Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 586462 14 pageshttpdxdoiorg1011552013586462

Review ArticleRecent Advances in Stimuli-Responsive PhotofunctionalMaterials Based on Accommodation of Chromophore intoLayered Double Hydroxide Nanogallery

Wu Li Dongpeng Yan Rui Gao Jun Lu Min Wei and Xue Duan

State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical Technology Beijing 100029 China

Correspondence should be addressed to Dongpeng Yan yandongpeng001163com

Received 29 October 2012 Accepted 27 December 2012

Academic Editor Su Chen

Copyright copy 2013 Wu Li et al This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The assembly of photofunctional molecules into host matrices has become an important strategy to achieve tunable fluorescenceand to develop intelligent materials The stimuli-responsive photofunctional materials based on chromophores-assembled layereddouble hydroxides (LDHs) have received much attention from both academic and industry fields as a result of their advantagessuch as high photothermal stability easy processing and well reversibility which can construct new types of smart luminescentnanomaterials (eg ultrathin film and nanocomposite) for sensor and switch applications In this paper external environmentalstimuli have mainly involved physical (such as temperature pressure light and electricity ) and chemical factors (such as pH andmetal ion) recent progress on the LDH-based organic-inorganic stimuli-responsive materials has been summarized Moreoverperspectives on further development of these materials are also discussed

1 Introduction

The functional material that can respond to different externalstimuli is the basis for developing a new generation of intel-ligent device Stimuli-responsive organic photofunctional(such as luminescent) materials have attracted significantattention from both fundamental research as well as industryduring the last few years because of their remarkable and sen-sitive response signal These photofunctional materials havepotential applications in the fields of fluorescent switchesand optical recording sensors [1] Generally the mechanismsfor changing in photofunction of organic materials consistof occurrence of chemical reactions and alteration of themolecular packing mode [2 3] Recently controlling andtuning the molecular packing mode become a main strategyfor the design of intelligent luminescent materials becausethe solid-state chemical reaction frequently involves relativelylow conversion efficiency Since 2005 several new types oforganic luminescent materials with stimuli-responsive prop-erties (such as piezochromic deformation-induced chromicphotochromic thermochromic and humidity colorimetricluminescent systems) have been developed [4ndash7] However

to meet the requirements of responsive luminescent devicesor optical sensors the assembly of ordered thin films with thechromophores on two-dimensional (2D) surfaces remains achallenge and examples are rather rare

For an idealized orderly system the photoactive mole-cules with regular molecular orientation and intermolecularpacking mode are more prone to exhibit systematicallyresponsive behaviors upon external stimuli Therefore thecontrol of high orientation of organic molecules is of criticalimportance to design and fabricate responsive luminescentmaterials As well from a perspective of luminescent effi-ciency the aggregates of luminescent molecules are usuallyreadily formed in the solid state which can lead to an emis-sion shift line broadening and even luminescence quench-ingMoreover the thermalchemical stability and service life-time of organic materials are generally low for optoelectronicdevice application [8] Therefore how to further enhancethe optical performance and stability also became majorgoals In addition from a viewpoint of practical applicationfast response high reversibility and stable repeatability areall necessary for such responsive materials as sensors andswitches

2 Journal of Nanomaterials

Nanosheets

Chromophores Nanogallery

Figure 1 A typical scheme for chromophores assembled into Mg-Al-LDH nanogallery

One effective way to realize the regulation and orien-tation of the organic chromophores is the incorporation oforganic photofunctional molecules into solid host matriceswhich can also supply a stable environment to enhance thethermo and photostabilities of organic species In this senselayered double hydroxides (LDHs) are typical layered hostmaterials which can be described by the general formula[MII1minus119909

MIII119909(OH)2]119911+

119860119899minus

119911119899sdot 119910H2O (MII and MIII are diva-

lent and trivalent metals ions respectively A119899minus is an anion)[9] The structure of the LDH layer is analogous to that ofthe brucite with edge-sharing M(OH)

6octahedra in which

partial substitution ofM3+ forM2+ induces positively chargedhost layers balanced by the interlayer anions Different frommost of the cationic clays the charge density and elementalcomposition of LDHs can be changed during the synthesisprocess favoring finely controlling properties of the hostlayer To meet the demands in applications hundreds of suit-able anions have been rationally chosen and intercalated intoLDHs for constructing new types of host-guest nanomaterials[10]

The LDH features 2D channel at the nanometer leveland the nanogallery is usually in the range of 03ndash4 nm [11]therefore most of anionic organic photoactive guests canbe incorporated into LDH hosts to obtain inorganic-organichybrid nanomaterials (as shown in Figure 1) These systemsshow specific physical and chemical performances comparedwith their individual counterparts which is beneficial forthe fabrication of novel optoelectronic and photofunctionalmaterials (1) chromophore guest molecules immobilized inthe LDH host matrix exhibit optical and thermal stabilityenvironmental compatibility and low operational risk [12](2) The orientation and arrangement of the chromophorescan be tuned by changing the layer charge density andchemical composition which can further adjust the opticalproperties of the nanocomposites [13 14] (3) LDH hostmatrix provides chromophoremolecules with a confined and

stable environment which reduces molecular thermal agi-tation (intermolecular collisions vibrations and rotations)by host-guest interactions and the fluorescence quenchingis therefore reduced [15 16] Recently according to theprinciple of molecular design and supramolecular assemblythe inorganic-organic nanomaterials (both powders andthin films) based on the accommodation of chromophoreguests into LDH host have been largely developed and havegradually become a fascinating field in luminescent hybridmaterials [17 18] For example the polyanion-assembledLDH films exhibit a better UV light resistance ability thanthe pure polyanionpolycation film By the use of in-situphotoluminescence technique [15] it was found that thenormalized fluorescence intensity of the anionic poly(p-phenylene) (APPP) assembled LDH was larger than thatof the APPPPDDA (poly(dimethyldiallylammonium chlo-ride)) counterpart demonstrating that the presence of theinorganic LDH nanosheets leads to an enhanced opticalstability of the conjugated anions compared with typicalorganicorganic films A previous review on LDH-basedfluorescent materials has mainly summarized the prepa-ration method and tunable photoluminescent properties[19] Recently the host-guest stimuli-responsive luminescentmaterials have also been studied successively since theorientation mode of the interlayer chromophores and host-guest interaction can be changed upon external stimuli [2021] In addition new physicalchemical phenomena have alsobeen obtained based on the theoretical calculations for thesehybrid nanomaterials We believe it is timely and necessaryto introduce these new advances to give a better under-standing and supply new insights for the design of organic-inorganic intelligent nanomaterials In this paper we focusour attention on recent progress of the stimuli-responsivephotofunctionalmaterials for opticalluminescent switch andsensor applications by assembling photofunctionalmoleculesinto LDH nanogallery by selecting representative stimuli-responsive examples two types of environmental stimulimdashphysical stimuli (such as light pressure heat electricity andpolarization) and chemical stimuli (pH value and heavemetal ions)mdashwere mainly introduced Finally perspectiveson future development for these materials are also discussed

2 LDH-Based PhysicalStimuli-Responsive Materials

21 Heat- and Pressure-Responsive Materials Temperatureand pressure are the most common and natural envire-mental factors therefore temperature- and pressure-inducedchromic (known as thermochromic and piezochromic)mate-rials can be potentially used in memory chips and secu-rity inks Stilbene-type compounds have attracted consid-erable interests due to their excellent optical and elec-tronic properties [22 23] Yan et al [24] have fabri-cated an inorganic-organic ultrathin film (UTF) systemwith thermochromic luminescence (TCL) based on thelayer-by-layer (LBL) assembly of anionic stilbene derivative(bis(2-sulfonatostyryl)biphenyl donated as BSB) and LDHnanosheets The thickness of the BSBLDH UTF can be

Journal of Nanomaterials 3

finely controlled in the range from 23 nm (8 bilayers) to67 nm (32 bilayers) indicating that the average thickness ofone BSBLDH unit is about 22 nm The UTF undergoes aremarkable change in luminescence color upon increasingtemperature On heating the BSBLDH from 20 to 100∘Cthe emissive band moves from 444 to 473 nm with a gradualdecrease in the luminescence intensity The emission colorchanges from blue to bluish green on heating the UTF andthe color change is also visible to the naked eye as shown inthe inset of Figure 2(a) When the UTF was cooled to 20∘Cover 2min the fluorescence emission can recover its originalblue color completely together with the associated reversespectral changesThe reversible change in luminescence colorcan also be repeated (Figure 2(a) inset) For the excited statesof the UTF the fluorescence decay at high temperature isslower than that at low temperature (Figure 2(b)) and thisbehavior can be assigned to the formation of an excimer inthe UTF The fluorescence lifetime of the UTFs at 100∘C is19 ns about twice the value at 20∘C (09 ns) These changesin fluorescence lifetime are repeatedly observed on cyclingbetween two typical temperatures (Figure 2(b) inset)

In-situ FTIRmeasurement shows that as the temperatureincreases themost significant change is that the bands at 1652and 1630 cmminus1 broaden and become unresolved for the UTFsuggesting that the skeleton vibration increases dramaticallyat high temperature and the system becomes relatively disor-dered compared with that at low temperature No character-istic band disappears in the whole range demonstrating nochemical reaction occurs during the heating process Furthermolecular dynamic simulation confirms that the TCL perfor-mance is mainly associated with the variations in orientationand molecular packing of BSB confined between the LDHnanosheets Based on TCL performance it is anticipated thatthe UTFs can be potentially used as luminescent sensors andmolecular thermometers

The study on the reversible thermochromic materialshas attracted more attention due to its wide applicationssuch as optical data storage security markers for notes anddocuments and color-variable clothing [26] 4-(4-anilino-phenylazo)benzenesulfonate (AO5) is a typical azo dye withthermochromic property which has been used as a thermalsensor pH indicator and molecular memory storage dueto its tautomerism between the azo A form and hydrazoneH form (Figure 3) Such tautomeric equilibrium is sensitiveto the external microenvironment (eg substituents andsolvents) An effective way to enhance the thermochromicperformances of this dye is to choose a suitable host matrixfor tuning its molecular environment Wang et al [25] havefabricated transparent thin films based on AO5 and sodiumdodecylbenzene sulfonate (SDS) cointercalated in LDHwhich show a fast and repeatable thermochromic behaviorBy the use of temperature-dependent UVvisible absorptionspectrophotometer it was observed that the 10 AO5-LDHthin film shows the highest thermochromic efficiency

At ambient temperature the AO5-LDH thin film has amaximal absorption at 363 nm (Figure 4(a)) Upon increas-ing temperature a spectral change occurs with a decreasein the intensity of the band at 363 nm and a new band

appears with increasing intensity at 445 nm Visually a colorchange from light yellow to reddish orange can be observedupon heating the 10 AO5-LDH film from 35 to 65∘C Asthe film is cooled to 35∘C it recovers its original color withthe associated converse spectral changes Figure 4(b) showsthe temperature-dependent absorbance at 445 nm over acomplete heating-cooling cycle confirming the reversibilityof the thermochromic performance Moreover the filmmaterial also shows high thermostability and photostabilityas a result of the host-guest structure As the temperaturerange for the thermochromism covers the body temperatureof human beings and the atmosphere it can be expected thatthis AO5-LDH film has potential applications in the fieldof physiological and environmental temperature designationand warning

Conjugated polydiacetylenes (PDAs) have attracted greatattention during the past few years owing to their signif-icant functionality and wide applicability in colorimetricdetection systems [27 28] It is highly desirable to achievesensor and array devices with high stability reusability andenvironmental compatibility by the immobilization of PDAsRecently Shi et al [29] have prepared the 13-diacetylene(DA) anion-intercalated LDH nanocomposite films withthe aid of a photolithography technique UV irradiationof the colorless DA-LDH film results in the formation ofpatterned bluecolorless image (Figure 5(a) A B) Heatingthe film at 130∘C results in the transition to yellowcolorlesspatterned image while it transfers to redcolorless patternedimage as the film is cooled down (Figure 5(a) C D) Theheat-treatment at 130∘C shows an orange-yellowcolorlessfluorescence image which displays a bluish greencolorlessfluorescence image when the sample is cooled (Figure 5(b)C D) For the corresponding film with physical mixture ofPDA and LDH no thermal response can be observed foroptical image By the analysis of in-situ Raman spectroscopythe thermochromic behavior of PDAsLDH is attributedto strong hydrogen bond interactions between LDH andPDAs

To date compared with those of temperature-sensitivematerials the study of piezochromic luminescence (PCL)materials remains in an early stage [30] The design ofPCL materials is of importance to monitor the change inpressure especially under extreme conditions It has beenrecognized that alternating themolecular arrangement modeis a promising strategy to tune the fluorescence of an organiccompound During last 10 years efforts have been put in thedevelopment of pure organic fluorophores with PCL prop-erties and these materials usually involve an aggregation-induced emission mechanism [31 32] However the rationaldesign and preparation of organic-inorganic hybrid PCLmaterials remain a considerable challenge

Recently we have fabricated a new type of PCL materialby the assembly of an organic fluorophore (221015840-(12-ethe-nediyl)bis[5-[4-(diethylamino)-6-[(25-disulfophenyl)ami-no]-135-triazin-2-yl] amino] benzene sulfonate anionBTZB) into the nanogalleries of LDHs [33] Such strategyfor construction of PCL material is based on the fact thatthe LDH nanosheets are flexible enough to deform overinterlayer bulky guests and slipping of LDH layer can occur

4 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

0 1 2 3 4 5440445450455460465470475

Inte

nsity

(au

)

Wavelength (nm)

20

100

20

Cycles

100

Heating

Cooling

1 cm

120582m

ax

∘C

∘C

∘C

∘C

(a)

10 15 20 25 30

10

100

1000

0 1 2 3 4 5

0608

112141618

22224

Cou

nts

Times (ns)

20100

100

20

Solution

Life

time (

ns)

Cycles (n)

∘C

∘C

∘C∘C

(b)

Figure 2 TCLof the BSBLDHUTF at 20 and 100∘C (a) Fluorescence spectra (inset the reversible fluorescence response over five consecutivecycles and photographs of the UTF before and after heating) (b) Fluorescence decay curve (inset fluorescence lifetimes over five consecutivecycles) [24]

A form H form

Figure 3 Tautomeric equilibrium between the A form and H formof AO5 [25]

on increasing the external pressure which can furtherinfluence the host-guest interactions [21] In additionthe long-chain BTZB anion has four rotatable aromaticamine units and thus its molecular conformation andintermolecular interactions can be tuned more easily byexternal perturbations than the rigid molecules Uponincreasing pressure BTZBLDH nanocomposites exhibitluminescent redshift with a concomitant broadening ofthe emission while the pristine BTZB shows no PCL atall The most significant PCL behavior is present in theBTZBMg

2Al-LDH sample and the maximum emissive

wavelength moves from 452 to 515 nm under differentstimuli (Figures 6(a) and 6(b)) The typical photographs ofthe BTZBMg

2Al-LDH pellet under UV light (Figure 6(a)

inset) display a visual luminescent change from blue togreen upon increasing pressure The redshift of spectra maybe attributed to the formation of J-type aggregates in thenanogallery of LDH An appreciable change in the UV-visabsorption band of BTZBMg

2Al-LDH nanocomposites was

also observed upon compression as shown in Figure 6(c)

Once the pressed BTZBMg2Al-LDH sample was ground

into powder heated at 100∘C and then cooled downthe luminescent peak at 515 nm moved back to 452 nmcompletely In addition the reversible luminescent colorchange can be readily repeated to switch between twopressures The reversible changes in fluorescence propertiescan be recycled at least 3 timesTherefore it can be concludedthat the BTZB-intercalated LDH material exhibits reversibleoptical responses (luminescent color absorption bandand fluorescent lifetime) upon changing external pressuremolecular dynamics and periodic density functionaltheoretical studies demonstrate that the PCL performanceoriginates from changes in the relative orientation andaggregation state of the interlayer BTZB Such materials mayserve as the fluorescent antiforgery devices

22 Photoinduced-Responsive Materials The photoinducedcis-trans isomerization of organic photofunctional materials(such as Schiff base and azobenzene derivative) has presentedmany interesting features and their applications range fromelectronics to nonlinear devices [34ndash37] In the solid state ofthese materials the penetration between adjacent functionalgroup and strong 120587-120587 stacking of chromophores may leadto a lack of sufficient free volume for the isomerization andlead to irreversibility or low efficiency of the process Thisis one of the main bottlenecks in developing optical deviceswith superior optical properties based on the molecularisomerization LDH nanosheets can provide the organic

Journal of Nanomaterials 5

02

04

06

08

Abso

rptio

n

300 350 400 450 500 550 600

363 nm

445 nm

65605550454035

Wavelength (nm)

∘C∘C∘C∘C∘C∘C∘C

(a)

04

045

05

055

06

065

Max

imum

abso

rptio

n at

445

nm

0 10 20 30 40 50 60 70Temperature

HeatingCooling

(b)

Figure 4 (a) In-situ absorption spectra of the 10 AO5-LDH film during heating in the temperature range 35ndash65∘C (b) The correlationbetween the absorbance of the band at 445 nm and temperature over a heating-cooling cycle [25]

Color

UVirradiation Heating

at 130

Coolingto room

temperature

Heatingto 130

∘C

∘C

(a)

Fluorescence

UVirradiation

Heatingat 130

Heatingto 130

Coolingto room

temperature∘C

∘C

(b)

Figure 5 PDA-LDH film induced by UV irradiation and its thermochromic behavior (a) and fluorescent transition (b) (A) the DA-LDHfilm (B) the PDA-LDH film obtained by UV irradiating (A) (C) the film by heating (B) at 130∘C for 1min (D) the film by cooling (C) toroom temperature [29]

chromophores with a rigid and ordered microenvironmentin which the severe interpenetration of the cis-trans groupsmay be restrained by the isolating effect of the 2D nanosheetsAn ordered distribution and alignment of the cis-transgroups with sufficient available free space in the nanogallerybetween the LDH nanosheets can also facilitate their pho-toisomerization efficiency In pioneering works Tagaya et al[38ndash40] have prepared sulfonated indolinespirobenzopyran(SP) intercalated into the MgAI and ZnAl LDHs whichwas premodified by toluene-p-sulfonic acid (PTS) The newintercalated nanocomposites exhibited reversible photoiso-merization between SP and merocyanine (MC) as shown inthe Figure 7 It was also noted that the presence of PTS play akey role in the reversible photoisomerization

Han et al [41] have reported the fabrication of hybridultrathin photoresponsive films based on LBL self-assemblyof LDH nanosheets and the azobenzene-containing polymer(PAZO) By irradiating the sample with UV light there isa progressive decrease in the maximum intensity of 120587-120587lowasttransition band and the 120587-120587lowast band nearly disappears aftersufficient irradiation time indicating an almost 100 trans-to-cis photoreaction The 120587-120587lowast absorption band increasesagainwith irradiation by visible light (120582 gt 450 nm) indicativeof the cis-trans back-isomerization of azobenzene Further-more alternate irradiation with UV and visible light resultsin a reversible switching between the trans- and cis-state ofthe azobenzene group with significant changes in film colorThe thin film of azobenzene derivative-intercalated LDH

6 Journal of Nanomaterials

400 450 500 550 6000

02

04

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08

1

Inte

nsity

(au

)

Wavelength (nm)

01 MPa313 Gpa625 Gpa938 Gpa

125 Gpa1563 Gpa1875 Gpa

(a)

450

460

470

480

490

500

510

520

0 5 10 15 20External pressure (GPa)

ZnAl = 3ZnAl = 2

MgAl = 3MgAl = 2Pristine BTZB

120582m

ax(n

m)

(b)

300 400 500 600 700 8000

02

04

06

08

1

01 MPa313 GPa625 GPa938 GPa

125 GPa1563 GPa1875 GPa

Abso

rptio

n

Wavelength (nm)

(c)

Figure 6 (a) Fluorescent spectra of the BTZBMg2Al-LDH at different pressures (inset fluorescent photographs under 365 nmUV light the

arrow shows the direction of the increasing pressure) (b) maximum emissive wavelength of BTZBLDHs at different pressures (c) UV-visspectra of the BTZBMg

2Al-LDH at different pressures [33]

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

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2 k

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12 k

01

02

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Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

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2 k

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5 k

6 k

0

02

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Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CompositesJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Biomaterials

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TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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BioMed Research International

MaterialsJournal of

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Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

2 Journal of Nanomaterials

Nanosheets

Chromophores Nanogallery

Figure 1 A typical scheme for chromophores assembled into Mg-Al-LDH nanogallery

One effective way to realize the regulation and orien-tation of the organic chromophores is the incorporation oforganic photofunctional molecules into solid host matriceswhich can also supply a stable environment to enhance thethermo and photostabilities of organic species In this senselayered double hydroxides (LDHs) are typical layered hostmaterials which can be described by the general formula[MII1minus119909

MIII119909(OH)2]119911+

119860119899minus

119911119899sdot 119910H2O (MII and MIII are diva-

lent and trivalent metals ions respectively A119899minus is an anion)[9] The structure of the LDH layer is analogous to that ofthe brucite with edge-sharing M(OH)

6octahedra in which

partial substitution ofM3+ forM2+ induces positively chargedhost layers balanced by the interlayer anions Different frommost of the cationic clays the charge density and elementalcomposition of LDHs can be changed during the synthesisprocess favoring finely controlling properties of the hostlayer To meet the demands in applications hundreds of suit-able anions have been rationally chosen and intercalated intoLDHs for constructing new types of host-guest nanomaterials[10]

The LDH features 2D channel at the nanometer leveland the nanogallery is usually in the range of 03ndash4 nm [11]therefore most of anionic organic photoactive guests canbe incorporated into LDH hosts to obtain inorganic-organichybrid nanomaterials (as shown in Figure 1) These systemsshow specific physical and chemical performances comparedwith their individual counterparts which is beneficial forthe fabrication of novel optoelectronic and photofunctionalmaterials (1) chromophore guest molecules immobilized inthe LDH host matrix exhibit optical and thermal stabilityenvironmental compatibility and low operational risk [12](2) The orientation and arrangement of the chromophorescan be tuned by changing the layer charge density andchemical composition which can further adjust the opticalproperties of the nanocomposites [13 14] (3) LDH hostmatrix provides chromophoremolecules with a confined and

stable environment which reduces molecular thermal agi-tation (intermolecular collisions vibrations and rotations)by host-guest interactions and the fluorescence quenchingis therefore reduced [15 16] Recently according to theprinciple of molecular design and supramolecular assemblythe inorganic-organic nanomaterials (both powders andthin films) based on the accommodation of chromophoreguests into LDH host have been largely developed and havegradually become a fascinating field in luminescent hybridmaterials [17 18] For example the polyanion-assembledLDH films exhibit a better UV light resistance ability thanthe pure polyanionpolycation film By the use of in-situphotoluminescence technique [15] it was found that thenormalized fluorescence intensity of the anionic poly(p-phenylene) (APPP) assembled LDH was larger than thatof the APPPPDDA (poly(dimethyldiallylammonium chlo-ride)) counterpart demonstrating that the presence of theinorganic LDH nanosheets leads to an enhanced opticalstability of the conjugated anions compared with typicalorganicorganic films A previous review on LDH-basedfluorescent materials has mainly summarized the prepa-ration method and tunable photoluminescent properties[19] Recently the host-guest stimuli-responsive luminescentmaterials have also been studied successively since theorientation mode of the interlayer chromophores and host-guest interaction can be changed upon external stimuli [2021] In addition new physicalchemical phenomena have alsobeen obtained based on the theoretical calculations for thesehybrid nanomaterials We believe it is timely and necessaryto introduce these new advances to give a better under-standing and supply new insights for the design of organic-inorganic intelligent nanomaterials In this paper we focusour attention on recent progress of the stimuli-responsivephotofunctionalmaterials for opticalluminescent switch andsensor applications by assembling photofunctionalmoleculesinto LDH nanogallery by selecting representative stimuli-responsive examples two types of environmental stimulimdashphysical stimuli (such as light pressure heat electricity andpolarization) and chemical stimuli (pH value and heavemetal ions)mdashwere mainly introduced Finally perspectiveson future development for these materials are also discussed

2 LDH-Based PhysicalStimuli-Responsive Materials

21 Heat- and Pressure-Responsive Materials Temperatureand pressure are the most common and natural envire-mental factors therefore temperature- and pressure-inducedchromic (known as thermochromic and piezochromic)mate-rials can be potentially used in memory chips and secu-rity inks Stilbene-type compounds have attracted consid-erable interests due to their excellent optical and elec-tronic properties [22 23] Yan et al [24] have fabri-cated an inorganic-organic ultrathin film (UTF) systemwith thermochromic luminescence (TCL) based on thelayer-by-layer (LBL) assembly of anionic stilbene derivative(bis(2-sulfonatostyryl)biphenyl donated as BSB) and LDHnanosheets The thickness of the BSBLDH UTF can be

Journal of Nanomaterials 3

finely controlled in the range from 23 nm (8 bilayers) to67 nm (32 bilayers) indicating that the average thickness ofone BSBLDH unit is about 22 nm The UTF undergoes aremarkable change in luminescence color upon increasingtemperature On heating the BSBLDH from 20 to 100∘Cthe emissive band moves from 444 to 473 nm with a gradualdecrease in the luminescence intensity The emission colorchanges from blue to bluish green on heating the UTF andthe color change is also visible to the naked eye as shown inthe inset of Figure 2(a) When the UTF was cooled to 20∘Cover 2min the fluorescence emission can recover its originalblue color completely together with the associated reversespectral changesThe reversible change in luminescence colorcan also be repeated (Figure 2(a) inset) For the excited statesof the UTF the fluorescence decay at high temperature isslower than that at low temperature (Figure 2(b)) and thisbehavior can be assigned to the formation of an excimer inthe UTF The fluorescence lifetime of the UTFs at 100∘C is19 ns about twice the value at 20∘C (09 ns) These changesin fluorescence lifetime are repeatedly observed on cyclingbetween two typical temperatures (Figure 2(b) inset)

In-situ FTIRmeasurement shows that as the temperatureincreases themost significant change is that the bands at 1652and 1630 cmminus1 broaden and become unresolved for the UTFsuggesting that the skeleton vibration increases dramaticallyat high temperature and the system becomes relatively disor-dered compared with that at low temperature No character-istic band disappears in the whole range demonstrating nochemical reaction occurs during the heating process Furthermolecular dynamic simulation confirms that the TCL perfor-mance is mainly associated with the variations in orientationand molecular packing of BSB confined between the LDHnanosheets Based on TCL performance it is anticipated thatthe UTFs can be potentially used as luminescent sensors andmolecular thermometers

The study on the reversible thermochromic materialshas attracted more attention due to its wide applicationssuch as optical data storage security markers for notes anddocuments and color-variable clothing [26] 4-(4-anilino-phenylazo)benzenesulfonate (AO5) is a typical azo dye withthermochromic property which has been used as a thermalsensor pH indicator and molecular memory storage dueto its tautomerism between the azo A form and hydrazoneH form (Figure 3) Such tautomeric equilibrium is sensitiveto the external microenvironment (eg substituents andsolvents) An effective way to enhance the thermochromicperformances of this dye is to choose a suitable host matrixfor tuning its molecular environment Wang et al [25] havefabricated transparent thin films based on AO5 and sodiumdodecylbenzene sulfonate (SDS) cointercalated in LDHwhich show a fast and repeatable thermochromic behaviorBy the use of temperature-dependent UVvisible absorptionspectrophotometer it was observed that the 10 AO5-LDHthin film shows the highest thermochromic efficiency

At ambient temperature the AO5-LDH thin film has amaximal absorption at 363 nm (Figure 4(a)) Upon increas-ing temperature a spectral change occurs with a decreasein the intensity of the band at 363 nm and a new band

appears with increasing intensity at 445 nm Visually a colorchange from light yellow to reddish orange can be observedupon heating the 10 AO5-LDH film from 35 to 65∘C Asthe film is cooled to 35∘C it recovers its original color withthe associated converse spectral changes Figure 4(b) showsthe temperature-dependent absorbance at 445 nm over acomplete heating-cooling cycle confirming the reversibilityof the thermochromic performance Moreover the filmmaterial also shows high thermostability and photostabilityas a result of the host-guest structure As the temperaturerange for the thermochromism covers the body temperatureof human beings and the atmosphere it can be expected thatthis AO5-LDH film has potential applications in the fieldof physiological and environmental temperature designationand warning

Conjugated polydiacetylenes (PDAs) have attracted greatattention during the past few years owing to their signif-icant functionality and wide applicability in colorimetricdetection systems [27 28] It is highly desirable to achievesensor and array devices with high stability reusability andenvironmental compatibility by the immobilization of PDAsRecently Shi et al [29] have prepared the 13-diacetylene(DA) anion-intercalated LDH nanocomposite films withthe aid of a photolithography technique UV irradiationof the colorless DA-LDH film results in the formation ofpatterned bluecolorless image (Figure 5(a) A B) Heatingthe film at 130∘C results in the transition to yellowcolorlesspatterned image while it transfers to redcolorless patternedimage as the film is cooled down (Figure 5(a) C D) Theheat-treatment at 130∘C shows an orange-yellowcolorlessfluorescence image which displays a bluish greencolorlessfluorescence image when the sample is cooled (Figure 5(b)C D) For the corresponding film with physical mixture ofPDA and LDH no thermal response can be observed foroptical image By the analysis of in-situ Raman spectroscopythe thermochromic behavior of PDAsLDH is attributedto strong hydrogen bond interactions between LDH andPDAs

To date compared with those of temperature-sensitivematerials the study of piezochromic luminescence (PCL)materials remains in an early stage [30] The design ofPCL materials is of importance to monitor the change inpressure especially under extreme conditions It has beenrecognized that alternating themolecular arrangement modeis a promising strategy to tune the fluorescence of an organiccompound During last 10 years efforts have been put in thedevelopment of pure organic fluorophores with PCL prop-erties and these materials usually involve an aggregation-induced emission mechanism [31 32] However the rationaldesign and preparation of organic-inorganic hybrid PCLmaterials remain a considerable challenge

Recently we have fabricated a new type of PCL materialby the assembly of an organic fluorophore (221015840-(12-ethe-nediyl)bis[5-[4-(diethylamino)-6-[(25-disulfophenyl)ami-no]-135-triazin-2-yl] amino] benzene sulfonate anionBTZB) into the nanogalleries of LDHs [33] Such strategyfor construction of PCL material is based on the fact thatthe LDH nanosheets are flexible enough to deform overinterlayer bulky guests and slipping of LDH layer can occur

4 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

0 1 2 3 4 5440445450455460465470475

Inte

nsity

(au

)

Wavelength (nm)

20

100

20

Cycles

100

Heating

Cooling

1 cm

120582m

ax

∘C

∘C

∘C

∘C

(a)

10 15 20 25 30

10

100

1000

0 1 2 3 4 5

0608

112141618

22224

Cou

nts

Times (ns)

20100

100

20

Solution

Life

time (

ns)

Cycles (n)

∘C

∘C

∘C∘C

(b)

Figure 2 TCLof the BSBLDHUTF at 20 and 100∘C (a) Fluorescence spectra (inset the reversible fluorescence response over five consecutivecycles and photographs of the UTF before and after heating) (b) Fluorescence decay curve (inset fluorescence lifetimes over five consecutivecycles) [24]

A form H form

Figure 3 Tautomeric equilibrium between the A form and H formof AO5 [25]

on increasing the external pressure which can furtherinfluence the host-guest interactions [21] In additionthe long-chain BTZB anion has four rotatable aromaticamine units and thus its molecular conformation andintermolecular interactions can be tuned more easily byexternal perturbations than the rigid molecules Uponincreasing pressure BTZBLDH nanocomposites exhibitluminescent redshift with a concomitant broadening ofthe emission while the pristine BTZB shows no PCL atall The most significant PCL behavior is present in theBTZBMg

2Al-LDH sample and the maximum emissive

wavelength moves from 452 to 515 nm under differentstimuli (Figures 6(a) and 6(b)) The typical photographs ofthe BTZBMg

2Al-LDH pellet under UV light (Figure 6(a)

inset) display a visual luminescent change from blue togreen upon increasing pressure The redshift of spectra maybe attributed to the formation of J-type aggregates in thenanogallery of LDH An appreciable change in the UV-visabsorption band of BTZBMg

2Al-LDH nanocomposites was

also observed upon compression as shown in Figure 6(c)

Once the pressed BTZBMg2Al-LDH sample was ground

into powder heated at 100∘C and then cooled downthe luminescent peak at 515 nm moved back to 452 nmcompletely In addition the reversible luminescent colorchange can be readily repeated to switch between twopressures The reversible changes in fluorescence propertiescan be recycled at least 3 timesTherefore it can be concludedthat the BTZB-intercalated LDH material exhibits reversibleoptical responses (luminescent color absorption bandand fluorescent lifetime) upon changing external pressuremolecular dynamics and periodic density functionaltheoretical studies demonstrate that the PCL performanceoriginates from changes in the relative orientation andaggregation state of the interlayer BTZB Such materials mayserve as the fluorescent antiforgery devices

22 Photoinduced-Responsive Materials The photoinducedcis-trans isomerization of organic photofunctional materials(such as Schiff base and azobenzene derivative) has presentedmany interesting features and their applications range fromelectronics to nonlinear devices [34ndash37] In the solid state ofthese materials the penetration between adjacent functionalgroup and strong 120587-120587 stacking of chromophores may leadto a lack of sufficient free volume for the isomerization andlead to irreversibility or low efficiency of the process Thisis one of the main bottlenecks in developing optical deviceswith superior optical properties based on the molecularisomerization LDH nanosheets can provide the organic

Journal of Nanomaterials 5

02

04

06

08

Abso

rptio

n

300 350 400 450 500 550 600

363 nm

445 nm

65605550454035

Wavelength (nm)

∘C∘C∘C∘C∘C∘C∘C

(a)

04

045

05

055

06

065

Max

imum

abso

rptio

n at

445

nm

0 10 20 30 40 50 60 70Temperature

HeatingCooling

(b)

Figure 4 (a) In-situ absorption spectra of the 10 AO5-LDH film during heating in the temperature range 35ndash65∘C (b) The correlationbetween the absorbance of the band at 445 nm and temperature over a heating-cooling cycle [25]

Color

UVirradiation Heating

at 130

Coolingto room

temperature

Heatingto 130

∘C

∘C

(a)

Fluorescence

UVirradiation

Heatingat 130

Heatingto 130

Coolingto room

temperature∘C

∘C

(b)

Figure 5 PDA-LDH film induced by UV irradiation and its thermochromic behavior (a) and fluorescent transition (b) (A) the DA-LDHfilm (B) the PDA-LDH film obtained by UV irradiating (A) (C) the film by heating (B) at 130∘C for 1min (D) the film by cooling (C) toroom temperature [29]

chromophores with a rigid and ordered microenvironmentin which the severe interpenetration of the cis-trans groupsmay be restrained by the isolating effect of the 2D nanosheetsAn ordered distribution and alignment of the cis-transgroups with sufficient available free space in the nanogallerybetween the LDH nanosheets can also facilitate their pho-toisomerization efficiency In pioneering works Tagaya et al[38ndash40] have prepared sulfonated indolinespirobenzopyran(SP) intercalated into the MgAI and ZnAl LDHs whichwas premodified by toluene-p-sulfonic acid (PTS) The newintercalated nanocomposites exhibited reversible photoiso-merization between SP and merocyanine (MC) as shown inthe Figure 7 It was also noted that the presence of PTS play akey role in the reversible photoisomerization

Han et al [41] have reported the fabrication of hybridultrathin photoresponsive films based on LBL self-assemblyof LDH nanosheets and the azobenzene-containing polymer(PAZO) By irradiating the sample with UV light there isa progressive decrease in the maximum intensity of 120587-120587lowasttransition band and the 120587-120587lowast band nearly disappears aftersufficient irradiation time indicating an almost 100 trans-to-cis photoreaction The 120587-120587lowast absorption band increasesagainwith irradiation by visible light (120582 gt 450 nm) indicativeof the cis-trans back-isomerization of azobenzene Further-more alternate irradiation with UV and visible light resultsin a reversible switching between the trans- and cis-state ofthe azobenzene group with significant changes in film colorThe thin film of azobenzene derivative-intercalated LDH

6 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)

01 MPa313 Gpa625 Gpa938 Gpa

125 Gpa1563 Gpa1875 Gpa

(a)

450

460

470

480

490

500

510

520

0 5 10 15 20External pressure (GPa)

ZnAl = 3ZnAl = 2

MgAl = 3MgAl = 2Pristine BTZB

120582m

ax(n

m)

(b)

300 400 500 600 700 8000

02

04

06

08

1

01 MPa313 GPa625 GPa938 GPa

125 GPa1563 GPa1875 GPa

Abso

rptio

n

Wavelength (nm)

(c)

Figure 6 (a) Fluorescent spectra of the BTZBMg2Al-LDH at different pressures (inset fluorescent photographs under 365 nmUV light the

arrow shows the direction of the increasing pressure) (b) maximum emissive wavelength of BTZBLDHs at different pressures (c) UV-visspectra of the BTZBMg

2Al-LDH at different pressures [33]

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MaterialsJournal of

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Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanomaterials 3

finely controlled in the range from 23 nm (8 bilayers) to67 nm (32 bilayers) indicating that the average thickness ofone BSBLDH unit is about 22 nm The UTF undergoes aremarkable change in luminescence color upon increasingtemperature On heating the BSBLDH from 20 to 100∘Cthe emissive band moves from 444 to 473 nm with a gradualdecrease in the luminescence intensity The emission colorchanges from blue to bluish green on heating the UTF andthe color change is also visible to the naked eye as shown inthe inset of Figure 2(a) When the UTF was cooled to 20∘Cover 2min the fluorescence emission can recover its originalblue color completely together with the associated reversespectral changesThe reversible change in luminescence colorcan also be repeated (Figure 2(a) inset) For the excited statesof the UTF the fluorescence decay at high temperature isslower than that at low temperature (Figure 2(b)) and thisbehavior can be assigned to the formation of an excimer inthe UTF The fluorescence lifetime of the UTFs at 100∘C is19 ns about twice the value at 20∘C (09 ns) These changesin fluorescence lifetime are repeatedly observed on cyclingbetween two typical temperatures (Figure 2(b) inset)

In-situ FTIRmeasurement shows that as the temperatureincreases themost significant change is that the bands at 1652and 1630 cmminus1 broaden and become unresolved for the UTFsuggesting that the skeleton vibration increases dramaticallyat high temperature and the system becomes relatively disor-dered compared with that at low temperature No character-istic band disappears in the whole range demonstrating nochemical reaction occurs during the heating process Furthermolecular dynamic simulation confirms that the TCL perfor-mance is mainly associated with the variations in orientationand molecular packing of BSB confined between the LDHnanosheets Based on TCL performance it is anticipated thatthe UTFs can be potentially used as luminescent sensors andmolecular thermometers

The study on the reversible thermochromic materialshas attracted more attention due to its wide applicationssuch as optical data storage security markers for notes anddocuments and color-variable clothing [26] 4-(4-anilino-phenylazo)benzenesulfonate (AO5) is a typical azo dye withthermochromic property which has been used as a thermalsensor pH indicator and molecular memory storage dueto its tautomerism between the azo A form and hydrazoneH form (Figure 3) Such tautomeric equilibrium is sensitiveto the external microenvironment (eg substituents andsolvents) An effective way to enhance the thermochromicperformances of this dye is to choose a suitable host matrixfor tuning its molecular environment Wang et al [25] havefabricated transparent thin films based on AO5 and sodiumdodecylbenzene sulfonate (SDS) cointercalated in LDHwhich show a fast and repeatable thermochromic behaviorBy the use of temperature-dependent UVvisible absorptionspectrophotometer it was observed that the 10 AO5-LDHthin film shows the highest thermochromic efficiency

At ambient temperature the AO5-LDH thin film has amaximal absorption at 363 nm (Figure 4(a)) Upon increas-ing temperature a spectral change occurs with a decreasein the intensity of the band at 363 nm and a new band

appears with increasing intensity at 445 nm Visually a colorchange from light yellow to reddish orange can be observedupon heating the 10 AO5-LDH film from 35 to 65∘C Asthe film is cooled to 35∘C it recovers its original color withthe associated converse spectral changes Figure 4(b) showsthe temperature-dependent absorbance at 445 nm over acomplete heating-cooling cycle confirming the reversibilityof the thermochromic performance Moreover the filmmaterial also shows high thermostability and photostabilityas a result of the host-guest structure As the temperaturerange for the thermochromism covers the body temperatureof human beings and the atmosphere it can be expected thatthis AO5-LDH film has potential applications in the fieldof physiological and environmental temperature designationand warning

Conjugated polydiacetylenes (PDAs) have attracted greatattention during the past few years owing to their signif-icant functionality and wide applicability in colorimetricdetection systems [27 28] It is highly desirable to achievesensor and array devices with high stability reusability andenvironmental compatibility by the immobilization of PDAsRecently Shi et al [29] have prepared the 13-diacetylene(DA) anion-intercalated LDH nanocomposite films withthe aid of a photolithography technique UV irradiationof the colorless DA-LDH film results in the formation ofpatterned bluecolorless image (Figure 5(a) A B) Heatingthe film at 130∘C results in the transition to yellowcolorlesspatterned image while it transfers to redcolorless patternedimage as the film is cooled down (Figure 5(a) C D) Theheat-treatment at 130∘C shows an orange-yellowcolorlessfluorescence image which displays a bluish greencolorlessfluorescence image when the sample is cooled (Figure 5(b)C D) For the corresponding film with physical mixture ofPDA and LDH no thermal response can be observed foroptical image By the analysis of in-situ Raman spectroscopythe thermochromic behavior of PDAsLDH is attributedto strong hydrogen bond interactions between LDH andPDAs

To date compared with those of temperature-sensitivematerials the study of piezochromic luminescence (PCL)materials remains in an early stage [30] The design ofPCL materials is of importance to monitor the change inpressure especially under extreme conditions It has beenrecognized that alternating themolecular arrangement modeis a promising strategy to tune the fluorescence of an organiccompound During last 10 years efforts have been put in thedevelopment of pure organic fluorophores with PCL prop-erties and these materials usually involve an aggregation-induced emission mechanism [31 32] However the rationaldesign and preparation of organic-inorganic hybrid PCLmaterials remain a considerable challenge

Recently we have fabricated a new type of PCL materialby the assembly of an organic fluorophore (221015840-(12-ethe-nediyl)bis[5-[4-(diethylamino)-6-[(25-disulfophenyl)ami-no]-135-triazin-2-yl] amino] benzene sulfonate anionBTZB) into the nanogalleries of LDHs [33] Such strategyfor construction of PCL material is based on the fact thatthe LDH nanosheets are flexible enough to deform overinterlayer bulky guests and slipping of LDH layer can occur

4 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

0 1 2 3 4 5440445450455460465470475

Inte

nsity

(au

)

Wavelength (nm)

20

100

20

Cycles

100

Heating

Cooling

1 cm

120582m

ax

∘C

∘C

∘C

∘C

(a)

10 15 20 25 30

10

100

1000

0 1 2 3 4 5

0608

112141618

22224

Cou

nts

Times (ns)

20100

100

20

Solution

Life

time (

ns)

Cycles (n)

∘C

∘C

∘C∘C

(b)

Figure 2 TCLof the BSBLDHUTF at 20 and 100∘C (a) Fluorescence spectra (inset the reversible fluorescence response over five consecutivecycles and photographs of the UTF before and after heating) (b) Fluorescence decay curve (inset fluorescence lifetimes over five consecutivecycles) [24]

A form H form

Figure 3 Tautomeric equilibrium between the A form and H formof AO5 [25]

on increasing the external pressure which can furtherinfluence the host-guest interactions [21] In additionthe long-chain BTZB anion has four rotatable aromaticamine units and thus its molecular conformation andintermolecular interactions can be tuned more easily byexternal perturbations than the rigid molecules Uponincreasing pressure BTZBLDH nanocomposites exhibitluminescent redshift with a concomitant broadening ofthe emission while the pristine BTZB shows no PCL atall The most significant PCL behavior is present in theBTZBMg

2Al-LDH sample and the maximum emissive

wavelength moves from 452 to 515 nm under differentstimuli (Figures 6(a) and 6(b)) The typical photographs ofthe BTZBMg

2Al-LDH pellet under UV light (Figure 6(a)

inset) display a visual luminescent change from blue togreen upon increasing pressure The redshift of spectra maybe attributed to the formation of J-type aggregates in thenanogallery of LDH An appreciable change in the UV-visabsorption band of BTZBMg

2Al-LDH nanocomposites was

also observed upon compression as shown in Figure 6(c)

Once the pressed BTZBMg2Al-LDH sample was ground

into powder heated at 100∘C and then cooled downthe luminescent peak at 515 nm moved back to 452 nmcompletely In addition the reversible luminescent colorchange can be readily repeated to switch between twopressures The reversible changes in fluorescence propertiescan be recycled at least 3 timesTherefore it can be concludedthat the BTZB-intercalated LDH material exhibits reversibleoptical responses (luminescent color absorption bandand fluorescent lifetime) upon changing external pressuremolecular dynamics and periodic density functionaltheoretical studies demonstrate that the PCL performanceoriginates from changes in the relative orientation andaggregation state of the interlayer BTZB Such materials mayserve as the fluorescent antiforgery devices

22 Photoinduced-Responsive Materials The photoinducedcis-trans isomerization of organic photofunctional materials(such as Schiff base and azobenzene derivative) has presentedmany interesting features and their applications range fromelectronics to nonlinear devices [34ndash37] In the solid state ofthese materials the penetration between adjacent functionalgroup and strong 120587-120587 stacking of chromophores may leadto a lack of sufficient free volume for the isomerization andlead to irreversibility or low efficiency of the process Thisis one of the main bottlenecks in developing optical deviceswith superior optical properties based on the molecularisomerization LDH nanosheets can provide the organic

Journal of Nanomaterials 5

02

04

06

08

Abso

rptio

n

300 350 400 450 500 550 600

363 nm

445 nm

65605550454035

Wavelength (nm)

∘C∘C∘C∘C∘C∘C∘C

(a)

04

045

05

055

06

065

Max

imum

abso

rptio

n at

445

nm

0 10 20 30 40 50 60 70Temperature

HeatingCooling

(b)

Figure 4 (a) In-situ absorption spectra of the 10 AO5-LDH film during heating in the temperature range 35ndash65∘C (b) The correlationbetween the absorbance of the band at 445 nm and temperature over a heating-cooling cycle [25]

Color

UVirradiation Heating

at 130

Coolingto room

temperature

Heatingto 130

∘C

∘C

(a)

Fluorescence

UVirradiation

Heatingat 130

Heatingto 130

Coolingto room

temperature∘C

∘C

(b)

Figure 5 PDA-LDH film induced by UV irradiation and its thermochromic behavior (a) and fluorescent transition (b) (A) the DA-LDHfilm (B) the PDA-LDH film obtained by UV irradiating (A) (C) the film by heating (B) at 130∘C for 1min (D) the film by cooling (C) toroom temperature [29]

chromophores with a rigid and ordered microenvironmentin which the severe interpenetration of the cis-trans groupsmay be restrained by the isolating effect of the 2D nanosheetsAn ordered distribution and alignment of the cis-transgroups with sufficient available free space in the nanogallerybetween the LDH nanosheets can also facilitate their pho-toisomerization efficiency In pioneering works Tagaya et al[38ndash40] have prepared sulfonated indolinespirobenzopyran(SP) intercalated into the MgAI and ZnAl LDHs whichwas premodified by toluene-p-sulfonic acid (PTS) The newintercalated nanocomposites exhibited reversible photoiso-merization between SP and merocyanine (MC) as shown inthe Figure 7 It was also noted that the presence of PTS play akey role in the reversible photoisomerization

Han et al [41] have reported the fabrication of hybridultrathin photoresponsive films based on LBL self-assemblyof LDH nanosheets and the azobenzene-containing polymer(PAZO) By irradiating the sample with UV light there isa progressive decrease in the maximum intensity of 120587-120587lowasttransition band and the 120587-120587lowast band nearly disappears aftersufficient irradiation time indicating an almost 100 trans-to-cis photoreaction The 120587-120587lowast absorption band increasesagainwith irradiation by visible light (120582 gt 450 nm) indicativeof the cis-trans back-isomerization of azobenzene Further-more alternate irradiation with UV and visible light resultsin a reversible switching between the trans- and cis-state ofthe azobenzene group with significant changes in film colorThe thin film of azobenzene derivative-intercalated LDH

6 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)

01 MPa313 Gpa625 Gpa938 Gpa

125 Gpa1563 Gpa1875 Gpa

(a)

450

460

470

480

490

500

510

520

0 5 10 15 20External pressure (GPa)

ZnAl = 3ZnAl = 2

MgAl = 3MgAl = 2Pristine BTZB

120582m

ax(n

m)

(b)

300 400 500 600 700 8000

02

04

06

08

1

01 MPa313 GPa625 GPa938 GPa

125 GPa1563 GPa1875 GPa

Abso

rptio

n

Wavelength (nm)

(c)

Figure 6 (a) Fluorescent spectra of the BTZBMg2Al-LDH at different pressures (inset fluorescent photographs under 365 nmUV light the

arrow shows the direction of the increasing pressure) (b) maximum emissive wavelength of BTZBLDHs at different pressures (c) UV-visspectra of the BTZBMg

2Al-LDH at different pressures [33]

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CeramicsJournal of

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CompositesJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Biomaterials

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NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

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MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

4 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

0 1 2 3 4 5440445450455460465470475

Inte

nsity

(au

)

Wavelength (nm)

20

100

20

Cycles

100

Heating

Cooling

1 cm

120582m

ax

∘C

∘C

∘C

∘C

(a)

10 15 20 25 30

10

100

1000

0 1 2 3 4 5

0608

112141618

22224

Cou

nts

Times (ns)

20100

100

20

Solution

Life

time (

ns)

Cycles (n)

∘C

∘C

∘C∘C

(b)

Figure 2 TCLof the BSBLDHUTF at 20 and 100∘C (a) Fluorescence spectra (inset the reversible fluorescence response over five consecutivecycles and photographs of the UTF before and after heating) (b) Fluorescence decay curve (inset fluorescence lifetimes over five consecutivecycles) [24]

A form H form

Figure 3 Tautomeric equilibrium between the A form and H formof AO5 [25]

on increasing the external pressure which can furtherinfluence the host-guest interactions [21] In additionthe long-chain BTZB anion has four rotatable aromaticamine units and thus its molecular conformation andintermolecular interactions can be tuned more easily byexternal perturbations than the rigid molecules Uponincreasing pressure BTZBLDH nanocomposites exhibitluminescent redshift with a concomitant broadening ofthe emission while the pristine BTZB shows no PCL atall The most significant PCL behavior is present in theBTZBMg

2Al-LDH sample and the maximum emissive

wavelength moves from 452 to 515 nm under differentstimuli (Figures 6(a) and 6(b)) The typical photographs ofthe BTZBMg

2Al-LDH pellet under UV light (Figure 6(a)

inset) display a visual luminescent change from blue togreen upon increasing pressure The redshift of spectra maybe attributed to the formation of J-type aggregates in thenanogallery of LDH An appreciable change in the UV-visabsorption band of BTZBMg

2Al-LDH nanocomposites was

also observed upon compression as shown in Figure 6(c)

Once the pressed BTZBMg2Al-LDH sample was ground

into powder heated at 100∘C and then cooled downthe luminescent peak at 515 nm moved back to 452 nmcompletely In addition the reversible luminescent colorchange can be readily repeated to switch between twopressures The reversible changes in fluorescence propertiescan be recycled at least 3 timesTherefore it can be concludedthat the BTZB-intercalated LDH material exhibits reversibleoptical responses (luminescent color absorption bandand fluorescent lifetime) upon changing external pressuremolecular dynamics and periodic density functionaltheoretical studies demonstrate that the PCL performanceoriginates from changes in the relative orientation andaggregation state of the interlayer BTZB Such materials mayserve as the fluorescent antiforgery devices

22 Photoinduced-Responsive Materials The photoinducedcis-trans isomerization of organic photofunctional materials(such as Schiff base and azobenzene derivative) has presentedmany interesting features and their applications range fromelectronics to nonlinear devices [34ndash37] In the solid state ofthese materials the penetration between adjacent functionalgroup and strong 120587-120587 stacking of chromophores may leadto a lack of sufficient free volume for the isomerization andlead to irreversibility or low efficiency of the process Thisis one of the main bottlenecks in developing optical deviceswith superior optical properties based on the molecularisomerization LDH nanosheets can provide the organic

Journal of Nanomaterials 5

02

04

06

08

Abso

rptio

n

300 350 400 450 500 550 600

363 nm

445 nm

65605550454035

Wavelength (nm)

∘C∘C∘C∘C∘C∘C∘C

(a)

04

045

05

055

06

065

Max

imum

abso

rptio

n at

445

nm

0 10 20 30 40 50 60 70Temperature

HeatingCooling

(b)

Figure 4 (a) In-situ absorption spectra of the 10 AO5-LDH film during heating in the temperature range 35ndash65∘C (b) The correlationbetween the absorbance of the band at 445 nm and temperature over a heating-cooling cycle [25]

Color

UVirradiation Heating

at 130

Coolingto room

temperature

Heatingto 130

∘C

∘C

(a)

Fluorescence

UVirradiation

Heatingat 130

Heatingto 130

Coolingto room

temperature∘C

∘C

(b)

Figure 5 PDA-LDH film induced by UV irradiation and its thermochromic behavior (a) and fluorescent transition (b) (A) the DA-LDHfilm (B) the PDA-LDH film obtained by UV irradiating (A) (C) the film by heating (B) at 130∘C for 1min (D) the film by cooling (C) toroom temperature [29]

chromophores with a rigid and ordered microenvironmentin which the severe interpenetration of the cis-trans groupsmay be restrained by the isolating effect of the 2D nanosheetsAn ordered distribution and alignment of the cis-transgroups with sufficient available free space in the nanogallerybetween the LDH nanosheets can also facilitate their pho-toisomerization efficiency In pioneering works Tagaya et al[38ndash40] have prepared sulfonated indolinespirobenzopyran(SP) intercalated into the MgAI and ZnAl LDHs whichwas premodified by toluene-p-sulfonic acid (PTS) The newintercalated nanocomposites exhibited reversible photoiso-merization between SP and merocyanine (MC) as shown inthe Figure 7 It was also noted that the presence of PTS play akey role in the reversible photoisomerization

Han et al [41] have reported the fabrication of hybridultrathin photoresponsive films based on LBL self-assemblyof LDH nanosheets and the azobenzene-containing polymer(PAZO) By irradiating the sample with UV light there isa progressive decrease in the maximum intensity of 120587-120587lowasttransition band and the 120587-120587lowast band nearly disappears aftersufficient irradiation time indicating an almost 100 trans-to-cis photoreaction The 120587-120587lowast absorption band increasesagainwith irradiation by visible light (120582 gt 450 nm) indicativeof the cis-trans back-isomerization of azobenzene Further-more alternate irradiation with UV and visible light resultsin a reversible switching between the trans- and cis-state ofthe azobenzene group with significant changes in film colorThe thin film of azobenzene derivative-intercalated LDH

6 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)

01 MPa313 Gpa625 Gpa938 Gpa

125 Gpa1563 Gpa1875 Gpa

(a)

450

460

470

480

490

500

510

520

0 5 10 15 20External pressure (GPa)

ZnAl = 3ZnAl = 2

MgAl = 3MgAl = 2Pristine BTZB

120582m

ax(n

m)

(b)

300 400 500 600 700 8000

02

04

06

08

1

01 MPa313 GPa625 GPa938 GPa

125 GPa1563 GPa1875 GPa

Abso

rptio

n

Wavelength (nm)

(c)

Figure 6 (a) Fluorescent spectra of the BTZBMg2Al-LDH at different pressures (inset fluorescent photographs under 365 nmUV light the

arrow shows the direction of the increasing pressure) (b) maximum emissive wavelength of BTZBLDHs at different pressures (c) UV-visspectra of the BTZBMg

2Al-LDH at different pressures [33]

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

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TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MetallurgyJournal of

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BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanomaterials 5

02

04

06

08

Abso

rptio

n

300 350 400 450 500 550 600

363 nm

445 nm

65605550454035

Wavelength (nm)

∘C∘C∘C∘C∘C∘C∘C

(a)

04

045

05

055

06

065

Max

imum

abso

rptio

n at

445

nm

0 10 20 30 40 50 60 70Temperature

HeatingCooling

(b)

Figure 4 (a) In-situ absorption spectra of the 10 AO5-LDH film during heating in the temperature range 35ndash65∘C (b) The correlationbetween the absorbance of the band at 445 nm and temperature over a heating-cooling cycle [25]

Color

UVirradiation Heating

at 130

Coolingto room

temperature

Heatingto 130

∘C

∘C

(a)

Fluorescence

UVirradiation

Heatingat 130

Heatingto 130

Coolingto room

temperature∘C

∘C

(b)

Figure 5 PDA-LDH film induced by UV irradiation and its thermochromic behavior (a) and fluorescent transition (b) (A) the DA-LDHfilm (B) the PDA-LDH film obtained by UV irradiating (A) (C) the film by heating (B) at 130∘C for 1min (D) the film by cooling (C) toroom temperature [29]

chromophores with a rigid and ordered microenvironmentin which the severe interpenetration of the cis-trans groupsmay be restrained by the isolating effect of the 2D nanosheetsAn ordered distribution and alignment of the cis-transgroups with sufficient available free space in the nanogallerybetween the LDH nanosheets can also facilitate their pho-toisomerization efficiency In pioneering works Tagaya et al[38ndash40] have prepared sulfonated indolinespirobenzopyran(SP) intercalated into the MgAI and ZnAl LDHs whichwas premodified by toluene-p-sulfonic acid (PTS) The newintercalated nanocomposites exhibited reversible photoiso-merization between SP and merocyanine (MC) as shown inthe Figure 7 It was also noted that the presence of PTS play akey role in the reversible photoisomerization

Han et al [41] have reported the fabrication of hybridultrathin photoresponsive films based on LBL self-assemblyof LDH nanosheets and the azobenzene-containing polymer(PAZO) By irradiating the sample with UV light there isa progressive decrease in the maximum intensity of 120587-120587lowasttransition band and the 120587-120587lowast band nearly disappears aftersufficient irradiation time indicating an almost 100 trans-to-cis photoreaction The 120587-120587lowast absorption band increasesagainwith irradiation by visible light (120582 gt 450 nm) indicativeof the cis-trans back-isomerization of azobenzene Further-more alternate irradiation with UV and visible light resultsin a reversible switching between the trans- and cis-state ofthe azobenzene group with significant changes in film colorThe thin film of azobenzene derivative-intercalated LDH

6 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)

01 MPa313 Gpa625 Gpa938 Gpa

125 Gpa1563 Gpa1875 Gpa

(a)

450

460

470

480

490

500

510

520

0 5 10 15 20External pressure (GPa)

ZnAl = 3ZnAl = 2

MgAl = 3MgAl = 2Pristine BTZB

120582m

ax(n

m)

(b)

300 400 500 600 700 8000

02

04

06

08

1

01 MPa313 GPa625 GPa938 GPa

125 GPa1563 GPa1875 GPa

Abso

rptio

n

Wavelength (nm)

(c)

Figure 6 (a) Fluorescent spectra of the BTZBMg2Al-LDH at different pressures (inset fluorescent photographs under 365 nmUV light the

arrow shows the direction of the increasing pressure) (b) maximum emissive wavelength of BTZBLDHs at different pressures (c) UV-visspectra of the BTZBMg

2Al-LDH at different pressures [33]

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

6 Journal of Nanomaterials

400 450 500 550 6000

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)

01 MPa313 Gpa625 Gpa938 Gpa

125 Gpa1563 Gpa1875 Gpa

(a)

450

460

470

480

490

500

510

520

0 5 10 15 20External pressure (GPa)

ZnAl = 3ZnAl = 2

MgAl = 3MgAl = 2Pristine BTZB

120582m

ax(n

m)

(b)

300 400 500 600 700 8000

02

04

06

08

1

01 MPa313 GPa625 GPa938 GPa

125 GPa1563 GPa1875 GPa

Abso

rptio

n

Wavelength (nm)

(c)

Figure 6 (a) Fluorescent spectra of the BTZBMg2Al-LDH at different pressures (inset fluorescent photographs under 365 nmUV light the

arrow shows the direction of the increasing pressure) (b) maximum emissive wavelength of BTZBLDHs at different pressures (c) UV-visspectra of the BTZBMg

2Al-LDH at different pressures [33]

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanomaterials 7

NO2N O

UV

VIS

CH3 CH3

NO2

Ominus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

SO3minus

CH3

CH3 CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3 CH3 CH3

(CH2)3

(CH2)3

+N

Figure 7 Possible mechanism for reversible photoisomerization of MC in LDH [40]

nanogallery can also influence the surface properties basedon the photoisomerization For example Chen et al [42] havefabricated a hybrid film with a fluorine-containing azoben-zene within the LDH on a porous anodic aluminaaluminumsubstrate Irradiation with UV light led to a switch inwettability of the film from superhydrophobic to hydrophilicas shown in Figure 8 and this process could be reversed bysubsequent irradiation with visible light Such behavior canbe assigned to the difference between the dipole moments oftrans- and cis-azobenzene isomers the film containing themore polar cis-isomer will become more hydrophilic whilethe trans-isomer makes the surface hydrophobic

Wang et al [43] have fabricated optically transparent thinfilms with photochromic properties by means of cointercala-tion of azomethine-H anions (AMH) and 1-pentanesulfonate(PS) with different molar ratios into the nanogallery of a Zn-Al-LDH XRD and SEM show that the film exhibits well-defined c-axis orientation Fluorescence spectra demonstratethat the sample with 2AMHmolar percentage with respectto the total organicmaterial exhibits the optimal luminescentintensity It was observed that the fluorescence lifetime oftrans-keto tautomer in the 2AMH-LDHfilm is shorter thanthat of AMH solution indicating the trans-keto tautomer ofAMH is less stable in the 2D confined environment and theground state of the enol tautomer is well stabilized in the LDHnanogallery The results demonstrate an effective methodfor the preparation of photochromic thin film materialsby co-intercalation of chromophore and dispersant into an

inorganic 2D host matrix which can be potentially appliedin the field of photoelectronic devices

23 Polarized and Electric-Induced Responsive LuminescenceThe device with polarized emission can significantly enhancethe quality of the back light of liquid-crystal displays [4445] The LDH nanosheets with a 2D layered structure areintrinsically anisotropic the luminescent guest with pre-ferred orientation between LDH nanogallery can exhibitspecial anisotropic emission characteristics Several exampleshave demonstrated that the ordered assembly of lumines-cent molecules into the LDH is undoubtedly favorable toproduce a uniform orientation of transition dipole momentfor polarized emission [12 15 46] Based on the differencein the emissive colors of the chromophores at differentpolarization direction it is possible to develop a new typeof color-switching materials upon stimuli by polarized lightRecently we have fabricated four types of heterogeneousmulticolor luminescentUTFmaterials (bluered blueyellowbluegreen and redgreen emission) by using differentphotofunctional anions [bis(N-methylacridinium)polyvi-nylsulfonate ion pairs and anionic derivatives of poly(p-phenylene) (APPP) poly(phenylenevinylene) (APPV) andpoly(thiophene) (APT)] and LDH nanosheets as buildingblocks [47] The strategy for fabricating multicolor lumi-nescent UTFs involves the stepwise assembly of individ-ual luminescent species and LDH nanosheets Therefore

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CeramicsJournal of

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CompositesJournal of

NanoparticlesJournal of

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Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

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BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

8 Journal of Nanomaterials

DSA measurement

UV

Vis

DSA measurement

Figure 8 Shapes of a water droplet on the LDH hybrid film surface showing reversible superhydrophobicity and hydrophilicity induced byUV and visible irradiation [42]

the composition and loading of the luminescent species arefinely controlled by adjusting the assembly sequence andcycle number which is beneficial to the tunable multicoloremission By changing the polarization direction of thetwo-color UTFs with a single excitation wavelength it wasobserved that the intensity ratios for the two lumines-cence spectral regions were different suggesting that therelative intensities of the two luminescence colors and theoverall emission color are tuned by changing the polariza-tion direction For the (APPPLDH)

12(APPVLDH)

9UTF

the ratio of the intensities of luminescence at 410 and550 nm (119868

410119868550) was 125 for the 119868VV polarization while

it was only 071 for the 119868VH polarization (Figure 9(a)) Forthe (APPPLDH)

12(APTLDH)

9UTF the intensity ratio

119868410119868575

had values of 165 (119868VV polarization mode) and094 (119868VH polarization mode) respectively (Figure 9(b)) Thevariation in intensity ratio with polarization mode can beassociated with the orientation and arrangement of the chro-mophores in the UTFs We anticipate that these polarized-responsive luminescent UTFs can act as a possible colorconversion layer in flat-panel displays for future lightingdevices

From a stimuli-responsive perspective the electrolu-minescence (EL) can be regarded as an electric-inducedresponsive luminescence behavior of device Quantum dots(QDs) with their tunable photoluminescence and band gapare expected to play an important role in future displays[48 49] However EL devices based on QDs have oftensuffered from relative low efficiency short lifetimes or theneed of specialized deposition technique Bendall et al [50]have developed an all-inorganic EL device based on highlyluminescent CdTe QD assembled LDH nanosheets by usinga simple wet chemical process The operating conditionswere chosen to mimic the situation within an automotiveenvironment and the architecture of the device is shown inFigure 10 EL emission peak of the device is located at 637 nmCompared with the photoluminescence (PL) emission peakof the bareQD no shift in the peak position is detected for theEL peak and no significant change in the peak width occursSuch evidence demonstrates that the emission is solely dueto the CdTe QD The advantage of this device is that theoperating temperatures can be over 80∘C due to the all-inorganic materials The authors believe the devices will haveapplications within harsh environments such as automobile

lighting and entertainment or outdoor signaling The ease offabricationwill also provide simple and low cost light sources

3 LDH-Based ChemicalStimuli-Responsive Properties

31 pH-Responsive Luminescent Materials The pH fluores-cence chemosensors play critical roles in studying physiolog-ical activities influenced by pH value widely used in fieldsof analytical chemistry bioanalytical chemistry cytobiologyandmedical science [53 54]The traditional solid hostmatrix(eg sol-gel polymer) has some inherent demerits such asrelatively poor thermal or optical stability as well as toxicitywhich have limited the practical application in pH sensorsto date LDHs with a stable interlayer structure have highlyenhanced the opticalthermal stability and environmentalcompatibility of the interlayer chromophore molecules andcan be used as a new host matrix in more potentialapplications Yan et al [51] have fabricated a luminescentordered UTF based on a anionic polythiophene (APT) andMg-Al-LDH nanosheets by the LBL assembly method Thedependence of the maximum emission wavelength (120582max)on the pH value is divided into three main zones the 120582maxdecreases sharply from 591 to 578 nm as the pH value isdecreased from 14 to 12 it decreases very slightly from578 to 574 nm when the pH value decreases from 12 to 8finally when the pH value is decreased from 8 to 4 the 120582maxundergoes a decrease from 574 to 562 nm which shows anearly linear relationship with the pH The sensitivity of thefluorescence performance of theAPTLDHUTFs to pHvaluecan be attributed to the varying extent of protonation anddeprotonation of APT between the LDH nanosheets Typicalphotographs of the luminescence of the UTF under two pHconditions are shown in the inset of Figure 11 from which itcan be observed that the UTF shows bright red luminescenceand a relatively dark orange color at pH = 13 and pH =4 respectively under UV illumination The APTLDH UTFalso exhibits reversible emissive response at different pHvalues indicating its potential application as a pH-sensitiveluminescence sensor

Base on the example above it can be known that the selec-tion of a suitable fluorescent compound with high responseto H+ in solution is of great importance for fabricatingpH-sensitive optical materials Shi et al [55] have reported

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanomaterials 9

400 450 500 550 600 6500

2 k

4 k

6 k

8 k

10 k

12 k

01

02

03

04

05

06

07

08

Inte

nsity

(au

)

Wavelength (nm)

VVVH

119903

119868410119868550 = 125

119868410119868550 = 071

(a)

400 450 500 550 600 6500

1 k

2 k

3 k

4 k

5 k

6 k

0

02

04

06

08

1

Inte

nsity

(au

)

Wavelength (nm)VVVH

119903

119868410119868575 = 165

119868410119868575 = 094

(b)

Figure 9 Polarized fluorescence profiles with glancing incidence geometry in the VV and VH modes and the anisotropy value (r) for two-color luminescent UTFs (a) the (APPPLDH)

12(APPVLDH)

9UTF (b) the (APPPLDH)

12(APTLDH)

9UTF [47]

Al electrode

ITO (patterned)Glass

Emitted light

Active layerLDHCdTe QDsLDHCdTe QDsLDHCdTe QDsLDH

Active layerndashLDH and CdTe

Figure 10 (a) Schematic of the architecture of the device which is based on a ldquosandwichrdquo structure with alternating LDH nanosheets andCdTe QDs [50]

a highly oriented photoluminescent film with film thicknessof 300 nm based on the fluorescein and 1-heptanesulfonicacid sodium co-intercalated into LDH matrix The filmexhibits a broad linear dynamic range for solution with pHvalue from 502 to 854 Good repeatability and reversibilityhave also been demonstrated its relative standard deviation(RSD) is less than 15 in 20 consecutive cycles

32 Metal Ion Responsive Luminescent Materials The recog-nition of heavy metal ions (HMIs) is important in the fieldsof chemistry biotechnology medicine and environmentalscience [56] For instance HMIs dispersed in an aqueoussolution system (such as Hg2+ and Cd2+) can induce severepollutions which give rise to toxication and several dis-eases of organisms [57] Thus fast and effective detectionof HMIs has drawn much attention from both scientificand engineering viewpoints during the last few years Thedetermination of HMIs has been generally carried out basedon atomic absorption spectrometry [58] and inductivelycoupled plasma spectroscopy technique [59] which not onlyhave good sensitivity and fast measurement capabilities but

also require expensive instruments well-controlled experi-mental conditions and complicated procedures Due to thehigh sensitivity selectivity fast response low cost and easysignal detection the fluorescence-based chemical analysisshould be a good method for determining and monitoringcontaminants In this sense organic luminescent moleculeshave recently become good candidates to detect themetal ionbased on the selective quenching effects of the metal ions inthe solution of the luminescent molecules [60] For exampleTao et al [61] have reported that the synthesized120587-conjugatedpolymer exhibits a selective fluorescence quenching by Cu2+Cao et al [62] found that a metal-organic framework pow-der exhibited fluorescence quenching by the solutions ofHMIs To date most of the reported organic luminescencesystems used for detecting metal ions are in the form ofsolution or powder systems whereas this is unfavorable forits facile manipulation and cycling utility Moreover mostof the luminescent dye solutions can induce environmentalpollution and even operational risk which are detrimental tohuman healthTherefore there continues to be a challenge todevelop new types of solid luminescent film systems to meet

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

10 Journal of Nanomaterials

4 6 8 10 12 14

560

565

570

575

580

585

590

595

pH value

120582m

ax(n

m)

(a)

0 1 2 3 4 5 6

552

560

568

576

584

592

600

pH = 4

Cycles number

pH = 13

120582m

ax(n

m)

(b)

Figure 11 (a) Variation of the maximum photoemission wavelength of the APTLDH film with different pH values (b) the reversiblephotoemission response upon alternation between pH = 4 and pH = 13 (the inset show the luminescence photographs of the film atthe two pH conditions) [51]

the need for the integration of high selectivity for the HMIsand efficient manipulation

Mercury is considered one of the most toxic elementswhich are widely distributed in air water and soil [63 64]As a consequence of this pollution mercury can accumulatein the human body which causes a wide variety of diseaseseven in a low concentration such as digestive kidney andneurological disorders Sun et al [65] have reported thatan optical thin film can serve as chemosensor based on1-amino-8-naphthol-36-disulfonic acid sodium (H-acid)intercalated LDH The H-acidLDH film chemosensorwas immersed into Hg2+ aqueous solutions with differentconcentrations at pH value 70 for 10min then was washedthoroughly and dried at 60∘C for 20min It was found thatthe fluorescence intensity increases at first to a maximumand then decreases along with the increase of pH valueWith the presence of other metal ions and commonanions (Cr3+ Mn2+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+Mg2+ Ca2+ Li+ Na+ K+ Al3+ Pb2+ Clminus and NO

3

minus)

which are possible competitive ions in practical determina-tion the results show no significant effect on the resultsdemonstrating a strong resistance to interference This filmcan be potentially used as a chemosensor for the detection ofHg2+ ion in the environmental and biological field Yan et al[66] have prepared the UTFs with blue luminescence basedon a styrylbiphenyl derivative (BTBS) and Mg-Al-LDHnanosheets The luminescence spectra of the (BTBS-LDH)

32

UTF measured after immersing it in different metal cationicaqueous solutions (Hg2+ Cu2+ Pb2+ Cd2+ Cr3+ Ca2+Mn2+ Co2+ Zn2+ and Fe3+) with varying concentrations(from 10minus5 to 10minus2M) showed the fluorescence intensityof the UTF decreases systematically upon increasing theion concentration and the Hg2+ has the most significanteffect on the luminescence quenching of the UTFs with adetection limit of 23 times 10minus7molsdotLminus1 After the UTF was

treated with 001M EDTA aqueous solution for 30 s followedby thorough washing and drying the fluorescence intensitycan nearly recover to its initial state with 5 cycles at least

Magnesium ion being the most abundant intracellulardivalent cation plays a major role in many cellular processesincluding stabilization of DNA conformation ion transportthrough the membrane and signal transduction Addition-ally the activity of magnesium in blood and serum is animportant clinical parameter that needs to be monitored indifferent situations All these provide sufficient impetus tofabricate chemical sensors for the detection of magnesium[67 68] Jin et al [69] have prepared a 8-aminonaphthalene-136-trisulfonate (ANTS)LDH fluorescent film by an elec-trophoretic deposition (EPD) method The ANTSLDH filmshows a good fluorescent response for Mg2+ ion In additionthe linear correlation (1198772) between the fluorescence intensityof the ANTSLDH and the concentration of Mg2+ is 0996with a detection limit of 237 times 10minus7M The results exhib-ited that ANTSLDH film has a considerable fluorescenceselectivity for Mg2+ ions with no significant response toother metal ions (Ca2+ Na+ K+ Fe3+ Co2+ Ni2+ or Cu2+)which indicated a high fluorescence selectivity for Mg2+ions

Compared with intensity-based sensors ratiometric flu-orescence systems are preferred in bioimaging applicationsbecause such measurement involves the change of intensityratio of emission at two wavelengths which eliminatesinterferences from environment and increases the selectivityand sensitivity effectively For example Ji et al [52] have builta fluorescence sensor for Be2+ with high selective response byalternate assembly of Beryllon II andMg-Al-LDHnanosheetson quartz substrates using the LBL deposition techniqueThe Beryllon IILDHUTFs displays ratiometric fluorescenceresponse for Be2+ (Figure 12(a)) with a linear response rangein 10 times 10minus7ndash19 times 10minus6molsdotLminus1 and a detection limit of

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanomaterials 11

360 405 450 495 540 585Wavelength (nm)

0

200

400

600

800

1000

Inte

nsity

(au

)

375 nm

425 nm

(a)

(k)

09

1

11

12

13

14

15

16

17

18

0 02 04 06 08 1 12 14 16 18 2 22 24 26

(a)

(b)

(a) [Be2+] = 0 120583m (b) [Be2+] = 01120583m(c) [Be2+] = 03 120583m (d) [Be2+] = 05120583m(e) [Be2+] = 07 120583m (f) [Be2+] = 09120583m

(g) [Be2+] = 11120583m (h) [Be2+] = 13120583m (i) [Be2+] = 15120583m (j) [Be2+] = 17120583m (k) [Be2+] = 19120583m (l) [Be2+] = 21120583m(m) [Be2+] = 23 120583m

1198772 = 0994

119868 425119868375

[Be2+] (120583M)

Figure 12 (a) Emission spectra of the (Beryllon IILDH)20UTF upon increasing Be2+ concentration at pH = 11 (b) Be2+ titration curve of

the chemosensor for emission ratio at 425ndash375 nm (119868425

119868375

) [52]

42 times 10minus9molsdotLminus1 (Figure 12(b)) Evaluated with other com-petitive species (Zn2+ Al3+ Co2+ Mg2+ Cd2+ Ca2+ Hg2+Cu2+ Pb2+ Ni2+ and Mn2+) the Beryllon IILDH UTF dis-plays a good selectivity towards Be2+ A high thermodynamicaffinity of Be2+ toward typical N and S-chelate ligands andfastmetal-to-ligand binding kinetics lead to the complexationof Be2+ with Beryllon II in the UTF which is the result offluorescence quenching

4 Conclusions and Outlook

The assembly of photoactive chromophore within the na-nogallery of LDH can provide a facile way to develop newtypes of stimuli-responsive materials with host-guest struc-tures which also present enhanced properties (such as highphoto-optical stability and good operability) By designingand choosing the suitable photoactive chromophores andLDH layers as basic building blocks these organic-inorganic

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

12 Journal of Nanomaterials

hybrid nanomaterials (ultrathin films and nanocomposites)have presented promising applications in the field of switchesof piezochromic photochromic thermochromic and polar-ized luminescence as well as pHmetal sensors To meet theneed of practical application further studies should be putin how to finely regular and control the arrangement andorientation of the guest chromophore and how to maintainthe uniform and ordered thin film system In addition chal-lenges for stimuli-responsive host-guest materials includehow to further enhance the photo-thermoisomerization effi-ciency and repeatability Moreover despite several researcheson single-stimulus-responsive property of such materialsdevelopment onmultistimuli-responsive smart materials stillremains in its fancy and has been very seldom studiedThis can be an important strategy and direction to developmultifunctional materials Last but not least the responsetime and onoff ratio of these switches and sensors for real-time applications should also be taken in account in next stepresearches

Acknowledgments

This work was supported by the National Natural Sci-ence Foundation of China the 973 Program (Grant no2011CBA00504) 111 Project (Grant no B07004) andProgramfor Changjiang Scholars and Innovative Research Team inUniversity (PCSIRT IRT1205)

References

[1] M Irie T Fukaminato T Sasaki N Tamai and T Kawai ldquoAdigital fluorescent molecular photoswitchrdquoNature vol 420 no6917 pp 759ndash760 2002

[2] C Lowe and C Weder ldquoOligo(p-phenylene vinylene) excimersas molecular probes deformation-induced color changes inphotoluminescent polymer blendsrdquoAdvancedMaterials vol 14no 22 pp 1625ndash1629 2002

[3] T Mutai H Tomoda T Ohkawa Y Yabe and K ArakildquoSwitching of polymorph-dependent ESIPT luminescence ofan imidazo[12-a]pyridine derivativerdquo Angewandte ChemiemdashInternational Edition vol 120 no 49 pp 9664ndash9666 2008

[4] J Kunzelman M Kinami B R Crenshaw J D Protasiewiczand C Weder ldquoOligo(p-phenylene vinylene)s as a rdquonewrdquo classof piezochromic fluorophoresrdquo Advanced Materials vol 20 no1 pp 119ndash122 2008

[5] T Fukaminato andM Irie ldquoReversible fluorescence wavelengthshift based on photoinduced aggregate formationrdquo AdvancedMaterials vol 18 no 24 pp 3225ndash3228 2006

[6] N Chandrasekharan and L A Kelly ldquoA dual fluorescence tem-perature sensor based on peryleneexciplex interconversionrdquoJournal of the American Chemical Society vol 123 no 40 pp9898ndash9899 2001

[7] J Kunzelman B R Crenshaw and C Weder ldquoSelf-assembly ofchromogenic dyesmdasha new mechanism for humidity sensorsrdquoJournal of Materials Chemistry vol 17 no 29 pp 2989ndash29912007

[8] C Xia and R C Advincula ldquoDecreased aggregation phenom-ena in polyfluorenes by introducing carbazole copolymer unitsrdquoMacromolecules vol 34 no 17 pp 5854ndash5859 2001

[9] V Rives Layered Double Hydroxides Present and Future NovaScience New York NY USA 2001

[10] F Li and X Duan ldquoApplications of layered double hydroxiderdquoStructure and Bonding vol 119 pp 193ndash223 2006

[11] S P Newman and W Jones ldquoSynthesis characterization andapplications of layered double hydroxides containing organicguestsrdquo New Journal of Chemistry vol 22 no 2 pp 105ndash1151998

[12] D P Yan J Lu M Wei D G Evans and X Duan ldquoSulforho-damine B intercalated layered double hydroxide thin film withpolarized photoluminescencerdquo Journal of Physical Chemistry Bvol 113 no 5 pp 1381ndash1388 2009

[13] D P Yan J Lu J Ma M Wei D G Evans and X DuanldquoBenzocarbazole anions intercalated layered double hydroxideand its tunable fluorescencerdquo Physical Chemistry ChemicalPhysics vol 12 no 45 pp 15085ndash15092 2010

[14] W Shi M Wei J Lu et al ldquoMolecular orientation andfluorescence studies on naphthalene acetate intercalated Zn

2Al

layered double hydroxiderdquo Journal of Physical Chemistry C vol112 no 50 pp 19886ndash19895 2008

[15] D P Yan J LuMWei et al ldquoPoly(p-phenylene) anionic deriva-tivelayered double hydroxides ordered ultra thin films withblue luminescence by layer-by-layer assemblyrdquo AngewandteChemiemdashInternational Edition vol 48 no 17 pp 3073ndash30762009

[16] D P Yan J Lu J Ma et al ldquoAnionic poly(p-phenylenevinyl-ene)layered double hydroxide ordered ultrathin films withmultiple quantumwell structure a combined experimental andtheoretical studyrdquo Langmuir vol 26 no 10 pp 7007ndash7014 2010

[17] S Li J Lu M Wei D G Evans and X Duan ldquoTris(8-hydroxyquinoline-5-sulfonate)aluminum intercalated Mg-Allayered double hydroxidewith blue luminescence by hydrother-mal synthesisrdquo Advanced Functional Materials vol 20 no 17pp 2848ndash2856 2010

[18] D P Yan J Lu M Wei J Ma D G Evans and X Duan ldquoAcombined study based on experiment and molecular dynam-ics perylene tetracarboxylate intercalated in a layered doublehydroxide matrixrdquo Physical Chemistry Chemical Physics vol 11no 40 pp 9200ndash9209 2009

[19] D P Yan J Lu M Wei D G Evans and X Duan ldquoRecentadvances in photofunctional guestlayered double hydroxidehost composite systems and their applications experimentaland theoretical perspectivesrdquo Journal of Materials Chemistryvol 21 pp 13128ndash13139 2011

[20] I McCulloch M Heeney C Bailey et al ldquoLiquid-crystallinesemiconducting polymers with high charge-carrier mobilityrdquoNature Materials vol 5 no 4 pp 328ndash333 2006

[21] M A Thyveetil P V Coveney H C Greenwell and J LSuter ldquoRole of host layer flexibility in DNA guest intercalationrevealed by computer simulation of layered nanomaterialsrdquoJournal of the American Chemical Society vol 130 no 37 pp12485ndash12495 2008

[22] L Tian F He H Zhang et al ldquoThermal cycloaddition facili-tated by orthogonal 120587-120587 organization through conformationaltransfer in a swivel-cruciform oligo (phenylenevinylene)rdquoAngewandte ChemiemdashInternational Edition vol 46 no 18 pp3245ndash3248 2007

[23] H Meier ldquoConjugated oligomers with terminal donor-acceptorsubstitutionrdquo Angewandte ChemiemdashInternational Edition vol44 no 17 pp 2482ndash2506 2005

[24] D P Yan J Lu M Wei J Ma D G Evans and XDuan ldquoReversibly thermochromic fluorescent ultrathin films

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanomaterials 13

with a supramolecular architecturerdquo Angewandte ChemiemdashInternational Edition vol 50 no 3 pp 720ndash723 2011

[25] X Wang J Lu W Shi et al ldquoA thermochromic thin filmbased on host-guest interactions in a layered double hydroxiderdquoLangmuir vol 26 no 2 pp 1247ndash1253 2010

[26] M Inouye K Tsuchiya and T Kitao ldquoNew thermo-responsedyes coloration by the claisen rearrangement and intramolec-ular acid-base reactionrdquo Angewandte ChemiemdashInternationalEdition vol 31 no 2 pp 204ndash205 1992

[27] A Sarkar S Okada H Matsuzawa HMatsuda and H Nakan-ishi ldquoNovel polydiacetylenes for optical materials beyond theconventional polydiacetylenesrdquo Journal of Materials Chemistryvol 10 no 4 pp 819ndash828 2000

[28] H J Cho K Seo C J Lee H Yun and J Y Chang ldquoRodlikemesogenic molecules consisting of two diacetylenic groupsmesomorphic behavior and photoimagingrdquo Journal ofMaterialsChemistry vol 13 no 5 pp 986ndash990 2003

[29] W Y Shi Y J Lin S He et al ldquoPatterned fluorescence filmswithreversible thermal response based on the host-guest superarch-itecturerdquo Journal of Materials Chemistry vol 21 pp 11116ndash111222011

[30] Z G Chi and J R Xu ldquoNew thermally stable piezofluo-rochromic aggregation-induced emission compoundsrdquoOrganicLetters vol 13 no 4 pp 556ndash559 2011

[31] X Zhang Z Chi H Li et al ldquoPiezofluorochromism of anaggregation-induced emission compound derived from tetra-phenylethylenerdquo Chemistry vol 6 no 3 pp 808ndash811 2011

[32] Z Chi X Zhang B Xu et al ldquoRecent advances in organic me-chanofluorochromic materialsrdquo Chemical Society Reviews vol41 no 10 pp 3878ndash3896 2012

[33] D P Yan J Lu J Ma et al ldquoLayered host-guest materials withreversible piezochromic luminescencerdquo Angewandte ChemiemdashInternational Edition vol 50 no 31 pp 7037ndash7040 2011

[34] J Zhang Q Zou and H Tian ldquoPhotochromic materials morethan meets the eyerdquo Advanced Materials vol 25 no 3 pp 378ndash399 2012

[35] T F Tan P L Chen H M Huang and J B Meng ldquoSyn-thesis characterization and photochromic studies in film ofheterocycle-containing spirooxazinesrdquo Tetrahedron vol 61 no34 pp 8192ndash8198 2005

[36] H Durr ldquoPerspective in photochromism-based on the l-5-eleetroeyclization of heteroanalogous pentadienyl anionsrdquoAngewandte ChemiemdashInternational Edition vol 28 pp 413ndash431 1989

[37] E H Kang T Bu P Jin J Sun Y Yang and J ShenldquoLayer-by-layer deposited organicinorganic hybrid multilayerfilms containing noncentrosymmetrically orientated azoben-zene chromophoresrdquo Langmuir vol 23 no 14 pp 7594ndash76012007

[38] H Tagaya T Kuwahara S Sato J I Kadokawa M Karasu andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inlayered double hydroxidesrdquo Journal of Materials Chemistry vol3 no 3 pp 317ndash318 1993

[39] T Kuwahara H Tagaya and K Chiba ldquoPhotochromism ofspiropyran dye in Li-Al layered double hydroxiderdquoMicroporousMaterials vol 4 no 2-3 pp 247ndash250 1995

[40] H Tagaya S Sato T Kuwahara J I Kadokawa K Masa andK Chiba ldquoPhotoisomerization of indolinespirobenzopyran inanionic clay matrices of layered double hydroxidesrdquo Journal ofMaterials Chemistry vol 4 no 12 pp 1907ndash1912 1994

[41] J B Han D P Yan W Y Shi et al ldquoLayer-by-layer ultra-thin films of azobenzene-containing polymerlayered doublehydroxides with reversible photoresponsive behaviorrdquo Journalof Physical Chemistry B vol 114 no 17 pp 5678ndash5685 2010

[42] T Chen S Xu F Zhang D G Evans and X Duan ldquoFormationof photo- and thermo-stable layered double hydroxide filmswith photo-responsive wettability by intercalation of function-alized azobenzenesrdquo Chemical Engineering Science vol 64 no21 pp 4350ndash4357 2009

[43] X R Wang J Lu D P Yan M Wei D G Evans and XDuan ldquoA photochromic thin film based on salicylideneanilinederivatives intercalated layered double hydroxiderdquo ChemicalPhysics Letters vol 493 no 4-6 pp 333ndash339 2010

[44] C Weder C Sarwa A Montali C Bastiaansen and P SmithldquoIncorporation of photoluminescent polarizers into liquid crys-tal displaysrdquo Science vol 279 no 5352 pp 835ndash837 1998

[45] B Zhou Y Lin L Monica Veca K A Shiral FernandoB A Harruff and Y P Sun ldquoLuminescence polarizationspectroscopy study of functionalized carbon nanotubes in apolymeric matrixrdquo Journal of Physical Chemistry B vol 110 no7 pp 3001ndash3006 2006

[46] D P Yan S Qin L Chen et al ldquoThin film of sulfonatedzinc phthalocyaninelayered double hydroxide for achievingmultiple quantum well structure and polarized luminescencerdquoChemical Communications vol 46 no 45 pp 8654ndash8656 2010

[47] D P Yan J Lu M Wei et al ldquoHeterogeneous transparentultrathin films with tunable-color luminescence based on theassembly of photoactive organic molecules and layered doublehyroxidesrdquo Advanced Functional Materials vol 21 no 13 pp2497ndash2505 2011

[48] G Mingyuan C Lesser S Kirstein E Mohwald A L Rogachand H Weller ldquoElectroluminescence of different colors frompolycationCdTe nanocrystal self-assembled filmsrdquo Journal ofApplied Physics vol 87 no 5 pp 2297ndash2302 2000

[49] W Chung K Park H J Yu J Kim B H Chun and S HKim ldquoWhite emission using mixtures of CdSe quantum dotsand PMMA as a phosphorrdquo Optical Materials vol 32 no 4 pp515ndash521 2010

[50] J S Bendall M Paderi F Ghigliotti et al ldquoLayer-by-layer all-inorganic quantum-dot-based LEDs a simple procedure withrobust performancerdquo Advanced Functional Materials vol 20no 19 pp 3298ndash3302 2010

[51] D P Yan J Lu J Ma M Wei D G Evans and X Duan ldquoFab-rication of an anionic polythiophenelayered double hydroxideultrathin film showing red luminescence and reversible pHphotoresponserdquo AIChE Journal vol 57 no 7 pp 1926ndash19352011

[52] X L JiW Y Shi S T ZhangMWei D G Evans and X DuanldquoA ratiometric fluorescence sensor for Be2+ based on BeryllonIIlayered double hydroxide ultrathin filmsrdquo Analytica ChimicaActa vol 728 pp 77ndash85 2012

[53] I Roy and M N Gupta ldquoSmart polymeric materials emergingbiochemical applicationsrdquo Chemistry amp Biology vol 10 no 12pp 1161ndash1171 2003

[54] E S Gil and S M Hudson ldquoStimuli-responsive polymers andtheir bio-conjugatesrdquo Progress in Polymer Science vol 29 no 12pp 1173ndash1222 2004

[55] W Y Shi S He MWei D G Evans and X Duan ldquoOptical pHsensor with rapid response based on a fluorescein-intercalatedlayered double hydroxiderdquo Advanced Functional Materials vol20 no 22 pp 3856ndash3863 2010

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

14 Journal of Nanomaterials

[56] H N Kim Z Guo W Zhu J Yoon and H Tian ldquoRecentprogress on polymer-based fluorescent and colorimetric che-mosensorsrdquo Chemical Society Reviews vol 40 no 1 pp 79ndash932011

[57] S Yoon EWMiller Q He P H Do and C J Chang ldquoA brightand specific fluorescent sensor for mercury in water cells andtissuerdquo Angewandte ChemiemdashInternational Edition vol 46 no35 pp 6658ndash6661 2007

[58] J V Cizdziel and S Gerstenberger ldquoDetermination of totalmercury in human hair and animal fur by combustion atomicabsorption spectrometryrdquo Talanta vol 64 no 4 pp 918ndash9212004

[59] S C Hight and J Cheng ldquoDetermination of methylmercuryand estimation of total mercury in seafood using high perfor-mance liquid chromatography (HPLC) and inductively coupledplasma-mass spectrometry (ICP-MS) method developmentand validationrdquoAnalytica Chimica Acta vol 567 no 2 pp 160ndash172 2006

[60] MWangG ZhangD ZhangD Zhu andB Z Tang ldquoFluores-cent biochemosensors based on silole and tetraphenyletheneluminogens with aggregation-induced emission featurerdquo Jour-nal of Materials Chemistry vol 20 no 10 pp 1858ndash1867 2010

[61] X Tao Y Liu and K S Schanze ldquoA conjugated polyelectrolyte-based fluorescence sensor for pyrophosphaterdquo Chemical Com-munications no 28 pp 2914ndash2916 2007

[62] Y Cao Y Cui Q Zheng S Xiang G Qian and B Chen ldquoAmicroporous luminescent metal-organic framework for highlyselective and sensitive sensing of Cu2+ in aqueous solutionrdquoChemical Communications vol 46 no 30 pp 5503ndash5505 2010

[63] I Onyido A R Norris and E Buncel ldquoBiomolecule-mercuryinteractions modalities of DNA base-mercury binding mecha-nisms Remediation strategiesrdquo Chemical Reviews vol 104 no12 pp 5911ndash5929 2004

[64] N S Bloom A K Grout and E M Prestbo ldquoDevelopmentand complete validation of a method for the determination ofdimethyl mercury in air and other mediardquo Analytica ChimicaActa vol 546 no 1 pp 92ndash101 2005

[65] Z Y Sun L Jin S T Zhang et al ldquoAn optical sensor based onH-acidlayered double hydroxide composite film for the selectivedetection of mercury ionrdquo Analytica Chimica Acta vol 702 no1 pp 95ndash101 2011

[66] D P Yan J LuMWei D G Evans andXDuan ldquoLuminescentultrathin film of the anionic styrylbiphenyl derivativeslayereddouble hydroxide and its reversible sensing for heavy metalionsrdquo Physical Chemistry Chemical Physics vol 14 no 24 pp8591ndash8598 2012

[67] M Ishida YNaruta andF Tani ldquoAPorphyrin-relatedmacrocy-cle with an embedded 110-phenanthroline moiety fluorescentmagnesium(II) ion sensorrdquoAngewandte ChemiemdashInternationalEdition vol 49 no 1 pp 91ndash94 2010

[68] J L Lopez A Tarraga A Espinosa et al ldquoA new multifunc-tional ferrocenyl-substituted ferrocenophane derivative opticaland electronic properties and selective recognition of Mg2+ionsrdquo Chemistry vol 10 no 7 pp 1815ndash1826 2004

[69] L Jin Z J Guo Z Y Sun A Li Q Jin and M Wei ldquoAssemblyof 8-aminonaphthalene-136-trisulfonate intercalated layereddouble hydroxide film for the selective detection of Mg2+ rdquoSensors and Actuators B vol 161 pp 714ndash720 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

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