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Patterning through Controlled Submolecular Motion: Rotaxane-Based Switches and Logic Gates th
at Function in Solution and Polymer Films
David A. Leigh et al.
Angew. Chem. Int. Ed. 2005, 44, 3062-3067
Tobe Lab.
Keiji Nishihara
Contents
・ Introduction
・ Results and Discussions
・ Summary
Rotaxane Structure
Molecular Switches
Materials Applications
Rotaxane Structure
・ Macrocycle and thread are mechanically interlocked but are not covalently bonded.
High mobility
ex. Shuttling, Circumrotation
・ Synthesis of rotaxane was very difficult for its peculiar structure.
・ By using host-guest interaction or self-assembly, synthesis of rotaxane becomes more easily and efficiently since the late 1980s.
Stopper
Macrocycle
ThreadRotaxane
Shuttling
Circumrotation
Concept of Molecular Switches
Response : conductivity, circular dichroism, fluorescence
External stimuli : light, redox, protonation, pH, temperature, solvent effect
Shuttling
Station: the site where the macrocyle exists stable or =
・ A rotaxane in which the positon of macrocycle can be controlled by changing the stability of station with external stimuli.
Molecular Switches
“Off state”
“On state”
Materials Applications
The electrochromic response of the solid-state polymer devices.
Green
ground-state:
after a +1 V oxidizing potential:
Red/Purple
relaxed back to the ground-state:
Green
Only simple rotaxanes have been used to create patterned surfaces.
・ There are few examples where shuttling has been demonstrated in polymer-based media.
Suitable for materials applications
J. R. Heath et al., Angew. Chem. Int. Ed. 2004, 43, 6486-6491.
D. A. Leigh et al., Science 2003, 299, 531.
Design of Thread 1
Anthracene: fluorophore
(also act as “stopper”)
Glycylglycine: hydrogen-bonding site, “station”
C11 alkyl chain: “solvophobic” station
Second stopper
Design of Rotaxane 2, 3, and 3 ・ 2H+ ・ 2CF3
CO2-
・ Quenching the fluorescence of anthracene though distance-dependent electron transfer
Partial 1H NMR spectra in CDCl3 (400
MHz, 298 K)
・ The signals for Hc and He of glycylglycine station are shielded by =1.2 and 0.4 ppm in the rotaxane.
The macrocycle resides principally over the peptide residue of the rotaxane.
rotaxane 2
thread 1
X-ray crystal structure of 3’(3’: a close structural analogue of rotaxane 3.)
・ the macrocycle binding to the glycylglycine station though a network of intercomponent hydrogen bonds.
Partial 1H NMR spectra in [D6]DMSO (400 MHz, 298 K)
thread 1
rotaxane 2
・ the signals of the alkyl chain: strongly shielded
・ the signals of the glycylglycine unit: essentially unchanged
The macrocycle encapsulates the alkyl chain.
alkyl chain
Functional group interaction in solution
・ Solvent effect
In CHCl3 (chloroform)
In DMSO (dimethylsulfoxide) S
O
H3C CH3
C
Cl
H
Cl
Cl
amide-amide hydogen bonding : more favorable
alkyl chain-phenyl ring solvophobic interaction: favorable
: nonpolar solvent
: aprotic polar solvent
DMSO molecule: solvation
CHCl3 molecule: solvation
the macrocycle held firmly on the peptide station
the macrocycle to be localized on alkyl-chain station
Fluorescence of rotaxane 2
in CH2Cl2
in DMSO
・ The ratio of fluorescence quantum yields is as high as 15: 1
(lex=340 nm, 1 x 10-5 M, 298 K)
・ The variations in intensity observed with the different solvents is caused by the change in the relative separation of the fluorophore and quencher.
The switching mechanism in solution:
Polymer analogues of 2 and 3
・ [2]rotaxane P5 and P6 contained approximately 10% w/w of peptide rotaxane endgroups.
The behavior of polymers P5 and P6 in solution exactly mirrored those of the small-molecule analogues, 2 and 3.
・ 1H NMR studies in CDCl3 and [D6]DMSO
Poly(methyl methacrylate) (PMMA)-based: nonpolar
・ The polymer films were of good optical quality!
Effect of exposing to DMSO vapor: shuttling
・ No fluorescence of the P5 film when illuminated with UV light
In the nonpolar environment of PMMA-like film
the macrocycle resides over the peptide portion of the thread
Efficient quenching of the anthracene fluorescence
Exposing the P5-coated slides to DMSO vapor: shuttling
the characteristic blue anthracene fluorescene
Masked with aluminium grids
・ The system is reversible.
DMSO vapor
DMSO
heating
P5-coated slides
for 5 min
before
after
Effect of exposing to CF3CO2H vapor: protonation
・ P6 films were fluorescent when illuminated with UV light.The pyridine units of the macrocycle need to be protonated to quench the excited state of anthracene.
Exposing P6-coated slides to CF3CO2H vapors (P6→P6 ・ (2H+ ・ 2CF3CO2
-)n: protonation)Fluorescence was no longer observed.
A distinct pattern of dark (nonfluorescent) bands resulting from P6 films upon exposure to CF3CO2H vapor through a striped aluminum mask (a).
CF3CO2H vapor
heating
P6-coated slides
for 5 min
CF3CO2H
before
after
The response of P6 to the different combination of two stimuli
1. rotation of the aluminum grid by 90º
2. exposure of the film shown in (b) to DMSO vapor
Criss-cross pattern was obtained.
・ The response of P6 to the different combinations of two stimuli (DMSO and protons) corresponds to an “INHIBIT” logic gate.
・ The effect of the acid stimulus involves some deterioration in the optical quality of the film.
Molecular logic gates: “INHIBIT” logic gate
Input Output
0
1
1
0
"NOT" CIRCUIT
Input1 Input2 Output
0
0
0
0
1
1
1 1 1
0
0
0
THE "AND" GATE
INHIBITOR: Input2・ A NOT circuit preceding one terminal of an AND gate acts as an INHIBITOR. Output = Input1・ Input2
・ In the case of rotaxane P6, exposing to DMSO vapor acts as INHIBITOR.
Input1 Input2 Output
0
0
0
0
1
1
1 1
1
0
0
0
THE "INHIBIT" OPERATION
MOLECULAR-SCALE LOGIC GATES
For a recent review: A. P. de Silva, N. D. McClenaghan, Chem.Eur. J. 2004, 10, 574-586
Summary
・ The authors have described a class of molecular shuttles in which translational isomerism of the components can be controlled to either permit or preclude fluorescence quenching by intercomponent electron transfer in both solution and polymer films.
・ The optical response can be unambiguously ascribed to changes in the relative positions of macrocycle and thread.
・ The present work demonstrates that some of the switching mechanisms, properties, and logic operations established for molecular shuttles in solution can be transferred to media that are more suitable for materials which function through controlled submolecular motion.
Molecular Switches 1: conductivity
External stimuli: Redox
A molecular switch tunnel junction in its Off and On states. (left) Structural formula of a bistable [2]rotaxane
・ at a specific voltage, this rotaxane switches from a stable Off state to metastable On state with a different conductivity.
A. H. Flood et al., Science 2004, 306, 2055-2056.
Molecular Switches 2: circular dichroismExternal stimuli: light
(E)-isomer
Only (Z)-isomer gives a CD response.
glycyl-L-leucine (Gly-Leu) unit:
well-exprssed chiral environment
・ Upon photoisomerism of the olefin station (E→Z), the macrocycle moves to the glycyl-L-leucine (Gly-Leu) unit.
(Z)-isomer
D. A. Leigh et al., J. Am.Chem. Soc. 2003, 125, 13360-13361.
Molecular Switches 3: fluorescence
External stumuli: light
・ (E)-isomer converted into (Z)-isomer by photoisomerism.
(E)-isomer
anthracene unit
(Z)-isomerelectron transfer
pyridinium unit
A remarkable 200:1 intensity ratio between (E)-and (Z)-isomer.
Because of distance-dependent electron transfer from anthracene unit to pyridinium units.
(Z) (E)
PSS
D. A. Leigh et al., J. Am. Chem. Soc. 2004, 126, 12210-12211.
Functional group interaction profiles (FGIP)
: hydrogen-bond donor constant
: hydrogen-bond acceptor constant
BlueGH-bond < 0
favorable interaction
RedGH-bond > 0
unfavorable interaction
contour lines
( 等高線 )
・ FGIP provide a benchmark for estimating the magnitudes of intermolecular interactions.
In chloroform: nonpolar In DMSO: polar C. A. Hunter Angew. Chem. Int. Ed. 2004, 43, 5310-5324
Functional group interaction profiles (FGIP) in chloroform
amide-amide interaction: favorable
alkyl chain-phenyl ring interaction: unfavorable
・ The authors expect the tertiary structure to feature the macrocycle held firmly on the peptide station by well-defined hydrogen-bonding network.
Strong quenching of the anthracene fluorescence
Functional group interaction profiles (FGIP) in DMSO
amide-amide interaction: unfavorable
alkyl chain-phenyl ring interaction: favorable
・ The authors expect the macrocycle to be localized on alkyl-chain station but in a variety of positions owing to the general solvophobic interactions.
Electron-transfer process in solution
The very efficient quenching observed in nonpolar solvents (ex. chloroform, dichloromethane)
The electron-transfer process in rotaxanes 2 and 3 ・ 2H+ is close to the Marcus optimal region.
・ The variations in intensity observed with the different solvents is caused by the change in the relative separation of the fluorophore and quencher.
・ The electron transfer process in the rotaxanes:
barrierless and insensitive to the polarity of the solvent.
The switching mechanism in solution: