Bistable SystemsBistable Systems

andandMolecular Molecular SwitchingSwitching

Supervisor:Supervisor: Prof.Davor Boghai Prof.Davor Boghai

By: By: SeyyedSeyyed MohammadMohammad Reza Reza Sanavi HosseiniSanavi Hosseini

Bistable SystemsBistable Systems

Any molecular-level system that can be reversibly Any molecular-level system that can be reversibly switched between two different states by use of an switched between two different states by use of an

external stimulus can be taken as a basis for external stimulus can be taken as a basis for storing information, i.e. for memory purposes. An storing information, i.e. for memory purposes. An

ideal molecular-level memory should be stable and ideal molecular-level memory should be stable and easy to write, and its switched form should be easy to write, and its switched form should be

stable, easy to read, and erasable when necessary. stable, easy to read, and erasable when necessary. Systems that undergo an irreversible change can be Systems that undergo an irreversible change can be

used as permanent memories (e.g. photography, used as permanent memories (e.g. photography, dosimetry) . In more complex systems switching can dosimetry) . In more complex systems switching can

be performed among more than two states. This be performed among more than two states. This possibility can be exploited to obtain memories possibility can be exploited to obtain memories which are permanent unless they are erased on which are permanent unless they are erased on

purpose, or for performing logic operations. purpose, or for performing logic operations.

Important types of Important types of stimulusstimulus

11 ) )Light energy (photons)Light energy (photons)

22 ) )Electrical energy (electrons/holes)Electrical energy (electrons/holes)

33))Chemical energy ( in the form of Chemical energy ( in the form of protons, metal ions, etc.)protons, metal ions, etc.)

NoteNote : :

In photochemical stimulation the most In photochemical stimulation the most common switching processes are related common switching processes are related to photoisomerization or photoinduced to photoisomerization or photoinduced redox reactions; for electrochemical redox reactions; for electrochemical inputs, the induced processes are, of inputs, the induced processes are, of course, redox reactions.course, redox reactions.

Comparison between Comparison between different types of different types of

stimulationstimulationCompared whit chemical stimulation, Compared whit chemical stimulation,

photochemical and, to some extent, photochemical and, to some extent, electrochemical stimuli can be switched on and electrochemical stimuli can be switched on and off easily and rapidly. A further advantage of off easily and rapidly. A further advantage of the use of photo chemical and electro chemical the use of photo chemical and electro chemical techniques is that photons and electrons, techniques is that photons and electrons, besides supplying the stimulus to make a besides supplying the stimulus to make a switch work (i.e. switch work (i.e. ””to writeto write”” the information the information bit), can also be useful bit), can also be useful ““to readto read”” the state of the state of system and thus to control and monitor its system and thus to control and monitor its operation. It should be also noted that operation. It should be also noted that photochemical and electrochemical inputs and photochemical and electrochemical inputs and outputs are among the easiest to interface to outputs are among the easiest to interface to microscopic systems, making them amenable microscopic systems, making them amenable to the multi-scale engineering required for the to the multi-scale engineering required for the eventual creation of real deviceseventual creation of real devices

Significant switching Significant switching systemssystems

1)Photochromic systems:1)Photochromic systems:The term The term ““photochromicphotochromic”” is applied to is applied to

molecules that can be reversibly inter molecules that can be reversibly inter converted, with at least one of the converted, with at least one of the reactions being induced by light reactions being induced by light excitation, between two forms whit excitation, between two forms whit different absorption spectra. The two different absorption spectra. The two forms, differ not only in their absorption forms, differ not only in their absorption spectra, but also in several other spectra, but also in several other properties such as redox potentials, properties such as redox potentials, dielectric constant, etc. dielectric constant, etc.

Representation of a photochromic Representation of a photochromic system (a) and of its energy profile (b)system (a) and of its energy profile (b)

Some Some important important families of families of photochromic photochromic compounds:compounds:

a) Diarylethenesa) Diarylethenesb) Flugidesb) Flugidesc) Spiropyransc) Spiropyransd) Azobenzenesd) Azobenzenese) dihydroazulenese) dihydroazulenes

2) Modulation of Host-Guest 2) Modulation of Host-Guest interactions:interactions:

Switching host-guest interactions by Switching host-guest interactions by means of photochromic reactions means of photochromic reactions might lead to a variety of sensors and might lead to a variety of sensors and to transport of guest molecules across to transport of guest molecules across a membrane. An example is shown a membrane. An example is shown next page.next page.

Photoswitchable recognition of Photoswitchable recognition of saccharides by diarylethene saccharides by diarylethene

derivative 1derivative 1

3)Fluorescent Switches:3)Fluorescent Switches:

Several photochromic compounds Several photochromic compounds have different fluorescence have different fluorescence properties in their two forms. properties in their two forms. Occasionally on/off switching is Occasionally on/off switching is observed. Two examples is shown observed. Two examples is shown next pagenext page

On/off switching of fluorescence in On/off switching of fluorescence in (a) fulgide derivative 3 and (b) (a) fulgide derivative 3 and (b)

diaryiethene derivativediaryiethene derivative

4) Chiroptical Switches:4) Chiroptical Switches:

Chiral photobistable molecules are a particularly Chiral photobistable molecules are a particularly interesting class of photochromic compounds. In interesting class of photochromic compounds. In such molecules reversible photochemical trans such molecules reversible photochemical trans formation can lead to a change in chirality. The formation can lead to a change in chirality. The importance of chiroptical switches is further importance of chiroptical switches is further emphasized since chirality controls most natural emphasized since chirality controls most natural chemical processes, including molecular chemical processes, including molecular recognition, transport, information storage, recognition, transport, information storage, catalysis, assembly, and replication.catalysis, assembly, and replication.

Chiral switches based on photochromic molecules Chiral switches based on photochromic molecules can be subdivided as follows:can be subdivided as follows:

a) Switching of enantiomersa) Switching of enantiomersb) Switching of diastereoisomersb) Switching of diastereoisomersc) Functional chiral switchesc) Functional chiral switchesd) Switching of macromolecules or d) Switching of macromolecules or

supramolecular organizationsupramolecular organization

Besides the general requirements needed for Besides the general requirements needed for photochromic switches, chiroptical photochromic switches, chiroptical switches must be stable towards thermal switches must be stable towards thermal racemization.racemization.

Thermal and photochemical Thermal and photochemical isomerization processes of isomerization processes of

chiroptical switchchiroptical switch

5)Photochemical Biomolecular 5)Photochemical Biomolecular Switches:Switches:

It is well known that many biological It is well known that many biological processes are triggered by light signals. processes are triggered by light signals. Such systems consist of a biological material Such systems consist of a biological material or an environment the innate function of or an environment the innate function of which can be activated/deactivated by which can be activated/deactivated by artificial photoresponsive units.artificial photoresponsive units.

6) Electrochromic Systems:6) Electrochromic Systems:Electrochromic is applied to compounds Electrochromic is applied to compounds

that can be inter converted, by reversible that can be inter converted, by reversible redox processes, between two forms whit redox processes, between two forms whit different absorption spectra.different absorption spectra.

In electrochromic systems the In electrochromic systems the interconverting species are not isomers, interconverting species are not isomers, because they have different number of because they have different number of electrons. In these systems several electrons. In these systems several successive switching processes can successive switching processes can occur.occur.

77 ) )Redox Switches:Redox Switches: an example of redox switch is an example of redox switch is shown belowshown below

Multistate-Multifunctional Multistate-Multifunctional SystemsSystems

1)Biphotochromic Supermolecular 1)Biphotochromic Supermolecular Systems:Systems:

Many attempts have been made to couple Many attempts have been made to couple two photochromic units in the same two photochromic units in the same supramolecular species. The objective of supramolecular species. The objective of these studies was to obtain a synergistic these studies was to obtain a synergistic effect between the properties of the two effect between the properties of the two units to create materials with novel units to create materials with novel photokinetic properties.photokinetic properties.

2)Photochemical Inputs 2)Photochemical Inputs Coupled whit Other Stimuli:Coupled whit Other Stimuli:

a) Three-state Systems. Write-Lock-Read-a) Three-state Systems. Write-Lock-Read-Unlock-Erase CycleUnlock-Erase Cycle

b) Orthogonal photochemical-Electrochemical b) Orthogonal photochemical-Electrochemical StimulationStimulation

c) Orthogonal Photochemical-(Acid-Base) c) Orthogonal Photochemical-(Acid-Base) StimulationStimulation

d) Molecular Shift Registerd) Molecular Shift Register

Schematic representation of Schematic representation of the behavior of three types of the behavior of three types of

photochromic systemsphotochromic systems

33 ) )Multielectron Redox Multielectron Redox ProcessesProcesses::

a) System whit Equivalent redox Unitsa) System whit Equivalent redox Unitsb) System whit Nonequivalent Redox Unitsb) System whit Nonequivalent Redox Units

4) Electrochemical inputs 4) Electrochemical inputs Coupled whit Chemical InputsCoupled whit Chemical Inputs

5) Multiple Chemical Inputs5) Multiple Chemical Inputs

Photochemical and Photochemical and electrochemical switching of a electrochemical switching of a

diarylethene derivative to perform diarylethene derivative to perform a write-lock-read-unlock-erase a write-lock-read-unlock-erase

cyclecycle

Schematic representation of the Schematic representation of the write-lock-read-unlock-erase cycle write-lock-read-unlock-erase cycle

of a systemof a system

Light-and Light-and redox-redox-driven driven switching of switching of the DHA-the DHA-VHF systemVHF system

Photo-switching materials

in following parts we can see some in following parts we can see some examples and applications of examples and applications of molecular switching.molecular switching.

Photo-magnetic molecular solids

1)Prussian blue analogues and CN-bridging compounds

aa) ) Fe–Co Prussian blue

b) b) CN-bridging compounds

(Right) Structure and (left) field-cooled magnetization curves at 5G

(Top) View of the molecular structure, a projection of the three-dimensional crystal packing, and (bottom) magnetic susceptibilities (MT) vs. temperature

before and after UV light illumination for Nd(DMF)4(H2O)3(-CN)Fe(CN)5·H2O

2)Light-induced excited spin state trapping

compounds(Top) View of

molecular structure and (bottom) temperature dependence

of the magnetization before and after light illumination for [FeIII(pap)2]·ClO4

Photo-chromic magnetic materials

Photo-controllable magnetic vesicles:

the first successful example ofthe preparation of photo-chromic magnetic (composite)materials. A commercially available double-chain ammoniumamphiphile, didodecyldimethylammonium bromide([CH3(CH2)11]2(CH3)2N+Br-), which forms a vesiclestructure in aqueous solution by sonication, and an

azobenzenecontainingamphiphile (C12AzoC5N+Br-), which wassynthesized according to a reported procedure, were mixedwith an aqueous solution of poly(vinyl alcohol) (PVA). Thephoto-chromic vesicle films were prepared by casting the

abovesolution on a clean glass plate at room temperature

Design of photo-responsive magnetic vesicles containing Prussian blue

and azobenzene

Photo-switchable magnetic films

1)Prussian blue intercalated in Langmuir–Blodgett

films consisting of an amphiphilic azobenzene and a clay

Mineral.

2) Anisotropic photo-induced magnetization effect in ultrathin Fe–Co Prussian blue films

Preparation of the hybrid multilayered films

Schematic representation of photo-switchable magnetic layer-by-layer

films.

(Bottom) Changes in the magnetization for the films induced by alternating

illumination with UV and visible light at 300K at 10G.

Molecular models of the gemini peptide lipid 1 evaluated by molecular mechanism calculation using the Cerius2 software based on DREIDING force field: (a) trans-form; (b) cis-form bound a metal ion.

An example of data An example of data storagestorage

Memory operation of the single-molecule system. The blue line

shows the write, read, and erase pulse pattern applied and the red

line demonstrates the resulting switching between "off" and "on"

states of the molecular system. As can be seen in the picture, the

system is initially in the "off" state. Then a write pulse of +1.6 V is

applied and the molecule switches to the "on" state. This state can be

read out using a voltage of +1.1 V. The molecule can be switched

back to the "off" state by another pulse (erase pulse) of -1.6 V.

( Source: IBM)

References:

1)Journal of Photochemistry and Photobiology C: Photochemistry Reviews7 (2006) 69–88

2)Electrochemistry Communications 9 (2007) 173–179

3)Journal of Photochemistry and Photobiology A: Chemistry 183 (2006) 309–314

4)Journal of Luminescence 119–120 (2006) 478–481

5)Composites: Part A 38 (2007) 747–7546)www.physorg.com7)Molecular Devices and Machines, a Journey into

the Nanoworld,V.Balzani, M.Venyuri, A.Credi

The EndThe End

Thanks for your attentionThanks for your attention