Photoisomerization monolayer

In the example shown in Fig. 4.39, a photoisomerizable command mono-layer was immobilized on a sohd surface and hquid crystalline layers were then deposited on the monolayer. Photoisomerization of the command monolayer can then change the orientation of the thick hquid crystalhne layer. Molecular... 

Nakahara H, Fukuda K, Shimomura M and Kunitake T 1988 Moleoular arrangements and photoisomerization of amphiphilio azobenzene derivatives in monolayers and multilayers Mppo/ Kagaku Ka/sh/1001-10... 

Fig. 12 In situ optical switching of the current flowing through a DAE monolayer assembled in a PEDOT PSS interlayer-based LAJ. (a) Comparison of the current densities flowing through as assembled open and closed isomer and upon in-situ photoisomerization.

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

The rate constant for the cis- trans photoisomerization can be calculated from the observed time dependence. The rate constants obtained at various monolayer surface pressures under identical conditions of illumination are plotted vs surface pressure in Figure 3. 

Photochemical Generation of an Interfacial Shock Wave. Both the an-thocyanidine and the thioindigo monolayers showed a decrease in surface pressure at constant area during the photoisomerization reaction. A different behavior is observed with mixed monolayers of the surface active spiropyran SP and octadecanol (OD), molar ratio SP 0D = 1 5, on illumination with UV radiation. The isomerization of the spiropyran to the merocyanine MC causes an increase in surface pressure at constant area (5, 14). This is shown in Figure 4, where the sudden rise in surface pressure it upon repeated 0.5 s exposures (as indicated by the arrows) can be seen to occur in a wide surface pressure range (15). The kinetics of the relaxation process following the surface pressure increase depends on the surface pressure. 

Figure 3. Rate constants of cis - -trans photoisomerization obtained from enhanced reflection measurements vs. surface pressure of mixed monolayers of the thioindigo TI and arachidic acid (AA), molar ratio TI AA = 1 3. Subphase bidistilled water, 22° C.

Monolayers representing two-dimensional arrays of membrane-mimetic assemblies, consisting of azobenzene (poly-L-lysine) with 43 % loading of the photoisomerizable units, were prepared.1441 The compressed trans-azobenzene polymer mono-layer exhibited a surface pressure of 7 mN m 1, whereas photoisomerization of the monolayer to the cis-azobenzene state by UV light decreased the surface pressure to... 

Frequency of the crystal after addition of the DNP-Ab to the dinitrospiropyran (31a)-functionalized crystal. (O) Frequency of the crystal after photoisomerization of the (31a)/DNP-Ab monolayer to the protonated dinitromerocyanine (31b), washing offof the DNP-Ab, and back isomerization to (31a) monolayer state. 

Fig. 15 Average thickness of the monolayer (determined from the respective surface plasmon resonance spectra), (a) The dinitrospiropyran (31a) monolayer, (b) The (31a) mono-layer after binding of the anti-DNP-Ab. (c) After photoisomerization of the (31a)/DNP-Ab monolayerto the (31b) state, and washing off of the DNP-Ab.

Photoisomerization of the monolayer to the c/s-azobenzene configuration removes the threaded Fc- i-CD to a spatially separated position which retards the electron transfer rate. Therefore, the assembly functions as a molecular optoelectronic system which records optical information and transduces it into an electronic signal. 

Figure 5.35 Schematic illustration of a photoswitch process in which the photoreaction, in this instance, photoisomerization, occurs at the SAM. This alters the ability of the monolayer species to recognize and interact with a redox-active solution-phase moiety...

Cyclic photoisomerization of the electron-acceptor between the trans- and cis-states permitted reversible piezoelectric transduction of the formation of the complexes with trans-A,A -bNA, and trans-3,3 -bN A at the monolayer interface, and their dissociation upon photoisomerization to czs-4,4 -bNA and c/s-3,3 -bNA. 

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