Photochemical switching devices

S. L. Gilat, S. H. Kawai, and J.-M. Lehn, Light-triggered molecular devices photochemical switching of optical and electrochemical properties in molecular wire-type diarylethene species, Chem. Eur. J1, 275-284 (1995). 

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]. 

Fig. 120a. Schematic view of the photochemical switching device and the compounds used in this study, b Absorption spectra of the LB films of APT(8-13) irradiated with UV (365 nm) and visible (436 nm) light before irradiation (a) and after irradiation with visible light (b) and UV light (c) [740]...

A multiple switching device can be fabricated by combining the two photochemical switching LB films noted above, consisting of molecules with different switching units, NAPT(8-14) and APT(12-12) 20 monolayers of APT(12-12) are first transferred onto a hydrophobized quartz plate on which 20 monolayers of NAPT(8-14) are deposited. 

A multiple switching device of this type can utilize all four types of control light as external stimuli. Actually, the conductivity of the multiple photochemical switching device is controlled by sequential photoirradiation, as shown in Fig. 19. Irradiation with VIS I causes trans-to-cis isomerization of the naphthylbenzyl azo dye of NAPT(8-14), the conductivity... 

The fabrication of LB FETs and photochemical switching devices is encouraging to researchers working in the field of molecular electronics. The active parts of devices really consist of LB films. The latter could be considered a molecular device. 

Xachibana, H., Manda, E., Azumi, R., Nakamura, X, Matsumoto, M., and Kawabata, Y. Multiple photochemical switching device based on Langmuir-Blodgett-films. Appl. Phys. Lett. 1992, 61, 2420-2421. 

The great demand for miniaturization of components in electrotechnical, medicinal or material applications has led to the development of a highly multidisciplinary scientific and technological field called nanotechnology to produce devices with critical dimensions within the range 1 100 nm. The ultimate solution to miniaturization is logically a functional molecular machine, an assembly of components capable of performing mechanical motions (rotation or linear translation) upon external stimulation, such as photoactivation.1103,1104,1239-1244 This motion should be controllable, efficient and occur periodically within an appropriate time-scale therefore, it involves photochromic behaviour discussed in the Special Topic 6.15. Such devices can also be called photochemical switches (Special Topics 6.18 and 6.15). Here we show two examples of molecular machines a molecular rotary motor and a molecular shuttle. 

Self-assembly of Au(I) complexes through weak Au(I) - - -Au(I) interactions is now recognized as an interesting feature of heavy transition metal chemistry whose wider implications are slowly being understood. The utility of these compounds as chemical and photochemical switches or as energy storage devices and photochemical sensors is one of the possible fruits of this research. Although a com-... 

Figure 14.55. Schematic view of a photochemical switching device. (Reproduced by permission of Elevier Sequoia from ref. 362.)...

Figure 14.58. Molecular structure of amphiphiles for multiple photochemical switching devices. (Reproduced by permission of the American Institute of Physics from ref. 368.)...

Let us consider molecular switches based on intramolecular electronic transition. Generally, transfer of energy or an electron within a molecule proceeds in femtoseconds. The aim is to produce molecular electronic devices that respond equally rapidly. Molecular switches that employ optically controlled, reversible electron-transfer reactions sometimes bring both speed and photostability advantages over molecular switches which are usually based on photochemical changes in their molecular structure. Important examples are the molecnlar switches depicted in Scheme 8.3 (Debreczeny et al. 1996). 

R. A. Marcus I have a question for Prof. Rice Do most industrial photochemical processes involve chain reactions If so, one suspects that they will be less susceptible to coherent control. Are there some industrial photochemical processes not involving free radical chains I gather that you hold the view, which seems reasonable, that the opportunities for coherent control are greater in devices such as electronic switches and generally in telecommunications ... 

Although photochemical reactions in general take place very rapidly, for application to switching devices it is essential to know the response times. The photoinduced coloration and decoloration rates of diarylethenes have been measured by using... 

Photochemical bistability is a conditio sine qua non, but a number of other requirements are essential for application of chiral switches in photonic materials or optical devices 11,4,101... 

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