Light-induced changes, reversal

The bisbarium complex of azobis(berizo-18-crown-6) ether 28 exhibits catalytic properties that can be reversibly activated-deactivated by light-induced changes in molecular geometry [32]. The azobenzene unit is a well-known photochromic [33], often used in the construction of molecular switches [34]. 

Ozawa, Y, Pressprich, M. R. and Coppens, P. (1998). On the analysis of reversible light-induced changes in molecular crystals. J. Appl. Crystallogr, 31, 128-35. [234]... 

The reversible light-induced changes in photoconductivity that have been observed in a variety of a-Si H films are also often used to compare the S - W effect in different films. The wide range of photoconductivity changes that have been reported exhibit dynamics during light exposure that are similar to those shown earlier in Fig. 1. However, results such as those shown in Fig. 

Three carotenoids, violaxanthin (3), antheraxanthin (18), and zeaxanthin (15), undergo rapid, light-induced changes in concentration. These interconversions sometimes are called the xanthophyll cycle (Fig. 26.11) (Demmig-Adams and Adams, 1993). The content of violaxanthin in leaves can be reversibly altered in plants by exposure to light. In the presence of light, violaxanthin is deepoxidized to produce first antheraxanthin and then zeaxanthin. This... 

The compound exists normally as the trans or ( )-isomer 21a. This molecule is essentially planar both in the solid state and in solution, although in the gas phase there is evidence that it deviates from planarity. When irradiated with UY light, the ( )-isomer undergoes conversion substantially into the cis or (Z)-isomer 21b which may be isolated as a pure compound. In darkness, the (Z)-isomer reverts thermally to the (F)-isomer which is thermodynamically more stable because of reduced steric congestion. Some early disperse dyes, which were relatively simple azobenzene derivatives introduced commercially initially for application to cellulose acetate fibres, were found to be prone to photochromism (formerly referred to as phototropy), a reversible light-induced colour change. C. I. Disperse Red 1 (22) is an example of a dye which has been observed, under certain circumstances, to give rise to this phenomenon. 

F. Photochromism or phototropism. In many compounds, light induced reversible colour change is observed. Such light induced reversible transitions lead to states with quantum-mechanical stability but thermodynamic instability... 

Large photoresponse effects could be observed in solvent mixtures, provided that the irradiation was carried out at appropriate solvent compositions. A copolypeptide composed of 33 mol% P-benzyl-L-aspartate and 67 mol% para-phenylazo-L-aspartate (X) was found to give different kinds of photoresponse, depending on the composition of the solvent in which irradiation was carried out. In dichloroethane (DCE)/ hexafluoropropanol (HFP) = 95/5, irradiation at 320-390 nm produced an increase in right-handed helix content in DCE/HFP = 54/26, a light-induced conformational change from left-handed helix to random coil was observed while, finally, reversal of the helix sense occurred in DCE/HFP = 65/35.150,511... 

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