Thermal processing photochromic behavior

Fackler et al. (1563) previously showed that the brown color of [Ni(S2CNBu2)3]" can be photochemicaUy and thermally bleached in acetonitrile. Thiuram disulfide and [Ni(S2CNBu2)2] are the products and the process reversible. Eckstein and Hoyer (1559) studied this photochromic behavior in some detail measuring rate constants and quantum yields as a function of the dithiocarbamate substituents and anions (Fig. 198). 

Structuration is not completely elucidated. It is well known that essentially for the surface structuration is the trans-cis isomerization process of the azo-groups, under UV-VIS irradiation. As a consequence, a very careful study regarding the pho-tochromic behavior of the azo-polysiloxanes was effectuated. The photochromic response at the light stimuli was evaluated in different conditions trans-cis isomerization under UV irradiation cis-trans relaxation in the presence of the natural visible light cis-trans relaxation only thermally activated (in the dark). It must be underlined that there are no reported studies in the literature concerning the cis-trans relaxation process in the presence of natural visible light, a very important aspect in our opinion regarding the elucidation of SRG formation mechanism. 

Kinetics in a Continuously Stirred Photochemical Tank Reactor. Gregoire, F. Lavabre, D. Micheau, 1. C. Gimenez, M. Laplante, J.P. (Lab. Interact. Mol. React. Chim. Photochim., Univ. Paul Sabatier, F-31062 Toulouse, Fr.). J. Photochem. 1985, 28 (2), 261-71 (Eng.). The continuously stirred photochem. tank reactor (REPAC) is a new semiautomatic app. for photochem. measurements. From the kinetic anal, of steady-state regimes, this open system allows detn. of the quantum yields, the thermal-return rate consts. and the spectra of photoproducts. Moreover, the kinetic anal, of transient regimes affords further information on the mechanism of the photochem. process. The possibUities of the REPAC are shown using various photochromic compds. Theor. anal, of the kinetic rate equations in the REPAC shows that quite unusual behavior, such as unstable steady states or photochem. oscillations, can be exhibited. Nonhnear photochem. reaction schemes are likely to show such behavior. 

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