PHOTOINDUCED REACTION OF DYE IN POLYMER MEDIA .3. KINETICS OF PHOTOCOLOURATION OF ABERCHROME-540 IN POLYMER MATRICES

Aberchrome 540 is a photochromic fulgide. It is amber in its ring-open ed E-form [(E)-alpha-(2,5-dimethyl-3-furylethylidene) (isopropylidene) succinic anhydride]. Upon irradiation with u.v. light at lambda > 300 nm, the dye undergoes a conrotatory ring closure to give the red C fo rm [7,7a-dihydro-2,4,7,7,7a-pentamethylbenzo [b] furan-5,6-dicarboxyli c anhydride]. The kinetics of the photocolouration (from E to C form) of the dye dispersed in a number of polymer matrices has been investig ated in the temperature range 298-338 K. The kinetics is followed spec trophotometrically by monitoring the amount of C form at its lambda(ma x) of 493 nm. The polymer matrices are poly(styrene), poly(p-t-butyl s tyrene), poly(methyl methacrylate), poly(n-butyl methacrylate) and pol y(vinyl acetate). The first-order plot of the results of each run show s two distinct linear lines whose slopes have led to the extraction of the pseudo first-order rate constants k(1) and k(2), at the beginning and toward the end of the reaction times, respectively. The values of k(2) are not shown, since for each kinetic run, the line covers so fe w data points to make k(2) value meaningful. Only k(1) s and the corre sponding overall thermal activation energies are presented. The kineti c results suggest the plausible presence of two conformers of the reac tant in its ring-opened E form.