Photo-induced reaction of dye in polymer media—III. Kinetics of photocolouration of aberchrome 540 in polymer matrices

Abstract

Aberchrome 540 is a photochromic fulgide. It is amber in its ring-opened E-form [(E)-α-(2,5-dimethyl-3-furylethylidene) (isopropylidene) succinic anhydride]. Upon irradiation with u.v. light at λ > 300 nm, the dye undergoes a conrotatory ring closure to give the red C form [7,7a-dihydro-2,4,7,7,7a-pentamethylbenzo [b] furan-5,6-dicarboxylic anhydride]. The kinetics of the photocolouration (from E to C form) of the dye dispersed in a number of polymer matrices has been investigated in the temperature range 298–338 K. The kinetics is followed spectrophotometrically by monitoring the amount of C form at its λ max of 493 nm. The polymer matrices are poly(styrene), poly(p-t-butyl styrene), poly(methyl methacrylate), poly(n-butyl methacrylate) and poly(vinyl acetate). The first-order plot of the results of each run shows 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 few data points to make k 2 value meaningful. Only k 1, s and the corresponding overall thermal activation energies are presented. The kinetic results suggest the plausible presence of two conformers of the reactant in its ring-opened E form.