Photo-induced reaction of dye in polymer media—IV. Kinetics of photoisomerization Z → E of Aberchrome 540 in polymer matrices

Abstract

A photochromic fulgide known as Aberchrome 540 is amber in its ring-opened Z-form [(Z)-α-(2,5-dimethyl-3-furylethylidene) (isopropylidene) succinic anhydride]. It is photoisomerized at λ > 300 nm to give another ring-opened amber E-form which subsequently 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 Z → E is obtained by fitting a consecutive kinetic model to the experimental data of Z → k 1 E → k 2 C , using the known k 2 from previous experimental work. Thin films of dye, dispersed in polymer matrices by the solution-cast technique, have been used in this investigation. The reaction is studied at 303–338 K by monitoring the absorbance at λ max of 493 nm of the final product (C) formed at various irradiation times. The polymer matrices are poly(styrene), poly(p-t-butyl styrène), poly(vinyl acetate), and poly(n-butyl methacrylate). The magnitudes of the calculated rate constants, k 1 s and the apparent (thermal) activation energies, E a s appear to be under the influences of the available free volume at the dye sites, molecular motions of media and dipolar interactions.