PHOTOINDUCED REACTION OF DYE IN POLYMER MEDIA .4. KINETICS OF PHOTOISOMERIZATION Z-]E OF ABERCHROME-540 IN POLYMER MATRICES

A photochromic fulgide known as Aberchrome 540 is amber in its ring-op ened Z-form [(Z)-alpha-(2,5-dimethyl-3-furylethylidene) (isopropyliden e) succinic anhydride]. It is photoisomerized at lambda > 300 nm to gi ve another ring-opened amber E-form which subsequently undergoes a con rotatory 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 exp erimental data of Z -->(kt) E -->(k2) C, using the known k(2) from pre vious experimental work. Thin films of dye, dispersed in polymer matri ces by the solution-cast technique, have been used in this investigati on. The reaction is studied at 303-338 K by monitoring the absorbance at lambda(max) of 493 nm of the final product (C) formed at various ir radiation times. The polymer matrices are poly(styrene), poly(p-t-buty l styrene), poly(vinyl acetate), and poly(n-butyl methacrylate). The m agnitudes of the calculated rate constants, k(l)s and the apparent (th ermal) activation energies, E(a)s appear to be under the influences of the available free volume at the dye sites, molecular motions of medi a and dipolar interactions.