PHOTOINDUCED REACTION OF DYE IN POLYMER MEDIA - V - LOW-TEMPERATURE PHOTOBLEACHING OF ABERCHROME-540 IN POLYMER MATRICES

Photochromic fulgide, commonly known as Aberchrome 540, in its red, C- form 4,7,7,7a-pentamethylbenzo[b]furan-5,6-dicarboxylic anhydride] is bleached with white light to its amber, E-form [(E)-alpha-(2,5-dimethy l-3-furylethylidene) (isopropylidene) succinic anhydride] in poly(styr ene) (PS) and in poly(carbonate bisphenol A) (PC) films at 83-283 K. T his temperature range falls apprximately in the sub-glass transition t emperatures of PS (gamma and beta relaxations) and PC (gamma relaxatio n). The experiments are conducted in a cryogenic system and the extent of the photobleaching at various irradiation times, is monitored at l ambda(max) = 493 nm of the red C-form. The reaction begins with a very slow induction period and is followed by a pseudo-first-order reactio n. The latter allows for the extraction of the rate constant, k. Compa rison of k values in both matrices has revealed that the cooperative m olecular motion responsible for the gamma relaxation of PC (resulting from the intra-and inter-chain interactions), may play a dominant role leading to the observed k in PC being greater than k in PS, at the sa me temperature. (C) 1997 Elsevier Science Ltd.