STUDY OF THE FATIGUE PROCESS AND THE YELLOWING OF POLYMERIC FILMS CONTAINING SPIROOXAZINE PHOTOCHROMIC COMPOUNDS

Photochromic polyurethane films containing 5-substituted [2H-indole-2, 3'-[3H]pyrido[3,2-f][1,4]benzoxazine] and ro[2H-indole-2,3'-[3H]-napht h-[2,1-b][1,4]oxazine] were degraded under xenon light exposure. The l oss of the photochromic response was monitored by spectrophotometry as a function of the irradiation time; meanwhile, the photoproduct forma tion and the amount of photochromic material still available were anal yzed by chromatography after liquid-solid extraction. At the same time , the fade rates were monitored after flash-excitation photolysis or a fter the photostationary state during degradation. It was clearly demo nstrated that the loss of photochromism was due exclusively to a photo oxidation process of the initial dye, and not to an acceleration of th e bleaching or a potential screen effect caused by the photoproducts.