Luminescence studies of macromolecular behaviour I. Photodecomposition of auramine O in poly(methyl methacrylate)

The photoreduction of auramine O in PMMA has been studied at concentrations between 10^-3 to 10^-5 mol kg^-1, and over a temperature range of 290 K to 415 K. Whilst the photodecomposition of auramine O precludes its use as a fluorescent probe of relaxation phenomena in PMMA, the rate of the photoreduction process is considerably affected by the physical state of the polymer. A marked decrease in the rate of photoreduction (leading to an apparent negative energy of activation) is observed above T_g. This reduced importance of photochemical decomposition above T_g is a consequence of enhanced radiationless deactivation of the singlet excited state of auramine O through internal rotations, and of the triplet state through internal and external quenching. © 1981.