Luminescence studies of polymer matrices: 4. Phosphorescence of benzophenone dispersed in acrylic acid based polymer films

The thermal dependence of the phosphorescence characteristics of benzopheno ne (BP) dispersed in thin films of poly(acrylic acid), PAA, and acrylic aci d-methyl methacrylate, AA-MMA, copolymers is described. At all temperatures (between 77 K and 410 K), and in each of the systems studied, the tripler state decay kinetics of the phosphor are complex: a minimum of three expone ntial terms is required for adequate modelling of the time dependence of BP phosphorescence. This complexity is considered to reflect the breadth and heterogeneity of the distribution of sites accessed by the probe within eac h of the polymer matrices. Both phosphorescence intensity and lifetime measurements are affected by th e onset of macromolecular relaxations within each of the film samples. Howe ver, the temperature dependence of the BP phosphorescence data seems to als o reflect the presence of specific interactions between the probe and polym er. Consequently the data do not allow a definitive picture of the relaxati on behaviour or phase morphology of the copolymer samples to be derived. Th e data also illustrate the fact that, in designing a high-performance phosp horescent coding system, trends in the photophysical characteristics of one dopant in a given matrix do not necessarily translate into predictions of the behaviour of another phosphor even in the same matrix.