Luminescence Studies of Polymer Matrices: 4. Phosphorescence of Benzophenone Dispersed in Acrylic Acid Based Polymer Films

Abstract

The thermal dependence of the phosphorescence characteristics of benzophenone (BP) dispersed in thin films of poly(acrylic acid), PAA, and acrylic acid-methyl methacrylate, AA-MMA, copolymers is described. At all temperatures (between 77 K and 410 K), and in each of the systems studied, the triplet state decay kinetics of the phosphor are complex: a minimum of three exponential 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 each of the polymer matrices. Both phosphorescence intensity and lifetime measurements are affected by the onset of macromolecular relaxations within each of the film samples. However, the temperature dependence of the BP phosphorescence data seems to also reflect the presence of specific interactions between the probe and polymer. Consequently the data do not allow a definitive picture of the relaxation behaviour or phase morphology of the copolymer samples to be derived. The data also illustrate the fact that, in designing a high-performance phosphorescent 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.