TEMPERATURE EFFECTS ON PHOSPHORESCENCE OF AROMATIC HYDROCARBONS IN POLY(METHYLMETHACRYLATE)

Temperature effects on the phosphorescence lifetimes and phosphorescence intensities of naphthalene, phenanthrene, pyrene, biphenyl, and the perdeuterated analogs of these four molecules were measured with the use of poly (methylmethacrylate) (PMM) as a rigid solvent matrix. The phosphorescence lifetimes of these molecules decreased by only 13%-37% upon warming from 77°K to room temperature. On the basis of direct measurements of the permeability of PMM to oxygen, we conclude that oxygen quenching is not responsible for the observed temperature effects on the phosphorescence lifetimes. Although we cannot exclude the possibility that the rate constants for both radiative and nonradiative decay vary with temperature, we show that our results are consistent with an analysis that assumes that only the nonradiative rate constant is temperature dependent. On the basis of this analysis, we estimate an activation energy of 500±100 cm-1 for the thermally activated nonradiative decay mode.