Environmental Effects on Phosphorescence. III. Oxygen Quenching of Naphthalene Triplets in Compressed Polymethylmethacrylate

Bimolecular, diffusion-controlled oxygen quenching shortens triplet lifetimes and reduces phosphorescence intensities of organic solutes embedded in polymethylmethacrylate at room temperature. Matrix compression reduces the quenching of naphthalene and naphthalene-d8 triplets until at pressures of about 12 kbar the presence of oxygen is no longer felt and the pressure dependence of the lifetime in the 12–30-kbar range is indistinguishable from measurements on thoroughly deaerated samples. The activation volume for oxygen diffusion in this polymer is approximately +12 cm3/mole, as measured from the phosphorescence lifetimes of naphthalene-d8. The high-pressure results confirm that diffusional quenching is not responsible for the effects of pressure on phosphorescence lifetimes in deaerated polymer matrices.