KINETICS OF QUENCHING OF KETONE PHOSPHORESCENCE BY OXYGEN IN A GLASSYMATRIX

Measurements of oxygen diffusion in polystyrene, poly(methyl methacryl ate), and poly(vinyl chloride) films varying in thickness from 7 to 57 mu m were obtained at 22 degrees C by following the kinetics of quenc hing of phosphorescence of camphorquinone dissolved in each polymer. V alues of diffusion coefficients D were (2.2 +/- 0.5) x 10(-7), (1.4 +/ - 0.3) x 10(-8), and (1.3 +/- 0.1) x 10(-8) cm(2) s(-1), respectively, in reasonable agreement with literature data. The decreasing trend in D in this series is consistent with increasing polymer properties inc luding cohesive energy density and diffusion activation energy. Compar ison of the diffusion-limited rate constant k(d), calculated from D, a nd the bimolecular rate coefficient k(q), determined from lifetime and steady state intensity measurements, indicates that triplet CQ immobi lized in glassy polymers is quenched with an efficiency k(q)/k(d) grea ter than or similar to 4/9. This result is subject to some uncertainty due to the errors in k(q) and k(d); however, a value of k(q)/k(d) > 4 /9 must be considered possible in view of recent reports implying that intersystem crossing between excited complexes of all multiplicity is important in systems where the phosphor is a ketone immobilized in a high-viscosity matrix.