Characterizing the Quenching Process for Phosphorescent Dyes in Poly[((n-butylamino)thionyl)phosphazene] Films

Abstract

We compare the results of oxygen quenching experiments for four phosphorescent dyes [platinum octaethylporphyrin (PtOEP), platinum octaethylporphyrin ketone (PtOEPK), platinum tetrakis(pentafluorophenyl)porphyrin (PtTFPP), and Ru(dpp)3Cl2 (dpp = 4,7-diphenyl-1,10-phenanthroline)] in a low-glass-transition-temperature polymer matrix [poly[((n-butylamino)thionyl)phosphazene] (C4PATP).] The Pt dyes have exponential unquenched decays, but nonexponential decays in the presence of O2. These data fit well to a two-site model in which the dyes in the short lifetime environment are more readily quenched by oxygen. Ru(dpp)3Cl2 in C4PATP has a nonexponential decay under all conditions and is much better described by a Gaussian distribution of decay rates with a common mean quenching rate. Time-scan experiments with PtOEP, PtTFPP, and Ru(dpp)3Cl2 gave very similar values for the diffusion coefficient for oxygen in the polymer (DO2 = (3.7−4.0) × 10-6 cm2 s-1). For each of these three dyes, lifetimes and intensities gave identical Stern−Volmer plots. From the slopes of these plots one can calculate the permeability PO2 and solubility SO2 = PO2/DO2 of oxygen in the matrix. In this calculation, one must assume a value (commonly taken to be 1.0 nm) for αReff, the probability of quenching per encounter times the effective quenching radius of the dye. We find differences in calculated PO2 values that can only be explained in terms different sensitivities of the dyes to quenching by oxygen.