Characterizing the quenching process for phosphorescent dyes in poly[((n-butylamino)thionyl)phosphazene] films

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)(3)Cl-2 (dpp = 4,7-diphenyl-1,10-phenanthroline)] in a low-glass-transition-temperature polymer matrix [poly [((n-butylamino)thionyl)phosphazene] (C(4)PATP).] The Pt dyes have exponential unquenched decays, but nonexponential decays in the presence of O-2. 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)(3)Cl-2 in C(4)PATP 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)(3)Cl-2 gave very similar values for the diffusion coefficient for oxygen in the polymer (D-O2 = (3.7-4.0) x 10(-6) cm(2) 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 P-O2 and solubility S-O2 = P-O2/D-O2 of oxygen in the matrix. In this calculation, one must assume a value (commonly taken to be 1.0 nm) for alphaR(eff), the probability of quenching per encounter times the effective quenching radius of the dye. We find differences in calculated P-O2 values that can only be explained in terms different sensitivities of the dyes to quenching by oxygen.