Evaluation of phosphorescent rhenium and iridium complexes in polythionylphosphazene films for oxygen sensor applications

Three metal complexes- [Re(bpy)(CO)(3)(CN-t-Bu)]CI (1) (where bpy = 2,2-bipyridine), BU4N[Ir(ppy)(2)-(CN)(2)] (2), and Ir(ppy)(3) (3) (where ppy = 2-phenylpyridine and Bu4N = tetrabutylammonium cation)-were evaluated as oxygen sensors in poly((n-butylamino)thionylphosphazene) (nBuPTP) matrixes. The phosphorescent dyes 2 and 3 exhibit long lifetimes and high quantum yields in degassed dichloromethane and toluene solutions and when dissolved in the polymer matrix. These two dyes exhibited exponential decays both in solution and in the polymer films, with somewhat longer lifetimes (for 2, tau(0) = 4.78 mu s; for 3, tau(0) = 1.40 mu s) in the polymer film. All three dyes gave linear Stern-Volmer plots, but 1 was rather sensitive to photodecomposition. The slopes of the Stern-Volmer plots for these dyes were compared to those measured previously for platinum octaethyl porphine (PtOEP) and ruthenium tris-diphenylphenanthroline chloride ([Ru(dpp)(3)]CI2. Attempts to explain the differences in slope using tau(0) as the sole scaling parameter were unsuccessful. To explain these results, we calculated the effective capture radius for quenching by oxygen, which was 1.7 nm for 2 and 2.7 nm for 3, relative to a value of 1.0 mn for PtOEP. Thus, dye 3 is 2.7 times more sensitive to quenching by oxygen than PtOEP and more than 5 times more sensitive than [Ru(dPP)(3)]CI2.