Excited-State Deactivation of Ruthenium(II) Polypyridyl Chromophores Bound to Nanocrystalline TiO₂ Mesoporous Thin Films

Abstract

Excitation of Ru(deeb)(bpy)22+, bis(2,2‘-bipyridine)(2,2‘-bipyridine-4,4‘-diethylester)ruthenium(II) hexafluorophosphate, bound to nanocrystalline TiO2 thin films and immersed in an acetonitrile bath at 25 °C under an argon atmosphere, results in the formation of a species, the transient spectral characteristics for which are, consistent with a metal-to-ligand charge transfer, MLCT, excited state. The spectrum decays by kinetics that are inconsistent with a simple first-order process. Modeling of the data as a function of irradiance has been accomplished assuming parallel unimolecular and bimolecular excited-state deactivation processes. The quantum yield for excited-state formation depends on the excitation irradiance, consistent with triplet−triplet annihilation processes that occur with k ≥ 1 × 108 s-1.