Excited-state deactivation of ruthenium(II) polypyridyl chromophores boundto nanocrystalline TiO2 mesoporous thin films

Excitation of Ru(deeb)(bpy)(2)(2+), 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 degrees 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 c harge transfer, MLCT, excited state. The spectrum decays by kinetics that a re inconsistent with a simple first-order process. Modeling of the data as a function of irradiance has been accomplished assuming parallel unimolecul ar and bimolecular excited-state deactivation processes. The quantum yield for excited-state formation depends on the excitation irradiance, consisten t with triplet-triplet annihilation processes that occur with k greater tha n or equal to 1 x 10(8) s(-1).