Hopping and Annihilation of³MLCT in the Crystalline Solid of [Ru(bpy)₃]X₂(X = Cl^-, ClO₄^-and PF₆^-)

Abstract

Emission decay measurements under various excitation intensities and time-resolved absorption spectroscopy were applied to investigate the bimolecular reactions of the triplet lowest excited metal-to-ligand charge-transfer state (3MLCT) in the neat crystals or doped crystals with energy acceptor. The rate of hopping to the nearest-neighbor site in the energy migration of 3MLCT in [Ru(bpy)3](PF6)2 was determined to be (3.5 ± 0.5) × 108 s-1 from the dependence of emission decay rates on the doping concentration of Os2+ and the rate constant of triplet−triplet (T−T) annihilation in the emission decay for the single-crystal or transparent mixed-crystal ground with KCl. The rate constants of hopping to the nearest-neighbor sites obtained for the crystals of [Ru(bpy)3]X2 (X = Cl-, ClO4-, and PF6-) showed a distance dependence. The diffusion constants of triplet exciton in the crystals were also estimated. Time-resolved absorption spectroscopy revealed that T−T annihilation produced the one-electron transferred products. The rate of electron transfer between 3MLCT in the crystal of [Ru(bpy)3](PF6)2 was estimated to be ≥5 × 1010 s-1 by time-resolved absorption spectroscopy.