The solvent effect on electronic energy transfer between excited [Ru(bpy)3]2+ donor and aromatic acceptors

The luminescence quenching of [Ru(bpy)(3)](2+) by a series of organic aromatic molecules in acetonitrile occurs by electronic energy transfer through exchange interaction, and the quenching rate constants obtained are below the diffusion-controlled limit. The measured free energy of activation for energy transfer between non-highly distorted excited states is ascribed, in part, to a solvation effect due to the dipolar nature of MLCT excited-state of the [Ru(bpy)(3)](2+) donor. The solvent reorganization energy, obtained from quenching data, is 5.5 +/- 0.5 kcal/mol, in agreement with the predicted value of 5.7 kcal/mol, assuming the electronic transition (d pi)(5)(L pi)(1) --> (d pi)(6) is the Ru complex as an internal electron transfer mediated by solvent reorganization, calculated using the one-sphere model for charge redistribution. (C) 1999 Elsevier Science S.A. All rights reserved.