We report the first experimental evidence of long-range nonradiative singlet-singlet resonance energy transfer from excited coumarin 460 molecules to [Ru(bpy)(3)](2+) accepters (bpy is 2,2＇-bipyridine), The molecules were randomly dispersed in fluid solutions of both high (glycerol) and low (CH3CN) viscosity at room temperature. The frequency-domain donor (coumarin 460) fluorescence decays were satisfactorily analyzed in terms of Forster theory incorporating a term for translational diffusion. Two different [Ru(bpy)(3)](2+) (quencher) concentrations in each solvent were used, and the coumarin 460 emission was measured and analyzed both independently and globally. In glycerol, diffusion does not play a significant role in the energy transfer process, whereas in CH3CN, diffusion is able to enhance the energy transfer reaction. In both solvents, mutual diffusion coefficients were determined from the experimental data and chi(2)R error surfaces were constructed to judge their statistical uncertainty. The results demonstrate that metal-to-ligand charge transfer compounds can serve as intermolecular energy transfer accepters in schemes utilizing long-range Forster-type processes.