The effect of H/D-bond solute–solvent interaction on deactivation channels of MLCT excited state of [Ru(bpy)(CN)4]2−

Photophysics of [Ru(bpy)(CN)4]2− (bpy=2,2′-bipyridine) in CH3OH, CH3OD, CD3OD, and CH3OH/C2H5OH and CH3OD/C2H5OD solvent mixtures has been investigated by steady state and time-resolved techniques at various temperatures. The Franck–Condon analysis of the emission spectra observed between 80 and 165 K indicates similar and significant decrease in energy of the luminescent excited state (E0–0) and a small difference in the increasing solvent reorganizational energies for solvent mixtures of CH3OH/C2H5OH and CH3OD/C2H5OD, respectively. The rate of non-radiative (knr) and radiative decay (kphos) to the ground state and the parameters of thermally activated deactivation pathways (A4th, ΔE4th and Add, ΔEdd) have been determined between 250 and 330 K in CH3OH, CH3OD and CD3OD. The rate of phosphorescence and apparent activation energy of temperature dependent deactivations are not sensitive to the replacement of H to D, while the knr and the pre-exponential factor of thermally activated decay through the 4thMLCT state decreases with the replacement of H to D in the OH group of the solvent. The deuteriation of the methyl group in the solvent results in a small change of knr. The results provide further experimental evidence of the hydrogen-bond determined specific solvent–solute interaction playing important role in the decay of the lowest energy MLCT excited state of [Ru(LL)(CN)4]2− complexes.