Temperature dependence study on photophysics of RuL(CN)4 2− complexes: effects of diimine ligand and solvent deuteration

Photophysics of [RuL(CN)4]2− complexes, where L=2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (dmb), 4,4′-diphenyl-2,2′-bypiridine (dpb), 1,10-phenantrolin (phen), has been investigated by luminescence spectroscopy and flash photolysis at various temperatures. Luminescence quantum yield and lifetime of the 3MLCT excited state have been measured in aqueous solutions and in D2O. The rate of direct deactivations to the ground state via radiative and non-radiative decay and the parameters of the thermally activated deactivation pathway have been determined. The rate coefficients of the radiative decay are quite close to each other (4×104–7×104 s−1) and are not sensitive to the replacement of H to D in the solvent, while the rate of non-radiative decay strongly depends on the nature of the polypyridyl ligand and on solvent deuteration. The activation energy and the pre-exponential factor of the thermally activated deactivation also depend on the nature of the α,α′-diimine ligand. The value of the potential barrier and the pre-exponential coefficient vary between 1010–1400 cm−1 and 5.5×108–14×108 s−1, respectively. Analysis of the emission spectra and the decay kinetics has confirmed that the excited state distortion and the interaction between the excited species and the solvent molecule through H or D bond are the factors that count in determining the rate of non-radiative deactivation pathways.