Temperature dependence study on photophysics of RuL(CN42-) 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'-diphenyl2,2'-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 (MLCT)-M-3 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 x 10(4)-7 x 10(4) 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 alpha,alpha-diimine ligand. The value of the potential barrier and the pre-exponential coefficient vary between 1010-1400 cm(-1) and 5.5 x 10(8)-14 x 10(8) 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. (C) 2002 Elsevier Science B.V. All rights reserved.