Some spectroscopic aspects of electron transfer in ruthenium(II) polypyridyl complexes

摘要

The metal-to-ligand charge transfer (MLCT) absorption and emission properties of several ruthenium(II)-bipyridine am(m)ine complexes are compared. The Gaussian deconvolution of the spectra indicates that: (a) the emission MLCT bandwidths are smaller than the absorption bandwidths for the first components of the apparent vibronic progressions; (b) the emission bands decrease in energy and width when a polypyridyl is replaced by an am(m)ine. The observations can be interpreted in terms of a two state model and the perturbation theory-based treatment of the attenuation of the effective reorganizational energy, λ_r approx=λ_r~o(1-4a_(DA)~2), where λ_r~o is the reorganizational energy corresponding to no mixing between the two electron transfer states and α_(DA) = (H_(DA)/E_(DA)) is the mixing coefficient. Both the solvent and molecular contributions to λ_r are attenuated. The MLCT excited state lifetimes also decrease with am(m)ine substitution, and the non-radiative decay rate constant at 77 K is roughly number of am(m)ine moieties coordinated to the ruthenium center.