Geometrical distortions in excited A₂' states of single-crystal [Ru(bpy)₃](PF₆)₂

Abstract

The absorption band pattern of the E || c-polarized metal-to-ligand charge-transfer transitions in [Ru(bpy)₃](PF₆)₂ have been investigated by a band profile analysis in terms of intensity distributions l(η; Δ, β) of vibrational progressions in totally symmetric normal modes. For a specific state at 18770 cm⁻¹ of A₂' symmetry (classified in the relevant double group D₃') the Δ parameter obtained corresponds mainly to a change in equilibrium geometry of the bipyridine ligands with an increase in average intra-ring C-C (or C-N) distances and a decrease of inter-ring distances. Different geometric distortions occur in higher-lying A₂' states. The results are in accordance with bond length changes determined by a Hückel treatment considering electron density transferred into the π* orbitals of the bipyridinc ligand. The importance of different CT transitions (Ru 4d —› bpy π₁*, π₂*) for the visible absorption band structures is indicated.