Electron Delocalization and Localization in Mixed-Ligand [Ru(LL)n(LL')3-n]2+ Complexes

Highly resolved emission spectra of isolated [Ru(LL)n(LL')3-nJ²⁺ complexes doped into [Zn(bpy)₃](ClO₄)₂ with LL and LL' representing the ligands bpy-h₈, bpy-d₈, and bpz are presented. The information displayed in the electronic origins and the vibrational satellite structures combined with the emission decay behavior is used to provide a clear distinction between localized and delocalized MLCT transitions to the lowest excited states. In particular, the appearance or nonappearance of ligand-centered vibrational modes belonging to different types of ligands provides crucial evidence for delocalization or localization. Thus, for a localized excitation in [Ru(bpy)₂(bpz)]²⁺ only the ligand-centered modes of bpz can be found in the emission spectra. In contrast, for [Ru(bpy-h₈)₂(bpy-d₈)]²⁺ the ligand-centered vibrations of bpy-h₈ and bpy-d₈ accompany the same electronic origin. This is strong evidence for the delocalization of the excited electron in mixed-ligand [Ru(bpy-h₈)₂(bpy-d₈)]²⁺. Consequently, the lowest MLCT excited states in homoleptic complexes like [Ru(bpy-h₈)₃]²⁺ and [Ru(bpy-d₈)₃]²⁺ are also delocalized over the metal and the different ligands.