[Ru(bpy)3]2+∗ revisited. Is it localized or delocalized? How does it decay?

The issue of localization/delocalization of electron spin density in Metal-to-Ligand Charge Transfer (MLCT) excited states of [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) has been debated for almost four decades. Localization/delocalization of MLCT excited states specifically addresses the question regarding electron configuration in the excited state and whether the excited electron in the dπ5π∗1 excited state was localized on one ligand, [RuIII(bpy)(bpy−)]2+∗, or delocalized over all three, [RuIII(bpy−1/3)3]2+∗. This contribution outlines the results of a detailed meta-analysis of available experimental data to delineate the factors that govern how the excited state electron density evolves over the time from excitation until final excited state equilibration. Given the nature of the analysis, a number of interwoven issues are discussed in this article. A cohesive evaluation of the existing data leads to a detailed mechanistic understanding of the events that accrue following excitation of [Ru(bpy)3]2+. The results of the meta-analysis are both remarkably systematic and consistent with existing theories of dynamic processes.