New Ru(II) Complexes for Dual Photoreactivity: Ligand Exchange and 1O2 Generation

ConspectusUncovering the factors that govern the electronic structure of Ru(II)–polypyridyl complexes is critical in designing new compounds for desired photochemical reactions, and strategies to tune excited states for ligand dissociation and 1O2 production are discussed herein. The generally accepted mechanism for photoinduced ligand dissociation proposes that population of the dissociative triplet ligand field (3LF) state proceeds through thermal population from the vibrationally cooled triplet metal-to-ligand charge transfer (3MLCT) state; however, temperature-dependent emission spectroscopy provides varied activation energies using the emission and ligand exchange quantum yields for [Ru(bpy)2(L)2]2+ (bpy = 2,2′-bipyridine; L = CH3CN or py). This suggests that population of the 3LF state proceeds from the vibrationally excited 3MLCT state. Because the quantum yield of ligand dissociation for nitriles is much more efficient than that for py, steric bulk was introduced into the ligand set to distort the...