Role of the Bridge Length and Structure in Photoinduced Mixed‐Valence Systems

The MLCT excited state of the Creutz–Taube analog [(NH 3 ) 5 Ru II ( μ −4,4′‐bpy)Ru II (NH 3 ) 5 ] 4+ was studied using femtosecond transient‐absorption spectroscopy in combination with DFT/TD‐DFT calculations. The computations show that strongly mixed d xz (Ru) orbitals, whose symmetry favors metal–metal interactions, are involved in the lowest‐energy 3 MLCT state. Detection of photoinduced IVCT transitions allowed to calculate, using comparative actinometry and the Mulliken–Hush formalism, an excited‐state electronic coupling of H DA > 1510 cm –1 . The influence of bridging‐ligand conformation was analyzed in the context of ground‐state versus excited‐state mixed‐valence interactions. Despite the long geometric donor–acceptor separation, hole delocalization promoted a two‐order‐of‐magnitude extension of MLCT lifetimes relative to monometallic analogs.