Metal to ligand charge transfer photochemistry of Re(I)-alkyl complexes

Abstract

A preliminary study has been carried out concerning the photochemistry and photophysics of a series of (bpy)Re I(CO) 3-R complexes, where bpy is 2,2′-bipyridine and R=−CH 3,−CH 2Ph and −Ph. Photolysis of the complexes into the lowest energy absorption band (436 nm) leads to a highly efficient ReC bond homolysis reaction for R=−CH 3 and −CH 2Ph. Absorption and low-temperature emission studies of the complexes suggest that the lowest excited state is based on dπ (Re)→π * (bpy) metal to ligand charge transfer (MLCT). Nanosecond transient absorption studies confirm that the MLCT stare is formed after near-UV excitation of (bpy)Re(CO) 3-Ph; however, only the reactive intermediate which is formed as a result of ReC bond homolysis is observed for (bpy)Re(CO) 3−CH 3 and (bpy)Re(CO) 3−CH 2Ph. The results are interpreted by a photochemical model in which the bond homolysis reaction occurs either directly from an unrelaxed MLCT excited state or from a spectroscopically silent state which is reached during non-radiative relaxation of the Franck-Condon MLCT state.