Luminescence and redox reactions of the metal-to-ligand charge-transfer excited state of tricarbonylchloro-(polypyridyl)rhenium(I) complexes

Abstract

The metal-to-ligand charge-transfer (MLCT) excited state of tricarbonylchloro(polypyridyl)rhenium(I) complexes, [Re(CO)₃(LL)(Cl)], (LL = 2,2-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 1,10-phenanthroline, 5-chloro-1,10-phenanthroline and 2,2′-bipyrazine) is emissive in solution at room temperature and undergoes facile electron-transfer reactions with a variety of electron donor and acceptor molecules. Laser photolysis studies on three aspects of the excited-state photophysics and photoredox chemistry are described in this work: (a) sensitivity of the room-temperature absorption and emission to variation in the nature of the polypyridyl ligand and solvent; (b) excited-state absorption spectral features and (c) reversible and irreversible ‘reductive’ quenching (using various amines as electron donors) and their relevance to the photocatalytic reduction of CO₂ to CO.