The Remarkable Properties of α-Diimine Rhenium Tricarbonyl Complexes in Their Metal-to-Ligand Charge-Transfer (MLCT) Excited States

Abstract

α-Diimine rhenium tricarbonyl complexes [(L)Re(CO)₃(α-diimine)]^α/+ are exceptional among organometallic complexes in showing emission from their MLCT states at room temperature in fluid solution. The properties of these states can be “fine-tuned” by variation of the α-diimine and co-ligand L, the solvent and the rigidity of the medium. Light-induced energy and electron transfer processes occur inter- and intramolecularly. Reductive quenching of the MLCT state leads to a charge-separated LLCT state. The excited state properties of these chromophore-quencher complexes seem to be related to those of the binuclear metal-metal bonded complexes [L_nMRe(CO)₃(α-diimine)] (L_nM = metal fragment).

Key Words:

• α-diimines
• rhenium tricarbonyls
• metal-to-ligand charge transfer
• emission
• ligand-to-ligand charge transfer
• energy and electron transfer
• ligand-bridged complexes
• metal-metal bonded complexes
• chromophore-quencher complexes