Luminescence and reactivity of a charge-transfer excited iron complex with nanosecond lifetime

Iron's abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer states of most iron complexes are limited by picosecond or subpicosecond deactivation through low-lying metal-centered states, resulting in inefficient electron-transfer reactivity and complete lack of photoluminescence. In this study, we show that octahedral coordination of iron(Ill) by two mono-anionic facial tris-carbene ligands can markedly suppress such deactivation. The resulting complex [Fe(phtmeimb)(2)](+), where phtmeimb is {phenyl[tris(3-methylimidazol-1-ylidene)]borate}(-), exhibits strong, visible, room temperature photoluminescence with a 2.0-nanosecond lifetime and 2% quantum yield via spin-allowed transition from a doublet ligand-to-metal charge-transfer ((LMCT)-L-2) state to the doublet ground state. Reductive and oxidative electron-transfer reactions were observed for the (2)LMCTstate of [Fe(phtmeimb)(2)](+) in bimolecular quenching studies with methylviologen and diphenylamine.