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(III) by two mono-anionic facial -carbene ligands can markedly suppress such deactivation. The resulting complex [Fe(phtmeimb)], 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) state to the doublet ground state. Reductive and oxidative electron-transfer reactions were observed for the LMCT state of [Fe(phtmeimb)] in bimolecular quenching studies with methylviologen and diphenylamine.
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