Air-Stable Nickel(0) Complexes with Room-Temperature Photoluminescence

Among first-row transition metals, copper-(I) plays a central role in photophysics and photochemistry due to its closed d¹⁰ subshell, which makes unwanted excited-state deactivation processes less prevalent than in metal complexes with incompletely filled 3d orbitals. Building on the isoelectronic analogy between nickel(0) and copper-(I), we develop photoactive nickel(0) complexes that, for the first time, approach the photophysical performance of their copper-(I) counterparts. By creating a coordination sphere that stabilizes the zero-valent oxidation state through strong π-backbonding and shielding it from the chemical environment, we obtain two nickel(0) complexes that are inert towards oxidation by air and show luminescence from a metal-to-ligand charge-transfer (MLCT) excited state with a quantum yield of near 0.03% and a lifetime of approximately 4 ns in solution at room temperature. The more electron-rich nature of nickel(0) compared to copper-(I), as well as the unique role of nickel in modern cross-coupling catalysis, open perspectives for new inner-sphere photocatalysis beyond conventional photoredox strategies relying on simple molecular collisions, in addition to luminescence-based applications. Overall, this work contributes to the advancement of photoactive complexes based on abundant first-row transition metals and identifies new opportunities for photophysics and photochemistry compared to well-established noble metal-based coordination compounds.