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

Abstract

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.