Electronic Control of Emission Behavior in Atomically Precise Copper Nanoclusters.

Atomically precise copper nanoclusters (Cu NCs) offer a compelling platform for elucidating structure-property relationships in quantum-confined materials, yet isolating ligand-induced electronic effects without altering core geometry remains a fundamental challenge. Herein, we report a systematic study of four compositionally identical Cu11 NCs in which the metal nuclearity and core architecture are strictly preserved, while only the substitution position and electronic nature of the thiolate ligands are varied. By employing methyl- and amino-substituted benzenethiols (ABT) in para and meta configurations, we precisely modulate the ligand-to-metal electronic communication without perturbing the Cu11 architecture. Despite their nearly identical atomic structures, these NCs exhibit strikingly different photoluminescence behaviors. Comprehensive steady-state and time-resolved spectroscopic analyses, complemented by transient absorption measurements and theoretical calculations, reveal that subtle changes in ligand substitution govern excited-state relaxation pathways, long-lived triplet-like excited-state stabilization, and oxygen sensitivity. Among the series, Cu11-3ABT achieves an exceptional photoluminescence quantum yield of 26.1% under inert conditions, arising from effective excited-state stabilization. This work establishes ligand positional engineering as a powerful and general strategy to control emission dynamics in atomically precise Cu NCs, providing fundamental insights into their excited-state physics and offering new design principles for highly emissive, earth-abundant metal NC systems.