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.