Dual Emission in Au2Cu6 Nanoclusters Regulated by Excited-State Structural Reorganization

Abstract

Atomically precise metal nanoclusters exhibiting dual triplet emission provide a molecular-level platform for probing environment-dependent triplet-state relaxation. However, how local microenvironments redirect triplet relaxation between competing emissive states remains unclear. Here, we report pronounced medium-dependent dual emission in a heterometallic Au2Cu6(S-Adm)6(PPh2Py)2 nanocluster, where S-Adm is 1-adamantanethiolate. In tetrahydrofuran (THF) and dichloromethane (DCM) solutions, Au2Cu6 exhibits two emission bands at ca. 680 and 840 nm, whereas the lower-energy 840 nm band is markedly attenuated in the rigid poly(methyl methacrylate) (PMMA) matrix and in a specific aggregate state in THF/H2O mixtures at φH2O = 60%. Steady-state and time-resolved spectroscopic measurements support the involvement of two triplet-related emissive configurations. The 680 nm emission is associated with a higher-energy locally excited (LE)-like triplet configuration exhibiting predominantly phosphorescent character, whereas the near-infrared 840 nm band is associated with a lower-energy charge-transfer (CT)-like triplet configuration. The balance between these channels is governed by microenvironment-dependent excited-state structural relaxation, associated with reorganization from LE-like to CT-like. These findings highlight microenvironmental regulation of competing triplet-emission pathways as a promising strategy for tuning dual emission in atomically precise metal nanoclusters.