Impact of the Peripheral Ligand Layer on the Excited-State Deactivation Mechanism of Au₃₈S₂(S-Adm)₂₀ and Au₃₀(S-Adm)₁₈ (S-Adm = Adamantanethiolate) Clusters

Gold nanoclusters are ideal fluorescent labels for biological imaging, disease diagnosis, and treatment. Understanding the origin of the photoluminescence phenomenon in ligand-protected gold nanoclusters is crucial for both basic science and practical applications. In this study, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed to study the mechanism of excited state deactivation of Au₃₈S₂(S-Adm)₂₀ and Au₃₀(S-Adm)₁₈ (S-Adm = adamantanethiolate) clusters, which have similar sizes and compositions. The computational results indicate that the differences in structural symmetry and peripheral ligand layer lead to quite different excited state deactivation mechanisms and excited state lifetimes in Au₃₈S₂(S-Adm)₂₀ and Au₃₀(S-Adm)₁₈. Specifically, the μ₃-S atoms and bridging thiolate (SR) in the ligand layer of Au₃₈S₂(S-Adm)₂₀ significantly suppress the structural relaxation of ligand motifs, resulting in a prolonged excited state lifetime and higher quantum yield. For the Au₃₀(S-Adm)₁₈, due to the symmetry forbidden and large structural relaxation of the ligand shell, a rapid nonradiative transition process resulted. This study provides new insights into how the photoluminescence of ligand-protected gold nanoclusters is influenced by their structure and symmetry.