Theoretical Insights into the Impact of the Central Atom on the Photoluminescence Mechanisms of Ligand-Protected Cu Nanoclusters

Ligand-protected copper nanoclusters (CuNCs) have attracted considerable attention in both fundamental research and practical applications due to their easy availability, environmental friendliness, and exceptional optical properties. In this study, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were employed to investigate the photoluminescence (PL) mechanism of two-electron (2<i>e</i>) cluster [Au@Cu₁₄(SCH₂CH₃)₁₂(P(CH₂CH₃)₃)₆]⁺ (<b>Au@Cu</b>_<b>14</b>) and zero-electron (0<i>e</i>) cluster [Cl@Cu₁₄(SCH₂CH₃)₁₂(P(CH₂CH₃)₃)₆]⁺ (<b>Cl@Cu</b>_<b>14</b>) to explore the impact of the central atom on the PL mechanisms of CuNCs. The accuracy of various exchange-correlation (XC) functionals used for fluorescence and phosphorescence energy calculations was evaluated. The BP86 and PBE0 functionals were used to calculate the radiative and nonradiative transition processes of the two clusters. Theoretical calculations showed that enhanced spin-orbit coupling, larger transition dipole moments, more significant orbital overlap, and smaller Huang-Rhys factors and reorganization energies were the main reasons for the higher PL quantum yield (PLQY) of <b>Au@Cu</b>_<b>14</b> than <b>Cl@Cu</b>_<b>14</b>. These findings provide important insights into the central atom effect of CuNCs and valuable guidance for their design and optimization in optical applications.