Excited State Modulation of Copper Clusters Realized by Single-Site Alteration Achieving Near-Infrared Luminescence

Modulating the excited states of coinage metal clusters can effectively improve their photophysical properties, and significant progress has been realized through ligand modification and heterometallic doping. However, precise substitution of individual atoms within the kernel remains a formidable challenge. Herein, we present three copper cluster analogs, namely Cu₄S, Cu₄Se, and Cu₄P, displaying distinct thermally activated delayed fluorescence (TADF), wherein Cu₄S and Cu₄Se display yellow luminescence with QYs of 99.2% and 89.0% respectively, while Cu₄P with the first HP^2- unit in copper clusters exhibits near-infrared (NIR) emission with a QY of 22.2%. Theoretical calculations have verified that the energy levels of excited states in copper clusters are modulated by substituting the central coordinating atoms. The spin-orbit coupling of Cu₄P, Cu₄S, and Cu₄Se, as well as the structural deformation differences between the excited state and the ground state, leads to the different luminescence quantum yields. This study not only reports the first HP^2--involved copper cluster but also establishes a platform for investigation on single-site modulation directed luminescence of copper clusters.