Ligand effects in photoluminescence of copper nanoclusters.

Copper nanoclusters have attracted significant interest in the field of materials science due to their high abundance, complex structure, and unique properties. However, there is a limited amount of research on the relationship between structure and properties. In this study, we synthesized and comprehensively characterized two new Cu 9 nanoclusters, [Cu 9 (PhSe) 6 (PPh 2 O 2 ) 3 ] (Cu9-1) and [Cu 9 (CH 3 OPhS) 6 (PPh 2 O 2 ) 3 ] (Cu9-2), in order to investigate the effect of ligands on photoluminescence. Both clusters have the same metal skeleton and similar distribution of ligands, with the only difference being the surface ligands (PhSe vs . CH 3 OPhS). Interestingly, the photoluminescence lifetime of Cu9-2 was found to be 3.2 times longer than that of Cu9-1. Furthermore, a notable Stokes shift (ST) was observed in the emission spectra of the two clusters. Single-crystal X-ray analysis revealed the formation of hydrogen bonds between neighboring clusters of Cu9-2, which influenced intramolecular interactions. Additionally, the methoxy groups in Cu9-2, acting as conjugated electron donors, promoted intramolecular charge transfer and π-π interaction. This study is expected to inspire further research on surface ligand engineering for controlling the properties of copper nanoclusters beyond photoluminescence.