Ligand effects in photoluminescence of copper nanoclusters

Abstract

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 Cu₉ nanoclusters, [Cu₉(PhSe)₆(PPh₂O₂)₃] (Cu₉-1) and [Cu₉(CH₃OPhS)₆(PPh₂O₂)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. CH₃OPhS). 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.