Heavy-Atom Effect Modulated Photoluminescence Properties of Trinuclear Copper(I) Clusters with Haloarylacetylene Ligands

Copper(I) clusters have attracted significant interest due to their ultrasmall size, excellent photostability, large Stokes shift, and long emission lifetime. However, research on their structure-property relationship remains limited. In this study, we synthesized and comprehensively characterized a series of trinuclear copper(I) clusters, [Cu₃(dppm)₃(C≡CC₆H₄X)₂]PF₆ [Cu₃-X, X = F, Cl, Br, and I, dppm = bis(diphenylphosphino)methane], in order to investigate the effect of ligands containing heavy atoms on photoluminescence. All clusters have the same triangular metal core and similar distribution of ligands, with the only difference being the substituent on the phenyl ring of the arylacetylene ligand. Owing to the heavy-atom effect, a notable Stokes shift was observed in the emission spectra of the clusters. Specifically, the emission peak of <b>Cu₃-I</b> reached 564 nm, representing a 73 nm red shift compared to that of <b>Cu₃-F</b>. Furthermore, <b>Cu₃-Br</b> showed an absolute photoluminescence quantum yield of 15.24% and a lifetime of 114.56 μs, corresponding to 3.3-fold and 3.7-fold increases over the values for <b>Cu₃-F</b>. This study provides novel insights into the heavy-atom effect of surface ligands on the luminescence of copper(I) clusters and offers a robust platform for probing their structure-property relationships.