Rapid screening and separation of fluorescent clusters: a case study of Au9Cu5

Abstract

The rapid pre-screening and separation of strongly fluorescent clusters are critical for advancing research on fluorescent cluster properties and applications. However, these methods remain unexplored for oil-soluble clusters. In this work, the strong fluorescence characteristics of clusters enable rapid screening and separation of Au₉Cu₅ from mixed clusters via thin-layer chromatography (TLC). The Au₉Cu₅ cluster features an icosahedral Au₉Cu₄ core, shielded by a (DPPP)₂CuCl₂ motif, four DPPP ligands, and two Cl atoms, with the overall charge stabilized by two BPh₄⁻ counterions. Using chair BDPP instead of DPPP, optically active R/S-Au₉Cu₅ clusters were synthesized, exhibiting a dissymmetry factor (g) of 0.75 × 10⁻⁴—a moderate value among clusters. This arises primarily because the introduction of R/S-BDPP distorts only the cluster's surface motif, while the core retains high symmetry, with chiral signals still predominantly originating from ligand-to-metal charge transfer (LMCT). Further comparison of fluorescence properties reveals a 3-fold enhancement in the quantum yield of R/S-Au₉Cu₅ over Au₉Cu₅ (6.5% vs. 2.0%). Structural analysis attributes this improvement to the closer proximity of peripheral metal atoms to the core in R/S-Au₉Cu₅.