Tuning the fluorescence property of copper nanoclusters

A study on tuning the fluorescence property of Cu nanoclusters by thiol ligands was presented. The photoluminescence (PL) measurements show that the luminescent wave-length of Cu nanoclusters capped by 2-mercapto-5-n-propylpyrimidine (MPP) is gradually blue-shifted from 623 nm to 584 nm, with increasing concentrations of dodecanethiol (C12SH) added into the solution. The added thiol ligands, as suggested by mass spectra, do not change the number of Cu atoms in the clusters, but replace some of the original MPP ligands. X-ray absorption fine structure (XAFS) spectra reveal that with the increment of C12SH ligands, the Cu—Cu bonds disappear, the Cu—S bond length is contracted from the original 0228 nm to 0.224 nm, and the charge transfer from Cu to S is enhanced. Moreover, the etching effect of C12SH ligands leads to the change of atomic configuration of the Cu cores from the tetrahedron-alike structure to the chain-like structure of —S—Cu—S—. As a result, the electronic features of the Cu clusters show a metallic-to-covalent transition, resulting in the blue-shift of the luminescence and optical absorption wavelengths.