Metal Nanocluster Protected By Hexanedithiol: Sythesis, Characterization, And Studies On Their Fluorescence

Based on the work of our group, Ag, Cu and Au nanoclusters protected by 1,6-hexanedithiol were synthesized by partially modified microemulsion technology. The prepared MPCs were analyzed by transmission electron microscope, ultraviolet-visible spectroscope and Fourier transform infrared spectroscope. The results showed that 1,6-hexanedithiol molecules were covalently adsorbed on the metal cluster surface and the MPC particles were dispersed quite well from each other. Furthermore, the fluorescence spectra of the prepared samples were measured out. It was then found that the samples exhibited blue-violet fluorescence, which denotes high-energy and bright emission. And surprisingly, the spectra of all MPCs samples were almost in agreement with one another. The fluorescence characteristics was made clear by the theory of the Solid-state and Molecular models for the mechanism of emitting. Moreover, when the ligand with two–SH adsorbed on the metal cluster surface, the three samples of metal MPCs formed a special structure that was similar to the dendrimer, the structure of which yielded a metal core atoms-limited environment that prevented further nanocluster growth. As the core size decreases, the spacings between discrete states in each band increase, leading to a blue shift in fluorescence. Simultaneity this special structure stabilizes and enhances the nanocluster fluorescence by preventing photodissociation and preventing interaction with quenchers in solution. Because of the formation of S-S bond, the emitting state is a mixed metal-centered transitions and LMCT character. We suggest that this should be a dominating factor for causing the analogical spectra. The backbone of the ligand molecular with two–SH is not important in the formation of luminescence where as the fashion of S-S bond and the structure like the dendrimer play a key role in generating the luminescent species.