Growth And Fluorescence Performance Of Gold Nanoclusters

Gold nanoparticles have been research hotspots for a long time mainly because of their applications in optical, electronic, magnetic, catalytic and biomedical fields, as well as their stability and extraordinary diversity of preparation methods. In recent years, the ultra-small nanoparticles, so-called gold nanoclusters, have gained tremendous research efforts based on the plentiful reports about gold nanoparticles. The ultra-small size of these nanoclusters induces distinctive quantum confinement effects, which result in discrete electronic structure and molecular-like properties. The recent advances in the synthesis and characterization of gold nanoclusters have opened an avenue to making truly monodisperse nanoclusters and attaining the precise control of their atomic composition. Structural determination by X-ray crystallography significantly promote our understanding of the underlying physics and the important structure-property relationships. Fluorescent gold nanoclusters have been attractive sensing and imaging materials for their large Stokes shift, good biocompatibility and obvious fluorescence. In this dissertation, based on the pre-existing work, we conducted some novel researches on the adsorption process of ligands on gold nanocrystals, the formation process of Au nanoclusters and the fluorescent properties of gold nanoclusters.This dissertation include:1. Adsorption kinetic process of thiol ligands on gold nanocrystalsGold nanoparticles(NPs) capped by triphenylphosphine(PPh3) were prepared by liquid phase synthesis method and the adsorption kinetics of dodecanethiol ligands on gold nanocrystals by an in-situ XAFS technique were studied. Ligand coverage shows a quick increase from 0 to 0.40 within the first 20min, followed by a much slower increase to the limiting value of 0.94. In-depth analysis suggests that the the first stage involves the quick adsorption of dodecanethiol to the corner and edge sites of Au NCs surfaces, leading to remarkable surface Au-Au bond length relaxation and pronounced gold-to-ligand charge transfer. The second step that corresponds to the much slower adsorption process to the surface facets could be described by the Langmuir kinetics equation with an adsorption rate constant of 0.0132 min-1 and an initial coverage of 0.41.2. In situ studies on controlling an atomically accurate formation process of goldnanoclusters.The "top-down" synthetic process of monodisperse Au13 nanoclusters via HC1 etching polydisperse Au13 clusters (15≤ n≤ 65) is traced by a combination of in-situ X-ray/UV-vis absorption spectroscopies and time-dependent mass spectrometry. It is revealed experimentally that the HC1-induced synthesis of Au13 is achieved by accurately controlling the etching process with two distinctive steps. The first step involves the direct fragmentation of the initial larger Aun clusters into metastable intermediate Au8-Au13 smaller clusters. This is a critical step, which allows for the second size-growth step of the intermediates to evolve into the atomically monodisperse Au13 clusters via incorporating the pre-existing Au(I)-Cl oligomers. Due to the second-growth step, the obtained monodisperse end product has a very high yield (-70%) relative to the polydisperse starting material, in sharp contrast to the low-yield of the thiol-etching cases where a large portion of excess Au atoms are dissolved as Au(I) species and are wasted.3. Fluorescent gold nanoclusters and their sensing applicationsFluorescent gold nanoclusters Au@DHLA NCs were prepared from larger gold nanoparticles through the ligand-induced etching method and the emission spectra were centered at 683 nm. The luminescence emission originates from the mechanism of aggregation-induced emission(AIE) through the analysis of the compositions and structures of the NCs. These water-soluble fluorescent gold nanoclusters can be used as probes for sensitive and selective detection of Fe2+, and the limit of detection(LOD) was estimated to be 4.06 μM. The fluorescence response mechanism was proposed through the analysis of the relationship between the concentration of the Fe2+ and the fluorescent intensity.4. Fluorescence of Au(I)-thiolate complexes affected by solventFluorescent Au(I)-thiolate complexes are synthesized in the weakly polar solvent of toluene and the composition was [Au1.5(SR)14-16]+. Through the analysis of the relationship between the fluorescence intensity and the polarity of reaction solvent, we propose that the fluorescence of Au(I)-SR complexes originates from the aggregation of the bilayer supramolecular structures induced by the weakly polar solvent. This aggregation strengthens the intra and intercomplex aurophilie Au(I)-Au(I) interactions and subsequently the luminescence intensity of the complexes.