A Study On The Aggregation-Induced Emission Of Gold Nanoclusters

AuNCs have gradually become a promising fluorescent functional material due to their good physical and chemical properties,low toxicity and good biocompatibility,they have been explored in various applications,such as fluorescent probes,chemical catalyst,and bioimaging agent.Many researchers have been working on synthesizing gold nanoclusters with high quantum yields.It was found recently that aggregation-induced emission(AIE)mechanism can increase the luminescence intensity of AuNCs by controlling the interaction between the capping ligands.The degree of aggregatioin is affected by several factors,such as the pH of the solution,the type of organic solvent and introducing large molecules as capping ligand.However,the detailed mechanism of AIE and how to use it to control the luminescence of AuNCs has not been thoroughly studied.In this thesis,the correlation between the structure and luminescence properties of AuNCs with AIE properties was studied by means of photoluminescence spectroscopy,transmission electron microscopy,infrared spectroscopy,dynamic light scattering,and photoelectron spectroscopy.The main research content include:(1)The effect of pH on the AIE properties of the synthesized gold nanoclusters.We synthesized AuNCs with glutathione as the capping ligand in an alkaline environment.The AuNCs then undergo several cycles of pH adjustment from basic to acid and back to basic.The associated luminescence was monitored,and the intensity of the luminescence is found closely related to the degree of aggregation of the clusters.(2)The effect of solvent species on the AIE properties of the synthesized gold nanoclusters.Two groups of solvents were selected to examine how they affect the luminescence of AuNCs.Group ? solvents contains methanol,ethanol and isopropanol,and they have the same functional groups but different dielectric constants.and Group ?solvents contains dimethyl sulfoxide,ethanol and acetone,which are of different dielectric constants and functional groups.The relationship between the solvent properties and the AIE characteristics of the nanoclusters was analyzed by systematically measuring the effect of the type of solvent and its concentration on PL.(3)The study on the AIE properties of AuNCs stabilized by N-acetyl-L-cysteine-Glycol-chitosan(NAC-GC)complexes.The cationic polymer GC and NAC was combined to form a complex by electrostatic interaction at a suitable pH,and then stabilize the gold nanoclusters by thiol groups on the NAC,The AuNCs@NAC-GC structure was finally synthesized.The gold nanoclusters synthesized by this method not only show improved the water solubility,but also emit stronger red light with a higer quantum yield.This chapter studies the luminescence mechanism and bioimaging application of AuNCs@NAC-GC.(4)The effect of luminescence upon formation bimetallic nanoclusters.Zn ions was introduced into AuNCs to form Au-Zn bimetallic nanoclusters.The luminescence can be further enhanced via the AIE mechanism by introducing GC ligands.