Characterizing the Optical and Electrochemical Properties of Monolayer-Protected Noble Metal Nanoclusters

Gold, silver, and other nanoclusters protected by a monolayer of monothiolate or dithiolate ligand can be synthesized into a variety of compositions and core structures depending on the type of ligand used and reaction conditions. Unique size or composition dependent physicochemical properties emerge ranging from being molecular-like to plasmonic toward bulk metal. This dissertation focuses on the characterization of optical and electrochemical and other related properties of newly synthesized and previously established Au and Ag nanoclusters. Chapter one provides an overview of the gold and silver nanoclusters including both fundamentals and applications. In chapter two, phase transfer strategy is adopted to overcome the restraints of using water as an electrochemical solvent. Redox activities in a much wider potential were resolved for newly synthesized aqueous soluble Au nanoclusters stabilized by mercaptosuccinic acid and lipoic acid (LA) and the previously reported Au22LA12. In chapter three, spectroelectrochemistry analysis reveals unprecedented details in electronic transitions from the Au130(p-MBT)50 nanoclusters (sample obtained through the collaboration with Jin’s group). An energy diagram is proposed from the combined optical and electrochemical characterizations in reference to the ultrafast spectroscopy results. Together with the Au130 stabilized by a mixed mono- and di-thiolate ligand monolayer reported earlier by our group, a significant conclusion is reached that up to Au130, a clear energy band gap remains corresponding to molecular energetics. Full transition to metallic will likely occur at larger sizes with appropriate lattice structures. In chapter four, a new silver nanocluster is synthesized with the lipoic acid as its protecting ligands. Optical, electrochemical, and other features were studied to characterize this new cluster. Intense absorbance features along with high but unstable luminescence were observed. Like its gold counterparts, ligand oxidation was observed by FTIR. Further mass spectrometry data is needed to propose a molecular composition