Nanocrystalline Gold Arylthiolate Molecules

• Main Author: Price, Ryan Cameron
• Format: Others
• Language: en_US
• Published: Georgia Institute of Technology 2007
• Subjects: Gold nanoparticles; Benzenethiolate; Quantum dots; Raman spectroscopy; Monolayer protected cluster; Electrochemistry; Exchange reactions; Nanocrystals; Nanoparticles
• Online Access: http://hdl.handle.net/1853/14051

This research focuses on generating, isolating, and characterizing nanophase gold clusters with diameters below two nanometers. In this size regime, the metal cores exhibit electronic and optical properties very different from those of colloidal and bulk gold, arising from quantum size confinement. The unoccupied molecular orbitals of the cores are known to accept electrons, analogous to a capacitor, but with discrete electrochemical potentials. This work describes the novel production of gold clusters with structurally rigid benzenethiolate bound to the surface, rather than typically used alkanethiolates. The Aux(benzenethiolate)y clusters are anionic and charged balanced by tetraoctylammonium cations. They are enriched in ~1.5 nm diameter cores, compared to a dominance of 1.7 nm cores when alkanethiols are used during synthesis. The Aux(benzenethiolate)y clusters are more likely to form bulk crystals and possess enhanced electrochemistry relative to Aux(alkylthiolate)y clusters. They are characterized by x-ray diffraction, carbon and proton NMR, FTIR, optical spectroscopy, mass spectrometry, elemental analysis, and thermogravimetric analysis. The etching of clusters in the presence of hydrogen peroxide and excess benzenethiol to yield smaller 1.1 nm clusters is reported for the first time in this work. These 1.1 nm clusters have a rich optical spectrum with clear electronic transitions at room temperature and orient spontaneously when deposited from solution. This oxidative etching process was applied to alkanethiolate clusters, converting ~2.0 nm polydisperse clusters into smaller clusters. This offers the potential to produce smaller gold clusters with more available charge states and may allow increase the types of thiols that can be bound to the surface of gold monolayer protected clusters (MPCs), known also as quantum dots. The use of the bulky thiol, tert-butylmercaptan to produce 1.5 nm core gold clusters is also reported, indicating sterically hindered alkanethiols can play a role in limiting the size of Aux(alkylthiolate)y clusters. These clusters were characterized by x-ray diffraction, proton NMR, FTIR, optical spectroscopy, and mass spectrometry. The clusters are potentially useful for thiolate exchange reactions to produce new types of Aux(thiolate)y clusters.