From monolayers to nanostructured materials: An organic chemist's view of self-assembly

Simple methods are described for the production of gold nanoparticles with narrow size distributions by reduction of tetrachloroaurate solutions in the presence of thiol-containing organic compounds which self-assemble on the gold surface. Stable solutions of somewhat larger particles can be produced if the thiol is absent. The thiol-derivatized materials are stable in air over long periods and can be handled in much the same way as simple organic compounds. Using dithiols as the derivatizing spacer units, ways have been developed for the preparation of materials in three dimensional form and as thin films attached to a solid substrate. Such materials show conductivities that mimic the behaviour of semiconductors and that depend markedly on the structure of the dithiol used to link the gold particles together. The increase in conductivity with increasing temperature probably involves activated electron hopping from particle to particle. Surfaces treated with a coating of the materials show electroreflectance changes with applied potential that also differ according to the structure of the dithiol spacer. Unusual effects have been observed on heterogeneous electron transfer from electrode surfaces treated with layers of the gold nanoparticles and dithiol spacers. Applications for these nanostructured materials can be envisaged, which range from submicroelectronic devices and circuitry to electrical modification of the reflectance of glass. Such applications will require a multidisciplinary approach with a substantial organic chemical research input.