Mechanism of electron transfer rate control in hybrid redox polyether molten salts. Part 2. Spectroelectrochemistry of monolayer protected gold clusters

Chapter I outlines the reasons for studying electron transfer in the solid state and gives an overview of the studies done in hybrid redox polyether molten salts. These model semisolids are used to systematically understand the effects of rigidity on electron transfer and mass transport. In Chapter II the fluidity of polypyridine Co(II) melts is manipulated by changing the oligomeric chain lengths and by adding unattached oligomers as plasticizers. The electrochemically measured mass transport and electron transfer properties of these melts are presented. In general, the barriers to electron transfer in melts are larger than predicted. This was presumed to be caused by a solvent dynamics contribution to the barrier. However, the Chapter II results reveal a 1:1 proportionality between both heterogeneous and homogeneous electron transfer rates and counterion diffusion in these materials. The unknown contribution to the energy barriers is now concluded to be the slow relaxation rate of the ion atmosphere after electron transfer. The electron transfer rate correlations with mass transport in cobaltocenium based melts described in Chapter III prove more general applicability of the ion atmosphere relaxation model for describing electron transfer in semi-solid materials.; The nature of electron transfer in melts is probed further by studying optically induced electron transfer. A newly developed in situ electrochemical method of producing the mixed-valence states necessary to observe optically induced electron transfer is characterized in Chapter IV. The near-IR spectroscopic characteristics of mixed-valence cobalt trisphenanthroline, ferrocenylmethyltrimethylammonium, and cobaltocenium melts are described. These results reveal low electronic coupling in these mononuclear melts. In addition, an analysis of the cobaltocenium results gives another prediction of smaller than observed thermally induced electron transfer energies.; Monolayer-protected gold clusters (MPCs) are nanoparticles made up of 10s--100s of atoms that mark the transition between molecular and bulk properties of metals and display interesting size-based properties. Spectroelectrochemical characterization of MPCs made up of 38 and 140 gold atoms is presented in Chapter V. The HOMO-LUMO band gap of Au38 clusters is verified by the low energy absorbance bleach upon oxidation. Applying positive potential to Au140 clusters causes spectroscopic changes indicative of ligand dissociation.