Electro-analytical studies of supramolecular assemblies
Iqbal, Javed (2006) Electro-analytical studies of supramolecular assemblies. Master of Science thesis, Dublin City University.
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Monolayers of [Os(adamantyl-terpy)(terpy-py)][PF6]2 and solid deposits of [Os(4,4'- Diphenyl-2,2’-dipyridyl)2Cl2] have characterised using electrochemical and spectroscopic techniques. Monolayers of osmium terpy complex have been formed by spontaneous adsorption onto chemically cleaned platinum microelectrodes in acetone-water solution and their voltammetric properties were investigated. The voltammetric response of these monolayers is nearly ideal with a peak-to-peak separation 20 ± 4 mV, and a full width at half maximum of 120 ± 8 mV was observed for scan rates less than 100 Vs'1. The effect of decreasing the percentage of acetone in deposition solution did not improve the surface coverage of monolayer. The formation of the monolayers of the complex by monitoring the time evolution and changing in the bulk concentration shows the reversible adsorption occurs and maximum time requires is about 100 minutes to reach the equilibrium conditions. The maximum surface, 1.35 ± 0.10 x 10'u mol cm'2 is achieved when the bulk concentration is 0.3 [iM. High speed chronoamperometry reveals that RC time constant values of bare and modified electrodes are approximately same in the faradaic region.
Mechanically attached, solid-state films of [Os(4,4T-Diphenyl-2,2'-dipyridyl)2Cl2] have been formed on gold macro- and microelectrodes and their voltammetric properties investigated. The voltammetric response of these films associated with the Os2+/3+ redox reaction is reminiscent of that observed for an ideal reversible, solution phase redox couple only when the contacting electrolyte contains of the order of 40% v/v of acetonitrile (ACN). Scanning electron microscopy reveals that voltammetric cycling induces the formation of micro crystals. Voltammetry conducted under semiinfinite linear diffusion conditions has been used to determine the apparent diffusion coefficient, Dapp, for homogeneous charge transport through the deposit. The dynamics of charge transport decrease with increasing film thickness but appear to increase with increasing electrolyte concentration. These observations suggest that ion transport rather than the rate of electron self exchange limit the overall rate of charge transport through these solids. Dapp values for oxidation and reduction are identical at 1.7±0.4xl0‘12 cmV1. In the same electrolyte, the standard heterogeneous electron transfer rate constant, k°, determined by fitting the full voltammogram using the Butler-Volmer formalism is 8.3±0.5xl0"7 cms‘l.
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