[Show abstract][Hide abstract] ABSTRACT: The characterization of the adsorption/desorption of water insoluble surfactants onto an electrified interface is reviewed. Electrochemical and spectroelectrochemical investigations of the role of potential in controlling the nature of the surfactant present at the interface is described. The adsorption of octadecanol, cis-9-octadecenol onto Au(1 1 1) and the adsorption of DOPC (from a monolayer or from a dispersion of liposomes) onto Hg are used as examples. A general mechanism was proposed to describe the potential-dependent phase changes, desorption and subsequent readsorption process that links the results from impedance, fluorescence and elastically scattered light measurements of the surfactant-modified interface. This proposed mechanism and results from fluorescence microscopy results were used to describe the creation of a hybrid adsorbed hemi-liposomal layer onto a Hg surface. The implications for thermodynamic analysis via the electrocapillary equation for this class of surfactants were discussed. The relevance of the general mechanism towards the reductive desorption of alkyl thiol SAMs was also outlined.
[Show abstract][Hide abstract] ABSTRACT: The study of heterodentate molecules adsorbed on metal electrodes provides an opportunity to expand the functionality of modified surfaces while offering insights into the surface and intramolecular electronic interactions of organic adsorbates. The adsorption of 2-(2'-thienyl)pyridine, a molecule containing both pyridine and thiophene moieties, on a Au(111) electrode is reported. Adsorption was characterized by electrochemistry in neutral and basic aqueous electrolyte and was compared to that of pyridine. The aqueous electrochemistry of thiophene on Au(111) was also characterized for comparison purposes. At negative potentials, in the presence of 2-(2'-thienyl)pyridine, a diffuse, pi-bonded monolayer was formed, and a phase transition to a close-packed N- and/or S-bonded configuration was observed near -0.4 V in a 1 mM solution of adsorbate, similar to that seen in pyridine on Au(111). The thiophene-like oxidative dimerization of the molecule was confirmed at positive potentials using in situ fluorescence microscopy by comparison with the spectrum of the chemically synthesized dimer.
[Show abstract][Hide abstract] ABSTRACT: The reductive desorption of a self-assembled monolayer (SAM) of a fluorescent thiol molecule (BodipyC10SH) from Au was characterized using electrochemistry and epi-fluorescence microscopy. Molecular luminescence is quenched near a metal surface, so fluorescence was only observed for molecules reductively desorbed and then separated from the electrode surface. Fluorescence imaging showed that reductive desorption was selective, with desorption occurring from different regions of the Au electrode depending on the extent of the negative potential excursion. When desorbed, the molecules were sufficiently mobile, diffusing away from the electrode surface, thereby preventing oxidative readsorption. At sufficiently negative desorption potentials, all of the thiol was desorbed from the electrode surface, resulting in fluorescence at the air/solution interface. The selective removal of the thiol monolayer from distinct regions was correlated to features on the electrode surface and was explained through potential-dependent interfacial energies. This in situ electrofluorescence microscopy technique may be useful in sensor development.
Journal of the American Chemical Society 08/2004; 126(26):8329-35. DOI:10.1021/ja0494095 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Switching between three different adsorbed states was achieved using potential control to separately induce electrochemical behaviour associated with changes in binding and orientation of the thiophene and pyridine moieties of 2-(2'-thienyl)pyridine adsorbed to Au(111) in neutral and basic solution.
Chemical Communications 01/2003; DOI:10.1039/b208912b · 6.83 Impact Factor