Electrochemical Regulation of the Dynamic Behavior of Mososcopic Molecular Assemblies at Solid-Liquid Interfaces

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(1) The dynamic behavior of a viologen monolayer on a Au electrode surface was investigated. It was found that the redox potential is strongly affected by ingress-egress of the counter anion coupled with the binding interaction and that the monolayer memorizes the anion present when forming the monolayer, though the memory is erased by the addition of a softer anion in the electrolyte solution. Significance of the dynamic ion transfer process was demonstrated in the terms of not only charge compensation but also monolayer structure.(2) It was found that a water-insoluble dye, hypericin, undergoes redox reaction on an electrode surface in an aqueous medium when the dye is incorporated into a cationic artificial lipid film. The redox potential was found to be controllable by regulating the lipid structure.(3) Octadecylrhodamine B gave rise to two types of electroreflectance responses, faradaic response due to the redox process and non-faradaic one due to, for example, dynamic adsorption-desorption process. Addition of a surfactant made the redox reaction be more reversible while annihilating the non-faradaic processes.(4) The voltammetric spike response of heptylviologen at a HOPG electrode horizontally-touched to gas/heptylviologen aqueous solution interface was investigated in detail. The conditions of the appearance of the spike were listed up. It was found that the spike response is due to the first-order faradaic phase-transition process between a Gibbs film at a gas/solution interface and a Langmuir monolayer. The dynamics was governed by nucleation-growth-collision kinetics.(5) Dynaunic processes of Au nano-particles immobilized on a monolayer-modified Au electrode were studied using electroreflectance methods. An electroreflectance response due to potential-dependent charging-discharging process of the Au nano-particle was clearly observed at the wavelength of surface plasmon absorption.