Voltammetric Study of Two-Dimensional Phase-Transition Processes of Carboxylated Viologens at an HOPG Electrode as a Typical Organization Process of Molecules Possessing Multiple Interaction Sites

Abstract

Abstract Two-dimensional (2D) phase-transition behavior of three different viologens, heptyl viologen and its mono- and dicarboxylated derivatives, is described using the results of voltammetric measurements at an HOPG electrode. The transition was regarded as a typical 2D molecular organization process under oxidation state control. In an acidic medium, the width of the bi-stable potential region of the phase-transition was found to increase by approximately 55 mV with each addition of a carboxylate group. This fact points to a dominant contribution from intermolecular hydrogen bonding to the reductive formation of the 2D condensed phase. The occurrence of an incomplete transition process resulting in the formation of a metastable phase at lower temperatures, higher potential sweep rates, and higher concentrations was observed for dicarboxylated viologen, but not for monocarboxylated one. These results were used to discuss the advantages and disadvantages of multiple intermolecular interaction sites in a molecule in relation to the 2D molecular organization processes.