Electrochemical behavior of viologens with long alkyl chains depending on their concentrations and the concentration of micelles and cyclodextrins

Abstract

The concentration dependence of the electrochemical behaviors of 1- methyl-1'-alkyl-4,4'-bipyridinium chloride (C1C(n)V2+: n = 14, 16, 18) was investigated using cyclic voltammetric, chronocoulometric and spectroelectrochemical techniques. The electrochemical behavior was investigated in terms of critical micelle concentrations (CMCs) of C1C(n)V2+ determined by spectroscopic methods. The voltammetric behavior of these three surfactant viologens at lower and higher concentrations than their CMC varied: the relieved adsorption/precipitation of 1e- reduction product was observed for C1C14V2+ with an increase in its concentration, whereas reorientation after adsorption/precipitation resulted in two anodic peak responses for C1C16V.+ and C1C18V.+. These phenomena were interpreted as the competition between electrodeposition and dissolution into the micelle. This was supported by the incorporation of C1C14V.+ into cetyltrimethylammonium bromide (CTAB) micelle despite their electrostatic repulsion. Stabilization of the viologen cation radical (V.+) by cyclodextrins (CDs) was also observed, where α-CD and methylated β-CD were more effective than β-CD in suppression of adsorption/dimerization of viologens having a long alkyl chain.