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

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.