Effect of α- and β-cyclodextrin on the electrochemistry of methylheptylviologen and dibenzylviologen

The electrochemistry of N-methyl-N′-heptyl-4,4′-bipyridinium (C₁C₇V²⁺) and N,N′-dibenzyl-4, 4′-bipyridinium (BBV²⁺) salts with α-cyclodextrin and β-cyclodextrin (CD) was studied. The cyclic voltammetric behavior of both viologens revealed a cyclodextrin-induced conproportionation reaction between the electrogenerated viologen neutral forms and viologen dications with β-CD, but not with the α form. Both α-CD and β-CD suppress dimerization of C₁C₇V²⁺, whereas only β-CD is effective for disruption of the BBV^.+ dimer. These results are interpreted in terms of the involvement of the bipyridine ring and benzyl group, depending on the oxidation state of viologen, in the inclusion complexation with β-CD, but not significantly with α-CD.