Electrochemical behaviour of viologen-cyclodextrin inclusion complexes. The case of non-alkyl group substituted viologen

Abstract

The electrochemical behavior of non-alkyl substituted viologen, 4,4′-dibenzyl bipyridinium (BzV), 4,4′-dicyanophenyl bipyridinium (CyV) and α-,β-,γ-cyclodextrin (α, β, γ-CD) was studied using cyclic voltammetry and a spectroelectrochemical method. It was found that BzV and Fe(CN) ⁴⁻₆ formed a charge-transfer (CT) complex with a ratio of 2∶1 and the colour of the solution faded with the addition of an electrolyte. This behaviour is the same as in then-heptyl viologen and ferrocyanide system [1]. BzV, α-CD and γ-CD formed an inclusion complex only in the reduced state, whilst BzV and β-CD formed an inclusion complex in both the oxidized and the reduced state. An EC scheme in which a chemical reaction follows an electrochemical reaction was considered to predominate in the BzV and α-, γ-CD systems, while a CE scheme in which a chemical reaction preceded an electrochemical reaction predominated in the BzV and β-CD system. On the other hand, CyV was found to form an inclusion complex with α-, β-, γ-CD in both the oxidized and the reduced states. therefore a CE scheme was considered to predominate in the CyV-α-, β-, γ-CD systems.