Inclusion of methylviologen in cucurbit[7]uril

Abstract

The inclusion behavior of methylviologen (N,N′-dimethyl-4,4′-bipyridinium, MV) dication in cucurbit[7]uril (CB[7]) has been studied by using various spectroscopic and electrochemical methods. The inclusion complex of MV dication in CB[7] is stable thermodynamically and kinetically. The electrochemical study reveals that unlike β-cyclodextrin, CB[7] prefers the charged species, MV dication (MV²⁺), and cation radical (MV^+⋅) to the fully reduced neutral (MV⁰ species as guests. Dimerization of MV^+⋅ is suppressed effectively by forming a stable complex with CB[7] in aqueous solution as confirmed by spectroelectrochemical experiments. Furthermore, the first redox process (MV²⁺/MV^+⋅) of the MV²⁺–CB[7] complex occurs predominantly via the direct electron transfer pathway, whereas the second redox process (MV^+⋅/MV⁰) occurs via both the direct and indirect pathway because of the low affinity of the fully reduced species MV⁰ to CB[7].