Proton and Electron Transfer Control of the Position of Cucurbit[n]uril Wheels in Pseudorotaxanes

This paper presents an overview of recent work on the binding interactions between a series of 4,4'‐bipyridinium (viologen) derivatives and the hosts cucurbit[6]uril (CB6) and cucurbit[7]uril (CB7), which give rise to stable ‘wheel‐on‐an‐axle' inclusion complexes (pseudorotaxanes) in aqueous solution. The carboxylic acid termini on the pseudorotaxane axle can be used as handles to control—via proton transfer reactions—the relative position of the CB wheel along the axle. We also report on a different type of pseudorotaxane in which the reversible oxidation of the axle's ferrocenyl end groups leads to controlled displacement of the CB7 wheel.