Viologen–cucurbituril host/guest chemistry – redox control of dimerization versus inclusion

Two calix[4]arene systems, C23(4+) and C24(4+) – where 2 corresponds to the number of viologen units and 3–4 corresponds to the number of carbon atoms connecting the viologen units to the macrocyclic core – have been synthesized and led to the formation of [3]pseudorotaxanes when combined with either CB[7] or CB[8]. The [3]pseudorotaxanes spontaneously dissociate upon reduction of the bipyridinium units as the result of intramolecular dimerization of the two face-to-face viologen radical cations. CB[7] and CB[8]-based [2]pseudorotaxanes containing monomeric viologen guest model compounds, MC3(2+) and MC(4+), do not undergo decomplexation and dimerization following electrochemical reduction of their bipyridinium units.