Cucurbituril complexes of redox active guests

This review summarizes recent work on the chemistry of inclusion complexes formed between redox active guests and cucurbit[n]uril hosts. The large majority of the surveyed research concerns the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8), while the guests are 4,4'-bipyridinium (viologen) and ferrocene derivatives. The work includes dendronized guests, in which a guest residue is attached to a dendron in such a way that host-guest binding interactions are still possible. The main focus of the review is on the electrochemical behavior of the included guests. In general terms complexation by CB7 has a more pronounced effect on the ferrocene derivatives, giving rise to a measurable attenuation of the electrochemical kinetics. In contrast to this, the electrochemical kinetics of the viologen derivatives remains fast (in the voltammetric time scale, with scan rates up to 2 V s^-1) upon inclusion complexation by CB7. The larger cavity host CB8 is extremely effective at mediating the redox-driven self-assembly of dendronized viologens.