The structure of the Viologen-Phenylene-Imidazole (VPI) guest, previously shown to be bound by cucurbit[7]uril (CB[7]) with binding modes depending on pH and silver ions, has been extended by adding hydrophobic groups on the two extremities of VPI before investigations of CB[7] binding by NMR, ITC, X-ray diffraction, UV-vis and fluorescence spectroscopies. With an imidazole station extended by a naphthalene group (VPI-N), binding modes of CB[7] are similar to those previously observed. However, with the viologen extended by a tolyl group (T-VPI), CB[7] preferentially sits on station T, shuttling between the T and P stations at acid pH or after Ag+ addition. The CB[7] ⋅ T-VPI complex thus behaves as a metal-actuated thermodynamic stop-and-go molecular shuttle featured by fast and autonomous ring translocation between two stations and a continuum for fractional station occupancy solely and easily controlled by Ag+ concentration.
Keywords: cucurbituril; heterocycles; host:guest chemistry; macrocycles; viologens.
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