Temperature-driven braking of γ-cyclodextrin-curcubit[6]uril-cowheeled [4]rotaxanes

A capping moiety, playing a role of the brake, slowed down the rotation speed of the cyclodextrin of a cyclodextrin-cucurbit[6]uril-cowheeled [3]rotaxane. Lowering the temperature further stopped the rotation at the NMR timescale. [Display omitted] Several cyclodextrin-cucurbit[6]uril-cowheeled [4]rotaxanes were synthesized through the cucurbit[6]uril-templated azide-alkyne 1,3-dipolar cycloaddition. The intramolecular interaction between the aromatic axle and the capping groups of cyclodextrin moieties was investigated by UV–vis, fluorescence, circular dichroism and NMR spectroscopic studies. The rotational kinetic of the wheel around the axle can be manipulated by adjusting the temperature. The capping group apparently slowed down the rotation of the wheel, playing a role of the brake, and lowering the temperature can stop the rotation of the wheel on the NMR timescale.