Light-Controllable Cucurbit[7]uril-Based Molecular Shuttle

The design and construction of novel artificial molecular machines can be categorized as a currently important field of modern chemistry. In the present work, a novel photoresponsive [3]rotaxane containing two cucurbit[7]uril (CB[7]) rings and a dumbbell component consisting of one trans-azobenzene unit along with two viologen units was developed. Each viologen group was encircled by a CB[7] ring with a rapid shuttling equilibration distribution extended to the trans-azobenzene unit located in the middle of the dumbbell component. Upon the trans-to-cis photoisomerization of the azobenzene unit under UV light irradiation, a shuttling restriction of the CB[7] rings along the dumbbell component was observed. The equilibration distribution of the macrocycles on the dumbbell component can be recovered by the cis-to-trans photoisomerization of the azobenzene unit under visible light irradiation. Such a controllable shuttling process was fully characterized by H-1 NMR spectroscopy and was easily indicated by fluorescent changes of the [3]rotaxane.