pH‐Controlled Multiple Interconversion between Cucurbit[7]uril‐Based Molecular Shuttle, [3]Pseudorotaxane and [2]Pseudorotaxane

An axle molecule 1 2+ containing one viologen nucleus and two identical p ‐toluic acid sides was synthesized. The sequential binding of the Q[7] wheels to the 1 2+ axle leads to the formation of a molecular shuttle and then a homowheel, [3]pseudorotaxane. The [3]pseudorotaxane can reversibly transform to [2]pseudorotaxane by acid‐base control. On the other hand, the initially formed molecular shuttle can also transform to [2]pseudorotaxane directly and reversibly under pH control. As a whole, a molecular shuttle and [3]/[2]pseudorotaxanes constructed a pH‐controlled multiple interconvertible system.