Synthetic molecular machine based on reversible end-to-interior and end-to-end loop formation triggered by electrochemical stimuli.

We have designed and synthesized a novel [2]pseudorotaxane-based molecular machine in which the interconversion between end-to-interior and end-to-end loop structures is reversibly controlled by electrochemical stimuli. Cucurbit[8]uril (CB[8]) and the thread molecule 3(4+) with an electron-rich hydroxynaphthalene unit and two electron-deficient viologen units form the 1:1 complex 4(4+) with an end-to-interior loop structure, which is reversibly converted into an end-to-end structure upon reduction. Large changes in shape and size of the molecule accompany the reversible redox process. The key feature of the machine-like behavior is the reversible interconversion between an intramolecular charge-transfer complex and viologen cation radical dimer inside CB[8] triggered by electrochemical stimuli.