An electric cyclophane: cavity control based on the rotation of a paraphenylene by redox switching

Although a free rotation around a single bond gives no mechanical output, it has let us imagine a molecular motor. A para-substituted aromatic ring can be regarded as a rotator with the para-rotation axis. When it is incorporated in a wider pi-conjugated system, a quinoidal structure is generated accompanied by oxidation on the substituted groups at the 1,4-position, and the axis is fixed. A paraphenylenediamine was selected as the nanomechanical molecular module capable of locking and releasing the free rotation using an electrode in solution. We inserted the module into a simple molecular system, cyclophane. It was clarified that the cyclophane was able to open and close its cavity in a reversible redox process repeatedly.