A Light-Stimulated Molecular Switch Driven by Radical-Radical Interactions in Water

A redox‐controllable bistable [2]rotaxane has been synthesized using templation and click chemistry. With assistance from a sacrificial electron donor, light‐triggered switching through numerous cycles can be initiated by radical‐pairing interactions between the reduced forms of the cyclophane and the bipyridinium unit in aqueous solution in the absence of air. In the presence of air (O2), the interactions are reset by donor–acceptor charge transfer.