[c2]Daisy Chain Rotaxanes as Molecular Muscles

Abstract

Bistable [ c2]daisy chain rotaxanes represent a particularly intriguing class of interlocked molecules that can produce internal sliding movements with a net contraction or extension at the single-molecule level. These nanometric motions show some analogies with the sliding motions of actin and myosin filaments in sarcomeres, and this is why [ c2]daisy chain rotaxanes have been also named as “molecular muscles,” as their first synthesis in 2000. In this minireview, the authors discuss the recent history of these molecules, their modular chemical structures, and the various synthetic pathways described in the literature to access them. The authors also detail how their internal motions can be controlled and characterized by a number of chemical and physical tools. The authors finally show that their integration within polymers and materials can give access to synchronized motions and amplifications up to the macroscopic scale. Overall, the numerous examples that have been described in the literature to date demonstrate that this family of molecules has already strongly influenced the entire field of research on artificial molecular machines, and has the potential to be implemented as actuators working at all scales, from nanometric-switchable devices to mechanically active soft matter materials.