Mechanically active [c2]daisy chain rotaxanes were functionalized with mesogens to display liquid-crystalline properties. It was shown that the mechanical actuation of such bistable rotaxanes (between their contracted and extended states) modifies the transition temperature between their isotropic and smectic phases. In addition, small angle X-ray scattering (SAXS) experiments revealed a modification of the smectic phase corresponding to the modification of the interlayer distance as controlled by the mechanical bond. The work described by N. Giuseppone and co-workers in their Research Article opens new opportunities to implement [c2]daisy chain rotaxanes in responsive materials.

A bistable [ c 2]daisy chain rotaxane bearing two mesogenic units was synthesized, and its liquid crystal phase diagram was characterized. As a remarkable result, this study demonstrates that, depending on the contracted or extended state of its mechanical bond, the system can convert between an isotropic and a smectic A mesophase at constant temperature.

Artificial molecular machines are able to produce and exploit precise nanoscale actuations in response to chemical or physical triggers. Recent scientific efforts have been devoted to the integration, orientation, and interfacing of large assemblies of molecular machines in order to harness their collective actuations at larger length scale and up to the generation of macroscopic motions. Making use of such "hierarchical mechanics" represents a fundamentally new approach for the conception of stimuli-responsive materials. Furthermore, because some molecular machines can function as molecular motors-which are capable of cycling a unidirectional motion out of thermodynamic equilibrium and progressively increasing the work delivered to their environment-one can expect unique opportunities to design new kinds of mechanically active materials and devices capable of autonomous behavior when supplied by an external source of energy. Recently reported achievements are summarized, including the integration of molecular machines at surfaces and interfaces, in 3D self-assembled materials, as well as in liquid crystals and polymer materials. Their detailed functioning principles as well as their functional properties are discussed along with their potential applications in various domains such as sensing, drug delivery, electronics, optics, plasmonics, and mechanics.