Macroscopic spiral rotation of microscopic objects induced by nanoscale rotaxane dynamics

The ability to relay mechanical effects and information from the nanoscale to larger-length scales has potential for the development of responsive and adaptive materials. Here, we describe how the light-mediated translocation of a macrocycle between different sites on a rotaxane axle, a dynamic process that switches shape at the nanoscale, can be used for generating directional microscopic transport. The effect results from the change in the expression of rotaxane chirality experienced by a liquid-crystal medium. The position of the macrocycle within the rotaxane determines not only the pitch of the liquid-crystal helix but also its handedness. The helix inversion sets topological defects in motion, and these cause macroscopic spiral rotation of the microparticles confined within the defects. The process can be used for collecting and cleaning a surface of microparticles and dust particles. The results illustrate how mechano-stereochemical changes can be transduced across length scales into directional transport.