Recent Developments on Rotaxane-Based Shuttles: An update to 2010

This update reviews the major developments on rotaxane-based shuttles during the period of August 2008 to October 2010 and is organized similarly to the previous review. The progress in the field of chemical controlled shuttles can be summarized as a significant increase of the shuttling rates, secondgeneration pH-switchable Pd(II)-complexed rotaxanes, and new synthetic approaches, especially those based on Diels-Alder cycloadditions. The new synthetic routes allow ready access to rotaxanes that feature the template site fully incorporated into the interlocked product. This template site is unusual for active-template reactions and produces shuttles that exhibit entropy-driven translational isomerism with remarkably improved positional discrimination as was shown by the incorporation of a hydrogen-bonding TEG-station into an imine-bridged rotaxane. With respect to photochemically powered molecular switches, the most important result originated from the synthesis of a degenerate, donor-acceptor, light-gated, STOP-GO molecular shuttle. For electrochemically controllable bistable rotaxanes, the first example of a molecular shuttle with three different stations, which dramatically increase the shuttling process rate, has been reported. Finally, the last study in this review involves redox-driven switching and electrochromic responses of LC films containing a bistable rotaxane. The presence of a polymer electrolyte provides new prospects for the further development of rotaxane-based molecular materials by exploiting the dynamic, anisotropic, and coherent properties of liquid crystals.