An electric molecular motor

Macroscopic electric motors continue to have a large impact on almost every aspect of modern society. Consequently, the effort towards developing molecular motors 1 – 3 that can be driven by electricity could not be more timely. Here we describe an electric molecular motor based on a [3]catenane 4 , 5 , in which two cyclobis(paraquat- p -phenylene) 6 (CBPQT 4+ ) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop. The constitution of the loop ensures that both rings undergo highly (85%) unidirectional movement under the guidance of a flashing energy ratchet 7 , 8 , whereas the interactions between the two rings give rise to a two-dimensional potential energy surface (PES) similar to that shown by F O F 1 ATP synthase 9 . The unidirectionality is powered by an oscillating 10 voltage 11 , 12 or external modulation of the redox potential 13 . Initially, we focused our attention on the homologous [2]catenane, only to find that the kinetic asymmetry was insufficient to support unidirectional movement of the sole ring. Accordingly, we incorporated a second CBPQT 4+ ring to provide further symmetry breaking by interactions between the two mobile rings. This demonstration of electrically driven continual circumrotatory motion of two rings around a loop in a [3]catenane is free from the production of waste products and represents an important step towards surface-bound 14 electric molecular motors.