Controlled Rotation and Manipulation of Individual Molecular Motors

The design of artificial molecular machines often takes inspiration from macroscopic machines, but the parallels between the two are frequently only superficial because many molecular machines are governed by quantum processes. Previously, chemically and light driven rotary molecular motors have been developed. For electrically driven motors, tunneling electrons from the tip of a scanning tunneling microscope (STM) have been used to drive rotation in a simple rotor into a single direction and to move a wheeled molecule across a surface. Here, we show that a single standalone molecular motor adsorbed on a gold surface can be made to rotate in a clockwise or counterclockwise direction [1] by selective inelastic electron tunneling through different sub-units of the motor. Our motor is composed of a tripodal stator for vertical positioning, a five-arm rotator for controlled rotations, and a Ru atomic ball bearing connecting the static and rotational parts. The directional rotation originates from saw-tooth-like rotational potentials, which are determined by the internal molecular structure and are independent of the surface adsorption site. This project is supported by the US DOE, BES grant: DE-FG02-02ER46012.