Turning on and off the rotational oscillation of a single porphine molecule by molecular charge state.

The rotation dynamics of single magnesium porphine molecules on an ultrathin NaCl bilayer is investigated with low-temperature scanning tunneling microscopy and density functional theory calculations. It is observed that the rotational oscillation between two stable orientations can be turned on and off by the molecular charge state, which can be manipulated with the tunneling electrons. The features of the charge states and the mechanism of molecular rotational on/off state control are revealed at the atomic scale. The dependence of molecular orientation switching rate on the tunneling electron energy and the current density illustrates the underlying resonant tunneling excitation and single-electron process. The drive and control of molecular motion with tunneling electrons demonstrated in this study suggests a novel approach toward electronically controlled molecular rotors and motors.