Rotation of a Single Molecule Within a Supramolecular Bearing

We report the first experimental visualization and verification of single-molecule rotors operating within a supramolecular bearing. Using a scanning tunneling microscope, single molecules were observed to exist in one of two spatially defined states laterally separated by 0.26 nm. One was identified as a rotating state and the other as an immobilized state. Calculations of the energy barrier for rotation of these two states, and for translation between them, show that it is below the thermal energy at room temperature, whereas that of the immobilized state exceeds the thermal energy.