Repetitive Rolling of Triptycene-Based Molecules on Cu Surfaces.

The metal surface-supported rotation of artificial molecular structures is technologically important for developing molecular-level devices. The key factors leading to the practical applications of these molecular machines on metal surfaces are the atomic-scale control of the rotation and the counterbalance of the temperature-driven instability of the molecules. In this work, we present a means by which triptycene-based molecular wheels can roll repetitively on a metal surface. Our results show that regularly stepped surfaces are the perfect candidate not only for stabilizing the molecule on the metal surface but also for providing the pivot points needed for repetitive vertical rotation of the molecule at higher temperatures. In addition to the geometrical compatibility of the substrate and the molecule, intermittent application of the external electric field is needed for rolling the molecule on a metal-stepped surface in a controllable manner.