Propelling single molecules in a controlled manner along an unmodified surface remains extremely challenging because it requires molecules that can use light, chemical or electrical energy to modulate their interaction with the surface in a way that generates motion. Nature’s motor proteins1,2 have mastered the art of converting conformational changes into directed motion, and have inspired the design of artificial systems3 such as DNA walkers4,5 and light- and redox-driven molecular motors6,7,8,9,10,11. But although controlled movement of single molecules along a surface has been reported12,13,14,15,16, the molecules in these examples act as passive elements that either diffuse along a preferential direction with equal probability for forward and backward movement or are dragged by an STM tip. Here we present a molecule with four functional units—our previously reported rotary motors6,8,17—that undergo continuous and defined conformational changes upon sequential electronic and vibrational excitation. Scanning tunnelling microscopy confirms that activation of the conformational changes of the rotors through inelastic electron tunnelling propels the molecule unidirectionally across a Cu(111) surface. The system can be adapted to follow either linear or random surface trajectories or to remain stationary, by tuning the chirality of the individual motor units. Our design provides a starting point for the exploration of more sophisticated molecular mechanical systems with directionally controlled motion.
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This research was supported by the Netherlands Organization for Scientific Research (NWO-CW) (B.L.F. and T.K. through a VENI grant), the Swiss Secretary for Education and Research and the Swiss National Science Foundation (K.-H.E. and M.P.), and the European Research Council (ERC advanced grant 227897 to B.L.F.).
In this movie we see preferentially linear movement of the meso-isomer of the four-wheeled molecule after excitation - see Supplementary Information for full legend.
In this movie we see changes in STM contrast induced by helix inversion of the motor units of the four-wheeled molecule after vibrational excitation - see Supplementary Information for full legend.
In this movie we see the random movement of one enantiomer of the racemic version of the four-wheeled molecule after excitation - see Supplementary Information for full legend.
In this movie we see a molecular model for the anticipated linear propulsion of the meso-form of the four-wheeled molecule - see Supplementary Information for full legend.
About this article
Nature Nanotechnology (2018)