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Adsorbate motors for unidirectional translation and transport


Artificial molecular motors are designed to transform external energy into useful work in the form of unidirectional motion1. They have been studied mainly in solution2,3,4, but also on solid surfaces5,6, which provide fixed reference points, allowing for tracking of their movement. However, these molecules require sophisticated design and synthesis, because the motor function must be imprinted into the chemical structure, and show reduced functionality on surfaces compared with in solution5,6,7,8. DNA walkers9,10, on the other hand, impart high directionality as they include the surface as part of the motor function, but they require chemical surface patterning and sequential solvent modification for motor activation. Here we show how efficient motors can operate at much smaller length scales on a homogeneous metal surface without any liquid. This is realized by combining a surface with a simple molecule, which, by itself, does not contain any motor unit. The motion, which is tracked at the single-molecule level, is triggered by intramolecular proton transfer with a corresponding modulation of the potential energy surface. Each molecule moves with 100 percent unidirectionality along an atomically defined straight line. Proof of the motor performing meaningful work is shown by controlled transport of single carbon monoxide molecules. This simplistic concept could form the basis for the controlled bottom-up assembly of nanostructures at the atomic scale.

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Fig. 1: Unidirectional motion of ditolyl-ATI molecules on Cu(110).
Fig. 2: N–H stretch vibration as trigger for molecular motion.
Fig. 3: Potential energy landscape for unidirectional motion.
Fig. 4: Adsorbate motor acts as ‘snowplough’ for single CO molecule.

Data availability

All data needed to evaluate the conclusions in the paper are available in the main text or the Supplementary Information. Additional data related to this paper may be requested from the corresponding author.


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We acknowledge J. Schachner for deuteration of the molecules and B. Werner for NMR measurements. We also thank L. Gross for careful reading of the manuscript and valuable feedback during the review process. We acknowledge The European Commission (FET open project no. 766864) as well as the Austrian Science fund FWF (Lise Meitner project no. M 2021-N36) for financial support and Barkla at the University of Liverpool for providing computer resources.

Author information

Authors and Affiliations



G.J.S. performed the experiments, G.J.S. and L.G. analysed the data. M.P. did the calculations. G.J.S. and L.G. wrote the paper with feedback from M.P.

Corresponding author

Correspondence to Leonhard Grill.

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The authors declare no competing interests.

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Peer review information

Nature thanks R. Dean Astumian, Leo Gross and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

This file contains details about molecular configurations of ditolyl-ATI, thermally activated diffusion, unidirectional motion as well as calculated vibrational energies, molecular states and reaction pathways, Supplementary Figs. 1–15, Table 1 and References.

Supplementary Video 1

STM tip-induced hopping of ditolyl-ATI on Cu(110). 44 consecutively acquired STM images (V = 690 mV, I = 150 pA, 368 × 368 Å2) showing ditolyl-ATI adsorbed on a Cu(110) surface. Hopping of individual molecules is induced by scanning with a bias above the threshold of about 390 mV and occurs along the close-packed rows of the surface (surface lattice overlaid as a grid).

Supplementary Video 2

Thermally activated diffusion of ditolyl-ATI on Cu(110). 74 consecutively acquired STM images (V = 100 mV, I = 250 pA, 368 × 368 Å2) in the temperature range 47.4–43.7 K showing random thermally induced diffusion of ditolyl-ATI along the close-packed Cu(110) rows. The numbering of the molecules corresponds to the numbering shown in Supplementary Fig. 6b.

Supplementary Video 3

Reaction pathway for unidirectional motion. The mechanism of unidirectional motion of ditolyl-ATI along the \(\left[\bar{1}10\right]\) direction on Cu(110). The molecule progresses from \({{\rm{R}}}_{{\rm{o}}}\to \,{\widetilde{{\rm{R}}}}_{{\rm{o}}}\to \,{{\rm{L}}}_{\downarrow }\to \,{{\rm{R}}}_{\downarrow }\) in one full hop along a close-packed row. This process then repeats. For simplicity, the molecule ends on the blue curve of the L tautomer after proton transfer (indicated by a vertical arrow). It is noted that this is different from the instantaneously created L* state that is higher in energy (see Supplementary Fig. 11 for details).

Supplementary Video 4

Unidirectional hopping of molecules moving in opposite directions. 24 consecutively acquired STM images (V = 390 mV, I = 20 pA). The two ditolyl-ATI molecules in the centre of the frame point in opposite directions (\(\left[1\bar{1}0\right]\) and \([\bar{1}10]\)). Accordingly, the two molecules translate in opposite directions when unidirectional hopping is induced.

Supplementary Video 5

Cargo transport by a single ditolyl-ATI molecule. STM images (V = 110 mV, I = 10 pA) showing a single ditolyl-ATI molecule moving over the Cu(110) surface. Individual hops are induced by voltage pulses from the STM tip. A CO molecule lies along the path of the molecule and is subsequently pushed further in the same direction in a snowplough-like manner.

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Simpson, G.J., Persson, M. & Grill, L. Adsorbate motors for unidirectional translation and transport. Nature 621, 82–86 (2023).

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