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Published online: 3 December 2008 | doi:10.1038/nchina.2008.284

Molecular machines: Rotor brigade

Felix Cheung

Introduction

© (2008) APS

A rotor is an important component in any machine, no matter how large or small. Several examples of molecular rotors have been reported. However, until now, none of them could rotate around a well-defined axis that is fixed on a surface. Hongjun Gao at the Chinese Academy of Sciences in Beijing and co-workers¹ have now made not one, or two, but an array of anchored molecular rotors with an off-centre rotation axis.

The researchers prepared an atomically clean gold surface, which was 'reconstructed' so that the atoms at the surface assumed a herringbone structure. They then deposited additional gold atoms and a minute quantity of tetra-tert-butyl zinc phthalocyanine, (t-Bu)₄-ZnPc — a molecule that structurally resembles a four-blade propeller — onto the gold surface. Using scanning tunnelling microscopy, they imaged the gold surface and found that a large array of rotors had self-assembled on top of the surface (pictured top).

Each rotor (pictured bottom) comprises a gold atom (marked in red) that is fixed on the gold surface (marked in light blue) and a (t-Bu)₄-ZnPc molecule that spins slightly off-axis around the gold atom. The rotors formed such an ordered array because the gold atoms were preferentially absorbed at the corners of the herringbone reconstruction.

Further imaging showed that, at 78 K, the rotors were indeed not stationary but rotated around the gold atoms. The finding represents an important step towards the eventual fabrication of molecular motors and generators.

The authors of this work are from:
Institute of Physics, Chinese Academy of Sciences, Beijing, China; Institute of Chemistry, Chinese Academy of Sciences, Beijing, China; Surface Science Research Centre, University of Liverpool, Liverpool, UK.

Reference

1. Gao, L. et al. Constructing an array of anchored single-molecule rotors on gold surfaces. Phys. Rev. Lett. 101, 197209 (2008).  | Article | ChemPort |