Light-driven molecular motors that rotate perpendicular to a surface can control the surface's properties, say scientists from the Netherlands and Canada.

Light causes the top part of the molecule to rotate

Rotating molecules are widely used as molecular motors in biological systems, for tasks such as moving molecules away from cell nuclei. Ben Feringa, at the University of Groningen, the Netherlands, and colleagues have attempted to mimic biomolecular rotors by attaching photosensitive molecules to solid surfaces, which enables them to take control of the molecules' orientations.

The group anchored the molecules to quartz and silicon surfaces. When they shone light on the surfaces, the molecules underwent a photochemical isomerisation followed by a thermal inversion, which caused the top part of them to rotate in concert perpendicular to the surface. The rotation can be used to alternately expose then hide functional groups, which can affect surface properties such as wettability and adhesion, explains Feringa.

'Our motivation for this work was to employ the collective action of many nanomotors on a surface to change the surface properties in a fully dynamic fashion,' says Feringa. The motor is three orders of magnitude faster than previous surface-supported motors, which is a major step towards getting them to perform work, he adds. The team's next goal is to use the motors to control surface hydrophobicity.

'The successful formation of fully functional surface-grafted molecular motors might be a first step towards the construction of more sophisticated and functional nanomolecular motors,' says Qing-Zheng Yang, an expert on photo-driven molecular motors at the University of Illinois, Urbana, US.

Feringa says he looks forward to attaching long polymer chains to the surface-bound motors to amplify the motion. 'We would like to have motors that rotate in the microsecond time frame to see a propulsion effect on solvents, polymers or other nano-objects on top of the layer.'

Christina Hodkinson 

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