Light Drives Molecular Motor

Aaron J. Hand

Scientists at the University of Groningen and Tohoku University in Sendai, Japan, have used light to power one of the first working single-molecule motors. When irradiated with ultraviolet light, the molecule rotates 360° in one direction only.

Converting energy into unidirectional rotary motion has not been a simple task. Although many molecular systems undergo translational or rotary motion, controlling the direction of that rotation is another matter, said Ben L. Feringa of Groningen. "If one wishes to build a molecular-type motor as the central element in future nanomachines, it is essential to be able to control the direction of rotation," he said.

The researchers use 280- or 300-nm lamps to rotate a chiral helical alkene around a central carbon-carbon double bond. In the four-step isomerization process, the UV light causes the molecule to rotate 180° twice, each time followed by heating to block the molecule's natural reverse rotation. In principle, this is an efficient process, Feringa said, because it uses direct light energy to control the motion.

Since publishing their results in the Sept. 9, 1999, issue of Nature, the researchers have redesigned the molecular motor to make it asymmetrical, which would enable more complex systems, Feringa said. They also are working to attach the motors to surfaces and to increase the speed of rotation.

Ultraviolet light activates four discrete isomerization steps, causing a helically shaped alkene
to rotate 360°.

The researchers hope to be able to combine several rotors to propel larger molecular objects. To achieve this, they will first make a layer of propellers on a surface, operating the motors in concert. "Another challenge is to couple rotation to translation in a molecular-type crankshaft," Feringa said.

Although the research is far from achieving the goal molecular machinery or robotics, "the nanotechnology holds great promise for the future," Feringa said. "We have proven a fundamental principle and will use these molecular rotors based on chiral alkenes to build more advanced systems."