January 26, 2006 – Researchers from Italy’s U. of Bologna and UCLA have designed and build a molecular-scale motor that runs continuously without external interference, powered only by sunlight.

The multicomponent nanomotor is built on a bistable rotaxane, an interlocked molecule consisting of one or more 1.3nm-diameter rings, trapped on a 6nm-long dumbbell-shaped rod by bulky stoppers on either end — similar to the setup of an abacus. The rod portion of the dumbbell contains two “stations,” designated A and B, to which the rings are attracted. Absorbing sunlight into one of the end stoppers causes a transfer of one electron to station A, which repels the ring toward station B. This action causes the electron to transfer back to the light-harvesting stopper, reactivating station A, and reattracting the ring back to that position. A full cycle takes just <0.001sec, translating to an operating frequency of 1000Hz.

Fraser Stoddart, prof. of nanosystems sciences at UCLA and director of the California Nanosystems Institute, said the mechanism of the nanometer operates according to a four-stroke cycle, reminiscent of the process in an internal combustion-engine vehicle. The first step is light excitation and subsequent transfers of an electron (i.e., combustion), followed by displacement of the ring along the rod (piston motion), removal of the electron received by the first station (exhaust removal), and relocation of the piston. (Using this car analogy, the 100Hz cycle frequency would translate into about 60,000 RPM.)

Potential applications for the solar-powered nanomotor include nanoelectronics and molecular computers, as well as nanovalves for delivering medicines. The first step, according to Stoddart, is incorporating them into surfaces and membranes. For now, the car/driver analogy is an apt one. The researchers “test-drive them much as an engineer would a new motor car,” said Stoddart. “It is as if we had managed to get a solar-powered motor car onto the road and running.