Light drives molecular motor

A molecular motor powered by sunlight alone has been prepared by chemists in Italy and in the U.S. (Proc. Natl. Acad. Sci. USA 2006, 103, 1178). Vincenzo Balzani and Alberto Credi of the University of Bologna, J. Fraser Stoddart of the University of California, Los Angeles, and their coworkers believe their device is unique for several reasons. Because it's powered solely by visible light, the motor's movement-the shuttling of a crown ether back and forth between two points on the handle of a dumbbell-shaped structure (shown in the schematic)-requires no additional chemicals and produces no waste products. Also, the shuttle's movement relies on intramolecular processes, so it could, in principle, be operated at the single-molecule level. The motor moves when a ruthenium complex (green sphere) at one end of the dumbbell absorbs a photon and transfers an electron to a 4,4'-bipyridinium moiety (blue bar) within the dumbbell's handle. This reduction prompts the crown ether (pink circle) to move 1.3 nm to a 3,3'-dimethyl-4,4'-bipyridinium unit (red bar) in the compound. The crown ether moves back to its original position via a back electron-transfer process.