Lasers coax large molecules to change shape

Chemists at Purdue Univ. (West Lafayette, IN) have found that laser light can prompt individual molecules to alter their structure. This may someday enable scientists to direct molecules to perform specific functions, reports professor Timothy Zwier.

Chemists have long been interested in using laser light to drive chemical reactions. The difficulty with this approach is that, although the laser initially excites a single bond or group of atoms, that energy generally dissipates throughout the molecule, and the laser "heats up" the molecule in much the same way a traditional heating source would.

Because of their size and complexity, large molecules present an opportunity for a different kind of chemistry that does not involve breaking chemical bonds. "Large molecules can reconfigure into many different shapes, or conformations," Zwier explains. "Such changes are reactions in their own right, but they also can serve to change a molecule's reactivity with other molecules."

He says that making conformational changes in a molecule involves less energy than that required to break a chemical bond, and can be done through multiple pathways. His group found that by choosing different infrared wavelengths, the laser could be used to selectively choose the molecule's new shape.