from the Molectronics dept.
Researchers led by Paul S. Weiss at Penn State and and James M. Tour at Rice University, report in the 22 June 2001 issue of Science have demonstrated single molecules that switch between "on" and "off" states, and then hold in a state for hours at a time. The function of their molecular switches is based in part on conformational changes — which happen when molecules alter their arrangement by rotation of their atoms around a single bond, effectively changing shape by moving or turning — determine how and when that conductance switching occurs in those molecules. Additional coverage can be found in this article ("Single-molecule computer switches advance", by K. Hearn, 21 June 2001) from United Press International.
As described in their report, they tracked over time the conductance switching of single and bundled phenylene ethynylene oligomers isolated in matrices of alkanethiolate monolayers. The persistence times for isolated and bundled molecules in either the ON or OFF switch state ranged from seconds to tens of hours. When the surrounding matrix is well ordered, the rate at which the inserted molecules switch is low. When the surrounding matrix is poorly ordered, the inserted molecules switch more often. As a result, the team concluded that the switching is a result of conformational changes in the molecules or bundles, rather than electrostatic effects of charge transfer.
Funding for the research was provided by the Army Research Office, the Defense Advanced Research Projects Agency, the National Science Foundation, the Office of Naval Research, and Zyvex LLC
Although the Science paper is not freely available on the web, supplemental data and images that show the single and bundled molecules switching on and off within the matrices, are available on the Weiss group website.