Stretching Livens Up Electron Transport

As some molecules elongate, it turns out that they have an easier time transporting electrons along their frameworks, according to a molecular simulation study (J. Am. Chem. Soc., DOI: 10.1021/ja205908q). This counterintuitive behavior—longer molecules usually have poor conductance compared with shorter ones—could open the door to mechanically activated molecular electronic devices, says the research team led by Mark A. Ratner and George C. Schatz of Northwestern University. Using molecular dynamics and electronic structural methods, the researchers simulated passing current along a cyclophane molecule they designed (shown) as it was stretched between the gold tip of an atomic force microscope and a gold electrode surface. The team found that the molecule’s electrical resistance decreased when stretched, especially taking a dive once the compound’s bulky tert-butyl groups moved out of the way to allow π-stacking between its aromatic rings. “What makes this so exciting,” says David N. Beratan, a theoretical chemist at Duke University, “is that the authors find applied force may strongly remodel electron tunneling pathways,” a result that bolsters earlier simulation work on electron transport in DNA and proteins.