Electromechanical and conductance switching properties of single oligothiophene molecules.

We have studied the electron transport and electromechanical properties of single oligothiophenes with three and four thiophene repeating units covalently linked to two Au electrodes. The four-repeating unit molecule is found to be more conductive than the three-repeating unit molecule. This unusual length dependence is due to the different electronic states of the molecules. Both molecules can be switched reversibly between a high and low conducting state by oxidizing and reducing the molecules using an electrochemical gate. The conductance of the molecules decreases upon stretching, which is attributed to a force-induced increase in the HOMO-LUMO gap.