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.

No abstract