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.

Radical-polymerized chemical vapor deposition, a new bottom-up method, was developed to produce graphene nanoribbons (GNRs) efficiently, despite the use of extremely low vacuum. Using this technique, a systematic synthesis of a multilayered high-density array of width-controlled sub-1 nm GNRs on a metal surface, with width-dependent band gap, is made possible. GNR films transferred onto insulating substrates behave as an excellent photoconductor.

The fabrication of organized molecular-scale structures is key to realizing high-performance molecular- and conjugated-polymer devices. Here, we demonstrate a unique single-molecular processing technique using electrochemistry, termed 'electrochemical epitaxial polymerization'. This technique is based on step-by-step electropolymerization of the monomer by applying voltage pulses to a monomer-electrolyte solution that also contains iodine. Using this technique, we observe the formation of high-density arrays of single conjugated-polymer wires as long as 75 nm on the surface of a Au(111) electrode. Our findings unveil the mechanism of electropolymerization, showing that the conjugated polymer wires grow from nuclei adsorbed on the iodine-covered Au(111) surface. The results may also open the door to mass-production of molecular-scale devices based on conjugated polymers.

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