Side Chains Insulate Polythiophene Wires

By sheathing polythiophene with its own cyclic side chains, chemists in Japan have created an insulated molecular wire that’s free from structural defects (J. Am. Chem. Soc., DOI: 10.1021/ja107444m). The insulating strategy results in a molecular wire (shown) with excellent charge-carrying properties that may find use as molecular electric cords in nanosized integrated circuits. Just as wires in building walls wear insulation to prevent short circuits and crossed connections, molecular wires need an insulating sheath to prevent them from reacting with oxygen and water in their surroundings and from bundling up with other wires. Most insulated molecular wires are made via a supramolecular approach, wrapping wires with linear polymers or stringing them through cyclodextrin beads. The trouble with that approach is that the supramolecular assembly processes inevitably lead to structural defects. Researchers led by Kazunori Sugiyasu and Masayuki Takeuchi of Japan’s National Institute for Materials Science devised a way to circumvent this problem by tying a polythiophene’s side chains together using olefin metathesis prior to polymerization. “The covalently linked cyclic side chains extend the effective conjugation length of the interior polythiophene backbone, which results in an excellent intrawire hole mobility,” the researchers note.