A single molecule wire, claimed to be the longest yet, has been made by UK scientists.

Geoff Ashwell at the University of Wales, Bangor, headed the research.  He believes that, at seven nanometres, the molecular wire made by Martin Bryce and colleagues at Durham University, is the longest ever to be used for single-molecule electrical current studies. 

The wire is a rigid, almost linear, conjugated molecule with thiol groups at each end, which allow the wire to dock between two gold electrodes.

The central part of the wire, a dipyridyl group, can be protonated to become a positively charged electron acceptor that can couple to a negatively charged electron donor.  The electronic switching of this acceptor-donor combination implies the wire could act as a rectifying junction, converting alternating current to direct current.   

Theoretical calculations by Colin Lambert at Lancaster University confirmed the electronic properties of the molecular wire.  Ashwell said the calculations suggest the exciting possibility of using molecular wires as single-molecule sensors.

Richard Nichols, an expert in molecular electronics at the University of Liverpool, UK, praised the sophisticated design of the wire. 'The electrical properties of the wire can be chemically switched for application in rectifying junctions,' said Nichols. 'Long molecular wires of this kind are attractive candidates for bridging nanofabricated contact pads or for acting as conduits of electrical charge in photovoltaic devices,' he added.

The collaborative effort between teams of scientists, making and modelling the wires and fabricating the devices, is crucial for the advancement of molecular electronics, explained Ashwell.  'The future development of the work is dependent on the design of functional conjugated molecules and their alignment across nano-sized electrode gaps,' said Ashwell. 

Alison Stoddart