A single molecule wire, claimed by scientists to be the longest to date, has electronic properties that can be chemically modified. 

With a length of 7 nm, it is the longest molecular wire ever to be used for single-molecule electrical current studies, believes Geoff Ashwell at the University of Wales in Bangor, the scientist heading the study. 

The molecular wire, made by Martin Bryce and colleagues at Durham University, is a rigid and almost linear, conjugated molecule with thiol groups at each end, allowing the wire to dock between two gold electrodes. 

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

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

Richard Nichols, an expert in molecular electronics at the University of Liverpool 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. 

This 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