Credit: © 2006 Nature

Exploiting the electronic properties of single molecules in computing devices is one of the main goals of nanotechnology. However, for this to happen we need to understand the transport of electrons through molecules in fine detail. Researchers at Columbia University in the US have taken a major step forward in this direction by showing that the conductance of certain molecules depends on their shape.

Latha Venkataraman and colleagues1 start by breaking a gold wire in a solution containing the molecules to form metal–molecule–metal junctions. The first challenge in such experiments is to make sure that there is just one molecule between the electrodes. It is also important to ensure that the properties of the molecules, not the electrodes, are being measured. Recently, the Columbia team showed that the use of amine groups (which contain nitrogen atoms) to link the molecules to the electrodes overcame many of the problems encountered in such experiments.

Now, they have measured the conductance of a variety of molecules that contain two rings of six carbon atoms (known as phenyl groups) linked together by a single carbon–carbon bond. The simplest of these molecules is essentially flat, but on adding different atoms onto the carbon rings the molecule twists to different angles about the carbon–carbon bond. Venkataraman and colleagues show that the conductance of the molecule decreases as the twist angle increases. Indeed, the conductance varies with the square of the cosine of the angle, as had been predicted by theorists.