Nano-sized electrical switches that can be turned on and off using light have been made by researchers in The Netherlands.

These switches, made by Ben Feringa and colleagues at the University of Groningen, can swap between conducting electricity and not, depending on the wavelength of light they are exposed to.  

The switches are diarylethene molecules that can be attached to gold nanoelectrodes. The nanoelectrodes are just a few nanometres wide - a tiny fraction of the width of a human hair, which is around 10,000 nanometres wide. 

Diarylethenes are carbon-carbon double bonds with aromatic rings at each end.  These molecules exist as two forms, a conjugated form that allows electrons to flow across and a non-conjugated form that doesn't.  The flow of electrons can be switched on by ultraviolet light, which causes the bonds in the non-conjugated form to rearrange, to become conjugated. Visible light reverses the bond rearrangement, turning the switch off.  These resilient molecules can be flicked on and off as required.

But interfacing the diarylethene with the macro world is still a major challenge, said Feringa.  Attempts to attach this molecule directly to gold electrodes affected the efficiency of the switch.  Feringa overcame this hurdle by placing conjugated spacer units between the electrode and the diarylethene molecule.  These spacers are chemical units that allow electrons to flow through them, just as wires connect a switch to a light.  

Ultimately, Feringa hopes to build an entire electric circuit composed of single molecule components.  The electric switch is a fundamental component needed to achieve this, he said.

Nina Athey-Pollard