Molecules ring for information

Researchers have developed the first nano-scale parallel processor in which one molecule influences the state of many others.

In the future, individual atoms or molecules could act as moving components in computers. Many of these ‘molecular machines’ have been built by rearranging organic molecules, and the next challenge is to control the transfer of information between different machines.

Now Anirban Bandyopadhyay and Somobrata Acharya at the National Institute for Materials Science in Tsukuba have built an assembly in which one molecule can simultaneously send instructions to 16 others.¹ The system represents multiple machines influenced by a central control unit—one of the major goals of nanocomputing.

In earlier work², the researchers discovered that a single ring-shaped organic molecule called DRQ could be switched between four logic states (0, 1, 2 and 3) when instructed by a pulse from a scanning tunneling microscope. The four states are encoded by adding one or two electrons, or changing the shape of the molecule itself.

“When DRQ flips between 0, 1, 2 and 3 it rotates in a particular direction and by a certain angle, making it perfect for processor applications,” says Bandyopadhyay. “Our work was the first demonstration of multilevel logic in a single molecule.”

Fig. 1: Ring of DRQ molecules connected to a central ‘control unit’ molecule that influences the state of all molecules in the outer ring.Copyright © Anirban Bandyopadhyay 2008

Now the researchers have managed to arrange a ring of sixteen DRQ molecules connected by hydrogen bonds to a central ‘control unit’ DRQ molecule (Fig. 1). They found that a single pulse applied to the central molecule could change the states of all 16 outer molecules. The system could potentially produce a possible 4¹⁶ (around 4.3 billion) arrays, as in a 16-bit parallel processor.

The radial arrangement of molecules has many advantages over systems of molecules connected in a line, which can only communicate one instruction at a time. In particular, Bandyopadhyay believes that the DRQ system gives an insight into the behavior of DNA.

“DNA is nice because it is linear in connecting its bases, yet because of its spiral shape, one base can influence bases other than its neighbors—an indirect way of one-to-many connection”, says Bandyopadhyay. “Our study on radial connections of molecules opens the door for mimicking some of these amazing biological operations at the nanoscale.”