Organizing Dumbbells for Nanotech Devices

Photo: A dumbbell

Chemist Fraser Stoddart and co-workers have designed and made numerous molecules based on hanging ring-shaped molecules on other chain-like molecules and loops. By incorporating functional chemical groups along the length of the chain or around these loops, they have shown that it is possible to make the molecular beads switch between these various functional groups using heat, light, or electricity.

A team of chemists from France, Italy, Spain, the UK, and the US recognized that in order to exploit their molecular machines they will need to find a way to organize them at interfaces, deposit them on functional surfaces, or immobilize them into membranes or porous materials. This will allow the molecular machines to work together. The researchers believe that modifying the surface of an electrode to incorporate an organized layer of molecular machines could be the key to success.

The team reports in the current issue of Advanced Materials how they have recently succeeded in applying an incredibly thin layer, just a few molecules thick, of a particular molecular machine to a glass surface. The molecular machine was a switchable rotaxane - a ring-shaped molecule held on a short chain by two blocking groups, making it resemble a dumbbell with a collar around the handle.

A special technique was used to make thin layers of this dumbbell-shaped component in solution on a glass slide coated with ITO (indium tin oxide). By using two solutions - one containing the dumbbells and the other a soapy surfactant compound - the researchers were able to force the molecules to organize themselves because of electrostatic repulsion and attraction between the surfactant, the molecules, and the surface, until ultimately they became attached with the same orientation to the ITO layer on the glass slide.

The researchers found that the thin film exhibited a reversible switching behavior when exposed cyclically to an acid and then a base. This, they explain, demonstrates that the thin film is capable of transducing a chemical input signal--the acid-base--into an electrical output signal. This bodes well for interfacing other molecular machines in a similar way.; Source: John Wiley & Sons, Inc.