A supramolecular switch that can remember whether it is switched on has been developed by Ken Shimizu and Judith Lavin at the University of South Carolina, Columbia, US. 

Supramolecular switches are usually host-guest complexes that stop working and switch off if the guest is removed. This instability limits their use in information and memory storage applications. 

The switch developed by Shimizu and Lavin can be switched on or off by the presence of a guest at high temperatures. When cooled to room temperature, the switch stays in the required state even when the guest is removed. 'This is like a traditional light switch that you can turn on and will stay on when you let go,' explained Shimizu. The removed guest can then be used to activate other molecular switches. 

Shimizu admits that there is still potential for improvement of this switch. 'Our systems actually switch quite slowly so they are not ideal for the more common information storage applications. However, the ability to switch conformations and properties could be a new method for introducing and dynamically controlling the properties of a molecule or material,' he said. He also hopes to develop systems that can provide more operations than on and off.

Robert Strongin of Louisana State University, Baton Rouge, US, welcomed the work. 'The researchers have devised a simple and unique molecular system which exhibits guest-induced interconvertible molecular states. Importantly, the varying states persist even after guest removal. This is a significant advance as it provides clear proof-of-concept that supramolecular materials may have potential applications as key components in next generation memory storage devices,' said Strongin. 

Rebecca Gillan