Exposure to two different wavelengths of light can cause the azobenzene molecule to switch back and forth between two different shapes. This molecular shape-changing works well in solution but until now has not worked with molecules attached to surfaces. Now scientists from Penn State University and Rice University have found a way to make the switching work when the molecules are tethered to a surface—a first step toward making this molecular switching useful for nanotech devices. From Penn State (via PhysOrg.com) “Tethered molecules act as light-driven reversible nanoswitches“:
The ability to see is based on molecules in the eye that flip from one conformation to another when exposed to visible light. Now, a new technique for attaching light-sensitive organic molecules to metal surfaces allows the molecules to be switched between two different configurations in response to exposure to different wavelengths of light. Because the configuration changes are reversible and can be controlled without direct contact, this technique could enable applications that can be controlled at the molecular scale.
The technology has been suggested as a possible basis for molecular motors, artificial muscles, and molecular electronics. The research results, obtained by a team led by Paul S. Weiss, distinguished professor of chemistry and physics at Penn and James M. Tour, Chao professor of chemistry at Rice University, are reported in the June issue of the journal Nano Letters [abstract].
…When the tethered molecules were exposed to ultraviolet light in a specially built scanning tunneling microscope, they switched from the trans to the more-compact cis state. This switch was confirmed by an apparent decrease in height of the molecule above the surrounding surface. The researchers further found that exposure to visible light caused a transition back to the more-extended trans state.
Weiss points out that this research advance is just the first step in designing a device that can be driven or actuated by such molecular change. In order to perform useful work as a switch or nanoscale-drive motor, it will be necessary to coordinate the motion of multiple molecules and to build moving parts into some sort of assembly. According to Weiss, further research by the team already has found some surprises when the molecules are lined up to work in unison, like a chorus line.