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Chirality Is Electronically Switchable

Photonics Spectra
Sep 2000
Daniel S. Burgess

A copper-based molecule with electronically switchable optical properties promises improved display technologies and application as a switch in molecular electronics. The complex changes its apparent chirality when an electron is added or removed from its structure, causing it to strongly polarize light in almost perfectly opposite ways.

James W. Canary, a professor at New York University and lead researcher, explained that chirality describes the inability to superimpose variant geometries of structures, such as these otherwise chemically identical copper molecules. In this case, the electronic effect is analogous to turning a counterclockwise spiral staircase into one that rises clockwise, or to reversing the angle of attack on a propeller's blades.

The result is that the optical properties of the complexes also change, particularly their circular dichroism, which is the ability to convert the polarization of incident light between planar and elliptical. Canary and his colleague, Steffen Zahn, found that they could produce mirror-image circular dichroism spectra across the ultraviolet and visible by alternately exposing the molecules to solutions of ascorbic acid and ammonium persulfate. This allows them to create a molecular switch with which they can modulate a polarization signal.

Such switches may find a place in nanotechnology and molecular computing and electronics, but other applications are closer at hand. Canary said that the compounds act like cholesteric liquid crystals that are used in displays, but with a difference. "Our compounds may offer better stability and faster switching rates," he said. The university has patented the chemists' work, reported in the May 26 issue of Science. Canary noted that there has been commercial interest in licensing the technology. Currently, however, they plan to continue the research in the interest of basic science, he said.

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