Adv. Mater.http://dx.doi.org/10.1002/adma.201103362 (2011)

The development of cholesteric liquid crystals that offer dynamic colour tuning of their reflection across the visible spectrum would be of great interest for many applications in imaging, display technology and electronics. Unfortunately, this task has so far required the use of three distinct liquid crystal films, each serving the red, green or blue regions separately and being switched on or off electronically. In contrast, using light as a means of tuning reflectivity is attractive because it offers remote, spatial and temporal control. So far, however, reports of such light-driven colour changes are dynamic and continuous; that is, the material remains a particular colour only for as long as the controlling light is incident on it. Quan Li and co-workers at Kent State University in the USA have now synthesized two light-driven chiral molecular switches with very high helical twisting powers that quickly and reversibly modulate their structural reflection from blue to red, via green, when irradiated with light of ultraviolet or visible wavelengths. Such wavelength-selective reflection provides a simple and easy way of simultaneously achieving red, green and blue reflection colours in a single light-driven self-organized thin film. The researchers say that this work will encourage the development of light-driven chiral molecular switches or motors for a range of practical applications.