Liquid Crystal Shines In Three Colors

A two-component liquid-crystal system containing just a single luminescent moiety responds to mild stimuli by reversibly switching among three colored states, according to researchers at the University of Tokyo (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201100914). The study may lead to new types of liquid-crystal-based displays and data storage applications. Liquid crystals typically switch between two states—for example, two colors. Switching among three colors in systems that contain just one type of luminescent compound has not been reported until now. Chemists Yoshimitsu Sagara and Takashi Kato came up with the tricolored system by blending a large dumbbell-shaped molecule featuring a phenylethynyl anthracene center (the luminescent segment) with an equimolar amount of a smaller organic compound. UV radiation causes films of the mixture to appear red-orange. That color changes to yellow if the films are sheared or rubbed at room temperature and to green if they are rubbed at 90 °C. Such properties may be useful for designing indicators of a material’s mechanical history, the team suggests.