Photo-switchable chiral liquid crystal with optical tristability enabled by a photoresponsive azo-chiral dopant.

A light-driven tristable chiral-tilted homeotropic nematic (TCHN) cell is demonstrated. The liquid-crystal cell is photo-switchable among the three stable states: the tilted-homeotropic, fingerprint, and the tilted-twist states. The inclusion of a photosensitive chiral bis(azobenzene) compound into a typical nematic liquid crystal makes the resulting material possible to switch from one to another stable state directly and reversibly owing to the photoinduced trans-cis isomerization of the azo-chiral dopant and, hence, the configurational change of the liquid crystal via the guest-host effect. By further introducing dichroic dyes into the TCHN system, we devised a polarizer-free display and light modulators. The novel TCHN composite material opens up new possible applications in light-driven optical elements and devices.