Photoinduced phase transition behaviours of the liquid crystal blue phase doped with azobenzene bent-shaped molecules

Abstract

A kind of azobenzene-based bent-shaped molecule is doped into a chiral nematic liquid crystal, so as to induce a 25°C blue phase range. As the sample is irradiated by 365 nm ultraviolet radiation, phase transitions from the blue phase to the chiral nematic, and then to the isotropic state are observed, because of the trans–cis isomerisation of the azobenzene moiety; on the other hand, the cis–trans isomerisation of azobenzene leads to the recovery from the isotropic to the blue phase. The transition time from the blue phase to the isotropic is about ∼1–2 minutes, and the time for the recovery is about 2 hours; these times are significantly faster than that of conventional materials. It is also found that the transition time from the blue phase to the isotropic is extended with increase of the material thickness and the weakening of ultraviolet intensity; however, no distinct effects on the time of the reverse process are seen. In addition, a stripe pattern is fabricated by photomask exposure, and such results indicate prospects for application of this material in light-driven displays and information storage.