Sign reversal of the spontaneous and induced polarisation in a mixture of achiral liquid crystal host and chiral azo dopant

Achiral liquid crystal, possessing orthogonal smectic A and tilted smectic C phases in its phase sequence, was doped with a chiral photochromic azo dopant. It was found that the spontaneous and induced polarisation in the tilted smectic C* phase and in the orthogonal smectic A phase, respectively, change their sign, as well as their magnitude, under illumination with UV light. The origin of this sign reversal effect is considered to be the different sign of the molecular net dipole moment component mu(y) of trans- and cis-isomers of the photochromic azo dopant, respectively. This light-induced sign reversal effect seems to have large potential for applications in the light-light controlled photonic liquid crystal devices, based on this effect.

Automated summary

It was discovered that the addition of a chiral photochromic azo dopant to an achiral liquid crystal leads to a reversal of spontaneous and induced polarization in the tilted smectic C* phase and the orthogonal smectic A phase, respectively, under UV light illumination. This sign reversal effect, attributed to the different dipole moment components of the trans- and cis-isomers of the photochromic azo dopant, shows promising potential for applications in light-controlled photonic liquid crystal devices.