Oblique helicoidal state of the twist-bend nematic doped by chiral azo-compound

A novel light-sensitive chiral dopant ChD-3816 (an azo-compound containing 4-hexanoyloxyphenyl and 2-isopropyl-5-methylcyclohexylbenzoate moieties) was used for inducing helical twisting in N-tb-forming mixtures of CB7CB/CB6OCB with 5CB added to decrease the phase transition temperatures. The effects of ChD-3816 upon phase transition temperatures, as well as effects of its concentration on the measured values of helical twisting, were determined. Most of the measured parameters could be varied due to light-induced trans-cis isomerisation of ChD-3816. Under electric field, selective reflection spectra in the visible range were obtained for the emerging oblique helicoidal cholesteric structures (Ch(OH)), with the wavelengths controllable both by electric field and appropriate UV irradiation. Possible applications for dynamic formation of contrast images are discussed.