Study on the helical twisting behaviour of chiral 1,2-propanediol derivatives inducing chiral nematic liquid crystals with a helix inversion and controllable pitch variation

In this study, a novel series of chiral dopants were synthesised via the esterification reaction between optically active (S)-1,2-propanediol and mesogenic carboxylic acids. The phenomenon of a helix inversion with temperature variation could be observed in the chiral nematic liquid crystals (N*-LCs) by doping the chiral dopants into a nematic liquid crystal host. The results show that the inversion temperature varies only slightly with terminal alkyl chain length, but can be influenced by the structural rigidity and molecular shape of the chiral dopants, while the molecular twisting power has an apparent dependence on terminal alkyl chain length and the number of chiral centres. Depending on the composition proportion of binary chiral mixtures prepared by the synthesised chiral dopants and the commercially-available chiral compounds, induced N*-LCs with controllable pitch variation could be easily achieved.