Mesomorphic and anisotropic properties of trans-4-(4-pentylcyclohexyl)benzonitrile doped with chiral (bis)camphoralidene-ethylenediamine

Abstract
Mesomorphic, optical, orientational and dielectric properties of the nematic liquid crystal (LC) 4-pentyl-cyclohexyl-4-benzonitrile (5PCH) doped with chiral (bis)camphoralidene-ethylenediamine (C2-bisCamN) have been studied. Based on the analysis of textures, the induction of helical nematics phase upon addition of the dopant was detected. The helical pitch of the induced chiral nematic in mixtures was measured using the Grandjean-Cano method and the helical twisting power was estimated. The efficiency of chiral induction was shown to decrease with increasing the dopant concentration due to association. The clearing temperatures of the mixtures were measured using polarization thermomicroscopy. The degree of mesophase destabilization upon introduction of the dopant was estimated. The effect of the chiral dopant on the mesophase anisotropic characteristics, such as dielectric susceptibility and birefringence, was studied. It was found that the introduction of C2-bisCamN and the induction of a chiral mesophase were accompanied by a decrease in the dielectric and optical anisotropy as well as orientational ordering. The main contribution to the change of the anisotropic characteristics is made by spiral twisting and local orientation of the "quasinematic" layers. The associative state of the mesophase of binary systems based on highly polar cyano derivatives of LC was estimated using the Kirkwood correlation parameter. A decrease in the degree of antiparallel dipole-dipole association of 5PCH with an increase in the concentration of the additive was shown. Using quantum chemical calculations, optimized structures of monomers and dimers of 5PCH, C2-bisCamN and solvates based on them were obtained. Analysis of geometric parameters (shape anisotropy and molar volumes), polarity, optical activity and stability energies of supermolecules allowed to identify camphorodiimine associates as the most probable structures responsible for the properties of the induced chiral mesophase in the 5PCH + C2-bisCamN system.

Keywords: cyano-derivative liquid crystals, induced helical nematics, chiral dopants, thermal stability, dielectric anisotropy, birefringence, helix pitch, order parameter