Liquid crystals, compounds and mixtures with positive dielectric anisotropies are reviewed. The mesogenic properties and physical chemical properties (viscosity, birefringence, refractive indices, dielectric anisotropy and elastic constants) of compounds being cyano, fluoro, isothiocyanato derivatives of biphenyl, terphenyl, quaterphenyl, tolane, phenyl tolane, phenyl ethynyl tolane, and biphenyl tolane are compared. The question of how to obtain liquid crystal with a broad range of nematic phases is discussed in detail. Influence of lateral substituent of different kinds of mesogenic and physicochemical properties is presented (demonstrated). Examples of mixtures with birefringence ∆n in the range of 0.2-0.5 are given.

The phase transition temperatures, birefringence and visco-elastic coefficient of several high birefringence isothiocyanato tolane compounds were evaluated. The polarizability of these compounds was calculated by the Austin Model 1 (AM1) and Modified Neglect of Diatomic Overlap (MNDO) methods. Using these compounds, we have formulated a eutectic mixture exhibiting a wide nematic range and high figure of merit.

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The paper reports temperature and external electrical field effects on propagation properties of a photonic liquid-crystal fibre composed of a solid-core photonic crystal fibre filled either with a prototype nematic liquid crystal characterized by extremely low (of the order of ∼0.05) material birefringence or with a typical nematic pentylo-cyano-biphenyl, PCB (birefringence of the order of ∼0.2). The nematic liquid crystal was introduced into the micro holes of the photonic crystal fibre by the capillary effect. Depending on the liquid crystal material introduced into the micro holes and due to anisotropic properties of the photonic liquid-crystal fibre, switching between different guiding mechanisms controlled by temperature and an external electric field has been demonstrated. This creates great potential in fibre optic sensing and optical processing application.

High birefringence (0 3 1 0 4) and relatively low-viscosity liquid crystal mixtures containing isothiocyanato tolane and isothiocyanato terphenyl liquid crystals are developed. A twisted-nematic (TN) 1.6-m thin cell for color-sequential liquid crystal display with 1-ms response time is demonstrated. Index Terms-Color sequential display, high-birefringence liquid crystals, liquid crystal display (LCD), response time.