New liquid-crystalline isothiocyanates with high clearing points, low viscosities and strong nematic character

Bi-, tri- and tetra-ring liquid-crystalline compounds with an isothiocyanate group in the terminal position of the molecule and with an ethylene group in the central position have been synthesized. Phenyl, cyclohexyl, bicyclo2,2,2]octyl, 1,3-dioxane and pyrimidinyl were used as the ring systems. Their transition temperatures and melting enthalpies have been determined. The relationship between the order of the rings in the molecule and the clearing points and melting points of the compounds is discussed. It is shown that these compounds are valuable components of liquid crystal mixtures, since they effectively raise their clearing points yet only have a small effect on the viscosity.