New liquid-crystalline compounds with negative dielectric anisotropy

Abstract

Until now, liquid-crystalline compounds with high negative dielectric anisotropy were usually realized by a lateral cyano group. A drawback to these cyano substituted liquid crystals, namely the considerable increase in the viscosity and the reduction of the thermodynamic stability of the mesophase, has been circumvented by preparing 2,3-difluorobenzene derivatives. A universal method to prepare a variety of classes of liquid-crystalline compounds containing the 2,3-difluoro-phenylene moiety has been developed. The new materials are characterized by high negative Δϵ values of up to -6, and viscosities comparable with the non-fluorinated compounds. The introduction of the two fluorine atoms also leads to an increase in K ₃₃/K ₁₁. They also suppress higher ordered smectic phases and transform S_A into S_c phases. The new compound classes are promising materials for liquid crystal mixtures for various applications as electrically controlled bire-fringent, supertwisted nematic and ferroelectric liquid crystal displays.