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 SA into Sc 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 ...

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