, with the exponent α either smaller than 1 (subdiffusion) or

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-difluorophenylene moiety has been developed. The new materials are characterized by high negative A& values of up to -6 , and viscosities comparable with the nonfluorinated compounds. The introduction of the two fluorine atoms also leads to an increase in K,3/K,i. 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 birefringent, supertwisted nematic and ferroelectric liquid crystal displays.

Despite their relatively uniform structural appearance, the synthesis of liquid crystalline materials for modern display applications involves a broad range of different synthetic methods, such as heterocyclic chemistry, ortho-metallation, transition metal catalyzed carbon-carbon coupling reactions or stereoselective hydrofluorination. This account aims to give an impression of the ongoing challenge to introduce these complex techniques into industrial practice, and to keep pace with the more and more rapid advance of display technology.

Optical and electro-optic properties of two highly conjugated diphenyldiacetylenic liquid crystals (LCs) [1.4-bis-(4-propylphenyl)-butadiyne, abbreviated as PTTP-mm] and their eutectic mixture were characterized in the nematic range. These LCs are found to exhibit extraordinarily high birefringence and very low viscoelastic coefficient. Their figure of merit is significantly higher than that of the widely used commercial LC mixture BDH-E7. Potential application of PTTP-mm in modulating infrared radiation is addressed.