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-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.

Parametrization of Substituents: Effects of Fluorine and Other Heteroatoms on OH, NH, and CH Acidities

“…For example, they increase the dielectrical anisotropy of liquid crystals and thus enable the design of improved thin film transistor liquid crystal displays. [120] The details of how fluorine alters all such physical properties are still poorly understood if not mysterious. In other words, much remains to be done until one can claim to have succeeded in the ªparametrizationº of fluorine.…”

Determination of Orientational Order Parameters of Two Tri-Component Mixtures from Optical Birefringence and X-Ray Diffraction Measurements

“…In contrast, the vertically aligned (VA) mode LCD's [1][2][3][4][5], based on liquid crystal materials with negative dielectric anisotropy, offers a superior picture quality with wide viewing angle [6,7], high contrast [8] and video-compatible switching times [9,10]. Liquid crystalline materials suitable for VA mode LCD's are mainly focused on dielectrically negative fluorinated liquid crystals comprising of 1,2-difluorobenzene building block [11] which combine the necessary polarity with chemical stability and low polarizability [12,13] suitable for their application in VA mode LCD's. Difluorinated alkoxy compounds are suitable for preparation of VA mixtures because of their large negative dielectric anisotropy and low optical birefringence.…”

Advances in liquid crystalline conjugated polymers

“…It is required for FLC molecule to satisfy the following conditions, for example, it must be optical active (chiral) and it has a large dipole moment whose component perpendicular to the molecular axis is nonzero. Since fluorine atom has a large electronegativity 33 and a small van der Waals radius, 34 it affords a large dipole moment and thermal stability, 35 giving rise to a favorable FLC molecule. This also holds for the side-chain-type FLC polymers.…”