2,3-difluorobiphenyls

Details 2,3-difluorobiphenyls 2,3-difluorobiphenyls

1989-05-15

1993-04-20

Stoll, Robert L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229963, 25229967, 25229961, 25229965, 560 65, 560102, C09K 1912, C09K 1920, C09K 1934, C09K 1930

Patent

active

052040194

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

The invention relates to 4-Q.sup.1 -4'-Q.sup.2 -2,3-difluorobiphenyls wherein -A.sup.2 -Z in which is unsubstituted or monosubstituted by cyano or at least monosubstituted by fluorine or chlorine, and in which in each case one or two non-adjacent CH.sub.2 groups can also be replaced by --O--, --CO--, --O--CO, --CO--O-- or --O--COO--, CH.sub.2 --or a single bond, and 1,4-phenylene which is unsubstituted or substituted by one or two fluorine atoms, and in which one or two CH groups can also be replaced by N, or trans-1,4-cyclohexylene wherein one or two non-adjacent CH.sub.2 groups can also be replaced by --O--, and one of the two groups A.sup.1 and A.sup.2 can also be a single bond, --CH.sub.2 CH.sub.2 --, if one of the groups Q.sup.1 or Q.sup.2 is alkyl or alkoxy and the other group Q.sup.1 or Q.sup.2 is R--A.sup.1 --A.sup.2 --Z wherein one of the two groups A.sup.1 and A.sup.2 is a single bond.
For the sake of simplicity in the following text Cyc is a 1,4-cyclohexylene group, Phe is a 1,4-phenylene group, Pyd is a pyridine-2,5-diyl group, Pyr is a pyrimidine-2,5-diyl group and Pyn is a pyrazine-2,5-diyl group, it being possible for these groups to be unsubstituted or substituted by one or two fluorine atoms. Preferably, these groups are unsubstituted.
BPF.sub.2 is a group of the formula ##STR1##
The compounds of the formula I can be used as components of liquid-crystal phases, especially for displays based on the principle of the twisted cell, the guest-host effect, the effect of the deformation of aligned phases or the effect of dynamic scattering.
The compounds of the formula I are distinguished by a markedly negative anisotropy of the dielectric constant and, in an electric field, are aligned with the longitudinal axes of their molecules perpendicular to the direction of the field. This effect is known and is utilized to control optical transparency in various liquid-crystal displays, for example in liquid-crystal cells of the light scattering type (dynamic scattering), of the so-called DAP type (deformation of aligned phases) or of the ECB type (electrically controlled birefringence) or the guest/host type (guest/host interaction).
Compounds of the formula I are also suitable for use as components of chirally tilted smectic phases. Chirally tilted smectic, liquid-crystal phases having ferroelectric properties can be prepared by adding a suitable chiral doping substance to base mixtures containing one or more tilted smectic phases (L. A. Veresnev et al., Mol. Cryst. Liq. Cryst. 89, 327 (1982); H. R. Brand et al., J. Physique 44 (lett.), L-771 (1983). Phases of this type can be used as dielectrics for high-speed displays based on the principle described by Clark and Lagerwall of SSFLC technology (N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett. 36, 899 (1980); U.S. Pat. No. 4,367,924) based on the ferroelectric properties of the chirally tilted phase.
At present a number of liquid-crystal compounds having a weakly negative dielectric anisotropy have already been synthesized. On the other hand, relatively few liquid crystal components having a large negative anisotropy of the dielectric constant are yet known. In addition, the latter generally exhibit disadvantages, such as, for example, poor solubility in mixtures, high viscosity, high melting points and chemical instability. There is, therefore, a need for further compounds having negative dielectric anisotropy which make it possible to improve further the properties of mixtures for a wide variety of electrooptical applications.
Liquid-crystal compounds having negative dielectric anisotropy and containing two or three rings linked via carboxyl groups or a covalent bond and one or more lateral groups, such as halogen, cyano or nitro groups, are known from German Patents 2,240,864, 2,613,293, 2,835,662 and 2,836,086 and European Patent 023,728.
The compounds claimed here are embraced within a wide formula in European Patent 084,194. No individual compounds of the formula according to the invention are mentioned in that text, h

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