2,3-difluorobenzene derivatives

Details 2,3-difluorobenzene derivatives 2,3-difluorobenzene derivatives

1989-05-15

1993-08-17

Stoll, Robert L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229963, 25229967, 25229965, 2522996, 359104, 544298, 544224, 546339, 568647, 560 65, 560 73, 560102, C09K 1934, C09K 1930, C09K 1906, G02F 113

Patent

active

052366200

DESCRIPTION:

BRIEF SUMMARY
SUMMARY OF THE INVENTION

The invention relates to 2,3-difluorobenzene derivatives of the formula I ##STR1## wherein R.sup.1 and R.sup.2 independently of one another are each alkyl having 1-15 C atoms or alkenyl having 3-15 C atoms each of which is unsubstituted, mono-substituted by cyano or at least mono-substituted by fluorine or chlorine, it being possible for a CH.sub.2 group in these radicals to be replaced by --O--, --CO--, --O--CO--, --CO--O-- or --O--CO--O--, trans-1,4-cyclohexylene wherein it is also possible for one or two non-adjacent CH.sub.2 groups to be replaced by --O--, or are 1,4-phenylene which is unsubstituted or mono-substituted or disubstituted by fluorine and in which it is also possible for one or two CH groups to be replaced by N, at least one of the groups A.sup.1 and A.sup.2 being 2,3-difluoro-1,4-phenylene, and --O--CO--, --CH.sub.2 O--, --OCH.sub.2 -- or --CH.sub.2 CH.sub.2, ##STR2## m=1 and ##STR3## Z.sup.1 or Z.sup.2 is selected from the group consisting of --CO--O--, --O--CO--, --CH.sub.2 O--and --OCH.sub.2 --.
In the following text, for the sake of simplicity, Cyc is a 1,4-cyclohexylene group, Dio is a dioxane-2,5-diyl group, Dit is a dithiane-2,5-diyl group, Pyd is a pyridine-2,5-diyl group, Pyr is a pyrimidin-2,5-diyl group, Pyz is a pyridazine-3,5-diyl group, Phe is a 1,4-phenylene group, PheF is group of the formula ##STR4## and PheF.sub.2 is a group of the formula ##STR5##
The compounds of the formula I can be used as components of liquid-crystal phases, particularly for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases or the effect of dynamic scattering.
Compounds of the formula I having negative anisotropy of the dielectric constant (.DELTA..epsilon.=.epsilon..sub..parallel. -.epsilon..sub..perp. <0, in which .epsilon..sub.81 is the dielectric constant along the longitudinal axis of the molecule and .epsilon..sub.81 is the dielectric constant perpendicular thereto) are aligned in an electric field with the longitudinal axis 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 guest/host type (guest-host interaction).
If a liquid crystal having positive dielectric anisotropy is used, its homogeneous orientation (which is obtained by treatment of the surface of the plate) is aligned in a homotropic manner by the application of the potential, that is to say the cell is switched from "colored" to "colorless". Colorless symbols on a colored background are displayed in this manner. On the other hand, if a liquid crystal having negative dielectric anisotropy is used, its homotropic orientation (caused by treatment of the surface of the plate) is aligned parallel to the surfaces of the electrodes by the application of a potential, as a result of which it becomes possible to display colored pictorial elements on a colorless background.
The ECB effect (electrically controlled birefringence) or the DAP effect (deformation of aligned phases) was described for the first time in 1971 (M. F. Schieckel and K. Fahrenschon, "Deformation of nematic liquid crystals with vertical orientation in electrical fields", (Appl. Phys. Lett. 19 (1971), 3912). This was followed by papers by J. F. Khan (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869).
The researches of J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982) 244) have shown that liquid-crystal phases must have high values of the ratio of the elastic constants K.sub.3 /K.sub.1, high values of the optical anisotropy .DELTA.n and values of the dielectric anisotropy .DELTA..epsilon. between -0.5 and -5, in order to be able to be employed for highly informative

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