Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1990-11-21
1993-04-20
Rotman, Alan L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
546290, 546302, 340810, C07D21362, C07D21363, C07D21364
Patent
active
052044777
DESCRIPTION:
BRIEF SUMMARY
The invention relates to pyridine derivatives of the formula I ##STR2## wherein R.sup.1 is a straight-chain alkyl, alkoxy, alkenyl or oxaalkyl group with up to 15 C atoms in the alkyl residue, in case of X=F, the R.sup.1 groups may also be branched, polysubstituted by F, and wherein one or two CH groups may also be replaced by N, in the alkyl residue
The invention also relates to liquid crystal media, especially for electrooptical display elements based on the ECB effect, which contain at least one compound of the pyridine derivatives of the formula I.
For the sake of simplicity in the following, Phe is an unsubstituted 1,4-phenylene group, PheF is a mono- or disubstituted 1,4-phenylene group, Cyc is a trans-1,4-cyclohexylene group, Pyd is a pyridine-2,5-diyl group and Pyr is a pyrimidine-2,5-diyl group.
The compounds of the formula I can be used as components of liquid crystalline media, in particular for displays which are 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.
Compounds of the formula I are preferably also suitable for the use as components in liquid crystalline media for displays which are based on the ECB effect. Furthermore, some of the compounds of the formula I are also suitable for the use as components of STN mixtures.
Similar pyridine compounds are disclosed, e.g. in WO 87/4158 or in DE 38 14 346. However, none of these disclosed pyridines show an oxygen atom near the N atom of the pyridine ring and they do not have the excellent properties of the compounds of the present invention.
The ECB (electrically controlled birefringence) effect or DAP (deformation of aligned phases) effect 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). Works by J. F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869) followed.
The works by 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 media must have high values for the ratio of the elastic constants K.sub.3 /K.sub.1, high values for the optical anisotropy .DELTA.n and negative values for the dielectrical anisotropy .DELTA..epsilon. in order to be able to be used for highly informative display elements based on the ECB effect.
Electrooptical display elements based on the ECB effect have a homoeotropic edge orientation, that is to say the liquid crystal medium has negative dielectric anisotropy.
For technical use of this effect in electrooptical display elements, LC media which must meet numerous requirements are required. The chemical stability towards moisture, air and physical influences, such as heat, infrared, visible and ultraviolet radiation and constant and alternating electrical fields, are particularly important here. A liquid crystal mesophase in a suitable temperature range and a low viscosity are furthermore required of technically useful LC media.
In none of the .series of compounds with a liquid crystal mesophase which are known to date is there a single compound which meets all these requirements. Mixtures of two to 25, preferably three to 18, compounds are therefore as a rule prepared in order to obtain substances which can be used as LC media. However, it has not been possible for optimum media to be easily prepared in this manner, since no liquid crystal materials with significantly negative dielectric anisotropy and/or correspondingly high optical anisotropy and/or particularly high values for K.sub.3 /K.sub.1 and adquate long-term stability have as yet been available.
There is thus still a great need for liquid crystal media with favorable meso ranges, high values of K.sub.3 /K.sub.1, high optical anisotropy .increment.n, negative dielectric anisotropy .increment..epsilon. and high long-term stabil
REFERENCES:
Chemical Abstracts, vol. 109, No. 2, p. 596, Abst. No. 15315-z, Jul. 11, 1988.
Chemical Abstracts, vol. 102, No. 19, p. 603, Abst. No. 166,578-u, May 13, 1985.
Meyer Volker
Plach Herbert
Poetsch Eike
Reiffenrath Volker
Merck Patent Gesellschaft mit beschrankter Haftung
Rotman Alan L.
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