EP0988286A1

EP0988286A1 - 2-fluoro-3-(1-fluoro-alkyl)-pyridine-6-yl derivatives and the use thereof in liquid crystal mixtures

Info

Publication number: EP0988286A1
Application number: EP98928240A
Authority: EP
Inventors: Javier Manero; Wolfgang Schmidt; Barbara Hornung
Original assignee: Aventis Research and Technologies GmbH and Co KG
Current assignee: Aventis Research and Technologies GmbH and Co KG
Priority date: 1997-06-06
Filing date: 1998-05-11
Publication date: 2000-03-29
Also published as: JP2002511072A; DE19723855A1; WO1998055458A1

Abstract

The invention relates to a 2-fluoro-3-(1-fluoro-alkyl)-pyridine-6-yl derivative of formula (I) R<1>(-A<1>-M<1>)a(-A<2>-M<2>)b-B-R<2> wherein the symbols and indices have the following meaning: group B is (a); wherein Q is F or H; R<1> (-A<1>-M<1>)a(-A<2>-M<2>)b is a mesogene radical and R<2> is an alkyl group for example. The compounds of formula (I) are particularly suitable as constituents of ferroelectric liquid crystal mixtures, especially for displays which operate in tau V(min)- mode.

Description

description

2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivatives and their use in liquid-crystalline mixtures.

In addition to nematic and cholesteric liquid crystals, optically active inclined smectic (ferroelectric) liquid crystals have also recently been used in commercial display devices.

Clark and Lagerwall were able to show that the use of ferroelectric

Liquid crystals (FLC) in very thin cells lead to optoelectric switching or display elements which, compared to conventional TN ("twisted nematic") cells, have switching times that are up to a factor of 1000 faster (see, for example, EP-A 0 032 362) . Because of these and other beneficial properties, e.g. the bistable switching option and the almost independent viewing angle

Contrasts, FLCs are generally well suited for application areas such as computer displays.

For the use of FLCs in electro-optical or completely optical components, one needs either connections that form inclined or orthogonal smectic phases and are themselves optically active, or one can by doping compounds that form such smectic phases, but not optically active are, induce ferroelectric smectic phases with optically active compounds. The desired phase should be stable over the largest possible temperature range.

A uniform planar orientation of the liquid crystals is necessary to achieve a good contrast ratio in electro-optical components. A good orientation in the S _A and S ^* _c -P ιase can be achieved, for example, if the phase sequence of the liquid crystal mixture with decreasing temperature is:

Isotropic → N ^'→ S _A → S _c ^* The prerequisite is that the pitch (pitch of the helix) in the N ^* phase is very large (greater than 10 μm) or, even better, completely compensated (see, for example, T. Matsumoto et al., Proc. Of the 6th Int. Display Research Conf., Japan Display, Sept. 30 - Oct. 2, 1986, Tokyo, Japan, pp. 468-470; M. Murakami et al., Ibid. Pp. 344-. 347). This is achieved, for example, by adding one or more optically active dopants, which induce a right-handed helix, to the chiral liquid crystal mixture, which has a left-handed helix in the N ^* phase, in such amounts that the helix is compensated.

For the use of the SSFLCD effect (Surface Stabilized Ferroelectric Liquid Crystal Display) from Clark and Lagerwall for uniform, planar orientation, it is also a prerequisite that the pitch in the smectic C ^* phase is significantly larger than the thickness of the display element (Mol. Cryst Liq. Cryst. 1983, 94, 213 and 1984, 114, 151.

The optical switching time τ [μs] of ferroelectric liquid crystal systems, which should be as short as possible, depends on the rotational viscosity of the system γ [mPas], the spontaneous polarization P _s [nC / cm ² ] and the electric field strength E [V / m] the relationship γ

P _s - E

Since the field strength E is determined by the distance between the electrodes in the electro-optical component and by the applied voltage, the ferroelectric

Display medium must be low-viscosity and have a high spontaneous polarization so that a short switching time is achieved.

Finally, in addition to thermal, chemical and photochemical stability, a small optical anisotropy Δn and a low positive or preferably negative dielectric anisotropy Δε are required (see, for example, ST Lagerwall et al., "Ferroelectric Liquid Crystals for Displays" SID Symposium, Oct. Meeting 1985, San Diego, Ca, UNITED STATES).

All of these requirements can only be met with mixtures of several components. The base (or matrix) is preferably compounds that possible themselves already have the desired phase sequence I → S _A → S _c N. Other components of the mixture are often added to lower the melting point and broaden the S _c - and usually also the N phase, to induce optical activity, to compensate for pitch and to adapt the optical and dielectric anisotropy, but, for example, do not increase the rotational viscosity if possible shall be.

Ferroelectric liquid crystal displays can also be operated using the DHF (Distorted Helix Formation) effect or the PSFLCD effect (Pitch Stabilized Ferroelectric Liquid Crystal Display, also called SBF = Short Pitch Bistable Ferroelectric Effect). The DHF effect was described by Bl Ostrovski in Advances in Liquid Crystal Research and Applications, Oxford / Budapest 1980, 469ff. described, the PSFLCD effect is described in DE-A 39 20 625 and EP-A 0405 346. In contrast to the SSFLCD effect, a liquid crystal material with a short S _c pitch is required to use these effects.

2-fluoropyridine derivatives for use in liquid crystal mixtures are known, for example, from DE-A 40 40 575 and WO-A-91/04 249.

However, since the development, in particular of ferroelectric liquid crystal mixtures, can in no way be regarded as complete, the manufacturers of displays are interested in the most diverse components for mixtures. This is partly because the interaction of the liquid-crystalline mixtures with the individual components of the display device or the cells (for example the orientation layer) allows conclusions to be drawn about the quality of the liquid-crystalline mixtures as well. The object of the present invention was therefore to provide new compounds which are suitable in liquid-crystalline mixtures for improving the property profile of these mixtures.

It has now surprisingly been found that 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivatives of the formula (I) are particularly suitable for use in liquid-crystal mixtures.

The invention therefore relates to 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivatives of the formula (I),

R ¹ (-A ¹ - M ¹ ) _a (-A ² - M ² ) _b - B - R ² (I)

where the symbols and indices have the following meanings: the group is B.

Q is hydrogen or fluorine;

R \ R ² are the same or different a) a straight-chain or branched alkyl radical (with or without asymmetrical carbon atom) with 1 to 20 carbon atoms, where a1) one or more non-adjacent and non-terminal CH ₂ groups by -O -, -S-, -CO-O-, -O-CO-, -O-CO-O- or -Si (CH ₃ ) ₂ - can be replaced and / or a2) one or more CH ₂ groups by -CH = CH-, -C≡C-,

Cyclopropan-1, 2-diyl, 1, 4-phenylene, 1, 4-cyclohexylene or 1, 3-cyclopentylene can be replaced and / or a3) the terminal CH ₃ group can be replaced by one of the following chiral groups (optically active or racemic):

H H H H

R R R R

Cl CH CN

H H

R

F F

b) R ^{1 is} also hydrogen;

R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ are the same or different a) hydrogen b) a straight-chain or branched alkyl radical (with or without asymmetric carbon atom) with 1 to 16 carbon atoms, b1) one or more not neighboring and non-terminal CH ₂ -

Groups can be replaced by -O- and / or b2) one or two CH ₂ groups can be replaced by -CH = CH-, c) R ⁴ and R ⁵ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - if they are bound to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or Vaierolactone system;

M ¹ , M ² are the same or different -CO-O-, -O-CO-, -CO-S-, -S-CO-,

-CS-O-, -O-CS-, -CH ₂ -O-, -O-CH ₂ -, -CH ₂ -S-, -S-CH ₂ -, -CH = CH-, -C≡C -, -CH ₂ -CH ₂ -CO-O-, -O-CO-CH ₂ -CH ₂ - or a single bond; A ¹ , A ² are identical or different 1, 4-phenylene, where one or more H atoms can be replaced by F, Cl and / or CN, pyrazine-2,5-diyl, where one or two H atoms by F, Cl and / or CN can be replaced, pyridazine-3,6-diyl, where one or two H atoms can be replaced by F, Cl and / or CN, pyridine-2,5-diyl, one or more H atoms can be replaced by F, Cl and / or CN, pyrimidine-2,5-diyl, where one or two H atoms can be replaced by F, Cl and / or CN, 1, 4-cyclohexylene, where one or two H atoms can be replaced by CN and / or CH ₃ and / or F, (1, 3,4) thiadiazole-2,5-diyl, 1, 3-dioxane-2,5-diyl, 1, 3-dithiane-2,5-diyl, 1,3-thiazole-2,4-diyl, where an H atom can be replaced by F, Cl and / or CN, 1,3-thiazole-2,5-diyl , where an H atom can be replaced by F, Cl and / or CN, thiophene-2,4-diyl, where an H atom can be replaced by F, Cl and / or CN, thiophene-2,5-diyl , where one or two H atoms by F, Cl and / or C N can be replaced, naphthalene-2,6-diyl, where one or more H atoms can be replaced by F, Cl and / or CN or 1, 3-dioxaborinane-2,5-diyl;

a, b are 0 or 1; with the proviso that the compound of formula (I) contains no more than four five or more membered ring systems.

The provision of compounds of the formula (I) broadly broadens the range of liquid-crystalline substances which are suitable for the preparation of liquid-crystalline mixtures from various application points of view.

In this connection, the compounds of formula (I) have a wide range of uses. Depending on the selection of the substituents, they can serve as base materials from which liquid-crystalline phases are predominantly composed; However, it is also possible to add compounds of the formula (I) to liquid-crystalline base materials from other classes of compounds, for example the dielectric and / or optical anisotropy to influence such a dielectric and / or to optimize its threshold voltage and / or its viscosity.

The compounds of the formula (I) are particularly suitable for influencing the dielectric anisotropy (Δε) in the direction of higher negative values even in small amounts.

The compounds of the formula (I) according to the invention are particularly suitable for use in FLC mixtures which are operated in inverse mode.

The symbols and indices in the formula (I) preferably have the following meanings:

Q is preferably hydrogen;

R \ R ² are preferably identical or different a) a straight-chain or branched alkyl radical (with or without asymmetrical carbon atom) with 1 to 18 carbon atoms, where a1) one or more non-adjacent and non-terminal CH ₂ groups by - O-, -CO-O-, -O-CO-, -O-CO-O or -Si (CH ₃ ) ₂ - can be replaced and / or a2) a CH ₂ group by cyclopropane-1, 2- diyl, 1, 4-phenylene or trans-1, 4-cyclohexylene can be replaced and / or a3) the terminal CH ₃ group can be replaced by one of the following chiral groups (optically active or racemic):

b) R ^{1 is} also hydrogen R ¹ , R ² are particularly preferably identical or different a) a straight-chain or branched alkyl radical (with or without asymmetrical carbon atom) with 1 to 16 carbon atoms, where a1) one or two non-adjacent and non-terminal CH ₂ groups by -O-, -CO-O-, -O-CO-, -O-CO-O- or -Si (CH ₃ ) ₂ - and / or a2) a CH ₂ group by 1, 4 -Phenylene or trans-1, 4-cyclohexylene can be replaced and / or a3) the terminal CH ₃ group by one of the following chiral

Groups (optically active or racemic) can be replaced:

b) R ^{1 is} also hydrogen.

R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ are preferably identical or different a) hydrogen b) a straight-chain or branched alkyl radical (with or without asymmetric carbon atom) having 1 to 14 carbon atoms, where b1) one or two non-adjacent and non-terminal CH ₂ groups can be replaced by -O- and / or b2) a CH ₂ group can be replaced by -CH = CH-, c) R ⁴ and R ⁵ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ -, if they are bound to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system.

R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ are particularly preferably the same or different a) hydrogen b) a straight-chain or branched alkyl radical (with or without asymmetric carbon atom) with 1 to 14 carbon atoms, where b1) a non-terminal CH ₂ group can be replaced by -O- and / or c) R ⁴ and R ⁵ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - if they are bound to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system.

M \ M ² are preferably identical or different -CO-O-, -O-CO-, -CH ₂ -O-, -O-CH ₂ -, -CH = CH-, -C≡C-, -CH ₂ -CH ₂ -CO-O-, -O-CO-CH ₂ -CH ₂ - or a single bond.

M ¹ , M ² are particularly preferably identical or different -CO-O-, -O-CO-, -CH ₂ -O-, -O-CH ₂ - or a single bond.

A ¹ , A ² are preferably identical or different 1, 4-phenylene, where one or two H atoms can be replaced by F and / or CN, pyridine-2,5-diyl, where one or two H atoms by F and / or CN can be replaced, pyrimidine-2,5-diyl, where one or two H atoms can be replaced by F, trans-1, 4-cyclohexylene, where one or two H atoms can be replaced by CN and / or CH ₃ and / or F can be replaced, (1, 3,4) thiadiazole-2,5-diyl, 1, 3-dioxane-2,5-diyl, 1, 3-thiazole-2,4-diyl, where an H atom can be replaced by F and / or CN, 1, 3-thiazole-2,5-diyl, where an H atom can be replaced by F and / or CN or thiophene-2,5-diyl, where one or two H atoms can be replaced by F and / or CN.

A ¹ , A ² are particularly preferably identical or different 1, 4-phenylene, where one or two H atoms can be replaced by F, pyridine-2,5-diyl, where one H atom can be replaced by F, pyrimidine -2,5-diyl, trans-1, 4-cyclohexylene, where one or two H atoms can be replaced by CN and / or CH ₃ and / or F.

The following compounds of the formula (Ia) to are very particularly preferred (Is):

where R ⁸ , R ^9, identical or different, are a straight-chain or branched alkyl or alkoxy chain with 1 to 14, preferably 4 to 12, C atoms and R ^{10 is} a straight-chain or branched alkyl chain with 1 to 14, preferably 4 to 12, C - is atoms.

The compounds according to the invention are prepared by methods known per se from the literature, as described in standard works on organic synthesis, e.g. Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart.

The preparation takes place under reaction conditions which are known and suitable for the reactions mentioned. Use can also be made here of variants which are known per se and are not mentioned here in detail.

If desired, the starting materials can also be formed in situ, in such a way that they are not isolated from the reaction mixture, but instead are immediately reacted further to give the compounds of the formula (I).

An example of a possible synthetic route for the is in the following scheme Synthesis of 2-fluoro-3- (1-fluoro-alkyl) -pyridin-6-yl derivatives and to give compounds of the formula I, although other processes are also conceivable and possible.

In the diagram, the group (-A ¹ -M ¹ ) _a (-A ² -M ² ) _b 1, 4-phenylene and OR ^y corresponds to the group R ¹ (with the proviso that the CH bordering the aromatic ring system ₂ group is replaced by -O-) or is a suitable, optionally protected precursor thereof which can be converted into this group in later steps, according to methods known per se and known to the person skilled in the art.

The group R ^x is equal to the grouping -CH ₂ -R ² or a suitable, optionally protected precursor thereof, which can be converted into this grouping in later steps according to methods known per se and known to the person skilled in the art. The preparation takes place under reaction conditions which are known and suitable for the reactions mentioned. Use can also be made here of variants which are known per se and are not mentioned here in detail.

Scheme 1

A)

B)

C)

A) + B) analog (WO-A 96/01246).

C) analogous to J. Org. Chem. 1975, 40, 574. D) analogous to J. Chem. Soc. 1954, 3569.

In general for the synthesis of the groups (-A -M ¹ ) _a (-A ² -M ² ) _b , R ¹ , -CH ₂ -R for example, refer to DE-A 23 44 732, 24 50 088, 24 29 093, 25 02 94, 26 36 684, 27 01 591 and 27 52 975 for compounds with 1,4-cyclohexylene and 1,4-phenylene groups; DE-A 26 41 724 for compounds with pyrimidine-2,5-diyl groups; DE-A 40 26 223 and EP-A 03 91 203 for compounds with pyridine-2,5-diyl groups; DE-A 32 31 462 for compounds with pyridazine-3,6-diyl groups; EP-A 309 514 for compounds with (1, 3,4) thiadiazole-2-5-diyl groups; WO-A 92/16500 for naphthalene-2,6-diyl groups; K. Seto et al, Journal of the Chemical Society, Chemical Communications 1988, 56 for dioxoborinan-2,5-diyl groups.

The production of disubstituted pyridines, disubstituted pyrazines, disubstituted pyrimidines and disubstituted pyridazines can also be found, for example, in the corresponding volumes of the series "The Chemistry of Heterocyclic Compounds" by A. Weissberger and E.C. Taylor (editor).

Dioxane derivatives are useful by reacting an appropriate one

Aldehyde (or one of its reactive derivatives) with a corresponding 1,3-diol (or one of its reactive derivatives), preferably in the presence of an inert solvent such as benzene or toluene, and / or a catalyst, e.g. a strong acid such as sulfuric acid, benzene or p-toluenesulfonic acid, at temperatures between about 20 ° C and about 150 ° C, preferably between 80 ° C and 120 ° C. Acetals are primarily suitable as reactive derivatives of the starting materials.

Some of the aldehydes and 1,3-diols mentioned and their reactive derivatives are known, and in some cases they can be prepared without difficulty from standard compounds of organic chemistry from compounds known from the literature. For example, the aldehydes can be obtained by oxidation of corresponding alcohols or by reduction of nitriles or corresponding carboxylic acids or their derivatives, and the diols can be obtained by reducing corresponding diesters.

Compounds in which an aromatic ring has at least one F atom can also be obtained from the corresponding diazonium salts by exchanging the diazonium group for a fluorine atom, for example by the methods of Balz and Schiemann.

Regarding the connection of the ring systems with each other, reference is made to:

N. Miyaura, T. Yanagai and A. Suzuki in Synthetic Communications 1981, 11, 513-519, DE-A 39 30 663, MJ Sharp, W. Cheng, V. Snieckus in Tetrahedron Letters 1987, 28, 5093; GW Gray in J. Chem. Soc. Perkin Trans II 1989, 2041 and Mol. Cryst. Liq. Cryst. 1989, 172, 165; 1991, 204, 43 and 91; EP-A 0 449 015; WO-A 89/12039; WO-A 89/03821; EP-A 0 354 434 and EP-A 0 694 530 for the direct linking of aromatics and heteroaromatics; DE-A 32 01 721 for connections with -CH ₂ CH ₂ bridge members and Koji Seto et al. in Liquid Crystals 1990, 8, 861-870 for connections with -C≡C bridge members.

Esters of the formula (I) can also be esterified by appropriate carboxylic acids (or their reactive derivatives) with alcohols or phenols (or their reactive derivatives), according to the DCC method

(DCC = dicyclohexylcarbodiimide) or analogous to DE-A 44 27 198. The corresponding carboxylic acids and alcohols or phenols are known or can be prepared analogously to known processes.

Suitable reactive derivatives of the carboxylic acids mentioned are in particular the acid halides, especially the chlorides and bromides, and also the anhydrides, e.g. also mixed anhydrides, azides or esters, in particular alkyl esters with 1-4 C atoms in the alkyl group.

Suitable reactive derivatives of the alcohols or phenols mentioned are in particular the corresponding metal alcoholates or phenolates, preferably an alkali metal, such as sodium or potassium.

The esterification is advantageous in the presence of an inert solvent carried out. In particular, ethers such as diethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones such as acetone, butanone or cyclohexanone, amides such as DMF or phosphoric acid hexamethyltriamide, hydrocarbons such as benzene, toluene or xylene, halogenated hydrocarbons such as carbon tetrachloride are particularly suitable , Dichloromethane or tetrachlorethylene and sulfoxides such as dimethyl sulfoxide or sulfolane.

Ethers of the formula (I) can be obtained by etherification of corresponding hydroxyl compounds, preferably corresponding phenols, the hydroxyl compound advantageously first being converted into a corresponding metal derivative, for example by treatment with NaH, NaNH ₂ , NaOH, KOH, Na ₂ CO ₃ or K ₂ CO ₃ is converted into the corresponding alkali metal alcoholate or alkali metal phenolate. This can then be reacted with the corresponding alkyl halide, alkyl sulfonate or dialkyl sulfate, advantageously in an inert solvent such as acetone, 1, 2-dimethoxyethane, DMF or dimethyl sulfoxide, or with an excess of aqueous or aqueous-alcoholic NaOH or KOH at temperatures between about 20 ° and 100 ° C.

With regard to the synthesis of special radicals R ¹ and R ² , reference is also made, for example, to

EP-B 0 355 008 for connections with silicon-containing side chains, EP-B 0 292 954 for optically active connections with oxirane ester unit, EP-B 0 263437 for optically active connections with oxirane ether unit, EP-B 0 361 272 for optically active connections with dioxolane ester unit, EP-B 0 351 746 for optically active compounds with dioxolane ether unit, US 5,051, 506 for optically active compounds with 2,3-difluoroalkyloxy unit, US 4,798,680 for optically active compounds with 2-fluoroalkyloxy unit, US 4,855,429 for optically active compounds with α-chlorocarboxylic acid unit, EP-A 0 552 658 for compounds with cyclohexylpropionic acid residues, EP-A 0 318 423 for compounds with cyclopropyl groups in the side chain. Compounds of the formula (I) with Q = H can be prepared according to the person skilled in the art known methods can be separated into the optical antipodes (for example at the alcohol level before fluorination).

Such optically active compounds can then be used as dopants. Racemic compounds of the formula (I) (with Q = H) are preferred.

The invention also relates to the use of compounds of the formula (I) in liquid-crystal mixtures, preferably ferroelectric and nematic, in particular ferroelectric.

The invention furthermore relates to liquid crystal mixtures, preferably ferroelectric and nematic, in particular ferroelectric, comprising one or more compounds of the formula (I). They are particularly suitable for use in normal and inverse mode.

The liquid crystal mixtures according to the invention generally contain 2 to 35, preferably 2 to 25, particularly preferably 2 to 20 components.

They generally contain 0.01 to 80% by weight, preferably 0J to 60% by weight, particularly preferably 0.1 to 30% by weight, of one or more, preferably 1 to 10, particularly preferably 1 to 5 , very particularly preferably 1 to 3, of the compounds of the formula (I) according to the invention.

Further components of liquid crystal mixtures which contain compounds of the formula (I) according to the invention are preferably selected from the known compounds with smectic and / or nematic and / or cholesteric phases. These include e.g. B .:

Derivatives of phenylpyrimidine, as described, for example, in WO 86/06401, US Pat. No. 4,874,542, metasubstituted six-ring aromatics, as described, for example, in EP-A 0 578 054,

Silicon compounds, as described for example in EP-A 0 355 008, mesogenic compounds with only one side chain, as described for example in EP-A 0 541 081,

Hydroquinone derivatives, as described, for example, in EP-A 0 603 786, phenylbenzoates, as described, for example, by P. Keller, Ferroelectrics 1984, 58, 3 and J. W. Goodby et al., Liquid Crystals and Ordered Fluids, Vol. 4, New York

1984 and thiadiazoles, as described for example in EP-A 0 309 514.

Examples of suitable chiral, non-racemic dopants are: optically active phenylbenzoates, such as, for example, P. Keller,

Ferroelectrics 1984, 58, 3 and J.W. Goodby et al., Liquid Crystals and

Ordered Fluids, Vol. 4, New York 1984, describes optically active oxirane ethers, such as, for example, in EP-A 0 263 437 and WO-A

93/13093, - optically active oxirane esters, as described for example in EP-A 0 292 954, optically active dioxolane ethers, as described for example in EP-A 0 351 746, optically active dioxolane esters, as described for example in EP-A 0 361 272 , optically active tetrahydrofuran-2-carboxylic acid esters, such as in EP

A 0 355 561 and optically active 2-fluoroalkyl ethers, such as in EP-A 0 237 007 and

U.S. 5,051,506.

Suitable further mixture components are listed in particular in the international patent application PCT / EP 96/03154, to which reference is hereby expressly made.

Preferred further components of FLC mixtures which are used in inverse mode are: Phenanthrene derivatives of the formula (II),

Fluoropyridines of the formula (III),

Difluorophenylene derivatives of the formula (IV)

Meta-substituted aromatic compounds of formula (V) Y

Q \ - (MA) _a (-MA) _b (-MA) _C R '(V)

4-cyanocyclohexyls of the formula (VI)

R- (AM) _a (-AM) _b - ^ ^ ^N _{(V |}}

where the symbols and indices have the following meanings

X ¹ , X ² are identical or different, independently of one another, CH, CF or N,

Y is F, CF ₃ or R

R, R '= have the same or different independently of one another the same

Meanings such as R ¹ in formula (I), A, M have the same or different independently of one another the same

Meanings as in formula (I), a, b, c, d are identical or different, independently of one another, 0 or 1, with the proviso that the compounds must not contain more than four ring systems and, with the exception of the formula (III), must contain at least two ring systems.

The mixtures in turn can be used in electro-optical or completely optical elements, e.g. B. display elements, switching elements, light modulators, elements for image processing and / or signal processing or generally in the field of non-linear optics.

Furthermore, the mixtures for field treatment, i.e. H. suitable for operation in quasi-bookshelf geometry (QBG) (see, for example, H. Rieger et al., SID 91 Digest (Anaheim) 1991, 396).

The ferroelectric liquid crystal mixtures according to the invention are particularly suitable for operation in the so-called inverse or τV _(min) mode (see, for example: JC Jones, MJ Towler, JR Hughes, Displays 1993, 14, No. 2, 86-93; M Koden, Ferroelectrics 1996, 179, 121-129).

Liquid-crystalline mixtures which contain compounds of the general formula (I) are particularly suitable for use in electro-optical switching and display devices (displays). These displays are usually constructed in such a way that a liquid crystal layer is enclosed on both sides by layers which, starting from the LC layer, are usually at least one orientation layer, electrodes and a boundary plate (e.g. made of glass). They can also contain spacers, adhesive frames, polarizers and thin color filter layers for color displays. Other possible components are antireflection, passivation, compensation and barrier layers as well as electrically nonlinear elements such as thin film transistors (TFT) and metal insulator metal (MIM) elements. The structure of

Liquid crystal displays have already been described in relevant monographs (see e.g. BE Kaneko, "Liquid Crystal TV Displays: Principles and Applications of Liquid Crystal Displays", KTK Scientific Publishers, 1987).

Another object of the invention is therefore a switching and / or display device, in particular a ferroelectric device containing one

Liquid crystal mixture which contains one or more compounds of the formula (I).

The switching and / or display device according to the invention is preferably operated in normal or inverse (τV _mm ) mode.

Ferroelectric switching and / or display devices operated by multiplex control can be operated, inter alia, in two different ways, the so-called normal (normal mode) or the so-called inverse (inverse mode also τV _(mιn) mode). The difference between the two lies in the control scheme and in the different requirements for the dielectric tensor of the FLC material, ie the FLC mixture. Give an overview z. BJ

C. Jones et al. in Displays 1993, 14, No. 2, 86-93 hereinafter referred to as "Jones", and M. Koden in Ferroelectrics 1996, 179, 121-129, and the literature listed there.

The switching characteristics of an FLC device can generally be represented by a diagram in which the drive voltage (V) is plotted horizontally and the width of the drive pulses (τ, time) is plotted vertically (see, for example, Jones, Fig. 4, 8, 10 and 11). A switching curve is determined experimentally and divides the V, τ area into a switching and a non-switching area. The pulse width usually shortens when the voltage is increased. This behavior characterizes the so-called normal mode (see e.g. Jones, Fig. 4).

With suitable materials, however, the Vτ curve has a minimum (at the voltage V _(min) ), such as. B. at Jones in Figures 8, 10 and 11. This minimum is achieved by superimposing dielectric and ferroelectric twists. FLC devices are operated in inverse mode if the sum of the row and column drive voltages in the working temperature range are higher than the minimum on the Vτ curve, ie V _(time) + V _(spa , _te) > V _(min) .

The invention is further illustrated by the following examples, without wishing to restrict it thereby.

The meanings are: X = crystalline state, S = smectic phase (the index indicates the phase type), N = nematic phase, 1 = isotropic phase. The numbers between these symbols indicate the transition temperatures. Values in parentheses were obtained on cooling. Phase transfer temperatures were determined by DTA, phase types by optical polarization microscopy. All temperatures are given in degrees Celsius.

Example 1 :

2-fluoro-3- (1-fluoro-octyl) -6- (4-hexyloxyphenyl) pyridine

From 1- [2-fluoro-6- (4-hexyloxy-phenyl) pyridin-3-yl] octan-1-ol after fluorination with DAST.

Phase sequence: X 51, 5 (S ₀ 31, 5 S _a 50) I

Example 2:

6- [4- (3-Butyl-oxiranylmethoxy) phenyl] -2-fluoro-3- (1-fluoro-decyl) pyridine

From 4- [6-fluoro-5- (1-fluoro-decyl) pyridin-2-yl] phenol and (3-butyl-oxiranyl) methanol using the Mitsunobu reaction.

Example 3:

2,3-difluoro-4- [6-fluoro-5- (1-fluoro-octyl) pyridin-2-yl] phenyl 4-pentyl-cyclohexanecarboxylic acid

From 2,3-difluoro-4- [6-fluoro-5- (1-fluoro-octyl) pyridin-2-yl] phenol and 4-pentylcyclohexane carboxylic acid by esterification with dicyclohexylcarbodiimide.

Example 4:

6- {6- [5- (Butyldimethylsilanyl) pentyloxy] naphthalen-2-yl} -2-fluoro-3- (1-fluoro-octyl) pyridine

From 6- [6-fluoro-5- (1-fluoro-octyl) pyridin-2-yl] -naphthalen-2-ol and 5- (butyl-dimethyl-silanyl) pentan-1-ol by means of a Mitsunobu reaction .

Example 5: 2-Fluoro-3- (1-fluoro-decyl) -6- [4- (4-pentylcyclohexyl) phenyl] pyridine

From 1- {2-fluoro-6- [4- (4-pentylcyclohexyl) phenyl] pyridin-3-yl} decan-1-ol after fluorination with DAST. Example 6: 2-Fluoro-3- (1-fluoro-decyl) -6- (4'-pentyl-biphenyl-4-yl) pyridine

From 1- [2-fluoro-6- (4'-pentyl-biphenyl-4-yl) pyridin-3-yl] decan-1-ol after fluorination with DAST.

Example 7:

3- (1,1-difluoro-hexyl) -2-fluoro-6- (4'-octyloxy-biphenyl-4-yl) pyridine

From 4 '- [5- (1, 1-difluoro-hexyl) -6-fluoropyridin-2-yl] biphenyl-4-ol and 1-bromooctane by means of ether synthesis according to Williamson.

Claims

Claims:

1. 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivative of the formula (I),

R ¹ (-A ¹ -M ¹ ) _a (-A ² -M ² ) _b -BR ² (I)

where the symbols and indices have the following meanings: the group is B.

Q is hydrogen or fluorine;

Cyclopropan-1, 2-diyl, 1, 4-phenylene, 1, 4-cyclohexylene or 1, 3-cyclopentylene and / or a3) the terminal CH ₃ group can be replaced by one of the following chiral groups (optically active or racemic ) can be replaced:

b) R also hydrogen;

Groups can be replaced by -O- and / or b2) one or two CH ₂ groups can be replaced by -CH = CH-, c) R ⁴ and R ⁵ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - if they are linked to an oxirane, dioxoian, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system;

M \ M ² are the same or different -CO-O-, -O-CO-, -CO-S-, -S-CO-,

-CS-O-, -O-CS-, -CH ₂ -O-, -O-CH ₂ -, -CH ₂ -S-, -S-CH ₂ -, -CH = CH-, -C≡C -, -CH ₂ -CH ₂ -CO-O-, -O-CO-CH ₂ -CH ₂ - or a single bond;

A ¹ , A ² are identical or different 1, 4-phenylene, where one or more H atoms can be replaced by F, Cl and / or CN, pyrazine-2,5-diyl, where one or two H atoms by F, Cl and / or CN may be replaced can, pyridazine-3,6-diyl, where one or two H atoms can be replaced by F, Cl and / or CN, pyridine-2,5-diyl, where one or more H atoms can be replaced by F, Cl and / or CN can be replaced, pyrimidine-2,5-diyl, where one or two H atoms can be replaced by F, Cl and / or CN, 1,4-cyclohexylene, where one or two H atoms can be replaced by CN and / or CH ₃ and / or F can be replaced, (1, 3,4) thiadiazole-2,5-diyl, 1, 3-dioxane-2,5-diyl, 1, 3-dithiane-2,5-diyl , 1,3-thiazole-2,4-diyl, where an H atom can be replaced by F, Cl and / or CN, 1,3-thiazole-2,5-diyl, where an H atom is replaced by F, Cl and / or CN can be replaced, thiophene-2,4-diyl, where an H atom can be replaced by F, Cl and / or CN, thiophene-2,5-diyl, where one or two H atoms can be replaced by F, Cl and / or CN can be replaced, naphthalene-2,6-diyl, where one or more H atoms can be replaced by F, Cl and / or CN or 1,3-dioxaborinane-2,5-diyl;

2. 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivative according to claim 1, wherein the symbols and indices in the formula (I) have the following meanings:

Q is H or F;

R \ R ² are the same or different a) a straight-chain or branched alkyl radical (with or without asymmetric carbon atom) with 1 to 18 carbon atoms, where a1) one or more non-adjacent and non-terminal CH ₂ -

Groups can be replaced by -O-, -CO-O-, -O-CO-, -O-CO-O or -Si (CH ₃ ) ₂ - and / or a2) a CH ₂ group by cyclopropane-1 , 2-diyl, 1, 4-phenylene or trans-1, 4-cyclohexylene can be replaced and / or a3) the terminal CH ₃ group by one of the following chiral

Groups (optically active or racemic) can be replaced:

b) R ^{1 is} also hydrogen

R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ are the same or different a) a straight-chain or branched alkyl radical (with or without asymmetric carbon atom) with 1 to 16 C atoms, where a1) one or more non-adjacent and not terminal CH ₂ groups can be replaced by -O- and / or a2) one or two CH ₂ groups can be replaced by -CH = CH-, c) R ⁴ and R ⁵ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - if they are bound to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system;

M \ M ² , M ³ , M ⁴ are identical or different -CO-O-, -O-CO-, -CO-S-, -S-CO-, -CS-O-, -O-CS-, -CH ₂ -O-, -O-CH ₂ -, -CH ₂ -S-, -S-CH ₂ -, -CH = CH-, -C≡C-, -CH ₂ -CH ₂ -CO-O -, -O-CO-CH ₂ -CH ₂ - or a single bond;

A ¹ , A ² , A ³ , A ⁴ are identical or different 1, 4-phenylene, where one or more H atoms can be replaced by F and / or CN, pyridine-2,5-diyl, one or two H atoms can be replaced by F and / or CN, Pyrimidine-2,5-diyl, where one or two H atoms can be replaced by F, trans-1, 4-cyclohexylene, where one or two H atoms can be replaced by CN and / or CH ₃ and / or F. , (1, 3,4) -Thiadiazol-2,5-diyl, 1, 3-dioxane-2,5-diyl, 1, 3-thiazole-2,4-diyl, where an H atom by F and / or CN can be replaced, 1, 3-thiazole-2,5-diyl, where an H atom can be replaced by F and / or CN, 1, 3-thiazole-2,5-diyl, where an H- Atom can be replaced by F and / or CN or thiophene-2,5-diyl, where one or two H atoms can be replaced by F and / or CN.

3. 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivative according to one or more of the preceding claims, characterized in that the symbols and indices in the formula (I) have the following meanings:

Q is H; R ¹ , R ² are identical or different a) a straight-chain or branched alkyl radical (with or without asymmetrical carbon atom) with 1 to 16 carbon atoms, where a1) one or two non-adjacent and non-terminal CH ₂ groups by - O-, -CO-O-, -O-CO-, -O-CO-O- or -Si (CH ₃ ) ₂ - can be replaced and / or a2) a CH ₂ group by 1, 4-phenylene or trans-1, 4-cyclohexylene and / or a3) the terminal CH ₃ group can be replaced by one of the following chiral groups (optically active or racemic):

b) R ^{1 is} also hydrogen;

R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ are the same or different a) hydrogen b) a straight-chain or branched alkyl radical (with or without an asymmetric carbon atom) with 1 to 14 carbon atoms, where b1) a non-terminal CH ₂ groups can be replaced by -O- and / or c) R ⁴ and R ⁵ together also - (CH ₂ ) ₄ - or - (CH ₂ ) ₅ - if they are bonded to an oxirane, dioxolane, tetrahydrofuran, tetrahydropyran, butyrolactone or valerolactone system;

M \ M ² , M ³ , M ⁴ are identical or different -CO-O-, -O-CO-, -CH ₂ -O-, -O-CH ₂ - or a single bond.

A ¹ , A ² , A ³ , A ⁴ are identical or different 1, 4-phenylene, where one or two H atoms can be replaced by F, pyridine-2,5-diyl, where one H atom is replaced by F. may be pyrimidine-2,5-diyl, trans-1,4-cyclohexylene, it being possible for one or two H atoms to be replaced by CN and / or CH ₃ and / or F.

4. 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivative according to one or more of the preceding claims, selected from the group (la) to (Is):

in the case of R ⁸ , R ^{9, the} same or different, are a straight-chain or branched alkyl or alkoxy chain having 1 to 14 C atoms and R ^{0 is} a straight-chain or branched Is alkyl chain with 1 to 14 carbon atoms.

5. Use of 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivatives according to one or more of claims 1 to 4 as components of liquid-crystalline mixtures.

6. A liquid crystal mixture comprising one or more 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivatives according to one or more of claims 1 to 4.

7. Liquid crystal mixture according to claim 6, characterized in that it is ferroelectric.

8. A liquid crystal mixture according to claim 6 and / or 7, characterized in that it contains 0.01 to 80% by weight of one or more 2-fluoro-3- (1-fluoroalkyl) pyridin-6-yl derivatives of formula (I) contains.

9. Ferroelectric switching and / or display device containing a ferroelectric liquid crystal mixture according to claim 7 and / or 8.

10. Ferroelectric switching and / or display device according to claim 9, characterized in that it is operated in τV _(min) mode.