DE4234089A1 - Pyridine derivs. - are useful for liq. crystal displays and have low viscosity and high dielectric anisotropy - Google Patents

Abstract

Pyridine derivs. of formula (I), (I1), (I21), (I3) and (I23) are new. Also claimed is (i) use of (I) as liq. crystalline components of an electrooptical display element (II); (ii) a liq. crystalline medium (III) with at least one component of formula (I); and (iii) (II) contg. (III) as a dielectric, where in the formulae R=1-15C alkylene or alkyl, opt. substd. with CN, halogen, or CF2, contg. -O-, -CO-, -CO-O-, -O-CO- or -O-CO-O-; n=0,1; Z=-CH2CH2-, -CH=CH- or -C=C-; L1,L2=H,F; Q=-CHF-, -OCHF-, -CF2-, -OCF2-, -C2F4-, -OC2F4-, a single bond; and Y=H, F, Cl. In formula (I) when n=0, Q=a single bond, Z=-CH2CH2- or -CH=CH- and at least one of L1 and L2=F. USE/ADVANTAGE - (I) are useful for liq. crystal displays. (I) have low viscosity, a relatively high dielectric anisotropy and are stable.

Description

The invention relates to pyridine derivatives of the formula I,

wherein
R is an unsubstituted or monosubstituted by CN, halogen or CF ₃ alkyl or alkenyl radical having up to 15 carbon atoms, wherein in these radicals also one or more CH ₂ groups each independently of one another by -O-, -CO- , -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another,
n 0 or 1,
z is -CH ₂ CH ₂ -, -CH = CH- or -C≡C- L ¹ and L ² independently of one another are H or F,
Q is -CHF-, -OCHF-, -CF ₂ , -OCF ₂ -, -C ₂ F ₄ -, -OC ₂ F ₄ -, or a single bond, and
YH, F or Cl
mean, with the proviso that
in the case n = O, Q = single bond, Z = -CH ₂ CH ₂ - or -CH = CH-, at least one of the radicals L ¹ and L ^{2 is} fluorine.

The invention further relates to the use of this Ver compounds as components of liquid-crystalline media as well as Liquid crystal and electro-optical display elements, the contain liquid crystalline media according to the invention.

The compounds of the formula I can be liquid as components crystalline media are used, especially for Dis plays based on the principle of the twisted cell, the guest Host effect, the effect of deformation of upright phases or the effect of dynamic dispersion.

Ethyl-substituted pyridines are already available from the JP 60-163 865 known:

However, the compounds often have a highly smectogenic character and are therefore useful in many practical applications less suitable.

The invention therefore an object of the invention, new stable to find liquid-crystalline or mesogenic compounds which are suitable as components of liquid-crystalline media and especially at the same time a comparatively small Possess viscosity as well as a relatively high dielectric Anisotropy.

It has now been found that compounds of the formula I as Components of liquid-crystalline media excellently suitable are. In particular, they have comparatively low high viscosities. With their help can be stable liquid-crystalline media with a broad mesophase range and advantageous values for the optical and dielectric Obtained anisotropy. These media also have a lot good low temperature behavior.

With the provision of compounds of the formula I is also quite generally the range of liquid crystalline Substances that vary in their application aspects of the production of liquid crystalline Mixtures are suitable, considerably widened.

The compounds of the formula I include the compounds of the Formulas I1-I20 with 2 rings,

Compounds of formulas I21 to I42 with 3 rings

R is preferably alkyl, furthermore alkoxy. QY is preferably F, OCF ₃ , CF ₃ , CF ₂ H, C ₂ F ₅ or CF ₂ Cl.

Preference is also given to compounds of the formula I which contain a mono- or disubstituted by F substituted 1,4-phenylene ring ent. Especially preferred are compounds where L ¹ = L ² = F.

Z is preferably -CH ₂ CH ₂ -.

If R is an alkyl radical and / or an alkoxy radical, this may be straight-chain or branched. Preferably if it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and therefore preferably denotes ethyl, propyl, butyl, pentyl, Hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or Heptoxy, furthermore methyl, octyl, nonyl, decyl, undecyl, Dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, Nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetra decoxy.  

Oxaalkyl is preferably straight-chain 2-oxapropyl (= Methoxymethyl), 2- (= ethoxymethyl) or 3-oxabutyl (= 2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxo-octyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

If R is an alkyl radical in which a CH ₂ group is replaced by -CH = CH-, then this may be straight-chain or branched ver. It is preferably straight-chain and has 2 to 10 C atoms. It therefore means especially vinyl, prop-1, or prop-2-enyl, but-1, 2- or but-3-enyl, pent-1, 2-, 3- or pent-4-enyl, hex 1-, 2-, 3-, 4- or hex-5-enyl, hept-1, 2-, 3-, 4-, 5- or hept-6-enyl, Oct-1, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, Dec-1 -, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl.

If R is an alkyl radical in which one CH ₂ group has been replaced by -O- and one by -CO-, these are preferably adjacent. Thus, these include an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. Preferably, these are straight-chain and have 2 to 6 carbon atoms.

They therefore mean especially acetyloxy, propionyloxy, Butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, Propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, Methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxy  carbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxy carbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4- (methoxycarbonyl) -butyl.

If R is an alkyl radical in which a CH ₂ group is replaced by unsubstituted or substituted -CH = CH- and a neigh disclosed CH ₂ group by CO or CO-O or O-CO-, it may be straight-chain or branched his. Preferably, it is straight-chain and has 4 to 13 carbon atoms. It therefore means especially acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyl oxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxyethyl, 2-metha cryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxy-butyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyl oxyoctyl, 9-methacryloyloxynonyl.

If R monosubstituted by CN or CF ₃ means an alkyl or alkenyl radical, this radical is preferably straight-chain and the substitution by CN or CF ₃ in ω-Posi tion.

If R is an alkyl radical in which two or more CH ₂ groups have been replaced by -O- and / or -CO-O-, this may be straight-chain or branched. Preferably, it is branched and has 3 to 12 carbon atoms. It therefore particularly means bis-carboxymethyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxy-pentyl, 6 , 6-bis-carboxy-hexyl, 7,7-bis-carboxy-heptyl, 8,8-bis-carboxy-octyl, 9,9-bis-carboxy-nonyl, 10,10-bis-carboxy decyl, bis- (methoxycarbonyl) methyl, 2,2-bis (methoxy carbonyl) ethyl, 3,3-bis (methoxycarbonyl) propyl, 4,4-bis (methoxycarbonyl) butyl, 5,5-bis ( methoxycarbonyl) pentyl, 6,6-bis (methoxycarbonyl) hexyl, 7,7-bis (methoxycarbonyl) heptyl, 8,8-bis (methoxycarbonyl) octyl, bis (ethoxycarbonyl) methyl , 2,2-bis- (ethoxycarbonyl) -ethyl, 3,3-bis (ethoxycarbonyl) -propyl, 4,4-bis (ethoxycarbonyl) -butyl, 5,5-bis (ethoxycarbonyl) -hexyl.

If R is at least one halogen substituted Alkyl or alkenyl radical, then this radical is preferred Were straight-chain and halogen is preferably F or Cl. at Multiple substitution is halogen preferably F. The resul ting residues also include perfluorinated residues. at Simple substitution can be the fluorine or chlorine substituent in be any position, but preferably in position.

Compounds of the formulas I with branched wing groups R occasionally because of better solubility in the Of conventional liquid-crystalline base materials of importance but especially as chiral dopants, if they are are optically active. Smectic compounds of this kind eig as components for ferroelectric materials.  

Branched groups of this type usually do not contain more than one chain branch. Preferred branched radicals R is isopropyl, 2-butyl (= 1-methylpropyl), isobutyl (= 2-methylpropyl), 2-methylbutyl, isopentyl (= 3-methyl butyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethyl hexoxy, 1-methylhexoxy, 1-methylheptoxy.

Compounds of the formula I which are more than suitable for polycondensations suitable wing groups R are suitable for presentation development of liquid crystalline polycondensates.

Formula I includes both the racemates of these compounds as also the optical antipodes and their mixtures.

Compounds of the formula I with S _A phases are, for example, for thermally addressed displays.

Among these compounds of the formula I and the sub Formulas are those in which at least one the radicals contained therein one of the specified preferred Has meanings.

In the compounds of formula I those are stereoisomes preferred in which the cyclohexane ring trans-1,4-disub is substituted.  

The compounds of the formula I are known per se Methods presented in the literature (eg in the Standard works such as Houben-Weyl, Methods of the Organic Chemistry, Georg Thieme Verlag, Stuttgart), and Although under reaction conditions, for the aforementioned Umset tongues are known and suitable.

It is also known by itself, not closer make use of the variants mentioned.

If desired, the starting materials may also be in situ be formed, such that they are from the reaction mixture not isolated but immediately further to the compounds of Formula I implements.

The compounds of the invention can be as follows Produce reaction schemes easily.

Scheme 1

Scheme 2

Scheme 3

The liquid-crystalline media according to the invention contain preferably in addition to one or more inventive Compounds as further constituents 2 to 40, in particular 4 to 30 components. Very particularly preferably included these media in addition to one or more inventive Compounds 7 to 25 components. This further inventory Parts are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, esp substances from the classes of azoxybenzenes, benzylidene anilines, biphenyls, terphenyls, phenyl- or cyclohexylbenes zoates, cyclohexane-carboxylic acid phenyl or cyclohexyl esters, Phenyl or cyclohexyl esters of cyclohexylbenzoic acid, Phenyl or cyclohexyl esters of Cyclohexylcyclohexancar bonsäure, Cyclohexyl-phenylester of benzoic acid, the cyclo hexanecarboxylic acid or cyclohexylcyclohexanecarboxylic acid, Phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcy clohexane, cyclohexylcyclohexane, cyclohexylcyclohexylcyclo hexanes, 1,4-bis-cyclohexylbenzenes, 4,4'-bis-cyclohexyl biphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyl-dioxanes, Phenyl or cyclohexyl-1,3-dithiane, 1,2-diphenylethane, 1,2-dicyclohexylethane, 1-phenyl-2-cyclohexylethane, 1-cyclo hexyl 2- (4-phenylcyclohexyl) ethanes, 1-cyclohexyl-2- biphenylylethane, 1-phenyl-2-cyclohexyl-phenylethanes, given optionally halogenated stilbenes, benzylphenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.

The most important as further constituents according to the invention Media eligible connections can be through the Formulas 1, 2, 3, 4 and 5 characterize:

R'-LER '' 1
R'-L-COO-ER '' 2
R'-L-OOC-ER "3
R'-L-CH ₂ CH ₂ -ER '' 4
R'-LC≡CER '' 5.

In formulas 1, 2, 3, 4 and 5, L and E are the same or may be different, each independently a bivalent radical from the group consisting of -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc, -Cyc-Cyc, -Pyr-, -Dio, -G-Phe- and -G-Cyc- and their mirror images formed group, where Phe unsubstitu substituted or fluorine-substituted 1,4-phenylene, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexylene, Pyr pyrimi din-2-5-diyl or pyridine-2,5-diyl, Bio 1,3-dioxane-2,5-diyl and G 2- (trans-1,4-cyclohexyl) -ethyl, pyrimidine-2,5-diyl, Pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

Preferably, one of L and E is Cyc, Phe or Pyr. e is preferably Cyc, Phe or Phe-Cyc. Preferably ent the media of the invention one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein L and E are selected from the group Cyc, Phe and Pyr and at the same time one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein one of L and E is selected from the group Cyc, Phe and Pyr and the other radical is selected from the Group -Phe-Phe, -Phe-Cyc, -Cyc-Cyc, -G-Phe and -G-Cyc-, and optionally one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, wherein the Radicals L and E are selected from the group -Phe-Cyc-, -Cyc-Cyc, -G-Phe and -G-Cyc.  

R 'and R' 'in a smaller subgroup of Ver compounds of formulas 1, 2, 3, 4 and 5 each independently alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy of up to 8 carbon atoms. Hereinafter this smaller subgroup is called group A and the Compounds are treated with the subformulae 1a, 2a, 3a, 4a and 5a designated. For most of these compounds, R 'and R '' different from each other, with one of these radicals usually Alkyl, alkenyl, alkoxy or alkoxyalkyl.

In a smaller subgroup of compounds of formulas 1, 2, 3, 4 and 5, other than group B, R '' is - F, -Cl, -NCS or - (O) _i CH _{3- (k + 1)} F _k Cl ₁ , where i is 0 or 1 and k + 1 is 1, 2 or 3; the compounds in which R "has this meaning are designated by the subformulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the subformulae 1b, 2b, 3b, 4b and 5b in which R "has the meaning -F, -Cl, -NCS, -CF ₃ , -OCHF ₂ or -OCF ₃ .

In the compounds of sub-formulas 1b, 2b, 3b, 4b and 5b has R 'indicated in the compounds of the sub-formulas 1a-5a Meaning and is preferably alkyl, alkenyl, alkoxy or Alkoxyalkyl.

In another smaller subgroup of compounds of Formulas 1, 2, 3, 4 and 5 represent R "-CN; this subgroup is hereinafter referred to as group C and the Verbindun of this subgroup are correspondingly subformulated 1c, 2c, 3c, 4c and 5c. In the compounds of Partial formulas 1c, 2c, 3c, 4c and 5c has R 'in the verbin of the sub-formulas 1a-5a given meaning and is preferably alkyl, alkoxy or alkenyl.  

In addition to the preferred compounds of groups A, B and C. are also other compounds of formulas 1, 2, 3, 4 and 5 with other variants of the proposed substituents common. All these substances are known from the literature methods or by analogy.

In addition to compounds of the formula I according to the invention, the media according to the invention preferably comprise one or more compounds which are selected from the group A and / or group B and / or group C. The mass fractions of the compounds from these groups on the media according to the invention are preferred
Group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90%,
Group B: 0 to 80%, preferably 10 to 80%, in particular 10 to 65%,
Group C: 0 to 80%, preferably 5 to 80%, in particular 5 to 50%,
wherein the sum of the mass fractions of the compounds of the groups A and / or B and / or C contained in the respective inventive media is preferably 5% -90% and in particular 10% to 90%.

The media according to the invention preferably contain 1 to 40%, in particular preferably 5 to 30% of erfindungs proper connections. Further preferred are media,  containing more than 40%, in particular 45 to 90% of inventions compounds according to the invention. The media preferably contain three, four or five compounds of the invention.

The preparation of the media according to the invention takes place in usual way. In general, the components are dissolved in each other, useful at elevated temperature. By Suitable additives can after the liquid crystalline phases of the invention are modified so that they are in all hitherto have become known types of liquid crystal display elements can be used. Such additives are those skilled in the art known and described in detail in the literature (H.Kalkker / R.Hatz, Handbook of Liquid Crystals, Verlag Chemistry, Weinheim, 1980). For example, pleochroiti dyestuffs for producing colored guest-host systems or substances for changing the dielectric anisotropy pie, the viscosity and / or the orientation of the nematic Phases are added.

In the present application and in the following examples, the structures of the liquid crystal compounds are indicated by acronyms, wherein the transformation into chemical formulas according to following Tables A and B takes place. All radicals C _n H _{2n + 1} and C _m H _{2m + 1} are straight-chain alkyl radicals with n or m C atoms. The coding according to Table B is self-evident. In Table A, only the acronym for the main body is given. In the individual case, a code for the substituents R ¹ , R ² , L ¹ and L ² follows separately from the acronym for the main body with a dash:

Table A

Table B

The following examples are intended to illustrate the invention without limiting it. Above and below mean percentages by weight. All temperatures are in degrees Celsius. Mp means melting point, bp = clearing point. Furthermore, K = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent the transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C) and the viscosity (mm ² / sec) was determined at 20 ° C.

"Conventional workup" means: water is optionally added, extracted with dichloromethane, diethyl ether or toluene, separated, the organic phase is dried, evaporated and the product is purified by distillation under reduced pressure or crystallization and / or chromatography. The following abbreviations are used:

DAST diethylaminosulfur DCC dicyclohexylcarbodiimide DDQ dichlorodicyanobenzoquinone DIBALH diisobutylaluminum KOT Potassium tert-butoxide PdCl₂ dppf 1,1'-bis (diphenylphosphino) ferrocene-palladium (II) chloride THF tetrahydrofuran pTSOH p-toluenesulfonic acid TMEDA tetramethylethylenediamine

Example 1

0.1 mol of II are at 0 ° C in 50 ml of THF / toluene (1: 4) initially charged and in portions with 0.105 mol of n-BuLi (15% in Hexane). After 0.5 h stirring at 0 ° C is a cooled solution consisting of 0.05 mol of zinc bromide in 50 ml of THF / toluene (1: 4) was added dropwise to the mixture and stirred for a further 0.5 h. Subsequently, at the same time 0.1 mol of 1 and 2 mol% of tetrakis (triphenylphosphine) palla dium (0) added to the reaction mixture. One leaves 24 h stir at room temperature, pour the mixture into a saturated ammonium chloride solution, separates the organic Phase off and works up as usual.

• b) 0.1 mol III are presented at 0 ° C in 100 ml of THF and with 0.105 mol in n-BuLi (15% in hexane) dropwise added. After 0.5 h stirring at 0 ° C 0.05 mol Zinc bromide in 50 ml of THF within 15 minutes to the Dropped reaction mixture. It is allowed to stand for 0.5 h at 0 ° C stir and at the same time gives 0.1 mol of 4-n-propylcyclo hexyl bromide and 2 mol% tetrakis (triphenylphosphine) palla dium (0) to the solution. It is stirred for 24 h at room temperature, Pour the mixture into a saturated ammonium chloride solution. Solution and works up as usual.

Analogously, the following compounds of the formula

manufactured:

example 2

The product of Example 1 (0.06 mol) is dissolved in 250 ml of THF dissolved and hydrogenated with 5 g Pd / C (5%). The catalyst becomes filtered off after complete hydrogenation. The solvent is removed in vacuo and the residue is purified by Kri cleaned.

Analogously, the following compounds of the formula

manufactured:

example 3

Analogously to Example 1a), from 0.3 mol of I, 0.33 mol of n-BuLi, 0.15 mol of ZnBr ₂ , 0.3 mol of II in 550 ml of THF and 2 mol% of tetrakis (triphenylphosphine) palladium (0) Vinylene compound III.

• b) 0.5 mol III are presented at 0 ° C in 500 ml of THF and with 0.525 mol of n-BuLi (15% in hexane) dropwise ver puts. The mixture is stirred for 0.5 h at 0 ° C and are portions 0.25 mol of zinc bromide in 250 ml of THF within 15 mi to the reaction mixture. It is allowed to stand for 0.5 h at 0 ° C stir and then gives a mixture consisting of 0.1 4-n-propylcyclohexylbromide and 2 mol% tetrakis (tri phenylphosphine) palladium (0) to the reaction solution. The mixture is then stirred at room temperature for 24 h. The Reaction mixture turns into a saturated one Poured ammonium chloride solution. The organic phase becomes separated and worked up as usual.

Analogously, the following compounds of the formula

manufactured:

example 4

According to the synthetic scheme above, after conversion of I (0.3 mol) in the organozinc compound by a Pd (II) -catalyzed coupling reaction with II (0.3 mol) the Obtained compound III.

• b) 0.1 mol of III are analogously to Example 1b) with 0.1 mol of 4-n- Coupled with pentylcyclohexylbromide.
• c) The hydrogenolytic cleavage of the benzyl ether (0.1 mol) with Pd / C (5%) in THF leads to phenol IV.
• d) 0.06 mol of the phenol from Example 4c) are at 40 ° C in 235 ml of THF submitted, 2.1 g of tetrabutylammonium hydrogen sulphate and 0.15 mol 32% sodium hydroxide solution. Under Stirring is chlorodifluoromethane (about 0.23 mol) as long until this is cooled on a dry ice cooled Cooler condenses. After cooling, it is mixed with 200 ml Diluted water and 200 ml of tert-butyl methyl ether. The organic phase is separated and aufgear as usual beitet.

Analogously, the following compounds of the formula

manufactured.

Claims (10)

1. pyridine derivatives of the formula I, in which
R is an unsubstituted or monosubstituted by CN, halogen or CF ₃ alkyl or alkylene radical having up to 15 carbon atoms, wherein in these radicals also one or more CH ₂ groups each independently of one another by -O-, -CO- , -CO-O-, -O-CO- or -O-CO-O- may be replaced so that O atoms are not directly linked to one another,
n 0 or 1,
z is -CH ₂ CH ₂ -, -CH = CH- or -C≡C-
L ¹ and L ^{2 are} independently H or F,
Q is -CHF-, -OCHF-, -CF ₂ -, -OCF ₂ -, -C ₂ F ₄ -, -OC ₂ F ₄ -, or a single bond, and
YH, F or Cl
means, with the proviso that in the case n = 0, Q = single bond and Z = -CH ₂ CH ₂ - or -CH = CH- at least one of the radicals L¹ and L² fluorine tet signified. 2. pyridine derivatives of the formula I1, wherein R, Z and L ^{2 have} the meaning given in claim 1. 3. pyridine derivatives of the formula I21, wherein R, Z, L ¹ and L ^{2 have} the meaning indicated in claim 1 significance. 4. pyridine derivatives of the formula I3, wherein R, Z, L ¹ and L ^{2 have} the meaning indicated in claim 1 significance. 5. pyridine derivatives of the formula I23, wherein R, Z, L ¹ and L ² have the significance given in claim 1 tung. 6. Compounds of the formula I, wherein Z is -CH ₂ CH ₂ -. 7. Use of the compounds of the formula I as components Liquid-crystalline media for electro-optical display elements. 8. Liquid-crystalline medium with at least two components th, characterized in that at least one compo nente is a compound of formula I. 9. Electro-optical display element, characterized that it is a liquid-crystalline medium as a dielectric according to claim 8 contains. 10. A matrix liquid crystal display element according to claim 7, characterized in that it is a dielectric Liquid-crystalline medium according to claim 8 contains.