DD207211A5 - FLUORINOUS CYCLOHEXYLBIPHENYL DERIVATIVES CONTAINING LIQUID CRYSTALLINE DIELECTRICS - Google Patents

Abstract

Fluorine-containing Cyclohexylbiphenylderivate of formula (&), wherein R below 1 alkyl having 1-12 C atoms, R below 6 alkyl or alkoxy having 1-12 C atoms, CN or fluorine, and R below 2, R below 3, R below 4 and R below 5 mean hydrogen or fluorine, with the proviso that at least one, but not more than two of the radicals R below 2, R bottom 3, R bottom 4, R bottom 5 and R 6 below fluorine are colorless compounds, which form a low-viscosity nematic-liquid-crystalline mesophase in a broad and favorable temperature range. They are valuable components of liquid-crystalline dielectrics for electro-optical display elements.

Description

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Merck Patent Limited Liability Company Darmstadt

Fluorine-containing cyclohexylbiphenyl derivatives containing liquid-crystalline dielectrics

a) Field of application of the invention

For electro-optical display elements, the properties of nematic or nematic

exploited cholesteric liquid crystalline materials to significantly change their optical properties such as light absorption, light scattering, Doppeibrechnung, reflectivity or color under the influence of electric fields. The function of such display elements

is based, for example, on the phenomena of dynamic scattering, the deformation of upright phases, the Schadt-Helfrich effect in the twisted cell or the cholesteric-nematic phase transition.

^ ⁵ For the technical application of these effects in electronic components liquid-crystalline dielectrics are required, which must meet a variety of requirements. Particularly important here are the chemical resistance to moisture, air and physical

Influences such as heat, radiation in the infrared, visible and ultraviolet range and electrical alternating and alternating fields. Furthermore, of technically usable liquid crystal dielectrics a liquid crystalline mesophase in the temperature range of at least +10 C to "+ 50 ° C ₁ preferably from 0 ° C to 60 ° C ₁ and a very low viscosity at room temperature, preferably

-3 not more than 70. 10 Pa.s should be required.

Finally, they must not show self-absorption in the visible light range, ie. they have to be colorless.

^ύ ) Characteristic of the known technical solutions;

There are already known a number of liquid-crystalline compounds which satisfy the stability requirements imposed on dielectrics for electronic components and are also colorless. These include, in particular, the p, p'-disubstituted phenyl benzoate described in DE-OS 2 139 628 and the ρ, ρ'-disubstituted phenylcyclohexane derivatives described in DE-OS 2 636 684. In both classes of compounds mentioned, as well as in other known series of compounds with liquid-crystalline mesophase, there are no individual compounds which form a liquid-crystalline nematic mesophase in the required temperature range from 10 ° C. to 60 ° C. As a rule, mixtures of two or more compounds are therefore produced in order to obtain substances which can be used as liquid-crystalline dielectrics. For this one mixes usually at least one compound with a low melting point and clearing point with another with a much higher melting and clearing point. Here, a mixture is usually obtained whose melting point is lower than that of the lower melting component

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while the clearing point lies between the clearing points of the components. Nevertheless, the production of optimum dielectrics always presents difficulties, since the components with the high melting and clearing points often also give the mixtures a high viscosity. As a result, the switching times of the electro-optical display elements produced in this way are undesirably prolonged. Furthermore, problems often arise in that the solubility of the various components into each other, especially at room temperature or lower temperatures is very limited.

c) Aim of the invention;

The invention has for its object to produce liquid-crystalline dielectrics, which have a nematic phase in the required temperature range and allow sufficiently short switching times in liquid crystal cells at room temperature.

d) presentation of the essence of the invention;

It has now been found that the cyclohexylbiphenyl derivatives of the formula (I)

(D

R ₂ R _a R ₄ R ₅

wherein R is alkyl having 1-12 C atoms, R, alkyl or alkoxy having 1-12 C atoms, CN or

Fluorine, and

RRR and R _{5 are} hydrogen or fluorine, provided that at least one but not more than two of R ₂ , R ₃ , R ₄ , R ₅ and R are fluorine.

are excellently suitable as components of liquid-crystalline dielectrics. These compounds have an extraordinarily broad field of application:

Depending on the choice of substituents, the compounds of formula (I) can serve both as base materials constituting predominantly liquid crystal dielectrics, but also compounds of formula (I) in minor proportions of, for example, 2 to 45 weight percent of liquid crystalline base materials may be added from other classes of compounds so as to prepare dielectrics with a broadened liquid-crystalline mesophase or to influence the size of the dielectric anisotropy of such a dielectric.

By suitable selection of the substituents R ₁ to _R may be with the compounds of formula (I) both dielectrics with a strong positive dielectric anisotropy Verwehdung in display elements based on the twisted nematic cell or the cholesteric-nematic. However, it is also possible to produce dielectrics with only slightly different or even negative dielectric anisotropy, which are used in display elements based on the dynamic scattering or the deformation of upright phases (DAP effect).

The compounds of the formula (I) are colorless in the pure state, and form low-viscosity nematic mesophases in a surprisingly wide and favorable for the electro-optical use temperature range.

The invention thus relates to liquid-crystalline dielectrics containing at least one fluorochemical cyclohexylbiphenyl derivative of the formula (I).

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The fluorine-containing cyclohexylbiphenyl derivatives of the formula (I) include, in particular, the'4- (trans-4-alkylcyclohexyl) -4'-fluorobiphenyls of the formula (Ia)

(La)

10

the 4- (trans-4-alkylcyclohexyl) -3'-fluoro-4 '- (R ₇ ) -biphenyls of the formula (Ib),

(Ib)

the 4- (trans-4-alkylcyclohexyl) -3 ', 4'-difluorobiphenyls of the formula (Ic),

(Ic)

the 4- (trans-4-alkylcyclohexyl) -2 ', 3'-difluoro-4' - (R ₇ ) -biphenyls of the formula (Id)

(Id)

the 2,3-difluoro-4- (trans-4-alkylcyclohexyl) -4 '- (R ₇ ) -biphenyls of the formula (Ie)

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and the 2-fluoro-4- (trans-4-alkylcyclohexyl) -4 '- (R ₇ ) -biphenyls of the formula (If),

(If)

wherein in these sub-formulas R _{7 is} alkyl or alkoxy having 1-12 C atoms or CN and R having the meaning given in the formula (I). The trans position of the substituents in the 1 and 4 positions of the cyclohexane ring is indicated in the formula pictures by a reinforced black dot on the right side of the ring. Although the compounds of formula (I) not encompassed by sub-formulas (Ia) to (If) have the same advantageous properties as those of the selected groups, their preparation is more difficult and therefore less economical; the compounds of sub-formulas (Ia) to (If) 5 are therefore preferred.

Among the compounds of the formula (I), those having the partial formulas (Ia) to (Ic) have a positive dielectric anisotropy; whereas the compounds of sub-formulas (Id) to (If) have a negative dielectric anisotropy or zero values when R _{7 is} alkyl or alkoxy and a reduced positive dielectric anisotropy when R _{7 is} CN.

In the compounds of the formula (I), the alkyl radical R and the alkyl or alkoxy radical R may be straight-chain or branched. If it is straight-chain, ie methyl, ethyl, n-propyl, η-butyl, n-pentyl, n-hexyl,

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- "7" ·

n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl or n-dodecyl, the compounds characterized thereby generally have higher clearing points than those with branched wing groups R. and / or R. .5 Therefore, usually at most one of the wing groups R ₁ and R _{6 contains} a branched carbon chain. Compounds of the formula (I) having a branched wing group R ₁ or R are occasionally of importance because of better solubility in the usual liquid-crystalline base materials, but in particular as chiral dopants, if they possess optical activity as a result of the chain branching. Such branched wing groups contain no more than one chain branch. Preferred branched hydrocarbon radicals are those in which there is a methyl or ethyl group on a longer carbon chain in the 1-, 2- or 3-position, for example 2-methylpropyl, 2-methylbutyl, 3-methylbutyl, 2-methylpentyl, 3-methylpentyl , 2-ethylhexyl or 1-methylhexyl. When R, is alkyl or alkoxy, the wing groups R and R can together _ß up to 24 carbon atoms. In the context of the present invention, those are preferred in which R.sup.1 and _R.sup.B together contain 3 to 14, in particular from 4 to 12, carbon atoms.

The compounds of formula (I) are prepared in a manner conventional for such substances. Thus, the 4- (trans-4-alkylcyclohexyl) -4'-fluorobiphenyls of the formula (Ia) are obtained by reacting the known 4- (trans-4-alkylcyclohexyl) biphenyls unsubstituted in the 4'-position to the corresponding Nitro compounds are nitrated, which are reduced to the 4'-amino compounds and converted in a conventional manner by Schiemann courts in the 4'-fluoro compounds. For the preparation of 3 ', 4'-difluoro compounds of the formula (Ic) is a

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4- (trans-4-alkylcyclohexyl) -4'-aminobiphenyl first acetylated, then nitrated to 3'-nitro ~ 4'-acetamidobiphenylderivat, which is then converted by reduction and hydrolysis in the 3 ', 4'-Diaminobiphenylderivat. From this is then again by diazotization, reaction with fluoborate and thermal decomposition, the 3 ', 4'-Difluorbiphenylderivat obtained.

The compounds of formula (I) wherein _R is an alkyl or alkoxy group, and R ₂ to R ₅ are one or two fluorine from residues, are prepared analogously from the appropriately substituted mono- or dinitro compounds. These starting materials are obtained by nitration of 4- (trans-4-alkylcyclohexyl) -4 '(alkyl or alkoxy) biphenyls. In this case, by suitable choice of the nitration conditions known per se from the literature, for example the type and concentration of the nitrating agent, solvent, temperature, reaction time and / or catalyst, the isomer distribution in the resulting mixture of nitration products can be influenced in the direction of the mainly desired products. From the isomer mixtures obtained, these can then be separated in a customary manner, for example by chromatographic methods. The reduction of the nitro compounds to the amino compounds is carried out according to standard methods, for example by catalytic hydrogenation, by treatment with aqueous dithionite or with tin (II) chloride and hydrochloric acid. The Schiemann-Balz synthesis is likewise carried out in a manner known per se, for example according to one of the process variants described in "Organic Reactions, Vol. 5 (1949), pages 193-228.

The dielectrics according to the invention consist of 2 to 15, preferably 3 to 12 components, including at least one fluorine-containing cyclohexylbiphenyl derivative

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of the formula (I). The other constituents are selected from the nematic or nematogenic substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, cyclohexanecarboxylic acid phenyl or cyclohexyl esters, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclohexalnaphthalenes, 1,4- Bis-cyclohexylbenzenes, 4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzylphenyl ethers, tolans and substituted cinnamic acids. The most important as constituents of such liquid-crystalline dielectrics in question compounds can be characterized by the formula (II).

(II)

Where A and C are each a carbo- or heterocyclic ring system consisting of 1,4-disubstituted benzene and cyclohexane rings, 4,4'-disubstituted biphenyl / phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1, 3-dioxane rings, 2,6-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline,

-CH = CH- -N (O) = N- -CH = CX -CH = N (O) -CeC- -CH ₂ -CH ₂ -CO-O- -CH ₂ -O- -CO-S- -CH ₂ -S- -N = N- -CH = N-

or a C-C single bond,

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- ίο -

X is halogen, preferably chlorine, or -CN, and R ₈ and R 9 are alkyl, alkoxy, alkanoyloxy or alkoxycarbonyloxy having up to 18, preferably up to 8 carbon atoms, or one of these radicals also -CN, -NC, -NC ·, -CF -, F, Cl or Br mean. For most of these compounds, R ₀ and R _Q are different from each other,

ο "

wherein one of these radicals is usually an alkyl or alkoxy group. But other variants of the proposed substituents are in use. Many such substances or mixtures thereof are commercially available.

The dielectrics according to the invention generally contain at least 30, preferably 50-99, in particular 60-98 parts by weight of the compounds of the formula (I) and (II). Of these, preferably at least 5 parts by weight, usually also 10 or more parts by weight, account for one or more compounds of the formula (I). The invention also encompasses those liquid-crystalline dielectrics to which, for example, for doping purposes, only less than 5 parts by weight, for example 0/1 to 3 parts by weight of one or more compounds of the formula (I) have been added. On the other hand, the compounds of formula (I) may account for up to 50% by weight of the dielectrics of the invention. The liquid-crystalline dielectrics according to the invention preferably contain 10 to 30% by weight of one or more compounds of the formula (I).

The preparation of the dielectrics according to the invention is carried out in a conventional manner. In general, the desired amount of Kompo-3Q components used in lesser amount is dissolved in the constituent of the main component, useful at elevated temperature. If a temperature above the clearing point of the main constituent is selected, the complete

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the dissolution process are particularly easy to observe.

However, it is also possible to mix solutions of the components of the formula (I) and (II) in a suitable organic solvent, for example acetone, chloroform or methanol, and to remove the solvent after thorough mixing, for example by distillation under reduced pressure , Of course, care must be taken in this procedure that no impurities or unwanted dopants are introduced by the solvent.

By means of suitable additives, the liquid-crystalline dielectrics according to the invention can be modified so that they can be used in all hitherto known types of .Y liquid crystal display elements.

Such additives are known to the person skilled in the art and are described in detail in the relevant literature. For example, dichroic dyes or substances for changing the dielectric anisotropy, the viscosity, the conductivity and / or the orientation of the nematic phases can be added. Such substances are described for example in DE-OS 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430, 28 53 728 and 29 02 177.

e) examples of application;

The following examples are intended to illustrate the invention without limiting it. In the examples, F. is the melting point and K. is the clearing point of a liquid crystalline substance in degrees Celsius; Boiling temperatures are designated by Kp. Unless otherwise indicated, parts are by weight or percentages by weight.

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Example A

(a) 15.3 g of 4- (trans-4-n-pentylcyclohexyl) -biphenyl are added portionwise to a 40-warm mixture of 5 ml of 65% nitric acid and 6 ml of 96% sulfuric acid. After the end of the addition, the reaction mixture is stirred for 1 hour at 60 ° and poured onto 150 g of ice. After thawing, the crystallized 4- (trans-4-n-pentylcyclohexyl) -4'-nitrobiphenyl is filtered off and recrystallized from ethanol; F. 115 °, K. 176 °.

(b) In a suspension of 3 g of palladium-carbon (10% Pd) in a solution of 10 g of 4- (trans-4-n-pentylcyclohexyl) -4'-nitrobiphenyl in 100 ml of tetrahydrofuran is stirred for one hour at normal pressure and room temperature Introduced hydrogen. The catalyst is then filtered off and the filtrate is evaporated. The remaining 4- (trans-4-n-pentylcyclohexyl) -4 ^/ -aminobiphenyl is recrystallized from petroleum ether (boiling range 40-60 °); F. 132 °, K. 215 °.

(°) 7.8 g of 4- (tranS-4-n-pentylcyclohexyl) -4'-aminobiphenyl are slurried in 5 ml of 36% aqueous hydrochloric acid.

After addition of 5 ml of dioxane, the solution of 1.9 g of sodium nitrite in 7.5 ml of water is added dropwise at 0 °.

Immediately thereafter, likewise at ⁰ , a solution of 6 g of sodium tetrafluoroborate in 10 ml of water is added dropwise. The precipitate formed is suctioned off 1/2 hour after the addition of the fluorine compound, washed with ice water and

3Q dried at room temperature in vacuo. The dried powder is heated to 120 °. After finishing

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3 -

After the BF ₃ development, the residue is dissolved in ethanol. From the solution crystallize 3.5 g of 4- (trans-4-n-pentylcyclohexyl) -4'-fluorobiphenyl, mp 99 °, K. 154 °.

Analog are produced:

4- (trans-4-methylcyclohexyl) -4'-fluorobiphenyl, 4- (trans-4-ethylcyclohexyl) -4'-fluorobiphenyl, 4- (trans-4-n-propylcyclohexyl) -4'-fluorobiphenyl, 4- (trans trans-4-n-butylcyclohexyl) -4'-fluorobiphenyl, 4- (trans-4-n-hexylcyclohexyl) -4'-fluorobiphenyl, 4- (trans-4-n-heptylcyclohexyl) -4'-fluorobiphenyl, 4- (trans-4-n-decylcyclohexyl) -4'-fluorobiphenyl, 4- (trans-4-n-dodecylcyclohexyl) -4'-fluorobiphenyl, 4- [trans-4- (2-methylbutyl) -cyclohexyl] -4 ' -fluorbiphenyl.

Example β

(a) 16.7 g of 4- (trans-4-n-pentylcyclohexyl) -4'-ethylbiphenyl are nitrated in the manner described in Example 1. (a). The mixture of isomeric nitration products filtered off after pouring into ice water is dissolved in toluene and separated by preparative high pressure liquid chromatography. There are 8.7 g of 4- (trans-4-n-pentylcyclohexyl) -2'-nitro-4'-ethylbiphenyl and 5.5 g of 4- (trans-4-n-pentylcyclohexyl) -2-nitro-4 ^/ obtained ethylbiphenyl.

(b) The nitro compounds prepared according to Example 2 (a) are reduced analogously to Example 1 (b) to give the corresponding amino compounds and this analogously to Example (Ic) in 4- (trans-4-n-pentylcyclohexyl) -2'-fluoro 4'-ethylbiphenyl, mp 27 °, K. 104 ° and 4- (trans-4-n-pentylcyclohexyl) -2-fluoro-4'-ethylbiphenyl, mp 26 °, K. 107 °.

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Analog are produced:

4- (trans-4-ethylcyclohexyl) -2'-fluoro-4'-n-butylbiphenyl, 4- (trans-4-n-propylcyclohexyl) -2'-fluoro-4'-n-propylbiphenyl, ^ - (trans ^ -n-propylcyclohexyl) ^ ¹ -fluoro ^ '- n-octylbi-

4- (trans-4-n-butylcyclohexyl) -2'-fluoro-4'-n-butylbiphenyl, 4- (trans-4-n-pentylcyclohexyl) -2'-fluoro-4'-n-propylbiphenyl, 4- (trans-4-n-pentylcyclohexyl) -2 ^l -fluoro-4'-n-pentylbiphenyl, transition smectic-nematic 52 °, K. 105 °; 4- (trans-4-n-heptylcyclohexyl) -2 ^l -fluoro-4'-n-butylbiphenyl,

4- (trans-4-n-0ctylcyclohexyl) - ² '-fluoro-4'-methylbiphenyl, and

4- (trans-4-ethylcyclohexyl) -2-fluoro-4'-n-butylbiphenyl, 4- (trans-4-n-propylcyclohexyl) -2- fluoro-4'-n-propylbiphenyl,

4- (trans-4-n-propylcyclohexyl) -2-fluoro-4'-n-octylbiphenyl, 4- (trans-4-n-butylcyclohexyl) -2-fluoro-4'-n-butylbiphenyl, 4- (trans 4-n-pentylcyclohexyl) -2-fluoro-4'-n-propylbiphenyl,,;

4- (trans-4-n-pentylcyclohexyl) -2-fluoro-4'-n-pentylbiphe-

4- (trans-4-n-heptylcyclohexyl) -2-fluoro-4'-n-butylbiphenyl,

4- (trans-4-n-octylcyclohexyl) -2- fluoro-4'-methylbiphenyl / 4- (trans-4-n-pentylcyclohexyl) -2 _/ 2'-difluoro-4'-ethylbiphenyl F. -2 °, K. 80 °.

4 6 83 8 -is

example 1

The liquid-crystalline dielectric from;

24% 4- (trans-4-n-propylcyclohexyl) benzonitrile, 36% 4- (trans-4-n-pentylcyclohexyl) benzonitrile _/ 25% 4- (trans-4-n-heptylcyclohexyl) benzonitrile and 15% 4- (trans-4-n-pentylcyclohexyl) biphenyl-4'-carbonitrile

has a nematic range of -6 ° to + 70 ° and a viscosity of 28. 10 ~ ³ Pa.s at 20 ° and from 97. 10 ~ Pa.s at 0 °. If the latter component is replaced by the same amount by weight of 4- (trans-4-n-pentylcyclohexyl) -4'-fluorobiphenyl, the temperature range of the nematic phase changes slightly from -10 ° to + 65 °; the viscosity values, which have a significant influence on the switching times, amount to 24 in the thus prepared dielectric 24 according to the invention. 10 " ³ Pa.s at 20 ° and only 68. 10 ~ ³ Pa.s at O ⁰ .

Example 2

The liquid crystal dielectric of 12% anisic acid 4-n-propylphenyl ester, 23% anisic acid 4-n-pentylphenyl ester, 9% 1- / 4- (trans-4-n-penty! Cyclohexyl) -phenylZ-pentanedione - (1,3),

21% 4- (trans-4-n-propylcyclohexyl) benzoic acid (4-n-butyl-2-cyanophenyl) ester and 35% 4- (trans-4-n-pentylcyclohexyl) -2 ^l -fluoro-4 ' ethyl

biphenyl;

has a nematic range of -11 ° to + 78 °, a viscosity of 65 · 10 Pa.s at 20 ° and a dielectric anisotropy of / \ 6 = -0.6. It is with it

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well suited for liquid crystal display elements based on dynamic scattering.

Example 3

The liquid-crystalline dielectric of 23% anisic acid 4-n-pentylphenyl ester,

11% 1/4 ~ (trans-4-n-pentylcyclohexyl) -phenyl-7-pentane

dion- (1,3), 21% 4- (trans-4-n-propylcyclohexyl) benzoic acid (4-n-butyl-2-cyanophenyl) ester

15% of 4- (trans-4-n-pentylcyclohexyl) -4 -ethylbiphenyl ^I and 30% 2-fluoro-4- (trans-4-n-pentylcyclohexyl) -4 ^l -ethylbiphenyl

has a nematic range of -13 ° to + 94 °, a viscosity of 69 x 10 "* ³ Pa.s at 20 ° and of 298 · 10 ^-3 Pa.s at 0 °. The dielectric anisotropy is / \ £ = The dielectric is therefore also very suitable for use in a wide temperature range, dynamically scattering liquid crystal display elements.

Example 4

The liquid crystalline dielectric of 17% 4- (trans-4-n-propylcyclohexyl) benzonitrile,

12% of 4- (trans-4-n-butylcyclohexyl) benzonitrile,

13% of 4- (trans-4-n-pentylcyclohexyl) benzonitrile 15% 4- (trans-4-n-propylcyclohexyl) -ethylbenzene, 21% of 4- (trans-4-n-pentylcyclohexyl) -4 ^I -ethylbiphenyl , 12% 4- (trans-4-n-pentylcyclohexyl) -4 ^l - (trans-4-n-propylcyclohexyl) -biphenyl

5% of 4- (trans-4-n-pentylcyclohexyl) -4'-cyanobiphenyl and 5% of 4- (trans-4-n-pentylcyclohexyl) -4'-fluorobiphenyl

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a nematic range of -11 to +92, a viscosity of 20 x 10 6 Pa.s at 20 °, 61 x 10 ^-3 Pa.s at 0 °, and 316 x 10 ^-3 Pa.s at -20 ° (in the supercooled melt) and a dielectric anisotropy of / \ ± £ = +5.4. It is suitable for strong temperature fluctuations exposed liquid crystal display elements based on the twisted cell.

Example 5

The liquid-crystalline dielectric made

17% of 4- (trans-4-n-propylcyclohexyl) benzonitrile, 12% of 4- (trans-4-n-butylcyclohexyl) benzonitrile,

18% 4- (trans-4-n-pentylcyclohexyl) benzonitrile,

15% of 4- (trans-4-n-propylcyclohexyl) -1-n-butylbenzene _/ 21% of 4- (trans-4-n-pentylcyclohexyl) -4 ^l -ethylbiphenyl, 12% of 4- (trans-4-n- pentylcyclohexyl) -4 '- (trans-4-n-

propylcyclohexylD-biphenyl and

5% of 4- (trans-4-n-propylcyclohexyl) -4 ^l -fluorobiphenyl has a nematic range of -11 to +84, a viscosity of 19 x 10 ^-3 Pa.s at 20 °, of 56 x 10 ^-3 Pa.s at 0 ° and 290 x 10 Pa.s at -20 ° (in the supercooled melt). The threshold voltage in a twisted cell is 2.0 volts at 20 °.

Example 6

The liquid-crystalline dielectric of 10% 4- (trans-4-n-propylcyclohexyl) benzonitrile _f 10% 4- (trans-4-n-propylcyclohexyl) -phenetol / 22% 4- (trans-4-n-propylcyclohexyl) - ethylbenzene, 15% 4- (trans-4-n-pentylcyclohexyl) -4'-ethylbiphenyl _f 9% 4- (trans-4-n-pentylcyclohexyl) -4 '- (trans-4-propyl-cyclohexyl) -biphenyl,

23 4 6 83 8

8% trans-4-n-pentylcyclohexanecarboxylic acid ^ 4- (trans-

4-n-propylcyclohexyl) -phenyl _: 7 ~ ester _f 8% 4- (trans-4-n-propylcyclohexyl) -4 ^l -ethylbiphenyl and 18% 4- (trans-4-n-propylcyclohexyl) -2 ^l fluoride -4 ^l- ethyl

biphenyl

has a nematic range of -17 to * 86, a viscosity of 18 x 10 ^-3 Pa.s at 20 °, 47 x 10 ^-3 Pa.s at 0 ° and 225 Pa.s at -20 ° (in the supercooled melt) and a threshold voltage in the twisted cell of 2.8V at 20 °.

Claims (1)

4 6 83 8 claim Liquid-crystalline dielectric having two or more liquid-crystalline components, characterized in that at least one component is a fluorochemical cyclohexylbiphenyl derivative of the formula (I) Rk (D in which R, alkyl having 1 to 12 C atoms, R _{6 is} alkyl or alkoxy nit 1 - 12 C atoms, CN or fluorine, and R_, R ₃ , R ₄ and R _{5 are} hydrogen or fluorine, with the proviso that at least one, but not more than two of the Radicals R ₂ , R ₃ ^ R ₄ , R ₅ and Mean fluorine, is.