DE4441963B4 - Cyclohexane derivatives and liquid crystalline medium - Google Patents

Abstract

A liquid-crystalline medium having at least two liquid-crystalline components, which comprises at least one compound of the formula I where R 1 is H or alkyl having 1 to 5 C atoms, R 2 is an unsubstituted or monosubstituted by CN or CF 2 or at least one halogen Alkyl or alkenyl radical having 1 to 10 C atoms, it also being possible for one or more CH 2 groups in this radical to be replaced by -O- or -CO- such that O atoms are not directly linked to one another, CN, F, Cl, OCN, NCS, m is 1 or 2 n is 0 to 6, and r is 0 or 1.

Description

wobei
R¹ H oder Alkyl mit 1 bis 5 C-Atomen,
R² einen unsubstituierten oder einen einfach durch CN oder CF₂ oder einen mindestens einfach durch Halogen substituierten Alkyl- oder Alkenylrest mit 1 bis 10 C-Atomen, wobei in diesem Rest auch eine oder mehrere CH₂-Gruppen durch -O- oder -CO- so ersetzt sein können, daß O-Atome nicht direkt miteinander verknüpft sind, CN, F, Cl, OCN, NCS,

m 1 oder 2
n 0 bis 6, und
r 0 oder 1
bedeuten.The invention relates to a liquid-crystalline medium containing at least one cyclohexane derivative of the formula I,

in which
R ^{1 is} H or alkyl having 1 to 5 C atoms,
R ^{2 is} an unsubstituted or substituted by CN or CF ₂ or at least one halogen-substituted alkyl or alkenyl radical having 1 to 10 carbon atoms, wherein in this radical also one or more CH ₂ groups by -O- or -CO - can be replaced so that O atoms are not directly linked, CN, F, Cl, OCN, NCS,

m 1 or 2
n 0 to 6, and
r 0 or 1
mean.

The invention further relates to the use of these compounds as components of liquid-crystalline media and to liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.

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 deformation of upright phases or the effect of dynamic scattering.

The invention had the object of finding stable liquid-crystalline or mesogenic compounds which are suitable as components of liquid-crystalline media and, in particular, at the same time have a comparatively low viscosity and a relatively high nematogeneity.

However, in view of the various uses of such compounds with low Δε, it was desirable to have available further compounds with high nematogeneity, which have precisely tailor-made properties for the respective applications. With the help of the compounds of the formula I STN mixtures can be realized with surprisingly good slope. In comparison to the corresponding saturated compounds, these substances have higher clearing points, better solubility, and a much lower tendency to form smectic phases.

Similar compounds are in the EP 571 916 A1 . DE 42 11 694 A1 and EP 0 256 097 B1 described. However, in contrast to the compounds according to the invention, the latter have an alkenyloxy radical instead of an alkenyl radical.

It has now been found that compounds of the formula I are excellently suitable as components of liquid-crystalline media. In particular, they have comparatively low viscosities. With your help It is possible to obtain stable liquid-crystalline media with a broad nematic mesophase range and advantageous values for the optical and dielectric anisotropy. These media also have a very good low temperature behavior.

With the provision of compounds of the formula I, the range of liquid-crystalline substances which are suitable for the production of liquid-crystalline mixtures from a variety of application-technical points of view is also broadly broader.

The compounds of the formula I have a wide range of applications. Depending on the choice of substituents, these compounds may serve as base materials from which liquid crystalline media 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 in order, for example, to influence the dielectric and / or optical anisotropy of such a dielectric and / or to optimize its threshold voltage and / or its viscosity.

The compounds of the formula I are colorless in the pure state and form liquid-crystalline mesophases in a temperature range which is favorably located for the electro-optical use. Chemically, thermally and against light, they are stable.

The invention relates to liquid-crystalline media containing at least one compound of the formula I and the use of these liquid-crystalline media in liquid crystal display elements, in particular electroopic display elements.

A very particularly preferred smaller group of compounds are those of the subformulae I1 and I6 (L: H or F, R ^{2 '} = alkyl):

R ¹ in sub-formulas I1 to I6 is preferably H or methyl. R ² is preferably alkyl, alkenyl, alkoxy, CN or a halogenated alkyl or alkenyl radical. Halogen is preferably F. In particular, R ² is F, Cl, OCF ₃ , OCF ₂ H, CF ₃ , OCH ₂ CF ₃ , OCHFCF ₃ , OC ₂ F ₅ , C ₂ F ₅ , OC ₂ F ₄ H, OCHF ₂ , CH = CH ₂ or CH = CH-CH ₃ . R ^{2 '} is H or alkyl of 1 to 5 carbon atoms, preferably H or methyl. o is 0 to 6

If R ^{2 is} an alkyl radical and / or an alkoxy radical, this may be straight-chain or branched. Preferably, it is straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and thus preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, furthermore methyl , Octyl, nonyl, decyl, methoxy, octoxy, nonoxy or 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 ^{2 is} an alkyl radical in which a CH ₂ group is replaced by -CH = CH-, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 C atoms. He 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 ^{2 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 particularly mean acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetylaxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, Propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2- (methoxycarbonyl) ethyl, 2- (ethoxycarbonyl) ethyl, 2- (propoxycarbonyl) ethyl, 3- (methoxycarbonyl) propyl, 3- (ethoxycarbonyl) propyl, 4 - (methoxycarbonyl) butyl.

If R ^{2 is} an alkyl radical in which a CH ₂ group is replaced by unsubstituted or substituted -CH = CH- and an adjacent CH ₂ group by CO or CO-O or O-CO, this may be straight-chain or branched , Preferably, it is straight-chain and has 4 to 13 carbon atoms. It therefore particularly means acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3 Methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl, 9-methacryloyloxynonyl.

If R ² is 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-position.

If R ^{2 is} an alkyl or alkenyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain and halogen is preferably F or Cl. In the case of multiple substitution, halogen is preferably F. The resulting radicals also include perfluorinated radicals. For single substitution, the fluoro or chloro substituent may be in any position, but preferably in the ω position.

Compounds of the formula I having branched wing groups R ¹ and R ² may occasionally be of importance because of better solubility in the customary liquid-crystalline base materials, but in particular as chiral dopants if they are optically active.

Branched groups of this type usually contain no more than one chain branch. Preferred branched radicals are 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-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy.

If R ^{2 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 denotes bis-carboxy-methyl, 2,2-bis-carboxy-ethyl, 3,3-bis-carboxy-propyl, 4,4-bis-carboxy-butyl, 5,5-bis-carboxypentyl, 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 (methoxycarbonyl) -ethyl, 3,3-bis (methoxycarbonyl) -propyl, 4,4-bis (methoxycarbonyl) -butyl, 5,5-bis (methoxy carbonyl) 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.

Compounds of the formula I which have wing groups R ¹ and R ² suitable for polycondensations are suitable for the preparation of liquid-crystalline polycondensates.

Formula I includes both the racemates of these compounds and the optical antipodes and mixtures thereof.

Preferred among these compounds of the formula I and the sub-formulas are those in which at least one of the radicals contained therein has one of the preferred meanings given.

In the compounds of formula I, those stereoisomers are preferred in which the rings are trans-1,4-disubstituted cyclohexane rings.

The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methods of Organic Chemistry, Georg-Thieme-Verlag, Stuttgart), namely under Reaction conditions which are known and suitable for the said reactions.

One can also make use of known per se, not mentioned here variants.

Schema 2

The compounds of the formula I can z. B. be prepared as follows: Scheme 1

Scheme 2

The liquid-crystalline media according to the invention preferably contain, in addition to one or more compounds according to the invention, as further constituents 2 to 40, in particular 4 to 30 components. With very particular preference these media contain, in addition to one or more compounds according to the invention, 7 to 25 components. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, cyclohexanecarboxylic acid phenyl or cyclohexyl esters, phenyl or cyclohexyl esters Cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, of cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexylbenzenes, 4,4'-biscyclohexylbiphenyls, 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-cyclohexyl-2- (4 -phenyl-cyclohexyl) -ethanes, 1-cycloh exyl-2-biphenylylethanes, 1-phenyl-2-cyclohexyl-phenylethanes, optionally halogenated stilbenes, benzylphenyl ethers, tolans and substituted cinnamic acids. The 1,4-phenylene groups in these compounds can also be fluorinated.

The most important compounds which may be used as further constituents of media according to the invention can be characterized by the formulas 1, 2, 3, 4 and 5: R'-LE-R '' 1 R'-L-COO-E-R "2 R'-L-OOC-E-R "3 R'-L-CH ₂ CH ₂ -E-R "4 R'-LC≡CE-R "5

In formulas 1, 2, 3, 4 and 5, L and E, which may be the same or different, each independently represents a bivalent radical selected 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, wherein Phe is unsubstituted or substituted by fluorine 1,4-phenylene, Cyc trans- 1,4-cyclohexylene or 1,4-cyclohexylene, Pyr pyrimidine-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. The media according to the invention preferably comprise one or more components selected from the compounds of the formulas 1, 2, 3, 4 and 5, in which L and E are selected from the group Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the Formulas 1, 2, 3, 4 and 5, wherein one of the radicals 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 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 the compounds of formulas 1, 2, 3, 4 and 5 are each independently alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy of up to 8 carbon atoms. In the following, this smaller subgroup will be called Group A and the compounds will be referred to as Partial Formulas 1a, 2a, 3a, 4a and 5a. In most of these compounds R 'and R "are different from each other, one of these radicals is 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, R 'has the meaning given for the compounds of sub-formulas 1a-5a and is preferably alkyl, alkenyl, alkoxy or alkoxyalkyl.

In another smaller subgroup of the compounds of formulas 1, 2, 3, 4 and 5, R "is -CN; this subgroup is referred to below as group C and the compounds of this subgroup are described respectively with sub-formulas 1c, 2c, 3c, 4c and 5c. In the compounds of sub-formulas 1c, 2c, 3c, 4c and 5c, R 'has the meaning given for the compounds of sub-formulas 1a-5a and is preferably alkyl, alkoxy or alkenyl.

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

In addition to the compounds of the formula I, the media according to the invention preferably contain one or more compounds which are selected from 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 preferably Group A: 0 to 90%, preferably 20 to 90%, in particular 30 to 90% Group B: 0 to 80%, preferably 10 to 80%, especially 10 to 65% Group C: 0 to 80%, preferably 5 to 80%, especially 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 to 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 compounds of the formula I. Further preferred are media containing more than 40%, in particular 45 to 90% of compounds of the formula I. The media preferably contain three, four or five compounds of the formula I.

The preparation of the media according to the invention is carried out in a conventional manner. In general, the components are dissolved in each other, useful at elevated temperature. By means of suitable additives, the liquid-crystalline phases according to the invention can be modified so that they can be used in all hitherto known types of liquid-crystal display elements. Such additives are known to the person skilled in the art and are described in detail in the literature (H. Kelker / R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be added to produce colored guest-host systems or to modify the dielectric anisotropy, viscosity and / or orientation of the nematic phases.

Tabelle B:

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: Code for R ¹ , R ² , L ¹ and L ² R ¹ R ² L ¹ L ² nm C _n H _{2n + 1} C _m H _{2m + 1} H H n Om C _n H _{2n + 1} OC _m H _{2m + 1} H H nO.m OC _n H _{2n + 1} C _m H _{2m + 1} H H n C _n H _{2n + 1} CN H H nN.F C _n H _{2n + 1} CN H F nF C _n H _{2n + 1} F H H nOF OC _n H _{2n + 1} F H H n Cl C _n H _{2n + 1} Cl H H nF.F C _n H _{2n + 1} F H F nF.FF C _n H _{2n + 1} F F F nCF ₃ C _n H _{2n + 1} CF ₃ H H nOCF ₃ C _n H _{2n + 1} OCF ₃ H H nOCF ₂ C _n H _{2n + 1} OCHF ₃ H H nS C _n H _{2n + 1} NCS H H RVSN C _r H _{2r + 1} -CH = CH-C _s H _2s - CN H H rESn C _r H _{2r + 1} OC _s H _2s - CN H H nAm C _n H _{2n + 1} COOC _m H _{2m + 1} H H nOCCF ₂ .FF C _n H _{2n + 1} OCH ₂ CF ₂ H F F Table A:

Table B:

The following examples are intended to illustrate the invention without limiting it. Above and below, percentages are 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 information between these symbols represents the Transition temperatures. Δn means optical anisotropy (589 nm, 20 ° C) and the viscosity (mm ² / sec) was determined at 20 ° C.

"Conventional work-up" means: water is optionally added, extracted with dichloromethane, diethyl ether, methyl tert-butyl 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.

DMF

N,N-Dimethylformamid

DMEU

1,3-Dimethyl-2-imidazolidinon

KOT

Kalium-tertiär-butanolat

THF

Tetrahydrofuran

pTsOH

p-Toluolsulfonsäure

The following abbreviations are used :.

DMF

N, N-dimethylformamide

DMEU

1,3-dimethyl-2-imidazolidinone

KOT

Potassium tert-butoxide

THF

tetrahydrofuran

pTsOH

p-toluenesulfonic acid

example 1

2.93 ml of methoxymethyltrimethyltriphenylphosphonium chloride and 2.93 mol of 4-cyclohexanonecarboxylic ester are dissolved in 4 l of THF in a nitrogen atmosphere, and 2.93 mol of potassium tert-butylate are added at room temperature with stirring. The mixture is stirred for 2 h, mixed with water and dilute hydrochloric acid and worked up as usual.

50.4 mmol of II, 1.0 g of 10% HCl, 20 ml of THF and 50.4 mmol of acetaldehyde are stirred for 0.75 h at room temperature. It is mixed with water and methyl tert-butyl ether and worked up as usual.

In a nitrogen atmosphere, 46.1 mmol of potassium tert.butylate in 20 ml of THF are added dropwise to 46.1 mmol of methyltriphenylphosphonium bromide in 50 ml of THF at 0 ° C. After stirring for 10 minutes, 46.1 mmol of III dissolved in 20 ml of THF are added dropwise to the solution. The mixture is allowed to warm to room temperature, mixed with water and dilute HCl and methyl tert-butyl ether and worked up as usual.

65.8 mmol of Vitride be presented at 0 ° C in 35 ml of toluene and dissolved under stirring with 72.3 mmol of morpholine in 20 ml of toluene. The solution is added dropwise at -40 ° C to 32.9 mmol IV dissolved in 30 ml of toluene and stirred at -40 to -50 ° for 70 min. It is mixed at -40 ° C with water and at -10 ° C with 10% HCl. Then it is worked up as usual.

0.04 mol of V, 0.04 mol of 4- [trans-4- (trans-4-propylcyclohexyl) cyclohexylmethyltriphenylphosphonium iodide and 1140 ml of THF are introduced and mixed in portions with 0.40 mol of potassium tert.butylat, the reaction temperature 35 ° C should not exceed. It is stirred overnight at room temperature, hydrolyzed, mixed with dil. HCl and worked up as usual. K -2 S _B 188 N 222.2 I; Δn = +0.888; Δε = 1.03

hergestellt:

Analogously, the following compounds of the formula

produced:

Claims (10)

Liquid-crystalline medium having at least two liquid-crystalline components, characterized in that it contains at least one compound of the formula I,

wherein R ^{1 is} H or alkyl having 1 to 5 C atoms, R ^{2 is} an unsubstituted or a simply by CN or CF ₂ or at least one halogen-substituted alkyl or alkenyl radical having 1 to 10 carbon atoms, in this rest also one or more CH ₂ groups can be replaced by -O- or -CO- so that O atoms are not directly linked to one another, CN, F, Cl, OCN, NCS,

m is 1 or 2 n is 0 to 6, and r is 0 or 1. Medium according to Claim 1, characterized in that it contains at least one compound of the formula I1,

wherein R ¹ , R ² and n have the meaning given in claim 1 contains. Medium according to Claim 1 or 2, characterized in that it contains at least one compound of the formula I2,

wherein R ¹ and n have the meaning given in claim 1 and R ^{2 'is} H or alkyl having 1 to 5 carbon atoms and o is 0 to 6, contains. Medium according to Claim 1, characterized in that it contains at least one compound of the formula I3,

wherein R ¹ , R ² and n have the meaning given in claim 1 contains. Medium according to Claim 1, characterized in that it contains at least one compound of the formula I4,

wherein R ¹ , R ² and n have the meaning given in claim 1 contains. Medium according to Claim 1, characterized in that it contains at least one compound of the formula I5,

wherein R ¹ , R ² and n have the meaning given in claim 1 contains. Medium according to Claim 1, characterized in that it contains at least one compound of the formula I6,

wherein R ¹ , R ² and n have the meaning given in claim 1 contains. Medium according to Claim 1, characterized in that it contains at least one compound of the formula I according to Claim 1, in which R ^{2 is} F, Cl, CN, OCHFCF ₃ , OCF ₃ , OCF ₂ H, alkyl, alkenyl or alkoxy. Use of compounds of the formula I or one or more of their sub-formulas, as defined in one or more of claims 1 to 8, as components of liquid-crystalline media. Use of a medium according to one or more of claims 1 to 8 in a liquid crystal display element.