JPH0625062A - Liquid crystal compound and composition - Google Patents

Abstract

PURPOSE:To obtain a new compound useful as a liquid crystal composition used in a liquid crystal display element. CONSTITUTION:The compound of formula 1 (R<1> is 1-18C alkyl; A is formula 6 to 10; R<2> is 1-18C alkyl or alkenyl). The compound of formula 1 in which A is formula 6 is obtained by reacting a compound of formula 4 derived from 6-bromo-2-naphthol with a compound of formula 5 in the presence of a Pd catalyst. When this compound is used as a component of a chiral smectic C phase liquid crystal composition, the orienting properties can be improved and the contrast ratio can be raised without zigzag defects. Since other smectic phases are not exhibited in a low-temperature region, this compound can be used as a component of the chiral smectic C phase liquid crystal composition to extend the temperature range of the chiral smectic C phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel liquid crystal compound useful as a component of a liquid crystal composition used for a liquid crystal display device and the like and a liquid crystal composition containing this liquid crystal compound. More specifically, the present invention provides a novel naphthalene-based liquid crystal compound exhibiting a non-chiral smectic C phase (hereinafter abbreviated as Sc phase) and a liquid crystal composition containing the liquid crystal compound.

[0002]

2. Description of the Related Art Recently, a display system using a ferroelectric liquid crystal compound has been reported by Meyer et al., And a high speed response and a memory effect of 100 to 1000 times that of a TN type can be obtained. Expectations are high, and research and development are currently underway. The liquid crystal phase of the ferroelectric liquid crystal compound belongs to the tilt type chiral smectic phase, but in practice, the chiral smectic C (hereinafter abbreviated as Sc *) phase, which has the lowest viscosity, is practically used. Is most desirable. A large number of liquid crystal compounds exhibiting the Sc * phase have already been synthesized and studied, but the conditions for use as a ferroelectric display element are: (a) showing Sc * in a wide temperature range including room temperature, b) showing uniform orientation and having a large helical pitch,
(C) having an appropriate tilt angle, (d) having low viscosity, and the like. However, no liquid crystal compound exhibiting the Sc * phase that satisfies these conditions alone has been known, and efforts have been made to satisfy these conditions by mixing. In addition, the development of new liquid crystal compounds exhibiting the Sc * phase is also in progress. On the other hand, as a method for preparing a liquid crystal composition exhibiting a Sc * phase (hereinafter referred to as a Sc * liquid crystal composition), a chiral compound is added to a liquid crystal compound or composition exhibiting a non-chiral Sc phase without showing ferroelectricity. There is also a method of addition, and development of a liquid crystal compound exhibiting a Sc phase is underway. Conventionally, phenylpyrimidine-based liquid crystal compounds represented by the following chemical formulas 7 and 8 are known as typical liquid crystal compounds exhibiting the Sc phase or Sc * phase.

[0003]

[Chemical 7]

[0004]

[Chemical 8]

In Chemical formula 8, C * represents an asymmetric carbon atom.

[0006]

However, since these phenylpyrimidine-based liquid crystal compounds and compositions using these compounds have poor orientation, zigzag defects are likely to occur when injected into a cell and the contrast ratio does not increase. There's a problem.

[0007]

Means for Solving the Problems As a result of intensive investigations by the present inventors on a liquid crystal compound exhibiting an Sc phase having a better orientation than the above compounds, a new liquid crystal compound having a structure different from the conventional one was found. The invention was reached. That is, the present invention is represented by the following general formula

[0008]

[Chemical 9] [In the formula, R ¹ represents an alkyl group having 1 to 18 carbon atoms,
A represents a group selected from the following chemical formulas 10 to 14, and NAP
Represents a 2,6-naphthylene group, R ² represents an alkyl group or an alkenyl group having 1 to 18 carbon atoms; and a liquid crystal composition containing at least one liquid crystal compound. Is.

[0009]

[Chemical 10]

[0010]

[Chemical 11]

[0011]

[Chemical 12]

[0012]

[Chemical 13]

[0013]

[Chemical 14]

In the general formula (1), the number of carbon atoms represented by R ¹ is 1.
Specific examples of the alkyl group of to 18 include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group,
n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tetradecyl group, n-hexadecyl group, n-octadecyl group, etc. Is mentioned. Of these, preferred is an alkyl group having 3 to 14 carbon atoms. Specific examples of the alkyl group and alkenyl group having 1 to 18 carbon atoms represented by R ² is an alkyl group and indicated above R ¹ 2-
Propenyl group, 3-butenyl group, 4-pentenyl group, 5-
Hexenyl group, 6-heptenyl group, 7-octenyl group, 8
-Nonenyl group, 9-decenyl group, 10-undecenyl group,
11-dodecenyl group, trans-2-hexenyl group, cis-2-
Hexenyl group, cis-3-hexenyl group, cis-4-hexenyl group, trans-2-heptenyl group, cis-3-nonenyl group, ci
Examples include s-6-nonenyl group, trans-2-decenyl group and trans-5-decenyl group. Preferred as R ² are alkyl and alkenyl groups having 3 to 14 carbon atoms. Specific examples of the liquid crystal compound of the present invention are shown in Table 1 below.
~ Compounds having groups as shown in Table 6 can be mentioned.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

[Table 5]

[0020]

[Table 6]

In the above Tables 1 to 6, each symbol represents the following group. _{PEN; nC 5 H 11 - HEX} ; nC 6 H 13 - H
_{EP; nC 7 H 15 - OCT} ; nC 8 H 17 - NON; nC 9 H 19 - D
_{EC; nC 10 H 21 - O} -HEP; CH 2 = CH- (CH 2) 5 - O-OCT; CH 2 = CH- (CH 2) 6 - O-NON; CH 2 = CH- (CH 2) _{7 - O-DEC; CH 2} = CH- (CH 2) 8 -

The compound of the present invention can be synthesized, for example, through the steps shown in the items <I> to <V> [R ¹ and N in the following formulas].
AP and R ² are the same as in general formula (1)]. <I> When A is a group represented by Chemical formula 10

[0023]

[Chemical 15]

That is, 6-bromo-2-naphthol was reacted with an alkylating agent (for example, an alkyl halide) in the presence of a base to obtain a compound of the general formula (3) prepared from a compound of the general formula (2) and metallic magnesium. The compound of the general formula (4) can be obtained by reacting the Grignard reagent of 4) with 4-bromo-2-fluoroiodobenzene in the presence of a palladium catalyst. By reacting the compound of the general formula (4) with the 1-alkyne represented by the general formula (5) in the presence of a palladium catalyst, the compound of the general formula (1)
The compound of a) can be obtained. <II> When A is a group represented by Chemical formula 11

[0025]

[Chemical 16]

That is, the compound of the general formula (3) and 2,5
-The compound of the general formula (6) can be obtained by reacting dibromopyridine in the presence of a palladium catalyst. The compound of the general formula (6) and 1 represented by the general formula (5)
-The compound of the general formula (1b), which is the compound of the present invention, can be obtained by reacting an alkyne in the presence of a palladium catalyst. <III> When A is a group represented by Chemical formula 12,

[0027]

[Chemical 17]

That is, a compound of the general formula (7) can be obtained by reacting 2,5-dibromopyridine with a 1-alkyne represented by the general formula (5) in the presence of a palladium catalyst. Compound of general formula (7) and general formula (3)
The compound of the general formula (1c), which is the compound of the present invention, can be obtained by reacting the compound of (1) in the presence of a palladium catalyst. <IV> When A is a group represented by Chemical formula 13,

[0029]

[Chemical 18]

That is, the compound of the general formula (8) can be obtained by reacting the Grignard reagent of the general formula (3) with 4-benzyloxy-2,3-difluoroiodobenzene in the presence of a palladium catalyst. General formula (8)
The compound of the general formula (9) can be obtained by hydrogenolysis of the compound of (1) using palladium carbon.
The compound of general formula (10) can be obtained by reacting the compound of general formula (9) with trifluoromethanesulfonic anhydride. The compound of the general formula (1d), which is the compound of the present invention, can be obtained by reacting the compound of the general formula (10) with the 1-alkyne represented by the general formula (5) in the presence of a palladium catalyst. Alternatively, it can be synthesized through the following steps.

[0031]

[Chemical 19]

That is, n-in ortho-difluorobenzene
2,3-Difluoroiodobenzene can be obtained by reacting iodine with butyllithium. A compound of the general formula (11) can be obtained by reacting 2,3-difluoroiodobenzene with a 1-alkyne represented by the general formula (5) in the presence of a palladium catalyst. The compound of the general formula (12) can be obtained by reacting the compound of the general formula (11) with n-butyllithium and then reacting it with trimethyl borate for hydrolysis. The compound of the general formula (3) and the general formula (1
The compound of the general formula (1d) which is the compound of the present invention can also be obtained by reacting the compound of 2) in the presence of a palladium catalyst. <V> When A is a group represented by Chemical formula 14,

[0033]

[Chemical 20]

That is, a compound of the general formula (11) is obtained by reacting 1-bromo-3-fluoro-4-iodobenzene with a 1-alkyne of the general formula (5) in the presence of a palladium catalyst. Can be done. By reacting the compound of general formula (3) with the compound of general formula (11) in the presence of a palladium catalyst, the compound of general formula (1e), which is the compound of the present invention, can be obtained.

The liquid crystal compound is generally used as a component of a liquid crystal composition composed of two or more kinds of components, and the liquid crystal compound of the present invention can also be used as a component of the liquid crystal composition. The liquid crystal composition of the present invention comprises a mixture of a plurality of compounds and contains at least one liquid crystal compound of the present invention. Examples of the composition of the present invention include the liquid crystal composition [1] of the present invention exhibiting the Sc phase and the liquid crystal composition [2] of the present invention exhibiting the Sc * phase. The liquid crystal composition [1] of the present invention contains at least 1 part of the liquid crystal compound of the present invention.
A liquid crystal compound (2-4′-alkyloxyphenyl-5-alkylpyrimidine, 2-4′-alkylphenyl-5-alkyloxypyrimidine, 2-4′-, which is an essential component of the seed and which exhibits another Sc phase as an optional component. Alkyloxyoxyphenyl-5-alkyloxypyrimidines, 2-p-alkyloxycarbonylphenyl-5-alkylpyrimidines, 2-
4'-alkyloxy-3'-fluorophenyl-5-alkylpyrimidine, 2-4'-alkyloxy-2 ', 3'-
Difluorophenyl-5-alkylpyrimidine, 2-4'-
Alkyloxyphenyl-5-alkylpyridine, 2-
4′-alkyloxy-3′-fluorophenyl-5-alkylpyridine, etc.), a smectic liquid crystal compound not exhibiting an Sc phase, and a liquid crystal compound exhibiting a nematic phase. In the liquid crystal composition [1] of the present invention, the content of one or more liquid crystal compounds of the present invention is usually 5 to 100% by weight.

The liquid crystal composition [2] of the present invention includes a liquid crystal compound (optically active 4-alkyloxy-4′-biphenylcarboxylic acid-p ′) exhibiting a Sc * phase with the liquid crystal composition [1] of the present invention.
-(2-Methylbutyloxycarbonyl) phenyl ester, optically active 4-n-alkyloxy-4'-biphenylcarboxylic acid-2-methylbutyl ester, etc. and / or a chiral compound (Japanese Patent Laid-Open No. 63-99032, JP Kaisho 63
-190843, JP-A-2-138274, JP-A-2-
256673, JP-A-2-262579, JP-A-2-2
86673, compounds described in JP-A-3-27374, etc.) and, if necessary, a dichroic dye (anthraquinone dye, azo dye, etc.).
In the liquid crystal composition [2] of the present invention, the content of the liquid crystal composition [1] of the present invention is usually 10 to 99% by weight.

A liquid crystal composition exhibiting ferroelectricity causes an optical switching phenomenon when a voltage is applied, and a liquid crystal display element having a fast response can be manufactured by utilizing this phenomenon [see, for example, JP-A-56-1].
07216, JP 59-118744, NA Clark, ST Lagawall (STLage)
rwall) ； Applied Phyth Letter
sics Letter) 36, 899 (1980), etc.].

Liquid crystal composition of the present invention showing Sc * [2]
Can be used as an optical switching element (liquid crystal display element) by vacuum-sealing in a liquid crystal cell having a cell interval of 0.5 to 10 μm, preferably 0.5 to 3 μm and installing polarizers on both sides. The above liquid crystal cell can be produced by providing a transparent electrode and bonding two glass substrates, the surfaces of which are aligned, with a spacer interposed therebetween. Examples of the spacer include alumina beads, glass fiber, and polyimide film. As the alignment treatment method, a normal alignment treatment, such as a rubbing treatment of a polyimide film or an oblique SiO vapor deposition, can be applied.

[0039]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited thereto. Example 1 No. 1 in Table 1 Preparation of 11 compound 6-bromo-2-octyloxynaphthalene (this compound was obtained by reacting an alkali metal salt of 6-bromo-2-naphthol with n-octyl bromide) 10.0 g
Diethyl ether solution of Grignard reagent prepared by
1-Bromo-3-fluoro-4-iodobenzene in 100 ml 9.
After 0 g was added and the atmosphere was replaced with nitrogen, the mixture was cooled to 10 ° C. or lower in an ice water bath, 180 mg of dichloro {1,4-bis (diphenylphosphino) butane} palladium (II) was added, and the mixture was stirred for 1 hour as it was. After removing the ice water bath and stirring for further 5 hours, water was added while cooling in the ice water bath. After adding toluene, the organic layer was washed with water and then the solvent was removed. The obtained solid was recrystallized from ethanol to obtain 8.2 g of the compound (a) represented by the following chemical formula 21.

[0040]

[Chemical 21]

2.5 g of the compound (a) obtained in 1 and 1-decyne
1.0 g was heated to reflux for 8 hours in a nitrogen atmosphere using 20 mg of dichlorobistriphenylphosphine palladium (II), 5 mg of copper (I) iodide and 40 mg of triphenylphosphine as catalysts in 50 ml of triethylamine. After completion of the reaction, triethylamine was removed and the mixture was extracted with toluene. The toluene layer was washed with 1N hydrochloric acid, washed with water, purified with a silica gel column, and then recrystallized three times with ethanol to give white crystals of the compound of the present invention (No. 1 in Table 1).
1.4 g of the compound of 11 are obtained. The structure of the compound is NMR (nuclear magnetic resonance spectrum analysis), MS (mass spectrometry), IR
(Infrared absorption spectrum analysis) and elemental analysis confirmed. IR (cm ^-1 ) 2924.0 2854.0 2226.0 1605.0 1549.0 1499.0 1468.0 1392.0 1257.0 1203.0 1170.0 1120.0 855.0 NMR (ppm) 0.84 to 0.95 (m, 6H) 1.20 to 1.55 (m, 20H) 1.55 to 1.67 (m, 2H) 1.79 to 1.91 (m, 2H) 2.42 (t, 2H) 4.08 (t, 2H) 7.11 to 7.29 (m, 4H) 7.44 (t, 1H) 7.62 (d, 1H) 7.75 (s, 1H) 7.78 (s, 1H) 7.93 (s, 1H) ¹⁹ F-NMR -42.4 (t, 1F) Elemental analysis value Theoretical value (%) Actual value (%) C: 83.95 C: 84.01 H: 8.85 H: 8.63 F: 3.91 F: 4.12

Example 2 In Table 2, No. Preparation of 26 compound 100 ml of diethyl ether solution of Grignard reagent prepared from 10.0 g of 6-bromo-2-octyloxynaphthalene
After adding 7.1 g of 2,5-dibromopyridine to the inside and purging with nitrogen, the mixture was cooled to 10 ° C or lower in an ice water bath, and then dichloro {1,4-bis (diphenylphosphino) butane} palladium (II) 180 mg Was added and the mixture was stirred as it was for 1 hour. After removing the ice water bath and stirring for further 5 hours, water was added while cooling in the ice water bath. After adding toluene,
The organic layer was washed with water and then the solvent was removed. The obtained solid was recrystallized from ethanol to obtain 8.7 g of the compound (b) represented by the following chemical formula 22.

[0043]

[Chemical formula 22]

3.0 g of the compound (b) obtained in (1) and 1.0 g of 1-octyne were used in 50 ml of triethylamine with 24 mg of dichlorobistriphenylphosphine palladium (II), 6 mg of copper (I) iodide and 48 mg of triphenylphosphine as catalysts. And refluxed under nitrogen atmosphere for 8 hours. After completion of the reaction, triethylamine was removed and the mixture was extracted with toluene. The toluene layer was washed with 1N hydrochloric acid water, washed with water, purified with a silica gel column, and then recrystallized three times with ethanol to give white crystals of the compound of the present invention N in Table 2.
o. 1.9 g of 26 compound was obtained. IR (cm ^-1 ) 2928.0 2856.0 2232.0 1628.0 1605.0 1466.0 1381.0 1274.0 1257.0 1205.0 1174.0 1044.0 841.0 NMR (ppm) 0.82 to 0.99 (m, 6H) 1.21 to 1.43 (m, 12H) 1.43 to 1.58 (m, 4H) 1.58 to 1.72 (m, 2H) 1.79 to 1.91 (m, 2H) 2.46 (t, 2H) 4.08 (t, 2H) 7.12 to 7.20 (m, 2H) 7.72 to 7.84 (m, 4H) 8.08 (dd, 1H) 8.40 (d , 1H) 8.72 (d, 1H) Elemental analysis value Theoretical value (%) Actual value (%) C: 84.36 C: 84.13 H: 8.84 H: 9.01 N: 3.17 N: 3.22

Example 3 No. 3 in Table 3 Preparation of compound 55. 2,5-dibromopyridine 10.0 g and 1-decyne 5.8 g in triethylamine 200 ml as a catalyst, dichlorobistriphenylphosphine palladium (II) 80 mg, copper iodide 2
The mixture was heated under reflux for 8 hours using 0 mg and 160 mg of triphenylphosphine under a nitrogen atmosphere. After completion of the reaction, triethylamine was removed and the mixture was extracted with hexane. The hexane layer was washed with a 1N hydrochloric acid solution and washed with water, and then hexane was removed to give an oily compound (c) 10.8
got g.

[0046]

[Chemical formula 23]

4.4 g of the compound (c) obtained in 50 ml of a diethyl ether solution of a Grignard reagent prepared from 5.0 g of 6-bromo-2-octyloxynaphthalene was added, and the atmosphere was replaced with nitrogen. After cooling to below, 90 mg of dichloro {1,4-bis (diphenylphosphino) butane} palladium (II) was added and the mixture was stirred for 1 hour as it was. After removing the ice water bath and stirring for further 5 hours, water was added while cooling in the ice water bath. After adding toluene, the organic layer was washed with water and then the solvent was removed. The obtained solid was dissolved in toluene, purified with a silica gel column, and recrystallized three times with ethanol to give a white crystalline compound of the present invention, No. 3 in Table 3. 1.7 g of 55 compound was obtained. IR (cm ^-1 ) 2926.0 2230.0 1628.0 1603.0 1549.0 1493.0 1468.0 1394.0 1255.0 1209.0 1174.0 1015.0 849.0 820.0 NMR (ppm) 0.84 to 0.96 (m, 6H) 1.22 to 1.58 (m, 20H) 1.59 to 1.72 (m, 2H) 1.78 to 1.92 (m, 2H) 2.47 (t, 2H) 4.08 (t, 2H) 7.12 ~ 7.23 (m, 2H) 7.46 (d, 1H) 7.65 (dd, 1H) 7.75 ~ 7.85 (m, 2H) 7.88 ~ 7.97 ( m, 2H) 8.89 (d, 1H) Elemental analysis value Theoretical value (%) Actual value (%) C: 84.43 C: 84.21 H: 9.17 H: 9.33 N: 2.99 N: 3.05

Example 4 In Table 4, No. Preparation of 75 Compound 1,2-Difluoro-3-iodobenzene (This compound was obtained by lithiation of ortho-difluorobenzene with n-butyllithium and subsequent reaction with iodine) 1
In 200 ml of triethylamine, 0.0 g and 1-nonine 5.2 g were used as catalysts for dichlorobistriphenylphosphine palladium (I
I) 80 mg and copper (I) iodide 20 mg were used and reacted at room temperature for 8 hours under a nitrogen atmosphere. After completion of the reaction, triethylamine was removed and the mixture was extracted with hexane. The hexane layer was washed with 1N hydrochloric acid water and washed with water, and then hexane was removed to give 9.2 g of an oily compound (d) represented by the following chemical formula 24.
Got

[0049]

[Chemical formula 24]

The compound (d) (9.2 g) obtained above was dissolved in anhydrous tetrahydrofuran (150 ml) and cooled to -60 ° C. or lower with a dry ice-acetone bath. Then, 26 ml of a hexane solution of n-butyllithium (15%) was added dropwise at -60 ° C or lower, and the mixture was stirred as it was for 3 hours. Next, 4.8 g of trimethyl borate-
Drop it below 60 ℃ and stir for another 30 minutes, then dry ice
-The acetone bath was removed, and the mixture was stirred until it reached 0 ° C. Water and then 1N hydrochloric acid were added, and the mixture was extracted with ether. The ether layer was washed with water and then the ether was removed to obtain 9.8 g of a compound (e) represented by the following chemical formula 25 as a white solid.

[0051]

[Chemical 25]

2.0 g of the compound (e) obtained in 6-bromo-
2-nonyloxynaphthalene (this compound is 6-bromo-
2.5 g of trinaphthylamine (obtained by reacting an alkali metal salt of 2-naphthol with n-nonyl bromide)
In 60 ml, 165 mg of tetrakistriphenylphosphine palladium (0) and 165 mg of triphenylphosphine were used as catalysts in a nitrogen atmosphere and heated under reflux for 10 hours. After completion of the reaction, triethylamine was removed and the mixture was extracted with toluene.
The toluene layer was washed with 1N hydrochloric acid, washed with water, purified with a silica gel column, and then recrystallized three times to obtain white crystals of the compound of the present invention.
o. 2.0 g of the compound of 75 are obtained. IR (cm ^-1 ) 2928.0 2858.0 2252.0 1630.0 1605.0 1502.0 1462.0 1218.0 1093.0 853.0 826.0 NMR (ppm) 0.84 to 0.95 (m, 6H) 1.18 to 1.41 (m, 16H) 1.41 to 1.58 (m, 4H) 1.58 to 1.70 (m , 2H) 1.79 to 1.91 (m, 2H) 2.47 (t, 2H) 4.09 (t, 2H) 7.11 to 7.22 (m, 4H) 7.57 to 7.64 (m, 1H) 7.78 (d, 1H) 7.92 (s, 1H ) ¹⁹ F-NMR -67.3 (dd, 1F) -59.9 (dd, 1F) Elemental analysis value Theoretical value (%) Actual value (%) C: 80.95 C: 81.09 H: 8.33 H: 8.17 F: 7.54 F: 7.38

The phase transition temperatures of the compounds obtained in Examples 1 to 4 are shown in Table 7 below.

[0054]

[Table 7]

The symbols in Table 7 above have the following meanings. Cry; Crystal phase Sc; Smectic C phase S _A ; Smectic A phase Nem; Nematic phase Iso; Isotropic liquid phase ・; Phase exists-; Phase does not exist

[0056]

By using the liquid crystal compound of the present invention as a component of the Sc * liquid crystal composition, the orientation of this composition can be improved and the contrast ratio can be increased.
Further, the liquid crystal compound of the present invention is a compound capable of extending the temperature range of the Sc * phase by being used as a component of the Sc * liquid crystal composition because it does not exhibit other smectic phases in the low temperature range. Therefore, the compounds and compositions of the present invention are useful as liquid crystal materials used in liquid crystal display devices.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kuniyoshi Yoshio 1-11, Hitotsubashi-honcho, Higashiyama-ku, Kyoto Sanyo Chemical Industry Co., Ltd. Industry Co., Ltd.

Claims (2)

[Claims] 1. The following general formula: [In the formula, R ¹ represents an alkyl group having 1 to 18 carbon atoms,
A represents a group selected from the following Chemical Formulas 2 to 6, NAP represents a 2,6-naphthylene group, and R ² represents an alkyl group or an alkenyl group having 1 to 18 carbon atoms]. [Chemical 2] [Chemical 3] [Chemical 4] [Chemical 5] [Chemical 6] 2. A liquid crystal composition comprising a mixture of a plurality of compounds and containing at least one liquid crystal compound according to claim 1.