DE3703651A1 - Liquid-crystalline mixtures of negative dielectric anisotropy - Google Patents

Abstract

The invention relates to liquid-crystalline mixtures for opto-electronic components which work on the basis of their dielectric and optical anisotropy, for the modulation of the light passing through or thrown back, and for the colour or black/white reproduction of numbers, symbols and images. The object of the invention comprises finding novel substances which are distinguished by negative dielectric anisotropy, a low melting point and a high clearing point or by positive dielectric anisotropy and a high clearing point, for liquid-crystalline mixtures for electro-optical components. It has been found that 2-substituted 5-(trans-4-n-alkylcyclo-hexyl)-1,3,4-thiadiazoles impart the desired properties to liquid-crystalline mixtures. Non-liquid-crystalline substances, in particular dyes, can be added to the mixtures according to the invention.

Description

The invention relates to crystalline-liquid mixtures for electro-optical arrangements for the modulation of the continuous or reflected light as well as for colored or black and white display of digits, characters and moving or still images in single and dual frequency.

Liquid crystals in passive optoelectronic components (Displays) must be used, certain Properties regarding melting and clearing point, electro-optical Threshold voltage, electrical conductivity, optical Anisotropy, viscosity as well as thermal and chemical Have stability.

So far, no pure substance is known, even remotely fulfills these requirements. That is why mixtures are used without exception applied, their properties through targeted choice the components are adapted to the respective purpose. To specifically modify the properties of the mixtures to be able to, new substances with cheaper Properties needed. A claim dealing with the substance classes previously available is easy to meet, is a wide temperature range, in which the substance mixtures can be used. This is especially true for guest-host mixes / T. Uchida, H. Seki, C. Shishido, M. Wade: Molecular Crystals and Liquid Crystals 54 (161 (1979), in which substances with negative dielectric Anisotropy are needed. Especially for substances that have no dipole moment in the direction of the molecular longitudinal axis, As an area of application, it is used in two-frequency mixtures to symmetrize the dielectric anisotropy.

The known 2-phenyl-5- (4-n-alkyloxyphenyl) -1,3,4-thiadiazoles (DD-WP 1 17 014) have high clearing points, mostly about 100 ° C, and high contrasts with the dynamic scattering effect, however their melting temperatures are too high. You result from that big disadvantage, the insufficient solubility at deeper Temperatures and consequently the insufficient property, the properties to modify mixtures. This very property is important for substances found in liquid crystalline Mixtures for the dielectric described above Orientation effects can be used.

The aim of the invention is new mixtures of crystalline liquid Substances for electro-optical assemblies that are due to a negative dielectric anisotropy, deep Melting temperatures and high clarification temperatures or one positive dielectric anisotropy and high clearing temperatures award.

It has been found that additives from one or more representatives the 2-subst.-5 (trans-4-n-alkylcyclohexyl) -1,3,4-thiadiazole the general formula

in which

R ₁ : C _m H _{2 m + 1} ,
X is a single bond or an oxygen atom and
R ₂ : H, Br, CN or CH ₃ as well
n and m are from 1 to 12,
in which
R _{2 is} not H when X is an oxygen atom,
are suitable for use in optoelectronic components for modulating the continuous or reflected light and for reproducing numbers, characters and images. Depending on the application, these mixtures can be mixed with cholesteric crystalline-liquid compounds, chiral smectic liquid crystals or non-liquid-crystalline substances, in particular dyes.

So far, of the 2- (4-subst.-phenyl) -5- (trans-4-n-alkylcyclohexyl) - 1,3,4-thiadiazoles only the compound

known / K. Dimikrowa, J. Hausschild, H. Zaschke, H. Schubert: J. Prakt. Chem. 322, 933 (1980) /.

Due to its melting point of 103 ° C, it is not very suitable for use in electro-optical arrangements. It was therefore surprising that the 2- (4-substituted-phenyl) -5- (trans-4-n-alkylcyclohexyl) -1,3,4-thiadiazoles according to the invention have low melting points and are therefore suitable for use in electro-optical arrangements are. The 2-substituted-5 (trans-4n-alkylcyclohexyl) -1,3,4-thiadiazole derivatives of the general formula I according to the invention are obtained by reacting 4-n-alkylcyclohexanecarboxylic acid hydrazides with substituted benzoic acid chlorides or substituted cyclohexanecarboxylic acid chlorides and subsequent cyclization with P ₄ S ₁₀ in the presence of tertiary nitrogen bases, e.g. B. pyridine, in an inert solvent, preferably benzene, at reaction temperatures of 60 to 80 ° C and reaction times of 4 to 6 h. Fractional crystallization from ethanol / butanol enables the crystalline liquid trans isomer to be obtained in high purity from the crude product.

Exemplary embodiments for the production of the invention links example 1 Preparation of 2- (4-n-butylphenyl) -5- (trans-4-n-hexylcyclohexyl) - 1,3,4-thiadiazole (Verb 1.7)

2.26 g (0.01 mol) of 4-n-hexylcyclohexane carboxylic acid hydrazide in 30 to 40 ml of benzene-pyridine mixture (ratio 7: 1) dissolved and cooled to a temperature between 0 and 5 ° C.

In this temperature interval, 1.97 g (0.01 mol) of 4-n-butylbenzoyl chloride are slowly added dropwise with stirring, the mixture is stirred for a further 45 to 60 minutes at this temperature and then again for 45 to 60 minutes at room temperature. The reaction mixture is then heated to about 80 to 85 ° C. within one hour and stirred at this temperature for three hours. After cooling to room temperature, 3.5 g of P ₄ S _{10 are} added. After the exothermic reaction has cooled, the mixture is heated to 50 ° C. within an hour and stirred at this temperature for another hour.

The reaction mixture is then within 30 to Heated to 80 ° C for 45 minutes and under these conditions Stirred for 4 to 6 hours.

After cooling, 20 ml of ethanol are added, the solution poured into about 250 ml of ice water and with aqueous Neutralized 10% sodium hydroxide solution. The reaction product is suctioned off, washed with plenty of water and dried. The crude product is made from a lot of ethanol / butanol (ratio 8: 1) recrystallized with the addition of activated carbon. The cis / trans isomers are separated by fractional ones Crystallization since the trans isomers are solid during the liquid cis isomers are dissolved in the solvent.

Yield:, 575% crude product, 536% trans product, 5K 58 S _A 117 N 151 I.

Example 2 Preparation of 2- (3-bromo-4-n-nonyloxyphenyl) -5- (trans-4-n- butylcyclohexyl) -1,3,4-thiadiazole (Verb 1.10)

1.98 g (0.01 mol) of 4-n-butylcyclohexane carboxylic acid hydrazide dissolved in 50 ml of benzene-pyridine mixture (ratio 7: 1) and cooled to 0 to 5 ° C by ice cooling.

Then 3.62 g (0.01 mol) of 3-bromo-4-n-nonyloxybenzoyl chloride are added dropwise and the mixture is stirred at this temperature for 90 minutes and then again at about 25 ° C. to 30 ° C. for 90 minutes. The reaction mixture is then heated to about 80 ° C. in the course of one hour and stirred at this temperature for four hours. After cooling to room temperature, 3.5 g of P ₄ S _{10 are} added. After the exothermic reaction has subsided, the mixture is heated to 50 ° C. within one hour and stirred at this temperature for about 90 minutes. Now the reaction mixture is heated to a temperature between 70 and 80 ° C, and it is stirred for 4 to 6 hours within this temperature interval. After cooling to room temperature, 25 ml of ethanol are added, the solution is poured into about 250 ml of ice water and neutralized with 10% sodium hydroxide solution. The product is filtered off, washed with 2 l of water (25 ° C), then dried and recrystallized from ethanol / butanol (ratio 6: 1) with activated carbon. The cis / trans isomer mixture is separated by fractional crystallization as in Example 1.

Yield:, 580% crude product, 540% trans product, 5K 81 S _A 113.5 N 117 I.

Example 3 Preparation of 2,5-bis (trans-4-n-butylcyclohexyl) -1,3,4- thiadiazole (Verb.3.1)

1.98 g (0.01 mol) of 4-n-butylcyclohexane carboxylic acid hydrazide are stirred in 50 ml of benzene-pyridine mixture (ratio 8: 1) and adjusted to a temperature of about 5 ° C. by ice cooling. Then 2.02 g (0.01 mol) of 4-n-butylcyclohexane carboxylic acid chloride are added dropwise, the mixture is stirred for one hour at this temperature and then for a further 30 minutes at room temperature. The reaction mixture is then heated to 80 ° C. in the course of 30 minutes and stirred at this temperature for 6 hours. After cooling to room temperature, 3.5 g of P ₄ S ₁₀ are slowly added.

After the exothermic reaction has subsided, the reaction mixture heated to 50 ° C within one hour and stirred at this temperature for an hour. Subsequently heated to 70 to 80 ° C and stirred at this Temperature about 6 hours. The approach is at room temperature cooled and mixed with 30 ml of ethanol. The solution is poured into 300 ml of ice water and with 10% sodium hydroxide solution neutralized. The raw product is suctioned off with plenty of water (25 ° C) washed, dried and then recrystallized from ethanol / activated carbon.

The cis / trans isomers are separated by fractional ones Crystallization analogous to example 1.

Yield:, 585% crude product, 541% trans product, 5K 65.5 S _B 162 I

Example 4 Preparation of 2- (trans-4-n-butylcyclohexyl) -5- (trans-4-n- heptylcyclohexyl) -1,3,4-thiadiazole (Verb.4.1)

1.98 g (0.01 mol) of 4-n-butylcyclohexanecarboxylic acid hydrazide are stirred in 100 ml of benzene-pyridine mixture (ratio 8: 1) and cooled to a temperature between 10 ° C. and 15 ° C. 2.45 g (0.01 mol) of 4-n-heptylcyclohexanecarboxylic acid chloride are slowly added dropwise within this temperature interval and the mixture is stirred at this temperature for 90 minutes. The reaction mixture is then heated to 80 ° C. and stirred at this temperature for 5 hours. After cooling to room temperature, 3.5 g of P ₄ S _{10 are} added. After the slightly exothermic reaction has subsided, the mixture is heated to 60 ° C. within one hour and stirred at this temperature for a further 1.5 hours.

The reaction mixture is then heated to 80 ° C. and stirred at this temperature for 6 hours. After cooling, about 30 ml of ethanol are added, the solution is stirred into 300 ml of ice water and neutralized with 10% aqueous NaOH solution. The crude product is filtered off, washed with plenty of cold water and taken up in diethyl ether. The ethereal solution is washed twice with 400 ml of cold water and then dried over Na ₂ SO ₄ .

The diethyl ether is distilled off on a rotary evaporator and the crude product is recrystallized from ethanol / activated carbon. The cis / trans isomers are separated by fractional ones Crystallization.

Yield:, 585% crude product, 538% trans product, 5K ¹⁾ S _B 174 I

¹⁾

Does not crystallize after 10 days at 30 ° C out.

The following were substituted analogously to Examples 1-4 1,3,4-thiadiazoles synthesized.

In the tables, K = crystalline-solid, S ₁ , S ₂ , S ₃ = unspecified smectic phases, S _A , S _B = smectic A or B, N = nematic, I = isotropic.

Table 1

Table 2

Table 3

Table 4

Exemplary embodiments for a more detailed explanation of the application Example I

For a basic mix of GM

27 mol%, 54-n-pentyloxybenzoic acid (4-n-octyloxyphenyl ester) 24 mol%, 54-n-methoxybenzoic acid (4-n-hexyloxyphenyl ester) 12 mol%, 54-n-hexyloxybenzoic acid (4-n-heptyloxyphenyl ester) 37 mol%, 54-n-hexylbenzoic acid (4-n-butyloxyphenyl ester)

15 mol% of 2- (trans-4-n-butylcyclohexyl) -5- (4-n-hexylphenyl) - 1,3,4-thiadiazole (compound 1.7) were added. The clarification temperature increases from 70 to 88 ° C. The dielectric anisotropy of the nematic mixtures decreases from Δε (basic mixture) = -0.37 to Δε = -1.02 at 23 ° C.

This corresponds to an effective dielectric anisotropy of Δε = -4.8 for compound 1.7

Example II

10 mol% of 2,5-bis- (trans-4-n- butylcyclohexyl) -1,3,4-thiadiazole (Verb.3.3) or

10 mol%, 52,5-bis (trans-4-n-hexylcyclohexyl) -1,3,4-thiadiazole (Verb. 3.5) or 10 mol%, 52, - (trans-4-n-hexylcyclohexyl) -5- (trans-4-n-octylcyclohexyl) - 1,3,4-thiadiazole (Verb. 4.2)

added.

The dielectric anisotropy of the nematic mixtures decreased from Δε (basic mixture) = -0.36 to Δε = -0.84 ( compound 3.3) or Δε = -0.91 compound 3.5) and Δε = -0.82 ( 3.2) at 25 ° C. This corresponds to an effective dielectric anisotropy of -5.2 (Verb. 3.3) or -5.9 (Verb. 3.5) and -5.0 (Verb. 4.2). The clarification temperatures increased by 5 ° C by adding the respective substances.

Example III

GM was added to the basic mixture mentioned in Example I. 43 mol% of a mixture of

8.1 mol%, 52- (trans-4-n-butylcyclohexyl) -5- (3-bromo-4-n- nonyloxyphenyl) -1,3,4-thiadiazole (Verb 1.10) 45.4 mol%, 52- (trans-4-n-pentylcyclohexyl) -5- (4-n-hexylphenyl) - 1,3,4-thiadiazole (Verb 1.8) 46.5 mol%, 52- (trans-4-n-butylcyclohexyl) -5- (4-n-hexylphenyl) - 1,3,4-thiadiazole (Verb 1.7)

added. The colorless mixture is nematic at 20 ° C and converts to the isotropic phase at 95 ° C. The dielectric anisotropy of the mixture is Δε = -2.7 at 20 ° C. The threshold voltage for the DAP effect is 1.8 V at 58 ° C and 2 V at 20 ° C. The dynamic scattering effect only occurs above U = 15 V.

Example IV

The mixture given in Example III is 1 percent by weight of the red dye

transferred. With homeotropic starting orientation, at Room temperature a color change from faint pink to red observed at U = 2 V.

Example V

The basic mixture mentioned in Example I are each

3 mol%, 52- (trans-4-n-butylcyclohexyl) -5- (4-cyanophenyl) - 1,3,4-thiadiazole (compound 2.1)
or 3 mol%, 52- (trans-4-n-hexylcyclohexyl) -5- (4-cyanphenyl) - 1,3,4-thiadiazole (Verb.2.2)

added.

The dielectric anisotropy rises to -0.05 or -0.07 at 20 ° C. The effective dielectric anisotropy of the dissolved components is Δε = 11 (Verb. 2.1) and Δε = 10.3 (Verb. 2.2). The clearing points increase by 5 degrees.

Example VI

To the basic mixture specified in Example I 52 mol% of a mixture of

52 mol%, 52,5-bis (trans-4-n-butylcyclohexyl) -1,3,4-thiadiazole (Verb 3.3) and 48 mol%, 52,5-bis (trans-4-n-hexylcyclohexyl) -1,3,4-thiadiazole (Verb.3.5)

added. The clarification temperature of the mixture increases by 26 ° C compared to the basic mixture. The dielectric anisotropy drops from Δε (basic mixture) = -0.35 to Δε = -2.6 at 46 ° C. The threshold voltages for the reorientation of a homeotropic to a planar orientation (DAP effect) are 1.6 V at 80 ° C and 2.5 V at 46 ° C (measuring frequency / 200 Hz). At 80 ° C the dynamic scattering effect is observed above 15 V, while at 46 ° C it only occurs above 30 V (measuring frequency: 20 Hz). Dielectric relaxation effects, which could be caused by connection 3.3 and 3.5, are not observed up to frequencies of 100 kHz.

Example VII

To ensure good miscibility with other substances, too have a high negative dielectric anisotropy, to demonstrate is a mix of

produced.

At 25 ° C, ε _II = 4.4 and Δε = -2.2 were found for the mixture. The threshold voltage for the DAP effect is 2.1 V.

The mixture changed from nematic at 80.5 ° C into the isotropic phase.

Claims (7)

1.Crystalline-liquid mixtures with negative dielectric anisotropy, low melting temperatures and high clarification temperatures or with positive dielectric anisotropy and high clarification temperatures for modulating the transmitted or reflected light and for reproducing numbers, characters and images, both in the single-frequency and in the two-frequency method in that, as the mixing partner, one or more representatives of the 2-sub-5- (trans-4-n-alkylcyclohexyl) 1,3,4-thiadiazoles of the general formula in which R ₁ = C _m H _{2 m + 1} ,
X is a single bond or an oxygen atom
and R ₂ = H, Br, CN or CH ₃
and n and m are from 1 to 12,
where R _{2 is} not H when X is an oxygen atom,
contain. 2. Crystalline-liquid mixtures according to claim 1, characterized in that these mixtures are cholesterol crystalline liquid compounds or chiral smectic Contain liquid crystals. 3. Crystalline-liquid mixtures according to claim 1, characterized in that these mixtures are not liquid-crystalline Contain substances, especially dyes. 4. Crystalline-liquid mixtures according to claims 1-3, characterized in that they are compounds of the formula as mixing partners wherein X is a single bond or an oxygen atom
R ₂ H, Br, CH or CH ₃
n and m represent 1 to 12,
where R _{2 is} not H when X is oxygen,
contain. 5. Crystalline-liquid mixtures according to claims 1-3, characterized in that they are compounds of the formula as mixing partners where n is 1 to 12,
contain. 6. Crystalline-liquid mixtures according to claims 1-3, characterized in that they are compounds of the formula as mixing partners where n and m are 1 to 12,
contain 7. Process for the preparation of 2-substituted-5 (trans-4n-alkylcyclohexyl) -1,3,4-thiadiazole derivatives of the general formulas in which R ¹ = C _n H _{2 n + 1} -,
R ² = Br, CH ₃ , CH, H
m, n = 1 to 12,
where R _{2 is} not H when X is an oxygen atom
from carboxylic acid hydrazides and cyclization with P ₄ S ₁₀ , for crystalline-liquid mixtures with negative dielectric anisotropy according to claim 1, characterized in that 4-n-alkylcyclohexanecarboxylic acid hydrazides are reacted with substituted benzoic acid chlorides or cyclohexanecarboxylic acid chlorides, subsequently in an inert solvent, preferably in benzene, at 60 to 80 ° C in the presence of tertiary nitrogen bases, e.g. B. pyridine, cyclized and the trans-Iosmeren are separated by fractional crystallization from ethanol / butanol.