JPS6126899B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel liquid crystal substance, and more particularly to a liquid crystal compound having a negative dielectric anisotropy and a significantly large value, and substances similar thereto.

Liquid crystal materials with negative dielectric anisotropy are used in light-scattering type liquid crystal display devices that take advantage of the fact that the liquid crystal layer causes dynamic scattering when a voltage is applied, and that utilize the birefringence of liquid crystals by controlling the tilt of the liquid crystal. The so-called DAP type liquid crystal display device displays multiple colors using a polarizing plate.
Furthermore, it is already well known that it is an important component of a so-called Guest-Host type color display device that uses a liquid crystal material containing a specific dye.

The present invention provides a novel liquid crystal compound having negative and large dielectric anisotropy and suitable for constituting liquid crystal materials used in these liquid crystal display devices.

In the above-mentioned liquid crystal display device, it is necessary to lower the minimum voltage required for the liquid crystal to start responding to applied voltage, that is, the threshold voltage, and to show sufficient contrast for visual viewing. In order to reduce the required operating voltage, the dielectric anisotropy (Δε) of the liquid crystal material is required to have a large negative value. However, for example, in MBBA (methoxybenzylidene butylaniline), which is well known as a liquid crystal with negative induced anisotropy, △ε is approximately -0.5, and in liquid crystals made of benzoic acid phenyl esters, △ε is at most -0.4. It is. Therefore, it is desired to develop a liquid crystal material in which Δε has an even larger negative value.
A substance having one cyano group on the side of the molecule has been proposed as one of the substances that can meet such demands.

i.e. bis-(4'-n-alkylbenzylidene)
-2-cyano-1,4-phenylenediamine or 4-alkyl-4'-biphenylcarboxylic acid 4-
Alkyl 2-cyanophenyl ester etc. have been applied for and published. The value of △ε for these substances with one CN group is certainly the same as that of the previous MBBA.
It shows a large negative value compared to , etc., but since the liquid crystal temperature range is higher than room temperature, it cannot be used alone.In order to maintain the liquid crystal state at room temperature, the liquid crystal temperature range must be at room temperature. It is used in combination with other liquid crystal materials that have a small Δε value. However, when these substances are added to such an extent as to bring about the effect of lowering the operating voltage as described above, other physical properties, such as response speed, are adversely affected. It is presumed that this is because these substances have relatively large molecular weights, which increases their viscosity. Therefore, in order to reduce the amount added as much as possible and obtain a sufficient effect, it is desirable to use a substance in which Δε has a larger negative value.

The present inventors focused on this point and searched for a liquid crystal compound having two CN groups on the same side, and as a result, invented a compound of the following formula and filed a patent application (Japanese Patent Application No. 115591-1985). issue).

(However, in the above formula, R ₁ and R ₂ are hydrogen or carbon number 1
~10 alkyl group or alkyloxy group) This compound has a dielectric anisotropy of more than -20 and the above-mentioned
As is clear from the fact that the dielectric anisotropy of the compound of formula () is -4, it can be said that it has an extremely large negative dielectric anisotropy value. However, since the compound of formula () has a relatively high melting point (C-N point), its amount (use ratio) should not be used too much as a component of a liquid crystal composition that maintains a liquid crystal state near room temperature. I couldn't raise it. Therefore, there is a practical limit to the magnitude of the negative dielectric anisotropy of a liquid crystal material containing the compound of formula ().

The present inventors have arrived at the present invention as a result of searching for a new compound with a low melting point and a large negative value of dielectric anisotropy that can further expand this limit value.

That is, the present invention is based on the general formula (However, in the above formula, R represents a linear alkyl group having 1 to 10 carbon atoms.) 3-n-pentyloxy-6-(trans-4'-alkylcyclohexanecarboxy)-phthalonitrile and its It is a manufacturing method.

The compound () of the present invention makes it possible to further expand the limit values that can be reached when using the compound (). That is, Compound () melts at a much lower melting point than Compound () and becomes an isotropic liquid, but when this isotropic liquid is cooled, it enters a smectic state at a temperature that is not too low. This is one of the reasons why this compound () has applicability to the above-mentioned purposes. Furthermore, as a second factor, the compound () has a large negative dielectric anisotropy reaching about -17 to -18. Furthermore, compound () is chemically stable and is a colorless substance that does not absorb light with a wavelength of 360 nm or longer, meaning that its stability will not be impaired when combined with any other known practical liquid crystals. It means that there is no. A specific example of this compound () is 3-n-pentyloxy-6-(trans-4'-
Methylcyclohexanecarboxy)-phthalonitrile, 3-n-pentyloxy-6-(trans-4'-
Ethylcyclohexanecarboxy)-phthalonitrile, 3-n-pentyloxy-6-(trans-4'-
3-n-pentyloxy-6-(trans-4'-
butylcyclohexanecarboxy)-fucuronitrile, [m・p, 82~83℃, SI point 66~67
°C] 3-n-pentyloxy-6-(trans-4'-
(pentylcyclohexacarboxy)-phthalonitrile, [m/p, 95-101.5°C, SI point 76-77
°C] 3-n-pentyloxy-6-(trans-4'-
3-n-pentyloxy-6-(trans-4'-
heptylcyclohexanecarboxy)-phthalonitrile, [m.p., 94-5°C. , S-I point 84-85
°C] etc.

These compounds are produced by the following method. First, 2,3-dicyano-p-hydroquinone is treated with a pentylating agent such as p-toluenesulfonic acid pentyl ester or pentyl bromide in the presence of an alkali to obtain its monopentyl ether, and trans-4- An alkylcyclohexanecarboxylic acid halide is reacted in a basic solvent such as pyridine. Alternatively, 2,3-dicyano-p-hydroquinone is monoesterified by reacting a little over 1 mole of trans-4-alkylcyclohexanecarboxylic acid halide in a basic solvent such as pyridine, and diazopentane is reacted with this monoester. . This raw material, 2,3-dicyano-p-hydroquinone, is a substance that has been known for a long time and has been published in the literature.
Thiele and Meisenheimer, Berichte, 33;
675, (1900). Trans-4-alkylcyclohexanecarboxylic acid is also synthesized by hydrogenating the corresponding substituted benzoic acid. All of these methods are n-
The same applies to alkyl ethers other than pentyl groups. That is, by using a butylating agent instead of a pentylating agent, 3-n-butyloxy-6(trans-4'-alkylcyclohexanecarboxy)phthalonitrile can be obtained. They are, for example, 3-n-butyloxy-6(trans-4'-butylcyclohexanecarboxy)phthalonitrile [m.p., 83°C, S-I
point 51.5℃ (monotropic)], 3-n-butyloxy-6(trans-4'-pentylcyclohexanecarboxy)phthalonitrile [m・p, 92℃,
SI point 64℃ (monotropic)], 3-n-butyloxy-6(trans-4'-hexylcyclohexanecarboxy)phthalonitrile [m/p, 87
℃, SI point of 70℃ (monotropic)], but these are outside the scope of the present invention.

The compound () of the present invention can be mixed with other nematic compounds to prepare a liquid crystal mixture having a large negative dielectric anisotropy. These liquid crystal mixtures allow use at lower voltages than conventional liquid crystal materials in display elements with the so-called guest-host effect, DAP effect, DSM effect.

The liquid crystal material that becomes the base for adding the compound () is a liquid crystal whose Δε has a negative value, or a liquid crystal whose value is small even if it is positive. For example, Schiff liquid crystal compounds represented by MBBA (methoxypenzylidene butylaniline) and EBBA (ethoxybenzylidene butylaniline), ester liquid crystals that do not have a cyano group in the para position (for example, p-methoxybenzoic acid p'-pentylphenyl ester) ), also p-methoxy-
p'-butylazoxybenzene, p-methoxy-
Examples include azoxybenzene-based liquid crystal compounds such as p'-ethylazoxybenzene. Compound
Because of the large negative dielectric anisotropy of (), by adding a small amount of this material to a liquid crystal material with positive dielectric anisotropy, the dielectric anisotropy can be reduced without changing the other properties of the base liquid crystal. It only helps to decrease the sexual value.

The present invention will be explained in more detail below using Examples.

Example 1 (Production of a product in which R is n-C ₅ H ₁₁ in ()) 50 g of 2,3-dicyano-p-hydroquinone,
After stirring and heating 375 ml of 5% aqueous sodium hydroxide solution and 113 g of p-toluenesulfonic acid n-pentyl ester under reflux in a three-necked flask for 7 hours,
The mixture was transferred to a separatory funnel, toluene and an aqueous caustic soda solution were added, and 2,3-dicyano-p-hydroquinone monopentyl ether and unreacted 2,3-dicyano-p-hydroquinone were extracted into the alkaline aqueous layer. The alkaline aqueous layer is acidified with hydrochloric acid, the precipitated solid is collected, and the solid is dissolved in toluene (1) and heated to remove most of the unreacted raw material 2,3-dicyanohydroquinone. When the filtered toluene solution is cooled, crude 2,
Since 3-dicyano-p-hydroquinone monopentyl ether was precipitated, it was filtered and recrystallized from water-containing methanol to obtain crystals with m.p. of 150 to 153°C (yield: 21 g). On the other hand, 19.8 g of trans-p-pentylcyclohexanecarboxylic acid was heated with 5.0 ml of thionyl chloride under reflux for 40 minutes, and excess thionyl chloride was distilled off to obtain an acid chloride. Add the above 2,3-dicyano-p- to 100ml of toluene solution.
Hydroquinone monopentyl ether 20g 300
ml of pyridine was added dropwise to the solution while cooling with water and stirring. After heating and stirring at 50℃ for 1 hour, cool and add to ice.
Add 6N hydrochloric acid to make it acidic, then add 200ml of toluene to separate the liquid, wash with water, wash with 2N caustic soda water, rehydrate, then distill off the toluene, and recrystallize the residue from ethanol to obtain the desired product. 31.7 g of colorless crystals of 3-pentyloxy-6-(trans-4'-n-pentylcyclohexanecarboxy)-phthalonitrile were obtained. This thing is once 95℃
During this melting, needle-like crystals are produced. The needle-like crystals melt at 101.5°C to form an isotropic liquid. When this isotropic liquid is cooled, it becomes a smectic liquid crystal (monotropic) at 76-77°C.

Example 2 (Production of formula () where R is n-C ₄ H ₉ ) 18.4 g of trans-p-butylcyclohexanecarboxylic acid and 50 ml of thionyl chloride were heated under reflux for 40 minutes, and excess thionyl chloride was distilled off. The acid chloride was obtained. On the other hand, 16 g of 2,3-dicyano-p-hydroquinone was dissolved in 60 ml of pyridine, and the toluene solution of the above acid chloride was added dropwise with stirring while cooling with water.
The mixture was heated to ℃ and stirred for 30 minutes. Ice and 6N hydrochloric acid were added to this, and the precipitate was collected by filtration, and this was recrystallized from water-containing methanol and then toluene to obtain 10.3 g of crystals with m.p. of 153-154°C. This is a monoester of trans-pn-butylcyclohexanecarboxylic acid of 2,3-dicyano-p-hydroquinone. 5 g of this was dissolved in 100 ml of ether, cooled to 0°C, and a small excess of an ether solution of diazopentane was added dropwise. After dripping 5
After standing at room temperature for an hour, the ether was distilled off under reduced pressure with a water jet pump, and the residue was recrystallized from ethanol to yield 5.1 g of colorless crystals, the desired product 3.
-n-pentyloxy-6-(trans-4'-n
-butylcyclohexanecarboxy)-phthalonitrile was obtained. This material becomes an isotropic liquid at m/p of 82 to 83°C and becomes a smectic liquid crystal (monotropic) at 66 to 67°C.

The diazopentanes used here were D, W,
Adamson and J. Kenner, J. Chem.
Soc・, 1935, 286, J.Chem・Soc・, 1937,
Synthesized as described in 1551.

Also, in the formula () obtained in the same manner as above, R is
The melting points and the like of the compounds C ₃ H ₇ , n-C ₆ H ₁₃ and n-C ₇ H ₁₅ are shown above in the examples of the compound names.

Example 3 (Use Example 1) A liquid crystal mixture consisting of 2 parts of p-methoxybenzoic acid p'-pentylphenyl ester and 1 part of p-hexyloxybenzoic acid p'-pentylphenyl ester had a nematic temperature of 15 to 48°C. has a range and △ε is +
It is 0.1. Using this as a base liquid crystal, its 9g
3-n-pentyloxy-6-(trans-4
A mixture of 0.9 g of -hexylcyclohexanecarboxy)-phthalonitrile (R = C ₆ H ₁₃ in the formula ()) was vertically aligned and the distance between the electrodes was approximately 10.
When the voltage-current characteristics were measured at a frequency of 1 KHz by enclosing it in a micrometer cell, a value of -1.5 was obtained for Δε. From this result, a value of -17 is determined as Δε of the compound of formula (2) (where R=C ₆ H ₁₃ ) itself by extrapolation. as a guest in this mixture
When we added 1% by weight of dye molecules called D-16 manufactured by BDH and observed the so-called guest-host effect, the threshold voltage for this effect was 3.0V and the saturation voltage was 4.0V.
It was hot. This shows that the compound of formula () has a high negative Δε value, and therefore the voltage required to change the alignment state of the liquid crystal is significantly reduced.

Example 4 (Use Example 2) 33.5 parts of p-methoxybenzoic acid p'-n-pentylphenyl ester, 16.5 parts of p-hexyloxybenzoic acid p'-n-pentylphenyl ester, trans-4-n-butyl 16.5 parts of cyclohexanecarboxylic acid p'-ethoxyphenyl ester, trans-4-n-butylcyclohexanecarboxylic acid p'-hexyloxyphenyl ester
The Δε of the liquid crystal composition consisting of 33.5 parts is negative, its NI point is 58.4°C, and no crystal precipitation is observed even if it is stored at -5°C for a long time. to this
1% by weight of anthraquinone dye D-16 manufactured by BDH Co., Ltd. was added as a guest and was sealed in a 10 μm thick cell that had been subjected to vertical alignment treatment.
The guest-host effect was observed by measuring the change in light transmittance due to voltage using 670 nm light, and its operating characteristics were determined, and the threshold voltage was found to be
The voltage was 4.8V, and the saturation voltage was 6.3V. On the other hand, to 80 parts of this base liquid crystal, 6 parts of 3-n-pentyloxy-6-(trans-4'-pentylcyclohexanecarboxy)phthalonitrile of the present invention, 3-n-
Pentyloxy-6-(trans-4'-hexylcyclohexanecarboxy)phthalonitrile 8
A total of 20 parts of a mixture of three types of compounds, 1 part and 6 parts of 3-n-pentyloxy-6-(trans-4'-heptylcyclohexanecarboxy)phthalonitrile, was added to obtain a liquid crystal composition. The Δε of this liquid crystal composition was -3.8, and the NI point was 50.5°C4.
Using this liquid crystal composition as a host, we added the same guest dye as before, observed the guest-host effect in the same way, and determined its operating characteristics.The threshold voltage was 1.7V, the saturation voltage was 2.6V. Ta. This value is much lower than the value when the compound of the present invention is not added.

The fact that the threshold voltage and saturation voltage can be lowered by adding the compound of formula () of the present invention in this way means that the operating voltage when performing positive color display due to the guest-host effect is significantly increased. This is a very significant point when using liquid crystals.

Claims (1)

[Claims] 1. General formula (However, in the above formula, R represents an alkyl group having 1 to 10 carbon atoms.) 3-n-pentyloxy-6-(trans-4'-alkylcyclohexanecarboxy)-phthalonitrile. 2 General formula characterized by reacting mono-n-bentyl ether of 2,3-dicyano-p-hydroquinone with trans-4-alkylcyclohexanecarboxylic acid halide in a basic solvent (However, in the above formula, R represents an alkyl group having 1 to 10 carbon atoms. 3-n-pentyloxy-6-trans-4'-alkylcyclohexanecarboxy)
-Production method of phthalonitrile. 3 4 of 2,3-dicyano-p-hydroquinone
-A general formula characterized by reacting 1-diazopentane with a monoester with alkylcyclohexanecarboxylic acid (However, in the above formula, R represents an alkyl group having 1 to 10 carbon atoms.) A method for producing 3-n-pentyloxy-6-(trans-4'-alkylcyclohexanecarboxy)-phthalonitrile. 4 General formula (However, in the above formula, R represents an alkyl group having 1 to 10 carbon atoms.) A liquid crystal of 3-n-pentyloxy-6-(trans-4'-alkylcyclohexanecarboxy)-phthalonitrile represented by Compounding agents for compositions.