JPH0546865B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a novel red to blue dichroic dye used in liquid crystals, a liquid crystal composition containing the dye, and a display device using this composition. Prior Art and Problems to be Solved by the Invention In recent years, liquid crystal display elements have come into widespread use from the viewpoints of energy saving and miniaturization. Most of the liquid crystal display elements currently in use utilize the electro-optic effect of twisted nematic liquid crystals, and are required to be combined with two polarizing plates for display. The reality is that there are many restrictions. As an alternative liquid crystal display method, a so-called guest-host type liquid crystal display that utilizes the electro-optic effect of a colored liquid crystal composition in which a dichroic dye is dissolved in a nematic liquid crystal is being considered, and some of these have already been used in watches and home appliances. It is beginning to be used as a display face for products, industrial instruments, etc. The principle of this guest-host type liquid crystal display method is
This is because dichroic dye molecules, which are guests, are aligned and arranged according to the arrangement of liquid crystal molecules, which are hosts. In other words, by applying an external stimulus, usually an electric field, the liquid crystal molecules change their orientation from the 'off' state to the 'on' state, and at the same time, the dichroic dye molecules also change their orientation. ,
It is based on the principle that the degree of light absorption by dye molecules in both states changes, and a display is produced. The dichroic dye used here (1) has sufficient coloring ability in a small amount, (2) has a large dichroic ratio and shows a large contrast between voltage application and no voltage application, (3) (4) It must be highly durable, stable, and do not deteriorate the performance of the device even after long-term use. It is necessary for a limited time. Various dichroic dyes have been proposed as meeting the above conditions, and some have already begun to be used in digital clocks, meters, etc., but those that exhibit a large dichroic ratio lack durability. At present, many of them still have shortcomings that need to be improved, such as having excellent durability but not having enough dichroism to provide clear display for practical use. . Means for Solving the Problems In light of the above circumstances, the inventors of the present invention have made extensive studies and have found a new dichroic dye that has a large dichroic ratio and is highly durable. I've reached it. That is, the present invention uses the general formula () as a dye for liquid crystals. (In the formula, X represents an alkyl group, an alkoxyalkyl group, a phenyl group or a cyclohexyl group which may be substituted with an alkyl or alkoxy group at the P position, and Y ₁ and Y ₂ are a hydrogen atom, a halogen atom, a cyano group, Represents a methyl group or a methoxy group.Z is a lower dialkylamino group, a hydroxyl group,
alkoxy group, P-alkylbenzyloxy group,
P-arylbenzylamino group or

[Formula], R is an alkyl group, a phenyl or cyclohexyl group which may be substituted with an alkyl or alkoxy group at the P position. ) The present invention provides a novel trisazo dye shown in the following. The feature of the dye of the present invention is that it is a trisazo dye in which a biphenyl skeleton having a 4-carbonyloxy group, two naphthyl skeletons, and a phenyl skeleton are introduced into the long axis of the molecule of an azo compound, and each of these is bonded with an azo group. As a result, the dichroism is significantly improved compared to similar known dyes. The general formula of the liquid crystal dye according to the present invention ()
Specific examples of X in -CH ₃ , -C ₂ H ₅ , -(CH ₂ ) ₃ CH ₃ , -(CH ₂ ) ₇ CH ₃ , -
_C2H4CH ( _CH3 )CH2 _{- C} ( _CH3 ) ₃ ,-
( _CH2 ) _{10CH3 ,}

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[Formula], -C ₂ H ₄ OC ₂ H ₅ , - C ₂ H ₄ O(CH ₂ ) ₃ CH ₃ and the like are mentioned. Here X
When having an alkyl group at the end, the number of carbon atoms is preferably 15 or less. Specific examples of Y ₁ and Y ₂ include -H, -Cl, -
F, -CN, _-OCH3 , _-CH3 , etc. Especially Y ₁
and when Y ₂ is −H, the dichroism effect is large;
Further, purification of the reactant is also easy and preferred. Specific examples _of Z include -N( _CH3 ) ₂ , -N( _C2H5 ) ₂ , -OH, _-OCH3 , -O
( _CH2 ) _6CH3 , _-O ( _CH2 ) _{9CH3 ,} Examples include groups having the following structural formula. The trisazo dye of the present invention can be synthesized by conventional methods. Specific representative examples of the dichroic dye of the present invention are shown in Table-1. The dichroic ratio shown in Table 1 is the characteristic value that most characterizes the usefulness of the novel dichroic dye of the present invention. Table -
The dichroic ratio shown in 1 is calculated by dissolving 1.0% by weight of each dye in Merck's liquid crystal (product number E-8), which is a typical nematic liquid crystal, and placing it in a 10 μm thick liquid crystal cell that has been previously treated to achieve homogeneous alignment. After being sealed, the absorbance (A″) was measured by placing it in the optical path of a spectrophotometer and shining linearly polarized light parallel to the liquid crystal alignment.
The absorbance (A⊥) was measured by applying linearly polarized light perpendicular to the liquid crystal alignment, and was calculated using the following formula: dichroic ratio = A″/A⊥.All of the dichroic dyes of the present invention It exhibits an extremely high dichroic ratio. The dichroic dye of the present invention can be incorporated into a liquid crystal and used as a liquid crystal composition for color display in display devices commonly used. The liquid crystal used is, for example, 4-cyano-
4'-n-pentylbiphenyl, 4-cyano4'-n
- Cyano-biphenyl such as propoxybiphenyl, 4-cyano-4'-n-pentoxybiphenyl, 4-cyano-4'-n-octoxybiphenyl, 4-cyano-4'-n-pentylta-phenyl Liquid crystal mixtures (e.g. Merck trade mark E-8), or trans-4-n-propyl-(4-cyanophenyl)-cyclohexane, trans-4-n-
Pentyl-(4-cyanophenyl)-cyclohexane, trans-4-n-heptyl-(4-cyanophenyl)-cyclohexane, trans-4-n
Examples include cyclohexane-based liquid crystal mixtures such as -pentyl-(4'-cyanobiphenyl)-cyclohexane (for example, Merck & Co., Ltd. product code: ZLI-1132). Furthermore, when an optically active substance such as cholesteryl nonanoate or photochromic 4-cyano-4'-isopentyl biphenyl is added to the liquid crystal mixture, it is in a cholesteric phase state when no electric field is applied, and it is in a nematic phase state when an electric field is applied. It is also possible to use so-called chiral nematic liquid crystal mixtures which undergo a phase transformation. The liquid crystal is not limited to the above examples, but may include other biphenyl-based liquid crystals, phenylcyclohexane-based liquid crystals, Schiff-based liquid crystals,
Ester liquid crystals, pyrimidine liquid crystals, tetrazine liquid crystals, and other liquid crystals can be used alone or as a mixture. The dyes according to the present invention may be used alone or in combination of two or more. The concentration of the dye to be used may be within the range where the dye can be dissolved in the liquid crystal and within the range where the dye molecules can be sufficiently controlled by the alignment of the liquid crystal molecules, but generally it is 0.01 to 0.01 to the liquid crystal. concentration of 10% by weight,
It is preferably used at a concentration of 0.01 to 5% by weight. Further, it is also possible to mix the dichroic dye according to the present invention with another dichroic dye or a dye without dichroism and use the mixture to obtain a desired hue, and there is no limitation at all. The dichroic dye is dissolved in the liquid crystal by mixing a predetermined amount of the dye with the liquid crystal and stirring for a long time, or by heating and stirring above the temperature at which the liquid crystal becomes an isotropic liquid, and the desired color display is achieved. It can be used as a liquid crystal composition for use. Examples of synthesis of trisazo dichroic dyes of the present invention are shown below, and Table 1 shows structures of typical dyes,
The dichroic ratio and toluene dissolution color in liquid crystal are shown. Example 1 Formula Dissolve 4.0 parts of the compound represented by in 250 parts of N,N-dimethylformamide, add 10 parts of 35% hydrochloric acid, cool to below 5°C, and dissolve 10% sodium nitrite aqueous solution.
After 10 parts of the mixture was added dropwise and stirred at the same temperature for 2 hours, 2 parts of sulfamic acid was added to obtain a diazotized solution. Add 1.7 parts of α-naphthylamine to this diazotized solution.
A solution dissolved in 5 parts of dimethylformamide was added dropwise, and the mixture was stirred at 0 to 5°C for 2 hours. After adjusting the pH to 4 with 45% caustic soda solution, washing with water and drying, 6.1 parts of a crude disazo dye represented by was obtained. 1.1 parts of the above disazo dye obtained above was dissolved in 50 parts of N,N-dimethylformamide, and 2.0 parts of 35% hydrochloric acid was added.
After cooling to below 5°C, 2.2 parts of 10% sodium nitrite aqueous solution was added dropwise, stirred at the same temperature for 2 hours, and 0.4 part of sulfamic acid was added to obtain a diazotized liquid. 100ml of 50% acetone water
was added to completely dissolve the diazotized solution. Add 100 parts of ice;
A solution of 0.3 parts of phenol dissolved in 30 parts of 10% caustic soda solution was added, and the mixture was stirred at 0 to 5°C for 2 hours to bring the pH to 7 to 9, then filtered, washed with water, dried, and the formula A trisazo dye represented by was obtained, which was dissolved in toluene and separated and purified by column chromatography using a column packed with silica gel to obtain the trisazo dye No. 1 in Table 1 below. Next, in a small beaker, add 43% 4-n-pentyl-4'-cyanobiphenyl, 4-n-propoxy-4'-
Cyanobiphenyl 17%, 4-n-pentoxy-
Add 0.1 part of the above trisazo dye to 10 parts of a liquid crystal mixture consisting of 13% 4'-cyanobiphenyl, 17% 4-n-octoxy-4'-cyanobiphenyl, and 10% 4-n-pentyl-4'-cyanoterphenyl. hand,
Heated to about 80°C to give a completely clear solution. Next, after the contents were left to cool, this colored liquid crystal solution was sealed inside a liquid crystal display element. This display device shows red when no voltage is applied,
When voltage was applied, only the electrode portion became colorless, showing good contrast. Further, the dichroic ratio was 12.0 at the maximum absorption wavelength of 531 nm. Example 2 The formula synthesized in Example 1 0.5 part of the compound in N,N-dimethylformamide
The mixture was heated and dissolved in 50 parts, 2.0 parts of pyridine and 0.8 parts of propionyl chloride were added, and the mixture was reacted at 80°C for 3 hours.
Cool to room temperature, add 200 parts of ice water, separate the precipitated crystals, wash with methanol, and use the formula A trisazo dye represented by was obtained. (Table-1
Dye No. 2) The dichroic ratio of this purified dye has a maximum absorption wavelength of 515 nm.
showed 12.8. Example 3 Formula Dissolve 1.1 parts of the compound represented by in 100 parts of N,N-dimethylformamide, add 5.0 parts of 35% hydrochloric acid, cool to below 5°C, and dissolve 10% sodium nitrite aqueous solution.
After adding 2.2 parts and stirring at 0 to 5°C for 3 hours, 0.3 parts of sulfamic acid was added. This diazotized solution contains N,
Add 0.7 parts of N-dimethylaniline and dilute with NaOH water.
After setting the pH to 4, I left it in the refrigerator overnight. Discharge into 500 parts of ice water, separate the precipitated crystals, wash with water,
dry and formula A trisazo dye represented by was obtained. (Table-1
Dye No. 3) The dichroic ratio of this purified dye has a maximum absorption wavelength of 592 nm.
15.1 was shown in Table 1 below shows the dichroic ratios of trisazo dyes synthesized and purified according to these methods.

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Claims (1)

[Claims] 1 Formula () (In the formula, X represents an alkyl group, an alkoxyalkyl group, a phenyl group or a cyclohexyl group which may be substituted with an alkyl or alkoxy group at the P position, and Y ₁ and Y ₂ are a hydrogen atom, a halogen atom, or a cyano group. , represents a methyl group or a methoxy group. Z represents a lower dialkylamino group, a hydroxyl group, an alkoxy group, a P-alkylbenzyloxy group, a P-arylbenzylamino group or -O
represents C‖O, and R is an alkyl group, a phenyl or cyclohexyl group which may be substituted with an alkyl or alkoxy group at the P position. ) Dichroic trisazo dye for liquid crystals.