JPH0635553B2 - Dichroic azo dye for liquid crystal display - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel dichroic dye of yellow to blue type used for liquid crystals, a liquid crystal composition containing the dye, and a display using this composition. It relates to the device.

Problems to be Solved by Conventional Techniques and Inventions In recent years, liquid crystal display devices have been widely used from the viewpoint of energy saving and miniaturization. Most of the currently used liquid crystal display elements utilize the electro-optical effect of twisted nematic type liquid crystal, and display is performed under the condition that it is combined with two polarizing plates. The reality is that there are many restrictions. As an alternative liquid crystal display method, a so-called guest-host liquid crystal display utilizing the electro-optical effect of a colored liquid crystal composition in which a dichroic dye is dissolved in a nematic liquid crystal has been studied, and a part of it is already used for watches and home appliances. , Are beginning to be used as display elements in industrial instruments and the like.

The principle of this guest-host liquid crystal display system is that the dichroic dye molecules that are guests are oriented and arranged according to the arrangement of the liquid crystal molecules that are hosts. That is, when an external stimulus, which is usually an electric field, is applied, the liquid crystal molecules change their alignment direction from the “off” state to the “on” state, but at the same time, the dichroic dye molecules also change their alignment direction. Based on the principle that the degree of light absorption by dye molecules in both states changes, and display is performed.

The dichroic dye used here has (1) sufficient coloring ability even in a small amount, (2) has a large dichroic ratio, and shows a large contrast when no voltage is applied. ) Basically, it must have sufficient compatibility with liquid crystal, (4) excellent durability, stability, and not deteriorate the performance of the device even if it is used for a long time. It is necessary.

As those having the above conditions, various dichroic dyes have been proposed, and although some have already begun to be used for digital clocks, meters, etc., those exhibiting a large dichroic ratio have poor durability, At present, many of them have drawbacks that need to be improved, such as excellent durability but not having dichroism enough for practically clear display.

Means for Solving the Problems The present inventors have conducted diligent studies in view of such circumstances, and as a result, have found a novel dichroic dye having a large dichroic ratio and excellent durability. It was

That is, the present invention is a liquid crystal dye, represented by the general formula (I) [In the formula, X is a halogen atom, a hydroxyl group, a cyano group, an alkoxy group, (Here, R ₁ is a hydrogen atom or a lower alkyl group,
₂ is a lower alkyl group or a benzyl group which may be substituted at the p-position with an alkyl, alkoxy, or phenyl group. ) Or Is.

(Here, R is a hydrogen atom, a lower alkyl group or a phenyl group.) Ar and Ar ′ are Is.

-W = is -N = or -CH =.

D, E ₁ and E ₂ represent a hydrogen atom, a halogen atom, an alkyl group having 4 or less carbon atoms, a cyano group, or an alkoxy group. ] The present invention provides a novel yellow to blue bisbenzoxazole-based dichroic azo dye for liquid crystal display.

The feature of the dichroic dye of the present invention is that a bisbenzoxazole skeleton is introduced at the center of the long axis of the molecule, whereby the dichroism is remarkably improved as compared with a similar known azo dichroic dye. . Further, a vivid blue color, which was very difficult to obtain with a conventional dichroic azo compound, can be easily obtained by using the dye according to the present invention.

The above X in the general formula (I) for liquid crystal dyes according to the present invention
Specific examples of -Br, -Cl, -F, -I, -O
_{H, -CN, -N (CH 3} ) 2, -N (C 2 H 5) 2, -N (C 3 H 7) 2, -N (C 4 H 9) 2, -OCH ₃ , -OC ₂ H ₅ , -O (CH ₂ ) ₃ CH ₃ , -O (CH ₂ ) ₇ CH ₃ , -OC ₂ H ₅ CH
_{(CH 3) CH 2 C (} CH 3) 3, -O (CH 2) 11 CH 3, And so on.

Further, as the D of the bisbenzoxazole ring and the E ₁ and E ₂ nuclear substituents of the benzene ring, —H, —CH ₃ , —C ₂ H ₅ , —OCH ₃ , —OC ₂ H ₅ , —Br, -Cl, -CN,
And so on.

The compound of the general formula (I) of the azo dye having the bisbenzoxazole skeleton of the present invention can be synthesized by a conventional method.

For example, formula (II) 1,4-bis (4-aminobenzoxa-
2-yl) benzene was diazotized according to a conventional method to give a compound of general formula (I
II) Or (IV) The compound of the general formula (II) is coupled to the compound represented by the formula (1) and then hydrolyzed to obtain the general formula (VII) or (VIII), or the diazotized compound of the general formula (II) is converted to the general formula (V). Or (VI) The compound represented by the general formula (V
II) Or (VIII) A disazo compound represented by

Next, this disazo compound was further diazotized to give a compound of the general formula
(IX) [Wherein X'is a hydroxy group, an amino group, or (Wherein. Show the same meaning as _R 1, _{R 2} of _R 1, _{R 2} is Formula (I)) represents the. ] The tetraazo dye can be obtained by coupling with a compound represented by

Further, when X ′ in the general formula (IX) is a hydroxy group, it is reacted with a desired alkylating agent or acylating agent after completion of the coupling to give a compound represented by the general formula (I).
X'can be converted into a substituent corresponding to X in the compound.

In addition, the compound of the general formula (VII) or (VIII) is added to the compound of the general formula (X) [In the formula, X has the same meaning as in formula (I). ] When the compound represented by the formula] is azomethine-modified, a compound of the general formula (I) in which -W = is a -CH = group can be obtained.

Further, when it is desired to obtain a compound in which X of the general formula (I) is a halogen atom, a cyano group or a phenyl group,
The diazotization decomposition reaction of the compound in which X in the general formula (I) is a —NH ₂ group may be carried out.

The crude dyestuff of general formula (I) thus obtained is recrystallized,
A highly pure dye can be obtained by purification by column chromatography or the like.

Table-1 shows specific representative examples of the dichroic dye of the present invention.

The dichroic ratio shown in Table 1 is a characteristic value that most characterizes the usefulness of the novel dichroic dye of the present invention. The dichroic ratio shown in Table 1 is 1.0% by weight of each dye, which is a typical nematic liquid crystal.
CK liquid crystal (Product No. ZLI-1840) dissolved and pre-treated for homogeneous alignment 10 μm thick
Absorbance measured by applying linearly polarized light parallel to the liquid crystal array after enclosing it in the liquid crystal cell of
(A) and the absorbance (A⊥) measured by applying linearly polarized light at right angles to the liquid crystal array, It is calculated from

The dichroic dye of the present invention exhibits an extremely high dichroic ratio.

The dichroic dye of the present invention can be contained in a liquid crystal and used in a display device usually used as a liquid crystal composition for color display.

Examples of the liquid crystal used include 4-cyano-4′-n-
Pentylbiphenyl, 4-cyano-4'-n-propoxybiphenyl, 4-cyano-4'-n-pentoxybiphenyl, 4-cyano-4'-n-octoxybiphenyl, 4-cyano-4'-n- A cyano-biphenyl liquid crystal mixture such as pentylterphenyl (for example, Merck's product code 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-pentyl- (4'-cyanobiphenyl) -cyclohexane and other cyclohexane-based liquid crystal mixtures (for example, Merck & Co. product symbols ZLI-1132, ZLI-1840) and the like.

Furthermore, when an electric field is not applied, in which an optically active substance such as cholesteryl nonanoate or optically active 4-cyano-4'-isopentylbiphenyl is added to the liquid crystal mixture, it is in a cholesteric phase state, and becomes a nematic phase state in an electric field applied state. It is also possible to use so-called chiral nematic liquid crystal mixtures which undergo phase inversion. The liquid crystal is not limited to the above examples, but other biphenyl liquid crystals, phenylcyclohexane liquid crystals, Schiff base crystals, ester liquid crystals, pyrimidine liquid crystals, tetrazine liquid crystals, other liquid crystals as a single substance or a mixture. Can be used.

The dye according to the present invention may be used alone or in combination of two or more. The concentration of the dye used is within a limit in which the dye is dissolved in the liquid crystal, and the dye molecule may be sufficiently controlled by the alignment of the liquid crystal molecule, but generally 0.01 to 10% by weight relative to the liquid crystal. %, Preferably 0.01 to 5% by weight.

It is also possible to mix the dichroic dye according to the present invention with another dichroic dye or a dye having no dichroism and use it as a desired hue, without any limitation.

The dichroic dye is dissolved in the liquid crystal by mixing a predetermined amount of the dye with the liquid crystal and stirring the mixture for a long time or by heating the liquid crystal to a temperature at which it becomes an isotropic liquid or higher.
The liquid crystal composition for desired color display can be obtained.

Examples Synthesis examples of the tetraazo dichroic dye of the present invention are shown below, and then Table 1 shows typical dye structures including the dyes of Examples 1 to 4 and liquid crystal (liquid crystal ZLI-manufactured by Merck). 1
840). "Parts" in the examples indicate parts by weight. "%" Indicates% by weight.

Example 1 Formula After dissolving 10.2 parts of the compound represented by the above in 600 parts of N, N-dimethylformamide (hereinafter abbreviated as "DMF"), 20 parts of 35% hydrochloric acid was added and the mixture was cooled to 5 ° C or lower and 10% nitrous acid was added. After 55 parts of a soda aqueous solution was added dropwise and stirred at the same temperature for 2 hours, sulfamic acid was added to obtain a diazotized solution. After adjusting the pH of this diazotized liquid to 4, α-naphthylamine 10.3
60 parts of a DMF solution in which 1 part was dissolved was added dropwise, and the mixture was stirred at 0 to 5 ° C for 2 hours.

The reaction solution was discharged into 3000 parts of ice water, filtered, washed with water, dried, 19 parts of a crude product of a disazo dye represented by

Further, 13 parts of this disazo compound obtained was dissolved in 300 parts of DMF, 30 parts of 35% hydrochloric acid was added, and the mixture was cooled to 5 ° C. or lower.
% Sodium nitrite aqueous solution (30 parts) was added dropwise, and the mixture was stirred at the same temperature for 2.5 hours, and then sulfamic acid was added to obtain a diazotized solution.

To this diazotized liquid, 30 parts of N, N-dimethylaniline was added dropwise, and the mixture was stirred at 0 to 5 ° C for 3 hours. After adjusting the pH to 4, 600 parts of ice water was added, filtered, washed with water and dried, 14 parts of an azo dye represented by This was dissolved in toluene and decomposed and purified by column chromatography using a column packed with silica gel to obtain the dye of Table 1 No. 1 described later.

Next, in a small beaker, Merck liquid crystal ZLI-1840 1
00 parts and 0.5 part of the above dye were added and heated to about 80 ° C. to form a completely clear solution. Then, after the contents were left to cool, the colored liquid crystal solution was sealed in the liquid crystal display device.

This display device exhibited a bluish purple color when no voltage was applied, and when the voltage was applied, only the electrode portions became colorless, showing good contrast. The dichroic ratio is at the maximum absorption wavelength of 592 nm.
It was 15.2.

Example 2 As in Example 1, the formula The compound represented by the formula (9) is diazotized and coupled with N- (4-ethoxybenzyl) -1-naphthylamine to give a compound of the formula An azo dye represented by the following formula was obtained (No. 2 dye in Table 1).

The dichroic ratio of this purified dye is 1 at the maximum absorption wavelength of 645 nm.
It showed 6.4.

Example 3 Similar to Example 1, the formula The compound represented by is diazotized and coupled with phenol at pH = 8-9, A compound represented by

This compound was reacted with p-phenylbenzoyl chloride in toluene to give the compound of formula A dye represented by the following formula was obtained (No. 4 dye in Table-1).

The dichroic ratio of this purified dye is 1 at the maximum absorption wavelength of 476 nm.
It showed 2.6.

Example 4 Similar to Example 1, the formula The compound represented by is diazotized and coupled with α-naphthylamine to give a compound of the formula To a disazo dye represented by the following formula, followed by diazo coupling reaction with N, N-dimethylaniline to give a compound of the formula An azo dye represented by the following formula was obtained (No. 8 dye in Table-1).

The dichroic ratio of this purified dye is 1 at the maximum absorption wavelength of 586 nm.
It showed 4.6.

Claims (1)

[Claims] 1. A general formula (I) [In the formula, X is a halogen atom, a hydroxyl group, a cyano group, an alkoxy group, (Here, R ₁ is a hydrogen atom or a lower alkyl group,
₂ is a lower alkyl group or a benzyl group which may be substituted at the p-position with an alkyl, alkoxy, or phenyl group. ) Or Is. (Here, R is a hydrogen atom, a lower alkyl group or a phenyl group.) Ar and Ar ′ are Is. -W = is -N = or -CH =. D, E ₁ and E ₂ represent a hydrogen atom, a halogen atom, an alkyl group having 4 or less carbon atoms, a cyano group or an alkoxy group. ] A bisbenzoxazole-based dichroic azo dye for liquid crystal display represented by: