JPS61221267A - Dichroic azo dye for liquid crystal display - Google Patents

Abstract

NEW MATERIAL:Bisbenzoxazole azo dye of formula I, wherein X is H, halogen, hydroxyl, cyano, alkoxy, etc.; Ar, Ar' are each a group of formula II or III; Y1, Y2 are each H, halogen, alkyl, alkoxy, etc.; W is N, CH; D, E1, E2 are each H, halogen, 4 C or lower alkyl, cyano, alkoxy. USE:Diochroic azo dyes which are yellow to blue, has a high dichroic ratio and excellent durability and is suitable for use as dichroic dyes for liquid crystal display. PREPARATION:1,4-Bis(4-aminozenzoxazol-2-yl) benzene of formula IV is diazotized and then coupled with a compd. of formula V. The resulting product is hydrolyzed to obtain a compd. of formula VI. The compd. of formula VI is diazotized and then coupled with a compd. of formula VII (wherein X' is hydroxy, amino, etc.) to obtain the a o dye of formula I.

Description

[Detailed description of the invention] ji! )=OflJ mJ''2 The present invention relates to a novel yellow to blue dichroic dye used in liquid crystals, a liquid crystal composition containing the dye, and a display device using this composition.

In recent years, liquid crystal display elements have become widely used from the viewpoint 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 element in products, industrial instruments, etc.

The principle of this guest-host type liquid crystal display system is that dichroic dye molecules, which are guests, are aligned and arranged according to the arrangement of liquid crystal molecules, which are hosts. That is, by applying an external stimulus, usually an electric field, the liquid crystal molecules change their alignment direction from the 'off' state to the I-on state, but at the same time, the dichroic dye molecules also change their alignment direction. This is based on the principle that the degree of absorption of light by dye molecules in both states changes to produce a display.

The dichroic dye used here (1) has sufficient coloring ability in a small amount, (2) has a large dichroic ratio and exhibits a large contrast between voltage application and no voltage application. (
3) It must have sufficient compatibility with liquid crystals, and (4) It must have basic conditions such as being highly durable and stable, and not deteriorating the performance of the device even when used for a long time. Minimum required.

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. Although they have excellent durability, they currently have many drawbacks that still need to be improved, such as not having enough dichroism to enable clear display for practical use.

, Means for determining the illumination point In light of the above circumstances, the present inventors have conducted intensive studies and have discovered a new dichroic dye that has a large dichroic ratio and is excellent in durability. reached.

That is, the present invention provides dyes for liquid crystals having general formula (I) [wherein, hydrogen atom, halogen atom, hydroxyl group, cyan group, alkoxy group, alkoxyalkoxy group, -N't:'',
rHere, R is a hydrogen atom or a lower alkyl group optionally substituted with a cyano group, or a lower alkyl group optionally substituted with a cyano group, or a p-position substituted with an alkyl, alkoxy, or aryl group. It is a benzyl group which may be ), +R where R is a hydrogen atom, a lower alkyl group or an aryl group. ), and these are penzene atoms, alkyl groups or alkoxy groups, cyano groups, and hydroxyl groups. ) W is =N- or =CH-.

D%E1 and EHydrogen resistant atom, halogen atom, carbon number 4
Indicates the following alkyl group, cyan group or alkoxy group. ] The present invention provides a novel bisbenzoxazole-based dichroic azo dye for liquid crystal displays with a yellow to blue color. A benzoxazole skeleton has been introduced, which significantly improves dichroism compared to similar known azo dichroic dyes. Furthermore, a vivid blue color, which was extremely difficult to obtain with conventional dichroic azo compounds, can be easily obtained using the dye according to the present invention.

X in the liquid crystal dye general formula CI) according to the present invention
Specific examples include -H, -Br, -CI, -F
, -I, -OH, -CN, -N(CH3)2
, -N(C2H5)2, -N(C3H7)2. -N(
C4H,)2, -N(C2H4CN)z, -NHC
HzC@, -0CHs, -0C2H5, -〇(CH
2) 3CH3, -0(CH2)70H31l-OC2H
40C2H5, 0C2H5CH(CHa)CH2C(C
H3) a.

Now◎-'OCH3%-08(CI(2)20H3゜-o
8(an2)gcH3, -08CH2CH(CH3)C
H2C(CH3)3, -ReC-〇-〇C2H5, -Test H
U-006)'13.

- Sum CH + 0CxoH21, - Trial H CzHs, - Ichito Htsu - C5Hu, U - - Cbe → - C2H5.

-KHeCsH13, -WataruH[Y]-0CzHs, Y
Specific examples of l and Y2 include -CHa, -C2, etc. However, when y and y are both hydrogen atoms, the dichroism effect is large, and the purity of the reactant is It is advantageous and preferable in terms of production costs such as raw materials and raw materials.

In addition, as for the bisbenzoxazole ring and El of the benzene ring, as well as the tetranuclear substituent, CH3s -C2Hs, -0CH3, -QC2H,
, -Br, -Cl, -CN and the like.

The compound of general formula (Il) of the azo dye having a bisbenzoxazole skeleton of the present invention can be synthesized by a conventional method. For example, 1,4-bis(4-aminobenzoxa-
2-yl)benzene was diazotized according to a conventional method.

General formula (g) or @) 工2 [In the formula, Yl and Y2 represent the same meanings as Yl and Y2 in the general formula CI). ] Coupling to a compound represented by formula (4) or (4) or diazotized compound of general formula (CV) [wherein, Yl and ■ are general formula Expressing the same meaning as formula (I)] It is directly coupled to a compound represented by the general formula (
Vl) or (■) [In the formula, η and ■ represent the same meanings as in general formula (I)]
A disazo compound represented by is obtained.

Next, this disazo compound is further diazotized, [in the formula,
X' is a hydroxy group, an amine group, or -<(where R
1, R21 has the same meaning as R1 and R2 in general formula (I). ). ] A tetraazo dye can be obtained by coupling to the compound shown below.

In addition, when X' in the general formula α) is a hydroxy group, after the coupling is completed, by subsequent reaction with a desired alkylating agent or acylating agent, a substitution corresponding to X of the compound of the general formula (I) can be performed. Based on this, X' can be converted.

In addition, the compound of general formula (Vl) or (■) may be added to the compound of general formula [
In the formula, X has the same meaning as in general formula (I). ] By azomethination with a compound represented by formula (I), a compound of general formula (I) in which W is a =CH- group can be obtained.

Furthermore, if you want to obtain a compound of general formula (I) in which X is H, a halogen atom, a cyan group, or a phenyl group,
A diazotization decomposition reaction of a compound in which X in the general formula chain is an -NH2 group may be carried out.

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

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. The dichroic ratios shown in Table 1 are obtained by dissolving 1.0% by weight of each dye in Merck liquid crystal (product number ZLI-1840), which is a typical nematic liquid crystal, and using a thickness lOI# of which the liquid crystal was previously treated to be homogeneously oriented. After being sealed in the liquid crystal cell of rrL, it was placed in the optical path of a spectrophotometer, and the absorbance (AI) was measured by shining linearly polarized light parallel to the liquid crystal alignment, and the absorbance (AI) was measured by shining linearly polarized light perpendicular to the liquid crystal alignment. above) was measured and calculated using the following formula. Some of the dichroic dyes of the present invention exhibit extremely high dichroic ratios.

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 commonly used display devices.

The liquid crystal used is, for example, 4-cyano-4'-n-
Pentylbiphenyl, 4-cyanoal-n+++propoxypiphenyl, 4-cyano4'-n-pentoxybiphenyl, 4-cyano-4'-n-octoxybiphenyl, 4-cyano-4'-n-pentyltaphenyl cyano-biphenyl liquid crystal mixtures such as (e.g. Merck product code E-4), or trans-4-n-pro and leu(4-cyanophenyl)-cyclohexane, trans-
4-n-pentyl-(4-cyanophenyltocyclohexane, trans-4?-n-hebutyl-(4-cyanophenyl)-cyclohexane, trans-4-n-pentyl-(4'-cyanobiphenyl)- Examples include cyclohexane-based liquid crystal mixtures such as cyclohexane (for example, Merck & Co. product codes ZLI-1132 and ZLI-1840).

Furthermore, when an optically active substance such as cholesteryl 7-nanoate or 4-cyano-4'-isopentylbiphenyl is added to the liquid crystal mixture, it is in a cholesteric phase state when no electric field is applied, and it shifts to a nematic phase state when an electric field is applied. It is also possible to use so-called chiral nematic liquid crystal mixtures. The liquid crystal is not limited to the above examples, and may include other biphenyl liquid crystals, phenylcyclohexane liquid crystals, Schiff base liquid crystals, ester liquid crystals, pyrimidine liquid crystals, dorazine liquid crystals, and other liquid crystals alone or in mixtures. Can be used.

Only one type of dye according to the present invention may be used.

It is also possible to use a mixture of two or more types. The concentration of the dye used is within the limit for the dye to dissolve in the liquid crystal, and 1
It is sufficient that the dye molecules are within a range where the alignment can be sufficiently controlled by the alignment of the liquid crystal molecules, but generally it is 0.01
It is preferable to use it at a concentration of 10 to 10% by weight, preferably 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 the liquid crystal to a temperature higher than the temperature at which the liquid crystal becomes an isotropic liquid. It can be a composition.

Synthesis examples of tetraazo dichroic dyes of the present invention are shown below, and Table 1 shows structures of typical dyes, liquid crystals (Meyc
The dichroic ratio and color tone in ZLI-1840 (manufactured by Company K) are shown. "Parts" in the examples indicate parts by weight.

Example 1 After dissolving 10.2 parts of the compound represented by the formula in 600 parts of DMF, 20 parts of 35-thihydrochloric acid was added, the mixture was cooled to below 5°C, and 3 drops of 55 parts of 10% sodium nitrite aqueous solution were added. After stirring 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, 60 parts of a DMF solution in which 10.3 parts of α-naphthylamine was dissolved was added dropwise, and the mixture was stirred at 0 to 5°C for 2 hours. Pour the reaction solution into ice water for 30 minutes.
00 parts, washed with water and dried to obtain 19 parts of a crude product of a disazo dye represented by the formula.

Furthermore, 13 parts of this obtained disazo compound was added to DMF 3
00 parts, add 30 parts of 35-thihydrochloric acid, cool to below 5°C, dropwise add 30 parts of 10% sodium nitrite aqueous solution, stir at the same temperature for 2.5 hours, then add sulfamic acid,
A diazotized solution was obtained.

30 parts of N,N-dimethylaniline was added dropwise to this diazotized liquid, 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 to obtain 14 parts of an azo dye represented by the formula. This was dissolved in toluene and separated and purified by column chromatography using a column packed with silica gel to obtain the dye shown in Table 141 below.

Next, place Merck's liquid crystal ZLI-1840 in a small beaker.
100 parts of the dye and 0.8 part of the above dye were added and heated to about 80°C to form a completely clear solution. After the contents were left to cool, the colored liquid crystal solution was sealed inside a liquid crystal display element.

This display device displayed a bluish-purple color when no voltage was applied, and when a voltage was applied, only the electric bridge portion became colorless, showing good contrast. Moreover, the dichroic ratio is 15. “It was 2.

Example 2 In the same manner as in Example 1, the compound represented by the formula was subjected to diazolysis and coupled with N-(4-ethoxybenzyl)-1-naphthylamine to obtain an azo dye represented by the formula. (7 (Dye No. 2 in Table 1)) The dichroic ratio of this purified dye was 16.4 at the maximum absorption wavelength of 645 nm.

Example 3 In the same manner as in Example 1, the compound represented by the formula was diazotized and coupled with phenol at pH = 8 to 9 to obtain the compound represented by the formula. This compound was p-diazotized in toluene. When reacted with phenylbenzoyl chloride, the dichroic ratio of this purified dye was 12.6 at a maximum absorption wavelength of 476 nm.

Example 4 In the same manner as in Example 1, the compound represented by the formula is coupled with diazo (aluminium, α-naphthylamine) to form a disazo dye represented by the formula, and then subjected to a diazo coupling reaction with N,N-dimethylaniline. An azo dye represented by the formula was obtained. (Dye No. 8 in Table 1) The dichroic ratio of this purified dye was 14.6 at the maximum absorption wavelength of 586nrn.

Table 1 below shows the dichroic ratio of the dyes synthesized and purified according to the method of Kore et al.

(Margin below)

Claims (1)

[Claims] 1 General formula (I) ▲ Numerical formula, chemical formula, table, etc. ▼ (I) [In the formula, X is a hydrogen atom, a halogen atom, a hydroxyl cyano group, an alkoxy group, an alkoxyalkoxy group, ▲Math , chemical formulas, tables, etc. ▼ (Here, R_1 is a hydrogen atom or a lower alkyl group that may be substituted with a cyano group,
Further, R_2 is a lower alkyl group which may be substituted with a cyano group, or a benzyl group which may be substituted at the p-position with an alkyl, alkoxy, or aryl group. ) or ▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲mathematical formulas,
There are chemical formulas, tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, ▲ Mathematical formulas, chemical formulas,
There are tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼
, ▲There are mathematical formulas, chemical formulas, tables, etc.▼,▲Mathematical formulas, chemical formulas,
There are tables, etc. ▼. (Here, R is a hydrogen atom, a lower alkyl group, or an aryl group.) These benzene rings may be replaced by cyclohexane rings. Ar and Ar' are ▲There are mathematical formulas, chemical formulas, tables, etc.▼, or ▲There are mathematical formulas, chemical formulas, tables, etc.▼. (Here, Y_1 and Y_2 are hydrogen atoms, halogen atoms,
They are an alkyl group, an alkoxy group, a cyano group, and a hydroxyl group. ) W is =N- or =CH-. D, E_1 and E_2 are hydrogen atoms, halogen atoms,
Indicates an alkyl group, cyano group, or alkoxy group having 4 or less carbon atoms. ] A bisbenzoxazole-based dichroic azo dye for liquid crystal display. 2. The dichroic azo dye for liquid crystal display according to claim 1, wherein Y_1 and Y_2 of the compound of general formula (I) are hydrogen atoms.