JPH0653854B2 - Polyazo dichroic dye for liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a novel violet to blue-violet type dichroic dye for use in liquid crystals, a liquid crystal composition containing the dye, and further to this composition. The present invention relates to a display device using.

(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 downsizing. Most of the liquid crystal display elements currently in use utilize the electro-optical effect of twisted nematic liquid crystal, and display is made with the requirement of combining two polarizing plates. The reality is that there are many restrictions. As an alternative liquid crystal display method, a so-called guest-host type liquid crystal display utilizing the electro-optical effect of a colored liquid crystal composition in which a dichroic dye is dissolved in nematic liquid crystal has been studied, and some of them have already been considered as watches and home appliances. It has begun to be used as a display element in products and industrial instruments.

The principle of this guest-host liquid crystal display system is that the dichroic dye molecules that are guests are aligned 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. , It is based on the principle that the degree of light absorption by the dye molecules applied to 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.

Various dichroic dyes have been proposed to meet the above conditions, and some have already begun to be used in digital clocks, meters, etc., but those exhibiting a large dichroic ratio have poor durability. In many cases, however, there are drawbacks that need to be improved, such as excellent durability but not dichroic enough to make a clear display practically.

(Means for Solving the Problems) The inventors of the present invention have made intensive studies as a result of such a situation, and as a result, have developed a novel dichroic dye having a large dichroic ratio and excellent durability. I came to find out.

That is, the present invention is a liquid crystal dye, represented by the general formula (I) [In the formula, Z _{1 to} Z ₂ are a hydrogen atom, an alkyl group, an alkoxy group, an optionally substituted cycloalkyl group, an alkoxyalkoxy group, a halogen atom, a cyano group, or a dialkylamino group, and Y ₁ is , A hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom, Ar is Is.

X is a hydrogen atom or an alkyl group, Y ₂ is a hydrogen atom, a halogen atom, a cyano group, an alkyl group, a dialkylamino group, an alkoxy group, an alkoxyalkoxy group,
Or Is. (Here, R is a hydrogen atom or a lower alkyl group.) N is 1 or 2, and when n = 2, the two naphthyl groups may be the same or different. ] A novel polyazo-based dichroic dye of purple to blue-violet represented by the following is provided.

A feature of the dye of the present invention is that a biphenyl benzoxazole skeleton at one end of the molecular long axis and a benzylamine skeleton at the other end are introduced in combination, whereby a similar known azo dichroic dye is obtained. In comparison, dichroism can be significantly improved.

Specific examples of Z ₁ and Z ₂ in the general formula (I) of the dye for liquid crystal according to the present invention include -H, -CH ₃ , -C ₂ H ₅ ,
_{- (CH 2) 2 CH 3} , -CH (CH 3) 2, - (CH 2) 7 CH 3, -CH 2 C (C
_{H 3) 3, - (CH} 2) 10 CH 3, alkyl group, such as, -O-CH _{3,
-O-C 2 H 5, -O-} (CH 2) 7 CH 3, -O-C 2 H 4 CH (CH 3) CH 2 C
_{(CH 3) 3, -O- (} CH 2) 12 CH 3, alkoxy groups such as, An optionally substituted cycloalkyl group such as -OCH ₂
Alkoxyalkoxy groups such as CH ₂ OC ₂ H ₅ , —OCH ₂ CH ₂ OCH ₂ CH (CH ₃ ) ₂ , halogen atoms such as —F, —Cl and —Br, cyano groups and And dialkylamino groups such as Z ₁ , Z ₂ ,
Even in the case of a hydrogen atom, that is, in the case of an unsubstituted benzoxazole ring, the dichroism does not deteriorate, which is advantageous from the viewpoint of production cost.

Specific examples of Y ₁ include -H, -CH ₃ , -C ₂ H ₅ , -OC.
H ₃ , —O—C ₂ H ₅ , —Br, —Cl, —F and the like, and specific examples of Ar include: Groups having a structure such as However, when both Y _{1 s} are hydrogen atoms, dichroism is particularly large, and it is also advantageous in terms of the purity of the reaction product and the purification and production costs of raw materials.

Specific examples of X are _{also, -H, -CH 3, -C 2} H 5, -CH 2
Examples of the benzyl group include CH (CH ₃ ) _{2 and the} like, as well as an unsubstituted benzyl group in which Y ₂ is a hydrogen atom, the following.

The polyazo dichroic dye of the present invention and the compound of the general formula (I) can be synthesized by the following method.

For example, in the general formula (I), the compound of n = 2 is represented by the general formula (I
I) [Wherein Z ₁ and Z ₂ have the same meanings as in the general formula (I)], a 2- (4′-aminobiphenyl) benzoxazole compound is diazotized by a conventional method to give a compound represented by the general formula (III) [In the formula, Y ₁ represents the same meaning as in the general formula (I). ] To the compound represented by the general formula (IV) [In the formula, Y ₁ , Z ₁ and Z ₂ have the same meanings as in formula (I). ] The monoazo dye represented by this is obtained. Next, this monoazo compound is similarly diazotized to give a compound of the general formula (IV) ′ [In the formula, Y ₁ ′ represents a substituent according to Y ₁ . ] When coupled to a compound represented by the general formula (V) A disazo compound represented by can be obtained.

Further, this compound is diazotized to give a compound of the general formula (VI) or (VII) [In the formula, X and Y ₂ have the same meanings as in formula (I). ] The compound of the general formula (I) can be obtained by coupling to the compound represented by

The crude dye of the general formula (I) thus obtained can be purified by recrystallization, column chromatography or the like to obtain a highly pure dye.

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 obtained by dissolving 1.0% by weight of each dye in a liquid crystal (product number ZLI-1565) manufactured by Merck Co., which is a typical nematic liquid crystal,
A thickness of 10μ, which has been processed in advance for homogeneous orientation.
Absorbance measured by applying linearly polarized light parallel to the liquid crystal array after enclosing it in the m liquid crystal cell and then placing it in the optical path of the spectrophotometer.
(A‖) and the absorbance (A⊥) measured by applying linearly polarized light at right angles to the liquid crystal array, and It is calculated from Each of the dichroic dyes 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.

As the liquid crystal to be used, liquid crystals such as biphenyl liquid crystal, phenyl cyclohexane liquid crystal, schiff base liquid crystal, azoxy liquid crystal, ester liquid crystal, pyrimidine liquid crystal and tetrazine liquid crystal can be used alone or as a mixture.

Furthermore, an optically active substance such as cholesteryl nonanoate or optical rotatory 4-cyano-4'-isopentylbiphenyl was added to the liquid crystal mixture, which was in a cholesteric phase state when no electric field was applied, and was in a nematic phase state when an electric field was applied. It is also possible to use a so-called chiral nematic liquid crystal mixture which undergoes a phase transformation into.

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 molecules may be sufficiently controlled by the alignment of the liquid crystal molecules, but generally 0.01 to 10 wt% 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 to use as a desired hue, and there is no 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 period of time or by heating the liquid crystal to a temperature above the temperature at which the liquid crystal becomes an isotropic liquid. It can be a composition.

The synthesis examples of the polyazo dichroic dye of the present invention are shown below,
Next, Table 1 shows the structures of typical dyes, dichroic ratio in liquid crystal (Merck & Co., Ltd., product code ZLI-1565), and dissolved colors.

In the examples, "part" means "part by weight".

Example 1 Formula After dissolving in 106 parts of the compound represented by the formula and 1000 parts of N, N-dimethylformamide (hereinafter referred to as DMF), 3
After adding 120 parts of 5% hydrochloric acid and cooling to 5 ° C. or lower, 125 parts of 20% sodium nitrite solution was added dropwise and stirred for 2 hours at the same temperature, and then sulfamic acid was added to obtain a diazotized solution. After adjusting the pH of the diazotized solution to 4, α-naphthylamine 36
A DMF solution in which parts were dissolved was added dropwise, and the mixture was stirred at 0 to 5 ° C for 3 hours. The reaction solution was discharged into 1500 parts of water, and the solid obtained by passing was washed with water and dried. 116 parts of a crude product of a disazo dye represented by

6 parts of the obtained disazo compound was dissolved in 150 parts of DMF, 10 parts of 35% hydrochloric acid was added, and the mixture was cooled to 5 ° C or lower. 10% sodium nitrite aqueous solution 10 with vigorous stirring
After adding dropwise, the mixture was stirred at the same temperature for 3 hours, and then sulfamic acid was added to obtain a diazotized solution. N-
A solution prepared by dissolving 3 parts of (p-ethoxybenzyl) -α-naphthylamine in 30 parts of DMF was added dropwise, and the mixture was stirred at 3 to 8 ° C for 3 hours. After discharging into 600 parts of water and adjusting the pH to 6 to 7, it was washed with water and dried. More methanol 1
Dispersed in 00 parts, stirred for 1 hour, dried and dried
formula 7.2 parts of a crude product of the trisazo dye represented by
This was dissolved in toluene and separated and purified by column chromatography using a column packed with silica gel to obtain 2.8 parts of the trisazo dye shown in Table 1 No. 1 described later.

Next, 1% by weight of the above trisazo dye was added to liquid crystal ZLI-1565 manufactured by Merck & Co., Inc. and heated to about 80 ° C. to obtain a completely clear solution. Then, after leaving the contents to cool,
This colored liquid crystal solution was enclosed in a liquid crystal display device.

This display device exhibited bluish purple when no voltage was applied, and when the voltage was applied, only the electrode portions became colorless, showing good contrast. The dichroic ratio in this case was 18.7 at the maximum absorption wavelength of 572 nm.

Example 2 Similar to Example 1, the formula Diazotization of the compound represented by Coupling with amine represented by A disazo dye represented by (Dye of No. 6 in Table-1) The dichroic ratio of this purified dye is at the absorption maximum wavelength of 575 nm.
It was 18.2.

[Example 3] Similar to Example 1, the formula After obtaining the disazo dye represented by And couple it with the formula A trisazo dye represented by (No. 12 of Table-1
This dye has a dichroic ratio at the maximum absorption wavelength of 582 nm.
It was 18.1.

[Example 4] Similar to Example 2, the formula After diazotization of the compound represented by The compound represented by A disazo dye represented by (No. 14 of Table-1
This dye has a dichroic ratio at the maximum absorption wavelength of 539 nm.
It showed 16.4.

[Comparative example]

In the same manner as in Example 1, the following formula having a skeleton in which a phenyl group is bonded to the terminal benzoxazole group instead of a biphenyl group When a dye represented by the formula (3) was synthesized and its dichroic ratio in liquid crystal was measured by the same method as in the example, the absorption maximum wavelength of 529 was obtained.
The value was 10.3 in nm, which was an extremely low value as compared with the dye of the present invention.

Claims (2)

[Claims] 1. A general formula (I) [In the formula, Z _{1 to} Z ₂ are a hydrogen atom, an alkyl group, an alkoxy group, an optionally substituted cycloalkyl group, an alkoxyalkoxy group, a halogen atom, a cyano group, or a dialkylamino group, and Y ₁ is , A hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom, Ar is Is. X is a hydrogen atom or an alkyl group, Y ₂ is a hydrogen atom, a halogen atom, a cyano group, an alkyl group, a dialkylamino group, an alkoxy group, an alkoxyalkoxy group, or Is. (Here, R is a hydrogen atom or a lower alkyl group.) N is 1 or 2, and when n = 2, the two naphthyl groups may be the same or different. ] The polyazo dichroic dye for liquid crystal display shown by these. 2. Y ₁ and Z _{1 to} Z of the compound of general formula (I).
_The dichroic dye according to claim 1, wherein both ₂ are hydrogen atoms.