JP2567057B2 - Dichroic dye for liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a novel red-based dichroic dye for use in liquid crystals,
And a liquid crystal composition containing the dye, and a display device using the composition.

[Problems to be Solved by Prior Art and Invention]

In recent years, liquid crystal display devices have been widely used from the viewpoint of energy saving and miniaturization. Most of the liquid crystal display elements currently in use utilize the electro-optical effect of twisted nematic type liquid crystal, and display is made as an indispensable condition in combination with two polarizing plates. The reality is that As an alternative liquid crystal display method, the electro-optical effect of a colored liquid crystal composition in which a dichroic dye is dissolved in a nematic liquid crystal is used.
So-called guest-host liquid crystal displays have been studied, and some of them have already begun to be used as display elements in watches, home appliances, 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 aligned and arranged according to the arrangement of the liquid crystal molecules that are hosts. That is, by applying an external stimulus, which is usually an electric field, 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) large contrast, (3) sufficient compatibility with liquid crystal,
(4) Basically, it is necessary to have conditions such as excellent durability, stability, and not deteriorating the performance of the device even when used for a long time.

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 problem]

As a result of intensive studies based on such a situation, the present inventors have found a new red dichroic dye having a large dichroic ratio and excellent durability.

That is, the present invention provides a liquid crystal dye of the formula (I) (In the formula, R ₁ represents a phenyl group which may be substituted with an alkyl group or an alkoxy group, or a cyclohexyl group which may be substituted with an alkyl group or an alkoxy group, and R ₂ is a hydrogen atom, an alkyl group or an alkoxy group. Group, an alkoxyalkoxy group, or an alkylcarbonyloxy group) is provided, which provides a reddish novel dichroic dye having a red anthraquinone skeleton.

The feature of the dichroic dye of the present invention is that a substituted benzyl group or a substituted cyclohexylmethyl group is introduced at the 2- and 6-positions of the anthraquinone skeleton and a phenylthio group which may be substituted at the p-position is introduced at the 4-position. Therefore, the dichroic property, the solubility in liquid crystal and the durability are remarkably improved as compared with the similar known anthraquinone type dichroic dye.

The liquid crystal dye according to the present invention is represented by the general formula (I), and specific examples of R ₁ in the general formula (I) are substituted with a methyl, ethyl, isopropyl, methoxy, ethoxy, isobutyloxy group or the like. Phenyl group and unsubstituted phenyl group, cyclohexyl group and unsubstituted cyclohexyl group substituted with methyl, ethyl, n-butyl, methoxy, ethoxy, n-butyloxy group and the like, and specific examples of R ₂ , Hydrogen atom, methyl, ethyl,
Alkyl group such as n-butyl group, methoxy, ethoxy, n
-Alkoxy group such as butyloxy group, alkoxyalkoxy group such as methoxymethoxy, methoxyethoxy and ethoxyethoxy group, acetyloxy group, ethylcarbonyloxy group, n-propylcarbonyloxy group, alkylcarbonyloxy group such as n-butylcarbonyloxy group A group can be mentioned.

The dichroic dye of the general formula (I) of the present invention can be easily synthesized by a conventional method.

That is, the 1,5-dihydroxy-4-nitro-2,6-substituted methylanthraquinone compound of the general formula (II) (Wherein, represents the same substituent as R ₁ R ₁ is in the formula (I))
Can be reacted with thiophenols in the presence of a base such as potassium carbonate or potassium hydroxide in a polar organic solvent such as dimethyl sulfoxide or isopropanol to obtain the compound of the general formula (I).

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.

The dichroic dye of the present invention can be contained in a liquid crystal and used in a display device which is 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- ( A cyclohexane-based liquid crystal mixture such as 4-cyanophenyl) -cyclohexane, trans-4-n-heptyl- (4-cyanophenyl) -cyclohexane, trans-4-n-pentyl- (4′-cyanobiphenyl) -cyclohexane (for example, Merck's product code 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, the state is a cholesteric phase state, and the phase is changed to a nematic phase state when an electric field is applied. It is also possible to use so-called chiral nematic liquid crystal mixtures which are converted. The liquid crystal is not limited to the above examples, other biphenyl liquid crystals, phenylcyclohexane liquid crystals, Schiff base liquid 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 the 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 0.1 to 10% by weight relative to the liquid crystal.
Is preferably used at a concentration of 0.1 to 5% by weight.

Further, the dichroic dye according to the present invention and other dichroic dyes,
Alternatively, a dye having no dichroism can be mixed and used as a desired hue, and there is no limitation. To dissolve a dichroic dye in a liquid crystal, mix a predetermined amount of dye with the liquid crystal,
The liquid crystal composition for a desired color display can be obtained by stirring for a long time or by heating the liquid crystal at a temperature higher than the temperature at which the liquid crystal becomes an isotropic liquid.

[Action and effect]

Various dichroic dyes used in conventional guest-host liquid crystal display systems have been proposed, but those exhibiting a large dichroic ratio have poor durability or excellent durability but are practical. However, the dichroic dye of the present invention represented by the general formula (I) has a large dichroic ratio and solubility. At the same time, the durability was significantly improved.

As described above, the dye is extremely valuable in practical use.

〔Example〕

Hereinafter, synthesis examples of the anthraquinone-based dichroic dye of the present invention are shown, and then Table 1 shows the structures of typical dyes, Merck.
The dichroic ratio and solubility in the liquid crystal ZLI-1840 manufactured by the same are shown. The dichroic ratio shown in Table-1 is a liquid crystal cell with a thickness of 10 μm in which 1.0% by weight of each dye is dissolved in a typical nematic liquid crystal manufactured by Merck (Product No. ZLI-1840) and preliminarily treated for homogeneous alignment. After enclosing it inside, place it in the optical path of the spectrophotometer and measure the absorbance (A ₁₁ ) measured by applying linearly polarized light parallel to the liquid crystal array and the absorbance (A ⊥) measured by applying linearly polarized light perpendicular to the liquid crystal array. Then It is calculated from Each of the dichroic dyes of the present invention exhibits an extremely high dichroic ratio. "Parts" in the examples indicate parts by weight.

Example-1 The following formula A compound represented by 2,6-biscyclohexylmethyl-
48 parts of 1,5-dihydroxy-4-nitroanthraquinone,
14 parts potassium carbonate and pn-butylthiophenol
17 parts was added to 1,500 parts of isopropyl alcohol, and the mixture was stirred under a nitrogen stream at 50 ° C. for 2 hours and then heated under reflux for 1 hour to complete the reaction. The solvent of this reaction mixture was distilled off under reduced pressure, 500 parts of water was added, and the mixture was stirred, filtered, washed with water and dried to obtain the compound of the following formula: Compound represented by 4- (4-n-butylphenylthio)
52 parts of a crude product of -2,6-biscyclohexylmethyl-1,5-dihydroxyanthraquinone were obtained. This was dissolved in toluene and separated and purified by column chromatography using a column packed with silica gel, and N in Table 1 below was used.
A dye of o.1 was obtained.

Next, 1 part of the above dye was added to 100 parts of liquid crystal ZLI-1840 manufactured by Merck & Co., Inc. in a small beaker and heated to about 80 ° C. to obtain a completely clear solution. Then, after the contents were left to cool, the colored liquid crystal was sealed in the liquid crystal display element under reduced pressure. This display device showed a red color when no voltage was applied, and when the voltage was applied, only the electrode portions became colorless, showing good contrast. The dichroic ratio was 15.3 at the maximum absorption wavelength of 522 nm. Further 200 by sunshine weather meter
After irradiation with light for hours, no change was observed and good light resistance was exhibited.

Example-2 The following formula 1,5-dihydroxy-2,6-bis (4-methylbenzyl) -4-nitroanthraquinone represented by the following formula was reacted with thiophenol in the same manner as in Example 1 to give the following formula: 1,5-dihydroxy-2,6-bis (4-methylbenzyl) -4-thiophenoxyantharaquinone represented by the following formula (No. 6 dye in Table 1) was obtained.

The dichroic ratio of this purified dye is 1 at the maximum absorption wavelength of 525 nm.
It showed 5.6. In a 200-hour light resistance test using a sunshine weather meter, no deterioration in performance was observed and good results were shown.

Example 3 2,6-bis (4-ethylbenzyl) -1,5-dihydroxy-4-nitroanthraquinone represented by
In the exactly same manner as in the method of, the reaction with 4-ethoxythiophenol 4- (4-ethoxyphenylthio) -2,6-
Bis (4-ethylbenzyl) -1,5-dihydroxyanthraquinone was obtained (No. 7 dye in Table-1). The dichroic ratio of this purified dye was 15.5 at the maximum absorption wavelength of 526 nm.
In a 200-hour light resistance test using a sunshine weather meter, no deterioration in performance was observed and good results were shown.

Hereinafter, the solubility and the dichroic ratio of the dye obtained by synthesis and purification according to these methods to liquid crystal are shown in Table-1.

Claims (1)

(57) [Claims] 1. A formula (I) (In the formula, R ₁ represents a phenyl group which may be substituted with an alkyl group or an alkoxy group, or a cyclohexyl group which may be substituted with an alkyl group or an alkoxy group, and R ₂ is a hydrogen atom, an alkyl group or an alkoxy group. Group, an alkoxyalkoxy group or an alkylcarbonyloxy group)) for a liquid crystal display.