JPH0269591A - Dichroic dye for liquid crystal display - Google Patents

Abstract

PURPOSE:To obtain the subject dye with high dichroic ratio excellent in durability and solubility in liquid crystals and consisting of a novel red-based dichroic dye having an anthraquinone skeleton. CONSTITUTION:Objective dyes represented by formula I [R1 is (alkyl or alkoxy substituted)phenyl, (alkyl or alkoxy substituted)cyclohexyl; R2 is H, alkyl, alkoxy, alkoxyalkoxy or alkylcarboxyloxy]. For synthesis of the above- mentioned dye, 1,5-dihydroxy-4-nitro-2,6-substituted methylanthraquinone compound of formula II is reacted with a thiophenol in the presence of a base such as potassium carbonate or potassium hydroxide in a polar organic solvent such as dimethyl sulfoxide or isopropanol.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a novel red dichroic dye used in liquid crystals, a liquid crystal composition containing the dye, and a display using this composition. It is related to the device.

[Problems to be solved by conventional techniques and inventions] 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 display requires a combination with two polarizing plates, and there are many restrictions when using them. The reality is that people are suffering from this. As an alternative liquid crystal display method, a so-called guest-host type liquid crystal display that utilizes the electro-optical 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 are already being used in watches and home appliances. , and are beginning to be used as display elements in industrial instruments and the like.

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. By applying this voltage, the liquid crystal molecules change their orientation from the "off" state to the "on" state, but at the same time, the dichroic dye molecules also change their orientation, resulting in absorption of light by the dye molecules in both states. It is based on the principle of varying degrees and indications.

The dichroic dye used here must (I) have sufficient coloring ability in a small amount, (2) exhibit large contrast, (3) have sufficient compatibility with liquid crystals, and (4)
) The minimum requirements are that the device has excellent durability, is stable, and does not deteriorate the performance of the device even after long periods of use.

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 provide clear display for practical use.

[Means to solve the problem]

The inventors of the present invention conducted extensive studies in light of the above circumstances, and as a result, they discovered a new red dichroic dye that has a large dichroic ratio and is excellent in durability.

That is, the present invention provides a liquid crystal dye having the formula (I) (wherein 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 h is a hydrogen atom, an alkyl group, an alkoxy group, an alkoxyalkoxy group, or an alkyl group. (represents carbonyloxy group)
The present invention provides a dichroic dye having a novel red anthraquinone skeleton represented by:

The dichroic dye of the present invention is characterized by its anthraquinone skeleton.
A substituted benzyl group or a substituted cyclohexylmethyl group is introduced at the 4-position and 6-position, and a p-substituted phenylthio group is introduced at the 4-position. The solubility and durability in liquid crystals are significantly improved.

The liquid crystal dye according to the present invention is represented by the general formula (I), and specific examples of R3 in the general formula (I) are substituted with methyl, ethyl, isopropyl, methoxy, ethoxy, isobutyloxy groups, etc. Examples include phenyl groups and cyclohexyl groups and cyclohexyl groups substituted with methyl, ethyl, n-butyl, methoxy, ethoxy, n-butyloxy groups, and specific examples of R2 include hydrogen atoms, methyl, ethyl, n- - Alkyl groups such as butyl groups, alkoxy groups such as methoxy, ethoxy, n-butyloxy groups, alkoxyalkoxy groups such as methoxymethoxy, methoxyethoxy, and ethoxyethoxy groups,
Examples include alkylcarbonyloxy groups such as an acetyloxy group, an ethylcarbonyloxy group, and an n-propylcarbonyloxy group.

The dichroic dye of general formula (I) of the present invention can be easily synthesized using conventional methods.

That is, the 1,5-dihydroxy-4-ditro-2,6-substituted methylanthraquinone compound of general formula (II) (wherein R1 represents the same substituent as R1 in general formula (I)) is converted to dimethyl sulfoxide. , in the presence of a base such as potassium carbonate or potassium hydroxide in a polar organic solvent such as isopropanol, to form a compound of the general formula (I
) can be obtained.

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.

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 a commonly used display device.

The liquid crystal used is, for example, 4-cyano-4'-n-
Pentylbiphenyl, 4-cyano-4'-n-7'lopoxybiphenyl, 4-cyano-4'-n-pentoxybiphenyl, 4-cyano-4'-n-octoxybiphenyl, 4-cyano-4 Cyano-biphenyl liquid crystal mixtures such as ゛-n-pentylterphenyl (for example, Merck & Co., Ltd. product code E-8), or trans-4-n-propyl (4-cyanophenyl)-cyclohexane, trans-4-n- Cyclohexane liquid crystals such as pentyl-(4-cyanophenyl)-cyclohexane, trans-4-n-hebutyl-(4-cyanophenyl)-cyclohexane, trans-4-n-pentyl-(4'-cyanobiphenyl)cyclohexane, etc. Examples include mixtures (for example, Merck & Co. product codes ZLI-1132 and ZL4-1840).

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

The liquid crystals are 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, tetrazine liquid crystals, and other liquid crystals alone or as a mixture. Can be used.

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 it is generally 0.1 to 1 O to the liquid crystal. It is advisable to use a concentration of 0.1 to 5% by weight, preferably 0.1 to 5% by weight.

Furthermore, it is also possible to mix the dichroic dye according to the present invention with other dichroic dyes or with a dye without dichroism and use it to obtain a desired hue, and there are no limitations on the dichroic dye. Dissolution into the liquid crystal is carried out 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 to obtain the desired liquid crystal composition for color display. be able to.

[Action and effect]

Various dichroic dyes have been proposed for use in conventional guest-host liquid crystal display systems, but those that exhibit a large dichroic ratio lack durability, while others have excellent durability but are not practical. Although it still has drawbacks such as not having enough dichroism to enable clear display, the dichroic dye of the present invention represented by the formula -i has a large dichroic ratio and solubility. At the same time, durability was significantly improved.

As described above, this dye is extremely valuable in practice.

〔Example〕

Synthesis examples of the andranquinone dichroic dye of the present invention are shown below, and Table 1 shows the structures of typical dyes, Merc
The dichroic ratio and solubility in liquid crystal ZLI-1840 manufactured by Company K are shown. 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 10μ thick liquid crystal that had been previously treated to achieve homogeneous alignment. After being sealed in a liquid crystal cell, the absorbance was measured by placing it in the optical path of a spectrophotometer and applying linearly polarized light parallel to the liquid crystal alignment (All), and the absorbance measured by applying linearly polarized light perpendicular to the liquid crystal alignment (A top) The dichroic dyes of the present invention all exhibit an extremely high dichroic ratio. "Parts" in the examples indicate parts by weight.

Compound shown in Example-1, 2,6-piscyclohexylmethyl-1,5-dihydroxy-4-nitroanthraquinone 4
8 parts, 14 parts of potassium carbonate and 17 parts of p-n-butylthiophenol! Isopropyl alcohol 1,500
After stirring at 50° C. for 2 hours under a nitrogen stream, the reaction was completed by heating under reflux for 1 hour. 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.

52 parts of a crude product of the compound 4-(4-n-butylphenylthio)2.6-piscyclohexylmethyl-1.5-dihydroxyanthraquinone represented by was obtained. This was dissolved in toluene and separated and purified by column chromatography using a column packed with silica gel to obtain the dye of sewage 1 shown in Table 1 below.

Next, place Merck's liquid crystal ZLI-18401 in a small beaker.
1 part of the above dye was added to 0 parts and heated to about 80°C to make a completely clear solution.Then, the contents were left to cool, and this colored liquid crystal was sealed in a liquid crystal display element under reduced pressure. . This display device showed a red color when no voltage was applied, and only the electrode portions became colorless when a voltage was applied, showing good contrast. Further, the dichroic ratio was 15.3 at a maximum absorption wavelength of 522 nm.

Further, light irradiation was performed for 200 hours using a sunshine weather meter, but no change was observed. Good Example - 1,5-dihydroxy-2,6-bis(4-
Methylbenzyl)-4-nitroanthraquinone was reacted with thiophenol in exactly the same manner as in Example 1 to form 1,5-dihydroxy-2,6-bis(4-
methylbenzyl)-4-thiophenoxyanthoaraquinone was obtained (dye number 6 in Table 1).

The dichroic ratio of this purified dye was 15.6 at the maximum absorption wavelength of 525rue. Further, 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 Table 1 shows the dichroic ratios of dyes synthesized and purified according to these methods.

2,6-bis(4-ethylbenzyl) -1 represented by
, 5-dihydroxy-4-nitroanthraquinone was reacted with 4-ethoxythiophenol in exactly the same manner as in Example 1 above to obtain 4-(4-ethoxyphenylthio) represented by the following formula: -2,
6-bis(4-ethylbenzyl)-1,5-dihydroxyanthraquinone was obtained (N117 dye in Table 1), and the dichroic ratio of this purified dye was 15.5 at the maximum absorption wavelength of 526rv. Further, in a 200 hour light resistance test using a sunshine weather meter, no deterioration in performance was observed and good results were shown.

Claims (1)

[Claims] Formula (I) ▲Mathematical formulas, chemical formulas, tables, etc.▼(I) (In the formula, R_1 is a phenyl group that may be substituted with an alkyl group or an alkoxy group, or an alkyl group or an alkoxy group. (represents a cyclohexyl group which may be substituted with , and R_2 represents a hydrogen atom, an alkyl group, an alkoxy group, an alkoxyalkoxy group, or an alkylcarbonyloxy group).