JPS6335193B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dichroic dye used in a guest-host type liquid crystal color display and a method for improving the dichroism of the dye. Dichroic dyes are indispensable materials in guest-host type liquid crystal color displays, and it is no exaggeration to say that the superiority or inferiority of this type of display element depends on the characteristics of such dyes. For this reason, research and development on dichroic dyes has become more active in recent years, and as a result, dyes that are considered to be of practical use have been proposed or developed. The main ones include JP-A No. 55-155054, JP-A No. 56-32578, and JP-A No. 56-62873.
Anthraquinone dyes disclosed in JP-A-Sho et al.
There are azo dyes disclosed in No. 56-57850, No. 56-104984, and the like. Today, research and development of guest-host type display devices using some of these dyes is actively being carried out from various angles with the aim of practical application. It is predicted that it could become the center of color displays in the world. However, when compared with conventional color display technology and peripheral similar technologies that have already been put into practical use, further improvement in display characteristics is desired in order for this device to outperform conventionally used devices. In addition, this type can be used in various ways, such as using one or two polarizing plates.
There are so-called white-tailor types that use polarizing plates, and those that do not use polarizing plates at all.
A system that does not use a polarizing plate is considerably inferior to a system that uses a polarizing plate in terms of contrast and appearance when the same dye is used, and improvements in display characteristics are desired. Measures to improve this include improving the dichroism of dichroic dyes or employing dyes with a larger dichroic ratio, and the development of better dichroic dyes is awaited. In view of such prior art, the present inventors have completed the present invention as a result of intensive studies on dyes with even better dichroism and methods for improving dichroism that can be put to practical use. - New dichroic dyes suitable for use in host-type liquid crystal color displays, methods for improving the dichroism of dyes, and liquid crystal compositions containing dichroic dyes.More specifically, regarding dichroic dyes for liquid crystals, 4 of the phenyl group or cyclohexyl group located at the molecular end of the long axis of the molecule
A method for improving the dichroism of a dye characterized by introducing an alkyl group, an alkoxy group, a cyclohexyl group having an alkyl group or an alkoxy group at the 4th position, or a cyclohexanecarbonyloxy group having another substituent, and such cyclohexane The present invention relates to a group of new and useful dichroic dyes having a carbonyloxy group, and further to liquid crystal compositions containing one or more of these dyes. A group of dichroic dyes having such a cyclohexanecarbonyloxy group include the general formula [],
There are pigments represented by [], [], [] and/or []. General formula [] General formula [] General formula [] General formula [] General formula [] In the above formula, R is a cyclohexanecarbonyloxy group substituted with an alkyl group at the 4-position,
R ₁ is an alkyl group, an alkoxy group, a trifluoromethyl group, a halogen, an alkyloxycarbonyloxy group, a phenyl group having these groups at the 4-position, or a dialkylamino group; R ₂ ,
R ₃ is a hydroxyl group, an alkyl-substituted or unsubstituted amino group, R ₄ , R ₅ are hydrogen, R ₆ , R ₇ ,
R ₈ and R ₉ are a hydroxyl group, an alkyl-substituted or unsubstituted amino group, R ₁₀ is a hydroxyl group, R ₁₁ is an amino group, R ₁₂ and R ₁₃ are hydrogen, and φ ₁ is 4
-R-phenyl group, and φ ₂ is an alkyl group with 4
It is a phenyl group in the position. Further, Y is hydrogen, X is an oxygen atom, and n is a positive number of 2. In addition, in the general formula (), if any one position of the benzene ring is substituted with a methyl group and/or two of the side positions of any one of the benzene rings form a naphthalene structure. This includes cases in which the compound is fused with a benzene ring in order to More specifically, the present invention relates to a dye represented by the following formula. General formula () General formula () General formula () General formula () In the formula, R is a cyclohexanecarbonyloxy group substituted with an alkyl group at the 4-position, R ₁ is a dialkylamino group, R ₂ and R ₃ are a hydroxyl group or an amino group, and R ₄ , R ₅ , R ₆ , R ₇ is a hydroxyl group,
It is an alkyl-substituted or unsubstituted amino group. In dichroic dyes for liquid crystals, the following methods are available for introducing a 4-substituted cyclohexanecarbonyloxy group into the 4-position of the phenyl group or cyclohexyl group present at the molecular end of the long axis of the dye. That is, a method in which a dye precursor having a phenyl group or a cyclohexyl group having a hydroxyl group at the 4-position is reacted with 4-substituted cyclohexane carbonyl halide in an inert solvent, and in the case of an azo dye, a 4-substituted cyclohexane carbonyloxy group is reacted with
A method for obtaining a desired dye by synthesizing in advance an aniline having a position at the position (hereinafter referred to as an aniline derivative), and repeating diazotization and coupling reactions using such a derivative in a conventional manner, general formula [],
For dyes such as [], there is a method of obtaining them by reacting an aniline derivative with a corresponding acid anhydride in an inert solvent. The dye synthesized in this manner is purified using methods such as column chromatography, recrystallization, sublimation, etc., and is used after being made highly pure. Next, the present invention will be explained by giving synthesis examples. [Synthesis example 1] Dissolve 2.2 g of 1-amino-4-{4-(4-pentylcyclohexacycarbonyloxy)phenylazo}naphthalene in 8 ml of dimethylformamide, pour in 18% aqueous hydrochloric acid solution, and stir thoroughly.
Cool to -5℃, add 0.34 g of sodium nitrite, 1.3 g of water.
ml of the solution was added dropwise to cause a diazotization reaction. After the reaction was completed, 0.73 g of N,N-dimethylaniline in an alcoholic solution was added at the same temperature to cause a coupling reaction, and after the reaction was completed, it was poured into a weak alkaline solution and dried to obtain 1.3 g of a crude product of dye number 1 in Table 1. Ta. This dye was purified and highly purified by passing it through a silica gel column several times. This material exhibits a maximum absorption wavelength of 516 nm in chloroform. [Synthesis example 2] Add 6 g of 1.4-diaminoanthraquinone-2,3-dicarboxylic anhydride and 8.5 g of 4-(trans-4-cyclohexanecarbonyloxy)aniline to 50 ml of dichlorobenzene and bring to an external temperature of 100 to 150 ml.
C. for several hours, and after the reaction was completed, 150 ml of methanol was added to the system to collect the resulting crystals, which were dried to obtain 5 g of a crude product of dye number 2 in Table 1. Since this product contained a considerable amount of impurities, it was purified using a silica gel column to achieve high purity. This material exhibits a maximum absorption wavelength of 680 nm in chloroform. [Synthesis example 3] 2-(4-hydroxyphenyl)-1,5-dihydroxy-4,8-diaminoanthraquinone
Dissolve 4.6g in 46ml of pyridine under stirring,
3.2 g of trans-4-heptylcyclohexane carbonyl chloride was added dropwise at ℃, and after the completion of dropping,
After the reaction was completed, 200 ml of methanol was added to collect the resulting crystals and dried to obtain 2.3 g of the crude product of dye number 3 in Table 1. This product was purified by passing it through a silica gel column several times to achieve high purity. This is the maximum absorption wavelength in chloroform.
578nm and 618nm are shown. Other dyes according to the present invention are also synthesized in these synthesis examples 1 to 3.
It is synthesized in the same manner according to either of the following. For example, the dye group of general formula [] is prepared according to Synthesis Example 1, the dye group of general formulas [] and [] is prepared according to Synthesis Example 2, and the dye group of general formulas [] and [] is prepared according to Synthesis Example 3. Synthesized accordingly. These dyes can also be synthesized by other methods mentioned above. Hereinafter, the present invention will be explained in more detail with reference to Examples. Examples Table 1 shows examples of dichroic dyes according to the present invention and the colors and dichroic ratios of the dyes in biphenyl mixed liquid crystal GR-41 (manufactured by Chitsuso Corporation).

【table】

[Table] The dichroic ratios listed in Table 1 are calculated by dissolving a dichroic dye in GR-41, sealing it between two glass substrates with transparent electrodes, and aligning it homogeneously. It was determined by calculating the absorbance in the long axis direction and short axis direction of the molecule at the maximum absorption wavelength of the dye when linearly polarized light with a vertical electric field is applied, and the ratio thereof. This dichroic ratio may vary somewhat depending on the properties of the host liquid crystal and the concentration of the dichroic dye. Next, the present invention will be explained by giving reference examples. Reference Examples Table 2 lists known dyes similar to the dyes listed in Table 1, and their properties are also listed for comparison.

【table】

【table】

[Table] The dichroism ratios listed in Table 2 were measured in the same manner as described above. As is clear from comparing Tables 1 and 2, the dichroism of the dye is achieved by introducing a cyclohexane carbonyloxy group into the 4-position of the phenyl group present at the molecular end of the long axis of the dichroic dye. It can be seen that the results are significantly improved. This difference in dichroism is an extremely significant difference in this technical field, and not only these representative examples but also other dyes according to the present invention have a similar significant difference. The above-mentioned phenyl group may be a cyclohexyl group, and these groups may also be biphenyl groups,
It may constitute a part of a group such as a terphenyl group, a cyclohexyl phenyl group, a phenylcyclohexyl group, or a cyclohexylcyclohexyl group. When these groups are directly connected to the dye backbone, it is commonly used in this field,
This is desirable for improving dichroism because it connects to a so-called "hard skeleton." The development of dyes with good dichroism is extremely important for the practical application of guest-host type display elements, and research and development have been carried out continuously since the beginning of practical research. This is clear from the history. More specifically, development of azo dyes progressed from mono-azo to di- and tri-azo.
Currently, diazo and trisazo dyes suitable for practical use have been discovered. As the number of azo groups increases,
Its synthesis requires more steps, making it even more difficult to develop a dye that has good properties in combination with other properties. A dye having an azo group larger than that of a tetrakisazo dye is likely to be impractical due to the synthesis process, complexity of content, solubility, and other characteristics. According to the present invention, the dichroism value can be easily increased by about 2. This has the same effect as increasing the number of azo groups by one. Among the anthraquinone dyes, those currently said to be practically useful are
There are the dyes described in No. 155054 (corresponding to Control 3 in the present invention) and those described in JP-A-56-32578.
The latter publication contains a large number of disclosures, but its dichroism value is at most 10. (corresponds to order parameter 0.75). Furthermore, those showing this value are found at both positions of the anthraquinone skeleton (2, 6
It is necessary to introduce a phenyl group into the dye (position), which poses various problems in terms of synthesis, yield, and practical use due to characteristics such as solubility of the dye. For anthraquinone dyes, the dichroic ratio is currently 7 to 9.
Most of them have this property, and improvement in dichroism is desired. In the present invention, the dichroism value can be easily reduced to 1.
This problem can be solved because it can be improved by ~2. Similar effects can be achieved with other dyes. As described above, the present invention is characterized by the fact that a phenyl group or a cyclohexyl group exists at the molecular end of the long axis of the dye molecule, and that a specific group is introduced into the 4-position of these groups, and that the dye group into which these groups are introduced is novel and useful. It is characterized by According to the present invention, a group of dyes with excellent dichroism is obtained, and by using these dyes, the display quality of displays using the guest-host system is significantly improved and improved, and the practical application of such technology is promoted.
Furthermore, in some technical fields that are already in practical use, it is possible to improve displays with even better characteristics. Dichroic dyes are usually 0.01 to 20% relative to the host liquid crystal.
It is used at a concentration of 0.1 to 5% by weight, and the selection is made depending on the purpose of use, method, host liquid crystal, etc. The dye group according to the present invention is also used within the above range. The dye according to the present invention may be used alone or in a mixture of two or more, or may be used in combination with a non-dichroic dye, an optically active substance, or other additives. In addition, these pigments include Schizuf, biphenyl, azo, cyclohexylcyclohexane,
It is used for any liquid crystal such as phenylcyclohexane and ester, and due to the structure of the dye, it is more effectively used for liquid crystals having a cyclohexane ring and ester-based liquid crystals. Further, the liquid crystal may be of a nematic type, a cholesteric-nematic phase transition type, a smectic type, or the like. As the display method, any method based on the positive or negative dielectric anisotropy of the liquid crystal may be employed. As explained above, according to the present invention, the dichroism of dichroic dyes can be easily further improved, and a new dye with excellent dichroism is provided. It is possible to improve the display quality, which was considered to be a drawback compared to conventional displays, and promote the practical application of guest-host type displays.
In addition, it can respond to diversification of application fields and technologies, and will greatly contribute to the development of color LCD displays.

Claims (1)

[Claims] 1 General formula (), (), (), or () General formula () General formula () General formula () General formula () (In the formula, R is a cyclohexanecarbonyloxy group substituted with an alkyl group at the 4-position, R ₁ is a dialkylamino group, R ₂ and R ₃ are a hydroxyl group,
or an amino group, and R ₄ , R ₅ , R ₆ , and R ₇ are a hydroxyl group, an alkyl-substituted or unsubstituted amino group. ) is a dichroic dye for liquid crystals.