JPS5993776A - Improvement of solubility of azo dyestuff in liquid crystal and two-color azo dyestuff for liquid crystal - Google Patents

Abstract

PURPOSE:To obtain a color display element having improved solubility of an azo dyestuff especially in a low-visocity nematic liquid crystal, improved display characteristics, and display quality, by introducing a group shown by a specific formula to the end position of a dyestuff molecule. CONSTITUTION:A group shown by the formula I (R1 and R2 are 4-12C alkyl; R3 is lower alkyl introduced to the ortho and meta position of amino group; m is 1-4) is introduced to the end position of a dyestuff molecule, to improve solubility of an azo dyestuff especially in a low-viscosity nematic liquid crystal. A compound shown by the formula II [X is azo dyestuff residue shown by the formula III (p is positive integer); Y is H, azo dyestuff residue, substituent group such as alkyl, alkoxy, (substituted)phenyl, etc.; R4-R7 are H, substituent group selected from hydroxy, amino, alkyl-substituted amino, alkoxy, cyano, nitro] is preferable as the azo dyestuff having the formula shown by the formula I .

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for improving the solubility of an ano-dye in a liquid crystal and a dichroic azo dye for a t-liquid crystal with improved solubility.

2. Description of the Related Art In recent years, there has been active research and development into technology for displaying color by dissolving dyes in liquid crystals and utilizing the color of the dyes or color changes based on the light absorption anisotropy of the dyes. A typical example of this is liquid crystal color display technology that utilizes the Kest-Phos 1-effect. In this technology, it is necessary that the dye (guest l-) has good dichroism, solubility, durability, etc.

Furthermore, dyes are used to improve display quality, especially the contrast of display elements.
Development has been progressing centering on the dichroic mucosa without affecting -. Dyes having a dichroic ratio of 8 to 10, which is at a practical level, have been proposed or developed, and there is currently a demand for the development of dyes having even higher values. In order to improve the dichroism ratio, it is necessary to increase the ratio of the long axis and short axis of the dye molecule as much as possible. However, if an attempt is made to increase this ratio, the dye molecules will gradually become larger, and the solubility of the dye in the liquid crystal will gradually decrease.

By the way, display elements require an appropriate dye concentration in the operating temperature range in order to degrade their display quality, and for this reason, dyes with low solubility in liquid crystals are unsuitable as dichroic dyes and cannot be put to practical use at all. Or, it will be used under restrictions regarding the liquid crystals used, methods, applications, etc. Therefore, the solubility of the ab dye in liquid crystal must be at least 1% or more at room temperature, preferably 2%.
% or more is desirable.

Akira Motoko et al. gave a detailed study on the expansion of dye molecules and the decrease in solubility. They discovered this and completed the present invention.

The present invention relates to a method for improving the solubility of an ab dye in liquid crystal, which is characterized by introducing a group represented by the general formula (CI) at the end of the dye molecule, and a method for improving the solubility of an ab dye in liquid crystal, which is characterized by introducing a group represented by the general formula (I) at the end of the dye molecule. This invention relates to dichroic dyes for liquid crystals with improved solubility characterized by having R8 and R7 in the L formula.
represent the same or different alkyl groups having 4 to 12 carbon atoms, and R3 represents a lower alkyl group such as a methyl group, ethyl group, or propyl group, which is introduced at the ortho or meta position to the amine group. , ITI represents a positive number from 1 to 4.

There are various types of dichroic ab dyes having specific groups according to the present invention, and representative ones include those represented by the following general formulas [■] and [111].

General formula [■] In formula [■], R1, R2, R3 and m are 'C' as above, and φ represents hydrogen or various substituents suitably used as a liquid crystal dye. These substituents include c,
Alkyl group, alkoxy group, halogen, 21.0 group, substituted sulfonyl group, cyano group, trifluoromethyl group, substituted ester group, or phenyl group, hyphenyl group, which may have a substituent such as alkyl or alkoxy, There are cycloalkyl groups and existing groups such as ida element 11 groups.

In addition, when two of the side positions of any one of the benzene rings are fused with benzene rings to form a 1-phthalene structure, and/or when the benzene ring has a methyl group, ethyl group, etc. in the vacant position of the benzene ring. The dichroic dyes may be substituted with a lower alkyl group, an alkoxy group having these lower alkyl groups, a)rogen, or the like.

Here, X represents an azo dye residue represented by the formula C[). R3, R2, R1
and m are the same as above, and P is a positive number. Y is hydrogen, an azo dye residue that is the same as or different from X, or
This represents a substituent such as an alkyl group, an alkoxy group, or a substituted or unsubstituted phenyl group. R4, R, , R6, and R7 represent a substituent selected from hydrogen, a hydroxy group, an amino group, an alkyl-substituted amino group, an alkoxy group, a cyano group, a dil·0 group, and the like.

In addition, in the formula [■], there is also a type of dye in which an azo group is substituted at the beta position of the anthraquinone skeleton, but an ano group S@ is substituted at the alpha position.

Next, the present invention will be explained in more detail with reference to Examples.

Table 1 shows the solubility of the dye of the present invention and the control dye, and also lists dichroism and the like.

The solubility of each compound was determined by preparing a saturated solution of each compound in liquid crystal ZLI 1565, filtering the resulting solution, and making a 0.0% solution of each compound.
Accurately take 1 ml, dissolve it in 200 ml of chloroform, measure the absorbance of this solution at 8 wavelengths of maximum absorption, and calculate t from the already known absorption coefficient for chloroform:

As is clear from Table 1, even dyes with large molecular weights such as trisazo and tetrakisano dyes into which the specific group of the present invention has been introduced are 1% L at room temperature (25°C).
uk, showing 3 to 6 times higher solubility than the control. The same applies to other dyes.

Dichroism is achieved by dissolving a dye in liquid crystal GR-41, sealing it between two glass substrates with transparent electrodes, aligning it in pomonia, and applying linearly polarized light with electric fields parallel and perpendicular to this alignment direction. The absorbance in the long axis direction and the short axis direction of the molecule at the maximum absorption wavelength of the dye was determined, and the ratio was determined. As can be seen from Table 1, the dyes of the present invention into which specific groups have been introduced tend to have slightly lower dichroism. The dichroism ratio at a practical level is said to be 81 Jl, and by devising the molecular structure design, it is possible to improve and improve solubility based on the present invention and at the same time bring the dichroism to a practical level ah. It's easy. The present inventors have already filed patent application No. 111j 57 4158 regarding the direction of dichroism.
No. 5, No. 57-160434 discloses that it is effective to introduce a hyphenyl group, a cuphenyl group, a cyclohexylphenyl group, a phenyl ester group, a noclohexyl ester group, etc. at the molecular end. Taking this technology into consideration makes it possible to develop dyes with excellent solubility and dichroism.

According to the present invention, a group of dyes with excellent solubility can be obtained, and devices using these dyes exhibit various effects. First, the phenomenon of dye precipitation in the device at low temperatures due to the soluble mucous membrane is eliminated, and display characteristics and device life can be improved. Second, the visual color density required by a color display element can be easily achieved and display quality can be maintained.

If a dye with low solubility is used, the color will be pale in a normal device and the display quality will be degraded. For this reason, if such a dye is unavoidably used due to absorption characteristics, etc., it becomes necessary to use a large amount of dye, and for this reason, the device thickness is designed to be large.This causes factors such as deterioration of the response characteristics of the device. In the case of dyes with excellent solubility, the desired color density can be easily achieved.Also, in response to the proposal to reduce the element thickness to improve response characteristics, dyes dissolved in liquid crystal ( By increasing IL, it is possible to easily achieve desired color density and improve display quality.

According to the present invention, it is possible to improve the solubility in liquid crystal. In particular, it has poor solubility in liquid crystals having low viscosity and wide temperature range, such as phenylcyclohexane-based liquid crystals, and mixed liquid crystals.

When the dye is used as a dichroic dye, it is usually 0.01 to 20% by weight, preferably 0.1% by weight based on the liquid crystal.
It is used at a concentration of up to 5% by weight, and its selection depends on the purpose of use, method, host liquid crystal, etc. The dye of the present invention may be used alone, or may be used as a mixture of two or two types, or may be used in combination with a non-dichroic dye, an optically active substance, or other additives. Further, these dyes can be used in any liquid crystal such as Schiff, hypohenyl, ano, cyclohekyne, cyclohexane, and ester.

Furthermore, the liquid crystal may be nematic, cholesteric, nematic-1-nosteric phase transition type, smectic, 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, a color display element with excellent display quality and display characteristics can be produced, and it greatly contributes to the progress and development of liquid crystal color display technology.

patent applicant Japan Photosensitive Dye Research Institute Co., Ltd.

Claims (1)

[Claims] 1) General formula [■] [In the formula, R and R2 represent the same or different argyl groups having 4 to 12 carbon atoms, and R3 is at the ortho or meta position with respect to the amino group. It represents a lower alkyl group to be introduced, and %I11 represents a positive number from 1 to 4. ] A method for improving the solubility of an ano-dye in a liquid crystal, characterized by introducing a group represented by the following into the terminal position of a dye molecule. 2) The method for improving the solubility of an ab dye in a liquid crystal according to claim 1, wherein the liquid crystal is a low-viscosity nematic liquid crystal. 3) General formula [I] In the C formula, R and R2 represent the same or different alkyl groups having 4 to 12 carbon atoms, and R3 is at the ortho position to the axyl group and is at the meta position. It represents a lower alkyl group to be introduced, and m represents a positive number from 1 to 4. A dichroic dye for liquid crystals, characterized in that it has a group represented by ] at the terminal position of the dye molecule.