JP4515059B2 - Dichroic azo dye for liquid crystal and production method thereof - Google Patents

Description

  The present invention relates to an azo dye for liquid crystal exhibiting dichroism and a method for producing the same.

  Liquid crystal display devices are widely used as display devices for notebook personal computers due to their space-saving and lightweight features, and in recent years they are also used as desktop monitors in place of CRTs. is doing. Most of the liquid crystal elements used in these liquid crystal display devices are transmissive elements using a backlight. However, recently developed personal digital assistants (PDAs) need to be able to be driven for a long time with a battery with a limited capacity, and thus a display element with low power consumption is required. As a display element for that purpose, a low power consumption type reflection type element that does not use a backlight is preferable. Among them, a display element using a guest host liquid crystal composition containing a dichroic dye (hereinafter referred to as a guest host type display). The element is excellent as a reflection type element because it does not use a polarizing plate and has high light utilization efficiency and a bright display.

  In order to produce a reflective liquid crystal element that is low in power consumption, bright, and capable of displaying high contrast, the guest host liquid crystal composition is required to have high order parameters, and the liquid crystal used It is necessary to satisfy various conditions such as high solubility of the dichroic dye for the. That is, the order parameter of the guest-host liquid crystal composition and the solubility of the dichroic dye in the liquid crystal greatly affect display quality such as contrast and color reproducibility of the host-guest display element using the liquid crystal composition. Among these, the contrast can be improved by increasing the concentration of the dichroic dye in the liquid crystal composition, but the transmittance (or reflectance) of the missing color is lowered accordingly, and the guest-host display The brightness of the display, which is a feature of the element, is impaired. Therefore, in order to achieve both the brightness of the liquid crystal display and the high contrast, it is necessary to increase the order parameter of the guest-host liquid crystal composition and increase the solubility of the dichroic dye in the liquid crystal.

  Many azo dichroic dyes for use in liquid crystal display elements have been known so far (see, for example, JP-A Nos. 11-228967 and 2000-236994), but the structure is complicated. And disadvantages such as the need to use expensive raw materials, and the solubility in the host liquid crystal was not sufficiently high.

  By the way, as a liquid crystal material used for liquid crystal display by active matrix driving having a large display capacity, a conventionally known liquid crystal material containing a cyano group (hereinafter referred to as a cyano liquid crystal material) is used instead of a fluorine atom, Fluorine-based liquid crystal materials that have a substituent containing a fluorine atom such as a fluoromethyl group such as a fluoromethyl group and a fluoromethoxy group such as a trifluoromethoxy group and are less likely to contain ionic impurities are used. This is to achieve a high voltage holding ratio required for active driving in the liquid crystal display element. However, in general, dichroic dyes have lower solubility in the fluorinated liquid crystal material than conventional cyano liquid crystal materials, and dichroic dyes that can express particularly high order parameters have significantly higher solubility in fluorinated liquid crystal materials. It was low (for example, refer Unexamined-Japanese-Patent No. 2000-239664). For this reason, it has been difficult to develop a guest-host liquid crystal composition having a high order parameter when using a dichroic dye and a fluorine-based liquid crystal material.

JP-A-11-228967 JP 2000-239664 A

  The present invention provides a dichroic dye having sufficient solubility in a liquid crystal material, particularly a fluorine-based liquid crystal material, and a method for producing the same, and a color liquid crystal having a high order parameter using the dichroic dye. It is an object of the present invention to provide a liquid crystal display device having a composition and high contrast.

The dichroic azo dye for liquid crystal of the present invention has the following formulas ( I) to (IX ):
It is characterized by being represented by .

The first preferred production method of the dichroic azo dye for liquid crystal of the present invention is represented by the following formula (2):
(In the formula (2), A is phenyl, represents pyridyl, and a group selected from the group consisting of thienyl, and X represents a group selected from H and -NO ₂ or Ranaru group, and Y is H and alkoxy It represents a group selected from shea or Ranaru group.)
A diazonium salt obtained by diazotizing the acrylonitrile derivative represented by the formula (1) is coupled with an azo component having no diazotizable primary amino group.

Furthermore, the second preferred method for producing the dichroic azo dye for liquid crystal of the present invention includes the following steps:
(Step 1): Formula (2) below:
(In the formula (2), A is phenyl, represents pyridyl, and a group selected from the group consisting of thienyl, and X represents a group selected from H and -NO ₂ or Ranaru group, and Y is H and alkoxy It represents a group selected from shea or Ranaru group.)
A diazonium salt of an acrylonitrile derivative represented by the formula:
(Step 2): Coupling product having a diazotizable primary amino group by coupling reaction of the diazonium salt obtained in the previous step with an azo component having a diazotizable primary amino group To obtain
(Step 3): The coupling product having a diazotizable primary amino group obtained in the previous step is diazotized into a diazonium salt; and (Step 4): The diazonium salt obtained in the previous step. Coupling reaction with an azo component which does not have a diazotizable primary amino group;
After performing step 1, the steps 2 and 3 are performed n times (n represents an integer of 1 or more) sequentially in this order, and finally the step 4 is performed. is there.
In the present specification, the azo component refers to a compound that can react with a diazonium salt to form an azo compound.

  The inventors have solved the problem that the order parameter of a guest-host liquid crystal composition using a fluorine-based liquid crystal material as a host liquid crystal does not have a sufficient size, so that the contrast of the guest-host display device does not increase. As a result of intensive studies, an azo dichroic dye having a specific molecular structure has high solubility in a fluorinated liquid crystal material, and the dichroic dye is used in combination with a fluorinated liquid crystal material to provide a guest-host liquid crystal The inventors have found that the value of the order parameter of the composition can be increased and completed the present invention.

  By using the dichroic azo dye of the present invention, a guest-host liquid crystal composition having a high order parameter can be obtained, and a liquid crystal display device using this host-guest liquid crystal composition can display with high contrast. It has the effect of being able to.

The dichroic azo dye for liquid crystal of the present invention has the following formula (1) in its molecular structure:
It has a residue having an α-phenyl-, α-pyridyl-, or α-thienyl-β-4-azophenylacrylonitrile structure represented by: In the above formula (1), A represents a group selected from the group consisting of phenyl, pyridyl, and thienyl. Here, the bonding position of the pyridyl and thienyl groups is not particularly limited, but the 2-position of these heterocyclic rings is preferably bonded to the α-position of the acrylonitrile residue. Further, in the above formula (1), X represents a group selected from the group consisting of H, —NO ₂ , halogen, —CN, alkoxy, alkyl, cycloalkyl, alkenyl, aryl, and heteroaryl. Here, the halogen is preferably fluorine, chlorine, bromine or iodine. The alkyl is preferably an alkyl having 1 to 4 carbon atoms. The alkoxy is preferably an alkoxy having 1 to 4 carbon atoms. X is particularly preferably H or —NO ₂ . Further, in the above formula (1), Y represents a group selected from the group consisting of H, alkyl, alkoxy, and halogen. Here, the alkyl is preferably an alkyl having 1 to 4 carbon atoms. In addition, alkoxy is preferably alkoxy having 1 to 4 carbon atoms, and halogen is preferably fluorine, chlorine, bromine, or iodine. It is particularly preferable that Y is H or methoxy. In addition, cis (Z) or trans (E) isomers may exist with respect to the ethylene bond to which the CN group of the above formula (1) is bonded, but the azo dye of the present invention may be either Z-form or E-form. Or a mixture of both. This point is the same in the acrylonitrile derivative represented by the following formula (2).

For example, in the above formula (1), when A is phenyl, the residue of the above formula (1) is represented by the following formula (1b):
Can be expressed as In the formula (1b), X and Y are the same as the substituents represented by X and Y in the formula (1).

  In the dichroic azo dye of the present invention, the compound to which the residue represented by the formula (1) is bonded is not particularly limited, but is selected from the group consisting of an aromatic compound and an aromatic azo compound. Compounds are preferred. The aromatic compound is preferably an aromatic compound having a mono- or dialkylamino group such as dialkylaminobenzene and monoalkylaminobenzene, and the alkyl group of the mono- or dialkylamino group is an alkyl group having 4 or less carbon atoms. It is particularly preferred. Further, when the aromatic compound is a benzene compound having a substituent such as a mono- or dialkylamino group, the residue represented by the above formula (1) with respect to the substituent originally possessed by the benzene compound Is particularly preferably bonded to the para-position of the substituent. When the aromatic compound to which the residue represented by the formula (1) is bonded is a naphthalene-based aromatic compound having a substituent, the substituent originally contained in the naphthalene skeleton and the above formula (1) It is particularly preferable that the residues represented by) are bonded so as to be arranged at the 1-position and 4-position of the naphthalene skeleton.

  When the structure of the dichroic azo dye for liquid crystal of the present invention has a structure in which the residue represented by the above formula (1) and an aromatic and / or heterocyclic azo compound are bonded, the aromatic And / or the heterocyclic azo compound has a structure in which two or more groups selected from the group consisting of a heterocyclic group, a mono- or dialkylaminophenyl group, and a naphthalene group are connected to each other by an azo group, and Preferably, at least one nitrogen-containing group such as a mono- or dialkylamino group or a nitrogen-containing heterocyclic group is present in the linked structure. Preferred examples of the aromatic and / or heterocyclic azo compound include (p-mono or dialkylaminophenylazo) -1-naphthalene and (p-mono or dialkylaminophenylazo) -1-naphthalene-4. -Azo-1'-naphthalene, urolidinylazo-1-naphthalene, etc. are mentioned. Therefore, as a preferable dichroic azo dye for liquid crystal of the present invention, a compound having a structure in which the residue represented by the above formula (1) is bonded to the azo compound can be exemplified.

  Although the structure of the partner compound to which the residue represented by formula (1) is bound has been described so far, the residue represented by formula (1) in the above description is bound to the compound. This means that the dichroic azo dye for liquid crystal of the present invention is a compound having such a bonded structure, and the chemical reaction route itself for actually obtaining the azo dye of the present invention is described. Not shown.

  Preferred specific examples of the dichroic azo dye for liquid crystal of the present invention include compounds represented by the following chemical formulas (I) to (XI), but the present invention is not limited to these. These compounds can be easily produced by those skilled in the art by appropriately selecting reaction conditions using appropriate compounds having a corresponding structure as raw materials in the synthesis method of the dichroic azo dye described below ( Can be synthesized).

  Furthermore, the color tone of the mixture obtained by dissolving the above compounds (I to XI) in a fluorine-based liquid crystal material (ZLI-4792 (trade name), manufactured by E. Merck), and the absorption maximum in the visible region of the mixture The wavelength (λmax = nm) is shown in Table 1. The wavelength of this absorption maximum is a value measured with a visible ultraviolet absorption spectrum measuring apparatus.

  Next, a method for producing (synthesizing) the dichroic azo dye for liquid crystal of the present invention will be described. As a method for producing the dichroic azo dye for liquid crystal of the present invention, any method may be used, but the following production method (synthesis method) is particularly preferable.

A preferred first production method of the dichroic azo dye for liquid crystal of the present invention is the following formula (2):
The diazonium salt obtained by diazotizing the acrylonitrile derivative represented by the above and a azo component having no diazotizable primary amino group are subjected to a coupling reaction.

  A, X, and Y in the formula (2) have the same meanings as A, X, and Y in the formula (1) described above, and preferred groups are also the same.

  The acrylonitrile derivative represented by the above formula (2) can be produced, for example, using the method described in Japanese Patent Publication No. 47-57107 (Patent No. 694279). For example, α-phenyl-β- (2-methoxy-4-aminophenyl) -acrylonitrile can be synthesized as shown below.

  A solution obtained by dissolving 2-methoxy-4-nitrotoluene (30 g) in 95% ethyl alcohol (200 g) is heated to boil, and with stirring, the above-described solution is subjected to crystalline sodium sulfide (18 g), caustic soda (16.5 g). , Sulfur (8.5 g), and water (200 g) are added dropwise over about 2 hours. After further stirring for 6 hours at the same temperature, the solution was cooled to 40 ° C., 21.1 g of benzyl cyanide was added, and the mixture was stirred for 3 hours at the same temperature and then allowed to cool. The precipitated yellow product was separated by filtration, and the resulting product was washed with water and a small amount of ethanol, and α-phenyl-β- (2-methoxy-4-aminophenyl)-having a melting point of 138 to 139 ° C. Acrylonitrile crystals (25.5 g) can be obtained.

  Α-phenyl-β- (4-aminophenyl) -acrylonitrile can be produced by using 4-nitrotoluene instead of 2-methoxy-4-nitrotoluene used in the above production method. Similarly, the synthesis of α-nitrophenyl-acrylonitrile derivatives, α-pyridyl-acrylonitrile derivatives and α-thienyl-acrylonitrile derivatives is produced by using the corresponding acetonitrile derivatives instead of benzyl cyanide used in the above production method. be able to.

  The compound represented by the above formula (2) has a primary amino group and can be converted into a diazonium salt by a known diazotization reaction such as a method using sodium nitrite. A dichroic azo of the present invention having a residue represented by the above formula (1) is obtained by coupling reaction of the obtained diazonium salt with an azo component having no diazotizable primary amino group. A dye can be synthesized. This diazotization reaction and coupling reaction are known methods, and those skilled in the art can use known reactants, and appropriately determine preferable reaction conditions such as reaction temperature, reaction time, etc. so as to increase the reaction yield. be able to. The azo component having no primary amino group that can be diazotized is an aromatic compound having no primary amino group or a heterocyclic compound having no primary amino group, which is a diazonium Examples thereof include compounds capable of azo coupling reaction by electrophilic substitution reaction with a salt. The aromatic compound having no primary amino group used as the azo component is particularly preferably a benzene-based or naphthalene-based aromatic compound having no primary amino group, and specifically, for example, N, N-dimethyl N, N-dialkylanilines such as aniline and N, N-dibutylaniline; and N-monoalkylanilines such as N-methyl, N-ethyl and N-butyl are preferred, and the heterocyclic azo component is urolidine. Etc. can be illustrated as preferable.

The second method for producing the dichroic azo dye for liquid crystal of the present invention includes the following steps:
(Step 1): Formula (2) below:
A diazonium salt of an acrylonitrile derivative represented by the formula:
(Step 2): Coupling product having a diazotizable primary amino group by coupling reaction of the diazonium salt obtained in the previous step with an azo component having a diazotizable primary amino group To obtain
(Step 3): The coupling product having a diazotizable primary amino group obtained in the previous step is diazotized into a diazonium salt; and (Step 4): The diazonium salt obtained in the previous step. Coupling reaction with an azo component which does not have a diazotizable primary amino group;
After performing step 1 above, steps 2 and 3 are performed n times (n represents an integer of 1 or more) in this order, and finally step 4 is performed. It is a method. That is, the reaction is performed in the order of step 1 → step 2 → step 3 → (step 2 → step 3) (n−1 times, n represents an integer of 1 or more) → step 4. When using the production method including step 2 twice or more in the whole production process, the azo component used in step 2 can be used in combination with a desired compound for each step, and the same compound can be used, or different compounds can be used. It can also be used. In each step, preferable reactants and reaction conditions can be appropriately used as is usually performed by those skilled in the art. The acrylonitrile derivative represented by the formula (2) used in the second production method is the same as the acrylonitrile derivative of the formula (2) in the first production method.

  Examples of the azo component having no diazotizable primary amino group used in the second production method include the azo component having no diazotizable primary amino group described in the first production method described above. Mention may be made of the same compounds.

  Examples of the azo component having a primary amino group capable of diazotization include aromatic primary amines such as aniline, toluidine, xylidine and α-naphthylamine, and 5- or 8-aminoquinoline. Primary amino group-containing heterocyclic compounds such as are preferable.

  Specific examples of the first and second production methods of the azo dye will be shown. The compound represented by the above formula (I) can be produced by diazotizing α-phenyl-β- (2-methoxy-4-aminophenyl) -acrylonitrile and coupling reaction with N, N-diethylaminoaniline ( First manufacturing method). The compound represented by the above formula (VIII) is obtained by diazotizing α-phenyl-β- (4-aminophenyl) -acrylonitrile and coupling with α-naphthylamine to obtain a coupling product. The product is obtained by diazotization and coupling with N, N-di-n-butylaniline (the second production method).

  All of the azo dyes of the present invention exhibit dichroism and provide a guest-host liquid crystal composition having excellent order parameters when used in a mixture with a fluorine-based liquid crystal material.

Next, a preferred liquid crystal material used for preparing a liquid crystal composition in combination with the dichroic azo dye of the present invention will be described. As this liquid crystal material, the following structural formulas (A) to (E):
Np-type liquid crystal material or Nn-type liquid crystal material whose main component is a liquid crystal material represented by

In the above formulas (A) to (E), the formula:
Represents a cyclohexane ring, a benzene ring, a dioxane ring, or a pyrimidine ring, and n represents an integer of 1 to 3. —Z— represents a single bond, —COO—, —CH ₂ CH ₂ —, —CH═CH— or —C≡C—. X ¹ is a halogen atom such as a fluorine atom or a chlorine atom; a substituted alkyl group having 1 to 7 carbon atoms, a substituted alkoxy group or a substituted alkenyl group having a halogen atom such as a fluorine atom or a chlorine atom as a substituent; a substituted alkyl group; A substituted cyclohexyl group or a substituted phenyl group having a substituted alkoxy group or a substituted alkenyl group as a substituent is represented, and X ² and X ³ each independently represent a hydrogen atom; or a halogen atom such as a fluorine atom or a chlorine atom. Y ¹ and Y ² each independently represent a cyano group; or a halogen atom such as a fluorine atom or a chlorine atom. R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ each independently represent an alkyl group, alkoxy group, alkoxyalkyl group or alkenyl group having 1 to 10 carbon atoms.

  As will be described below, a liquid crystal composition is prepared by adding the dichroic azo dye of the present invention to the above liquid crystal compound. Further, the above liquid crystal compound can be used by adding an additive such as an optically active substance such as cholesteryl nonanoate, an ultraviolet absorber, an antioxidant, and the like, and the addition amount thereof is appropriately determined. Can do.

  A liquid crystal composition can be easily prepared by dissolving at least one dichroic azo dye of the present invention in the above liquid crystal compound by a known method. Generally, in order to obtain a liquid crystal composition having a desired hue, it is preferable to add two or more of the azo dyes of the present invention to a liquid crystal material. In addition, a dichroic dye other than the dichroic azo dye of the present invention can be used in the liquid crystal composition in combination with the dichroic azo dye of the present invention as long as the effects of the present invention are not impaired. The amount of the dichroic azo dye of the present invention added to the liquid crystal compound when preparing the liquid crystal composition can be appropriately selected according to the desired hue, for example, a hue such as black, brown, or dark blue In order to obtain a liquid crystal composition having a content of 0.1 to 5.0 parts by mass with respect to 100 parts by mass of the host liquid crystal compound (liquid crystal material) to be used.

  Various liquid crystal display elements can be constructed by sandwiching the liquid crystal composition thus prepared between a pair of electrode substrates, at least one of which is transparent. Examples of such display elements include the “Liquid Crystal Device Handbook” Guest host effect such as Heilmeier type guest host or phase transition type guest host described in the Japan Society for the Promotion of Science 142nd Committee edition, published by Nikkan Kogyo Shimbun, pages 315 to 329, etc. Various display elements applying the guest host effect such as a polymer dispersed guest host described in Device Handbook, Japan Society for the Promotion of Science 142nd edition, published by Nikkan Kogyo Shimbun, pages 367 to 370 Can be illustrated.

  As described above, the dichroic azo dye of the present invention can be used for various modes of devices as a material for a liquid crystal display element. In the phase transition mode obtained by adding an active substance, a bright display with high contrast can be obtained without using a polarizing plate. Therefore, the dichroic azo dye of the present invention can be used for a reflective liquid crystal display element. Particularly preferred.

  As an example of an embodiment of the liquid crystal display element of the present invention, FIG. 1 and FIG. 2 schematically show cross-sectional views of an active drive type phase transition mode guest-host type liquid crystal display element. FIG. 1 shows a liquid crystal display element in a voltage applied state, and FIG. 2 shows a liquid crystal display element in a no voltage applied state. In FIG. 1, 1 is incident light, 3 is a glass substrate, 4 is a transparent electrode, 5 is an alignment film, 6 is a dichroic azo dye molecule, 7 is a liquid crystal molecule, 9 is a reflective layer, and 10 is reflected light. .

  When no voltage is applied (FIG. 2), host liquid crystal molecules (hereinafter also simply referred to as liquid crystal molecules) (7) exhibit a cholesteric phase. Since the dichroic azo dye molecule (6) exhibits a cholesteric structure together with the liquid crystal molecule (7), even if the incident light (1) is natural light and no polarizing plate is used, the incident light (1) is It is absorbed by the chromatic dye molecule (6). On the other hand, when a voltage is applied to the liquid crystal display element (FIG. 1), the liquid crystal molecules (7) and the dichroic azo dye molecules (6) are aligned in the direction of the electric field, so that light is transmitted through the liquid crystal composition and reflected layer. Reflected by (9). As described above, in the liquid crystal display element, it is possible to control whether the display element reflects (or transmits) or absorbs light depending on the presence / absence of voltage application, that is, the presence / absence of an electric field.

The present invention will be described below based on examples, but the present invention is not limited to the examples.
[Creation of liquid crystal element using guest-host liquid crystal composition and measurement of order parameter]
(Preparation of liquid crystal composition)
As shown in the following Examples 1 to 4 and Comparative Examples, guest-host type liquid crystal compositions were prepared. The following compounds I to XI are the same as the compounds represented by the above structural formulas I to XI as preferred examples of the dichroic azo dye of the present invention.

[Examples 1 to 4 and Comparative Example]
For each example and comparative example, each described amount of the compound described below is dissolved in 100 g of ZLI-4792 (trade name, manufactured by E. Merck), which is a liquid crystal mixture containing a fluorine-based compound as a main component, A liquid crystal composition was prepared. Therefore, each liquid crystal composition contains four types of dichroic azo dyes. The obtained liquid crystal compositions are referred to as “Example 1” to “Example 4” or “Comparative Example” liquid crystal compositions.

Example 1 0.4 g of compound I
0.7 g of compound VIII,
Compound IX 0.5 g,
And Compound XI 0.4 g.

Example 2 0.5 g of compound II
0.5 g of compound III,
0.4 g of compound V,
And 0.7 g of compound X.

Example 3 0.4 g of compound I
Compound IV 0.5g,
0.5 g of compound VII,
And 0.7 g of compound VIII.

Example 4 0.4 g of compound I
0.5 g of compound VI,
Compound IX 0.5 g,
And Compound XI 0.7 g.

[Comparative example]
The following structural formula:
0.64 g of a dye represented by
The following structural formula:
0.25 g of a dye represented by
The following structural formula:
0.44 g of a dye represented by
The following structural formula:
1.30 g of a dye represented by the following formula:
1.43 g of a dye represented by
The prescription of the comparative example is one of general prescriptions using a commercially available azo dichroic dye and anthraquinone dichroic dye.

  The liquid crystal display elements used for measuring the characteristics of the liquid crystal compositions prepared in each Example and Comparative Example are Heilmeier mode transmissive liquid crystal elements using an Np type liquid crystal composition, and FIG. 3 and FIG. It is the figure which showed notionally the cross section of the liquid crystal element. 3 and 4 are the same as those shown in FIGS. 1 and 2 and are not described here. 3 and 4, 2 represents a polarizing plate, and 8 represents transmitted light.

  As shown in FIGS. 3 and 4, the liquid crystal element used in this example and the comparative example has a transparent electrode (4) on one side of a glass substrate (3), and further on the surface of the transparent electrode (4). Two glass substrates having an alignment film (5) are arranged opposite to each other with the alignment film (5) facing inward, and further on the outer surface of the glass substrate on one side of the cell where light enters. A polarizing plate (2) is arranged. The alignment film (5) is obtained by applying a polyimide resin solution on a transparent electrode (4) of a glass substrate and drying it, followed by rubbing and homogeneous alignment treatment. In this cell, the liquid crystal compositions of Examples 1 to 4 or Comparative Examples were sealed to prepare liquid crystal elements including the respective liquid crystal compositions.

[Measurement of order parameters]
The order parameter was measured using each liquid crystal element described above.
In this liquid crystal element, when no voltage is applied (FIG. 4), the liquid crystal molecules are in a homogeneous alignment state parallel to the electrode surface and arranged in a certain direction, and the dye molecules have the same alignment as the host liquid crystal molecules. The measurement of the order parameter was performed by measuring the light absorption spectrum when light was transmitted through the liquid crystal element without applying a voltage to the liquid crystal element, and measuring the absorbance of the dye in the liquid crystal composition.

  The light absorption spectrum of the liquid crystal element was measured in two ways using light polarized parallel to the alignment direction of liquid crystal molecules or light polarized perpendicularly. That is, the absorbance (A //) of the dye with respect to light polarized parallel to the alignment direction of the liquid crystal molecules and the absorbance (A⊥) of the dye with respect to light polarized perpendicular to the alignment direction of the liquid crystal molecules were measured. . In measuring the absorbance of the dye, correction was made for light absorption by the host liquid crystal composition and the glass substrate and light loss due to reflection of the element itself, and the absorbance by the dye alone was calculated.

For each liquid crystal element using the liquid crystal compositions of Examples 1 to 4 and Comparative Example, A // and A⊥ were measured, and based on the obtained spectra, 450 nm, 500 nm, 550 nm, 600 nm, and 650 nm The order parameter S (S value) at the wavelength is expressed by the following formula:
S = (A // − A⊥) / (2A⊥ + A //)
It calculated using.
The obtained results are shown in Table 2.

  As shown in Table 2, the liquid crystal composition using the dichroic azo dye of the present invention has an order parameter (S value) 0.02 to 0.06 higher than the conventionally used dye at each wavelength. Furthermore, the liquid crystal display element produced using the liquid crystal composition using the dichroic azo dye of the present invention has a significantly superior visual recognition than the liquid crystal display element produced using the conventionally known liquid crystal composition It was visually observable to have sex.

  The dichroic azo dye of the present invention can be used as a dichroic azo dye for liquid crystal materials, and is particularly excellent as a dye for use in a color liquid crystal composition using a fluorine-based liquid crystal material. Furthermore, the color liquid crystal composition using the dichroic azo dye of the present invention can be used for a liquid crystal display device.

FIG. 2 is a diagram schematically showing a cross section of a phase change mode reflective liquid crystal element using an Np type liquid crystal composition in an applied voltage state as one embodiment of a liquid crystal display element using the dichroic azo dye of the present invention. is there. The figure which showed typically the cross section of the reflection type liquid crystal element of the phase transition mode using the Np type liquid crystal composition in the voltage-less application state as one embodiment of the liquid crystal display element using the dichroic azo dye of this invention It is. The figure which showed typically the cross section of the transmissive liquid crystal element of Heilmeier mode using the Np type liquid crystal composition in a voltage application state as another embodiment of the liquid crystal display element using the dichroic azo dye of this invention. It is. As another embodiment of the liquid crystal display device using the dichroic azo dye of the present invention, a cross section of a transmissive liquid crystal device in Heilmeier mode using an Np type liquid crystal composition in a state where no voltage is applied is schematically shown. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Incident light 2 ... Polarizing plate 3 ... Glass substrate 4 ... Transparent electrode 5 ... Orientation film 6 ... Dichroic azo dye molecule 7 ... Host liquid crystal molecule 8 ... Transmitted light 9 ... Reflective layer 10 ... Reflected light

Claims (3)

The following formulas ( I) to (IX ):
A dichroic azo dye for liquid crystal represented by The following formula (2):
(In the formula (2), A is phenyl, represents pyridyl, and a group selected from the group consisting of thienyl, and X represents a group selected from H and -NO ₂ or Ranaru group, and Y is H and alkoxy It represents a group selected from shea or Ranaru group.)
A dichroic salt for liquid crystal according to claim 1, wherein a diazonium salt obtained by diazotizing the acrylonitrile derivative represented by formula (1) is coupled with an azo component having no diazotizable primary amino group. A manufacturing method of azo dyes. The following steps:
(Step 1): Formula (2) below:
(In the formula (2), A is phenyl, represents pyridyl, and a group selected from the group consisting of thienyl, and X represents a group selected from H and -NO ₂ or Ranaru group, and Y is H and alkoxy It represents a group selected from shea or Ranaru group.)
A diazonium salt of an acrylonitrile derivative represented by the formula:
(Step 2): Coupling product having a diazotizable primary amino group by coupling reaction of the diazonium salt obtained in the previous step with an azo component having a diazotizable primary amino group To obtain
(Step 3): The coupling product having a diazotizable primary amino group obtained in the previous step is diazotized to form a diazonium salt; and (Step 4): The diazonium salt obtained in the previous step is converted into a diazonium salt. Coupling reaction with an azo component having no diazotizable primary amino group;
The step 2 and the step 3 are performed n times (n represents an integer of 1 or more) sequentially in this order, and the step 4 is finally performed. 2. A process for producing a dichroic azo dye for liquid crystal according to 1.