Azo dichroic dye and preparation and application thereof

Abstract

The invention discloses an azo dichroic dye and preparation and application thereof, the azo dichroic dye has high solubility, high dichroic ratio and high stability, can be compounded with other azo dichroic dyes to obtain a black dichroic dye composition, has good adaptability with a liquid crystal system, and can be used for preparing a liquid crystal display device. The prepared polaroid has an excellent polarization effect, realizes full coverage of absorption in a visible light range, and can be directly applied to a liquid crystal display and a flexible display screen.

Description

Technical Field

[0001] The present invention relates to the technical field of azo dichroic dyes, and in particular to an azo dichroic dye and a preparation and application thereof. Background Art

[0002] With the rapid development and innovative iteration of optoelectronic display technology, the new generation of display devices has continued to make breakthroughs in core performance indicators such as color reproduction, energy conversion efficiency and response speed, improving the display effects of smart terminal devices such as smartphones, tablets, and smart car terminals. At present, liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs), as the two mainstream technologies in the display field, still have good development prospects due to their mature process systems and diversified application scenarios. However, as display technology develops towards higher resolution, wider color gamut coverage and lower energy consumption, how to further improve display performance has become a major issue that needs to be urgently addressed in the display field.

[0003] Polarizers, as core optical control components of display devices, play an irreplaceable role in various display technologies. In traditional LCDs, two polarizers control the polarization direction of backlight through a precise light modulation process, creating a contrast between light and dark to achieve image display. In emerging organic light-emitting diode (OLED) technology, despite the elimination of a backlight module, a polarizer is still required to suppress light reflected from the screen surface, thereby improving display contrast and image clarity. Therefore, the performance of polarizers directly affects core display indicators such as color rendering, contrast, and viewing angle, and improving their performance plays a key role in the overall performance of the display device.

[0004] The optical performance of polarizers essentially depends on the molecular properties of the dichroic dye system. An ideal dichroic dye should possess a variety of excellent properties, such as good solvent compatibility to ensure uniform film formation, an ultra-high dichroic ratio to achieve selective transmission of light with a specific polarization direction, and good environmental stability to extend the life of the device. However, currently commercial dichroic dyes generally suffer from technical bottlenecks such as insufficient dichroic ratio and poor photothermal stability. These issues lead to a significant decrease in the optical performance of polarizers in hot and humid environments, severely limiting the application of high-end display devices in wide temperature ranges.

[0005] Therefore, in order to meet the stringent requirements of optical films in emerging fields such as ultra-high-definition display and flexible display, it is urgent to develop dichroic dyes with high solubility, high dichroic ratio and high photothermal stability. Summary of the Invention

[0006] To solve the above technical problems, the object of the present invention is to provide an azo dichroic dye and its preparation and application. The azo dichroic dye has excellent optical properties and thermal stability and can be widely used in the fields of liquid crystal display, optical devices, optoelectronic materials, etc.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] An azo dichroic dye, the structural formula of the azo dichroic dye is shown as formula A:

[0009]

[0010] Wherein, R1 is selected from one or more of trifluoromethyl, cyano, ethoxycarbonyl and halogen; R2 is

[0011] Further, the azo dichroic dye is selected from one of the following structural formulas:

[0012]

[0013]

[0014] The present invention provides a preparation method of the above azo dichroic dye, including the following steps:

[0015] (1) Dissolve in a solvent, add sodium nitrite and a catalyst at 0 - 5 °C to obtain solution A; add phenylamino-N-methylsulfonate and a base to solution A and react to obtain a compound shown as formula a; wherein, R is selected from one or more of trifluoromethyl, cyano, ethoxycarbonyl and halogen;

[0016] (2) Dissolve the compound shown as formula a in an organic solvent, add nitrosyl sulfuric acid at 0 - 5 °C, and then add phenylmorpholine or N,N-dimethylaniline and react to obtain a compound shown as formula A;

[0017] The structural formula of the above formula a is shown as follows:

[0018]

[0019] Further, in step (1), is 4-trifluoromethylaniline, 2,4-difluoroaniline, 4-cyanoaniline, 4-ethoxycarbonylaniline or 3,4,5-trifluoroaniline.

[0020] Further, in step (1), the solvent is an aqueous hydrochloric acid solution.

[0021] Further, in step (1), the catalyst is sulfamic acid.

[0022] Further, in step (1), the base is sodium bicarbonate.

[0023] Further, in step (1), the structural formula of phenylamino-N-methylsulfonate is

[0024] In a specific embodiment, in step (1), is dissolved in a solvent, sodium nitrite is added at 0 - 5°C, after stirring for 1 - 2 h, a catalyst is added and stirred for 10 - 20 min to obtain solution A; phenylamino-N-methylsulfonate and a base are added to the solution A, the temperature is raised to 23 - 27°C and the reaction is carried out for 10 - 12 h, and the obtained crude product is purified to finally obtain the compound shown by formula a.

[0025] Further, the specific manner of the purification treatment is: the obtained crude product is washed and then dissolved in water, an alkali solution is added, stirred at 65 - 75°C for 3 - 4 h, and after filtration, washing, and drying, the compound shown by formula a is obtained.

[0026] Further, the alkali solution is an aqueous solution of sodium carbonate or an aqueous solution of sodium hydroxide.

[0027] Further, in step (2), the organic solvent is selected from one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc).

[0028] Further, in step (2), the structural formula of phenylmorpholine is The structural formula of N,N-dimethylaniline is

[0029] Further, in step (2), a step of adding an acid is further included while adding phenylmorpholine or N,N-dimethylaniline.

[0030] Further, the acid is selected from one or more of formic acid, acetic acid, and propionic acid, and a small amount of the acid has a catalytic effect.

[0031] In a specific embodiment, in step (2), the compound shown by formula a is dissolved in an organic solvent, nitrosylsulfuric acid is added at 0 - 5°C, after stirring for 1 - 2 h, phenylmorpholine or N,N-dimethylaniline is added, and the reaction is carried out for 3 - 4 h, and the obtained crude product is purified to obtain the compound shown by formula A.

[0032] Further, the specific manner of the purification treatment is: the obtained crude product is dissolved in an alkali solution, filtered and washed, petroleum ether is added and stirred for 2 - 3 h, and after filtration and drying, the compound shown by formula A is obtained.

[0033] Further, the alkali solution is an aqueous solution of sodium carbonate.

[0034] The present invention provides a dichroic dye composition, comprising the above-mentioned azo dichroic dye and wherein, R is selected from one or more of trifluoromethyl, cyano, ethoxycarbonyl, and halogen.

[0035] The azo dichroic dye provided by the present invention and other azo dichroic dyes are compounded to obtain a black dichroic dye composition.

[0036] The present invention provides a liquid crystal material composition, comprising the above-mentioned azo dichroic dye

[0037] The liquid crystal material composition provided by the present invention may also comprise the above-mentioned dichroic dye composition.

[0038] The present invention protects the application of the above-mentioned azo dichroic dye, dichroic dye composition or liquid crystal material composition in the preparation of a polarizer or a filter, and the polarizer or filter can be used in a liquid crystal display and a flexible display screen.

[0039] The beneficial effects of the present invention are as follows:

[0040] The present invention provides an azo dichroic dye and a black azo dichroic dye mixture, and the dye and the dye mixture have the following characteristics: high solubility, high dichroic ratio, high compatibility, and high stability, have good adaptability to a liquid crystal system, the obtained polarizer has an excellent polarization effect, and realizes full coverage of absorption in the visible light range, and can be directly applied to a liquid crystal display and a flexible display screen. Description of the Drawings

[0041] Figure 1 1H NMR spectrum of the azo dichroic dye prepared in Example 1.

[0042] Figure 2 1H NMR spectrum of the azo dichroic dye prepared in Example 2.

[0043] Figure 3 1H NMR spectrum of the azo dichroic dye prepared in Example 3.

[0044] Figure 4 1H NMR spectrum of the azo dichroic dye prepared in Example 4.

[0045] Figure 5 Absorbance data graph of the solution of the dichroic dye composition prepared in Example 5 in the visible light range.

[0046] Figure 6 Absorbance data graph of the solution of the dichroic dye composition prepared in Example 7 in the visible light range.

[0047] Figure 7 Ultraviolet absorption spectrum graph of the polarizing plate coated with a polarizing film in Application Example 7 in the visible light range. Detailed implementation manners

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used in the description of this invention herein are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0049] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples given are not intended to limit the present invention.

[0050] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels.

[0051] The structural formula of liquid crystal LC242 in the following application examples and test examples is:

[0052]

[0053] The structural formula of liquid crystal C11-3 in the following application examples and test examples is:

[0054]

[0055] Example 1

[0056] A preparation method of an azo dichroic dye, comprising the following steps:

[0057] (1) Dissolve 16.2 g of 3,4,5-trifluoroaniline in 27 mL of concentrated hydrochloric acid and 500 mL of water. At 5 °C, dropwise add a 50 mL aqueous solution containing 8 g of sodium nitrite, stir at 5 °C for 2 h, add 1.5 g of sulfamic acid and stir for 10 min, and filter to obtain solution A. Dissolve 23 g of phenylamino-N-methylsulfonate sodium and 23 g of sodium bicarbonate in 300 mL of water, cool to 5 °C, then dropwise add solution A, gradually warm up to about 25 °C and react overnight, filter, and wash the solid with 200 mL of 20% brine. Transfer the crude product to 350 mL of water, dropwise add 50 g of sodium hydroxide (30%) solution within 10 min, and stir at 75 °C for 5 h. Filter the reaction system while it is hot, wash the solid with 300 mL of water, and dry to obtain 24.3 g of an orange-yellow product, namely the compound shown in formula 1a, and the structural formula is as follows:

[0058]

[0059] (2) Dissolve 5 g of the compound shown in formula 1a in 60 mL of N-methylpyrrolidone. At 5 °C, dropwise add 6.96 g of nitrosyl sulfuric acid (40%) and stir for 1 h. At 5 °C, add a 10 mL N-methylpyrrolidone solution containing 3.25 g of phenylmorpholine and 1.4 g of acetic acid, and react overnight. Add 200 mL of 50% aqueous sodium carbonate solution to the system, filter to obtain a solid, and wash with 250 mL of water to obtain the crude product. Add the crude product to 70 mL of petroleum ether, stir at 25 °C for 2 h, filter, and dry to obtain 6.03 g of a red product, namely the compound shown in formula 1b, and the structural formula is as follows:

[0060]

[0061] The δ (CDCl3) data of the 1H nuclear magnetic resonance spectrum (1H NMR) of the compound shown in formula 1b are: 8.03 (4H), 7.75–7.54 (4H), 7.11 (2H), 3.95 (4H), 3.41 (4H), and the 1H nuclear magnetic resonance spectrum is as shown in Figure 1 shown.

[0062] Example 2

[0063] A preparation method of an azo dichroic dye, comprising the following steps:

[0064] (1) Dissolve 20 g of 2,4-difluoroaniline in 31 mL of concentrated hydrochloric acid and 600 mL of water. At 5 °C, dropwise add a 60 mL aqueous solution containing 11.3 g of sodium nitrite, stir at 5 °C for 2 h, add 1.6 g of sulfamic acid and stir for 10 min, and filter to obtain solution A. Dissolve 32.43 g of phenylamino-N-methylsulfonate sodium and 32.43 g of sodium bicarbonate in 400 mL of water. After cooling to 5 °C, dropwise add solution A, gradually warm up to about 25 °C and react overnight. Filter, and wash the solid with 300 mL of 20% brine. Transfer the crude product to 300 mL of water, dropwise add 60 g of sodium hydroxide (30%) solution within 10 min, and stir at 75 °C for 5 h. Filter the reaction system while it is hot, wash the solid with 300 mL of water, and dry to obtain 34.52 g of an orange-yellow product, which is the compound shown in Formula 2a, and the structural formula is as follows:

[0065]

[0066] (2) Dissolve 7.14 g of the compound shown in Formula 2a in 92 mL of N-methylpyrrolidone. At 5 °C, dropwise add 9.73 g of nitrosyl sulfuric acid (40%) and stir for 1 h. At 5 °C, add a 15 mL N-methylpyrrolidone solution containing 5 g of phenylmorpholine, and react overnight. Add 400 mL of 50% aqueous sodium carbonate solution to the system, filter to obtain a solid, wash with 250 mL of water and 250 mL of methanol to obtain the crude product. Add the crude product to 200 mL of petroleum ether, stir at 50 °C for 2 h, filter, and dry to obtain 7.83 g of a dark red product, which is the compound shown in Formula 2b, and the structural formula is as follows:

[0067]

[0068] The δ (CDCl3) data of the 1H nuclear magnetic resonance spectrum (1H NMR) of the compound shown in Formula 2b are: 8.12–8.04 (6H), 7.86 (2H), 7.33 (1H), 7.08–6.90 (4H), 4.05 (4H), 3.53–3.44 (4H). The 1H nuclear magnetic resonance spectrum is as Figure 2 shown.

[0069] Example 3

[0070] A preparation method of an azo dichroic dye, comprising the following steps:

[0071] (1) Dissolve 16.2 g of 3,4,5-trifluoroaniline in 27 mL of concentrated hydrochloric acid and 500 mL of water. At 5 °C, dropwise add a 50 mL aqueous solution containing 8 g of sodium nitrite, stir at 5 °C for 2 h, add 1.5 g of sulfamic acid and stir for 10 min, and filter to obtain solution A. Dissolve 23 g of phenylamino-N-methylsulfonate sodium and 23 g of sodium bicarbonate in 300 mL of water, cool to 5 °C, then dropwise add solution A, gradually warm up to about 25 °C and react overnight, filter, and wash the solid with 200 mL of 20% brine. Transfer the crude product to 350 mL of water, dropwise add 50 g of sodium hydroxide (30%) solution within 10 min, and stir at 75 °C for 5 h. Filter the reaction system while it is hot, wash the solid with 300 mL of water, and dry to obtain 24.3 g of an orange-yellow product, which is the compound shown in formula 3a, and the structural formula is as follows:

[0072]

[0073] (2) Dissolve 5.5 g of the compound shown in formula 1a in 60 mL of N-methylpyrrolidone. At 5 °C, dropwise add 7.65 g of nitrosyl sulfuric acid (40%) and stir for 1 h. At 5 °C, add a 10 mL N-methylpyrrolidone solution containing 2.41 g of N,N-dimethylaniline and 1.6 g of acetic acid, and react overnight. Add 200 mL of 50% aqueous sodium carbonate solution to the system, filter to obtain a solid, and wash with 250 mL of water to obtain the crude product. Add the crude product to 60 mL of petroleum ether, stir at 50 °C for 2 h, filter, and dry to obtain 5.98 g of a yellow product, which is the compound shown in formula 3b, and the structural formula is as follows:

[0074]

[0075] The δ (CDCl3) data of the 1H nuclear magnetic resonance spectrum (1H NMR) of the compound shown in formula 3b are: 8.02 (6H), 7.67–7.61 (2H), 6.83 (2H), 3.16 (6H). The 1H nuclear magnetic resonance spectrum is as shown in Figure 3 shown.

[0076] Example 4

[0077] A preparation method of an azo dichroic dye, comprising the following steps:

[0078] (1) Dissolve 20 g of 2,4-difluoroaniline in 31 mL of concentrated hydrochloric acid and 600 mL of water. At 5 °C, add dropwise a 60 mL aqueous solution containing 11.3 g of sodium nitrite, stir at 5 °C for 2 h, add 1.6 g of sulfamic acid and stir for 10 min, then filter to obtain solution A. Dissolve 32.43 g of phenylamino-N-methylsulfonate sodium and 32.43 g of sodium bicarbonate in 400 mL of water, cool to 5 °C, then add dropwise solution A, gradually warm up to about 25 °C and react overnight, filter, and wash the solid with 300 mL of 20% brine. Transfer the crude product to 300 mL of water, add dropwise a 60 g sodium hydroxide (30%) solution within 10 min, and stir at 75 °C for 5 h. Filter the reaction system while it is hot, wash the solid with 300 mL of water, and dry to obtain 33.26 g of an orange-yellow product, which is the compound shown in Formula 4a, and the structural formula is as follows:

[0079]

[0080] (2) Dissolve 7.00 g of the compound shown in Formula 4a in 100 mL of N-methylpyrrolidone. At 5 °C, add dropwise 10.40 g of nitrosyl sulfuric acid (40%) and stir for 1 h. At 5 °C, add a 15 mL N-methylpyrrolidone solution containing 3.64 g of N,N-dimethylaniline, and react overnight. Add 300 mL of 50% sodium carbonate aqueous solution to the system, filter to obtain a solid, wash with 250 mL of water and 250 mL of methanol to obtain the crude product. Add the crude product to 200 mL of petroleum ether, stir at 50 °C for 2 h, filter, and dry to obtain 7.9 g of a dark yellow product, which is the compound shown in Formula 4b, and the structural formula is as follows:

[0081]

[0082] The δ (CDCl3) data of the 1H nuclear magnetic resonance spectrum (1H NMR) of the compound shown in Formula 4b are as follows: 8.33 (d, J = 8.6 Hz, 1H), 8.09 (d, J = 2.8 Hz, 1H), 8.03 (s, 1H), 7.93 (, J = 8.4 Hz, 1H), 7.89–7.74 (m, 2H), 7.55–7.48 (m, 1H), 7.16–6.85 (m, 4H), 3.33 (d, J = 14.3 Hz, 6H). The 1H nuclear magnetic resonance spectrum is as shown in Figure 4 shown.

[0083] Example 5

[0084] A dichroic dye composition, by mass, comprises 100 parts of an azo dichroic dye and 45 parts of the azo dichroic dye prepared in Example 1.

[0085] Example 6

[0086] A dichroic dye composition, by mass, comprises 100 parts of an azo dichroic dye and 45 parts of the azo dichroic dye prepared in Example 1.

[0087] Example 7

[0088] A dichroic dye composition, by mass, comprises 100 parts of an azo dichroic dye and 45 parts of the azo dichroic dye prepared in Example 2.

[0089] Example 8

[0090] A dichroic dye composition, by mass, comprises 100 parts of an azo dichroic dye and 45 parts of the azo dichroic dye prepared in Example 3.

[0091] Application Example

[0092] Dissolve the aligning agent SD1 (Mediary Yellow 26) in ethylene glycol monomethyl ether to prepare an SD1 solution with a concentration of 1 mg / mL; separately mix the azo dichroic dyes of Examples 1-4 or the dichroic dye compositions of Examples 5-8 with liquid crystal LC242, liquid crystal C11-3, and initiator 369, and dissolve the obtained liquid crystal material composition in a mixed solvent of cyclohexanone and cyclopentanone (the mass ratio of cyclohexanone to cyclopentanone is 1:4, and the mass ratio of the liquid crystal material composition to the mixed solvent is 1:4) to obtain a liquid crystal material composition solution. The contents of each component in the liquid crystal material composition are shown in Table 1:

[0093] Table 1

[0094]

[0095] At room temperature, uniformly scrape the SD1 solution on the glass plate substrate with a 10-micron wire bar. After keeping it in an oven at 120 °C for 3 min, place a polarizer above the film. The direction of the polarizer is parallel to the scraping direction, and irradiate it with a UV lamp at 25 °C for 1 min for alignment to form an SD1 layer;

[0096] At room temperature, uniformly scrape the liquid crystal material composition solutions of Application Examples 1-8 on the surface of the SD1 layer with a 30-micron wire bar respectively. After placing it in an oven at 120 °C for 20 s, transfer it to a hot stage at 75 °C and keep it warm for 10 min. Then set the hot stage temperature to 65 °C, keep it warm for 15 min, transfer it to a hot stage at 30 °C, and irradiate it with a UV lamp for 5 s in a nitrogen atmosphere to cure it, obtaining a polarizer coated with a polarizing film.

[0097] Test Example 1

[0098] The maximum absorption wavelength and dichroic ratio of the azo dichroic dyes prepared in Test Examples 1-4 were measured by the following method:

[0099] The azo dichroic dye was dissolved in ethyl acetate, and the absorption band of the azo dichroic dye solution was measured using a UV spectrophotometer to obtain the maximum absorption wavelength.

[0100] The dichroic ratio was measured using the polarizer coated with a polarizing film in Application Examples 1-4 on a UV spectrophotometer: A polarizer was placed in front of the optical path, and the maximum absorbances D ⊥ and D || of the polarizer for polarized light parallel and perpendicular to the liquid crystal director were measured respectively. The dichroic ratio D ⊥ was calculated through D || and D A = D / / / D ⊥ .

[0101] The test results are shown in Table 2:

[0102] Table 2

[0103]

[0104] In addition, after the azo dichroic dyes prepared in the present invention were stored for more than half a year, their absorption bands did not change; moreover, through observation with a polarized light microscope (POM), the melting points of the dyes were all above 100 °C, proving that the azo dichroic dyes have excellent thermal stability.

[0105] Test Example 2

[0106] The visible light absorption band of the dichroic dye composition prepared in Example 5 and Example 7 was measured using a UV spectrophotometer. The test method was as follows: The dichroic dye composition was dissolved in ethyl acetate, and the absorption band of the solution of the dichroic dye composition in the visible light range was measured. The solution of the dichroic dye composition and the polarizing film prepared therefrom were both black.

[0107] The test results are as shown in Figure 5 and Figure 6 . Figure 5 and Figure 6 show the absorption spectral characteristics of the solution of the dichroic dye composition compounded in the present invention in the visible light range. It can be seen that the absorbance is relatively stable within a small range from 400 nm to 650 nm and decreases after 650 nm, indicating the unique optical absorption properties of the dichroic dye composition in the visible light range, which is suitable for the preparation of polarizers for new display devices and can achieve excellent effects.

[0108] Test Example 3

[0109] The dichroic ratio of the dichroic dye composition was measured using the polarizer coated with a polarizing film in Application Examples 5 - 8 on an ultraviolet spectrophotometer. The measurement method was as follows: A polarizer was placed in front of the light path, and the maximum absorbances D ⊥ and D || of the polarizer for polarized light parallel and perpendicular to the liquid crystal director were measured respectively. ⊥ and D || were used to calculate the dichroic ratio D A = D / / / D ⊥ . The solubility refers to the mass percentage of the dichroic dye composition in the liquid crystal material composition (the maximum solubility was achieved in Application Examples 5 - 8).

[0110] The test results are shown in Table 3 and Figure 7 as follows:

[0111] Table 3

[0112]

[0113]

[0114] Figure 7 is the ultraviolet absorption spectrum of the polarizer coated with a polarizing film in Application Example 7 in the visible light range.

[0115] Obviously, the above - mentioned embodiments of the present invention are only examples for clearly explaining the present invention, and are not limitations on the implementation modes of the present invention. Those skilled in the art should understand that other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all implementation modes here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. An azo dichroic dye, characterized in that, The structural formula of the azo dichroic dye is shown in Formula A as follows: Among them, R1 is selected from one or more of trifluoromethyl, cyano, ethoxycarbonyl and halogen; R2 is 2. The azo dichroic dye according to claim 1, characterized in that, The azo dichroic dye is selected from one of the following structural formulas:

3. A method for preparing the azo dichroic dye according to claim 1, characterized in that, It includes the following steps: (1) Dissolve in a solvent, add sodium nitrite and a catalyst at 0 - 5 °C to obtain solution A; add phenylamino-N-methylsulfonate and a base to the solution A and react to obtain the compound shown in formula a; wherein, R is selected from one or more of trifluoromethyl, cyano, ethoxycarbonyl, and halogen; (2) Dissolve the compound shown in Formula a in an organic solvent, add nitrosylsulfuric acid at 0 - 5°C, and then add phenylmorpholine or N,N-dimethylaniline, and react to obtain the compound shown in Formula A; The structural formula of the above Formula a is shown as follows:

4. The preparation method according to claim 3, characterized in that, In step (2), it also includes the step of adding an acid while adding phenylmorpholine or N,N-dimethylaniline.

5. The preparation method according to claim 4, wherein The acid is selected from one or more of formic acid, acetic acid, and propionic acid.

6. The preparation method according to claim 3, characterized in that, In step (2), dissolve the compound shown in Formula a in an organic solvent, add nitrosylsulfuric acid at 0 - 5°C, stir for 1 - 2 h, then add phenylmorpholine or N,N-dimethylaniline, react for 3 - 4 h, and purify the obtained crude product to obtain the compound shown in Formula A.

7. The preparation method according to claim 6, characterized in that, The specific method of the purification treatment is: dissolve the obtained crude product in an alkaline solution, filter and wash it, then add petroleum ether and stir for 2 - 3 h, and obtain the compound shown in Formula A after filtration and drying.

8. A dichroic dye composition, characterized in that, including the azo dichroic dye described in claim 1 and wherein R is selected from one or more of trifluoromethyl, nitrile group, ethoxycarbonyl and halogen.

9. A liquid crystal material composition, characterized in that, It includes the azo dichroic dye described in Claim 1.

10. The azo dichroic dye described in Claim 1, the dichroic dye described in Claim 8 The application of the composition or the liquid crystal material composition described in Claim 9 in the preparation of a polarizing plate or a filter.

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