Azo compound, photo-alignment film and liquid crystal display device

Abstract

The invention discloses an azo compound, a photo-alignment film and a liquid crystal display device. The azo compound provided by the invention has the following structural formula: # imgabs0 #. The azo compound has the characteristics of good orientation performance, high light sensitivity, low temperature and humidity sensitivity and low chromaticity.

Description

Technical Field

[0001] The present invention relates to the technical field of organic compounds, and particularly to an azo compound, a photo-alignment film, and a liquid crystal display device. Background Art

[0002] Photo-alignment technology usually uses photosensitive materials as a medium, and utilizes the physical / chemical reactions of photosensitive materials under light irradiation to produce different-direction anchoring effects on liquid crystal molecules in contact with the photosensitive materials. In theory, it can make the liquid crystals arrange in an arbitrary orientation angle distribution. Compared with rubbing alignment, photo-alignment technology can effectively avoid problems such as impurity contamination, mechanical damage, and electrostatic accumulation, with higher precision and better quality. In recent years, the preparation of film layers by photo-alignment technology has been studied by many research scholars. Photo-controllable alignment materials can be classified according to different light response mechanisms: photoisomerization, photocrosslinking, photodegradation, and photoinduced rearrangement of azobenzene dye molecules. Among these photo-alignment methods, the method using azobenzene is the optimal way to obtain high sensitivity and high orientation control. Azo compounds are used to manufacture photo-alignment films by irradiating anisotropic light. For example, commonly used azobenzene photo-alignment materials SD1 and BY on the market all contain azobenzene structures.

[0003] However, the photo-alignment performance, photosensitivity, temperature and humidity sensitivity, and chromaticity of BY molecules sold on the market are inferior to those of SD1 molecules. However, the SD1 alignment material has a high cost, a high chromaticity value, is relatively sensitive to temperature and humidity, and has a low yield when aligned with liquid crystals.

[0004] Therefore, it is necessary to develop an azo compound with good alignment performance, high photosensitivity, low temperature and humidity sensitivity, and low chromaticity. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides an azo compound, which has the characteristics of good alignment performance, high photosensitivity, low temperature and humidity sensitivity, and low chromaticity.

[0006] The second aspect of the present invention further provides a photo-alignment film.

[0007] The third aspect of the present invention further provides a liquid crystal display device.

[0008] The azo compound according to the embodiment of the first aspect of the present invention has the following structural formula:

[0009]

[0010] Wherein, X is selected from -O, -S, -NH;

[0011] R1 and R2 are each independently selected from H, Among them, R5, R6, and R7 are independently selected from H or an alkyl group of C 1～6 ; n, m, y, z, p, or q are each independently selected from integers of 1 to 20;

[0012] R3 and R4 are independently selected from C 1～6 haloalkyl, C 1～6 carboxyl, or C 1～6 sodium carboxylate.

[0013] The azo compound according to the embodiment of the present invention has at least the following beneficial effects:

[0014] The present invention provides a novel-structured azo compound, which has the characteristics of good orientation performance, low photosensitivity, low temperature and humidity sensitivity, and low chromaticity.

[0015] According to some embodiments of the present invention, R3 and R4 are independently selected from C 1～3 haloalkyl, C 1～3 carboxyl, or C 1～3 sodium carboxylate.

[0016] According to some embodiments of the present invention, R1 and R2 are each independently selected from H, Among them, R5, R6, and R7 are independently selected from H or an alkyl group of C 1～3 ; n, m, y, z, p, or q are each independently selected from integers of 3 to 10.

[0017] According to some embodiments of the present invention, R1 and R2 are the same.

[0018] According to some embodiments of the present invention, R3 and R4 are the same.

[0019] According to some embodiments of the present invention, the azo compound is selected from the following structural formulas:

[0020]

[0021]

[0022] The azo compound described in the present invention can be prepared by literature or conventional methods. For example, the azo compound of the present invention is prepared by the following method, including the following steps:

[0023] S1. Mix and react compound I, an acidic substance, and sodium nitrite to obtain intermediate I;

[0024] S2. React the intermediate I with compound II to obtain the product.

[0025] Alternatively; reacting the product obtained in step S2 with compound III to obtain intermediate II;

[0026] Reacting the intermediate II, compound IV, a base, and an organic solvent in reaction II to obtain the product;

[0027] Among them, the structural formulas of compound I, compound II, compound III, and compound IV are as follows:

[0028]

[0029] According to some embodiments of the present invention, the acidic substance includes at least one of hydrochloric acid and sulfuric acid.

[0030] According to some embodiments of the present invention, the base includes at least one of triethylamine, sodium carbonate, sodium bicarbonate, pyridine, and triethanolamine.

[0031] According to some embodiments of the present invention, in step S1, the temperature of the reaction is 0°C to 5°C.

[0032] According to some embodiments of the present invention, in step S1, the molar ratio of compound I to sodium nitrite is 1:(1.5 - 3).

[0033] According to some embodiments of the present invention, the molar ratio of the product obtained in step S2 to compound III is 1:(1.5 - 3).

[0034] According to some embodiments of the present invention, the organic solvent includes at least one of tetrahydrofuran, sodium carbonate, sodium bicarbonate, pyridine, and triethanolamine.

[0035] According to some embodiments of the present invention, the temperature of reaction I is 60 - 90°C.

[0036] According to some embodiments of the present invention, the temperature of reaction II is 10 - 20°C.

[0037] The third aspect of the present invention provides a photo-alignment film, which includes the azo compound described in the first aspect of the present invention.

[0038] According to some embodiments of the present invention, the thickness of the photo-alignment film is 20 nm to 100 nm. For example, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any sub-range composed of any two of these values can be selected.

[0039] According to some embodiments of the present invention, the photo-alignment film is prepared by the following method:

[0040] First, mix the azo compound described in the first aspect of the present invention with a solvent to obtain a coating; then coat the coating on a substrate, irradiate with polarized light to endow the liquid crystal alignment function, and then obtain the product by heating or light irradiation.

[0041] According to some embodiments of the present invention, the solvent includes toluene, tetrahydrofuran, chlorobenzene, ethylene glycol, dimethyl sulfoxide, N-methylpyrrolidone, γ-butyrolactone, N,N-dimethylformamide.

[0042] The third aspect of the present invention provides a liquid crystal display device, including the photo-alignment film described in the second aspect of the present invention.

[0043] The additional aspects and advantages of the present invention will be partly given in the following description, partly become obvious from the following description, or be understood through the practice of the present invention. Detailed Description of Embodiments

[0044] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention.

[0045] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0046] In the description of the present invention, the meaning of several is more than one, the meaning of multiple is more than two, greater than, less than, exceeding, etc. are understood as not including the recited number, and above, below, within, etc. are understood as including the recited number. If the first and second are described only for the purpose of distinguishing technical features, they should not be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or the sequence of the indicated technical features.

[0047] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific content of the technical solution.

[0048] In the description of the present invention, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0049] Example 1

[0050] This example provides an azo compound, and its reaction equation and preparation method are as follows:

[0051]

[0052] S1. Diphenyl[b,d]thiophene-3,7-diamine (100 g, 467 mmol), 100 g of concentrated sulfuric acid (98% concentrated sulfuric acid), and 120 g of sodium bisulfate are successively added to a stirrer, stirred for 1 hour, then dispersed into a uniform material and placed in a baking tray, and placed in a vacuum drying oven. After heating to 200 °C and holding for 18 hours, the material is poured into 600 ml of water, and 1 g of activated carbon is added and heated to 80 °C for decolorization. After filtering out the activated carbon while it is hot, the solution is cooled to room temperature, crystallized, and filtered to obtain 72 g of white solid of Compound 2 (yield 41%).

[0053] S2. 210 mL of 2% hydrochloric acid is added to Compound 2 (10 g, 23.9 mmol), and an aqueous solution of 3.5 g (51 mmol) of sodium nitrite is added dropwise little by little each time while maintaining the temperature at 0 - 5 °C. After reacting and stirring for 2 hours, a diazonium salt is formed. Then, 6.9 g (50 mmol) of salicylic acid is dissolved in 300 ml of 5% sodium carbonate aqueous solution, and the above-mentioned mixed solution is slowly added dropwise thereto. A 20% aqueous NaCl solution is added, and a precipitate will be obtained. The precipitate is washed 3 times with 50 ml of dichloromethane to remove by-products such as unreacted salicylic acid, and then the precipitate is recrystallized with a mixed solution of ethanol and water to obtain Compound 4 (3.8 g, yield 21%).

[0054] The NMR data of Compound 4 are as follows:

[0055] 11H NMR (DMSO, 400 MHz): δ 7.18 - 7.32 (2H, 7.24 (dd, J = 8.3, 0.5 Hz), 7.25 (dd, J = 8.3, 0.5 Hz)), 7.95 (1H, d, J = 5.4 Hz), 8.32 - 8.45 (2H, 8.39 (dd, J = 8.3, 1.8 Hz), 8.39 (dd, J = 8.3, 1.8 Hz)), 8.69 - 8.83 (3H, 8.74 (dd, J = 1.8, 0.5 Hz), 8.74 (dd, J = 1.8, 0.5 Hz), 8.78 (dd, J = 5.4, 0.5 Hz)), 8.90 (1H, t, J = 0.5 Hz), 9.27 (1H, d, J = 0.5 Hz).

[0056] Example 2

[0057] This example provides an azo compound (Compound 5), whose structural formula is as follows; its preparation method is basically the same as that of Example 1, the difference is that dibenzo[b,d]pyridine-3,7-diamine is used instead of dibenzo[b,d]thiophene-3,7-diamine.

[0058]

[0059] Its nuclear magnetic data is as follows:

[0060] 1 1H NMR (DMSO, 400 MHz): δ 7.17 - 7.30 (2H, 7.23 (dd, J = 8.3, 0.5 Hz), 7.24 (dd, J = 8.3, 0.5 Hz)), 7.55 - 7.74 (2H, 7.60 (d, J = 0.5 Hz), 7.68 (d, J = 5.4 Hz)), 8.24 - 8.37 (2H, 8.31 (dd, J = 8.3, 1.9 Hz), 8.31 (dd, J = 8.3, 1.9 Hz)), 8.61 - 8.86 (4H, 8.66 (t, J = 0.5 Hz), 8.70 (dd, J = 1.9, 0.5 Hz), 8.71 (dd, J = 1.9, 0.5 Hz), 8.81 (dd, J = 5.4, 0.5 Hz)).

[0061] Example 3

[0062] This example provides an azo compound (Compound 6), whose structural formula is as follows; its preparation method is basically the same as that of Example 1, the difference is that in step S1, dibenzo[b,d]furan-3,7-diamine is used instead of dibenzo[b,d]thiophene-3,7-diamine.

[0063]

[0064] Its NMR data is as follows:

[0065] 1 H NMR(DMSO, 400 MHz): δ 7.20 - 7.32(2H, 7.26(dd, J = 8.3, 0.5 Hz), 7.26(dd, J = 8.3, 0.5 Hz)), 7.77(1H, d, J = 0.5 Hz), 8.08(1H, d, J = 5.4 Hz), 8.32 - 8.44(2H, 8.38(dd, J = 8.3, 1.8 Hz), 8.38(dd, J = 8.3, 1.8 Hz)), 8.68 - 8.95(4H, 8.74(dd, J = 1.8, 0.5 Hz), 8.74(dd, J = 1.8, 0.5 Hz), 8.83(dd, J = 5.4, 0.5 Hz), 8.90(t, J = 0.5 Hz)).

[0066] Furthermore, by referring to the preparation method of Example 1, the present invention can prepare the following azo compounds by changing the raw materials.

[0067]

[0068] Example 4

[0069] This example provides an azo compound (Compound 8), and its reaction equation and preparation method are as follows:

[0070]

[0071] S1. Add the compound 4 (3 g, 3.94 mmol) prepared in the above Example 1 and 6 - bromo - 1 - hexanol (1.45 g, 8 mmol) to DMF (30 mL), add K2CO3 (2.25 g, 16 mmol), and stir the mixture at 80 °C for 1 hour. Dilute the reaction mixture with ethyl acetate, wash it with water and brine, and then dry it with Na2SO4. Filter and concentrate under vacuum and purify by flash chromatography on silica gel (PE / EA 2 / 1) to obtain compound 7 (2.06 g; yield 54.4%).

[0072] S2. Under nitrogen protection, compound 7 (2.06 g, 2.14 mmol), 1.5 equiv of triethylamine (0.29 g, 3.21 mmol) and THF (30 mL) were stirred in an ice bath. Acryloyl chloride (0.43 g, 4.28 mmol) was added dropwise to the mixture, and the mixture was stirred at 15 °C for 5 h. The solution was filtered, and the filtrate was concentrated in vacuo. The residue was dissolved in ethyl acetate, washed with saturated ammonium chloride solution, and dried over anhydrous magnesium sulfate. After removing the solvent in vacuo, it was purified by silica gel column chromatography (hexane / ethyl acetate = 5 / 1) and recrystallized from a mixed solvent (PE / DCM = 3 / 1) to obtain yellow solid compound 8 (0.9 g; yield 39.3%).

[0073] Its NMR data are as follows:

[0074] 11H NMR (DMSO, 400 MHz): δ 1.28 - 1.48 (8H, 1.35 (tt, J = 7.5, 7.0 Hz), 1.35 (tt, J = 7.5, 7.0 Hz), 1.41 (tt, J = 7.4, 7.0 Hz), 1.41 (tt, J = 7.4, 7.0 Hz)), 1.66 - 1.92 (8H, 1.73 (tt, J = 7.4, 7.1 Hz), 1.73 (tt, J = 7.4, 7.1 Hz), 1.85 (tt, J = 7.5, 7.2 Hz), 1.85 (tt, J = 7.5, 7.1 Hz)), 4.13 - 4.26 (4H, 4.19 (t, J = 7.1 Hz), 4.20 (t, J = 7.1 Hz)), 4.43 - 4.63 (4H, 4.49 (t, J = 7.1 Hz), 4.57 (t, J = 7.2 Hz)), 5.95 - 6.08 (2H, 6.02 (dd, J = 10.9, 1.5 Hz), 6.02 (dd, J = 10.9, 1.5 Hz)), 6.29 - 6.44 (2H, 6.37 (dd, J = 17.0, 1.5 Hz), 6.37 (dd, J = 17.0, 1.5 Hz)), 6.78 - 7.08 (2H, 6.86 (dd, J = 17.0, 10.9 Hz), 6.99 (dd, J = 17.0, 10.9 Hz)), 7.23 - 7.36 (2H, 7.29 (dd, J = 8.3, 0.5 Hz), 7.30 (dd, J = 8.3, 0.5 Hz)), 7.95 (1H, d, J = 5.4 Hz), 8.27 - 8.40 (2H, 8.34 (dd, J = 8.3, 1.9 Hz), 8.34 (dd, J = 8.3, 1.9 Hz)), 8.68 - 8.83 (3H, 8.73 (dd, J = 1.9, 0.5 Hz), 8.73 (dd, J = 1.9, 0.5 Hz), 8.77 (dd, J = 5.4, 0.5 Hz)), 8.90 (1H, t, J = 0.5 Hz), 9.26 (1H, d, J = 0.5 Hz).

[0075] Example 5

[0076] This example provides an azo compound (Compound 9) with the following structural formula. The preparation method is the same as that in Example 4. The difference is that in step S1, the azo compound (Compound 6) of Example 3 is used to replace Compound 4 prepared in Example 1.

[0077]

[0078] Its NMR data is as follows:

[0079] 11H NMR (DMSO, 400 MHz): δ 1.27 - 1.45 (8H, 1.34 (tt, J = 7.5, 7.1 Hz), 1.35 (tt, J = 7.4, 7.1 Hz), 1.38 (tt, J = 7.5, 7.1 Hz), 1.38 (tt, J = 7.5, 7.1 Hz)), 1.63 - 1.93 (8H, 1.70 (tt, J = 7.5, 6.8 Hz), 1.73 (tt, J = 7.7, 7.5 Hz), 1.85 (tt, J = 7.5, 7.1 Hz), 1.86 (tt, J = 7.4, 7.2 Hz)), 3.35 (2H, t, J = 6.8 Hz), 3.92 (2H, t, J = 7.7 Hz), 4.42 - 4.56 (4H, 4.47 (t, J = 7.1 Hz), 4.50 (t, J = 7.2 Hz)), 7.34 - 7.55 (2H, 7.40 (dd, J = 8.3, 0.5 Hz), 7.49 (dd, J = 8.3, 0.5 Hz)), 7.75 (1H, d, J = 0.5 Hz), 8.08 (1H, d, J = 5.4 Hz), 8.19 - 8.41 (2H, 8.25 (dd, J = 8.3, 1.8 Hz), 8.35 (dd, J = 8.3, 1.9 Hz)), 8.62 - 8.95 (4H, 8.67 (dd, J = 1.8, 0.5 Hz), 8.73 (dd, J = 1.9, 0.5 Hz), 8.83 (dd, J = 5.4, 0.5 Hz), 8.90 (t, J = 0.5 Hz)).

[0080] Example 6

[0081] This example provides an azo compound (Compound 10) with the following structural formula. The preparation method is the same as that in Example 4. The difference lies in that in step S1, the azo compound (Compound 5) of Example 2 is used to replace Compound 4 prepared in Example 1.

[0082]

[0083] Its nuclear magnetic data is as follows:

[0084] 11H NMR (DMSO, 400 MHz): δ 1.27 - 1.45 (8H, 1.34 (tt, J = 7.5, 7.1 Hz), 1.35 (tt, J = 7.4, 7.1 Hz), 1.38 (tt, J = 7.5, 7.1 Hz), 1.38 (tt, J = 7.5, 7.1 Hz)), 1.63 - 1.92 (8H, 1.70 (tt, J = 7.5, 6.8 Hz), 1.73 (tt, J = 7.7, 7.5 Hz), 1.84 (tt, J = 7.5, 7.2 Hz), 1.85 (tt, J = 7.4, 7.2 Hz)), 3.35 (2H, t, J = 6.8 Hz), 3.91 (2H, t, J = 7.7 Hz), 4.43 - 4.56 (4H, 4.49 (t, J = 7.2 Hz), 4.50 (t, J = 7.2 Hz)), 7.33 - 7.53 (2H, 7.39 (dd, J = 8.3, 0.5 Hz), 7.47 (dd, J = 8.3, 0.5 Hz)), 7.53 - 7.74 (2H, 7.58 (d, J = 0.5 Hz), 7.68 (d, J = 5.4 Hz)), 8.09 - 8.30 (2H, 8.15 (dd, J = 8.3, 1.9 Hz), 8.24 (dd, J = 8.3, 1.9 Hz)), 8.58 - 8.86 (4H, 8.63 (dd, J = 1.9, 0.5 Hz), 8.65 (t, J = 0.5 Hz), 8.70 (dd, J = 1.9, 0.5 Hz), 8.80 (dd, J = 5.4, 0.5 Hz)).

[0085] Furthermore, the present invention can prepare the following azo compounds by referring to the preparation method of Example 4 and changing the raw materials.

[0086]

[0087]

[0088] Comparative Example 1

[0089] Comparative Example 1 provides an alignment dye BY (CAS: 3051 - 11 - 4; commercially available).

[0090] Comparative Example 2

[0091] Comparative Example 2 provides an alignment dye SD1 (CAS: 6232 - 49 - 1; commercially available).

[0092] Performance Test

[0093] The azo compounds provided in Examples 1 - 6 of the present invention and Comparative Examples 1 - 2 were prepared into photo - alignment films by the following method:

[0094] First, use the azo compounds provided in Examples 1-6 and Comparative Examples 1-2 of the present invention as the alignment layer material, and dissolve 1 wt.% of the alignment layer material in the DMF solution. After preparing the solution, filter impurities using a 0.2 μm filter element, then pre-treat the glass substrate, and then spin-coat the solution on the glass substrate as the photo-alignment layer. Spin-coat the prepared alignment layer solution on the pre-treated glass substrate by spin coating. During the operation of the spin coater, first set the rotation speed to a slow speed (500 mpm) and spin-coat the solution for 5 s to ensure that the solution spreads evenly on the substrate. Subsequently, increase the rotation speed to a fast speed (3000 rpm) and continuously spin-coat for 25 s to promote the evaporation of the solvent in the alignment layer, thereby forming a film layer with the desired thickness. After completing the spin coating of the alignment layer, place the substrate on a heating table and perform a heat treatment at 100 °C for 10 minutes to further remove the residual solvent and achieve thermal curing, thereby forming a stable alignment film layer. During this process, ensure the cleanliness of the glass substrate and the surface of the alignment film layer as much as possible, otherwise it will affect the final grating structure and display effect.

[0095] Perform the following experimental tests on the prepared photo-alignment film: The results are shown in Table 1.

[0096] Photo-alignment performance: After spin coating the alignment layer, irradiate with a specific exposure energy, and then spin coat the liquid crystal material in the next step. A grating will appear. Observe whether the grating structure is clear through a polarizing microscope, and observe the texture of the liquid crystal under polarized light to see if there are unaligned liquid crystal molecules.

[0097] Photosensitivity: Measure according to the method of GB 10557-89. Under specific temperature and humidity conditions, test the lowest exposure energy to produce a perfect grating. The higher the photosensitivity, the smaller the exposure energy required and the shorter the exposure time, and the more sensitive the alignment.

[0098] Temperature sensitivity: Under the conditions of an exposure energy of 2.0 J and a humidity of 40%, explore the widest temperature range capable of forming a perfect grating.

[0099] Humidity sensitivity: Under the conditions of an exposure energy of 2.0 J and a temperature of 23 °C, explore the widest humidity range capable of forming a perfect grating.

[0100] Chromaticity: Detect the b value of the above-prepared alignment layer using a color difference meter. The results are shown in Table 1.

[0101] Table 1

[0102]

[0103] Judging from the data in Table 1, the azo compounds provided in Examples 1-6 of the present invention have the characteristics of good photo-alignment performance, low photosensitivity, low temperature and humidity sensitivity, and low chromaticity.

[0104] The above has been described in detail in connection with the embodiments of the present invention. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. An azo compound, characterized in that, It has the following structural formula: Wherein, X is selected from -O, -S, -NH; R1 and R2 are each independently selected from H, wherein, R5, R6, and R7 are independently selected from H or C 1～6 alkyl; n, m, y, z, p, or q are each independently selected from integers of 1 to 20; R3 and R4 are independently selected from a haloalkyl group of C 1～6 , a carboxyl group of C 1～6 , or a sodium carboxylate of C 1～6 .

2. The azo compound according to claim 1, wherein R3 and R4 are independently selected from a haloalkyl group of C 1～3 , a carboxyl group of C 1～3 , or a sodium carboxylate salt of C 1～3 .

3. The azo compound according to claim 1 or 2, characterized in that, R1 and R2 are each independently selected from H, wherein, R5, R6, and R7 are independently selected from H or C 1～3 alkyl; n, m, y, z, p, or q are each independently selected from integers of 3 to 10.

4. The azo compound according to claim 1 or 2, characterized in that, R1 and R2 are the same.

5. The azo compound according to claim 1 or 2, characterized in that, R3 and R4 are the same.

6. The azo compound according to claim 1 or 2, characterized in that, The azo compound is selected from the following structural formulas:

7. An optical alignment film, characterized in that It includes the azo compound according to any one of claims 1 to 6.

8. The photo-alignment film according to claim 7, wherein The thickness of the photo-alignment film is 20 nm to 100 nm.

9. The photo-alignment film according to claim 7, wherein The photo-alignment film is prepared by the following method: Mix the azo compound according to any one of claims 1 to 6 with a solvent to obtain a coating; then coat the coating on a substrate, irradiate with polarized light to endow the liquid crystal alignment function, and then obtain it by heating or light irradiation.

10. A liquid crystal display device, characterized in that, It includes the photo-alignment film according to any one of claims 7 to 9.

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