CN117486744A - Diamine compound, polyimide, and liquid crystal display panel - Google Patents

Abstract

Provided are a diamine compound, polyimide, and a liquid crystal display panel. The diamine compound has a molecular structure represented by the following formula (1): wherein R is ₁ And R is ₂ Respectively selected from alkylene groups with 1-5 carbon atoms. The diamine compound of the present application contains diphenylethynyl group capable of undergoing polymerization reaction to form a dimer structure, the dimer structure of diphenylethynyl group has an anchoring effect on liquid crystal, and since the dimer structure of diphenylethynyl group has coplanarity, it is possible to reduce when polyimide synthesized from the diamine compound as a raw material is used as an alignment filmLow pretilt angle of the liquid crystal.

Description

Diamine compounds, polyimide and liquid crystal display panels

Technical field

The present application relates to the field of display, and in particular to a diamine compound, polyimide and a liquid crystal display panel.

Background technique

Thin film transistor liquid crystal display (TFT-LCD) devices with wide viewing angles and high display quality have become mainstream display products on the market. Among them, In-Plane Switching (IPS) and Fringe Field Switching (FFS) type TFT-LCDs have been widely used as portable mobile devices due to their fast response, wide viewing angle, and low power consumption. Display panels for communication devices such as mobile phones and tablets. For IPS-LCD or FFS-LCD, a close to zero and stable pretilt angle value is usually required to avoid the problem of light leakage in the dark state of the panel. Since the deflection and alignment of liquid crystal are affected by the alignment layer, the structure and processing design of the alignment layer play an important role in realizing high-quality TFT-LCD in practical applications.

In order to obtain high-quality display effects, stable and uniform alignment of liquid crystals is one of the most important factors. In order to achieve uniform alignment of liquid crystals (LC), many alignment methods have been developed. For example, directional rubbing (Rubbing) of polymer films, evaporation of silica, ultraviolet (UV) exposure of photopolymers, ion beam treatment of polymer substrates, and surface modification of surfactants or micro-groove patterns, etc. Among them, the rubbing method is the most widely used and can provide the best electro-optical performance and good thermal stability of liquid crystal switches. However, corresponding impurities, electrostatic charges, and mechanical damage may cause liquid crystals to deflect abnormally under voltage.

In order to overcome these problems, non-contact alignment methods have been developed in recent years, especially the Patternless Optical Alignment (PA) method, which has many advantages compared with the rubbing method. In the photoalignment method, anisotropic polymer films can be used to achieve uniform alignment of liquid crystals. The anisotropy of the photoalignment layer is generated by polarized UV irradiation. However, using the chemical reaction of photodegradation, photosensitive polyimide (PI) can produce a uniform arrangement of liquid crystal molecules perpendicular to linearly polarized ultraviolet (LPUV) light, but the resulting polyimide The surface anisotropy is small, so the azimuthal anchoring energy of the liquid crystal layer attached to the surface is also small, and it is easy to cause the problem of unstable pretilt angle.

Contents of the invention

In view of this, the present application provides a diamine compound, polyimide and liquid crystal display panel that can increase anchoring energy and reduce pretilt angle.

The diamine compound of the present application has a molecular structure represented by the following formula (1):

Among them, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms.

Optionally, the diamine compound is any one of the following:

The present application also provides a polyimide having a molecular structure represented by the following formula (2):

Wherein, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms;

R ₃ is a structure derived from tetracarboxylic dianhydride;

R ₄ is selected from benzene ring, single heterocyclic ring, aromatic group containing two or more single rings or heteroaryl group containing two or more single rings.

Optional, R ₃ is selected from benzene ring, single heterocycle, two or more benzene rings connected by single bond, carbon atom or oxygen atom, two or more single heterocyclic rings connected by single bond, carbon atom or oxygen atom, single bond , the total number of rings connected to carbon atoms or oxygen atoms is more than two benzene rings and a single heterocyclic ring, two or more fused benzene rings, two or more fused single heterocyclic rings, the total number of fused rings is two The above benzene ring and single heterocyclic ring.

Optionally, R ₃ is selected from 2 to 3 benzene rings connected by a single bond, carbon atom or oxygen atom, 2 to 3 single heterocyclic rings connected by a single bond, carbon atom or oxygen atom, a single bond, carbon atom or oxygen atom. The combination of a benzene ring and a single heterocyclic ring with a total number of 2 to 3 rings connected by atoms, a fused 2 to 3 benzene ring, a fused 2 to 3 single heterocyclic ring, a combination of a fused ring with a total number of 2 to 3 rings Benzene ring and single heterocycle.

Optionally, R ₄ is selected from two or more benzene rings connected by a single bond, carbon atom or oxygen atom, two or more single heterocyclic rings connected by a single bond, carbon atom or oxygen atom, and two or more single heterocyclic rings connected by a single bond, carbon atom or oxygen atom. The total number of rings is a combination of two or more benzene rings and a single heterocyclic ring. The total number of fused rings is a combination of two or more benzene rings and a single heterocyclic ring. The total number of fused rings is a combination of two or more benzene rings and a single heterocyclic ring. Heterocycle.

Optionally, R ₃ is selected from one of the following groups:

Among them, the wavy line between two carbon atoms indicates that the connection site between _R3 and the dianhydride is not fixed.

Optionally, R ₄ is selected from one of the following groups:

Optionally, the polyimide has one of the following structural units:

The present application also provides a liquid crystal display panel, which includes an alignment film, and the alignment film includes the polyimide as described above.

The diamine compound provided by the present application has a molecular structure represented by the following formula (1):

Among them, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms. The diphenylacetylene contained in the diamine compound of the present application can polymerize to form a dimer structure. The dimer structure of diphenylacetylene has an anchoring effect on liquid crystals, and because the dimer structure of diphenylacetylene has Coplanarity can reduce the pretilt angle of liquid crystal when the polyimide synthesized using the diamine compound as a raw material is used as an alignment film.

Description of the drawings

In order to explain the technical solutions in the present application more clearly, the drawings needed to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, other drawings can also be obtained based on these drawings without exerting creative efforts.

Figure 1 is the NMR spectrum of diamine compound A synthesized in Example 1 of the present application.

Figure 2 is the NMR spectrum of the diamine compound A1 synthesized in Example 4 of the present application.

Figure 3 is a schematic structural diagram of a liquid crystal display panel according to some embodiments of the present application.

Detailed ways

The technical solutions in this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of this application.

In this application, unless otherwise explicitly stated and limited, the term "above" or "below" a first feature to a second feature may include the first and second features being directly connected, or may include the first and second features being directly connected. Not directly connected but through additional characteristic contact between them. Furthermore, the terms "above", "above" and "above" a first feature on a second feature include the first feature being directly above and diagonally above the second feature, or simply mean that the first feature is higher in level than the second feature. “Below”, “under” and “under” the first feature is the second feature includes the first feature being directly below and diagonally below the second feature, or simply means that the first feature is less horizontally than the second feature. In addition, the terms “first” and “second” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Therefore, the features defined as “first” and “second” may explicitly or implicitly include one or more features.

The present application provides a polyimide having a molecular structure represented by the following formula (1):

Wherein, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms;

R ₃ is a structure derived from tetracarboxylic dianhydride;

R ₄ is selected from benzene ring, single heterocyclic ring, aromatic group containing two or more single rings or heteroaryl group containing two or more single rings.

Specifically, examples of aromatic groups include: benzene, naphthalene, anthracene, phenanthrene, perylene, tetracene, pyrene, benzopyrene, triphenylene, acenaphthylene, fluorene, spirofluorene and derivatives thereof. Examples of heteroaryl groups are: furan, benzofuran, dibenzofuran, thiophene, benzothiophene, dibenzothiophene, pyrrole, pyrazole, triazole, imidazole, oxazole, oxadiazole, thiazole, tetrazole , indole, carbazole, pyrroloimidazole, pyrrolopyrrole, thienopyrrole, thienothiophene, furopyrrole, furanofuran, thienofuran, benzisoxazole, benzisothiazole, benzimidazole, Pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, naphthalene, quinoxaline, phenanthridine, primidine, quinazoline, quinazolinone, and their derivatives.

The polyimide includes a plurality of structural units (a), and each structural unit (a) has a horizontal skeleton derived from two diamine compounds. Two diamine compounds polymerize to form a polyphenyl ring rigid structure (b) between two adjacent rows of skeletons. The two diamine compounds are connected on one side in the vertical direction through the small molecule structure _R4 , and on the other side through the structure (c) derived from tetracarboxylic dianhydride. Therefore, the polyphenyl ring rigid structure (b) between two adjacent rows of skeletons is located between the structure (c) derived from tetracarboxylic dianhydride and R ₄ in the horizontal direction. Furthermore, adjacent structural units (a) are connected on one side by the small molecule structure _R4 , and on the other side by the structure (c) derived from tetracarboxylic dianhydride.

The polyphenyl ring rigid structure (b) of the present application has coplanarity, and the polymerizable groups at both ends of the diamine compound react with tetracarboxylic dianhydride and the small molecule structure R ₄ derived from small molecules to form a stable polymerization It can be used in the liquid crystal alignment layer to improve the alignment stability with the liquid crystal, that is, the anchoring effect. Liquid crystal cells using this alignment material can achieve a lower liquid crystal pretilt angle and can be applied to LCD display panels with horizontal electric fields such as IPS.

Specifically, the polyimide of some embodiments of the present application has one of the following structural units:

Hereinafter, each component and its source of the above-mentioned polyimide will be described in detail.

(A) Diamine compound

The diamine compound used to synthesize polyimide in this application is a new type of diamine compound, which has a molecular structure represented by the following formula (2):

Among them, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms.

The diphenylethynyl group of the diamine compound of formula (2) is a photo-alignment group, and the amine groups and vinyl groups at both ends are polymerizable groups. Under the irradiation of linearly polarized ultraviolet light (for example, 365nm linearly polarized ultraviolet light), the diphenylethynyl group in the diamine compound of formula (2) is cleaved and a dimerization reaction occurs to form a dimer. The specific reaction process is as follows:

Among them, the wavy lines in the reaction formula represent omitted structures.

The above reaction can only occur when the transition dipole moment of the diphenylethynyl group is parallel to the electric vector direction of LPUV, that is, the reaction has optical axis selectivity. This reaction can produce anisotropic polymers. The dimer structure of diphenylacetylene generated by the above method has an anchoring effect on the liquid crystal, and because the dimer structure of diphenylacetylene is coplanar, the pretilt angle of the liquid crystal can be reduced by using this alignment layer material , suitable for LCD display panels with horizontal electric fields such as IPS. In addition, the polymerizable groups at both ends of the diamine compound can undergo a polymerization reaction with tetracarboxylic dianhydride to form a stable polymer, thereby improving the alignment stability with the liquid crystal, that is, the anchoring effect.

Optionally, R ₁ is selected from an alkylene group having 1 to 5 carbon atoms, and R ₂ is selected from an alkylene group having 1 to 3 carbon atoms.

Optionally, the diamine compound is any one of the following diamine compounds:

(B) Tetracarboxylic dianhydride compound

All tetracarboxylic dianhydride compounds commonly used in this field can be used as the tetracarboxylic dianhydride compound in this application. That is, this application does not specifically limit the structure derived from tetracarboxylic dianhydride.

Optionally, R ₃ is selected from a benzene ring, a single heterocyclic ring, two or more benzene rings connected by a single bond, a carbon atom or an oxygen atom, two or more single heterocyclic rings connected by a single bond, a carbon atom or an oxygen atom, or a single ring. The total number of rings connected by bonds, carbon atoms or oxygen atoms is more than two benzene rings and a single heterocyclic ring, two or more fused benzene rings, two or more fused single heterocyclic rings, the total number of fused rings is two More than one benzene ring and single heterocyclic ring. The benzene ring or single heterocyclic ring can provide rigidity to the molecule, thus improving the anchoring force.

Specifically, examples of R ₃ are: furan, benzofuran, dibenzofuran, thiophene, benzothiophene, dibenzothiophene, pyrrole, pyrazole, triazole, imidazole, oxazole, oxadiazole, thiazole, Tetrazole, indole, carbazole, pyrroloimidazole, pyrrolopyrrole, thienopyrrole, thienothiophene, furopyrrole, furanofuran, thienofuran, benzisoxazole, benzisothiazole, benzo Imidazole, pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, o-naphthalene, quinoxaline, phenanthridine, primidine, quinazoline, quinazolinone, and their derivatives .

Optionally, R ₃ is selected from 2 to 3 benzene rings connected by a single bond, carbon atom or oxygen atom, 2 to 3 single heterocyclic rings connected by a single bond, carbon atom or oxygen atom, a single bond, carbon atom or oxygen atom. The combination of a benzene ring and a single heterocyclic ring with a total number of 2 to 3 rings connected by atoms, a fused 2 to 3 benzene ring, a fused 2 to 3 single heterocyclic ring, a combination of a fused ring with a total number of 2 to 3 rings Benzene ring and single heterocycle. The number of benzene rings or single heterocycles determines the rigidity of the group and the length of the group. Therefore, the structure (c) derived from tetracarboxylic dianhydride and the polyphenyl ring rigid structure (b) are equally rigid and similar in length, which is beneficial to improving structural stability.

Specifically, R ₃ can be one of the following groups:

Among them, the wavy line between two carbon atoms indicates that the connection site between _R3 and the dianhydride is not fixed.

Correspondingly, the tetracarboxylic dianhydride compound is selected from one of the following compounds:

(C)Small molecule structure

R ₄ is derived from small molecules with vinyl groups as described below:

Among them, R ₄ is selected from two or more benzene rings connected by a single bond, carbon atom or oxygen atom, two or more single heterocyclic rings connected by a single bond, carbon atom or oxygen atom, a ring connected by a single bond, carbon atom or oxygen atom. The total number of fused rings is a combination of two or more benzene rings and a single heterocyclic ring, two or more fused benzene rings, a fused two or more single heterocyclic rings, the total number of fused rings is a combination of two or more benzene rings and a single heterocyclic ring .

The double bond on one side of the diamine compound in (A) undergoes a free radical polymerization reaction with the above small molecular structure under irradiation of 365 nm ultraviolet light. The specific reaction process is as follows:

Optional, R ₄ selects two benzene rings connected by a single bond, carbon atom or oxygen atom, two single heterocycles connected by a single bond, carbon atom or oxygen atom, the total number of rings connected by a single bond, carbon atom or oxygen atom is The combination of two benzene rings and a single heterocyclic ring, two fused benzene rings, two fused single heterocyclic rings, the total number of fused rings is two benzene rings and a single heterocyclic ring. Therefore, the linking group R ₄ and the polyphenyl ring rigid structure (b) have equivalent rigidities and similar lengths, which is beneficial to improving structural stability.

Optionally, R ₄ is selected from one of the following groups:

Optionally, R ₄ is selected from para-biphenyl or para-terphenyl.

In some embodiments, R ₃ is selected from 2 to 3 benzene rings connected by single bonds, carbon atoms or oxygen atoms, 2 to 3 single heterocycles connected by single bonds, carbon atoms or oxygen atoms, single bonds, carbon atoms Or a combination of a benzene ring and a single heterocyclic ring with a total number of 2 to 3 rings connected to the oxygen atom, 2 to 3 fused benzene rings, 2 to 3 fused single heterocyclic rings, and a total of 2 to fused rings. 3’s benzene ring and single heterocyclic ring, and R ₄ is selected from two benzene rings connected by a single bond, carbon atom or oxygen atom, two single heterocyclic rings connected by a single bond, carbon atom or oxygen atom, single bond, carbon atom Or a combination of a benzene ring with two fused rings and a single heterocycle, two fused benzene rings, two fused monoheterocycles, a benzene ring with a single fused ring in total. Heterocycle. Therefore, R ₃ and R ₄ have the same rigidity and similar lengths, and are similar in length to the connecting group in the middle, and the structure of the obtained polyimide is more stable.

In this application, by polymerizing the above-mentioned (A) diamine compound, (B) dianhydride compound and (C) small molecular structure, and through the cross-linking reaction of double bonds, the generated polyimide side chains can be arranged in an orderly manner. , further fixing the polyphenyl ring structure formed by the polymerization of the core alignment group diphenylalkyne, which improves the anisotropy of the film and enhances the anchoring stability to the liquid crystal, thereby improving the LCD's imaging sticking (IS) problem.

The present invention will be described below with reference to the preferred embodiments, but the present invention is not limited to the following embodiments. It should be understood that the appended claims summarize the scope of the present invention. Under the guidance of the concept of the present invention, those skilled in the art should It is appreciated that certain changes may be made to the various embodiments of the present invention and will be covered by the spirit and scope of the claims of the present invention.

Example 1

1.1 Synthesis of new diamine compound A

Example 1 Taking R ₁ as an alkylene group with a carbon number of 3 and R ₂ as an alkylene group with a carbon number of 2 as an example, the synthesis flow chart of the new diamine compound A is as follows:

Among them, (1) to (8) are all intermediate products, and all starting materials can be high-purity (>99%) commercial products.

Synthesis of (1): Add 16.6g (0.1mol) ethyl 4-hydroxybenzoate to 300 ml of 2-butanone dissolved in 4g (0.12mol) NaOH. After adding 15g (0.1mol) NaI and 11.4g (0.12mol) 3-chloro-1-propanol, the mixture was heated at 60°C for 10h and evaporated to obtain (1).

Synthesis of (2): Add intermediate product (1) to 300 ml of 0.5 mol/L KOH solution and reflux for 5 hours. Residual 3-chloro-1-propanol was removed by washing with diethyl ether, and the aqueous phase was neutralized with HCI to obtain precipitate (2) and filtered.

Synthesis of (3): After recrystallizing the precipitate (2) from ethanol, dissolve 13.9g (0.11mol) of N,N-dimethylaniline in 230 ml of 1,4-dioxane, Another 19.6 g (0.1 mol) of precipitate (2) was added. At 60°C, 10.4g (0.11mol) acryloyl chloride was slowly added. After 2 h, (3) was isolated by washing with water and recrystallized from 2-propanol.

Synthesis of (4): Add 10g (0.04mol) of (3) obtained by recrystallization into a flask containing 80ml of methylene chloride, stir and dissolve, add 8.8g (0.04mol) of 4-iodophenol, and continue to stir evenly. Add 0.1g (0.4mmol) dicyclohexylcarbodiimide and 0.05g (0.4mmol) 4-dimethylaminopyridine, continue stirring and dissolving, then place the flask in a 60°C water bath and continue stirring for 10 hours. (4) was then separated by washing with water, and recrystallized in 2-propanol to obtain 15.2 g of pure product (4), with a yield of 81%.

Synthesis of (5): Add 9.92g (40.0mmol) p-iodobenzoic acid, 17.36g (280.0mmol) ethylene glycol and a few drops of methanesulfonic acid to a 500mL flask. After stirring at 115 °C for 4 h, the mixture was poured into 1 liter of water and extracted several times with ethyl acetate. The combined organic solutions were washed several times with deionized water, washed with saturated aqueous _NaHCO solution, and then dried over anhydrous sodium sulfate. The solution was evaporated to obtain crude product (5). The crude product (5) was purified by chromatography (dichloromethane:ethyl acetate=1:1) to obtain a dark yellow oily product (5). Yield: 88%.

Synthesis of (6): Into a 100mL flask, add 8.76g (30.0mmol) compound (5), 80mL triethylamine, 114.3mg (0.6mmol) copper iodide (I) and 693.3mg (0.6mmol) tetrakis (triethylamine) Phenylphosphine)palladium(0). The mixture was flushed with nitrogen and 4.4 g (45.0 mmol) of trimethylsilyl acetylene was added with magnetic stirring. After stirring at 40°C for 24 h, 14.4 ml of 75% (w/w) tetrabutylammonium fluoride aqueous solution was added to deprotect the silane part. After stirring for a further 30 minutes, the solvent was evaporated in vacuo, the residual mixture was dissolved in dichloromethane and filtered. The obtained organic phase was washed several times with aqueous HCl solution and dried over anhydrous magnesium sulfate. The solvent was evaporated to obtain a crude product, which was further purified by chromatography (dichloromethane:ethyl acetate=2:1) to obtain product (6) as a dark yellow liquid, yield: 72%.

Synthesis of (7): Add 3.8g (20.0mmol) compound (6), 3.0g (30.0mmol) triethylamine and 40mL dichloromethane into a 100mL flask. The mixture was flushed with nitrogen, and 5.5 g (24.0 mmol) 3,5-dinitrobenzoyl chloride was slowly added in an ice bath under magnetic stirring. After stirring at room temperature for 12 h, the solution was diluted with 40 mL of dichloromethane, and then washed with 20 mL of 1 mol/L HCl aqueous solution and deionized water respectively. The organic phase was dried over anhydrous sodium sulfate, and the solvent was evaporated to obtain crude product (7). The crude product (7) was purified by chromatography (dichloromethane) to obtain the product (7) as a pale yellow liquid. Yield: 41%.

Synthesis of (8): In a 250ml flask, weigh 3.5g (0.01mol) of purified (7) and disperse it in a mixed solvent of 70ml ethanol and 5g (0.1mol) hydrazine hydrate while stirring magnetically and bubbling nitrogen to remove 0.5 of the oxygen. h, after bubbling, add 80mg palladium carbon. Quickly place the reaction bottle into a 90°C oil bath and condense and reflux for 4 hours. After the reaction is completed, cool to room temperature, and filter to remove the palladium carbon catalyst. Add water to precipitate, and filter to obtain a filter residue. The filter residue is purified by recrystallization with DMF, washed with water, and dried in a vacuum oven for 2 hours to obtain (8) with a yield of 95%.

Synthesis of diamine compound A: Add 1.8g (4.0mmol) compound (4), 1.43g (4.4mmol) compound (8), 25ml triethylamine, 25.4mg (0.13mmol) copper iodide (I) to a 50ml flask. ) and 154.1 mg (0.13 mol) tetrakis(triphenylphosphine)palladium(0). The flask was flushed with nitrogen and placed under magnetic stirring. After stirring at 45 °C for 24 h, the solvent was evaporated in vacuo, the residual mixture was dissolved in dichloromethane and filtered. The obtained organic phase was washed with 0.5 mol/L HCl aqueous solution, dried over anhydrous magnesium sulfate, and the solvent was evaporated to obtain a crude product. The crude product was purified by chromatography (ethyl acetate: dichloromethane: petroleum ether = 1:10:10) and recrystallized with ethanol several times to obtain the final product A as white crystals. Yield: 70%.

The synthesized diamine compound A was confirmed, and the 1H-NMR (Nuclear Magnetic Resonance: Nuclear Magnetic Resonance) spectrum of the diammonium compound A is shown in Figure 1.

The test conditions for 1H-NMR are as follows:

Solvent: Deuterated DMSO

Frequency: 300MHz

1.2 Polyamic acid polymerization

For the dianhydride compound, take pyromellitic dianhydride as an example. Weigh 6.49g (10mmol) diamine compound A and add it to 90g N-methylpyrrolidone NMP. After it is completely dissolved, add 2.18g (10mmol) pyromellitic acid dianhydride. Anhydride, stir in a 300 mL three-necked flask while flowing nitrogen, and stir at room temperature for 12 hours to obtain a polyamic acid solution.

1.3 Dispersion of active small molecules

For small molecules, take paradienebenzene as an example. Weigh 1.3g (10mmol) of paradienebenzene and add it to 15g of NMP. Ultrasonicate the mixed system to completely dissolve it. Then slowly add the dispersed solution to the rapidly stirring polyethylene glycol. In the polyamic acid (PAA) solution, stir for another 6 hours to obtain a polyamic acid (PAA) solution that can be used for spin coating.

1.4 Panel preparation and performance testing

(1) Spin-coat the PAA prepared above on the 5×5cm array substrate and color filter substrate respectively, pre-bake at 90°C for 5 minutes to evaporate the solvent, then increase the temperature to 230°C and bake for 30 minutes , to obtain a polyimide film.

(2) Irradiate the baked substrate with ultraviolet light with an energy of 500mJ/cm ² and a wavelength of 365nm, so that the photodimerization reaction occurs and an anisotropic thin film is generated.

(3) Dispense glue on the surface of the CF substrate and form a box with the TFT substrate.

(4) In a vacuum environment, a horizontally aligned liquid crystal cell can be obtained by injecting negative liquid crystal.

(5) Test the pretilt angle and afterimage of the liquid crystal cell.

Example 2

The difference between Example 2 and Example 1 lies in the dianhydride used. Specifically, the steps after the synthesis of diamine compound A include:

2.2 Polyamic acid polymerization

Add 6.49g (10mmol) diamine compound A to 100ml NMP, stir until completely dissolved, then add 2.94g (10mmol) 3,3,4,4-biphenyltetracarboxylic dianhydride, and continue stirring under nitrogen atmosphere protection.

2.3 Dispersion of active small molecules

Add 1.3g (10mmol) paradienebenzene to 15g NMP, use ultrasound to completely dissolve it, then slowly add the dispersed solution to the rapidly stirring PAA solution, and stir for another 12 hours to obtain a PAA solution with a certain viscosity. , can be used for spin coating.

2.4 Panel preparation and performance testing

The PAA solution was spin-coated on a 5×5cm array substrate and color filter substrate and thermally cured, followed by 365nm illumination treatment with a condition of 500mJ/cm ² .

After preparing the liquid crystal cell, its pretilt angle and afterimage were tested.

Example 3

The difference between Example 3 and Example 1 lies in the dianhydride compound used. Specifically, the steps after the synthesis of diamine compound A include:

3.2 Polyamic acid polymerization

Add 6.49g (10mmol) diamine compound A to 100ml NMP, stir until completely dissolved, then add 3.10g (10mmol) 4,4-oxybisphthalic anhydride, and continue stirring under nitrogen atmosphere protection.

3.3 Dispersion of active small molecules

Add 1.3g (10mmol) paradienebenzene to 15g NMP, use ultrasound to completely dissolve it, then slowly add the dispersed solution to the rapidly stirring PAA solution, and stir for another 12 hours to obtain a PAA solution with a certain viscosity. , can be used for spin coating.

3.4 Panel preparation and performance testing

The PAA solution was spin-coated on a 5×5cm TFT substrate and a CF substrate and thermally cured, followed by 365nm illumination treatment with a condition of 500mJ/cm ² .

After preparing the liquid crystal cell, its pretilt angle and afterimage were tested.

Example 4

The difference between Example 4 and Example 1 lies in the diamine compound used. Example 4 Synthesis of diamine compound A1 using the same steps as Example 1 (1) to (8):

The synthesized diamine compound A1 was confirmed, and the nuclear magnetic resonance spectrum of the diammonium compound A1 is shown in Figure 2.

The test conditions for 1H-NMR are as follows:

Solvent: Deuterated DMSO

Frequency: 300MHz

The steps following the synthesis of diamine compound A1 include:

4.2 Polyamic acid polymerization

Add 6.91g (10mmol) diamine compound A1 to 100ml NMP, stir until completely dissolved, then add 3.10g (10mmol) 4,4-oxybisphthalic anhydride, and continue stirring under nitrogen atmosphere protection.

4.3 Dispersion of active small molecules

Add 1.3g (10mmol) paradienebenzene to 15g NMP, use ultrasound to completely dissolve it, then slowly add the dispersed solution to the rapidly stirring PAA solution, and stir for another 12 hours to obtain a PAA solution with a certain viscosity. , can be used for spin coating.

4.4 Panel preparation and performance testing

The PAA solution was spin-coated on a 5×5cm TFT substrate and a CF substrate and thermally cured, followed by 365nm illumination treatment with a condition of 500mJ/cm ² .

After preparing the liquid crystal cell, its pretilt angle and afterimage were tested.

Example 5

The difference between Example 5 and Example 1 lies in the small molecules used. The small molecule compounds in Example 5 are:

The steps following the synthesis of diamine compound A include:

5.2 Polyamic acid polymerization

Add 6.49g (10mmol) diamine compound A to 100ml NMP, stir until completely dissolved, then add 3.10g (10mmol) 4,4-oxybisphthalic anhydride, and continue stirring under nitrogen atmosphere protection.

5.3 Dispersion of active small molecules

Add 1.8g (10mmol) paradiene naphthalene to 15g NMP, use ultrasound to completely dissolve it, then slowly add the dispersed solution to the rapidly stirring PAA solution, and stir for another 12 hours to obtain a PAA solution with a certain viscosity. , can be used for spin coating.

5.4 Panel preparation and performance testing

The PAA solution was spin-coated on a 5×5cm TFT substrate and a CF substrate and thermally cured, followed by 365nm illumination treatment with a condition of 500mJ/cm ² .

After preparing the liquid crystal cell, its pretilt angle and afterimage were tested.

Comparative ratio

Weigh 2.00g (10mmol) 4,4'-diaminodiphenyl ether ODA and add it to 25.7g NMP. Stir thoroughly to dissolve and then add 2.24g (10mmol) cyclobutane tetracarboxylic dianhydride CBDA. Continue stirring under the protection of nitrogen atmosphere. After 12 hours, a PAA solution suitable for spin coating is obtained and can be used for spin coating.

This is followed by thermal curing, followed by 254nm LPUV illumination treatment at a condition of 500mJ/cm ² . After preparing the Cell, test its pretilt angle.

The pretilt angle and afterimage detection conditions of Examples 1 to 5 and the Comparative Example are shown in Table 1 below.

Table 1

Example number/performance parameters pretilt angle 8V, 24h IS evaluation Example 1 0.08° A Example 2 0.16° A Example 3 0.21° A Example 4 0.25° A Example 5 0.10° A Comparative ratio 0.51° B

Among them, the afterimage evaluation was performed at 8V voltage and after 12 hours of power-on. If no afterimage is observed, it will be graded A, and if there is slight afterimage, it will be graded B.

As can be seen from Table 1, compared to the comparative examples, in Examples 1 to 5 of the present application, by using the dimer structure of diphenylacetylene with rigidity, derived from tetracarboxylic dianhydride and containing R ₃ With a rigid structure and a rigid linker R ₄ , the pretilt angle of the alignment film is significantly reduced, and the probability of afterimages can be reduced.

The present application also provides a liquid crystal display panel, which includes an alignment film, and the alignment film includes the polyimide as described in any one of the above. Please refer to FIG. 3 . The liquid crystal display panel 1 includes an array substrate 100 , a color filter substrate 200 and a liquid crystal layer 300 . The array substrate 100 and the color filter substrate 200 are arranged opposite to each other. The liquid crystal layer 300 is disposed between the array substrate 100 and the color filter substrate 200 . The array substrate 100 includes a first alignment film 101, and the color filter substrate includes a second alignment film 201. The liquid crystal display panel 1 may be an IPS or FFS type liquid crystal display panel.

The above provides a detailed introduction to the implementation of the present application. This article uses specific examples to illustrate the principles and implementations of the present application. The above description of the implementation is only used to help understand the present application. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the ideas of the present application. In summary, the content of this description should not be understood as a limitation of the present application.

Claims (10)

1. A diamine compound, characterized in that the diamine compound has a molecular structure represented by the following formula (1): Among them, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms. 2. The diamine compound as claimed in claim 1, wherein the diamine compound is any one of the following: 3. A polyimide, characterized in that the polyimide has a molecular structure represented by the following formula (2): Wherein, R ₁ and R ₂ are respectively selected from alkylene groups with 1 to 5 carbon atoms; R ₃ is a structure derived from tetracarboxylic dianhydride; R ₄ is selected from benzene ring, single heterocyclic ring, aromatic group containing two or more single rings or heteroaryl group containing two or more single rings. 4. The polyimide as claimed in claim 3, wherein _R3 is selected from benzene rings, single heterocycles, two or more benzene rings connected by single bonds, carbon atoms or oxygen atoms, single bonds, carbon atoms. Or the combination of two or more single heterocyclic rings connected by oxygen atoms, the total number of rings connected by single bonds, carbon atoms or oxygen atoms is two or more benzene rings and single heterocyclic rings, two or more fused benzene rings, fused Two or more single heterocyclic rings, the total number of fused rings is more than two benzene rings and single heterocyclic rings. 5. The polyimide of claim 3, wherein _R3 is selected from 2 to 3 benzene rings connected by single bonds, carbon atoms or oxygen atoms, and 2 benzene rings connected by single bonds, carbon atoms or oxygen atoms. ~3 single heterocyclic rings, a combination of benzene rings and single heterocyclic rings with a total number of 2 to 3 rings connected by single bonds, carbon atoms or oxygen atoms, 2 to 3 fused benzene rings, 2 to 3 fused benzene rings Single heterocyclic ring, a benzene ring and a single heterocyclic ring with a total number of fused rings of 2 to 3. 6. The polyimide according to any one of claims 3 to 5, wherein _R4 is selected from two or more benzene rings connected by a single bond, a carbon atom or an oxygen atom, a single bond, a carbon atom or an oxygen atom. Two or more single heterocyclic rings connected by atoms, the total number of rings connected by single bonds, carbon atoms or oxygen atoms is a combination of more than two benzene rings and single heterocyclic rings, two or more fused benzene rings, two fused benzene rings For the above single heterocyclic ring, the total number of fused rings is two or more benzene rings and single heterocyclic ring. 7. The polyimide _of claim 3, wherein R is selected from one of the following groups: Among them, the wavy line between two carbon atoms indicates that the connection site between _R3 and the dianhydride is not fixed. 8. The polyimide as claimed in claim 3, characterized in that R ₄ is selected from one of the following groups: 9. The polyimide of claim 3, wherein the polyimide has one of the following structural units: 10. A liquid crystal display panel, characterized in that it includes an alignment film, and the alignment film includes the polyimide according to any one of claims 3 to 9.