A negative liquid crystal compound and its preparation method and application

Abstract

The present application relates to the field of liquid crystal material technology, and specifically to a negative liquid crystal compound and its preparation method and application. The preparation method of the negative liquid crystal compound of the present application comprises: obtaining a first compound; dissolving the first compound, 2,7-dibromocarbazole, an alkaline compound, and a catalyst in a mixed solvent of tetrahydrofuran and water, filtering under a nitrogen atmosphere, refluxing at a temperature of 70 to 80°C, and washing and drying the filter residue to obtain a second compound; reacting the second compound with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and separating and purifying the reaction product to obtain a negative liquid crystal compound. The negative liquid crystal compound of the present application contains a benzene ring and a carbazole ring with a large conjugated structure, which can increase the degree of conjugation of the molecule, so that the liquid crystal compound has a larger birefringence, and the nitrogen atom on the carbazole ring can increase the dipole moment of the liquid crystal molecule in the vertical direction, so that the molecule has a larger negative dielectric anisotropy.

Description

Technical Field

[0001] The present application relates to the technical field of liquid crystal materials, and in particular to a negative liquid crystal compound and a preparation method and application thereof. Background Art

[0002] Negative liquid crystal has the advantages of high contrast and high transmittance, and is widely used in liquid crystal display devices. In order to improve the response speed of negative liquid crystal display devices, the following schemes can be adopted: (i) Develop liquid crystal materials with large dielectric anisotropy. The dielectric anisotropy of liquid crystal materials is related to the response time of liquid crystal display devices, that is, the larger the dielectric anisotropy of liquid crystal materials, the smaller the response time of liquid crystal display devices, and the faster the response speed; (ii) Develop liquid crystal materials with low viscosity. The viscosity of liquid crystal materials is closely related to the response time of liquid crystal devices, that is, the smaller the viscosity of liquid crystal materials, the faster the response speed; (iii) Reduce the thickness of liquid crystal device box. The lower the thickness of liquid crystal device box, the faster the response speed. Liquid crystal materials with large optical anisotropy (Δn) can ensure that the thickness of liquid crystal device box is effectively reduced in practical applications. Therefore, liquid crystal materials with large birefringence and large dielectric anisotropy are one of the keys to achieve fast response of liquid crystal optoelectronic devices.

[0003] At present, in order to improve the response speed of liquid crystal optoelectronic devices, negative liquid crystals with large birefringence or negative liquid crystals with large dielectric anisotropy are usually used. However, there are few liquid crystal molecules that have both large birefringence and large negative dielectric anisotropy. Summary of the invention

[0004] The purpose of the present application is to provide a negative liquid crystal compound and a preparation method and application thereof, so as to solve the problem that the negative liquid crystal used to improve the response speed of liquid crystal display devices in the prior art only has a large birefringence or a large negative dielectric anisotropy, but there are very few negative liquid crystals that have both a large birefringence or a large negative dielectric anisotropy, thereby further improving the response speed of liquid crystal display devices.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions to achieve it.

[0006] In one aspect, the present invention provides a negative liquid crystal compound, the chemical structure of which is shown in formula (1):

[0007]

[0008] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms;

[0009] Ring A is selected from Any one of .

[0010] Preferably, the negative liquid crystal compound includes:

[0011]

[0012] Another aspect of the present application provides a method for preparing the above-mentioned negative liquid crystal compound, when ring A is When, the preparation method comprises:

[0013] A first compound is obtained, wherein the chemical structure of the first compound is shown in formula (2):

[0014]

[0015] The first compound, 2,7-dibromocarbazole, a basic compound and a catalyst are dissolved in a mixed solvent of tetrahydrofuran and water, and the mixture is refluxed at 70-80° C. under a nitrogen atmosphere, and then filtered, and the filter residue is washed and dried to obtain a second compound;

[0016] The chemical structure of the second compound is shown in formula (3):

[0017]

[0018] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms;

[0019] The second compound is reacted with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and the reaction product is separated and purified to obtain a negative liquid crystal compound.

[0020] The preparation method of the above negative liquid crystal compound, when ring A is When, the preparation method comprises:

[0021] A fourth compound is prepared, whose chemical formula is:

[0022]

[0023] The preparation method of the fourth compound comprises:

[0024] Monofluoro-substituted p-bromophenol, 1-bromoalkane and alkaline compound are added to acetone, refluxed at 60-80°C, and separated and purified to obtain an intermediate product;

[0025] In a nitrogen atmosphere, add tetrahydrofuran to the intermediate product, slowly add n-butyl lithium at -90°C to -75°C for reaction, slowly add tributyl borate, raise the temperature to room temperature, separate and purify to obtain;

[0026] The molar ratio of the monofluoro-substituted p-bromophenol, 1-bromoalkane and alkaline compound is 1:1.05-1.50:1.5-3.0, and the molar ratio of the intermediate product, n-butyl lithium and tributyl borate is 1:1.1-1.8:2.5-3.5;

[0027] The fourth compound, 2,7-dibromocarbazole, a basic compound, and a catalyst are dissolved in a mixed solvent of tetrahydrofuran and water, and the mixture is refluxed at 70 to 80° C. under a nitrogen atmosphere, and then filtered, and the filter residue is washed and dried to obtain a fifth compound;

[0028] The chemical structure of the fifth compound is shown in Formula (4-1) or Formula (4-2):

[0029]

[0030] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms;

[0031] The fifth compound is reacted with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and the reaction product is separated and purified to obtain a negative liquid crystal compound.

[0032] As a preference of the second aspect of the present application, the molar ratio of the first compound or the fourth compound, 2,7-dibromocarbazole, the basic compound, and the catalyst is 1:2.5-3.5:7.0-9.0:0.07-0.18.

[0033] As a further preference of the second aspect of the present application, the alkaline compound is any one of sodium hydroxide, potassium hydroxide, anhydrous sodium carbonate or anhydrous potassium carbonate, or a mixture of two or more thereof; the catalyst includes tetrakis(triphenylphosphine)palladium and methyltrioctylammonium chloride, and the molar ratio of methyltrioctylammonium chloride to tetrakis(triphenylphosphine)palladium is 2-8:5-10.

[0034] As a preferred aspect of the second aspect of the present application, the separation and purification is:

[0035] The second compound or the fifth compound is dissolved in N,N-dimethylformamide, iodomethane is added dropwise for reaction, water is added for sedimentation, suction filtration is performed, and the filter residue is recrystallized and dried.

[0036] As a preference of the second aspect of the present application, the molar ratio of the second compound or the fifth compound, potassium hydroxide and methyl iodide is 1:6-8:1-2.

[0037] As a further preference of the second aspect of the present application, the recrystallization solvent is a mixed solution of petroleum ether and ethanol in a volume ratio of 1:1.

[0038] The third aspect of the present application provides the use of a negative liquid crystal compound in a liquid crystal display device.

[0039] Compared with the prior art, the beneficial effects of this application are:

[0040] The liquid crystal compound of the present application is a negative liquid crystal, and contains a benzene ring and a carbazole ring in the molecule, which can increase the conjugation degree of the liquid crystal compound molecule, thereby making the liquid crystal compound have a larger birefringence; the nitrogen atom on the carbazole ring can increase the dipole moment of the liquid crystal molecule in the vertical direction, so that the molecule has a larger negative dielectric anisotropy. The fluorine substituent on the benzene ring further increases the dipole moment of the liquid crystal compound molecule in the vertical direction, and increases the negative dielectric anisotropy value of the liquid crystal compound. The liquid crystal compound of the present invention has both a large birefringence and a negative dielectric anisotropy, and has a wide nematic phase temperature range, and the prepared liquid crystal optoelectronic device has a fast response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0042] Figure 1 It is the DSC curve of the liquid crystal compound prepared in Example 3 (heating and cooling rate 5°C / min).

[0043] Figure 2 This is a polarizing microscope (POM) test photograph (100×) of the liquid crystal compound prepared in Example 3 when the temperature was raised to 168.5°C.

[0044] Figure 3 This is a polarizing microscope (POM) test photograph (100×) of the liquid crystal compound prepared in Example 3 when the temperature was lowered to 191.5°C. DETAILED DESCRIPTION

[0045] In the following description of this embodiment, the terms "include", "comprising", "having" and "containing" are all open terms, meaning including but not limited to.

[0046] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0047] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0048] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0049] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0050] Those skilled in the art will appreciate that the numerical ranges in the embodiments of the present application are to be understood as each intermediate value between the upper and lower limits of the scope also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded in the scope.

[0051] Unless otherwise specified, the technical / scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs. Although this application only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of this application. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0052] In a first aspect of the present application, a negative liquid crystal compound is provided, the chemical structure of which is shown in formula (1):

[0053]

[0054] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms;

[0055] Ring A is selected from One of them.

[0056] Negative liquid crystal compounds contain benzene rings and carbazole rings, which can increase the conjugation degree of the liquid crystal compound molecules, thereby making the liquid crystal compounds have a larger birefringence; in addition, the nitrogen atoms on the carbazole ring can increase the dipole moment of the liquid crystal molecules in the vertical direction, making the molecules have a larger negative dielectric anisotropy. The fluorine substituents on the benzene rings further increase the dipole moment of the liquid crystal compound molecules in the vertical direction and increase the negative dielectric anisotropy value of the liquid crystal compound. The organic combination of the above functional groups makes the negative liquid crystal compounds have a larger dielectric anisotropy and a larger birefringence.

[0057] In the embodiments of the present application, the liquid crystal compound preferably has the following structure:

[0058]

[0059] The negative liquid crystal compound of the above structure has a large dielectric anisotropy and a large birefringence, a fast response speed and a high transmittance through the synergistic effect of the hexyloxyalkyl substituent, the benzene ring, the carbazole ring and the fluorine substituent.

[0060] The negative liquid crystal compound of the present application can be used to prepare a liquid crystal display device with a fast response speed.

[0061] The second aspect of the present application provides a method for preparing the above negative liquid crystal compound. According to the different structures of ring A, the present application includes two preparation methods.

[0062] (1) When ring A is When, the preparation method comprises:

[0063] Step 1: Obtain a first compound, the chemical structure of which is shown below:

[0064]

[0065] In an embodiment of the present application, the first compound is 4-(alkoxy)phenylboronic acid, including any one of 4-methoxyphenylboronic acid, 4-ethoxyphenylboronic acid, 4-propoxyphenylboronic acid, 4-butoxyphenylboronic acid, 4-pentyloxyphenylboronic acid or 4-hexyloxyphenylboronic acid, which is obtained by purchasing a commodity.

[0066] Step 2: dissolving the first compound, 2,7-dibromocarbazole, a basic compound and a catalyst in a mixed solvent of tetrahydrofuran and water, refluxing at 70 to 80° C. under a nitrogen atmosphere, filtering, and washing and drying the filter residue to obtain a second compound;

[0067] The reaction formula for preparing the second compound is as follows:

[0068]

[0069] Step 3: reacting the second compound with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and separating and purifying the reaction product to obtain a negative liquid crystal compound.

[0070] The reaction formula for preparing the negative liquid crystal compound is as follows:

[0071]

[0072] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms.

[0073] (2) Ring A is When, the preparation method comprises:

[0074] Step 1: Prepare a fourth compound having the chemical structural formula:

[0075]

[0076] The fourth compound is mono-fluorinated 4-(alkoxy)phenylboronic acid, and its preparation method comprises:

[0077] Monofluoro-substituted p-bromophenol, 1-bromoalkane and alkaline compounds are added to acetone, refluxed at 60-80° C., and subjected to distillation, separation and purification to obtain an intermediate product; the monofluoro-substituted p-bromophenol is 4-bromo-2-fluorophenol or 4-bromo-3-fluorophenol.

[0078] In a nitrogen atmosphere, add tetrahydrofuran to the intermediate product, slowly add n-butyl lithium at -90°C to -75°C for reaction, slowly add tributyl borate, raise the temperature to room temperature, separate and purify to obtain;

[0079] The molar ratio of the monofluoro-substituted p-bromophenol, 1-bromoalkane and alkaline compound is 1:1.05-1.50:1.5-3.0, and the molar ratio of the intermediate product, n-butyl lithium and tributyl borate is 1:1.1-1.8:2.5-3.5;

[0080] The reaction formula for preparing monofluoro-substituted 4-(alkoxy)phenylboronic acid is as follows:

[0081]

[0082] Wherein, RBr is 1-bromoalkane, including any one of 1-bromomethane, 1-bromoethane, 1-bromopropane, 1-bromobutane, 1-bromopentane or 1-bromohexane, preferably 1-bromohexane.

[0083] Step 2: dissolving the fourth compound, 2,7-dibromocarbazole, a basic compound and a catalyst in a mixed solvent of tetrahydrofuran and water, refluxing at 70 to 80° C. under a nitrogen atmosphere, filtering, and washing and drying the filter residue to obtain a fifth compound;

[0084] The chemical structure of the fifth compound is shown in Formula (4-1) or Formula (4-2):

[0085]

[0086] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms;

[0087] The reaction formula for preparing the fifth compound is as follows:

[0088]

[0089] Step 3: reacting the fifth compound with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and separating and purifying the reaction product to obtain a negative liquid crystal compound.

[0090] The reaction formula for preparing the negative liquid crystal compound is as follows:

[0091]

[0092] Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms.

[0093] In the embodiments of the present application, in the preparation method of (1) or (2) above:

[0094] The alkaline compound is any one of sodium hydroxide, potassium hydroxide, anhydrous sodium carbonate or anhydrous potassium carbonate, or a mixture of two or more thereof, preferably anhydrous potassium carbonate; the catalyst includes methyl trioctyl ammonium chloride and tetrakis(triphenylphosphine) palladium, and the molar ratio of methyl trioctyl ammonium chloride to tetrakis(triphenylphosphine) palladium is 2-8:5-10. Anhydrous potassium carbonate, methyl trioctyl ammonium chloride and tetrakis(triphenylphosphine) palladium are combined to promote the removal of bromide ions from 2,7-dibromocarbazole and the formation of an ether bond with the first compound or the fourth compound; and reduce the degree of elimination reaction of 2,7-dibromocarbazole.

[0095] In the embodiment of the present application, the molar ratio of the first compound or the fourth compound, 2,7-dibromocarbazole, the basic compound, and the catalyst is 1:2.5-3.5:7.0-9.0:0.07-0.18. Under this molar ratio, the degree of the etherification reaction is high, which can improve the dielectric anisotropy and birefringence of the subsequent negative liquid crystal compound.

[0096] In the embodiment of the present application, the molar ratio of the second compound or the fifth compound, potassium hydroxide and methyl iodide is 1:6 to 8:1 to 2. Under this molar ratio, the negative liquid crystal compound has a higher dielectric anisotropy and a larger birefringence.

[0097] In an embodiment of the present application, the separation and purification is specifically as follows: dissolving the second compound or the fifth compound in N,N-dimethylformamide, adding iodomethane dropwise for reaction, adding water for sedimentation, suction filtration, and recrystallizing and drying the filter residue. The solvent for recrystallization is a mixed solution of petroleum ether and ethanol in a volume ratio of 1:1. Separation and purification can remove unreacted raw materials, improve the purity of the negative liquid crystal compound, and thereby improve the dielectric anisotropy and birefringence of the negative liquid crystal compound.

[0098] The present invention is further described below by taking R as a hexyl group as an example.

[0099] Example 1

[0100] Step 1, obtaining 4-hexyloxyphenylboronic acid by purchasing existing products;

[0101] Step 2, Preparation of 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole

[0102] 3.10mmol of 2,7-dibromocarbazole, 7.75mmol of 4-hexyloxyphenylboronic acid, 23.3mmol of anhydrous potassium carbonate, 0.15mmol of methyl trioctyl ammonium chloride and 36mL of dry tetrahydrofuran were added to a 100mL three-necked flask equipped with a condenser, placed on a magnetic stirrer with constant temperature heating, and stirred at room temperature for 45min under nitrogen protection. Then 0.31mmol of tetrakis(triphenylphosphine)palladium was added to the system under nitrogen protection, and stirred and refluxed at 75°C for 24h. After the reaction system was cooled to room temperature, it was filtered under pressure with a Buchner funnel, and the filter residue was repeatedly washed with dichloromethane and ethanol. The filter residue was collected and dried in a vacuum oven to obtain 1.12g of white solid 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole with a yield of 70%. Its chemical structure is as follows:

[0103]

[0104] Step 3, preparation of liquid crystal compound 2,7-bis(4-(hexyloxy)phenyl)-9-methyl-9H-carbazole

[0105] 0.39 mmol of 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole, 2.50 mmol of potassium hydroxide powder and 10 mL of dry N,N-dimethylformamide were added to a single-necked flask in sequence, and stirred at 30°C for 30 min. 0.56 mmol of iodomethane was added dropwise and the reaction was continued for 3 h before stopping the reaction. The reaction solution was transferred to a beaker, 50 mL of deionized water was added, and the mixture was stirred for 2 h to settle. Then, the mixture was filtered under reduced pressure using a Buchner funnel. The residue was recrystallized with petroleum ether: ethanol = 1:1 and dried in a vacuum oven to obtain 0.11 g of a white solid 2,7-bis(4-(hexyloxy)phenyl)-9-methyl-9H-carbazole, i.e., a liquid crystal compound, with a yield of 53%. Its chemical structure is shown in formula (5):

[0106]

[0107] The spectral data of the liquid crystal compound are as follows:

[0108] H NMR 1 H-NMR (400MHz, CDCl3, TMS) δ (ppm) 8.11 (dd, J = 8.0, 0.6Hz, 2H), 7.71-7.62 (m, 4H), 7.54 (dd, J = 1.5, 0.6Hz, 2H), 7.45 (dd, J = 8.1, 1.5Hz, 2H ),7.07-6.98(m,4H),4.03(t,J=6.6Hz,4H),3.92(s,3H),1.82(m,J=8.5Hz,4H),1.52-1.46(m,4H),1.43-1.30(m,8H),0.98-0.86(m,6H).

[0109] Infrared spectrum IR(KBr,pellet,cm -1 ):3042,2932,2865,1895,1607,1521,1458,1402,1332,1306,1246,1183,1110,1016,940,911,805,731,710.

[0110] The theoretical value of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) m / z mass-to-charge ratio was 533.33, and the measured value was 533.17.

[0111] through 1 H-NMR, IR and MALDI-TOF-MS spectral analyses showed that the product had a correct structure and was the compound represented by formula (5).

[0112] Example 2

[0113] Step 1, preparation of (3-fluoro-4-(hexyloxy)phenyl)boronic acid

[0114] 26.32mmol of 4-bromo-2-fluorophenol, 28.96mmol of 1-bromohexane, 52.67mmol of anhydrous potassium carbonate and 100mL of acetone were added to a single-necked flask, placed on a magnetic stirrer with constant temperature heating, reacted at 61°C for 8h and then cooled to room temperature. The reaction solution was extracted three times with water and dichloromethane, the organic phases were combined and dried with anhydrous sodium sulfate, the solvent was removed by vacuum distillation, 7g of silica gel was added to prepare the sample and column chromatography was performed, the eluent was petroleum ether: ethyl acetate = 100: 1, and 6.10g of colorless transparent liquid, i.e., intermediate product, was obtained, with a yield of 91%.

[0115] The three-necked flask was filled with nitrogen three times, 14.60mmol of the intermediate product and 75mL of dry tetrahydrofuran were added and nitrogen was continuously passed into the three-necked flask. The three-necked flask was placed in liquid nitrogen and cooled to -80°C, 23.36mmol of n-butyl lithium was added dropwise for 45min, and the reaction was continued at -80°C for 3h, and 43.80mmol of tributyl borate was added dropwise for 60min, and the reaction was continued in a nitrogen atmosphere until the system temperature reached room temperature, 1mol / L dilute hydrochloric acid was added, and the pH was adjusted to neutral in 30min. The reaction solution was extracted with water and dichloromethane three times, and the organic phases were combined and dried with anhydrous sodium sulfate. After the solvent was removed by distillation under reduced pressure, 3.10g of white transparent liquid (3-fluoro-4-(hexyloxy)phenyl)boric acid was obtained, and its chemical structure is as follows:

[0116]

[0117] Step 2, Preparation of 2,7-bis((3-fluoro-4-(hexyloxy)phenyl)-9H-carbazole

[0118] 3.10mmol of 2,7-dibromocarbazole, 10.8mmol of 3-fluoro-4-(hexyloxy)phenylboronic acid, 27.9mmol of anhydrous potassium carbonate, 0.24mmol of methyl trioctyl ammonium chloride and 36mL of dry tetrahydrofuran were added to a three-necked flask, and placed on a magnetic stirrer with constant temperature heating, and stirred at room temperature for 45min under nitrogen protection. Then 0.15mmol of tetrakis(triphenylphosphine)palladium was added to the system under nitrogen protection, and stirred and refluxed at 80℃ for 24h. After the reaction system was cooled to room temperature, it was filtered under pressure with a Buchner funnel, and the filter residue was repeatedly washed with dichloromethane and ethanol, the filter residue was collected, and dried in a vacuum oven to obtain 0.95g of white solid 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole, with a yield of 55%. The reaction equation is as follows:

[0119]

[0120] Step 3, preparation of liquid crystal compound 2,7-bis(3-fluoro-4-(hexyloxy)phenyl)-9-methyl-9H-carbazole

[0121] 0.39 mmol of 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole, 3.10 mmol of potassium hydroxide powder and 10 mL of dry N,N-dimethylformamide were added to a single-necked flask in sequence. After stirring at 30°C for 30 min, 0.42 mmol of iodomethane was added dropwise and the reaction was continued for 5 h before stopping the reaction. The reaction solution was transferred to a 100 mL beaker, 50 mL of deionized water was added, and the mixture was stirred for 2 h to settle. Then, the mixture was filtered under reduced pressure using a Buchner funnel. The residue was recrystallized with petroleum ether: ethanol = 1:1 and dried in a vacuum oven to obtain 0.10 g of a white solid 2,7-bis(4-(hexyloxy)phenyl)-9-methyl-9H-carbazole, i.e., a liquid crystal compound, with a yield of 50%. Its chemical structure is shown in formula (6):

[0122]

[0123] The spectral data of the liquid crystal compound are as follows:

[0124] H NMR 1 H NMR(400MHz, CDCl3, TMS)δ(ppm)δ8.11(dd,J=8.1,0.6Hz,2H),7.53-7.51(m,2H),7.48(dd,J=12.5,2.2Hz,2H),7.43(dt,J=8.0,1.4Hz,4H),7.06 (t,J=8.6Hz,2H),4.09(t,J=6.6Hz,4H),3.93(s,3H),1.86(m,J=8.5,6.7 Hz, 4H), 1.51 (s, 4H), 1.37 (m, J=7.3, 3.6, 1.5Hz, 8H), 0.95-0.89 (m, 6H).

[0125] Infrared spectrum IR(KBr,pellet,cm -1 ):3057,2928,2856,1870,1607,1521,1468,1412,1277,1182,1153,1130,1018,947,842,800,723.

[0126] Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) m / z: theoretical mass-to-charge ratio 569.31, measured value 568.68.

[0127] through 1 H-NMR, IR and MALDI-TOF-MS spectral analyses showed that the product had a correct structure and was the compound represented by formula (6).

[0128] Example 3

[0129] Step 1, preparation of (2-fluoro-4-(hexyloxy)phenyl)boronic acid

[0130] 26.32mmol of 4-bromo-3-fluorophenol, 39.45mmol of 1-bromohexane, 78.95mmol of anhydrous potassium carbonate and 100mL of acetone were added to a single-necked flask, placed on a magnetic stirrer with constant temperature heating, reacted at 80°C for 6h and then cooled to room temperature. The reaction solution was extracted three times with water and dichloromethane, the organic phases were combined and dried with anhydrous sodium sulfate, the solvent was removed by vacuum distillation, 7g of silica gel was added to prepare the sample and column chromatography was performed, the eluent was petroleum ether: ethyl acetate = 100: 1, and 6.18g of colorless transparent liquid, i.e., intermediate product, was obtained, with a yield of 87%.

[0131] The three-necked flask was charged and discharged with nitrogen three times, and 14.60mmol of the intermediate product and 75mL of dry tetrahydrofuran were added and nitrogen was continuously passed into the three-necked flask. The three-necked flask was placed in liquid nitrogen and cooled to -90°C. 16.05mmol of n-butyl lithium was added dropwise over 45min. After continuing to react at -90°C for 2h, 51.10mmol of tributyl borate was added dropwise over 60min. The reaction was continued in a nitrogen atmosphere until the system temperature reached room temperature. 1mol / L dilute hydrochloric acid was slowly added, and the pH was adjusted to neutral over 30min. The reaction solution was extracted three times with water and dichloromethane, and the organic phases were combined and dried over anhydrous sodium sulfate. After removing the solvent by distillation under reduced pressure, 3.15g of white transparent liquid (3-fluoro-4-(hexyloxy)phenyl)boric acid was obtained; its chemical structure is as follows:

[0132]

[0133] Step 2, Preparation of 2,7-bis(2-fluoro-4-(hexyloxy)phenyl)-9H-carbazole

[0134] 3.10mmol of 2,7-dibromocarbazole, 9.3mmol of 2-fluoro-4-(hexyloxy)phenyl, 24.8mmol of anhydrous potassium carbonate, 0.24mmol of methyl trioctyl ammonium chloride and 36mL of dry tetrahydrofuran were added to a three-necked flask, and placed on a magnetic stirrer with constant temperature heating, and stirred at room temperature for 45min under nitrogen protection. Then 0.21mmol of tetrakis(triphenylphosphine)palladium was added to the system under nitrogen protection, and stirred and refluxed at 75℃ for 24h. After the reaction system was cooled to room temperature, it was filtered under pressure with a Buchner funnel, and the filter residue was repeatedly washed with dichloromethane and ethanol, the filter residue was collected, and dried in a vacuum oven to obtain 1.03g of white solid 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole, with a yield of 60%; its chemical structure is as follows:

[0135]

[0136] Step 3, preparation of liquid crystal compound 2,7-bis(2-fluoro-4-(hexyloxy)phenyl)-9-methyl-9H-carbazole

[0137] 0.39 mmol of 2,7-bis(4-(hexyloxy)phenyl)-9H-carbazole, 2.73 mmol of potassium hydroxide powder and 10 mL of dry N,N-dimethylformamide were added to a single-necked flask in sequence, and stirred at 30°C for 30 min. 0.74 mmol of iodomethane was added dropwise and the reaction was continued for 4 h before stopping the reaction. The reaction solution was transferred to a 100 mL beaker, 50 mL of deionized water was added, and the mixture was stirred for 2 h to settle. Then, the mixture was filtered under reduced pressure using a Buchner funnel. The residue was recrystallized with petroleum ether: ethanol = 1:1 and dried in a vacuum oven to obtain 0.10 g of a white solid 2,7-bis(4-(hexyloxy)phenyl)-9-methyl-9H-carbazole, i.e., a liquid crystal compound, with a yield of 50%. Its chemical structure is shown in formula (7):

[0138]

[0139] The spectral data of the liquid crystal compound are as follows:

[0140] H NMR 1 H NMR(400MHz, CDCl3, TMS)δ(ppm)δ8.13(dd,J=8.0,0.7Hz,2H),7.54(d,J=1.6Hz,2H),7.49(t,J=8.8Hz,2H),7.39(dt,J=8.1,1.5Hz,2H),6.84-6.79(m,2 H),6.76(dd,J=12.5,2.5Hz,2H),4.00(t,J=6.6Hz,4H),3.90(s,3H),1.87-1 .77(m,4H),1.48(q,J=7.3Hz,4H),1.36(h,J=3.5Hz,8H),0.95-0.89(m,6H).

[0141] Infrared spectrum IR(KBr,pellet,cm -1 ):3070,2918,2855,1829,1621,1574,1514,1461,1428,1410,1395,1368,1333,1315,1288,1247,1224,1163,1107,1035,999,980,901,803.

[0142] Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) m / z: theoretical mass-to-charge ratio 569.31, measured value 569.26.

[0143] through 1 H-NMR, IR and MALDI-TOF-MS spectral analyses showed that the product had a correct structure and was the compound represented by formula (7).

[0144] The optical anisotropy, dielectric anisotropy and thermal properties of the liquid crystal compounds prepared in Examples 1-3 were tested respectively to obtain their birefringence (Δn), dielectric anisotropy (Δε), phase transition temperature and phase transition enthalpy. Among them, the birefringence was obtained by Gaussian09 software to obtain a theoretical value, and the experimental value was obtained by Abbe refractometer extrapolation method; the dielectric anisotropy was obtained by dissolving the liquid crystal compound in a mixed crystal and then testing it by extrapolation method; the phase transition temperature and phase transition enthalpy were obtained by scanning calorimeter testing.

[0145] The test data of birefringence and dielectric anisotropy are shown in Table 1.

[0146] Table 1 Birefringence and dielectric anisotropy data

[0147]

[0148] As can be seen from Table 1, the liquid crystal compounds of Examples 1-3 have large birefringence and negative dielectric anisotropy. The birefringence of the liquid crystal compound is related to the degree of conjugation of the molecule. The benzene ring and carbazole ring with large conjugated structures in the liquid crystal molecules of Examples 1-3 can increase the degree of conjugation of the molecule, thereby making the liquid crystal compound have a large birefringence. The dielectric anisotropy of the liquid crystal compound is related to the dipole moment of the liquid crystal molecule. Increasing the dipole moment can increase the dielectric anisotropy of the compound. The nitrogen atoms on the carbazole ring can increase the dipole moment of the liquid crystal molecule in the vertical direction, so that the molecule has a large negative dielectric anisotropy. The introduction of side fluorine further increases the dipole moment of the liquid crystal molecule in the vertical direction, thereby increasing the negative dielectric anisotropy value of the liquid crystal compound.

[0149] The test data of phase transition temperature and phase transition enthalpy are shown in Table 2.

[0150] Table 2 Phase change temperature and phase change enthalpy data

[0151]

[0152]

[0153] In Table 2, Cr represents a crystalline phase; SmC represents a smectic C phase; N represents a nematic phase; and I represents isotropy. As can be seen from Table 2, the liquid crystal compounds of Examples 1-3 all have a liquid crystal phase, and the liquid crystal compounds of Examples 1 and 2 are smectic phases, and the liquid crystal compound of Example 3 has a wide nematic phase temperature range of 95.33°C. Nematic liquid crystals with a wide temperature range can be used in display devices under more extreme conditions.

[0154] The liquid crystal compound prepared in Example 3 was subjected to DSC test at a heating and cooling rate of 5°C / min. The test results are as follows: Figure 1 The liquid crystal compound of Example 3 was tested by polarizing microscope (POM). Figure 2 This is a POM photograph of the liquid crystal compound prepared in Example 3 when the temperature is raised to 168.5°C. Figure 3 This is a POM photograph of the liquid crystal compound prepared in Example 3 when the temperature is lowered to 191.5°C. Figure 1 , Figure 2 , Figure 3 It can be seen that the liquid crystal compound of Example 3 has a nematic liquid crystal texture and a liquid crystal texture.

[0155] Although the present invention has been described in detail in general terms and in specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements may be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A negative liquid crystal compound, the chemical structure of which is shown in formula (1): in, R is a straight chain alkyl group containing 5 to 10 carbon atoms; Ring A is selected from Any one of .

2. The negative liquid crystal compound according to claim 1, wherein the chemical structure thereof is as follows:

3. The method for preparing the negative liquid crystal compound according to claim 1, characterized in that: When ring A is When, the preparation method comprises: A first compound is obtained, wherein the chemical structure of the first compound is shown in formula (2): The first compound, 2,7-dibromocarbazole, an alkaline compound and a catalyst are dissolved in a mixed solvent of tetrahydrofuran and water, and the mixture is refluxed at 70 to 80° C. under a nitrogen atmosphere, and then filtered, and the filter residue is washed and dried to obtain a second compound; wherein the catalyst comprises methyl trioctyl ammonium chloride and tetrakis(triphenylphosphine)palladium, and the molar ratio of the methyl trioctyl ammonium chloride to the tetrakis(triphenylphosphine)palladium is 2 to 8:5 to 10; The chemical structure of the second compound is shown in formula (3): Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms; The second compound is reacted with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and the reaction product is separated and purified to obtain a negative liquid crystal compound.

4. The method for preparing a negative liquid crystal compound according to claim 1, characterized in that: When ring A is When, the preparation method comprises: A fourth compound is prepared, whose chemical formula is: The preparation method of the fourth compound comprises: Monofluoro-substituted p-bromophenol, 1-bromoalkane and alkaline compound are added to acetone, refluxed at 60-80°C, and separated and purified to obtain an intermediate product; In a nitrogen atmosphere, add tetrahydrofuran to the intermediate product, slowly add n-butyl lithium at -90°C to -75°C for reaction, slowly add tributyl borate, raise the temperature to room temperature, separate and purify to obtain; The molar ratio of the monofluoro-substituted p-bromophenol, 1-bromoalkane and alkaline compound is 1:1.05-1.50:1.5-3.0, and the molar ratio of the intermediate product, n-butyl lithium and tributyl borate is 1:1.1-1.8:2.5-3.5; The fourth compound, 2,7-dibromocarbazole, an alkaline compound and a catalyst are dissolved in a mixed solvent of tetrahydrofuran and water, refluxed at 70 to 80° C. under a nitrogen atmosphere, filtered, and the filter residue is washed and dried to obtain a fifth compound; wherein the catalyst comprises methyl trioctyl ammonium chloride and tetrakis(triphenylphosphine)palladium, and the molar ratio of the methyl trioctyl ammonium chloride to tetrakis(triphenylphosphine)palladium is 2 to 8:5 to 10; the chemical structure of the fifth compound is shown in Formula (4-1) or Formula (4-2): Wherein, R is a straight chain alkyl group containing 5 to 10 carbon atoms; The fifth compound is reacted with methyl iodide in N,N-dimethylformamide containing potassium hydroxide, and the reaction product is separated and purified to obtain a negative liquid crystal compound.

5. The preparation method according to claim 3 or 4, characterized in that: The molar ratio of the first compound or the fourth compound, 2,7-dibromocarbazole, the basic compound and the catalyst is 1:2.5-3.5:7.0-9.0:0.07-0.

18.

6. The preparation method according to claim 5, characterized in that: The alkaline compound is any one of sodium hydroxide, potassium hydroxide, anhydrous sodium carbonate or anhydrous potassium carbonate, or a mixture of two or more thereof.

7. The preparation method according to claim 3 or 4, characterized in that: The separation and purification is as follows: The second compound or the fifth compound is dissolved in N,N-dimethylformamide, iodomethane is added dropwise for reaction, water is added for sedimentation, suction filtration is performed, and the filter residue is recrystallized and dried.

8. The preparation method according to claim 3 or 4, characterized in that: The molar ratio of the second compound or the fifth compound, potassium hydroxide and methyl iodide is 1:6-8:1-2.

9. The preparation method according to claim 7, characterized in that: The solvent for the recrystallization is a mixed solution of petroleum ether and ethanol in a volume ratio of 1:

1.

10. Use of the negative liquid crystal compound according to claim 1 or 2 in a liquid crystal display device.

Images