Liquid crystal material containing 4-bromo-4'-n-heptylbiphenyl and preparation and application thereof

Abstract

The application relates to a liquid crystal material containing 4-bromo-4'-n-heptyl biphenyl and preparation and application thereof, relates to the technical field of liquid crystal monomer synthesis, and solves the problems of poor selectivity, many by-products, unstable yield and high cost of the preparation process of existing 4-bromo-4'-n-heptyl biphenyl, thereby leading to the problems of poor structural stability and performance consistency of thiofene-containing liquid crystal materials and high cost. The application takes 4-bromobiphenyl as raw material, and 4-bromo-4'-n-heptyl biphenyl is prepared through a Friedel-Crafts acylation reaction and a reduction reaction; finally, liquid crystal molecule 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylate molecule is prepared through a coupling reaction and a condensation reaction. The preparation process is simple, the conditions are mild, the novel liquid crystal molecule has excellent thermal stability and stable thermotropic liquid crystal phase behavior, and can be applied to the field of photoelectric devices.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal monomer synthesis technology, specifically to a liquid crystal material containing 4-bromo-4'-n-heptylbiphenyl and its preparation and application. Background Technology

[0002] Liquid crystal materials, existing between solid and liquid states, possess unique optical, electrical, and dielectric properties and are widely used in liquid crystal displays, sensors, and optoelectronic materials, becoming one of the core foundations of information display and smart material systems. With the continuous improvement of display resolution, response speed, and energy efficiency requirements, traditional biphenyl or cyanobiphenyl liquid crystal materials have gradually revealed performance bottlenecks in terms of birefringence, phase transition temperature range, and molecular tunability, making it difficult to meet the development needs of next-generation high-performance displays and optoelectronic devices. Against this backdrop, liquid crystal molecular systems containing conjugated heterocyclic structures, especially liquid crystal materials incorporating thiophene units, have shown significant advantages in improving birefringence, widening the phase transition temperature range, and enhancing solubility and processing performance due to their excellent π-electron delocalization ability and molecular structure designability, thus becoming an important development direction in current liquid crystal material research.

[0003] However, the construction of existing thiophene-containing liquid crystal materials relies on key reaction intermediates, particularly 4-bromo-4'-n-heptylbiphenyl. Current techniques typically employ a coupling reaction between 4,4'-dibromobiphenyl and a dialkyl copper lithium reagent to obtain 4-bromo-4'-n-heptylbiphenyl. However, due to the presence of two equivalent active sites in the substrate, selective substitution at a single site is difficult to achieve during the reaction, easily generating byproducts and consuming the substrate. This not only reduces the selectivity of the target product but also increases raw material consumption and leads to unstable yields, making stable and controllable industrial production difficult. Furthermore, this type of method relies on the dialkyl copper lithium reagent, whose preparation process is complex, requires stringent reaction conditions, and has poor commercial availability, increasing process costs and making it unsuitable for large-scale production. Due to the technical defects in the preparation of 4-bromo-4'-n-heptylbiphenyl, the purity and compositional stability of this key monomer are difficult to guarantee. Consequently, in the subsequent construction of thiophene-containing liquid crystal molecules, the controllability of liquid crystal phase behavior is easily affected, making it difficult to guarantee the performance consistency and repeatability of the target liquid crystal material. This significantly increases the complexity and cost of the synthesis route, restricting its large-scale preparation and practical application.

[0004] Therefore, it is necessary to develop a highly selective, high-yield, and process-feasible method for preparing 4-bromo-4'-n-heptylbiphenyl monomer to overcome the problems of numerous side reactions, unstable yields, and limited key reagents in existing technologies. Based on this, a novel liquid crystal molecule material with excellent photoelectric properties can be further constructed, thereby providing a more reliable material basis and technical support for high-performance liquid crystal displays and optoelectronic devices. Summary of the Invention

[0005] To address the problems of poor selectivity, numerous byproducts, unstable yields, and high costs associated with existing 4-bromo-4'-n-heptylbiphenyl preparation processes, which consequently lead to poor structural stability and performance consistency in thiophene-containing liquid crystal materials, this invention proposes a liquid crystal material containing 4-bromo-4'-n-heptylbiphenyl, its preparation, and its applications. The technical solution of this invention is as follows: A method for preparing 4-bromo-4'-n-heptylbiphenyl includes the following preparation steps: S1: Add heptanyl chloride and aluminum trichloride to a 4-bromobiphenyl solution to carry out Friedel-Crafts acylation reaction. After the reaction is completed, post-treatment is performed to obtain a yellow solid crude product. After purification, a yellow solid intermediate 1 is obtained, which is 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone. S2: Trifluoroacetic acid and triethylsilane were added to 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone for reduction reaction. After the reaction was completed, post-treatment was performed to obtain an oily liquid crude product. After purification, a yellow solid intermediate 2 was obtained, which is 4-bromo-4'-n-heptylbiphenyl.

[0006] Further, the solvent of the 4-bromobiphenyl solution in S1 is any one of dichloromethane, chloroform, and ethyl acetate; the molar ratio of 4-bromobiphenyl, heptanyl chloride, and aluminum trichloride is 1:1.1:1.2; the Friedel-Crafts acylation reaction is carried out under a nitrogen atmosphere at a reaction temperature of 20-30°C for 18-20 h.

[0007] Further, the post-processing steps in S1 are as follows: quench the reaction system in ice water, extract with dichloromethane 2-3 times, dry the organic phase, filter, and evaporate the solvent under reduced pressure. The purification steps are as follows: dissolve the crude product in methanol, pulp the crude product at 60-70℃ for 1-2 h, and filter.

[0008] Furthermore, in S2, the molar ratio of 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone to triethylsilane is 1:3; the reduction reaction temperature is 25°C, and the reduction reaction time is 24~36 h; Further, the post-treatment steps in S2 are as follows: quenching the reaction system with water, stopping the quenching when the system temperature is controlled at 0~10℃, extracting with dichloromethane 2~3 times, drying the organic phase, filtering, and evaporating the solvent under reduced pressure; the purification steps are as follows: distilling the crude product under reduced pressure at a temperature of 40℃ for 40~50 min; continuing to raise the temperature to 110℃ and recrystallizing with isopropanol, wherein the mass-volume ratio of crude product to isopropanol is 1g:5mL.

[0009] A liquid crystal material containing 4-bromo-4'-n-heptylbiphenyl is prepared using 4-bromo-4'-n-heptylbiphenyl obtained by the above preparation method as a raw material, and its structural formula is shown in Formula I: Formula I.

[0010] A method for preparing the above-mentioned liquid crystal material containing 4-bromo-4'-n-heptylbiphenyl includes the following preparation steps: P1: Add 4-bromo-4'-n-heptylbiphenyl and 5-carboxythiophene-2-boronic acid to a mixed solution, heat the solution, add tetra(triphenylphosphine)palladium to react, and perform post-treatment after the reaction to obtain a light yellow viscous liquid intermediate 3, which is 5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid; P2: Intermediate 3,3,4,5-trifluorophenol and N,N'-dicyclohexylcarbodiimide were added to a solvent, and a dichloromethane solution of 4-dimethylaminopyridine was added under ice bath conditions. After the ice bath was completed, the reaction was continued. After the reaction was completed, post-treatment was performed to obtain a crude product, which was purified to obtain 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylate (ETA316), denoted as liquid crystal molecule ETA316.

[0011] Further, the mixed solution in P1 is a mixture of acetonitrile and sodium carbonate aqueous solution, with a volume ratio of acetonitrile to sodium carbonate aqueous solution of 54:55; the molar ratio of 4-bromo-4'-n-heptylbiphenyl, 5-carboxythiophene-2-boronic acid and tetrakis(triphenylphosphine)palladium is 1:1.1:0.03; the heating is raised to 80°C; and the reaction time is 24~36 h.

[0012] Furthermore, the post-processing steps described in P1 are as follows: the reaction system is extracted with ethyl acetate and saturated sodium bicarbonate solution, separated, the aqueous phase is acidified with hydrochloric acid to precipitate a white solid, filtered, and dried.

[0013] Further, in P2, the molar ratio of 5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid, 3,4,5-trifluorophenol, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 1:1.2:1.8:0.08; the solvent is any one of anhydrous dichloromethane, chloroform, and ethyl acetate; the ice bath time is 1~1.5 h; and the reaction time is 24~36 h.

[0014] Further, the post-processing steps described in P2 are as follows: the reaction system is added to a saturated sodium chloride aqueous solution, the reaction system is extracted 2-3 times with the saturated sodium chloride aqueous solution, the liquid is separated, anhydrous sodium sulfate is added to the organic phase for drying, the mixture is filtered, and the solvent is evaporated under reduced pressure. The purification steps are as follows: the crude product is purified by column chromatography, using a petroleum ether-dichloromethane system as the eluent with a volume ratio of 1:1.

[0015] An application of the above-mentioned liquid crystal material containing 4-bromo-4'-n-heptylbiphenyl is found in the field of optoelectronic devices.

[0016] Furthermore, the field of optoelectronic devices includes communication equipment, liquid crystal display units, and nonlinear optical elements.

[0017] Compared with existing technologies, this invention solves the problems of poor selectivity, numerous byproducts, unstable yield, and high cost in the preparation process of 4-bromo-4'-n-heptylbiphenyl, which in turn leads to poor structural stability and performance consistency of thiophene-containing liquid crystal materials and high cost. The specific beneficial effects are as follows: 1. This invention uses 4-bromobiphenyl and heptanoyl chloride as raw materials to prepare 4-bromo-4'-n-heptylbiphenyl via Friedel-Crafts acylation combined with reduction. This synthetic route is simple, with widely available and inexpensive raw materials. Through the rational design of the reaction pathway, the selective transformation of the target site is effectively achieved, the non-selective substitution reaction initiated by the dual active sites of the substrate is effectively suppressed, and the generation of byproducts is significantly reduced. This improves the selectivity and yield of the target product and makes the obtained monomer more stable and controllable in terms of structure, composition and purity, providing a reliable guarantee for the consistency and reproducibility of subsequent reactions.

[0018] 2. This invention uses 4-bromo-4'-n-heptylbiphenyl as a key intermediate to further construct a novel liquid crystal molecule, 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylate. In the construction of this liquid crystal molecule, dependence on complex organometallic reagents is avoided from the outset, the overall reaction conditions are mild and controllable, and the process adaptability is strong. While ensuring reaction efficiency, the difficulty of obtaining raw materials and the overall process cost are effectively reduced, and the stability and scalability of the reaction process are improved. This novel liquid crystal molecule has significant potential for industrial application.

[0019] 3. Based on a high-purity and structurally stable key intermediate, the novel liquid crystal molecule 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylate provided by this invention exhibits excellent thermal stability and stable thermotropic liquid crystal phase behavior. It can stably maintain its ordered liquid crystal structure over a wide liquid crystal phase temperature range (132℃~152℃), thereby improving the phase stability of the liquid crystal molecule under thermal conditions. This effectively ensures the molecular structural regularity and compositional consistency of the thiophene-containing liquid crystal molecule ETA316 provided by this invention, further enhancing the stability and repeatability of the liquid crystal material in terms of phase transition behavior and photoelectric properties. This better meets the material performance requirements of high-performance liquid crystal displays and related optoelectronic devices, expanding the application applicability of liquid crystal molecule materials in high-end optoelectronic fields. Attached Figure Description

[0020] Figure 1 The 1H NMR spectrum of intermediate 1; Figure 2 The 1H NMR spectrum of intermediate 2; Figure 3 The 1H NMR spectrum of intermediate 3; Figure 4 A schematic diagram of the reaction pathway structure of liquid crystal molecule ETA316; Figure 5 The hydrogen NMR spectrum of the liquid crystal molecule ETA316; Figure 6 Differential scanning calorimetry curve of liquid crystal molecule ETA316; Figure 7 Thermogravimetric analysis (TG) curve of liquid crystal molecule ETA316. Detailed Implementation

[0021] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0022] Example 1. S1: 4-Bromobiphenyl (806 g, 3.46 mol, 1 eq) and 12 L of dichloromethane (DCM) were added to a reactor. After the 4-bromobiphenyl dissolved completely, heptanyl chloride (565.3 g, 3.80 mol, 1.1 eq) was added. Aluminum trichloride (AlCl3, total AlCl3 input: 553.24 g, 4.15 mol, 1.2 eq) was added in three batches every 30 min. After the addition was complete, a nitrogen stream was introduced, and the reaction was carried out at 25 °C for 18 h under a nitrogen atmosphere. After the reaction was complete, the aluminum trichloride was quenched in 12 L of ice water, followed by extraction three times with dichloromethane to remove aluminum salt impurities. Anhydrous sodium sulfate was added to the organic phase for drying, and the mixture was filtered and the solvent was evaporated under reduced pressure to obtain a yellow solid crude product. The crude yellow solid product was dissolved in 10 L of methanol and hot-beaten at a constant temperature of 60 °C for 1 h. The mixture was then filtered while hot to obtain intermediate 1, a yellow solid, which is 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone, with a yield of 75.39%. The structural formula of intermediate 1 is shown in Formula II below. Figure 1 The image shows the 1H NMR spectrum of intermediate 1. The 1H NMR spectrum results are as follows: 1 H NMR (300 MHz, CDCl3) δ 8.03 (d,J = 8.4 Hz, 2H), 7.68-7.45 (m, 6H), 2.99 (t, J = 7.4 Hz, 2H), 1.74 (dd, J =14.6, 7.4 Hz, 2H), 1.35 (s, 6H), 0.90 (t, J = 6.7 Hz, 3H). Formula II.

[0023] S2: Intermediate 1 (900 g, 2.61 mol, 1 eq) was added to the reaction flask, followed by 2.2 L of trifluoroacetic acid (TFA). The temperature was lowered to 10 °C, and triethylsilane (Et3SiH, 909.28 g, 7.82 mol, 3 eq) was added dropwise. After the addition was complete, the reaction was carried out at 10 °C for 30 min. After the reaction was completed, the temperature was restored to room temperature (25 °C) and the reaction was continued for 24 h. After the reaction was completed, the reaction system was quenched with water until the temperature of the reaction system was maintained at 10 °C. Subsequently, the mixture was extracted three times with dichloromethane. Anhydrous sodium sulfate was added to the organic phase for drying, filtration, and solvent evaporation under reduced pressure to obtain an oily liquid crude product. Due to the low melting point of the crude product, it was in an oily liquid state during rotary evaporation. When the temperature was restored to room temperature, a pale yellow viscous solid precipitated out. This solid contained hexaethyldisiloxane impurities. The crude product was added to a 5 L three-necked flask and distilled under reduced pressure using a vacuum distillation apparatus. The temperature was raised to 40°C and maintained for 40 min. During the reaction, bubbles appeared in the system, and liquid flowed out of the receiving flask. After the bubbles stabilized, the temperature was raised to 110°C to remove the hexaethyldisiloxane impurity. Isopropanol was then added for recrystallization, with a mass-to-volume ratio of crude product to isopropanol of 1 g:5 mL. After cooling, a solid precipitated. The solid was filtered and dried to obtain a yellow solid intermediate 2, which is 4-bromo-4'-n-heptylbiphenyl, with a yield of 82.22%. The following formula (III) shows the structural formula of intermediate 2. Figure 2 The image shows the 1H NMR spectrum of intermediate 2. The 1H NMR spectrum results are as follows: 1 H NMR (300 MHz, CDCl3) δ 7.57-7.52 (m, 2H), 7.51-7.42 (m, 4H), 7.27 (s,1H), 7.24 (s, 1H), 2.70-2.58 (m, 2H), 1.64 (dd, J = 15.0, 7.5 Hz, 2H), 1.42-1.24 (m, 8H), 0.89 (t, J = 6.8 Hz, 3H). Formula III.

[0024] S3: 5.4 L of acetonitrile and 5.5 L of sodium carbonate aqueous solution (0.4 M sodium carbonate concentration) were added to a reaction flask. Under a nitrogen atmosphere, intermediate 2 (710 g, 2.14 mol, 1 eq) and 5-carboxythiophene-2-boronic acid (405.38 g, 2.36 mol, 1.1 eq) were added. The temperature was raised to 80 °C, followed by the addition of tetrakis(triphenylphosphine)palladium (74.18 g, 64.2 mmol, 0.03 eq) and the reaction was carried out for 24 h. After the reaction was completed, the reaction system was extracted with ethyl acetate and saturated sodium bicarbonate solution to separate the organic and aqueous phases. The aqueous phase was acidified with hydrochloric acid (1 M) to precipitate a white solid. After filtration, a light yellow viscous liquid intermediate 3 was obtained, which was 5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid, with a yield of 85.3%. The following formula IV is the structural formula of intermediate 3, such as Figure 3 The image shows the 1H NMR spectrum of intermediate 3. The 1H NMR spectrum results are as follows: 1 H NMR (500 MHz, CDCl3) δ 8.06 (s, 1H), 8.01-7.94 (m, 3H), 7.66-7.60 (m,2H), 7.41-7.34 (m, 2H), 7.29-7.23 (m, 2H), 2.69 (s, 2H), 1.70 (s, 2H), 1.39-1.24 (m, 8H), 0.96 (s, 3H). Formula IV.

[0025] S4: Add 2 L of anhydrous dichloromethane to the reaction flask, and add intermediate 3 (690 g, 1.82 mol, 1 eq), 3,4,5-trifluorophenol (324 g, 2.18 mol, 1.2 eq), and N,N'-dicyclohexylcarbodiimide (DCC, 676 g, 3.28 mol, 1.8 eq). Place the mixture in an ice bath, and under a nitrogen atmosphere, continue to add a dichloromethane solution of 4-dimethylaminopyridine (DMAP, 17.8 g, 145.6 mmol, 0.08 eq). React in an ice bath for 1 h, then return to room temperature and continue the reaction for 24 h. After the reaction was complete, the reaction system was added to a saturated sodium chloride aqueous solution, and the reaction system was extracted three times with the saturated sodium chloride aqueous solution. Anhydrous sodium sulfate was added to the organic phase for drying, followed by filtration and solvent evaporation under reduced pressure to obtain the crude product. The crude product was purified by column chromatography using a petroleum ether-dichloromethane system as the eluent, wherein the volume ratio of petroleum ether to dichloromethane was 1:1, to obtain a yellow solid 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylate, denoted as liquid crystal molecule ETA316. Figure 4 The diagram shows the reaction pathway for preparing the liquid crystal molecule ETA316 in Example 1, with a yield of 78.8%. The following formula V represents the structural formula of the liquid crystal molecule ETA316. Figure 5 The image shows the 1H NMR spectrum of the liquid crystal molecule ETA316. The 1H NMR spectrum results are as follows: 1 H NMR (500 MHz, CDCl3) δ 8.05-7.93 (m, 3H), 7.75-7.58 (m,3H), 7.41-7.23 (m, 4H), 7.06-6.99 (m, 2H), 2.69 (s, 2H), 1.70 (s, 2H), 1.49-1.16 (m, 8H), 0.96 (s, 3H). Formula V.

[0026] The thermodynamic properties of the liquid crystal molecule ETA316 prepared in Example 1 were characterized, such as... Figure 6 The figure shows the differential scanning calorimetry (DSC) curve of the liquid crystal molecule ETA316, used to analyze its phase transition behavior and phase transition temperature range. As can be seen from the figure, under a heating / cooling rate of 10℃ / min, the liquid crystal molecule ETA316 exhibits a clear thermally induced liquid crystal phase transition characteristic. The solid line represents the cooling curve; when the temperature drops to 132℃, a significant exothermic peak appears. This exothermic behavior corresponds to the process of transforming from the liquid crystal phase to an isotropic liquid phase, and this temperature range represents the formation temperature range of the liquid crystal phase. Furthermore, as the temperature further decreases, the system maintains a stable liquid crystal phase. The dashed line represents the heating curve; when the temperature rises to 152℃, the system undergoes a transformation from the liquid crystal phase to an isotropic liquid phase. This temperature corresponds to the clearing temperature of the liquid crystal material, indicating that the ordered structure of the liquid crystal completely disappears. The DSC test results show that the liquid crystal molecule ETA316 has a wide liquid crystal phase temperature range (132℃~152℃), which belongs to the medium-high temperature type liquid crystal material. It can stably maintain the ordered liquid crystal structure in environments above 100℃, demonstrating good thermally induced phase stability. It is suitable for applications with high requirements for thermal stability, such as automotive displays and high-temperature industrial testing.

[0027] like Figure 7The thermogravimetric analysis (TG) curve of the liquid crystal molecule ETA316 is shown, used to evaluate the thermal decomposition behavior of the liquid crystal molecule. As can be seen from the figure, during the heating process, when the mass loss of the liquid crystal molecule ETA316 reaches 5%, the corresponding thermal decomposition temperature is 310℃. This indicates that the liquid crystal molecule ETA316 can maintain molecular structural stability within a high temperature range, exhibiting excellent thermal stability. This demonstrates that the liquid crystal molecule ETA316 provided by this invention not only possesses a clear and stable thermotropic liquid crystal phase behavior but also has a high thermal decomposition temperature and good thermal stability. It is suitable for optoelectronic applications with strict temperature requirements, significantly expanding the application range of liquid crystal materials in the optoelectronic field. The liquid crystal molecule ETA316 provided by this invention can be widely adapted to flexible display panels, optical switching devices, laser modulators, and other optoelectronic components, meeting the urgent need for high-performance materials in future optoelectronic devices.

[0028] In summary, this invention uses 4-bromobiphenyl and heptanoyl chloride as raw materials to prepare 4-bromo-4'-n-heptylbiphenyl via Friedel-Crafts acylation combined with reduction, further constructing a novel liquid crystal molecule, 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylate. This synthetic route is simple, uses widely available and inexpensive raw materials, effectively achieves selective conversion of the target site, avoids dependence on complex organometallic reagents from the source, and provides mild and controllable overall reaction conditions with strong process adaptability, thus expanding the applicability of liquid crystal molecular materials in high-end optoelectronic fields.

[0029] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0030] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A liquid crystal material, characterized in that, The liquid crystal material was prepared using 4-bromo-4'-n-heptylbiphenyl as a raw material, and its structural formula is shown in Formula I: Formula I.

2. A method for preparing the liquid crystal material as described in claim 1, characterized in that, The preparation steps include the following: P1: 4-Bromo-4'-n-heptylbiphenyl and 5-carboxythiophene-2-boronic acid were added to a mixed solution, heated, and tetra(triphenylphosphine)palladium was added to react. After the reaction was completed, post-treatment was performed to obtain 5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid; P2: 5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid, 3,4,5-trifluorophenol, and N,N'-dicyclohexylcarbodiimide were added to a solvent, and a dichloromethane solution of 4-dimethylaminopyridine was added under ice bath conditions. After the ice bath was completed, the reaction was continued. After the reaction was completed, post-treatment was performed to obtain the crude product, which was purified to obtain 3,4,5-trifluorophenyl-5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid ester; The preparation method of the 4-bromo-4'-n-heptylbiphenyl includes the following preparation steps: S1: Add heptanyl chloride and aluminum trichloride to a 4-bromobiphenyl solution to carry out Friedel-Crafts acylation reaction. After the reaction is completed, perform post-treatment to obtain a crude product, which is then purified to obtain 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone. S2: Trifluoroacetic acid and triethylsilane were added to 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone for reduction reaction. After the reaction was completed, post-treatment was performed to obtain crude product, which was then purified to obtain 4-bromo-4'-n-heptylbiphenyl. The solvent for the 4-bromobiphenyl solution in S1 is any one of dichloromethane, trichloromethane, and ethyl acetate; the molar ratio of 4-bromobiphenyl, heptanyl chloride, and aluminum trichloride is 1:1.1:1.2; the Friedel-Crafts acylation reaction is carried out under a nitrogen atmosphere at a temperature of 20-30°C for 18-20 h; the post-treatment steps are: quenching the reaction system in ice water, extracting with dichloromethane, drying the organic phase, filtering, and evaporating the solvent under reduced pressure; the purification steps are: dissolving the crude product in methanol, slurrying the crude product at 60-70°C for 1-2 h, and filtering. The molar ratio of 1-(4'-bromo[1,1'-biphenyl]-4-yl)-1-heptanone, triethylsilane, and trifluoroacetic acid in S2 is 1:3:11; the reduction reaction temperature is 25℃, and the reduction reaction time is 24~36 h; the post-treatment steps in S2 are: quenching the reaction system with water, extracting with dichloromethane, drying the organic phase, filtering, and evaporating the solvent under reduced pressure; the purification steps are: distilling the crude product under reduced pressure at a temperature of 40℃ for 40~50 min; further heating to 110℃ and recrystallizing with isopropanol, wherein the mass-volume ratio of crude product to isopropanol is 1 g:5 mL.

3. The method for preparing liquid crystal material according to claim 2, characterized in that, The mixed solution described in P1 is a mixture of acetonitrile and sodium carbonate aqueous solution, with a volume ratio of acetonitrile to sodium carbonate aqueous solution of 54:55; the molar ratio of 4-bromo-4'-n-heptylbiphenyl, 5-carboxythiophene-2-boronic acid, and tetrakis(triphenylphosphine)palladium is 1:1.1:0.03; the temperature is raised to 80°C; the reaction time is 24~36 h; the post-treatment steps are as follows: the reaction system is extracted with ethyl acetate and saturated sodium bicarbonate solution, separated, the aqueous phase is acidified with hydrochloric acid to precipitate a white solid, filtered, and dried.

4. The method for preparing liquid crystal material according to claim 2, characterized in that, The molar ratio of 5-(4'-heptyl-[1,1'-biphenyl]-4-yl)thiophene-2-carboxylic acid, 3,4,5-trifluorophenol, N,N'-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine in P2 is 1:1.2:1.8:0.08; the solvent is any one of anhydrous dichloromethane, chloroform, and ethyl acetate; the ice bath time is 1-1.5 h; and the reaction time is 24-36 h.

5. The method for preparing liquid crystal material according to claim 2, characterized in that, The post-processing steps described in P2 are as follows: the reaction system is added to a saturated sodium chloride aqueous solution, the reaction system is extracted using the saturated sodium chloride aqueous solution, separated, anhydrous sodium sulfate is added to the organic phase for drying, filtered, and the solvent is evaporated under reduced pressure; the purification steps are as follows: the crude product is purified by column chromatography, using a petroleum ether-dichloromethane system as the eluent, with an eluent volume ratio of 1:

1.

6. The application of a liquid crystal material as described in claim 1 or a liquid crystal material prepared by any one of claims 2-5, characterized in that, It is used in the field of optoelectronic devices.

7. The application of the liquid crystal material according to claim 6, characterized in that, The field of optoelectronic devices includes communication equipment, liquid crystal display units, and nonlinear optical elements.

Images