A negative liquid crystal compound based on a 4,5,6,7-tetrahydrobenzo[b]thiophene skeleton, a related liquid crystal composition, and applications thereof

Abstract

The application discloses a negative liquid crystal compound based on a 4,5,6,7-tetrahydrobenzo[b]thiophene skeleton, a related liquid crystal composition and application thereof. The structure of the disclosed liquid crystal compound is shown in a general formula (1), and the disclosed liquid crystal composition contains the liquid crystal compound shown in the general formula (1). The liquid crystal compound has the advantages of large negative dielectric anisotropy, low viscosity and the like. The liquid crystal composition containing the liquid crystal compound has the advantages of high response speed, good light stability, large negative dielectric anisotropy and the like, and can be used in various displays of different display modes.

Description

Technical Field

[0001] This invention belongs to the field of liquid crystal materials technology, specifically relating to a negative liquid crystal compound based on a 4,5,6,7-tetrahydrobenzene[b]thiophene skeleton, related liquid crystal compositions and their applications, mainly applied in the field of liquid crystal displays. Background Technology

[0002] Negative dielectric anisotropic liquid crystal materials (Δε < 0) are one of the key functional materials in vertically aligned (VA) liquid crystal displays. By utilizing the high electronegativity and small spatial size of fluorine atoms, the dielectric anisotropy of liquid crystal molecules can be regulated by introducing lateral fluorine substituents into these materials, thereby obtaining negative dielectric anisotropic liquid crystal materials. Furthermore, the introduction of lateral fluorine substituents has also improved the stability and safety issues of traditional cyano-substituted liquid crystal materials to some extent, and has been successfully applied in automotive displays and large-size displays. With the development of display devices towards higher refresh rates (240Hz+ for gaming screens), wider operating temperature ranges (-40℃ to 85℃ for automotive displays), and lower power consumption (mobile terminals), higher requirements are placed on the dielectric properties, viscosity, and response speed of negative dielectric anisotropic liquid crystal materials. Existing fluorine-substituted negative liquid crystal materials generally suffer from limited dielectric anisotropy values ​​and relatively high molecular viscosity. Under low-temperature conditions or high-speed driving conditions, their dynamic response performance and operational stability still have room for improvement. Therefore, the existing technology system still faces certain challenges in meeting the comprehensive performance requirements of next-generation display devices.

[0003] Liquid crystal molecules are typically composed of nucleation units, bridging bonds, lateral substituents, and terminal groups. The nucleation unit has a decisive influence on the molecular configuration, phase transition behavior, and dielectric properties of liquid crystal materials. Currently, typical rod-shaped nucleation structures such as 1,4-disubstituted benzene, trans-1,4-disubstituted cyclohexane, and 2,6-disubstituted naphthalene have been widely used in negative dielectric anisotropic liquid crystal materials, forming relatively mature technological systems. However, the potential for performance improvement in liquid crystal materials based on these nucleation structures is gradually becoming limited. Simply changing the number or substitution position of aromatic rings is insufficient to simultaneously achieve dielectric properties, thermal stability, and dynamic response characteristics. In recent years, designing and synthesizing novel liquid crystal nucleation units to obtain novel liquid crystal molecules with diverse properties has become a widely studied technological solution. By introducing heteroatoms such as sulfur, oxygen, and nitrogen into the nucleus—that is, replacing traditional aromatic rings or saturated aliphatic rings with heterocyclic or fused heterocyclic rings—the electronic structure and spatial configuration of liquid crystal molecules can be altered, thereby affecting the dipole moment distribution, phase transition temperature, and dielectric constant of the liquid crystal material. Based on this idea, existing literature has reported a variety of liquid crystal compounds containing fused heterocyclic structures such as benzofuran, benzothiophene, thiophene-thiophene, and cyclopentanopthiophene, which exhibit physical properties different from traditional crystal nuclei structures.

[0004] However, existing negative dielectric anisotropic liquid crystal materials containing fused heterocyclic nuclei still have certain limitations in practical applications. On the one hand, the introduction of heterocyclic structures often leads to an increase in the melting point of liquid crystal molecules, affecting their low-temperature performance; on the other hand, the increased rigidity of the molecular structure may cause an increase in the viscosity of the liquid crystal, which is not conducive to improving the response speed. Summary of the Invention

[0005] Based on the urgent need for novel heterocyclic nuclei to construct high-performance negative dielectric anisotropic liquid crystal materials, this invention provides a negative liquid crystal compound based on a 4,5,6,7-tetrahydrobenzyl[b]thiophene skeleton, related liquid crystal compositions, and their applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A liquid crystal compound based on the 4,5,6,7-tetrahydrobenz[b]thiophene skeleton, characterized in that the compound structure is as shown in general formula (1): (1) Wherein, R1 is a saturated alkyl group with 1 to 9 carbon atoms, an unsaturated alkyl group with 1 to 9 carbon atoms, a saturated alkoxy group with 1 to 9 carbon atoms, or an unsaturated alkoxy group with 1 to 9 carbon atoms; the ring H is a benzene ring or trans-cyclohexane; A1, A2, A3, and A4 are each independently a hydrogen atom or a fluorine atom; m and n are each independently 0 or 1; R2 and R3 are each independently a hydrogen atom, a saturated alkyl group with 1 to 9 carbon atoms, or an unsaturated alkyl group.

[0008] The novel 4,5,6,7-tetrahydrobenzyl[b]thiophene-based negative liquid crystal molecule of this invention possesses advantages such as a wide phase transition temperature, high birefringence, and large negative dielectric anisotropy, without causing a significant increase in melting point or viscosity. The preferred structure is shown in the following general formula:

[0009] The present invention also provides a method for synthesizing the liquid crystal compound based on the 4,5,6,7-tetrahydrobenz[b]thiophene skeleton, as follows:

[0010] This synthetic route uses substituted cyclohexanone-thiophene as the starting material, which is reduced by hydrazine hydrate to obtain a substituted 4,5,6,7-tetrahydrobenzene[b]thiophene intermediate. The latter is further reacted with NBS to obtain a thiophene 2-brominated intermediate. Finally, this brominated intermediate is coupled to the left-side liquid crystal intermediate boric acid via a palladium-catalyzed coupling reaction, successfully preparing the compound of the above-described general formula. This method has advantages such as simple steps, readily available raw materials, easy operation, and excellent yield, and the synthesis cost is controllable, showing good application prospects.

[0011] The present invention also provides a liquid crystal composition, characterized in that it comprises one or more 4,5,6,7-tetrahydrobenz[b]thiophene liquid crystal compounds of preferred structural formula (1). Optionally, the mass fraction of the compound of formula (1) in the liquid crystal composition of the present invention is 1% to 100%.

[0012] The liquid crystal composition provided by the present invention further includes one or more liquid crystal compounds of general formula (2) as a second component. Optionally, the mass fraction of the second component is 0-99%.

[0013] (2) Among them, R4 and R5 are independently saturated alkyl groups with 1 to 9 carbon atoms, unsaturated alkyl groups with 1 to 9 carbon atoms, saturated alkoxy groups with 1 to 9 carbon atoms, and unsaturated alkoxy groups with 1 to 9 carbon atoms, respectively; L1 bridge bond is a single bond, ethylene bridge bond (-C=C-), ethane bridge bond (-CC-), and acetylene bridge bond (-C≡C-); ring O and ring P are independently benzene ring, transcyclohexane, cyclohexene, or benzene ring substituted with fluorine (F), chlorine (Cl), trifluoromethyl (CF3), methyl (CH3), or ethyl (CH3CH2); i and j are independently 0, 1, and 2, respectively.

[0014] The preferred structure of general formula (2) is as follows:

[0015] R4 and R5 are, respectively, saturated alkyl groups with 1 to 9 carbon atoms, unsaturated alkyl groups with 1 to 9 carbon atoms, saturated alkoxy groups with 1 to 9 carbon atoms, and unsaturated alkoxy groups with 1 to 9 carbon atoms; X is a fluorine atom substituted in the ortho or meta position of an alkyne bond.

[0016] The liquid crystal composition of the present invention may further contain one or more chiral additives, the amount of which is 0.01%-1% of the liquid crystal composition; preferably 0.1%-0.5%. The chiral additive is preferably derived from the following structures:

[0017] In each of these, R is an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms.

[0018] The liquid crystal composition of the present invention further comprises a plurality of hindered phenols as an antioxidant stabilizer, wherein the content in the liquid crystal composition is 1ppm-10000ppm; preferably 10ppm-1000ppm. The antioxidant stabilizer preferably has the following structure:

[0019] In this case, each R′ is an alkyl group having 1 to 9 carbon atoms.

[0020] The liquid crystal composition of the present invention further comprises one or more ultraviolet light stabilizers, wherein the content in the liquid crystal composition is 1 ppm to 10000 ppm; preferably 10 ppm to 1000 ppm. The ultraviolet light stabilizer preferably has the following structure:

[0021] The liquid crystal compounds and compositions obtained by this invention have large dielectric anisotropy, high birefringence, wide operating temperature range, and low material cost, making them suitable for high-performance liquid crystal display panels. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, and are not intended to limit the scope of the present invention.

[0023] Liquid crystal formulation preparation method: A thermal dissolution method is adopted. First, monomer liquid crystals of different weight ratios are weighed using a precision balance, heated to 60℃~100℃, and stirred for 1~2 hours to ensure uniform dissolution of all components. After cooling, the mixture is filtered, and the resulting liquid is degassed under high vacuum (≤100Pa). Finally, it is encapsulated with high-purity nitrogen to obtain the target mixed liquid crystal.

[0024] Unless otherwise specified, all liquid crystal compositions involved in this invention are prepared according to this method.

[0025] The detailed test method for testing the physical and photoelectric properties of the mixed liquid crystal involved in this invention is as follows: (1) Liquid crystal phase transition temperature and liquid crystal phase state: Differential scanning calorimetry (DSC): Under nitrogen atmosphere, the heating rate was set to 2℃ / min.

[0026] Polarizing hot stage method (POM): The liquid crystal sample is coated on a glass slide and placed in an orthogonal polarizing microscopic hot stage, with a heating rate of 2℃ / min. The changes in the texture of the liquid crystal sample are observed under a polarizing microscope to determine the liquid crystal phase.

[0027] (2) Birefringence (Δn): Using an Abbe refractometer, under constant temperature conditions of 25℃, the birefringence (Δn) of the ordinary ray was measured separately. o ) and unusual light (n e The refractive index of ) and the birefringence Δn = n e -n o .

[0028] (3) Dielectric constant (Δε): Tested using an LCR meter under constant temperature conditions of 25℃. Δε = ε ∥ -ε ⊥ That is, the dielectric constant along the long axis of the molecule (ε)∥ ) and the dielectric constant along the short axis of the molecule (ε) ⊥ The difference between ).

[0029] (4) Elastic constant (K) 11 K 33 Under constant temperature conditions of 25℃, K was obtained by fitting the capacitance-voltage (CV) curve of the liquid crystal. 11 and K 33 .

[0030] (5) Rotational viscosity (γ1): Under constant temperature of 25℃, the transient current value I of liquid crystal molecules deflected by electric field was measured by applying voltage to the liquid crystal test cell. p The rotational viscosity γ1 was calculated.

[0031] (6) Low Temperature Storage (LTS): Pour approximately 1 mL of the mixed liquid crystal into a transparent glass bottle and place it in a low-temperature freezer. Set the temperature to -20℃, -30℃, and -40℃, and store for 10 days respectively, observing whether crystals precipitate or smectic phases appear. If no crystals precipitate at -30℃, the LTS is ≤ -30℃.

[0032] The negative base formulation HOST in the following examples is obtained by mixing the following liquid crystal monomers (Table 1) in the corresponding mass ratios.

[0033] Table 1. Composition and mass ratio of negative formulation HOST

[0034] The codes and descriptions involved in this invention are shown in Table 2-4: Table 2 Physical Parameters

[0035] Table 3 Structural Abbreviations

[0036] Table 4 Examples of Structural Abbreviations

[0037] Example 1: This example is 2-(2,3-difluoro-4-propoxyphenyl)-4,5,6,7-tetrahydrobenzo[ b The synthesis of thiophene, with the following structural formula:

[0038] The synthetic route is shown below:

[0039] The specific method is as follows: Step 1: Add 6,7-dihydrobenzo[] to each of the three-necked round-bottom flasks. b Thiophene-4(5H)-one (10.0 g), hydrazine hydrate (13.5 g), potassium hydroxide (12.9 g), and diethylene glycol (100 mL) were used to heat the reaction mixture at 200 °C for 6 hours. After cooling to room temperature, the mixture was diluted with water and extracted three times with toluene. The organic phases were combined, washed once with water, dried over anhydrous magnesium sulfate, and filtered to obtain the filtrate. The solvent was removed under reduced pressure, and the residue was purified by silica gel column chromatography (eluent: n-heptane / toluene = 10 / 1, V / V) to give the intermediate 4,5,6,7-tetrahydrobenzo[ b Thiophene was a light yellow oily substance (8.8 g, yield 80%).

[0040] The compound characterization data are as follows: 1 H NMR (500 MHz, CDCl3): δ = 7.07 (d, J = 5.00 Hz, 1H), 6.78 (d, J = 5.00 Hz, 1H), 2.81 (t, J = 6.00 Hz, 2H), 2.66 (t, J = 6.00 Hz, 2H),1.90–1.82 (m, 4H) ppm. 13 C NMR (125 MHz, CDCl3): δ = 135.6, 135.3, 127.8,121.6, 25.7, 25.1, 23.9, 23.1 ppm. MS m / z (RI, %): 138.2 (M + , 68.1), 110.2(100.0), 137.1 (25.9), 97.1 (16.4), 111.1 (13.8), 139.1 (9.3). Step 2: Add 4,5,6,7-tetrahydrobenzo[] to the round-bottom flask. b Thiophene (8.8 g) and dichloromethane (100 mL). The reaction system was cooled to -15 °C, and then... N - Bromosuccinimide (10.8 g), followed by continued reaction at the same temperature for 2 hours; after the reaction was complete, 100 mL of water was added to quench the reaction, followed by extraction with dichloromethane, washing the organic phase with water, drying with anhydrous magnesium sulfate, filtering to obtain the filtrate, and removing the solvent under reduced pressure to obtain 2-bromo-4,5,6,7-tetrahydrobenzo[ b Thiophene was a pale yellow oil (13.8 g). The crude compound could be used directly in the next coupling reaction without further purification.

[0041] The compound characterization data are as follows: MS m / z (RI, %): 137.1 (M + , 100.0), 190.0 (67.6), 188.0 (66.9), 218.1 (54.2), 216.1 (53.6), 109.1 (29.3). Step 3: Under nitrogen protection, add (2,3-difluoro-4-propoxyphenyl)boric acid (1.05 g) and 2-bromo-4,5,6,7-tetrahydrobenzo[] to a round-bottom flask. b Thiophene (1.00 g), potassium carbonate (1.27 g), Pd(PPh3)2Cl2 (0.03 g), tetrabutylammonium bromide (0.1 g), and solvent (toluene / ethanol / water, 100 mL, V / V / V = 1 / 1 / 1) were reacted. The reaction system was heated at 100 °C for 6 hours and then cooled to room temperature. The reaction system was extracted with toluene to obtain an organic phase. After washing the organic phase with water, the solvent in the organic phase was removed under reduced pressure. The residue was purified by silica gel column chromatography (eluent: n-heptane / toluene = 8 / 1, V / V) to give compound 2-(2,3-difluoro-4-propoxyphenyl)-4,5,6,7-tetrahydrobenzo[ b Thiophene is a white solid (1.1 g, 77% yield).

[0042] The compound characterization data are as follows: 1 H NMR (800 MHz, CDCl3): d = 7.17 (td, J = 8.80 Hz, J =2.40 Hz, 1H), 7.03 (s, 1H), 6.72 (td, J = 9.60 Hz, J = 2.40 Hz, 1H), 4.01 (t, J =6.40 Hz, 2H), 2.78 (t, J = 4.80 Hz, 2H), 2.63 (t, J = 6.40 Hz, 2H), 1.88–1.84 (m,4H), 1.83–1.80 (m, 2H), 1.06 (t, J = 7.20 Hz, 3H) ppm. 13 C NMR (200 MHz, CDCl3): δ = 148.4 (dd, J = 248.00 Hz, J= 12.00 Hz), 147.4 (dd, J = 8.00 Hz, J = 4.00 Hz), 142.1 (dd, J = 244.00 Hz, J = 14.00 Hz), 136.3, 136.0 (d, J = 4.00 Hz), 132.5 (t, J =2.00 Hz), 126.8 (d, J = 8.00 Hz), 121.8 (t, J = 4.00 Hz), 117.1 (d, J = 10.00 Hz), 109.8 (d, J = 4.00 Hz),71.5, 25.7, 25.1, 23.7, 23.0, 22.7, 10.5 ppm. MS m / z(RI, %): 308.3 (M + , 80.3), 238.2 (100.0), 266.2 (92.3), 265.2 (37.1), 267.2 (18.7), 309.3 (17.6). DSC and POM tests revealed that the phase transition temperature and phase transition type of this compound are: Cr 94.1 I (no liquid crystal phase).

[0043] When the compound was added to the negative base formulation HOST at a mass fraction of 10%, the compound dissolved well and showed no obvious room temperature crystallization.

[0044] Further testing of its physical properties yields the birefringence Δ of this compound. n = 0.1471, dielectric anisotropy Δ e = -4.88.

[0045] Example 2: This example is 2-(2,3-difluoro-4-(pentoxy)phenyl)-4,5,6,7-tetrahydrobenzo[ b Thiophene, with the following structural formula:

[0046] Using the same preparation method as in Example 1, but replacing (2,3-difluoro-4-(pentoxy)phenyl)boronic acid with (2,3-difluoro-4-propoxyphenyl)boronic acid, 2-(2,3-difluoro-4-(pentoxy)phenyl)-4,5,6,7-tetrahydrobenzo[ bThiophene is a white solid.

[0047] The compound characterization data are as follows: 1 H NMR (500 MHz, CDCl3): d = 7.17 (td, J = 8.50 Hz, J =2.50 Hz, 1H), 7.03 (s, 1H), 6.71 (td, J = 9.00 Hz, J = 2.00 Hz, 1H), 4.05 (t, J =6.50 Hz, 2H), 2.78 (t, J = 6.00 Hz, 2H), 2.63 (t, J = 6.50 Hz, 2H), 1.89–1.80 (m,6H), 1.49–1.36 (m, 4H), 0.94 (t, J = 7.50 Hz, 3H) ppm. 13 C NMR (125 MHz, CDCl3): δ = 148.4 (dd, J = 248.75 Hz, J = 12.50 Hz), 147.4 (dd, J = 8.75 Hz, J = 3.75 Hz), 142.2 (dd, J = 245.00 Hz, J = 15.00 Hz), 136.3, 136.0 (d, J = 2.50 Hz), 132.5 (t, J =2.50 Hz), 126.8 (d, J = 7.50 Hz), 121.8 (t, J = 3.75 Hz), 117.1 (d, J = 10.00 Hz), 109.8 (d, J = 2.50 Hz), 70.1,29.0, 28.2, 25.7, 25.1, 23.7, 23.0, 22.6, 14.1ppm. MS m / z (RI, %): 336.3 (M +, 60.6), 266.3 (100.0), 238.2 (89.7), 265.3 (29.3), 267.3 (23.7), 239.2 (17.0). DSC and POM tests revealed that the phase transition temperature and phase transition type of this compound are: Cr 56.7 I (no liquid crystal phase).

[0048] When the compound was added to the negative base formulation HOST at a mass fraction of 10%, the compound dissolved well and showed no obvious room temperature crystallization.

[0049] Further testing of its physical properties yields the birefringence Δ of this compound. n = 0.1261, dielectric anisotropy Δ e = -4.49.

[0050] Example 3: This embodiment is 2-(2',3,3'-trifluoro-4'-propoxy-[1,1'-biphenyl]-4-yl)-4,5,6,7-tetrahydrobenzo[ b Thiophene, with the following structural formula:

[0051] Using the same preparation method as in Example 1, but replacing (2,3-difluoro-4-propoxy-[1,1'-biphenyl]-4-yl)boronic acid with (2',3,3'-trifluoro-4'-propoxy-[1,1'-biphenyl]-4-yl)boronic acid, 2-(2',3,3'-trifluoro-4'-propoxy-[1,1'-biphenyl]-4-yl)-4,5,6,7-tetrahydrobenzo[ b Thiophene is a white solid.

[0052] The compound characterization data are as follows: 1 H NMR (500 MHz, CDCl3): d = 7.60 (t, J = 8.00 Hz, 1H),7.31–7.28 (m, 2H), 7.18 (s, 1H), 7.11 (td, J = 8.50 Hz, J = 2.50 Hz, 1H), 6.82–6.79 (m, 1H), 4.09 (t, J = 6.50 Hz, 2H), 2.81 (t, J = 6.00 Hz, 2H), 2.66 (t, J=6.00 Hz, 2H), 1.91–1.81 (m, 6H), 1.57–1.50 (m, 2H), 1.00 (t, J = 7.50 Hz, 3H)ppm. 13 C NMR (125 MHz, CDCl3): δ = 158.9 (d, J = 247.50 Hz), 149.1 (dd, J = 247.50Hz, J = 11.25 Hz), 148.4 (dd, J = 8.75 Hz, J = 3.75 Hz), 142.0 (dd, J = 246.25 Hz, J =15.00 Hz), 136.9 (d, J = 3.75 Hz), 136.4, 134.8 (d, J = 8.75 Hz), 132.9 (d, J =3.75 Hz), 128.5 (d, J = 5.00 Hz), 127.6 (d, J = 6.25 Hz), 124.6 (t, J = 2.50 Hz), 123.4 (t, J = 3.75 Hz), 122.0 (d, J = 12.50 Hz), 121.4 (d, J = 10.00 Hz), 116.5 (dd, J = 23.75 Hz, J = 3.75 Hz), 109.8 (d, J = 3.75 Hz), 69.7, 31.3, 25.7, 25.1,23.7, 23.0, 19.3, 13.9 ppm. MS m / z (RI, %): 416.3 (M + , 100.0), 332.2 (73.4), 360.2 (44.2), 417.3 (27.9), 359.2 (22.8), 333.2 (15.5). DSC and POM tests revealed that the phase transition temperature and phase transition type of this compound are: Cr 110.7 I (no liquid crystal phase).

[0053] When the compound was added to the negative base formulation HOST at a mass fraction of 10%, the compound dissolved well and showed no obvious room temperature crystallization.

[0054] Further testing of its physical properties yields the birefringence Δ of this compound. n = 0.2435, dielectric anisotropy Δ e = -5.26.

[0055] Example 4: This embodiment is 2-(2,3-difluoro-4'-propyl-[1,1'-biphenyl]-4-yl)-4,5,6,7-tetrahydrobenzo[ b Thiophene, with the following structural formula:

[0056] Using the same preparation method as in Example 1, but replacing (2,3-difluoro-4'-propyl-[1,1'-biphenyl]-4-yl)boronic acid with (2,3-difluoro-4'-propyl-[1,1'-biphenyl]-4-yl)boronic acid, 2-(2,3-difluoro-4'-propyl-[1,1'-biphenyl]-4-yl)-4,5,6,7-tetrahydrobenzo[ b Thiophene is a white solid.

[0057] The compound characterization data are as follows: 1 H NMR (500 MHz, CDCl3): d = 7.51 (d, J = 6.50 Hz, 2H),7.37–7.34 (m, 1H), 7.29 (d, J = 8.00 Hz, 2H), 7.21–7.17 (m, 2H), 2.83 (t, J =6.00 Hz, 2H), 2.69–2.65 (m,4H), 1.93–1.83 (m, 4H), 1.76–1.68 (m, 2H), 1.01(t, J = 7.00 Hz, 3H) ppm. 13 C NMR (125 MHz, CDCl3): δ = 148.8 (dd, J = 247.50 Hz, J =13.75 Hz), 147.9 (dd, J = 250.00 Hz, J = 15.00 Hz), 142.9, 137.2 (d, J= 3.75 Hz), 136.5, 132.2 (t, J = 3.75 Hz), 132.0 (d, J = 2.50 Hz), 128.9, 128.8 (d, J = 12.50Hz), 128.7 (d, J = 2.50 Hz), 127.9 (d, J = 7.50 Hz), 124.7 (t, J = 3.75 Hz), 123.3(d, J = 10.00 Hz), 122.5 (t, J = 3.75 Hz), 37.9, 25.7, 25.1, 24.6, 23.7, 23.0,14.0 ppm. MS m / z (RI, %): 368.2 (M + , 100.0), 340.1 (45.9), 369.1 (32.4), 311.0 (31.1), 339.1 (28.8), 155.5 (20.1). DSC and POM tests revealed that the phase transition temperature and phase transition type of the compound are: Cr 85.1 N 90.3 I.

[0058] When the compound was added to the negative base formulation HOST at a mass fraction of 10%, the compound dissolved well and showed no obvious room temperature crystallization.

[0059] Further testing of its physical properties yields the birefringence Δ of this compound. n = 0.2831, dielectric anisotropy Δ e = -1.47.

[0060] Example 5: This embodiment is 2-(2,3-difluoro-4'-pentyl-[1,1'-biphenyl]-4-yl)-4,5,6,7-tetrahydrobenzo[ b Thiophene, with the following structural formula:

[0061] Using the same preparation method as in Example 1, but replacing (2,3-difluoro-4'-pentyl-[1,1'-biphenyl]-4-yl)boronic acid with (2,3-difluoro-4'-propoxyphenyl)boronic acid, 2-(2,3-difluoro-4'-pentyl-[1,1'-biphenyl]-4-yl)-4,5,6,7-tetrahydrobenzo[ b Thiophene is a white solid.

[0062] The compound characterization data are as follows: 1 H NMR (500 MHz, CDCl3): d = 7.52 (d, J = 7.00 Hz, 2H),7.38–7.34 (m, 1H), 7.30 (d, J = 8.00 Hz, 2H), 7.22–7.17 (m, 2H), 2.84 (t, J =6.00 Hz, 2H), 2.70–2.67 (m,4H), 1.94–1.83 (m, 4H), 1.73–1.67 (m, 2H), 1.41–1.38 (m, 4H), 0.96 (t, J = 6.50 Hz, 3H) ppm. 13 C NMR (125 MHz, CDCl3): δ = 148.8(dd, J = 247.50 Hz, J = 13.75 Hz), 147.9 (dd, J = 250.00 Hz, J = 13.75 Hz), 143.2,137.2 (d, J = 3.75 Hz), 136.5, 132.2 (t, J = 3.75 Hz), 132.0, 128.79, 128.78 (d, J = 10.00 Hz), 128.7 (d, J = 2.50 Hz), 127.9 (d, J = 7.50 Hz), 124.6 (t, J = 3.75Hz), 123.3 (d, J = 10.00 Hz), 122.5 (t, J = 3.75 Hz), 35.8, 31.7, 31.2, 25.7,25.1, 23.7, 23.0, 22.7, 14.2 ppm. MS m / z (RI, %): 396.3 (M + , 100.0), 339.1(40.4), 397.2 (37.2), 311.0 (31.4), 368.1 (28.2), 398.2 (11.1). DSC and POM tests revealed that the phase transition temperature and phase transition type of this compound are: Cr 71.2 N 97.1 I.

[0063] When the compound was added to the negative base formulation HOST at a mass fraction of 10%, the compound dissolved well and showed no obvious room temperature crystallization.

[0064] Further testing of its physical properties yields the birefringence Δ of this compound. n = 0.2671, dielectric anisotropy Δ e = -1.19.

[0065] Example 6: The liquid crystal composition, its mass ratio and performance parameters are shown in Table 5 below.

[0066] Table 5

[0067] The liquid crystal composition exhibits good low-temperature performance, retaining the nematic phase at -20 °C.

[0068] Comparative Example 1: Comparative Example 1 compound is 2-(2,3-difluoro-4'-propyl-[1,1'-biphenyl]-4-yl)benzo[b]thiophene, with the following structural formula:

[0069] The same preparation method as in Example 4 was used, but 2-bromobenzothiophene was used instead of 2-bromo-4,5,6,7-tetrahydrobenzo[ b Thiophene yields 2-(2,3-difluoro-4'-propyl-[1,1'-biphenyl]-4-yl)benzo[b]thiophene, a white solid.

[0070] The compound characterization data are as follows: 1 H NMR (800 MHz, CDCl3): d = 7.87 (d, J = 8.00 Hz, 1H), 7.84 (d, J = 7.20 Hz, 1H), 7.79 (s, 1H), 7.52 (d, J = 6.40 Hz, 2H), 7.49 (t, J =6.40 Hz, 1H), 7.41–7.36 (m, 2H), 7.30 (d, J = 8.00 Hz, 2H), 7.27 (t, J = 6.40 Hz, 1H), 2.67 (t,J = 7.20 Hz, 2H), 1.74–1.69 (m, 2H), 1.00 (t, J = 7.20 Hz, 3H)ppm. 13 C NMR (200 MHz, CDCl3): δ = 148.8 (dd, J = 248.00 Hz, J = 14.00 Hz), 148.6 (dd, J = 232.00 Hz, J = 16.00 Hz), 143.3, 140.5, 139.6 (d, J = 4.00 Hz), 136.3 (t, J = 2.00 Hz), 131.8, 130.4 (d, J = 10.00 Hz), 129.0, 128.8 (d, J = 4.00 Hz), 125.1, 124.9 (t, J = 4.00 Hz), 124.8, 124.2, 124.0 (d, J = 8.00 Hz), 123.6 (t, J = 4.00Hz), 122.8 (d, J = 10.00 Hz), 122.2, 38.0, 24.6, 14.0 ppm. MS m / z (RI, %): 364.0 (M + , 96.5), 335.0 (100.0), 167.4 (27.6), 365.0 (25.7), 336.0 (24.0), 313.0 (7.6). DSC and POM tests revealed that the phase transition temperature and phase transition type of the compound are: Cr 154.8 N 193.8 I.

[0071] Compound 1 of Comparative Example 1 was added to the negative base formulation HOST at a mass fraction of 10%. The compound exhibited poor solubility and significant room-temperature crystallization. Subsequently, the concentration was reduced, and the compound was added to the negative base formulation HOST at a mass fraction of 5%. The compound still showed poor solubility and crystals precipitated after standing at room temperature. Compared to the compound of Example 4, Comparative Example 1 used benzothiophene as the crystal nucleus structure. The melting point of the compound of Comparative Example 1 was 154.8 °C. o C) is much higher than in Example 4 (85.1) oC), and there is no liquid crystal phase. This highlights the technical advantages of 4,5,6,7-tetrahydrobenz[b]thiophene in this invention: it can significantly improve the solubility of negative liquid crystals, lower the melting point of the compound, and facilitate the formation of nematic liquid crystal phases.

[0072] Comparative Example 2: Comparative Example 2 compound is 2-(2,3-difluoro-4-propoxyphenyl)benzo[b]thiophene, with the following structural formula:

[0073] The same preparation method as in Example 1 was used, but 2-bromobenzothiophene was used instead of 2-bromo-4,5,6,7-tetrahydrobenzo[ b Thiophene can be used to obtain 2-(2,3-difluoro-4-propoxyphenyl)benzo[b]thiophene, which is a white solid.

[0074] The compound characterization data are as follows: 1 H NMR (800 MHz, CDCl3): d = 7.83 (d, J = 8.00 Hz, 1H), 7.79 (d, J = 8.00 Hz, 1H), 7.63, 7.37 (t, J = 8.80 Hz, 1H), 7.33 (t, J = 8.00 Hz, 2H), 6.78 (t, J = 10.00 Hz, 1H), 4.05 (t, J = 6.40 Hz, 2H), 1.90–1.86 (m, 2H), 1.08 (t, J = 7.20 Hz, 3H) ppm. 13 C NMR (200 MHz, CDCl3): δ = 149.0 (dd, J = 252.00Hz, J = 10.00 Hz), 148.5 (dd, J = 8.00 Hz, J = 4.00 Hz), 142.1 (dd, J = 248.00 Hz, J =16.00 Hz), 140.6, 139.2 (d, J = 2.00 Hz), 136.6 (t, J = 2.00 Hz), 125.0 (d, J=26.00 Hz), 124.7 (d, J = 4.00 Hz), 123.9, 122.9 (t, J = 4.00 Hz), 122.7 (d, J =8.00 Hz), 122.1, 116.4 (d, J = 10.00 Hz), 109.7, 71.5, 22.6, 10.5 ppm. MS m / z(RI, %): 304.0 (M + , 25.3), 261.9 (100.0), 262.9 (15.9), 260.9 (10.1), 200.9 (8.9), 212.9 (6.5). DSC and POM tests revealed that the phase transition temperature and phase transition type of this compound are: Cr 114.7 I (no liquid crystal phase).

[0075] When the compound of Comparative Example 2 was added to the negative base formulation HOST at a mass fraction of 10%, the compound showed very poor solubility and obvious room temperature crystallization. Subsequently, the concentration was reduced, and the compound was added to the negative base formulation HOST at a mass fraction of 5%. The compound dissolved and showed no obvious room temperature crystallization after standing.

[0076] Further testing of its physical properties yielded the birefringence Δ of the compound in Comparative Example 2. n = 0.2541, dielectric anisotropy Δ e = -4.44.

[0077] Compared to the compound of Example 1, the compound of Comparative Example 2 uses conventional benzothiophene as the crystal nucleus structure. As shown in Table 6 below, its negative dielectric anisotropy is less than that of the compound of Example 1, and its melting point is higher than that of the compound of Example 2. This highlights the technical advantages of the novel liquid crystal nucleus of 4,5,6,7-tetrahydrobenzo[b]thiophene, which can improve the negative dielectric anisotropy while lowering the melting point of the molecule.

[0078] Table 6

Claims

1. A negative liquid crystal compound based on a 4,5,6,7-tetrahydrobenzene[b]thiophene skeleton, characterized in that, The structure of the compound is shown in general formula (1): （1） Wherein, R1 is a saturated alkyl group with 1 to 9 carbon atoms, an unsaturated alkyl group with 1 to 9 carbon atoms, a saturated alkoxy group with 1 to 9 carbon atoms, or an unsaturated alkoxy group with 1 to 9 carbon atoms; the ring H is a benzene ring or trans-cyclohexane; A1, A2, A3, and A4 are each independently a hydrogen atom or a fluorine atom; m and n are each independently 0 or 1; R2 and R3 are each independently a hydrogen atom, a saturated alkyl group with 1 to 9 carbon atoms, or an unsaturated alkyl group.

2. The negative liquid crystal compound according to claim 1, characterized in that, The compound is selected from the structures shown in formulas (1)-1 to (1)-6: 。 3. The method for synthesizing the negative liquid crystal compound according to claim 1, characterized in that, The synthesis method includes: Step 1: Using substituted cyclohexanone thiophene as the starting material, the intermediate substituted 4,5,6,7-tetrahydrobenz[b]thiophene was prepared by reduction with hydrazine hydrate. Step 2: The substituted 4,5,6,7-tetrahydrobenzene[b]thiophene intermediate is reacted with NBS to give the 2-brominated thiophene intermediate; Step 3: The thiophene 2-brominated intermediate is coupled with a substituted fluorinated arylboronic acid via a palladium-catalyzed coupling reaction to obtain the negative liquid crystal compound.

4. A negative liquid crystal composition, characterized in that, The composition comprises one or more of the liquid crystal compounds of claim 1.

5. The negative liquid crystal composition according to claim 4, characterized in that, It also includes a second component, which is one or more liquid crystal compounds as described in general formula (2): （2） Wherein, R4 and R5 are independently saturated alkyl groups with 1 to 9 carbon atoms, unsaturated alkyl groups with 1 to 9 carbon atoms, saturated alkoxy groups with 1 to 9 carbon atoms, or unsaturated alkoxy groups with 1 to 9 carbon atoms, respectively; L1 bridging bond is a single bond, ethylene bridging bond, ethane bridging bond, or acetylene bridging bond; ring O and ring P are independently benzene rings, transcyclohexane, cyclohexene, or benzene rings substituted with fluorine, chlorine, trifluoromethyl, methyl, or ethyl, respectively; i and j are independently 0, 1, and 2, respectively.

6. The negative liquid crystal composition according to claim 4, characterized in that, The mass fraction of the liquid crystal compound according to claim 1 is 1 to 100%.

7. The liquid crystal composition according to claim 4, characterized in that, The mass fraction of the second component is 0-99%.

8. A liquid crystal display element, characterized in that... The negative liquid crystal composition comprising any one of claims 4 to 7.

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