Liquid crystal compound containing 2, 4, 5-trifluorobenzene, preparation method and composition thereof

Abstract

The invention discloses a liquid crystal compound containing 2, 4, 5-trifluorobenzene, a preparation method and a composition thereof. The structure of the compound disclosed by the invention is shown as a general formula I; and the liquid crystal composition disclosed by the invention comprises the liquid crystal compound disclosed as the general formula I. The liquid crystal compound has the advantages of low dielectric loss, good light stability, wide nematic liquid crystal phase, high birefringence, low viscosity, good low-temperature intermiscibility and the like. The composition based on the liquid crystal compound provided by the invention obtains relatively high dielectric tuning rate, extremely low dielectric loss and low rotary viscosity under high frequency; and the material has the advantages of good light stability, large birefringence, wide working temperature range and the like. The liquid crystal composition provided by the invention has the characteristics of large birefringence, low viscosity and the like, so that the liquid crystal composition is suitable for manufacturing liquid crystal optical elements and high-frequency assemblies. # imgabs0 #

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal materials, and particularly relates to a liquid crystal compound containing 2,4,5-trifluorobenzene, a liquid crystal composition, a liquid crystal high-frequency component, a liquid crystal optical element, and a synthesis method thereof. Background Art

[0002] Liquid crystal materials have been widely used in optoelectronic display devices, such as various liquid crystal TVs, desktop liquid crystal displays, mobile display terminals, etc. In recent years, with the continuous development of technologies such as microwave and terahertz communication, optical communication, and laser phased array, there is an urgent need for liquid crystal materials with high birefringence. The higher the birefringence (Δn) of the liquid crystal, the greater the dielectric anisotropy value in the microwave (1 - 100G) band. In addition, in liquid crystal devices such as optical communication and laser phased array, by using a liquid crystal with high birefringence (Δn), the response time can be significantly shortened on the premise of ensuring the optical phase modulation amount.

[0003] To improve the birefringence of liquid crystal materials, a structure with a long conjugated chain needs to be adopted in the liquid crystal molecules. For example, the molecular skeleton adopts a long conjugated structure of biphenyl, terphenyl, quaterphenyl, or diphenylacetylene. Among them, liquid crystal molecules containing an alkyne bond (-C≡C-) have a high polarizability anisotropy, so the birefringence is relatively high. Further, by introducing an isothiocyanate group (NCS) at the end of the liquid crystal molecule, the conjugation degree of the liquid crystal is greatly increased, and the dielectric constant in the microwave frequency band is greatly increased. Patents CN107955630A, CN105368465A, CN110499163A, US2019292458A1, and CN113528154A disclose compositions of liquid crystal compounds containing a diphenylacetylene molecular skeleton and an NCS group at the end group, which have the advantage of large dielectric constant tunability in the microwave frequency band. However, liquid crystal compounds and their compositions containing an NCS group have poor photo-stability. When irradiated with ultraviolet light and visible light, they are prone to photochemical reactions, resulting in a rapid deterioration of performance. Due to the poor photo-stability of NCS liquid crystals, many problems are brought about in the production process and application process. Especially for antenna devices that are transparent to visible light or optical devices in application scenarios such as visible light, NCS liquid crystals are not applicable. In addition, liquid crystals containing an NCS group also have a relatively low resistivity.

[0004] Patents CN 104011175 A and CN108865179A disclose compositions of fluorine-substituted diphenylacetylene-based liquid crystal compounds. These liquid crystal compounds do not contain an NCS group and have relatively good photo-stability, but there is still a problem of large dielectric loss.

[0005] To further meet the working performance requirements such as light stability for microwave, optical and other components, it is urgent to research and develop new liquid crystal structures and compositions with good light stability, low dielectric loss, wide nematic phase temperature range, low viscosity, high birefringence and high resistivity. Summary of the Invention

[0006] In order to overcome the defects or deficiencies in the background art, the present invention provides a liquid crystal compound containing 2,4,5-trifluorobenzene and its composition.

[0007] To achieve the above tasks, the present invention adopts the following technical solutions:

[0008] The liquid crystal compound containing 2,4,5-trifluorobenzene of the present invention has a structure as shown in General Formula I:

[0009]

[0010] Wherein:

[0011] R is an alkyl group with 1-10 carbon atoms, an alkyl group with 1-10 carbon atoms in which hydrogen is substituted by fluorine, an alkoxy group with 1-10 carbon atoms, an alkoxy group with 1-10 carbon atoms in which hydrogen is substituted by fluorine, an alkenyl group with 2-10 carbon atoms, an alkenyl group with 2-10 carbon atoms in which hydrogen is substituted by fluorine, an alkenyloxy group with 2-10 carbon atoms, an alkenyloxy group with 2-10 carbon atoms in which hydrogen is substituted by fluorine, a cycloalkyl group with 3-8 carbon atoms or a cycloalkyl group with 3-8 carbon atoms in which hydrogen is substituted by fluorine;

[0012] Z1 and Z2 are each independently a single bond or -C≡C-;

[0013] Ring A is a benzene ring, cyclohexane, cyclohexene or a benzene ring in which hydrogen is substituted by fluorine, chlorine, methyl or / and ethyl;

[0014] n = 0, 1, 2.

[0015] An alternative is that n = 1. Or n = 1 and ring A is a benzene ring.

[0016] An alternative is that the structural formula of the compound is shown as any one of the structural formulas of I-1 to I-10;

[0017]

[0018] For the liquid crystal compound of the present invention, by introducing fluorine substituents at specific positions on the benzene ring, compared with similar liquid crystal compounds disclosed in the prior art, surprising results are obtained. The dielectric loss at high frequencies is greatly reduced, the quality factor is greatly improved, and it has high light stability. The above advantages are very beneficial for microwave antennas, liquid crystal optical devices, etc.

[0019] The present invention also provides a method for synthesizing the above-mentioned liquid crystal compound containing 2,4,5-trifluorobenzene. The preparation method includes: coupling reaction of 2,4,5-trifluoroiodo(bromo)benzene with a phenylacetylene derivative in the presence of a transition metal catalyst and a copper salt catalyst A to obtain a diphenylacetylene liquid crystal compound;

[0020] Or:

[0021] Coupling reaction of 2,4,5-trifluoroiodo(bromo)benzene with an arylboronic acid derivative under the catalysis of a transition metal catalyst B to obtain a biphenyl liquid crystal compound;

[0022] It is also possible to use 2,4,5-trifluorobenzeneboronic acid or 2,4,5-trifluorobenzeneboronate ester, and carry out a coupling reaction with an aryl bromide under the catalysis of a transition metal catalyst C to obtain a liquid crystal compound containing a biphenyl unit.

[0023] Further optional is that the transition metal catalysts A, B, and C are each independently selected from a palladium-containing complex or a nickel-containing complex. The palladium-containing complex is tetrakis(triphenylphosphine)palladium or dichlorobis(triphenylphosphine)palladium. The copper salt catalyst is cuprous halide.

[0024] The present invention also provides a liquid crystal composition, which contains one or more liquid crystal compounds selected from those shown in the general structural formula I. Optionally, the mass percentage of the liquid crystal compound shown in the general structural formula I contained in the liquid crystal composition is 10% - 100%. Further optionally, the liquid crystal composition further contains one or more liquid crystal compounds selected from those shown in the general structural formula II as a second component, and the mass percentage of the second component is 0 - 95% (excluding the endpoint value 0);

[0025]

[0026] Wherein:

[0027] R3 and R4 are each independently an alkyl group having 1 - 10 carbon atoms, an alkoxy group having 1 - 10 carbon atoms, an alkenyl group having 2 - 10 carbon atoms, an alkenyloxy group having 2 - 10 carbon atoms, fluorine, chlorine, cyano (-C≡N), isothiocyanate group (-N=C=S), trifluoromethyl (-CF3) or trifluoromethoxy (-OCF3);

[0028] Z3 and Z4 are each independently a single bond, -C≡C-, -CH=CH-, -CF=CF-, -CF2O- or -CH2CH2;

[0029] Ring C, ring D, and ring E are each independently a benzene ring, cyclohexane, cyclohexene or a benzene ring in which hydrogen is substituted by fluorine, chlorine, methyl or / and ethyl;

[0030] m = 0, 1, 2.

[0031] Preferably, the liquid crystal composition further contains one or more liquid crystal compounds selected from those represented by Structural Formulas II-1 to II-8:

[0032]

[0033] Wherein:

[0034] R5 in Formulas II-1 to II-8 are each independently an alkyl group having 1 to 7 carbon atoms or an alkoxy group having 1 to 7 carbon atoms; R6 in Formulas II-1 and II-6 are each independently an alkyl group having 1 to 7 carbon atoms or an alkoxy group having 1 to 7 carbon atoms; R7 in Formulas II-6 to II-8 are each independently fluorine, chlorine, methyl or ethyl;

[0035] Ring C in Formulas II-1 and II-2 are each independently a benzene ring or a cyclohexane ring;

[0036] m in Formulas II-1, II-2 and II-4 are each independently 0, 1 or 2.

[0037] The liquid crystal compounds of the present invention have the advantages of low dielectric loss, good light stability, a relatively wide nematic liquid crystal phase, high birefringence, low viscosity, good low-temperature compatibility, etc. The composition based on the liquid crystal compounds of the present invention obtains a large dielectric tuning rate, extremely low dielectric loss, and low rotational viscosity at high frequencies; and has the advantages of good light stability, large birefringence, and a wide operating temperature range.

[0038] The liquid crystal composition of the present invention, due to its characteristics such as large birefringence and low viscosity, is suitable for making liquid crystal optical elements and high-frequency components, including phase modulation devices, gratings, wavelength selective switches (WSS), etc. The liquid crystal compounds and compositions of the present invention have high light stability and are particularly suitable for making transparent antennas. Detailed Embodiments

[0039] Unless otherwise specified, the scientific and technical terms and methods in this article are understood or implemented according to the understanding of those of ordinary skill in the relevant art or using existing related methods.

[0040] According to the disclosure of the present invention, those skilled in the art can select appropriate components and ratios to achieve the effects of the present invention. The liquid crystal composition of the present invention contains one or more compounds of Structural Formula I. In some other preferred embodiments of the present invention, the liquid crystal composition contains one or more compounds of Structural Formula I and one or more compounds of Structural Formula II. In specific embodiments, those skilled in the art can make optimized selections based on the disclosure of the present invention.

[0041] In a specific embodiment, the liquid crystal composition of the present invention is composed of a plurality of compounds, preferably 3 to 20 compounds, more preferably 5 to 18 compounds, and even more preferably 7 to 15 compounds. These compounds can be mixed in a conventional manner: various compounds are weighed according to a predetermined mass ratio, then heated, and at the same time, homogenously mixed by means of magnetic stirring or ultrasonic stirring until all components are completely dissolved; and then obtained after filtration. The liquid crystal composition can also be prepared by other conventional methods, such as using a so-called premix, or using a so-called "multi-bottle" system, in which the components themselves are ready-to-use mixtures.

[0042] The preferred liquid crystal composition of the present invention has a dielectric tuning rate τ≥0.20 at high frequencies, such as 19 to 30 GHz, more preferably ≥0.22; the dielectric loss tangent tanδ of the preferred liquid crystal material in the vertical direction ⊥ ≤0.010, more preferably tanδ ⊥ ≤0.008; the material quality factor η≥20, preferably η≥30.

[0043] The nematic temperature range of the preferred liquid crystal composition of the present invention is 0 to 70 °C or above, more preferably the nematic temperature range is -10 to 90 °C or above; the rotational viscosity γ1 of the preferred liquid crystal composition ≤500 mPa·s, more preferably ≤400 mPa·s.

[0044] The liquid crystal composition of the present invention has a high birefringence (Δn). The preferred liquid crystal composition of the present invention has Δn≥0.30 at 25 °C and 589 nm, more preferably Δn≥0.32.

[0045] In some other embodiments, the liquid crystal composition of the present invention may further contain 0.001% to 1% of additives, such as hindered phenol antioxidants, hindered amine light stabilizers, etc. The hindered phenol antioxidants are preferably selected from the following structures:

[0046]

[0047] In the above three structural formulas, R' is independently an alkyl or alkoxy group having 1 to 9 carbon atoms.

[0048] The hindered amine light stabilizers are preferably selected from the following structures:

[0049]

[0050] The preferred addition amounts of the hindered phenol antioxidants and hindered amine light stabilizers are 0.01% to 0.5%, more preferably 0.02% to 0.2%.

[0051] The liquid crystal composition of the present invention may further comprise one or more chiral additives, with a content of 0.01% to 1%; preferably 0.1% to 0.5%. The chiral additive is preferably selected from the following structures:

[0052]

[0053] In the above formula, each R″ is independently an alkyl group having 1 to 9 carbon atoms or an alkoxy group having 1 to 9 carbon atoms.

[0054] The performance of the liquid crystals described herein at high frequencies is measured using the test methods reported in the literature: Penirschke, A. (2004). Cavity perturbation method for characterization of liquid crystals up to 35 GHz. Microwave Conference,2004.34th European .

[0055] The liquid crystal is introduced into a polytetrafluoroethylene (PTFE) or fused silica capillary, and the filled capillary is introduced into the middle of a chamber having a resonance frequency of 19 GHz. Then, an input signal source is applied, and the results of the output signal are recorded using a vector network analyzer. The changes in the resonance frequency and Q factor between the capillary filled with the liquid crystal and the blank capillary are measured, and the dielectric constant and loss tangent value are calculated. The dielectric constant components perpendicular and parallel to the liquid crystal director are obtained by aligning the liquid crystal in a magnetic field, and the direction of the magnetic field is set accordingly and then rotated by 90° accordingly.

[0056] The liquid crystal composition according to the present invention is very suitable for preparing microwave components, such as phase shifters that can be tuned by applying an external magnetic field or electric field. These phase shifters can operate in the UHF-band (0.3 - 1 GHz), L-band (1 - 2 GHz), S-band (2 - 4 GHz), C-band (4 - 8 GHz), X-band (8 - 12 GHz), Ku-band (12 - 18 GHz), K-band (18 - 27 GHz), Ka-band (27 - 40 GHz), V-band (50 - 75 GHz), W-band (75 - 110 GHz), and up to 1 THz. The construction of the phase shifters according to the present application is known to those skilled in the art. Typically, loaded line phase shifters, inverted microstrip lines, finline phase shifters, preferably antipodal finline phase shifters, slotted phase shifters, microstrip line phase shifters, or coplanar waveguide (CPW) phase shifters are used. These components can achieve reconfigurable antenna arrays.

[0057] The present invention will be further described in detail below with reference to specific embodiments.

[0058] It should be noted that the detailed test methods for the physical properties and optoelectronic properties involved in the present invention are as follows:

[0059] (1) Liquid crystal phase transition temperature:

[0060] Differential scanning calorimetry (DSC) was used: Under a nitrogen atmosphere, the heating (cooling) rate was set at 5 °C / min.

[0061] Polarizing hot stage method: The liquid crystal sample was placed in an orthogonal polarizing microscope hot stage, and the heating rate was set at 2 °C / min. Observe the texture image of the liquid crystal phase transition in a polarizing microscope to determine the liquid crystal phase state.

[0062] (2) Birefringence (Δn): The liquid crystal monomer was added to the basic formulation HOST in a mass ratio of 15:85%, and heated and mixed evenly. Using an Abbe refractometer, at a constant temperature of 25 °C and a light source of 589 nm, measure the refractive indices of the ordinary light (n o ) and extraordinary light (n e ) respectively, and extrapolate to obtain the birefringence.

[0063] (3) Dielectric constant (Δε, 1 KHz): The liquid crystal monomer was added to the basic formulation HOST in a mass ratio of 15:85%, and heated and mixed evenly. Under a constant temperature condition of 25 °C, it was tested using an LCR meter. Δε = ε ∥ - ε ⊥ , that is, the difference between the dielectric constant (ε ∥ ) in the direction of the long axis of the molecule and the dielectric constant (ε ⊥ ) in the direction of the short axis of the molecule, and extrapolate to obtain the dielectric anisotropy value Δε.

[0064] (4) Rotational viscosity (γ1): The liquid crystal monomer was added to the basic formulation HOST in a mass ratio of 15:85%, and heated and mixed evenly. Under a constant temperature condition of 25 °C, by applying a voltage to the liquid crystal test cell, measure the transient current value Ip of the deflection of the liquid crystal molecules moving with the electric field, and calculate and extrapolate to obtain the rotational viscosity γ1.

[0065] (5) Dielectric constant and dielectric loss (Δε, tanδ, 19 GHz): The liquid crystal monomer was added to the basic formulation M0 in a mass ratio of 15:85%, and heated and mixed evenly. Under a constant temperature condition of 25 °C, the liquid crystal was poured into a polytetrafluoroethylene (PTFE) or fused quartz capillary tube, and the capillary tube filled with the liquid crystal was inserted into the middle of the resonant cavity chamber. Then apply an input signal source, and use a vector network analyzer to record the results of the output signal. Measure the changes in the resonance frequency and Q factor between the capillary tube filled with the liquid crystal and the blank capillary tube, and calculate to obtain the dielectric constant and loss tangent value. The dielectric constant components perpendicular and parallel to the liquid crystal director are obtained by the orientation of the liquid crystal in a magnetic field, and the direction of the magnetic field is set accordingly, and then rotated by 90° accordingly.

[0066] The base formulation HOST described in the following examples is obtained by uniformly mixing the following three monomeric liquid crystals in a mass ratio of 1:1:1.

[0067]

[0068] The relevant explanations for the codes involved in this article are as follows:

[0069] Table 1 Physical Parameters

[0070] Code Description Unit <![CDATA[ε ⊥ > Dielectric constant perpendicular to the director <![CDATA[ε ∥ > Dielectric constant parallel to the director Δε Dielectric anisotropy <![CDATA[tanδ ⊥ > Dielectric loss tangent perpendicular to the director <![CDATA[tanδ ∥ > Dielectric loss tangent parallel to the director Δn Birefringence <![CDATA[γ1]]> Rotational viscosity mPa·s τ <![CDATA[Dielectric tuning rate; τ = Δε / ε ∥ > η <![CDATA[Microwave quality factor; η = Δε / (ε ∥ *tanδ ⊥ )]]>

[0071] Liquid crystal phase transition temperature: C represents melting point, S represents smectic phase, N represents nematic phase, and I represents liquid state.

[0072] Table 2 Structure Abbreviations

[0073]

[0074]

[0075] Table 3 Abbreviation Examples

[0076]

[0077] Example 1:

[0078] This example is 2,4,5-trifluoro-4'-((4-n-pentylphenyl)ethynyl)-1,1'-biphenyl, and its structural formula is as follows:

[0079]

[0080] Its synthesis route is as follows:

[0081]

[0082] The specific method is as follows:

[0083] (1) Under nitrogen protection, add 14.1 g of 4-bromoiodobenzene, 100 mL of triethylamine, 0.35 g of dichlorobis(triphenylphosphine)palladium(II), 0.29 g of copper(I) iodide, and 0.39 g of triphenylphosphine to the reaction flask. At room temperature, slowly add a 30 mL triethylamine solution containing 8.6 g of 4-n-pentylphenylacetylene dropwise. After dropping, react at room temperature for 4 h, filter, concentrate the filtrate to dryness, add 100 mL of toluene, wash with water, dry, remove toluene under reduced pressure, and recrystallize with ethanol to obtain 15.2 g of white solid 4-bromo-1-((4-n-pentylphenyl)ethynyl)benzene;

[0084] (2) Under nitrogen protection, 13.1 g of 4-bromo-1-((4-n-pentylphenyl)ethynyl)benzene, 7.0 g of 2,4,5-trifluorobenzeneboronic acid, 0.46 g of tetrakis(triphenylphosphine)palladium, 11.1 g of potassium carbonate, 60 mL of toluene, 60 mL of ethanol, and 60 mL of water were added to a reaction flask, and the mixture was heated under reflux for 8 h. After cooling, 100 mL of toluene was added, washed with water, dried, and toluene was removed under reduced pressure. The product was dissolved in n-heptane, passed through a silica gel column, and eluted with n-heptane. The eluate was concentrated to dryness under reduced pressure and recrystallized from n-heptane to obtain 11.8 g of white solid 2,4,5-trifluoro-4'-((4-n-pentylphenyl)ethynyl)-1,1'-biphenyl.

[0085] The structure identification data of the product are as follows:

[0086] 1 H NMR(500MHz,CDCl3)δ(ppm): 0.941(t,3H,J = 7Hz),1.346~1.406(m,4H),1.636~1.694(m,2H),2.660(t,2H,J = 8Hz),7.034~7.086(m,1H),7.217(d,2H,J = 7.5Hz),7.272~7.325(m,1H),7.493~7.512(m,4H),7.627(d,2H,J = 8Hz).

[0087] 13 C NMR(125MHz,CDCl3)δ(ppm): 14.0,22.5,30.9,31.5,35.9,88.3,90.9,106.2,118.0,120.2,123.6,124.9,128.7(2C),131.6(2C),131.8(2C),133.5,143.7,147.0(J C-F = 250Hz),149.5(J C-F = 250Hz),154.8(J C-F = 250Hz).

[0088] MS m / z(RI,%): 378.2(M + ,68),321.1(100).

[0089] DSC: C 49.8S 57.2N 111.4I.

[0090] The compound was mixed with the above basic formulation in a mass percentage of 15%, and further tests were carried out to obtain the physical property parameters of the compound: Δn = 0.308, Δε = 4.4, γ1 = 228 mPa·s.

[0091] Example 2:

[0092] This example is 4-n-butyl-4'-((2,4,5-trifluorophenyl)ethynyl)-1,1'-biphenyl, and its structural formula is as follows:

[0093]

[0094] Its synthetic route is as follows:

[0095]

[0096] The specific synthesis method is as follows:

[0097] Under nitrogen protection, add 12.9 g of 2,4,5-trifluoroiodobenzene, 100 mL of triethylamine, 0.35 g of dichlorobis(triphenylphosphine)palladium(II), 0.29 g of copper(I) iodide, and 0.39 g of triphenylphosphine to the reaction flask. At room temperature, slowly add a 30 mL triethylamine solution containing 11.7 g of 4-n-butylphenylacetylene. After the addition is complete, stir the reaction mixture at room temperature for 4 h. Filter the reaction mixture, concentrate the filtrate to dryness, add 100 mL of toluene, wash with water, dry, remove toluene under reduced pressure, and recrystallize with n-heptane to obtain 14.9 g of white solid 4-n-butyl-4'-((2,4,5-trifluorophenyl)ethynyl)-1,1'-biphenyl.

[0098] The structure identification data are as follows:

[0099] 1 H NMR(500MHz,CDCl3)δ(ppm): 0.999(t,3H,J=7Hz),1.417~1.447(m,2H),1.655~1.716(m,2H),2.705(t,2H,J=8Hz),6.991~7.041(m,1H),7.310(d,2H,J=8Hz),7.348~7.398(m,1H),7.565(d,2H,J=8Hz),7.632(s,4H).

[0100] 13 C NMR(125MHz,CDCl3)δ(ppm): 14.0,22.4,33.6,35.3,81.0,95.2,106.0,108.5,120.5,120.7,126.9(4C),129.0(2C),132.1(2C),137.5,141.7,142.8,146.5(J C-F =250Hz),150.1(J C-F =250Hz),158.3(J C-F =250Hz).

[0101] MS m / z (RI, %): 364.2 (M + , 70), 321.2 (100).

[0102] DSC: C 62.7 S 98.7 S143.9 N 144.8 I.

[0103] The compound was mixed with the above basic formulation at a mass percentage of 15%, and further tests were carried out to obtain the physical property parameters of the compound: Δn = 0.323, Δε = 5.9, γ1 = 146 mPa·s.

[0104] Example 3:

[0105] This example is 2,4,5-trifluoro-1-((4-(trans-4-propylcyclohexyl)phenyl)ethynyl)benzene, and its structural formula is as follows:

[0106]

[0107] Its synthetic route is as follows:

[0108]

[0109] 4-(trans-4-Propylcyclohexyl)phenylacetylene was used to replace 4-butylbiphenylacetylene in Example 2, and the same synthetic method as in Example 2 was adopted for other operations to obtain 2,4,5-trifluoro-1-((4-(trans-4-propylcyclohexyl)phenyl)ethynyl)benzene.

[0110] The structure identification data are as follows:

[0111] DSC: C 56.4 N 141.8 I.

[0112] The compound was mixed with the above basic formulation at a mass percentage of 15%, and further tests were carried out to obtain the physical property parameters of the compound: Δn = 0.230, Δε = 5.1, γ1 = 202 mPa·s.

[0113] Example 4:

[0114] This example is 2,4,5-trifluoro-4”-n-pentyl-1,1':4',1”-terphenyl, and its structural formula is as follows:

[0115]

[0116] Its synthetic route is as follows:

[0117]

[0118] The specific synthetic method is as follows:

[0119] Under nitrogen protection, 13.4 g of 4-n-pentylbiphenylboronic acid, 10.6 g of 2,4,5-trifluorobromobenzene, 0.58 g of tetrakis(triphenylphosphine)palladium, 13.8 g of potassium carbonate, 60 mL of toluene, 60 mL of ethanol, and 60 mL of water were added to a reaction flask, and the mixture was heated under reflux for 8 h. The organic layer was separated and washed with water until neutral. Toluene was removed under reduced pressure, and the product was passed through a silica gel column and eluted with n-heptane. The product was concentrated to dryness, and recrystallized with n-heptane to obtain 12.9 g of white solid 2,4,5-trifluoro-4”-n-pentyl-1,1':4',1”-terphenyl.

[0120] The structure identification data are as follows:

[0121] DSC: C 75.0S102.0I.

[0122] This compound was mixed with the above basic formulation in a mass percentage of 15%, and further tests were carried out to obtain the physical property parameters of this compound: Δn = 0.222, Δε = 4.1, γ1 = 184 mPa·s.

[0123] Example 5:

[0124] The liquid crystal composition of this example, its mass ratio and performance parameters are as shown in Table 4 below:

[0125] Table 4

[0126]

[0127] This liquid crystal composition has very low dielectric loss and a large quality factor at a high frequency of 19 GHz.

[0128] Example 6:

[0129] The liquid crystal composition of this example, its mass ratio and performance parameters are as shown in Table 5 below:

[0130] Table 5

[0131]

[0132]

[0133] This liquid crystal composition has very low dielectric loss and a large quality factor at a high frequency of 19 GHz.

[0134] Example 7:

[0135] The liquid crystal composition of this example, its mass ratio and performance parameters are as shown in Table 6 below:

[0136] Table 6

[0137]

[0138]

[0139] This liquid crystal composition has very low dielectric loss and a large quality factor at a high frequency of 19 GHz.

[0140] Comparative Example 1:

[0141] This comparative example is a liquid crystal composition containing a fluorinated diphenylacetylene structure disclosed in Patent CN104087309A. The dielectric properties at 19 GHz were tested, and the data are shown in Table 7 below:

[0142] Table 7

[0143]

[0144] Compared with Comparative Example 1, although Example 5 and Comparative Example 1 both have a similar molecular skeleton, when the substitution position of the lateral fluorine atoms is adjusted, the dielectric loss at a high frequency of 19 GHz is greatly reduced; among them, the reduction rate of the dielectric loss in the vertical direction reaches 81%; at the same time, the dielectric anisotropy Δη and the dielectric tuning rate τ at a high frequency of 19 GHz also increase significantly; the corresponding quality factor η also doubles. It can be seen that the liquid crystal compounds and their compositions of the present invention have unexpected technical effects.

Claims

1. A liquid crystal compound containing 2,4,5-trifluorobenzene, characterized in that, The structure of the said compound is shown in general formula Ⅰ: Wherein: R is an alkyl group with 1 to 10 carbon atoms, an alkyl group with 1 to 10 carbon atoms in which hydrogen is substituted by fluorine, an alkoxy group with 1 to 10 carbon atoms, an alkoxy group with 1 to 10 carbon atoms in which hydrogen is substituted by fluorine, an alkenyl group with 2 - 10 carbon atoms, an alkenyl group with 2 - 10 carbon atoms in which hydrogen is substituted by fluorine, an alkenyloxy group with 2 - 10 carbon atoms, an alkenyloxy group with 2 - 10 carbon atoms in which hydrogen is substituted by fluorine, a cycloalkyl group with 3 - 8 carbon atoms or a cycloalkyl group with 3 - 8 carbon atoms in which hydrogen is substituted by fluorine; Z1 and Z2 are each independently a single bond or -C≡C-; Ring A is a benzene ring, cyclohexane, cyclohexene or a benzene ring in which hydrogen is substituted by fluorine, chlorine, methyl or / and ethyl; n＝0，1，2。 2. The liquid crystal compound according to claim 1, wherein n＝1。 3. The liquid crystal compound according to claim 1, wherein n = 1 and ring A is a benzene ring.

4. The liquid crystal compound according to claim 1, characterized in that, The structural formula of the said compound is shown as any one of the structural formulas of Ⅰ-1 to Ⅰ-10; 5. The synthesis method of the 2,4,5-trifluorobenzene-containing liquid crystal compound according to claim 1, characterized in that, The method includes: 2,4,5-trifluoroiodo(bromo)benzene undergoes a coupling reaction with a phenylacetylene derivative in the presence of a transition metal catalyst A and a copper salt catalyst to obtain a diphenylacetylene-based liquid crystal compound; Or: 2,4,5-trifluoroiodo(bromo)benzene undergoes a coupling reaction with an arylboronic acid derivative under the catalytic action of a transition metal catalyst B to obtain a biphenyl-based liquid crystal compound; Or: Using 2,4,5-trifluorobenzeneboronic acid or 2,4,5-trifluorobenzeneborate, under the catalytic action of a transition metal catalyst C, undergoes a coupling reaction with an aryl bromide to obtain a liquid crystal compound containing a biphenyl unit.

6. The synthesis method according to claim 5, characterized in that, The said transition metal catalysts A, B and C are each independently selected from a palladium-containing complex or a nickel-containing complex.

7. The synthesis method according to claim 6, characterized in that, The said palladium-containing complex is tetrakis(triphenylphosphine)palladium or dichlorobis(triphenylphosphine)palladium.

8. The synthesis method according to claim 5, characterized in that, The said copper salt catalyst is cuprous halide.

9. A liquid crystal composition, characterized in that, The said liquid crystal composition contains one or more liquid crystal compounds selected from those shown in general formula Ⅰ.

10. The liquid crystal composition according to claim 9, characterized in that, The mass percentage of the liquid crystal compound shown in general formula Ⅰ contained in the said liquid crystal composition is 10% - 100%.

11. The liquid crystal composition according to claim 9, wherein The said liquid crystal composition further contains one or more liquid crystal compounds selected from those shown in general formula Ⅱ as the second component, and the mass percentage of the second component is 0 - 95%; Wherein: R3 and R4 are each independently an alkyl group with 1 to 10 carbon atoms, an alkoxy group with 1 to 10 carbon atoms, an alkenyl group with 2 - 10 carbon atoms, an alkenyloxy group with 2 - 10 carbon atoms, fluorine, chlorine, cyano group, isothiocyanate group, trifluoromethyl group or trifluoromethoxy group; Z3 and Z4 are each independently a single bond, -C≡C-, -CH=CH-, -CF=CF-, -CF2O- or -CH2CH2; Ring C, ring D and ring E are each independently a benzene ring, cyclohexane, cyclohexene or a benzene ring in which hydrogen is substituted by fluorine, chlorine, methyl or / and ethyl; m＝0，1，2。 12. The liquid crystal composition according to claim 9, characterized in that, The said liquid crystal composition further contains one or more liquid crystal compounds selected from those shown in general formula Ⅱ-1 to Ⅱ-8: Wherein: R5 in formulas Ⅱ-1 to Ⅱ-8 are each independently an alkyl group with 1 to 7 carbon atoms or an alkoxy group with 1 to 7 carbon atoms; R6 in formulas Ⅱ-1 and Ⅱ-6 are each independently an alkyl group with 1 to 7 carbon atoms or an alkoxy group with 1 to 7 carbon atoms; R7 in Formulae II-6 to II-8 is each independently fluorine, chlorine, methyl or ethyl; Ring C in Formulae II-1 and II-2 is each independently a benzene ring or a cyclohexane; m in Formulae II-1, II-2 and II-4 is each independently 0, 1 or 2.

13. A liquid crystal high-frequency component, characterized in that, The liquid crystal high-frequency component is prepared by using the liquid crystal compound according to any one of claims 1-4 or a liquid crystal composition containing the liquid crystal compound according to any one of claims 9-12.

14. A liquid crystal optical element, characterized in that, The liquid crystal optical element is prepared by using the liquid crystal compound according to any one of claims 1-4 or a liquid crystal composition containing the liquid crystal compound according to any one of claims 9-12.

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