Liquid crystal composition with low viscoelastic ratio, large dielectric tunability, low dielectric loss and high-frequency component

Abstract

The application discloses a liquid crystal composition with low viscoelastic ratio, large dielectric adjustability and low dielectric loss and a high-frequency component, and the liquid crystal composition comprises one or more compounds represented by a general structure I; wherein R is alkyl with 1-10 carbon atoms, alkoxy, fluorinated alkyl, alkenyl with 2-10 carbon atoms, alkenyloxy, fluorinated alkenyl, fluorinated alkenyloxy, cycloalkyl with 3-8 carbon atoms or cycloalkyl-containing substituted alkyl; Z1 and Z2 are single bond, -C=C-, -CH=CH-, -CF=CF-, -CH2CH2; ring A and ring B are benzene ring or cyclohexane, cyclohexene, wherein the hydrogen on the benzene ring can be substituted by fluorine, chlorine, methyl or ethyl; and n=0 or 1. The liquid crystal composition has the advantages of large dielectric tuning rate, extremely low dielectric loss, low rotational viscosity, large elastic constant, wide nematic phase working temperature range and large low-frequency dielectric constant.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of liquid crystal materials, and particularly relates to a liquid crystal composition and a high-frequency component containing the same, which are mainly suitable for the fields of filters, adjustable frequency selection surfaces, microwave phase shifters, microwave phased array antennas, etc. BACKGROUND

[0002] Liquid crystal materials have been widely used in optoelectronic display devices, such as various liquid crystal televisions, desktop liquid crystal displays, mobile display terminals, etc.

[0003] Based on the property that the effective dielectric constant of liquid crystal materials changes under the action of an applied electric field or magnetic field, new high-frequency (1 GHz-100 GHz) components based on liquid crystal materials have been developed, such as microwave phase shifters based on liquid crystal materials.

[0004] In a microwave phase shifter, the dielectric tuning rate (which can also be referred to as dielectric adjustability) of the liquid crystal material determines the tuning ability of the microwave device. For a liquid crystal material, its dielectric tuning rate (τ) is determined by the dielectric anisotropy (Δε) of the liquid crystal material at high frequencies and the dielectric constant (ε ∥ ) of the parallel direction of the molecules:

[0005] τ = Δε / ε ∥

[0006] The dielectric loss of a liquid crystal material is an important factor affecting the insertion loss of its microwave device. In order to obtain a high-performance liquid crystal microwave device, it is necessary to reduce the dielectric loss of the liquid crystal material. For a liquid crystal material, the loss tangent is different when the direction of the liquid crystal molecules changes with the electric field, i.e., the loss is different in the long-axis and short-axis directions of the liquid crystal molecules. When calculating the loss of a liquid crystal material, the maximum value of the loss tangent, i.e., max(tanδ ∥ ,tanδ ⊥ ), is generally used as the loss of the liquid crystal material.

[0007] In order to comprehensively evaluate the performance parameters of a liquid crystal material at microwaves, a quality factor (η) parameter is introduced:

[0008] η = τ / max(tanδ ∥ ,tanδ ⊥ )

[0009] A liquid crystal material used for high-frequency components requires a large dielectric tuning rate (τ), low loss (tanδ ∥ ,tanδ ⊥ ), and a high quality factor (η).

[0010] With the rapid development of high, medium and low orbit satellite communication technology, the moving antennas that track low orbit satellites need to have fast microwave beam switching speed. Therefore, high-frequency components based on liquid crystals must also have the ability to respond quickly. The response speed of liquid crystals mainly depends on the cell thickness (d) of the liquid crystal device, the rotational viscosity (γ1) of the liquid crystal material, and the elastic constant (K 11 ), as shown below:

[0011]

[0012]

[0013] Where: t on is the on-state (power-on) response time, t off is the off-state (power-off) response time; V th is the threshold voltage of the liquid crystal, V is the external driving voltage; when the cell thickness d is fixed, to improve the response speed of the liquid crystal device, the liquid crystal material must have low rotational viscosity (γ1), large elastic constant (K 11 ), that is, a low viscosity-elastic constant ratio (γ1 / K 11 ).

[0014] In order for high-frequency components to operate under electric field drive, the liquid crystal material must also have an appropriate dielectric constant at low frequencies, such as 1KHz.

[0015] To meet practical applications, liquid crystal materials used in high-frequency components also need to have a wider operating temperature range, such as -20 to +90°C, and the low-temperature operating temperature of existing liquid crystal materials needs to be improved.

[0016] Existing commercial high birefringence liquid crystal materials, such as those reported in the paper “Characterisation and Applications of Nematic Liquid Crystals in Microwave Devices” in Molecular Crystals and Liquid Crystals, 2011, 542(1):196 /

[718] -203 /

[725] , contain cyanobiphenyl and terphenyl liquid crystals, such as E7 and E44. They have low dielectric tuning rate (τ) at high frequencies and low dielectric loss (tanδ ∥ ,tanδ ⊥ ) major disadvantages.

[0017] Patent CN103443245A discloses a liquid crystal medium containing a bis(phenylacetylene) liquid crystal material, such as the structure shown in the following formula:

[0018]

[0019] Although the compound has a higher quality factor at high frequencies, its rotational viscosity (γ1) is as high as 2100 mPa·s, resulting in the defect of slow response speed. Moreover, the compound has a small dielectric anisotropy value at low frequencies, only 0.8.

[0020] The fluorophenylacetylene liquid crystal compound in patent CN 103429704 A:

[0021]

[0022] Although the compound has a large birefringence (Δn = 0.35) and good performance at high frequencies, its rotational viscosity γ1 = 1300 mPa·s, resulting in slow response speed.

[0023] CN107955630A, CN105368465A discloses a liquid crystal composition with NCS group at the molecular end and fluorine-substituted benzene ring in the molecular skeleton, which has a large dielectric constant and tuning rate at high frequencies, but has a large dielectric loss value; in the disclosed embodiments, the maximum dielectric loss tanδ ⊥ (19GHz) is above 0.01; at the same time, the rotational viscosity is large.

[0024] CN110499163A, US2019292458A1 discloses a liquid crystal composition based on a molecule with NCS group at the end and fluorine-substituted benzene ring in the molecular skeleton, in the disclosed embodiments, the maximum dielectric loss tanδ ⊥ (19GHz) is greater than or equal to 0.083; at the same time, the rotational viscosity is large.

[0025] It can be found in the existing disclosed literature that there is a contradiction between the performance parameters of the liquid crystal material for microwaves. Some liquid crystals with low dielectric loss have very large rotational viscosity and rotational viscosity / elastic constant ratio (γ1 / K 11 ), which cannot meet the demand for fast response. On the other hand, the increase of dielectric tunability often leads to the increase of rotational viscosity, further leading to slow response speed. SUMMARY

[0026] In view of the defects or deficiencies of the prior art, the present application provides a liquid crystal composition with low viscoelastic ratio, large dielectric tunability and low dielectric loss.

[0027] To this end, the liquid crystal composition provided by the present application comprises one or more compounds selected from the compounds represented by the general structure I:

[0028]

[0029] Wherein:

[0030] R is an alkyl group having 1 to 10 carbon atoms, an alkyl group in which hydrogen is substituted with fluorine, an alkoxy group, or an alkoxy group in which hydrogen is substituted with fluorine; an alkenyl group having 2 to 10 carbon atoms, an alkenyl group in which hydrogen is substituted with fluorine, an alkenyloxy group, or an alkenyloxy group in which hydrogen is substituted with fluorine; or a cycloalkyl group having 3 to 8 carbon atoms, a cycloalkyl group in which hydrogen is substituted with fluorine, a cycloalkyl group substituted alkyl group, or a cycloalkyl group substituted alkyl group in which hydrogen is substituted with fluorine;

[0031] Z1 is a single bond, -C≡C-, -CH=CH-, -CF=CF-, or -CH2CH2-;

[0032] Z2 is a single bond, -C≡C-, -CH=CH-, -CF=CF-, or -CH2CH2-;

[0033] Ring A is a benzene ring, a cyclohexane, a cyclohexene, or a benzene ring in which hydrogen is substituted with fluorine, chlorine, methyl, or / and ethyl; n = 0 or 1;

[0034] Ring B is a benzene ring, a cyclohexane, a cyclohexene, or a benzene ring in which hydrogen is substituted with fluorine, chlorine, methyl, or / and ethyl.

[0035] Optionally, the liquid crystal composition of the present application comprises one or more compounds selected from the group consisting of compounds represented by structural general formulae I-1 to I-8:

[0036]

[0037] Further, the liquid crystal composition of the present application further comprises one or more compounds selected from the group consisting of compounds represented by structural general formula II:

[0038]

[0039] wherein: R2 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, or a fluorinated alkyl group; or an alkenyl group having 2 to 10 carbon atoms, an alkenyloxy group, a fluorinated alkenyl group, or a fluorinated alkenyloxy group; or a halogen; or NCS;

[0040] R3 is an alkyl group having 1 to 10 carbon atoms, an alkoxy group, or a fluorinated alkyl group; or an alkenyl group having 2 to 10 carbon atoms, an alkenyloxy group, a fluorinated alkenyl group, or a fluorinated alkenyloxy group; or a halogen; or NCS;

[0041] Ring C is a benzene ring, a cyclohexane, a cyclohexene, or a benzene ring in which hydrogen is substituted with fluorine;

[0042] Ring D is a benzene ring, a cyclohexane, a cyclohexene, or a benzene ring in which hydrogen is substituted with fluorine.

[0043] Optionally, the compound of the general formula II is selected from the group consisting of compounds represented by general formulae II-A, II-B, or II-C:

[0044]

[0045] Furthermore, the liquid crystal composition of the present invention further comprises one or more compounds selected from the group consisting of:

[0046]

[0047] in:

[0048] R1 is an alkyl group, an alkoxy group or a fluorinated alkyl group having 1 to 10 carbon atoms; or an alkenyl group, an alkenyloxy group, a fluorinated alkenyl group or a fluorinated alkenyloxy group having 2 to 10 carbon atoms;

[0049] X4 is H or F; X5 is H or F; X6 is H or F;

[0050] K is 0 or 1; m is 0 or 1; r is 0 or 1;

[0051] Ring E is a benzene ring, cyclohexane or cyclohexene.

[0052] Optionally, the mass proportion of the compound represented by the general structural formula I is 50% to 100%, the mass proportion of the compound represented by the general structural formula II is 0% to 40%, and the mass proportion of the compound represented by the general structural formula III is 0% to 50%.

[0053] Furthermore, the vertical dielectric loss value tanδ of the liquid crystal composition at high frequency 19 GHz is ⊥ ≤0.010, quality factor η≥30, rotational viscosity ≤300mPa·s, elastic constant K 11 ≥12pN.

[0054] The liquid crystal composition of the present invention not only achieves a high dielectric tuning rate, extremely low dielectric loss, low rotational viscosity, and a large elastic constant at high frequencies, but also possesses advantageous properties such as a wide nematic phase operating temperature range and a large low-frequency dielectric constant. The liquid crystal composition of the present invention can be used to prepare optoelectronic display devices and high-frequency components. DETAILED DESCRIPTION

[0055] Unless otherwise specified, the scientific and technical terms used herein are understood according to the common understanding of those skilled in the art.

[0056] In a preferred embodiment of the present invention, the liquid crystal composition comprises one or more compounds of the general formula (I). In another preferred embodiment of the present invention, the liquid crystal composition comprises one or more compounds of the general formula (I) and one or more compounds of the general formula (II). In yet another preferred embodiment of the present invention, the liquid crystal composition comprises one or more compounds of the general formula (I), one or more compounds of the general formula (II) and one or more compounds of the general formula (III).

[0057] The liquid crystal composition of the present invention preferably comprises 50-100%, preferably 60-95%, and more preferably 70-90%, of the compound of formula I, based on the total amount of the mixture; and 0-40%, preferably 5-30%, and particularly preferably 10-20%, of the compound of formula II, based on the total amount of the mixture. The liquid crystal composition of the present invention may also comprise 0-50%, preferably 5-40%, and particularly preferably 10-30%, of the compound of formula III, based on the total amount of the mixture. In specific embodiments, those skilled in the art can make optimized selections based on the disclosure of this invention.

[0058] The liquid crystal composition according to the present invention is composed of a plurality of compounds, preferably 3 to 20 compounds, more preferably 5 to 18, and even more preferably 7 to 15 compounds. These compounds can be mixed in a conventional manner: the various compounds are weighed according to predetermined mass ratios, heated to a high temperature, and homogenized by stirring, such as magnetic stirring or ultrasonic stirring, until the components are completely dissolved; and then filtered. Liquid crystal compositions can also be prepared in other conventional ways, such as using so-called premixes or so-called "multi-bottle" systems, in which the components are provided as a ready-to-use mixture.

[0059] The preparation method of the compound of general formula I of the present invention is:

[0060] (1) 2,5-difluoroaniline reacts with a halogenating agent to obtain 4-halogen-substituted-2,5-difluoroaniline;

[0061] (2) 4-halogen-substituted-2,5-difluoroaniline undergoes a coupling reaction with an aryl boronic acid derivative or a derivative containing a terminal alkynyl group under transition metal catalysis to obtain a benzidine intermediate or an alkynylaniline intermediate;

[0062] (3) A benzidine intermediate or an alkynylaniline intermediate is subjected to a phosgenation reaction to obtain an isothiocyanate liquid crystal compound.

[0063] Wherein, the halogenating agent in step (1) is selected from iodine, bromine or N-bromosuccinimide. The transition metal catalyst in step (2) is selected from a complex containing palladium or nickel.

[0064] Example 1 for the preparation of compounds of Formula I: Synthesis of 2,5-difluoro-1-isothiocyanate-4-((4-n-pentyl)ethynyl)benzene. The specific method is as follows:

[0065] (1) 12.9 g of 2,5-difluoroaniline, 100 mL of dichloromethane, and 8.4 g of sodium bicarbonate were added to a reaction vessel and stirred at room temperature. 25.4 g of iodine was added in batches and stirred overnight. The organic layer was separated and washed with aqueous sodium bisulfite and then with water until neutral. The solvent was removed by concentration, and the resulting product was recrystallized from petroleum ether to obtain 19 g of 2,5-difluoro-4-iodoaniline.

[0066] (2) Under nitrogen protection, 12.8 g of 2,5-difluoro-4-iodoaniline, 100 mL of triethylamine, 0.35 g of ditriphenylphosphine palladium chloride, 0.29 g of cuprous iodide, and 0.39 g of triphenylphosphine were added to the reactor, and the temperature was raised to 50° C. 30 mL of triethylamine solution containing 8.6 g of 4-pentylphenylacetylene was added dropwise. After the addition was complete, the mixture was kept warm for 4 h, cooled to room temperature, filtered, and the filtrate was concentrated to dryness. 100 mL of toluene was added, washed with water, dried, and the toluene was removed under reduced pressure. Petroleum ether was added for recrystallization to obtain 12.6 g of a brown solid.

[0067] (3) 12.6 g of the brown solid obtained in the previous step, 100 mL of chloroform, and 25 mL of water were added to a reaction vessel, cooled to below 5°C, and 7.2 g of thiophosgene was slowly added dropwise. After the addition was complete, the temperature was raised to reflux for 2 h, cooled to room temperature, and the liquids were separated. The organic layer was washed with an aqueous sodium bicarbonate solution and then washed with water until neutral. The solvent was removed by distillation under reduced pressure, and the resulting product was passed through a silica gel column and eluted with n-heptane. The product was recrystallized from n-heptane to obtain 10.9 g of a white solid with a gas chromatographic purity of 99.9%.

[0068] The above method synthesis route is as follows:

[0069]

[0070] The product structure identification data are as follows:

[0071] 1 H NMR (500MHz, CDCl3) δ (ppm): 0.887 (t, 3H, J = 7Hz), 1.265 ~ 1.339 (m, 4H), 1.575 ~ 1.635 (m, 2H), 2.604 (t, 2H, J = 7.5Hz), 6.868 (dd, 1H, J1 = 8.5Hz, J2 = 6Hz), 7.159 (d, 2H, J = 8.5Hz), 7.229 (dd, 1H, J1 = 9.5Hz, J2 = 6.5Hz), 7.429 (d, 2H, J = 8Hz).

[0072] 13C NMR (125MHz, CDCl3) δ (ppm): 14.0, 22.6, 30.9, 31.5, 36.0, 80.5, 97.5, 111.9 (dd, J1=18.5Hz, J2=8.5Hz), 113.0 (d, J=26Hz), 119.3, 119.7 (dd, J1=22Hz, J2=2.4Hz), 120.9 (dd, J1=16Hz, J2=11Hz), 128.7, 131.7, 143.6, 144.3, 154.6 (d, J=250Hz), 158.3 (d, J=250Hz).

[0073] MS m / z (RI,%): 341.1 (M + ,100),284.1(92).

[0074] DSC: C 51.5N(44.9)I.

[0075] According to DSC test data, the liquid crystal compound is a single-phase liquid crystal, and a nematic phase appears when the temperature is lowered to 44.9°C.

[0076] Preparation Example 2 of the compound of Formula I: Synthesis of 2,5-difluoro-1-isothiocyanate-4-((4-(4-n-pentylcyclohexyl)phenyl)ethynyl)benzene, the specific method is as follows:

[0077]

[0078] 4-(4-n-pentylcyclohexyl)phenylacetylene was used to replace the 4-pentylphenylacetylene in Preparation Example 1. Other operations were performed using the same synthesis method as in Preparation Example 1 to obtain 2,5-difluoro-1-isothiocyanate-4-((4-(4-n-pentylcyclohexyl)phenyl)ethynyl)benzene.

[0079] The structural identification data are as follows:

[0080] 1 H NMR (500MHz, CDCl3) δ (ppm): 0.896 (t, 3H, J = 7.5Hz), 1.002 ~ 1.084 (m, 2H), 1.197 ~ 1.352 (m, 9H), 1.391 ~ 1.474 (m, 2H), 1.864 ~ 1.885 (m, 4H), 2 .474(t,3H,J=12Hz),6.898(dd,1H,J1=8.5Hz,J2=6.5Hz),7.198(d,2H,J=8Hz),7.252(dd,1H,J1=9.5Hz,J2=6.0Hz),7.447(d,2H,J=8.5Hz).

[0081] 13 C NMR (125 MHz, CDC13) δ (ppm): 14.1, 22.7, 26.7, 32.2, 33.5, 34.1, 37.3, 37.4, 44.7, 80.4, 97.5, 112.0 (dd, Ji = 19 Hz, J2 = 10 Hz), 113.1 (d, J = 26 Hz), 119.3, 119.7 (dd, Ji = 22 Hz, J2 = 4.5 Hz), 120.9 (dd, Ji = 21 Hz, J2 = 14 Hz), 127.1, 131.8, 143.5, 149.5, 154.7 (d, J = 252.5 Hz), 158.3 (d, J = 265 Hz).

[0082] MS m / z (Rl, %): 423.2 (M + , 100.0), 310.1 (11.6), 297.1 (39.3), 284.1 (25.1), 252.1 (13.1).

[0083] DSC: C 61.5 N 23 6.3 I.

[0084] According to the DSC test data, the nematic phase temperature range of the liquid crystal compound reaches 174.8°C.

[0085] Other specific compounds of general formula I can be prepared on the basis of the above disclosure of the preparation method by selecting corresponding raw materials.

[0086] The compound of structural general formula I has two fluorine atom substituents at the 2,5-positions of the benzene ring connected with -NCS, compared with the high-frequency liquid crystal composition based on isothiocyanide disclosed in the current literature. The compound of structural general formula I not only has extremely low dielectric loss and large dielectric anisotropy, but also has the excellent characteristics of low viscosity, large elastic constant, and wide liquid crystal phase range.

[0087] The molecular structure of the compound of structural general formula II is composed of two rings, has the characteristics of low viscosity, low melting point, and low dielectric loss, can further improve the low-temperature phase solubility of the liquid crystal composition, greatly reduce the viscosity of the liquid crystal composition, and reduce the dielectric loss.

[0088] The component of general formula II, preferably the specific compound structure is as follows:

[0089]

[0090] The more preferred specific compound of general formula II-A is as follows:

[0091]

[0092] The general formula II-B further preferably has the following structural compounds:

[0093]

[0094] The general formula II-C further preferably has the following structural compounds:

[0095]

[0096] The compound of the general structural formula III in the composition of the present invention has the following preferred specific compound structure:

[0097]

[0098] The compound of the general structural formula III in the composition of the present invention has a wider liquid crystal phase range, lower viscosity, and a larger dielectric constant, especially a larger dielectric constant at a low frequency of 1 kHz, which can play a role in regulating the liquid crystal phase range and dielectric constant of the composition at low frequency.

[0099] In a further embodiment, the liquid crystal composition according to the present invention may further comprise 0.001 to 1% of an additive selected from a hindered phenol antioxidant and / or a hindered amine light stabilizer. The hindered phenol antioxidant is preferably selected from the following structures:

[0100]

[0101] wherein R' is an alkyl group or alkoxy group having 1 to 9 carbon atoms.

[0102] The hindered amine light stabilizer is preferably selected from the following structures:

[0103]

[0104] The preferred added amount of the hindered phenol antioxidant and the amine light stabilizer in the liquid crystal composition is 0.01% to 0.5% by weight, more preferably 0.02% to 0.2% by weight.

[0105] In some further embodiments, 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 additives are preferably selected from the following structures:

[0106]

[0107] Wherein R" is an alkyl group or an alkoxy group having 1 to 9 carbon atoms.

[0108] The preferred liquid crystal composition of the present invention has a tuning rate τ≥0.25, more preferably ≥0.28; the preferred liquid crystal material has a vertical dielectric loss tanδ ⊥≤0.010, more preferably tanδ ⊥ ≤0.009; material quality factor η ≥ 30, preferably η ≥ 40. The preferred liquid crystal composition of the present invention has a nematic phase temperature range of 0 to 90°C or above, more preferably a nematic phase temperature range of -10 to 100°C or above; the preferred liquid crystal composition has a rotational viscosity γ1 ≤ 300 mPa·s, more preferably ≤ 280 mPa·s; the preferred liquid crystal composition has an elastic constant K 11 ≥12pN, more preferably K 11 ≥14pN; γ1 / K of the preferred liquid crystal composition 11 ≤18, more preferably γ1 / K of the liquid crystal composition 11 ≤17. The preferred liquid crystal composition has a dielectric constant of ≥6.0, more preferably ≥7.0 at a low frequency of 1 kHz.

[0109] The liquid crystal composition according to the present invention is suitable for preparing high-frequency components, such as microwave components, more specifically phase shifters that can be tuned by applying an external magnetic field or electric field. These phase shifters can operate in the UHF-band (0.3-1GHz), L-band (1-2GHz), S-band (2-4GHz), C-band (4-8GHz), X-band (8-12GHz), Ku-band (12-18GHz), K-band (18-27GHz), Ka-band (27-40GHz), V-band (50-75GHz), W-band (75-110GHz) and up to 1THz. The construction of the phase shifter according to the present application is known to experts. Typically, a loaded line phase shifter, an inverted microstrip line, a fin line phase shifter is used, preferably an antipodal fin line phase shifter, a slotted phase shifter, a microstrip line phase shifter or a coplanar waveguide (CPW) phase shifter. These components enable reconfigurable antenna arrays.

[0110] The high-frequency performance (dielectric constant, dielectric loss) of the liquid crystal composition in this article is based on the literature (Penirschke, A. (2004). Cavity perturbation method for characterization of liquid crystals up to 35GHz. Microwave Conference,2004.34th European.) reported test method: liquid crystal is introduced into a polytetrafluoroethylene (PTFE) or fused quartz capillary, and the filled capillary is introduced into the middle of a chamber with a resonance frequency of 19 GHz. Then an input signal source is applied, and the output signal is recorded by a vector network analyzer. The change of resonance frequency and Q factor between the capillary filled with liquid crystal and the blank capillary is measured, and the dielectric constant and loss tangent value are calculated. The dielectric constant components perpendicular and parallel to the director of the liquid crystal are obtained by the alignment of the liquid crystal in the magnetic field, and the direction of the magnetic field is set accordingly, and then rotated by 90° accordingly.

[0111] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with examples. Obviously, the described examples are only some of the examples of the present application, but not all. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0112] The mixed liquid crystal in the following examples is tested for physical properties and photoelectric properties. The detailed test methods for the physical properties and photoelectric properties involved in the present application are as follows:

[0113] (1) Clearing point (Tni):

[0114] Polarizing hot stage method: The liquid crystal sample is coated on a glass slide and placed in a crossed polarizing microscope hot stage, and the temperature rising rate is set to 2℃ / min. The temperature at which the liquid crystal sample starts to turn black from bright in the polarizing microscope is the clearing point.

[0115] Or differential scanning calorimetry method: under nitrogen atmosphere, set the temperature rising rate to 2℃ / min.

[0116] (2) Low temperature storage temperature (LTS): about 1 mL of mixed liquid crystal is placed in a transparent glass bottle and placed in a low temperature refrigerator. The temperature is set to -20℃, -30℃ and -40℃, respectively, and stored for 120h, 500h and 1000h, respectively, to observe whether crystals are precipitated or smectic phase is formed. If no crystals are precipitated at -30℃, LTS≤-30℃.

[0117] (3) Birefringence (Δn): Abbe refractometer is used to measure the refractive index of ordinary light (n o ) and extraordinary light (n e ) respectively under constant temperature condition of 25℃, light source 589nm, and birefringence Δn=n e -n o .

[0118] (4) Dielectric constant (Δε): LCR meter is used to test under constant temperature condition of 25℃. Δε=ε ∥ -ε⊥ i.e. the difference between the dielectric constant (ε ∥ ) in the long molecular axis direction and the dielectric constant (ε ⊥ ) in the short molecular axis direction.

[0119] (5) Elastic constant (K 11 , K 33 ): under the condition of constant temperature at 25°C, K 11 and K 33 are obtained by fitting the liquid crystal capacitance-voltage (C-V) curve.

[0120] (6) Rotational viscosity (γ1): under the condition of constant temperature at 25°C, the rotational viscosity γ1 is obtained by testing the transient current value Ip of the liquid crystal molecules deflected by the electric field movement by applying voltage to the liquid crystal test cell.

[0121] Code and explanation see Table 1-3 below:

[0122] Table 1 Physical parameters

[0123] code name illustrate unit [CAT ni ]]> Clear Point ℃ LTS Low temperature storage temperature ℃ <![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 perpendicular to the director Δn Birefringence <![CDATA[γ1]]> Rotational viscosity mPa·s K 11 ]]> splay elastic constant pN <![CDATA[K 33 ]]> Bending elastic constant pN τ Dielectric tuning rate η Quality Factor

[0124] Table 2 Abbreviations of structural units in this paper

[0125]

[0126]

[0127] Table 3 Examples of structure abbreviations

[0128]

[0129] Example 1:

[0130] Table 4 Composition and performance of Example 1

[0131]

[0132] The monomer liquid crystal component in Example 1 is selected from the liquid crystal compound shown in structural general formula I. The test performance shows that it not only has a wider liquid crystal phase temperature range, but also has a larger dielectric tuning rate, a lower dielectric loss, a low rotational viscosity, and a larger elastic constant. The liquid crystal composition of Example 1 has a low rotational viscosity / elastic constant ratio (γ1 / K 11 ), and has an advantageous response speed.

[0133] Example 2:

[0134] Table 5 Composition and performance of Example 2

[0135]

[0136]

[0137] The monomeric liquid crystal components in Example 2 are selected from liquid crystal compounds represented by general structural formulas I, II, and III. Performance tests revealed that the liquid crystal composition not only exhibits a wide liquid crystal phase temperature range, but also exhibits a large dielectric tuning rate, low dielectric loss, extremely low rotational viscosity, and a large elastic constant. The liquid crystal composition of Example 2 has an extremely low rotational viscosity / elastic constant ratio (γ1 / K 11 ), with a very favorable response speed.

[0138] Example 3:

[0139] Table 6 Composition and performance of Example 3

[0140]

[0141]

[0142] The monomeric liquid crystal components in Example 3 are selected from the liquid crystal compounds represented by the general structural formulas I and II. Performance tests revealed that the liquid crystal composition not only exhibits a wide liquid crystal phase temperature range, but also exhibits a large dielectric tuning rate, extremely low dielectric loss, low rotational viscosity, and a large elastic constant. The liquid crystal composition of Example 3 has an extremely low rotational viscosity / elastic constant ratio (γ1 / K 11 ), with a favorable response speed.

[0143] Comparative Example 1:

[0144] This comparative example is different from the above-mentioned Example 1 in that the corresponding monomer liquid crystal is replaced by the existing known 2,6-difluoro-substituted NCS monomer liquid crystal. The performance test data thereof are shown in Table 7 below.

[0145] Table 7

[0146]

[0147]

[0148] Compared with comparative example 1, the clearing point of the liquid crystal in Example 1 is 24°C higher, the birefringence is increased, the rotational viscosity is reduced, the elastic constant is increased, and the viscoelastic ratio (γ1 / K 11 ) is greatly reduced; the high-frequency dielectric anisotropy value at 19 GHz also increases significantly, while the dielectric loss is greatly reduced; the dielectric tuning rate of the liquid crystal increases, and the quality factor increases significantly.

[0149] Comparative Example 2:

[0150] US2019292458A1 discloses a liquid crystal composition for high-frequency components, wherein the components are selected from 2,6-difluoro-substituted isothiocyanate liquid crystal compounds. In Example N4, the composition and performance parameters are disclosed as shown in Table 8 below:

[0151] Table 8

[0152]

[0153] The liquid crystal component in Comparative Example 2 is entirely 2,6-difluoro-substituted isothiocyanate liquid crystal compounds. Compared with Examples 1 to 3 of the present invention, Comparative Example 2 has a large dielectric loss and a low quality factor; at the same time, the rotational viscosity is high, and the rotational viscosity / elastic constant (γ1 / K 11 ) is much higher than the embodiment of the present invention.

Claims

1. A liquid crystal composition, characterized in that Contains one or more compounds selected from the group consisting of compounds represented by the general structural formula I and one or more compounds selected from the group consisting of compounds represented by the general structural formula II: in: R is an alkyl group having 1 to 10 carbon atoms, an alkyl group in which hydrogen is substituted by fluorine, an alkoxy group, or an alkoxy group in which hydrogen is substituted by fluorine; an alkenyl group having 2 to 10 carbon atoms, an alkenyl group in which hydrogen is substituted by fluorine, an alkenyloxy group, or an alkenyloxy group in which hydrogen is substituted by fluorine; or a cycloalkyl group having 3 to 8 carbon atoms, a cycloalkyl group in which hydrogen is substituted by fluorine, an alkyl group substituted with a cycloalkyl group, or an alkyl group substituted with a cycloalkyl group in which hydrogen is substituted by fluorine; Z1 is a single bond, -C≡C-, -CH=CH-, -CF=CF- or -CH2CH2; Z2 is a single bond, -C≡C-, -CH=CH-, -CF=CF- or -CH2CH2; 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 or 1; Ring B is a benzene ring, cyclohexane, cyclohexene, or a benzene ring in which hydrogen is substituted by fluorine, chlorine, methyl, or / and ethyl; Wherein: R2 is an alkyl, alkoxy or fluorinated alkyl group having 1 to 10 carbon atoms; or an alkenyl, alkenyloxy, fluorinated alkenyl or fluorinated alkenyloxy group having 2 to 10 carbon atoms; or a halogen; or NCS; R3 is an alkyl, alkoxy or fluorinated alkyl group having 1 to 10 carbon atoms; or an alkenyl, alkenyloxy, fluorinated alkenyl or fluorinated alkenyloxy group having 2 to 10 carbon atoms; or a halogen; or NCS; Ring C is a benzene ring, cyclohexane, cyclohexene, or a benzene ring in which hydrogen atoms are replaced by fluorine atoms; Ring D is a benzene ring, cyclohexane, cyclohexene, or a benzene ring in which a hydrogen atom is substituted by a fluorine atom.

2. The liquid crystal composition according to claim 1, wherein Contains one or more compounds selected from the group consisting of compounds represented by general structural formulas Ⅰ-1 to Ⅰ-8:

3. The liquid crystal composition according to claim 1, wherein The compound of general formula II is selected from the compounds represented by general formula II-A, II-B or II-C:

4. The liquid crystal composition according to claim 1, wherein It also contains one or more compounds selected from the group consisting of: in: R1 is an alkyl group, an alkoxy group or a fluorinated alkyl group having 1 to 10 carbon atoms; or an alkenyl group, an alkenyloxy group, a fluorinated alkenyl group or a fluorinated alkenyloxy group having 2 to 10 carbon atoms; X4 is H or F; X5 is H or F; X6 is H or F; k is 0 or 1; m is 0 or 1; r is 0 or 1; Ring E is a benzene ring, cyclohexane or cyclohexene.

5. The liquid crystal composition according to claim 1, wherein The mass proportion of the compound represented by the general structural formula I is 50% to 100%, the mass proportion of the compound represented by the general structural formula II is 0% to 40%, and the mass proportion of the compound represented by the general structural formula III is 0% to 50%.

6. The liquid crystal composition according to claim 1, wherein The high frequency 19 GHz vertical dielectric loss value tan δ of the liquid crystal composition ⊥ ≤0.010, quality factor η≥30, rotational viscosity ≤300mPa·s, elastic constant K 11 ≥12pN.

7. Use of the liquid crystal composition according to claim 1 in preparing optoelectronic and display devices.

8. Use of the liquid crystal composition according to claim 1 in preparing high-frequency components.

9. A high-frequency component, characterized in that: The high-frequency component is prepared using the liquid crystal composition according to any one of claims 1 to 6.

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