Indane biphenyl liquid crystal composition and its application

Abstract

The present invention discloses a dihydroindene cyclobiphenyl liquid crystal composition and its application. The liquid crystal composition uses a dihydroindene cyclobiphenyl liquid crystal compound as a first component, and the first component contains at least one compound shown in structural formula (I): wherein R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1-10 carbon atoms; X1-X5 are each independently selected from -H, -F, -Cl or -CH3; X6 is selected from -H, -F or -Cl; Y is selected from -F, -OCF3 or -NCS; the liquid crystal composition also includes a second component, and three or more components in a third component, a fourth component and a fifth component. The liquid crystal composition of the present invention uses a dihydroindene cyclobiphenyl liquid crystal compound as a main component, and its Δn value is ≥0.37, and the maximum dielectric loss in the microwave frequency band (10-40GHz) is less than 6.7×10 ‑3 , dielectric anisotropy is greater than 1.00, phase tunability coefficient is greater than 0.285, and quality factor is greater than 45. It can be used as a low-freezing point, high-dielectric and low-loss, wide-temperature nematic liquid crystal material for use in microwave K-band phase shifters.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid crystal materials, and particularly relates to a dihydroindane biphenyl liquid crystal composition and application thereof. Background Art

[0002] The research on the use of liquid crystals in microwave phase shifters and other communication devices began at the end of the 20th century and developed rapidly at the beginning of this century. In particular, it has received widespread attention from the world in recent years. Its research covers important fields such as tunable filters, reconfigurable antennas, tunable frequency selectors and tunable phase shifters. However, due to the common problems of large dielectric loss, high melting point, slow response speed and poor thermal stability of liquid crystal materials for microwaves, the technical development of devices such as microwave phase shifters has been restricted, becoming a technical bottleneck for the development of liquid crystal microwave communication devices. Therefore, it is urgent to develop new low melting point, low viscosity, high stability, high birefringence, high dielectric anisotropy, low dielectric loss, wide temperature nematic phase liquid crystal compounds and liquid crystal composite materials.

[0003] In recent years, it has been reported that indene ring structure liquid crystal compounds are used in the field of flat panel displays. For example, Jiangsu Hecheng New Materials Co., Ltd. has designed and synthesized a series of low-melting-point indene ring structure liquid crystal compounds with a birefringence of less than 0.2, see Chinese invention patents CN102690167A and CN105085151A. This series of liquid crystal compounds has a low birefringence and a small dielectric constant. Beijing Yanhua Jilian Optoelectronics Technology Co., Ltd. applied for a Chinese invention patent for a negative liquid crystal compound material with an indene ring structure (CN115806466A (2022.12.28)), and its birefringence is only less than 0.133. They are not suitable for microwave high-frequency dielectric materials and cannot meet the use of microwave phase shifters at high frequencies.

[0004] Therefore, the indene ring is introduced into the biphenyl structure system, and the dihydroindene ring structure and cyclopentyl morphology characteristics are utilized to increase the π-electron plane conjugated system of the molecule and reduce the molecular aspect ratio. By adding substituents to the side positions of the benzene ring, the melting point and viscosity of the compound are reduced, the stability of the liquid crystal molecules in high-frequency electromagnetic fields is improved, and the dielectric loss is reduced. A new type of wide-temperature nematic liquid crystal compound with low melting point, low viscosity, high stability, high birefringence, high dielectric anisotropy, and low dielectric loss is designed and synthesized, and it is formulated into a mixed liquid crystal material, in order to improve the low-temperature performance of the liquid crystal material and obtain a "high dielectric and low loss" wide-temperature nematic liquid crystal material, so as to promote the research and development of my country's liquid crystal microwave phase shifters and microwave communication technology. Summary of the invention

[0005] The present invention aims to provide a dihydroindane cyclobiphenyl liquid crystal composition and its application. The liquid crystal composition is composed of a dihydroindane cyclobiphenyl liquid crystal compound as a main component, and its Δn value is ≥ 0.37, and the maximum dielectric loss in the microwave frequency band (10-40GHz) is less than 6.7×10 -3 , dielectric anisotropy is greater than 1.00, phase tunability coefficient is greater than 0.285, and quality factor is greater than 45. It can be used as a low-freezing point, high-dielectric and low-loss, wide-temperature nematic liquid crystal material for use in microwave K-band phase shifters.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In the technical solution of the present invention, the proposed liquid crystal composition is a type of dihydroindene ring fluorinated biphenyl type nematic phase liquid crystal compound (I) as the first component (main component); the composition also contains a tetracyclic biphenyl type liquid crystal compound (II) with a high birefringence as the second component, a polyphenylacetylene isothiocyanate compound (III) as the third component, and an optional fourth component tricyclic biphenyl type liquid crystal (IV) and a fifth component two-ring liquid crystal compound (V).

[0008] The first component is composed of a type of dihydroindene biphenyl liquid crystal compound (I) having the following structure:

[0009]

[0010] Among them, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1-10 carbon atoms; X1-X5 are each independently selected from H, F, Cl atoms or CH3; X6 is selected from H, F or Cl atoms; Y is selected from polar groups such as NCS, F, OCF3, etc.

[0011] The second component of the composition is a fluorine-containing tetracyclic biphenyl liquid crystal compound (II), and the molecular structure of the compound (II) is as follows:

[0012]

[0013] Wherein, R1 is a saturated alkyl group containing 1-10 carbon atoms, or an unsaturated alkyl group, or a dl-(±)-2-methylbutyl group; X1-X3 are each independently selected from -H, or -F, or CH3; X7 is a H atom, or a F atom, or a Cl atom, or -CH3, or -C2H5; Y1 is -NCS, or a -F atom, or -OCF3, a saturated alkyl chain containing 1-5 carbon atoms; Ring A is selected from trans-cyclohexylene or phenylene.

[0014] The third component includes at least one of the compounds represented by the following structural formula (III):

[0015]

[0016] Wherein, R2 is selected from a saturated alkyl group containing 1-10 carbon atoms; X7, X8 are selected from -H, or -F atoms, or CH3, or C2H5; m, k are selected from 0 or 1; and ring B is selected from trans-cyclohexylene or phenylene.

[0017] The fourth component includes at least one of the compounds represented by the following structural formula (IV);

[0018]

[0019] Wherein, R3 is a saturated alkyl or unsaturated alkyl group containing 1-10 carbon atoms; X1-X4 are each independently selected from -H or -F, Y2 is -NCS, or -F, or -OCF3; Ring C is selected from trans-cyclohexylene or phenylene.

[0020] The fifth component includes at least one of the compounds represented by the following structural formula (V);

[0021]

[0022] Wherein, R4 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; Ring A and Ring B are independently 1,4-phenylene or 1,4-cyclohexylene; Y3 is selected from -F, -Cl, -NCS, -OCF3 or -R4; X9 is selected from -H, -F, or -Cl.

[0023] The liquid crystal composition of the present invention comprises at least three of the above-mentioned components and compounds of three or more different components; based on the total weight of the composition, the liquid crystal composition includes 10-40wt% of the first component compound (I), 5-30wt% of the second component compound (II), 10-30wt% of the third component compound (III), 0-20wt% of the fourth component compound (IV), and 0-15wt% of the fifth component compound (V).

[0024] As a preferred embodiment, in the liquid crystal composition of the present invention, the first component contains one or more liquid crystal compounds (I) having a molecular structure of dihydroindene ring terphenyl in an amount of 1-20 wt%, preferably 5-15 wt%;

[0025] As a preferred embodiment, the liquid crystal composition of the present invention also includes: the content of any one of the tetraphenyl compounds (II) in the second component is 1-15wt%, preferably 5-15wt%; the content of any one of the diphenylacetylene and triphenylacetylene isothiocyanate liquid crystal compounds (III) in the third component is 1-20wt%, preferably 5-15wt%; the content of any one of the tricyclic biphenyl liquid crystal compounds (IV) in the fourth component is 0-15wt%, preferably 5-10wt%; the content of any one of the bicyclic liquid crystal compounds (V) in the fifth component is 0-10wt%, preferably 3-6wt%.

[0026] Preferably, when Y in the first component dihydroindene terphenyl liquid crystal compound structural formula (I) is selected from -NCS, the liquid crystal compound (I) is selected from one or more of the compounds of the following structural formulas (Ia-i):

[0027]

[0028] Wherein, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; X1-X5 are each independently selected from a H atom, a F atom, a Cl atom or CH3; and X6 is selected from a H atom, a F atom or a Cl atom.

[0029] The dihydroindene terphenyl liquid crystal compound (Ia-in) (n in the code represents the number of carbon atoms in the alkyl chain R1) includes the following structural compounds, but is not limited thereto:

[0030]

[0031]

[0032] The indane isothiocyanate liquid crystal compound (Ia-i) has the following advantages: the indane structure is used to ensure molecular rigidity and a larger π-conjugated system, increase the light and heat stability of the molecule, and improve the aspect ratio of the liquid crystal molecule. reduce The molecular dielectric loss is reduced; the -NCS group increases the π-electron conjugation system of the molecule, increases the dipole moment or polarity of the molecule, and makes the target compound (Ia-i) have a larger dielectric anisotropy (Δε) and optical anisotropy (Δn); Introduce F atoms, Cl atoms or -CH3 substituents on the side of the benzene ring of the molecule to reduce the intermolecular force and orderly arrangement degree, making its compound The melting point is low and the temperature range of the nematic phase liquid crystal state is wide, which is conducive to the outdoor low-temperature operation of microwave devices.

[0033] When Y in the first component dihydroindene terphenyl liquid crystal compound structural formula (I) is selected from OCF3, the liquid crystal compound (I) is selected from one or more of the following compounds of structural formula (Ib-i):

[0034]

[0035] Wherein, R1 is selected from an alkyl group containing 1-10 carbon atoms; X1-X5 are each independently selected from a H atom, a F atom, a Cl atom or CH3; and X6 is selected from a H atom, a F atom or a Cl atom.

[0036] The trifluoromethoxy indane terphenyl liquid crystal compound (Ib-in) (n in the code represents the number of carbon atoms in the alkyl chain R1) includes the following compounds, but is not limited thereto:

[0037]

[0038] The trifluoromethoxy indane biphenyl liquid crystal compound (Ib-in) has the following advantages: this type of liquid crystal compound contains an -OCF3 group, which increases the π-electron conjugation system and molecular polarity of indane biphenyl, reduces the polarizability of the molecule, makes the molecule highly thermally stable, has low viscosity and melting point, and increases the dielectric constant; it is beneficial to improve the low-temperature dielectric properties and temperature dependence of liquid crystal materials.

[0039] When Y in the first component dihydroindene terphenyl liquid crystal compound structural formula (I) is selected from F atom, the liquid crystal compound (I) is selected from one or more of the following compounds of structural formula (Ic-i):

[0040]

[0041] Wherein, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; X1-X5 are each independently selected from a H atom, a F atom, a Cl atom or CH3; and X6 is selected from a H atom, a F atom or a Cl atom.

[0042] The dihydroindene ring fluorinated biphenyl liquid crystal compound (Ic-in) comprises the following molecular structure, but is not limited thereto (n in the code represents the number of carbon atoms in the alkyl chain R1):

[0043]

[0044]

[0045] In the technical solution of the present invention, the selected indene ring fluorinated biphenyl liquid crystal compound (Ic-i) has the following advantages: relative to -NCS and -OCF3, although the introduction of F atoms into the terminal benzene ring will cause a certain decrease in molecular polarity, a decrease in birefringence and dielectric constant, the molecular structure of the compound (Ic-i) is stable, and the melting point and viscosity are relatively low, which is beneficial to reducing the eutectic point, viscosity and microwave dielectric loss of the liquid crystal composition; it can be used as a viscosity reducing additive for liquid crystal composition materials for microwave devices.

[0046] The synthesis method of the indane biphenyl liquid crystal compound (I) is to use alkyl carboxylic acid ethyl ester and p-bromobenzyl bromide as main raw materials, and after ring closure through condensation reaction of lithium diisopropylamide (LDA), alkyl indane borate is obtained through reduction reaction and preparation of boric acid reaction with Grignard reagent, and then Suzuki coupling reaction is carried out with different brominated or iodinated biphenyl intermediates to obtain intermediates (i)-(v) (whose structural formula is as follows) and liquid crystal compounds (Ib-i) or (Ic-i) respectively, and finally isothiocyanato reaction is carried out on the intermediate (v) and thiophosgene to obtain isothiocyanato indane fluorinated biphenyl liquid crystal compounds (Ia-i).

[0047]

[0048] In the preparation process of the dihydroindene biphenyl liquid crystal compound (I), column chromatography and recrystallization are usually used to remove trace impurities and color, and electric field adsorption is used to remove trace ions or polar ions to improve the resistivity and charge retention rate of the liquid crystal compound (I), so as to obtain a liquid crystal having a resistivity (ρ) higher than 1.0×10 12 The composition can only be mixed and prepared after the liquid crystal compound sample with a particle size of more than Ω.cm is obtained.

[0049] The liquid crystal composition further comprises a second component of a fluorinated tetracyclic biphenyl liquid crystal compound (II); the component comprises at least one of the compounds represented by the following structural formula (II):

[0050]

[0051] In the structural formula (II), R1 is a saturated alkyl group or an unsaturated alkyl group containing 2 to 10 carbon atoms, or a dl-(±)-2-methylbutyl group; X1-X3 are each independently selected from -H, or -F, or CH3; X7 is an H atom, or an F atom, or a Cl atom, or -CH3, or -C2H5; Y1 is -NCS, or a -F atom, or -OCF3, a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; and Ring A is selected from trans-cyclohexylene or phenylene.

[0052] The second component includes any one or at least one of the following compounds of structural formula (IIa-i), (IIb-i) and (IIc-i)-(IIh-i):

[0053]

[0054] The advantages of the second component, the fluorinated tetracyclic biphenyl liquid crystal compound (II), are: stable molecular structure, high birefringence, and a wide nematic phase, which can effectively broaden the nematic phase width of the liquid crystal composition, increase the clearing point of the composition, effectively improve the phase tunability of the microwave device, reduce the dielectric loss of the liquid crystal composition, and improve the quality factor of the liquid crystal composition.

[0055] The preparation method of the selected tetracyclic polyphenyl liquid crystal compounds (IIa-n)-(IIh-n) is mainly derived from Chinese invention patents CN110746982B, CN110776927B, CN110746981B, CN110760311B, CN109735348B, CN110699091B, CN110776396B, CN109825307B, CN109679666B, etc.

[0056] The liquid crystal composition further comprises a third component of a diphenylacetylene and / or triphenylacetylene isothiocyanate liquid crystal compound (III) having a high birefringence, wherein the component comprises at least one of the compounds represented by the following structural formula (III):

[0057]

[0058] Wherein, R2 is selected from a saturated alkyl group containing 1-10 carbon atoms; X7, X8 are selected from -H, or -F atoms, or CH3, or C2H5; m, k are selected from 0 or 1; and ring B is selected from trans-cyclohexylene or phenylene.

[0059] The third component compound includes any one or more of the following structures (IIIa-n)-(IIIf-n):

[0060]

[0061] The third component, isothiocyanato polyphenylacetylene liquid crystal compound (III), has the following advantages: wide nematic phase temperature range, large planar conjugated π-electron cloud density of the molecule, high birefringence, low viscosity and melting point. For example, the melting point of 4(1)PPTUS in compound (IIIc-n) is only 43.5°C, the clearing point is 171.3°C, Δn=0.460 (589.2nm, 20°C), and the rotational viscosity γ1=455mPa.s. It is beneficial to improve the phase tunability of microwave phase shifters and improve the quality factor of the device.

[0062] The preparation method of the selected isothiocyanato polyphenylacetylene liquid crystal compounds (IIIa-n)-(IIIf-n) is mainly derived from Chinese invention patents CN109852400B, CN109943350B, CN113528048A, etc.

[0063] The liquid crystal composition further comprises a fluorinated tricyclic biphenyl liquid crystal compound (IV) with a low melting point and a stable structure as a fourth component; the molecular structure of the component compound (IV) is as follows:

[0064]

[0065] In the structural formula (IV), R3 is a saturated alkyl or unsaturated alkyl group containing 1 to 10 carbon atoms; X1-X3 are each independently selected from -H, -F or -CH3 groups; Y2 is -NCS, or -F, or -OCF3; and ring C is selected from trans-cyclohexylene or phenylene.

[0066] The fourth component compound includes any one or at least one of the following structural compounds (IVa-n)-(IVf-n):

[0067]

[0068] The tricyclic polyphenyl liquid crystal compound (IV) in the fourth component has the following advantages: stable molecular structure, good π-electron plane conjugation, low rotational viscosity and melting point of the molecule, and birefringence that meets the requirements of microwave phase shifters; for example, the melting point of 4(1)PGUS in compound (IVc-4) is only 38°C, the clearing point is 109°C, Δn=0.385 (589.2nm, 20°C), and the rotational viscosity γ1=245mPa.s; and it has good miscibility with other compounds, which is beneficial to reducing the high-frequency dielectric loss of the composition, improving the low-temperature performance of the composition and improving the quality factor.

[0069] The preparation technology of the tricyclic biphenyl liquid crystal compounds (IVa-n)-(IVf-n) selected in the fourth component is mainly derived from Chinese invention patents CN110746983B, CN110760311B, CN108603121A, etc.

[0070] The liquid crystal composition also contains a low melting point, low viscosity bicyclic liquid crystal compound as a fifth component, which is mainly used to reduce viscosity and adjust low temperature performance. The component includes a compound represented by the following structural formula (V):

[0071]

[0072] In structural formula (V), ring A and ring B are independently 1,4-phenylene or 1,4-cyclohexylene, R4 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; Y3 is selected from F, a Cl atom, or -NCS, or -OCF3, or an R4 group; X9 is selected from a -H atom, or a -F atom, or a Cl atom, etc.

[0073] The fifth component includes any one or at least one of the following compounds of structural formula (Va-n)-(Vh-n):

[0074]

[0075] The advantages of the bicyclic liquid crystal compound (V) selected in the fifth component are that the molecular structure of the bicyclic liquid crystal compound (Va-i)-(Vh-i) is stable, the rotational viscosity and melting point of the molecule are very low, and it has good miscibility with other compounds. It is used to reduce the rotational viscosity of the liquid crystal composition, increase the response speed and improve the low-temperature performance.

[0076] The liquid crystal composition comprises at least three components of the above-mentioned component compounds and three or more different structural compounds thereof. The component compounds in the liquid crystal composition are purified and refined by electric field adsorption to remove ions, so as to improve the resistivity and charge retention rate of the liquid crystal compound, and then mixed and prepared to obtain a high-dielectric and low-loss nematic liquid crystal composition that can meet the microwave K band. The application of the above-mentioned liquid crystal composition as a liquid crystal material for a microwave phase shifter component is also provided.

[0077] In order to improve the thermal stability of the liquid crystal composition, a small amount of thermal stabilizer may be added to the composition of the present invention to prevent or reduce the influence of high temperature on the dielectric properties of the liquid crystal composition. The molecular structure of the stabilizer is shown below:

[0078]

[0079] The content of a small amount of heat stabilizer added to the liquid crystal composition accounts for 0.01-0.5 wt % of the total mass of the composition, and preferably 0.05-0.15 wt %.

[0080] The birefringence (Δn) value of the prepared liquid crystal composition is in the range of 0.37-0.41, and the freezing point is below -50°C; the results of the dielectric properties tested in the microwave frequency band (10-35GHz) using the rectangular resonant cavity perturbation method show that the phase modulation amount (τ) of the liquid crystal composition is ≥0.285, and the dielectric constant (Δε r )≥0.95, maximum dielectric loss (tanδε r max) is less than 0.0067, and the quality factor (η) is greater than 45. It can be seen that the liquid crystal composition of the present invention increases the microwave phase modulation amount, reduces the microwave insertion loss phenomenon, and further reduces the dielectric loss of the microwave device.

[0081] The liquid crystal composition of the present invention can be applied to liquid crystal material medium of microwave high frequency devices. Preferably, it can be used in microwave phase shifters. In the manufacture of microwave liquid crystal devices, a small amount of chiral dopant can be added to adjust the orientation arrangement of high birefringence liquid crystal composition material molecules.

[0082] The beneficial effects of the present invention are:

[0083] (1) The liquid crystal composition of the present invention uses a dihydroindene ring terphenyl liquid crystal compound (I) as a main component. The liquid crystal compound (I) utilizes the five-membered ring structure and morphological characteristics of the dihydroindene ring to not only lower the melting point and broaden the low temperature range of the nematic phase, but also improve the chemical stability of the liquid crystal molecules in high-frequency electromagnetic fields such as microwaves, reduce the microwave absorption coefficient, and reduce microwave dielectric loss;

[0084] (2) The present invention prepares a mixed liquid crystal material by mixing the dihydroindene terphenyl liquid crystal compound (I) with other liquid crystal compounds to obtain a "high dielectric and low loss" wide temperature nematic liquid crystal material; the maximum dielectric loss (tan δε r,max ) value is lower than 0.0067, the phase modulation (τ) is greater than 0.285, and the quality factor is greater than 45.0.

[0085] (3) The liquid crystal composition of the present invention uses the low-melting-point dihydroindene terphenyl liquid crystal compound (I) as the main component and other component compounds to form a composite liquid crystal material, which reduces the low eutectic point of the liquid crystal composition and makes the freezing point of the liquid crystal composition below -50°C, meeting the requirements of the outdoor low-temperature working environment of microwave devices. DETAILED DESCRIPTION

[0086] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and the concept of the present invention will be fully conveyed to those skilled in the art, and the present invention will only be limited by the claims.

[0087] The abbreviations of the test technical index items in the following embodiments and comparative examples are as follows:

[0088] △n is the optical anisotropy of the liquid crystal material, that is, the birefringence (589.2nm, 25℃); it means that after light passes through the liquid crystal material, it is refracted and scattered by the liquid crystal to form ordinary light and extraordinary light. The ordinary light refractive index is expressed as "n o ", the extraordinary refractive index represents "n e ”,Δn=n o -n e Microwave devices require a Δn value ≥ 0.35. The higher the Δn value, the more beneficial it is to improve the microwave phase shift.

[0089] Cr. is the melting point of the liquid crystal composition or the transition temperature from the solid state to the liquid crystal state; N. is the liquid crystal nematic phase transition temperature; Iso. is the clearing point temperature (°C) of the phase state of the liquid crystal composition;

[0090] mp is the eutectic point of the mixed liquid crystal material;

[0091] ρ is the resistivity of the liquid crystal material; γ1 is the rotational viscosity of the liquid crystal material;

[0092] △ε represents the dielectric constant of liquid crystal at low frequency (1KHz); Δε≡(ε || -ε ⊥ ); ∥ Represents the parallel component of the dielectric constant of liquid crystal at low frequency (1KHz); ε ⊥ It represents the vertical component of the dielectric constant of liquid crystal at low frequency (1KHz);

[0093] The dielectric anisotropy in the microwave range is defined as: Δε r ≡(ε r|| -ε r⊥ );△ε r The dielectric constant under microwave high frequency is generally required to be between 0.75 and 1.35; ε r⊥ is the vertical component of microwave high-frequency dielectric constant; ε r∥ is the parallel component of microwave high frequency dielectric constant;

[0094] tanδε r⊥ It is the dielectric loss expression of the vertical component of liquid crystal molecules under microwave high frequency; tanδε r∥ is the dielectric loss expression of the parallel component of liquid crystal molecules under microwave high frequency; τ is the phase modulatable coefficient of microwave frequency; η is the dielectric quality factor of microwave high frequency device;

[0095] The microwave phase tunability, or the phase tunability coefficient (τ) of the microwave frequency, is defined as: τ≡(Δε r / ε r|| ). It is the main parameter that reflects the phase tuning ability of liquid crystal materials to microwave frequencies, and generally requires τ ≥ 0.15; it can be seen that Δε r The larger it is, the more beneficial it is to increase the microwave phase shift amount.

[0096] The term "dielectric loss" refers to the loss of microwave frequency caused by the absorption of microwave frequency when microwaves are irradiated or pass through liquid crystal materials. It is the phenomenon that the liquid crystal material absorbs microwaves and causes the loss of microwave frequency. In liquid crystal materials, dielectric loss is usually manifested as parallel dielectric loss (tanδε r|| ) and vertical dielectric loss (tanδε r⊥ ),

[0097] The maximum dielectric loss of liquid crystal material is: tanδε r .max≡max{tanδε r⊥ , tanδε r||}. Among them, the parallel dielectric loss (tanδε r|| ) refers to the microwave frequency loss value along the molecular long axis direction in the liquid crystal material, which is usually small; the vertical dielectric loss (tanδε r⊥ ) refers to the loss value of microwave frequency along the short axis of the molecule in the liquid crystal material, which is usually larger. Therefore, physically, the maximum dielectric loss value of the liquid crystal material (tanδε r .max) often uses "tanδε r⊥ " value is used as a quantitative expression of microwave "dielectric loss". It is the main performance index parameter reflecting the liquid crystal material in the microwave field. Generally, the tanδε of the liquid crystal material is required to be r⊥ (or tanδε r .max) value ≤0.012 or less.

[0098] The "quality factor" (η, or FOM) mentioned in the term refers to the comprehensive evaluation result of the dielectric properties of liquid crystal as a microwave dielectric material, reflecting the performance and quality of liquid crystal materials in microwave devices. The material quality factor (η) is defined as: η≡τ / tanδε r max≈τ / tanδε r⊥ . Generally, η≥25 is required.

[0099] The term "high dielectric and low loss" liquid crystal material refers to a liquid crystal material with high dielectric anisotropy (Δε r ≥1.0), high optical anisotropy (△n≥0.37), low dielectric loss (tanδε r⊥ ≤0.0075 or 7.5E-03) of liquid crystal material.

[0100] The microwave dielectric properties of liquid crystals were tested by Chengdu Enchi Microwave Technology Co., Ltd. using the rectangular resonant cavity perturbation method. The test method is to introduce liquid crystal into polytetrafluoroethylene (PTFE) or quartz glass capillaries; the inner diameter of the capillary is 1.5mm, the outer diameter is 2.78mm, and the effective length of the sample is 2.0cm; the filled capillary is introduced into the center of the cylindrical resonant cavity, and the resonant frequency is 10GHz-35GHz; the vector network analyzer (N5227APNA microwave network analyzer, Keysight Technologies Inc.USA) is used for testing, and the magnetic field strength is 0.3T-1.0T.

[0101] For ease of expression, the different structural groups of each compound molecule are represented below according to the structural units and codes shown in Table 1:

[0102] Table 1 Group structure and code representation method in molecules

[0103]

[0104]

[0105] In the liquid crystal components of the embodiments of the present invention, a type of dihydroindene biphenyl liquid crystal compound (I) with a lower melting point, lower dielectric loss and higher birefringence is prepared as the main component compound, which is also the first component compound (Ia-i), (Ib-i), (Ic-i) The structure code, molecular structure, phase state and dielectric properties are listed in Table 2 below:

[0106]

[0107] Wherein, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; X1 to X6 are each independently selected from a H atom, a F atom, a Cl atom or CH3.

[0108] Table 2 Physical properties of some indene terphenyl series liquid crystal compounds

[0109]

[0110]

[0111]

[0112]

[0113]

[0114] The specific molecular structural formulas and structural codes of the second, third, fourth and fifth component compounds (IIa-n)-(IIg-n); (IIIa-1)-(IIIf-n); (IVa-n)-(IVd-n); (Va-n)-(Vf-n) etc. are as follows:

[0115]

[0116]

[0117]

[0118]

[0119] A small amount of heat stabilizer may be added to the composition, and its amount accounts for 0.01-0.5wt% of the total weight of the composition, preferably 0.10-0.15wt%. The molecular structure of the stabilizer (ST-i) is as follows:

[0120]

[0121]

[0122] Since the liquid crystal composition of the present invention can be used in a microwave phase shifter, a small amount of chiral dopant may be used in the liquid crystal composition to adjust the molecular orientation of the high birefringence liquid crystal composition in the manufacture of a microwave liquid crystal device. The molecular structure of the chiral dopant and its name code are as follows:

[0123]

[0124] In the present invention, each component compound of the composition, as well as its thermal stabilizer and chiral adsorbent, are purified and deionized by electric field adsorption method [Chinese invention patent CN101760203 B (2009)] or deionizing adsorbent to improve the resistivity and charge retention rate of the liquid crystal compound and its additives, and the resistivity reaches (ρ≥1.0×10 12 Ω.cm). Then, they are mixed and prepared according to a certain mass percentage to obtain a high dielectric and low loss nematic liquid crystal composition that can meet the microwave K band; and the liquid crystal composition is used as a liquid crystal material for a microwave phase shifter component.

[0125] The operation method of the electric field adsorption purification treatment has been described in detail in Chinese patent literature and will not be repeated here.

[0126] Example 1: Preparation of Liquid Crystal Composition (M-1)

[0127] Different liquid crystal compounds of the first component, the second component, the third component, the fourth component and the fifth component were selected, sampled and weighed according to a certain mass ratio, mixed, heated and stirred for 0.5 hours to prepare a liquid crystal composition (M-1). Its microwave dielectric properties were tested by Chengdu Enchi Microwave Technology Co., Ltd. using a rectangular resonant cavity perturbation method. The specific content (wt%) of each component and the high-frequency dielectric properties are shown in Table 3 below:

[0128] Table 3 Composition and dielectric properties of mixed liquid crystal material (M-1)

[0129]

[0130] Example 2: Preparation of Liquid Crystal Composition (M-2)

[0131] Referring to the preparation method of Example 1, a liquid crystal composition M-2 was obtained. The composition content and dielectric properties of the composition are shown in Table 4:

[0132] Table 4 Composition and dielectric properties of mixed liquid crystal material (M-2)

[0133]

[0134]

[0135] Example 3: Preparation of Liquid Crystal Composition (M-3)

[0136] Referring to the preparation method of Example 1, a liquid crystal composition M-3 was obtained. The composition content and dielectric properties of the composition are shown in Table 5:

[0137] Table 5 Composition and dielectric properties of mixed liquid crystal material (M-3)

[0138]

[0139] Example 4: Preparation of Liquid Crystal Composition (M-4)

[0140] Referring to the preparation method of Example 1, the liquid crystal composition M-4 was obtained. The composition content and dielectric properties of the composition are shown in Table 6:

[0141] Table 6 Composition and dielectric properties of mixed liquid crystal material (M-4)

[0142]

[0143]

[0144] Example 5: Preparation of Liquid Crystal Composition (M-5)

[0145] Referring to the preparation method of Example 1, a liquid crystal composition M-5 was obtained. The composition content and dielectric properties of the composition are shown in Table 7:

[0146] Table 7 Composition and dielectric properties of mixed liquid crystal material (M-5)

[0147]

[0148] Example 6: Preparation of Liquid Crystal Composition (M-6)

[0149] Referring to the preparation method of Example 1, a liquid crystal composition M-6 was obtained. The composition content and dielectric properties of the composition are shown in Table 8:

[0150] Table 8 Composition and dielectric properties of mixed liquid crystal material (M-6)

[0151]

[0152]

[0153] Example 7: Preparation of Liquid Crystal Composition (M-7)

[0154] Referring to the preparation method of Example 1, a liquid crystal composition M-7 was obtained. The composition content and dielectric properties of the composition are shown in Table 9:

[0155] Table 9 Composition and dielectric properties of mixed liquid crystal material (M-7)

[0156]

[0157] Test Example 1: Thermal stability test of liquid crystal composition:

[0158] Select the above liquid crystal compositions M-2, M-4, M-5, M-6, M-7, accurately weigh a small amount of antioxidants or heat stabilizers ST-7, ST-8, ST-11, ST-13 and ST-16 by mass percentage (wt%), and add them to the above liquid crystal compositions M-2, M-4, M-5, M-6, M-7 independently, heat to 80°C in a clean and dry environment, stir for 15 minutes, mix evenly, and cool to room temperature 25°C. Select 25°C, 60°C and 90°C for microwave dielectric thermal stability test experiments. The test data are shown in Table 10 below:

[0159] Table 10. Dielectric properties of the liquid crystal composition after adding stabilizer at 19.6 GHz

[0160]

[0161] Comparative Example

[0162] Comparative Example of Liquid Crystal Composition (D-1):

[0163] Comparative Example Composition D-1 comes from the “Composition in Example 10 (M-10)” in Chinese Patent US10711197A (July 14, 2020, Merck, Germany). The data is shown in Table 11:

[0164] Table 11. Composition and dielectric properties of liquid crystal composition material comparison example (D-1)

[0165]

[0166] Comparative Example 2: Composition D-2

[0167] Comparative Example Composition D-2 comes from "Composition (M-3) in Example 7" in Chinese Patent CN110776396A (2019.10.31). The data is shown in Table 12:

[0168] Table 12. Composition and dielectric properties of liquid crystal composition material comparison example (D-2)

[0169]

[0170] It can be seen from the performance parameter results of the liquid crystal compositions in the above embodiments that the liquid crystal compositions provided in the embodiments of the present invention have large optical anisotropy, low dielectric loss and large quality factor under microwaves, and can be used as liquid crystal materials in microwave communication devices, especially as nematic liquid crystal materials for microwave phase shifters. It is a nematic phase liquid crystal material with high Δn value, low melting point, low dielectric loss and high stability.

[0171] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A liquid crystal composition, characterized in that: The liquid crystal composition uses a dihydroindene biphenyl liquid crystal compound as the first component, and the first component contains at least one compound represented by structural formula (I): Wherein, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; X1-X5 are each independently selected from -H, -F, -Cl or -CH3; X6 is selected from -H, -F or -Cl; Y is selected from -F, -OCF3 or -NCS; and the first component is selected from at least one of the following compounds of structural formula (Ia-i), (Ib-i) and (Ic-i): in, R1 in Formula Ia-i is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; X1 is -H, -Cl, or -CH3; X2-X5 are each independently selected from -H, -Cl, -F or -CH3; X6 is selected from -H, -F or -Cl; In formula Ib-i, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms, X1 to X5 are independently selected from -H, -Cl, -F or -CH3; X6 is selected from -H, -F or -Cl; In formula Ic-i, R1 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms, X1 to X5 are independently selected from -H, -Cl, -F or -CH3; X6 is selected from -H, -F or -Cl; The liquid crystal composition further comprises three or more components among a second component, a third component, a fourth component and a fifth component; The second component includes at least one of the compounds represented by the following structural formula (II); Wherein, R1 is a saturated alkyl group containing 1 to 10 carbon atoms, or an unsaturated alkyl group, or an alkyl group with a branched methyl group; X1-X3 are each independently selected from -H, -F or -CH3; X7 is -F, -CH3 or -C2H5; Y1 is -NCS, -F or -OCF3; Ring A is selected from trans-cyclohexylene or phenylene; The third component includes at least one of the compounds represented by the following structural formula (III); Wherein, R2 is selected from a saturated alkyl group containing 1 to 10 carbon atoms; X7, X8 are selected from -H, -F, -CH3 or -C2H5; m, k are selected from 0, 1; Ring B is selected from trans-cyclohexyl or phenyl; The fourth component includes at least one of the compounds represented by the following structural formula (IV); Wherein, R3 is a saturated alkyl or unsaturated alkyl group containing 1 to 10 carbon atoms; X1 to X4 are each independently selected from -H or -F, Y2 is -NCS, -F or -OCF3; Ring C is selected from trans-cyclohexylene or phenylene; The fifth component includes at least one of the compounds represented by the following structural formula (V); Wherein, R4 is selected from a saturated alkyl group or an unsaturated alkyl group containing 1 to 10 carbon atoms; Ring A and Ring B are independently 1,4-phenylene or 1,4-cyclohexylene; Y3 is selected from -F, -Cl, -NCS, -OCF3 or alkyl R4; X9 is selected from -H, -F or -Cl.

2. The liquid crystal composition according to claim 1, characterized in that: The second component is at least one of the compounds of molecular structural formula (IIa-i)-(IIh-i): The third component is at least one of the compounds of molecular structural formula (IIIa-i)-(IIIf-i): The fourth component (IV) is at least one of the compounds of molecular structural formula (IVa-i) to (IVf-i): The fifth component (V) is at least one of the compounds of molecular structural formula (Va-i) to (Vh-i):

3. The liquid crystal composition according to claim 1, characterized in that: The liquid crystal composition contains 10-40 wt% of the first component, 5-30 wt% of the second component, 10-40 wt% of the third component, 0-20 wt% of the fourth component and 0-15 wt% of the fifth component.

4. The liquid crystal composition according to claim 1, characterized in that: Each component in the liquid crystal composition is a compound purified by electric field adsorption method.

5. The liquid crystal composition according to claim 1, characterized in that: The maximum dielectric loss of the liquid crystal composition at 19.6 GHz is less than 6.7×10 -3 , dielectric anisotropy is greater than 1.00, phase tunability coefficient is greater than 0.285, and quality factor is greater than 45.

6. The liquid crystal composition according to claim 1, characterized in that: A small amount of stabilizer may be added to the liquid crystal of the composition, and the amount thereof accounts for 0.01-0.5 wt % of the total mass of the composition.

7. A microwave device, characterized in that: The microwave device comprises the liquid crystal composition according to any one of claims 1 to 6.

8. Use of the liquid crystal composition according to any one of claims 1 to 6 in liquid crystal material medium of microwave high frequency devices.

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