Liquid crystal composition for radio wave control element and radio wave control element

Abstract

The present invention provides a liquid crystal composition for a radio wave control element. The composition forms a material demonstrating a high refractive index anisotropy when exposed to radio waves, and exhibits liquid crystallinity at a low temperature. This liquid crystal composition for a radio wave control element contains a compound represented by formula (1).

Description

Liquid crystal composition for radio wave control element, radio wave control element

[0001] The present invention relates to a liquid crystal composition for a radio wave control element and a radio wave control element.

[0002] High-frequency radio waves (e.g., millimeter waves and terahertz waves) required for high-capacity wireless communication have a tendency to propagate in a straight line. Therefore, a radio wave control element that can bend the direction of radio waves in any direction is required. However, for example, a typical reflector reflects radio waves in a fixed direction, and the reflection direction is a specular reflection in which the incident angle and the outgoing angle are equal. This significantly limits the range in which the direction of radio waves can be changed, making it difficult to deliver radio waves to the desired destination.

[0003] Non-Patent Document 1 discloses a radio wave control element using a liquid crystal composition for a radio wave control element, and discloses a predetermined polychromatic compound as the liquid crystal compound.

[0004] Response Improvement of Liquid Crystal-Loaded NRD Waveguide Type Terahertz Variable Phase Shifter, Crystals 2020, 10, 307.

[0005] On the other hand, there has been a demand for a radio wave control element using a liquid crystal composition for a radio wave control element to be thinner and have a shorter operating time. To obtain a radio wave control element exhibiting such characteristics, a liquid crystal composition for a radio wave control element that is a material with a larger refractive index anisotropy with respect to radio waves was required. It was also required to exhibit liquid crystallinity at low temperatures. The present inventors evaluated the characteristics of the liquid crystal composition for a radio wave control element described in Non-Patent Document 1 and found that there was room for further improvement in at least one of the refractive index anisotropy with respect to radio waves and the liquid crystallinity at low temperatures.

[0006] In view of the above circumstances, an object of the present invention is to provide a liquid crystal composition for a radio wave control device, which is a material having a large refractive index anisotropy with respect to radio waves and exhibits liquid crystallinity at low temperatures. Another object of the present invention is to provide a radio wave control device.

[0007] As a result of extensive research into solving the above problems, the present inventors have found that the problems can be solved by the following configuration.

[0008] [1] A liquid crystal composition for a radio wave control element, comprising a compound represented by formula (1) described below. [2] The liquid crystal composition for a radio wave control element according to [1], further comprising a dichroic azo dye compound. [3] The liquid crystal composition for a radio wave control element according to [1] or [2], wherein the maximum absorption wavelength in a chloroform solution of the compound represented by formula (1) is 370 nm or more. [4] A radio wave control element having, in this order: a first electrode; a liquid crystal composition layer composed of the liquid crystal composition for a radio wave control element according to any one of [1] to [3]; and a second electrode.

[0009] According to the present invention, it is possible to provide a liquid crystal composition for a radio wave control element, which is a material having a large refractive index anisotropy with respect to radio waves and exhibits liquid crystallinity at low temperatures. Also, according to the present invention, it is possible to provide a radio wave control element.

[0010] FIG. 1 is a diagram showing an example of use of a radio wave control element. FIG. 2 is a diagram showing an example of a metasurface structure used in a radio wave control element. FIG. 3 is a diagram explaining the mechanism by which the emission direction of radio waves is changed in a radio wave control element. FIG. 4 is a diagram conceptually showing an example of a radio wave control element. FIG. 5 is a diagram conceptually showing an example of a liquid crystal orientation pattern in a radio wave control element. FIG. 6 is a diagram showing the relationship between the applied voltage and the amount of phase delay of radio waves.

[0011] The present invention will be described in detail below. The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] In this specification, parallel and perpendicular do not mean parallel and perpendicular in the strict sense, but mean a range of parallel ±5° and a range of perpendicular ±5°, respectively.

[0013] In this specification, each component may be a single substance corresponding to the component, or two or more substances may be used in combination. When two or more substances are used in combination for each component, the content of the component means the total content of the substances used in combination, unless otherwise specified.

[0014] In this specification, the bonding direction of a divalent group (e.g., -CO-O-, etc.) is not limited unless otherwise specified. For example, when Y is -CO-O- in a compound represented by the formula "X-Y-Z," the compound may be either "X-O-CO-Z" or "X-CO-O-Z."

[0015] <Liquid crystal composition for radio wave control element> The liquid crystal composition for radio wave control element of the present invention (hereinafter also simply referred to as "the composition") contains a compound represented by formula (1) described below (hereinafter also referred to as "specific compound").

[0016] Although the mechanism by which the present composition becomes a material with large refractive index anisotropy with respect to radio waves and exhibits liquid crystallinity at low temperatures is unclear, the present inventors speculate as follows. Hereinafter, "exhibiting liquid crystallinity at low temperatures" means that the composition exhibits liquid crystallinity when observed at 70°C, and preferably exhibits liquid crystallinity when observed at 25°C. Hereinafter, liquid crystallinity at low temperatures will also be referred to simply as "low-temperature liquid crystallinity." The specific compound contained in the present composition is a compound having a so-called polyene structure, where n is an integer of 2 or greater. It is speculated that such a specific compound having a polyene structure will exhibit the desired effects. Hereinafter, superiority in at least one of the effects of refractive index anisotropy with respect to radio waves and the effect of low-temperature liquid crystallinity will also be referred to as "excellent effects of the present invention."

[0017] (Specific Compound) The present composition contains a specific compound. The specific compound is a compound represented by formula (1).

[0018]

[0019] In formula (1), Ar １ and Ar ２ each independently represents an aromatic ring which may have a substituent.１ and X ２ each independently represents an alkyl group, an alkoxy group, an alkoxycarbonyl group, an alkylcarbonyloxy group, a dialkylamino group, a halogen group, a cyano group, a nitro group, an isocyanate group, or a group represented by formula (XA). １ and X ２ The oxygen atom in the group represented by R may be replaced by a sulfur atom. １ and R ２ each independently represents a hydrogen atom, a fluorine atom, an alkyl group or a cyano group, and n represents an integer of 2 or more.

[0020] Ar １ and Ar ２The aromatic ring represented by the formula (I) may be either a monocyclic ring or a polycyclic ring, or may be a fused ring. Examples of the aromatic ring include an aromatic hydrocarbon ring and an aromatic heterocyclic ring. Examples of the aromatic hydrocarbon ring include a benzene ring, a naphthalene ring, an anthracene ring, a pyrene ring, a phenanthrene ring, and a fluorene ring, with a benzene ring or a naphthalene ring being preferred. Examples of the aromatic heterocycle include a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring (e.g., a 1,2,3-triazine ring, a 1,2,4-triazine ring, and a 1,3,5-triazine ring), a tetrazine ring (e.g., a 1,2,4,5-tetrazine ring), a quinoxaline ring, a pyrrole ring, a furan ring, a thiophene ring, an imidazole ring, an oxazole ring, a thiazole ring, a benzopyrrole ring, a benzofuran ring, a benzothiophene ring, a benzimidazole ring, a benzoxazole ring, a benzothiazole ring, a naphthopyrrole ring, a naphthofuran ring, a naphthothiophene ring, a naphthoimidazole ring, a naphthoxazole ring, a pyrroloimidazole ring (e.g., a 5H-pyrrolo[1,2-a]imidazole ring), and an imidazooxazole ring (e.g., an imidazo[2,1-b]oxazole ring). , thienothiazole ring (for example, thieno[2,3-d]thiazole ring, etc.), benzothiadiazole ring, benzodithiophene ring (for example, benzo[1,2-b:4,5-b']dithiophene ring, etc.), thienothiophene ring (for example, thieno[3,2-b]thiophene ring, etc.), thiazolothiazole ring (for example, thiazolo[5,4-d]thiazole ring, etc.), naphthodithiophene ring (for example, naphtho[2,3- [b:6,7-b']dithiophene ring, naphtho[2,1-b:6,5-b']dithiophene ring, naphtho[1,2-b:5,6-b']dithiophene ring, 1,8-dithiadicyclopenta[b,g]naphthalene ring, etc.), benzothienobenzothiophene ring, dithieno[3,2-b:2',3'-d]thiophene ring, and 3,4,7,8-tetrathiadicyclopenta[a,e]pentalene ring. Among these, the aromatic heterocycle is preferably a thiophene ring, a furan ring, a benzofuran ring, a benzothiophene ring, a thienothiophene ring, or a thienothiazole ring.

[0021] Examples of the substituent that the aromatic ring may have include halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc.), hydrocarbon groups (alkyl groups (including cycloalkyl groups, bicycloalkyl groups, and tricycloalkyl groups), alkenyl groups (including cycloalkenyl groups and bicycloalkenyl groups), alkynyl groups, and aryl groups), heterocyclic groups, cyano groups, isothiocyanate groups, nitro groups, alkoxy groups, aryloxy groups, silyl groups, silyloxy groups, heterocyclic oxy groups, acyloxy groups, carbamoyloxy groups, alkoxycarbonyloxy groups, aryloxycarbonyl groups, and the like. Examples of the substituent include an alkyl group, a primary, secondary, or tertiary amino group (including an anilino group), an alkylthio group, an arylthio group, a heterocyclic thio group, an alkyl or arylsulfinyl group, an alkyl or arylsulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, an aryl or heterocyclic azo group, an imido group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a phosphono group, a carboxy group, a phosphoric acid group, a sulfonic acid group, a hydroxy group, a thiol group, an acylamino group, a carbamoyl group, a ureido group, a boronic acid group, and a group combining these. Among these, the substituent is preferably an alkyl group which may have an oxygen atom, a nitrogen atom, or a sulfur atom, an alkoxy group which may have an oxygen atom, a nitrogen atom, or a sulfur atom, a halogen atom, a cyano group, or an isothiocyanate group, and more preferably an alkyl group or a halogen atom.

[0022] Ar １ and Ar ２ As the ring, an aromatic hydrocarbon ring is preferable, and a benzene ring is more preferable.

[0023] X １ and X ２The alkyl group represented by the formula (I) may be linear, branched, or cyclic, and is preferably linear or branched. The number of carbon atoms in the alkyl group is preferably 1 to 30, more preferably 1 to 10, and even more preferably 1 to 8. Any carbon atom in the alkyl group may be substituted with an oxygen atom, a sulfur atom, a silicon atom, a carbonyl group, or the like, and adjacent carbon atoms may be bonded by an unsaturated bond such as a double bond or a triple bond. Furthermore, any hydrogen atom in the alkyl group may be substituted with a halogen group such as a fluorine atom. X １ and X ２ The alkyl group in the alkoxy group, alkoxycarbonyl group, alkylcarbonyloxy group, and dialkylamino group represented by the formula: １ and X ２ The two alkyl groups in the dialkylamino group may be the same or different, may form a ring together, or may be an alkyl group represented by Ar １ and Ar ２ may bond to at least one of the following to form a fused ring structure. １ and X ２ Examples of the halogen group represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. １ and X ２ The group represented by formula (XA) will be described.

[0024]

[0025] In formula (XA), * represents a bonding position. ３ and R ４ R each independently represents a hydrogen atom, an alkyl group, or a cyano group. ５ Is -COOR Ａ or a cyano group. Ａ represents an alkyl group which may have a substituent.

[0026] R ３ and R ４ Examples of the alkyl group represented by the formula: X １ and X ２ Examples of the alkyl group include alkyl groups represented by the following formula: ＡExamples of the alkyl group represented by the formula: X １ and X ２ Examples of the substituent that the alkyl group may have include alkyl groups represented by the following formula: １ and Ar ２ Examples of the substituent that can be possessed by an aromatic ring represented by the formula: R ３ is preferably a hydrogen atom. ４ and R ５ Preferably, at least one of R is a cyano group. ４ and R ５ is more preferably a cyano group.

[0027] The above-mentioned X １ and X ２ The oxygen atom in the group represented by the formula (I) may be replaced by a sulfur atom. １ and X ２ Specifically, the oxygen atoms in the alkoxy group, alkoxycarbonyl group, and alkylcarbonyloxy group may be replaced with sulfur atoms to form any of -S-alkyl group, -CS-O-alkyl group, -CO-S-alkyl group, -CS-S-alkyl group, -S-CO-alkyl group, -O-CS-alkyl group, and -S-CS-alkyl group. X substituted with sulfur atoms １ and X ２ There are no particular limitations on the groups represented by the formula: and examples thereof include an --S-alkyl group.

[0028] X １ and X ２ As the X, an alkyl group, an alkoxy group, a dialkylamino group, a cyano group, a nitro group, an isocyanate group, or a group represented by formula (XA) is preferred, and an alkoxy group, a dialkylamino group, a cyano group, a nitro group, an isocyanate group, or a group represented by formula (XA) is more preferred. １ and X ２ It is preferred that at least one of these groups represents an alkoxy group or a dialkylamino group, and the other group represents a cyano group, a nitro group, an isocyanate group or a group represented by formula (XA).

[0029] R １ and R ２ Examples of the alkyl group represented by the formula: X １ and X ２ Examples of the alkyl group include alkyl groups represented by the following formula: １ and R ２ is preferably a hydrogen atom or a cyano group, more preferably a hydrogen atom. １ If there are multiple １ R may be the same or different. ２ If there are multiple ２ They may be the same or different.

[0030] n is preferably an integer of 2 to 5, more preferably 2 or 3.

[0031] The maximum absorption wavelength of the specific compound in a chloroform solution is preferably 350 nm or more, more preferably 370 nm or more, and even more preferably 380 nm or more, in terms of better effects of the present invention. The upper limit is preferably 500 nm or less, more preferably 450 nm or less. In addition, when the specific compound has multiple maximum absorption wavelengths, it is preferable that at least one of the multiple maximum absorption wavelengths is within the above range. The method for measuring the maximum absorption wavelength is to dissolve the specific compound in chloroform to obtain a chloroform solution of the specific compound at a concentration of approximately 10 mg / L. The obtained chloroform solution can be measured using a known spectrophotometer.

[0032] The specific compound may be used alone or in combination of two or more. The content of the specific compound is preferably 1% by mass or more, more preferably 10% by mass or more, and even more preferably 30% by mass or more, based on the total solid content of the liquid crystal composition for radio wave control elements. The upper limit is preferably 100% by mass or less, more preferably 80% by mass or less, and even more preferably 60% by mass or less, based on the total solid content of the liquid crystal composition for radio wave control elements. The solid content refers to components excluding the solvent, and components other than the solvent are considered to be solids even if they are in a liquid state.

[0033] (Dichroic Material) The present composition may contain a dichroic material. Here, the dichroic material refers to a dye whose absorbance varies depending on the direction. The dichroic material may or may not exhibit liquid crystallinity.

[0034] The dichroic material is not particularly limited, and examples thereof include visible light absorbing materials (e.g., dichroic dyes), luminescent materials (e.g., fluorescent materials and phosphorescent materials), ultraviolet absorbing materials, infrared absorbing materials, nonlinear optical materials, carbon nanotubes, and inorganic materials (e.g., quantum rods), and any conventionally known dichroic material (dichroic dye) can be used. Specifically, for example, paragraphs

[0067] to

[0071] of JP 2013-228706 A, paragraphs

[0008] to

[0026] of JP 2013-227532 A, paragraphs

[0008] to

[0015] of JP 2013-209367 A, paragraphs

[0045] to

[0058] of JP 2013-014883 A, paragraphs

[0012] to

[0029] of JP 2013-109090 A, paragraphs

[0009] to

[0017] of JP 2013-101328 A, Paragraphs

[0051] to

[0065] of JP 2013-037353 A, paragraphs

[0049] to

[0073] of JP 2012-063387 A, paragraphs

[0016] to

[0018] of JP 11-305036 A, paragraphs

[0009] to

[0011] of JP 2001-133630 A, paragraphs

[0030] to

[0169] of JP 2011-215337 A, paragraphs

[0021] to

[0075] of JP 2010-106242 A, paragraphs

[0022] to

[0023] of JP 2010-215846 A Paragraphs

[0011] to

[0025] of JP 2011-048311 A, paragraphs

[0017] to

[0069] of JP 2011-213610 A, paragraphs

[0013] to

[0133] of JP 2011-237513 A, paragraphs

[0074] to

[0246] of JP 2016-006502 A, paragraphs

[0005] to

[0051] of JP 2018-053167 A, paragraphs

[0014] to

[0032] of JP 2020-011716 A 3], paragraphs

[0005] to

[0041] of International Publication No. 2016 / 060173, paragraphs

[0008] to

[0062] of International Publication No. 2016 / 136561, paragraphs

[0014] to

[0033] of International Publication No. 2017 / 154835, paragraphs

[0014] to

[0033] of International Publication No. 2017 / 154695, paragraphs

[0013] to

[0037] of International Publication No. 2017 / 195833, paragraphs

[0014] to

[0034] of International Publication No. 2018 / 164252,Examples of the dichroic substances include those described in paragraphs

[0021] to

[0030] of WO 2018 / 186503, paragraphs

[0043] to

[0063] of WO 2019 / 189345, paragraphs

[0043] to

[0085] of WO 2019 / 225468, paragraphs

[0050] to

[0074] of WO 2020 / 004106, and paragraphs

[0015] to

[0038] of WO 2021 / 044843.

[0035] The dichroic substance is preferably a dichroic azo dye compound. A dichroic azo dye compound refers to an azo dye compound whose absorbance varies depending on the direction. A dichroic azo dye compound may or may not exhibit liquid crystallinity. When a dichroic azo dye compound exhibits liquid crystallinity, it may exhibit either nematic or smectic properties. The temperature range in which the liquid crystal phase is exhibited is preferably room temperature (approximately 20 to 28°C) to 300°C, and more preferably 50 to 200°C from the viewpoints of handleability and manufacturing suitability.

[0036] The dichroic azo dye compound may have a crosslinkable group, such as an acryloyl group, a methacryloyl group, an epoxy group, an oxetanyl group, or a styryl group, and preferably an acryloyl group or a methacryloyl group.

[0037] The dichroic substance is preferably a compound represented by formula (Z1) or a compound represented by formula (Z2).

[0038]

[0039] In formula (Z1), Ar ｚ１ and Ar ｚ２ R each independently represents a benzene ring which may have a substituent, or a naphthalene ring which may have a substituent. ｚ１represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may have a substituent, an alkoxy group, an alkylthio group, an alkylsulfonyl group, an alkylcarbonyl group, an alkyloxycarbonyl group, an acyloxy group, an alkylcarbonate group, an alkylamino group, an acylamino group, an alkylcarbonylamino group, an alkoxycarbonylamino group, an alkylsulfonylamino group, an alkylsulfamoyl group, an alkylcarbamoyl group, an alkylsulfinyl group, an alkylureido group, an alkylphosphoric acid amide group, an alkylimino group, or an alkylsilyl group. ｚ２ and R ｚ３ each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may have a substituent, an alkoxy group, an acyl group, an alkyloxycarbonyl group, an alkylamide group, an alkylsulfonyl group, an aryl group, an arylcarbonyl group, an arylsulfonyl group, an aryloxycarbonyl group, or an arylamide group.

[0040] Ar ｚ１ and Ar ｚ２ Examples of the substituent that the benzene ring or naphthalene ring represented by the formula (I) may have include Ar １ and Ar ２ Examples of the substituent that can be possessed by the aromatic ring represented by Ar ｚ１ and Ar ｚ２ As the ring, a benzene ring is preferred.

[0041] R ｚ１ The alkyl group represented by R may be any of linear, branched, and cyclic, and is preferably linear or branched. ｚ１ -CH constituting the alkyl group in the group represented by ２ - is -O-, -CO-, -C(O)-O-, -O-C(O)-, -Si(CH ３ ) ２ —O—Si(CH ３ ) ２ -, -N(R ｚ１’ ) -, -N(R ｚ１’ )-CO-, -CO-N(R ｚ１’ ) -, -N(R ｚ１’ )-C(O)-O-, -O-C(O)-N(R ｚ１’ ) -, -N(R ｚ１’)-C(O)-N(R ｚ１’ )-, -CH=CH-, -C≡C-, -N=N-, -C(R ｚ１’ )=CH—C(O)— or —O—C(O)—O—. ｚ１ is a group other than a hydrogen atom, the hydrogen atom of each group may be replaced by a halogen atom, a nitro group, a cyano group, -N(R ｚ１’ ) ２ , amino group, —C(R ｚ１’ ) = C(R ｚ１’ ) -NO ２ , -C(R ｚ１’ ) = C(R ｚ１’ )-CN or -C(R ｚ１’ ) = C(CN) ２ , may be substituted by R ｚ１’ represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms. ｚ１’ If there are multiple ｚ１’ R may be the same or different. ｚ１ As the alkyl group, an alkyl group having 1 to 20 carbon atoms which may have a substituent, or an alkoxy group is preferred.

[0042] R ｚ２ and R ｚ３ Examples of the alkyl group represented by R ｚ１ In addition, R ｚ２ and R ｚ３ -CH constituting the alkyl group in the group represented by ２ - is -O-, -S-, -C(O)-, -C(O)-O-, -O-C(O)-, -C(O)-S-, -S-C(O)-, -Si(CH ３ ) ２ —O—Si(CH ３ ) ２ -, -NR ｚ２’ -, -NR ｚ２’ -CO-, -CO-NR ｚ２’ -, -NR ｚ２’ -C(O)-O-, -OC(O)-NR ｚ２’ -, -NR ｚ２’ —C(O)—NR ｚ２’-, -CH=CH-, -C≡C-, -N=N-, -C(R ｚ２’ )=CH—C(O)— or —O—C(O)—O—. ｚ２ and R ｚ３ is a group other than a hydrogen atom, the hydrogen atom of each group may be replaced by a halogen atom, a nitro group, a cyano group, an —OH group, or —N(R ｚ２’ ) ２ , amino group, —C(R ｚ２’ ) = C(R ｚ２’ ) -NO ２ , -C(R ｚ２’ ) = C(R ｚ２’ )-CN or -C(R ｚ２’ ) = C(CN) ２ R ｚ２’ represents a hydrogen atom or a linear or branched alkyl group having 1 to 6 carbon atoms. ｚ２’ When a plurality of R are present, they may be the same or different. ｚ２ and R ｚ３ may be bonded to each other to form a ring, or R ｚ２ or R ｚ３ may be bonded to Ar2 to form a ring. ｚ２ and R ｚ３ As the alkyl group, an alkyl group having 1 to 20 carbon atoms which may have a substituent is preferred, and an alkyl group having 1 to 10 carbon atoms is more preferred.

[0043]

[0044] In formula (Z2), nz represents 1 or 2. ｚ３ , Ar ｚ４ and Ar ｚ５ R each independently represents an optionally substituted benzene ring, an optionally substituted naphthalene ring, or an optionally substituted heterocycle. ｚ４ and R ｚ５represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may have a substituent, an alkoxy group, an alkylthio group, an alkylsulfonyl group, an alkylcarbonyl group, an alkyloxycarbonyl group, an acyloxy group, an alkylcarbonate group, an alkylamino group, an acylamino group, an alkylcarbonylamino group, an alkoxycarbonylamino group, an alkylsulfonylamino group, an alkylsulfamoyl group, an alkylcarbamoyl group, an alkylsulfinyl group, an alkylureido group, an alkylphosphoric acid amide group, an alkylimino group, or an alkylsilyl group.

[0045] Ar ｚ３ , Ar ｚ４ and Ar ｚ５ Examples of the substituent that the group represented by the formula (I) may have include Ar １ and Ar ２ Examples of the substituent that can be possessed by the aromatic ring represented by Ar ｚ３ , Ar ｚ４ and Ar ｚ５ The heterocyclic group represented by the formula (I) may be either aromatic or non-aromatic. Atoms other than carbon constituting the aromatic heterocyclic group include nitrogen atoms, sulfur atoms, and oxygen atoms. When the aromatic heterocyclic group has multiple atoms constituting the ring other than carbon, these atoms may be the same or different. Specific examples of aromatic heterocyclic groups include a pyridylene group (pyridine-diyl group), a pyridazine-diyl group, an imidazole-diyl group, a thienylene (thiophene-diyl group), a quinolylene group (quinoline-diyl group), an isoquinolylene group (isoquinoline-diyl group), an oxazole-diyl group, a thiazole-diyl group, an oxadiazole-diyl group, a benzothiazole-diyl group, a benzothiadiazole-diyl group, a phthalimido-diyl group, a thienothiazole-diyl group, a thiazolothiazole-diyl group, a thienothiophene-diyl group, and a thienoxazole-diyl group.

[0046] R ｚ４ and R ｚ５ are each represented by R in formula (Z1). ｚ１ The preferred embodiments are also the same.

[0047] The dichroic substance may be used alone or in combination of two or more. The content of the dichroic substance is preferably 3% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, based on the total solid content of the composition. The upper limit is preferably 50% by mass or less.

[0048] (Liquid Crystal Compound) The present composition may contain a liquid crystal compound other than the various components described above. Generally, liquid crystal compounds can be classified into rod-shaped and discotic types based on their shape. Furthermore, each type can be divided into low-molecular-weight and high-molecular-weight types. The high-molecular-weight type generally refers to a compound with a degree of polymerization of 100 or more (Polymer Physics / Phase Transition Dynamics, Masao Doi, p. 2, Iwanami Shoten, 1992).

[0049] The liquid crystal compound is preferably a rod-shaped liquid crystal compound or a discotic liquid crystal compound (discotic liquid crystal compound). The liquid crystal compound may be any of two or more rod-shaped liquid crystal compounds, two or more discotic liquid crystal compounds, or a mixture of a rod-shaped liquid crystal compound and a discotic liquid crystal compound. The liquid crystal compound may have either forward wavelength dispersion or reverse wavelength dispersion.

[0050] The liquid crystal compound may be a liquid crystal compound having a polymerizable group (polymerizable liquid crystal compound). The polymerizable liquid crystal compound is preferably at least one polymerizable liquid crystal compound selected from the group consisting of polymerizable rod-shaped liquid crystal compounds and polymerizable discotic liquid crystal compounds. Examples of the polymerizable group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl group. The orientation of the liquid crystal compound can be fixed by polymerizing the polymerizable liquid crystal compound. It is not necessary for the liquid crystal compound to exhibit liquid crystallinity after being fixed by polymerization.

[0051] Examples of rod-shaped liquid crystal compounds include those described in claim 1 of JP-A No. 11-513019 and paragraphs

[0026] to

[0098] of JP-A No. 2005-289980. Examples of discotic liquid crystal compounds include those described in paragraphs

[0020] to

[0067] of JP-A No. 2007-108732 and paragraphs

[0013] to

[0108] of JP-A No. 2010-244038.

[0052] The liquid crystal compound may be used alone or in combination of two or more. The content of the liquid crystal compound is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 70% by mass or less, based on the total solid content of the liquid crystal composition for radio wave control elements. The lower limit of the content is preferably 0% by mass or more, more preferably 20% by mass or more, and even more preferably 60% by mass or more, based on the total solid content of the liquid crystal composition for radio wave control elements.

[0053] (Other Components) The present composition preferably contains substantially no solvent. "Substantially no solvent" means that the solvent content is 5% by mass or less, preferably 3% by mass or less, relative to the total mass of the liquid crystal composition for radio wave control elements. The lower limit is not particularly limited, but an example is 0% by mass. In other words, the solid content of the present composition is preferably 95% by mass or more, relative to the total mass of the liquid crystal composition for radio wave control elements. The upper limit is not particularly limited, but an example is 100% by mass.

[0054] <Radio wave control element> The composition can be applied to a radio wave control element. The radio wave control element acts on radio waves. Examples of radio waves include radio waves with a frequency of 0.007 to 0.3 THz. Radio waves in this frequency band (RW) are called high-frequency radio waves (centimeter waves, millimeter waves, terahertz waves, etc.), and are capable of high-capacity wireless communication while also having a high degree of directional propagation.

[0055] An example of a radio wave control element is a radio wave control element having, in this order, a first electrode, a liquid crystal composition layer made of the present composition, and a second electrode. In the radio wave control element, applying a voltage between the first and second electrodes controls the alignment state of the compound LC exhibiting liquid crystallinity contained in the liquid crystal composition layer, thereby adjusting the refractive index anisotropy of the liquid crystal composition layer and thereby adjusting the direction of radio wave propagation. The compound LC is not particularly limited as long as it is a compound exhibiting liquid crystallinity among the components contained in the present composition. Specifically, when the present composition contains a specific compound, a dichroic substance, and a liquid crystal compound, the compound LC may be at least one compound selected from the group consisting of the specific compound, the dichroic substance, and the liquid crystal compound. A liquid crystal composition layer made of the present composition can change the alignment state of the compound LC depending on the applied voltage. In particular, when the compound LC exhibits liquid crystallinity, the above characteristics are likely to be exhibited. In a liquid crystal composition layer made of the present composition, controlling the alignment state of the compound LC can achieve a state exhibiting large refractive index anisotropy. Typically, the response speed of a radio wave control element depends on the film thickness of the liquid crystal composition layer. Since a liquid crystal composition layer made of the present composition can assume a state exhibiting large refractive index anisotropy, the thickness of the liquid crystal composition layer can be reduced, resulting in an improved response speed, and therefore the reflection direction of incident radio waves can be switched in a short time.

[0056] Specific examples of radio wave control elements will be described below with reference to the drawings. A radio wave control element 10 according to the technology of the present disclosure is used in a radio wave reflecting device 2 shown in FIG. 1 . The radio wave reflecting device 2 is capable of reflecting highly directional radio waves RW emitted from an antenna ANT located behind a building BL toward an area AR1 in front of the building BL, which is in the shadow of the antenna ANT. The radio wave reflecting device 2 is also capable of changing the reflection direction of the radio waves RW to different directions in multiple areas AR1 and AR2. For example, the area where many users are present may change depending on the time of day, such as when many wireless communication users are present in area AR1 during the daytime and in area AR2 during the nighttime. In such cases, the radio wave reflecting device 2 can change the area to which the radio waves RW are supplied by changing the reflection direction of the radio waves RW depending on the time of day.

[0057] As shown in FIG. 2 , the radio wave control element 10 has a metasurface structure 12 and is a reflective radio wave control element that reflects the propagation direction of radio waves RW in a desired direction. The metasurface structure 12 is a structure that uses metamaterials. Metamaterials are artificial materials that exhibit properties not found in natural materials, such as a negative refractive index for radio waves. The radio wave control element 10 is configured with a plurality of unit cells UC arranged two-dimensionally, and the two-dimensional plane formed by the arrangement of the plurality of unit cells UC serves as a reflection surface for the radio waves RW. Each unit cell UC includes a microstructure 14 as a metamaterial, and constitutes the smallest unit on the reflection surface that can actively change the phase of the radio waves RW. The microstructure 14 is made of metal, for example. The microstructure 14 is sized on the order of the wavelength of the incident radio waves RW or less and functions as a resonator that resonates through interaction with the incident radio waves RW. Electrically, the microstructure 14 can be considered equivalent to a resonant circuit, for example, a coil and a capacitor connected in series to resonate an alternating current. The phase of the incident radio wave RW changes due to the resonance action of the microstructure 14. Furthermore, by actively changing the resonance conditions of the microstructure 14 using various methods, it is also possible to control the amount of phase delay of the radio wave RW.

[0058] The radio wave control element 10 mainly acts on radio waves RW with a frequency of 0.007 to 0.3 THz. In the radio wave control element 10, the metasurface structure 12 is configured to act on radio waves RW with a frequency of 0.1 to 0.3 THz. The wavelength of radio waves RW with a frequency of 0.1 to 0.3 THz is 1 to 3 mm, and the size of the microstructures 14 that make up the metasurface structure 12 is, for example, on the order of about half the wavelength. By making the size of the microstructures 14 equal to or less than the wavelength of the radio waves RW, the microstructures 14 resonate with the radio waves RW that pass through them, and function as a phase modulation element that modulates the phase of the radio waves RW.

[0059] As shown in FIG. 3 by the incident direction IN and the outgoing direction OUT, the overall traveling direction of the radio wave RW can be considered as the normal direction to the line connecting the wavefronts of the multiple radio waves RW. In the radio wave control element 10, for example, consider gradually increasing the phase delay of the radio wave RW incident on and reflected from each of the multiple unit cells UC arranged in a one-dimensional manner from the right-hand unit cell UC to the left-hand unit cell UC. In this case, even if the line connecting the wavefronts of the individual incident radio waves RW is parallel to the reflecting surface, the line connecting the wavefronts of the individual radio waves RW reflected by each unit cell UC is inclined with respect to the reflecting surface. In other words, the outgoing direction OUT, which is the traveling direction of the radio wave RW emitted from the reflecting surface, changes by an angle θ with respect to the incident direction IN of the radio wave RW. In this way, the traveling direction of the radio wave RW can be controlled by performing phase modulation, i.e., controlling the phase delay, for each unit cell UC.

[0060] As a result, while a normal reflector can only change the direction of propagation of the radio wave RW in the direction of specular reflection, the radio wave reflecting device 2 can change the direction of propagation of the radio wave RW in a direction other than specular reflection by using the metasurface structure 12. In addition, by actively changing the amount of phase delay in each unit cell UC, it becomes possible to actively change the direction of propagation of the radio wave RW.

[0061] As an example, as conceptually shown in Figure 4, a radio wave control element 10 uses a liquid crystal composition layer 20 as an element that changes the resonance conditions of the microstructures 14 of the metasurface structure 12. The radio wave control element 10 has, from the bottom in the figure, a first electrode layer 26, a liquid crystal composition layer 20, and the metasurface structure 12, in this order. The liquid crystal composition layer 20 is provided on a support 24. Furthermore, the first electrode layer 26 is provided so as to entirely cover the surface of the support 24 opposite to the liquid crystal composition layer 20. The liquid crystal composition layer 20 contains a compound LC.

[0062] Each unit cell UC is configured to include a microstructure 14, a liquid crystal composition layer 20, and a first electrode layer 26. Of these, the microstructure 14 is provided individually for each unit cell UC. The remaining components, the support 16, the liquid crystal composition layer 20, the support 24, and the first electrode layer 26, are not independent components for each unit cell UC, but are integrally formed in regions corresponding to a plurality of unit cells UC.

[0063] In the radio wave control element 10, the first electrode layer 26 and the support 24, and the liquid crystal composition layer 20 and the support 16 are attached using an adhesive (pressure-sensitive adhesive or adhesive) as necessary. There are no limitations on the attachment method, and various known methods that are permeable to the radio waves that the radio wave control element 10 targets, such as a method that uses an OCA (Optical Clear Adhesive) that is permeable to the radio waves that the radio wave control element 10 targets, can be used.

[0064] As an example, the microstructure 14 is formed of a conductive material and doubles as an electrode that forms an electrode pair with the first electrode layer 26. Furthermore, a power supply 28 is connected to each microstructure 14 for applying a voltage between the microstructure 14 and the first electrode layer 26. This makes it possible to control the magnitude of the voltage applied to each unit cell UC. The first electrode layer 26 is a common electrode shared by each unit cell UC, and the microstructure 14 of each unit cell UC functions as an individual electrode. The first electrode layer 26 functioning as a common electrode is an example of a "first electrode" according to the technology of the present disclosure, and the individual electrode shared by the microstructure 14 is an example of a "second electrode." The microstructure 14 as the second electrode and the first electrode layer 26 as the first electrode are an example of an "electrode pair for applying a voltage."

[0065] The radio wave control element 10 is of a reflective type, and the first electrode layer 26 also serves as a reflective layer that reflects the radio wave RW.

[0066] In the liquid crystal composition layer 20, the orientation state (hereinafter also referred to as the orientation pattern) of the liquid crystal compound changes upon application of a voltage. The alignment direction of the microstructures 14 of each unit cell UC is a direction (X direction or Y direction in the figure) perpendicular to the thickness direction of the liquid crystal composition layer 20 (Z direction in the figure). Here, the microstructures 14 and the first electrode layer 26 are disposed on both sides of the thickness direction of the liquid crystal composition layer 20. By supplying power from a power source 28, a voltage is applied between the microstructures 14 and the first electrode layer 26 of each unit cell UC. The application of the voltage generates an electric field in the thickness direction of the liquid crystal composition layer 20, changing the orientation state of the compound LC in each unit cell UC. Furthermore, the orientation state of the compound LC in each unit cell UC can be adjusted by adjusting the voltage applied to each unit cell UC.

[0067] As shown in Fig. 5, the compound LC has a cross section of a substantially elliptical shape having a major axis and a minor axis. As an example, when no voltage is applied between the microstructure 14 and the first electrode layer 26, which function as an electrode pair, the compound LC is aligned in a direction perpendicular to the thickness direction of the liquid crystal composition layer 20, as conceptually shown in the upper part of Fig. 5. In the following description, this alignment state will also be referred to as "horizontal alignment."

[0068] When a voltage is applied between the microstructures 14 and the first electrode layer 26 from this state, an electric field is generated in the liquid crystal composition layer 20, and the alignment state of the compound LC changes. Specifically, as conceptually shown in the lower part of Figure 5, the alignment state of the compound LC in the region corresponding to the microstructures 14 changes depending on the magnitude of the applied voltage, and the compound LC is tilted with respect to a direction (the main surface direction) perpendicular to the thickness direction of the liquid crystal composition layer 20. The example shown in the lower part of Figure 5 shows a state in which the tilt angle of the compound LC is maximum. When the tilt angle is maximum, the compound LC is aligned with its major axis along the thickness direction of the liquid crystal composition layer 20. In the following description, this alignment state will also be referred to as "vertical alignment".

[0069] The refractive index of the liquid crystal composition layer 20 increases as the tilt of the compound LC decreases, i.e., as the angle of the long axis of the compound LC decreases toward the principal surface direction of the liquid crystal composition layer 20 (the X or Y direction in FIG. 5 ). Conversely, the refractive index of the liquid crystal composition layer 20 decreases as the tilt of the compound LC decreases, i.e., as the angle of the long axis of the compound LC decreases toward the thickness direction of the liquid crystal composition layer 20 (the Z direction in the figure). Such changes in the refractive index of the liquid crystal composition layer 20 of each unit cell UC change the resonance conditions of the microstructure 14, changing the amount of phase delay of the incident radio wave RW. In this example, the amount of phase delay of the unit cell UC in the upper row of FIG. 5 is greater than that of the unit cell UC in the lower row of FIG. 5 .

[0070] That is, when the alignment state of the compound LC in the liquid crystal composition layer 20 located around the microstructures 14 of each unit cell UC changes, the refractive index of the liquid crystal composition layer 20 changes with respect to the radio wave RW transmitted through each unit cell UC. Because the refractive index and the dielectric constant are positively correlated, a change in the refractive index of the liquid crystal composition layer 20 changes the resonance conditions of the microstructures 14, which function as a resonator. The change in the resonance conditions of the microstructures 14 manifests as a change in the phase delay of the radio wave RW. Therefore, changing the refractive index of the liquid crystal composition layer 20 can change the phase delay of the radio wave RW. Furthermore, a change in the refractive index of the liquid crystal composition layer 20 itself also causes a change in the phase delay of the radio wave RW. Because the refractive index of the liquid crystal composition layer 20 of each unit cell UC changes depending on the voltage V applied to each unit cell UC, the relationship between the voltage V and the phase delay of the radio wave RW is, for example, as shown in FIG. 6 .

[0071] As shown in FIG. 3 , when a radio wave RW is incident on the radio wave control element 10 from the microstructure 14 side, the radio wave RW passes through the microstructure 14 and the liquid crystal composition layer 20 in this order. Furthermore, the radio wave RW is reflected by the first electrode layer 26, which also serves as a reflective layer, and again passes through the liquid crystal composition layer 20 and the microstructure 14 in this order before exiting the radio wave control element 10. The radio wave RW is reflected along this incident / exit path. Along the incident / exit path, the radio wave RW passing through each unit cell UC is phase-modulated by resonance with the microstructure 14 and also phase-modulated by passing through the liquid crystal composition layer 20. More specifically, in each unit cell UC, the resonance condition of the microstructure 14 is determined according to the refractive index of the liquid crystal composition layer 20, and the phase modulation of the radio wave RW occurs due to resonance according to the condition. In addition, the phase modulation of the radio wave RW also occurs according to the magnitude of the refractive index of the liquid crystal composition layer 20.

[0072] Based on the relationship shown in FIG. 6, the reflection direction of the radio wave RW reflected at the radio wave control element 10 is controlled by controlling the amount of phase delay of the radio wave RW for each unit cell UC through the applied voltage V.

[0073] 3, while a normal reflector can only change the direction of propagation of the radio wave RW in the direction of specular reflection, the radio wave control element 10 can change the direction of propagation of the radio wave RW in a direction other than specular reflection by using the metasurface structure 12. In addition, by actively changing the amount of phase delay in each unit cell UC, it is possible to actively change the direction of propagation of the radio wave RW.

[0074] Furthermore, various examples of controlling the traveling direction of the radio wave RW emitted from the radio wave control element 10 are possible other than controlling the reflected radio wave RW so that it travels straight in one direction as a whole as in the example shown in Figure 3. For example, the radio wave RW emitted from the radio wave control element 10 may be made to converge toward a single focal point, or conversely, may be made to diverge. The traveling direction of the emitted radio wave RW can be controlled by adjusting the voltage applied to each unit cell UC, thereby adjusting the amount of phase delay of the radio wave RW for each unit cell UC.

[0075] For example, in the case of a plurality of unit cells UC arranged in one direction as shown in FIG. 3 , consider increasing the phase delay of the central unit cell UC and decreasing the phase delay toward both sides. In this case, connecting the wavefronts of the radio waves RW passing through each unit cell UC forms a V-shape, allowing the emitted radio waves RW to be focused. Conversely, consider decreasing the phase delay of the central unit cell UC and increasing the phase delay toward both sides. In this case, connecting the wavefronts of the radio waves RW passing through each unit cell UC forms a mountain-like shape (inverted V-shape), allowing the emitted radio waves RW to be diverged. The degree of such focusing and divergence can also be adjusted by controlling the phase delay of the radio waves RW passing through each unit cell UC through adjusting the magnitude of the applied voltage.

[0076] Similar to known metasurface structures, the metasurface structure 12 is formed by two-dimensionally arranging microstructures 14, which are metamaterials, on a support 16. In the illustrated metasurface structure 12, as shown in Fig. 2, the microstructures 14 are two-dimensionally arranged at equal intervals in the X and Y directions, which are orthogonal to each other. In this metasurface structure 12, all of the microstructures 14 are, for example, the same.

[0077] There are no limitations on the support 16, and various known sheet-like materials can be used as long as they can support the microstructure 14 and can transmit radio waves RW of 0.007 to 0.3 THz, which is the frequency targeted by the radio wave control element 10. Examples of the support 16 include a metal substrate having an oxide insulating layer such as a silicon substrate having silicon oxide, a support made of an oxide such as silicon oxide, a support made of a semiconductor such as germanium and chalcogenide glass, a polyacrylic resin film such as polymethyl methacrylate, a cellulose resin film such as cellulose triacetate, a cycloolefin polymer film (for example, a product under the trade name "Arton" manufactured by JSR Corporation, or a product under the trade name "Zeonor" manufactured by Zeon Corporation), a resin film such as a polyethylene terephthalate (PET) film, a polycarbonate film, and a polyvinyl chloride film, and a glass plate.

[0078] There is no limitation on the thickness of the support 16, as long as it can support the microstructure 14, has sufficient transparency to radio waves RW with a frequency of 0.007 to 0.3 THz, and further has sufficient strength depending on the application of the radio wave control element 10. The thickness of the support 16 is set appropriately depending on the material from which the support 16 is made so as to satisfy these conditions.

[0079] In the radio wave control element 10 according to the technology of the present disclosure, the support 16 is not an essential component of the metasurface structure 12, and the support 16 may be omitted. For example, if possible, the metasurface structure 12 may be formed by arranging the microstructures 14 directly on the surface of the liquid crystal composition layer 20.

[0080] As described above, the metasurface structure 12 is composed of microstructures 14, which are metamaterials, spaced apart and arranged two-dimensionally on a plane, and more specifically, is composed of an arrangement of unit cells UC, each of which basically consists of one microstructure 14 and the space surrounding the microstructure 14.

[0081] In the radio wave control element 10 according to the technology of the present disclosure, the shape of the metasurface structure is basically the same as that of known metasurface structures. Therefore, various known metasurface structures can be used in the radio wave control element 10 according to the technology of the present disclosure. That is, in the technology of the present disclosure, there are no limitations on the shape and material of the microstructures 14, the arrangement of the microstructures 14, or the pitch (the spacing between the microstructures 14). Furthermore, the metasurface structure 12 may be designed using known methods depending on the wavelength of the radio wave RW to be controlled by the radio wave control element 10 and the target reflection characteristics (e.g., the range of controllable reflection directions). As an example, the amplitude and phase of the radio wave RW reflected by the microstructures 14 used may be calculated using commercially available simulation software, and the arrangement of the microstructures 14 may be set to achieve the desired distribution of phase modulation amounts. When a liquid crystal composition layer 20 is used as in this example, phase modulation occurs due to the refractive index and further the interaction between the refractive index and the microstructures 14. The amount of phase modulation is determined by the resonance characteristics of the microstructures 14, which change depending on the refractive index.

[0082] The radio wave control element 10 according to the technology of the present disclosure is intended to control radio waves RW with frequencies of 0.007 to 0.3 THz. Therefore, the metasurface structure 12 has microstructures 14 selected so as to impart a desired phase difference to the radio waves RW of this frequency, and the arrangement of the microstructures is also set. Specifically, when radio waves RW with frequencies of 0.1 to 0.3 THz are to be controlled, the wavelength range of the radio waves RW is approximately 1 to 3 mm, so the size of the microstructures 14 is selected to be equal to or smaller than this wavelength range.

[0083] Although one unit cell UC basically has one microstructure 14, the technology of the present disclosure is not limited to this. That is, in the radio wave control element according to the technology of the present disclosure, one unit cell UC may have multiple microstructures 14 as necessary depending on the reflection characteristics, the size, material and shape of the microstructures 14, and the size of the unit cell UC. In this case, one unit cell UC may have different microstructures 14. However, because the unit cell UC is the smallest unit capable of actively changing the phase of the radio wave RW, even when one unit cell UC has multiple microstructures 14, the amount of phase modulation is determined for each unit cell UC.

[0084] Furthermore, there are no limitations on the material for forming the microstructure 14, and various materials used as microstructures in known metasurface structures can be used. Examples of materials for forming the microstructure 14 include metals and dielectrics. In the case of metals, copper, gold, and silver are preferred due to their low optical loss. In addition, composites consisting of metal particles and binders and oxide semiconductors can also be used as materials for forming the microstructure 14. On the other hand, in the case of dielectrics, silicon, titanium oxide, and germanium are preferred due to their high refractive index and the ability to increase the amount of phase modulation. Note that, as shown in FIG. 4 , when the microstructure 14 also serves as an electrode that forms an electrode pair with the first electrode layer 26, the microstructure 14 is formed from a conductor.

[0085] Similarly, the shape of the microstructure 14 is not limited, and various shapes used as microstructures in known metasurface structures can be used. Examples include a cross-shaped solid like a crossed rectangular parallelepiped, a rectangular parallelepiped, a cylindrical shape, a V-shaped solid like a rectangular parallelepiped connected at its ends as shown in JP 2018-046395 A, an approximately H-shaped solid like an H-beam, and an approximately C-shaped solid like a C-channel. Furthermore, as shown in JP 2018-046395 A, various shapes can be used for the V-shaped solid and the cross-shaped solid by adjusting the angle between the two rectangular parallelepipeds. Other shapes that can be used include a solid with a bottom shape such as that shown in Figure 5 of "Appl. Sci. 2018, 8(9), 1689; https: / / doi.org / 10.3390 / app8091689."

[0086] In the metasurface structure 12, the microstructures 14 may be of the same type, or multiple types may be used in combination. Furthermore, the same microstructures 14 may be arranged in the same orientation in the XY plane, or in different orientations. Furthermore, microstructures 14 of the same orientation and those of different orientations may be mixed. However, in the radio wave control element 10 according to the technology of the present disclosure, it is preferable to use only one type of microstructure 14 and to arrange all of the microstructures 14 in the same orientation.

[0087] 3, a preferred embodiment of the metasurface structure 12 is one in which the same microstructures 14, all of which have the same structure, are arranged two-dimensionally at equal intervals in the X and Y directions, which are orthogonal to each other. However, the technology of the present disclosure is not limited to this, and multiple types of microstructures may be used in combination as described above. Furthermore, the arrangement intervals and arrangement of the microstructures 14 may also differ in the surface direction of the support 16. However, considering the controllability of the reflection direction of the radio wave RW when a voltage is applied to the liquid crystal composition layer 20, it is preferable that the metasurface structure 12 use all the same microstructures 14. Furthermore, it is more preferable that the microstructures 14 in the metasurface structure 12 are spaced at equal intervals, and even more preferably at equal intervals in both the X and Y directions, which are orthogonal to each other.

[0088] The liquid crystal composition layer 20 is a layer in which the compound LC is aligned in a preset state, and as described above, the alignment state of the compound LC changes when a voltage is applied.

[0089] In the liquid crystal composition layer 20 illustrated in Fig. 4, when no voltage is applied, the compound LC is horizontally aligned. When a voltage is applied to the liquid crystal composition layer 20, the compound LC is aligned at an angle with respect to the principal surface direction of the liquid crystal composition layer 20 in accordance with the voltage, and becomes vertically aligned at maximum. In the radio wave control element 10, the change in alignment of the compound LC is not limited to a change from horizontal alignment to vertical alignment or vice versa, but may be a change from a state tilted with respect to the thickness direction to horizontal or vertical alignment, a change from horizontal or vertical alignment to a state tilted with respect to the thickness direction, or a change at an angle from a state tilted with respect to the thickness direction to a state tilted with respect to the thickness direction.

[0090] The liquid crystal composition layer 20 may be formed, for example, on the surface of an alignment film described later by a known method. In the radio wave control element 10, the liquid crystal composition layer 20 is formed on a support 24. The support 24 is basically the same as the support 16 described above.

[0091] Here, the support 24 on which the liquid crystal composition layer 20 is formed may further include an alignment film for aligning the compound LC in a predetermined state on the surface of the support 16 described above as the main body on which the liquid crystal composition layer 20 is formed. Various known alignment films can be used. Examples include rubbed films made of organic compounds such as polymers, obliquely evaporated films of inorganic compounds, films with microgrooves, and films formed by accumulating LB (Langmuir-Blodgett) films formed by the Langmuir-Blodgett method using organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate. Furthermore, so-called photoalignment films, which are formed by irradiating a photoalignable material with polarized or unpolarized light, can also be used as the alignment film. These alignment films can be formed by known methods depending on the material forming the main body.

[0092] The surface of the support 24 on which the liquid crystal composition layer 20 is formed, opposite to the liquid crystal composition layer 20, is entirely covered with a first electrode layer 26. The first electrode layer 26 is an electrode that changes the alignment of the compound LC in the liquid crystal composition layer 20, and also functions as a reflective layer that reflects radio waves RW with a frequency of 0.007 to 0.3 THz that are incident from the metasurface structure 12 side, as described above.

[0093] There are no limitations on the first electrode layer 26, and a sheet-like material made of various known materials can be used as long as it has sufficient conductivity and is capable of reflecting radio waves RW. Examples of the first electrode layer 26 include metal layers such as copper, aluminum, gold, and silver; inorganic conductive materials such as ITO (tin-doped indium oxide); organic conductive materials such as polythiophenes, typified by PEDOT (poly 3,4-ethylenedioxythiophene); and graphene. Inorganic conductive materials, organic conductive materials, and graphene are transparent to visible light, but act as reflective layers for radio waves of the above frequencies.

[0094] There is no limitation on the thickness of the first electrode layer 26, and the thickness may be set appropriately depending on the material from which the first electrode layer 26 is made so that the target radio waves can be reflected with the required reflectivity.

[0095] As described above, the radio wave control element 10 according to the technology of the present disclosure is a reflective radio wave control element having a metasurface structure 12 and a liquid crystal composition layer 20. In the radio wave control element 10, power is supplied to each microstructure 14 to change the alignment state of the compound LC in the corresponding region of the liquid crystal composition layer 20, thereby forming regions with different refractive indices for each unit cell UC, thereby reflecting the radio wave RW in a desired direction. Furthermore, by changing the power supplied to each microstructure 14, i.e., the voltage applied to the liquid crystal composition layer 20, the reflection direction of the incident radio wave RW can be switched.

[0096] In the radio wave control element 10 according to the technology of the present disclosure, the refractive index anisotropy of the liquid crystal composition layer 20 with respect to radio waves is not limited, but is preferably large. Here, in the reflective radio wave control element 10 of this example, the refractive index anisotropy of the liquid crystal composition layer 20 with respect to radio waves of 100 GHz is preferably 0.35 or more. By making the refractive index anisotropy of the liquid crystal composition layer 20 with respect to radio waves of 100 GHz 0.35 or more, the liquid crystal composition layer 20 can be made thinner, which is preferable in that the reflection direction of the radio waves RW can be switched more quickly.

[0097] Furthermore, there is no limitation on the thickness of the liquid crystal composition layer 20, and a thickness that provides the necessary phase difference for the radio wave RW may be appropriately set depending on the material for forming the liquid crystal composition layer 20. As described above, in the radio wave control element 10 according to the technology of the present disclosure, the liquid crystal composition layer 20 is made of the present composition containing a predetermined amount of liquid crystal compound, and therefore the liquid crystal composition layer 20 can be made thin. In consideration of this point, the thickness of the liquid crystal composition layer 20 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. Setting the thickness of the liquid crystal composition layer 20 to 200 μm or less is preferable in that the reflection direction of the radio wave RW can be switched more quickly, for example.

[0098] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0099] <Compounds> (Compound 1) Specific Compound 1 was synthesized according to the method described in J. Chem. Soc., Perkin Trans. 1, 1993, 775-781. Specific Compound 1 had a λmax of 366 nm in a chloroform solution.

[0100] (Compound 2) Specific Compound 2 was obtained by a reaction under the same conditions as those of Specific Compound 1, except that the phosphate ester used in the final step of the synthesis of Specific Compound 1 was changed to Intermediate 1 in the following scheme. Specific Compound 2 had a λmax of 381 nm in a chloroform solution.

[0101]

[0102] (Compound 3) Compound 3 was obtained by changing the phosphate ester used in the final step in the synthesis of Specific Compound 1 to Intermediate 2 in the following scheme, and then carrying out a Horner-Wadsworth-Emmons reaction, followed by a hydrolysis reaction and a condensation reaction with malononitrile. Specific Compound 3 had a λmax of 434 nm in a chloroform solution.

[0103]

[0104] (Compound 4) Compound 4 was obtained by a reaction under the same conditions as in the synthesis of Specific Compound 1, except that the phosphate ester used in the final step was changed to Intermediate 3 in the following scheme. Specific Compound 4 had a λmax of 404 nm in a chloroform solution.

[0105]

[0106] (Compound 5) Compound 5 was obtained by reducing specific compound 4 with tin chloride and then thiocarbonylating it with 1,1'-thiocarbonyldi-2(1H)-pyridone. The λmax of specific compound 5 in a chloroform solution was 366 nm.

[0107]

[0108] (Compound 6) Compound 6 was synthesized using N-methylaniline as a starting material according to the following scheme: Specific Compound 6 had a λmax of 412 nm in a chloroform solution.

[0109]

[0110] (Synthesis of Intermediate 4) 20.0 g of N-methylaniline, 30.8 g of 1-bromohexane, and 25.8 g of potassium carbonate were mixed and stirred at 100°C for 4 hours. After cooling to room temperature, water and ethyl acetate were added and the mixture was separated. The mixture was dried over magnesium sulfate and concentrated to obtain 34.1 g of Intermediate 4.

[0111] (Synthesis of Intermediate 5) 10.4 mL of DMF (N,N-dimethylformamide) was ice-cooled, and 10.3 g of phosphorus oxychloride was added dropwise, followed by stirring at room temperature for 30 minutes. 10.0 g of Intermediate 4 was dissolved in 50 mL of DMF and added dropwise. The reaction solution was stirred at 60°C for 3 hours, then neutralized with sodium hydroxide under ice-cooling. After confirming hydrolysis, ethyl acetate and water were added and the mixture was separated. The mixture was dried over magnesium sulfate and concentrated to obtain 15.2 g of Intermediate 5 as a liquid containing DMF.

[0112] (Synthesis of Intermediate 6) 36.6 g of methyltriphenylphosphine bromide was dissolved in 150 mL of THF and cooled to 0°C under a nitrogen atmosphere. 102.6 mL of a 1 mol / L THF solution of potassium tert-butoxide was then added dropwise. 15.0 g of Intermediate 5 diluted in 15 mL of THF was then added dropwise. After completion of the reaction, 150 mL of 1 mol / L aqueous hydrochloric acid was added, and ethyl acetate was added to separate the layers. After neutralization and washing with sodium bicarbonate water and brine, the mixture was dried over magnesium sulfate and concentrated. The precipitated triphenylphosphine was filtered and concentrated to obtain 16.5 g of Intermediate 6.

[0113] (Synthesis of Intermediate 7) 10.5 mL of DMF was ice-cooled, and 11.8 g of phosphorus oxychloride was added dropwise, followed by stirring at room temperature for 30 minutes. 16.0 g of Intermediate 6 was dissolved in 48 mL of DMF and added dropwise. The reaction solution was stirred at 60°C for 3 hours, then neutralized with sodium hydroxide under ice-cooling. After confirming hydrolysis, ethyl acetate and water were added and the mixture was separated. The mixture was dried over magnesium sulfate, concentrated, and isolated and purified by silica gel chromatography to obtain 5.7 g of Intermediate 7.

[0114] (Compound 6) Compound 6 was obtained by reaction under the same conditions as in the synthesis of Compound 1, except that the aldehyde used in the final step was changed to Intermediate 7.

[0115] (Compound 7) Compound 7 was obtained by condensing intermediate 7 with 4-cyanomethylbenzonitrile. λmax of specific compound 7 in a chloroform solution was 449 nm.

[0116]

[0117] All of Compounds 1 to 7 are specific compounds.

[0118]

[0119] The maximum absorption wavelengths of Compounds 1 to 7 were measured using a spectrophotometer UV-3100PC manufactured by Shimadzu Corporation. Compounds 1 to 7 were each dissolved in chloroform at a concentration of 10 mg / L, and the measurement was carried out in a quartz cell.

[0120] <Dichroic Material> As a dichroic material, azo dye mixture A was prepared by mixing azo dye 1 and azo dye 2, which were dichroic azo dye compounds, in a mass ratio of 36:64.

[0121]

[0122] <Preparation of Liquid Crystal Compositions for Radio Wave Control Devices> A nematic liquid crystal compound (DIC Corporation, RDP-94990), the above azo dye mixture A, and each of Compounds 1 to 7 were mixed according to the table below to prepare each liquid crystal composition for radio wave control devices.

[0123] <Evaluation> (Refractive index anisotropy (Δn)) The refractive index anisotropy Δn at 10 GHz radio waves was measured by the method disclosed in Applied Optics, Vol. 44, No. 7, p. 1150 (2005). The refractive index anisotropy Δn was measured by filling a variable short-circuit waveguide with the composition, inputting 10 GHz radio waves into the waveguide while heating the waveguide to 70°C, and measuring the amplitude ratio of the reflected wave to the incident wave. Measurements were performed by changing the direction of the static magnetic field and the length of the short-circuit tube, and the refractive indices n e and n o were determined. The refractive index anisotropy (Δn) was calculated from n e - n o. Note that Δn is preferably 0.17 or more, more preferably 0.20 or more, and even more preferably 0.30 or more.

[0124] (Low-temperature liquid crystallinity) Each liquid crystal composition for radio wave control elements obtained above was observed using a polarizing microscope equipped with a hot stage to determine whether it exhibited liquid crystallinity at temperatures of 25°C and 70°C, and the low-temperature liquid crystallinity was evaluated according to the following evaluation criteria: "A": Exhibited liquid crystallinity at both 25°C and 70°C. "B": Exhibited no liquid crystallinity at 25°C (exhibited crystallinity), and exhibited liquid crystallinity at 70°C. "C": Exhibited no liquid crystallinity at both 25°C and 70°C (exhibited crystallinity).

[0125] In the table, the content of each component is shown as a value (% by mass) relative to the total solid content of each liquid crystal composition for radio wave control elements.

[0126]

[0127]

[0128]

[0129] From the results in the above table, it was confirmed that the present composition is a material with large refractive index anisotropy with respect to radio waves and exhibits liquid crystallinity at low temperatures (Examples 1 to 15).

[0130] 2 Radio wave reflecting device 10 Radio wave control element 12 Metasurface structure 14 Microstructure 16, 24 Support 20 Liquid crystal layer 26 First electrode layer 28 Power supply ANT Antenna AR1, AR2 Area BL Building LD Liquid crystal compound RW Radio wave UC Unit cell

Claims

1. A liquid crystal composition for a radio wave control device, comprising a compound represented by formula (1). In formula (1), Ar １ and Ar ２ each independently represents an aromatic ring which may have a substituent. １ and X ２ each independently represents an alkyl group, an alkoxy group, an alkoxycarbonyl group, an alkylcarbonyloxy group, a dialkylamino group, a halogen group, a cyano group, a nitro group, an isocyanate group, or a group represented by formula (XA). １ and X ２ The oxygen atom in the group represented by R may be replaced by a sulfur atom. １ and R ２ each independently represents a hydrogen atom, a fluorine atom, an alkyl group or a cyano group, and n represents an integer of 2 or more. In formula (XA), * represents a bonding position. ３ and R ４ R each independently represents a hydrogen atom, an alkyl group, or a cyano group. ５ Is -COOR Ａ or a cyano group. Ａ represents an alkyl group which may have a substituent.

2. The liquid crystal composition for a radio wave control device according to claim 1, further comprising a dichroic azo dye compound.

3. The liquid crystal composition for radio wave control devices according to claim 1, wherein the compound represented by formula (1) has a maximum absorption wavelength in a chloroform solution of 370 nm or more.

4. A radio wave control element having, in this order: a first electrode; a liquid crystal composition layer made of the liquid crystal composition for radio wave control elements according to any one of claims 1 to 3; and a second electrode.

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