Anthraquinone compounds, liquid crystal compositions containing the same, and light-adjusting elements

Abstract

The present application relates to an anthraquinone compound which is an anthraquinone compound represented by formula (1), wherein R1 and R4 represent a hydrogen atom, a C1-12 alkyl group, a C1-12 alkoxy group, a halogen atom, -CO2R9, -OCOR9, -COR9, a cyano group or a trifluoromethyl group; R2, R3, R5 and R6 represent a hydrogen atom, a C1-4 alkyl group, a C1-4 alkoxy group, a halogen atom, -CO2R9, -OCOR9, -COR9, a cyano group or a trifluoromethyl group; R7 and R8 represent a hydrogen atom or a C1-8 alkyl group; and R9 represents a C1-12 alkyl group, a substituent represented by formula (a) (wherein R 10 represents a hydrogen atom, a C1-8 alkyl group or a C1-8 alkoxy group) or a substituent represented by formula (b) (wherein R 11 represents a hydrogen atom or a C1-8 alkyl group).

Description

Technical Field

[0001] This invention relates to novel anthraquinone compounds, liquid crystal compositions containing such compounds, and dimming elements. Background Technology

[0002] Various technologies related to dimming films that control the transmission of external light have been proposed for the purpose of protecting privacy in windows, doors, and partitions of vehicles such as trams and automobiles, and buildings such as commercial buildings and hospitals (see Patent Documents 1 and 2). Among such dimming films, one technology utilizes liquid crystals. Typically, liquid crystal dimming films can block vision by controlling the transmission and scattering of light by applying voltage, but because they cannot block the light itself, there is a tendency for glare to increase due to light scattering. Therefore, in order to reduce glare and improve contrast, some researchers have tried to use pigments in the materials of dimming panels (see Patent Documents 3 and 4). For example, when such dimming panels are used in automobile window glass, from a practical and design point of view, in addition to ensuring good visibility without fogging or residual color when transparent, the demand for black elements that can block visible light is increased. Furthermore, in outdoor applications, when exposed to light or voltage for a long time at high temperatures, there is a strong demand for lightfastness and heat resistance with minimal color change, whether under voltage or not.

[0003] The pigments used in liquid crystal dimming films are generally dichroic pigments. As dimming elements using liquid crystal compositions containing dichroic pigments, guest-host (GH) types are known, and various dichroic pigments have been proposed (see Patent Document 5).

[0004] For dichroic pigments, there are inherent requirements for contrast and dichroism ratio when used as display elements, as well as lightfastness, UV resistance, heat resistance, and compatibility (solubility) of the dichroic pigment with the components of the liquid crystal composition. Currently, research is underway to improve these properties. On the other hand, light-shielding performance as a black dimming element has become a challenge. Black dimming elements made by adding pigments are generally manufactured by mixing yellow, red, and blue pigments. From a practical and design point of view, ideally, black dimming elements should absorb a wide range of wavelengths of light when opaque, especially controlling the transmission of light in the long wavelength region above 650nm, which is important for suppressing light leakage. For example, the blue dichroic pigment described in Patent Document 5, as shown in the comparative example in this application, does not meet the market demand for black dimming elements that require high light-shielding performance because its maximum absorption wavelength (λmax) is on the short wavelength side. Furthermore, while the blue dichroic pigment described in Patent Document 6 has an absorption peak in the long wavelength region, its low contrast makes it impractical. There is an urgent need for dichroic pigments that possess these characteristics.

[0005] [Existing Technical Documents]

[0006] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Publication No. 63-501512

[0008] [Patent Document 2] Japanese Patent Application Publication No. 03-47392

[0009] [Patent Document 3] Japanese Patent Application Publication No. 2018-205746

[0010] [Patent Document 4] Japanese Patent Application Publication No. 2011-190314

[0011] [Patent Document 5] Japanese Patent Application Publication No. 62-5941

[0012] [Patent Document 6] Japanese Patent Application Publication No. 04-264193. Summary of the Invention

[0013] [The problem that the invention aims to solve]

[0014] The primary objective of this invention is to provide a novel anthraquinone compound with excellent spectroscopic properties, exhibiting maximum absorption wavelength in the long wavelength region above 650 nm.

[0015] Another object of the present invention is to provide a dimming element with excellent contrast comprising the novel anthraquinone compound, a liquid crystal composition containing the compound, and a curing of the liquid crystal composition or the liquid crystal composition.

[0016] [Methods for solving the problem]

[0017] The inventors of this application have successfully obtained a novel anthraquinone compound with a specific structure that has the maximum absorption wavelength in the long wavelength region above 650 nm.

[0018] In addition, the inventors of this application have discovered that a dimming element with excellent contrast can be obtained by using this novel anthraquinone compound.

[0019] That is, the various forms or embodiments of the present invention are as described below.

[0020] [1] An anthraquinone compound, which is an anthraquinone compound of the following formula (1):

[0021]

[0022] (In the formula, R1 and R4 independently represent hydrogen atoms, straight-chain or branched alkyl groups having 1 to 12 carbon atoms, straight-chain or branched alkoxy groups having 1 to 12 carbon atoms, halogen atoms, -CO2R9, -OCOR9, -COR9, cyano or trifluoromethyl; R2, R3, R5 and R6 independently represent hydrogen atoms, straight-chain or branched alkyl groups having 1 to 4 carbon atoms, straight-chain or branched alkoxy groups having 1 to 4 carbon atoms, halogen atoms, -CO2R9, -OCOR9, -COR9, cyano or trifluoromethyl; R7 and R8 independently represent hydrogen atoms or straight-chain or branched alkyl groups having 1 to 8 carbon atoms; R9 independently represents straight-chain or branched alkyl groups having 1 to 12 carbon atoms, a substituent shown in formula (a) below or a substituent shown in formula (b) below;)

[0023]

[0024] (where R is in the formula) 10 (representing a hydrogen atom, a straight-chain or branched alkyl group having 1 to 8 carbon atoms, or a straight-chain or branched alkoxy group having 1 to 8 carbon atoms);

[0025]

[0026] (where R is in the formula) 11 (representing hydrogen atoms or straight-chain or branched alkyl groups having 1 to 8 carbon atoms).

[0027] [2] The anthraquinone compound as described in [1] above, wherein at least one of R1 to R6 is a non-hydrogen atom.

[0028] [3] The anthraquinone compound as described in [1] or [2] above, wherein R9 is independently a straight-chain or branched alkyl group having 1 to 8 carbon atoms.

[0029] [4] The anthraquinone compound as described in any one of [1] to [3] above, wherein R1 and R4 are each independently hydrogen atom, a straight-chain or branched alkyl group having 1 to 8 carbon atoms, a straight-chain or branched alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, cyano or trifluoromethyl, and R2, R3, R5 and R6 are each independently hydrogen atom, a straight-chain alkyl group having 1 to 4 carbon atoms, a straight-chain alkoxy group having 1 to 4 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, cyano or trifluoromethyl.

[0030] [5] An anthraquinone compound as described in any one of [1] to [4] above, wherein at least one of R1, R2, R4 and R5 is a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano or trifluoromethyl group.

[0031] [6] The anthraquinone compound as described above [5], wherein at least one of R1, R2, R4 and R5 is a fluorine atom, -CO2R9 or a cyano group.

[0032] [7] The anthraquinone compound as described in any one of [1] to [6] above, wherein R3 and R6 are hydrogen atoms.

[0033] [8] An anthraquinone compound as described in any one of [1] to [7] above, wherein either R1 or R2 is a hydrogen atom and either R4 or R5 is a hydrogen atom.

[0034] [9] The anthraquinone compound as described in any one of [1] to [8] above, wherein R2 and R5 are hydrogen atoms.

[0035]

[10] The anthraquinone compound as described in any one of [1] to [9] above, wherein R4 is a straight-chain or branched alkyl group having 3 to 8 carbon atoms.

[0036]

[11] The anthraquinone compound as described in any one of [1] to

[10] above, wherein R7 and R8 are each independently a straight-chain alkyl group having 3 to 8 carbon atoms.

[0037]

[12] The anthraquinone compound as described in any one of the preceding items [1] to

[11] has a maximum absorption wavelength of 650 nm or more.

[0038]

[13] A liquid crystal composition comprising an anthraquinone compound as described in any one of the preceding items [1] to

[12] and a liquid crystal material.

[0039]

[14] The liquid crystal composition as described in

[13] above contains a photocurable compound and a photopolymerization initiator.

[0040]

[15] The liquid crystal composition as described in

[13] or

[14] above contains a pigment compound other than the anthraquinone compound shown in formula (1).

[0041]

[16] A photocurable material, which is a photocurable form of the liquid crystal composition described in

[14] or

[15] above.

[0042]

[17] A dimming element is formed by sandwiching a liquid crystal composition as described in any one of the preceding items

[13] to

[15] or a photocurable material as described in the preceding item

[16] between a pair of opposing substrates, wherein at least one of the opposing substrates is a transparent substrate having a transparent electrode.

[0043]

[18] The dimming element as described in the preceding item

[17] , wherein, of the pair of substrates, both are transparent substrates having transparent electrodes.

[0044] [The effects of the invention]

[0045] By using the anthraquinone compound of the present invention as a dichroic pigment for liquid crystal dimming elements, dimming elements that suppress light leakage during light blocking and have excellent contrast can be obtained. Detailed Implementation

[0046] The present invention will be described in detail below.

[0047] The anthraquinone compounds of the present invention are shown in formula (1).

[0048]

[0049] In formula (1), R1 and R4 independently represent a hydrogen atom, a straight-chain or branched alkyl group having 1 to 12 carbon atoms, a straight-chain or branched alkoxy group having 1 to 12 carbon atoms, a halogen atom, -CO2R9 group, -OCOR9 group, -COR9 group, cyano group, or trifluoromethyl group, respectively. R2, R3, R5, and R6 independently represent a hydrogen atom, a straight-chain or branched alkyl group having 1 to 4 carbon atoms, a straight-chain or branched alkoxy group having 1 to 4 carbon atoms, a halogen atom, -CO2R9, -OCOR9, -COR9, cyano group, or trifluoromethyl group, respectively. R7 and R8 independently represent a hydrogen atom or a straight-chain or branched alkyl group having 1 to 8 carbon atoms, respectively.

[0050] In formula (1), R1 and R4 represent alkyl groups having 1 to 12 carbon atoms, which can be either straight-chain or branched-chain. Specific examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, 2-ethylhexyl, 2-propylhexyl, 2-butylhexyl, 2-pentylhexyl, and 2-pentylheptyl. Among these, straight-chain or branched-chain alkyl groups having 1 to 8 carbon atoms are preferred, straight-chain or branched-chain alkyl groups having 3 to 8 carbon atoms are more preferred, and straight-chain alkyl groups having 3 to 8 carbon atoms are even more preferred.

[0051] In formula (1), R1 and R4 represent alkoxy groups having 1 to 12 carbon atoms, which can be either straight-chain or branched-chain. Specific examples include: methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, neopentoxy, tert-pentoxy, hexoxy, heptoxy, octoxy, nonoxy, decoxy, undecoxy, dodecaoxy, 2-ethylhexoxy, 2-propylhexoxy, 2-butylhexoxy, 2-pentylhexoxy, and 2-pentylheptoxy. Among these, straight-chain or branched-chain alkoxy groups having 1 to 8 carbon atoms are preferred.

[0052] Specific examples of halogen atoms represented by R1 and R4 in formula (1) include: fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Chlorine atoms or fluorine atoms are preferred, and fluorine atoms are more preferred.

[0053] In the options -CO2R9, -OCOR9 and -COR9 for R1 and R4 in formula (1), R9 represents a straight-chain or branched alkyl group having 1 to 12 carbon atoms, a substituent shown in formula (a) or a substituent shown in formula (b). Furthermore, when there are multiple R9s in formula (1), each R9 may be the same or different.

[0054]

[0055] In equation (a), R 10 It represents a hydrogen atom, a straight-chain or branched alkyl group having 1 to 8 carbon atoms, or a straight-chain or branched alkoxy group having 1 to 8 carbon atoms.

[0056] In equation (b), R 11 It represents a hydrogen atom or a straight-chain or branched alkyl group having 1 to 8 carbon atoms.

[0057] The alkyl group represented by R9, having 1 to 12 carbon atoms, can be either straight-chain or branched-chain. Specific examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, 2-ethylhexyl, 2-propylhexyl, 2-butylhexyl, 2-pentylhexyl, and 2-pentylheptyl. Among these, straight-chain or branched-chain alkyl groups having 1 to 8 carbon atoms are preferred, straight-chain or branched-chain alkyl groups having 1 to 4 carbon atoms are more preferred, and straight-chain alkyl groups having 1 to 4 carbon atoms are even more preferred.

[0058] R in equations (a) and (b) 10 and R 11 The alkyl group having 1 to 8 carbon atoms can be either straight-chain or branched-chain. Specific examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, heptyl, octyl, and 2-ethylhexyl. A straight-chain or branched-chain alkyl group having 4 to 8 carbon atoms is preferred, and a straight-chain alkyl group having 4 to 8 carbon atoms is more preferred.

[0059] R in equation (a) 10 The alkoxy group having 1 to 8 carbon atoms can be either straight-chain or branched-chain. Specific examples include: methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, n-pentoxy, isopentoxy, neopentoxy, tert-pentoxy, hexoxy, heptoxy, octoxy, and 2-ethylhexoxy. Among these, straight-chain or branched-chain alkoxy groups having 4 to 8 carbon atoms are preferred, and straight-chain alkoxy groups having 4 to 8 carbon atoms are more preferred.

[0060] Regarding R1 and R4 in formula (1), it is more preferably that they are each independently a straight-chain or branched alkyl group having 1 to 12 carbon atoms, a straight-chain or branched alkoxy group having 1 to 12 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano, or a trifluoromethyl group. Regarding R1 and R4 in formula (1), it is more preferably that they are each independently a straight-chain or branched alkyl group having 1 to 8 carbon atoms, a straight-chain or branched alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano, or a trifluoromethyl group. Regarding R1 and R4 in formula (1), it is even more preferably that they are each independently a straight-chain or branched alkyl group having 1 to 8 carbon atoms, a straight-chain or branched alkoxy group having 1 to 8 carbon atoms, a fluorine atom, -CO2R9, or a cyano group. Furthermore, regarding R4 in formula (1), it is particularly preferably a straight-chain or branched alkyl group having 3 to 8 carbon atoms.

[0061] The alkyl groups representing 1 to 4 carbon atoms in formula (1) such as R2, R3, R5, and R6 can be either straight-chain or branched-chain. Specific examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl. Methyl or ethyl is preferred.

[0062] The alkoxy groups represented by R2, R3, R5, and R6 in formula (1) having 1 to 4 carbon atoms can be either straight-chain or branched-chain. Specific examples include: methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, sec-butoxy, and tert-butoxy. Methoxy or ethoxy is preferred.

[0063] Specific examples of halogen atoms represented by R2, R3, R5 and R6 in formula (1) include: fluorine atoms, chlorine atoms, bromine atoms and iodine atoms. Chlorine atoms or fluorine atoms are preferred, and fluorine atoms are more preferred.

[0064] R9 in -CO2R9, -OCOR9, and -COR9, which are options for R2, R3, R5, and R6 in equation (1), is synonymous with R9 in -CO2R9, -OCOR9, and -COR9, which are options for R1 and R4. A preferred embodiment of R9 in -CO2R9, -OCOR9, and -COR9, which are options for R2, R3, R5, and R6, is the same as a preferred embodiment of R9 in -CO2R9, -OCOR9, and -COR9, which are options for R1 and R4.

[0065] With regard to R2, R3, R5, and R6 in formula (1), it is more preferably that each is independently a hydrogen atom, a straight-chain or branched alkyl group having 1 to 4 carbon atoms, a straight-chain or branched alkoxy group having 1 to 4 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano, or a trifluoromethyl group. With regard to R2, R3, R5, and R6 in formula (1), it is more preferably that R2 and R5 are independently hydrogen atoms, a straight-chain alkyl group having 1 to 4 carbon atoms, a straight-chain alkoxy group having 1 to 4 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano, or a trifluoromethyl group, while R3 and R6 are hydrogen atoms. With regard to R2, R3, R5, and R6 in formula (1), it is even more preferably that R2 and R5 are independently hydrogen atoms, a straight-chain alkyl group having 1 to 4 carbon atoms, a fluorine atom, -CO2R9, or a cyano group, while R3 and R6 are hydrogen atoms.

[0066] In formula (1), the number of substituents other than the hydrogen atom of the phenyl group having R1 and the number of substituents other than the hydrogen atom of the phenyl group having R4 are independently 0 to 2, that is, preferably at least one of R1 to R3 is a hydrogen atom, and at least one of R4 to R6 is a hydrogen atom. More preferably, the number of substituents of at least one of these phenyl groups is 0 or 1, that is, R1 to R6 is a hydrogen atom. 33 At least two of the phenyl groups are hydrogen atoms, and / or at least two of R4 to R6 are hydrogen atoms. More preferably, the number of substituents in two of these phenyl groups is 0 or 1, that is, at least two of R1 to R3 are hydrogen atoms and at least two of R4 to R6 are hydrogen atoms.

[0067] In formula (1), the positions of the substituents other than the hydrogen atom on the phenyl with R1 and the phenyl with R4 are independent. If the numbering is described as shown in formula (3), it is more preferably only 2-position, only 3-position, only 4-position, 2-position and 4-position or 3-position and 4-position, more preferably only 2-position, only 3-position or only 4-position, and even more preferably only 2-position or only 4-position.

[0068]

[0069] In formula (1), it is more preferred that at least one of R1, R2, R4 and R5 is a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano or a trifluoromethyl, and more preferably that at least one of them is a fluorine atom, -CO2R9 or a cyano.

[0070] In formula (1), R7 and R8 represent alkyl groups having 1 to 8 carbon atoms, which can be either straight-chain or branched-chain. Specific examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, heptyl, octyl, and 2-ethylhexyl. Among these, straight-chain alkyl groups having 3 to 8 carbon atoms are more preferred.

[0071] With regard to preferred examples of the compounds shown in formula (1) above, the following compounds can be listed, but the present invention is not limited to these. In addition, in the structural formulas described in this specification, alkyl groups that are only indicated by the number of carbons and hydrogens and whose structure is not limited are all straight-chain alkyl groups.

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087] The anthraquinone compound represented by formula (1) is preferably an anthraquinone compound that has the maximum absorption wavelength in the wavelength region above 650 nm.

[0088] Next, the method for synthesizing the anthraquinone compound represented by formula (1) of the present invention will be described.

[0089] The anthraquinone compound represented by formula (1) can be synthesized, for example, by reacting the anthraquinone compound represented by formula (A) synthesized by a conventionally known method as disclosed in Japanese Patent Application Publication No. 62-5941 with the iodobenzene derivative (or a bromobenzene derivative) represented by formula (B) at 140 to 160 °C under alkaline conditions such as potassium carbonate and in the presence of a copper catalyst such as copper powder, in the presence of a copper catalyst such as copper powder, in the presence of a copper catalyst such as potassium carbonate, in the presence of a solvent such as N-methyl-2-pyrrolidone.

[0090] Furthermore, R1 to R8 in formulas (A) and (B) below are synonymous with R1 to R8 in formula (1). Regarding other methods of synthesis, a reaction introducing a benzene ring having R1 to R3 as substituents to act as an iodobenzene derivative (e.g., the reaction illustrated in Example 4 below) can be carried out instead of a reaction introducing a benzene ring having R4 to R6 as substituents to act as an iodobenzene derivative (e.g., the reactions illustrated in Examples 1 to 3 below).

[0091]

[0092] The liquid crystal composition of the present invention (hereinafter sometimes referred to simply as "the composition of the present invention") contains an anthraquinone compound represented by formula (1) and a liquid crystal material.

[0093] The proportion of the anthraquinone compound represented by formula (1) in the liquid crystal composition is not particularly limited, but is preferably 0.5 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of liquid crystal material. Furthermore, when using dichroic pigments other than the compound represented by formula (1) (described later), the total content of the anthraquinone compound represented by formula (1) and the dichroic pigments other than the compound represented by formula (1) relative to 100 parts by mass of liquid crystal material is preferably within the aforementioned range (0.5 to 10 parts by mass).

[0094] The liquid crystal material contained in the liquid crystal composition of the present invention is not particularly limited as long as it is a liquid crystal material (a liquid crystal compound) such as nematic liquid crystal, cholesteric liquid crystal, or saturated liquid crystal, but nematic liquid crystal is preferred. Examples of liquid crystal compounds include those described in items 154 to 192 and 715 to 722 of the "Handbook of Liquid Crystal Components" (edited by Committee 142 of the Japan Society for the Promotion of Science, Nikkan Kogyo Shimbun Co., Ltd., 1989).

[0095] The liquid crystal composition of the present invention may also contain various additives such as dichroic pigments other than the anthraquinone compounds shown in formula (1) or cholesterol nonanoate, which may or may not exhibit a liquid crystal phase, ultraviolet absorbers and antioxidants, photocurable compounds and photopolymerization initiators, etc.

[0096] The liquid crystal composition of the present invention may contain photocurable compounds, and is not particularly limited as long as the compounds have functional groups that polymerize upon exposure to light due to the action of a photopolymerization initiator described later. Examples of photocurable compounds include compounds having (meth)acrylate groups, compounds having vinyl groups, and compounds having allyl groups. Compounds having (meth)acrylate groups are preferred. Furthermore, in this specification, the term "(meth)acrylate" refers to "methacrylate and / or acrylate".

[0097] The liquid crystal composition of the present invention contains (meth)acrylate compounds, including, for example, a mono(meth)acrylate compound having one (meth)acrylate group in one molecule and a di(meth)acrylate compound having two (meth)acrylate groups in one molecule, but is not limited thereto.

[0098] With regard to mono(meth)acrylate compounds, mono(meth)acrylates having a straight-chain, cyclic, or branched alkyl group having 5 to 13 carbon atoms are more preferred. Specific examples include: straight-chain alkyl mono(meth)acrylates such as amyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate, and tridecyl methacrylate; cyclic alkyl mono(meth)acrylates such as isoborneol methacrylate; and branched alkyl mono(meth)acrylates such as 2-methylhexyl methacrylate, 2-ethylhexyl methacrylate, 2-propylhexyl methacrylate, 2-methylheptyl methacrylate, 2-ethylheptyl methacrylate, and 2-propylheptyl methacrylate.

[0099] Examples of di(meth)acrylate compounds include: 1,4-butanediol di(meth)acrylate, 1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,7-heptanediol di(meth)acrylate, 1,8-octanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, 1,11-undecanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, and 1,13-tridecanediol di(meth)acrylate. Further examples include triethylene glycol di(meth)acrylate and other trialkylene glycol di(meth)acrylates.

[0100] In the liquid crystal composition of the present invention, both mono(meth)acrylate compounds and di(meth)acrylate compounds may be used together. When using mono(meth)acrylate compounds to di(meth)acrylate compounds, the preferred mass ratio is 10:90 to 96:4, more preferably 50:50 to 95:5.

[0101] The composition of the present invention may contain a photopolymerization initiator, which is not particularly limited as long as it is a compound that can polymerize photocurable compounds by irradiation. It is more preferably a photopolymerization initiator that will not remain in the cured material after irradiation and cause deterioration of dichroic pigments such as anthraquinone compounds represented by formula (1).

[0102] Regarding photopolymerization initiators, alkyl phenyl ketone-based photopolymerization initiators such as Darocur 1173, Irgacure 651, and Irgacure 184, and phosphine oxide-based photopolymerization initiators such as Irgacure TPO are preferred.

[0103] When the composition contains a photocurable compound and a photopolymerization initiator, the mixing ratio of the total amount of the anthraquinone compound (1) and the liquid crystal material in the composition of the present invention to the photocurable compound, by mass ratio, is preferably 90:10 to 50:50, more preferably 80:20 to 50:50, and even more preferably 60:40 to 50:50. By keeping the mixing ratio of the photocurable compound within the aforementioned range, separation of the liquid crystal material and the photocurable compound before photocuring and a reduction in the light-shielding properties of the cured material can be prevented.

[0104] Furthermore, when using dichroic pigments other than those shown in Formula (1) (described later), the mixing ratio of the total amount of all dichroic pigments and liquid crystal materials containing the anthraquinone compound shown in Formula (1) in the composition of the present invention to the photocurable compound is preferably within the range described above (90:10 to 50:50 by mass ratio), and even more preferred and more preferred ranges are the same as described above.

[0105] When the composition contains a photocurable compound and a photopolymerization initiator, the content of the photopolymerization initiator in the composition of the present invention is preferably 0.1 to 5 parts by mass relative to 100 parts by mass of the photocurable compound.

[0106] In the compositions of the present invention, dichroic pigments other than the anthraquinone compounds shown in formula (1) may be used.

[0107] The dichroic pigments that can be used in combination are not particularly limited, as long as they are selected from, for example, azo pigments, anthraquinone pigments, perylene pigments, quinophthalone pigments, merocyanine pigments, azomethine pigments, phthaloperylene pigments, indigo pigments, azulene pigments, dioxazine pigments, polythiophene pigments, etc. Specific examples include the pigments described in "Dichroic dyes for Liquid Crystal Display" (AVIvashchenko, CRC Corporation, 1994). Among these, it is more preferable to use azo pigments, anthraquinone pigments, perylene pigments, or quinophthalone yellow pigments in combination, and more preferably, azo pigments and anthraquinone pigments in combination.

[0108] When using dichroic pigments other than the anthraquinone compound shown in formula (1), the content of the anthraquinone compound shown in formula (1) in all dichroic pigments is not particularly limited, as long as it does not impair the effect of the present invention. The amount is preferably 1 to 80% by mass, more preferably 5 to 70% by mass, and even more preferably 10 to 50% by mass.

[0109] The compositions of the present invention may further incorporate light stabilizers such as benzotriazole, benzophenone and hindered amine, antioxidants such as phosphite and hindered phenol, thermal polymerization inhibitors, thiols, photosensitizers, photosensitizers, chain transfer inhibitors, polymerization inhibitors, adhesion promoters, defoamers, crosslinking agents, surfactants, thermosetting accelerators, thermoplastic resins, thermosetting resins, tackifiers such as urethane diacrylate, etc.

[0110] In addition, to control the unit gaps of the dimming elements, spherical or cylindrical spacers such as silica, glass, plastic, or ceramic can be added. The unit gaps can then be set in the range of 2 to 100 μm.

[0111] The dimming liquid crystal composition of the present invention can be obtained by mixing and stirring anthraquinone compound of formula (1) and liquid crystal material, which are essential components, and other arbitrary components such as photocurable compounds and photopolymerization initiators added as needed. As for mixing and stirring, it is acceptable to put all the components into a container and stir manually in the simplest way, but stirring can be carried out effectively using equipment such as a magnetic stirrer.

[0112] By irradiating the composition of the present invention containing a photocurable compound and a photopolymerization initiator with light, a cured liquid crystal composition formed by the curing (polymerization) of the photocurable compound can be obtained. Furthermore, the term "cured product" in the present invention refers to a state in which the functional groups of the photocurable compound are polymerized or copolymerized by irradiation, and does not refer to cured products such as anthraquinone compounds as shown in formula (1) or liquid crystal materials, which may not contribute to the curing reaction.

[0113] Regarding the light source, there is no particular limitation as long as it is a light source capable of irradiating the absorption wavelength of the photopolymerization initiator. Preferred light sources include: high-pressure mercury lamps, metal halide lamps, xenon lamps, and halogen lamps that can irradiate ultraviolet light.

[0114] The dimming element of the present invention is formed by sandwiching a layer of the aforementioned liquid crystal composition or its photocurable form between a pair of opposing substrates, wherein at least one of the pair of substrates is a transparent substrate having a transparent electrode. Examples of substrates include: inorganic transparent materials such as glass and quartz; metals; metal oxides; semiconductors; ceramics; plastic sheets; plastic films; and other colorless, transparent, colored, or opaque substrates. The electrode is formed on the substrate as a thin film of metal oxide, metal, semiconductor, organic conductive material, etc., on the entire surface or a portion of the substrate using well-known methods such as coating, printing, or sputtering. Especially for obtaining a large-area dimming element, from a production and processability perspective, it is desirable to use an electrode substrate in which ITO (indium tin oxide) electrodes are formed on a transparent polymer film such as PET using methods such as sputtering or printing. A more preferred embodiment is that both of the pair of substrates are transparent substrates having transparent electrodes. Furthermore, wiring for connecting the electrodes to each other or to the outside can also be provided on the substrate. For example, electrode substrates for segmented driving, electrode substrates for matrix driving, and electrode substrates for active matrix driving can also be used. In addition, a protective film or alignment film formed of organic compounds such as polyimide, polyamide, polysiloxane, and cyanide, inorganic compounds such as SiO2, TiO2, and ZrO2, or mixtures thereof can be coated on the entire surface or part of the electrode surface disposed on the substrate.

[0115] By using a plastic film as a substrate, flexible and lightweight dimming elements can be obtained. Therefore, dimming elements can be sandwiched between a pair of planar or curved glass or rigid plastic surfaces using adhesive layers such as polyvinyl butyral, vinyl acetate, double-sided tape, or other adhesives. Alternatively, dimming elements can be laid on the surface of a planar or curved glass or rigid plastic surface using double-sided tape or other adhesives. They can also be sandwiched between flexible plastics or laid on one or both sides. Furthermore, protective layers such as hard coatings, ultraviolet or infrared blocking layers, and semi-mirror layers can be provided on the substrate surface opposite the electrode surface in the dimming element, or color filters can be stacked, or polarizing element filters can be installed. Additionally, it can be used as a laminate for electroluminescent display elements, light-emitting diode display elements, electrochromic display elements, and other liquid crystal display elements.

[0116] The driving device used to apply voltage to the dimming element of the present invention is a device capable of applying a DC voltage of 2 to 100V or an AC voltage of 10 to 1000Hz, and can be open-circuited or short-circuited between electrodes when no voltage is applied. Alternatively, this driving device may also include a voltage application circuit for segment driving, a voltage application circuit for matrix driving, a voltage application circuit for active matrix, etc.

[0117] The anthraquinone compound represented by formula (1) of the present invention has a maximum absorption wavelength in the long wavelength region above 650 nm and excellent spectral characteristics. Therefore, by using this compound, a dimming element that suppresses light leakage during shading and has excellent contrast can be obtained. Therefore, the dimming element of the present invention is most suitable for use in building materials such as windows, partitions, and doors; automotive materials such as car windows and sunroofs; display materials such as displays for text or numbers; and display windows.

[0118] [Example]

[0119] The present invention will be described in more detail below through examples, but the invention is not limited thereto. Furthermore, unless otherwise specified, "parts" and "%" in this document refer to mass. The maximum absorption wavelength in the examples is a value measured using a Shimadzu UV-3150 spectrophotometer manufactured by Shimadzu Corporation.

[0120] Example 1 (Synthesis of the compound represented by Specific Example No. 3)

[0121] 20 parts of NMP, 0.02 parts of copper powder, 0.02 parts of copper iodide, 2.0 parts of iodobenzene, 0.02 parts of potassium carbonate, and 0.15 parts of sodium acetate were added to 0.9 parts of the compound shown in formula (C) synthesized by the method described in Japanese Patent Application Publication No. 62-5941 (Patent Document 5). The mixture was stirred at 140 to 150°C for 12 hours, then cooled to 25°C, and 200 parts of methanol were added. The mixture was stirred for 1 hour. The reaction product was filtered, washed with methanol, and dried in a hot air dryer at 50°C for 24 hours. The resulting crude product was dissolved in toluene, and column purification was performed using toluene as the developing solvent. The solvent was removed from the purified solution by vacuum distillation, and the solution was dried in a hot air dryer at 50°C for 24 hours to obtain 0.3 parts of the compound shown in Specific Example No. 3 above, which is a blue solid.

[0122]

[0123] Example 2 (Synthesis of the compound shown in Specific Example No. 14)

[0124] Using 2.1 parts of 2-methyliodobenzene instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.4 parts of the compound shown in Specific Example No. 14 above were obtained, which was a blue solid.

[0125] Example 3 (Synthesis of the compound shown in Example No. 9)

[0126] Using 3.2 parts of 1-((2-ethylhexyl)oxy)-4-iodobenzene instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.5 parts of the compound shown in Specific Example No. 9 above were obtained, which was a blue solid.

[0127] Example 4 (Synthesis of the compound shown in Specific Example No. 25)

[0128] Using 2.2 parts of 4-iodobenzonitrile instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.3 parts of the compound shown in Specific Example No. 25 above were obtained, which was a blue solid.

[0129] Example 5 (Synthesis of the compound shown in Specific Example No. 19)

[0130] Using 2.4 parts of 4-iodochlorobenzene instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.2 parts of the compound shown in Specific Example No. 19 above were obtained, which was a blue solid.

[0131] Example 6 (Synthesis of the compound shown in Specific Example No. 26)

[0132] Using 2.8 parts of ethyl 4-iodobenzoate instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.4 parts of the compound shown in Specific Example No. 26 above were obtained, which was a blue solid.

[0133] Example 7 (Synthesis of the compound shown in Specific Example No. 41)

[0134] Using 2.3 parts of 2-iodobenzonitrile instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.2 parts of the compound shown in Specific Example No. 41 above were obtained, which was a blue solid.

[0135] Example 8 (Synthesis of the compound shown in Specific Example No. 49)

[0136] Using 0.9 parts of the compound shown in formula (E) below instead of 0.9 parts of the compound shown in formula (C) above, and using 2.0 parts of 4-bromo-3-fluorobenzonitrile instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.4 parts of the compound shown in Specific Example No. 49 above were obtained, which was a blue solid.

[0137]

[0138] Example 9 (Synthesis of the compound shown in Specific Example No. 33)

[0139] Using 2.5 parts of 3-iodoacetophenone instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.3 parts of the compound represented by Specific Example No. 33 above were obtained, which was a blue solid.

[0140] Example 10 (Synthesis of the compound shown in Specific Example No. 20)

[0141] Using 0.9 parts of the compound represented by formula (F) below instead of 0.9 parts of the compound represented by formula (C) above, and using 2.2 parts of 4-iodofluorobenzene instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.3 parts of the compound shown in Specific Example No. 20 above were obtained, which was a blue solid.

[0142]

[0143] Example 11 (Synthesis of the compound shown in Specific Example No. 28)

[0144] Using 0.9 parts of the compound represented by formula (G) below instead of 0.9 parts of the compound represented by formula (C) above, and using 2.3 parts of 4-bromobenzotrifluoride instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.3 parts of the compound shown in Specific Example No. 28 above were obtained, which was a blue solid.

[0145]

[0146] Example 12 (Synthesis of the compound shown in Specific Example No. 67)

[0147] Using 0.9 parts of the compound shown in formula (H) below instead of 0.9 parts of the compound shown in formula (C) above, and using 2.3 parts of 4-iodobenzonitrile instead of 2.0 parts of iodobenzene, otherwise the same as in Example 1, 0.3 parts of the compound shown in Specific Example No. 67 above were obtained, which was a blue solid.

[0148]

[0149] Comparative Example 1 (Synthesis of the Comparative Example Compounds)

[0150] The compound shown in formula (C) above was obtained by the method described in Japanese Patent Application Publication No. 1987-5941 (Patent Document 5).

[0151] (Evaluation of λmax of anthraquinone compounds)

[0152] 10 mg of the anthraquinone compounds obtained in Examples 1 to 12 and Comparative Example 1 were weighed and dissolved in 20 mL of N-methylpyrrolidone. 1 mL of the solution was diluted with 50 mL of toluene, and the maximum absorption wavelength (λmax) was measured using a Shimadzu UV-3150 spectrophotometer. The results are shown in Tables 1 and 2.

[0153] [Table 1]

[0154] Table 1. Maximum absorption wavelengths (λmax) of anthraquinone compounds.

[0155]

[0156]

[0157] [Table 2-1]

[0158] Table 2. Maximum absorption wavelengths (λmax) of anthraquinone compounds.

[0159]

[0160]

[0161] [Table 2-2]

[0162]

[0163] As can be seen from Tables 1 and 2, the anthraquinone compounds of the present invention have a maximum absorption wavelength (λmax) of 650 nm or more, which is higher than that of the compound of Comparative Example 1, and has a maximum absorption wavelength in the long wavelength region.

[0164] Example 13 (Preparation of the liquid crystal composition of the present invention)

[0165] The liquid crystal composition of the present invention was prepared by mixing 0.006 parts of the compound shown in Specific Example No. 3 obtained in Example 1 and liquid crystal materials (0.306 parts of 1-cyano-4'-n-pentylbiphenyl, 0.15 parts of 1-cyano-4'-n-heptylbiphenyl, 0.096 parts of 1-cyano-4'-n-octyloxybiphenyl, and 0.048 parts of 1-cyano-4'-n-pentyltriphenyl) at room temperature.

[0166] Examples 14 to 24 (Preparation of the liquid crystal compositions of the present invention)

[0167] The compound shown in Specific Example No. 3 obtained in Example 1 was replaced with the compounds shown in Specific Examples No. 14, No. 9, No. 25, No. 19, No. 26, No. 41, No. 49, No. 33, No. 20, No. 28, and No. 67 obtained in Examples 2 to 12, respectively. Otherwise, the liquid crystal compositions of the present invention were prepared according to Example 13.

[0168] Comparative Example 2 (Preparation of the liquid crystal composition used for comparison)

[0169] The compound shown in Specific Example No. 3 obtained in Example 1 was replaced with the compound No. 8 disclosed in Japanese Patent Application Publication No. 04-264193, which is shown in the following formula (D). Otherwise, a comparative liquid crystal composition was prepared according to Example 13.

[0170]

[0171] Examples 25 to 36 and Comparative Example 3 (Fabrication of the dimming element used in the present invention and comparison)

[0172] The liquid crystal compositions obtained in Examples 13 to 24 and Comparative Example 2 were respectively encapsulated into an element with a substrate gap of 15 μm, consisting of two glass substrates having transparent electrodes and surface-rubbed polyamide resins in contact with the liquid crystal and subjected to horizontal alignment treatment. In the above-mentioned aligned elements, when no voltage is applied, the liquid crystal is in a horizontal alignment state, and the pigment molecules also exhibit the same alignment state as the bulk liquid crystal.

[0173] (Comparative evaluation of the dimming elements of the present invention and comparative examples)

[0174] For the dimming elements obtained in Examples 25 to 36 and Comparative Example 3, the transmittance (Kz) for linearly polarized light parallel to the alignment direction and the transmittance (Ky) for polarized light perpendicular to the alignment direction were measured, and the comparison (C) at 650 nm was calculated using the following formula. The results are recorded in Tables 3 and 4.

[0175] C = Ky / Kz

[0176] [Table 3]

[0177] Table 3 Comparison of the maximum absorption wavelength of anthraquinone compounds and dimming elements

[0178] Compound No. λmax(nm) C(650nm) Example 25 3 656nm 10.5 Example 26 14 654nm 10.3 Example 27 9 658nm 10.1 Example 28 25 652nm 12.1 Comparative Example 3 Formula (D) 665nm 7.0

[0179] [Table 4]

[0180] Table 4 Comparison of the maximum absorption wavelength of anthraquinone compounds and dimming elements

[0181] Compound No. λmax(nm) C(650nm) Example 29 19 653nm 11.2 Example 30 26 654nm 12.1 Example 31 41 651nm 11.4 Example 32 49 651nm 10.8 Example 33 33 653nm 10.8 Example 34 20 653nm 11.8 Example 35 28 650nm 11.7 Example 36 67 650nm 10.6

[0182] As shown in Tables 3 and 4, the dimming elements of Examples 25 to 36 obtained using the anthraquinone compounds of the present invention have the same maximum absorption wavelength as the dimming elements of the comparative examples, but exhibit high contrast, indicating that they achieve both long wavelength and high contrast.

[0183] Example 37 (Fabrication of a Black Dimming Element)

[0184] A liquid crystal composition was prepared by mixing 0.003 parts of the compound shown in Specific Example No. 14 obtained in Example 2, 0.015 parts of LCD212 (an anthraquinone compound, manufactured by Nippon Kayaku Co., Ltd.), 0.008 parts of the pigment compound shown in formula (X), 0.306 parts of 1-cyano-4'-n-pentylbiphenyl, 0.15 parts of 1-cyano-4'-n-heptylbiphenyl, 0.096 parts of 1-cyano-4'-n-octyloxybiphenyl, and 0.048 parts of 1-cyano-4'-n-pentyltriphenyl at room temperature. The resulting liquid crystal composition was then encapsulated in an element with a substrate gap of 15 μm, consisting of two glass substrates with transparent electrodes and surface-rubbed polyamide resin in contact with the liquid crystal, which had undergone horizontal alignment treatment. In the aforementioned element, the liquid crystal is in a horizontally aligned state when no voltage is applied, and the pigment molecules also exhibit the same alignment state following the liquid crystal.

[0185]

[0186] Example 38 (Fabrication of a Black Dimming Element)

[0187] The following components were used: 0.467 parts of isoborneol acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd.), a monofunctional monomer used as a photocurable compound; 0.024 parts of triethylene glycol dimethacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.), a difunctional monomer used as a photocurable compound; 0.255 parts of 1-cyano-4'-n-pentylbiphenyl, a liquid crystal material; 0.125 parts of 1-cyano-4'-n-heptylbiphenyl; 0.080 parts of 1-cyano-4'-n-octyloxybiphenyl; 0.040 parts of 1-cyano-4'-n-pentyltriphenyl; 0.005 parts of Irgacure TPO (manufactured by BASF Co., Ltd.), a photopolymerization initiator; and 0.005 parts of Irgacure... The liquid crystal composition of the present invention was prepared by stirring at room temperature for 2 hours with 0.003 parts of the compound shown in Specific Example No. 3 obtained in Example 1, 0.015 parts of LCD212 (anthraquinone compound, manufactured by Nippon Kayaku Co., Ltd.), and 0.008 parts of the yellow pigment compound shown in formula (X) above. At room temperature, 0.010 parts of a spacer with a diameter of 20 μm ("Micropearl (registered trademark) SP220" manufactured by Sekisui Chemicals Co., Ltd.) was mixed into the obtained... In a liquid crystal composition, the liquid crystal composition containing the aforementioned spacer is coated onto a 5 square centimeter PET film containing an ITO film using a coater, forming a liquid crystal composition layer. Next, this film is laminated with another 5 square centimeter PET film containing an ITO film, with the liquid crystal composition layer on the ITO film facing the other ITO film. Then, the laminate of the two films and the liquid crystal composition layer obtained in this way is mounted on a heated plate at 23°C and subjected to a 365nm light intensity of 9mW / cm² on an LED lamp, achieving a light intensity of 9mW / cm². 2 The location is illuminated for 1 minute to photocur the photocurable compound, and a black dimming element is made accordingly.

[0188] [Industry availability]

[0189] By using the anthraquinone compound of the present invention as a dichroic pigment for liquid crystal dimming elements, dimming elements that suppress light leakage during light blocking and have excellent contrast can be obtained. The dimming elements obtained by the present invention are applicable to building materials such as windows, partitions, and doors; automotive materials such as car windows and sunroofs; display materials such as displays for text or numbers; and display windows.

Claims

1. An anthraquinone compound, which is an anthraquinone compound represented by formula (1) below, In the formula, R1 and R4 independently represent hydrogen atoms, straight-chain alkyl groups having 1 to 8 carbon atoms or branched-chain alkyl groups having 3 to 8 carbon atoms, straight-chain alkoxy groups having 1 to 8 carbon atoms or branched-chain alkoxy groups having 3 to 8 carbon atoms, halogen atoms, -CO2R9, -OCOR9, -COR9, cyano or trifluoromethyl; R2, R3, R5 and R6 independently represent hydrogen atoms, methyl, halogen atoms, -CO2R9, -OCOR9, -COR9, cyano or trifluoromethyl; R7 and R8 independently represent hydrogen atoms or straight-chain alkyl groups having 1 to 8 carbon atoms or branched-chain alkyl groups having 3 to 8 carbon atoms; R9 independently represents straight-chain alkyl groups having 1 to 5 carbon atoms or branched-chain alkyl groups having 3 to 5 carbon atoms.

2. The anthraquinone compound according to claim 1, wherein, At least one of R1 to R6 is a non-hydrogen atom.

3. The anthraquinone compound according to claim 1, wherein, R1 and R4 are each independently a hydrogen atom, a straight-chain alkyl group having 1 to 8 carbon atoms or a branched-chain alkyl group having 3 to 8 carbon atoms, a straight-chain alkoxy group having 1 to 8 carbon atoms or a branched-chain alkoxy group having 3 to 8 carbon atoms, a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano or a trifluoromethyl group, and R2, R3, R5 and R6 are each independently a hydrogen atom, a methyl group, a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano or a trifluoromethyl group.

4. The anthraquinone compound according to claim 3, wherein, At least one of R1, R2, R4, and R5 is a fluorine atom, a chlorine atom, -CO2R9, -COR9, a cyano group, or a trifluoromethyl group.

5. The anthraquinone compound according to claim 4, wherein, At least one of R1, R2, R4, and R5 is a fluorine atom, -CO2R9, or a cyano group.

6. The anthraquinone compound according to claim 3, wherein R3 and R6 are hydrogen atoms.

7. The anthraquinone compound according to claim 6, wherein only one of R1 and R2 is a hydrogen atom, and only one of R4 and R5 is a hydrogen atom.

8. The anthraquinone compound according to claim 6, wherein R2 and R5 are hydrogen atoms.

9. The anthraquinone compound according to claim 8, wherein R4 is a straight-chain or branched alkyl group having 3 to 8 carbon atoms.

10. The anthraquinone compound according to claim 3, wherein R7 and R8 are each independently a straight-chain alkyl group having 3 to 8 carbon atoms.

11. The anthraquinone compound according to claim 1, wherein the maximum absorption wavelength is above 650 nm.

12. A liquid crystal composition comprising an anthraquinone compound and a liquid crystal material according to any one of claims 1 to 11.

13. The liquid crystal composition according to claim 12, wherein it contains a photocurable compound and a photopolymerization initiator.

14. The liquid crystal composition according to claim 12, wherein it contains a pigment compound other than the anthraquinone compound shown in formula (1).

15. A photocurable material, which is a photocurable form of the liquid crystal composition according to claim 13.

16. A dimming element comprising sandwiching the liquid crystal composition according to claim 12 between a pair of opposing substrates, wherein, In the pair of opposing substrates, at least one is a transparent substrate with a transparent electrode.

17. The dimming element according to claim 16, wherein, In a pair of substrates, both are transparent substrates with transparent electrodes.

18. A dimming element comprising sandwiching the photocurable material according to claim 15 between a pair of opposing substrates, wherein, In the pair of opposing substrates, at least one is a transparent substrate with a transparent electrode.

19. The dimming element according to claim 18, wherein, In a pair of substrates, both are transparent substrates with transparent electrodes.

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