Chiral dopant, liquid crystal composition, and liquid crystal element

Abstract

To provide a chiral dopant which is optically reversible in a liquid crystal and has a good torsional force change width, a liquid crystal composition, and a liquid crystal element.SOLUTION: The chiral dopant is represented by formula (1). Wherein X1, X2, X3 and X4 are each independently benzene or cyclohexane, and R is each independently an alkyl group having 1 to 12 carbon atoms. ) SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a chiral dopant, a liquid crystal composition, and a liquid crystal device. [Background technology]

[0002] Liquid crystals are classified according to the way their molecules are oriented, and for example, nematic liquid crystals and cholesteric liquid crystals (CLC) are known. Figure 1 shows a schematic diagram of nematic liquid crystals and cholesteric liquid crystals.

[0003] In nematic liquid crystals, the long axes (orientation axes) of the molecules are oriented in the same direction. On the other hand, in cholesteric liquid crystals, liquid crystal phases in which the long axes of the molecules are oriented in one direction are twisted in a spiral and stacked. The thickness of the liquid crystal layer when the spiral twist rotates 360° is called the pitch (P). When white light is irradiated onto cholesteric liquid crystals, a phenomenon called "selective reflection" occurs, in which circularly polarized light of the same handedness is selectively reflected at a wavelength proportional to the pitch according to the Bragg equation. Here, if the angle of incidence with respect to the spiral axis is θ, the selective reflection wavelength is λ, and the refractive index of the liquid crystal is n, the following equation (A) holds: λ=nPcosθ (A)

[0004] Cholesteric liquid crystals form a molecular arrangement with a helical structure, and have the characteristic of selectively reflecting circularly polarized light of a wavelength that corresponds to the period (pitch) of the helical structure. Cholesteric liquid crystals are prepared by adding chiral dopants, which are optically active guest molecules, to nematic liquid crystals, which are liquid crystals with low structural order. Chiral dopants have the power to twist the arrangement of the liquid crystal molecules, and this power is called "helical twisting power (HTP)."

[0005] By using a compound that can reversibly switch between two states by light as the chiral dopant mentioned above, the helical pitch of cholesteric liquid crystals can be reversibly changed. The length of the helical pitch is derived from the twisting power of the chiral dopant. The larger the difference in the twisting power between the two states that can be reversibly switched by light, the larger the range of change in the helical pitch of the cholesteric liquid crystal can be. To realize full-color, controllable selective reflection in cholesteric liquid crystals, the development of chiral dopants with a large range of twisting power change is expected.

[0006] Non-Patent Document 1 discloses a synthesis example of chiral dopant (2) having an anthracene moiety, as shown in Figure 2. The chiral dopant (2) described in Non-Patent Document 1 is a compound (bisanthracene) in which two anthracene groups are connected to binaphthyl via an alkyl spacer. The chiral dopant (2) was dimerized in a dilute solution by irradiation with 365 nm light, and dedimerized by irradiation with 254 nm light and heat. The twisting power of the chiral dopant (2) in 4-cyano-4'-pentylbiphenyl (5CB) was +51.4 μm by irradiation with 365 nm light. -1 to -100.9 μm -1 Furthermore, when an auxiliary dopant was added to this cholesteric liquid crystal, the selective reflection wavelength changed from 769 nm to 445 nm upon irradiation with 365 nm light, successfully controlling the full-color selective reflection wavelength. However, the 254 nm light required for dedimerization of dimerized anthracene was absorbed by 5CB, making this photoreversible in the liquid crystal.

[0007] Non-Patent Document 2 discloses a synthesis example of chiral dopant (3) having a pyrenylethene moiety, as shown in Figure 3. The chiral dopant (3) described in Non-Patent Document 2 is a compound in which a binaphthyl skeleton and a pyrenylethene are crosslinked without an alkyl spacer. In a dilute solution and in a liquid crystal, chiral dopant (3) was intramolecularly dimerized by irradiation with 436 nm light, and subsequently dedimerized by irradiation with 334 nm light. However, in a liquid crystal (5CB), the twisting power was reduced to -19.5 μm by irradiation with 436 nm light. -1 to -58.0 μm -1 and then, by irradiation with 334 nm light, the -1 The torsional force recovered to a level below 100%, and the range of torsional force change was not satisfactory. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Rino Yokokura, "Creation of Stealth Photochromic Chiral Dopants Based on Bisanthracene," Master's Thesis, Graduate School of Engineering, Yokohama National University, FY2017 [Non-patent document 2] Ryo Nakamura, "Photoresponse properties of pyrenylethenes bridged by binaphthyl moieties in solution and liquid crystal," Master's thesis, Graduate School of Science and Engineering, Yokohama National University, FY2022 [Non-patent document 3] HariKrishnaBisoyi and QuanLi, “Light-DrivenLiquidCrystallineMaterials:FromPhoto-InducedPhase TransitionsandPropertyModulationstoApplications”, Chem. Rev. 2016, 116, 15089-15166 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above problems, the present embodiment aims to provide a chiral dopant, a liquid crystal composition, and a liquid crystal device which are photoreversible in liquid crystal and have a good range of change in twisting power. [Means for solving the problem]

[0010] The above problems can be solved by the embodiments specified below. 1. A chiral dopant represented by the following formula (1): [ka] (In the formula, X 1 , X 2 , X 3 and X 4 are each independently benzene or cyclohexane, and each R is independently an alkyl group having 1 to 12 carbon atoms. 2. A liquid crystal composition comprising the chiral dopant described in 1 above and a host liquid crystal. 3. A pair of glass substrates that have been subjected to surface alignment treatment; 2. The liquid crystal composition according to 2, which is provided between the pair of glass substrates; A liquid crystal element having: [Effects of the Invention]

[0011] According to this embodiment, it is possible to provide a chiral dopant, a liquid crystal composition, and a liquid crystal device which are photoreversible in liquid crystal and have a good range of change in twisting power. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic diagrams of nematic liquid crystal and cholesteric liquid crystal. [Figure 2] This is a synthesis example of chiral dopant (2) having an anthracene moiety disclosed in Non-Patent Document 1. [Figure 3] This is a synthesis example of chiral dopant (3) having a pyrenylethene moiety disclosed in Non-Patent Document 2. [Figure 4] 1 is a synthesis scheme of chiral dopant (11). [Figure 5] 1 is a graph of 1H NMR of chiral dopant (11). [Figure 6] 1 is a graph of 1H NMR of chiral dopant (11). [Figure 7] 1 is a graph showing the change in absorption spectrum of chiral dopant (11). [Figure 8] FIG. 1 is a schematic diagram for explaining the Grandjean-Cano method. [Figure 9] This is a polarized light microscope (POM) image of the change in the Kano line of a cholesteric liquid crystal prepared by adding chiral dopant (11) to a nematic liquid crystal 5CB upon irradiation with 436 nm light. [Figure 10] The change in the Kano line upon irradiation with 436 nm light is shown as a linear line plotting the reciprocal of the pitch P against the concentration c. [Figure 11] This is a polarized optical microscope (POM) image obtained during contact testing of a cholesteric liquid crystal with chiral dopant (11). DETAILED DESCRIPTION OF THE INVENTION

[0013] Next, embodiments of the present disclosure will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes, modifications, and the like may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0014] <Chiral dopants> The chiral dopant according to the embodiment of the present invention is represented by the following formula (1).

[0015] [ka] (In the formula, X 1 , X 2 , X 3 and X 4 are each independently benzene or cyclohexane, and each R is independently an alkyl group having 1 to 12 carbon atoms. Furthermore, each R may independently be an alkyl group having 3 to 10 carbon atoms, an alkyl group having 3 to 7 carbon atoms, or an alkyl group having 3 to 5 carbon atoms.

[0016] The chiral dopant shown in formula (1) is a chiral dopant with a photoresponsive moiety that can photoreversibly change its molecular structure, and a compound that exhibits a reversible photodimerization reaction is used as the photoresponsive moiety. As shown below, the chiral dopant shown in formula (1) is dimerized by visible light to take the structure of compound (1'), and can be dedimerized by ultraviolet light to return to the original structure of formula (1).

[0017] [ka]

[0018] The chiral dopant according to an embodiment of the present invention is a compound in which a 4-pentylbiphenyl group, a substituent similar to the liquid crystal molecule (5CB), is attached to the pyrene end of a compound in which pyrenylethene is crosslinked via a binaphthyl skeleton. This configuration allows the chiral dopant to be photoreversible in the liquid crystal, as described above, and provides a good range of change in the "twisting power," which is the power that twists the alignment of the liquid crystal molecules. The reason for the good range of change in the twisting power is that the chiral dopant has a substituent with a structure similar to that of the liquid crystal molecule, which improves the compatibility between the chiral dopant and the host liquid crystal molecule, 5CB, and thus facilitates the transfer of changes in the properties of the chiral dopant to the liquid crystal.

[0019] -X in formula (1) 1 -X 2 -R and -X 3 -X 4 Specific examples of the structural formula of -R are shown in the following formulas (4) to (7). -X in formula (1) 1 -X 2 -R and -X 3 -X 4 Each —R can independently have any of the structural formulas (4) to (7) below.

[0020] [ka]

[0021] -X in formula (1) 1 -X 2 -R and -X 3 -X 4 Even when -R has not only the structural formula (4) but also any of the structural formulas (5) to (7), the chiral dopant is photoreversible in liquid crystal and exhibits a good range of change in "twisting power," which is the power to twist the alignment of liquid crystal molecules. An example of a chiral dopant in which one benzene ring of the chiral dopant is replaced with a cyclohexane ring and is photoreversible in liquid crystal and exhibits a good range of change in "twisting power," which is the power to twist the alignment of liquid crystal molecules, is disclosed in Non-Patent Document 3: Hari Krishna Bisoyi and Quan Li, "Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications," Chem. Rev. 2016, 116, 15089-15166.

[0022] <Liquid Crystal Composition> The liquid crystal composition according to the embodiment of the present invention contains a chiral dopant represented by the above formula (1) and a host liquid crystal. Since the chiral dopant represented by formula (1) has the ability to induce a helical structure in the liquid crystal, the liquid crystal composition according to the embodiment of the present invention can exhibit cholesteric liquid crystal.

[0023] The concentration of the chiral dopant in the liquid crystal composition according to the embodiment of the present invention is preferably 0.1 to 20 mmol / mol. With this configuration, the liquid crystal composition can have a predetermined selective reflection wavelength range using only a predetermined chiral dopant.

[0024] Examples of the host liquid crystal include liquid crystal compounds exhibiting a nematic phase (nematic liquid crystals). Specific examples include azomethine compounds, cyanobiphenyl compounds, cyanophenyl esters, fluorine-substituted phenyl esters, cyclohexanecarboxylic acid phenyl esters, fluorine-substituted cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexane, fluorine-substituted phenylcyclohexane, cyano-substituted phenylpyrimidines, fluorine-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, fluorine-substituted alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolan-based compounds, fluorine-substituted tolan-based compounds, and alkenylcyclohexylbenzonitriles. 4-cyano-4'-pentylbiphenyl (5CB) is particularly preferred.

[0025] The liquid crystal composition according to the embodiment of the present invention can be added with various liquid crystal or non-liquid crystal compounds to change the physical properties of the host liquid crystal (e.g., the temperature range of the liquid crystal phase) to a desired range. Compounds such as ultraviolet absorbers and antioxidants may also be added. The liquid crystal composition according to the present invention may also contain a chiral dopant other than the chiral dopant represented by the above formula (1).

[0026] <Liquid crystal element> A liquid crystal element according to an embodiment of the present invention has a pair of glass substrates that have been subjected to a surface alignment treatment, and a liquid crystal composition according to an embodiment of the present invention provided between the pair of glass substrates. In another embodiment, the liquid crystal element according to the present invention may include a liquid crystal composition according to the present invention and a pair of electrodes, at least one of which is a transparent electrode. More specifically, the liquid crystal element according to the present invention includes a pair of electrodes, at least one of which is a transparent electrode, and a liquid crystal layer containing the liquid crystal composition according to the present invention between the electrodes. The liquid crystal element may further include a black plate, an anti-reflection film, a brightness enhancement film, etc. Note that, if no electric field response is required, these electrodes are not necessary, and the liquid crystal element is configured to include a pair of glass substrates that have been subjected to the above-mentioned surface alignment treatment and a liquid crystal composition according to the present invention provided between the pair of glass substrates.

[0027] The electrodes of the liquid crystal element can be glass substrates or plastic substrates such as acrylic resin, polycarbonate resin, or epoxy resin, with an electrode layer formed on the surface. Materials that can be used for the electrode layer include indium oxide, indium tin oxide (ITO), tin oxide, PEDOT-PSS, silver nanorods, and carbon nanotubes.

[0028] The liquid crystal element according to the embodiment of the present invention can be constructed by providing a gap (cell gap) between a pair of electrodes via a spacer or the like, and injecting a liquid crystal composition into the gap.

[0029] The liquid crystal element according to the embodiment of the present invention may also include other members such as a barrier film, an ultraviolet absorbing layer, an anti-reflection layer, a hard coat layer, an anti-fouling layer, an organic interlayer insulating film, a metal reflector, a retardation film, an alignment film, etc. These may be used alone or in combination of two or more.

[0030] The liquid crystal element according to the embodiment of the present invention can be driven by a simple matrix driving method or an active matrix driving method using thin film transistors (TFTs) or the like. [Example]

[0031] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0032] <Test Example 1: Synthesis of chiral dopant (11)> In Test Example 1, a chiral dopant represented by formula (11) was prepared based on the synthesis scheme shown in FIG.

[0033] 1. Synthesis of compound (8) A 50 mL two-necked recovery flask was equipped with a Dimroth tube and a base balloon, placed in an oil bath, and charged with a spinner and the raw materials (441.2 mg (1.00 mmol, 1.00 eq.) of (R)-2,2'-bis(bromomethyl)-1,1'-binaphthalene and 421.0 mg (5.01 mmol, 5.01 eq.) of sodium bicarbonate. A septum was then attached, and the mixture was subjected to vacuum drying and nitrogen substitution three times, alternating to create a nitrogen atmosphere. Using a 20 mL syringe, 16.0 mL of DMSO (dimethyl sulfoxide) was added, and the mixture was stirred for 6 hours while maintaining the temperature at approximately 100 °C. The DMSO used was not subjected to any pretreatment, such as dehydration. The mixture was then extracted with diethyl ether, washed with water, and dehydrated over anhydrous sodium sulfate. The resulting solution was transferred to a 50 mL two-necked recovery flask, and the solvent was removed under reduced pressure using a rotary evaporator. The mixture was then evacuated overnight. The next day, oxidation was carried out using PCC (pyridinium chlorochromate). A 50 mL two-necked eggplant flask containing the crude product was charged with 656.6 mg (3.04 mmol, 3.04 eq.) of pyridinium chlorochromate, 653.2 mg of Celite, a spinner, a septum, and a balloon. After evacuating and replacing the atmosphere with nitrogen three times, 15.0 mL of dehydrated dichloromethane (pre-dehydrated with 4A molecular sieves) was added and stirred at room temperature for approximately 4 hours. The mixture was then filtered, extracted with dichloromethane, washed with saturated saline, and dehydrated over anhydrous sodium sulfate. The crude product was dissolved in toluene and purified by column chromatography using a 15 / 85 (v / v) ethyl acetate / hexane eluent to obtain 233.7 mg of compound (8') as a white solid. 1 The H NMR spectrum confirmed that the target compound (8) and ethyl acetate were mixed in a 2:1 ratio by mass, and the calculated yield of compound (8) was 204.6 mg (0.659 mmol, yield = 66%). 1 Details of the H NMR are shown below. 1H NMR (500 MHz, CHLOROFORM-D,TMS) δ = 7.23 (dd, J = 8.6, 1.2, 2H), 7.38(ddd, J= 8.2, 6.8, 1.3, 2H), 7.65(ddd, J = 8.2, 6.7, 1.2, 2H), 8.02 (d, J = 8.2, 2H), 8.13(d, J = 8.7,2H), 8.20 (d, J = 8.6, 2H), 9.62 (d, J = 1.0, 2H).

[0034] 2. Synthesis of compound (9) A 50 mL Schlenk flask was charged with 1079.2 mg (3.04 mmol, 4.61 eq.) of methyltriphenylphosphonium bromide and 338.0 mg (3.05 mmol, 4.62 eq.) of potassium tert-butoxide. The flask was placed in an ice bath and evacuated and purged with nitrogen three times. Then, 10.0 mL of dehydrated tetrahydrofuran (THF) was added, followed by 233.7 mg of compound (8'), a mixture of (R)-1,1-binaphthyl-2,2'-dicarboxaldehyde and ethyl acetate (calculated amount of compound (8) was 204.6 mg (0.659 mmol, 1.00 eq.)), using a total of 6 mL of dehydrated THF. The ice was removed, the mixture was stirred for 10 minutes, and then quenched with dilute hydrochloric acid. The mixture was extracted with dichloromethane, washed with saturated saline, dehydrated with anhydrous sodium sulfate, and purified by column chromatography using a toluene / hexane = 10 / 90 (v / v) developing solvent, yielding 171.9 mg (0.561 mmol, yield = 85%) of the target compound (9) as a white solid. 1 The details of the 1 H NMR spectrum are shown below. 1H NMR (500 MHz, CHLOROFORM-D) δ = 5.07 (dd, J = 11.0, 1.0, 2H), 5.78 (dd, J =17.6, 1.0, 2H), 6.27 (dd, J = 17.5, 11.1, 2H), 7.05 (d, J = 10.6, 2H), 7.21 (ddd, J = 8.3, 6.9,1.4, 2H), 7.42 (ddd, J = 8.2, 6.8, 1.4, 2H), 7.90 (d, J = 8.2, 2H), 7.92 (d, J = 8.8, 2H), 7.96(d, J = 8.7, 1H).

[0035] 3. Synthesis of compound (10) A 100 mL two-necked recovery flask was equipped with a Dimroth tube and a base balloon. Then, 90.1 mg (0.250 mmol, 1.0 eq.) of 1,6-dibromopyrene, 139.4 mg (1.01 mmol, 4.04 eq.) of potassium carbonate, 14.2 mg (0.0202 mmol, 0.0808 eq.) of dichlorobistriphenylphosphine palladium, and 67.4 mg (0.251 mmol, 1.00 eq.) of 4'-pentyl-4-biphenylboronic acid were added. The flask was then evacuated and purged with nitrogen three times. Then, 10 mL of pure water, 3.50 mL of toluene, and 0.80 mL of ethanol were added as solvents using a 20 mL syringe, a 10 mL syringe, and a 2 mL syringe, respectively, purged with nitrogen. The mixture was stirred for 1 hour while maintaining the temperature at 100 °C in an oil bath. After stirring, the mixture was cooled to room temperature, quenched with water, extracted with dichloromethane, washed with saturated saline, and dehydrated with anhydrous magnesium sulfate. Due to the poor solubility of the crude product, it was purified using a column chromatography. The mobile phase was (chloroform / hexane) = (5 / 95 (v / v)), and 47.3 mg (0.094 mmol, yield = 38%) of colorless solid compound (10) was obtained. 1 The details of the 1 H NMR spectrum are shown below. 1H NMR (500 MHz, CHLOROFORM-D) δ = 0.93 (t, J = 7.1, 3H), 1.38 - 1.40 (m, 4H), 1.68 - 1.71 (m, 2H), 2.69 (t, J = 7.8, 2H), 7.33 (d, J = 8.3, 2H), 7.65 (d, J = 8.2, 2H), 7.69(d, J = 8.3, 2H), 7.79 (d, J = 8.3, 2H), 8.01 (d, J = 9.2, 1H), 8.02 (d, J = 8.2, 1H), 8.07 (d, J= 7.9, 1H), 8.22 (d, J = 9.3, 1H), 8.26 (d, J = 8.2, 1H), 8.28 (d, J = 9.2, 1H), 8.30 (d, J = 7.9,1H), 8.48 (d, J = 9.2, 1H).

[0036] 4. Synthesis of compound (11) N,N-dimethylformamide (DMF) was dehydrated using molecular sieves 4A in advance. In a 20 mL two-necked flask, 30.7 mg (0.100 mmol, 1.00 eq.) of (R)-2,2'-divinyl-1,1'-binaphthyl (2), 256.1 mg (0.51 mmol, 5.1 eq.) of 1-bromo-6-(4'-pentyl-4-biphenyl)pyrene (compound (10)), 5.86 mg (0.026 mmol, 0.26 eq.) of palladium(II) acetate, and phosphine ligand X were added. 24.3 mg (0.051 mmol, 0.50 eq.) of Phos (2-(dicyclohexylphosphino)-2',4',6'-triisopropyl-1,1'-biphenyl) and 121.6 mg (0.88 mmol, 0.88 eq.) of potassium carbonate were added, and a spinner, septum, Dimroth condenser, and balloon were installed. After evacuation and nitrogen substitution three times, 5.0 mL of dehydrated DMF was added, and the mixture was heated and stirred at 100 °C for approximately 48 hours using an aluminum bath and a cooling water circulator. After 24 hours, 0.5 mL of dehydrated DMF was added. The mixture was quenched with hydrochloric acid, extracted with toluene, washed with saturated brine, and dehydrated over anhydrous sodium sulfate. A column was run using a developing solvent of toluene / hexane = 30 / 70 (v / v), yielding 43.5 mg (0.0378 mmol, yield = 38%) of compound (11) as a yellow solid. 1 The details of the 1 H NMR spectrum are shown below. 1 H NMR (500 MHz, METHYLENE-CHLORI) δ = 0.84 (t, J = 6.1, 6H), 1.29 - 1.30 (m, 8H), 1.59 (t, J = 7.2, 4H), 2.59 (t, J = 7.5, 4H), 7.01 (d, J = 15.8, 2H), 7.17 (d, J = 8.6, 2H),7.24 (d, J = 7.0, 6H), 7.43 (t, J = 7.2, 2H), 7.56 (d, J = 7.3, 4H), 7.59 (d, J = 7.4, 4H), 7.70(d, J = 8.6, 4H), 7.73 (d, J = 9.0, 2H), 7.81 (d, J = 9.6, 2H), 7.83 - 7.88 (m, 6H), 7.96 (d, J= 8.6, 2H), 8.02 (d, J = 8.3, 2H), 8.09 (t, J = 10.0, 4H), 8.15 (d, J = 17.5, 2H), 8.18 (d, J =10.1, 2H), 8.27 (d, J = 9.2, 2H).

[0037] 1 The synthesis of chiral dopant (11) was confirmed by H NMR measurement. A signal from the ethene moiety with a coupling constant of 16.0 Hz was observed near 7.0 ppm, suggesting that the stereoisomer is E (Figures 5 and 6). Another signal from the ethene moiety, overlapping with other peaks, was also observed near 8.2 ppm, with a coupling constant of 16.2 Hz, suggesting that the stereoisomer is E.

[0038] <Test Example 2: Measurement of absorption spectrum accompanying photoreaction of chiral dopant (11)> A dilute chloroform solution of the chiral dopant (11) prepared in Test Example 1 was prepared, and the solution was irradiated with light at 436 nm and 334 nm to measure the absorption spectrum. The changes in the absorption spectrum upon irradiation with light at 436 nm and 334 nm are shown in Figure 7. Upon irradiation with 436 nm light, the absorption bands at 398 nm and 270 nm decreased, and when the photostationary state (PSS) was reached, the absorption band at 353 nm increased. This is thought to be due to a decrease in the conjugation length caused by [2+2] dimerization of the ethene moiety. Upon irradiation with 334 nm light, the absorption band at the maximum absorption wavelength of 353 nm decreased, and when the photostationary state (PSS) was reached, the absorption bands at the maximum absorption wavelengths of 270 nm and 398 nm increased. This is thought to be due to an increase in the conjugation length caused by dedimerization of the ethene moiety.

[0039] <Test Example 3: Measurement of photoresponse of chiral dopant (11) in liquid crystal> The photoresponse of chiral dopant (11) in liquid crystal was measured by the Grandjean-Cano method as follows. The Grandjean-Cano method is a method for measuring the pitch of cholesteric liquid crystals. When cholesteric liquid crystals are injected into a wedge-shaped cell with alignment treatment applied to the top and bottom substrates, the liquid crystal molecules align so that their helical axis is perpendicular to the substrates (Figure 8). Within a certain range of cell thickness, the number of twists is determined to satisfy the alignment on the cell surface, but at slightly thicker thicknesses the number of twists increases by half a turn, and at slightly thinner thicknesses the number of twists decreases by half a turn. When this cell is viewed from above, periodic parallel lines (Cano's lines) can be observed inside the cell, corresponding to the discontinuity in the number of twists of the liquid crystal. The following formula (B) holds between the spacing a of the Kano lines, the pitch P, and the wedge angle θ in FIG. P=2atanθ (B) Furthermore, the twisting power (β M ) is calculated. β M [μm -1 ]=1 / Pc (C)

[0040] The cholesteric liquid crystal prepared by adding the chiral dopant (11) prepared in Test Example 1 to nematic liquid crystal 5CB was injected into a wedge-shaped cell, and the spacing of the Kano lines was measured before and after light irradiation, and the pitch P was calculated using equation (B). A wedge-shaped cell with tan θ = 0.0200 was used here. Experiments were conducted at two concentrations, and the length of the pitch P was measured before and after irradiation with 436 nm light at each concentration, and the twisting force was calculated. Polarized light microscope (POM) images of the change in the Kano lines upon irradiation with 436 nm light at c = 0.53 mmol / mol are shown in Figure 9. The spacing of the Kano lines widened with 436 nm light irradiation, then disappeared and then reappeared. The slope of the linear line in Figure 10, which plots the reciprocal of the pitch P against each concentration c [mmol / mol], represents the torsional strength in each state. From the slope of the linear line in Figure 10, the torsional force (β M ) is 290μm in the initial state -1 , 110 μm in PSS irradiated with 436 nm light -1 was asked. In addition, when the torsional force is calculated using the mass ratio c [wt%] as the concentration unit, the β wt% The absolute value of is 63 μm in the initial state -1 , 23 μm in PSS irradiated with 436 nm light -1 was asked.

[0041] <Test Example 4: Contact test of cholesteric liquid crystal using chiral dopant (11)> A contact test of the cholesteric liquid crystal using the chiral dopant (11) prepared in Test Example 1 was carried out as follows. Contact testing is a method for determining the helical sense of cholesteric liquid crystals. When two cholesteric liquid crystals are brought into contact, if they have the same helical sense, the boundary between the two phases will be continuous. If they have opposite helical senses, the boundary between the two phases will be discontinuous, and nematic liquid crystals will appear at the boundary, resulting in defects when observed under crossed Nicols with a polarizing microscope. In this test example, the above-mentioned contact test was performed using S1011 (manufactured by Merck), a compound known to induce cholesteric liquid crystals with left-handed helical sense. The resulting polarized light microscope (POM) images are shown in Figure 11. As shown in Figure 11, in a contact test between a cholesteric liquid crystal consisting of S1011 and 5CB and a cholesteric liquid crystal consisting of chiral dopant (11) and 5CB before irradiation with 436 nm light, defects were observed at the boundary between the two phases. This confirmed that the cholesteric liquid crystal consisting of chiral dopant (11) and 5CB has a right-handed helical sense in the initial state. Similarly, in a contact test between a cholesteric liquid crystal consisting of chiral dopant (11) and 5CB that had reached the PSS state by irradiation with 436 nm light and the initial state, defects were also observed. In other words, when the cholesteric liquid crystal consisting of chiral dopant (11) and 5CB was continuously irradiated with 436 nm light and reached the PSS state, the helical sense changed from right-handed to left-handed, confirming that helix reversal had occurred. In other words, it was confirmed that the cholesteric liquid crystal consisting of chiral dopant (11) and 5CB has a positive twisting power in the initial state and a negative twisting power in the PSS state (PSS 436) irradiated with 436 nm light. The contact test determined the sign of the torsional force in the initial state and in the state of PSS irradiated with 436 nm light (PSS 436), and also determined the range of change in the torsional force. The evaluation results are shown in Table 1 below.

[0042] <Test Example 5: Evaluation of chiral dopant (12)> A chiral dopant (12) having the structural formula shown in the following formula (12) was prepared. Next, the photoresponse of the chiral dopant (12) in the liquid crystal was measured in the same manner as in the above-mentioned Test Example 3. As a result, the twisting power (β M ) is 19.5μm in the initial state -1 , 58.0 μm for PSS irradiated with 436 nm light -1 was asked. Furthermore, by conducting a contact test of a cholesteric liquid crystal using chiral dopant (12) in the same manner as in Test Example 4, the sign of the twisting power in the initial state and in the PSS state (PSS 436) irradiated with 436 nm light was determined, and the range of change in the twisting power was also calculated. The evaluation results are shown in Table 1 below.

[0043] [Table 1]

[0044] <Evaluation results> As shown in Table 1, the absolute values ​​of the twisting power in the initial state and the change in twisting power from the initial state to the PSS state (PSS 436) for chiral dopant (11) were larger than those for chiral dopant (12). When (R)-binaphthyl was used as the chiral dopant, the dihedral angle θ was 0°.

Claims

1. A chiral dopant represented by the following formula (1): 【Chemistry 1】 (In the formula, X 1 , X 2 , X 3 and X 4 are each independently benzene or cyclohexane, and each R is independently an alkyl group having 1 to 12 carbon atoms.

2. A liquid crystal composition comprising the chiral dopant according to claim 1 and a host liquid crystal.

3. A pair of glass substrates that have been subjected to surface alignment treatment; The liquid crystal composition according to claim 2 provided between the pair of glass substrates; A liquid crystal element having:

Images