Liquid crystal material, thin film, and organic electroluminescence device

Abstract

To provide a liquid crystal material suitable for constructing a linearly or circularly polarized light-emitting organic electroluminescence device.SOLUTION: A liquid crystal material according to the present invention contains a compound having a predetermined tricarbazole structure and satisfies the following condition at 25°C that: (i) the material exhibits a nematic liquid crystal phase or a chiral nematic liquid crystal phase; or (ii) the material has a molecular orientation reflecting a nematic liquid crystal phase or a chiral nematic liquid crystal phase and exhibits a glassy state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid crystal material, and to a thin film and an organic electroluminescent device using the liquid crystal material. [Background technology]

[0002] Organic electroluminescence technology has been put to practical use in a wide range of applications, including smartphones, televisions, head-mounted displays, and lighting. In many organic electroluminescence displays, phase conversion to polarized or circularly polarized light is performed using polarizers and quarter-wave retarders to improve visibility and for optical control.

[0003] However, phase conversion using polarizers in principle results in a 50% attenuation of light intensity, which leads to a decrease in the energy efficiency of the entire device and is a major challenge in the development of display devices.

[0004] To solve this problem, polarizer-less device structures and polarized organic electroluminescent devices have been proposed. The former are cost-inefficient because they require the benefits of polarized light, such as improved viewing angle and anti-reflection, to be implemented in separate components. The latter has been actively explored for polymer organic electroluminescent materials, but it is difficult to impart polarization properties to materials that utilize the energy-efficient triplet excited state, and they have not yet been put to practical use.

[0005] Furthermore, circularly polarized light emission using polymer organic electroluminescent light-emitting materials has not yet been achieved in a manner that combines circularly polarized light emission characteristics with electrical properties and external quantum yield. Therefore, the development of light-emitting materials that are endowed with polarized and circularly polarized light emission characteristics is expected to contribute to the further development of organic electroluminescence technology.

[0006] Utilizing the helical structure of chiral nematic liquid crystals to impart circular polarization properties to light-emitting materials is a promising technology due to its high circular polarization purity. Chiral nematic liquid crystals are characterized by the presence of optically active molecules in nematic liquid crystals with an orderly orientation, which causes a twist between adjacent molecules, resulting in a helical periodic structure perpendicular to the molecular axis. This periodic structure exhibits long-range correlation, and the period can persist over several centimeters. The pitch of the periodic structure (i.e., the helical pitch p) ranges from several hundred nanometers to infinity.

[0007] In order to use circularly polarized light-emitting materials as the light-emitting layer of organic electroluminescence devices, they must be made into thin films to keep the driving voltage low, and the film thickness must be kept on the order of nanometers. It is generally known that most circularly polarized light-emitting materials using chiral nematic liquid crystals lose their circular polarization properties when the film thickness is on the order of nanometers or less.

[0008] As an example of a device that exhibits circular polarization properties on the order of nanometers or less, Non-Patent Document 1 describes a liquid crystalline conjugated polymer, F8BT, which is combined with helicene as a chiral inducer to induce a special chiral structure, resulting in circularly polarized light emission in a thin film. This chiral structure is only generated in a limited combination, and a more versatile method of circularly polarized light emission is desired. Meanwhile, Non-Patent Document 2 describes a device in which a chiral nematic liquid crystal is partially oriented, thereby inducing an ideal phase change and achieving circularly polarized light emission. However, this method requires the formation of an alignment film on the device, which deteriorates the electrical characteristics of the organic electroluminescence device when it is operated, so a method that does not use an alignment film is desired.

[0009] In Non-Patent Document 3, a tricarbazole-type liquid crystal compound is used as a charge transport layer of an organic electroluminescent device, and charge transport properties are improved by controlling the intermolecular orientation through the formation of a liquid crystal phase. However, this compound is not used as a host material, and does not form linear alignment or chiral nematic liquid crystals, so linearly polarized or circularly polarized light emission properties are not demonstrated. In order to impart linearly polarized or circularly polarized light emission properties using a liquid crystal compound as a host material, it is necessary to stably maintain the orientation state derived from the liquid crystal phase even after thin film formation, and a method for achieving this is desired.

[0010] Generally, there are no circularly polarized luminescent materials that can produce pure circularly polarized light; only those that produce elliptically polarized light, a mixture of right- and left-handed circularly polarized light, have been reported. The g value, which indicates the degree of polarization of left-handed circularly polarized light, is widely used as an index of the purity of circular polarization. The g value is expressed as g = 2(IL - IR) / (IL + IR), where IL is the left-handed circularly polarized light intensity and IR is the right-handed circularly polarized light intensity. The g value ranges from -2 to 2, with g = 0 indicating non-circularly polarized light and |g| = 2 indicating pure circular polarization. [Prior art documents] [Non-patent literature]

[0011] [Non-Patent Document 1] Nature Communications, 2020, 11, 6137 [Non-patent document 2] Adv. Optical. Mater., 2021, 2101674 [Non-patent document 3] Liquid Crystals, 2021, 48, 1, 63-74 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a liquid crystal material suitable for constructing a linearly polarized or circularly polarized light-emitting organic electroluminescent device. [Means for solving the problem]

[0013] Specific means for solving the above problems include the following embodiments. <1> A liquid crystal material containing two or more compounds having a structure of the following formula (1): At 25°C, either (i) or (ii) below: (i) exhibiting a nematic or chiral nematic liquid crystal phase; (ii) The liquid crystal has molecular orientation reflecting a nematic liquid crystal phase or a chiral nematic liquid crystal phase and exhibits a glassy state; Liquid crystal material that meets the above conditions. [ka] [In the formula, R 1 Ha-(CH2) n R represents a group represented by CH3, and n represents an integer of 0 or more. 2 represents a group represented by the following formula (4) or (5). [ka] [In the formula, m1 represents an integer of 2 or more and 7 or less, m2 represents an integer of 0 or more and 4 or less, and m3 represents an integer of 0 or more and 2 or less.]

[0014] <2> A liquid crystal material for an organic electroluminescence device, comprising a compound having a structure of the following formula (1): At 25°C, either (i) or (ii) below: (i) exhibiting a nematic or chiral nematic liquid crystal phase; (ii) The liquid crystal has molecular orientation reflecting a nematic liquid crystal phase or a chiral nematic liquid crystal phase and exhibits a glassy state; Liquid crystal material that meets the above conditions. [ka] [In the formula, R 1 Ha-(CH2) n R represents a group represented by CH3, and n represents an integer of 0 or more. 2 represents a group represented by the following formula (4) or (5). [ka] [In the formula, m1 represents an integer of 2 or more and 7 or less, m2 represents an integer of 0 or more and 4 or less, and m3 represents an integer of 0 or more and 2 or less.]

[0015] <3> R in the formula (1) 2 is a group represented by formula (5), <1> or <2> The liquid crystal material according to claim 1.

[0016] <4> The compound (B) not having the structure of the formula (1) is contained in an amount of 0.01 mol % or more and 50 mol % or less relative to the compound having the structure of the formula (1), At 25°C, the following (i-1) or (ii-1): (i-1) exhibits a nematic liquid crystal phase; (ii-1) It has molecular orientation reflecting the nematic liquid crystal phase and exhibits a glassy state; Meet the conditions of <1> ~ <3> 1. A liquid crystal material according to any one of claims 1 to 9.

[0017] <5> The compound (B) has a chiral structure, The compound (B) functions as a chiral dopant for nematic liquid crystal, and thereby the following (i-2) or (ii-2) is obtained at 25°C: (i-2) exhibits a chiral nematic liquid crystal phase; (ii-2) It has molecular orientation reflecting the chiral nematic liquid crystal phase and exhibits a glassy state; Meet the conditions of <4> The liquid crystal material according to claim 1.

[0018] <6> The compound (B) is a light-emitting material that exhibits fluorescent emission characteristics, phosphorescent emission characteristics, or TADF (thermally activated delayed fluorescence) emission characteristics in a wavelength region of 400 nm or more and 1200 nm or less. <4> The liquid crystal material according to claim 1.

[0019] <7> exhibiting linearly polarized or circularly polarized luminescence properties, <1> ~ <6> 1. A liquid crystal material according to any one of claims 1 to 9.

[0020] <8> <1> ~ <7> 1. A thin film comprising the liquid crystal material according to any one of claims 1 to 9, having a thickness of 10 nm to 500 nm.

[0021] <9> exhibiting linearly polarized or circularly polarized luminescence properties, <8> The thin film according to claim 1.

[0022] <10> It exhibits linearly polarized luminescence properties and has a linear dichroic ratio of 2.0 or more. <8> or <9> The thin film according to claim 1.

[0023] <11> It exhibits circularly polarized luminescence characteristics and has an absolute value of the asymmetry factor g of 0.1 or more. <8> or <9> The thin film according to claim 1.

[0024] <12> <1> ~ <7> 1. An alignment thin film comprising the liquid crystal material according to any one of claims 1 to 8, having a film thickness of 10 nm to 500 nm.

[0025] <13> formed on the surface of the coating film having liquid crystal alignment properties, <12> The oriented thin film according to claim 1.

[0026] <14> <8> ~ <11> 1. An organic electroluminescence device comprising the thin film according to any one of claims 1 to 9 as a light-emitting layer. [Effects of the Invention]

[0027] By using the liquid crystal material of the present invention in an organic electroluminescence device, it is possible to achieve both light emitting properties and linearly polarized light emission properties or circularly polarized light emission properties. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an organic electroluminescence element. DETAILED DESCRIPTION OF THE INVENTION

[0029] The liquid crystal material according to this embodiment includes a compound having a structure of the following formula (1), and exhibits the following (i) or (ii) at 25° C.: (i) exhibiting a nematic or chiral nematic liquid crystal phase; (ii) The liquid crystal has molecular orientation reflecting a nematic liquid crystal phase or a chiral nematic liquid crystal phase and exhibits a glassy state; A liquid crystal material that satisfies the above condition (ii) is one that exhibits a nematic liquid crystal phase or a chiral nematic liquid crystal phase at high temperatures and exhibits a glassy state while maintaining the orientation state when cooled.

[0030] [ka] [In the formula, R 1 Ha-(CH2) n R represents a group represented by CH3, and n represents an integer of 0 or more. 2 represents a group represented by the following formula (4) or (5).

[0031] [ka] [In the formula, m1 represents an integer of 2 or more and 7 or less, m2 represents an integer of 0 or more and 4 or less, and m3 represents an integer of 0 or more and 2 or less.]

[0032] The compound having the structure of the above formula (1) has a tricarbazole structure bonded at the 2- and 7-positions, an ether structure at the terminal, and further has R 1 and R 2The compound has an alkyl structure at the position of 1.5. Due to the tricarbazole structure and the alkyl structure of an appropriate chain length, the compound tends to exhibit a nematic liquid crystal phase both alone and in a mixture, and tends to exhibit a glassy state at room temperature (25°C). The compound also exhibits fluorescent or organic electroluminescent properties.

[0033] Examples of compounds having the structure of the above formula (1) include compounds represented by the following formulas (1-1) to (1-8).

[0034] [ka]

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] [ka]

[0041] [ka]

[0042] R in the above formula (1) 1 The alkyl chain length in the formula (1) significantly affects the phase transition temperature. When n is 5 or more and 9 or less, the compound alone having the structure of formula (1) exhibits a stable nematic liquid crystal phase and a glassy state at room temperature. By setting n to 5 or more, the crystallinity is prevented from becoming too high, and it becomes possible to exhibit a glassy state at room temperature. By setting n to 9 or less, it becomes possible to prevent the glass transition temperature from becoming too low, and it becomes possible to exhibit a glassy state at room temperature.

[0043] R in the above formula (1) 2 When m1 represents a group represented by the above formula (4), it is preferable that m1 is 2 or more and 7 or less, since the glassy state tends to exist stably. By making m1 2 or more, it is possible to increase the number of factors that inhibit the intermolecular interactions of the tricarbazole moiety, thereby preventing the promotion of crystallization and suppressing the instability of the glassy state. By making m1 7 or less, it is possible to prevent the orientation of the tricarbazole moiety in the main chain direction from increasing, and suppress the instability of the glassy state that accompanies crystallization.

[0044] R in the above formula (1) 2 When R represents a group represented by the above formula (5), if m2 is 0 or more and 4 or less and m3 is 0 or more and 2 or less, the crystallinity of the tricarbazole moiety is inhibited, and the crystallinity and glass transition temperature are reduced, so that a stable nematic liquid crystal phase and a glass state at room temperature can be exhibited. 2 may have chirality.

[0045] Among the compounds having the structure of the above formula (1), the compounds represented by the above formula (1-3), (1-7), or (1-8) are preferred because they exhibit a stable nematic liquid crystal phase and a glassy state at room temperature when used alone.

[0046] When two or more compounds having the structure of the above formula (1) are mixed, the mixing ratio can be set arbitrarily as long as the resulting mixture exhibits a nematic liquid crystal phase and a glassy state at room temperature. 1 and R 2 is not particularly limited.

[0047] When two or more compounds having the structure of formula (1) are mixed, it is preferable that the mixture contains a compound that exhibits a stable nematic liquid crystal phase and a glassy state at room temperature by itself. For example, it is preferable that the mixture contains a compound represented by formula (1-3), (1-7), or (1-8). The proportion of the compound represented by formula (1-3), (1-7), or (1-8) in the mixture is preferably 10 mol% or more, more preferably 25 mol% or more, even more preferably 35 mol% or more, and particularly preferably 45 mol% or more.

[0048] In addition, R in the above formula (1) 2 is a group represented by the above formula (4), and R 2 A mixture obtained by mixing a compound in which R in the above formula (1) is a group represented by the above formula (5) in a molar ratio that shows an appropriate phase transition temperature is preferred because it exhibits a stable nematic liquid crystal phase and a glassy state at room temperature. 2 is a group represented by the above formula (4), and R 2 The molar ratio of the compound represented by formula (5) to the compound represented by formula (5) is, for example, preferably 10:90 to 90:10, more preferably 25:75 to 75:25, even more preferably 35:65 to 65:35, and particularly preferably 45:55 to 55:45.

[0049] The liquid crystal material according to this embodiment further contains a compound (B) that does not have the structure of the above formula (1), and has the following (i-1) or (ii-1) at 25° C.: (i-1) exhibits a nematic liquid crystal phase; (ii-1) It has molecular orientation reflecting the nematic liquid crystal phase and exhibits a glassy state; The above conditions may be satisfied.

[0050] The proportion of compound (B) in the liquid crystal material is preferably 0.01 mol% to 50 mol%, more preferably 0.05 mol% to 30 mol%, and even more preferably 0.1 mol% to 10 mol%. A proportion of compound (B) of 0.01 mol% or more can affect the physical properties of the liquid crystal material. On the other hand, a proportion of compound (B) of 50 mol% or less can prevent the charge transport properties derived from the structure of formula (1) from being impaired. Furthermore, a proportion of compound (B) of 50 mol% or less can exhibit a stable nematic liquid crystal phase and a glassy state at room temperature even when compound (B) does not exhibit a liquid crystal phase.

[0051] When compound (B) is a chiral compound having a chiral structure, it acts as a chiral dopant that induces chirality in the nematic liquid crystal phase. The direction of the induced helical structure depends on the chiral configuration of the chiral compound added. That is, the liquid crystal material according to this embodiment has compound (B) having a chiral structure and functions as a chiral dopant for the nematic liquid crystal, and therefore exhibits the following (i-2) or (ii-2) at 25°C: (i-2) exhibits a chiral nematic liquid crystal phase; (ii-2) It has molecular orientation reflecting the chiral nematic liquid crystal phase and exhibits a glassy state; The above conditions may be satisfied.

[0052] The structure of the chiral compound is not particularly limited, but the use of an axially asymmetric compound having a binaphthyl structure is preferred because the desired chiral nematic liquid crystal phase can be obtained even with a small amount of addition. Examples of the chiral compound include a compound represented by the following formula (2-1) or (2-2) having a binaphthyl structure; a compound represented by the following formula (2-3) having an asymmetric center structure; and the like.

[0053] [ka]

[0054] [ka]

[0055] [ka]

[0056] The chiral nematic liquid crystal in this embodiment preferably has a helical pitch of 0.1 μm or more and 20 μm or less. A helical pitch of 20 μm or less can form a stable helical structure, preventing the inclusion of nematic liquid crystal portions. This can suppress a decrease in the asymmetry factor g value. To obtain a higher g value, the helical pitch is more preferably 10 μm or less, and even more preferably 5 μm or less. Furthermore, a helical pitch of 0.1 μm or more makes the liquid crystal more susceptible to phase changes due to the birefringence of the liquid crystal molecules, allowing it to exhibit circular polarization.

[0057] When compound (B) is a light-emitting material, light can be emitted from the light-emitting material in addition to the light emitted from the compound having the structure of formula (1). This light can be obtained as linearly polarized light or circularly polarized light depending on the orientation state of the host material.

[0058] When compound (B) is a light-emitting material, the structure of the light-emitting material is not particularly limited. However, it is preferable that the maximum emission wavelength of the light-emitting material is longer than the maximum emission wavelength of the compound having the structure of formula (1) above, since charge or energy transfer is more likely to occur. Furthermore, the emission wavelength of the light-emitting material is preferably 400 nm or more and 1200 nm or less. Visible light or near-infrared light can be obtained when the emission wavelength is within this range, making it possible to apply the liquid crystal material according to this embodiment to optical devices. Furthermore, it is preferable that the light-emitting material exhibits phosphorescence or TADF properties, since this leads to improved external quantum yield when used in an organic electroluminescence device. Examples of light-emitting materials include a compound represented by formula (3-1) below, which has fluorescent properties; and a compound represented by formula (3-2) below, which has TADF properties. TADF properties refer to the property of being thermally excited from the lowest triplet excited state (T1) to the lowest singlet excited state (S1) at room temperature. When a light-emitting material has phosphorescence or TADF properties, it can achieve highly efficient light emission by utilizing the triplet excited state when used in the light-emitting layer of an organic electroluminescence device.

[0059] [ka]

[0060] [ka]

[0061] To apply the liquid crystal material according to this embodiment to an organic electroluminescence device, a thin film must be formed. The method for forming the thin film is not limited, and spin coating, slit coating, vacuum deposition, inkjet technology, and the like can be employed. When forming the thin film, a solution of the compound or mixture used as the liquid crystal material dissolved in any organic solvent may be used. The organic solvent is not particularly limited as long as it can dissolve the compound or mixture. Examples of the organic solvent that can be used include chloroform, tetrahydrofuran, dimethylformamide, 1,4-dioxane, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, and N-methylpyrrolidone.

[0062] The thickness of the coating film after drying is preferably 10 nm to 500 nm. The thickness is more preferably 200 nm or less, and even more preferably 100 nm or less. A thickness of 500 nm or less can prevent the driving voltage of the organic electroluminescent device from increasing. Furthermore, a thickness of 10 nm or more can avoid the influence of disordered liquid crystal alignment occurring near the interface, allowing a stable liquid crystal phase to be exhibited.

[0063] In this embodiment, an annealing step is preferably performed after thin film formation to facilitate the formation of long-range order in the liquid crystal. This annealing step can significantly improve the linear dichroic ratio and g-value. Annealing at a temperature equal to or higher than the isotropic phase transition temperature is particularly preferable.

[0064] When the liquid crystal phase exhibited by the liquid crystal material is a nematic liquid crystal phase, linearly polarized light can be obtained in the wavelength region originating from the host material or the added light-emitting material by subjecting the resulting coating film to an alignment treatment. The method of alignment treatment is not particularly limited, and examples include rubbing treatment; and a method of forming a coating film on a substrate provided with an alignment film that has the property of aligning liquid crystals. Furthermore, when the liquid crystal phase exhibited by the liquid crystal material is a chiral nematic liquid crystal phase, circularly polarized light can be obtained in the wavelength region originating from the host material or the added light-emitting material.

[0065] When a glassy state is formed by a continuous glass transition from a nematic or chiral nematic liquid crystal phase without any other phase transition, the orientation state of the nematic or chiral nematic liquid crystal phase is maintained. Light emitted in this glassy state also provides linearly polarized or circularly polarized light, similar to that of a nematic or chiral nematic liquid crystal phase. However, when the orientation state derived from the nematic or chiral nematic liquid crystal phase is not maintained due to crystallization, phase transition, or the like, linearly polarized or circularly polarized light is not obtained.

[0066] By using the liquid crystal material according to this embodiment as the light-emitting layer of an organic electroluminescence device, it is possible to obtain an organic electroluminescence device that emits linearly polarized or circularly polarized light, depending on the orientation state of the liquid crystal phase. The configuration of the organic electroluminescence device is not limited, and materials commonly used for the charge transport layer, charge injection layer, hole transport layer, hole injection layer, and electrodes can be arbitrarily combined.

[0067] The present invention is not limited to the present embodiment and examples, and various modifications are possible without departing from the spirit of the present invention. [Example]

[0068] The chemical structures of the liquid crystal compounds, chiral compounds, and light-emitting materials exemplified in the Examples and Comparative Examples are shown below.

[0069] [Liquid crystal compound] [ka]

[0070] [ka]

[0071] [ka]

[0072] [ka]

[0073] [ka]

[0074] [ka]

[0075] [ka]

[0076] [ka]

[0077] [Chiral compounds] [ka]

[0078] [ka]

[0079] [ka]

[0080] [Luminescent materials] [ka]

[0081] [ka]

[0082] The glass transition temperature Tg and the nematic-isotropic phase transition temperature TN-I shown in each of the examples and comparative examples were determined by observation using a polarizing microscope equipped with a temperature-variable HP (AXIO IMAGER M1M, manufactured by Carl Zeiss) and measurement using a differential scanning calorimeter (DSC-8000, manufactured by Kitahama Seisakusho Co., Ltd.).

[0083] <Examples 1 to 14, Comparative Examples 2 to 4, 6> The liquid crystal compound, chiral compound, and luminescent material were mixed at the molar ratios shown in Tables 1 and 2, and dissolved in chloroform to a concentration of 13 mg / mL to prepare a homogeneous solution. The resulting solution was spin-coated onto an ITO-evaporated quartz glass substrate at 1000 rpm for 60 seconds using a spin coater (Opticoat MS-A150, manufactured by Mikasa Co., Ltd.). The resulting solution was then annealed on a hot plate at 130°C for 30 minutes and cooled to room temperature to prepare a sample.

[0084] <Example 5, Comparative Example 1> The samples were prepared in the same manner as above, except that the annealing temperature was set to 180°C.

[0085] <Comparative Example 5> The samples were prepared in the same manner as above, except that the annealing temperature was set to 200°C.

[0086] <Evaluation> [Evaluation of film-forming properties] The spin-coated sample was observed under a microscope, and the film-forming properties were evaluated according to the following evaluation criteria. -Evaluation criteria- ◯: Formed uniformly over the entire substrate surface. △: The particles are formed uniformly in the center of the substrate, but aggregated and non-uniform at the edges of the substrate. ×: Aggregation occurs and the surface is non-uniform.

[0087] [Evaluation of glassy state stability] The sample after spin coating was observed at room temperature (25°C), and the stability of the glass state was evaluated according to the following evaluation criteria. -Evaluation criteria- ◯: No crystalline structure is observed even after leaving the film for 24 hours or more after film formation. △: Crystal structure is not observed even after leaving the film for 24 hours after film formation, but is observed thereafter. ×: Crystal structure is observed immediately after film formation.

[0088] [Evaluation of linear dichroic ratio] The spin-coated sample was subjected to a rubbing treatment. The sample was then placed in a spectrofluorometer (FP-8550, manufactured by JASCO Corporation) equipped with a polarizing plate on the light-receiving side, with the rubbing direction of the sample parallel or perpendicular to the polarization direction of the polarizing plate. The intensity ratio of the two obtained emission spectra was taken as the linear dichroic ratio.

[0089] [G-value evaluation] The g value was calculated from the circularly polarized luminescence spectrum obtained using a circularly polarized luminescence measurement system (CPL-2000, manufactured by JASCO Corporation).

[0090] [Evaluation of electroluminescence] An evaluation cell with the configuration shown in Figure 1 was fabricated in a glove box, and organic electroluminescence (EL) emission was evaluated according to the following criteria. In the organic electroluminescence device 10 shown in Figure 1, the PEDOT / PSS layer 2 serving as the hole injection / transport layer, the BPOPB layer 4 serving as the charge transport layer, and the light-emitting layer 3 were formed by spin coating, while the ITO layer 1 serving as the anode, the CsF layer 5 serving as the charge injection layer, and the Al layer 6 serving as the cathode were formed by vapor deposition. The thicknesses of the layers were as follows: ITO layer: 150 nm, PEDOT / PSS layer: 40 nm, light-emitting layer: 60 nm, BPOPB layer: 40 nm, CsF layer: 0.5 nm, and Al layer: 250 nm. -Evaluation criteria- ◯: EL light emission is stable. △: EL luminescence is present, but the luminescence is extinguished in about 30 minutes. ×: No EL luminescence.

[0091] [Table 1]

[0092] [Table 2]

[0093] Examples 1 to 7 satisfy the requirements of the present invention, and the liquid crystal compound functions as a polarized light-emitting organic electroluminescent material. It was confirmed that the obtained device serves as a polarized light-emitting organic electroluminescent light-emitting material that achieves both linear dichroic ratio and organic electroluminescent light-emitting property. In particular, it was confirmed that, in Examples 4 to 7, the linear dichroic ratio and organic electroluminescent light-emitting property were improved by using multiple types of liquid crystal compounds to increase the stability of the glass state. Furthermore, in Examples 5 to 7, the R 2 By mixing a compound having a linear alkyl structure with a compound having a branched alkyl structure as the crystalline polymer, it was possible to achieve both a high glass transition temperature and stability in the glass state.

[0094] In Examples 8 to 11, the liquid crystal compound satisfies the requirements of the present invention, and functions as a circularly polarized light-emitting organic electroluminescent material. It was confirmed that the obtained device serves as a circularly polarized light-emitting organic electroluminescent light-emitting material that satisfies both circular dichroic ratio and organic electroluminescent light-emitting property.

[0095] Example 12 satisfies the requirements of the present invention, and is a composition in which a light-emitting material having an emission maximum wavelength longer than that of the liquid crystal compound is mixed. It was confirmed that the resulting device is a linearly polarized organic electroluminescent light-emitting material that combines linear dichroic ratio and light-emitting characteristics derived from the light-emitting material.

[0096] Examples 13 and 14 satisfy the requirements of the present invention, and are obtained by mixing a light-emitting material having a maximum emission wavelength longer than that of the liquid crystal compound into the composition. It was confirmed that the obtained device is a circularly polarized organic electroluminescent light-emitting material that combines a high g value with the light-emitting characteristics derived from the light-emitting material.

[0097] In Comparative Examples 1 to 5, films were formed from mixtures that had the structure of formula (1) but did not exhibit a glassy state at room temperature or that crystallized during thin film formation and did not exhibit a glassy state. The resulting devices did not exhibit linearly polarized or circularly polarized light emission.

[0098] Comparative Example 6 used a mixture containing 50 mol % or more of a chiral compound not having the structure of formula (1). This mixture aggregated after spin coating, making it difficult to form a uniform coating film. [Explanation of symbols]

[0099] 1 ITO layer 2 PEDOT / PSS layer 3. Light-emitting layer 4 BPOPB layer 5 CsF layer 6 Al layer 10 Organic electroluminescence element

Claims

1. A liquid crystal material containing two or more compounds having a structure of the following formula (1): At 25°C, the following (i) or (ii): (i) exhibits a nematic liquid crystal phase or a chiral nematic liquid crystal phase; (ii) It has molecular orientation reflecting a nematic liquid crystal phase or a chiral nematic liquid crystal phase and exhibits a glassy state; Liquid crystal material that meets the above conditions. 【Chemical Formula 1】 [In the formula, R １ Ha-(CH ２ ) ｎ CH ３ where n is an integer of 0 or more. ２ represents a group represented by the following formula (4) or (5): 【Chemistry 2】 [In the formula, m1 represents an integer of 2 or more and 7 or less, m2 represents an integer of 0 or more and 4 or less, and m3 represents an integer of 0 or more and 2 or less.]

2. A liquid crystal material for an organic electroluminescent device, comprising a compound having a structure of the following formula (1): At 25°C, the following (i) or (ii): (i) exhibits a nematic liquid crystal phase or a chiral nematic liquid crystal phase; (ii) It has molecular orientation reflecting a nematic liquid crystal phase or a chiral nematic liquid crystal phase and exhibits a glassy state; Liquid crystal material that meets the above conditions. 【Chemistry 3】 [In the formula, R １ Ha-(CH ２ ) ｎ CH ３ where n is an integer of 0 or more. ２ represents a group represented by the following formula (4) or (5): 【Chemistry 4】 [In the formula, m1 represents an integer of 2 or more and 7 or less, m2 represents an integer of 0 or more and 4 or less, and m3 represents an integer of 0 or more and 2 or less.]

3. R in the formula (1) ２ The liquid crystal material according to claim 1 , comprising a compound in which is a group represented by formula (5).

4. The compound (B) not having the structure of the formula (1) is contained in an amount of 0.01 mol % or more and 50 mol % or less relative to the compound having the structure of the formula (1), The following (i-1) or (ii-1) at 25°C: (i-1) exhibits a nematic liquid crystal phase; (ii-1) It has molecular orientation reflecting a nematic liquid crystal phase and exhibits a glassy state; The liquid crystal material according to claim 1 , which satisfies the condition:

5. The compound (B) has a chiral structure, The compound (B) functions as a chiral dopant for nematic liquid crystal, and thereby the following (i-2) or (ii-2) is obtained at 25° C.: (i-2) exhibits a chiral nematic liquid crystal phase; (ii-2) It has molecular orientation reflecting a chiral nematic liquid crystal phase and exhibits a glassy state; The liquid crystal material according to claim 4, which satisfies the condition:

6. The liquid crystal material according to claim 4, wherein the compound (B) is a light-emitting material that exhibits fluorescent light emission characteristics, phosphorescent light emission characteristics, or TADF (thermally activated delayed fluorescence) light emission characteristics in a wavelength region of 400 nm or more and 1200 nm or less.

7. The liquid crystal material according to claim 1 , which exhibits linearly polarized light emission properties or circularly polarized light emission properties.

8. A thin film comprising the liquid crystal material according to any one of claims 1 to 7, having a film thickness of 10 nm to 500 nm.

9. The thin film according to claim 8, which exhibits linearly polarized or circularly polarized luminescence properties.

10. The thin film according to claim 8 , which exhibits linearly polarized luminescence properties and has a linear dichroic ratio of 2.0 or more.

11. The thin film according to claim 8, which exhibits circularly polarized luminescence properties and has an asymmetry factor g of 0.1 or more in absolute value.

12. An oriented thin film comprising the liquid crystal material according to any one of claims 1 to 7, having a film thickness of 10 nm to 500 nm.

13. The alignment film according to claim 12 formed on a coating film having liquid crystal alignment properties.

14. An organic electroluminescent device comprising the thin film according to claim 8 as a light-emitting layer.

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