WO2018008673A1 - Organic electroluminescent material and organic electroluminescent element using same - Google Patents

Abstract

A compound represented by general formula (Cz)_n-Ar is excellent as a hole-blocking material. Cz denotes a 9-carbazolyl group substituted in at least 2 positions with substituent groups selected from the group consisting of fluoroalkyl groups and cyano groups, Ar denotes a triazine ring, a pyridazine ring, a pyrimidine ring or a pyrazine ring, and these rings may have substituent groups other than the 9-carbazolyl group. n is 1 or 2.

Description

Organic electroluminescent material and organic electroluminescent device using the same

The present invention relates to an organic electroluminescent material and an organic electroluminescent element using the same. In particular, the present invention relates to an excellent compound as a hole block material, a hole block material, and an organic light emitting device using the compound.

Researches for increasing the light emission efficiency of organic light emitting devices such as organic electroluminescence devices (organic EL devices) are being actively conducted. In particular, various contrivances for improving luminous efficiency have been made by newly developing and combining light-emitting materials and other functional materials constituting organic electroluminescence elements. Among them, a hole block that is contained in a layer in contact with the cathode side of the light emitting layer and prevents the holes injected into the light emitting layer and excitons (excitons) generated in the light emitting layer from diffusing outside the light emitting layer. There are also studies on materials.

For example, Patent Document 1 discloses that triplet excitation of a blue phosphorescent material generated in a light-emitting layer occurs when the layer in contact with the light-emitting layer contains an m-phenyl-pyridyl type compound such as TmPyPB represented by the following formula: It is described that the child can be prevented from moving out of the light emitting layer from the side in contact with the layer.

Further, an example in which PPT and DPEPO represented by the following formula are used for the hole block layer is also known (for example, see Patent Document 2).

JP 2013-115066 A JP 2016-036025 A

As described above, TmPyPB, PPT, and DPEPO are conventionally known as compounds that can function as a hole blocking material. However, when the present inventors used these compounds as a hole block material and combined with a blue light emitting material to produce an organic EL device, none of them could provide sufficiently satisfactory light emission efficiency or blue purity. found. In particular, it has been found that phosphine oxide type compounds are easily oxidized, and there is a risk of impairing the durability of the device when used as a hole block material.
Therefore, the present inventors have repeated research aiming to find a new compound that is excellent as a hole block material. And the general formula of the compound useful as a hole block material was derived | led-out, and the earnest examination was advanced in order to generalize the structure of the organic light emitting element with high luminous efficiency.

The inventors of the present invention need to have a hole blocking property, exciton blocking property, high electron transporting property, and stability in a compound used for the hole blocking material, and in particular, the lowest excited triplet energy level T ₁ is high. In order to achieve a sufficient exciton blocking property even for a blue light-emitting material, it is considered important that the lowest excited triplet energy level T ₁ is sufficiently high. And based on such an idea, the compound was designed combining various aromatic rings and substituents, and the examination which evaluates the exciton block property and the hole block property was performed comprehensively. As a result, it was first discovered that a compound group having a carbazolyl group substituted with an electron-withdrawing group is useful as a hole blocking material, and further investigation was made.
As mentioned above, TmPyPBm is a phenyl-pyridyl type compound. PPT and DPEPO are phosphine oxide type compounds. None of these compounds has a carbazolyl group substituted with an electron-withdrawing group. Therefore, the usefulness of a compound having a carbazolyl group substituted with an electron-withdrawing group as a hole blocking material cannot be predicted from these compounds.

As a result of diligent investigation under such circumstances, the present inventors have obtained a compound having a structure in which a 9-carbazolyl group substituted with a fluoroalkyl group or a cyano group is substituted with a specific nitrogen-containing aromatic 6-membered ring However, it has been found that the lowest excited triplet energy level T1 is remarkably high and exciton blocking property and hole blocking property are excellent. And it was clarified that an organic light emitting device with high luminous efficiency can be provided by using such a compound for the hole blocking layer. Based on these findings, the present inventors have provided the following present invention as means for solving the above problems.

[1] A compound represented by the following general formula (1).
General formula (1)
(Cz) _n -Ar
[In the general formula (1), Cz represents a 9-carbazolyl group substituted at least two positions with a substituent selected from the group consisting of a fluoroalkyl group and a cyano group, Ar represents a triazine ring, a pyridazine ring, It represents a pyrimidine ring or a pyrazine ring, and these rings may have a substituent other than the 9-carbazolyl group. n is an integer of 1 or 2. ]
[2] The substitution position in the 9-carbazolyl group of the substituent selected from the group consisting of the fluoroalkyl group and the cyano group is 2-position and 7-position, 3-position, 6-position, 2-position, The compound according to [1], which is in the 3rd, 6th and 7th positions.
[3] The compound according to [1] or [2], wherein the substitution position in the 9-carbazolyl group of the substituent selected from the group consisting of the fluoroalkyl group and the cyano group is the 3-position and the 6-position.
[4] The compound according to any one of [1] to [3], wherein the ring represented by Ar is a triazine ring or a pyrimidine ring.
[5] The compound according to any one of [1] to [4], wherein the ring represented by Ar is a triazine ring.
[6] The compound according to any one of [1] to [5], wherein the ring represented by Ar is a 1,3,5-triazine ring.
[7] The compound according to any one of [1] to [4], wherein the ring represented by Ar is a pyrimidine ring.
[8] The compound according to [7], wherein the ring represented by Ar is a pyrimidine ring and the 4-position and 6-position of the pyrimidine ring are substituted with the 9-carbazolyl group.
[9] The compound according to any one of [1] to [8], wherein n is 1.
[10] The compound according to any one of [1] to [9], wherein the ring represented by Ar has a substituent other than the 9-carbazolyl group.
[11] The compound according to [10], wherein the substituent other than the 9-carbazolyl group is a substituent selected from the group consisting of an aryl group and a fluoroalkyl group.
[12] The compound according to any one of [1] to [11], wherein the HOMO level is less than −6.1 eV.
[13] The compound according to any one of [1] to [12], wherein the lowest excited triplet energy level T ₁ is greater than 2.8 eV.
[14] A hole block material containing the compound according to any one of [1] to [13].
[15] An organic light-emitting device using the compound according to any one of [1] to [13] and a light-emitting material.
[16] The organic light emitting device according to [15], wherein the light emitting material is a blue light emitting material.
[17] The organic light-emitting device according to [15] or [16], wherein the light-emitting material is a delayed fluorescent material.
[18] The organic light-emitting device according to any one of [15] to [17], wherein the light-emitting material and the compound are contained in separate layers.
[19] The organic light-emitting device according to any one of [15] to [18], wherein the layer containing the compound is formed so as to be in contact with the cathode side of the layer containing the light-emitting material.
[20] The organic light-emitting device according to any one of [15] to [19], which is an organic electroluminescence device.

The compound of the present invention is excellent in exciton blocking property and hole blocking property and is useful as a hole blocking material. An organic light emitting device using the compound of the present invention as a hole block material can realize high luminous efficiency.

It is a schematic sectional drawing which shows the layer structural example of an organic electroluminescent element. 6 is a graph showing voltage-current density characteristics of the electronic-only devices manufactured in Example 1 and Comparative Examples 1, 2, and 3. It is a graph which shows the voltage change characteristic with time at the time of flowing an electron with the fixed current density to the electronic only element manufactured in Example 1 and Comparative Examples 1 and 2. FIG. It is an energy level diagram which shows the HOMO level and LUMO level of the compound used in Example 2 and Comparative Examples 4 and 5. It is an emission spectrum of the organic electroluminescent element manufactured in Example 2 and Comparative Examples 4 and 5. 6 is a graph showing voltage-current density-luminance characteristics of organic electroluminescence elements manufactured in Example 2 and Comparative Examples 4 and 5. 6 is a graph showing luminance-external quantum efficiency characteristics of organic electroluminescence elements manufactured in Example 2 and Comparative Examples 4 and 5. It is an energy level diagram which shows the HOMO level and LUMO level of the compound used in Example 3 and Comparative Example 6. 2 is an emission spectrum of organic electroluminescence elements manufactured in Example 3 and Comparative Example 6. 6 is a graph showing voltage-current density-luminance characteristics of organic electroluminescence elements manufactured in Example 3 and Comparative Example 6.

Hereinafter, the contents of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. In addition, the isotope species of the hydrogen atom present in the molecule of the compound used in the present invention is not particularly limited. For example, all the hydrogen atoms in the molecule may be ¹ H, or a part or all of them are ² H. (Deuterium D) may be used.

[Compound represented by general formula (1)]
The compound of the present invention has a structure in which a 9-carbazolyl group substituted with at least two substituents selected from the group consisting of a fluoroalkyl group and a cyano group is substituted with a specific nitrogen-containing aromatic 6-membered ring . Such a compound is excellent in exciton block property and hole block property, and has high utility as a hole block material. The reason why the compound of the present invention is excellent as a hole block material is not limited to any theory, but is presumed to be due to the following mechanism.
First, the “hole block material” realizes efficient light emission in the light emitting layer by suppressing the leakage (diffusion) of holes and excitons from the light emitting layer. For this reason, a compound useful as a hole blocking material is a compound having exciton blocking properties as well as hole blocking properties. Here, the HOMO level is an index for the hole block property of the compound, and the lowest excited triplet energy level T ₁ is an index for the exciton block property. That is, as the HOMO level is lower (deeper), holes from the light emitting layer are less likely to be injected into the HOMO and the hole blocking property tends to be higher, and as the lowest excited triplet energy level T ₁ is higher, the light emitting layer. It is difficult to receive exciton energy, and exciton block property tends to be high.
In view of the above, TmPyPB, which has been conventionally used as a hole block material, has a low HOMO level (−6.4 eV), but it cannot be said that the lowest excited triplet energy level T ₁ is sufficiently high. (2.78 eV). Therefore, especially when the lowest excited triplet energy level T ₁ is comprises a high blue light-emitting material emitting layer, the energy of the exciton easily receive hole blocking material is sufficiently suppress diffusion of excitons from the luminescent layer I guess it can't be done.
In contrast, in the compound of the present invention, the 9-carbazolyl group has a high lowest excited triplet energy level T ₁ , and the 9-carbazolyl group has an electron withdrawing property such as a fluoroalkyl group or a cyano group. The HOMO level is low because the group is substituted. In addition, nitrogen-containing aromatic six-membered rings such as triazine ring and pyrimidine ring contain nitrogen atoms with high electronegativity, so that the π electron density on carbon atoms is low, and it is presumed to have high electron transport properties. Since the compound of the present invention has such a partial structure, it is less susceptible to hole injection from the light emitting layer and exciton energy transfer from the light emitting layer, and exhibits excellent hole blocking properties and exciton blocking properties. In particular, it is presumed that having the 9-carbazolyl group as described above greatly contributes to the prevention of exciton diffusion of a light emitting material having a high lowest excited triplet energy level T ₁ like a blue light emitting material. From the above, the compound of the present invention is very excellent in hole blocking property and exciton blocking property, and has extremely high utility as a hole blocking material.
Furthermore, since the compound of the present invention does not have a structure vulnerable to oxidation like phosphine oxide, it has high stability and excellent electron transport properties. For this reason, it can also be widely used as a functional material of various elements.

Hereinafter, the compound of the present invention will be specifically described.
The compound of the present invention is represented by the following general formula (1).
General formula (1)
(Cz) _n -Ar
In the general formula (1), Cz represents a 9-carbazolyl group substituted at least at two positions with a substituent selected from the group consisting of a fluoroalkyl group and a cyano group. In the following description, “9-carbazolyl group substituted at least at two positions with a substituent selected from the group consisting of a fluoroalkyl group and a cyano group” may be referred to as “substituent modified 9-carbazolyl group”.
The 9-carbazolyl group may be substituted only with a fluoroalkyl group, may be substituted only with a cyano group, or may be substituted with both a fluoroalkyl group and a cyano group.
The fluoroalkyl group may be a perfluoroalkyl group in which all hydrogen atoms of the alkyl group are substituted with fluorine atoms, or a partially fluorinated alkyl in which only some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms It may be a group. The fluoroalkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, still more preferably 1 to 5 carbon atoms, and particularly preferably 1 to 3 carbon atoms. When the fluoroalkyl group has 3 or more carbon atoms, the fluoroalkyl group may be linear or branched.

The substituent selected from the group consisting of a fluoroalkyl group and a cyano group is substituted at at least 2 positions of the 9-carbazolyl group, preferably substituted at 2-6 positions, and substituted at 2-4 positions. More preferably, it is most preferably substituted at two positions. In addition, the substituent selected from the group consisting of a fluoroalkyl group and a cyano group may be substituted with the same number on both benzene rings of the carbazolyl group, or with a different number on both benzene rings of the carbazolyl group. The substituent may be bonded to only one benzene ring, and the substituent may not be substituted on the other benzene ring.
The substitution position in the carbazolyl group of the substituent selected from the group consisting of a fluoroalkyl group and a cyano group is preferably any of the 2 to 7 positions, the 2nd and 7th positions, the 3rd and 6th positions, or 2 It is more preferable that they are the 3rd, 6th and 7th positions. When the 3-position and 6-position of the 9-carbazolyl group are substituted with a cyano group, the HOMO level of the compound tends to decrease. When the 2-position and 7-position of the 9-carbazolyl group are substituted with a fluoroalkyl group, the HOMO level of the compound tends to decrease.

The 9-carbazolyl group fluoroalkyl group and the methine group not substituted with a cyano group may be substituted or unsubstituted, but are preferably unsubstituted. Examples of the substituent other than the fluoroalkyl group and the cyano group that can be substituted on the 9-carbazolyl group include an aryl group, a heteroaryl group, and an alkyl group (for example, a methyl group and a tert-butyl group).

Ar represents a triazine ring, a pyridazine ring, a pyrimidine ring or a pyrazine ring, and these rings are substituent-modified 9-carbazolyl groups (that is, at least two substituents selected from the group consisting of a fluoroalkyl group and a cyano group). It may have a substituent other than (substituted 9-carbazolyl group). Ar is preferably a triazine ring or a pyrimidine ring. The triazine ring may be any of 1,2,3-triazine ring, 1,2,4-triazine ring and 1,3,5-triazine ring, but it must be 1,3,5-triazine ring. Is most preferred.

N represents the number of substitutions of the substituent-modified 9-carbazolyl group on the ring represented by Ar, and is 1 or 2. When the ring represented by Ar is any ring, n is particularly preferably 1. A compound in which n is 1 or 2 exhibits better electron transport properties than a compound in which n is 3 or more. This is presumably because the compound in which n is 1 or 2 has a more planar structure than the compound in which n is 3 or more, and has good packing properties when deposited on a substrate to form a layer. Further, the compound in which n is 1 or 2 has a sublimation temperature lower than that of a compound in which n is 3 or more, and is excellent in solubility in various solvents, so that either vapor deposition method or coating method is used. Even film formation is possible, and it is excellent in handling. For example, in the case of a compound having a 9-carbazolyl group modified with a cyano group and n is 3 or more, thermal decomposition occurs before reaching the sublimation temperature. Therefore, the film formation by the vapor deposition method cannot be performed, and the coating film formation is limited due to poor solubility in various solvents. When n = 1 or 2, these problems hardly occur. The modified substitution position is not particularly limited, but when the ring represented by Ar is a pyrimidine ring, the substitution position of the substituent-modified 9-carbazolyl group is at least one of 4-position and 6-position, or 4-position and 6-position. Both are preferred.

The methine group not substituted with the substituent-modified 9-carbazolyl group of the ring represented by Ar may be substituted with a substituent other than the substituent-modified 9-carbazolyl group, or may be unsubstituted. A substituent other than the substituent-modified 9-carbazolyl group that may be substituted on the ring represented by Ar is not particularly limited, but is preferably an aryl group, a heteroaryl group, an alkyl group, or a cyano group. The aryl group is preferably an aryl group having 6 to 40 carbon atoms, more preferably a phenyl group or a naphthyl group. The heteroaryl group is preferably a heteroaryl group having 3 to 40 carbon atoms, more preferably a pyridyl group or a pyrimidyl group. The alkyl group is preferably an alkyl group having 1 to 20 carbon atoms, and more preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group is preferably a fluoroalkyl group in which at least a part of the hydrogen atoms are substituted with fluorine atoms. The fluoroalkyl group may be a perfluoroalkyl group in which all hydrogen atoms of the alkyl group are substituted with fluorine atoms, or a partially fluorinated alkyl in which only some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms It may be a group. Among these substituents, those that can be further substituted with a substituent may be substituted with a substituent selected from these substituent groups.

As described above, the compound of the present invention has a low HOMO level and a high lowest excited triplet energy level T ₁ is presumed to contribute to the hole blocking property and the exciton blocking property. Specifically, the HOMO level of the compound of the present invention is preferably less than −6.1 eV, and more preferably less than −6.2 eV. A compound having a HOMO level in the above range is less likely to inject holes from the light emitting layer into the HOMO, and can more effectively prevent the diffusion of holes outside the light emitting layer. On the other hand, the lowest excited triplet energy level T ₁ of the compound of the present invention is preferably larger than 2.8 eV, more preferably larger than 2.87 eV. Compounds having the lowest excited triplet energy level T ₁ in the above range are less likely to receive the energy of triplet excitons (excitons) generated in the light emitting layer, and are more effective in diffusing triplet excitons outside the light emitting layer. Can be blocked. In addition, since the compound having the lowest excited triplet energy level T ₁ in the above range also has a higher lowest excited triplet energy level S _1, it is difficult to receive energy of singlet excitons (excitons) generated in the light emitting layer. Further, it is possible to effectively prevent the diffusion of singlet excitons outside the light emitting layer.
The LUMO level of the compound of the present invention may be, for example, in the range of −2.7 eV or lower, in the range of −3.3 eV or higher, and in the range of −2.8 eV or lower, for example. , −3.2 eV or more.
Here, “HOMO level”, “LUMO level”, and “lowest excited triplet energy level T ₁ ” in this specification are measured values measured by the method described in the section of the examples. And

Specific examples of the carbazolyl group constituting the partial structure of the compound according to the present invention are shown below as Z01 to Z22, and specific examples of the compound according to the present invention having these partial structures are exemplified as Ar01 to Ar30. The compound represented by the general formula (1) that can be used in the present invention should not be construed as being limited by these specific examples. Note that * shown in the structural formulas of Z01 to Z22 represents a binding site. ZXX shown in the structural formulas of Ar01 to Ar30 represents any one of carbazolyl groups of Z01 to Z22.

The molecular weight of the compound represented by the general formula (1) is, for example, 1500 or less when the organic layer containing the compound represented by the general formula (1) is intended to be formed by vapor deposition. Preferably, it is preferably 1200 or less, more preferably 1000 or less, and even more preferably 800 or less. The lower limit of the molecular weight is usually 247 or more, preferably 290 or more. A particularly preferred combination is a combination of Z01 and A01.
The compound represented by the general formula (1) may be formed by a coating method regardless of the molecular weight.

By applying the present invention, it is also conceivable to use a compound containing a plurality of structures represented by the general formula (1) in the molecule for the hole blocking layer of the organic light emitting device.
For example, it is conceivable to use a polymer obtained by polymerizing a polymerizable monomer having a structure represented by the general formula (1) for a hole blocking layer of an organic light emitting device. Specifically, a monomer having a polymerizable functional group in either Cz or Ar in the general formula (1) is prepared, and this is polymerized alone or copolymerized with other monomers to repeat units. It is conceivable to obtain a polymer having the above and use the polymer for a hole blocking layer of an organic light emitting device. Alternatively, it is also conceivable that dimers and trimers are obtained by coupling compounds having a structure represented by the general formula (1) and used in the hole blocking layer of the organic light emitting device.

As a structural example of the repeating unit constituting the polymer including the structure represented by the general formula (1), a substituent in any one of Cz and Ar in the general formula (1) is represented by the following general formula (10) or (11). What is a structure represented by these can be mentioned.

In the general formulas (10) and (11), L ¹ and L ² each represent a linking group. The linking group preferably has 0 to 20 carbon atoms, more preferably 1 to 15 carbon atoms, and still more preferably 2 to 10 carbon atoms. And preferably has a structure represented by - linking group -X ¹¹ -L ^11. Here, X ¹¹ represents an oxygen atom or a sulfur atom, and is preferably an oxygen atom. L ¹¹ represents a linking group, and is preferably a substituted or unsubstituted alkylene group, or a substituted or unsubstituted arylene group, and is a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, or a substituted or unsubstituted group A phenylene group is more preferable.
In the general formulas (10) and (11), R ¹⁰¹ , R ¹⁰² , R ¹⁰³ and R ¹⁰⁴ each independently represent a substituent. Preferably, it is a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 6 carbon atoms, or a halogen atom, more preferably an unsubstituted alkyl group having 1 to 3 carbon atoms. An unsubstituted alkoxy group having 1 to 3 carbon atoms, a fluorine atom, and a chlorine atom, and more preferably an unsubstituted alkyl group having 1 to 3 carbon atoms and an unsubstituted alkoxy group having 1 to 3 carbon atoms.

Specific examples of the structure of the repeating unit include those in which the substituent in any one of Cz and Ar in the general formula (1) is represented by the following formulas (12) to (15). Two or more of the substituents may be represented by the following formulas (12) to (15), but it is preferable that one of the substituents is any of the following formulas (12) to (15). .

In the polymer having a repeating unit containing these formulas (12) to (15), the substituent in either Cz or Ar in the general formula (1) is made into a hydroxy group, and the following compounds are reacted using it as a linker. It can be synthesized by introducing a polymerizable group and polymerizing the polymerizable group.

The polymer containing the structure represented by the general formula (1) in the molecule may be a polymer composed only of repeating units having the structure represented by the general formula (1), or other structures may be used. It may be a polymer containing repeating units. The repeating unit having a structure represented by the general formula (1) contained in the polymer may be a single type or two or more types. Examples of the repeating unit not having the structure represented by the general formula (1) include those derived from monomers used in ordinary copolymerization. Examples thereof include a repeating unit derived from a monomer having an ethylenically unsaturated bond such as ethylene and styrene.

[Synthesis Method of Compound Represented by General Formula (1)]
The compound represented by the above general formula (1) is a novel compound.
The compound represented by the general formula (1) can be synthesized by combining known reactions. For example, Cz in the general formula (1) is a 9-carbazolyl group substituted at the 3-position and 6-position with a substituent selected from the group consisting of a fluoroalkyl group and a cyano group, and Ar is a triazine ring. A compound having a structure in which one methine group is substituted with the above 9-carbazolyl group and the remaining two methine groups are substituted with a substituent other than the above 9-carbazolyl group is represented by the following two compounds: It can be synthesized by reacting.

For the explanation of R ¹ and R ² in the above reaction formula, the explanation of “substituent selected from the group consisting of a fluoroalkyl group and a cyano group” in the general formula (1) can be referred to, R ³ , For the description of R ⁴ , reference can be made to the description of “substituents other than the substituent-modified 9-carbazolyl group” which may be substituted on the ring represented by Ar. X represents a halogen atom, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a chlorine atom, a bromine atom, and an iodine atom are preferable.
The details of the above reaction can be referred to the synthesis examples described below. The compound represented by the general formula (1) can also be synthesized by combining other known synthesis reactions.

[Organic light emitting device]
The compound represented by the general formula (1) of the present invention is excellent in hole blocking property and exciton blocking property, and in particular, a light emitting material having a high lowest excited triplet energy level T ₁ such as a blue light emitting material. Even when the light emitting layer is included, the exciton can be effectively prevented from diffusing from the light emitting layer. For this reason, the compound represented by General formula (1) of this invention is useful as a hole block material, and can be used effectively as a hole block material of an organic light emitting element. And in an organic light emitting device using such a compound as a hole blocking material, diffusion of holes injected into the light emitting layer from the light emitting layer is prevented, so that recombination of holes and electrons occurs with a high probability, Recombination energy can be generated efficiently. Further, since the exciton of the light emitting material generated by the recombination energy is effectively prevented from diffusing from the light emitting layer, the energy of the exciton can be efficiently used for light emission. From the above, by using the compound represented by the general formula (1) of the present invention as the hole block material, the light emission efficiency of the organic light emitting device can be dramatically improved.

The compound represented by the general formula (1) of the present invention may be applied to either an organic photoluminescence element (organic PL element) or an organic electroluminescence element (organic EL element), but is applicable to an organic electroluminescence element. In this case, a higher effect can be obtained.
The organic photoluminescence device to which the compound represented by the general formula (1) of the present invention is applied has a structure in which at least a light emitting layer and a layer containing the compound represented by the general formula (1) are formed on a substrate. Here, the layer containing the compound represented by the general formula (1) is disposed, for example, between the light emitting layer and the substrate and at least one side of the light emitting layer opposite to the substrate, and excitons are formed outside the light emitting layer. It functions as an exciton block layer that diffuses the element.
The organic electroluminescence element has a structure in which an organic layer is formed at least between an anode, a cathode, and an anode and a cathode. The organic layer includes at least a light emitting layer and a hole blocking layer formed so as to be in contact with the cathode side of the light emitting layer, and the hole blocking layer includes a compound represented by the general formula (1) of the present invention. . The organic layer may be composed of only the light emitting layer and the hole blocking layer, or may have one or more organic layers in addition to the light emitting layer and the hole blocking layer. Examples of such other organic layers include a hole transport layer, a hole injection layer, an electron block layer, an electron injection layer, an electron transport layer, and an exciton block layer. The hole transport layer may be a hole injection / transport layer having a hole injection function, and the electron transport layer may be an electron injection / transport layer having an electron injection function. A specific example of the structure of an organic electroluminescence element is shown in FIG. In FIG. 1, 1 is a substrate, 2 is an anode, 3 is a hole injection layer, 4 is a hole transport layer, 5 is a light emitting layer, 6 is a hole block layer, 7 is an electron transport layer, and 8 is a cathode.
Below, each member and each layer of an organic electroluminescent element are demonstrated. In addition, description of a board | substrate and a light emitting layer corresponds also to the board | substrate and light emitting layer of an organic photo-luminescence element.

(substrate)
The organic electroluminescence device of the present invention is preferably supported on a substrate. The substrate is not particularly limited and may be any substrate conventionally used for organic electroluminescence elements. For example, a substrate made of glass, transparent plastic, quartz, silicon, or the like can be used.

(anode)
As the anode in the organic electroluminescence element, an electrode material made of a metal, an alloy, an electrically conductive compound, or a mixture thereof having a high work function (4 eV or more) is preferably used. Specific examples of such electrode materials include metals such as Au, and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Alternatively, an amorphous material such as IDIXO (In ₂ O ₃ —ZnO) that can form a transparent conductive film may be used. For the anode, a thin film may be formed by vapor deposition or sputtering of these electrode materials, and a pattern of a desired shape may be formed by photolithography, or when pattern accuracy is not so high (about 100 μm or more) ), A pattern may be formed through a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. Or when using the material which can be apply | coated like an organic electroconductivity compound, wet film-forming methods, such as a printing system and a coating system, can also be used. When light emission is extracted from the anode, it is desirable that the transmittance be greater than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually selected in the range of 10 to 1000 nm, preferably 10 to 200 nm.

(cathode)
On the other hand, as the cathode, a material having a low work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O ₃ ) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among these, from the point of durability against electron injection and oxidation, a mixture of an electron injecting metal and a second metal which is a stable metal having a larger work function value than this, for example, a magnesium / silver mixture, Suitable are a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, a lithium / aluminum mixture, aluminum and the like. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. The sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm. In order to transmit the emitted light, if either one of the anode or the cathode of the organic electroluminescence element is transparent or translucent, the emission luminance is advantageously improved.
In addition, by using the conductive transparent material mentioned in the description of the anode as a cathode, a transparent or semi-transparent cathode can be produced. By applying this, an element in which both the anode and the cathode are transparent is used. Can be produced.

(Light emitting layer)
The light emitting layer is a layer that emits light after exciton is generated by recombination of holes and electrons injected from each of the anode and the cathode, and the light emitting material may be used alone for the light emitting layer, Preferably, a luminescent material and a host material are included.
The light emitting material contained in the light emitting layer may be a fluorescent light emitting material or a phosphorescent light emitting material. The light emitting material may be a delayed fluorescent material that emits delayed fluorescence together with normal fluorescence. Among these, high luminous efficiency can be obtained by using the delayed fluorescent material as the light emitting material.
In order for the organic electroluminescence device of the present invention to exhibit high luminous efficiency, it is important to confine singlet and triplet excitons generated in the light emitting material in the light emitting material. Therefore, it is preferable to use a host material in addition to the light emitting material in the light emitting layer. As the host material, an organic compound in which at least one of excited singlet energy and excited triplet energy has a value higher than that of the light-emitting material can be used. As a result, singlet and triplet excitons generated in the light-emitting material can be confined in the molecules of the light-emitting material of the present invention, and the light emission efficiency can be sufficiently extracted. However, even if the singlet state excitons and the triplet state excitons cannot be sufficiently confined, high emission efficiency may be obtained, so any host material that can achieve high emission efficiency may be used. It can use for this invention without a restriction | limiting especially. In the organic electroluminescence device of the present invention, light emission is generated from the light emitting material of the present invention contained in the light emitting layer. This light emission may be any of fluorescent light emission, delayed fluorescent light emission, and phosphorescent light emission, and these light emission may be mixed. In addition, light emission from the host material may be partly or partly emitted.
When the host material is used, the amount of the light emitting material contained in the light emitting layer is preferably 0.1% by weight or more, more preferably 1% by weight or more, and 50% by weight or less. Is preferably 20% by weight or less, more preferably 10% by weight or less.
The host material in the light-emitting layer is preferably an organic compound that has a hole transporting ability and an electron transporting ability, prevents the emission of longer wavelengths, and has a high glass transition temperature.

As described above, the light emitting material of the light emitting layer is preferably a delayed fluorescent material because high light emission efficiency can be obtained. High luminous efficiency can be obtained by the delayed fluorescent material based on the following principle.
In an organic electroluminescence element, carriers are injected into a light emitting material from both positive and negative electrodes to generate an excited light emitting material and emit light. In general, in the case of a carrier injection type organic electroluminescence element, 25% of the generated excitons are excited to an excited singlet state, and the remaining 75% are excited to an excited triplet state. Therefore, the use efficiency of energy is higher when phosphorescence, which is light emission from an excited triplet state, is used. However, since the excited triplet state has a long lifetime, energy saturation occurs due to saturation of the excited state and interaction with excitons in the excited triplet state, and in general, the quantum yield of phosphorescence is often not high. On the other hand, delayed fluorescent materials, after energy transition to an excited triplet state due to intersystem crossing, etc., are then crossed back to an excited singlet state due to triplet-triplet annihilation or absorption of thermal energy, and emit fluorescence. To do. In the organic electroluminescence device, it is considered that a thermally activated delayed fluorescent material by absorption of thermal energy is particularly useful. When a delayed fluorescent material is used for the organic electroluminescence element, the excited singlet exciton emits fluorescence as usual. On the other hand, exciton in the excited triplet state absorbs heat generated by the device and crosses the excited singlet to emit fluorescence. At this time, since the light is emitted from the excited singlet, the light is emitted at the same wavelength as the fluorescence, but the light lifetime (luminescence lifetime) generated by the reverse intersystem crossing from the excited triplet state to the excited singlet state is normal. Since the fluorescence becomes longer than the fluorescence and phosphorescence, it is observed as fluorescence delayed from these. This can be defined as delayed fluorescence. If such a heat-activated exciton transfer mechanism is used, the ratio of the compound in the excited singlet state, which normally produced only 25%, is raised to 25% or more by absorbing thermal energy after carrier injection. It becomes possible. If a compound that emits strong fluorescence and delayed fluorescence even at a low temperature of less than 100 ° C is used, the heat of the device will sufficiently cause intersystem crossing from the excited triplet state to the excited singlet state and emit delayed fluorescence. Efficiency can be improved dramatically.
In the present invention, the hole blocking layer containing the compound represented by the general formula (1) is formed so as to be in contact with the cathode side of the light emitting layer, so that the excited triplet state generated in the light emitting layer is obtained. Exciton and excited singlet state excitons are prevented from diffusing to the cathode side, and the reverse triplet state to excited singlet state crossing from the excited triplet state to the excited singlet state excitons in the light emitting layer. It occurs with high probability. For this reason, luminous efficiency can be further improved.
Hereinafter, preferred delayed fluorescent materials that can be used for the light emitting layer are listed. However, the light-emitting material that can be used in the present invention is not limited to the following delayed fluorescent material.

As delayed fluorescent materials that emit delayed fluorescence, paragraphs 0008 to 0048 and 0095 to 0133 of WO2013 / 154064, paragraphs 0007 to 0047 and 0073 to 0085 of WO2013 / 011954, and paragraphs 0007 to 0033 of WO2013 / 011955 are disclosed. And 0059 to 0066, paragraphs 0008 to 0071 and 0118 to 0133 of WO2013 / 081088, paragraphs 0009 to 0046 and 0093 to 0134 of JP2013-256490A, paragraphs 0008 to 0020 of JP2013-116975A and 0038 to 0040, paragraphs 0007 to 0032 and 0079 to 0084 of WO 2013/133359, paragraphs 0008 to 005 of WO 2013/161437 And 0101 to 0121, paragraphs 0007 to 0041 and 0060 to 0069 of JP 2014-9352 A, compounds included in the general formulas described in paragraphs 0008 to 0048 and 0067 to 0076 of JP 2014-9224 A, In particular, exemplary compounds can be mentioned preferably. These publications are hereby incorporated by reference as part of this specification.
Further, as delayed fluorescent materials that emit delayed fluorescence, JP2013-253121A, WO2013 / 133359, WO2014 / 034535, WO2014 / 115743, WO2014 / 122895, WO2014 / 126200, WO2014 / 136758, WO2014 / 133121, WO2014 / 136860, WO2014 / 196585, WO2014 / 189122, WO2014 / 168101, WO2015 / 008580, WO2014 / 203840, WO2015 / No. 002213, WO2015 / 016200, WO2015 / 019725, WO2015 / 072470, WO201 No. / 108049, WO2015 / 080182, WO2015 / 072537, WO2015 / 080183, JP2015-129240, WO2015 / 129714, WO2015 / 129715, WO2015 / 133501, WO2015 / 136880, WO2015 / 137244, WO2015 / 137202, WO2015 / 137136, WO2015 / 146541, and WO2015 / 159541, particularly exemplified compounds. Preferable examples can be given. These publications are also cited herein as part of this specification.

(Injection layer)
The injection layer is a layer provided between the electrode and the organic layer for lowering the driving voltage and improving the light emission luminance. There are a hole injection layer and an electron injection layer, and between the anode and the light emitting layer or the hole transport layer, and the cathode. Between the light emitting layer and the electron transport layer. The injection layer can be provided as necessary.

(Block layer)
The block layer is a layer that can prevent electric charges (electrons or holes) and / or excitons existing in the light emitting layer from diffusing outside the light emitting layer. The hole blocking layer can be disposed between the light emitting layer and the electron transport layer, and prevents holes from passing through the light emitting layer toward the electron transport layer. Similarly, the electron blocking layer can be disposed between the light emitting layer and the hole transport layer and prevents electrons from passing through the light emitting layer toward the hole transport layer. The blocking layer can also be used to prevent excitons from diffusing outside the emissive layer. That is, each of the electron block layer and the hole block layer can also function as an exciton block layer. The hole block layer or exciton block layer used in the present specification is used in the sense of including a layer having the functions of a hole block layer and an exciton block layer in one layer, and the electron block layer or exciton block layer is also a single layer. It is used in the meaning including a layer having a function of an electron block layer and an exciton block layer.

(Hall block layer)
The hole block layer has a function of an electron transport layer in a broad sense. The hole blocking layer has a role of blocking holes from reaching the electron transporting layer while transporting electrons, thereby improving the recombination probability of electrons and holes in the light emitting layer.

(Electronic block layer)
The electron blocking layer has a function of transporting holes in a broad sense. The electron blocking layer has a role of blocking electrons from reaching the hole transporting layer while transporting holes, thereby improving the probability of recombination of electrons and holes in the light emitting layer.

(Exciton block layer)
The exciton block layer is a layer to prevent exciton generated by recombination of holes and electrons in the light emitting layer from diffusing into the charge transport layer. It becomes possible to confine in the layer, and the luminous efficiency of the device can be improved. The exciton block layer can be inserted on either the anode side or the cathode side adjacent to the light emitting layer, or both can be inserted simultaneously. That is, when the exciton block layer is provided on the anode side, the layer can be inserted adjacent to the light emitting layer between the hole transport layer and the light emitting layer, and when inserted on the cathode side, In between, the layer can be inserted adjacent to the light emitting layer. Further, a hole injection layer, an electron blocking layer, or the like can be provided between the anode and the exciton block layer adjacent to the anode side of the light emitting layer, and the exciton block layer adjacent to the cathode and the cathode side of the light emitting layer. And an electron injection layer, an electron transport layer, a hole block layer, and the like. When the block layer is arranged, it is preferable that at least one of the excited singlet energy and the excited triplet energy of the material used as the block layer is higher than the excited singlet energy and the excited triplet energy of the light emitting material.
As described above, the hole block layer or exciton block layer referred to in this specification is used in the sense of including a layer having the functions of a hole block layer and an exciton block layer in one layer. That is, the organic electroluminescent element may have a hole block layer and an exciton block layer separately, or the hole block layer may have the function of an exciton block layer. In the former case, one or more compounds selected from the compound group represented by the general formula (1) of the present invention can be used as the material for the hole block layer and the exciton block layer. Here, the compounds used for the hole block layer and the exciton block layer are preferably different compounds. Specifically, a compound having a lower HOMO level is preferably used for the hole block layer, and a compound having a higher lowest excited triplet energy level T ₁ is preferably used for the exciton block layer. When the hole block layer and the exciton block layer are provided separately, the exciton block layer is formed so as to be in contact with the cathode side of the light emitting layer, and the hole block layer is formed on the cathode side of the exciton block layer. preferable. On the other hand, when the latter hole block layer also serves as the exciton block layer, one or more compounds selected from the compound group represented by the general formula (1) of the present invention are used as the material of the hole block layer. Can be used. Since the compound represented by the general formula (1) of the present invention is excellent in both the hole blocking property and the exciton blocking property, it is effective as a material for the hole blocking layer when the hole blocking layer also functions as the exciton blocking layer. Can be used.

(Hall transport layer)
The hole transport layer is made of a hole transport material having a function of transporting holes, and the hole transport layer can be provided as a single layer or a plurality of layers.
The hole transport material has any of hole injection or transport and electron barrier properties, and may be either organic or inorganic. Examples of known hole transport materials that can be used include triazole derivatives, oxadiazole derivatives, imidazole derivatives, carbazole derivatives, indolocarbazole derivatives, polyarylalkane derivatives, pyrazoline derivatives and pyrazolone derivatives, phenylenediamine derivatives, arylamine derivatives, amino acids Substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline-based copolymers, and conductive polymer oligomers, particularly thiophene oligomers, include porphyrin compounds, aromatics It is preferable to use a tertiary amine compound and a styrylamine compound, and it is more preferable to use an aromatic tertiary amine compound.

(Electron transport layer)
The electron transport layer is made of a material having a function of transporting electrons, and the electron transport layer can be provided as a single layer or a plurality of layers.
The electron transport material (which may also serve as a hole blocking material) may have a function of transmitting electrons injected from the cathode to the light emitting layer. Examples of the electron transport layer that can be used include nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide oxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, oxadiazole derivatives, and the like. Furthermore, in the above oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as an electron transport material. Furthermore, a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain can also be used.

When producing an organic electroluminescence device, the compound represented by the general formula (1) may be used not only for the hole block layer and the exciton block layer but also for layers other than these layers. At that time, the compound represented by the general formula (1) used for the hole block layer and the exciton block layer and the compound represented by the general formula (1) used for a layer other than these layers may be the same or different. It may be. For example, you may use the compound represented by General formula (1) as a host material of a light emitting layer, or said injection | pouring layer, an electron carrying layer, etc. The method for forming these layers is not particularly limited, and the layer may be formed by either a dry process or a wet process.

Below, the preferable material which can be used for an organic electroluminescent element is illustrated concretely. However, the material that can be used in the present invention is not limited to the following exemplary compounds. Moreover, even if it is a compound illustrated as a material which has a specific function, it can also be diverted as a material which has another function. In the structural formulas of the following exemplary compounds, R and R ₂ to R ₇ each independently represent a hydrogen atom or a substituent, and n represents an integer of 3 to 5.

First, preferred compounds that can also be used as a host material for the light emitting layer are listed. The host material may be bipolar (both holes and electrons flow well) or unipolar, and preferably has a higher T ₁ level than the light-emitting material. More preferably, it is bipolar and has a T ₁ level higher than that of the light emitting material.

Next, preferred compound examples that can be used as the hole injection material are given.

Next, preferred examples of compounds that can be used as a hole transport material are given.

Next, preferred examples of compounds that can be used as an electron blocking material are given.

Next, preferred compound examples that can be used as an electron transporting material are listed.

Next, preferred examples of compounds that can be used as an electron injection material will be given.

Further preferred compound examples are given as materials that can be added. For example, adding as a stabilizing material can be considered.

The organic electroluminescent device produced by the above-described method emits light by applying an electric field between the anode and the cathode of the obtained device. At this time, if the light is emitted by excited singlet energy, light having a wavelength corresponding to the energy level is confirmed as fluorescence emission and delayed fluorescence emission. In addition, in the case of light emission by excited triplet energy, a wavelength corresponding to the energy level is confirmed as phosphorescence. Since normal fluorescence has a shorter fluorescence lifetime than delayed fluorescence, the emission lifetime can be distinguished from fluorescence and delayed fluorescence.
On the other hand, phosphorescence is hardly observable at room temperature in ordinary organic compounds such as the compounds of the present invention because the excited triplet energy is unstable and converted to heat, etc., and has a short lifetime and immediately deactivates. In order to measure the excited triplet energy of a normal organic compound, it can be measured by observing light emission under extremely low temperature conditions.

The organic electroluminescence element of the present invention can be applied to any of a single element, an element having a structure arranged in an array, and a structure in which an anode and a cathode are arranged in an XY matrix. According to the present invention, an organic light emitting device with greatly improved luminous efficiency can be obtained by incorporating the compound represented by the general formula (1) into the hole blocking layer. The organic light emitting device such as the organic electroluminescence device of the present invention can be further applied to various uses. For example, it is possible to produce an organic electroluminescence display device using the organic electroluminescence element of the present invention. For details, see “Organic EL Display” (Ohm Co., Ltd.) written by Shizushi Tokito, Chiba Adachi and Hideyuki Murata. ) Can be referred to. In particular, the organic electroluminescence device of the present invention can be applied to organic electroluminescence illumination and backlights that are in great demand.

The features of the present invention will be described more specifically with reference to synthesis examples and examples. The following materials, processing details, processing procedures, and the like can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.
The light emission characteristics were evaluated using a source meter (Keithley: 2400 series), an absolute external quantum efficiency measurement system (Hamamatsu Photonics: C9920-12), and a spectrometer (Hamamatsu Photonics: PMA-12). I went. For measurement of the emission spectrum, a nitrogen laser (Lasertechnik Berlin, MNL200) was used as an excitation light source, and a streak camera (Hamamatsu Photonics, C4334) was used as a detector.
Moreover, the energy level and sublimation point of each material were measured by the following methods.

Regarding the HOMO level, the ionization potential of the measurement target compound was measured using a photoelectron spectrometer (manufactured by Riken Keiki Co., Ltd .: AC-3), and the value of the measured ionization potential was defined as the HOMO level. The LUMO level is estimated from the optical absorption edge of a spectrophotometer (LAMBDA950-PKA manufactured by PerkinElmer), and the band gap of the measurement target compound is estimated. Obtained by adding.

The lowest excited triplet energy level T ₁ was calculated by the following method.
A sample having a thickness of 100 nm was produced on a Si substrate by vapor-depositing the measurement target compound. The sample was cooled to 5 [K], the sample for phosphorescence measurement was irradiated with excitation light (337 nm), and the phosphorescence intensity was measured using a streak camera. By integrating the luminescence from 1 millisecond after the excitation light incidence to 10 milliseconds after the incidence, a phosphorescence spectrum having the luminescence intensity on the vertical axis and the wavelength on the horizontal axis was obtained. A tangent line was drawn with respect to the rising edge of the phosphorescence spectrum on the short wavelength side, and a wavelength value λ edge [nm] at the intersection of the tangent line and the horizontal axis was obtained. A value obtained by converting this wavelength value into an energy value by the following conversion formula was defined as T ₁ .
Conversion formula: T ₁ [eV] = 1239.85 / λedge
The tangent to the short wavelength rising edge of the phosphorescence spectrum was drawn as follows. When moving on the spectrum curve from the short wavelength side of the phosphorescence spectrum to the maximum value on the shortest wavelength side among the maximum values of the spectrum, tangents at each point on the curve are considered toward the long wavelength side. The slope of this tangent line increases as the curve rises (that is, as the vertical axis increases). The tangent drawn at the point where the value of the slope takes the maximum value was taken as the tangent to the rising edge of the phosphorescence spectrum on the short wavelength side.
In addition, the maximum point having a peak intensity of 10% or less of the maximum peak intensity of the spectrum is not included in the above-mentioned maximum value on the shortest wavelength side, and has the maximum slope value closest to the maximum value on the shortest wavelength side. The tangent drawn at the point where the value was taken was taken as the tangent to the rising edge of the phosphorescence spectrum on the short wavelength side.

As for the sublimation point, a temperature at which the weight of the compound to be measured was reduced by 5% by weight under 1 Pa was measured using a thermogravimetric measuring instrument (TG-DTA2400SA manufactured by Bruker), and the temperature was defined as the sublimation point.

Synthesis Example 1 Synthesis of Compound 1

The raw material 3,6-dicyanocarbazole was synthesized from 3,6-dibromocarbazole with reference to a known method (Macromolecules, 2014, 47, 2875-2882.). Sodium hydride (60 wt% oil, 480 mg) was placed in a 200 mL eggplant flask and purged with nitrogen. Dehydrated hexane (20 mL) was added, and the mixture was stirred at room temperature and allowed to stand, and the supernatant was removed. N-methylpyrrolidone (NMP, 100 mL) was added, and 3,6-dicyanocarbazole (2.17 g) was added with stirring at room temperature. After stirring at room temperature for 1 hour, 2-chloro-4,6-diphenyl-1,3,5-triazine (2.14 g) was added. The reaction vessel was transferred into an oil bath and stirred for 14 hours while heating to 170 ° C. After allowing to cool, water (100 mL) was added with stirring. The precipitate was collected by filtration with a Kiriyama funnel, washed successively with water and acetone, and purified by sublimation to obtain the desired product (850 mg, yield 24%).

Synthesis Example 2 Synthesis of Compound 2

The raw material 2,7-ditrifluoromethylcarbazole was synthesized with reference to a known method (Chem. Mater., 2015, 27 (5), 1772-1779.). Sodium hydride (60 wt% oil, 288 mg) was placed in a 100 mL eggplant flask and purged with nitrogen. Dehydrated hexane (20 mL) was added, and the mixture was stirred at room temperature and allowed to stand, and the supernatant was removed. N-methylpyrrolidone (NMP, 60 mL) was added, and 2,7-ditrifluoromethylcarbazole (1.82 g) was added with stirring at room temperature. After stirring at room temperature for 1 hour, 2-chloro-4,6-diphenyl-1,3,5-triazine (1.28 g) was added. The reaction vessel was transferred into an oil bath and stirred for 14 hours while heating to 170 ° C. After standing to cool, water (60 mL) was added with stirring. The precipitate was collected by filtration with a Kiriyama funnel, washed in turn with water and ethyl acetate, and purified by sublimation to obtain the desired product (987 mg, 38% yield).

Synthesis Example 3 Synthesis of Compound 3

Sodium hydride (60 wt% oil, 480 mg) was placed in a 200 mL eggplant flask and purged with nitrogen. Dehydrated hexane (20 mL) was added, and the mixture was stirred at room temperature and allowed to stand, and the supernatant was removed. Tetrahydrofuran (THF, 100 mL) was added, and 3,6-dicyanocarbazole (2.17 g) was added with stirring at room temperature. After stirring at room temperature for 1 hour, 4,6-dichloro-2-trifluoromethyl-1,3-pyrimidine (870 mg) was added. The reaction vessel was transferred into an oil bath and stirred for 9 hours while heating under reflux. After allowing to cool, water (100 mL) was added with stirring. The precipitate was collected by filtration with a Kiriyama funnel, washed successively with water and acetone, and purified by sublimation to obtain the desired product (508 mg, yield 22%).

(Synthesis Example 4) Synthesis of Compound 4

Sodium hydride (60 wt% oil, 288 mg) was placed in a 100 mL eggplant flask and purged with nitrogen. Dehydrated hexane (20 mL) was added, and the mixture was stirred at room temperature and allowed to stand, and the supernatant was removed. Tetrahydrofuran (THF, 60 mL) was added, and 2,7-ditrifluoromethylcarbazole (1.82 g) was added with stirring at room temperature. After stirring at room temperature for 1 hour, 4,6-dichloro-2-trifluoromethyl-1,3-pyrimidine (521 mg) was added. The reaction vessel was transferred into an oil bath and stirred for 20 hours while heating to 70 ° C. The reaction liquid was concentrated after standing_to_cool. The residue was washed successively with water and ethyl acetate, and purified by sublimation to obtain the desired product (325 mg, yield 18%).

Synthesis Example 5 Synthesis of Comparative Compound 1

Sodium hydride (60 wt% oil, 480 mg) was placed in a 100 mL eggplant flask and purged with nitrogen. Dehydrated hexane (20 mL) was added, and the mixture was stirred at room temperature and allowed to stand, and the supernatant was removed. N-methylpyrrolidone (NMP, 100 mL) was added, and 3,6-dicyanocarbazole (2.17 g) was added with stirring at room temperature. After stirring for 1 hour at room temperature, 2,4,6-trichloro-1,3,5-triazine (500 mg) was added. The reaction vessel was transferred into an oil bath and stirred for 14 hours while heating to 170 ° C. After standing to cool, water (300 mL) was added with stirring. The precipitate was collected by filtration with a Kiriyama funnel and washed in turn with water, chloroform, and methanol to obtain the desired product (1.5 g, yield 90%).

Synthesis Example 6 Synthesis of Comparative Compound 2

The reaction was conducted in the same manner as in Synthesis Example 5 except that 2,7-dicyanocarbazole was used as a raw material.

Table 1 shows the results of measuring the HOMO level, LUMO level, lowest excited triplet energy level T ₁ , and sublimation point of Compounds 1 to 4 and Comparative Compounds 1 and 2 synthesized in Synthesis Examples 1 to 6. Comparative compounds 1 and 2 could not be sublimated due to thermal decomposition. In addition, since it was insoluble in various solvents such as chloroform and acetone, it was difficult to form a film by both the vapor deposition method and the coating method. Therefore, the HOMO level, LUMO level, and lowest excited triplet energy level T ₁ could not be measured using a thin film.

As shown in Table 1, all of Compounds 1 to 4 had a deep HOMO level and a high lowest excited triplet energy level T ₁ .

[Production of electron-only devices and evaluation of electron transport properties]
Example 1 Production of an Electronic Only Element Using Compound 1 Each thin film was vacuum-deposited on a glass substrate on which an anode made of indium tin oxide (ITO) having a film thickness of 150 nm was formed by a vacuum deposition method. Lamination was performed at 10 ⁻⁴ to 10 ⁻⁵ Pa. First, Compound 1 is formed to a thickness of 100 nm on ITO, on which lithium fluoride (LiF) is vapor-deposited to a thickness of 0.8 nm, and then aluminum (Al) is deposited to a thickness of 100 nm. By vapor deposition, an electronic only element was obtained.

(Comparative Examples 1, 2, 3) Preparation of an electronic-only device using comparative compounds 3, 4, 5 As in Example 1, except that comparative compounds 3, 4, 5 were used instead of compound 1, electronic-only devices were used. An element was produced.

FIG. 2 shows the voltage-current density characteristics of the electron-only devices manufactured in Example 1 and Comparative Examples 1, 2, and 3. The voltage change characteristics over time when electrons are passed at a constant current density of 100 mAh / cm ² are shown in FIG. As shown in FIG. “Compound 1” shown in FIGS. 2 and 3 indicates that it is an electronic only device manufactured in Example 1, “PPT” indicates that it is an electronic only device manufactured in Comparative Example 1, and “TPBi”. Represents an electronic-only device manufactured in Comparative Example 2, and “DPEPO” represents an electronic-only device manufactured in Comparative Example 3.
From FIG. 2, the electronic-only device using Compound 1 has a lower threshold voltage at which current starts to flow and the obtained current value is higher than that of the electronic-only device using Comparative Compounds 3, 4, and 5; It can be seen that it exhibits electron transport properties. In addition, since the electron-only device using the comparative compound 4 shows a gentle increase in current (leakage current) in a low voltage region of 1 V or less, the flatness of the film of the comparative compound 4 is predicted to be low. On the other hand, since no leak current is observed in the electron-only device using Compound 1, it can be seen that the film-forming property of Compound 1 is good.
From FIG. 3, it can be seen that the voltage change during driving of the electronic-only device using the compound 1 is extremely small compared to the electronic-only device using the comparative compounds 3 and 4, and the stability of the compound 1 is very high. The electron-only device using the comparative compound 5 has low electron transport characteristics, and has not been able to pass a current of 100 mA / cm ² , and thus does not exhibit characteristics.

[Production of organic electroluminescence device and evaluation of light emission characteristics]
(Example 2) Production of organic electroluminescence device using compound 1 Each thin film was vacuum-deposited by vacuum deposition on a glass substrate on which an anode made of indium tin oxide (ITO) having a thickness of 150 nm was formed. The layers were laminated at a degree of 10 ⁻⁴ to 10 ⁻⁵ Pa. First, α-NPD was formed to a thickness of 40 nm on ITO, and mCP was formed to a thickness of 10 nm thereon. Next, 2CzPN and mCP were co-evaporated from different vapor deposition sources to form a 20 nm thick layer as a light emitting layer. At this time, the concentration of 2CzPN was 10% by weight. Next, Compound 1 was formed to a thickness of 10 nm to form a hole blocking layer, and TPBi was formed thereon to a thickness of 40 nm. Further, lithium fluoride (LiF) was vapor-deposited to a thickness of 0.8 nm, and aluminum (Al) was vapor-deposited thereon to a thickness of 100 nm to form a cathode, whereby an organic electroluminescence element was obtained.

(Comparative Examples 4 and 5) Production of Organic Electroluminescence Device Using Comparative Compounds 3 and 4 A hole blocking layer having a thickness of 10 nm using Comparative Compound 3 (PPT) or Comparative Compound 4 (TPBi) instead of Compound 1 An organic electroluminescence element was produced in the same manner as in Example 1 except that the above was formed.
The HOMO level and LUMO level of the compounds used in Example 2 and Comparative Examples 4 and 5 are shown in FIG. In FIG. 4, the numerical value above each column indicates the absolute value of the LUMO level, the numerical value below each column indicates the absolute value of the HOMO level, and the numerical values below ITO and LiF / Al are the Fermi level. Indicates an absolute value.
In addition, the emission spectrum of the organic electroluminescence device manufactured in Example 2 and Comparative Examples 4 and 5 is shown in FIG. 5, the voltage-current density-luminance characteristic is shown in FIG. 6, and the luminance-external quantum efficiency (EQE) characteristic is shown. As shown in FIG. “Compound 1” shown in FIGS. 4 to 7 represents the organic electroluminescence device produced in Example 2, and “PPT (Comparative Compound 3)” is the organic electroluminescence device produced in Comparative Example 4. “TPBi (Comparative Compound 4)” represents the organic electroluminescence device produced in Comparative Example 5.
From FIG. 5, the organic electroluminescent device using Compound 1 for the hole blocking layer has an emission wavelength on the blue wavelength side (short wavelength side) as compared with the organic electroluminescent device using Comparative Compounds 3 and 4 for the hole blocking layer. You can see that there is a shift. Moreover, in the organic electroluminescent element using the comparative compound 4, light emission derived from the comparative compound 4 is observed, whereas in the organic electroluminescent element using the compound 1, such a hole block material (compound 1) is used. The derived luminescence is not recognized. From this, it was found that by using Compound 1 as a hole blocking material, blue light emission with high purity becomes possible. The reason why the emission wavelength is shifted to the blue wavelength side is considered that the good electron transport property of Compound 1 is involved. Compound 1 is well matched with the LUMO level of the surrounding material, and has higher electron mobility than Comparative Compounds 3 and 4, and therefore has high electron injection properties into the light emitting layer. Since the recombination region of holes and electrons is away from the interface, it is considered that excitons are not easily affected by the charge and are blue-shifted.
6, the organic electroluminescence device using Compound 1 for the hole blocking layer has a higher current density and luminance rising voltage than the organic electroluminescence device using Comparative Compounds 3 and 4 for the hole blocking layer. It is clearly low, and it can be seen that a high current density and a high luminance can be obtained at a low voltage. From this, it was found that the use of Compound 1 as a hole block material improves the electron injection property.
Furthermore, it can be seen from FIG. 7 that the organic electroluminescence device using Compound 1 as the hole blocking layer has higher external quantum efficiency than the organic electroluminescence device using Comparative Compounds 3 and 4 as the hole blocking layer. I was able to confirm.

(Example 3) Production of other organic electroluminescence elements using compound 1 Each thin film was formed by vacuum deposition on a glass substrate on which an anode made of indium tin oxide (ITO) having a thickness of 150 nm was formed. And a degree of vacuum of 10 ⁻⁴ to 10 ⁻⁵ Pa. First, α-NPD was formed to a thickness of 30 nm on ITO. Next, TCTA was formed to a thickness of 20 nm, and mCBP was formed thereon to a thickness of 15 nm. Next, TCC01 and DPEPO were co-evaporated from different vapor deposition sources to form a 20 nm thick layer as a light emitting layer. At this time, the concentration of TCC01 was 15% by weight. Next, Compound 1 was formed to a thickness of 10 nm to form a hole blocking layer, and TPBi was formed thereon to a thickness of 30 nm. Furthermore, lithium fluoride (LiF) was vapor-deposited to a thickness of 0.7 nm, and aluminum (Al) was vapor-deposited thereon to a thickness of 100 nm to form a cathode, whereby an organic electroluminescence element was obtained.

(Comparative example 6) Preparation of the organic electroluminescent element using the comparative compound 5 It replaced with the compound 1 and Example 3 except having formed the 10-nm-thick hole block layer using the comparative compound 5 (DPEPO). Similarly, an organic electroluminescence element was produced.
FIG. 8 shows HOMO levels and LUMO levels of the compounds used in Example 3 and Comparative Example 6. In FIG. 8, the numerical value above each column indicates the absolute value of the LUMO level, the numerical value below each column indicates the absolute value of the HOMO level, and the numerical values below ITO and LiF / Al are the Fermi level. Indicates an absolute value.
In addition, FIG. 9 shows an emission spectrum of the organic electroluminescence elements produced in Example 3 and Comparative Example 6, and FIG. 10 shows voltage-current density-luminance characteristics. “Compound 1” shown in the figure represents the organic electroluminescence device produced in Example 3, and “DPEPO (Comparative Compound 5)” represents the organic electroluminescence device produced in Comparative Example 6. .
Similar to the tendency shown in FIGS. 5 to 7, the organic electroluminescence device using Compound 1 for the hole blocking layer has an emission wavelength that is larger than that of the organic electroluminescence device using Comparative Compound 6 for the hole blocking layer. It shifted to the blue wavelength side (short wavelength side), and a high current density and a high luminance could be obtained at a low voltage. Moreover, the external quantum efficiency was equivalent to DPEPO, and a maximum value of 18% could be realized.

The compound of the present invention is excellent in hole blocking property and exciton blocking property, and is useful as a hole blocking material. By using the compound of the present invention for the hole blocking layer of the organic light emitting device, high luminous efficiency can be realized. For this reason, this invention has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Hole block layer 7 Electron transport layer 8 Cathode

Claims (20)

1. A compound represented by the following general formula (1).
   General formula (1)
   (Cz) _n -Ar
   [In the general formula (1), Cz represents a 9-carbazolyl group substituted at least two positions with a substituent selected from the group consisting of a fluoroalkyl group and a cyano group, Ar represents a triazine ring, a pyridazine ring, It represents a pyrimidine ring or a pyrazine ring, and these rings may have a substituent other than the 9-carbazolyl group. n is an integer of 1 or 2. ]
2. The substitution position in the 9-carbazolyl group of the substituent selected from the group consisting of the fluoroalkyl group and the cyano group is 2-position and 7-position, 3-position and 6-position, 2-position and 3-position, The compound according to claim 1, which is in the 6th and 7th positions.
3. The compound according to claim 1 or 2, wherein substitution positions in the 9-carbazolyl group of the substituent selected from the group consisting of the fluoroalkyl group and the cyano group are the 3-position and the 6-position.
4. The compound according to any one of claims 1 to 3, wherein the ring represented by Ar is a triazine ring or a pyrimidine ring.
5. The compound according to any one of claims 1 to 4, wherein the ring represented by Ar is a triazine ring.
6. The compound according to any one of claims 1 to 5, wherein the ring represented by Ar is a 1,3,5-triazine ring.
7. The compound according to any one of claims 1 to 4, wherein the ring represented by Ar is a pyrimidine ring.
8. The compound according to claim 7, wherein the ring represented by Ar is a pyrimidine ring, and the 4-position and the 6-position of the pyrimidine ring are substituted with the 9-carbazolyl group.
9. The compound according to any one of claims 1 to 8, wherein n is 1.
10. The compound according to any one of claims 1 to 9, wherein the ring represented by Ar has a substituent other than the 9-carbazolyl group.
11. The compound according to claim 10, wherein the substituent other than the 9-carbazolyl group is a substituent selected from the group consisting of an aryl group and a fluoroalkyl group.
12. The compound according to any one of claims 1 to 11, wherein the HOMO level is less than -6.1 eV.
13. The compound according to any one of claims 1 to 12, wherein the lowest excited triplet energy level T ₁ is larger than 2.8 eV.
14. A hole block material containing the compound according to any one of claims 1 to 13.
15. An organic light emitting device using the compound according to any one of claims 1 to 13 and a light emitting material.
16. The organic light emitting device according to claim 15, wherein the light emitting material is a blue light emitting material.
17. The organic light emitting device according to claim 15 or 16, wherein the light emitting material is a delayed fluorescent material.
18. The organic light emitting device according to any one of claims 15 to 17, wherein the light emitting material and the compound are contained in separate layers.
19. The organic light emitting device according to any one of claims 15 to 18, wherein the layer containing the compound is formed so as to be in contact with the cathode side of the layer containing the light emitting material.
20. The organic light-emitting device according to any one of claims 15 to 19, which is an organic electroluminescence device.

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