JP7465119B2 - Organic electroluminescence device, display device, and lighting device - Google Patents

Description

The present invention relates to organic electroluminescence (hereinafter, electroluminescence (field emission) may be abbreviated as "EL") elements, display devices, and lighting devices.

Organic EL elements have the characteristics that they can be driven at a low voltage, and can be made thin, lightweight, flexible, etc. For these reasons, organic EL elements are suitably used in display devices, lighting devices, etc.
An organic EL element has a structure in which a plurality of layers, such as an electron transport layer, a light-emitting layer, and a hole transport layer, are laminated between a cathode and an anode (see, for example, Patent Document 1, Patent Document 2, and Non-Patent Document 3). Organic EL elements include those with a forward structure in which an anode is disposed between a substrate and a light-emitting layer, and those with an inverted structure in which a cathode is disposed between a substrate and a light-emitting layer. When an organic EL element with an inverted structure is used in a display device or the like, the cathode can be easily connected to a transistor or the like.

Conventionally, metal oxide electrodes such as ITO have been used as the cathode material for inverted-structure organic EL elements.
In recent years, an organic EL element with an inverted structure has been proposed in which a metal oxide film, which is stable in air and has a small work function, is formed on the cathode surface (see, for example, Non-Patent Documents 1 and 2). In this organic EL element, electrons can be efficiently injected into the organic layer. In addition, this organic EL element has high operational stability in air.

JP 2011-184430 A JP 2012-151148 A

APPLIED PHYSICS LETTERS, Volume 89, page 183510 (2006) Advanced Materials, Volume 23, page 1829 (2011) H. Cho et al., Science, vol. 350, p. 1222 (2015)

In conventional organic EL elements, the electrode material is deteriorated by the influence of moisture and oxygen in the atmosphere, which causes a problem of the formation of non-light-emitting areas. For this reason, conventional organic EL elements are strictly sealed to prevent the deterioration of the electrode material.
In addition, since an inverted-structure organic EL element has significantly higher atmospheric stability than a normal-structure organic EL element, there is less need for strict sealing. However, when a practical metal that is easily oxidized, such as Al, is used for the anode, in an unsealed environment in which no barrier film is used, deterioration of the anode/hole-injection layer interface occurs, and the hole-injection ability decreases, causing deterioration of the light-emitting surface.
Therefore, in order to popularize flexible displays, in which deterioration and destruction of the barrier film due to bending can easily occur, it is necessary to realize inverted-structure organic EL elements that have higher atmospheric stability and suppress deterioration of the anode/hole injection layer interface.
Therefore, in order to improve the stability of organic EL elements in the atmosphere, it is necessary to form an anode/hole injection layer interface capable of maintaining the hole injection property.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an organic EL element that has good storage stability in the atmosphere and suppresses deterioration of the light-emitting surface even in a state where a low level of sealing is performed.
Another object of the present invention is to provide a display device and a lighting device using the organic EL element having good storage stability in the atmosphere.

Means for Solving the Problems The present inventors have conducted extensive research to solve the above problems, and as a result have found that by doping a host material of a hole injection layer located between an emission layer and an anode with an electron-withdrawing dopant at a high concentration, it is possible to suppress deterioration of hole injection ability and to sustain light emission for a long period of time even in a state where a low level of sealing is performed, and have arrived at the present invention.
The gist of the present invention to solve the above problems is as follows.

The organic electroluminescent device of the present invention comprises, in this order, a substrate, a cathode, a light-emitting layer, a hole injection layer, and an anode.
Sealing is performed to provide a water vapor transmission rate (WVTR) of 3×10 ⁻³ g/m ² /day or more,
the hole injection layer comprises an organic host material for the hole injection layer and an electron-withdrawing dopant having a hole injection ability,
The ratio of the electron-withdrawing dopant to the total amount of the host material of the hole injection layer and the electron-withdrawing dopant is 12% by mass or more and 50% by mass or less.
The organic electroluminescence element of the present invention has good storage stability in the atmosphere and is inhibited from deteriorating in the light-emitting surface.

In a preferred embodiment of the organic electroluminescence element of the present invention, the hole injection layer and the anode are adjacent to each other,
The anode is made of a metal element alone, a transparent conductive oxide alone, or a laminate of a metal element and a transparent conductive oxide. Even in this case, the storage stability in the atmosphere is good, and deterioration of the light-emitting surface can be suppressed.

In another preferred embodiment of the organic electroluminescent element of the present invention, the ratio of the electron-withdrawing dopant is 18% by mass or more and 50% by mass or less with respect to the total amount of the hole injection layer host material and the electron-withdrawing dopant. In this case, storage stability in the atmosphere is further improved, and deterioration of the light-emitting surface can be further suppressed.

In another preferred embodiment of the organic electroluminescent element of the present invention, the electron-withdrawing dopant is a material having tetracyanoquinodimethane as a functional group. In this case, storage stability in the atmosphere is further improved, and deterioration of the light-emitting surface can be further suppressed.

The organic electroluminescent element of the present invention includes at least a first material, which is an organic material having an acid dissociation constant pKa of 1 or more, and a second material that transports electrons, and it is preferable that the first material further includes an organic thin film between the cathode and the light-emitting layer, the organic thin film being one or more selected from tertiary amines, phosphazene compounds, guanidine compounds, heterocyclic compounds containing an amidine structure, hydrocarbon compounds having a ring structure, and ketone compounds. In this case, storage stability in the atmosphere is further improved, and deterioration of the light-emitting surface can be further suppressed.

The display device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a display device of the present invention has a long shelf life and can be used stably for a long period of time.

The lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a lighting device of the present invention has a long shelf life and can be used stably for a long period of time.

According to the present invention, it is possible to provide an organic EL element which has good storage stability in the atmosphere even when sealed at a low level, and in which deterioration of the light-emitting surface is suppressed.
Moreover, according to the present invention, it is possible to provide a display device and a lighting device using such an organic EL element having good storage stability in the atmosphere.

FIG. 2 is a schematic cross-sectional view illustrating an example of an organic EL element according to the present embodiment. 1 shows images of the light-emitting surface of the organic EL element of Example 1-4 taken immediately after preparation and 2500 hours after the start of the storage life test (0 hours). In the storage life test, the organic EL element was stored under normal temperature and humidity, and was lit only when the light-emitting surface image was obtained to perform the evaluation. 13 is an image of the light-emitting surface of the organic EL element of Example 5-8 taken under the same conditions as above. 13 is an image of the light-emitting surface of the organic EL element of Example 9-10 taken under the same conditions as above. 13 is an image of the light-emitting surface of the organic EL element of Comparative Example 1-3 taken under the same conditions as above. 13 is an image of the light-emitting surface of the organic EL element of Comparative Example 4-7 taken under the same conditions as above. 13 is an image of the light-emitting surface of the organic EL element of Comparative Example 8-10 taken under the same conditions as above.

The organic electroluminescence element, display device, and lighting device of the present invention will be described in detail below with reference to their embodiments.

<Organic electroluminescence element>
The organic electroluminescent device of the present invention comprises, in this order, a substrate, a cathode, a light-emitting layer, a hole injection layer, and an anode.
Sealing is performed to provide a water vapor transmission rate (WVTR) of 3×10 ⁻³ g/m ² /day or more,
the hole injection layer comprises an organic host material for the hole injection layer and an electron-withdrawing dopant having a hole injection ability,
The ratio of the electron-withdrawing dopant to the total amount of the host material of the hole injection layer and the electron-withdrawing dopant is 12% by mass or more and 50% by mass or less.

In the organic electroluminescence device of the present invention, since the hole injection layer contains a high concentration of an electron-withdrawing dopant having hole injection ability, deterioration of the interface between the hole injection layer and the anode is suppressed, and high hole injection performance can be maintained. Therefore, the organic electroluminescence device of the present invention has good storage stability in the atmosphere, and even in a state where only low-level sealing (i.e., sealing with a water vapor transmission rate (WVTR) of 3×10 ^-3 g/m ² /day or more) is performed, the storage stability in the atmosphere is good and deterioration of the light-emitting surface can be suppressed.

Next, one embodiment of the organic electroluminescence element of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view illustrating an example of an organic EL element of this embodiment.

In the organic EL element 1 of the present embodiment shown in FIG. 1, a cathode 3, a light-emitting layer 7, a hole injection layer 9, and an anode 10 are provided in this order on a substrate 2, and a laminated structure including the light-emitting layer 7 is formed between the cathode 3 (electrode) and the anode 10 (electrode).
The organic EL element 1 of this embodiment has a laminated structure in which an inorganic electron injection layer 4, an organic electron injection layer 5, an electron transport layer 6, a light emitting layer 7, a hole transport layer 8, and a hole injection layer 9 are formed in this order. The hole injection layer 9 is disposed between the hole transport layer 8 and an anode 10. Here, the hole injection layer 9 and the hole transport layer 8 may be made of the same material and have the same composition.
The organic EL element 1 of this embodiment has an inverted structure in which a cathode 3 is disposed between a substrate 2 and a light-emitting layer 7. The organic EL element 1 shown in Fig. 1 may be a top-emission type in which light is extracted to the side opposite to the substrate 2, or a bottom-emission type in which light is extracted to the substrate 2 side.

(substrate)
Examples of the material for the substrate 2 include a resin material, a glass material, etc. The material for the substrate 2 may be one type alone or a combination of two or more types.
Examples of the resin material used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, polyamide, polyethersulfone, polymethyl methacrylate, polycarbonate, polyarylate, etc. When a resin material is used as the material for the substrate 2, it is preferable because an organic EL element 1 having excellent flexibility can be obtained.
On the other hand, examples of the glass material used for the substrate 2 include quartz glass, soda glass, and the like.

When the organic EL element 1 is of a bottom emission type, the substrate 2 is made of a transparent material.
On the other hand, when the organic EL element 1 is of a top emission type, not only a transparent substrate but also an opaque substrate may be used as the material of the substrate 2. Examples of opaque substrates include a substrate made of a ceramic material such as alumina, a substrate in which an oxide film (insulating film) is formed on the surface of a metal plate such as stainless steel, and a substrate made of a resin material.

The average thickness of the substrate 2 is not particularly limited, but is preferably 0.1 to 30 mm, and more preferably 0.1 to 10 mm. The average thickness of the substrate 2 can be measured using a digital multimeter and calipers.

(cathode)
The material of the cathode 3 is preferably an oxide _conductive material such as ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorine tin oxide), InSnZnO (indium zinc tin oxide, ITZO), _In3O3 , _SnO2 , Sb-containing _SnO2 , and Al-containing ZnO. Of these, it is particularly preferable to use ITO, IZO, or FTO as the material of the cathode 3. These conductive materials are preferable as the cathode material for a bottom emission type organic EL element.

On the other hand, in the case of a top-emission organic EL element, it is preferable to use an electrode with high reflectivity, such as an Ag alloy, for the cathode.

The average thickness of the cathode 3 is not particularly limited, but is preferably 10 to 500 nm, and more preferably 100 to 200 nm.

(Inorganic Electron Injection Layer)
The inorganic electron injection layer 4 is preferably made of, for example, an oxide of one or more elements selected from the group consisting of metal oxides having a low work function, such as zinc, tin, zirconium, silicon, germanium, titanium, and hafnium.

The average thickness of the inorganic electron injection layer 4 is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 2 to 100 nm. If the average thickness of the inorganic electron injection layer 4 is 1 nm or more, the effect of having the inorganic electron injection layer 4 can be sufficiently obtained. Furthermore, if the average thickness of the inorganic electron injection layer 4 is 1000 nm or less, the inorganic electron injection layer 4 can be formed efficiently. The average thickness of the inorganic electron injection layer 4 can be measured by a stylus step gauge or spectroscopic ellipsometry.

(Organic Electron Injection Layer)
Examples of materials for the organic electron injection layer 5 include polyacetylene compounds such as trans-polyacetylene, cis-polyacetylene, poly(di-phenylacetylene) (PDPA), and poly(alkyl, phenylacetylene) (PAPA); poly(para-phenylenevinylene) (PPV), poly(2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly(para-phenylenevinylene) (CN-PPV), and poly(2-dimethylphenylacetylene) (PDPA). polyparaphenylenevinylene compounds such as poly(2-methoxy,5-(2'-ethylhexoxy)-para-phenylenevinylene) (DMOS-PPV) and poly(2-methoxy,5-(2'-ethylhexoxy)-para-phenylenevinylene) (MEH-PPV); polythiophene compounds such as poly(3-alkylthiophene) (PAT) and poly(oxypropylene)triol (POPT); poly(9,9-dialkylfluorene compounds such as poly(9,9-dioctylfluorene); ) (PDAF), poly(dioctylfluorene-alt-benzothiadiazole) (F8BT), α,ω-bis[N,N'-di(methylphenyl)aminophenyl]-poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6am4), poly(9,9-dioctyl-2,7-divinylenefluorenyl-ortho-co(anthracene-9,10-diyl), and other polyfluorene-based compounds; poly(para-phenylene) ( Examples of such compounds include polyparaphenylene compounds such as poly(1,5-dialkoxy-para-phenylene) (RO-PPP) and polyparaphenylene compounds such as poly(N-vinylcarbazole) (PVK); and polysilane compounds such as poly(methylphenylsilane) (PMPS), poly(naphthylphenylsilane) (PNPS), and poly(biphenylylphenylsilane) (PBPS). These compounds may be used alone or in combination of two or more.

The average thickness of the organic electron injection layer 5 is not particularly limited, but is preferably 5 to 100 nm, and more preferably 10 to 60 nm. The average thickness of the organic electron injection layer 5 can be measured by a stylus step gauge or spectroscopic ellipsometry. Alternatively, it can be measured during deposition using a quartz crystal thickness gauge.

As the organic electron injection layer 5, an organic thin film is preferred that contains at least a first material, which is an organic material having an acid dissociation constant pKa of 1 or more, and a second material that transports electrons, and the first material is one or more selected from tertiary amines, phosphazene compounds, guanidine compounds, heterocyclic compounds containing an amidine structure, hydrocarbon compounds having a ring structure, and ketone compounds. In this embodiment, the organic thin film constitutes the organic electron injection layer 5, but in other embodiments, the organic thin film may be located anywhere between the cathode and the light-emitting layer.

The first material is an organic material having a pKa of 1 or more, and therefore has the ability to extract protons (H ⁺ ) from the second material. The first material preferably has a pKa of 5 or more, more preferably 11 or more. The higher the pKa of the first material, the higher the ability of the first material to extract protons from the second material. As a result, when the organic thin film is used as the organic electron injection layer 5, excellent electron injection properties are obtained. In addition, the first material is suitably coordinated to the defective portion of the inorganic compound, and therefore has the effect of preventing reactions at the interface with oxygen or water entering from the outside, thereby enhancing the atmospheric stability of the element.
The above-mentioned "pKa" usually means "acid dissociation constant in water", but if it cannot be measured in water, it means "acid dissociation constant in dimethyl sulfoxide (DMSO)", and if it cannot be measured even in DMSO, it means "acid dissociation constant in acetonitrile". Preferably, it means "acid dissociation constant in water".

The tertiary amine (tertiary amine derivative) used in the first material may be a chain or cyclic amine compound, and if cyclic, may be a heterocyclic amine compound, or may be a heterocyclic amine compound such as an aliphatic amine or aromatic amine. The tertiary amine preferably has 1 to 4 amino groups, and more preferably has 1 or 2. The amine compound may be a compound having an alkyl group, an alkylamino group, or an alkoxy group. Specific examples include (mono-, di-, tri-) alkylamines; aromatic amines having 1 to 3 alkylamino groups; and aromatic amines having 1 to 3 alkoxy groups.

The tertiary amine is preferably one that does not contain a primary amine or a secondary amine.Specific examples of the tertiary amine include dialkylaminopyridines such as dimethylaminopyridine (DMAP) represented by the following structural formula (1-1) or (1-2), amines having a structure represented by NR ¹ R ² R ³ such as triethylamine represented by the following structural formula (1-3) (wherein R ¹ , R ² , and R ³ are the same or different and each represents a hydrocarbon group which may have a substituent), and acridine orange (AOB) represented by the following structural formula (1-4).

The hydrocarbon group preferably has 1 to 30 carbon atoms, more preferably 1 to 8 carbon atoms, even more preferably 1 to 4 carbon atoms, and even more preferably 1 or 2 carbon atoms. When the hydrocarbon group has a substituent, it is preferable that the total number of carbon atoms including the substituent is the above number. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, and an alkynyl group, and an alkyl group is preferable. Examples of the substituent in the substituted hydrocarbon group include a halogen atom, a heterocyclic group, a cyano group, a hydroxyl group, an alkoxy group, an aryloxy group, and an amino group. As for dimethylaminopyridine, it is preferable that the position at which the dimethylamino group, which is an electron donating group, is bonded to the pyridine ring is the 2-position (2-DMAP) or the 4-position (4-DMAP). In particular, 4-dimethylaminopyridine, in which a dimethylamino group is bonded to the 4-position of the pyridine ring, is preferable because it has a high pKa and, moreover, when an organic thin film containing this is used as the organic electron injection layer 5 of an organic EL element, a long life can be obtained.

As the tertiary amine, an alkoxypyridine derivative such as a methoxypyridine derivative can also be used. As the alkoxy group, an alkoxy group having 1 to 30 carbon atoms is preferable, an alkoxy group having 1 to 8 carbon atoms is more preferable, an alkoxy group having 1 to 4 carbon atoms is even more preferable, and an alkoxy group having 1 or 2 carbon atoms is even more preferable. The alkoxypyridine derivative also includes a compound having a structure in which one or more hydrogen atoms of an alkoxypyridine are substituted with a substituent. Examples of the substituent include the same as those of the substituent of the hydrocarbon group of the above-mentioned tertiary amine.
The methoxypyridine derivative is preferably 4-methoxypyridine (4-MeOP) represented by the following structural formula (2-1) in which the methoxy group is bonded to the pyridine ring at position 4, or 3-methoxypyridine (3-MeOP) represented by the following structural formula (2-2) in which the methoxy group is bonded to position 3. In particular, 4-methoxypyridine in which a methoxy group is bonded to position 4 of the pyridine ring is preferred because of its high pKa.

As the tertiary amine, it is preferable to use one or more selected from heterocyclic aromatic amines having a dialkylamino group and/or an alkoxy group, and trialkylamines. From the viewpoint of improving electron injection properties and life, it is particularly preferable to use one or more selected from dialkylaminopyridines, trialkylamines, and alkoxypyridine derivatives.

In the heterocyclic compound containing an amidine structure, the amidine structure is ^a structure represented by ^R4 -C(= ^NR5 ) ^-NR6R7 (wherein ^R4 to ^R7 are the same or different and represent a hydrogen atom or a hydrocarbon group.) Examples of the heterocyclic compound containing an amidine structure include diazabicyclononene derivatives and diazabicycloundecene derivatives.

The diazabicyclononene derivatives include 1,5-diazabicyclo[4.3.0]nonene-5 (DBN, also called "diazabicyclononene") represented by the following structural formula (3-1). DBN is preferable because it provides a long life when an organic thin film containing DBN is used as the organic electron injection layer 5 of an organic EL element.
The diazabicycloundecene derivatives include 1,8-diazabicyclo[5.4.0]undecene-7 (DBU) represented by the following structural formula (3-2).

The diazabicyclononene derivatives include compounds in which one or more of the hydrogen atoms of diazabicyclononene are substituted with a substituent, and the diazabicycloundecene derivatives include compounds in which one or more of the hydrogen atoms of diazabicycloundecene are substituted with a substituent. Examples of the substituent include the same ones as those of the hydrocarbon group of the tertiary amine described above.

The phosphazene compound (phosphazene base derivative) is, for example, a compound containing a structure represented by the following general formula (4).

In the above formula (4), R ⁸ represents a hydrogen atom or a hydrocarbon group, and R ⁹ to R ¹¹ represent a hydrogen atom, a hydrocarbon group, -NR'R" (wherein R' and R" each independently represent a hydrogen atom or a hydrocarbon group), or a group represented by the following formula (5), and n represents a number from 1 to 5.

In the above formula (5), R ¹² to R ¹⁴ represent a hydrogen atom, a hydrocarbon group, or --NR'R" (wherein R' and R" each independently represent a hydrogen atom or a hydrocarbon group), and m represents a number from 1 to 5.

The hydrocarbon group in the above formulas (4) and (5) is preferably a group having 1 to 8 carbon atoms, more preferably a group having 1 to 4 carbon atoms. Moreover, the hydrocarbon group is preferably an alkyl group. The above R ¹¹ is particularly preferably a tertiary butyl group.

The phosphazene base derivative includes a compound represented by the following structural formula (6).

The guanidine compound is a compound containing a structure represented by the following general formula (7).

In the above formula (7), R ¹⁵ to R ¹⁹ are the same or different and represent a hydrogen atom or a hydrocarbon group, and two or more of R ¹⁵ to R ¹⁹ may be bonded to form a cyclic structure.

The guanidine compound may be a guanidine cyclic derivative, etc. Examples of the guanidine cyclic derivative include 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) represented by the following formula (8-1) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) represented by the following formula (8-2).

The hydrocarbon compound having a ring structure is preferably a compound having a 5-membered or 6-membered ring as a ring structure, and is also preferably a compound having a ring structure in which a 5-membered ring and a 6-membered ring are condensed, or a ring structure in which multiple 6-membered rings are condensed. Examples of the 5-membered ring include a cyclopentane ring and a cyclopentadiene ring, and examples of the 6-membered ring include a benzene ring.
Preferred examples of hydrocarbon compounds having a ring structure include compounds having only a ring structure, compounds having a structure in which an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10, and more preferably 1 to 5 carbon atoms, is bonded to a ring structure, and compounds having a structure in which multiple ring structures are bonded directly or via a hydrocarbon linking group having 1 to 20 carbon atoms, preferably 1 to 10, and more preferably 1 to 5 carbon atoms. Specific examples of hydrocarbon compounds having a ring structure include compounds of the following formulas (9-1) to (9-14). In the formulas, Ph represents a phenyl group.

The ketone compound is preferably a ketone having 2 to 30 carbon atoms, and may have a cyclic structure. Specific examples include methyl ethyl ketone (MEK), acetone, diethyl ketone, methyl isobutyl ketone (MIBK), methyl isopropyl ketone (MIPK), diisobutyl ketone (DIBK), 3,5,5-trimethylcyclohexanone, diacetone alcohol, cyclopentanone, cyclohexanone, etc.

で示される化合物のようなホスフィンオキサイド誘導体、トリス－１，３，５－（３’－（ピリジン－３”－イル）フェニル）ベンゼン（ＴｍＰｈＰｙＢ）のようなピリジン誘導体、（２－（３－（９－カルバゾリル）フェニル）キノリン（ｍＣＱ））のようなキノリン誘導体、２－フェニル－４，６－ビス（３，５－ジピリジルフェニル）ピリミジン（ＢＰｙＰＰＭ）のようなピリミジン誘導体、ピラジン誘導体、バソフェナントロリン（ＢＰｈｅｎ）のようなフェナントロリン誘導体、２，４－ビス（４－ビフェニル）－６－（４’－（２－ピリジニル）－４－ビフェニル）－［１，３，５］トリアジン（ＭＰＴ）のようなトリアジン誘導体、３－フェニル－４－（１’－ナフチル）－５－フェニル－１，２，４－トリアゾール（ＴＡＺ）のようなトリアゾール誘導体、オキサゾール誘導体、２－（４－ビフェニリル）－５－（４－ｔｅｒｔ－ブチルフェニル－１，３，４－オキサジアゾール）（ＰＢＤ）のようなオキサジアゾール誘導体、２，２’，２”－（１，３，５－ベントリイル）－トリス（１－フェニル－１－Ｈ－ベンズイミダゾール）（ＴＰＢＩ）のようなイミダゾール誘導体、ナフタレン、ペリレン等の芳香環テトラカルボン酸無水物、ビス［２－（２－ヒドロキシフェニル）ベンゾチアゾラト］亜鉛（Ｚｎ（ＢＴＺ）２）、トリス（８－ヒドロキシキノリナト）アルミニウム（Ａｌｑ₃）などに代表される各種金属錯体、２，５－ビス（６’－（２’，２”－ビピリジル））－１，１－ジメチル－３，４－ジフェニルシロール（ＰｙＰｙＳＰｙＰｙ）等のシロール誘導体に代表される有機シラン誘導体、更には、後述するホウ素含有化合物等が挙げられ、これらの１種又は２種以上を用いることができる。
これらの第２材料の中でも、ＰＯＰｙ₂、構造式（１０）で示される化合物等のホスフィンオキサイド誘導体、ホウ素含有化合物、Ａｌｑ₃等の金属錯体、ＴｍＰｈＰｙＢ等のピリジン誘導体を用いることがより好ましい。 The second material may be any material capable of transporting electrons, and is preferably an organic material. More preferably, the second material is an organic material having a lowest unoccupied molecular orbital (LUMO) level of 2.0 eV to 4.0 eV, and among these, an n-type organic semiconductor material having a LUMO level of 2.5 eV to 3.5 eV. For example, any of the conventionally known materials shown below may be used as the material for the electron transport layer of the organic EL element, and among these, a material that satisfies the above LUMO level requirement is preferred.
Specifically, the second material is phenyl-dipyrenylphosphine oxide (POPy ₂ ), which is represented by the following structural formula (10):

pyridine derivatives such as tris-1,3,5-(3'-(pyridin-3"-yl)phenyl)benzene (TmPhPyB); quinoline derivatives such as (2-(3-(9-carbazolyl)phenyl)quinoline (mCQ)); pyrimidine derivatives such as 2-phenyl-4,6-bis(3,5-dipyridylphenyl)pyrimidine (BPyPPM); pyrazine derivatives; phenanthroline derivatives such as bathophenanthroline (BPhen); triazine derivatives such as 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3,5]triazine (MPT); triazole derivatives such as phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole (TAZ), oxazole derivatives, oxadiazole derivatives such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole) (PBD), imidazole derivatives such as 2,2',2"-(1,3,5-benzotriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI), aromatic ring tetracarboxylic anhydrides such as naphthalene and perylene, bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (Zn(BTZ)2), tris(8-hydroxyquinolinato)aluminum (Alq ₃ ), organic silane derivatives such as silole derivatives such as 2,5-bis(6'-(2',2"-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy), and further boron-containing compounds described below. These may be used alone or in combination.
Among these second materials, it is more preferable to use POPy ₂ , phosphine oxide derivatives such as the compound represented by structural formula (10), boron-containing compounds, metal complexes such as Alq ₃ , and pyridine derivatives such as TmPhPyB.

An example of the boron-containing compound used in the second material is a boron-containing compound represented by the following general formula (11).

In the general formula (11), the dotted arc represents a ring structure formed together with the solid line skeleton portion. The dotted portion in the solid line skeleton portion represents that a pair of atoms connected by the dotted line may be connected by a double bond. The arrow from the nitrogen atom to the boron atom represents that the nitrogen atom is coordinated to the boron atom. Q ¹ and Q ² are the same or different and are linking groups in the solid line skeleton portion, at least a part of which forms a ring structure together with the dotted arc portion and may have a substituent. X ¹ , X ² , X ³ and X ⁴ are the same or different and represent a hydrogen atom or a monovalent substituent that becomes a substituent of the ring structure, and a plurality of them may be bonded to the ring structure forming the dotted arc portion. ^{n 1} represents an integer of 2 to 10. ^Y1 is a direct bond or an ⁿ¹ -valent linking group, and is bonded to each of the ⁿ¹ structural moieties other than ^Y1 at any one of the ring structures forming the dotted arc portion, ^Q1 , ^Q2 , ^X1 , ^X2 , ^X3 , and ^X4 , independently.

In the above general formula (11), the dotted arc represents that a ring structure is formed together with the skeletal portion represented by the solid line, i.e., a part of the skeletal portion connecting the boron atom, ^Q1 , and the nitrogen atom, or a part of the skeletal portion connecting the boron atom and ^Q2 . This represents that the compound represented by the above general formula (11) has at least four ring structures in the structure, and in the above general formula (11), the skeletal portion connecting the boron atom, ^Q1 , and the nitrogen atom and the skeletal portion connecting the boron atom and ^Q2 are included as parts of the ring structure. Note that it is preferable that the ring structure to which ^X1 is bonded is one in which the ring structure skeleton does not contain atoms other than carbon atoms and is composed of carbon atoms.
In the above general formula (11), the dotted lines in the skeletal moieties represented by solid lines, i.e., the skeletal moieties connecting the boron atom, ^Q1 , and the nitrogen atom and the skeletal moieties connecting the boron atom and ^Q2 , indicate that a pair of atoms connected by the dotted line in each skeletal moiety may be connected by a double bond.

In the above general formula (11), the arrow from the nitrogen atom to the boron atom indicates that the nitrogen atom is coordinated to the boron atom. Here, "coordinated" means that the nitrogen atom acts on the boron atom in the same way as a ligand and chemically influences it, and may or may not form a coordinate bond (covalent bond). Preferably, it is a coordinate bond.

In the above general formula (11), ^Q1 and ^Q2 are the same or different and are linking groups in the skeleton portion represented by the solid line, at least a part of which forms a ring structure together with the arc portion of the dotted line, and may have a substituent. This means that ^Q1 and ^Q2 are each incorporated as a part of the ring structure.

In the above general formula (11), X ¹ , X ² , X ³ and X ⁴ are the same or different and represent a hydrogen atom or a monovalent substituent that is a substituent of a ring structure, and may be bonded to a ring structure forming a dotted arc portion in a plurality of units. That is, when X ¹ , X ² , X ³ and X ⁴ are hydrogen atoms, the four ring structures having X ¹ , X ² , X ³ and X ⁴ in the structure of the compound represented by the above general formula (11) do not have a substituent, and when any or all of X ¹ , X ² , X ³ and X ⁴ are monovalent substituents, any or all of the four ring structures have a substituent. In that case, the number of substituents that one ring structure has may be one or may be two or more.
Here, the term "substituent" refers to groups including organic groups containing carbon and groups not containing carbon such as halogen atoms and hydroxyl groups.

In the above general formula (11), ⁿ¹ represents an integer of 2 to 10, and ^Y1 is a direct bond or an ⁿ¹ -valent linking group. That is, in the compound represented by the above general formula (11), ^Y1 is a direct bond, and the two structural moieties other than ^Y1 are each independently bonded to each other at one of the ring structures forming the dotted arc portion, ^Q1 , ^Q2 , ^X1 , ^X2 , ^X3 , and ^X4 , or ^Y1 is an ⁿ¹ -valent linking group, and there are a plurality of structural moieties other than ^Y1 in the above general formula (11), and they are bonded via ^Y1 , which is a linking group.

In the above general formula (11), when Y ¹ is a direct bond, the above general formula (11) represents that one of the ring structures Q ¹ , Q ² , X ¹ , X ² , X ³ , and X ⁴ forming the dotted arc portion of one of the two structural parts other than Y ¹ is directly bonded to one of the ring structures Q ¹ , Q ² , X ¹ , X ² , X ³ , and X ⁴ forming the dotted arc portion of the other. The bonding position is not particularly limited, but it is preferable ^{that the ring to which one of the structural parts other than Y 1 is bonded or the ring to which X 2 is bonded is directly bonded to the ring to which the other X 1 is bonded or the ring to which X 2 is bonded . More} preferably, the ring to which one of the structural parts other than Y ¹ is bonded and the ring to which the other ^{X 2 is} bonded are directly bonded. In this case, the structures of the structural moieties other than the two Y ^1s may be the same or different.

In the above general formula (11), ^Y1 is a linking group having a valence of ⁿ¹ , and when a plurality of structural moieties other than ^Y1 in the above general formula (11) are present and are bonded via the linking group ^Y1 , this is preferred because it is more resistant to oxidation and has improved film formability than a structure in which the structural moieties other than ^Y1 are directly bonded.

In addition, when ^Y1 is a ⁿ¹ -valent linking group, ^Y1 is bonded to each of the ⁿ¹ structural moieties other than ^Y1 at one of the ring structures forming the arc portion of the dotted line, ^Q1 , ^Q2 , ^X1 , ^X2 , ^X3 , and ^X4 , independently. This means that the structural moiety other than ^Y1 is bonded to ^Y1 at one of the ring structures forming the arc portion of the dotted line, ^Q1 , ^Q2 , ^X1 , ^X2 , ^X3 , and ^X4 , and the bonding sites of the structural moieties other than ^Y1 to ^Y1 are independent of each of the ⁿ¹ structural moieties other than ^Y1 , and may all be the same site, some may be the same site, or all may be different sites.
The bonding position is not particularly limited, but it is preferable that all of the ⁿ¹ structural moieties other than ^Y1 are bonded to Y1 at the ring to which ^X1 is bonded or the ring to which ^X2 is bonded. It is more preferable that all of the ⁿ¹ structural moieties other than ^Y1 are bonded ^{to Y1} at the ring to which ^X2 is bonded.
Furthermore, the structures of the structural portions other than ^Y1 , which are present in an amount of ⁿ¹ , may all be the same, some may be the same, or all may be different.

When Y ¹ in the above general formula (11) is a linking group having a valence of n ¹ , the linking group may be, for example, a chain-like, branched or cyclic hydrocarbon group which may have a substituent, a group containing a hetero element which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent. Among these, a group having an aromatic ring, such as an aryl group which may have a substituent or a heterocyclic group which may have a substituent, is preferable. That is, Y ¹ in the above general formula (11) being a group having an aromatic ring is also one of the preferred embodiments of the present invention.
Furthermore, Y ¹ may be a linking group having a structure in which a plurality of the above-mentioned linking groups are combined.

The linear, branched or cyclic hydrocarbon group is preferably a group represented by any one of the following formulae (12-1) to (12-8). Among these, the following formulae (12-1) and (12-7) are more preferred.
The group containing a hetero element is preferably a group represented by any one of the following formulae (12-9) to (12-13). Among these, the following formulae (12-12) and (12-13) are more preferable.
The aryl group is preferably a group represented by any one of the following formulae (12-14) to (12-20). Among these, the following formulae (12-14) and (12-20) are more preferable.
The heterocyclic group is preferably a group represented by any one of the following formulae (12-21) to (12-33). Among these, the following formulae (12-23) and (12-24) are more preferable.

Examples of the substituents possessed by the above-mentioned linear, branched or cyclic hydrocarbon groups, groups containing a hetero element, aryl groups and heterocyclic groups include halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms and iodine atoms; haloalkyl groups such as fluoromethyl groups, difluoromethyl groups and trifluoromethyl groups; linear or branched alkyl groups having 1 to 20 carbon atoms such as methyl groups, ethyl groups, propyl groups, isopropyl groups, butyl groups, isobutyl groups and tert-butyl groups; cyclic alkyl groups having 5 to 7 carbon atoms such as cyclopentyl groups, cyclohexyl groups and cycloheptyl groups; linear or branched alkoxy groups having 1 to 20 carbon atoms such as methoxy groups, ethoxy groups, propoxy groups, isopropoxy groups, butoxy groups, isobutoxy groups, tert-butoxy groups, pentyloxy groups, hexyloxy groups, heptyloxy groups and octyloxy groups; a nitro group; a cyano group; a methylamino group, an ethylamino group, a dimethylamino group, a diene group, acyl groups such as acetyl, propionyl and butyryl groups; alkenyl groups having 2 to 30 carbon atoms such as vinyl, 1-propenyl, allyl and styryl groups; alkynyl groups having 2 to 30 carbon atoms such as ethynyl, 1-propynyl and propargyl groups; aryl groups which may be substituted with a halogen atom, an alkyl group, an alkoxy group, an alkenyl group, an alkynyl group or the like; heterocyclic groups which may be substituted with a halogen atom, an alkyl group, an alkoxy group, an alkenyl group or an alkynyl group; N,N-dialkylcarbamoyl groups such as N,N-dimethylcarbamoyl and N,N-diethylcarbamoyl groups; dioxaborolanyl groups, stannyl groups, silyl groups, ester groups, formyl groups, thioether groups, epoxy groups, isocyanate groups and the like. These groups may be substituted with a halogen atom, a hetero element, an alkyl group, an aromatic ring, or the like.
Among these, the substituent of the chain, branched or cyclic hydrocarbon group, group containing a hetero element, aryl group or heterocyclic group in ^Y1 is preferably a halogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, a linear or branched alkoxy group having 1 to 20 carbon atoms, an aryl group, a heterocyclic group or a diarylamino group, more preferably an alkyl group, an aryl group, an alkoxy group or a diarylamino group.
When the linear, branched or cyclic hydrocarbon group, group containing a hetero element, aryl group or heterocyclic group in Y ¹ has a substituent, the position or number to which the substituent is bonded is not particularly limited.

In the above general formula (11), ⁿ¹ represents an integer of 2 to 10, and is preferably an integer of 2 to 6. More preferably, n1 is an integer of 2 to 5, and even more preferably, an integer of 2 to 4, and from the viewpoint of solubility in a solvent, particularly preferably, n1 is 2 or 3. Most preferably, n1 is 2. In other words, it is most preferable that the boron-containing compound represented by the above general formula (11) is a dimer.

Q ¹ and Q ² in the above general formula (11) include structures represented by the following formulas (13-1) to (13-8):

In addition, the above formula (13-2) is a structure in which two hydrogen atoms are bonded to a carbon atom, and three more atoms are bonded to the carbon atom, but the three atoms bonded to the carbon atom other than the hydrogen atoms are all atoms other than hydrogen atoms. Among the above formulas (13-1) to (13-8), any of (13-1), (13-7), and (13-8) is preferable. More preferably, it is (13-1). That is, a case in which Q ¹ and Q ² are the same or different and represent a linking group having one carbon atom is also one of the preferred embodiments of the present invention.

In the above general formula (11), the ring structure formed by the dotted arc and a part of the skeletal portion represented by the solid line is not particularly limited as long as the skeleton of the ring structure to which ^X1 is bonded is composed of carbon atoms.

In the above general formula (11), when Y ¹ is a direct bond and n ¹ is 2, examples of the ring to which X ¹ is bonded include a benzene ring, a naphthalene ring, an anthracene ring, a tetracene ring, a pentacene ring, a triphenylene ring, a pyrene ring, a fluorene ring, an indene ring, a thiophene ring, a furan ring, a pyrrole ring, a benzothiophene ring, a benzofuran ring, an indole ring, a dibenzothiophene ring, a dibenzofuran ring, a carbazole ring, a thiazole ring, a benzothiazole ring, an oxazole ring, a benzoxazole ring, an imidazole ring, a pyrazole ring, a benzimidazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a pyridazine ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, a benzothiadiazole ring, a phenanthridine ring, an oxadiazole ring, and a thiadiazole ring, which are respectively represented by the following formulas (14-1) to (14-36).

Among these, those in which the ring structure skeleton consists only of carbon atoms are preferred, and benzene ring, naphthalene ring, anthracene ring, tetracene ring, pentacene ring, triphenylene ring, pyrene ring, fluorene ring, and indene ring are preferred. Benzene ring, naphthalene ring, and fluorene ring are more preferred, and benzene ring is even more preferred.

In the above general formula (11), when ^Y1 is a direct bond and ⁿ¹ is 2, examples of the ring to which ^X2 is bonded include an imidazole ring, a benzimidazole ring, a pyridine ring, a pyridazine ring, a pyrazine ring, a pyrimidine ring, a quinoline ring, an isoquinoline ring, a phenanthridine ring, a quinoxaline ring, a benzothiadiazole ring, a thiazole ring, a benzothiazole ring, an oxazole ring, a benzoxazole ring, an oxadiazole ring, and a thiadiazole ring. These are respectively represented by the following formulas (15-1) to (15-17).

In addition, the marks * in the above formulae (15-1) to (15-17) indicate that the carbon atom constituting the ring to which ^X1 is bonded and constituting the skeleton portion connecting the boron atom, ^Q1 , and the nitrogen atom in the above general formula (11) is bonded to any one of the carbon atoms marked with *. In addition, the ring may be condensed with another ring structure at a position other than the carbon atom marked with *. Among these, a pyridine ring, a pyrimidine ring, a quinoline ring, and a phenanthridine ring are preferred. More preferred are a pyridine ring, a pyrimidine ring, and a quinoline ring. Even more preferred is a pyridine ring.

In addition, in the above general formula (11), when ^Y1 is a direct bond and ⁿ¹ is 2, the ring to which ^X3 is bonded and the ring to which ^X4 is bonded include the rings represented by the above formulas (14-1) to (14-33). Among these, a benzene ring, a naphthalene ring, and a benzothiophene ring are preferred. A benzene ring is more preferred.

In the above general formula (11), ^X1 , ^X2 , ^X3 and ^X4 are the same or different and each represents a hydrogen atom or a monovalent substituent that is a substituent of a ring structure. The monovalent substituent is not particularly limited, but ^X1 , ^X2 , ^X3 and X4 are Examples of ⁴ include a hydrogen atom, an aryl group which may have a substituent, a heterocyclic group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryloxy group, an arylalkoxy group, a silyl group, a hydroxy group, an amino group, an alkylamino group, an arylamino group, a halogen atom, a carboxyl group, a thiol group, an epoxy group, an acyl group, an oligoaryl group which may have a substituent, a monovalent oligoheterocyclic group, an alkylthio group, an arylthio group, an arylalkyl group, an arylalkoxy group, an arylalkylthio group, an azo group, a stannyl group, a phosphino group, an arylphosphino group which may have a substituent, an alkylphosphino group which may have a substituent, an arylphosphinyl group, an alkylphosphinyl group which may have a substituent, a silyloxy group, an aryloxycarbonyl group which may have a substituent, an alkoxycarbonyl group which may have a substituent, a Examples of the alkyl group include a carbamoyl group which may have a substituent, an arylcarbonyl group which may have a substituent, an alkylcarbonyl group which may have a substituent, an arylsulfonyl group which may have a substituent, an alkylsulfonyl group which may have a substituent, an arylsulfinyl group which may have a substituent, an alkylsulfinyl group which may have a substituent, a formyl group, a cyano group, a nitro group, an arylsulfonyloxy group, an alkylsulfonyloxy group; alkylsulfonate groups such as a methanesulfonate group, an ethanesulfonate group, and a trifluoromethanesulfonate group; arylsulfonate groups such as a benzenesulfonate group and a p-toluenesulfonate group; arylalkylsulfonate groups such as a benzylsulfonate group, a boryl group, a sulfonium methyl group, a phosphonium methyl group, a phosphonate methyl group, an arylsulfonate group, an aldehyde group, and an acetonitrile group.

Examples of the substituents in X ¹ , X ² , X ³ and X ⁴ include halogen atoms such as fluorine atom, chlorine atom, bromine atom and iodine atom; haloalkyl groups such as methyl chloride group, methyl bromide group, methyl iodide group, fluoromethyl group, difluoromethyl group and trifluoromethyl group; linear or branched alkyl groups having 1 to 20 carbon atoms such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group and tert-butyl group; cyclic alkyl groups having 5 to 7 carbon atoms such as cyclopentyl group, cyclohexyl group and cycloheptyl group; methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group and isobutoxy group. linear or branched alkoxy groups having 1 to 20 carbon atoms, such as tert-butoxy, pentyloxy, hexyloxy, heptyloxy, and octyloxy groups; hydroxyl groups; thiol groups; nitro groups; cyano groups; amino groups; azo groups; mono- or dialkylamino groups having an alkyl group having 1 to 40 carbon atoms, such as methylamino, ethylamino, dimethylamino, and diethylamino groups; amino groups such as diphenylamino and carbazolyl groups; acyl groups such as acetyl, propionyl, and butyryl groups; aryl groups having 2 to 20 carbon atoms, such as vinyl, 1-propenyl, allyl, butenyl, and styryl groups. alkynyl groups having 2 to 20 carbon atoms, such as ethynyl, 1-propynyl, propargyl, and phenylacetynyl; alkenyloxy groups, such as vinyloxy and allyloxy; alkynyloxy groups, such as ethynyloxy and phenylacetyloxy; aryloxy groups, such as phenoxy, naphthoxy, biphenyloxy, and pyrenyloxy; perfluoro groups, such as trifluoromethyl, trifluoromethoxy, pentafluoroethoxy, and perfluorophenyl, and longer-chain perfluoro groups; diphenylboryl, dimesitylboryl, and bis(perfluorophenyl)boryl. boryl groups such as 4,4,5,5-tetramethyl-1,3,2-dioxaborolanyl group; carbonyl groups such as acetyl group and benzoyl group; carbonyloxy groups such as acetoxy group and benzoyloxy group; alkoxycarbonyl groups such as methoxycarbonyl group, ethoxycarbonyl group and phenoxycarbonyl group; sulfinyl groups such as methylsulfinyl group and phenylsulfinyl group; sulfonyl groups such as methylsulfonyl group and phenylsulfonyl group; alkylsulfonyloxy groups; arylsulfonyloxy groups; phosphino groups; phosphinyl groups such as diethylphosphinyl group and diphenylphosphinyl group; silyl groups such as trimethylsilyl, triisopropylsilyl, dimethyl-tert-butylsilyl, trimethoxysilyl and triphenylsilyl; silyloxy groups; stannyl groups; phenyl groups which may be substituted with halogen atoms, alkyl groups, alkoxy groups and the like, 2,6-xylyl, mesityl, duryl, biphenyl, terphenyl, naphthyl, anthryl, pyrenyl, toluyl, anisyl, fluorophenyl, diphenylaminophenyl, dimethylaminophenyl, diethylaminophenyl and phenanthrenyl groups (aryl groups which may be substituted); thienyl, furyl and silacyclopentane groups which may be substituted with halogen atoms, alkyl groups, alkoxy groups and the like. Examples of the heterocyclic group include a heterocyclic group (an aromatic heterocyclic group which may be substituted) such as a thadienyl group, an oxazolyl group, an oxadiazolyl group, a thiazolyl group, a thiadiazolyl group, an acridinyl group, a quinolyl group, a quinoxaloyl group, a phenanthrolyl group, a benzothienyl group, a benzothiazolyl group, an indolyl group, a carbazolyl group, a pyridyl group, a pyrrolyl group, a benzoxazolyl group, a pyrimidyl group, and an imidazolyl group; a carboxyl group; a carboxylic acid ester; an epoxy group; an isocyanate group; an isocyanate group; a thiocyanate group; an isothiocyanate group; a carbamoyl group; an N,N-dialkylcarbamoyl group such as an N,N-dimethylcarbamoyl group or an N,N-diethylcarbamoyl group; a formyl group; a nitroso group; and a formyloxy group. These groups may be substituted with a halogen atom, an alkyl group, an aryl group, or the like. Furthermore, these groups may be bonded to each other at any position to form a ring.

Among these, X ¹ , X ² , X ³ and X ⁴ are preferably a hydrogen atom; a reactive group such as a halogen atom, a carboxyl group, a hydroxyl group, a thiol group, an epoxy group, an amino group, an azo group, an acyl group, an allyl group, a nitro group, an alkoxycarbonyl group, a formyl group, a cyano group, a silyl group, a stannyl group, a boryl group, a phosphino group, a silyloxy group, an arylsulfonyloxy group or an alkylsulfonyloxy group; a linear or branched alkyl group having 1 to 20 carbon atoms; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms or a linear or branched alkoxy group having 1 to 8 carbon atoms. a silyl group, an aryl group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or a linear or branched alkyl group having 1 to 20 carbon atoms substituted with said reactive group; a linear or branched alkoxy group having 1 to 20 carbon atoms; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or a linear or branched alkoxy group having 1 to 20 carbon atoms substituted with said reactive group; an aryl group; A linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an aryl group substituted with said reactive group; an oligoaryl group; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an oligoaryl group substituted with said reactive group; a monovalent Heterocyclic groups; monovalent heterocyclic groups substituted with a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or the reactive group; monovalent oligoheterocyclic groups; monovalent oligoheterocyclic groups substituted with a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or the reactive group. Oligoheterocyclic groups; alkylthio groups; aryloxy groups; arylthio groups; arylalkyl groups; arylalkoxy groups; arylalkylthio groups; alkenyl groups; linear or branched alkyl groups having 1 to 8 carbon atoms, linear or branched alkoxy groups having 1 to 8 carbon atoms, aryl groups, heterocyclic groups, alkenyl groups having 2 to 8 carbon atoms, alkynyl groups having 2 to 8 carbon atoms, or alkenyl groups substituted with said reactive groups; alkynyl groups; linear or branched alkyl groups having 1 to 8 carbon atoms, linear or branched alkoxy groups having 1 to 8 carbon atoms, A chain alkoxy group, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an alkynyl group substituted with said reactive group; an alkylamino group; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an alkylamino group substituted with said reactive group; an arylamino group; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an arylamino group substituted with said reactive group; an arylphosphino group; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an arylphosphino group substituted with said reactive group; an arylphosphinyl group; a linear or branched alkyl group having 1 to 8 carbon atoms, [0043] Preferred are any of a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an arylphosphinyl group substituted with said reactive group; an arylsulfonyl group; a linear or branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkoxy group having 1 to 8 carbon atoms, an aryl group, a heterocyclic group, an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 2 to 8 carbon atoms, or an arylsulfonyl group substituted with said reactive group.
More preferred are a hydrogen atom, a bromine atom, an iodine atom, an amino group, a boryl group, an alkynyl group, an alkenyl group, a formyl group, a silyl group, a stannyl group, a phosphino group, an aryl group substituted with the reactive group, an oligoaryl group substituted with the reactive group, a monovalent heterocyclic group or a monovalent heterocyclic group substituted with the reactive group, a monovalent oligoheterocyclic group substituted with the reactive group, an alkenyl group or an alkenyl group substituted with the reactive group, an alkynyl group or an alkynyl group substituted with the reactive group.

Among them, ^X1 and ^X2 are more preferably functional groups that are resistant to reduction, such as a hydrogen atom, an alkyl group, an aryl group, a nitrogen-containing heteroaromatic group, an alkenyl group, an alkoxy group, an aryloxy group, and a silyl group, and are particularly preferably a hydrogen atom, an aryl group, or a nitrogen-containing heteroaromatic group.
More preferably, ^X3 and ^X4 are functional groups that are resistant to oxidation, such as a hydrogen atom, a carbazolyl group, a triphenylamino group, a thienyl group, a furanyl group, an alkyl group, an aryl group, an indolyl group, etc. Particularly preferably, X3 and X4 are a hydrogen atom, a carbazolyl group, a triphenylamino group, and a thienyl group.
In this way, when ^X1 and ^X2 have functional groups resistant to reduction, and ^X3 and ^X4 have functional groups resistant to oxidation, the boron-containing compound as a whole is considered to be a compound further resistant to both reduction and oxidation.
In the above X ¹ to X ⁴ and the substituents in X ¹ to X ⁴ , examples of the heterocyclic ring forming the heterocyclic group include those represented by the above formulae (14-10) to (14-36). Examples of the oligoheterocycle forming the oligoheterocyclic group and the nitrogen-containing heteroaromatic ring forming the nitrogen-containing heteroaromatic group include those corresponding to the oligoheterocycle and the nitrogen-containing heteroaromatic ring in the above formulae (14-10) to (14-36), respectively.
In the above general formula (11), when X ¹ , X ² , X ³ and X ⁴ are monovalent substituents, the bonding positions and the number of bonds of X ¹ , X ² , X ³ and X ⁴ to the ring structure are not particularly limited.

In the above general formula (11), when Y ¹ is an n ¹ -valent linking group and n ¹ is 2 to 10, the ring to which X ¹ is bonded is the same as the ring to which X ¹ is bonded in the above general formula (11) when Y ¹ is a direct bond and n ¹ is 2. Among these rings, a benzene ring, a naphthalene ring, and a benzothiophene ring are preferred. A benzene ring is more preferred.

In the above general formula (11), when Y ¹ is an n ¹ -valent linking group and n ¹ is 2 to 10, the ring to which X ² is bonded, the ring to which X ³ is bonded, and the ring to which X ⁴ is bonded are respectively similar to the rings exemplified as the ring to which X ² is bonded, the ring to which X ³ is bonded, and the ring to which X ⁴ is bonded when Y ¹ is a direct bond and n ¹ is 2 in the above general formula (11), and the preferred structures are also similar.

That is, in either case where Y ¹ in the above general formula (11) is a direct bond and n ¹ is 2, or where Y ¹ is an ⁿ¹ -valent linking group and n ¹ is 2 to 10, the boron-containing compound represented by the above general formula (11) is also a boron-containing compound represented by the following general formula (16), which is also one of the preferred embodiments of the present invention.

In formula (16), the arrow from the nitrogen atom to the boron atom, X ¹ , X ² , X ³ , X ⁴ , n ¹ and Y ¹ are the same as in formula (11).

The boron-containing compound represented by the above general formula (11) is preferably a boron-containing compound represented by general formula (11-1) or (11-2), and most preferably a boron-containing compound represented by general formula (11-2).

As the boron-containing compound used for the second material, a boron-containing compound represented by the following general formula (17) is also preferable.

In the general formula (17), the dotted arcs, which may be the same or different, represent a ring structure formed together with the skeletal portion represented by the solid line. The dotted portion in the skeletal portion represented by the solid line represents that a pair of atoms connected by the dotted line may be connected by a double bond. The arrow from the nitrogen atom to the boron atom represents that the nitrogen atom is coordinated to the boron atom. R ¹⁸ to R ²¹ , which may be the same or different, represent a hydrogen atom, a monovalent substituent that becomes a substituent of the ring structure, a divalent group, or a direct bond. Each of R ¹⁸ , R ¹⁹ , and R ²¹ may be bonded in a plurality to the ring structure that forms the dotted arc portion. A plurality of R ²⁰ may be bonded to the pyridine ring structure. The ring to which R ²¹ is bonded is an aromatic heterocycle. n ⁶ is an integer of 1 to 4. n ⁷ is 0 or 1. When ⁿ⁷ is 1, ^Y2 represents an ⁿ⁶ -valent linking group or a direct bond, and is bonded independently to the ⁿ⁶ structural moieties other than ^Y2 at one of ^R18 , ^R19 , ^R20 , or ^R21 . When ⁿ⁷ is 0, ⁿ⁶ is 1, and at least one of ^R18 to ^R21 represents a monovalent substituent that is a substituent of a ring structure.

The boron-containing compound represented by the above general formula (17) is a compound having high stability due to the structure in which a nitrogen atom is coordinated to a boron atom and the rigid ring structure represented by the above general formula (17). In addition, the boron-containing compound represented by the above general formula (17) has good solubility in various solvents and can easily form a good coating film by coating or the like. Furthermore, the boron-containing compound has a specific ring structure on the boron, so that the LUMO energy level is low, and it is considered to have excellent performance as an organic EL element.
First, the structural moieties other than ^Y2 in the above general formula (17) will be described.

In the above general formula (17), the dotted arc represents the formation of a ring structure together with the skeletal portion represented by the solid line. The skeletal portion represented by the solid line is the portion in which dotted lines are written along the solid line. There are three such ring structures, and in this specification, each of the ring structures is referred to as the ring to which R ¹⁸ is bonded, the ring to which R ¹⁹ is bonded, and the ring to which R ²¹ is bonded.
In the above general formula (17), the dotted line portion in the skeleton portion represented by a solid line and the arrow from the nitrogen atom to the boron atom have the same meanings as those in the above general formula (11).

In the above general formula (17), the ring to which ^R21 is bonded is an aromatic heterocycle. The aromatic heterocycle has one or more hetero elements in the ring. The hetero elements are preferably a nitrogen atom, a sulfur atom, or an oxygen atom, and more preferably a nitrogen atom or a sulfur atom.
The aromatic heterocycle may be a monocycle or a condensed ring.
Examples of the aromatic heterocycle include a thiophene ring, a furan ring, a pyrrole ring, a benzothiophene ring, a benzofuran ring, an indole ring, a dibenzothiophene ring, a dibenzofuran ring, a carbazole ring, a thiazole ring, a benzothiazole ring, an oxazole ring, a benzoxazole ring, an imidazole ring, a pyrazole ring, a benzimidazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a pyridazine ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, a benzothiadiazole ring, a phenanthridine ring, an oxadiazole ring, and a thiadiazole ring. These are respectively represented by the above formulas (14-10) to (14-36).

In one preferred embodiment of the boron-containing compound represented by the general formula (17), the aromatic heterocycle is a monocycle (monocyclic aromatic heterocycle). The monocyclic aromatic heterocycle is preferably a 5- to 7-membered ring, and more preferably a 5- or 6-membered ring. Examples of the monocyclic aromatic heterocycle include a thiophene ring, a furan ring, a pyrrole ring, a thiazole ring, an oxazole ring, an imidazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a pyridazine ring, an oxadiazole ring, and a thiadiazole ring. These are represented by the formulas (14-10) to (14-12), (14-19), (14-21), (14-23), (14-26) to (14-29), (14-35), and (14-36), respectively. Among these, a thiophene ring, a pyridine ring, and a pyrimidine ring are preferred, and a thiophene ring and a pyridine ring are more preferred.

In the above general formula (17), the ring to which R ¹⁸ and R ¹⁹ are bonded may be a ring having no aromaticity, but from the viewpoint of stabilizing the boron-containing compound, it is preferable that the ring is an aromatic ring such as an aromatic hydrocarbon ring or an aromatic heterocycle. Examples of the aromatic ring include the same as the ring to which X ¹ is bonded in the above general formula (11) when Y ¹ is a direct bond and n ¹ is 2.

In the above general formula (17), ^R to ^R are the same or different and represent a hydrogen atom, a monovalent substituent that is a substituent of a ring structure, a divalent group, or a direct bond. The monovalent substituent is not particularly limited, and examples thereof include the same groups as specific examples when ^X , ^X , ^X , and ^X are monovalent substituents in the above general formula (11).

Among the above, R ¹⁸ to R ²¹ are preferably the same groups as the preferred groups for X ¹ , X ² , X ³ and X ⁴ in the above general formula (11).
R ^{to R} are more preferably any one of a hydrogen atom; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; a silyl group; an alkylamino group; an arylamino group; a boryl group; a stannyl group; a linear or branched alkyl group having 1 to 8 carbon atoms; an aryl group; an oligoaryl group; a monovalent heterocyclic group; a monovalent oligoheterocyclic group; an arylphosphinyl group; or an arylsulfonyl group.

As the divalent group, for example, a group in which one hydrogen atom has been removed from a monovalent substituent that serves as a substituent for the above-mentioned ring structure can be used.
R ¹⁸ , R ¹⁹ , and R ²¹ may be the same or different and may be bonded in multiple numbers to the ring structure forming the arc portion of the dotted line. R ²⁰ may be the same or different and may be bonded in multiple numbers to the pyridine ring structure. In addition, the bonding position of the monovalent substituent to the ring structure is not particularly limited.

In the above general formula (17), R ²⁰ and R ²¹ are the same or different and represent a hydrogen atom, a monovalent substituent that becomes a substituent of a ring structure, a divalent group, or a direct bond. Among them, it is preferable that at least one of R ²⁰ and R ²¹ is a monovalent electron transporting substituent that becomes a substituent of a ring structure. By having an electron transporting substituent as R ²⁰ and R ²¹ , the boron-containing compound represented by the above general formula (17) becomes a material with excellent electron transport properties.
The electron-transporting monovalent substituent preferably has an aromatic ring. Examples of the electron-transporting monovalent substituent having an aromatic ring include a monovalent group derived from a nitrogen atom-containing heterocycle having a carbon-nitrogen double bond (C=N) in the ring, such as an imidazole ring, a thiazole ring, an oxazole ring, an oxadiazole ring, a triazole ring, a pyrazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a benzimidazole ring, a benzothiazole ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, or a benzothiadiazole ring; a monovalent group derived from an aromatic hydrocarbon ring or aromatic heterocycle having no carbon-nitrogen double bond in the ring, such as a benzene ring, a naphthalene ring, a fluorene ring, a thiophene ring, a benzothiophene ring, or a carbazole ring, having one or more electron-withdrawing substituents; a dibenzothiophene dioxide ring, a dibenzophosphole oxide ring, or a silole ring.
Examples of the electron-withdrawing substituent include -CN, -COR, -COOR, -CHO, _-CF3 , _-SO2Ph , and -PO(Ph) ₂ , where R represents a hydrogen atom or a monovalent hydrocarbon group.
The electron-transporting monovalent substituent preferably has an aromatic heterocycle, such as a monovalent group derived from a nitrogen-atom-containing heterocycle having a carbon-nitrogen double bond in the ring, or a monovalent group derived from an aromatic heterocycle not having a carbon-nitrogen double bond in the ring.
Among these, the electron-transporting monovalent substituent more preferably has a nitrogen-atom-containing aromatic heterocycle having a carbon-nitrogen double bond in the ring. The nitrogen-atom-containing aromatic heterocycle having a carbon-nitrogen double bond in the ring is preferably a pyridine ring, a pyrimidine ring, or a quinoline ring, and more preferably a pyridine ring.
In another preferred embodiment of the present invention, at least one of R ²⁰ and R ²¹ is a silyl group such as a trimethylsilyl group, a triisopropylsilyl group, a dimethyl-tert-butylsilyl group, a trimethoxysilyl group, or a triphenylsilyl group.

The substituents in R ¹⁸ to R ²¹ include the same groups as the substituents in X ¹ , X ² , X ³ and X ⁴ in the general formula (11) above.
Among these, it is preferable that the substituents in the above R ¹⁸ to R ²¹ are groups having an aromatic ring, such as an aromatic hydrocarbon ring group or an aromatic heterocyclic group.
For example, it is preferred that at least one of R ¹⁸ to R ²¹ in the above general formula (17) is a ring in which an aromatic ring is further bonded to one of the carbon atoms constituting the aromatic heterocycle. Examples of the aromatic ring further bonded to one of the carbon atoms constituting the aromatic heterocycle include an aromatic hydrocarbon ring group and an aromatic heterocyclic group. Preferred examples of the aromatic hydrocarbon ring group include a phenyl group, a naphthyl group, an anthracenyl group, a pyrenyl group, and a fluorenyl group. Preferred examples of the aromatic heterocyclic group include a pyridyl group, a quinolyl group, a pyrimidyl group, a thiazole group, and an imidazole group.
The above-mentioned substituents may be further substituted with a halogen atom, an alkyl group, an aryl group, etc., and are preferably substituted with, for example, a linear or branched alkyl group having 1 to 8 carbon atoms. Furthermore, these substituents may be bonded to each other at any position to form a ring.

Y ² , n ⁶ and n ⁷ in the above general formula (17) will be explained below.
The above ⁿ⁶ is an integer of 1 to 4. ⁿ⁷ is 0 or 1. When ⁿ⁷ is 1, ^Y2 represents an ⁿ⁶ -valent linking group or a direct bond, and is bonded to the ⁿ⁶ structural moieties other than ^Y2 independently at one of ^R18 , ^R19 , ^R20 , or ^R21 .

In the above general formula (17), when ⁿ⁶ is 1, ⁿ⁷ is 0, and the compound is composed only of the structural portion other than ^Y2 in the above general formula (17). In this case, at least one of ^R18 to ^R21 represents a monovalent substituent that becomes a substituent of the ring structure. In particular, it is preferable that at least one of ^R20 and ^R21 represents a monovalent electron-transporting substituent that becomes a substituent of the ring structure.
In the above general formula (17), when ⁿ⁶ is 2, there are two structural moieties other than ^Y2 in the above general formula (17). Here, when ^Y2 is a divalent linking group, the two structural moieties other than ^Y2 are bonded via ^Y2 , which is a divalent linking group. When ^Y2 is a direct bond, the two structural moieties other than ^Y2 are bonded directly.
In the compound represented by the above general formula (17), when ⁿ⁶ is 3 or more, ^Y2 is an ⁿ⁶ -valent linking group, and there are ⁿ⁶ structural moieties other than ^Y2 in the above general formula (17), and they are bonded via ^Y2 which is the linking group.

In the above general formula (17), ⁿ⁶ is preferably 1 to 3, and more preferably 1 to 2. That is, the boron-containing compound is more preferably a monomer or a dimer.

In addition, when ^Y2 is a ⁿ⁶ -valent linking group, ^Y2 is bonded to the ⁿ⁶ structural moieties other than ^Y2 independently at one of ^R18 , ^R19 , ^R20 , or ^R21 , which means that the bonding site of the structural moiety other than ^Y2 to ^Y2 is independent of the ⁿ⁶ structural moieties other than ^Y2 , and may be all the same site, may be partly the same site, or may be all different sites. The bonding position is not particularly limited, but it is preferable that all of the ⁿ⁶ structural moieties other than ^Y2 are bonded to ^R20 or ^R21 .
Furthermore, the structures of the structural portions other than the ⁿ⁶ present ^Y2 may all be the same, some may be the same, or all may be different.

When ^Y2 in the above general formula (17) is a linking group having a valence of ⁿ⁶ , the linking group may be, for example, a chain-like, branched or cyclic hydrocarbon group which may have a substituent, a group containing a hetero element which may have a substituent, an aromatic hydrocarbon ring group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. Among these, a group having an aromatic ring, such as an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group which may have a substituent, is preferable. That is, ^Y2 in the above general formula (17) being a group having an aromatic ring is also one of the preferred embodiments of the present invention.
Furthermore, ^Y2 may be a linking group having a structure in which a plurality of the above-mentioned linking groups are combined.

The linear, branched or cyclic hydrocarbon group is preferably a group represented by any one of the above formulae (12-1) to (12-8). Among these, the above formulae (12-1) and (12-7) are more preferred.
The group containing a hetero element is preferably a group represented by any one of the above formulae (12-9) to (12-13), with the above formulae (12-12) and (12-13) being more preferred.
The aromatic hydrocarbon ring group is preferably a group represented by any one of the above formulae (12-14) to (12-20), with the above formulae (12-14), (12-19) and (12-20) being more preferred.
The aromatic heterocyclic group is preferably a group represented by any one of the above formulae (12-21) to (12-33), and among these, the above formulae (12-24) and (12-32) are more preferred.

Examples of the substituent that the linear, branched or cyclic hydrocarbon group, the group containing a hetero element, the aromatic hydrocarbon ring group and the aromatic heterocyclic group may have include the same substituents that may be possessed by R ¹⁸ , R ¹⁹ , R ²⁰ and R ²¹ in the above general formula (17).
Among these, the substituent of the chain, branched or cyclic hydrocarbon group, group containing a hetero element, aromatic hydrocarbon ring group or aromatic heterocyclic group in ^Y2 is preferably a halogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, a linear or branched alkoxy group having 1 to 20 carbon atoms, an aromatic hydrocarbon ring group, an aromatic heterocyclic group or a diarylamino group. More preferably, it is an alkyl group, an aromatic hydrocarbon ring group, an aromatic heterocyclic group or a diarylamino group.
When the linear, branched or cyclic hydrocarbon group, the group containing a hetero element, the aromatic hydrocarbon ring group or the aromatic heterocyclic group in ^Y2 has a substituent, the position or the number of the substituent to be bonded is not particularly limited.

（式中、窒素原子からホウ素原子への矢印、Ｒ¹⁸、Ｒ¹⁹、Ｒ²⁰及びＲ²¹は一般式（１７）と同様である。）で表されるホウ素含有化合物であることもまた、本発明の好適な実施形態の１つである。 The boron-containing compound represented by the general formula (17) may be a compound represented by the following formula (18-1) or (18-2):

(wherein the arrows from the nitrogen atom to the boron atom, R ¹⁸ , R ¹⁹ , R ²⁰ and R ²¹ are the same as in general formula (17)) is also one of the preferred embodiments of the present invention.

As the boron-containing compound used for the second material, a boron-containing compound represented by the following general formula (19) is also preferable.

In the general formula (19), the dotted arc represents that a ring structure is formed together with the boron atom or the skeletal portion represented by the solid line, and the ring structure may be a monocyclic structure composed of one ring, or a condensed ring structure composed of multiple rings, which may be the same or different. The dotted portion in the skeletal portion represented by the solid line represents that a pair of atoms connected by the dotted line may be connected by a double bond. The arrow from the nitrogen atom to the boron atom represents that the nitrogen atom is coordinated to the boron atom. ^Q7 is a linking group in the skeletal portion represented by the solid line, and at least a part of the linking group forms a ring structure together with the dotted arc portion, and may have a substituent. ^R22 and ^R23 are the same or different and represent a hydrogen atom, a monovalent substituent that becomes a substituent of the ring structure, a divalent group, or a direct bond, and may be bonded to the ring structure forming the dotted arc portion. ^R24 and ^R25 are the same or different and represent a hydrogen atom, a monovalent substituent, a divalent group, or a direct bond. R ²⁴ and R ²⁵ are not bonded to each other to form a ring structure together with the skeletal portion represented by the double line. n ⁸ is an integer from 1 to 4. n ⁹ is 0 or 1. When ^{n 9} is 1, Y ³ represents an n ⁸ -valent linking group or a direct bond, and is bonded to each of the n ⁸ structural portions other than Y ³ independently at one of R ²² , R ²³ , R ²⁴ , or R ²⁵ .

The boron-containing compound represented by the general formula (19) has a structure in which a nitrogen atom is coordinated to a boron atom, and also has a rigid ring structure represented by the general formula (19), and thus has high stability. The boron-containing compound represented by the general formula (19) has good solubility in various solvents, and can easily form a good coating film by coating or the like. Furthermore, the boron-containing compound has a specific ring structure on the boron, and therefore has a low LUMO energy level, which is considered to provide excellent performance as an organic EL element.
First, the structural moieties other than ^Y3 in the above general formula (19) will be described.

In the above general formula (19), the meanings of the dotted arc, the dotted portion in the skeletal portion represented by the solid line, and the arrow from the nitrogen atom to the boron atom are the same as those in the above general formula (17). In the above general formula (19), there are two ring structures formed by the dotted arc and the boron atom or the skeletal portion represented by the solid line, and these ring structures are referred to herein as the ring to which R ²² is bonded and the ring to which R ²³ is bonded.

In the above general formula (19), ^Q7 is a linking group in the skeleton portion represented by the solid line, and at least a part of it forms a ring structure together with the arc portion of the dotted line, and may have a substituent. This means that ^Q7 is incorporated as a part of the ring structure.
^Q7 in the above general formula (19) may be any of the structures represented by the above formulas (13-1) to (13-8), and among these, any of formulas (13-1), (13-7), and (13-8) is preferred. More preferably, it is formula (13-1). That is, a case in which ^Q7 represents a linking group having one carbon atom is also one of the preferred embodiments of the present invention.

In the above general formula (19), the ring to which R ²² is bonded may be a ring that does not have aromaticity, but is preferably an aromatic ring.In addition, the ring to which R ²² is bonded may be a monocyclic structure composed of one ring, but is preferably a condensed ring structure composed of multiple rings, and is more preferably a condensed ring structure composed of at least three rings, such as the boron-containing compound represented by general formula (20) described later.In addition, the ring to which R ²² is bonded may or may not have a hetero element other than a boron atom in the ring.

In the above general formula (19), the ring to which R ²³ is bonded may be a nitrogen-containing heterocycle having no aromaticity, but is preferably a nitrogen-containing aromatic heterocycle from the viewpoint of stabilizing the boron-containing compound and exhibiting excellent performance as an organic electroluminescent device material. Examples of the nitrogen-containing aromatic heterocycle include an imidazole ring, a benzimidazole ring, a pyridine ring, a pyridazine ring, a pyrazine ring, a pyrimidine ring, a quinoline ring, an isoquinoline ring, a phenanthridine ring, a quinoxaline ring, a benzothiadiazole ring, a thiazole ring, a benzothiazole ring, an oxazole ring, a benzoxazole ring, an oxadiazole ring, and a thiadiazole ring. These are respectively represented by the above formulas (15-1) to (15-17). In addition, the * mark in the formulas (15-1) to (15-17) indicates that the carbon atom bonded to R ²⁴ is bonded to any one of the carbon atoms marked with the * mark. In addition, the rings represented by formulae (15-1) to (15-17) may be condensed with other ring structures at positions other than the carbon atoms marked with *. Among these, nitrogen-containing heteroaromatic rings containing six-membered rings such as a pyridine ring, a pyrazine ring, a pyrimidine ring, a quinoline ring, and a phenanthridine ring are preferred. The ring to which R ²³ is bonded is more preferably a pyridine ring, a pyrazine ring, a pyrimidine ring, or a quinoline ring, and even more preferably a pyridine ring.

In the above general formula (19), R ²² and R ²³ are the same or different and represent a hydrogen atom, a monovalent substituent that becomes a substituent of a ring structure, a divalent group, or a direct bond. R ²⁴ and R ²⁵ are the same or different and represent a hydrogen atom, a monovalent substituent, a divalent group, or a direct bond. The monovalent substituent that becomes a substituent of the ring structure in R ²² and R ²³ , and the monovalent substituent in R ²⁴ and R ²⁵ are not particularly limited, but the same substituents as the specific examples when X ¹ , X ² , X ³ and X ⁴ in the above general formula (11) are monovalent substituents that become a substituent of a ring structure can be mentioned, and among them, the preferred substituents are also the same as the preferred substituents of X ¹ , X ² , X ³ and X ⁴ .

In the above general formula (19), R ²⁴ and R ²⁵ are not bonded to each other to form a ring structure together with the skeletal portion represented by the double line. The ring structure includes those having a coordinate bond in the skeletal portion.
It is more preferable that R ²⁴ be an atom other than an oxygen atom that is directly bonded to the carbon atom in the skeleton portion represented by the double line in the above general formula (19).
R ²² , R ²³ , R ²⁴ , and R ²⁵ are particularly preferably any one of a hydrogen atom; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; a silyl group; an alkylamino group; an arylamino group; a boryl group; a stannyl group; a linear or branched alkyl group having 1 to 8 carbon atoms; an aryl group; an oligoaryl group; a monovalent heterocyclic group; a monovalent oligoheterocyclic group; an arylphosphinyl group; or an arylsulfonyl group.

The divalent groups for R ²² , R ²³ , R ²⁴ and R ²⁵ may be, for example, the above-mentioned monovalent substituents from which one hydrogen atom has been removed.
R ²² and R ²³ may be the same or different and may be bonded in plurality to the ring structure forming the arc portion of the dotted line. The bonding position of the monovalent substituent to the ring structure is not particularly limited.

In the above general formula (19), it is preferable that at least one of R ²³ , R ²⁴ , and R ²⁵ represents a monovalent electron transporting substituent that becomes a substituent of a ring structure. By having an electron transporting substituent as R ²³ , R ²⁴ , or R ²⁵ , the boron-containing compound becomes a material with excellent electron transport properties. Among them, it is more preferable that R ²⁵ has an electron transporting substituent.
The electron-transporting monovalent substituent preferably has an aromatic ring. For example, R ²⁵ preferably represents a monovalent substituent having an aromatic ring. Examples of the monovalent substituent having an aromatic ring include a monovalent group derived from a nitrogen atom-containing heterocycle having a carbon-nitrogen double bond (C=N) in the ring, such as an imidazole ring, a thiazole ring, an oxazole ring, an oxadiazole ring, a triazole ring, a pyrazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a benzimidazole ring, a benzothiazole ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, or a benzothiadiazole ring; a monovalent group derived from an aromatic hydrocarbon ring or aromatic heterocycle having no carbon-nitrogen double bond in the ring, such as a benzene ring, a naphthalene ring, a fluorene ring, a thiophene ring, a benzothiophene ring, or a carbazole ring, having one or more electron-withdrawing substituents; a dibenzothiophene dioxide ring, a dibenzophosphole oxide ring, a diarylphosphine oxide group, or a silole ring.
Examples of the electron-withdrawing substituent include -CN, -COR, -COOR, -CHO, _-CF3 , _-SO2Ph , and -PO(Ph) ₂ , where R represents a hydrogen atom or a monovalent hydrocarbon group.
The electron-transporting monovalent substituent preferably has an aromatic heterocycle, such as a monovalent group derived from a nitrogen-atom-containing heterocycle having a carbon-nitrogen double bond in the ring, or a monovalent group derived from an aromatic heterocycle not having a carbon-nitrogen double bond in the ring.
Among these, the electron-transporting monovalent substituent more preferably has a nitrogen-atom-containing aromatic heterocycle having a carbon-nitrogen double bond in the ring. The nitrogen-atom-containing aromatic heterocycle having a carbon-nitrogen double bond in the ring is preferably a pyridine ring, a pyrimidine ring, or a quinoline ring, and more preferably a pyridine ring.
From the viewpoint of increasing the electron mobility of the boron-containing compound, it is particularly preferable that in the general formula (19), the ring to which R ²³ is bonded is a nitrogen-containing aromatic heterocycle, and R ²⁵ represents a monovalent substituent having an aromatic ring. Among them, it is most preferable that the ring to which R ²³ is bonded is a pyridine ring, and R ²⁵ represents a benzene ring.

The substituents in R ²² , R ²³ , R ²⁴ and R ²⁵ include the same groups as the substituents in X ¹ , X ² , X ³ and X ⁴ in the above general formula (11).
Among these, it is preferable that the substituents in the above R ²³ , R ²⁴ and R ²⁵ are groups having an aromatic ring, such as an aromatic hydrocarbon ring group or an aromatic heterocyclic group.
For example, it is preferable that at least one of R ²³ , R ²⁴ and R ²⁵ in the above general formula (19) is a ring in which an aromatic ring is further bonded to one of the carbon atoms constituting the aromatic heterocycle. Examples of the aromatic ring further bonded to one of the carbon atoms constituting the aromatic heterocycle include an aromatic hydrocarbon ring group and an aromatic heterocycle group. The aromatic hydrocarbon ring group is preferably a phenyl group, a naphthyl group, an anthracenyl group, a pyrenyl group, or a fluorenyl group. The aromatic heterocycle group is preferably a pyridyl group, a pyrrolyl group, a quinolyl group, a pyrimidyl group, a thiazole group, or an imidazole group. Specifically, it is a preferable example that at least one of R ²³ , R ²⁴ and R ²⁵ is bipyridine from the viewpoint of improving electron injection properties.
The above-mentioned substituents may be further substituted with a halogen atom, an alkyl group, an aryl group, etc., and are preferably substituted with, for example, a linear or branched alkyl group having 1 to 8 carbon atoms. Furthermore, these substituents may be bonded to each other at any position to form a ring.

Y ³ , n ⁸ and n ⁹ in the above general formula (19) will be explained below.
The above ⁿ⁸ is an integer of 1 to 4. ⁿ⁹ is 0 or 1. When ⁿ⁹ is 1, ^Y3 represents an ⁿ⁸ -valent linking group or a direct bond, and is bonded to each of the ⁿ⁸ structural moieties other than ^Y3 independently at one of ^R22 , ^R23 , ^R24 , or ^R25 .

In the above general formula (19), when ⁿ⁸ is 1, ⁿ⁹ is 0, and the compound is composed only of the structural portion other than ^Y3 in the above general formula (19).
From the viewpoint of improving the thermal stability of the boron-containing compound, it is preferable that n ⁸ is an integer of 2 to 4, and n ⁹ is 1 in the above general formula (19).
In the above general formula (19), when ⁿ⁸ is 2, there are two structural moieties other than ^Y3 in the above general formula (19). Here, when ^Y3 is a divalent linking group, the two structural moieties other than ^Y3 are bonded via ^Y3 , which is a divalent linking group. When ^Y3 is a direct bond, the two structural moieties other than ^Y3 are bonded directly.
In the compound represented by the above general formula (19), when ⁿ⁸ is 3 or more, ^Y3 is an ⁿ⁸ -valent linking group, and there are ⁿ⁸ structural moieties other than ^Y3 in the above general formula (19), and they are bonded via ^Y3 which is the linking group.

In addition, when ^Y3 is an ⁿ⁸ -valent linking group, ^Y3 is bonded to the ⁿ⁸ structural moieties other than ^Y3 independently at one of ^R22 , ^R23 , ^R24 , or ^R25 , which means that the bonding site of the structural moiety other than ^Y3 with ^Y3 is independent of the ⁿ⁸ structural moieties other than ^Y3 , and may be all the same site, may be partly the same site, or may be all different sites. The bonding position ^{is not particularly limited, but it is preferable that all of the structural moieties other than Y3 are} bonded with ^R23 , ^R24 , or ^R25 .
Furthermore, the structures of the structural portions other than the n ⁸ present Y ³ may all be the same, some may be the same, or all may be different.

When ^Y3 in the above general formula (19) is a ⁿ⁸ -valent linking group, the linking group may be, for example, a chain-like, branched or cyclic hydrocarbon group which may have a substituent, a group containing a hetero element which may have a substituent, an aromatic hydrocarbon ring group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. Among these, a group having an aromatic ring, such as an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group which may have a substituent, is preferable. That is, it is also one of the preferred embodiments of the present invention that ^Y3 in the above general formula (19) represents an ⁿ⁸ -valent linking group having an aromatic ring.
Furthermore, ^Y3 may be a linking group having a structure in which a plurality of the above-mentioned linking groups are combined.

The linear, branched or cyclic hydrocarbon group is preferably a group represented by any one of the above formulae (12-1) to (12-8). Among these, formulae (12-1) and (12-7) are more preferred.
The group containing a hetero element is preferably a group represented by any one of the above formulae (12-9) to (12-13). Among these, the groups represented by formulae (12-12) and (12-13) are more preferable.
The aromatic hydrocarbon ring group is preferably a group represented by any one of the above formulae (12-14) to (12-20), of which formulae (12-14), (12-19) and (12-20) are more preferred.
The aromatic heterocyclic group is preferably a group represented by any one of the above formulae (12-21) to (12-33), with the formulae (12-24) and (12-32) being more preferred.

Examples of the substituent that the linear, branched or cyclic hydrocarbon group, the group containing a hetero element, the aromatic hydrocarbon ring group and the aromatic heterocyclic group may have include the same as the substituents that R ²³ , R ²⁴ and R ²⁵ in the above general formula (19) may have.
Among these, the substituent of the linear, branched or cyclic hydrocarbon group, group containing a hetero element, aromatic hydrocarbon ring group or aromatic heterocyclic group in ^Y3 is preferably a halogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, a linear or branched alkoxy group having 1 to 20 carbon atoms, an aromatic hydrocarbon ring group, an aromatic heterocyclic group or a diarylamino group. More preferably, it is an alkyl group, an aromatic hydrocarbon ring group, an aromatic heterocyclic group or a diarylamino group.
When the linear, branched or cyclic hydrocarbon group, the group containing a hetero element, the aromatic hydrocarbon ring group or the aromatic heterocyclic group in ^Y3 has a substituent, the position or the number of the substituent to be bonded is not particularly limited.

（式中、点線の円弧は、同一又は異なって、実線で表される骨格部分と共に環構造が形成されていることを表す。Ｑ⁸は、実線で表される骨格部分における連結基であり、少なくとも一部が点線の円弧部分と共に環構造を形成しており、置換基を有していてもよい。Ｒ²²¹及びＲ²²²は、同一又は異なって、水素原子、環構造の置換基となる１価の置換基、２価の基、又は、直接結合を表し、点線の円弧部分を形成する環構造に複数個結合していてもよい。ｎ⁹が１の場合、Ｙ³は、ｎ⁸価の連結基、又は、直接結合を表し、ｎ⁸個存在するＹ³以外の構造部分とそれぞれ独立に、Ｒ²²¹、Ｒ²²²、Ｒ²³、Ｒ²⁴、又は、Ｒ²⁵のいずれか１箇所で結合していることを表す。実線で表される骨格部分における点線部分、窒素原子からホウ素原子への矢印、Ｑ⁷、Ｒ²³、Ｒ²⁴、Ｒ²⁵、ｎ⁸、及び、ｎ⁹は一般式（１９）と同様である。）で表されることがより好ましい。 As described above, in the above general formula (19), it is more preferable that the ring to which R ²² is bonded is a condensed ring structure composed of at least three rings. That is, the boron-containing compound is preferably a compound represented by the following general formula (20):

(In the formula, the dotted arcs are the same or different and represent a ring structure formed together with the skeletal portion represented by the solid line. ^Q8 is a linking group in the skeletal portion represented by the solid line, at least a part of which forms a ring structure together with the dotted arc portion and may have a substituent. ^R221 and ^R222 are the same or different and represent a hydrogen atom, a monovalent substituent that becomes a substituent of the ring structure, a divalent group, or a direct bond, and may be bonded to the ring structure forming the dotted arc portion. When ⁿ⁹ is 1, ^Y3 represents an ⁿ⁸ -valent linking group or a direct bond, and represents that it is bonded to the ⁿ⁸ structural portions other than ^Y3 at any one of ^R221 , R222, ^R23 , ^R24 , or ^R25 independently. The dotted line portion in the skeletal portion represented by ^the solid line, the arrow from the nitrogen atom to the boron atom, ^Q7 , ^R23 , ^R24 , ^R25 , ⁿ⁸ and ⁿ⁹ is the same as in general formula (19).

In the above general formula (20), the dotted arc represents the formation of a ring structure together with the skeletal portion represented by the solid line. The skeletal portion represented by the solid line is the portion in which dotted lines are written along the solid line. There are three ring structures, and each of the ring structures is referred to herein as the ring to which R ²²¹ is bonded, the ring to which R ²²² is bonded, and the ring to which R ²³ is bonded.
In the above general formula (20), the dotted line portion in the skeleton portion represented by the solid line indicates that a pair of atoms connected by the dotted line may be connected by a double bond.

In the above general formula (20), the ring to which R ²²¹ and R ²²² are bonded may be a ring that does not have aromaticity. However, from the viewpoint of stabilizing the boron-containing compound, it is preferable that the ring is an aromatic ring such as an aromatic hydrocarbon ring or an aromatic heterocycle. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, a tetracene ring, a pentacene ring, a triphenylene ring, a pyrene ring, a fluorene ring, an indene ring, a thiophene ring, a furan ring, a pyrrole ring, a benzothiophene ring, a benzofuran ring, an indole ring, a dibenzothiophene ring, a dibenzofuran ring, a carbazole ring, a thiazole ring, a benzothiazole ring, an oxazole ring, a benzoxazole ring, an imidazole ring, a pyrazole ring, a benzimidazole ring, a pyridine ring, a pyrimidine ring, a pyrazine ring, a pyridazine ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, a benzothiadiazole ring, a phenanthridine ring, an oxadiazole ring, and a thiadiazole ring, each of which is represented by the above-mentioned formulas (14-1) to (14-36). Among these, a benzene ring, a naphthalene ring, and a benzothiophene ring are preferred. A benzene ring is more preferred.

In the above general formula (20), the ring to which R ²³ is bonded is the same as the ring to which R ²³ is bonded in the above general formula (19).
In the above general formula (20), R ²²¹ and R ²²² are each the same as R ²² in the above general formula (19).
In the above general formula (20), Q ⁸ is the same as Q ⁷ in the above general formula (19). For example, it is preferable that at least one of Q ⁷ and Q ⁸ represents a linking group having 1 carbon atom.

In the above general formula (20), when Y ³ is an n ⁸ -valent linking group, Y ³ is bonded to the n ⁸ structural moieties other than Y ³ independently at one of R ²²¹ , R ²²² , R ²³ , R ²⁴ , or R ²⁵ , which means that the bonding site of the structural moiety other than Y ³ with Y ³ is independent of the n ⁸ structural moieties other than Y ³ , and may be all the same site, may be partly the same site, or may be all different sites. The bonding position is not particularly limited, but it is preferable that all of the structural moieties other than Y ³ that exist in the n ⁸ numbers are bonded with R ²³ , R ²⁴ , or R ²⁵ .
Furthermore, the structures of the structural portions other than the n ⁸ present Y ³ may all be the same, some may be the same, or all may be different.

（式中、窒素原子からホウ素原子への矢印、点線の円弧、実線で表される骨格部分における点線部分、Ｑ⁷、Ｒ²²¹、Ｒ²²²、Ｒ²³、Ｒ²⁴、Ｒ²⁵、及び、Ｙ³は一般式（２０）と同様である。）のいずれかで表されるホウ素含有化合物であることもまた、本発明の好適な実施形態の１つである。これにより、熱安定性が向上する。中でも、前記ホウ素含有化合物が、上記式（２１－２）で表されることがより好ましい。 The boron-containing compound is represented by the following formulas (21-1) to (21-3):

(wherein the arrow from the nitrogen atom to the boron atom, the dotted arc, the dotted line portion in the solid line skeleton, Q ⁷ , R ²²¹ , R ²²² , R ²³ , R ²⁴ , R ²⁵ , and Y ³ are the same as in general formula (20).) This improves thermal stability. Of these, it is more preferable that the boron-containing compound is represented by the above formula (21-2).

As the boron-containing compound used for the second material, a boron-containing compound represented by the following general formula (22) is also preferable.

In the general formula (22), the dotted arc represents that a ring structure is formed together with the solid line skeleton portion. The dotted portion in the solid line skeleton portion represents that a pair of atoms connected by the dotted line may be connected by a double bond. The arrow from the nitrogen atom to the boron atom represents that the nitrogen atom is coordinated to the boron atom. ^Q3 and ^Q4 are the same or different and are linking groups in the solid line skeleton portion, at least a part of which forms a ring structure together with the dotted arc portion and may have a substituent. ^X5 and ^X6 are the same or different and represent a hydrogen atom or a monovalent substituent that becomes a substituent of the ring structure. ^X7 and ^X8 are the same or different and represent a monovalent electron transporting substituent that becomes a substituent of the ring structure. ^X5 , ^X6 , ^X7 , and ^X8 may each be bonded to a ring structure forming the dotted arc portion in a plurality of units.

In the above general formula (22), the dotted arc represents that a ring structure is formed together with the skeletal portion represented by the solid line, i.e., a part of the skeletal portion connecting the boron atom and ^Q3 , or a part of the skeletal portion connecting the boron atom, ^Q4 , and the nitrogen atom. This represents that the compound represented by general formula (22) has at least four ring structures in the structure, and in general formula (22), the skeletal portion connecting the boron atom and ^Q3 and the skeletal portion connecting the boron atom, ^Q4 , and the nitrogen atom are included as parts of the ring structure.

In the above general formula (22), the skeletal moieties represented by solid lines, i.e., the skeletal moieties connecting the boron atom and ^Q3 , and the dotted lines in the skeletal moieties connecting the boron atom, ^Q4 , and the nitrogen atom, indicate that a pair of atoms connected by the dotted line in each skeletal moiety may be connected by a double bond.

In the above general formula (22), the arrow from the nitrogen atom to the boron atom indicates that the nitrogen atom is coordinated to the boron atom. Here, "coordinated" means that the nitrogen atom acts like a ligand on the boron atom and chemically influences it.

In the above general formula (22), ^Q3 and ^Q4 are the same or different and are linking groups in the skeleton portion represented by the solid line, at least a part of which forms a ring structure together with the dotted arc portion and may have a substituent. This means that ^Q3 and ^Q4 are each incorporated as a part of the ring structure.

Q ³ and Q ⁴ in the above general formula (22) include structures represented by the above formulas (13-1) to (13-8). In addition, general formula (13-2) is a structure in which two hydrogen atoms are bonded to a carbon atom and three more atoms are bonded to the carbon atom, but the three atoms bonded to the carbon atom other than the hydrogen atoms are all atoms other than hydrogen atoms. Among the above formulas (13-1) to (13-8), any of formulas (13-1), (13-7), and (13-8) is preferred. More preferably, formula (13-1). That is, Q ³ and Q ⁴ may be the same or different and represent a linking group having one carbon atom, which is also one of the preferred embodiments of the present invention.

In the above general formula (22), examples of the ring to which ^X5 to ^X7 are bonded include the same rings as the specific examples of the ring to which ^X1 is bonded in the above general formula (11) when ^Y1 is a direct bond and ⁿ¹ is 2. Among these, a benzene ring, a naphthalene ring, a thiophene ring, and a benzothiophene ring are preferred. A benzene ring and a thiophene ring are more preferred.

In the above general formula (22), the ring to which ^X8 is bonded may be the same as the specific example of the ring to which X2 is bonded in the above general formula (11) when ^Y1 is a direct bond and ⁿ¹ is 2, and the preferred ring structure among them is also the same. The * mark in the above formulas (15-1) to (15-17) indicates that the carbon atom constituting the ring to which ^X7 is bonded and constituting the skeleton portion connecting the boron atom, ^Q4 , and the nitrogen atom in general formula (22) is bonded to any one of the carbon atoms marked with *. In addition, it may be condensed with another ring structure at a position other than the carbon atom marked with *.

That is, in one preferred embodiment of the present invention, the boron-containing compound represented by the above general formula (22) is a boron-containing compound represented by the following general formula (23):

In formula (23), the arrow from the nitrogen atom to the boron atom, and X ⁵ , X ⁶ , X ⁷ and X ⁸ are the same as in formula (22).

In the boron-containing compound represented by the above general formula (23), the ring to which ^X5 , ^X6 , ^X7 , and ^X8 are bonded is composed only of carbon atoms, except for the nitrogen atom coordinated to the boron atom, and therefore the orbital spread is smaller and the HOMO-LUMO energy gap is generally kept wide, compared with a compound containing a heteroatom such as S in the ring. Therefore, for example, the compound can be suitably used as an electron injection layer of an organic EL device.

In the above general formula (22), ^X5 and ^X6 are the same or different and represent a hydrogen atom or a monovalent substituent that is a substituent of a ring structure. The monovalent substituent is not particularly limited, and examples thereof include the same as the specific examples of the monovalent substituents of ^X1 , ^X2 , ^X3 , and ^X4 in the above general formula (11). More preferred substituents include an oligoaryl group, a monovalent heterocyclic group, and a monovalent oligoheterocyclic group, and the preferred substituents are also the same.
In the above general formula (22), when X ⁵ , X ⁶ , X ⁷ and X ⁸ are monovalent substituents, the bonding positions and bonding numbers of X ⁵ , X ⁶ , X ⁷ and X ⁸ to the ring structure are not particularly limited.

In the above general formula (22), ^X7 and ^X8 are the same or different and each represents a monovalent electron-transporting substituent that becomes a substituent of the ring structure. By having an electron-transporting substituent as ^X7 and ^X8 , the boron-containing compound represented by the above general formula (22) becomes a material with excellent electron transport properties.
Examples of the electron-transporting monovalent substituent include a monovalent group derived from a nitrogen-atom-containing heterocycle having a carbon-nitrogen double bond (C═N) in the ring, such as an imidazole ring, a thiazole ring, an oxazole ring, an oxadiazole ring, a triazole ring, a pyrazole ring, a pyridine ring, a pyrazine ring, a triazine ring, a benzimidazole ring, a benzothiazole ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, or a benzothiadiazole ring; a monovalent group derived from an aromatic hydrocarbon ring or aromatic heterocycle not having a carbon-nitrogen double bond in the ring, such as a benzene ring, a naphthalene ring, a fluorene ring, a thiophene ring, a benzothiophene ring, or a carbazole ring, which has one or more electron-withdrawing substituents; a dibenzothiophene dioxide ring, a dibenzophosphole oxide ring, a silole ring, and the like.

Examples of the electron-withdrawing substituent include -CN, -COR, -COOR, -CHO, _-CF3 , _-SO2Ph , and -PO(Ph) ₂ , where R represents a hydrogen atom or a monovalent hydrocarbon group.
Among these, the electron-transporting monovalent substituent is preferably a group derived from a nitrogen-atom-containing heterocycle having a carbon-nitrogen double bond (C═N) in the ring.
The electron-transporting monovalent substituent is more preferably any monovalent group derived from a heteroaromatic ring compound having a carbon-nitrogen double bond in the ring.

The substituents in X ⁵ , X ⁶ , X ⁷ and X ⁸ are the same as those in X ¹ , X ² , X ³ and X ⁴ in the general formula (11) above.

The boron-containing compound represented by the above general formula (22) is most preferably a boron-containing compound represented by the following structural formula (22-1).

As the boron-containing compound used for the second material, a boron-containing compound represented by the following general formula (24) is also preferable.

In the general formula (24), the dotted arc represents that a ring structure is formed together with the solid line skeleton portion. The dotted portion in the solid line skeleton portion represents that a pair of atoms connected by the dotted line may be connected by a double bond. The arrow from the nitrogen atom to the boron atom represents that the nitrogen atom is coordinated to the boron atom. ^Q5 and ^Q6 are the same or different and are linking groups in the solid line skeleton portion, at least a part of which forms a ring structure together with the dotted arc portion and may have a substituent. ^X9 , ^X10 , ^X11 , and ^X12 are the same or different and represent a hydrogen atom, a monovalent substituent that becomes a substituent of the ring structure, or a direct bond, and may be bonded to the ring structure forming the dotted arc portion. ^A1 is the same or different and represents a divalent group. The structural unit in the parentheses with ⁿ² is bonded to the adjacent structural unit at any two of ^X9 , ^X10 , ^X11 , and ^X12 . ⁿ² and ⁿ³ are each independently the same or different and each represents a number of 1 or more.

^Q5 and ^Q6 in the above general formula (24) are the same as ^Q3 and ^Q4 in the above general formula (22), and the preferred embodiments are also the same. That is, it is preferable that ^Q5 and ^Q6 are the same or different and represent a linking group having 1 carbon atom.
In the above general formula (24), the dotted arc, the dotted portion in the solid-line skeleton, and the arrow from the nitrogen atom to the boron atom have the same meanings as in the above general formula (22), and the preferred structure of the dotted arc is also the same as in the above general formula (22). That is, the boron-containing compound represented by the general formula (24) is preferably a boron-containing compound represented by the following general formula (25).

In general formula (25), the arrow from the nitrogen atom to the boron atom, ^X9 , ^X10 , ^X11 , ^X12 , ^A1 , ⁿ² and ⁿ³ are the same as in general formula (24). The bond between the structural unit in parentheses with ⁿ² and the adjacent structural unit is also the same as in general formula (24).

In the above general formula (24), ⁿ² represents the number of structural units in the parentheses with ⁿ² attached, and represents a number of 1 or more. ⁿ³ represents the number of structural units in the parentheses with ⁿ³ attached, and represents a number of 1 or more. ⁿ² and ⁿ³ are each independently, the same or different, and represent a number of 1 or more, which has the following meaning. ⁿ² and ⁿ³ are each independent numbers. Therefore, ⁿ² and ⁿ³ may be the same number or different numbers.

The boron-containing compound represented by the general formula (24) may have one or more repeating units represented by the general formula (24). When the boron-containing compound has more than one repeating units represented by the general formula (24), ⁿ² and ⁿ³ in one unit may be the same as or different from ⁿ² and ⁿ³ in the adjacent units.

Therefore, the boron-containing compound represented by the general formula (24) includes any of the following structures: an alternating copolymer (having two or more repeating structures represented by the general formula (24) above, in which ⁿ² is the same number and ⁿ³ is the same number in all structures represented by the general formula (24) above), a block copolymer (having one repeating structure represented by the general formula (24) above, in which at least one of ⁿ² and ⁿ³ is 2 or more), and a random copolymer (having two or more repeating structures represented by the general formula (24) above, in which at least one of the structures represented by the multiple general formula (24) has either or both of ⁿ² and ⁿ³ that are different from the ⁿ² and ⁿ³ in the other structures).
Of these, the boron-containing compound represented by the above general formula (24) is preferably an alternating copolymer.

In the above formula (24), X ⁹ , X ¹⁰ , X ¹¹ and X ¹² are the same or different and each represent a hydrogen atom, a monovalent substituent that serves as a substituent of a ring structure, or a direct bond.
In the above general formula (24), any two of ^X9 , ^X10 , ^X11 , and ^X12 form a bond as a part of the main chain of the polymer. Among ^X9 to ^X12 , those that form a bond as a part of the main chain of the polymer are direct bonds. Among ^X9 , ^X10 , ^X11 , and ^X12 , those that do not participate in polymerization are hydrogen atoms or monovalent substituents.
Among ^X9 , ^X10 , ^X11 and ^X12 , specific examples and preferred ones of the monovalent group not involved in polymerization are the same as the specific examples and preferred ones of ^X5 and ^X6 of the boron-containing compound represented by the above-mentioned general formula (22).

In the boron-containing compound represented by the above general formula (24), among ^X9 , ^X10 , ^X11 and ^X12 , the direct bond may be any of ^X9 , ^X10 , ^X11 and ^X12 , but it is preferable that ^X9 and ^X10 , or ^X11 and ^X12 are directly bonded. In this case, the boron-containing compound represented by the above general formula (24) becomes a polymer having a repeating unit structure represented by the following general formula (26) or general formula (27).

In general formulae (26) and (27), the dotted arc, the dotted portion in the solid-line skeleton, the arrow from the nitrogen atom to the boron atom, ^Q5 , ^Q6 , ^A1 , ⁿ² , and ⁿ³ are the same as those in general formula (24). In general formula (26), ^X9 and ^X10 represent a direct bond, and ^X11 and ^X12 represent a hydrogen atom or a monovalent substituent. In general formula (27), ^X11 and ^X12 represent a direct bond, and ^X9 and ^X10 represent a hydrogen atom or a monovalent substituent.

When the boron-containing compound used as the second material is a polymer, the weight average molecular weight is preferably 5,000 to 1,000,000. When the weight average molecular weight is in this range, the organic thin film can be easily thinned when produced by applying a coating composition containing the second material and the first material. The weight average molecular weight is more preferably 10,000 to 500,000, and even more preferably 30,000 to 200,000.

The weight average molecular weight can be measured by gel permeation chromatography (GPC) in terms of polystyrene using the following apparatus and under the following measurement conditions.
High-speed GPC device: HLC-8220GPC (manufactured by Tosoh Corporation)
Developing solvent: chloroform Column: TSK-gel GMHXL x 2 Eluent flow rate: 1 ml/min
Column temperature: 40°C

A ¹ in the above general formula (24) is not particularly limited so long as it is a divalent group, but is preferably any one of an alkenyl group, an arylene group, and a divalent aromatic heterocyclic group.
The arylene group is an atomic group obtained by removing two hydrogen atoms from an aromatic hydrocarbon, and the number of carbon atoms constituting the ring is usually about 6 to 60, and preferably 6 to 20. The aromatic hydrocarbon also includes those having a condensed ring, and those in which two or more independent benzene rings or condensed rings are bonded directly or via a group such as vinylene.

The arylene group may, for example, be any of the groups represented by the following general formulas (28-1) to (28-23). Among these, a phenylene group, a biphenylene group, a fluorene-diyl group, and a stilbene-diyl group are preferred.

In the general formulae (28-1) to (28-23), R may be the same or different and represent a hydrogen atom, a halogen atom, an alkyl group, an alkyloxy group, an alkylthio group, an alkylamino group, an aryl group, an aryloxy group, an arylthio group, an arylalkyl group, an arylalkyloxy group, an arylalkylthio group, an acyl group, an acyloxy group, an amido group, an imide group, an imine residue, an amino group, a substituted amino group, a substituted silyl group, a substituted silyloxy group, a substituted silylthio group, a substituted silylamino group, a monovalent heterocyclic group, a heteroaryloxy group, a heteroarylthio group, an arylalkenyl group, an arylethynyl group, a carboxyl group, an alkyloxycarbonyl group, an aryloxycarbonyl group, an arylalkyloxycarbonyl group, a heteroaryloxycarbonyl group, or a cyano group.

In general formulae (28-1) to (28-23), a line intersecting a ring structure, such as the line indicated by x-y in general formula (28-1), means that the ring structure is directly bonded to an atom in the bonded portion. That is, in general formula (28-1), the line indicated by x-y means that the ring structure is directly bonded to any of the carbon atoms constituting the ring, and the bonding position in the ring structure is not limited.
In addition, in the general formulae (28-1) to (28-23), a line attached to a vertex of a ring structure, such as the line indicated by z- in the general formula (28-10), means that the ring structure is directly bonded to an atom in the bonded portion at that position.
In addition, a line with R attached thereto crossing a ring structure means that one or more R may be bonded to the ring structure, and the bonding position of the R may be unlimited.

In addition, in general formulae (28-1) to (28-10) and (28-15) to (28-20), the carbon atoms may be replaced with nitrogen atoms, and the hydrogen atoms may be replaced with fluorine atoms.

The above-mentioned divalent aromatic heterocyclic group refers to the atomic group remaining after removing two hydrogen atoms from an aromatic heterocyclic compound, and the number of carbon atoms constituting the ring is usually about 3 to 60. The aromatic heterocyclic compound includes aromatic organic compounds having a cyclic structure in which the elements constituting the ring are not only carbon atoms, but also heteroatoms such as oxygen, sulfur, nitrogen, phosphorus, boron, and arsenic in the ring.

Examples of the divalent aromatic heterocyclic group include the heterocyclic groups represented by the following general formulas (29-1) to (29-38).

In the general formulae (29-1) to (29-38), R is the same as R in the above arylene group. Y represents O, S, SO, _SO2 , Se, or Te. The lines intersecting the ring structure, the lines at the vertices of the ring structure, and the lines with R intersecting the ring structure are the same as in the general formulae (28-1) to (28-23).
In addition, in the general formulae (29-1) to (29-38), a carbon atom may be replaced with a nitrogen atom, and a hydrogen atom may be replaced with a fluorine atom.

As A ¹ in the above general formula (24), among those mentioned above, the formulas (28-1), (28-9), (29-1), (29-9), (29-16), and (29-17) are preferred, and the formulas (28-1) and (28-9) are more preferred. In this case, when an organic thin film is produced by a method of applying a coating composition containing the second material, which is a boron-containing compound represented by the above general formula (24), and the first material, excellent film formability is obtained.

The boron-containing compound represented by the general formula (24) is most preferably a boron-containing compound represented by the general formula (24-1) or (24-2). As the boron-containing compound represented by the general formula (24), the boron-containing compound represented by the general formula (24-2) is particularly preferred, which is easily soluble in a solvent and can be used to easily prepare a coating composition containing the first material and the second material.

In the general formula (24-1), ⁿ⁵ represents a number of 1 or more.
In formula (24-2), ⁿ⁴ represents a number of 1 or more.

When the above-mentioned boron-containing compound is used as the second material having electron transport properties, a uniform organic thin film can be easily obtained by applying a coating composition containing the first material and the second material.
In addition, the above-mentioned boron-containing compounds have deep lowest unoccupied molecular orbital (LUMO) energies, making them suitable materials for the electron injection layer of an organic EL device, and therefore organic thin films containing these boron-containing compounds as the second material are particularly suitable for the electron injection layer of an organic EL device.
The above-mentioned boron-containing compound can be synthesized, for example, according to the method described in WO 2016/181705.

The mixing ratio of the first material and the second material contained in the organic thin film of this embodiment is not particularly limited, and can be appropriately determined depending on the type of compound used for each of the first material and the second material. The mixing ratio of the first material and the second material is preferably 0.01:99.9 to 10:1 in mass ratio (first material:second material). For example, when dimethylaminopyridine (DMAP) is used as the first material and a boron-containing compound represented by general formula (22-1) is used as the second material, the mixing ratio of the first material and the second material is preferably 0.5:1 to 40:1 in mass ratio (first material:second material), and more preferably 2:1 to 20:1. With the above mixing ratio, the effect of improving the electron transport property and the electron injection property due to the inclusion of the first material and the second material in the organic thin film becomes significant.

The organic thin film may be composed of only the first material and the second material, or may contain other materials than the first material and the second material as long as the effects of the present invention are obtained. When the organic thin film contains other materials than the first material and the second material, for example, the content (mass %) of the other materials in the organic thin film is preferably equal to or less than the content (mass %) of the second material.
It is preferable to use an electron transport material as the material other than the first material and the second material. As the electron transport material, for example, any material conventionally known as a material for the electron transport layer of an organic EL element may be used.

(Electron Transport Layer)
As the material for the electron transport layer 6, any material that can be usually used as the material for the electron transport layer 6 can be used, and these materials may be used in combination.
Examples of low molecular weight compounds that can be used as the material for the electron transport layer 6 include bis[2-(o-hydroxyphenylbenzothiazole)zinc(II) (Zn(BTZ) ₂ ), tris(8-hydroxyquinolinato)aluminum (Alq ₃ boron-containing compounds; pyridine derivatives such as tris-1,3,5-(3'-(pyridin-3"-yl)phenyl)benzene (TmPyPhB); quinoline derivatives such as (2-(3-(9-carbazolyl)phenyl)quinoline (mCQ)); pyrimidine derivatives such as 2-phenyl-4,6-bis(3,5-dipyridylphenyl)pyrimidine (BPyPPM); pyrazine derivatives; phenanthroline derivatives such as bathophenanthroline (BPhen); triazine derivatives such as 2,4-bis(4-biphenyl)-6-(4'-(2-pyridinyl)-4-biphenyl)-[1,3,5]triazine (MPT); Examples of the organic silane derivatives include triazole derivatives such as Zn(BTZ) and the like, oxazole derivatives, oxadiazole derivatives such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole) (PBD) and the like, imidazole derivatives such as 2,2',2"-(1,3,5-bentriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI) and the like, aromatic ring tetracarboxylic acid anhydrides such as naphthalene and perylene, and silole derivatives such as 2,5-bis(6'-(2',2"-bipyridyl))-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy) and the like. One or more of these can be used. Among these, Zn(BTZ) ₂ is preferred.

The average thickness of the electron transport layer 6 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 40 to 100 nm. The average thickness of the electron transport layer 6 can be measured during deposition using a quartz crystal thickness gauge.

(Light Emitting Layer)
The material for forming the light-emitting layer 7 may be a low molecular weight compound, a high molecular weight compound, or a mixture of these.

Examples of the polymer compound forming the light-emitting layer 7 include polyacetylene-based compounds such as trans-polyacetylene, cis-polyacetylene, poly(di-phenylacetylene) (PDPA), and poly(alkylphenylacetylene) (PAPA); polyparaphenylenevinylene-based compounds such as poly(para-phenvinylene) (PPV), poly(2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly(para-phenvinylene) (CN-PPV), poly(2-dimethyloctylsilyl-para-phenylenevinylene) (DMOS-PPV), and poly(2-methoxy,5-(2'-ethylhexoxy)-para-phenylenevinylene) (MEH-PPV); polythiophene-based compounds such as poly(3-alkylthiophene) (PAT) and poly(oxypropylene)triol (POPT); and poly(9,9-dialkylfluorene) (PD polyfluorene-based compounds such as poly(dioctylfluorene-alt-benzothiadiazole) (F8BT), α,ω-bis[N,N'-di(methylphenyl)aminophenyl]-poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6am4), poly(9,9-dioctyl-2,7-divinylenefluorenyl-ortho-co(anthracene-9,10-diyl); poly(para-phenyl Examples of such compounds include polyparaphenylene compounds such as poly(1,5-dialkoxy-para-phenylene) (PPP) and poly(1,5-dialkoxy-para-phenylene) (RO-PPP); polycarbazole compounds such as poly(N-vinylcarbazole) (PVK); polysilane compounds such as poly(methylphenylsilane) (PMPS), poly(naphthylphenylsilane) (PNPS), and poly(biphenylylphenylsilane) (PBPS); and boron compound-based polymer compounds.

Examples of low molecular weight compounds forming the light emitting layer 7 include phosphorescent materials, as well as 8-hydroxyquinoline aluminum (Alq ₃ ), tris[1-phenylisoquinoline-C2,N]iridium(III) (Ir(piq) ₃ ), bis[2-(o-hydroxyphenylbenzothiazole)zinc(II) (Zn(BTZ) ₂ ), tris(4-methyl-8-quinolinolato)aluminum(III) (Almq ₃ ), 8-hydroxyquinoline zinc (Znq ₂ ), (1,10-phenanthroline)-tris-(4,4,4-trifluoro-1-(2-thienyl)-butane-1,3-dionate)europium(III) (Eu(TTA) ₃ ). (phen)), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (II), and various other metal complexes; benzene-based compounds such as distyrylbenzene (DSB) and diaminodistyrylbenzene (DADSB), naphthalene-based compounds such as naphthalene and Nile Red, phenanthrene-based compounds such as phenanthrene, chrysene-based compounds such as chrysene and 6-nitrochrysene, perylene, N,N'-bis(2,5-di-t-butylphenyl)-3,4,9,10-perylene-di-carboximide (BPPC), and other perylene-based compounds; anthracene-based compounds, such as coronene; anthracene-based compounds, such as anthracene and bisstyrylanthracene; pyrene-based compounds, such as pyrene; pyran-based compounds, such as 4-(di-cyanomethylene)-2-methyl-6-(para-dimethylaminostyryl)-4H-pyran (DCM); acridine-based compounds, such as acridine; stilbene-based compounds, such as stilbene; carbazolyl compounds, such as 4,4'-bis[9-dicarbazolyl]-2,2'-biphenyl (CBP) and 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'-biphenyl (BCzVBi); thiophene compounds such as 2,5-dibenzoxazolethiophene, benzoxazole compounds such as benzoxazole, benzimidazole compounds such as benzimidazole, benzothiazole compounds such as 2,2'-(para-phenylenedivinylene)-bisbenzothiazole, butadiene compounds such as bistyryl(1,4-diphenyl-1,3-butadiene) and tetraphenylbutadiene, naphthalimide compounds such as naphthalimide, coumarin compounds such as coumarin, perinone compounds such as perinone, and oxadiazole and other olefin compounds. Examples of the compound include oxadiazole-based compounds, aldazine-based compounds, cyclopentadiene-based compounds such as 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), quinacridone-based compounds such as quinacridone and quinacridone red, pyridine-based compounds such as pyrrolopyridine and thiadiazolopyridine, spiro compounds such as 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene, and metal or metal-free phthalocyanine-based compounds such as phthalocyanine (H2Pc) and copper phthalocyanine. One or more of these compounds may be used.

As the light-emitting layer 7, in addition to a material that emits visible light, for example, an organic material that emits infrared light can be used. As the material of the light-emitting layer 7, in addition to an organic material, for example, a quantum dot or a material with a _{perovskite structure represented by CH3NH3PbBr3 (} for example, see Non-Patent Document ₃ ) can be used. As the material of the light-emitting layer 7, in addition to a fluorescent material or a phosphorescent material, a thermally activated delayed fluorescent material can be used.

The average thickness of the light-emitting layer 7 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 20 to 100 nm. The average thickness of the light-emitting layer 7 can be measured with a quartz crystal film thickness gauge when the material of the light-emitting layer 7 is a low molecular weight compound, and can be measured with a contact step gauge when the material of the light-emitting layer 7 is a high molecular weight compound.

(Hole transport layer)
As the material for the hole transport layer 8, any material that can be usually used as the material for the hole transport layer 8 can be used, and these materials may be used in combination.
Examples of materials for the hole transport layer 8 include arylcycloalkane compounds such as 1,1-bis(4-di-para-triaminophenyl)cyclohexane and 1,1′-bis(4-di-para-tolylaminophenyl)-4-phenyl-cyclohexane, N4,N4′-bis(dibenzo[b,d]thiophen-4-yl)-N4,N4′-diphenylbiphenyl-4,4′-diamine (DBTPB), and 4,4′,4″-trimethyltriphenyl Amines, N,N,N',N'-tetraphenyl-1,1'-biphenyl-4,4'-diamine, N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD1), N,N'-diphenyl-N,N'-bis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (TPD2), N,N,N',N'-tetrakis(4-methoxyphenyl)-1,1'- Arylamine compounds such as biphenyl-4,4'-diamine (TPD3), N,N'-di(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD), triphenylamine tetramer (TPTE), and 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA); phenylenediamine compounds such as N,N,N',N'-tetraphenyl-para-phenylenediamine, N,N,N',N'-tetra(para-tolyl)-para-phenylenediamine, and N,N,N',N'-tetra(meta-tolyl)-meta-phenylenediamine (PDA); carbazole compounds such as carbazole, N-isopropylcarbazole, and N-phenylcarbazole; stilbene compounds such as stilbene and 4-di-para-tolylaminostilbene; oxazole compounds such as OxZ; triphenylmethane, m- triphenylmethane compounds such as MTDATA, pyrazoline compounds such as 1-phenyl-3-(para-dimethylaminophenyl)pyrazoline, benzine (cyclohexadiene) compounds, triazole compounds such as triazole, imidazole compounds such as imidazole, oxadiazole compounds such as 1,3,4-oxadiazole and 2,5-di(4-dimethylaminophenyl)-1,3,4-oxadiazole, anthracene compounds such as anthracene and 9-(4-diethylaminostyryl)anthracene, fluorenone compounds such as fluorenone, 2,4,7-trinitro-9-fluorenone, and 2,7-bis(2-hydroxy-3-(2-chlorophenylcarbamoyl)-1-naphthylazo)fluorenone, aniline compounds such as polyaniline, silane compounds, 1,4-dithioketo-3,6-diphenyl-pyrrolo-(3,4-c)pyrrolo Examples of the compound include pyrrole-based compounds such as pyrrole, fluorene-based compounds such as fluorene, porphyrin-based compounds such as porphyrin and metal tetraphenylporphyrin, quinacridone-based compounds such as quinacridone, metallic or non-metallic phthalocyanine-based compounds such as phthalocyanine, copper phthalocyanine, tetra(t-butyl)copper phthalocyanine, and iron phthalocyanine, metallic or non-metallic naphthalocyanine-based compounds such as copper naphthalocyanine, vanadyl naphthalocyanine, and monochlorogallium naphthalocyanine, benzidine-based compounds such as N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine and N,N,N',N'-tetraphenylbenzidine, and 9-(2-ethylhexyl)-N,N,N,N-tetrakis(4-metaoxyphenyl)-9H-carbazole-2,7-diamine) (EH44). One or more of these compounds may be used. Among these, arylamine compounds such as DBTPB, α-NPD, TCTA, etc. are preferable. These materials that can be used for the hole transport layer 8 can also be suitably used as the host material for the hole injection layer described later.

The average thickness of the hole transport layer 8 is not particularly limited, but is preferably 10 to 150 nm, and more preferably 40 to 100 nm. The average thickness of the hole transport layer 8 can be measured during deposition using a quartz crystal thickness gauge.

(Hole Injection Layer)
The hole injection layer 9 includes an organic host material and an electron-withdrawing dopant having hole injection capability, wherein the ratio of the electron-withdrawing dopant is from 12% by mass to 50% by mass, preferably from 18% by mass to 50% by mass, based on the total amount of the host material and the electron-withdrawing dopant.
The concentration of the electron-withdrawing dopant can be determined depending on the conditions of the organic EL element 1 to be used, such as the carrier balance of the organic EL element 1 and the HOMO and hole mobility of the host material of the hole-injection layer. When doped at 12% by mass or more, the performance of suppressing deterioration of the light-emitting surface is high even when stored in air, and when doped at 18% by mass or more, the performance of suppressing deterioration of the light-emitting surface is particularly high.

The organic hole injection layer host material is not particularly limited, but is preferably a material having hole transport capability, such as the organic material described in the above section on hole transport layer 8. The above-mentioned arylamine compounds such as DBTPB, α-NPD, and TCTA are also preferred as the hole injection layer host material.

On the other hand, the electron-withdrawing dopant of the hole injection layer 9 is an electron-withdrawing material having hole injection ability. The electron-withdrawing dopant preferably has an electron-withdrawing functional group such as a cyano group, a nitro group, or a halogen. As the electron-withdrawing dopant material, for example, tetrafluorotetracyanoquinodimethane (F4-TCNQ), 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN), 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TCCNNQ), etc. can be used. Among these, materials having tetracyanoquinodimethane as a functional group, such as F4-TCNQ and F6-TCCNNQ, are particularly preferred. Here, tetracyanoquinodimethane has a structure in which two cyano groups and two groups formed by carbon [(N≡C) _2C =] are bonded to an aromatic ring by a double bond, and a "material having tetracyanoquinodimethane as a functional group" is a material that has such a structure as a functional group.

The average thickness of the hole injection layer 9 is not particularly limited, but is preferably 1 to 1000 nm, and more preferably 5 to 50 nm. The average thickness of the hole injection layer 9 can be measured during film formation using a quartz crystal film thickness meter.
In addition, some kind of buffer layer may be sandwiched between the hole injection layer 9 and the anode 10 described later.

(anode)
Examples of materials for the anode 10 include metal elements such as Au, Pt, Ag, Cu, Pd, Mo, Ni, Mg, and Bi, or alloys containing these, transparent conductive oxides such as ITO, IZO, and AZO, conductive carbons such as graphene and carbon nanotubes (CNT), conductive polymers such as poly(3,4-ethylenedioxythiophene):polystyrenesulfonic acid (PEDOT:PSS), and mixtures thereof. Among these, it is preferable to use any of Ag, Au, Pd, ITO, and IZO as the material for the anode 10, and Pd, Pt, Ag, and Au are more preferable because they are less susceptible to oxidation, and Ag and Au are particularly preferable.
In particular, when the hole injection layer 9 and the anode 10 are adjacent to each other, the anode 10 is preferably made of a metal element alone, a transparent conductive oxide alone, or a laminate of a metal element and a transparent conductive oxide.

The average thickness of the anode 10 is not particularly limited, but is preferably, for example, 10 to 1000 nm, and more preferably 30 to 150 nm.
When the organic EL element 1 is of a top emission type, it is preferable to use a transparent material as the material of the anode 10. When the organic EL element 1 is of a top emission type and a material that is opaque to irradiated light is used as the material of the anode 10, the anode 10 can be used as a transparent anode by setting the average thickness to about 8 to 30 nm.
The average thickness of the anode 10 can be measured during deposition using a quartz crystal film thickness gauge.

(Sealing)
The organic EL element of the present invention is sealed at a low level, with a water vapor transmission rate (WVTR) of 3×10 ⁻³ g/m ² /day or more.
Thus, the organic EL element of the present invention has high storage stability even with low-level sealing, so it can be made flexible and inexpensive to manufacture. In addition, it has the advantage of being able to reduce the quality variation between products and to easily increase the area. The water vapor transmission rate can be measured, for example, by the Ca corrosion method.
Regarding the sealing of the organic EL element of the present invention, there is no upper limit to the water vapor transmission rate (WVTR), and, for example, the sealing may be performed by covering the components (substrate, cathode, light-emitting layer, hole injection layer, anode, etc.) with a film or the like, or the sealing may be performed by simply surrounding the components with a case. Moreover, sealing with a water vapor transmission rate (WVTR) of 3×10 ^-3 g/m ² /day or more also includes non-sealing.

(Formation method)
In the organic EL element 1 shown in FIG. 1, the method for forming all the layers is not particularly limited, and examples of the method that can be used include chemical vapor deposition (CVD) methods such as plasma CVD, thermal CVD, and laser CVD, which are gas phase film formation methods, dry plating methods such as vacuum deposition, sputtering, and ion plating, and thermal spraying methods, and liquid phase film formation methods such as wet plating methods such as electrolytic plating, immersion plating, and electroless plating, the sol-gel method, the MOD method, the spray pyrolysis method, a doctor blade method using a fine particle dispersion, and printing techniques such as a spin coating method, an inkjet method, and a screen printing method. An appropriate method can be selected and used depending on the material.
It is preferable to select these methods depending on the characteristics of the material of each layer, and the manufacturing method may differ for each layer.

<Display Device>
The display device of the present invention is characterized by comprising the organic electroluminescence element described above. The display device of the present invention comprises the organic EL element having good storage stability (storage life) in the atmosphere described above, and therefore has a long storage life and can be used stably for a long period of time. In addition to the organic EL element described above, the display device of the present invention can comprise other components that are generally used in display devices.

<Lighting equipment>
The lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. The lighting device of the present invention comprises the organic EL element having good storage stability (storage life) in the atmosphere described above, and therefore has a long storage life and can be used stably for a long period of time. In addition to the organic EL element described above, the lighting device of the present invention can comprise other components that are generally used in lighting devices.

The following describes examples and comparative examples of the present invention. Note that the present invention is not limited to the examples shown below.

Example 1
[1] A commercially available transparent glass substrate (hereinafter also simply referred to as substrate) 2 having an average thickness of 0.7 mm and having a cathode 3 made of an ITO film (patterned to a thickness of 150 nm and a width of 3 mm) was prepared.

[2] Next, the substrate 2 having the cathode 3 was scrubbed with an alkaline cleaner and a PVA sponge, then ultrasonically cleaned in acetone and isopropanol for 10 minutes each, and further cleaned in isopropanol vapor for 5 minutes. The substrate 2 was then removed from the isopropanol, dried by nitrogen blowing, and UV ozone cleaned for 20 minutes.

[3] Next, the substrate was set on a substrate holder in a Millertron sputtering device (manufactured by Choshu Sangyo Co., Ltd.), and a zinc oxide film was formed to a thickness of 3 nm using reactive sputtering by Millertron sputtering with a Zn target. Next, the substrate 2 with the zinc oxide film formed on the cathode 3 was heat-treated in the atmosphere on a hot plate at 400°C for 1 hour. This formed an inorganic electron injection layer 4.

で示されるホウ素含有化合物（ＳＰＢ－ＢＰｙ２）の１．０質量％シクロペンタノン溶液を作製した。なお、該ホウ素含有化合物は、特開２０１６－５４１７３号公報の合成例４に記載の方法に従って合成した。無機電子注入層４まで形成した基板２をスピンコーターにセットし、上記ホウ素含有化合物のシクロペンタノン溶液を滴下し、毎分３０００回転で３０秒間回転させて塗布した。更に、上記ホウ素含有化合物のシクロペンタノン溶液を塗布した基板２を、窒素雰囲気中で１５０℃にセットしたホットプレートを用いて、１時間アニールした。これにより、平均膜厚が２５ｎｍのホウ素含有化合物からなる有機電子注入層５を形成した。 [4] Next, the following structural formula (30):

A 1.0 mass% cyclopentanone solution of a boron-containing compound (SPB-BPy2) represented by the formula (1) was prepared. The boron-containing compound was synthesized according to the method described in Synthesis Example 4 of JP-A-2016-54173. The substrate 2 on which the inorganic electron injection layer 4 was formed was set on a spin coater, and the cyclopentanone solution of the boron-containing compound was dropped onto the substrate, which was then rotated at 3000 rpm for 30 seconds to coat the substrate. Furthermore, the substrate 2 on which the cyclopentanone solution of the boron-containing compound was coated was annealed for 1 hour using a hot plate set at 150° C. in a nitrogen atmosphere. This resulted in the formation of an organic electron injection layer 5 made of a boron-containing compound with an average film thickness of 25 nm.

[5] Next, the substrate 2 on which the organic electron injection layer 5 had been formed was fixed to a substrate holder in a chamber of a vacuum deposition apparatus. Bis[2-(o-hydroxyphenylbenzothiazole)zinc(II) (Zn(BTZ) ₂ ) represented by the following structural formula (31), tris[1-phenylisoquinoline-C2,N]iridium(III) (Ir(piq) ₃ ) represented by the following structural formula (32), a hole transport material HTM-081 manufactured by Merck & Co., 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TCCNNQ) represented by the following structural formula (33), and Ag were each placed in a crucible and set as a deposition source.

[6] The inside of the vacuum deposition apparatus was reduced in pressure to about 1×10 ⁻⁵ Pa, and Zn(BTZ) ₂ was deposited to a thickness of 10 nm to form an electron transport layer 6 .
Further, Zn(BTZ) ₂ as a host and Ir(piq) ₃ as a dopant were co-evaporated to a thickness of 20 nm to form the light-emitting layer 7. At this time, the doping concentration of Ir(piq) ₃ was set to 6 mass% with respect to the entire light-emitting layer 7.
Next, a hole transport layer 8 was formed by depositing HTM-081 to a thickness of 50 nm.
Furthermore, HTM-081 was co-deposited as a host and F6-TCNNQ as a dopant to a thickness of 10 nm to form a hole injection layer 9. At this time, the doping concentration of F6-TCNNQ was set to 18% by mass with respect to the entire hole injection layer 9.
Finally, Ag was evaporated to a thickness of 100 nm to form the anode 10. By the above steps, the organic EL element 1 of Example 1 was obtained.
When the anode 10 was evaporated, a stainless steel evaporation mask was used so that the evaporation surface would be in the shape of a strip having a width of 3 mm. As a result, the light-emitting area of the organic EL element 1 was set to ⁹ mm2.
Moreover, the organic EL element 1 is not sealed at all, and its water vapor transmission rate (WVTR) is 3×10 ⁻³ g/m ² /day or more.

Example 2
An organic EL element 1 of Example 2 was obtained in the same manner as in Example 1, except that the doping concentration of F6-TCNNQ in the hole injection layer 9 was 12 mass % with respect to the entire hole injection layer 9.

Example 3
An organic EL device 1 of Example 3 was obtained in the same manner as in Example 1, except that 1,4,5,8,9,12-hexaazatriphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) represented by the following structural formula (34) was used as the guest material of the hole injection layer 9 and the doping concentration was set to 40 mass % with respect to the entire hole injection layer 9.

Example 4
An organic EL device 1 of Example 4 was obtained in the same manner as in Example 1, except that 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) represented by the following structural formula (35) was used as the guest material of the hole injection layer 9 and the doping concentration was set to 40 mass % with respect to the entire hole injection layer 9.

Example 5
An organic EL element 1 of Example 5 was obtained in the same manner as in Example 1, except that N4,N4'-bis(dibenzo[b,d]thiophen-4-yl)-N4,N4'-diphenylbiphenyl-4,4'-diamine (DBTPB) represented by the following structural formula (36) was used as the host material of the hole injection layer 9.

Example 6
An organic EL element 1 of Example 6 was obtained in the same manner as in Example 1, except that 9-(2-ethylhexyl)-N,N,N,N-tetrakis(4-metaoxyphenyl)-9H-carbazole-2,7-diamine) (EH44) represented by the following structural formula (37) was used as the host material of the hole injection layer 9.

(Example 7)
The doping concentration of F6-TCNNQ in the hole injection layer 9 was set to 12 mass % with respect to the entire hole injection layer 9, and the anode 10 was formed by co-evaporating Ag and Bi in a mass ratio of 9:1 to a thickness of 100 nm. The organic EL element 1 of Example 7 was obtained in the same manner as in Example 1.

(Example 8)
The doping concentration of F6-TCNNQ in the hole injection layer 9 was set to 12 mass % with respect to the entire hole injection layer 9, and then Pd was evaporated to a thickness of 2 nm. The organic EL element 1 of Example 8 was obtained in the same manner as in Example 1, except that the anode 10 was formed by sputtering an IZO film to a thickness of 60 nm and depositing the IZO film thereon.

Example 9
To form the organic electron injection layer 5, a mixed solution of 1.0 mass % of a boron-containing compound (SPB-BPy2) and 2.0 mass % of diazabicyclononene (DBN) in cyclopentanone was prepared.
The substrate 2 on which the inorganic electron injection layer 4 had been formed was set on a spin coater, and the cyclopentanone mixed solution of the boron-containing compound and DBN was dropped onto the substrate, which was then rotated at 3000 rpm for 30 seconds to coat the substrate. The substrate 2 on which the cyclopentanone solution of the boron-containing compound had been coated was then annealed for 1 hour using a hot plate set at 150° C. in a nitrogen atmosphere. An organic EL device 1 of Example 9 was obtained in the same manner as in Example 1, except that an organic electron injection layer 5 made of a boron-containing compound doped with DBN and having an average thickness of 30 nm was thus formed.

Example 10
An organic EL element 1 of Example 10 was obtained in the same manner as in Example 1, except that a thermosetting resin was applied onto the anode and a sealing film manufactured by Oike Kogyo Co., Ltd. (water vapor transmission rate WVTR: 3×10 ⁻³ g/m ² /day) was attached to form a sealing structure.

(Comparative Examples 1 and 2)
Organic EL elements 1 of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the doping concentration of F6-TCNNQ in the hole injection layer 9 was 4 mass % or 10 mass % with respect to the entire hole injection layer 9.

(Comparative Example 3)
An organic EL element 1 of Comparative Example 3 was obtained in the same manner as in Example 1, except that F4-TCNQ was used as the guest material of the hole injection layer 9 and the doping concentration was set to 5 mass % with respect to the entire hole injection layer 9.

(Comparative Examples 4 to 7)
The organic EL elements 1 of Comparative Examples 4, 5, 6 and 7 were obtained in the same manner as in Example 1, except that the hole injection layer 9 was formed by depositing HAT-CN to a thickness of 10 nm, molybdenum oxide (MoOx) to a thickness of 5 nm, F4-TCNQ to a thickness of 1 nm, and F6-TCNQ to a thickness of 1 nm.

(Comparative Example 8)
An organic EL element 1 of Comparative Example 8 was obtained in the same manner as in Example 1, except that the doping concentration of F6-TCNNQ in the hole injection layer 9 was set to 4 mass % with respect to the entire hole injection layer 9, and the anode 10 was formed by co-evaporating Ag and Bi in a mass ratio of 9:1 to a thickness of 100 nm.

(Comparative Example 9)
The doping concentration of F6-TCNNQ in the hole injection layer 9 was set to 4 mass % with respect to the entire hole injection layer 9, and then Pd was evaporated to a thickness of 2 nm. The resultant was then transported to a Millitron sputtering device and an IZO film was sputtered to a thickness of 60 nm to form an anode 10. Except for this, an organic EL element 1 of Comparative Example 9 was obtained in the same manner as in Example 1.

(Comparative Example 10)
An organic EL element 1 of Comparative Example 10 was obtained in the same manner as Comparative Example 1, except that a thermosetting resin was applied onto the anode and a sealing film manufactured by Oike Kogyo Co., Ltd. (water vapor transmission rate WVTR: 3×10 ⁻³ g/m ² /day) was attached to form a sealing structure.

<Storage life test>
The organic EL elements of the examples and comparative examples were stored at normal temperature and humidity, and 2500 hours after the start of the storage life test (0 hours), images of the light-emitting surface of the organic EL elements were taken. In this test, the organic EL elements were lit only when the light-emitting surface images were taken, and the evaluation was performed. The light-emitting surface images are shown in Figures 2 to 7. Note that Ag anode lines are present in the vertical direction of the screen, and the hole injection layer 9 is exposed on the left and right of the light-emitting part of the light-emitting surface image.
As an index for evaluating deterioration of the light-emitting surface, the light-emitting surface image after 2500 hours was binarized with the maximum in-plane luminance value set to 1, and the area ratio of the light-emitting part was calculated with the light-emitting area after 0 hours set to 100%. The evaluation results of the light-emitting area ratio after 2500 hours are shown in Table 1.
The area ratio is indicated by the symbol ◎ if 95% or more, ◯ if 90% or more but less than 95%, △ if 80% or more but less than 90%, and × if less than 80%.

2 to 7 and a comparison of Comparative Examples 1 to 3 with Examples 1 to 4 and 9 in Table 1 shows that by using Ag as the anode and adding a high concentration of the hole injection layer dopant material, deterioration of the light emitting surface (shrinkage from the lateral direction where the hole injection layer is exposed) is suppressed even after a long-term deterioration test of 2,500 hours.
In particular, it is clear that the atmospheric stability is significantly improved as compared with Comparative Examples 4 to 7 in which the hole injection layer 9 was formed using a single material having hole injection properties.
Furthermore, a comparison of Examples 7 and 8 with Comparative Examples 8 and 9 shows that even when an oxide anode or an alloy anode was used, the deterioration of the light-emitting surface was similarly suppressed, and that adding a high concentration of a hole injection layer dopant material is effective in improving the atmospheric stability of an organic EL element.

1: Organic EL (electroluminescence) element 2: Substrate 3: Cathode 4: Inorganic electron injection layer 5: Organic electron injection layer 6: Electron transport layer 7: Light-emitting layer 8: Hole transport layer 9: Hole injection layer 10: Anode

Claims (7)

A device comprising, in this order, a substrate, a cathode, a light-emitting layer, a hole injection layer, and an anode;
Sealing is performed with a water vapor transmission rate (WVTR) of 3×10 ⁻³ g/m ² /day or more,
The hole injection layer and the anode are adjacent to each other,
the hole injection layer comprises an organic host material for the hole injection layer and an electron-withdrawing dopant having a hole injection ability,
1. An organic electroluminescence device, comprising: a hole injection layer host material and an electron-withdrawing dopant, the electron-withdrawing dopant being present in a proportion of 12% by mass or more and 50% by mass or less based on a total amount of the hole injection layer host material and the electron-withdrawing dopant. 2. The organic electroluminescence device according to claim 1, wherein the anode is made of a metal element alone, a transparent conductive oxide alone, or a laminate of a metal element and a transparent conductive oxide. The organic electroluminescence element according to claim 1 or 2, wherein the ratio of the electron-withdrawing dopant is 18% by mass or more and 50% by mass or less with respect to the total amount of the hole injection layer host material and the electron-withdrawing dopant. The organic electroluminescence element according to any one of claims 1 to 3, wherein the electron-withdrawing dopant is a material having tetracyanoquinodimethane as a functional group. The organic electroluminescence element according to any one of claims 1 to 4, further comprising an organic thin film between the cathode and the light-emitting layer, the organic thin film including at least a first material that is an organic material having an acid dissociation constant pKa of 1 or more and a second material that transports electrons, the first material being one or more selected from a tertiary amine, a phosphazene compound, a guanidine compound, a heterocyclic compound having an amidine structure, a hydrocarbon compound having a ring structure, and a ketone compound. A display device comprising an organic electroluminescence element according to any one of claims 1 to 5. A lighting device comprising an organic electroluminescence element according to any one of claims 1 to 5.

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