JP6516892B2 - Organic dopant compound and organic electroluminescent device using them - Google Patents

Description

  The present invention relates to organic dopant compounds and organic electroluminescent devices using them.

  An organic electroluminescent element (organic EL element) is an element which emits light by sandwiching an organic material between electrodes and applying a voltage. The organic material used here is generally called an organic semiconductor. Unlike an inorganic semiconductor such as a silicon semiconductor, an organic semiconductor is a semiconductor made of an organic molecule or an organic polymer. As typical organic semiconductor materials, polyacetylene, polythiophene and the like are mentioned, and have been actively developed in the fields such as organic TFT materials, organic solar cell materials, organic EL materials and the like from the past.

Such an organic semiconductor material generally has low electrical conductivity by itself and is difficult to apply as a device. Therefore, it has been considered to mix (dope) another compound (dopant) in order to impart conductivity to the organic semiconductor material as a substrate. Examples of organic compound dopants include (4- (1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl) phenyl) dimethylamine (N-DMBI). It has been confirmed that this material releases hydrogen by energy such as heat and becomes a radical or a cation to improve the electrical conductivity of the organic semiconductor material (Non-Patent Documents 1 and 2; Patent Document 3).
In addition, it is also known that when the organic EL is added to the electron transport layer, the light emission characteristic is improved (Patent Document 4).

International Publication No. 2011/127075 JP 2014-49697

Mingtao Lu, Herman T. Nicolai, Gert-Jan A. H. Wetzelaer, and Paul W. M. Blom, “N-type doping of poly (p-phenylene vinylene) with air-stable dopants”, APPLIED PHYSICS LETTERS 99, 173302 (2011) Peng Wei, Joon Hak Oh, Guifang Dong, and Zhenen Bao, "Use of 1H-Benzoimidazole Derivatives as an n-Type Dopant and To-Enable Air-Stable Solution-Processed n-Channnel Organic Thin-Film Transistor", JOURNAL Of the American Chemical Society 132, 8852-8853 (2010)

As mentioned above, various dopants have been proposed to improve the electrical conductivity of organic semiconductor materials. However, those dopants have a problem that storage stability is not enough. Furthermore, there has been a problem that the provision of electrical conductivity is not sufficient.
The present invention has been made in view of the above-mentioned present situation, and when it is used as an organic dopant compound, it is possible to impart good electric conductivity to organic semiconductor materials, and it has good storage stability. In particular, it is an object of the present invention to provide a compound capable of imparting good luminescence characteristics to an organic electroluminescent device.

  The inventor made various studies in order to solve the above problems. As a result, when a compound having a predetermined structure has good stability and is used as an organic dopant compound, it has good doping performance, and the driving stability of the organic semiconductor device containing the organic dopant is improved. The present invention has been completed.

  That is, the present invention is a compound represented by the general formula (1).

In formula (1), R ^{1 to} R ⁴ and R ^{7 to} R ¹⁰ each independently represent a hydrogen atom or an alkyl group which may have a substituent, an aryl group or a heteroaryl group, and each other May form a ring. R ^{5 to} R ⁶ each represent an alkyl group which may have a substituent, an aryl group or a heteroaryl group. X represents either a carbon atom or a nitrogen atom, Y represents an atom having a noncovalent electron pair, and represents any of nitrogen, oxygen and sulfur atoms. The arc represents a mother skeleton which is a 5- or 6-membered aromatic ring containing X and Y. This mother skeleton may have a substituent or may be condensed.

  The compound of the present invention has high storage stability and can impart high electrical conductivity when used as an organic dopant compound of an organic semiconductor material. In particular, it is possible to impart good light emission characteristics to the organic electroluminescent device. In addition, the driving stability of the organic electroluminescent device using the organic material can be improved.

FIG. 1 is a ¹ H-NMR chart of ¹ -methyl-2-phenyl-1H-benzo [d] imidazole. Figure 2 is the 1-methyl-2- (2- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl)-1H-benzo [d] ^imidazol-1 H- It is a NMR chart figure. FIG. 3 is a ¹ H-NMR chart of ¹ -methyl-2- (2- (pyridin-2-yl) phenyl) 4-1H-benzo [d] imidazole. FIG. 4 is a ¹ H-NMR chart of 1,3-dimethyl-2- (2- (pyridin-2-yl) phenyl) -1H-benzo [d] imidazol-3-ium iodide. FIG. 5 is a ¹ H-NMR chart of 1,3-dimethyl-2- (2- (pyridin-2-yl) phenyl) -2,3-dihydro-1H-benzo [d] imidazole (Py-DMBI). is there. FIG. 6 is a comparison diagram of voltage-current characteristics of the first embodiment and the first comparative example. FIG. 7 is a comparison diagram of voltage-luminance characteristics of the first embodiment and the first comparative example.

Hereinafter, the present invention will be described in detail.
In addition, what combined two or more of each preferable form of this invention described below is also a preferable form of this invention.

[Compound of the present invention]
The compound of the present invention is represented by the above general formula (1).
The compound of the present invention is a hydrogen-releasing compound, in which an electron donating substituent (a substituent having a noncovalent electron pair and atom) is adjacent to or coordinated to a carbocation or carboradical releasing hydrogen. In particular, higher emissivity (doping performance) and stability can be imparted. That is, when the compound represented by the above general formula (1) is used as a dopant, Y in the above general formula (1) approaches or coordinates to a cation or a radical remaining when hydrogen at 2-position is released. Donate electrons and stabilize.

In the above formula (1), R ^{1 to} R ⁴ and R ^{7 to} R ¹⁰ each represent a hydrogen atom, or an alkyl group which may have a substituent, an aryl group or a heteroaryl group, and each other May form a ring.

The alkyl group which may have a substituent is preferably a group having 1 to 30 carbon atoms, and more preferably a group having 1 to 18 carbon atoms.
The alkyl group having a substituent is a group in which one or two or more of the hydrogen atoms of the alkyl group is substituted with another substituent, and as the substituent, an aryl group, a heteroaryl group, a halogen atom, a hydroxyl group And carboxyl group, carboxylic acid ester group, amino group, alkoxy group and the like.

The aryl group which may have a substituent is preferably a group having 6 to 30 carbon atoms, and more preferably a group having 6 to 18 carbon atoms.
The aryl group having a substituent is a group in which one or two or more of the hydrogen atoms of the aryl group are substituted with another substituent, and as the substituent, an alkyl group, a heteroaryl group, a halogen atom, a hydroxyl group And carboxyl group, carboxylic acid ester group, amino group, alkoxy group and the like.

The heteroaryl group which may have a substituent is preferably a group having 3 to 30 carbon atoms, and more preferably 3 to 18 carbon atoms.
The heteroaryl group having a substituent is a group in which one or two or more of the hydrogen atoms of the heteroaryl group are substituted with another substituent, and as the substituent, an alkyl group, an aryl group, a halogen atom, Examples thereof include a hydroxyl group, a carboxyl group, a carboxylic acid ester group, an amino group and an alkoxy group.

In the above formula (1), X represents either a carbon atom or a nitrogen atom.
In the above formula (1), Y is an atom having a non-covalent electron pair and represents any of nitrogen, oxygen and sulfur atoms. When Y is any one of nitrogen atom, oxygen atom and sulfur atom, the carbocation or carboradical from which the compound of the formula (1) releases hydrogen tends to be stable. As a result, the doping performance is increased, and the effect of imparting electrical conductivity to the organic semiconductor material etc. is improved. Y is preferably a nitrogen atom.

  In the above formula (1), the circular arc represents a mother skeleton which is a 5- or 6-membered aromatic ring containing X and Y. This mother skeleton may have a substituent or may be condensed. When the arc has the above structure, the carbocation or carboradical from which the compound of the formula (1) releases hydrogen tends to be stable. As a result, the doping performance is increased, and the effect of imparting electrical conductivity to the organic semiconductor material and the like is improved.

  The mother skeleton of the 6-membered ring and 5-membered ring constituting the arc in the above formula (1) includes, for example, a 5- to 6-membered ring containing 1 to 3 nitrogen atoms, 1 nitrogen atom and 1 oxygen atom A 5-membered ring, a 5-membered ring containing one nitrogen atom and one sulfur atom, a 5-membered ring containing two nitrogen atoms and one sulfur atom, etc. are exemplified, and more specifically, for example, the following structures are exemplified. . In the following structural formulae, * represents a bond to a benzene ring, and R represents any of an alkyl group which may have a substituent, an aryl group and a heteroaryl group. The alkyl group which may have a substituent, the aryl group and the heteroaryl group are as described above. In addition, it also includes a structure in which another aromatic ring is condensed to the mother skeleton as described above. Examples of the structure in which another aromatic ring is fused to the mother skeleton include, for example, a quinolyl group and an isoquinolyl group in which a benzene ring as another aromatic ring is condensed when the mother skeleton is a pyridyl group. Ru.

  The compound represented by following General formula (2) as a preferable form of a compound of this invention is illustrated.

In the formula (2), each of R ^{1 to} R ⁴ , R ^{7 to} R ¹⁰ and R ^{11 to} R ¹⁴ is a hydrogen atom or any of an alkyl group which may have a substituent, an aryl group and a heteroaryl group. And may form a ring with each other. R ^{5 to} R ⁶ each represent an alkyl group which may have a substituent, an aryl group or a heteroaryl group.
Preferred forms of R ^{1 to} R ⁴ , R ^{7 to} R ¹⁰ and R ^{11 to} R ^{14 in} the formula (2) are the same as the preferred forms of R ^{1 to} R ⁴ and R ^{7 to} R ^{10 in} the general formula (1) is there.

[Method of producing the compound of the present invention]
The method for producing the compound of the present invention is not particularly limited, but 2-aryl-1H-benzo [d] imidazole such as 2-phenyl-1H-benzo [d] imidazole and alkyl borate compounds such as trialkyl borate By reaction, the ortho hydrogen atom of the aryl group of 2-aryl-1H-benzo [d] imidazole is substituted with a boronate group (Step 1), and the compound is reacted with a halogen heteroaryl compound such as bromoheteroaryl compound. Then replace the boronate group with a heteroaryl group (Step 2), quaternize the nitrogen at position 3 of the imidazole ring of the compound with a halogenated alkyl compound or a hypervalent halogenated heteroaryl compound (Step 3), Preferably, the compound is produced by reducing the imidazole ring of the compound (Step 4).

  The above steps 1 to 4 may be carried out in the presence of a solvent, and usable solvents include, for example, diethyl ether, tetrahydrofuran etc. in step 1, toluene, tetrahydrofuran etc. in step 2, ethanol, methanol, tetrahydrofuran in step 3. In the step 4, ethanol, methanol, tetrahydrofuran and the like are exemplified.

In the above steps 1 to 4, a reaction catalyst may be used. For example, in step 1, an organic lithium compound such as n-butyllithium, etc., in step 2, a palladium catalyst such as tetrakistriphenylphosphine palladium, etc. Alkali metal hydroxides such as potassium oxide, organometallic catalysts such as nickel, copper, palladium and the like are, in step 4, hydride reducing agents such as sodium borohydride, lithium aluminum hydride and calcium hydride.
It is preferable to use 0.01-10 mol with respect to 1 mol of imidazole compounds which are the raw materials of each process of the said reaction catalyst.

  It is preferable to perform the said process 1 at reaction temperature -100-30 degreeC. The above step 2 is preferably performed at a reaction temperature of 30 to 120 ° C. The above step 3 is preferably performed at a reaction temperature of 30 to 100 ° C. The above step 4 is preferably performed at a reaction temperature of 0 to 100 ° C.

  A purification step may be performed between each of the above steps 1 to 4. Examples of purification include extraction, washing with a solvent, separation by column chromatography, recrystallization and the like.

  The above steps 1 to 4 may be performed under a low moisture atmosphere or a low oxygen atmosphere.

  Prior to the step 1, in order to enhance the selectivity of boronation,-(NH)-group of the imidazole ring may be alkylated with a halogenated alkyl compound or the like, or arylated with a halogenated heteroaryl compound or the like.

  The trialkyl borate compound in the above step 1 is not particularly limited as long as it is a trialkyl borate compound in which an alkoxy group is bonded to a boron atom, but a compound having 1 to 12 carbon atoms is preferable as the alkoxy group.

[Organic electroluminescent device of the present invention]
The organic electroluminescent device of the present invention comprises the compound of the present invention. Usually, the compound of the present invention is contained in the organic semiconductor layer.
The organic electroluminescent device of the present invention has at least a cathode, an anode, and a light emitting layer present between the cathode and the anode.
The organic electroluminescent layer of the present invention may have, in addition to the above, a hole injection layer, a hole transport layer, an electron transport layer, an electron injection layer, a buffer layer, a substrate, and the like.

The material of the electrode (first electrode) of the organic electroluminescent device of the present invention is ITO (indium tin oxide), IZO (indium zinc oxide), FTO (fluorinated tin oxide), In3O ₃ , SnO ₂ , Sb-containing SnO _And oxides such as Al-containing ZnO. Among these, ITO, IZO and FTO are preferable.
The average thickness of the first electrode is not particularly limited, but is preferably 10 to 500 nm, and more preferably 100 to 200 nm. The average thickness of the first electrode can be measured by a stylus profilometer, spectroscopic ellipsometry.
The first electrode of the organic electroluminescent device of the present invention is preferably a cathode.

Examples of the material of the electrode (second electrode) of the organic electroluminescent device of the present invention include Au, Pt, Ag, Cu, Al, and alloys containing these, and the like. Among these, Au, Ag and Al are preferable.
The average thickness of the second electrode is not particularly limited, but is preferably 10 to 1000 nm. More preferably, it is 30 to 150 nm. Further, even in the case of using an opaque material, for example, by setting the average thickness to about 10 to 30 nm, it can be used as a transparent electrode.
The second electrode of the organic electroluminescent device of the present invention is preferably an anode.

As a material of a light emitting layer, any compound which can usually be used as a material of a light emitting layer can be used, and these may be mixed and used. As a material of the light emitting layer, it is preferable to include a phosphorescent light emitting material.
As a material of the light emitting layer, for example, a tricoordinate iridium complex having 2,2′-bipyridine-4,4′-dicarboxylic acid as a ligand, factory (2-phenylpyridine) iridium (Ir (ppy) 3), 8-hydroxyquinoline aluminum (Alq 3), tris (4-methyl-8 quinolinolate) aluminum (III) (Almq 3), 8-hydroxyquinoline zinc (Znq 2), (1, 10-phenanthroline)-tris- (4) 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, various metal complexes such as platinum (II); distyrylbenzene (DSB), diamino Benzene compounds such as styryl benzene (DADSB), naphthalene compounds such as naphthalene and nile red, phenanthrene compounds such as phenanthrene, chrysene, chrysene compounds such as 6-nitrochrysene, perylene, N, N ' Perylene compounds such as -bis (2,5-di-t-butylphenyl) -3,4,9,10-perylene-di-carboximide (BPPC), coronene compounds such as coronene, anthracene, bis Anthracene compounds such as styryl anthracene, pyrene compounds such as pyrene, and pyrans such as 4- (di-cyanomethylene) -2-methyl-6- (para-dimethylaminostyryl) -4H-pyran (DCM) Compounds, acridine compounds such as acridine, stilbene Tilbene compounds, carbazole compounds such as 4,4'-bis [9-dicarbazolyl] -2,2'-biphenyl (CBP), thiophene compounds such as 2,5-dibenzoxazole thiophene, benzoxazole Benzoxazole compounds, benzimidazole compounds such as benzimidazole, benzothiazole compounds such as 2,2 '-(para-phenylene divinylene) -bisbenzothiazole, bistyryl (1,4-diphenyl-1,1,4 Butadiene compounds such as 3-butadiene), tetraphenyl butadiene, naphthalimide compounds such as naphthalimide, coumarin compounds such as coumarin, perinone compounds such as perinone, oxadiazoles such as oxadiazole Compounds, aldazine systemization Compounds, cyclopentadiene compounds such as 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), quinacridones, quinacridone compounds such as quinacridone red, pyrrolopyridines, thiadiazolo compounds Pyridine compounds such as pyridine, spiro compounds such as 2,2 ', 7,7'-tetraphenyl-9,9'-spirobifluorene, metals such as phthalocyanine (H2Pc) and copper phthalocyanine or metal-free The phthalocyanine compound and the boron compound material etc. which are described further in Unexamined-Japanese-Patent No. 2009-155325 and Japanese Patent Application No. 2010-28273 are mentioned, and 1 type (s) or 2 or more types of these can be used.
The average thickness of the light emitting layer is not particularly limited, but is preferably 10 to 150 nm. More preferably, it is 20 to 100 nm. The average thickness of the light emitting layer can be measured at the time of film formation by a quartz oscillator film thickness meter.

  The organic electroluminescent device of the present invention comprises the compound of the present invention. The compound of the present invention is generally contained in the organic semiconductor layer, but when the organic electroluminescent element of the present invention has a buffer layer described later, it is preferably contained in the buffer layer. At least one organic semiconductor layer of the organic electroluminescent device of the present invention comprises 0.1 to 15% of the compound of the present invention based on 100% by mass of the organic compound forming the organic semiconductor layer (the organic semiconductor layer of 1). It is preferable to contain mass%, it is more preferable to contain 0.5-10 mass%, and it is especially preferable to contain 1 to 5 mass% or more. By including the content in the above range, the driving stability of the organic electroluminescent device tends to be further improved.

  The organic electroluminescent device of the present invention may have a buffer layer between the light emitting layer and the cathode. In the organic electroluminescent device, holes are supplied from the anode and electrons are supplied from the cathode, and these are recombined in the light emitting layer to emit light, but a part of the holes supplied from the anode passes through each layer to be the cathode. It is believed that this is one of the causes of lowering the efficiency of the organic electroluminescent device. By providing the buffer layer, it is possible to suppress the holes from reaching the cathode, and the efficiency of the device can be increased. Materials for the buffer layer include polyacetylene compounds such as trans-type polyacetylene, cis-type polyacetylene, poly (di-phenylacetylene) (PDPA), poly (alkyl, phenylacetylene) (PAPA); poly (para-phenvinylene) ) (PPV), poly (2,5-dialkoxy-para-phenylenevinylene) (RO-PPV), cyano-substituted-poly (para-phenvinylene) (CN-PPV), poly (2-dimethyloctylsilyl-) Poly-p-phenylene-vinylene compounds such as p-phenylene vinylene) (DMOS-PPV), poly (2-methoxy, 5- (2'-ethylhexoxy) -p-phenylene vinylene) (MEH-PPV); Alkyl thiophene) (PAT), poly (oxypropylene) tri Polythiophene compounds such as poly (POPT); poly (9, 9-dialkyl fluorenes) such as poly (9, 9- dioctyl fluorene) (PDAF), poly (dioctyl fluorene-alto-benzothiadiazole) (F8 BT), α, ω-Bis [N, N′-di (methylphenyl) aminophenyl] -poly [9,9-bis (2-ethylhexyl) fluorene-2,7-dyl] (PF2 / 6am4), poly (9, Polyfluorene compounds such as 9-dioctyl-2,7-divinylene fluorenyl-ortho-co (anthracene-9,10-diyl); poly (para-phenylene) (PPP), poly (1,5- Polyparaphenylene-based compounds such as dialkoxy-para-phenylene) (RO-PPP); poly (N-vinylcarbazole) (PV) Polycarbazole compounds such as poly); polysilane compounds such as poly (methylphenylsilane) (PMPS), poly (naphthylphenylsilane) (PNPS), poly (biphenylylphenylsilane) (PBPS), and the following formula The boron containing compound etc. which are represented by (3) etc. are mentioned, These may use 1 type and may use 2 or more types.

The buffer layer preferably has an average thickness of 5 to 100 nm. The average thickness of the buffer layer can be measured by a stylus type profilometer and spectroscopic ellipsometry.

In the above-mentioned formula (3), the dotted circular arc represents that a ring structure is formed together with the skeleton represented by the solid line. The dotted line in the skeleton represented by a solid line represents that a pair of atoms connected by a dotted line may be connected by a double bond. The arrow from the nitrogen atom to the boron atom indicates that the nitrogen atom is coordinated to the boron atom. Q1 and Q2 are the same or different and are a linking group in the skeleton part represented by a solid line, at least a part of which forms a ring structure with a dotted arc part, and may have a substituent. X ¹ , X ² , X ³ and X ⁴ are the same or different and each represents a hydrogen atom or a monovalent substituent to be a substituent of a ring structure, and a plurality of ring structures forming a dotted arc portion It may be combined. n ¹ represents an integer of 2 to 10; Y ¹ is a direct bond or an n ¹ -valent linking group, and a ring structure Q ¹ , Q ² , X ¹ , which independently forms an arc part of a dotted line independently of the n ¹ structural moiety other than Y ¹ present indicating that it is attached at any one location in the ^{X 2, X 3, X 4} . It is preferable that it is a boron containing compound represented by these.

The organic electroluminescent device of the present invention may be one in which each layer constituting the organic electroluminescent device is laminated on a substrate. When each layer is stacked on the substrate, each layer is preferably formed on the first electrode formed on the substrate. In this case, the organic electroluminescent device of the present invention may be a top emission type that extracts light on the side opposite to the side on which the substrate is located, or a bottom emission type that extracts light on the side on which the substrate is side May be
The material of the substrate is a resin material such as polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyether sulfone, polymethyl methacrylate, polycarbonate, polyarylate, quartz glass, soda glass, etc. A glass material etc. are mentioned and 1 type (s) or 2 or more types of these can be used.
In the case of top emission type, an opaque substrate can also be used. For example, a substrate made of a ceramic material such as alumina, or an oxide film (insulating film) is formed on the surface of a metal substrate such as stainless steel. Also, substrates made of resin materials can be used.
The average thickness of the substrate is preferably 0.1 to 30 mm. More preferably, it is 0.1 to 10 mm.
The average thickness of the substrate can be measured with a digital multimeter, vernier calipers.

As a material of the said hole transport layer, any compound which can usually be used as a material of a hole transport layer can also be used, and you may mix and use these. As a material of the hole transport layer, for example, N, N'-di (1-naphthyl) -N, N'-diphenyl-1,1'-biphenyl-4,4'-diamine (α-NPD), etc. An arylamine compound etc. are illustrated.
When the organic electroluminescent element of the present invention has a hole transport layer, the average thickness of the hole transport layer is not particularly limited, but is preferably 10 to 150 nm. More preferably, it is 40-100 nm. The average thickness of the hole transport layer can be measured at the time of film formation by a quartz oscillator film thickness meter.

As a material of the said electron carrying layer, any compound which can usually be used as a material of an electron carrying layer can also be used, and these may be mixed and used. Examples of the material of the electron transport layer include pyridine derivatives such as tris-1,3,5- (3 ′-(pyridine-3 ′ ′-yl) phenyl) benzene (TmPyPhB), tris (8-hydroxy-quinolinate) ) Metal complexes such as aluminum (Alq3) are exemplified.
When the organic electroluminescent element of the present invention has an electron transport layer, the average thickness of the electron transport layer is not particularly limited, but is preferably 10 to 150 nm. More preferably, it is 40-100 nm. The average thickness of the electron transport layer can be measured at the time of film formation by a quartz oscillator film thickness meter.

The material of the electron injection layer is not particularly limited, but titanium oxide (TiO ₂ ), zinc oxide (ZnO), tungsten oxide (WO ₃ ), niobium oxide (Nb ₂ O ₅ ), iron oxide (Fe ₂ O) ₃ ) One or more metal oxides such as tin oxide (SnO ₂ ), magnesium oxide (MgO), hafnium oxide (HfO ₂ ), zirconium oxide (ZrO ₂ ), etc. can be used, and hole injection The material of the layer is not particularly limited, but one or more of metal oxides such as vanadium oxide (V ₂ O ₅ ), molybdenum oxide (MoO ₃ ) and ruthenium oxide (RuO ₂ ) can be used. .
When the organic electroluminescent element of the present invention has an electron injection layer, the average thickness of the electron injection layer is not particularly limited, but is preferably 1 to 1000 nm. More preferably, it is 2 to 100 nm. The average thickness of the electron injection layer can be measured by a stylus profilometer, spectroscopic ellipsometry. When the organic electroluminescent element of the present invention has a hole injection layer, the average thickness of the hole injection layer is not particularly limited, but is preferably 1 to 1000 nm. More preferably, it is 5 to 50 nm. The film thickness can be measured at the time of film formation by a quartz oscillator film thickness meter of the hole injection layer.

  In the organic electroluminescent device of the present invention, the method for forming the electrode, the light emitting layer, and in the case, the hole injecting layer, the hole transporting layer, the electron transporting layer, and the electron injecting layer, is not particularly limited. Chemical vapor deposition (CVD) such as plasma CVD, thermal CVD, laser CVD etc. which are film methods, dry plating such as vacuum evaporation, sputtering, ion plating etc., thermal spraying, electrolytic plating which is liquid phase film formation, immersion Plating, wet plating such as electroless plating, sol-gel method, MOD method, spray thermal decomposition method, doctor blade method using fine particle dispersion, printing technology such as spin coating method, ink jet method, screen printing method etc. It can be used, and an appropriate method according to material can be selected and used.

When the organic electroluminescent element of the present invention includes a buffer layer, it is preferably formed by applying a solution containing an organic compound. By forming the buffer layer having a predetermined thickness by coating, the driving stability of the organic electroluminescent device of the present invention becomes better.
The method of applying the solution containing the organic compound that is the material of the buffer layer is not particularly limited, and spin coating, casting, gravure coating, bar coating, roll coating, dip coating, spray coating, screen Various coating methods such as a printing method, an offset printing method, and an inkjet printing method can be used. Among these, spin coating is preferred. The solvent used to prepare the solution containing the organic compound is not particularly limited as long as it can dissolve the organic compound, but tetrahydrofuran (THF), toluene, xylene, chloroform, dichloromethane, dichloroethane, chlorobenzene One or two or more of them can be used. Among these, THF, toluene, chloroform and dichloroethane are preferable.

Hereinafter, the present invention will be specifically described by way of production examples and examples, but the present invention is not limited to these production examples and examples.
Preparation Example 1 Preparation of 1-Methyl-2-phenyl-1H-benzo [d] imidazole 1-methyl-2-phenyl-1H-benzo [d] imidazole was synthesized according to the following reaction formula.

Dissolve 2-phenyl-1H-benzo [d] imidazole (10 g, Tokyo Chemical Industry Co., Ltd.) in dehydrated tetrahydrofuran (200 ml, Wako Pure Chemical Industries, Ltd.), and add potassium t-butoxide (6.07 g, Wako Pure Chemical Industries) thereto, iodination Methyl (3.85 ml, Wako Pure Chemical Industries, Ltd.) was added and stirred overnight at room temperature. After the reaction, the reaction solution was extracted with chloroform (Wako Pure Chemical Industries, Ltd.), washed twice with water, the organic layer was recovered, and the organic layer was dried with anhydrous sodium sulfate (Wako Pure Chemical Industries, Ltd.) and concentrated. The residue was purified by silica gel column chromatography to obtain 8 g of 1-methyl-2-phenyl-1H-benzo [d] imidazole.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 7.8-7.83 (1H), 7.74-7.77 (2H), 7.49-7.53 (3H), 7.37-7 .39 (1H), 7.28-7.33 (2H), 3.86 (3H)
Preparation Example 2 1-Methyl-2- (2- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl) -1H-benzo [d] imidazole Production 1-Methyl-2- (2- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl) -1H-benzo [d] imidazole according to the following reaction formula Was synthesized.

It was dissolved in 1-methyl-2-phenyl-1H-benzo [d] imidazole (4.16 g) and tetrahydrofuran (30 ml) to −78 °. Thereto, n-butyllithium (1.6 M, n-hexane solution, 15 ml, Kanto Chemical) was added and allowed to stir for 30 minutes. After setting the temperature to 0 ° C., the mixture was further stirred for 1 hour. Thereto, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (4.85 ml, Tokyo Chemical Industry Co., Ltd.) was added dropwise, and allowed to react overnight at room temperature. After the reaction, the reaction solution was quenched with water, extracted with chloroform (Wako Pure Chemical Industries, Ltd.), washed twice with water, the organic layer was recovered, and the organic layer was dried over anhydrous sodium sulfate (Wako Pure Chemical Industries, Ltd.) and concentrated. The residue is purified by silica gel column chromatography and 1-methyl-2- (2- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl) -1H-benzo 4 g of [d] imidazole was obtained.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 7.82 to 7.84 (1 H), 7.75 to 7.77 (1 H), 7.47 to 7.51 (3 H), 7.34 to 7 .37 (1H), 7.24-7.31 (2H), 3.67 (3H), 1.10 (12H)
Preparation Example 3 Preparation of 1-Methyl-2- (2- (pyridin-2-yl) phenyl) 4-1H-benzo [d] imidazole According to the following reaction formula, 1-methyl-2- (2-) (Pyridin-2-yl) phenyl) 4-1H-benzo [d] imidazole was synthesized.

1-Methyl-2- (2- (4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl) phenyl) -1H-benzo [d] imidazole (1.87 g), 2 -Bromopyridine (1.25 ml, Wako Pure Chemical Industries, Ltd.), tetrakis (triphenylphosphine) palladium (0) (0.65 g, Tokyo Chemical Industry Co., Ltd.) is dissolved in dehydrated toluene (28 ml, Wako Pure Chemical Industries, Ltd.) A solution of (2.33 g, Wako Pure Chemical Industries, Ltd.) dissolved in water (5.6 ml) was added and allowed to react overnight at 110 ° C. After the reaction, the reaction solution was extracted with chloroform (Wako Pure Chemical Industries, Ltd.), washed twice with water, the organic layer was recovered, and the organic layer was dried over anhydrous sodium sulfate (Wako Pure Chemical Industries, Ltd.) and concentrated. The residue was purified by silica gel column chromatography to obtain 1.4 g of 1-methyl-2- (2- (pyridin-2-yl) phenyl) 4-1H-benzo [d] imidazole.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 8.59 (1 H), 7.88 (1 H), 7.82 (1 H), 7.68 (1 H), 7.65 (1 H), 7.55 (1H), 7.35 (1H), 7.24-7.31 (2H), 7.16 (1H), 7.10 (1H), 6.94 (1H), 3.06 (3H)
Preparation Example 4: Preparation of 1,3-Dimethyl-2- (2- (pyridin-2-yl) phenyl) -1H-benzo [d] imidazol-3-ium iodide According to the following reaction formula, 1,3- Dimethyl-2- (2- (pyridin-2-yl) phenyl) -1H-benzo [d] imidazol-3-ium iodide was synthesized.

1-Methyl-2- (2- (pyridin-2-yl) phenyl) 4-1H-benzo [d] imidazole (1.4 g) is dissolved in ethanol (10 ml, Wako Pure Chemical Industries, Ltd.) and potassium hydroxide is added thereto (1.4 g, Wako Pure Chemical Industries, Ltd.) was added. Further, methyl iodide (3.1 ml, Wako Pure Chemical Industries, Ltd.) was added and allowed to react overnight at 45 ° C. The resulting solid was washed with ethanol to give 1 g of 1,3-dimethyl-2- (2- (pyridin-2-yl) phenyl) -1H-benzo [d] imidazol-3-ium iodide.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 8.22 (1 H), 8.02 (1 H), 7.83-7.90 (3 H), 7.82 (1 H), 7.76-7. 79 (3H), 7.63-7.66 (2H), 7.12 (1H), 3.60 (6H)
Preparation Example 5 Preparation of 1,3-Dimethyl-2- (2- (pyridin-2-yl) phenyl) -2,3-dihydro-1H-benzo [d] imidazole (Py-DMBI) The following reaction 1,3-Dimethyl-2- (2- (pyridin-2-yl) phenyl) -2,3-dihydro-1H-benzo [d] imidazole (Py-DMBI) was synthesized according to the formula.

Dissolve 1,3-dimethyl-2- (2- (pyridin-2-yl) phenyl) -1H-benzo [d] imidazol-3-ium iodide (1 g) in dehydrated methanol (20 ml, Wako Pure Chemical Industries, Ltd.), hydrogen Sodium borohydride (0.4 g, Wako Pure Chemical Industries, Ltd.) was added little by little and allowed to react at room temperature for 2 hours. After the reaction, the reaction solution was extracted with chloroform (Wako Pure Chemical Industries, Ltd.), washed twice with water, the organic layer was recovered, and the organic layer was dried over anhydrous sodium sulfate (Wako Pure Chemical Industries, Ltd.) and concentrated. The residue is purified by silica gel column chromatography, and 1,3-dimethyl-2- (2- (pyridin-2-yl) phenyl) -2,3-dihydro-1H-benzo [d] imidazole (Py-DMBI) 0.3g was obtained.
¹ H-NMR (400 MHz, CDCl ₃ ) δ = 8.61 (1 H), 8.02 (1 H), 7.66 (1 H), 7.49 (1 H), 7.45 (1 H), 7.37 (2H), 7.21 (1H), 6.64 (2H), 6.31 (2H), 5.34 (1H), 2.49 (6H)
(Preparation of organic electroluminescent device)
Example 1
[1] A commercially available transparent glass substrate with an ITO electrode layer having an average thickness of 0.7 mm was prepared. At this time, the ITO electrode (first electrode) of the substrate used was patterned to a width of 2 mm. The substrate was ultrasonically cleaned in acetone for 10 minutes each in isopropanol and then boiled for 5 minutes in isopropanol. The substrate was removed from isopropanol, dried by nitrogen blow, and subjected to UV ozone cleaning for 20 minutes.
[2] This substrate was fixed to a substrate holder of a miratron sputtering apparatus having a zinc metal target. After reducing the pressure to about 1 × 10 −4 Pa, sputtering was performed in a state of introducing argon and oxygen to form a zinc oxide layer having a film thickness of about 2 nm. At this time, a metal mask was used in combination so that zinc oxide was not formed on a part of the ITO electrode for taking out the electrode. The zinc oxide layer was formed by baking this on the hot plate set to 400 degreeC in air | atmosphere for 1 hour.
[3] 2,7-bis (6- (2- (5H-dibenzo [b, d] borol-5-yl) phenyl) pyridin-3-yl) -9,9'-spirobi [fluorene] (hereinafter referred to as It is called "boron compound 1"). The boron compound 1 was manufactured with reference to Patent Document 2. The compound in the literature is written as 2,7-bis (3-dibenzoborolyl-4-pyridylphenyl) -9,9'-spirofluorene. A mixed solution of 1.0% of (1), 0.01% of 1, 2- dichloroethane of Py-DMBI was prepared. The substrate with a zinc oxide thin film prepared in the step [2] was set in a spin coater. A boron-containing compound 1 / Py-DMBI mixed solution was dropped onto the substrate, and rotated at 3000 rpm for 30 seconds to form a second layer containing a boron-containing organic compound. Further, it was annealed for 2 hours on a hot plate set at 125 ° C. in a nitrogen atmosphere. The average thickness of the second layer was 30 nm.
[4] The substrate formed up to the second layer was fixed to the substrate holder of the vacuum deposition apparatus. Bis [2- (2-benzothiazolyl) phenolato] zinc (II)
(ZnBTZ2), iridium tris (1-phenylisoquinoline) (Ir (piq) 3), N, N'-di (1-naphthyl) -N, N'-diphenyl-1,1'-biphenyl-4,4 ' -The diamine ((alpha) -NPD) was put into the alumina crucible, respectively, and was set to the vapor deposition source. The inside of the vacuum deposition apparatus was depressurized to about 1 × 10 −5 Pa, ZnBTZ 2 was co-deposited with 20 nm of IrTB as a host and Ir (piq) 3 as a dopant to form a light emitting layer. At this time, the doping concentration was such that Ir (piq) 3 was 6% by weight with respect to the entire light emitting layer. Next, 30 nm of α-NPD was vapor deposited to form a hole transport layer.
[5] Next, molybdenum trioxide and aluminum were placed in an alumina crucible and set as an evaporation source. The inside of the vacuum deposition apparatus was depressurized to about 1 × 10 −5 Pa, and molybdenum trioxide was deposited to a film thickness of 10 nm. Next, aluminum was vapor-deposited to a film thickness of 100 nm to fabricate an organic electroluminescent element (1). At the time of vapor deposition of aluminum, a vapor deposition surface made of a stainless steel vapor deposition mask was made to be a strip having a width of 2 mm. That is, the light emission area of the produced organic electroluminescent element was 4 mm 2. A voltage was applied between ITO and aluminum to cause light emission, and voltage-current characteristics and voltage-luminance characteristics of the device were measured. The characteristic diagrams are shown in FIGS. The current voltage was a source meter 2400 manufactured by Keithley, and the luminance was measured by LS-100 manufactured by Konica Minolta.

Example 2
Py-DMBI was dissolved in 1,2-dichloroethane to a 1% solution. The solution was placed in 3 ml of a sample tube and sealed, and left at room temperature for 3 days. After 3 days the solution remained clear and colorless.

Comparative Example 1
A comparative organic electroluminescent device (1) was produced in the same manner as in Example 1 except that N-DMBI was used in place of Py-DMBI in the second layer of Example 1. The characteristic diagrams are shown in FIGS.

Comparative Example 2
N-DMBI was dissolved in 1,2-dichloroethane to make a 1% solution. The solution was placed in 3 ml of a sample tube and sealed, and left at room temperature for 3 days. After 3 days, the solution turned brown and partially insoluble matter was precipitated.

  As apparent from FIGS. 6 and 7, in Example 1 in which Py-DMBI is used, the conductivity is improved compared to Comparative Example 1, and it is confirmed that light emission is performed with high current at low voltage and high luminance. The

  As apparent from the results of Example 2 and Comparative Example 2, it was confirmed that the compound of the present invention has high storage stability.

The present material can be applied to organic semiconductor devices in general as well as organic electroluminescent devices. For example, an organic TFT element, an organic thermoelectric element, an organic solar cell or the like.

Claims (4)

An organic electroluminescent device comprising a buffer layer between a light emitting layer and a cathode, wherein the buffer layer comprises a compound represented by the general formula (1).

(R ^{1 to} R ⁴ and R ^{7 to} R ¹⁰ each independently represent a hydrogen atom, or an alkyl group which may have a substituent, an aryl group or a heteroaryl group, and they form a ring with each other R ^{5 to} R ⁶ each represents an alkyl group, an aryl group or a heteroaryl group which may have a substituent, X represents a carbon atom or a nitrogen atom, and Y represents a noncovalent electron A paired atom represents any of nitrogen, oxygen, and sulfur atoms, and an arc represents a mother skeleton which is a 5- or 6-membered aromatic ring containing X and Y. This mother skeleton has a substituent. And may be fused.) An organic electroluminescent device comprising a buffer layer between a light emitting layer and a cathode, wherein the buffer layer comprises a compound represented by the general formula (2).

(R ^{1 to} R ⁴ and R ^{7 to} R ¹⁴ each independently represent a hydrogen atom, or an alkyl group which may have a substituent, an aryl group or a heteroaryl group, and they form a ring with each other R ^{5 to} R ⁶ each represent an alkyl group which may have a substituent, an aryl group or a heteroaryl group.) Content of the compound represented with General formula (1) or (2) is 0.1-15 mass% with respect to 100 mass% of organic compounds which form the said buffer layer. Organic electroluminescent device. The organic electroluminescent device according to any one of claims 1 to 3, wherein the buffer layer is formed by coating.

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