JP5109236B2 - Hole blocking material and organic electroluminescent device - Google Patents

Description

  The present invention relates to a hole blocking material and an organic electroluminescent device, and more specifically, a hole blocking material capable of providing an organic electroluminescent device having high luminous efficiency and low luminance reduction during continuous driving, and the hole. The present invention relates to an organic electroluminescence device using a blocking material for a hole blocking layer.

  In recent years, organic electroluminescent elements using organic thin films have been developed as thin film type electroluminescent (EL) elements instead of using inorganic materials. In addition, as an attempt to increase the light emission efficiency of the organic electroluminescence device, it has been studied to use phosphorescence (light emission by triplet excitons) instead of fluorescence (light emission by singlet excitons). When phosphorescence is used, it is considered that the efficiency is improved about three times as compared with an element using fluorescence, and it has been reported that europium complex, platinum complex or the like is used as phosphorescent molecule. However, the conventional organic electroluminescent device using phosphorescent molecules is highly efficient, but is insufficient for practical use in terms of driving stability, and it is difficult to realize a highly efficient display device. .

  In the organic electroluminescence device reported so far, light emission is basically obtained by a combination of a hole transport layer and an electron transport layer. That is, the holes injected from the anode move through the hole transport layer, recombine with the electrons injected from the cathode and moving through the electron transport layer near the interface between the two layers, and the hole transport layer and The principle is that the electron transport layer is excited to emit light, and a device that improves the light emission efficiency by providing a light emitting layer between the hole transport layer and the electron transport layer is common. is there.

  Furthermore, a hole blocking layer may be provided in contact with the cathode side interface of the light emitting layer for the purpose of promoting the generation of excitons in the light emitting layer and improving the efficiency of light emission and the purity of the light emission color. For example, a device using a triarylamine compound for the hole injection / transport layer and an aluminum complex for the electron injection / transport layer has a tendency that the hole mobility exceeds the electron mobility. There has been a problem that the light passes through the cathode without contributing to light emission. In order to solve this problem, it is considered preferable to provide a hole blocking layer at the cathode side interface of the light emitting layer.

  In particular, when the oxidation potential of the light emitting layer is large, a blue light emitting device or a phosphorescent light emitting device having an electron transport layer such as a commonly used aluminum complex of 8-hydroxyquinoline, which is difficult to contain holes in the light emitting layer, The need for a hole blocking layer is high.

  Patent Document 1 describes an organic electroluminescence device provided with a hole blocking layer having an ionization potential larger than the ionization potential of the light emitting layer. This document proposes the use of tris (5,7-dichloro-8-hydroxyquinolino) aluminum as the hole blocking material used in the hole blocking layer. Patent Document 2 proposes the use of silacyclopentadiene as a hole blocking material. However, none of these has sufficient driving stability. The reason why the stability at the time of driving is insufficient is that the hole blocking material is thermally deteriorated due to the low glass transition temperature (Tg), or the electrical property of the hole blocking material caused by injection of electrons and holes. Chemical modification has been pointed out.

  On the other hand, extending the lifetime of organic electroluminescent elements has been studied, and improvement of hole blocking materials for this purpose has also been studied. In Non-Patent Document 1, Balq (aluminum (III) bis (2-methyl-8-quinolinate) 4-phenylphenolate) or SAlq (aluminum (III) bis (2) is used for the purpose of improving the lifetime of the phosphorescent device. Aluminum complex-based hole blocking materials such as -methyl-8-quinolinate) triphenylsilanolate) have been actively used and have achieved a certain long life. However, in the above compound, since the hole blocking ability is not sufficient, the luminous efficiency of the device is insufficient, or some of the holes pass through the hole blocking layer and escape to the electron transport layer. There has been a problem that the electron transport material is oxidized and deteriorated.

  As another method for improving the lifetime of the phosphorescent element, Patent Document 3 discloses NPD (N, N′-diphenyl-N, N′-bis-α-naphthylbenzidine) and Alq3 (8 -A host material mixed with an aluminum complex of hydroxyquinoline) and PtOEP (2,3,7,8,12,12,17,18-octaethyl-21H, 23H-porphine platinum (II) or BTPIr ( Bis (2- (2′-benzo [4,5-a] thienylpyridinate-N, C3 ′) iridium (III) -acetylacetonate) is described as a phosphorescent dopant. Can only be applied to red dopant materials, and it has not been possible to extend the life of green phosphors and blue phosphors required for full-color display.

For the above reasons, there has been a demand for an organic electroluminescent device having high luminous efficiency and high hole blocking ability. In particular, the hole blocking material itself has been required to have electrical redox durability, particularly electrical reduction durability.
Japanese Patent Laid-Open No. 2-195683 Japanese Patent Laid-Open No. 9-87616 US Patent Application Publication No. 2002/0074935 Appl. Phys. Lett., 81, 162, 2002

  The present invention can provide a long-lived hole blocking material that maintains a high luminous efficiency and has a low luminance drop during continuous driving, and has a high hole blocking ability and electrical redox durability, particularly electrical reduction. It is an object of the present invention to provide a hole blocking material excellent in durability and a long-life organic electroluminescence device using the hole blocking material and having a high luminous efficiency and a low luminance decrease during continuous driving.

  As a result of intensive studies by the present inventors, the ratio of the reduction current value (Ipc) and oxidation current value (Ipa) of the first reduction wave obtained by cyclic voltammetry measurement is a hole blocking material having a molecular weight of 400 or more. By using a hole blocking material having (Ipa / Ipc) of 0.1 or more, in an organic electroluminescent device, while maintaining high efficiency light emission, there is little decrease in luminance during continuous driving and long life is achieved. The present invention has been found.

  That is, as a general knowledge so far, it has been preferable that an electron transporting material such as a hole blocking material is electrochemically stable, particularly stable against reduction. However, it has been very difficult to specify such a material specifically. Therefore, the present inventors tried various measurements and material designs to identify this electrochemically stable material, and reached the conclusion that the Ipa / Ipc ratio was useful. As the conventional hole blocking material, a material having an Ipa / Ipc ratio of less than 0.1 is usually used for a material having a molecular weight of 400 or more that can obtain a high glass transition temperature. However, when the present inventors dared to use a hole blocking material having an Ipa / Ipc ratio of 0.1 or more for the hole blocking layer instead, the electrical reduction durability of the device was dramatically improved. And it has been found that the service life is extended. That is, when the Ipa / Ipc ratio is 0.1 or higher, not only is it electrochemically stable as a hole blocking material, but it also maintains high luminous efficiency when used in an organic electroluminescent device. However, the inventors have found that it is possible to provide an element having a long lifetime with little decrease in luminance during continuous driving, and the present invention has been achieved.

（一般式（Ｉ）中、Ｒ^１〜Ｒ^３は、各々独立に、置換基を有していてもよい芳香族炭化水素基を表す。ｍは、２であり、Ｑ^１は、置換基を有していてもよい２価の芳香族炭化水素基であり、ピリジン環の２〜６位のいずれか１つと直接結合する。但し、Ｑ^１がピリジン環の２，４，６位のいずれかに結合する場合は、その結合位置にあるＲ^１〜Ｒ^３のいずれかがＱ^１となる。又、複数個含まれるＲ^１〜Ｒ^３は、それぞれ同一であつても異なっていてもよく、ピリジン環がＱ^１ と結合する位置は、それぞれ同一の位置であつても異なった位置であってもよい。） The first gist of the present invention resides in a hole blocking material which is a compound represented by the following general formula (I) and has a molecular weight of 400 or more.

(In General Formula (I), R ^{1 to} R ³ each independently represents an optionally substituted aromatic hydrocarbon group . M is 2 , and Q ¹ represents a substituent. A divalent aromatic hydrocarbon group which may be present and directly bonded to any one of positions 2 to 6 of the pyridine ring, provided that Q ¹ is any of positions 2, 4 and 6 of the pyridine ring; If attached, either R ¹ to R ³ is Q ¹ in its coupled position in. Further, R ¹ to R ³ which contained several double may be different even shall apply the same respectively The position at which the pyridine ring is bonded to Q ¹ may be the same position or different positions.)

  The second aspect of the present invention is an organic electroluminescence device comprising a light emitting layer sandwiched between an anode and a cathode on a substrate, and a hole blocking layer provided on the cathode side interface of the light emitting layer. In the device, the hole blocking layer resides in an organic electroluminescent device characterized by containing the hole blocking material of the present invention.

  According to the hole blocking material of the present invention, it is possible to realize a long-life organic electroluminescence device that is highly efficient and has a low luminance decrease during continuous driving.

  Therefore, the organic electroluminescent device according to the present invention is a flat panel display (for example, for OA computers and wall-mounted televisions), an in-vehicle display device, a light source utilizing characteristics of a mobile phone display or a surface light emitter (for example, a light source of a copying machine, It can be applied to liquid crystal displays and back light sources for instruments, display panels, and indicator lights, and its technical value is great.

  Embodiments of the present invention will be described in detail below, but the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention does not exceed the gist thereof. The content of is not specified.

[Hole blocking material]
First, the hole blocking material of the present invention will be described.
The hole blocking material of the present invention is a hole blocking material having a molecular weight of 400 or more, and is a ratio of the reduction current value (Ipc) and the oxidation current value (Ipa) of the first reduction wave obtained by cyclic voltammetry measurement ( Ipa / Ipc) is usually 0.1 or more. In an organic electroluminescence device having a light emitting layer sandwiched between an anode and a cathode on a substrate, a layer provided in contact with the cathode side interface of the light emitting layer Used as a material for (usually hole blocking layer).

  Here, the cyclic voltammetry measurement is carried out by the method described in “Electrochemical Measurement Manual Basics” (Electrical Society of Japan, Maruzen P.13-44) (or a measurement method equivalent thereto) Specifically, using a three-electrode measurement system, for example, as a supporting electrolyte, tetrabutylammonium perchlorate 0.1 M acetonitrile solution, tetrabutylammonium perchlorate 0.1 M dichloromethane solution, Using a mixed solvent of tetrabutylammonium perchlorate 0.1M dimethylformamide solution or tetrabutylammonium perchlorate 0.1M acetonitrile solution and tetrabutylammonium perchlorate 0.1M tetrahydrofuran solution as working electrode Measured using BAS GCE, Pt wire as counter electrode and Ag wire as reference electrode Determined.

  In addition, the equipment used for cyclic voltammetry measurement is not specified, and for example, “Electrochemical Analyzer 650A” manufactured by BAS can be used. Can do.

  As measurement conditions, the sweep speed is preferably measured at 10 V / sec or less, and can be measured at, for example, about 100 mV / sec. Also, it is desirable not to make the sweep region unnecessarily large in order to prevent as much as possible the adhesion of redox substances other than the sample to the electrode surface. The concentration of the sample is usually preferably 0.5 to 5 mM, and can be measured, for example, at a sample concentration of 1 mM.

The supporting electrolyte, solvent, working electrode, counter electrode, reference electrode, and the like can be appropriately changed according to the object to be measured. For the reference electrode, an Ag / Ag ⁺ electrode, an Ag / AgCl electrode, or the like is used. Also good.

  The reduction current value (Ipc) and the oxidation current value (Ipa) defined in the present invention mean those described in “Electrochemistry” (Masayoshi Watanabe et al., Ikuo Inoue et al., Maruzen P. 90-93). To do.

  The hole blocking material is responsible for transport of electrons, and thus is required to have stability against electrons. In other words, reduction stability is required. In the hole blocking material of the present invention, the ratio (Ipa / Ipc) of the reduction current value (Ipc) and the oxidation current value (Ipa) of the first reduction wave is 0.1 or more, preferably 0.2 or more, Most preferably, it is 0.3 or more. Below this lower limit, the electrical reduction stability is remarkably inferior, which is not preferable. It is estimated that Ipa / Ipc is closer to 1 and has better electroreduction stability.

In the present invention, the first oxidation potential and the first reduction potential are ferrocene / ferrocenium (Fc / Fc ⁺ ) as an internal standard, and +0.41 V vs. The potential was determined as SCE.

The difference (energy gap) in redox potential defined by the calculated redox potential is:
The thing of 3.5V or more is preferable.

  The molecular weight of the hole blocking material of the present invention is usually 4000 or less, preferably 3000 or less, more preferably 2000 or less, and usually 400 or more, more preferably 500 or more. If the molecular weight exceeds the above upper limit, the sublimation property is remarkably lowered, which may cause trouble when using an evaporation method when producing an organic electroluminescent device, or a decrease in solubility in an organic solvent, or a synthesis process. With the increase in impurity components generated in the process, it may be difficult to increase the purity of the material (that is, to remove the deterioration-causing substance). On the other hand, if the molecular weight is below the lower limit, the glass transition temperature, melting point, vaporization temperature and the like are lowered, so that the heat resistance is remarkably impaired, the crystallinity is improved due to a decrease in amorphousness, and the film stability is lowered. Since there are cases, it is not preferable.

  The glass transition temperature (Tg) of the hole blocking material is preferably 70 ° C. or higher, more preferably 100 ° C. or higher. When the glass transition temperature is below this lower limit, the heat resistance is remarkably impaired, and the driving life when applied to an organic electroluminescent device is also adversely affected.

  The hole blocking material used for the hole blocking layer of the organic electroluminescence device is required to be able to efficiently move the charges (in this case, electrons) moved from the cathode side into the light emitting layer. Therefore, it is preferable that the hole blocking layer has few energy barriers with the adjacent light emitting layer and electron transport layer. Furthermore, if the mobility with respect to the charge (in this case, the electron mobility) is high, the charge moving from the cathode side can be efficiently taken into the light emitting layer, and the drive voltage of the element can be lowered. ,preferable.

  In addition, the hole blocking material of the present invention preferably has an excited triplet level of 2.2 eV or higher. The excited triplet level correlates with the emission color and the luminous efficiency, and in particular, a higher excited triplet level is necessary for efficiently emitting a dopant material that exhibits phosphorescence at a short wavelength such as blue. . The excited triplet level of the hole blocking material is preferably 2.2 eV or more, more preferably 2.4 eV or more, and particularly preferably 2.6 eV or more. Moreover, it is preferably 3.4 eV or less, more preferably 3.2 eV or less.

Note that phosphorescence is light emission generated by transition from an excited triplet state to a ground state, and the excited triplet level (T1) can be obtained by experimentally measuring the phosphorescence spectrum of a substance. The excited triplet level can be obtained from the following relational expression using λT1 of the phosphorescence spectrum measured by cooling to about 5 to 10K.
T1 [eV] = 1240 / λT1 [nm]
Usually, it is calculated from the peak wavelength (λT1 [nm]) having the highest energy (short wavelength) in the obtained phosphorescence spectrum.

  The hole blocking material of the present invention may be any material having a molecular weight of 400 or more and Ipa / Ipc of 0.1 or more. Specifically, oxadiazole derivatives, triazole derivatives, distyrylbiphenyl derivatives, silole derivatives A benzoxazole metal complex, a benzothiazole metal complex, trisbenzimidazolylbenzene, a quinoxaline compound, a phenanthroline derivative, a boron-containing compound, a pyridine-containing ring compound, or the like is used as a hole blocking material for an organic electroluminescent device. Good. Among these, a compound having a pyridine ring exhibits high electroreduction stability, and further has a high excited triplet rank (T1) and is more preferable.

（一般式（Ｉ）中、Ｒ^１〜Ｒ^３は、各々独立に、任意の置換基を表す。ピリジン環の３位、５位は、置換されていてもよい。ｍは、１〜８の整数である。
Ｑ^１は、ｍが１の時、ピリジン環の置換基或いは水素原子であり、ｍが２以上の時、ｍ価の連結基である。Ｑ^１は、ピリジン環の２〜６位のいずれか１つと直接結合する。但し、Ｑ^１が、ピリジン環の２，４，６位のいずれかに結合する場合は、その結合位置にあるＲ^１〜Ｒ^３のいずれかがＱ^１となる。
ｍが２以上の時、化合物中に複数個含まれるＲ^１〜Ｒ^３は、それぞれ同一であつても異なっていてもよい。また、ｍが２以上の時、ピリジン環がＱ^１と結合する位置は、それぞれ同一の位置であつても異なっていてもよい。） Of the compounds having a pyridine ring, compounds represented by the following general formula (I) are more preferred.

(In General Formula (I), R ^{1 to} R ³ each independently represents an arbitrary substituent. The 3-position and 5-position of the pyridine ring may be substituted. It is an integer.
Q ¹ is a substituent of the pyridine ring or a hydrogen atom when m is 1, and an m-valent linking group when m is 2 or more. Q ¹ is directly bonded to any one of positions 2 to 6 of the pyridine ring. However, when Q ¹ is bonded to any of the 2, 4 and 6 positions of the pyridine ring, any one of R ^{1 to} R ^{3 at} the bonding position is Q ¹ .
When m is 2 or more, a plurality of R ^{1 to} R ³ contained in the compound may be the same or different. When m is 2 or more, the position at which the pyridine ring is bonded to Q ¹ may be the same position or different. )

The value of m that can be taken by the compound represented by the general formula (I) is an integer of 1 to 8, but it can exhibit excellent durability when it has two or more pyridine rings in the molecule. As a result, it exhibits excellent electron transport properties and a wide redox potential difference. On the other hand, when there are too many pyridine rings, the basicity as a compound becomes too strong, and when it is contained in the hole blocking layer, there is a risk of causing ligand exchange by applying a long electric field. From such a viewpoint, m representing the number of pyridine rings bonded to Q ¹ is preferably 2 or more, preferably 6 or less, more preferably 4 or less, and most preferably 3 or less.

The molecular weight of the compound represented by the general formula (I) is usually 4000 or less, preferably 3000 or less, more preferably 2000 or less, and usually 400 or more for the same reason as the molecular weight of the hole blocking layer described above. More preferably, it is 500 or more.
The preferred total carbon number of the compound represented by the general formula (I) is usually 300 or less, preferably 200 or less, more preferably 100 or less, and usually 15 or more, preferably 20 or more, more preferably 30 or more.

In the general formula (I), when m representing the number of pyridine rings is 2 or more, the linking group Q ¹ is a direct bond connecting the pyridine rings or preferably any linking group having no diarylamine skeleton. Is possible.

In the general formula (I), the linking group Q ¹ is preferably
Direct bond,
Alkene group (group derived from alkene) which may have a substituent,
Alkyne group (group derived from alkyne) which may have a substituent,
An aromatic hydrocarbon group which may have a substituent (for example, derived from benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, perylene ring, tetracene ring, pyrene ring, benzpyrene ring, chrysene ring, triphenylene ring, fluoranthene, etc. m-valent groups are included)
Or an aromatic heterocyclic group which may have a substituent (for example, furan ring, thiophene ring, pyrrole ring, pyrazole ring, imidazole ring, oxadiazole ring, pyridine ring, pyrazine ring, pyridazine ring, pyrimidine ring, M-valent groups derived from triazine ring, quinoline ring, isoquinoline ring, sinoline ring, quinoxaline ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring, etc.),
Or a group formed by connecting two or more of these,
Etc.

又は、これらを組み合わせてなる部分構造で連結されている場合が好ましい。なお、上記式において、Ｇ¹〜Ｇ³は各々独立に、水素原子又は任意の置換基を表すか、或いは、Ｑ¹の例として前述した芳香族炭化水素や芳香族複素環の一部を構成する。同一のＱ¹基中に含まれるＧ¹〜Ｇ³は、各々、同一であっても異なっていてもよい。 From the viewpoint of the electrical redox durability of the compound, in the compound represented by the general formula (I), two or more pyridine rings contained in one molecule are conjugated with each other through a linking group Q ^1. A compound is preferred. In order to make such a compound, a direct bond between pyridine rings,

Or the case where it connects with the partial structure which combines these is preferable. In the above formula, G ^{1 to} G ³ each independently represent a hydrogen atom or an arbitrary substituent, or constitute a part of the aromatic hydrocarbon or aromatic heterocycle described above as an example of Q ^1. To do. G ^{1 to} G ³ contained in the same Q ¹ group may be the same or different from each other.

で表される構造で結合されている場合がより好ましく、更にＧ¹及びＧ²が、Ｑ¹基における芳香族炭化水素基の一部を構成する場合が、特に好ましい。 Among these, the space between the pyridine rings

Is more preferable, and it is particularly preferable that G ¹ and G ² constitute a part of the aromatic hydrocarbon group in the Q ¹ group.

Preferable specific examples of the linking group Q ¹ are shown in the following Z-1 to Z-173, but are not limited thereto.

Among them, from the viewpoint of sufficiently widening the redox potential difference and the viewpoint of repeated electric redox durability, as the linking group Q ¹ ,
Z-1 (direct coupling), Z-2 to 69, 79, 82, 84, 89, 96, 103, 105, 108, 109, 111 to 114, 117, 118, 121, 124, 167, 170
Is preferred,
Z-2, 8, 11-13, 15, 17, 19, 20, 22, 23-25, 27-30, 34, 37, 44, 47-61, 63-69, 89, 105, 109, 114, 124, 167, 170
Is more preferred,
Z-2, 8, 12, 13, 15, 17, 19, 20, 22, 23, 25, 27-30, 34, 37, 44, 47-50, 63, 64, 66, 67, 89, 109, 114, 124, 167
Is more preferred,
Z-2, 8, 12, 13, 15, 17, 19, 20, 23, 28-30, 34, 66
Is most preferred.

（上記式中、Ｒ^aは任意の置換基であり、好ましくは置換基を有していてもよい炭素数１〜８のアルキル基、アラルキル基、アリール基の何れかである。Ｒ^bは水素原子又は任意の置換基であり、好ましくは置換基を有していてもよい炭素数１〜８のアルキル基、アラルキル基、アリール基の何れかである。）

（上記式中、Ｒ^c、Ｒ^dは水素原子又は任意の置換基であり、好ましくは置換基を有していてもよい炭素数１〜８のアルキル基、アラルキル基、アリール基の何れかである。）
シアノ基
置換基を有していてもよいシリル基（例えばトリメチルシリル基、トリフェニルシリル基などが挙げられる。）
置換基を有していてもよいボリル基（例えばジメシチルボリル基などが挙げられる。）
置換基を有していてもよいホスフィノ基（例えばジフェニルホスフィノ基などが挙げられる。）
置換基を有していてもよい芳香族炭化水素基（例えばベンゼン環、ナフタレン環、アントラセン環、フェナントレン環、ペリレン環、テトラセン環、ピレン環、ベンズピレン環、クリセン環、トリフェニレン環、フルオランテン環などが挙げられる。）
置換基を有していてもよい芳香族複素環基（例えばフラン環、チオフェン環、ピロール環、ピラゾール環、イミダゾール環、オキサジアゾール環、ピリジン環、ピラジン環、ピリダジン環、ピリミジン環、トリアジン環、キノリン環、イソキノリン環、シノリン環、キノキサリン環、ペリミジン環、キナゾリン環、キナゾリノン環、アズレン環などが挙げられる。） The linking group Q ^{1 in the} above specific example may have an arbitrary substituent (having no diarylamine skeleton, aryloxide skeleton and arylsulfide skeleton). Examples of such a substituent are as follows: The thing is mentioned.
Halogen atom (fluorine atom, chlorine atom, bromine atom, iodine atom)
An alkyl group which may have a substituent (preferably a linear or branched alkyl group having 1 to 8 carbon atoms, such as methyl, ethyl, n-propyl, 2-propyl, n-butyl, isobutyl, tert -A butyl group etc. are mentioned.)
An alkenyl group which may have a substituent (preferably an alkenyl group having 1 to 8 carbon atoms, such as vinyl, allyl and 1-butenyl groups).
An alkynyl group which may have a substituent (preferably an alkynyl group having 1 to 8 carbon atoms, such as ethynyl and propargyl groups).
Aralkyl group which may have a substituent (preferably an aralkyl group having 1 to 8 carbon atoms, such as benzyl group).
An acyl group which may have a substituent (preferably an acyl group having 1 to 8 carbon atoms which may have a substituent, such as formyl, acetyl and benzoyl groups).
An alkoxycarbonyl group which may have a substituent (preferably an alkoxycarbonyl group having 2 to 13 carbon atoms which may have a substituent, such as methoxycarbonyl and ethoxycarbonyl groups).
Aryloxycarbonyl group which may have a substituent (preferably an aryloxycarbonyl group having 2 to 13 carbon atoms which may have a substituent, including, for example, an acetoxy group)
Carboxyl group

(In the above formula, R ^a is an arbitrary substituent, preferably an alkyl group having 1 to 8 carbon atoms, an aralkyl group or an aryl group which may have a substituent. R ^b is hydrogen. An atom or an arbitrary substituent, preferably an alkyl group having 1 to 8 carbon atoms which may have a substituent, an aralkyl group, or an aryl group.

(In the above formula, R ^c and R ^d are a hydrogen atom or an arbitrary substituent, preferably an alkyl group having 1 to 8 carbon atoms, an aralkyl group or an aryl group which may have a substituent. is there.)
Cyano group A silyl group which may have a substituent (for example, a trimethylsilyl group, a triphenylsilyl group, etc.).
An optionally substituted boryl group (eg, a dimesitylboryl group).
A phosphino group which may have a substituent (for example, a diphenylphosphino group).
An aromatic hydrocarbon group which may have a substituent (for example, benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, perylene ring, tetracene ring, pyrene ring, benzpyrene ring, chrysene ring, triphenylene ring, fluoranthene ring, etc. Can be mentioned.)
An aromatic heterocyclic group which may have a substituent (for example, furan ring, thiophene ring, pyrrole ring, pyrazole ring, imidazole ring, oxadiazole ring, pyridine ring, pyrazine ring, pyridazine ring, pyrimidine ring, triazine ring) Quinoline ring, isoquinoline ring, sinoline ring, quinoxaline ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring and the like.

From the viewpoint of limiting molecular vibration, the linking group Q ¹ does not have a substituent, or has a methyl group or a phenyl group as a substituent, and most preferably has no substituent. .

R ¹ to R ³ in the general formula (I) each independently represents an arbitrary substituent. When m is 2 or more, R ¹ to R ³ contained in the compound may be the same or different. Specific examples of the optional group that can be used for R ¹ to R ³ include the following.
An alkyl group which may have a substituent (preferably a linear or branched alkyl group having 1 to 8 carbon atoms, such as methyl, ethyl, n-propyl, 2-propyl, n-butyl, isobutyl, tert -A butyl group etc. are mentioned.)
An alkenyl group which may have a substituent (preferably an alkenyl group having 2 to 9 carbon atoms, such as vinyl, allyl and 1-butenyl groups).
An alkynyl group which may have a substituent (preferably an alkynyl group having 2 to 9 carbon atoms, such as ethynyl and propargyl groups).
An aralkyl group which may have a substituent (preferably an aralkyl group having 7 to 15 carbon atoms, such as a benzyl group).
An amino group which may have a substituent as described below (an alkylamino group having one or more alkyl groups having 1 to 8 carbon atoms which may have a substituent, such as methylamino, dimethylamino , Diethylamino, dibenzylamino group and the like.
An arylamino group having an aromatic hydrocarbon group having 6 to 12 carbon atoms which may have a substituent, such as phenylamino, diphenylamino, and ditolylamino groups.
A heteroarylamino group having a 5- or 6-membered aromatic heterocyclic ring which may have a substituent, such as pyridylamino, thienylamino, dithienylamino group and the like.
An acylamino group having an acyl group having 2 to 10 carbon atoms, which may have a substituent, such as acetylamino and benzoylamino groups. )
An alkoxy group that may have a substituent (preferably an alkoxy group having 1 to 8 carbon atoms that may have a substituent, such as methoxy, ethoxy, and butoxy groups).
An aryloxy group which may have a substituent (preferably an aromatic hydrocarbon group having 6 to 12 carbon atoms, such as phenyloxy, 1-naphthyloxy, 2-naphthyloxy group and the like. .)
A heteroaryloxy group which may have a substituent (preferably has a 5- or 6-membered aromatic heterocyclic group, and examples thereof include a pyridyloxy and thienyloxy group).
An acyl group which may have a substituent (preferably an acyl group having 2 to 10 carbon atoms which may have a substituent, such as formyl, acetyl and benzoyl groups).
An alkoxycarbonyl group which may have a substituent (preferably an alkoxycarbonyl group having 2 to 10 carbon atoms which may have a substituent, such as methoxycarbonyl and ethoxycarbonyl groups).
An aryloxycarbonyl group which may have a substituent (preferably an aryloxycarbonyl group having 7 to 13 carbon atoms which may have a substituent, such as a phenoxycarbonyl group).
An alkylcarbonyloxy group which may have a substituent (preferably an alkylcarbonyloxy group having 2 to 10 carbon atoms which may have a substituent, such as an acetoxy group).
Halogen atom (especially fluorine atom or chlorine atom)
Carboxyl group Cyano group Hydroxyl group Mercapto group Alkylthio group which may have a substituent (preferably an alkylthio group having 1 to 8 carbon atoms, such as methylthio group and ethylthio group).
An arylthio group which may have a substituent (preferably an arylthio group having 6 to 12 carbon atoms, such as a phenylthio group and a 1-naphthylthio group).
A sulfonyl group which may have a substituent (for example, a mesyl group, a tosyl group, etc.).
A silyl group which may have a substituent (for example, a trimethylsilyl group, a triphenylsilyl group, etc.).
An optionally substituted boryl group (eg, a dimesitylboryl group).
A phosphino group which may have a substituent (for example, a diphenylphosphino group).
An aromatic hydrocarbon group which may have a substituent (for example, benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, perylene ring, tetracene ring, pyrene ring, benzpyrene ring, chrysene ring, triphenylene ring, fluoranthene ring, etc. And monovalent groups derived from 5- or 6-membered monocyclic rings or 2 to 5 condensed rings.)
An aromatic heterocyclic group which may have a substituent (for example, furan ring, benzofuran ring, thiophene ring, benzothiophene ring, pyrrole ring, pyrazole ring, imidazole ring, oxadiazole ring, indole ring, carbazole ring, pyrrolo) Imidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring, furopyrrole ring, furofuran ring, thienofuran ring, benzisoxazole ring, benzoisothiazole ring, benzimidazole ring, pyridine ring, pyrazine ring, pyridazine ring, Monovalent groups derived from 5- or 6-membered monocyclic or 2-4 condensed rings such as pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring, sinoline ring, quinoxaline ring, benzimidazole ring, perimidine ring, quinazoline ring Can be mentioned.)

The substituent that these R ^{1 to} R ³ groups may have is not particularly limited as long as the performance of the compound represented by the general formula (I) is not impaired, but preferably an alkyl group, an aromatic hydrocarbon group, Or an alkyl-substituted aromatic hydrocarbon group, and specific examples thereof include alkyl groups having about 1 to 6 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, and a tert-butyl group; a phenyl group and a naphthyl group. An aromatic hydrocarbon group having about 6 to 18 carbon atoms such as fluorenyl group; an alkyl-substituted aromatic hydrocarbon group having about 7 to 30 carbon atoms such as tolyl group, mesityl group and 2,6-dimethylphenyl group , Etc.

Specific examples R-1 to R-55 in the case where R ^{1 to} R ³ are aromatic hydrocarbon groups or aromatic heterocyclic groups are shown below, but are not limited thereto.

（上記各式中、Ｌ₁〜Ｌ₃は各々独立に、置換基を有していてもよい、アルキル基、芳香族炭化水素基、又はアルキル置換芳香族炭化水素基を表す。Ｌ₄及びＬ₅は各々独立に、置換基を有していてもよい、水素原子、アルキル基、芳香族炭化水素基、又はアルキル置換芳香族炭化水素基を表す。
Ｌ₁〜Ｌ₅のアルキル基、芳香族炭化水素基、又はアルキル置換芳香族炭化水素基として、具体的には、メチル基、エチル基、イソプロピル基、ｔｅｒｔ−ブチル基などの、炭素数１〜６程度のアルキル基；フェニル基、ナフチル基、フルオレニル基などの、炭素数６〜１８程度の芳香族炭化水素基；トリル基、メシチル基、２，６−ジメチルフェニル基などの、総炭素数７〜３０程度のアルキル置換芳香族炭化水素基、などが挙げられる。
なお、上記構造はいずれも、Ｌ₁〜Ｌ₅の他にも置換基を有していてもよいが、自身が結合しているピリジン環上の電子状態に強く影響を及ぼしてしまうと、酸化還元電位差が狭くなってしまうおそれがあるため、置換基としては、電子供与性・電子吸引性が共に小さく、かつ、分子内共役長の広がりをもたらしにくい基を選択することが好ましい。このような置換基の具体例としても、やはりアルキル基、芳香族炭化水素基、アルキル置換芳香族炭化水素基等が挙げられる。
なお、１分子中に上記構造を２個以上有する化合物の場合、１分子中に含まれる２個以上のＬ₁〜Ｌ₅は、同一であっても異なっていてもよい。）

(In the above formulas, L _{1 to} L ₃ each independently represents an alkyl group, an aromatic hydrocarbon group, or an alkyl-substituted aromatic hydrocarbon group which may have a substituent. L ₄ and L Each ₅ independently represents a hydrogen atom, an alkyl group, an aromatic hydrocarbon group, or an alkyl-substituted aromatic hydrocarbon group, which may have a substituent.
Specific examples of the alkyl group, aromatic hydrocarbon group, or alkyl-substituted aromatic hydrocarbon group represented by L _{1 to} L ₅ include a methyl group, an ethyl group, an isopropyl group, and a tert-butyl group. An alkyl group of about 6; an aromatic hydrocarbon group of about 6 to 18 carbon atoms such as a phenyl group, a naphthyl group and a fluorenyl group; a total carbon number of 7 such as a tolyl group, a mesityl group and a 2,6-dimethylphenyl group And about 30 alkyl-substituted aromatic hydrocarbon groups.
Any of the above structures may have a substituent in addition to L _{1 to} L ₅ , but if it strongly affects the electronic state on the pyridine ring to which it is bonded, oxidation will occur. Since the reduction potential difference may be narrowed, it is preferable to select a group that has a small electron donating property and electron withdrawing property and does not easily cause an increase in intramolecular conjugated length. Specific examples of such substituents also include alkyl groups, aromatic hydrocarbon groups, alkyl-substituted aromatic hydrocarbon groups, and the like.
In the case of a compound having two or more of the above structures in one molecule, two or more L _{1 to} L ₅ contained in one molecule may be the same or different. )

Among the exemplary structures of R ^{1 to} R ³ , R- ¹ to 6, 10 to 13, 33, 34, 38, 45, and 48 are preferable, and R-1 to 6, 48, from the viewpoint of giving a wide redox potential difference. Are more preferable, and R-1 to 3 and 48 are most preferable.

For example, when the hole blocking material of the present invention is applied to the hole blocking layer of the organic electroluminescent element, R ^{1 to} R ³ may have a substituent from the viewpoint of sublimation and heat resistance improvement. An alkyl group or an aromatic hydrocarbon group which may have a substituent (especially an aromatic hydrocarbon group having about 6 to 12 carbon atoms) is preferable. From the viewpoint of giving a large oxidation potential, a hydrogen atom or phenyl The group is particularly preferred.

In the general formula (I), the 3-position and 5-position of the pyridine ring may be substituted with any group specifically exemplified as an arbitrary group that can be used for R ^{1 to} R ^3. From the viewpoint of improving redox durability and improving heat resistance, the substituent is preferably an aromatic hydrocarbon group or an aromatic heterocyclic group.

  Specific examples preferable as the compound represented by the general formula (I) are shown below, but the hole blocking material of the present invention is not limited thereto.

[Organic electroluminescence device]
Next, the organic electroluminescent element of the present invention using such a hole blocking material of the present invention will be described.

  The organic electroluminescent device of the present invention is an organic electroluminescent device having a light-emitting layer sandwiched between an anode and a cathode on a substrate and provided with a hole blocking layer in contact with the cathode-side interface of the light-emitting layer. The hole blocking layer contains the hole blocking material of the present invention.

  When the hole blocking material of the present invention is used as the hole blocking material of the hole blocking layer of the organic electroluminescence device as described above, one kind may be used alone, or two or more kinds may be used in combination. .

  In the hole blocking material of the present invention, in particular, the first oxidation potential obtained in the cyclic voltammetry measurement of the hole blocking material of the hole blocking layer is higher than the first oxidation potential of the light emitting substance in the light emitting layer. In the case where a plurality of light emitting substances are included in the light emitting layer, it is most preferable that the first oxidation potential of the hole blocking material is higher than that of the light emitting substance having the highest first oxidation potential. Further, when a plurality of hole blocking materials are included in the hole blocking layer, the one with the lowest first oxidation potential among the hole blocking materials is more than the first oxidation potential of the light emitting substance in the light emitting layer. Larger is preferred. Here, the light emitting substance in the present invention means a compound that emits light in the light emitting layer. In the case of a light emitting layer containing a dopant material and a host material, the dopant material is usually referred to as a light emitting substance.

  The first oxidation potential obtained in the cyclic voltammetry measurement of the hole blocking material in the hole blocking layer is preferably 0.1 V or more higher than the first oxidation potential of the light emitting substance in the light emitting layer. When the light emitting layer includes a host material and a dopant material, the first oxidation potential of the hole blocking material is preferably 0.1 V or more higher than the first oxidation potential of the dopant material, and is more positive than the oxidation potential of the host material. It is more preferable that the first oxidation potential of the hole blocking material is 0.1 V or more.

  Since these hole blocking materials are used in the hole blocking layer adjacent to the light emitting layer, when the oxidation potential of the hole blocking material and the light emitting material satisfies the above relationship, the holes carried from the anode side emit light. The effect of confining in the layer is further increased, and holes carried from the anode side can be further contributed to light emission, and high light emission efficiency can be achieved.

Hereinafter, an example of the structure of the organic electroluminescent element of the present invention will be described with reference to the drawings. However, the structure of the organic electroluminescent element of the present invention is not limited to the one shown in the drawings.
1 to 3 are cross-sectional views schematically showing an example of the structure of the organic electroluminescent device of the present invention, wherein 1 is a substrate, 2 is an anode, 3 is an anode buffer layer, 4 is a hole transport layer, and 5 is a light emitting layer. , 6 represents a hole blocking layer, 7 represents an electron transport layer, and 8 represents a cathode.

(substrate)
The substrate 1 serves as a support for the organic electroluminescent element, and a quartz or glass plate, a metal plate or a metal foil, a plastic film, a sheet, or the like is used. In particular, a glass plate, a transparent synthetic resin plate such as polyester, polymethacrylate, polycarbonate, polysulfone, or a film is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too small, the organic electroluminescent element may be deteriorated by the outside air that has passed through the substrate, which is not preferable. For this reason, a method of providing a gas barrier property by providing a dense silicon oxide film or the like on at least one surface of the synthetic resin substrate is also a preferable method.

(anode)
An anode 2 is provided on the substrate 1. The anode 2 plays a role of hole injection into the hole transport layer 4. The anode 2 is usually a metal such as aluminum, gold, silver, nickel, palladium, or platinum, a metal oxide such as an oxide of indium and / or tin, a metal halide such as copper iodide, carbon black, or poly It is composed of conductive polymers such as (3-methylthiophene), polypyrrole, and polyaniline. In general, the anode 2 is often formed by a sputtering method, a vacuum deposition method, or the like. Further, when the anode 2 is formed of metal fine particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, and conductive polymer fine powder, It can also be formed by dispersing and coating on the substrate 1. Further, when the anode 2 is formed with a conductive polymer, a polymerized thin film can be formed directly on the substrate 1 by electrolytic polymerization, or a conductive polymer can be applied on the substrate 1 (Appl). Phys. Lett., 60, 2711, 1992).

The anode 2 usually has a single-layer structure, but it can also have a laminated structure made of a plurality of materials if desired.

  The thickness of the anode 2 varies depending on the required transparency. When transparency is required, the visible light transmittance is usually 60% or more, preferably 80% or more. In this case, the thickness of the anode is usually 5 nm or more, preferably 10 nm or more, and usually 1000 nm or less, preferably about 500 nm or less. When it may be opaque, the thickness of the anode 2 is arbitrary, and if desired, it may be formed of metal to serve as the substrate 1.

(Hole transport layer)
In the element having the configuration shown in FIG. 1, a hole transport layer 4 is provided on the anode 2. As conditions required for the material of the hole transport layer, it is necessary that the material has a high hole injection efficiency from the anode 2 and can efficiently transport the injected holes. For this purpose, the ionization potential is low, the transparency to visible light is high, the hole mobility is high, the stability is high, and impurities that become traps are unlikely to be generated during manufacturing or use. Required. Further, in order to contact the light emitting layer 5, it is required not to quench the light emitted from the light emitting layer 5 or to form an exciplex with the light emitting layer 5 to reduce the efficiency. In addition to the above general requirements, when the application for in-vehicle display is considered, the element is further required to have heat resistance. Therefore, a material having a glass transition temperature of 85 ° C. or higher is desirable.

  As such a hole transporting material, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl is used similarly to the hole transporting material used for the host material of the light emitting layer 5. Aromatic diamines containing two or more representative tertiary amines and having two or more condensed aromatic rings substituted with nitrogen atoms (Japanese Patent Laid-Open No. 5-234681), 4,4 ′, 4 ″ -tris ( Aromatic amine compounds having a starburst structure such as 1-naphthylphenylamino) triphenylamine (J. Lumin., 72-74, 985, 1997), a triphenylamine tetramer Spiro compounds such as compounds (Chem. Commun., 2175, 1996), 2,2 ′, 7,7′-tetrakis- (diphenylamino) -9,9′-spirobifluorene (Synth. Metals, 91, pp. 209 pp., 1997), 4,4'-N, such as a carbazole derivative such as N'- dicarbazole biphenyl. These compounds may be used individually by 1 type, and may be used in mixture of multiple types as needed.

  In addition to the above compounds, polyarylene ether sulfone (Polym. Adv. Tech.) Containing polyvinyl carbazole, polyvinyl triphenylamine (Japanese Patent Laid-Open No. 7-53953), and tetraphenylbenzidine as the material of the hole transport layer 4 is used. , 7, p. 33, 1996).

  The hole transport layer 4 may be formed by a normal coating method such as a spray method, a printing method, a spin coating method, a dip coating method, or a die coating method, a wet film forming method such as various printing methods such as an ink jet method or a screen printing method, or a vacuum. It can be formed by a dry film formation method such as a vapor deposition method.

  In the case of the coating method, an additive such as a binder resin or a coating property improving agent that does not trap holes is added to one or more of the hole transport materials, if necessary, and dissolved in a suitable solvent. A solution is prepared, applied onto the anode 2 by a method such as spin coating, and dried to form the hole transport layer 4. Examples of the binder resin include polycarbonate, polyarylate, and polyester. When the amount of the binder resin added is large, the hole mobility is lowered. Therefore, the smaller amount is desirable, and the content in the hole transport layer is usually preferably 50% by weight or less.

In the case of the vacuum evaporation method, the hole transport material is put in a crucible installed in a vacuum vessel, the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa with a suitable vacuum pump, and then the crucible is heated, The hole transport material is evaporated and a hole transport layer 4 is formed on the substrate 1 on which the anode 2 is formed, which is placed facing the crucible.

  The thickness of the hole transport layer 4 is usually 5 nm or more, preferably 10 nm or more, and is usually 300 nm or less, preferably 100 nm or less. In order to uniformly form such a thin film, a vacuum deposition method is generally used.

(Light emitting layer)
In the element shown in FIG. 1, a light emitting layer 5 is provided on the hole transport layer 4. The light emitting layer 5 is a recombination of holes injected from the anode 2 and moving through the hole transport layer 4 and electrons injected from the cathode and moved through the hole blocking layer 6 between the electrodes to which an electric field is applied. It is formed of a luminescent material that emits strong light when excited by. Usually, the light emitting layer 5 includes a dopant material and a host material, which are light emitting substances, as described above. In the present invention, a material contained in the light emitting layer such as a dopant material or a host material is referred to as a light emitting layer material.

  The light-emitting substance used in the light-emitting layer 5 is a compound that has a stable thin film shape, exhibits high emission (fluorescence or phosphorescence) quantum yield in the solid state, and can efficiently transport holes and / or electrons. It is necessary to be. Further, it is required to be a compound that is electrochemically and chemically stable and does not easily generate impurities as traps during production or use.

Furthermore, in the present invention, as described above, a luminescent material having a first oxidation potential smaller than the first oxidation potential of the hole blocking material of the hole blocking layer, particularly (oxidation potential of the hole blocking material) − (luminescent material). Oxidation potential) ≧ 0.1V
(Reduction potential of hole blocking material) ≧ (Reduction potential of luminescent substance)
It is preferable to use a light-emitting substance that satisfies the above.

  As a material that satisfies such conditions and forms a light emitting layer that emits fluorescence, a metal complex such as an aluminum complex of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393), 10-hydroxybenzo [h] quinoline Metal complexes (JP-A-6-322362), bisstyrylbenzene derivatives (JP-A-1-245087, JP-A-2-222484), bisstyrylarylene derivatives (JP-A-2-247278), (2- Hydroxyphenyl) benzothiazole metal complexes (Japanese Patent Laid-Open No. 8-315983), silole derivatives, and the like. These light emitting layer materials are usually laminated on the hole transport layer by a vacuum deposition method. Of the hole transport layer materials described above, an aromatic amine compound having a light-emitting property can also be used as the light-emitting layer material.

  For the purpose of improving the luminous efficiency of the device and changing the emission color, for example, doping a fluorescent dye for lasers such as coumarin with an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phys., Volume 65). 3610 (1989)). This doping technique can also be applied to the light emitting layer 5, and various fluorescent dyes can be used as a doping material in addition to coumarin. Examples of fluorescent dyes that emit blue light include perylene, pyrene, anthracene, coumarin, and derivatives thereof. Examples of the green fluorescent dye include quinacridone derivatives and coumarin derivatives. Examples of yellow fluorescent dyes include rubrene and perimidone derivatives. Examples of red fluorescent dyes include DCM compounds, benzopyran derivatives, rhodamine derivatives, benzothioxanthene derivatives, azabenzothioxanthene and the like.

  Other than the above-mentioned fluorescent dyes for doping, depending on the host material, listed in Laser Research, 8, 694, 803, 958 (1980); 9, 9, 85 (1981). Fluorescent dyes and the like that can be used as a doping material for the light emitting layer.

The amount by which the fluorescent dye is doped with respect to the host material is preferably 10 ⁻³ wt% or more, more preferably 0.1 wt% or more. Moreover, 10 weight% or less is preferable and 3 weight% or less is more preferable. If the lower limit is not reached, it may not be possible to contribute to improving the luminous efficiency of the device. If the upper limit is exceeded, concentration quenching may occur, leading to a reduction in luminous efficiency.

  In the present invention, the dopant material used for the light emitting layer is preferably an organometallic complex containing a metal selected from Groups 7 to 11 of the periodic table. The T1 (excited triplet level) of the metal complex is preferably higher than the T1 of the charge transporting compound used as the host material from the viewpoint of light emission efficiency. Furthermore, since light emission occurs in the dopant material, chemical stabilization such as redox is also required.

Preferred examples of the metal in the phosphorescent organometallic complex containing a metal selected from Groups 7 to 11 of the periodic table include ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, and gold. Preferred examples of these organometallic complexes include compounds represented by the following general formula (II) or general formula (VI).
MLn-jL'j (II)
(In the formula, M represents a metal, n represents a valence of the metal, L and L ′ represent a bidentate ligand, and j represents 0, 1 or 2.)

（式中、Ｍ⁷は金属、Ｔは炭素又は窒素を表す。Ｔが窒素の場合はＲ¹⁴、Ｒ¹⁵は無く、Ｔが炭素の場合はＲ¹⁴、Ｒ¹⁵は水素原子、ハロゲン原子、アルキル基、アラルキル基、アルケニル基、シアノ基、アミノ基、アシル基、アルコキシカルボニル基、カルボキシル基、アルコキシ基、アルキルアミノ基、アラルキルアミノ基、ハロアルキル基、水酸基、アリールオキシ基、置換基を有していてもよい芳香族炭化水素基又は芳香族複素環基を表す。
Ｒ¹²、Ｒ¹³は水素原子、ハロゲン原子、アルキル基、アラルキル基、アルケニル基、シアノ基、アミノ基、アシル基、アルコキシカルボニル基、カルボキシル基、アルコキシ基、アルキルアミノ基、アラルキルアミノ基、ハロアルキル基、水酸基、アリールオキシ基、置換基を有していてもよい芳香族炭化水素基又は芳香族複素環基を表し、互いに連結して環を形成しても良い。）

(In the formula, M ⁷ represents a metal, T represents carbon or nitrogen. When T is nitrogen, there are no R ¹⁴ and R ¹⁵ , and when T is carbon, R ¹⁴ and R ¹⁵ represent a hydrogen atom, a halogen atom, and an alkyl. Group, aralkyl group, alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, alkylamino group, aralkylamino group, haloalkyl group, hydroxyl group, aryloxy group, substituent Represents an aromatic hydrocarbon group or an aromatic heterocyclic group.
R ¹² and R ¹³ are hydrogen atom, halogen atom, alkyl group, aralkyl group, alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, alkylamino group, aralkylamino group, haloalkyl group Represents an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a hydroxyl group, an aryloxy group or a substituent, and may be linked to each other to form a ring. )

  In the general formula (II), bidentate ligands L and L ′ each represent a ligand having the following partial structure.

（環Ａ１及び環Ａ１’は各々独立に、芳香族炭化水素基又は芳香族複素環基を表し、置換基を有していてもよい。環Ａ２及び環Ａ２’は含窒素芳香族複素環基を表し、置換基を有していてもよい。Ｒ’、Ｒ’’及びＲ’’’はそれぞれハロゲン原子；アルキル基；アルケニル基；アルコキシカルボニル基；メトキシ基；アルコキシ基；アリールオキシ基；ジアルキルアミノ基；ジアリールアミノ基；カルバゾリル基；アシル基；ハロアルキル基又はシアノ基を表す。）

(Ring A1 and Ring A1 ′ each independently represents an aromatic hydrocarbon group or an aromatic heterocyclic group, which may have a substituent. Ring A2 and Ring A2 ′ are nitrogen-containing aromatic heterocyclic groups. Each of R ′, R ″ and R ′ ″ represents a halogen atom; an alkyl group; an alkenyl group; an alkoxycarbonyl group; a methoxy group; an alkoxy group; an aryloxy group; (Amino group; diarylamino group; carbazolyl group; acyl group; haloalkyl group or cyano group)

  More preferable examples of the compound represented by the general formula (II) include compounds represented by the following general formulas (Va), (Vb) and (Vc).

（式中、Ｍ⁴は金属、ｎは該金属の価数を表す。環Ａ１は置換基を有していてもよい芳香族炭化水素基を表し、環Ａ２は置換基を有していてもよい含窒素芳香族複素環基を表す。）

(In the formula, M ⁴ represents a metal, and n represents a valence of the metal. Ring A1 represents an aromatic hydrocarbon group which may have a substituent, and ring A2 may have a substituent. Represents a good nitrogen-containing aromatic heterocyclic group.)

（式中、Ｍ⁵は金属、ｎは該金属の価数を表す。環Ａ１は置換基を有していてもよい芳香族炭化水素基又は芳香族複素環基を表し、環Ａ２は置換基を有していてもよい含窒素芳香族複素環基を表す。）

(In the formula, M ⁵ represents a metal, and n represents a valence of the metal. Ring A1 represents an optionally substituted aromatic hydrocarbon group or aromatic heterocyclic group, and ring A2 represents a substituent. Represents a nitrogen-containing aromatic heterocyclic group which may have

（式中、Ｍ⁶は金属、ｎは該金属の価数を表し、ｊは０又は１又は２を表す。環Ａ１及び環Ａ１’は各々独立に、置換基を有していてもよい芳香族炭化水素基又は芳香族複素環基を表し、環Ａ２及び環Ａ２’は各々独立に、置換基を有していてもよい含窒素芳香族複素環基を表す。）

(Wherein M ⁶ represents a metal, n represents a valence of the metal, and j represents 0, 1 or 2. Each of ring A1 and ring A1 ′ is independently an aromatic group optionally having a substituent. Represents an aromatic hydrocarbon group or an aromatic heterocyclic group, and ring A2 and ring A2 ′ each independently represent a nitrogen-containing aromatic heterocyclic group which may have a substituent.)

  The ring A1 and ring A1 ′ of the compounds represented by the general formulas (Va), (Vb), and (Vc) are preferably phenyl group, biphenyl group, naphthyl group, anthryl group, thienyl group, furyl group, benzothienyl. Group, benzofuryl group, pyridyl group, quinolyl group, isoquinolyl group, or carbazolyl group.

  Ring A2 and ring A2 ′ are preferably a pyridyl group, pyrimidyl group, pyrazyl group, triazyl group, benzothiazole group, benzoxazole group, benzimidazole group, quinolyl group, isoquinolyl group, quinoxalyl group, or phenanthridyl group. Can be mentioned.

  Examples of the substituent that the compounds represented by the general formulas (Va), (Vb), and (Vc) may have include a halogen atom such as a fluorine atom; a C 1-6 carbon atom such as a methyl group and an ethyl group An alkyl group; an alkenyl group having 2 to 6 carbon atoms such as a vinyl group; an alkoxycarbonyl group having 2 to 6 carbon atoms such as a methoxycarbonyl group and an ethoxycarbonyl group; an alkoxy group having 1 to 6 carbon atoms such as a methoxy group and an ethoxy group; An aryloxy group such as a phenoxy group and a benzyloxy group; a dialkylamino group such as a dimethylamino group and a diethylamino group; a diarylamino group such as a diphenylamino group; a carbazolyl group; an acyl group such as an acetyl group; A haloalkyl group; a cyano group, and the like, which may be linked to each other to form a ring.

  In addition, the substituent which ring A1 and the substituent which ring A2 has may combine, or the substituent which ring A1 'and the substituent which ring A2' may combine may form one condensed ring, Examples of such a condensed ring include a 7,8-benzoquinoline group.

  More preferably, the substituent for ring A1, ring A1 ′, ring A2 and ring A2 ′ is an alkyl group, an alkoxy group, an aromatic hydrocarbon group, a cyano group, a halogen atom, a haloalkyl group, a diarylamino group, or a carbazolyl group. Can be mentioned.

M ⁴ to M ⁵ in the formulas (Va) and (Vb) are preferably ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum or gold. M ⁷ in the formula (VI) is preferably ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum or gold, and particularly preferably a divalent metal such as platinum or palladium.

  Specific examples of the organometallic complexes represented by the general formulas (II), (Va), (Vb) and (Vc) are shown below, but are not limited to the following compounds.

  Among the organometallic complexes represented by the general formulas (II), (Va), (Vb) and (Vc), a 2-arylpyridine ligand (2- A compound having an arylpyridine, a compound in which an arbitrary substituent is bonded to the arylpyridine, or a compound in which an arbitrary gas is condensed thereto is preferable.

  Specific examples of the organometallic complex represented by the general formula (VI) are shown below, but are not limited to the following compounds.

  The molecular weight of such a phosphorescent dopant material is usually 4000 or less, preferably 3000 or less, more preferably 2000 or less, and usually 200 or more, preferably 300 or more, more preferably 400 or more. If the molecular weight exceeds this upper limit, the sublimation property is significantly reduced, which may cause problems when using an evaporation method when producing an electroluminescent device, or decrease in solubility in an organic solvent, or a synthesis process. With the increase in the impurity components generated in the process, it may be difficult to improve the purity of the material (that is, to remove the deterioration-causing substance), and when the molecular weight is below the lower limit, the glass transition temperature, the melting point, and the vaporization temperature. Etc., the heat resistance may be significantly impaired.

  When two or more of these dopant materials are used, as described above, the oxidation potential of the hole blocking material in the hole blocking layer is higher than that having the highest oxidation potential among the plurality of types of dopant materials. Larger is preferred.

  As a host material used for a light emitting layer that exhibits phosphorescence using such an organometallic complex as a dopant material, in addition to the materials described above as a host material used for a light emitting layer that exhibits fluorescence, Carbazole derivatives such as 4′-N, N′-dicarbazole biphenyl (WO 00/70655), tris (8-hydroxyquinoline) aluminum (USP 6,303,238), 2, 2 ′, 2 ′ '-(1,3,5-benzenetolyl) tris [1-phenyl-1H-benzimidazole] (Appl. Phys. Lett., 78, 1622, 2001), polyvinylcarbazole (Japanese Patent Laid-Open No. 2001-257076) Gazette) and the like. The hole blocking material of the present invention can also be used as a host material.

  The amount of the organometallic complex contained as a dopant material in the light emitting layer is preferably 0.1% by weight or more, and more preferably 30% by weight or less. If the lower limit is not reached, it may not be possible to contribute to improving the luminous efficiency of the device. If the upper limit is exceeded, concentration quenching may occur due to the formation of dimers between organometallic complexes, etc., leading to a decrease in luminous efficiency. There is sex.

  The amount of the dopant material in the light emitting layer exhibiting phosphorescence tends to be preferably slightly larger than the amount of the fluorescent dye contained in the light emitting layer in a conventional device using fluorescence (singlet). Moreover, when a fluorescent pigment | dye is contained in a light emitting layer with a phosphorescent dopant material, 0.05 weight% or more is preferable and 0.1 weight% or more is more preferable. Moreover, 10 weight% or less is preferable and 3 weight% or less is more preferable.

  The thickness of the light emitting layer 5 is usually 3 nm or more, preferably 5 nm or more, and is usually 200 nm or less, preferably 100 nm or less.

  The light emitting layer 5 can also be formed by the same method as the hole transport layer 4.

  A method of doping the above-described fluorescent dye and / or phosphorescent dye (phosphorescent dopant material) as a dopant material into the host material of the light emitting layer will be described below.

  In the case of coating, the light emitting layer host material, the dopant material, and if necessary, additives such as a binder resin that does not serve as an electron trap or light emission quencher, and a coating property improving agent such as a leveling agent were added and dissolved. A coating solution is prepared, applied onto the hole transport layer 4 by a method such as spin coating, and dried to form the light emitting layer 5. Examples of the binder resin include polycarbonate, polyarylate, and polyester. When the amount of the binder resin added is large, the hole / electron mobility is lowered. Therefore, it is desirable that the amount is small, and the content in the light emitting layer is preferably 50 wt% or less.

In the case of the vacuum deposition method, the host material is put in a crucible installed in a vacuum vessel, the dopant material is put in another crucible, and the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa by an appropriate vacuum pump. Thereafter, each crucible is heated and evaporated simultaneously to form a layer on the substrate placed facing the crucible. As another method, a mixture of the above materials in a predetermined ratio may be evaporated using the same crucible.

  When each of the above dopant materials is doped into the light emitting layer 5, it is uniformly doped in the film thickness direction of the light emitting layer, but there may be a concentration distribution in the film thickness direction. For example, it may be doped only in the vicinity of the interface with the hole transport layer 4, or conversely, it may be doped in the vicinity of the interface of the hole blocking layer 6.

The light emitting layer 5 can also be formed by the same method as the hole transport layer 4, but usually a vacuum deposition method is used.
In addition, the light emitting layer 5 may contain components other than the above in the range which does not impair the performance of this invention.

(Hole blocking layer)
In the element shown in FIG. 1, the hole blocking layer 6 is laminated on the light emitting layer 5 so as to be in contact with the cathode side interface of the light emitting layer 5.

  The hole blocking layer 6 serves to block the holes moving from the hole transport layer 4 from reaching the cathode 8 and efficiently transports electrons injected from the cathode 8 toward the light emitting layer 5. Preferably, it is formed from a compound that can be used. In the present invention, the hole blocking material constituting the hole blocking layer 6 is required to satisfy the above molecular weight and the value of Ipa / Ipc, and to have high electron mobility and low hole mobility. The hole blocking layer 6 has a function of confining holes and electrons in the light emitting layer 5 and improving luminous efficiency.

  In particular, a compound having a pyridine ring represented by the above general formula (I) as a hole blocking material has a high excited triplet level (T1), and thus has a high effect of confining excitons in the light emitting layer 5 and emits light. From the viewpoint of efficiency, it is more preferable as a hole blocking material. The compound represented by the general formula (I) may be used alone or in combination of two or more in the hole blocking layer. The hole blocking layer 6 may be used in combination with another known compound having a hole blocking function as long as the performance of the hole blocking material according to the present invention is not impaired.

  The ionization potential of the hole blocking layer 6 used in the present invention is preferably greater than the ionization potential of the light emitting layer 5 by 0.1 eV or more. When the light emitting layer 5 includes a host material and a dopant material, the hole blocking material is preferably 0.1 eV or more larger than the ionization potential of the dopant material, and 0.1 eV or more larger than the ionization potential of the host material, More preferred.

The ionization potential is defined by the energy required to emit electrons at the HOMO (highest occupied molecular orbital) level of the material to the vacuum level. The ionization potential can be defined directly by photoelectron spectroscopy or can be determined by correcting the electrochemically measured oxidation potential relative to the reference electrode. In the case of the latter method, for example, when a saturated sweet potato electrode (SCE) is used as a reference electrode,
Ionization potential = oxidation potential (vs. SCE) + 4.3 eV
Defined by ("Molecular Semiconductors", Springer-Verlag, 1985, page 98).

Furthermore, the electron affinity (EA) of the hole blocking material constituting the hole blocking layer 6 is equal to or greater than the electron affinity of the light emitting layer (the electron affinity of the electron transporting compound among the host materials in the light emitting layer). It is preferable that Similar to the ionization potential, the electron affinity is also defined by the energy at which the electrons in the vacuum level fall to the LUMO (lowest unoccupied molecular orbital) level of the material and stabilize, with the vacuum level as a reference. The electron affinity can be obtained by subtracting the optical band gap from the above-mentioned ionization potential, or similarly obtained from the electrochemical reduction potential by the following formula.
Electron affinity = reduction potential (vs. SCE) +4.3 eV

  The hole blocking layer 6 is formed by laminating on the light emitting layer 5 by a coating method or a vacuum vapor deposition method in the same manner as the hole transport layer 4, but a vacuum vapor deposition method is usually used.

The thickness of the hole blocking layer 6 is usually 5 nm or more, preferably 10 nm or more, and usually 3
00 nm or less, preferably 100 nm or less. In order to uniformly form such a thin film, a vacuum deposition method is generally used.

(cathode)
The cathode 8 serves to inject electrons into the light emitting layer 5 through the hole blocking layer 6. The material used for the cathode 8 can be the material used for the anode 2, but a metal having a low work function is preferable for efficient electron injection, such as tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include low work function alloy electrodes such as magnesium-silver alloy, magnesium-indium alloy, and aluminum-lithium alloy.

The film thickness of the cathode 8 is usually the same as that of the anode 2.
For the purpose of protecting the cathode 8 made of a low work function metal, further laminating a metal layer having a high work function and stable to the atmosphere increases the stability of the device. For this purpose, metals such as aluminum, silver, copper, nickel, chromium, gold, platinum are used.

Furthermore, it is also possible to insert a very thin insulating film (0.1 to 5 nm) such as LiF, MgF ₂ , Li ₂ O at the interface between the cathode 8 and the light emitting layer 5 or the electron transport layer 7 to be described later. It is an effective method to improve (Appl. Phys. Lett., 70, 152, 1997; JP-A-10-74586; IEEE Trans. Electron. Devices, 44, 1245, 1997).

(Electron transport layer)
For the purpose of further improving the luminous efficiency of the device, it is preferable to provide an electron transport layer 7 between the hole blocking layer 6 and the cathode 8 as shown in FIGS. The electron transport layer 7 is formed of a compound that can efficiently transport electrons injected from the cathode 8 between electrodes to which an electric field is applied in the direction of the hole blocking layer 6.

Materials satisfying such conditions include metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Laid-Open No. 59-194393), metal complexes of 10-hydroxybenzo [h] quinoline, oxadiazole derivatives, Styryl biphenyl derivative, silole derivative, 3- or 5-hydroxyflavone metal complex, benzoxazole metal complex, benzothiazole metal complex, trisbenzimidazolylbenzene (US Pat. No. 5,645,948), quinoxaline compound No. 207169), phenanthroline derivatives (Japanese Patent Laid-Open No. 5-331459), 2-t-butyl-9,10-N, N′-dicyanoanthraquinonediimine, n-type hydrogenated amorphous silicon carbide, n-type sulfide Examples include zinc and n-type zinc selenide.

  Further, the electron transport material is doped with an alkali metal (described in Japanese Patent Application Laid-Open No. 10-270171, Japanese Patent Application No. 2000-285656, Japanese Patent Application No. 2000-285657, etc.), thereby improving the electron transport property. Therefore, it is preferable.

  When such an electron transport layer 7 is formed, the electron affinity of the hole blocking layer 6 is preferably equal to or less than the electron affinity of the electron transport layer 7.

In addition, the reduction potential of the light emitting layer material in the light emitting layer 5, the hole blocking material of the hole blocking layer 6 and the electron transport material used for the electron transport layer satisfies the following relationship to adjust the light emitting region and drive This is preferable from the viewpoint of lowering the voltage.
(Reduction potential of electron transport material) ≧ (Reduction potential of hole blocking material) ≧ (Reduction potential of light emitting layer material)
Here, when a plurality of electron transport materials, hole blocking materials, or light emitting layer materials are used, the one having the lowest reduction potential is used for comparison.

  The hole blocking material of the present invention may be used for this electron transport layer 7. In that case, the electron transport layer 7 may be formed using only the hole blocking material of the present invention, or may be used in combination with the various known materials described above.

  When the hole blocking material of the present invention is used for the electron transport layer 7, the hole blocking material of the present invention may be used for the hole blocking layer 6 described above, or the present invention is applied only to the electron transport layer 7. Other known hole blocking materials may be used for the hole blocking layer 6.

  The thickness of the electron transport layer 6 is usually 5 nm or more, preferably 10 nm or more, and is usually 200 nm or less, preferably 100 nm or less.

  The electron transport layer 7 is formed by laminating on the hole blocking layer 6 by a coating method or a vacuum vapor deposition method in the same manner as the hole transport layer 4, but a vacuum vapor deposition method is usually used.

(Anode buffer layer)
For the purpose of further improving the efficiency of hole injection and improving the adhesion of the entire organic layer to the anode 2, an anode buffer layer is provided between the hole transport layer 4 and the anode 2 as shown in FIG. 3 is also inserted. By inserting the anode buffer layer 3, the driving voltage of the initial element is lowered, and at the same time, an increase in voltage when the element is continuously driven with a constant current is suppressed.

  Conditions required for the material used for the anode buffer layer 3 include that the contact with the anode 2 is good, a uniform thin film can be formed, and that the material is thermally stable. The melting point and glass transition temperature are high. Is preferably 300 ° C. or higher, and the glass transition temperature is preferably 100 ° C. or higher. Furthermore, the ionization potential is low, hole injection from the anode 2 is easy, and the hole mobility is high.

  For this purpose, porphyrin derivatives, phthalocyanine compounds (JP-A 63-295695), hydrazone compounds, alkoxy-substituted aromatic diamine derivatives, p- (9-anthryl) have been used as materials for the anode buffer layer 3 so far. ) -N, N'-di-p-tolylaniline, polythienylene vinylene or poly-p-phenylene vinylene, polyaniline (Appl. Phys. Lett., 64, 1245, 1994), polythiophene (Optical Materials, 9 Vol. 125, 1998), organic compounds such as starbust aromatic triamine (JP-A-4-308688), sputtered carbon film (Synth. Met. 91, 73, 1997) Metal oxides such as vanadium oxide, ruthenium oxide, molybdenum oxide (J. Phys. D, 29, 2750, 1996) have been reported.

In addition, a layer containing a hole injection / transporting low molecular organic compound and an electron accepting compound (described in JP-A-11-251067, JP-A-2000-159221, etc.), an aromatic amino group, etc. A layer obtained by doping the contained non-conjugated polymer compound with an electron-accepting compound as necessary (JP-A-11-135262, JP-A-11-283750, JP-A-2)
No. 000-36390, JP-A 2000-150168, JP-A 2001-223084, and WO 97/33193), or a layer containing a conductive polymer such as polythiophene (JP-A 10-92584) However, it is not limited to these.

  As the material of the anode buffer layer 3, it is possible to use either low molecular or high molecular compounds.

Of the low molecular weight compounds, those often used include porphine compounds and phthalocyanine compounds. These compounds may have a central metal or may be metal-free. Preferable examples of these compounds include the following compounds.
Porphin,
5,10,15,20-tetraphenyl-21H, 23H-porphine,
5,10,15,20-tetraphenyl-21H, 23H-porphine cobalt (II),
5,10,15,20-tetraphenyl-21H, 23H-porphine copper (II),
5,10,15,20-tetraphenyl-21H, 23H-porphine zinc (II),
5,10,15,20-tetraphenyl-21H, 23H-porphine vanadium (IV) oxide,
5,10,15,20-tetra (4-pyridyl) -21H, 23H-porphine,
29H, 31H-phthalocyanine,
Copper (II) phthalocyanine,
Zinc (II) phthalocyanine,
Titanium phthalocyanine oxide,
Magnesium phthalocyanine,
Lead phthalocyanine,
Copper (II) 4,4'4 '', 4 '''-tetraaza-29H, 31H-phthalocyanine

  The anode buffer layer 3 can also be formed as a thin film in the same manner as the hole transport layer 4, but in the case of an inorganic material, a sputtering method, an electron beam evaporation method, or a plasma CVD method is further used.

  When the anode buffer layer 3 formed as described above is formed using a low molecular weight compound, the lower limit is usually 3 nm, preferably about 10 nm, and the upper limit is usually 100 nm, preferably about 50 nm. is there.

  When a polymer compound is used as the material of the anode buffer layer 3, for example, the polymer compound or the electron-accepting compound, and if necessary, a coating resin such as a binder resin or a leveling agent that does not trap holes if necessary. A coating solution in which the above additives are added and dissolved is prepared, applied to the anode 2 by a normal coating method such as a spray method, a printing method, a spin coating method, a dip coating method, a die coating method, or an ink jet method, and then dried. By doing so, the anode buffer layer 3 can be formed into a thin film. Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the binder resin is high in the layer, the hole mobility may be lowered. Therefore, it is desirable that the binder resin is low, and the content in the anode buffer layer 3 is preferably 50% by weight or less.

  Alternatively, a thin film may be formed in advance on a medium such as a film, a support substrate, or a roll by the above-described thin film forming method, and the thin film on the medium is thermally or pressure transferred onto the anode 2. it can.

  As described above, the lower limit of the film thickness of the anode buffer layer 3 formed using the polymer compound is usually 5 nm, preferably about 10 nm, and the upper limit is usually about 1000 nm, preferably about 500 nm.

(Layer structure)
The organic electroluminescent device of the present invention has a structure opposite to that shown in FIG. 1, that is, a cathode 8, a hole blocking layer 6, a light emitting layer 5, a hole transport layer 4, and an anode 2 are laminated on the substrate 1 in this order. As described above, the organic electroluminescent element of the present invention can be provided between two substrates, at least one of which is highly transparent. Similarly, the layers can be stacked in the reverse order to the above-described layer configuration shown in FIG. Moreover, in any layer structure of FIGS. 1-3, in the range which does not deviate from the meaning of this invention, it may have arbitrary layers other than the above-mentioned, and the layer which has the function of several said layers together By providing, it is possible to appropriately modify the layer structure, for example.

Alternatively, a top emission structure or a transmission type using a transparent electrode for both the cathode and anode, and a structure in which the layer configuration shown in FIG. 1 is stacked in multiple layers (a structure in which a plurality of light emitting units are stacked) is used. Is also possible. In that case, instead of the interfacial layer (between the light emitting units) (when the anode is ITO and the cathode is Al, the two layers), for example, V ₂ O ₅ is used as the charge generation layer (CGL). This is more preferable from the viewpoint of luminous efficiency and driving voltage.

  The present invention can be applied to any of an organic electroluminescent element having a single element, an element having a structure arranged in an array, and a structure having an anode and a cathode arranged in an XY matrix.

  EXAMPLES Next, although an Example demonstrates this invention further more concretely, this invention is not limited to description of a following example, unless the summary is exceeded.

<Example 1>
As a hole blocking material, 1 × 10 ⁻³ mol / l of the following compound 1 and 0.1 mol / l of tetrabutylammonium perchlorate as a supporting electrolyte were completely dissolved in acetonitrile.

Cyclic voltammetry was measured using BAS GCE as the working electrode, Pt line as the counter electrode, and Ag line as the reference electrode. The sweep rate during this measurement was 100 mV / sec, and the scanning potential region was −2.0 V to 1.4 V. The first reduction potential was determined by using ferrocene / ferrocenium (Fc / Fc ⁺ ) as an internal standard and +0.41 V vs. The potential was converted as SCE. The first oxidation potential was measured in the same manner as the above-mentioned first reduction potential by completely dissolving Compound 1 in 1 × 10 ⁻³ mol / l and tetrabutylammonium perchlorate 0.1 mol / l in dichloromethane as the supporting electrolyte. Converted. Table 1 shows the oxidation-reduction potential of Compound 1 and the value of Ipa / Ipc of the first reduction wave, which were obtained by converting the obtained potential using a saturated sweet potato electrode (SCE) as a reference electrode.

(Production of element)
Using the compound 1, an organic electroluminescent device having the structure shown in FIG. 3 was produced by the following method.

  An indium tin oxide (ITO) transparent conductive film deposited on a glass substrate 1 having a thickness of 150 nm (sputtered film; sheet resistance 15 Ω) is patterned into a 2 mm wide stripe using normal photolithography and hydrochloric acid etching. Thus, an anode 2 was formed. The patterned ITO substrate was cleaned in the order of ultrasonic cleaning with acetone, water with pure water, and ultrasonic cleaning with isopropyl alcohol, then dried with nitrogen blow, and finally subjected to ultraviolet ozone cleaning.

  As a material for the anode buffer layer 3, a non-conjugated polymer compound (PB-1) having an aromatic amino group represented by the following structural formula (weight average molecular weight: 29400, number average molecular weight: 12600) is shown below. Spin coating was carried out under the following conditions together with the active compound (A-1).

Solvent: Ethyl benzoate Coating solution concentration: 2 [wt%]
PB-1: A-1 = 10: 1 (molar ratio)
Spinner speed: 1500 [rpm]
Spinner rotation time: 30 [seconds]
Drying conditions: 100 ° C, 1 hour

  An anode buffer layer 3 made of a uniform thin film having a thickness of 30 nm was formed by the above spin coating.

Next, the substrate on which the anode buffer layer 3 was formed was placed in a vacuum deposition apparatus. After performing rough exhaust of the above apparatus with an oil rotary pump, exhaust using an oil diffusion pump until the degree of vacuum in the apparatus becomes 1.1 × 10 ⁻⁶ Torr (about 1.5 × 10 ⁻⁴ Pa) or less. did. The following arylamine compound (H-1) placed in a ceramic crucible arranged in the above apparatus was heated by a tantalum wire heater around the crucible to perform vapor deposition. At this time, the temperature of the crucible was controlled in the range of 318 to 334 ° C. The degree of vacuum at the time of vapor deposition was 1.1 × 10 ⁻⁶ Torr (about 1.4 × 10 ⁻⁴ Pa), the vapor deposition rate was 0.15 nm / second, and a hole transport layer 4 having a film thickness of 60 nm was obtained.

  Subsequently, the carbazole derivative (E-1) (excited triplet level 2.6 eV) shown below as the host material of the light-emitting layer 5 is used, and the organic iridium complex (D-1) (reduction potential − (1.88 V, oxidation potential 1.29 V, excited triplet level 2.6 eV) were placed in separate ceramic crucibles, and film formation was performed by binary co-evaporation.

The crucible temperature of the compound (E-1) is 200 to 205 ° C., the vapor deposition rate is controlled to 0.11 nm / second, the crucible temperature of the compound (D-1) is controlled to 306 to 309 ° C., and the compound ( The light emitting layer 5 containing 6 wt% of D-1) was laminated on the hole transport layer 4. The degree of vacuum at the time of vapor deposition was 1.0 × 10 ⁻⁶ Torr (about 1.3 × 10 ⁻⁴ Pa).

Further, as the hole blocking layer 6, the above-described compound 1 was laminated at a crucible temperature of 190 to 196 ° C. and a film thickness of 10 nm at a deposition rate of 0.13 nm / second. The degree of vacuum during vapor deposition was 0.7 × 10 ⁻⁶ Torr (about 0.9 × 10 ⁻⁴ Pa).

On the hole blocking layer 6 thus formed, an aluminum 8-hydroxyquinoline complex (ET-1) (reduction potential—1.87 V) shown below was deposited as the electron transport layer 7 in the same manner. At this time, the crucible temperature of the aluminum 8-hydroxyquinoline complex is controlled in the range of 250 to 262 ° C., and the degree of vacuum during the deposition is 0.7 × 10 ⁻⁶ Torr (about 0.9 × 10 ⁻⁴ Pa), The deposition rate was 0.21 nm / second and the film thickness was 35 nm.

Here, the element that has been vapor-deposited up to the electron transport layer 6 is once taken out from the vacuum vapor deposition apparatus to the atmosphere, and a 2 mm wide stripe-shaped shadow mask is used as the cathode stripe mask as a cathode vapor deposition mask. Are in close contact with the element so as to be orthogonal to each other, and are installed in another vacuum deposition apparatus, and the degree of vacuum in the apparatus is 2.7 × 10 ⁻⁶ Torr (about 2.0 × 10 ^{−4) in the same} manner as the organic layer. Pa) was exhausted to below. As the cathode 8, first, lithium fluoride (LiF) was deposited at a deposition rate of 0.01 nm / second and a degree of vacuum of 3.0 × 10 ⁻⁶ Torr (about 4.0 × 10 ⁻⁴ Pa) using a molybdenum boat. A film having a thickness of 0.5 nm was formed on the electron transport layer 7. Next, aluminum was similarly heated by a molybdenum boat, and an aluminum layer having a film thickness of 80 nm at a deposition rate of 0.48 nm / second and a degree of vacuum of 8.5 × 10 ⁻⁶ Torr (about 1.1 × 10 ⁻³ Pa). Thus, the cathode 8 was completed. The substrate temperature at the time of vapor deposition of the above two-layer cathode 8 was kept at room temperature.

  As described above, an organic electroluminescent element having a light emitting area portion having a size of 2 mm × 2 mm was obtained. The maximum wavelength of the emission spectrum of this device was 471 nm, which was identified as that from the organic iridium complex (D-1). The chromaticity was CIE (X, Y) = (0.15, 0.35).

Further, as the driving life, at room temperature, a constant DC current is continuously energized with a constant current emission luminance at the start of energization is 200 cd / m ^2, examine the current time when the light emission luminance becomes 100 cd / m ^2, The results are shown in Table 1.

<Example 2>
The following compound 2 as a hole blocking material is 1 × 10 ⁻³ mol / l and tetrabutylammonium perchlorate 0.1 mol / l as a supporting electrolyte completely in a mixed solvent of acetonitrile and tetrahydrofuran (mixing ratio 1: 1). Dissolved.

  Cyclic voltammetry is measured in the same manner as in Example 1, the sweep speed is 10 V / sec, and the scanning potential region during measurement is -2.3 V to 0.6 V. The oxidation-reduction potential was measured in the same manner as in Example 1 at a sweep rate of 100 mV / sec. Table 1 shows the redox potential of Compound 2 and the Ipa / Ipc value of the first reduction wave.

(Element creation)
In Example 1, the compound 2 was used instead of the compound 1, and the organic iridium complex (D-2) (reduction) shown below instead of the organic iridium complex (D-1) as the light-emitting substance (dopant material) of the light-emitting layer 5 An organic electroluminescence device having a light emitting area portion of 2 mm × 2 mm in the same manner as in Example 1 except that a potential of −2.30 V, an oxidation potential of 0.72 V, and an excited triplet level of 2.3 eV were used. Got.

  The maximum wavelength of the emission spectrum of this device was 510 nm, which was identified as that from the organic iridium complex (D-2). The chromaticity was CIE (x, y) = (0.28, 0.62).

In addition, as a driving life, a constant current with a constant current at which light emission luminance at the start of energization is 2000 cd / m ² at room temperature and a constant current at a constant current value are investigated, and an energization time when the light emission luminance becomes 1000 cd / m ² is investigated. The results are shown in Table 1.

<Example 3>
1 × 10 ⁻³ mol / l of the following compound 3 as a hole blocking material and 0.1 mol / l of tetrabutylammonium perchlorate as a supporting electrolyte were completely dissolved in dimethylformamide.

  Cyclic voltammetry is measured in the same manner as in Example 1, the sweep speed is 100 mV / sec, and the scanning potential region at the time of measurement is −2.0 V to 1.0 V. The oxidation-reduction potential was measured in the same manner as in Example 1 at a sweep rate of 100 mV / sec. Table 1 shows the redox potential of Compound 3 and the value of Ipa / Ipc of the first reduction wave.

(Element creation)
In Example 2, an organic electroluminescence device having a light emitting area portion of 2 mm × 2 mm in size was obtained in the same manner as in Example 2 except that Compound 3 was used instead of Compound 2.

  The maximum wavelength of the emission spectrum of this device was 510 nm, which was identified as that from the organic iridium complex (D-2). The chromaticity was CIE (x, y) = (0.28, 0.62).

  The drive life obtained in the same manner as in Example 2 was as shown in Table 1.

<Example 4>
1 × 10 ⁻³ mol / l of the following compound 4 as a hole blocking material and 0.1 mol / l of tetrabutylammonium perchlorate as a supporting electrolyte were completely dissolved in dimethylformamide.

  Cyclic voltammetry is measured in the same manner as in Example 1, the sweep speed is 100 mV / sec, and the scanning potential region at the time of measurement is −2.0 V to 1.0 V. The oxidation-reduction potential was measured in the same manner as in Example 1 at a sweep rate of 100 mV / sec. Table 1 shows the oxidation-reduction potential of this compound 4 and the value of Ipa / Ipc of the first reduction wave.

(Element creation)
In Example 2, an organic electroluminescence device having a light emitting area portion having a size of 2 mm × 2 mm was obtained in the same manner as in Example 2 except that Compound 4 was used instead of Compound 2.

  The maximum wavelength of the emission spectrum of this device was 512 nm, which was identified as that from the organic iridium complex (D-2). The chromaticity was CIE (x, y) = (0.29, 0.61).

  The drive life obtained in the same manner as in Example 2 was as shown in Table 1.

<Comparative Example 1>
1 × 10 ⁻³ mol / l of the following compound (HB-1) and 0.1 mol / l of tetrabutylammonium perchlorate as a supporting electrolyte were completely dissolved in acetonitrile.

  Cyclic voltammetry is measured in the same manner as in Example 1, the sweep speed is 100 mV / sec, and the scanning potential region at the time of measurement is −1.8 V to 1.6 V. The oxidation-reduction potential was measured in the same manner as in Example 1 at a sweep rate of 100 mV / sec. Table 1 shows the oxidation-reduction potential of this compound (HB-1) and the value of Ipa / Ipc of the first reduction wave.

(Element creation)
In Example 1, except that HB-1 was used in place of Compound 1, an organic electroluminescent device having a light emitting area portion having a size of 2 mm × 2 mm was obtained in the same manner as Example 1.

  The maximum wavelength of the emission spectrum of this device was 471 nm, which was identified as that from the organic iridium complex (D-1). The chromaticity was CIE (x, y) = (0.16, 0.33).

  Further, the drive life obtained in the same manner as in Example 1 was as shown in Table 1.

<Comparative example 2>
1 × 10 ⁻³ mol / l of the following compound (HB-2) and 0.1 mol / l of tetrabutylammonium perchlorate as a supporting electrolyte were completely dissolved in a mixed solvent of acetonitrile and tetrahydrofuran (mixing ratio 1: 1). .

  Cyclic voltammetry is measured in the same manner as in Example 1, the sweep speed is 10 V / sec, and the scanning potential region during measurement is -2.3 V to 1.35 V. The oxidation-reduction potential was measured in the same manner as in Example 1 at a sweep rate of 100 mV / sec. Table 1 shows the oxidation-reduction potential of this compound (HB-2) and the value of Ipa / Ipc of the first reduction wave.

(Element creation)
In Example 2, an organic electroluminescence device having a light emitting area portion of 2 mm × 2 mm in size was obtained in the same manner as in Example 2 except that the compound (HB-2) was used instead of the compound 2. The maximum wavelength of the emission spectrum of this device was 512 nm, which was identified as that from the organic iridium complex (D-2). The chromaticity was CIE (x, y) = (0.30, 0.62).

  The drive life obtained in the same manner as in Example 2 was as shown in Table 1.

  From Table 1, it can be seen that an organic electroluminescence device having a long driving life can be obtained by using a hole blocking material having an Ipa / Ipc value of 0.1 or more.

It is typical sectional drawing which showed an example of the organic electroluminescent element of this invention. It is typical sectional drawing which showed another example of the organic electroluminescent element of this invention. It is typical sectional drawing which showed another example of the organic electroluminescent element of this invention.

Explanation of symbols

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

Claims (7)

A hole blocking material, which is a compound represented by the following general formula (I) and has a molecular weight of 400 or more.

(In General Formula (I), R ^{1 to} R ³ each independently represents an optionally substituted aromatic hydrocarbon group . M is 2 , and Q ¹ represents a substituent. A divalent aromatic hydrocarbon group which may be present and directly bonded to any one of positions 2 to 6 of the pyridine ring, provided that Q ¹ is any of positions 2, 4 and 6 of the pyridine ring; If attached, either R ¹ to R ³ is Q ¹ in its coupled position in. Further, R ¹ to R ³ which contained several double may be different even shall apply the same respectively The position at which the pyridine ring is bonded to Q ¹ may be the same position or different positions.) 2. The hole blocking material according to claim 1, wherein in the general formula (I), R ^{1 to} R ³ are a phenyl group which may have a substituent. The hole blocking material according to claim 1 or 2 , wherein in the general formula (I), Q ¹ is a phenylene group which may have a substituent. In an organic electroluminescent device having a light-emitting layer sandwiched between an anode and a cathode on a substrate and provided with a hole-blocking layer in contact with the cathode-side interface of the light-emitting layer, the hole-blocking layer is claimed. Item 4. An organic electroluminescence device comprising the hole blocking material according to any one of Items 1 to 3 . The organic electroluminescent element according to claim 4 , wherein a first oxidation potential obtained by cyclic voltammetry measurement of the hole blocking material is larger than a first oxidation potential of a light emitting substance used for the light emitting layer. Wherein between the hole blocking layer and the cathode, the organic electroluminescent device according to claim 4 or 5 electron-transporting layer is provided. The organic electroluminescent element according to claim 6 , wherein the reduction potentials of the light emitting layer material used for the light emitting layer, the hole blocking material, and the electron transport material used for the electron transport layer satisfy the following relationship.
(Reduction potential of electron transport material) ≧ (Reduction potential of hole blocking material) ≧ (Reduction potential of light emitting layer material)

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