JP2000003788A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high heat resistance, further improved blue luminescence with excellent color purity and improved stability by using specified compound having hydrogen or an arbitrary substitutional group as a luminescent layer and having a high melting point aromatic ring. SOLUTION: An organic electroluminescent element is formed by holding a luminescent layer and an electron hole transport layer by an anode and a cathode on a substrate. In the luminescent layer, compound having a structure shown by formula I is included. In the formula I, X1, X2 are hydrogen or an arbitrary substitutional group each aromatic ring may be substituted by an arbitrary substitutional group. As compound shown by the formula I, for example it is preferable that a compound shown by formula II is used. In the formula II, X1, X2 represent alkyl groups, aromatic hydrocarbon ring groups and aromatic heterocyclic ring groups, each of which independently may have hydrogen atoms and a substitutional group. R1 to R8 represent hydrogen atoms, halogen atoms, alkyl groups and alkenyl groups. It is preferably that a hole inhibiting layer made of metallic complex styryl compound be provided between this luminescent layer and the cathode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to a thin film device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn, which is a group II-VI compound semiconductor of an inorganic material, is used.
In general, S, CaS, SrS, and the like are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, or the like) which is a luminescence center. However, EL devices manufactured from the above inorganic materials include: 1) AC drive is required (50-1000 Hz), 2) High drive voltage (up to 200 V), 3) Full color is difficult (especially blue), 4) Peripheral drive circuit is expensive. I have.

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has been started. In particular, in order to enhance the luminous efficiency, the type of the electrode was optimized for the purpose of improving the efficiency of carrier injection from the electrode, and a hole transport layer composed of an aromatic diamine and a luminescent layer composed of an aluminum complex of 8-hydroxyquinoline were used. Of an organic electroluminescent device provided with an electrode (Appl. Phys. Lett., 51
Vol., Pp. 913, 1987), the luminous efficiency has been greatly improved as compared with a conventional EL device using a single crystal such as anthracene. For example, doping a fluorescent dye for laser such as coumarin using an aluminum complex of 8-hydroxyquinoline as a host material (J. Appl. Phy.
s., 65, p. 3610, 1989), the improvement of luminous efficiency, conversion of luminous wavelength, and the like are also performed. In addition to the electroluminescent device using a low molecular material as described above, poly (p-phenylenevinylene) and poly [2-methoxy-5- (2-
Development of electroluminescent devices using polymer materials such as [ethylhexyloxy) -1,4-phenylenevinylene] and poly (3-alkylthiophene), and light-emitting materials and electron-transfer materials of polymers such as polyvinylcarbazole with low molecular weight The development of the element which mixed is.

[0004]

In order to apply an organic electroluminescent device to a display device such as a flat panel display, it is necessary to ensure sufficient reliability of the device. However, the heat resistance of the conventional organic electroluminescent device is insufficient, and the current-voltage characteristic shifts to a higher voltage side due to an increase in the ambient temperature or process temperature of the device, or local Joule heat generated when the device is driven. Deterioration such as shortening of service life and generation and increase of non-light emitting portions (dark spots) was inevitable. As for the blue light emitting element, 8-
At present, the stability of the device is further inferior to that of a green light-emitting device using an aluminum complex of hydroxyquinoline.

The main cause of the above-mentioned element deterioration is deterioration of the thin film shape of the organic layer. This deterioration of the thin film shape is caused by crystallization (or aggregation) of the organic amorphous thin film due to heat generated during driving of the element.
It is thought to be caused by such factors. This low heat resistance is considered to be due to the low glass transition temperature (hereinafter abbreviated as Tg) of the material. Tg generally has a linear correlation with the melting point. Further, with respect to the blue light-emitting element, many compounds used in the light-emitting layer have a small molecular weight and a low melting point and a low Tg due to the restriction that the pi electron conjugation cannot be expanded. At present, it is not sufficiently stable chemically.

[0006] Compounds that have been used in blue organic electroluminescent devices so far include anthracene, tetraphenylbutadiene, pentaphenylcyclopentadiene, distyrylbenzene derivative, oxadiazole derivative, azomethine zinc complex, benzazole metal complex (particularly). Kaihei 8-8
No. 1472), mixed ligand type aluminum complex (J.SID,
5, p. 11, 1997), N, N'-diphenyl-N, N '-(3-
Methylphenyl) -1,1'-biphenyl-4,4'-diamine, polyvinylcarbazole, 1,2,4-triazole derivative, aminopyrene dimer, distyrylbiphenyl derivative (App
l. Phys. Lett., vol. 67, p. 3853, 1995), silole derivatives and the like. Among the above blue light-emitting materials, representative compounds whose device characteristics are well studied are shown below:

[0007]

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[0008]

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[0009]

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Distyrylbiphenyl derivative (B-1)
Has a strong fluorescence intensity and does not form an exciplex even when used in a device, and has been reported to emit blue light (Appl.
Phys. Lett., Vol. 67, p. 3853, 1995), the ionization potential in a thin film state is as high as 5.9 eV, it is difficult for holes to be injected from the hole transport layer, and in the EL spectrum, the emission maximum is around 480 nm. And has a problem that the blue color purity is not good. This color purity is not improved by doping. Bis (2-methyl-8-
The quinolinolato) (p-phenylphenolato) aluminum complex (B-2) also has insufficient blue color purity, and although the color purity is improved by doping with perylene, the driving stability is reduced to a practical level. Not reached (JP-A-5-1983)
No. 77 gazette). N, N'-diphenyl- which is an aromatic diamine
N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (usually referred to as TPD) (B-3), when combined with a triazole derivative as a hole blocking layer Four
An EL spectrum having an emission peak at 64 nm is shown (Jp
n. J. Appl. Phys., 32, L917, 1993), TPD
Has a thermal instability such as crystallization because its Tg is as low as 63 ° C.

For the reasons described above, the organic electroluminescent device has a serious problem in terms of the heat resistance of the device and the color purity of blue light emission for practical use. The fact that the heat resistance and driving characteristics of the organic electroluminescent device are unstable and the blue purity is not improved is the reason that flat panels and
This is an undesirable characteristic for a display element such as a display. In view of the above situation, the present inventor has a high heat resistance, furthermore, as a result of intensive study for the purpose of providing an organic electroluminescent element that emits blue light with good color purity, as a result specific to the organic electroluminescent element It has been found that the above problems can be solved by using a compound, and the present invention has been completed.

[0012]

That is, the gist of the present invention is that of the general formula (I)

[0013]

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(X ₁ and X ₂ are hydrogen or an optional substituent, and each aromatic ring may be substituted with an optional substituent.) The feature resides in an organic electroluminescent device. Hereinafter, the organic electroluminescent device of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing an example of the structure of a general organic electroluminescent element used in the present invention.
2 represents an anode, 4 represents a hole transport layer, 5 represents a light emitting layer, 7 represents an electron transport layer, and 8 represents a cathode.

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

An anode 2 is provided on a substrate 1, and the anode 2 plays a role of injecting holes into a hole transport layer. This anode is usually made of a metal such as aluminum, gold, silver, nickel, palladium, and platinum; a metal oxide such as an oxide of indium and / or tin; a metal halide such as copper iodide; carbon black; (3-methylthiophene), conductive polymers such as polypyrrole and polyaniline. Usually, the formation of the anode 2 is often performed by a sputtering method, a vacuum evaporation method, or the like. In the case of fine metal particles such as silver, fine particles such as copper iodide, carbon black, conductive metal oxide fine particles, or conductive polymer fine powder, they are dispersed in a suitable binder resin solution and To form the anode 2. Further, in the case of a conductive polymer, a thin film can be formed directly on the substrate 1 by electrolytic polymerization, or the conductive polymer can be applied on the substrate 1 to form the anode 2 (Appl. Phys. Lett. 60, 2711,
1992). The anode 2 can be formed by laminating different materials. The thickness of the anode 2 depends on the required transparency. When transparency is required, the transmittance of visible light is usually 60% or more, preferably 80% or more. In this case, the thickness is usually 5 to 1000 nm, preferably 10 to 10 nm. It is about 500 nm. If opaque, the anode 2 may be the same as the substrate 1. Further, it is also possible to laminate a different conductive material on the anode 2.

On the anode 2, a hole transport layer 4 is provided. As a condition required for the material of the hole transport layer, it is necessary that the material has a high hole injection efficiency from the anode and can efficiently transport the injected holes. For that purpose, the ionization potential is small, the transparency to visible light is high, the hole mobility is large, the stability is high, and impurities serving as traps are unlikely to be generated during production or use. Required. In addition to the above general requirements, when considering applications for in-vehicle display, the element is required to have further heat resistance. Therefore, Tg is 85
A material having a value of at least C is desirable.

Examples of the material for such a hole transport layer include 1,1-bis (4-di-p-tolylaminophenyl) cyclohexane and 4,4′-bis [N- (1-naphthyl)- Aromatic amines containing two or more tertiary amines represented by [N-phenylamino] biphenyl and having two or more condensed aromatic rings substituted by nitrogen atoms (JP-A-5-234681); An aromatic triamine having a starburst structure as a derivative (US Pat. No. 4,923,774), N, N′-diphenyl-N, N′-bis (3-methylphenyl) biphenyl-4,
Compounds in which a pyrenyl group is substituted with a plurality of aromatic diamino groups, such as 4'-diamine, aromatic diamines having a styryl structure (JP-A-4-290851), and aromatic tertiary amine units linked by a thiophene group (JP-A-4-304466)
JP-A-5-239455), a starburst type aromatic triamine (JP-A-4-308688), a tertiary amine linked by a fluorene group (JP-A-5-25473), and a triamine compound (JP-A-5-239455) ), Bisdipyridylaminobiphenyl, N, N, N-triphenylamine derivatives (JP-A-6-1972), aromatic diamines having a phenoxazine structure (JP-A-7-138562), diaminophenylphenanthridine Derivatives (JP-A-7-252474), silazane compounds (US Pat. No. 4,950,950), silanamine derivatives (JP-A-6-49079),
And phosphamine derivatives (JP-A-6-25659). These compounds may be used alone,
If necessary, they may be mixed and used.

In addition to the above compounds, materials for the hole transport layer 4 include polyvinyl carbazole, polysilane, polyphosphazene (JP-A-5-310949), polyamide (JP-A-5-310949), and polyvinyl triphenyl. Polymer materials such as amines (JP-A-7-53953), polymers having a triphenylamine skeleton (JP-A-4-1303065), and polymethacrylates containing aromatic amines are exemplified.

The hole transport layer 4 is formed by laminating the above hole transport material on the anode 2 by a coating method or a vacuum evaporation method. In the case of the coating method, one hole transport material is used.
A seed or two or more, and if necessary, an additive such as a binder resin or a coatability improver that does not trap holes are added and dissolved to prepare a coating solution, and the solution is formed on the anode 2 by a method such as spin coating. To the hole transport layer 3b
To form Examples of the binder resin include polycarbonate, polyarylate, and polyester. If the amount of the binder resin is large, the hole mobility is reduced, so that a small amount is desirable, and usually 50% by weight or less is preferable.

In the case of the vacuum evaporation method, the hole transporting material is put into a crucible installed in a vacuum vessel, and the inside of the vacuum vessel is evacuated to about 10 ^-4 Pa by a suitable vacuum pump, and then the crucible is heated. Then, the hole transport material is evaporated, and the hole transport layer 4 is formed on the substrate 1 on which the anode is formed, which is placed facing the crucible.
Is formed. The thickness of the hole transport layer 4 is usually 10 to 300 n
m, preferably 30-100 nm. In order to uniformly form such a thin film, generally, a vacuum deposition method is often used. The light emitting layer 5 is formed on the hole transport layer 4.

The organic electroluminescent device of the present invention is characterized in that the light emitting layer contains a compound having a structure represented by the general formula (I). In the present invention, by using a compound having a high melting point for the light-emitting layer, the heat resistance of the device is improved and blue light emission is enabled. The compound having the structure represented by the general formula (I) enables strong fluorescence in the blue region by suppressing the spread of the pi-electron conjugated system, and at the same time, forms a dimer by introducing a rigid planar structure. Quenching due to concentration, and furthermore, it is possible to produce a stable light-emitting element having a high melting point and thus a high Tg and having a stable and high blue purity.

Among the compounds having the structure represented by the above general formula (I), in particular, the following general formula (II)

[0024]

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The compound represented by the following formula is preferred. General formula (I
In I), X ¹ and X ² are preferably each independently a hydrogen atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group or an ethyl group which may have a substituent; Optionally substituted phenyl group, biphenyl group, naphthyl group, anthryl group, phenanthryl group, pyrenyl group, etc. aromatic hydrocarbon ring group; optionally substituted pyridyl group, triazyl group, pyrazyl group, And an aromatic heterocyclic group such as a quinoxalyl group and a thienyl group. Examples of the substituent include a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group;
C1-C6 alkoxycarbonyl groups such as methoxycarbonyl group and ethoxycarbonyl group; C1-C6 alkoxy groups such as methoxy group and ethoxy group; aryloxy groups such as phenoxy group and benzyloxy group; dimethylamino group , A dialkylamino group such as a diethylamino group, an acyl group such as an acetyl group, a haloalkyl group such as a trifluoromethyl group, and a cyano group. Particularly preferred examples of the substituent include a methyl group, a phenyl group and a methoxy group.

In the general formula (I), R ^{1 to} R
⁸ is preferably each independently a hydrogen atom; a halogen atom such as a fluorine atom;
6 alkyl groups; cyclohexyl groups; aralkyl groups such as benzyl group and phenethyl group; alkenyl groups such as vinyl group; alkoxycarbonyl groups having 1 to 6 carbon atoms such as methoxycarbonyl group and ethoxycarbonyl group;
An alkoxy group having 1 to 6 carbon atoms such as an ethoxy group; an aryloxy group such as a phenoxy group and a benzyloxy group; a dimethylamino group; a dialkylamino group such as a diethylamino group; an acyl group such as an acetyl group; Haloalkyl group; cyano group; aromatic hydrocarbon ring group such as phenyl group, biphenyl group, naphthyl group, anthryl group, phenanthryl group, pyrenyl group; carbazolyl group, pyridyl group, triazyl group, pyrazyl group, quinoxalyl group, thienyl group, etc. Represents an aromatic heterocyclic group. Any of these may be further substituted. Among them, even if the aromatic hydrocarbon group and the aromatic heterocyclic group have a substituent, a compound having good characteristics can be obtained.

The substituent includes a halogen atom such as a fluorine atom; an alkyl group having 1 to 6 carbon atoms such as a methyl group and an ethyl group; an alkenyl group such as a vinyl group; and a carbon atom such as a methoxycarbonyl group and an ethoxycarbonyl group. 6 to 6 alkoxycarbonyl groups; a methoxy group, an ethoxy group, etc., having 1 carbon atom
Aryloxy groups such as phenoxy group and benzyloxy group; dialkylamino groups such as dimethylamino group and diethylamino group; acyl groups such as acetyl group; haloalkyl groups such as trifluoromethyl group; and cyano group. . Particularly preferred examples of the substituent include a methyl group, a phenyl group and a methoxy group. Note that R
¹ and R ² , R ³ and R ⁴ , R ⁵ and R ⁶ or R ⁷ and R
⁸ may be taken together to form a ring.
In this case, the formed ring preferably includes a naphthalene ring and an anthracene ring. The compound having the structure represented by the general formula (I) is, for example, a compound represented by the following general formula (II)

[0028]

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The product was prepared using the method described in J. Org. Chem., 55, 4190 (1990).
Year), and then the Anales de C
A compound having a structure represented by the general formula (I) is obtained by a photooxidation reaction shown in himie, 4, 365-426, 1959. Preferred specific examples of the compound having the structure represented by the general formula (I) are shown below, but are not limited thereto.

[0030]

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[0031]

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[0032]

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These compounds may be used alone or, if necessary, may be used as a mixture. The thickness of the light emitting layer 5 is usually 10 to 200 nm, preferably 30 to 100 nm.
nm. The light emitting layer 5 is formed by laminating on the hole transport layer 4 by a coating method or a vacuum evaporation method in the same manner as the hole transport layer 4. It is necessary to use a solvent that does not dissolve the hole transport layer. Doping a fluorescent dye with the light emitting layer material as a host material is an effective method for improving the luminous efficiency of blue light, improving the color purity, and further improving the driving life of the device. As doped dyes having blue fluorescence, condensed polycyclic aromatic rings such as perylene (JP-A-5-198377), coumarin derivatives, naphthalimide derivatives (JP-A-4-320486), and aromatic amine derivatives ( JP-A-8-199162).
The proportion of these doped dyes contained in the host material is
Preferably it is in the range of 0.1 to 10% by weight. Of course, in order to obtain green or red light emission, it is also possible to dope a green fluorescent dye or a red fluorescent dye. As a method of performing the above-mentioned doping by a vacuum evaporation method, there are a method of co-evaporation and a method of previously mixing an evaporation source at a predetermined concentration.

When the above dopants are doped in the light emitting layer, they are uniformly doped in the thickness direction of the light emitting layer, but may have a concentration distribution in the film thickness direction. For example, doping may be performed only near the interface with the hole transport layer, or conversely, may be doped near the interface with the electron transport layer. Light emitting layer 5
The electron transport layer 7 is provided on the substrate. The electron transport layer 7
It is formed of a compound capable of efficiently transporting electrons injected from the cathode between the electrodes to which an electric field is applied in the direction of the light emitting layer 5 and efficiently performing recombination with holes. The electron transporting compound used in the electron transporting layer 7 is preferably a compound having high electron injection efficiency from the cathode 8 and having high electron mobility and capable of efficiently transporting injected electrons. is necessary.

Materials satisfying such conditions include 8
Metal complexes such as aluminum complexes of -hydroxyquinoline (JP-A-59-194393), 10-hydroxybenzo
[h] quinoline metal complex, oxadiazole derivative, distyrylbiphenyl derivative, silole derivative, 3- or
5-hydroxyflavone metal complex, benzoxazole metal complex, benzothiazole metal complex, trisbenzimidazolylbenzene (US Pat. No. 5,645,948), quinoxaline compound (JP-A-6-207169), phenanthroline derivative (JP-A-5-331459) Gazette), 2-t-butyl
-9,10-N, N′-dicyanoanthraquinone diimine, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide and the like. The thickness of the electron transport layer 6 is usually
It is 5 to 200 nm, preferably 10 to 100 nm.

The electron transporting layer 7 is laminated on the light emitting layer 5 by a coating method or a vacuum evaporation method in the same manner as the hole transporting layer 4, but usually, a vacuum evaporation method is used. The cathode 8 is
It serves to inject electrons into the electron transport layer 7. As the material used for the cathode 8, the material used for the anode 2 can be used, but for efficient electron injection, a metal having a low work function is preferable, and tin, magnesium, indium, calcium, A suitable metal such as aluminum or silver or an alloy thereof is used. Specific examples include a low work function alloy electrode such as a magnesium-silver alloy, a magnesium-indium alloy, and an aluminum-lithium alloy. Further, an ultra-thin insulating film such as LiF, MgF ₂ , or Li ₂ O (0.
Insertion of 1 to 5 nm) is also an effective method for improving the efficiency of the device (Appl. Phys. Lett., Vol. 70, 152).
Page, 1997; JP-A-10-74586; IEEE Trans. El.
ectron. Devices, 44, 1245, 1997). The thickness of the cathode 8 is usually the same as that of the anode 2. In order to protect the cathode made of a low work function metal, further laminating a metal layer having a high work function and being stable to the atmosphere increases the stability of the device. For this purpose, aluminum,
Metals such as silver, copper, nickel, chromium, gold, and platinum are used.

In the present invention, in order to further increase the luminous efficiency and color purity of a device provided with a luminescent layer containing a compound having a structure represented by the general formula (I), as shown in FIG.
It is very effective to provide the hole blocking layer 6 between the electron transport layer 7 and the light emitting layer 5. The hole blocking layer 6 has a role of preventing holes moving from the hole transport layer from reaching the cathode, and a compound capable of efficiently transporting electrons injected from the cathode toward the light emitting layer. Formed. The physical properties required for the material constituting the hole blocking layer are that the electron mobility is high and the hole mobility is low, and in order to efficiently confine holes in the light emitting layer, the ionization potential of the light emitting layer is It is preferable to have a large value of the ionization potential or an optical band gap larger than the optical band gap of the light emitting layer. The hole blocking layer has a function of confining holes and electrons in the light emitting layer and improving luminous efficiency. As a hole blocking layer material satisfying such conditions, a mixed ligand complex represented by the following general formula (IV):

[0038]

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(Wherein R ^{9 to} R ¹⁴ represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group , An alkylsulfonyl group, an α-haloalkyl group, a hydroxyl group, an amide group which may have a substituent, an aromatic hydrocarbon ring group which may have a substituent or an aromatic which may have a substituent Represents a group heterocyclic group, M represents an Al atom or a Ga atom, and L is represented by any of the following general formulas (IVa), (IVb) and (IVc))

[0040]

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(Wherein, Y represents any atom of Si, Ge, and Sn, and Ar ^{1 to} Ar ⁵ represent an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent. A binuclear metal complex represented by the following general formula (V):

[0042]

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(Wherein R ^{9 to} R ¹⁴ represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group An alkylsulfonyl group, an α-haloalkyl group, a hydroxyl group, an amide group which may have a substituent, an aromatic hydrocarbon ring group which may have a substituent or an aromatic heterocyclic group, wherein M is An Al atom or a Ga atom.) A styryl compound represented by the following general formula (VI):

[0044]

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(Wherein Z is an optionally substituted 2
Represents a divalent aromatic hydrocarbon ring group or an aromatic heterocyclic group,
Ar ^{6 to} Ar ⁹ represent an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent. A) a compound having at least one 1,2,4-triazole ring represented by the following structural formula:

[0046]

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Examples include compounds having at least one phenanthroline ring represented by the following structural formula.

[0048]

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As a specific example of the mixed ligand complex represented by the general formula (IV), bis (2-methyl-8-quinolinolato)
(Phenolato) aluminum, bis (2-methyl-8-quinolinolato) (ortho-cresolato) aluminum, bis (2-methyl-8-quinolinolato) (meta-cresolato) aluminum, bis (2-methyl-8-quinolinolato) ( Para-cresolato) aluminum, bis (2-methyl-8-quinolinolato) (ortho-phenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (meta-phenylphenolato) aluminum, bis (2-methyl-) 8-quinolinolato) (para-phenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,3-dimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,6-dimethyl Phenolato) aluminum, bis (2-methyl-8-quinolinolato) (3,4-dimethylphenolato) aluminum, bis (2-methyl-8-quino) Norat) (3,5-dimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (3,5-di-tert-butylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2 , 6-Diphenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,4,6-triphenylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,4,6- Trimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,3,6-trimethylphenolato) aluminum, bis (2-methyl-8-quinolinolato) (2,3,5,6-tetramethyl Phenolato) aluminum, bis (2-methyl-8-quinolinolato) (1-naphthrat) aluminum, bis (2-methyl-8-quinolinolato) (2-naphthrat) aluminum, bis (2-methyl-8)
-Quinolinolato) (triphenylsilanolato) aluminum, bis (2-methyl-8-quinolinolato) (triphenylgermanolato) aluminum, bis (2-methyl-8-quinolinolato) (tris (4,4-biphenyl) silanolato )
Aluminum, bis (2,4-dimethyl-8-quinolinolato)
(Ortho-phenylphenolato) aluminum, bis (2,4-dimethyl-8-quinolinolato) (para-phenylphenolato) aluminum, bis (2,4-dimethyl-8-quinolinolato) (meta-phenylphenolato) aluminum , Bis (2,4-dimethyl-8-quinolinolato) (3,5-dimethylphenolato) aluminum, bis (2,4-dimethyl-8
-Quinolinolato) (3,5-di-tert-butylphenolato) aluminum, bis (2-methyl-4-ethyl-8-quinolinolato) (para-cresolato) aluminum, bis (2-methyl-4-methoxy-8) -Quinolinolato) (para-phenylphenolato) aluminum, bis (2-methyl-5-cyano-8)
-Quinolinolato) (ortho-cresolato) aluminum, bis (2-methyl-6-trifluoromethyl-8-quinolinolato) (2-naphthrat) aluminum, bis (2-methyl-8-quinolinolato) (phenolato) gallium, bis ( 2-methyl-8-quinolinolato) (ortho-cresolate)
Gallium, bis (2-methyl-8-quinolinolato) (para-
Phenylphenolatogallium, bis (2-methyl-8-quinolinolato) (1-naphthrat) gallium, bis (2-methyl)
-8-quinolinolato) (2-naphthrat) gallium, bis (2-methyl-8-quinolinolato) (triphenylsilanolato) gallium, bis (2-methyl-8-quinolinolato) (tris (4,4-biphenyl) silanolate Gallium). Particularly preferably, bis (2-methyl-8-quinolinolato) (2-naphthrat) aluminum, bis (2-methyl
-8-quinolinolato) (triphenylsilanolato) aluminum.

Specific examples of the binuclear metal complex represented by the general formula (V) include bis (2-methyl-8-quinolato) aluminum-μ-oxo-bis- (2-methyl-8-quinolinolato) aluminum. Bis (2,4-dimethyl-8-quinolato)
Aluminum-μ-oxo-bis- (2,4-dimethyl-8-
Quinolilat) aluminum, bis (4-ethyl-2-methyl)
-8-quinolinolato) aluminum-μ-oxo-bis-
(4-ethyl-2-methyl-8-quinolinolato) aluminum, bis (2-methyl-4-methoxyquinolinolato) aluminum-μ-oxo-bis- (2-methyl-4-methoxyquinolinolato) aluminum, Bis (5-cyano-2-methyl
-8-quinolinolato) aluminum-μ-oxo-bis-
(5-cyano-2-methyl-8-quinolinolato) aluminum, bis (5-chloro-2-methyl-8-quinolinolato) aluminum-μ-oxo-bis- (5-chloro-2-methyl-8)
-Quinolinolato) aluminum, bis (2-methyl-5-trifluoromethyl-8-quinolinolato) aluminum-μ
-Oxo-bis- (2-methyl-5-trifluoromethyl-8
-Quinolinolato) aluminum and the like. Particularly preferred is bis (2-methyl-8-quinolato) aluminum
-μ-oxo-bis- (2-methyl-8-quinolylato) aluminum. Specific examples of the styryl compound represented by the general formula (VI) include a distyrylbiphenyl compound (B-1) exemplified as a conventional blue light-emitting material. Specific examples of the compound having at least one 1,2,4-triazole ring represented by the above structural formula are shown below.

[0051]

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Specific examples of the compound having at least one phenanthroline ring represented by the above structural formula are shown below.

[0053]

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The thickness of the hole blocking layer 6 is usually 0.3 to 100
nm, preferably 0.5 to 10 nm. The hole blocking layer can be formed in the same manner as the hole transporting layer, but usually, a vacuum evaporation method is used. It is conceivable to provide an anode buffer layer 3 to improve the contact between the anode 2 and the hole transport layer 4 as shown in FIG. 3 in order to reduce the drive voltage of the device and improve the drive stability. . The conditions required for the material used for the anode buffer layer are that a uniform thin film can be formed with good contact with the anode and thermally stable, that is, the melting point and the glass transition temperature are high.
300 ° C or higher and glass transition temperature of 100 ° C or higher are required. In addition, the ionization potential is low, holes can be easily injected from the anode, and the hole mobility is high. For this purpose, porphyrin derivatives and phthalocyanine compounds (JP-A-63-295695) and star-bust-type aromatic triamines (JP-A-4-3069) have been used.
No. 8688), a hydrazone compound, an alkoxy-substituted aromatic diamine derivative, p- (9-anthryl) -N, N-di-p-
Tolylaniline, polythienylenevinylene and poly-p-
Organic compounds such as phenylene vinylene and polyaniline,
Sputtered carbon films and metal oxides such as vanadium oxide, ruthenium oxide and molybdenum oxide have been reported. Examples of the compound often used as the material of the anode buffer layer include a porphyrin compound and a phthalocyanine compound. These compounds may have a central metal or may be non-metallic.

Specific examples of preferred such compounds include the following compounds: porphine 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 Thin films can be formed, but in the case of inorganic materials, Jitter method or an electron beam deposition method, a plasma CVD method is used.

The thickness of the anode buffer layer 3 formed as described above is usually 3 to 100 nm, preferably 10 to 50 nm. It is to be noted that the structure opposite to that of FIG. 1, that is, the cathode 8, the electron transporting layer 7, the light emitting layer 5, the hole transporting layer 4, and the anode 2 can be laminated on the substrate in this order. It is also possible to provide the organic electroluminescent device of the present invention between two substrates, at least one of which is highly transparent. Similarly, FIG.
And it is also possible to laminate | stack in the structure opposite to the said each layer structure shown in FIG. According to the organic electroluminescent device of the present invention, since a compound having a specific skeleton having a high melting point is used for the light emitting layer or the hole blocking layer, the heat resistance of the device is improved, and blue light emission with good color purity is obtained. It is possible not only to function as a full-color or multi-color blue sub-pixel, but also to produce a full-color display element by combining with a fluorescent conversion dye (Japanese Patent Laid-Open No. 3-152897).

[0057]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist. Synthesis Example 1 Synthesis of Compound (3) 0.51 g of rubrene was dissolved in 25 ml of DMF by heating at 120 ° C., and a DMF solution of 0.2 g of N-bromosuccinimide was added dropwise, followed by heating and stirring at 120 ° C. for 8 hours. After completion of the reaction, the reaction solution was allowed to cool, and the resulting white precipitate was washed with methanol, dried, and purified by sublimation to obtain 0.27 g of a white powder (yield: 54%).
This compound was subjected to mass spectrometry. As a result, the compound was found to have a molecular weight of 530 and to be the target compound by NMR spectrum. The powder sample of the compound (3) was subjected to differential thermal analysis measurement using TG / DTA-320 manufactured by Seiko Instruments Inc., and as a result, the melting point was as high as 432 ° C.

Reference Example 1 A glass substrate was ultrasonically washed with acetone, washed with pure water, ultrasonically washed with isopropyl alcohol, dried with dry nitrogen, and dried.
After performing the V / ozone cleaning, the apparatus was set in a vacuum evaporation apparatus, and evacuated using an oil diffusion pump until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less. Exemplified compound (3) was placed in a ceramic crucible, and heated by a tantalum wire heater around the crucible to perform vapor deposition. The temperature of the crucible at this time is 29
Control was performed in the range of 0 to 300 ° C. Vacuum degree during evaporation is 7 × 10
^-7 Torr (approximately 9.3 x 10 ^-5 Pa) at a deposition rate of 0.3 nm / sec.
A 3 nm uniform and transparent film was obtained. The ionization potential of this thin film sample was measured using an ultraviolet electron analyzer (AC-1) manufactured by Riken Keiki Co., Ltd., and showed a value of 5.32 eV. The maximum of the fluorescence wavelength measured by exciting this vapor-deposited film with a mercury lamp (wavelength 350 nm) was 430 nm, which was blue-violet fluorescence.

Example 1 An organic electroluminescent device having the structure shown in FIG. 2 was manufactured by the following method. A transparent conductive film of indium tin oxide (ITO) deposited on a glass substrate with a thickness of 120 nm (Geomatec Co., Ltd .; electron beam filmed product; sheet resistance of 15Ω) was fabricated using ordinary photolithography and hydrochloric acid etching.
An anode was formed by patterning into a stripe having a width of mm.
The patterned ITO substrate is cleaned in the order of ultrasonic cleaning with acetone, water cleaning with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally cleaned with ultraviolet and ozone, and placed in a vacuum evaporation apparatus. installed. After performing rough exhaust of the above device by an oil rotary pump,
Evacuation was performed using an oil diffusion pump equipped with a liquid nitrogen trap until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) or less. As a material of the hole transport layer 4, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (H-1) of the following structural formula was put in a ceramic crucible,
Crucible

[0060]

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Deposition by heating with a surrounding tantalum wire heater
Was done. The temperature of the crucible at this time is in the range of 255 to 270 ° C.
Controlled by the box. The degree of vacuum during evaporation is 1.5 × 10^-6Torr (about 2.
0x10 ^-FourPa) at a deposition rate of 0.4 nm / sec and a hole thickness of 60 nm
Transport layer 4 was obtained. Next, the material of the light emitting layer 5 is exemplified.
The compound (3) is deposited on the hole transport layer 4 in the same manner.
Done. The temperature of the crucible at this time is in the range of 290 to 295 ° C.
Controlled by The degree of vacuum during evaporation is 1.1 × 10^-6Torr (about 1.5
× 10^-FourPa), a deposition rate of 0.3 nm / sec, and a film thickness of 30 nm.
Was. Next, as a material of the hole blocking layer 6, the following structural formula
(2-methyl-8-quinolinolato) (trif
Enyl silanolato) aluminum complex (HB-1)

[0062]

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The evaporation was performed on the light emitting layer 5. The temperature of the crucible when forming the hole blocking layer was 245 ° C, and the degree of vacuum was 1.1 ×
At 10 ⁻⁶ Torr (about 1.5 × 10 ⁻⁴ Pa), the deposition rate was 0.2 nm / sec, and the film thickness was 20 nm. E Subsequently, as a material of the electron transport layer 7, an 8-hydroxyquinoline complex of aluminum (E-1) shown below was vapor-deposited on the hole blocking layer in the same manner.

[0064]

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At this time, the temperature of the crucible was controlled in the range of 270 to 280 ° C. The degree of vacuum during vapor deposition is 9.0 × 10 ^-7 Torr (about 1.2
x10 ^-4 Pa), the deposition rate was 0.3 nm / sec, and the film thickness was 25 nm. The substrate temperature during vacuum deposition of the electron transport layer 7 from the hole transport layer 4 was kept at room temperature. Here, the element on which the electron transport layer 7 was deposited was once taken out of the vacuum deposition apparatus into the atmosphere, and used as a mask for cathode deposition.
A mm-wide stripe-shaped shadow mask is
It is closely attached to the element so as to be perpendicular to the stripe, and placed in another vacuum evaporation apparatus, and the degree of vacuum in the apparatus is 2 × 10 ⁻⁶ Torr (about 2.7 × 10 ⁻⁴ Pa) in the same manner as for the organic layer. Evacuation was performed until the following. As the cathode 8, first, magnesium fluoride (MgF ₂ ) was deposited using a molybdenum boat at a deposition rate of 0.1 nm.
/ S at a vacuum of 6.0 × 10 ^-6 Torr (approximately 8.0 × 10 ^-4 Pa).
A film was formed on the electron transport layer 7 to a thickness of 5 nm. Next, the aluminum was similarly heated by a molybdenum boat, and the deposition rate was 0.4 nm / sec and the degree of vacuum was 1.0 × 10 ⁻⁵ Torr (about 1.3 × 10 ⁵ Torr).
^-3 Pa) to form an aluminum layer having a thickness of 40 nm. Furthermore, copper was further heated thereon using a molybdenum boat to increase the conductivity of the cathode, and the deposition rate was 0.5 nm.
/ Sec, vacuum at 8.0 × 10 ^-6 Torr (about 1.1 × 10 ^-3 Pa)
A cathode 8 was completed by forming a 40 nm copper layer. The substrate temperature during vapor deposition of the above three-layer cathode 8 was kept at room temperature.

As described above, an organic electroluminescent device having a light emitting area of 2 mm × 2 mm was manufactured. Table 1 shows the light emission characteristics of this device. In Table 1, the light emission luminance is a value at a current density of 250 mA / cm ² , and the light emission efficiency is 100
The value at cd / m ² , the luminance / current indicate the slope of the luminance-current density characteristic, and the voltage indicates the value at 100 cd / m ² . This element is 6
Even after storage for months, no remarkable rise in drive voltage was observed, and there was no decrease in luminous efficiency or luminance, and stable storage stability of the device was obtained. Even when stored at a temperature of 60 ° C and a humidity of 90% for 96 hours. The light emission characteristics of the device did not deteriorate for practical use.

Comparative Example 1 A distyrylbiphenyl derivative (B-1) was used as a light emitting layer.
A device was produced in the same manner as in Example 1, except that the device was used. Table 1 shows the light emission characteristics of this device. The blue purity decreased and the driving voltage increased.

[0068]

[Table 1]

[0069]

According to the organic electroluminescent device of the present invention, it is possible to achieve blue light emission and to obtain a device with improved stability, since it has a light emitting layer containing a specific compound. Accordingly, the organic electroluminescent device according to the present invention can be used as a flat panel display (for example, for an OA computer or a wall-mounted television), a multi-color display device, or a light source (for example, a light source of a copier, a liquid crystal display) utilizing a feature as a surface light emitter. And instrument backlight),
It can be applied to display boards and marker lights, and particularly has a great technical value as an in-vehicle or outdoor display element requiring high heat resistance.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescent device.

FIG. 2 is a schematic sectional view showing another example of the organic electroluminescent device.

FIG. 3 is a schematic sectional view showing another example of the organic electroluminescent device.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 33/22 H05B 33/22 B

Claims (4)

[Claims] 1. A compound of the general formula (I) (X ₁ and X ₂ are hydrogen or an optional substituent, and each aromatic ring may be substituted with an optional substituent.) ,
Organic electroluminescent device. 2. A compound having a structure represented by the general formula (I): (Wherein X ¹ and X ² each independently represent a hydrogen atom or an alkyl group, an aromatic hydrocarbon ring group or an aromatic heterocyclic group which may have a substituent, and R ¹ to R ⁸ is independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, an allyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, an alkylsulfonyl group, α- Represents a haloalkyl group, a hydroxyl group, an amide group, an aromatic hydrocarbon ring group, or an aromatic heterocyclic group, all of which may be further substituted, and R ¹ and R ² , R ³ and R ⁴ ,
R ⁵ and R ⁶ or R ⁷ and R ⁸ may be bonded to each other to form a ring. 2. The organic electroluminescent device according to claim 1, wherein 3. An organic electroluminescent device comprising at least a light emitting layer sandwiched between an anode and a cathode on a substrate,
The light-emitting layer contains a compound represented by the general formula (I) or (II).
The organic electroluminescent device according to claim 1. 4. A hole blocking layer comprising at least one compound selected from a metal complex, a styryl compound, a triazole derivative and a phenanthroline derivative is provided between the light emitting layer and the cathode. The organic electroluminescent device according to claim 1.