JP2003082341A - Electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic luminescent element which can emit light with high luminance at various chromaticities so that it can be adaptable to a color display. SOLUTION: The electroluminescent element has an anode, a cathode and at least one organic layer installed between these electrodes, wherein the organic layer comprises a metal complex having a compound represented by general formula (1) (wherein X is O, S or NH; and R<1> to R<8> are each a lower alkyl, a lower alkoxy, a halogeno, or H, wherein R<1> and R<2> , R<2> and R<3> , R<3> and R<4> , R<5> and R<6> , R<6> and R<7> , and R<7> and R<8> may be combined with each other to form an aromatic ring) as a ligand.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroluminescent device, and more particularly to an electroluminescent device having a metal complex having a specific structure as a constituent material and having an excellent light emitting function.

[0002]

2. Description of the Related Art In recent years, attention has been paid to high fluorescence efficiency of organic compounds, and researches on light emitting devices of organic compounds have been actively conducted.

An organic light emitting device has a structure in which an organic light emitting layer is sandwiched between two electrodes, and holes injected from an anode and electrons injected from a cathode are recombined in the light emitting layer to emit light. These organic light emitting devices are basically said to be of two types. One is C. W. A fluorescent dye disclosed by Tang et al. (J. App.
l. Phys. 65, 3610 (1989)) and the other one using a fluorescent dye alone (Jpn. J. Appl. Phys.
27, L269 (1988)). The latter device has been shown to have improved luminous efficiency when the fluorescent dye is arranged to stack with a hole transport layer that transports only holes and / or an electron transport layer that transports only electrons. ing.

A wide variety of materials such as triphenylamine derivatives are known as hole transport materials used in organic light emitting devices.

In comparison with this, there are very few electron transport materials, but for example, in 1987, an oxynate metal complex composed of oxine (official name: 8-hydroxyquinoline) and aluminum and emitting green light was introduced. Since the report, research aiming at application to displays and the like has been extensively studied, and development of materials for obtaining highly efficient light emission has been actively conducted.

For example, Japanese Patent Laid-Open No. 8-81472 discloses the following structure.

[0007]

[Chemical 6]

(Wherein M ^a is a divalent metal, M ^b is a trivalent metal, X is O, S, NH or CH ₂ , R ^{1 to} R ⁸ and L ^{1 to} L.
⁵ represents a hydrogen atom, a hydrocarbon group or a functional group. A hole transport layer or an electron transport layer using an organometallic complex having a) is proposed.

[0009]

However, the metal complex having the above structural formula has a low heat resistance and an insufficient electronic transport efficiency. Therefore, the emission intensity and the stability during repeated use tend to be poor.

Further, recently, not only high-efficiency light emission but also electroluminescent device material for lowering driving voltage has been vigorously developed, but a light-emitting material capable of realizing both is still available. The current situation is that there are none.

The present invention has been made in view of the above problems, and an object thereof is to provide an organic light emitting device capable of emitting light with various chromaticities and high brightness so as to cope with colorization. To do.

[0012]

As a result of various studies on light emitting materials, a specific metal complex having a specific ligand has a high glass transition temperature, is amorphous, and has good film properties and high properties. The inventors have found that they have an electron transporting property and a thermal stability, and accordingly, high fluorescence, high brightness and high stability as an electroluminescent device can be obtained, and the present invention has been completed.

That is, according to the present invention, there is provided an electroluminescent device having an anode, a cathode and at least one organic layer arranged between these electrodes, wherein the organic layer is represented by the general formula (1):

[0014]

[Chemical 7]

(Wherein X is O, S or NH, R ^{1 to} R ⁸ are lower alkyl group, lower alkoxy group, halogen atom or hydrogen atom, R ¹ and R ² , R ² and R ³ , R ³ and R ⁴ , R ⁵ and R ⁶ ,
R ⁶ and R ⁷ , and R ⁷ and R ⁸ may combine with each other to form an aromatic ring. The present invention provides an electroluminescent device comprising a metal complex having a compound represented by the formula (1) as a ligand.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The electroluminescent device of the present invention is mainly composed of an organic layer and an anode and a cathode formed on both sides of the organic layer.

The organic layer may be formed of a single layer or a laminated layer which functions as a light emitting layer, an electron transporting layer, a hole transporting layer or the like, but at least one layer is represented by the general formula (1). ) Is composed of a metal complex having a compound represented by the formula as a ligand. In particular, the light emitting layer and / or the electron transporting layer is preferably composed of a metal complex.

In the general formula (1), the lower alkyl group is an alkyl group having 1 to 5 carbon atoms, for example, methyl,
Ethyl, propyl, isopropyl, t-, n-, sec
-Butyl, n-pentyl, isopentyl, neopentyl and the like. The lower alkoxy group has 1 carbon atom
To alkoxy groups such as methoxy, ethoxy, propoxy, butoxy, pentoxy and the like. Examples of the halogen atom include fluorine, chlorine, bromine, iodine and the like. Further, examples of the aromatic ring which may be bonded to each other include phenyl and naphthyl.

Among them, the following general formulas (2) and (3)
A metal complex having a compound represented by as a ligand is preferable.

[0020]

[Chemical 8]

[0021]

[Chemical 9]

(In the formula, X is O, S or NH.) The compounds represented by the general formulas (1) to (3) are divalent and trivalent.
Complexes with valent metals are preferred.

When the compound of the general formula (1) is coordinated with a divalent metal, the compound of the general formula (4)

[0024]

[Chemical 10]

(Wherein M ¹ is a divalent metal, X and R ^{1 to} R
⁸ has the same meaning as defined in formula (1). ) Shown in 4
It becomes a coordination compound.

When the compound of the general formula (1) is coordinated with a trivalent metal, most of them do not have the hexadentate coordination, and the reaction stops at the tetradentate compound. Therefore, the outermost shell electron is stabilized by an ionic bond with an anion having a relatively small structure, and the general formula (5)

[0027]

[Chemical 11]

[0028] (In the formula, A-substituted, aromatic ring unsubstituted C ₆ ~ _14, M ² is a trivalent metal, X and R ¹ to R ⁸ are defined as defined in the general formula (1) )). As the anion, a hydroxyl group, a halogen atom,
Hypochlorous acid group, perchloric acid group, thiocyanato (-SCN)
Although group and the like, among others, from the emission intensity with time of (stability to humidity), C ₆ hydroxy groups substituted to ₁₄
The aromatic ring of (especially phenyl derivative) is preferable.

In the general formulas (4) and (5),
Divalent metals include zinc, magnesium, beryllium,
Examples include nickel and mercury. In particular, beryllium and zinc, which have high emission intensity, are preferable. As a trivalent metal,
Aluminum, indium, ruthenium, boron, osnium, etc. are mentioned. Particularly, aluminum and osmium, which have high emission intensity, are preferable.

In the general formula (5), the number of carbon atoms is 6 to
Examples of the aromatic ring of 14 include phenyl, naphthalene, phenanthrene, indene and the like. Also,
A substituent may be substituted on these aromatic rings. The position and number of the substituents are not particularly limited and can be appropriately adjusted depending on the characteristics. As the substituent, a lower alkyl group (eg, methyl, ethyl, iso-propyl etc.), a lower alkoxy group (methoxy, ethoxy etc.), a methylenedioxy group, a halogen atom (chlorine, bromine etc.), a cyano group, α, Examples include α, α-trifluoromethyl group, phenyl group and diphenyl. Among these substituents, the electron donating group is preferable from the viewpoint of characteristics such as emission intensity and applied voltage, and the substitution of the ortho position is preferable from the viewpoint of amorphousness (adhesion). It should be noted that this is the characteristic of the charge generating material of the so-called function-separated electrophotographic photoreceptor (effect of anilide substitution of naphthol AS: ortho effect).
Shows similar characteristics to. On the other hand, many electron-withdrawing groups generally improve the properties such as emission intensity and applied voltage regardless of the position of the substituent (however, the ortho effect is recognized even in the case of electron-withdrawing group substitution). ). Further, from the viewpoint of emission intensity, it is preferable that the same element (especially chlorine) is substituted by 2 or less. Since this has a steric hindrance due to a large number of substitutions, it is presumed that desorption of elements (particularly chlorine) occurred during the conversion of the vapor phase. Furthermore, the phenyl and diphenyl groups, which are electron withdrawing groups in a broad sense, are highly preferable because the substituents themselves also have high electron transporting properties and also have excellent thermal stability.

Specific compounds of the general formulas (4) and (5) are shown below.

[0032]

[Chemical 12]

[0033]

[Chemical 13]

[0034]

[Chemical 14]

[0035]

[Chemical 15]

[0036]

[Chemical 16]

[0037]

[Chemical 17]

[0038]

[Chemical 18]

[0039]

[Chemical 19]

[0040]

[Chemical 20]

Among them, 2- (2-hydroxynaphthyl) benzoxazole, 2- (2-hydroxyanthryl) benzoxazole, 2- (2-hydroxyphenanthryl) benzoxazole, 2- (2-hydroxyphenyl). Oxazole derivatives such as benzoxazole; 2- (2-hydroxynaphthyl) benzimidazole, 2- (2-hydroxyanthryl) benzimidazole, 2- (2-hydroxyphenanthryl) benzimidazole, 2- (2-hydroxyphenyl) ) Imidazole derivatives such as benzimidazole; 2- (2-hydroxynaphthyl) benzothiazole, 2- (2-hydroxyanthryl) benzothiazole, 2- (2-hydroxyphenanthryl) benzothiazole, 2- (2-hydroxy) Phenyl) Is preferably one thiazole derivative as a ligand such as Zochiazoru, particularly oxazole derivatives is more preferable. More specifically, Exemplified Compound 2
-3, 2-8, 2-9, 2-10, 2-12, 2-15
Etc. are preferred.

The metal complexes represented by the general formulas (4) and (5) can be synthesized by the following method.

First, a ligand compound represented by the general formula (1) is obtained.

[0044]

[Chemical 21]

(Y is hydrogen or an alkali metal.) In the esterification here, alcohol may be used instead of phenol. If necessary, the reaction may be carried out in a solvent such as chlorobenzene or dichlorobenzene.
The reaction time is preferably about 6 hours and the temperature is preferably about 100 to 120 ° C. In order to accelerate the reaction, it is preferable to add a dehydrating agent (phosphorus oxychloride, phosphorus trichloride, etc.) to the reaction system again if necessary. After the reaction, alcohol or the like is added and the precipitated powder is recrystallized with ethyl acetate or the like.

The thus obtained ester form is reacted with ortho-aminophenol form, ortho-diamino form and the like at high temperature (150 ° C. or higher). It is preferable to add nitrobenzene or the like as a reaction solvent to homogenize the reaction. The compound of general formula (1) can be obtained by recrystallizing the obtained reaction product from toluene, chlorobenzene or the like. Although this reaction is a two-step reaction,
Proceeds almost quantitatively.

Then, the compound thus obtained (eg, oxazole, thiazole, imidazole compound) is dissolved in a suitable solvent (NMP, DMF, DMSO, alcohol or a mixed solvent thereof) to prepare 1. After adding 5- to 2.0-fold molar amount of potassium hydroxide or sodium hydroxide or the like, and finally gradually adding a divalent or trivalent metal salt, heating and stirring are performed. At this time, the reaction temperature is preferably relatively high (150 ° C. or higher).

[0048]

[Chemical formula 22]

Examples of the metal salt used here include aluminum chloride, aluminum nitrate, aluminum sulfate, gallium chloride, indium chloride, scandim chloride, osmium chloride and the like. Generally, a halide is easily available, and a chloride is more preferable.

There is also a method of directly obtaining the ligand compound represented by the general formula (1) without undergoing esterification. However, from the viewpoint of reactivity and control of by-products, esterification was performed. A stepwise synthesis method is preferred.

When a trivalent metal salt is used, A-
By reacting with OH, the compound of the general formula (5) can be obtained.

[0052]

[Chemical formula 23]

In this reaction, A-OH (for example, phenol derivative) is added at the end of the step of gradually adding a trivalent metal salt and heating and stirring. The reaction proceeds smoothly when the phenol derivative or the like is added in a state of being dissolved in alcohol or the like. Further, it is appropriate to add about 1.5 times the theoretical amount.

The reaction product thus obtained is repeatedly washed with water and washed with alcohol, and optionally purified by sublimation to obtain the metal complex of the present invention.

For the synthesis of these, US Pat.
50,006 and Analytical Chemistry 1938P (19
68) and the like.

A metal complex having the general formula (1) as a ligand is
It has excellent fluorescence and emission characteristics and can be applied to various product forms utilizing these characteristics. Fluorescent paint is a typical one utilizing the fluorescent property, and organic electroluminescent element is a typical one utilizing the light emitting property. In particular, it can be effectively used as a component of an organic electroluminescent device capable of emitting light with high brightness at a low voltage. Further, applications such as photoelectric materials for photovoltaic devices and materials for video devices are also conceivable.

In the present invention, the organic layer has the general formula (1)
It is effective to mix a plurality of kinds of metal complexes having the above compound as a ligand, and it is particularly preferable to mix and use metal complexes having the same core metal but different ligand compounds.
For example, a core metal such as aluminum or beryllium,
A mixture of a plurality of types of metal complexes having the above-mentioned oxazole derivatives as ligands, and a mixture of a plurality of types of metal complexes having the same imidazole derivatives as ligands, respectively.
Similarly, a mixture of a plurality of types of metal complexes having a thiazole derivative as a ligand can be used. Thus, by mixing (co-evaporating) the metal complex having the compound of the general formula (1) as a ligand, panchromatic emission wavelength and further improvement in adhesion due to amorphization are brought about.
The mixing ratio of the metal complex in this case can be arbitrarily set depending on the purpose of use such as adjustment of the emission wavelength, but it is preferable that each metal complex is in an equivalent amount.

The organic layer, particularly the light emitting layer, may be formed by further mixing with another metal complex (for example, an oxynate derivative), and any of the compounds usually used for the organic layer of the electroluminescent element may be used. It may be formed by mixing. For example, the structure

[0059]

[Chemical formula 24]

4-dicyanomethylene-6- (p having
Fluorescent substances such as -diethylaminostyryl) -2-methyl-4H-pyran, anthracene, phenanthrene, birene, perylene, coumarin, acridine, stilbene and their derivatives can be used. When a fluorescent substance is used, it is appropriate that the amount is about 2% by weight or less based on the total weight of the organic layer (that is, the light emitting layer). Moreover, you may use 1 type or 2 types or more of an alkali metal containing compound. The alkali metal-containing compound is a light-emitting material (for example, a compound represented by the general formula (1)) contained in the organic layer in consideration of a decrease in glass transition point, occurrence of thermal deterioration, increase in light-emission start voltage, and the like. 1 equivalent or less per 1 equivalent of a metal complex used as a ligand is suitable. Further, it is preferably 0.01 equivalent or more. Further, the organic layer may be doped with an electron transport material. The doping amount of the electron transport material is preferably about 2% by weight or less based on the total weight of the organic layer (light emitting layer).

In the case of having an electron transport layer, examples of the material for forming the electron transport layer include condensed polycyclic hydrocarbon compounds such as tetracene, pentacene, tetraphenylene, diphenyloxadiazole, and heterocyclic compounds. To be The film thickness of the electron transport layer is not particularly limited and may be the same as that of the light emitting layer. The electron transport layer is preferably doped with an alkali metal-containing compound together with the electron transport material. Examples of the alkali metal-containing compound include phenol, benzoic acid, organic metal salts such as lithium salts such as acetic acid, and further inorganic metal salts such as lithium chloride, lithium fluoride and lithium iodide. . The appropriate doping ratio is about 30 mol% or more with respect to the electron transport material.

Further, in the case of having a hole transport layer, an aromatic compound having an enamine structure can be mentioned as a material for forming the hole transport layer. The film thickness of the hole transport layer is not particularly limited and may be the same as that of the light emitting layer.

The anode in the organic electroluminescent element of the present invention is usually formed on a substrate and is formed of, for example, a single layer or a laminated layer of a metal, an alloy, or a transparent conductive material having a large work function (about 4 eV or more). can do. Specifically, aluminum, vanadium, cobalt, nickel,
Tungsten, silver, gold and their alloys, CuI, S
Examples include transparent conductive materials such as nO, ZnO, and ITO. Among them, it is common to take out light emission from the anode side, and therefore, a material formed of a transparent conductive material is preferable. The thickness of the anode depends on the material used,
For example, 500 nm or less, preferably 10 to 300 nm
The degree can be mentioned.

The cathode has, for example, a low work function (4e).
It can be formed of a single layer or a laminated layer of metal, alloy, transparent conductive material, or the like. Specifically, calcium, aluminum, silver, titanium, yttrium, sodium, ruthenium, manganese, indium,
Metals such as magnesium, lithium, ytterbium, LiF and magnesium / copper, magnesium / silver, sodium / potassium, At / AtO ₂ , lithium / aluminum, lithium / calcium / aluminum, LiF /
Examples include alloys of calcium / aluminum and the like, single layers or laminated layers of the transparent conductive material as described above. The thickness of the cathode depends on the material used, but is, for example, 5
The thickness is not more than 00 nm, preferably about 10 to 300 nm.

Further, in the present invention, optionally between the substrate and the anode, between the anode and the organic layer, between the organic layer and the cathode,
When the organic layer has a plurality of layers, other layers such as a buffer layer and an intermediate layer may be provided between them. In particular, the electron injection effect can be enhanced by providing the electron barrier layer between the cathode and the organic layer. The electron barrier layer may basically have a film thickness necessary to form a monomolecular array, for example,
It is about 10 Å or more. Examples of the material for the electron barrier layer include inorganic salts and organic salts of metals that have a large ionization tendency and lower the molar level. Specifically, α, α, α-
Lithium salt of trifluoroacetic acid, lithium phenolate,
Examples thereof include lithium sulfonate. Further, in order to improve the stability of the device, a part or the whole of the device may be covered with a protective layer, and a color filter may be incorporated in order to adjust the emission color. The materials, film thicknesses, etc. of these layers are not particularly limited as long as they are usually used for forming an electroluminescent device, and can be appropriately selected depending on their functions and the like.

The electroluminescent element of the present invention is, for example,
As shown in FIG. 1, on a substrate (for example, a glass substrate) 1, an anode (ITO transparent electrode) 2, a hole transport layer 3, a light emitting layer 4, an electron barrier layer 5, a cathode (for example, an aluminum or aluminum alloy electrode). ) 6 are laminated in this order. The light emitting layer 4 usually has an electron transporting function, but as shown in FIG. 2, an electron transporting layer 7 may be separately provided between the light emitting layer 4 and the electron barrier layer 5. Further, as shown in FIG. 3, the light emitting layer 4 may be directly adjacent to the cathode 6. Further, as shown in FIG. 4, only the electron transport layer 7 may be provided between the light emitting layer 4 and the cathode 6.

In the electroluminescent device having such a structure, by selectively applying a DC voltage between the anode and the cathode, holes injected from the anode pass through the hole transport layer and from the cathode. The injected electrons optionally reach the light emitting layer through the electron barrier layer and the electron transport layer to cause electron-hole recombination, which is observed as light emission from the substrate side.

This electroluminescent device can be manufactured as follows.

First, an anode is formed on the substrate. The anode is
It can be formed by various methods such as a sputtering method, a vacuum deposition method, and a sol-gel method.

Next, a hole transport layer is formed on the anode.

A light emitting layer is formed thereon. For example, when the light emitting layer is formed by vapor deposition, an alkali metal-containing compound (for example, lithium-α-naphtholate) or another metal complex (for example, A
(1q ₃ etc.) may be vapor-deposited, or a plurality of kinds of the above-mentioned metal complexes may be vapor-deposited simultaneously. At this time, since there is a difference in vapor deposition rate among the metal complexes, it is appropriate to vapor deposit a metal complex having a low vapor deposition rate and then sequentially vaporize a fast metal complex, an alkali metal-containing compound and the like. When a plurality of materials are vapor-deposited at the same time, they may be vapor-deposited in any number of times from the same direction or different directions.
Further, by utilizing the difference in vapor deposition rate of the light emitting material, a light emitting layer having a laminated structure of two layers or more may be formed.

As another method for forming the light emitting layer, the above metal complex is added to a suitable organic solvent (eg DMSO, NMP).
Etc.) and a method of coating with a spin coater or the like. At this time, the metal complex may be used in combination with another metal complex, a fluorescent substance, or a plurality of types of the above metal complexes. Further, in order to improve solubility and adhesion, it is preferable that the light emitting material is in an amorphous state. Therefore, in order to apply this method, it is preferable to use, as the light emitting material, a material having an asymmetric structure and further substituted with a long-chain alkyl or branched alkyl group.

An electron transport layer, an electron barrier layer, a cathode and the like are optionally formed on the light emitting layer by a known method.

The organic electroluminescent device of the present invention will be specifically described below with reference to examples, but the contents of the present invention are not limited thereby.

Examples 1 to 5 A glass substrate on which an ITO film (anode) having a film thickness of 50 nm was vapor-deposited by vacuum vapor deposition was vacuum-deposited to have a film thickness of about 35 n.
m hole-transporting layer was formed. For the hole transport layer, a bis enamine compound having the following structural formula was used.

[0076]

[Chemical 25]

Next, on this hole transport layer, five kinds of metal complexes consisting of the exemplified compounds shown in Table 1 and berylium were laminated by vacuum vapor deposition to form an electronic light emitting layer. The thickness of these films was between 40 nm and 50 nm.

A DMF solution of a lithium salt of α-naphthol was spin-coated on the electronic light emitting layer so as to have a film thickness of about 40 nm, and then a Mg—Ag alloy (cathode) was laminated by vacuum vapor deposition to form an organic layer. An electroluminescent device was created.

The conditions for vacuum deposition of the above layers were as follows. The maximum wavelength of the emission spectrum of each obtained organic electroluminescent device was measured by a photomultiplier tube. The applied voltage at this time is 18V. When the applied voltage was 18 V, the flowing current value and the light emission start applied voltage were measured, and these measured values are shown in Table 1.

[0080]

[Table 1]

From Table 1, it was found that all of these devices emitted blue light and had a low light emission starting voltage of 10 V or less.

Examples 6 to 10 As an electroluminescent material, instead of the metal complex of Examples 1 to 5, a metal complex 5 containing the exemplified compounds shown in Table 2 and zinc.
Organic electroluminescent devices were prepared according to Examples 1 to 5 except that the respective types were used.

A film thickness 2 of diphenyloxazole was formed between the lithium salt layer and the light emitting layer as the electron transport layer.
A 0 nm layer was formed by the vacuum evaporation method. However, the interface between the electron transport layer and the lithium salt layer was slightly broken from the cross-sectional photograph. This indicates that lithium ions are in a state of being diffused in the electron transport layer.

[0084]

[Table 2]

From Table 2, it was found that all of these devices emitted blue light and had a low light emission starting voltage of 10 V or less. Regarding the current value, the device using a complex containing a oxazole compound as a ligand showed a high value. This suggests that these devices have high brightness.

Examples 11 and 12 With respect to the organic electroluminescent devices of Examples 5 and 10, the current value and luminance which flowed at the applied voltage of 18 V and the emission start applied voltage were measured for the devices in the system free of the lithium salt layer. did. These measured values are shown in Table 3. The brightness was measured with a brightness meter (CS-100, manufactured by Minolta). Example 11 corresponds to Example 5, and Example 12 corresponds to Example 10.

[0087]

[Table 3]

From Table 3, it was confirmed that providing the lithium salt layer on the cathode side had the effect of lowering the light emission starting voltage. Further, the maximum emission wavelength is the same as in Example 5.
And 10 were almost the same.

Examples 13 to 18 As electroluminescent materials, in Examples 13 to 16 instead of the metal complexes of Examples 1 to 5, metal complexes of the exemplified compounds shown in Table 4 and aluminum, Examples 17 and 18 were used. Then, an organic electroluminescence device was prepared according to Examples 1 to 5 except that the exemplified compounds shown in Table 4 and the metal complex consisting of osmium were used respectively.

An electron transport layer made of rubrene having a film thickness of 20 nm was provided between the lithium salt layer and the light emitting layer by a vacuum vapor deposition method. However, at this time, the interface between the electron transport layer and the lithium salt layer was a little distorted from the cross-sectional photograph. This indicates that lithium ions are in a state of being diffused in the electron transport layer. However, the interface between the electron transport layer and the light emitting layer made of a metal complex was clearly recognized.

An applied voltage of 18 V was applied to these organic electroluminescent elements in the same manner as in Examples 1 to 5, 11 and 12.
The current value, luminance at that time, maximum emission wavelength, and emission start voltage were measured. The results are shown in Table 4.

[0092]

[Table 4]

From Table 4, most of the organic electroluminescent elements using the metal complex composed of these trivalent metals as the light emitting material exhibited blue to slightly purpleish light emission. In particular, an organic electroluminescent device in which a ligand is composed of a light emitting material composed of benzoxazole and a polyvalent phenolate such as biphenolate and terphenolate tends to have a large brightness as a whole. Further, it is recognized that the aromatic ring aggregated type has high brightness due to the arrangement of π electrons and the improvement of electron mobility due to an appropriate electron withdrawing property (Examples 15 and 1).
7, 18).

Examples 19 to 21 Three types of organic electroluminescent elements of Examples 5, 15 and 17 were measured at an applied voltage of 18 V for the time required for the initial emission luminance to disappear. As a result, they were about 7 hours, 23 hours, and 25 hours, respectively. It is considered that this is because an empty wall is formed between the light emitting layer and the hole transporting layer or the electron blocking layer, which causes decomposition of the light emitting material due to the flow of an excessive current. From this, it can be said that the trivalent metal complex has relatively better adhesion.

Examples 22 and 23 The core metal is beryllium and the ligand is 2- (2-hydroxynaphthyl) benzoxazole, 2- (2-hydroxyanthryl) benzoxazole or 2- (2-
An organic electroluminescent device was prepared in the same manner as in Example 1 except that three kinds of metal complexes composed of hydroxyphenyl) benzoxazole were weighed in equivalent amounts and well mixed together to form a light emitting layer having a film thickness of 50 nm. It was created.

The core metal is aluminum and the ligand is 2- (2-hydroxynaphthyl) benzoxazole, 2- (2-hydroxyanthryl) benzoxazole or 2- (2-hydroxyphenyl) benzoxazole. And a metal complex composed of a biphenyl group as a phenolate (Exemplified compound 2-3, Exemplified compound 2-8)
In the same manner as above, an organic electroluminescent element was prepared in the same manner as in Example 1 except that the light emitting layer having a film thickness of 50 nm was used.

When the organic EL device having the light emitting layer composed of a plurality of materials was prepared as described above, and the brightness, the light emission drive voltage, the light emission wavelength, and the adhesiveness were compared with each other, the brightness was 5100 ( cd / m ² ), 6
It was 800 (cd / m ² ) and improved by 10% or more. Further, in the device using the complex in which the core metal is beryllium, the time required for the initial emission brightness to disappear was improved to 18 hours. It is considered that this is because the adhesion between layers is improved. No significant improvement was observed in the light emission drive voltage.

A similar tendency was observed when the ligand was a benzimidazole or benzothiazole type.

Particularly, the melting point effect of mixing a metal complex having a high glass transition temperature can be expected to maintain heat resistance and improve adhesion, and is preferable from the viewpoint of stability.

[0100]

According to the present invention, since the organic layer contains a light emitting material which emits purple to green light, an electroluminescent device having high brightness and low voltage can be obtained. Further, by appropriately blending these light emitting materials, it is possible to obtain an electroluminescent element with little deterioration and excellent stability. Moreover, since such a light-emitting material can be easily synthesized from existing general-purpose raw materials, it is possible to reduce the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing an example of an electroluminescent device of the present invention.

FIG. 2 is a schematic cross-sectional view of a main part showing another example of the electroluminescent element of the present invention.

FIG. 3 is a schematic cross-sectional view of a main part showing still another example of the electroluminescent element of the present invention.

FIG. 4 is a schematic cross-sectional view of a main part showing still another example of the electroluminescent element of the present invention.

[Explanation of symbols]

1 substrate 2 anode 3 Hole transport layer 4 Light emitting layer 5 Electron barrier layer 6 cathode 7 Electron transport layer

Claims (12)

[Claims] 1. An electroluminescent device comprising an anode, a cathode and at least one organic layer arranged between these electrodes, wherein the organic layer is represented by the general formula (1): (In the formula, X is O, S or NH, R ^{1 to} R ⁸ are a lower alkyl group, a lower alkoxy group, a halogen atom or a hydrogen atom, and R ¹ and R ² , R ² and R ³ , R ³ And R ⁴ , R ⁵ and R ⁶ ,
R ⁶ and R ⁷ , and R ⁷ and R ⁸ may combine with each other to form an aromatic ring. An electroluminescent device comprising a metal complex having a compound represented by the formula (1) as a ligand. 2. A compound represented by the general formula (1) has the formula (2): The electroluminescent device according to claim 1, which is a compound represented by the formula: wherein X is O, S, or NH. 3. A compound represented by the general formula (1) is represented by the formula (3): The electroluminescent device according to claim 1, which is a compound represented by the formula: wherein X is O, S, or NH. 4. The electroluminescent device according to claim 1, wherein the metal complex is composed of a divalent or trivalent metal. 5. The metal complex has the general formula (4) or (5): [Chemical 5] (In the formula, A substitutions, unsubstituted C ₆ ~ ₁₄ aromatic ring, M ¹ is a divalent metal, M ² is a trivalent metal,
X is O, S or NH, R ^{1 to} R ⁸ are a lower alkyl group, a lower alkoxy group, a halogen atom or a hydrogen atom, R ¹ and R ² , R ² and R ³ , R ³ and R ⁴ , R ⁵ and R ⁶ , R ⁶ and R ⁷ , and R ⁷ and R ⁸ may be bonded to each other to form an aromatic ring. The electroluminescent element according to claim 1 or 4. 6. The metal complex is 2- (2-hydroxynaphthyl) benzoxazole, 2- (2-hydroxyanthryl) benzoxazole, 2- (2-hydroxyphenanthryl) benzoxazole, 2- (2-hydroxy). The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is composed of a complex of metal complexes composed of the same metal each having phenyl) benzoxazole as a ligand. 7. The metal complex is 2- (2-hydroxynaphthyl) benzimidazole, 2- (2-hydroxyanthryl) benzimidazole, 2- (2-hydroxyphenanthryl) benzimidazole, 2- (2-hydroxy). The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is composed of a complex of metal complexes composed of the same metal having phenyl) benzimidazole as a ligand. 8. The metal complex is 2- (2-hydroxynaphthyl) benzothiazole, 2- (2-hydroxyanthryl) benzothiazole, 2- (2-hydroxyphenanthryl) benzothiazole, 2- (2-hydroxy). The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device comprises a complex of a metal complex composed of the same metal having phenyl) benzothiazole as a ligand. 9. The organic electroluminescent element according to claim 1, wherein the trivalent metal is aluminum. 10. The organic electroluminescent device according to claim 1, wherein the divalent metal is zinc or beryllium. 11. The organic electroluminescent device according to claim 1, wherein an electron barrier layer made of an organic lithium salt is provided between the organic layer and the cathode. 12. The method according to claim 1, wherein a hole transport layer is formed between the anode and the organic layer, and an aromatic compound having an enamine structure is used as a hole transport material forming the hole transport layer. 11. The organic electroluminescent device according to any one of 11.