JPH11322723A - Enamine group-containing hydrazone compound and organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject new compound containing plural enamine groups in one molecule and capable of providing an organic EL element having good luminescent efficiency, luminescence with high luminance and luminescence at a low driving voltage and hardly causing deterioration by a substance such as water or oxygen. SOLUTION: This compound is represented by formula I Ar is (CH2 )n or a (substituted)arylene; R<1> and R<2> are each H, a (substituted)aryl or a lower alkyl; R<3> is a (substituted)aryl; R<4> is H or a (substituted)alkyl; X is O, S or the like; A<1> and A<2> are each H, a lower alkyl or the like; (n) is 0-4}, e.g. a compound of formula II. Furthermore, the compound is preferably obtained by heating an aldehyde compound or ketone compound of formula III and a hydrazone compound of formula IV under reflux in an organic solvent such as ethanol in acidic atmosphere and heating the resultant compound and an aldehyde of formula V under reflux in an aromatic organic solvent such as benzene in the presence of a catalyst such as nitric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an enamine group-containing hydrazone compound and an organic electroluminescent device. More specifically, the present invention relates to a novel enamine group-containing hydrazone compound and a driving voltage using the compound which is small and good luminous efficiency. The present invention relates to an organic electroluminescent device having:

[0002]

2. Description of the Related Art In recent years, electroluminescent devices (hereinafter, EL devices) have been developed.
Because of its self-luminous properties, it has high visual recognition and is a solid-state device, and has features such as excellent impact resistance.Therefore, its use in various displays and backlight lamps is attracting attention. ing.

[0003] As the EL element, there are an inorganic EL element using an inorganic compound for a light emitting layer and an organic EL element using an organic compound. Above all, research on practical use of organic EL elements has been actively conducted in order to reduce the applied voltage and support full-color display. The organic EL element has an anode / light-emitting layer / cathode as its basic structure, and a hole injection / transport layer having a function of efficiently transferring holes injected from the anode to the light-emitting layer, and electrons injected from the cathode. Is appropriately provided with an electron injection / transport layer having a function of efficiently transmitting the electron transport layer to the light emitting layer.

Among the organic EL devices having such a structure, various devices having a structure of anode / hole injection / transport layer / light emitting layer / cathode have been proposed as having particularly excellent performance. (U.S. Pat.Nos. 4,539,507 and 4,769,292
JP-A-59-194393, JP-A-63-295695, etc.). For example, in the organic EL device having the above structure, by using a material having excellent thin film forming properties for the hole injecting and transporting layer, the total thickness of the hole injecting and transporting layer and the light emitting layer can be reduced to 150 n.
m, and as a result, high-luminance light emission has been successfully obtained with a drive voltage of 20 V or less.

[0005] Further, a triphenylamine-based hole injection / transport compound which does not transport electrons and acts as a barrier against electrons is used for the hole injection / transport layer, and an interface between the hole injection / transport layer and the light emitting layer is formed. Electrons accumulate at this interface in the light emitting layer due to the electron barrier existing in the light emitting layer, and further, by using an oxime complex of aluminum (III) as a material of the light emitting layer, 1000 cd / m 2 at a low applied voltage of 10 V or less. ^Two
High-luminance green color development with a high luminous efficiency of 1.5 lumen / V (Appl. Phys. Letter, Vol.
51, p913 (1987)).

Incidentally, since the organic EL element has a light-emitting mechanism of recombination of electrons and holes, it should be possible to drive at a low voltage (2 to 6 V) as much as a light-emitting diode.
However, at present, the driving voltage is 8 V or more. This is due to the energy barrier against hole injection existing at the interface between the anode and the hole injection transport layer or the energy barrier against electron injection existing at the interface between the light emitting layer and the cathode. Furthermore, it is said that the upper limit of the general quantum efficiency of light emission is about 40%, but it is still about 3% in an organic EL device.

As described above, the organic EL device having the structure of the anode / hole injection / transport layer / light emitting layer / cathode has better performance than the organic EL devices of other structures, The luminous efficiency is not always satisfactory. Further, the organic EL element is an inorganic EL element.
The problem that the deterioration characteristics of the constituent material is not as good as that of the element and the problem that the element cannot withstand long-time use has not been solved yet.

The present invention has been made in view of the above problems, and has good luminous efficiency, high-luminance luminescence, luminescence at a low driving voltage, chemicals such as water or oxygen, and physical phenomena such as light and heat. An object is to provide an organic EL element with small deterioration.

[0009]

The inventor of the present invention has conducted intensive studies to develop an EL device having the above-mentioned excellent characteristics. An EL device having a transport layer formed in
When a hydrazone compound having two enamine groups in one molecule represented by the following formula (I) is used as at least the hole injection transport layer compound or the electron injection transport layer compound in the transport layer, The present inventors have found that the energy barrier of the existing charge injection is alleviated, a lower driving voltage can be achieved, and an organic EL device having high luminous efficiency and stable for a long time can be obtained. Thus, the present invention has been completed.

That is, according to the present invention, formula (I)

[0011]

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(Wherein, Ar is-(CH ₂ ) _n- , an optionally substituted arylene group, R ¹ and R ² are the same or different and are each a hydrogen atom, an optionally substituted aryl group or A lower alkyl group, R ³ is an optionally substituted aryl group, R ⁴ is a hydrogen atom, an optionally substituted alkyl group, or an optionally substituted aryl group, or a combination of R ³ and R ⁴ May be linked together to form a ring with the carbon atom to which they are attached, X is an oxygen atom,
A sulfur atom or —NR ⁵ — (where R ⁵ is a hydrogen atom,
An alkyl group which may be substituted or an aryl group which may be substituted), A ¹ and A ² are the same or different,
A hydrogen atom, a lower alkyl group, an aryl group which may be substituted, or A ¹ and A ² may be connected to each other to form a ring together with the carbon atom to which they are bonded, and n is 0
And an hydrazone compound having an enamine group represented by the formula:

Further, according to the present invention, there is provided an organic electroluminescent device in which an anode, a hole injecting and transporting layer, a light emitting layer and a cathode are laminated in this order, wherein the hole injecting and transporting layer has the formula (I) And an organic electroluminescent device containing the compound represented by the formula:

Further, according to the present invention, an anode, a hole injecting and transporting layer, a light emitting layer, an electron injecting and transporting layer, and a cathode are laminated in this order. There is provided an organic electroluminescent device containing an enamine group-containing hydrazone compound represented by the formula (I).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrazone compound containing an enamine group of the present invention is a compound having a novel structure. These hydrazone compounds can be suitably used as a transport material in an organic EL light emitting device, an electrophotographic photoreceptor, and the like. In addition to the transport material such as an organic EL device, the photoconductor material and the waveguide material can be suitably used.

The enamine group-containing hydrazone compound of the formula (I) of the present invention has the following structure:

[0017]

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(Wherein, Ar is-(CH ₂ ) _n- , an optionally substituted arylene group, R ¹ and R ² are the same or different and are each a hydrogen atom, an optionally substituted aryl group or A lower alkyl group, R ³ is an optionally substituted aryl group, R ⁴ is a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group, or R ³ and R ⁴ are X may be linked to each other to form a ring together with the carbon atom to which they are bonded, and X is an oxygen atom, a sulfur atom, or -NR ^5- (where R ⁵ is a hydrogen atom, an optionally substituted alkyl group or a substituted A ¹ and A ² are the same or different and are each a hydrogen atom, a lower alkyl group or an optionally substituted aryl group, or A ¹ and A ² are linked to each other. The carbon atoms to which they are attached And n may form a ring together with
Which is an integer of 4).

The "arylene group which may be substituted" in Ar includes an arylene group having 6 to 12 carbon atoms and an arylene group having 6 to 12 carbon atoms having a substituent. As the "arylene group", for example,
Examples include phenylene, biphenylene, tolylene, and naphthylene groups. Among them, a 1,4-phenylene group is preferred. Examples of the “substituted arylene group” include a hydrogen atom, a halogen atom, a methyl group, a methoxy group, a trifluoromethyl group, a dichloro group, and a methylenedioxy group.

As the “substituted arylene group”, for example,
2 or 3-chloro-1,4-phenylene group, 2,3-dichloro-1,4-phenylene group, 2 or 3-bromo-
1,4-phenylene group, 2,3-dibromo-1,4-phenylene group, 2 or 3-methyl-1,4-phenylene group, 2,3-dimethyl-1,4-phenylene group, 2 or 3- Methoxy-1,4-phenylene group, 2,3-dimethoxy-1,4-phenylene group, 2 or 3-trifluoromethyl-1,4-phenylene group, 2,3-di (trifluoromethyl) -1, 4-phenylene group, 4-methyl-1,3
-Phenylene group, 4-chloro-1,3-phenylene group and the like. Among them, an electron-donating substituted arylene such as a methyl group or a methoxy group is preferable.

The "optionally substituted aryl group" for R ¹ and R ² includes an aryl group having 6 to 12 carbon atoms and an aryl group having 6 to 12 carbon atoms having a substituent. Examples of the “aryl group” include a phenyl group, a tolyl group, a naphthyl group, a biphenylene group and the like. Examples of the “substituent of an aryl group” include a hydrogen atom, a halogen atom, a methyl group, a methoxy group, a trifluoromethyl group, an ethyl group, a dimethyl group, an ethylenedioxy group, and the like.

As the “substituted aryl group”, for example, 2
Or 3-chlorophenyl group, 2,3-dichlorophenyl group, 2 or 3-bromophenyl group, 2,3-dibromophenyl group, 2 or 3-methylphenyl group, 2,3-dimethylphenyl group, 2 or 3-methoxy Phenyl group, 2,
Examples include a 3-dimethoxyphenyl group, a 3,4-methylenedioxyphenyl group, and a 2-methyl-3-chlorophenyl group. Among them, methyl group, methoxy group, 3,4-
An electron donating substituent such as a dimethoxy group and an ethyl group is preferred.

As the "lower alkyl group", there are 1 to 1 carbon atoms.
And 5 alkyl groups. Examples of the “alkyl group” include a methyl group, an ethyl group, a propyl group, a t-butyl group, an n-butyl group, a pentyl group and the like.

Note that R ¹ and R ² may be the same substituent or different substituents.

[0025] As the "optionally substituted aryl group" for R ³ include the same as R ¹ and R ^2. Among them, methoxy group, methyl group, ethoxy group,
An aryl group having a substituent such as an ethyl group is preferred.

The "optionally substituted alkyl group" for R ⁴ includes an alkyl group having 1 to 5 carbon atoms or an alkyl group having a substituent. As the “alkyl group”, for example, a methyl group, an ethyl group, a propyl group, a t
-Butyl group, n-butyl group and pentyl group.

Examples of the "substituted alkyl group" include a benzyl group, a phenethyl group, a 2-hydroxyethyl group and the like. Among them, a benzyl group and its electron-donating substituent are preferred.

As the "optionally substituted aryl group", those similar to R ¹ and R ² can be mentioned. Among them, a 3-methylphenyl group, a 4-methylphenyl group,
A 3,4-dimethoxyphenyl group and a 4-methyl-1-naphthyl group are preferred.

R ³ and R ⁴ may be connected to each other to form a ring together with the carbon atom to which they are bonded. Examples of the ring include a 5-membered ring and a 6-membered ring. In particular,

[0030]

Embedded image Is mentioned. Among them, the latter three are preferred because they are easily available as raw materials and the synthesis is relatively easy.

[0031] As the "optionally substituted alkyl group" and "optionally substituted aryl group" for R ⁵ include the same as R ^4. Among them, as the “optionally substituted alkyl group”, α, α, α-
Trifluoroethyl group, benzyl group, phenyl group, 2-
A methoxyethyl group is preferable, and as the “optionally substituted aryl group”, a 4-methylphenyl group, a 3,4-dimethoxyphenyl group, a 3,4-methylenedioxyphenyl group, a 4-methoxyphenyl group, a 4-phenyl -Phenyl groups are preferred.

The “lower alkyl group” and the “optionally substituted aryl group” in A ¹ and A ² include R ¹
And include the same R ^2. Among them, the "lower alkyl group" is preferably a methyl group, an ethyl group, or an n-propyl group, and the "optionally substituted aryl group" is preferably a 4-methylphenyl group or a phenyl group. Note that A ¹ and A ² may be the same or different.

A ¹ and A ² may be linked together to form a ring together with the carbon atom to which they are bonded.
Examples of the ring include phenylene, tolylene, naphthylene and the like. Further, this ring may have a substituent represented by (Y) m. Y is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a methylenedioxy group, and m is an integer of 1-4.

As the "lower alkyl group" for Y,
The same as R ¹ and R ² can be mentioned. Of these, a methyl group and an ethyl group are preferred. Examples of the “lower alkoxy group” include an alkoxy group having 1 to 5 carbon atoms, and specific examples include a methoxy group, an ethoxy group, a propoxy group, a t-butoxy group, an n-butoxy group, and a pentoxy group. Of these, a methoxy group and an ethoxy group are preferred. In the above, when m is 2 to 4, each Y may be the same or different.

Among the above compounds (I), those represented by the formula (IIa)

[0036]

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Wherein Y is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a methylenedioxy group, and m is an integer of 1-4, wherein m is 2-4.
In the formula, Y may be the same or different; Ar, R ¹ ,
R ³ , R ⁴ and X have the same meanings as in formula (I)) and formula (IIb)

[0038]

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(Wherein, Ar, R ¹ , R ² and X have the same meanings as in the formula (I), and Y and m have the same meanings as in the formula (IIa)).

Among the compounds of the general formula (I), Ar is an arylene group, A ¹ and A ² are an aryl group or a compound forming a benzene ring or a naphthalene ring by bonding to each other, and further R ³ and R ⁴ are In general, many compounds that are aryl groups have a high melting point and a high glass transition point, have a good transport efficiency, and are suitable as organic EL materials. On the other hand, as the transport material for electrophotography, A ¹ and A ² are preferably a hydrogen atom or a lower alkyl group.

Specific examples of the compounds of the general formulas (I), (IIa) and (IIb) are shown below.

[0042]

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[0043]

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[0044]

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[0045]

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[0046]

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[0047]

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[0048]

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[0049]

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[0050]

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Of the above compounds, particularly compounds 2 to 5,
7, 10 to 14, 18 to 22, 25, 29, 34 and 3
No. 9 is a compound excellent as a transport material for an organic electroluminescent device in terms of transport efficiency, thermal stability, and synthesis.

Next, a method for synthesizing the enamine group-containing hydrazone compound of the present invention will be described according to a generally known synthesis method.

[0053]

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(Wherein R ¹ , R ² , A ¹ , A ² , Ar and X
Has the same meaning as in formula (I). First, an aldehyde compound of the formula (III) [for example, a compound of the formula (II)
In I), R ₁ and R ₂ are hydrogen] or a ketone compound (eg, in the formula (II), R ₁ and R ₂ are an alkyl group or an aryl group) and a hydrazone compound of the formula (IV): Two
At a molar ratio of about 1: 3, an organic solvent (for example, alcohols such as isopropyl alcohol and ethanol, benzene,
The hydrazone compound of the formula (V) can be obtained by heating to reflux in an acidic atmosphere in ethyl acetate or the like).

Next, the obtained hydrazone compound (V)
And an aldehyde represented by the formula (VI):
Heat reflux in a molar ratio of about 5 in an aromatic organic solvent (benzene, toluene, etc.), optionally in the presence of a catalyst (nitric acid, p-toluenesulfonic acid, acetic acid, inorganic acid or organic acid such as titanium tetrachloride). Then, by removing water as a by-product out of the system, the hydrazone compound containing two enamine groups of the present invention can be easily obtained.

Since the hydrazone compound of the present invention often has poor solubility, it is difficult to perform recrystallization or column separation with a common organic solvent (eg, alcohol, ethyl acetate, toluene, etc.), and dimethylformamide, chloroform Recrystallization or reprecipitation using a solvent such as the above or a mixed solvent to which alcohol is added, and in some cases, purification by sublimation purification are appropriate. In particular, among the compounds shown in the above table, 10 to 14, 18 to 22, 25, 29 and 3
The compound of No. 4 can be produced, for example, from a known starting compound (available from Aldrich) by the above synthesis method.

The organic EL device of the present invention is mainly constituted by laminating an anode, a hole injection / transport layer, a light emitting layer and a cathode in this order. In addition, these anode-hole injection transport layer,
An intermediate layer such as an electron injection / transport layer, a charge blocking layer, and a buffer layer may be provided between the hole injection / transport layer and the light emitting layer, and between the light emitting layer and the cathode. When an electron injection / transport layer is provided between the light emitting layer and the cathode, a charge barrier layer may be further provided between the light emitting layer and the electron injection / transport layer. Above all,
An electron injection / transport layer is preferably formed between the light emitting layer and the cathode as a charge barrier layer facing the light emitting layer.

It is preferable that the organic EL element is supported on a substrate. The substrate is not particularly limited as long as it is generally used for an organic EL device, and examples thereof include a substrate made of glass, transparent plastic, and quartz. Further, a desired insulating layer, an element, a circuit, and the like, a desired insulating layer, and the like may be formed over these substrates. However, when the layer configuration is multi-layered, the organic EL
Since problems such as difficulty in controlling the production of the element also increase, it is preferable to make the element structure as simple as possible.

Examples of the anode in the present invention include a metal, an alloy, a conductive compound, a transparent conductive compound, and a mixture thereof having a large work function (4 eV or more) as an electrode material. Specific examples of such substances include A
and a transparent conductive compound such as CuI, SnO, and ZnO. Above all, it is common to take out light emission from the anode side, and thus a transparent conductive compound is preferable. The anode can be formed in a thin film shape by the above-mentioned metal or the like by a method such as vapor deposition or sputtering. The thickness of the anode varies depending on the electrode material used, for example, 10 to 10
About 200 nm is preferable.

The hole injection / transport layer according to the present invention has a function of transmitting holes injected from the anode to the light emitting layer described later. The hole injection transport layer may contain the compound represented by the above formula (I). These compounds have a good hole mobility of 10 ⁻⁶ cm ² / V · S or more, and have excellent thermal stability, low driving voltage, and non-crystalline properties. It is optimal as the main material of the hole injection transport layer.

The compound represented by the above formula (I) is
By optionally using it in combination with another transporting material, an organic EL element having higher luminance and lower driving voltage and higher luminous efficiency may be obtained in some cases. Examples of such a transport material include those conventionally known as a hole injection / transport compound of an organic optical semiconductor and those conventionally known as an organic EL.
It can be selected from those used as hole injection / transport compounds of the device and used.

For example, triazole derivatives (as described in US Pat. No. 3,112,197), oxadiazole derivatives (as described in US Pat. No. 3,189,447), imidazole derivatives (Described in JP-B-37-16095) and polyarylalkane derivatives (US Pat. No. 3,615,402).
No. 3,820,989, No. 3,54
2,544, JP-B-45-555, and JP-B-5-555.
1-110983, JP-A-51-93224, JP-A-55-17105, JP-A-56-4148, JP-A-55-108667, and JP-A-55-15695.
Nos. 3 and 56-36656).

Further, pyrazoline derivatives and pyrazolone derivatives (see US Pat. Nos. 3,180,729 and 4,180,729).
278,746, JP-A-55-88064, JP-A-55-88065, and 49-105537.
JP-A-55-51086 and JP-A-56-8005
Nos. 1, 56-88141, 57-455
No. 45, No. 54-112637, No. 55-7
No. 4546), phenylenediamine derivatives (U.S. Pat. No. 3,615,404, JP-B-51-10105, JP-B-46-3712, JP-A-47-25336), 1954-5343
No. 5, No. 54-110536, No. 54-11
No. 9925).

Further, arylamine derivatives (US Pat. Nos. 3,567,450 and 3,180,703)
No. 3,240,597, No. 3,655
8,520, 4,232,103,
4,175,961 and 4,012,376
No., JP-B-49-35702, JP-B-39-2
No. 7577, JP-A-55-144250, JP-A-56-119132, JP-A-56-22437, West German Patent No. 1,110,518, etc.), amine-substituted chalcone derivatives ( U.S. Patent No. 3,
526,501), oxazole derivatives (as described in U.S. Pat. No. 3,257,203), and styryl anthracene derivatives (as described in JP-A-56-46234). ).

Further, fluorenone derivatives (Japanese Patent Application Laid-Open No.
No. 110837), hydrazone derivatives (U.S. Pat. No. 3,717,462, JP-A-54-59143, JP-A-55-52063),
JP-A-55-52064, JP-A-55-46760, JP-A-55-85495, JP-A-57-11350, JP-A-57-148749, etc.), stilbene derivatives (Japanese Unexamined Patent Application Publication No. Sho 61) −21036
No. 3, No. 61-228451, No. 61-14
Nos. 642, 61-72255, 62-4
Nos. 7646, 62-36674, 62-
Nos. 10652, 62-30255, 60
-93445, 60-94462, 6
Nos. 0-174749 and 60-175052).

Further, a porphyrin compound (JP-A-63
No. 2,295,695) and aromatic tertiary amine compounds and styrylamine compounds (U.S. Pat. No. 4,127,412, JP-A-53-2703).
No. 3, No. 54-58445, No. 54-149
Nos. 634, 54-64299, 55-7
9450, 55-144250, 56
JP-119132, JP-A-61-295558,
Nos. 61-98353 and 63-295695) and the like. Among them, aromatic tertiary amine compounds are preferred.

When these transport materials are used in combination, the enamine group-containing hydrazone compound of the formula (I) of the present invention is used in an amount of 3 to 40 for both the hole and electron transport materials.
% Is preferable. Addition of a larger amount tends to cause a decrease in thermal stability and a decrease in transport efficiency.
%, The effect cannot be expected. Alternatively, the hole injection transport layer may be formed into two layers, and the above transport material may be used as one material.

The light emitting layer according to the present invention is composed of an organic compound having a light emitting property in a solid state. At least (1) holes can be injected from an anode or a hole injection layer when an electric field is applied, and a cathode or an electron can be injected. Injection performance that can inject electrons from the injection transport layer, (2) a transport function of moving injected charges (electrons or holes) by the force of an electric field, or (3) a field of recombination of electrons and holes. It has any one, and preferably all, of the light-emitting functions provided and connected to light emission.

The thickness of the light emitting layer is preferably a thin film having a thickness of about 5 nm to 5000 nm. Note that the light-emitting layer may have a difference between the ease with which holes are injected and the ease with which electrons are injected, and may have a large or small transport function represented by the mobility of electrons and holes. It is preferable that at least one of the charges can be moved.

In the above-described injection function, the ionization energy of the light emitting layer is preferably 6.0 eV or less from the viewpoint of relatively easy injection of holes if an appropriate anode material is selected, while the electron affinity is appropriate. If a suitable cathode material is selected, it is preferably 2.5 eV or more from the viewpoint that electrons can be relatively easily injected. Further, it is desirable that the solid-state fluorescence is strong for the light emitting function. This is because such a light-emitting layer has a large ability to convert an excited state, such as a compound forming the compound itself, an aggregate of the compound or a crystal, into light.

The organic compound constituting the light emitting layer is not particularly limited, and any one of known compounds can be used. For example, polycyclic fused aromatic compounds; fluorescent brighteners such as benzothiazole, benzimidazole, and benzoxazole; metal chelated oxinoid compounds; styryl compounds.

Examples of the polycyclic condensed compound include a condensed ring light emitting compound having an anthracene, naphthalene, phenathrene, pyrene, and perylene skeleton, and other condensed ring light emitting materials having eight condensed rings.

As the fluorescent whitening agent, for example, JP-A-59
No. 194393.

Examples of the metal chelated okinoid compound include those described in JP-A-63-295695.

As the styryl compound, for example, those described in JP-A-62-31356 or JP-A-63-80257 can be exemplified.

The light emitting layer may have a laminated structure of two or more layers. For example, U.S. Pat.
As described in No. 292, a laminated structure of a host substance and a fluorescent substance may be used. In this case, the host material is a thin film-like layer, which is responsible for part of the functions of the light emitting layer, such as the injection / transport function and the light emitting function. The fluorescent material is present in the host material layer in a small amount (several%). In addition, it has only a part of the light emitting function of emitting light in accordance with the combination of electrons and holes.

The method for thinning these organic light emitting materials is as follows.
For example, a spin coating method, a casting method, an LB method, an evaporation method and the like can be mentioned. Among them, the evaporation method is preferable from the viewpoint that a uniform film is easily obtained and a pinhole is hardly generated. When using the evaporation method, the evaporation conditions vary depending on the sublimation temperature of the organic material used for the light-emitting layer, the state of the target thin film, for example, selection of microcrystal or amorphous, crystallinity, crystal orientation, and the like. Temperature 50 to 500 ° C., degree of vacuum 10 ⁻⁵ to 10 ⁻³ Pa, deposition rate 0.01 to 50 nm / sec, substrate temperature −50 to +30
It is preferable to appropriately select the temperature within a range of 0 ° C. and a thickness of 5 nm to 500 nm.

As the cathode in the present invention, metals, alloys, conductive compounds, and the like having a small work function (about 4 eV or less) can be used.
Examples thereof include those using a transparent conductive compound and a mixture thereof as an electrode material. In general, it is preferable that one of the anode and the cathode is transparent or translucent because the efficiency of extracting light emission is high. Specific examples of such materials include sodium, sodium-potassium alloys, magnesium, lithium, magnesium / copper mixtures, At / A
tO ₂ , ytterbium, indium and the like. Further, the sheet resistance as an electrode is preferably several hundred Ω / □ or less, and the film thickness is usually 500 nm or less, preferably 10 nm or less.
It can be selected in the range of -200 nm. The above substance can be formed into a thin film by a method such as evaporation or sputtering.

In the present invention, the optional electron injecting and transporting layer is made of an electron transporting compound, and has a function of transmitting electrons injected from the cathode to the light emitting layer. The electron transfer compound is not particularly limited, and may be appropriately selected from known compounds. Such compounds include, for example,

[0080]

Embedded image Nitro-substituted fluorenone compounds such as

[0081]

Embedded image Thiovirane dioxide compounds such as

[0082]

Embedded image Diphenylquinone compounds [Polymer Preprints, Japan, Vol. 37, No. 3,
No., page 681 (1988)],

[0083]

Embedded image [Journal of Applied Physics, Vol. 27, L269 (198
8) and anthraquinodimethane derivatives (JP-A-57-149259, 58-554).
No. 50, No. 61-225151, No. 61-2
Nos. 33750 and 63-104061), and fluorenylidenemethane derivatives (those described in JP-A-60-69657, JP-A-61-143764, and JP-A-61-148159). ),
Anthrone derivatives (JP-A-61-225151,
No. 61-233750) and the like.

As the charge barrier layer facing the light emitting layer in the present invention, there are two types, a hole barrier layer and an electron barrier layer. The electron barrier layer is preferable because it is more efficient. The expression “formed so as to face the light emitting layer” means that in the case of an electron barrier layer, it is preferably provided between the light emitting layer and the hole injection / transport layer, preferably in contact with the anode side surface of the light emitting layer. In the case of a hole blocking layer, it is preferably provided between the light emitting layer and the cathode, preferably in contact with the cathode side surface of the light emitting layer. Specifically, (1) anode / hole injection / transport layer / electron barrier layer / emission layer / cathode (2) anode / emission layer / hole barrier layer / electron injection / transport layer / cathode (3) anode / hole Injection / transport layer / electron barrier layer / emission layer / hole barrier layer / electron injection / transport layer / cathode.

In the present invention, among the charge barrier layers that can be provided arbitrarily, the electron barrier layer has a role of retaining electrons that are going to the anode side from the light emitting layer in the light emitting layer. Preferably, the layer has an electron mobility lower than the electron mobility of the layer or a layer having an electron affinity lower than the electron affinity of the light emitting layer.

Such an electron barrier layer is a layer composed of a triphenyldiamine-based compound [“Applied Physics Letters (Appl, Phys, dett.)”, Vol. 51, No. 91).
3 (1987)], and a hole injection / transport layer of an aromatic tertiary amine compound (JP-A-59-194393 and JP-A-63-295695). These layers act as barriers by not transporting electrons.

Further, in the present invention, a-Si _1-x -C _x (0.4 <x <1, more preferably 0.4 <x <0.6) or a-Si _1-y −N _y
(0.4 <y <1, more preferably 0.4 <y <0.
6), wherein the value of x or y is determined so that the electron affinity of this layer is smaller than the electron affinity of the light-emitting layer, or the layer obtained by determining the range of manufacturing conditions is an electron barrier layer. Suitable as. Note that the inorganic amorphous material used for the electron barrier layer does not need to be a P-type semiconductor.

These electron barrier layers have ionization energies of (1) a value between the ionization energy of the hole injection / transport layer and the ionization energy of the light-emitting layer, and (2) a larger value than the ionization energy of the light-emitting layer. Values are classified into two types. In the (1) type electron barrier layer, the ionization energy increases in the order of anode / hole injection / transport layer / electron barrier layer / light-emitting layer, thereby facilitating hole injection. The hole mobility of the electron barrier layer is 10 ⁻⁶ cm.
It is preferably larger than ² / VS. In the (2) type electron barrier layer, it is necessary for holes to pass through by a tunnel effect.
It is preferably 0 nm or less.

On the other hand, the hole blocking layer has a role of retaining holes which are going to exit from the light emitting layer to the cathode side in the light emitting layer, and is usually provided so as to be in contact with the cathode side surface of the light emitting layer. Thereby, the luminous efficiency is improved. This hole barrier layer
It is preferable that the hole mobility of the layer is lower than that of the light-emitting layer or that the layer has lower ionization energy. In the present invention, as the hole barrier layer, the inorganic amorphous a-Si _{1- x} (0.4 <x <1)
The mold type is preferable because the hole mobility is small. The hole barrier layer made of such an inorganic amorphous material has, as its electron affinity, one having a value between (1) the electron affinity of the hole injection / transport layer and the light emitting layer, and (2) the electron affinity of the light emitting layer. They are categorized into two types with small values.
The (1) type and (2) type have substantially the same effects as those of the electron barrier layer.

The inorganic amorphous thin film can be formed by a known method,
For example, H ₂ , SiH ₄ , CH ₄ , C ₄
It can be made from a gas such as ₂ H ₆ or NH ₃ . For example a-SiC may be made of H _2, SiH _4, said method than CH ₄ gas. Moreover, a-SiC and a-
When controlling the electric conductivity by controlling valence electrons with Si or the like, a gas such as B ₂ H ₆ or PH ₃ is usually added to form a thin film, and B or B is added to the film of a-SiC or a-SiC. It can also be produced by doping P or the like.

Usually, the above SiH ₄ , CH ₄ , C ₂ H ₆ , N
The H ₃ gas is used in a state of being diluted to about 10% by hydrogen gas, and B ₂ H ₆ and PH ₃ are used in a state of being diluted to about 500 ppm, and the raw material gas mixture is passed through a mass flow controller. Adjust the mixing ratio, pressure, etc.
It is introduced into a CVD furnace. Thereafter, by applying energy such as high frequency, light, electric discharge and the like to decompose the gas in the furnace, a thin film can be formed on the substrate.

In the present invention, an optional buffer layer may be further provided. The buffer layer is a layer for the purpose of preventing the separation phenomenon and improving the injection efficiency of holes or electrons. These buffer layers are composed of various phthalocyanine pigments,
Various organic metal compounds (for example, trialkoxyaluminum, zinc stearate, aluminum triacetylacetone, magnesium diacetylacetone), carbon black, and the like. The position where the buffer layer is provided is not particularly limited. For example, in the case of the configuration (1), in which peeling is particularly likely to occur, between the anode and the hole injection / transport layer, between the light emitting layer and the cathode, In the case of the configuration (2), between the anode and the light emitting layer, between the electron donor injection layer and the cathode, and in the case of the configuration (3), between the anode and the hole injection and transport layer, It is effective to provide between the injection transport layer and the cathode. The thickness of the buffer layer varies depending on where it is provided, but is preferably, for example, about 10 to 500 nm.

The organic EL of the present invention thus obtained
When a DC voltage is applied to the device, when a voltage of about 1 to 30 V is applied with a positive polarity of the anode and a negative polarity of the cathode, light emission can be observed from the transparent or translucent electrode side. Note that no light emission occurs even when a voltage is applied with the opposite polarity. When an AC voltage is applied, light is emitted when the anode is in the positive state and the cathode is in the negative state. The waveform of the applied AC voltage may be arbitrary.

[0094]

EXAMPLES The following examples illustrate the synthesis of an enamine group-containing hydrazone compound of the present invention and an organic electroluminescent device.

Synthesis Example 1 (Synthesis of Exemplified Compound 11) 6.7 g of terephthalaldehyde and 16.5 g of 2-hydrazinobenzoxazole are dissolved in 100 ml of ethanol, and 2 drops of glacial acetic acid are added. Then, the mixture was heated and refluxed for about 2 hours in a water bath, whereby the precipitated yellow-white powder 14.3 was obtained.
g. From the IR measurement, the absorption of the aldehyde compound at 1690 cm ^-1 had disappeared.

Next, the terephthalaldehyde-di- (2-benzoxazole hydrazone) thus obtained is obtained.
4.0 g and 6.5 g of diphenylacetaldehyde are dissolved in 150 ml of benzene, a small amount of p-toluenesulfonic acid is added, and the mixture is heated under reflux. When the generated water is taken out of the reaction system by azeotropic distillation and the remaining reaction solution is left at room temperature, a yellowish white powder is precipitated. This was dissolved in chloroform to remove insolubles, and recrystallized by adding a small amount of alcohol to obtain 6.8 g of a yellowish white powder. Melting point: 245 to 247 ° C. A peak was observed at MS: 752 (M ⁺ ) by mass spectrometry.

Example 1 (In the case of using a hydrazone compound as a hole injecting / transporting material) As shown in FIG. 1, a glass substrate (25 mm) provided with a 100 nm-thick ITO transparent electrode as the anode 2 was used.
× 75 mm × 1.1 mm (manufactured by HOYA) 1 was used as a transparent support substrate, which was subjected to ultrasonic cleaning with isopropyl alcohol for 30 minutes and further immersed for cleaning. The transparent support substrate was dried with dry nitrogen gas and fixed to a substrate holder of a commercially available vacuum vapor deposition device.

On the other hand, a hydrazone compound of the present invention (exemplified compound No. 7) was placed in a molybdenum resistance heating boat for 200 m.
g, 200 mg of the following 4,4′-bis (2,2-diphenylvinyl) biphenyl (BDVB) is placed in another molybdenum resistance heating boat, and bis [( 200 mg of 2-methyl-8-quinolinolate), (2-naphtholate)] aluminum complex was placed in a vacuum evaporation apparatus.

[0099]

Embedded image

First, after reducing the pressure of the vacuum layer to 4 × 10 ⁻⁴ Pa, the heating boat containing Exemplified Compound No. 7 (melting point: 245 to 247.5 ° C.) was energized and heated to 280 ° C. The hole injecting and transporting layer 3 having a thickness of 60 nm was formed by vapor deposition on the transparent supporting substrate at a rate of 0.1 to 0.3 nm / sec.

Next, the heating boat containing the BDVB was energized and heated to 240 ° C.
The light emitting layer 4 having a thickness of 40 nm was deposited on the hole injecting and transporting layer 3 at a rate of 0.3 nm / sec.

Further, the heating boat containing the compound obtained from the above aluminum complex was energized and heated to 314 ° C., and was vapor-deposited on the light-emitting layer 4 at a vapor deposition rate of 0.1 nm / sec. An electron injection transport layer 5 of 20 nm was provided.
In addition, the substrate temperature at the time of vapor deposition was room temperature. Next, a vacuum layer was opened and a stainless steel mask was placed on the electron injection / transport layer 5, while 3 g of magnesium was placed in a molybdenum resistance heating boat, and 0.5 g of silver was placed in a tungsten deposition basket. After the pressure in the vacuum chamber was reduced again to 2 × 10 ⁻⁴ Pa, the boat containing magnesium was energized to deposit magnesium at a deposition rate of 1.5 to 2.0 nm / sec. Speed 0.1n
Silver was vapor-deposited at a rate of m / sec to form a counter electrode serving as a cathode 6 made of a mixture of magnesium and silver, thereby producing a target organic EL device. When a direct current of 11 volts was applied to the ITO electrode of this device as the anode 2 and the counter electrode made of a mixture of magnesium and silver as the cathode 6, a current having a current density of 5.8 mA / cm ² flowed and a blue color (chromaticity coordinates) was obtained. : 0.18, 0.20) were obtained.

The maximum wavelength of this light emission was 468 nm, the luminance was 215 cd / m ² , and the light emission efficiency was 0.48 lumen / W. Even after 100 hours from the energization under an argon gas flow, there was no peeling or clouding of the electrode surface, and blue light emission was still observed.

Examples 2 to 7 Example 1 was repeated except that Exemplified Compound No. 7 was used instead of Exemplified Compound No. 7 as a hole injecting and transporting layer, and that the heating temperature during vapor deposition was changed as shown in Table 1. A device was prepared and evaluated in the same manner as described above. Table 1 shows the obtained results.

[0105]

[Table 1]

Example 8 (When a hydrazone compound is used as an electron injecting / transporting material) Using the transparent support substrate prepared in Example 1, an aromatic diamino compound represented by the following structural formula and an aromatic diamino compound used in Example 1 were used. B
Each DVB was placed in another molybdenum resistance heating boat and attached to a vacuum evaporation apparatus. BDVB was laminated on the hole injection transport layer shown below in the same manner as in Example 1, then Exemplified Compound No. 11 of the present invention was laminated, and finally a counter electrode composed of a mixture of magnesium and silver was laminated. A layer type organic EL device was prepared.

[0107]

Embedded image

The thicknesses of the hole injection transport layer, the light emitting layer and the electron injection transport layer were 40 nm, 45 nm and 40 nm, respectively. As for the characteristics, the light emission luminance showed a large value of 2800 cd / m ² , and the light emission inactivation was stable even for 200 hours or more. In addition, other characteristics such as applied voltage hardly decreased. Thus, it can be seen that the hydrazone compound of the present invention provides excellent EL characteristics even as an electron transport material.

Example 9 (In the case of using a hydrazone compound as a hole injecting and transporting material and providing an electron barrier layer) In Example 1, a hole injecting and transporting layer (exemplified compound No. 7)
By diluting SiH ₄ and CH ₄ into 10% hydrogen gas, respectively, and further introducing B ₂ H ₆ diluted to 5 × 10 ³ ppm into the chamber through the master flow controller between the and the light emitting layer, RF A P-type a-SiC layer as an electron barrier layer was formed with a plasma output of 40 W. At this time, the thickness of the electron barrier layer was 10 nm. When a DC voltage of 11 V was applied to the EL device in the same manner as in Example 1, a current having a current density of 5.3 mA / cm ² flowed, and blue-green color was obtained. The maximum wavelength of this light emission was 518 nm, the luminance was 1020 cd / m ^{2, and the} light emission efficiency was 1.8 lumen / W. From these results, high luminance and high efficiency were achieved by stacking the electron barrier layers.

Example 10: (When a hydrazone compound is used as an electron injecting and transporting material and an electron barrier layer is provided) In Example 7, an electron injecting and transporting layer (Exemplary Compound No. 11)
Each gas is continuously introduced by a mass flow controller at a flow ratio of NH ₃ / SiH ₄ = 5 between the gas and the light emitting layer, and the pressure is 0.3.
An a-SiN film having a thickness of 10 nm was formed under the conditions of Torr, RF output of 15 W, and substrate temperature of 250 ° C. When a DC voltage of 7.5 V was applied to this device, the same luminous efficiency and luminance as in Example 7 were obtained.

According to the enamine group-containing hydrazone compound of the present invention, it has excellent hole transporting and electron transporting properties, so that it has excellent close contact with the electrode, high brightness, high luminous efficiency, An organic EL device having a long life characteristic can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of the organic electroluminescent device of the present invention. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 ITO electrode 3 Hole injection / transport layer 4 Light emitting layer electrode 5 Electron injection / transport layer 6 Cathode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09K 11/06 650 C09K 11/06 650 655 655 H05B 33/14 H05B 33/14 A 33/22 33/22 D B

Claims (7)

[Claims] 1. A compound of the formula (I) (Wherein, Ar is — (CH ₂ ) _n —, an optionally substituted arylene group, R ¹ and R ² are the same or different and are a hydrogen atom, an optionally substituted aryl group or a lower alkyl group; , R ³ is an optionally substituted aryl group,
R ⁴ is a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group, or R ³ and R ⁴ are connected to each other to form a ring together with the carbon atom to which they are bonded; X is an oxygen atom, a sulfur atom, or -NR ^5- (where R ⁵ is a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group), A ¹ and A ² are The same or different, a hydrogen atom, a lower alkyl group, an aryl group which may be substituted, or A ¹ and A ² may be connected to each other to form a ring together with the carbon atom to which they are bonded, n is an integer of 0 to 4). 2. The compound according to claim 1, wherein both or one of A ¹ and A ^{2 in} the formula (I) is an optionally substituted aryl group. 3. A ¹ and A ² are connected to each other to form a phenylene group together with the carbon atom to which they are bonded (the phenylene group may be substituted, and the substituent is represented by (Y) m:
Y is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a methylenedioxy group, m is an integer of 1-4, provided that when m is 2-4, m may be the same or different ), The following sub-formula (IIa): (Wherein Ar, R ¹ , R ³ , R ⁴ and X have the same meanings as in the formula (I)). 4. A ¹ and A ² are linked to each other to form a phenylene group together with the carbon atom to which they are bonded (the phenylene group may be substituted, and the substituent is represented by (Y) m:
Y is a hydrogen atom, a halogen atom, a lower alkyl group, a lower alkoxy group or a methylenedioxy group, m is an integer of 1-4, provided that when m is 2-4, m may be the same or different ), R ³ and R ⁴ are linked together with the carbon atom to which they are attached To form the following sub-formula (IIb): (Wherein, Ar, R ¹ , R ² and X have the same meanings as in formula (I))
The compound according to claim 1, which is represented by the formula: 5. An anode, a hole injecting and transporting layer, a light emitting layer and a cathode are laminated in this order, wherein the hole injecting and transporting layer contains an enamine group-containing hydrazone compound represented by the formula (I). An organic electroluminescent device comprising: 6. An anode, a hole injecting and transporting layer, a light emitting layer, an electron injecting and transporting layer, and a cathode are laminated in this order, wherein the hole injecting and transporting layer or the electron injecting and transporting layer is represented by the formula (I). An organic electroluminescent device comprising an enamine group-containing hydrazone compound. 7. The organic electroluminescent device according to claim 5, wherein an electron barrier layer is provided facing the light emitting layer.