JP3099468B2 - Organic electroluminescence device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device (hereinafter referred to as an organic EL device). For more information,
The present invention relates to an organic EL device using a benzene derivative having four vinylene groups as a light emitting material.

[0002]

2. Description of the Related Art Inorganic electroluminescent devices (hereinafter, inorganic EL devices) using an inorganic phosphor as a light emitting material.
Are used in, for example, a planar light source as a backlight or a display device such as a flat panel display, but a high voltage AC is required to emit light.

Recently, Tang et al. Have a two-layer organic EL layer in which an organic fluorescent dye is used as a light-emitting layer, and an organic hole transport compound used for an electrophotographic photoreceptor is laminated.
Organic EL with low voltage drive, high efficiency and high brightness
The device was realized (Japanese Patent Laid-Open No. 59-194393). Compared to inorganic EL devices, organic EL devices have the characteristics that they can easily emit light of many colors in addition to low voltage driving and high brightness. Attempts have been reported [Japanese Journal of Applied Physics (Jpn. J. Appl. Phys.) 27: L269 (1988
Year)], [Journal of Applied Physics (J. Appl. Phys.) Vol. 65, p. 3610 (1989)].

[0004]

The organic EL devices reported so far have high luminance, but have a problem that the life of the light emitting device is short. It is said that the heat generation of the element causes a structural change in the light emitting layer and causes deterioration. Therefore, a light-emitting material constituting a thermally stable light-emitting layer has been demanded.

[0005]

Means for Solving the Problems The present inventors have proposed an organic EL device.
As a result of intensive studies on the light-emitting material of the device, a uniform light-emitting layer was formed by using a compound containing four vinylene groups among aromatic vinylene compounds having a benzene ring as a skeleton as a light-emitting compound, The present inventors have found that an organic EL device that emits light uniformly can be obtained, and have reached the present invention.
That is, the present invention relates to an organic electroluminescent device having at least one light-emitting layer between a pair of transparent or translucent electrodes, wherein the light-emitting layer is

[0006]

Embedded image [In the formula, A ₁ , A ₂ , A ₃ , and A ₄ each independently represent a group selected from the following chemical formulas 5 and 6.

[0007]

Embedded image as well as

[0008]

Embedded image (R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ ,
R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ each independently represent hydrogen, an alkyl group or an alkoxy group having 1 to 12 carbon atoms, an aryl group or an aryloxy group having 6 to 14 carbon atoms, and a nitro group. , A heterocyclic compound group. It is an object of the present invention to provide an organic electroluminescence device comprising at least one aromatic compound selected from the compounds represented by the formula (1). Less than,
The organic EL device of the present invention will be described in detail.

The luminescent material used in the present invention is an aromatic compound represented by the formula (4), wherein A ₁ , A ₂ ,
A ₃ and A ₄ are a phenyl group, a naphthyl group,
Derivatives in which an anthryl group, a pyridyl group, a thienyl group, or an alkyl or alkoxy group having 1 to 12 carbon atoms, an aryl or aryloxy group having 6 to 14 carbon atoms, a nitro group or a heterocyclic compound group are substituted with nuclei. . Among these, a phenyl group, a pyridyl group, and their derivatives having good film formability are preferable. Here, examples of the alkyl group having 1 to 12 carbon atoms include methyl, ethyl, butyl, and octyl, and methyl and ethyl are preferable. Alternatively, the alkoxy group having 1 to 12 carbon atoms includes methoxy, ethoxy, butoxy, heptyloxy and the like, and methoxy and ethoxy are preferred. Examples of the aryl group include a phenyl group, a 4-methylphenyl group, a 4-ethylphenyl group, a 4-propylphenyl group, a 4-butylphenyl group, a 4-pentylphenyl group, a 4-hexylphenyl group, a 1-naphthalene group, Examples of the naphthalene group and the aryloxy group include a 4-methoxyphenyl group, a 4-ethoxyphenyl group, a 4-propoxyphenyl group, a 4-butoxyphenyl group, a 4-pentyloxyphenyl group, a 4-hexyloxyphenyl group, and a phenoxy group. Is done. Examples of the heterocyclic compound group include a thienyl group, a pyridin-2-yl group, a pyridin-3-yl group, and a pyridin-4-yl group.

[0010] Specific compounds 1,2,4,5-tetrakis (Fenirue Te) benzene, 1,2,4,
5- tetrakis (2'Pirijirue Te) benzene,
1,2,4,5-tetrakis (p-methoxyphenyle
Te) benzene, 1,2,4,5-tetrakis (2,
5-dimethoxyphenyl d Te) benzene, 1,2,
4,5-tetrakis (Nafuchirue Te) benzene,
1,2,4,5-tetrakis (Antoranirue Te nil)
Benzene, 1,2,4,5-tetrakis (Chienirue Te <br/> sulfonyl) the like benzene, 1,2,4,5
Tetrakis (Fenirue Te) benzene, 1,2,
4,5-tetrakis (p- methoxyphenyl d Te sulfonyl)
Benzene, 1,2,4,5-tetrakis (2,5-dimethoxyphenyl d Te) benzene fluorescence intensity, from the viewpoint of film forming property.

The aromatic compound represented by the above formula (4) is a benzene derivative, and its synthesis method is not particularly limited. Generally, a reaction for forming a carbon-carbon double bond is used, and a Wittig reaction, Examples thereof include a sulfonium salt decomposition method and a dehydrohalogenation method. Specifically, for example, the compound is synthesized by reacting 1,2,4,5-tetrakis (bromomethyl) benzene with triphenylphosphine to form a phosphonium salt, and then reacting the corresponding aldehyde (Wittig reaction). When these compounds are used as a light-emitting layer of an organic EL device, it is desirable to purify such as reprecipitation purification, sublimation purification, etc. after synthesis since the purity affects the light emission characteristics.

The light-emitting layer containing an aromatic compound represented by the above formula (4) can be formed by a vacuum evaporation method or a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method, or the like. And can be formed by a known method. In the case where the film is formed into a thin film by a coating method, the solvent is removed under reduced pressure or an inert atmosphere at 30 to 200 ° C., preferably 60 to 200 ° C.
It is desirable to heat-treat at a temperature of 100 ° C. It is preferable to use a vacuum deposition method in that fine control of the film thickness is performed.

The present invention also includes the use of a layer in which the above-mentioned aromatic compound and a known polymer compound are mixed as the light-emitting layer. In this case, the polymer compound used is not particularly limited, but is preferably one that does not extremely impair the charge transporting property and the light emitting property. For example, poly (N-vinyl carbazole), polyaniline and its derivatives, polythiophene and its derivatives, poly (P-phenylenevinylene) and its derivatives, poly (2,5-thienylenevinylene) and its derivatives, polycarbonate, polysiloxane, and vinyl polymers such as polymethyl acrylate, polymethyl methacrylate, polystyrene, and polyvinyl chloride Is exemplified. Here, poly (N-
Vinylcarbazole), polyaniline and its derivatives,
Polythiophene and its derivatives, poly (p-phenylenevinylene) and its derivatives, poly (2,5-thienylenevinylene) and its derivatives also have an action as a charge transporting compound described below.

The mixed layer of the aromatic compound and the high molecular compound is formed by mixing the high molecular compound and the aromatic compound in a solution state or a molten state, dispersing the aromatic compound, You can use the law. In this case, the amount of the aromatic compound dispersed in the polymer is not particularly limited.
Parts by weight, preferably 20 to 70 parts by weight.

When precursor polymers such as poly (p-phenylenevinylene) and its derivatives and poly (2,5-thienylenevinylene) and its derivatives are used, they are mixed with the aromatic amine compound in a solution state, Under an active atmosphere,
Heat treatment is performed at a temperature of 30 to 200 ° C., preferably 60 to 100 ° C., to convert the polymer into a target polymer.

In the present invention, a charge transporting layer is provided between the light emitting layer and one of the electrodes (the charge transporting layer in the present invention means a hole transporting layer and an electron transporting layer unless otherwise specified). It may be provided. The charge transporting material (generic term for the hole transporting material and the electron transporting material) used at this time is not particularly limited, and examples thereof include a triphenyldiamine derivative, an oxadiazole derivative, a pyrazoline derivative, an arylamine derivative, a stilbene derivative, and an anthracene derivative. A quinodimethane derivative or the like can be used. In particular,
For example, JP-A-2-209988 and JP-A-3-3799
Known ones such as those described in JP-A No. 2 can be used. Among them, one or both of the electron transporting compound and the hole transporting compound may be used simultaneously. The thickness of the charge transport layer varies depending on the type of the compound used and the like, and thus may be appropriately determined in consideration of a sufficient range in which the film formability and the light emission characteristics are not impaired.

These charge transporting materials can be formed into compounds by a known method, for example, a vacuum evaporation method, or a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method or the like of a solution of the charge transporting material. The charge transport layer can be formed by appropriately adopting the method. When the charge transporting material is not a polymer compound, it is preferable to use a vacuum deposition method in that fine control of the film thickness is performed.

In the present invention, the light emitting layer further comprises:
It is also possible to use a mixture of the aromatic compound as the light emitting material and the charge transporting material, or to use the mixture as a layer dispersed in a known polymer compound as a medium. . The mixing ratio between the light emitting material and the charge transport material is not particularly limited, but is preferably 0.1:
The ratio is in the range of 100 to 1: 1 (weight), and the ratio of the sum of the polymer compound and these materials is not particularly limited, but is preferably in the range of 100: 0.01 to 1: 3 (weight).
In this case, as the polymer compound to be used, those described above which do not strongly absorb visible light are preferably used. Specifically, poly (N-vinylcarbazole), polythiophene and its derivatives, poly (p-phenylenevinylene) and its derivatives, poly (2,5-thienylenevinylene) and its derivatives, polycarbonate, polymethyl acrylate, polymethyl Examples thereof include methacrylate, polystyrene, polyvinyl chloride, and polysiloxane. The formation of the mixed layer can employ the same method as described above. In addition, these layers can be used alone, but another layer of a charge transporting material may be provided as necessary.

The structure of the organic EL device of the present invention will be described below. The structure of the element itself can be a known structure. For example, the anode / charge (hole) transport layer / light-emitting layer / cathode (/ indicates that the layers are stacked) or the anode / charge (hole or electron) transport / emission (charge transport material and In addition to the luminescent material and mixture) layer / cathode structure,
A combination structure having a conductive polymer layer between an anode and a charge (hole) transport layer can be employed, and a combination structure having a charge (electron) transport layer between a light emitting layer and a cathode can be employed. Can also be taken. Furthermore, anode / conductive polymer /
It may have a structure of a charge (hole) transport layer / a light emitting layer / a charge (electron) transport layer / a cathode.

Hereinafter, the production of an organic EL device will be described.
The fabrication method will be described below with an example of a charge (hole) transport layer / light-emitting layer / cathode structure. Transparent out of a pair of electrodes,
Alternatively, as the translucent electrode, a transparent or translucent electrode is formed on a transparent substrate such as glass or transparent plastic.
This is used as the anode. As a material of the electrode, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, indium tin oxide (ITO), tin oxide (NESA), Au, Pt, Ag, Cu and the like are used. As a manufacturing method, a vacuum evaporation method, a sputtering method, a plating method, or the like is used.

Next, the above-mentioned charge transport layer is provided, and the thickness is 5 to 10 μm, preferably 10 to 1 μm. In order to increase the light emission luminance by increasing the current density, 20
A range of up to 5000 ° is preferred.

Next, a light emitting layer is provided on the charge transport layer.
The thickness of the light-emitting layer is required to be at least such that pinholes do not occur. However, if the thickness is too large, the resistance of the element increases, and a high driving voltage is required, which is not preferable. Therefore, the thickness of the light emitting layer is 5 to 10 μm, preferably 10 to 10 μm.
Å-1 μm, more preferably 50-2000Å. This range is also preferable in the case of a mixed layer of a charge transport material and a light emitting material.

Next, an electrode is provided on the light emitting layer. This electrode becomes an electron injection cathode. The material is not particularly limited, but a material having a small ionization energy is preferable. For example, Al, In, Mg, Mg-Ag alloy, M
A g-In alloy, a graphite thin film or the like is used. As a method for producing the cathode, a known vacuum deposition method, sputtering method, or the like is used.

Although the organic EL device of the present invention can be manufactured as described above, a device having another structure can be manufactured by the same method.

[0025]

The benzene derivative having four vinylene groups used as a light emitting material in the present invention has a π-conjugated system extended to the four vinylene groups, and even if one or two of the substituents are modified for some reason. The molecule is considered to be thermally stable because of its ability as a light emitting material and its relatively high melting point and decomposition temperature.

[0026]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples.

[0027] Reference Example 1 (1,2,4,5-tetrakis (p- Synthesis methoxyphenyl d Te) benzene) 1,2,4,5 tetrakis (bromomethyl) benzene and triphenylphosphine N, N -Reaction was carried out at 150 ° C for 3 hours in dimethylformamide (DMF). The reaction solution was cooled to room temperature, and the resulting precipitate was filtered and filtered.
After washing with MF, it was dried under reduced pressure to obtain a phosphonium salt. This phosphonium salt and p-methoxybenzaldehyde were dissolved in ethanol, and an ethanol solution of lithium ethoxide was added dropwise at room temperature. After the dropwise addition, the mixture was further stirred for 1 hour and reacted (Wittig reaction ). The resulting precipitate was filtered, successively ethanol, washed with ethanol / water ,, ethanol, dried under reduced pressure to 1,2,4,5-tetrakis (p- methoxyphenyl d Te sulfonyl) give benzene.

[0028] In Reference Example 2 (1,2,4,5-tetrakis (Fenirue Te yl) Synthesis of benzene) p-methoxybenzaldehyde, except that the reaction was carried out using benzaldehyde in place of Reference Example 1 and the same methods 1,2,4,5-tetrakis (Fenirue Te nil)
Benzene was synthesized.

[0029] A reaction is conducted by using Reference Example 3 (1,2,4,5-tetrakis (2,5-dimethoxyphenyl d Te yl) Synthesis of benzene) p-2,5-dimethoxybenzaldehyde instead of methoxybenzaldehyde other than the was synthesized 1,2,4,5-tetrakis (2,5-dimethoxyphenyl d Te) benzene in the same manner as in reference example 1.

Example 1 A glass substrate provided with an ITO film having a thickness of 200 ° by sputtering was charged with 4,4′-bis (3-methyl-diphenylamino) biphenyl (hereinafter referred to as TPD) 3 × as a charge (hole) transport layer. 1 by evaporation under a vacuum of 10 ^-6 Torr
A film was formed with a thickness of 000 mm. Then the upper synthesized in Reference Example 1 as a light-emitting layer 1,2,4,5-tetrakis (p- methoxyphenyl d Te) benzene 600
{Circle around (2)}, and indium as a cathode was vapor-deposited at 6000 mm to form an organic EL device. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 20 V was applied to this element, the current density was 16.8 mA / c
A current of m ² flowed and uniform blue-white EL emission with a luminance of 0.011 cd / m ² was observed. Brightness was proportional to current density.

Example 2 On a glass substrate provided with an ITO film having a thickness of 200 ° by sputtering, 3,4′-bis (3-methyl-diphenylamino) biphenyl (hereinafter referred to as TPD) was used as a charge (hole) transporting layer at 3 ×. 1 by evaporation under a vacuum of 10 ^-6 Torr
A film was formed with a thickness of 000 mm. Then, thereon 1000Å the synthesized 1,2,4,5-tetrakis (Fenirue Te) benzene in Reference Example 2 as a light emitting layer, further an organic E and indium was 6000Å deposited as a cathode thereon
An L element was produced. The degree of vacuum at the time of vapor deposition is all 3 × 1
0 ^-6 Torr or less. When a voltage of 18 V was applied to this device, a current having a current density of 156 mA / cm ² flowed and uniform blue-white EL light emission with a luminance of 0.692 cd / m ² was observed. Brightness was proportional to current density.

Example 3 A 200% charge (holes) was obtained by spin-coating a 0.1% solution of polyaniline in N-methylpyrrolidone on a glass substrate having an ITO film having a thickness of 200 ° by sputtering and then drying. A transport layer was prepared. Next, on top of this, 1,2,2 synthesized in Reference Example 3 as a light emitting layer
4,5-tetrakis (2,5-dimethoxyphenyl et te <br/> sulfonyl) 1000 Å benzene, to produce an organic EL device was further 6000Å depositing indium as a cathode thereon. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 16 V was applied to this element,
A current with a current density of 119 mA / cm ² flows, and a luminance of 3 cd
/ M ^2, a blue-white uniform EL emission was observed. Brightness was proportional to current density.

[0033]

The organic EL element using the light emitting material of the present invention exhibits excellent light emission characteristics such as uniformity and stability of light emission, and is suitable for a planar light source as a backlight and a display device such as a flat panel display. Can be used.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-296595 (JP, A) JP-A-59-194393 (JP, A) JP-A-5-178842 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) C09K 11/06 CA (STN) REGISTRY (STN)

Claims (7)

(57) [Claims] 1. An organic electroluminescent device having at least one light-emitting layer between a pair of transparent or translucent electrodes, wherein the light-emitting layer is represented by the following formula: [In the formula, A ₁ , A ₂ , A ₃ , and A ₄ each independently represent a group selected from the following chemical formulas 2 and 3. Embedded image And (R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R ₉ , R
₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄ each independently represent hydrogen, an alkyl or alkoxy group having 1 to 12 carbon atoms, an aryl or aryloxy group having 6 to 14 carbon atoms, a nitro group, a heterocyclic compound It means a group represented by a group. An organic electroluminescent device comprising at least one aromatic compound selected from the compounds represented by the formula (1): 2. A light-emitting layer comprising the aromatic compound and a charge transport material.
2. The organic electric device according to claim 1, further comprising:
Troll luminescence element. 3. The method according to claim 1, wherein the light emitting layer comprises the aromatic compound and a charge transport material.
Characterized in that it is a layer in which is dispersed in a polymer compound
The organic electroluminescence according to claim 1 or 2.
element. 4. The method according to claim 1 , wherein the light emitting layer is disposed between the cathode and the light emitting layer.
3. An electron transport layer according to claim 1, wherein
Or the organic electroluminescent device according to 3. 5. A light emitting device, comprising: a light emitting layer between an anode and a light emitting layer;
And a hole transporting layer is provided.
Or the organic electroluminescent device according to 3. 6. A light emitting device, comprising:
The electron transporting layer, and the light emitting layer between the anode and the light emitting layer.
A hole transport layer is provided adjacent to the substrate.
Organic electroluminescent element according to 1, 2, or 3
Child. 7. A conductive polymer is provided between the anode and the hole transport layer.
7. The method according to claim 5, wherein a layer is provided.
Electroluminescent element.