JP3237282B2 - 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 sometimes referred to as an organic EL device). Specifically, the present invention relates to an organic EL device using a viologen-based compound having an aromatic ring in the center of a molecule.

[0002]

2. Description of the Related Art An inorganic electroluminescent element (hereinafter sometimes referred to as an inorganic EL element) using an inorganic phosphor as a light-emitting material is used, for example, in a planar light source as a backlight or a display device such as a flat panel display. However, a high-voltage alternating current was required to emit light.

[0003] Tang et al. Use an organic fluorescent dye as a light emitting layer,
An organic EL device having a two-layer structure is fabricated by laminating this and an organic hole transporting compound used for an electrophotographic photoreceptor and the like, and an organic EL device with low voltage drive, high efficiency, and high brightness is realized. (JP-A-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 (JP
n. J. Appl. Phys.) 27, L269 (1988), Journal of Applied Physics (J. Appl.
ys.) 65, 3610 (1989)]. In addition, oxidation-reduction properties of a viologen compound having an aromatic ring,
It has been reported that cations generated by oxidation show strong fluorescence [Journal of Chemical Society Chemical Communications (J. Che)
m. Soc., Chem. Commun.), No. 8, p. 620 (199)
2 years)]. However, there is no description about the electroluminescence of the viologen-based compound or the transfer of injected charge in the solid-state device.

[0004]

Although the organic EL devices which have been reported to date have high brightness, many of them emit green or red light, and light emission used for the organic EL device which emits blue light for full colorization. Materials were sought. In addition, combinations of light emitting materials and charge transport materials are limited, and new charge transport materials have 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 viologen-based compound having an aromatic ring in the center of the molecule is used not only as a light-emitting material, but also as a charge-transporting material. The material also functions as a material and an electron transporting material. In addition, the uniform light emitting layer or the charge transporting layer (hereinafter, the charge transporting layer means a hole transporting layer and an electron transporting layer unless otherwise specified. ) Can be formed and emits light uniformly
The inventors have found that an element can be obtained, and have reached the present invention.

That is, the present invention comprises the following inventions. (1) An organic electroluminescence device having at least one organic material layer between a pair of electrodes, at least one of which is transparent or translucent, wherein the organic material layer is

Embedded image(Where Ar is an aromatic hydrocarbon group having 6 to 18 carbon atoms or
A heteroaromatic group having 4 to 14 carbon atoms, X^-Indicates a counter anion
You. Also, R₁, R_Two, R_Three, R_Four, R_Five, R ₆,
R₇, R₈, R₉, R_TenAre each independently hydrogen or
And represents an alkyl group having 1 to 20 carbon atoms. Compound represented by)
At least one viologen system selected from products
Organic electroluminescence characterized by containing a compound
Sense element. (2) The organic layer containing the viologen compound is a light emitting layer
The organic electroluminescent device according to (1), wherein
Luminescence element. (3) The organic layer containing the viologen-based compound is
(1) characterized in that it is laminated with an optical layer.
Electroluminescent element.

Hereinafter, the organic EL device of the present invention will be described in detail. In the organic EL device of the present invention,
Can be used both as a light emitting material and a charge transport material. The viologen-based compound is a viologen-based compound having an aromatic ring at the center of the molecule represented by Chemical Formula 2. Here, as the aromatic hydrocarbon group having 6 to 18 carbon atoms, 1,4-phenylene group, 2,5-dimethylphenylene group, 2,5-diethylphenylene group, 1,5-naphthylene group, 2,6-
Examples include a naphthylene group and a 1,4-naphthylene group. As the heteroaromatic group having 4 to 14 carbon atoms, 2,5-thienylene group, 2,5-furylene group, thieno [3,2-
b] thienylene group and the like. X ⁻ is Cl ⁻ , Br ⁻ , I ⁻ , F ⁻ , BF ₄ ⁻ , ClO ₄
^And p-toluenesulfonic acid ions.
Among them, Ar is 1,4-phenylene group, 2,
5-thienylene group, 2,5-furylene group, thieno [3,
2-b] a thienylene group is preferred. Further, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ , R ₈ , R
₉ and R ₁₀ are groups selected from hydrogen and an alkyl group having 1 to 20 carbon atoms as described above. Here, carbon number 1-2
Examples of the 0 alkyl group include a methyl group, an ethyl group, a butyl group, and an octyl group. Among them, preferred are hydrogen, methyl group and ethyl group, and more preferred are hydrogen and methyl group.

The viologen compounds specifically include the following chemical formulas (3) to (7).

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[0009]

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[0010]

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[0011]

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[0012]

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The method of synthesizing the viologen compound having an aromatic ring at the center of the molecule represented by Chemical formula 2 is not particularly limited, but may be selected from Journal of Chemical Society Chemical Communications (J. Chem.
Soc., Chem. Commun.) No. 8, p. 620 (1992)
Year) or Bulletin of the Chemical Society of Japan (Bull. Chem. Soc. Jpn.
), Vol. 65, p. 1855 (1992). Specifically, for example, 4- (trimethyltin) pyridine and 2,5-dibromothiophene are subjected to a coupling reaction using tetrakis (triphenylphosphine) palladium as a catalyst, and then reacted with methyl bromide to form a pyridine ring. By quaternizing the nitrogen atom, the above formula 3 is obtained. These compounds are used in organic EL
When used for an element, since its purity affects the charge transporting property and the light emitting property, it is desirable to purify such as reprecipitation purification and sublimation purification after synthesis.

In the present invention, the organic material layer containing a viologen compound having an aromatic ring at the center of the molecule represented by the above formula (2) is a layer composed of only the viologen compound,
A layer in which a viologen compound and another charge transporting material are mixed, a layer in which a viologen compound and another light emitting material are mixed, and a layer in which a viologen compound and another charge transporting material and another light emitting material are mixed It may be a layer or a layer in which a polymer compound is further mixed with any one of these four. Here, the main functions of the charge transport material and the luminescent material are improvement of the charge transport property and the luminescence property, respectively, and the main function of the polymer compound is improvement of the film forming property.
Further, an organic material layer containing a viologen-based compound may be used alone, or another charge transport layer, another light emitting layer,
Alternatively, it may be laminated with both.

The charge transport material used together with the viologen compound is not particularly limited, and examples thereof include triphenyldiamine derivatives, oxadiazole derivatives, pyrazoline derivatives, arylamine derivatives, stilbene derivatives, anthraquinodimethane derivatives and the like. Can be used. Specifically, for example, those described in JP-A-2-209988 and JP-A-3-37992,
Known ones can be used. Among them, one or both of the electron transporting compound and the hole transporting compound may be used simultaneously.

The luminescent material used together with the viologen compound is not particularly limited, and examples thereof include dyes such as naphthalene derivatives, anthracene and its derivatives, perylene and its derivatives, polymethine, xanthene, coumarin, and cyanine dyes. And metal complexes of 8-hydroxyquinoline and its derivatives, aromatic amines, tetraphenylcyclopentadiene and its derivatives, tetraphenylbutadiene and its derivatives, and the like.
Known ones described in, for example, Japanese Patent Nos. 51781 and 59-194393 can be used.

Further, conjugated polymers such as poly (p-phenylenevinylene) and poly (2,5-diheptyloxy-p-phenylenevinylene) having relatively short conjugated chains described in JP-A-3-71453 are disclosed. Molecules can also be used as light emitting materials.

The polymer compound used together with the viologen compound is not particularly limited, but those which do not extremely impair the charge transporting property and the luminescent property are preferable. For example, poly (N-vinylcarbazole), polyaniline, Derivatives, polythiophene and its derivatives, poly (p-phenylenevinylene) and its derivatives, poly (2,5-thienylenevinylene) and its derivatives, polycarbonate, polysiloxane, polymethyl acrylate, polymethyl methacrylate, polystyrene and polyvinyl chloride And the like.
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 have the above-mentioned electric charge. Also acts as a transportable compound.

The organic layer containing the viologen compound can be formed by a known method such as a vacuum evaporation method or a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method or a roll coating method of a solution of the viologen compound. Can be formed. When mixed with another charge transporting material or a light emitting material, they may be mixed in advance and formed into a film by the above method, or in the case of a vacuum evaporation method, they may be co-evaporated from separate evaporation sources. . In the case where the film is formed into a thin film by a coating method, 30 to 200 ° C., preferably 60 to 1 ° C., under reduced pressure or an inert atmosphere is used to remove the solvent.
It is desirable to heat-treat at a temperature of 00 ° C. It is preferable to use a vacuum deposition method in that fine control of the film thickness is performed.

In the present invention, a mixed layer of a viologen compound and a high molecular compound can also be used. The formation of a mixed layer of a viologen compound and a polymer compound is performed by mixing the polymer compound and the viologen compound in a solution state or a molten state, dispersing the viologen compound, and then applying the coating method described above. Can be used.

In this case, the amount of the viologen compound is preferably from 0.5 to 80% by weight, more preferably from 1 to 50% by weight, and still more preferably from 1 to 30% by weight, based on the polymer compound used. It is.

Poly (p-phenylenevinylene) and its derivatives and poly (2,5-thienylenevinylene)
And when a precursor polymer such as a derivative thereof is used, mixed with the viologen compound in a solution state, and then heat-treated at a temperature of 30 to 300 ° C., preferably 60 to 200 ° C. in an inert atmosphere to achieve the intended purpose. Convert to polymer.

In the present invention, a mixture of the viologen compound of the present invention and the above-mentioned light emitting material or charge transporting material can be used as a layer in which the above polymer compound is used as a medium and dispersed. In this case, the mixing ratio of the viologen compound to the light emitting material or the charge transporting material and the ratio of the sum of the polymer compound and these materials are not particularly limited. It is preferably from 5 to 80% by weight, more preferably from 1 to 50% by weight, still more preferably from 1 to 30% by weight.
% By weight. The formation of the mixed layer can employ the same method as described above.

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, anode / light-emitting layer / cathode (/ indicates that the layers are laminated), anode / hole transport layer / light-emitting layer / cathode, anode / (mixture layer of charge transport material and light-emitting material) / cathode, or It can have a structure of anode / hole transport layer / (mixture layer of charge transport material and luminescent material) / cathode. Also,
A structure having a combination of a conductive polymer layer between an anode and a hole transport layer may be employed, or a structure having an electron transport layer between a light emitting layer and a cathode may be employed. Further, a structure of anode / conductive polymer / hole transport layer / light-emitting layer / electron transport layer / cathode can be adopted.

When the viologen compound is used in the light emitting layer, a charge transport layer may be provided between the light emitting layer and any one of the electrodes, or between each electrode. A structure in which a layer and an electron transporting layer are stacked is more preferable because it exhibits good EL characteristics. In this case, the charge transport material used in the charge transport layer is exemplified by the above-described charge transport materials. 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.

The formation of the charge transport layer can be performed by a known method, for example, a vacuum deposition 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 transport material. Can be carried out by appropriately adopting it according to 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.

When a light emitting layer is provided separately from the organic substance layer containing the viologen compound and laminated, the light emitting material used for the light emitting layer is exemplified by the light emitting materials described above. Since the thickness of the light emitting layer varies depending on the kind of the compound to be used and the like, the thickness may be appropriately determined in consideration of the sufficient film formability and the light emission characteristic within a range of the amount.

The light-emitting layer is formed by a known method, for example, a vacuum evaporation method or a coating method such as spin coating method, casting method, dipping method, bar coating method and roll coating method after dissolving in a solution, depending on the compound to be used. The light emitting layer can be formed by adopting the light emitting layer appropriately. When the light-emitting material is not a high molecular compound, it is preferable to use a vacuum deposition method in that fine control of the film thickness is performed.

Hereinafter, a method of manufacturing an organic EL device will be described with reference to a structure having an anode / hole transport layer / light emitting layer / cathode as an example. As a transparent or translucent electrode of the pair of electrodes, 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, an indium tin oxide film (ITO film), a tin oxide film (NESA film), a thin film of Au, Pt, Ag, Cu, or the like is used. As a manufacturing method, a vacuum evaporation method, a sputtering method, a plating method, or the like is used.

Next, the above-mentioned hole transport layer is provided, and the film thickness is 0.5 nm to 10 μm, preferably 1 nm to 1 μm. 2 to 50 to increase current density to increase light emission brightness
A range of 0 nm is preferred.

Next, a light emitting layer is provided on the hole 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 0.5 nm to 10 μm, preferably 1 nm to
It is 1 μm, more preferably 5 to 200 nm. This range is also preferable in the case of a mixed layer of a hole transporting 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 in the same manner.

In the present invention, the viologen compound having an aromatic ring at the center of the molecule represented by the chemical formula 2 has both strong blue fluorescence and excellent charge transport properties.
Organic EL devices containing these compounds are considered to have excellent light-emitting properties.

[0035]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Example 1 <Synthesis of Viologen Compound> Journal of Chemical Society Chemical Communications (J. Chem. Soc., Chem. Commun.), No. 8, 62
In accordance with the method described on page 0 (1992), 4- (trimethyltin) pyridine and 2,5-dibromothiophene are subjected to a coupling reaction using tetrakis (triphenylphosphine) palladium as a catalyst, and then reacted with methyl bromide. To quaternize the nitrogen atom of the pyridine ring,
5-Bis (N-methyl-4-pyridinium) thiophene dibromide was obtained. This was purified by recrystallization from an ethanol solution.

<Preparation and Evaluation of Device> 4,4′-bis (3-methyl-diphenylamino) biphenyl (hereinafter referred to as a charge (hole) transport layer) was formed on a glass substrate having a 400 nm-thick ITO film formed thereon by sputtering. TPD) was deposited to a thickness of 50 nm by vapor deposition. Then, the 2,5-bis (N-
Methyl-4-pyridinium) thiophene dibromide
m, and further, 2- (4-biphenylyl) -5- (4-t
-Butylphenyl) -1,3,4-oxadiazole
50 nm was deposited. The organic substance was deposited at a rate of 0.1 to 0.2 nm / s. Finally, a magnesium-silver alloy (Mg: Ag = 9: 1 weight ratio) was deposited thereon as a cathode to a thickness of 150 nm to produce an organic EL device. The degree of vacuum at the time of vapor deposition was 8 × 10 ⁻⁶ Torr or less. 13.3
When a voltage of V was applied, a current of about 100 mA / cm ² flowed, and uniform EL emission was observed. The peak of the emission spectrum was at 492 nm, and the emission color was blue.

Example 2 A 400 nm thick ITO was used as the anode by sputtering.
On a glass substrate with a film, a charge (hole) transport layer T
PD was deposited to a thickness of 50 nm by vapor deposition, and then 2,5-bis (N-methyl-synthesized in the same manner as in Example 1).
(4-pyridinium) thiophene dibromide by evaporation
The film was formed with a thickness of nm. As a light-emitting layer thereon, (sometimes hereinafter referred to as Alq _3.) Tris (8-quinolinol) aluminum was deposited 50 nm. Organic deposition is 0.1 ~
The test was performed at a speed of 0.2 nm / s. Finally, a magnesium-silver alloy (Mg: Ag = 9: 1 weight ratio) was formed thereon as a cathode.
An organic EL device was produced by vapor deposition at 150 nm. The degree of vacuum at the time of vapor deposition was 8 × 10 ⁻⁶ Torr or less. When a voltage of 11.6 V was applied to this element, 160 mA / cm ²
And a uniform EL emission of 70 cd / m ² was observed. The emission spectrum is substantially coincident with the fluorescence spectrum of Alq _3, the emission color was green. The brightness was almost proportional to the current density.

[0038]

The organic EL device using the light emitting material of the present invention can emit blue light, and has uniform light emission, stability,
It exhibits excellent characteristics of low power consumption and can be suitably used for a planar light source as a backlight and a display device such as a flat panel display.

Continuation of the front page (56) References JP-A-5-70455 (JP, A) JP-A-55-65285 (JP, A) JP-A-6-248260 (JP, A) JP-A-6-240246 (JP) JP-A-6-240245 (JP, A) JP-A-4-334894 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 11/06 CA (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] At least one is transparent or translucent.
Having at least one organic layer between a pair of electrodes
In the organic electroluminescence element, the organic substance
The layer has the following formula 1(Where Ar is an aromatic hydrocarbon group having 6 to 18 carbon atoms or
A heteroaromatic group having 4 to 14 carbon atoms, X^-Indicates a counter anion
You. Also, R₁, R_Two, R_Three, R_Four, R_Five, R ₆,
R₇, R₈, R₉, R_TenAre each independently hydrogen or
And represents an alkyl group having 1 to 20 carbon atoms. Compound represented by)
At least one viologen system selected from products
Organic electroluminescence characterized by containing a compound
Sense element. 2. The organic electroluminescent device according to claim 1, wherein the organic layer containing the viologen compound is a light emitting layer. 3. An organic layer containing a viologen compound is laminated on another light emitting layer.
The organic electroluminescent device according to the above.