JP2000231988A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive this organic electroluminescent element at a low voltage by a zinc complex having 5-hydroxy-quinoxaline as a ligand contained in a component of an organic electroluminescent layer intervened between an anode and a cathode facing each other. SOLUTION: This zinc complex is shown by the formula. An organic electroluminescent layer with a specified thickness between an anode of a ITO transparent electrode and a cathode of a metal such as Mg with a low work function protected by platinum, together with a positive hole transporting layer and an electron transporting layer comprises mainly the zinc complex. In this organic electroluminescent element, luminescence with 635-617 nm is observed by applying a dc voltage of 7.5 V for example or a pulse voltage. [In the formula, R1, R2, R3, R4, R5: hydrogen, a halogen atom, an alkyl group containing a substituent or containing no substituent, an aralkyl group, an alkenyl group, an allyl group, an alkoxyl group, an aromatic hydrocarbon group, an aromatic heteloocyclic group, or a part of cyclic constructions of an alicyclic compound, an aromatic hydrocarbon compound and a hetelocyclic compound formed by mutually adjacent compounds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventional thin-film electroluminescent devices (hereinafter sometimes abbreviated as EL devices) include ZnS, CaS, which are II-VI group compound semiconductors made of inorganic materials.
In SrS, etc., Mn as a luminescence center and rare earth elements (Eu,
Although elements doped with Ce, Tb, Sm, etc.) were generally used, EL devices made from the above inorganic materials require: 1) AC drive (50 to 1000 Hz) 2) High drive voltage (up to 200 V) 3) It is difficult to achieve full color (especially blue) 4) There is a problem that the cost of the peripheral drive circuit is high. Therefore, a high voltage and an AC power source are required, so that a usable place is limited, and a light emitting material is limited. In addition, the light emitting efficiency is low in spite of the need for power, and the sign is dark. Further, the drive circuit and the like are expensive in terms of equipment, and the cost of the entire product is high.

[0003] Therefore, an EL that emits light at low voltage and high efficiency
Various metal complexes such as a zinc complex and an aluminum complex have been proposed as materials for the device. In recent years, 1),
A new organic electroluminescent device that is conscious of the problems 2) and 4) (hereinafter, may be abbreviated as an organic EL device).
And an organic EL device (Applied Physics Letters, Inc.) provided with an organic hole transport layer composed of an aromatic diamine and an organic light emitting layer composed of an aluminum complex of 8-hydroxyquinoline developed by Tang et al. Of Kodak Company. Appl. Phys. Lett.), 51, 913
(1987, p. 1987), a significant improvement in luminous efficiency has been observed as compared to earlier EL devices using single crystals such as anthracene. However, even with the organic EL element developed by Tang et al. And having a relatively high luminance, it cannot be said that a sufficient luminescent color that can be driven stably is obtained, and in terms of driving voltage,
In order to stably drive the organic EL element, a high driving voltage is still required, and it cannot be said that the driving voltage has been reduced to a practically usable level. Accordingly, an object of the present invention is to provide an organic EL device which can solve the above problems and can be driven at a low voltage.
In the development of devices.

[0004]

According to the present invention, in an electroluminescent device having an organic electroluminescent layer interposed between an anode and a cathode facing each other, a material constituting the organic electroluminescent layer is represented by the following general formula ( I)

[0005]

Embedded image

(Wherein R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an aralkyl group, an alkenyl group, an allyl group, A part of the ring structure of an alicyclic compound, an aromatic hydrocarbon compound or a heterocyclic compound, which represents an alkoxyl group, an aromatic hydrocarbon group or an aromatic heterocyclic group; The above object can be attained by providing an organic EL device including a zinc complex having a 5-hydroxyquinoxaline as a ligand represented by the following formula:

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an organic EL device according to the present invention will be described. The organic EL device of the present invention has an organic electroluminescent layer interposed between the opposed anode and cathode. As the anode of the present invention, a transparent material for extracting light, for example, a conductive metal oxide such as tin oxide, indium oxide, and indium tin oxide (hereinafter referred to as ITO transparent electrode); or gold or silver And metals such as chromium; inorganic conductive substances such as copper iodide and copper sulfide; conductive polymers such as polythiophene, polypyrrole, and polyaniline; and the like, and are not particularly limited.
Among them, it is particularly preferable to use an ITO transparent electrode. The electrical resistance of the ITO transparent electrode is preferably low from the viewpoint of power consumption of the element, as long as the electrical resistance to the element can be ensured and a sufficient current can be supplied to maintain light emission. For example, an ITO transparent electrode having a resistance of 500 Ω / □ or less can function as an anode.
□ The following transparent electrodes are more preferred. The thickness of the ITO transparent electrode can be arbitrarily selected in accordance with a suitable resistance value, and usually, a thickness between 100 and 300 nm is used. I
The TO transparent electrode is formed by forming a film on a transparent glass plate. As the film forming method, an electron beam method, a sputtering method, a chemical reaction method, or the like is used. Soda lime glass, non-alkali glass, or the like is used as the transparent glass plate. Alkali-free glass is preferred in that few ions elute from the glass when a voltage is applied, but soda-lime glass barrier coated with SiO ₂ or the like can also be used. The thickness of the glass substrate may be a thickness sufficient to maintain mechanical strength,
It is 0.1 to 5 mm, preferably 0.5 to 3 mm.

The cathode is not particularly limited as long as it is a metal capable of efficiently injecting electrons into the organic electroluminescent layer. Generally, platinum, gold, silver, copper, iron, tin, aluminum, indium,
Examples include lithium, sodium, potassium, calcium, and magnesium. In order to increase the electron injection efficiency and improve the device characteristics, metals having a low work function such as lithium, sodium, potassium, calcium, magnesium, and aluminum or alloys containing these metals are effective. In addition, platinum, gold, silver, copper,
Iron, tin, aluminum, metals such as indium, and alloys composed of these metals, and silica, inorganic compounds such as titania, polyvinyl alcohol, vinyl chloride,
It is preferable to laminate a hydrocarbon polymer or the like on the surface of the cathode. The method for producing these electrodes is not particularly limited as long as electrical conduction can be achieved, such as resistance heating, electron beam, sputtering, ion plating, and coating.

[0009] The organic EL device of the present invention is an organic EL device having an organic electroluminescent layer interposed between an anode and a cathode facing each other. Alternatively, an organic EL device having an electron transport layer is also included. As an organic EL device having such a multilayer structure, an anode (ITO transparent electrode) / hole transport layer / organic electroluminescent layer / cathode, anode (ITO transparent electrode) / hole transport layer / electron transport layer / organic electroluminescence Layers / cathodes can be exemplified.

The hole transporting layer is formed by singly or laminating a hole transporting substance alone or a mixture of a hole transporting substance and a polymer adhesive. As the hole transport material, N, N'-diphenyl-
Triphenylamines such as N, N'-di (3-methylphenyl) -4,4'-diphenyl-1,1'-diamine, bis (N-allylcarbazole) s, pyrazoline derivatives, stilbene compounds, oxadi Heterocyclic compounds represented by azole derivatives, phthalocyanine derivatives, porphyrin derivatives, and in the polymer system, polycarbonates having the above monomers in the side chain, styrene derivatives, polyvinyl carbazole, polysilane, polythiophene, and the like are preferable, but thin films necessary for device fabrication are preferable. Is not particularly limited as long as it is a compound capable of injecting holes from the anode and transporting holes. The thickness of the hole transporting layer varies depending on the resistance value of the hole transporting material used for producing the device, but is usually in the range of 10 to 1000 nm.

The organic electroluminescent layer and the electron transporting layer are made of the following general formula (I):

[0012]

Embedded image

(Wherein R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an aralkyl group, an alkenyl group, an allyl group, A part of the ring structure of an alicyclic compound, an aromatic hydrocarbon compound or a heterocyclic compound, which represents an alkoxyl group, an aromatic hydrocarbon group or an aromatic heterocyclic group; Or a zinc complex having a 5-hydroxyquinoxaline as a ligand.

As the organic electroluminescent layer, a substance having high fluorescence in a solid state as a general property is used. For example, fluorescent dyes such as quinacridone and coumarin can be mentioned. When used as a constituent material of an organic EL element, it is used in a thickness of about 10 to 1000 nm.

As the electron transport layer, a substance which forms a stable radical anion and has a high ionization potential is generally used. For example, oxadiazoles, aluminum quinolinol complexes and the like can be mentioned. When used as a constituent material of an organic EL element, it is used in a thickness of about 10 to 1000 nm.

The organic electroluminescent layer and the electron transporting layer are each formed by a method such as resistance heating evaporation, electron beam evaporation, sputtering, molecular lamination, or coating, and are not particularly limited. Evaporation,
Those formed by electron beam evaporation are preferable in terms of characteristics.

The electron transport layer may be formed by depositing only one kind of the above metal complex, by depositing several kinds of the above metal complexes, or by co-depositing several kinds of the above metal complexes.

Hereinafter, the present invention will be described in detail with reference to Reference Examples and Examples, but the present invention is not limited to the following Examples.

Reference Example 1 12.4 g of 2,3-diaminophenol was placed in a three-necked flask.
(0.1 mol), 21.2 g of 2,2-dipyridyl
(0.11 mol), and 200 g of toluene was added. The generated water was removed while heating and stirring for 2 hours in a reactor equipped with Gene Stark. After the reaction,
The mixture was cooled to room temperature and allowed to stand at 5 ° C. for 12 hours. The precipitated crystals were collected by filtration, rinsed with toluene, and dried under reduced pressure to obtain 16.8 g (0.056 mol, yield 56%) of the objective 5-oxy-2,3-dipyridylquinoxaline. 9.0 g (0.03 mol) of the obtained 2,3-dipyridyl-5-oxyquinoxaline was dissolved in 20 ml of tetrahydrofuran (hereinafter sometimes abbreviated as THF) and heated to 40 ° C. 2.0 g of zinc chloride
(0.015 mol) was added. Heat the mixture to reflux,
Thereto, 2 ml of an aqueous ammonia solution was added, and the mixture was further heated and stirred for 2 hours. After the reaction solution was cooled to room temperature, THF was distilled off, and 10 ml of dimethylformamide was added to the residue to dissolve the residue. After removing insoluble materials, 5 ml of water was added. 5. Precipitated crystals are collected and dried under reduced pressure to obtain the desired di- (5-oxy-2,3-dipyridylquinoxaline) zinc complex.
56 g (66% yield) were obtained. ¹ H-NMR (DMSO) δ 8.33 (d, 4H, J = 0.2 Hz) 8.04 (d, 4H, J = 1.6 Hz) 7.96 (d, 4H, J = 1.9 Hz) 7.8-7.9 (m, 8H) 7.21-7.33 (m, 6H) UV (nm) 207,235,307,442 MASS 663 (M ⁺ ) m. p. 205 ° C

Reference Example 2 A di- (5-oxy-2,3-diphenylquinoxaline) zinc complex was obtained in a yield of 59% in the same manner as in Reference Example 1, except that the starting material was changed from 2,2-dipyridyl to benzyl. Was. ¹ H-NMR (DMSO) δ 7.96 (d, 2H, J = 1.0 Hz) 7.72 (dd, 2H, J = 1.4, 1.0 Hz) 7.46 (d, 8H, J = 3.130) 7.30 to 7.36 (m, 12H) 7.20 to 7.22 (m, 2H) UV (nm) 210, 242, 305, 435 MASS 659 (M ⁺ ) m. p. 147 ° C

Reference Example 3 The procedure of Reference Example 1 was repeated except that the starting material was changed from 2,2-dipyridyl to 9,10-phenanthrolenquinone.
A (10-oxy-dibenzo (a, c) phenazine) zinc complex was obtained with a yield of 61%. ¹ H-NMR (CDCl ₃ ) δ 9.40 (d, 1H, J = 3.2) 9.30 (d, 1H, J = 3.2) 8.50 (d, 2H, J = 2.8 Hz) 7.70-7.90 (m, 6H) 7.32 (m, 1H) UV (nm) 207,248,325,494 MASS 655 (M ⁺ ) m. p. 221 ° C

Example 1 A transparent electrode made of an indium oxide alloy formed on a transparent glass plate 11 (hereinafter referred to as an ITO transparent electrode).
12, a hole transport layer 13 composed of a tetraphenylenediamine derivative, and di- (10-oxy-dibenzo (a, c)).
A light emitting layer 14 made of a phenazine) zinc complex and an upper electrode 15 made of a metal such as magnesium were sequentially formed to manufacture the organic EL device 10 shown in FIG. These hole transport layer 13, light emitting layer 14, and upper metal electrode 15
Was formed by a vacuum evaporation method. The hole transport layer 13 and the light emitting layer 14 were formed by continuous vapor deposition under a high vacuum of about 10 ^-6 Torr without breaking a vacuum state. The hole transport layer, the light emitting layer, and the upper metal electrode
Elements were formed by vapor deposition of 0 nm, 50 nm, and 200 nm.
When a direct current or a pulse voltage of 7.5 V was applied from a power supply using the ITO transparent electrode 12 as an anode and the upper electrode 15 as a cathode in the organic EL element 10 shown in FIG.
m was observed.

Example 2 A hole transport layer 1 made of a tetraphenylenediamine derivative was formed on an ITO transparent electrode 12 formed on a transparent glass plate 11.
3, a light emitting layer 14 made of a di- (5-oxy-2,3-diphenylquinoxaline) zinc complex and an upper electrode 15 made of a metal such as magnesium are sequentially formed.
Was manufactured. These hole transport layer 13, light emitting layer 14, and upper metal electrode 15 were formed by a vacuum evaporation method. The hole transport layer 13 and the light emitting layer 14 were formed by continuous vapor deposition under a high vacuum of about 10 ^-6 Torr without breaking a vacuum state. The hole transport layer, the light emitting layer, and the upper metal electrode were each 50 nm thick by vacuum evaporation.
Elements were formed by vapor deposition of 50 nm and 20 nm. When a direct current or a pulse voltage of 7.5 V was applied from a power supply using the ITO transparent electrode 12 of the organic EL element 10 shown in FIG. 1 as an anode and the upper electrode 15 as a cathode, emission of 617 nm was observed.

Example 3 A hole transport layer 1 made of a tetraphenylenediamine derivative was formed on an ITO transparent electrode 12 formed on a transparent glass plate 11.
3, a light-emitting layer 14 composed of a di- (5-oxy-2,3-dipyridylquinoxaline) zinc complex and an upper electrode 15 composed of a metal such as magnesium are sequentially formed.
Was manufactured. These hole transport layer 13, light emitting layer 14, and upper metal electrode 15 were formed by a vacuum evaporation method. The hole transport layer 13 and the light emitting layer 14 were formed by continuous vapor deposition under a high vacuum of about 10 ^-6 Torr without breaking a vacuum state. The hole transport layer, the light emitting layer, and the upper metal electrode were each 50 nm thick by vacuum evaporation.
Elements were formed by vapor deposition of 50 nm and 20 nm. When a direct current or a pulse voltage of 7.5 V was applied from a power supply using the ITO transparent electrode 12 of the organic EL element 10 shown in FIG. 1 as an anode and the upper electrode 15 as a cathode, emission of 622 nm was observed.

[0025]

According to the present invention, in an organic EL device in which an organic electroluminescent layer is interposed between the opposed anode and cathode, 5-hydroxyquinoxaline represented by the general formula (I) is used as a material constituting the organic electroluminescent layer. By finding an organic EL device containing a zinc complex having a compound as a ligand, an organic EL device that can be driven at a low voltage can be provided.

[0026]

[Brief description of the drawings]

FIG. 1 shows the structure of an organic EL device and the IT of the organic EL device.
The connection using the O transparent electrode 12 as an anode and the upper electrode 15 as a cathode is shown.

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 transparent glass plate 12 ITO transparent electrode 13 hole transport layer 14 light emitting layer comprising zinc complex of the present invention 15 upper electrode

Claims (1)

[Claims] 1. An organic electroluminescent device having an organic electroluminescent layer interposed between an anode and a cathode opposed to each other, wherein a material constituting the organic electroluminescent layer is represented by the following general formula (I): (Wherein R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an aralkyl group, an alkenyl group, an allyl group, an alkoxyl group, Represents an aromatic hydrocarbon group or an aromatic heterocyclic group, or a group adjacent to each other forms a part of a ring structure of an alicyclic compound, an aromatic hydrocarbon compound or a heterocyclic compound; An organic electroluminescent device comprising a zinc complex having a 5-hydroxyquinoxaline as a ligand represented by the formula: