JP2002334786A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element which accelerates recombination of positive holes with electrons in a luminescent layer and of emitting light with high luminance and high efficiency. SOLUTION: In this organic electroluminescent element, an organic layer having a luminescent region is formed between a positive electrode and a negative electrode. The organic electroluminescent element is characterized in that at least part of the organic layer is formed of a mixed ligand complex such as a bis (bathophenanthroline) (toluene dithiolate) zinc complex expressed by structural formula (1) for instance.

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 (EL device) in which an organic layer having a light emitting region is provided between an anode and a cathode.

[0002]

2. Description of the Related Art Flat panel displays having a light weight and high efficiency have been actively researched and developed, for example, for displaying screens of computers and televisions.

First, a cathode ray tube (CRT) is currently used most frequently as a display because of its high luminance and good color reproducibility, but has a problem that it is bulky, heavy and consumes high power.

Further, as a lightweight and highly efficient flat panel display, a liquid crystal display such as an active matrix drive has been commercialized. However, liquid crystal displays have a narrow viewing angle and are not self-luminous, so in a dark environment the consumption electrodes of the backlight are large and high-definition high-speed video signals expected to be put to practical use in the future And does not have sufficient response performance. In particular, it is difficult to manufacture a display having a large screen size, and there are also problems such as high cost.

[0005] As an alternative to this, there is a possibility of a display using light emitting diodes, but there are also problems such as high manufacturing costs and difficulty in forming a matrix structure of light emitting diodes on one substrate. However, as a low-cost display candidate to replace a cathode ray tube, there is a large problem until commercialization.

Recently, an organic electroluminescent device (organic EL device) using an organic luminescent material has been attracting attention as a flat panel display that can solve these problems. That is, by using an organic compound as a light emitting material, realization of a flat panel display which is self-luminous, has a high response speed, and has no viewing angle dependence is expected.

The structure of the organic electroluminescent device is such that an organic thin film containing a light emitting material which emits light by current injection is formed between a translucent positive electrode and a metal cathode. CWTang,
SAVanSlyke et al. Reported in a research report published in Applied Physics Letters, Vol. 51, No. 12, pp. 913-915 (1987) that an organic thin film had a two-layer structure of a thin film made of a hole transporting material and a thin film made of an electron transporting material. A device structure that emits light by recombination of holes and electrons injected into the organic film from the respective electrodes has been developed (single heterostructure organic EL device).

In this device structure, either the hole transporting material or the electron transporting material also functions as a light emitting material, and light emission occurs in a wavelength band corresponding to an energy gap between a ground state and an excited state of the light emitting material. With such a two-layer structure, a drastic reduction in driving voltage and an improvement in luminous efficiency were performed.

Thereafter, C. Adachi, S. Tokita, T. Tsuhuthu
Japanese Journal of Applied Physics such as i, S. Saito
As described in a research report published in Vol. 27, No. 2, L269-L271 (1988), a hole transport material,
A three-layer structure (organic EL device with a double heterostructure) consisting of a light emitting material and an electron transport material has been developed. Further, CWTang, SAVA
As described in a research report published in Journal of Applied Physics, Vol. 65, No. 9, pp. 3610-3616 (1989) by nSlyke, CHChen et al., an element structure in which a light emitting material is included in an electron transport material has been developed. Was done. These studies have verified the possibility of high-luminance light emission at low voltage, and in recent years, research and development have been very active.

The diversity of the organic compounds used for the light emitting material has the advantage that the emission color can be arbitrarily changed by changing the molecular structure theoretically. Therefore, by performing molecular design, R (red) and G with good color purity required for full color display can be obtained.
It can be said that it is easier to make the three colors (green) and B (blue) uniform than a thin film EL element using an inorganic substance.

[0011]

Although it cannot be said that it is an organic material in a strict sense, a metal complex material in which an organic compound is coordinated around a metal ion is also used as an electroluminescent element material. Generally, it is treated as a category of the organic EL light emitting material. A typical example is that aluminum ion is the central metal and 8-quinolinol is 3
Molecularly coordinated tris (8-quinolinol) aluminum [hereinafter abbreviated as Alq ₃ ] may be mentioned. This emission of Alq ₃ is attributed to the fluorescence from the ππ ^* excited state localized in coordinated 8-quinolinol, and it may not be a problem even if it is equivalent to the emission from an organic substance. However, A
Emission with lq ₃ is not satisfactory as a display material in terms of both maximum brightness and reliability.

Further, in recent years, with the diversification of materials, it is a complex material centered on a transition metal and a rare earth metal, and has a charge-transfer excited state (metal-to-ligand) between a metal and a ligand.
charge transfer; MLCT, ligand-to-metal charge transf
er; LMCT) has been treated as well, and when this metal complex material is used as a light emitting material in the same manner as the organic compound described above,
Theoretically, it can be said that there is an advantage that the emission color can be arbitrarily changed by changing the molecular structure or combination of the ligand which is an organic substance, and further by changing the central metal.

Further, from the viewpoint of improving the luminous efficiency, research and development using phosphorescence instead of fluorescence as light emission has recently started to stand out. In the case of a metal complex, the atomic weight of the central metal is large, and the electron cloud of the electron cloud is large. Because of the spread, the establishment of the intersystem crossing between the excited states is increased, and light emission from the triplet excited state lower than the singlet excited state, that is, phosphorescence is expected.

An object of the present invention is to provide an electroluminescent device containing a metal complex having an inherently high quantum yield, which promotes the recombination of holes and electrons in the light emitting layer, and further achieves high-luminance and high-efficiency light emission. An object of the present invention is to provide an organic electroluminescent device exhibiting the following.

[0015]

Means for Solving the Problems As a result of diligent studies to solve the above-mentioned problems, the present invention has revealed that a metal complex having a specific excited state between ligands in the lowest excited state can be used as a luminescent material, thereby stabilizing the stability. The present inventors have found that a highly reliable light-emitting element extremely useful for a high-luminance full-color display can be provided, and have reached the present invention.

That is, the present invention provides an organic electroluminescent device in which an organic layer having a light emitting region is provided between an anode and a cathode, wherein at least a part of the organic layer has the following general formula [I] At least one of the mixed ligand complexes represented by
An organic electroluminescent device comprising a seed.

Embedded image [However, the α-diimine is represented by the following general formula (1):
It has a molecular structure represented by (2) or (3),

Embedded image (However, in the general formulas (1) to (3), the substituent R
¹ and R ² are an alkyl group, a halogen atom, an ether group,
A group selected from an oxyalkyl group, a carboxyl group, a carboxylic acid ester group, a nitro group, a phenyl group, and a benzyl group, which may be the same or different. R ¹ and R ² are substituents, and m and n are integers of 0 or more. Further, the aromatic dithiolate has a molecular structure represented by the following general formula (4), (5), (6), (7) or (8);

Embedded image (However, in the general formulas (4) to (8), the substituent R
³ and R ⁴ are groups selected from an alkyl group, a halogen atom, an ether group, an oxyalkyl group, a carboxyl group, a carboxylate group, a nitro group, a phenyl group, and a benzyl group. You may. R ³ and R ⁴ are substituents, and m ′ and n ′ are integers of 0 or more. )] The metal ion is d ¹⁰ transition metal ions. ｝

According to the present invention, since at least one kind of the mixed ligand complex represented by the general formula [I] is used as a light emitting material, high luminance and stable light emission can be obtained, and electrical and thermal properties can be obtained. An element excellent in stability either chemically or chemically can be provided.

Further, the mixed ligand complex represented by the general formula [I] emits light from an interligand excited state.
By introducing a substituent into the ligand, changing the combination of the ligand, and changing the combination with the central metal ion, the emission wavelength can be tuned relatively easily, and the conventional organic light-emitting material can be used. More various emission wavelengths can be selected.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically based on embodiments.

In the mixed ligand complex represented by the general formula [I] used for the organic electroluminescent device according to the present invention,
The central metal ion is preferably Zn ²⁺ , Cd ²⁺ or Hg ²⁺ . In this case, the four nitrogen atoms and two sulfur atoms serving as coordination atoms have an octahedral coordination structure with respect to the central metal. Can be taken. These highest occupied orbits (HOM
O: highest occupied molecular orbital is an electron orbit localized in the aromatic dithiolate, and is the lowest unoccupied orbital (LUMO).
(orbital) is an electron orbit localized in the α-diimine. Therefore, the lowest excited state has been assigned to be the interligand excited state (LLCT) from the aromatic dithiolate to the α-diimine. And the H
OMO is localized at two sulfur atoms of the aromatic dithiolate, and at the very least, it can be said that the LLCT is from the sulfur atom of the aromatic dithiolate to the α-diimine. The metal ions constituting these mixed ligand complex, large spread of the electron cloud of sulfur atoms, still these heavy atom effect, singlet ¹ LLCT further energy level is low triplet excitation from the excited state ³ The transition to the LLCT state is promoted and ³ LL
Light emission from CT, that is, phosphorescence is observed.

Accordingly, since the organic electroluminescent device according to the present invention uses the mixed ligand complex represented by the general formula [I], it is possible to obtain light emission by phosphorescence as described above. Compared to the case of light emission by fluorescence, stable light emission with a longer life, higher luminance and higher stability are obtained in terms of electrical, thermal or chemical properties.

As the central metal ion, Zn ²⁺ ,
Co ²⁺ is known to have an octahedral coordination structure in the same manner as Cd ²⁺ and Hg ²⁺ .
However, since Co ²⁺ is a d ⁷ transition metal ion in which ^seven electrons are occupied in the d orbital, when such a transition metal ion is used as the central metal, dd in which the lowest excited state is a non-emission transition ^* May not emit light.

In the general formulas (1) to (3) and the general formulas (4) to (8), the alkyl group is preferably an alkyl group having 10 or less carbon atoms. , An ethyl group and a propyl group.

The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
The ether group is preferably an ether group having 10 or less carbon atoms. Examples thereof include a methoxy group and an ethoxy group. The oxyalkyl group and the carboxylate group preferably have 10 or less carbon atoms.

Since the mixed ligand complex represented by the general formula [I] emits light from an excited state between the ligands, it is possible to introduce the above-mentioned various substituents into the ligand, By changing the combination of the ligands of the general formulas (1) to (3) and the general formulas (4) to (8), and by changing the combination with the central metal ion, the tuning of the emission wavelength is relatively easy. It can be easily performed and more various emission wavelengths can be selected.

In the present invention, it is also possible to provide a hole blocking layer in contact with the cathode side of the layer composed of the mixed ligand complex. By arranging the hole blocking layer, recombination of holes and electrons is performed more efficiently in the layer composed of the mixed ligand complex, and pure luminescence unique to the luminescent material is increased in brightness and efficiency. It is possible to obtain.

The material suitable for the hole blocking layer preferably has the following energy state. That is, the highest occupied molecular orbital level of the material forming the hole blocking layer is at an energy level lower than the highest occupied molecular orbital level of the material forming the layer in contact with the anode side of the hole blocking layer, and the hole blocking The lowest unoccupied molecular orbital level of the material forming the layer is at an energy level higher than the lowest unoccupied molecular orbital level of the material forming the layer in contact with the anode side of the hole blocking layer;
Further, the energy level is lower than the lowest unoccupied molecular orbital level of the material forming the layer in contact with the cathode side of the hole blocking layer.

As such a material, Japanese Patent Application Laid-Open No. H10-79
297, JP-A-11-204258, JP-A-11-20
4264 and phenanthroline derivatives described in JP-A-11-204259, but are not limited to the phenanthroline derivatives as long as they satisfy the above-mentioned energy level conditions.

FIGS. 1 to 4 and FIGS. 5 to 8 show examples of an organic electroluminescent device according to the present invention.

FIG. 1 shows a transmissive organic electroluminescent element A in which emitted light 20 passes through a cathode 3, wherein the emitted light 20 is applied to a protective layer 4.
Observable from the side. FIG. 2 shows a reflective organic electroluminescent element B in which the reflected light from the cathode 3 is also obtained as the emitted light 20.

In the figure, reference numeral 1 denotes a substrate for forming an organic electroluminescent device, which can be made of glass, plastic or other appropriate material. When the organic electroluminescent device is used in combination with another display device, the substrate can be shared. 2 is a transparent electrode (anode);
TO (Indium tin oxide), SnO ₂ or the like can be used.

Reference numeral 5 denotes an organic light-emitting layer, which contains the mixed ligand complex as a light-emitting material. With respect to this light emitting layer, the layer configuration for obtaining the organic electroluminescence 20 includes:
Various conventionally known configurations can be used. As will be described later, for example, when a material constituting either the hole transport layer or the electron transport layer has a light emitting property, a structure in which these thin films are laminated can be used. Further, in order to improve the charge transporting performance in a range satisfying the object of the present invention, one or both of the hole transporting layer and the electron transporting layer has a structure in which thin films of a plurality of types of materials are stacked, or a plurality of types of materials. It does not prevent the use of a thin film having a mixed composition. Further, in order to improve the light emitting performance, at least one kind of fluorescent material is used, and the thin film is sandwiched between the hole transport layer and the electron transport layer. May be used in the hole transport layer, the electron transport layer, or both. In these cases, a thin film for controlling the transport of holes or electrons can be included in the layer structure in order to improve the luminous efficiency.

For example, since the compound comprising the mixed ligand complex represented by the above general formula [I] has both electron transporting performance and hole transporting performance, it also serves as an electron transporting layer in the device structure. It can be used as a light emitting layer composed of the mixed ligand complex or a light emitting layer composed of the mixed ligand complex also serving as a hole transport layer. In addition, it is also possible to adopt a configuration in which the mixed ligand complex is used as a light-emitting layer and sandwiched between an electron transport layer and a hole transport layer. FIGS. 5 and 6 show a structure in which a hole blocking layer 21 made of a phenanthroline derivative or the like is provided in contact with the light emitting layer 5 on the cathode side in addition to the above-described structure.

In FIGS. 1 and 2, and FIGS. 5 and 6, 3
Denotes a cathode, and as an electrode material, an alloy of an active metal such as Li, Mg, Ca and the like and a metal such as Ag, Al, In or the like, or a structure in which these are laminated can be used. In a transmission type organic electroluminescent device, by adjusting the thickness of the cathode, a light transmittance suitable for the intended use can be obtained. Further, reference numeral 4 in the drawing denotes a sealing / protecting layer, and its effect is improved by adopting a structure that covers the entire organic electroluminescent element.
If airtightness is maintained, an appropriate material can be used. Reference numeral 8 denotes a drive power supply for current injection.

In the organic electroluminescent device according to the present invention, the organic layer has an organic laminated structure (single heterostructure) in which a hole transport layer and an electron transport layer are laminated, and The mixed ligand complex may be used as a material for forming the electron transport layer. Alternatively, the organic layer has an organic laminated structure (double hetero structure) in which a hole transport layer, a light emitting layer, and an electron transport layer are sequentially laminated, and the mixed ligand complex is used as a material for forming the light emitting layer. May be used.

FIG. 3 shows an example of an organic electroluminescent device having such an organic laminated structure.
It has a laminated structure in which a translucent anode 2, an organic layer 5 a including a hole transport layer 6 and an electron transport layer 7, and a cathode 3 are sequentially laminated, and this laminated structure is sealed with a protective film 4. This is an organic electroluminescent device C having a single hetero structure.
In FIG. 7, a hole blocking layer 21 is provided in contact with the electron transport layer 7 and / or the hole transport layer 6 on the cathode side.

As shown in FIGS. 3 and 7, when the light emitting layer is omitted, light emission 20 of a predetermined wavelength is generated from the interface between the hole transport layer 6 and the electron transport layer 7. These light emissions are observed from the substrate 1 side.

FIG. 4 shows a light-transmitting anode 2, an organic layer 5 b composed of a hole transport layer 10, a light-emitting layer 11 and an electron transport layer 12, and a cathode 3 on a light-transmitting substrate 1. Are sequentially laminated, and this laminated structure is sealed with a protective layer 4 to provide an organic electroluminescent element D having a double hetero structure. 8, a hole blocking layer 21 is provided in contact with the light emitting layer 11 on the cathode side.

In the organic electroluminescent device shown in FIG. 4, by applying a DC voltage between the anode 2 and the cathode 3, holes injected from the anode 2 pass through the hole transport layer 10, and The electrons injected from 3 reach the light emitting layer 11 via the electron transport layer 12 respectively. As a result, in the light-emitting layer 11, electron / hole recombination occurs to generate singlet excitons, which are relaxed in the molecule to triplet excitons, and emit light of a predetermined wavelength from the triplet excitons. .

In each of the organic electroluminescent elements C and D described above, the substrate 1 can be made of a light-transmissive material such as glass or plastic. In the case where the display device is used in combination with another display element, or in the case of FIGS.
In the case where the stacked structures shown in FIG. 8 and the stacked structure shown in FIG. 8 are arranged in a matrix, the substrate may be shared. Also, element C,
D can take any of a transmission type and a reflection type structure.

The anode 2 is a transparent electrode and is made of ITO.
(Indium tin oxide) or SnO ₂ can be used. Between the anode 2 and the hole transport layer 6 (or the hole transport layer 10), a thin film made of an organic substance or an organometallic compound (metal complex or the like) may be provided for the purpose of improving charge injection efficiency. Good. When the protective layer 4 is formed of a conductive material such as a metal, an insulating film may be provided on a side surface of the anode 2.

The organic layer 5a in the organic electroluminescent device C is an organic layer in which a hole transport layer 6 and an electron transport layer 7 are laminated, and one or both of them are the mixed ligand complex described above. And the light-emitting hole transport layer 6 or the electron transport layer 7 may be used. The organic layer 5b in the organic electroluminescent element D is an organic layer in which the hole transport layer 10, the light emitting layer 11 containing the mixed ligand complex described above, and the electron transport layer 12 are laminated, A laminated structure can be adopted. For example, one or both of the hole transport layer and the electron transport layer may have a light emitting property.

In the hole transport layer, a hole transport layer in which a plurality of types of hole transport materials are laminated may be formed in order to improve hole transport performance.

In the organic electroluminescent device C, the light emitting layer may be the electron transporting light emitting layer 7. However, depending on the voltage applied from the power supply 8, the light emitting layer may emit light at the hole transporting layer 6 or its interface. There is. Similarly, in the organic electroluminescent device D, the light emitting layer may be the electron transport layer 12 or the hole transport layer 10 other than the layer 11. In order to improve the light emitting performance, it is preferable that the light emitting layer 11 using at least one kind of fluorescent material is sandwiched between the hole transport layer and the electron transport layer. Further, a structure in which this fluorescent material is contained in the hole transport layer or the electron transport layer, or in both of these layers, may be configured. In such a case, in order to improve the luminous efficiency, a thin film (such as a hole blocking layer or an exciton generation layer) for controlling the transport of holes or electrons can be included in the layer configuration.

The material used for the cathode 3 is L
An alloy of an active metal such as i, Mg, Ca or the like and a metal such as Ag, Al, In or the like can be used, and a structure in which these metal layers are laminated may be used. Incidentally, by appropriately selecting the thickness and material of the cathode, an organic electroluminescent device suitable for the intended use can be produced.

The protective layer 4 functions as a sealing film, and has a structure that covers the entire organic electroluminescent element, so that charge injection efficiency and luminous efficiency can be improved. As long as the airtightness is maintained, the material can be appropriately selected, such as a single metal such as aluminum, gold, and chromium, or an alloy.

The current applied to each of the above-mentioned organic electroluminescent elements is usually a direct current, but a pulse current or an alternating current may be used. The current value and the voltage value are not particularly limited as long as they are within a range that does not cause element destruction. However, in consideration of power consumption and life of the organic electroluminescent element, it is desirable to emit light efficiently with as little electric energy as possible.

Next, FIG. 9 shows an example of the configuration of a flat panel display using the organic electroluminescent device of the present invention. As shown, for example, in the case of a full color display, an organic layer 5 (5a, 5b) capable of emitting three primary colors of red (R), green (G) and blue (B) is provided between the cathode 3 and the anode 2. It is arranged in. The cathode 3 and the anode 2 can be provided in a stripe shape crossing each other, and are selected by the luminance signal circuit 14 and the control circuit 15 with a built-in shift register, and a signal voltage is applied to each of them. The organic layer at a position (pixel) where the anode 3 and the anode 2 intersect is configured to emit light.

That is, FIG. 9 shows, for example, an 8 × 3 RGB simple matrix in which a laminate 5 composed of a hole transport layer and at least one of a light emitting layer and an electron transport layer is placed between the cathode 3 and the anode 2. It is arranged (see FIGS. 3 and 7 or FIGS. 4 and 8). The cathode and the anode are both patterned in a stripe shape and are orthogonal to each other in a matrix to form a control circuit 15 with a built-in shift register.
And 14, a signal voltage is applied in chronological order, and light is emitted at the intersection. The EL element having such a configuration can be used not only as a display for characters and symbols, but also as an image reproducing device. Cathode 3
By arranging the stripe pattern of the anode 2 and each of the red (R), green (G), and blue (B) colors, a multi-color or full-color all solid-state flat panel display can be configured.

[0050]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

<Synthesis example of mixed ligand complex: bis (basophenanthroline) (toluene dithiolate) zinc complex>
1 mmol of Zn (CH ₃ COO) ₂ .2H ₂ O was dissolved in 5 ml of dehydrated DMF (dimethylformamide). To this, 1 mmol of 3,4-toluenedithiol (t) was added to 10 ml of dehydrated ethanol.
It was added dropwise while heating those dt-H ₂₎ dissolved. Furthermore, 2 mmol of 1,10-phenanthroline (phen) is added to 10 ml of dehydrated ethanol.
Was added dropwise while further heating. After heating for 1 hour and cooling to room temperature, a red-pink solid began to precipitate.
This was filtered and the solid was washed with ethanol. This solid was purified with an alumina column using dichloromethane as a developing solvent, and recrystallized three times with dehydrated DMF and ethanol. As a result, a bis (basophenanthroline) (toluene dithiolate) zinc complex (Zn (tdt) (phen) ₂ ) represented by the following structural formula (1), which is the target product, is obtained in a high yield of 60 to 70%. I got it.

Embedded image Structural formula (1): bis (basophenanthroline)
(Toluene dithiolate) zinc complex (Zn (tdt)
(Phen) ₂ )

By the same procedure, the desired α-diimine compound is substituted for 1,10-phenanthroline,
By using a desired aromatic dithiol instead of 4-toluenedithiol and cadmium acetate instead of zinc acetate, the desired mixed ligand complex can be obtained.

Example 1 In this example, a mixed ligand complex (bis (basophenanthroline) represented by the above structural formula (1) obtained by the above method among the compounds of the above general formula [I] was prepared. This is an example in which (toluene dithiolate) zinc complex) was used as a hole transport layer (also serving as a light emitting layer) to produce an organic electroluminescent device having a single hetero structure.

First, in a vacuum deposition apparatus, a 30 mm-thick anode made of ITO having a thickness of 100 nm was formed on one surface.
A 30 mm glass substrate was set. A plurality of metal masks each having a unit opening of 2.0 mm × 2.0 mm as a vapor deposition mask are arranged close to the substrate, and are represented by the above structural formula (1) under a vacuum of 10 ⁻⁴ Pa or less by a vacuum vapor deposition method. Zn (tdt) (phen) ₂ was formed as a hole transport layer (also serving as a light emitting layer) to a thickness of, for example, 50 nm. The deposition rates were each 0.1 nm / sec.

As a material for the electron transport layer, Alq ₃ (tris (8-quinolinol) aluminum) represented by the following structural formula (2) was deposited in contact with the hole transport layer. A
The thickness of this electron transport layer made of lq _{3 is} also, for example, 50 nm.
And the deposition rate was 0.2 nm / sec.

Embedded image

As a cathode material, a laminated film of Mg and Ag is adopted, and this is also deposited by vapor deposition at a deposition rate of 1 nm / sec, for example, 50 nm (Mg film) and 150 nm (Ag film).
To produce an organic electroluminescent device as shown in FIG. 3 according to Example 1.

The organic electroluminescent device of Example 1 thus manufactured was evaluated for luminous characteristics by applying a forward bias DC voltage in a nitrogen atmosphere. It emitted a red light, which was found by spectrometry to have a peak at about 637 nm. For spectrometry, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. When voltage-luminance measurement was performed, 190 cd / m ^{2 at} 8 V was measured.
Was obtained.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when current was supplied at a constant value at an initial luminance of 50 cd / m ² to continuously emit light and was forcibly deteriorated, it took 130 hours until the luminance was reduced by half.

Example 2 In this example, a mixed ligand complex (bis (basophenanthroline) represented by the above structural formula (1) obtained by the above method among the compounds of the above general formula [I] This is an example in which (toluene dithiolate) zinc complex) was used as a light emitting layer to produce an organic electroluminescent device having a double hetero structure.

First, a 30 mm-thick anode formed of ITO having a thickness of 100 nm was formed on one surface in a vacuum evaporation apparatus.
A 30 mm glass substrate was set. A plurality of metal masks each having a unit opening of 2.0 mm × 2.0 mm as a vapor deposition mask are arranged close to the substrate, and a vacuum vapor deposition method under a vacuum of 10 ⁻⁴ Pa or less is used as a hole transport layer material described below. The α-NPD represented by the structural formula (3) is, for example, 30
The film was formed to a thickness of nm. The deposition rate was 0.1 nm / sec.

Embedded image

Further, in contact with the hole transport layer, Zn (tdt) (phen) ₂ represented by the structural formula (1) was formed as a light emitting layer to a thickness of, for example, 30 nm. The deposition rates were each 0.2 nm / sec.

Further, using Alq ₃ represented by the structural formula (2) as an electron transport layer material, vapor deposition was performed in contact with the light emitting layer. The thickness of this electron transport layer made of Alq ₃ was also, for example, 30 nm, and the deposition rate was 0.2 nm / sec.

As a cathode material, a laminated film of Mg and Ag is employed, which is also deposited by vapor deposition at a deposition rate of 1 nm / sec, for example, 50 nm (Mg film) and 150 nm (Ag film).
To produce an organic electroluminescent device as shown in FIG.

The organic electroluminescent device of Example 2 manufactured as described above was evaluated for luminous characteristics by applying a forward bias DC voltage under a nitrogen atmosphere. It emitted a red light, which was found by spectrometry (as in Example 1) to have a peak at about 637 nm. When voltage-luminance measurement was performed, a luminance of 140 cd / m ² was obtained at 8 V.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when the current value was kept constant at an initial luminance of 50 cd / m ² to continuously emit light and was forcibly deteriorated, it took 110 hours until the luminance was reduced by half.

Example 3 In this example, a mixed ligand complex (bis (basophenanthroline) represented by the above structural formula (1) obtained by the above-mentioned method was selected from the compounds of the above general formula [I]. This is an example in which (toluene dithiolate) zinc complex) was used as a hole transport layer (also serving as a light emitting layer) to produce an organic electroluminescent device based on a single heterostructure.

First, in a vacuum evaporation apparatus, a 30 mm-thick anode made of ITO having a thickness of 100 nm was formed on one surface.
A 30 mm glass substrate was set. A plurality of metal masks each having a unit opening of 2.0 mm × 2.0 mm as a vapor deposition mask are arranged close to the substrate, and are represented by the above structural formula (1) under a vacuum of 10 ⁻⁴ Pa or less by a vacuum vapor deposition method. Zn (tdt) (phen) ₂ was formed as a hole transport layer (also serving as a light emitting layer) to a thickness of, for example, 50 nm. The deposition rates were each 0.1 nm / sec.

Further, bathocuproine represented by the following structural formula (4) was deposited as a hole blocking layer material in contact with the hole transport layer. The thickness of the hole blocking layer made of bathocuproine was, for example, 15 nm, and the deposition rate was 0.1 nm / sec.

Further, the above structure as an electron transport layer material
Alq represented by formula (2)_Three(Tris (8-quinolino
E) aluminum) was deposited in contact with the hole transport layer. A
lq _ThreeThe thickness of the electron transport layer made of
And the deposition rate was 0.2 nm / sec.

Embedded image

As a cathode material, a laminated film of Mg and Ag is employed, which is also deposited by vapor deposition at a deposition rate of 1 nm / sec, for example, 50 nm (Mg film) and 150 nm (Ag film).
Then, an organic electroluminescent device as shown in FIG. 7 according to Example 3 was produced.

The organic electroluminescent device of Example 3 manufactured as described above was evaluated by applying a forward bias DC voltage under a nitrogen atmosphere to the light emitting characteristics. It emitted a red light, which was found by spectrometry to have a peak at about 637 nm. For spectrometry, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. Further, when voltage-luminance measurement was performed, 180 cd / m ^{2 at} 8 V was obtained.
Was obtained.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when the current was supplied at a constant value at an initial luminance of 50 cd / m ² to continuously emit light and was forcibly deteriorated, it took 200 hours until the luminance was reduced to half.

Example 4 In this example, a mixed ligand complex (bis (basophenanthroline) represented by the above structural formula (1) obtained by the above method among the compounds of the above general formula [I] This is an example in which (toluene dithiolate) zinc complex) was used as a light emitting layer to produce an organic electroluminescent device based on a double hetero structure.

First, in a vacuum deposition apparatus, a 30 mm-thick anode made of ITO having a thickness of 100 nm was formed on one surface.
A 30 mm glass substrate was set. A plurality of metal masks each having a unit opening of 2.0 mm × 2.0 mm are arranged in close proximity to the substrate as a vapor deposition mask, and the above-described material as a hole transport layer material is formed under a vacuum of 10 ⁻⁴ Pa or less by a vacuum vapor deposition method. The α-NPD represented by the structural formula (3) is, for example, 30
The film was formed to a thickness of nm. The deposition rate was 0.1 nm / sec.

Further, in contact with the hole transport layer, Zn (tdt) (phen) ₂ represented by the structural formula (1) was formed as a light emitting layer to a thickness of, for example, 30 nm. The deposition rates were each 0.2 nm / sec.

Further, bathocuproine represented by the structural formula (4) was deposited as a hole blocking layer material in contact with the light emitting layer. The thickness of the hole blocking layer made of bathocuproine was, for example, 15 nm, and the deposition rate was 0.1 nm / sec.

Further, Alq ₃ represented by the above structural formula (2) was used as an electron transport layer material, and was deposited in contact with the hole blocking layer. The thickness of this electron transport layer made of Alq _{3 is} also, for example, 30 nm, and the deposition rate is 0.2 n.
m / sec.

As the cathode material, a laminated film of Mg and Ag is employed, and this is also deposited by vapor deposition at a deposition rate of 1 nm / sec, for example, 50 nm (Mg film) and 150 nm (Ag film).
To produce an organic electroluminescent device as shown in FIG.

The organic electroluminescent device of Example 4 manufactured as described above was evaluated for luminous characteristics by applying a forward bias DC voltage under a nitrogen atmosphere. It emitted a red light, which was found by spectrometry (as in Example 3) to have a peak at about 637 nm. Further, when voltage-luminance measurement was performed, a luminance of 165 cd / m ² was obtained at 8 V.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when the current was supplied at a constant value at an initial luminance of 50 cd / m ² to continuously emit light and was forcibly deteriorated, it took 140 hours until the luminance was reduced by half.

Examples 5 to 17 In this example, of the mixed ligand complex represented by the general formula [I], the following structural formula (5) was used as the α-diimine.
1,8-phenanthroline derivatives represented by the following structural formulas (9) to (11);
A bipyridine derivative and a 2,2′-bipyrazine derivative represented by the following structural formula (12) are used, and as the aromatic dithiolate, the following structural formulas (13) to (1)
Using a benzenedithiolate derivative represented by 5) and a naphthalenedithiolate derivative represented by the following structural formula (16), and combining Zn ²⁺ or Cd ²⁺ as a central metal, as shown in Table 1 below This is an example in which an organic electroluminescent device based on a double hetero structure as shown in FIG. 8 was manufactured using a mixed ligand complex as a light emitting layer material.

Embedded image

An organic electroluminescent device was manufactured according to Example 4 in both the layer structure and the film forming method.

The organic electroluminescent devices of Examples 5 to 17 manufactured as described above were evaluated for light emission characteristics by applying a forward bias DC voltage under a nitrogen atmosphere. The results are summarized in Table 1 below.

[0084]

[Table 1] * Brightness is the result when 8V is applied.

Comparative Example 1 Instead of the mixed ligand complex (bis (basophenanthroline) (toluene dithiolate) zinc complex) represented by the structural formula (1), a compound represented by the following structural formula (17) was used. , 3,
7,8,12,13,17,18-octaethyl-21
H, 23H-porphyrin platinum (II) complex (PtOE
An organic electroluminescent device having a single hetero structure as shown in FIG. 3 was produced in the same manner as in Example 1 except that P) was used as a hole transport layer (also serving as a light emitting layer). In addition, the following structural formula (1
2,3,7,8,12,13,17,1 represented by 7)
The 8-octaethyl-21H, 23H-porphyrin platinum (II) complex is a conventionally known phosphorescent material for emitting red light.

Embedded image

The organic electroluminescent device of Comparative Example 1 thus manufactured was evaluated for light emission characteristics by applying a forward bias DC voltage under a nitrogen atmosphere. It emitted a red light, which was found by spectrometry to have a peak at about 650 nm. For spectrometry, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. When voltage-luminance measurement was performed, a luminance of 80 cd / m ² was obtained at 8 V.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when the current was continuously supplied at a constant current value at an initial luminance of 50 cd / m ² to continuously emit light and was forcibly deteriorated, it took 100 hours until the luminance was reduced by half.

Comparative Example 2 Instead of the mixed ligand complex (bis (basophenanthroline) (toluene dithiolate) zinc complex) represented by the structural formula (1), a compound represented by the structural formula (17) was used. ,
3,7,8,12,13,17,18-octaethyl-
An organic electroluminescent device having a double hetero structure as shown in FIG. 4 was produced in the same manner as in Example 2 except that the 21H, 23H-porphyrin platinum (II) complex was used for the light emitting layer.

The organic electroluminescent device of Comparative Example 2 thus manufactured was evaluated for luminous characteristics by applying a forward bias DC voltage in a nitrogen atmosphere. It emitted a red light, which was found by spectrometry to have a peak at about 650 nm. For spectrometry, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. When voltage-luminance measurement was performed, a luminance of 90 cd / m ² was obtained at 8 V.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when the current value was kept constant at an initial luminance of 50 cd / m ² to continuously emit light and was forcibly deteriorated, it took 110 hours until the luminance was reduced by half.

Comparative Example 3 Instead of the mixed ligand complex (bis (basophenanthroline) (toluene dithiolate) zinc complex) represented by the structural formula (1), a compound represented by the structural formula (17) ,
3,7,8,12,13,17,18-octaethyl-
An organic electroluminescent device based on a single heterostructure as shown in FIG. 7 in the same manner as in Example 3 except that a 21H, 23H-porphyrin platinum (II) complex was used for a hole transport layer (also serving as a light emitting layer). Was prepared.

The organic electroluminescent device of Comparative Example 3 manufactured as described above was evaluated for light emission characteristics by applying a forward bias DC voltage in a nitrogen atmosphere. It emitted a red light, which was found by spectrometry to have a peak at about 650 nm. For spectrometry, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. Also, when voltage-luminance measurement was performed, 120 cd / m ^{2 at} 8 V was measured.
Was obtained.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when current was supplied at a constant value at an initial luminance of 110 cd / m ² to continuously emit light and was forcibly deteriorated, it took 90 hours until the luminance was reduced to half.

Comparative Example 4 Instead of the mixed ligand complex (bis (basophenanthroline) (toluene dithiolate) zinc complex) represented by the structural formula (1), the compound represented by the structural formula (17) ,
3,7,8,12,13,17,18-octaethyl-
An organic electroluminescent device based on a double hetero structure as shown in FIG. 8 was produced in the same manner as in Example 4 except that the 21H, 23H-porphyrin platinum (II) complex was used for the light emitting layer.

The organic electroluminescent device of Comparative Example 4 fabricated as described above was evaluated for light emission characteristics by applying a forward bias DC voltage under a nitrogen atmosphere. It emitted a red light, which was found by spectrometry to have a peak at about 650 nm. For spectrometry, a spectroscope using a photodiode array manufactured by Otsuka Electronics Co., Ltd. as a detector was used. When voltage-luminance measurement was performed, 110 cd / m ^{2 at} 8 V was measured.
Was obtained.

After this organic electroluminescent device was manufactured, it was left under a nitrogen atmosphere for one month, but no device deterioration was observed. In addition, when the current was supplied at a constant value at an initial luminance of 100 cd / m ² to continuously emit light and was forcibly deteriorated, it took 80 hours until the luminance was reduced by half.

As is clear from the above, the organic electroluminescent device according to the present invention has the above general formula [I] as a luminescent material.
For example, a bis (basophenanthroline) (toluene dithiolate) zinc complex represented by the structural formula (1) can be used as the mixed ligand complex represented by the formula (1), so that light emission by phosphorescence can be obtained. In addition, stable light emission with longer life, higher luminance and higher stability can be obtained, and the stability is improved more electrically, thermally or chemically.

The mixed ligand complex represented by the general formula [I] emits light from an excited state between ligands.
By introducing the above-mentioned various substituents to the ligand, changing the combination of the ligand, and changing the combination with the central metal, tuning of the emission wavelength can be relatively easily performed, and more diverse. It is possible to select an appropriate emission wavelength.

[0099]

According to the present invention, since at least one kind of the mixed ligand complex represented by the general formula [I] is used as a light emitting material, high luminance and stable light emission can be obtained, In addition, an element having excellent thermal or chemical stability can be provided.

The mixed-ligand complex represented by the general formula [I] emits light from an excited state between ligands.
Tuning the emission wavelength is relatively easy by introducing a substituent into the ligand, changing the combination of the ligands, and changing the combination with the central metal ion. You can choose.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a main part of an example of an organic electroluminescent device according to the present invention.

FIG. 2 is a schematic sectional view of a main part of another example of the organic electroluminescent device.

FIG. 3 is a schematic sectional view of a main part of another example of the organic electroluminescent device.

FIG. 4 is a schematic cross-sectional view of a main part of another example of the organic electroluminescent device.

FIG. 5 is a schematic sectional view of a main part of another example of the organic electroluminescent device.

FIG. 6 is a schematic sectional view of a main part of another example of the organic electroluminescent device.

FIG. 7 is a schematic sectional view of a main part of another example of the organic electroluminescent device.

FIG. 8 is a schematic cross-sectional view of a main part of still another example of the organic electroluminescent device.

FIG. 9 is a configuration diagram of a full-color flat display using the organic electroluminescent device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Transparent electrode (anode), 3 ... Cathode, 4 ... Protective film, 5 5a, 5b ... Organic layer, 6 ... Hole transport layer, 7 ... Electron transport layer, 8 ... Power supply, 10 ... Positive Hole transport layer, 11 light emitting layer, 12 electron transport layer, 14 luminance signal circuit, 15 control circuit, 20 light emission, 21 hole (hole) blocking layer, A, B, C, D organic EL device

Claims (12)

[Claims] 1. An organic electroluminescent device in which an organic layer having a light emitting region is provided between an anode and a cathode, at least a part of the organic layer is represented by the following general formula [I]. An organic electroluminescent device comprising at least one kind of mixed ligand complex. Embedded image [However, the α-diimine is represented by the following general formula (1):
It has a molecular structure represented by (2) or (3), (However, in the general formulas (1) to (3), the substituent R
¹ and R ² are an alkyl group, a halogen atom, an ether group,
A group selected from an oxyalkyl group, a carboxyl group, a carboxylic ester group, a nitro group, a phenyl group, and a benzyl group, which may be the same or different. R ¹ and R ² are substituents, and m and n are integers of 0 or more. In addition, the aromatic dithiolate has a molecular structure represented by the following general formula (4), (5), (6), (7) or (8): (However, in the general formulas (4) to (8), the substituent R
³ and R ⁴ are groups selected from an alkyl group, a halogen atom, an ether group, an oxyalkyl group, a carboxyl group, a carboxylate group, a nitro group, a phenyl group, and a benzyl group. You may. R ³ and R ⁴ are substituents, and m ′ and n ′ are integers of 0 or more. )] The metal ion is d ¹⁰ transition metal ions. ｝ 2. The alkyl group is an alkyl group having 10 or less carbon atoms, the ether group is an ether group having 10 or less carbon atoms, and the oxyalkyl group is an oxyalkyl group having 10 or less carbon atoms. The organic electroluminescent device according to claim 1, wherein the carboxylate group is a carboxylate group having 10 or less carbon atoms. 3. The organic electroluminescence according to claim 1, wherein the metal ion of the mixed ligand complex represented by the general formula [I] is represented by Zn ²⁺ , Cd ²⁺ or Hg ^2+. element. 4. The organic layer has an organic laminated structure in which a hole transporting layer and an electron transporting layer are laminated, and at least the electron transporting layer of the organic layer has the general formula [I]
The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device is a layer containing at least one kind of a mixed ligand complex represented by the following formula: 5. The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are laminated, and at least the hole transport layer of the organic layer is represented by the general formula [I]. The organic electroluminescent device according to claim 1, wherein the organic electroluminescent device is a layer containing at least one kind of the mixed ligand complex represented. 6. The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are laminated, and the hole transport layer has a mixed coordination represented by the general formula [I]. 2. The layer according to claim 1, wherein the electron transport layer is a layer containing at least one kind of the mixed ligand complex represented by the general formula [I]. 3. The described organic electroluminescent device. 7. The organic layer has an organic laminated structure in which a hole transport layer, a light emitting layer, and an electron transport layer are laminated,
The organic electroluminescent device according to claim 1, wherein at least the light-emitting layer among the organic layers is a layer containing at least one kind of the mixed ligand complex represented by the general formula [I]. 8. The organic electroluminescent device according to claim 1, wherein a hole blocking layer is present in contact with a cathode side of the layer composed of the mixed ligand complex. 9. The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are laminated, and at least the electron transport layer of the organic layer has the general formula [I]
The organic electroluminescent device according to claim 8, wherein the organic EL device is a layer containing at least one kind of the mixed ligand complex represented by the formula: and the hole blocking layer is in contact with the cathode side of the layer. 10. The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are laminated, and at least the hole transport layer of the organic layer is represented by the general formula [I]. The organic electroluminescent device according to claim 8, wherein the organic EL device is a layer containing at least one kind of the mixed ligand complex represented by the formula, and wherein the hole blocking layer is present in contact with the cathode side of the layer. 11. The organic layer has an organic laminated structure in which a hole transport layer and an electron transport layer are laminated, and the hole transport layer has a mixed coordination represented by the general formula [I]. The electron transporting layer is a layer containing at least one kind of the mixed ligand complex represented by the general formula [I], and the electron transporting layer is a layer containing at least one kind of the complex ligand. The organic electroluminescent device according to claim 8, wherein the hole blocking layer is present in contact with the cathode side of the layer. 12. The organic layer has an organic laminated structure in which a hole transporting layer, a light emitting layer, and an electron transporting layer are laminated, and at least the light emitting layer of the organic layer has the general formula [ At least one of the mixed ligand complexes represented by I]
9. The organic electroluminescent device according to claim 8, wherein the hole blocking layer is a layer containing a seed and is in contact with the cathode side of the layer.