JPH11329729A - Luminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminescent element capable of emitting orange - red light, with high luminescent efficiency, and high brightness by containing a metal complex having a quinoxaline skeleton. SOLUTION: A metal complex is represented by formula. Where, R1 -R5 may be the same or different, and are selected from hydrogen, alkyl group, cycloalkyl group, aralkyl group, alkenyl group, cycloalkenyl group, alkynyl group, hydroxyl group, mercapt group, alkoxy group, alkylthio group, arylether group, arylthio ether group, aryl group, heterocyclic group, halogen, haloalkane, haloalkene, haloalkine, cyano group, aldehyde group, carbonyl group, carboxyl group, ester group, carbamoyl group, amino group, nitro group, silyl group, siloxanyl group, a fused ring formed between adjacent substitution groups, heterocyclic ring, and aliphatic ring. M represents (m) valent metal, (m) represents natural number of 1-3. Since the preparation of the complex is easy, zinc is preferably used as the center metal M.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element capable of converting electric energy into light, and relates to a display element, a flat panel display, a backlight, lighting, an interior, a sign, a sign, an electrophotographic device, an optical signal generator, and the like. The present invention relates to a light emitting element that can be used in the field of (1).

[0002]

2. Description of the Related Art In recent years, active research has been conducted on organic thin-film light emitting devices that emit light when electrons injected from a negative electrode and holes injected from a positive electrode recombine in an organic phosphor sandwiched between both electrodes. I have. This element is characterized by thinness, high luminance light emission under a low driving voltage, and multicolor light emission by selecting a fluorescent material.

[0003] It is known from Kodak's C.I. W. Tang et al. (Appl. Phys. Lett. 51 (12)
21, p. 913, 1987). A typical configuration of the organic laminated thin-film light emitting device presented by Kodak Company is a hole transporting diamine compound and a light emitting layer on an ITO glass substrate,
Tris (8-quinolinolato) aluminum, which also has an electron transporting property, and Mg: Ag were sequentially provided as a negative electrode, and green light emission of 1000 candela / m 2 was possible at a driving voltage of about 10V. The current organic laminated thin-film light-emitting device has a different configuration, such as a device provided with an electron transport layer, in addition to the above-described device components, but basically follows the configuration of Kodak. I have.

As a host material of the light emitting layer, tris (8
-Quinolinolato) aluminum and other metal-chelating oxinoid compounds, diarylbutadiene derivatives, stilbene derivatives, benzoxazole derivatives, benzothiazole derivatives (JP-A-63-264692) and the like.

On the other hand, as dopant materials as guest materials, fluorescent coumarin dyes such as 7-dimethylamino-4-methylcoumarin, dicyanomethylenepyran dye, and the like, which are known to be useful as laser dyes, Dicyanomethylenethiopyran dye, polymethine dye, cyanine dye, oxobenzanthracene dye, xanthene dye, rhodamine dye, fluorescein dye,
Pyrylium dye, carbostyril dye, perylene dye,
Acridine dye, bis (styryl) benzene dye, pyrene dye, oxazine dye, phenylene oxide dye (JP-A-63-264892), perylene, tetracene, pentacene (JP-A-2-261889), quinacridone compounds, quinazoline compounds (JP-A-5-70773) pyrrolopyridine compound, furopyridine compound (JP-A-5-222360),
2,5-thiadiazolopyrene derivatives (JP-A-5-222)
No. 361), perinone derivatives (JP-A-5-2796)
62, a pyrrolopyrrole compound (JP-A-5-32)
No. 0663), squarylium compounds (Japanese Unexamined Patent Publication No.
93257), a biolanthrone compound (Japanese Unexamined Patent Publication No.
-90259), phenazine derivatives (Japanese Unexamined Patent Publication No.
102250), an acridone compound (Japanese Unexamined Patent Publication No.
No. 67873), diazaflavin derivatives (Japanese Unexamined Patent Publication No.
-78058) and the like.

[0006]

However, the luminescent materials (host materials and dopant materials) used in the prior art include those having low luminous efficiency and high power consumption, and those having low durability of the compound and short element life. There were many. Among the three primary colors required for a full-color display, a high-performance light-emitting material has been found for green light emission, but a light-emitting material having sufficient characteristics for blue or red, particularly red has not been obtained. An object of the present invention is to solve the problems of the prior art and to provide a light-emitting element that can emit orange to red light, has high luminous efficiency, and can obtain high luminance.

[0007]

In order to achieve the above object, the present invention provides an element which emits light by electric energy, wherein a substance which controls light emission exists between a positive electrode and a negative electrode, and the element has a quinoxaline skeleton. A light-emitting element characterized by including a metal complex having the same.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A positive electrode according to the present invention is made of a conductive metal oxide such as tin oxide, indium oxide, indium tin oxide (ITO), or gold, silver, chromium, if it is transparent to extract light. Metals such as, for example, inorganic conductive substances such as copper iodide and copper sulfide, and conductive polymers such as polythiophene, polypyrrole, and polyaniline are not particularly limited, but it is particularly preferable to use ITO glass or Nesa glass. The resistance of the transparent electrode is not limited as long as a current sufficient for light emission of the element can be supplied, but is preferably low from the viewpoint of power consumption of the element. For example, an ITO substrate having a resistance of 300Ω / □ or less functions as an element electrode, but a substrate having a resistance of about 20Ω / □ or less should be used because a substrate of about 10Ω / □ can be supplied at present. Is particularly desirable. The thickness of the ITO can be arbitrarily selected according to the resistance value.
It is often used between ３００300 nm. Further, as the glass substrate, soda lime glass, non-alkali glass or the like is used, and the thickness only needs to be sufficient to maintain the mechanical strength.
As for the material of the glass, alkali-free glass is preferable because it is better that ions eluted from the glass are small,
Soda lime glass provided with a barrier coat such as SiO ₂ is also commercially available and can be used. The method of forming the ITO film is not particularly limited, such as an electron beam evaporation method, a sputtering method, and a chemical reaction method.

The negative electrode in the present invention is not particularly limited as long as it can efficiently inject electrons into a substance that efficiently emits light or a substance adjacent to the substance that emits light (for example, an electron transport layer). Generally, platinum, gold, silver, copper, iron, tin, aluminum, indium, lithium, sodium, potassium, calcium, magnesium and the like can be mentioned. In order to improve the device characteristics by increasing the electron injection efficiency, lithium, sodium, potassium, calcium, magnesium or an alloy containing these low work function metals is effective. However, these low work function metals are generally unstable in the atmosphere, and platinum, gold,
Metals such as silver, copper, iron, tin, aluminum and indium, or alloys using these metals, and silica,
It is preferable to laminate an inorganic substance such as titania and a polymer such as polyvinyl alcohol and vinyl chloride. These electrodes are also manufactured by resistance heating method evaporation, electron beam evaporation method,
There is no particular limitation as long as electrical continuity such as a sputtering method, an ion plating method, and a coating method can be achieved.

The composition of the substance that controls light emission in the present invention is as follows:
1) a hole transporting material / a light emitting material, 2) a hole transporting material / a light emitting material / an electron transporting material, 3) a light emitting material / an electron transporting material, and 4) a form in which a combination of the above substances is mixed.
Any of these may be used. That is, in addition to the multi-layer structure of 1) to 3), a layer containing a luminescent material alone or a luminescent material and a hole transporting material, or a layer containing a luminescent material, a hole transporting material and an electron transporting material as in 4) is further provided. It may just be provided.

The light emitting material may be either a host material alone or a combination of a host material and a dopant material. In addition, the dopant material may be included in the entire host material, partially, or may be included. The dopant material may be stacked, dispersed, or the like.

The hole transporting material in the present invention is required to efficiently transport holes from the positive electrode between the electrodes to which an electric field is applied, and has a high hole injection efficiency. Good transport is desirable. For that purpose, it is required that the ionization potential be small, the hole mobility be large, the stability be further improved, and impurities serving as traps be hardly generated during production and use. The substance satisfying such conditions is not particularly limited, but is a biscarbazolyl derivative,
Known triphenylamine derivatives such as TPD, m-MTDATA, α-NPD, pyrazoline derivatives, stilbene compounds, hydrazone compounds, heterocyclic compounds represented by oxadiazole derivatives and phthalocyanine derivatives, polyvinyl carbazole, polysilane and the like Hole transport materials can be used. These hole transport materials may be used alone or may be laminated or mixed with different hole transport materials.

The luminescent material of the present invention contains a metal complex having a quinoxaline skeleton. The metal complex having the quinoxaline skeleton may be used as a dopant material, but is preferably used as a host material. Also, because the quinoxaline skeleton has good electron transporting ability,
It is also preferably used as an electron transporting light emitting layer, and may be used as an electron transporting layer. As the metal complex having the quinoxaline skeleton, a compound represented by the following general formula can be given because of easy synthesis.

[0014]

Embedded image Here, R1 to R5 may be the same or different, and may be hydrogen, alkyl, cycloalkyl, aralkyl, alkenyl, cycloalkenyl, alkynyl, hydroxyl, mercapto, alkoxy, alkylthio, aryl Ether group, arylthioether group,
Aryl group, heterocyclic group, halogen, haloalkane, haloalkene, haloalkyne, cyano group, aldehyde group, carbonyl group, carboxyl group, ester group, carbamoyl group, amino group, nitro group, silyl group, siloxanyl group, with adjacent substituent It is selected from a condensed ring, a heterocyclic ring and an aliphatic ring formed therebetween. M represents an m-valent metal,
m represents a natural number of 1 to 3.

Among these substituents, the alkyl group means a saturated aliphatic hydrocarbon group such as a methyl group, an ethyl group, a propyl group, a butyl group and the like, which may be unsubstituted or substituted. The cycloalkyl group is, for example, a saturated alicyclic hydrocarbon group such as cyclopropyl, cyclohexyl, norbornyl, and adamantyl, which may be unsubstituted or substituted. The aralkyl group refers to an aromatic hydrocarbon group via an aliphatic hydrocarbon such as a benzyl group and a phenylethyl group, and the aliphatic hydrocarbon and the aromatic hydrocarbon may be unsubstituted or substituted. I don't care. The alkenyl group refers to an unsaturated aliphatic hydrocarbon group containing a double bond such as a vinyl group, an allyl group and a butadienyl group, which may be unsubstituted or substituted. The cycloalkenyl group refers to an unsaturated alicyclic hydrocarbon group containing a double bond such as a cyclopentenyl group, a cyclopentadienyl group, and a cyclohexene group, which may be unsubstituted or substituted. . The alkynyl group means an unsaturated aliphatic hydrocarbon group containing a triple bond such as an acetylenyl group, which may be unsubstituted or substituted. The alkoxy group refers to an aliphatic hydrocarbon group via an ether bond such as a methoxy group, and the aliphatic hydrocarbon group may be unsubstituted or substituted. The alkylthio group is obtained by substituting the oxygen atom of the ether bond of the alkoxy group with a sulfur atom. Further, the aryl ether group refers to an aromatic hydrocarbon group via an ether bond such as a phenoxy group, and the aromatic hydrocarbon group may be unsubstituted or substituted. Also,
The arylthioether group is a group in which an oxygen atom of an ether bond of the arylether group is substituted with a sulfur atom. The aryl group refers to, for example, an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, a biphenyl group, a phenanthryl group, a terphenyl group, and a pyrenyl group, which may be unsubstituted or substituted. Further, the heterocyclic group refers to a cyclic structural group having an atom other than carbon, such as a furanyl group, a thiophenyl group, an oxazolyl group, a pyridyl group, a quinolinyl group, and a carbazolyl group, which may be unsubstituted or substituted. Absent. Halogen refers to fluorine, chlorine, bromine and iodine. Haloalkanes, haloalkenes, and haloalkynes are those in which some or all of the aforementioned alkyl, alkenyl, and alkynyl groups, such as trifluoromethyl, have been substituted with the aforementioned halogens, and the rest are unsubstituted. It may be replaced. Aldehyde groups, carbonyl groups, ester groups, carbamoyl groups, and amino groups include those substituted with aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, heterocycles, and the like. The cyclic hydrocarbon, aromatic hydrocarbon and heterocyclic ring may be unsubstituted or substituted. The silyl group means a silicon compound group such as a trimethylsilyl group, which may be unsubstituted or substituted. The siloxanyl group means a silicon compound group via an ether bond such as a trimethylsiloxanyl group, which may be unsubstituted or substituted.

Examples of the central metal M include, but are not particularly limited to, lithium, beryllium, sodium, magnesium, aluminum, potassium, calcium, zinc, gallium and the like. The valence of the central metal M is preferably 1 or 2, and zinc is more preferably used as the central metal because complex adjustment is easy.

The above-mentioned metal complex having a quinoxaline skeleton specifically has the following structure.

[0018]

Embedded image

Embedded image

The host material is not limited to one kind of the metal complex having the quinoxaline skeleton, and a mixture of a plurality of metal complexes having the quinoxaline skeleton may be used. It may be used as a mixture with a metal complex having a skeleton. Specifically, condensed ring derivatives such as anthracene and pyrene which have been known as luminous bodies, metal chelated oxinoid compounds such as tris (8-quinolinolato) aluminum, bisstyrylanthracene derivatives, distyrylbenzene derivatives, etc. Bisstyryl derivative, tetraphenylbutadiene derivative, coumarin derivative, oxadiazole derivative, pyrrolopyridine derivative, perinone derivative, cyclopentadiene derivative, oxadiazole derivative, thiadiazolopyridine derivative, polymer system, polyphenylenevinylene derivative, polyparaphenylene Derivatives and polythiophene derivatives can be used, but are not particularly limited.

The dopant material to be added to the light emitting material is not particularly limited, but a known dopant material can be used. Specifically, conventionally known,
Condensed ring derivatives such as perylene and rubrene, quinacridone derivatives, phenoxazone 660, DCM1, perinone,
Coumarin derivatives and the like can be used as they are.

As the electron transporting material in the present invention, it is necessary to efficiently transport electrons from the negative electrode between the electrodes to which an electric field is applied, and it is necessary to have a high electron injection efficiency and to efficiently transport the injected electrons. Is desirable. For that purpose, electron affinity is large, and electron mobility is large,
Further, it is required that the substance be excellent in stability and hardly generate impurities serving as traps during production and use. As a substance satisfying such a condition, a metal complex having the quinoxaline skeleton or tris (8-quinolinolato)
There are quinolinol derivative metal complexes represented by aluminum, tropolone metal complexes, flavonol metal complexes, perylene derivatives, perinone derivatives, naphthalene, coumarin derivatives, oxadiazole derivatives, aldazine derivatives, bisstyryl derivatives, pyrazine derivatives, phenanthroline derivatives, and the like. It is not limited. These electron transporting materials may be used alone or may be laminated or mixed with different electron transporting materials.

The above materials used for the hole transporting layer, the light emitting layer and the electron transporting layer can be used alone to form each layer. Examples of the polymer binder include polyvinyl chloride, polycarbonate, polystyrene, and the like. Poly (N-vinyl carbazo-
), Polymethyl methacrylate, polybutyl methacrylate, polyester, polysulfone, polyphenylene oxide, polybutadiene, hydrocarbon resin, ketone resin, phenoxy resin, polyamide, ethyl cellulose
Curing of solvent-soluble resins such as water, vinyl acetate, ABS resin and polyurethane resin, phenol resin, xylene resin, petroleum resin, urea resin, melamine resin, unsaturated polyester resin, alkyd resin, epoxy resin, silicone resin, etc. It is also possible to use it by dispersing it in a conductive resin or the like.

The method of forming the substance which controls light emission in the present invention is not particularly limited, such as resistance heating evaporation, electron beam evaporation, sputtering, molecular lamination, and coating. Beam evaporation is preferred in terms of properties. The thickness of the layer depends on the resistance of the substance that controls light emission and cannot be limited, but is selected from the range of 10 to 1000 nm.

The electric energy in the present invention mainly refers to a direct current, but it is also possible to use a pulse current or an alternating current. The current value and voltage value are not particularly limited,
In consideration of the power consumption and life of the device, it is necessary to obtain the maximum brightness with the lowest possible energy.

It is preferable that the light emitting device of the present invention constitutes a display for displaying by a matrix or segment system or a combination of both.

The matrix according to the present invention is a matrix in which pixels for display are arranged in a lattice, and displays a character or an image by a set of pixels. The shape and size of the pixel depend on the application. For example, for the display of images and characters on personal computers, monitors, televisions, and the like, generally square pixels with a side of 300 μm or less are used, and in the case of a large display such as a display panel, pixels with a side on the order of mm are used. Become. In the case of monochrome display, pixels of the same color may be arranged, but in the case of color display, red, green and blue pixels are displayed side by side. In this case, there are typically a delta type and a stripe type. Note that the light-emitting element of the present invention can emit red, green, and blue light, so that multi-color or full-color display can be performed by using the display method. The matrix may be driven by either a line-sequential driving method or an active matrix. The line-sequential driving has the advantage of a simpler structure, but the active matrix is sometimes superior in consideration of the operating characteristics. Therefore, it is necessary to use this depending on the application.

In the segment type according to the present invention, a pattern is formed so as to display predetermined information, and a predetermined area emits light. For example, there are a time display and a temperature display on a digital clock or a thermometer, an operation state display of an audio device, an electromagnetic cooker, or the like, and a panel display of an automobile. The matrix display and the segment display may coexist in the same panel.

The light emitting device of the present invention is also preferably used as a backlight. The backlight in the present invention,
It is mainly used for improving the visibility of a display device that does not emit light, and is used for a liquid crystal display device, a clock, an audio device, an automobile panel, a display panel, a sign, and the like. In particular, as for the backlight for liquid crystal display devices, particularly for personal computer applications where thinning is an issue, the present invention is considered to be difficult because the conventional type is made of a fluorescent lamp or a light guide plate, and it is difficult to make it thin. Is characterized by its thinness and light weight.

[0029]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 A glass substrate (15 Ω / □, electron beam vapor-deposited product, manufactured by Asahi Glass Co., Ltd.) on which an ITO transparent conductive film was deposited to 150 nm was used for 30
The wafer was cut into a size of 40 mm and etched. The obtained substrate was subjected to ultrasonic cleaning with acetone and semicocrine 56 for 15 minutes each, and then with ultrapure water. Subsequently, the substrate was subjected to ultrasonic cleaning with isopropyl alcohol for 15 minutes, immersed in hot methanol for 15 minutes, and dried. This substrate was subjected to UV-ozone treatment for 1 hour immediately before producing the element, placed in a vacuum evaporation apparatus, and evacuated until the degree of vacuum in the apparatus became 5 × 10 ⁻⁵ Pa or less. First, 4,4′-bis (N- (m-tolyl) -N-phenylamino) biphenyl was deposited as a hole transporting material to a thickness of 100 nm by a resistance heating method. Next, bis (2,3-bis (p-dimethylaminophenyl) -8-quinoxalinolate) zinc (solid fluorescence: 577 nm) as a light emitting material was laminated to a thickness of 100 nm. Next, 2 nm of lithium and 150 nm of silver were deposited to form a cathode,
A 5 × 5 mm square device was produced. The film thickness referred to here is a value displayed on a crystal oscillation type film thickness monitor corrected by a value measured by a surface roughness meter. The light-emitting voltage of this light-emitting element was 6 V, the maximum luminance was 45 candelas / square meter, and favorable orange light emission with a light emission peak wavelength of 587 nm was obtained.

Example 2 Light emission of a device manufactured in exactly the same manner as in Example 1 except that bis (2,3-diphenyl-8-quinoxalinolate) zinc (solid fluorescence: 608 nm) was used as a light emitting material. The voltage was 7 V, the maximum luminance was 9 candela / square meter, and good red light emission with an emission peak wavelength of 619 nm was obtained.

Example 3 Example 1 was repeated except that tris (8-quinoxalinolate) aluminum (solid fluorescence: 577 nm) was used as the light emitting material.
The light emission starting voltage of the device manufactured in exactly the same
The highest luminance was 23 candela / square meter, and good orange light emission with an emission peak wavelength of 585 nm was obtained.

Comparative Example 1 Tris (benzoyltrifluoroacetonate) europium was deposited as a light emitting material to a thickness of 1500 nm on an ITO substrate treated in the same manner as in Example 1. Next, 100 nm of gold was vapor-deposited to form a cathode, and a 5 × 5 mm square device was produced. The light emission starting voltage of this light emitting element is 16 V
In this case, red light emission having a light emission peak wavelength of 618 nm was obtained, but the maximum luminance was only 5 candela / square meter.

[0034]

According to the present invention, it is possible to provide a light emitting device which can emit orange to red light, has high luminous efficiency, and can obtain high luminance.

Claims (8)

[Claims] 1. A light-emitting element in which a substance which emits light is present between a positive electrode and a negative electrode and which emits light by electric energy, wherein the element contains a metal complex having a quinoxaline skeleton. 2. The light emitting device according to claim 1, wherein the metal complex having a quinoxaline skeleton is represented by the following general formula. Embedded image (Where R1 to R5 may be the same or different, and each represents a hydrogen, an alkyl group, a cycloalkyl group, an aralkyl group, an alkenyl group, a cycloalkenyl group, an alkynyl group, a hydroxyl group, a mercapto group, an alkoxy group, an alkylthio group, Aryl ether group, aryl thioether group, aryl group, heterocyclic group, halogen, haloalkane,
Haloalkenes, haloalkynes, cyano groups, aldehyde groups, carbonyl groups, carboxyl groups, ester groups, carbamoyl groups, amino groups, nitro groups, silyl groups, siloxanyl groups, fused rings formed between adjacent substituents, heterocycles and Selected from aliphatic rings. M represents an m-valent metal, and m represents a natural number of 1 to 3. ) 3. The light emitting device according to claim 2, wherein M is a monovalent or divalent metal. 4. The method according to claim 2, wherein M is zinc.
The light-emitting element according to any one of the preceding claims. 5. The light emitting device according to claim 1, wherein the metal complex having a quinoxaline skeleton is a light emitting material. 6. The light emitting device according to claim 1, wherein the metal complex having a quinoxaline skeleton is a host material. 7. The light emitting device according to claim 1, wherein the light emitting device constitutes a display for displaying by a matrix and / or segment method. 8. The light emitting device according to claim 1, wherein the light emitting device is a backlight.