JP2005235787A - Organic electroluminescence element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a long-life and highly efficient organic electroluminescence element (organic EL element), where for example a change in a luminescent color is small even after a long drive. <P>SOLUTION: The organic electroluminescence element has an organic compound layer, having at least a recombination region in which holes and electrons are recombined, and an emission region that emits light in response to the recombination, and a pair of electrodes for pinching the organic compound layer. In the organic electroluminescence element, diphenylbenzofluoranthene is contained by a ratio of 0.1-8 wt.% as a fluorescent dopant in the recombination region and/or emission region. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic electroluminescence (hereinafter abbreviated as EL) element, and more particularly to an organic EL element having a long life and high efficiency such as little change in emission color even when driven for a long time. It is.

EL elements using electroluminescence are highly visible due to self-emission and are completely solid elements, so they have features such as excellent impact resistance, so they are attracting attention as light emitting elements in various display devices. Has been.
In this EL element, there are an inorganic EL element using an inorganic compound as a light emitting material and an organic EL element using an organic compound. Among these, the organic EL element can greatly reduce the applied voltage. As a next-generation display element, research into practical use has been actively conducted.

By the way, in this organic EL device, in order to develop a long-life and high-efficiency blue light-emitting device, research on blue light-emitting materials has been focused on various blue light-emitting materials such as high luminance and high efficiency. Distyrylarylene-based blue light-emitting materials (Patent Document 1), high-brightness chelate-based blue light-emitting materials (Patent Document 2), and high-brightness diamine-based blue light-emitting materials (Patent Document 3) are disclosed. However, these blue light-emitting materials are usually used in the configuration of anode / hole injection / transport layer / light-emitting layer / electron injection / transport layer / cathode and have been demonstrated in performance, but they are always satisfactory in terms of lifetime. Rather, for example, (1) as the driving time elapses, the color changes to green and the emission color changes. (2) The half-life at an initial luminance of 100 cd / m ² is as short as about 1000 hours (practically several). There are problems such as that more than 1000 hours are required).

On the other hand, an element using a compound having a perylene structure with a different substituent similar to the fluorescent dopant in the present invention as a material of the light emitting layer has been proposed (Patent Documents 4 and 5). No mention is made of the function.
Patent Documents 6 and 7 listed below disclose distyrylarylene-based materials that are charge injection auxiliary agents added to the light emitting layer. Although this material also functions as a fluorescent dopant, the half-life of an element using this material is as short as about 1000 hours (initial luminance 100 cd / m ² ), and improvement has been demanded.
Furthermore, in the following Patent Document 8, a technique for containing a condensed polycyclic hydrocarbon compound in an aluminum chelate represented by (R ⁵ -Q) ₂ Al—OL is disclosed. A technique in which the condensed polycyclic hydrocarbon compound is incorporated into an aluminum chelate represented by (R ⁵ -Q) ₂ Al—O—Al (Q—R ⁵ ) ₂ is disclosed. These emit blue light by doping with an unsubstituted condensed polycyclic hydrocarbon. Even in the best combination of these, the half-life is 2000 hours or less and the efficiency is about 1 lm / W. Improvement was required because it was low.

JP-A-2-247278 JP-A-5-198378 JP-A-6-220437 JP-A-3-791 Japanese Patent Laid-Open No. 3-162485 JP-A-6-9953 International Patent Publication No. 94-6157 Japanese Patent Laid-Open No. 5-214332 JP-A-5-198377

  The present invention provides a long-life and high-efficiency organic EL element that improves such drawbacks of the conventional organic EL element and has a small change in emission color even when driven for a long time. It is intended.

As a result of intensive studies to develop a long-life and high-efficiency organic EL device, the present inventors, as a fluorescent dopant, in at least one of a bonding region or a light-emitting region of holes and electrons of the device, It has been found that the purpose can be achieved by containing a specific compound in a predetermined ratio. The present invention has been completed based on such findings.
That is, the present invention includes an organic compound layer having at least a recombination region in which holes and electrons recombine, a light emitting region that emits light in response to the recombination, and a pair of electrodes that hold the organic compound layer. In the organic electroluminescence device provided, each of the above-mentioned recombination region and / or light-emitting region has diphenylbenzo having only a secondary or tertiary alkyl group having 3 to 10 carbon atoms or a substituent having 1 to 4 cycloalkyl groups. The present invention provides an organic electroluminescence device characterized by containing fluoranthene as a fluorescent dopant in a proportion of 0.1 to 8% by weight.

The organic EL device of the present invention contains a fluorescent dopant having a specific structure in at least one of a recombination region where holes and electrons recombine or a light emitting region which emits light in response to the recombination. However, even if it is driven for a long time, it has a long life, such as little change in emission color, and has a high light emission efficiency, and is suitably used for, for example, displays of information industry equipment.
Hereinafter, the present invention will be described in more detail.

で表され、１以上の置換基Ｒでのみ置換された構造である化合物の中から選ばれた少なくとも一種を0.１〜８重量％の割合で含有させることが好ましい。上記一般式（１）の母骨格構造を有する化合物において、置換基Ｒはそれぞれ炭素数１〜１０のアルキル基又はシクロアルキル基である。ここで、炭素数１〜１０のアルキル基の具体例としては、例えばメチル基，エチル基，ｎ−プロピル基，イソプロピル基，ｎ−ブチル基，イソブチル基，ｓｅｃ−ブチル基，ｔ−ブチル基，イソオクチル基などが挙げられる。また、シクロアルキル基の具体例としては、例えばシクロヘキシル基，シクロペンチル基などが挙げられる。 As the fluorescent dopant of the present invention, the mother skeleton has the following general formula (1)

It is preferable that at least one compound selected from the compounds represented by the above formula and substituted only with one or more substituents R is contained in a proportion of 0.1 to 8% by weight. In the compound having the mother skeleton structure of the general formula (1), the substituents R are each an alkyl group or a cycloalkyl group having 1 to 10 carbon atoms. Here, specific examples of the alkyl group having 1 to 10 carbon atoms include, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butyl group, An isooctyl group etc. are mentioned. Specific examples of the cycloalkyl group include a cyclohexyl group and a cyclopentyl group.

Specific examples of the compound having the mother skeleton structure of the general formula (1) include compounds having the following structures.

  In the above compound, the number n of substituents is preferably an integer of 1 to 6, and the position of these substituents is not particularly limited. Accordingly, it may be a structural isomer or a mixture of n of 1 to 6.

  In the present invention, these compounds may be used as a fluorescent dopant, or two or more of them may be used in combination.

  The fluorescent dopant in the present invention is a compound that emits light in response to recombination of holes and electrons in the recombination region or light emitting region of the organic EL element. The substance to be formed (host material) contains a trace amount. Here, the recombination region is a place in the device where holes and electrons meet and combine to form an excited state. In addition, the light emitting region is a place where the excited state formed in the recombination region moves and diffuses depending on the case, but specifies the diffusion range.

  In the present invention, the fluorescent dopant is at least one of the recombination region and the light-emitting region, that is, only in the recombination region, only in the light-emitting region, or in both regions at a ratio of 0.1 to 8% by weight. It is necessary to contain. When the content is less than 0.1% by weight, the effect of the fluorescent dopant is not sufficiently exhibited, and the object of the present invention cannot be achieved. On the other hand, if it exceeds 8% by weight, the disappearance phenomenon may occur due to the association between the fluorescent dopants, and the effect may not be sufficiently exhibited. From the viewpoint of extending the life and efficiency of the device, the preferred content of the fluorescent dopant is in the range of 0.3 to 4% by weight, and particularly preferably in the range of 0.8 to 3% by weight.

  Although there is no restriction | limiting in particular about the method of making this fluorescent dopant contain in a recombination area | region or a light emission area | region, For example, it is preferable to employ | adopt the co-evaporation method with the material (host material) which forms a recombination area | region or a light emission area | region. . In this method, the host material and the fluorescent dopant are vacuum-deposited from separate boats in which the host material and the fluorescent dopant are accommodated to form a recombination region and a light emitting region.

  In the organic EL device of the present invention, an organic compound layer having at least a recombination region and a light emitting region is used. Since the recombination region and the light emitting region are usually present in the light emitting layer, in the present invention, only the light emitting layer may be used as the organic compound layer, but if necessary, other than the light emitting layer, for example, a hole injection layer. An electron injection layer, an organic semiconductor layer, an electron barrier layer, an adhesion improving layer, and the like can also be used.

Next, the typical structural example of the organic EL element of this invention is shown. Of course, it is not limited to this.
(I) Anode / hole injection layer / light emitting layer / cathode (II) Anode / hole injection layer / light emitting layer / electron injection layer / cathode (III) Anode / light emitting layer / electron injection layer / cathode (IV) Anode / Organic semiconductor layer / light emitting layer / cathode (V) Anode / organic semiconductor layer / electron barrier layer / light emitting layer / cathode (VI) Anode / hole injection layer / light emitting layer / adhesion improving layer / cathode The structure of II) is preferably used.

  As described above, the recombination region and the light emitting region in the element of the present invention are usually present in the light emitting layer. Therefore, the fluorescent dopant is usually contained in the light emitting layer. However, in some cases, other layers such as a hole injection layer, an electron injection layer, an organic semiconductor layer, an electron barrier layer, and an adhesion improving layer may be involved in recombination and light emission. In this case, these layers are also preferably contained.

The organic EL device of the present invention has a structure in which the organic compound layer is sandwiched between a pair of electrodes, that is, an anode and a cathode. The anode has a work function (4 eV or more) metal, alloy, What uses an electroconductive compound and a mixture thereof as an electrode material is preferably used. Specific examples of such electrode materials include metals such as Au, and dielectric transparent materials such as CuI, ITO, SnO ₂ and ZnO. The anode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. When taking out light emission from this electrode, it is desirable to make the transmittance greater than 10%, and the sheet resistance as the electrode is preferably several hundred Ω / □ or less. Further, although the film thickness depends on the material, it is usually preferably in the range of 10 nm to 1 μm, particularly 10 to 200 nm.

On the other hand, as the cathode, those using an electrode material of a metal, an alloy, an electrically conductive compound and a mixture thereof having a small work function (4 eV or less) are used. Specific examples of such an electrode material include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / silver alloy, Al / AlO ₂ , aluminum-lithium alloy, indium, rare earth metal, and the like. The cathode can be produced by forming a thin film of these electrode materials by a method such as vapor deposition or sputtering. Further, the sheet resistance as an electrode is preferably several hundred Ω / □ or less, and the film thickness is usually in the range of 10 nm to 1 μm, particularly 50 to 200 nm. In the element of the present invention, although not particularly defined, it is preferable that either one of the anode and the cathode is transparent or translucent because the light can be transmitted and extracted efficiently.

  In the light emitting layer in the element of the present invention, as the light emitting material (host material), the general formula (I)

A distyrylarylene compound represented by the formula is preferably used. This compound is disclosed in JP-A-2-247278.

In the general formula (I), Y ^{1 to} Y ⁴ are each a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aralkyl group having 7 to 8 carbon atoms, a substituted or unsubstituted group. An aryl group having 6 to 18 carbon atoms, a substituted or unsubstituted cyclohexyl group, a substituted or unsubstituted aryloxy group having 6 to 18 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms are shown. Here, the substituent is an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aralkyl group having 7 to 8 carbon atoms, an aryloxy group having 6 to 18 carbon atoms, or an acyl having 1 to 6 carbon atoms. Group, C1-C6 acyloxy group, carboxyl group, styryl group, C6-C20 arylcarbonyl group, C6-C20 aryloxycarbonyl group, C1-C6 alkoxycarbonyl group, vinyl group , Anilinocarbonyl group, carbamoyl group, phenyl group, nitro group, hydroxyl group or halogen. These substituents may be single or plural. Y ^{1 to} Y ⁴ may be the same or different from each other, and Y ¹ and Y ² and Y ³ and Y ⁴ are bonded to a group that is substituted with each other to form a substituted or unsubstituted saturated five-membered member. A ring or a substituted or unsubstituted saturated six-membered ring may be formed. Ar represents a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, which may be single-substituted or plural-substituted, and the bonding site may be any of ortho, para, and meta. However, when Ar is an unsubstituted phenylene group, Y ^{1 to} Y ⁴ are each an alkoxy group having 1 to 6 carbon atoms, an aralkyl group having 7 to 8 carbon atoms, a substituted or unsubstituted naphthyl group, a biphenyl group, a cyclohexyl group, It is selected from aryloxy groups.

Examples of such distyrylarylene-based compounds include:

Etc.

  Another preferable light-emitting material (host material) is 8-hydroxyquinoline or a metal complex of a derivative thereof. Specifically, it is a metal chelate oxinoid compound containing a chelate of oxine (generally 8-quinolinol or 8-hydroxyquinoline). Such compounds exhibit a high level of performance and are easily formed into thin film forms. Examples of this oxinoid compound satisfy the following structural formula.

(In the formula, Mt represents a metal, n is an integer of 1 to 3, and Z represents an atom necessary for completing at least two condensed aromatic rings, each of which is independent at each position. .)

  Here, the metal represented by Mt can be a monovalent, divalent or trivalent metal, for example, an alkali metal such as lithium, sodium or potassium, or an alkaline earth metal such as magnesium or calcium. Or an earth metal such as boron or aluminum.

  In general, any monovalent, divalent or trivalent metal known to be a useful chelate compound can be used.

  Z represents an atom that forms a heterocyclic ring in which one of at least two condensed aromatic rings is an azole or an azine. Here, if necessary, it is possible to add another different ring to the condensed aromatic ring. In order to avoid adding bulky molecules without functional improvement, it is preferable to maintain the number of atoms represented by Z at 18 or less.

  Furthermore, specific examples of chelated oxinoid compounds include tris (8-quinolinol) aluminum, bis (8-quinolinol) magnesium, bis (benzo-8-quinolinol) zinc, bis (2-methyl-8-quinolylato) aluminum. Oxides, tris (8-quinolinol) indium, tris (5-methyl-8-quinolinol) aluminum, 8-quinolinol lithium, tris (5-chloro-8-quinolinol) gallium, bis (5-chloro-8-quinolinol) calcium 5,7-dichloro-8-quinolinol aluminum, tris (5,7-dibromo-8-hydroxyquinolinol) aluminum, and the like.

Further, a phenolate-substituted 8-hydroxyquinoline metal complex described in JP-A-5-198378 is preferable as a blue light-emitting material. Specific examples of the metal complex of the phenolate-substituted 8-hydroxyquinoline include bis (2-methyl-8-quinolinolato) (phenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (o-cresolate) aluminum. (III), bis (2-methyl-8-quinolinolato) (m-cresolate) aluminum (III), bis (2-methyl-8-quinolinolato) (p-cresolate) aluminum (III), bis (2-methyl- 8-quinolinolato) (o-phenylphenolato) aluminum (III), bis (2-methyl-8-quinolinolato) (m-phenylphenolato) aluminum (III), bis (2-methyl-8-quinolinolato) (p -Phenylphenolate) Aluminum (III), Bis (2-methyl-8-quinolinolate) ( 2,3-dimethylphenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (2,6-dimethylphenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (3 4-dimethylphenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (3,5-dimethylphenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (3,5- Di-t-butylphenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (2,6-diphenylphenolate) aluminum (III), bis (2-methyl-8-quinolinolato) (2, 4,6-triphenylphenolate) aluminum (III) and the like.
These light emitting materials may be used alone or in combination of two or more.

As a method for forming the light emitting layer in the element of the present invention, for example, it can be formed by thinning by a known method such as vapor deposition, spin coating, casting, LB, etc., but it is particularly a molecular deposited film. It is preferable. Here, the molecular deposited film is a thin film formed by deposition from the vapor phase state of the compound or a film formed by solidification from the molten state or liquid phase state of the compound. Usually, this molecular deposited film can be distinguished from a thin film (molecular accumulated film) formed by the LB method, a difference in aggregation structure and higher order structure, and a functional difference resulting therefrom.
In addition, the light emitting layer can be formed by dissolving in a solvent together with a binder such as a resin to form a solution, and then reducing the film by a spin coating method or the like.
There is no restriction | limiting in particular about the film thickness of the light emitting layer formed in this way, Although it can select suitably according to a condition, Preferably it is 1 nm-10 micrometers, Especially preferably, the range of 5 nm-5 micrometers is good.

Next, the hole injection layer is not necessarily required for the device of the present invention, but is preferably used for improving the light emitting performance. This hole injection layer is a layer that assists the injection of holes into the light emitting layer, has a high hole mobility, and has a small ionization energy of usually 5.5 eV or less. As such a hole injection layer, a material that transports holes to the light emitting layer with a lower electric field is preferable, and the mobility of holes is, for example, at least 10 when an electric field of 10 ⁴ to 10 ⁶ V / cm is applied. ^-6 cm ² / V · sec is more preferable.
Such a hole injection material is not particularly limited as long as it has the above-mentioned preferable properties, and conventionally used as a charge transport material for a hole in an optical transmission material or a hole of an EL element. Any known material used for the injection layer can be selected and used.

Examples of the hole injection material include triazole derivatives (see, for example, US Pat. No. 3,112,197), oxadiazole derivatives (see, for example, US Pat. No. 3,189,447), and imidazole derivatives (Japanese Patent Publication No. 37-16096). Reference), polyarylalkane derivatives (US Pat. Nos. 3,615,402, 3,820,989, 3,542,544, JP-B-45-555, JP-A-51-10983, JP-A-51-93224) Publication, 55-17105 publication, 56-4148 publication, 55-108667 publication, 55-156953 publication, 56-36656 publication, etc.), pyrazoline derivatives and pyrazolone derivatives (US Pat. No. 3,180,729) No. 4,278,746, JP-A-55-88064, JP-A-55-88065, JP-A-49-10. No. 537, No. 55-51086, No. 56-80051, No. 56-88141, No. 57-45545, No. 54-112737, No. 55-74546, etc.), phenylene Diamine derivatives (U.S. Pat. No. 3,615,404, Japanese Patent Publication No. 51-10105, Japanese Patent Publication No. 46-3712, Japanese Patent Publication 47-25336, Japanese Patent Publication No. 54-53435, Japanese Patent Publication No. 54-110536, 54-1119925), arylamine derivatives (US Pat. Nos. 3,567,450, 3,180,703, 3,240,597, 3,658,520, 4,232,103, 4,175,961) No. 4,012,376, JP-B-49-35702, JP-A-39-27577, JP-A-55-144250, JP-A-56-1. 19132, 56-22437, West German Patent 1,110,518, etc.), amino-substituted chalcone derivatives (see US Pat. No. 3,526,501, etc.), oxazole derivatives (US Pat. No. 3,257,203, etc.) Styryl anthracene derivatives (see JP 56-46234 A), fluorenone derivatives (see JP 54-110837 A, etc.), hydrazone derivatives (US Pat. No. 3,717,462, JP A) 54-59143, 55-52063, 55-52064, 55-46760, 55-85495, 57-11350, 57-148749, etc.) , Stilbene derivatives (Japanese Patent Laid-Open Nos. 61-210363, 61-228451, 61-14642) Gazette, 61-72255 gazette, 62-47646 gazette, 62-36674 gazette, 62-10652 gazette, 62-30255 gazette, 60-93445 gazette, 60-94462 gazette. Gazette, 60-174749 gazette, 60-175052 gazette, etc.).
Further, silazane derivatives (US Pat. No. 4,950,950), polysilanes (JP-A-2-204996), aniline-based copolymers (JP-A-2-282263), conductive polymer oligomers (JP-A-1 1992). -2139999), especially thiophene-containing oligomers.

  In the present invention, these compounds can be used as a hole injecting material. The following porphyrin compounds (described in JP-A-63-295965), aromatic tertiary amine compounds and Styrylamine compounds (US Pat. No. 4,127,412, JP-A-53-27033, 54-58445, 54-149634, 54-64299, 55-79450, 55-144250, 56-119132, 61-295558, 61-98353, 63-295695, etc.), especially the use of aromatic tertiary amine compounds. preferable.

  Representative examples of the porphyrin compounds include porphine, 1,10,15,20-tetraphenyl-21H, 23H-porphine copper (II); 1,10,15,20-tetraphenyl 21H, 23H-porphine zinc (II ); 5,10,15,20-tetrakis (pentafluorophenyl) -21H, 23H-porphine; silicon phthalocyanine oxide; aluminum phthalocyanine chloride; phthalocyanine (metal free); dilithium phthalocyanine; copper tetramethylphthalocyanine; Examples thereof include phthalocyanine; zinc phthalocyanine; lead phthalocyanine; titanium phthalocyanine oxide; magnesium phthalocyanine; copper octamethylphthalocyanine.

  As typical examples of the aromatic tertiary amine compound and styrylamine compound, N, N, N ′, N′-tetraphenyl-4,4′-diaminophenyl, N, N′-diphenyl-N, N '-Di (3-methylphenyl) -4,4'-diaminobiphenyl, 2,2-bis (4-di-p-tolylaminophenyl) propane, 1,1-bis (4-di-p-tolylamino) Phenyl) cyclohexane, N, N, N ′, N′-tetra-p-tolyl-4,4′-diaminobiphenyl, 1,1-bis (4-di-p-tolylaminophenyl) -4-phenylcyclohexane, Bis (4-dimethylamino-2-methylphenyl) phenylmethane, bis (4-di-p-tolylaminophenyl) phenylmethane, N, N′-diphenyl-N, N′-di (4-methoxypheny) ) -4,4′-diaminobiphenyl, N, N, N ′, N′-tetraphenyl-4,4′-diaminodiphenyl ether, 4,4′-bis (diphenylamino) quadriphenyl, N, N, N -Tri (P-tolyl) amine, 4- (di-p-tolylamino) -4 '-[4 (di-p-tolylamino) styryl] stilbene, 4-N, N-diphenylamino- (2-diphenylvinyl) Examples include benzene, 3-methoxy-4′-N, N-diphenylaminostilbenzene, N-phenylcarbazole, and aromatic dimethylidin compounds.

The hole injection layer in the EL device of the present invention can be formed by forming the above compound by a known thin film method such as a vacuum deposition method, a spin coating method, or an LB method. The thickness of the hole injection layer is not particularly limited, but is usually 5 nm to 5 μm. This hole injection layer may be composed of one or more of the above hole injection materials, or a hole injection layer made of a compound different from the hole injection layer is laminated. It may be a thing.
The organic semiconductor layer is a layer that assists hole injection or electron injection into the light emitting layer, and preferably has a conductivity of 10 ⁻¹⁰ S / cm or more. As a material for such an organic semiconductor layer, a conductive oligomer such as a thiophene-containing oligomer or an arylamine oligomer, a conductive dendrimer such as an arylamine dendrimer, or the like can be used.

On the other hand, the electron injection layer is a layer that assists the injection of electrons into the light emitting layer and has a high electron mobility, and the adhesion improving layer is made of a material that adheres particularly well to the cathode among the electron injection layers. It is a layer. Preferred examples of the material used for the electron injection layer include 8-hydroxyquinoline or a metal complex of a derivative thereof, or an oxadiazole derivative. In addition, as a material used for the adhesion improving layer, 8-hydroxyquinoline or a metal complex thereof is particularly suitable.
Specific examples of the metal complex of 8-hydroxyquinoline or a derivative thereof include metal chelate oxinoid compounds containing a chelate of oxine (generally 8-quinolinol or 8-hydroxyquinoline).
On the other hand, as oxadiazole derivatives, general formulas (II), (III) and (IV)

(Each of Ar ¹⁰ to Ar ¹³ has the formula a substituted or unsubstituted aryl group, Ar ¹⁰ and Ar ¹¹ and Ar ¹² and Ar ¹³ may be mutually different, even the same in each, Ar ¹⁴ is Represents a substituted or unsubstituted arylene group.)
The electron transfer compound represented by these is mentioned. Here, examples of the aryl group include a phenyl group, a biphenyl group, an anthranyl group, a perylenyl group, and a pyrenyl group. Examples of the arylene group include a phenylene group, a naphthylene group, a biphenylene group, an anthracenylene group, a peryleneylene group, and a pyrenylene group. It is done. Moreover, as a substituent, a C1-C10 alkyl group, a C1-C10 alkoxy group, a cyano group, etc. are mentioned. The electron transfer compound is preferably a thin film-forming compound. Specific examples of the electron transfer compound include

などが挙げられる。

Etc.

In the method for producing a dopant used in the present invention, pyrene, perylene, benzoperylene, pentacene, fluoranthene or the like is selected as a mother skeleton as a condensed polycyclic hydrocarbon ring, and a bulky alkyl such as isopropyl group, t-butyl group or cyclohexyl group is selected. Introduce a group. By introducing a bulky alkyl group, the interaction with the host is avoided and excimer emission is prevented.
In addition, the introduction of an alkyl group has the advantage that the sublimation temperature is increased and the doping rate can be easily controlled during device fabrication. Introducing an alkyl group is Friedel-Crafts The alkylation reaction is a reaction in which a carbonium cation is formed as an intermediate, and therefore, an alkyl group that may transfer such as a primary halide cannot be introduced. To introduce a primary alkyl group, a Grignard coupling reaction must be used. The Friedel-Crafts alkylation reaction is generally difficult to control and polyalkylation occurs. Further, since the olefin generated from the carbonium cation intermediate is polymerized to produce a large amount of polyolefin as a by-product, the stoichiometric reaction is generally difficult, and the halide must be used in a large excess as a solvent.

  Further, the position of the substituent is often different depending on the size of the alkyl group to be introduced. For example, in the following formula, the perylene-based compound has the highest reactivity at the 3-position, and when an acyl group or the like is introduced, a substituent is introduced at the 3-position, but the t-butyl group is bulky and thus the 2-position. However, there is a tendency of selectivity such that only substituents are contained.

ピレン系の化合物は下記式において１位の位置が最も反応性が高く、イソプロピル基などの導入を行うと１位に置換基が入るが、ｔ−ブチル基は嵩高いために２位にしか置換基が入らないなどの選択性の傾向がある。

The pyrene-based compound is most reactive at the 1-position in the following formula, and when an isopropyl group or the like is introduced, a substituent is introduced at the 1-position, but the t-butyl group is bulky and is substituted only at the 2-position. There is a tendency of selectivity such as no group.

フリーデルクラフツアルキル化反応の触媒としては、特に制限はないが、塩化アルミニウムなどの固体酸を用いることができる。

The catalyst for the Friedel-Crafts alkylation reaction is not particularly limited, but a solid acid such as aluminum chloride can be used.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. In the production examples, examples of synthesis using alkylation and phenylation reactions using compounds having a typical skeleton of the present invention as raw materials are given, but other compounds can be synthesized by the same method.

Production Example 1 [Synthesis of Diphenylbenzofluoranthene (IK-1)]
1.5 g (5.5 mmol) of diphenylisobenzofuran and 0.8 g (5.3 mmol) of acenaphthylene were dissolved in 15 ml of xylene and refluxed for 7 hours. The solvent was distilled off from the reaction mixture to obtain a brown oil. Since it crystallized by rubbing the wall of the flask, it was filtered and washed with hexane to obtain 1.8 g of a pale yellow solid (intermediate yield: 80%). The obtained solid was suspended in 8 ml of acetic acid, 1 ml of 47% hydrobromic acid was added, and the mixture was refluxed for 2 hours. The solid was filtered off and recrystallized from 60 ml of acetic acid to obtain 1.1 g of light brown needle crystals (IK-1 yield: 83%).
The physical properties of the obtained acicular crystals were as follows.
Melting point: 270-271 ° C
¹ H-NMR (CDCl ₃ , TMS)
6.61 (2H, d)
7.92 to 7.7 (18H, m)
The outline of the reaction of Production Example 1 is shown in the following reaction formula.

Production Example 2 [Synthesis of tributyldiphenylbenzofluoranthene (IK-2)]
1.1 g (2.7 mmol) of diphenylbenzofluoranthene was suspended in 100 ml of t-butyl chloride, 0.4 g (3.0 mmol) of pulverized aluminum chloride was added, and the mixture was refluxed for 2 hours. The reaction mixture was washed with 60 ml of water and 60 ml of a saturated aqueous sodium hydrogen carbonate solution, dried over magnesium sulfate and evaporated to give a light brown liquid. When this was left overnight, a solid was formed, which was filtered off and recrystallized from hexane containing a small amount of dichloromethane to obtain 0.4 g of a white solid (IK-2 yield: 26%).
The physical properties of the obtained solid were as follows.
Melting point: 300 ° C or higher
¹ H-NMR (CDCl ₃ , TMS)
1.19 (18H, s)
1.30 (9H, s)
6.64 (2H, d)
7.4 to 7.7 (15H, m)
The outline of the reaction of Production Example 2 is shown in the following reaction formula.

Examples 1-2 and Comparative Examples 1, 2
A transparent support substrate was formed by depositing ITO with a thickness of 100 nm on a glass substrate of 25 mm × 75 mm × 1.1 mm by a vapor deposition method (manufactured by Geomatic). This substrate was ultrasonically cleaned in isopropyl alcohol for 5 minutes, dried by blowing nitrogen and UV ozone cleaning (UV300, manufactured by Samco International) for 30 minutes.

This transparent support substrate is fixed to a substrate holder of a commercially available vapor deposition apparatus (manufactured by Nippon Vacuum Technology Co., Ltd.), MTDATA 200 mg is put into a molybdenum resistance heating boat, DPVBi 200 mg is put into another molybdenum resistance heating boat, and another molybdenum 200 mg of NPD as a hole transport material is put into a resistance heating boat, and 200 mg of the fluorescent dopant [compound (A)] shown in Table 1 is put into another resistance heating boat made of molybdenum. ^The pressure was reduced to ^-4 Pa. Thereafter, the boat containing MTDATA was heated to 215 to 220 ° C. and deposited on a transparent support substrate at a deposition rate of 0.1 to 0.3 nm / second to form a hole injection layer having a thickness of 60 nm. .

  Next, without removing the substrate from the vacuum chamber, the boat containing NPD was heated to form a 20 nm-thick hole transport layer on the hole injection layer. At this time, the temperature of the substrate was room temperature. Without removing this from the vacuum chamber, 40 nm of DPVBi was laminated as a host material on the NPD layer. At the same time, the boat of compound (A) was heated, and compound (A) was mixed in the light emitting layer. At this time, the deposition rate of the compound (A) was (C) (shown in Table 1) with respect to the deposition rate of DPVBi ((B) shown in Table 1). Therefore, the mixing ratio [ratio of compound (A) to host material] was (D) (shown in Table 1).

After that, the vacuum chamber is returned to atmospheric pressure, and an 8-hydroxyquinoline / aluminum complex, which is a material for the electron injection layer, is newly added to a resistance heating boat made of molybdenum, and 1 g of a magnesium ribbon is further added to the resistance heating boat made of molybdenum. 500 mg of silver wire was put in the basket, and the vacuum chamber was depressurized to 1 × 10 ⁻⁴ Pa.

  Subsequently, an 8-hydroxyquinoline / aluminum complex was deposited at a deposition rate of 0.01 to 0.03 nm / second to form an electron injection layer of 20 nm. Further, silver was co-evaporated at a deposition rate of 0.1 nm / second and magnesium was deposited at a deposition rate of 1.4 nm / second to form a silver: magnesium mixed electrode as a cathode. The film thickness was 150 nm.

Luminous efficiency was calculated by applying a voltage of 8 V to the resulting device and measuring the amount of current and the luminance of the device. The results obtained are shown in Table 2.
The structures of MTDATA, DPVBi, and NPD are as follows.

As a result, the device of the present invention is superior in luminous efficiency as compared with those of Comparative Examples 1 and 2 using perylene (fluorescent dopant described in JP-A-5-198378) as the fluorescent dopant. I understand that.
Next, each element was driven in an atmosphere of dry nitrogen at an initial luminance of 300 cd / m ² to obtain a half life (time for the initial luminance to be halved). The results are shown in Table 3. As a result of testing at an initial luminance of 100 cd / m ² , a life of about 3.5 times that of Table 3 was obtained. Therefore, the device of the present invention can have a lifetime of 2500 hours to 1100 hours under the condition of initial luminance of 100 cd / m ² .

  As can be seen from Table 3, the lifetime of the device of the present invention is significantly improved as compared with those of Comparative Examples 1 and 2.

The organic EL device of the present invention contains a fluorescent dopant having a specific structure in at least one of a recombination region where holes and electrons recombine or a light emitting region which emits light in response to the recombination. However, even if it is driven for a long time, it has a long life, such as little change in emission color, and has a high light emission efficiency, and is suitably used for, for example, displays of information industry equipment.

Claims (4)

Organic electroluminescence device comprising an organic compound layer having at least a recombination region in which holes and electrons recombine, a light emitting region that emits light in response to the recombination, and a pair of electrodes that hold the organic compound layer In the recombination region and / or the light emitting region, each has only a secondary or tertiary alkyl group having 3 to 10 carbon atoms or a substituent having 1 to 4 cycloalkyl groups.

An organic electroluminescent device comprising 0.1 to 8% by weight of diphenylbenzofluoranthene represented by the formula: Organic electroluminescence device comprising an organic compound layer having at least a recombination region in which holes and electrons recombine, a light emitting region that emits light in response to the recombination, and a pair of electrodes that hold the organic compound layer In the recombination region and / or the light emitting region, the following formula

An organic electroluminescent device comprising 0.1 to 8% by weight of diphenylbenzofluoranthene represented by the formula: The organic electroluminescent element according to claim 1 or 2, wherein a fluorescent dopant is contained in the light emitting layer. 3. The element structure is anode / hole injection layer / light emitting layer / electron injection layer / cathode, or anode / hole injection layer / hole transport layer / light emitting layer / electron injection layer / cathode. Organic electroluminescence element.