JP5934570B2 - Luminescent material and organic EL device - Google Patents

Description

  The present invention relates to a light emitting material and an organic EL device using the same.

  An organic EL element has attracted attention as a light emitting element used in a flat display panel or a lighting device. The organic EL element can emit light of various wavelengths by appropriately selecting the material constituting the light emitting layer. Specifically, the organic light-emitting compound can change the excitation and emission wavelength by derivatization by introducing a substituent or the like. For this reason, the discovery of a novel basic skeleton structure (key structure) exhibiting luminescent properties brings about various developments, and research has been conducted energetically.

  For example, perylene and distyrylarylene are known as blue light-emitting materials, and many distyrylarylene derivatives have been developed as blue light-emitting elements or white light-emitting element materials by a color mixing method (for example, patents). Literature 1 and Patent literature 2). However, although a distyrylarylene derivative exhibits high emission quantum efficiency in a solution, it tends to cause quenching in the solid state and decrease emission quantum efficiency. Therefore, in an organic EL device in which a luminescent material is used as a solid thin film, a compound that causes quenching in a solid state, such as a distyrylarylene derivative, is used as a dopant added to another compound (host material). Yes. On the other hand, Patent Document 3 discloses that a tetraphenylethene derivative having a specific substituent has high luminous efficiency in a solid state.

JP 2000-7604 A JP 2009-10408 A International Publication No. 2010/047335

  As described above, basic knowledge has been obtained that a tetraphenylethene derivative can be applied as a light-emitting material. However, there has been no example in which a tetraphenylethene derivative is applied as a light emitting material of an organic EL device, and it has not been clear what problems exist in practical use.

  In view of such a current situation, the present inventors manufactured and evaluated an organic EL element including a light emitting layer made of a thin film of a tetraphenylethene derivative having a specific substituent, and confirmed that the EL element emitted light. It was done. On the other hand, it has been found that it is difficult to increase the luminance of the element because the luminous efficiency is lower than that of an organic EL element that has already been put into practical use, and the element is destroyed when the drive current density is increased. Further, it has been found that the tetraphenylethene derivative having a specific substituent is likely to be crystallized at the time of vacuum vapor deposition, and the organic EL element does not emit light when the thickness of the light emitting layer exceeds 5 nm.

  In view of such a new problem, the present invention provides a light-emitting material having high emission intensity using a tetraphenylethene derivative having a specific substituent, and provides an organic EL element using the light-emitting material. For the purpose.

  As a result of investigations by the present inventors, it has been found that a light emitting material using another light emitting material as a host material and containing a tetraphenylethene derivative as a dopant compound exhibits high light emission intensity, and has led to the present invention.

  The present invention relates to a light emitting material containing a host compound and a dopant compound. In the light-emitting material of the present invention, the host compound is an anthracene derivative, and the dopant compound is a tetraphenylethene derivative represented by the following general formula (1Z) or (1E).

In the above formulas (1Z) and (1E), R ₁ is an electron donating group and R ₂ is an electron withdrawing group.

  The luminescent material of the present invention preferably contains a total of 1 to 50 parts by weight of the tetraphenylethene derivative with respect to 100 parts by weight of the anthracene derivative.

  Furthermore, this invention relates to the organic EL element containing a luminescent material as a light emitting layer.

  By using the light emitting material of the present invention, an organic EL device having excellent light emission efficiency can be provided.

It is a typical sectional view showing an example of layer composition of an organic EL device. It is typical sectional drawing which shows an example of the layer structure of the organic EL element in the organic EL apparatus of FIG. It is the light emission intensity spectrum in the current density of 10 mA / cm < ² > of the organic EL element of an Example and a comparative example. Each emission intensity spectrum of FIG. 3 is normalized by the intensity at the emission maximum wavelength. It is the graph which plotted the brightness | luminance of the organic EL element of the Example and the comparative example with respect to the current density.

  The light emitting material of the present invention contains an anthracene derivative as a host compound, and contains a tetraphenylethene derivative represented by the following general formula (1E) or (1Z) as a dopant compound.

[Dopant compound]
The compound represented by the general formula (1Z) and the compound represented by the general formula (1E) are geometric isomers (cis-trans isomers), and the general formula (1Z) is a Z isomer and the general formula (1E ) Is the E body. In the luminescent material of the present invention, the dopant compound may be either Z-form or E-form alone, or may be a mixture of both. In general, the E and Z forms are obtained as a 1: 1 mixture. In the present invention, these mixtures can be used as a dopant of the light emitting material in the state of the mixture without separating and purifying them into E form or Z form alone. When the dopant compound is a mixture of the E body and the Z body, the mixing ratio is not particularly limited. From an industrial point of view, an equivalent mixture of E-form and Z-form is preferably used. In addition, the equivalence mixture of E body and Z body is not limited to the one whose mixing ratio is strictly 1: 1, for example, the mixing ratio may be in the range of 4: 6 to 6: 4.
Hereinafter, the substituents R ₁ and R ₂ of the tetraphenylethene derivative as the dopant compound will be described.

R ₁ is a substituent having a high electron donating property (electron extrudability). Examples of R ₁ include a lower alkyl group, a lower alkoxy group, a lower alkylthio group, an amino group which may have a substituent, a nitrogen-containing saturated heterocyclic group, and a triorganosilyl group.

  Examples of the lower alkyl group include linear or branched alkyl groups having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, sec-butyl group, n-pentyl group, 1-ethylpropyl group, isopentyl group , Neopentyl group, n-hexyl group, 1,2,2-trimethylpropyl group, 3,3-dimethylbutyl group, 2-ethylbutyl group, isohexyl group, 3-methylpentyl group, and the like.

  Examples of the lower alkoxy group include linear or branched alkoxy groups having 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. Specifically, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, tert-butoxy group, sec-butoxy group, n-pentyloxy group, isopentyloxy group, neo A pentyloxy group, an n-hexyloxy group, an isohexyloxy group, a 3-methylpentyloxy group, and the like can be given.

  Examples of the lower alkylthio group include linear or branched alkylthio groups having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. Specific examples include a methylthio group, an ethylthio group, an n-propylthio group, an isopropylthio group, an n-butylthio group, a tert-butylthio group, an n-pentylthio group, and an n-hexylthio group.

The amino group which may have a substituent may have 1 or 2 substituents in addition to —NH ₂ . When an amino group can form a hydrogen bond, concentration quenching occurs and the light emission efficiency tends to decrease. Therefore, the amino group preferably has two substituents. When the amino group has two substituents, these may be the same or different. Examples of the substituent include an aryl group and the lower alkyl group exemplified above, and among them, an aryl group is preferable. That is, as the amino group which may have a substituent, a diarylamino group is particularly preferable.

  Examples of the nitrogen-containing saturated heterocyclic group include 5- or 6-membered nitrogen-containing heterocyclic groups which may contain other heteroatoms such as oxygen atoms and sulfur atoms. More specifically, pyrrolidino group, piperidino group, piperazinyl group, morpholino group, thiomorpholino group and the like can be mentioned.

  Examples of the triorganosilyl group include trimethylsilyl group, dimethylvinylsilyl group, dimethylphenylsilyl group, methyldiphenylsilyl group, dimethyl (tert-butyl) silyl group, methyldivinylsilyl group, methylphenylvinylsilyl group, and trivinylsilyl group. , Triethylsilyl group, ethoxydimethylsilyl group and the like.

R ₂ is a substituent having a high electron withdrawing property. R ₂ is halogen, a halogen-substituted lower alkyl group, a lower alkylcarbonyl group, a lower alkoxycarbonyl group, a formyl group, an aminocarbonyl group which may have a substituent, a carbamoyl group which may have a substituent, A cyano group, a nitro group, etc. are mentioned. From the viewpoint of suppressing fluorescence quenching due to intersystem crossing from a singlet to a triplet and obtaining a material with high luminous efficiency, R ₂ has a halogen, a halogen-substituted lower alkyl group, a lower alkoxycarbonyl group, and a substituent. It is preferably either an aminocarbonyl group or a cyano group.

  Examples of the halogen include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these halogens, a fluorine atom or a chlorine atom is preferable from the viewpoint of suppressing fluorescence quenching due to intersystem crossing from a singlet to a triplet.

  Examples of the halogen-substituted lower alkyl group include the exemplified lower alkyl groups substituted with 1 to 5, more preferably 1 to 3, halogen atoms. Specifically, fluoromethyl group, difluoromethyl group, trifluoromethyl group, chloromethyl group, dichloromethyl group, trichloromethyl group, bromomethyl group, dibromomethyl group, dichlorofluoromethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, pentafluoroethyl group, 2-fluoroethyl group, 2-chloroethyl group, 3,3,3-trifluoropropyl group, heptafluoropropyl group, 2,2,3,3 , 3-pentafluoropropyl group, heptafluoroisopropyl group, 3-chloropropyl group, 2-chloropropyl group, 3-bromopropyl group, 4,4,4-trifluorobutyl group, 4,4,4,3, 3-pentafluorobutyl group, 4-chlorobutyl group, 4-bromobutyl group, 2-chlorobutyl group, 5, 5, 5 Trifluoro-pentyl group, 5-chloropentyl group, 6,6,6-trifluoro hexyl, 6-chloro-hexyl group, perfluorohexyl group, and the like.

  Examples of the lower alkoxycarbonyl group include alkoxycarbonyl groups in which the lower alkoxy moiety is the lower alkoxy group exemplified above. Specifically, methoxycarbonyl group, ethoxycarbonyl group, n-propoxycarbonyl group, isopropoxycarbonyl group, n-butoxycarbonyl group, isobutoxycarbonyl group, tert-butoxycarbonyl group, sec-butoxycarbonyl group, n-pentyl Examples include oxycarbonyl group, neopentyloxy group, n-hexyloxycarbonyl group, isohexyloxycarbonyl group, 3-methylpentyloxycarbonyl group and the like.

  Examples of the aminocarbonyl group which may have a substituent include an aminocarbonyl group whose amino group portion is an amino group which may have the exemplified substituent. Specific examples include a dimethylaminocarbonyl group, a diethylaminocarbonyl group, an ethylmethylaminocarbonyl group, a diarylaminocarbonyl group, and the like.

The tetraphenylethene derivative used as a dopant compound has an electron-donating substituent R ₁ and an electron-withdrawing substituent R ₂ on the phenyl ring, and the π-electron density in the molecular plane is localized. Thus, a blue light emitting material having a light emission maximum at a wavelength shorter than 500 nm can be obtained. That is, the tetraphenylethene derivative represented by the general formulas (1Z) and (1E) can change the light emission characteristics of the material depending on the type of the substituent.

From the viewpoint of obtaining a blue light emitting material having an emission maximum at a wavelength shorter than 500 nm, R ₁ is preferably a diarylamino group, a lower alkoxy group, or the like, and particularly preferably a lower alkoxy group. R ₂ is preferably a fluoro group, a trifluoromethyl group, a cyano group, or the like.

(Synthesis method)
The method for synthesizing the tetraphenylethene derivative is not particularly limited, and a target compound can be obtained by combining various known reactions. For example, bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene, where R ₁ is a methoxy group and R ₂ is a trifluoromethyl group, starts with a benzophenone derivative as shown in the following scheme: As a raw material, it is obtained by McMurray coupling.

  In the above scheme, the starting material is a known compound or is produced by a known method (for example, a method described in Synthetic Communications, 1998, 28, 1065.). In the above reaction scheme, an equivalent mixture of E-form and Z-form is obtained, but each can be separated and purified by treating with chromatography or the like after the reaction.

[Host compound]
The anthracene derivative serving as the host compound is not particularly limited as long as it can be used as a light emitting material, and various known compounds can be used. Examples include 9,10-di (naphth-2-yl) anthracene (abbreviation: ADN), 2-tert-butyl-9,10-di (naphth-2-yl) anthracene (abbreviation: TBADN), 2- Methyl-9,10-bis (naphthalen-2-yl) anthracene (abbreviation: MADN), 2,2'-di (9,10-diphenylanthracene) (abbreviation: TPBA), 4,4'-di (10- (Naphthalen-1-yl) anthracen-9-yl) biphenyl (abbreviation: BUBH-3), and the like.

  The addition ratio of the tetraphenylethene derivative (dopant compound) to the anthracene derivative (host compound) in the light emitting material of the present invention is not particularly limited. The content of the tetraphenylethene derivative is preferably 1 to 50 parts by weight, more preferably 2 to 20 parts by weight, still more preferably 2.5 to 15 parts by weight, particularly preferably 100 parts by weight of the anthracene derivative. 3 to 10 parts by weight. In addition, when a dopant compound is a mixture of the compound (Z body) represented by the said general formula (1Z), and the compound (E body) represented by the said general formula (1E), content which totaled both has the content. It is preferable that it is the said range.

  In the light-emitting material of the present invention, by using a tetraphenylethene derivative having a specific substituent as a dopant compound, the light emission efficiency is improved and the emission wavelength is shorter than when the compound is used alone. There is a tendency to become blue (blue shift). For example, as shown later using Examples and Comparative Examples, when bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene is used alone as a light emitting material, a long wavelength of 470 to 480 nm ( There is an emission peak in the blue region. On the other hand, when bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene is used as a dopant compound, an emission peak exists on the shorter wavelength side of 445 to 455 nm.

  In addition, when a tetraphenylethene derivative is used as a dopant compound, the half-value width of the emission spectrum is reduced, and high current emission efficiency is maintained even when the drive current density is high. In the light-emitting material of the present invention, energy transfer from the anthracene derivative which is the host material to the tetraphenylethene derivative is sufficiently performed, and it can be said that the two are functionally interacting.

  The light emitting material of the present invention may further contain components other than the anthracene derivative (host compound) and the tetraphenylethene derivative (dopant compound). Examples of other components include compounds that exhibit electron transport properties. As the compound exhibiting the electron transporting property, those exemplified later as the material constituting the electron transporting layer 15 are used.

  Examples of the method for producing the light emitting material of the present invention include a method of forming a film on a support such as a substrate and obtaining it as a thin film. Typically, a method of co-evaporating an anthracene derivative and a tetraphenylethene derivative is used.

[Organic EL device]
The organic EL device of the present invention comprises at least a light emitting layer between a pair of electrodes composed of an anode 4 and a cathode 6, and the light emitting layer has the above-described light emitting material of the present invention. FIG. 1 is an example of a layer configuration of an organic EL device. The organic EL device shown in FIG. 1 has a configuration called “bottom emission type” in which light is extracted from the transparent substrate 3 side. The organic EL device 1 has an organic EL element 2 on a transparent substrate 3, and the organic EL element is sealed by a sealing portion 7. The organic EL element 2 has a functional layer 5 between a pair of electrodes composed of a transparent electrode layer (anode) 4 and a back electrode layer (cathode) 6.

  The functional layer 5 is formed by laminating a plurality of organic compound thin films. FIG. 2 is an example of a layer configuration of the functional layer 5. In the organic EL element 2 shown in FIG. 2, the functional layer 5 includes a hole injection layer 10, a hole transport layer 11, a light emitting layer 12, an electron transport layer 15, and an electron injection layer 16. That is, in the organic EL element 2, the light emitting layer 12 is located between the transparent electrode layer 4 and the back electrode layer 6.

(Transparent substrate)
The transparent substrate 3 is not particularly limited as long as it is made of a material having translucency. In the embodiment shown in FIG. 1, since light is extracted from the transparent substrate 3 side (bottom emission method), the transparent substrate 3 preferably has a transmittance in the visible light region of 80% or more, and 90% or more. Is more preferable, and it is further more preferable that it is 95% or more. As the transparent substrate 3, a glass substrate, a flexible transparent film substrate, or the like may be used. When the organic EL device adopts a top emission method, the substrate may be opaque.

(Transparent electrode)
A transparent electrode layer (anode) 4 is laminated on the transparent substrate 3. The material which comprises the transparent electrode layer 4 is not specifically limited, A well-known thing can be used. Examples thereof include those made of materials such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO ₂ ), and zinc oxide (ZnO). Among these, ITO or IZO is preferably used from the viewpoint of the light extraction efficiency from the light emitting layer 12 and the ease of electrode patterning.

  The transparent electrode layer 4 may be doped with one or more dopants such as aluminum, gallium, silicon, boron, and niobium as necessary. The transmittance of the transparent electrode layer 4 is preferably 70% or more, more preferably 80% or more, and further preferably 90% or more in the visible light region. The transparent electrode layer 4 is formed on the transparent substrate 3 by a dry process such as sputtering or CVD. The film thickness of the transparent electrode layer 4 may be appropriately selected in consideration of light transmittance and electrical conductivity, and is, for example, 80 to 300 nm, preferably 100 to 150 nm, and more preferably 120 to 150 nm.

(Hole injection layer)
A hole injection layer 10 is stacked on the transparent electrode layer 4. The hole injection layer 10 is not particularly limited, and a known material used as the hole injection layer of the organic EL element can be employed. Examples thereof include metal oxides such as molybdenum oxide, vanadium oxide, ruthenium oxide, and manganese oxide. In addition, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (abbreviation: F4-TCNQ) can be given. Further, a mixed layer of molybdenum trioxide and N, N-bis (naphthalen-1-yl) -N, N′-phenylbenzidine (abbreviation: NPB) can be employed as the hole injection layer 10.

  The hole injection layer 10 is formed by, for example, a vacuum evaporation method. The thickness of the hole injection layer 10 may be appropriately selected in consideration of the light interference effect, the leakage current suppression effect, and the like, but is preferably 10 nm or more, and more preferably 30 nm or more.

(Hole transport layer)
A hole transport layer 11 is stacked on the hole injection layer 10. There is no limitation in particular as the positive hole transport layer 11, The well-known material used as a positive hole transport layer of an organic EL element is employable. Examples thereof include arylamine compounds represented by the following general formula (2).

上記式（２）中、Ａｒ₁、Ａｒ₂およびＡｒ₃は、それぞれ独立に置換基を有してよい芳香族炭化水素基を示す。

In the above formula (2), Ar ₁ , Ar ₂ and Ar ₃ each independently represent an aromatic hydrocarbon group which may have a substituent.

  Specific examples of such arylamine compounds include 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, N, N, N ′, N′-tetra-p-tolyl-4,4 ′ -Diaminobiphenyl, bis (4-di-p-tolylaminophenyl) phenylmethane, N, N'-diphenyl-N, N'-di (4-methoxyphenyl) -4,4'-diaminobiphenyl, N, N , N ′, N′-tetraphenyl-4,4′-diaminodiphenyl ether, 4,4′-bis (diphenylamino) quadriphenyl, 4-N, N′-diphenylamino- (2-diphenylvinyl) benzene, 3-methoxy-4'- , N-diphenylaminostilbenzene, N-phenylcarbazole, 1,1-bis (4-di-p-triaminophenyl) cyclohexane, 1,1-bis (4-di-p-triphenyl) cyclohexane, 1, 1-bis (4-di-p-triaminophenyl) -4-phenylcyclohexane, bis (4-dimethylamino-2-methylphenyl) phenylmethane, N, N, N-N-tri (p-tolyl) amine 4- (di-p-tolylamino) -4 ′-[4 (di-p-triamino) styryl] stilbene, N, N, N ′, N′-tetraphenyl-4,4′-diamino-biphenyl N— Phenylscarbazole, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl, 4,4′-bis [N- (1-naphthyl) -N-phenylamino] p-ter Phenyl, 4,4′-bis [N- (3-acenaphthenyl) -N-phenylamino] biphenyl, 1,5-bis [N- (1-naphthyl) -N-phenylamino] naphthalene, 4,4′- Bis [N- (9-anthrin) -N-phenylamino] biphenyl, 4,4′-bis [N- (1-anthryl) -N-phenylamino] p-terphenyl, 4,4′-bis [ N- (2-phenanthryl) -N-phenylamino] biphenyl, 4,4′-bis [N- (8-fluoranthenyl) -N-phenylamino] biphenyl, 4,4′-bis [N- (2 -Pyrenyl) -N-phenylamino] biphenyl, 4,4'-bis [N- (2-perylenyl) -N-phenylamino] biphenyl, 4,4'-bis [N- (1-colonenyl) -N- Phenylamino] biphenyl, 2, -Bis [di- (1-naphthyl) amino] naphthalene, 2,6-bis [N- (1-naphthyl) -N- (2-naphthyl) amino] naphthalene, 4,4'-bis [N, N- Di (2-naphthyl) amino] terphenyl, 4,4′-bis {N-phenyl-N- [4- (1-naphthyl) phenyl] amino} biphenyl, 4,4′-bis [N-phenyl- N- (2-pyrenyl) amino] biphenyl, 2,6-bis [N, N-di (2-naphthyl) amino] fluorene, 4,4′-bis [N-phenyl-N- (2-pyrenyl) amino ] Biphenyl, 2,6-bis [N, N-di-p-triamino] terphenyl, bis (N-1-naphthyl) (N-2-naphthyl) amine, and the like.

  The hole transport layer 11 is formed by, for example, a vacuum deposition method.

(Light emitting layer)
A light emitting layer 12 is laminated on the hole transport layer 11. The light-emitting layer 12 is mainly composed of the above-described light-emitting material of the present invention, that is, a light-emitting material in which a tetraphenylethene derivative is doped into an anthracene derivative as a host compound. Examples of a method for forming the light emitting layer 12 include a method in which an anthracene derivative and a tetraphenylethene derivative are simultaneously deposited. Specifically, a method of co-evaporating an anthracene derivative and a tetraphenylethene derivative using a vacuum vapor deposition method can be given. At this time, a desired vapor deposition ratio (dope concentration) can be realized by controlling the vapor deposition rates of the host compound and the dopant compound. Examples of methods other than the vacuum deposition method include a method of applying a solution containing a light emitting material (a coating method, a printing method, etc.) and a transfer method (laser transfer, thermal transfer, etc.).

  The thickness of the light emitting layer 12 may be appropriately selected in consideration of current efficiency and the like. The film thickness of the light emitting layer is, for example, 5 nm to 400 nm, preferably 7 nm to 350 nm, and more preferably 10 nm to 250 nm. When a tetraphenylethene derivative is used as a single host compound, it tends to be difficult to obtain a high-quality amorphous film having the above film thickness. On the other hand, according to the configuration of the present invention using a tetraphenylethene derivative as a dopant compound, it is easy to obtain a high-quality amorphous film suitable as a light emitting layer even with the above film thickness.

(Electron transport layer)
An electron transport layer 15 is stacked on the light emitting layer 12. The material of the electron transport layer 15 is not specifically limited, The well-known material used as an electron transport layer of an organic EL element is employable. For example, tris (8-hydroxyquinolinato) aluminum (abbreviation: Alq ₃ ) or 1,3-bis [2- (2,2′-bipyridin-6-yl) -1,3,4-oxadiazo-5-yl ] Benzene (abbreviation: Bpy-OXD), 4,7-diphenyl-1,10-phenanthroline (abbreviation: Bphen), 2,2 ′, 2 ″-(1,3,5-benzynetriyl) -tris ( 1-phenyl-1-H-benzimidazole) (abbreviation: TPBi), 2- (4-biphenyl) -5- (4-tert-butyphenyl) -1,3,4-oxadiazole (abbreviation: PBD), Bis (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum (abbreviation: BAlq), 3- (4-biphenyl) -4-phenyl-5-tert-butylphenyl-1,2,4 Triazole (abbreviation: TAZ), and the like.

  The electron transport layer 15 is formed by, for example, a vacuum evaporation method. The film thickness of the electron transport layer 15 may be appropriately selected in consideration of interference effects, mobility, and the like, but is, for example, 10 to 100 nm, preferably 20 to 80 nm, and more preferably 40 to 60 nm.

(Electron injection layer)
An electron injection layer 16 is stacked on the electron transport layer 15. The electron injection layer 16 is not particularly limited, and a known material used as the electron injection layer of the organic EL element can be used. Examples thereof include alkali metals such as Li; alkaline earth metals such as Mg and Ca; alloys containing one or more of the metals; oxides, halides, and carbonates of the metals; and mixtures thereof. Specific examples include 8-hydroxyquinolinolato (lithium) (Liq) and lithium fluoride (LiF).

  The electron injection layer 16 is formed by, for example, a vacuum evaporation method. The thickness of the electron injection layer 16 may be appropriately selected in consideration of mobility and the like, and is, for example, 0.1 to 5 nm, preferably 0.5 to 3 nm, and more preferably 1 to 2 nm.

(Back electrode layer)
A back electrode layer (cathode) 6 is stacked on the electron injection layer 16. The material used for the back electrode layer 6 is preferably a metal having a low work function, or an alloy or metal oxide containing these metals. For example, the alkali metal is Li or the like, and the alkaline earth metal is Mg or Ca. In addition, a simple metal made of rare earth metal or the like, or an alloy such as Al, In, or Ag with these metals can be used. In addition, an organic metal complex containing at least one selected from the group consisting of alkaline earth metal ions and alkali metal ions as an organic layer in contact with the cathode, using the technology disclosed in Japanese Patent Application Laid-Open No. 2001-102175 In the case of using a compound, a metal that reduces metal ions contained in the complex compound to a metal in a vacuum, such as Al, Zr, Ti, Si, or an alloy containing these metals can also be used. .

  As described above, the organic EL element 2 of the present embodiment has the hole injection layer 10, the hole transport layer 11, and the like formed on the transparent electrode layer 4 formed on the transparent substrate 3 by a technique such as vacuum deposition. It can be manufactured by sequentially laminating the light emitting layer 12, the electron transport layer 15, the electron injection layer 16, and the back electrode layer 6. The organic EL element 2 manufactured in this way is sealed by providing the sealing portion 7 to become the organic EL device 1.

  Although the above demonstrated the structure in which the functional layer 5 consists of five layers, this invention is not limited to the said embodiment. For example, a configuration in which some or all of the hole injection layer 10, the hole transport layer 11, the electron transport layer 15, and the electron injection layer 16 are omitted may be employed. Further, a hole blocking layer or an electron blocking layer may be provided before and after the light emitting layer 12.

  The organic EL element of the present invention is suitably used for organic EL lighting, organic EL display devices and the like. Organic EL lighting is used not only for general lighting such as houses, but also for backlights of liquid crystal display devices, electronic devices such as digital still cameras, light sources for endoscopes, medical fields such as image processing, exposure devices, communication equipment, etc. Application as special lighting for industrial equipment is also possible.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

[Synthesis example]
Zinc powder (0.65 g, 10 mmol), pyridine (0.20 mL, 2.5 mmol) and THF (4 mL) were introduced into Schlenk (20 mL) equipped with a stir bar and a reflux condenser under an argon atmosphere. The mixture was cooled to 0 ° C. and titanium tetrachloride (0.30 mL, 2.7 mmol) was slowly added thereto with a syringe. The resulting suspension was refluxed for 1 hour. After the mixture was cooled again to 0 ° C., 4-bromo-4 ′-(trifluoromethyl) benzophenone (0.33 g, 1.0 mmol) was added thereto and refluxed for 21 hours. The mixture was allowed to cool to room temperature and filtered through a short column of Florisil with ethyl acetate. The filtrate was washed with saturated brine and dried over anhydrous magnesium sulfate. The crude product obtained by distilling off the organic solvent under reduced pressure was purified by silica gel column chromatography to obtain 1,2-bis (4-bromophenyl) -1,2-bis [4- (trifluoromethyl) phenyl]. Ethene (0.28 g, 90% yield) was obtained as a mixture with an E / Z ratio of approximately 1: 1.

  1,2-bis (4-bromophenyl) -1,2-bis [4- (trifluoromethyl) phenyl] ethene (0.25 g, 0.4 mmol) to Schlenk (20 mL) equipped with stir bar and reflux condenser. , Copper iodide (7.6 mg, 0.04 mmol), sodium methoxide (5 M methanol solution 1.6 mL, 8.0 mmol), dimethylformamide (1.2 mL) and ethyl acetate (1.2 mL) were introduced under an argon atmosphere. did. The mixture was heated at 100 ° C. for 17 hours. Saturated aqueous ammonium chloride solution (2 mL) was added to stop the reaction, and the aqueous layer was extracted with dichloromethane (3 mL × 3 times). The organic layer was washed with saturated brine, dried over anhydrous magnesium sulfate, and then the organic solvent was distilled off with an evaporator. The obtained crude product was purified by silica gel column chromatography to obtain 1,2-bis [4- (trifluoromethyl) phenyl] -1,2-bis represented by the following formulas (3Z) and (3E). (4-Methoxyphenyl) ethene was obtained as a mixture with an E / Z ratio of about 1: 1 (0.11 g, yield 51%).

[Example 1]
On a glass substrate having a patterned ITO electrode (film thickness 150 nm), a bottom emission type evaluation element having a light emitting region of 2 mm × 2 mm was produced by the following procedure.

On the ITO electrode (anode), molybdenum trioxide (MoO ₃ ) and a hole transport material (EL-301 manufactured by Hodogaya Chemical Co., Ltd.) were co-evaporated to form a hole injection layer (film thickness 60 nm). On the hole injection layer, EL-301 was vacuum-deposited to form a hole transport layer (film thickness 20 nm). Next, an anthracene derivative (SH03 manufactured by SFC) and bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene obtained in the above production example were co-deposited on the hole transport layer. A light emitting layer (film thickness 20 nm) was formed. The doping concentration of bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene was 5 parts by weight with respect to 100 parts by weight of the anthracene derivative.

  An electron transport material (ETM-033 manufactured by Merck & Co., Inc.) was vacuum-deposited on the light emitting layer to form an electron transport layer (40 nm). Next, LiF was vacuum-deposited on the electron transport layer to form an electron injection layer (film thickness: 10 nm). On the electron injection layer, aluminum was formed to a thickness of 150 nm as a cathode.

  After forming the cathode, the organic EL element after vapor deposition was moved to an inert glove box, a UV curable resin was applied to the glass cap, and the substrate and the cap were bonded together. After the UV irradiation, the bonded substrates were taken out under atmospheric pressure, a current was applied, and current-voltage-luminance (IVL) characteristics and emission intensity spectra were measured.

[Example 2]
In the formation of the light emitting layer of Example 1, the doping concentration of bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene was 7 parts by weight with respect to 100 parts by weight of the anthracene derivative. Other than that was carried out similarly to Example 1, and produced the evaluation element, and measured the IV characteristic and the light emission intensity spectrum.

[Comparative Example 1]
In the formation of the light emitting layer of Example 1, only the bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene was vacuum deposited to form a light emitting layer (film thickness 5 nm). Other than that was carried out similarly to Example 1, and produced the evaluation element, and measured the IV characteristic and the light emission intensity spectrum.

[Comparative Example 2]
In the formation of the light-emitting layer in Example 1, the light-emitting layer (thickness 20 nm) was formed by vacuum deposition of only the anthracene derivative without using bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene. . Other than that was carried out similarly to Example 1, and produced the evaluation element and measured the IVL characteristic.

[Evaluation results]
Table 1 shows the current efficiency (cd / A) in the case where the organic EL elements of the examples and the comparative examples have a luminance of 2000 cd / m ² . Moreover, the emission intensity spectrum of each organic EL element at a current density of 10 mA / cm ² is shown in FIG. 3, and each emission intensity spectrum normalized by the intensity (peak intensity) at the emission maximum wavelength is shown in FIG. Moreover, the graph which plotted the brightness | luminance of the organic EL element of Example 2 and the comparative example 1 with respect to the current density is shown in FIG.

  As is apparent from Table 1, the organic EL device of the example using an anthracene derivative as a host compound and bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene as a dopant is bis (4-methoxy). Compared to the organic EL device of Comparative Example 1 using phenyl) bis (4-trifluoromethylphenyl) ethene alone, it has a luminous efficiency of about 1.5 times. Moreover, the organic EL element of an Example has the luminous efficiency of 2 times or more compared with the element of the comparative example 2 which used the anthracene derivative independently. According to the comparison between Example 1 and Example 2, an increase in luminous efficiency was observed by increasing the content of the dopant compound.

  Thus, when a tetraphenylethene derivative is used as a dopant compound, it exhibits high luminous efficiency compared to either the case of a tetraphenylethene derivative alone or the case of an anthracene derivative alone, and the concentration dependence of the luminous efficiency is observed. It has been. Moreover, according to FIGS. 3 and 4, when bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene is used as a dopant, the light emission maximum is larger than when the light emitting material is used alone. As the wavelength becomes wavelength (blue shift), the spectrum width (half-value width) becomes smaller. From these results, it is considered that the luminous efficiency of the light emitting material of the present invention is improved by sufficiently transferring the energy of the tetraphenylethene derivative from the anthracene derivative as the host material.

As shown in FIG. 5, in Comparative Example 1 using bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene alone, the current efficiency decreases as the current density increases, and the current density is 300 mA / cm. ² caused device breakdown. On the other hand, in Example 2 in which bis (4-methoxyphenyl) bis (4-trifluoromethylphenyl) ethene was used as a dopant, a decrease in current efficiency was suppressed compared to Comparative Example 1, Even when the current density was increased to 1000 mA / cm ² , high luminous efficiency was exhibited.

  As described above, the light-emitting material of the present invention has high luminous efficiency and a small spectrum half-value width as compared with conventional light-emitting materials. Furthermore, the light-emitting material of the present invention is suitable for practical use as an organic EL element because it has little decrease in current density efficiency even when driven at a high current density (high voltage).

2 Organic EL element 4 Transparent electrode layer (anode)
5 Functional layer 6 Back electrode layer (cathode)
12 Light emitting layer

Claims (3)

A blue light-emitting material containing a blue host compound and a dopant compound and having a light emission maximum at a wavelength shorter than 500 nm ,
Before SL dopant compound, Ri tetraphenyl ethene derivatives der represented by the following general formula (1Z) or (1E),

Wherein (1Z) and (1E), _{R 1} is a lower alkoxy group having 1 to 6 carbon atoms, _{R 2} is a 1-5 halogens substituted lower alkyl group having 1 to 6 carbon atoms Yes,
A light emitting material, wherein the blue host compound is an anthracene derivative.   The luminescent material according to claim 1, wherein the tetraphenylethene derivative is contained in a total amount of 1 to 50 parts by weight with respect to 100 parts by weight of the anthracene derivative. An organic EL device comprising at least a light emitting layer between a pair of electrodes consisting of an anode and a cathode, the light-emitting layer, the organic EL element having a light-emitting material according to claim 1 or 2.

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