ORGANIC ELECTROLUMINESCENT DEVICE

Abstract

The present invention provides an organic electroluminescent device having a capping layer comprising a material having a high absorption coefficient in the wavelength range of 400 nm to 410 nm and no absorption in the respective wavelength ranges of blue, green and red in order to prevent the light in the 400 nm to 410 nm wavelength of sunlight from being absorbed and affecting the materials inside the device and to improve the light extraction efficiency. Since the arylamine compound having a specific structure in the present invention is excellent in stability and durability of the thin film, an organic EL device obtained by selecting amine compounds with high absorbance in the absorption spectrum at concentration 10.sup.−5 mol/L at wavelengths of 400 nm to 410 nm, from amine compounds having a specific benzoazole ring structure with a high refractive index as a material of a capping layer, exhibits good characteristics.

Claims

1. An organic electroluminescence device comprising at least an anode electrode, a hole transport layer, an emission layer, an electron transport layer, a cathode electrode, and a capping layer in this order, wherein the capping layer has a refractive index of 1.90 or more higher at a wavelength of 500 nm to 570 nm and comprises an amine compound having a benzoazole ring structure represented by the following general formula (1): ##STR00017## wherein R.sub.1 to R.sub.3 may be the same or different, and represent a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, a linear or branched alkyl group of 1 to 6 carbon atoms that may have a substituent, a cycloalkyl group of 5 to 10 carbon atoms that may have a substituent, a linear or branched alkenyl group of 2 to 6 carbon atoms that may have a substituent, a linear or branched alkyloxy group of 1 to 6 carbon atoms that may have a substituent, a cycloalkyloxy group of 5 to 10 carbon atoms that may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, or a substituted or unsubstituted aryloxy group, and when more than one of these groups are bonded to the same benzene ring, they may be bonded to each other to form a ring, or each group may be bonded to the benzene ring to which it is bonded to form a ring. X, Y, and Z may be the same or different, and represent an oxygen atom or a sulfur atom, and Ar.sub.1 to Ar.sub.3 may be the same or different and represent a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted aromatic heterocyclic ring, or a divalent group of substituted or unsubstituted condensed polycyclic aromatics. r.sub.1 to r.sub.3 may be the same or different, and represent integers from 0 to 4.

2. The organic electroluminescent device according to claim 1, wherein the amine compound having the benzoazole ring structure is represented by the following general formula (1a): ##STR00018## wherein R.sub.1 to R.sub.3, X, Y, and Z, r.sub.1 to r.sub.3 represent as defined by the general formula (1).

3. The organic electroluminescent device according to claim 1, wherein all r.sub.1 to r.sub.3 in the general formula (1) represents 0.

4. The organic electroluminescent device according to claim 1, wherein the thickness of the capping layer is within a range of 30 nm to 120 nm.

5. A method of using an amine compound having a refractive index of 1.90 or higher at a wavelength of 500 nm to 570 nm and having a benzoazole ring structure represented by the following general formula (1) or the following general formula (1a) in the capping layer of an organic electroluminescent device: ##STR00019## wherein R.sub.1 to R.sub.3 may be the same or different, and represent a deuterium atom, a fluorine atom, a chlorine atom, a cyano group, a nitro group, a linear or branched alkyl group of 1 to 6 carbon atoms that may have a substituent, a cycloalkyl group of 5 to 10 carbon atoms that may have a substituent, a linear or branched alkenyl group of 2 to 6 carbon atoms that may have a substituent, a linear or branched alkyloxy group of 1 to 6 carbon atoms that may have a substituent, a cycloalkyloxy group of 5 to 10 carbon atoms that may have a substituent, a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, or a substituted or unsubstituted aryloxy group, and when more than one of these groups are bonded to the same benzene ring, they may be bonded to each other to form a ring, or each group may be bonded to the benzene ring to which it is bonded to form a ring. X, Y, and Z may be the same or different, and represent an oxygen atom or a sulfur atom, and Ar.sub.1 to Ar.sub.3 may be the same or different and represent a divalent group of a substituted or unsubstituted aromatic hydrocarbon, a divalent group of a substituted or unsubstituted aromatic heterocyclic ring, or a divalent group of substituted or unsubstituted condensed polycyclic aromatics. r.sub.1 to r.sub.3 may be the same or different and represent integers from 0 to 4. ##STR00020## wherein R.sub.1 to R.sub.3, X, Y, and Z, r.sub.1 to r.sub.3 represent as defined by the general formula (1).

6. The organic electroluminescent device according to claim 2, wherein all r.sub.1 to r.sub.3 in the general formula (1a) represents 0.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG. 1 is a figure showing the structures of compounds (1-1) through (1-12) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0062] FIG. 2 is a figure showing the structures of compounds (1-13) to (1-24) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0063] FIG. 3 is a figure showing the structures of compounds (1-25) to (1-36) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0064] FIG. 4 is a figure showing the structures of compounds (1-37) to (1-48) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0065] FIG. 5 is a figure showing the structures of compounds (1-49) to (1-60) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0066] FIG. 6 is a figure showing the structures of compounds (1-61) to (1-72) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0067] FIG. 7 is a figure showing the structures of compounds (1-73) to (1-84) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0068] FIG. 8 is a figure showing the structures of compounds (1-85) to (1-96) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0069] FIG. 9 is a figure showing the structures of compounds (1-97) to (1-106) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0070] FIG. 10 is a figure showing the structures of compounds (1-107) to (1-120) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0071] FIG. 11 is a figure showing the structures of compounds (1-121) to (1-132) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0072] FIG. 12 is a figure showing the structures of compounds (1-133) to (1-140) as amine compounds having the benzoazole ring structure represented by the general formula (1).

[0073] FIG. 13 is a diagram illustrating the configuration of organic EL device of Examples 7 to 9 and Comparative Examples 1 to 4.

MODE FOR CARRYING OUT THE INVENTION

[0074] The amine compounds having the benzoazole ring structure represented by the general formula (1) or (1a) are novel compounds, and the benzoazole derivatives that are the main skeleton of these compounds are, for example, themselves synthesized by known methods (refer to Non-Patent Document 4, for example). Furthermore, by conducting a coupling reaction between the synthesized halogenated benzoazole derivative and an arylamine using a copper catalyst or palladium catalyst, the benzoazole amine compounds having the ring structure represented by the aforementioned general formula (1) or (1a) can be synthesized.

[0075] In the same way, amine compounds having the benzoazole ring structure represented by the general formula (1) or (1a) can be synthesized by derivatizing halogenated benzoazole derivatives into boronic acid derivatives or boronic acid ester derivatives, followed by coupling reaction with halogenated arylamine (refer to non-Patent Document 5 and Non-Patent Document 6, for example).

##STR00005##

[0076] The specific examples of preferred compounds among the amine compounds having a benzoazole ring structure represented by the general formula (1) or (1a) preferably used in the organic EL devices of the present invention is shown in FIGS. 1 to 12. The present invention, however, is not restricted to these compounds.

[0077] The amine compounds having the benzoazole ring structure represented by the general formula (1) or (1a), which are suitably used for the organic EL devices of the present invention, are purified by column chromatography, adsorption purification using, for example, a silica gel, activated carbon, activated white clay, recrystallization or crystallization using a solvent, and finally purification by the sublimation purification method. The compounds were identified by NMR analysis. The melting point, glass transition point (Tg), refractive index and extinction coefficient, and absorbance were measured as material property values. The melting point can be used as an index of deposition properties, the glass transition point (Tg) can be used as an index of the stability in a thin film state, the refractive index and extinction coefficient can be used as an index of improved light extraction efficiency, and absorbance can be used as an index of color purity and improved light extraction efficiency.

[0078] Melting points and glass transition points (Tg) were measured by a high-sensitivity differential scanning calorimeter (DSC3100SA produced by Bruker AXS).

[0079] The refractive index and extinction coefficient were measured using a spectrometer (F10-RT-UV produced by Philmetrics) for 80 nm thin film formed on a silicon substrate.

[0080] The absorbance was measured in toluene solution at a prepared concentration of 1.0×10.sup.−5 mol/L, and the absorption coefficients were measured in toluene solution at prepared four concentrations of 5.0×10.sup.−6 mol/L, 1.0×10.sup.−5 mol/L, 1.5×10.sup.−5 mol/L, and 2.5×10.sup.−5 mol/L using a UV-visible-near-infrared spectrophotometer (V-650 produced by JASCO Corporation).

[0081] The organic EL device of the present invention, for example, in the case of a top emission light emitting device, may have a structure including an anode, a hole transport layer, an emission layer, an electron transport layer, a cathode, and a capping layer successively formed on a glass substrate, optionally with a hole injection layer between the anode and hole transport layer, an electron blocking layer between the hole transport layer and the light emitting layer, a hole blocking layer between the light emitting layer and an electron transport layer, and an electron injection layer between the electron transport layer and the cathode. Some of the organic layers in the multilayer structure may be omitted or may serve more than one function. For example, a single organic layer may serve as a hole injection layer and a hole transport layer, a hole transport layer and an electron blocking layer, a hole blocking layer and an electron transport layer, or an electron transport layer and an electron injection layer, and so on. Further, any of the layers may be configured to laminate two or more organic layers having the same function, and the hole transport layer may have a two-layer laminated structure, the light emitting layer may have a two-layer laminated structure, the electron transport layer may have a two-layer laminated structure, capping layer may have a two-layer laminated structure, and so on.

[0082] The total thickness of each layer of the organic EL device is preferably 200 nm to 750 nm, more preferably 350 nm to 600 nm.

[0083] The thickness of the capping layer, for example, is preferably 30 nm to 120 nm, more preferably 40 nm to 80 nm.

[0084] In this case, good light extraction efficiency can be obtained. The thickness of the capping layer can be changed according to the type of light-emitting material used in the light-emitting device, the thickness of each layer of the organic EL device other than the capping layer, and other factors.

[0085] Electrode materials with a large work function, such as ITO and gold, are used as the anode of the organic EL device.

[0086] The hole injection layer of the organic EL device of the present invention may be made of, for example, arylamine compounds having a structure in which three or more triphenylamine structures are joined within a molecule via a single bond or a divalent group that does not contain a heteroatom, for example, material such as starburst-type triphenylamine derivatives and various triphenylamine tetramers; porphyrin compounds such as copper phthalocyanine; accepting heterocyclic compounds such as hexacyanoazatriphenylene; coating-type polymer materials. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin film by a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0087] The hole transport layer of the organic EL device of this invention may be made of, preferably, arylamine compounds having a structure in which two triphenylamine structures are joined within a molecule via a single bond or a divalent group that does not contain a heteroatom, such as N,N′-diphenyl-N,N′-di(m-tolyl)benzidine (TPD), N,N′-diphenyl-N,N′-di(α-naphthyl)benzidine (NPD), N,N,N′,N′-tetrabiphenylylbenzidine, and 1,1-bis[4-di(4-tolylamino)phenyl]cyclohexane (TAPC). It is also preferable to use arylamine compounds having three or more triphenylamine structures in the molecule linked by a single bond or a divalent group that does not contain a heteroatom, such as various triphenylamine trimers or tetramers and the like. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. In addition, a coating-type polymer material such as poly (3,4-ethylenedioxythiophene) (PEDOT)/poly (styrene sulfonate) (PSS) may be used as the injection/transport layer of the hole. These materials may be formed into a thin film by a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0088] The material used for the hole injection layer, or the hole transport layer may be obtained by p-doping materials such as tri sbromophenylaminehexachloroantimony, and radialene derivatives (refer to Patent Document 3, for example) into a material commonly used for these layers, or may be, for example, polymer compounds each having, as a part of the compound structure, a structure of a benzidine derivative such as TPD.

[0089] The electron-blocking layer of the organic EL device of this invention may be made of a compounds having an electron blocking effect, including, for example, carbazole derivatives such as 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA), 9,9-bis[4-(carbazol-9-yl)phenyl]fluorene, 1,3-bis(carbazol-9-yl)benzene (mCP), and 2,2-bis[4-(carbazol-9-yl)phenyl]adamantane (Ad-Cz); and compounds having a triphenylsilyl group and a triarylamine structure, as represented by 9-[4-(carbazol-9-yl)phenyl]-9-[4-(triphenylsilyl)phenyl]-9H-fluorene. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin film by a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0090] The light emitting layer of the organic EL device of this invention may be made of various metal complexes of quinolinol derivatives, such as Alq.sub.3, as well as various anthracene derivatives, bis(styryl)benzene derivatives, pyrene derivatives, oxazole derivatives, polyparaphenylene vinylene derivatives, etc. may be used. Further, the light emitting layer made of a host material and a dopant material. Anthracene derivatives are preferably used as the host material, but various metal complexes, bis(styryl)benzene derivatives, pyrene derivatives, oxazole derivatives, polyparaphenylene vinylene derivatives, heterocyclic compound having an indole ring as a partial structure of the fused ring, heterocyclic compound having a carbazole ring as a partial structure of fused ring, carbazole derivatives, thiazole derivatives, benzimidazole derivatives, polydialkylfluorene derivatives may be used. Further, as dopant materials, quinacridone, coumarin, rubrene, perylene and their derivatives, benzopyran derivatives, rhodamine derivatives, amino styryl derivatives may be used, and green light emitting materials are particularly preferred. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer.

[0091] Further, the light-emitting material may be a phosphorescent material. Phosphorescent materials as metal complexes of metals such as iridium and platinum may be used. Examples of the phosphorescent materials include green phosphorescent materials such as Ir(ppy).sub.3, blue phosphorescent materials such as Flrpic and FIr6, and red phosphorescent materials such as Btp.sub.2Ir(acac), and green phosphorescent materials are particularly preferred. Here, as the hole injecting and transporting host material, 4,4′-di(N-carbazolyl)biphenyl (CBP), and carbazole derivatives such as TCTA and mCP may be used. As electron transporting host materials, p-bis(triphenyl silyl)benzene (UGH2), 2, 2′,2″-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) (TPBI) may be used. In this way, a high-performance organic EL device can be produced.

[0092] To avoid concentration quenching, the doping of the host material with the phosphorescent light-emitting material should preferably be made by co-evaporation in a range of 1 to 30 weight percent with respect to the whole light emitting layer.

[0093] Further, Examples of the light-emitting material may be delayed fluorescent-emitting material such as a CDCB derivative of PIC-TRZ, CC2TA, PXZ-TRZ, 4CzIPN or the like (refer to Non-Patent Document 7, for example) These materials may be formed into a thin film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0094] The hole blocking layer of the organic EL device of the present invention may be formed by using hole blocking compounds such as various rare earth complexes, triazole derivatives, triazine derivatives, and oxadiazole derivatives, in addition to the metal complexes of phenanthroline derivatives such as bathocuproin (BCP), and the metal complexes of quinolinol derivatives such as aluminum(III) bis(2-methyl-8-quinolinate)-4-phenylphenolate (BAlq). These materials may also serve as the material of the electron transport layer. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0095] The electron transport layer of the organic EL device of the present invention may be formed by using metal complexes of quinolinol derivatives such as Alq.sub.3 and BAlq, various metal complexes, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, pyridine derivatives, benzimidazole derivatives, benzoazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and silole derivatives. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0096] Examples of material used for the electron injection layer of the organic EL device of the present invention can be alkali metal salts such as lithium fluoride and cesium fluoride; alkaline earth metal salts such as magnesium fluoride; metal complexes of quinolinol derivatives such as lithium quinolinol; metal oxides such as aluminum oxide; and metals such as itterbium (Yb), samarium (Sm), calcium (Ca), strontium (Sr), cesium (Cs). However, the electron injection layer may be omitted in the preferred selection of the electron transport layer and the cathode.

[0097] Further, in the electron injection layer or the electron transport layer, a material obtained by further N-doping a material which is commonly used for the layer with a metal such as cecium, or the like can be used.

[0098] The cathode of the organic EL device of the present invention may be made of an electrode material with a low work function such as aluminum, or an alloy of an electrode material with an even lower work function such as a magnesium-silver alloy, magnesium calcium alloys, a magnesium-indium alloy, or an aluminum-magnesium alloy, and furthermore ITO, IZO.

[0099] The amine compound having a benzoazole ring structure represented by the above general formula (1) or (1a) are preferably used as the capping layer of the organic EL device of the present invention. These may be individually deposited for film forming, may be used as a single layer deposited mixed with other materials, or may be formed as a laminate of individually deposited layers, a laminate of mixedly deposited layers, or a laminate of the individually deposited layer and the mixedly deposited layer. These materials may be formed into a thin film by using a vapor deposition method or other known methods such as a spin coating method and an inkjet method.

[0100] The above description refers to an organic EL device with a top emission structure, but the invention is not limited to this, and can also be applied to organic EL devices with bottom emission structures, and organic EL devices with dual emission structures that emit light from both the top and the bottom. In these cases, the electrode in the direction from which light is extracted from the light emitting device to the outside must be transparent or translucent.

[0101] The refractive index of the material comprising the capping layer is preferably greater than the refractive index of the adjacent electrode. In other words, the capping layer improves the light extraction efficiency in the organic EL device, but the effect is more effective when the reflective index at the interface between the capping layer and the material in contact with the capping layer is larger, because the effect of light interference is greater. Therefore, the refractive index of the material comprising the capping layer is preferably greater than the refractive index of the adjacent electrode, and a refractive index of 1.90 or greater is preferable, while 2.00 or higher is far preferable.

[0102] The following describes an embodiment of the present invention in more detail based on Examples. The present invention, however, is not restricted to the following Examples as long as they do not go beyond the gist of the invention.

Example 1

Synthesis of Example Compound (1-1)

[0103] Bis[4-(benzoxazol-2-yl)-phenyl]amine: 12.3 g, 2-(4-bromophenyl)benzoxazole:9.2 g, tert-butoxy sodium: 4.4 g, toluene: 130 ml were added into a reaction vessel, and the mixture was aerated with nitrogen gas under ultrasonic irradiation for 30 minutes. Then, palladium (II) acetate: 0.1 g, tri-(tert-butyl)phosphine in 50% (w/v) toluene solution: 0.3 g were added thereto, and the mixture was stirred refluxed and stirred for overnight. After allowing to cool, dispersion washing was carried out at 80° C., and the insoluble material was filtered off, and the resulting filtrate was concentrated to obtain a crude product. The crude product was purified by recrystallizing with a mixed solvent of toluene/acetone, whereby a yellow powder of example compound (1-1): 10.0 g (yield: 54.9%) was obtained.

##STR00006##

[0104] The structure of the obtained yellow powder was identified by NMR. .sup.1H-NMR (CDCl.sub.3) detected 24 hydrogen signals, as follows. δ (ppm)=8.25-8.21(6H), 7.82-7.76(3H), 7.63-7.57(3H), 7.41-7.32(12H).

Example 2

Synthesis of Example Compound (1-2)

[0105] Bis[4-(benzoxazol-2-yl)-phenyl]amine: 12.3 g, 2-(4-bromophenyl)benzothiazole: 9.7 g, tert-butoxy sodium: 4.4 g, toluene: 130 mL were added into a reaction vessel, and the mixture was aerated with nitrogen gas under ultrasonic irradiation for 30 minutes. Then, palladium (II) acetate: 0.1 g, tri-(tert-butyl)phosphine in 50% (w/v) toluene solution: 0.3 g were added thereto, and the mixture was refluxed and stirred for overnight. After allowing to cool, dispersion washing was carried out at 80° C., and the insoluble material was filtered off, and the resulting filtrate was concentrated to obtain a crude product. The crude product was purified by recrystallizing with a mixed solvent of toluene/acetone, whereby a yellow powder of example compound (1-2): 14.5 g (yield: 77.5%) was obtained.

##STR00007##

[0106] The structure of the obtained yellow powder was identified by NMR. .sup.1H-NMR (CDCl.sub.3) detected 24 hydrogen signals, as follows. δ (ppm)=8.24-8.21(4H), 8.09-8.06(3H), 7.92-7.89(1H), 7.80-7.77(2H), 7.60-7.58(2H), 7.51(1H), 741-7.29(11H).

Example 3

Synthesis of Example Compound (1-4)

[0107] 2-(4-aminophenyl)benzothiazole: 6.0 g, 2 (4-bromophenyl)benzothiazole: 16.2 g, tert-butoxy sodium: 7.6 g, toluene: 150 mL were added into a reaction vessel, and the mixture was aerated with nitrogen gas under ultrasonic irradiation for 30 minutes. Then, tris(dibenzylideneacetone)palladium (0): 0.2 g, tri-(tert-butyl)phosphine in 50% (w/v) toluene solution: 0.2 g were added thereto, and the mixture was refluxed and stirred for overnight. After allowing to cool, dispersion washing was carried out at 80° C., and the insoluble material was filtered off, and the resulting filtrate was concentrated to obtain a crude product. The crude product was purified by recrystallizing with a mixed solvent of toluene/acetone, whereby a yellow powder of example compound (1-4): 10.2 g (yield: 59.6%) was obtained.

##STR00008##

[0108] The structure of the obtained yellow powder was identified by NMR. .sup.1H-NMR (CDCl.sub.3) detected the following 24 hydrogen signals. δ (ppm)=8.10-8.05(9H), 7.92-7.90(3H), 7.54-7.48(3H), 7.42-7.37(3H), 7.31-7.27(6H).

Example 4

[0109] The melting points and glass transition points (Tg) of amine compounds having a benzoazole ring structure represented by the general formula (1) or (1a) were determined using a high-sensitivity differential scanning calorimeter (DSC3100SA produced by Bruker AXS).

TABLE-US-00001 Melting point Glass transition point (Tg) Compound of Example 1 277° C. 126° C. Compound of Example 2 274° C. 123° C. Compound of Example 3 270° C. 119° C.

[0110] Amine compounds having a benzoazole ring structure represented by the general formula (1) or (1a) have a glass transition points (Tg) of 100° C. or higher, demonstrating that the compounds have a stable thin-film state.

Example 5

[0111] An 80 nm-thick vapor-deposited film was fabricated on a silicon substrate using the amine compound having a benzoazole ring structure of the general formula (1) or (1a), and the refractive index n at wavelengths of 400 nm, 410 nm, 500 nm, and 570 nm, and the extinction coefficient k at wavelengths of 400 nm and 410 nm were also measured with spectrometer (F10-RT-UV produced by Philmetrics). For comparison, comparative compounds (2-1), (2-2), (2-3), and (2-4) of the following structural formula were also measured (refer to Patent Document 4, for example). The measurement results are summarized in Table 1.

##STR00009##

TABLE-US-00002 TABLE 1 Extinction Extinction Refractive index n Refractive index n Refractive index n Refractive index n coefficient k coefficient k (λ: 400 nm) (λ: 410 nm) (λ: 500 nm) (λ: 570 nm) (λ: 400 nm) (λ: 410 nm) Example 2.54 2.59 2.09 1.97 0.85 0.56 Compound(1-1) Example 2.47 2.62 2.14 2.01 1.03 0.72 Compound(1-2) Example 2.09 2.41 2.19 2.04 1.16 1.07 Compound(1-4) Comparative 2.05 2.04 1.88 1.84 0.05 0.03 Compound(2-1) Comparative 2.35 2.27 1.94 1.88 0.14 0.06 Compound(2-2) Comparative 2.30 2.20 1.91 1.87 0.45 0.31 Compound(2-3) Comparative 2.37 2.31 1.87 1.80 0.32 0.11 Compound(2-4)

[0112] Thus, the compounds of the present invention have a larger refractive index of 1.90 or higher at wavelength of 500 nm to 570 nm, and more than the comparative compounds (2-1), (2-2), (2-3) and (2-4). This indicates that an improvement in light extraction efficiency in organic EL device can be expected.

[0113] In addition, the extinction coefficient of the comparative compounds (2-1), (2-2), (2-3) and (2-4) at wavelengths of 400 nm to 410 nm are less than 0.5, while the compounds of the present invention have larger values of extinction coefficient. This indicates that the compound absorbs light at wavelengths between 400 nm and 410 nm of sunlight well and do not affect the material inside the device.

Example 6

[0114] A toluene solution at a concentration of 1.0×10.sup.−5 mol/L using the compounds of the present invention were prepared, and the absorbance thereof at 400 nm and 410 nm was measured with a UV-visible-near-infrared spectrophotometer (V-650 produced by JASCO Corporation). For the absorption coefficient, four different concentrations, 5.0×10.sup.−6 mol/L, 1.0×10.sup.−5 mol/L, 1.5×10.sup.−5 mol/L, and 2.0×10.sup.−5 mol/L of toluene solutions were prepared, and measured using a UV-visible-near-infrared spectrophotometer (V-650 produced by JASCO Corporation), and the absorption coefficient was calculated from the calibration curve. For comparison, comparative compounds (2-1), (2-2), (2-3), and (2-4) of the above structural formula were also measured. The measurement results are summarized in Table 2.

TABLE-US-00003 TABLE 2 Peak wave- length Absorbance Absorbance Absorption (λ max) (λ: 400 nm) (λ: 410 nm) coefficient Example 386 nm 0.75 0.14 149608 Compound(1-1) Example 387 nm 1.11 0.41 150416 Compound(1-2) Example 396 nm 1.55 1.13 156411 Compound(1-4) Comparative 305 nm 0.02 0.01 114814 compound(2-1) Comparative 305 nm 0.02 0.00 98970 compound(2-2) Comparative 345 nm 0.60 0.21 100841 compound(2-3) Comparative 373 nm 0.28 0.08 88182 compound(2-4)

[0115] Thus, the absorbance at wavelengths of 400 nm to 410 nm of comparative compounds (2-1), (2-2), (2-3) and (2-4) were less than 0.7, whereas the compounds of the present invention larger than 0.7, which indicates that they absorb light at wavelengths of 400 nm to 410 nm of sunlight well. In terms of absorption coefficient, absorption coefficient of compounds of this invention is larger than that of comparative compounds (2-1), (2-2), (2-3), and (2-4). This indicates that if the concentration is the same, the compounds of the present invention show that they absorb light well, and regarding thin films, it is shown that the thicker the film thickens, the better the light absorbs and is an excellent light fastness.

Example 7

[0116] The organic EL device, as shown in FIG. 13, was fabricated by vapor-depositing a hole injection layer 3, first hole transport layer 4, second hole transport layer 5, emission layer 6, electron transport layer 7, electron injection layer 8, cathode 9, and capping layer 10 in this order on a glass substrate 1 on which a reflective ITO electrode as metal anode 2 beforehand.

[0117] Specifically, as the metal anode 2, an ITO film with a thickness of 50 mm, a silver alloy reflective film with a thickness of 100 nm, and an ITO film with a thickness of 5 nm were deposited on the glass substrate 1 in this order. After ultrasonic cleaning in isopropyl alcohol for 20 minutes, the film was dried on a hot plate heated to 250° C. for 10 minutes. After UV ozone treatment for 2 minutes, the glass substrate with ITO was installed in a vacuum vapor deposition apparatus, and the pressure was reduced to 0.001 Pa or lower. Subsequently, as the hole injection layer 3 covering the metal anode 2, an electron acceptor (Acceptor-1) of the structural formula below and compound (3-1) of the structural formula below were formed in a film thickness of 10 nm by dual vapor deposition at a vapor deposition rate ratio of Acceptor-1: compound (3-1)=3:97. The first hole transport layer 4 was formed on the hole injection layer 3 by forming the compounds (3-1) of the structural formula below in a film thickness of 70 nm. The second hole transport layer 5 was formed on the first hole transport layer 4 by forming the compound (3-2) of the structural formula below in a film thickness of 10 nm. Then, the light emitting layer 6 was formed on the second hole transport layer 5 in a film thickness of 40 nm by dual vapor deposition of the compound (3-3) of the structural formula below and Compound (3-4) of the structural formula below at a vapor deposition rate ratio of the compound (3-3): Compound (3-4)=5:95. The electron transport layer 7 was formed on the light emitting layer 6 in a film thickness of 30 nm by dual vapor deposition of the compound (3-5) of the structural formula below and Compound (3-6) of the structural formula below at a vapor deposition rate ratio of the compound (3-5): Compound (3-6)=50:50. The electron injection layer 8 was formed on the electron transport layer 7 by forming lithium fluoride in a film thickness of 1 nm. On top of the electron injection layer 8, a magnesium silver alloy was formed as the cathode 9 with a thickness of 12 nm. Finally, compound (1-1) of Example 1 was formed as the capping layer 10 with a film thickness of 60 nm. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0118] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00010##

Example 8

[0119] An organic EL device was fabricated under the same conditions used in Example 7, except that the capping layer 10 was formed by forming the compound (1-2) of Example 2, instead of using the compound (1-1) of Example 1. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0120] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00011##

Example 9

[0121] An organic EL device was fabricated under the same conditions used in Example 7, except that the capping layer 10 was formed by forming the compound (1-4) of Example 3, instead of using the compound (1-1) of Example 1. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0122] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00012##

Comparative Example 1

[0123] For comparison, an organic EL device was fabricated under the same conditions used in Example 7, except that the capping layer 10 was formed by forming a comparative compound (2-1) of the following structural formula, instead of using the compound (1-1) of Example 1. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0124] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00013##

Comparative Example 2

[0125] For comparison, an organic EL device was fabricated under the same conditions used in Example 7, except that the capping layer 10 was formed by forming a comparative compound (2-2) of the following structural formula, instead of using the compound (1-1) of Example 1. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0126] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00014##

Comparative Example 3

[0127] For comparison, an organic EL device was fabricated under the same conditions used in Example 7, except that the capping layer 10 was formed by forming a comparative compound (2-3) of the following structural formula, instead of using the compound (1-1) of Example 1. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0128] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00015##

Comparative Example 4

[0129] For comparison, an organic EL device was fabricated under the same conditions used in Example 7, except that the capping layer 10 was formed by forming a comparative compound (2-4) of the following structural formula, instead of using the compound (1-1) of Example 1. The characteristics of the organic EL device thus fabricated were measured in the atmosphere at an ordinary temperature.

[0130] Table 3 summarizes the results of emission characteristics measurements performed by applying a DC voltage to the fabricated organic EL device.

##STR00016##

[0131] Table 3 summarizes the results of the device lifetime measurements performed with the organic EL devices fabricated in Examples 7 to 9 and Comparative Examples 1 to 4. A device lifetime was measured as the time (attenuation to 95%) taken for the initial luminance to decay to 95%, with the initial brightness as 100%, when carrying out constant current drive of 10 mA/cm.sup.2.

TABLE-US-00004 TABLE 3 Current Efficiency Power Efficiency Voltage [V] Luminance[ /m2] [ /A] [ ] Device lifetime Capping Layer (@10 mA/cm2) (@10 mA/cm2) (@10 mA/cm2) (@10 mA/cm2) Attenuation to 95% Example 7 Example 4.04 16370 163.85 127.36 385 Time H compound(1-1) Example 8 Example 4.05 16625 166.43 129.07 396 Time H compound(1-2) Example 9 Example 4.03 17025 170.36 133.01 378 Time H compound(1-4) Comparative Comparative 4.02 13139 131.45 102.78 291 Time H Example 1 compound(2-1) Comparative Comparative 4.01 14625 146.30 114.55 302 Time H Example 2 compound(2-2) Comparative Comparative 4.06 13814 138.29 107.02 301 Time H Example 3 compound(2-3) Comparative Comparative 4.03 13022 130.31 101.68 257 Time H Example 4 compound(2-4) indicates data missing or illegible when filed

[0132] As shown in Table 3, the driving voltage at a current density of 10 mA/cm.sup.2 is almost the same for the devices in Comparative Examples 1 to 4 and Examples 7 to 9. However, luminance, current efficacy, power efficiency, and device lifetime were improved in the devices of Examples 7 to 9 compared with those of Comparative Examples 1 to 4. This indicates that the light extraction efficiency can be significantly improved by including a material with a high refractive index, which is suitably used for the organic EL devices of the present invention, in the capping layer.

INDUSTRIAL APPLICABILITY

[0133] As described above, the amine compound having the benzoazole ring structure represented by general formula (1), which is suitably used for the organic EL device of the present invention, has a high absorption coefficient of light at the wavelength range of 400 nm to 410 nm, high refractive index, which can significantly improve light extraction efficiency and stability in thin film state. The compound is excellent as a compound for organic EL device. By using this compound to fabricate organic EL devices, high efficiency can be obtained, and durability and lightfastness can be improved so that sunlight light is not absorbed and affects the materials inside the device. The use of this compound, which has no absorption in the blue, green, and red wavelength regions, makes it particularly suitable for displaying clear, bright images with good color purity. For example, it is now possible to develop applications in home appliances and lighting.

DESCRIPTION OF REFERENCE NUMERAL

[0134] 1 Glass substrate [0135] 2 Metal Anode [0136] 3 Hole injection layer [0137] 4 First hole transport layer [0138] 5 Second hole transport layer [0139] 6 Light emitting layer [0140] 7 Electron transport layer [0141] 8 Electron injection layer [0142] 9 Cathode [0143] 10 Capping layer