JP4802671B2 - Organic EL device with low molecular organic thin film - Google Patents

Description

The present invention relates to an organic EL device having a coating-type low-molecular organic thin film, and particularly, trans-1,2-bis (9H-carbazol-9-yl) cyclobutane represented by the following formula (2) as a core. The present invention relates to an electroluminescent (hereinafter abbreviated as EL) device including an organic thin film made of a low molecular compound. More specifically, the present invention comprises a low-molecular compound having trans-1,2-bis (9H-carbazol-9-yl) cyclobutane represented by the following formula (4) as a nucleus, and a wet method such as printing. The present invention relates to an organic EL element including a formed organic thin film.

 The organic EL element has at least one layer of an organic carrier transport layer and an organic light emitting layer between opposed electrodes. As a method for forming these organic films, there are a vapor deposition method and a wet film formation method.

 For example, a method for producing an organic EL element in which an organic film is formed by a vapor deposition method is such that a light emitting layer material is formed by vacuum vapor deposition on a transparent anode substrate having indium tin composite oxide (ITO) or the like patterned on the substrate. And depositing a cathode on it. In addition, for the purpose of improving performance, functional separation of the cathode, such as a hole injection layer, a hole transport layer, an electron block layer, a light emitting layer, a hole block layer, an electron transport layer, and an electron injection layer, is performed on the anode substrate. In some cases, laminated multilayer films are laminated.

 In the wet film formation method, an ink in which a conjugated polymer material such as polyparaphenylene vinylene, polyparaphenylene, polyfluorene, or polythiophene is dissolved in an organic solvent or dispersed in water, or a low molecular material is polyvinyl An organic film is formed by applying ink dissolved with carbazole or a conjugated polymer material. A method for manufacturing an EL element using a wet film forming method is to form a film by printing or applying a hole transport layer and a light emitting layer in this order on a substrate having a transparent anode such as patterned ITO, The cathode is formed by vapor deposition or sputtering.

 Specific film forming methods in the wet film forming method include printing methods such as an ink jet method, a gravure printing method, a relief printing method, an offset printing method, and a coating method such as spin coating, die coating, and cap coating. In some cases, the organic film is formed on the substrate in the reverse order from the cathode, and finally the anode is formed.

 The low molecular weight hole transport material and the light emitting material are preferably compounds having a molecular weight (Mw) of at least about 350 in order to prevent re-evaporation from the substrate in vacuum. In order to prevent decomposition and carbonization, a material having a molecular weight of about 1200 or less is usually used so that a sufficient vapor deposition rate can be obtained at a low evaporation source temperature of 500 ° C. or less.

  Examples of general vapor deposition materials include Al oxine complexes (abbreviated as Alq, Mw = 459), bis-N, N′-diphenyl-N, N′-di (2-naphthyl) benzidine (abbreviated as α-NPD, Mw = 588), rubrene (Mw = 583), fac-tris (2-phenylpyridine) Ir (Mw = 655), 4,4 ', 4 "-tris (N-2-naphthyl-N-phenyl) amino-tri In many cases, a material having a molecular weight of about 450 to 1000 such as phenylamine (abbreviated as 2-TNATA, Mw = 897) is used.

 A general low-molecular material formed by a vapor deposition method does not have a large molecular structure like a polymer material or a higher-order dendrimer material, so that molecules are not entangled and are easy to move. An organic film formed using a solution obtained by dissolving such a compound in an organic solvent tends to cause unevenness in the film due to the association of molecules with each other over time. Therefore, when an EL element is manufactured using such an organic film, there is a problem that a pinhole is generated in the film and a short circuit occurs.

 In contrast, even a low molecular weight material can prevent crystallization by forming a rigid, asymmetric and steric amorphous molecular structure having a high glass transition temperature (for example, non-patent literature). Therefore, it is conceivable to form an organic film by applying or printing a low molecular material having such a molecular structure.

 In addition, high molecular weight polymer materials capable of wet film formation and high-generation dendrimer materials have a problem that they are difficult to purify and synthesize, so they are low-molecular compounds that can be easily synthesized, have high solubility in solvents, There is a demand for materials having good film properties.

 Furthermore, when producing a color display by three-color coating by low-molecular material mask vapor deposition, if the substrate size becomes a metric size, it becomes difficult to align the mask and the substrate, and a large vacuum film forming apparatus is required. Therefore, there is a problem that the manufacturing cost increases. Therefore, in order to produce a color display with a large area at a low cost, it is desired to develop a technique using a printing method capable of performing multicolor coating of light emitting layers at a low cost under normal pressure.

 In this case, one pixel is usually divided into three colors of red, blue, and green. Further, in order to improve the light utilization efficiency, there are cases where the four colors of red, green, blue, and white are separately applied. Furthermore, in order to further expand the color reproduction region, it is possible to separately coat the five sub-pixels of red, yellow-green, green, blue, and white.

 As a method for forming these sub-pixels, there is a method in which a monochromatic blue light-emitting element or a white light-emitting element is spectrally separated by a color filter, in addition to a method in which a light emitting layer is directly applied.

  On the other hand, a polythiophene-based or polyaniline-based conductive polymer is usually used as a polymer hole transport material that can be applied and printed. Poly (3,4-ethylenedioxythiophene) / poly (styrenesulfonic acid) (hereinafter abbreviated as PEDOT / PSS), which is a polythiophene-based conductive polymer, is an aqueous dispersion of fine particles. The PEDOT / PSS film has an advantage that when the light emitting layer is laminated thereon, the film is not dissolved by the organic solvent of the light emitting layer.

 The PEDOT / PSS film has a low electrical resistance, and can increase the ionization energy of the surface from about 4.8 eV, which is the ionization energy of ITO, to 5.1 to 5.3 eV to promote hole injection. Further, there is an advantage that the unevenness on the surface of the ITO electrode is smoothed to prevent a short circuit.

 However, the PEDOT / PSS film has a high acidity of about pH 1 due to the sulfonic acid group in the PSS, so it corrodes the metal part of the device, dissolves the ITO surface, and diffuses indium ions to the light emitting layer. There was a problem of causing deterioration of the light emitting layer. In addition, since PEDOT / PSS is an aqueous dispersion, it takes time to completely remove the water in the film.

 Therefore, after forming a film using a highly volatile organic solvent instead of a strong acid, it can be insolubilized in an organic solvent by cross-linking with light or heat, or by self-organization using the formation of hydrogen bonds between substituents. Development of a positive hole transport material is also desired.

  In addition, when a conjugated polymer light emitting material such as a polyfluorene copolymer is used as a blue light emitting material, the lifetime is currently an order of magnitude shorter than that of a low molecular weight material, and the color purity of a high brightness blue material is inferior. was there. Therefore, development of materials having high brightness, long life, and high color purity that can be printed and applied at low cost is desired, not limited to polymer materials.

 Furthermore, when an EL device is manufactured using a printing method, the solubility of the polymer material may be insufficient, or the ink may not be highly concentrated due to high viscosity and may not be printed to a desired thickness. there were. It is also desired to reduce the environmental burden by making a high-concentration ink using a low-molecular-weight low-molecular compound and reducing the amount of volatile solvent during printing.

 Furthermore, depending on the type of polyfluorene, there is a concern that the polymer may be oxidized during the polymerization or by heating in the subsequent device manufacturing process to generate fluorenone, resulting in a long wavelength shift of the spectrum (for example, Non-Patent Document 3). reference). On the other hand, when a polymer material is handled in an inert atmosphere, there is a problem that the manufacturing cost of the material itself and the manufacturing cost of the EL element increase, and a material that is stable even in the air has been demanded.

The synthesis of trans-1,2-bis (9H-carbazol-9-yl) cyclobutane was reported in 1965 by Bawn et al. (See, for example, Non-Patent Document 4). Trans-1,2-bis (9H-carbazol-9-yl) cyclobutane (yield 40-50%) and 9- (1-methoxyethyl) from a dry methanol solution of N-vinylcarbazole containing Fe (NO ₃ ) ₃ ) Carbazole can be obtained.

 The photodimerization reaction of N-vinylcarbazole was also reported by Ellinger in 1965 (see, for example, Non-Patent Document 5). Furthermore, continuous production is also possible by using a synthesis method by photodimerization and dissolving the raw material in acetone and continuously feeding it (see, for example, Patent Document 1).

 Trans-1,2-bis (9H-carbazol-9-yl) cyclobutane has a high hole transporting property, and can be formed by coating with a binder resin as an organic photoconductor for electrophotography (for example, Patent Documents). 2) or mixed with a Lewis acid to form a coating film (for example, see Patent Document 3).

The hole mobility of trans-1,2-bis (9H-carbazol-9-yl) cyclobutane is 1.6 × 10 ⁻⁶ cm ² / V · sec when 51 wt% is dispersed in poly (bisphenol A carbonate). (1.6 × 10 ⁵ Vcm ⁻¹ ) (see, for example, Non-Patent Document 6) and 7.0 × 10 ⁻⁶ cm ² / V · sec (2. 5 × 10 ⁵ Vcm ⁻¹ ) (for example, see Patent Document 4). Their values are an order of magnitude greater than poly N-vinylcarbazole.

  However, a film formed by dispersing and coating a low molecular hole transport material in a polymer binder has the ability to transport holes by aggregating the low molecular hole transport material in the film or thinning it with the binder. Will drop significantly. Although its hole transport capability is sufficient for electrophotographic applications, it is insufficient for EL device applications. If the transport capability is insufficient, there is a problem that charges are accumulated in the film and the deterioration is accelerated, so that a high hole transport capability is required.

 As an example of using trans-1,2-bis (9H-carbazol-9-yl) cyclobutane as a hole transport material of an EL element, in the DuPont patent (for example, see Patent Documents 5, 6, 7, and 8) The metal complex is used for the hole transport layer of the phosphorescent EL device. However, the glass transition temperature (Tg) of trans-1,2-bis (9H-carbazol-9-yl) cyclobutane is 59 ° C. (temperature at the beginning of the transition, measured at a heating rate of 20 ° C./min by differential scanning calorimetry) Therefore, the heat resistance was quite insufficient for use as an EL display material.

 In order to put the EL element into practical use as a vehicle-mounted display or the like, the hole transport material preferably requires Tg of 120 ° C. or higher.

 In addition, trans-1,2-bis is added to the main chain of polyurethane, polyester, polyurea, polyamide (see, for example, Patent Document 9), the main chain of polyazomethine, and the side chain of a vinyl polymer (see, for example, Patent Document 10). There is also an example in which (9H-carbazol-9-yl) cyclobutane is introduced into a polymer to improve flexibility and printing durability. However, as in the case of being dispersed in the binder, the carrier hopping distance is increased as compared with the performance of a film composed of only low molecules, so that there is a problem that the hole transport capability is lowered.

Furthermore, due to impurities incorporated into the polymer during the polymerization, charges are accumulated in the film, or charge transfer complexes with acceptors such as Lewis acids added for resistance reduction, and carbazole rings in the polymer are Since they are close to each other, it is easy to form an excimer and there is a problem in that excitons in the light emitting layer are deactivated.
U.S. Pat. No. 3,846,264 U.S. Pat. No. 3,684,506 JP 49-8236 A Japanese Patent Application Laid-Open No. 60-213851 Japanese translation of PCT publication No. 2004-503059 JP-T-2004-536133 JP 2005-508437 A JP 2005-519988 JP 56-47431 A Japanese Patent Laid-Open No. 2-9586 B E. Koene, D E. Loy and ME. Thompson, Chem. Mater., 10, 2235 (1998). Yuichi Ito, M & BE, 11, 32 (2000). Xiong Gonga, Daniel Mosesa, Alan J. Heeger and Steven Xiao, Synthetic Metals, 141, 17 (2003). CEH Bawn, A. Ledwitth and Yang Shih-Lin, Chem. Ind., 18, 769 (1965). LPEllinger, Polymer, 6,549 (1965) N. Tsutsumi, M. Yamamoto, Y. Nishijima, Journal of Polymer Science, Part B: Polymer Physics, 25 (10), 2139 (1987)

 As described above, conventionally, PEDOT / PSS has been used as a polymer hole transport material for organic EL elements capable of wet coating, but as described above, this substance has strong acidity. Since there is a problem of dissolving the ITO transparent electrode surface, a hole transport material that does not corrode the ITO transparent electrode has been demanded.

 Conjugated polymer light-emitting materials can be formed on a large-area substrate at a lower cost than a vacuum evaporation method because wet film formation is possible by an inkjet method, a printing method, or the like. However, there is still a problem with the lifetime of the blue material, and it has not yet been put into practical use for large-screen TV applications.

 Although an EL element excellent in durability, luminance characteristics, and color purity can be produced by a vacuum evaporation method of a low molecular EL material, high-definition multicolor coating by mask evaporation on a large area substrate is difficult. Therefore, when a large color display is manufactured, the light use efficiency is deteriorated, but colorization is performed by overlaying a color filter on a white light emitting element.

 If a low molecular weight EL material having excellent EL element performance can be formed into a wet film, there is a possibility that both performance and a large area can be achieved. However, conventional low-molecular EL materials have low solubility or are often easily crystallized by wet film formation, and it is often difficult to form an amorphous film that is smooth and has high heat resistance.

 Therefore, the development of amorphous low-molecular-weight EL materials that can be applied to wet film formation using coating methods such as spin coating, cap coating, slit coating, nozzle dispenser, etc., inkjet, letterpress printing, offset printing, intaglio printing, etc. It has become a challenge.

 Thus, there is a demand for an organic EL element that can be applied to a large-area substrate and can emit blue light at a low cost by coating and forming an ink made of an amorphous low-molecular EL material.

 In addition, it can be coated with a low molecular weight material without the need for a binder, has high amorphousness and heat resistance, has high carrier transportability, or can be used as a light emitting material or a host material for a light emitting layer. There is a need for an EL element using a material having a high light-emitting property.

 In the case of a high molecular compound, since the viscosity of the solution is high and the solubility is low, a high-concentration ink cannot be produced, and an ink having a solid content of about 1 to 2 wt% is usually used. For this reason, a large amount of organic solvent of 98% or more of the ink weight is volatilized in the atmosphere by coating and drying, which adversely affects the environment.

 In this case, if the solid concentration can be increased 10 times to form the same film thickness, the amount of the volatile organic solvent can be reduced to 1/10, and the influence on the environment can be minimized. Even when the solvent adsorption filter is installed in the clean room where the printing machine is installed, it is only necessary to install a small adsorption device, and the life of the filter can be extended. Therefore, development of an EL element using an amorphous low molecular EL material capable of producing a high concentration ink is desired.

 The present invention has been made under the circumstances as described above, and an object thereof is to provide an organic EL element with low cost, large area, high reliability, and low environmental load.

R ₁ 、R ₂ はそれぞれ独立に炭素数４以下のアルキル基または水素で、R ₁ 、R ₂ が同時に水素にならない。R ₃ は炭素数４以下のアルキル基である。
A ₁ 、A ₂ はそれぞれ独立に炭素数６から１２の芳香族６員環を含む単環または縮合環から誘導された置換基である。) In order to solve the above problems, the present invention provides an organic EL device comprising an organic carrier transport layer and / or an organic light emitting layer between opposing electrodes, wherein at least one of the organic carrier transport layer and the organic light emitting layer is: It is represented by the following formula (1) having a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane structure, has a molecular weight of 1271.7 or more and 1864.3 or less , and can be formed by spin coating. Provided is an organic EL element comprising an organic layer formed by coating or printing using a simple material .

R ₁ and R ₂ are each independently an alkyl group having 4 or less carbon atoms or hydrogen, and R ₁ and R ₂ do not simultaneously become hydrogen. R ₃ is an alkyl group having 4 or less carbon atoms.
A ₁ and A ₂ are each independently a substituent derived from a monocyclic or condensed ring containing a 6- to 12-carbon aromatic 6-membered ring. )

The organic EL device of the present invention is represented by the formula (1) having a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane structure and has a molecular weight of 1271.7 or more and 1864.3 or less. A hole transport layer containing the compound can be provided.

The organic EL device of the present invention is represented by the formula (1) having a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane structure and has a molecular weight of 1271.7 or more and 1864.3 or less. A hole transport layer containing the compound can be provided.

The organic EL device of the present invention is represented by the formula (1), and includes a carrier transport layer and / or an organic light emitting layer containing a compound having a molecular weight of 1271.7 or more and 1864.3 or less, and the cathode. The hole blocking electron transport layer may be interposed.

 Conventionally, a low molecular weight material is likely to be a crystalline film and has a problem that an EL element is short-circuited due to a film defect. However, a compound represented by the above formula (1) having a molecular weight of 690 to 5000 is Since a smooth amorphous film can be easily formed by printing or coating, there are few film defects. The organic EL device of the present invention in which such a film is used for a carrier transport layer such as a hole transport layer and / or a light-emitting layer is not short-circuited due to a film defect, and a coating or printing method is used for film formation Since it can be used, a large-area display can be manufactured at low cost.

 In addition, since conventional conjugated polymer EL materials such as polyfluorene are large in molecular weight, they are often difficult to dissolve and apply in high concentrations in organic solvents due to solubility and viscosity. An ink with a low solid content concentration was used. Therefore, when a film is formed by an ink jet method or a printing method, it is necessary to form a high bank for storing ink or to apply a plurality of times in order to obtain a certain dry film thickness.

   On the other hand, since the compound represented by the above formula (1) having a molecular weight of 690 or more and 5000 or less used in the present invention is a low-viscosity, high-amorphous low-molecular compound, a general organic solvent such as toluene. It can be dissolved at a high concentration, for example, as high as 10 to 50 wt%. Therefore, it is possible to reduce the number of ink droplets to be ejected or to eliminate the need for overcoating and to increase the film formation speed. Further, since the formation of a low bank is sufficient, there is an advantage that a step can be reduced, defects in the wiring film and the sealing film are reduced, and an EL element having a high aperture ratio is possible.

 Moreover, since the amount of the volatile organic solvent at the time of drying can be greatly reduced by using a high-concentration ink, there is an effect of reducing damage to the environment.

 Furthermore, when a light emitting layer is formed by coating or printing, it is only necessary to dissolve a certain concentration of dopant in the ink, so the dopant concentration is not uniform on the substrate due to the difference in distance from the evaporation source as in the case of co-evaporation. There is an effect that an EL light emitting surface with high uniformity can be obtained.

  The best mode for carrying out the invention will be described below.

The organic EL device of the present invention is an organic EL device comprising an organic carrier transport layer and / or an organic light emitting layer between opposed electrodes, wherein at least one of the organic carrier transport layer and the organic light emitting layer is trans-1 , 2-bis (9H-carbazol-9-yl) cyclobutane structure, represented by the following formula (1), and having a molecular weight of 690 or more and 5000 or less.

(In the formula, A1 to A4 represent substituents, at least two of which are substituents including one or more aromatic rings or condensed aromatic rings, and hydrogen may be substituted with deuterium. )
The trans-1,2-bis (9H-carbazol-9-yl) cyclobutane nucleus of the compound represented by the above formula (1) has two rigid carbazole rings bonded to a flexible cyclobutane ring at the trans position. Therefore, it has a bent molecular structure. Moreover, the compound represented by Formula (1) by a substituent of A1-A4 takes a more three-dimensional molecular structure, and since it is highly amorphous, it is easy to melt | dissolve in an organic solvent. A highly amorphous material exhibits a glass transition by DSC (Differential Scanning Thermal Analysis) measurement, and can form a transparent and smooth film by vacuum deposition or coating. Therefore, a solution containing the compound represented by the formula (1) can be formed by a coating method or a printing method.

 Since the compound represented by the formula (1) contains a rigid aromatic ring or condensed aromatic ring in the molecular structure, it has a high glass transition temperature and heat resistance. In addition, since the compound represented by the formula (1) is a low molecular weight amorphous material having a molecular weight of 690 to 5,000, the compound has high solubility in an organic solvent, and the product is not obtained by column chromatography compared to a polymer material. It has the advantage that the separation of the reactants and side reactants is relatively easy.

 Further, purification of a compound having a molecular weight within this range is relatively easy by a combination of methods such as filtration, adsorption, dialysis, extraction, column chromatography, sublimation, reprecipitation, and recrystallization depending on the molecular weight and solubility. Therefore, there is an advantage that a relatively high purity material can be synthesized at a low cost.

An example of the molecular weight of the compound represented by the above formula (1) used in the organic EL device of the present invention is a compound in which two o-biphenyl groups are substituted, the molecular formula is C ₅₂ H ₃₈ N ₂ , and the molecular weight is 690. 87, which is the lowest molecular weight compound of the present invention. When the molecular weight is less than 690, there is one biphenyl substituent, and the film has a high crystallinity, making it difficult to form a smooth film.

When all of A1 to A4 in the above formula (1) are o-biphenyl groups, the molecular formula is C ₇₆ H ₅₄ N ₂ and the molecular weight is 995.26. Up to a molecular weight of about 1000, it is possible to form a film by vacuum deposition at a deposition source temperature of about 400 to 450 ° C. However, a compound in which all the positions of A1 to A4 are substituted has a three-dimensional molecular association. The film can be formed by a coating method such as spin coating, die coating or cap coating after dissolving in a solvent, or a printing method such as ink jet, letterpress printing, offset printing or gravure printing.

In addition, the molecular formula of the compound in which all of A1 to A4 in the formula (1) are substituted with a substituent represented by the following formula (3) (a substituent shown in No. 36 of Table 1) is C ₃₄₀ H ₃₄₂ N _2. And the molecular weight is 4456.37.

 If the molecular weight is greater than 5000, it may be difficult to dissolve in a solvent, or the synthesis yield may be reduced due to steric hindrance of the substituent, making it difficult to introduce the substituent. Therefore, the molecular weight is desirably in the range of 690 to 5000.

 Substituents used for A1 to A4 in the above formula (1) are each independently at least two or more substituents other than hydrogen and containing two or more aromatic rings or one or more condensed aromatic rings. It is a group. Further, hydrogen in the formula (1) may be substituted with deuterium in order to suppress thermal vibration and increase luminous efficiency.

  Examples of the aromatic ring and condensed aromatic ring in the substituents A1 to A4 of the formula (1) include 1,3,4-oxadiazole ring, oxazole ring, thiophene ring, thiazole ring, benzothiazole ring, benzo Thiadiazole ring, benzene ring, naphthalene ring, anthracene ring, pyridine ring, quinoline ring, pyrazole ring, imidazole ring, benzimidazole ring, 1,3,4-triazole ring, pyrazine ring, pyrimidine ring, pyridazine ring, 1,3, 5-triazine ring, fluorene ring, carbazole ring, β-carboline ring, phenanthridine ring, acridine ring, perimidine ring, 4,7-phenanthroline ring, 3,8-phenanthroline ring, 3,7-phenanthroline ring, 2, 9-phenanthroline ring, 2,8-phenanthroline ring, 2,7-phenanthroline ring, 1,1 -Phenanthroline ring, neocuproine ring, bathocuproine ring, 1,9-phenanthroline ring, 1,8-phenanthroline ring, 1,7-phenanthroline ring, phenazine ring, phenothiazine ring, phenoxazine ring, antilysine ring, naphthalimide ring, silole A ring, a borol ring, a 9-borafluorene ring, which are directly connected to each other, or via a group derived from a vinylene group, an ethynylene group, a nitrogen atom, a boron atom, a silicon atom, or an adamantane ring. May be linked in a straight chain or branched form.

  In addition, one or more alkyl groups, alkoxy groups, polyether groups, adamantyl groups, or polyhedral oligomeric silyls may be added to the aromatic rings of these substituents in order to improve solubility, adhesion, and film formability. A sesquioxane (POSS) group may be substituted.

 Examples of the structural formula of the substituent are listed in N0.1 to 86 in Tables 1 to 8 below, but are not limited to these examples.

  Further, all of the substituents of A1 to A4 may be the same substituent, but a compound having a structure in which two or three are the same substituents can be synthesized, and a compound having a structure in which all are different substituents can also be synthesized. It can be synthesized.

R in Tables 1 to 8 below is a linear or branched alkyl group having 20 or less carbon atoms such as hydrogen, methyl group, isopropyl group, t-butyl group, octyl group; methoxy group, 2-ethyl-octyloxy An alkoxy group having 20 or less carbon atoms such as a group; fluorine, cyano group, phenyl group, tolyl group; vinyl group, allyl group, allyloxy group, glycidyl group, glycidyloxy group, acryloxy group, (oxetan-2-yl) methyl It is a group selected from crosslinkable groups such as an oxy group, a styryl group, and a thiol group.

 The trans-1,2-bis (9H-carbazol-9-yl) cyclobutane nucleus of the low molecular weight compound represented by the above formula (1) has two carbazole rings and has a hole transport capability. Therefore, an organic EL device having excellent performance can be obtained by forming this compound into a hole transport layer.

 In addition, at least two of the substituents A1 to A4 of the low molecular weight compound represented by the above formula (1) are from an aromatic ring in a substituted or unsubstituted aromatic tertiary amine, or aromatic secondary. By using a monovalent group derived from a nitrogen atom of an amine, the density of hole transport units is increased, and an EL device having a hole transport layer having a higher hole transport capability can be obtained.

 The aromatic group in the aromatic tertiary amine of the substituents A1 to A4 is preferably a ring having 20 or less carbon atoms such as a phenyl group, a tolyl group, a naphthyl group, an anthryl group, a biphenyl group, and a pyridyl group, An alkyl group or an alkoxy group having 20 or less carbon atoms may be substituted. In other cases, it may be irradiated with light or heat such as a vinyl group, a styryl group, a thiol group, an acrylate group, a methacryl group, a glycidyl group, or an oxetane group. It may be substituted with a group that polymerizes, or may be substituted by connecting them with a linking group such as an ether bond, a methylene chain, or an oxymethylene chain.

 As examples of monovalent substituents derived from the aromatic ring of the aromatic tertiary amine, Nos. 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 64, 82.

 Examples of monovalent substituents derived from the nitrogen atom of the aromatic secondary amine include Nos. 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81 in the above table. It is done.

 A compound containing a condensed aromatic ring such as naphthalene or anthracene in the aromatic ring in the aromatic amine group in the substituents A1 to A4 exhibits strong fluorescence in the visible region, and is therefore used as a hole transporting light emitting layer. An EL element can also be manufactured. A compound that does not contain a condensed aromatic ring can also be used as a host material for a light-emitting layer by doping a light-emitting material that has absorption in the ultraviolet region and has strong fluorescence or phosphorescence in the visible region.

In the present invention, the organic carrier transport layer and / or the organic light emitting layer may contain a compound represented by the following formula (4). This compound has a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane nucleus with a No. in the above table. The aromatic tertiary amine group shown in 46 is 4-substituted, and exhibits higher hole transport ability. Moreover, this compound is different from three aromatic groups bonded to the nitrogen of the aromatic tertiary amine, and exhibits an extremely high amorphous property due to an asymmetric three-dimensional structure.

 When the compound represented by the above formula (4) is used alone or mixed with another hole transport material to form a hole transport layer, a low molecular light emitting layer such as an Al oxine complex is deposited on the hole transport layer. An organic EL element having excellent performance can be produced by laminating or applying a water-soluble or alcohol-soluble low-molecular or high-molecular light-emitting material to form a light-emitting layer.

 In the present invention, a compound containing a condensed aromatic ring such as naphthalene or anthracene in the substituents of A1 to A4, or two or more conjugated non-condensed aromatic rings in the substituent, preferably three or more conjugated non-cyclic rings Since a compound having a condensed aromatic ring exhibits fluorescence in the visible portion, it can be used as a light-emitting layer having a hole transporting property.

 As examples of substituents having a substituent containing a condensed aromatic ring such as naphthalene, anthracene, acridine, etc., No. 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 in the above table 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 46, 47, 48, 49, 50, 51 , 54, 59, 66, 72, 73, 74, 75, 76, 78, 79, 80, 83, 84, etc., but are not limited to these examples.

 Examples of the substituent having a substituent containing three or more conjugated non-condensed aromatic rings include No. 5, 67 (n ≧ 2), 68 (n ≧ 2), 85, 86 in the above table. Although not limited to these examples.

 When the condensed aromatic ring or the conjugated non-condensed aromatic ring is not included as in the substituent No. 77 in the above table, the low molecular weight compound represented by the formula (1) is used as the host material of the light emitting layer. By doping a region with a luminescent material having strong fluorescence or phosphorescence, an EL element using the low molecular compound represented by the formula (1) for the light emitting layer can be manufactured.

 More specifically, a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane nucleus in which the aromatic tertiary amine group indicated by No. 46 in the above table is 4-substituted is represented by the above formula ( The compound represented by 4) has strong blue-violet fluorescence having a peak at around 413 nm, and this compound is used as a light-emitting layer, and 1,3,5-tris (N-phenylbenzimidazole-2) is formed on the light-emitting layer. -Il) By depositing an electron transporting hole blocking layer such as benzene (TPBI), a blue light-emitting EL element can be obtained. An electron transporting hole blocking layer is formed by applying a solution obtained by dissolving a low molecular weight or high molecular weight electron transporting hole blocking material in a solvent that does not dissolve the light emitting layer onto the light emitting layer. You can also

 In addition, a compound in which at least two, preferably four of the substituents A1 to A4 of the low molecular weight compound represented by the formula (1) are groups having a 1,3,4-oxadiazole ring is used for hole transport. And both electron transport properties. In this case, the electron transporting property is further improved by using a group having 2,5-diaryl-1,3,4-oxadiazole more preferably.

 Examples of the substituent having a 1,3,4-oxadiazole ring include Nos. 65 and 66 in the above table, but are not limited to this example.

Further, the low molecular weight compound represented by the following formula (5), that is, the hole transporting trans-1,2-bis (9H-carbazol-9-yl) cyclobutane nucleus represented by the formula (1) 4- [5- (4-tert-butylphenyl) -1,3,4-oxadiazole-2 having an electron-transporting 1,3,4-oxadiazole ring having the structure shown in No. 65 of the table The compound in which the 4-yl] phenyl group is substituted has strong blue fluorescence having a peak in the vicinity of 433 nm, hole transportability and electron transportability. Therefore, an EL element in which the compound represented by the formula (5) is used alone as a light-emitting layer, or an EL element that is mixed with another hole transport material, an electron transport material, or another light-emitting material to form a light-emitting layer is manufactured. It is possible.

 In order to absorb the blue light emission of the compound represented by the above formula (5) and convert it into a blue having a narrower spectrum width, this compound may contain 2,5,8,11-tetra-t-butylperylene or the like. Quantum dot materials that are surface-modified with a solvent-soluble group with fine inorganic semiconductors such as condensed aromatic compounds or nanometer-sized CdSe, ZnSe, NiO, CuS, etc. as nuclei may be mixed as a dopant in a proportion of less than 50 wt% it can.

 Further, the compound represented by the above formula (5) comprises an organic fluorescent material, an Ir complex, or a Pt complex that absorbs blue light emission and converts it into other colors such as green, red, white, yellow, and emits fluorescence or phosphorescence. A phosphorescent material can also be mixed as a dopant.

  Doping requires co-evaporation in the vapor deposition method, and it was difficult to co-evaporate a large area substrate with a uniform concentration and thickness. However, a wet concentration method using an inkjet or printing method has a predetermined concentration of dopant. Is previously mixed with ink, a film having a uniform dopant concentration can be easily obtained even on a large substrate.

 Moreover, it is also possible to laminate | stack and use the organic layer containing the compound represented by Formula (1) demonstrated above, and a hole block electron carrying layer.

 That is, when the compound represented by the formula (1) is used as the light emitting layer, when the light emitting layer material has a hole transporting property stronger than the electron transporting property, the electron-hole recombination region is a region close to the cathode side. become. When recombination occurs in the vicinity of the cathode and excitons are generated, energy is transferred to the cathode metal, the excitons are deactivated, and the EL luminous efficiency is reduced. In order to prevent deactivation, a hole blocking electron transport layer such as TPBI is preferably laminated between the light emitting layer and the cathode in a thickness of preferably 10 nm or more and about 100 nm or less to prevent energy transfer to the cathode. Can do.

 The electron transporting hole blocking layer can be formed by vacuum depositing a low molecular weight material or by dissolving an amorphous low molecular weight material or polymer material in a solvent that does not dissolve the light emitting layer and applying this solution on the light emitting layer. Can be formed.

 Furthermore, in order to optimize the carrier balance between holes and electrons in the light emitting layer and improve the light emission efficiency and lifetime, the light emitting layer is mixed with an electron transport material composed of other low molecules or polymers in a proportion of less than 50 wt%. You can also

  The synthesis of the compound represented by the formula (1) described above can be performed by the following procedure.

First, according to the method described in Japanese Patent Application No. 2-9586, trans-1,2-bis (9H-carbazol-9-yl) cyclobutane represented by the following formula (2) is photodimerized. Synthesize by reaction.

Next, the synthesized trans-1,2-bis (9H-carbazol-9-yl) cyclobutane represented by the above formula (2) is brominated, iodinated, or chlorinated, according to the following formula (6). Trans-1,2-bis (3,6-dibromo-9H-carbazol-9-yl) cyclobutane, trans-1,2-bis (3,6-diiodo-9H-carbazol-9-yl) cyclobutane, Alternatively, trans-1,2-bis (3,6-dichloro-9H-carbazol-9-yl) cyclobutane is synthesized.

(Wherein X is a halogen atom selected from iodine, bromine, and chlorine)
At this time, it is also possible to obtain a disubstituted or trisubstituted halogen by adjusting the amount of bromine or iodine added.

 Thereafter, boronic acid is synthesized from the Li-substituted product of the aromatic ring in the carrier transporting group or luminescent group substituted for A1 to A4, or the Grignard reagent and boric acid ester of those groups. Alternatively, a bromine-substituted, iodine-substituted, or triflate-substituted aromatic ring in a carrier transporting group or a luminescent group is synthesized and then reacted with bis (pinacolato) diboron or the like to synthesize a boronic ester.

  Next, by carrying out a Suzuki coupling reaction of the halogen 4-substituted or 2-3 substituted represented by the above formula (6) with the boronic acid or boronic ester, the carrier transporting group or the luminescent substituent is converted into 2 4-Substituted carrier transporting material and luminescent material are synthesized.

Examples of the light emitting material in which the light emitting group consisting of a condensed aromatic ring is substituted with 4 are shown in the following formulas (7), (8), (9), and (10). These have a hole-transporting carbazole ring and become a hole-transporting light-emitting material. During the coupling reaction, it is possible to promote the reaction by irradiating microwaves, reduce the amount of Pd catalyst or Ni catalyst added, and reduce the cost.

Further, by reacting the boronic acid or boronic acid ester in an amount less than an equivalent amount, an unreacted halogen is left, and a crosslinkable substituent such as styrylboronic acid is introduced after the reaction, and the following formula ( It is also possible to synthesize the compound represented by 11).

Further, when the carrier transporting group or the luminescent group of the substituents A1 to A4 is a carbazole derivative or an acridone derivative, the aromatic amino group of the carbazole derivative or the acridone derivative is substituted with bromine or iodine represented by the above formula (6). A compound represented by the following formulas (12), (13), and (14) can be synthesized by binding to a body or the like by an Ullmann reaction.

 In another case, the substituents of A1 to A4 may contain a group that is polymerized by light or heat, such as a vinyl group, a styryl group, a thiol group, an acrylic group, a methacryl group, an epoxy group, or an oxetane group.

Examples of compounds having a substituent containing a vinyl group are shown in the following (15) and (16).

 Furthermore, it is possible to synthesize compounds having substituents having different structures in any of A1 to A4.

 By including two or more aromatic rings or condensed aromatic rings in the substituent, the degree of conjugation is adjusted, the energy gap, and the energy levels of HOMO (highest occupied orbit) and LUMO (lowest unoccupied orbit) By controlling, a hole transporting property, an electron transporting property, or a light emitting property can be provided.

 A substituent having an aromatic tertiary amine structure or a thiophene ring has a hole transporting property, and a substituent having a condensed ring such as a naphthalene ring, an anthracene ring, a benzothiazole ring, or a naphthalimide ring has a light emitting property. A nitrogen-containing heterocycle such as a triazole ring, a triazine ring, a quinoxaline ring, a pyridine ring, a silole ring, a benzothiadiazole ring, an oxadiazole ring, an oxazole ring, or a substituent having a boron atom has an electron transporting property.

 The substituents A1 to A4 are preferably substituted with a substituent having a formula weight of 1500 or less from the viewpoint of improving the yield of the synthesis because large substituents are difficult to introduce due to steric hindrance. When two or three aromatic substituents are introduced, the remaining two or less substituents are unsubstituted hydrogen, unreacted halogen atoms, or other non-aromatic substituents. It may be substituted with a group.

  Examples of other substituents are alkyl groups having 1 to 10 carbon atoms such as a methyl group, tertiary butyl group, octyl group, heptyl group and 2-ethylhexyl group; 1 carbon atoms such as methoxy group and 2-ethylhexoxy group Or a alkoxy group having 1 to 10 carbon atoms such as a 3,6-dioxaheptyl group, or a substituent that imparts solubility such as a dialkoxyphenyl group, a vinyl group, a styryl group, It is a crosslinking group that can be crosslinked by light, heat, or radiation, such as an acrylic group, a methyl acrylate group, a glycidyl group, a cinnamic acid group, a mercapto group, and a maleimide group.

  Hereinafter, an organic EL device using the compounds represented by the above formulas (4) and (5) as a hole transport layer or a light emitting layer will be specifically described.

  When the compounds represented by the above formulas (4) and (5) are heated at a rate of 20 ° C./min by DSC (differential scanning calorimetry), the glass transition temperature (Tg) is 140 ° C. (transition start temperature). Furthermore, the compound represented by the above formula (13) has Tg of 224 ° C. (transition start temperature) and high heat resistance.

 In addition, the ionization energy of the compounds represented by the formulas (4) and (5) is 5.8 eV, and in the case of the compound represented by the formula (13), it is 5.9 eV. The energy gaps determined from the absorption edge wavelength are 3.1 eV, 2.95 eV, and 3.1 eV, respectively. The emission peak wavelengths are blue to violet emission near 415 nm, 433 nm, and 405 nm, respectively, and can be used as a light emitting material by itself.

 Such ionization energies of the compounds represented by formula (4), formula (5), and formula (13) are such that holes are generated from the ionization energy 5.1 eV of copper phthalocyanine or PEDOT / PSS which are hole injection / transport materials. It is at an ionization energy level that can be injected and transported. The LUMO levels are 2.7 eV, 2.85 eV, and 2.81 eV, respectively, obtained by subtracting the absorption edge wavelength energy gap from the ionization energy, and Li alloy cathodes or fluorides containing Li with an ionization energy of 2.93 eV. The energy level is such that electrons can be easily injected from the Li / Al laminated cathode.

  FIG. 1 shows a cross-sectional view of an organic EL device according to an embodiment of the present invention.

  In FIG. 1, an anode 2 is formed on a substrate 1, and a hole transport layer 3, a light emitting layer 4, and a cathode 6 are sequentially stacked on the electrode 2 to constitute an EL element.

 On the substrate 1, a cathode extraction electrode 7 electrically connected to the cathode of the power source 8 through the wiring 9 is formed. The cathode extraction electrode 7 is electrically connected to the cathode 6. The anode of the power source 8 is electrically connected to the electrode 2 through the wiring 10.

  In FIG. 1, only one hole transport layer is formed, but a plurality of layers may be stacked.

  FIG. 2 shows a cross-sectional view of an EL device according to another embodiment of the present invention.

  In the EL element shown in FIG. 2, the hole block electron transport layer 5 is interposed between the light emitting layer 4 and the cathode 6 of the EL element shown in FIG.

  The EL elements shown in FIGS. 1 and 2 contain a compound represented by the above formula (1) in at least one of the hole transport layer and the light emitting layer.

  Next, as a specific example of the compound represented by the above formula (1), a case where an EL device is produced using the compounds represented by the above formulas (4) and (5) as a hole transport layer and a light emitting layer will be described. .

  As a board | substrate used for the organic thin film EL element which concerns on one Embodiment of this invention, a metal substrate, a semiconductor substrate, and an insulating substrate can be mentioned.

 When the substrate is composed of a metal substrate, the metal substrate itself acts as an electrode. Characters and graphics can be displayed by masking the substrate with an insulating film except for the portion that emits light to produce an EL element.

 When a metal substrate is used as an anode, a substrate made of a metal having a work function of 4.6 eV or more such as gold, platinum, palladium and nickel, or a metal such as stainless steel foil or copper or aluminum having good heat dissipation. A substrate formed over the substrate can be used. When the metal substrate acts as a cathode, a low work selected from magnesium alloy, lithium, cesium, calcium, and barium having a work function of 2.5 to 4 eV on a stainless steel foil substrate, an aluminum substrate, or a copper substrate. A substrate on which an alloy containing a functional metal component, a rare earth metal such as ytterbium, or an alloy containing a rare earth metal can be used.

 Examples of the semiconductor substrate include semiconductor wafer substrates such as silicon, gallium phosphide, gallium nitride, diamond, and zinc oxide. The non-light-emitting portion can be masked by forming an insulating film such as an oxide film or a nitride film.

 As the insulating substrate, a transparent insulating material such as an opaque insulating substrate made of a ceramic substrate such as aluminum nitride, a glass substrate such as alkali glass or non-alkali glass, a single crystal alumina substrate, a plastic film such as polyethersulfone, etc. A substrate can be mentioned.

 Examples of the electrode formed as an anode on the insulating substrate include an opaque electrode, a semitransparent electrode, and a transparent electrode. Examples of the material constituting the opaque electrode include the above-described materials constituting the metal substrate and the semiconductor substrate. When light is emitted from the substrate side, the anode is formed in a mesh shape or stripe shape, and the light is the anode. Try to get out of the gap.

 Examples of the semitransparent electrode include a semitransparent metal film formed by thinly depositing gold or platinum.

 As the transparent electrode, amorphous or microcrystalline transparent conductive material such as ITO (work function 4.6 to 4.8 eV), indium zinc composite oxide (IZO), zinc aluminum composite oxide, or copper aluminum composite oxide is used. Examples thereof include a film and a transparent conductive film made of a conductive polymer such as polyaniline or PEDOT / PSS.

 When a transparent insulating substrate is used as the substrate and the anode is a transparent electrode or a semi-transparent electrode, display can be performed from the substrate side. In this case, at least one surface of the transparent insulating substrate may be colored in order to improve contrast and durability, such as a circularly polarizing filter, a multilayer antireflection filter, an ultraviolet absorption filter, a color filter, and a fluorescence wavelength conversion filter. And a silica coating may be provided. Further, in order to improve the light extraction efficiency, a microlens or a low refractive index layer may be formed on the substrate surface.

 When displaying from the substrate side, the electrode formed on the transparent insulating substrate is preferably a transparent electrode having a surface resistance of 1 to 50Ω / □ and a visible light transmittance of 80% or more.

 In order to reduce resistance, a layer having a thickness of about 10 nm made of silver, copper, or an alloy of silver and copper is mainly composed of ITO, indium zinc composite oxide (IZO), titanium oxide, tin oxide, or the like. A film having a structure sandwiched between amorphous or microcrystalline transparent conductive films may be used as the transparent electrode. These transparent electrodes can be formed on the substrate by a method such as vacuum vapor deposition or sputtering.

 When the organic thin film EL element using the transparent electrode described above is used as a simple matrix drive display, a metal bus line made of a low resistivity metal such as Cu or Al is provided in contact with the transparent electrode line, and the It is desirable to make resistance.

In the EL device according to one embodiment of the present invention, as a material used for the hole transport layer, in addition to the compound represented by the above formula (1), copper phthalocyanine, chlorinated copper phthalocyanine, tetra (t-butyl) copper Metal phthalocyanines such as phthalocyanines, metal free phthalocyanines, low molecular hole transport materials such as quinacridone, polymer hole transport materials such as poly (para-phenylene vinylene) and polyaniline, PEDOT / PSS, and CHF ₃ plasma polymerized films In addition, other known hole transport materials can be mentioned.

 As long as the hole transport layer used in the EL device according to an embodiment of the present invention contains at least one compound represented by the formula (1), other hole transport materials as described above. A structure in which a plurality of films made of

 For example, the hole transport layer has a three-layer structure for the purpose of improving the adhesion between the layers, preventing the deterioration of the element, adjusting the color tone, etc., and in order from the anode side, the first hole transport layer, In the case of the second hole transport layer and the third hole transport layer, the work function or ionization energy value of the hole transport layer, the organic light emitting layer, and the anode is expressed as follows: anode <first hole transport layer It is preferable to control in the order of <second hole transport layer <third hole transport layer <organic light emitting layer.

 By laminating each layer in this way, the difference in work function value between the anode and the organic light emitting layer is reduced, the efficiency of hole injection into the organic light emitting layer is improved, and EL light emission can be obtained at a low voltage.

 There is no restriction | limiting in particular in the number of lamination | stacking of a positive hole transport layer, Different types of positive hole transport materials can be mixed or laminated | stacked and used.

 As a film forming method of the hole transport layer of the EL device according to the embodiment of the present invention, an appropriate method is selected depending on the molecular weight of the material, the solubility in a solvent, the sublimation property, and the like. For example, various coating printing methods such as vacuum deposition method, spin coating method, dip coating method, roll coating method, die coating method, ink jet method, relief printing method, offset printing, gravure printing, etc. Can be membrane.

 For example, copper phthalocyanine is deposited on the anode to a thickness of 10 nm by vacuum deposition, then PEDOT / PSS is laminated to a thickness of 30 nm by a die coating method, and is further expressed by, for example, formula (4) A compound may be laminated to a thickness of 20 nm by a relief printing method to form a three-layer hole transport layer.

 The light emitting layer of the EL device according to one embodiment of the present invention is a layer containing at least one arbitrary organic or inorganic light emitter that emits strong fluorescence in the visible light region when a voltage is applied to the device. If this light emitter emits strong fluorescence or phosphorescence in a solid state and a smooth film can be formed, a light emitting layer can be formed only by the light emitter.

 However, when the concentration of light emission is quenched in the solid state or it is difficult to form a smooth film, the light emitter is mixed with a hole transport material, an electron transport material, or a predetermined resin binder. A light emitting layer can be comprised.

 In the EL device according to one embodiment of the present invention, examples of the organic phosphor that can be used in the light emitting layer include salicylate, pyrene, coronene, 2, 5, and 8 in addition to the compound represented by the above formula (1). , 11-tetra-t-butylperylene, rubrene, tetraphenylbutadiene, 9,10-bis (phenylethynyl) anthracene, 8-quinolinolatolithium, Al trisoxine complex, bis (8-quinolinolato) zinc complex, tris ( 5-fluoro-8-quinolinolato) aluminum complex, tris (4-methyl-5-trifluoromethyl-8-quinolinolato) aluminum complex, tris (4-methyl-5-cyano-8-quinolinolato) aluminum complex, bis (2 -Methyl-5-trifluoromethyl-8-quinolinolate) (4-cyano Phenylphenolate) aluminum complex, bis (2-methyl-5-cyano-8-quinolinolato) (4-cyanophenylphenolate) aluminum complex, tris (8-quinolinolato) scandium complex, 2-t-butyl-9,10 -Di (2-naphthyl) anthracene, poly (2,5-diheptyloxy-p-phenylenevinylene), N 2, N′-diaryl-substituted pyrrolopyrrole compound, JP-A-4-31488 (patented by Idemitsu Kosan Co., Ltd.) The described bisstyrylarylene-based phosphor compound, the phosphor described in US Pat. No. 5,141,671, US Pat. No. 4,769,292 (Eastman Kodak Company patent), and other American DYE Sources H. W. Examples thereof include polymer compounds, low molecular phosphors, low molecular phosphors, and inorganic quantum dot light emitters described in catalogs of Sands and Sensent.

 The light emitting layer of the EL device according to an embodiment of the present invention can be composed of a mixture of different types of light emitters. Organic fluorescence of coumarin-based, quinacridone-based, perylene-based, and pyran-based products commercially available from Lambda Fizzic Co., Eastman Kodak Company, Inc., and American Dice Source Company, using the compound represented by the general formula (1) as a blue light emitting host. A body or an inorganic quantum dot light emitter may be doped as a guest light emitter. Further, the light emitting layer may have a stacked structure in which a plurality of films made of different types of light emitters are stacked.

 Such a light emitting layer has a thickness of preferably 100 nm or less, and more preferably 5 to 50 nm in both a single layer structure and a laminated structure. If it is too thick, the driving voltage becomes high, and if it is too thin, the light emission efficiency decreases.

 As described above, by using another appropriate light emitter as a dopant, conversion of the emission spectrum, reduction of the half-value width of the emission spectrum, and improvement of the emission efficiency can be achieved. Note that the light emitter used as the dopant may emit light in the ultraviolet region or the infrared region.

 As a method for forming a light emitting layer of an EL element according to an embodiment of the present invention, an appropriate method is selected according to physical properties such as molecular weight of a material, solubility in a solvent, and sublimation. For example, a method selected from various coating and printing methods such as vacuum deposition method, spin coating method, dip coating method, roll coating method, die coating method, ink jet method, relief printing method, offset printing, gravure printing, etc. Application and film formation are possible.

 In the EL device according to one embodiment of the present invention, the compound represented by the formula (1) used for the light emitting layer has two carbazole rings in the nucleus of the compound, and thus has a hole transporting property. Therefore, when the substituents A1 to A4 have an electron-transporting group having a large electron mobility and the injection balance of holes and electrons into the light-emitting layer is larger, the number of electrons and holes The recombination region is on the hole transport layer side in the light emitting layer, but when the electron transport ability of the substituents A1 to A4 is low, recombination is performed on the cathode side. In that case, it is desirable to provide a hole-blocking electron transport layer between the light emitting layer and the cathode to avoid deactivation of excitons by the cathode.

 The material used for the hole-blocking electron injecting and transporting layer is preferably an amorphous material capable of obtaining a smooth film, and has a high electron mobility, a large LUMO state density, and an LUMO energy level (electron affinity). It is preferable that the material be between the same level as the LUMO energy level and the Fermi level (work function) of the cathode material and the energy gap between the HOMO-LUMO is preferably 1 eV or more larger than that of the light emitting layer.

 Providing such a hole-blocking electron transport layer can increase the efficiency of electron injection into the organic light-emitting layer and suppress the holes and excitons in the light-emitting layer from reaching the cathode.

 Examples of materials used for the hole blocking electron transport layer include TPBI, bis (8-hydroxyquinaldine) aluminum biphenoxide (hereinafter abbreviated as BAlq), 2,2 ′-(1,3-phenylene) bis [5- [4- (1,1-dimethylethyl) phenyl] -1,3,4-oxadiazole (hereinafter abbreviated as OXD-7) and 2,5-bis (1-naphthyl) -1,3,4 Oxadiazole, triazole compounds disclosed in JP-A-7-90260, and the like can be used.

 Alternatively, a film can be formed by applying an electron transporting polymer or oligomer having an electron transporting oxadiazole ring, triazole ring, silole ring or triarylborane group that dissolves in a solvent that does not dissolve the light emitting layer.

 The hole-blocking electron transport layer is formed by a method such as coating / printing such as vacuum deposition, CVD, spin coating, letterpress printing, etc., and preferably has a thickness of 10 nm to 100 nm, a single layer or a multilayer Preferably formed as a structure.

 In the organic thin film EL device according to one embodiment of the present invention, the electrode provided as a cathode on the organic light emitting layer is preferably composed of a material having a low work function. As the material having a low work function, a single metal such as Mg or Al and a metal such as Li, Mg, Ca, Ar, La, Ce, Er, Eu, Sc, Y, and Y b are used. The alloy etc. which are contained above can be mentioned.

 When these materials having a low work function are used for the cathode, electron injection is effectively performed. In particular, when the above alloy is used, both the low work function and the stability can be achieved.

 Although there is no restriction | limiting in particular in the thickness of a cathode, When the cathode is formed in the thickness of 5-10 nm, sufficient transmittance | permeability of visible light will be obtained and the cathode side can be made into a display surface. At that time, a protective transparent electrode made of ITO or IZO can be laminated on the cathode metal.

 The cathode can be formed by a resistance heating vapor deposition method, an electron beam vapor deposition method, a reactive vapor deposition method, an ion plating method, or the like according to a material to be used, or a sputtering method using an alloy target or the like.

When the cathode is composed of a multi-component alloy, it can be measured by a co-evaporation method using a resistance heating method under a vacuum of the order of 10 ⁻³ Pa or less and monitoring from a separate vapor deposition source for each component with a quartz crystal film thickness meter. Alternatively, it can be formed by flash deposition of the alloy material little by little.

 When the EL element is a simple matrix drive display and the cathode needs to be formed in stripes, the cathode material is deposited by adhering a mask with slits to the substrate in close contact with the substrate, or the cathode material is formed as a cathode. After vapor deposition over the entire surface, the cathode material film is patterned by laser ablation method, ion beam etching method, reactive etching method, partition wall method or the like, whereby the cathode can be formed in a stripe shape.

 As described above, the structure in which the anode, the hole transport layer, the light emitting layer, and the hole block electron transport layer and the cathode are laminated in order from the substrate side has been shown, but the EL element of the present invention is in order from the substrate side. , A cathode, an electron injecting and transporting layer, a light emitting layer, a hole transporting layer, and an anode may be laminated.

 Further, although omitted in FIGS. 1 and 2, preferably, germanium monoxide, one layer is formed on the electrode 6 of the EL element, that is, covering the hole injection transport layer 3, the light emitting layer 4, and the cathode 6. Metal oxide films such as silicon oxide, magnesium oxide, and alumina; metal fluoride films such as magnesium fluoride, calcium fluoride, lithium fluoride, aluminum fluoride, and barium fluoride; or metal nitride films such as silicon nitride; By forming a sealing layer in which an inorganic insulating film and a metal film of aluminum, copper, zinc, or the like are alternately laminated in a thickness of 50 to 500 nm at least one inorganic insulating film and one metal film, respectively. The element can be moisture-proof. The sealing layer can be formed by vapor deposition, sputtering, or CVD.

 Further, in order to prevent long-term entry of water vapor into the EL device, the device is sealed with a hermetic seal or the like in a vacuum or with an inert gas, or a sealing plate such as a glass plate is formed on the device. It is preferable to adhere and seal the surface with an adhesive material such as a commercially available low-hygroscopic photocurable adhesive, thermosetting epoxy adhesive, and low-melting glass.

  As a sealing plate, a metal plate, a plastic plate, a film, etc. other than the above-mentioned glass plate can be used. In addition, a desiccant such as calcia can be mixed in the adhesive material. You may form the layer of the getter agent which consists of metals, rare earths, etc.

  The organic thin film EL device according to an embodiment of the present invention configured as described above emits light by applying a DC voltage with the hole injection / transport layer side being positive, but even when an AC voltage is applied, the hole is emitted. Light is emitted while a positive voltage is applied to the injection transport layer side.

 The thin film display which can display a character and an image can be formed by arrange | positioning the organic thin-film EL element which concerns on one Embodiment of this invention demonstrated above on a board | substrate two-dimensionally.

 Furthermore, the color display can be realized by two-dimensionally arranging light emitting elements of three colors of red, blue and green, or by using a white light emitting element and a four-color filter of red, blue, green and white. It becomes possible.

  Hereinafter, various synthesis examples of the compound represented by the formula (1) and having a molecular weight of 690 or more and 5000 or less used for the organic EL device of the present invention will be described.

Synthesis example 1
Trans-1,2-bis (3,6-di {3- [N- (2-biphenyl) -1-naphthylamino] phenyl} -9H-carbazole-9- which is a compound represented by the above formula (4) Synthesis of yl) cyclobutane 1.19 g (1.7 mmol) of trans-1,2-bis (3,6-dibromo-9H-carbazol-9-yl) cyclobutane, N- (2-biphenylyl) -N- [3 -(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl] -1-naphthylamine 4.03 g (8.1 mmol) and PdCl ₂ (dppf) 0.051 g ( 0.062 mmol) was dissolved in 70 ml of tetrahydrofuran (hereinafter abbreviated as THF), and 35 ml of a saturated aqueous solution of sodium bicarbonate was added thereto.

  The mixture was heated to reflux for 8 hours under a nitrogen atmosphere and cooled, and then THF was distilled off, followed by extraction with 30 ml of chloroform. The organic layer was concentrated and the concentrate was dissolved in 10 ml of chloroform and added dropwise to 100 ml of methanol. The precipitated crystals were collected by filtration and purified by silica gel column chromatography. 2.08 g of trans-1,2-bis (3,6-di {3- [N-- (2-Biphenyl) -1-naphthylamino] phenyl} -9H-carbazol-9-yl) cyclobutane was obtained (yield 65.8%).

The mass spectrum of this compound had a molecular ion peak of 1863 (C ₁₄₀ H ₉₈ N ₆ ), which was consistent with the structural formula.

 The solubility of this compound was about 0.6 g / ml for toluene, about 0.4 g / ml for 1,2-dichloroethane, and about 0.1 g / ml for 2-methylanisole. Further, Tg was 164 ° C. (intermediate temperature of transition, 140 ° C. at the transition start temperature) (DSC measurement value at a rate of 20 ° C./mim with a SSC5200 thermal analysis system manufactured by Seiko Denshi Kogyo).

  The result of measuring the IR absorption spectrum of this compound by the KBr method using FT / IR-460plus (manufactured by JASCO Corporation) is shown in FIG. In addition, FIG. 4 shows the results of measuring the corrected fluorescence excitation spectrum (light receiving 440 nm) and the corrected fluorescence spectrum (365 nm excitation) of the film formed on the quartz plate with RF-5300PC (manufactured by Shimadzu Corporation). In FIG. 4, the broken line indicates the corrected fluorescence excitation spectrum, and the solid line indicates the corrected fluorescence spectrum.

 FIG. 4 shows that strong blue-violet fluorescence is shown in the vicinity of the peak wavelength of 415 nm. From the absorption edge energy, the energy gap was 3.1 eV. Moreover, the ionization energy measured by surface analyzer AC-1 (made by Riken Keiki Co., Ltd.) was 5.8 eV.

Synthesis example 2
Trans-1,2-bis (3,6-bis {4- [5- (4-tert-butylphenyl) -1,3,4-oxadiazole-2, which is a compound represented by the above formula (5) Synthesis of -yl] phenyl} -9H-carbazol-9-yl) cyclobutane 1.17 g (1.7 mmol) of trans-1,2-bis (3,6-dibromo-9H-carbazol-9-yl) cyclobutane, 2 -(4-tert-butylphenyl) -5- [4- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) phenyl] -1,3,4-oxadi 4.04 g (10 mmol) of azole and 0.08 g (0.1 mmol) of PdCl ₂ (dppf) were added to a mixture of 80 ml of THF and 40 ml of a saturated aqueous solution of sodium bicarbonate. The mixture was refluxed for 8 hours under a nitrogen atmosphere. After completion of the reaction, THF was distilled off, and 30 ml of chloroform was added thereto for extraction. The organic layer was concentrated to obtain crude crystals, which were purified by silica gel column chromatography, and 1.26 g of trans-1,2-bis (3,6-bis { 4- [5- (4-tert-butylphenyl) -1,3,4-oxadiazol-2-yl] phenyl} -9H-carbazol-9-yl) cyclobutane was obtained (yield 50.7%). ).

The mass spectrum of this compound had a molecular ion peak of 1491 (C ₁₀₀ H ₈₆ N ₁₀ O ₄ ), which was consistent with the structural formula.

 The solubility of this compound was about 0.5 g / ml with respect to 1,2-dichloroethane. Further, Tg was 149 ° C. (intermediate temperature of transition, 140 ° C. at the transition start temperature). (DSC measurement value at a rate of 20 ° C./min with a SSC5200 thermal analysis system manufactured by Seiko Denshi Kogyo).

  FIG. 5 shows the results of measuring the IR absorption spectrum of this compound by the KBr method using FT / IR-460 plus (manufactured by JASCO Corporation). In addition, FIG. 6 shows the results of measuring the corrected fluorescence excitation spectrum (light receiving 440 nm) and the corrected fluorescence spectrum (365 nm excitation) of the film formed on the quartz plate with RF-5300PC (manufactured by Shimadzu Corporation). In FIG. 6, a broken line shows a corrected fluorescence excitation spectrum, and a solid line shows a corrected fluorescence spectrum.

 FIG. 6 shows that strong blue-violet fluorescence is shown in the vicinity of the peak wavelength of 433 nm. From the absorption edge energy, the energy gap was 2.95 eV. Moreover, the ionization energy measured by surface analyzer AC-1 (made by Riken Keiki Co., Ltd.) was 5.8 eV.

Synthesis example 3
Trans-1,2-bis [3,6-di (3-tert-butyl-9H-carbazol-9-yl) -9H-carbazol-9-yl] which is a compound represented by the above formula (13) Synthesis of cyclobutane trans-1,2-bis (3,6-dibromo-9H-carbazol-9-yl) cyclobutane 2.09 g (3 mmol), 3-tert-butyl-9H-carbazole 3.48 g (15.6 mmol) Then, 18 ml of dichlorotoluene was added to 3.30 g (24 mmol) of potassium carbonate, 0.03 g (0.47 mmol) of copper powder, and 0.03 g (0.16 mmol) of copper iodide, and the mixture was heated to reflux for 30 hours. The solution was cooled, filtered by adding 30 ml of toluene, and the filter residue was washed with 30 ml of toluene. The filtrate was concentrated, purified by silica gel column chromatography, recrystallized with a mixed solvent of ethyl acetate / chloroform, and the collected crystals were dried to obtain 1.83 g of trans-form represented by the above formula (13). 1,2-bis [3,6-di (3-tert-butyl-9H-carbazol-9-yl) -9H-carbazol-9-yl] cyclobutane was obtained (yield 48.0%).

The mass spectrum of this compound had a molecular ion peak of 1271 (C ₉₂ H ₈₂ N ₆ ), which was consistent with the structural formula. The solubility of this compound was 0.15 g / ml with respect to toluene.

  Hereinafter, various examples of the present invention will be shown to describe the present invention more specifically.

Example 1
Using the compound represented by the above formula (4) for the hole transport layer, an EL device was produced as follows.

 First, an ITO film having a thickness of 140 nm was formed on a blue glass plate having a thickness of 0.7 mm by a sputtering method to form an anode. The glass plate on which this ITO film was formed was washed with water and plasma, and then a 46 nm thick first hole transport layer made of PEDOT / PSS (Baytron P CH8000) was formed on the ITO film by spin coating. Was deposited.

 Next, a solution in which the hole transport material represented by the above formula (4) is dissolved in 2-methylanisole is formed on the first hole transport layer by spin coating, and a second film having a thickness of 46 nm is formed. The hole transport layer was formed.

 Subsequently, after drying in vacuum at 200 ° C., an organic light-emitting layer made of Alq was vacuum-deposited to a thickness of 30 nm on the second hole transport layer. On this organic light emitting layer, LiF was vacuum-deposited to a thickness of 0.5 nm, and Al was further evaporated to a thickness of 200 nm to form a cathode.

 Furthermore, G e O is added as an insulating sealing layer on the obtained structure to a thickness of 0. After performing Ar plasma assisted vapor deposition to a thickness of 6 μm, Al was vapor deposited to a thickness of 200 nm to seal the device, thereby producing an organic EL device.

When the organic EL element manufactured as described above was made to emit light by applying a DC voltage, yellow-green light emission from the Alq light emitting layer was stably obtained when a DC voltage of 3 V or more was applied, and a DC voltage of 10 V was applied. Sometimes a maximum brightness of 8,690 cd / m ² was obtained.

 A graph showing the luminance-voltage characteristics of the organic EL element obtained as described above is shown by a curve A in FIG. Further, the EL emission spectrum is shown by a curve C in FIG.

Example 2
In the same manner as in Example 1, except that the compound represented by the above formula (5) was used in the hole transport layer instead of the compound represented by the above formula (4) used in Example 1, an organic EL device was used. Was made.

When the produced EL element was made to emit light by applying a DC voltage, when a DC voltage of 4 V or higher was applied, the second light emission composed mainly of yellow-green light from the Alq light emitting layer and composed of the compound represented by the formula (5) Light emission in which the blue light emission of the hole transport layer was mixed a little was stably obtained. When a DC voltage of 13 V was applied, a maximum luminance of 3,730 cd / m ² was obtained.

 A graph of luminance-voltage characteristics of this element is shown by a curve B in FIG. Further, the EL emission spectrum is shown by a curve D in FIG.

Example 3
An EL device was fabricated in the same manner as in Example 1, except that a hole blocking electron transport layer made of TPBI was vacuum-deposited to a thickness of 40 nm instead of the Alq light-emitting layer of Example 1. In this EL element, the compound layer represented by the above formula (4) is a light emitting layer.

When the produced EL element was made to emit light by applying a DC voltage, when a DC voltage of 4 V or more was applied, the light emitting layer made of the compound represented by the formula (4) had a CIE1931 chromaticity (0.164, 0.082). Blue emission was stably obtained. When a DC voltage of 11 V was applied, the maximum luminance of 421 cd / m ² was obtained. Further, this EL element emitted light stably even at a temperature of 100 ° C.

 A graph of luminance-voltage characteristics of this element is shown by a curve a in FIG. An EL emission spectrum is shown by a curve e in FIG.

Comparative Example 1
An EL device was produced in the same manner as in Example 3 except that the hole block electron transport layer made of TPBI in Example 3 was removed.

When the produced organic EL element was made to emit light by applying a direct current voltage, blue light emission was obtained from the light emitting layer made of the compound represented by the formula (4) when 4 V or more was applied. When a DC voltage of 9 V was applied, only a maximum luminance of 5 cd / m ² was obtained.

 A graph of luminance-voltage characteristics of this element is shown by a curve c in FIG. Further, the EL emission spectrum is shown by a curve g in FIG.

Example 4
An EL device was produced in the same manner as in Example 1 except that a hole blocking electron transport layer made of TPBI was vacuum-deposited by 40 nm instead of the Alq light-emitting layer of Example 2. In this EL device, the layer of the compound represented by the formula (5) is a light emitting layer.

When the produced organic EL element was made to emit light by applying a direct current voltage, the CIE1931 chromaticity (0.176, 0.128) from the light emitting layer made of the compound represented by the formula (5) was applied when 4 V or more was applied. Blue emission was stably obtained. When a DC voltage of 13 V was applied, the maximum luminance of 634 cd / m ² was obtained. Moreover, it emitted light stably even at a temperature of 100 ° C.

 A graph of luminance-voltage characteristics of this EL element is shown in a curve b in FIG. An EL emission spectrum is shown by a curve f in FIG.

Comparative Example 2
An EL device was produced in the same manner as in Example 4 except that the hole block electron transport layer made of TPBI of Example 4 was removed.

When the produced organic EL element was made to emit light by applying a DC voltage, blue light emission from the light emitting layer made of the compound represented by the formula (5) was obtained when a voltage of 4 V or more was applied. When a DC voltage of 10 V was applied, the maximum luminance of 177 cd / m ² was obtained.

 Since the compound represented by the formula (5) has an electron transporting group, electrons are easily injected into the light emitting layer, and higher brightness was obtained than the element of Comparative Example 1, but a hole blocking electron transport layer made of TPBI. The luminance was lower than that of the device of Example 4 having

 A graph of luminance-voltage characteristics of this EL element is shown by a curve d in FIG. An EL emission spectrum is shown by a curve h in FIG.

Example 5
Using the compound represented by the above formula (13) for the hole transport layer, an EL device was produced as follows.

 First, an ITO film having a thickness of 140 nm formed by sputtering on a blue plate glass plate having a thickness of 0.7 mm was used as an anode. The glass plate on which the ITO film is formed is washed with water and plasma, and then a first hole transport layer having a thickness of 46 nm made of PEDOT / PSS (Baytron P CH8000) is formed on the ITO film by spin coating. Was formed and dried at 130 ° C. in air.

 Next, a light emitting layer having a thickness of 68 nm is formed on the first hole transport layer by spin coating from a 1,2-dichloroethane solution using the material represented by the formula (13). Dry at 130 ° C. Next, a hole blocking electron transport layer made of TPBI was vacuum deposited to a thickness of 40 nm.

 Next, in order to improve the electron injection property, LiF was vacuum-deposited to a thickness of 0.5 nm, and A 1 was further deposited to a thickness of 200 nm to form a cathode.

 Further, Ge plasma was deposited on the device as an insulating sealing layer by Ar plasma assisted deposition to a thickness of 0.6 μm, and then Al was deposited to a thickness of 200 nm and sealed to prepare an EL device.

When the produced organic EL device was made to emit light by applying a DC voltage, when a DC voltage of 4 V or higher was applied, ultraviolet to blue light emission was obtained from the light emitting layer made of the compound represented by the formula (13), and 14 V A luminance of 355 cd / m ² was obtained when a DC voltage was applied. The CIE 1931 chromaticity at 6V was (0.17, 0.10).

 A graph of luminance-voltage characteristics of this element is shown by a curve E in FIG. The EL emission spectrum is shown by curve e in FIG.

Example 6
Instead of the light emitting layer of Example 5, a material represented by the formula (13) doped with 8 wt% of 2-tertiarybutyl-9,10-di (2-naphthyl) anthracene (hereinafter abbreviated as TBDNA) was used. Then, an EL device was produced in the same manner as in Example 5 except that a light emitting layer having a thickness of 68 nm was formed from a 1,2-dichloroethane solution by spin coating.

When the produced organic EL device was made to emit light by applying a DC voltage, blue light emission from TBDNA was obtained when a DC voltage of 4 V or more was applied, and a luminance of 898 cd / m ² was obtained when a DC voltage of 15 V was applied. . The CIE 1931 chromaticity at 6V was (0.15, 0.09).

 A graph of luminance-voltage characteristics of this element is shown by a curve F in FIG. The EL emission spectrum is shown by the curve f in FIG.

 Since the EL element of the present invention uses a low molecular weight ink that can be dissolved at a high concentration in the carrier transport layer and / or the light emitting layer, it can be produced at low cost, large area, and high reliability by an appropriate coating method and printing method. It is possible to manufacture organic EL elements and color displays with low environmental impact.

It is sectional drawing of the EL element which concerns on one Embodiment of this invention. It is sectional drawing of the EL element which concerns on one Embodiment of this invention. It is a FT-IR spectrum measured by KBr method of the compound represented by Formula (4) used for the EL element which concerns on one Embodiment of this invention. It is a fluorescence excitation spectrum and a fluorescence spectrum of the compound represented by Formula (4) used for the EL element which concerns on one Embodiment of this invention. It is a FT-IR spectrum measured by the KBr method of the compound represented by Formula (5) used for the EL element which concerns on one Embodiment of this invention. It is a fluorescence excitation spectrum and a fluorescence spectrum of the compound represented by Formula (5) used for the EL element which concerns on one Embodiment of this invention. It is a characteristic view which shows the voltage-luminance characteristic of the EL element in Example 1 and 2. It is a characteristic view which shows the EL spectrum of the EL element in Example 1 and 2. It is a characteristic view which shows the voltage-luminance characteristic of the EL element in Examples 3 and 4 and Comparative Examples 1 and 2. It is a characteristic view which shows the EL spectrum of the EL element in Examples 3 and 4 and Comparative Examples 1 and 2. It is a characteristic view which shows the voltage-luminance characteristic of the EL element in Example 5 and 6. It is a characteristic view which shows the EL spectrum of the EL element in Example 5 and 6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Anode, 3 ... Hole transport layer, 4 ... Light emitting layer, 5 ... Hole block electron transport layer, 6 ... Cathode, 7 ... Cathode Extraction electrode, 8... Power source, 9, 10.

Claims (4)

In an organic EL device including an organic carrier transport layer and / or an organic light emitting layer between opposed electrodes, at least one of the organic carrier transport layer and the organic light emitting layer is trans-1,2-bis (9H-carbazole). It was formed by coating or printing using a material having a molecular weight of 1271.7 or more and 1864.3 or less and having a molecular weight of 1271.7 to 1864.3 , which is represented by the following formula (1) having a -9-yl) cyclobutane structure . An organic EL element comprising an organic layer.

R ₁ and R ₂ are each independently an alkyl group having 4 or less carbon atoms or hydrogen, and R ₁ and R ₂ do not simultaneously become hydrogen. R ₃ is an alkyl group having 4 or less carbon atoms.
A ₁ and A ₂ are each independently a substituent derived from a monocyclic or condensed ring containing a 6- to 12-carbon aromatic 6-membered ring. ) Represented by the formula has a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane structure (1), a hole transport layer comprising a compound having a molecular weight of 1271.7 or 1864.3 less The organic EL device according to claim 1, wherein the organic EL device is provided. A light emitting layer comprising a compound represented by the formula (1) having a trans-1,2-bis (9H-carbazol-9-yl) cyclobutane structure and having a molecular weight of 1271.7 or more and 1864.3 or less is provided. The organic EL element according to claim 1. A hole-blocking electron transport layer is provided between the carrier transport layer and / or the organic light emitting layer containing the compound represented by the formula (1) and having a molecular weight of 1271.7 or more and 1864.3 or less and the cathode. The organic EL element according to claim 1 , wherein the organic EL element is interposed.

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