JP5943467B2 - Diphenylsulfone derivative, host material comprising the same, and organic electroluminescence device using the same - Google Patents

Description

  The present invention relates to a novel diphenylsulfone derivative, a host material comprising the same, and an organic electroluminescence device (hereinafter referred to as an organic EL device) using the same.

The organic EL element is a current injection type self-luminous element, and has features such as a high viewing angle, high contrast, ultra-thin structure, low voltage drive, and high response speed. In recent years, research and development has been actively conducted.
Organic EL elements have been put into practical use in some products, but for application to the large display and lighting fields, further increasing the efficiency of the elements is one of the most important issues. In particular, in order to realize white light emission with high color purity and high efficiency, high efficiency and long life of blue organic EL elements are important issues.

  In order to solve this problem, attention has been focused on phosphorescent organic EL elements capable of increasing efficiency four times as compared with conventional fluorescent elements. In general, an iridium complex that is a light-emitting material of a phosphorescent element has high symmetry and high cohesion. For this reason, in order to improve the efficiency of the phosphorescent element, it is very important to develop an appropriate host material. This host material is required to have high triplet energy from the viewpoint of energy confinement and characteristics such as aggregation suppression of the guest material from the viewpoint of improving the light emission quantum efficiency. Furthermore, for low voltage driving which is one of the characteristics of the organic EL element, it is desired to have bipolar properties, that is, excellent carrier injection / transport properties.

However, it is very difficult to express these characteristics simultaneously.
Recently, a bipolar host material having a sulfone moiety has been developed (see Non-Patent Document 1).

Fang-Ming Hsu, et al., J. Mater. Chem., 2009, 19, 8002-8008

  However, although the host material described in Non-Patent Document 1 exhibits a high electron injection property due to the introduction of the sulfone moiety, the color purity is reduced due to the triplet energy reduction accompanying the reduction of the energy gap due to intramolecular charge transfer. It does not have enough triplet energy to be applied to a high blue phosphorescent organic EL device.

  The present invention has been made to solve the above technical problem, and is capable of being driven at a low voltage and highly efficient by a host material suitable for a phosphorescent material that maintains a high triplet energy while exhibiting a bipolar property. It is an object of the present invention to provide a novel diphenylsulfone derivative useful for obtaining a simple organic EL device, a host material comprising the same, and an organic EL device using the same.

Diphenyl sulfone derivatives according to the present invention is represented by any one of the below following formula.

According to the diphenylsulfone derivative having the structure as described above, since it has a bipolar property, the hole injection / transport property and the electron injection / transport property are enhanced, and high triplet energy is maintained by suppressing the expansion of the π-conjugated system. can do.

Moreover, according to this invention, the host material which consists of the said diphenyl sulfone derivative is provided.
The diphenylsulfone derivative is suitable as a host material for a phosphorescent material.

  The organic EL device according to the present invention is an organic EL device in which at least one organic layer is laminated between a pair of electrodes, and includes a layer containing the diphenylsulfone derivative. .

Alternatively, the organic EL device according to the present invention is an organic EL device in which one or more organic layers are laminated between a pair of electrodes, and the light emitting layer in which the host material is doped with a phosphorescent material It is characterized by having.
Thus, by using the diphenylsulfone derivative according to the present invention, it is possible to obtain a highly efficient organic EL element driven at a low voltage.

Since the novel diphenylsulfone derivative according to the present invention has bipolar properties and high triplet energy, it is suitable as a host material for efficiently emitting blue phosphorescent material.
Therefore, a highly efficient organic EL device can be provided by using the diphenylsulfone derivative according to the present invention.

5 is a schematic cross-sectional view schematically showing a layer structure of an organic EL element according to Example 2. FIG. 6 is a graph showing a current density-external quantum efficiency curve of each organic EL element in Example 2.

Hereinafter, the present invention will be described in more detail.
The diphenylsulfone derivative according to the present invention is a compound represented by the general formula (1).
In the formula (1), at least one of a carbazole group of the substituents R ¹ to R ^10, the substituents R ¹ to R ¹⁰ other than it are each independently, hydrogen, straight-1 to 6 carbon atoms Any of a chain or branched alkyl group, an alkoxy group containing a linear or branched alkyl group having 1 to 6 carbon atoms, a linear or branched alkylamino group having 1 to 6 carbon atoms, a cyano group, and a phenyl group It is a group selected from these.
Such a diphenylsulfone derivative is a novel compound and is characterized by having a carbazole group having a hole transporting property and a high triplet energy and a sulfone site having a high electron accepting property.

  Among the compounds represented by the general formula (1), specific examples include those shown below.

Among the diphenylsulfone derivatives exemplified above, it is preferable that at least one of the substituents R ^{2 to} R ⁴ and R ^{7 to} R ^{9 in} the general formula (1) is a carbazole group. In particular, the compounds shown below (in order, abbreviated as 1CzSO, 2CzSO, 3CzSO, 4CzSO) are given as typical examples.

  The method for synthesizing the diphenylsulfone derivative according to the present invention as described above is not particularly limited, and for example, it can be synthesized by a method as shown in the following Examples.

The diphenylsulfone derivative according to the present invention can improve the hole injection / transport property by the carbazole group and the electron injection property by the sulfone moiety, and can maintain high triplet energy by suppressing the π-conjugated system expansion. it can.
Therefore, it can be suitably used as a host material for a dopant of a phosphorescent material.

The organic EL device according to the present invention having a layer containing a diphenylsulfone derivative as described above has a structure in which at least one organic layer is laminated between a pair of electrodes. Specific layer structures include anode / light emitting layer / cathode, anode / hole transport layer / light emitting layer / electron transport layer / cathode, anode / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode. And the like.
Furthermore, a known laminated structure including a hole injection layer, a hole transporting light emitting layer, an electron transporting light emitting layer, and the like may be used.
The organic EL element according to the present invention may be an element having a multi-photon emission structure in which a plurality of light emitting units including one light emitting layer are stacked in series via a charge generation layer.

  In the organic EL device, the diphenylsulfone derivative according to the present invention may be used in any of the organic layers, and may be used by being dispersed together with a hole transport material, a light emitting material, or an electron transport material. It is also possible to dope a luminescent dye into the layer. Furthermore, it can also be used as an electron injecting and transporting layer by allowing an oxidizing dopant to act on the diphenylsulfone derivative, and as an electron injecting and transporting layer by acting a reducing dopant.

  In particular, by using the diphenylsulfone derivative as a host material and forming a light emitting layer doped with the phosphorescent material, the phosphorescent material can emit light efficiently.

In the organic EL element, the constituent material of each layer other than the diphenylsulfone derivative according to the present invention is not particularly limited, and can be appropriately selected from known ones. Any of molecular systems may be used.
The film thickness of each of the layers is appropriately determined depending on the situation in consideration of adaptability between the layers and the required total layer thickness, but is usually preferably in the range of 5 nm to 5 μm.

  The formation method of each of the above-mentioned layers is an ink jet method, a casting method, a dip coating method, a bar coating method, a blade coating method, a roll coating method, a gravure coating method, a flexographic printing method, a spraying method even in a drive process such as a vapor deposition method and a sputtering method. A wet process such as a coating method may be used.

  Also, the electrode may be a known material and configuration, and is not particularly limited. For example, a so-called ITO substrate is generally used in which a transparent conductive thin film is formed on a transparent substrate made of glass or polymer, and an indium tin oxide (ITO) electrode is formed as an anode on the glass substrate. On the other hand, the cathode is composed of a metal, alloy, or conductive compound having a small work function (4 eV or less) such as Al.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited by the following Example.
A representative example of the diphenylsulfone derivative according to the present invention was synthesized by the steps shown in Synthesis Examples 1 to 4 below.
(Synthesis Example 1) Synthesis of 1CzSO 1CzSO was synthesized by a reaction with phenylboronic acid after synthesizing a precursor by the following steps.

First, in a 200 ml four-necked flask equipped with a thermometer, a nitrogen inlet tube and a reflux tube, 8.49 g (30.0 mmol) of 3-bromoiodobenzene, 571 mg (3.00 mmol) of copper (I) iodide, potassium carbonate 8.29 g (60.0 mmol) and N, N-dimethylformamide (DMF) 150 ml were added, and the mixture was heated and stirred to 100 ° C. under a nitrogen atmosphere. 5.37 g (30.0 mmol) of 3,5-dichlorobenzenethiol was added and reacted for 4 hours. The disappearance of the raw material was confirmed by thin layer chromatography (TLC).
100 ml of water was added to the reaction solution, transferred to a separatory funnel, extracted with a mixed solvent of hexane: ethyl acetate = 1: 1 (100 ml × 2 times), and the organic layer was washed with 100 ml of saturated brine. The organic layer was dried over sodium sulfate, and then the solvent was distilled off to obtain a transparent yellow liquid (yield 9.51 g, yield 95.1%). The target product (mBrDClS) was identified by ¹ H-NMR spectrum.

Next, 250 ml of dichloromethane (DCM) was added to a 500 ml four-necked flask equipped with a thermometer, a reflux condenser, a calcium chloride tube and a dropping funnel, cooled to 0 to 5 ° C., and then 30% m-chloroperbenzoic acid. 32.7 g (56.8 mmol) of acid was added. While stirring, a solution prepared by dissolving 9.50 g (28.4 mmol) of mBrDC1S in 100 ml of dichloromethane was added dropwise at 0 to 10 ° C. over 30 minutes. After completion of dropping, the reaction was allowed to proceed at room temperature for 2 hours. The disappearance of the raw material was confirmed by TLC.
To the reaction vessel, 175 ml of saturated sodium bicarbonate solution was added little by little with stirring. After the addition was completed, the mixture was stirred for 30 minutes, transferred to a separatory funnel, and the organic layer was recovered. The obtained organic layer was dried over anhydrous sodium sulfate and filtered, and then the solvent was distilled off. The product was purified by dispersion washing using ethanol and dried under reduced pressure to obtain a white solid (yield 8.76 g, yield 84.2%). The target product (mBrDClSO) was identified by ¹ H-NMR spectrum.

Then, in a 200 ml four-necked flask equipped with a thermometer, a nitrogen introduction tube and a reflux tube, mBrDClSO 3.66 g (10.0 mmol), carbazole 1.67 g (10.0 mmol), potassium carbonate 4.15 g (30.0 mmol) Was added and nitrogen flowed. To this, 150 ml of dry xylene was added, and nitrogen was bubbled for 1 hour. 89.8 mg (0.40 mmol) of palladium (II) acetate and 0.376 ml (1.60 mmol) of tri-tert-butylphosphine were added and refluxed for 20 hours. The disappearance of the raw material was confirmed by TLC.
100 ml of water was added to the reaction solution, transferred to a separatory funnel, extracted with a mixed solvent of hexane: ethyl acetate = 1: 1 (100 ml × 2 times), and the organic layer was washed with 100 ml of saturated brine. The organic layer was dried over sodium sulfate and the solvent was distilled off. The obtained brown solid was purified by a recrystallization method using toluene (yield 1.80 g, yield 39.8%). The target product (CzDClSO) was identified by ¹ H-NMR and mass spectrum.

Further, 1.58 g (3.50 mmol) of CzDClSO (3.50 mmol), 2-phenyl-4,4,5,5-tetramethyl-1,3,2- was added to a 100 ml four-necked flask equipped with a thermometer, a nitrogen inlet tube and a reflux tube. Dioxaborolane (PhDOB) 1.43 g (7.00 mmol) and 1.35 M tripotassium phosphate aqueous solution 15.6 ml (21.0 mmol) were added, and nitrogen bubbling was performed for 1 hour. To this, 0.160 g (0.175 mmol) of tris (dibenzylideneacetone) dipalladium (0) and 0.147 g (0.525 mmol) of tricyclohexylphosphine were added and refluxed for 1 hour. The disappearance of the raw material was confirmed by TLC.
100 ml of water was added to the reaction solution, transferred to a separatory funnel, and extracted with a mixed solvent of hexane: ethyl acetate = 1: 1. The organic layer was dried over sodium sulfate, and the solvent was concentrated to about 15 ml under reduced pressure. Purification by silica gel column chromatography using a mixed solvent of hexane: ethyl acetate = 5: 1 gave a brown solid. It was purified again with silica gel column chromatography using toluene to obtain a colorless transparent viscous body. This was purified by dispersion washing with methanol to obtain a white solid (yield 0.53 g, yield 28.3%). The target product (1CzSO) was identified by ¹ H-NMR and mass spectrum.
Further, the obtained white solid (1CzSO) was purified by sublimation and then identified by elemental analysis.

(Synthesis Example 2) Synthesis of 2CzSO 2CzSO was synthesized by a reaction with a corresponding carbazole after the precursor was synthesized by the following steps.

First, in a 200 ml four-necked flask equipped with a thermometer, a nitrogen introduction tube and a reflux tube, 15.0 g (73.5 mmol) of iodobenzene, 15.8 g (88.2 mmol) of 3,5-dichlorobenzenethiol, copper powder 4 .67 g (73.5 mmol), cesium carbonate 28.7 g (88.2 mmol), and dimethyl sulfoxide (DMSO) 100 ml were added and reacted at 170 ° C. in a nitrogen atmosphere for 20 hours. The disappearance of the raw material was confirmed by TLC.
The reaction solution was filtered through Celite, and the filtrate was washed twice with 200 ml of water. The organic layer was dried over sodium sulfate and the solvent was distilled off. Purification by silica gel column chromatography using hexane gave 4.50 g of a colorless transparent solution (yield 23.9%). The target product (2ClS) was identified by ¹ H-NMR.

Next, 100 ml of dichloromethane (DCM) was added to a 300 ml four-necked flask equipped with a thermometer, reflux condenser, calcium chloride tube and dropping funnel, cooled to 0 to 5 ° C., and then 30% m-chloroperbenzoic acid. 21.3 g (37.0 mmol) of acid was added. While stirring, a solution prepared by dissolving 4.50 g (17.6 mmol) of 2ClS in 50 ml of dichloromethane was added dropwise at 0 to 10 ° C. over 20 minutes. After completion of dropping, the reaction was allowed to proceed at room temperature for 1 hour. The disappearance of the raw material was confirmed by TLC.
To the reaction vessel, 80 ml of saturated sodium bicarbonate solution was added little by little with stirring. After the addition was completed, the mixture was stirred for 30 minutes, transferred to a separatory funnel and washed with water (100 ml × 4 times). The organic layer was dried over anhydrous sodium sulfate and filtered, and then the solvent was distilled off. The obtained white solid was dispersed and washed with ethanol, and the insoluble matter was isolated by suction filtration. The isolated solid was purified by a recrystallization method using toluene to obtain a yellowish white solid (yield 3.13 g, yield 62.0%). The target product (2ClSO) was identified by ¹ H-NMR and mass spectrum.

Then, in a 100 ml four-necked flask equipped with a thermometer, a nitrogen introduction tube and a reflux tube, 1.15 g (4.00 mmol) of 2ClSO, 1.34 g (8.40 mmol) of carbazole, 3.32 g (24.0 mmol) of potassium carbonate. Was added and nitrogen flowed. To this, 70 ml of dry xylene was added and nitrogen bubbling was performed for 1 hour. Next, 35.9 mg (0.16 mmol) of palladium (II) acetate and 0.15 ml (0.64 mmol) of tri-tert-butylphosphine were added and refluxed for 14 hours. The disappearance of the raw material was confirmed by TLC.
The reaction solution was suction filtered using silica gel. The filtrate was washed with water (100 ml × 2 times), the organic layer was dried over sodium sulfate, and the solvent was distilled off. The obtained yellow solid was purified by silica gel column chromatography using toluene to obtain a bowl-like solid. This was dispersed and washed with 30 ml of methanol to obtain a white solid. The obtained white solid was dried under reduced pressure (yield 1.46 g, yield 66.7%). The target product (2CzSO) was identified by ¹ H-NMR and mass spectrum.
Furthermore, the obtained white solid (2CzSO) was purified by sublimation and then identified by elemental analysis.

(Synthesis Example 3) Synthesis of 3CzSO After the precursor was synthesized by the following steps, 3CzSO was synthesized by reaction with the corresponding carbazole.

First, in a 100 ml four-necked flask equipped with a thermometer, a nitrogen introduction tube and a reflux tube, 5.00 g (21.0 mmol) of 1-chloro-4-iodobenzene, 3.75 g of 3,5-dichlorobenzenethiol (21 0.0 mmol), 8.71 g (63.0 mmol) of potassium carbonate and 70 ml of DMF were added, and nitrogen was bubbled for 30 minutes. To this, 0.40 g (2.10 mmol) of copper (I) iodide was added and reacted at 100 ° C. under a nitrogen atmosphere for 22 hours. The disappearance of the raw material was confirmed by TLC.
The reaction solution was suction filtered and washed with 50 ml of DMF. The filtrate was concentrated, 60 ml of chloroform was added, and insoluble matters were isolated. Further, the filtrate was concentrated to about 30 ml and purified by silica gel column chromatography to obtain an orange liquid (yield 6.48 g, yield 96.0%). The target product (3ClS) was identified by ¹ H-NMR and mass spectrum.

Next, 100 ml of dichloromethane (DCM) was added to a 200 ml four-necked flask equipped with a thermometer, a reflux condenser, a calcium chloride tube and a dropping funnel, cooled to 0 to 5 ° C., and then 30% m-chloroperbenzoic acid. 23.8 g (41.4 mmol) of acid was added. While stirring, a solution prepared by dissolving 6.00 g (20.7 mmol) of 3ClS in 50 ml of dichloromethane was added dropwise at 0 to 10 ° C. over 15 minutes. After completion of dropping, the reaction was allowed to proceed at room temperature for 1 hour. The disappearance of the raw material was confirmed by TLC.
To the reaction vessel, 115 ml of saturated sodium bicarbonate solution was added little by little with stirring. After the addition was completed, the mixture was stirred for 30 minutes, transferred to a separatory funnel, and the organic layer was recovered. The obtained organic layer was dried over anhydrous sodium sulfate and filtered, and then the solvent was distilled off. The obtained white solid was dispersed and washed with ethanol, and the insoluble matter was isolated by suction filtration. The obtained pink solid was dried under reduced pressure (yield 5.08 g, yield 76.3%). The target product (3ClSO) was identified by ¹ H-NMR and mass spectrum.

Then, in a 200 ml four-necked flask equipped with a thermometer, a nitrogen introduction tube and a reflux tube, 3ClSO 2.57 g (8.00 mmol), carbazole 4.01 g (24.0 mmol), potassium carbonate 9.95 g (73.0 mmol) Was added and nitrogen flowed. To this, 160 ml of dry xylene was added, and nitrogen was bubbled for 1 hour. Next, 71.8 mg (0.32 mmol) of palladium (II) acetate and 0.301 ml (1.28 mmol) of tri-tert-butylphosphine were added and refluxed for 9 hours. The disappearance of the raw material was confirmed by TLC.
The reaction solution was suction filtered using silica gel. The filtrate was washed with water (100 ml × 2 times), the organic layer was dried over sodium sulfate, and the solvent was distilled off. The obtained black-green soot-like solid was dispersed and washed with 15 ml of a mixed solvent of hexane: toluene = 2: 1 to isolate insoluble matter. Furthermore, the obtained white solid was dissolved by heating in 160 ml of toluene, and the insoluble matter was isolated. The filtrate was concentrated and purified with silica gel column chromatography using toluene to obtain a bowl-like solid. This was dispersed and washed with 30 ml of methanol to obtain a white solid. The obtained white solid was dried under reduced pressure (yield 2.28 g, yield 39.9%). The target product (3CzSO) was identified by ¹ H-NMR and mass spectrum.
Furthermore, the obtained white solid (3CzSO) was purified by sublimation and then identified by elemental analysis.

(Synthesis Example 4) Synthesis of 4CzSO The starting material 1-chloro-4-iodobenzene in Synthesis Example 3 was changed to 3,5-dichloroiodobenzene, and bis (3 , 5-dichlorophenyl) sulfide and then bis (3,5-dichlorophenyl) sulfone (see International Publication WO2010 / 018858 A1). 4CzSO was synthesized by reacting the synthesized bis (3,5-dichlorophenyl) sulfide with the corresponding carbazole.

In a 100 ml four-necked flask equipped with a thermometer, a nitrogen inlet tube and a reflux tube, 1.42 g (4.00 mmol) of bis (3,5-dichlorophenyl) sulfone, 2.74 g (16.4 mmol) of carbazole, potassium carbonate 6 .63 g (48.0 mmol) was added and nitrogen flowed. To this, 80 ml of dry xylene was added, and nitrogen was bubbled for 1 hour. Next, 35.9 mg (0.16 mmol) of palladium (II) acetate and 0.15 ml (0.64 mmol) of tri-tert-butylphosphine were added and refluxed for 3.5 hours. The disappearance of the raw material was confirmed by TLC.
The reaction solution was suction filtered using silica gel. The filtrate was washed with water (50 ml × 2 times), the organic layer was dried over sodium sulfate, and the solvent was distilled off. The obtained brown solid was dispersed and washed with 15 ml of chloroform, and the insoluble matter was isolated by suction filtration. The isolated white solid was purified by recrystallization using toluene (yield 1.63 g, yield 46.3%). The target product (4CzSO) was identified by ¹ H-NMR.
Further, the obtained white solid (4CzSO) was purified by sublimation and then identified by elemental analysis.

(Example 1) Phosphorescence spectrum measurement About each diphenylsulfone derivative synthesize | combined above, the phosphorescence spectrum measurement of the co-deposition film | membrane of diphenylsulfone derivative: 5 wt% Ir (ppz) ₃ is performed, and triplet energy is measured from the rise of a spectrum. Estimated.
As a result, each derivative showed a triplet energy of 2.8 eV or more, and it was confirmed that sufficient triplet exciton confinement in the blue phosphorescent material was possible.
The structure of Ir (ppz) ₃ is shown below.

(Example 2) Device evaluation Using each diphenylsulfone derivative synthesized above as a host material, an organic EL device having a light emitting layer doped with FIrpic which is a blue phosphorescent material was produced. As shown in FIG. 1, the device configuration is substrate 1 / anode 2 / hole transport layer 3 / light emitting layer 4 / electron transport layer 5 / electron injection layer 6 / cathode 7. Specifically, ITO / TAPC (20 nm) / host: 11 wt% FIrpic (10 nm) / B3PyPB (50 nm) / Liq (1.5 nm) / Al.
In addition, the structure of each compound of FIrpic, TAPC, and B3PyPB is shown below.

For each element, measurement of drive voltage, power efficiency, current efficiency, and external quantum efficiency at emission luminance of 100 cd / m ² and 1000 cd / m ² was performed.
These measurement results are summarized in Table 1.
FIG. 2 shows a current density-external quantum efficiency curve of each element.

  From the above evaluation results, the diphenylsulfone derivative synthesized in this example has high triplet energy, and therefore, when used as a host material, a blue phosphorescent material can be made to emit light efficiently, and a highly efficient organic EL device. It was recognized that it could be provided.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole transport layer 4 Light emitting layer 5 Electron transport layer 6 Electron injection layer 7 Cathode

Claims (4)

Diphenyl sulfone derivative represented by any one of the below following formula.

A host material comprising the diphenylsulfone derivative according to claim 1 . An organic electroluminescent device comprising at least one organic layer laminated between a pair of electrodes, the organic electroluminescent device comprising a layer containing the diphenylsulfone derivative according to claim 1 . An organic electroluminescence device comprising one or more organic layers laminated between a pair of electrodes, wherein the host material according to claim 2 comprises a light emitting layer doped with a phosphorescent material. An organic electroluminescence element.

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