JP2018127424A - Novel imidazole derivative, and organic el element prepared therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel imidazole derivative that emits light with high efficiency, and an organic EL element prepared therewith.SOLUTION: The present invention provides a benzoimidazophenanthridine compound represented by the following formula, and an imidazole derivative containing the same.SELECTED DRAWING: None

Description

  The present invention relates to a novel imidazole derivative having high luminous efficiency and an organic EL device using the same.

  In an organic EL (electronics) element, by applying a voltage between a pair of electrodes, holes from the anode, electrons from the cathode, and a light-emitting layer containing an organic compound as a light-emitting material are injected. When holes recombine, excitons are formed in the light-emitting organic compound, and light emission can be obtained from the excited organic compound.

One means for improving the practicality of such an organic EL element is to increase the luminous efficiency. Excitons formed by organic compounds include singlet excitons (E _S1 ) and triplet excitons (E _T1 ). Fluorescence emission from singlet excitons (E _S1 ) and triplet excitons (E Although there are a phosphorescence from _T1), these statistical generation ratio in _{elements, E S1: E T1 = 1} : 3, and limit the internal quantum efficiency of 25% on an organic EL element using the fluorescent emission It is said. Therefore, in order to improve the conversion efficiency (internal quantum efficiency) from electrons to photons, a phosphorescent material capable of converting the triplet excited state into light emission has been developed. Recently, an organic material utilizing this phosphorescence emission has been developed. EL devices have been reported.

  In addition, when such a light emitting material is used in an organic EL element, a method of doping a host material with a dopant material is known. In the light emitting layer formed by the doping method, excitons can be efficiently generated from the charge injected into the host. And the exciton energy of the produced | generated exciton can be moved to a dopant, and highly efficient light emission can be obtained from a dopant.

Here, in order to perform intermolecular energy transfer from the host to the phosphorescent phosphorescent dopant, it is necessary that the triplet energy E _gH of the host is larger than the triplet energy E _gD of the phosphorescent dopant. .

For example, CBP (4,4′-bis (N-carbazolyl) biphenyl) is known as a material having a large triplet energy E _gH . When such a material is used as a host, a highly efficient light-emitting element can be obtained by transferring energy between triplet excitons to a phosphorescent dopant having a predetermined emission wavelength (for example, red or green).

  By the way, although the thermally activated delayed fluorescence (TADF) material described in Non-Patent Document 1 is a fluorescent material, it can theoretically realize an exciton generation probability of 100%, similarly to a phosphorescent material. It is possible to improve the efficiency. Furthermore, it is possible to reduce the development cost for molecular designs that do not require noble metals such as Ir and Pt. Therefore, it is considered that a light-emitting element with low cost and high efficiency can be obtained by developing a light-emitting material using this TADF.

Patent Document 1 reports that a pyridinecarbonitrile compound containing a carbazole structure can be a TADF material as a light-emitting material used in an organic EL element.
Non-Patent Document 2 describes a blue organic EL device using a carbazole / pyridinedicarbonitrile derivative as a TADF material, and reports that it has a luminous efficiency of 21.2%.

  In these organic EL devices, the theoretical external quantum efficiency is improved by about 4 times compared to conventional fluorescent materials, but in order to obtain delayed fluorescence with high efficiency, precise molecular design is required. There are few.

Japanese Patent Laying-Open No. 2015-172166

H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature 2012,492, 234. Wei Liu, Cai-Jun Zheng, Kai Wang, Zhan Chen, Dong-Yang Chen, Fan Li, Xue-Mei Ou, Yu-Ping Dong, and Xiao-Hong Zhang, Applied Materials & Interfaces 2015, 7, 18930

  An object of the present invention is to provide a novel imidazole derivative that emits light with high efficiency, and an organic EL device using the same.

The present invention comprises the following items.
The imidazole derivative of the present invention is represented by the following general formula (1).

In the general formula (1), R ^{1 to} R ⁸ and R ^{12 to} R ¹⁵ each independently represent a hydrogen atom, an aliphatic substituent or an aromatic substituent, and R ¹ and R ² are connected to each other to form a ring. it may be formed, X is -O -, - S -, - NR 9 - or -CR ¹⁰ R ¹¹ - represents, R ⁹ represents a hydrogen atom, an alkyl group having a carbon number of 1 to 20, R ¹⁰ And R ¹¹ each independently represents an aromatic substituent or an alkyl group having 1 to 20 carbon atoms, and R ¹⁰ and R ¹¹ may be linked to each other to form a ring.

In the general formula (1), R ¹ and R ² are hydrogen atoms, or R ¹ and R ² are connected to each other to form a phenyl group, and R ^{3 to} R ¹⁵ are hydrogen atoms or carbon atoms. It is preferably an aliphatic hydrocarbon group having 1 to 4 atoms.

  The organic EL device of the present invention is characterized by using the imidazole derivative.

  The imidazole derivative of the present invention exhibits thermally activated delayed fluorescence (TADF), and can improve the external quantum efficiency by a factor of 4 or more as compared with conventional fluorescent materials, thereby improving the light emission efficiency. Since the imidazole derivative exhibits the same efficiency as the second generation phosphorescent material, it can be suitably used for an organic EL device.

FIG. 1 represents the ¹ HNMR spectrum of Ac-BIP. FIG. 2 represents the ¹ HNMR spectrum of PXZ-BIP. FIG. 3 represents the ¹ HNMR spectrum of PXZ-IP. FIG. 4 represents an ultraviolet-visible (UV-vis) absorption spectrum of each toluene solution (10 ⁻⁵ M) of Ac-BIP, PXZ-BIP and PXZ-IP. FIG. 5 shows the ultraviolet-visible (UV-vis) absorption spectrum of each of the single films of Ac-BIP, PXZ-BIP and PXZ-IP. FIG. 6 shows UV-vis absorption spectra of 10 wt% DPEPO co-deposited films of Ac-BIP, PXZ-BIP and PXZ-IP. FIG. 7 represents the PL-transient spectrum of Ac-BIP measured using a streak camera at 300K and 5K. Fig.7 (a) represents PL spectrum and FIG.7 (b) represents a mode that PL attenuate | damps with time. The fluorescence spectrum (Flu.) Was measured with a 10 wt% DPEPO co-deposited film, and the phosphorescence spectrum (Phos.) Was measured with a single film. FIG. 8 represents the PL transient spectrum of PXZ-BIP measured with a streak camera at 300K and 5K. FIG. 8A shows a PL spectrum, and FIG. 8B shows a PL attenuation curve. Both the fluorescence spectrum (Flu.) And the phosphorescence spectrum (Phos.) Were measured using a 10 wt% DPEPO co-deposited film. FIG. 9 represents the PL transient spectrum of PXZ-IP measured with a streak camera at 300K and 5K. FIG. 9A shows a PL spectrum, and FIG. 9B shows a PL attenuation curve. Both fluorescence spectrum (Flu.) And phosphorescence spectrum (Phos.) Were measured using a 10 wt% DPEPO co-deposited film. FIG. 10 shows the PYS measurement results of the Ac-BIP single film. FIG. 11 shows the PYS measurement results of the PXZ-BIP single film. FIG. 12 shows the PYS measurement results of the PXZ-IP single film. FIG. 13 shows an EL emission spectrum when a current of 1 mA is passed through a device formed from a single light-emitting layer containing each of Ac-BIP, PXZ-BIP, and PXZ-IP. FIG. 14A shows the relationship between external quantum efficiency and luminance characteristics of a device formed from a single light-emitting layer including each of Ac-BIP, PXZ-BIP, and PXZ-IP, and FIG. FIG. 14C shows the relationship between the current density-voltage characteristic and the luminance-voltage characteristic of the device, FIG. 14C shows the relationship between the power efficiency-luminance characteristic of the device, and FIG. 14C shows the current of the device. This represents the relationship between efficiency and luminance characteristics. FIG. 15 shows EL spectra when a current of 1 mA is passed through a device including PXZ-BIP by comparing a single light emitting layer and a double light emitting layer. FIG. 16A represents the relationship between external quantum efficiency and luminance characteristics of a device including PXZ-BIP, and FIG. 16B represents the relationship between current density-voltage characteristics and luminance-voltage characteristics of the device. FIG. 16C shows the relationship between the power efficiency and luminance characteristics of the device, and FIG. 16D shows the relationship between the current efficiency and luminance characteristics of the device. FIGS. 16A to 16D show a single light emitting layer and a double light emitting layer in comparison. FIG. 17 shows a typical configuration of an organic EL element.

Hereinafter, the present invention will be described in detail.
[Imidazole derivatives]
The imidazole derivative of the present invention is represented by the following general formula (1).

In the general formula (1), R ^{1 to} R ⁸ and R ^{12 to} R ¹⁵ each independently represent a hydrogen atom, an aliphatic substituent or an aromatic substituent, and R ¹ and R ² are connected to each other to form a ring. it may be formed, X is -O -, - S -, - NR 9 - or -CR ¹⁰ R ¹¹ - represents, R ⁹ represents a hydrogen atom, an alkyl group having a carbon number of 1 to 20, R ¹⁰ And R ¹¹ each independently represents an aromatic substituent or an alkyl group having 1 to 20 carbon atoms, and R ¹⁰ and R ¹¹ may be linked to each other to form a ring.

The aliphatic substituent includes a hydrocarbon group having 1 to 20 carbon atoms, specifically, an alkyl group having 1 to 20 carbon atoms. Methyl group, ethyl group, propyl group, 2-propyl group, a butyl group, an isobutyl group, a t- butyl group are preferred, the aliphatic substituents of R ^2, a methyl group, an ethyl group, a propyl group, 2-propyl group , A butyl group, an isobutyl group, and a t-butyl group are preferable.
In addition, a part of the hydrogen atoms of the aliphatic substituent and the alkyl group may be substituted with a nitrogen atom, an oxygen atom, a sulfur atom or the like within a range not impairing the effects of the present invention.
The aromatic substituent includes aromatic substituents having 6 to 22 carbon atoms, specifically, phenyl group, biphenyl group, naphthyl group, anthracenyl group, phenanthrenyl group, triphenylenyl group, and terphenyl. Groups and the like. Among these, a phenyl group, a biphenyl group, a terphenyl group, and a triphenylenyl group are preferable. A part of the hydrogen atoms constituting the aromatic substituent may be substituted with a nitrogen atom, an oxygen atom, a sulfur atom or the like within a range not impairing the effects of the present invention.
R ¹ and R ² and R ¹⁰ and R ¹¹ may be connected to each other to form a 4- to 6-membered ring.

The imidazole derivative has a π-conjugated system. It is known that molecules having a π-conjugated system have a light absorption band in the visible region, and many of them can function as a dye. Furthermore, the energy gap can be adjusted by appropriately adding functional groups to such molecules to change the electronic properties. That is, in the present invention, the molecular design is performed so that the energy gap between the singlet excited state (E _S1 ) and the triplet excited state (E _T1 ) in the imidazole derivative is as small as possible, so that the triplet excited state is once shifted. Energy can be returned to the singlet excited state again, and highly efficient fluorescence can be extracted.

The imidazole derivative of the present invention is a thermally activated delayed fluorescence (TADF) molecule and a compound that emits light in blue (430 to 480 nm).
Furthermore, when n is 1 or 2 in the general formula (1), the imidazole derivative can stably maintain a π-conjugated system, and thus can exhibit long-life blue light emission.

そして、上記一般式（１）で表されるイミダゾール誘導体には、以下の化合物がより好ましい。 The imidazole derivative represented by the general formula (1) is preferably a compound represented by the following structural formula.

The following compounds are more preferable for the imidazole derivative represented by the general formula (1).

[Method for producing imidazole derivative]
The imidazole derivative of the present invention can be produced, for example, by the method shown below. A method for producing Ac-BIP is shown as an example.

2- (4-Chlorophenyl) benzimidazole and 1,2-dibromobenzene are heated to reflux in DMF in the presence of potassium carbonate using Pd (II) and XPhos ligands to give 6-chlorobenzo [4 , 5] imidazo [1,2-f] phenanthridine (BIP). Further, BIP and 9,10-dihydro-9,9-dimethylacridine are heated and refluxed in xylene in the presence of potassium carbonate using Pd (II) and P (t-Bu) ₃ HBF ₄ . Ac-BIP is obtained with a yield of 58%.
However, the imidazole derivative represented by the general formula (1) is not limited to the above-described method, and can be produced by various known methods.

[Organic EL device]
The organic EL element of the present invention uses the imidazole derivative.
Here, FIG. 17 shows a typical layer structure of the organic EL element.
The organic EL element typically has, for example, an indium tin oxide (ITO) film formed on the substrate 1 as the anode 2, and a hole injection layer 3, a hole transport layer 4, and a light emitting layer thereon. 5, the electron transport layer 6, the electron injection layer 7, and the cathode 8 are laminated | stacked in this order.

  The substrate 1 is transparent and smooth and has a total light transmittance of at least 70%. Specifically, the substrate 1 is a flexible transparent substrate such as a glass substrate having a thickness of several μm or a special transparent substrate. Plastic or the like is used.

Thin films such as the anode 2, the hole injection layer 3, the hole transport layer 4, the light emitting layer 5, the electron transport layer 6, the electron injection layer 7 and the cathode 8 formed on the substrate are laminated by a vacuum deposition method or a coating method. Is done. When using a vacuum vapor deposition method, the deposited material is usually heated in an atmosphere reduced to 10 ⁻³ Pa or lower. The thickness of each layer varies depending on the type of layer and the material used, but usually the anode 2 and the cathode 8 are about 100 nm, and the other layers including the light emitting layer 5 are less than 50 nm. The electron injection layer 7 or the like may be formed with a thickness of 1 nm or less, for example.

  The anode 2 has a large work function and a total light transmittance of usually 80% or more. Specifically, in order to transmit light emitted from the anode 2, transparent conductive ceramics such as ITO and ZnO, transparent conductive polymers such as PEDOT / PSS and polyaniline, and other transparent conductive materials are used. The film thickness of the anode 2 is usually 10 to 200 nm.

  In the light emitting layer 5, like the other light emitting layers used in the organic EL device, it is preferable to use a host compound together with the imidazole derivative which is the light emitting material of the present invention. The host compound is not limited as long as it does not impair the emission characteristics based on fluorescence and TADF. For example, bis [2- (diphenylphosphino) phenyl] ether oxide (DPEPO), 3,6-bis (diphenyl) Forphoryl) -9-phenylcarbazole (PO9), 4,4′-bis (N-carbazolyl) -1,1′-biphenyl (CBP), tris (4-carbazoyl-9-ylphenyl) amine (TCTA) 2,8-bis (diphenylphosphoryl) dibenzothiophene (PPT), adamantane anthracene (Ad-Ant), rubrene, and 2,2′-bi (9,10-diphenylanthracene) (TPBA). In the components constituting the light emitting layer 5, the content of the light emitting material (imidazole derivative) and the host compound of the present invention is 1 to 50 wt%, preferably 5 to 10 wt%.

  In order to efficiently transport holes from the anode 2 to the light emitting layer, a hole transport layer 4 is provided between the anode 2 and the light emitting layer 5. Examples of the hole transport material forming the hole transport layer 4 include 4,4′-cyclohexylidenebis [N, N-bis (4-methylphenyl) benzeneamine] (TAPC), N, N′—. Diphenyl-N, N′-di (m-tolyl) benzidine (TPD), N, N′-di (1-naphthyl) -N, N′-diphenylbenzidine (α-NPD), 1,3-di (carbazolyl) -9-yl) benzene) (mCP) and 4,4 ′, 4 ″ -tris [phenyl (m-tolyl) amino] triphenylamine. Although the film thickness of the positive hole transport layer 4 can be suitably changed according to the target design, it is 5-100 nm normally.

  An electron transport layer 6 is provided between the cathode 8 and the light emitting layer 5 in order to efficiently transport electrons from the cathode to the light emitting layer. Examples of the electron transport material forming the electron transport layer 6 include 4,6-bis (3,5-di (pyridin-3-yl) phenyl) -2-methylpyrimidine (B3PymPm), 4,6-bis ( 3,5-di (pyridin-4-yl) phenyl) -2-phenylpyrimidine (B4PyPPm), 2- (4-biphenylyl) -5- (pt-butylphenyl) -1,3,4-oxadi Azole (tBu-PBD), 1,3-bis [5- (4-t-butylphenyl) -2- [1,3,4] oxadiazolyl] benzene (OXD-7), 3- (biphenyl-4-yl) ) -5- (4-tert-butylphenyl) -4-phenyl-4H-1,2,4-triazole (TAZ), bathocuproine (BCP), 1,3,5-tris (1-phenyl-1H-benz Imidazole-2- Le) benzene (TPBi), and the like. Although the film thickness of the electron carrying layer 6 can be suitably changed according to the target design, it is 5-100 nm normally.

As the cathode 8, a cathode having a low work function (4 eV or less) and chemically stable is used.
Specifically, a cathode material such as Al, MgAg alloy, or an alloy of Al and an alkali metal such as AlLi or AlCa is used. These cathode materials are formed by, for example, resistance heating vapor deposition, electron beam vapor deposition, sputtering, or ion plating. The thickness of the cathode is usually 10 nm to 1 μm, preferably 50 to 500 nm.

  Of the hole transport layer 4 and the electron transport layer 6, a layer having a function of improving the charge injection efficiency from the anode 2 or the cathode 8, respectively, and exhibiting an effect of lowering the driving voltage of the organic EL element, A hole injection layer 3 and an electron injection layer 7 may be provided.

  Examples of the hole injection material for forming the hole injection layer 3 include phthalocyanine complexes such as copper phthalocyanine, and aromatic amine derivatives such as 4,4 ′, 4 ″ -tris (3-methylphenylphenylamino) triphenylamine. , Hydrazone derivatives, carbazole derivatives, triazole derivatives, imidazole derivatives, oxadiazole derivatives having an amino group, polythiophene, etc. The thickness of the hole injection layer 3 is usually 5 to 300 nm.

  Examples of the electron transport material forming the electron injection layer 7 include Ba, Ca, CaF, LiF, Li, and NaF. The film thickness of the electron injection layer 7 is usually 3 to 50 nm.

  In addition, layers such as a hole blocking layer, an electron blocking layer, and an exciton blocking layer are further formed as necessary.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.

[Synthesis of imidazole derivatives]
The equipment used for product purification and identification is as follows.
(1) ¹ H nuclear magnetic resonance (NMR) apparatus JEOL Ltd. (400 MHz) JNM-EX270FT-NMR type (2) mass spectrometry (MS) apparatus JEOL Ltd. JMS-K9 [desktop GCQMS] and Zspray (SQ detector 2) manufactured by Waters
(3) Sublimation refining equipment Temperature gradient electric furnace, model: NPF80-500, company name: Cosmo Tech Co., Ltd.
Thermal constant flow rate device, model: MC-1A, company name: Coflock Co., Ltd.
Rotary pump, model: GLD-136C, company name: ULVAC Kiko Co., Ltd.
(4) Elemental analyzer Perkin Elmer 2400II CHNS / O analyzer Measurement mode: CHN mode (5) Thermal analyzer TGA diamond and DSCDTA manufactured by PerkinElmer Japan Co., Ltd.

[Example 1] Synthesis of Ac-BIP

[Step 1] Synthesis of 6-chloro-benzo [4,5] imidazo [1,2-f] phenanthridine (BIP) In a 50 mL four-necked flask equipped with a thermometer and a reflux tube, add 2- (4- Chlorophenyl) benzimidazole (1.83 g, 8 mmol) and K ₂ CO ₃ (20 mL, 24 mmol) were added and a nitrogen flow was performed for 15 minutes. Subsequently, 1,2-dibromobenzene (20 mL, 41 mmol) and DMF (70 mL) were added, and nitrogen bubbling was performed for 1 hour, and then Pd (OAc) ₂ (269 mg, 1.5 mmol), XPhos (1.14 g, 2.4 mmol) And heated to 140 ° C. After 87 hours, the reaction was stopped, liquid-separated with ethyl acetate and water, dehydrated with anhydrous sodium sulfate, and dried. The product was purified by silica gel chromatography (hexane: ethyl acetate = 10: 2) and dispersed and washed with methanol to obtain 0.6 g of a white solid. The target product was identified by ASAP-MS and ¹ HNMR. ASAP-MS: m / z = 303.1 [M ⁺ ]

[Step 2] Synthesis of Ac-BIP 6-Chloro-benzo [4,5] imidazo [1,2-f] phenanthridine (BIP) (561mg) in a 25mL 4-neck flask with thermometer and reflux tube , 1.85 mmol), 9,10-dihydro-9,9-dimethylacridine (464 mg, 2.22 mmol) and K ₂ CO ₃ (767 mg, 5.55 mmol) were added, and nitrogen flow was performed for 15 minutes. Subsequently, xylene (30 mL) was added, nitrogen bubbling was performed for 1 hour, and Pd (OAc) ₂ (44.3 mg, 0.2 mmol) and [( ^t Bu) ₃ PH] BF ₄ (163.3 mg, 0.56 mmol) were added. And heated to reflux. After 20 hours, the progress of the reaction was not observed, so Pd (OAc) ₂ (44.3 mg, 0.2 mmol), [( ^t Bu) ₃ PH] BF ₄ (163.3 mg, 0.56 mmol), and xylene (10 mL) were added. did. After 42 hours, the reaction was stopped, suction filtration was performed with ethyl acetate, and the organic layer was extracted with liquid separation (water: 50 mL × 3, saturated saline: 50 mL × 5). The organic layer was dried over anhydrous sodium sulfate and the solution was concentrated. Purification by silica gel chromatography (toluene: ethyl acetate / 10: 1) gave 365 mg of a white solid.
They were identified by ASAP-MS, TGA / DSC measurement, elemental analysis, and ¹ HNMR.
The results are shown below. FIG. 1 shows the ¹ HNMR spectrum.
ASAP-MS: m / z = 476.4 [M ⁺ ]
Melting point ( _Tm ) 310 ℃
5% weight decay temperature (T _d5 ) 393 ℃
Elemental analysis: Theoretical value C, 85.87%; H, 5.30%; N, 8.84%,
Found C, 85.88%; H, 5.01%; N, 8.81%

[Example 2] Synthesis of PXZ-BIP

[Step 1] Synthesis of BIP The BIP was synthesized by the method described in Step 1 of Example 1.
[Step 2] Synthesis of PXZ-BIP 6-Chloro-benzo [4,5] imidazo [1,2-f] phenanthridine (BIP) (910mg) in a 50mL 4-neck flask equipped with a thermometer and a reflux tube 3 mmol), phenoxazine (659 mg, 3.6 mmol) and K ₂ CO ₃ (1.24 g, 9 mmol) were added, and nitrogen flow was performed for 40 minutes. Subsequently, xylene (30 mL) was added and nitrogen bubbling was performed for 1.4 hours. Pd (OAc) ₂ (33.7 mg, 0.15 mmol) and [( ^t Bu) ₃ PH] BF ₄ (131 mg, 0.45 mmol) were added and heated. Refluxed. After 20 hours, since the progress of the reaction was not observed, Pd (OAc) ₂ (44.3 mg, 0.2 mmol), [( ^t Bu) ₃ PH] BF ₄ (163.3 mg, 0.56 mmol), and xylene (50 mL) were added. Added. After 15 hours, the reaction was stopped, and suction filtration was performed with toluene, followed by liquid separation with water, saturated brine and toluene, the organic layer was dehydrated with anhydrous sodium sulfate, and the solution was concentrated. Purification by silica gel chromatography (toluene: ethyl acetate / 40: 1) gave 460 mg of a yellow solid.
They were identified by ASAP-MS, TGA / DSC measurement, elemental analysis, and ¹ HNMR.
The results are shown below. FIG. 2 shows the ¹ HNMR spectrum.
ASAP-MS: m / z = 450.5 [M ⁺ ]
Melting point ( _Tm ) 313 ℃
5% weight decay temperature (T _d5 ) 395 ° C
Elemental analysis: Theoretical value C, 82.83%; H, 4.26%; N, 9.35%
Measured value C, 82.67%; H, 4.14%; N, 9.29%

[Example 3] Synthesis of PXZ-IP

[Step 1] Synthesis of 2- (4-chlorophenyl) imidazole Methanol (200 mL) was placed in a 200 mL four-necked flask that had previously been flowed with nitrogen, and nitrogen bubbling was performed for 10 minutes. 4-Chlorobenzaldehyde (8.43 g, 60 mmol), ammonium acetate (9.25 g, 120 mmol), L-proline (1.04 g, 9 mmol), and glyoxal (6.83 mL, 60 mmol) were added thereto and stirred for 18 hours. After stopping the reaction, methanol was removed by concentration, and dispersion washing was performed with ethyl acetate. Since one spot was observed from TLC and only the peak of the target product was observed from ASAP-MS, purification was completed and the residue was dried under reduced pressure to obtain 3.6 g of a white solid. ASAP-MS: m / z = 179.8 [M ⁺ ]

[Step 2] Synthesis of imidazophenanthridine (IP) In a 100 mL four-necked flask equipped with a thermometer and a reflux tube, 2- (4-chlorophenyl) imidazole (3.00 g, 16.8 mmol), K ₂ CO ₃ (7.0 g, 50.4 mmol) was added, and a nitrogen flow was performed for 10 minutes. Then, 1,2-dibromobenzene (10 mL, 84 mmol) and DMF (50 mL) were added and nitrogen bubbling was performed for 1 hour. Thereafter, Pd (OAc) ₂ (377 mg, 1.68 mmol) and Xphos (1.6 g, 3.36 mmol) were added and heated to reflux. After 216 hours, the reaction was stopped, suction filtration was performed with ethyl acetate, liquid separation was performed with ethyl acetate, water and saturated brine, the organic layer was dehydrated with anhydrous sodium sulfate, and the solution was concentrated to obtain a black solid. . Purification by silica gel chromatography (toluene: ethyl acetate = 10: 7) gave 500 mg of the desired product. ASAP — MS: m / z = 253.6 [M ⁺ ]

[Step 3] Synthesis of PXZ-IP In a 50 mL four-necked flask equipped with a thermometer and a reflux tube, chloroimidazophenanthridine (IP) (500 mg, 2 mmol), phenoxazine (366 mg, 2 mmol), and K ₂ CO ₃ (833 mg, 6 mmol) was added, nitrogen flow was performed for 10 minutes, xylene (10 mL) was added, and nitrogen bubbling was performed for 1 hour. Then, Pd (OAc) ₂ (23 mg, 0.1 mmol) and [( ^t Bu) ₃ PH] BF ₄ (187 mg, 0.3 mmol) were added and heated to reflux. After 22 hours, the reaction was stopped, suction filtration was performed with toluene, and separation and extraction were performed with toluene, water, and saturated saline. The organic layer was dehydrated with anhydrous sodium sulfate, and the solution was concentrated. The product was purified by silica gel chromatography (toluene: ethyl acetate = 10: 7) and dried under reduced pressure overnight to obtain 521 mg of a black yellow solid.
They were identified by ASAP-MS, TGA / DSC measurement, elemental analysis, and ¹ HNMR.
The results are shown below. FIG. 3 shows the ¹ HNMR spectrum.
ASAP-MS: m / z = 400.3 [M ⁺ ]
Melting point (T _m ) 249 ° C,
5% weight decay temperature (T _d5 ) 360 ° C
Elemental analysis: Theoretical value C, 81.19%; H, 4.29%; N, 10.52%,
Measured value C, 80.95%; H, 4.08%; N, 10.50%

[Optical characteristics evaluation]
The equipment and measurement conditions used for the optical property evaluation are as follows.
(1) Ultraviolet / visible (UV-vis) spectrophotometer UV-3150 manufactured by Shimadzu Corporation
Measurement conditions: medium scan speed, measurement range 200 to 800 nm, sampling pitch 0.5 nm, slit width 0.5 nm
(2) Photoluminescence (PL) measuring device Fluoro MAX-2 manufactured by HORIBA, Ltd.
A PL spectrum and a time-resolved PL spectrum (PL transient spectrum) using a streak camera (C4334 manufactured by Hamamatsu Photonics Co., Ltd.) were measured at normal temperature (300K) and low temperature (5K).
(3) Photoelectron Yield Spectroscopy (PYS) Device Ionization Potential Measurement Device manufactured by Sumitomo Heavy Industries, Ltd. Ionization potential (Ip) was measured in vacuum using an ionization potential measurement device.
The electron affinity (E _a ) was calculated by estimating the energy gap (E _g ) from the absorption edge of the UV-vis absorption spectrum.

[Example 4]
Toluene solutions (10 ⁻⁵ M) of Ac-BIP, PXZ-BIP, and PXZ-IP synthesized in Examples 1 to 3 were prepared, and absorption (UV-vis) and emission (PL) spectra were measured. . The results are shown in FIG.
In addition, a single film (neatfilm) of Ac-BIP, PXZ-BIP, and PXZ-IP, and a 10 wt: DPEPO film obtained by doping 10 wt% of each into DPEPO are prepared, and absorption (UV-vis) / luminescence (PL) The spectrum was measured. The results are shown in FIGS.
From the results of UV-vis absorption spectra, peaks derived from these π-conjugated systems were observed for all of the imidazole derivatives. In particular, in PXZ-BIP and PXZ-IP having a phenoxazine skeleton, λ _max was observed on the longer wavelength side compared to Ac-BIP having a 9,10-dihydro-9,9-dimethylacridine skeleton.
From the results of the PL spectrum, the single film showed blue to green emission with an emission wavelength of λ _max = 440 to 540 nm. In the DPEPO-doped film, since the imidazole derivative was dispersed, no red shift due to aggregation was observed, and blue to green light emission of λ _max = 440 to 540 nm was exhibited.

[Example 5]
For each of Ac-BIP, PXZ-BIP, and PXZ-IP synthesized in Examples 1 to 3, fluorescence / phosphorescence spectrum at low temperature (5K) and time-resolved PL spectrum (PL transient spectrum) at room temperature (300K) Was measured using a streak camera. The results are shown in FIGS. 7 (a) and 7 (b).
In addition, although the fluorescence spectrum of Ac-BIP was able to be measured using the DPEPO dope film | membrane, the intensity | strength was low and the phosphorescence spectrum was unmeasurable. Therefore, only the phosphorescence spectrum was measured with a single film.
In PXZ-BIP and PXZ-IP, both fluorescence and phosphorescence were measured using a DPEPO-doped film. The results are shown in FIGS. 8A and 8B and FIGS. 9A and 9B, respectively.

[Example 6]
The respective ionization potentials of the solid thin films (single film) of Ac-BIP, PXZ-BIP, and PXZ-IP were measured by photoelectron yield spectroscopy (PYS). The results of PYS are shown in FIGS.
From the PYS results, the ionization potentials (I _p) of Ac-BIP, PXZ-BIP and PXZ-IP were calculated. Table 2 shows I _p , electron affinity (E _a) , and E _g , respectively. I _p was calculated from the rise of the photoelectron yield, and E _g was calculated from the absorption edge of the UV-vis absorption spectrum of the solid thin film (single film).

In addition, since the discontinuity of the plot of the photoelectron yield of 5 eV vicinity in FIGS. 10-12 is detected by all the samples, it is thought that it originates in an apparatus.
[Production and Evaluation of Organic EL Element]
The equipment used for the evaluation of the light emission characteristics of the organic EL element is as follows.
Equipment: PHOTONIC MULTI-CHANNEL ANALYZER PMA-1 manufactured by Hamamatsu Photonics Co., Ltd.

[Example 7] Element having a single light emitting layer For Ac-BIP, PXZ-BIP, and PXZ-IP, elements having the following structures were prepared.
[ITO (130 nm) / Triphenylamine-containing polymer: 4-isopropyl-4'-methyldiphenyliodonium tetrakis (pentafluorophenyl) borate (PPBI) (20 nm) / di [4- (N, N-ditolylamino) phenyl] Cyclohexane (TAPC) (20 nm) / N, N-dicarbazoyl-3,5-benzene (mCP) (5 nm) / 10 wt% Guest: Bis [2- (diphenylphosphino) diphenyl] ether oxide (DPEPO) (20 nm) / 3,3 ”, 5,5'-tetra (3-pyridyl) -1,1 ';3',1" -terphenyl B3PyPB (50 nm) / LiF (0.5 nm) / Al (100 nm) ]
Note that “guest” in the above-described element structure corresponds to Ac-BIP, PXZ-BIP, or PXZ-IP. Further, the structural formulas of TAPC, mCP, DPEPO, and B3PyPB used for manufacturing the element are as follows.

The luminous efficiency of the element having the above single light emitting layer was measured. EL emission spectra are shown in FIGS. 13 and 14 (a) to (d).
Table 3 shows the element characteristics.

λ_EL＝４４０〜４８５ｎｍにドーパント由来の発光が確認された（図１３）。Ac-BIPに比べ、より強い電子供与性部位を有するPXZ-BIPでは長波長化し、電子受容性部位のπ共役の拡張の抑制をしたPXZ-IPではLUMO準位が浅くなったためPXZ-BIPに比べ短波長化した。

Luminescence derived from the dopant was confirmed at λ _EL = 440 to 485 nm (FIG. 13). Compared to Ac-BIP, the PXZ-BIP with a stronger electron donating site has a longer wavelength, and the PXZ-IP with suppressed π-conjugate expansion of the electron accepting site has a shallow LUMO level. Compared to a shorter wavelength.

[Example 8] Element having a double light-emitting layer An element having a double light-emitting layer was produced for PXZ-BIP.
An element having the structure shown below was manufactured and compared with the element of the single light emitting layer of Example 7.
[ITO (130 nm) / Triphenylamine-containing polymer: 4-isopropyl-4'-methyldiphenylindoniumtetrakis (pentafluorophenyl) borate (PPBI) (20 nm) / di [4- (N, N-ditolylamino) phenyl ] Cyclohexane (TAPC) (20 nm) / 10 wt% Guest: N, N-Dicarbazoyl-3,5-benzene (mCP) (10 nm) / 10 wt% Guest: Bis [2- (diphenylphosphino) phenyl] ether oxide (DPEPO) (10 nm) / 3,3 ”, 5,5'-tetra (3-pyridyl) -1,1 ';3',1" -terphenyl B3PyPB (50 nm) / LiF (0.5 nm) / Al (100 nm)]
Note that “guest” in the element structure described above corresponds to PXZ-BIP.
The luminous efficiency of the element having the above-described double light emitting layer was measured. The EL emission spectra are shown in FIGS. 15 and 16 (a) to (d).
Table 4 shows the element characteristics.

シングル発光層、ダブル発光層のいずれを有する素子も、λ_EL＝４８０〜５００ｎｍにドーパント由来の発光が確認された（図１５）。発光層の構成によらず、本デバイス構造では、キャリアと励起子の閉じ込めが十分可能であるため、周辺材料からの発光は見られなかったと考えられる。

In the device having both the single light emitting layer and the double light emitting layer, light emission derived from the dopant was confirmed at λ _EL = 480 to 500 nm (FIG. 15). Regardless of the structure of the light-emitting layer, in this device structure, it is considered that light emission from peripheral materials was not observed because carriers and excitons can be sufficiently confined.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Anode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 Electron injection layer 8 Cathode

Claims (3)

Imidazole derivatives represented by the following general formula (1).

(In the general formula (1), R ^{1 to} R ⁸ and R ^{12 to} R ¹⁵ each independently represent a hydrogen atom, an aliphatic substituent or an aromatic substituent, and R ¹ and R ² are linked to each other to form a ring. X represents —O—, —S—, —NR ⁹ — or —CR ¹⁰ R ¹¹ —, R ⁹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, R ¹⁰ and R ¹¹ each independently represents an aromatic substituent or an alkyl group having 1 to 20 carbon atoms, and R ¹⁰ and R ¹¹ may be linked to each other to form a ring. In the general formula (1), R ¹ and R ² are hydrogen atoms, or R ¹ and R ² are connected to each other to form a phenyl group, R ^{3 to} R ⁸ and R ^{12 to} R ^2. Each of ¹⁵ is independently a hydrogen atom or an aliphatic hydrocarbon group having 1 to 20 carbon atoms, and R ⁹ , R ^10, and R ¹¹ are each independently an aromatic substituent. Imidazole derivatives.   An organic EL device using the imidazole derivative according to claim 1.

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