CN112028879B - An electron transport material, an organic electroluminescent device and a display device - Google Patents

Abstract

The invention discloses an electron transport material of general formula I, which can be used as an electron transport layer of an organic electroluminescent device in a display device. The electron transport material has a parent structure of diversified condensed heterocycles, has high bond energy among atoms, good thermal stability, favorability for solid accumulation among molecules and strong electron transition capability, can effectively reduce the driving voltage of an organic electroluminescent device when being used as an electron transport layer material, improves the current efficiency of the organic electroluminescent device and prolongs the service life of the organic electroluminescent device.

Description

Electron transport material, organic electroluminescent device and display device

Technical Field

The present invention relates to the field of light-emitting display technology, and in particular to an electron transport material, an organic electroluminescent device and a display device.

Background Art

Electroluminescence (EL) refers to the phenomenon that luminescent materials emit light under the action of electric field, stimulated by current and voltage. It is the luminescence process of directly converting electrical energy into light energy. Organic electroluminescent displays (hereinafter referred to as OLEDs) have a series of advantages such as autonomous luminescence, low-voltage DC drive, full curing, wide viewing angle, light weight, simple composition and process. Compared with liquid crystal displays, organic electroluminescent displays do not require backlight sources, have large viewing angles, low power consumption, and their response speed can reach 1000 times that of liquid crystal displays, but their manufacturing cost is lower than that of liquid crystal displays with the same resolution. Therefore, organic electroluminescent devices have a very broad application prospect.

With the continuous advancement of OLED technology in the two major fields of lighting and display, people are paying more attention to the research on high-efficiency organic materials that affect the performance of OLED devices. An organic electroluminescent device with high efficiency and long life is usually the result of an optimized combination of device structure and various organic materials. This provides great opportunities and challenges for chemists to design and develop functional materials of various structures.

Compared with inorganic luminescent materials, organic electroluminescent materials have many advantages, such as good processing performance, can be formed into films on any substrate by evaporation or spin coating, can realize flexible display and large-area display; can adjust the optical properties, electrical properties and stability of materials by changing the molecular structure, and there is a lot of room for material selection. In the most common OLED device structure, the following types of organic materials are usually included: hole injection materials, hole transport materials, electron transport materials, and various luminescent materials (dyes or doped guest materials) and corresponding host materials. At present, electron transport materials, as an important functional material, have a direct impact on the mobility of electrons and ultimately affect the luminous efficiency of OLEDs. However, the electron transport materials currently used in OLEDs can achieve a low electron migration rate and poor matching with the energy levels of adjacent layers, which seriously restricts the luminous efficiency of OLEDs and the display function of OLED display devices.

Summary of the invention

In order to improve the luminous efficiency of an organic light-emitting electroluminescent device and prolong its life, the present invention provides an electron transport material, an organic electroluminescent device and a display device.

The electron transport material of the present invention has a structure as shown in Formula I:

in,

Ar ¹ -Ar ⁴ are selected from C ₆ -C ₃₀ aromatic groups or C ₅ -C ₃₀ heteroaromatic groups, and the hydrogen atoms of the aromatic groups and heteroaromatic groups may be independently substituted by Ra;

L is selected from a chemical bond, a C ₆ -C ₃₀ arylene group or a C ₃ -C ₃₀ heteroarylene group, and the hydrogen atoms on the arylene group and the heteroarylene group can each independently be replaced by Ra;

R ¹ -R ⁴ are selected from hydrogen, C ₁ -C ₆ alkyl, C ₆ -C ₃₀ arylene or C ₃ -C ₃₀ heteroarylene, the hydrogen atoms on the arylene and heteroarylene groups can be independently replaced by Ra, and adjacent R substituents can be connected to form a ring;

The heteroatoms on the heteroaryl or the heteroarylene are each independently selected from O, S or N;

Each Ra is independently selected from deuterium, halogen, nitro, cyano, C ₁ -C ₄ alkyl, phenyl, biphenyl, terphenyl or naphthyl.

Preferably, Ar ¹ -Ar ⁴ are selected from one of the following groups which are unsubstituted or substituted by Ra: phenyl, biphenyl, terphenyl, naphthyl, phenanthrenyl, triphenylene, fluorenyl, 9,9-dimethylfluorenyl, spirofluorenyl, dibenzofuranyl, dibenzothienyl, pyridyl, pyrazine, quinoline, isoquinoline, quinazoline, quinoxaline, cinnoline, naphthyridine or benzimidazole; L is selected from one of the subunits of the following compounds which are unsubstituted or substituted by Ra: 1. Benzene, biphenyl, terphenyl, naphthalene, phenanthrene, triphenylene, fluorene, pyridine, pyridazine, pyrimidine, pyrazine, quinoline, isoquinoline, quinazoline, quinoxaline, cinnoline, naphthyridine, triazine, pyridopyrazine, furan, benzofuran, dibenzofuran, aza-dibenzofuran, thiophene, benzothiophene, dibenzothiophene, aza-dibenzothiophene, 9,9-dimethylfluorene, spirofluorene, aromatic amine or carbazole; R ^R1 - ^R4 are each independently selected from hydrogen, methyl, ethyl, isopropyl, tert-butyl, one of the following groups which are unsubstituted or substituted by Ra: phenyl, biphenyl, terphenyl, naphthyl, phenanthrenyl, triphenylene, fluorenyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, quinolyl, isoquinolyl, quinazolinyl, quinoxalinyl, cinnolinyl, naphthyridinyl, triazinyl, pyridopyrazinyl, furanyl, benzofuranyl, dibenzofuranyl, aza-dibenzofuranyl, thienyl, benzothienyl, dibenzothienyl, aza-dibenzothienyl, 9,9-dimethylfluorenyl, arylamine or carbazolyl.

The present invention also discloses the specific structure of the electron transport material shown in Formula A1-A30:

The electron transport material of the present invention has a matrix structure of diversified condensed heterocycles, high bond energy between atoms, good thermal stability, and is conducive to solid-state stacking between molecules. It has strong electron transition ability and can be used as an electron transport layer material to effectively reduce the driving voltage of an organic electroluminescent device, improve the current efficiency of the organic electroluminescent device, and extend its service life. The electron transport material of the present invention is used in the electron transport layer and has a suitable energy level between adjacent layers, which is conducive to the injection and migration of electrons, can effectively reduce the starting and falling voltage, and has a high electron migration rate, and can achieve good luminous efficiency in the organic electroluminescent device. The electron transport material of the present invention has a larger conjugated plane, is conducive to molecular stacking, exhibits good thermodynamic stability, and exhibits a long service life in the organic electroluminescent device.

The present invention also provides an organic electroluminescent device, comprising at least an anode electrode, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode electrode, wherein the electron transport layer is selected from at least one of the above compounds. In the present invention, there is no particular restriction on the type and structure of the organic electroluminescent device, as long as the electron transport material provided by the present invention can be used. The organic electroluminescent device of the present invention can be a light-emitting device with a top emission structure, which can be exemplified by a light-emitting device including an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, a transparent or semi-transparent cathode in sequence on a substrate. The organic electroluminescent device of the present invention can also be a light-emitting device with a bottom emission structure, which can be exemplified by a light-emitting device including a transparent or semi-transparent anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode structure in sequence on a substrate. The organic electroluminescent device of the present invention can also be a light-emitting device with a double-sided emission structure, which can be exemplified by a light-emitting device including a transparent or semi-transparent anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a transparent or semi-transparent cathode structure in sequence on a substrate.

Figure 1 is a schematic diagram of the structure of a typical organic electroluminescent device in accordance with the organic electroluminescent device of the present invention, which comprises, from bottom to top: a substrate 1, a reflective anode electrode 2, a hole injection layer 3, a hole transport layer 4, a light-emitting layer 5, an electron transport layer 6, an electron injection layer 7 and a cathode electrode 8.

For convenience, the organic electroluminescent device of the present invention is described below with reference to FIG1 , but this does not mean any limitation on the protection scope of the present invention. It is understood that all organic electroluminescent devices that can use the electron transport material of the present invention are within the protection scope of the present invention.

In the present invention, the substrate 1 is not particularly limited, and conventional substrates used in organic electroluminescent devices in the prior art, such as glass, polymer materials, glass and polymer materials with TFT components, etc., can be used.

In the present invention, the reflective anode electrode 2 is not particularly limited, and can be selected from transparent conductive materials such as indium tin oxide (ITO), indium zinc oxide (IZO), tin dioxide (SnO ₂ ), zinc oxide (ZnO) known in the prior art, or metal materials such as silver and its alloys, aluminum and its alloys, or organic conductive materials such as PEDOT (poly 3,4-ethylenedioxythiophene), multilayer structures of the above materials, etc. In the present invention, the hole injection layer 3 is not particularly limited, and can be made of hole injection layer materials known in the art, for example, a hole transport material (HTM) is selected as the main material, and a p-type dopant is added. The type of the p-type dopant is not particularly limited, and various p-type dopants known in the art can be used, for example, the following p-type dopants can be used:

In the present invention, the hole transport layer 4 is not particularly limited, and at least one of the hole transport materials (HTM) known in the art can be selected. For example, the material for the hole injection layer main body and the material for the hole transport layer can be selected from at least one of the following HT-1 to HT-32 compounds:

In the present invention, the luminescent material in the luminescent layer 5 is not particularly limited, and any luminescent material known to those skilled in the art can be used. For example, the luminescent material can include a host material and a luminescent dye. The host material can be selected from at least one of the following GPH-1 to GPH-80 compounds:

Preferably, the light-emitting layer 5 contains a phosphorescent dopant, and the dopant can be selected from at least one of the following RPD-1 to RPD-28 compounds. The amount of the dopant is not particularly limited and can be an amount known to those skilled in the art.

In the present invention, the electron transport layer 6 comprises at least one of the electron transport materials of the present invention. The electron transport layer 6 may also comprise a combination of at least one of the electron transport materials of the present invention and at least one of the following known electron transport materials ET-1 to ET-57:

The electron injection layer 7 is not particularly limited and may be made of any electron injection material known in the art, for example, including but not limited to at least one of LiQ, LiF, NaCl, CsF, _Li2O , _Cs2CO3 , BaO, Na, Li, _Ca and other materials in the prior art.

The cathode electrode 8 is not particularly limited and may be selected from, but not limited to, metals such as magnesium-silver mixture, LiF/Al, ITO, Al, metal mixtures, oxides, and the like.

The method for preparing the organic electroluminescent device of the present invention is not particularly limited, and any method known in the art may be used, for example:

(1) cleaning the reflective anode electrode 2 on the substrate 1 of the top-emitting OLED device by using a cleaning machine through steps such as chemical cleaning, water cleaning, brushing, high-pressure water cleaning, and air knife cleaning, and then performing a heat treatment;

(2) vacuum evaporating a hole injection layer 3 on the reflective anode electrode 2, wherein the main material of the hole injection layer is HTM, which contains a P-type dopant (p-dopant) and has a thickness of 10-50 nm;

(3) vacuum evaporating a hole transport material (HTM) on the hole injection layer 3 as a hole transport layer 4 with a thickness of 80-150 nm;

(4) vacuum evaporating a light-emitting layer 5 on the hole transport layer 4, wherein the light-emitting layer comprises a host material (GPH) and a guest material (RPD) and has a thickness of 20-50 nm;

(5) vacuum evaporating an electron transport material (ETM) on the light emitting layer 5 as an electron transport layer 6;

(6) vacuum evaporating an electron injection material on the electron transport layer 6 to form an electron injection layer 7;

(7) A cathode material is vacuum-deposited on the electron injection layer 7 to form a cathode electrode 8 .

A third aspect of the present invention provides a display device, comprising the above-mentioned organic electroluminescent device. The display device of the present invention includes but is not limited to a monitor, a television, a tablet computer, a mobile communication terminal, etc.

DETAILED DESCRIPTION

The present invention is described below in conjunction with examples, which are only used to explain the present invention and are not used to limit the scope of the present invention.

1. Synthesis of Electron Transport Materials

Example 1, Synthesis of A1

100 mmol of 2-chloro-3-phenylquinoxaline, 100 mmol of 2-chlorophenylboronic acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of tetrahydrofuran (THF), 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 60° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was purified by recrystallization with toluene to obtain a white powder M1, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2-chloro-3-phenylquinoxaline;

100 mmol of M1, 150 mmol of biboric acid pinacol ester, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the mixture was reacted at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M2, wherein the amount of Pd(dppf)Cl ₂ added was 1 mol% of M1;

100 mmol of 2-(3-chloro-5-bromophenyl)-4,6-diphenyltriazine, 100 mmol of phenylboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was purified by recrystallization with toluene to obtain a white powder M3, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2-(3-chloro-5-bromophenyl)-4,6-diphenyltriazine;

100 mmol of M2, 100 mmol of M3, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask and reacted at 80°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered and washed with water. The obtained solid was recrystallized and purified with toluene to obtain white powder A1, wherein the added amount of Pd(PPh ₃ ) ₄ was 1 mol% of M2.

The hydrogen spectrum characterization results of A1 are as follows:

¹ HNMR (400MHz, Chloroform) δ8.86 (s, 1H), 8.46–8.34 (m, 3H), 8.23 (s, 1H), 7.96 (d, J＝10.0Hz, 2H), 7.88 (d, J＝ 8.4Hz,6H),7.80(s,1H),7.75-7.59(m,8H),7.52–7.40(m,8H),7.39(s,1H).

The reaction process is as follows:

Example 2, Synthesis of A9

100 mmol of 2,3-dichloroquinoxaline, 100 mmol of 4-dibenzofuran boronic acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of tetrahydrofuran (THF), 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 60° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was purified by recrystallization with toluene to obtain a white powder M1, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2,4-dichloroquinoxaline;

100 mmol of M1, 100 mmol of 4-chlorophenylboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M2, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of M1;

100 mmol of M2, 150 mmol of biboric acid pinacol ester, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the mixture was reacted at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M3, wherein the amount of Pd(dppf)Cl ₂ added was 1 mol% of M2;

100 mmol of 2-(3-chloro-5-bromophenyl)-4,6-diphenyltriazine, 100 mmol of 2-naphthaleneboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M4, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2-(3-chloro-5-bromophenyl)-4,6-diphenyltriazine;

100 mmol of M3, 100 mmol of M4, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask and reacted at 80°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered and washed with water. The obtained solid was purified by recrystallization with toluene to obtain white powder A9, wherein the added amount of Pd(PPh ₃ ) ₄ was 1 mol% of M2.

The hydrogen spectrum characterization results of A9 are as follows:

¹ HNMR(400MHz,Chloroform)δ8.62(s,1H),8.51(s,1H),8.42(d,J＝9.6Hz,1H),8.39(d,J＝8.8Hz,4H),8.13(s ,1H),8.08(d,J＝12.0Hz,4H),8.03(s,1H),7.99–7.82(m,5H),7.79(d,J＝6.4Hz,2H),7.63(s,1H) ,7.58(d,J＝8.0Hz,2H),7.55–7.45(m,5H),7.36(d,J＝7.6Hz,2H),7.24(s,1H).

The reaction process is as follows:

Example 3, Synthesis of A11

100 mmol of 2,3-dichloroquinoxaline, 100 mmol of (3-(pyridin-3-yl)phenyl)boric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was purified by recrystallization with toluene to obtain a white powder M1, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2,3-dichloroquinoxaline;

100 mmol of M1, 100 mmol of 4-chlorophenylboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M2, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of M1;

100 mmol of M2, 150 mmol of biboric acid pinacol ester, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the mixture was reacted at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M3, wherein the amount of Pd(dppf)Cl ₂ added was 1 mol% of M2;

100 mmol of M3, 100 mmol of 3-bromo-5-chloro-1,1'-biphenyl, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M4, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of M3;

100 mmol of M4, 150 mmol of biboric acid pinacol ester, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the mixture was reacted at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M5, wherein the amount of Pd(dppf)Cl ₂ added was 1 mol% of M4;

100 mmol of 2,4-dichloro-6-phenyltriazine, 100 mmol of 2-boric acid-9,9-dimethylfluorene, 41.4 g of potassium carbonate (300 mmol), 800 ml of tetrahydrofuran (THF), 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction bottle, and the mixture was reacted at 60° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was purified by recrystallization with toluene to obtain a white powder M6, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2,4-dichloro-6-phenyltriazine;

100 mmol of M5, 100 mmol of M6, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask and reacted at 80°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered and washed with water. The obtained solid was purified by recrystallization with toluene to obtain white powder A11, wherein the added amount of Pd(PPh ₃ ) ₄ was 1 mol% of M5.

The hydrogen spectrum characterization results of A11 are as follows:

¹ HNMR (400MHz, Chloroform) δ8.45(d,J＝8.4Hz,2H),8.36(s,1H),8.25(d,J＝6.4Hz,2H),8.09(s,1H),7.97(d ,J＝10.0Hz,2H),7.90(s,1H),7.78(t,J＝12.4Hz,4H),7.63(d,J＝10.8Hz,4H),7.60(d,J＝9.6Hz,2H ),7.49(d,J＝8.0Hz,6H),7.41(s,1H),7.38–7.16(m,8H),1.69(s,6H).

The reaction process is as follows:

Example 4, Synthesis of A19

100 mmol of 2,3-dichloroquinoxaline, 100 mmol of isopropylboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of tetrahydrofuran (THF), 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 60° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M1, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2,4-dichloroquinoxaline;

100 mmol of M1, 100 mmol of 4-chlorophenylboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M2, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of M1;

100 mmol of M2, 150 mmol of bipyraclostrobin, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the mixture was reacted at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M3, wherein the amount of Pd(dppf)Cl ₂ added was 1 mol% of M2;

100 mmol of 2-(3-chloro-5-bromophenyl)-4,6-diphenyltriazine, 100 mmol of 2-naphthaleneboric acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M4, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of 2-(3-chloro-5-bromophenyl)-4,6-diphenyltriazine;

100 mmol of M4, 150 mmol of biboric acid pinacol ester, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the reaction was carried out at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, water was added, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M5, wherein the amount of Pd(dppf)Cl ₂₄ added was 1 mol% of M2;

100 mmol of M3, 100 mmol of M5, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask and reacted at 80°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered and washed with water. The obtained solid was purified by recrystallization with toluene to obtain white powder A19, wherein the added amount of Pd(PPh ₃ ) ₄ was 1 mol% of M3.

The hydrogen spectrum characterization results of A19 are as follows:

¹ HNMR(400MHz,Chloroform)δ8.61(d,J＝8.0Hz,3H),8.55(s,1H),8.36-8.13(m,3H),8.01(s,1H),7.92(s,1H) ,7.80(d,J＝7.6Hz,4H),7.65-7.54(m,8H),7.49(d,J＝8.0Hz,4H),3.44(s,1H),1.33(s,6H).

The reaction process is as follows:

Example 5. Synthesis of A27

100 mmol of 2-(3-chloro-5-bromophenyl)-4-phenyl-6-(4-biphenyl)triazine, 150 mmol of biphenyl pinacol diboron, 41.4 g of potassium carbonate (300 mmol), 800 ml of DMF, and 1 mol% of Pd(dppf)Cl ₂ were added to a reaction flask, and the mixture was reacted at 120°C for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M1, wherein the amount of Pd(dppf)Cl ₂ added was 1 mol% of 2-(3-chloro-5-bromophenyl)-4-phenyl-6-(4-biphenyl)triazine;

100 mmol of M1, 100 mmol of 2,3-dichloroquinoxaline, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask, and the mixture was reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered, and washed with water. The obtained solid was recrystallized and purified with toluene to obtain a white powder M2, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of M1;

100 mmol of M2, 100 mmol of (4-(1-phenyl-1H-benzo[d]imidazole-2-yl)phenyl)phenylboronic acid, 41.4 g of potassium carbonate (300 mmol), 800 ml of THF, 200 ml of water and Pd(PPh ₃ ) ₄ were added to a reaction flask and reacted at 80° C. for 12 h. After the reaction was completed, the reactant was cooled to room temperature, added with water, filtered and washed with water. The obtained solid was purified by recrystallization with toluene to obtain white powder A27, wherein the amount of Pd(PPh ₃ ) ₄ added was 1 mol% of M2.

The hydrogen spectrum characterization results of A27 are as follows:

¹ HNMR(400MHz,Chloroform)δ8.56(s,1H),8.49(s,1H),8.36(d,J＝8.4Hz,3H),8.30(s,1H),8.28–7.96(m,6H) ,7.88–7.77(m,4H),7.75(s,2H),7.63(d,J＝12.0Hz,3H),7.56–7.40(m,11H),7.38(s,2H),7.27(d,J =11.6Hz,4H).

The reaction process is as follows:

2. Preparation of organic electroluminescent devices

The glass plate coated with the ITO transparent conductive layer was ultrasonically treated in a commercial cleaning agent, rinsed in deionized water, ultrasonically degreased in an acetone-ethanol mixed solvent, baked in a clean environment to completely remove the water, cleaned with ultraviolet light and ozone, and bombarded with a low-energy cation beam;

The glass substrate with the anode is placed in a vacuum chamber, and the vacuum is evacuated to less than 10 ^-5 Torr. A hole injection layer is vacuum-deposited on the anode layer. The hole injection layer material is HT-4 and a p-type dopant (p-dopant) with a mass ratio of 3%. The evaporation rate is 0.1 nm/s, the evaporation film thickness is 10 nm, and the hole injection layer material and p-type dopant are:

Vacuum evaporation of a hole transport material HT-5 material on the hole injection layer as a hole transport layer, wherein the evaporation rate is 0.1 nm/s and the evaporation film thickness is 80 nm;

A light-emitting layer is vacuum-deposited on the hole transport layer, wherein the light-emitting layer includes a main material GHP-16 and a dye material RPD-1, and the evaporation is performed by a multi-source co-evaporation method, wherein the evaporation rate of the main material GHP-16 is adjusted to 0.1 nm/s, the evaporation rate of the dye RPD-1 is adjusted to 3% of the evaporation rate of the main material, and the total evaporation film thickness is 30 nm;

An electron transport layer (ETL) was vacuum evaporated on the light-emitting layer, wherein the electron transport layer was the electron transport material prepared in Examples 1-5, and LiF with a thickness of 0.5 nm was vacuum evaporated on the electron transport layer (ETL) as an electron injection layer, wherein the evaporation rate was 0.1 nm/s and the evaporation film thickness was 10 nm; finally, an aluminum layer with a thickness of 150 nm was vacuum evaporated on the electron injection layer as the cathode electrode of the organic electroluminescent device, wherein the evaporation rate was 1 nm/s and the evaporation film thickness was 50 nm.

Comparative Example 1

The electron transport material ET-16 of the above organic electroluminescent device is replaced by a material with the following structure, while the rest remains unchanged.

The organic electroluminescent devices of Examples 1-4 and Comparative Example 1 were subjected to the following performance tests:

At the same brightness, the driving voltage and current efficiency of the organic electroluminescent device and the life of the device are measured using a digital source meter and a brightness meter. Specifically, the voltage is increased at a rate of 0.1V per second, and the voltage when the brightness of the organic electroluminescent device reaches 5000cd/ ^m2 , that is, the driving voltage, is measured, and the current density at this time is measured; the ratio of brightness to current density is the current efficiency; the life test of LT95 is as follows: using a brightness meter at a brightness of 5000cd/ ^m2 , maintaining a constant current, and measuring the time in hours when the brightness of the organic electroluminescent device drops to 4750cd/ ^m2 . The results are shown in Table 1.

Table 1. Organic electroluminescent device performance

Required brightness (cd/m ² ) Driving voltage/V Current efficiency (cd/A) Lifespan (LT95)/h Example 1 5000.00 4.1 42.5 260 Example 2 5000.00 3.8 42.8 275 Example 3 5000.00 4.0 41.6 270 Example 4 5000.00 3.9 43.2 280 Example 5 5000.00 4.0 42.5 270 Comparative Example 1 5000.00 4.4 37.4 215

As can be seen from Table 1, the compounds A1, A9, A11, A19 and A27 prepared in the present application are used as electron transport materials for organic electroluminescent devices, which can effectively reduce the driving voltage, improve the current efficiency, and extend the life of the device, and are electron transport materials with good performance.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. An electron transport material characterized by having a structure represented by the formulas A1, A9, a11, a19, and a 27:

2. an organic electroluminescent device comprising an anode electrode, a hole transporting layer, a light emitting layer, an electron transporting layer, and a cathode electrode, wherein the electron transporting layer comprises at least one of the electron transporting materials of claim 1.

3. The organic electroluminescent device of claim 2, wherein the electron transport layer further comprises at least one transport material of the formulae ET-1 to ET-57, the formulae ET-1 to ET-57 having the structure,

4. a display device comprising the organic electroluminescent device as claimed in claim 2 or 3.