Organic electroluminescent material, its manufacturing process and organic electroluminescent device

Abstract

An organic electroluminescent material which is the compound having the following structural formula I, wherein Ar, L and R are defined such that the compound having the structural formula I is one of the following compounds 18, 21 or 29:

Description

Technical area

[0001] The invention relates to the field of organic electroluminescent materials, in particular to a compound based on imidazole [1,5-a] [1,8] naphthyridine and also to a light-emitting device. Background of the technology

[0002] OLED stands for organic light-emitting diode (OLE) or organic light-emitting device (OLE). OLED is a self-luminous device that requires no backlight and has many special features such as fast response time, low operating voltage, high luminous efficiency, high resolution, and wide viewing angle. It has already become a new generation of display and lighting technologies, particularly with great application prospects for mobile phones, computers, televisions, and bendable and foldable electronic products.

[0003] Currently, two types of light-emitting materials are used in OLEDs: fluorescent materials and phosphorescent materials. The light-emitting materials used in early devices are mainly organic low-molecular-weight fluorescent materials, and spin statistics quantum theory shows that the theoretical internal quantum efficiency of fluorescent materials is only 25%. In 1998, Professor Forrest of Princeton University and Professor Thompson of the University of Southern California discovered the phosphorescence-electroluminescence phenomenon of molecular materials of organometallic complexes at room temperature. The strong spin-orbit coupling of heavy metal atoms can effectively promote intersystem crossing (ISC) of electrons from singlet to triplet.This allows OLED devices to fully utilize the singlet and triplet excitons generated by electronic excitation, so that the theoretical internal quantum efficiency of light-emitting materials can reach 100% (Nature, 1998, 395, 151).

[0004] Since the hole transport rate of most organic electroluminescent materials used in OLEDs is one or two orders of magnitude higher than the electron transport rate, this easily leads to an imbalance between the number of electrons and holes in the light-emitting layer, resulting in low device efficiency. Therefore, the selection and optimization of the host material in the light-emitting layer has a significant impact on improving the efficiency and lifetime of organic electroluminescent devices. CBP has been widely used in the light-emitting layer of phosphorescent devices since its invention. Although the carbazole group of CBP causes it to exhibit a higher triplet state, it can be used in the light-emitting layer of phosphorescent materials.However, it is primarily a hole-transporting material, exhibiting a low electron transport rate, which can easily lead to imbalanced charge carrier injection and transfer. In addition, the glass transition temperature Tg of CBP is low, which does not promote stable device use. Therefore, the development of host materials for the light-emitting layer with high stability and balanced charge carrier transport is of great importance for the widespread use of organic electroluminescent devices.

[0005] Die Dokumente EP 2 169 028 A2, Tan, Z., et al.: Aerobic copper-catalyzed halocyclization of methyl N-heteroaromatics with aliphatic amines: Access to functionalized imidazo-fused N-heterocycles. The journal of organic chemistry, Vol. 81, 2016, S. 9939-9946, und Qian, P., et al.: Electrocatalytic intermolecular C (sp3) - H / N-H coupling of methyl N-heteroaromatics with amines and amino acids: Access to imidazo-fused N-heterocycles. Organic letters, Vol. 20, 2018, S. 6359-6363 offenbaren weitere Beispiele organischer Elektrolumineszenz-Materialien. Inhalt der Erfindung

[0006] The present invention provides a compound based on imidazole [1,5-a][1,8] naphthyridine, which exhibits good thermal stability and high hole / electron transport equilibrium. The present invention also provides the application of the material in organic light-emitting diodes (OLEDs), and the device made from the organic electroluminescent compound exhibits advantages such as good electroluminescence efficiency, excellent color purity, and a long lifetime.

[0007] Organic electroluminescent material is the compound with the following structural formula I:wherein Ar, L and R are defined such that the compound with the structural formula I is one of the following compounds 18, 21 or 29:

[0008] The manufacturing process of the above organic electroluminescent material includes the following steps: (1) connection A is available, (2) under an alkaline condition, with tetrakis(triphenylphosphine)palladium as catalyst, the Ar-containing borate or Ar-containing pinacol borate is reacted with the compound A to obtain the compound of formula (I).

[0009] The preparation process of compound A is as follows: A) under the action of n-butyllithium, 2-bromo-1,8-dinaphthyridine is reacted with the formate of R to obtain compound B. B) Compound B is reacted with the formaldehyde compound of brominated L CHO-L-Br to obtain compound A.

[0010] The formate of R is methyl formate of R.

[0011] The imidazole [1,5-a][1,8] naphthyridine compound of the present invention can be applied to the fields of organic electroluminescent devices, solar cells, organic thin film transistors or organic receptors.

[0012] The present invention also provides an organic electroluminescent device comprising an anode, a cathode and an organic layer, wherein the organic layer comprises at least one of a light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-injection layer and an electron-transport layer, and at least one of the organic layers contains the imidazole [1,5-a] [1,8] naphthyridine compound as shown in structural formula I.

[0013] The definitions of Ar, L and R are as mentioned before.

[0014] The organic layer consists of a light-emitting layer and an electron-transport layer; or the organic layer consists of a light-emitting layer, a hole-injection layer, a hole-transport layer, and an electron-transport layer; or the organic layer consists of a light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-transport layer and an electron-injection layer; or the organic layer consists of a light-emitting layer, a hole-transport layer, an electron-transport layer, an electron-injection layer; or the organic layer consists of a light-emitting layer, a hole transport layer, an electron injection layer.

[0015] Preferably, the layer in which the compound based on imidazole [1,5-a][1,8] naphthyridine shown in the structural formula I is located is a light-emitting layer.

[0016] Preferably, the compound depicted in structural formula I containing imidazole [1,5-a] [1,8] naphthyridine is a compound of structural formula 1-36;

[0017] When the compound shown in structural formula I containing imidazole [1,5-a][1,8] naphthyridine is used to prepare light-emitting devices, it can be used alone or in combination with other compounds, or two or more compounds shown in structural formula I can be used at the same time.

[0018] The organic electroluminescent device of the present invention is further preferred that the organic electroluminescent device comprises an anode, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer and a cathode, wherein the light-emitting layer contains the compound of structural formula I, more preferably contains a compound of structure I-36.

[0019] The total thickness of the organic layer of the organic electroluminescent device of the present invention is 1-1000 nm, preferably 50-500 nm.

[0020] When the organic electroluminescent device of the present invention uses the compound having the structural formula I of the present invention, other materials may be used in combination to obtain blue light, green light, yellow light, red light or white light.

[0021] Each layer of the organic layer in the organic electroluminescent device of the present invention can be formed by a vacuum deposition method, a molecular beam deposition method, a solvent-soluble dip coating method, a bar coating method, or an inkjet printing method. For the metal electrode, vapor deposition or sputtering can be used for fabrication.

[0022] Device experiments show that the compound of the present invention, as shown in structural formula I, containing imidazole [1,5-a] [1,8] naphthyridine, exhibits superior thermal stability and high hole / electron transport equilibrium. The device made from the organic electroluminescent compound has advantages such as good electroluminescence efficiency, excellent color purity, and a long lifetime. Short description of the drawings Fig. 1 is DSC spectrum of compound 29, Fig. Fig. 2 is a schematic representation of the structure of an organic electroluminescent device, where 110 is a glass substrate, 120 is an anode, 130 is a hole injection layer, 140 is a hole transport layer, 150 is a light emitting layer, 160 is an electron transport layer, 170 is an electron injection layer, and 180 is a cathode. Detailed embodiments

[0023] The following are examples that illustrate embodiments of the present invention. These examples should not be construed as limiting. Unless otherwise stated, all percentages are by weight and all solvent mixture ratios are by volume. Synthesis of intermediates

[0024] 2-Bromo-1,8-dinaphthyridine (10 g, 47.84 mmol) and anhydrous THF (100 mL) were added to a three-necked flask under nitrogen and stirred at -50°C for 20 minutes. Then, an n-hexane solution of n-butyllithium (2.2 M, 26 mL, 57 mmol) was added dropwise through a pressure-equalizing dropping funnel. After the addition, the mixture was further stirred at room temperature for half an hour, and a THF solution of methyl benzoate (6.84 g, 50.2 mmol) was added dropwise. Then, the mixture was slowly warmed to room temperature and stirred overnight. After the reaction was complete, the mixture was quenched with saturated ammonium chloride solution. The organic phase was separated, the inorganic phase was extracted with ethyl acetate, and the organic phases were combined. A product 7.7 g with a yield of 71% is obtained by purification by column chromatography.

[0025] The starting material for the synthesis is methyl 4-picolinate. The synthesis procedure is the same as that for intermediate 1, and the yield is 68%.

[0026] Intermediate 1 (3 g, 12.8 mmol), p-bromobenzaldehyde (2.37 g, 12.8 mmol), ammonium acetate (29.6 g, 0.38 mol), and 60 mL of acetic acid were added to a flask, heated to 130 °C under nitrogen, and reacted for 15 hours. After the reaction, the mixture was cooled to room temperature, acetic acid was removed under reduced pressure, water was added, and the mixture was extracted with dichloromethane. The organic phases were combined, dried, and concentrated to obtain a crude product. Purification of the crude product by silica gel column chromatography gave a product (3.5 g) with a yield of 70%.

[0027] The starting material for the synthesis is m-bromobenzaldehyde. The synthesis procedure is the same as that for intermediate 3, and the yield is 65%.

[0028] Intermediate 2 (6 g, 25.5 mmol), m-bromobenzaldehyde (4.7 g, 25.5 mmol), ammonium acetate (49 g, 0.64 mol), and 100 mL of acetic acid were added to a flask, heated to 130°C under nitrogen, and reacted for 16 hours. After the reaction, the mixture was cooled, acetic acid was removed under reduced pressure, water was added, and the mixture was extracted with dichloromethane. The organic phases were combined, dried, and concentrated to obtain a crude product. The crude product was purified by silica gel column chromatography, yielding 6 g of product with a yield of 59%.

[0029] Intermediate 4 (1 g, 2.5 mmol), 2,4-diphenyl-6-((3-pinacolborate)phenyl)-1,3,5-triazine (1.2 g, 2.75 mmol), tetrakis(triphenylphosphine)palladium (0.29 g, 0.25 mmol), potassium carbonate (0.86 g, 6.2 mmol), and dioxane / water (10 mL / 2 mL) were added to a round-bottom flask. The reaction mixture was heated to 110 °C under a nitrogen atmosphere and stirred for 10 hours. After the reaction, it was washed with water, extracted with dichloromethane, and concentrated to obtain a crude product. Purification by silica gel column chromatography afforded a product (1.27 g) with a yield of 81%. MS (ESI): 629.2 (M + 1).

[0030] Intermediate 3 (1 g, 2.5 mmol), N-phenyl-3-carbazoleboronic acid (0.79 g, 2.75 mmol), tetrakis(triphenylphosphine)palladium (0.29 g, 0.25 mmol), potassium carbonate (0.86 g, 6.2 mmol), and toluene / water (10 mL / 2 mL) were added to a round-bottom flask. The reaction mixture was heated to 110°C under a nitrogen atmosphere and stirred for 8 hours. After the reaction, it was washed with water, extracted with dichloromethane, and concentrated to obtain a crude product. Purification by silica gel column chromatography yielded 1.04 g of product with a yield of 74%. MS (ESI): 563.2 (M + 1).

[0031] Intermediate 5 (2 g, 5 mmol), (3-(10H-spiro[acridin-9,9'-fluorene]-10-yl)phenyl)boronic acid (2.47 g, 6 mmol), tetrakis(triphenylphosphine)palladium (0.58 g, 0.5 mmol), potassium carbonate (1.7 g, 12.5 mmol), and dioxane / water (20 mL / 4 mL) were added to a round-bottom flask. The reaction mixture was heated to 110 °C under a nitrogen atmosphere and stirred for 10 hours. After the reaction, it was washed with water, extracted with dichloromethane, and concentrated to obtain a crude product. Purification by silica gel column chromatography afforded a product (3.08 g) with a yield of 85%. MS (ESI): 728.3 (M+1). The glass transition temperature was 99 °C. Fig. Figure 1 shows the DSC spectrum of compound 29. Example 4-6

[0032] Fabrication of organic electroluminescent devices

[0033] The OLEDs are prepared from the compounds in the examples of the present invention.

[0034] First, a transparent conductive ITO glass substrate 110 (with the anode 120 on it) is washed sequentially with deionized water, ethanol, acetone, and deionized water, and then treated with oxygen plasma for 30 seconds.

[0035] Then, a hole injection layer 130 (HATCN) with a thickness of 5 nm is evaporated.

[0036] Then, a hole transport layer 140 (TAPC) with a thickness of 50 nm is evaporated onto the hole injection layer.

[0037] Then, on the hole transport layer, a compound of the examples with a thickness of 10 nm doped with 10 wt% Pt-1 is evaporated as the light-emitting layer 150.

[0038] Then, an electron transport layer 160 (TmPyPb) with a thickness of 50 nm is evaporated onto the light-emitting layer.

[0039] Finally, 1.2nm LiF is deposited as the electron injection layer 160 and 100nm Al as the device cathode 180.

[0040] The efficiency of the manufactured device (see Fig. 2 for a schematic representation of the structure), which was measured with a Photo Reasearch PR650 spectrometer at a current density of 1000 cd / m 2 measured is shown in Table 1. Comparison example 1

[0041] Except that CBP is used as the light-emitting layer instead of the compound of the invention, everything else remains the same as in Example 4.

[0042] The efficiency of the manufactured device (see Fig. 2 for a schematic representation of the structure), which was measured with a Photo Reasearch PR650 spectrometer at a current density of 1000 cd / m 2 measured is shown in Table 1. Table 1 Example Connection CE (cd / A) PE (lm / W) EQE (%) CIE (x, y) at 20 mA / cm 2 4 18 58.7 43 16.2 (0.33, 0.62) 5 21 89.8 68.0 24.6 (0.31, 0.64) 6 29 95.6 71.7 26.1 (0.31, 0.64) Comparison example 1 CBP 41.9 29.1 12.1 (0.30, 0.65)

[0043] From Table 1, it can be seen that under the same conditions, the efficiency of the organic electroluminescent device prepared from the imidazole[1,5-a][1,8]naphthyridine compound of the present invention is higher than that of the comparative example. As described above, the compound of the present invention has high stability, and the organic electroluminescent device prepared according to the present invention has high efficiency.

[0044] The structural formulas in the device are listed as follows:

[0045] Therefore, using the imidazole[1,5-a][1,8]naphthyridine compound of the present invention as a host, a higher device efficiency can be obtained than using CBP. Under the same test condition at 1000 cd / m 2The current efficiency of the device made of CBP is 41.9 cd / A, the power efficiency is 29.1 lm / W, and the external quantum efficiency is 12.1%. However, the devices made of the compound of Examples of the present invention can achieve better efficiency than the above. In addition, the glass transition temperature Tg of CBP is 62°C, and the compound of Example 29 of the present invention has a higher glass transition temperature Tg (99°C). When the glass transition temperature is higher, the light-emitting layer of the device has good morphological stability and better application prospects, which better meets the requirements for organic light-emitting diodes for host materials.

Claims

[1] An organic electroluminescent material which is the compound having the following structural formula I, wherein Ar, L and R are defined such that the compound having the structural formula I is one of the following compounds 18, 21 or 29: [2] A method for producing the organic electroluminescent material according to claim 1, comprising the following steps: (1) connection A is available, (2) under an alkaline condition, with tetrakis(triphenylphosphine)palladium as catalyst, the Ar-containing borate or Ar-containing pinacol borate is reacted with the compound A to obtain the compound of formula (I). [3] The manufacturing process according to claim 2, wherein the process for producing compound A is as follows: A) under the action of n-butyllithium, 2-bromo-1,8-dinaphthyridine is reacted with the formate of R to obtain compound B. B) Compound B is reacted with formaldehyde compound of brominated-L CHO-L-Br to obtain compound A. [4] The manufacturing process according to claim 3, wherein the formate of R is methyl formate of R. [5] Use of the organic electroluminescent material according to claim 1 in organic electroluminescent devices. [6] An organic electroluminescent device comprising an anode, a cathode, and an organic layer, wherein the organic layer comprises at least one of a light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-injection layer, and an electron-transport layer, and at least one of the organic layers contains the organic electroluminescent material according to claim 1. [7] The organic electroluminescent device according to claim 6, wherein the organic layer consists of a light-emitting layer, a hole-injection layer, a hole-transport layer, an electron-injection layer and an electron-transport layer, and the layer in which the organic electroluminescent material is located is the light-emitting layer. [8] The organic electroluminescent device according to claim 7, wherein the organic electroluminescent material is used alone or in combination with other compounds in the light-emitting layer. [9] The organic electroluminescent device according to claim 6, wherein the total thickness of the organic layer is 1-1000nm and the organic layer is formed by a vacuum deposition method, a molecular beam deposition method, a solvent-soluble dip coating method, a bar coating method or an inkjet printing method.

Images