Organic electroluminescent material and its applications

Abstract

Organic electroluminescent material which is the compound of formula (I), where B and X1-X4 are defined so that the organic electroluminescent material is the following compound

Description

Technical area

[0001] The present invention relates to the field of organic electroluminescent materials, in particular to an electroluminescent material containing pyrazine and cyano, and its application. Background of the technology

[0002] In recent years, organic light-emitting diodes (OLEDs) have attracted considerable attention in academia and industry as a lighting and display technology with excellent application prospects. OLEDs feature self-illumination, a wide viewing angle, and a short response time, as well as potential applications in flexible devices. They will be a strong contender in the next generation of display and lighting technologies. Currently, OLEDs still suffer from problems such as low efficiency and short lifetime, so further research is needed.

[0003] Since Forrest et al. reported electrophosphorescent devices (PHOLEDs) in 1998, industrial applications of organic electroluminescent devices have already been realized. Their advantage is that they break the limit of organic electroluminescence quantum efficiency of less than 25% and increase the quantum efficiency to 100%. High-efficiency PHOLED devices typically have a multilayer structure comprising a cathode, an anode, and an organic layer. The organic layer consists of one or more layers of a hole-injection layer, a hole-transport layer, a light-emitting layer, a hole-blocking layer, an electron-injection layer, and an electron-transport layer. Each of these organic layers need not be present, and some organic layers can be added or reduced according to actual conditions.The advantage is that it is convenient to adjust the injection, transfer and recombination of charge carriers to improve the efficiency of transfer and recombination of charge carriers.

[0004] An important aspect of optimizing the performance of organic electroluminescent devices is to promote exciton formation and improve light yield by adjusting charge injection between adjacent functional organic layers. TCNQF4 is often used as a hole-injection layer, effectively promoting hole injection and reducing the operating voltage. However, due to its low molecular weight and good volatility, it is prone to contaminating evaporation equipment and devices during vapor deposition.

[0005] Document EP 2 213 662 A1 discloses an example of an organic electroluminescent material. Content of the invention

[0006] The object of the present invention is to provide an organic electroluminescent material containing pyrazine and cyano, which can effectively reduce the voltage of the device while improving the efficiency.

[0007] Organic electroluminescent material is the compound having the structure of formula (I):where B and X1-X4 are defined so that the organic electroluminescent material is the following compound

[0008] The above-mentioned compound 1 can be used in organic electroluminescent devices, mechanoluminescent devices, organic field-effect transistors, organic solar cells and chemical sensors.

[0009] The present invention does not specifically limit the preparation process of the compound of chemical formula (I). The synthesis and preparation of compound 1 can be as follows: Synthesis route: Synthesis process:

[0010] Reactant 1a (1 eq.) and benzofuran-2-boronic acid ester 1b (2.1 eq.) are reacted under nitrogen protection by a Pd-catalyzed coupling reaction to obtain intermediate 1c. Intermediate 1d is obtained from 1c by an intramolecular ring closure reaction. Compound 1 is then obtained by a condensation reaction.

[0011] It should be understood by those skilled in the art that the above preparation method is merely an illustrative example. Those skilled in the art can obtain other compounds of the present invention by improving the technique.

[0012] The organic electroluminescent device of the present invention comprises a cathode, an anode, and an organic layer, wherein the organic layer consists of one or more layers of a hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron injection layer, and an electron transport layer, and each layer of this organic layer need not be present.

[0013] At least one of the hole injection layer, the hole transport layer, the hole blocking layer, the light emitting layer and / or the electron transport layer contains the compound of formula (I).

[0014] Preferably, the layer in which the compound of structural formula (1) is located is a hole injection layer or an electron transport layer.

[0015] The total thickness of the organic layer of the device of the present invention is 1-1000 nm, preferably 1-500 nm, and more preferably 5-300 nm.

[0016] The organic layer can be formed into a thin film by vapor deposition or a solution process.

[0017] The experimental results show that the organic electroluminescent material of the present invention can effectively reduce the voltage of the device while improving the optoelectric efficiency of the device and is potentially applied in the field of organic electroluminescent devices. Short description of the drawings Fig. 1 is a structural diagram of the organic electroluminescent device of the present invention, wherein 10 is a glass substrate, 20 is an anode, 30 is a hole injection layer, 40 is a hole transport layer, 50 is a light emitting layer, 60 is an electron transport layer, 70 is an electron injection layer and 80 is a cathode. Detailed embodiments

[0018] In the following, the present invention is explained in more detail with reference to the embodiments. Example 1Synthesis of compound 1 Synthesis of intermediate 1c:

[0019] Under nitrogen protection, compound 1a (3.3 g, 10.0 mmol) (see synthesis in patent WO 2007 / 149478), benzofuran-2-borate 1b (5.2 g, 21.0 mmol) (see synthesis in patent US 2009 / 54454), Pd(PPh3)4 (0.58 g, 0.5 mmol), K2CO3 (6.9 g, 50.0 mmol), tetrahydrofuran (30 mL), and water (5 mL) were added sequentially to a Schlenk tube. The reaction mixture was heated to 80°C and allowed to react for 24 hours. After cooling to room temperature, the above reaction liquid was poured into water, and the pH was adjusted to neutral with hydrochloric acid. A light yellow solid then precipitated. Recrystallization from n-hexane and methanol yielded intermediate 1c (2.5 g, yield 62%). Synthesis of compound 1d:

[0020] Under nitrogen protection, compound 1c (1.5 g, 3.8 mmol) was dissolved in oxalyl chloride (20 mL). DMF (0.5 mL) was added dropwise. The mixture was heated to reflux and reacted for 6 hours. Oxalyl chloride was distilled off under reduced pressure. The residue was dissolved in dichloromethane, cooled to 0°C, and aluminum trichloride (20.0 g, 15 mmol) was added. Then, it was gradually warmed to room temperature and stirred for 24 hours. The reaction liquid was added to hydrochloric acid (2 M, 20 mL), stirred for 1 hour, and filtered. A purple solid was obtained (1.1 g, yield 80%). Synthesis of compound 1:

[0021] Under nitrogen protection, compound 1d (1.0 g, 3.8 mmol) and malononitrile (3.3 g, 50 mmol) were dissolved in pyridine (50 mL) and stirred overnight at room temperature. A purple solid was obtained after filtration. Recrystallization from methanol afforded compound 1 (0.6 g, yield 34%). ESI-MS (m / z): 461.1 (M + 1). Example 2

[0022] The organic light-emitting material of the present invention is used to fabricate an electroluminescent device. The structure of the electroluminescent device is shown in Fig. 1 shown.

[0023] First, a transparent conductive ITO glass substrate 10 (with an anode 20 thereon) is washed successively with a detergent solution, deionized water, ethanol, acetone, and deionized water, and then treated with oxygen plasma for 30 seconds.

[0024] Then, a hole-injection layer 30 with a thickness of 10 nm is evaporated onto ITO. The hole-injection layer consists of a doped composition of compound 1 (3%) and HT1 (97%).

[0025] Then, the compound HT1 is evaporated to form a hole transport layer 40 with a thickness of 40 nm.

[0026] Then, a light-emitting layer 50 with a thickness of 30 nm is evaporated onto the hole-transport layer. The light-emitting layer consists of a doped composition of Ir(PPy)3 (10%) and CBP (90%).

[0027] Thereafter, the compound AlQ3 with a thickness of 50 nm is evaporated as an electron transport layer 60 on the light-emitting layer.

[0028] Finally, 1nm LiF is deposited as an electron injection layer 70 and 100nm Al as a device cathode 80. Comparison example

[0029] HT1 with a thickness of 10 nm is deposited as a hole-injection layer, and the remaining layers are the same as described in Example 2. The organic light-emitting devices are fabricated using the same process.

[0030] The structural formulas of the compounds in the device are listed as follows:

[0031] The performance parameters of the organic electroluminescent device in Example 2 and Comparative Example are shown in the following table: Light-emitting device Hole injection layer Maximum power efficiency (lm / W) Turn-on voltage (V) Fluorescent paint Example 2 Compound 1 (3%) / HT 1 (97%) 51.2 3.2 Green light Comparison example HT1 37.8 3.9 Green light

[0032] Under the same conditions, the power efficiency of the organic electroluminescent device prepared by doping with the compound of the present invention is significantly better than the comparative example, and the turn-on voltage can be reduced, which is of great importance for optimizing the performance of the organic optoelectronic devices.

Claims

[1] Organic electroluminescent material which is the compound of formula (I), where B and X1-X4 are defined so that the organic electroluminescent material is the following compound [2] An organic electroluminescent device comprising a cathode, an anode and an organic layer, wherein the organic layer consists of one or more layers of a hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron injection layer and an electron transport layer, and the organic layer contains the organic electroluminescent material according to claim 1. [3] The organic electroluminescent device according to claim 2, wherein the layer of the organic electroluminescent material is a hole injection layer or an electron transport layer, and the organic electroluminescent material is used alone or in combination with other compounds. [4] The organic electroluminescent device according to claim 2, wherein the total thickness of the organic layer is 1 to 1000 nm and the organic layer is formed into a thin film by vapor deposition or a solution method.

Images