Thermal activation delayed fluorescent material based on acenaphthene quinoxaline dinitrile, red light electroluminescent device and preparation method of red light electroluminescent device

Abstract

The invention relates to a thermally activated delayed fluorescent material based on acenaphthene quinoxaline dinitrile, a red light electroluminescent device and a preparation method of the red light electroluminescent device. A molecular structure is optimized, so that the ANQDC-BiCzPh and the ANQDC-tPTZ are obtained. 26.7% of external quantum efficiency is achieved through a bicarbazole group, and the doping concentration is 5-30 wt%; the efficiency of the latter roll down to 14.7% under the brightness of 100 cd / m < 2 > by using phenothiazine groups, and 10-90 wt% doping is supported. The two compounds have the advantages of high thermal stability, simple synthesis, high yield and low cost. The materials are used for red light electroluminescent devices, so that the brightness of the devices reaches 4946 cd / m < 2 > when the turn-on voltage is less than or equal to 3.6 V, the maximum emission wavelength is 565-714 nm, and the color purity is high. The technology solves the problems of fast efficiency attenuation and narrow process window of a traditional red light OLED, and is suitable for the fields of flexible display, Micro-LED and high-brightness illumination.

Description

Technical Field

[0001] The present invention relates to the technical field of organic light-emitting materials, and in particular, to a thermally activated delayed fluorescence material based on acenaphthoquinoxaline dinitrile, a red organic light-emitting device, and a preparation method thereof. Background Art

[0002] In the fields of display and lighting, organic light-emitting diode (OLED) technology has attracted much attention due to its characteristics such as not relying on a backlight source and active light emission. However, current OLED devices mainly rely on fluorescent materials and thermally activated delayed fluorescence (TADF) materials as the light-emitting layer, and their performance limitations are gradually emerging. Traditional fluorescent materials are limited by the spin statistics rule, and the theoretical maximum internal quantum efficiency is only 25%, which is difficult to meet the application requirements of high brightness and high efficiency. Although TADF materials can theoretically achieve 100% internal quantum efficiency through the reverse intersystem crossing (RISC) mechanism, there are still significant problems in actual applications, which limit their wide application in the fields of high-end display and lighting.

[0003] First of all, existing TADF materials generally show a serious efficiency roll-off phenomenon at high brightness. For example, when the brightness increases from 1 cd / m 2 to 100 cd / m 2 , the external quantum efficiency often drops by more than 50%. This efficiency roll-off stems from the bimolecular loss mechanism under high excitation density, resulting in unstable device performance and shortened lifespan during high-brightness operation, directly affecting the user experience of high-end display devices (such as large-screen TVs) and lighting products. Secondly, the synthesis process of TADF materials is complex, usually involving multiple steps of reactions and expensive raw materials, with difficult purification and high production costs. These factors significantly increase the industrialization difficulty of device preparation and limit their popularity in cost-sensitive markets.

[0004] In addition, the design of red TADF materials faces greater challenges. Since red light materials usually have a relatively wide singlet-triplet energy gap, the reverse intersystem crossing rate is slow, the utilization efficiency of triplet excitons is low, and the non-radiative loss increases due to the energy gap law, making the development of highly efficient red TADF materials particularly difficult. At the same time, the molecular structure of red light materials is complex, and the synthesis difficulty is further increased, limiting their practical application in full-color displays, especially in fields that require precise color performance, such as medical displays and professional graphic design, where the deficiency of red light performance has become a technical bottleneck.

[0005] Therefore, the above-mentioned defects of existing luminescent materials, namely high efficiency roll-off, complex synthesis process, and insufficient red light performance, seriously hinder the further development of OLED technology in high-performance applications. Developing a red TADF material with high fluorescence quantum yield, low efficiency roll-off characteristics, and easy synthesis can not only improve the stability and lifespan of devices at high brightness but also promote the industrialization process of OLED technology in the fields of high-end display and lighting, which has important research significance and application value. Summary of the Invention

[0006] The present invention discloses a thermally activated delayed fluorescence material based on acenaphthoquinoxaline dinitrile, a red electro-luminescent device, and a preparation method thereof. The aim is to solve the problems existing in existing red TADF materials, such as low luminescence efficiency and severe efficiency roll-off when brightness is increased. At the same time, it overcomes the problems of cumbersome synthesis and preparation steps, high raw material costs, complex synthesis and purification processes, low yield, and difficulty in large-scale production of existing red TADF materials. Among them, the device prepared from molecule 1 achieved a high external quantum efficiency (EQE) of 26.7%, significantly improving the luminescence performance of the device; while the device prepared from molecule 2 exhibited low efficiency roll-off characteristics, with an efficiency roll-off of only 14.7% at a brightness of 100 cd / m 2 When the brightness is 100 cd / m², the efficiency roll-off is only 14.7%, effectively reducing the decrease in efficiency as brightness increases. The excellent characteristics of these two molecules, as well as their co-design through ΔE ST optimization and doping compatibility breakthrough, jointly contribute to the improvement of the efficiency and stability of red OLEDs, providing strong support for enhancing the performance of electro-luminescent devices and showing good application prospects in the field of electro-luminescent devices.

[0007] The present invention provides a thermally activated delayed fluorescence material based on acenaphthoquinoxaline dinitrile molecules, and its structural general formula is shown as follows:

[0008]

[0009] wherein R is 9-phenyl-3,3'-bicarbazole or 3,6-di-tert-butylphenothiazine respectively, corresponding to two compounds 3-(9'-phenyl-9H,9'H-[3,3'-bicarbazole]-9-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC-BiCzPh) and 3-(3,7-di-tert-butyl-10H-phenothiazine-10-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC-tPTZ), and their structural formulas are shown in the following figure:

[0010]

[0011] The material needs to satisfy at least one of the following characteristics: (1) singlet-triplet energy level difference ΔE ST≤0.15 eV, for example: ΔE of ANQDC - BiCzPh ST is +0.13 eV (Example 6), and ΔE of ANQDC - tPTZ ST is -0.05 eV (Example 7); (2) In the light - emitting layer of an organic electroluminescent device, when the doping concentration is 10 - 90 wt%, the external quantum efficiency (EQE) ≥ 20%. Among them, the EQE of ANQDC - BiCzPh reaches 26.7% at a doping concentration of 25 wt% (Example 10), and the EQE of ANQDC - tPTZ is 9.2% at the same concentration (Example 11), but the efficiency roll - off of the latter drops to 14.7% at a brightness of 100 cd / m 2 brightness.

[0012] The present invention provides a light - emitting layer formed by doping a host material (such as mCP) with an acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence material. The doping concentration is 5 - 90 wt%, preferably 25 - 90 wt%, which refers to the mass percentage of the acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence material in the total amount of the light - emitting layer. This light - emitting layer exhibits excellent optoelectronic properties, such as high external quantum efficiency (EQE) and low efficiency roll - off.

[0013] In a further preferred technical solution:

[0014] The preferred solution for ANQDC - BiCzPh is: R is 9 - phenyl - 3,3'-bicarbazole, and the external quantum efficiency (EQE) ≥ 25% at a doping concentration of 5 - 30 wt% (Example 10);

[0015] The preferred solutions for ANQDC - tPTZ include:

[0016] (a) R is 3,6 - di - tert - butylphenothiazine, and the singlet - triplet energy level difference ΔE ST ≤0 eV (Example 7);

[0017] (b) At a doping concentration of 10 - 90 wt%, the efficiency roll - off ≤ 15% at a brightness of 100 cd / m 2 (Example 11);

[0018] (c) At a high doping concentration of 25 - 90 wt%, the maximum emission wavelength ≥ 650 nm (696 nm in Example 11). The compound ANQDC - BiCzPh achieves high EQE and narrow full - width at half - maximum through the rigid conjugate structure of the bicarbazole group, while ANQDC - tPTZ utilizes the strong electron - donating effect of the phenothiazine group and the steric hindrance of the tert - butyl group to break through the traditional ΔE ST limit (ΔE ST≤0 eV), significantly suppressing the efficiency roll-off at high brightness. Through the design of differentiated substituents, they respectively target the efficiency and stability bottlenecks of red OLEDs, forming complementary technical solutions.

[0019] The present invention provides a red electro-luminescent device based on acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence materials, the structure of which includes the following functional layers:

[0020] 1. Overall structure of the electro-luminescent device

[0021] The overall structure of the electro-luminescent device includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), an electron / exciton blocking layer (EBL), an emission layer (EML), another electron / exciton blocking layer (EBL), an electron transport layer (ETL), an electron injection layer (EIL), and a cathode. The emission layer of the red electro-luminescent device is prepared by doping a host material (such as mCP) with acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence materials (ANQDC-BiCzPh or ANQDC-tPTZ).

[0022] 2. Host material of the electro-luminescent device

[0023] In the present invention, the host material is a bipolar fluorescent material, specifically 1,3-bis(9H-carbazol-9-yl)benzene (mCP). The bipolar material has excellent electron and hole transport capabilities, can effectively balance the injection and transport of carriers, thereby improving the luminescence efficiency and stability of the device. The energy level structure of mCP matches well with ANQDC-BiCzPh and ANQDC-tPTZ, enabling efficient energy transfer and exciton utilization.

[0024] The diode includes an anode layer, a hole injection layer, at least one hole transport layer, an emission layer, at least one electron transport layer, an electron injection layer, and a cathode layer stacked in sequence.

[0025] 3. Materials and functions of each layer of the electro-luminescent device

[0026] For the electro-luminescent device based on 3-(9'-phenyl-9H,9'H-[3,3'-bicarbazole]-9-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC-BiCzPh) and 3-(3,7-di-tert-butyl-10H-phenothiazin-10-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC-tPTZ) red thermally activated delayed fluorescence materials disclosed in the present invention, the materials and functions of each layer are as follows:

[0027] Anode: Indium tin oxide (ITO).

[0028] Hole injection layer (HIL): Dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HATCN).

[0029] Hole transport layer (HTL): 4,4'-(Cyclohexane-1,1-diyl)bis(N,N-di-p-toluidine) (TAPC).

[0030] Electron / exciton blocking layer (EBL): Tris(4-(9H-carbazol-9-yl)phenyl)amine (TCTA) and 1,3-bis(9H-carbazol-9-yl)benzene (mCP).

[0031] Emitting layer (EML): Formed by doping mCP host material with ANQDC-BiCzPh or ANQDC-tPTZ as guest materials, with a doping concentration of 5 - 90 wt%, preferably 25 - 90 wt%.

[0032] Hole / exciton blocking layer (EBL): 2,2',2"-(1,3,5-Benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi).

[0033] Electron transport layer (ETL): Tris[3-(3-pyridyl)mesityl]borane (3TPYMB).

[0034] Electron injection layer (EIL): Lithium fluoride (LiF).

[0035] Cathode: Aluminum (Al).

[0036] 4. Specific specifications of each layer of the device

[0037] As an example, the specifications of each layer of the organic electroluminescent device are as follows:

[0038] ITO (anode): The thickness is a conventional value (usually 100 - 150 nm).

[0039] HATCN (hole injection layer): 5 nm.

[0040] TAPC (hole transport layer): 20 nm.

[0041] TCTA (electron / exciton blocking layer): 5 nm.

[0042] mCP (electron / exciton blocking layer): 5 nm.

[0043] mCP:TADF material (emitting layer): 20 nm, with a doping concentration of 25 - 90 wt%.

[0044] TPBi (hole / exciton blocking layer): 10 nm.

[0045] 3TPYMB (Electron Transport Layer): 55 nm.

[0046] LiF (Electron Injection Layer): 1 nm.

[0047] Al (Cathode): 200 nm.

[0048] The preparation method of this device uses conventional techniques, such as vacuum evaporation. The specific process parameters are as follows: the vacuum degree ≤ 2×10 -4 Pa; the deposition rates are for the functional layers host material LiF layer and Al layer The selection and preparation parameters of each layer of materials have been optimized to ensure the best device performance. In particular, the mass percentage of the multi-resonant small molecule luminescent material in the light-emitting layer is set to 5% - 90%, and its thickness range is 10 nm to 200 nm.

[0049] The specific preparation process is as follows: sequentially prepare a hole injection layer, a hole transport layer, an electron / exciton blocking layer, a light-emitting layer, another electron / exciton blocking layer, an electron transport layer, an electron injection layer, and a cathode on the anode, and finally complete the fabrication of a red electro-luminescent device based on acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence material.

[0050] In a further preferred technical solution, the preparation process includes the following steps:

[0051] (1) Sequentially vacuum deposit a hole injection layer, a hole transport layer, and an electron / exciton blocking layer on the anode;

[0052] (2) Deposit the light-emitting layer, where the doping concentration of the fluorescent material is 5 - 90 wt%;

[0053] (3) Continue to deposit a hole / exciton blocking layer, an electron transport layer, an electron injection layer, and a cathode;

[0054] Among them, the deposition rate of the functional layer is the deposition rate of the host material is the deposition rate of the LiF layer is the deposition rate of the Al layer is

[0055] An application of acenaphthoquinoxaline dinitrile small molecule luminescent material in electro-luminescence. The electro-luminescent device of the present invention shows good application prospects in the fields of display and lighting, especially maintaining high efficiency and stable performance even at high brightness.

[0056] Experimental data show that the device fabricated with ANQDC-BiCzPh achieved an external quantum efficiency (EQE) of 26.7%, while the device fabricated with ANQDC-tPTZ had an efficiency roll-off of only 14.7% at a brightness of 100 cd / m 2 ².

[0057] Advantages of the present invention compared with the prior art:

[0058] The present invention proposes a red organic light-emitting device based on an acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence material, which exhibits significant advantages in many aspects. First of all, in terms of performance, an external quantum efficiency as high as 26.7% is achieved, and the efficiency roll-off is reduced to 14.7% at high brightness, far superior to the prior art. Its excellent luminescence performance and high fluorescence quantum yield enable the excited-state energy to be more effectively converted into photons while maintaining a stable luminescence effect. In addition, the material has a wide doping concentration range (5 - 90 wt%), as well as good thermal stability (Td5% up to 425 °C and 454 °C), supporting the requirements of different application scenarios.

[0059] In terms of the synthesis process, the present invention adopts a simplified synthesis route with a relatively high yield, reducing costs, and using conventional commercially available raw materials, which is environmentally friendly and suitable for large-scale production. The energy levels are well matched, and efficient energy transfer and exciton utilization are achieved in cooperation with the host material, improving the luminescence efficiency. In particular, its microsecond-level delayed fluorescence lifetime indicates efficient thermally activated delayed fluorescence characteristics, further improving the device efficiency.

[0060] In terms of device design, by optimizing the selection of materials and thickness design for each layer, the injection, transport, and recombination processes of carriers are effectively balanced, thus improving the overall performance. The maximum emission wavelengths are 565 nm and 696 nm respectively, meeting the requirements of red OLEDs, while the narrow full width at half maximum ensures excellent color purity. In addition, the present invention also demonstrates a low turn-on voltage, a long device lifetime, and adjustable luminescence characteristics, suitable for high-brightness, high-efficiency, and long-life red OLED applications, with broad application prospects and high scalability. Description of the Drawings

[0061] Figure 1 It is the thermogravimetric curve diagram of Example 1 and Example 2 of the present invention.

[0062] Figure 2 It is the ultraviolet-visible absorption spectrum diagram of Example 1 of the present invention in n-hexane, toluene, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, methanol, and N,N-dimethylformamide solutions.

[0063] Figure 3It is the UV-Vis absorption spectrum of Example 2 of the present invention in n-hexane, toluene, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, methanol and N,N-dimethylformamide solutions.

[0064] Figure 4 It is the molecular structure diagram of the host material mCP.

[0065] Figure 5 It is the fluorescence and phosphorescence emission spectra of Example 1 of the present invention doped with 25 wt% in the host material mCP at 77K.

[0066] Figure 6 It is the fluorescence and phosphorescence emission spectra of Example 2 of the present invention doped with 25 wt% in the host material mCP at 77K.

[0067] Figure 7 It is the transient fluorescence and delayed fluorescence lifetime diagrams of Example 1 of the present invention doped with 25 wt% in the host material mCP.

[0068] Figure 8 It is the transient fluorescence and delayed fluorescence lifetime diagrams of Example 2 of the present invention doped with 25 wt% in the host material mCP.

[0069] Figure 9 It is the organic light-emitting diode device structure and energy level diagram of Example 10 of the present invention.

[0070] Figure 10 It is the organic light-emitting diode device structure and energy level diagram of Example 11 of the present invention.

[0071] Figure 11 It is the current density-voltage-brightness curve of the organic light-emitting diode of Example 10 of the present invention.

[0072] Figure 12 It is the current density-voltage-brightness curve of the organic light-emitting diode of Example 11 of the present invention.

[0073] Figure 13 It is the brightness-external quantum efficiency curve of the organic light-emitting diode of Example 10 of the present invention.

[0074] Figure 14 It is the brightness-external quantum efficiency curve of the organic light-emitting diode of Example 11 of the present invention.

[0075] Figure 15 It is the electroluminescence spectrum of the organic light-emitting diode of Example 10 of the present invention.

[0076] Figure 16 It is the electroluminescence spectrum of the organic light-emitting diode of Example 11 of the present invention. Detailed implementation mode

[0077] The raw materials involved in the present invention are all commercially available products, and the specific operation methods and testing methods are conventional methods in the art; in particular, the specific preparation process of the electroluminescent device based on the thermally activated delayed fluorescence red light material of acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile receptor of the present invention and the materials of each layer are prior art, such as vacuum evaporation, and the vacuum degree ≤ 2×10 -4 Pa, and the deposition rate of the functional layer is The deposition rate of the host material is The deposition rate of the LiF layer is The deposition rate of Al

[0078] The creativity of the present invention lies in providing a thermally activated delayed fluorescence material based on acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile receptor to prepare an OLED device with high external quantum efficiency and low efficiency roll-off. To further understand the present invention, the preferred implementation modes of the present invention are described below in conjunction with embodiments, but it should be understood that these

[0079] The present invention provides a thermally activated delayed fluorescence material based on acenaphthoquinoxaline dinitrile, and the structural general formula is as follows:

[0080]

[0081] wherein R is 9-phenyl-3,3'-bicarbazole or 3,6-di-tert-butylphenothiazine respectively, corresponding to two compounds 3-(9'-phenyl-9H,9'H-[3,3'-bicarbazole]-9-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC-BiCzPh) and 3-(3,7-di-tert-butyl-10H-phenothiazin-10-yl)acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (ANQDC-tPTZ), and their structural formulas are shown in the following figure:

[0082]

[0083] In the present invention, the acenaphthoquinoxaline dinitrile thermally activated delayed fluorescence material is ANQDC-BiCzPh or ANQDC-tPTZ.

[0084] Using 11-fluorobipyridine[3,2-a:2',3'-c]phenazine and 9,9-dimethyl-9,10-dihydroacridine as raw materials, ANQDC-BiCzPh is prepared by reaction; using 11,12-fluorobipyridine[3,2-a:2',3'-c]phenazine and 9,9-dimethyl-9,10-dihydroacridine as raw materials, ANQDC-tPTZ is prepared by reaction.

[0085] Example 1: The synthetic route of ANQDC-BiCzPh is as follows:

[0086]

[0087] Step 1: Mix 5-bromoacenaphthylene-1,2-dione (2.14 g, 8.5 mmol), hydrochloric acid (7 mL), tetrahydrofuran (70 mL), ethanol (70 mL) and 4,5-diaminophthalonitrile (1.96 g, 12.4 mmol), and heat the reaction system at 40 °C for 18 hours. After the reaction is completed, cool the system to room temperature and collect the generated precipitate by filtration. Subsequently, wash the precipitate with ethanol to remove residual impurities. Finally, dry the precipitate under vacuum to obtain a brown powdery product (2.82 g, yield 87%).

[0088] Step 2: Mix tris(dibenzylideneacetone)dipalladium (229 mg, 0.25 mmol), 2,2'-(diphenylphosphino)diphenyl ether (162 mg, 0.30 mmol), cesium carbonate (4.07 g, 12.5 mmol), xylene (60 mL), 3-bromobenzo[3,4]indeno[1,2-b]quinoxaline-9,10-dicarbonitrile (955 mg, 2.5 mmol) and 9-phenyl-3,3'-bicarbazole (1.43 g, 3.5 mmol). Under a nitrogen atmosphere, heat the reaction mixture to 130 °C and stir for 24 hours. After the reaction is completed, cool to room temperature, extract the reaction mixture with brine and dichloromethane (3 × 60 mL), and dry with anhydrous sodium sulfate. After removing the solvent, purify by silica gel column chromatography using dichloromethane / petroleum ether (1:1, v:v) as the eluent to obtain an orange powder (763 mg, yield 43%).

[0089] The nuclear magnetic resonance spectrum of ANQDC-BiCzPh is as follows: 11H NMR (600 MHz, DMF) δ (ppm): 9.07 (d, J = 6.4 Hz, 1H), 8.88 (s, 1H), 8.83 (d, J = 7.1 Hz, 1H), 8.78 (s, 1H), 8.67 (d, J = 6.9 Hz, 1H), 8.55 (d, J = 7.7 Hz, 1H), 8.42 (d, J = 7.7 Hz, 1H), 8.38 (d, J = 7.5 Hz, 1H), 8.01 (d, J = 7.1 Hz, 2H), 7.95 (d, J = 8.1 Hz, 1H), 7.92 (dd, J = 8.3, 2.9 Hz, 2H), 7.80 (d, J = 8.3 Hz, 1H), 7.79 (d, J = 3.0 Hz, 3H), 7.62 (dq, J = 6.1, 3.1 Hz, 1H), 7.55 (d, J = 8.5 Hz, 1H), 7.47 (ddd, J = 30.5, 14.1, 8.2 Hz, 5H), 7.36 (dd, J = 7.9, 5.3 Hz, 2H). MALDI-TOF: Found at 710.2213.

[0090] Example 2: The synthetic route of ANQDC-tPTZ is as follows:

[0091]

[0092] Step 1: Mix 5-bromoacenaphthylene-1,2-dione (2.14 g, 8.5 mmol), hydrochloric acid (7 mL), tetrahydrofuran (70 mL), ethanol (70 mL), and 4,5-diaminophthalonitrile (1.96 g, 12.4 mmol), and heat the reaction system at 40 °C for 18 hours. After the reaction is completed, cool the system to room temperature and collect the resulting precipitate by filtration. Subsequently, wash the precipitate with ethanol to remove residual impurities. Finally, dry the precipitate under vacuum to obtain a brown powder product (2.82 g, yield 87%).

[0093] Step 2: Under a nitrogen atmosphere, maintain the reaction temperature at 0 °C and slowly add tert-butyl chloride (3.33 mL, 3.2 mmol) dropwise to a stirred mixture of phenothiazine (200 mg, 1 mmol) and anhydrous aluminum chloride (400 mg, 3 mmol) in anhydrous dichloromethane (4 mL). After the addition is complete, continue to stir the mixture at 0 °C for 15 minutes. Subsequently, carry out hydrolysis treatment by adding water (1 L) and sodium acetate. The crude product is extracted with dichloromethane (3 × 60 mL), and then the organic layer is separated from the water. Wash the organic layer with water to remove the residual aqueous phase, and then dry it with anhydrous sodium sulfate. Concentrate the dried organic layer under vacuum. Finally, recrystallize the product three times from n-hexane to obtain a white solid (149 mg, yield 48%).

[0094] Step 3: Mix tris(dibenzylideneacetone)dipalladium(0) (229 mg, 0.25 mmol), 2,2'-(diphenylphosphino)diphenylether (162 mg, 0.30 mmol), cesium carbonate (4.07 g, 12.5 mmol), xylene (60 mL), 3-bromobenzo[3,4]indeno[1,2-b]quinoxaline-9,10-dicarbonitrile (955 mg, 2.5 mmol) and 3,6-di-tert-butylphenothiazine (1.09 g, 3.5 mmol). Under a nitrogen atmosphere, heat the reaction mixture to 130 °C and stir continuously for 24 h. After completion of the reaction, cool to room temperature, extract the reaction mixture with brine and dichloromethane (3 × 60 mL), and dry over anhydrous sodium sulfate. After removal of the solvent, purify by silica column chromatography using dichloromethane / petroleum ether (1:1, v:v) as the eluent to obtain a red powder (935 mg, yield 61%).

[0095] The NMR spectrum of ANQDC-tPTZ is as follows: 1 HNMR (400 MHz, CD2Cl2) δ (ppm): 8.69 (d, J = 4.0 Hz, 3H), 8.53 (d, J = 7.0 Hz, 1H), 8.36 (d, J = 8.4 Hz, 1H), 8.07 (s, 1H), 7.88 (t, J = 7.7 Hz, 1H), 7.15 (s, 2H), 6.80 (s, 2H), 6.13 (s, 2H), 1.22 (s, 18H). 13 C NMR (101 MHz, CD2Cl2) δ (ppm): 158.78, 157.97, 143.75, 143.67, 138.27, 138.24, 132.30, 131.75, 131.32, 129.44, 126.09, 125.70, 125.15, 116.85, 116.68, 114.90, 114.86. MALDI-TOF: found at 613.2295.

[0096] Example 3: Heat the compounds ANQDC-BiCzPh and ANQDC-tPTZ in Examples 1 and 2 at a rate of 10 °C / min in the range of 50 - 800 °C under N 2 protection, and measure the thermogravimetric curve using a differential scanning calorimeter of model DSC 204. It can be Figure 1 seen that the temperature at which the compound ANQDC-BiCzPh decomposes with a 5% weight loss is 425 °C, and the temperature at which the compound ANQDC-tPTZ decomposes 5% is 454 °C, indicating that the two materials have good thermal stability.

[0097] Example 4: Test on the ultraviolet-visible light absorption performance of compound ANQDC-BiCzPh in different solutions. Compound ANQDC-BiCzPh was dissolved in n-hexane, toluene, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, methanol and N,N-dimethylformamide solutions (with a concentration of 10 -5 M), and the ultraviolet-visible light absorption performance in different solutions was tested using an ultraviolet-visible absorption spectrometer. As Figure 2 shown, with the increase in solvent polarity, there was no obvious change in the ultraviolet-visible light absorption spectrum of compound ANQDC-BiCzPh.

[0098] Example 5: Test on the ultraviolet-visible light absorption performance of compound ANQDC-tPTZ in different solutions. Compound ANQDC-tPTZ was dissolved in n-hexane, toluene, dichloromethane, chloroform, tetrahydrofuran, acetonitrile, methanol and N,N-dimethylformamide solutions (with a concentration of 10 -5 M), and the ultraviolet-visible light absorption performance in different solutions was tested using an ultraviolet-visible absorption spectrometer. As Figure 3 shown, with the increase in solvent polarity, there was no obvious change in the ultraviolet-visible light absorption spectrum of compound ANQDC-tPTZ.

[0099] Example 6: Energy level test of the doped film of compound ANQDC-BiCzPh. The host material mCP (as Figure 4 shown) and compound ANQDC-BiCzPh were mixed at a mass ratio of 3:1 and dissolved in dichloromethane, and then spin-coated using a film spin coater. The ITO glass plate used was washed and then subjected to plasma treatment. The prepared doped film was used to test the fluorescence spectrum and phosphorescence spectrum of the film at 77K in the range of 390nm - 800nm using a FLS1000, and the gate setting of the phosphorescence spectrum was 5ms. Tangents were made to the fluorescence spectrum and phosphorescence spectrum at 77K respectively to obtain the S1 and T1 energy levels of compound ANQDC-BiCzPh. As Figure 5 shown, S1 was 2.56eV, T1 was 2.43eV, and the energy level difference was 0.13eV, meeting the energy level requirements of thermally activated delayed fluorescence molecules.

[0100] Example 7: Energy level test of the doped film of compound ANQDC-tPTZ. The host material mCP (as Figure 3As shown in the figure, the compound ANQDC-tPTZ is mixed with a mass ratio of 3:1 and dissolved in dichloromethane, and then spin-coated using a film spin coater. The ITO glass plate used is washed and then subjected to plasma treatment. The prepared doped film is tested for its fluorescence spectrum and phosphorescence spectrum at 77K in the range of 390nm - 800nm using a FLS1000, and the gate setting for the phosphorescence spectrum is 5ms. Tangents are drawn for the fluorescence spectrum and phosphorescence spectrum at 77K respectively to obtain the S1 and T1 energy levels of the compound ANQDC-tPTZ. As Figure 6 shown, S1 is 2.18eV, T1 is 2.23eV, and the energy level difference is -0.05eV. Since the energy level difference is negative, the reverse intersystem crossing rate can be significantly accelerated, reducing the efficiency roll-off problem caused by increased brightness.

[0101] Example 8: Measurement of the delayed fluorescence lifetime of the compound ANQDC-BiCzPh doped film. The film preparation method is the same as in Example 6. Using the VPL 375 laser of FLS1000, with a slit width of 2nm, the test time range is 1ms, and the test temperature is 25°C at room temperature. The delayed fluorescence lifetime is determined by double exponential fitting. As Figure 7 shown, the delayed fluorescence lifetime of the compound ANQDC-BiCzPh doped film is 133.08μs, reaching the microsecond level, indicating that it has thermally activated delayed fluorescence.

[0102] Example 9: Measurement of the delayed fluorescence lifetime of the compound ANQDC-tPTZ doped film. The film preparation method is the same as in Example 7. Using the VPL 375 laser of FLS1000, with a slit width of 5nm, the test time range is 1ms, and the test temperature is 25°C at room temperature. The delayed fluorescence lifetime is determined by double exponential fitting. As Figure 8 shown, the delayed fluorescence lifetime of the compound ANQDC-tPTZ doped film is 6.37μs, reaching the microsecond level, indicating that it has thermally activated delayed fluorescence.

[0103] Example 10: The preparation steps of the organic light-emitting diode in this example are as follows:

[0104] Step 10-1: Clean the conductive ITO glass with a cleaning agent, dry it, and then subject it to ozone treatment for 30 minutes, and transfer it to a glove box filled with nitrogen for standby;

[0105] Step 10-2: Under high vacuum (1X 10 -6In an environment of Pa), a HATCN hole injection layer, a TAPC hole transport layer, a TCTA electron blocking layer, an mCP electron blocking layer, a light-emitting layer, a TPBi hole blocking layer, a 3TPYMB electron transport layer, a LiF electron injection layer, and an Al cathode layer were sequentially evaporated onto the ITO anode layer; among them, the light-emitting layer includes a host material mCP (75%) and ANQDC-BiCzPh (25%). Two devices were fabricated respectively, where device A has a TPBi hole blocking layer, while device B does not have a TPBi hole blocking layer. Thus, the structure of the organic light-emitting diode device A prepared is: ITO / HATCN(5nm) / TAPC(20nm) / TCTA(5nm) / mCP(5nm) / light-emitting layer(20nm) / TPBi(10nm) / 3TPYMB(55nm) / LiF(1nm) / Al(200nm); the structure of the organic light-emitting diode device B is: ITO / HATCN(5nm) / TAPC(20nm) / TCTA(5nm) / mCP(5nm) / light-emitting layer(20nm) / 3TPYMB(55nm) / LiF(1nm) / Al(200nm).

[0106] Step 10-3, testing of the OLED device: After the overall fabrication of the device is completed, the vacuum chamber of the vacuum coating machine needs to cool down naturally for 30 minutes, and then the molecular pump and the mechanical pump are turned off in sequence. Finally, the device is taken out from the vacuum chamber, and a spectrophotometer CS200 and a power meter Keithley 236 are used to test the voltage-current-brightness data of the device. Then, a spectrophotometer PR705 is used to test the electroluminescence spectrum (EL) and color coordinates (CIE) of the device. Using the above data, the current density, current efficiency, power efficiency, and external quantum efficiency of the device under different driving voltages are calculated, and key performance data such as current density-voltage-brightness, current density-external quantum efficiency, and electroluminescence spectrum are obtained.

[0107] Example 11: In this example, on the basis of Example 10, step 10-2 is replaced with step 11-2: In a high vacuum (1X10 -6In the environment of Pa), a HATCN hole injection layer, a TAPC hole transport layer, an mCP electron blocking layer, a light-emitting layer, a TPBi hole blocking layer, a 3TPYMB electron transport layer, a TCTA electron blocking layer, a LiF electron injection layer, and an Al cathode layer are sequentially evaporated onto the ITO anode layer. Two devices are fabricated respectively. The light-emitting layer of device C includes a host material mCP (75%) and ANQDC-tPTZ (25%), while the light-emitting layer of device D includes a host material mCP (10%) and ANQDC-tPTZ (90%). The structures of the organic light-emitting diode devices C and D prepared thereby are: ITO / HATCN(5nm) / TAPC(20nm) / TCTA(5nm) / mCP(5nm) / light-emitting layer(20nm) / TPBi(10nm) / 3TPYMB(55nm) / LiF(1nm) / Al(200nm).

[0108] Figure 9 and Figure 10 are the device structures and energy level diagrams of the above-mentioned Examples 10 - 11. Figure 11 and Figure 12 are the current density-voltage-luminance curves of the organic light-emitting diodes of the above-mentioned Examples 10 and 11. As can be seen from the figure, the turn-on voltages of the organic light-emitting diodes A and B of Example 10 are 3.5V and 3.6V respectively; the maximum luminances reach 4946 cd / m 2 and 2989 cd / m 2 respectively. The turn-on voltages of the organic light-emitting diodes C and D of Example 11 are both 4.8V; the maximum luminances reach 1221 cd / m 2 and 542 cd / m 2

[0109] Figure 13 and Figure 14 are the luminance-external quantum efficiency curves of the organic light-emitting diodes of Examples 10 and 11. As can be seen from the figure, the maximum external quantum efficiencies of the organic light-emitting diodes A and B of Example 10 are 26.7% and 24.6% respectively, and the maximum external quantum efficiencies of the organic light-emitting diodes C and D of Example 11 are 9.2% and 4.6% respectively. And when the luminance is 100 cd / m 2 , the efficiency roll-off is only 14.7% and 31.9%.

[0110] Figure 15 and Figure 16Electroluminescence spectra of the organic light-emitting diodes of Example 10 and Example 11. As can be seen from the figure, the maximum emission wavelengths of the electroluminescence of the organic light-emitting diodes A and B of Example 10 are 565 nm and 577 nm respectively, and the maximum emission wavelengths of the electroluminescence of the organic light-emitting diodes C and D of Example 11 are 696 nm and 714 nm respectively.

[0111] Although the present disclosure is disclosed as above, the scope of protection of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A thermally activated delayed fluorescent material based on an acenaphthenequinoxaline dinitrile skeleton, characterized in that: The general structural formula I is as follows: wherein R is selected from a 9-phenyl-3,3'-bicarbazole group or a 3,6-di-tert-butylphenothiazine group; The material meets at least one of the following characteristics: (a) Singlet-triplet energy level difference (ΔE ST )≤0.15eV; (b) In the light-emitting layer of an organic electroluminescent device, when the doping concentration is 10-90 wt %, the external quantum efficiency (EQE) is ≥ 20%.

2. The fluorescent material according to claim 1, wherein: R is 9-phenyl-3,3'-bicarbazole group, and the corresponding compound is ANQDC-BiCzPh; or R is 3,6-di-tert-butyl phenothiazine group, and the corresponding compound is ANQDC-tPTZ; 3. The fluorescent material according to claim 1, characterized in that: R is a 9-phenyl-3,3'-bicarbazole group, and when the doping concentration of the material in the light-emitting layer is 5-30wt%, the external quantum efficiency (EQE) is ≥25%.

4. The fluorescent material according to claim 1, characterized in that: R is a 3,6-di-tert-butylphenothiazine group and satisfies at least one of the following: (a) Singlet-triplet energy level difference (ΔE ST )≤0eV; (b) At a doping concentration of 10-90wt%, the brightness is 100cd / m 2 The efficiency roll-off is ≤15%; (c) At a doping concentration of 25-90wt%, the maximum emission wavelength is ≥650nm.

5. A light-emitting layer, comprising the fluorescent material according to any one of claims 1 to 4 and a host material, wherein the doping concentration of the fluorescent material is 5-90 wt%.

6. A red light electroluminescent device comprising an anode, a hole injection layer, a hole transport layer, an electron / exciton blocking layer, a light emitting layer, a hole / exciton blocking layer, an electron transport layer, an electron injection layer and a cathode, characterized in that: The light-emitting layer is composed of the light-emitting layer according to claim 5.

7. The device of claim 6, wherein: The hole injection layer is bipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanenitrile; The hole transport layer is 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline); The main material is 1,3-di(9H-carbazole-9-yl)benzene; The electron transport layer is tris[3-(3-pyridyl)-mesityl]borane.

8. The device of claim 6, wherein the thickness of each layer is: Hole injection layer: 5nm; Hole transport layer: 20nm; Light-emitting layer: 20nm; Electron transport layer: 55nm; Electron injection layer: 1nm; Cathode: 200nm.

9. A method for preparing the red light electroluminescent device according to any one of claims 6 to 8, comprising the following steps: (1) vacuum evaporating a hole injection layer, a hole transport layer, and an electron / exciton blocking layer on the anode in sequence; (2) evaporating a light-emitting layer, wherein the doping concentration of the fluorescent material is 5-90wt%; (3) continuing to evaporate the hole / exciton blocking layer, electron transport layer, electron injection layer and cathode; Among them, the evaporation rate of the functional layer is The evaporation rate of the main material is The LiF layer evaporation rate is The Al layer evaporation rate is 10. Use of the fluorescent material according to any one of claims 1 to 4 in preparing a red electroluminescent device, wherein the device is used in the field of display or lighting.

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