Highly efficient thermally activated delayed fluorescence host material, preparation method and application thereof

Abstract

The application provides a high-efficiency thermally activated delayed fluorescence host material and a preparation method and application thereof, belongs to the technical field of organic photoelectric materials, and is obtained by combining 5,7-dihydro-7,7-dimethylindeno[2,1-b]carbazole and 2-(3-bromophenyl)-4,6-diphenyl-1,3,5-triazine, has the advantages of simple synthesis method, easily obtained raw materials, stable material structure, easy storage, and the like. The synthesized thermally activated delayed fluorescence host material is applied to an OLED device, the bromine atom attached to the triazine fragment enhances single-triplet state exciton conversion, improves high-efficiency energy transmission to a guest light-emitting material, and thus improves device efficiency. Compared with a traditional host material CBP, the application has obvious advantages, and thus has a wide application prospect and is optimistic, and is expected to be widely applied in the fields of flat panel display and solid-state lighting.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronic materials technology, specifically relating to high-efficiency thermally activated delayed fluorescence host materials, their preparation methods, and applications. Background Technology

[0002] Since Tang and Vanslyke's discovery of organic light-emitting diodes (OLEDs) in 1987, they have become a hot research topic in the lighting and display fields due to their advantages such as self-emission, full-color display, low-voltage driving, low power consumption, and fast response. The electroluminescence of OLEDs originates from the exciton radiative decay formed by the recombination of electrons and holes injected into the electrodes in the emissive layer. According to the spin statistics rule, the ratio of singlet to triplet excitons generated by electron-hole recombination under electrical excitation is 1:3. Researchers have done extensive work to fully utilize singlet and triplet excitons to achieve 100% internal quantum efficiency (IQE). Materials with thermally activated delayed fluorescence (TADF) mechanisms show great potential, as they can effectively utilize triplet excitons through reverse intersystem crossing to achieve a theoretical 100% IQE. Over the years, research on TADF materials has been booming, and researchers have developed a large number of TADF luminescent materials. However, the development of TADF host materials is relatively limited. Currently, most OLED devices still use traditional host materials, such as CBP. Therefore, designing and developing high-efficiency TADF host materials is of great significance. Summary of the Invention

[0003] This invention addresses the technical problems existing in the prior art by proposing a high-efficiency thermally activated delayed fluorescence host material, its preparation method, and its application, which helps to improve the efficiency of OLED devices.

[0004] The technical solution adopted in this invention is as follows:

[0005] A high-efficiency thermally activated delayed fluorescence host material, characterized by having a structure as shown in formula (1):

[0006]

[0007] A method for preparing a high-efficiency thermally activated delayed fluorescence host material, characterized by comprising the following steps:

[0008] Step 1: 3-Bromobenzylamine hydrochloride, benzaldehyde, and potassium hydroxide were added to anhydrous ethanol in a molar ratio of 1:0.5:(1-2) under nitrogen protection to obtain a mixed solution A with a benzaldehyde concentration of 0.06-0.07 mmol / mL. The mixture was heated to 70℃ and reacted for 8-10 h to obtain mixture A. After cooling to room temperature, the mixture was poured into ice water to precipitate the precipitate, which was then filtered to obtain crude product A. Crude product A was then purified by silica gel column chromatography using a 1:1 volume ratio of dichloromethane and petroleum ether as the eluent. After recrystallization, filtration, and drying, the intermediate material was obtained.

[0009] Step 2: The intermediate material, 5,7-dihydro-7,7-dimethylindo[2,1-b]carbazole, cuprous iodide, 1,10-phenanthroline, and potassium carbonate were added to dehydrated dimethylformamide in a molar ratio of 1:1:(2-2.5):(1-2):(3-4) under nitrogen protection to obtain a mixed solution B with an intermediate material concentration of 0.05 mmol / mL. The mixture was heated to 130℃ and reacted for 10-12 h to obtain mixture B. After cooling to room temperature, mixture B was extracted with saturated sodium chloride aqueous solution and dichloromethane. Then, dichloromethane and toluene were removed, and a mixed solution of dichloromethane and petroleum ether in a volume ratio of 1:6 was used as the eluent to purify mixture B by silica gel column chromatography. After recrystallization, filtration, and drying, a high-efficiency thermally activated delayed fluorescence host material was obtained.

[0010] An organic electroluminescent device containing a high-efficiency thermally activated delayed fluorescence host material includes, from bottom to top, a substrate, an anode electrode, a hole transport layer, an electron blocking layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode electrode; characterized in that the light-emitting layer is a hybrid thin film composed of a high-efficiency thermally activated delayed fluorescence host material and a guest light-emitting material, wherein the mass percentage of the high-efficiency thermally activated delayed fluorescence host material in the light-emitting layer is 90-99%.

[0011] Furthermore, the anode electrode is ITO; the hole transport layer is TAPC; the electron blocking layer is TCTA; the electron transport layer is TmPyPB; the electron injection layer is LiF; and the cathode electrode is Al metal.

[0012] Furthermore, the guest luminescent material possesses excellent thermal stability, high electrochemical reversibility, and high TL. g Furthermore, they do not degrade during vacuum deposition, specifically SAF-2NP, DCJTB, or APDC-DTPT.

[0013] Furthermore, the thickness of the light-emitting layer is 20–30 nm.

[0014] Furthermore, ITO conductive glass is used as the substrate and anode electrode.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. This invention obtains a high-efficiency thermally activated delayed fluorescence host material by combining 5,7-dihydro-7,7-dimethylindo[2,1-b]carbazole with 2-(3-bromophenyl)-4,6-diphenyl-1,3,5-triazine. The synthesis method is simple, the raw materials are readily available, and the material structure is stable and easy to store.

[0017] 2. This invention applies the synthesized thermally activated delayed fluorescence host material to OLED devices. Due to the bromine atom attached to the triazine fragment of 2-(3-bromophenyl)-4,6-diphenyl-1,3,5-triazine, the heavy atom effect is introduced, which enhances the singlet-trittite exciton conversion and improves the high-efficiency energy transfer to the guest light-emitting material, thereby improving the efficiency of OLED devices. The application prospects are broad and optimistic, and it is expected to be widely used in flat panel displays and solid-state lighting. Attached Figure Description

[0018] Figure 1 This is the absorption-emission (Abs-PL) spectrum of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention at room temperature;

[0019] Figure 2 The emission spectra of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention in solvents of different polarities at room temperature;

[0020] Figure 3 The redox potential curve of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of this invention;

[0021] Figure 4 The EQE curves of the organic electroluminescent devices of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention and the traditional host material CBP-sensitized luminescent material SAF-2NP are shown.

[0022] Figure 5 The JVL curves of the organic electroluminescent devices of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention and the traditional host material CBP-sensitized luminescent material SAF-2NP are shown.

[0023] Figure 6 The images show the EL spectra of the organic electroluminescent devices using the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of this invention and the conventional host material CBP-sensitized luminescent material SAF-2NP.

[0024] Figure 7The EQE curves of the organic electroluminescent devices of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention and the conventional host material CBP-sensitized luminescent material DCJTB are shown.

[0025] Figure 8 The JVL curves of the organic electroluminescent devices using the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of this invention and the conventional host material CBP-sensitized luminescent material DCJTB are shown.

[0026] Figure 9 The EL spectra of the organic electroluminescent devices of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention and the conventional host material CBP-sensitized luminescent material DCJTB are shown.

[0027] Figure 10 The EQE curves of the organic electroluminescent devices of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention and the traditional host material CBP-sensitized luminescent material APDC-DTPA are shown.

[0028] Figure 11 The JVL curves of the organic electroluminescent devices of the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of the present invention and the traditional host material CBP-sensitized luminescent material APDC-DTPA are shown.

[0029] Figure 12 The images show the EL spectra of the organic electroluminescent devices made from the high-efficiency thermally activated delayed fluorescence host material obtained in Example 1 of this invention and the traditional host material CBP-sensitized luminescent material APDC-DTPA. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in conjunction with the following specific embodiments and with reference to the accompanying drawings.

[0031] Example 1

[0032] This embodiment proposes a high-efficiency thermally activated delayed fluorescence host material with the following structure: Br-DMIC-TRZ:

[0033]

[0034] The synthetic route of the thermally activated delayed fluorescence host material (Br-DMIC-TRZ) is as follows:

[0035]

[0036] Specifically, the following steps are included:

[0037] Step 1: Add 3-bromobenzylamidinium hydrochloride (1.99 g, 10 mmol), benzaldehyde (0.53 g, 5 mmol), and potassium hydroxide (0.84 g, 15 mmol) to a 250 mL two-necked round-bottom flask equipped with a magnetic stirrer. Purge the flask three times with nitrogen. Under nitrogen protection, inject a total of 80 mL of anhydrous ethanol into the flask using a 50 mL syringe. Rotate the flask during the reaction at 70 °C in an oil bath. Detect the reaction using thin-layer chromatography (TCL). After the 3-bromobenzylamidine hydrochloride had completely reacted (9 hours), the heating switch of the heating plate was turned off, and the mixture was cooled to room temperature. The precipitate was poured into ice water and filtered to obtain crude product A. Then, crude product A was purified by silica gel column chromatography using a 1:1 volume ratio of dichloromethane and petroleum ether as the eluent. After recrystallization with a mixture of dichloromethane and anhydrous ethanol, filtration, and drying, 1.95 g of a white solid intermediate material was obtained, with a yield of 83.5%.

[0038] Step 2: Add the above-mentioned white intermediate material (0.94 g, 2 mmol), 5,7-dihydro-7,7-dimethylindeno[2,1-b]carbazole (0.57 g, 2 mmol), cuprous iodide (0.76 g, 4 mmol), 1,10-phenanthroline (0.36 g, 2.00 mmol), and potassium carbonate (1.11 g, 8 mmol) to a 100 mL two-necked round-bottom flask equipped with a magnetic stirrer. Replace the nitrogen gas three times. Under nitrogen protection, use a 50 mL syringe to inject 40 mL of dehydrated dimethylformamide into the round-bottom flask. Rotate the flask during the reaction at 130 °C in an oil bath. Analyze the reaction using thin-layer chromatography. (TCL) TLC detection was performed. After the intermediate material had completely reacted (11 hours), the heating switch of the heating stage was turned off, and the mixture was cooled to room temperature. The mixture was extracted with saturated sodium chloride aqueous solution and dichloromethane. The reaction solution was concentrated under vacuum, and the residual solid was purified by column chromatography. A mixture of dichloromethane and petroleum ether at a volume ratio of 1:6 was used as the eluent. Impurities and byproducts were removed by silica gel column chromatography. Then, the mixture was recrystallized with a mixture of dichloromethane and ethanol, filtered, and dried to obtain 1.15 g of white solid, which is the high-efficiency thermally activated delayed fluorescence host material (Br-DMIC-TRZ), with a yield of approximately 85.8%.

[0039] In 10 -5 The absorption and emission spectra of the thermally activated delayed fluorescence host material were measured in a dilute toluene solution at room temperature using mol / L, as shown below. Figure 1 As shown, the absorption from 340 nm to 370 nm is a distinct CT absorption band, indicating that it has good TADF characteristics; the emission peak in dilute toluene solution is 495 nm.

[0040] The emission spectra of the thermally activated delayed fluorescence host material in different polar solvents (specifically, toluene, tetrahydrofuran (THF), and dichloromethane (DCM) with polarity increasing from low to high) were measured at room temperature. Figure 2 As shown, the emission spectrum of the thermally activated delayed fluorescence host material red-shifts with increasing solvent polarity, indicating that the thermally activated delayed fluorescence host material has a solvent color-changing effect, which demonstrates that the thermally activated delayed fluorescence host material has TADF properties. Figure 3 The redox potential curves of the thermally activated delayed fluorescence host material are obtained by cyclic voltammetry (CV). The HOMO and LUMO energy levels are 5.75 eV and 3.25 eV, respectively, from the initial oxidation and initial reduction positions.

[0041] In this embodiment, the obtained high-efficiency thermally activated delayed fluorescence host material is used to sensitize three different luminescent guest materials, SAF-2NP, DCJTB, and APDC-DTPA, to prepare an organic electroluminescent device. The device includes, from bottom to top, a glass substrate, an ITO anode electrode, a 30 nm thick TAPC hole transport layer, a 10 nm thick TCTA electron blocking layer, a 30 nm thick Br-DMIC-TRZ:emitter luminescent layer, a 65 nm thick TmPyPB electron transport layer, a 0.8 nm thick LiF electron injection layer, and a 100 nm thick Al cathode electrode. The Br-DMIC-TRZ:emitter luminescent layer is a hybrid thin film formed by mixing the thermally activated delayed fluorescence host material (Br-DMIC-TRZ) with the luminescent guest material SAF-2NP, DCJTB, or APDC-DTPA, respectively.

[0042] To compare with the traditional host material CBP, comparative organic electroluminescent devices were fabricated by sensitizing SAF-2NP, DCJTB, and APDC-DTPA with CBP, respectively. The devices consist of a glass substrate, an ITO anode electrode, a 30 nm thick TAPC hole transport layer, a 10 nm thick TCTA electron blocking layer, a 30 nm thick CBP:emitter light-emitting layer, a 65 nm thick TmPyPB electron transport layer, a 0.8 nm thick LiF electron injection layer, and a 100 nm thick Al cathode electrode, arranged from bottom to top. The CBP:emitter light-emitting layer is a hybrid thin film formed by mixing the traditional host material CBP with the light-emitting guest material SAF-2NP, DCJTB, or APDC-DTPA, respectively.

[0043] like Figure 4 As shown, the organic electroluminescent device fabricated based on the highly efficient thermally activated delayed fluorescence host material Br-DMIC-TRZ and the sensitized luminescent guest material SAF-2NP exhibits a maximum external quantum efficiency of 34.1%, and the emission peak is as follows: Figure 6The image shows a wavelength of 580 nm, which represents a significant improvement over the 25.4% maximum external quantum efficiency of organic electroluminescent devices sensitized by SAF-2NP with the traditional host material CBP; simultaneously, as... Figure 5 As shown, the turn-on voltage (3.0V) of the organic electroluminescent device prepared by sensitizing the luminescent guest material SAF-2NP with the high-efficiency thermally activated delayed fluorescence host material Br-DMIC-TRZ is lower than that of the organic electroluminescent device sensitized with the conventional host CBP to SAF-2NP (3.5V).

[0044] like Figure 7 As shown, the organic electroluminescent device fabricated based on the highly efficient thermally activated delayed fluorescence host material Br-DMIC-TRZ and the sensitized luminescent guest material DCJTB has a maximum external quantum efficiency of 7.65%, and the emission peak is as follows: Figure 9 The image shows a wavelength of 592 nm, which represents a significant improvement over the 4.53% maximum external quantum efficiency of organic light-emitting devices sensitized by DCJTB with the traditional host material CBP; simultaneously, as... Figure 8 As shown, the turn-on voltage (3.3V) of the organic electroluminescent device based on the highly efficient thermally activated delayed fluorescence host material Br-DMIC-TRZ sensitized luminescent guest material DCJTB is lower than that of the organic electroluminescent device sensitized with the conventional host material CBP sensitized DCJTB (4.7V).

[0045] like Figure 10 As shown, the organic electroluminescent device fabricated based on the highly efficient thermally activated delayed fluorescence host material Br-DMIC-TRZ and the sensitized luminescent guest material APDC-DTPA exhibits a maximum external quantum efficiency of 21.4%, and the emission peak is as follows: Figure 12 The image shows a wavelength of 652 nm, which represents a significant improvement over the 15.8% maximum external quantum efficiency of organic light-emitting devices sensitized with CBP as the host material for APDC-DTPA; simultaneously, as... Figure 11 As shown, the turn-on voltage (3.2V) of the organic electroluminescent device prepared by sensitizing the luminescent guest material APDC-DTPA with the high-efficiency thermally activated delayed fluorescence host material Br-DMIC-TRZ is lower than that of the organic electroluminescent device sensitized with the conventional host material CBP to sensitize APDC-DTPA (3.5V).

[0046] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A method for preparing a high-efficiency thermally activated delayed fluorescence host material, characterized by, The molecular structure of the high-efficiency thermally activated delayed fluorescence host material is as follows: The preparation method comprises the following steps: Step 1: 3-bromobenzyl amidine hydrochloride, benzaldehyde and potassium hydroxide are added into anhydrous ethanol in a molar ratio of 1:0.5:(1-2) under nitrogen protection to obtain a mixed solution A of benzaldehyde with a concentration of 0.06-0.07 mmol / mL, and the mixed solution A is reacted at 70 DEG C for 8-10 h, and then the mixture A is obtained; after cooling to room temperature, precipitates are separated out, and the crude product A is obtained by filtration; then a mixed solution of dichloromethane and petroleum ether with a volume ratio of 1:1 is used as an eluent to purify the crude product A by silica gel column chromatography, and after recrystallization, suction filtration and drying, the intermediate material is obtained; Step 2: the intermediate material, 5,7-dihydro-7,7-dimethylindeno[2,1-b]carbazole, cuprous iodide, 1,10-phenanthroline and potassium carbonate are added into anhydrous dimethylformamide in a molar ratio of 1:1:(2-2.5):(1-2):(3-4) under nitrogen protection to obtain a mixed solution B of the intermediate material with a concentration of 0.05 mmol / mL, and the mixed solution B is reacted at 130 DEG C for 10-12 h to obtain mixture B; after cooling to room temperature, the mixture B is extracted with saturated sodium chloride aqueous solution and dichloromethane; then dichloromethane and toluene are removed, a mixed solution of dichloromethane and petroleum ether with a volume ratio of 1:6 is used as an eluent to purify the mixture B by silica gel column chromatography, and after recrystallization, suction filtration and drying, the high-efficiency thermally activated delayed fluorescence host material is obtained.

2. An organic electroluminescent device comprising a high-efficiency thermally activated delayed fluorescence host material, comprising, in this order from bottom to top, a substrate, an anode electrode, a hole transport layer, an electron blocking layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode electrode; characterized in that, The light-emitting layer is a mixed film formed by mixing the high-efficiency thermally activated delayed fluorescence host material obtained by the preparation method of claim 1 and a guest light-emitting material, and the mass ratio of the high-efficiency thermally activated delayed fluorescence host material in the light-emitting layer is 90-99%; the guest light-emitting material is SAF-2NP, DCJTB or APDC-DTPT.

3. The organic electroluminescent device comprising a high-efficiency thermally activated delayed fluorescence host material according to claim 2, wherein The thickness of the light-emitting layer is 20-30 nm.

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