Boron-containing thermally activated delayed fluorescence material and applications thereof

Abstract

A kind of boron-containing thermally activated delayed fluorescence material and its application belong to electroluminescent material technical field.The present application relates to organic electroluminescent technical field.In the material, boron-nitrogen resonance skeleton is integrated with donor-acceptor unit in molecular design, boron-nitrogen resonance skeleton is used as electron acceptor unit, and strong electron donor unit is connected by reasonable space and electronic structure, and unique synergistic effect is generated.The material can accurately control the distribution and overlap degree of highest occupied molecular orbital and lowest unoccupied molecular orbital, promote efficient reverse intersystem crossing (RISC), and effectively inhibit the molecular structure relaxation when electron transition, so as to realize narrow-band emission.In the prepared OLED device, narrow-band emission and high external quantum efficiency are realized at the same time.This kind of material has broad application prospect in next-generation high-definition display and lighting devices.

Description

Technical Field

[0001] This invention belongs to the field of electroluminescent materials technology, and relates to a method for synthesizing a class of boron-containing thermally activated delayed fluorescence materials and their applications. Background Technology

[0002] The evolution of organic light-emitting diode (OLED) technology has always been closely linked to the innovation of luminescent materials. In the history of materials development, first-generation traditional fluorescent materials could only utilize 25% of the singlet excitons generated by electrical excitation, making it difficult to break through the theoretical ceiling of their internal quantum efficiency. Subsequently, second-generation phosphorescent materials, based on the noble metals iridium and platinum, successfully captured triplet excitons by leveraging the strong spin-orbit coupling brought about by the heavy atom effect, achieving a theoretical 100% exciton utilization rate. However, this technological path is not only constrained by the scarcity and high cost of precious metals, but its core patents are also monopolized by foreign manufacturers, posing a significant obstacle to the independent development and technological breakthrough of my country's OLED industry. Therefore, developing a next-generation luminescent material that can achieve both high-efficiency light emission and circumvent patent and resource limitations has become an urgent research focus for both academia and industry.

[0003] To overcome these challenges, thermally activated delayed fluorescence (TADF) materials emerged and are considered representative of third-generation OLED light-emitting materials. Their core light-emitting mechanism lies in the fact that, through ingenious molecular design, the energy difference between the singlet and triplet states of the material is extremely small. This allows triplet excitons to use ambient thermal energy to reverse their trajectory to the singlet state and emit light, ultimately achieving near-100% exciton utilization without relying on any precious metals. However, early TADF materials (mainly donor-acceptor structures) revealed two fatal weaknesses during their commercialization: first, their strong intramolecular charge transfer effect resulted in an excessively broad emission spectrum and insufficient color purity, failing to meet the color requirements of ultra-high-definition displays; second, their long exciton lifetime easily led to severe efficiency roll-off at high brightness. These defects severely restricted the practical application of TADF technology.

[0004] It is precisely in addressing these core challenges that boron-containing TADF materials, due to the vacancies in boron's p orbitals, have been widely used as efficient electron acceptors in organic optoelectronic materials. By constructing an electron push-pull system within an aromatic framework using heteroatoms such as boron and nitrogen, the frontier orbitals of the molecule can be effectively separated in space to achieve small energy level differences, while maintaining a certain degree of overlap to ensure a high radiative rate. This unique electronic structure has overcome the broad-spectral challenge of traditional TADF materials, achieving efficient narrow-band emission and making it possible to obtain high color purity. Furthermore, the empty p orbitals of boron atoms endow the molecular structure with extremely high tunability, facilitating systematic optimization of emission color, efficiency, and stability. Therefore, boron-containing TADF materials have not only become one of the most promising breakthroughs in overcoming the commercialization challenges of TADF and breaking the foreign technological monopoly, but have also rightfully become a key strategic research direction for promoting the development of next-generation display and lighting technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a class of boron-containing thermally activated delayed fluorescence materials. By integrally bonding a strong electron donor unit with a boron-nitrogen resonance acceptor framework, it is possible to reduce the singlet-triplet energy level difference (Δ) while maintaining frontier orbital spatial separation. E ST While promoting efficient reverse system crossing (RISC), the boron-nitrogen resonance effect is used to effectively suppress excited-state structural relaxation, thereby obtaining narrow-band emission and high color purity, and making the final OLED device have higher external quantum efficiency (EQE).

[0006] The technical solution of the present invention is as follows: a boron-containing thermally activated delayed fluorescence material, which has the following structure:

[0007]

[0008] The method for preparing the boron-containing thermally activated delayed fluorescence material includes the following steps:

[0009]

[0010] Wherein, R is carbazole or tert-butylcarbazole; R2 is hydrogen or alkyl;

[0011] In a nitrogen glove box, tris(pentafluorophenyl)borane, compound A, and toluene were added sequentially to the reaction vessel; then, the mixture was heated in an oil bath at 80℃-100℃ for 20-30 hours; after the reaction was completed, the mixture was cooled to room temperature, the solvent was removed by vacuum distillation at room temperature, and the product was obtained by silica gel column chromatography at 200-300 mesh and vacuum drying to obtain the target product B.

[0012] Furthermore, the molar ratio of the tris(pentafluorophenyl)borane to compound A is 1:1.

[0013] Application of a class of boron-containing thermally activated delayed fluorescent materials, wherein the fluorescent materials are used to prepare electroluminescent devices.

[0014] An organic electroluminescent device, wherein the light-emitting device comprises the aforementioned boron-containing thermally activated delayed fluorescence material.

[0015] Furthermore, the light-emitting device includes a light-emitting layer containing the fluorescent material.

[0016] The beneficial effects of this invention are as follows: the fluorescent material focuses on the synergistic effect of the boron-nitrogen resonance effect and the donor-acceptor (DA) structure. Its core advantage lies in utilizing the boron-nitrogen resonance framework as the electron acceptor unit, which is connected to the strong electron donor unit through a reasonable spatial and electronic structure, generating a unique synergistic effect. This design can precisely control the distribution and overlap of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals: on the one hand, the boron-nitrogen resonance effect is used to restrict structural relaxation in the excited state, thereby maintaining narrow-band emission characteristics; on the other hand, through the charge transfer interaction between the donor and acceptor, the singlet-triple energy level difference is further reduced, thereby greatly promoting the triplet exciton to the singlet state through the thermally activated reverse intersystem crossing process, achieving efficient exciton utilization. Ultimately, this results in an OLED luminescent material that combines narrow-band emission and high external quantum efficiency. The successful implementation of this project opens up new avenues for the design of TADF materials. Attached Figure Description

[0017] Figure 1 This is the HOMO and LUMO orbital distribution diagram of compound B2 calculated using Gaussian 09.

[0018] Figure 2 This is the HOMO and LUMO orbital distribution diagram of compound B3 calculated using Gaussian 09.

[0019] Figure 3 The figures show the UV-Vis absorption and fluorescence emission spectra of the compounds in toluene solution. In the figure, (a) is the UV-Vis absorption and fluorescence emission spectrum of compound B2 in toluene solution, and (b) is the UV-Vis absorption and fluorescence emission spectrum of compound B3 in toluene solution.

[0020] Figure 4 These are the fluorescence and phosphorescence spectra of the compounds at 77 K. Among them, (a) is the fluorescence and phosphorescence spectrum of compound B2 at 77 K, and (b) is the fluorescence and phosphorescence spectrum of compound B3 at 77 K.

[0021] Figure 5These are the transient fluorescence spectra of the compounds. Among them, (a) is the transient fluorescence spectrum of compound B2, and (b) is the transient fluorescence spectrum of compound B3.

[0022] Figure 6 These are the cyclic voltammetry diagrams for compounds B2 and B3.

[0023] Figure 7 These are the electroluminescence spectra of blue light devices B2 and B3.

[0024] Figure 8 These are the current density-voltage-brightness curves for blue light devices B2 and B3.

[0025] Figure 9 These are the external quantum efficiency-brightness curves for blue light devices B2 and B3.

[0026] Figure 10 The spectrum is the current efficiency-luminance-power efficiency spectrum of the blue light device. Among them, (a) is the current efficiency-luminance-power efficiency spectrum of blue light device B2, and (b) is the current efficiency-luminance-power efficiency spectrum of blue light device B3. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0028] This invention provides a class of boron-containing thermally activated delayed fluorescence materials having the following structural formula:

[0029]

[0030] The synthesis of the compound comprises the following steps:

[0031] Step 1: Synthesis of Intermediate 1:

[0032]

[0033] Carbazole (or tert-butylcarbazole) (1.0 equiv) and cesium carbonate (4.0 equiv) were weighed into round-bottom flasks, and N,N-dimethylformamide (DMF) was added. While stirring, p-fluoroiodobenzene (2.0–4.0 equiv) was added, and the mixture was heated and refluxed at 150 °C for 24 hours. The reaction was monitored by TLC. After the reaction was complete, saturated brine was added to the system, and the mixture was extracted with ethyl acetate (EA). The organic phase was dried and concentrated to obtain the crude product. Finally, the crude product was purified by silica gel column chromatography and dried in a vacuum oven to obtain the target product.

[0034] Step 2: Synthesis of Intermediate 2:

[0035]

[0036] Under nitrogen atmosphere, intermediate 1 (1.0 equiv), p-methylbenzylamine or benzylamine (1.0~1.5 equiv), cuprous iodide (0.01~0.05 equiv), L-ligand (0.1~0.2 equiv), and base (1.0~3.0 equiv) were added to a dry Schlenk tube and dissolved in diethylene glycol (DEG). The mixture was stirred at 25~150℃ for 24 hours. After the reaction was completed, the reaction solution was extracted with ethyl acetate (EA) and saturated brine. The organic phase was dried and concentrated to obtain the crude product. Finally, the crude product was purified by silica gel column chromatography using petroleum ether and ethyl acetate as the mobile phase to obtain the target product. After drying, intermediate 2 was obtained as a white solid.

[0037] The L-ligands mentioned therein are the following:

[0038]

[0039] The alkali is sodium hydroxide or cesium carbonate.

[0040] Step 3: Synthesis of Compound A:

[0041]

[0042] Potassium carbonate (2.0 equiv) and potassium iodide (1.1 equiv) were weighed into round-bottom flasks, and 40 mL of N,N-dimethylformamide (DMF) was added. While stirring, intermediate 2 (1.0 equiv) was added, followed by 1-bromo-2-butyne (1.2 equiv). The mixture was stirred at 66 °C for 24 hours. The reaction was monitored by TLC until completion. Saturated brine and ethyl acetate were added to the system for extraction. The organic phase was collected, dried, and concentrated to obtain the crude product. Finally, the crude product was purified using a silica gel column with petroleum ether and ethyl acetate as the mobile phase. After drying in a vacuum oven, a white solid A was obtained.

[0043] Step 4: Synthesis of compounds B1, B2, and B3:

[0044]

[0045] In a nitrogen-filled glove box, tris(pentafluorophenyl)borane [B(C6F5)3] (1.0 equiv), compound A (1.0 equiv), and toluene were sequentially added to a 100 mL pressure-resistant bottle. The mixture was then heated in an oil bath at 100 °C for 24 hours. After the reaction was complete, the mixture was cooled to room temperature, and TLC was performed to confirm the polarity of the target product. The solvent was removed directly under reduced pressure at room temperature. The crude product was then subjected to silica gel column chromatography (200-300 mesh) using petroleum ether and ethyl acetate as the mobile phase, and dried under vacuum to obtain the target product B.

[0046] The present invention will be further illustrated below through examples, with the aim of providing a better understanding of its contents. Therefore, the examples given do not limit the scope of protection of the present invention.

[0047] Example 1: Synthesis of compound B1:

[0048] Carbazole (418 mg, 2.5 mmol, 1.0 equiv) and cesium carbonate (3.258 g, 10 mmol, 4.0 equiv) were weighed into round-bottom flasks, and 40 ml of N,N-dimethylformamide (DMF) was added. While stirring, p-fluoroiodobenzene (2.220 g, 10 mmol, 4.0 equiv) was added, and the mixture was heated and refluxed at 150 °C for 24 hours. The reaction was monitored by TLC until completion. After cooling to room temperature, saturated brine was added to the system, and extraction was performed with ethyl acetate (EA). The organic phase was dried and concentrated to obtain the crude product. Finally, the target product was purified by silica gel column chromatography (pure petroleum ether). The product was dried in a vacuum oven to obtain a white solid intermediate 1 (yield: 41%). TOF-EI-MS: 369.0006 [M] + ].

[0049]

[0050] Under nitrogen atmosphere, intermediate 1 (1.0 g, 2.71 mmol, 1.0 equiv), p-methylbenzylamine (361 mg, 2.98 mmol, 1.1 equiv), cuprous iodide (5 mg, 2.71 mmol%, 0.01 equiv), L3 ligand (218 mg, 0.542 mmol, 0.2 equiv), and NaOH (120 mg, 2.98 mmol, 1.1 equiv) were dissolved in 10 ml of diethylene glycol (DEG) and stirred at room temperature for 24 hours. The reaction solution was extracted with ethyl acetate (EA) and saturated brine. The organic phase was dried and concentrated to obtain the crude product. Finally, the target product was purified by silica gel column chromatography with petroleum ether:ethyl acetate = 10:1 (V:V). After drying, a white solid intermediate 2 was obtained (yield: 45.68%). TOF-EI-MS: 362.1773 [M] + ]

[0051] Potassium carbonate (180 mg, 1.3 mmol, 2.0 equiv) and potassium iodide (119 mg, 0.715 mmol, 1.1 equiv) were weighed into round-bottom flasks, and 40 mL of DMF was added. Intermediate 2 (235 mg, 0.65 mmol, 1.0 equiv) was added with stirring, followed by 1-bromo-2-butyne (104 mg, 0.78 mmol, 1.2 equiv). The mixture was stirred and refluxed at 66 °C for 24 hours. The reaction was monitored by TLC until completion. Water and ethyl acetate (EA) were added for extraction, and the organic phase was collected, dried, and concentrated to obtain the crude product. The crude product was then purified by silica gel column chromatography with petroleum ether:ethyl acetate = 15:1 (V:V) to obtain the target product. The crude product was dried in a vacuum oven to obtain a white solid intermediate 3 (yield: 33%). TOF-EI-MS: 414.2086 [M] + ]

[0052] In a nitrogen-filled glove box, borane B(C6F5)3 (600 mg, 1.2 mmol, 1.0 equiv), intermediate 3 (500 mg, 1.2 mmol, 1.0 equiv), and toluene (10.0 mL) were sequentially added to a 100 mL pressure-resistant bottle. The mixture was then heated in an oil bath at 100 °C for 24 hours. After cooling to room temperature, the polarity of the target product was confirmed by TLC. The solvent was removed directly under reduced pressure at room temperature, and the product was purified by column chromatography using petroleum ether:dichloromethane = 2:1 (V:V) as eluent. The target product was then dried in a vacuum oven to obtain a yellow solid B1 (yield: 67%). TOF-EI-MS: 924.1789 [M]+ ].

[0053] Example 2: Synthesis of compound B2:

[0054]

[0055] Carbazole (418 mg, 2.5 mmol, 1.0 equiv) and cesium carbonate (3.258 g, 10 mmol, 4.0 equiv) were weighed into round-bottom flasks, and 40 ml of N,N-dimethylformamide (DMF) was added. While stirring, p-fluoroiodobenzene (2.220 g, 10 mmol, 4.0 equiv) was added, and the mixture was heated and refluxed at 150 °C for 24 hours. The reaction was monitored by TLC until completion. After cooling to room temperature, saturated brine was added to the system, and extraction was performed with ethyl acetate (EA). The organic phase was dried and concentrated to obtain the crude product. Finally, the target product was purified by silica gel column chromatography (pure petroleum ether). The product was dried in a vacuum oven to obtain a white solid intermediate 1 (yield: 41%). TOF-EI-MS: 369.0006 [M] + ].

[0056] Under nitrogen atmosphere, intermediate 1 (1.0 g, 10 mmol, 1.0 equiv), benzylamine (1.605 g, 15 mmol, 1.5 equiv), cuprous iodide (1 mg, 0.5 mmol%, 0.05 equiv), L1 ligand (342 mg, 1 mmol, 0.1 equiv), and NaOH (880 mg, 22 mmol, 2.2 equiv) were added to a dry Schlenk tube and dissolved in 10 mL of diethylene glycol (DEG). The mixture was stirred at room temperature for 24 hours. The reaction solution was extracted with ethyl acetate (EA) and saturated brine. The organic phase was dried and concentrated to obtain the crude product. Finally, the crude product was purified by silica gel column chromatography with petroleum ether:ethyl acetate = 20:1 (V:V) to obtain the target product. After drying, intermediate 2 (yield: 42.55%) was obtained as a white solid. TOF-EI-MS: 348.1617 [M] + ].

[0057] Potassium carbonate (2.760 g, 20 mmol, 2.0 equiv) and potassium iodide (1.826 g, 11 mmol, 1.1 equiv) were weighed into a round-bottom flask, and 40 mL of DMF was added. Intermediate 2 (3.482 g, 10 mmol, 1.0 equiv) was added with stirring, followed by 1-bromo-2-butyne (1.596 g, 12 mmol, 1.2 equiv). The mixture was stirred and refluxed at 66 °C for 24 hours. The reaction was monitored by TLC until completion. Water and ethyl acetate (EA) were added to the system for extraction. The organic phase was collected, dried, and concentrated to obtain the crude product. Finally, the crude product was purified by silica gel column chromatography with petroleum ether:ethyl acetate = 15:1 (V:V) to obtain the target product. The crude product was dried in a vacuum oven to obtain a white solid intermediate 3 (yield: 73%). TOF-EI-MS: 400.1929 [M] + ].

[0058] In a nitrogen-filled glove box, borane B(C6F5)3 (2.560 g, 5 mmol, 1.0 equiv), intermediate 3 (2.0 g, 5 mmol, 1.0 equiv), and toluene (10 mL) were sequentially added to a 100 mL pressure-resistant bottle. The mixture was then heated in an oil bath at 100 °C for 24 hours. After cooling to room temperature, the polarity of the target product was confirmed by TLC. The solvent was removed directly under reduced pressure at room temperature, and the product was purified by column chromatography using petroleum ether:dichloromethane = 2:1 (V:V) as eluent. The target product was then dried in a vacuum oven to obtain a yellow solid B2 (yield: 64%). TOF-EI-MS: 910.1631 [M] + ].

[0059] Example 3: Synthesis of compound B3:

[0060] 2.220 g (10 mmol, 2.0 equiv.) of p-fluoroiodobenzene, 1.4 g (5 mmol, 1.0 equiv.) of 3,6-di-tert-butylcarbazole, and 6.520 g (20 mmol, 4.0 equiv.) of cesium carbonate were weighed and added to a 100 mL flask. 10 mL of N,N-dimethylformamide (DMF) was added as a solvent. The reaction was carried out at 150 °C under reflux for 24 hours. TLC was used to monitor the reaction until completion. The mixture was poured into saturated brine, and the crude product was extracted three times with ethyl acetate. The mixture was then dried over anhydrous Na₂SO₄, and the solvent was removed by vacuum distillation. The target product was purified by silica gel column chromatography using petroleum ether:ethyl acetate = 50:1 (V:V) as the eluent. The product was dried in a vacuum oven to obtain a white solid intermediate 1 (yield 21.14%). TOF-EI-MS: 481.1256 [M] + ].

[0061]

[0062] Intermediate 1 (500 mg, 1.0386 mmol, 1.0 equiv), benzylamine (166 mg, 1.5579 mmol, 1.5 equiv), cuprous iodide (10 mg, 0.0519 mmol, 0.05 equiv), ligand L5 (33 mg, 0.1039 mmol, 0.1 equiv), and cesium carbonate (677 mg, 2.0772 mmol, 2.0 equiv) were added to a 100 mL flask, followed by 10 mL of DEG as solvent. After three purgings with nitrogen, the mixture was heated to 150 °C and refluxed with stirring for 24 hours. The reaction was monitored by TLC until completion. After cooling to room temperature, the mixture was poured into saturated brine. The crude product was extracted three times with ethyl acetate. The mixture was then dried over anhydrous Na₂SO₄, and the solvent was removed by vacuum distillation of the filtrate. The target product was purified by silica gel column chromatography using petroleum ether:ethyl acetate = 20:1 (V:V) as eluent, and dried in a vacuum oven to give a white solid intermediate 2 (yield: 21.89%). TOF-EI-MS: 460.2872 [M] + ] .

[0063] At room temperature, intermediate 2 (133 mg, 0.2884 mmol, 1.0 equiv), 1-bromobut-2-yne (46 mg, 0.3461 mmol, 1.2 equiv), potassium iodide (53 mg, 0.3173 mmol, 1.1 equiv), and potassium carbonate (80 mg, 0.5768 mmol, 2.0 equiv) were added to a 100 mL flask, followed by 5 mL of DMF as solvent. The mixture was stirred and refluxed at 66 °C for 12 hours. The reaction mixture was monitored by TLC until completion. The reaction solution was then poured into saturated brine, and the crude product was extracted three times with ethyl acetate. The mixture was dried over Na₂SO₄, and the solvent was removed by vacuum distillation of the filtrate. The target product was purified by silica gel column chromatography using petroleum ether:ethyl acetate = 15:1 (V:V) as eluent. After air-drying, a white solid intermediate 3 was obtained (yield: 67.96%). TOF-EI-MS: 512.3183 [M] + ].

[0064] In a nitrogen-filled glove box, intermediate 3 (73 mg, 0.1420 mmol, 1.0 equiv) and tris(pentafluorophenyl)borane B(C6F5)3 (77 mg, 0.1504 mmol, 1.0 equiv) were added to a 100 mL pressure-resistant flask, followed by 20 mL of toluene as solvent. The mixture was then heated in an oil bath at 100 °C for 24 hours. After the reaction was complete, the mixture was poured into saturated brine, and the crude product was extracted three times with DCM. The mixture was dried over anhydrous Na2SO4, and the filtrate was distilled under reduced pressure to remove the solvent. The target product was obtained by silica gel column chromatography with petroleum ether:dichloromethane = 2:1 (V:V) as eluent; the product was dried in a vacuum oven to obtain a yellow solid B3 (yield: 85.11%). TOF-EI-MS: 1022.2879 [M] + ].

[0065] Example 4:

[0066] Density functional theory simulations of the structures of B2 and B3 molecules were performed using the Gaussian09 program. The HOMO and LUMO distributions of the molecules are shown below. Figure 1 As shown, the LUMO electron cloud of the molecule is mainly distributed on the quinoline acceptor. The HOMO electron cloud, on the other hand, is mainly distributed on carbazole and 3,6-di-tert-butylcarbazole. More importantly, compared to similar molecules, due to the resonance between nitrogen and boron atoms on the quinoline, some electrons are delocalized to the boron atom and its attached group, prolonging π-conjugation. This promotes the separation of the HOMO and LUMO electron clouds while also allowing for partial overlap, resulting in a smaller Δ... E STAnd a large oscillator strength. On the other hand, the introduction of the resonance effect of nitrogen and boron atoms also increases the rigidity of the molecule, suppresses molecular vibrational relaxation, and improves luminescence efficiency. Therefore, combining the above two points, all molecules maintain high molecular rigidity, enabling the molecule to maintain a high radiative transition rate, a small energy level difference, and a high fluorescence quantum yield.

[0067] Example 5:

[0068] At room temperature, using dry toluene as a solvent, the solution concentration is 1 × 10⁻⁶. -5 The UV-Vis absorption and fluorescence spectra of B2 and B3 at room temperature were measured using mol / L, as shown below. Figure 3 As shown, the absorption range of 350-400 nm indicates that this is the ICT absorption from electron donor to electron acceptor. The fluorescence spectra of B2 and B3 measured in toluene both exhibit the characteristic of lacking fine vibrational structure, confirming the CT luminescence feature. Compared with the PL spectrum of B2 in toluene solvent, the maximum emission peak of B3 shows a red shift. This is because the electron-donating ability of tert-butylcarbazole is stronger than that of carbazole.

[0069] To further estimate the excited state energy levels of this series of molecules, their LT-FL and LT-PH spectra were measured. Figure 4 As shown. Based on the tangents of each fluorescence spectrum and the first emission peak of the phosphorescence spectrum, the energy levels of B1 and B2 were calculated to be 2.86 / 2.60 eV and 2.80 / 2.56 eV, respectively.

[0070] Example 6:

[0071] The transient spectra of this series of molecularly doped films were tested. Figure 5 As shown, at room temperature, the transient spectra of all molecules exhibit a double exponential decay characteristic of the transient and delayed components, proving the existence of TADF properties. The lifetimes of compounds B2 and B3 are 102 µs and 97 µs, respectively.

[0072] Example 7:

[0073] A blank scan was performed at a scan rate of 100 mV / s, followed by the addition of B2 and B3, respectively, in dry dichloromethane and N , N Using dimethylformamide as the solvent and tetrabutylammonium hexafluorophosphate (Bu4NPF6) as the electrolyte, after nitrogen bubbling for 10 min to remove oxygen, the positive and negative cyclic voltammetry curves of B2 and B3 were measured on a CHI610E electrochemical analyzer. Figure 6 Based on the initial oxidation and reduction peak potentials, and the formula... and The HOMO and LUMO energy levels of B2 and B3 were calculated to be 5.65 / 2.69 eV and 5.53 / 2.68 eV, respectively.

[0074] Example 8:

[0075] Spin-coated electroluminescent devices were fabricated using the boron-containing thermally activated delayed fluorescence materials prepared in Examples 1, 2, and 3 as guest materials for the luminescent layer, and the devices were characterized. The specific structure of the electroluminescent device is: IITO / PEDOT:PSS (40nm) / TAPC (20nm) / 5 wt% dopants:mCP (20nm) / TmPyPb (40nm) / LiF (1nm) / Al (200nm), (dopants: B2 and B3). In the device, PEDOT:PSS and LiF serve as hole and electron injection layers, respectively; TAPC and TmPyPB serve as hole and electron transport layers, respectively; furthermore, mCP is chosen as the host material because its triplet energy level is higher than that of the luminescent material, ensuring energy transfer from host to guest and effectively preventing the reverse energy transfer from luminescent material to host. Figure 8 The current density-voltage-luminance curves of blue light-emitting devices fabricated using B2 and B3 as guest materials are shown in the figure. From this figure, it can be seen that the turn-on voltages of the devices are 3.6 V and 3.7 V, and the maximum luminances are 1497 and 1526 cd / m², respectively. 2 The efficiency curve and electroluminescence spectrum of the device are as follows: Figure 9 and 10 As shown, the maximum external quantum equivalences of the devices (B2 and B3) are 12.3% and 15.8%, respectively. CIE (0.17, 0.26) and CIE (0.17, 0.28) values ​​are used. The electroluminescence spectra of the devices show that the emission peaks are only those of the guest materials B2 and B3, with no emission peaks from the host material or other materials. Compared to similar reported devices, the doped devices prepared using small molecules B2 and B3 as luminescent materials exhibit excellent efficiency. Therefore, combining theoretical calculations and photophysical testing results, it can be inferred that B2 and B3 possess both high efficiency and low roll-off characteristics.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A class of boron-containing thermally activated delayed fluorescence materials, characterized in that, The material has the following structure: 。 2. A method for preparing a boron-containing thermally activated delayed fluorescence material as described in claim 1, characterized in that, Includes the following steps: ； Where R is or R2 is hydrogen or methyl; In a nitrogen glove box, tris(pentafluorophenyl)borane, compound A, and toluene were added sequentially to the reaction vessel; then, the mixture was heated in an oil bath at 80℃-100℃ for 20-30 hours; after the reaction was completed, the mixture was cooled to room temperature, the solvent was removed by vacuum distillation at room temperature, and the product was obtained by silica gel column chromatography at 200-300 mesh and vacuum drying to obtain the target product B.

3. The preparation method according to claim 2, characterized in that: The molar ratio of tris(pentafluorophenyl)borane to compound A is 1:

1.

4. The application of the boron-containing thermally activated delayed fluorescence material as described in claim 1, characterized in that, The fluorescent material is used to prepare electroluminescent devices.

5. A type of organic electroluminescent device, characterized in that: The light-emitting device includes the boron-containing thermally activated delayed fluorescence material as described in claim 1.

6. The electroluminescent device according to claim 5, characterized in that, The light-emitting device includes a light-emitting layer containing the fluorescent material.

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