Thermally activated delayed fluorescent material containing intramolecular hydrogen bonds and application of thermally activated delayed fluorescent material

Abstract

The invention discloses a thermally activated delayed fluorescent material containing intramolecular hydrogen bonds and application thereof, and belongs to the technical field of electroluminescent materials. According to the material, the advantage that a six-membered ring donor has a large dihedral angle is utilized, nitrogen atoms are introduced to the 1-position of the six-membered ring donor, and through intramolecular hydrogen bonds, on one hand, the dihedral angle between the donor and an acceptor is finely adjusted, the orbital overlap integral between electrons and holes is improved, and the radiative transition rate is improved while the small energy level difference and the high anti-intersystem crossing rate are maintained; therefore, the balance between the anti-intersystem crossing rate and the radiative transition rate is promoted. On the other hand, the rigidity of molecules is improved, excited state vibration relaxation is inhibited, and the luminous efficiency is improved. The material disclosed by the invention has excellent photoelectric properties, and an ideal material solution is provided for preparing OLED devices with high efficiency and low roll-off.

Description

Technical Field

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

[0002] Organic light-emitting diodes (OLEDs) possess unique advantages such as ultra-thinness, high color saturation, and low energy consumption. Since Dr. CW Tang of Kodak reported on OLED layered devices in 1987, they have received considerable attention from the scientific and industrial communities. After more than 30 years of development, although OLEDs have made breakthroughs in both basic research and practical applications, they are still plagued by high cost, low efficiency, and poor stability.

[0003] Following traditional fluorescent and phosphorescent materials, Adachi reported a high-efficiency pure organic thermally activated delayed fluorescence (TADF) material in 2012. Unlike fluorescent materials, it employs a donor-acceptor (DA) linkage, effectively separating the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO), resulting in an energy level difference (Δ) between its triplet (T1) and singlet (S1) states. E ST With a relatively small exciton size, and aided by ambient heat, T1-state excitons can cross over to the S1 state via antisystem crossing (RISC), thereby emitting light and achieving nearly 100% exciton utilization. Therefore, to meet the development needs of OLEDs, using TADF materials, which combine low cost and high efficiency, to replace fluorescent and phosphorescent materials undoubtedly has significant scientific and practical value.

[0004] However, the efficiency roll-off remains severe, hindering industrial applications. The main reason is that current high-performance small-molecule TADF materials primarily rely on small Δ... E ST This process results in a smaller orbital overlap integral between electrons and holes, typically exhibiting an intersystem crossing rate ( k ISC ) higher than the anti-system crossover rate ( k RISC ) and radiative transition rate ( k r This leads to a significant efficiency roll-off. Therefore, the pre-fabrication of TADF materials with both high efficiency and low roll-off needs to simultaneously meet the requirements of high PLQY and fast efficiency. k r and k RISCIt is obvious that currently mainstream bond charge transfer (TBCT) and space charge transfer (TSCT) TADF materials with small orbital overlap integrals cannot meet the above conditions. This project aims to design and synthesize a class of materials that possess both small Δ... E ST Heda k r The core of TADF materials lies in utilizing the large dihedral angle advantage of the six-membered ring donor by introducing a nitrogen atom at its 1-position. This fine-tunes the dihedral angle between the donor and acceptor through intramolecular hydrogen bonding, thereby increasing the orbital overlap integral between electrons and holes and maintaining a small Δ E ST At the same time improve k r On the other hand, increasing molecular rigidity and suppressing excited-state relaxation can improve fluorescence quantum yield (PLQY). Against this backdrop, this invention aims to resolve the aforementioned technical contradictions through innovative molecular design strategies, providing a key material foundation for advancing the low-cost, large-area, and flexible development of OLED technology. Summary of the Invention

[0005] The purpose of this invention is to provide a class of thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds. By utilizing the large dihedral angle advantage of the six-membered ring donor and introducing a nitrogen atom at its 1-position, intramolecular hydrogen bonding is used to finely adjust the dihedral angle between the donor and acceptor, thereby increasing the orbital overlap integral between electrons and holes and maintaining a small Δ fluorescence. E ST At the same time improve k r Simultaneously, it increases molecular rigidity, effectively suppresses π-π stacking and molecular vibrational relaxation, and significantly improves material stability and luminescence efficiency. Thus, Δ... E ST , k r and k RISC An effective balance is achieved, providing an ideal material solution for fabricating high-performance, low-roll-off OLED devices.

[0006] The technical solution of this invention is as follows: A type of thermally activated delayed fluorescence material containing intramolecular hydrogen bonds, the material having the following structure:

[0007] A method for preparing thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds includes the following steps:

[0008] An organic solvent is added to compound A1 or compound A2, donor C1, catalyst, ligand, and base, wherein the molar ratio of compound A1 or compound A2, donor C1, palladium catalyst, ligand, and base is 1:1.5~2:0.05:0.1~0.5:5; the reaction is heated, and after the reaction is completed, the mixture is extracted, dried, and purified to obtain compounds M1 and M2.

[0009] Furthermore, the catalyst is palladium acetate, tris(dibenzylacetone)dipalladium, or cuprous iodide; the base is K2CO3, sodium tert-butoxide, or Cs2CO3; the ligand is 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl; and the organic solvent is N,N-dimethylformamide.

[0010] Furthermore, the preparation process of the donor C1 includes the following steps:

[0011] (1) Preparation of intermediate 1: o-fluoronitrobenzene, 2-chloro-3-hydroxypyridine and potassium carbonate were dissolved in N,N-DMF and the reaction mixture was stirred overnight; the reaction mixture was poured into ice water, the precipitate was precipitated, filtered and washed to obtain intermediate 1; (2) Preparation of donor C1: Add intermediate 1 and stannous chloride to a round-bottom flask and dissolve them in anhydrous ethanol; stir and reflux the reaction mixture; then pour the reactants into hydrochloric acid, precipitate out, filter, wash and dry to obtain crude product; then purify to obtain donor C1.

[0012] The application of the thermally activated delayed fluorescent material containing intramolecular hydrogen bonds, wherein the fluorescent material is used to prepare electroluminescent devices.

[0013] An organic electroluminescent device, wherein the light-emitting device includes the fluorescent material described above.

[0014] Furthermore, the light-emitting device includes a light-emitting layer containing the fluorescent material.

[0015] The beneficial effects of this invention are as follows: This invention provides a class of thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds, the core advantage of which lies in achieving a "balanced Δ" E ST , k r and k RISC The molecular design principle of "high performance and high stability" was successfully implemented. Firstly, by introducing a nitrogen atom at the 1-position of a six-membered ring donor with large steric hindrance, an intramolecular hydrogen bond was formed between the nitrogen atom at the 1-position and the hydrogen atom on the bridging benzene ring. This allowed for the adjustment of the dihedral angle between the donor and acceptor, thereby regulating the orbital overlap between electrons and holes, and ultimately maintaining a small Δ...E ST At the same time improve k r On the other hand, the presence of intramolecular hydrogen bonds increases molecular rigidity, effectively suppressing concentration quenching caused by π-π stacking and nonradiative energy loss caused by molecular vibrational relaxation, thereby contributing to improved photoluminescence quantum yield and material stability. Finally, a class of OLED devices with both high efficiency and low roll-off was fabricated. The successful implementation of this project opens up new avenues for the design of TADF materials. Attached Figure Description

[0016] Figure 1 This is the HOMO and LUMO orbital distribution diagram of compound M1 calculated using Gaussian 09.

[0017] Figure 2 This is the HOMO and LUMO orbital distribution diagram of compound M2 calculated using Gaussian 09.

[0018] Figure 3 These are the UV-Vis absorption and fluorescence emission spectra of the compounds in toluene solution. Among them, (a) is the UV-Vis absorption and fluorescence emission spectrum of compound M1, and (b) is the UV-Vis absorption and fluorescence emission spectrum of compound M2.

[0019] Figure 4 These are the fluorescence and phosphorescence spectra of the compounds at 77K. Among them, (a) is the fluorescence and phosphorescence spectrum of compound M1, and (b) is the fluorescence and phosphorescence spectrum of compound M2.

[0020] Figure 5 These are the transient fluorescence spectra of the compounds. Among them, (a) is the transient fluorescence spectrum of compound M1, and (b) is the transient fluorescence spectrum of compound M2.

[0021] Figure 6 These are the cyclic voltammetry diagrams for compounds M1 and M2.

[0022] Figure 7 These are the electroluminescence spectra of sky-blue light devices M1 and M2.

[0023] Figure 8 These are the current density-voltage-brightness curves for sky-blue light devices M1 and M2.

[0024] Figure 9 These are the external quantum efficiency-brightness curves of sky-blue light devices M1 and M2.

[0025] Figure 10These are the current efficiency-brightness-power efficiency spectra of the devices. Among them, (a) is the current efficiency-brightness-power efficiency spectrum of the sky-blue light device M1, and (b) is the current efficiency-brightness-power efficiency spectrum of the sky-blue light device M2.

[0026] Figure 11 These are the chemical structural formulas of compounds M1 and M2. 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 discloses a class of thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds, the structural formula of which is as follows:

[0029] This invention provides a method for synthesizing a class of thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds, comprising the following steps:

[0030] An organic solvent was added to compound A1 (2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine) or compound A2 (4-(4-bromophenyl)-2,6-diphenylpyrimidine), donor C1, catalyst, ligand, and base. The molar ratio of compound A1 or compound A2, donor C1, palladium catalyst, ligand, and base was 1:1.5~2:0.05:0.1~0.5:5. After three vacuum-nitrogen purgings, the mixture was heated to 165℃ and reacted for 12~24 h. The reaction was monitored by TLC until completion. The solvent was then evaporated under reduced pressure. The crude product was extracted three times with ethyl acetate, dried with anhydrous sodium sulfate, and filtered. The filtrate was subjected to reduced pressure distillation to remove the solvent. The crude product was purified by silica gel column chromatography (200-300 mesh) and recrystallization from chloroform / methanol using petroleum ether and ethyl acetate as the mobile phase to obtain compounds M1 and M2.

[0031] The catalyst is palladium acetate, tris(dibenzylacetone)dipalladium, and cuprous iodide; the base is K2CO3, sodium tert-butoxide, and Cs2CO3; the ligand is 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl; and the organic solvent is N,N-dimethylformamide.

[0032] This invention provides a class of compounds, C1: 10H-benzo[b]pyrido[2,3-e][1,4]oxazine, for preparing thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds. The preparation process includes the following steps:

[0033] (1) Preparation of intermediate 1: o-fluoronitrobenzene, 2-chloro-3-hydroxypyridine and potassium carbonate were dissolved in N,N-dimethylformamide (DMF), and the reaction mixture was stirred overnight at 50°C. The reaction mixture was then poured into ice water, and the resulting precipitate was filtered out and washed with a large amount of water to obtain crude product 1.

[0034] (2) Preparation of C1: Intermediate 1 and stannous chloride were added to a round-bottom flask and dissolved in anhydrous ethanol. The reaction mixture was stirred and refluxed at 80°C for 12 h; then the reaction mixture was poured into hydrochloric acid, the precipitate was filtered out and washed with water, and dried to obtain crude product; then purified by silica gel column chromatography with petroleum ether and ethyl acetate as mobile phase to obtain white solid C1.

[0035] This invention relates to a class of thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds. The materials of this invention are used as guest materials for the luminescent layer in the fabrication of electroluminescent devices.

[0036] 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.

[0037] Example 1: Synthesis of compound M1:

[0038] Add o-fluoronitrobenzene (1.41 g, 1 equiv), 1,2-chloro-3-hydroxypyridine (2.58 g, 2 equiv) and potassium carbonate (4.1 g, 3 equiv) to a round-bottom flask and dissolve them in N,N-dimethylformamide (DMF). Stir the reaction mixture overnight at 50 °C. Then pour the reaction mixture into ice water. The resulting precipitate is filtered out and washed with a large amount of water. After vacuum drying, crude intermediate 1 is obtained.

[0039] Next, intermediate 1 (2.25 g, 1 equiv) and stannous chloride (8.56 g, 5 equiv) were added sequentially to a round-bottom flask and dissolved in anhydrous ethanol (100 mL). The reaction mixture was stirred and refluxed at 80 °C for 12 h; then the reaction mixture was poured into 1 mol / L hydrochloric acid, filtered to obtain a precipitate, washed with plenty of water, and dried to obtain a crude product; then purified by silica gel column chromatography using petroleum ether:ethyl acetate = 10:1 (V:V) as the mobile phase to obtain a white solid Cl.

[0040] In a three-necked flask, C1 (498 mg, 1.5 equiv), 2-(4-bromophenyl)-4,6-diphenyl-1,3,5-triazine (700 mg, 1 equiv), palladium acetate (20 mg, 0.05 equiv), potassium carbonate (1.25 g, 5 equiv), and 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl (85 mg, 0.1 equiv), and dissolved in DMF; after three vacuum-nitrogen purgings, heated to 165℃ and reacted for 12-24 h; the reaction was monitored by TLC until completion, cooled to room temperature, and the solvent was evaporated under reduced pressure; the crude product was extracted three times with ethyl acetate, dried with anhydrous sodium sulfate and filtered; the filtrate was distilled under reduced pressure to remove the solvent, and the crude product was purified by silica gel column chromatography (200-300 mesh) and recrystallization from chloroform / methanol using petroleum ether:ethyl acetate = 30:1 (V:V) as the mobile phase to obtain yellow solid M1 (yield: 40%), TOF-EI-MS: 491.1744 [M + ].

[0041] Example 2: Synthesis of compound M2:

[0042] Add o-fluoronitrobenzene (1.41 g, 1 equiv), 1,2-chloro-3-hydroxypyridine (2.58 g, 2 equiv) and potassium carbonate (4.1 g, 3 equiv) to a round-bottom flask and dissolve them in N,N-dimethylformamide (DMF). Stir the reaction mixture overnight at 50 °C. Then pour the reaction mixture into ice water. The resulting precipitate is filtered out and washed with a large amount of water. After vacuum drying, crude intermediate 1 is obtained.

[0043] Next, intermediate 1 (2.25 g, 1 equiv) and stannous chloride (8.56 g, 5 equiv) were added sequentially to a round-bottom flask and dissolved in anhydrous ethanol (100 mL). The reaction mixture was stirred and refluxed at 80 °C for 12 h; then the reaction mixture was poured into 1 mol / L hydrochloric acid, filtered to obtain a precipitate, washed with plenty of water, and dried to obtain a crude product; then purified by silica gel column chromatography using petroleum ether:ethyl acetate = 10:1 (V:V) as the mobile phase to obtain a white solid Cl.

[0044] Add C1 (171 mg, 1.8 equiv), 4-(4-bromophenyl)-2,6-diphenylpyrimidine (200 mg, 1 equiv), palladium acetate (7 mg, 0.05 equiv), potassium carbonate (356 mg, 5 equiv), and 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl (49 mg, ...) sequentially to a three-necked flask. 0.2 equiv), and dissolved in DMF; after three vacuum-nitrogen purgings, heated to 165℃ and reacted for 12-24 h; the reaction was monitored by TLC until completion, cooled to room temperature, and the solvent was evaporated under reduced pressure; the crude product was extracted three times with ethyl acetate, dried with anhydrous sodium sulfate and filtered; the filtrate was distilled under reduced pressure to remove the solvent, and the crude product was purified by silica gel column chromatography (200-300 mesh) and recrystallization from chloroform / methanol using petroleum ether:ethyl acetate = 50:1 (V:V) as the mobile phase to obtain a yellow solid M2 (yield: 61%), TOF-EI-MS: 49.1783 [M + ].

[0045] Example 3: Density Functional Theory Simulation Density functional theory simulations of the structures of molecules M1 and M2 were performed using the Gaussian09 program. The HOMO and LUMO distributions of the molecules are as follows: Figure 1 As shown, the LUMO electron cloud of the molecule is mainly distributed on the triazine, while the HOMO electron cloud is mainly distributed on the nitrogen-containing phenoxazine donor group at the 1-position. The bridging benzene rings between the donor and acceptor overlap, theoretically demonstrating the molecule's electron and hole transport capabilities. More importantly, compared to similar molecules, the introduction of intramolecular hydrogen bonds reduces the dihedral angle between the donor and acceptor to 63.6° and 65.6°, respectively. This promotes the separation of the HOMO and LUMO while maintaining partial overlap, resulting in a smaller Δ... E ST And a large oscillator strength. On the other hand, the introduction of hydrogen bonds 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.

[0046] Example 4: Photophysical properties: 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 M1 and M2 at room temperature were measured using mol / L, as shown below. Figure 3As shown, the absorption range of 400-450 nm indicates that this is the ICT absorption from electron donor to electron acceptor. The fluorescence spectra of M1 and M2 measured in toluene both exhibit the characteristic of lacking fine vibrational structure, confirming the CT luminescence feature. Compared with the PL spectrum of M1 in toluene solvent, the maximum emission peak of M2 shows a blue shift, because the electron-withdrawing ability of the pyrimidine electron acceptor is weaker than that of triazine.

[0047] To further estimate the excited-state energy levels of this series of molecules, their LT-FL and LT-PH spectra were measured. The low-temperature spectra of all molecules in this series did not reveal fine vibrational structures, indicating that their S1 and T1 states originate from charge states and exhibit relatively small energy differences. Figure 4 As shown. Based on the highest peaks of their respective spectra, the energy levels of M1 and M2 were calculated to be 2.31 / 2.30 eV and 2.38 / 2.38 eV, respectively.

[0048] Example 5: 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 M1 and M2 are 4.9 µs and 10.2 µs, respectively.

[0049] Example 6: A blank scan was performed at a scan rate of 100 mV / s, followed by the addition of M1 and M2, 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 M1 and M2 were measured on a CHI610E electrochemical analyzer. Figure 6 Based on the half-wave potentials of the initial oxidation and reduction peak pairs, and the formula... and The HOMO and LUMO energy levels of M1 and M2 were calculated to be 5.13 / 2.73 eV and 5.11 / 2.65 eV, respectively.

[0050] Example 7: Spin-coated electroluminescent devices were fabricated using the thermally activated delayed fluorescence material containing intramolecular hydrogen bonds prepared in Examples 1 and 2 as the guest material 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:CBP (20nm) / TmPyPb (40nm) / LiF (1nm) / Al (200nm), (dopants: M1 and M2). In the device, PEDOT:PSS and LiF serve as the hole and electron injection layers, respectively; TAPC and TmPyPB serve as the hole and electron transport layers, respectively; furthermore, CBP is chosen as the host material because its triplet energy level is higher than that of the luminescent material, ensuring energy transfer from the host to the guest and effectively preventing the reverse energy transfer from the luminescent material to the host. Figure 8 The current density-voltage-luminance curves of blue-green light-emitting devices fabricated using M1 and M2 as guest materials are shown in the figure. As can be seen from the figure, the turn-on voltages of the devices are 2.3 and 3.0 V, and the maximum luminance is 13000 cd / m². 2 And 54000. 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 device are 21.0% and 18.2%, respectively. CIE values ​​(0.32, 0.57) and CIE values ​​(0.27, 0.53) are also shown. From the electroluminescence spectrum of the device, it can be seen that the emission peaks are only those of the guest materials M1 and M2, with no emission peaks from the host material or other materials. It is noteworthy that devices M1 and M2 exhibit emission peaks at a brightness of 100 cd / m². -2 and at 1000 cdm -2 The out-of-time quantum efficiencies were 20.0% / 17.2% and 17.2% / 13.0%, respectively. Compared with similar devices reported previously, the doped devices fabricated using small molecules M1 and M2 as luminescent materials exhibited excellent efficiency roll-off. Therefore, combining theoretical calculations and photophysical testing results, it can be inferred that M1 and M2 possess both high efficiency and low roll-off characteristics.

[0051] 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 thermally activated delayed fluorescence materials containing intramolecular hydrogen bonds, characterized in that, The material has the following structure: 。 2. A method for preparing a thermally activated delayed fluorescence material containing intramolecular hydrogen bonds as described in claim 1, characterized in that, Includes the following steps: ； Add donor C1, catalyst, ligand, base, and organic solvent to compound A1 or compound A2, wherein the molar ratio of compound A1 or compound A2 to donor C1, palladium catalyst, ligand, and base is 1:1.5~2:0.05:0.1~0.5:5; heat the reaction, and after the reaction is completed, extract, dry, and purify to obtain compounds M1 and M2.

3. The preparation method according to claim 2, characterized in that: The catalyst is palladium acetate, tris(dibenzylacetone)dipalladium, and cuprous iodide; the base is K2CO3, sodium tert-butoxide, and Cs2CO3; the ligand is 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl; and the organic solvent is N,N-dimethylformamide.

4. The preparation method according to claim 2, characterized in that: The preparation process of the donor C1 includes the following steps: ； (1) Preparation of intermediate 1: o-fluoronitrobenzene, 2-chloro-3-hydroxypyridine and potassium carbonate were dissolved in N,N-dimethylformamide and the reaction mixture was stirred overnight; the reaction mixture was poured into ice water, the precipitate was precipitated, filtered and washed to obtain intermediate 1; (2) Preparation of donor C1: Add intermediate 1 and stannous chloride to a round-bottom flask and dissolve them in anhydrous ethanol; stir and reflux the reaction mixture; then pour the reactants into hydrochloric acid, precipitate out, filter, wash and dry to obtain crude product; then purify to obtain donor C1.

5. The application of a type of thermally activated delayed fluorescence material containing intramolecular hydrogen bonds as described in claim 1, characterized in that, The fluorescent material is used to prepare electroluminescent devices.

6. A type of organic electroluminescent device, characterized in that: The light-emitting device includes the fluorescent material as described in claim 1.

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

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