Thermally activated delayed fluorescence material containing intramolecular hydrogen bond and application thereof

Abstract

The application discloses a kind of thermally activated delayed fluorescence material containing intramolecular hydrogen bond and its application, and belongs to the technical field of electroluminescent material.The material has a large dihedral angle advantage by using six-membered ring donor, introduces nitrogen atom at its 1-position, and through intramolecular hydrogen bond, on the one hand, fine-tunes the dihedral angle between the donor and the acceptor, improves the orbital overlap integral between the electron and the hole, maintains small energy level difference and fast reverse intersystem crossing rate, while improving the radiation transition rate, so as to promote the balance of reverse intersystem crossing rate and radiation transition rate.On the other hand, the rigidity of the molecule is improved to suppress excited state vibration relaxation and improve the light-emitting efficiency.The material of the application has excellent photoelectric performance, and provides an ideal material solution for preparing high-efficiency and low-rolling OLED devices.

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 the current mainstream track overlap integral of the small key charge transfer type (TBCT) and space charge transfer type (TSCT) TADF material cannot meet the above conditions. The present project aims to design and synthesize a kind of TADF material with small E ST and large k r The core is to use the six-membered ring donor with large dihedral angle advantage, introduce nitrogen atom at 1-position, on the one hand, through intramolecular hydrogen bond, fine-tune the dihedral angle between the donor and the acceptor, improve the orbital overlap integral between the electron and the hole, maintain small E ST , and improve k r ; on the other hand, improve the rigidity of the molecule, inhibit the relaxation of the excited state of the molecule, thereby improve the fluorescence quantum yield (PLQY). The present application is in this background, aims to solve the above technical contradiction through innovative molecular design strategy, to provide key material basis for promoting the low-cost, large-area and flexible development of OLED technology. SUMMARY

[0005] The purpose of the present application is to provide a kind of thermal activated delayed fluorescence material containing intramolecular hydrogen bond. By using the six-membered ring donor with large dihedral angle advantage, introducing nitrogen atom at 1-position, through intramolecular hydrogen bond, on the one hand, fine-tune the dihedral angle between the donor and the acceptor, improve the orbital overlap integral between the electron and the hole, maintain small E ST , and improve k r ; at the same time, improve the rigidity of the molecule, effectively inhibit π-π stacking and molecular vibration relaxation, significantly improve the material stability and luminous efficiency. Thus realize the effective balance of Δ E ST , k r and k RISC on TADF small molecule system, provide ideal material solution for preparing high-performance, low-rolling OLED device.

[0006] The technical scheme of the present application is as follows: a kind of thermal activated delayed fluorescence material containing intramolecular hydrogen bond, which has the following structure:

[0007]

[0008] The preparation method of the thermal activated delayed fluorescence material containing intramolecular hydrogen bond comprises the following steps:

[0009]

[0010] The compound A1 or compound A2, the donor C1, the catalyst, the ligand, the base are added into an organic solvent, and the molar ratio of the compound A1 or compound A2, the donor C1, the palladium catalyst, the ligand, the base is 1:1.5-2:0.05:0.1-0.5:5; the reaction is heated, after the reaction is completed, extraction, drying, purification, to obtain the compound M1 and M2.

[0011] Further, the catalyst is palladium acetate, tris(dibenzylideneacetone)dipalladium, cuprous iodide; the base is K2CO3, sodium tert-butoxide, Cs2CO3; the ligand is 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl; the organic solvent is N,N-dimethylformamide.

[0012] Further, the preparation process of the donor C1 includes the following steps:

[0013]

[0014] (1) Preparation of intermediate 1: o-fluoronitrobenzene, 2-chloro-3-hydroxypyridine and potassium carbonate are dissolved in N,N-DMF, and the reaction mixture is stirred overnight; the reaction mixture is poured into ice water, and a precipitate is separated out, filtered, and washed to obtain intermediate 1;

[0015] (2) Preparation of donor C1: intermediate 1 and stannous chloride are added to a round-bottom flask and dissolved with anhydrous ethanol; the reaction mixture is stirred and refluxed; then the reaction is poured into hydrochloric acid, a precipitate is separated out, filtered, washed, and dried to obtain a crude product; and then purified to obtain donor C1.

[0016] The application of the thermally activated delayed fluorescence material containing intramolecular hydrogen bonds, the fluorescent material is used for preparing an electroluminescent device.

[0017] An organic electroluminescent device, the luminescent device comprises the fluorescent material.

[0018] Further, the luminescent device comprises a luminescent layer, and the luminescent layer contains the fluorescent material.

[0019] The application has the following beneficial effects: the application provides a thermally activated delayed fluorescence material containing intramolecular hydrogen bonds, and the core advantage is that the “equilibrium Δ E ST 、 k r and k RISCThe molecular design principle of "high performance and high stability" is successfully realized. First, by introducing a nitrogen atom at the 1-position of the six-membered ring donor with large steric hindrance characteristics, the intramolecular hydrogen bond is formed between the 1-position nitrogen atom and the hydrogen atom on the bridging phenyl ring. On the one hand, the dihedral angle between the donor and the acceptor can be adjusted, thereby adjusting the degree of orbital overlap between the electrons and the holes, and then maintaining a small Δ E ST , while improving k r On the other hand, due to the existence of intramolecular hydrogen bond, the rigidity of the molecule is improved, which effectively suppresses the concentration quenching caused by π-π stacking and the non-radiative energy loss caused by molecular vibration relaxation, thereby helping to improve the photoluminescence quantum yield of the material and the stability of the material. Finally, a kind of OLED device with high efficiency and low roll-off is prepared. The successful implementation of this project opens up a new way for the design of TADF materials. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the HOMO and LUMO orbital distribution diagram of compound M1 calculated by Gaussian 09.

[0021] Figure 2 is the HOMO and LUMO orbital distribution diagram of compound M2 calculated by Gaussian 09.

[0022] Figure 3 is the ultraviolet-visible absorption spectrum and fluorescence emission spectrum of the compound in toluene solution. Among them, (a) is the ultraviolet-visible absorption spectrum and fluorescence emission spectrum of compound M1, (b) is the ultraviolet-visible absorption spectrum and fluorescence emission spectrum of compound M2.

[0023] Figure 4 is the fluorescence spectrum and phosphorescence spectrum of the compound under the condition of 77K. Among them, (a) is the fluorescence spectrum and phosphorescence spectrum of compound M1, (b) is the fluorescence spectrum and phosphorescence spectrum of compound M2.

[0024] Figure 5 is the transient fluorescence spectrum of the compound. Among them, (a) is the transient fluorescence spectrum of compound M1, (b) is the transient fluorescence spectrum of compound M2.

[0025] Figure 6 is the cyclic voltammogram of compounds M1 and M2.

[0026] Figure 7 is the electroluminescence spectrum of the sky blue light device M1 and M2.

[0027] Figure 8 is the current density-voltage-brightness curve of the sky blue light device M1 and M2.

[0028] Figure 9 is the external quantum efficiency-luminance curve of the sky blue light device M1 and M2.

[0029] Figure 10 is the current efficiency-luminance-power efficiency spectrum of the device. Wherein, (a) is the current efficiency-luminance-power efficiency spectrum of the sky blue light device M1, (b) is the current efficiency-luminance-power efficiency spectrum of the sky blue light device M2.

[0030] Figure 11 is the chemical structural formula of the compounds M1 and M2. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the present application will be clearly and completely described below with reference to the drawings.

[0032] The present application provides a kind of thermal activation delayed fluorescence material containing intramolecular hydrogen bond, its structural formula is as follows,

[0033]

[0034] The present application provides a kind of synthesis method of thermal activation delayed fluorescence material containing intramolecular hydrogen bond, comprising the following steps:

[0035]

[0036] 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, base are added into organic solvent, and the molar ratio of the compound A1 or compound A2, donor C1, palladium catalyst, ligand, base is 1:1.5~2:0.05:0.1~0.5:5. After vacuum-nitrogen replacement three times, it is heated to 165 DEG C and reacted for 12~24h;After reaction is detected by TLC to the end, the solvent is distilled under reduced pressure;The crude product is extracted with ethyl acetate three times, dried with anhydrous sodium sulfate and filtered;The filtrate is distilled under reduced pressure to remove the solvent, and the obtained crude product is purified by silica gel column chromatography with petroleum ether and ethyl acetate as mobile phase, chloroform / methanol recrystallization, to obtain compounds M1 and M2.

[0037] The catalyst is palladium acetate, tris (dibenzylideneacetone) dipalladium, cuprous iodide;The base is K2CO3, sodium tert-butoxide, Cs2CO3;The ligand is 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl;The organic solvent is N,N-dimethylformamide.

[0038] The present application provides a kind of compound C1 for preparing the thermal activation delayed fluorescent material containing intramolecular hydrogen bond: 10H-benzo [b] pyridine [2, 3-e] [1, 4] oxazine. The preparation process comprises the following steps:

[0039]

[0040] (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 at 50°C overnight. Then the reaction mixture was poured into ice water, and the obtained precipitate was filtered out and washed with a large amount of water to obtain crude product 1.

[0041] (2) Preparation of C1: intermediate 1 and stannous chloride were added to a round-bottom flask and dissolved with anhydrous ethanol. The reaction mixture was stirred at 80°C under reflux for 12h; then the reaction was poured into hydrochloric acid, and the obtained precipitate was filtered out and washed with water, 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.

[0042] The thermal activation delayed fluorescent material containing intramolecular hydrogen bond of the present application The material of the present application is used as a guest material of a light-emitting layer for preparing an electroluminescent device.

[0043] The present application is further illustrated by examples, which are intended to better understand the content of the present application. Therefore, the examples do not limit the protection scope of the present application.

[0044] Example 1 Synthesis of compound M1:

[0045]

[0046] o-fluoronitrobenzene (1.41g, 1 equiv), 1, 2-chloro-3-hydroxypyridine (2.58g, 2 equiv) and potassium carbonate (4.1g, 3 equiv) were added to a round-bottom flask and dissolved in N,N-dimethylformamide (DMF), and the reaction mixture was stirred at 50°C overnight; then the reaction mixture was poured into ice water, and the obtained precipitate was filtered out and washed with a large amount of water, and dried under vacuum to obtain crude product intermediate 1.

[0047] To the round bottom flask, intermediate 1 (2.25 g, 1 equiv) and stannous chloride (8.56 g, 5 equiv) were added successively and dissolved with anhydrous ethanol (100 mL). The reaction mixture was stirred at 80 °C for 12 h under reflux; then the reaction was poured into 1 mol / L hydrochloric acid, the precipitate was filtered and washed with a large amount of water, and the crude product was obtained after drying; then purified by silica gel column chromatography with petroleum ether: ethyl acetate = 10:1 (V:V) as the mobile phase, and C1 was obtained as a white solid.

[0048] To the 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-dicyclohexylphospho-2',4',6'-triisopropylbiphenyl (85 mg, 0.1 equiv) were added successively and dissolved with DMF; after vacuum-nitrogen replacement for three times, it was heated to 165 °C for 12-24 h; after TLC detection of the reaction to the end, it was cooled to room temperature, and the solvent was evaporated under reduced pressure; the crude product was extracted with ethyl acetate three times, dried with anhydrous sodium sulfate and filtered; the filtrate was distilled under reduced pressure to remove the solvent, and the obtained crude product was purified by silica gel column chromatography with petroleum ether: ethyl acetate = 30:1 (V:V) as the mobile phase, and recrystallized with chloroform / methanol to obtain M1 (yield: 40%) as a yellow solid, TOF-EI-MS: 491.1744 [M + ]。

[0049] Synthesis of compound M2 in Example 2:

[0050]

[0051] To the round bottom flask, 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) were added and dissolved in N,N-dimethylformamide (DMF), and the reaction mixture was stirred at 50 °C overnight; then the reaction mixture was poured into ice water, the obtained precipitate was filtered out and washed with a large amount of water, and the crude product intermediate 1 was obtained after vacuum drying.

[0052] To the round bottom flask, intermediate 1 (2.25 g, 1 equiv) and stannous chloride (8.56 g, 5 equiv) were added successively and dissolved with anhydrous ethanol (100 mL). The reaction mixture was stirred at 80 °C for 12 h under reflux; then the reaction was poured into 1 mol / L hydrochloric acid, the precipitate was filtered and washed with a large amount of water, and dried to obtain the crude product; then purified by silica gel column chromatography with petroleum ether: ethyl acetate = 10:1 (V:V) as the mobile phase to obtain white solid C1.

[0053] To the three-necked flask, 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-dicyclohexylphospho-2',4',6'- triisopropylbiphenyl (49 mg, 0.2 equiv) were added successively and dissolved with DMF; after three vacuum-nitrogen replacements, heated to 165 °C for 12-24 h; after TLC detection of the reaction to the end of the reaction, cooled to room temperature, and the solvent was evaporated under reduced pressure; the crude product was extracted with ethyl acetate three times, dried with anhydrous sodium sulfate and filtered; the filtrate was distilled under reduced pressure to remove the solvent, and the obtained crude product was purified by silica gel column chromatography with petroleum ether: ethyl acetate = 50:1 (V:V) as the mobile phase, chloroform / methanol recrystallization to obtain yellow solid M2 (yield: 61%), TOF-EI-MS: 49.1783 [M + ].

[0054] Example 3 Density functional theory simulation:

[0055] The density functional theory simulation of the structure of M1 and M2 molecules was carried out by Gaussian09 program, and the HOMO and LUMO distribution of the molecules was shown in Figure 1 The LUMO electron cloud of the molecule was mainly distributed on the triazine, and the HOMO electron cloud was mainly distributed on the 1-nitrogen-containing phenoxazine donor group, and there was overlap on the bridging benzene ring between the donor and acceptor, which theoretically proved that the molecule had electron and hole transport ability. More importantly, compared with similar molecules, due to the introduction of intramolecular hydrogen bond, the dihedral angle between the donor and acceptor was reduced to 63.6° and 65.6°, which promoted the separation of HOMO and LUMO of the molecule while accompanied by partial overlap, realizing small Δ E ST and large oscillator strength. On the other hand, the introduction of hydrogen bond also improved the rigidity of the molecule to inhibit the molecular vibration relaxation, and improved the light-emitting efficiency, so combining the above two points, all the molecules maintained a high molecular rigidity, so that the molecule maintained a high radiation transition rate, small energy level difference and high fluorescence quantum yield.

[0056] Photophysical properties of Example 4:

[0057] The UV-Vis absorption and fluorescence spectra of M1 and M2 were measured in dry toluene at room temperature with a concentration of 1 × 10 -5 Figure 3 The absorption range from 400 to 450 nm is assigned to the ICT absorption from electron donor to electron acceptor. The fluorescence spectra of M1 and M2 in toluene both show no fine vibrational structure, which is the characteristic of CT emission. Compared with the PL spectrum of M1 in toluene, the maximum emission peak of M2 has a blue shift, which is because the electron-withdrawing ability of the pyrimidine electron acceptor is weaker than that of the triazine.

[0058] To further estimate the excited state energy levels of the series of molecules, the LT-FL spectra and LT-PH spectra were tested. The low-temperature spectra of the series of molecules all show no fine vibrational structure, which proves that their S1 and T1 come from the charge state and show a small energy gap. As shown in Figure 4 According to the highest peak of each spectrum, the energy levels of M1 and M2 are calculated to be 2.31 / 2.30 eV and 2.38 / 2.38 eV.

[0059] Example 5:

[0060] The transient spectra of the doped films of the series of molecules were tested. As shown in Figure 5 At room temperature, the transient spectra of all molecules show the double-exponential decay characteristics of the transient component and the delayed component, which proves the existence of TADF properties, and the lifetimes of M1 and M2 are 4.9 µs and 10.2 µs, respectively.

[0061] Example 6:

[0062] At a scan rate of 100 mV / s, a blank scan was performed, and then M1 and M2 were added, respectively, in dry dichloromethane and N , N -dimethylformamide as the solvent, and tetra-n-butylammonium hexafluorophosphate (Bu4NPF6) as the electrolyte, after deoxygenation by nitrogen bubbling for 10 min, the positive and negative cyclic voltammetry curves of M1 and M2 were measured on a CHI610E type electrochemical analyzer, as shown in Figure 6 .According to the half-wave potentials of the initial oxidation and reduction peak pairs, and the formulas and , the HOMO energy level and the LUMO energy level of M1 and M2 are calculated to be 5.13 / 2.73 eV and 5.11 / 2.65 eV, respectively.

[0063] Example 7: ​

[0064] The spin-coated electroluminescent devices were prepared by using the thermally activated delayed fluorescence materials with intramolecular hydrogen bond prepared in Example 1 and 2 as guest materials of the light-emitting layer, and the devices were characterized. The specific structure of the electroluminescent device was: IITO / PEDOT:PSS (40 nm) / TAPC (20 nm) / 5 wt% dopants:CBP (20 nm) / TmPyPb (40 nm) / LiF (1 nm) / Al (200 nm), (dopants: M1 and M2). In the device, PEDOT:PSS and LiF were used as the hole and electron injection layers, respectively; TAPC and TmPyPB were used as the hole and electron transport layers, respectively; in addition, CBP was selected as the host material because the triplet energy level of the material was higher and far higher than the triplet energy level of the light-emitting material, which not only ensured the energy transfer from the host to the guest, but also effectively prevented the energy back transfer process from the light-emitting material to the host. As shown in Figure 8 The current density-voltage-brightness curves of the blue-green light-emitting devices prepared by using M1 and M2 as guest materials were obtained, and it can be seen from the graph that the turn-on voltage of the device was 2.3 and 3.0 V, and the maximum brightness was 13000 cd / m 2 and 54000. The efficiency curve and electroluminescent spectrum of the device are shown in Figure 9 and 10 The maximum external quantum of the device was 21.0% and 18.2%, respectively. CIE (0.32, 0.57) and CIE (0.27, 0.53) can be seen from the electroluminescent spectrum of the device, and the light-emitting peak of the device is only the light-emitting peak of the guest material M1 and M2, without the light-emitting peak of the host material or other light-emitting peaks. It is worth noting that the external quantum efficiency of the devices M1 and M2 was 20.0% / 17.2% and 17.2% / 13.0% at the brightness of 100 cd m -2 and 1000 cd m -2 , respectively, which was at an excellent level compared with the similar devices reported. Therefore, combined with the theoretical calculation results and the photophysical test results, it can be inferred that M1 and M2 have the characteristics of high efficiency and low roll-off.

[0065] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

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: 。 3. The preparation method according to claim 2, characterized in that, The specific steps are as follows: add an organic solvent to compound A1 or compound A2, donor C1, catalyst, ligand, and base, wherein the molar ratio of compound A1 or compound A2, donor C1, 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.

4. The preparation method according to claim 3, 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.

5. The preparation method according to claim 2, characterized in that: The preparation process of the donor C1 includes the following steps: 。 6. The preparation method according to claim 5, characterized in that: The preparation process of the donor C1 is as follows: (1) Preparation of intermediate 1: o-fluoronitrobenzene, 2-chloro-3-hydroxypyridine and potassium carbonate were dissolved in 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; Further purification yields donor C1.

7. An 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.

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

9. The electroluminescent device according to claim 8, characterized in that, The light-emitting device includes a light-emitting layer containing the fluorescent material.

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