TADF luminescent material and preparation method thereof

Abstract

The invention discloses a TADF luminescent material and a preparation method thereof, and relates to the technical field of organic optoelectronics, the molecular structure of the material comprises a phenyl triazine derivative electron-deficient core as an electron acceptor and a carbazole or tert-butyl carbazole electron-rich group as an electron donor; an aggregation-induced emission mechanism is introduced into the thermally activated delayed fluorescence material, so that the aggregation-induced quenching problem of a traditional thermally activated delayed fluorescence material and the exciton annihilation effect under high brightness are effectively solved, and meanwhile, the defect that a traditional aggregation-induced emission molecule is low in electroluminescence efficiency is overcome; the material can be used for preparing a non-doped organic electroluminescent device, the process is simplified, the cost is reduced, and the material has application potential in the field of intelligent response materials.

Description

Technical Field

[0001] This invention relates to the field of organic optoelectronics, and more particularly to a TADF luminescent material and its preparation method. Background Technology

[0002] Organic light-emitting diodes (OLEDs) based on organic semiconductor materials possess advantages such as flexibility, light weight, fast response speed, high brightness, wide viewing angle, good color quality, and low cost, attracting widespread attention from academia and industry. Since the pioneering work on bilayer fluorescent OLEDs reported by Ching W. Tang et al. of Kodak in 1987, related research has progressed rapidly. After years of effort, organic light-emitting materials have evolved from first-generation traditional fluorescent materials, second-generation organic electrophosphorescent materials based on metal complexes, to the third-generation thermally activated delayed fluorescence (TADF) materials, which have the most promising applications. New OLED materials with higher efficiency, lower cost, and more vibrant colors have become a hot topic in the industry.

[0003] TADF materials can serve as host and guest materials for the luminescent layer. Their chemical structure, thermal stability, photophysical properties, and quantum yield (PLQY) directly determine the final device efficiency. Intramolecular and intermolecular charge transfer luminescence is a common design approach for luminescent materials. It requires a charge-deficient core as an electron acceptor and a charge-rich group as an electron donor, emitting fluorescence through intramolecular and intermolecular charge transfer.

[0004] Traditional TADF materials, due to their conjugated structure, exhibit aggregation-induced quenching (ACQ) due to π-π molecular stacking during aggregation. Therefore, complex techniques and doping methods are required to distribute the material into the host matrix and eliminate the adverse effects of ACQ. Furthermore, doped OLED devices based on TADF materials suffer from exciton annihilation at high brightness, causing a sharp decrease in electroluminescence efficiency with increasing current, significantly hindering their practical application. Summary of the Invention

[0005] This application provides a TADF luminescent material and its preparation method, introducing the AIE mechanism into the TADF material. This not only solves the problems caused by concentration quenching and exciton annihilation effects in TADF devices, but also reduces the device fabrication cost by using non-doping technology. At the same time, it also solves the problem of low efficiency of traditional AIE molecular electroluminescence.

[0006] This application includes a TADF luminescent material having the structures shown in general formulas (I) and (II):

[0007] Where X can be either a C atom or a N atom; R 1 R 2 R 3 L 1 L 2 L 3 Each of these can be independently alkyl, amino, imino, deuterated, unsubstituted or substituted five-membered aromatic ring, six-membered aromatic ring, fused ring, aniline, aniline derivative, diphenylamine, or diphenylamine derivative.

[0008] Where L 1 L 2 L 3 It can have the following general formula:

[0009] Where R 1 R 2 R 3 R 4 R 5 R 6 R 7 R 8 R 9 R 10 R 11 R 12 R 13 R 14 Each can be independently a hydrogen atom, a deuterium atom, an alkyl group, a deuterated product, an aromatic ring, a fused ring, an aniline, an aniline derivative, a diphenylamine, or a diphenylamine derivative, and Y can be an O atom or an S atom.

[0010] Furthermore, including but not limited to the following structures:

[0011]

[0012] The above materials are used as functional materials in organic electronic devices, which include: organic electroluminescent devices, optical sensors, solar cells, lighting elements, organic thin-film transistors, organic field-effect transistors, organic thin-film solar cells, information tags, electronic artificial skin sheets, sheet-type scanners, or electronic paper.

[0013] The method for preparing the above-mentioned TADF luminescent material is characterized in that the reaction equation occurring during the preparation process is as follows:

[0014] In the reaction equation, X and Y represent chlorine atoms, bromine atoms, or iodine atoms; The specific reaction steps in the reaction equation are as follows: In a nitrogen or argon atmosphere, a halogenated compound with bis(triazol)triazine as its core and R are reacted. 2 H, palladium acetate, tri-tert-butylphosphine tetrafluoroborate, and potassium carbonate are reacted in toluene solution. The mixture of the above reactants is refluxed for 24-60 hours, cooled, filtered through diatomaceous earth, evaporated under reduced pressure, and subjected to silica gel column chromatography to obtain the target product.

[0015] The halogenated compound with bis(triazol)-triazine as its core: R 2 The molar ratio of H:palladium acetate:tri-tert-butylphosphine tetrafluoroborate:potassium carbonate is 1:(0.5~5):(0.05~0.5):(0.05~1):(2~10).

[0016] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: The material can be used directly as an undoped light-emitting layer, which simplifies the device structure and reduces the manufacturing cost. The novel bis(triazol)triazine (BTT) acceptor provided by this invention fuses hexagonal triazine (TRZ) and two pentagonal triazoles (TAZ). Due to the fusion of the electron-deficient TAZ fragments, BTT exhibits a stronger electron-withdrawing ability than the TRZ backbone, resulting in well-separated distribution of FMOs and thus reducing the ΔEST of the target TADF material. Furthermore, the BTT acceptor significantly enhances the rigidity of the molecular structure, effectively weakening intermolecular interactions and improving exciton utilization. The symmetry breaking and strong molecular rigidity of the novel TADF material based on the BTT acceptor suppress intramolecular motion in the solid state, thereby generating AIEE. The novel TADF material molecule with bis(triazol)triazine as its core exhibits mechanofluorescence (MCL).

[0017] This invention utilizes a novel TADF material molecule with bis(triazol)triazine as its core as a design unit to construct a non-traditional TADF material with multi-stimulus response, providing a new design approach. It effectively avoids the aggregation-induced quenching phenomenon caused by π-π stacking in traditional TADF materials; significantly suppresses the exciton annihilation effect of doped OLED devices at high brightness; improves the efficiency and stability of devices at high current densities; and possesses mechanoluminescent color-changing properties, with its emission color reversibly changing under mechanical force and thermal annealing treatment, expanding its applications in the fields of intelligent sensing and display. Attached Figure Description

[0018] Figure 1 The H NMR spectrum of M3 in this invention; Figure 2 The H NMR spectrum of M5 in this invention; Figure 3 The H NMR spectrum of M6 in this invention; Figure 4 The C NMR spectrum of M6 in this invention; Figure 5 The XRD pattern of M5 in this invention; Figure 6 This is the XRD pattern of M6 in this invention. Detailed Implementation

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] The following provides a method for preparing the compounds disclosed in this invention. However, this disclosure is not intended to limit it to any of the methods described herein. Those skilled in the art can readily modify the described methods or use different methods to prepare one or more of the disclosed compounds. The following aspects are merely exemplary and are not intended to limit the scope of this disclosure. Temperature, catalyst, concentration, reactant composition, and other process conditions can be varied, and those skilled in the art can readily select suitable reactants and conditions for the desired compounds.

[0021] Example 1:

[0022]

[0023] Synthesis of intermediate M1: A stir bar was placed in a round-bottom flask, and 2,4-dichloro-6-phenyl-1,3,5-triazine (2.26 g, 10 mmol), hydrazine hydrate (24 mL, 80%), and ethanol (6 mL) were added sequentially. The mixture was stirred under reflux for 6 hours, cooled to 0 °C, and filtered. The resulting solid was washed with ethanol to pH 7.0 and could be used in the next reaction without further purification. A brown solid (1.6 g, 73% yield) was given.

[0024] Example 2:

[0025]

[0026] Synthesis of intermediate M2: M1 (1.30 g, 6 mmol) and 4-bromobenzaldehyde (2.22 g, 12 mmol) were dissolved in ethanol (30 mL). The solution was stirred and heated to 90 °C for 6 hours under a nitrogen atmosphere. After the reaction was complete, the mixture was cooled, filtered, and washed with ethanol. The resulting hydrazone could be used in the next reaction without any purification. A grayish-white solid (2.69 g, 90% yield) was given.

[0027] Example 3:

[0028]

[0029] Synthesis of intermediate M3: To a solution of M2 (1.30 g, 2 mmol) in dichloromethane, iodobenzene diacetate (1.29 g, 4 mmol) was added. The reaction mixture was stirred at room temperature for 6 hours, the resulting solid was collected by filtration and washed with dichloromethane. The crude product, without further purification, was used directly in the subsequent rearrangement reaction to give a yellowish-white solid (0.38 g, 35% yield).

[0030] like Figure 1 Characterization of intermediate M3: 1 H NMR (400 MHz, Chloroform- d ) δ 8.77 – 8.72 (m,2H), 8.31 (dd, J = 8.5, 1.9 Hz, 2H), 8.10 (dd, J = 8.5, 1.9 Hz, 2H), 7.79(dd, J = 8.6, 1.9 Hz, 2H), 7.75 – 7.63 (m, 5H). Example 4:

[0031]

[0032] Synthesis of intermediate M4: DBU (487.1 μL) was added fractionally to a methanol (14 mL) solution of M3 (0.6 g, 1.1 mmol). The mixture was stirred at room temperature for 4 hours, followed by solvent removal by rotary evaporation. A mixture of ethyl acetate and dichloromethane was then added, and the mixture was distilled under reduced pressure until a large amount of solid was obtained. The solid was then washed with ethyl acetate until white (this step was repeated several times). Finally, the collected product was analyzed by thin-layer chromatography. After confirming the absence of visible impurities, the purified product could be directly used for the synthesis of the target compound. A white solid (0.36 g, 60% yield) was obtained.

[0033] Synthesis of the target product via Buchwald-Hartwig amination reaction: Example 5:

[0034]

[0035] Synthesis of compound M5: M4 (55 mg, 0.1 mmol), palladium acetate (5 mg, 0.02 mmol), carbazole (0.22 mmol), tris(tert-butyl)phosphine tetrafluoroborate (12 mg, 0.04 mmol), and potassium carbonate (55 mg, 0.4 mmol) were added sequentially to a Schlenk tube. The mixture was purged with nitrogen at least three times, and then 5 mL of dried, degassed toluene was added. The mixture was then refluxed under a nitrogen atmosphere for 60 hours. After the reaction was complete, the mixture was cooled to room temperature, and the solvent was removed by rotary evaporation. The crude product was purified by column chromatography to give a yellowish-white solid (50 mg, 69%).

[0036] like Figure 2 Characterization of target product M5: 1 H NMR (400 MHz, Chloroform- d ) δ 8.86 – 8.66(m, 4H), 8.49 (d, J = 8.4 Hz, 1H), 8.39 – 8.25 (m, 2H), 8.21 – 8.06 (m, 4H), 7.94 – 7.82 (m, 2H), 7.82 – 7.58 (m, 7H), 7.56 – 7.28 (m, 9H). HRMS(ESI)m / z:[M+H] + Calcd.for C 47 H 30 N9 + :720.2624; found,720.2619. Example 6:

[0037]

[0038] Synthesis of compound M6: M4 (55 mg, 0.1 mmol), palladium acetate (5 mg, 0.02 mmol), 3,6-di-tert-butyl-9H-carbazole (0.22 mmol), tris(tert-butyl)phosphine tetrafluoroborate (12 mg, 0.04 mmol), and potassium carbonate (55 mg, 0.4 mmol) were added sequentially to a Schlenk tube. The mixture was purged with nitrogen at least three times, and then 5 mL of dried, degassed toluene was added. The mixture was then refluxed under a nitrogen atmosphere for 60 hours. After the reaction was complete, the mixture was cooled to room temperature, and the solvent was removed by rotary evaporation. The crude product was purified by column chromatography to give a yellowish-white solid (56.6 mg, 60%).

[0039] like Figure 3 Characterization of target product M6: 1 H NMR (400 MHz, Chloroform- d ) δ 8.84 (d, J =7.6 Hz, 2H), 8.71 (d, J = 8.6 Hz, 2H), 8.47 (d, J = 8.4 Hz, 2H), 8.17 – 8.13(m, 3H), 7.91 (d, J = 8.5 Hz, 2H), 7.81 – 7.68 (m, 6H), 7.57 (d, J = 8.7 Hz,2H), 7.54 – 7.45 (m, 6H), 1.55 (s, 36H). HRMS(ESI)m / z:[M+H] + Calcd.for C 63 H 62 N9 + :944.5128; found, 944.5123. The carbon NMR spectrum of the target product M6 is as follows: Figure 4 ; The mechanofluorescence of target products M5 and M6 was verified by XRD analysis. Figure 5 , Figure 6 After mechanical grinding, the XRD pattern of the sample underwent significant changes. The originally sharp diffraction peaks broadened considerably or even disappeared, while a broad diffuse scattering packet appeared across the entire diffraction angle range. This indicates that the material transformed from a long-range ordered crystalline structure to a short-range ordered amorphous structure. The near disappearance of the diffraction peaks in product M6 demonstrates that mechanical force disrupted the long-range ordered structure of the material, causing it to transform into an amorphous state. The original crystallinity was significantly reduced, and the regularly arranged lattice was destroyed. This process can be reversibly switched through thermal annealing, showcasing its application potential in smart response materials.

[0040] This material introduces the AIE (aggregation-induced emission) mechanism into TADF (thermally activated delayed fluorescence) materials. Its molecular structure includes an electron-deficient core (phenyltriazine derivative) as an electron acceptor and an electron-rich group (carbazole or tert-butylcarbazole) as an electron donor. Emission is achieved through intramolecular / intermolecular charge transfer, while avoiding the ACQ (aggregation-induced quenching) problem of traditional TADF materials. The AIE property enhances the luminescence of the material in the aggregated state (amorphous state), avoiding the ACQ problem. The TADF property achieves efficient delayed fluorescence through reverse intersystem crossing (RISC), improving the luminescence efficiency. After mechanical force disrupts the molecular arrangement, the amorphous structure can change the charge transfer path or energy level difference, thereby modulating the emission color.

[0041] The luminescence performance of OLEDs prepared using the above materials is verified; an example is provided, which should not be regarded as a limitation of the present invention. In order to facilitate those skilled in the art to understand the technical advantages and device principles of the present invention, the examples in the present invention are all illustrated with the simplest device structure.

[0042] A multilayer organic light-emitting diode device is provided, consisting of an anode / hole injection layer (HIL) / hole transport layer (HTL) / emitting layer (EML) / electron transport layer (ETL) / electron injection layer (EIL) / cathode. Using ITO glass as the substrate, the substrate was ultrasonically cleaned sequentially in acetone, ethanol, and deionized water to remove surface organic matter and particulate contaminants. After cleaning, it was dried with nitrogen and then treated in a UV ozone cleaner for 15-20 minutes. The treated ITO substrate was then placed on the sample stage of a vacuum evaporation machine, and a high vacuum was applied until the pressure was below 5 × 10⁻⁶. -4 Pa; Then, the organic functional layers are deposited sequentially: Hole injection layer (HIL): HATCN is deposited by heating a molybdenum boat; Hole transport layer (HTL): TAPC is deposited by evaporation; Emissive layer (EML): TADF material (M5, M6) is directly deposited by evaporation; Electron transport layer (ETL): TPBi (approximately 30-50 nm) is deposited by evaporation; Electron injection layer (EIL): A very thin layer of LiF (approximately 1 nm) is deposited by evaporation; Cathode evaporation: Finally, an opaque metal cathode, aluminum (Al, approximately 100 nm), is deposited by evaporation through a mask to complete the device fabrication; Immediately encapsulate the device in a glove box (filled with high-purity nitrogen, with a water and oxygen content of <0.1 ppm); use UV-curing adhesive to bond the cover sheet (which usually also contains a desiccant) to the device substrate, and cure it with UV light to completely isolate the device from the external environment.

[0043] The external quantum efficiency obtained above was tested in accordance with GB / T 39492-2020; it was found that the external electron efficiency was 19%±2% when M5 was used as the light-emitting layer and 22%±1% when M6 was used as the light-emitting layer.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A TADF light-emitting material, characterized by, It has the structure shown in general formula (I), (II): wherein X can be a C atom or a N atom, respectively; R 1 , R 2 , R 3 , L 1 , L 2 , L 3 each independently is alkyl, amino, imino, deuterium, unsubstituted or substituted five-membered aromatic ring, six-membered aromatic ring, fused ring, aniline, aniline derivative, diphenylamine, diphenylamine derivative; wherein L 1 , L 2 , L 3 may have the general formula: wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 , R 11 , R 12 , R 13 , R 14 each independently is a hydrogen atom, a deuterium atom, an alkyl group, a deuterium group, an aromatic ring, a fused ring, an aniline, an aniline derivative, a diphenylamine, and a diphenylamine derivative, and Y can be an O atom or an S atom.

2. The material of claim 1, wherein structures including, but not limited to, one of the following.

3. Use of a material according to any of claims 1 to 2 as a functional material in an organic electronic device, characterized in that, The organic electronic device includes an organic electroluminescent device, an optical sensor, a solar cell, an illumination element, an organic thin film transistor, an organic field effect transistor, an organic thin film solar cell, an information tag, an electronic artificial skin sheet, a sheet-type scanner, or electronic paper.

4. A method for preparing the TADF light-emitting material according to any one of claims 1-2, characterized in that, wherein the reaction equation specifically represents the following steps: under nitrogen or argon atmosphere, halogenated compound with bistrizoletriazine as core and R 2 H, palladium acetate, tri-tert-butylphosphine tetrafluoroborate, potassium carbonate in toluene solution, the above reaction mixture solution is refluxed for 24-60 hours, cooled, filtered by diatomite, rotary evaporation under reduced pressure, and silica gel column chromatography to obtain the target product. The halogenated compound with a bistrizoletriazole core: R 2 H: palladium acetate: tri-tert-butylphosphine tetrafluoroborate: potassium carbonate in a molar ratio of 1 : (0.5-5): (0.05-0.5): (0.05-1): (2-10).

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