Blue organic delayed fluorescent material as well as preparation method and application thereof

Abstract

The invention belongs to the field of organic photoelectric materials, and particularly relates to a blue organic delayed fluorescent material and a preparation method and application thereof. The material integrates a space charge transfer mechanism and a chemical bond charge transfer mechanism, and shows unique luminescence performance. Through an elaborately designed molecular structure, effective energy transfer from an excited state to a ground state is realized, and a remarkable blue delayed fluorescence effect is generated. An innovative synthesis path is adopted and comprises the steps of raw material selection, reaction condition optimization and post-treatment, so that the purity, stability and luminous efficiency of the obtained material are ensured. The preparation process is simple, has high yield and repeatability, and is suitable for large-scale industrial production. The material has good luminescence performance and thermal stability in a solid state, the luminescence wavelength is located in a blue spectrum range, the luminescence life is long, excellent charge transmission performance and photoelectric conversion efficiency are shown, and the material has wide application prospects in organic light-emitting diodes, solid-state illumination, display technologies and the like.

Description

Technical Field

[0001] The present invention belongs to the field of organic optoelectronic materials, and particularly relates to a blue organic delayed fluorescence material, a preparation method thereof, and an application thereof. Background Art

[0002] In the technical field of organic optoelectronic materials where blue organic light-emitting materials are located, there has been a long development process from basic theoretical exploration to extensive practical applications. In the early stage, traditional fluorescent materials, as the main carriers of blue light emission, under electrical excitation, since singlet and triplet excitons are generated in a ratio of 1:3, and traditional fluorescent materials can only utilize 25% of the singlet excitons for radiative decay, resulting in low luminescence efficiency, which greatly limits the application expansion of related technologies. However, this stage laid the foundation for subsequent research, and researchers gradually realized the key significance of improving exciton utilization efficiency for enhancing luminescence efficiency.

[0003] With the in-depth research, scientists continuously sought breakthroughs, and metal complex phosphorescent materials emerged as the representatives of the second-generation organic light-emitting materials. By means of the spin-orbit coupling effect induced by heavy metals, triplet excitons can directly return to the ground state through the radiative transition process to emit phosphorescence, and the internal quantum efficiency can theoretically reach 100%. However, precious metals such as iridium and platinum used therein are scarce and costly, and most phosphorescent devices have a large efficiency roll-off problem at high brightness, which to a certain extent hinders their large-scale application. Nevertheless, this technological breakthrough brought new ideas to the field of organic optoelectronics and promoted the research to develop in a more efficient and stable direction.

[0004] In recent years, thermally activated delayed fluorescence (TADF) materials have become a research hotspot. As the third-generation organic electroluminescent materials, they convert the majority of non-luminescent triplet excitons into singlet excitons through the reverse intersystem crossing (RISC) process, thereby achieving 100% exciton utilization efficiency. In terms of blue TADF materials, although there are some innovative achievements, such as some molecular designs based on the intramolecular space charge transfer mechanism, there are still many problems. For example, TSCT-TADF molecules face problems such as long radiative decay time and low radiative rate, resulting in the overall luminescence efficiency being difficult to meet the actual requirements. Nevertheless, the emergence of TADF materials has injected new vitality into the development of blue light materials, prompting researchers to continuously optimize the molecular structure and preparation process.

[0005] In the display field, with the growing demand for high-definition and wide color gamut displays, the requirements for the color purity of blue light materials are becoming increasingly stringent. Early blue light materials using fluorescence technology had problems with impure chromaticity, seriously affecting color reproducibility and display effects. To solve this problem, researchers have started from various aspects such as molecular structure design and material synthesis processes. They have achieved an extremely narrow emission spectrum and rapid spin flipping of blue light materials. The corresponding OLED devices have excellent color coordinates and high external quantum efficiency, providing strong support for the development of wide color gamut ultra-high definition OLED displays.

[0006] In the lighting field, white organic light-emitting diodes (WOLEDs) are regarded as highly potential next-generation intelligent lighting sources due to their advantages such as flexibility, bendability, low power consumption, and eye protection. However, the lack of long-lived blue light materials and devices that can efficiently utilize triplet excitons for luminescence has limited the power efficiency and device lifetime of WOLEDs. Therefore, the research team has continuously explored and precisely regulated the complementary blue light color to achieve full-spectrum coverage. While improving the quality of white light, it has effectively solved the problems of efficiency and lifetime, enabling WOLED devices to achieve significant improvements in maximum external quantum efficiency and maximum power efficiency, and the device lifetime has also reached a relatively high level.

[0007] In addition, in other emerging application fields, such as quantum dot displays, scientists have been continuously working hard on the research of electroluminescent quantum dot light-emitting diodes (QLEDs). The performance of red and green QLEDs can already be comparable to that of commercial OLEDs. However, due to reasons such as higher operating voltages and the need to overcome larger hole injection barriers, the performance progress of blue QLED devices lags behind, especially the development of environmentally friendly heavy-metal-free devices is slow.

[0008] Generally speaking, the blue light material technology field is continuously innovating and developing in the process of solving existing problems. From the enrichment of material types to the gradual optimization of performance, from the deep cultivation of traditional application fields to the expansion of emerging fields, the unremitting efforts of researchers are making blue light materials play an increasingly important role in the field of organic optoelectronics, and there is also hope for greater breakthroughs and applications in more fields in the future.

[0009] Organic light-emitting diode (OLED) technology, with its outstanding performance in low energy consumption, fast response, and flexibility, has shown great market potential in cutting-edge fields such as flat panel displays, virtual reality (VR), augmented reality (AR), and wearable devices (a) D. Zhang, T. Huang, L. Duan, Adv. Mater. 2020, 32, 1902391; b) H. J. Jang, J. Y. Lee, J. Kim, J. Kwak, J.-H. Park, J. Inf. Disp. 2020, 21, 1; c) C. Kang, H. Lee, J. Inf. Disp. 2021, 23, 19; d) H. J. Jang, J. Y. Lee, G. W. Baek, J. Kwak, J.-H. Park, J. Inf. Disp. 2022, 23, 1.). However, one of the core challenges of OLED technology is that singlet (S1) and triplet (T1) excitons are generated in a 1:3 ratio under electrical excitation, and traditional fluorescent materials can only utilize 25% of the (S1) excitons for radiative decay, which greatly limits the performance improvement of OLEDs. To address this limitation, phosphorescent materials have achieved 100% internal quantum efficiency (IQE) by introducing noble metals to enhance the spin-orbit coupling (SOC) effect (a) M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151; b) Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, S. R. Forrest, Nature 2006, 440, 908.). However, the high cost, potential toxicity, and resource scarcity of noble metals pose severe challenges to their large-scale and sustainable applications.

[0010] To overcome the limitations of phosphorescent materials, the emergence of pure organic thermally activated delayed fluorescence (TADF) molecules in 2011 brought a revolutionary breakthrough to OLED technology. Adachi et al. found that by reducing the singlet-triplet energy splitting (ΔE ST),The T1 exciton can transition to the S1 exciton, thus enabling an efficient reverse intersystem crossing (RISC) process ((a) Q. Zhang, et al. Nat. Photon. 2014, 8, 326; b) S. Hirata, et al. Nat. Mater. 2015, 14, 330; c) M. Sarma, K.-T. Wong, ACS Appl. Mater. Interfaces 2018, 10, 19279; d) Q. Xue, G. Xie, Adv. Opt. Mater. 2021, 9, 2002204.)). To achieve this goal, it is necessary to ensure that ΔE ST is as small as possible, so the sufficient separation of the frontier molecular orbitals (FMO) is crucial.

[0011] TADF materials are generally divided into two categories: intermolecular charge transfer and intramolecular charge transfer. OLEDs based on exciplexes of intermolecular charge transfer theoretically also have the potential to achieve 100% IQE. The formation of exciplexes is a bimolecular process in which electronically excited species form a complex with another ground-state molecule through Coulombic attraction. Among them, intramolecular space charge transfer (TSCT)-TADF materials have attracted much attention due to their large highest occupied molecular orbital - lowest unoccupied molecular orbital (HOMO-LUMO) separation distance (a) X. Tang, et al. Nat. Mater. 2020, 19, 1332; b) S. Y. Yang, et al. Angew. Chem., Int. Ed. 2022, 61, e202206861; c) C. C. Peng, et al. Adv. Mater. 2020, 32, 2003885; d) X. Q. Wang, et al. Angew. Chem., Int. Ed. 2021, 60, 5213; e) F. C. Kong, et al. Angew. Chem., Int. Ed. 2022, 61, e202207204; f) S. Y. Yang, et al. Adv. Mater. 2022, 34, 2104125; g) T. Huang, et al. Angew. Chem., Int. Ed. 2022, 61, e202200059; h) Z. Zhao, et al. Angew. Chem., Int. Ed. 2022, 61, e202210864; i) Y. Wada, et al. Nat. Photon. 2020, 14, 643; j) C. Wu, et al. Angew. Chem., Int. Ed. 2021, 60, 3994; k) X. K. Chen, et al. Phys. Chem. Lett. 2019, 10, 3260.). In the TSCT-TADF molecule, the extremely close distance between the donor and the acceptor can open the TSCT channel, generating effective charge interaction or charge transfer, and significantly accelerating the RISC rate (k RISC ). The spatial confinement strategy with a rigid molecular structure provides an effective way to solve the problem of relatively low photoluminescence quantum yield (PLQY) in the TSCT-TADF molecular system.

[0012] In principle, a helical structure with a large volume and a rigid molecular structure will lead to the separation of HOMO and LUMO, thus generating a small ΔE STand slight geometric deformations (W. Li, et al. Angew. Chem., Int. Ed. 2019, 58, 582; W. Li, et al. Angew. Chem., Int. Ed. 2019, 58, 11301; W. Li, et al. ACS Appl. Mater. Interfaces 2021, 13, 5302.). Meanwhile, the bulky molecular structure can hinder π-π stacking and reduce the non-radiative decay rate, while the "inert" non-conjugated end segments limit the electron exchange interaction in the collision Dexter energy transfer (DET) model, thus restricting severe aggregation-caused quenching (ACQ). Therefore, such TADF materials can achieve high PLQY. (a) W. Li, X. Cai, B. Li, L. Gan, Y. He, K. Liu, D. Chen, Y. C. Wu, S. J. Su, Angew. Chem., Int. Ed. 2019, 58, 582; (b) W. Li, B. Li, X. Cai, L. Gan, Z. Xu, W. Li, K. Liu, D. Chen, S. J. Su, Angew. Chem., Int. Ed. 2019, 58, 11301; (c) W. Li, M. Li, W. Li, Z. Xu, L. Gan, K. Liu, N. Zheng, C. Ning, D. Chen, Y. C. Wu, S. J. Su, ACS Appl. Mater. Interfaces 2021, 13, 5302.). However, according to Fermi's golden rule, the spin-orbit coupling (SOC) of this type of emitter is small, resulting in a slower RISC rate k RISC (P. K. Samanta, et al. Am. Chem. Soc. 2017, 139, 4042; T. J. Penfold, et al. Chem. Rev. 2018, 118, 6975.). Therefore, in the pursuit of high PLQY and fast k RISC , how to balance the two becomes the key prerequisite for constructing excellent TADF materials.

[0013] The research on TSCT-TADF materials in the prior art has been widely reported and explored, providing a solid theoretical basis and practical experience for the present invention. These studies not only reveal the great potential of blue TSCT-TADF materials in OLED technology but also point out the challenges they face in practical applications.

[0014] Traditional blue fluorescent materials: Most of the currently mass-produced blue light materials still adopt fluorescence technology, which has a low luminous efficiency. Since singlet and triplet excitons are generated in a ratio of 1:3 under electrical excitation, and traditional fluorescent materials can only utilize 25% of the singlet excitons for radiative decay, this greatly limits the improvement of the overall luminous efficiency, resulting in the need to consume more energy to achieve the desired luminous brightness in practical applications.

[0015] Some blue TADF materials: TSCT-TADF molecules, although innovative in the charge transfer mechanism, still face the problems of long τ P and low radiative rate. This results in large energy losses during the conversion of electrical energy into light energy, making it impossible to achieve efficient luminescence and difficult to meet the demand for high luminous efficiency.

[0016] Low color purity:

[0017] Blue light materials using existing fluorescence technology have the problem of impure chromaticity. The emitted blue light is not a pure blue spectrum and is often accompanied by other colors, which will seriously affect the color rendering and display effect in the display field with extremely high requirements for color accuracy, such as OLED display panels, and cannot accurately present a high-quality blue picture.

[0018] Material category:

[0019] The types of blue thermally activated delayed fluorescence materials are relatively scarce, making it difficult to meet the diverse market demands and complex application scenarios. Different OLED devices, solid-state lighting, and display technologies have different performance requirements for blue light materials, and currently, the available high-performance blue light materials are limited, restricting the innovation and development of related industries and product iteration.

[0020] Difficult preparation and high cost:

[0021] Complex preparation process: The preparation process of some high-performance blue light materials involves complex processes and stringent conditions. For example, when preparing certain blue TADF materials, precise control is required for reaction temperature, duration, catalyst, solvent system, etc. This not only increases the preparation difficulty but also raises the requirements for production equipment and the professional skills of operators, which is not conducive to large-scale production and promotion.

[0022] High cost: The raw materials for the preparation of some blue light materials are scarce or the preparation process has high energy consumption, resulting in high costs. For example, in metal complex phosphorescent materials, precious metals (such as iridium, platinum, etc.) are scarce, greatly increasing the material cost and being unfavorable for realizing low-cost OLED applications. Summary of the Invention

[0023] The present invention aims to specifically address a series of key technical problems faced in the field of existing organic optoelectronic materials technology, especially in the aspect of blue thermally activated delayed fluorescence materials.

[0024] On the one hand, in view of the scarcity of blue thermally activated delayed fluorescence materials, the existing materials are difficult to meet the diverse market demands and complex application scenarios. Different OLED devices, solid-state lighting, and display technologies have different performance requirements for blue materials, while the currently available high-performance blue materials are very limited, restricting the innovative development and product iteration of related industries.

[0025] On the other hand, focusing on the core performance index of luminous efficiency, traditional blue thermally activated delayed fluorescence materials have serious drawbacks. Although TSCT-TADF materials have certain advantages, as mentioned above, their problems of long τ P and low radiative rate are prominent, which directly leads to low overall luminous efficiency. In the pursuit of high luminous efficiency, the existing technology cannot effectively balance PLQY and k RISC , making it difficult for the materials to simultaneously possess efficient energy conversion and fast exciton transition capabilities, unable to fully exert the performance potential of blue materials in devices such as OLEDs, and thus hindering the advancement of display and lighting technologies towards higher performance and lower energy consumption.

[0026] In OLED display and lighting technologies that pursue high image quality and long lifespan, the precise combination of the three primary colors of red, green, and blue (RGB) is the key to achieving full-color display or white OLEDs. Among them, blue materials have become a hot topic and challenge in current research due to their strict requirements for color purity and stability. Blue TADF materials, with their unique luminescence mechanism, are regarded as powerful candidates for improving the performance of OLED devices, especially color purity, quantum efficiency, and long-term device stability. With the continuous in-depth research on blue materials in the scientific community, the research progress in this field is rapid, but the existing materials still need to be improved in terms of luminous efficiency and stability. Therefore, developing new blue light-emitting materials has become the most direct and effective method to improve the light-emitting ability of OLED devices. At the same time, the optimization of device processing technology and functional materials also plays an indispensable role.

[0027] In view of the above problems, the present invention is dedicated to developing a brand-new blue delayed fluorescence material. By innovatively designing the molecular structure to integrate the TBCT and TSCT mechanisms, and simultaneously combining a practical and easily industrialized preparation method, the material can achieve a synergistic improvement in various aspects such as luminescence performance, stability, and charge transport, comprehensively overcoming the thorny problems faced by existing blue thermally activated delayed fluorescence materials, such as single variety and low luminescence efficiency, injecting new vitality into cutting-edge fields such as solid-state lighting and display technologies, and providing strong material support and technical guarantee. The proposal of the present invention is precisely based on an in-depth understanding and analysis of the existing technology, aiming to solve the problems of the blue TSCT-TADF material in terms of radiative decay time and radiative rate through innovative technical means, and further improve the performance and efficiency of OLEDs.

[0028] To solve the above existing technical problems, the present application provides the following technical solutions:

[0029] The present invention provides a blue organic delayed fluorescence material, including compound A, and the chemical structural formula of compound A is as follows:

[0030] Wherein, R1 and R2 are independently selected from hydrogen, methyl, tert-butyl, cyclohexyl, phenyl or 4-tert-butylphenyl;

[0031] A1 and A2 are independently selected from arylamines or heteroaryl groups of C6-C60;

[0032] X is selected from absent, single bond, double bond, O, S, Se, S(=O)2 or CR'R″;

[0033] In CR'R″, R' and R″ are independently selected from alkyl groups of C1-C10, monocyclic aromatic hydrocarbons of C6-C30, polycyclic aromatic hydrocarbons of C6-C30, monocyclic heteroaromatic hydrocarbons of C3-C30 or polycyclic heteroaromatic hydrocarbons of C3-C30; R' and R″ are substituted or unsubstituted.

[0034] Preferably, in CR'R″, the substituents of R' and R″ are independently selected from one of deuterium, trifluoromethyl, halogen, alkyl or cycloalkyl groups of C1-C10, aryl groups of C6-C30 and heteroaryl groups of C3-C30.

[0035] Preferably, the chemical structural formula of compound A is selected from one of the following formulas:

[0036]

[0037] The chemical structural formula of the present invention has the above specific structure. This unique structure combines the mechanisms of through-space charge transfer (TSCT) and through-bond charge transfer (TBCT), which is the basis for achieving excellent luminescent properties of the material, bringing about effective energy transfer from the excited state to the ground state of the material, and thus generating a significant blue delayed fluorescence effect.

[0038] Details of CR′R″: In CR′R″, such a delicate group setting further optimizes the electronic structure and properties of the molecule.

[0039] The present invention also provides a method for preparing the above blue organic delayed fluorescence material, comprising the following steps:

[0040] S1: React raw material I and raw material II at 5 - 40 °C for 6 - 12 h in the presence of a lithium reagent, and then react at 100 - 120 °C for 12 - 15 h in the presence of an acid to obtain intermediate III;

[0041] The chemical structural formula of the said raw material I is as follows:

[0042]

[0043] The chemical structural formula of the said raw material II is as follows:

[0044]

[0045] The chemical structural formula of the said intermediate III is as follows:

[0046] Wherein, R1 and R2 are independently selected from hydrogen, methyl, tert-butyl, cyclohexyl, phenyl or 4-tert-butylphenyl;

[0047] X is selected from absent, single bond, double bond, O, S, Se, S(=O)2 or CR'R″;

[0048] In CR'R″, R' and R″ are independently selected from C1-C10 alkyl, C6-C30 monocyclic aromatic hydrocarbon, C6-C30 polycyclic aromatic hydrocarbon, C3-C30 monocyclic heteroaromatic hydrocarbon or C3-C30 polycyclic heteroaromatic hydrocarbon; R' and R″ are substituted or unsubstituted;

[0049] S2: Under an inert gas atmosphere and alkaline conditions, carry out a Suzuki reaction on the said intermediate III and raw material IV in a solvent to obtain the blue organic delayed fluorescence material; the Suzuki reaction uses tetrakis(triphenylphosphine)palladium(0) as a catalyst, the temperature is 70 - 100 °C, and the time is 20 - 24 h; the raw material IV is selected from boric acid or boric acid ester derivatives of A2; A1 and A2 are independently selected from C6-C60 aromatic amines or heteroaryl groups.

[0050] Preferably, in the step S1, the lithium reagent is selected from n-butyllithium, and the acid is hydrochloric acid containing 30-37 wt% concentration and glacial acetic acid. The reaction is carried out as a continuous one-pot method for ring-closure reaction.

[0051] Preferably, in the step S2, the alkaline condition is an aqueous solution of cesium carbonate, potassium carbonate or sodium carbonate.

[0052] Preferably, the inert gas atmosphere is selected from nitrogen or argon.

[0053] Preferably, in the step S2, the solvent is selected from tetrahydrofuran, 1,4-dioxane or dimethyl sulfoxide.

[0054] Preferably, in the step S2, the solvent is tetrahydrofuran / water (v:v = 6 - 4:1), 1,4-dioxane / water (v:v = 10 - 4:1) or toluene / ethanol / water (v:v:v = 10 - 8:1:1).

[0055] Specifically, the preparation method includes the following steps:

[0056] (1) Under the protection of an inert gas, dissolve raw material I in an anhydrous and anaerobic organic solvent, with the help of a lithium reagent, add raw material II. After the reaction is completed, spin-dry the solvent, add the solid to the acid for reaction to obtain intermediate III; the lithium reagent is n-butyllithium (concentration 1 - 2.5 M); the anhydrous and anaerobic organic solvent is any one of ultra-dry tetrahydrofuran, 1,4-dioxane and dimethyl sulfoxide; the acid is glacial acetic acid and hydrochloric acid with a concentration of 30% - 37%.

[0057] (2) React the obtained intermediate III and raw material IV in the presence of a catalyst tetrakis(triphenylphosphine)palladium(0) in an alkaline environment and under the protection of an inert gas in a solvent to prepare a blue delayed fluorescence material with mixed space charge transfer and single bond charge transfer; the molar ratio of intermediate III to raw material IV is 1 - 1.1 mol:1 mol. The alkaline condition is provided by one of cesium carbonate, potassium carbonate and sodium carbonate, and the solvent is tetrahydrofuran / water (v:v = 6 - 4:1), 1,4-dioxane / water (v:v = 10 - 4:1) or toluene / ethanol / water (v:v:v = 10 - 8:1:1); the reaction temperature is 70 - 100 °C, and the reaction duration is 20 - 24 h.

[0058] All raw materials of the present invention are existing products, and the specific preparation method and testing method are conventional technologies. The preparation schematic diagram of the blue organic delayed fluorescence material based on mixed space charge transfer and single bond charge transfer of the present invention is as Figure 9 shown.

[0059] The key of the preparation method of the present invention is two-step reactions: precise control of each link ensures the quality and yield of the intermediate, laying the foundation for subsequent reactions.

[0060] Subsequently, the intermediate reacts with the raw material (boronic acid or boronic acid ester derivative of A2) under the action of the catalyst tetrakis(triphenylphosphine)palladium(0) in an inert gas (such as nitrogen or argon) protection and an alkaline solvent (provided by one of cesium carbonate, potassium carbonate, and sodium carbonate, and the solvent is a specific ratio mixture such as tetrahydrofuran / water (v:v = 6 - 4:1), etc.) to obtain the target blue delayed fluorescence material. This process ensures the material purity, stability, and luminescence efficiency, and has a high yield and good repeatability, suitable for industrial production.

[0061] The present invention also provides an organic electroluminescent device, comprising a light-emitting layer prepared from the above blue organic delayed fluorescence material; in the light-emitting layer, the blue organic delayed fluorescence material is doped or not doped in 3,3'-bis(9H-carbazol-9-yl)-1,1'-biphenyl (mCBP).

[0062] Preferably, the preparation method of the light-emitting layer is evaporation method or solution method.

[0063] Preferably, the light-emitting layer is composed of a cathode, an electron injection layer, an electron transport layer, a hole blocking layer, a light-emitting layer, an exciton blocking layer, a hole transport layer, a hole injection layer, and an anode arranged in sequence.

[0064] The key to the application field lies in the application of the device: the application of this material in the preparation of thermally activated delayed fluorescence devices or the light-emitting layer of thermally activated delayed fluorescence devices is an important protection point. The specific structure of the thermally activated delayed fluorescence device includes a cathode, an electron injection layer, an electron transport layer, a hole blocking layer, a light-emitting layer (containing the material of the present invention), an exciton blocking layer, a hole transport layer, a hole injection layer, and an anode. Each layer cooperates with each other, and the material of the present invention plays a key role in the light-emitting layer, endowing the device with advantages such as low turn-on voltage, high luminescence efficiency, high color purity, and better service life, and expanding its application prospects in the fields of solid-state lighting and display technology, etc.

[0065] The above technical key points and protection points are interrelated and supportive, jointly constructing the core value of the present invention in the aspect of blue delayed fluorescence materials and their preparation and application, protecting from molecular design, synthesis process to practical application in all aspects, and ensuring the full embodiment of the innovation and practicality of the invention.

[0066] The present invention is closely related to the prior art, aiming to solve the deficiencies of blue TSCT-TADF materials in terms of radiative decay time and radiative rate, and promoting the continuous development of OLED technology through innovative technical means.

[0067] The technical solution of the present invention has the following advantages compared with the prior art:

[0068] Excellent luminescence performance:

[0069] The blue delayed fluorescence material of the present invention incorporates the dual mechanisms of TBCT and TSCT. This unique design enables the molecular structure to achieve efficient energy transfer from the excited state to the ground state, thereby generating a significant blue delayed fluorescence effect. Compared with traditional materials that rely solely on a single charge transfer mechanism, the luminous efficiency is greatly improved, effectively solving the problem of low luminous efficiency of existing blue thermally activated delayed fluorescence materials and better meeting the requirements of devices such as OLEDs for high-brightness blue light.

[0070] In the solid state, the material still maintains good luminous performance, and the emission wavelength is stably within the blue spectral range, ensuring color purity, that is, high color purity, which is crucial for full-color displays or white OLED applications, avoiding color deviation caused by emission wavelength shift and providing a guarantee for accurate color rendering.

[0071] Outstanding preparation advantages:

[0072] The preparation process is simple and easy to implement. By adopting an innovative synthesis route, through specific raw material selection, precise reaction condition optimization, and reasonable post-treatment steps, the complex material preparation process is simplified. Taking the two-step method of reacting raw material one and raw material two to prepare intermediate three and then performing a Suzuki reaction with raw material four as an example, the reagents required for each step are common and the operation process is clear, reducing the strict requirements for production equipment and the professional skills of operators, and being easy to promote and implement in laboratories or factories of different scales.

[0073] The raw materials are easily available. The selected raw materials are all existing products, without special customization or complex synthesis, and the market supply is stable, greatly reducing the production cost and the difficulty of raw material procurement, avoiding production restrictions caused by scarce raw materials, and laying a solid foundation for large-scale industrial production.

[0074] It has a high yield and good reproducibility. Strictly controlled reaction temperature, duration, and a suitable catalyst and solvent system enable the materials prepared in each batch to maintain stability in terms of both yield and quality, reducing product performance fluctuations caused by batch differences, ensuring the consistency of product quality, and being conducive to continuous industrial production and quality control.

[0075] Excellent device applications:

[0076] When the blue delayed fluorescence material is applied to a thermally activated delayed fluorescence device, it can significantly improve the device performance. The prepared OLED device has the characteristic of a low turn-on voltage. Compared with traditional devices, it can operate normally under a lower voltage drive, effectively reducing energy consumption, which is particularly crucial for mobile devices and wearable devices powered by batteries, extending the battery life of the devices and enhancing the user experience.

[0077] The device is given a high luminous efficiency. Combining the high luminous characteristics of the material itself and its synergistic effect with the structures of each layer of the device enables the device to convert more electrical energy into light energy output, improving the energy utilization rate, achieving a brighter display effect under the same power consumption, and enhancing the competitiveness of the product in the market.

[0078] The efficiency roll-off of the device is optimized. Thanks to the good stability and long luminescence lifetime of the material, the aging risk of the device caused by material aging and performance decline is reduced, enabling the device to maintain stable performance during long-term use, reducing the after-sales maintenance cost, and improving the market reputation and economic benefits of the product.

[0079] The present invention not only reveals the unique chemical structure of the above-mentioned blue organic delayed fluorescence material with hybrid space charge transfer and single-bond charge transfer and its preparation method, but also deeply explores the broad application potential of this material in the preparation of organic electroluminescent devices. Specifically, as a luminescent layer material, this material exhibits excellent performance and is particularly suitable as a luminescent dye and / or sensitizer, providing a significant improvement in the luminescent performance of OLED devices.

[0080] The OLED device prepared by using the compound of the present invention exhibits a low turn-on voltage, high luminous efficiency, and longer service life compared with traditional materials. These advantages enable this material to have broad application prospects in the fields of display technology and lighting, can promote the further development of OLED technology, and meet the urgent needs of the market for high-performance, low-power, and long-life display and lighting products.

[0081] In addition, the preparation process of the compound of the present invention is simple and easy to implement, the required raw materials are easy to obtain, and the entire preparation process is easy to control, which provides a strong guarantee for large-scale production. By optimizing the preparation conditions, the purity and yield of the product can be further improved, and the production cost can be reduced, making this material more competitive in commercial applications.

[0082] In summary, the present invention demonstrates significant advantages in terms of material properties, preparation process, and device applications, overcomes many defects of the prior art, injects strong impetus into the development of the organic optoelectronic field, especially the OLED-related industries, and has broad market prospects and application values. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 1H NMR spectrum of compound BOTCZ-BO prepared in Example 1 of the present invention;

[0084] Figure 2 13C NMR spectrum of compound BOTCZ-BO prepared in Example 1 of the present invention;

[0085] Figure 3Mass spectrum of compound BOTCZ-BO prepared in Example 1 of the present invention;

[0086] Figure 4 1H NMR spectrum of compound BOTCZ-TRZ prepared in Example 2 of the present invention;

[0087] Figure 5 13C NMR spectrum of compound BOTCZ-TRZ prepared in Example 2 of the present invention;

[0088] Figure 6 Mass spectrum of compound BOTCZ-TRZ prepared in Example 2 of the present invention;

[0089] Figure 7 Device efficiency graphs of devices D1 and D2 prepared in the examples of the present invention;

[0090] Figure 8 Electroluminescence spectra of devices D1 and D2 prepared in the examples of the present invention;

[0091] Figure 9 Schematic diagram for the preparation of a blue organic delayed fluorescence material based on hybrid space charge transfer and single-bond charge transfer of the present invention;

[0092] Figure 10 Synthesis route diagram of compound BOTCZ-BO in Example 1;

[0093] Figure 11 Synthesis route diagram of compound BOTCZ-TRZ in Example 2. Detailed implementation manners

[0094] In the OLED display and lighting technologies pursuing high picture quality and long lifespan, the precise combination of the three primary colors of red, green, and blue (RGB) is the key to achieving full-color display or white OLED. Among them, blue light materials have become the current research focus and challenge due to their strict requirements in terms of color purity and stability. TADF blue light materials, with their unique luminescence mechanism, are regarded as powerful candidates for improving the performance of OLED devices, especially in terms of color purity, quantum efficiency, and long-term device stability. With the continuous in-depth research on blue light materials in the scientific community, the research in this field has advanced rapidly, but the existing materials still need to be improved in terms of luminescence efficiency and stability. Therefore, developing new blue light-emitting materials has become the most direct and effective method to improve the light-emitting ability of OLED devices. At the same time, the optimization of device processing technology and functional materials also plays an indispensable role.

[0095] The present invention will be further described below in conjunction with the accompanying drawings and specific examples, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples given are not intended to limit the present invention.

[0096] Synthesis of Compound BOTCZ-BO in Example 1

[0097] The synthetic route of this Example 1 is as follows Figure 10 shown

[0098] Under a nitrogen atmosphere, n-butyllithium (2.2 M, 1.60 mL) was added dropwise to a low-temperature (-78 °C) solution of raw material A (2.00 g, 3.58 mmol) in tetrahydrofuran. After stirring at -78 °C for 30 minutes, raw material B (2.00 g, 3.57 mmol) dissolved in a tetrahydrofuran solution was added. Then, the mixture was stirred at room temperature for 12 hours. The solvent was removed under reduced pressure. Then, acetic acid (80 mL) and hydrochloric acid (36%, 5 mL) were added, and the reaction was carried out at 120 °C for 12 hours. After the reaction was completed, the reaction solution was poured into water and filtered under reduced pressure. The filter residue was purified by silica gel column chromatography (the developing agent was dichloromethane∶petroleum ether = 2:1, v / v) to obtain intermediate C (1.91 g, yield: 55%).

[0099] Under nitrogen protection, intermediate C (1.91 g, 1.96 mmol), raw material D (1.10 g, 2.17 mmol), and potassium carbonate (0.83 g, 6.01 mmol) were dissolved in a mixed solvent of 30 mL of tetrahydrofuran and 3 mL of water, and 5% equi of tetrakis(triphenylphosphine)palladium was added. The mixed solution was heated to 70 °C and stirred for 24 h. Then, the reaction solution was poured into brine, and the filter residue was obtained by filtration. The filter residue was purified by silica gel column chromatography (the developing agent was dichloromethane∶petroleum ether = 1:5, v / v) to obtain product BOTCZ-BO (2.10 g, 1.65 mmol), with a yield of 84.1%.

[0100] NMR results 1 H NMR (400 MHz, CDCl3) δ 8.74 (d, J = 2.5 Hz, 2H), 8.51 (d, J = 2.6 Hz, 2H), 8.02 - 7.99 (m, 2H), 7.85 (d, J = 8.7 Hz, 1H), 7.79 - 7.70 (m, 5H), 7.58 (d, J = 1.7 Hz, 1H), 7.52 - 7.45 (m, 4H), 7.37 (d, J = 2.0 Hz, 1H), 7.32 (d, J = 8.7 Hz, 2H), 7.24 (d, J = 1.2 Hz, 1H), 7.21 (d, J = 7.7 Hz, 3H), 7.11 - 7.04 (m, 2H), 7.00 (d, J = 2.2 Hz, 1H), 6.69 (dd, J = 8.7, 2.1 Hz, 1H), 6.44 (d, J = 1.6 Hz, 1H), 5.93 (s, 2H), 1.50 (d, J = 4.2 Hz, 36H), 1.28 (s, 9H), 1.15 (s, 9H); 13CNMR(101MHz,CDCl3)δ158.82,158.38,157.78,155.50,155.23,147.02,145.46,144.92,143.98,142.61,140.44,139.90,139.16,137.60,135.73,134.84,131.32,130.99,130.26,130.03,129.61,128.91,128.81,128.56,127.94,127.70,126.86,126.40,125.06,123.21,121.95,121.87,121.02,120.08,119.79,117.92,117.60,114.51,111.79,108.48,106.35,56.48,34.80,34.55,34.51,34.18,31.99,31.86,31.59,31.58。

[0101] Matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) result: molecular ion peak 1278.069. Figure 1 1H NMR of compound BOTCZ-BO; Figure 2 13C NMR of compound BOTCZ-BO; Figure 3 Mass spectrum of compound BOTCZ-BO.

[0102] Synthesis of compound BOTCZ-TRZ in Example 2

[0103] The synthetic route of this Example 2 is as Figure 11 shown.

[0104] On the basis of Example 1, raw material D was replaced with raw material E (1.00 g, 2.30 mmol), and other conditions remained unchanged. Finally, product BOTCZ-TRZ (2.04 g, 1.69 mmol) was obtained with a yield of 86.3%. NMR results: 1 H NMR(400MHz,CDCl3)δ8.82 - 8.72(m,6H),8.51(d,J = 2.6Hz,2H),7.98(d,J = 7.7Hz,2H),7.76 - 7.43(m,15H),7.40 - 7.27(m,4H),7.23(d,J = 7.4Hz,1H),7.07(dd,J = 14.0,7.5Hz,2H),6.95(s,1H),6.69(s,1H),6.48(s,1H),5.95(s,2H),1.50(s,18H),1.29(s,9H),1.15(s,9H); 1313C NMR (101 MHz, CDCl3) δ 171.58, 158.38, 155.22, 145.43, 143.99, 140.46, 139.96, 139.10, 136.37, 132.45, 131.00, 130.05, 129.40, 128.98, 128.82, 128.63, 128.56, 127.91, 127.71, 126.45, 121.88, 119.90, 119.66, 117.58, 114.15, 108.43, 34.82, 34.51, 34.18, 32.02, 31.88, 31.59. MALDI-TOF-MS result: molecular ion peak 1204.511. Figure 4 1H NMR of compound BOTCZ-TRZ; Figure 5 13C NMR of compound BOTCZ-TRZ; Figure 6 Mass spectrum of compound BOTCZ-TRZ.

[0105] The present invention discloses that the above compound is used as a guest material doped into a host material as a light-emitting layer, or directly as a light-emitting layer, for preparing a thermally activated delayed fluorescence device; further, when the above compound is used as a guest material doped into a host material to jointly serve as a light-emitting layer, the doping concentration of the compound is 20 wt%, and the doping concentration refers to the percentage of the guest material in the sum of the masses of the guest material and the host material.

[0106] Application Example 1

[0107] The specific structure of the organic electroluminescent device prepared in the device is as follows: indium tin oxide (ITO) is used as the anode, bipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanitrile (HATCN) is used as the hole injection layer (HIL), 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylbenzenamine) (TAPC) is used as the hole transport layer (HTL), 4,4',4''-tris(carbazol-9-yl)triphenylamine (TCTA) is used as the electron blocking layer (EBL), the compound BOTCZ-BO obtained in Example 1 is used as a guest material doped into 3,3'-bis(9H-carbazol-9-yl)-1,1'-biphenyl (mCBP) as the host material to jointly serve as the light-emitting layer (EML), 4,6-bis(3,5-bis(pyridin-3-yl)phenyl)-2-methylpyrimidine (TmPyPB) is used as the electron transport layer (ETL), lithium fluoride (LiF) is used as the electron injection layer (EIL), and aluminum (Al) is used as the cathode, as Device D1;

[0108] The specifications of each layer of the thermally activated delayed fluorescence device are as follows: ITO / HATCN (10 nm) / TAPC (40 nm) / TCTA (10 nm) / mCBP: guest material (20 wt%) (20 nm) / TmPyPB (40 nm) / LiF (1 nm) / Al (100 nm). The specific preparation process is a conventional technique and is prepared by vacuum evaporation.

[0109] The test method is based on GB / T 20871.61-2013 "Organic Light-Emitting Diode Displays, Part 6-1: Test Methods for Optical and Optoelectronic Parameters", and the external quantum efficiency of the thermally activated delayed fluorescence device is tested according to the light distribution method. The computer is used to control the power meter to apply a driving voltage to the light-emitting device, so that current passes through the device to make it emit light. The brightness in the normal direction is measured by a luminance meter, and the EQE value of the device is calculated with the help of the standard Lambertian distribution theory. The external quantum efficiency is the ratio of the number of photons emitted by the device per unit time to the number of injected carriers, and the calculation formula is:

[0110]

[0111] In the formula, where N photon represents the number of photons generated per second, I is the current in the device (unit: A), and e is the unit electron constant, with a value of 1.6×10 -19 C.

[0112]

[0113] Among them, is the luminous radiant flux, and E average is the average photon energy.

[0114] The measuring equipment is the Photo Research spectrophotometer radiometer PR-670 from the United States: the spectral range is 380-780 nm, which can accurately collect the radiant intensity and spectral data of the light emission, providing key optical signal data support for the calculation of the external quantum efficiency. This equipment is widely used in the field of optical measurement, and its performance has been verified by a large number of experiments, and it can meet the requirements of this test for the accurate measurement of external light signals. The power meter Keithley 2400: the current measurement can be accurate to 0.001 μA, ensuring the accurate acquisition of the device operating current. Its high-precision current measurement ability is an important basis for ensuring the accuracy of the external quantum efficiency calculation. This power meter has good stability and accuracy in electrical measurement, meeting the strict requirements of this test for current measurement accuracy.

[0115] Test conditions: The ambient temperature range is set to 25±3 °C, and the relative humidity range is 25-85%.

[0116] Test steps: The area is 10 mm 2The thermally activated delayed fluorescence device is placed in the electrode fixture and connected to the power meter. Ensure that the device is firmly installed and the electrodes are well connected to avoid abnormal current transmission caused by poor contact, which may affect the test results.

[0117] Place the light-emitting device vertically in front of the spectrophotometric radiometer PR670, ensuring that the test environment is free from ambient light interference. Ambient light will superimpose on the measured optical signal, resulting in deviations in the measured radiation intensity and spectral data, thus affecting the accuracy of the external quantum efficiency calculation.

[0118] Set the light-emitting area of the test device to 10 mm 2 in the computer program, with a voltage range from 0 V to 15 V and a step size of 0.5 V, and perform the test using the automatic exposure method.

[0119] The original test data and data processing are as follows:

[0120] Luminance; unit: cd m-2, error ±2%;

[0121] Current; unit: mA, accurate to 0.001 μA;

[0122] Current density; unit: mAcm -2 accurate to 0.0001 mAcm -2 ;

[0123] External quantum efficiency; unit: %, accurate to 0.001;

[0124] Emission peak wavelength; for blue light, 450 - 480 nm, error ±1 nm;

[0125] The above data do not require processing, and the test equipment directly gives the values.

[0126] Application Example 2

[0127] The preparation scheme is the same as that of Application Example 1, except that the guest material in the light-emitting layer is the compound BOTCZ-TRZ in Example 2.

[0128] Effect Evaluation 1

[0129] The specific performance data of the thermally activated delayed fluorescence devices prepared based on the compounds in the above various examples are shown in Table 1, and the specific test method is the prior art.

[0130] Table 1 Performance of Thermally Activated Delayed Fluorescence Devices

[0131] Device Host material <![CDATA[EQE max (%)]]> <![CDATA[Luminance (cdm -2 )]]> EL (nm) CIE (x, y) D1 BOTCZ - BO 15.2 3737 438 (0.15,0.06) D2 BOTCZ - TRZ 20.3 18360 484 (0.20,0.36)

[0132] The above experimental data indicate that after the blue organic delayed fluorescence material with hybrid spatial charge transfer and single-bond charge transfer provided by the present invention is applied to an electroluminescent device, deep blue light emission is successfully achieved. More importantly, the application of this material significantly improves the efficiency and maximum brightness of the device, bringing substantial progress to the performance optimization of fluorescent devices. Therefore, this type of novel compound of the present invention is an organic light-emitting functional material with good performance and is expected to be promoted for commercial application. Figure 7 Device efficiency diagrams for devices D1 and D2; Figure 8 Electroluminescence spectra diagrams for devices D1 and D2.

[0133] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A blue organic delayed fluorescence material, characterized in that, Comprising compound A, the chemical structural formula of which is as follows: Wherein, R1 and R2 are independently selected from hydrogen, methyl, tert-butyl, cyclohexyl, phenyl or 4-tert-butylphenyl; A1 and A2 are independently selected from arylamines or heteroaryls having 6 to 60 carbon atoms; X is selected from absent, single bond, double bond, O, S, Se, S(=O)2 or CR'R″; In CR'R″, R' and R″ are independently selected from alkyl groups having 1 to 10 carbon atoms, monocyclic aromatic hydrocarbons having 6 to 30 carbon atoms, polycyclic aromatic hydrocarbons having 6 to 30 carbon atoms, monocyclic heteroaromatic hydrocarbons having 3 to 30 carbon atoms or polycyclic heteroaromatic hydrocarbons having 3 to 30 carbon atoms; R' and R″ are substituted or unsubstituted.

2. The blue organic delayed fluorescence material according to claim 1, wherein In CR'R″, the substituents of R' and R″ are independently selected from one of deuterium, trifluoromethyl, halogen, alkyl or cycloalkyl groups having 1 to 10 carbon atoms, aryl groups having 6 to 30 carbon atoms and heteroaryl groups having 3 to 30 carbon atoms.

3. The blue organic delayed fluorescence material according to claim 1, characterized in that, The chemical structural formula of the compound A is selected from one of the following formulas:

4. A method for preparing the blue organic delayed fluorescence material according to any one of claims 1-3, characterized in that, Comprising the following steps: S1: React raw material I and raw material II at 5 - 40 °C for 6 - 12 h in the presence of a lithium reagent and then react at 100 - 120 °C for 12 - 15 h in the presence of an acid to obtain intermediate III; The chemical structural formula of the raw material I is as follows: The chemical structural formula of the raw material II is as follows: The chemical structural formula of the intermediate III is as follows: Wherein, R1 and R2 are independently selected from hydrogen, methyl, tert-butyl, cyclohexyl, phenyl or 4-tert-butylphenyl; X is selected from absent, single bond, double bond, O, S, Se, S(=O)2 or CR'R″; In CR'R″, R' and R″ are independently selected from alkyl groups having 1 to 10 carbon atoms, monocyclic aromatic hydrocarbons having 6 to 30 carbon atoms, polycyclic aromatic hydrocarbons having 6 to 30 carbon atoms, monocyclic heteroaromatic hydrocarbons having 3 to 30 carbon atoms or polycyclic heteroaromatic hydrocarbons having 3 to 30 carbon atoms; R' and R″ are substituted or unsubstituted; S2: Under an inert gas atmosphere and basic conditions, carry out a Suzuki reaction on the intermediate III and raw material IV in a solvent to obtain the blue organic delayed fluorescence material; the Suzuki reaction uses tetrakis(triphenylphosphine)palladium(0) as a catalyst, the temperature is 70 - 100 °C, and the time is 20 - 24 h; the raw material IV is selected from boric acid or boric acid ester derivatives of A2; A1 and A2 are independently selected from arylamines or heteroaryls having 6 to 60 carbon atoms.

5. The preparation method according to claim 4, wherein In the step S1, the lithium reagent is selected from n-butyllithium, and the acid is an aqueous solution containing hydrochloric acid with a concentration of 30 - 37 wt% and glacial acetic acid.

6. The preparation method according to claim 4, characterized in that, In the step S2, the basic condition is an aqueous solution of cesium carbonate, potassium carbonate or sodium carbonate.

7. The preparation method according to claim 4, characterized in that, The inert gas atmosphere is selected from nitrogen or argon.

8. The preparation method according to claim 4, characterized in that, In the step S2, the solvent is selected from tetrahydrofuran, 1,4-dioxane or dimethyl sulfoxide.

9. An organic electroluminescent device, characterized in that, Comprising a light-emitting layer prepared from the blue organic delayed fluorescence material according to any one of claims 1 - 3; in the light-emitting layer, the blue organic delayed fluorescence material is doped or not doped in 3,3'-bis(9H-carbazol-9-yl)-1,1'-biphenyl.

10. The organic electroluminescent device according to claim 9, wherein The preparation method of the light-emitting layer is evaporation method or solution method.

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