Near ultraviolet light organic electroluminescent device

Abstract

The invention belongs to the field of electroluminescent devices, and particularly relates to a near ultraviolet light organic electroluminescent device. The invention innovatively provides an A-D-D 'type near ultraviolet light organic compound which has the characteristic of thermal activation delayed fluorescence. A unique face-to-face acceptor-donor-auxiliary donor (A-D-D ') arrangement mode is adopted in the spatial layout of the monomolecular structure. The interaction in molecules is ingeniously realized through spatial non-conjugated connection, and the luminescence property of the material is remarkably improved through the unique spatial interaction. The donor and the auxiliary donor are elaborately connected to the meta position of the same benzene ring, charge transfer in molecules is effectively weakened, and then blue shift of the light-emitting wavelength of the material is promoted to successfully cover a near ultraviolet region. The compound shows extremely high application value and application potential in a near ultraviolet organic light-emitting device, especially in the aspect of serving as a light-emitting material or a sensitizer of an organic material layer, and indicates a wide market prospect.

Description

Technical Field

[0001] The invention belongs to the field of electroluminescent devices, and in particular relates to a near-ultraviolet organic electroluminescent device. Background Art

[0002] Organic Light Emitting Diodes (OLEDs) are current-driven light-emitting devices that utilize organic materials as the light-emitting layer, generating light radiation through current excitation. OLED devices employ a sandwich structure, consisting of positive and negative electrode layers interposed with an organic functional material layer. This structure enables efficient and stable light emission.

[0003] Throughout the development of OLED technology, continuous innovation in device structure and fabrication processes has been key to driving performance improvements. However, even more crucial is the in-depth research and innovation of optoelectronic functional materials. Compared to inorganic materials, organic materials offer unique advantages in the OLED field due to their low synthesis cost, wide functional tunability, flexibility, and excellent film-forming properties. These characteristics make OLED devices based on organic materials not only relatively simple to manufacture and easy to fabricate on a large scale, but also environmentally friendly and promising for broad application prospects.

[0004] While OLED technology has achieved significant commercial success in the lighting and display sectors, it still faces numerous challenges in the near-UV OLED sector. In particular, the performance of the luminescent layer material directly determines the luminous efficiency, stability, and lifespan of near-UV OLEDs. Therefore, developing novel organic luminescent materials to improve the overall performance of near-UV OLEDs has become a key research priority.

[0005] Near-ultraviolet organic electroluminescence (NEEL) technology, with its unique spectral properties, holds broad application prospects in a variety of fields. In the display field, it promises to enable more efficient and energy-efficient display technology; in optoelectronics, it can serve as an excitation light source; in biological and medical applications, it can be used in biosensing, medical diagnosis and treatment, sterilization, and disinfection; and in information storage, it facilitates high-density information storage. For example, in biosensing, near-ultraviolet light is used to excite specific biomolecules to produce fluorescent signals, enabling their detection and analysis. In high-density information storage, the short wavelength of NEL can increase storage density and enhance the amount of information stored.

[0006] Near-ultraviolet organic electroluminescence (NEEL) technology has developed rapidly in the field of organic optoelectronic materials, achieving remarkable results from its early exploration to its current widespread application in various fields. This progress is primarily reflected in material research and development, device structure optimization, and application expansion.

[0007] Early organic electroluminescent materials were primarily traditional fluorescent materials. Limited by spin statistics theory, they could only utilize 25% of singlet excitons for luminescence, resulting in low internal quantum efficiency and an efficiency bottleneck in near-ultraviolet emission, limiting their application in related fields. To address the low efficiency of traditional fluorescent materials, researchers introduced the hot exciton mechanism. By creating charge transfer states at high energy levels to achieve the conversion of triplet excitons to singlet excitons, while retaining localized luminescent states at low energy levels, this mechanism resolves the conflict between short-wavelength emission from donor-acceptor materials and high exciton utilization, bringing breakthroughs in the development of near-ultraviolet materials. For example, the carbazole-containing near-ultraviolet / ultraviolet organic semiconductor materials developed by Tang Benzhong's team at South China University of Technology achieve high near-ultraviolet / ultraviolet luminescence, high electrically excited exciton utilization, and bipolarity by attaching different modifying groups to the carbazole moiety. The resulting OLED devices exhibit low turn-on voltage, high external quantum efficiency, and low efficiency roll-off. In recent years, materials with a "donor'-donor-acceptor" (D'-DA) structure using carbazole as a donor bridge have been designed. These materials effectively guarantee near-ultraviolet and ultraviolet emission, high color purity, high fluorescence efficiency, and bipolarity. OLED devices fabricated with these materials exhibit excellent performance, including an electroluminescence peak below 420nm, low turn-on voltage, and high efficiency. These materials hold great promise for applications in areas such as anti-counterfeiting and UV curing.

[0008] In addition, early near-ultraviolet organic electroluminescent devices had problems with hole injection and carrier imbalance. To address these issues, researchers introduced multilayer structures, such as ultraviolet organic electroluminescent devices based on gradient hole injection and transport. A gradient hole injection and transport system layer is set between the anode and the light-emitting layer to promote hole injection and transport, increase the number of holes in the light-emitting layer, and improve the irradiance and luminous efficiency of the device. Doping technology is widely used in device preparation. By co-evaporating the host material with p-type or n-type dopants, p-type or n-type doped hole and electron transport layers are formed, which improves the material's conductivity, reduces the driving voltage, and increases the device's luminous efficiency and lifespan. For example, the near-ultraviolet organic electroluminescent material based on benzocyanate prepared by South China University of Technology is used as the light-emitting layer of OLED in a doped or undoped manner. The resulting doped OLED devices have high efficiency and a small efficiency roll-off.

[0009] Since OLED has the advantages of self-luminescence, low energy consumption, wide color gamut, large viewing angle, high resolution, high contrast, short response time, simple device structure, and can achieve pure black display and transparent display, and with the development of blue light (Ahn DH, Kim S.W., Lee H., et al. Nature Photonics, 2019, 13(8): 540-546.;Guo X., Yuan P., Fan J., et al. Advanced Materials, 2021, 33(11): 2006953.), green light (Chen X., Ma D., Liu T., et al. CCS Chemistry, 2021, 4(4): 1284-1294.;Peng C.-C., Yang S.-Y., Li H.-C., et al. Advanced Materials, 2020, 32(48): 2003885.) and red light (Cai Z., Wu With the improvement of the performance of pure organic materials, OLEDs have gradually become the representative and main force of advanced display and solid-state lighting technologies (Liu Y., Li C., Ren Z., et al. Nature Reviews Materials, 2018, 3(4): 18020.). Currently, researchers are committed to further broadening the emission band of organic light-emitting materials to improve the performance of OLEDs and open up new application scenarios for OLEDs. For example, near-infrared (NIR)-OLEDs are used in night vision displays, chemical sensing, and medical diagnosis (Zampetti A., Minotto A., Cacialli F. Advanced Functional Materials, 2019, 29(21): 1807623.); the development of near-ultraviolet (NUV)-OLEDs has also attracted much attention due to its application prospects in excitation light sources, biological and chemical sensors, ultraviolet communications, high-density information storage, biomedicine, and other fields (Chen M., Liao Y., Lin Y., et al. Journal of Materials Chemistry C, 2020, 8(42): 14665-14694.).

[0010] In order to achieve efficient NUV-OLED emission, it is very important to develop efficient NUV luminescent materials. However, the maximum external quantum efficiency (EQE max ) is generally below 5%, lower EQE max This has always been one of the urgent problems that NUV-OLED needs to solve (Lee HL, Chung W.J., Lee JY Small, 2020, 16 (14): 1907569.; Liu H., Bai Q., Yao L., et al. Chemical Science, 2015, 6 (7): 3797-3804.). On the one hand, this is because the wide band gap of short-wavelength organic light-emitting materials is not conducive to the injection of carriers; on the other hand, the structure of NUV pure organic materials often needs to limit their degree of conjugation, and the smaller molecular weight leads to low thermal stability and morphological stability. The stability and uniformity of the thin film deposited during the evaporation process of OLED are poor, which limits the improvement of device performance. More importantly, the lower exciton utilization rate of NUV pure organic materials will cause the EQE of its corresponding device to be lower. max The NUV molecular structure is difficult to meet the design requirements of the TADF mechanism. This is because the NUV molecule is usually constructed with weaker donors and acceptors to increase the singlet state (S1) energy level, but at the same time this construction strategy will significantly reduce the CT characteristics of S1, resulting in its ΔE ST It is difficult to achieve efficient TADF. RISC ) mechanism, it is easier to realize the effective utilization of triplet (T1) excitons: 1) The weak ICT state of NUV luminescent materials is conducive to the construction of h RISC The energy level of the mechanism is also beneficial to improve the purity of the luminescent color; 2) The high energy level T1 exciton passes through h RISC The process is converted to S1 excitons, which does not require a small ΔE ST , so there is no need to reduce the overlap of the molecular frontier orbital (FMO), S1 can be a local excited state with high luminescence efficiency. In theory, this type of molecule can achieve high exciton utilization and high fluorescence efficiency at the same time; 3) At the same time, the fast h RISC The process can effectively alleviate the aggregation and annihilation of triplet excitons and reduce the device efficiency roll-off; 4) Due to h RISC The process is fast, so these molecules are less susceptible to concentration quenching of excitons. Undoped OLED devices using these luminescent materials exhibit excellent performance, are simple to prepare, and are relatively low-cost. However, high-performance NUV-OLED devices with a CIEy below 0.04 are still rare and require further research and development.

[0011] Materials that utilize meta-N-π-N to weaken CT to achieve near-ultraviolet emission offer numerous performance advantages. These materials can achieve high fluorescence efficiency and exhibit strong luminescence in the near-ultraviolet region. Due to the effective weakening of the CT effect, the color purity of the material is significantly improved, and the emission spectrum is purer, which is of great significance for applications requiring high color purity, such as bioimaging and optical detection. By rationally designing the molecular structure, the construction of space charge transfer (TSCT)-TADF materials can also exhibit excellent stability and carrier transport properties, laying a solid foundation for the preparation of high-performance organic electroluminescent devices. In practical applications, the stability and carrier transport properties of the material directly affect the device's service life and luminescence efficiency. Materials with excellent stability and carrier transport properties can enable the device to maintain a stable luminescence effect during long-term use, reduce energy consumption, and improve the overall performance of the device.

[0012] Current near-ultraviolet OLED technology has many shortcomings in materials and device performance, which limits its development and application.

[0013] Low luminous efficiency and exciton utilization: Traditional near-ultraviolet fluorescent materials are limited by quantum spin statistics and can only utilize 25% of singlet excitons for emission. This low theoretical upper limit for internal quantum efficiency limits the overall luminous efficiency of OLED devices, making them unable to meet the requirements of high-brightness displays or lighting. In practical applications, achieving the desired brightness requires more electricity, resulting in energy waste.

[0014] Designing and synthesizing NUV-TADF materials is difficult: The development of near-ultraviolet TADF materials faces challenges. Achieving near-ultraviolet emission requires weakening the ICT effect, while high-efficiency TADF requires enhancing the ICT effect and reducing the FMO overlap integral. The two requirements conflict. At the same time, the charge transfer triplet energy level of this type of material is high, and the local triplet energy level is difficult to increase to a level close to it, resulting in ΔE ST The larger the RISC rate, the longer the excited state lifetime, the more serious the non-radiative channel and exciton annihilation, which reduces the device efficiency and increases the efficiency roll-off.

[0015] Limitations of other materials: Although triplet-triplet annihilation (TTA) materials can utilize some triplet excitons, the theoretical exciton utilization rate is only 62.5%, and their luminescence process is significantly dependent on current density. Under high voltage and high current density, annihilation is enhanced and the luminescence lifetime is shortened, which limits the performance and stability of the device.

[0016] Poor color purity: Existing near-UV OLED devices generally have low color purity and a broad emission spectrum. For example, the full width at half maximum (FWHM) of some TADF emission OLEDs is generally around 60nm, which cannot meet the color accuracy requirements of high color gamut display applications, affecting display clarity and color reproduction.

[0017] Severe efficiency roll-off: At high current densities, most near-UV OLED devices suffer from severe efficiency roll-off. This is due to the inefficient RISC process and the long excited-state lifetime. This results in excessively high triplet exciton concentrations in the luminescent molecules at high current densities, making processes such as TTA, singlet-triplet annihilation (STA), and triplet-polaron annihilation (TPA) more likely to occur. This leads to a significant drop in device efficiency, impacting device lifespan and user experience. Summary of the Invention

[0018] This invention focuses on the field of OLEDs and aims to solve many key problems existing in existing near-ultraviolet / deep-blue luminescent materials and devices, including:

[0019] Improve exciton utilization and luminous efficiency: In existing OLEDs, the theoretical maximum exciton utilization of traditional fluorescent materials is only 25%, which greatly limits the development of high-efficiency OLED displays. The external quantum efficiency of near-ultraviolet OLEDs is generally less than 5%, which is mainly because the wide band gap of short-wavelength organic light-emitting materials is not conducive to carrier injection, and the structural limitations of pure organic materials lead to poor thermal stability and morphological stability, and low exciton utilization. This invention is committed to developing high-performance near-ultraviolet / deep blue fluorescent materials. Through innovative molecular design, the use of TADF and h RISC Mechanisms such as these can effectively improve the utilization rate of triplet excitons, thereby improving the luminous efficiency of OLED devices and breaking through the bottleneck of existing materials in exciton utilization and luminous efficiency.

[0020] Optimizing luminescent color and color purity: In the field of near-ultraviolet / deep-blue luminescent materials, achieving high-color-purity emission is difficult. For example, when pursuing high efficiency, traditional TADF materials have a conflict between their molecular structure design and the realization of short-wavelength emission, making it difficult to ensure color purity. The present invention achieves high-color-purity luminescence from deep blue to near-ultraviolet wavelengths by rationally designing the molecular structure, such as introducing specific groups and conjugated bridges, and precisely controlling the emission energy level and frontier orbital of the molecule, meeting the demand for high-quality light color in fields such as display and lighting.

[0021] Reducing efficiency roll-off: Currently, near-ultraviolet OLED devices suffer from severe efficiency roll-off at high current density, which is caused by the aggregation and annihilation of triplet excitons and the low efficiency of the RISC process.

[0022] This invention addresses the current technical challenges of near-ultraviolet (NUV) electroluminescent devices in terms of luminescence performance, efficiency, and roll-off characteristics. The core of this invention is the design and introduction of a novel NUV thermally activated delayed fluorescence material, aiming to create an NUV electroluminescent device with superior performance.

[0023] The present invention provides a near-ultraviolet organic electroluminescent device, which is prepared by vacuum evaporation method and comprises an anode, a cathode and a light-emitting layer arranged between the anode and the cathode;

[0024] The light-emitting layer includes compound A, which is doped or undoped with bis[2-(diphenylphosphine)phenyl]oxyether. The structure of compound A is shown in Formula I:

[0025]

[0026] wherein R1, R2, R3 and R4 are independently selected from one of hydrogen, methyl, tert-butyl, cyclohexyl, phenyl, 4-tert-butylphenyl, diphenylamino and nitrogen-containing aromatic rings;

[0027] A is selected from C6-C60 aromatic amine or heteroaryl;

[0028] X1 and X2 are independently selected from absence, a single bond, a double bond, O, S, S(=O)2, CR'R" or Se;

[0029] In CR′R″, R′ and R″ are independently selected from one of a C1-C10 alkyl group, a C6-C30 monocyclic aromatic hydrocarbon, a C6-C30 condensed-ring aromatic hydrocarbon, a C5-C30 monocyclic heteroaromatic hydrocarbon and a C5-C30 condensed-ring heteroaromatic hydrocarbon; and R′ and R″ are substituted or unsubstituted.

[0030] The light-emitting layer can be composed solely of the compound of Formula I, or it can be mixed with the host material as a dopant. When the compound of Formula I is used as a dopant, the doping concentration is precisely controlled between 5-40 wt%, preferably 20 wt%. This design optimizes the performance of the light-emitting layer, balancing factors such as luminous efficiency, color purity, and stability, thereby improving the overall performance of the device. The present invention uses the compound of Formula I as the light-emitting layer or as a dopant material for the light-emitting layer, resulting in OLED devices with low turn-on voltage, high luminous efficiency, high color purity, and improved service life.

[0031] The choice of these groups provides rich tunability in device performance.

[0032] Preferably, in the light-emitting layer, the doping concentration of compound A is 5-40 wt %.

[0033] Preferably, the heteroaryl group is selected from carbazolyl.

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

[0035] Preferably, in the heteroaryl group, monocyclic heteroaromatic hydrocarbon or condensed-ring heteroaromatic hydrocarbon, the heteroatom is selected from N, O, S, P, Si or Se.

[0036] Furthermore, in the heteroaryl group, monocyclic heteroaromatic hydrocarbon or condensed-ring heteroaromatic hydrocarbon, the heteroatom is selected from N, O or S.

[0037] Preferably, the compound A is selected from one of the following compounds:

[0038]

[0039] Preferably, the compound A is obtained by mixing compound B and a lithium reagent at -78°C for 2 hours, reacting with compound C at room temperature (25±5°C) for 12 hours, and then heating to 120°C for 12 hours;

[0040] The chemical formula of compound B is:

[0041] wherein R1, R2, R3 and R4 are independently selected from one of hydrogen, methyl, tert-butyl, cyclohexyl, phenyl, 4-tert-butylphenyl, diphenylamino and nitrogen-containing aromatic rings;

[0042] X1 and X2 are independently selected from non-existence, a single bond, a double bond, O, S, S(=O)2, CR′R″ or Se; in CR′R″, R′ and R″ are independently selected from one of a C1-C10 alkyl group, a C6-C30 monocyclic aromatic hydrocarbon, a C6-C30 condensed aromatic hydrocarbon, a C5-C30 monocyclic heteroaromatic hydrocarbon and a C5-C30 condensed heteroaromatic hydrocarbon; and R′ and R″ are substituted or unsubstituted.

[0043] The chemical formula of the compound C is:

[0044] Wherein, A is selected from C6-C60 aromatic amine or heteroaryl.

[0045] Specifically, the reaction formula is as follows:

[0046]

[0047] In the raw materials, the substituents are the same as those in the compound of formula I above, and Y is a halogen, such as Cl, Br or I.

[0048] The core of the present invention is a compound having the structure of Formula I, which has a unique ADD'-type spatial layout and adopts a face-to-face acceptor-donor-auxiliary donor arrangement mode. The donor and auxiliary donor are connected at the meta position of the same benzene ring, and realize intramolecular interaction through spatial non-conjugated connection. This structural design effectively weakens the intramolecular charge transfer, promotes the blue shift of the emission wavelength to the near-ultraviolet light region, and improves the luminescence performance of the material. It is a key structural feature for achieving efficient near-ultraviolet light emission. In the structure of Formula I, the various optional groups of R1, R2, R3, R4, X1, X2 and A provide rich possibilities for regulating the properties of the compound. R1, R2, R3 and R4 can be independently selected from various groups such as hydrogen and methyl; X1 and / or X2 are unsubstituted or selected from single bonds, double bonds, etc.; A is selected from C6-C60 aromatic amines or heteroaryl groups. Different choices of these groups can adjust the electron cloud distribution, energy level structure and steric hindrance of the molecule, thereby optimizing the luminescence performance, thermal stability and solubility of the compound to meet the needs of different application scenarios.

[0049] Preferably, the near-ultraviolet organic electroluminescent device includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), an electron blocking layer (EBL), an emitting layer (EML), a hole blocking layer (HBL), an electron transport layer (ETL), an electron injection layer (EIL), and a cathode, arranged in sequence. The synergistic effect of these layers ensures efficient operation of the device.

[0050] Preferably, the anode is indium tin oxide (ITO), the hole injection layer is bipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanenitrile (HATCN), the hole transport layer is 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC), the electron blocking layer is 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA) and 1,3-bis(N-carbazolyl)benzene (mCP), the hole blocking layer is bis[2-(diphenylphosphine)phenyl]oxide (DPEPO), the electron transport layer is 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (TmPyPB), the electron injection layer is lithium fluoride (LiF), and the cathode is aluminum (Al).

[0051] Near-ultraviolet organic electroluminescent devices consist of an anode, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode, all working together. This comprehensive device structure ensures efficient carrier injection, transport, and recombination, laying the foundation for efficient luminescence. The device is fabricated using vacuum evaporation, precisely controlling the deposition conditions of each layer, such as ensuring a vacuum level of no more than 2×10 -4 Pa, functional layer The main material is deposited at a rate of The LiF layer and the Al layer were deposited at a rate of and Precise process parameters ensure uniform deposition of each layer of material and high-quality film formation, helping to improve device performance and stability.

[0052] Furthermore, the thickness of 4,4′,4″-tri(carbazol-9-yl)triphenylamine in the electron blocking layer (EBL) is 10 nm, and the thickness of 1,3-bis(N-carbazyl)benzene is 10 nm; the thickness of the hole injection layer (HIL) is 10 nm, the thickness of the hole transport layer (HTL) is 40 nm, the thickness of the light emitting layer (EML) is 20 nm, the thickness of the hole blocking layer (HBL) is 10 nm, the thickness of the electron transport layer (ETL) is 40 nm, the thickness of the electron injection layer (EIL) is 1 nm, and the thickness of the cathode is 100 nm.

[0053] The present invention also provides the use of the near-ultraviolet organic electroluminescent device in the preparation of an organic electroluminescent device.

[0054] The core innovation of this invention lies in providing a novel near-ultraviolet (UV) compound as a dopant host material for constructing the light-emitting layer of a near-UV organic electroluminescent device. This innovation is not limited to using the new compound directly as the light-emitting layer; it also encompasses the strategy of using it as a guest material, co-doped with a host material to form the light-emitting layer at a dopant concentration of 5 to 40 wt% (preferably 20 wt%). This ratio range ensures an optimal balance of light-emitting layer performance. Here, the doping concentration refers to the percentage of the guest material in the total mass of the guest and host materials.

[0055] To comprehensively evaluate the luminescence performance of the fabricated device, a direct current was applied and brightness was evaluated using a PhotoResearch PR670 luminance meter. Simultaneously, the device's current-voltage characteristics were measured using a computer-controlled Keithley 2400 source-meter instrument. These tests were performed while varying the applied DC voltage to fully reveal the device's luminescence properties.

[0056] In summary, this invention not only reveals the potential application of compounds with novel structures as light-emitting layers in near-UV organic electroluminescent devices, but also optimizes the device's luminescent performance through a sophisticated doping strategy. This innovation not only broadens the material selection range for near-UV organic electroluminescent devices but also provides new ideas and methods for improving device performance.

[0057] The technical solution of the present invention has the following advantages over the prior art:

[0058] The present invention has made significant progress in the field of near-ultraviolet organic electroluminescent devices by designing a new near-ultraviolet light-heat-activated delayed fluorescent material and optimizing the device structure and preparation process, bringing many beneficial effects.

[0059] Improved luminous efficiency: The present invention uses a near-ultraviolet organic compound with a unique ADD' structure as the luminescent layer material. The single-molecule structure of this compound adopts a face-to-face acceptor-donor-auxiliary donor arrangement mode in spatial layout, and realizes intra-molecular interaction through spatial non-conjugated connection, thereby improving the luminous performance of the material. From the data of Example 1, the device D1 with m-2tCz-tBO as the guest material has an external quantum efficiency EQE max It can reach 11.5%, which is a significant improvement compared to the generally low efficiency of existing near-ultraviolet light OLED devices, effectively improving the conversion efficiency of electrical energy to light energy.

[0060] Lower turn-on voltage: The fabricated OLED device has the advantage of a low turn-on voltage. The device structure and material design of this invention optimize the carrier injection and transport processes, enabling the device to achieve efficient luminescence at a lower voltage. This not only reduces device energy consumption but also improves its response speed, enabling the device to reach a stable luminescence state more quickly, thus enhancing the user experience.

[0061] Improved color purity: The donor and co-donor are attached at the meta position of the same benzene ring. This design effectively reduces charge transfer within the molecule, shifting the emission wavelength to the near-ultraviolet region and achieving high color purity. For example, device D1, with its CIE coordinates of (0.162, 0.028), exhibits high color purity and can more accurately represent near-ultraviolet light colors, meeting the requirements for color accuracy in applications such as biological testing and photochemical experiments.

[0062] The present invention aims to provide a novel organic light-emitting material and its application in near-ultraviolet OLEDs. This material has excellent luminescence performance, stability, and processing properties, and can meet the stringent requirements of near-ultraviolet OLEDs for light-emitting layer materials. Through the implementation of this patent, the present invention hopes to promote the further development of near-ultraviolet OLED technology and bring more efficient, environmentally friendly, and economical solutions to the lighting and display fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The specific chemical structural formula of the compound of formula I of the present invention;

[0064] Figure 2 This is a diagram of device efficiency of device D1 prepared according to an embodiment of the present invention;

[0065] Figure 3This is an electroluminescence spectrum of the device D1 prepared in an embodiment of the present invention;

[0066] Figure 4 The hydrogen spectrum of the compound m-2tCz-tBO prepared in the embodiment of the present invention;

[0067] Figure 5 This is the mass spectrum of the compound m-2tCz-tBO prepared in an example of the present invention. DETAILED DESCRIPTION

[0068] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0069] The specific chemical structure of the compound of formula I disclosed in the present invention is as follows: Figure 1 As shown, it shows a unique design idea.

[0070] The following examples will be used to describe in detail the preparation method of this novel compound. However, it is worth noting that the preparation strategy of the present invention is not limited to these examples, but has a wider range of applicability.

[0071] In the preparation process, all raw materials used in the present invention are readily available products in the market, and the preparation process and testing methods all follow the industry conventions. For example, in the vacuum evaporation process, the vacuum degree is ensured not to exceed 2×10 -4 Pa, in order to precisely control the deposition rate of each functional layer: the functional layer is The main material is deposited at a rate of The LiF layer and the Al layer were respectively and rate of deposition.

[0072] Example 1 Synthesis of Guest Material Compound m-2tCz-tBO

[0073] Under a nitrogen atmosphere, n-butyllithium solution (2.0 M, 1.50 ml) was added dropwise to a solution of raw material A1 (1.00 g, 1.41 mmol) in anhydrous tetrahydrofuran at a low temperature (-78°C). After stirring at -78°C for 2 hours, raw material B (0.88 g, 1.57 mmol) dissolved in anhydrous tetrahydrofuran solution was added, and then stirred at room temperature for 12 hours. The solvent was removed under reduced pressure, and then acetic acid (40 ml) and hydrochloric acid (36%, 5 ml) were added. ), reacted at 120°C for 12 hours. After completion of the reaction, the reaction solution was poured into ice water and filtered under reduced pressure. The filter residue was purified by silica gel column chromatography (developing solvent: dichloromethane: petroleum ether = 1:2, v / v) to obtain compound m-2tCz-tBO (yield: 0.54 g, yield: 46%) as a white powder. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) results showed: molecular ion peak 1174.4724. Figure 4 is the hydrogen spectrum of compound m-2tCz-tBO; Figure 5 This is the mass spectrum of compound m-2tCz-tBO.

[0074]

[0075] Example 2 Synthesis of Guest Material Compound m-2Cz-tBO

[0076] On the basis of Example 1, raw material A was replaced by raw material C (0.68 g, 1.40 mmol), and other conditions remained unchanged. Finally, the product m-2Cz-tBO (0.80 g, 0.85 mmol) was obtained with a yield of 60.7%.

[0077]

[0078] Example 3 Preparation of device D1

[0079] The device uses indium tin oxide (ITO) as the anode, starting with a hole injection layer (HIL) composed of bipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanenitrile (HATCN), followed by a hole transport layer (HTL) composed of 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC). Next, the device uses a combination of 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA) and 1,3-bis(N-carbazolyl)benzene (mCP) as an electron blocking layer (EBL), effectively preventing unwanted electron migration.

[0080] Notably, the device's emitting layer (EML) consists of m-2tCz-tBO, the guest material compound from Example 1, doped into a bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO) host material at a 20 wt% concentration. This design not only optimizes luminescence performance but also enhances device stability. Subsequently, the device utilizes DPEPO as a hole-blocking layer (HBL), further improving luminescence efficiency.

[0081] For electron transport, the device uses 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (TmPyPB) as the electron transport layer (ETL), ensuring smooth electron transfer. Lithium fluoride (LiF) serves as the electron injection layer (EIL), providing a convenient pathway for electrons to enter the cathode. Finally, aluminum (Al) is used as the cathode to complete the device's structure.

[0082] In terms of preparation process, this device adopts the conventional technology of vacuum evaporation, and the thickness of each layer of material is precisely controlled, which is: ITO / HATCN (10nm) / TAPC (40nm) / TCTA (10nm) / mCP (10nm) / DPEPO: guest material (doped 20wt% in DPEPO) (20nm) / DPEPO (10nm) / TmPyPB (40nm) / LiF (1nm) / Al (100nm).

[0083] 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 uses the light distribution method to test the external quantum efficiency of thermally activated delayed fluorescence devices. A computer-controlled power meter applies a driving voltage to the light-emitting device, causing current to flow through the device, causing it to emit light. A luminance meter measures the luminance in the normal direction, and the device's EQE is calculated using the standard Lambertian body 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. The calculation formula is:

[0084]

[0085] In the formula, 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, which is 1.6×10 -19 C.

[0086]

[0087] in, is the light radiation flux, E average is the average photon energy.

[0088] The measurement equipment used is a Photo Research PR-670 spectrophotometer from the United States. Its spectral range is 380-780nm, allowing it to accurately capture radiant intensity and spectral data, providing crucial optical signal data for external quantum efficiency calculations. This instrument is widely used in optical measurement, and its performance has been verified through extensive experiments to meet the precise external optical signal measurement requirements of this test. The Keithley 2400 power meter measures current with an accuracy of 0.001μA, ensuring accurate measurement of device operating current. Its high-precision current measurement capability is crucial for ensuring the accuracy of external quantum efficiency calculations. This power meter demonstrates excellent stability and accuracy in electrical measurements, meeting the stringent current measurement accuracy requirements of this test.

[0089] Test conditions: The ambient temperature range is set to 25±3℃, and the relative humidity range is 25-85%.

[0090] Test steps: The area is 10mm 2 Place the thermally activated delayed fluorescence device in the electrode fixture and connect it to the power meter. Ensure that the device is firmly installed and the electrodes are well connected to avoid poor contact that may cause abnormal current transmission and affect the test results.

[0091] Place the light-emitting device vertically in front of the PR670 spectrophotometer to ensure that the test environment is free of ambient light interference. Ambient light can superimpose on the measured optical signal, causing deviations in the measured radiation intensity and spectral data, thus affecting the accuracy of the external quantum efficiency calculation.

[0092] Set the test device's luminous area to 10mm in the computer program. 2 , voltage range 0V to 15V, step size 0.5V, automatic exposure mode is used for testing.

[0093] The test original data and data processing are as follows:

[0094] Brightness; unit: cd m -2 , error ±2%;

[0095] Current; unit: mA, accurate to 0.001μA;

[0096] Current density; unit: mAcm -2 , accurate to 0.0001mAcm -2 ;

[0097] External quantum efficiency; unit: %, accurate to 0.001;

[0098] Luminescence peak wavelength: blue light 450-480nm, error ±1nm;

[0099] The above data does not need to be processed, and the test equipment directly gives the value.

[0100] Example 4 Preparation of device D2

[0101] The preparation scheme of device D2 is the same as that of Example 3, except that the guest material compound m-2Cz-tBO of Example 2 is doped into the main material of bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO).

[0102] Effect evaluation 1

[0103] Detailed performance data for this device is listed in Table 1. The testing methods are based on existing technologies, ensuring the accuracy and reliability of the data. This innovative near-ultraviolet organic electroluminescent device not only demonstrates excellent luminescence performance but also provides new insights into the research and application of organic electroluminescence.

[0104] Table 1 Performance of near-ultraviolet organic electroluminescent devices

[0105]

[0106] The experimental data clearly demonstrate that the novel near-UV TADF materials proposed in this invention, when applied to near-UV organic electroluminescent devices, not only successfully impart exceptional luminous efficiency and significantly reduced efficiency roll-off, but also achieve a dramatic increase in the brightness of the electroluminescent devices, reaching exceptionally high levels. This achievement fully demonstrates the exceptional overall performance of these novel compounds as organic light-emitting functional materials. Consequently, these materials demonstrate broad commercial application prospects and have great potential for expansion into a wider range of industrial fields. Figure 2 is the device efficiency diagram of device D1; Figure 3 This is the electroluminescence spectrum of device D1.

[0107] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A near-ultraviolet organic electroluminescent device, characterized in that: It is prepared by vacuum evaporation method, comprising an anode, a cathode and a light-emitting layer arranged between the anode and the cathode; The light-emitting layer includes compound A, which is doped or undoped with bis[2-(diphenylphosphine)phenyl]oxyether. The structure of compound A is shown in Formula I: Wherein, R1, R2, R3 and R4 are independently selected from one of hydrogen, methyl, tert-butyl, cyclohexyl, phenyl, 4-tert-butylphenyl, diphenylamine and nitrogen-containing aromatic ring; A is selected from C6-C60 aromatic amine or heteroaryl; X1 and X2 are independently selected from non-existence, single bond, double bond, O, S, S(=O)2, CR′R″ or Se; in CR′R″, R′ and R″ are independently selected from one of C1-C10 alkyl, C6-C30 monocyclic aromatic hydrocarbon, C6-C30 condensed-ring aromatic hydrocarbon, C5-C30 monocyclic heteroaromatic hydrocarbon and C5-C30 condensed-ring heteroaromatic hydrocarbon; R′ and R″ are substituted or unsubstituted.

2. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: In the light-emitting layer, the doping concentration of compound A is 5-40 wt %.

3. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: The heteroaryl group is selected from carbazolyl.

4. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: In CR′R″, the substituents of R′ and R″ are independently selected from one of deuterium, trifluoromethyl, cyano, halogen, C1-C10 alkyl, C1-C10 cycloalkyl, C6-C30 aryl and C3-C30 heteroaryl.

5. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: In the heteroaryl group, monocyclic heteroaromatic hydrocarbon or condensed-ring heteroaromatic hydrocarbon, the heteroatom is selected from N, O, S, P, Si or Se.

6. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: The compound A is selected from one of the following compounds:

7. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: Compound A is obtained by mixing compound B and lithium reagent at -78°C for 2 hours, adding compound C and reacting at room temperature for 12 hours, and then heating to 120°C and reacting for 12 hours; The chemical formula of compound B is: wherein R1, R2, R3 and R4 are independently selected from one of hydrogen, methyl, tert-butyl, cyclohexyl, phenyl, 4-tert-butylphenyl, diphenylamino and nitrogen-containing aromatic rings; X1 and X2 are independently selected from one of the following groups: absence, single bond, double bond, O, S, S(=O)2, CR'R" or Se; in CR'R", R' and R" are independently selected from one of C1-C10 alkyl, C6-C30 monocyclic aromatic hydrocarbon, C6-C30 condensed aromatic hydrocarbon, C5-C30 monocyclic heteroaromatic hydrocarbon and C5-C30 condensed heteroaromatic hydrocarbon; R' and R" are substituted or unsubstituted; The chemical formula of the compound C is: Wherein, A is selected from C6-C60 aromatic amine or heteroaryl.

8. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: The near-ultraviolet organic electroluminescent device comprises an anode, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a cathode which are arranged in sequence.

9. The near-ultraviolet organic electroluminescent device according to claim 1, wherein: The anode is indium tin oxide, the hole injection layer is bipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanenitrile, the hole transport layer is 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline), the electron blocking layer is 4,4',4"-tri(carbazol-9-yl)triphenylamine and 1,3-bis(N-carbazolyl)benzene, the hole blocking layer is bis[2-(diphenylphosphine)phenyl]oxide, the electron transport layer is 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine, the electron injection layer is lithium fluoride, and the cathode is aluminum.

10. The near-ultraviolet organic electroluminescent device according to claim 9, characterized in that: The thickness of 4,4′,4″-tri(carbazol-9-yl)triphenylamine in the electron blocking layer is 10 nm, and the thickness of 1,3-bis(N-carbazyl)benzene is 10 nm; the thickness of the hole injection layer is 10 nm, the thickness of the hole transport layer is 40 nm, the thickness of the light-emitting layer is 20 nm, the thickness of the hole blocking layer is 10 nm, the thickness of the electron transport layer is 40 nm, the thickness of the electron injection layer is 1 nm, and the thickness of the cathode is 100 nm.

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