An electron transport layer material, a preparation method thereof and an organic electroluminescent device

Abstract

The application provides an electron transport layer material, a preparation method thereof and an organic electroluminescent device, and the electron transport layer material has a structure shown in chemical formula I. The material of the application synergistically acts with a 9-alkyl-9-phenylfluorenyl group and a bistrizine group, is used as an electron transport layer material in a blue light device, has good thermal stability and a film morphology, can improve the light-emitting efficiency of the device, prolong the service life, and reduce the driving voltage.

Description

Technical Field

[0001] This invention belongs to the field of organic electroluminescence technology, specifically relating to an electron transport layer material, its preparation method, and an organic electroluminescence device. Background Technology

[0002] Organic light-emitting diode (OLED) displays have attracted considerable attention from researchers due to their advantages, including active light emission without the need for a backlight, high luminous efficiency, wide viewing angle, fast response speed, wide temperature adaptability, relatively simple manufacturing process, low driving voltage, low power consumption, lighter and thinner profile, and flexible display capabilities, as well as their enormous application prospects. Existing OLED displays typically include: a substrate, an anode on the substrate, an organic light-emitting layer on the anode, an electron transport layer on the organic light-emitting layer, and a cathode on the electron transport layer. During operation, holes from the anode and electrons from the cathode are emitted into the organic light-emitting layer. These electrons and holes combine to generate excited electron-hole pairs, and the excited electron-hole pairs are then converted from an excited state to a ground state to achieve light emission.

[0003] To improve the luminous efficiency of organic light-emitting diodes (OLEDs), various fluorescent and phosphorescent luminescent material systems have been developed. However, the development of excellent blue light-emitting materials, whether fluorescent or phosphorescent, remains a significant challenge. Generally speaking, OLEDs using blue fluorescent materials currently offer higher reliability. While many materials are used as electron transport materials in blue light-emitting devices, several problems exist. For example, the electron mobility is typically lower than the hole mobility in the hole transport layer, leading to carrier imbalance, reduced current efficiency, and ineffective electron transport to the luminescent layer, thus affecting light generation. Furthermore, poor energy level matching between the electron transport layer and the cathode results in difficult or inefficient electron injection, increasing interface resistance, reducing the device's driving voltage, and consequently affecting efficiency and lifetime. Some electron transport materials also degrade after prolonged operation, especially at high current densities. This degradation, caused by thermal effects, chemical reactions, or charge accumulation, leads to performance degradation, such as brightness decay and shortened lifetime.

[0004] Therefore, developing a stable and efficient compound as an electron transport layer material for use in blue organic electroluminescent devices, enabling the devices to achieve longer lifespans and higher efficiency, facilitating large-scale production, and applying it to high-end displays, is a key focus of future research and development. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an electron transport layer material, its preparation method, and an organic electroluminescent device. The present invention provides a structural compound with a synergistic effect of 9-alkyl-9-phenylfluorenyl and bis(triazine) groups, which can be used as an electron transport layer material in blue light devices. This compound exhibits good thermal stability and thin film morphology, and can improve the luminous efficiency of the device, extend its lifespan, and reduce the driving voltage.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] On one hand, the present invention provides an electron transport layer material having the structure shown in chemical formula I:

[0008] ;

[0009] in,

[0010] Ar1, Ar2, Ar3, and Ar4 are each independently selected from substituted or unsubstituted C6-C30 (e.g., C6, C8, C9, C10, C12, C13, C15, C16, C18, C19, C21, C22, C24, C25, C28, or C30, etc.) aryl groups and substituted or unsubstituted C3-C30 (e.g., C3, C4, C5, C6, C8, C9, C10, C12, C13, C15, C16, C18, C19, C21, C22, C24, C25, C28, or C30, etc.) heteroaryl groups, wherein the heteroatom contains at least one of O, S, N, Si, and Se;

[0011] R is independently selected from substituted or unsubstituted C1-C8 alkyl groups (e.g., C1, C2, C3, C4, C5, C6, C7, or C8);

[0012] R1, R2, and R3 are each independently selected from hydrogen or cyano groups; n1 and n2 are each independently selected from 0, 1, 2, and 3.

[0013] n3 is independently selected from 0, 1, 2, 3, 4, and 5.

[0014] Furthermore, Ar1, Ar2, Ar3, and Ar4 are each independently selected from substituted or unsubstituted C6-C20 (e.g., C3, C4, C5, C6, C8, C9, C10, C12, C13, C15, C16, C18, C19, or C20) aryl groups and substituted or unsubstituted C5-C18 (e.g., C5, C6, C8, C9, C10, C12, C13, C15, C16, or C18) heteroaryl groups, wherein the heteroatom contains at least one of O, S, N, Si, or Se.

[0015] Furthermore, R is independently selected from substituted or unsubstituted methyl, substituted or unsubstituted ethyl, substituted or unsubstituted propyl, substituted or unsubstituted isopropyl, and substituted or unsubstituted tert-butyl.

[0016] Furthermore, Ar1, Ar2, Ar3, and Ar4 are each independently selected from the following structures:

[0017]

[0018] * indicates the linking site of a functional group.

[0019] The term "substituted or unsubstituted" as mentioned above means substituted by one, two or more substituents selected from the following: cyano, halogen, methyl, ethyl, propyl, butyl, tert-butyl, cyclopentane, cyclohexane, phenyl, biphenyl, naphthyl, fluorenyl, dimethylfluorenyl, phenanthrene, triphenylene, carbazolyl, furanyl, thiophene, pyrrole, pyridyl, benzofuranyl, benzothiophene, isobenzofuranyl, dibenzofuranyl, dibenzothiophene, or substituted by two or more substituents linked together from the substituents shown above, or without substituents.

[0020] Furthermore, the electron transport layer material is any one of the following compounds 1-520:

[0021] .

[0022] The electron transport layer material of this invention can be prepared by methods known to those skilled in the art. Alternatively, the following reaction process is preferred for preparation, with the specific synthetic route as follows:

[0023]

[0024] Among them, R, R1-R3, n1-n3, Ar1-Ar4 are as defined in chemical formula I, and Hal1-Hal4 are selected from Cl, Br, and I.

[0025] The specific steps are as follows:

[0026] Step 1 is as follows:

[0027] At -78°C, raw material A (1.1-1.3 eq) was added to a reaction flask containing THF (tetrahydrofuran), and stirred for 15-30 min under nitrogen protection. Then, n-butyllithium (1.1-1.3 eq) was added dropwise to the reaction flask, and the reaction was allowed to proceed for 0.5-3 h. Next, a solution of raw material B (1.0 eq) in THF was gradually added dropwise to the reaction flask, and the mixture was stirred for 30 min. The mixture was then stirred overnight at room temperature, and the reaction was quenched with water. The aqueous phase was then extracted with dichloromethane, and the organic phases were combined and concentrated. The intermediate 1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:2-1:6).

[0028] Step 2 is as follows:

[0029] At room temperature, intermediate 1 (1.0 eq) was added to a reaction flask containing a mixed solution of toluene (4.0-8.0 eq) and THF (4.0-8.0 eq), stirred to dissolve, and then methanesulfonic acid (2.0-6.0 eq) was added and reacted for 20-90 min. After the reaction was completed, water and dichloromethane were added for extraction, the liquid was separated, the organic phases were combined and concentrated, and intermediate 2 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:3-1:8).

[0030] Step 3 is as follows:

[0031] Intermediate 2 (1.0 eq), pinacol diborate (1.0-1.5 eq), and potassium acetate (2.0-4.0 eq) were added to a reaction flask containing 1,4-dioxane. Under nitrogen protection, [1,1'-bis(phenylphosphine)(ferrocene)palladium dichloride] (0.02-0.10 eq) was added, and the reaction was carried out at 100-110 °C for 2-30 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 3 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:3-1:8).

[0032] Step 4 is as follows:

[0033] Intermediate 3 (1.0 eq) and starting material C (1.0-1.3 eq) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Under nitrogen protection, tetrakis(triphenylphosphine)palladium (0.01-0.05 eq) and potassium carbonate (2.0-4.0 eq) were added, and the reaction was carried out at 80℃-100℃ for 2-30 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 4 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:3-1:10).

[0034] Step 5 is as follows:

[0035] Intermediate 4 (1.0 eq), pinacol diborate (1.0-1.5 eq), and potassium acetate (2.0-4.0 eq) were added to a reaction flask containing 1,4-dioxane. Under nitrogen protection, tris(dibenzylacetone)palladium (0.02-0.10 eq), X-Phos (2-bicyclohexylphosphine-2',4',6'-triisopropylbiphenyl, 0.1-0.2 eq) or [1,1'-bis(phenylphosphine)(ferrocene)palladium dichloride] (0.02-0.10 eq) were added, and the reaction was carried out at 110-120 °C for 2-30 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 5 was obtained by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:3-1:8).

[0036] Step 6 is as follows:

[0037] Intermediate 5 (1.0 eq) and starting material D (1.0-1.3 eq) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Under nitrogen protection, tetrakis(triphenylphosphine)palladium (0.01-0.05 eq) and potassium carbonate (2.0-4.0 eq) were added, and the reaction was carried out at 80℃-100℃ for 2-30 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. The solution of dichloromethane and petroleum ether (V:V = 1:3-1:10) was purified by column chromatography to obtain chemical formula I.

[0038] Another object of the present invention is to provide an organic electroluminescent device, the organic electroluminescent device comprising an anode, a cathode and an organic layer disposed between the anode and the cathode, the organic layer comprising an electron transport layer containing an electron transport layer material as described above.

[0039] It should be noted that the organic material layer of the organic electroluminescent device in this invention can be formed as a single-layer structure or as a multilayer structure with two or more organic material layers. For example, the organic electroluminescent device may have a structure comprising a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting auxiliary layer, a light-emitting layer, a hole blocking layer, an electron transport layer, and an electron injection layer as organic material layers. However, the structure of the organic electroluminescent device is not limited to this, and may include fewer or more organic material layers.

[0040] Furthermore, the organic electroluminescent device can be used in organic electroluminescent apparatuses, including but not limited to flat panel displays, computer monitors, medical monitors, televisions, billboards, lamps for internal or external lighting and / or signals, head-up displays, fully transparent or partially transparent displays, flexible displays, laser printers, telephones, mobile phones, tablets, photo albums, personal digital assistants (PDAs), wearable devices, laptops, digital cameras, camcorders, viewfinders, microdisplays, 3D displays, virtual reality or augmented reality displays, vehicles, video walls including multiple displays tiled together, theater or stadium screens, phototherapy devices, and signs.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The compound of this invention, as an electron transport layer material, possesses excellent electron transport capabilities, superior thermal stability, and morphological stability. Organic electroluminescent devices prepared using this compound exhibit low driving voltage, high luminous efficiency with a slow efficiency roll-off, and long lifespan. The compound's structure mainly consists of 9-alkyl-9-phenyl and two triazine groups, wherein the 9-alkyl-9-phenyl acts as a bridging group, and the two triazine groups are respectively attached to the two phenyl groups in the fluorene group below the 9-alkyl-9-phenyl fluorene group.

[0043] The fluorene core in the structure possesses a high triplet energy level, effectively confining excitons within the emissive layer and reducing efficiency roll-off and spectral changes caused by exciton annihilation or diffusion into the electron transport layer at high current densities. The rigid fluorene ring also endows the material with a high melting point and high glass transition temperature. The introduction of the phenyl group further increases the Tg (glass transition temperature) and provides crucial steric hindrance, effectively suppressing close packing between molecules and ensuring the formation of a stable, uniform amorphous film, preventing crystallization during device use. The flexibility of the alkyl group contributes to good film-forming properties during evaporation with minimal impact on the distortion of the molecular skeleton. Therefore, 9-alkyl-9-phenylfluorene provides asymmetric and moderate steric hindrance to suppress crystallization without excessively distorting the molecular skeleton, thus achieving good thermal stability and film morphology while maintaining good electron mobility. This gives the material both good thermal stability and process adaptability, ensuring that the ETL (electron transport layer) film will not crystallize or degrade in morphology during long-term device operation and heating, which is key to improving device operating life. Furthermore, a uniform and stable thin film also helps maintain the uniformity of the electric field, avoiding luminescence quenching and color shift caused by local high current.

[0044] The synergistic effect of the two triazine groups generates a stronger electron-pulling effect on the central fluorene nucleus, lowering the LUMO energy level of the entire molecule. This results in a smaller barrier for electron injection from the cathode to the electron transport layer, significantly improving injection efficiency, leading to lower device power consumption and driving voltage. It also facilitates the formation of more efficient electron transport channels, promoting electron transitions within and between molecules. The strong electron supply capability of the bistriazine ensures more complete and balanced recombination of electrons and holes within the emissive layer, increasing exciton generation rate and leading to a significant improvement in maximum external quantum efficiency and luminous efficiency. Maintaining carrier balance even at high current densities results in a flatter efficiency-luminosity curve. The larger molecular weight and more rigid ends of the bistriazine groups typically significantly increase the glass transition temperature of the material. A high thermal glass transition temperature means that the material is less prone to molecular relaxation or rearrangement during device operation. The triazine group contains multiple nitrogen atoms, which can generate certain dipole-dipole interactions. The bistriazine structure enhances these intermolecular forces (but must be controlled to avoid excessive crystallization), which helps to form a denser and more robust thin film, thereby improving the long-term operational stability of the device. In addition, the further substitution of a cyano group on the three benzene rings in the 9-alkyl-9-phenylfluorenyl group changes the energy level, thus playing a role in adjusting the device performance, resulting in a lower driving voltage and higher luminous efficiency. Attached Figure Description

[0045] Figure 1 This is the 1H NMR spectrum of compound 1.

[0046] Figure 2 The image shows the proton NMR spectrum of compound 501. Detailed Implementation

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0048] Additionally, it should be noted that the values ​​given in the following embodiments are as accurate as possible. However, those skilled in the art will understand that due to unavoidable measurement errors and experimental issues, each number should be understood as an approximation rather than an absolutely accurate value.

[0049] Example 1

[0050]

[0051] Step 1 is as follows:

[0052] At -78°C, raw material A-1 (1.2 eq, CAS No.: 1801701-07-4) was added to a reaction flask containing THF. The mixture was stirred for 20 min under nitrogen protection. Then, n-butyllithium (1.2 eq) was added dropwise to the reaction flask, and the reaction was allowed to proceed for 2 h. Next, a solution of raw material B-1 (1.0 eq, CAS No.: 98-86-2) in THF was gradually added dropwise to the reaction flask, and the mixture was stirred for 30 min. The mixture was then stirred overnight at room temperature. The reaction was quenched with water, and the aqueous phase was extracted with dichloromethane. The combined organic phases were concentrated, and the intermediate 1-1 was purified by column chromatography using a mixture of dichloromethane and petroleum ether (V:V = 1:2) to obtain intermediate 1-1 (yield: 71.2%).

[0053] Step 2 is as follows:

[0054] At room temperature, intermediate 1-1 (1.0 eq) was added to a reaction flask containing a mixed solution of toluene (5.0 eq) and THF (5.0 eq), stirred to dissolve, and then methanesulfonic acid (5.0 eq) was added and reacted for 60 min. After the reaction was completed, water and dichloromethane were added for extraction, the liquid was separated, the organic phases were combined and concentrated, and intermediate 2-1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4) (yield: 78.9%).

[0055] Step 3 is as follows:

[0056] Intermediate 2-1 (1.0 eq), pinacol diborate (1.2 eq), and potassium acetate (3.0 eq) were added to a reaction flask containing 1,4-dioxane. Under nitrogen protection, [1,1'-bis(phenylphosphine)(ferrocene)palladium dichloride] (0.03 eq) was added, and the reaction was carried out at 100 °C for 15 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 3-1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:5) (yield: 78.2%).

[0057] Step 4 is as follows:

[0058] Intermediate 3-1 (1.0 eq) and starting material C-1 (1.0 eq, CAS No.: 3842-55-5) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Tetra(triphenylphosphine)palladium (0.03 eq) and potassium carbonate (3.0 eq) were added under nitrogen protection, and the reaction was carried out at 95 °C for 20 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 4-1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:4) (yield: 83.3%).

[0059] Step 5 is as follows:

[0060] Intermediate 4-1 (1.0 eq), pinacol diborate (1.2 eq), and potassium acetate (4.0 eq) were added to a reaction flask containing 1,4-dioxane. Tris(dibenzylacetone)dipalladium (0.05 eq) and X-Phos (0.2 eq) were added under nitrogen protection, and the reaction was carried out at 120 °C for 18 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 5-1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4) (yield: 79.8%).

[0061] Step 6 is as follows:

[0062] Intermediate 5-1 (1.0 eq) and starting material D-1 (1.0 eq, CAS No.: 3842-55-5) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Tetra(triphenylphosphine)palladium (0.05 eq) and potassium carbonate (4.0 eq) were added under nitrogen protection, and the reaction was carried out at 95 °C for 23 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Compound 1 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:5) (yield: 85.6%).

[0063] The obtained compound 1 was analyzed, and the results are as follows:

[0064] HPLC purity: >99.8%.

[0065] Mass spectrometry test: Waters XEVO TQD mass spectrometer with ESI source.

[0066] Test value MS(ESI, m / Z): [M+H] + =719.29.

[0067] Elemental analysis:

[0068] The test values ​​are: C, 83.32; H, 4.88; N, 11.81.

[0069] The proton NMR spectrum of compound 1 is shown below. Figure 1 As shown.

[0070] Example 2

[0071]

[0072] Raw material A-501 is not existing technology and needs to be synthesized first. The synthesis process is as follows:

[0073] Raw material a-501 (1.0 eq, CAS No.: 89598-96-9) and raw material b-501 (1.2 eq, CAS No.: 148836-41-3) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Tetra(triphenylphosphine)palladium (0.03 eq) and potassium carbonate (3.0 eq) were added under nitrogen protection, and the reaction was carried out at 80 °C for 3 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Raw material A-501 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:6) (yield: 74.3%).

[0074] Note: In this reaction step, the starting material b-501 contains three halogens. Utilizing the characteristic of reactivity I>Br>Cl in the Suzuki coupling reaction, and by controlling the reaction conditions and reaction sites, the intermediate of the target structure was prepared. The reaction was then purified using column chromatography or a silica gel funnel to remove byproducts, yielding the target compound. For the reaction mechanism, see: *Organometallic Chemistry* (6th Edition), Robert H. Crabtree, Shanghai: East China University of Science and Technology Press, 2017-09-00, ISBN: 978-7-5628-5111-0, page 388; and *Experimental Tutorial on Organic Chemistry and Optoelectronic Materials*, Chen Runfeng, Southeast University Press, 2019-11-0, ISBN: 9787564184230, page 174.

[0075] Step 1 is as follows:

[0076] At -78°C, raw material A-501 (1.2 eq) was added to a reaction flask containing THF, and stirred for 20 min under nitrogen protection. Then, n-butyllithium (1.2 eq) was added dropwise to the reaction flask, and the reaction was allowed to proceed for 2 h. Next, a solution of raw material B-501 (1.0 eq, CAS No.: 1443-80-7) in THF was gradually added dropwise to the reaction flask, and the mixture was stirred for 30 min. The mixture was then stirred overnight at room temperature, and the reaction was quenched with water. The aqueous phase was then extracted with dichloromethane, and the organic phases were combined and concentrated. The intermediate 1-501 (yield: 70.1%) was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:2).

[0077] Step 2 is as follows:

[0078] At room temperature, intermediate 1-501 (1.0 eq) was added to a reaction flask containing a mixed solution of toluene (5.0 eq) and THF (5.0 eq), stirred to dissolve, and then methanesulfonic acid (5.0 eq) was added and reacted for 60 min. After the reaction was completed, water and dichloromethane were added for extraction, the liquid was separated, the organic phases were combined and concentrated, and intermediate 2-501 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:5) (yield: 77.4%).

[0079] Step 3 is as follows:

[0080] Intermediate 2-501 (1.0 eq), pinacol diborate (1.2 eq), and potassium acetate (3.0 eq) were added to a reaction flask containing 1,4-dioxane. Under nitrogen protection, [1,1'-bis(phenylphosphine)(ferrocene)palladium dichloride] (0.03 eq) was added, and the reaction was carried out at 100 °C for 16 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 3-501 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:5) (yield: 77.9%).

[0081] Step 4 is as follows:

[0082] Intermediate 3-501 (1.0 eq) and starting material C-501 (1.0 eq, CAS No.: 3842-55-5) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Tetra(triphenylphosphine)palladium (0.03 eq) and potassium carbonate (3.0 eq) were added under nitrogen protection, and the reaction was carried out at 95 °C for 22 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 4-501 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:4) (yield: 82.1%).

[0083] Step 5 is as follows:

[0084] Intermediate 4-501 (1.0 eq), pinacol diborate (1.2 eq), and potassium acetate (4.0 eq) were added to a reaction flask containing 1,4-dioxane. Tris(dibenzylacetone)dipalladium (0.05 eq) and X-Phos (0.2 eq) were added under nitrogen protection, and the reaction was carried out at 120 °C for 19 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Intermediate 5-501 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V=1:4) (yield: 78.2%).

[0085] Step 6 is as follows:

[0086] Intermediate 5-501 (1.0 eq) and starting material D-501 (1.0 eq, CAS No.: 3842-55-5) were added to a reaction flask containing a mixed solution of toluene, ethanol and water (V:V:V = 3:1:1). Tetra(triphenylphosphine)palladium (0.05 eq) and potassium carbonate (4.0 eq) were added under nitrogen protection, and the reaction was carried out at 95 °C for 24 h. After the reaction was completed, water and dichloromethane were added for separation and extraction. The organic phase was retained and concentrated. Compound 501 was purified by column chromatography using a mixed solution of dichloromethane and petroleum ether (V:V = 1:5) (yield: 85.0%).

[0087] The obtained compound 501 was analyzed, and the results are as follows:

[0088] HPLC purity: >99.7%.

[0089] Mass spectrometry test: Waters XEVO TQD mass spectrometer with ESI source.

[0090] Test value MS(ESI, m / Z): [M+H] + =744.36.

[0091] Elemental analysis:

[0092] The test values ​​are: C, 82.11; H, 4.61; N, 13.31.

[0093] The proton NMR spectrum of compound 501 is shown below. Figure 2 As shown.

[0094] In addition, it should be noted that other compounds of the present invention can be obtained by referring to the preparation methods of the examples listed above, so they will not be listed one by one here.

[0095] Device Example 1: Fabrication of Organic Electroluminescent Devices

[0096] The coating thickness is 1500. The ITO (indium tin oxide)-Ag-ITO (indium tin oxide) glass substrate was cleaned three times in distilled water, ultrasonically washed for 30 minutes, then repeatedly cleaned three times in distilled water, ultrasonically washed for 10 minutes. After washing, it was ultrasonically washed sequentially with methanol, acetone, and isopropanol (5 minutes each time), dried, and then transferred to a plasma cleaner for 5 minutes. It was then sent to an evaporation machine, where other functional layers were sequentially deposited on the substrate as the anode.

[0097] (1) with 1 Hole injection layer materials HT and P-dopant are vacuum evaporated at a evaporation rate of / s, wherein the evaporation rate ratio of HT and P-dopant is 97:3, and the thickness is 10nm.

[0098] (2) with 1.5 A 130nm HT layer was vacuum-deposited at a deposition rate of / s as a hole transport layer.

[0099] (3) with 0.5 Prime was vacuum-deposited at a deposition rate of / s to a 5nm layer as a light-emitting auxiliary layer.

[0100] (4) with 1 Vacuum evaporation of host material and dopant material as light-emitting layer at a evaporation rate of / s, with a thickness of 30nm, wherein the evaporation rate ratio of host to dopant is 98:2.

[0101] (5) with 0.5 A vacuum evaporation process with a deposition rate of / s was used to deposit HB with a thickness of 5nm as a hole blocking layer.

[0102] (6) with 1 Compound 1 and Liq were vacuum-deposited at a deposition rate of / s as an electron transport layer with a thickness of 30nm, wherein the deposition rate ratio of compound 1 to Liq was 50:50.

[0103] (7) with 0.5 A Yb film with a thickness of 1 nm was vacuum-deposited at a deposition rate of / s as an electron injection layer.

[0104] (8) with 1 Magnesium and silver were vacuum-deposited at a deposition rate of / s as cathodes, with a thickness of 13nm, and the deposition rate ratio of magnesium to silver was 1:9.

[0105] (9) with 1 At a evaporation rate of / s, CPL is vacuum-deposited on the cathode as a light extraction layer with a thickness of 70nm. The substrate after evaporation is then encapsulated: first, a UV adhesive is applied to the cleaned cover plate using a coating equipment; then, the coated cover plate is moved to the lamination section, and the evaporated substrate is placed on top of the cover plate; finally, the substrate and cover plate are laminated under the action of a bonding equipment, while simultaneously curing the UV adhesive by light.

[0106] The required material structure is shown below:

[0107] .

[0108] Device Example 2-144

[0109] Referring to the method provided in Device Example 1 above, the corresponding compounds in Table 1 below were selected to replace compound 1, and the electron transport layer was deposited to prepare the corresponding organic electroluminescent devices, which are respectively referred to as Device Examples 2-144.

[0110] Device Comparison Examples 1-7

[0111] The device comparative example was prepared according to the method provided in Device Example 1 above, except that the electron transport layer (compound 1) in Device Example 1 was replaced with the existing comparative compound ag, wherein the structural formula of compound ag is as follows:

[0112] .

[0113] The driving voltage, BI value, and lifetime of the organic electroluminescent devices obtained in Examples 1-144 and Comparative Examples 1-7 were characterized at a brightness of 1000 nits. The test results are shown in Table 1 below.

[0114] Table 1 Device Test Results

[0115]

[0116] Those skilled in the art will know that in blue top-emitting devices, luminous efficiency is greatly affected by chromaticity. Therefore, taking into account the influence of chromaticity on efficiency, the ratio of luminous efficiency to CIEy is defined as the BI value, i.e., BI = (cd / A) / CIEy. In the test, the CIEy value is adjusted to be between 0.043 and 0.045.

[0117] As can be seen from the data in the table above, the organic electroluminescent devices prepared using the compounds of this invention as electron transport layer materials exhibit superior device performance compared to those prepared using the comparative compounds, with high thermal stability, low driving voltage (below 3.81V), high luminous efficiency (above 180 cd / A), and long service life (T95 above 540h).

[0118] Comparative compounds a, b, c, d, and e are parallel comparative examples to compounds 489, 491, 488, 503, and 2 of this invention. The difference lies in the structure of the compounds in this invention: two triazine groups are respectively attached to two benzene groups below 9-methyl-9-phenylfluorene, with 9-methyl-9-phenylfluorene acting as a bridging group. In contrast, the corresponding bridging groups in comparative compounds a, b, c, d, and e are spirodifluorenyl, 9,9-diphenylfluorenyl, 9,9-dimethylfluorenyl, a fluorenyl group attached to adamantane, and a phenyl group, respectively. The spirodifluorenyl group contains a spirocarbon center, causing the two benzene rings to be nearly perpendicular, resulting in excessive molecular twisting, severely disrupting conjugation, and lower electron mobility. The two large phenyl groups in the 9,9-diphenylfluorenyl group further exacerbate molecular twisting, widening the molecular bandgap, and potentially resulting in insufficient LUMO energy level depth, thus slightly weakening electron injection capability, and lower conjugation and mobility compared to the 9-methyl-9-phenylfluorene structure. The steric hindrance of the 9,9-dimethylfluorene group is too small, making the molecule prone to regular arrangement, resulting in a strong tendency to crystallize, poor thin film stability, and shortened device lifespan during long-term high-temperature operation. Meanwhile, the single phenyl group lacks a rigid fused ring structure, and its thermal stability, morphological stability, and high triplet energy levels are inferior to the fluorene series structures, thus leading to low device performance. The large adamantane group exhibits a three-dimensional structure, severely distorting and disrupting molecular planarity and conjugation, significantly impairing electron mobility and affecting electron transport capabilities.

[0119] Comparative compounds f and g are parallel comparative examples of compounds 37 and 399 of this invention. The difference lies in the following: in comparative compounds f and g, only one triazine group is attached to the fluorene atom below the 9-alkyl-9-phenylfluorene, while in compounds 37 and 399 of this invention, each of the two benzene atom groups below the 9-alkyl-9-phenylfluorene atom is attached to a triazine group. The two triazine groups work synergistically to generate a stronger electron-pulling effect on the central fluorene nucleus, resulting in a lower LUMO energy level for the entire molecule, smoother electron injection, and higher mobility, leading to lower power consumption and lower driving voltage in the device. It also achieves a perfect balance between electron and hole injection, resulting in higher efficiency and a slower roll-off. The bis-triazine structure makes the overall structure more rigid, enhances molecular forces, makes the film more robust, and extends the device's lifespan.

[0120] The applicant declares that this invention illustrates the electron transport layer material, its preparation method, and the organic electroluminescent device through the above embodiments. However, this invention is not limited to the above embodiments, meaning that this invention does not necessarily rely on the above embodiments for implementation. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. An electron transport layer material, characterized in that, The electron transport layer material has the structure shown in chemical formula I: ； in, Ar1, Ar2, Ar3, and Ar4 are each independently selected from the following structures: ； * indicates the linking site of a functional group; R is independently selected from unsubstituted methyl, unsubstituted ethyl, unsubstituted propyl, unsubstituted isopropyl, and unsubstituted tert-butyl; R1, R2, and R3 are each independently selected from hydrogen or cyano groups; n1 and n2 are independently selected from 0, 1, 2, and 3; n3 is independently selected from 0, 1, 2, 3, 4, and 5.

2. The electron transport layer material according to claim 1, characterized in that, The electron transport layer material is any one of the following compounds 1-520: 。 3. An organic electroluminescent device, characterized in that, The organic electroluminescent device includes an anode, a cathode, and an organic layer disposed between the anode and the cathode, the organic layer including an electron transport layer, the electron transport layer containing the electron transport layer material as described in claim 1 or 2.

4. The organic electroluminescent device according to claim 3, characterized in that, The organic layer further includes at least one of a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting auxiliary layer, a light-emitting layer, a hole blocking layer, or an electron injection layer.

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