Electron transport material, electron transport layer, and organic electroluminescent device

Abstract

The application discloses an electron transport material, an electron transport layer and an organic electroluminescent device, and belongs to the technical field of organic electroluminescent materials.The electron transport material is a compound containing a nitrogen-containing heterocycle, and simultaneously contains a pyridine ring and a pyrimidine ring connected with the pyridine ring.By introducing a power supply group with a steric effect, the nucleophilicity of similar nitrogen atoms on the pyrimidine ring connected with the pyridine ring can be shielded, so that the coordination activation n-doping effect of the target chelated nitrogen atom with the n-type dopant is enhanced, and the coordination stability in the coordination activation n-doping effect is promoted; and by introducing the power supply group to modify the nitrogen-containing heterocycle unit, the electronic nucleophilicity of the nitrogen-containing heterocycle unit is enhanced, so that the electron transport material can form a more stable complex with the n-type dopant, the conductivity of the electron transport layer of the light-emitting device is improved, so that the driving voltage of the organic electroluminescent device can be reduced, and the efficiency and service life of the device are improved.

Description

Technical Field

[0001] This invention relates to the field of organic electroluminescent materials technology, and more particularly to electron transport materials, electron transport layers, and organic electroluminescent devices. Background Technology

[0002] Organic light-emitting diode (OLED) technology is a display and lighting technology based on the emission of light from organic semiconductor thin films under an applied electric field. It boasts advantages such as self-illumination, thinness, flexibility, low power consumption, wide viewing angle, and excellent color saturation, and has been widely applied in high-end fields such as smartphones, televisions, automotive displays, and OLED lighting. In the OLED industry chain, organic light-emitting materials are a core technology, and their performance directly restricts the overall performance of the device, becoming one of the key technological barriers currently facing the industry. Therefore, developing high-performance materials that meet the needs of next-generation display panels is of great significance.

[0003] With the continuous development and iteration of OLED technology, the market has placed higher demands on the performance of organic light-emitting devices (OLEDs), including low driving voltage, high luminous efficiency, long operating lifetime, and high color purity. Currently, researchers have made significant progress in the design and optimization of emissive layer materials, achieving high external quantum efficiency (EQE). For commercial applications, power efficiency (PE) is also a key indicator affecting the practicality of OLEDs. OLEDs often face the problem of power efficiency decreasing with increasing brightness, known as the efficiency roll-off phenomenon, which is essentially due to increased resistive losses. To maintain high PE under high brightness conditions, it is necessary to achieve high current density at low voltage.

[0004] The performance of organic electroluminescent devices is highly dependent on the properties of the materials in each functional layer. Among them, electron transport materials play a decisive role in balancing carrier injection and transport, reducing driving voltage, improving efficiency, and extending lifetime. An ideal electron transport material needs to possess high electron mobility, matched HOMO and LUMO energy levels, good film-forming properties, high triplet energy levels, and excellent thermal stability. Currently, commercially available materials such as TPBi and BPhen suffer from insufficient electron mobility and easy crystallization, leading to poor device stability. Furthermore, some nitrogen-based heterocyclic electron transport materials may generate isomers during synthesis, causing purification difficulties and poor performance consistency, thereby increasing process complexity and production costs. Existing nitrogen-containing heterocyclic electron transport materials are mostly based on pyridine-based phenanthroline structures; however, this type of material system is singular and difficult to adapt to the needs of multi-functional devices. Therefore, developing a new type of electron transport material with a well-defined molecular structure, no isomerization defects, high thermal stability, high electron affinity, excellent electron transport performance, and the ability to achieve efficient n-type doping with metals is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide an electron transport material, an electron transport layer, and an organic electroluminescent device, aiming to solve the problems of poor electron mobility and thermal stability of existing electron transport materials.

[0006] The first aspect of this invention provides an electron transport material having a molecular structure as shown in Formula I or Formula II:

[0007]

[0008] Wherein, X1 to X4 are each independently selected from substituted or unsubstituted sterically hindered power-emitting groups, wherein the sterically hindered power-emitting groups are selected from straight-chain alkyl groups containing 1 to 6 carbon atoms, silyl groups containing 1 to 6 carbon atoms, aryl groups containing 1 to 12 carbon atoms, alkyl groups with branches containing 3 to 10 carbon atoms, cyclic alkyl groups with branches containing 3 to 10 carbon atoms, and alkoxy groups with branches containing 3 to 10 carbon atoms;

[0009] Wherein, R is selected from at least one power-producing group, which is selected from substituted or unsubstituted power-producing groups, and the power-producing group is selected from straight-chain alkyl containing 1 to 20 carbon atoms, silyl containing 1 to 20 carbon atoms, cyclic alkyl containing 3 to 20 carbon atoms, alkoxy containing 3 to 20 carbon atoms, trimethylsilyl containing 3 to 20 carbon atoms, six-membered spirocyclic rings and six-membered spirocyclic ring derivatives, spirodifluorene and spirodifluorene derivatives, silicone and silicone derivatives, fluorenyl and fluorenyl derivatives, carbazole and carbazole derivatives, aniline and aniline derivatives.

[0010] Optionally, the straight-chain alkyl group containing 1 to 6 carbon atoms is selected from methyl, ethyl, and propyl.

[0011] Optionally, the alkyl group containing 3 to 10 carbon atoms is selected from isopropyl or tert-butyl.

[0012] Optionally, the aryl group containing 1 to 12 carbon atoms is selected from phenyl.

[0013] Optionally, the silane containing 1 to 6 carbon atoms is selected from trimethylsilyl, triethylsilyl, and triisopropylsilyl.

[0014] Optionally, X1 to X4 are selected from the same group.

[0015] Optionally, the electron transport material is selected from any of the following molecular structural formulas:

[0016] .

[0017] A second aspect of the present invention provides an electron transport layer applied to an organic electroluminescent device, wherein the electron transport layer comprises an n-type dopant and the electron transport material described above.

[0018] Optionally, the n-type dopant is selected from at least one of Li, Na, Rb, Cs, Yb, Ag, Mg, Zn, Ta, Pt, Au, Li3N, Cs2CO3, and Li2CO3; the doping concentration of the n-type dopant is 0.2 to 10 wt%.

[0019] A third aspect of the present invention provides an organic electroluminescent device, comprising, from bottom to top, an anode layer, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, the electron transport layer, the electron injection layer, and a cathode layer.

[0020] Optionally, the thickness of the electron transport layer is 15–200 nm; the material of the electron injection layer is selected from at least one of Li, Na, Yb, Ag, Mg, LiF, Cs2CO3, and Li2CO3.

[0021] The beneficial effects of this invention are:

[0022] The first aspect of this invention provides an electron transport material, which is a nitrogen-containing heterocyclic compound with a unique molecular structure design. It contains a pyridine ring and a pyrimidine ring connected to the pyridine ring. By introducing a sterically hindered electron-donating group at the inter-nitrogen position of the pyridine ring, the nucleophilicity of adjacent nitrogen atoms on the pyrimidine ring connected to the pyridine ring can be shielded. This reduces the nucleophilic competition between the shielded nitrogen atom and the unshielded chelated nitrogen atom, thereby enhancing the coordination activation of the target chelated nitrogen atom with the n-type dopant. This promotes coordination stability in the coordination activation of the n-type dopant, improving the conductivity of the electron transport layer of the device, reducing the driving voltage of the organic electroluminescent device, and extending the device's lifespan.

[0023] This invention also enhances the electron nucleophilicity of nitrogen-containing heterocyclic units by introducing electron-emitting groups to modify them, thereby enhancing the coordination stability in coordination-activated n-doping. This allows the electron transport material to serve as the host material for n-type doping, forming a stable complex with the n-type dopant through coordination-activated n-doping, further improving the conductivity of the electron transport layer of the device. This effectively reduces the driving voltage of organic electroluminescent devices, improves device efficiency, and extends operating life, solving the problems of low electron mobility and poor thermal stability of electron transport materials in the prior art.

[0024] The second aspect of the present invention provides an electron transport layer applicable to organic electroluminescent devices. Compared with the existing electron transport layers of organic electroluminescent devices, the electron transport layer provided by the present invention can significantly improve electron conductivity and achieve efficient electron transport, thereby effectively reducing the driving voltage of organic electroluminescent devices, improving the luminous efficiency of light-emitting devices, and extending the working life of light-emitting devices.

[0025] The third aspect of the present invention provides an organic electroluminescent device. Compared with existing organic electroluminescent devices, the organic electroluminescent device provided by the present invention has advantages such as low driving voltage, high luminous efficiency, and long working life, and can adapt to the needs of the ever-developing and iterative updates of OLED technology. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation of compound ETL-18 from Example 1.

[0027] Figure 2 This is a flowchart illustrating the preparation of compound ETL-24 from Example 2.

[0028] Figure 3 This is a flowchart illustrating the preparation of compound ETL-29 from Example 3.

[0029] Figure 4 This is a flowchart of the preparation process of compound ETL-33 in Example 4.

[0030] Figure 5 This is a flowchart illustrating the preparation of compound ETL-37 from Example 5.

[0031] Figure 6 This is a flowchart illustrating the preparation of compound ETL-38 from Example 6.

[0032] Figure 7 This is a flowchart of the preparation process of compound ETL-39 in Example 7.

[0033] Figure 8 This is a flowchart of the preparation process of compound ETL-40 in Example 8.

[0034] Figure 9 This is a flowchart illustrating the preparation of compound ETL-45 from Example 9.

[0035] Figure 10 This is a flowchart illustrating the preparation of compound ETL-46 from Example 10.

[0036] Figure 11 This is a schematic diagram of the layered structure of the organic electroluminescent device provided in Example 11.

[0037] Figure 12 This is a molecular structure diagram of some of the raw materials used in Example 11.

[0038] Figure 13 These are the molecular structure diagrams of comparative compound 1, comparative compound 2, and comparative compound 3. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] The first aspect of this invention provides an electron transport material having a molecular structure as shown in Formula I or Formula II:

[0041] Wherein, X1 to X4 are each independently selected from substituted or unsubstituted sterically hindered power-emitting groups, wherein the sterically hindered power-emitting groups are selected from straight-chain alkyl groups containing 1 to 6 carbon atoms, silyl groups containing 1 to 6 carbon atoms, aryl groups containing 1 to 12 carbon atoms, alkyl groups with branches containing 3 to 10 carbon atoms, cyclic alkyl groups with branches containing 3 to 10 carbon atoms, and alkoxy groups with branches containing 3 to 10 carbon atoms;

[0042] Wherein, R is selected from at least one power-producing group, which is selected from substituted or unsubstituted power-producing groups, and the power-producing group is selected from straight-chain alkyl containing 1 to 20 carbon atoms, silyl containing 1 to 20 carbon atoms, cyclic alkyl containing 3 to 20 carbon atoms, alkoxy containing 3 to 20 carbon atoms, trimethylsilyl containing 3 to 20 carbon atoms, six-membered spirocyclic rings and six-membered spirocyclic ring derivatives, spirodifluorene and spirodifluorene derivatives, silicone and silicone derivatives, fluorenyl and fluorenyl derivatives, carbazole and carbazole derivatives, aniline and aniline derivatives.

[0043] The electron transport material provided by this invention is a nitrogen-containing heterocyclic compound. The molecular structure of this compound contains both a pyridine ring and a pyrimidine ring linked to the pyridine ring, and the nitrogen atom possesses a lone pair of electrons, resulting in strong nucleophilicity and coordination ability of the electrons near the nitrogen atom. This allows it to form a complex with an n-type dopant through coordination, thereby activating the n-doping process. The activated n-type dopant significantly increases the free electron concentration in the electron transport layer, while the structure of the complex optimizes the electron transport path and reduces scattering losses during electron transport. This, in turn, improves the electron transport performance of organic light-emitting devices and reduces device voltage.

[0044] To enhance the coordination activation of n-type dopant, this invention introduces a sterically hindered electron-donating group at the inter-nitrogen position (one carbon atom away from the nitrogen atom) of the pyridine ring. This shields the nucleophilicity of nearby nitrogen atoms on the pyrimidine ring (e.g., nitrogen atoms 2 and 5 in Formula III), reducing the nucleophilic competition between the shielded nitrogen atoms and the unshielded chelated nitrogen atoms (e.g., nitrogen atoms 1, 3, and 4 in Formula III). This enhances the coordination ability of the unshielded chelated nitrogen atoms, strengthens the coordination activation of n-type dopant between the chelated nitrogen atoms and the n-type dopant, promotes coordination stability in the coordination activation of n-type dopant, improves the conductivity of the electron transport layer of the device, reduces the driving voltage of the organic electroluminescent device, and extends the device's lifespan.

[0045] Furthermore, by introducing an electron-donating group (i.e., R in Formula III) to modify the nitrogen-containing heterocyclic unit and linking the electron-donating group to the pyridine ring, this invention can enhance the electron nucleophilicity of the nitrogen-containing heterocyclic unit, thereby enhancing the coordination stability in the coordination activation n-doping process, forming a stable complex, and further improving the conductivity of the electron transport layer of the device. This effectively reduces the driving voltage of the organic electroluminescent device, improves device efficiency, and extends its operating life, solving the problems of low electron mobility and poor thermal stability of electron transport materials in the prior art.

[0046] Formula III:

[0047]

[0048] In an optional embodiment, X1 to X4 can be selected from the same functional group, in which case the molecular structural formula of the electron transport material is shown in Formulas iv and V below:

[0049]

[0050] In optional embodiments, the straight-chain alkyl group containing 1 to 6 carbon atoms is selected from methyl, ethyl, and propyl. The branched alkyl group containing 3 to 10 carbon atoms is selected from isopropyl and tert-butyl. The aryl group containing 1 to 12 carbon atoms is selected from phenyl. The silyl group containing 1 to 6 carbon atoms is selected from trimethylsilyl, triethylsilyl, and triisopropylsilyl. These optional groups have steric hindrance effects while also considering electron donor characteristics, which can enhance the interaction between the electron transport material and the n-type dopant, thereby more effectively achieving n-doping and improving the electron transport capability of the material.

[0051] In an optional embodiment, the electron transport material is selected from any of the following molecular structural formulas:

[0052] .

[0053] A second aspect of this invention provides an electron transport layer applied to an organic electroluminescent device, wherein the electron transport layer comprises an n-type dopant and the electron transport material described above. Compared with existing electron transport layers in organic electroluminescent devices, the electron transport layer provided by this invention can significantly improve electron conductivity, achieve efficient electron transport, thereby effectively reducing the driving voltage of the organic electroluminescent device, improving the luminous efficiency of the device, and extending the operating life of the device.

[0054] In an optional embodiment, the n-type dopant is selected from at least one of Li, Na, Rb, Cs, Yb, Ag, Mg, Zn, Ta, Pt, Au, Li3N, Cs2CO3, and Li2CO3; the doping concentration of the n-type dopant is 0.2 to 10 wt%, which can improve electron mobility and reduce the quenching effect of the n-type dopant on the light-emitting layer, thereby improving the luminous efficiency of the light-emitting device and reducing the power consumption of the light-emitting device. At the same time, when the doping concentration of the n-type dopant is controlled within the above range, it can avoid excessively fast electron transport in the electron transport layer, thereby preventing exciton imbalance in the recombination region and optimizing the driving voltage and efficiency of the light-emitting device.

[0055] A third aspect of this invention provides an organic electroluminescent device, comprising, from bottom to top, an anode layer, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, the aforementioned electron transport layer, the electron injection layer, and a cathode layer. The light-emitting layer can be a binary blend of a host material and a light-emitting guest material, or a ternary blend of a host material, a sensitizer, and a light-emitting guest material. Compared with existing organic electroluminescent devices, the organic electroluminescent device provided by this invention has advantages such as low driving voltage, high luminous efficiency, and long operating life, and can adapt to the ever-evolving and iterative needs of OLED technology.

[0056] In an optional embodiment, the thickness of the electron transport layer is 15–200 nm, which can improve the luminous efficiency of the light-emitting device and reduce its power consumption. To improve electron injection capability and accelerate electron injection from the cathode layer, the material of the electron injection layer is selected from at least one of Li, Na, Yb, Ag, Mg, LiF, Cs₂CO₃, and Li₂CO₃.

[0057] The present invention will be further illustrated by specific embodiments below.

[0058] Example 1

[0059] Please see Figure 1 This embodiment provides compound ETL-18 and its synthesis method, the preparation method of which is as follows:

[0060] 2-Bromo-9,9-spirodifluorene T1 (1.5 g, 3.79 mmol) was refluxed with Magnesium Grignard reagent (0.1 g, 4.17 mmol) in 10 mL of tetrahydrofuran for 16 hours to obtain a thick suspension. 2 mL of DMF (N,N-dimethylformamide) was added under low-temperature water bath conditions, followed by warming to room temperature and continuing the reaction for 5 hours. The reaction was then terminated with 2 mol / L hydrochloric acid aqueous solution. After the reaction was complete, the product was extracted with ethyl acetate, dried over magnesium sulfate, and concentrated under reduced pressure. The crude product was purified by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) to give a white solid product T2 (1.05 g), with a yield of 81%.

[0061] Next, under a nitrogen atmosphere, T2 (0.59 g, 1.50 mmol), 1-(pyrimidin-2-yl)prop-1-one (0.41 g, 3.00 mmol), ammonium acetate (0.12 g, 1.51 mmol), and 10 mol% phosphorus-based ionic liquid PIL1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-18 (0.48 g), with a yield of 55%.

[0062] Example 2

[0063] Please see Figure 2 This embodiment provides the compound ETL-24 and its synthesis and preparation method, the preparation method is as follows:

[0064] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (24 mL, 39 mmol, 1.6 mol / L) was slowly added dropwise to 300 mL of tetrahydrofuran solution containing 2,7-dibromo-9,9'-spirodifluorene T3 (7.40 g, 15.60 mmol) while stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide (DMF) was slowly added, and the mixture was gradually heated to room temperature and stirred for 2 hours. After the reaction was complete, the reaction was quenched with 2 mol / L dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, and the organic phase was dried over magnesium sulfate and concentrated under reduced pressure. The crude product was purified by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 4) to give a white solid product T4 (4.1 g), in 69% yield.

[0065] Under a nitrogen atmosphere, T4 (0.81 g, 2.17 mmol), 1-(pyrimidin-2-yl)prop-1-one (1.18 g, 8.68 mmol), ammonium acetate (0.17 g, 2.20 mmol), and 20 mol% phosphorus-based ionic liquid PIL 1 were added to a 50 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 20 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-24 (0.93 g), with a yield of 51%.

[0066] Example 3

[0067] Please see Figure 3 This embodiment provides compound ETL-29 and its synthesis and preparation method, the preparation method is as follows:

[0068] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (14 mL, 22.4 mmol, 1.6 mol / L) was slowly added dropwise to 200 mL of tetrahydrofuran solution containing 3-bromo-9,9-dimethylfluorene T5 (5.57 g, 20.4 mmol) while stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide was slowly added, and the mixture was gradually heated to room temperature and stirred for 2 hours. After the reaction was complete, the reaction was quenched with 2 mol / L dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, and the organic phase was dried over magnesium sulfate and concentrated under reduced pressure. The crude product was purified by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) to give a grayish-white solid product T6 (2.84 g), in 63% yield.

[0069] Under a nitrogen atmosphere, T6 (0.35 g, 1.57 mmol), 1-(pyrimidin-2-yl)prop-1-one (0.43 g, 3.14 mmol), ammonium acetate (0.12 g, 1.51 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-29 (0.44 g), with a yield of 62%.

[0070] Example 4

[0071] Please see Figure 4 This embodiment provides compound ETL-33 and its synthesis and preparation method, the preparation method is as follows:

[0072] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (14 mL, 22.4 mmol, 1.6 mol / L) was slowly added dropwise to 200 mL of tetrahydrofuran solution containing 3-bromo-9,9-dimethylfluorene T5 (5.57 g, 20.4 mmol) while stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide was slowly added, and the mixture was gradually heated to room temperature and stirred for 2 hours. After the reaction was complete, the reaction was quenched with 2 mol / L dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, and the organic phase was dried over magnesium sulfate and concentrated under reduced pressure. The crude product was purified by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) to give a grayish-white solid product T6 (2.84 g), in 63% yield.

[0073] Under a nitrogen atmosphere, T6 (0.35 g, 1.57 mmol), 1-(pyrimidin-2-yl)phenyl-1-one (0.62 g, 3.14 mmol), ammonium acetate (0.12 g, 1.51 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a grayish-white solid product ETL-33 (0.44 g), with a yield of 48%.

[0074] Example 5

[0075] Please see Figure 5 This embodiment provides compound ETL-37 and its synthesis and preparation method, the preparation method is as follows:

[0076] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (14 mL, 22.4 mmol, 1.6 mol / L) was slowly added dropwise to 200 mL of tetrahydrofuran solution containing 5.57 g (20.4 mmol) of 2-bromo-9,9-dimethylfluorene T7, with stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide was slowly added, and the mixture was gradually heated to room temperature with stirring for another 2 hours. After the reaction was complete, the reaction was quenched with 2 mol of dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, dried over magnesium sulfate, and concentrated under reduced pressure. Purification by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) yielded a pale yellow viscous liquid product T8 (3.21 g), in 71% yield.

[0077] Under a nitrogen atmosphere, T8 (0.41 g, 1.84 mmol), 1-(pyrimidin-2-yl)prop-1-one (0.51 g, 3.68 mmol), ammonium acetate (0.14 g, 1.85 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-37 (0.51 g), with a yield of 61%.

[0078] Example 6

[0079] Please see Figure 6 This embodiment provides compound ETL-38 and its synthesis and preparation method, the preparation method is as follows:

[0080] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (14 mL, 22.4 mmol, 1.6 mol / L) was slowly added dropwise to 200 mL of tetrahydrofuran solution containing 5.57 g (20.4 mmol) of 2-bromo-9,9-dimethylfluorene T7, with stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide was slowly added, and the mixture was gradually heated to room temperature with stirring for another 2 hours. After the reaction was complete, the reaction was quenched with 2 mol of dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, dried over magnesium sulfate, and concentrated under reduced pressure. Purification by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) yielded a pale yellow viscous liquid product T8 (3.21 g), in 71% yield.

[0081] Under a nitrogen atmosphere, T8 (0.41 g, 1.84 mmol), 1-(pyrimidin-2-yl)but-1-one (0.55 g, 3.68 mmol), ammonium acetate (0.14 g, 1.85 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-38 (0.56 g), with a yield of 63%.

[0082] Example 7

[0083] Please see Figure 7 This embodiment provides compound ETL-39 and its synthesis and preparation method, the preparation method is as follows:

[0084] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (14 mL, 22.4 mmol, 1.6 mol / L) was slowly added dropwise to 200 mL of tetrahydrofuran solution containing 5.57 g (20.4 mmol) of 2-bromo-9,9-dimethylfluorene T7, with stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide was slowly added, and the mixture was gradually heated to room temperature with stirring for another 2 hours. After the reaction was complete, the reaction was quenched with 2 mol of dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, dried over magnesium sulfate, and concentrated under reduced pressure. Purification by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) yielded a pale yellow viscous liquid product T8 (3.21 g), in 71% yield.

[0085] Under a nitrogen atmosphere, T8 (0.41 g, 1.84 mmol), 2-cyclohexyl-1-(pyrimidin-2-yl)ethyl-1-one (0.75 g, 3.68 mmol), ammonium acetate (0.14 g, 1.85 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-39 (0.50 g), with a yield of 46%.

[0086] Example 8

[0087] Please see Figure 8 This embodiment provides compound ETL-40 and its synthesis and preparation method, the preparation method is as follows:

[0088] Under a nitrogen atmosphere, a solution of n-butyllithium in n-hexane (14 mL, 22.4 mmol, 1.6 mol / L) was slowly added dropwise to 200 mL of tetrahydrofuran solution containing 5.57 g (20.4 mmol) of 2-bromo-9,9-dimethylfluorene T7, with stirring for 1 hour. Then, 10 mL of N,N-dimethylformamide was slowly added, and the mixture was gradually heated to room temperature with stirring for another 2 hours. After the reaction was complete, the reaction was quenched with 2 mol of dilute hydrochloric acid aqueous solution, extracted with ethyl acetate, dried over magnesium sulfate, and concentrated under reduced pressure. Purification by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 10) yielded a pale yellow viscous liquid product T8 (3.21 g), in 71% yield.

[0089] Under a nitrogen atmosphere, T8 (0.41 g, 1.84 mmol), 1-(pyrimidin-2-yl)phenyl-1-one (0.73 g, 3.68 mmol), ammonium acetate (0.14 g, 1.85 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-40 (0.62 g), with a yield of 58%.

[0090] Example 9

[0091] Please see Figure 9 This embodiment provides compound ETL-45 and its synthesis and preparation method, the preparation method is as follows:

[0092] Under nitrogen protection, 2,7-dibromo-9,9-dimethylfluorene T9 (10.0 g, 28.4 mmol) and magnesium Grignard reagent (1.73 g, 71.0 mmol) were refluxed in 150 mL of tetrahydrofuran for 16 hours to obtain a thick suspension. This suspension was then placed in a low-temperature water bath, and 6 mL of N,N-dimethylformamide was added. The mixture was then brought to room temperature and reacted for another 5 hours. The reaction was terminated with 2 mol / L hydrochloric acid aqueous solution. After the reaction was complete, the product was extracted with ethyl acetate, and the organic phase was concentrated under reduced pressure using magnesium sulfate drying solution. The crude product was purified by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 4) to give a white solid product T10 (4.33 g), in 61% yield.

[0093] Under a nitrogen atmosphere, T10 (0.52 g, 2.08 mmol), 1-(pyrimidin-2-yl)prop-1-one (1.14 g, 8.31 mmol), ammonium acetate (0.16 g, 2.12 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-45 (0.60 g), with a yield of 40%.

[0094] Example 10

[0095] Please see Figure 10 This embodiment provides compound ETL-46 and its synthesis method, the preparation method of which is as follows:

[0096] Under nitrogen protection, 10 g (28.4 mmol) of 3,6-dibromo-9,9-dimethylfluorene (T11) was refluxed with a magnesium Grignard reagent (1.73 g, 71.0 mmol) in 150 mL of tetrahydrofuran for 16 h. The resulting concentrated suspension was then added to 6 mL of N,N-dimethylformamide in a low-temperature water bath, followed by a return to room temperature and a further reaction time of 5 h. The reaction was then terminated with 2 mol / L hydrochloric acid solution. After the reaction was complete, the product was extracted with ethyl acetate, and the organic phase was concentrated under reduced pressure using magnesium sulfate drying solution. The crude product was purified by rapid column chromatography (silica gel, ethyl acetate / n-hexane = 1 / 4). A white solid, T12 (4.68 g), was obtained, in 66% yield.

[0097] Under a nitrogen atmosphere, T12 (0.54 g, 2.16 mmol), 1-(pyrimidin-2-yl)prop-1-one (1.14 g, 8.63 mmol), ammonium acetate (0.16 g, 2.12 mmol), and 10 mol% phosphorus-based ionic liquid PIL 1 were added to a 20 mL round-bottom flask and reacted at 80 °C for 1 hour. After the reaction was complete, 10 mL of water was added to the flask, and the catalyst was separated. The remaining solid was then washed with hot ethanol and dried at 80 °C to give a white solid product ETL-46 (0.63 g), with a yield of 41%.

[0098] The compounds provided in the above examples were subjected to elemental analysis and molecular weight determination using a PerkinElmer 2400 Series II elemental analyzer and a ThermoFisher ISQ 7000 gas chromatograph-mass spectrometer, respectively. The test results are shown in Table 1 below.

[0099] Table 1

[0100]

[0101] As can be seen from the elemental analysis results in Table 1 above, the molecular structures of the compounds provided in the above embodiments contain only three elements: C, H, and N. This indicates that the prepared electron transport materials have high purity, thus ensuring that their molecular structures are well-defined.

[0102] To further test the performance of the electron transport material provided by the present invention, the following embodiments are provided.

[0103] Example 11

[0104] This embodiment provides an organic electroluminescent (OLED) device using the compound ETL-18 provided in Example 1. The structure of this organic electroluminescent device is as follows: Figure 11 As shown, from bottom to top, the structure includes an anode layer 1 (ITO conductive glass), a hole injection layer 2, a hole transport layer 3, an electron blocking layer 4, a light-emitting layer 5, a hole blocking layer 6, an electron transport layer 7, an electron injection layer 8, and an anode layer 9. The fabrication method of the organic electroluminescent device includes the following steps:

[0105] Step S001: The 30 mm × 30 mm × 0.7 mm thick transparent conductive ITO (indium tin oxide) glass substrate is ultrasonically cleaned in cleaning agent, water and isopropanol respectively. After cleaning, the ITO glass substrate is placed in an oven at 75°C and baked for 4 hours. After baking, the ITO glass substrate is subjected to vacuum plasma treatment for 20 minutes. After treatment, the anode layer is obtained.

[0106] Step S002: Place the obtained anode layer on the substrate rack of a vacuum evaporation equipment, perform vacuum treatment, and then deposit a 10nm HI-9 / BPBPA binary composition on the surface of the anode layer to form a hole injection layer on the anode layer, wherein the doping concentration of HI-9 in the binary composition is 2wt%;

[0107] Step S003: A 50 nm thick compound BPBPA is deposited on the hole injection layer to form a hole transport layer;

[0108] Step S004: A 10 nm thick compound Prime is deposited on the hole transport layer to form an electron blocking layer;

[0109] Step S005: A 40 nm thick light-emitting layer is deposited on the electron blocking layer. The light-emitting layer includes a host light-emitting material (GH) and a phosphorescent doped guest material (GD), wherein the doping concentration of the phosphorescent doped guest material is 5 wt%.

[0110] Step S006: A 10 nm thick compound HBL is deposited on the light-emitting layer to form a hole blocking layer;

[0111] Step S007: Deposit a 30 nm thick electron transport layer on the hole blocking layer. The electron transport layer includes an n-type dopant and ETL-18; wherein the n-type dopant is Ag, and the doping concentration of the n-type dopant is 5 wt%.

[0112] Step S008: Deposit a 1 nm thick layer of Yb on the electron transport layer to form an electron injection layer;

[0113] Step S009: Evaporate 100 nm thick Al on the electron injection layer to form a cathode layer.

[0114] Examples 12 to 20

[0115] Examples 12 to 20 all provide an organic electroluminescent device. The difference from Example 11 is that other types of electron transport materials were selected in step S007, as shown in Table 2 below.

[0116] Examples 21 to 23

[0117] Examples 21 to 23 all provide an organic electroluminescent device. The difference between them and Example 11 is that the doping concentration of the n-type dopant is different, as shown in Table 2 below.

[0118] Table 2:

[0119]

[0120] Comparative Examples 1 to 3

[0121] The difference between Comparative Examples 1 to 3 and Example 11 is that, in step S007, Comparative Compound 1, Comparative Compound 2, and Comparative Compound 3 were used respectively to replace ETL-18 as the electron transport material (as shown in Table 3 below), while the thickness of the electron transport layer remained 30 nm. The molecular structural formulas of Comparative Compound 1, Comparative Compound 2, and Comparative Compound 3 are attached. Figure 13 As shown.

[0122] Table 3:

[0123]

[0124] The organic electroluminescent devices provided in Examples 11 to 24 above were compared with the organic electroluminescent devices provided in Comparative Examples 1 to 3 in terms of performance. A spectroradiometer CS was used in the tests. 2000 (Konica Minolta) and 2400 (Keithley) digital source meters were used to measure organic electroluminescent devices at 1000 cd / m². 2 External quantum efficiency at luminance was measured in an organic electroluminescent device at 10 mA / cm². 2 The driving voltage at current density. Specifically, the OLED device lifetime testing system was used at 10 mA / cm². 2 The lifetime of the constant current driven measuring device when it decays to 95% of its initial brightness under the current density is shown in Table 4 below.

[0125] Table 4:

[0126]

[0127] As shown in Table 4 above, when other materials in the structure of an organic electroluminescent device are the same, the organic electroluminescent device has a long working life when using the electron transport material provided by the present invention, and can achieve low driving voltage and high luminous efficiency, thus meeting the market demand for high-performance organic electroluminescent devices.

[0128] Further comparison of the device test results provided in Example 11 with those in Comparative Example 2 revealed that, under the same current density, the organic electroluminescent device provided in Example 11 exhibits a lower driving voltage, higher external quantum efficiency, and longer operating life. This is because the electron transport material ETL-18 used in Example 11 incorporates a steric hindrance effect-producing group, which shields the nucleophilicity of the nitrogen atoms on the pyrimidine ring connected to the pyridine ring in the material's molecular structure. This enhances the coordination activation of other chelated nitrogen atoms with the n-dopant, resulting in better electron transport capabilities. Consequently, the organic electroluminescent device exhibits a lower driving voltage and higher luminous efficiency. Furthermore, due to the lower power consumption during operation, the device's lifespan is also extended.

[0129] Further comparison of the device test results provided in Examples 11 to 20 with those in Comparative Example 1 revealed that the organic electroluminescent devices provided in Examples 11 to 20 exhibited lower driving voltage, higher external quantum efficiency, and longer operating lifetime. This is because the electron transport materials used in Examples 11 to 20 incorporated steric hindrance-induced electron-donating groups, and the introduction of these groups further enhanced the electron nucleophilicity of the nitrogen-containing heterocyclic units, thereby improving the coordination stability in the coordination-activated n-doping process and further improving the conductivity of the material.

[0130] Further comparison of the device test results provided in Examples 11 to 20 with the device test results in Comparative Example 3 revealed that the driving voltage, external quantum efficiency, and operating lifetime of the organic electroluminescent devices provided in Examples 11 to 20 were superior to those of the organic electroluminescent devices provided in Comparative Example 3. Furthermore, the electron transport material used in Comparative Example 3 was based on phenanthroline material, indicating that the electron transport material provided by the present invention has superior device performance.

[0131] Further comparison of the device test results provided in Examples 11 and 21 to 23 revealed that when the doping ratio of n-type dopant is too high, the driving voltage of the organic electroluminescent device will increase and the working life will be shortened. Therefore, when n-type dopant is doped into electron transport materials, its doping amount should not be too high.

[0132] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An electron transport material, characterized in that, The electron transport material is selected from any of the following molecular structural formulas: 。 2. An electron transport layer, characterized in that, The electron transport layer is applied to an organic electroluminescent device, and the electron transport layer includes an n-type dopant and the electron transport material as described in claim 1.

3. The electron transport layer according to claim 2, characterized in that, The n-type dopant is selected from at least one of Li, Na, Rb, Cs, Yb, Ag, Mg, Zn, Ta, Pt, Au, Li3N, Cs2CO3, and Li2CO3; the doping concentration of the n-type dopant is 0.2 to 10 wt%.

4. An organic electroluminescent device, characterized in that, From bottom to top, it includes an anode layer, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer as described in any one of claims 2-3, an electron injection layer, and a cathode layer.

5. The organic electroluminescent device according to claim 4, characterized in that, The thickness of the electron transport layer is 15–200 nm; the material of the electron injection layer is selected from at least one of Li, Na, Yb, Ag, Mg, LiF, Cs2CO3, and Li2CO3.

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