Styrene hybrid-based carbazole derivative, preparation method and application thereof

Abstract

This invention belongs to the field of organic optoelectronics and discloses a class of styrene-hybridized carbazole derivatives, their preparation methods, and their application in preparing hole transport layers for electroluminescent devices. The styrene-hybridized carbazole derivatives can be prepared into functional thin films with excellent solvent resistance through thermal crosslinking, while also possessing excellent hole transport capabilities and high triplet energy levels. They can be used as hole transport layers in organic electroluminescent devices. Furthermore, the styrene-hybridized carbazole derivatives have a low crosslinking temperature, allowing for convenient thermal annealing to facilitate the preparation of multilayer light-emitting devices using solution methods. The prepared multilayer light-emitting devices exhibit excellent luminescent properties and show promising application prospects in solar cells and flexible light-emitting devices.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronics, and relates to a class of carbazole derivatives based on styrene hybridization, their preparation methods, and their application in preparing hole transport layers for electroluminescent devices. Technical Background

[0002] Organic light-emitting diodes (OLEDs) have been widely studied by academia and industry due to their superior image quality and contrast, fast response time, and high refresh rate. They are also lighter, thinner, and have great potential for applications in optoelectronics. Furthermore, OLED devices show great promise for use on flexible substrates, such as in electronic skin and wearable devices. OLEDs are also a more energy-efficient technology.

[0003] In OLED devices, the hole transport layer plays a crucial role in hole injection from the anode to the emissive layer, making the molecular design of hole transport materials particularly important. The designed molecules must possess not only high triplet energy levels but also suitable orbital energy levels (HOMO, LUMO levels) to ensure hole entry into the emissive layer and electron blocking from the anode, thereby improving device efficiency. Currently, OLED device fabrication processes are mainly divided into solution methods and vacuum evaporation methods, and the main difference between these two processes lies in the fabrication of the hole transport layer. While vacuum evaporation produces uniform semiconductor films, its high cost and inability to fabricate large-area devices limit its development. Conversely, solution methods require milder conditions, consume less energy, and are less expensive, making them suitable for large-scale semiconductor device fabrication.

[0004] Thermal crosslinking has become a common method for solution-based fabrication of organic semiconductor devices. However, current designs for crosslinking materials still have shortcomings, such as solvent resistance and long-term stability. Our research group previously disclosed patent CN114560851B, which provides a class of carbazole derivatives based on epoxide, their preparation methods, and applications. The disclosed carbazole derivatives based on epoxide are crosslinkable compounds with hole transport capabilities. Carbazole hole transport materials based on epoxide possess hole transport performance and high triplet energy. The introduction of crosslinkable epoxide gives the material strong thermal stability and solvent resistance. Although no initiator is required, the disclosed Oxe-DCzTPA (hereinafter referred to as Oxe-TPA) still needs annealing at 180℃ to maintain its strong thermal stability and solvent resistance. Therefore, the problem of excessively high crosslinking temperatures in existing thermal crosslinking methods remains unresolved.

[0005] As another type of thermally crosslinked functional material, styrene groups generally require high heat treatment temperatures, such as above 170°C, to achieve complete crosslinking even without the need for additional initiators. For example, see the published literature Meng-Ju Tsai, Wei-Lun Huang, Li-Ming Chen, Guo-Lun Ruan, Dian Luo, Zong-Liang Tseng and Ken-Tsung Wong. Journal of Materials Chemistry C, 2023, 1056-1066. Chen et al. designed a thermally crosslinked hole transport material (BCzC4Sy), which requires a heat treatment temperature of 170°C to achieve complete crosslinking. This greatly hinders the application of thermal crosslinking methods in organic semiconductor devices.

[0006] Lowering the heat treatment temperature in the thermal crosslinking process is crucial for the fabrication of organic semiconductor devices. Relevant research (see R. Kiebooms, A. Aleshin, K. Hutchison, F. Wudl, A. Heeger. Synthetic Metals, 1999, 436-437) indicates that heat treatment temperatures above 150°C can damage the hole injection layer (PEDOT:PSS), thereby reducing device efficiency. Therefore, lowering the thermal crosslinking temperature not only reduces the manufacturing cost of organic semiconductor devices but also minimizes damage to organic molecules within the device, thus expanding its application range. Summary of the Invention

[0007] To address the above problems, this invention provides a class of styrene-hybridized carbazole derivatives (R-VBCz) and their preparation method. This application uses thermally crosslinked functional material styrene groups, which are hybridized with the carbazole derivative core provided in this application. Crosslinking can be carried out at a relatively low heat treatment temperature without the need for additional initiators. At the same time, the formed network film has excellent solvent resistance and long-term stability. The styrene-hybridized carbazole derivatives provided in this invention have high triplet energy levels and suitable HOMO energy levels, and can be used to fabricate hole transport layers in organic electroluminescent devices, thereby preparing high-efficiency organic electroluminescent devices.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a class of carbazole derivatives based on styrene hybridization, having the following general structural formula:

[0010]

[0011] Where n is any positive integer, and R is selected from any of the following structures:

[0012]

[0013] As a preferred embodiment of the styrene-hybridized carbazole derivative described in this application, the structure is selected from any one of the following compounds:

[0014]

[0015] Secondly, the present invention also provides a method for preparing the above-mentioned type of carbazole derivatives based on styrene hybridization, the preparation method being as follows:

[0016]

[0017] Wherein, RH can be any of the following structural formulas:

[0018]

[0019] The preparation method of the styrene-hybridized carbazole derivative (R-VBCz) is as follows:

[0020] Preparation of intermediate compound 1: Compound 4-hydroxycarbazole, tetrabutylammonium bromide (TBAB), and potassium carbonate were added to a reaction flask containing ethyl acetate. After stirring at room temperature for 2 hours, the starting material iodomethane was added, and the mixture was refluxed at 80°C for 24 hours. After the reaction was completed and cooled to room temperature, dichloromethane and water were added for liquid-liquid extraction. The organic phase was collected, and the organic solvent was evaporated to dryness using a rotary evaporator. Finally, the mixture was purified by silica gel column chromatography to obtain a white solid, namely compound 1.

[0021] Preparation of intermediate compound 2: Intermediate compound 1 and potassium tert-butoxide were added to a reaction flask containing dried dimethyl sulfoxide solvent. After thorough stirring, the starting material 1-bromo-3,5-difluorobenzene was added, and the mixture was heated to 80°C and reacted for 12 hours. After the reaction was completed and cooled to room temperature, excess water was added, and then excess dimethyl sulfoxide was removed by filtration. The precipitate was collected and purified by silica gel chromatography to obtain a white solid, namely intermediate compound 2.

[0022] Preparation of intermediate compound 3: Intermediate compound 2, starting material RH, tri-tert-butylphosphine tetrafluoroborate, tris(dibenzylacetone)dipalladium, and sodium tert-butoxide were added to a reaction flask. Toluene solvent, after being repeatedly deoxygenated by nitrogen evacuation, was added, and the mixture was heated to 115°C and stirred under reflux. After the reaction was completed and cooled to room temperature, dichloromethane and water were added for liquid-liquid extraction. The organic phase was collected, and the organic solvent was evaporated to dryness using a rotary evaporator. Finally, the mixture was purified by silica gel column chromatography to obtain a white solid, which is intermediate compound 3.

[0023] Preparation of intermediate compound 4: Intermediate compound 3 was added to a reaction flask containing dried dichloromethane. After the reaction flask was cooled to 0°C in an ice-water bath, boron tribromide was slowly added dropwise. After the reaction was carried out in an ice-water bath for 2 hours, the mixture was transferred to room temperature and reacted for 6 hours. After the reaction was completed, excess water was added to quench the reaction, and then saturated sodium bicarbonate solvent was added to adjust the pH of the reaction solution to neutral. Finally, dichloromethane and water were added for liquid-liquid extraction, and the organic phase was collected. The organic solvent was evaporated using a rotary evaporator to obtain a brown solid, which was intermediate compound 4.

[0024] Preparation of the intermediate compound BOVBr: 4-hydroxystyrene, the starting material 1,6-dibromohexane, and potassium carbonate were added to a reaction flask containing acetone solvent, and the mixture was heated to 70°C and reacted for 12 hours. After the reaction was completed and cooled to room temperature, dichloromethane and water were added for liquid-liquid extraction. The organic phase was collected, and the organic solvent was evaporated to dryness using a rotary evaporator. Finally, the solution was purified by silica gel column chromatography to obtain a colorless liquid, which is the intermediate compound BOVBr.

[0025] Preparation of compound R-VBCz: Intermediate compound 4, compound BOVBr, tetrabutylammonium bromide (TBAB), and potassium carbonate were added to a reaction flask containing acetonitrile solvent and reacted at 85°C for 26 hours. After the reaction was completed and cooled to room temperature, ethyl acetate and water were added for liquid-liquid extraction. The organic phase was collected, dried over anhydrous sodium sulfate, and then the organic solvent was evaporated by rotary evaporation. Finally, the mixture was purified by silica gel column chromatography to obtain a pale yellow solid, namely compound R-VBCz.

[0026] Thirdly, the present invention provides the application of the above-mentioned styrene-hybridized carbazole derivatives in the fabrication of hole transport layers for organic electroluminescent devices. The hole transport layer is a thin film structure prepared by coating the styrene-hybridized carbazole derivatives onto a hole injection layer using a solution method and then performing a thermal crosslinking reaction through annealing. The annealing temperature is not lower than 120°C and the annealing time is not less than 30 minutes.

[0027] The styrene-hybridized carbazole derivatives provided by this invention, as hole transport materials, possess high triplet energy levels and suitable highest occupied molecular orbital (HOMO) energy levels, enabling them to transport holes and block exciton overflow from the light-emitting layer. This allows them to be used as hole transport layers in organic electroluminescent devices. Furthermore, the styrene-hybridized carbazole derivatives provided by this invention also have low thermal crosslinking temperatures, greatly optimizing the process conditions for solution-based electroluminescent device fabrication. When used to fabricate hole transport layers, they can improve the device efficiency of organic electroluminescent devices.

[0028] Fourthly, the present invention provides a type of organic electroluminescent device, wherein the hole transport layer of the organic electroluminescent device is the hole transport layer provided in the third aspect of the present invention; such as Figure 1 As shown, the organic electroluminescent device comprises, from anode to cathode, a metal anode, an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an ITO cathode. The metal anode layer is Ag, deposited using a vacuum evaporation process to a thickness of 100 nm. The electron injection layer is Ca, deposited using a vacuum evaporation process to a thickness of 10 nm. The electron transport layer is 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)phenyl TPBi, also deposited using a vacuum evaporation process to a thickness of 3 nm. The light-emitting layer is prepared by solution method using 26DCzPPy and thermally activated delayed fluorescence material in different mass ratios; the hole injection layer is a poly(3,4-ethyldioxythiophene):polystyrene sulfonate PEDOT:PSS film, which is prepared by spin-coating the hole injection layer onto an ITO glass substrate using a solution process, with a film thickness of approximately 30nm; the anode substrate is ITO glass, where ITO is the conductive anode, and the required ITO glass substrate is cleaned, dried, and then subjected to ozone treatment.

[0029] As one embodiment of the organic electroluminescent device of the present invention, the light-emitting layer material is 26DCzPPy:4CzIPN, and the mass concentrations of 26DCzPPy and 4CzIPN are 90% and 10%, respectively, and the organic electroluminescent device is a device that emits green light.

[0030] As one embodiment of the organic electroluminescent device of the present invention, the light-emitting layer material is 26DCzPPy:4TCzBN, and the mass concentrations of 26DCzPPy and 4TCzBN are 60% and 40%, respectively. The organic electroluminescent device is a device that emits blue light.

[0031] As one embodiment of the organic electroluminescent device of the present invention, the light-emitting layer material is 26DCzPPy:TXO-TPA, and the mass concentrations of 26DCzPPy and TXO-TPA are 60% and 40%, respectively; the organic electroluminescent device is a red light emitting device.

[0032] The beneficial effects of this invention are:

[0033] First, the styrene-hybridized carbazole derivatives provided in this application are constructed by introducing thermally crosslinked styrene functional groups into a molecular core with a high HOMO energy level through alkyl chains. The constructed styrene-hybridized carbazole derivatives can still maintain a high HOMO energy level and also have a high triplet energy level. In addition, the characterization of the carbazole derivatives provided in this application using photophysics, electrochemistry and thermodynamics can verify that the styrene-hybridized carbazole derivatives provided in this application can be completely crosslinked under thermal initiation as thermally crosslinked hole transport materials, and the film formed after crosslinking has good solvent resistance and film-forming properties.

[0034] Secondly, the carbazole derivatives based on styrene hybrids provided in this application, as thermally crosslinked hole transport materials, can be used to prepare electroluminescent devices with excellent device efficiency.

[0035] Finally, the styrene-hybridized carbazole derivatives provided in this application, as thermally crosslinked hole transport materials, can obtain thin films with good solvent resistance and film-forming properties as hole transport layers for electroluminescent devices under relatively low heat treatment conditions; thereby reducing the processing time of electroluminescent devices, making the process simple, efficient, and environmentally friendly.

[0036] Moreover, the thermally cross-linked hole transport material disclosed in this invention can be applied to the fabrication of large-area, large-scale devices in the field of optoelectronic information, and also has good application prospects in the fields of solar cells, flexible materials, and electrochromic materials. Attached Figure Description

[0037] Figure 1 This is a structural diagram of the organic electroluminescent device described in this invention;

[0038] Figure 2 The UV absorption, fluorescence, and low-temperature phosphorescence spectra of the compound solution in Example 1 of this invention are shown below.

[0039] Figure 3 The following are fluorescence spectra of the compound in different solutions in Example 1 of this invention;

[0040] Figure 4 This is an oxidation curve of the compound in Example 1 of the present invention;

[0041] Figure 5a Thermogravimetric analysis (TGA) curves of the compounds after crosslinking in Example 1 of this invention;

[0042] Figure 5b The differential scanning calorimetry (DSC) curve of the compound after crosslinking in Example 1 of this invention;

[0043] Figure 6 This is an atomic force microscope (AFM) image of the compound in Example 1 of the present invention after crosslinking;

[0044] Figure 7a Comparison of UV absorption spectra of HTPA-VBCz before and after film formation and elution after thermal crosslinking treatment at 120℃;

[0045] Figure 7b Comparison of UV absorption spectra of OXE-TPA before and after film formation and elution after thermal crosslinking treatment at 120℃;

[0046] Figure 7c Comparison of UV absorption spectra of OXE-TPA before and after film formation and elution after thermal crosslinking treatment at 140℃;

[0047] Figure 7d Comparison of UV absorption spectra of OXE-TPA before and after film formation and elution after thermal crosslinking treatment at 160℃;

[0048] Figure 8a The current density-voltage-brightness characteristic curve of the green light device fabricated in the specific implementation embodiment is shown.

[0049] Figure 8b The current efficiency-brightness-external quantum efficiency characteristic curves of the green light device fabricated in the specific implementation embodiment are shown.

[0050] Figure 8c The electroluminescence spectrum of the green light device fabricated in the specific implementation embodiment;

[0051] Figure 9a The current density-voltage-brightness characteristic curve of the blue light device fabricated in the specific implementation embodiment is shown.

[0052] Figure 9b The current efficiency-brightness-external quantum efficiency characteristic curves of the blue light device fabricated in the specific implementation embodiment are shown.

[0053] Figure 9c The electroluminescence spectrum of the blue light device fabricated in the specific implementation embodiment;

[0054] Figure 10a The figure shows the current density-voltage-brightness characteristic curve of the red light device fabricated in the specific implementation embodiment;

[0055] Figure 10b The graph shows the current efficiency-brightness-external quantum efficiency characteristics of the red light device fabricated in the specific implementation method.

[0056] Figure 10c The electroluminescence spectrum of the red light device fabricated in the specific implementation embodiment. Detailed Implementation

[0057] The present invention will be further illustrated below with specific examples, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described below shall be carried out under conventional conditions or manufacturer's recommended conditions. Instruments and reagents whose manufacturers are not specified can be purchased commercially.

[0058] Example 1: Preparation of HTPA-VBCz

[0059] The synthetic route of HTPA-VBCz is shown below:

[0060]

[0061] Synthesis of Intermediate 1: 5.0 g of 4-hydroxycarbazole, 1.0 g of tetrabutylammonium bromide (TBAB), and 7.6 g of potassium carbonate (K₂CO₃) were added to a 250 mL three-necked flask equipped with a condenser. 50 mL of ethyl acetate (EA) was added, and the mixture was stirred at room temperature for 2 h. Then, 7.7 g of iodomethane (CH₃I) was added using a syringe, and the mixture was stirred and refluxed at 80 °C for 24 h. After stirring, the reaction was allowed to cool to room temperature. 100 mL of dichloromethane was added to the organic phase, and 100 mL of water was added to dissolve the inorganic salt. This process was repeated three times to obtain the organic phase. After removing the solvent, the organic phase was purified by silica gel column chromatography (DCM:PE = 1:2, V:V) to obtain the crude product, a white solid intermediate 1. Further purification was achieved by recrystallization from dichloromethane to obtain 3.9 g of the solid intermediate 1, with a yield of 72%. 1H NMR spectrum: 1 H NMR(400MHz,Chloroform-d)δ8.32(d,J=7.8Hz,1H),8.06(s,1H),7.39(d,J=7.8Hz,2H),7.35(t ,J=7.8Hz,1H),7.23(d,J=7.5Hz,1H),7.05(d,J=8.0Hz,1H),6.69(d,J=7.9Hz,1H),4.08(s,3H).

[0062] Synthesis of Intermediate 2: 1.0 g of Intermediate 1 and 0.56 g of potassium tert-butoxide (t-BuOK) were added to a 50 mL three-necked flask. After three purgings using a double-row tube, 50 mL of dried dimethyl sulfoxide (DMSO) was added. Then, 0.44 g of the starting material 1-bromo-3,5-difluorobenzene was added using a syringe. The mixture was stirred at 80 °C for 12 h. After the reaction was completely cooled, 100 mL of water was added to obtain a precipitate. The precipitate was filtered, dried, and purified by silica gel column chromatography (DCM:PE = 1:2, V:V) to obtain 0.77 g of white solid Intermediate 2, with a yield of 55%. 1H NMR spectrum: 1H NMR(400MHz,Chloroform-d)δ8.32(d,J=7.7Hz,2H),7.77(s,2H),7.71(s,1H),7.43(d,J=8.2Hz,2H),7.38-7.32 (m,2H),7.29(d,J=8.2Hz,2H),7.25(t,J=7.4Hz,2H),7.06(d,J=8.2Hz,2H),6.70(d,J=8.0Hz,2H),4.04(s,6H).

[0063] Synthesis of Intermediate 3: 2.8 g of Intermediate 2, 1.9 g of diphenylamine, 0.2 g of tri-tert-butylphosphine tetrafluoroborate (P(t-Bu)3BF4), 0.1 g of tris(dibenzylacetone)dipalladium (Pd(dba)3), and 1.9 g of sodium tert-butoxide (t-BuONa) were added to a 250 mL flask equipped with a condenser. The mixture was evacuated three times using a double-row tube to maintain a nitrogen atmosphere. 35 mL of toluene solvent that had undergone deoxygenation was added. The mixture was heated to 115 °C, stirred, and refluxed. After the reaction was complete, 250 mL of dichloromethane was added, and the mixture was extracted with 200 mL of water to obtain the organic phase. After removing the solvent, the organic phase was purified by silica gel column chromatography (DCM:PE = 1:2, V:V) to obtain 2.7 g of white solid Intermediate 3, with a yield of 82%. 1H NMR spectrum: 1 HNMR(400MHz,Chloroform-d)δ8.36(d,J=7.0Hz,2H),7.50(d,J=8.0Hz,2H),7.37-7. 24(m,17H),7.18-7.10(m,2H),7.09-7.02(m,2H),6.68(d,J=7.9Hz,2H),4.03(s,6H).

[0064] Synthesis of Intermediate 4: 5.0 g of Intermediate 3 was dissolved in 50 mL of ultra-dry dichloromethane solvent (CH2Cl2), added to a flask with a nitrogen balloon inserted, and placed on an ice-water mixture to cool to 0 °C. Then, 10.0 g of boron tribromide (BBr3) was slowly added dropwise, paying attention to the volume change of the balloon during the addition. After the addition was complete, the reaction was carried out in ice water for 2 hours, and then transferred to room temperature for 6 hours. After the reaction was completed, a drop of the reaction solution was taken, and water was used to test whether BBr3 had reacted completely. After verification, water was slowly added dropwise to quench the reaction. Finally, the pH of the reaction solution was adjusted to neutral with a 1 mol / L sodium bicarbonate solution. The organic phase was extracted three times with 100 mL of dichloromethane and 100 mL of water, and the organic phase was collected. After the organic solvent was evaporated by rotary evaporation, a dark brown product, namely Intermediate 4, was obtained, with a mass of 4.5 g and a yield of 96%. 1H NMR spectrum: 1H NMR(400MHz,Chloroform-d)δ8.25(d,J=7.6Hz,2H),7.42(d,J=8.2Hz,2H),7.33(d,J=7.2Hz,2H),7.29(s,1H),7.2 8-7.22(m,8H),7.21-7.18(m,4H),7.15(d,J=7.9Hz,2H),7.03(d,J=8.2Hz,4H),6.55(d,J=7.7Hz,2H),5.50(s,2H).

[0065] Intermediate BOVBr: 5.0 g of 4-hydroxystyrene and 27.3 g of potassium carbonate (K₂CO₃) were added to a 250 mL three-necked flask, followed by 60 mL of acetone. The mixture was stirred at room temperature for 30 minutes, then 30.5 g of 1,6-dibromohexane was slowly added, and the mixture was heated to 70 °C and reacted for 12 h. After the reaction was complete, the mixture was cooled to room temperature, and 100 mL of dichloromethane and 100 mL of water were added for extraction. The collected organic phase was then evaporated to dryness and purified by silica gel chromatography (petroleum ether:dichloromethane = 10:1, V:V) to obtain a colorless liquid, BOVBr, with a mass of 1.2 g and a yield of 10.2%. 1H NMR spectrum: 1 H NMR (400MHz, Chloroform-d) δ7.25(d,J=8.6Hz,2H),6.76(d,J=8.6Hz,2H),6.57(dd,J=17.6,10.9Hz,1H),5.52(d,J=17.5Hz,1H),5.03(d,J =10.8Hz,1H),3.87(t,J=6.4Hz,2H),3.34-3.31(m,2H),1.82-1.78(m,2H),1.79-1.63(m,2H),1.42(d,J=3.8Hz,2H),1.20(d,J=11.1Hz,2H).

[0066] The final product, HTPA-VBCz, was prepared by adding 1.0 g of intermediate 4, 1.5 g of potassium carbonate (K₂CO₃), 0.4 g of tetrabutylammonium bromide (TBAB), and 30 mL of acetonitrile to a 50 mL three-necked flask equipped with a condenser. After thorough stirring, 1.0 g of BOVBr was added, and the mixture was refluxed at 85 °C for 26 h until the reaction was complete. After cooling, the mixture was extracted three times with 100 mL of dichloromethane and 100 mL of water. The solvent was then removed by vacuum rotary distillation, and the product was purified by silica gel column chromatography (ethyl acetate:PE = 1:5, V:V) to obtain 0.7 g of the pale yellow solid, HTPA-VBCz. The yield was 41%.

[0067] 1H NMR spectrum:1 H NMR(400MHz,Chloroform-d)δ8.40-8.33(m,2H),7.51(d,J=8.2Hz,2H),7.45-7.39(m,1H),7.37(dt,J=6.3,1.5Hz,3H),7.35(d ,J=1.9Hz,4H),7.33(d,J=2.3Hz,8H),7.30(d,J=1.9Hz,2H),7.28(d,J=2.0Hz,3H),7.16-7.06(m,4H),6.88-6.83(m,4H),6.72 (dd,J=8.1,3.9Hz,2H),6.66(dd,J=17.6,10.9Hz,2H),5.61(dd,J=17.6,0.9Hz,2H),5.12(dd,J=10.9,0.9Hz,2H),4.26(t,J=6 .3Hz,4H),3.99(t,J=6.5Hz,4H),2.04(t,J=7.2Hz,4H),1.90-1.84(m,4H),1.73-1.68(m,4H),1.64(tt,J=8.4,6.0,5.3Hz,4H).

[0068] Carbon NMR spectrum: 13 C NMR (101MHz, CDCl3) δ158.96,155.80,150.68,146.94,141.81,139.85,139.65,136.34,130.30,129.71,127.43,126.84, 125.34,125.09,124.32,123.26,123.11,120.45,114.54,112.85,111.48,109.32,102.66,101.98,67.91,29.31,25.95.

[0069] Mass spectrometry: MS (MALDI-TOF) [m / z]: C 70 H 65 N3O4:1011.9,found:1012.3.Anal.Calcd(%)for C 70 H 65 N3O4:C,83.05;H,6.47;N,4.15;O,6.32.

[0070] To prepare other types of styrene-based carbazole hole transport materials, simply replace the diphenylamine group with other groups in Example 1; meanwhile, for the preparation of styrene crosslinked materials with different chain lengths, the preparation process of BOVBr in Example 1 can also be referred to, and will not be repeated here.

[0071] Example 2: Photophysical properties of HTPA-VBCz solution

[0072] Figure 2 The UV absorption spectrum, fluorescence spectrum, and low-temperature phosphorescence spectrum of compound HTPA-VBCz in solution are presented. The compound was dissolved in dichloromethane to prepare a solution with a concentration of 10... -5 A 0.7 mL solution of mol / L was pipetted into a cuvette, and absorption and emission spectra were measured using a UV-Vis spectrophotometer and a fluorophotometer. Similarly, a 10 mol / L solution was prepared using dichloromethane as a solvent. -5 A mol / L solution was prepared, and 2 mL of solvent was added to a sample tube. After cooling to 77 K with liquid nitrogen, the low-temperature phosphorescence spectrum was measured using a phosphorescence spectrophotometer. In solution, the ultraviolet absorption peaks of the compound HTPA-VBCz were located at 284 nm and 337 nm, respectively, and the fluorescence spectrum peaks of the compound were located at 365 nm. The triplet energy level of HTPA-VBCz could be calculated to be 3.00 eV from the low-temperature phosphorescence spectrum. The compound HTPA-VBCz prepared in this embodiment has a high triplet energy level and can be used to fabricate a hole transport layer, which can effectively confine the excitons in the light-emitting layer, thereby improving the efficiency of organic semiconductor devices.

[0073] Example 3: Fluorescence spectral changes of HTPA-VBCz in different solvents

[0074] Figure 3 Fluorescence spectra of compound HTPA-VBCz in solvents of different polarities are presented. The compound was prepared into 10... -5 Dilute solutions of acetone, dichloromethane (DCM), N,N-dimethylformamide (DMF), and tetrahydrofuran (THF) were prepared, and 0.7 mL of each solution with different polarities was pipetted into cuvettes for testing. The spectra showed that the fluorescence peak of compound HTPA-VBCz remained around 348 nm in all solvents with different polarities, indicating that the solvent polarity had little effect on the HTPA-VBCz material.

[0075] Example 4: Electrochemical performance testing of HTPA-VBCz

[0076] Figure 4 Oxidation curves of compound HTPA-VBCz are presented. Cyclic voltammetry was used to determine the energy levels of the compound. Dichloromethane was used during the oxidation process. Ag / AgNO3 solution was used as the reference electrode, and ferrocene solution (concentration greater than 10) was used as the standard solution. -3(mol / L is sufficient). Based on the oxidation potential of the compound HTPA-VBCz, the corresponding HOMO energy level can be calculated to be -5.25 eV, which is almost unchanged from the theoretically calculated HOMO energy level.

[0077] Example 5: Thermal stability test of HTPA-VBCz

[0078] Figure 5a Differential thermal scanning (DSC) curves of compound HTPA-VBCz are presented. It can be seen that the glass transition temperature of compound HTPA-VBCz is 120℃, indicating that the two materials can be cross-linked without high heat treatment conditions. Figure 5b Thermogravimetric analysis (TGA) of the compound HTPA-VBCz is presented. The TGA shows that the material has a thermal decomposition temperature as high as 400℃ and good thermal stability. The good thermal stability is attributed to the three-dimensional network structure formed after the styrene groups are cross-linked.

[0079] Example 6: Atomic force microscopy image of HTPA-VBCz thermally cross-linked film

[0080] Figure 6 Atomic force microscopy images of the film formed by compound HTPA-VBCz under heat treatment at 120℃ are presented. It can be seen that the compound is completely cross-linked at 120℃ and no pinholes appear. The mean square roughness of the compound is less than 1 nm, indicating that the HTPA-VBCz material has excellent film morphology.

[0081] Example 7: Solvent resistance test of HTPA-VBCz and OXE-TPA - absorbance test

[0082] Figure 7a The UV absorption spectra of compound HTPA-VBCz after crosslinking at 120℃ and after elution with chlorobenzene are presented. To test the solvent resistance of the crosslinked film, the compound was coated on PEDOT:PSS. For HTPA-VBCz, complete crosslinking was achieved after only 30 minutes of heat treatment at 120℃. The crosslinked film was then eluted three times with chlorobenzene, and the UV absorption spectra before and after elution were measured. The results showed that the absorbance of the film after solvent elution after crosslinking remained almost unchanged, indicating that the material was completely crosslinked at this temperature and exhibited excellent solvent resistance. For the previously disclosed OXE-TPA molecule, complete crosslinking also requires 60 minutes of heat treatment at 180℃ without an initiator. OXE-TPA molecules were heat-treated for 30 minutes at 120℃, 140℃, and 160℃, respectively, and then eluted three times with chlorobenzene. The UV absorption spectra before and after elution were then measured. Figure 7b , 7cAs shown in Figure 7d, the absorbance of the film after elution changed significantly, indicating that OXE-TPA was not fully crosslinked at temperatures of 120℃, 140℃ and 160℃. Therefore, the resulting film had poor solvent resistance.

[0083] Using the HTPA-VBCz material prepared in Example 1 above, as a hole transport material, organic electroluminescent devices with different emission colors were fabricated according to the preparation methods in Examples 8 to 10. It should be noted that the organic electroluminescent devices prepared below are all preferred embodiments provided by the present invention and do not limit the application scope of the derivatives described in the present invention in organic electroluminescent devices.

[0084] For example Figure 1 Taking the organic electroluminescent device with the structure shown as an example, the structure and fabrication method of the organic electroluminescent device described in this embodiment are illustrated. The structure of the organic electroluminescent device used, from top to bottom, is as follows: anode ITO glass (tin oxide), hole injection layer PEDOT:PSS, hole transport layer, light-emitting layer, electron transport layer TPBi, electron injection layer Ca, and metal cathode Ag.

[0085] Example 8: Fabrication of green light devices using HTPA-VBCz thin films as hole transport layers

[0086] The device structure in this embodiment can be simply represented as follows:

[0087] Device 1 (Green): ITO / PEDOT:PSS / HTPA-VBCz / 26DCzPPy:4CzIPN (90:10wt%) / TPBi / Ca:Ag, wherein the transparent conductive substrate is the ITO glass substrate with the anode, PEDOT:PSS is the hole injection layer, HTPA-VBCz is the crosslinked hole transport layer, 26DCzPPy:4CzIPN (90:10wt%) and TPBi are the electron transport layer, Ca is the electron injection layer and Ag is the cathode.

[0088] The specific fabrication steps of the device in this embodiment are as follows:

[0089] First, the ITO substrate was sonicated with dichloromethane for 20 minutes, then cleaned with detergent, followed by sonication with ultrapure water, acetone, and ethanol for 20 minutes each, and finally dried at 80°C. After cleaning, the ITO substrate was treated with ozone for 20 minutes, and then a hole injection layer, PEDOT:PSS, was spin-coated at 3000 rpm for 30 seconds, followed by annealing at 120°C for 20 minutes on a hot plate. Next, a hole transport layer was prepared using a solution method. All operations were performed inside a glove box. A chloroform solution of HTPA-VBCz was spin-coated onto the hole injection layer. The concentration of z was 4 mg / mL. The solution was spin-coated at 3000 rpm for 30 seconds, then transferred to a hot plate and heat-treated at 120°C for 30 minutes to prepare the HTPA-VBCz film. The luminescent layer was also prepared using a solution method: a luminescent layer solution, namely a 4 mg / mL 26DCzPPy:4CzIPN chloroform solution, was spin-coated onto the prepared cross-linked hole transport layer at 3000 rpm for 30 seconds, and then annealed at 120°C for 20 minutes on a hot plate to prepare the film. Finally, a vacuum evaporation process was used: [The text abruptly ends here, so the translation stops as well.] -5 Below Pa pressure, the electron transport layer TPBi, the electron injection layer Ca, and the metal cathode Ag are deposited sequentially by vapor deposition.

[0090] like Figure 8a The figure shows the current density-voltage-brightness characteristic curves of the green light device. It can be observed that with the addition of the cross-linked hole transport layer, although the device's turn-on voltage increases slightly and its maximum brightness decreases, both still meet the requirements. Figure 8b The figure shows the current efficiency-luminance-external quantum efficiency characteristic curves of a green light device. Compared with the device without a hole transport layer, the device with a cross-linked hole transport layer has a maximum current efficiency of 38.3 cdA. -1 Increased to 78.3 cdA -1 The external quantum efficiency increased from 12.0% to 24.6%, and the device exhibited excellent efficiency and stability; for example... Figure 8c The image shows the electroluminescence spectrum of the green light-emitting device. It can be observed that the addition of the hole transport layer has almost no effect on the device's luminescence. In summary, HTPA-VBCz, as a thermally cross-linked hole transport layer, significantly improves the performance of green light-emitting devices, while requiring a lower fabrication temperature.

[0091] Example 9: Fabrication of Blue Light Devices Using HTPA-VBCz Thin Films as Hole Transport Layers

[0092] This embodiment is identical to Example 8 except for the light-emitting layer material; all other structural components and preparation steps are the same. Therefore, the preparation process will not be described in detail. The device structure of this embodiment can be simply represented as follows:

[0093] Device 2 (Blue Light): ITO / PEDOT:PSS / HTPA-VBCz / 26DCzPPy:4TCzBN(60:40wt%) / TPBi / Ca:Ag

[0094] like Figure 9a The figure shows the current density-voltage-brightness characteristic curves of a blue light-emitting device. It can be observed from the figure that, compared to the device without a hole transport layer, the start-up voltage and maximum brightness of the device with a hole transport layer remain almost unchanged. Figure 9b The figure shows the current efficiency-luminance-external quantum efficiency characteristic curves of the green light device. Compared with the device without a hole transport layer, using HTPA-VBCz as the hole transport layer increases both the current efficiency and external quantum efficiency to 31.1 cdA. -1 and 11.3%; such as Figure 9c The figure shows the electroluminescence spectrum of the blue light-emitting device. It can be observed that with the addition of the hole transport layer, the electroluminescence spectra of the two almost overlap, indicating that the addition of the hole transport layer has almost no impact on the luminescence of the blue light-emitting material. Therefore, in summary, HTPA-VBCz as a cross-linked hole transport layer does improve the performance of the blue light-emitting device to some extent.

[0095] Example 10: Fabrication of a red light device using HTPA-VBCz thin film as the hole transport layer.

[0096] This embodiment is identical to Embodiment 8 except for the light-emitting layer material; all other structural components and fabrication steps are the same. Therefore, the preparation process will not be described in detail. The device structure of this embodiment can be simply represented as follows:

[0097] Device 3 (Red): ITO / PEDOT:PSS / HTPA-VBCz / 26DCzPPy:TXO-TPA (60:40wt%) / TPBi / Ca:Ag

[0098] like Figure 10a The figure shows the current density-voltage-brightness characteristic curves of the red light device. It can be seen from the figure that the addition of the hole transport layer reduced the turn-on voltage of the red light device from 5.0V to 4.6V, while simultaneously increasing the maximum brightness; Figure 10b The current efficiency-luminance-external quantum efficiency characteristic curves of the red light device are shown. Compared with the device without a hole transport layer, the device containing the cross-linked hole transport layer HTPA-VBCz has a current efficiency of 9.0 cdA. -1 This increased to 20.9 cdA. -1 Meanwhile, the external quantum efficiency increased from 6.6% to 10.5%; Figure 10cThe electroluminescence spectrum of the red light device is shown. It can be seen from the figure that after the addition of the hole transport layer, the electroluminescence spectra of the two are almost identical, indicating that the addition of the hole transport layer has almost no effect on the luminescence of the red light material.

[0099] Therefore, in general, HTPA-VBCz has certain universality in improving the performance of various devices using cross-linked hole transport layers.

[0100] The above are merely preferred embodiments of the present invention, but do not limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of the present invention's specification and drawings, whether directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of the present invention.

Claims

1. A class of carbazole derivatives based on styrene hybridization, characterized in that, The molecular structural formula of the carbazole derivative is shown below: 。 2. The method for preparing a type of carbazole derivative based on styrene hybridization as described in claim 1, characterized in that, The synthetic route for the carbazole derivatives is shown below: 。 3. The application of the styrene-hybridized carbazole derivative as described in claim 1 in the fabrication of the hole transport layer of an organic electroluminescent device, characterized in that, The hole transport layer is a thin film structure prepared by coating the styrene-based carbazole derivative onto the hole injection layer using a solution method, followed by a thermal crosslinking reaction through annealing. The annealing temperature is not lower than 120°C, and the annealing time is not less than 30 minutes.

4. A type of organic electroluminescent device, characterized in that, The hole transport layer of the organic electroluminescent device is the hole transport layer described in claim 3; the organic electroluminescent device comprises, from cathode to anode, a metal cathode, an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an ITO anode.

5. The organic electroluminescent device as described in claim 4, characterized in that, The metal cathode layer is made of Ag metal, and the film thickness is 100 nm, prepared by vacuum evaporation. The electron injection layer is made of Ca metal, and the film thickness is 10 nm, prepared by vacuum evaporation. The electron transport layer is 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), and the film thickness is 30 nm, prepared by vacuum evaporation. The light-emitting layer is prepared by solution method using 26DCzPPy and thermally activated delayed fluorescence material. The hole injection layer is a thin film prepared by spin-coating PEDOT:PSS on an ITO glass substrate using solution method, and the film thickness is 30 nm. The ITO anode is conductive glass, and the ITO anode is a conductive anode. The ITO anode, as a substrate, is cleaned, dried, and then subjected to ozone treatment.

6. The organic electroluminescent device as described in claim 5, characterized in that, The light-emitting layer material is 26DCzPPy:4CzIPN, and the mass concentrations of 26DCzPPy and 4CzIPN are 90% and 10%, respectively. The organic electroluminescent device is a green light-emitting device.

7. The organic electroluminescent device as described in claim 5, characterized in that, The light-emitting layer material is 26DCzPPy:4TCzBN, and the mass concentrations of 26DCzPPy and 4TCzBN are 60% and 40%, respectively. The organic electroluminescent device is a blue light emitting device.

8. The organic electroluminescent device as described in claim 5, characterized in that, The light-emitting layer material is 26DCzPPy:TXO-TPA, and the mass concentrations of 26DCzPPy and TXO-TPA are 60% and 40%, respectively; the organic electroluminescent device is a red light-emitting device.

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