Phosphorus-oxygen group-containing alcohol-soluble small molecule as well as preparation method and application thereof

Abstract

The invention discloses alcohol-soluble micromolecules containing phosphorus and oxygen groups as well as a preparation method and application thereof. Phosphorus-oxygen groups have high electron withdrawing performance, and after the phosphorus-oxygen groups are introduced into conjugated molecules, the electron transmission performance is further enhanced. The group with better electron transport characteristic can make up the defect of electron mobility of common electron transport materials, and has the advantage of high chemical stability. According to the principle of'similar dissolvability ', the introduction of the polar PO group enables the electron transport material to have higher solubility in an alcohol solvent. The alcohol-soluble micromolecule containing the phosphorus and oxygen groups has relatively high potential when being used as an electron transport layer in photoelectric devices such as a quantum dot light-emitting diode. The polymer has good alcohol solubility, and can be used for preparing a large-area film through solution processing methods such as spin coating, ink-jet printing, printing and the like.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronics, specifically relating to a class of alcohol-soluble small molecules containing phosphoroyl groups, their preparation methods, and applications. Background Technology

[0002] With the continuous innovation of display and lighting technologies, quantum dot light-emitting diodes (QLEDs) have come into view. QLEDs possess characteristics such as flexibility, thinness, excellent luminous performance, high color purity, optimal color temperature, long lifespan, and simple fabrication processes, making them highly promising for the lighting and display fields. Furthermore, with improvements in quantum dot synthesis processes and optimization of device structures, QLED performance has achieved significant breakthroughs, and its properties now preliminarily meet the requirements for commercial applications. However, the large-area, high-efficiency fabrication of QLED devices remains a challenge. Currently used methods for preparing quantum dot thin films still suffer from problems such as raw material waste, complex processes, and low fabrication efficiency. Therefore, researching and developing more advanced quantum dot light-emitting diode technology is of great significance to both the display and lighting fields.

[0003] Solution-processed QLEDs offer advantages such as low cost and mass production capability, making them suitable for flexible devices and large-size flat panel displays. The most serious problem in solution-based multilayer device fabrication is the solvent erosion effect between layers, leading to poor device performance. One effective solution is to use an orthogonal solvent method during spin-coating. Previous research reported that alcohol-soluble polymer dielectrics were used to prepare electron transport layers in continuous wet fabrication of multilayer devices; however, studies have shown that polymer dielectrics with ionic side chains can induce negative electrochemical deposition effects. Small-molecule electron transport materials are easier to synthesize and purify, making them an ideal choice for preparing electron transport layers in wet multilayer devices using the orthogonal solvent method. Therefore, developing a small-molecule electron transport material with good dispersibility in alcohol solutions is of great significance for promoting the large-scale production of QLEDs. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a class of alcohol-soluble small molecules containing phosphorothoxy groups. Organic electron transport materials are classified into polymers and small molecules. Ionic groups readily attach to the side chains of alcohol-soluble polymers, which may lead to electrochemical doping effects, thus affecting device performance. In contrast, alcohol-soluble small molecules are easier to synthesize and purify, making them more suitable for solution-based fabrication of quantum dot light-emitting diodes. These phosphorothoxy group-containing small molecules exhibit excellent alcohol solubility and can be used to prepare large-area thin films through solution processing methods such as spin coating, inkjet printing, and printing.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned small molecules containing phosphoro groups.

[0006] Another object of the present invention is to provide the application of the above-mentioned small molecules containing phosphoro groups as electron transport materials in the field of organic optoelectronics.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A class of alcohol-soluble small molecules containing phospho groups have chemical structural formulas that satisfy one of the following general formulas:

[0009]

[0010] In the formula, each of the multiple Ar groups is relatively independent and is one of an aromatic hydrocarbon group with 6 to 30 carbon atoms or an aromatic heterocyclic group with 3 to 30 carbon atoms.

[0011] Furthermore, the plurality of Ar atoms are preferably, relatively independently, one of the following chemical structures or derivatives thereof:

[0012]

[0013] Wherein, R is one of H, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 4 to 12 carbon atoms, an aromatic hydrocarbon group having 6 to 30 carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms; R1 is one of H, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 4 to 12 carbon atoms, an aromatic hydrocarbon group having 6 to 30 carbon atoms, or an aromatic heterocyclic group having 3 to 30 carbon atoms.

[0014] Preferably, the above-mentioned small molecule containing a phosphorus group has a chemical structural formula of one of the following:

[0015]

[0016]

[0017] The aforementioned class of small molecules containing phospho groups have good alcohol solubility and are soluble in common alcohol solvents such as methanol, ethanol, dipropanol, isopropanol, and n-butanol.

[0018] A method for preparing the above-mentioned small molecule containing a phosphorus group includes the following steps:

[0019] (1) Under the protection of light and inert gas, diphenylphosphine chloride and DMF were added, then the temperature was lowered to -20℃ and NBS solution was added and stirred. After the reaction was completed, the mixture was stirred at room temperature until it was raised to room temperature. After filtration and washing, intermediate (a) was obtained.

[0020] (2) Add p-dibromobenzene or 4,4'-dibromobiphenyl and anhydrous diethyl ether into a container, adjust the temperature to -78℃, add n-butyllithium and stir to react. After the reaction is completed, add intermediate (a) and continue to stir to react at room temperature. After the reaction is completed, purify to obtain compound (1) or compound (2). The starting material p-dibromobenzene corresponds to compound (1), and the starting material 4,4'-dibromobiphenyl corresponds to compound (2).

[0021] (3) Under an inert atmosphere, compound (1) or compound (2) reacts with pinacol ester containing Ar-group borate in the presence of a catalyst and a base to produce general formula ① or general formula ②.

[0022] The solvent for the NBS solution in step (1) is an alcohol, preferably a mixture of ethylene glycol and ethanol.

[0023] The molar ratio of diphenylphosphine chloride and NBS in step (1) is 1:2; the stirring reaction time is 3-6 h.

[0024] The stirring time for adding n-butyllithium in step (2) is 3-4 hours; the stirring time at room temperature is 12-14 hours.

[0025] The reaction described in step (3) refers to the reaction at 25°C (room temperature) for 2-5 hours.

[0026] The specific reaction route is as follows:

[0027]

[0028] The above-mentioned type of small molecules containing phosphoro groups are used as electron transport materials in the electron transport layer of quantum dot light-emitting diodes.

[0029] Furthermore, the preparation of the electron transport layer of a quantum dot light-emitting diode using the aforementioned type of small molecules containing phosphorus groups includes the following steps: dissolving the aforementioned type of small molecules containing phosphorus groups in an alcohol solvent, and then forming a film by spin coating, inkjet printing, or printing to obtain the electron transport layer of the quantum dot light-emitting diode. The alcohol solvent is at least one selected from methanol, ethanol, dipropanol, isopropanol, and n-butanol.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] (1) The small molecules containing phosphorooxy groups described in this invention have strong electron transport properties, which can make up for the problem of low electron mobility of traditional electron transport polymers and obtain higher electron transport properties.

[0032] (2) The small molecules containing phosphoroyl groups described in this invention have high optical transparency and electron mobility, and have great potential as electron transport materials. These electron transport materials have good alcohol solubility and can be prepared into large-area thin films by solution processing methods such as spin coating, inkjet printing, and printing. Attached Figure Description

[0033] Figure 1 The thermogravimetric curve of compound M1 is shown.

[0034] Figure 2 The cyclic voltammetry curves for polymer M3 are shown. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0036] Unless otherwise specified, all reagents used in the examples are commercially available.

[0037] Example 1: Preparation of compound M1

[0038] 1) Preparation of compound (1)

[0039] A 100 ml round-bottom flask was wrapped with aluminum foil to prevent light from entering. Diphenylphosphine chloride (20 mmol) and DMF (15 ml) were added, and the mixture was purged with nitrogen. NBS (40 mmol) was dissolved in a solution prepared with ethylene glycol and ethanol at a ratio of 9:1. The flask was placed in a dry ice bath and cooled to -20°C. The NBS solution was then added dropwise, and the reaction was stirred for 4 hours. After the reaction was complete, the flask was transferred to an ice bath for cooling and stirred at room temperature until the temperature rose to room temperature. The mixture was filtered, washed with methanol, and finally dried to obtain intermediate (a).

[0040] 30 mmol of p-dibromobenzene was placed in a round-bottom flask, and 20 mL of anhydrous diethyl ether was added. The temperature was adjusted to -78 °C, and 0.8 mL (0.0016 mol) of n-butyllithium was added, followed by stirring for 3 hours. After the reaction was complete, intermediate (a) (14 mmol) was added, and the mixture was stirred at room temperature for approximately 12 hours. After the reaction was complete, the reactants were heated in a water bath and then extracted with diethyl ether. The concentrated product was purified by column chromatography using petroleum ether:ethyl acetate (3:1, v:v) as eluent, yielding 19.55 g of a white solid.

[0041] 2) Preparation of compound (2)

[0042] 30 mmol of 4,4'-dibromobiphenyl was placed in a round-bottom flask, and 20 mL of anhydrous diethyl ether was added. The temperature was adjusted to -78°C, and 0.8 mL (0.0016 mol) of n-butyllithium was added, followed by stirring for 3 hours. After the reaction was complete, intermediate (a) (14 mmol) was added, and the mixture was stirred at room temperature for approximately 12 hours. After the reaction was complete, the reactants were heated in a water bath and extracted with diethyl ether. The concentrate was then purified by column chromatography using petroleum ether:ethyl acetate (4:1, v:v) as eluent, yielding 20.68 g of a pale yellow solid, with a yield of 79.25%.

[0043] The chemical reaction equation for intermediate (a) is shown below:

[0044]

[0045] The chemical reaction equation for the synthesis of compound (1) is shown below:

[0046]

[0047] The chemical reaction equation for the synthesis of compound (2) is shown below:

[0048]

[0049] (3) Preparation of compound M1

[0050] Under nitrogen protection, 2.5 mmol of 4,4,5,5-tetramethyl-2-ylphenyl-1,3-dioxoborane, 12.5 mmol of compound 1, 6 mg of palladium acetate, and 6 mg of potassium carbonate were dissolved in 15 mL of ethylene glycol monomethyl ether and 2 mL of water, and the reaction was carried out at room temperature for 3 hours. After the reaction was completed, the product was extracted with ethyl acetate, washed five times with saturated sodium chloride aqueous solution to remove the organic solvent, and the crude product was purified by column chromatography using ethyl acetate:methanol (20:1, v:v) as eluent to give 1.02 g of a pale white solid, with a yield of 52%. 1 ¹H NMR (400 MHz, CDCl₃) δ 8.01–7.95 (m, 20H), 7.79–7.70 (m, 8H), 7.48–7.45 (m, 8H), 7.43–7.35 (m, 4H). The relative molecular mass was determined to be 782.25 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0051] The chemical reaction equation for the synthesis of compound M1 is shown below:

[0052]

[0053] Figure 1The thermogravimetric curve of compound M1 shows that the temperature at which compound M1 loses 5% of its mass (and its thermal decomposition temperature) reaches 437℃, indicating that the material has good thermal stability.

[0054] Example 2: Synthesis of compound M2

[0055] The synthesis of compound M2 was similar to that of M1. Following the synthesis method of compound M1 in Example 1, the reactants were replaced with pinacol 4-pyridineboronic acid ester (2.5 mmol) and compound 1 (12.5 mmol). 1 ¹H NMR (400MHz, CDCl₃) δ 8.75 (d, 8H), 8.05–7.90 (m, 28H). The relative molecular mass was determined to be 786.23 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0056]

[0057] Example 3: Synthesis of compound M3

[0058] The synthesis of compound M3 was similar to that of M1. Following the synthesis method of compound M1 in Example 1, the reactants were replaced with 4-(4-pyridyl)phenylboronic acid pinacol ester (2.5 mmol) and compound 1 (12.5 mmol). 1 ¹H NMR (400MHz, CDCl₃) δ 8.74 (d, 8H), 8.05–7.93 (m, 28H), 7.23 (d, 16H). The relative molecular mass was determined to be 1090.36 by MS. 1 HNMR and MS analyses showed that the obtained compound was the target product.

[0059]

[0060] Figure 2 The cyclic voltammetry curves of polymer M3 show that the oxidation potential of compound M3 is 1.40 V, the reduction potential is -1.62 eV, and the calibrated oxidation potential of ferrocene is 0.43 V. The calculated HOMO level of compound M3 is -5.51 eV, and the LUMO level is -2.75 eV. It has a deep LUMO level, making it suitable as an electron transport layer material.

[0061] Example 4: Preparation of compound M4

[0062] The synthesis of compound M4 was similar to that of M1. Following the synthesis method of compound M1 in Example 1, the reactants were replaced with 3,5-diphenylphenylboronic acid pinacol ester (2.5 mmol) and compound 1 (12.5 mmol).1 ¹H NMR (400MHz, CDCl₃) δ 8.10 (s, 12H), 8.02–7.93 (m, 20H), 7.80–7.72 (m, 16H), 7.50–7.40 (d, 24H). The relative molecular mass was determined to be 1390.51 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0063]

[0064] Example 5: Synthesis of compound M5

[0065] The synthesis of compound M5 was similar to that of M1. The reactants were replaced with 7-(4,4,5,5-tetramethyl-1,3-dioxo-2-borylyl)quinoline (2.5 mmol) and compound 1 (12.5 mmol) according to the synthesis method of compound M1 in Example 1. 1 ¹H NMR (400 MHz, CDCl₃) δ 9.02–8.92 (m, 4H), 8.66–8.58 (m, 4H), 8.38–8.26 (m, 8H), 8.02–7.93 (m, 24H), 7.76–7.70 (m, 4H). The relative molecular mass was determined to be 986.30 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0066]

[0067] Example 6: Synthesis of compound M6

[0068] The synthesis of compound M6 was similar to that of M1. Following the synthesis method of compound M1 in Example 1, the reactants were replaced with 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborhecyclopentan-2-yl)phenyl)-1,3,4-oxadiazole (2.5 mmol) and compound 1 (12.5 mmol). 1 ¹H NMR (400MHz, CDCl₃) δ 8.25 (s, 4H), 8.05–7.92 (m, 28H), 7.25–7.18 (m, 8H). The relative molecular mass was determined to be 1062.33 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0069]

[0070] Example 7: Synthesis of Polymer M7

[0071] The synthesis of compound M7 was similar to that of M1. Following the synthesis method of compound M1 in Example 1, the reactants were replaced with 4,4,5,5-tetramethyl-2-ylphenyl-1,3-dioxoborane (2.5 mmol) and compound 2 (12.5 mmol). 1 ¹H NMR (400MHz, CDCl₃) δ 8.01–7.95 (m, 24H), 7.80–7.70 (m, 8H), 7.49–7.40 (m, 12H). The relative molecular mass was determined to be 858.28 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0072]

[0073] Example 8: Synthesis of Polymer M8

[0074] The synthesis of compound M8 was similar to that of M1. Following the synthesis method for compound M1 in Example 1, the reactants were replaced with pinacol 4-pyridineboronic acid ester (2.5 mmol) and compound 2 (12.5 mmol). 1 ¹H NMR (400MHz, CDCl₃) δ 8.75 (d, 8H), 8.05–7.90 (m, 32H). The relative molecular mass was determined to be 862.25 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0075]

[0076] Example 9: Synthesis of Polymer M9

[0077] The synthesis of compound M9 was similar to that of M1. The reactants were replaced with 7-(4,4,5,5-tetramethyl-1,3-dioxo-2-borylyl)quinoline (2.5 mmol) and compound 2 (12.5 mmol) according to the synthesis method of compound M1 in Example 1. 1 ¹H NMR (400 MHz, CDCl₃) δ 9.00–8.91 (m, 4H), 8.65–8.58 (m, 4H), 8.38–8.25 (m, 8H), 8.02–7.93 (m, 28H), 7.76–7.70 (m, 4H). The relative molecular mass was determined to be 1062.33 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0078] Example 10: Synthesis of Polymer M10

[0079] The synthesis of compound M10 was similar to that of M1. Following the synthesis method of compound M1 in Example 1, the reactants were replaced with 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborhecyclopentan-2-yl)phenyl)-1,3,4-oxadiazole (2.5 mmol) and compound 2 (12.5 mmol). 1 ¹H NMR (400MHz, CDCl₃) δ 8.26 (s, 4H), 8.04–7.92 (m, 32H), 7.26–7.18 (m, 8H). The relative molecular mass was determined to be 1130.29 by MS. 1 ¹H NMR and MS analyses showed that the obtained compound was the target product.

[0080]

[0081] Example 11: Fabrication of Quantum Dot Light Emitting Diodes

[0082] The ITO substrate was ultrasonically cleaned sequentially with tetrahydrofuran, deionized water, and isopropanol (10 minutes each), and then dried. After plasma treatment, PEDOT:PSS was spin-coated onto the ITO surface. The resulting PEDOT:PSS film (~40 nm) was baked at 150 °C for 10 min. The PEDOT:PSS coated substrate was transferred in a glove box with oxygen and humidity <10 ppm. Then, a 40 nm layer of poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl)diphenylamine)] (TFB, CAS: 220797-16-0) was spin-coated onto the PEDOT:PSS layer as a hole transport layer, and the resulting hole transport layer was baked at 100 °C for 10 min. A 15 nm layer of red quantum dots (CdSe / ZnS, octane solution) was then spin-coated onto the hole transport layer and baked at 90 °C for 10 min. M1–M10 were dissolved in ethanol solution at a concentration of 8 mg / ml, spin-coated to form a 20 nm thick film, and baked at 90 °C for 10 min to obtain the electron transport layer. Finally, the device was transferred to a vacuum level <1×10⁻⁶. -4 In a vacuum chamber, 0.5 nm LiF and 120 nm Al were sequentially deposited as electrodes, and encapsulated using epoxy resin and a cover glass. QLED devices based on small molecules M1–M10 as electron transport layers were designated D1–D10. Simultaneously, a QLED device based on 2,7-bis(diphenylphospho)-9,9′-spirobi[fluorene](SPPO13, CAS: 1234510-13-4) as the electron transport layer was also fabricated as a control, designated D0.

[0083] Table 1 Performance of Quantum Dot Light-Emitting Devices

[0084]

[0085] As shown in Table 1, the devices based on M1 to M10 all exhibited lower turn-on voltages and higher current efficiencies, and the efficiency of the fabricated QLED devices was higher than that of the control electron transport material SPPO13. This indicates that these materials can be used as electron transport materials to fabricate high-efficiency quantum dot light-emitting diodes.

[0086] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A small molecule containing a phosphorus-containing oxy group characterized in that The chemical structural formula satisfies one of the following general formulae: In the formula, each of the plurality of Ar is independently one of a C6-30 aromatic hydrocarbon group or a C3-30 aromatic heterocyclic group.

2. The small molecule containing a phosphorus-containing oxygen group according to claim 1, wherein: Each of the plurality of Ar is independently one of the following chemical structures or a derivative of the following structures: In the formula, R is one of H, a C1-6 alkyl group, a C4-12 cycloalkyl group, a C6-30 aromatic hydrocarbon group, or a C3-30 aromatic heterocyclic group; and R1 is one of H, a C1-6 alkyl group, a C4-12 cycloalkyl group, a C6-30 aromatic hydrocarbon group, or a C3-30 aromatic heterocyclic group.

3. The small molecule containing phosphorus oxyradical of claim 1, wherein The chemical structural formula is one of the following structural formulae:

4. A preparation method of the small molecule containing a phosphorus-containing oxygen group according to any one of claims 1-3, comprising the following steps: (1) under light protection and inert gas protection, diphenyl phosphinic chloride and DMF are added, then the temperature is lowered to -20°C, NBS solution is added, and stirring reaction is performed, after the reaction is completed, stirring is performed at room temperature until the temperature is raised to room temperature, and after filtration and washing, an intermediate (a) is obtained; (2) p-dibromobenzene or 4,4'-dibromobiphenyl and anhydrous ether are added to a container, the temperature is adjusted to -78°C, n-butyllithium is added, stirring reaction is performed, after the reaction is completed, the intermediate (a) is added, and stirring reaction is continuously performed at room temperature, after the reaction is completed, purification is performed, and compound (1) or compound (2) is obtained, wherein compound (1) is obtained when p-dibromobenzene is used as the raw material, and compound (2) is obtained when 4,4'-dibromobiphenyl is used as the raw material; (3) under inert atmosphere protection, compound (1) or compound (2) is reacted with Ar group-pinacol borate in the presence of a catalyst and a base, and general formula ① or general formula ② is obtained; The reaction route is as follows:

5. The preparation method of the small molecule containing a phosphorus-containing oxygen group according to claim 4, wherein: In step (1), the solvent of the NBS solution is alcohol; In step (1), the molar ratio of diphenyl phosphinic chloride to NBS is 1:2, and the stirring reaction time is 3-6 h.

6. The preparation method of the small molecule containing a phosphorus-containing oxygen group according to claim 4, wherein: In step (2), the stirring reaction time of the n-butyllithium is 3-4 h, and the stirring reaction time at room temperature is 12-14 h.

7. The preparation method of the small molecule containing a phosphorus-containing oxygen group according to claim 4, wherein: In step (3), the reaction is performed at room temperature for 2-5 h.

8. Use of the small molecule containing a phosphorus-containing oxygen group according to any one of claims 1-3 in preparation of an electron transport layer of a quantum dot light-emitting diode.

9. Use of the small molecule containing a phosphorus-containing oxygen group according to claim 8 in preparation of an electron transport layer of a quantum dot light-emitting diode, wherein: The preparation of the electron transport layer of the quantum dot light emitting diode comprises the following steps: dissolving the small molecule containing the phosphorus-containing oxy group in an alcohol solvent, and then forming a film by spin coating, inkjet printing or printing, thereby obtaining the electron transport layer of the quantum dot light emitting diode.

10. The small molecule containing the phosphorus-containing oxy group according to claim 9 is used for preparing an electron transport layer of a quantum dot light emitting diode. The alcohol solvent is at least one of methanol, ethanol, dipropyl alcohol, isopropyl alcohol and n-butyl alcohol.

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