Blue fluorescent molecules, methods of making and uses thereof

Abstract

The application discloses a blue fluorescent molecule, which has a D-pi-A structure, contains an oxadiazole as an acceptor group and a phenyl carbazole as a donor group, and connects the acceptor group and the donor group with an aromatic ring having a thermal excitation energy level arrangement characteristic as a pi bridge. The application also provides a preparation method and application of the blue fluorescent molecule. The application uses the aromatic ring having the thermal excitation energy level arrangement characteristic as the pi bridge, reasonably regulates a high-energy excited state of the acceptor by introducing the donor, activates a thermal excitation channel of the molecule, breaks through a limitation of 25% of an excitation utilization rate of a fluorescent material, and thus improves the excitation utilization rate.

Description

Technical Field

[0001] This invention relates to the field of organic optoelectronic materials technology, specifically to blue fluorescent molecules, their preparation methods, and applications. Background Technology

[0002] Organic Light Emitting Diode (OLED), as a next-generation display and lighting technology, boasts advantages such as self-emission, abundant material sources, wide color gamut, pure color, eye protection, and flexibility. Therefore, it has received widespread attention since its commercialization and is currently widely used in full-color flat panel displays and lighting. OLED luminescent materials, as the core of OLED display technology, have also continuously evolved with the development of OLED. Currently, compared to red and green OLED materials, blue OLED materials lag significantly behind in both efficiency and lifespan, especially at high brightness levels. This seriously hinders the development of the OLED industry.

[0003] The core scientific challenge in achieving high exciton utilization in OLED luminescent materials is the triplet excited state. Limited by spin statistics, 75% of the excited states in traditional OLEDs are non-luminescent triplet states, resulting in low efficiency for devices utilizing only singlet excitons. To address this issue, international researchers have proposed thermally activated delayed fluorescence (TADF) materials based on triplet anti-intersystem crossing (RISC) (Nature 2012, 492, 234–238) and TTA fluorescent materials based on triplet annihilation upconversion (Adv. Funct. Mater. 2013, 23, 739–746). TADF materials can utilize triplet excitons through anti-intersystem crossing processes of hyperfine interactions, achieving a maximum theoretical internal quantum efficiency (IQE) of 100%. However, deep blue TADF materials are particularly rare, and device efficiency roll-off is significant. The TTA materials reported so far can annihilate two triplet excitons and convert them into a singlet exciton. This principle can improve the utilization rate of excitons to a certain extent, but the maximum IQE of the device is only 62.5%.

[0004] In contrast, Academician Ma Yuguang's research group proposed a new mechanism in 2011 called the "thermal exciton mechanism," which can also fully utilize singlet and triplet excitons, theoretically achieving 100% exciton utilization. These materials are characterized by a large T2-T1 bandgap and a small T2-S1 bandgap. The large T2-T1 bandgap hinders the internal conversion process (IC) from T2 to T1, accelerating the high-energy reverse intersystem crossing process from T2 to S1, thus achieving high exciton utilization and low efficiency roll-off. However, the efficiency of currently reported thermal exciton materials lags significantly behind that of contemporary TADF materials, necessitating effective molecular modifications.

[0005] Besides efficiency, device stability at high brightness is also a major bottleneck for current blue OLED materials. A significant reason for this is the low carrier mobility of organic semiconductor materials, especially electron mobility, which is typically more than two orders of magnitude lower than hole mobility, affecting carrier balance in OLED devices. Furthermore, low carrier mobility also leads to significant Joule heating during device operation, further impacting device lifespan. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the purpose of this application is to provide a blue fluorescent molecule that uses an aromatic ring with thermal exciton energy level arrangement characteristics as a π bridge. By introducing donors and acceptors to reasonably regulate their high-energy excited states, the thermal exciton channels of the molecule are activated, thereby breaking through the 25% exciton utilization limit of fluorescent materials and thus improving the exciton utilization rate.

[0007] To solve the above problems, the technical solution adopted in this application is as follows:

[0008] A class of blue fluorescent molecules with a D-π-A structure, containing oxadiazole as an acceptor group and phenylcarbazole as a donor group, with an aromatic ring having thermal exciton energy level arrangement characteristics as a π bridge connecting the acceptor group and the donor group.

[0009] As a further preferred embodiment, in this application, the blue fluorescent molecule has one of the following structural formulas or one of the following structural formulas substituted with halogens or alkyl groups, or is a homologue or derivative thereof:

[0010]

[0011] Ar represents the aramid ring π-bridge structure.

[0012] As a further preferred embodiment, in this application, Ar represents one of the following structural formulas or one of the following halogenated or alkyl-substituted homologues or derivatives:

[0013]

[0014] This application also provides a method for preparing a blue fluorescent molecule. By selecting a suitable donor and acceptor and connecting them through an aromatic ring π-bridge, a blue fluorescent molecule with high exciton utilization is obtained, which breaks through the limitation of exciton utilization of existing fluorescent materials and thus improves the exciton utilization.

[0015] The preparation method includes the following steps:

[0016] Select reactants and reaction conditions to synthesize an oxadiazole intermediate having one of the following structural formulas or derivatives of the following structural formulas:

[0017]

[0018] Synthesize phenylcarbazole intermediate I by selecting reactants and reaction conditions based on one of the following structural formulas or derivatives thereof:

[0019]

[0020] The above-mentioned phenylcarbazole intermediate I was reacted with pinacol diboronate to synthesize phenylcarbazole intermediate II having one of the following structural formulas or derivatives thereof:

[0021]

[0022] The above-mentioned phenylcarbazole intermediate II was reacted with the above-mentioned oxadiazole intermediate to synthesize a blue fluorescent molecule.

[0023] This application also provides a blue organic electroluminescent material with high exciton utilization, having a D-π-A structure, comprising an oxadiazole as an acceptor group and a phenylcarbazole as a donor group, with an aromatic ring having thermal exciton energy level arrangement characteristics serving as a π bridge connecting the acceptor group and the donor group.

[0024] As a further preferred embodiment, in this application, the high exciton utilization blue fluorescent material has one of the following structural formulas or one of the following structural formulas substituted with halogens or alkyl groups, or a homologue or derivative thereof:

[0025]

[0026] Ar represents the aramid ring π-bridge structure.

[0027] The blue fluorescent molecule described in this application can be used as a high exciton utilization blue fluorescent material in light-emitting diode devices or organic electroluminescent devices.

[0028] Another objective of this application is to provide an organic electroluminescent device, comprising, from bottom to top, an anode, a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, an electron injection layer, and a cathode; characterized in that the light-emitting layer contains the blue fluorescent molecules described in this application.

[0029] As a further preferred embodiment, in this application, the organic light-emitting layer is a pure film of blue fluorescent molecules, or a composite film of blue fluorescent molecules and guest doped.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The blue fluorescent molecule described in this application uses an aromatic ring with thermal exciton energy level distribution characteristics as its core. By introducing suitable donors and acceptors to regulate its high-energy excited state, it can open the high-energy reverse intersystem crossing channel of excitons, realize the "thermal exciton" mechanism, and achieve 100% utilization of excitons.

[0032] 2. The blue fluorescent molecule described in this application uses an oxadiazole group as an acceptor. The oxadiazole group has a high LUMO energy level, making it suitable as a blue light building block. Furthermore, oxadiazole is bipolar, which is beneficial for improving carrier mobility, especially electron mobility, and the balance of electron and hole transport when used as a building block for the luminescent layer.

[0033] 3. The blue fluorescent molecule described in this application has an asymmetric structure. The torsion between the donor and acceptor and the π-bridge can inhibit molecular aggregation and reduce exciton quenching, which is beneficial to achieving high efficiency.

[0034] The present invention will be further described in detail below with reference to specific embodiments. Attached Figure Description

[0035] Figure 1 The fluorescence emission spectra of blue fluorescent molecules M1, M2, M3, and M4 in tetrahydrofuran solution are shown.

[0036] Figure 2 This is a schematic diagram of an organic electroluminescent device.

[0037] Figure 3 The electroluminescence spectra of undoped devices fabricated based on blue fluorescent molecules M1, M2, M3, and M4 are shown.

[0038] Figure 4 The electroluminescence spectra of doped devices fabricated based on blue fluorescent molecules M1, M2, M3, and M4 are shown. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] The term "comprising" and other equivalent descriptive terms used in the specification and claims of this application are intended to cover a non-exclusive inclusion, which includes both the contents explicitly described in the specification and claims and steps or units that are not described in the specification and claims but are inherent in the product, method or structure.

[0041] This application provides a class of blue fluorescent molecules with a D-π-A structure, comprising an oxadiazole as an acceptor group and a phenylcarbazole as a donor group, with an aromatic ring having thermal exciton energy level arrangement characteristics serving as a π-bridge connecting the acceptor and donor groups. The oxadiazole acceptor molecule used in this application has a high LUMO energy level, making it suitable as a blue light building block; furthermore, the bipolarity of oxadiazole as a building block for the luminescent layer material is beneficial for improving carrier mobility, especially electron mobility, and the balance of electron and hole transport. Carbazole has a small ionic potential, i.e., a strong electron-donating ability, which is beneficial for enhancing charge transfer between acceptor and donor molecules, thereby shifting the co-crystal fluorescence to a longer direction. The phenylcarbazole donor molecule used in this application has a significantly enhanced electron-donating ability due to the presence of the π-conjugated group. Therefore, in this application, by selecting suitable acceptors and donors and connecting them through an aromatic ring-type π-bridge, the high-energy excited state of the fluorescent compound can be effectively controlled, activating the thermal exciton channels of the molecule, thereby overcoming the limitation of exciton utilization.

[0042] In the embodiments of this application, the blue fluorescent molecule has one of the following structural formulas, or one of the following structural formulas being replaced by halogens or alkyl groups, or a homologue or derivative thereof:

[0043]

[0044] Where Ar represents an aromatic ring π-bridge structure. In some embodiments, halogen substitution means that the H atom on the benzene ring in the above structural formula is replaced by one or more halogen atoms. This substitution can occur on one or more benzene rings, or it can be the same halogen atom or different halogen atoms. Preferably, the halogen is Cl or / and Br. In some embodiments, alkyl substitution means that the H atom on any one or more benzene rings in the above structural formula is replaced by an alkyl group. This can be multiple H atoms on one benzene ring being replaced by the same alkyl group or different alkyl groups, or multiple H atoms on multiple benzene rings being replaced by the same alkyl group or different alkyl groups. In some embodiments, the alkyl group is a C1-C30 straight-chain alkyl group or a branched alkyl group. Preferably, the alkyl group is C1-C30. 15 It is a straight-chain alkyl or branched alkyl, or a C1-C8 straight-chain alkyl or branched alkyl.

[0045] As a further preferred embodiment, Ar represents an aromatic ring π-bridge. Specifically, in the embodiments of this application, Ar represents a fused ring structure composed of multiple aromatic rings. In some embodiments, the aromatic ring π-bridge represented by Ar may be selected from, but is not limited to, one of the following structural formulas or one of the halogenated or alkyl-substituted homologues or derivatives of the following structural formulas:

[0046]

[0047] Similarly, in the Ar-representing aromatic ring π-bridge, the halogens and alkyl groups involved in halogenation and alkyl substitution are the same as those listed above.

[0048] This application also provides a method for preparing a blue fluorescent molecule. By selecting a suitable donor and acceptor and connecting them through an aromatic ring π-bridge, a blue fluorescent molecule with high exciton utilization is obtained, which breaks through the limitation of exciton utilization of existing fluorescent materials and thus improves the exciton utilization.

[0049] The preparation method includes the following steps:

[0050] Select reactants and reaction conditions to synthesize an oxadiazole intermediate having one of the following structural formulas or derivatives of the following structural formulas:

[0051]

[0052] Synthesize phenylcarbazole intermediate I by selecting reactants and reaction conditions based on one of the following structural formulas or derivatives thereof:

[0053]

[0054] The above-mentioned phenylcarbazole intermediate I was reacted with pinacol diboronate to synthesize phenylcarbazole intermediate II having one of the following structural formulas or derivatives thereof:

[0055]

[0056] The above-mentioned phenylcarbazole intermediate II was reacted with the above-mentioned oxadiazole intermediate to synthesize a blue fluorescent molecule.

[0057] This application also provides a blue organic electroluminescent material with high exciton utilization, having a D-π-A structure, comprising an oxadiazole as an acceptor group and a phenylcarbazole as a donor group, with an aromatic ring having thermal exciton energy level arrangement characteristics serving as a π bridge connecting the acceptor group and the donor group.

[0058] As a further preferred embodiment, in this application, the high exciton utilization blue fluorescent material has one of the following structural formulas or one of the following structural formulas substituted with halogens or alkyl groups, or a homologue or derivative thereof:

[0059]

[0060] Ar represents the aramid ring π-bridge structure.

[0061] This application also provides a blue fluorescent small molecule having the following structural formula or a derivative thereof, or a fragment containing the following structural formula or a derivative thereof.

[0062]

[0063] The blue fluorescent molecules, high exciton utilization blue fluorescent materials, and small blue fluorescent molecules described in this application can all be used in light-emitting diode devices or organic electroluminescent devices.

[0064] like Figure 2 As shown, another objective of this application is to provide an organic electroluminescent device, comprising, from bottom to top, an anode, a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, an electron injection layer, and a cathode; characterized in that the light-emitting layer contains the blue fluorescent molecules described in this application, or the high exciton utilization blue fluorescent material described in this application, or the blue fluorescent small molecules described in this application.

[0065] As a further preferred embodiment, in this application, the organic light-emitting layer is a pure film of blue fluorescent molecules, high exciton utilization blue fluorescent materials, or small blue fluorescent molecules, or a composite film doped with a guest.

[0066] Example 1

[0067] This embodiment provides a blue fluorescent molecule M1 with the molecular formula C1. 48 H 29 N3O, structural formula:

[0068]

[0069] The specific synthetic route and steps are as follows:

[0070]

[0071] (1) Synthesis of Compound 1

[0072] 4-Bromobenzoyl chloride (10 mmol), benzoyl hydrazine (10 mmol), and triethylamine (8.00 mL) were dissolved in dichloromethane. The mixture was stirred at 20 °C for 4 h, washed with water, filtered, and recrystallized to give a white solid intermediate. The intermediate was then dissolved in POCl3 (20 mL) and reacted at 90 °C for 12 h under a nitrogen atmosphere. After the reaction was complete and cooled to room temperature, the mixture was slowly added to ice water, precipitating a white solid. The solid was then extracted with water and dichloromethane, dried over MgSO4, and filtered. Recrystallization from n-hexane and water gave a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0073] (2) Synthesis of compound 2

[0074] 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester (6 mmol), 2,7-dibromopyrene (6 mmol), tetra(triphenylphosphine)palladium (0.5 mmol), potassium carbonate (12 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, the reaction solution was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to give a yellow solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0075] (3) Synthesis of compound 3

[0076] A mixture of compound 2 (3 mmol), pinacol diborate (4.5 mmol), potassium acetate (9 mmol), and [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride (0.66 mmol) was placed in a 100 mL round-bottom flask and placed under nitrogen atmosphere. Then, 60 mL of dioxane was injected into the flask, and the reaction mixture was refluxed at 90 °C for 24 hours. When the reaction mixture cooled to room temperature, it was poured into an aqueous solution and extracted several times with dichloromethane. The extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0077] (4) Synthesis of compound M1

[0078] Compound 3 (2.5 mmol), compound 1 (3 mmol), tetrakis(triphenylphosphine)palladium (0.075 mmol), and potassium carbonate (6 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, it was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to obtain a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0079] Example 2

[0080] This embodiment provides a blue fluorescent molecule M2 with the molecular formula C2. 46 H 29 N3O, structural formula:

[0081]

[0082] The specific synthesis route and steps are as follows:

[0083]

[0084] (1) Synthesis of compound 4

[0085] Benzylamidine hydrochloride (10 mmol), p-bromotoluene (10 mmol), Cu(OAc)₂ (1 mmol), K₃PO₄ (30 mmol), 70% TBHP (30 mmol), and DCE (100 mL) were mixed in a 250 mL round-bottom flask and stirred at room temperature for 12 h. After the reaction was complete, the reaction solution was evaporated under reduced pressure. The mixture was then extracted with ethyl acetate and water. The extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to give a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0086] (2) Synthesis of compound 5

[0087] 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester (6 mmol), 9,10-dibromoanthracene (6 mmol), tetra(triphenylphosphine)palladium (0.5 mmol), potassium carbonate (12 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, the reaction solution was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to give a yellow solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0088] (3) Synthesis of compound 6

[0089] A mixture of compound 5 (3 mmol), pinacol diborate (4.5 mmol), potassium acetate (9 mmol), and [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride (0.66 mmol) was placed in a 100 mL round-bottom flask under nitrogen atmosphere. Then, 60 mL of dioxane was injected into the flask, and the reaction mixture was refluxed at 90 °C for 24 hours. When the reaction mixture cooled to room temperature, it was poured into an aqueous solution and extracted several times with dichloromethane. The extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to a white solid. ¹H NMR, ¹³C NMR, MS, and elemental analysis indicated that the obtained compound was the target product.

[0090] (4) Synthesis of compound M2

[0091] Compound 6 (2.5 mmol), compound 4 (3 mmol), tetra(triphenylphosphine)palladium (0.075 mmol), and potassium carbonate (6 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, it was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product. Figure 1 The UV absorption and fluorescence emission spectra of M2 in solution and thin film are shown.

[0092] Example 3

[0093] This embodiment provides a blue fluorescent molecule M3, whose molecular formula is C3. 50 H 31 N3O, structural formula:

[0094]

[0095] The specific synthesis route and steps are as follows:

[0096]

[0097] (1) Synthesis of compound 7

[0098] 4-Bromobenzylamidine hydrochloride (10 mmol), toluene (10 mmol), Cu(OAc)₂ (1 mmol), K₃PO₄ (30 mmol), 70% TBHP (30 mmol), and DCE (100 mL) were mixed in a 250 mL round-bottom flask and stirred at room temperature for 12 h. After the reaction was complete, the reaction solution was evaporated under reduced pressure. The mixture was then extracted with ethyl acetate and water. The extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to give a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0099] (2) Synthesis of compound 8

[0100] 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester (6 mmol), 6,12-dibromochloropyrrolidone (6 mmol), tetra(triphenylphosphine)palladium (0.5 mmol), potassium carbonate (12 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, the reaction solution was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to give a yellow solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0101] (3) Synthesis of compound 9

[0102] A mixture of compound 8 (3 mmol), pinacol diborate (4.5 mmol), potassium acetate (9 mmol), and [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride (0.66 mmol) was placed in a 100 mL round-bottom flask and placed under nitrogen atmosphere. Then, 60 mL of dioxane was injected into the flask, and the reaction mixture was refluxed at 90 °C for 24 hours. When the reaction mixture cooled to room temperature, it was poured into an aqueous solution and extracted several times with dichloromethane. The extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0103] (4) Synthesis of compound M3

[0104] Compound 9 (2.5 mmol), compound 7 (3 mmol), tetra(triphenylphosphine)palladium (0.075 mmol), and potassium carbonate (6 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, it was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0105] Example 4

[0106] This embodiment provides a blue fluorescent molecule M4, whose molecular formula is C4. 50 H 31 N3O, structural formula:

[0107]

[0108] The specific preparation steps are as follows:

[0109]

[0110] (1) Synthesis of compound 10

[0111] 10 mmol of 4-bromodiphenylglyoxime and 50 mmol of succinic anhydride were mixed in a 250 mL round-bottom flask and reacted at 180–180 °C for 10 min. After the reaction was complete, the reactants were cooled to room temperature, poured into deionized water, and neutralized with sodium bicarbonate solution until the solution was neutral. The mixture was then extracted with ethyl acetate and water. The organic phase was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to obtain a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0112] (2) Synthesis of compound 11

[0113] 4-(9H-carbazole-9-yl)phenylboronic acid pinacol ester (6 mmol), 2,11-dibromobenzophenanthrene (6 mmol), tetra(triphenylphosphine)palladium (0.5 mmol), potassium carbonate (12 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, the reaction solution was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to give a yellow solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0114] (3) Synthesis of compound 12

[0115] A mixture of compound 11 (3 mmol), pinacol diborate (4.5 mmol), potassium acetate (9 mmol), and [1,1'-bis(diphenylphosphine)ferrocene]palladium dichloride (0.66 mmol) was placed in a 100 mL round-bottom flask and placed under nitrogen atmosphere. Then, 60 mL of dioxane was injected into the flask, and the reaction mixture was refluxed at 90 °C for 24 hours. When the reaction mixture cooled to room temperature, it was poured into an aqueous solution and extracted several times with dichloromethane. The extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to obtain a crude product, which was purified by silica gel column chromatography to give a white solid. ¹H NMR, ¹³C NMR, MS, and elemental analysis indicated that the obtained compound was the target product.

[0116] (4) Synthesis of compound M4

[0117] Compound 12 (2.5 mmol), compound 10 (3 mmol), tetra(triphenylphosphine)palladium (0.075 mmol), and potassium carbonate (6 mmol) were placed in a 250 mL round-bottom flask under nitrogen atmosphere. Then, a mixed solvent system of 60 mL tetrahydrofuran and 15 mL H₂O was injected into the flask, and the reaction mixture was refluxed at 70 °C for 24 hours. When the reaction mixture cooled to room temperature, it was evaporated under reduced pressure. The mixture was then poured into an aqueous solution and extracted several times with dichloromethane. Finally, the extract was dried over anhydrous magnesium sulfate and evaporated under reduced pressure to give a crude product, which was purified by silica gel column chromatography to a white solid. 1 HNMR, 13 CNMR, MS and elemental analysis results indicate that the obtained compound is the target product.

[0118] Figure 1The four blue fluorescent molecules described in Examples 1-4 above emit light at a wavelength of approximately 450 nm in THF, exhibiting pure blue light emission, indicating that these four compounds are good blue fluorescent materials.

[0119] Application Example 1

[0120] This application example provides an undoped organic light-emitting device, the fabrication method of which is as follows:

[0121] Take a pre-made indium tin oxide (ITO) glass with a sheet resistance of 15Ω, and clean it ultrasonically with acetone, detergent, deionized water and isopropanol in sequence, followed by plasma treatment for 10 minutes. Then, in a vacuum evaporation apparatus, a 40 nm thick layer of polyethylene dioxythiophene-doped poly(styrene sulfonate) (PEDOT:PSS) is spin-coated onto the ITO surface as a hole injection layer. Next, a 40 nm thick layer of 4,4',4” tris(carbazole 9-yl)triphenylamine (TCTA) is sequentially deposited as a hole transport layer. Blue light-emitting compounds M1–M4 are used as emitting layers with a thickness of 20 nm. A 30 nm thick layer of 1,3,5-tris(1-phenyl 1H-benzimidazole 2-ylbenzene) (TPBi) is used as an electron transport layer, a 1 nm thick layer of lithium fluoride (LiF) is used as an electron injection layer, and a 100 nm thick layer of aluminum (Al) is used as the cathode. The device structure is: ITO / PEDOT:PSS / TCTA / emitting layer (M1-M4) / TPBi / LiF / Al.

[0122] The performance data of the fabricated undoped organic light-emitting devices are shown in Table 1.

[0123] Table 1: Performance Test Results of Undoped Organic Light-Emitting Devices

[0124]

[0125] The results in Table 1 show that all devices exhibit good color purity, with y-coordinate values ​​generally below 0.14, demonstrating pure blue or deep blue light emission. Furthermore, these devices all possess low turn-on voltages (<3.5V) and high brightness (>15000 cd / m²). -2 This indicates that the blue light "thermal exciton" small molecules with benzoxazole and oxadiazole as donors and acceptors provided by this invention can be used to construct high-efficiency blue organic light-emitting diodes with low turn-on voltage.

[0126] Figure 4 The electroluminescence spectra of undoped organic light-emitting devices prepared using blue fluorescent molecules M1, M2, M3, and M4 as the emitting layer are shown. The emission wavelength of the undoped organic light-emitting devices is red-shifted relative to the solution, with emission peaks around 460 nm. However, compared to the solution, the electroluminescence color purity of the organic light-emitting devices increases, and the full width at half maximum (FWHM) decreases.

[0127] Application Example 2

[0128] This application example provides a doped organic light-emitting device, the fabrication method of which is as follows:

[0129] Take a pre-made indium tin oxide (ITO) glass with a sheet resistance of 15Ω, and ultrasonically clean it sequentially with acetone, detergent, deionized water, and isopropanol, followed by plasma treatment for 10 minutes. Then, in a vacuum evaporation equipment, sequentially deposit the following layers onto the ITO surface: a 5nm thick layer of 2,3,6,7,10,11 hexacyano-1,4,5,8,9,12 hexaazabenzophenanthrene (HATCN) as a hole injection layer; a 40nm thick layer of N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB) as a hole transport layer; a 5nm thick layer of 4,4',4"tri(carbazole-9"triphenylamine) (TCTA) as a hole transport layer; and a 20nm thick layer of luminescent small molecules M1-M4 (98% by mass) (and 4,4'-diphenylamine). A bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi) (2% by mass) mixed film is used as the light-emitting layer, a 40 nm thick 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) is used as the electron transport layer, a 1 nm thick lithium fluoride (LiF) is used as the electron injection layer, and a 100 nm thick aluminum (Al) is used as the cathode. The device structure is ITO / PEDOT:PSS / NPB / TCTA / light-emitting layer (M1-M4 (98%):BD (2%)) / TPBi / LiF / Al.

[0130] The performance test data of the doped organic light-emitting device are shown in Table 2.

[0131] Table 2: Performance Test Results of Doped Organic Light-Emitting Devices

[0132]

[0133] The results in Table 2 show that the performance of doped organic light-emitting devices is further improved compared to undoped devices. The y-coordinate values ​​are generally below 0.10, indicating very high color purity. Furthermore, the maximum external quantum efficiency of all devices is close to 10%, breaking through the 5% external quantum efficiency limit of traditional light-emitting materials. This demonstrates that the blue light-emitting small molecules using benzoxazole and oxadiazole as donors and acceptors provided in this invention possess "thermal exciton" characteristics and their superiority in high exciton utilization.

[0134] Figure 4 The electroluminescence spectra of doped organic light-emitting devices (OLEDs) based on blue fluorescent molecules M1, M2, M3, and M4 are shown. The doped OLEDs, using these four Lysear fluorescent molecules as the main emitting layer, all exhibit emission peaks around 460 nm, with further increases in color purity and decreases in full width at half maximum (FWHM) compared to undoped devices. They demonstrate excellent blue light performance.

[0135] The embodiments described in this application are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A class of blue fluorescent molecules, characterized in that, It has a D-π-A structure, comprising an oxadiazole as an acceptor group and a phenylcarbazole as a donor group, with an aromatic ring having thermal exciton level arrangement characteristics serving as a π-bridge connecting the acceptor and donor groups; it has one of the following structural formulas M1-M4: 。 2. A method for preparing the blue fluorescent molecule as described in claim 1, characterized in that, Includes the following steps: An oxadiazole intermediate having one of the following structural formulas is used: Phenylacetazole intermediate I with one of the following structural formulas is used: The above-mentioned phenylcarbazole intermediate I was reacted with pinacol diboronate to synthesize phenylcarbazole intermediate II having one of the following structures: The above-mentioned phenylcarbazole intermediate II was reacted with the above-mentioned oxadiazole intermediate to synthesize a blue fluorescent molecule.

3. The application of the blue fluorescent molecule as described in claim 1 in light-emitting diode devices or organic electroluminescent devices.

4. An organic electroluminescent device, comprising, from bottom to top, an anode, a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, an electron injection layer, and a cathode; characterized in that, The luminescent layer contains the blue fluorescent molecules as described in claim 1.

5. The organic electroluminescent device according to claim 4, characterized in that, The organic light-emitting layer is a pure film of blue fluorescent molecules or a composite film doped with a guest.

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