Narrow-emission fluorescent compound and preparation method and application thereof

Abstract

The present application relates to the technical field of organic electroluminescent material, especially refers to a narrow emission fluorescent compound and a preparation method and application thereof. The present application provides a kind of narrow emission fluorescent compound with semi-enclosed / fully enclosed structure, which has the characteristics of thermally activated delayed fluorescence (TADF) and the coating structure of spatial orthogonal barrier. Different protective groups can be introduced by spatial orthogonal double screw lock unit to form semi-enclosed / fully enclosed structure, which can significantly increase the intermolecular distance between adjacent MR light emitting units, protect the electron cloud of light emitting core from overlapping, thereby inhibit harmful Dexter energy transfer, fundamentally avoid the problems of aggregation-induced quenching (ACQ) and spectral broadening; it has narrow-band emission and anti-aggregation, and the OLED device prepared by using the light emitting layer material of the organic electroluminescent device has high luminous efficiency and high color purity.

Description

Technical Field

[0001] This invention relates to the field of organic electroluminescent materials technology, and in particular to a narrow emission fluorescent compound, its preparation method, and its application. Background Technology

[0002] In recent years, the emergence of thermally activated delayed fluorescence (TADF) materials has provided a novel approach to achieving 100% exciton utilization efficiency in purely organic materials. TADF materials achieve an extremely small singlet-triplet bandgap by designing a distorted donor-acceptor structure, thereby utilizing ambient thermal energy to induce triplet excitons to undergo reverse intersystem crossing to emit light in the singlet state, theoretically achieving a balance between low cost and high efficiency. However, as display technology advances towards higher resolution, lower power consumption, and more realistic colors, TADF materials with broad emission spectra (FWHM > 60 nm) cannot meet commercial demands. Therefore, developing luminescent material systems with high efficiency, long lifetime, and high color purity has become the most crucial issue in the current OLED field. Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have emerged, constructing short-range charge transfer states at the molecular level through precise alternating boron and nitrogen atom arrangements. Their highly conjugated polycyclic aromatic hydrocarbon structure effectively suppresses structural relaxation in the excited state. The most prominent advantages of this type of material are: (1) high color purity, with its emission half-width typically as narrow as below 30 nm, easily meeting the requirements of ultra-high-definition display standards such as BT.2020; and (2) high efficiency, effectively suppressing non-radiative transitions while also achieving efficient exciton utilization, exhibiting excellent device performance in the blue and green light regions. Therefore, MR-TADF material is considered an ideal emitting layer material for realizing next-generation ultra-high-definition displays.

[0003] However, despite the promising prospects of MR-TADF materials, they still face a critical bottleneck problem in practical device applications—severe concentration aggregation quenching effect. This is because MR-TADF molecules usually have a highly planar and rigid molecular skeleton. Although this structural feature is beneficial for narrowband luminescence, it also makes them prone to dense π-π stacking in solid films. Harmful Dexter energy transfer is easily induced between luminescent molecules, resulting in nonradiative transitions and affecting device performance. When the doping concentration of MR-TADF material in the device is high, the intermolecular interaction will cause the following major drawbacks: (1) As the doping concentration increases, the luminescence efficiency drops sharply. In order to avoid this problem, the existing technology usually forces the doping concentration of MR-TADF luminescent material to be strictly limited to a very low level (usually below 5 wt% or even 1 wt%), but this brings new problems, such as insufficient energy transfer from host to guest and easy carrier trapping effect. (2) As the doping concentration increases, the device spectrum broadens. Intermolecular aggregation and interactions can lead to red shift of the emission peak, a significant increase in the half-width at half-maximum (WHM), and bimolecular emission, thus failing to meet the stringent requirements for color purity in ultra-high-definition displays.

[0004] Although researchers have proposed two solutions, both have significant drawbacks: (1) Macrocyclic covalent encapsulation strategy: By introducing covalently linked macrocycles outside the MR luminescent unit, the entire luminescent core is enclosed like a "cage" to isolate the interaction between MR units. However, compared with the traditional strategy of directly connecting sterically hindered groups, the construction of macrocycles requires multi-step synthesis and the route is complex. At the same time, compared with the all-aromatic ring structure, the introduction of flexible alkyl chains will bring unavoidable structural relaxation, resulting in unavoidable spectral broadening. (2) Using a "spatial wrapping" strategy (such as carbazole unit wrapping): The MR core is wrapped with large-volume conjugated units to isolate aggregation. Although the PLQY (photoluminescence quantum efficiency) is still >90% under high doping (20 wt%), the multi-step precise synthesis leads to complex processes, and the peripheral units are prone to weak conjugation with the core, which broadens the FWHM to 28-30 nm; at the same time, the energy level matching is difficult, which can easily cause charge transport imbalance and reduce device efficiency.

[0005] Therefore, developing an MR-TADF material and device that combines narrowband emission, high anti-aggregation properties, and high efficiency has become the key to promoting the development of ultra-high-definition OLEDs. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a narrow-emission fluorescent compound based on a spatial orthogonal barrier strategy, along with its preparation method and applications. The narrow-emission fluorescent compound based on the spatial orthogonal barrier strategy exhibits thermally activated delayed fluorescence properties, narrow-band emission (FWHM < 30 nm), and minimal decay of the maximum external quantum efficiency as the doping concentration increases. It can be used as a light-emitting layer material for organic electroluminescent devices, and simultaneously enables the acquisition of light-emitting devices with high-efficiency narrow emission spectra, demonstrating promising application prospects and economic value.

[0007] To address the aforementioned technical problems, the present invention provides a narrow-emission fluorescent compound, wherein the structure of the narrow-emission fluorescent compound is one of the following formulas: , ; Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl.

[0008] Preferably, the structure of the narrow-emission fluorescent compound is one of the following formulas: .

[0009] The present invention also provides a method for preparing the above-mentioned narrow-emission fluorescent compound, comprising the following steps: S11: Under a protective atmosphere, compound A1 and lithium reagent I are mixed in organic solvent I at -80°C to -76°C for 1-3 h, then compound A2 is added and reacted at 20-30°C for 10-14 h. The solvent is removed by vacuum distillation to obtain a solid. The structure of compound A1 is as follows: ; The structure of compound A2 is one of the following formulas: , ; Wherein, X is selected from phenyl, tolyl, or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl, or 1,3,5-trimethylphenyl; S12: Add the solid obtained in step S11 to acid and carry out a condensation cyclization reaction at 100-140℃ for 10-14h to obtain intermediate B1; The intermediate B1 has a structure that is one of the following: , ; Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl; S13: Under light-protected conditions, the intermediate B1 and the brominating reagent are added to organic solvent II and reacted at 20-30°C for 10-14 h to obtain intermediate C1; The intermediate C1 has a structure of one of the following formulas: , ; Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl; S14: Under a protective atmosphere, the intermediate C1 and lithium reagent II are added to organic solvent III and reacted at 85-95°C for 2-4 h. Then boron halide is added and mixed at 20-30°C for 2-4 h to obtain a mixture. S15: Add an organic amine to the mixture, react at 160-180℃ for 22-26 h, and purify to obtain the narrow emission fluorescent compound.

[0010] Preferably, lithium reagent I is n-butyllithium and lithium reagent II is tert-butyllithium.

[0011] n-Butyllithium (n-BuLi) is a commonly used organolithium reagent with moderate basicity and strong nucleophilicity. It has both deprotonation and nucleophilic addition properties and is mainly used for hydrogen removal from moderately acidic CH bonds, halogen-lithium exchange, nucleophilic addition of carbonyl compounds, and polymerization initiation. It has wide applicability and relatively mild operation. Tert-Butyllithium (t-BuLi) is extremely basic with large steric hindrance and significantly weakened nucleophilicity. It hardly undergoes nucleophilic side reactions and is more suitable for metallization of weakly acidic CH bonds that are difficult to remove hydrogen from, and for the preparation of aryl lithium through efficient halogen-lithium exchange. It has higher reactivity but is flammable and explosive, and has more stringent safety requirements.

[0012] Preferably, in step S12, the acid is hydrochloric acid and acetic acid (glacial acetic acid).

[0013] In steps S11 and S12, compound A1 first undergoes a metal-halogen exchange substitution reaction with a lithium reagent, then undergoes a nucleophilic addition reaction with compound A2, and finally completes a condensation cyclization reaction under acidic conditions to obtain intermediate compound B1.

[0014] Preferably, the brominating agent is N-bromosuccinimide or liquid bromine, and the boron halide is boron tribromide or boron triiodide.

[0015] In steps S13 and S14, intermediate B1 undergoes an electrophilic substitution reaction with a bromide reagent to obtain intermediate C1; intermediate C1 first undergoes a metal-halogen exchange substitution reaction with tert-butyllithium, and then undergoes a nucleophilic borylation reaction with boron halide.

[0016] Furthermore, in step S14, lithium reagent II is added to organic solvent III at -45°C to -35°C, and boron halide is added at -25°C to -15°C.

[0017] Preferably, the organic amine is N,N-diisopropylethylamine.

[0018] In step S15, the mixture undergoes an intramolecular nucleophilic aromatic substitution cyclization reaction with N,N-diisopropylethylamine to obtain a narrow-emission fluorescent compound based on a spatial orthogonal barrier strategy.

[0019] Preferably, the organic solvent I is one or more of tetrahydrofuran, 1,4-dioxane and dimethyl sulfoxide; the organic solvent II is one or more of dichloromethane, chloroform and N,N-dimethylformamide; and the organic solvent III is one or more of tert-butylbenzene, o-xylene and mesitylene.

[0020] Preferably, the protective atmosphere is a nitrogen atmosphere.

[0021] Preferably, the molar ratio of compound A1 to compound A2 is 1:4-5.

[0022] Preferably, the purification method involves extraction three times with sodium acetate aqueous solution and dichloromethane, drying the organic phase with anhydrous magnesium sulfate, filtering, and concentrating under reduced pressure. The crude product is then further purified by silica gel column chromatography.

[0023] The present invention also provides an organic electroluminescent device, the organic electroluminescent device comprising an emissive layer, the emissive layer being prepared from the above-mentioned narrow-emission fluorescent compound.

[0024] This invention protects the electron cloud of the luminescent core from overlapping, thereby suppressing harmful Dexter energy transfer and fundamentally avoiding induced quenching (ACQ) and spectral broadening problems. This invention can be used as a luminescent layer material in organic electroluminescent devices, and at the same time, it can obtain luminescent devices with high efficiency and narrow emission spectra.

[0025] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: This invention relates to a narrow-emission fluorescent compound with a semi-enclosed / fully enclosed structure based on a dual-spiral locking strategy. This compound exhibits thermally activated delayed fluorescence properties. Furthermore, its unique spatial orthogonal barrier three-dimensional encapsulation configuration significantly increases the intermolecular distance between adjacent MR luminescent units, thereby preventing the overlap of frontier orbitals between luminescent molecules and suppressing harmful Dexter energy transfer between luminescent cores, reducing nonradiative transitions, and fundamentally avoiding aggregation-induced quenching and spectral broadening. It also features narrow-band emission (FWHM < 30 nm) and high anti-aggregation properties (no significant ACQ under 5-20 wt% high doping), making it suitable as a luminescent layer material for organic electroluminescent devices. The OLED devices prepared from this compound exhibit high luminous efficiency and high color purity. Attached Figure Description

[0026] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] Figure 1 The proton NMR spectrum of compound 2tPh-BN prepared in Example 1 of this invention; Figure 2 The carbon spectrum of compound 2tPh-BN prepared in Example 1 of this invention; Figure 3 The mass spectrum of compound 2tPh-BN prepared in Example 1 of this invention; wherein, the vertical axis is the peak intensity and the horizontal axis is the mass-to-charge ratio m / z; Figure 4 The proton NMR spectrum of compound mPh-BN-mPh prepared in Example 2 of this invention; Figure 5 The carbon spectrum of compound mPh-BN-mPh prepared in Example 2 of this invention; Figure 6 The mass spectrum of compound mPh-BN-mPh prepared in Example 2 of this invention; wherein, the vertical axis is the peak intensity and the horizontal axis is the mass-to-charge ratio m / z; Figure 7 This is a device efficiency graph for device D1 with a 5wt% doping concentration in Application Example 1 of the present invention; Figure 8 This is the electroluminescence spectrum of device D1 with a 5wt% doping concentration in Application Example 1 of the present invention; Figure 9 This is a device efficiency graph for device D2 with a 5wt% doping concentration in Application Example 1 of this invention; Figure 10 This is the electroluminescence spectrum of device D2 with a 5wt% doping concentration in Application Example 1 of this invention; Figure 11 This is a synthetic route diagram of compound 2tPh-BN prepared in Example 1 of the present invention; Figure 12 This is a synthetic route diagram for the compound mPh-BN-mPh prepared in Example 2 of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0029] Example 1:

[0030] This embodiment relates to a method for preparing a narrow-emission fluorescent compound 2tPh-BN with a semi-enclosed structure, the synthetic route of which is as follows: Figure 11 As shown (where tBu is tert-butyl): Specifically, the steps include the following: (1) Under a nitrogen atmosphere, compound 9,9'-(4,6-dibromo-1,3-phenyl)bis(3,6-di-tert-butyl-9H-carbazole) (3.00 g, 3.81 mmol) was dissolved in 60 mL of tetrahydrofuran (THF). The solution was cooled to -78°C, and a 2.20 M solution of n-butyllithium (n-BuLi, 6.90 mL, 15.24 mmol) was added dropwise using a syringe. After stirring for 2 hours, compound 1-(4-(tert-butyl)phenyl)-9H-fluorene-9-one (4.75 g, 15.24 mmol) was added. After reacting for 12 hours, 5 mL of water was added to terminate the reaction, and then the solvent was removed under reduced pressure. The resulting solid was dissolved in 160 mL of glacial acetic acid (AcOH), heated to 120°C and stirred for half an hour, and then 15 mL of 36... The reaction mixture was added to hydrochloric acid (HCl) at wt% and reacted for 12 hours. The reaction mixture was then poured into ice water, resulting in the precipitation of a large amount of solid. The solid was separated by silica gel column chromatography (dichloromethane:n-hexane = 1:10) to obtain intermediate A (1.49 g, 1.22 mmol), yield: 32.1%. Matrix-assisted laser desorption / ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) showed a molecular ion peak at 1221.399.

[0031] (2) Under strictly light-protected conditions, intermediate A (3.00 g, 2.46 mmol) was dissolved in 50 mL of dichloromethane (DCM), and the solution was cooled to 0 °C. Then, N-bromosuccinimide (NBS) (0.66 g, 3.69 mmol) was added in portions. The reaction was maintained at 0 °C for 30 minutes, and then stirred overnight at room temperature. Subsequently, the solvent was removed under reduced pressure, and the resulting solid was separated by silica gel column chromatography (dichloromethane: n-hexane = 1:10) to obtain intermediate B (1.32 g, 1.01 mmol), yield: 42.48%. Matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) showed a molecular ion peak at 1300.196.

[0032] (3) Under a nitrogen atmosphere, intermediate B (3.00 g, 2.31 mmol) was dissolved in 50 mL of mesitylene solution and cooled to -40 °C. Then, 1.30 M tert-butyllithium solution (t-BuLi, 3.55 mL, 4.62 mmol) was slowly added. The reaction mixture was slowly heated to room temperature (25 ± 5 °C) and stirred at 90 °C for 3 hours. After completion, 1.00 M boron tribromide solution (BBr3, 4.62 mL, 4.62 mmol) was slowly added at -20 °C, and stirring was continued at room temperature for 3 hours. Finally, 5.00 M boron tribromide solution was added at 0 °C. After adding mL of N,N-diisopropylethylamine (DIPEA), the reaction mixture was stirred at 170 °C for 24 hours. After the reaction was completed, the mixture was extracted three times with sodium acetate aqueous solution and dichloromethane. The organic phase was dried over anhydrous magnesium sulfate, filtered, and concentrated under reduced pressure. The crude product was further purified by silica gel column chromatography (dichloromethane:n-hexane = 1:10) to obtain the target compound 2tPh-BN (0.48 g, 0.38 mmol), with a yield of 16.4%. Matrix-assisted laser desorption / ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) showed a molecular ion peak at 1228.392. Figure 1 The hydrogen spectrum of compound 2tPh-BN; Figure 2 The carbon spectrum of compound 2tPh-BN; Figure 3 This is the mass spectrum of compound 2tPh-BN.

[0033] Example 2:

[0034] This embodiment relates to a method for preparing a narrow-emission fluorescent compound mPh-BN-mPh with a fully enclosed structure, the synthetic route of which is as follows: Figure 12 As shown: Specifically, the steps include the following: The preparation method differs from that in Example 1 in that: in step (1), 1-(4-(tert-butyl)phenyl)-9H-fluorene-9-one is replaced with an equivalent amount of 1-(3,5-dimethylphenyl)-9H-fluorene-9-one, while other steps and parameters remain unchanged, to obtain compound mPh-BN-mPh (yield: 15.0%). The matrix-assisted laser desorption / ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) results show that the molecular ion peak is 1172.592. Figure 4 The hydrogen spectrum of compound mPh-BN-mPh; Figure 5 The carbon spectrum of compound mPh-BN-mPh; Figure 6 This is the mass spectrum of compound mPh-BN-mPh.

[0035] Comparative Example 1: Di-tert-butylcarbazole boron (DtBuCzB, CAS 2170487-30-4) was used directly.

[0036] Application Example 1: The organic electroluminescent device based on the compounds obtained in the examples has the following specific structure: indium tin oxide (ITO) is used as the anode, bispyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanonitrile (HATCN) is used as the hole injection layer (HIL), 4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC) is used as the hole transport layer (HTL), and 4,4',4”-tris(carbazole-9-yl)triphenylamine (TCTA) is used as the anode. The electron blocking layer (EBL), the example compound as the guest material, and 3,3'-bis(9H-carbazole-9-yl)-1,1'-biphenyl (mCBP) as the host material are used together as the emissive layer (EML); 4,6-bis(3,5-bis(pyridin-3-yl)phenyl)-2-methylpyrimidine (TmPyPb) are used as the electron transport layer (ETL); lithium fluoride (LiF) is used as the electron injection layer (EIL); and aluminum (Al) is used as the cathode. The specifications of each layer of the organic electroluminescent device are: ITO / HATCN (10 nm) / TAPC (40 nm) / TCTA (10 nm) / mCBP: guest material (5-20 wt%) (20 nm) / TmPyPb (40 nm) / LiF (1 nm) / Al (100 nm). The specific preparation process is a conventional technique, using vacuum evaporation.

[0037] Figure 7 The device efficiency diagram is for device D1 with a doping concentration of 5 wt%. Figure 8 The electroluminescence spectrum of device D1 with a doping concentration of 5 wt% is shown. Figure 9 The device efficiency diagram is for device D2 with a doping concentration of 5 wt%. Figure 10The electroluminescence spectrum of device D2 (5 wt% doping concentration) is shown in Table 1; device D3 is a comparative example. All data are from previously reported literature. Specific performance parameters of the organic electroluminescent devices are shown in Table 1, where EL is the electroluminescence wavelength, FWHM is the full width at half maximum (FWHM), and EQE is the maximum emission value. max This represents the maximum external quantum efficiency.

[0038] Table 1 Performance Tests of Different Devices

[0039] As shown in Table 1, the narrow-emission fluorescent compounds with semi-enclosed and fully enclosed structures provided by this invention successfully achieved narrow-band green light emission when applied to electroluminescent devices. More importantly, compared to comparative examples, the OLED devices fabricated based on the narrow-emission fluorescent compounds of this invention exhibit a higher maximum external quantum efficiency (EQE) over a wide doping concentration range of 5-20 wt%. max The material exhibits low attenuation and maintains an efficiency consistently above 26%, indicating excellent resistance to aggregation-induced quenching (ACQ). Furthermore, with increasing doping concentration, the device's electroluminescence (EL) spectrum retains a narrow emission band of 25 nm, effectively suppressing spectral broadening, redshift, and bimolecular emission caused by ACQ. These results demonstrate that the spiro-ring-locked semi-enclosed / fully enclosed structure strategy offers significant insights for designing luminescent molecules that balance high efficiency and high color purity.

[0040] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A narrow-emission fluorescent compound, characterized in that, The narrow-emission fluorescent compound has a structure of one of the following formulas: 、 ； Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl.

2. The narrow-emission fluorescent compound according to claim 1, characterized in that, The narrow-emission fluorescent compound has a structure of one of the following formulas: 。 3. A method for preparing the narrow-emission fluorescent compound according to claim 1 or 2, characterized in that, The steps include the following: S11: Under a protective atmosphere, compound A1 and lithium reagent I are mixed in organic solvent I at -80°C to -76°C for 1-3 h, then compound A2 is added and reacted at 20-30°C for 10-14 h. The solvent is removed by vacuum distillation to obtain a solid. The structure of compound A1 is as follows: ; The structure of compound A2 is one of the following formulas: , ; Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl; S12: Add the solid obtained in step S11 to acid and carry out a condensation cyclization reaction at 100-140℃ for 10-14 h to obtain intermediate B1; The intermediate B1 has a structure that is one of the following: 、 ； Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl; S13: Under light-protected conditions, the intermediate B1 and the brominating reagent are added to organic solvent II and reacted at 20-30°C for 10-14 hours to obtain intermediate C1; The intermediate C1 has a structure of one of the following formulas: 、 ； Wherein, X is selected from phenyl, tolyl or tert-butylphenyl; Y is selected from 2,6-dimethylphenyl, 3,5-dimethylphenyl or 1,3,5-trimethylphenyl; S14: Under a protective atmosphere, the intermediate C1 and lithium reagent II are added to organic solvent III and reacted at 85-95°C for 2-4 hours. Then boron halide is added and mixed at 20-30°C for 2-4 hours to obtain a mixture. S15: Add an organic amine to the mixture, react at 160-180℃ for 22-26 h, and purify to obtain the narrow emission fluorescent compound.

4. The preparation method according to claim 3, characterized in that: The lithium reagent I is n-butyllithium, and the lithium reagent II is tert-butyllithium.

5. The preparation method according to claim 3, characterized in that: In step S12, the acids are hydrochloric acid and acetic acid.

6. The preparation method according to claim 3, characterized in that: The brominating reagent is N-bromosuccinimide or liquid bromine, and the boron halide is boron tribromide or boron triiodide.

7. The preparation method according to claim 3, characterized in that: The organic amine is N,N-diisopropylethylamine.

8. The preparation method according to claim 3, characterized in that: The organic solvent I is one or more of tetrahydrofuran, 1,4-dioxane and dimethyl sulfoxide; the organic solvent II is one or more of dichloromethane, chloroform and N,N-dimethylformamide; and the organic solvent III is one or more of tert-butylbenzene, o-xylene and mesitylene.

9. The preparation method according to claim 3, characterized in that: The molar ratio of compound A1 to compound A2 is 1:4-5.

10. An organic electroluminescent device, characterized in that: The organic electroluminescent device includes a light-emitting layer, which is prepared from the narrow-emission fluorescent compound of claim 1 or 2.

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