Narrow-emission fluorescent compound based on double-spiro skeleton as well as preparation method and application of narrow-emission fluorescent compound

Abstract

The invention discloses a narrow-emission fluorescent compound based on a double-spiro skeleton as well as a preparation method and application thereof, the narrow-emission fluorescent compound has a structural general formula shown in the specification, and X is selected from a carbon-carbon single bond, oxygen, sulfur or selenium. The narrow-emission fluorescent compound based on the double-spiro skeleton has a thermally activated delayed fluorescence property, and meanwhile, due to a unique biorthogonal strategy, the molecular distance between adjacent MR cores is remarkably increased, so that the interaction between molecules is effectively inhibited, and the phenomena of aggregation-induced quenching and spectrum broadening are avoided; the organic light-emitting diode (OLED) device prepared by using the material as the light-emitting layer material of the organic light-emitting device has high light-emitting efficiency and high color purity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic electroluminescent materials, in particular to a narrow-emission fluorescent compound based on a double-spiro skeleton and a preparation method and application thereof. BACKGROUND

[0002] Organic light-emitting diodes (OLEDs) have advantages such as flexibility, bendability, high contrast, fast response, etc., and narrow-band full-color emission is a key prerequisite for realizing ultra-high-definition display. Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have become a core candidate for breaking through the performance bottleneck of traditional fluorescent / phosphorescent materials because they have theoretical 100% internal quantum efficiency (IQE) and narrow-band emission characteristics (full width at half maximum (FWHM) < 30 nm).

[0003] However, existing MR-TADF devices still face two major technical bottlenecks: 1. Aggregation-induced emission quenching (ACQ) is serious: traditional MR-TADF materials are based on planar B, N-doped polycyclic aromatic hydrocarbons (B, N-PAHs), which are prone to form strong π-π stacking between molecules, leading to ACQ, and the device efficiency drops by more than 50% at high doping concentrations (> 10 wt%); 2. Poor spectral stability: under high doping or high brightness, excimers are easily formed, leading to red shift of the emission peak (> 20 nm) and widening of the FWHM (e.g., from 25 nm in solution to more than 40 nm in thin film), which destroys the color purity and cannot meet the requirements of color coordinate accuracy for ultra-high-definition display.

[0004] Although researchers have proposed two solutions, both have significant defects: 1. Introducing small steric substituents (such as tert-butyl groups): slightly increasing the intermolecular distance through peripheral small-volume groups can only alleviate ACQ at low doping (< 5 wt%); at high doping (> 10 wt%) or high brightness, aggregation and excimer formation still occur, leading to a drop in efficiency of more than 30% and a red shift of the emission peak of > 15 nm, which cannot meet the needs of mass production for high-doping compatibility and spectral stability. 2. Using a "spatial wrapping" strategy (such as a carbazole unit wrapping): wrapping the MR core with a large-volume conjugated unit to isolate aggregation, although the PLQY (photoluminescence quantum yield) is still > 90% at high doping (20 wt%), but the multi-step precise synthesis leads to complex process, and the peripheral unit is prone to weak conjugation with the core, widening the FWHM to 28-30 nm; meanwhile, it is difficult to match the energy levels, which can easily cause imbalance of charge transport and reduce the efficiency of the device.

[0005] Therefore, it is crucial to develop an MR-TADF material and device that has narrow-band emission, high resistance to aggregation, and high efficiency, which is key to promoting the development of ultra-high-definition OLEDs. SUMMARY

[0006] The present application aims at the deficiencies in the prior art, and provides a narrow-emission fluorescent compound based on a double-spiro skeleton as well as a preparation method and application thereof.The narrow-emission fluorescent compound based on the double-spiro skeleton has a thermally activated delayed fluorescence property, has a narrow-band emission (FWHM<30 nm) and high anti-aggregation (no obvious ACQ under high doping of 5-50 wt %), can be used as a light-emitting layer material of an organic electroluminescent device, and can obtain a light-emitting device with a high-efficiency narrow-emission spectrum, and has good application prospect and economic value.

[0007] To solve the above technical problems, the present application provides, in a first aspect, a narrow-emission fluorescent compound based on a double-spiro skeleton, which has a general structure as shown in the following formula:

[0008]

[0009] In the formula, X is selected from a carbon-carbon single bond, oxygen, sulfur or selenium.

[0010] The narrow-emission fluorescent compound based on the double-spiro skeleton has a thermally activated delayed fluorescence property, and due to its unique double-perpendicular strategy, the molecular distance between adjacent MR cores is significantly increased, so as to effectively inhibit the intermolecular interaction, and meanwhile, the aggregation-induced quenching and spectral broadening phenomena are avoided; the compound has a narrow-band emission (FWHM<30 nm) and high anti-aggregation (no obvious ACQ under high doping of 5-50 wt %), can be used as a light-emitting layer material of an organic electroluminescent device, and can obtain a light-emitting device with a high-efficiency narrow-emission spectrum.

[0011] Further, the narrow-emission fluorescent compound is selected from one of the following structural formulas:

[0012]

[0013] The present application provides, in a second aspect, a preparation method of the narrow-emission fluorescent compound based on the double-spiro skeleton according to the first aspect, which comprises the following steps:

[0014] S1, in an organic solvent, a compound of formula 1 is first reacted with a lithium reagent, then a compound of formula 2 is added for reaction, and finally acid is added for condensation cyclization to obtain a compound of formula 3;

[0015] S2, in an organic solvent, a compound of formula 4 is first reacted with a lithium reagent, then a compound of formula 3 is added for reaction, and finally acid is added for condensation cyclization to obtain a compound of formula 5;

[0016] S3, in an organic solvent, a compound of formula 5, a lithium reagent, a boron halide and an organic amine are sequentially added for reaction to obtain the narrow-emission fluorescent compound;

[0017] The structural formulas of the compounds of formula 1 to formula 5 are as follows:

[0018]

[0019] wherein R is X is selected from a carbon-carbon single bond, oxygen, sulfur or selenium.

[0020] The present application is based on a preparation method of a narrow-emission fluorescent compound based on a double-spiro skeleton, in S1, a compound of formula 1 is first subjected to a metal-halogen exchange substitution reaction with a lithium reagent, then subjected to a nucleophilic addition reaction with a compound of formula 2, and finally subjected to a condensation cyclization reaction under acidic conditions to obtain a compound of formula 3; in S2, a compound of formula 4 is first subjected to a metal-halogen exchange substitution reaction with a lithium reagent, then subjected to a nucleophilic addition reaction with a compound of formula 3, and finally subjected to a condensation cyclization reaction under acidic conditions to obtain a compound of formula 5; the compound of formula 5 is first subjected to a metal-halogen exchange substitution reaction with tert-butyllithium, then subjected to a nucleophilic boronation reaction with boron halide, and finally subjected to an intramolecular nucleophilic aromatic substitution cyclization reaction with N,N-diisopropylethylamine to obtain a narrow-emission fluorescent compound based on a double-spiro skeleton.

[0021] Further, in S1-S2, the lithium reagent is n-butyllithium.

[0022] Further, in S1-S2, the acid is hydrochloric acid and glacial acetic acid.

[0023] Further, in S1-S2, the organic solvent is one or more of tetrahydrofuran, 1,4-dioxane and dimethyl sulfoxide.

[0024] Further, in S3, the lithium reagent is tert-butyllithium.

[0025] Further, in S3, the boron halide is boron tribromide or boron triiodide.

[0026] Further, in S3, the organic amine is N,N-diisopropylethylamine.

[0027] Further, in S3, the organic solvent is one or more of anhydrous and oxygen-free tert-butylbenzene, o-xylene and mesitylene.

[0028] The third aspect of the present application provides the use of the narrow-emission fluorescent compound based on a double-spiro skeleton according to the first aspect in an organic electroluminescent device.

[0029] Further, the narrow-emission fluorescent compound is used for preparing a light-emitting layer of an organic electroluminescent device, and the light-emitting layer is prepared by a vapor deposition method or a solution method.

[0030] The present application has the following beneficial effects:

[0031] The present application is based on a narrow-emission fluorescent compound with a double-spiro skeleton, which has the property of thermally activated delayed fluorescence, and due to its unique double-perpendicular strategy, the intermolecular distance between adjacent MR cores is significantly increased, thereby effectively inhibiting intermolecular interaction, and avoiding the phenomena of aggregation-induced quenching and spectral broadening; it has the properties of narrow-band emission (FWHM<30 nm) and high anti-aggregation (no obvious ACQ under high doping of 5-50 wt%), and can be used as a light-emitting layer material for organic electroluminescent devices, and the prepared OLED device has high luminous efficiency and high color purity. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the present application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application, and other drawings can also be obtained according to these drawings without creative labor for those skilled in the art.

[0033] Figure 1 The hydrogen spectrum of the compound DSB-1 prepared in Example 1 of the present application;

[0034] Figure 2 The carbon spectrum of the compound DSB-1 prepared in Example 1 of the present application;

[0035] Figure 3 The mass spectrum of the compound DSB-1 prepared in Example 1 of the present application;

[0036] Figure 4 The hydrogen spectrum of the compound DSB-2 prepared in Example 2 of the present application;

[0037] Figure 5 The carbon spectrum of the compound DSB-2 prepared in Example 2 of the present application;

[0038] Figure 6 The mass spectrum of the compound DSB-2 prepared in Example 2 of the present application;

[0039] Figure 7 The hydrogen spectrum of the compound DSG-1 prepared in Example 3 of the present application;

[0040] Figure 8 The carbon spectrum of the compound DSG-1 prepared in Example 3 of the present application;

[0041] Figure 9 The mass spectrum of the compound DSG-1 prepared in Example 3 of the present application;

[0042] Figure 10 The hydrogen spectrum of the compound DSG-2 prepared in Example 4 of the present application;

[0043] Figure 11Carbon spectrum of compound DSG-2 prepared in Example 4 of the present application;

[0044] Figure 12 Mass spectrum of compound DSG-2 prepared in Example 4 of the present application;

[0045] Figure 13 Device efficiency graph and electroluminescence spectrum graph of device D1 in Application Example 1 of the present application;

[0046] Figure 14 Device efficiency graph and electroluminescence spectrum graph of device D2 in Application Example 1 of the present application;

[0047] Figure 15 Device efficiency graph and electroluminescence spectrum graph of device D3 in Application Example 1 of the present application;

[0048] Figure 16 Device efficiency graph and electroluminescence spectrum graph of device D4 in Application Example 1 of the present application. DETAILED DESCRIPTION

[0049] The technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0050] Example 1

[0051] This example relates to a preparation method of a narrow-emission fluorescent compound DSB-1 based on a double-spiro skeleton, and the synthetic route is as follows:

[0052]

[0053] Specifically includes the following steps:

[0054] (1) Under a nitrogen atmosphere, compound 9-(6-bromo-3-(4-tert-butylphenoxy)-2- chlorophenyl)-3,6-di-tert-butyl-9H-carbazole (9.00 g, 14.63 mmol) was dissolved in 60 mL of tetrahydrofuran, and the solution was cooled to -78°C. A 2.20 M concentration of n-butyllithium solution (8.00 mL, 17.60 mmol) was slowly added dropwise using a syringe. After stirring for 2 hours, compound anthracene-9,10-dione (6.09 g, 29.25 mmol) was added. After 12 hours of reaction, the reaction was terminated by adding 5 mL of water, and then the solvent was removed under reduced pressure. The resulting solid was dissolved in 160 mL of glacial acetic acid, heated to 120°C, and stirred for half an hour. Then, 15 mL of 36% hydrochloric acid was added, and the reaction was allowed to proceed for 24 hours. The reaction mixture was poured into ice water, and a large amount of solid was precipitated. The solid was separated by silica gel column chromatography (dichloromethane: n-hexane = 1:5) to obtain intermediate A (5.58 g, 7.68 mmol) at a yield of 52.34%, and the results of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) were as follows: molecular ion peak 727.233.

[0055] (2) Under a nitrogen atmosphere, 2-bromo-1,1'-biphenyl (2.87 g, 12.38 mmol) was dissolved in 60 mL of tetrahydrofuran, and the solution was cooled to -78°C. A 2.20 M concentration of n-butyllithium solution (6.75 mL, 14.85 mmol) was slowly added dropwise using a syringe. After stirring for 2 hours, intermediate A (4.50 g, 6.18 mmol) was added. After 12 hours of reaction, the reaction was terminated by adding 5 mL of water, and then the solvent was removed under reduced pressure. The resulting solid was dissolved in 80 mL of glacial acetic acid, heated to 120°C, and stirred for half an hour. Then, 9 mL of 36% hydrochloric acid was added, and the reaction was allowed to proceed for 24 hours. The reaction mixture was poured into ice water, and a large amount of solid was precipitated. The solid was separated by silica gel column chromatography (dichloromethane: n-hexane = 1:10) to obtain intermediate B (3.55 g, 4.11 mmol) at a yield of 42.48%, and the results of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) were as follows: molecular ion peak 863.082.

[0056] (3) under nitrogen atmosphere, intermediate B (2.89 g, 3.35 mmol) was dissolved in 50 mL of mesitylene solution, cooled to -40 °C, then 1.30 M tert-butyllithium solution (5.20 mL, 6.76 mmol) was slowly added, the reaction mixture was slowly warmed to room temperature, then stirred at 90 °C for 3 hours; after completion, 1.00 M boron tribromide solution (7.00 mL, 7.00 mmol) was slowly added at -20 °C, and stirring was continued at room temperature for 3 hours; after 5.00 mL of N,N-diisopropylethylamine was added at 0 °C, the reaction mixture was further stirred at 170 °C for 24 hours; after the reaction was completed, the mixture was extracted with aqueous sodium acetate and dichloromethane three times, 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 DSB-1 (0.61 g, 0.73 mmol) with a yield of 21.68%, and the matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) result: molecular ion peak 837.322. Figure 1 is the hydrogen spectrum of compound DSB-1; Figure 2 is the carbon spectrum of compound DSB-1; Figure 3 is the mass spectrum of compound DSB-1.

[0057] Example 2

[0058] This example relates to a preparation method of a narrow-emission fluorescent compound DSB-2 based on a double-spiro skeleton, and the synthetic route is as follows:

[0059]

[0060] The difference between the preparation method and Example 1 is that 2-bromo-1,1'-biphenyl in step (2) is replaced by an equivalent amount of 2-bromophenyl phenyl sulfide, and other steps and parameters remain unchanged to obtain compound DSB-2 (yield: 25.42%), and the matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) result: molecular ion peak 869.174. Figure 4 is the hydrogen spectrum of compound DSB-2; Figure 5 is the carbon spectrum of compound DSB-2; Figure 6 is the mass spectrum of compound DSB-2.

[0061] Example 3

[0062] This example relates to a preparation method of a narrow-emission fluorescent compound DSG-1 based on a double-spiro skeleton, and the synthetic route is as follows:

[0063]

[0064] The preparation method thereof is different from that of Example 1 in that 9-(6-bromo-3-(4-tert-butylphenoxy)-2-chlorophenyl)-3,6-di-tert-butyl-9H-carbazole is replaced by equivalent amount of 9,9'-(4-bromo-2-chloro-1,3-phenylene)bis(3,6-di-tert-butyl-9H-carbazole) in step (1), and other steps and parameters are unchanged, to obtain compound DSG-1 (yield: 27.82%), and the matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) result is: molecular ion peak 966.443. Figure 7 is the hydrogen spectrum of compound DSG-1; Figure 8 is the carbon spectrum of compound DSG-1; Figure 9 is the mass spectrum of compound DSG-1.

[0065] Example 4

[0066] This example relates to a preparation method of a narrow-emission fluorescent compound DSG-2 based on a double-spiro skeleton, and the synthetic route thereof is as follows:

[0067]

[0068] The preparation method thereof is different from that of Example 3 in that 2-bromo-1,1'-biphenyl is replaced by equivalent amount of 2-bromophenyl phenyl sulfide in step (2), and other steps and parameters are unchanged, to obtain compound DSG-2 (yield 26.33%), and the matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) result is: molecular ion peak 998.139. Figure 10 is the hydrogen spectrum of compound DSG-2; Figure 11 is the carbon spectrum of compound DSG-2; Figure 12 is the mass spectrum of compound DSG-2.

[0069] Comparative Example 1

[0070] This comparative example relates to a preparation method of compound SB, and the synthetic route thereof is as follows:

[0071]

[0072] The preparation method thereof comprises the following steps:

[0073] Under a nitrogen atmosphere, compound 9-(6-bromo-3-(4-tert-butylphenoxy)-2- chlorophenyl)-3,6-di-tert-butyl-9H-carbazole (6.00 g, 9.76 mmol) was dissolved in 60 mL of tetrahydrofuran, and the solution was cooled to -78°C. A 2.20 M concentration of n-butyllithium solution (5.00 mL, 11.00 mmol) was slowly added dropwise using a syringe. After stirring for 2 hours, compound thioxanthone (2.48 g, 11.72 mmol) was added, and the reaction was allowed to proceed for 12 hours. After 5 mL of water was added to terminate the reaction, the solvent was removed under reduced pressure. The resulting solid was dissolved in 80 mL of glacial acetic acid, and the solution was heated to 120°C and stirred for half an hour. Then, 9 mL of 36% hydrochloric acid was added, and the reaction was allowed to proceed for 24 hours. The reaction mixture was poured into ice water, and a large amount of solid was precipitated. The solid was separated by silica gel column chromatography (dichloromethane: n-hexane = 1:5) to obtain intermediate C (4.46 g, yield: 61.01%), and the results of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) were as follows: molecular ion peak 731.719.

[0074] (2) Under a nitrogen atmosphere, intermediate C (2.05 g, 2.73 mmol) was dissolved in 50 mL of mesitylene solution, and the solution was cooled to -40°C. Then, a 1.30 M tert-butyllithium solution (4.20 mL, 5.46 mmol) was slowly added. After the reaction mixture was slowly warmed to room temperature, it was stirred at 90°C for 3 hours. After completion, a 1.00 M boron tribromide solution (7.00 mL, 7.00 mmol) was slowly added at -20°C, and the reaction mixture was further stirred at room temperature for 3 hours. After 5.00 mL of N,N-diisopropylethylamine was added at 0°C, the reaction mixture was further stirred at 170°C for 24 hours. After the reaction was completed, the reaction mixture was extracted with aqueous sodium acetate and dichloromethane three times, and the organic phase was dried over anhydrous magnesium sulfate. After filtration, the organic phase was concentrated under reduced pressure. The crude product was further purified by silica gel column chromatography (dichloromethane: n-hexane = 1:10) to obtain compound SB (0.42 g, 0.57 mmol) as an orange solid, and the yield was 20.51%. The results of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) were as follows: molecular ion peak 705.080.

[0075] Comparative Example 2

[0076] This comparative example relates to a method for preparing compound SG, and the synthetic route thereof is as follows:

[0077]

[0078] The preparation method is different from Comparative Example 1 in that 9-(6-bromo-3-(4-tert-butylphenoxy)-2-chlorophenyl)-3,6-di-tert-butyl-9H-carbazole in step (1) is replaced by equivalent amount of 9,9'-(4-bromo-2-chloro-1,3-phenylene) bis(3,6-di-tert-butyl-9H-carbazole), and other steps and parameters remain unchanged, finally obtaining compound SG (yield: 30.26%). Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS) result: molecular ion peak 834.113.

[0079] Application Example 1

[0080] The organic electroluminescent device based on the compound obtained from the examples and comparative examples has the following specific structure: indium tin oxide (ITO) is used as an anode, bispyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanitrile (HATCN) is used as a hole injection layer (HIL), 4,4'-(cyclohexane-1,1-diyl) bis(N,N-di-p-tolylbenzenamine) (TAPC) is used as a hole transport layer (HTL), 4,4',4"-tris(9H-carbazol-9-yl)triphenylamine (TCTA) is used as an electron blocking layer (EBL), the compound of the examples and comparative examples is used as a guest material doped in 3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl (mCBP) host material as a light-emitting layer (EML), 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine (TmPyPB) is used as an electron transport layer (ETL), lithium fluoride (LiF) is used as an electron injection layer (EIL), and aluminum (Al) is used as a 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 (5-50 wt%) (20 nm) / TmPyPB (40 nm) / LiF (1 nm) / Al (100 nm). The specific preparation process is a conventional technique, and vacuum evaporation is used for preparation.

[0081] Figure 13 The device efficiency graph and electroluminescence spectrum graph of the device D1 with a doping concentration of 5 wt% are shown in FIG. 1; Figure 14 The device efficiency graph and electroluminescence spectrum graph of the device D2 with a doping concentration of 5 wt% are shown in FIG. 2; Figure 15 The device efficiency graph and electroluminescence spectrum graph of the device D3 with a doping concentration of 5 wt% are shown in FIG. 3; Figure 16 The device efficiency graph and electroluminescence spectrum graph of the device D4 with a doping concentration of 5 wt% are shown in FIG. 4. The specific performance parameters of the organic electroluminescent device are shown in Table 1, wherein EL is the electroluminescence wavelength, FWHM is the full width at half maximum, and EQE is the maximum external quantum efficiency. max

[0082] Table 1​

[0083]

[0084]

[0085] As can be seen from Table 1, after the double-spiro narrow-emission fluorescent compound provided by the present application is applied to an electroluminescent device, blue light and green light narrow emission are successfully achieved. More importantly, the application of the material significantly improves the efficiency and color purity of the device, and has the advantages of narrow-band emission (FWHM < 30 nm), high anti-aggregation (no obvious ACQ under high doping of 5-50 wt%), which brings substantial progress to the performance optimization of OLED devices. At the same time, compared with the compound obtained in Comparative Example 1-2, the compound obtained in the present application has better molecular orientation, larger light coupling rate, larger external group, better anti-concentration quenching effect, and obvious improvement in light-emitting external quantum efficiency.

[0086] The present application has been described in detail with reference to specific embodiments and exemplary examples, but these descriptions are not to be construed as limiting the present application. Those skilled in the art understand that various equivalent substitutions, modifications or improvements can be made to the technical solutions and embodiments of the present application without departing from the spirit and scope of the present application, and these all fall within the scope of the present application. The scope of protection of the present application is subject to the appended claims.

Claims

1. A narrow-emission fluorescent compound based on a bispirocyclic framework, characterized in that, The narrow-emission fluorescent compound has the following general structural formula: X is selected from carbon-carbon single bonds, oxygen, sulfur, or selenium.

2. The narrow-emission fluorescent compound based on a bispirocyclic framework as described in claim 1, characterized in that, The narrow-emission fluorescent compound is selected from one of the following structural formulas:

3. A method for preparing a narrow-emission fluorescent compound based on a bispirocyclic framework as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. In an organic solvent, compound 1 reacts with a lithium reagent, then compound 2 is added and reacted, and finally acid is added to perform condensation cyclization to obtain compound 3. S2. In an organic solvent, compound 4 is first reacted with a lithium reagent, then compound 3 is added and reacted, and finally acid is added to carry out condensation cyclization to obtain compound 5. S3. In an organic solvent, add the compound of formula 5, lithium reagent, boron halide, and organic amine in sequence, and react to obtain the narrow emission fluorescent compound; The structural formulas of compounds 1-5 are as follows: Where R is X is selected from carbon-carbon single bonds, oxygen, sulfur, or selenium.

4. The method for preparing a narrow-emission fluorescent compound based on a bispirocyclic framework as described in claim 3, characterized in that, In S1-S2, the lithium reagent is n-butyllithium.

5. The method for preparing a narrow-emission fluorescent compound based on a bispirocyclic framework as described in claim 3, characterized in that, In S1-S2, the acid is hydrochloric acid and glacial acetic acid.

6. The method for preparing a narrow-emission fluorescent compound based on a bispirocyclic framework as described in claim 3, characterized in that, In S3, the lithium reagent is tert-butyllithium.

7. The method for preparing a narrow-emission fluorescent compound based on a bispirocyclic framework as described in claim 3, characterized in that, In S3, the boron halide is boron tribromide or boron triiodide.

8. The method for preparing a narrow-emission fluorescent compound based on a bispirocyclic framework as described in claim 3, characterized in that, In S3, the organic amine is N,N-diisopropylethylamine.

9. The application of a narrow-emission fluorescent compound based on a bispiral framework as described in any one of claims 1-2 in an organic electroluminescent device.

10. The application as described in claim 9, characterized in that, The narrow-emission fluorescent compound is used to prepare the light-emitting layer of an organic electroluminescent device, which is prepared by vapor deposition or solution deposition.

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