Cycloheptatriene pyrrole salt fluorescent dye and preparation method thereof

Abstract

The invention provides a cycloheptatriene pyrrole salt fluorescent dye and a preparation method thereof, overcomes a series of defects of the existing hemicyanine fluorescent dye, and compared with the traditional hemicyanine dye, the cycloheptatriene pyrrole salt fluorescent dye provided by the invention has certain red shift in the maximum absorption wavelength and emission wavelength; the compound C1 and the compound C2 prepared by the embodiment of the invention are verified by a spectrum test, the fluorescence emission wavelength of the compound C1 and the compound C2 is 1020-1050 nm, and the compound C1 and the compound C2 can be well suitable for a scene of long-wavelength fluorescence detection; the cycloheptatriene pyrrole salt fluorescent dye has the advantages of easily available raw materials, low preparation cost, simple operation, high yield, mild reaction conditions, simple synthesis steps, and high commercial application value.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and in particular relates to a cycloheptatriene pyrrole salt fluorescent dye and a preparation method thereof. Background Art

[0002] Since fluorescence imaging technology has the characteristics of non-destructive, high sensitivity and real-time spatial imaging, it is widely used in the identification of various biological small molecules and the study of their biological effects. As the cornerstone of fluorescence imaging technology, fluorescent dyes have also received extensive attention and research from scientific researchers.

[0003] Hemicyanine fluorophores contain a nitrogen heterocyclic electron acceptor, a conjugated linker, and an aromatic donor with a functional end, which together form a unique D-π-A structure. However, especially xanthene-type hemicyanine dyes have absorption and emission in the NIR region, flexible and tunable spectral properties, and good stability. Based on hemicyanines, researchers can develop multifunctional fluorescent probes to monitor important biomolecules or enzymes in living systems through changes in fluorescence and photoacoustic signals, and use chemotherapy, photothermal, photodynamic or combined therapy for diagnosis and treatment.

[0004] At present, the preparation of hemicyanine fluorescent dyes usually adopts quaternary salts with active (acidic) methyl at the 2-position or 4-position, such as quaternary salts of 2-methylpyridine (α-pyridine / 2-pyridine), 2-methylquinoline (quinoline), 4-methylpyridine (γ-pyridine / 4-pyridine) and 4-methylquinoline. Most of them are quaternary salts with five-membered rings and six-membered rings as the main components, while the present invention introduces a seven-membered heterocyclic pyrrole quaternary salt to construct a hemicyanine fluorescent dye. The emission wavelength of existing hemicyanine fluorescent molecules is usually short, and they are easily interfered by biological background fluorescence during imaging and analysis. The fluorescence emission wavelength of the cycloheptatriene pyrrole salt and its fluorescent dye of the present invention can reach the near-infrared region II. Summary of the invention

[0005] To overcome a series of defects of existing fluorescent dyes, the present invention provides a class of cycloheptatriene pyrrole salt fluorescent dyes and preparation methods thereof. The present invention is a hemicyanine fluorescent dye of a seven-membered heterocyclic pyrrole salt, which is not a traditional five-membered ring or six-membered ring pyrrole or pyridinium salt category. The cycloheptatriene pyrrole salt fluorescent dye of the present invention has a certain red shift compared to the maximum absorption wavelength and emission wavelength of traditional hemicyanine dyes. Compound C1 and compound C2 prepared in the embodiments of the present application are verified by spectral testing, and their fluorescence emission wavelength is between 1020nm-1050nm, which can be well applied to the scene of long-wavelength fluorescence detection. This class of cycloheptatriene pyrrole salts and their fluorescent dyes are easy to obtain and have low cost, simple operation, high yield, mild reaction conditions and simple synthesis steps, and have high commercial application value.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A type of cycloheptatriene pyrrole salt fluorescent dye, the general structural formula is as follows:

[0008]

[0009] R1 is selected from hydrogen, alkyl with 1-18 carbons; R2 is selected from hydrogen, alkyl with 1-18 carbons, aryl, benzyl; R3 is selected from hydrogen, hydroxyl, methoxy; Y is selected from halogen ion, ClO4 - 、BF4 - 、CH3COO - CF3COO - or OTs - .

[0010] A method for preparing a cycloheptatriene pyrrole salt fluorescent dye, comprising:

[0011] Step S1: Preparation of intermediate compound A-1

[0012] 2,5-hexanedione, an amine containing a substituent R1, and aminosulfonic acid are stirred at room temperature, and after extraction, a compound A-1 containing a substituent R1 is obtained;

[0013] Step S2: Preparation of intermediate compound A-2

[0014] Dissolve compound A-1 in DMF, add POCl3 and stir at room temperature. After the reaction is completed, pour the solution into a mixture of sodium acetate and ice water and stir. After forming a solid suspension, filter, wash and air-dry to obtain intermediate compound A-2.

[0015] Step S3: Preparation of intermediate compound A-3

[0016] Dissolve compound A-2 in ethanol, add a ketone containing a substituent R2, and then add a sodium hydroxide aqueous solution; stir the mixture at room temperature, then extract, concentrate, and purify to obtain an intermediate compound A-3 containing R1 and R2 substitutions;

[0017] Step S4: Preparation of intermediate compound A-4

[0018] Compound A-3 is dissolved in THF under anhydrous and oxygen-free conditions, CH3MgCl is added, and then an inorganic acid is added, and after extraction, concentration, and purification, an intermediate compound A-4 containing R1 and R2 substituents is obtained;

[0019] Step S5: Preparation of intermediate compound B-1

[0020] PBr3, DMF and CHCl3 are added to cyclohexanone and stirred at room temperature for neutralization reaction; then compound B-1 is obtained by extraction, washing and drying;

[0021] Step S6: Preparation of intermediate compound B-2

[0022] Compound B-1, salicylaldehyde containing R3 substituent, and Cs2CO3 are dissolved in DMF and stirred at room temperature, and then extracted, concentrated, and purified to obtain intermediate compound B-2 containing R3 substituent;

[0023] Step S7: Preparation of Compound C

[0024] Compound B-2 and compound A-4 are dissolved in acetic anhydride, triethylamine is added, and the mixture is heated, condensed and refluxed. Compound C is obtained after extraction, concentration and purification;

[0025] The reaction process is as follows:

[0026]

[0027] R1 is selected from hydrogen, alkyl with 1-18 carbon atoms; R2 is selected from hydrogen, alkyl with 1-18 carbon atoms, aryl, benzyl; R3 is selected from hydrogen, hydroxyl, methoxy; Y is selected from halogen ion, ClO4 - 、BF4 - 、CH3COO - CF3COO - or OTs - .

[0028] Furthermore, in the step S1, the prepared compound A-1 is extracted with ether, then extracted with dichloromethane and water, the organic layer is dried over Na2SO4, filtered, and concentrated in vacuo to obtain compound A-1; in the step S1, the molar ratio of 2,5-hexanedione and the amine containing the substituent R1 is 1:1.1-1.5 equivalents, and aminosulfonic acid is a catalytic amount.

[0029] Furthermore, in step S2, the mass ratio of sodium acetate to ice in the sodium acetate-ice-water mixture is 1:6; the mass ratio of compound A-1 to sodium acetate is 12.24:100; and the washing solvent is distilled water.

[0030] Furthermore, in step S3, the molar ratio of compound A-2 to the ketone containing the substituent R2 is 1:1.1; the mass concentration of the sodium hydroxide aqueous solution is 10%; extraction is performed with distilled water and dichloromethane; the concentration method is reduced pressure distillation; the crude product is purified by column chromatography, and the column chromatography eluent is petroleum ether and ethyl acetate.

[0031] Furthermore, in step S4, extraction is performed using distilled water and dichloromethane; the concentration method is vacuum distillation; and the crude product is purified by recrystallization.

[0032] Furthermore, in step S5, the molar ratio of PBr3 to cyclohexanone is 130.5:48.4; the reaction is neutralized with a saturated sodium bicarbonate solution, and extracted with dichloromethane and distilled water.

[0033] Furthermore, in step S6, the molar ratio of compound B-1, salicylaldehyde containing R3 substituent, and Cs2CO3 is 5.4:4.5:13.5; washing with H2O; drying the organic layer over Na2SO4, filtering, and concentrating in vacuo; and purification by silica gel column chromatography.

[0034] Furthermore, in step S7, the molar ratio of compound B-2 to compound A-4 is 1:1.2; after extraction with dichloromethane solvent and water, the solvent is evaporated and concentrated, purified by silica gel column chromatography, and then recrystallized with dichloromethane and ethyl acetate to obtain compound C.

[0035] The fluorescent dye is applied in the scenario of long-wavelength fluorescence detection.

[0036] Beneficial Effects

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. The fluorescent dye raw materials of the cycloheptatrienolpyrrole salt described in the present invention are easily available, easy to operate, high in yield and simple in synthesis steps, and have high commercial application value.

[0039] 2. The maximum absorption wavelength and emission wavelength of the cycloheptatriene pyrrole salt fluorescent dye of the present invention are red-shifted compared to the traditional hemicyanine dye. Compound C1 and Compound C2 prepared in the examples of the present application were verified by spectral testing, and their fluorescence emission wavelengths were between 1020nm-1050nm, which can be well applied to the scene of long-wavelength fluorescence detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a general synthesis route of cycloheptatrienolpyrrole salt fluorescent dyes in the embodiments of the present invention;

[0041] Figure 2 is a synthetic route diagram of compound C1 in Example 1 of the present invention;

[0042] Figure 3 is the H NMR spectrum of compound C1 prepared in Example 1 of the present invention;

[0043] Figure 4 is the NMR carbon spectrum of compound C1 prepared in Example 1 of the present invention;

[0044] Figure 5 is the mass spectrum of compound C1 prepared in Example 1 of the present invention;

[0045] Figure 6 is the fluorescence emission spectrum of compound C1 prepared in Example 1 of the present invention at an excitation wavelength of 808 nm;

[0046] Figure 7 is a synthetic route diagram of compound C2 in Example 2 of the present invention;

[0047] Figure 8 is the H NMR spectrum of compound C2 prepared in Example 2 of the present invention;

[0048] Fig. 9 is the NMR carbon spectrum of compound C2 prepared in Example 2 of the present invention;

[0049] Fig.10 is the mass spectrum of compound C2 prepared in Example 2 of the present invention;

[0050] Fig.11 This is the fluorescence emission spectrum of compound C2 prepared in Example 1 of the present invention at an excitation wavelength of 808 nm. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] Embodiment 1:

[0053] Figure 1 The general synthesis route of the cycloheptatriene pyrrolidine salt fluorescent dye in the embodiments of the present invention is shown in FIG. 1 ; the synthesis of compound C1 is performed as an example:

[0054] The synthetic route of compound C1 is as follows Figure 2 As shown, the synthesis of compound C1 was carried out according to the synthetic route:

[0055] 1. Preparation of Compound A-1

[0056] 2,5-Hexanedione (5.70 g, 0.05 mmol) and n-butylamine (4.38 g, 0.06 mmol) were added to a 100 mL round-bottom flask equipped with a magnetic stirrer, and 10 mol% aminosulfonic acid was added. Stir at room temperature for 12 h, and after the reaction, the mixture was extracted with ether (2×10 mL), followed by extraction with dichloromethane and water. The organic layer was dried over Na2SO4, filtered, and concentrated in vacuo to obtain compound A-1 (4.3 g, Y=57.0%).

[0057] 2. Preparation of Compound A-2

[0058] In a 250 mL round bottom flask equipped with a magnetic stir bar and a thermometer, 12.24 g of compound A-1 was added, followed by 60 mL of DMF. The flask was cooled in an ice bath, and the mixture was treated with 19 mL of POCl3 in 1 mL units. In the first 8 mL, a strong exotherm was generated for each 1 mL, causing the solution to warm from 10 degrees Celsius to 20 degrees Celsius. After the first 8 mL, the addition of phosphorus oxychloride produced almost no temperature increase. After the addition of POCl3, the ice bath was removed, and the flask containing the light orange solution was placed in an oil bath, which was then heated to 100 degrees Celsius. After heating for two hours, the oil bath was removed and the solution was allowed to cool for 15 minutes. The solution was then poured into a mixture of 600 grams of ice cubes and 100 grams of sodium acetate and stirred. After 25 minutes, a gray solid suspension was formed. The mixture was filtered, and the solid was washed with 2×100 ml of water and air-dried to obtain compound A-2 (10.24 g, Y=60.99%).

[0059] 3. Preparation of Compound A-3

[0060] The material of compound A-2 (1.03 g, 5 mmol) was dissolved in ethanol at room temperature, 5.5 mmol 3-pentanone was added to the solution in 3 ml ethanol very slowly in the form of drops (3 hours), and then 4 ml of a mixture of water and sodium hydroxide solution (10% mass concentration) was added. The mixture was stirred at room temperature, and then 10 ml of water was added. The aqueous phase was extracted 5 times, each time with 15 ml of chloroform. The organic phase was dried over anhydrous MgSO4 and then evaporated. The residue was chromatographed on an aluminum column using thioether / chloroform = 75 / 25 as eluent. Compound A-3 (0.37 g, Y = 28.9%) was collected.

[0061] 4. Preparation of Compound A-4

[0062] Compound A-3 (2.58 g, 10 mmol) was added to anhydrous ether (15 mL), and the Grignard reagent prepared by conventional methods by adding magnesium (1.03 g, 43.5 mmol) and methyl iodide (6.2 g, 174 mmol) to anhydrous reagent-grade ether (50 mL) was added dropwise under argon at room temperature. The solution partially changed color due to the precipitation of a yellow solid. The obtained mixture was stirred at 40 ° C, and then the solvent was evaporated in vacuo, and then a mixture of acetic acid (20 mL) and HBF4 (50%, 15 mL) was added. The obtained blue solution was poured into water (250 mL). After 12 h, it was extracted with dichloromethane (3*50 ml) and dried with Na2SO4. After the solvent was evaporated, the solid was fermented with ether and then recrystallized from isopropanol to obtain compound A-4 (2.37 g, Y=75.2%).

[0063] 5. Preparation of Compound B-1

[0064] At 0°C, PBr3 (12.4 mL, 130.5 mmol) was dropped into a mixture of DMF (11.2 mL) and chloroform (50 mL). After stirring for 45 min, cyclohexanone (5 mL, 48.4 mmol) was added. The resulting solution was stirred at room temperature for 16 h, then poured into 50 mL of ice water, neutralized with solid NaHCO3, and extracted with dichloromethane. The layers were separated and the aqueous layer was extracted with CH2Cl2 (100 mL). The organic layer was dried over Na2SO4, filtered, and concentrated in vacuo to obtain the target compound B-1 (7.2 g, 38.52 mmol, Y = 75.7%).

[0065] 6. Preparation of Compound B-2

[0066] At room temperature, compound B-1 (1.02 g, 5.4 mmol) was dissolved in DMF (30 mL) and 2-hydroxy-4-methoxybenzaldehyde (685 mg, 4.5 mmol) and Cs2CO3 (4.4 g, 13.5 mmol) were added. Stirring was carried out at 25 °C for 16 h, and a strong yellow spot appeared on the TLC plate (hexane: AcOEt = 8:2). The insoluble matter was filtered on a silica gel pad and the filtrate was concentrated. The obtained residue was diluted with dichloromethane (150 ml) and washed with H2O (10×15 mL). The organic layer was dried over Na2SO4, filtered, and concentrated in vacuo. Purified by silica gel column chromatography (CH2Cl2: AcOEt = 20:1), compound B-2 was a dark yellow solid (0.72 g, Y = 65.8%).

[0067] 7. Preparation of Compound C1

[0068] At 100°C, compound B-2 (484 mg, 2 mmol, 1 eq) and compound A-4 (857 mg, 2.4 mmol, 1.2 eq) were dissolved in 30 mL of acetic anhydride, and 2 mL of triethylamine was added to catalyze the reaction. The reaction progress was monitored by TLC, and the reaction was stopped after stirring for 1-24 h. The solvent was then evaporated after extraction with dichloromethane solvent and water, and the mixture was purified by silica gel column chromatography (CH2Cl2:MeOH=20:1), and then recrystallized from dichloromethane and ethyl acetate to obtain compound C1 (403 mg, 0.84 mmol, Y=42.0%).

[0069] Figure 3 is the H NMR spectrum of compound C1 prepared in Example 1 of the present invention; Figure 4 is the NMR carbon spectrum of compound C1 prepared in Example 1 of the present invention; Figure 5 It is the mass spectrum of compound C1 prepared in Example 1 of the present invention.

[0070] 1 H NMR (600MHz, CDCl3) δ = 8.20 (s, 2H), 7.93 (d, J = 15.0Hz 1H),7.14(d,J=8.5Hz,1H),6.82(s,1H),6.77(s,1H),6.65-6.70(m,2H),4.29(t,J=7.2Hz,2H),3.88(s,3H),2.72(s,6H),2.71(s, 6H),2.64(t,J=5.4Hz,2H),2.59(t,J=6.0Hz,2H),1.87-1.90(m,2H),1.84-1.86(m,2H),1.40-1.47(m,2H),0.98(t,J=7.8Hz,3H).

[0071] 13 C NMR (100MHz, CDCl3) δ = 168.5, 162.9, 156.3, 154.3, 141.9, 140.4, 134.7, 130.8, 128.9, 127.7, 127.2, 124.8, 124.0, 116. 0,115.0,113.5,112.4,101.6,100.4,68.0,56.1,46.3,41.0,32.3,29.7,29.4,29.0,25.6,24.1,21.1,20.1,13.7,10.1.

[0072] ESI-MS (m / z): calculated value: 480.29, spectrum display: 480.3.

[0073] Embodiment 2:

[0074] Figure 1 The general synthesis route of the cycloheptatriene pyrrolidine salt fluorescent dye in the embodiment of the present invention is shown; the synthesis of compound C2 is performed as an example:

[0075] Synthesis route diagram Figure 7 As shown, the synthesis of compound C2 was carried out according to the synthetic route:

[0076] 1. Preparation of compound B-3

[0077] At 0°C, a mixed solution of BBr3 (1.5 mL) and CH2Cl2 (3 mL) was added to a solution of compound B-2 (2.42 g, 10 mmol) in anhydrous CH2Cl2 (25 mL) in Example 1. The resulting mixture was stirred at 0°C overnight, and then quenched with water. After filtration, silica gel chromatography was performed using CH2Cl2:CH3OH (20:1) as the eluent to obtain compound B-3 (1.45 g, Y=63.5%).

[0078] 2. Preparation of Compound C2

[0079] At 100°C, compound B-3 (338 mg, 1.5 mmol, 1 eq) and compound A-4 (589 mg, 1.65 mmol, 1.1 eq) were dissolved in 20 mL of acetic anhydride, and 1.0-2.0 mL of triethylamine was added to catalyze the reaction. The reaction progress was monitored by TLC, and the reaction was stopped after stirring for 1-24 h. The solvent was then evaporated after extraction with dichloromethane solvent and water, and the mixture was purified by silica gel column chromatography (CH2Cl2:MeOH=20:1), and then recrystallized from dichloromethane and ethyl acetate to obtain compound 2 (324 mg, 0.73 mmol, Y=48.4%).

[0080] Figure 8 is the H NMR spectrum of compound C2 prepared in Example 2 of the present invention; Fig. 9 is the NMR carbon spectrum of compound C2 prepared in Example 2 of the present invention; Fig.10 is the mass spectrum of compound C2 prepared in Example 2 of the present invention;

[0081] 1H NMR (400MHz, CDCl3) δ = 8.49 (s, 2H), 7.54 (d, J = 15.9Hz, 1H), 7.11 (d, J = 8.0Hz, 1H),6.86(s,1H),6.76-6.79(m,1H),6.70(d,J=16.0Hz,1H),6.54(s,1H),4.45 (t,J=8.0Hz,2H),2.84(s,6H),2.74(s,6H),2.57-2.65(m,2H),2.30(s,2H),1 .85-1.93(m,2H),1.76-1.84(m,2H),1.44-1.54(m,2H),1.02(t,J=7.2Hz,3H).

[0082] 13 C NMR (100MHz, CDCl3) δ = 169.1, 168.0, 153.1, 151.5, 144.9 (3C), 136.2 (2C), 132.1 (2C), 130.1 (2C), 126.7, 126. 3,125.5,124.0,119.8,116.9,112.1,109.1,47.3,32.2,29.7,28.9,24.4,21.1,20.7,20.1,18.39,13.6,10.2.

[0083] ESI-MS (m / z): [M+MeCN] + Calculated value: 508.27, spectrum display: 508.3.

[0084] Embodiment 3:

[0085] Fluorescence spectrum test of compound C1 and compound C2:

[0086] like Figure 6 As shown, 10.0 μM compound C1 was placed in dichloromethane, dimethyl sulfoxide, and PBS buffer, and the fluorescence emission spectra of different solutions were measured under 808 nm laser excitation. Compound C1 exhibited strong fluorescence in the NIR-II region, with the maximum emission peak between 1000 and 1200 nm.

[0087] like Fig.11 As shown, 10.0 μM compound C2 was placed in dichloromethane, dimethyl sulfoxide, and PBS buffer, and the fluorescence emission spectra of different solutions were measured under 808 nm laser excitation. Compound C2 exhibited strong fluorescence in the NIR-II region, with the maximum emission peak between 1000 and 1200 nm.

[0088] In summary, the present invention discloses a method for preparing a cycloheptatriene pyrrole salt fluorescent dye. The cycloheptatriene pyrrole salt and its fluorescent dye of the present invention have a certain red shift compared to the maximum absorption wavelength and emission wavelength of traditional hemicyanine dyes. Compound C1 and compound C2 prepared in the embodiment of the present application are verified by spectral testing, and their fluorescence emission wavelength is between 1020nm-1050nm, which can be well applied to the scene of long-wavelength fluorescence detection. Such cycloheptatriene pyrrole salt and its fluorescent dye raw materials are easy to obtain and low in cost, easy to operate, high in yield, mild in reaction conditions and simple in synthesis steps, and have high commercial application value.

[0089] Finally, it should be noted that the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article, or apparatus.

[0090] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0091] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A cycloheptatriene pyrrole salt fluorescent dye, characterized in that: The cycloheptatriene pyrrole salt fluorescent dye has the following general structural formula: R1 is selected from hydrogen, alkyl with 1-18 carbons; R2 is selected from hydrogen, alkyl with 1-18 carbons, aryl, benzyl; R3 is selected from hydrogen, hydroxyl, methoxy; Y is selected from halogen ion, ClO4 - 、BF4 - 、CH3COO - CF3COO - or OTs - .

2. A method for preparing a cycloheptatriene pyrrole salt fluorescent dye, characterized in that: The preparation method comprises: Step S1: Preparation of intermediate compound A-1 2,5-hexanedione, an amine containing a substituent R1, and aminosulfonic acid are stirred at room temperature, and after extraction, a compound A-1 containing a substituent R1 is obtained; Step S2: Preparation of intermediate compound A-2 Dissolve compound A-1 in DMF, add POCl3 and stir at room temperature. After the reaction is completed, pour the solution into a mixture of sodium acetate and ice water and stir. After forming a solid suspension, filter, wash and air-dry to obtain intermediate compound A-2. Step S3: Preparation of intermediate compound A-3 Dissolve compound A-2 in ethanol, add a ketone containing a substituent R2, and then add a sodium hydroxide aqueous solution; stir the mixture at room temperature, then extract, concentrate, and purify to obtain an intermediate compound A-3 containing R1 and R2 substitutions; Step S4: Preparation of intermediate compound A-4 Compound A-3 is dissolved in THF under anhydrous and oxygen-free conditions, CH3MgCl is added, and then an inorganic acid is added, and after extraction, concentration, and purification, an intermediate compound A-4 containing R1 and R2 substituents is obtained; Step S5: Preparation of intermediate compound B-1 PBr3, DMF and CHCl3 are added to cyclohexanone and stirred at room temperature for neutralization reaction; then compound B-1 is obtained by extraction, washing and drying; Step S6: Preparation of intermediate compound B-2 Compound B-1, salicylaldehyde containing R3 substituent, and Cs2CO3 are dissolved in DMF and stirred at room temperature, and then extracted, concentrated, and purified to obtain intermediate compound B-2 containing R3 substituent; Step S7: Preparation of Compound C Compound B-2 and compound A-4 are dissolved in acetic anhydride, triethylamine is added, and the mixture is heated, condensed and refluxed. Compound C is obtained after extraction, concentration and purification; The reaction process is as follows: R1 is selected from hydrogen, alkyl with 1-18 carbon atoms; R2 is selected from hydrogen, alkyl with 1-18 carbon atoms, aryl, benzyl; R3 is selected from hydrogen, hydroxyl, methoxy; Y is selected from halogen ion, ClO4 - 、BF4 - 、CH3COO - CF3COO - or OTs - .

3. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In the step S1, the prepared compound A-1 is extracted with ether, then extracted with dichloromethane and water, the organic layer is dried over Na2SO4, filtered, and concentrated in vacuo to obtain compound A-1; in the step S1, the molar ratio of 2,5-hexanedione and the amine containing the substituent R1 is 1:1.1-1.5 equivalents, and aminosulfonic acid is a catalytic amount.

4. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In step S2, the mass ratio of sodium acetate to ice in the sodium acetate-ice-water mixture is 1:6; the mass ratio of compound A-1 to sodium acetate is 12.24:100; and the washing solvent is distilled water.

5. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In the step S3, the molar ratio of compound A-2 to the ketone containing the substituent R2 is 1:1.1; the mass concentration of the sodium hydroxide aqueous solution is 10%; extraction is performed with distilled water and dichloromethane; the concentration method is reduced pressure distillation; the crude product is purified by column chromatography, and the column chromatography eluent is petroleum ether and ethyl acetate.

6. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In the step S4, extraction is performed using distilled water and dichloromethane; the concentration method is vacuum distillation; and the crude product is purified by recrystallization.

7. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In the step S5, the molar ratio of PBr3 to cyclohexanone is 130.5:48.4; the reaction is neutralized with a saturated sodium bicarbonate solution, and extracted with dichloromethane and distilled water.

8. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In the step S6, the molar ratio of compound B-1, salicylaldehyde containing R3 substituent and Cs2CO3 is 5.4:4.5:13.5; washing with H2O; the organic layer is dried over Na2SO4, filtered, concentrated in vacuo and purified by silica gel column chromatography.

9. The method for preparing a cycloheptatriene pyrrole salt fluorescent dye as claimed in claim 2, characterized in that: In the step S7, the molar ratio of compound B-2 to compound A-4 is 1:1.2; after extraction with dichloromethane solvent and water, the solvent is evaporated and concentrated, purified by silica gel column chromatography, and then recrystallized by dichloromethane and ethyl acetate to obtain compound C.

10. The cycloheptatrienolpyrrole salt fluorescent dye as claimed in claim 1 or the cycloheptatrienolpyrrole salt fluorescent dye prepared by the preparation method of any one of claims 2 to 9, characterized in that: The fluorescent dye is applied in the scenario of long-wavelength fluorescence detection.

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