Preparation method and application of flexible fluorescent sensing film based on fluorescent probe

Abstract

The application discloses a preparation method of a flexible fluorescent sensing film based on a fluorescent probe. The molecule of the fluorescent probe is a 1,8-naphthalimide derivative as a core unit, a nitrogen heterocyclic butane modified naphthalene acetylene is introduced at one end of the molecule, and an alkyl chain with different lengths is connected at the other end through a condensation reaction. The fluorescent probe is uniformly mixed with triacetate cellulose by a physical mixing method to prepare a spinning solution, and a flexible fluorescent sensing film is prepared by an electrostatic spinning technology. The preparation method of the flexible fluorescent sensing film based on the fluorescent probe is used for sensitive detection of a peroxide explosive TATP.

Description

Technical Field

[0001] This invention belongs to the field of concealed explosive detection technology, specifically relating to a method for preparing and applying a flexible fluorescent sensing film based on a fluorescent probe. Background Technology

[0002] TATP (triacetone triperoxide, chemical formula C9H6O6) is a high-energy compound, also known as triacetone triperoxide. It is a white or pale yellow crystal with high explosiveness and sensitivity, requiring extreme care in handling and storage. In contrast to its destructive power, TATP is relatively simple to prepare, generated directly from hydrogen peroxide (H2O2) and acetone (C3H6O) under acidic conditions. The explosiveness of TATP primarily stems from the peroxy bonds in its molecule. These bonds are easily broken by impact, friction, or high temperatures, leading to rapid decomposition and the release of large amounts of gas and energy, thus triggering an explosion. Due to its ease of preparation, high destructive power, and lack of nitrogen, it easily evades detection by most explosive detectors, making TATP a key target for security checks.

[0003] Fluorescent molecular probe technology, due to its high sensitivity and fast response speed, has gradually become an important means of detecting trace amounts of hazardous chemicals. Fluorescent sensing films, prepared by fixing sensing units onto the surface of a flexible substrate using physical or chemical methods, represent a promising device for detecting trace substances. They offer advantages such as simple operation, portability, adjustable size, and non-contamination of the analyte system, greatly promoting research into the currently popular field of smart wearable materials. In particular, the combination of fluorescence sensing technology and electrospinning technology to prepare nanofiber fluorescent sensing films has become a research hotspot in recent years.

[0004] TATP exhibits poor stability at room temperature, readily decomposing into acetone and H2O2. Therefore, researchers often detect TATP by detecting acetone or H2O2. For example, the research groups of Cheng Jiangong and He Qingguo at the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, developed a novel fluorescent hyperbranched polymer with a borate ester-terminated pyrene-fluorene alternating copolymer backbone, achieving rapid and sensitive detection of TATP through its sensitive response to H2O2 vapor. The research group of Fang Yu at Shaanxi Normal University synthesized a fluorescent compound based on a naphthalimide structure (DNNDI), using it in the preparation of fluorescent sensing films. They successfully developed a low-cost, highly sensitive, portable, and reusable paper-based fluorescent sensor for detecting TATP through vapor sampling.

[0005] Although thin-film fluorescent sensors have made some progress in the field of explosives detection, many problems still exist, such as the limited range of detectable explosives, poor photochemical stability of the films, and low ability to distinguish and identify complex samples. Therefore, there is an urgent need to develop a fluorescent sensing film with good photochemical stability, reusability, and strong anti-interference ability, as well as to accelerate the deviceization and integration of thin-film fluorescent sensors to promote their industrial application. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a flexible fluorescent sensing film based on a fluorescent probe for the sensitive detection of TATP, a peroxide-based explosive.

[0007] To address the aforementioned technical problems, this invention discloses a method for preparing a flexible fluorescent sensing film based on a fluorescent probe. The fluorescent probe molecule uses a 1,8-naphthalimide derivative as the core unit, with a naphthaleneacetylene modified with azacyclobutane introduced at one end, and alkyl chains of different lengths introduced at the other end via a condensation reaction. The fluorescent probe is uniformly mixed with triacetate cellulose using a physical mixing method to prepare a spinning solution, and the flexible fluorescent sensing film is prepared by electrospinning technology. The structural formula of the fluorescent probe is as follows:

[0008]

[0009] In the structural formula, n is 1, 2, 3, or 4.

[0010] The technical solution of the present invention also has the following characteristics:

[0011] As a preferred embodiment of the present invention, the synthesis of the fluorescent probe is specifically carried out according to the following steps:

[0012] Step 1, Synthesis of compound N2: 6-Bromo-2-naphthol was weighed and placed in a round-bottom flask. Redistilled dichloromethane and anhydrous pyridine were added. Trifluoromethanesulfonate was added dropwise to the reaction solution under ice bath conditions, and the mixture was stirred at room temperature for 12 hours. The molar ratio of 6-Bromo-2-naphthol, trifluoromethanesulfonate, pyridine, and dichloromethane was 1:(1-2):(5-10):(10-30). The reaction was monitored throughout by TLC. After the reactants had completely reacted, the reaction solution was transferred to a pear-shaped flask and the solvent was evaporated. After dilution with ethyl acetate, the solution was extracted, dried, concentrated, and purified by column chromatography to obtain compound N2.

[0013]

[0014] Step 2, Synthesis of Compound N3: Compound N2, palladium acetate, 1,1′-binaphthyl-2,2′-bis(diphenylphosphine) (BINAP), and cesium carbonate were weighed and placed in a two-necked flask equipped with a condenser. The reaction apparatus was sealed and connected to a double-row tube system. Three evacuations and nitrogen replacements were performed to ensure the reaction system was in an anhydrous and oxygen-free environment. Then, toluene and azacyclobutane were injected separately. The molar ratio of compound N2, palladium acetate, 1,1′-binaphthyl-2,2′-bis(diphenylphosphine) (BINAP), cesium carbonate, azacyclobutane, and toluene was... The reaction ratio was 1:(0.1~0.3):(0.2~0.4):(1.5~3):(1.5~3):(30~50). The reaction was observed after heating to 100℃ in an oil bath, followed by reflux and stirring for 18 hours. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored by TLC. After the reactants had completely reacted, the reaction was terminated. The mixture was allowed to cool naturally to room temperature, then transferred to a pear-shaped flask and the solvent was evaporated. After dilution with dichloromethane, the mixture was extracted, dried, concentrated, and purified by column chromatography to obtain compound N3.

[0015]

[0016] Step 3, Synthesis of Compound N4: Compound N3, tetra(triphenylphosphine)palladium, and cuprous iodide were weighed and placed in a two-necked flask equipped with a condenser. The reaction apparatus was connected to a double-row tube system and evacuated three times to ensure the reaction system was in an anhydrous and oxygen-free environment. Diisopropylamine, toluene, and trimethylsilylacetylene were then sequentially added to the two-necked flask. The molar ratio of compound N3, tetra(triphenylphosphine)palladium, cuprous iodide, trimethylsilylacetylene, diisopropylamine, and toluene was 1:(0.05–0.2):( The reaction mixture was prepared by heating the oil bath to 100°C until reflux occurred, followed by continuous stirring for 12 hours. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored by TLC. After the reactants had completely reacted, the reaction was terminated. The mixture was allowed to cool to room temperature, then transferred to a pear-shaped flask and the solvent was evaporated. After dilution with dichloromethane, the mixture was extracted, dried, concentrated, and purified by column chromatography to obtain compound N4.

[0017]

[0018] Step 4, Synthesis of compound N5: Compound N4 was weighed and placed in a round-bottom flask, dissolved in anhydrous tetrahydrofuran, and then a 1 mol / L tetrabutylammonium fluoride tetrahydrofuran solution was added. The molar ratio of compound N4, tetrabutylammonium fluoride, and tetrahydrofuran was 1:(5-10):(30-50). The mixture was stirred at room temperature for 4 hours, and the reaction was monitored by TLC. The reaction was terminated after complete reaction. After dilution with dichloromethane, the product was extracted, dried, concentrated, and purified by column chromatography to obtain compound N5.

[0019]

[0020] Step 5, Synthesis of Compound 2: Weigh 4-bromo-1,8-naphthalenedicarboxylic anhydride and place it in a two-necked flask equipped with a condenser. Add anhydrous ethanol and N-Boc-diaminoalkane sequentially. The molar ratio of 4-Br-1,8-naphthalenedicarboxylic anhydride, N-Boc-diaminoalkane, and anhydrous ethanol is 1:(1.5~2):(30~50). Heat the mixture in an oil bath to 100℃, reflux the system, and stir continuously for 12 hours. Monitor the entire reaction process using a TLC plate. After the reactants have completely reacted, terminate the reaction. Allow the mixture to cool to room temperature naturally, then filter, wash, and collect the filter cake. Transfer the cake to a pear-shaped flask and remove residual dichloromethane and ethanol solvent by rotary evaporation to obtain Compound 2.

[0021]

[0022] In the above formula, n is 1, 2, 3, or 4.

[0023] Step 6, Synthesis of compound NADCA: Compound 2, compound N5, tetratetraphenylphosphine palladium, and cuprous iodide were weighed and placed in a two-necked flask. The reaction apparatus was connected to a double-row tube system and evacuated three times for nitrogen exchange. Toluene and triethylamine were injected into the reaction flask respectively. The molar ratio of compound N5, compound 2, tetratetraphenylphosphine palladium, cuprous iodide, triethylamine, and toluene was 1:(1.2-1.5):(0.1-0.2):(0.1-0.3):(10-20):(30-50). The system was heated to 100°C in an oil bath and stirred continuously for 12 hours after reflux. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored by TLC plate. After the reactants had completely reacted, the reaction was terminated. After cooling to room temperature, the reaction solution was transferred to a pear-shaped flask and the solvent was evaporated. After dilution with dichloromethane, the solution was extracted, dried, concentrated, and purified by column chromatography to obtain compound NADCA.

[0024] As a preferred embodiment of the present invention, the preparation of the flexible fluorescent sensing film specifically involves:

[0025] Step 7: Weigh out the fluorescent compound NADCA and cellulose triacetate (CTA) separately, dissolve them in a mixed solvent of dimethyl sulfoxide and dichloromethane, stir at room temperature, and after standing / ultrasonic degassing, obtain CTA@NADCA spinning solutions with different mass fractions.

[0026] Step 8: Using a JDF 05 electrospinning apparatus, CTA@NADCA spinning solution was drawn into the syringe and fixed onto the injection pump. The distance between the needle and the receiver was adjusted, and the receiving roller was selected as the receiving device. A layer of release paper was applied to the receiving roller. The spinning chamber door was closed, the origin of the needle movement was set, and the spinning parameters were adjusted before starting the electrospinning machine. The solution was collected at room temperature for 4 hours. After collection, the power was turned off, the release paper was removed, and the solution was placed in a vacuum oven at 40°C for at least 2 hours to remove the solvent. Finally, the prepared film was placed in a dark and dry place for use.

[0027] In a preferred embodiment of the present invention, in step 1, the extraction is carried out sequentially using a 5% hydrochloric acid aqueous solution, a saturated sodium bicarbonate aqueous solution, and a saturated sodium chloride aqueous solution; the drying is performed using anhydrous sodium sulfate for 2 hours; and the column chromatography separation and purification is carried out using petroleum ether as the eluent.

[0028] In step 2, the extraction is carried out sequentially using distilled water and saturated sodium chloride solution; the drying is carried out using anhydrous sodium sulfate for 2 hours; the column chromatography separation and purification is carried out using a mixed solvent of petroleum ether and ethyl acetate at a volume ratio of (15-30):1 as the eluent for column separation.

[0029] In step 3, the extraction is carried out sequentially using saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution; the drying is carried out by drying with anhydrous sodium sulfate for 2 hours; the column chromatography separation and purification is carried out by using a mixed solvent of petroleum ether and dichloromethane at a volume ratio of (6-10):1 as the eluent for column separation.

[0030] In a preferred embodiment of the present invention, in step 4, the extraction is carried out sequentially using saturated sodium bicarbonate solution and saturated sodium chloride solution; the drying is carried out by drying with anhydrous sodium sulfate for 2 hours; and the column chromatography separation and purification is carried out by using a mixed solvent of petroleum ether and dichloromethane in a volume ratio of (6-10):1 as the eluent for column separation.

[0031] In a preferred embodiment of the present invention, in step 5, the washing is performed 6 to 7 times with ethanol and dichloromethane. The N-Boc-diaminoalkane is any one of N-Boc-1,2-diaminoethane, N-Boc-1,4-diaminobutane, N-Boc-1,6-diaminohexane, and N-Boc-1,8-diaminooctane.

[0032] In a preferred embodiment of the present invention, in step 6, the extraction is carried out sequentially using saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution; the drying is carried out by drying with anhydrous sodium sulfate for 2 hours; and the column chromatography separation and purification is carried out by using a mixed solvent of dichloromethane and ethyl acetate in a volume ratio of (10-20):1 as the eluent for column separation.

[0033] In a preferred embodiment of the present invention, in step 7, the stirring time is 12h to 20h.

[0034] In a preferred embodiment of the present invention, in step 8, the extraction volume is 6 ml to 8 mL; the receiving distance is 10 cm to 15 cm; and the spinning parameters are: roller speed of 300 r / min, spinning voltage of 14 kV to 20 kV, needle reciprocating distance of 80 mm to 100 mm, and syringe advance speed of 0.6 mL / h to 1.0 mL / h.

[0035] As a preferred embodiment of the present invention, the flexible fluorescent sensing film obtained by the preparation method of the flexible fluorescent sensing film based on the fluorescent probe is applied in the detection of peroxide explosives, wherein the explosive is triacetone triperoxide (TATP).

[0036] Compared with existing technologies, this invention provides a method for preparing a flexible fluorescent sensing film based on a fluorescent probe. The 1,8-naphthalimide derivative possesses characteristics such as a large Stokes shift, good photochemical stability, ease of modification, sensitivity to the microenvironment, and rich fluorescence output signals, making it an ideal sensing unit for preparing fluorescent sensing films. We designed and synthesized a D-π-A type fluorescent molecular probe (NADCA) by incorporating a naphthaleneacetylene with a nitrogen-containing butane end at the 4 position of 1,8-naphthalimide. Photophysical studies showed that this fluorescent compound exhibits strong sensitivity to the polarity of its environment. Subsequently, a film was prepared using electrospinning technology, and its photophysical properties were systematically tested. Furthermore, the CTA@NADCA film can achieve a rapid (<1s), sensitive (detection limit as low as 10.9 ppb), and highly selective response to trace amounts of acetone vapor, and can be reused multiple times. Since acetone is the main decomposition product of TATP, a peroxide-based explosive, we investigated the sensing behavior of the thin film for trace amounts of TATP. The results showed that the prepared CTA@NADCA thin film can be used for the field detection of explosive TATP. Attached Figure Description

[0037] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0038] Figure 1 This is the UV-Vis absorption spectrum of the fluorescent probe based on 1,8-naphthalimide derivative prepared in Example 1 of this invention;

[0039] Figure 2 This is the fluorescence spectrum of the fluorescent probe based on the 1,8-naphthalimide derivative prepared in Example 1 of the present invention;

[0040] Figure 3 This is an experimental spectrum of the sensitivity of the flexible fluorescent film prepared in Example 1 of the present invention to acetone vapor;

[0041] Figure 4 This is a repeatable experimental spectrum of the flexible fluorescent film prepared in Example 1 of the present invention for acetone vapor;

[0042] Figure 5 This is an experimental spectrum of the resistance to acetone vapor of the flexible fluorescent film prepared in Example 1 of the present invention;

[0043] Figure 6 This is the sensitivity spectrum of the flexible fluorescent film prepared in Example 1 of this invention to TATP. Detailed Implementation

[0044] The flexible fluorescent sensing film obtained by the preparation method of the flexible fluorescent probe based on the present invention has high sensitivity, good selectivity and rapid response; the synthesis method of the fluorescent probe and the preparation method of the film are simple to operate, have low equipment requirements and are suitable for large-scale production; the fluorescent film can be widely used in the detection of TATP.

[0045] This invention is achieved through the following technical solution:

[0046] First, a 1,8-naphthalimide derivative fluorescent probe was synthesized. The structural formula of the fluorescent probe is as follows:

[0047]

[0048] In the formula, n is 1, 2, 3, or 4. The specific synthesis route is as follows:

[0049]

[0050] The method for synthesizing the 1,8-naphthalimide derivative fluorescent probe of the present invention includes the following steps:

[0051] Step 1: Synthesize compound N2;

[0052] Weigh 6-Br-2-naphthol into a 100 mL round-bottom flask, add 25 mL of redistilled dichloromethane and 3.6 mL of anhydrous pyridine. Under ice bath conditions, add trifluoromethanesulfonate dropwise to the reaction solution. The molar ratio of 6-bromo-2-naphthol, trifluoromethanesulfonate, pyridine, and dichloromethane used in the reaction is 1:(1–2):(5–10):(10–30), and stir at room temperature for 12 h. Monitor the entire reaction process using TLC. After the reactants have completely reacted, transfer the reaction solution to a pear-shaped flask and evaporate the solvent. Dilute with 200 mL of ethyl acetate, and extract successively with 5% hydrochloric acid aqueous solution, saturated sodium bicarbonate aqueous solution, and saturated sodium chloride aqueous solution. Collect the organic phase and dry it with anhydrous sodium sulfate for 2 h. After drying, filter using a sintered glass funnel. Collect the filtrate, concentrate it, and separate it by column chromatography (eluent: petroleum ether) to obtain compound N2.

[0053]

[0054] Step 2, synthesize compound N3;

[0055] Compound N2, palladium acetate, 1,1′-binaphthyl-2,2′-bis(diphenylphosphine) (BINAP), and cesium carbonate were weighed and placed in a 250 mL two-necked flask equipped with a condenser. The reaction apparatus was sealed and connected to a double-row tube system, and the system was evacuated three times to ensure an anhydrous and oxygen-free environment. Toluene and azacyclobutane were then injected. The molar ratio of N2, palladium acetate, 1,1′-binaphthyl-2,2′-bis(diphenylphosphine) (BINAP), cesium carbonate, azacyclobutane, and toluene was 1:(0.1–0.3):(0.2–0.4):(1.5–3):(1.5–3):(30–50). The reaction was observed to produce reflux after being heated to 100 °C in an oil bath, and then stirred continuously for 18 h. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored throughout by TLC. Once the reactants had completely reacted, the reaction was terminated. After cooling to room temperature, the reaction solution was transferred to a pear-shaped flask and the solvent was evaporated. The solution was diluted with 100 mL of dichloromethane and extracted successively with distilled water and saturated sodium chloride solution. The organic phase was dried over anhydrous sodium sulfate for 2 h. After drying, the solution was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and then separated by column chromatography (eluent: petroleum ether: ethyl acetate = 15–30: 1) to obtain compound N3.

[0056]

[0057] Step 3: Synthesize compound N4;

[0058] Compound N3, tetraphenylphosphine palladium, and cuprous iodide were weighed and placed in a 100 mL two-necked flask equipped with a condenser. The reaction apparatus was connected to a double-row tube system and evacuated three times to ensure an anhydrous and oxygen-free environment. 10 mL of diisopropylamine, 25 mL of toluene, and trimethylsilylacetylene were then sequentially added to the flask. The molar ratio of N3, tetraphenylphosphine palladium, cuprous iodide, trimethylsilylacetylene, diisopropylamine, and toluene was 1:(0.05–0.2):(0.05–0.2):(1.5–2):(10–20):(30–50). The system was heated in an oil bath to 100 °C until reflux occurred, and then stirred continuously for 12 h. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored by TLC. After the reactants had completely reacted, the reaction was terminated. The mixture was allowed to cool to room temperature, then transferred to a pear-shaped flask and the solvent was evaporated. After dilution with dichloromethane (100 mL), the organic phase was extracted sequentially with saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the mixture was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and then separated by column chromatography (eluent: petroleum ether: dichloromethane = 6–10:1) to obtain compound N4.

[0059]

[0060] Step 4: Synthesize compound N5;

[0061] A certain amount of compound N4 was weighed and placed in a 50 mL round-bottom flask, dissolved in anhydrous tetrahydrofuran (15 mL), and then a 1 mol / L tetrabutylammonium fluoride tetrahydrofuran solution (5 mL) was added. The molar ratio of compound N4, tetrabutylammonium fluoride, and tetrahydrofuran was 1:(5-10):(30-50). The mixture was stirred at room temperature for 4 h, and the reaction was monitored by TLC. The reaction was terminated after the reactants had completely reacted. The mixture was diluted with dichloromethane, and then extracted successively with saturated sodium bicarbonate solution and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the mixture was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and separated by column chromatography (eluent: petroleum ether: dichloromethane = 6-10:1) to obtain compound N5.

[0062]

[0063] Step 5, synthesize compound 2;

[0064] Weigh 4-Br-1,8-naphthalenedicarboxylic anhydride into a 100 mL two-necked flask equipped with a condenser. Add anhydrous ethanol and N-Boc-diaminoalkane sequentially. The molar ratio of 4-Br-1,8-naphthalenedicarboxylic anhydride, N-Boc-diaminoalkane, and anhydrous ethanol used in the reaction is 1:(1.5–2):(30–50). Heat the system in an oil bath to 100 °C until reflux occurs, then stir continuously for 12 h. Monitor the entire reaction process using a TLC plate. After the reactants have completely reacted, terminate the reaction and allow it to cool to room temperature. Filter the mixture, washing away impurities with ethanol and dichloromethane, respectively. Collect the filter cake and transfer it to a pear-shaped flask. Rotary evaporation removes residual dichloromethane and ethanol solvent, yielding compound 2.

[0065]

[0066] The aforementioned N-Boc-diaminoalkane is any one of N-Boc-1,2-diaminoethane, N-Boc-1,4-diaminobutane, N-Boc-1,6-diaminohexane, and N-Boc-1,8-diaminooctane.

[0067] Step 6: Synthesize compound NADCA;

[0068] Compound N5, compound 2, tetraphenylphosphine palladium, and cuprous iodide were weighed into 25 mL two-necked flasks according to a molar ratio of 1:(1.2~1.5):(0.1~0.2):(0.1~0.3). The reaction apparatus was connected to a double-row tube system and evacuated three times for nitrogen replacement. Toluene and triethylamine were injected into the reaction flasks respectively. The molar ratio of compound N5, compound 2, tetraphenylphosphine palladium, cuprous iodide, triethylamine and toluene was 1:(1.2~1.5):(0.1~0.2):(0.1~0.3):(10~20):(30~50). The system was heated to 100℃ in an oil bath and stirred continuously for 12 h after reflux. The entire reaction was carried out in a nitrogen atmosphere. After dilution with dichloromethane (50 mL), the organic phase was extracted sequentially with saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the organic phase was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and separated by column chromatography (eluent: dichloromethane: ethyl acetate = 10-20:1) to obtain the compound NADCA.

[0069] A method for preparing a flexible fluorescent sensing film includes the following steps:

[0070] Step 7, Preparation of spinning solution;

[0071] A mixed solution of fluorescent probe NADCA and triacetyl cellulose (CTA) in dimethyl sulfoxide (DMSO) and dichloromethane (DCM) was prepared, wherein the mass ratio of NADCA, CTA, DMSO and DCM was 1:(300-400):(2000-2500):(700-800). The solution was stirred on a stirrer at room temperature for 12-20 hours, and after standing / ultrasonic degassing, CTA@NADCA spinning solutions with different mass fractions were obtained.

[0072] Step 8, Thin film preparation;

[0073] A JDF 05 electrospinning apparatus was used. 6–8 mL of LTA@NADCA spinning solution was drawn using a 10 mL syringe and fixed to the syringe pump. A 20G spinneret was selected, and the distance between the needle and receiver was adjusted to 10–15 cm. A receiving roller was selected as the receiving device, and a layer of release paper was applied to it. The spinning chamber door was then closed, the origin of the needle movement was set, and the spinning parameters were adjusted (roller speed 300 r / min, spinning voltage 14–20 kV, needle reciprocating distance 80–100 mm, syringe advance speed 0.6–1.0 mL / h). The electrospinning machine was then started, and the solution was collected for 4 hours at room temperature and 45% humidity. After collection, the power was turned off, the release paper was carefully removed, and the solution was placed in a vacuum oven at 40°C for at least 2 hours to remove the solvent. The solution was then collected and stored in a dark, dry place for later use.

[0074] The above-mentioned electrospun thin film based on a 1,8-naphthalimide derivative fluorescent probe is used in the detection of peroxide explosives, wherein the peroxide explosive is triacetone triperoxide (TATP), and the detection method is as follows:

[0075] 1. Preparation of TATP

[0076] Under ice bath conditions, 0.2 mL (2.7 mmol) of acetone was added to a 5 mL test tube. While stirring with a magnetic stirrer, 0.348 mL (3.375 mmol) of 30% hydrogen peroxide was added. Then, under ice bath conditions, 0.225 mL (2.7 mmol) of 37% concentrated hydrochloric acid was added dropwise. A white flocculent precipitate gradually appeared in the test tube. The mixture was kept in an ice bath with continuous stirring for 1 hour, then allowed to rise naturally to room temperature, and stirring continued for 24 hours. After the reaction was complete, the filter cake was collected after multiple washes with water and allowed to dry naturally at room temperature. Then, TATP was transferred to a sample vial using a non-metallic spatula and sealed for storage in a refrigerator at 2-8°C for later use. All utensils used in the reaction, filtration, and transfer processes were washed with 5% hydrochloric acid aqueous solution to decompose residual TATP.

[0077] 2. Detect the sample to be tested

[0078] We placed different masses of TATP powder into multiple 500mL glass sample vials and sealed them to prevent leakage. The vials were then sealed and placed in a dark, dry place for 24 hours. The gas above the solid inside the vial was considered to be the saturated vapor of acetone and hydrogen peroxide released during the decomposition of TATP. For sensing tests, fluorescence characterization was performed using an FS5 fluorescence spectrometer. The fluorescent film was cut to an appropriate size, placed in a dedicated four-way cuvette, and fitted with a silicone cap with a pinhole. A 20mL syringe with a metal needle was used to draw gas from the headspace of the sealed sample vial, which was then injected into the cuvette. The gas was then blown directly onto the surface of the fluorescent film. After stabilization for a period of time, fluorescence testing was performed. To ensure accuracy and repeatability, the temperature, humidity, and atmospheric pressure of the testing environment were recorded in real time during the tests, and the sensing test for each gas was repeated at least five times.

[0079] The electrospun thin film based on the 1,8-naphthalimide derivative fluorescent probe of this invention has good chemical stability, fast response speed and good selectivity, and can be directly detected. Using FS5, handheld ultraviolet lamp or other similar optical detectors, efficient detection of TATP can be achieved.

[0080] Example 1

[0081] This invention discloses a method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe.

[0082] First, a 1,8-naphthalimide derivative fluorescent probe with the following structural formula was synthesized:

[0083]

[0084] Its synthesis method includes the following steps:

[0085] Step 1: Synthesize compound N2;

[0086] Weigh 6-Br-2-naphthol into a 100 mL round-bottom flask, add 25 mL of redistilled dichloromethane and 3.6 mL of anhydrous pyridine. Under ice bath conditions, add trifluoromethanesulfonate dropwise to the reaction solution. The molar ratio of 6-bromo-2-naphthol, trifluoromethanesulfonate, pyridine, and dichloromethane used in the reaction is 1:1:5:10, and stir at room temperature for 12 h. Monitor the entire reaction process using TLC. After the reactants have completely reacted, transfer the reaction solution to a pear-shaped flask and evaporate the solvent. Dilute with 200 mL of ethyl acetate, and extract successively with 5% hydrochloric acid aqueous solution, saturated sodium bicarbonate aqueous solution, and saturated sodium chloride aqueous solution. Collect the organic phase and dry it with anhydrous sodium sulfate for 2 h. After drying, filter using a sintered glass funnel. Collect the filtrate, concentrate it, and separate it by column chromatography (eluent: petroleum ether) to obtain compound N2.

[0087]

[0088] Step 2, synthesize compound N3;

[0089] Compound N2, palladium acetate, 1,1′-binaphthyl-2,2′-bis(diphenylphosphine) (BINAP), and cesium carbonate were weighed and placed in a 250 mL two-necked flask equipped with a condenser. The reaction apparatus was sealed and connected to a double-row tube system, and the system was evacuated three times to ensure an anhydrous and oxygen-free environment. Toluene and azacyclobutane were then added. The molar ratio of N2, palladium acetate, 1,1′-binaphthyl-2,2′-bis(diphenylphosphine) (BINAP), cesium carbonate, azacyclobutane, and toluene was 1:0.1:0.2:1.5:1.5:30. The reaction was observed to be heated to 100 °C in an oil bath until reflux occurred, and then stirred continuously for 18 h. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored by TLC. After the reactants had completely reacted, the reaction was terminated, allowed to cool naturally to room temperature, and then transferred to a pear-shaped flask and the solvent was evaporated. After dilution with dichloromethane (100 mL), the organic phase was extracted successively with distilled water and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the mixture was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and separated by column chromatography (eluent: petroleum ether: ethyl acetate = 15:1) to obtain compound N3.

[0090]

[0091] Step 3: Synthesize compound N4;

[0092] Compound N3, tetraphenylphosphine palladium, and cuprous iodide were weighed and placed in a 100 mL two-necked flask equipped with a condenser. The reaction apparatus was connected to a double-row tube system and evacuated three times to ensure an anhydrous and oxygen-free environment. 10 mL of diisopropylamine, 25 mL of toluene, and trimethylsilylacetylene were then added sequentially to the flask. The molar ratio of N3, tetraphenylphosphine palladium, cuprous iodide, trimethylsilylacetylene, diisopropylamine, and toluene was 1:0.05:0.05:1.5:10:30. The system was heated in an oil bath to 100 °C until reflux occurred, and then stirred continuously for 12 h. The entire reaction was carried out under a nitrogen atmosphere. The reaction was monitored by TLC. After the reactants had completely reacted, the reaction was terminated. The mixture was allowed to cool to room temperature, then transferred to a pear-shaped flask and the solvent was evaporated. After dilution with dichloromethane (100 mL), the organic phase was extracted sequentially with saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the mixture was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and then separated by column chromatography (eluent: petroleum ether: dichloromethane = 6:1) to obtain compound N4.

[0093]

[0094] Step 4: Synthesize compound N5;

[0095] A certain amount of compound N4 was weighed and placed in a 50 mL round-bottom flask, dissolved in anhydrous tetrahydrofuran (15 mL), and then a 1 mol / L tetrabutylammonium fluoride tetrahydrofuran solution (5 mL) was added. The molar ratio of compound N4, tetrabutylammonium fluoride, and tetrahydrofuran was 1:5:30. The mixture was stirred at room temperature for 4 h, and the reaction was monitored by TLC. The reaction was terminated after the reactants had completely reacted. The mixture was diluted with dichloromethane, and then extracted successively with saturated sodium bicarbonate solution and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the mixture was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and separated by column chromatography (eluent: petroleum ether: dichloromethane = 6:1) to obtain compound N5.

[0096]

[0097] Step 5, synthesize compound 2;

[0098] Weigh 4-Br-1,8-naphthalenedicarboxylic anhydride into a 100 mL two-necked flask equipped with a condenser. Add anhydrous ethanol and N-Boc-diaminoalkane sequentially. The molar ratio of 4-Br-1,8-naphthalenedicarboxylic anhydride, N-Boc-diaminoalkane, and anhydrous ethanol used in the reaction is 1:1.5:30. Heat the system in an oil bath to 100 °C until reflux occurs, then stir continuously for 12 h. Monitor the entire reaction process using a TLC plate. After the reactants have completely reacted, terminate the reaction and allow it to cool to room temperature. Filter the mixture, washing away impurities with ethanol and dichloromethane, respectively. Collect the filter cake and transfer it to a pear-shaped flask. Rotary evaporation removes residual dichloromethane and ethanol solvent, yielding compound 2.

[0099]

[0100] Step 6: Synthesize NADCA;

[0101] Compound N5, compound 2, tetraphenylphosphine palladium, and cuprous iodide were weighed into 25 mL two-necked flasks in a molar ratio of 1:1.2:0.1:0.1. The reaction apparatus was connected to a double-row tube system and evacuated three times for nitrogen replacement. Toluene and triethylamine were injected into the reaction flasks respectively. The molar ratio of compound N5, compound 2, tetraphenylphosphine palladium, cuprous iodide, triethylamine, and toluene was 1:1.2:0.1:0.1:10:30. The system was heated in an oil bath to 100 °C until reflux occurred, and then stirred continuously for 12 h. The entire reaction was carried out under a nitrogen atmosphere. After dilution with dichloromethane (50 mL), the mixture was extracted sequentially with saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The organic phase was dried with anhydrous sodium sulfate for 2 h. After drying, the mixture was filtered using a sintered glass funnel. The filtrate was collected, concentrated, and separated by column chromatography (eluent: dichloromethane: ethyl acetate = 10:1) to obtain compound NADCA.

[0102]

[0103] The above NMR data based on the 1,8-naphthalimide derivative fluorescent probe NADCA are as follows: 1 H NMR(400MHz,Chloroform-d)δ8.80(t,J=6.4Hz,1H),8.63(d,J=6.3Hz,1H),8.55(t,J=6.6Hz,1H),8.04(d, J=4.9Hz,1H),7.95(t,J=6.6Hz,1H),7.84(q,J=7.1Hz,1H),7.71(t,J=6.7Hz,1H),7.64(t,J=6.6Hz,1H),7. 57(t,J=6.7Hz,1H),6.83(t,J=6.6Hz,1H),6.64(s,1H),4.17(q,J=6.9Hz,2H),4.04(q,J=6.8Hz,4H),3.23– 2.99(m,2H),2.45(h,J=7.3,6.9Hz,2H),1.80–1.69(m,2H),1.44(d,J=4.9Hz,12H),0.85(d,J=22.3Hz,2H).

[0104] Step 7, Preparation of spinning solution;

[0105] A mixed solution of fluorescent probe NADCA and triacetyl cellulose (CTA) in dimethyl sulfoxide (DMSO) and dichloromethane (DCM) was prepared, wherein the mass ratio of NADCA, CTA, DMSO and DCM was 1:(300-400):(2000-2500):(700-800). The solution was stirred on a stirrer at room temperature for 12-20 hours, and after standing / ultrasonic degassing, CTA@NADCA spinning solutions with different mass fractions were obtained.

[0106] Step 8, Thin film preparation;

[0107] A JDF 05 electrospinning apparatus was used. 6–8 mL of LTA@NADCA spinning solution was drawn using a 10 mL syringe and fixed to the syringe pump. A 20G spinneret was selected, and the distance between the needle and receiver was adjusted to 10–15 cm. A receiving roller was selected as the receiving device, and a layer of release paper was applied to it. The spinning chamber door was then closed, the origin of the needle movement was set, and the spinning parameters were adjusted (spinning voltage 14–20 kV, needle reciprocating distance 40–100 mm, syringe advance speed 0.4–1.0 mL / h). The electrospinning machine was then started, and the solution was collected for 4 hours at room temperature and 45% humidity. After collection, the power was turned off, the release paper was carefully removed, and the solution was placed in a vacuum oven to dry for at least 2 hours to remove the solvent. The solution was then collected and stored in a dark, dry place for later use.

[0108] The photophysical properties of the synthesized fluorescent probe based on 1,8-naphthalimide derivatives were tested using the following methods:

[0109] (1) Prepare the solution.

[0110] The basic photophysical properties of NADCA in homogeneous phase were tested, including its UV / Vis absorption and fluorescence spectra in different solvents and at different concentrations in the same solvent. First, a stock solution was prepared by weighing 1 mg of NADCA powder and placing it in a 5 mL sample vial. 1.7 mL of dichloromethane, a good solvent, was then used to dissolve the powder, resulting in a 1×10⁻⁶ solution. -3 The mother liquor of M is diluted as needed for subsequent experiments.

[0111] (2) Ultraviolet-visible absorption spectroscopy test.

[0112] First, we examined the compound at a concentration of 1×10⁻⁶. -5 The UV-Vis absorption spectra of M in different solvents are shown in the following figures. Figure 1 As shown in Figure a, it was found that the shape of the absorption spectrum and the position of the strongest absorption peak of the compound did not show a regular change in different solvents, indicating that the absorption properties of this compound are not significantly affected by the polarity or structure of the solvent. Subsequently, its UV-Vis absorption spectra in 1,4-dioxane solutions of different concentrations were tested, as shown in Figure a. Figure 1 As shown in b, the absorption spectrum of NADCA is mainly distributed in two bands: 280-340 nm and 390-520 nm. Its strongest absorption peaks are located at 330 nm and 440 nm, corresponding to the electronic transition processes π→π* and n→π*, respectively.

[0113] (3) Fluorescence spectroscopy test.

[0114] To investigate the fluorescence properties of NADCA in solution, we tested its fluorescence spectra as a function of concentration in different solvent systems and within the same solvent system, using 440 nm as the excitation light. Figure 2 As shown in Figure a, with increasing solvent polarity, the fluorescence emission wavelength of NADCA exhibits a significant red shift (500 nm to 603 nm), demonstrating that NADCA is highly sensitive to changes in solvent polarity, showing a large fluorescence change even with small polarity variations. Figure 2 Figure b shows the change in fluorescence intensity of NADCA in 1,4-dioxane solvent as a function of solution concentration. Initially, the fluorescence intensity of compound NADCA gradually increases with increasing solution concentration. When the concentration is 2 × 10⁻⁶, the fluorescence intensity increases further. -5 Its fluorescence intensity reaches its maximum at concentration M, and the fluorescence intensity gradually weakens as the concentration continues to increase, proving that there is an aggregation-induced fluorescence quenching (ACQ) phenomenon.

[0115] The above-mentioned electrospun thin film based on a 1,8-naphthalimide derivative fluorescent probe is used in the detection of peroxide explosives, wherein the peroxide explosive is triacetone triperoxide (TATP), and the detection method is as follows:

[0116] (1) Preparation of TATP

[0117] Under ice bath conditions, 0.2 mL (2.7 mmol) of acetone was added to a 5 mL test tube. While stirring with a magnetic stirrer, 0.348 mL (3.375 mmol) of 30% hydrogen peroxide was added. Then, under ice bath conditions, 0.225 mL (2.7 mmol) of 37% concentrated hydrochloric acid was added dropwise. A white flocculent precipitate gradually appeared in the test tube. The mixture was kept in an ice bath with continuous stirring for 1 hour, then allowed to rise naturally to room temperature, and stirring continued for 24 hours. After the reaction was complete, the filter cake was collected after multiple washes with water and allowed to dry naturally at room temperature. Then, TATP was transferred to a sample vial using a non-metallic spatula and sealed for storage in a refrigerator at 2-8°C for later use. All utensils used in the reaction, filtration, and transfer processes were washed with 5% hydrochloric acid aqueous solution to decompose residual TATP.

[0118] (2) Detecting the sample to be tested

[0119] To investigate the photophysical properties of NADCA, we detected different types of volatile organic gases. Our study revealed that the prepared CTA@NADCA film exhibited a significant quenching response to acetone vapor. Since acetone is a decomposition product of the peroxide explosive TATP, we first examined the film's response to acetone vapor using fluorescence sensing on an FS5 fluorescence spectrometer.

[0120] First, equal masses of acetone were placed in ten glass sample vials with volume gradients ranging from 20 to 500 mL. The vials were sealed with rubber stoppers to prevent gas leakage. The vials were then placed in a dark, dry place for 24 hours. Under these conditions, the gas above the liquid inside the vial was considered its saturated vapor. A fluorescent film was placed in a cuvette, and different concentrations of acetone gas were injected using a syringe. After stabilization for a period of time, fluorescence testing was performed. To ensure accuracy and repeatability, the temperature, humidity, and atmospheric pressure of the testing environment were recorded in real time during the testing period, and the tests for different concentrations of acetone gas were repeated at least five times.

[0121] The test of the detection limit of the thin film for acetone gas, such as Figure 3 As shown, the film still exhibits fluorescence quenching at an acetone gas concentration of 27 ppb, with a more pronounced quenching effect as the concentration increases. Within the concentration range of 27 ppb to 3.4 ppm, the fluorescence intensity of the CTA@NADCA nanofiber film shows a good linear correlation with the acetone gas concentration; when the concentration increases to 221 ppm, the film fluorescence is completely quenched. Based on the test results, the theoretical detection limit DL for acetone gas of the CTA@NADCA film can be calculated to be 10.9 ppb.

[0122] Repeatability testing of the thin film for acetone gas detection, such as... Figure 4 As shown, we conducted more than ten detection / recovery cycle tests on the prepared CTA@NADCA fluorescent film and recorded the data from the first ten cycles. It can be seen that the CTA@NADCA film's response to acetone gas is almost instantaneous and completely quenched, and the sensing process is completely reversible. After each detection, the fluorescence intensity can be almost completely recovered to the initial value. After ten cycles, the fluorescence intensity of the film showed no significant attenuation, indicating that the film has excellent repeatability and meets the requirements for long-term use.

[0123] Selectivity testing of the thin film for acetone gas detection was conducted, selecting 18 potential interfering substances for detection at a concentration of 300 ppm for each gas. TATP was also tested, and the results are as follows. Figure 5 As shown in the figure, the CTA@NADCA nanofiber film we prepared can achieve selective detection of acetone gas in practical applications. Furthermore, the film also exhibits a sensitive response to TATP, with a quenching efficiency of approximately 51% for TATP and a quenching efficiency as high as 99% for acetone, indicating that this fluorescent film can achieve highly selective detection of trace amounts of TATP in the environment.

[0124] A systematic study of the sensing behavior of the prepared fluorescent thin film showed that the CTA@NADCA film can achieve rapid, sensitive, repeatable, and highly selective detection of acetone gas, and can be extended to the field detection of peroxide explosives (TATP). To further determine the sensitivity of the film for TATP detection, we synthesized trace amounts of TATP and placed different masses of TATP in glass containers of the same volume, stored them in a dark place for 24 hours to allow them to decompose, and then performed sensitivity tests. The results are as follows: Figure 6 As shown, it can achieve sensitive detection of at least 8 μg of TATP in the environment.

[0125] In summary, the electrospun nanofiber membrane based on 1,8-naphthalimide derivatives of this invention has good photochemical stability and strong fluorescence quantum efficiency, and can achieve highly selective and sensitive response to trace amounts of acetone gas and peroxide explosives TATP, and can be reused.

[0126] Example 2

[0127] The present invention provides a method for preparing a flexible fluorescent sensing film based on a fluorescent probe, which differs from Example 1 in that the synthesized fluorescent probe based on a 1,8-naphthalimide derivative has the following structural formula:

[0128]

[0129] The synthesis method steps are as follows:

[0130] In step 5 of the synthesis based on the 1,8-naphthalimide derivative in Example 1, the N-Boc-diaminohexane used was replaced with an equimolar mass of N-Boc-1,2-diaminoethane, and the other steps were the same as in the corresponding Example 1.

[0131] Example 3

[0132] The present invention provides a method for preparing a flexible fluorescent sensing film based on a fluorescent probe, which differs from Example 1 in that the synthesized fluorescent probe based on a 1,8-naphthalimide derivative has the following structural formula:

[0133]

[0134] In step 5 of the synthesis based on the 1,8-naphthalimide derivative in Example 1, the N-Boc-diaminohexane used was replaced with an equimolar mass of N-Boc-1,4-diaminobutane, and the other steps were the same as in the corresponding Example 1.

[0135] Example 4

[0136] The present invention provides a method for preparing a flexible fluorescent sensing film based on a fluorescent probe, which differs from Example 1 in that the synthesized fluorescent probe based on a 1,8-naphthalimide derivative has the following structural formula:

[0137]

[0138] In step 5 of the synthesis based on the 1,8-naphthalimide derivative in Example 1, the N-Boc-diaminohexane used was replaced with an equimolar mass of N-Boc-1,8-diaminooctane, and the other steps were the same as in the corresponding Example 1.

Claims

1. A method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe, characterized in that, The fluorescent probe molecule uses a 1,8-naphthalimide derivative as its core unit, with a naphthaleneacetylene modified with azacyclobutane introduced at one end and alkyl chains of different lengths introduced at the other end via a condensation reaction. The fluorescent probe is uniformly mixed with triacetate cellulose using a physical mixing method to prepare a spinning solution, and a flexible fluorescent sensing film is prepared by electrospinning. The structural formula of the fluorescent probe is as follows: ； In the structural formula, n is 1, 2, 3, or 4; The synthesis of the fluorescent probe is carried out according to the following steps: Step 1, Synthesis of compound N2: 6-Bromo-2-naphthol was weighed and placed in a round-bottom flask. Redistilled dichloromethane and anhydrous pyridine were added. Trifluoromethanesulfonate was added dropwise to the reaction solution under ice bath conditions, and the mixture was stirred at room temperature for 12 hours. The molar ratio of 6-Bromo-2-naphthol, trifluoromethanesulfonate, pyridine, and dichloromethane was 1:(1~2):(5~10):(10~30). The reaction was monitored throughout by TLC. After the reactants had completely reacted, the reaction solution was transferred to a pear-shaped flask and the solvent was evaporated. After dilution with ethyl acetate, the solution was extracted, dried, concentrated, and purified by column chromatography to obtain compound N2. ； Step 2, Synthesis of Compound N3: Compound N2, palladium acetate, 1,1'-binaphthyl-2,2'-bis(diphenylphosphine) (BINAP), and cesium carbonate were weighed and placed in a two-necked flask equipped with a condenser. The reaction apparatus was sealed and connected to a double-row tube system. Three evacuations and nitrogen replacements were performed to ensure the reaction system was in an anhydrous and oxygen-free environment. Toluene and azacyclobutane were then injected. The molar ratio of compound N2, palladium acetate, 1,1'-binaphthyl-2,2'-bis(diphenylphosphine) (BINAP), cesium carbonate, azacyclobutane, and toluene was 1:(0.1~0.3):(0.2~0.4):(1.5~3):(1.5~3):(30~50). The reaction was observed. After heating to 100 °C in an oil bath, the system refluxed and was continuously stirred for 18 minutes. The reaction was carried out entirely under a nitrogen atmosphere. The reaction was monitored by TLC. Once the reactants had completely reacted, the reaction was terminated, allowed to cool naturally to room temperature, and then transferred to a pear-shaped flask with the solvent evaporated. After dilution with dichloromethane, the solution was extracted, dried, concentrated, and then purified by column chromatography to obtain compound N3. ； Step 3, Synthesis of Compound N4: Compound N3, tetra(triphenylphosphine)palladium, and cuprous iodide were weighed and placed in a two-necked flask equipped with a condenser. The reaction apparatus was connected to a double-row tube system and evacuated three times to ensure the reaction system was in an anhydrous and oxygen-free environment. Diisopropylamine, toluene, and trimethylsilylacetylene were sequentially added to the two-necked flask. The molar ratio of compound N3, tetra(triphenylphosphine)palladium, cuprous iodide, trimethylsilylacetylene, diisopropylamine, and toluene was 1:(0.05~0.2):(0.05~0.2):(1.5~2):(10~20):(30~50). After heating in an oil bath to 100 °C and the system refluxed, stirring was continued for 12 minutes. The reaction was carried out entirely under a nitrogen atmosphere. The reaction was monitored by TLC. Once the reactants had completely reacted, the reaction was terminated, allowed to cool to room temperature, and then transferred to a pear-shaped flask with the solvent evaporated. After dilution with dichloromethane, the solution was extracted, dried, concentrated, and purified by column chromatography to obtain compound N4. ； Step 4, Synthesis of compound N5: Compound N4 was weighed and placed in a round-bottom flask, dissolved in anhydrous tetrahydrofuran, and then a 1 mol / L tetrabutylammonium fluoride tetrahydrofuran solution was added. The molar ratio of compound N4, tetrabutylammonium fluoride, and tetrahydrofuran was 1:(5~10):(30~50). The mixture was stirred at room temperature for 4 h, and the reaction was monitored by TLC. The reaction was terminated after the reactants had completely reacted. After dilution with dichloromethane, the product was extracted, dried, concentrated, and purified by column chromatography to obtain compound N5. ； Step 5, Synthesis of Compound 2: Weigh 4-bromo-1,8-naphthalenedicarboxylic anhydride and place it in a two-necked flask equipped with a condenser. Add anhydrous ethanol and N-Boc-diaminoalkane sequentially. The molar ratio of 4-Br-1,8-naphthalenedicarboxylic anhydride, N-Boc-diaminoalkane, and anhydrous ethanol is 1:(1.5~2):(30~50). Heat the mixture in an oil bath to 100 °C, reflux the mixture, and stir continuously for 12 h. Monitor the entire reaction process using a TLC plate. After the reactants have completely reacted, terminate the reaction. Allow the mixture to cool to room temperature naturally, then filter, wash, and collect the filter cake. Transfer the cake to a pear-shaped flask and remove residual dichloromethane and ethanol solvent by rotary evaporation to obtain Compound 2. ； In the above formula, n is 1, 2, 3, or 4; Step 6, Synthesis of compound NADCA: Weigh compound 2, compound N5, tetraphenylphosphine palladium, and cuprous iodide into a two-necked flask. Connect the reaction apparatus to a double-row tube system and perform three evacuation and nitrogen replacement cycles. Inject toluene and triethylamine into the reaction flask. The molar ratio of compound N5, compound 2, tetraphenylphosphine palladium, cuprous iodide, triethylamine, and toluene is 1:(1.2~1.5):(0.1~0.2):(0.1~0.3):(10~20):(30~50). Heat the system in an oil bath to 100 °C until reflux occurs, then stir continuously for 12 h. The entire reaction is carried out under a nitrogen atmosphere. Monitor the entire reaction process using a TLC plate. After the reactants have completely reacted, terminate the reaction. Allow the mixture to cool to room temperature naturally, then transfer the reaction solution to a pear-shaped flask and evaporate the solvent. The compound NADCA was obtained by dilution with dichloromethane followed by extraction, drying, concentration, and separation and purification by column chromatography.

2. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 1, characterized in that, The specific steps for preparing flexible fluorescent sensing films are as follows: Step 7: Weigh out the fluorescent compound NADCA and cellulose triacetate (CTA) respectively, dissolve them in a mixed solvent of dimethyl sulfoxide and dichloromethane, stir at room temperature, and after standing / ultrasonic degassing, obtain CTA@NADCA spinning solutions with different mass fractions; Step 8: Using a JDF 05 electrospinning machine, draw CTA@NADCA spinning solution with a syringe and fix it on the injection pump; adjust the distance between the needle and the receiver, select the receiving roller as the receiving device, and cover the receiving roller with a layer of release paper; close the spinning box door, set the origin of the needle movement and adjust the spinning parameters, then start the electrospinning machine and collect the solution at room temperature for 4 hours. After collection, turn off the power, remove the release paper, and place it in a vacuum oven at 40 ℃ for more than 2 hours to remove the solvent. Finally, place the prepared film in a dark and dry place for use.

3. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 2, characterized in that, In step 1, the extraction is carried out sequentially using a 5% hydrochloric acid aqueous solution, a saturated sodium bicarbonate aqueous solution, and a saturated sodium chloride aqueous solution; the drying is performed using anhydrous sodium sulfate for 2 hours; and the column chromatography separation and purification is carried out using petroleum ether as the eluent. In step 2, the extraction is carried out sequentially using distilled water and saturated sodium chloride solution; the drying is carried out using anhydrous sodium sulfate for 2 hours; the column chromatography separation and purification is carried out using a mixed solvent of petroleum ether and ethyl acetate at a volume ratio of (15~30):1 as the eluent for column separation. In step 3, the extraction is carried out sequentially using saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution; the drying is carried out by drying with anhydrous sodium sulfate for 2 hours; the column chromatography separation and purification is carried out by using a mixed solvent of petroleum ether and dichloromethane in a volume ratio of (6~10):1 as the eluent for column separation.

4. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 3, characterized in that, In step 4, the extraction is carried out sequentially using saturated sodium bicarbonate solution and saturated sodium chloride solution; the drying is carried out by drying with anhydrous sodium sulfate for 2 hours; the column chromatography separation and purification is carried out by using a mixed solvent of petroleum ether and dichloromethane in a volume ratio of (6~10):1 as the eluent for column separation.

5. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 4, characterized in that, In step 5, the washing is performed by washing with ethanol and dichloromethane 6 to 7 times; the N-Boc-diaminoalkane is any one of N-Boc-1,2-diaminoethane, N-Boc-1,4-diaminobutane, N-Boc-1,6-diaminohexane, and N-Boc-1,8-diaminooctane.

6. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 5, characterized in that, In step 6, the extraction is carried out sequentially using saturated ammonium chloride solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution; the drying is carried out by drying with anhydrous sodium sulfate for 2 hours; the column chromatography separation and purification is carried out by using a mixed solvent of dichloromethane and ethyl acetate in a volume ratio of (10~20):1 as the eluent for column separation.

7. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 6, characterized in that, In step 7, the stirring time is 12 h to 20 h.

8. The method for preparing a flexible fluorescent sensing thin film based on a fluorescent probe according to claim 7, characterized in that, In step 8, the extraction volume is 6 ml to 8 mL; the receiving distance is 10 cm to 15 cm; the spinning parameters are: roller speed is 300 r / min, spinning voltage is 14 kV to 20 kV, needle reciprocating distance is 80 mm to 100 mm, and syringe advance speed is 0.6 mL / h to 1.0 mL / h.

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