PH response type organic fluorescent probe as well as preparation method and application thereof

Abstract

According to the pH response type organic fluorescent probe and the preparation method and application thereof, the probe has good pH responsiveness, the linear pH response range of the probe is 4.0-8.0, and the pH range of the whole physiological environment is covered. The pH response type fluorescent probe P-pH provided by the invention can quickly respond to acidic pH in the environment; the probe can be specifically activated in an acidic pH environment; meanwhile, the acid pH of the environment can be specifically responded, and interference of related ions is avoided. In addition, the pH response type fluorescent probe P-pH provided by the invention also has good pH response stability and relatively long response time.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and in particular to a pH-responsive organic fluorescent probe (P-pH) and a preparation method and application thereof. Background Art

[0002] Small molecule organic fluorescent materials have attracted extensive attention in the fields of optical imaging and information encryption due to their advantages such as modifiable structure, adjustable color and luminescence intensity, diversified synthesis methods, and excellent photophysical properties. However, due to the aggregation-induced quenching effect of traditional organic fluorescent materials, the fluorescence of fluorescent materials is easily quenched under physiological conditions, which limits their further application in the chemical industry. In recent years, pH-responsive organic fluorescent probes for environmental detection have been increasingly used in the chemical industry.

[0003] At present, most of the developed pH organic fluorescent probes have poor photostability and selectivity and are easily interfered by other related substances. Therefore, how to establish a pH-responsive signal amplification strategy to achieve accurate detection and response of pH in environmental detection is the focus of current research. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a pH-responsive organic fluorescent probe (P-pH) having good pH responsiveness and a linear pH response range of 4.0 to 8.0, covering the pH range of the entire physiological environment.

[0005] The invention also provides a method for preparing the pH-responsive organic fluorescent probe P-pH.

[0006] The invention also provides application of the pH-responsive organic fluorescent probe P-pH in environmental detection.

[0007] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0008] A pH-responsive organic fluorescent probe P-pH, the structural formula of which is shown below:

[0009]

[0010] Where R=H.

[0011] The present invention is further designed in that the linear pH response range of the organic fluorescent probe P-pH is 4.0 to 8.0.

[0012] The present invention is further designed in that the organic fluorescent probe P-pH can be specifically activated in an acidic environment with a pH value of 4-8.

[0013] The present invention is further designed in that the organic fluorescent probe P-pH has a good linear response in the range of pH 4-8.

[0014] The present invention provides a method for preparing a pH-responsive organic fluorescent probe, comprising the following steps:

[0015] Step 1, synthesis of the first intermediate: adding o-phenanthroline to a mixed solvent of an appropriate amount of sulfuric acid and nitric acid, adding a small amount of potassium bromide, and reflux reacting at 100-120° C. for 6-12 hours to obtain the first intermediate 1,10-o-phenanthroline-5,6-dione;

[0016] Step 2, synthesis of auxiliary ligand: dissolving the first intermediate prepared in step 1, diphenylamino-4-benzaldehyde and ammonium acetate in glacial acetic acid, reflux reaction at 60-70° C. for 12-24 hours, neutralizing with ammonia water after the reaction, and then filtering and drying, purifying the product by silica gel column chromatography to purify the crude product to obtain an auxiliary ligand; the molar ratio of the first intermediate, diphenylamino-4-benzaldehyde and ammonium acetate is: 1:1:0.01;

[0017] Step 3, synthesis of the second intermediate: dissolve naproxenic acid impurity, diboryl bis(pentanoyl)diboron, ferrocenyl palladium dichloride and potassium acetate in an appropriate amount of dioxane solvent, fill the system with nitrogen, and react for more than 24 hours. After the reaction, filter and extract the product, collect the organic phase, dry it, and purify it by column chromatography to obtain the second intermediate 2-(6-methoxynaphthalen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborane, wherein the molar ratio of naproxenic acid impurity, diboryl bis(pentanoyl)diboron, ferrocenyl palladium dichloride and potassium acetate is (1.4-2.25):(1.4-2.25):0.1:(14-22.5);

[0018] Step 4, synthesis of the third intermediate: dissolve the second intermediate obtained in step 3, 1-chloroisoquinoline, tetrakis-triphenylphosphine palladium and potassium carbonate in a suitable amount of toluene and a mixed solvent of ethanol and water, inject nitrogen and react at 90-100° C. for 12-24 hours, filter and extract the product, collect the organic phase, dry it, and purify it by column chromatography to obtain the third intermediate 1-(6-methoxynaphthalen-2-yl)isoquinoline, wherein the molar ratio of the second intermediate, 1-chloroisoquinoline and tetrakis-triphenylphosphine palladium to potassium carbonate is 1:1:(0.06-0.08):(40-50);

[0019] Step 5, synthesis of iridium chloride bridge dimer: dissolving iridium chloride trihydrate and the third intermediate prepared in step 4 in a mixed solution of water and ethylene glycol ethyl ether, protecting with nitrogen, and reacting at 110-120° C. for 40-60 hours; after the reaction is completed, filtering and drying to obtain iridium chloride bridge dimer, wherein the molar ratio of iridium chloride trihydrate to the third intermediate is (0.9-1):2;

[0020] Step 6, synthesis of P-pH: dissolve the iridium-chloro bridge dimer, auxiliary ligand and potassium hexafluorophosphate obtained in step 5 in a mixed solvent of an appropriate amount of methanol and dichloromethane, fill the system with nitrogen, and react at 20-30° C. for 8-24 hours; after the reaction, purify the crude product by silica gel column chromatography to obtain a complex P-pH, wherein the molar ratio of the iridium-chloro bridge dimer, auxiliary ligand and potassium hexafluorophosphate is 0.5:1:4.

[0021] The present invention is further designed that the volume ratio of sulfuric acid to nitric acid in the mixed solvent of sulfuric acid and nitric acid in step 1 is 1:1; the volume ratio of toluene to ethanol in the mixed solvent of toluene, ethanol and water in step 4 is 2:1; the volume ratio of methanol to dichloromethane in the mixed solvent of methanol and dichloromethane in step 6 is 2:1.

[0022] The present invention is further designed that, in step 3, the solvent for column chromatography purification is water.

[0023] The present invention is further designed that, in step 6, the solvent for the silica gel column chromatography purification is methanol or anhydrous dichloromethane.

[0024] The above-mentioned pH-responsive organic fluorescent probe P-pH is applied in environmental detection.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The pH-responsive organic fluorescent probe P-pH provided by the present invention is widely used in the fields of optical imaging, photocatalysis and information encryption due to the advantages of good photophysical and photochemical properties and excellent photostability of transition metal iridium complexes. However, the research on metal iridium complexes in the field of pH responsive detection is still in its infancy. Therefore, the study of the application of iridium complexes in the field of pH responsive environment has important significance and development prospects.

[0027] The pH-responsive organic fluorescent probe P-pH has good pH responsiveness, with a linear pH response range of 4.0 to 8.0, covering the entire pH range of the physiological environment and having the potential for environmental detection.

[0028] The pH-responsive organic fluorescent probe P-pH synthesized by the present invention has pH responsiveness, and its linear pH response range is 4.0 to 8.0, covering the pH range of the entire physiological environment, and has the potential for environmental detection.

[0029] The pH-responsive organic fluorescent probe material P-pH of the present invention realizes the fluorescence switch (OFF-ON) detection of different pH values, and examines the luminescence performance of the fluorescent probe P-pH under different pH values, metal ions, redox substances, temperatures and viscosities. The present invention lays a certain foundation for promoting the application of metal-based organic materials in related pH detection and further developing environmental detection materials.

[0030] The pH-responsive fluorescent probe P-pH provided by the present invention can respond quickly to the acidic pH in the environment; can be specifically activated in the acidic pH environment; and can specifically respond to the acidic pH of the environment without being interfered by related ions. The pH-responsive fluorescent probe P-pH provided by the present invention also has good pH response stability and a relatively long response time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The synthetic route of the pH-responsive organic fluorescent probe in the embodiment is as follows:

[0032] Figure 2 The synthetic route for the auxiliary ligand is:

[0033] Figure 3 The synthetic route for the second intermediate is:

[0034] Figure 4 The synthetic route for the third intermediate is:

[0035] Figure 5 The synthetic route of iridium-chloride bridged dimer is shown in FIG.

[0036] Figure 6 The synthetic route of P-pH is:

[0037] Figure 7 It is a mechanism diagram of the P-pH response to pH of the present invention;

[0038] Figure 8 is the hydrogen nuclear magnetic resonance spectrum of the probe P-pH of the present invention;

[0039] Fig. 9 It is the fluorescence spectrum of P-pH in response to pH of the present invention;

[0040] Fig.10 It is the ion interference spectrum of P-pH response to pH of the present invention;

[0041] Fig.11 It is the time stability fluorescence spectrum of the P-pH of the present invention in response to different pH;

[0042] Fig.12 The temperature stability fluorescence spectrum of the P-pH of the present invention in response to different pH values;

[0043] Fig.13 This is the fluorescence spectrum of viscosity stability of P-pH in response to different pH values ​​of the present invention. DETAILED DESCRIPTION

[0044] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. For those skilled in the art, modifications and substitutions made to the method, steps or conditions of the present invention without departing from the essence of the present invention all fall within the scope of the present invention.

[0045] Description of reagents used in the present invention: The raw materials used in the present invention were purchased from suppliers such as Sinopharm and Aladdin, and the raw materials were used directly without any special treatment.

[0046] The synthesis route of the pH-responsive organic fluorescent probe (called fluorescent probe P-pH) in the present invention is shown in 1:

[0047] Among them, the synthetic route of auxiliary ligand is as follows Figure 2 As shown:

[0048] The synthetic route of the second intermediate is as follows Figure 3 As shown:

[0049] The synthetic route of the third intermediate is as follows Figure 4 As shown:

[0050] The synthetic route of iridium chloride bridged dimer is as follows Figure 5 As shown;

[0051] The synthetic route of P-pH is as follows Figure 6 shown.

[0052] Embodiment 1:

[0053] Synthesis of pH-responsive organic fluorescent probe P-pH in this example:

[0054] Step 1, synthesis of the first intermediate 1,10-phenanthroline-5,6-dione: add phenanthroline (2.7 g, 15 mmol) to a mixed solvent of 30 mL of sulfuric acid and nitric acid, add a small amount of potassium bromide, heat to 110° C. in an oil bath, and reflux for 12 hours to obtain the first intermediate 1,10-phenanthroline-5,6-dione; wherein the volume ratio of sulfuric acid to nitric acid in the mixed solvent of sulfuric acid and nitric acid is 1:1.

[0055] Step 2, synthesis of auxiliary ligand: Weigh the first intermediate 1,10-phenanthroline-5,6-dione (1.95 g, 9 mmol), diphenylamino-4-benzaldehyde (2.55 g, 9 mmol) and ammonium acetate (6.9 g, 0.09 mol) prepared in step 1 and dissolve them in 30 mL of glacial acetic acid, and reflux in an oil bath at 60°C for 12 h. After the reaction is completed, neutralize it with ammonia water in an ice bath, wait until the pH value in the reaction bottle reaches 6 and no solid precipitates, filter it with a funnel, wash it with water continuously during this period, put it in an oven for drying after the filtration is completed, and then purify the product, the volume ratio of petroleum ether to ethyl acetate is 6:1.

[0056] Step 3, synthesis of the second intermediate 2-(6-methoxynaphthalen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborane: Naphoxic acid impurity (0.1 g, 0.45 mmol), bis(pentanoyl)diboron (0.15 g, 0.45 mmol), 0.02 mmol (diphenylphosphino) ferrocene palladium dichloride and potassium acetate (0.85 g, 4.5 mmol) were dissolved in 6 mL of dioxane solvent, nitrogen was introduced into the system and the reaction was carried out for 12 h. After the reaction was completed, the product was filtered and extracted, and the organic phase was collected and dried and then purified by column chromatography. The solvents for column chromatography purification were petroleum ether and dichloromethane, and the purification solvent ratio was 3:1 by volume of petroleum ether and dichloromethane.

[0057] Step 4, synthesis of the third intermediate 1-(6-methoxynaphthalen-2-yl)isoquinoline: weigh the second intermediate 2-(6-methoxynaphthalen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborane (0.4 g, 1.5 mmol), 1-chloroisoquinoline (0.3 g, 1.5 mmol) and tetrakis-triphenylphosphine palladium (0.1 g, 0.09 mmol) and potassium carbonate (8.2 g, 60 mmol) prepared in step 3, and dissolve them in 30 mL of toluene and a mixed solvent of ethanol and water, fill with nitrogen and react at 96° C. for 24 h, then filter and extract the product, collect the organic phase, dry it, and purify it by column chromatography, the purification solvent ratio is petroleum ether and dichloromethane volume ratio 3:1. The volume ratio of toluene to ethanol in the mixed solvent of toluene and ethanol and water is: 2:1.

[0058] Step 5, synthesis of iridium chloride bridged dimer: Weigh iridium chloride trihydrate (0.4 g, 1.4 mmol) and the third intermediate prepared in step 4 (0.8 g, 3 mmol), dissolve in a mixed solution of ethylene glycol ether and water, fill with nitrogen and react at 120° C. for 48 h. Filter with suction and put in an oven to dry.

[0059] Step 6, synthesis of P-pH: The above iridium-chloro bridge dimer (0.32 g, 0.2 mmol), the above auxiliary ligand (0.18 g, 0.4 mmol) and potassium hexafluorophosphate (0.3 g, 1.6 mmol) were dissolved in 10 mL of a mixed solvent of methanol and dichloromethane, wherein the volume ratio of methanol to dichloromethane in the mixed solvent was 2: 1. The reaction system was filled with nitrogen, reacted at 25° C. for 12 h, and purified by column chromatography with dichloromethane and methanol to obtain the product pH-responsive organic fluorescent probe P-pH, referred to as fluorescent probe P-pH.

[0060] The response mechanism of the fluorescent probe P-pH prepared in this example is as follows Figure 7 As shown in the figure, it can be seen that under acidic conditions, the fluorescence intensity of the probe is significantly enhanced and the red light intensity is significantly improved.

[0061] Embodiment 2:

[0062] The preparation method of the pH-responsive organic fluorescent probe of the present invention comprises the following steps:

[0063] Step 1, synthesis of the first intermediate: add o-phenanthroline (6 mmol) to a mixed solvent of 15 mL of sulfuric acid and nitric acid, add a small amount of potassium bromide and reflux at 110° C. for 6 hours to obtain the first intermediate 1,10-o-phenanthroline-5,6-dione; the volume ratio of sulfuric acid to nitric acid in the mixed solvent of sulfuric acid and nitric acid is 1:1.

[0064] Step 2, synthesis of auxiliary ligand: dissolve the first intermediate (7mmol), diphenylamino-4-benzaldehyde (7mmol) and ammonium acetate (0.07mol) prepared in step 1 in 10mL of glacial acetic acid, and reflux at 70°C for 15h. After the reaction, neutralize with ammonia water, and then filter and dry. Purify the product. Purify the crude product by silica gel column chromatography to obtain an auxiliary ligand; the molar ratio of the first intermediate, diphenylamino-4-benzaldehyde, and ammonium acetate is: 1:1:0.01;

[0065] Step 3, synthesis of the second intermediate: dissolve naproxenic acid impurity (0.7 mmol), bis(pentanoyl)diboron (0.7 mmol), (bis(phenylphosphino)ferrocenepalladium dichloride) (0.05 mmol) and potassium acetate (7 mmol) in 5 mL of dioxane solvent, fill the system with nitrogen, and react for more than 24 hours. After the reaction, filter and extract the product, collect the organic phase, dry it, and purify it by column chromatography to obtain the second intermediate 2-(6-methoxynaphthalen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborane, wherein the molar ratio of naproxenic acid impurity, bis(pentanoyl)diboron, ferrocenepalladium dichloride and potassium acetate is 0.7:0.7:0.05:7;

[0066] Step 4, synthesis of the third intermediate: the second intermediate (1 mmol) obtained in step 3, 1-chloroisoquinoline (1 mmol) and tetrakis-triphenylphosphine palladium (0.08 mmol) and potassium carbonate (50 mmol) are dissolved in 20 mL of toluene and a mixed solvent of ethanol and water, nitrogen is introduced, and the reaction is carried out at 98° C. for 15 hours, the product is filtered and extracted, the organic phase is collected and dried, and then purified by column chromatography to obtain the third intermediate 1-(6-methoxynaphthalen-2-yl)isoquinoline, the molar ratio of the second intermediate, 1-chloroisoquinoline and tetrakis-triphenylphosphine palladium to potassium carbonate is 1:1:0.08:50; wherein the volume ratio of toluene to ethanol in the mixed solvent of toluene, ethanol and water is: 2:1.

[0067] Step 5, synthesis of iridium chloride bridge dimer: dissolve iridium chloride trihydrate (0.9 mmol) and the third intermediate (1.8 mmol) prepared in step 4 in a mixed solution of water and ethylene glycol ether, protect with nitrogen, and react at 115°C for 48 hours. After the reaction is completed, filter and dry to obtain iridium chloride bridge dimer, wherein the molar ratio of iridium chloride trihydrate to the third intermediate is 1:2;

[0068] Step 6, synthesis of P-pH: Take iridium-chloro bridge dimer (0.15mmol), auxiliary ligand (0.3mmol) and potassium hexafluorophosphate (1.2mmol) and dissolve them in 30mL of a mixed solvent of methanol and dichloromethane, where the volume ratio of methanol to dichloromethane in the mixed solvent is 2:1. Nitrogen is filled into the system and reacted at 25°C for 12h; after the reaction, the crude product is purified by silica gel column chromatography to obtain an organic fluorescent probe P-pH. The solvent for silica gel column chromatography purification is methanol or dichloromethane, and the molar ratio of the main ligand, auxiliary ligand 1, and potassium hexafluorophosphate is 0.5:1:4;

[0069] Test Example 1: P-pH H NMR Spectrum

[0070] The following is the analysis data of the nuclear magnetic resonance hydrogen spectrum of the fluorescent probe P-pH prepared in Example 1, Figure 8 shown. 1HNMR(500MHz,Chloroform-d)δ12.26(s,1H),9.22(d,J=73.8Hz,2H),9.13(d,J=7.8Hz,2H),8.78(s,2H),8.11(dd,J=32.8,13.3Hz,4H),7.92-7.75 (m,8H),7.65(s,2H),7.32(d,J=6.0Hz,2H),7.13(d,J=7.7Hz,6H),7.07(t ,J=7.5Hz,2H),7.05-6.96(m,2H),6.72(d,J=33.0Hz,2H),6.56(d,J=6.2H z,2H),3.76(s,6H).

[0071] Test Example 2: pH Response of Iridium Complex

[0072] The fluorescent probe P-pH prepared in Example 1 was dissolved in dimethyl sulfoxide (DMSO) to obtain a stock solution with a concentration of 1 mM, and then a detection solution with a concentration of 10 mM was prepared using buffer solutions of different pH values. The changes in its absorption spectrum and emission spectrum under different pH conditions were detected using a UV-visible spectrophotometer and a fluorescence spectrometer, respectively. The results showed that P-pH had a significant responsiveness to pH, and the fluorescence intensity gradually increased with the decrease of pH value, and had a good linear relationship in the pH range of 4-8, such as Fig. 9 shown.

[0073] Test Example 3: Selective Detection of P-pH

[0074] Prepare 1mM concentration of interfering ion stock solutions, including aluminum chloride, calcium chloride, copper chloride, ferric chloride, ferrous chloride, potassium chloride, magnesium chloride, sodium chloride, zinc chloride, hydrogen peroxide, glutathione, cysteine, and homocysteine; prepare 1mM concentration of the fluorescent probe P-pH prepared in Example 1. In the test solution, the concentration of the interfering ions is 100μM, and the concentration of the complex is 10μM. After adding the interfering ions for 5 minutes, detect the fluorescence intensity of the sample. Fig.10 As shown, the detection results show that the fluorescent probe P-pH responds specifically to pH and can effectively eliminate the interference of the above ions.

[0075] Test Example 4: pH response stability under different P-pH conditions

[0076] The fluorescent probe P-pH prepared in Example 1 was dissolved in DMSO to prepare a stock solution with a concentration of 1 mM. Subsequently, a detection solution with a concentration of 10 μM was prepared using PBS (phosphate buffer solution) with pH values ​​of 4 and 8. The changes in its emission spectrum at different times, temperatures, and viscosities were detected using a UV-visible spectrophotometer and a fluorescence spectrometer. The test results show that the probe has good stability under different conditions.

[0077] Test Example 5: P-pH photostability test

[0078] The fluorescent probe P-pH prepared in Example 1 was prepared into a detection solution with a concentration of 10 μM using PBS (phosphate buffer solution) with a pH of 7. In order to simulate the responsiveness of pH under physiological conditions, Fig.11 , Fig.12 ,and Fig.13As shown, the stability of the pH response of the fluorescent probe P-pH at different times (0-24 hours), temperatures (20-42 degrees) and viscosities (0-20% glycerol) indicates that under different conditions, specifically in terms of the time stability of the response at different pH values, the temperature stability of the response at different pH values, and the viscosity stability of the response at different pH values, the fluorescent probe P-pH has good stability.

[0079] The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A pH-responsive organic fluorescent probe P-pH, characterized in that: Its structural formula is as follows: Where R=H.

2. The pH-responsive organic fluorescent probe P-pH according to claim 1, characterized in that: The organic fluorescent probe P-pH has a linear pH response range from 4.0 to 8.

0.

3. The pH-responsive organic fluorescent probe P-pH according to claim 1, characterized in that: The organic fluorescent probe P-pH can be specifically activated in an acidic environment with a pH value of 4-8.

4. The pH-responsive organic fluorescent probe P-pH according to claim 1, characterized in that: The organic fluorescent probe P-pH has a good linear response in the pH range of 4-8.

5. The method for preparing the pH-responsive organic fluorescent probe according to claim 1, characterized in that: The steps include: Step 1, synthesis of the first intermediate: adding o-phenanthroline to a mixed solvent of an appropriate amount of sulfuric acid and nitric acid, adding a small amount of potassium bromide, and reflux reacting at 100-120° C. for 6-12 hours to obtain the first intermediate 1,10-o-phenanthroline-5,6-dione; Step 2, synthesis of auxiliary ligand: dissolving the first intermediate prepared in step 1, diphenylamino-4-benzaldehyde and ammonium acetate in glacial acetic acid, reflux reaction at 60-70° C. for 12-24 hours, neutralizing with ammonia water after the reaction, and then filtering and drying, purifying the product by silica gel column chromatography to purify the crude product to obtain an auxiliary ligand; the molar ratio of the first intermediate, diphenylamino-4-benzaldehyde and ammonium acetate is: 1:1:0.01; Step 3, synthesis of the second intermediate: dissolve naproxenic acid impurity, diboryl bis(pentanoyl)diboron, ferrocenyl palladium dichloride and potassium acetate in an appropriate amount of dioxane solvent, fill the system with nitrogen, and react for more than 24 hours. After the reaction, filter and extract the product, collect the organic phase, dry it, and purify it by column chromatography to obtain the second intermediate 2-(6-methoxynaphthalen-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborane, wherein the molar ratio of naproxenic acid impurity, diboryl bis(pentanoyl)diboron, ferrocenyl palladium dichloride and potassium acetate is (1.4-2.25):(1.4-2.25):0.1:(14-22.5); Step 4, synthesis of the third intermediate: dissolve the second intermediate obtained in step 3, 1-chloroisoquinoline, tetrakis-triphenylphosphine palladium and potassium carbonate in a suitable amount of toluene and a mixed solvent of ethanol and water, inject nitrogen and react at 90-100° C. for 12-24 hours, filter and extract the product, collect the organic phase, dry it, and purify it by column chromatography to obtain the third intermediate 1-(6-methoxynaphthalen-2-yl)isoquinoline, wherein the molar ratio of the second intermediate, 1-chloroisoquinoline and tetrakis-triphenylphosphine palladium to potassium carbonate is 1:1:(0.06-0.08):(40-50); Step 5, synthesis of iridium chloride bridge dimer: dissolving iridium chloride trihydrate and the third intermediate prepared in step 4 in a mixed solution of water and ethylene glycol ethyl ether, protecting with nitrogen, and reacting at 110-120° C. for 40-60 hours; after the reaction is completed, filtering and drying to obtain iridium chloride bridge dimer, wherein the molar ratio of iridium chloride trihydrate to the third intermediate is (0.9-1):2; Step 6, synthesis of P-pH: dissolve the iridium-chloro bridge dimer, auxiliary ligand and potassium hexafluorophosphate obtained in step 5 in a mixed solvent of an appropriate amount of methanol and dichloromethane, fill the system with nitrogen, and react at 20-30° C. for 8-24 hours; after the reaction, purify the crude product by silica gel column chromatography to obtain a complex P-pH, wherein the molar ratio of the iridium-chloro bridge dimer, auxiliary ligand and potassium hexafluorophosphate is 0.5:1:

4.

6. The method for preparing a pH-responsive organic fluorescent probe according to claim 5, characterized in that: The volume ratio of sulfuric acid to nitric acid in the mixed solvent of sulfuric acid and nitric acid in step 1 is 1:1; the volume ratio of toluene to ethanol in the mixed solvent of toluene, ethanol and water in step 4 is 2:1; the volume ratio of methanol to dichloromethane in the mixed solvent of methanol and dichloromethane in step 6 is 2:

1.

7. The method for preparing a pH-responsive organic fluorescent probe according to claim 5, characterized in that: In step 3, the solvent for column chromatography purification is water.

8. The method for preparing a pH-responsive organic fluorescent probe according to claim 5, characterized in that: In step 6, the solvent for the silica gel column chromatography purification is methanol or anhydrous dichloromethane.

9. Application of the pH-responsive organic fluorescent probe P-pH according to claim 1 in environmental detection.

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