A multi-aromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor, its preparation method and applications

Abstract

A multi-aromatic-ring bridged bis-benzimidazole-based pH fluorescence sensor, its preparation method and application, and a pH fluorescence sensor, its preparation method and application. It aims to solve the technical problems of the existing pH fluorescence sensors, such as low sensitivity, poor anti-interference ability and non-reusability. The structural formula of the pH fluorescence sensor of the present invention is: Preparation method: First, use 4,4'-dihydroxybiphenyl and 4-fluorobenzaldehyde to prepare a dicarbonyl intermediate, and then the intermediate reacts with o-phenylenediamine to obtain it. This pH fluorescence sensor determines whether the pH value in the solution to be measured is greater than 11.5 through fluorescence emission spectroscopy, nuclear magnetic resonance hydrogen spectrum, and naked-eye fluorescence detection, and qualitatively detects the pH value of the solution to be measured. It can resist the interference of halogen ions, acid radical ions, and metal ions, and the sensor can be reused, and can be used in the field of qualitative detection of pH values.

Description

Technical Field

[0001] The present invention relates to a fluorescence sensor and a preparation method thereof. Background Art

[0002] For a long time, the pH value, as an important parameter, has been widely used in many fields (such as environmental, biomedical, and industrial fields). Although existing methods have been mature, there are still problems that cannot be accurately detected under certain conditions (such as insufficient anti-electromagnetic interference ability and weak anti-interference ability). Therefore, it is still meaningful to use a fluorescence sensor for pH detection, mainly because of its fast, real-time, high sensitivity, especially strong anti-electromagnetic interference ability. Therefore, in recent years, fluorescence sensors for pH detection have made significant developments. However, some fluorescence sensors have defects such as low sensitivity, poor anti-interference ability, and non-reusable, which limit their applications. Therefore, it is very important to develop a highly reversible "on-off-on" fluorescence switch for pH detection. Summary of the Invention

[0003] The present invention aims to solve the technical problems of the existing pH fluorescence sensors with low sensitivity, poor anti-interference ability, and non-reusable, and provides a polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor, a preparation method thereof, and an application thereof. The pH fluorescence sensor of the present invention is a fluorescence color-changing pH sensor with high repeatability constructed by polyaromatic-ring-bridged bisbenzimidazole. This type of compound has the advantages of simple preparation, rapid detection, and visual resolution.

[0004] The polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor of the present invention has the following structural formula:

[0005]

[0006] The preparation method of the above polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor is carried out according to the following steps:

[0007] I. Preparation of dicarbonyl intermediate: 4,4'-dihydroxybiphenyl and 4-fluorobenzaldehyde are added to a reactor according to a molar ratio of 1:(2.3 - 3), potassium carbonate is used as a catalyst, N,N-dimethoxyacetamide is used as a solvent, and after stirring at room temperature for 24 - 48 h, water is added to the reaction system to precipitate the product, and the crude product is obtained by filtration. Then, it is recrystallized successively with N,N-dimethoxyacetamide and isopropanol to obtain a pure dicarbonyl intermediate compound;

[0008] II. Add the dicarbonyl intermediate compound and o-phenylenediamine into a reactor at a molar ratio of 1:(2.3 - 3). Using acetic acid as a catalyst and dimethyl sulfoxide as a solvent, heat the mixture to 100 - 120 °C and stir for 24 - 48 h. Then cool it to room temperature, add water to the reaction system, and then perform suction filtration and wash the solid phase with water and dichloromethane solution to obtain a polyaromatic ring-bridged bisbenzimidazole pH fluorescence sensor.

[0009] Further, the structural formula of the dicarbonyl intermediate compound described in step I is

[0010]

[0011] The application of the above polyaromatic ring-bridged bisbenzimidazole pH fluorescence sensor is to use the polyaromatic ring-bridged bisbenzimidazole pH fluorescence sensor for qualitative detection of pH value. Specifically as follows:

[0012] (1) Mix the polyaromatic ring-bridged bisbenzimidazole pH fluorescence sensor solution with the solution to be tested to obtain a mixed solution;

[0013] (2) Test the ultraviolet absorption spectra of the fluorescence sensor solution and the mixed solution. If the maximum absorption wavelength is at 313 nm, the pH of the mixed solution is between 5 and 11. If the maximum absorption wavelength is at 326 nm, the pH of the mixed solution is higher than 11.5.

[0014] Or test the fluorescence emission spectra of the fluorescence sensor solution and the mixed solution. If the fluorescence emission peak intensity of the mixed solution decreases by more than 75% compared with the fluorescence sensor solution and a new peak appears, and the maximum emission wavelength of this new peak is at 490 nm, it is determined that the pH value of the solution to be tested is greater than 11.5;

[0015] Or test the nuclear magnetic resonance hydrogen spectra of the fluorescence sensor solution and the mixed solution. If the hydrogen of benzimidazole in the nuclear magnetic resonance hydrogen spectrum of the mixed solution moves to a higher field compared with the fluorescence sensor solution, it is determined that the pH value of the solution to be tested is greater than 11.5;

[0016] Or observe the naked-eye fluorescence of the fluorescence sensor solution and the mixed solution. The naked-eye fluorescence of the fluorescence sensor solution shows colorless. If the naked-eye fluorescence of the mixed solution turns cyan-blue, it is determined that the pH value of the solution to be tested is greater than 11.5.

[0017] Further, the concentration of the pH fluorescence sensor in the mixed solution in step (1) is 10 -6 ~~10 -3 mol / L.

[0018] The multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor of the present invention is constructed by utilizing the electron - accepting and aromatic - ring - bridging characteristics of benzimidazole. It can change the electron cloud density on its aromatic ring by losing hydrogen ions under alkaline conditions, thereby changing its luminescence ability. By using the property that its luminescence ability is changed, after mixing it with the unknown solution to be measured, the fluorescence emission spectrum, or nuclear magnetic resonance hydrogen spectrum, or naked - eye fluorescence is detected. Qualitative recognition of pH value is achieved through the decrease of the fluorescence emission peak and the appearance of a new peak at a long - wavelength position, or the shift of the hydrogen of benzimidazole to a higher magnetic field in the nuclear magnetic resonance hydrogen spectrum, or obvious fluorescence changes observed by naked - eye fluorescence. The multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor of the present invention can be used in the field of qualitative detection of pH value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the ultraviolet absorption spectra of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1 at different pH values;

[0020] Figure 2 is the fluorescence emission spectra of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1 at different pH values;

[0021] Figure 3 is the analysis chart of the fluorescence anti - interference ability of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1;

[0022] Figure 4 is the analysis chart of the fluorescence reusability of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1;

[0023] Figure 5 is the nuclear magnetic resonance hydrogen spectra of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1 in deuterated solution at different pH values;

[0024] Figure 6 is Figure 5 the corresponding hydrogen position chart of peaks a, b, c, d, e, f, g, h, j, k in

[0025] Figure 7 is the naked - eye analysis test chart of the test paper of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1;

[0026] Figure 8 is the naked - eye analysis test chart of the solution of the multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescence sensor prepared in Example 1;

[0027] Figure 9 is the naked - eye analysis test chart of the solution of Comparative Compound 2. DETAILED DESCRIPTION OF THE INVENTION

[0028] The beneficial effects of the present invention are verified by the following examples.

[0029] Example 1: The preparation method of the multi-aromatic-ring bridged bisbenzimidazole pH fluorescent sensor in this example is carried out according to the following steps:

[0030] I. Preparation of the dicarbonyl biphenyl intermediate:

[0031] 0.186 g of 4,4'-dihydroxybiphenyl and 0.32 g of 4-fluorobenzaldehyde (their molar ratio is 1:2.5) are added to a reactor. Using 0.345 g of potassium carbonate as the base and 20 mL of N,N-dimethoxyacetamide as the solvent, after stirring at room temperature for 24 h, filtration is carried out to obtain a crude product; then recrystallization is carried out with a mixed solution of N,N-dimethoxyacetamide and isopropanol with a volume ratio of 1:4 to obtain a pure dicarbonyl biphenyl intermediate compound; the structural formula of the dicarbonyl biphenyl intermediate compound is: Denoted as compound 3;

[0032] II. 0.197 g of the dicarbonyl intermediate compound 3 and 0.135 g of o-phenylenediamine (their molar ratio is 1:2.5) are added to a reactor. Using 0.5 mL of glacial acetic acid as the catalyst and 15 mL of dimethyl sulfoxide as the solvent, the temperature is raised to 100 °C and stirred for 24 h, then cooled to room temperature. 25 mL of water is added to the reaction to quench the reaction, and then suction filtration is carried out and the solid product is washed 5 times with 50 mL of dichloromethane solution. After natural drying, a multi-aromatic-ring bridged bisbenzimidazole pH fluorescent sensor is obtained, denoted as compound 1.

[0033] The chemical synthesis expression of the multi-aromatic-ring bridged bisbenzimidazole pH fluorescent sensor in Example 1 is:

[0034]

[0035] The melting point of the multi-aromatic-ring bridged bisbenzimidazole pH fluorescent sensor obtained in this Example 1 is greater than 300 °C. It is characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy and mass spectrometry, and the obtained results are as follows:

[0036] IR(KBr,cm -1 ):3058,1598,1489,1398,1239,1168,853,744.

[0037] 1 H NMR(600MHz,DMSO-d6):δ12.88(s,2H); 8.22(q,J=6.6,4H); 7.75(d,J=8.4,4H); 7.59(s,4H); 7.23-7.18(m,12H).

[0038] 1313C NMR (150 MHz, DMSO-d6) δ 158.2, 155.4, 150.8, 135.6, 128.4, 128.3, 125.4, 121.9, 119.7, 118.6.

[0039] MS (ESI): m / z 571.2123 ([M+H] + ), calculated 571.2056.

[0040] From the above characterization results, the structural formula of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor prepared in Example 1 is as follows:

[0041] The polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor prepared in this example was prepared as a stock solution with a concentration of 1.0×10 -2 mol / L using dimethyl sulfoxide (DMSO) as the solvent. Subsequently, 1 mL of the stock solution of the host with a concentration of 1.0×10 -2 mol / L was added to a 500.0 mL volumetric flask, and then 449 mL of dimethyl sulfoxide and 50 mL of water were added to make up the volume to prepare 500 mL of the stock solution of the host with a concentration of 2.0×10 -5 mol / L. The stock solution of the host was dispensed into 10 mL volumetric flasks. Subsequently, the pH of the stock solution of the host was adjusted to 5, 5.5, 6, 6.5, 7... 13 by adding 1.0×10 -3 mol / L sodium hydroxide (NaOH) and hydrochloric acid (HCl) respectively. After maintaining a constant temperature for 2 h, the ultraviolet absorption spectrum was detected. The ultraviolet absorption spectra of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor under different pH conditions are as shown in Figure 1 . As can be seen from Figure 1 , the maximum absorption wavelength of the host is at 313 nm and does not change between pH 5 and 11. When the pH is higher than 11, the maximum absorption wavelength of the host undergoes a red shift to 326 nm. Therefore, it can be preliminarily speculated from the ultraviolet absorption spectrum that when the pH of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor is higher than 11, the imidazole hydrogen ion in benzimidazole is stripped under alkaline conditions, resulting in a phenomenon of red shift of the absorption peak.

[0042] The polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor prepared in Example 1 was prepared as a stock solution with a concentration of 1.0×10 -2 mol / L using dimethyl sulfoxide (DMSO) as the solvent. Subsequently, 1 mL of the stock solution of the host with a concentration of 1.0×10 -2 mol / L was added to a 500.0 mL volumetric flask, and then 449 mL of dimethyl sulfoxide and 50 mL of water were added to make up the volume to prepare -5 500 mL of the main stock solution at mol / L. The main stock solution was dispensed into 10 mL volumetric flasks, and then the pH of the main stock solution was adjusted to 5, 5.5, 6, 6.5, 7... 13 by adding 1.0×10 - 3 mol / L of sodium hydroxide (NaOH) and hydrochloric acid (HCl), respectively. After maintaining a constant temperature for 2 h, the fluorescence emission spectrum was detected. At an excitation wavelength of 313 nm and an excitation slit width of 1.0 nm, the fluorescence intensities at pH values of 5, 5.5, 6, 6.5, 7... 13 were measured. The fluorescence emission spectra of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor prepared in Example 1 under different pH conditions are as shown in Figure 2 shown. As can be seen from Figure 2 , when the pH is between 5 and 10.5, the maximum fluorescence emission wavelength of the main body is 352 nm, and with the change of pH, the change in fluorescence intensity is not obvious. When the pH is higher than 11, the fluorescence intensity decreases significantly, and the fluorescence intensity decreases by 75% - 85%. At the same time, a new peak appears at 490 nm for the main body. Therefore, it can be further speculated from the fluorescence emission spectrum that when the pH is higher than 11 for the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor, the imidazole hydrogen ion in benzimidazole is stripped under alkaline conditions, resulting in a red shift of the absorption peak.

[0043] To further verify the fluorescence anti-interference ability of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor, at an excitation wavelength of 313 nm, an excitation slit width of 1.0 nm, and a pH of 7, the interference of various cations and anions (F - , Cl - , Br - , I - , ClO4 - , H2PO4 - , HSO4 - , CH3COO - , Al 3+ , Cu 2+ , Ca 2+ , Cd 2+ , Co 2+ , Cr 3+ , Mg 2+ , Na + , Ni 2+ , Pb 2+ and Zn 2+ ) on the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor was measured. The analysis diagram of the fluorescence anti-interference ability of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescence sensor prepared in Example 1 is as shown in Figure 3 shown. As can be seen from Figure 3As can be seen, under neutral conditions without adjusting the pH value, various interfering ions are added to a solution of a polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor with a concentration of 2.0×10 -5 mol / L. The concentration of the interfering ions is 10 -3 mol / L, and there will be no significant change in the luminescence performance. When various interfering ions are added to a solution of a polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor with a concentration of 2.0×10 -5 mol / L at a pH value of 11.5, and the concentration of the interfering ions is 10 -3 mol / L, it will not affect the luminescence performance of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor, further confirming the stability of this type of compound.

[0044] Next, in order to verify the reusable ability of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor, at an excitation wavelength of 313 nm and an excitation slit width of 1.0 nm, continuously cyclically adjust the pH to vary between 10 and 12. The fluorescence reusable analysis diagram of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor obtained is as Figure 4 shown. As can be seen from Figure 4 , 10 cycles basically have no effect on the overall luminescence performance of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor, demonstrating the reusable ability of this type of compound.

[0045] To further prove the influence of pH, the changes in the NMR spectra under different pH conditions were measured by NMR hydrogen spectrum experiments here. A main body stock solution with a concentration of 1.0×10 -3 mol / L and a dimethyl sulfoxide:water ratio of 9:1 was prepared. Five 0.5 mL solutions were taken out and placed in NMR tubes respectively. Subsequently, sodium hydroxide (NaOH) was added to adjust the ratio of the main body to sodium hydroxide (NaOH) to 1:0.5, 1:1, and 1:5. Hydrochloric acid (HCl) was added to adjust the ratio of the main body to hydrochloric acid (HCl) to 1:0.5 and 1:1 respectively. Then, the NMR hydrogen spectra of the main body and the samples with different acid-base ratios of the main body were detected. The NMR hydrogen spectra of the polyaromatic-ring-bridged bisbenzimidazole-based pH fluorescent sensor prepared in Example 1 in deuterated solutions with different pH values are as Figure 5 shown. Figure 5 The diagrams of the hydrogen positions corresponding to peaks a, b, c, d, e, f, g, h, j, and k in Figure 6 are as Figure 5As can be seen, with the increase of pH, both the hydrogens Ha and Hb of the benzimidazole moiety of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor show a large upfield shift. The peak of Ha shifts from 7.50 to 6.77, and the peak of Hb shifts from 7.76 to 7.39. This further indicates that when the pH value is high, the imidazole hydrogen ions in benzimidazole are stripped off under alkaline conditions, thereby increasing the electron cloud density of the benzimidazole moiety of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor and changing its own properties and luminescence ability.

[0046] The practical application ability of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor prepared in Example 1 stems from visual detection. Using a mixed solution with a volume ratio of dimethyl sulfoxide: water of 9:1 as the solvent, the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor prepared in Example 1 was formulated into a host solution with a concentration of 1.0×10 -2 mol / L. The filter paper was immersed in the host solution for 2 h and then dried. It was irradiated and photographed with a 365 nm fluorescent lamp. The results are as Figure 7 shown. As can be seen from Figure 7 , when sodium hydroxide (NaOH) solutions with pH values of 7 and 12 and a dimethyl sulfoxide: water ratio of 9:1 were dropped onto the test paper, the generation of fluorescence color could be clearly observed with the naked eye. At pH 7, basically no fluorescence was observed, and the color at pH 12 was cyan blue. This is because the human naked eye observes wavelengths in the range of 390 - 780 nm. Under neutral pH, the fluorescence emission wavelength of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor is lower than 390 nm and does not show color with the naked eye. Under alkaline conditions, a new peak appears at 490 nm for the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor, thereby generating fluorescence.

[0047] Finally, using a mixed solution with a volume ratio of dimethyl sulfoxide: water of 9:1 as the solvent, the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor prepared in Example 1 was formulated into a host solution with a concentration of 1.0×10 -2 mol / L. Subsequently, its pH was adjusted to 7 and 12 respectively, and it was irradiated and photographed with a 365 nm fluorescent lamp. The results are as Figure 8 shown. As can be seen from Figure 8 , when the solution pH was adjusted to 7 and 12, the generation of fluorescence color could be clearly observed with the naked eye. At pH 7, basically no fluorescence was observed, and the fluorescence generated at pH 12 was cyan blue. This further expands the practical application scope of the polyaromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor.

[0048] The reason for the fluorescence change of the multi-aromatic-ring bridged bisbenzimidazole pH fluorescence sensor prepared in Example 1 under alkaline conditions is that its molecule is composed of a biphenyl structure inside. Under alkaline conditions, the electron cloud density of its aromatic ring increases, which further triggers the aggregation effect and generates a large conjugated system, resulting in fluorescence change. To prove this conclusion, Compound 2 was synthesized as a comparison. The preparation method of this comparative compound 2 is carried out according to the following steps: 0.226 g of 4,4'-dicarbonyl phenyl ether and 0.27 g of o-phenylenediamine were added to the reactor in a molar ratio of 1:2.5. Using 1 mL of acetic acid as a catalyst and 30 mL of dimethyl sulfoxide as a solvent, the temperature was raised to 100 °C and stirred for 24 h, then cooled to room temperature. 50 mL of water was added to the reaction to quench the reaction. Subsequently, it was filtered by suction and the solid product was washed 5 times with 100 mL of dichloromethane solution and dried naturally to obtain a pure comparative compound. The structural formula of this compound is: Denoted as Compound 2.

[0049] The chemical synthesis expression of the comparative compound is:

[0050]

[0051] The melting point of the comparative compound 2 is greater than 300 °C. It was characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy and mass spectrometry, and the results obtained are as follows:

[0052] IR(KBr,cm -1 ): 3067, 1605, 1545, 1478, 1247, 835, 743.

[0053] 1 H NMR(600MHz,DMSO-d6): δ12.89(s,2H); 8.25 - 8.22(m,4H); 7.59(q,J = 7.8,4H); 7.29 - 7.27(m,4H); 7.23 - 7.17(m,4H).

[0054] 13 C NMR(150MHz,DMSO-d6) δ157.6, 150.8, 128.5, 125.8, 122.0, 119.2.

[0055] MS(ESI): m / z 403.1550([M + H] + ), calculated 403.1481.

[0056] From the above characterization results, the structural formula of the comparative compound 2 is:

[0057]

[0058] In order to detect the responsiveness of the comparative compound 2 to pH, the ultraviolet absorption spectra of the compound at different pH were detected. Compared with the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor molecule of Example 1, the pH response range of the oxygen-bridged benzimidazole comparative compound 2 is relatively narrow, and red shift only occurs when the pH is above 12, which limits the scope of use of this type of compound. At the same time, it is proved that the polyaromatic ring-bridged bisbenzimidazole compound has a stronger detection ability than the oxygen-bridged benzimidazole comparative compound.

[0059] In addition, in order to detect the luminescence ability of comparative compound 2, the fluorescence emission spectrum of the comparative compound was detected. When the pH is higher than 11.5, the fluorescence luminescence partially red-shifts, and when the pH is higher than 12, the fluorescence luminescence completely red-shifts. However, the change in red-shift is not large, and the maximum absorption wavelength is still less than 390nm, which is difficult to observe with the naked eye, which greatly affects the observation of the phenomenon, and further proves that the polyaromatic ring bridged bisbenzimidazole compound of Example 1 has a stronger detection ability than the oxygen-bridged benzimidazole comparative compound.

[0060] In order to further prove that the pH detection ability of the comparative compound 2 was weak, a mixture of dimethyl sulfoxide and water with a volume ratio of 9:1 was used as the solvent to prepare 1.0×10 -2 mol / L solution of comparative compound 2, and then adjusted its pH to 7 and 12, and photographed using a 365nm fluorescent lamp. The results are as follows Figure 9 As shown. Figure 9 It can be seen that compared with the polyaromatic ring-bridged bisbenzimidazole compounds, the luminescence intensity of the oxygen-bridged benzimidazole comparative compound 2 is weaker and difficult to detect with the naked eye. This further proves the practicality and application ability of the polyaromatic ring-bridged bisbenzimidazole compounds.

[0061] The polyaromatic ring bridged bisbenzimidazole pH fluorescence sensor of Example 1 can determine whether the pH value of the solution to be tested is greater than 11.5 by fluorescence emission spectroscopy, nuclear magnetic resonance hydrogen spectrum, and naked eye fluorescence detection, and perform qualitative detection of the pH value of the solution to be tested.

Claims

1. A multi-aromatic-ring bridged bisbenzimidazole-based pH fluorescence sensor, characterized in that The structural formula of the pH fluorescent sensor is as follows:

2. A method for preparing a multi - aromatic - ring - bridged bis - benzimidazole - based pH fluorescent sensor as claimed in claim 1, characterized in that The method is carried out according to the following steps: I. Preparation of Dicarbonyl Intermediate: 4,4'-Dihydroxybiphenyl and 4-fluorobenzaldehyde were added to a reactor in a molar ratio of 1:(2.3 - 3). Using potassium carbonate as a catalyst and N,N-dimethoxyacetamide as a solvent, the mixture was stirred at room temperature for 24 - 48 h. Then, water was added to the reaction system to precipitate the product. The crude product was obtained by filtration and then recrystallized successively with N,N-dimethoxyacetamide and isopropanol to obtain a pure dicarbonyl intermediate compound. The structural formula of the dicarbonyl intermediate compound is: Second, add the dicarbonyl intermediate compound and o-phenylenediamine into the reactor in a molar ratio of 1:(2.3 - 3), use acetic acid as the catalyst, dimethyl sulfoxide as the solvent, heat up to 100 - 120 °C and stir for 24 - 48 h, then cool to room temperature, add water to the reaction system, and then filter and wash the solid phase with water and dichloromethane solution to obtain the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor.

3. The preparation method of a multi-aromatic-ring bridged bis-benzimidazole-based pH fluorescent sensor according to claim 2, characterized in that In the mixed solution of N,N-dimethoxyacetamide and isopropanol for recrystallization in Step 1, the volume ratio of N,N-dimethoxyacetamide to isopropanol is 1:(4 - 5).

4. Use of a multi-aromatic-ring bridged bisbenzimidazole-based pH fluorescence sensor according to claim 1, characterized in that This application is to use the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor for the qualitative detection of pH value.

5. Use of a multi-aromatic-ring bridged bis-benzimidazole-based pH fluorescence sensor according to claim 4, characterized in that The method for the qualitative detection of pH value using the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor by ultraviolet absorption spectroscopy is carried out according to the following steps: (1) After mixing the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor solution with the solution to be measured, a mixed solution is obtained; (2) Test the ultraviolet absorption spectra of the fluorescent sensor solution and the mixed solution. If the maximum absorption wavelength is at 313 nm, the pH of the mixed solution is between 5 and 11; if the maximum absorption wavelength is at 326 nm, the pH of the mixed solution is higher than 11.

5.

6. Use of a multi-aromatic-ring bridged bisbenzimidazole-based pH fluorescent sensor according to claim 4, characterized in that The method for the qualitative detection of pH value using the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor by fluorescence emission spectroscopy is carried out according to the following steps: (1) After mixing the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor solution with the solution to be measured, a mixed solution is obtained; (2) Test the fluorescence emission spectra of the fluorescent sensor solution and the mixed solution. If the fluorescence emission peak intensity of the mixed solution decreases by more than 75% compared with the fluorescent sensor solution and a new peak appears, and the maximum emission wavelength of this new peak is at 490 nm, it is judged that the pH value of the solution to be measured is greater than 11.

5.

7. Use of a multi-aromatic-ring bridged bis-benzimidazole-based pH fluorescent sensor according to claim 4, characterized in that The method for the qualitative detection of pH value using the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor by nuclear magnetic resonance hydrogen spectrum is carried out according to the following steps: (1) After mixing the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor solution with the solution to be measured, a mixed solution is obtained; (2) Test the nuclear magnetic resonance hydrogen spectra of the fluorescent sensor solution and the mixed solution. If the hydrogen of benzimidazole in the nuclear magnetic resonance hydrogen spectrum of the mixed solution moves to the high field compared with the fluorescent sensor solution, it is judged that the pH value in the solution to be measured is greater than 11.

5.

8. Use of a multi-aromatic-ring bridged bisbenzimidazole-based pH fluorescence sensor according to claim 4, characterized in that The method for the qualitative detection of pH value using the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor by nuclear magnetic resonance hydrogen spectrum is carried out according to the following steps: (1) After mixing the polyaromatic ring-bridged bisbenzimidazole pH fluorescent sensor solution with the solution to be measured, a mixed solution is obtained; (2) Observe the naked-eye fluorescence of the fluorescent sensor solution and the mixed solution. If the naked-eye fluorescence of the fluorescent sensor solution is colorless compared with the fluorescent sensor solution, and the naked-eye fluorescence of the mixed solution turns cyan-blue, it is judged that the pH value of the solution to be measured is greater than 11.

5.

9. Use of a multi-aromatic-ring bridged bis-benzimidazole-based pH fluorescence sensor according to claim 5, 6, 7 or 8, characterized in that, The concentration of the pH fluorescence sensor in the mixed solution in step (1) is 10 -6 ~10 -3 mol / L.

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