A halogenated Schiff base as a fluorescent probe for detecting water content in ethanol or DMF

Abstract

The present invention discloses a halogenated Schiff base as a fluorescent probe for detecting water content in ethanol or DMF. The detection method using the fluorescent probe of the present invention for detecting water content in DMF and ethanol is rapid, convenient and low-cost. Among them, the 3,5-Cl Salen probe can achieve full-range detection of water content (0-100 wt%) in ethanol and DMF. At the same time, the probe also has the advantages of fast response speed (within 10 s), high stability (180 days) and extraordinary repeatability (15 cycles). The fluorescence sensing test paper based on the halogenated Schiff base 3,5-Cl Salen of the present invention combined with a smartphone realizes rapid, sensitive, accurate, simple and economical on-site detection of different water contents in DMF and ethanol, can also be effectively applied in actual samples, and can be reused, promising to bring higher efficiency and reliability to fields such as industrial production and environmental monitoring.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluorescent probes, and particularly relates to a halogenated Schiff base as a fluorescent probe for detecting the water content in ethanol or DMF. Background Art

[0002] The detection of water content is an important part of the brewing industry and chemical production. Precise control of the water content can directly affect the catalytic and regulatory fermentation and the growth process of microorganisms, and plays a decisive role in ensuring the quality, taste and appearance of products. In addition, the real-time monitoring of water content can reduce corruption and pollution in the production process, extend the service life of equipment and save costs. Therefore, it is of great significance to develop a water content detection probe that is effective, fast, convenient and has a wide detection range.

[0003] So far, there have been various methods for the determination of water content in organic solvents, including gas chromatography, infrared spectroscopy, Raman spectroscopy, solid-phase extraction, impedance-based electrochemical methods, Karl Fischer titration, etc. However, these methods have various disadvantages to varying degrees, such as slow reaction speed, narrow detection range, high cost of materials used or lack of convenience for on-site detection. In recent years, the fluorescence detection technology of molecular water content detection probes based on the changes in the aggregation state (aggregation-induced emission (AIE) and aggregation fluorescence quenching (ACQ) mechanisms) has received extensive attention due to its advantages such as simplicity, high efficiency and intuitiveness. However, the formation of the aggregation state of molecular water content detection probes depends on the response of molecules to the change in the external environment polarity and the strength of intermolecular interactions. And it is difficult to avoid the participation of many and strong H bonds from excitation to the completion of the aggregation state change for traditional probes. They are relatively sensitive to the change in polarity, and the response range of the driving force is relatively limited. Therefore, the signal response range of traditional probes is generally small. In addition, the change in the aggregation state of the same type of molecular probes is usually attributed to the relatively fixed intermolecular interaction mode. The regulation strategy of the detection range of traditional probes often focuses on the redesign of the probe molecular skeleton. However, the change in the molecular skeleton often leads to a fundamental change in the action mode, making it difficult to further regulate the detection range. How to rationally and efficiently improve the detection range of probe molecules and achieve wide-range detection of molecular probes is still a huge challenge. Summary of the Invention

[0004] The purpose of the present invention is to provide a halogenated Schiff base as a fluorescent probe for detecting the water content in ethanol or DMF, which has high sensitivity, a wide detection range and strong practicability.

[0005] The purpose of the present invention is achieved as follows. The halogenated Schiff base is 3,5-Cl Salen ((3,5 Cl-L 2 H 2)[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene]), 3,5-Br Salen ((3,5Br-L 2 H 2 )[N,N'-bis(3,5-bromosalicylaldehyde)-m-xylene]), or 3,5-I Salen ((3,5I-L 2 H 2 )[N,N'-bis(3,5-Iodosalicylaldehyde)-m-xylene]); wherein, (3,5 Cl-L 2 H 2 )[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene] is used as a probe to detect the water content in ethanol or DMF, and the detection range is 0-100% vol%.

[0006] The change of different halogen atoms can linearly change the charge distribution on the benzene ring, precisely control the strength of intermolecular interactions, and thus linearly change the detection range of the molecular probe. The intermolecular π-involved interaction is the main driving force for the change of the aggregation state, and the halogen atom can affect the electronic structure of the benzene ring through the p-π conjugation effect or the inductive effect. That is to say, the substitution of different halogens can achieve the control of the electronic distribution on the benzene ring surface. The present invention precisely regulates the strength of intermolecular interactions by changing the charge distribution on the benzene ring surface through halogen atoms. Not only is the method simple, but also since the regular change of different halogen atoms will not fundamentally affect the intermolecular interaction mode, it provides a regular regulation for the interaction strength of compounds and provides another way for the design of molecular fluorescence probes.

[0007] The detection method for detecting the water content in DMF and ethanol using the fluorescence probe of the present invention is fast, convenient, and low-cost. Among them, the 3,5-Cl Salen probe can achieve full-range detection of the water content (0-100 wt%) in ethanol and DMF. At the same time, the probe also has the advantages of fast response speed (within 10 s), high stability (180 days), and excellent repeatability (15 cycles).

[0008] In addition, the fluorescence sensing test paper based on the halogenated Schiff base 3,5-Cl Salen of the present invention combined with a smartphone realizes rapid, sensitive, accurate, simple, and economical on-site detection of different water contents in DMF and ethanol, can also be effectively applied in actual samples, and can be reused, promising to bring higher efficiency and reliability to fields such as industrial production and environmental monitoring. Description of the Drawings

[0009] Figure 1 FT-IR spectrum of 3,5-Cl Salen;

[0010] Figure 2 of 3,5-Cl Salen 1 H NMR spectrum;

[0011] Figure 3 of 3,5-Cl Salen 13 C NMR spectrum;

[0012] Figure 4 FT-IR spectrum of 3,5-Br Salen;

[0013] Figure 5 of 3,5-Br Salen 1 H NMR spectrum;

[0014] Figure 6 of 3,5-Br Salen 13 C NMR spectrum;

[0015] Figure 7 FT-IR spectrum of 3,5-I Salen;

[0016] Figure 8 of 3,5-I Salen 1 H NMR spectrum;

[0017] Figure 9 of 3,5-I Salen 13 C NMR spectrum;

[0018] Figure 10 Comparison of the H NMR spectra of 3,5-Cl Salen, 3,5-Br Salen and 3,5-I Salen 1 ;

[0019] Figure 11 Comparison of the C NMR spectra of 3,5-Cl Salen, 3,5-Br Salen and 3,5-I Salen 13 ;

[0020] Figure 12 Comparison of the (a) FT-IR and (b) XRD spectra of 3,5-Cl Salen, 3,5-Br Salen and 3,5-I Salen;

[0021] Figure 13Among them, Figures a, b, and c are the fluorescence emission spectra of 3,5-Cl Salen, 3,5-Br Salen, and 3,5-I Salen in DMF with different water contents; Figures d, e, and f are the fluorescence emission spectra of 3,5-Cl Salen, 3,5-Br Salen, and 3,5-I Salen in ethanol with different water contents;

[0022] Figure 14 Among them, Figures a and b are the fluorescence emission spectra of 3,5-Cl Salen in DMF and ethanol with different water contents (0 - 100 wt%); Figures c and d are the fluorescence photographs of 3,5-Cl Salen, 3,5-Br Salen, and 3,5-I Salen in ethanol with different water contents (0 - 100 wt%) under 365 nm ultraviolet light;

[0023] Figure 15 Among them, Figures a, b, and c are the linear graphs of the fluorescence intensities of 3,5-Cl Salen, 3,5-Br Salen, and 3,5-I Salen in DMF with different concentrations of water (0 - 100 wt%); Figures d, e, and f are the linear relationship graphs of 3,5-Cl Salen, 3,5-Br Salen, and 3,5-I Salen in ethanol with different concentrations of water (0 - 100 wt%); The insets are the corresponding linear fittings;

[0024] Figure 16 Among them, a is the ball-and-stick model of 3,5-Cl Salen; b is the two dihedral angles formed by the three benzene ring planes of 3,5-Cl Salen; c is the dimer structure diagram of 3,5-Cl Salen (left) and 3,5-Br Salen (right);

[0025] Figure 17 Among them, a and b are the schematic diagrams of the two-dimensional structures formed by the one-dimensional supramolecular chains of 3,5-Cl Salen and 3,5-Br Salen through C-H...O and X...π interactions respectively;

[0026] Figure 18 It is a visualization schematic diagram of intermolecular interactions: a is the electrostatic interaction, b is the dispersion force, and c is the total interaction;

[0027] Figure 19 Among them, a is the schematic diagram of the MEP surface of 3,5-Cl Salen (upper) and 3,5-Br Salen (lower). b is the schematic diagram of the binding energy of the self-assembled dimer of 3,5-Cl Salen (upper) and 3,5-Br Salen (lower) given by the MEP value in kJ / mol at the selected points on the surface;

[0028] Figure 20 In it, a and b are respectively the curves of the fluorescence intensity of 3,5-Cl Salen varying with time at different water contents in DMF and ethanol; c and d are respectively the fluorescence stability tests of 3,5-Cl Salen at different water contents in DMF and ethanol;

[0029] Figure 21 In it, a, b, and c are respectively the graphs of the interference experiment results of different anions, organic substances, and metal ions on 3,5-Cl Salen; d is the fluorescence photograph corresponding to c;

[0030] Figure 22 In it, a and b are respectively the response fluorescence color changes of the 3,5-Cl Salen test paper to different water contents in DMF and EtOH; c is the schematic diagram of the reversibility of the fluorescence color change after the 3,5-Cl Salen test paper is simply dried; d is the schematic diagram of the self-made portable smartphone vision detection device in Experimental Example 4; e and f are respectively the linear relationships between the G value and different water concentrations in DMF and ethanol;

[0031] Figure 23 In it, a are several kinds of commercially available alcoholic products with different water contents, b is the picture of dropping different brand wine samples into the fluorescence test paper based on 3,5-Cl Salen, c is the schematic diagram of the comparison between the water content values measured by the smartphone-assisted test paper colorimetric detection method in Experimental Example 4 and the labeled water content values, and d is the schematic diagram of the recovery rate of the method in Experimental Example 4;

[0032] Figure 24 In it, a and b are respectively the graphs of the changes in the relative fluorescence intensity values of the 3,5-Cl Salen test paper and the blank test paper during the process of dropping 10% (v / v) water-containing ethanol and drying in cycles;

[0033] Figure 25 is the graph of the fluorescence color change after the blank test paper is simply dried. Detailed implementation manners

[0034] The present invention will be further described in detail below in conjunction with the drawings and embodiments, but the present invention is not limited in any way. Any transformation or improvement based on the teachings of the present invention falls within the protection scope of the present invention.

[0035] The present invention provides a halogenated Schiff base as a fluorescence probe for detecting the water content in ethanol or DMF, and the halogenated Schiff base is (3,5 Cl-L 2 H 2 )[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene], (3,5 Br-L 2 H 2)[N,N'-bis(3,5-bromosalicylaldehyde)-m-xylene] or (3,5 I-L 2 H 2 )[N,N'-bis(3,5-Iodosalicylaldehyde)-m-xylene]; wherein, (3,5 Cl-L 2 H 2 )[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene] as a fluorescence probe for detecting the water content in ethanol or DMF has a detection range of 0 - 100% vol%.

[0036] (3,5 Cl-L 2 H 2 )[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene] as a fluorescence probe to achieve full-range detection of the water content in ethanol or DMF. The principle is that the introduction of Cl atoms reduces the intensity of π+-π- between benzene rings. Therefore, a larger external polarity change is required to drive the change of the Cl-containing probe to fully form an aggregated state.

[0037] The said (3,5 Cl-L 2 H 2 )[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene] as a fluorescence probe can reach fluorescence equilibrium within 10 s after being added to a quantitative solvent, and the fluorescence intensity remains unchanged within 180 days, being in a stable state.

[0038] (3,5 Cl-L 2 H 2 )[N,N'-bis(3,5-chlorosalicylaldehyde)-m-xylene] as a fluorescence probe has detection limits of 0.45 vol% and 0.59 vol% in DMF or ethanol solutions respectively.

[0039] The present invention also provides a detection reagent or test paper for detecting the water content in ethanol or DMF based on the said halogenated Schiff base.

[0040] The preparation method of the detection test paper is as follows: soak the test paper in the solution of the halogenated Schiff base for 24 hours, and then dry it in an oven at 105 °C for 30 minutes to obtain the detection test paper.

[0041] The fluorescence of the said detection test paper quenches after dropping ethanol with 10% water content, but the fluorescence will recover after redrying, and its cyclic process can reach more than 15 times.

[0042] During detection, the volume of the solution to be detected dropped is 1 - 10 μL.

[0043] The present invention will be further described below in conjunction with embodiments.

[0044] Example 1 Synthesis of 3,5-Cl Salen (Compound 1)

[0045]

[0046] A mixture of 3,5-dichlorosalicylaldehyde (0.191 g, 1 mmol) and m-xylylenediamine (62 μL, 0.5 mmol) was dissolved in ethanol (50 mL), stirred at room temperature for 2 hours and filtered. After slow evaporation for 3 days, brown transparent crystals of 3,5-Cl Salen were obtained, washed with ethanol and dried in air (yield: 68.3%). FT-IR (KBr, cm -1 ): 1631 (C=N), 1292 (C-O), 1107 (C-N), 737 (O-H), 613 (C-Cl)( Figure 1 ); 1 H NMR (600 MHz, Chloroform-d) δ 14.34 (s, 2H), 8.37 (s, 2H), 7.45 – 7.36 (m, 3H), 7.29 – 7.18 (m, 5H), 4.85 (s, 4H) ( Figure 2 ); 13C NMR (151 MHz, CDCl3) δ 164.07, 156.64, 137.77, 132.36, 129.45, 129.13, 127.30, 127.25, 122.90, 122.75, 119.52, 62.27( Figure 3 ).

[0047] Example 2 Synthesis of 3,5-Br Salen (Compound 2)

[0048]

[0049] Except for using 3,5-dibromosalicylaldehyde (0.280 g, 1 mmol) instead, the other steps were the same as in Example 1, and finally brownish-yellow crystals of 3,5-Br Salen were obtained (yield: 65.6%). FT-IR (KBr, cm -1 ): 1612 (C=N), 1288 (C-O), 1107 (C-N), 752 (O-H), 613 (C-Br) (Figure 4 ); 1 1H NMR (600 MHz, Chloroform-d) δ 14.51 (s, 2H), 8.32 (s, 2H), 7.70 (d, J = 2.3 Hz, 2H), 7.40 – 7.34 (m, 3H), 7.27 – 7.20 (m, 3H), 4.83 (s, 4H) ( Figure 5 ); 13C NMR (151 MHz, CDCl3) δ 163.88, 158.15, 137.79, 137.69, 132.87, 129.46, 127.37, 127.33, 119.93, 112.42, 109.51, 62.06( Figure 6 )。

[0050] Example 3 Synthesis of 3,5-I Salen (Compound 3)

[0051]

[0052] Except for using 3,5-diiodosalicylaldehyde (0.374 g, 1 mmol) instead, other steps were the same as in Example 1. Finally, a yellowish-brown powder of 3,5-I Salen was obtained (yield: 63.1%). FT-IR (KBr, cm-1): 1610 (C=N), 1120 (C-O), 1111 (C-N), 763 (O-H), 613 (C-I)( Figure 7 ); 1H NMR (600 MHz, Chloroform-d) δ 14.71 (s, 2H), 8.24 (s, 2H), 8.07 (d, J = 2.1 Hz, 2H), 7.55 (d, J = 2.1 Hz, 2H), 7.41 – 7.23 (m, 4H), 4.83 (s, 4H) ( Figure 8 ). 13C NMR (151 MHz, CDCl3) δ 163.55, 161.30, 148.84, 139.94, 137.63, 129.48, 127.45, 127.41, 119.76, 88.08, 78.93, 61.80( Figure 9 ).

[0053] The obtained powder was characterized in detail, such as Figure 10 and 11 , and it was found that the three halogenated Schiff bases in Examples 1-3 showed similar chemical shifts in the NMR spectrum, and most of the chemical shifts were almost exactly the same. At the same time, a similar phenomenon was also observed in the infrared spectrum ( Figure 12 a), especially the C=N double bond, which is the most important signature of Schiff base. This indicates that the three Schiff bases are identical in structure. In addition, by comparing the XRD diffraction peaks of the three halogenated Schiff base powders, it can be found that their structures are highly similar ( Figure 12 b). The above data can fully prove that the three halogenated Schiff bases synthesized in the present invention are identical in structure.

[0054] Example 4 Preparation of a colorimetric sensing test strip based on 3,5-Cl Salen prepared in Example 1

[0055] A circular test strip with a radius of 4 cm was placed in a DMF solution of 3,5-Cl Salen (concentration: 1×10 -2 mmol / ml) and soaked for 24 h to ensure that 3,5-Cl Salen could be fully absorbed onto the surface of the test strip and enter all the pores of the test strip. Then, it was dried in an oven at 80 °C for 30 min to obtain a fluorescence sensing test strip.

[0056] Experimental Example 1 Detection of water content in organic solvents using the halogenated Schiff bases prepared in Examples 1-3

[0057] 1. Prepare 10 ml of ethanol and DMF aqueous solutions with water contents of 0-90 vol.% in reagent bottles. Then, the halogenated Schiff bases prepared in Examples 1-3 were respectively added to the above solutions to a concentration of 1×10 -5 mmol / ml, and then shaken at room temperature for 10 s to ensure thorough mixing. The fluorescence emission spectra in the range of 400-700 nm were collected using a fluorescence spectrometer (Edinburgh FS-5), with an excitation wavelength of 400 nm and a slit width of 1.5 nm. Photos of the above solutions under a 365 nm ultraviolet lamp were taken using a smartphone (Oppo Reno Ace). The detection of the water content in other organic solvents was carried out in the same manner as the above steps.

[0058] Results and analysis: With the increase in water content, in DMF, the fluorescence behaviors of both 3,5-Br Salen and 3,5-I Salen molecules showed a trend of first increasing and then decreasing, but the water content ranges for fluorescence enhancement and attenuation were different. Specifically, in DMF, when the water content changed from 0% to 30%, the fluorescence intensity of 3,5-Br Salen molecules gradually increased, but showed fluorescence attenuation in the water content range of 30-100 wt% ( Figure 13b). 3,5-I Salen is similar, but the fluorescence enhancement and quenching intervals are 0 - 40 wt% and 40 - 100 wt% water content respectively ( Figure 13 c). In ethanol, although the fluorescence behavior of 3,5-Br Salen gradually decays with the increase of water content, its change is relatively large in the water content range of 0 - 10 wt% ( Figure 13 e). In contrast, in ethanol, the fluorescence enhancement and quenching intervals of 3,5-I Salen are 0 - 30 wt% and 30 - 100 wt% water content respectively ( Figure 13 f). However, the fluorescence behavior of 3,5-Cl Salen molecules is completely different. Whether in DMF or ethanol, the fluorescence behavior of 3,5-Cl Salen molecules only shows a gradually decaying trend, and this phenomenon is very obvious in the water content range of 0 - 100 wt% ( Figure 14 a and 14b).

[0059] 2. Observe the change of fluorescence intensity of three halogenated Schiff bases in DMF and ethanol solutions with the increase of water content under the irradiation of a 365 nm ultraviolet lamp.

[0060] The results are as Figure 14 shown in c and 14d, which are completely consistent with the phenomena shown in the fluorescence emission spectra.

[0061] 3. Fit the peak values of fluorescence intensity at different water contents ( Figure 15 ), and use them to describe the change of the detection range of the chemical sensors studied caused by the introduction of water in the above solvents.

[0062] Results: As Figure 15 shown in a and 15d, 3,5-Cl Salen shows a good linear relationship (R 2 = 0.993; R 2 = 0.997) with the change of water content from 0 to 100% in DMF or ethanol solutions, and its detection limits are 0.45 vol% and 0.59 vol% respectively (D = 3N / S, where D is the detection limit, N is the standard deviation of the blank sample, and S is the slope of the linear regression equation). However, due to the sudden change of the fluorescence intensity of 3,5-Br Salen and 3,5-I Salen at certain water contents, their detection ranges are relatively narrow. As Figure 15 shown in b and 15c, the detection ranges of 3,5-Br Salen and 3,5-I Salen in DMF are 30 - 100 wt% (R 2 = 0.961) and 40 - 100 wt% (R 2 = 0.940) respectively, and in ethanol are 10 - 100 wt% (R 2= 0.989) and 30 - 100 wt% (R 2 = 0.978) ( Figure 15 e and 15f). The detection range described above is exactly the same as the fluorescence behavior of the previously mentioned halogenated Schiff bases at different water contents in DMF and ethanol.

[0063] It can be seen from the above experiments that the change of halogen atoms plays a decisive role in the regulation of the response range. However, it is difficult to give a convincing explanation for the regulation mechanism of halogen atoms through optical experiments. As is well known, the molecular packing structure of luminescent materials plays an important role in their fluorescence properties and luminescence process. Therefore, in-depth study of the single crystal structure of L-X and the intermolecular interactions and packing arrangements is very valuable for understanding the relationship between halogen atoms and photophysical properties.

[0064] Experimental Example 2 X-ray Single Crystal Diffraction Analysis

[0065] In this experimental example, X-ray single crystal diffraction analysis was performed on the crystal structures of Compound 1 and Compound 2. Based on high-quality single crystal data, the regulation of the packing structure by different halogen atoms was compared to try to find out the mechanism affecting the detection range of the probe.

[0066] Single crystal analysis shows that Compound 1 and Compound 2 have the same crystal form, except that the halogen atom in Compound 2 is replaced by Br. The unit cell parameters are shown in Table 1.

[0067] Table 1 Crystallographic data and structure refinement of 3,5-Cl Salen and 3,5-Br Salen

[0068]

[0069] Compound 1 crystallizes in the monoclinic space group P21 / c, and the molecular structure is as Figure 16 shown. The main body of the molecule contains a plane formed by three benzene rings, that is, a large conjugated plane 1 and 1' formed by the benzene rings on both sides of the molecule as the main body (the S(6) ring plane formed by the intramolecular hydrogen bond between the phenolic oxygen atom and the diamine nitrogen atom and the plane formed by the bromobenzene ring in the same plane as the S(6) ring), and a small plane 2 formed by m-xylylenediamine in the center of the molecule. The dihedral angles between 1 and 1' and 2 are 76.152(42) and 75.528(40) respectively (Compound 2: 77.213(66), 75.609(72)). In addition, it is also different from the common salen-type Schiff bases. The benzene ring planes on both sides of the molecule are not parallel and the torsion angle is relatively large and close to perpendicular, reaching 71.826(14) [(Compound 2: 72.507(46))]. Therefore, the whole molecule has a twisted conformation.

[0070] Different from the high degree of twist inside the molecule ( Figure 17), good parallelism was exhibited between adjacent halogenated benzene rings, strong π-π stacking interactions were generated between the rings in the crystal packing of the molecule, and a one-dimensional supramolecular structure was formed thereby. The centroid-centroid separation of the type-I stacking mode of the compound 1 molecule occurred at the Cg1 ring at (x, y, z) to the Cg at (1 / 2 - X, 3 / 2 - Y, 1 - Z) i . The interplanar distance between the relevant centroids was 3.8379(11), the slip angle was 28.81, and the offset distance of the ring center was 1.850. Therefore, the stacking mode was offset ( Figure 16 c left). In addition, there were also additional C-H...π interactions [C(4)-H(4)i...Cg2] between the halogenated benzene ring and the benzene ring of the central diamine moiety among adjacent benzene rings. Under these two strong interactions, adjacent molecules were firmly bound together to form supramolecular chains. Different from the strong intra-chain interactions in one dimension, the interactions between supramolecular chains were significantly smaller, which could also be proven in the subsequent Hirshfeld energy analysis. The interactions maintaining the two-dimensional structure were only C-H...O (C-H ii ...O = 2.478(3), ii = 1 / 2 - X, -1 / 2 + y, 3 / 2 - Z) and X-H...Pi (C(3)-Cl(1)...Cg(1) iii = 3.3754(9)). Symmetry code: iii = X, 1 - Y, 1 / 2 + Z].

[0071] Although the single-molecule structure of compound 2 was exactly the same as that of compound 1, stronger interactions were significantly formed between adjacent molecules in compound 2. The interplanar distance between the centroids of adjacent benzene rings was further shortened to 3.753(2) ( Figure 16 c right).

[0072] Closer intermolecular distances often mean stronger intermolecular interactions. In this experiment, the CrystalExplorer software was first used to analyze the intermolecular repulsion, electrostatics, dispersion, and polarization, etc. The molecular environment of compound 1 was established at its center and around, with a maximum distance of 3.4 Å. The energy benchmark was calculated according to Mackenzie's method to scale different energy frameworks. The results showed that the scaling factors of electrostatics, dispersion, polarization, and repulsion were 1.057, 0.740, 0.871, and 0.618 respectively ( Figure 18 ).

[0073] The relative strength of the interaction energy of the obtained molecular packing in all directions exhibited a cylindrical energy framework (see Figure 19). For clarity, some insignificant contacts weaker than the threshold energy value of 20 kcal / mol were omitted in the original calculation. From the calculation results of the interaction energy, the Hirshfeld calculation results are consistent with the structural analysis results. It can be seen that the adjacent intermolecular π-π interaction related to the electrostatic interaction is of fundamental importance for the formation of the stacking structure. By removing the interactions less than 30 kJ / mol, the energy framework of the intermolecular interaction between adjacent molecules can be seen more clearly. Only the colom forming a one-dimensional supramolecular chain remains, with an interaction energy of 71.5 KJ / mol, while the interaction between one-dimensional supramolecular chains is only about 1 / 3 of the intermolecular energy (-28.7). In addition, through comparison, it is found that the introduction of Br in compound 2 significantly increases the intermolecular interaction strength and further increases the intermolecular interaction energy to -79.1 KJ / mol, that is, the substitution of Br atoms can enhance the intermolecular interaction.

[0074] The above results show that the change of different halogen atoms can linearly change the charge distribution on the benzene ring, precisely control the strength of intermolecular interaction, and thus linearly change the detection range of the molecular probe.

[0075] Experimental Example 3 Sensitivity, Stability and Anti-interference of 3,5-Cl Salen for Detecting Water Content in Organic Solvents

[0076] The detection of supramolecular aggregates and monomers is very sensitive to the solvent environment and can continuously self-assemble into supramolecular aggregates with the change of the external environment, having a very wide detection range. However, if this technology wants to find a way out in industrial applications, their sensitivity and stability are also crucial.

[0077] 1. Sensitivity Detection

[0078] Determination of the response time of 3,5-Cl Salen.

[0079] As Figure 20 shown in a and 20c, when a certain amount of water is added to the DMF and ethanol solutions of the probe, the reaction can be completed quickly, and the fluorescence remains constant rapidly within 10 seconds. With the increase of water content, the sensitivity decreases slightly, which may be due to the formation of aggregates being unfavorable for the diffusion of molecules.

[0080] 2. Stability Detection

[0081] Determine the stability of the fluorescence intensity of 3,5-Cl Salen over time.

[0082] As Figure 20As shown in Figures 18b and 20d, within 180 days, the fluorescence of 3,5-Cl Salen in DMF and ethanol solutions with different water contents hardly changed, indicating that the halogenated Schiff base 3,5-Cl Salen has excellent sensitivity and stability.

[0083] 3. Anti-interference detection

[0084] Since the use cost of distilled water is too high, tap water is mostly used in industrial production. There are various impurities in tap water, which may have an important impact on the detection of its content when added to ethanol or DMF. In this experiment, referring to the National Standard for Drinking Water Quality of the People's Republic of China (GB 5749-2022), anti-interference experiments were carried out on common metal ions, anions and organic substances involved, and the results are as Figure 21 shown.

[0085] Results: As can be seen from Figure 21 it, after adding the above-mentioned interfering substances, the fluorescence did not change significantly, indicating that 3,5-Cl Salen has high anti-interference ability and is expected to be applied in practice.

[0086] Experimental Example 4 Detection of water content in DMF and ethanol using the test paper prepared in Example 4

[0087] 1. The prepared test paper was placed under a 365 nm ultraviolet lamp, and then DMF solutions (5 μL) with different water contents (0%-100%) were dropped, and then these test papers were visually observed in the dark. The detection of the test paper for ethanol water content was the same as the above steps. Results: As shown in Figure 22 Figures 21a and 22b, it can be seen with the naked eye that as the water content increases, the fluorescence intensity at the center of the test paper gradually weakens and finally completely quenches, which is consistent with the water concentration and the same as the phenomenon mentioned above.

[0088] 2. In order to explore a rapid, reliable and convenient real-time colorimetric water content sensing method using 3,5-Cl Salen, the present invention conducted experiments using a mobile phone imaging system. The RGB values ( Figure 22 d) were extracted through a color analysis application program on the mobile phone and plotted together with the water content values. As the water content increases, the color gradually changes from blue to black, resulting in a significant decrease in complementary green, from which the water content value can be quantitatively calculated. The slope fitting is based on the green channel ( Figure 22 e and 22f), and the correlation coefficients (R 2 ) are 0.991 (DMF) and 0.998 (ethanol) respectively. And the water content value of the unknown solution can be accurately calculated from the numerical green channel through the imaging system using the fitting formula.

[0089] 3. Analysis of actual samples

[0090] To verify the feasibility and accuracy of the 3,5-Cl Salen-based fluorescent probe for detecting water content in practical applications, ten alcohol products with different water contents were purchased from the market in this experiment ( Figure 23 a), and the smartphone-assisted test strip colorimetric detection method mentioned above was used to measure the actual samples ( Figure 23 b), from which color parameters were obtained and directly replaced with linear values ( Figure 23 c).

[0091] Results: As Figure 23 shown in d and Table 2, the water content measured in the present invention was compared with the water content marked in the actual samples, and the recovery rate was between 92.9% and 104.3%. Although there were small errors, the recovery rate obtained satisfactory results. This indicates that the smartphone-assisted test strip colorimetric detection method has excellent accuracy and reliability and has important application value for rapid on-site detection of water content.

[0092] Table 2 Determination of water content in actual samples (ethanol products)

[0093]

[0094] Experimental Example 5 Detection of the reusability of the test strip prepared in Example 4

[0095] The reusability of the test strip was detected by repeatedly adding 10% ethanol solution to the test strip and then drying it.

[0096] Results: As can be seen from Figure 22 c, the test strip prepared in Example 4 is a recoverable test strip and can be used for repeated water detection more than 15 times ( Figure 24 a), while the blank test strip used as a control does not have recoverable performance ( Figure 24 b and 25).

Claims

1. Use of a halogenated Schiff base as a fluorescent probe for detecting water content in ethanol or DMF, wherein the halogenated Schiff base is 3,5-Cl Salen, and its structural formula is as follows: ； It is characterized in that when the halogenated Schiff base is used as a fluorescent probe for detecting water content in ethanol or DMF, the detection range is 0 - 100 vol%.

2. The use according to claim 1, It is characterized in that when the halogenated Schiff base is added as a fluorescent probe to a quantitative solvent, it can reach fluorescence equilibrium within 10 s, and the fluorescence intensity remains unchanged within 180 days, being in a stable state.

3. The use according to claim 1, It is characterized in that the detection limits of the halogenated Schiff base as a fluorescent probe for water content in DMF and ethanol solutions are 0.45 vol% and 0.59 vol% respectively.

4. The use according to claim 1, It is characterized in that a detection reagent or test paper for detecting water content in ethanol or DMF is prepared based on the halogenated Schiff base.

5. The use according to claim 4, It is characterized in that the preparation method of the test paper is to soak the test paper in the solution of the halogenated Schiff base for 24 hours, and then dry it in an oven at 105 °C for 30 minutes to obtain the test paper.

6. The use according to claim 4 or 5, It is characterized in that when 10% water-containing ethanol is dropped on the test paper, the fluorescence is quenched, and the fluorescence will recover after re-drying, and the cycle process can reach more than 15 times.

7. The use according to claim 4 or 5, It is characterized in that when using the test paper, the volume of the detected solution dropped is 1 - 10 μL.

8. The use according to claim 4 or 5, It is characterized in that the method for detecting water content in an organic solvent by mobile phone imaging based on the test paper is to extract the green channel (G) value on the test paper by using a mobile phone camera and a color channel extraction application program, and accurately calculate the water content value of the unknown solution through data analysis software.

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