A tridentate schiff base compound, a preparation method and application thereof

Abstract

The application belongs to the technical field of fluorescent analysis and detection, and particularly relates to a tridentate Schiff base compound and a preparation method and application thereof. 2 The formylhydrazine Schiff base compound is widely applied in coordination chemistry, and a parent structure thereof can be used to better study the transformation of a complex under light stimulation, and the imino group also has good photoisomerization performance, at this time, the light stimulation can catalyze the ligand to produce more rich coordination modes, so the isomerization phenomenon of the compound under the action of ultraviolet light is tested, and the application of the compound in a colorimetric chemical sensor is studied. Further research is conducted on whether the compound has different ion selectivity after the conversion configuration under the action of ultraviolet light and the change of the coordination mode, and finally, the complex of the ligand Ni 2+ , Cu 2+ metal is synthesized.

Description

Technical Field

[0001] This invention belongs to the field of fluorescence analysis and detection technology, specifically relating to a tridentate Schiff base compound, its preparation method, and its application. Background Technology

[0002] Acylhydrazones are a class of compounds containing the -CONHN=CH- group. Due to the presence of C=N, acylhydrazones belong to a special class of Schiff bases. They are products of nucleophilic addition and subsequent elimination dehydration of acylhydrazides with aldehydes or ketones. Acylhydrazone groups include acyl groups linked by a subamino group and imine groups (hydrazone groups). The lone pair electrons on the subamino group readily form p-π conjugation with the carbonyl group and the C=N group, making acylhydrazones more stable and less prone to hydrolysis compared to other Schiff bases. The N and O atoms in acylhydrazone compounds can act as electron donors, providing coordination sites for metal ions (including rare earth metals, transition metals, and main group metals). This closely resembles the biological environment and provides a good basis for biological activity. Studies have shown that the complexes formed after the N and O atoms in the group coordinate with metal ions exhibit superior biological activity compared to free ligands. At the same time, it has a stronger coordination ability. Complexes based on acylhydrazone ligands have excellent biological and pharmaceutical activities and have wide applications in medicine, pesticides and analytical chemistry.

[0003] Fluorescent probe analysis, with its advantages of simple equipment, easy operation, high sensitivity, good selectivity, and rapid reaction, has been widely used in the detection of various cations, anions, biomolecules, neutral small molecules, and free radicals in fields such as bioanalysis, environmental monitoring, and life sciences. The development of highly selective and highly sensitive fluorescent probes is of great significance. Summary of the Invention

[0004] In view of this, the first objective of the present invention is to provide a tripentate Schiff base compound with good photostability, addressing the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A tripentate Schiff base compound with the following structural formula:

[0007]

[0008] It is worth noting that azobenzene compounds can exist in either cis or trans conformations. Trans-to-cis isomerization occurs after UV-Vis irradiation, mechanical stress, or electrostatic stimulation. Due to the thermodynamic stability of the trans isomer, thermal cis-to-trans isomerization occurs spontaneously in the dark. Azobenzene compounds exhibit remarkable photostability, as negligible decomposition occurs even after prolonged irradiation.

[0009] Obtaining colorimetric chemical sensors simply and inexpensively has always been a research focus in this field. This invention designs and synthesizes the azophenyl hydrazone compound HL. 2 Furthermore, simpler Schiff bases with additional photoactive functional groups, such as azo functional groups (–N=N–), are used as chromophores to enhance the molar extinction coefficient, making them more sensitive to the detection of metal ions.

[0010] The second objective of this invention is to provide a method for preparing the tripentate Schiff base compound as described above.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A method for preparing a tripentate Schiff base compound as described above includes the following steps:

[0013] Synthesis of S1, methyl o-nitrobenzoate

[0014] Accurately weigh methyl anthranilate aniline and dissolve it in dichloromethane to obtain solution A. Then weigh potassium peroxymonosulfonate and dissolve it in water to obtain solution B. Mix solution A and solution B and stir. Extract the aqueous layer twice with dichloromethane. After extraction, wash with 1 mol / L HCl, saturated sodium bicarbonate solution, water and brine in sequence. Finally, dry with anhydrous magnesium sulfate and remove the solvent under vacuum to obtain methyl anthranilate.

[0015] Synthesis of S2, methyl 1-o-azophenylbenzoate

[0016] Methyl o-nitrobenzoate and aniline were added to a mixed solution of ethanol and acetic acid in a volume ratio of 1:3. The solution was heated to 85°C and kept at that temperature for 24 hours. The resulting mixture was cooled to room temperature in an open container, quenched with water, extracted with ethyl acetate, dried with anhydrous Na2SO4, and filtered to obtain methyl o-azophenylbenzoate.

[0017] Synthesis of S3, o-azophenylbenzoyl hydrazine

[0018] Methyl o-azophenylbenzoate was added to methanol, followed by the addition of 80% hydrazine hydrate. The solution was heated to 65°C and reacted for 6 hours to obtain o-azophenylbenzoylhydrazine.

[0019] Synthesis of S4, o-azophenylbenzoylpyridinium hydrazone

[0020] Add o-azobenzoyl hydrazide and 2-pyridine carboxaldehyde to ethanol, and heat the solution to 80°C for 6 hours.

[0021] Preferably, in S1, the molar ratio of methyl anthranilate aniline to potassium peroxymonosulfonate is 1:2, the concentration of solution A is 1 mmol / 3 mL, and the concentration of solution B is 1 mmol / 6 mL.

[0022] In S2, the molar ratio of methyl o-nitrobenzoate to aniline is 13:15, and the concentration of aniline in the mixed solution is 3 mmol / 8 mL.

[0023] The methanol solution concentration of methyl o-azophenylbenzoate in S3 is 1 mmol / 3 mL, and the molar ratio of methyl o-azophenylbenzoate to 80% hydrazine hydrate is 10:52.

[0024] In S4, the molar ratio of o-azobenzoyl hydrazide to 2-pyridine carboxaldehyde is 1:1, and the concentration of the o-azobenzoyl hydrazide ethanol solution is 1 mmol / 15 mL.

[0025] A third object of the present invention is to provide the application of the tripodish Schiff base compound as described above.

[0026] A tridentate Schiff base compound as described above is used as a fluorescent probe in acetonitrile solution for Co 2+ Cu 2+ Applications of ion detection.

[0027] Cobalt is an essential trace element for the human body, but excessive amounts can be harmful. Simple, reliable, sensitive, and selective detection at trace levels using chemical sensors is crucial. Currently, many methods exist for measuring metal ions, with colorimetric detection being the most effective. Therefore, this invention simplifies and improves metal detection by utilizing a method where the binding of metal ions to probe molecules causes a significant change in absorbance within the visible light range. Furthermore, the compounds disclosed in this invention are the first to achieve simultaneous detection of copper and cobalt ions, providing a new research approach for the multi-scenario, multi-target application of the same colorimetric probe.

[0028] A tripentate Schiff base compound, as described above, is used as a ligand in the synthesis of photoresponsive compounds.

[0029] Given that acylhydrazones are more robust and resistant to oxidation, and are readily synthesized from esters or acyl chlorides via their acylhydrazine precursors, the combination of extremely simple preparation, chemical stability of precursors and products, and a modular approach to acylhydrazone design paves the way for novel optical switching platforms with a multitude of tunable "on-demand" properties.

[0030] Furthermore, the photoresponsive compound is a Ni compound with a tripentate Schiff base as a ligand. 2+ Cu 2+ Metal complexes.

[0031] The Ni2+ The metal complex is Ni Ⅱ (L 2 The preparation method for nickel acetate tetrahydrate (25 mg, 0.1 mmol) and ligand L2·2H2O is as follows: 2 (33 mg, 0.1 mmol) was dissolved in a mixture of 8 mL acetonitrile and 2 mL water. The solution was placed in a glass bottle and stirred at room temperature until it became clear. After being placed in a refrigerator for 1 day, brownish-red crystals were produced.

[0032] The Cu 2+ The metal complex is Cu Ⅱ (L 2 )2. The preparation method is as follows: copper chloride dihydrate (17 mg, 0.1 mmol) and ligand (33 mg, 0.1 mmol) are dissolved in 20 mL of acetonitrile solution, heated under reflux for 2 hours and volatilized at room temperature to obtain yellow cluster crystals.

[0033] This invention synthesizes o-azophenylbenzoylpyridinium hydrazone from methyl aniline o-aminobenzoate and utilizes the excellent coordination properties of tripentate Schiff bases and the photoisomerization properties of imine groups to realize the application of azophenylylhydrazone compounds in colorimetric chemical sensors. The o-azophenylbenzoylpyridinium hydrazone disclosed in this invention achieves Co in acetonitrile solution. 2+ Cu 2+ The selective detection of ions provides a new approach and method for detecting environmental pollutants based on the tunability of tridentate Schiff base ligands in their coordination chemistry. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0035] Figure 1 This is a synthetic route diagram of the tripentate Schiff base compound in Example 1 of the present invention.

[0036] Figure 2 The infrared spectrum of the tridentate Schiff base compound in Example 2 of this invention is shown.

[0037] Figure 3 This is the NMR spectrum of the tripentate Schiff base compound in Example 3 of the present invention.

[0038] Figure 4 This is the ultraviolet isomerism spectrum of the tridentate Schiff base compound in Example 4 of the present invention.

[0039] Figure 5 The probe L in Embodiment 5 of the present invention 2 The ultraviolet-visible absorption spectrum.

[0040] Figure 6 The metal complex Ni in Example 6 of this invention Ⅱ (L 2 The molecular structure of 2·2H2O.

[0041] Figure 7 The metal complex Ni in Example 6 of this invention Ⅱ (L 2 Infrared spectrum of 2·2H2O.

[0042] Figure 8 The metal complex Ni in Example 6 of this invention Ⅱ (L 2 PXRD pattern of 2·2H2O.

[0043] Figure 9 The metal complex Ni in Example 6 of this invention Ⅱ (L 2 Thermogravimetric analysis spectrum of 2·2H2O.

[0044] Figure 10 For ligand L 2 The ultraviolet spectrum. Figure 11 The graph shows the changes in the UV-Vis spectrum of the complex after irradiation with acetonitrile solution at 365 nm. Detailed Implementation

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0047] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0048] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0049] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0050] To better understand the present invention, the following embodiments are provided for further detailed description of the invention, but they should not be construed as limiting the invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description are also considered to fall within the protection scope of the present invention.

[0051] Example 1 Tridentate Schiff base compound (HL) 2 Synthesis of )

[0052] Synthesis of methyl o-nitrobenzoate

[0053] 2.25 g (15 mmol) of methyl anthranilate aniline was dissolved in 45 mL of dichloromethane. 18 g (30 mmol) of potassium peroxymonosulfonate was then dissolved in 180 mL of water. The mixture was stirred, and the aqueous layer was extracted twice with DCM. After extraction, the solution was washed with 1 M HCl, saturated sodium bicarbonate solution, water, and brine, and finally dried over anhydrous magnesium sulfate. The solvent was removed under vacuum to obtain methyl anthranilate.

[0054] Synthesis of methyl o-azophenylbenzoate

[0055] 2.2 g (13 mmol) of methyl o-nitrobenzoate and 1.35 g (15 mmol) of aniline were added to a mixture of 10 mL of ethanol and 30 mL of acetic acid. The solution was heated to 85 °C and maintained for 24 hours. The resulting mixture was cooled to room temperature in an open container, quenched with 50 mL of water, extracted with 80 mL of ethyl acetate, dried over anhydrous Na₂SO₄, and filtered to obtain methyl o-azophenylbenzoate.

[0056] Synthesis of o-azophenylbenzoyl hydrazide

[0057] Methyl o-azophenylbenzoate (2.5 g, 10 mmol) was added to 30 mL of methanol, followed by the addition of 80% hydrazine hydrate (3.3 g, 52 mmol). The solution was heated to 65 °C and reacted for 6 hours to obtain o-azophenylbenzoylhydrazine.

[0058] Synthesis of o-azophenylbenzoylpyridine hydrazone

[0059] 0.5 g (2 mmol) of o-azobenzoyl hydrazide and 0.24 g (2 mmol) of 2-pyridinecarboxaldehyde were added to 30 mL of ethanol and the solution was heated to 80 °C for 6 hours.

[0060] Example 2 Infrared Spectroscopic Characterization

[0061] Approximately 1 mg of sample was thoroughly ground and mixed with dry potassium bromide or potassium chloride powder in a smooth agate mortar. The mixture was then pounded using a specially designed mold at a pressure of 800–1000 kg / cm². 2 The mixture is pressed into discs under pressure. The discs are carefully removed, placed on a salt disc holder, and then placed in an infrared spectrometer to record the infrared spectrum.

[0062] Tridentate Schiff base compound HL 2 Infrared spectrum ( Figure 2 ) at 3434cm -1 There is a relatively broad absorption peak at 1677 cm⁻¹, which can be attributed to the absorption peak of (NH) in the compound molecule. Due to the strong conjugation effect of (C=O) in the compound being connected to the secondary amine and benzene ring, the characteristic peak of (C=O) in the compound molecule appears at 1677 cm⁻¹. -1 The characteristic infrared peak of the compound (C=N) is at 1542 cm⁻¹. -1 Finally, the characteristic peak belonging to azo compounds appears at 776 cm⁻¹ in the fingerprint region. -1 The weaker peaks appearing in the remaining infrared spectra can all be attributed to the aromatic rings in the compound molecule.

[0063] Example 3: NMR Characterization

[0064] ligand HL 2 The proton NMR spectrum was measured on a Varian 640 400 MHz NMR spectrometer, and the result was obtained using d... 6 -CDCl3 is the solvent, and the chemical shifts of all hydrogen atoms are assigned as follows: Figure 3 As shown. 7.26-7.27 (1H, d) belongs to the hydrogen at position 3; 7.56-7.60 (5H, q) belongs to the hydrogen at positions 8-12; 7.70-7.73 (1H, t) belongs to the hydrogen at position 4; 7.80-7.81 (1H, d) belongs to the hydrogen at position 20; 7.82-7.86 (2H, t) belongs to the hydrogen at positions 24 and 25; 8.18 (1H, s) belongs to the hydrogen at position 7; 8.22-8.24 (1H, d) belongs to the hydrogen at position 5; 8.44-8.46 (1H, t) belongs to the hydrogen at position 23; 8.56-8.58 (1H, d) belongs to the hydrogen at position 2; 11.88 (1H, s) belongs to the hydrogen at position 17.

[0065] Example 4: Determination of the UV isomerism properties of tridentate Schiff base compounds

[0066] The photoisomerization properties of this tridentate Schiff base compound were determined using ultraviolet light at 365 nm, obtained from an LP300WE 120-140V source. Detection was performed using a TU-1901 double-beam UV-Vis spectrophotometer. Photoisomerization measurements were conducted using a quartz cell with a 1 cm optical path length. The sample concentration was 4.0 × 10⁻⁵ M.

[0067] Figure 4 The tridentate Schiff base compound L was shown. 2 The changes in the absorption spectrum over time in ethanol solution revealed that the UV-Vis absorption spectrum of the tripentate Schiff base compound exhibited a broad and strong π–π* transition band at 296 nm, with a molar extinction coefficient ε of 3.48 × 10⁻⁶. 4 When the tridentate Schiff base compound L 2 Without UV irradiation, the n-π* transition band of the azo group in the 400-500 nm range is very weak. When the solution is irradiated with 365 nm UV light, the intensity of the π–π* absorption band at 296 nm gradually decreases with increasing irradiation time. Although the n-π* transition band of the azo group is extremely weak, absorption changes in the weak n-π* forbidden transition band can still be observed during irradiation. The spectral changes indicate that the azophenyl group of the tridentate Schiff base compound transforms from the trans to the cis form. The most dramatic and obvious isomerization change is observed in the first minute of irradiation with 365 nm UV light, and the solution reaches a essentially photostable state after 30 minutes of irradiation. Subsequently, the isomerized tridentate Schiff base compound L... 2 When placed at room temperature, the final absorption spectrum recovers 75%.

[0068] Example 5: Tridentate Schiff base compound as a fluorescent probe for Co in acetonitrile solution 2+ Cu 2+ Detection of ions

[0069] probe L 2 The ultraviolet-visible absorption spectrum is as follows Figure 5 As shown, when the excitation wavelength is scanned in the range of 200-600 nm, the probe L... 2 The UV-Vis absorption spectrum shows a distinct absorption peak at 296 nm, followed by a weaker absorption peak in the 400-450 nm range. Subsequently, upon adding twice the equivalent amount of different metal ions, it was observed that the addition of Co... 2+ Cu 2+ Hg 2+ The solution underwent a significant color change upon the addition of Co. 2+ The ion probe solution turned light green upon addition of Cu. 2+The solution of the ion becomes darker yellow upon addition of Hg. 2+ The pale yellow tinge of the ion probe molecules faded, and the solution became colorless, transparent, and turbid. Subsequently, they were measured using a UV analyzer at 200-600 nm, revealing that Ca... 2+ Al 3+ Cr 3+ Fe 2+ Co 2+ Ni 2+ Cu 2 + Zn 2+ Cd 2+ Ag + Pb 2+ All curves exhibited varying degrees of redshift. Among these redshifted curves, CoCl2 and CuCl2 showed significant increases in their peaks within the 400-405 nm range, followed by a slight increase in CrCl3. Meanwhile, Fe... 3+ This leads to a significant increase in the absorption peak. Finally, there's Hg. 2+ The addition of ions causes the absorption peak to disappear because the metal coordinates with the probe molecules in the solution and precipitates.

[0070] Example 6 Metal Complex Ni Ⅱ (L 2 Characterization of 2·2H2O

[0071] (1) Crystal structure determination

[0072] Compound crystals of appropriate sizes were observed under a microscope at room temperature, and then X-ray diffraction experiments were performed at room temperature. X-ray diffraction data of the crystals were collected on an Oxford Diffraction Gemini R Ultra diffractometer using Cu-Kα rays monochromated with a graphite monochromator. At a temperature of 296K Diffraction data were collected using various methods. Diffraction data for some structures were corrected for absorption using the SADABS program. The crystal structure was determined by a combination of the direct method and the Fourier transform. All non-hydrogen atom coordinates and anisotropic parameters were corrected using full-matrix least squares. The positions of C–H atoms were calculated according to the theoretical model. OH atoms were first located using the Fourier transform, and then their hydrogen atom coordinates and isotropic parameters were corrected using full-matrix least squares, participating in the final structure refinement.

[0073] As can be seen, the complex belongs to the triclinic crystal system, and its space group is P. -1 The molecular structure of the complex is as follows Figure 6 As shown. This complex consists of two deprotonated ligand molecules and Ni. 2+The L anion is chelated with Ni(II) ions in a tridentate manner via its enolized oxygen atom and two nitrogen atoms provided by the pyridylbenzohydrazine group, forming an octahedral geometry. During coordination, the two ligand molecules are in different environments. The benzene ring of one ligand molecule is essentially in the same plane as the pyridine ring of the ligand, and forms a large angle with the benzene ring of its azophenyl group. Their dihedral angles are 10.3(1) and 59.1(9), respectively. In this ligand, the N=N double bond length is... Another ligand molecule has a benzene ring that forms a large angle with the pyridine ring in its main body, while its azophenyl ring is essentially in the same plane, with dihedral angles of 71.7(3) and 9.1(3), respectively. In this ligand molecule, its N=N is slightly elongated to...

[0074] Table 1. Complex Ni Ⅱ (L 2 Crystallographic data of 2·2H2O

[0075]

[0076]

[0077] (2) Infrared spectroscopy analysis

[0078] Infrared spectrum of the complex ( Figure 7 It can be found that the ligand is 3434cm. -1 The moderate intensity peak is at 3423 cm⁻¹ -1 The weak peak was replaced by the 1677cm peak. -1 The strong peak at (C=O) disappears, revealing the weak peak on the previously obscured aromatic ring. These two points together indicate that the HNC=O on the ligand is transformed into its enol form NC-OH, and then the H is removed to form a negatively charged ligand molecule. Therefore, the peak at 3434 cm⁻¹ in the infrared spectrum... -1 and 1677cm -1 The peaks disappeared, and the disappearance of these two characteristic peaks at 1337 cm⁻¹ was also observed. -1 A strong peak appeared, which may be attributed to the newly generated (C=N) peak. Originally, the peak at 1542 cm⁻¹ was observed in the ligand. -1 In the complex, it became 1486cm. -1 and 1462cm -1 The two peaks are due to the association of N in the original (C=N) matrix, which shifts to lower wavelengths, and the presence of peaks in the Ni metal complex. Ⅱ (L 2 In 2·2H₂O, the two ligand molecules are in different states, thus showing two peaks in the infrared spectrum (C=N). Similarly, at 773 cm⁻¹...-1 The (N=N) group at the location also showed splitting.

[0079] (3) Powder X-ray diffraction (PXRD) analysis

[0080] Powder X-ray diffraction (PXRD) was performed on a DX-2600 spectrometer. Metal complex Ni Ⅱ (L 2 Powder X-ray diffraction (PXRD) pattern of 2·2H2O Figure 8 The experimental results are basically consistent with the simulation results, indicating that the blocky product of the compound has high phase purity.

[0081] (4) Thermogravimetric analysis

[0082] Analysis of Ni metal complex using an SDT 2960 thermogravimetric analyzer Ⅱ (L 2 The structural stability of 2·2H2O was tested using N2 as the carrier gas in a temperature range of 25-1000℃ at a heating rate of 10℃·min. -1 Appendix Figure 9 The complex exhibits good thermal stability. Below 325°C, the main framework of the complex essentially does not decompose. The 5.2% mass loss was calculated to be due to two molecules of water of crystallization within the crystal, compared to a theoretical loss of 5.0%. As the test temperature increased, the crystal framework gradually collapsed, eventually reaching a constant mass at 750°C.

[0083] (5) Metal complex Ni Ⅱ (L 2 UV-Vis Spectroscopic Study of 2·2H2O

[0084] Depend on Figure 10 It can be seen that the absorbance intensity of the complex phase is significantly lower and the range is significantly wider compared to that of the ligand phase. The molar absorptivity of the strongest peak is more than halved. At the same time, the absorption at 388 nm is significantly enhanced. This is due to the effect of coordination between the ligand molecule and the metal.

[0085] Furthermore, the complex exhibited interaction with ligand L 2 Similar photoisomerism properties were observed when the complex was dissolved in acetonitrile (5 × 10⁻⁶). -5 mol·L -1 Its ultraviolet isomerism properties were also tested at a wavelength of 365 nm. Figure 11The maximum absorption wavelength of the complex appears at 304 nm, and a large absorption peak also appears at 389 nm. After ultraviolet irradiation, the absorption peak at the maximum absorption wavelength of 304 nm decreases, and the absorption peak decreases significantly after 5 minutes. After 15 minutes, it reaches a photostatic state. At the same time, the absorption peak at 389 nm shows a slight increase, indicating that the azo group in the complex also undergoes photoisomerization.

[0086] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A tripentate Schiff base compound, characterized in that, The structural formula of the compound is:

2. A method for preparing the tridentate Schiff base compound as described in claim 1, characterized in that, Includes the following steps: Synthesis of S1, methyl o-nitrobenzoate Accurately weigh methyl anthranilate aniline and dissolve it in dichloromethane to obtain solution A. Then weigh potassium peroxymonosulfonate and dissolve it in water to obtain solution B. Mix solution A and solution B and stir. Extract the aqueous layer twice with dichloromethane. After extraction, wash with 1 mol / L HCl, saturated sodium bicarbonate solution, water and brine in sequence. Finally, dry with anhydrous magnesium sulfate and remove the solvent under vacuum to obtain methyl anthranilate. Synthesis of S2, methyl 1-o-azophenylbenzoate Methyl o-nitrobenzoate and aniline were added to a mixed solution of ethanol and acetic acid in a volume ratio of 1:

3. The solution was heated to 85°C and kept at that temperature for 24 hours. The resulting mixture was cooled to room temperature in an open container, quenched with water, extracted with ethyl acetate, dried with anhydrous Na2SO4, and filtered to obtain methyl o-azophenylbenzoate. Synthesis of S3, o-azophenylbenzoyl hydrazine Methyl o-azophenylbenzoate was added to methanol, followed by the addition of 80% hydrazine hydrate. The solution was heated to 65°C and reacted for 6 hours to obtain o-azophenylbenzoylhydrazine. Synthesis of S4, o-azophenylbenzoylpyridinium hydrazone Add o-azobenzoyl hydrazide and 2-pyridine carboxaldehyde to ethanol, and heat the solution to 80°C for 6 hours.

3. The preparation method according to claim 2, characterized in that, In S1, the molar ratio of methyl anthranilate aniline to potassium peroxymonosulfonate is 1:2, the concentration of solution A is 1 mmol / 3 mL, and the concentration of solution B is 1 mmol / 6 mL. In S2, the molar ratio of methyl o-nitrobenzoate to aniline is 13:15, and the concentration of aniline in the mixed solution is 3 mmol / 8 mL. The methanol solution concentration of methyl o-azophenylbenzoate in S3 is 1 mmol / 3 mL, and the molar ratio of methyl o-azophenylbenzoate to 80% hydrazine hydrate is 10:

52. In S4, the molar ratio of o-azobenzoyl hydrazide to 2-pyridine carboxaldehyde is 1:1, and the concentration of the o-azobenzoyl hydrazide ethanol solution is 1 mmol / 15 mL.

4. An application of the tripentate Schiff base compound as described in claim 1, characterized in that, The compound was used as a fluorescent probe in acetonitrile solution for Co. 2+ Cu 2+ Ion detection.

5. An application of the tripentate Schiff base compound as described in claim 1, characterized in that, The compound is used as a ligand in the synthesis of photoresponsive compounds.

6. The application according to claim 5, characterized in that, The photoresponsive compound is a Ni compound with a tridentate Schiff base ligand. 2+ Cu 2+ Metal complexes.

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