AIE Schiff base gel and its preparation method and application

Abstract

The present invention discloses an AIE Schiff base gel and its preparation method and application, belonging to the field of supramolecular chemistry technology. The Schiff base derivative of the AIE Schiff base gel of the present invention has a structure shown in Formula I, and the Schiff base derivative can form a gel in a variety of organic solvents and mixed solvents. Whether the metal ion solution contains Cu is judged by whether the gel is formed again. 2+ At the same time, the tetrahydrofuran solution of AIE Schiff base derivatives containing different alkoxy chains was mixed with the metal ion aqueous solution, and the ultraviolet-visible light absorption and fluorescence emission tests showed that Cu 2+ The AIE Schiff base gel containing different alkoxy chains of the present invention can achieve visible Cu 2+ The selective test is performed using the bottle inversion method of the gel test, which does not require complex instruments. The AIE Schiff base gel has broad application prospects in the analysis and detection of metal ions.

Description

Technical Field

[0001] The present invention relates to the technical field of supramolecular chemistry, and in particular to an AIE Schiff base gel and a preparation method and application thereof. Background Art

[0002] Most traditional organic small molecules exhibit significant fluorescence in solution, but in the solid state, their fluorescence intensity is easily reduced due to aggregation-induced quenching (ACQ). In recent years, fluorescent materials exhibiting aggregation-induced emission (AIE) have become a research hotspot in the cutting-edge materials field due to their unique luminescence properties and excellent solid-state photophysical properties. Gels are an ideal platform for constructing AIE fluorescent materials.

[0003] Schiff bases are aldehyde- and ketone-like compounds in which the carbonyl group is replaced by an imine or methyleneamine group. Due to their mild synthesis conditions, short reaction times, excellent optical properties, and robust ligand performance, Schiff bases are among the most widely used organic compounds in organic synthesis intermediates, chemical sensors, industrial fuels, and catalysts. Gels containing Schiff base units are of great significance in metal cation sensing. Schiff base units can perfectly integrate with the self-assembly of gels, resulting in aggregation-induced emission (AIE) properties. Copper is an essential trace element for the human body, participating in important physiological reactions such as enzyme catalysis and electron transfer. However, as copper ions accumulate, excessive copper ion concentrations in the human body can cause gastrointestinal disorders and liver and kidney damage.

[0004] Therefore, the detection of copper ions is extremely important. Currently, copper ion detection has evolved from instrumental detection to visual detection, achieving high efficiency and convenience. The use of gel as a multifunctional visual probe will greatly facilitate the detection field. The prepared gel can be used as a multifunctional material for visual detection of copper ions. Summary of the Invention

[0005] The present invention aims to address the current problem of excessive copper ion content in environmental water sources, which poses a significant threat to people's lives. The present invention proposes an AIE Schiff base gel, its preparation method, and its application. The gel of the present invention has the advantages of simple raw materials, convenient preparation, and easy storage. It solves the problems of the prior art at a low cost.

[0006] The technical solution of the present invention is:

[0007] An AIE Schiff base gel, characterized in that it contains a Schiff base derivative, wherein the Schiff base derivative has a structure shown in Formula I:

[0008]

[0009] Where R = C n H 2n+1 or Cm F 2m+1 ,

[0010] n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18 or 20,

[0011] m is 4, 6, 8 or 10.

[0012] A method for preparing the AIE Schiff base gel as described above comprises the following steps:

[0013] (1) reacting an aniline derivative with 2-hydroxy-1-naphthaldehyde to obtain a Schiff base derivative;

[0014]

[0015] Where R = C n H 2n+1 or C m F 2m+1 ,

[0016] n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18 or 20,

[0017] m is 4, 6, 8 or 10;

[0018] (2) The Schiff base derivative is heated and dissolved in a solvent, cooled and allowed to stand, and a gel is obtained by judging by the bottle inversion method.

[0019] As a further improvement of this scheme, the synthesis steps of step (1) are as follows: dissolving aniline derivatives containing different alkoxy chains and 2-hydroxy-1-naphthaldehyde in anhydrous ethanol solution, adding glacial acetic acid, and stirring and refluxing for 12 hours to obtain a series of Schiff base derivatives.

[0020] As a further improvement of this solution, in step (2), the solvent is selected from a single organic solvent or a mixed solvent consisting of an organic solvent and water; when the solvent is a single organic solvent, the gel is an organic gel; when the solvent is a mixed solvent consisting of an organic solvent and water, the gel is a hydrogel.

[0021] As a further improvement of this solution, the single organic solvent is any one of polyethylene glycol 400, dimethyl silicone oil, mineral oil, liquid paraffin, pump oil, diesel, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, and tetrahydrofuran.

[0022] As a further improvement of this solution, the mixed solvent is any one of tetrahydrofuran / water (1:5-5:1) and dimethyl sulfoxide / water (1:9-9:1).

[0023] As a further improvement of this solution, in step (2), after the heating temperature reaches 90° C., the standing time is 30 minutes.

[0024] A further improvement of this solution is that the AIE Schiff base hydrogel is applied to Cu 2+ The detection method is to heat and dissolve the Schiff base derivative and the mixed solvent (proportionate to water) at a mass concentration of 5%. After the gel is formed, a metal ion solution of not less than 0.05 mmol / L is added and mixed. Whether the metal ion solution contains Cu is determined by whether a gel is formed again. 2+ , wherein the volume ratio of the 5% Schiff base derivative mixed solvent solution and the metal ion solution is 4:1, and the mixed solvent is any one of tetrahydrofuran / water (1:5 to 5:1) and dimethyl sulfoxide / water (1:9 to 9:1).

[0025] As a further improvement of this scheme, a UV-visible absorption test method is used. A tetrahydrofuran solution of a Schiff base derivative is added to a cuvette, and then a metal ion aqueous solution is added. The concentration of the metal ion aqueous solution is 1:1 with the concentration of the Schiff base derivative tetrahydrofuran solution. The absorption peak of the UV absorption spectrum is red-shifted at 386 nm and blue-shifted at 320 nm to determine whether the metal ion solution contains Cu. 2+ .

[0026] As a further improvement of this scheme, a fluorescence emission test method is used. A tetrahydrofuran solution of a Schiff base derivative is added to a cuvette, and then a metal ion aqueous solution is added. The concentration of the metal ion aqueous solution is 1:1 with the concentration of the Schiff base derivative tetrahydrofuran solution. The fluorescence emission spectrum shows a significant decrease in the emission peak intensity at 530 nm and a blue shift to determine whether the metal ion solution contains Cu. 2+ .

[0027] Advantages of the present invention:

[0028] 1. The AIE Schiff base derivatives containing different alkoxy chains disclosed in the present invention have imine dynamic bonds, hydrogen bonding, and π-π stacking between aromatic rings. Due to the characteristics of proton transfer within the excited state, the Schiff base derivatives can undergo phototautomerization through intramolecular hydrogen bonding and exhibit aggregation-induced emission characteristics. The AIE Schiff base gel containing different alkoxy chains of the present invention detects copper ions mainly through the coordination between the oxygen atom on the hydroxyl group and the nitrogen atom of the Schiff base unit, resulting in changes in its ultraviolet-visible light absorption spectrum and fluorescence emission spectrum. Due to the coordination with the copper ion, the Schiff base derivative cannot undergo intramolecular rotation, resulting in fluorescence quenching. At the same time, in the gel system, the presence of copper ions weakens the hydrogen bonding of the Schiff base derivative, resulting in the lack of gel properties.

[0029] The AIE Schiff base gel containing different alkoxy chains of the present invention can achieve visible Cu 2+ The detection method is simple and quick. The Schiff base derivative is heated and dissolved in a mixed solvent with a mass concentration of 5%. After forming a gel, a metal ion solution of not less than 0.05 mmol / L is added and mixed. Whether the metal ion solution contains Cu is determined by whether a gel is formed again. 2+ At the same time, the AIE Schiff base derivatives containing different alkoxy chains can also be detected by UV-visible absorption spectrum and fluorescence emission spectrum for their Cu 2+ selectivity.

[0030] This invention provides an ion-responsive gel constructed using molecular self-assembly and a method for preparing the same. By designing the hydroxyl group on the naphthalene ring ortho to the Schiff base unit, the resonance between the hydroxyl group (OH) and the imine bond (C=N) is utilized to more easily construct a nitrogen oxide ligand, thereby coordinating with copper ions. The gel has the advantages of simple raw materials, easy preparation, and easy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0032] H4 is an AIE Schiff base derivative containing a 6-carbon alkoxy chain; F4 is an AIE Schiff base derivative containing a 6-carbon alkoxy chain.

[0033] Figure 1 For compound H4 1 H NMR spectrum;

[0034] Figure 2 For compound H4 13 C NMR spectrum;

[0035] Figure 3 Compound F4 1 H NMR spectrum;

[0036] Figure 4 For compound F4 13 C NMR spectrum;

[0037] Figure 5 For compound F4 19 F NMR spectrum;

[0038] Figure 6 Schematic diagram of the gel formed by compounds H4 and F4 in an organic solvent in Example 2;

[0039] Figure 7 Schematic diagram of the gel formed by compounds H4 and F4 in a mixed solvent in Example 3;

[0040] Figure 8 Schematic diagram of the morphology of the gel formed by compounds H4 and F4 in a mixed solvent of dimethyl sulfoxide / water (9:1) in Example 3;

[0041] Figure 9 This is a gel image after adding 5% dimethyl sulfoxide solution of compound H4 to the 0.05 M metal ion aqueous solution in Example 4 (the volume ratio of 5% dimethyl sulfoxide solution of compound H4 to 0.05 M metal ion solution is 9:1).

[0042] Figure 10 UV-visible absorption spectra after adding a tetrahydrofuran solution of Compound H4 (concentration ratio of Schiff base derivative to metal ion 1:1) to the different metal ion solutions in Example 5;

[0043] Figure 11 Cu in Example 5 2+ UV-visible absorption spectrum after the addition of an ion gradient (0-1.0 equivalent) of a tetrahydrofuran solution of compound H4;

[0044] Figure 12 Graphs showing fluorescence emission spectra after adding a tetrahydrofuran solution of Compound H4 (with a concentration ratio of Schiff base derivative to metal ion of 1:1) to different metal ion solutions in Example 6;

[0045] Figure 13 Cu in Example 6 2+ Fluorescence emission spectrum after the addition of an ion gradient (0-1.0 equivalent) of a tetrahydrofuran solution of compound H4.

[0046] Figure 14 The tetrahydrofuran solution of compound H4 in Example 7, compound H4 and Cu 2+ FT-IR spectrum of the xerogel formed by the ionic complex, compound H4, in dimethyl sulfoxide and distilled water (volume ratio 9:1). DETAILED DESCRIPTION

[0047] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and preferred embodiments.

[0048] Example 1

[0049] A method for preparing an AIE Schiff base gel, comprising the following steps:

[0050] (1) reacting an aniline derivative with 2-hydroxy-1-naphthaldehyde to obtain a Schiff base derivative;

[0051]

[0052] Where R = C n H 2n+1 or C m F 2m+1 ,

[0053] n is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18 or 20,

[0054] m is 4, 6, 8 or 10;

[0055] (2) The Schiff base derivative is heated and dissolved in a solvent, cooled and allowed to stand, and a gel is obtained by judging by the bottle inversion method.

[0056] In a specific embodiment, the synthesis routes of AIE Schiff base derivatives H4 and F4 containing 6 carbon alkoxy chains are as follows:

[0057]

[0058] The synthesis steps of H4 are as follows: 10.35 mmol of aniline containing a 6-carbon perhydroalkoxy chain and 10.35 mmol of 2-hydroxy-1-naphthaldehyde are dissolved in 30 mL of anhydrous ethanol, 1 mL of glacial acetic acid is added, and the mixture is stirred and refluxed for 12 hours. After the reaction is completed, a yellow solid is directly filtered and then recrystallized from ethanol to obtain 3.26 g of yellow solid powder. 1H NMR (400MHz, CDCl3) δ15.71 (s, 1H), 9.30 (s, 1H), 8.09 (d, J = 8.4Hz, 1H), 7.78 ( d,J=9.2Hz,1H),7.71(d,J=8.0Hz,1H),7.51(t,J=7.6Hz,1H),7.32(d,J=8.8H z,3H),7.09(d,J=8.8Hz,1H),6.97(d,J=8.8Hz,2H),3.99(t,J=6.6Hz,2H),1. 88–1.75(m,2H),1.54–1.44(m,2H),1.44–1.27(m,4H),0.94(d,J=6.8Hz,3H). 13 C NMR (101 MHz, CDCl3) δ 169.5, 158.3, 153.8, 138.5, 136.1, 133.3, 129.5, 128.0, 127.4, 123.5, 122.2, 121.6, 119.0, 115.6, 109.0, 68.6, 31.7, 29.4, 25.8, 22.7, 14.2 ppm. Yield: 91%, melting point: 82-83°C.

[0059] The synthesis steps of F4 are as follows: 5.63 mmol of aniline containing a 6-carbon perfluoroalkoxy chain and 5.63 mmol of 2-hydroxy-1-naphthaldehyde are dissolved in 25 mL of anhydrous ethanol, and 1 mL of glacial acetic acid is added. The mixture is stirred and refluxed for 12 hours. After the reaction is completed, a yellow solid is directly filtered and recrystallized from ethanol to obtain 2.66 g of bright yellow solid powder. 1 H NMR (400MHz, CDCl3) δ15.60(s,1H),9.31(s,1H),8.10(d,J=8.4Hz,1H),7.79(d,J=9.2Hz,1H),7.72(d,J=8.0Hz,1H),7.52(t ,J=7.6Hz,1H),7.34(d,J=8.8Hz,3H),7.11(d,J=9.2Hz,1H),6.98(d,J=8.4Hz,2H),4.31(t,J=6.4Hz,2H),2.76–2.54(m,2H). 13 C NMR (101MHz, CDCl3) δ168.9,157.0,154.5,139.8,136.2,133.3,129.5,128.1,127.5,123.6,121.9,121.8,119.0,115.7,109.0,60.5(t,J FC =4.6Hz),31.3(t,J FC =21.6Hz). 19F NMR (376 MHz, CDCl3) δ -80.99 (t, J = 9.4 Hz), -113.49 (t, J = 14.5 Hz), -124.29–-124.60 (m), -125.95 (t, J = 14.3 Hz) ppm. Yield: 93%, melting point: 143-144°C.

[0060] AIE Schiff base derivative H4 containing 6 carbon alkoxy chains 1 H NMR spectrum Figure 1 As shown, its 13 C NMR spectrum Figure 2 As shown; AIE Schiff base derivative F4 containing 6 carbon alkoxy chains 1 H NMR spectrum Figure 3 As shown, its 13 C NMR spectrum Figure 4 As shown, its 19 F NMR spectrum Figure 5 shown.

[0061] Example 2

[0062] The AIE Schiff base derivatives H4 and F4 containing 6 carbon alkoxy chains synthesized in Example 1 were tested for their gel properties respectively with a single organic solvent. In step (2), the solvent is selected from a single organic solvent or a mixed solvent consisting of an organic solvent and water; when the solvent is a single organic solvent, the gel is an organic gel; when the solvent is a mixed solvent consisting of an organic solvent and water, the gel is a hydrogel. The organic solvent includes any one of polyethylene glycol 400, dimethyl silicone oil, mineral oil, liquid paraffin, pump oil, diesel, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, and tetrahydrofuran. Specifically, H4 or F4 was heated to 90°C in a single organic solvent to dissolve H4 or F4, and then allowed to cool to 25°C and allowed to stand to observe its gelling ability. H4 formed an organic gel in pump oil and dimethyl silicone oil, and the organic gel had good stability and was a yellow gel. F4 formed an organic gel in pump oil, mineral oil, dimethyl silicone oil and liquid paraffin, all of which were yellow gels. The gel schematic diagram is shown as follows. Figure 6 shown.

[0063] Example 3

[0064] The gel properties of H4 and F4 synthesized in Example 1 were tested in mixed solvents (in proportion to water), and the mixed solvents were any one of tetrahydrofuran / water (1:1), dimethyl sulfoxide / water (1:1), dimethyl sulfoxide / water (2:1), dimethyl sulfoxide / water (7:3), dimethyl sulfoxide / water (8:2), and dimethyl sulfoxide / water (9:1). H4 or F4 was heated to above 90°C in a mixed organic solvent to dissolve H4 or F4, and then allowed to cool to 25°C and allowed to stand to observe its gelling ability. H4 formed gel in the mixed solvents dimethyl sulfoxide / water (8:2) and dimethyl sulfoxide / water (9:1), while F4 only formed gel in dimethyl sulfoxide / water (9:1). The schematic diagram of H4 and F4 gel is shown in the figure below. Figure 7 As shown in Figure 2, the gel morphology formed by H4 and F4 in dimethyl sulfoxide / water (9:1) is as follows: Figure 8 shown.

[0065] Example 4

[0066] The detection of metal ions by AIE Schiff base gels containing different alkoxy chains shown in formula I was studied, and Na + , K + Mg 2+ , Ca 2+ 、Ba 2+ 、Al 3+ 、Mn 2+ 、Fe 3+ 、Fe 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Zn 2+ 、Cd 2+ 、Hg 2+ This example describes the detailed study of H4.

[0067] The AIE Schiff base derivative H4 was used to form a gel in a mixed solvent of dimethyl sulfoxide / water (9:1) as a blank control. The total concentration of H4 in dimethyl sulfoxide was fixed and only the type of metal ion solution added was changed. The effects of the added ions on the entire gel system were determined in turn. + , K + Mg 2+ , Ca 2+ 、Ba 2+ 、Al 3+ 、Mn 2+ 、Fe 3+ 、Fe 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Zn 2+ 、Cd2+ 、Hg 2+ The aqueous solution of H4 was added to the dimethyl sulfoxide solution, heated to 90 ° C, and allowed to cool to 25 ° C. The solution was left to stand and observed to see if it formed a gel. The molar concentration of the metal ion aqueous solution was 0.05 mol / L. The results showed that only the solution containing Cu 2+ The system with the highest concentration of H4 could not form gel, while the other reaction systems could form gel. The gel test after adding 5% dimethyl sulfoxide solution of compound H4 (5% dimethyl sulfoxide solution of compound H4 and 0.05M metal ion solution in a volume ratio of 9:1) to aqueous solutions of different metal ions is shown in the following figure: Figure 9 shown.

[0068] Example 5

[0069] The effect of H4 on Cu was studied in detail by the change characteristics of the UV-visible absorption spectrum of compound H4. 2+ This example describes a detailed study of H4. 3.0 mL of a 25 μmol / L H4 tetrahydrofuran solution was added to a cuvette, followed by 25 μmol / L metal ion aqueous solutions. The differences in UV-visible absorption spectra were observed when different metal ions were present. The concentration of the metal ion aqueous solution was 1:1 with the concentration of the compound H4 tetrahydrofuran solution. + , K + Mg 2+ , Ca 2+ 、Ba 2+ 、Al 3 + 、Mn 2+ 、Fe 3+ 、Fe 2+ 、Co 2+ 、Ni 2+ 、Cu 2+ 、Zn 2+ The aqueous solutions are all chloride salts, Cd 2+ and Hg 2+ The results show that only the presence of Cu 2+ When the absorption peak is red-shifted at 386 nm and blue-shifted at 320 nm, the results are as follows. Figure 10 As shown. 2+ With the increase of concentration, the absorption peak has a cross point at 452nm, the absorption at 465nm gradually decreases and the absorption at 442nm gradually increases; at the same time, the absorption peak at 386nm obviously red-shifts to 389nm, and the absorption peak at 325nm blue-shifts to 320nm. It can be seen that compound H4 is obviously related to Cu 2+ Complexation occurs, and the results are as follows Figure 11 shown.

[0070] Example 6

[0071] The fluorescence emission spectrum of compound H4 was used to study the relationship between compound H4 and Cu 2+ When complexation occurs, fluorescence quenching occurs. This example describes a detailed study of H4. 3.0 mL of a 25 μmol / L tetrahydrofuran solution of H4 was added to a cuvette, followed by 25 μmol / L aqueous metal ion solutions. The differences in fluorescence emission spectra in the presence of different metal ions were observed. The same metal ions as in Example 5 were used, and the concentration of the metal ion aqueous solution was 1:1 with that of the compound H4 tetrahydrofuran solution. The results showed that only in the presence of Cu 2+ When the fluorescence emission spectrum is 530 nm, the emission peak intensity is significantly reduced and a blue shift occurs. Figure 12 As shown. 2+ Gradient test, from 0.1 equivalent to 1.0 equivalent, the emission peak obviously shifted to blue and the fluorescence intensity gradually decreased. 2+ The addition of can complex with H4 and reduce its fluorescence intensity until it is quenched. Figure 13 shown.

[0072] Example 7

[0073] Compound H4 tetrahydrofuran solution, compound H4 and Cu 2+ FT-IR spectra of the ionic complex and the xerogel formed by compound H4 in a 9:1 ratio of dimethyl sulfoxide to distilled water. The H4 solution in tetrahydrofuran and the H4 xerogel were at 1624 cm -1 The C=N stretching vibration characteristic peak also appeared at 1256 cm -1 The results show that there is hydrogen bonding between molecules. 2+ After complexation, the characteristic peak of hydroxyl group changes from 3424cm -1 Blue shift to 3391 cm -1 The characteristic peak of C=N changes from the original 1624cm -1 The sharp peak at 1599 cm-1 becomes a broad peak and -1 A new peak appears. The change in the infrared spectrum shows that the N atom on the C=N group and the O atom on the OH group participate in the Cu 2+ The results are as follows Figure 14 shown.

[0074] The present invention is described through preferred embodiments. Those skilled in the art will appreciate that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. The present invention is not limited to the specific embodiments disclosed herein, and other embodiments falling within the claims of this application fall within the scope of protection of the present invention. The present invention has multiple implementation methods, and all technical solutions formed by equivalent transformations or equivalent transformations fall within the scope of protection of the present invention.

Claims

1. An AIE Schiff base gel, characterized in that: It contains a Schiff base derivative having a structure shown in Formula I: Where R = C n H 2n+1 or C m F 2m+1 , n is 4, m is 4; the preparation method comprises the following steps: (1) reacting an aniline derivative with 2-hydroxy-1-naphthaldehyde to obtain a Schiff base derivative; Where R = C n H 2n+1 or C m F 2m+1 , n is 4, m is 4; (2) heating and dissolving the Schiff base derivative in a solvent, cooling and then allowing it to stand, and obtaining a gel by judging by the bottle inversion method; the solvent is selected from a single organic solvent or a mixed solvent consisting of an organic solvent and water; The single organic solvent is any one of dimethyl silicone oil, mineral oil, liquid paraffin, and pump oil; the mixed solvent is a mixed solution of tetrahydrofuran and water in a volume ratio of 1:5 to 5:1, or a mixed solution of dimethyl sulfoxide and water in a volume ratio of 1:9 to 9:

1.

2. The AIE Schiff base gel according to claim 1, wherein: The synthesis steps of step (1) are as follows: dissolving aniline derivatives containing different alkoxy chains and 2-hydroxy-1-naphthaldehyde in anhydrous ethanol solution, adding glacial acetic acid, stirring and refluxing for 12 hours to obtain a Schiff base derivative.

3. The AIE Schiff base gel according to claim 1, wherein: In step (2), when the solvent is a single organic solvent, the gel is an organogel; When the solvent is a mixed solvent consisting of an organic solvent and water, the gel is a hydrogel.

4. The AIE Schiff base gel according to claim 3, wherein: In step (2), the heating temperature is not less than 90° C. and the standing time is 30 minutes.

5. AIE Schiff base gel according to claim 1 on Cu 2+ Application in detection.

6. The use according to claim 5, characterized in that: The AIE Schiff base gel is applied to Cu 2+ The detection method is to heat and dissolve the Schiff base derivative and the mixed solvent. The mass concentration of the Schiff base derivative in the mixed solvent is 1-10%. After the gel is formed, 0.05mmol / L metal ion solution is added and mixed. Whether the metal ion solution contains Cu is determined by whether the gel is formed again. 2+ , wherein the mixed solvent is any ratio of tetrahydrofuran / water or dimethyl sulfoxide / water.

7. The use according to claim 5, characterized in that: Using the UV-visible absorption test method, a tetrahydrofuran solution of a Schiff base derivative was added to a cuvette, and then a metal ion aqueous solution was added. The concentration of the metal ion aqueous solution was 1:1 with that of the Schiff base derivative tetrahydrofuran solution. The absorption peak of the UV absorption spectrum was red-shifted at 386 nm and blue-shifted at 320 nm to determine whether the metal ion solution contained Cu. 2+ .

8. The use according to claim 5, characterized in that: Using the fluorescence emission test method, a tetrahydrofuran solution of a Schiff base derivative is added to a cuvette, and then a metal ion aqueous solution is added. The concentration of the metal ion aqueous solution is 1:1 with the concentration of the Schiff base derivative tetrahydrofuran solution. The fluorescence emission spectrum shows a significant decrease in the emission peak intensity at 530nm and a blue shift to determine whether the metal ion solution contains Cu. 2+ .

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