A dabsa molecular switch of dibenzylamine bridged salicylaldehyde acylhydrazone and a preparation method thereof

Abstract

This invention discloses a dibenzylamine-bridged DASA molecular switch for salicylaldehyde hydrazone and its preparation method. The DASA molecule has the structure 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidine-5(2H)-ylidene)-4-hydroxypentan-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylene)benzoylhydrazide, which is prepared by reacting the donor (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylene)benzoylhydrazide with the acceptor 5-(furan-2-methylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione in methanol. Its advantages include: exhibiting excellent negative photochromic behavior in moderately strong aprotic polar solvents such as dichloromethane and acetonitrile; undergoing reversible linear-ring isomerization under visible light irradiation; showing significant changes in absorption peaks; and exhibiting good cyclic fatigue resistance. Furthermore, the introduced salicylaldehyde hydrazone group enhances its responsiveness to acids, bases, and metal ions, enabling reversible switching in various protic and aprotic solvents and selective recognition of different metal ions, thus showing broad application prospects in colorimetric sensing and metal ion detection.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology and relates to a dibenzylamine-bridged DASA molecular switch for salicylaldehyde hydrazone and its preparation method. Background Technology

[0002] Photoresponsive molecular switches are a key component in the construction of advanced photosensitive materials. Their core lies in the presence of organic functional groups within the molecule that can absorb light energy, enabling reversible transitions between different states under specific wavelengths of light excitation. Compared to other stimulus responses such as temperature, pH, and redox reactions, photostimulation offers unique advantages such as non-contact operation, high spatiotemporal precision, and remote controllability. However, most traditional photochromic molecules rely on ultraviolet light for activation, and the high energy of ultraviolet light can easily damage materials and biological systems, significantly limiting their applications. Therefore, developing visible light-driven photochromic systems has become an important research direction. Among them, DASA molecular switches (Donor-Acceptor Stenhouse Adducts, DASAs), as a novel class of negative photochromic molecules, exhibit excellent performance: they undergo reversible isomerization from a colored linear structure to a colorless ring structure under visible light irradiation and spontaneously recover in the dark, accompanied by significant changes in molecular configuration, size, and polarity. Since their introduction, DASA derivatives have shown broad application prospects in fields such as light-controlled switches, information storage, metal probes, drug delivery, and controlled release.

[0003] However, current DASAs systems still have significant limitations: their photochromic properties typically perform well in low- to medium-polarity solvents, but in highly polar media such as water, alcohols, and acetonitrile, they often exhibit reduced response efficiency, weakened reversibility, or insufficient cycle stability, severely limiting their practical application in biocompatible environments and complex polar systems. Meanwhile, traditional metal ion probes also have significant shortcomings: on the one hand, their recognition performance is highly dependent on the solvent environment, especially in polar organic phases (such as methanol and acetonitrile), where changes in the coordination microenvironment often lead to reduced recognition activity, decreased sensitivity, or sluggish response; on the other hand, traditional metal ion probes are mostly based on a single coordination mode, lacking specific recognition sites, resulting in poor selectivity and weak anti-interference ability in complex systems, and insufficient chemical stability of the resulting complexes. Therefore, developing a novel multifunctional molecule that can operate stably in highly polar solvents, possess visible light-driven reversible switching characteristics, and can synergistically couple light modulation with metal ion recognition signals would have significant scientific and application value for developing intelligent sensing materials adapted to complex environments and with dynamic response capabilities. Summary of the Invention

[0004] This invention, through innovative molecular structure, designs a dibenzylamine-bridged DASA compound of salicylhydrazone, which to some extent overcomes the limitation of traditional photochromic materials in performance degradation in medium- to high-aprotic polar solvents, achieving highly efficient and reversible light-driven switching behavior. Simultaneously, the introduced salicylhydrazone group endows it with specific metal ion recognition capabilities. This molecule possesses both photoresponsive and metal ion recognition properties, showing application potential in fields such as optical information encryption (e.g., anti-counterfeiting in polar solvent systems) and environmental monitoring (e.g., metal ion detection in complex solution matrices).

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

[0006] The dibenzylamine-bridged salicylhydrazone (DASA) molecule described in this invention is (4-((benzyl((1E,3Z)-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxacyclopentan-5-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylmethylene)benzoylhydrazine, and its structural formula is shown in (III) below:

[0007]

[0008] The above-mentioned method for synthesizing DASA molecular switches includes the following steps:

[0009] (1) Using hydrazine hydrate as a reducing agent and reaction solvent, methyl 4-((benzylamino)methyl)benzoate and hydrazine hydrate were reacted at 115±5℃. After the reaction was completed, the mixture was cooled and allowed to stand. The precipitated solid product was separated by filtration and dried to obtain 4-((benzylamino)methyl)benzoyl hydrazine (compound (I)). The synthetic route is as follows:

[0010]

[0011] (2) Using methanol as the reaction solvent, 4-((benzylamino)methyl)benzoyl hydrazide and salicylaldehyde were refluxed at 75±5℃. After the reaction was completed, the organic solvent was removed by rotary evaporation, and the mixture was washed and dried to obtain (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoyl hydrazide (compound (II)). The synthetic route is as follows:

[0012]

[0013] (3) Using water as the reaction solvent, 1,3-dimethylbarbituric acid and 2-furan carbaldehyde were mixed in water to undergo a nucleophilic substitution reaction to prepare 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (BAF), synthetic route;

[0014]

[0015] (4) Using methanol and dichloromethane as reaction solvents, (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoylhydrazide and 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidin-2,4,6(1H,3H,5H)-trione (BAF) were reacted at room temperature. After the reaction was completed, the precipitate was collected by filtration, ground, washed, and dried to obtain the DASA molecule of dibenzylamine-bridged salicylhydrazone, namely 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylidene)benzoylhydrazide (compound (III)). The synthetic route is as follows:

[0016]

[0017] Furthermore, in step (1), the reaction time is more than 8 hours, and the washing method is washing with ice-cold ethanol more than three times;

[0018] Further, in step (2), the molar ratio of 3-dimethylbarbituric acid to 2-furan carboxaldehyde is 1:1, and the product is extracted with dichloromethane;

[0019] Further, in step (3), the molar ratio of 3-dimethylbarbituric acid to 2-furan carboxaldehyde is 1:1, and the product is extracted with dichloromethane;

[0020] Further, in step (4), the molar ratio of (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoylhydrazine and 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione is 1:1, the reaction time is 2-4 h, and the purification method is to grind and filter with ethyl acetate and then wash with glacial ethyl acetate more than three times.

[0021] Furthermore, the present invention provides a DASA molecular switch with dibenzylamine bridging salicylhydrazone that exhibits good photochromic switching performance in a variety of aprotic solvents of different polarities and can be applied to metal ion sensing and detection in various polar solvent environments.

[0022] Specifically, the methods for testing photochromic properties and detecting metal ions include the following:

[0023] (1) 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylidene)benzoylhydrazine was prepared into test solutions using dichloromethane, tetrahydrofuran, and acetonitrile, respectively. The test solutions were irradiated with a xenon lamp as a visible light source to induce a transition from an open-ring state to a closed-ring state. The irradiated solutions were then placed in the dark to allow them to spontaneously revert to the open-ring state. The changes in the intensity of the characteristic absorption peak of the open-ring state were monitored by repeatedly performing the irradiation and dark-placement cycles using a UV-Vis spectrometer to characterize the reversibility and cycle stability of the photochromic reaction.

[0024] Furthermore, 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylene)benzoylhydrazine was dissolved in dichloromethane, tetrahydrofuran, and acetonitrile. The solution was then irradiated with white light to fade from colored to colorless, and then restored to its original color under darkness. This process was repeated multiple times.

[0025] (2) Prepare solutions of 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylidene)benzoylhydrazine with methanol or dimethyl sulfoxide, respectively, and add the metal ion compound to be tested dropwise to the solution; by observing the changes in solution color and absorbance, the specific metal ion can be detected and identified.

[0026] Further, the metal ion to be tested is fully dissolved in methanol or dimethyl sulfoxide and prepared to an appropriate concentration. The solution is then added dropwise to a methanol or acetonitrile solution of 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidine-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylidene)benzoylhydrazine.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) To address the aforementioned shortcomings of existing photochromic materials, the dibenzylamine-bridged salicylaldehyde hydrazone DASA molecule designed in this invention, through precise molecular structure modification, not only maintains excellent visible light-driven isomerization characteristics but also successfully achieves efficient and reversible photochromic switching behavior in solvents of different polarities. More importantly, the salicylaldehyde benzoylhydrazone group introduced into this molecule acts as a highly efficient coordination unit, endowing it with specific metal ion recognition capabilities, enabling it to exhibit specific responses to different metals through coordination in various solvents.

[0029] (2) The synthesis method of the present invention is efficient, green and suitable for industrialization. It has a short reaction time, high yield and few side reactions, which demonstrates excellent selectivity and atom economy; at the same time, the solution method adopted is simple, energy-saving and environmentally friendly, and has the potential for large-scale production. Attached Figure Description

[0030] Figure 1 The image shows the proton NMR spectrum of compound (III).

[0031] Figure 2 The image shows the two-dimensional COSY NMR spectrum of compound (III).

[0032] Figure 3 The image shows the infrared spectrum of compound (III).

[0033] Figure 4 The absorbance of compound (III) in acetonitrile, tetrahydrofuran, and dichloromethane solutions changes over time and is shown in cyclic UV plots.

[0034] Figure 5 The UV response spectrum of compound (III) in methanol solvent for promoted ring-opening metal ions is shown.

[0035] Figure 6 The UV response spectrum of compound (III) in methanol solvent for the promoted closed-ring state of metal ions is shown.

[0036] Figure 7 The image shows the UV response spectrum of compound (III) in dimethyl sulfoxide solvent with metal ions. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0038] In the following examples, the preparation of methyl 4-((benzylamino)methyl)benzoate was carried out in accordance with the reference [Nidufexor (LMB763), a Novel FXR Modulator for the Treatment of Nonalcoholic Steatohepatitis, 2020, 63, 8, 3868-3880], and the specific steps are as follows:

[0039] Methyl p-methylbenzoate and benzylamine were reacted at room temperature for 0.5 h using methanol as solvent. After the reaction was complete, a white flocculent solid was filtered off and then added to methanol while stirring with sodium borohydride. After the reaction was complete, the mixture was extracted with dichloromethane, and the organic solvent was removed by rotary evaporation under reduced pressure. The mixture was washed and dried to obtain methyl 4-((benzylamino)methyl)benzoate. The synthetic route is as follows:

[0040]

[0041] The preparation of 5-(furan-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (MAF) is described in reference [Photoswitching Using Visible Light: A New Class of Organic Photochromic Molecules, 2014, 136, 8169-817]. The specific steps are as follows:

[0042] Using water as the reaction solvent, 1,3-dimethylbarbituric acid and 2-furancarbaldehyde were mixed in water to undergo a nucleophilic substitution reaction to prepare 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (BAF). Synthetic route:

[0043]

[0044] Example 1

[0045] (1) Compound (I) is 4-((benzylamino)methyl)benzoylhydrazide, and its molecular structure is shown below:

[0046]

[0047] Prepared by the following steps:

[0048] In a single-necked flask, methyl 4-((benzylamino)methyl)benzoate (2.55 g, 0.01 mol) was dissolved in 20 mL of 85% hydrazine hydrate solution and refluxed at 120 °C for 12 h with stirring. The reaction was monitored by TLC (Vo). 乙酸乙酯 V 甲醇=2:1), after the reaction was complete, the reaction mixture was cooled to room temperature. 150 mL of deionized water was added, and the mixture was allowed to stand for 12 h. The insoluble product was separated by filtration, and the obtained solid was washed with ice-cold ethanol. The mixture was dried in air to give a white solid compound (I).

[0049] (2) Compound (II) is (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoylhydrazide, and its molecular structure is shown below:

[0050]

[0051] Prepared by the following steps:

[0052] In a single-necked flask, according to the molar ratio of compound (I) The solvent was added to anhydrous ethanol and heated under reflux at 80°C for 8 hours with stirring. The solvent was then evaporated to dryness by rotary evaporation to give a yellow solid. The solid was washed three times with ice-cold ethyl acetate and dried in air to give a pale yellow solid compound (II).

[0053] (3) Compound (III), a DASA ligand grafted with salicylaldehyde hydrazone, is 4-((benzyl((1E,3Z)-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxane-5-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylmethyl)benzoylhydrazine, with the molecular structure shown below:

[0054]

[0055] Prepared by the following steps:

[0056] In a single-necked flask, according to the molar ratio of compound (II) The mixture was added to methanol, stirred at 25°C for 2 hours, and then filtered to obtain a precipitate. The crude solid product was washed with a mixed solvent (V... 乙酸乙酯 V 无水乙醚 =1:20) Washing by pulping: First, dissolve in a trace amount of ethyl acetate, then add anhydrous diethyl ether and stir for 30 minutes. After filtration, wash repeatedly with cold ethyl acetate and dry to obtain a dark purple compound (III).

[0057] Example 1

[0058] Photochromic behavior of compound III in different solvents

[0059] Compound (III) was dissolved in toluene, tetrahydrofuran, dichloromethane, and acetonitrile under white light irradiation with a xenon lamp equipped with a cutoff filter below 450 nm, respectively, to prepare a concentration c = 1 × 10⁻⁶.-5 A solution of mol / L was prepared. To assess its dark stability and fatigue resistance, the solution was placed in the dark, and the UV-Vis absorption spectrum was periodically measured to monitor structural changes. After dark equilibrium was reached, illumination was applied to reduce the absorbance of the ring-opening characteristic absorption peaks (λ = 566 nm in acetonitrile, λ = 571 nm in tetrahydrofuran, and λ = 572 nm in dichloromethane) to near baseline. The solution was then placed in the dark to allow it to recover, and this process was repeated.

[0060] The results showed that the intensity of the characteristic absorption peaks decreased significantly after light irradiation in all three solvents, indicating that compound (III) could efficiently complete the photo-driven isomerization from the open-ring to the closed-ring state and reversibly recover it in the dark. Figure 4 As shown in the figure. During the cyclic test, the absorbance of the open-ring state did not show a significant decrease, proving that compound (III) has good reversible light-switching performance and cyclic stability in tetrahydrofuran, dichloromethane and acetonitrile.

[0061] Example 2

[0062] Promoter of the ring-opening metal ion response test of compound (III)

[0063] This embodiment discloses a metal ion detection method based on DASA-L1 molecules. The DASA-L1 is prepared at a concentration of 1.0 × 10⁻⁶. -5 A methanol solution of the metal ion to be tested was prepared, and after reaching dark equilibrium, it was gradually added dropwise in equal amounts under light-protected conditions until excess (concentration 1.0 × 10⁻⁶ mol / L). -5 (mol / L), and monitor changes in the UV-Vis spectrum, such as Figure 4 As shown, after adding the above ions to the DASA-L1 methanol solution, the ring-opening characteristic absorption peak at 560 nm was significantly enhanced, and simultaneously, specific coordination characteristic absorption peaks were generated in the 390 nm to 400 nm range. The intensity of these coordination peaks showed a certain linear relationship with the corresponding ion concentration (R0). 2 =0.9785, R 2 =0.93882, R 2 =0.88423), based on which quantitative detection of each target ion can be achieved; for Al 3+ The system also exhibited a regular enhancement of the open-ring characteristic absorption peak at 560 nm, but no new coordination characteristic peak was generated. Nevertheless, the intensity of this open-ring peak is similar to that of Al. 3+ The concentrations still showed a good linear relationship (R0). 2 =0.98049). By comparing the linear fitting slope (Slopez... n2+ >Slope Al3+ >Slope Ni2+ >SlopeFe2+ It was found that different metal ions promoted the ring-opening state of DASA-L1 to varying degrees, resulting in different intensities of the characteristic purple color of the ring-opening state in the solution. Therefore, this embodiment demonstrates that by utilizing the differentiated spectral response of this single sensor molecule to metal ions, it is possible to identify and detect multiple metal ions in the protic solvent methanol.

[0064] DASA-L1 was prepared at a concentration of 1.0 × 10⁻⁶. -5 mo l A dimethyl sulfoxide solution of / L was stabilized in a closed-ring state by irradiation with white light above 450 nm for 1 hour (the absorbance at the characteristic peak of ring opening at 567 nm decreased to 0.08), forming a colorless or light-colored background detection system. Al was then added dropwise to this closed-ring system. 3+ Subsequently, a significant enhancement of the ring-opening characteristic absorption peak at 567 nm was observed, along with a clear coordination characteristic peak appearing in the 376-403 nm range, indicating that Al 3+ The molecule transitions from a colorless closed-ring state to a colored open-ring state via direct coordination, and the absorbance of the open-ring peak is similar to that of Al. 3+ The concentration showed a good linear relationship (R0). 2 =0.98773), such as Figure 5 As shown. Zn was added dropwise to the same system. 2+ It can also induce a significant enhancement of the ring-opening peak at 567 nm, and the absorbance is similar to that of Zn. 2+ Concentration linear correlation (R) 2 =0.99069), such as Figure 5 As shown. However, unlike in methanol solvent, no obvious coordination characteristic peaks were observed in this process, indicating that Zn in DMSO... 2+ The conversion is primarily driven by influencing the open-ring-closed-ring equilibrium. This method utilizes a pre-established closed-ring background and monitors the colorless-to-colored conversion induced by specific metal ions and its spectral linear response to achieve the control of Al in aprotic solvents. 3+ With Zn 2+ Specific identification and quantitative detection.

[0065] Example 3

[0066] Promotes the closed-ring metal ion response test of compound (III)

[0067] This embodiment provides a method for metal ion detection based on the "closed-ring decolorization" effect of the DASA-L1 molecule. This method reveals that Fe... 3+ The regulation of this process is concentration-dependent: when 1-2 equivalents are added, the absorbance of the ring-opening absorption peak (560 nm) increases slightly, which is related to the local acidity change caused by ion hydrolysis; further increasing Fe... 3+Concentration significantly suppresses ring-opening absorption, causing a rapid decrease in absorbance and driving the system's transition from colored to colorless. Within the concentration range of 20 μm to 60 μm, ring-opening absorbance and Fe... 3+ There was a good linear relationship between the concentrations (R0). 2 =0.99744), such as Figure 6 As shown. The unique concentration dependence of this "closed-loop decolorization" response is for Fe 3+ The specific identification and quantitative analysis provides a visible light detection method based on absorbance changes.

Claims

1. A dibenzylamine-bridged DASA molecular switch for salicylaldehyde hydrazone, characterized in that, The molecular formula is C 33 H 31 N5O6, with a relative molecular mass of 593.23, has the structural formula (III):

2. The method for synthesizing the DASA molecular switch of dibenzylamine-bridged salicylhydrazone according to claim 1, characterized in that, Includes the following steps: (1) Using hydrazine hydrate as a reducing agent and reaction solvent, methyl 4-((benzylamino)methyl)benzoate and hydrazine hydrate were reacted at 115±5℃. After the reaction was completed, the mixture was cooled and allowed to stand. The crystalline product was separated by filtration, dissolved, and dried to obtain 4-((benzylamino)methyl)benzoyl hydrazine (compound (I)). (2) Using methanol as the reaction solvent, 4-((benzylamino)methyl)benzoylhydrazide and salicylaldehyde were refluxed at 75±5℃. After the reaction was completed, the reaction solvent was removed by rotary evaporation under reduced pressure, washed and dried to obtain (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoylhydrazide (compound (II)). (3) Using water as the reaction solvent, 1,3-dimethylbarbituric acid and 2-furan carbaldehyde were mixed in water to undergo a nucleophilic substitution reaction to prepare 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (BAF); (4) Using methanol and dichloromethane as reaction solvents, (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoylhydrazine and 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (BAF) were reacted at room temperature. After the reaction was completed, the precipitate was collected by filtration, ground, washed and dried to obtain the DASA molecule of dibenzylamine-bridged salicylaldehyde hydrazone, namely 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidine-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′--((E)-2-hydroxybenzylene)benzoylhydrazine (compound (III)).

3. The synthesis method according to claim 2, characterized in that, In step (1), the reaction time is more than 10 hours and the standing time is more than 10 hours; in step (2), the reaction time is more than 8 hours and the washing method is washing with ice-cold ethanol more than three times; in step (3), the molar ratio of 3-dimethylbarbituric acid to 2-furan carbaldehyde is 1:1, and the product is extracted with dichloromethane; in step (4), 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3-) (H,5H)-trione was dissolved in a mixed solvent of methanol and dichloromethane. The molar ratio of (E)-4-((benzylamino)methyl)-N′-(2-hydroxybenzylmethyl)benzoylhydrazine and 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione was 1:

1. The reaction time was 2-4 h. The purification method was to grind and filter with ethyl acetate and then wash with glacial ethyl acetate three times or more.

4. The dibenzylamine-bridged salicylhydrazone-based DASA molecular switch according to claim 1 exhibits excellent photochromic switching performance in a variety of aprotic solvents with different polarities.

5. A method for testing the photochromic properties of the DASA molecular switch as described in claim 4, characterized in that, Includes the following steps: 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylene)benzoylhydrazine was prepared into test solutions using toluene, dichloromethane, tetrahydrofuran, and acetonitrile, respectively. The solution was then irradiated with a xenon lamp to convert it from an open-ring state to a closed-ring state, followed by spontaneous reversion to the open-ring state in the dark. The intensity changes of the characteristic absorption peak during multiple "light-dark" cycles were monitored using a UV-Vis spectrometer to characterize the reversibility and cycling stability of the photochromic reaction.

6. The dibenzylamine-bridged salicylhydrazone DASA molecular switch according to claim 1 can be applied to metal ion sensing and detection in various polar solvent environments.

7. The application according to claim 6, characterized in that, 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylidene)benzoylhydrazine was dissolved in dichloromethane, tetrahydrofuran, and acetonitrile. The solution was then irradiated with white light to fade from colored to colorless, and then restored to its original color in the dark. This process was repeated multiple times.

8. A method for testing the selective recognition of metal ions by the DASA molecular switch as described in claim 7, characterized in that, Specific methods include the following: 4-((benzyl((1E,3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylene)benzoylhydrazine was prepared into solutions with methanol and dimethyl sulfoxide, respectively. The metal ion to be tested was added dropwise to the solutions. The metal ion was detected and identified by observing the changes in the color and absorbance of the solution.

9. The application according to claim 8, characterized in that, The metal ions to be tested were thoroughly dissolved in methanol and dimethyl sulfoxide and prepared to an appropriate concentration. The solution was then added dropwise to a methanol or dimethyl sulfoxide solution of 4-((benzyl((1E3Z)-5-(1,3-dimethyl-2,4,6-trioxotetrahydropyrimidine-5(2H)-ylidene)-4-hydroxypent-1,3-dien-1-yl)amino)methyl)-N′-((E)-2-hydroxybenzylidene)benzoylhydrazine.

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