Multiple stimuli-responsive Zn(ii)-dasa complex molecular switch, preparation method and application thereof

Abstract

The application discloses a kind of multiple stimulus response type Zn (II) -DASA complex molecular switch and preparation method and application thereof.The Zn (II) -DASA complex molecular switch is prepared by grafting DASA ligand with salicylaldehyde acylhydrazone and ZnCl2 in methanol, and crystal is obtained by solution evaporation method.The Zn (II) -DASA complex molecular switch of the application exhibits multifunctional switching characteristics of solid-state light, heat and water-induced color change and fluorescence emission, and has wide application prospect in the field of information storage medium such as photo-thermal color-reproducible erasable material, intelligent display material or anti-fake encryption material.

Description

Technical Field

[0001] The present invention belongs to the technical field of multifunctional rewritable color-changing materials, and relates to a multi-stimulus responsive Zn(II)-DASA complex molecular switch, and a preparation method and application thereof. Background Art

[0002] Stimuli-responsive materials, which are sensitive to various external stimuli such as light irradiation, temperature, mechanical pressure, voltage, and pH, have become an important development direction in the field of smart materials. In particular, photoresponsive materials can instantly change their chemical and physical properties under light irradiation, so they have great application potential in optical storage systems and optical switching molecular devices (Photochromic Benzo[b]phosphole Alkynylgold(I) Complexes with Mechanochromic Property to Serve as Multistimuli-Responsive Materials. 2018, 58(10), 3027-3031).

[0003] With the growing demand for smart materials and high-density digital storage systems with multiple addressable states, multi-stimulus-responsive functional materials are becoming increasingly important and show unique application potential in smart writing and encryption. One of the main strategies for developing multi-stimulus-responsive materials with multiple states is to integrate two or more stimuli-responsive units into a single molecule. Existing research has mainly focused on traditional organic photochromic molecules such as diarylethenes, azobenzenes, and spiropyrans. These molecules have shown broad application potential in various fields such as optical storage and optical switching, but they also have limitations such as a limited photoresponse range and poor fatigue resistance.

[0004] DASA, a novel negative photochromic molecular switch that has garnered considerable attention in recent years, boasts high color-changing efficiency, fast response, and vibrant colors. Furthermore, it responds to long-wavelength visible light, eliminating the need for short-wavelength ultraviolet light, which can damage organic materials. However, due to its complex EZ isomerization and structural rearrangements during 4π electrocyclization, solid-state photoswitching of DASA remains challenging, even hindering switching behavior in concentrated solutions. Therefore, achieving multi-stimulus responsiveness in solid-state materials through rational molecular design would greatly enhance their application in intelligent information storage systems. Summary of the Invention

[0005] The present invention aims to provide a multi-stimulus-responsive Zn(II)-DASA complex molecular switch, its preparation method, and applications. The molecular switch comprises a closed-ring salicylaldehyde acylhydrazone-grafted DASA ligand coordinated with Zn(II). The molecular switch responds to multiple environmental stimuli, including light, heat, humidity, and vacuum, and can reversibly recover. Its significant color and fluorescence changes can be exploited as an intelligent material for applications in dynamic erasable smart coatings, information anti-counterfeiting, and encryption.

[0006] The technical solutions for achieving the purpose of the present invention are as follows:

[0007] The multi-stimulus responsive Zn(II)-DASA complex molecular switch is composed of a closed-ring salicylaldehyde acylhydrazone-grafted DASA ligand coordinated with Zn(II). The coordination structure is [Zn2(DASA)2(H2O)2]·(MeOH)2, and the molecular formula is Zn2C 68 H 70 N6O 18 , the relative molecular mass is 1390.04, and the structural formula is shown in formula (IV):

[0008]

[0009] Furthermore, the Zn(II)-DASA complex molecular switch crystal of the present invention is a monoclinic crystal system with a space group of C2 / c; the unit cell parameters are a=26.966(2), b=16.5628(15), c=14.5093(11), β=93.963(11), Z=4,ρ calc =1.432mg mm -3 .

[0010] The salicylaldehyde acylhydrazone-grafted DASA ligand of the present invention is (4-((benzyl((1E,3Z)-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxolane-5-ylidene)-4-hydroxypenta-1,3-dien-1-yl)amino)methyl)-N'-((E)-2-hydroxybenzylidene)benzohydrazide, and its structural formula is shown below (III):

[0011]

[0012] The synthesis method of the Zn(II)-DASA complex molecular switch comprises the following steps:

[0013] (1) Using hydrazine hydrate as a reducing agent and reaction solvent, methyl 4-((benzylamino)methyl)benzoate and hydrazine hydrate were reacted at 120±5°C. After the reaction, water was added, the mixture was allowed to stand, and the insoluble product was separated by filtration. After drying, 4-((benzylamino)methyl)benzoic acid hydrazide (Compound (I)) was obtained. The synthetic route is as follows:

[0014]

[0015] (2) Using anhydrous ethanol as the reaction solvent, 4-((benzylamino)methyl)benzohydrazide and salicylaldehyde were refluxed at 80±5°C. After the reaction, the organic solvent was removed by rotary evaporation, and the mixture was washed and dried to obtain (E)-4-((benzylamino)methyl)-N'-(2-hydroxybenzylidene)benzohydrazide (Compound (II)). The synthetic route is as follows:

[0016]

[0017] (3) Using methanol as the reaction solvent, (E)-4-((benzylamino)methyl)-N'-(2-hydroxybenzylidene)benzohydrazide and 5-(furan-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (MAF) were reacted at room temperature. After the reaction, the precipitate was collected by filtration, washed, dried, and purified to obtain a salicylaldehyde acylhydrazone-grafted DASA ligand, namely 4-((benzyl((1E,3Z)-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxolane-5-ylidene)-4-hydroxypenta-1,3-dien-1-yl)amino)methyl)-N'-((E)-2-hydroxybenzylidene)benzohydrazide. The synthesis route is as follows:

[0018]

[0019] (4) The salicylaldehyde acylhydrazone-grafted DASA ligand is dissolved in methanol. After irradiation with visible light, the linear open-ring state is converted into a closed-ring state. A weak base is then added dropwise to deprotonate the DASA ligand. A methanol solution of ZnCl2 is then added at a molar ratio of 1:1 between the salicylaldehyde acylhydrazone-grafted DASA ligand and anhydrous ZnCl2 to react. After the reaction is completed, the solution is filtered to obtain a saturated closed-ring solution containing the Zn(II)-DASA complex molecular switch. The solution is allowed to stand at room temperature and the solvent is evaporated naturally to obtain the Zn(II)-DASA complex molecular switch. The synthesis route is as follows:

[0020]

[0021] In step (3), the structural formula of MAF is

[0022] Furthermore, in step (1), the reaction time is more than 12 hours, and the standing time is more than 12 hours; in step (2), the reaction time is more than 8 hours, and the washing method is washing with ethyl acetate more than three times; in step (3), the molar ratio of (E)-4-((benzylamino)methyl)-N'-(2-hydroxybenzylidene)benzohydrazide to MAF is 1:1.1-1.2, and the reaction time is 40-60 minutes.

[0023] Furthermore, in step (4), the weak base is triethylamine.

[0024] The Zn(II)-DASA complex molecular switch of the present invention initially exhibits a yellow closed-ring state. Upon heating within a temperature range of 60-80°C, the complex molecular switch effectively removes coordinated water molecules, resulting in reduced fluorescence and a pink partially open-ring state. This process is fully reversible. Upon exposure to the atmosphere, the treated complex molecular switch absorbs airborne water molecules and reforms the coordination, with the color and fluorescence properties fully restored to their initial state. This change can be repeated multiple times without loss of performance. Heating the pink partially open-ring state Zn(II)-DASA complex molecular switch to 120°C significantly changes its color from pink to bright red, accompanied by complete fluorescence quenching. Subsequently, upon irradiation of the bright red complex powder with a 500nm light source, the bright red complex powder returns to yellow. This color change from red to yellow induced by heating and irradiation is also fully reversible and can be repeated multiple times. Therefore, through photothermal regulation, the reversible switching of the Zn(II)-DASA complex molecular switch between different states can be achieved, including color changes between yellow, pink, and red, and the turning on and off of fluorescence.

[0025] Furthermore, the present invention provides the use of the above-mentioned Zn(II)-DASA complex molecular switch in the preparation of information storage media such as photothermochromic rewritable materials, smart display materials or anti-counterfeiting encryption materials.

[0026] Specifically, the application methods include the following:

[0027] (1) The Zn(II)-DASA complex molecular switch crystal was ground into powder, dispersed in a volatile organic solvent to form a uniform suspension, and then the suspension was coated on the surface of the substrate by blade coating to prepare the Zn(II)-DASA complex molecular switch crystal with a surface coverage concentration of ≤0.4 mg / cm 2The smart display coating can be used to emit fluorescence under ultraviolet irradiation in a dark environment. The coordinated water molecules in the coating are removed by heating and drying, thereby eliminating the fluorescence. Information is written on the coating surface using water as smart ink. The written coating is exposed to moist air or a light breath is used to erase the fluorescent information. This allows repeated storage and display of different fluorescent patterns, forming a dynamic erasable smart coating. Alternatively, a heated mold with an information pattern is used to imprint the coating. The contact area loses its fluorescence due to dehydration, thereby revealing specific graphic information. The fluorescent erased information is then restored by moist air or a light breath. Multiple rounds of erasing and writing are also possible.

[0028] or (2) grinding the Zn(II)-DASA complex molecular switch crystal into powder, dispersing it in a volatile organic solvent to form a uniform suspension, and then applying the suspension to the surface of the substrate by blade coating to prepare the Zn(II)-DASA complex molecular switch crystal with a surface coverage concentration of ≥1 mg / cm 2 Smart display coating; the smart display coating responds to fluorescence and color discernible to the naked eye induced by photothermal stimulation in the following way: the coating is briefly heated and then allowed to cool naturally in an atmospheric environment. This process is repeated, and two different color states can be observed to alternate in the solid phase as the temperature rises and falls, accompanied by reversible switching of fluorescence. After pretreatment at a base temperature of 60-80°C, the temperature is further raised to 120°C and irradiated with a light source of 500nm wavelength. Through periodic photothermal cycle treatment, reversible changes in fluorescence and color discernible to the naked eye are achieved in the solid state.

[0029] In a specific embodiment of the present invention, the organic solvent is exemplified by isopropyl alcohol.

[0030] In a specific embodiment of the present invention, the base material is paper as an example.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) The present invention cleverly introduces an organic photochromic DASA unit into the acylhydrazone ligand framework, achieving integration with coordination chemistry technology, thereby enabling the Zn(II)-DASA complex molecular switch to exhibit multifunctional switching properties of solid-state light-, heat-, and water-induced color change and fluorescence emission. Through clear single crystal structure analysis, it was confirmed that the water molecules and DASA units in the molecular switch complex achieve efficient synergistic coordination. This coordination effect not only effectively solves the problem of the DASA unit itself being difficult to photochromic due to solid-state aggregation, but also gives the material the additional ability to change color in response to changes in ambient temperature and humidity.

[0033] (2) The preparation method of the present invention is simple, the reaction conditions are mild, and the yield is more than 55%. Since the natural evaporation and crystallization occur at room temperature, it is green and environmentally friendly with little pollution, and is suitable for industrial application.

[0034] (3) The Zn(II)-DASA complex molecular switch of the present invention has dynamic regulation characteristics and can exhibit material properties of multiple stimulus responses, including light stimulation, temperature, humidity change stimulation, etc. It is sensitive to environmental changes and has the advantages of rapid response and no side reactions. In addition, unlike conventional solvent-driven color changes, the Zn(II)-DASA complex molecular switch of the present invention is used as an information storage medium such as a photothermochromic rewritable material, an intelligent display material or an anti-counterfeiting encryption material. It can achieve environmentally friendly and harmless reversible response switching of fluorescence and color through a cyclic process of water absorption and dehydration. It will not cause harm to the human body in practical applications and has great application potential in the fields of intelligent writing and anti-counterfeiting encryption. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the single crystal structure of the Zn(II)-DASA complex molecular switch.

[0036] Figure 2 This is the H NMR spectrum of the Zn(II)-DASA complex molecular switch.

[0037] Figure 3 This is the NMR two-dimensional COSY spectrum of the Zn(II)-DASA complex molecular switch.

[0038] Figure 4 This is the NMR two-dimensional DOSY spectrum of the Zn(II)-DASA complex molecular switch.

[0039] Figure 5 This is the PXRD pattern of the Zn(II)-DASA complex molecular switch.

[0040] Figure 6 Schematic diagram of the dual stimulus response process of thermochromism and photochromism, fluorescence switching and reversible recovery process of the Zn(II)-DASA complex molecular switch.

[0041] Figure 7 Actual diagram of the dual stimulus response process of thermochromism and photochromism, fluorescence switching and reversible recovery process of the Zn(II)-DASA complex molecular switch.

[0042] Figure 8 This is the fluorescence spectrum of the Zn(II)-DASA complex molecular switch.

[0043] Figure 9This is the TGA-DSC analysis diagram of the Zn(II)-DASA complex molecular switch.

[0044] Figure 10 The temperature and light reflectivity changes and cycle diagram of the Zn(II)-DASA complex molecular switch solid.

[0045] Figure 11 Demonstration of practical application of fluorescence switching by writing information on Zn(II)-DASA complex molecular switch.

[0046] Figure 12 This is a diagram of the temperature-changing and light-induced color conversion process of the solid-state coating of the Zn(II)-DASA complex molecular switch. DETAILED DESCRIPTION

[0047] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0048] In the following examples, the preparation of methyl 4-((benzylamino)methyl)benzoate was based on the literature [Nidufexor (LMB763), a Novel FXR Modulator for the Treatment of Nonalcoholic Steatohepatitis, 2020, 63, 8, 3868–3880]. The specific steps are as follows:

[0049] Methyl p-toluate and benzylamine were reacted at room temperature using methanol as solvent. After the reaction, the mixture was extracted, washed, dried, and the organic solvent was removed by rotary evaporation to obtain methyl 4-((benzylamino)methyl)benzoate. The synthetic route is as follows:

[0050]

[0051] The preparation of 5-(furan-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (MAF) was carried out according to the literature [Photoswitching Using Visible Light: A New Class of Organic Photochromic Molecules, 2014, 136, 8169-817]. The specific steps are as follows:

[0052] Using water as solvent, 2-furaldehyde and cycloisopropyl malonate were reacted at room temperature. After the reaction, the mixture was extracted, washed, dried, and the organic solvent was removed by rotary evaporation to obtain 5-(furan-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione. The synthesis route is as follows:

[0053]

[0054] Example 1

[0055] (1) Compound (I) is 4-((benzylamino)methyl)benzohydrazide, and its molecular structure is shown below:

[0056]

[0057] Prepared by the following steps:

[0058] 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 under stirring. The reaction was monitored by TLC (V 乙酸乙酯 :V 甲醇 =2:1), after the reaction was completed, 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 resulting solid was washed with ice-cold ethanol. The mixture was dried in air to obtain a white solid compound (I).

[0059] (2) Compound (II) is (E)-4-((benzylamino)methyl)-N'-(2-hydroxybenzylidene)benzohydrazide, and its molecular structure is shown below:

[0060]

[0061] Prepared by the following steps:

[0062] In a single-necked flask, compound (I) was added according to the molar ratio Salicylaldehyde (1:1) was added to anhydrous ethanol and heated under reflux at 80°C for 8 h with stirring. The solvent was then evaporated to dryness by rotary evaporation to obtain a yellow solid. The solid was washed three times with ice-cold ethyl acetate and dried in air to obtain a light yellow solid compound (II).

[0063] (3) Compound (III), a DASA ligand grafted with salicylaldehyde acylhydrazone, is 4-((benzyl((1E,3Z)-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxolane-5-ylidene)-4-hydroxypenta-1,3-dien-1-yl)amino)methyl)-N'-((E)-2-hydroxybenzylidene)benzohydrazide, and its molecular structure is shown below:

[0064]

[0065] Prepared by the following steps:

[0066] In a single-necked flask, compound (II) was added according to the molar ratio MAF Methanol was added, and the mixture was stirred at 25°C for 1 hour and then filtered to obtain a precipitate. The solid was washed with cold ethyl acetate and dried to obtain a dark purple compound (III).

[0067] (4) Target compound, Zn(II)-DASA complex molecular switch, single crystal structure as shown in the figure Figure 1 As shown, the structural formula is shown in formula (IV):

[0068]

[0069] Prepared by the following steps:

[0070] Using methanol as the reaction solvent, in a single-necked flask, the salicylaldehyde acylhydrazone-grafted DASA ligand 4-((benzyl((1E,3Z)-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxolane-5-ylidene)-4-hydroxypenta-1,3-dien-1-yl)amino)methyl)-N'-((E)-2-hydroxybenzylidene)benzohydrazide (0.05 mmol) was added to methanol (15 ml) and heated with stirring to completely dissolve it. Next, 0.025 g (0.025 mmol) of triethylamine (Et3N) was added and stirred for 5 minutes. A solution of ZnCl2 (0.0068 g, 0.05 mmol) in methanol (3 ml) was added to the reaction mixture. The reaction mixture was then filtered to obtain a saturated closed-loop solution in which the Zn(II)-DASA complex molecular switch was dissolved. The solution was placed in an open beaker and sealed with a microporous plastic wrap. The solution was allowed to stand at room temperature and the solvent was naturally evaporated. After three days, a well-shaped yellow single crystal (square plate) was obtained with a yield of 55%. The solution was characterized by NMR, single crystal diffraction, and XRD at room temperature. The results were as follows: Figure 2-5 shown.

[0071] Comparative Example 1

[0072] This comparative example is essentially the same as Example 1, except that the reaction solvent, methanol, is replaced with ethanol or acetonitrile. The saturated filtrate obtained by filtering the reaction mixture of DASA and ZnCl2 and then standing for three days yields only a complex precipitate, without precipitation of yellow crystals.

[0073] Example 2

[0074] The structure of the Zn(II)-DASA complex molecular switch crystal prepared in Example 1 was determined, and the crystal data obtained after the complex crystallized are shown in Table 1 below.

[0075] Table 1 Crystallographic parameters of Zn(II)-DASA complexes

[0076]

[0077]

[0078] Example 3

[0079] Solid-state color change property test of Zn(II)-DASA complex molecular switch:

[0080] The Zn(II)-DASA complex molecular switch exhibits multiple responsive stimuli, so its structure is switched according to the open and closed ring states of its DASA part and the desorption and adsorption states of the complex solvent, resulting in four solid products with different colors, accompanied by significant fluorescence changes.

[0081] The initial Zn(II)-DASA complex molecular switch is characterized by a pale yellow color and strong fluorescence at 471 nm. After heat treatment at 60-80°C for 10 minutes, the color reversibly changes to pink and the fluorescence intensity decays significantly. This transition is easily reversed in ambient air, and the sample can return to its initial yellow state within 5 minutes, and the high-intensity fluorescence is restored. The recovery of the pink sample to its original color depends largely on the presence of water. Further heating of the pink solid at 130°C for 20 minutes changes its color to a brighter red, accompanied by complete fluorescence quenching. Irradiation of the red powder at a wavelength of 500 nm at room temperature causes it to bleach into a yellow powder. The overall color change process is as follows Figure 6 and Figure 7 shown.

[0082] During the temperature change process, fluorescence test was performed on the solid phase powder of Zn(II)-DASA complex molecular switch, and the performance characterization results are as follows: Figure 8 As shown in the figure, it can be clearly seen that the fluorescence emission intensity at 470nm gradually decreases as the temperature rises, which also corresponds to the transition of the three states of the complex during the temperature change process. TG and DSC tests were also carried out, and the results are shown as follows: Figure 9 As shown, it is proved that the reversible fluorescence switching process of the complex is due to the adsorption and desorption of solvent water.

[0083] Example 4

[0084] Zn(II)-DASA complex molecular switch reflection property test:

[0085] By tracking the reflectivity changes of the Zn(II)-DASA complex molecular switch solid powder, its response behavior under photothermal stimulation was monitored in detail. Figure 10 As shown in the figure, we observed that during the temperature-dependent solid-state color change process, the reflectivity at 550nm gradually decreased as the color of the complex changed from initial yellow to pink and finally to bright red. This phenomenon reveals the changes in the optical properties of the complex in different color states.

[0086] Furthermore, when the complex is transformed into the DASA unit open-ring red state, the continuous use of 505 nm, 14 mW cm -2 When exposed to light of a specific wavelength, the color of the complex gradually changed from bright red to khaki, accompanied by a gradual increase in reflectivity. This result shows that the complex can achieve further color changes under light of a specific wavelength.

[0087] To test the stability of the Zn(II)-DASA complex as a molecular switch, it was subjected to multiple cycles of testing, including continuous 500nm illumination and heating. Under continuous 500nm illumination, the normalized reflectance spectrum revealed a significant increase in the complex's emissivity, approaching 1. Upon heating to 120°C, the emissivity decayed to near 0, accompanied by a reversible color shift from bright red to khaki. Importantly, even after multiple cycles, the emissivity decay was minimal, demonstrating the excellent reversible performance of the Zn(II)-DASA complex as a molecular switch.

[0088] In summary, we not only demonstrated the optical property changes of Zn(II)-DASA under photothermal stimulation, but also verified its stability and reversibility as a molecular switch. These findings provide important theoretical and experimental basis for the design and development of new photothermal responsive materials.

[0089] Example 5

[0090] Intelligent reversible color development system based on Zn(II)-DASA complex molecular switch and water-based ink:

[0091] The Zn(II)-DASA complex molecular switch prepared above was ground into powder, 20 mg was taken and mixed in 20 ml of isopropanol, and a coating solution with a standard concentration of 0.00003 mol / L was prepared using a volumetric flask. The solution was modularly applied on a stencil rice paper to coat the paper with a concentration of 0.1 mg / cm 2The low-concentration Zn(II)-DASA complex molecular switch is illuminated by ultraviolet light in the dark, and the paper soaked in the complex solution will produce a strong fluorescence effect. When the coating module is heated and dried, the coordinated water is removed, causing the fluorescence to disappear, forming a rewritable smart "whiteboard". Subsequently, use a pen containing water molecules to write English letters such as "A", "B", "C", etc. on this "whiteboard", and the fluorescence will immediately reappear, forming a clearly visible fluorescent letter pattern. The coated paper can also be heated with a stamp heated to about 80°C to quench the fluorescence in the covered area, thereby clearly showing a highly recognizable stamp pattern. Then, just place the treated paper in humid air, or blow on it gently, and the fluorescent material on the surface of the paper will absorb water. This water absorption will cause the previously displayed fluorescent pattern to gradually disappear, restoring the coated paper to its original state, as if it were a brand new fluorescent copy board. For example, Figure 11 As shown in Figure 2, the repeatability of these two processes creates a stable cycle of disappearance and reappearance of the fluorescent pattern, making information encryption and storage both secure and efficient. Each disappearance and reappearance of the fluorescent pattern is reversible, which not only ensures the confidentiality of the information but also demonstrates an innovative information hiding technique. This technique is not limited to one-time information hiding but can be used multiple times, greatly enhancing its practicality and flexibility.

[0092] When applying a pattern with an "NJUST" stamp stained with the complex suspension, the pattern coating concentration on the smear paper was increased to 1 mg / cm 2 By utilizing the strong color rendering ability of the material, there is no need to pay attention to the color change of fluorescence. The naked eye can capture clear patterns and achieve rich color information expression. Then, by subjecting it to dual stimulation of light and heat, such as drying with a hair dryer and irradiating it with a 500nm LED portable flashlight, it can achieve very sensitive environmental response color switching. By using this change, it is given a unique state code, which allows the information to be displayed dynamically. It can flexibly select and access the different state information of the material, thus achieving very sophisticated information encryption and anti-counterfeiting storage. Demonstration example Figure 12 As shown in the figure, during the reversible recovery process of the coordinated water solvent, the "NJUST" letter pattern can be clearly seen cyclically switching from yellow to pink under visible light. When the letter coating changes from yellow to pink, heating to 120°C further turns the color of the letters to bright red, at which point the fluorescence completely disappears. Then, allowing the coating pattern to cool naturally and irradiating it with a 500nm wavelength LED flashlight for 15 minutes, the bright red letters gradually return to yellow. Heating again to 120°C deepens the color, returning to deep red.

[0093] Finally, the material's sensitivity to water in fluorescence switching allows for the use of natural, harmless water solvents as reversible writing "ink," which is highly consistent with the current technological development direction of environmental friendliness and green chemistry. It eliminates the need for organic solvents that are harmful to human health to serve as writing fluids, and demonstrates potential value for large-scale practical applications.

Claims

1. A multi-stimulus responsive Zn(II)-DASA complex molecular switch, characterized in that: The coordination structure is [Zn2(DASA)2(H2O)2]·(MeOH)2, and the molecular formula is Zn2C 68 H 70 N6O 18 , the relative molecular mass is 1390.04, and the structural formula is shown in formula (IV): 。 2. The Zn(II)-DASA complex molecular switch according to claim 1, wherein The crystal is monoclinic and the space group is: C 2 / c ; The unit cell parameters are: a = 26.966(2), b = 16.5628(15), c = 14.5093(11), β = 93.963(11), V = 6449.0(10)Å 3 , Z = 4, ρ calc = 1.432 mg mm -3 .

3. The method for synthesizing the Zn(II)-DASA complex molecular switch according to claim 1 or 2, characterized in that: The steps include: (1) Using hydrazine hydrate as a reducing agent and reaction solvent, methyl 4-((benzylamino)methyl)benzoate and hydrazine hydrate were reacted at 120±5°C. After the reaction, water was added, the mixture was allowed to stand, and the insoluble product was separated by filtration. After drying, 4-((benzylamino)methyl)benzoic acid hydrazide was obtained. (2) Using anhydrous ethanol as the reaction solvent, 4-((benzylamino)methyl)benzoylhydrazide and salicylaldehyde were refluxed at 80±5°C. 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-hydroxybenzylidene)benzohydrazide; (3) Using methanol as the reaction solvent, E )-4-((Benzylamino)methyl)- N' -(2-Hydroxybenzylidene)benzoylhydrazide and 5-(furan-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (MAF) were reacted at room temperature. After the reaction, the precipitate was collected by filtration, washed, dried and purified to obtain the DASA ligand grafted with salicylaldehyde acylhydrazone, i.e., 4-((benzyl((1 E ,3 Z )-5-(2,2-dimethyl-4,6-dioxo-1,3-dioxolane-5-ylidene)-4-hydroxypenta-1,3-dien-1-yl)amino)methyl)- N' -(( E )-2-hydroxybenzylidene)benzohydrazide; (4) The salicylaldehyde acylhydrazone-grafted DASA ligand is dissolved in methanol. After irradiation with visible light, the linear open-ring state is converted into a closed-ring state. A weak base is then added to deprotonate the ligand. A methanol solution of ZnCl2 is then added at a molar ratio of 1:1 between the salicylaldehyde acylhydrazone-grafted DASA ligand and ZnCl2 to react. After the reaction is completed, the solution is filtered to obtain a saturated closed-ring solution containing the Zn(II)-DASA complex molecular switch. The solution is allowed to stand at room temperature and the solvent is evaporated naturally to obtain the Zn(II)-DASA complex molecular switch.

4. The synthesis method according to claim 3, characterized in that In step (1), the reaction time is more than 12 hours, and the standing time is more than 12 hours; in step (2), the reaction time is more than 8 hours, and the washing method is washing with ethyl acetate for more than three times; in step (3), ( E )-4-((Benzylamino)methyl)- N The molar ratio of '-(2-hydroxybenzylidene)benzoylhydrazide to MAF is 1:1.1~1.2, and the reaction time is 40~60min.

5. The synthesis method according to claim 3, characterized in that In step (4), the weak base is triethylamine.

6. Use of the Zn(II)-DASA complex molecular switch according to claim 1 or 2 in the preparation of photothermochromic rewritable materials, smart display materials or anti-counterfeiting encryption materials.

7. The use according to claim 6, characterized in that Application methods include the following: (1) The Zn(II)-DASA complex molecular switch crystal was ground into powder and dispersed in a volatile organic solvent to form a uniform suspension. The suspension was then coated on the surface of the substrate by blade coating to prepare a surface coverage concentration of ≤0.4 mg / cm2 of the Zn(II)-DASA complex molecular switch crystal. 2 The smart display coating can be used to emit fluorescence under ultraviolet irradiation in a dark environment. The coordinated water molecules in the coating are removed by heating and drying, thereby eliminating the fluorescence. Information is written on the coating surface using water as smart ink. The written coating is exposed to moist air or a light breath is used to erase the fluorescent information. This allows repeated storage and display of different fluorescent patterns, forming a dynamic erasable smart coating. Alternatively, a heated mold with an information pattern is used to imprint the coating. The contact area loses its fluorescence due to dehydration, thereby revealing specific graphic information. The fluorescent erased information is then restored by moist air or a light breath. Multiple rounds of erasing and writing are also possible. (2) The Zn(II)-DASA complex molecular switch crystal was ground into powder and dispersed in a volatile organic solvent to form a uniform suspension. The suspension was then coated on the surface of the substrate by blade coating to prepare a surface coverage concentration of ≥1 mg / cm2 of the Zn(II)-DASA complex molecular switch crystal. 2 Smart display coating; The smart display coating responds to fluorescence and color discernible to the naked eye induced by photothermal stimulation in the following way: the coating is briefly heated and then allowed to cool naturally in an atmospheric environment. This process is repeated, and two different color states can be observed to alternate in the solid phase as the temperature rises and falls, accompanied by reversible switching of fluorescence. After pretreatment at a base temperature of 60-80°C, the temperature is further raised to 120°C and irradiated with a light source of 500nm wavelength. Through periodic photothermal cycle treatment, reversible changes in fluorescence and color discernible to the naked eye are achieved in the solid state.

8. The use according to claim 7, characterized in that The organic solvent was isopropyl alcohol.

9. The use according to claim 7, characterized in that The base material is paper.

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