A MOF-based photothermal dual-responsive material, a preparation method therefor and an application thereof

Abstract

The application belongs to the technical field of color-changing materials, and particularly relates to a MOF-based photo-thermal dual-response material and a preparation method and application thereof, which has a chemical formula of 3-BP@Cd-MOF and comprises guest 3-bromopropynyl and host Cd-MOF material; the Cd-MOF material is a three-dimensional porous structure; the 3-bromopropynyl is fixed in a one-dimensional pore of the Cd-MOF material through C≡C-H...O hydrogen bond interaction; and adjacent 3-bromopropynyl molecules are connected into a guest molecular chain through C-Br...pi halogen bond interaction. The system has thermal discoloration and photo-fading dual discoloration performance, and has potential application values in super-temperature indication, information encryption, anti-counterfeiting technology and intelligent temperature control materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of color-changing materials, and specifically relates to a MOF-based photothermal dual-response material and a preparation method and application thereof. Background Art

[0002] Color-changing materials have the property of reversibly switching between two stable states with different colors and electronic / molecular structures. This color change can be regulated by external stimuli such as light, temperature, pH, redox, and pressure. Among various stimuli-responsive materials, photochromic and thermochromic materials have attracted great attention in the field of smart materials due to their potential applications in protection, decoration, display, storage, switching, photography, etc. Some common organic photochromic molecules (such as azobenzene, spiropyran and spiroxazine, diarylethenes and fulgide) and diarylethene coordination compounds achieve color changes through molecular structure isomerization, such as cis-trans or ring opening-closing. However, viologen compounds and viologen-based metal-organic frameworks (MOFs) and some other composite systems cause their photochromism through electron transfer (ET).

[0003] So far, most photochromic compounds caused by isomerization or ET processes will only undergo thermochromism as the temperature rises. Materials that have both photochromism and thermochromism are rare. If a material has both thermochromic and photochromic properties, it is expected to have a wider range of applications. For example, it is well known that sunlight helps humans use vitamin D to promote bone growth and helps plants to photosynthesize. But if exposed to sunlight for a long time, it may cause the body temperature of animals and plants to rise, leading to heatstroke or sunburn. This color-changing material with dual functions of thermochromism and photochromism will have potential application value in smart temperature control materials. The material allows more sunlight to enter in the light state, changes color as the temperature rises, and issues an overtemperature indication at higher temperatures (such as 50°C), but such research has not yet been reported. Summary of the Invention

[0004] The present invention aims to provide a MOF-based dual-responsive photothermal material, its preparation method, and its application, overcoming the shortcomings of existing technologies. A novel host-guest system, 3-BP@Cd-MOF, is constructed using Cd-MOF and 3-bromopropyne. This system exhibits both thermochromic and photochromic properties, and has potential applications in over-temperature indication, information encryption, anti-counterfeiting technology, and intelligent temperature control materials.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] In the first aspect, the present invention provides a MOF-based photothermal dual-response material, named 3-BP@Cd-MOF, which includes a guest 3-bromopropyne and a host Cd-MOF material. The Cd-MOF material is a three-dimensional porous structure, and the 3-bromopropyne is fixed in the one-dimensional channel of the Cd-MOF material through C≡C–H···O hydrogen bonding; adjacent 3-bromopropyne molecules are connected into guest molecular chains through C–Br···π halogen bonding.

[0007] The Cd-MOF material is ([CdL2(ClO4)2]·2CH2Cl2), where L is 4-amino-3,5-di(4-pyridine-3-phenyl)-1,2,4-triazole), and a stable Cd-MOF with nanopores ([CdL2(ClO4)2]·H2O) is obtained by losing a guest dichloromethane molecule at 150°C.

[0008] The inventive concept adopted by the present invention is: Cd-MOF is a highly stable MOF material with a three-dimensional porous structure formed by Cd(ClO4)2 and 4-amino-3,5-bis(4-pyridyl-3-phenyl)-1,2,4-triazole (the preparation method can refer to the synthesis and photocatalytic hydrogen production of photosensitive Cd-MOF and fluorescence recognition of Pt-based supramolecules [D], Han Congcong, Shandong Normal University, 2022 or the self-assembly chemistry and property research based on five-membered heterocyclic bridged organic ligands and fluorescent organic ligands [D], Liu Qikui, Shandong Normal University, 2010) and can adsorb propyne molecules in its one-dimensional pores through host-guest C≡C–H···O hydrogen bond interactions, where the close contact between CH3 and the adjacent alkynyl groups is determined to be

[0009] This invention utilizes 3-bromopropyne (3-BP) instead of propyne to introduce guest molecular chains connected by halogen bonds (C–Br···π) into the pores of Cd-MOF. Bromine atoms readily generate free radicals under light stimulation. More importantly, Cd-MOF generates a guest-promoted, long-lived charge-separated state and characteristic absorption across the visible light region through a thermally induced ET process. Therefore, a new host-guest system, 3-BP@Cd-MOF, was constructed using Cd-MOF and 3-bromopropyne. This system exhibits dual color-changing properties, both thermochromic and photochromic, and has potential applications in overtemperature indication, information encryption, anti-counterfeiting technology, and intelligent temperature-control materials.

[0010] In some other embodiments, the Cd-MOF material is [CdL2(ClO4)2]·H2O, where L is 4-amino-3,5-di(4-pyridine-3-phenyl)-1,2,4-triazole).

[0011] In some other embodiments, the MOF-based photothermal dual-response material has the following response characteristics:

[0012] Under heating conditions of 45-55℃, it responds to thermochromism, changing from colorless to blue, and the response time is 20min-8h;

[0013] Under cold light irradiation, the photochromic response fades from blue to colorless, and the response time is 2-3 minutes;

[0014] Under heating conditions of 90-110℃, it responds to thermochromism, changing from blue or colorless to brown, with a response time of 0.5-1h;

[0015] Under cold light irradiation, the color will fade from brown to orange and cannot be restored to blue or colorless. The response time is 12-24 hours.

[0016] Under heating conditions of 90-110℃, it responds thermochromically, changing from orange to brown, and the response time is 0.5-1h.

[0017] In some other embodiments, the 3-BP@Cd-MOF can maintain a blue color stably for more than one month under sealed and light-proof conditions.

[0018] In a second aspect, the present invention provides a method for preparing the MOF-based photothermal dual-responsive material described in the first aspect, wherein the activated Cd-MOF crystal and 3-bromopropyne are sealed and heated to obtain a blue or brown MOF-based photothermal dual-responsive material.

[0019] In some other embodiments, when the heating temperature is 45-55° C. and the heating time is 1-10 h, a blue MOF-based photothermal dual-responsive material is obtained;

[0020] When the heating temperature is 90-110°C and the heating time is 0.5-1h, a brown MOF-based photothermal dual-responsive material is obtained.

[0021] In some other embodiments, the activation method of the Cd-MOF crystals is to activate the colorless Cd-MOF crystals at 100-150° C. for 2-5 hours.

[0022] In a third aspect, the present invention provides applications of the MOF-based photothermal dual-response material described in the first aspect in over-temperature indication, information encryption, anti-counterfeiting technology, and intelligent temperature control materials.

[0023] In a fourth aspect, the present invention provides a 3-BP@Cd-MOF doped polyvinylidene fluoride film, comprising a matrix material and a filler material uniformly dispersed in the matrix material;

[0024] The matrix material is polyvinylidene fluoride; the filling material is the MOF-based photothermal dual-response smart material described in the first aspect.

[0025] In some other embodiments, the 3-BP@Cd-MOF doped PVDF film has the following response characteristics:

[0026] Under heating conditions of 45-55℃, it responds to thermochromism and turns purple. The response time is 5-8 minutes.

[0027] Under cold light irradiation, the photochromic response fades from purple to colorless, and the response time is 2-3 minutes;

[0028] Under heating conditions of 45-55℃, it responds to thermochromism, changing from colorless to purple, and the response time is 5-8 minutes;

[0029] Under heating conditions of 90-110℃, it responds to thermochromism, changing from purple to brown, with a response time of 0.5-1h;

[0030] Under cold light irradiation, the photofading response changes from brown to orange, and the response time is 12-24h;

[0031] Under heating conditions of 90-110℃, it responds thermochromically, changing from orange to brown, and the response time is 0.5-1h.

[0032] Beneficial effects of the present invention:

[0033] (1) This invention creatively constructs a new host-guest system, 3-BP@Cd-MOF, by combining Cd-MOF and 3-bromopropyne. This system exhibits dual color-changing properties, including thermochromism and photochromism, and has potential applications in over-temperature indication, information encryption, anti-counterfeiting technology, and intelligent temperature control materials.

[0034] (2) The host-guest system 3-BP@Cd-MOF in the present invention exhibits very strong visible light absorption in the range of 400-800 nm. The 3-BP@Cd-MOF-Blue crystals are kept in airtight and light-free conditions and can be stable for at least one month.

[0035] (3) The preparation method of the host-guest system 3-BP@Cd-MOF of the present invention is simple, easy, economical and non-toxic. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0037] Figure 1The color responses of Cd-MOF and 3-BP@Cd-MOF crystals under light and heat stimulation in the embodiment of the present invention;

[0038] Figure 2 These are the performance characterization diagrams of solid-state 3-BP@Cd-MOF-Blue, 3-BP@Cd-MOF-Colorless, 3-BP@Cd-MOF-Brown, 3-BP@Cd-MOF-Light Orange, and Cd-MOF in the embodiments of the present invention, where (a) is the Fourier transform infrared spectrum, (b) is the UV-visible spectrum, (c) is the EPR spectrum, and (d) is the fluorescence emission spectrum (λ ex =315 nm), (e)-(h) are X-ray photoelectron spectroscopy (XPS);

[0039] Figure 3 The crystal structure, hydrogen bonding and C–Br…π halogen bonding diagrams of the 3-BP@Cd-MOF host-guest system in the embodiment of the present invention are shown, where (A) is the crystal structure and (B) is the hydrogen bonding C≡C–H…O(ClO4 - )(pink dashed line), N(amino)–H...Br(3-BP)(blue-green dashed line), Cpyridyl–H...O(ClO4 - )(green dashed line)and N(amino)–H…O(ClO4 - )(orange dashed line), (C) is the halogen bond effect C–Br…π;

[0040] Figure 4 This is a photograph of the color response of the 3-BP@Cd-MOF doped PVDF film under the stimulation of heat and light in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The reagents and materials used in the present invention are all common commercial products and can be purchased in the market.

[0042] The present invention will be further described below in conjunction with the embodiments:

[0043] Example 1

[0044] (1) Construction and color response of 3-BP@Cd-MOF materials

[0045] First, the colorless Cd-MOF crystals were activated at 403K for 3 hours. Then, the activated Cd-MOF crystals and 3-bromopropyne (3-BP) were sealed in a vial and placed in an oven (50°C). After about 8 hours, the blue crystals (3-BP@Cd-MOF-Blue) were obtained. Figure 1When 3-BP@Cd-MOF-Blue crystals were exposed to cold light (5W, the wavelength of the cold light source was mainly concentrated in the visible light region, that is, from approximately 400 nanometers (blue light) to 700 nanometers (red light)), a significant photochromic phenomenon occurred, and the blue color quickly faded to almost colorless within 2-3 minutes, resulting in colorless crystals (3-BP@Cd-MOF-Colorless). If the 3-BP@Cd-MOF-Blue crystals were kept in an airtight and lightless environment, the 3-BP@Cd-MOF-Blue crystals were stable for at least one month. When the nearly colorless 3-BP@Cd-MOF-Colorless crystals were heated at 50°C for 20 minutes, the blue color was restored. Further experiments showed that when heated at a higher temperature (100°C for approximately 1 hour), both 3-BP@Cd-MOF-Blue and 3-BP@Cd-MOF-Colorless crystals turned brown, resulting in brown crystals (3-BP@Cd-MOF-Brown). When exposed to cold light (5W), 3-BP@Cd-MOF-Brown crystals slowly faded to light orange, resulting in light orange crystals (3-BP@Cd-MOF-Light Orange), and could not revert to blue or colorless. Orange crystals (3-BP@Cd-MOF-Light Orange) turned brown when heated at 100°C for about an hour. The study found that exposing 3-BP@Cd-MOF-Blue and 3-BP@Cd-MOF-Colorless crystals to a 3-BP atmosphere significantly enhanced the browning effect.

[0046] (2) Structural characterization of 3-BP@Cd-MOF color-changing materials

[0047] The performance of 3-BP@Cd-MOF-Blue, 3-BP@Cd-MOF-Colorless, 3-BP@Cd-MOF-Brown, 3-BP@Cd-MOF-Light Orange and Cd-MOF were characterized. Figure 2 As shown, (a) is the Fourier transform infrared spectrum, (b) is the UV-visible spectrum, (c) is the EPR spectrum, and (d) is the fluorescence emission spectrum (λ ex =315nm), (e)-(h) are X-ray photoelectron spectroscopy (XPS). Fourier transform infrared (FT-IR) spectroscopy analysis ( Figure 2 a) Analysis showed that after Cd-MOF captured 3-BP, the Cd-MOF-induced ions at approximately 3258 (C–H) and 2125 (C≡C) cm -1 The characteristic absorption peak is located at 1606cm -1 The C=N stretching vibration absorption peaks are split into 1636 and 1606 cm-1 The two peaks reflect the strong host-guest interaction and its influence on the ligand heterocycle.

[0048] Solid-state UV-Vis absorption spectroscopy ( Figure 2 b) shows that compared with Cd-MOF, the blue 3-BP@Cd-MOF-Blue exhibits visible light absorption with maximum absorption at 580nm and 625nm, and the brown 3-BP@Cd-MOF-Brown exhibits very strong visible light absorption in the range of 400-800nm. After irradiation with cold light (5W), both blue and brown crystalline materials fade to colorless and light orange. Among them, the colorless 3-BP@Cd-MOF-Colorless shows very weak absorption near 620nm, while the light orange 3-BP@Cd-MOF-Light shows strong absorption in the range of 350-600nm, with maximum absorption around 400nm. The light absorption characteristics of all host-guest systems are consistent with their color response.

[0049] Electron paramagnetic resonance (EPR) spectroscopy ( Figure 2 c) The study showed that no free radical signal was observed in the Cd-MOF sample, while the blue 3-BP@Cd-MOF-Blue exhibited a weak free radical signal at g = 2.0050. As the color deepened, the brown 3-BP@Cd-MOF-Brown exhibited a strong free radical signal. This EPR signal persisted for at least one month under sealed conditions and in the dark. However, upon irradiation with cold light, as the color changed from blue to colorless and from brown to light orange, the EPR signal also weakened accordingly. These findings suggest that heating of 3-BP@Cd-MOF generates free radicals on the MOF framework, and upon irradiation with cold light, new free radicals are generated, partially quenching the original host free radicals.

[0050] Solid-state fluorescence emission spectroscopy ( Figure 2 d) The study showed that the fluorescence emission of blue and brown 3-BP@Cd-MOF crystals was significantly quenched, indicating the generation of free radicals in the main framework. However, the fluorescence emission of colorless and light orange crystals recovered to varying degrees, indicating that the newly generated free radicals partially quenched the original free radicals, leading to a recovery of fluorescence emission. This is consistent with the EPR results.

[0051] In order to gain a deeper understanding of the changes in the valence state of bromine elements before and after heating and light irradiation, X-ray photoelectron spectroscopy (XPS) tests were performed on the color-changing materials. In 3-BP@Cd-MOF-Blue and 3-BP@Cd-MOF-Brown, the Br3d binding energy peaks are located at 68.44, 67.49 eV and 67.81, 66.86 eV, respectively, corresponding to the CH2-Br( Figure 2 e-2f). The shift of the Br3d peak to lower binding energy in the brown system is also attributed to the increase in electron cloud density on the skeleton. 3 / 2 and Br3d 5 / 2 The peaks shifted toward higher binding energies in both photobleaching systems, indicating an overall decrease in the electron cloud density on the guest molecule. Furthermore, two distinct satellite peaks appeared at 70.43 and 69.48 eV for 3-BP@Cd-MOF-Colorless and 70.19 and 69.14 eV for 3-BP@Cd-MOF-Light Orange, respectively. This result suggests that the valence state of some Br elements in the photobleaching system increased, indicating the generation of guest Br radicals after photoinduced bleaching. This result is highly consistent with the results from EPR and solid-state fluorescence emission experiments.

[0052] (3) Crystal structure analysis and mechanism

[0053] To elucidate the thermally induced discoloration and light-induced fading mechanisms of host-guest materials, single crystal X-ray diffraction analysis was performed on four new host-guest MOFs, namely 3-BP@Cd-MOF-Blue, 3-BP@Cd-MOF-Colorless, 3-BP@Cd-MOF-Brown, and 3-BP@Cd-MOF-Light Orange. Figure 3 A) Single crystal structure analysis shows that all 3-BP@Cd-MOF host-guest systems have the same P41212 or P43212 space group and tetragonal crystal system as Cd-MOF. Specifically: 3-BP@Cd-MOF-Blue is P41212V: a: b: c: 3-BP@Cd-MOF-Colorless is P43212,V: a: b: ,c: 3-BP@Cd-MOF-Brown is P43212, V: a: b: c: 3-BP@Cd-MOF-Light Orange is P43212, V: a: b: c:

[0054] like Figure 3 As shown in B, 3-BP molecules pass through C≡C–H…O(ClO4- ) Hydrogen bond interactions Fixed in the 1D pores of the skeleton. There are two arrangement directions for the 3-BP guest molecules in the 1D pores. Among them, the arrangement direction of the 3-BP guest molecules that affects the photothermal dual response characteristics is: there is an N–H…Br hydrogen bond interaction between the propargyl Br and the amino group of the ligand For the blue, colorless, brown, and light orange host-guest complexes, the short contacts between Br atoms and alkynyl groups in adjacent guest molecules were determined to be 2.8197, 2.8164, 2.9197, and (Based on H2CC≡C…Br distance), the C–Br…C bond angle is 174-175° close to 180°, and it can be considered that there is a C–Br…π halogen bond interaction between the guest molecules ( Figure 3 C).

[0055] Based on the above experimental results, it is inferred that the thermochromic and photofading mechanisms of the 3-BP@Cd-MOF host-guest system should be: under heating conditions, ClO4 - The anion undergoes electron transfer to the organic linker of the framework and generates a host free radical on the MOF framework, C≡C–H…O(ClO4 - ), C pyridyl –H…O(ClO4 - ) and N(amino)–H…O(ClO4 - ) hydrogen bonding interactions facilitate this electron transfer. As the temperature increases, more host radicals are generated on the framework, as evidenced by the greatly enhanced EPR signal of the brown system. Under illumination, the halogen-linked guest 3-BP molecules are excited to produce Br radicals, which interact with the MOF backbone through N–H…Br hydrogen bonds and partially quench the host radicals. The abundant hydrogen and halogen bonding in the 3-BP@Cd-MOF system leads to its unique light- and heat-induced dual-functional color-changing properties.

[0056] Preparation of dual-responsive PVDF films

[0057] (4) Application

[0058] A 3-BP@Cd-MOF-Blue-doped polyvinylidene fluoride (PVDF) film was prepared using polyvinylidene fluoride (PVDF) as a matrix. After drying at 50°C, the film exhibited a purple color. Upon exposure to a cold light source (5W), the purple film rapidly transformed into a colorless film, which then returned to purple upon heating at 50°C. However, if the purple film was heated at 100°C for one hour, it exhibited a darker brown color. This temperature-dependent color change makes it potentially useful for overtemperature warning applications. The brown film slowly faded to a light orange color upon exposure to cold light and returned to brown upon heating. These unique thermochromic and photochromic properties make the 3-BP@Cd-MOF crystal material potentially useful in information encryption and anti-counterfeiting technologies.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that 3-bromopropyne (3-BP) is replaced with propyne or 3-chloropropyne. The other preparation methods are the same as those in Example 1. The study found that the Cd-MOF crystals adsorbing propyne did not change color. Under the same adsorption conditions as in Example 1, the Cd-MOF crystals adsorbing chloropropyne did not show obvious color change, that is, they did not have the photothermal dual response characteristic.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that the Cd-MOF crystal is replaced with a Cu-MOF crystal, and the other preparation methods are the same as those in Example 1. Among them, the preparation method of the Cu-MOF crystal (molecular formula is ([CuL2(ClO4)2]·H2O), L is 4-amino-3,5-di(4-pyridine-3-phenyl)-1,2,4-triazole) is different from the preparation method of the Cd-MOF crystal in that Cu(ClO4)2 is used to replace Cd(ClO4)2, and the other preparation methods are the same as those of the Cd-MOF crystal. The study found that the 3-bromopropyne or 3-chloropropyne crystal material after Cu-MOF adsorption did not change color due to light and heat. It may be that the weak interaction between Cu-MOF and propyne or 3-chloropropyne is not conducive to the electron transfer to produce the host free radical that responds, resulting in the color change phenomenon.

[0063] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A MOF-based photothermal dual-response material, characterized in that: The system, named 3-BP@Cd-MOF, includes a guest 3-bromopropyne and a host Cd-MOF material. The Cd-MOF material has a three-dimensional porous structure. The 3-bromopropyne is fixed in the one-dimensional channels of the Cd-MOF material through C≡C–H···O hydrogen bonds. Adjacent 3-bromopropyne molecules are connected to form guest molecular chains through C–Br···π halogen bonds. The Cd-MOF material is [CdL2(ClO4)2]∙H2O, where L is 4-amino-3,5-di(4-pyridine-3-phenyl)-1,2,4-triazole).

2. The MOF-based photothermal dual-response material according to claim 1, characterized in that: The MOF-based photothermal dual-response material has the following response characteristics: Under heating conditions of 45-55℃, it responds to thermochromism, changing from colorless to blue, with a response time of 20 min-8 h; Under cold light irradiation, the photochromic response fades from blue to colorless, and the response time is 2-3 minutes; Under heating conditions of 90-110℃, it responds to thermochromism, changing from blue or colorless to brown, with a response time of 0.5-1h; Under cold light irradiation, it responds to photofading, fading from brown to orange and cannot be restored to blue or colorless. The response time is 12-24 hours. Under heating conditions of 90-110℃, it responds to thermochromism, changing from orange to brown, with a response time of 0.5-1h; The cold light irradiation conditions are as follows: the power of the cold light source is 5 W, and the wavelength of the cold light source is 400-700 nanometers.

3. The MOF-based photothermal dual-response material according to claim 1, characterized in that: The 3-BP@Cd-MOF can maintain a blue color stably for more than one month under sealed and light-proof conditions.

4. A method for preparing the MOF-based photothermal dual-response material according to any one of claims 1 to 3, characterized in that: After sealing the activated Cd-MOF crystals and 3-bromopropyne, heating them resulted in a blue or brown MOF-based photothermal dual-responsive material.

5. The method for preparing the MOF-based photothermal dual-response material according to claim 4, characterized in that: When the heating temperature is 45-55°C and the heating time is 1-10h, a blue MOF-based photothermal dual-response material is obtained; When the heating temperature is 90-110°C and the heating time is 0.5-1h, a brown MOF-based photothermal dual-responsive material is obtained.

6. The method for preparing the MOF-based photothermal dual-response material according to claim 4, characterized in that: The activation method of the Cd-MOF crystal is to activate the colorless Cd-MOF crystal at 100-150° C. for 2-5 hours.

7. Use of the MOF-based photothermal dual-response material according to any one of claims 1 to 3 in over-temperature indication, information encryption, anti-counterfeiting technology and intelligent temperature control materials.

8. A 3-BP@Cd-MOF doped polyvinylidene fluoride film, characterized in that: comprising a matrix material and a filler material uniformly dispersed in the matrix material; The matrix material is polyvinylidene fluoride; the filling material is the MOF-based photothermal dual-response material according to any one of claims 1 to 3.

9. The 3-BP@Cd-MOF doped polyvinylidene fluoride film according to claim 8, characterized in that: The 3-BP@Cd-MOF doped polyvinylidene fluoride film has the following response characteristics: Under heating conditions of 45-55℃, it responds to thermochromism and turns purple. The response time is 5-8 minutes. Under cold light irradiation, the photofading response fades from purple to colorless, and the response time is 2-3 minutes; Under heating conditions of 45-55℃, it responds to thermochromism, changing from colorless to purple, and the response time is 5-8 minutes; Under heating conditions of 90-110℃, it responds to thermochromism, changing from purple to brown, with a response time of 0.5-1h; Under cold light irradiation, the color changes from brown to orange in a photofading response, and the response time is 12-24 h. Under heating conditions of 90-110℃, it responds to thermochromism, changing from orange to brown, with a response time of 0.5-1h; The cold light irradiation conditions are as follows: the power of the cold light source is 5 W, and the wavelength of the cold light source is 400-700 nanometers.

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