A polyheptamethine imide-based photochromic thin film and its preparation method

Abstract

This invention provides a polyheptamethrinimide-based photochromic thin film and its preparation method, relating to the field of smart materials technology. The polyheptamethrinimide-based photochromic thin film includes a film matrix, a photoreducing agent, and a redox dye. The photoreducing agent is polyheptamethrinimide, and the redox dye is methylene blue. Polyheptamethrinimide can be excited by 405nm visible light to generate photogenerated electrons, reducing and decolorizing the methylene blue, changing the film from blue to white. When oxygen is present in the environment, the film adsorbs oxygen, which oxidizes the decolorized methylene blue, restoring the color, and the film returns to blue from white, enabling naked-eye detection of oxygen. It can detect oxygen concentration changes from 0% to 20%, exhibiting high sensitivity; the film decolorizes completely within 8 seconds after photoexcitation, and the color recovery time in air is 12 minutes, demonstrating a short response time; the repeatability reaches 20 times, indicating good detection stability.

Description

Technical Field

[0001] This invention relates to the field of smart materials technology, and more specifically, to a polyheptamethine imide-based photochromic thin film and its preparation method. Background Technology

[0002] Currently, food safety and quality assurance have become a focus of attention for consumers and regulatory agencies worldwide. As a key factor affecting the shelf life and flavor stability of food, the precise monitoring of oxygen is particularly important in the food packaging sector. Oxygen promotes the growth of aerobic microorganisms and accelerates food spoilage; therefore, controlling the oxygen concentration within packaging is crucial for extending food shelf life. This has led to extensive research both domestically and internationally on oxygen detection methods in food packaging, such as electrochemical and fluorescent oxygen indicator technologies. However, these traditional gas detection methods often require destructive sampling or rely on expensive analytical equipment, failing to achieve real-time, non-destructive monitoring. This limits the ability to continuously track oxygen levels during food distribution.

[0003] Therefore, visual oxygen indicator films and their supporting real-time monitoring technologies have emerged, providing an intuitive and efficient solution for controlling oxygen content during food storage and transportation. Visual oxygen indicator films are typically composed of oxygen-sensitive pigments or chemical indicators that change color upon contact with oxygen. This change is visible to the naked eye, allowing for the determination of oxygen levels within the packaging without the need for additional tools. Currently, photo-driven redox oxygen indicators are widely used, such as WO3 / polyacrylonitrile nanofiber films synthesized through electrospinning technology or colorimetric oxygen indicators based on titanium dioxide composite materials. These technologies show promise in the field of oxygen detection, but also suffer from problems such as poor stability, long response time, and low sensitivity. Summary of the Invention

[0004] The problem addressed by this invention is how to solve the issues of poor oxygen detection stability, long response time, and low sensitivity of visual oxygen indicator films.

[0005] To address the above problems, this invention provides a polyheptamethine imide-based photochromic film and its preparation method.

[0006] In a first aspect, the present invention provides a polyheptamethrin imide-based photochromic film, comprising a film matrix, a photoreducing agent and a redox dye, wherein the photoreducing agent is polyheptamethrin imide, the redox dye is methylene blue, and the film matrix is ​​a polyvinyl alcohol and ethylene glycol crosslinked polymer film.

[0007] Optionally, the polyheptamethrinimide is selected from a polyheptamethrinimide solution with a concentration of 1.2-1.8 g / L, and the methylene blue is selected from a methylene blue solution with a concentration of 8-12 mg / L. The mass ratio of the polyheptamethrinimide solution to the methylene blue solution is 2.5:1.6-2.4.

[0008] Optionally, polyvinyl alcohol is selected from polyvinyl alcohol solution with a mass fraction of 8-12%, ethylene glycol is selected from ethylene glycol solution, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2, and the mass ratio of polyvinyl alcohol solution to ethylene glycol solution is 3.6-4.4:1.

[0009] In a second aspect, the present invention provides a method for preparing a polyheptamethrin-imide-based photochromic film, comprising the following steps:

[0010] Take polyvinyl alcohol solution and ethylene glycol solution, mix them evenly, heat to above 100℃, and stir for more than 10 minutes to obtain membrane matrix solution;

[0011] Take polyheptamethrin imide solution and methylene blue solution, mix them evenly, add them to the membrane matrix solution, heat to above 85°C, stir for more than 45 minutes, and cool to room temperature;

[0012] Pour into a mold and heat at 25-35℃ for more than 6 hours to obtain a polyheptamethine imide-based photochromic film.

[0013] Optionally, the concentration of the polyheptamethrinimide solution is 1.2-1.8 g / L.

[0014] Optionally, the concentration of the methylene blue solution is 8-12 mg / L.

[0015] Optionally, the mass ratio of polyheptamethrinimide solution to methylene blue solution is 2.5:1.6-2.4.

[0016] Optionally, the polyvinyl alcohol solution has a mass fraction of 8-12%.

[0017] Optionally, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2.

[0018] Optionally, the mass ratio of polyvinyl alcohol solution to ethylene glycol solution is 3.6-4.4:1.

[0019] The beneficial effects of the polyheptamethrin-imide-based photochromic film and its preparation method of the present invention are as follows: Polyheptamethrin-imide (PHI) is a highly crystalline carbon nitride (CN) prepared by the eutectic molten salt method. Compared with ordinary CN, PHI has a higher carrier mobility, improves the utilization rate of photogenerated carriers, solves the problem of high electron-hole recombination rate of CN, enhances photoreduction activity, and broadens the light absorption range to 280nm-460nm. The photoreducing agent polyheptamethrin-imide can be excited by 405nm visible light to generate photogenerated electrons, thereby reducing and decolorizing the redox dye methylene blue, turning the photochromic film from blue to white. When oxygen is present in the environment, the film adsorbs oxygen, which diffuses in the film, and the decolorized film is then treated by the oxygen. Methylene blue oxidation restores the color, causing the photochromic film to change from white to blue, enabling naked-eye detection of oxygen. This visual color change of the film helps ensure food safety. Within a specified time, different oxygen concentrations correspond to different film colors, with the color deepening as the oxygen concentration increases. It can detect concentration changes from 0% to 20%, and a noticeable color change is visible at an oxygen concentration of 5%, demonstrating high sensitivity. The film completely decolorizes after being excited by 405nm light in 8 seconds, and the color recovery time is 12 minutes in an air environment (oxygen content of approximately 20%), showing a short response time. The polyheptamethrinimide-based photochromic film can achieve a repeatability of up to 20 times while maintaining good color-changing performance and good stability in oxygen detection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the design and mechanism of the polyheptamethrin imide-based photochromic film according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the color change of the polyheptamethrin imide-based photochromic film in Example 1 of the present invention;

[0022] Figure 3 This is a schematic diagram showing the color change time of the polyheptamethrin imide-based photochromic film under visible light irradiation in Example 1 of the present invention.

[0023] Figure 4 This is a schematic diagram showing the time it takes for the polyheptamethrin imide-based photochromic film of Example 1 of the present invention to recover its blue color in an air environment;

[0024] Figure 5 This is a schematic diagram showing the number of color-changing cycles of the polyheptamethrin imide-based photochromic film in Example 1 of the present invention.

[0025] Figure 6 This is a digital photograph of the colorimetric response time of the polyheptamethine imide-based photochromic film of Example 1 of the present invention to oxygen.

[0026] Figure 7 This is a curve showing the B value versus oxygen concentration of the polyheptamethrin imide-based photochromic film of Example 1 of the present invention over a certain period of time.

[0027] Figure 8 This is a schematic diagram showing the oxygen concentration of the film at 9 minutes calculated by equation in Embodiment 1 of the present invention. Detailed Implementation

[0028] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0029] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this invention's description is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0030] The term "comprising" and its variations as used herein are open-ended inclusion, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below.

[0031] In related technologies, the selection of semiconductor photoreducing agents requires not only suitable preparation costs, good chemical stability and resistance to photocorrosion, and the ability to be used efficiently for a long time, but also high solar energy utilization and photoreduction activity. Currently, the widely used photoreducing agent TiO2 suffers from problems such as a wide band gap (3.0 eV-3.2 eV), resulting in low solar energy utilization, a limited light absorption range (280 nm-400 nm), and an inability to respond to visible light.

[0032] Organic semiconductor material carbon nitride (CN) has attracted widespread attention due to its good chemical stability, thermal stability, suitable conduction band and valence band positions, a suitable band gap (2.7 eV), and visible light response.

[0033] Polyheptamethrinimide (PHI) is a highly crystalline CN prepared by the eutectic molten salt method. Compared with ordinary CN, PHI has a higher carrier mobility, improves the utilization rate of photogenerated carriers, solves the problem of high electron-hole recombination rate of CN, enhances photoreduction activity, and broadens the light absorption range (280nm-460nm).

[0034] To address the problems existing in the aforementioned related technologies, this embodiment provides a polyheptamethine imide-based photochromic film and its preparation method.

[0035] The present invention provides a polyheptamethrin-based photochromic film, comprising a film matrix, a photoreducing agent and a redox dye, wherein the photoreducing agent is polyheptamethrin-imide, the redox dye is methylene blue, and the film matrix is ​​a polyvinyl alcohol and ethylene glycol crosslinked polymer film.

[0036] In this embodiment, polyheptamethrinimide (PHI) is a highly crystalline carbon nitride (CN) prepared by a eutectic molten salt method. Compared with ordinary CN, PHI has a higher carrier mobility, improves the utilization rate of photogenerated carriers, solves the problem of high electron-hole recombination rate in CN, enhances photoreduction activity, and broadens the light absorption range to 280nm-460nm; Figure 1 As shown, the photoreducing agent polyheptamethrinimide can be excited by 405nm visible light to generate photo-electrons, thereby reducing and decolorizing the redox dye methylene blue, causing the photochromic film to change from blue to white. When oxygen is present in the environment, the film adsorbs oxygen, which diffuses within the film. The oxygen then oxidizes the decolorized methylene blue, restoring the color and causing the photochromic film to return from white to blue, enabling naked-eye detection of oxygen. This method of visually detecting oxygen through film color changes can ensure food safety. Within a specified time, different oxygen concentrations correspond to different film colors, with the color becoming increasingly darker as the oxygen concentration increases. It can detect concentration changes from 0% to 20%, and a noticeable color change is visible at an oxygen concentration of 5%, demonstrating high sensitivity. The film decolorizes completely within 8 seconds after being excited by 405nm light, and in an air environment (oxygen content of approximately 20%), the color recovery time is 12 minutes, exhibiting a short response time. The polyheptamethrinimide-based photochromic film can achieve a repetition rate of 20 times while maintaining good color-changing performance and good stability in oxygen detection.

[0037] Specifically, Figure 1The design and mechanism of the polyheptamethrinimide-based photochromic film in this embodiment are as follows: the photoreducing agent polyheptamethrinimide (PHI) can be excited by 405nm visible light to generate photogenerated electrons, thereby reducing and decolorizing the redox dye methylene blue, and the film changes from blue to white. The key to the film's recovery from white to blue is the diffusion of oxygen in the film, that is, the adsorption of oxygen by the film. The film restores its color by oxidizing the decolorized methylene blue with oxygen. Therefore, oxygen inside the packaging can be detected by visually observing the change in film color, and naked-eye detection of oxygen can be achieved.

[0038] Optionally, the polyheptamethrinimide is selected from a polyheptamethrinimide solution with a concentration of 1.2-1.8 g / L, and the methylene blue is selected from a methylene blue solution with a concentration of 8-12 mg / L. The mass ratio of the polyheptamethrinimide solution to the methylene blue solution is 2.5:1.6-2.4.

[0039] In this optional embodiment, the mass ratio of polyheptamethrinimide and methylene blue is such that the photoreducing agent polyheptamethrinimide is excited by 405nm visible light to generate photogenerated electrons, which can completely reduce and decolorize the redox dye methylene blue, causing the photochromic film to change from blue to white. Furthermore, when oxygen is present in the environment, the film adsorbs oxygen, and the decolorized methylene blue is oxidized by oxygen to restore the color, causing the photochromic film to return from white to blue, thus enabling naked-eye detection of oxygen.

[0040] Optionally, polyvinyl alcohol is selected from polyvinyl alcohol solution with a mass fraction of 8-12%, ethylene glycol is selected from ethylene glycol solution, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2, and the mass ratio of polyvinyl alcohol solution to ethylene glycol solution is 3.6-4.4:1.

[0041] In this optional embodiment, the mass ratio of polyvinyl alcohol and ethylene glycol as membrane matrix materials has good film-forming properties, and the prepared membrane can meet the requirements of food packaging.

[0042] This invention provides a method for preparing a polyheptamethrin-imide-based photochromic film, comprising the following steps:

[0043] Take polyvinyl alcohol solution and ethylene glycol solution, mix them evenly, heat to above 100℃, and stir for more than 10 minutes to obtain membrane matrix solution;

[0044] Take polyheptamethrin imide solution and methylene blue solution, mix them evenly, add them to the membrane matrix solution, heat to above 85°C, stir for more than 45 minutes, and cool to room temperature;

[0045] Pour into a mold and heat at 25-35℃ for more than 6 hours to obtain a polyheptamethine imide-based photochromic film.

[0046] In this embodiment, polyvinyl alcohol and ethylene glycol are prepared into solutions before mixing to make the mixing more uniform and the resulting membrane matrix solution has uniform quality. Polyheptamethimide and methylene blue are prepared into solutions before mixing. During the mixing process, polyheptamethimide and methylene blue can be mixed more quickly and uniformly. The photoreducing agent polyheptamethimide is excited by 405nm visible light to generate photogenerated electrons, and the redox dye methylene blue is rapidly decolorized with a short response time.

[0047] Optionally, the concentration of the polyheptamethrinimide solution is 1.2-1.8 g / L.

[0048] Optionally, the concentration of the methylene blue solution is 8-12 mg / L.

[0049] Optionally, the mass ratio of polyheptamethrinimide solution to methylene blue solution is 2.5:1.6-2.4.

[0050] In this optional embodiment, the polyheptamethrinimide solution and methylene blue solution are in such a volume ratio that the photoreducing agent polyheptamethrinimide is excited by 405nm visible light to generate photogenerated electrons, which can completely reduce and decolorize the redox dye methylene blue, causing the photochromic film to change from blue to white. Furthermore, when oxygen is present in the environment, the film adsorbs oxygen, and the decolorized methylene blue is oxidized by oxygen to restore the color, causing the photochromic film to return from white to blue, thus enabling naked-eye detection of oxygen.

[0051] Optionally, the polyvinyl alcohol solution has a mass fraction of 8-12%.

[0052] In this optional embodiment, the polyvinyl alcohol solution has a moderate concentration, resulting in fast film formation and good film quality. If the concentration is too low, the film formation process will be slow, while if the concentration is too high, the film quality will decrease due to increased solution viscosity.

[0053] Optionally, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2.

[0054] In this optional embodiment, the concentration of the ethylene glycol solution is moderate, which can improve the durability and stability of the membrane and prevent the membrane from aging and being damaged. At the same time, ethylene glycol can also reduce the plasticizing effect of the membrane and prevent the membrane from deforming and losing stability.

[0055] Optionally, the mass ratio of polyvinyl alcohol solution to ethylene glycol solution is 3.6-4.4:1.

[0056] In this optional embodiment, the polyvinyl alcohol solution and ethylene glycol solution in this mass ratio serve as membrane matrix materials, exhibiting good film-forming properties, and the prepared membrane can meet the requirements of food packaging.

[0057] The present invention will be further described below with reference to specific embodiments.

[0058] Example 1: A method for preparing a polyheptamethine imide-based photochromic film.

[0059] (1) Weigh 8g of polyvinyl alcohol granules and dissolve them in 72g of pure water. Heat and stir at 85℃ for 45min until completely dissolved. Cool the solution. The mass fraction of the polyvinyl alcohol solution is 10%.

[0060] (2) At the same time, take another 20 ml of ethylene glycol (ethylene glycol is used as a polyvinyl alcohol crosslinking agent) and dissolve it in 10 ml of pure water. Stir at room temperature until completely mixed. The volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:1.

[0061] (3) Weigh 12g of polyvinyl alcohol solution and 3g of ethylene glycol solution, mix them evenly, heat and stir at 100℃ for 10min to obtain membrane matrix solution. The mass ratio of polyvinyl alcohol solution to ethylene glycol solution is 4:1.

[0062] (4) Take another 30 mg of polyheptamethrin imide powder and mix it with 20 ml of pure water, and sonicate for 5 h. The concentration of the polyheptamethrin imide solution is 1.5 g / L.

[0063] (5) At the same time, weigh 5 mg of methylene blue powder and dissolve it in 500 ml of pure water. Stir at room temperature until completely dissolved. The concentration of the methylene blue solution is 10 mg / L.

[0064] (6) Weigh 12g of polyheptamethimide upper suspension and 9.6g of methylene blue solution, mix them, add them to the membrane matrix solution in step (3), heat and stir at 85℃ for 45min, cool, and the mass ratio of polyheptamethimide solution to methylene blue solution is 2.5:2;

[0065] (7) Measure 3 ml of the mixed solution obtained in step (6) and pour it into a 4 cm × 4 cm × 1 mm mold. Place it in an oven and heat it at 30 °C for 6 hours to obtain a polyheptamethrin imide photochromic film.

[0066] Example 2: A method for preparing a polyheptamethine imide-based photochromic film.

[0067] (1) Weigh 8g of polyvinyl alcohol granules and dissolve them in 92g of pure water. Heat and stir at 85℃ for 45min until completely dissolved, then cool.

[0068] (2) At the same time, take another 20 ml of ethylene glycol (ethylene glycol is used as a polyvinyl alcohol crosslinking agent) and dissolve it in 12 ml of pure water, and stir at room temperature until completely mixed;

[0069] (3) Weigh 10.8g of polyvinyl alcohol solution and 3g of ethylene glycol solution, mix them evenly, heat and stir at 100℃ for 10min to obtain membrane matrix solution;

[0070] (4) Take another 24 mg of polyheptamethrin imide powder and mix it with 20 ml of pure water, and sonicate for 5 h.

[0071] (5) Weigh 4 mg of methylene blue powder and dissolve it in 500 ml of pure water. Stir at room temperature until completely dissolved.

[0072] (6) Weigh 12g of polyheptamethrin imide upper suspension and 7.68g of methylene blue solution, mix them, add them to the membrane matrix solution in step (3), heat and stir at 85℃ for 45min, and then cool.

[0073] (7) Measure 3 ml of the mixed solution obtained in step (6) and pour it into a 4 cm × 4 cm × 1 mm mold. Place it in an oven and heat it at 25 °C for 6 hours to obtain a polyheptamethrin imide photochromic film.

[0074] Example 3: A method for preparing a polyheptamethine imide-based photochromic film.

[0075] (1) Weigh 8g of polyvinyl alcohol granules and dissolve them in 60g of pure water. Heat and stir at 85℃ for 45min until completely dissolved, then cool.

[0076] (2) At the same time, take another 20 ml of ethylene glycol (ethylene glycol is used as a polyvinyl alcohol crosslinking agent) and dissolve it in 8 ml of pure water, and stir at room temperature until completely mixed;

[0077] (3) Weigh 13.2g of polyvinyl alcohol solution and 3g of ethylene glycol solution, mix them evenly, heat and stir at 100℃ for 10min to obtain membrane matrix solution;

[0078] (4) Take another 36mg of polyheptamethrin imide powder and mix it with 20ml of pure water, and sonicate for 5h;

[0079] (5) At the same time, weigh 6 mg of methylene blue powder and dissolve it in 500 ml of pure water, stirring at room temperature until completely dissolved;

[0080] (6) Weigh 12g of polyheptamethrin imide upper suspension and 11.5g of methylene blue solution, mix them, add them to the membrane matrix solution in step (3), heat and stir at 85℃ for 45min, and then cool.

[0081] (7) Measure 3 ml of the mixed solution obtained in step (6) and pour it into a 4 cm × 4 cm × 1 mm mold. Place it in an oven and heat it at 35 °C for 6 hours to obtain a polyheptamethrin imide photochromic film.

[0082] Effect Example

[0083] The color-changing properties of the polyheptamethrin imide-based photochromic film prepared in Example 1 were tested, and the test results are as follows: Figures 2 to 5As shown, Figure 2 The discoloration of the film is visible in the image. Figure 3 As can be seen, the film decolorizes completely and becomes colorless 8 seconds after being irradiated with 405nm visible light. Figure 4 As can be seen, in an air environment (oxygen content of approximately 20%), the film can completely recover its blue color in about 12 minutes. Figure 5 As can be seen, this film can be repeated up to 20 times while still maintaining good color-changing performance.

[0084] The colorimetric response time of the polyheptamethrin imide-based photochromic film prepared in Example 1 to oxygen was tested, and the test results are as follows: Figure 6 As shown, after the film is decolorized by photoexcitation, it remains white in a completely Ar environment. However, as the oxygen concentration increases, the time for the film to fully recover its color becomes shorter and shorter.

[0085] The B-value corresponding to the color of the polyheptamethrin imide-based photochromic film prepared in Example 1 was tested against the fitting curve of oxygen concentration. The test results are as follows: Figure 7 As shown, at different oxygen concentrations at every 3 oxygen concentration points, the B value (RGB color space, where R represents the red component, G represents the green component, and B represents the blue component, and the three components are combined to form the color of a pixel) of the film color is obtained by a smart device (such as a smartphone), and linear fitting is performed to obtain the relationship between the B value and the oxygen concentration.

[0086] Based on the fitting curve of the B value corresponding to the film color and the oxygen concentration, an equation is obtained. The oxygen concentration at the film location after 9 minutes is then calculated using this equation. Figure 8 As shown, by substituting the B value of the film color at different oxygen concentrations at 9 minutes into the fitted equation, the oxygen concentration of the environment in which the film was located can be calculated. The oxygen content inside the packaging can be evaluated by using a smart device (such as a smartphone).

[0087] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A polyheptamethine imide-based photochromic film, characterized in that, The membrane comprises a membrane matrix, a photoreducing agent, and a redox dye, wherein the photoreducing agent is polyheptamethrinimide, the redox dye is methylene blue, and the membrane matrix is ​​a cross-linked polymer film of polyvinyl alcohol and ethylene glycol; the polyheptamethrinimide is selected from polyheptamethrinimide solutions with a concentration of 1.2-1.8 g / L, the methylene blue is selected from methylene blue solutions with a concentration of 8-12 mg / L, and the mass ratio of the polyheptamethrinimide solution to the methylene blue solution is 2.5:1.6-2.

4.

2. The polyheptaazine imide-based photochromic film according to claim 1, characterized in that, The polyvinyl alcohol is selected from polyvinyl alcohol solutions with a mass fraction of 8-12%, the ethylene glycol is selected from ethylene glycol solutions, the volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.2, and the mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:

1.

3. A method for preparing a polyheptamethine imide-based photochromic thin film, characterized in that, The preparation of the polyheptamethine imide-based photochromic film as described in any one of claims 1-2 comprises the following steps: Take polyvinyl alcohol solution and ethylene glycol solution, mix them evenly, heat to above 100℃, and stir for more than 10 minutes to obtain membrane matrix solution; Take polyheptamethrin imide solution and methylene blue solution, mix them evenly, add them to the membrane matrix solution, heat to above 85°C, stir for more than 45 min, and cool to room temperature; Pour into a mold and heat at 25-35℃ for more than 6 hours to obtain a polyheptamethine imide-based photochromic film.

4. The method for preparing the polyheptamethrin imide-based photochromic film according to claim 3, characterized in that, The concentration of the polyheptamethrin imide solution is 1.2-1.8 g / L.

5. The method for preparing the polyheptamethrin imide-based photochromic film according to claim 4, characterized in that, The concentration of the methylene blue solution is 8-12 mg / L.

6. The method for preparing the polyheptamethrin imide-based photochromic film according to claim 5, characterized in that, The mass ratio of the polyheptamethrin imide solution to the methylene blue solution is 2.5:1.6-2.

4.

7. The method for preparing the polyheptamethrin imide-based photochromic film according to claim 3, characterized in that, The polyvinyl alcohol solution has a mass fraction of 8-12%.

8. The method for preparing the polyheptamethrin imide-based photochromic film according to claim 7, characterized in that, The volume ratio of ethylene glycol to water in the ethylene glycol solution is 2:0.8-1.

2.

9. The method for preparing the polyheptamethrin imide-based photochromic film according to claim 8, characterized in that, The mass ratio of the polyvinyl alcohol solution to the ethylene glycol solution is 3.6-4.4:1.

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