Preparation method and application of phenylethanone viologen based on tetraphenyl borate as counter anion and flexible composite material thereof

Abstract

The application discloses a preparation method and application of phenylethanone viologen based on tetraphenylborate as a counter anion and a flexible composite material thereof, and takes phenylethanone to replace viologen VioBr2*2Cl as a precursor, replaces Cl − with tetraphenylborate BPh4 − by anion exchange to obtain VioBr2*2B(Ph)4. The electron-rich BPh4 − transfers electron density to a viologen cation skeleton, so that the compound generates a viologen radical cation under the stimulation of ultraviolet light irradiation for 5s, heating at 80-140 DEG C and a pressure of 15 MPa, the colored state is maintained for dozens of days, and the discoloration and fading cycle is stable, and a VioBr2*2B(Ph)4@PVA flexible photochromic film and a VioBr2*2B(Ph)4@PVA eutectic gel are constructed. The application solves the bottleneck problems of traditional viologen materials, such as easy quenching of a free radical, difficulty in processing in a solid state and difficulty in device integration, and has a wide application prospect.

Description

Technical Field

[0002] This invention belongs to the field of inorganic synthesis technology, specifically relating to an acetophenone violet compound regulated by tetraphenylborate anion, its composite film with a polyvinyl alcohol (PVA) matrix and a eutectic gel, and its application in photochromic glasses and smart windows. Background Technology

[0004] Viologen compounds, as a classic class of organic redox reactive molecules, have attracted widespread attention in fields such as intelligent dimming, information anti-counterfeiting, biosensing, and energy storage due to their reversible two-step electron transfer characteristics and accompanying significant color changes. Modifying the viologen framework through molecular engineering can effectively control its electronic structure, stacking mode, and stimulus-response behavior, thereby developing multifunctional material systems such as photochromic, thermochromic, and piezochromic materials. In recent years, researchers have made significant progress in improving the fluorescence emission performance and color-changing sensitivity of viologen materials by introducing substituents such as acetophenone and thiazole into viologen molecules, and by utilizing strategies such as host-guest self-assembly and metal halide hybridization. However, the intrinsic instability of viologen radical cations in the solid state and the aggregation quenching effect caused by intermolecular π-π stacking remain core scientific problems restricting the practical application of these materials.

[0005] To address the challenge of insufficient free radical stability, counterion regulation strategies have demonstrated unique advantages in recent years. Studies have shown that replacing small-sized halogen anions (such as Cl−, Br−) with large-volume weakly coordinated anions (such as PF6−, ClO4−) in viologen through anion exchange can effectively modulate the local electric field environment, molecular packing mode, and electron donor-acceptor distance of the viologen cation. In particular, the electron-rich tetraphenylborate not only provides additional electron density to the electron-deficient viologen framework to reduce redox potential, but its large benzene ring can also construct a spatial shielding layer and a hydrophobic microenvironment, simultaneously inhibiting free radical dimerization and oxidative quenching from both kinetic and thermodynamic perspectives, thereby significantly extending the lifetime of colored free radicals. However, current viologen systems based on BPh4− anion regulation are still mainly in crystalline powder form, and systematic research on multi-stimulus response behavior is relatively weak. Furthermore, the powder morphology has significant limitations in terms of processability and device integration.

[0006] In the field of composite materials, combining viologen active components with polymer matrices is an effective way to overcome processing difficulties and achieve flexibility and stabilization. Polyvinyl alcohol (PVA), due to its excellent film-forming properties, high light transmittance, abundant hydroxyl sites, and good biocompatibility, has been widely used to construct viologen-based electrochromic and photochromic composite films. In addition, PVA gel systems plasticized with deeutectic solvents (DES) possess ionic conductivity, flexibility, and strong adhesion, providing an ideal matrix for the immobilization and interfacial encapsulation of photofunctional active molecules.

[0007] In summary, there is an urgent need to develop a novel viologen-polymer composite material system that can achieve rapid, stable, and reversible color change under multiple stimuli, while also possessing good processability and device integration capabilities. This invention addresses this background by modulating the electronic structure and stacking mode of acetophenone viologen through tetraphenylborate anions and synergistically combining it with PVA films and PVA deep eutectic gel matrices. The aim is to systematically solve the bottleneck problems of viologen aggregation without luminescence, difficulties in solid-state processing, and insufficient compatibility with practical devices, providing a new technical solution for the engineering application of high-performance solid-state multi-stimulus responsive photochromic materials. Summary of the Invention

[0009] The purpose of this invention is to overcome the bottlenecks of existing viologen color-changing materials, such as poor free radical stability, difficulty in solid-state processing, low integration of multi-stimulus response, and insufficient device compatibility, and to provide a novel viologen-polymer composite material system and its application that combines photo / thermal / pressure multi-stimulus response color-changing ability, long free radical lifetime, good processability, and flexible device integration performance.

[0010] This was achieved through the following technical solution:

[0011] Acetophenone violet based on tetraphenylborate as the counter anion, namely violet compound VioBr2·2B(Ph)4, uses acetophenone to replace violet VioBr2 as the cationic skeleton and tetraphenylborate BPh4⁻ as the counter anion. The two form a close-packed structure through ion pair interactions.

[0012] A method for preparing a flexible composite material based on tetraphenylborate as a counterion anion of acetophenone violet involves using VioBr2·2Cl as a precursor and replacing Cl⁻ with BPh4⁻ through an anion exchange strategy.

[0013] Furthermore, in the preparation method of the flexible composite material based on tetraphenylborate as the counter anion of acetophenone violet, in specific operation, NaBPh4 is dissolved in ultrapure water and combined with a mixture of acetonitrile / water in VioBr2·2Cl. The mixture is stirred at room temperature for 3 hours. After the precipitate is generated, it is washed with pure water and acetone in sequence, filtered, and then vacuum dried to obtain the target product in the form of a deep yellow powder.

[0014] A flexible composite material based on tetraphenylborate as the counter anion of acetophenone violet is comprising two solid composite material systems: VioBr2·2B(Ph)4@PVA film and VioBr2·2B(Ph)4@PVA deep eutectic gel.

[0015] Furthermore, the VioBr2·2B(Ph)4@PVA film is prepared by uniformly mixing viologen with polyvinyl alcohol (PVA) and glycerol in a solution and then casting it into a film. The resulting film has transparency, flexibility, fluorescence emission and rapid photochromic ability. It changes from pale yellow to blue within 5 seconds under sunlight, and spontaneously fades after 10 minutes indoors. Moreover, its performance does not significantly decrease after multiple cycles, making it suitable for photochromic coated glasses.

[0016] Furthermore, the VioBr2·2B(Ph)4@PVA deep eutectic gel incorporates viologen into a PVA low eutectic solvent (ZnCl2 ethylene glycol water) system, and prepares a physically cross-linked eutectic gel through repeated freeze-thaw cycles. This gel exhibits excellent adhesion, can be directly sandwiched in a glass interlayer, turns purple after 5 seconds of UV irradiation, achieves color saturation after 1 minute, and spontaneously fades after 3 hours in the dark. It also demonstrates excellent cycle stability and is suitable for passively driven adaptive smart windows.

[0017] Application of flexible composite materials based on tetraphenylborate as a counterion anion, acetophenone viologen, in photochromic coated glasses and smart windows.

[0018] Beneficial effects:

[0019] This invention systematically solves key bottlenecks in the practical application of viologen-based photochromic materials, such as free radical quenching, processing difficulties, and device integration, through a strategy of co-designing anion engineering and polymer matrix. It provides a practical material solution and application example for the development of high-performance, multi-stimulus-responsive intelligent optical devices, specifically in the following aspects:

[0020] (1) Regarding the stability of free radicals, this invention utilizes the large-volume, electron-rich characteristics of tetraphenylborate to synergistically stabilize viologen free radical cations from two dimensions: electronic regulation and spatial shielding. The spatial shielding and hydrophobic microenvironment of tetraphenylborate (BPh4⁻) effectively inhibit free radical dimerization and oxidation, allowing the colored state to be maintained in the air for tens of days without complete fading, far exceeding the traditional halogen anion viologen system. Highly stable free radicals: the colored state can be maintained for tens of days in the solid state without fading.

[0021] (2) In terms of response performance, the VioBr2·2B(Ph)4 obtained in this invention can produce sensitive color change response to three types of external stimuli: ultraviolet light, heating (80-140℃) and pressure (15 MPa). It has a fast color change speed (color appears after 5 s of light exposure), a wide absorption band (500-800 nm), and good reversibility (no decay after more than 8 cycles). It achieves a high degree of integration of multi-stimulus response and realizes wide and strong absorption in the visible region and long free radical lifetime.

[0022] (3) In terms of processability and device fabrication, this invention disperses the active components in a PVA film or a deep eutectic gel matrix. Through PVA film formation or deep eutectic gelation, it endows the solid powder with fluorescent properties that it did not originally possess. On the other hand, it significantly improves processability and stability through polymer composites, fundamentally solving the technical problem of the difficulty in device fabrication of crystalline viologen materials. The resulting composite material has flexibility, transparency, adhesion, and long-term photostability. It can be directly coated onto lenses or encapsulated in glass interlayers without the need for complex circuits and external power supplies, significantly reducing the cost of device fabrication and maintenance.

[0023] (4) In terms of multifunctional integration, the composite material system of the present invention is accompanied by obvious fluorescence quenching and recovery during the color change process, providing a dual signal output mode of "color change" and "fluorescence switch", which provides new technical possibilities for real-time status monitoring and multi-level information encryption. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the synthetic route of VioBr2·2B(Ph)4 in this invention.

[0026] Figure 2 shows the infrared and nuclear magnetic resonance spectra of VioBr2·2B(Ph)4 in this invention.

[0027] Figure 3 This is a schematic diagram of the crystal structure of VioBr2·2B(Ph)4 in this invention.

[0028] Figure 4 This is the photochromic property of VioBr2·2B(Ph)4 in this invention and its ultraviolet-visible absorption spectrum under 365 nm illumination.

[0029] Figure 5 This is a schematic diagram of the ultraviolet spectrum and reversibility cycle test of VioBr2·2B(Ph)4 fading in the dark after light exposure and fading after spraying with HCl in this invention.

[0030] Figure 6 The thermochromic properties of VioBr2·2B(Ph)4 and its ultraviolet-visible spectra at different temperatures are shown in this invention.

[0031] Figure 7 This is a schematic diagram of the ultraviolet spectrum and reversible cycle test of VioBr2·2B(Ph)4 after heating to 100℃ and fading in the dark and after spraying with HCl in this invention.

[0032] Figure 8 These are photographs and ultraviolet-visible spectra of samples under different pressures in this invention.

[0033] Figure 9 This is a schematic diagram of the ultraviolet spectrum and reversible cycle test of VioBr2·2B(Ph)4 after pressure-induced color change, followed by fading in the dark and fading after spraying with HCl in this invention.

[0034] Figure 10 This invention provides a comparison of infrared and PXRD spectra before and after stimulation.

[0035] Figure 11 This is the EPR spectrum used in this invention.

[0036] Figure 12 The images show the UV-Vis and fluorescence spectra of the VioBr2·2B(Ph)4@PVA film before and after the color change in sunlight in this invention.

[0037] Figure 13 This is a schematic diagram of the VioBr2·2B(Ph)4@PVA coated glasses of the present invention before and after the color change in sunlight.

[0038] Figure 14 This is a schematic diagram illustrating the synthesis of VioBr2·2B(Ph)4@PVA eutectic gel in this invention.

[0039] Figure 15 The images show the UV-Vis absorption and fluorescence spectra of the VioBr2·2B(Ph)4@PVA eutectic gel before and after color change in this invention.

[0040] Figure 16 The images show photographs of VioBr2·2B(Ph)4@PVA eutectic gel adhering to different substrates, comparison images of glass interlayer before and after discoloration, and a schematic diagram of a simulated smart window. Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0043] Example 1: Synthesis of VioBr2·2B(Ph)4 (Compound 5):

[0044] Raw materials: VioBr2·2Cl (0.1500 g, about 0.26 mmol), sodium tetraphenylborate NaBPh4 (0.2470 g, about 0.72 mmol).

[0045] Operation steps (synthesis route as follows) Figure 1 (as shown)

[0046] 1. Dissolve VioBr2·2Cl in a mixed solvent of 10 mL ultrapure water and 10 mL acetonitrile to obtain a clear yellow solution;

[0047] 2. Dissolve NaBPh4 in 5 mL of ultrapure water;

[0048] 3. While stirring at room temperature, slowly add NaBPh4 aqueous solution dropwise to VioBr2·2Cl solution. After the addition is complete, continue stirring for 3 hours. A precipitate gradually precipitates in the system.

[0049] 4. After the reaction is complete, filter the precipitate and wash it with ultrapure water 1–2 times and acetone 1–2 times in sequence. After filtration, dry it in a vacuum drying oven to obtain a dark yellow powdery solid with a yield of about 80%.

[0050] Structural assessment:

[0051] •like Figure 2a As shown, FT IR (KBr tablet, cm⁻¹): 3051.5 (aromatic ring C–H stretching), 2983.75 (saturated C–H stretching), 1694.4 (C=O stretching), 1628.69, 1576.13 (pyridine ring C=C / C=N⁺), 1473.63, 1418.43 (BPh4⁻ characteristic skeleton), 1329.07 (pyridine ring in-plane bending), 1221.32, 1171.38, 1066.25 (aromatic ring C–H bending and skeleton vibration), 984.78 (pyridine ring out-of-plane bending), 811.31 (monosubstituted benzene ring C–H out-of-plane bending), 708.81 (BPh4⁻ monosubstituted benzene ring characteristic out-of-plane bending), 561.63, 495.93, 453.87 (B–Ph bond and ion pair interaction).

[0052] •like Figure 2bAs shown, the ¹H NMR (600 MHz, d6-DMSO) δ / ppm values ​​are: 9.22 (2H, pyridine ring α-H), 8.85 (2H, pyridine ring β-H), 8.02 (2H, bromine meta-H), 7.94 (2H, bromine ortho-H), 7.16 (16H), 6.92 (16H), 6.79 (8H, all BPh4⁻ aryl hydrogens), and 6.50 (4H, methylene H). Compared to VioBr2·2Cl, the pyridine ring α-H shifted from 9.28 to 9.22, the β-H from 8.92 to 8.85, and the bromine meta-H from 8.11 to 8.02, all exhibiting high-field shifts, indicating that BPh4⁻ transfers electron density to the viologen cation skeleton.

[0053] • Single-crystal X-ray diffraction, such as Figure 3 As shown: The crystals were obtained by solvent diffusion (acetone / water / acetonitrile mixed solvent, left to stand at room temperature for 30 days). They belong to the monoclinic crystal system, space group C2 / c, with cell parameters a=18.463(15) Å, b=9.390(7) Å, c=38.65(3) Å, β=94.73(3)°. One asymmetric unit contains half a VioBr2²⁺, one BPh4⁻, and two acetonitrile solvent molecules. The inter-carbon distance between the pyridine nitrogen and the BPh4⁻ benzene ring is 3.38–3.82 Å, indicating a close packing of ion pairs between the cations and anions, providing a geometric basis for intramolecular electron transfer.

[0054] Color-changing performance verification:

[0055] • Photochromic, such as Figures 4-5 As shown: after 5 seconds of exposure to 365 nm ultraviolet light, the color changes from deep yellow to deep dark green, and a broad and strong absorption band (λmax≈600 nm) is produced at 500–800 nm. In the dark, the color basically fades back to its original color after 30 days, while the color fades completely within 1 second when sprayed with HCl vapor.

[0056] •Thermochromic Figures 6-7 As shown: It begins to change color from dark yellow to grayish brown at 80°C, and reaches saturated black at 140°C.

[0057] • Pressure-induced color change, such as Figures 8-9 As shown: the yellow color turns brown under 15 MPa pressure, and the color fades in 30 days. Spraying with HCl can quickly fade the color.

[0058] •like Figures 10-11 As shown, EPR testing confirmed that the color change originated from the generation of free radical cations, while IR and PXRD confirmed that the molecular skeleton remained unchanged before and after the color change.

[0059] Example 2: Preparation of VioBr2·2B(Ph)4@PVA thin film:

[0060] Formula: 10 mL deionized water, 10 wt% polyvinyl alcohol (PVA, degree of alcoholysis approximately 99%), 5 wt% glycerol, and an appropriate amount of VioBr2·2B(Ph)4 (dissolved in 10 mL acetone).

[0061] Operating steps:

[0062] 1. Weigh 1.0 g PVA and 0.5 g glycerol and add them to 10 mL of deionized water. Heat and stir in a 60°C water bath until completely dissolved to obtain a transparent and viscous PVA solution.

[0063] 2. Weigh approximately 0.1 g of VioBr2·2B(Ph)4 solid powder and dissolve it in 10 mL of acetone, stirring until homogeneous;

[0064] 3. Mix the two solutions together and continue stirring until homogeneous. Sonicate for 10 minutes to eliminate air bubbles.

[0065] 4. Use a dropper to evenly coat the mixture onto a glass slide (or other required substrate), and allow it to air dry naturally or at 40°C under light-protected conditions to obtain VioBr2·2B(Ph)4@PVA film.

[0066] Thin film properties:

[0067] • Appearance and optical properties: The film is pale yellow and exhibits yellow-green fluorescence emission (approximately 540 nm). PXRD testing confirmed that compound 5 was successfully dispersed in the PVA matrix.

[0068] • Mechanical properties: It can automatically recover its original state after being stretched, exhibiting excellent flexibility and self-recovery.

[0069] • Photostability: After being placed in air for 120 days, the fluorescence emission curve remained almost unchanged.

[0070] • Photochromic (e.g.) Figure 12 As shown in the figure): the pale yellow color turns blue within 5 seconds of sunlight exposure, and fades back to its original color after 10 minutes indoors; the color change is accompanied by obvious fluorescence quenching, and the fluorescence recovers after fading.

[0071] • Thermochromic: It exhibits different degrees of coloration at different temperatures, and ultraviolet-visible spectroscopy confirms that the absorption band at 500–800 nm increases with increasing temperature.

[0072] Example 3: Preparation of VioBr2·2B(Ph)4@PVA eutectic gel:

[0073] Preparation of eutectic solvent (DES) (e.g.) Figure 14 (as shown)

[0074] 1. Weigh 6.81 g of anhydrous zinc chloride (ZnCl2) and 6.20 g of ethylene glycol (approximately 5.57 mL, mass fraction 41.86 wt%), and mix them in a sealed container;

[0075] 2. Stir at 60°C until the system is completely clear and transparent;

[0076] 3. Slowly add 1.8 mL of deionized water and continue stirring for 30 min to obtain a homogeneous and transparent eutectic solvent (ZnCl2 concentration of approximately 4.4 mol / L). Cool and set aside.

[0077] PVA sol preparation:

[0078] 1. Weigh 1.0 g PVA and add it to 9 mL of deionized water. Stir in a 90°C oil bath for 2 h until completely dissolved to obtain a transparent viscous solution.

[0079] 2. Cool to 50°C before use.

[0080] Gel preparation:

[0081] 1. Under light-protected conditions, add 0.1 g VioBr2·2B(Ph)4 (approximately 0.90 wt%) to a PVA solution cooled to 50°C and stir until homogeneous.

[0082] 2. Add 1.0 g of the eutectic solvent prepared above, and stir at 30°C until completely dissolved and mixed to obtain a homogeneous sol.

[0083] 3. Transfer the sol to a mold and freeze at −20°C for 12 h. Remove and thaw at room temperature. Repeat the freeze-thaw cycle a total of 4 times.

[0084] 4. Immerse the obtained gel in a eutectic solvent, changing the solvent every 24 hours for a total of two changes.

[0085] 5. After removing the gel, blot off any excess solvent from the surface to obtain the target VioBr2·2B(Ph)4@PVA eutectic gel.

[0086] Gel properties (e.g.) Figure 15 (as shown)

[0087] • Structural characterization: FT IR simultaneously showed characteristic peaks of PVA (O–H stretching approximately 3300 cm⁻¹, C–H stretching approximately 2900 cm⁻¹) and characteristic peaks of compound 5 (1694 cm⁻¹ C=O, 1473 / 1418 cm⁻¹ BPh4⁻ skeleton), and the broadening and redshift of the O–H peak confirmed the presence of hydrogen bond interactions between the components.

[0088] • Appearance and Adhesion: The gel is pale yellow and transparent, and can be directly adhered to various substrates such as glass, plastic, metal, and paper without the need for additional adhesives.

[0089] • Fluorescence properties: It exhibits yellow-green fluorescence emission at approximately 540 nm. Under 365 nm ultraviolet light, the fluorescence intensity gradually decreases with prolonged illumination time and is almost completely quenched after 15 s.

[0090] • Photochromic: After 5 seconds of exposure to 365 nm ultraviolet light, it changes from pale yellow to blue-violet, and a broad free radical absorption band appears at 500–800 nm; it spontaneously fades back to its original color after 3 hours in dark air.

[0091] • Cyclic stability: No significant performance degradation after multiple color change-fading cycles.

[0092] Application Example 1: Photochromic Coated Glasses

[0093] The VioBr2·2B(Ph)4@PVA sol (solution before drying) prepared in Example 2 was uniformly coated onto the surface of the finished resin lens. After drying in the dark, a photochromic functional coating was formed. Figure 13 As shown, under direct sunlight outdoors, the coating changes from pale yellow to blue within 5 seconds; upon entering an indoor environment, it spontaneously fades back to its initial state in about 10 minutes, accompanied by the fluorescence quenching and then recovering. This solution does not require changes to the lens substrate structure and can be directly coated onto the surface of existing finished lenses, resulting in low cost and simple processing. Compared to the limitations of traditional silver halide photochromic glass, which requires overall doping and has a slow color-changing response (typically exceeding 30 seconds), this solution has significant advantages in response speed, substrate compatibility, and long-term stability, making it suitable for adaptive dimming scenarios such as outdoor goggles and industrial protective masks.

[0094] Application Example 2: Powerless Photochromic Smart Window

[0095] Under direct sunlight, the VioBr2·2B(Ph)4@PVA eutectic gel develops color within 5 seconds and becomes saturated within 1 minute, exhibiting a blue-purple hue, effectively blocking glare and ultraviolet rays. After being moved to a dark environment, it spontaneously fades to transparency within 3 hours, restoring its transparency. The VioBr2·2B(Ph)4@PVA eutectic gel prepared in Example 3 is encapsulated between two pieces of glass (e.g., ...). Figure 16As shown in the image, this simulates a smart window that changes color (purple) under sunlight and fades when placed in the air. The entire process requires no external power supply or circuitry, achieving completely passive operation. Compared to the complex structure of traditional electrochromic smart windows, which require external circuitry and transparent conductive films, this solution is simple in structure and low in cost, showing broad application prospects in scenarios such as building energy-saving dimming and car sunroofs. This smart window has a simple structure and is easy to integrate, and can be directly used for the renovation of existing building glass curtain walls or windows, demonstrating application potential in residential, office building, and car sunroof scenarios.

[0096] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. Acetophenone violet based on tetraphenylborate as the counter anion, namely violet compound VioBr2·2B(Ph)4, characterized in that, This compound uses acetophenone instead of violetine (VioBr2) as the cationic skeleton and tetraphenylborate (BPh4⁻) as the counter anion. The two form a close-packed structure through ion pair interactions.

2. The method for preparing the flexible composite material based on tetraphenylborate as the counter anion of acetophenone violet as described in claim 1, characterized in that, Using VioBr2·2Cl as a precursor, Cl⁻ was replaced with BPh4⁻ through an anion exchange strategy.

3. The preparation method of the flexible composite material based on tetraphenylborate as the counter anion of acetophenone violet as described in claim 2, in specific operation, NaBPh4 is dissolved in ultrapure water and combined with a mixture of acetonitrile / water in VioBr2·2Cl, and stirred at room temperature for 3 hours. After precipitation, it is washed with pure water and acetone in sequence, filtered and vacuum dried to obtain the target product in the form of a deep yellow powder.

4. The flexible composite material based on tetraphenylborate as the counter anion of acetophenone violet as described in claim 1, wherein the flexible composite material is a system of two solid composite materials, namely VioBr2·2B(Ph)4@PVA film and VioBr2·2B(Ph)4@PVA deep eutectic gel.

5. The flexible composite material based on tetraphenylborate as the counter anion of acetophenone viologen according to claim 4, characterized in that, The VioBr2·2B(Ph)4@PVA film is formed by uniformly mixing viologen with polyvinyl alcohol (PVA) and glycerol in a solution and then casting it into a film. The resulting film has transparency, flexibility, fluorescence emission and rapid photochromic ability. It changes from pale yellow to blue within 5 seconds under sunlight, and spontaneously fades after 10 minutes indoors. Its performance does not significantly decrease after multiple cycles, making it suitable for photochromic coated glasses.

6. The flexible composite material based on acetophenone violet as a counter anion according to claim 4, characterized in that, The VioBr2·2B(Ph)4@PVA deep eutectic gel incorporates viologen into a PVA low eutectic solvent (ZnCl2 ethylene glycol water) system. Physically cross-linked eutectic gels are prepared through repeated freeze-thaw cycles. This gel exhibits excellent adhesion, can be directly sandwiched within glass interlayers, turns purple after 5 seconds of UV irradiation, achieves color saturation after 1 minute, and spontaneously fades after 3 hours in the dark. It also demonstrates excellent cycle stability and is suitable for passively driven adaptive smart windows.

7. Application of flexible composite materials based on tetraphenylborate as a counterion anion, acetophenone viologen, in photochromic coated glasses and smart windows.

Images