Preparation method of colorless-orange red reversible switching electrochromic material based on phenothiazine

Abstract

The invention belongs to the field of electrochromic materials, and relates to a preparation method of a colorless-orange red reversible switching electrochromic material based on phenothiazine. The method comprises the following steps: functionalization of phenothiazine micromolecules, introduction of polymerizable functional groups on a phenothiazine structure, ring-opening polymerization in which phenothiazine derivatives participate, dehydration of cyclization polymerization intermediates, and preparation of the electrochromic material. Due to the conjugated electron-rich structure of phenothiazine, phenothiazine has advantages as an electroactive group of an electrochromic material; in addition, a plurality of active sites provide synthesis advantages for polymer structure regulation and control. A non-coplanar propeller configuration and a polymeric monomer are introduced into a phenothiazine skeleton through a synthesis reaction, and the electrochromic film prepared after polymerization has the electrochromic characteristics of reversible switching between colorless color and orange red color, good stability and the like, and has huge application potential in the fields of intelligent windows, camouflage materials and the like.

Description

Technical Field

[0001] The present invention belongs to the field of electrochromic materials and relates to a preparation method of a colorless - orange - red reversible switching electrochromic material based on phenothiazine. Background Art

[0002] In recent years, electrochromic materials have received extensive attention because they can undergo reversible color changes under the action of an external electric field. Such materials show important application potential in the fields of smart windows, information displays, camouflage materials, etc. Polyimide is a type of polymer material with excellent comprehensive properties. Due to its excellent mechanical strength, heat resistance, chemical corrosion resistance, and good electrical insulation properties, it has been widely used in the fields of aerospace, electronics, flexible displays, etc. The excellent comprehensive properties of polyimide make it show advantages as the backbone material of electrochromic materials. However, the main chain of traditional polyimide molecules is usually non - conjugated and does not have electrochromic properties. Therefore, it is necessary to introduce reversibly redox - active groups through grafting or copolymerization to achieve its electrochromic function. In addition, because most polyimides have high rigidity and intermolecular interactions, the molecular chains are closely packed, enhancing the charge transfer effect, thus forming a charge - transfer complex, making the material show yellow or brown in the neutral state. This intrinsic color affects the controllability of the visual effect. Therefore, achieving a colorless neutral state color is of great significance. However, limited by the molecular structure characteristics of polyimide, achieving ideal color regulation still faces many challenges.

[0003] To further broaden the color regulation range and prepare a colorless - orange - red electrochromic polyimide material with reversible switching ability, several key problems still need to be solved. First, the colorlessization of the neutral state color requires effectively suppressing the formation of CTC, which depends on reasonable molecular structure design, such as reducing the main - chain rigidity, adjusting intermolecular forces, or introducing special substituents to disrupt the regular packing. Second, achieving the reversible switching between colorless and orange - red requires balancing key parameters such as the electrochemical stability, response rate, and cycle life of the material, while enabling the material to have efficient electron - transfer ability and appropriate energy - level regulation to ensure its stable color - changing behavior during multiple redox cycles. Therefore, developing polyimide materials with simultaneous colorless - orange - red reversible color - changing performance, high electrochemical stability, and excellent optical tunability, and breaking through the limitations of existing materials in color regulation, has important research value and application prospects. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an electrochromic material for red - transparent display in order to overcome the deficiencies of existing research.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A preparation method of a colorless - orange - red reversible switching electrochromic material based on phenothiazine, the specific steps are as follows:

[0007] Step (1): Functionalization of phenothiazine small molecules

[0008] Add phenothiazine monomer a and p - fluorobenzaldehyde as solutes into a solvent, mix them evenly and react fully under the action of a basic catalyst. The action of the basic catalyst causes the nucleophilic substitution reaction of p - halogenobenzaldehyde at the 10 - H position of phenothiazine, introducing a benzaldehyde structure to obtain a functionalized phenothiazine derivative b;

[0009] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0010] Add the functionalized phenothiazine derivative b obtained in step (1) and o - toluidine as solutes into a solvent, mix them evenly, and react in an acidic environment to obtain a phenothiazine - type derivative c with a polymerizable functional group amino, which is a monomer compound with an electroactive group;

[0011] Step (3): Ring - opening polymerization involving phenothiazine derivatives

[0012] Fully mix the phenothiazine - type derivative c with a polymerizable functional group amino obtained in step (2) and an acid anhydride in an aprotic polar solvent to obtain a polymerization intermediate after the ring - opening of the acid anhydride structure;

[0013] Step (4): Dehydration of the polymerization intermediate

[0014] First, raise the temperature of the system of the polymerization intermediate obtained in step (3), then continue to stir - react in the reaction system of step (3), and add a basic catalyst and a dehydrating agent to remove the water in the structure of the polymerization intermediate. After the reaction, precipitate the product into absolute ethanol to obtain a polyimide powder based on electroactive group phenothiazine, that is, an electrochromic polymer;

[0015] Step (5): Preparation of the electrochromic material

[0016] Prepare the electrochromic material by spin - coating technology; first, add the polyimide powder obtained in step (4) as a solute into a solvent, mix it evenly under ultrasonic action to obtain a mixed solution A; then, drop - coat the mixed solution A onto a conductive glass (ITO glass) with an indium tin oxide layer; turn on the spin coater, and under the action of centrifugal force, the solution spreads evenly and forms a film, and then the solvent is volatilized to obtain a uniform coating; finally, put the conductive glass with the electrochromic coating into an oven to dry the solvent to obtain the electrochromic material.

[0017] Preferably, the molar ratio of the phenothiazine monomer a to p-fluorobenzaldehyde in step (1) is 1:1 to 5; the reaction temperature is 120°C to 160°C; the reaction time is 10 h to 30 h; the basic catalyst is one or a mixture of two of potassium phosphate and potassium carbonate; the solvent is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and tetrahydrofuran.

[0018] Preferably, the molar ratio of the functionalized phenothiazine derivative b to o-toluidine in step (2) is 1:4 to 9; the reaction temperature is 70°C to 150°C; the reaction time is 5 h to 30 h; the acidic environment is obtained by mixing one or two or more of phosphoric acid, nitric acid, and hydrochloric acid; the reaction solvent is one or a mixture of two or more of pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and tetrahydrofuran.

[0019] Preferably, the molar ratio of the phenothiazine derivative c with a polymerizable functional group amino to the acid anhydride in step (3) is 1:1 to 2; the reaction temperature is -10°C to 50°C; the reaction time is 5 h to 30 h; the reaction is carried out under a protective atmosphere, and the protective atmosphere is a nitrogen atmosphere or an argon atmosphere; the aprotic polar solvent is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; the acid anhydride monomer is one or a mixture of two or more of pyromellitic dianhydride, hexafluorodiacid anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic dianhydride.

[0020] Preferably, the reaction temperature in step (4) is 120°C to 200°C; the reaction time is 2 h to 8 h; the molar ratio of the phenothiazine derivative c with a polymerizable functional group amino to the basic catalyst or dehydrating agent is 1:2 to 4.

[0021] Preferably, the solvent in step (5) is one or a mixture of two or more of acetone, dichloromethane, chloroform, ethyl acetate, tetrahydrofuran, and methanol; the ultrasonic time is 10 min to 60 min; the temperature for drying the film is set at 20°C to 80°C; the drying time is 2 h to 16 h.

[0022] The principle of the present invention:

[0023] The present invention adopts a simple synthesis method. Through a design strategy of integrating a conjugated electron-rich structure with a non-coplanar molecular configuration, a two-step reaction path of first condensing into aldehyde and then performing directional diamination is used to synthesize a diamine monomer with an electroactive group of phenothiazine and obtain a phenothiazine-based electrochromic polyimide material through polymerization. The non-coplanar propeller configuration formed by carbon atoms during the synthesis process will disrupt the regular arrangement of molecular chains, greatly improving the optical transparency of the system after polymerization of such monomers; the conjugated electron-rich structure of phenothiazine makes it have advantages as an electroactive group of electrochromic materials; in addition, its multiple active sites provide synthetic advantages for polymer structure regulation. At the same time, the introduction of electroactive groups into the polymer main chain will endow the polyimide system with electrochromic functionality, realizing color switching between colorless and orange-red. The present invention has great application potential in the fields of smart windows, camouflage materials, etc.

[0024] Advantages of the present invention:

[0025] (1) The polyimide based on the phenothiazine electroactive group in the present invention shows good solubility in high-boiling-point polar solvents (such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide) and low-boiling-point polar solvents (such as dichloromethane, chloroform, tetrahydrofuran, acetone), and the processing performance is greatly improved; the neutral-state thin film prepared therefrom has a high transmittance in the visible light region and is close to the colorless point in the center under the CIE coordinates. The high transmittance makes it suitable for the application of optoelectronic materials.

[0026] (2) The redox and electrochromic behaviors of the polyimide based on the phenothiazine electroactive group in the present invention result from the reversible redox process of the phenothiazine unit under the action of an electric field, and the transfer reaction of the lone pair electrons on its nitrogen atom dominates the formation of radical cations. A pair of obvious reversible redox pairs are shown in the voltage range of 0 - 1.4V, and it has good cycle stability. The thin film realizes a clear reversible color switching of "colorless - orange-red" after applying voltage, corresponding to a characteristic wavelength of about 519nm. Its lower oxidation potential (1.0V) and reduction potential (0.8V) can effectively save energy consumption, and during the long-term continuous coloring-fading reversible switching process, the high coloring retention, current density stability, and optical contrast shown by the phenothiazine-based polyimide material make it have potential application value in the fields of indoor comfort adjustment and energy-saving smart windows. Description of the drawings

[0027] Figure 1 It is the infrared-visible spectrum diagram of the electrochromic monomer and polymer in Example 1;

[0028] Figure 2 It is the cyclic voltammogram of the polyimide based on the phenothiazine electroactive group in Example 1;

[0029] Figure 3 Electrical cycling stability diagram of the polyimide based on phenothiazine electroactive groups in Example 1;

[0030] Figure 4 UV-visible spectroscopy diagram of the polyimide based on phenothiazine electroactive groups in Example 1 at different voltages;

[0031] Figure 5 Spectral kinetic stability diagram of the polyimide based on phenothiazine electroactive groups in Example 1 at 519 nm wavelength band;

[0032] Figure 6 Current density kinetic stability diagram recorded by an electrochemical workstation of the polyimide based on phenothiazine electroactive groups in Example 1 at 519 nm wavelength band;

[0033] Figure 7 Chromaticity comparison diagram of the polyimide based on phenothiazine electroactive groups in Example 1 before and after color change under CIE coordinates at 519 nm wavelength band. Detailed implementation manners

[0034] The following further illustrates the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0035] A preparation method of a colorless - orange - red reversible switching electrochromic material based on phenothiazine. The electrochromic polymer used is obtained by reacting monomer compounds with electroactive groups. The polymerization route of the electrochromic polymer is as follows:

[0036]

[0037] The synthesis route of the monomer compound with electroactive groups is as follows:

[0038]

[0039] In the present invention, the molar ratio of the phenothiazine monomer a and p - fluorobenzaldehyde in step (1) is 1:1 to 5, further preferably 1:1 to 3, and more preferably 1:1.5; the reaction temperature is 120°C to 160°C, further preferably 140°C to 160°C, and more preferably 150°C; the reaction time is 10 h to 30 h, further preferably 20 h to 30 h, and more preferably 25 h.

[0040] In the present invention, in step (2), the molar ratio of the functionalized phenothiazine derivative b to o-toluidine is 1:4 to 9, further preferably 1:5 to 8, and more preferably 1:8; the reaction temperature is 70°C to 150°C, further preferably 70°C to 120°C, and more preferably 110°C; the reaction time is 5 h to 30 h, further preferably 18 h to 24 h, and more preferably 20 h.

[0041] In the present invention, in step (3), the molar ratio of the phenothiazine derivative c with a polymerizable functional group amino to the acid anhydride is 1:1 to 2, further preferably 1:1 to 1.8, and more preferably 1:1.2; the reaction temperature is -10°C to 50°C, further preferably 0°C to 40°C, and more preferably 25°C; the reaction time is 5 h to 30 h, further preferably 18 h to 24 h, and more preferably 24 h.

[0042] In the present invention, in step (4), the reaction temperature is 120°C to 200°C, further preferably 160°C to 200°C, and more preferably 180°C; the substitution reaction time is preferably 2 h to 8 h, further preferably 4 h to 8 h, and more preferably 5 h; the ratio of the phenothiazine derivative c with a polymerizable functional group amino to the basic catalyst or dehydrating agent is 1:2 to 4, further preferably 1:2.5 to 3.5, and more preferably 1:3.

[0043] In the present invention, in step (5), the ultrasonic time is preferably 10 min to 60 min, further preferably 20 min to 40 min, and more preferably 30 min; the temperature for drying the film is preferably 20°C to 80°C, further preferably 30°C to 60°C, and more preferably 50°C; the drying time is preferably 2 h to 16 h, further preferably 4 h to 15 h, and more preferably 12 h.

[0044] Example 1:

[0045] Step (1): Functionalization of phenothiazine small molecules

[0046] The phenothiazine monomer a and p-fluorobenzaldehyde (the molar ratio of the reactant feed is 1:4) are added as solutes to the solvent N,N-dimethylformamide, mixed evenly, and heated to 150°C under the action of the basic catalyst potassium phosphate and reacted for 25 h to obtain the functionalized phenothiazine derivative b;

[0047] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0048] The product b obtained in step (1) and o-toluidine (molar ratio of 1:8) are added as solutes to the solvent N,N-dimethylformamide, mixed evenly, and heated to 110°C under the action of hydrochloric acid and reacted for 24 h to obtain the phenothiazine derivative c with a polymerizable functional group amino;

[0049] Step (3): Ring-opening polymerization involving phenothiazine derivatives

[0050] First, the phenothiazine derivative c with a polymerizable functional group amino obtained in step (2) is fully mixed with the acid anhydride 3,3',4,4'-biphenyltetracarboxylic dianhydride (molar ratio 1:1.2) in the aprotic polar solvent N,N-dimethylacetamide, and reacted at 25 °C under a nitrogen atmosphere for 24 h to obtain a polymerization intermediate after the ring-opening of the acid anhydride structure;

[0051] Step (4): Dehydration process of the polymerization intermediate

[0052] First, the system of the polymerization intermediate obtained in step (3) is heated to 180 °C, then a basic catalyst pyridine and a dehydrating agent acetic anhydride with a molar ratio of 1:3 to the phenothiazine derivative c are added, and the reaction is continued under stirring for 5 h to remove the water on the structure of the ring-opening polymerization intermediate. After the reaction, it is sedimented into absolute ethanol to obtain polyimide powder based on the electroactive group phenothiazine;

[0053] Step (5): Preparation of electrochromic materials

[0054] The electrochromic material is prepared by a spin-coating process; first, the polyimide powder obtained in step (4) is added as a solute to the solvent dichloromethane, and uniformly mixed under ultrasonic action for 30 min to obtain a mixed solution A; subsequently, the mixed solution A is drop-coated onto a conductive glass (ITO glass) with an indium tin oxide layer; the spin coater is turned on, and under the action of centrifugal force, the solution spreads uniformly and forms a film, and then a uniform coating is obtained after the solvent volatilizes; finally, the conductive glass with the electrochromic coating is placed in an oven and dried at 50 °C for 12 h to obtain an electrochromic film.

[0055] From Figure 1 it can be seen that no doublet of the stretching vibration of the N-H bond on the amino group is observed at 3459 and 3363 cm -1 . The stretching vibration peaks of the methyl group and the aliphatic C-H bond connecting three non-coplanar aromatic fragments are located in the range of 2921 - 2850 cm -1 . At the same time, an asymmetric stretching vibration peak and a symmetric stretching vibration peak of the carbonyl C=O on the imide ring structure are observed at 1778 cm -1 and 1722 cm -1 ; a stretching vibration peak of C-N on the imide ring is observed at 1373 cm -1 ; a stretching vibration peak of C-N on the imide ring is observed at 743 cm -1The angular vibration peak of the carbonyl group, that is, the deformation vibration peak of the imide ring, was observed, confirming the introduction of the imide ring. In addition, the characteristic peaks (carbonyl stretching vibration of the amide group at 1660 cm -1 and stretching vibration of the C-N bond at 1550 cm -1 ) of the polyamic acid, the polymerization intermediate, were not detected in the infrared curves of the three polymers. In summary, infrared spectroscopy analysis shows that the polymerization structure of the polyimide is clear and the reaction has been completed completely.

[0056] From Figure 2 , it can be found that the phenothiazine-based polyimide film shows obvious and reversible redox peak pairs, and no additional redox peaks are observed. From Figure 3 , it can be found that the results of the repeated cycle evaluation of the stability of the polyimide film show that the current value attenuation of the electrochromic polymer material is small, showing excellent redox reversibility and stability.

[0057] By using a combination of an ultraviolet-visible spectrometer and an electrochemical workstation, the optical response of the film under different voltages applied by the electrochemical workstation was recorded by the spectrometer. From Figure 4 , it can be found that as the voltage gradually increases, the polymer is gradually oxidized; when the voltage increases to 0.8 V, a new absorption peak appears at 519 nm, and the absorbance of this characteristic peak increases significantly with the further increase of the voltage.

[0058] To further evaluate the electrochromic cycling performance of the three phenothiazine-based polyimide films, based on the characteristic peak positions corresponding to the electrochromic process determined by ultraviolet-visible spectroscopy, a square wave voltage was applied at this fixed wavelength (i.e., 519 nm) to drive the polyimide film to switch between the colored state and the faded state, and its transmittance ( Figure 5 ) and the change of current density with time ( Figure 6 ) were monitored. After a long time of color reversible switching, the colorless - orange-red reversible switching electrochromic material based on phenothiazine shows a very low attenuation degree, presenting excellent electrochromic cycling performance.

[0059] From Figure 7 , it can be found that the color of the phenothiazine-based polyimide film before color change is in the central region of the CIE coordinate, close to the colorless point, showing a colorless neutral state color; after color change, its CIE coordinate is located in the orange-red region, and the coordinate difference before and after color change is obvious, indicating that the film has undergone a significant color change under the action of voltage.

[0060] Example 2

[0061] Step (1): Functionalization of phenothiazine small molecules

[0062] Phenothiazine monomer a and p-fluorobenzaldehyde (the molar ratio of reactant feeding is 1:4) were added as solutes into the solvent N,N-dimethylacetamide, and mixed evenly. Under the action of the alkaline catalyst potassium phosphate, the temperature was raised to 120 °C and reacted for 30 h to obtain the functionalized phenothiazine derivative b;

[0063] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0064] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (molar ratio of 1:9) were added as solutes into the solvent N,N-dimethylformamide, mixed evenly, and under the action of hydrochloric acid, the temperature was raised to 70 °C and reacted for 30 h to obtain the phenothiazine derivative c with polymerizable functional group amino;

[0065] Step (3): Ring-opening polymerization involving phenothiazine derivatives

[0066] First, the phenothiazine derivative c with polymerizable functional group amino obtained in step (2) and the acid anhydride 1,4,5,8-naphthalenetetracarboxylic dianhydride (molar ratio of 1:1.2) were fully mixed in the aprotic polar solvent N,N-dimethylformamide, and reacted at -10 °C under a nitrogen atmosphere for 30 h to obtain the polymerization intermediate after the ring-opening of the acid anhydride structure;

[0067] Step (4): Dehydration process of the ring-opening polymerization intermediate

[0068] First, the system of the polymerization intermediate obtained in step (3) was heated to 120 °C, then the alkaline catalyst pyridine and the dehydrating agent acetic anhydride with a molar ratio of 1:3 to the phenothiazine derivative c were added, and the reaction was continued under stirring for 8 h to remove the water on the structure of the ring-opening polymerization intermediate. After the reaction, it was sedimented into absolute ethanol to obtain the polyimide powder based on the electroactive group phenothiazine;

[0069] Step (5): Preparation of electrochromic film

[0070] The electrochromic material was prepared by a spin-coating process; First, the polyimide powder obtained in step (4) was added as a solute into the solvent chloroform, and mixed evenly under ultrasonic action for 10 min to obtain the mixed solution A; Subsequently, the mixed solution A was drop-coated onto the conductive glass with an indium tin oxide layer (ITO glass); The spin coater was turned on, and under the action of centrifugal force, the solution spread evenly and formed a film, and then a uniform coating was obtained after the solvent volatilized; Finally, the conductive glass with the electrochromic coating was placed in an oven and dried at 20 °C for 16 h to obtain the electrochromic film.

[0071] Example 3:

[0072] Step (1): Functionalization of phenothiazine small molecules

[0073] Phenothiazine monomer a and p-fluorobenzaldehyde (the molar ratio of reactant feeding is 1:4) were added as solutes into the solvent tetrahydrofuran, and they were mixed evenly. Under the action of the alkaline catalyst potassium phosphate, the temperature was raised to 160 °C and reacted for 10 h to obtain the functionalized phenothiazine derivative b;

[0074] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0075] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (molar ratio of 1:4) were added as solutes into the solvent N-methylpyrrolidone, and they were mixed evenly. Under the action of hydrochloric acid, the temperature was raised to 150 °C and reacted for 5 h to obtain the phenothiazine derivative c with polymerizable functional group amino;

[0076] Step (3): Ring-opening polymerization involving phenothiazine derivatives

[0077] First, the phenothiazine derivative c with polymerizable functional group amino obtained in step (2) and the acid anhydride 3,3',4,4'-benzophenone tetracarboxylic dianhydride (molar ratio of 1:1) were fully mixed in the aprotic polar solvent N,N-dimethylformamide, and reacted at 50 °C under a nitrogen atmosphere for 5 h to obtain the polymerization intermediate after the ring-opening of the acid anhydride structure;

[0078] Step (4): Dehydration process of the ring-opening polymerization intermediate

[0079] First, the system of the polymerization intermediate obtained in step (3) was heated to 200 °C, then the basic catalyst pyridine and the dehydrating agent acetic anhydride with a molar ratio of 1:3 to the phenothiazine derivative c were added, and the reaction was continued under stirring for 2 h to remove the water on the structure of the ring-opening polymerization intermediate. After the reaction, it was precipitated into absolute ethanol to obtain the polyimide powder based on the electroactive group phenothiazine;

[0080] Step (5): Preparation of electrochromic film

[0081] The electrochromic material was prepared by spin coating process; First, the polyimide powder obtained in step (4) was added as a solute into the solvent acetone, and it was mixed evenly under ultrasonic action for 10 min to obtain the mixed solution A; Subsequently, the mixed solution A was drop-coated onto the conductive glass (ITO glass) with an indium tin oxide layer; The spin coater was turned on, and under the action of centrifugal force, the solution spread evenly and formed a film, and then a uniform coating was obtained after the solvent volatilized; Finally, the conductive glass with the electrochromic coating was placed in an oven and dried at 80 °C for 60 h to obtain the electrochromic film.

[0082] Example 4:

[0083] Step (1): Functionalization of phenothiazine small molecules

[0084] Phenothiazine monomer a and p-fluorobenzaldehyde (the molar ratio of reactant feeding is 1:1) were added as solutes into the solvent N,N-dimethylformamide, and they were mixed evenly. Under the action of the alkaline catalyst potassium phosphate, the temperature was raised to 150 °C and the reaction was carried out for 25 h to obtain the functionalized phenothiazine derivative b;

[0085] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0086] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (molar ratio of 1:4) were added as solutes into the solvent tetrahydrofuran, and they were mixed evenly. Under the action of nitric acid, the temperature was raised to 150 °C and the reaction was carried out for 5 h to obtain the phenothiazine derivative c with a polymerizable functional group amino;

[0087] Step (3): Ring-opening polymerization involving phenothiazine derivatives

[0088] First, the phenothiazine derivative c with a polymerizable functional group amino obtained in step (2) and the acid anhydride hexafluorodiacetic anhydride (molar ratio of 1:2) were fully mixed in the aprotic polar solvent N,N-dimethylacetamide, and the reaction was carried out at 25 °C under a nitrogen atmosphere for 24 h to obtain a polymerization intermediate after the ring-opening of the acid anhydride structure;

[0089] Step (4): Dehydration process of the ring-opening polymerization intermediate

[0090] First, the system of the polymerization intermediate obtained in step (3) was heated to 200 °C, and then the basic catalyst pyridine and the dehydrating agent acetic anhydride with a molar ratio of 1:2 to the phenothiazine derivative c were added. The reaction was continued under stirring for 2 h to remove the water on the structure of the ring-opening polymerization intermediate. After the reaction, it was sedimented into absolute ethanol to obtain polyimide powder based on the electroactive group phenothiazine;

[0091] Step (5): Preparation of electrochromic film

[0092] The electrochromic film was prepared by a spin-coating process; First, the polyimide powder obtained in step (4) was added as a solute into the solvent ethyl acetate, and it was mixed evenly under ultrasonic action for 60 min to obtain a mixed solution A; Subsequently, the mixed solution A was drop-coated onto the conductive glass with an indium tin oxide layer (ITO glass); The spin coater was turned on, and under the action of centrifugal force, the solution spread evenly and formed a film, and then a uniform coating was obtained after the solvent volatilized; Finally, the conductive glass with the electrochromic coating was placed in an oven and dried at 80 °C for 2 h to obtain the electrochromic film.

[0093] Example 5:

[0094] Step (1): Functionalization of phenothiazine small molecules

[0095] The phenothiazine monomer (and p-fluorobenzaldehyde with a molar ratio of reactant feed of 1:5) was added as a solute to the solvent N-methylpyrrolidone, and they were mixed evenly. Under the action of the alkaline catalyst potassium phosphate, the temperature was raised to 150 °C and the reaction was carried out for 25 h to obtain the functionalized phenothiazine derivative b;

[0096] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0097] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (molar ratio of 1:4) were added as solutes to the solvent N,N-dimethylacetamide, and they were mixed evenly. Under the action of phosphoric acid, the temperature was raised to 150 °C and the reaction was carried out for 5 h to obtain the phenothiazine derivative c with a polymerizable functional group amino;

[0098] Step (3): Ring-opening polymerization involving phenothiazine derivatives

[0099] First, the phenothiazine derivative c with a polymerizable functional group amino obtained in step (2) and the acid anhydride pyromellitic dianhydride (molar ratio of 1:2) were fully mixed in the aprotic polar solvent N-methylpyrrolidone, and the reaction was carried out at 25 °C in a nitrogen environment for 24 h to obtain a polymerization intermediate after the ring-opening of the acid anhydride structure;

[0100] Step (4): Dehydration process of the ring-opening polymerization intermediate

[0101] First, the system of the polymerization intermediate obtained in step (3) was heated to 120 °C, then the alkaline catalyst pyridine and the dehydrating agent acetic anhydride with a molar ratio of 1:4 to the feed of the phenothiazine derivative c were added, and the reaction was continued under stirring for 8 h to remove the water on the structure of the ring-opening polymerization intermediate. After the reaction, it was sedimented into absolute ethanol to obtain the polyimide powder based on the electroactive group phenothiazine;

[0102] Step (5): Preparation of electrochromic film

[0103] The electrochromic film was prepared by a spin-coating process; first, the polyimide powder obtained in step (4) was added as a solute to the solvent tetrahydrofuran, and it was mixed evenly under ultrasonic action for 30 min to obtain a mixed solution A; subsequently, the mixed solution A was drop-coated onto the conductive glass (ITO glass) with an indium tin oxide layer; the spin coater was turned on, and under the action of centrifugal force, the solution spread evenly and formed a film, and then a uniform coating was obtained after the solvent volatilized; finally, the conductive glass with the electrochromic coating was placed in an oven and dried at 80 °C for 2 h to obtain the electrochromic film.

[0104] Example 6:

[0105] Step (1): Functionalization of phenothiazine small molecules

[0106] Phenothiazine monomer a and p-fluorobenzaldehyde (the molar ratio of reactant feeding is 1:5) were added as solutes into the solvent tetrahydrofuran, and they were mixed evenly. Under the action of the alkaline catalyst potassium phosphate, the temperature was raised to 150 °C and reacted for 25 h to obtain the functionalized phenothiazine derivative b;

[0107] Step (2): Introduction of polymerizable functional groups onto the phenothiazine structure

[0108] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (molar ratio of 1:8) were added as solutes into the solvent tetrahydrofuran, and they were mixed evenly. Under the action of hydrochloric acid, the temperature was raised to 110 °C and reacted for 24 h to obtain the phenothiazine derivative c with a polymerizable functional group amino;

[0109] Step (3): Ring-opening polymerization involving phenothiazine derivatives

[0110] First, the phenothiazine derivative c with a polymerizable functional group amino obtained in step (2) and the acid anhydride pyromellitic dianhydride (molar ratio of 1:2) were fully mixed in the aprotic polar solvent dimethyl sulfoxide, and reacted at 25 °C under a nitrogen atmosphere for 24 h to obtain a polymerization intermediate after the ring-opening of the acid anhydride structure;

[0111] Step (4): Dehydration process of the ring-opening polymerization intermediate

[0112] First, the system of the polymerization intermediate obtained in step (3) was heated to 200 °C, then a basic catalyst pyridine and a dehydrating agent acetic anhydride with a molar ratio of 1:3 to the phenothiazine derivative c were added, and the reaction was continued under stirring for 8 h to remove the water on the structure of the ring-opening polymerization intermediate. After the reaction, it was sedimented into absolute ethanol to obtain polyimide powder based on the electroactive group phenothiazine;

[0113] Step (5): Preparation of electrochromic film

[0114] The electrochromic material was prepared by a spin-coating process; first, the polyimide powder obtained in step (4) was added as a solute into the solvent methanol, and mixed evenly under ultrasonic action for 30 min to obtain a mixed solution A; subsequently, the mixed solution A was drop-coated onto the conductive glass with an indium tin oxide layer (ITO glass); the spin coater was turned on, and under the action of centrifugal force, the solution spread evenly and formed a film, and then a uniform coating was obtained after the solvent volatilized; finally, the conductive glass with the electrochromic coating was placed in an oven and dried at 50 °C for 12 h to obtain the electrochromic film.

[0115] The films of Examples 2 - 6 showed asymmetric stretching vibration peaks and symmetric stretching vibration peaks attributed to the carbonyl C=O on the imide ring structure at 1778 cm -1 and 1722 cm -1 ; at 1373 cm-1 The stretching vibration peak attributed to C-N on the imide ring was observed at 743 cm -1 The angular deformation vibration peak of the carbonyl group, that is, the deformation vibration peak of the imide ring, was observed at [specific value], confirming the introduction of the imide ring. In addition, no characteristic peaks of the polymerization intermediate (the stretching vibration of the carbonyl group on the amide group at 1660 cm -1 and the stretching vibration of the C-N bond at 1550 cm -1 ) were detected in the infrared curve. It was proved that the reaction was complete. At the same time, its neutral state color was close to the center position of the CIE coordinates, confirming its colorless state; its color after electrooxidation was located in the orange-red region of the CIE coordinates.

Claims

1. A method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine, characterized in that: The electrochromic polymer used is obtained by reacting a monomer compound with an electroactive group. The polymerization route of the electrochromic polymer is: The synthetic route of the monomer compound with electroactive groups is:

2. The method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine according to claim 1, characterized in that: The specific steps are as follows: Step (1): Functionalization of phenothiazine small molecules Phenothiazine monomer a and p-fluorobenzaldehyde are added as solutes into a solvent, mixed evenly and reacted fully under the action of an alkaline catalyst. The alkaline catalyst causes p-halogen benzaldehyde to undergo a nucleophilic substitution reaction at the 10-H position of phenothiazine, introducing a benzaldehyde structure to obtain a functionalized phenothiazine derivative b. Step (2): Introduction of polymerizable functional groups into the phenothiazine structure The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine as a solute are added to a solvent, mixed evenly, and reacted in an acidic environment to obtain a phenothiazine derivative c with a polymerizable functional group amino group, i.e., a monomer compound with an electroactive group; Step (3): Ring-opening polymerization involving phenothiazine derivatives The phenothiazine derivative c with a polymerizable functional group amino group obtained in step (2) is fully mixed with an acid anhydride in a non-protonic polar solvent to obtain a polymerizable intermediate after the acid anhydride structure is ring-opened; Step (4): Dehydration of the polymerization intermediate First, the system of the polymer intermediate obtained in step (3) is heated, then, the reaction is continued in the reaction system of step (3) by stirring, and an alkaline catalyst and a dehydrating agent are added to remove water in the structure of the polymer intermediate, and after the reaction is completed, the product is precipitated into anhydrous ethanol to obtain a polyimide powder based on an electroactive group phenothiazine, i.e., an electrochromic polymer; Step (5): Preparation of electrochromic material The electrochromic material is prepared by a spin coating process; first, the polyimide powder obtained in step (4) is added as a solute into a solvent, and mixed evenly under the action of ultrasound to obtain a mixed solution A; then, the mixed solution A is drop-coated onto a conductive glass with an indium tin oxide layer; a coating machine is turned on, and under the action of centrifugal force, the solution is evenly spread to form a thin film, and then the solvent is evaporated to obtain a uniform coating; finally, the conductive glass with the electrochromic coating is placed in an oven to dry the solvent to obtain the electrochromic material.

3. The method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine according to claim 2, characterized in that: The molar ratio of the phenothiazine monomer a to p-fluorobenzaldehyde in step (1) is 1:1-5; the reaction temperature is 120°C-160°C; the reaction time is 10h-30h; the alkaline catalyst is one or a mixture of potassium phosphate and potassium carbonate; and the solvent is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and tetrahydrofuran.

4. The method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine according to claim 2, characterized in that: The molar ratio of the functionalized phenothiazine derivative b to o-toluidine in step (2) is 1:4-9; the reaction temperature is 70°C-150°C; the reaction time is 5h-30h; the acidic environment is obtained by using one or a mixture of two or more of phosphoric acid, nitric acid and hydrochloric acid; the reaction solvent is one or a mixture of two or more of pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and tetrahydrofuran.

5. The method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine according to claim 2, characterized in that: In step (3), the molar ratio of the phenothiazine derivative c with a polymerizable functional amino group to the acid anhydride is 1:1-2; the reaction temperature is -10°C-50°C; the reaction time is 5h-30h; the reaction is carried out under a protective atmosphere, which is a nitrogen atmosphere or an argon atmosphere; the non-protonic polar solvent is one or a mixture of two or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; the acid anhydride monomer is one or a mixture of two or more of pyromellitic dianhydride, hexafluorodianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic anhydride.

6. The method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine according to claim 2, characterized in that: The reaction temperature in step (4) is 120°C to 200°C; the reaction time is 2h to 8h; the molar ratio of the phenothiazine derivative c with a polymerizable amino functional group to the alkaline catalyst or dehydrating agent is 1:2 to 4;.

7. The method for preparing a colorless-orange-red reversibly switchable electrochromic material based on phenothiazine according to claim 2, characterized in that: The solvent described in step (5) is one or a mixture of two or more of acetone, dichloromethane, chloroform, ethyl acetate, tetrahydrofuran, and methanol; the ultrasonic time is 10 min to 60 min; the temperature of the drying film is set to 20° C. to 80° C.; and the drying time is 2 h to 16 h.

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