A preparation method of a colorless-orange red reversible switching electrochromic material based on phenothiazine

Abstract

The application 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 a phenothiazine small molecule, introduction of a polymerizable functional group on the phenothiazine structure, ring-opening polymerization of a phenothiazine derivative, dehydration of a cyclization polymerization intermediate, and preparation of an electrochromic material. The conjugated electron-rich structure of phenothiazine makes it have an advantage as an electroactive group of an electrochromic material. In addition, the multiple active sites provide advantages for the synthesis of polymer structure regulation. The application introduces a non-coplanar propeller configuration and a polymerization monomer into the phenothiazine skeleton through a synthesis reaction, and the electrochromic film prepared after polymerization has electrochromic characteristics such as colorless-orange red reversible switching and good stability, and has great application potential in the fields of smart windows, camouflage materials and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrochromic materials, and relates to a preparation method of a colorless-orange red reversibly switchable electrochromic material based on phenothiazine. BACKGROUND

[0002] In recent years, electrochromic materials have attracted extensive attention due to their reversible color change under the action of an external electric field. Such materials have important application potential in the fields of smart windows, information display, camouflage materials and the like. Polyimide is a kind of polymer material with excellent comprehensive performance, and is widely used in the fields of aerospace, electronics, flexible display and the like due to its excellent mechanical strength, heat resistance, chemical corrosion resistance and good electrical insulation. The excellent comprehensive performance of polyimide enables it to have advantages as a skeleton material of electrochromic materials. However, the traditional polyimide molecular main chain usually has a non-conjugated structure and does not have electrochromic properties, and therefore it is necessary to introduce reversible redox electroactive groups by grafting or copolymerization and the like to realize the electrochromic function. In addition, due to the high rigidity and molecular chain interaction of most polyimides, the molecular chains are tightly packed, the charge transfer effect is enhanced, and a charge transfer complex is formed, so that the material presents a yellow or brown color in the neutral state. This intrinsic color affects the controllability of the visual effect, and therefore it is of great significance to realize the colorless neutral state. However, due to the molecular structure characteristics of polyimide, there are still many challenges in realizing ideal color regulation.

[0003] In order to further broaden the color regulation range and prepare a colorless-orange red electrochromic polyimide material with reversible switching capability, a plurality of key problems still need to be solved. First, the colorless neutral state color needs to effectively inhibit the formation of CTC, which depends on reasonable molecular structure design, such as reducing the rigidity of the main chain, adjusting the intermolecular force or introducing special substituents to destroy the regular packing. Second, in order to realize the reversible switching of colorless-orange red, it is necessary to balance the key parameters such as electrochemical stability, response rate and cycle life of the material, and at the same time, to enable the material to have efficient electron transfer capability and suitable energy level regulation, so as to ensure that it still has stable color change behavior in multiple redox cycles. Therefore, it is of great research value and application prospect to develop a polyimide material with reversible colorless-orange red color, high electrochemical stability and excellent optical tunability, and to break through the limitations of existing materials in color regulation. SUMMARY

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

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

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

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

[0008] Phenothiazine monomer a and p-fluorobenzaldehyde are added as solutes to the solvent, mixed uniformly and reacted under the action of a basic catalyst. The action of the basic catalyst causes the nucleophilic substitution reaction of p-halogen benzaldehyde at the 10-H position of phenothiazine, introducing the benzaldehyde structure, to obtain the functionalized phenothiazine derivative b;

[0009] Step (2): introduction of a polymerizable functional group on the phenothiazine structure

[0010] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine are added as solutes to the solvent, mixed uniformly, and reacted in an acidic environment to obtain a phenothiazine derivative c with a polymerizable amino group, i.e. a monomer compound with an electroactive group;

[0011] Step (3): ring-opening polymerization of phenothiazine derivatives

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

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

[0014] First, the system of the polymerization intermediate obtained in step (3) is warmed, then the reaction system of step (3) is continuously stirred and reacted, and a basic catalyst and a dehydrating agent are added to remove water from the structure of the polymerization intermediate. After the reaction is completed, the product is settled in anhydrous ethanol to obtain a polyimide powder based on the electroactive group phenothiazine, i.e. an electrochromic polymer;

[0015] Step (5): preparation of an electrochromic material

[0016] An electrochromic material is prepared by a spin coating process. First, the polyimide powder obtained in step (4) is added as a solute to a solvent, mixed uniformly under ultrasonic action to obtain a mixed solution A; then, the mixed solution A is drop-coated onto 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 thin film, and then a uniform coating is obtained after solvent evaporation; finally, the conductive glass with the electrochromic coating is placed in an oven to dry the solvent, obtaining an electrochromic material.

[0017] As preferred, the molar ratio of the phenothiazine monomer a and p-fluorobenzaldehyde in step (1) is 1:1-5; the reaction temperature is 120-160℃; the reaction time is 10-30h; the basic catalyst is one or a mixture of both 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.

[0018] As preferred, the molar ratio of the functionalized phenothiazine derivative b and o-toluidine in step (2) is 1:4-9; the reaction temperature is 70-150℃; the reaction time is 5-30h; the acidic environment is obtained by using one or a mixture of two or more of phosphoric acid, nitric acid and hydrochloric acid; and 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] As preferred, the molar ratio of the phenothiazine derivative c with polymeric functional group amino and anhydride in step (3) is 1:1-2; the reaction temperature is -10-50℃; the reaction time is 5-30h; the reaction is carried out in a protective atmosphere, which is nitrogen atmosphere or 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; and the anhydride monomer is one or a mixture of two or more of pyromellitic dianhydride, hexafluoro dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride and 1,4,5,8-naphthalene tetracarboxylic anhydride.

[0020] As preferred, the reaction temperature in step (4) is 120-200℃; the reaction time is 2-8h; and the molar ratio of the phenothiazine derivative c with polymeric functional group amino and the basic catalyst or dehydrating agent is 1:2-4.

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

[0022] Principle of the present application:

[0023] The application adopts a simple synthesis method, a design strategy of integrating conjugated electron-rich structure and non-coplanar molecular configuration, a two-step reaction path of synthesizing aldehyde first and then directing double amino, synthesizes a diamin monomer with an electrically active group phenothiazine, and obtains an electrochromic polyimide material based on phenothiazine by polymerization. The non-coplanar propeller configuration formed by carbon atoms in the synthesis process can destroy the regular arrangement of the molecular chain, so that the optical transparency of the system after polymerization of the monomer is greatly improved; the conjugated electron-rich structure of phenothiazine makes it have an advantage as an electrically active group of electrochromic material; in addition, the multiple active sites provide advantages for the synthesis of polymer structure regulation. At the same time, the introduction of the electrically active group into the polymer main chain will endow the polyimide system with electrochromic function, realizing the color switching of colorless-orange red. The application has great application potential in the fields of smart windows, camouflage materials and the like.

[0024] The beneficial effects of the application are as follows:

[0025] (1) The polyimide based on the phenothiazine electrically active group in the application has 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, trichloromethane, tetrahydrofuran, acetone), and the processing performance is greatly improved; the neutral state thin film prepared therefrom has high light transmittance in the visible light region, and is close to the colorless point in the CIE coordinate, so that it is suitable for application in optoelectronic materials.

[0026] (2) The redox and electrochromic behavior of the polyimide based on the phenothiazine electrically active group in the application is derived 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 the nitrogen atom dominates the formation of free radical cations. In the voltage range of 0-1.4V, a pair of obvious reversible redox couples is exhibited, and good cycle stability is also exhibited. The thin film realizes clear “colorless-orange red” reversible color switching after applying voltage, corresponding to a characteristic wavelength of about 519nm. The low oxidation potential (1.0V) and reduction potential (0.8V) can effectively save energy, and in the long-term continuous coloring-fading reversible switching process, the polyimide material based on phenothiazine exhibits high coloration maintenance, current density stability and optical contrast, so that it has potential application value in the fields of indoor comfort adjustment and energy-saving smart windows. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The infrared visible spectrum of the electrochromic monomer and polymer of Example 1 is shown in the figure;

[0028] Figure 2 The cyclic voltammogram of the polyimide based on the phenothiazine electrically active group of Example 1 is shown in the figure.

[0029] Figure 3 Figure for electrocyclic stability of the phenothiazine-based electroactive group-based polyimide of Example 1;

[0030] Figure 4 Figure for UV-Vis spectra of the phenothiazine-based electroactive group-based polyimide of Example 1 at different voltages;

[0031] Figure 5 Figure for spectral kinetic stability of the phenothiazine-based electroactive group-based polyimide of Example 1 at 519 nm wavelength;

[0032] Figure 6 Figure for current density kinetic stability recorded by electrochemical workstation of the phenothiazine-based electroactive group-based polyimide of Example 1 at 519 nm wavelength;

[0033] Figure 7 Figure for chroma contrast of CIE coordinates before and after color change of the phenothiazine-based electroactive group-based polyimide of Example 1 at 519 nm wavelength. DETAILED DESCRIPTION

[0034] The specific embodiments of the present application are further illustrated in the following with reference to the accompanying drawings.

[0035] A preparation method of a phenothiazine-based colorless-orange red reversible switching electrochromic material, the electrochromic polymer used is obtained by reacting a monomer compound with an electroactive group, and the polymerization route of the electrochromic polymer is as follows:

[0036]

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

[0038]

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

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

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

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

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

[0044] Example 1:

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

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

[0047] Step (2): introduction of polymerizable functional group on phenothiazine structure

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

[0049] Step (3): ring-opening polymerization of phenothiazine derivative

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

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

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

[0053] Step (5): preparation of electrochromic material

[0054] The electrochromic material was prepared by spin coating process. First, the polyimide powder obtained in step (4) was added as a solute to the solvent dichloromethane, and mixed uniformly under ultrasonic action for 30min to obtain a mixed solution A. Then, 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 uniformly and formed a thin film, and then a uniform coating was obtained after solvent evaporation. Finally, the conductive glass with electrochromic coating was placed in an oven and dried at 50°C for 12h to obtain an electrochromic film.

[0055] From Figure 1 It can be seen that the polyimide does not observe the N-H bond stretching vibration doublet belonging to the amino group at 3459 and 3363cm -1 . The stretching vibration peaks of methyl and aliphatic C-H bonds connecting three non-planar aromatic fragments are located in the range of 2921-2850cm -1 . At the same time, the asymmetric stretching vibration peak and the symmetric stretching vibration peak belonging to the carbonyl C=O on the imide ring structure are observed at 1778cm -1 and 1722cm -1 . The stretching vibration peak belonging to C-N on the imide ring is observed at 1373cm -1 . The stretching vibration peak belonging to C-N on the imide ring is observed at 1373cm -1The introduction of the imide ring was confirmed by the observation of the carbonyl variable angle vibration peak, i.e. the deformation vibration peak of the imide ring. In addition, the characteristic peaks of the polymerization intermediate, polyamic acid (1660 cm -1 The stretching vibration of the carbonyl group on the amide group and the stretching vibration of the C-N bond at 1550 cm -1 The infrared spectrum analysis showed that the polymerization structure of the polyimide was clear and the reaction had been completed.

[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 repeated cycle evaluation of the stability of the polyimide film shows that the attenuation value of the current value of the electrochromic polymer material is small, and it exhibits excellent redox reversibility and stability.

[0057] By using the ultraviolet visible spectrometer in combination with the 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 the characteristic peak is significantly enhanced as the voltage further increases.

[0058] To further evaluate the electrochromic cycle performance of the three phenothiazine-based polyimide films, based on the characteristic peak position determined by the ultraviolet visible spectrum corresponding to the electrochromic process, a square wave voltage was applied at the fixed wavelength (i.e. 519 nm) to drive the polyimide film to switch between the colored state and the bleached state, and the transmittance ( Figure 5 ) and the current density ( Figure 6 ) were monitored over time. After long-term color reversible switching, the colorless-orange red reversible switching electrochromic material based on phenothiazine showed very low attenuation degree, and exhibited excellent electrochromic cycle 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, and exhibits 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 significant color change under the action of voltage.

[0060] Example 2

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

[0062] The phenothiazine monomer a and p-fluorobenzaldehyde (molar ratio of reactant feedings is 1:4) are added as solutes into solvent N,N-dimethylacetamide, mixed uniformly, and reacted at 120°C for 30 h under the action of basic catalyst potassium phosphate to obtain functionalized phenothiazine derivative b;

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

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

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

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

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

[0068] The polymerization intermediate system obtained in step (3) is first heated to 120°C, and then the basic catalyst pyridine and the dehydrating agent acetic anhydride are added at a molar ratio of 1:3 to the phenothiazine derivative c, and the reaction is continued for 8 h under stirring to remove water from the structure of the ring-opening polymerization intermediate. After the reaction is completed, the product is precipitated into anhydrous ethanol to obtain a polyimide powder based on the electroactive group phenothiazine;

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

[0070] An electrochromic material is prepared by a spin coating process. First, the polyimide powder obtained in step (4) is added as a solute into solvent trichloromethane, mixed uniformly under ultrasonic action for 10 min to obtain a mixed solution A. Subsequently, the mixed solution A is drop-coated onto 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. Subsequently, a uniform coating is obtained by solvent evaporation. Finally, the conductive glass with the electrochromic coating is placed in an oven and dried at 20°C for 16 h to obtain an electrochromic film.

[0071] Example 3:

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

[0073] The phenothiazine monomer a and p-fluorobenzaldehyde (molar ratio of reactant feedings is 1:4) are added as solutes into the solvent tetrahydrofuran, mixed uniformly, and reacted at 160°C for 10 h under the action of the basic catalyst potassium phosphate to obtain the functionalized phenothiazine derivative b;

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

[0075] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (molar ratio is 1:4) are added as solutes into the solvent N-methylpyrrolidone, mixed uniformly, and reacted at 150°C for 5 h under the action of hydrochloric acid to obtain the phenothiazine derivative c with a polymerizable amino functional group;

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

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

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

[0079] The polymerization intermediate system obtained in step (3) is first heated to 200°C, and then the basic catalyst pyridine and the dehydrating agent acetic anhydride (molar ratio of phenothiazine derivative c is 1:3) are added, and the reaction is continued for 2 h under stirring to remove water from the ring-opening polymerization intermediate structure. After the reaction is completed, the product is precipitated into anhydrous ethanol to obtain the electroactive group phenothiazine-based polyimide powder;

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

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

[0082] Example 4:

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

[0084] The phenothiazine monomer a and p-fluorobenzaldehyde (the molar ratio of reactant is 1:1) are added as solutes into solvent N,N-dimethylformamide, mixed uniformly, heated to 150°C under the action of basic catalyst potassium phosphate, and reacted for 25 h to obtain functionalized phenothiazine derivative b;

[0085] Step (2): Introduction of polymerizable functional group on phenothiazine structure

[0086] The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine (the molar ratio is 1:4) are added as solutes into solvent tetrahydrofuran, mixed uniformly, heated to 150°C under the action of nitric acid, and reacted for 5 h to obtain phenothiazine derivative c with a polymerizable functional group amino;

[0087] Step (3): Ring-opening polymerization participated by phenothiazine derivative

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

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

[0090] First, the polymerization intermediate system obtained in step (3) is 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 are added, and the reaction is continued for 2 h under stirring to remove water on the structure of the ring-opening polymerization intermediate. After the reaction is completed, it is settled in anhydrous ethanol to obtain a polyimide powder based on an electroactive group phenothiazine;

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

[0092] An electrochromic film is prepared by a spin coating process. First, the polyimide powder obtained in step (4) is added as a solute into solvent ethyl acetate, mixed uniformly under ultrasonic action for 60 min to obtain a mixed solution A. Then, the mixed solution A is drop-coated onto conductive glass (ITO glass) with an indium tin oxide layer. The spin coater is started, and under the action of centrifugal force, the solution spreads uniformly and forms a film. Then, a uniform coating is obtained by solvent evaporation. Finally, the conductive glass with the electrochromic coating is placed in an oven and dried at 80°C for 2 h to obtain an electrochromic film.

[0093] Example 5:

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

[0095] The phenothiazine monomer (and p-fluorobenzaldehyde (the molar ratio of reactant feedings is 1:5) is added as a solute into the solvent N-methyl pyrrolidone, mixed uniformly, and reacted at 150°C for 25 h under the action of the basic catalyst potassium phosphate to obtain the functionalized phenothiazine derivative b;

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

[0097] The functionalized phenothiazine derivative b obtained in step (1) is added as a solute into the solvent N,N-dimethylacetamide together with o-toluidine (the molar ratio is 1:4), mixed uniformly, and reacted at 150°C for 5 h under the action of phosphoric acid to obtain the phenothiazine derivative c with a polymerizable amino functional group;

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

[0099] The phenothiazine derivative c with a polymerizable amino functional group obtained in step (2) is first mixed with anhydride pyromellitic dianhydride (the molar ratio is 1:2) in the aprotic polar solvent N-methyl pyrrolidone, and reacted at 25°C for 24 h under a nitrogen atmosphere to obtain a polymerization intermediate after ring-opening of the anhydride structure;

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

[0101] The system of the polymerization intermediate obtained in step (3) is first heated to 120°C, and then the basic catalyst pyridine and the dehydrating agent acetic anhydride are added at a molar ratio of 1:4 to the phenothiazine derivative c, and the reaction is continued for 8 h under stirring to remove water from the structure of the ring-opening polymerization intermediate. After the reaction is completed, the product is precipitated into anhydrous ethanol to obtain a polyimide powder based on the electroactive group phenothiazine;

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

[0103] An electrochromic film is prepared by a spin coating process. First, the polyimide powder obtained in step (4) is added as a solute into the solvent tetrahydrofuran, mixed uniformly 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. Subsequently, a uniform coating is obtained by solvent evaporation. Finally, the conductive glass with the electrochromic coating is placed in an oven and dried at 80°C for 2 h to obtain an electrochromic film.

[0104] Example 6:

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

[0106] The phenothiazine monomer a and p-fluorobenzaldehyde (molar ratio of reactant feedings is 1:5) are added as solutes into the solvent tetrahydrofuran, mixed uniformly, and reacted at 150°C for 25 h under the action of the basic catalyst potassium phosphate to obtain the functionalized phenothiazine derivative b;

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

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

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

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

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

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

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

[0114] The electrochromic material is prepared by a spin coating process. First, the polyimide powder obtained in step (4) is added as a solute into the solvent methanol, mixed uniformly under ultrasonic action for 30 min to obtain a mixed solution A. Subsequently, the mixed solution A is drop-coated onto the conductive glass (ITO glass) with an indium tin oxide layer. The spin coater is started, and under the action of centrifugal force, the solution is uniformly spread and a thin film is formed. Subsequently, a uniform coating is obtained through solvent evaporation. Finally, the conductive glass with the electrochromic coating is placed in an oven and dried at 50°C for 12 h to obtain the electrochromic film.

[0115] The films of Examples 2-6 exhibit asymmetric stretching vibration peaks and symmetric stretching vibration peaks belonging to the carbonyl C=O on the imide ring structure at 1778 cm -1 and 1722 cm -1 ; and 1373 cm-1 a stretching vibration peak of C-N belonging to the imide ring was observed at 743 cm -1 a bending vibration peak of carbonyl, i.e. a deformation vibration peak of the imide ring, was observed at 1330 cm -1 a stretching vibration of carbonyl on the amide group and 1550 cm -1 a stretching vibration of C-N bond) were not detected in the infrared curve. The reaction was proved to be complete. At the same time, the color of the neutral state was close to the center position of the CIE coordinates, which confirmed its colorless state; the color after the oxidation of the electrified state was located in the orange-red region of the CIE coordinates.

Claims

1. A process for the preparation of a colorless-orange red reversible switching electrochromic material based on phenothiazine, characterized in that, The electrochromic polymer is obtained by reacting monomer compounds with electroactive groups, and the polymerization route of the electrochromic polymer is as follows: The synthesis route of the monomer compounds with electroactive groups is as follows:

2. A process for the preparation of a non-colorless-orange red reversible 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 uniformly and reacted under the action of a basic catalyst. The action of the basic catalyst causes the nucleophilic substitution reaction of p-halogen benzaldehyde at the 10-H position of phenothiazine, introduces the benzaldehyde structure, and obtains the functionalized phenothiazine derivative b; Step (2): introduction of polymerizable functional groups on the structure of phenothiazine The functionalized phenothiazine derivative b obtained in step (1) and o-toluidine are added as solutes into a solvent, mixed uniformly, and reacted in an acidic environment to obtain a phenothiazine derivative c with a polymerizable amino group, i.e., a monomer compound with electroactive groups; Step (3): ring-opening polymerization of phenothiazine derivatives The phenothiazine derivative c with a polymerizable amino group obtained in step (2) is mixed with an anhydride in an aprotic polar solvent to obtain a polymerization intermediate after the ring-opening of the anhydride structure; Step (4): dehydration of the polymerization intermediate First, the system of the polymerization intermediate obtained in step (3) is heated, then the reaction system in step (3) is continuously stirred and reacted, and a basic catalyst and a dehydrating agent are added to remove water in the structure of the polymerization intermediate. After the reaction is completed, the product is precipitated into anhydrous ethanol to obtain a phenothiazine-based polyimide powder based on electroactive groups, i.e., an electrochromic polymer; Step (5): preparation of an electrochromic material An 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, mixed uniformly under ultrasonic action 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 film is uniformly spread and formed under the action of centrifugal force by opening the film applicator, and then a uniform coating is obtained after solvent evaporation; finally, the conductive glass with the electrochromic coating is placed in an oven to dry the solvent, and an electrochromic material is obtained.

3. A process for the preparation of a non-colorless-orange red reversible electrochromic material based on phenothiazine according to claim 2, characterized in that, The molar ratio of the phenothiazine monomer a and p-fluorobenzaldehyde in step (1) is 1:1-5; the reaction temperature is 120-160°C; the reaction time is 10-30h; the basic 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. A process for the preparation of a non-colorless-orange red reversible electrochromic material based on phenothiazine according to claim 2, characterized in that, In step (2), the molar ratio of the functionalized phenothiazine derivative b and o-toluidine is 1:4-9; the reaction temperature is 70-150°C; the reaction time is 5-30h; the acidic environment is obtained by using one or a mixture of two or more of phosphoric acid, nitric acid, and hydrochloric acid; and 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 process for the preparation of a colorless-orange red reversible electrochromic material based on phenothiazine according to claim 2, characterized in that, The molar ratio of the phenothiazine derivative c with polymeric functional group amino in step (3) to acid anhydride is 1:1-2; the reaction temperature is-10℃-50℃; the reaction time is 5h-30h; the reaction is carried out in a protective atmosphere, which is nitrogen atmosphere or argon atmosphere; the aprotic polar solvent is one or more than two kinds of mixture of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide; the acid anhydride monomer is one or more than two kinds of mixture of pyromellitic dianhydride, hexafluorodiphthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic anhydride.

6. A process for the preparation of a non-colorless-orange red reversible electrochromic material based on phenothiazine according to claim 2, characterized in that, The reaction temperature in step (4) is 120℃-200℃; the reaction time is 2h-8h; the molar ratio of the phenothiazine derivative c with polymeric functional group amino to basic catalyst or dehydrating agent is 1:2-4.

7. A process for the preparation of a colorless-orange red reversible electrochromic material based on phenothiazine according to claim 2, characterized in that, The solvent in step (5) is one or more than two kinds of mixture of acetone, dichloromethane, chloroform, ethyl acetate, tetrahydrofuran, methanol; the ultrasonic time is 10min-60min; the temperature setting of the dried film is 20℃-80℃; the drying time is 2h-16h.

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