Pyrrolopyrrole Schiff base organic photochromic material and preparation method thereof

Abstract

The invention discloses a pyrrolopyrrole Schiff base organic photochromic material and a preparation method thereof, diketopyrrolopyrrole is used as a mother nucleus, and a triphenylamine structure and a Schiff base unit are introduced to construct a novel photochromic compound of pyrrolopyrrole Schiff base. Under the irradiation of ultraviolet light (365 nm), the material shows remarkable color change and spectral response in a solution and a polymethyl methacrylate (PMMA) film, and has excellent photochromic performance. The preparation method disclosed by the invention is simple in step, mild in condition and easy in structure modification and function regulation and control, and the obtained material is stable in structure before and after illumination, can quickly respond within 30 seconds, and shows a wide application prospect in the fields of optical information storage, molecular switches, intelligent sensing, flexible photoelectric devices and the like along with obvious signal changes of ultraviolet spectrum, fluorescence and the like.

Description

A pyrrolopyrrole Schiff base organic photochromic material and its preparation method Technical Field

[0001] This invention belongs to the field of organic small molecule photochromic materials, and relates to a pyrrolopyrrolo Schiff base photochromic material and its preparation method. Background Technology

[0002] Photochromism generally refers to the phenomenon where certain compounds undergo reversible structural transformations under specific wavelengths of light, accompanied by a significant color change. These reactions typically involve a photochemical transition between two states (A and B): light of one wavelength induces the transformation of A into B, while external energy input such as light of another wavelength or heat can restore the system to its initial state. The photoresponse behavior of photochromic materials is usually based on two different microscopic mechanisms: photophysical processes and photochemical reactions. Photophysical mechanisms primarily arise from the energy level transitions of electrons within the material after absorbing photons, directly causing changes in the absorption spectrum. These processes generally do not involve the breaking or formation of chemical bonds, have a relatively fast response speed, and are common in some inorganic compounds and organic conjugated systems. Photochemical mechanisms, on the other hand, often involve structural transformations or chemical reactions in the excited state. After a compound is photoexcited, electrons transition to the excited state, subsequently undergoing photochemical reactions such as bond isomerization, ring opening / closing, or proton transfer, ultimately leading to significant changes in spectral characteristics. These processes are usually accompanied by changes in molecular configuration or chemical structure. Due to their unique photoresponsive properties, these materials show significant application potential in fields such as optical information storage, molecular switches, optical devices, and smart sensors. Among numerous photochromic systems, azo compounds (N=N) are typical representatives due to their well-defined cis-trans isomerism photoconversion mechanism. Their trans isomers can be converted to the cis structure via n–π* transitions under ultraviolet light excitation; while the cis isomers can revert to the more stable trans configuration under blue light irradiation or thermal excitation. Azobenzene derivatives possess characteristics such as fast response speed and good fatigue resistance. By introducing them into the polymer backbone through chemical modification, functional materials that combine the photoactivity of azobenzene with the processing properties of polymer materials can be prepared.

[0003] Similarly, Schiff bases are a class of organic compounds containing characteristic carbon-nitrogen double bonds (C=N). Their structures are flexible and tunable. Due to the electronic properties of the C=N bond and its coordination ability as a cation ligand, these compounds typically exhibit high chemical reactivity and can be used as multifunctional ligands to construct functional materials, showing potential application value in fields such as luminescence, catalysis, magnetism, and electrochemistry. Notably, some Schiff bases and their metal complexes also exhibit photochromic behavior. Under photoexcitation, their C=N bonds or overall molecular configuration can undergo reversible changes, accompanied by significant color or spectral changes. However, existing photochromic materials suffer from drawbacks such as complex molecular design, numerous synthesis steps, slow photoresponse rates, and poor fatigue resistance. For example, while the cis-trans isomerization process of traditional azobenzene compounds is reversible, their poor thermal stability limits their application in information storage; and the photochromism of ordinary Schiff bases largely depends on proton transfer or configurational changes, resulting in poor environmental adaptability and low color contrast. Furthermore, the photochromic efficiency of most materials in the solid or aggregated state decreases significantly or even disappears completely due to the tight intermolecular packing and limited free volume. This severely hinders their application in practical scenarios such as thin-film devices, smart coatings, and wearable devices. Therefore, it is of great significance to develop a new material with a well-defined structure, simple synthesis, and the ability to achieve efficient, reversible, and high-contrast photochromism in both solution and thin-film states. Summary of the Invention

[0004] The purpose of this invention is to provide a pyrrolopyrrole Schiff base organic photochromic material with significant photochromic properties, the structural formula of which is shown below:

[0005] This material uses pyrrolopyrroledione as the parent core and introduces a triphenylamine structure and a Schiff base unit to construct a novel photochromic compound with a synergistic mechanism of photoinduced electron transfer and configuration change.

[0006] The preparation method includes the following steps: (1) After chopping sodium, put it into a reaction flask, add tert-amyl alcohol to the flask, and add an iron catalyst under the protection of nitrogen. The iron catalyst can be FeCl3, Fe2(SO4)3, FeCl2, or FeSO4. Heat to 90-110℃, and after the sodium is completely dissolved, add the raw material TPA-CN. The ratio of its amount to sodium is 1:2.4. Then add 0.5-1.5 times the amount of diisopropyl succinate. After the reaction is completed, cool down, add an alcohol solvent, precipitate the solid, filter, wash the solid with water and alcohol, and dry to obtain the intermediate compound DPP-TPA; (2) Add the intermediate DPP-TPA and 4-6 times the equivalent of 5-((trimethylsilyl)ethynyl)pyridine-2-amine to the reaction flask, and add a high-boiling solvent, including toluene, chlorobenzene, o-dichlorobenzene, dimethylformamide, xylene, or dimethyl sulfoxide. Under nitrogen protection, heat to 60-90℃, then add 5-7 equivalents of TiCl4 and 25-27 equivalents of ultra-dry triethylamine. Continue heating to 100-120℃, stop the reaction after 2-5 hours, cool to room temperature, add methanol to precipitate the solid, recrystallize and purify to obtain compound TPA-H.

[0007] Preferably, the iron catalyst in step (1) is one of FeCl3, Fe2(SO4)3, FeCl2, and FeSO4.

[0008] More preferably, the iron catalyst in step (1) is FeCl3.

[0009] Preferably, the alcohol solvent in step (1) can be one of methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, and n-hexanol.

[0010] More preferably, the alcohol in step (1) is methanol.

[0011] Preferably, the high-boiling-point solvent in step (2) includes one of toluene, chlorobenzene, o-dichlorobenzene, dimethylformamide, xylene, and dimethyl sulfoxide.

[0012] More preferably, the high-boiling-point solvent in step (2) is toluene.

[0013] The preparation process of pyrrolopyrrole Schiff base organic photochromic materials is as follows:

[0014] As can be seen from the above technical solution, compared with the prior art, the present invention provides a pyrrolopyrrole Schiff base organic photochromic material and its preparation method, which has the following beneficial effects: 1. By modifying the carbonyl part of pyrrolopyrrole dione and conducting a condensation reaction with an aromatic amine compound, a Schiff base-based photochromic material is constructed. This compound undergoes a change in molecular configuration and electron transfer after being irradiated with a UV lamp in chloroform, ultimately exhibiting obvious spectral and color changes.

[0015] 2. The obtained material exhibits excellent thermal stability, maintaining structural stability before and after light exposure, and responds rapidly within 30 seconds, accompanied by significant changes in ultraviolet spectral and fluorescence signals. This material demonstrates significant color changes and spectral responses in both solutions and polymethyl methacrylate (PMMA) films.

[0016] 3. The material's structure is easily derived, providing an ideal platform for subsequent functional expansion and device integration. It also exhibits excellent photochromic properties.

[0017] 4. The preparation method provided by this invention has simple steps and mild conditions. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 shows the time-of-flight mass spectrum of the TPA-H prepared in the example.

[0020] Figure 2 shows the 1H-NMR spectrum of TPA-H prepared in the example.

[0021] Figure 3 shows the single crystal structure of TPA-H prepared in the example.

[0022] Figure 4 shows the photochromic ultraviolet absorption spectrum of the TPA-H prepared in the example and photos before and after the color change. The ultraviolet light wavelength used for irradiation was 365 nm.

[0023] Figure 5 shows the photochromic fluorescence spectrum of the TPA-H prepared in the example and fluorescence photographs before and after irradiation.

[0024] Figure 6 shows the ultraviolet absorption spectrum of the TPA-H polymethyl methacrylate (PMMA) film prepared in the example after illumination, as well as photos before and after color change. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Embodiments

[0026] A pyrrolopyrroloschiff base organic photochromic material and its preparation method, comprising the following steps: 5-((trimethylsilyl)ethynyl)pyridine-2-amine is synthesized according to literature.

[0027] (1) 4-(diphenylamino)benzaldehyde (4 g, 14.63 mmol) and 60 mL of tetrahydrofuran were added to a round-bottom flask and stirred until dissolved. Iodine (7.6 g, 29.70 mmol) was then added, followed by 120 mL of ammonia. The flask was sealed and reacted at room temperature for 12 h. After the reaction was complete, sodium thiosulfate was added and stirred until the solution became clear. The tetrahydrofuran was removed, and the resulting solution was transferred to a separatory funnel and extracted with ethyl acetate and water. The organic layers were combined, dried over anhydrous sodium sulfate, and filtered. The crude product was purified by column chromatography to give a pale yellow solid, TPA-CN (3.61 g), in 91% yield.

[0028]

[0029] (2) Sodium (0.81 g, 0.035 mol) was cut into pea-sized particles and placed in a 150 mL round-bottom flask. 20 mL of tert-amyl alcohol was added to the flask, followed by anhydrous ferric chloride (catalytic amount) under nitrogen protection. The mixture was heated to 110 °C until the sodium was completely dissolved. Then, compound TPA-CN (3.98 g, 0.0147 mol) was added. Subsequently, diisopropyl succinate (1.49 g, 0.0074 mol) was added dropwise. The reaction was stopped after 7 hours. After the reaction solution cooled, a large amount of methanol was added to precipitate the solid. The solid was then obtained by vacuum filtration, and the filter cake was washed alternately with methanol and water until the filtrate was clear. The filter cake was collected and dried to obtain a brown solid, DPP-TPA (2.45 g), with a yield of 53%.

[0030] (3) DPP-TPA (200 mg, 0.32 mmol), 5-((trimethylsilyl)ethynyl)pyridine-2-amine (365 mg, 1.92 mmol), and 20 mL of anhydrous toluene were added to a 100 mL reaction flask. The mixture was heated to 60 °C under nitrogen protection, followed by the addition of TiCl4 (0.25 mL, 2.24 mmol) and ultradry NET3 (1.2 mL, 8.64 mmol), and then heated to 100 °C. After 2 h of reaction, the reaction was stopped, the reaction solution was cooled to room temperature, and methanol was added to precipitate the solid, yielding a crude solid. The crude product was purified by recrystallization from a mixture of methanol and dichloromethane, finally yielding a green solid TPA-H (105 mg), with a yield of 34%. The time-of-flight mass spectrum, proton NMR spectrum, and single crystal structure of TPA-H are shown in Figures 1-3. The NMR results are as follows: 1 H NMR (400 MHz, CDCl3): δ 13.01 (s, 2H), 8.43 (m, 4H), 7.62 (d,J= 8.4 Hz,2H), 7.34 (t, J = 8.0 Hz, 10H), 7.20 (d,J= 8.0 Hz, 10H), 7.15 (t,J= 7.2Hz, 8H), 0.25 (s, 18H). MALDI-TOF (%): Calcd. for [M+H] + C 62 H 55 N8Si2, m / z:967.4083; found, 967.2714.

[0031]

[0032] First, a 1 cm wide quartz cuvette was selected, and 2 mL of a 10⁻⁵ M chloroform solution of TPA-H was added. The UV-Vis absorption spectrum was then measured. Under 365 nm UV irradiation, the color of the TPA-H solution gradually changed from an initial light green to a deep purple. Accompanying this color change, the UV-Vis absorption spectrum underwent significant changes: the intensity of the characteristic absorption peak at 450 nm gradually decreased with increasing irradiation time, while a new absorption band appeared in the 500-580 nm range, as shown in Figure 4. This redshift of the absorption peak and the appearance of the new absorption band indicate that the molecule underwent conjugated structural rearrangement and intramolecular charge transfer under photoexcitation, confirming that the compound possesses excellent photochromic properties.

[0033] In fluorescence spectroscopy, the chloroform solution of TPA-H initially exhibited a shoulder peak at 700 nm, emitting red light. Upon irradiation with 365 nm ultraviolet light, a fluorescence emission peak appeared at 510 nm, while the intensity of the shoulder peak at 700 nm decreased significantly, demonstrating a clear photoinduced fluorescence response, as shown in Figure 5. This trend indicates that light-induced changes in molecular conformation and electron transfer processes caused the TPA-H molecule to transition from red fluorescence to yellow fluorescence.

[0034] Finally, we doped TPA-H molecules into polymethyl methacrylate (PMMA) films. Under UV irradiation, we observed obvious photochromic phenomena and spectral changes. Under 365 nm UV irradiation, the film color gradually changed from an initial light green to purple, with a uniform and obvious change. UV-Vis absorption spectroscopy showed that the photochromic behavior in the film state was similar to that in solution: initially, the film had a strong absorption peak at approximately 460 nm; with prolonged irradiation, the intensity of this absorption peak gradually decreased, while a new broad absorption band appeared in the 500 nm-580 nm range, with its intensity gradually increasing. Compared to solution, the color change rate in the film state was slightly slower, but the film could slowly recover to its original color after the irradiation was stopped, exhibiting good reversibility and film-forming adaptability.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A pyrrolopyrrole Schiff base material capable of achieving photochromism, characterized in that, Its structural formula is: 。 2. The pyrrolopyrrole Schiff base material for achieving photochromism according to claim 1, characterized in that, The synthetic route is shown below: 。 3. The method for preparing photochromic pyrrolopyrrole Schiff base materials according to claim 1, characterized in that, The steps include: (1) After chopping sodium, put it into a reaction flask, add tert-amyl alcohol to the flask, add iron catalyst under nitrogen protection, heat to 90-110℃, and after the sodium is completely dissolved, add raw material TPA-CN, the molar ratio of which to sodium is 1:2.4, and then add 0.5-1.5 times the molar amount of diisopropyl succinate. After the reaction is complete, cool down, add alcohol solvent, precipitate solid, filter, wash with water and alcohol, dry, and obtain intermediate compound DPP-TPA; (2) Add intermediate DPP-TPA and 4-6 times the molar amount of 5-((trimethylsilyl)ethynyl)pyridine-2-amine to a reaction flask, add high-boiling solvent, under nitrogen protection, heat to 60-90℃, then add 5-7 times the molar amount of TiCl4 and 25-27 times the equivalent of ultra-dry triethylamine, continue heating to 100-120℃, 2-5 After h, the reaction was stopped, cooled to room temperature, methanol was added to precipitate the solid, and recrystallized to purify the compound TPA-H.

4. The method for preparing pyrrolopyrrolo Schiff base material for photochromism according to claim 3, wherein the iron catalyst in step (1) is selected from one of FeCl3, Fe2(SO4)3, FeCl2, and FeSO4.

5. The method for preparing photochromic pyrrolopyrrole Schiff base material according to claim 3, wherein the alcohol solvent in step (1) is selected from one of methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, and n-hexanol.

6. The method for preparing photochromic pyrrolopyrrole Schiff base material according to claim 3, wherein the high-boiling solvent in step (2) is selected from toluene, chlorobenzene, o-dichlorobenzene, dimethylformamide, xylene, and dimethyl sulfoxide.

7. The application of the pyrrolopyrrole Schiff base material for achieving photochromism according to claim 1, characterized in that, After loading the material onto a photochromic film of polymethyl methacrylate, the photochromic film is irradiated with ultraviolet light, and the film can change from green to purple.

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