An alkyne-modified covalent organic framework, a stable radical covalent organic framework based on D-A structure and a preparation method and application thereof

Abstract

The application discloses an alkynyl-modified covalent organic framework, a stable radical covalent organic framework based on a D-A structure, and a preparation method and application thereof; the alkynyl-modified covalent organic framework comprises an alkynyl-functionalized main structure with a benzene ring as a center, provides a large condensed ring pi system to adjust electronic properties, and the main framework has high crystallinity and is rich in alkynyl; the strong intermolecular pi-pi stacking caused by the highly conjugated rigid planar skeleton of the main framework leads to high charge carrier mobility; and the alkynyl in the alkynyl-functionalized main chain can undergo an addition reaction to form a stable radical framework and a COF two-dimensional layered structure of a strong electron donor-acceptor structure, has a wide absorption spectrum, and is favorable to absorption of sunlight. After irradiation with simulated sunlight, the temperature can reach 76.8 DEG C, and the alkynyl-modified covalent organic framework has a good application prospect as a light-heat conversion material; the preparation method for post-synthetic modification of the alkynyl has high yield and can be used for large-scale preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic framework functional materials, and specifically relates to an alkyne-modified covalent organic framework, a stable free radical covalent organic framework based on a DA structure, and a preparation method and application thereof. Background Art

[0002] Two-dimensional layered covalent organic frameworks (2D COFs) materials have an electronic system with a high degree of π-orbital overlap and high charge carrier mobility, making them ideal for charge transport; they also have open porous channels parallel to the stacking direction. To further reduce the band gap, the currently widely used method is donor-acceptor copolymerization, that is, the alternating introduction of electron-rich units and electron-deficient units into the polymer backbone. Donor-acceptor COFs are donor (D) and acceptor (A) chain segments connected by covalent bonds and finely arranged to form a highly ordered network structure. Covalently bonded donor-acceptor pairs with tunable band gaps and optoelectronic properties give COFs materials potential applications in optoelectronics, fluorescent bioimaging, and sensors. The unique structural features of DA-type COFs enable the formation of individual DA stacks, providing a way for efficient charge separation and having broad prospects for photothermal applications. Summary of the Invention

[0003] In order to overcome the shortcomings of the prior art, the first object of the present invention is to provide an alkynyl-modified covalent organic framework, which comprises an alkynyl-functionalized ligand unit centered on a benzene ring, provides a large fused ring π system to regulate electronic properties, and the main framework has high crystallinity and is rich in alkynyl groups, so the charge carrier mobility is high.

[0004] The second object of the present invention is to provide a method for preparing the above-mentioned alkynyl-modified covalent organic framework.

[0005] The third object of the present invention is to provide a stable free radical covalent organic framework based on DA structure.

[0006] The fourth object of the present invention is to provide a method for preparing a stable free radical covalent organic framework based on a DA structure.

[0007] The fifth purpose of the present invention is to provide applications of an alkyne-modified covalent organic framework and a stable free radical covalent organic framework based on a DA structure.

[0008] The first object of the present invention can be achieved by adopting the following technical solutions:

[0009] An alkyne-modified covalent organic framework having a structural unit shown in Formula I:

[0010]

[0011] The second object of the present invention can be achieved by adopting the following technical solutions:

[0012] A method for preparing an alkyne-modified covalent organic framework comprises the following steps:

[0013] The organic ligand of the structure represented by formula II and trialdehyde phloroglucinol are uniformly dispersed in a mixed solvent of mesitylene and 1,4-dioxane, aniline and acetic acid are added, and then reacted in a closed environment. After the reaction is completed, solid-liquid separation is performed, and the obtained solid is washed and dried to obtain the alkynyl-modified covalent organic framework;

[0014]

[0015] Furthermore, the molar ratio of the organic ligand of the structure shown in Formula II to trialdehyde phloroglucinol is 1:(0.8-1.2).

[0016] Furthermore, the concentration of the added acetic acid is 5-7 mol / L, and the amount of the added acetic acid is 5%-15% of the volume of the mixed solvent.

[0017] Furthermore, the amount of aniline added is 0.5-1.5% of the volume of the mixed solvent.

[0018] Furthermore, the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:(0.5-1.5).

[0019] Furthermore, the ratio of the added amount of the organic ligand of the structure represented by Formula II to the mixed solvent is 1 mmol: (10-40 mL).

[0020] Furthermore, the reaction conditions are 100-140° C. for 24-96 hours.

[0021] The third object of the present invention can be achieved by adopting the following technical solutions:

[0022] A stable free radical covalent organic framework based on a DA structure having a structural unit shown in Formula III:

[0023]

[0024] The fourth object of the present invention can be achieved by adopting the following technical solutions:

[0025] A method for preparing a stable free radical covalent organic framework based on a DA structure comprises the following steps:

[0026] The alkynyl-modified covalent organic framework is heated and reacted with 7,7,8,8-tetracyanoquinodimethane under vacuum, and the stable free radical covalent organic framework based on the DA structure is obtained after the reaction is completed.

[0027] Furthermore, the heating reaction condition is 150-200° C.; and the reaction time is 6-72 h.

[0028] Furthermore, the mass ratio of the alkynyl-modified covalent organic framework of claim 1 to 7,7,8,8-tetracyanobenzoquinodimethane is 1:(0.73-1.1).

[0029] The fifth object of the present invention can be achieved by adopting the following technical solutions:

[0030] Application of the above-mentioned alkyne-modified covalent organic framework or the above-mentioned stable free radical covalent organic framework based on DA structure as a photothermal conversion material.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention provides an alkynyl-modified covalent organic framework, comprising an alkynyl-functionalized main structure centered on a benzene ring, which provides a large fused-ring π system for regulating electronic properties. The main framework is highly crystalline and rich in alkynyl groups. Its highly conjugated rigid planar skeleton leads to strong intermolecular π-π stacking, resulting in high charge carrier mobility and certain photothermal conversion performance. In addition, the alkynyl groups in the alkynyl-functionalized main chain can undergo addition reactions, providing sites for post-functionalization modification.

[0033] 2. The present invention discloses a method for preparing an alkynyl-modified covalent organic framework. Through an amino-aldehyde condensation reaction, an alkynyl-functionalized organic ligand centered on a benzene ring and trialdehyde phloroglucinol are sequentially linked to form a hexagonal ring-like covalent organic framework unit, generating an ordered two-dimensional honeycomb network with high crystallinity. The preparation process is a solvothermal reaction, which is mild and easy to initiate, without requiring harsh reaction conditions, and thus can be prepared on a large scale.

[0034] 3. The stable radical covalent organic framework based on the DA structure of the present invention, on the basis of the alkyne-modified covalent organic framework, undergoes a [2+2]CA-RE reaction between 7,7,8,8-tetracyanoquinodimethane and alkyne to achieve post-synthetic modification, forming a stable radical framework and a two-dimensional layered structure, optimizing light capture and charge separation properties; the strong π-π stacking between molecules enhances the stability of the free radicals, so the stable radical covalent organic framework of the DA structure has a wide absorption spectrum, high conductivity and is rich in free radicals, which is conducive to the absorption of sunlight.

[0035] 4. The present invention's method for preparing a stable free radical covalent organic framework based on a DA structure involves post-synthetic modification of the alkynyl groups on the basis of an alkynyl-modified covalent organic framework. The alkynyl-modified covalent organic framework has a macrocyclic structure, forming material pores that are more conducive to the entry of 7,7,8,8-tetracyanoquinodimethane into the pores and reaction with the alkynyl groups. This post-synthetic modification process provides high yield and is suitable for large-scale production.

[0036] 5. The alkyne-modified covalent organic framework or the stable free radical covalent organic framework based on the DA structure of the present invention has a wide absorption spectrum, high conductivity and is rich in free radicals, which is conducive to the absorption of sunlight and photothermal conversion. Therefore, it can be used as a photothermal conversion material. After simulated sunlight irradiation, the temperature can reach 76.8°C, which has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of Ph-3Ph-3NH2 prepared in Example 1;

[0038] Figure 2 This is the carbon NMR spectrum of Ph-3Ph-3NH2 prepared in Example 1;

[0039] Figure 3 The X-ray powder diffraction patterns of Ph-3Ph-3NH2 prepared in Example 1 and TF-4 COF prepared in Example 2;

[0040] Figure 4 The X-ray powder diffraction patterns of TF-4 COF prepared in Example 2 and TF-4 COF-TCNQ prepared in Example 5;

[0041] Figure 5 Fourier transform-infrared spectra of Ph-3Ph-3NH2 prepared in Example 1 and TF-4 COF prepared in Example 2;

[0042] Figure 6 Fourier transform-infrared spectra of TF-4 COF prepared in Example 2 and TF-4 COF-TCNQ prepared in Example 5;

[0043] Figure 7 UV-Vis-NIR absorption spectra of TF-4 COF prepared in Example 2 and TF-4 COF-TCNQ prepared in Example 5 at room temperature;

[0044] Figure 8 The solid EPR test results of TF-4 COF prepared in Example 2 and TF-4 COF-TCNQ prepared in Example 5 are shown;

[0045] Figure 9 Graph showing temperature changes over time of TF-4 COF prepared in Example 2 and TF-4 COF-TCNQ prepared in Example 5 under simulated sunlight irradiation. DETAILED DESCRIPTION

[0046] The technical solutions of the present invention will be described clearly and completely below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0047] Covalent organic frameworks (COFs) possess an electron system with high π-orbital overlap and high charge carrier mobility, but their poor intrinsic conductivity and solution processability still pose significant challenges for their application in flexible electronics. Current approaches to improving the conductivity of COFs are generally through doping with guest molecules (such as iodine and LiClO4) and designing semiconducting groups in the ligands (such as tetrathiafulvan and porphyrin). Due to the inherent hydrophobicity and limited light absorption of COFs, their application as photothermal conversion materials for solar water evaporation is still in its infancy.

[0048] Therefore, the present invention provides an alkyne-modified covalent organic framework and a stable free radical covalent organic framework based on a DA structure to optimize light capture and charge separation properties. Its wide absorption spectrum of 200-1300nm is conducive to the absorption of sunlight, which gives it photothermal conversion capability.

[0049] An alkyne-modified covalent organic framework having a structural unit shown in Formula I:

[0050]

[0051] The alkynyl-modified covalent organic framework (COF) with the structural unit represented by Formula I comprises a macrocyclic structure formed by an alkynyl-functionalized organic ligand centered on 1,3,5-triphenylbenzene and a trialdehyde-phloroglucinol ligand, forming an ordered two-dimensional honeycomb network. The macrocyclic structure provides a large fused-ring π system to modulate electronic properties. The COF is highly crystalline and rich in alkynyl groups. Its highly conjugated, rigid planar backbone results in strong intermolecular π-π stacking, resulting in high charge carrier mobility and promising photothermal conversion performance. Furthermore, the alkynyl groups in the alkynyl-functionalized backbone are capable of undergoing addition reactions, providing sites for post-functionalization modifications.

[0052] A method for preparing an alkyne-modified covalent organic framework comprises the following steps:

[0053] The organic ligand of the structure represented by formula II and trialdehyde phloroglucinol are uniformly dispersed in a mixed solvent of mesitylene and 1,4-dioxane, aniline and acetic acid are added, and then reacted in a closed environment. After the reaction is completed, solid-liquid separation is performed, and the obtained solid is washed and dried to obtain the alkynyl-modified covalent organic framework;

[0054]

[0055] Alkynyl-modified covalent organic frameworks (COFs) form covalent bonds through an ammaldehyde condensation reaction between amino groups on the ligands and aldehyde groups. Alkynyl-functionalized organic ligands centered around 1,3,5-triphenylbenzene and trialdehyde phloroglucinol are sequentially linked to form hexagonal ring-like COF units, resulting in an ordered, two-dimensional honeycomb network with high crystallinity. The ammaldehyde condensation reaction can proceed even under solvothermal conditions, making the synthesis of alkynyl-modified COFs mild and easy, requiring no harsh reaction conditions and thus amenable to large-scale production.

[0056] As one embodiment, the molar ratio of the organic ligand of the structure shown in Formula II to trialdehyde phloroglucinol is 1:(0.8-1.2).

[0057] As one embodiment, the concentration of the added acetic acid is 5-7 mol / L, and the amount of the added acetic acid is 5%-15% of the volume of the mixed solvent.

[0058] As one embodiment, the amount of aniline added is 0.5-1.5% of the volume of the mixed solvent.

[0059] As one embodiment, the volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:(0.5-1.5).

[0060] As one embodiment, the ratio of the organic ligand having the structure shown in Formula II to the mixed solvent is 1 mmol: (10-40 mL).

[0061] As one embodiment, the reaction conditions are 100-140° C. for 24-96 hours.

[0062] As one embodiment, the reaction is carried out in a glass tube. After the materials are added into the glass tube, the glass tube is sealed with an oxyhydrogen flame and then heated.

[0063] In one embodiment, after solid-liquid separation, the solid is purified. In this embodiment, purification includes washing and / or Soxhlet extraction. The solvent used for washing is DMF and / or ethyl acetate; the solvent used for Soxhlet extraction is tetrahydrofuran.

[0064] As one of the embodiments, after the solid-liquid separation, the solid is washed with DMF (5 mL x 5) and ethyl acetate (5 mL x 5), and then Soxhlet extraction in THF solution for 1-5 days, and after vacuum drying, the acetylenyl-modified covalent organic framework is obtained.

[0065] As one of the embodiments, the organic ligand with the structure shown in formula II is prepared by the following preparation process:

[0066]

[0067] wherein X is Br or I.

[0068] In the present embodiment, the molar ratio of 1,3,5-tri(4-X phenyl) benzene to 4-ethynyl aniline is 1: (3.5-4.5).

[0069] In the present embodiment, the reaction is carried out under a Cu + / Pd +2 catalytic system, and the catalyst includes cuprous iodide, dichlorobis(triphenylphosphine)palladium, and triphenylphosphine ligand; the molar ratio of cuprous iodide, dichlorobis(triphenylphosphine)palladium, and triphenylphosphine ligand is (1.5-2.5):1:(2-3); and the molar ratio of 1,3,5-tri(4-X phenyl) benzene to dichlorobis(triphenylphosphine)palladium is (10-50):1.

[0070] In the present embodiment, the solvent is tetrahydrofuran; and the amount of the solvent is such that the molar concentration of 1,3,5-tri(4-X phenyl) benzene is 0.04-0.15 mmol / mL.

[0071] In the present embodiment, the reaction occurs in the presence of a base; the base is an inorganic base or an organic base, and potassium carbonate is preferred; and the amount of the base added is 1-8 times the molar amount of 1,3,5-tri(4-X phenyl) benzene.

[0072] In the present embodiment, the reaction is carried out in anhydrous and anaerobic conditions, including the use of anhydrous solvent and the use of inert gas to displace oxygen in the reaction system, and nitrogen is preferred as the inert gas.

[0073] In the present embodiment, the reaction is carried out at 50-66°C for 6-72 h.

[0074] In the present embodiment, the product after the reaction is purified by silica gel chromatography. The eluent is petroleum ether / ethyl acetate prepared according to a volume ratio of 1:2.

[0075] A stable radical covalent organic framework based on D-A structure has a structural unit shown in formula III:

[0076]

[0077] Based on a stable radical covalent organic framework (MOF) with a DA structure, 7,7,8,8-tetracyanoquinodimethane undergoes a [2+2]CA-RE reaction with alkynyl groups on the basis of an alkyne-modified covalent organic framework, achieving post-synthetic modification. This results in a stable radical framework and a two-dimensional layered structure, optimizing light harvesting and charge separation properties. The alkyne-functionalized organic ligands in the alkyne-modified covalent organic framework, centered around 1,3,5-triphenylbenzene, form a macrocyclic structure, which gives the MOF material larger pores, facilitating the entry of 7,7,8,8-tetracyanoquinodimethane into the pores and reacting with the alkyne groups to form a photothermal COF rich in stable radicals. Furthermore, the strong π-π stacking between MOF molecules enhances the stability of the radicals. As a result, the stable radical covalent organic framework with a DA structure exhibits a broad absorption spectrum, high conductivity, and is rich in free radicals, which is beneficial for the absorption of sunlight.

[0078] As one embodiment, the stable radical covalent organic framework based on the DA structure has a broad absorption spectrum of 220-1300 nm.

[0079] A method for preparing a stable free radical covalent organic framework based on a DA structure comprises the following steps:

[0080] The alkynyl-modified covalent organic framework is heated and reacted with 7,7,8,8-tetracyanoquinodimethane under vacuum, and the stable free radical covalent organic framework based on the DA structure is obtained after the reaction is completed.

[0081] The alkynyl-modified covalent organic framework contains abundant alkynyl groups, which can undergo a [2+2]CA-RE reaction to modify the organic framework. Therefore, in the present invention, 7,7,8,8-tetracyanoquinodimethane is used to react with alkynyl groups to undergo a [2+2]CA-RE reaction to achieve post-synthetic modification, forming a stable free radical framework and a two-dimensional layered structure, thereby optimizing light capture and charge separation properties. The alkynyl-modified covalent organic framework contains pores. In order to allow 7,7,8,8-tetracyanoquinodimethane to enter the pores and react with the alkynyl groups, 7,7,8,8-tetracyanoquinodimethane is sublimated into a gas, and the gas molecules diffuse. The adsorption of the gas by the alkynyl-modified covalent organic framework pores allows 7,7,8,8-tetracyanoquinodimethane gas molecules to enter the pores and adsorb on the surface, thereby generating an addition reaction under thermal conditions. Based on the alkyne-modified covalent organic framework, the alkyne is post-synthetically modified. This post-synthetic modification process has high yield and can be prepared on a large scale.

[0082] In one embodiment, the heating reaction is carried out at 150-200° C. and the reaction time is 6-72 hours. In this embodiment, the vacuum condition is a vacuum degree of 0.1 MPa.

[0083] As one embodiment thereof, the mass ratio of the alkyne-modified covalent organic framework of claim 1 to 7,7,8,8-tetracyanobenzoquinodimethane is 1:(0.73-1.1).

[0084] As one embodiment, after the reaction is completed, post-processing is performed, and the post-processing process includes purifying the reaction product using an organic reagent, and then vacuum drying it after purification.

[0085] In this embodiment, the purification process is to first wash the reaction product with an organic reagent, and the washing method includes dissolution, solid-liquid separation, Soxhlet extraction, etc. Preferably, the washing is to first dissolve the reaction product in an organic solvent, and after solid-liquid separation, the solid matter is processed by Soxhlet extraction.

[0086] In one embodiment, the organic reagent is one or more of acetonitrile, ethyl acetate or tetrahydrofuran.

[0087] As one embodiment, the product obtained by the reaction is washed with acetonitrile, subjected to Soxhlet extraction with tetrahydrofuran for 1-5 days, and vacuum dried to obtain a stable free radical covalent organic framework based on the DA structure.

[0088] The above-mentioned alkyne-modified covalent organic framework or the above-mentioned stable free radical covalent organic framework based on DA structure is used as a light-to-heat conversion material.

[0089] The following is a further description with reference to specific embodiments.

[0090] Example 1

[0091] The raw materials, 1,3,5-tris(4-bromophenyl)benzene (0.737 mmol), 4-ethynylaniline (3.095 mmol), cuprous iodide (0.058 mmol), bis(triphenylphosphine)palladium dichloride (0.030 mmol), triphenylphosphine (0.074 mmol), and potassium carbonate (4.422 mmol), were weighed into a 25 mL two-necked round-bottom flask. The mixture was then evacuated and purged with nitrogen five times. Under nitrogen, 12 mL of ultra-dry tetrahydrofuran (THF) was added, followed by stirring at 65°C for 24 hours. After the reaction, the mixture was allowed to cool to room temperature, and the solvent was removed by rotary evaporation. The mixture was purified by silica gel chromatography using petroleum ether / ethyl acetate (1:2, v / v) as the eluent to obtain the organic ligand represented by Formula II, designated Ph-3Ph-3NH2, in an 82% yield.

[0092] The ligand Ph-3Ph-3NH2was tested by nuclear magnetic resonance hydrogen spectrum and carbon spectrum, and the test results are shown in Figure 1 and Figure 2 . 1 HNMR (400 MHz, DMSO-d6) δ 7.97 - 7.87 (m, 9H), 7.58 (d, J = 8.2 Hz, 6H), 7.26 (d, J = 8.3 Hz, 6H), 6.60 (d, J = 8.4 Hz, 6H), 5.60 (s, 6H).

[0093] 13 C NMR (101 MHz, DMSO-d6) δ 150.05, 141.33, 139.41, 133.14, 131.83, 127.81, 124.73, 123.38, 114.18, 108.64, 92.87, 87.05.

[0094] Example 2

[0095] Take 28 mg of Ph-3Ph-3NH2and 9 mg of tri-aldehyde m-phloroglucinol in a glass tube (8 x 150 mm), add 0.5 mL of mesitylene, 0.5 mL of 1,4-dioxane, 10 μL of aniline and 0.1 mL of 6M aqueous acetic acid, then ultrasonic the mixture for 10 min; seal the glass tube with hydrogen flame and heat in a 120°C oven for 72 h, then naturally cool to room temperature; collect the powder by filtration, wash the powder sample with DMF (5 mL x 5) and ethyl acetate (5 mL x 5), then Soxhlet extract in THF solution for 3 days and dry in vacuum to obtain the alkynyl-modified covalent organic framework, recorded as TF-4 COF.

[0096] Example 3

[0097] Take 28 mg of Ph-3Ph-3NH2and 7.2 mg of tri-aldehyde m-phloroglucinol in a glass tube (8 x 150 mm), add 0.29 mL of mesitylene, 0.14 mL of 1,4-dioxane, 2.2 μL of aniline and 21.5 μL of 7M aqueous acetic acid, then ultrasonic the mixture for 10 min; seal the glass tube with hydrogen flame and heat in a 100°C oven for 96 h, then naturally cool to room temperature; collect the powder by filtration, wash the powder sample with DMF (5 mL x 5) and ethyl acetate (5 mL x 5), then Soxhlet extract in THF solution for 3 days and dry in vacuum to obtain the alkynyl-modified covalent organic framework, recorded as TF-4 COF.

[0098] Example 4

[0099] 28 mg of Ph-3Ph-3NH2 and 10.8 mg of trialdehyde phloroglucinol were weighed into a glass tube (8×150 mm), and 0.69 mL of trimethylbenzene, 1.03 mL of 1,4-dioxane, 25.8 μL of aniline and 258 μL of 5 M acetic acid aqueous solution were added. The mixture was then sonicated for 10 min; the glass tube was sealed with an oxyhydrogen flame and heated in an oven at 140°C for 24 h, and then naturally cooled to room temperature; the powder was collected by filtration, and the powder sample was washed with DMF (5 mL×5) and ethyl acetate (5 mL×5), then Soxhlet extracted in THF solution for 3 days and dried in vacuum to obtain an alkynyl-modified covalent organic framework, designated as TF-4 COF.

[0100] Example 5

[0101] 15 mg of TF-4 COF and 18 mg of 7,7,8,8-tetracyanoquinodimethane were weighed and placed in a glass tube (8×150 mm) to ensure full contact between the two. After the air was evacuated from the glass tube, the tube was kept in a vacuum state and sealed with an oxyhydrogen flame. The tube was then placed in a tube furnace preheated to 180°C to promote the sublimation of 7,7,8,8-tetracyanoquinodimethane. After 24 hours, the tube was removed from the oven and cooled to room temperature. The resulting powder was washed with MeCN, Soxhlet extracted with THF for 3 days, and dried in vacuum at 100°C for 5 hours to obtain a stable free radical covalent organic framework based on a DA structure, designated TF-4 COF-TCNQ.

[0102] Example 6

[0103] 15 mg of TF-4 COF and 10.95 mg of 7,7,8,8-tetracyanoquinodimethane were weighed and placed in a glass tube (8×150 mm) to ensure full contact between the two. After the air was evacuated from the glass tube, the tube was kept in a vacuum state and sealed with an oxyhydrogen flame. The tube was then placed in a tube furnace preheated to 150°C to promote the sublimation of 7,7,8,8-tetracyanoquinodimethane. After 72 hours, the tube was removed from the oven and cooled to room temperature. The resulting powder was washed with MeCN, Soxhlet extracted with THF for 3 days, and dried in vacuum at 100°C for 5 hours to obtain a stable free radical covalent organic framework based on the DA structure, which was designated TF-4 COF-TCNQ.

[0104] Example 7

[0105] Take 15 mg of TF-4 COF and 16.5 mg of 7,7,8,8-tetracyanoquinodimethane, place them in a glass tube (8x150 mm), and make them fully contact; after the air in the glass tube is extracted, the tube is kept in a vacuum state, and the glass tube is sealed with a hydrogen oxygen flame; then it is placed in a tube furnace preheated to 200°C to promote the sublimation of 7,7,8,8-tetracyanoquinodimethane; after 6 h, the tube is taken out of the oven to cool to room temperature; the obtained powder is washed with MeCN, Soxhlet extracted with THF for 3 days, and vacuum dried at 100°C for 5 h to obtain a stable free radical covalent organic framework based on D-A structure, denoted as TF-4 COF-TCNQ.

[0106] Test Example:

[0107] (1) The TF-4 COF prepared in Example 2 and the TF-4 COF-TCNQ prepared in Example 5 were subjected to X-ray powder diffraction test, and the X-ray powder diffraction is shown in Figure 3 and Figure 4 .

[0108] Figure 3 The X-ray powder diffraction pattern of the TF-4 COF prepared in Example 2 and the X-ray powder diffraction pattern of the simulated AA stacking structure, where a is the TF-4 COF prepared in Example 2, and b is the simulated AA stacking structure;

[0109] Figure 4 The X-ray powder diffraction pattern of the TF-4 COF prepared in Example 2 and the TF-4 COF-TCNQ prepared in Example 5, where a is the TF-4 COF prepared in Example 2, and b is the TF-4 COF-TCNQ prepared in Example 5.

[0110] From the results of the X-ray powder diffraction test of Figure 3 , it can be seen that the diffraction spectrum of the synthesized TF-4 COF is highly consistent with the X-ray powder diffraction of the simulated AA stacking structure in peak position, indicating that the synthesized TF-4 COF is an AA-stacked two-dimensional layered structure, and from the diffraction spectrum, it can also be seen that the diffraction peak of the TF-4 COF is very strong and sharp, indicating that the synthesized covalent organic framework TF-4 COF has a high degree of crystallinity. From Figure 4 , it can be seen that the TF-4 COF-TCNQ obtained by post-functionalization modification still maintains good crystallinity, and the diffraction peak position is highly consistent with that of the TF-4 COF, indicating that during the post-functionalization modification process, the COFs material maintains good crystallinity.

[0111] (2) The Ph-3Ph-3NH2 ligand prepared in Example 1, the TF-4 COF prepared in Example 2, and the TF-4 COF-TCNQ prepared in Example 5 were subjected to Fourier transform infrared spectroscopy. The infrared spectra are shown in FIG. Figure 5 and Figure 6 shown.

[0112] from Figure 5 It can be seen that in the Fourier transform infrared spectrum of TF-4 COF, the original amino monomer Ph-3Ph-3NH2 has a wavelength of about 3300-3400 cm -1 The NH stretching vibration absorption peak at 2200 cm -1 The C≡C stretching vibration at 1617cm -1 、1566cm -1 and 1294cm -1 The C=O stretching vibration, C=C stretching vibration and CN vibration peaks observed at α-α-ketoenamine bonded structures were formed, indicating that the monomers successfully underwent an aminaldehyde condensation reaction to form TF-4 COF.

[0113] Figure 6 The TF-4 COF-TCNQ powder obtained by treatment with 7,7,8,8-tetracyanoquinodimethane showed a peak at 2214 cm -1 The C≡N stretching vibration peak appears at the center, while the C≡C stretching vibration peak disappears, indicating that the alkynyl functional group successfully reacts with the 7,7,8,8-tetracyanobenzoquinodimethane molecule to achieve post-synthetic modification.

[0114] (3) The TF-4 COF prepared in Example 2 and the TF-4 COF-TCNQ prepared in Example 5 were subjected to UV-Vis-NIR absorption spectrum test. The results are as follows: Figure 7 shown.

[0115] from Figure 7 As can be seen in the figure, the UV-Vis-NIR absorption spectra of the post-synthesized TF-4COF-TCNQ powder measured at room temperature show significant differences compared to the original TF-4 COF. The TF-4 COF-TCNQ powder exhibits a broad absorption spectrum from 220 to 1300 nm, covering the visible and near-infrared ranges, which is beneficial for sunlight absorption. The introduction of a donor-acceptor (DA) structure into the TF-4 COF-TCNQ framework results in strong intramolecular charge transfer and a low band gap, significantly enhancing non-radiative decay. Therefore, the TF-4 COF-TCNQ powder has great potential for applications in solar-thermal and thermoelectric conversion.

[0116] (4) The TF-4 COF prepared in Example 2 and the TF-4 COF-TCNQ prepared in Example 5 were subjected to electron paramagnetic resonance (EPR) activity test. The results are as follows: Figure 8 shown.

[0117] The TF-4 COF prepared in Example 21 and the TF-4COF-TCNQ solid prepared in Example 5 were tested for electron paramagnetic resonance (EPR) activity. Each sample was 2.0 mg. Figure 8 The TF-4 COF-TCNQ solid shown in Figure 4 exhibits obvious EPR signals, while the TF-4 COF solid shows negligible EPR signals, indicating that TF-4 COF-TCNQ is rich in stable free radicals.

[0118] Test example:

[0119] The xenon lamp simulated sunlight (420-2500 nm) with a light intensity of 0.1 W cm -2 50 mg of TF-4 COF prepared in Example 2 and TF-4 COF-TCNQ prepared in Example 5 were irradiated at room temperature for 5 minutes, and then the light was removed. The changes of TF-4 COF and TF-4 COF-TCNQ with the irradiation time and temperature are shown in Figure 2. Figure 9 shown.

[0120] from Figure 9 As can be seen from the figure, the BTT-COF-T powder exhibits efficient photothermal conversion. After 5 minutes of light irradiation, the maximum temperature of TF-4COF-TCNQ reached 76.8°C, while the temperature of the original TF-4 COF under the same conditions was 50°C. After 5 minutes, the light was removed, and the surface temperature of the powder dropped rapidly. This shows that the TF-4 COF prepared in Example 2 and the TF-4 COF-TCNQ prepared in Example 5 have photothermal conversion performance, and the TF-4 COF-TCNQ obtained after post-synthesis modification exhibits even superior photothermal conversion performance.

[0121] In summary, the alkynyl-modified covalent organic framework and the stable free radical covalent organic framework based on the DA structure of the present invention, wherein the alkynyl groups in the alkynyl-modified covalent organic framework are post-synthetically modified to form a covalent organic framework material rich in stable free radicals, exhibit a broad absorption spectrum from 220 to 1300 nm and can reach a temperature of 76.8°C under simulated sunlight irradiation, showing excellent photothermal conversion performance and promising application prospects as photothermal conversion materials. This method utilizes a green and efficient post-synthetic modification method, resulting in high yield and scalable production.

[0122] The above embodiments are only the preferred embodiments of the present application, and cannot be used to limit the protection scope of the present application, and any non-essential changes and replacements made by those skilled in the art on the basis of the present application shall fall within the protection scope of the present application.

Claims

1. A stable free radical covalent organic framework based on DA structure, characterized in that: Having the structural unit shown in formula III:

2. The method for preparing a stable free radical covalent organic framework based on a DA structure according to claim 1, characterized in that: The following steps are involved: The alkynyl-modified covalent organic framework is heated to react with 7,7,8,8-tetracyanoquinodimethane under vacuum, and the stable free radical covalent organic framework based on the DA structure is obtained after the reaction is completed; The alkyne-modified covalent organic framework has a structural unit shown in Formula I: 。 3. The method for preparing a stable free radical covalent organic framework based on a DA structure according to claim 2, characterized in that: The heating reaction conditions are 150-200° C. and the reaction time is 6-72 h.

4. The method for preparing a stable free radical covalent organic framework based on a DA structure according to claim 2, characterized in that: The mass ratio of the alkynyl-modified covalent organic framework to 7,7,8,8-tetracyanobenzoquinodimethane is 1:(0.73-1.1).

5. The method for preparing a stable free radical covalent organic framework based on DA structure according to claim 2, characterized in that: The preparation method of the alkyne-modified covalent organic framework comprises the following steps: The organic ligand of the structure represented by formula II and trialdehyde phloroglucinol are uniformly dispersed in a mixed solvent of mesitylene and 1,4-dioxane, aniline and acetic acid are added, and then reacted in a closed environment. After the reaction is completed, solid-liquid separation is performed, and the obtained solid is washed and dried to obtain the alkynyl-modified covalent organic framework; 6. The method for preparing a stable free radical covalent organic framework based on a DA structure according to claim 5, characterized in that: The molar ratio of the organic ligand of the structure shown in formula II to trialdehyde phloroglucinol is 1:(0.8-1.2); the concentration of the added acetic acid is 5-7 mol / L, and the amount of the added acetic acid is 5%-15% of the volume of the mixed solvent; and the amount of the added aniline is 0.5-1.5% of the volume of the mixed solvent.

7. The method for preparing a stable free radical covalent organic framework based on DA structure according to claim 5, characterized in that: The volume ratio of mesitylene to 1,4-dioxane in the mixed solvent is 1:(0.5-1.5); the ratio of the added amount of the organic ligand with the structure shown in Formula II to the mixed solvent is 1 mmol:(10-40 mL).

8. The method for preparing a stable free radical covalent organic framework based on a DA structure according to claim 5, characterized in that: The reaction conditions are 100-140°C for 24-96 hours.

9. Use of the stable free radical covalent organic framework based on DA structure as claimed in claim 1 as a photothermal conversion material.

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