Preparation method of thienyl metal organic framework material and application thereof

Abstract

The application discloses a preparation method and application of a thienyl metal organic framework material, and synthesizes a 1,2,4,5-tetra(5-bromothiophene) benzene intermediate through a Stiller reaction and an NBS bromination reaction, and obtains a long-size 1,2,4,5-tetra(2-(5-(4-carboxyl phenyl))thiophene) benzene with a large conjugate system by reacting the intermediate with 4-methoxycarbonyl phenylboronic acid, and then obtains a MOF with stable structure and excellent fluorescence properties by self-assembly through a solvothermal method with Zr 4+ The fluorescence-enhanced metal organic framework material prepared by the application has excellent chemical and hydrothermal stability, the quenching rate and recognition sensitivity of the metal organic framework material to Fe 3+ and aromatic nitro compounds are kept at 95% and 10 4 orders of magnitude or more, and the prepared MOF has good application in selective fluorescence detection of Fe 3+ and aromatic nitro compounds.

Description

Technical Field

[0001] This invention relates to the field of metal-organic framework materials technology, and in particular to a method for preparing a thiophene-based metal-organic framework material and its application. Background Technology

[0002] Heavy metal ions exhibit bioaccumulation in the environment, gradually accumulating in the food chain to reach high concentrations. This accumulation not only increases the toxicity of heavy metal ions to organisms but also further complicates the removal of heavy metal ions through biodegradation. Furthermore, nitro explosives, widely used in mining and railway construction, release harmful substances during explosions, causing damage to the environment and ecosystems.

[0003] Metal-organic frameworks (MOFs) are multidimensional ordered frameworks formed by the self-assembly of organic ligands and metal ions or metal clusters. They combine the porous structure of inorganic materials with the functional advantages of organic materials, attracting significant attention in many fields such as recognition, adsorption, and host-guest chemistry. In particular, the development of fluorescent MOFs, primarily utilizing their fluorescence properties to recognize and adsorb pollutants, including heavy metal ions and aromatic nitro compounds, offers new and potential solutions to increasingly serious environmental pollution and health safety issues.

[0004] The main structure of MOFs is constructed by interconnecting secondary structural units through organic ligands. Therefore, the selection of metal ions and ligands plays a crucial role in the structural construction and property regulation of MOF materials. Currently, most fluorescent MOF materials are constructed using ligands containing O and N, while ligands containing S heteroatoms are rare, limiting their synthesis and application. In addition, the bonding mode of coordinate bonds makes most MOFs relatively unstable. How to combine functionality and stability in MOFs has become an important issue.

[0005] In addition to their inherent luminescent properties, conjugated thiophene compounds can enhance the structural stability of porous materials by strengthening intermolecular π-π interactions and hydrogen bonding with certain small molecules through the lone pair electrons of sulfur atoms on the thiophene ring. However, there are very few reports on the construction of organic bridging ligands for MOFs using conjugated thiophene compounds to date. Therefore, designing novel conjugated thiophene ligands as organic linking units to construct porous materials with novel structures and functions will provide a new research paradigm for improving the stability of MOFs and expanding their fluorescent recognition applications. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for preparing thiophene-based metal-organic framework materials and their applications. A 1,2,4,5-tetra(5-bromothiophene)benzene intermediate is synthesized via the Stiller reaction and NBS bromination reaction. This intermediate is then reacted with 4-methoxycarbonylphenylboronic acid to obtain a long-sized 1,2,4,5-tetra(2-(5-(4-carboxyphenyl))thiophene)benzene with a large conjugated system. Finally, a solvothermal method is used to react with Zr... 4+ Self-assembly yielded MOFs with stable structures and excellent fluorescence properties. The prepared MOFs were used for selective fluorescence detection of Fe. 3+ It has excellent applications in aromatic nitro compounds.

[0007] A thiophene-based metal-organic framework material, wherein the thiophene-based metal-organic framework is a zirconium metal-organic framework compound obtained by coordination of a thiophene carboxylic acid ligand with a zirconium metal ion;

[0008] The thiophene carboxylic acid ligand is 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene; its structural formula is as follows:

[0009]

[0010] The crystal structure of the thiophene-based metal-organic framework is orthorhombic Fmmm space group. α=β=γ=90°, Z = 4.

[0011] A second objective of this invention is to provide a method for preparing the above-mentioned 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene organic ligand, comprising the following steps:

[0012] 1) 1,2,4,5-Tetrabromobenzene and tributyl(2-thienyl)tin were reacted to prepare 1,2,4,5-tetra(thienyl)benzene intermediate (1);

[0013] 2) Intermediate 1 was brominated by NBS to prepare 1,2,4,5-tetra(5-bromothiophene)benzene intermediate (2);

[0014]

[0015] 3) Intermediate 2 was reacted with 4-methoxycarbonylphenylboronic acid to prepare 1,2,4,5-tetrakis(2-(5-(4-methyl benzoate))thienyl)benzene intermediate (3);

[0016] 4) Intermediate 3 is hydrolyzed under acidic conditions to give 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene organic ligand (TPP);

[0017]

[0018] Further, the preparation method includes the following steps: 1) 1,2,4,5-tetrabromobenzene, PdCl2 and triphenylphosphine are added to the reaction system to remove oxygen in the reaction system, and tributyl(2-thienyl)tin and N,N-dimethylformamide solvent are added to the reaction system. After dispersion, the temperature is raised to 120-150℃ and reacted for 12-18h. After the reaction is completed, the temperature is cooled to room temperature, filtered and washed with n-hexane to obtain a gray-black crude product. Dichloromethane is used as the eluent to purify the product to obtain a white 1,2,4,5-tetra(thienyl)benzene (1);

[0019] 2) The (1) obtained in step 1), N-bromosuccinimide and tetrahydrofuran solvent were reacted in the reaction system at room temperature for 24-36 h. The solvent was removed by vacuum distillation, and the mixture was washed with water and acetone to obtain a pale yellow powder 1,2,4,5-tetra(5-bromothiophene)benzene (2).

[0020] 3) The (2) obtained in step 2), 4-methoxycarbonylphenylboronic acid, tetra-triphenylphosphine palladium, potassium carbonate and 1,4-dioxane were placed in the reaction system and reacted at 90-120℃ for 48-96h under N2 protection. After the solvent was distilled under reduced pressure, it was extracted multiple times with a mixed solvent of CH2Cl2 and water. After evaporating the solvent, it was purified with CH2Cl2 as the eluent to obtain the bright yellow product 1,2,4,5-tetra(2-(5-(4-methyl benzoate))thiophene)benzene (3);

[0021] 4) Place the (3) obtained in step 3) into a reaction system containing a mixed solvent, slowly add 1-3M KOH solution at 50-70℃ until the solution is clear, remove the solvent, slowly add dilute hydrochloric acid until a large amount of yellow flocculent precipitate appears, filter and rinse with water until neutral to obtain 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene TPP;

[0022] 5) Mix the TPP obtained in step 4) with anhydrous ZrCl4, anhydrous DMF and trifluoroacetic acid in a certain proportion, seal it and put it in an oven at 100-120℃ for 48-72h to obtain the thiophene-based metal-organic framework material TPP-1.

[0023] Further, in step 1), the molar ratio of 1,2,4,5-tetrabromobenzene, PdCl2, triphenylphosphine, tributyl(2-thienyl)tin and N,N-dimethylformamide is 14:1:2:56-84:35.

[0024] Further, in step 2), the molar ratio of (1), N-bromosuccinimide and tetrahydrofuran is 1:4-6:220.

[0025] Further, in step 3), the molar ratio of (2), 4-methoxycarbonylphenylboronic acid, tetra-triphenylphosphine palladium, potassium carbonate and 1,4-dioxane is 12:48-72:1:420:27000, and the volume ratio of CH2Cl2 and water is 1:1.

[0026] Further, in step 4), the mass-to-volume ratio of (3) to the mixed solvent is 1-2.5:100g / ml, and the volume ratio of CH3OH to THF in the mixed solvent is 1:1.

[0027] Furthermore, in step 5), the molar ratio of TPP, anhydrous ZrCl4, and trifluoroacetic acid is 1-3:12:500.

[0028] A third objective of this invention is to provide the above-mentioned thiophene-based metal-organic framework material for the fluorescence detection of Fe. 3+ Applications in [the field].

[0029] A fourth objective of this invention is to provide the application of thiophene-based metal-organic framework materials in the fluorescence detection of aromatic nitro compounds.

[0030] Furthermore, during fluorescence detection, the thiophene-based metal-organic framework material TPP-1 obtained from the reaction is dispersed in DMF, a solution containing the ions and compounds to be detected is added, and after mixing evenly, fluorescence emission spectroscopy is used for detection.

[0031] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0032] The beneficial effects of this invention are as follows:

[0033] 1. This invention designs and synthesizes a novel 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene organic ligand with a large conjugated system and long ligand size through Stiller reaction and NBS bromination reaction. The prepared thienyl metal-organic framework material has a novel structure, and the large conjugated bonds of the ligand endow it with strong fluorescence intensity. While maintaining the inherent luminescent properties of conjugated thienyl compounds, it can enhance the structural stability of porous materials and exhibit excellent chemical and hydrothermal stability.

[0034] 2. The preparation method of the thiophene-based metal-organic framework fluorescent material provided by the present invention is a solvothermal method, which has the advantages of simple operation, controllable structure and composition, easy reproducibility and mass production in obtaining crystalline materials;

[0035] 3. This invention designs novel conjugated thiophene ligands. The S atom exhibits stronger polarization ability than the C and N atoms, which are the more commonly studied elements, thus endowing porous materials with Fe... 3+ Hg 2+ The selective recognition and adsorption of metal ions;

[0036] 4. This invention utilizes a structurally stable and fluorescence-enhanced thiophene-based metal-organic framework material to address the effects of Fe... 3+ The quenching rate and recognition sensitivity of aromatic nitro compounds remained at 95% and 10%, respectively. 4 Orders above 100,000, exhibiting excellent selectivity and anti-interference ability, enabling the identification of Fe 3+ Aromatic nitro compounds provide an excellent new fluorescent material that can rapidly detect and eliminate heavy metal ions and nitro explosives, thus providing strong technical support for environmental protection. Attached Figure Description

[0037] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A three-dimensional structural diagram of the thiophene-based metal-organic framework material provided by the present invention;

[0039] Figure 2 X-ray diffraction patterns of the thiophene-based metal-organic framework material provided by the present invention under different environmental treatments, wherein (a) is the powder X-ray diffraction test after treatment in H2O for 14 h and before treatment, (b) is after soaking in solutions with different pH values ​​for a certain time, and (c) is after heating treatment at different temperatures for a certain time;

[0040] Figure 3 The solid-state and fluorescence emission spectra of the thiophene-based metal-organic framework material provided by the present invention in different solvents;

[0041] Figure 4 The fluorescence spectra and quenching efficiencies of the thiophene-based metal-organic framework material provided by the present invention for different metal ions are shown in (a) and (b) respectively.

[0042] Figure 5 Fluorescence spectra and quenching efficiencies of different aromatic nitro compounds in the thiophene-based metal-organic framework material provided by the present invention are shown, wherein (a) is the recognition effect of 2,4-dinitrophenylhydrazine at different concentrations; (b) is the recognition effect of 4-nitroaniline at different concentrations; and (c) is the recognition effect of 2-nitro-1,4-phenylenediamine at different concentrations. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0044] Example 1

[0045] 1) Weigh 10.0 g of 1,2,4,5-tetrabromobenzene, 0.32 g of PdCl2, and 0.95 g of triphenylphosphine into a 100 mL round-bottom flask. Remove oxygen from the system by three vacuum-nitrogen circulation cycles. Then add 41 mL of tributyl(2-thienyl)tin and 5 mL of N,N-dimethylformamide, heat to 130 °C and react for 16 h. After the reaction is complete, cool to room temperature, filter, and wash with n-hexane to obtain a gray-black crude product. Finally, purify by silica gel column chromatography (CH2Cl2 as eluent) to obtain white 1,2,4,5-tetra(thienyl)benzene (1) with a yield of 90%.

[0046] 2) Weigh 1g (1) and 2.7g NBS into a 500mL round-bottom flask, add 45mL tetrahydrofuran, react at room temperature for 24h, remove the solvent by vacuum distillation, and then wash with water and acetone to obtain a pale yellow powder 1,2,4,5-tetra(5-bromothiophene)benzene (2), with a yield of 98%.

[0047] 3) Weigh 0.36g (2), 0.45g 4-methoxycarbonylphenylboronic acid, 0.05g tetrakis(triphenylphosphine)palladium and 2.50g potassium carbonate into a 100mL round-bottom flask, perform three vacuum-nitrogen-purging operations, add 100mL of 1,4-dioxane, heat and stir at 95℃ for 48h under N2 protection, cool to room temperature and remove solvent by vacuum distillation, add a small amount of water and extract three times with a mixed solvent of CH2Cl2 and water (V / V=1 / 1), collect the CH2Cl2 organic layer, evaporate to remove solvent to obtain crude product, and then purify with silica gel column (CH2Cl2 as eluent) to obtain bright yellow product 1,2,4,5-tetrakis(2-(5-(4-methyl benzoate))thiophene)benzene (3), yield 50%.

[0048] 4) Weigh 0.4 g (3) and place it in a 250 mL round-bottom flask. Add 40 mL of a mixed solution of methanol and tetrahydrofuran (V / V = 1 / 1). Slowly add 30 mL of the prepared 2M KOH solution to the flask and stir at 60 °C until the reaction solution becomes clear. Remove the solvent by rotary evaporation and slowly add dilute hydrochloric acid to adjust until a large amount of yellow flocculent precipitate appears. Filter and rinse the filtrate with plenty of water until neutral. Dry at 80 °C for 24 h to obtain the product 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene (TPP), with a yield of 95%.

[0049] 5) 10 mg of TPP ligand and 20 mg of anhydrous ZrCl4 were placed in a 4 mL glass vial, 3 mL of anhydrous DMF solvent and 275 μL of trifluoroacetic acid were added, the vial was sealed and placed in an oven at 120 °C. Crystals were obtained after 72 h with a yield of 80%.

[0050] Example 2

[0051] The difference between this embodiment and Embodiment 1 is that the reaction temperature in step 5) is 100°C, and the crystals are obtained by filtration after 72 hours of reaction, with a yield of 60%.

[0052] Example 3

[0053] The difference between this embodiment and Embodiment 1 is that the reaction temperature in step 5) is 110°C, and the crystals are obtained by filtration after 72 hours of reaction, with a yield of 70%.

[0054] Example 4

[0055] The difference between this embodiment and embodiment 3 is that the reaction time in step 5) is 48 hours. After the reaction is completed, the crystals are obtained by filtration, with a yield of 50%.

[0056] Example 5

[0057] 1) Weigh 10.0 g of 1,2,4,5-tetrabromobenzene, 0.32 g of PdCl2, and 0.95 g of triphenylphosphine into a 100 mL round-bottom flask. Remove oxygen from the system by three vacuum-nitrogen circulation cycles. Then add 41 mL of tributyl(2-thienyl)tin and 5 mL of N,N-dimethylformamide, heat to 130 °C and react for 16 h. After the reaction is complete, cool to room temperature, filter, and wash with n-hexane to obtain a gray-black crude product. Finally, purify by silica gel column chromatography (CH2Cl2 as eluent) to obtain white 1,2,4,5-tetra(thienyl)benzene (1) with a yield of 90%.

[0058] 2) Weigh 1g (1) and 2.7g NBS into a 500mL round-bottom flask, add 45mL tetrahydrofuran, react at room temperature for 24h, remove the solvent by vacuum distillation, and then wash with water and acetone to obtain a pale yellow powder 1,2,4,5-tetra(5-bromothiophene)benzene (2), with a yield of 98%.

[0059] 3) Weigh 0.36g (2), 0.45g 4-methoxycarbonylphenylboronic acid, 0.05g tetrakis(triphenylphosphine)palladium and 2.50g potassium carbonate into a 100mL round-bottom flask, perform three vacuum-nitrogen-purging operations, add 100mL of 1,4-dioxane, heat and stir at 95℃ for 48h under N2 protection, cool to room temperature and remove solvent by vacuum distillation, add a small amount of water and extract three times with a mixed solvent of CH2Cl2 and water (V / V=1 / 1), collect the CH2Cl2 organic layer, evaporate to remove solvent to obtain crude product, and then purify with silica gel column (CH2Cl2 as eluent) to obtain bright yellow product 1,2,4,5-tetrakis(2-(5-(4-methyl benzoate))thiophene)benzene (3), yield 50%.

[0060] 4) Weigh 1 g (3) and place it in a 250 mL round-bottom flask. Add 40 mL of a mixed solution of methanol and tetrahydrofuran (V / V = 1 / 1). Slowly add 30 mL of the prepared 2M KOH solution to the flask and stir at 60 °C until the reaction solution becomes clear. Remove the solvent by rotary evaporation and slowly add dilute hydrochloric acid to adjust until a large amount of yellow flocculent precipitate appears. Filter and wash the filtrate with plenty of water until neutral. Dry at 80 °C for 24 h to obtain the product 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene (TPP), with a yield of 95%.

[0061] 5) 20 mg of TPP ligand and 20 mg of anhydrous ZrCl4 were placed in a 4 mL glass vial, 3 mL of anhydrous DMF solvent and 275 μL of trifluoroacetic acid were added, the vial was sealed and placed in an oven at 120 °C. Crystals were obtained after 72 h with a yield of 70%.

[0062] Unlike Example 1, the molar ratio of the organic ligand 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene to the metal source in this Example 1 is 1:4.

[0063] To further illustrate the superior performance of the thiophene metal-organic framework material prepared in this invention in fluorescence detection, the following experiments were conducted.

[0064] Example 6

[0065] Single-crystal diffraction data of the thiophene-based MOFs material provided in Example 1 were collected using an Agilent SuperNova X-ray single-crystal diffraction system. High-quality crystals were selected and mounted on a loop. Cu-Kα rays were monochromated using a graphite monochromator at a low temperature of 150 K. As a diffraction source, diffraction point data of the crystal under test were collected using an ω-scan method. Structure analysis was performed using the Superflip method in the Olex2 software package, and structure refinement was achieved using the ShelXL method. Results are shown below. Figure 1 .

[0066] Thiophene-based MOFs belong to the cubic crystal system and the Fmmm space group. Z=4, forming a six-core, eight-linked Zr6(μ3-O)8(COO)8(H2O)8 SBU, which further connects with ligands to construct a 3D ordered framework with large pores in the c-axis direction.

[0067] Example 7

[0068] Appropriate amounts of MOF samples were weighed and immersed in water, solutions of different pH levels, and heated. After a certain period of time, the samples were removed and subjected to powder X-ray diffraction analysis. The results are shown below. Figure 2 .

[0069] Thiophene-based MOFs exhibit good structural stability after immersion in water for 14 hours. At pH 0, the crystal structure of thiophene-based MOFs partially collapses, while at pH 1 and 2, the crystal structure is well preserved. Compared to acidic conditions, thiophene-based MOFs are more stable under alkaline conditions; even after immersion in increasingly alkaline solutions with pH values ​​ranging from 9 to 11 for 14 hours, the crystal structure remains well maintained. Heating thiophene-based MOFs to 120℃ for 12 hours resulted in a change in peak shape, indicating that the crystal structure was partially disrupted, but the overall framework has not completely collapsed.

[0070] Example 8

[0071] Fluorescence spectra of thiophene MOFs were collected at room temperature using a Hitachi F-7000 fluorescence spectrophotometer. The scan rate was 1200 nm·min⁻¹, the voltage was 400 V, and both the excitation and emission slits were 5 nm. Fluorescence and emission spectra of thiophene MOFs in different solvents were obtained by dispersing 2 mg of the material in 2 mL of different solvents. Results are shown below. Figure 3 .

[0072] Solid-state fluorescence emission spectra of thienyl MOFs and ligand TPP show that their maximum emission peaks are basically the same, both appearing around 518 nm (λex = 350 nm). However, under the same test conditions, the fluorescence of MOFs is significantly stronger than that of the ligand. This is mainly because after the ligand and metal ions form a polymer network, the ordered orientation of the conjugated groups and the fixation of the organic ligands reduce non-radiative energy transitions and enhance fluorescence. The maximum emission peaks of thiophene MOFs in different solvents are all around 500 nm (λex = 350 nm). The order of fluorescence intensity is: EtOH (ethanol) > CH3CN (acetonitrile) > DMF (N,N-dimethylformamide) > Acetone (acetone) > Toluene (toluene) > DMA (N,N-diethylformamide) > THF (tetrahydrofuran) > CH2Cl2 (dichloromethane) > TCM (chloroform) > DMSO (dimethyl sulfoxide). This may be because the polymer backbone of MOFs is rich in sulfur, which can form hydrogen bonds with nitrogen, oxygen, etc., resulting in differences in their dispersibility and fluorescence emission peak intensity in different solvents. Among these solvents, ethanol is the most likely to form strong hydrogen bonds, which enhances the rigidity of the polymer network and reduces non-radiative transitions, thus exhibiting the strongest fluorescence in ethanol.

[0073] Example 9

[0074] Thiophene-based MOFs selected 13 metal ions, including Ag, for recognition. + Li + Zn 2+ Pd 2+ Zn 2+ Mn 2+ Pb 2+ Cu 2+ Ni 2+ Ba 2+ Hg 2+ Fe 2+ Al 2+ 10 mM DMF solutions of different metal ions were prepared. Using DMF as the dispersion solvent, 2 mg of thiophene-based MOF material was uniformly dispersed in 2 mL of DMF. The mixture was sonicated for 10 minutes, and then the fluorescence emission spectra of a series of solutions with different volumes of metal ions were measured. The results are shown below. Figure 4 .

[0075] When Fe 3+ The quenching rate reached 84% when the solution was added to 100 μL, and 94% when added to 200 μL, further demonstrating the high recognition efficiency of thienyl MOFs. Furthermore, thienyl MOFs showed good recognition of Pd. 2+ Ag + Cu 2+ Hg2+ It also exhibits some fluorescence response, but shows almost no recognition of the other eight metal ions. This result is mainly attributed to the photoinduced electron transfer mechanism, because Fe... 3+ Fe has a valence electron orbital configuration of 3d⁵4s⁰, exhibiting a very high charge density compared to other ions. 3+ It exhibits strong electron-withdrawing properties, with electron-rich conjugated thiophene ligands and electron-withdrawing Fe in the thiophene-based MOF framework. 3+ Electron transfer occurred between them, leading to fluorescence quenching.

[0076] Example 10

[0077] Twelve nitro compounds were selected, including 2-nitro-1,4-phenylenediamine, 4-nitro-o-phenylenediamine, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline, 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenylhydrazine, 1,3-dinitrobenzene, 2,4-dinitrotoluene, and 4-nitrotoluene. 10 mM DMF solutions of different nitro compounds were prepared. 2 mg of thienyl MOF material was uniformly dispersed in 2 mL of DMF and sonicated for 10 minutes. The fluorescence emission spectra of the thienyl MOFs after adding different volumes of nitro compound solutions were then measured. The results are shown below. Figure 5 .

[0078] Thiophene-based MOFs exhibit high sensitivity in recognizing phenylenediamine and phenylhydrazine-type nitro compounds, and also show significant recognition of 4-nitroaniline among aniline-type nitro compounds. They demonstrate good recognition of 4-nitrophenol among phenol-type nitro compounds, but show poor recognition of toluene-type nitro compounds. The sensitivity ranking is: 2,4-dinitrophenylhydrazine > 4-nitroaniline > 2-nitro-1,4-phenylenediamine > 4-nitro-o-phenylenediamine; the quenching efficiency ranking is: 2,4-dinitrophenylhydrazine (96%) > 4-nitroaniline (93.2%) > 2-nitro-1,4-phenylenediamine (92.1%) > 4-nitro-o-phenylenediamine (89.12%). The fluorescence quenching mechanism mainly involves hydrogen bonds and π-π interactions between the large π-conjugated MOF backbone and electron-deficient nitro compounds. These interactions cause electrons in the LUMO orbitals of the backbone to transfer from the MOF ligands to the explosive molecule, resulting in fluorescence quenching. The differences in fluorescence recognition performance for different nitro compounds primarily stem from the number and strength of hydrogen bonds formed. For example, the strength of hydrogen bond formation by different groups is: amino > hydroxy > methyl. Therefore, thiophene MOFs exhibit higher sensitivity for phenylhydrazine and aniline compounds than for phenol and toluene compounds.

[0079] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A thiophene-based metal-organic framework material, characterized in that, The thiophene-based metal-organic framework is a zirconium metal-organic framework compound obtained by coordination of thiophene carboxylic acid ligands with zirconium ions. The thiophene carboxylic acid ligand is 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene; its structural formula is as follows: ； The crystal structure of the thiophene-based metal-organic framework is an orthorhombic Fmmm space group, a = 38.1015 Å, b = 33.9856 Å, c = 16.1219 Å, α = β = γ = 90°, V = 20876.4 Å3, Z = 4.

2. A method for preparing a thiophene-based metal-organic framework material as described in claim 1, characterized in that, The preparation method includes the following steps: 1) Add 1,2,4,5-tetrabromobenzene, PdCl2 and triphenylphosphine to the reaction system to remove oxygen from the reaction system. Then add tributyl(2-thienyl)tin and N,N-dimethylformamide solvent to the reaction system. After dispersion, heat to 120-150℃ and react for 12-18 h. After the reaction is completed, cool to room temperature, filter and wash with n-hexane to obtain a gray-black crude product. Purify with dichloromethane as eluent to obtain white 1,2,4,5-tetra(thienyl)benzene (1); 2) The (1) obtained in step 1), N-bromosuccinimide and tetrahydrofuran solvent were reacted in the reaction system at room temperature for 24-36 h. The solvent was removed by vacuum distillation, and the mixture was washed with water and acetone to obtain a pale yellow powder 1,2,4,5-tetra(5-bromothiophene)benzene (2). 3) The (2) obtained in step 2), 4-methoxycarbonylphenylboronic acid, tetra-triphenylphosphine palladium, potassium carbonate and 1,4-dioxane were placed in the reaction system and reacted at 90-120 °C for 48-96 h under N2 protection. After distilling the solvent under reduced pressure, the product was extracted multiple times with a mixed solvent of CH2Cl2 and water. After evaporating the solvent, the product was purified with CH2Cl2 as the eluent to obtain the bright yellow product 1,2,4,5-tetrakis(2-(5-(4-methyl benzoate))thiophene)benzene (3); 4) Place the (3) obtained in step 3) into a reaction system containing a mixed solvent, slowly add 1-3 MKOH solution at 50-70 °C until the solution is clear, remove the solvent, slowly add dilute hydrochloric acid until a large amount of yellow flocculent precipitate appears, filter and rinse with water until neutral to obtain 1,2,4,5-tetrakis(2-(5-(4-carboxyphenyl))thienyl)benzene TPP; 5) Mix the TPP obtained in step 4) with anhydrous ZrCl4, anhydrous DMF and trifluoroacetic acid in a certain proportion, seal it and put it in an oven at 100-120 ℃ for 48-72 h to obtain the thiophene-based metal-organic framework material TPP-1. In step 1), the molar ratio of 1,2,4,5-tetrabromobenzene, PdCl2, triphenylphosphine, tributyl(2-thienyl)tin, and N,N-dimethylformamide is 14:1:2:56-84:

35.

3. The method for preparing the thiophene-based metal-organic framework material according to claim 2, characterized in that: In step 2), the molar ratio of (1), N-bromosuccinimide and tetrahydrofuran is 1:4-6:

220.

4. The method for preparing the thiophene-based metal-organic framework material according to claim 2, characterized in that: In step 3), the molar ratio of (2), 4-methoxycarbonylphenylboronic acid, tetra-triphenylphosphine palladium, potassium carbonate and 1,4-dioxane is 12:48-72:1:420:27000, and the volume ratio of CH2Cl2 and water is 1:

1.

5. The method for preparing the thiophene-based metal-organic framework material according to claim 2, characterized in that: In step 4), the mass-to-volume ratio of (3) to the mixed solvent is 1~2.5:100 g / ml, and the volume ratio of CH3OH to THF in the mixed solvent is 1:

1.

6. The method for preparing the thiophene-based metal-organic framework material according to claim 2, characterized in that: In step 5), the molar ratio of TPP, anhydrous ZrCl4, and trifluoroacetic acid is 1-3: 8-15: 300-500.

7. A thiophene-based metal-organic framework material as described in claim 1 for the fluorescence detection of Fe. 3+ Applications in [the field].

8. The application of a thiophene-based metal-organic framework material as described in claim 1 in the fluorescence detection of aromatic nitro compounds.

9. The application according to any one of claims 7 or 8, characterized in that: In fluorescence detection, the thiophene-based metal-organic framework material TPP-1 obtained from the reaction is dispersed in DMF, a solution containing the ions and compounds to be detected is added, and after mixing evenly, fluorescence emission spectroscopy is used for detection.

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