Preparation method and application of a kind of metal-organic framework material with photochromic and long persistent luminescence characteristics

Abstract

The application relates to a preparation method and application of a metal-organic framework (MOFs) material with photochromic and long persistent luminescence (LPL) characteristics. Specifically, X-MOFs (X=Cl, Br) are prepared by high-temperature self-assembly of ligand 1,1'- (6-hydroxy-1,3,5-triazine-2,4-diyl) bis (pyridine-4 (1H)-ketone) and CdCl2.2.5H2O and CdBr2. Research finds that, under the continuous irradiation of ultraviolet light, the X-MOFs realize photochromic behavior from yellow to gray. In addition, after the removal of different excitation light sources, the X-MOFs exhibit multicolor LPL which is dependent on excitation, temperature and time evolution. The X-MOFs material synthesized by the application provides potential application value in the fields of data encryption and anti-fake patterns.

Description

Technical Field

[0001] This invention belongs to the field of luminescent MOF materials technology. It constructs X-MOF materials with photochromic and LPL properties through the self-assembly of organic ligands and metal salts, and illustrates their application value in data encryption and anti-counterfeiting patterns. Background Technology

[0002] LPL materials, due to their highly tunable optical properties, possess unique advantages in fields such as bioimaging, anti-counterfeiting, information encryption, and optical recording. However, the development of LPL materials still faces many challenges. At room temperature, nonradiative transitions significantly reduce phosphorescence efficiency. Furthermore, triplet excitons are highly susceptible to environmental quenching and readily decay through nonradiative pathways, making the simultaneous achievement of long lifetimes and high efficiency in most LPL systems a significant challenge. To develop efficient LPL materials, researchers often employ strategies such as heavy atom doping to enhance spin-orbit coupling (SOC) to promote intersystem crossing (ISC). In addition, strategies such as crystal engineering, host-guest doping, and H aggregation aim to improve ISC rates and stabilize triplet excitons. Among numerous material platforms, MOFs stand out due to their high crystallinity, structural rigidity, and periodic porous structure. The metal-ligand coordination bonds in MOFs can effectively suppress nonradiative transitions, providing a feasible strategy for achieving long phosphorescence lifetimes and high environmental stability. However, traditional LPL MOFs are often functionally limited and struggle to meet the growing and diverse demands of advanced applications. This has driven research into single-component multifunctional LPL MOFs to become a current hot topic.

[0003] In recent years, photoresponsive luminescent materials (especially electron-transfer photochromic systems) have attracted much attention due to their reversible color conversion characteristics under illumination. During electron transfer, the generation or annihilation of free radicals triggers reversible changes in the material's structure, electronic or energy states, thereby modulating properties such as photoluminescence. This combination of the LPL effect and photochromic effect opens up innovative pathways for high-end optical applications. Because triazine groups possess π-electron-deficient properties and are rich in heteroatoms, they become ideal electron acceptors and phosphorescent groups for constructing MOFs that combine both LPL and photochromic properties.

[0004] Based on this, the present invention synthesizes a series of X-MOFs integrating photochromism and multicolor LPL. Through a rigid framework and halogen engineering, the X-MOFs can achieve tunable multipath luminescence. Simultaneously, the participation of halogens and the charge distribution of ligands promote electron transfer. Therefore, under continuous ultraviolet light irradiation, the X-MOFs exhibit photochromic behavior ranging from yellow to gray. Interestingly, after removing different excitation sources, the X-MOFs exhibit multicolor LPLs from green to orange, dependent on excitation, temperature, and time evolution. These X-MOFs show great promise for high-security information encryption and anti-counterfeiting. Summary of the Invention

[0005] This invention aims to synthesize MOF materials possessing both photochromic and photochromic ligand (LPL) properties. The invention generates HL via the reaction of 4-hydroxypyridine and cyanuric chloride, and then uses HL to self-assemble with metal salts CdCl₂·H₂O and CdBr₂ to construct X-MOFs, achieving multi-path, multi-color LPL. Furthermore, Cl-MOFs and Br-MOFs exhibit photochromic properties due to the generation of photoradicals. A further objective of this invention is to provide a method for preparing the photochromic ligand HL; a more significant objective is to provide a method for preparing and applying the aforementioned X-MOFs.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] An organic ligand HL, with the molecular formula: C 13 H9N5O3 has the following structure:

[0008] .

[0009] The preparation method of HL includes the following steps:

[0010] Step 1: Dissolve 4-hydroxypyridine and cyanuric chloride in CH3CN in a round-bottom flask, and stir with a magnetic stirrer at room temperature for 10 h. The molar ratio of 4-hydroxypyridine to cyanuric chloride is 1 mol: 1 mol.

[0011] Step 2: Heat the mixture to 70°C on a magnetic stirrer and maintain a speed of 500 r / min for 8 hours to allow it to react fully (with magnetic stirring throughout).

[0012] Step 3: After the reaction is complete, filter the solution, wash it with CH3OH and CH2Cl, and then dry it to obtain a light yellow powder, which is HL.

[0013] A class of MOFs materials exhibiting photochromic and LPL properties is characterized by comprising two compounds, Cl-MOF and Br-MOF, with molecular formulas C0, C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C21, C22, C3, C4, C5, C6, C7, C8, C9, C11, C21, C 13 H10 CdClN5O4 and C 13 H 10 CdBrN5O4, with molecular weights of 448.11 and 492.57 respectively, both belong to the triclinic crystal system and have space group P-1.

[0014] Furthermore, compounds X-MOFs were obtained by high-temperature self-assembly of HL with CdCl2·2.5H2O and CdBr2, respectively.

[0015] Furthermore, the preparation method of compound Cl-MOF includes the following steps:

[0016] Step 1: Add HL to a PTFE-lined stainless steel reaction vessel, then add DMF and sonicate to dissolve. After complete dissolution, add CdCl2·2.5H2O and H2O, and sonicate again to dissolve. The volume ratio of H2O to DMF is 1 ml: 1.5~2 ml, and the molar ratio of HL to CdCl2·2.5H2O is 1~1.2 mmol: 1 mmol.

[0017] Step 2: After complete dissolution, place the reaction vessel into the matching stainless steel high-temperature reactor, and then place the reactor into an electric heating drying oven. Heat the reactor from room temperature to 80-100 ℃ for 1-2 hours, maintain this temperature for 40-50 hours, and then cool it down to room temperature for 8-10 hours.

[0018] Step 3: After cooling to room temperature, yellow crystals are obtained. After filtration and washing with DMF, pure crystals of Cl-MOF are obtained.

[0019] Furthermore, in step 1, the molar ratio of HL to CdCl2·2.5H2O is 1 mmol: 1 mmol, and the volume ratio of H2O to DMF is 1 ml: 1.5 ml.

[0020] Furthermore, in step 2, the temperature is raised to 90°C for 2 hours, maintained at this temperature for 48 hours, and then cooled to room temperature for 10 hours.

[0021] As an alternative embodiment, the preparation method of the compound Cl-MOF includes the following steps: a mixture of HL (28 mg, 0.1 mmol) and CdCl2·2.5H2O (23 mg, 0.1 mmol) is added to a 25 ml polytetrafluoroethylene-lined stainless steel reaction vessel, along with 1.5 ml of DMF and 1 ml of H2O. The mixture is then sonicated to dissolve the dissolved substances. After dissolution, the mixture is placed in a matching stainless steel high-temperature reactor. The reactor is then placed in an electrically heated drying oven and heated from room temperature to 90 °C for 2 h, reacted for 48 h, and cooled to room temperature for 10 h. Finally, the mixture is filtered and washed with DMF to obtain Cl-MOF.

[0022] Furthermore, the preparation method of the compound Br-MOF includes the following steps:

[0023] Step 1: Add HL to a PTFE-lined stainless steel reaction vessel, then add DMF and sonicate to dissolve. After complete dissolution, add H2O, CdBr2, and CH3CH2OH, and sonicate again to dissolve. The volume ratio of H2O, CH3CH2OH, and DMF is 1 ml: 1 ml: 0.5 ml, and the molar ratio of HL to CdBr2 is 1 mmol: 1~1.2 mmol.

[0024] Step 2: After complete dissolution, place the reaction vessel into the matching stainless steel high-temperature reactor, and then place the reactor into an electric heating drying oven. Heat the reactor from room temperature to 80-100 ℃ for 1-2 hours, maintain this temperature for 40-50 hours, and then cool it down to room temperature for 8-10 hours.

[0025] Step 3: After cooling to room temperature, yellow crystals are obtained. After filtration and washing with DMF, pure crystals of Br-MOF are obtained.

[0026] Furthermore, in step 1, the molar ratio of HL to CdBr2 is 1 mmol: 1 mmol.

[0027] Furthermore, in step 2, the temperature is raised to 90°C for 2 hours, maintained at this temperature for 48 hours, and then cooled to room temperature for 10 hours.

[0028] As an alternative embodiment, the preparation method of the compound Br-MOF includes the following steps: a mixture of HL (28 mg, 0.1 mmol) and CdBr2 (27 mg, 0.1 mmol) is added to a 25 ml polytetrafluoroethylene-lined stainless steel reaction vessel, along with 0.5 ml DMF, 1 ml H2O, and 1 ml CH3CH2OH. The mixture is then sonicated to dissolve the Br-MOF. After dissolution, the mixture is placed in a matching stainless steel high-temperature reactor, which is then placed in an electrically heated drying oven and heated from room temperature to 90 °C for 2 h. The reaction is carried out for 48 h, followed by cooling to room temperature for 10 h. Finally, the mixture is filtered and washed with DMF to obtain pure single crystals of Br-MOF.

[0029] This invention, based on extensive research and exploration, aims to provide methods for preparing Cl-MOF and Br-MOF. Another objective is to provide applications based on Cl-MOF and Br-MOF, specifically in anti-counterfeiting and encryption.

[0030] The present invention has the following beneficial effects:

[0031] By introducing halogen atoms to provide abundant intermolecular interactions, the triplet exciton is stabilized, thereby enhancing LPL performance.

[0032] The triazine group possesses π-electron-deficient properties and is rich in heteroatoms, which endows X-MOFs with photochromic effects. Attached Figure Description

[0033] Figure 1 This is the hydrogen NMR spectrum of HL.

[0034] Figure 2 TGA curves for HL and X-MOFs.

[0035] Figure 3 The simulation of X-MOFs and their PXRD spectra before and after ultraviolet irradiation.

[0036] Figure 4 Crystal structures of X-MOFs. a) Asymmetric unit cell. b, e) 2D and 3D structures. c, d) π-π stacking and halogen bond interactions.

[0037] Figure 5 The instantaneous and delayed (1 ms) emission spectra of HL, X-MOFs are given.

[0038] Figure 6 Phosphorescence lifetime decay curves for HL, X-MOFs.

[0039] Figure 7 The fluorescence lifetime decay curves of X-MOFs are shown.

[0040] Figure 8 The gating spectra of X-MOFs under 365 nm excitation at different delay times are shown.

[0041] Figure 9 This is a crystal photograph showing how X-MOFs change over time under ultraviolet irradiation.

[0042] Figure 10 The EPR spectra of X-MOFs before and after UV irradiation are shown.

[0043] Figure 11 The image shows the XPS spectrum of Cl-MOF.

[0044] Figure 12 The XPS spectra of O1s and N1s of Cl-MOF before and after UV irradiation are shown.

[0045] Figure 13 The LPL spectrum and photographs of Cl-MOF at 300 K after removing different radiation sources.

[0046] Figure 14 The LPL spectrum and photographs of Br-MOF at 300 K after removing different radiation sources.

[0047] Figure 15 The LPL spectrum and photographs of Cl-MOF at 77 K after removing different radiation sources.

[0048] Figure 16 The LPL spectrum and photographs of Br-MOF at 77 K after removing different radiation sources.

[0049] Figure 17 The temperature-dependent delayed emission spectra of X-MOFs in the range of 300–77 K.

[0050] Figure 18 A schematic diagram of creating anti-counterfeiting patterns for the molding of X-MOFs.

[0051] Figure 19 A schematic diagram illustrating multiple data encryption and time-resolved data encryption for X-MOFs. Detailed Implementation

[0052] The following examples will help to understand the present invention, but the examples do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0053] Example 1: Preparation of organic ligand HL

[0054] 4-Hydroxypyridine (1.84 g, 19 mmol) and cyanuric chloride (3.8 g, 20 mmol) were mixed in a round-bottom flask. 50 mL of CH3CN was then added to dissolve the solid, and the mixture was stirred at room temperature for 10 h. The reaction mixture was then heated to 70 °C and reacted for 8 h. After cooling, the mixture was filtered, washed with CH3OH and CH2Cl2, and then dried to obtain HL.

[0055] Example 2: Synthesis of Cl-MOF and Br-MOF

[0056] (1) Synthesis of Cl-MOF.

[0057] A mixture of HL (28 mg, 0.1 mmol) and CdCl2·2.5H2O (23 mg, 0.1 mmol) was added to a 25 mL PTFE-lined stainless steel reaction vessel, along with 1.5 mL of DMF and 1 mL of H2O. The mixture was then sonicated to dissolve the precipitate. After dissolution, the solution was transferred to a matching stainless steel high-temperature reactor. The reactor was then placed in an electrically heated drying oven and heated from room temperature to 90 °C for 2 h, reacted for 48 h, and then cooled to room temperature for 10 h. Finally, the solution was filtered and washed with DMF to obtain Cl-MOF single crystals.

[0058] (2) Synthesis of Br-MOF.

[0059] A mixture of ligand HL (28 mg, 0.1 mmol) and CdBr2 (27 mg, 0.1 mmol) was added to a 25 mL PTFE-lined stainless steel reaction vessel, along with 0.5 mL DMF, 1 mL H2O, and 1 mL CH3CH2OH. The mixture was then sonicated to dissolve the ligand. After dissolution, the vessel was placed in an oven and heated from room temperature to 90 °C for 48 h, followed by 10 h of cooling to room temperature. Finally, the mixture was filtered and washed with DMF to obtain Br-MOF.

[0060] Example 3: Crystallographic data of Cl-MOF and Br-MOF

[0061] Table 1. Crystal data for Cl-MOF and Br-MOF.

[0062]

[0063]

[0064] Example 4: Structural Analysis of Cl-MOF and Br-MOF Crystals

[0065] The molecular structure of HL is obtained through 1H NMR confirmed ( Figure 1 A series of novel halogen-tuned MOFs (X-MOFs, X = Cl, Br) were synthesized via a three-day hydrothermal reaction at 90 °C using HL and CdX2 in a mixed solvent. Thermogravimetric analysis showed that the X-MOFs remained stable below approximately 350 °C, with a weight loss of approximately 3.5% at about 150 °C corresponding to the release of one water molecule. Upon reaching 350 °C, the framework began to decompose as the HL units burned. Figure 2 The phase purity of X-MOFs was confirmed by PXRD. Figure 3 Single-crystal X-ray diffraction analysis showed that the X-MOFs crystallized in a triclinic system (space group P-1). The asymmetric unit contained a Cd atom. 2+ One coordination L - Ligand, an X - and a coordinated water molecule ( Figure 4 a) The metal center is five-coordinated, surrounded by three oxygen atoms, one water molecule, and one halogen atom of three ligands, exhibiting a trigonal bipyramidal geometry. Adjacent ligands are connected via μ3-η 1 : η 1 : η 1 These polyhedra are connected in a way that forms a two-dimensional layered structure. Figure 4 b). As is well known, intermolecular interactions play a crucial role in stabilizing the framework and promoting luminescence. Two-dimensional planes are further assembled into ordered three-dimensional supramolecular networks through extensive intermolecular halogen bonds and p-p stacking interactions. Figure 4 It is noteworthy that the stacking interaction of pp between the donor and acceptor is crucial for promoting electron transfer, thereby synergistically promoting the photochromic process.

[0066] Example 5: Photophysical properties of Cl-MOF and Br-MOF

[0067] The photoluminescence properties of HL and X-MOFs were characterized under solid-state conditions. At excitation wavelength of 360 nm, both the instantaneous emission spectrum and the delayed emission spectrum of HL were within 515 nm. Figure 5 The corresponding emission decay curve shows a lifetime of 5.15 ms, which is consistent with the phosphorescent origin. Figure 6 In contrast, the instantaneous emission spectra of X-MOFs show a weak emission band at 420 nm and a strong emission band in the 525-535 nm range, with the maximum emission peaks of Cl-MOF and Br-MOF located at 525 and 530 nm, respectively. After a 1 ms delay, the short-wavelength emission peaks disappear, while the long-wavelength peaks persist. Figure 5The transient spectrum indicates that the emission at 420 nm is fluorescence, with lifetimes of 2.78 and 2.37 ns, respectively. Figure 7 The lifetimes corresponding to the long-wavelength emission peaks are 11.32 and 9.18 ms, further confirming its phosphorescent origin. Figure 6 The similarity between the delayed emission spectra of X-MOFs and those of HL under 360 nm excitation suggests that the long-lived emission originates from the ligand. Notably, when the delay time is increased to 80 ms, Cl-MOF and Br-MOF also exhibit new emission peaks at 580 nm and 582 nm, respectively. Figure 8 Low-energy phosphorescence lifetime measurements showed that Cl-MOF had a lifetime of 10.39 ms, and Br-MOF had a lifetime of 8.99 ms. Clearly, X-MOFs exhibited dual phosphorescence emission. High-energy phosphorescence emitted phosphorescence from the ligand center, as its emission peak position closely matched the phosphorescence peak position of the ligand. In contrast, low-energy phosphorescence only appeared in X-MOFs and gradually redshifted with increasing halogen atomic number; it is speculated that the emission band near 580 nm can be attributed to aggregated-state phosphorescence.

[0068] Triazine-based HL ligands, with their strong conjugation and electron-accepting abilities, make X-MOFs an ideal system for studying photochromism in crystals at room temperature. After 2 hours of ultraviolet irradiation, X-MOFs exhibit a distinct color change from yellow to gray. Figure 9 This color change can be attributed to photogenerated HL radicals. Electron paramagnetic resonance spectroscopy showed almost no signal before irradiation. However, after irradiation with 365 nm and 60 W ultraviolet light, a sharp peak appeared at g = 2.0067, confirming the generation of free radicals under photostimulation. Figure 10 Further X-ray photoelectron spectroscopy was used to study the electron transfer pathway. For Cl-MOF, the energy level spectra of C 1s, Cl 2p, and Cd 3d did not show a significant shift in binding energy before and after UV irradiation. Figure 11 This indicates that the chemical environment of these elements remains stable. In contrast, the core energy level spectra of O 1s and N 1s show significant changes under ultraviolet irradiation. For example... Figure 12 As shown, the binding energies of oxygen atoms increased from 531.59 eV and 531.00 eV to 531.65 eV and 531.19 eV, respectively, while the binding energies of nitrogen atoms decreased from 405.92 eV and 405.49 eV to 405.81 eV and 405.37 eV. Since higher binding energies around atoms correspond to lower electron densities, and lower binding energies indicate higher electron densities, these changes confirm that oxygen atoms lost electrons during the coloring process, while nitrogen atoms gained electrons. In summary, these results indicate that the photochromism of X-MOFs originates from electron transfer from oxygen atoms to nitrogen atoms, ultimately leading to the formation of HL radicals.

[0069] Interestingly, X-MOFs exhibited bright LPL emission after the excitation source was removed. Based on the existence of multiple excited states, five excitation wavelengths (311, 365, 385, 405, and 450 nm) were selected for investigation. Under different excitation conditions at 300 K, X-MOFs exhibited halide-dependent long afterglow colors: green (Cl-MOF) and yellow-green (Br-MOF). Figure 13 ,14). Upon cooling to 77 K, the LPL intensity of X-MOFs significantly increased. From high-energy excitation to low-energy excitation, the LPL gradually changed from cyan to green and then to yellow or orange ( Figure 15 Interestingly, as the temperature decreases, the emission peak of X-MOFs at 545 nm (LPL1) slowly increases, while a significantly enhanced new peak (LPL2) gradually emerges in the 575-585 nm range. This result is in high agreement with the trend observed in temperature-dependent time-gated spectra. Figure 17 When these excitation sources are removed, the camera can capture the LPL of these X-MOFs, demonstrating the multicolor tunability of the LPL. Therefore, the introduction of halogens induces excitation-dependent, temperature-responsive, and time-evolving LPL characteristics.

[0070] Example 6: Specific applications of Cl-MOF and Br-MOF

[0071] (1) Molding to create anti-counterfeiting patterns

[0072] like Figure 18 As shown, star-shaped and flower-shaped structures were fabricated using Cl-MOF and Br-MOF, respectively. After turning off the 365 nm and 450 nm UV light, clear green or yellow LPL images were displayed. Notably, after irradiation with 365 nm (60 W) UV light for 400 s and subsequent removal of the excitation source, the LPL signal from the flower-shaped structure disappeared, while the LPL signal from the star-shaped structure became weaker. These dynamic LPL variations can significantly increase the barrier to anti-counterfeiting technology, fundamentally reducing the feasibility of counterfeiting.

[0073] (2) Multiple data encryption and time-resolved data encryption

[0074] like Figure 19As shown, fast-response QR codes with dual information (Cl-MOF: F; Br-MOF: L) were drawn on different sides of a cube based on ink printing. For example, only after excitation with 365 nm ultraviolet light could the green and yellow-green LPLs be displayed on the F and L sides, simultaneously obtaining the encrypted information (EI-1: LA). However, when the scanning order was incorrect, incorrect information (AL) was obtained. Furthermore, after 0.5 s and 1 s, EI-2 (LL) and EI-3 (L) could be seen, respectively. Therefore, true dual information (LA→LL→L) can only be obtained when the correct excitation wavelength, LPL color, and scanning order are met, demonstrating the potential of X-MOFs in multi-body information encryption.

[0075]

[0076]

[0077]

[0078]

[0079]

Claims

1. An organic ligand HL, characterized in that, The ligand HL is named 1,1'-(6-hydroxy-1,3,5-triazine-2,4-diyl)bis(pyridin-4(1H)-one), with the molecular formula: C 13 H9N5O3 has the following structure: 。 2. A class of MOFs materials exhibiting photochromic and long-lasting luminescence properties, characterized in that, It includes two compounds, Cl-MOF and Br-MOF, with molecular formulas C1, C2, and C3, respectively. 13 H 10 CdClN5O4 and C 13 H 10 CdBrN5O4, with molecular weights of 448.11 and 492.57 respectively, both belong to the triclinic crystal system and have space group P-1.

3. The method for preparing a type of MOF material with photochromic and long-lasting luminescence properties according to claim 2, characterized in that, Compounds X-MOFs (X = Cl, Br) were obtained by high-temperature self-assembly of HL with CdCl2·2.5H2O and CdBr2, respectively.

4. The method for preparing the organic ligand HL according to claim 1, characterized in that, The preparation process of HL is as follows: Step 1: Dissolve 4-hydroxypyridine and cyanuric chloride in CH3CN in a round-bottom flask, and stir on a magnetic stirrer at room temperature for 10 h. The molar ratio of 4-hydroxypyridine to cyanuric chloride is 1 mol: 1 mol. Step 2: Heat the mixture to 70°C on a magnetic stirrer and maintain a speed of 500 r / min for 8 hours to allow it to react fully (with magnetic stirring throughout the process). Step 3: After the reaction is complete, filter the solution, wash it with CH3OH and CH2Cl2, and then dry it to obtain a light yellow powder, which is HL.

5. The compound Cl-MOF according to claim 3, characterized in that, The preparation method of compound Cl-MOF includes the following steps: Step 1: Add HL to a PTFE-lined stainless steel reaction vessel, then add DMF and sonicate to dissolve. After complete dissolution, add CdCl2·2.5H2O and H2O, and sonicate again to dissolve. The volume ratio of H2O to DMF is 1 ml:1.5~2 ml, and the molar ratio of HL to CdCl2·2.5H2O is 1~1.2 mmol:1 mmol. Step 2: After complete dissolution, place the reaction vessel into the matching stainless steel high-temperature reactor, and then place the reactor into an electric heating drying oven. Heat the reactor from room temperature to 80-100 ℃ for 1-2 hours, maintain this temperature for 40-50 hours, and then cool it down to room temperature for 8-10 hours. Step 3: After cooling to room temperature, yellow crystals are obtained. After filtration and washing with DMF, pure crystals of Cl-MOF are obtained.

6. The method for preparing the compound Cl-MOF according to claim 5, characterized in that, In step 1, the molar ratio of HL and CdCl2·2.5H2O is 1 mmol: 1 mmol, and the volume ratio of H2O and DMF is 1 ml: 1.5 ml.

7. The method for preparing the compound Cl-MOF according to claim 5, characterized in that, In step 2, the temperature is raised to 90°C for 2 hours, maintained at this temperature for 48 hours, and then cooled to room temperature for 10 hours.

8. The compound Br-MOF according to claim 3, characterized in that, The preparation method of compound Br-MOF includes the following steps: Step 1: Add HL to a PTFE-lined stainless steel reaction vessel, then add DMF and sonicate to dissolve. After complete dissolution, add H2O, CdBr2, and CH3CH2OH, and sonicate again. The volume ratio of H2O, CH3CH2OH, and DMF is 1 ml: 1 ml: 0.5 ml, and the molar ratio of HL to CdBr2 is 1 mmol: 1~1.2 mmol. Step 2: After complete dissolution, place the reaction vessel into the matching stainless steel high-temperature reactor, and then place the reactor into an electric heating drying oven. Heat the reactor from room temperature to 80-100 ℃ for 1-2 hours, maintain this temperature for 40-50 hours, and then cool it down to room temperature for 8-10 hours. Step 3: After cooling to room temperature, yellow crystals are obtained. After filtration and washing with DMF, pure crystals of Br-MOF are obtained.

9. The method for preparing the compound Br-MOF according to claim 8, characterized in that, The molar ratio of HL and CdBr2 in step 1 is 1 mmol: 1 mmol.

10. The method for preparing the compound Br-MOF according to claim 8, characterized in that, In step 2, the temperature is raised to 90°C for 2 hours, maintained at this temperature for 48 hours, and then cooled to room temperature for 10 hours.

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