Chiral porphyrinyl COF nanosheet as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of chiral nano materials, and particularly relates to a chiral porphyrinyl COF nanosheet as well as a preparation method and application thereof. The ultrathin chiral porphyrin-based COF nanosheet is prepared through induction of phenylethylamine which is an isomer by adopting an acoustochemical room-temperature ultrasonic synthesis method, is uniform in thickness, has good crystallinity and large transverse size, has opposite circular dichroism (CD) signals, can be used as a chiral solid fluorescence detector, and can be used as a solid fluorescence detector. The method is used for detecting enantiomers of the same chiral compound.

Description

Technical Field

[0001] The invention belongs to the technical field of chiral nanomaterials, and specifically relates to a chiral porphyrin-based COF nanosheet and a preparation method and application thereof. Background Art

[0002] Covalent organic frameworks (COFs) are a new class of lightweight porous materials with large specific surface area, tunable periodic pores, designable and predictable structures, and a long-range ordered thermodynamically stable framework.

[0003] Since its first report in 2005, covalent organic frameworks (COFs) have attracted widespread attention. At the same time, the successful separation of single-layer graphene has provided important inspiration for this field and stimulated the research enthusiasm for the design and synthesis of two-dimensional polymers. Compared with bulk materials, the advantages of ultrathin nanosheets are mainly manifested in: the substrate molecules in the reaction process and the electrons with lower diffusion / transmission barriers can more easily approach the active sites on the surface of the material; it is conducive to the modification and regulation of the material by doping metal atoms or clusters; ultrathin nanosheets have better dispersibility in solvents, which is conducive to chemical reactions such as catalysis or recognition. As an important branch, two-dimensional ultrathin COFs have shown excellent performance in many fields such as drug separation, photoelectrocatalysis, chemical energy storage and semiconductor preparation.

[0004] Chirality, as one of the most important properties of nature, is widely present on Earth. Chiral functionalization is of great significance to biomedicine and materials. Chiral COFs have been shown to be effective in the recognition and separation of chiral substances. In fact, there are many studies on chiral COFs, and their preparation strategies mainly include direct synthesis, chiral induced synthesis, and post-modification. Chiral induction is to change the mirror symmetry of the module by adding chiral molecules to the building blocks. Compared with the direct synthesis method, the chiral induction method gets rid of the difficulty of synthesizing chiral molecules in the early stage; compared with the post-modification method, it avoids the damage to the framework structure caused by subsequent processing; chiral induced synthesis as an ideal method has great exploration value.

[0005] Most of the COFs materials prepared so far are synthesized under solvothermal conditions, and their microscopic morphology mostly presents blocky stacking of sheets. The preparation of chiral COFs is also subject to many limitations: one reason is that the construction of chiral ligands is difficult, and the other reason is that some chiral modules will undergo spatial twisting under high temperature of solvothermal. The large-scale and high-yield preparation of chiral ultra-thin COFs nanosheets is still a huge challenge. This limits the exploration of the unique functions and wide application potential of this type of material. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a chiral porphyrin-based COF nanosheet and a preparation method and application thereof.

[0007] The present invention is achieved through the following technical solutions: A chiral porphyrin-based COF nanosheet having a basic structural unit shown in formula I; , named COF-367.

[0008] Formula I The chiral porphyrin-based COF nanosheet has a uniform thickness of 3-4 nm and a large lateral size of micrometer level.

[0009] The second object of the present invention is to provide a method for preparing the chiral porphyrin-based COF nanosheets, comprising the following steps: S1. Dissolve 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (H2TAPP) and terephthalaldehyde (BPDA) in a mixed solvent of mesitylene and ethanol, and fully mix them by ultrasonic to form a uniform dispersion; the uniformity is conducive to the smooth progress of the subsequent reaction and avoids agglomeration or incomplete reaction.

[0010] S2. Add chiral organic ligand: (S)-(-)-1-phenylethylamine (S-PEA) or (R)-(+)-1-phenylethylamine (R-PEA), shake well to form a uniformly mixed dispersion; S3, add 6 mol / L acetic acid aqueous solution, place in ultrasonic cleaner and continue ultrasonication for 8 hours; S4. After the reaction is completed, solid-liquid separation is performed to obtain a dark purple fluffy solid, which is a chiral porphyrin-based COF nanosheet.

[0011] Furthermore, in step S1, the molar ratio of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin to terephthalaldehyde is 1:2; the volume ratio of mesitylene to ethanol in the mixed solvent is 1:1; and the amount of the mixed solvent added is 1 mL of the mixed solvent for every 0.01 mmol of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin.

[0012] Furthermore, in step S2, the molar ratio of the chiral organic ligand (S)-(-)-1-phenylethylamine or (R)-(+)-1-phenylethylamine to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin is (10-40):1.

[0013] Furthermore, in step S3, the volume ratio of the 6 mol / L acetic acid aqueous solution to the mixed solvent is 1: 10. The acetic acid aqueous solution can not only adjust the pH of the reaction environment but also act as a reaction catalyst to promote the binding of porphyrin and ligand while maintaining the stability of the reactants.

[0014] Further, in step S4, the material is collected by high-speed centrifugation at a speed of 8000 rpm for 5 minutes, and washed with tetrahydrofuran and ethanol for 3-5 times respectively to remove unreacted organic ligand molecules and soluble fragments to obtain a dark purple fluffy solid. The product is separated by high-speed centrifugation and washed with tetrahydrofuran and ethanol to remove unreacted organic ligand molecules and other soluble fragments, thereby improving the purity of the final product and avoiding interference from impurities.

[0015] The present invention also provides the application of the chiral porphyrin-based COF nanosheet as a chiral solid fluorescence detector in identifying the enantiomers of 1,2-cyclohexanediamine.

[0016] Furthermore, by adding an ethanol solution of (1S, 2S)-1,2-cyclohexanediamine or (1R, 2R)-1,2-cyclohexanediamine to the ethanol dispersion of the chiral porphyrin-based COF nanosheets, the fluorescence intensity of the system is enhanced to varying degrees.

[0017] Compared with the prior art, the present invention has the following technical effects: (1) The present invention adopts a sonochemical room temperature ultrasound synthesis method. Compared with the traditional solvothermal method, this method is more economical and convenient, and it also effectively avoids the axial π-π stacking of COFs and the spatial torsion of chiral ligands caused by high temperature. Based on the dynamic reversible properties of the imine bond, chirality is induced in the COF-367 module, and continuous ultrasound is applied at room temperature to achieve the preparation of chiral nanosheets. This method for synthesizing ultrathin two-dimensional chiral porphyrin-based COF nanosheets based on chirality induction under room temperature ultrasound is universal and simple in process.

[0018] (2) The ultrathin chiral porphyrin-based COF nanosheet material is a dark purple fluffy solid with uniform thickness, good crystallinity and large lateral size.

[0019] (3) During the preparation process, the chiral COF-367 nanosheets induced by isomers of phenylethylamine have opposite circular dichroism (CD) signals.

[0020] (4) The chiral porphyrin-based COF nanosheet material can be used as a chiral solid fluorescence detector to detect enantiomers of the same chiral compound.

[0021] (5) The chiral ultrathin nanosheet material has good dispersibility and can be evenly dispersed in ethanol solvent as a chiral fluorescence detector to detect chiral 1,2-cyclohexanediamine, which has the function of identification and identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 HR-TEM image of S40-COF367 NSs obtained in Example 1; Figure 2 HR-TEM image of R40-COF367 NSs obtained in Example 1; Figure 3 FT-IR spectrum of S40-COF367 NSs obtained in Example 1; Figure 4 FT-IR spectrum of R40-COF367 NSs obtained in Example 1; Figure 5 TEM image of S40-COF367 NSs obtained in Example 1; Figure 6 TEM image of R40-COF367 NSs obtained in Example 1; Figure 7 is the SEM image of S40-COF367 NSs obtained in Example 1; Figure 8 is the SEM image of R40-COF367 NSs obtained in Example 1; Fig. 9 is the AFM image of S40-COF367 NSs obtained in Example 1; Fig.10 is the AFM image of R40-COF367 NSs obtained in Example 1; Fig.11 The UV-vis spectrum of S / R40-COF367 NSs obtained in Example 1; Fig.12 The UV-vis spectrum of S / R30-COF367 NSs obtained in Example 2; Fig.13 The UV-vis spectrum of S / R20-COF367 NSs obtained in Example 3; Fig.14 The UV-vis spectrum of S / R10-COF367 NSs obtained in Example 4; Fig.15 The UV-vis spectrum of COF367 NSs obtained in Example 5; Fig.16 The CD spectrum of S / R40-COF367 NSs obtained in Example 1; Fig.17 The CD spectrum of S / R30-COF367 NSs obtained in Example 2; Fig.18 The CD spectrum of S / R20-COF367 NSs obtained in Example 3; Fig.19The CD spectrum of S / R10-COF367 NSs obtained in Example 4; Fig. 20 is the CD spectrum of COF367 NSs obtained in Example 5; Fig.21 is the fluorescence emission spectrum of S40-COF367 NSs dispersion with the addition of (R)-(+)-1-phenylethylamine; Fig. 22 is the fluorescence emission spectrum of S40-COF367 NSs dispersion with the addition of (S)-(-)-1-phenylethylamine; Fig.23 Based on Fig.21 and 22 The fluorescence enhancement curve of S40-COF367 NSs detecting chiral 1,2-cyclohexanediamine is plotted; Fig.24 is the fluorescence emission spectrum of R40-COF367 NSs dispersion with the addition of (R)-(+)-1-phenylethylamine; Fig.25 is the fluorescence emission spectrum of R40-COF367 NSs dispersion with the addition of (S)-(-)-1-phenylethylamine; Fig.26 Based on Fig.24 and 25 The fluorescence enhancement curve of R40-COF367 NSs detecting chiral 1,2-cyclohexanediamine is plotted. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the embodiments.

[0024] Example 1 S1. Weigh two portions of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (6.75 mg, 0.01 mmol) and terephthalaldehyde (4.2 mg, 0.02 mmol) and add them to glass vials respectively. Add 1 mL of a mixed solvent of mesitylene and ethanol respectively and mix them thoroughly by ultrasonication to form a uniformly mixed dispersion.

[0025] S2. Add chiral organic ligands separately: add (S)-(-)-1-phenylethylamine (52 μL, 0.4 mmol) to one portion and (R)-(+)-1-phenylethylamine (52 μL, 0.4 mmol) to the other portion, shake well to form a uniformly mixed dispersion.

[0026] S3. Add 100 μL of 6 mol / L acetic acid aqueous solution respectively, place in an ultrasonic cleaner and continue ultrasonication at room temperature for 8 h.

[0027] S4. After the reaction is completed, the material is collected by high-speed centrifugation at 8000 rpm for 5 minutes, and washed with tetrahydrofuran and ethanol for 3-5 times respectively to remove unreacted organic ligand molecules and soluble fragments to obtain a dark purple fluffy solid, which is a chiral porphyrin-based COF nanosheet material, named S40-COF367 NSs and R40-COF367 NSs.

[0028] Example 2 S1. Weigh two portions of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (6.75 mg, 0.01 mmol) and terephthalaldehyde (4.2 mg, 0.02 mmol) and add them to glass vials respectively. Add 1 mL of a mixed solvent of mesitylene and ethanol respectively and mix them thoroughly by ultrasonication to form a uniformly mixed dispersion.

[0029] S2. Add chiral organic ligands separately: add (S)-(-)-1-phenylethylamine (39 μL, 0.3 mmol) to one portion and (R)-(+)-1-phenylethylamine (39 μL, 0.3 mmol) to the other portion, shake well to form a uniformly mixed dispersion.

[0030] S3. Add 100 μL of 6 mol / L acetic acid aqueous solution respectively, place in an ultrasonic cleaner and continue ultrasonication at room temperature for 8 h.

[0031] S4. After the reaction is completed, the material is collected by high-speed centrifugation at 8000 rpm for 5 minutes, and washed with tetrahydrofuran and ethanol for 3-5 times respectively to remove unreacted organic ligand molecules and soluble fragments to obtain a dark purple fluffy solid, which is a chiral porphyrin-based COF nanosheet material, named S30-COF367 NSs and R30-COF367 NSs.

[0032] Example 3 S1. Weigh two portions of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (6.75 mg, 0.01 mmol) and terephthalaldehyde (4.2 mg, 0.02 mmol) and add them to glass vials respectively. Add 1 mL of a mixed solvent of mesitylene and ethanol respectively and mix them thoroughly by ultrasonication to form a uniformly mixed dispersion.

[0033] S2. Add chiral organic ligands separately: add (S)-(-)-1-phenylethylamine (26 μL, 0.2 mmol) to one portion and (R)-(+)-1-phenylethylamine (26 μL, 0.2 mmol) to the other portion, shake well to form a uniformly mixed dispersion.

[0034] S3. Add 100 μL of 6 mol / L acetic acid aqueous solution respectively, place in an ultrasonic cleaner and continue ultrasonication at room temperature for 8 h.

[0035] S4. After the reaction is completed, the material is collected by high-speed centrifugation at 8000 rpm for 5 minutes, and washed with tetrahydrofuran and ethanol for 3-5 times respectively to remove unreacted organic ligand molecules and soluble fragments to obtain a dark purple fluffy solid, which is a chiral porphyrin-based COF nanosheet material, named S20-COF367 NSs and R20-COF367 NSs.

[0036] Example 4 S1. Weigh two portions of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (6.75 mg, 0.01 mmol) and terephthalaldehyde (4.2 mg, 0.02 mmol) and add them to glass vials respectively. Add 1 mL of a mixed solvent of mesitylene and ethanol respectively and mix them thoroughly by ultrasonication to form a uniformly mixed dispersion.

[0037] S2. Add chiral organic ligands separately: add (S)-(-)-1-phenylethylamine (13 μL, 0.1 mmol) to one portion and (R)-(+)-1-phenylethylamine (13 μL, 0.1 mmol) to the other portion, shake well to form a uniformly mixed dispersion.

[0038] S3. Add 100 μL of 6 mol / L acetic acid aqueous solution respectively, place in an ultrasonic cleaner and continue ultrasonication at room temperature for 8 h.

[0039] S4. After the reaction is completed, the material is collected by high-speed centrifugation at 8000 rpm for 5 minutes, and washed with tetrahydrofuran and ethanol for 3-5 times respectively to remove unreacted organic ligand molecules and soluble fragments to obtain a dark purple fluffy solid, which is a chiral porphyrin-based COF nanosheet material, named S10-COF367 NSs and R10-COF367 NSs.

[0040] Example 5 S1. Add 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (6.75 mg, 0.01 mmol) and terephthalaldehyde (4.2 mg, 0.02 mmol) into a glass vial, add 1 mL of a mixed solvent of mesitylene and ethanol, and mix thoroughly by ultrasonication to form a uniformly mixed dispersion.

[0041] S2. Add 100 μL of 6 mol / L acetic acid aqueous solution and place in an ultrasonic cleaner for continuous ultrasonication at room temperature for 8 h.

[0042] S3. After the reaction is completed, solid-liquid separation is performed to obtain an achiral porphyrin-based COF nanosheet material, named COF367 NSs.

[0043] Chiral COF nanosheets were synthesized by adding chiral modifiers and using room temperature ultrasonic chiral induction. However, the addition of excessive chiral modifiers caused most of the aldehyde ligands in the reaction system to react preferentially with chiral amino groups, thereby forming fragmented organic molecular polymers. Experiments have confirmed that when more than 40 equivalents of (S)-(-)-1-phenylethylamine or (R)-(+)-1-phenylethylamine were added relative to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin, the yield of COF nanosheets was extremely low. Most of the solids obtained after the reaction were dissolved and removed by tetrahydrofuran, and the small amount of material obtained did not have obvious circular dichroism spectral signals.

[0044] Characterize the morphology of the material: The morphology of the materials obtained in Examples 1-5 is the same, and the characteristics are as follows: (1) HR-TEM images of S40-COF367 NSs and R40-COF367 NSs obtained in Example 1 are shown in Figure 1 and Figure 2 As shown, it is shown that the target COF material has been successfully prepared in this embodiment, and the COF material has long-range order.

[0045] (2) The FT-IR spectra of S40-COF367 NSs and R40-COF367 NSs obtained in Example 1 are shown in Figure 3 and Figure 4 As shown, compared with the monomer, the material has -1 Obvious characteristic peaks appeared on the left and right, which were attributed to the C=N stretching vibration peaks, indicating the successful synthesis of COF.

[0046] (3) TEM images of S40-COF367 NSs and R40-COF367 NSs obtained in Example 1 are shown in Figure 5 and Figure 6 As shown, it is demonstrated that both materials have large lateral dimensions of micrometer level and uniform ultra-thin radial thickness.

[0047] (4) The SEM images of S40-COF367 NSs and R40-COF367 NSs obtained in Example 1 are as follows: Figure 7 and Figure 8 As shown, it indicates that the material has ultra-thin radial thickness and good dispersibility.

[0048] (5) The AFM images of S40-COF367 NSs and R40-COF367 NSs obtained in Example 1 are shown in FIG. Fig. 9 and Fig.10 As shown, it is shown that the material has large lateral dimensions reaching the micrometer level and a uniform thickness of about 3-4 nanometers.

[0049] The materials obtained in Examples 1-5 were subjected to UV absorption and CD spectrum tests: (1) The UV-vis spectrum of S / R40-COF367 NSs obtained in Example 1 is as follows Fig.11 As shown, it is shown that the material has good light absorption in the wavelength range of 300-750nm, and the maximum ultraviolet absorption occurs at around 450nm.

[0050] (2) The UV-vis spectrum of S / R30-COF367 NSs obtained in Example 2 is as follows: Fig.12 As shown, it is shown that the material has good light absorption in the wavelength range of 300-750nm, and the maximum ultraviolet absorption occurs at around 450nm.

[0051] (3) The UV-vis spectrum of S / R20-COF367 NSs obtained in Example 3 is as follows: Fig.13 As shown, it is shown that the material has good light absorption in the wavelength range of 300-750nm, and the maximum ultraviolet absorption occurs at around 460nm.

[0052] (4) The UV-vis spectrum of S / R100-COF367 NSs obtained in Example 4 is shown in Fig.14 As shown, it is shown that the material has good light absorption in the wavelength range of 300-750nm, and the maximum ultraviolet absorption occurs at around 430nm.

[0053] (5) The UV-vis spectrum of COF367 NSs obtained in Example 5 is as follows Fig.15 As shown, it is shown that the material has good light absorption in the wavelength range of 300-750nm, and the maximum ultraviolet absorption occurs at around 450nm.

[0054] (6) The CD spectrum of S / R40-COF367 NSs obtained in Example 1 is as follows: Fig.16 As shown, the two materials have CD signals with similar intensities but are mirror images of each other, indicating that the two structures induced by chirality have a certain mirror symmetry in space.

[0055] (7) The CD spectrum of S / R30-COF367 NSs obtained in Example 2 is as follows: Fig.17 As shown, the two materials have CD signals with similar intensities but are mirror images of each other, indicating that the two structures induced by chirality have a certain mirror symmetry in space.

[0056] (8) The CD spectrum of S / R20-COF367 NSs obtained in Example 3 is as follows: Fig.18The two materials have CD signals with similar intensities but are mirror images of each other, indicating that the two structures induced by chirality have a certain mirror symmetry in space.

[0057] (9) The CD spectrum of S / R100-COF367 NSs obtained in Example 4 is shown in Fig.19 As shown, the two materials have CD signals with similar intensities but are mirror images of each other, indicating that the two structures induced by chirality have a certain mirror symmetry in space.

[0058] (10) The CD spectrum of COF367 NSs obtained in Example 5 is shown in Fig. 20 As shown, the material has no obvious CD spectrum signal, indicating that the material prepared without the presence of a chiral inducing agent does not have chiral characteristics.

[0059] Example 6 Application of the S40-COF367 NSs nanosheets obtained in Example 1 for fluorescence detection of chiral substances: Under the condition of excitation wavelength of 415nm, the maximum fluorescence emission peak position of S40-COF367 NSs is at 660nm. S40-COF367NSs nanosheets were dispersed in ethanol. 5μL of 0.1mol / L (1S,2S)-1,2-cyclohexanediamine ethanol dispersion was added to 2.5mL of S40-COF367 NSs ethanol dispersion in batches, and the change of fluorescence intensity was detected. The addition was cumulatively 6 times.

[0060] Under the same conditions, 5 μL of 0.1 mol / L (1R,2R)-1,2-cyclohexanediamine ethanol dispersion was added to 2.5 mL of S40-COF367 NSs ethanol dispersion in batches, and the change in fluorescence intensity was detected in time. A total of 6 additions were made.

[0061] Compare the changes in the maximum fluorescence emission peak of S40-COF367NSs after adding equal amounts of (1S,2S)-1,2-cyclohexanediamine and (1R,2R)-1,2-cyclohexanediamine. Although the position of the maximum fluorescence emission peak has not changed, the intensity of the fluorescence emission peak has been enhanced to varying degrees. For specific results, refer to Fig.21 and 22 , Fig.21 This is the fluorescence emission spectrum of S40-COF367 NSs dispersion after adding (R)-(+)-1-phenylethylamine. Fig. 22The fluorescence emission spectrum of S40-COF367 NSs dispersion with (S)-(-)-1-phenylethylamine is shown, indicating that the fluorescence response of S40-COF367 NSs to (1S,2S)-1,2-cyclohexanediamine and (1R,2R)-1,2-cyclohexanediamine is significantly different.

[0062] The fluorescence enhancement curve was drawn using the maximum fluorescence emission peak intensity at 660 nm, and the equation was defined as I / I0=K EC [X]+1, where I / I0 is the ratio of the maximum fluorescence intensity before and after the addition of the analyte, [X] is the concentration of the analyte, and K EC is the fluorescence enhancement efficiency. Fig.23 For S40-COF367 NSs, the fluorescence enhancement efficiency K EC[（S,R）-Dia] =0.21L / mmol; Under different amounts of (1R,2R)-1,2-cyclohexanediamine, the fluorescence enhancement efficiency K EC[（S,S）-Dia] =0.10L / mmol; selectivity coefficient α (α=K EC[（S,R）-Dia] / K EC[（S,S）-Dia] ) is 2.1. It is proved that S40-COF367 NSs responds more obviously to (1R, 2R)-1,2-cyclohexanediamine.

[0063] Example 7 Application of the R40-COF367 NSs obtained in Example 1 for fluorescence detection of chiral substances: Under the condition of excitation wavelength of 415nm, the maximum fluorescence emission peak position of R40-COF367 NSs is at 660nm. The nanosheets were dispersed in ethanol. 5μL of 0.1mol / L (1S,2S)-1,2-cyclohexanediamine ethanol dispersion was added to 2.5mL of R40-COF367 NSs ethanol dispersion in batches, and the change of fluorescence intensity was detected. The addition was cumulatively 6 times.

[0064] Under the same conditions, 5 μL of 0.1 mol / L (1R,2R)-1,2-cyclohexanediamine ethanol dispersion was added to 2.5 mL of R40-COF367 NSs ethanol dispersion in batches, and the change in fluorescence intensity was detected in time. A total of 6 additions were made.

[0065] Compare the changes in the maximum fluorescence emission peak of R40-COF367NSs after adding equal amounts of (1S,2S)-1,2-cyclohexanediamine and (1R,2R)-1,2-cyclohexanediamine. Although the position of the maximum fluorescence emission peak has not changed, the intensity of the fluorescence emission peak has been enhanced to varying degrees. For specific results, refer to Fig.24 and Fig.25 , indicating that the fluorescence response ability of R40-COF367 NSs to (1S,2S)-1,2-cyclohexanediamine and (1R,2R)-1,2-cyclohexanediamine is significantly different.

[0066] The fluorescence enhancement curve was drawn using the maximum fluorescence emission peak intensity at 660 nm, and the equation was defined as I / I0=K EC [X]+1, where I / I0 is the ratio of the maximum fluorescence intensity before and after the addition of the analyte, [X] is the concentration of the analyte, and K EC is the fluorescence enhancement efficiency. Fig.26 For R40-COF367 NSs, the fluorescence enhancement efficiency K EC[（R,S）-Dia] =0.28L / mmol; Under different amounts of (1R,2R)-1,2-cyclohexanediamine, the fluorescence enhancement efficiency K EC[（R,R）-Dia] =0.13L / mmol; selectivity coefficient α (α=K EC[（R,S）-Dia] / K EC[（R,R）-Dia] ) is 2.2. It is proved that R40-COF367 NSs responds more obviously to (1S, 2S)-1,2-cyclohexanediamine.

Claims

1. A chiral porphyrin-based COF nanosheet, characterized in that: Having a basic structural unit shown in formula I; , named COF-367; Formula I The chiral porphyrin-based COF nanosheets have uniform thickness, a size of 3-4 nm, and a large lateral size of micrometer level.

2. A method for preparing a chiral porphyrin-based COF nanosheet according to claim 1, characterized in that: The steps include: S1. Dissolve 5,10,15,20-tetrakis(4-aminophenyl)porphyrin H2TAPP and terephthalaldehyde BPDA in a mixed solvent of mesitylene and ethanol, and mix them thoroughly by ultrasonication to form a uniform dispersion; S2. Add chiral organic ligand: (S)-(-)-1-phenylethylamine or (R)-(+)-1-phenylethylamine, shake well to form a uniformly mixed dispersion; S3, add 6 mol / L acetic acid aqueous solution, place in ultrasonic cleaner and continue ultrasonication for 8 hours; S4. After the reaction is completed, solid-liquid separation is performed to obtain a dark purple fluffy solid, which is a chiral porphyrin-based COF nanosheet.

3. The method for preparing chiral porphyrin-based COF nanosheets according to claim 1, characterized in that: In step S1, the molar ratio of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin to terephthalaldehyde is 1:2; the volume ratio of mesitylene to ethanol in the mixed solvent is 1:1; and the amount of the mixed solvent added is 1 mL of the mixed solvent for every 0.01 mmol of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin.

4. The method for preparing chiral porphyrin-based COF nanosheets according to claim 1, characterized in that: In step S2, the molar ratio of the chiral organic ligand (S)-(-)-1-phenylethylamine or (R)-(+)-1-phenylethylamine to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin is (10-40):

1.

5. The method for preparing chiral porphyrin-based COF nanosheets according to claim 1, characterized in that: In step S3, the volume ratio of the 6 mol / L acetic acid aqueous solution to the mixed solvent is 1:

10.

6. The method for preparing chiral porphyrin-based COF nanosheets according to claim 1, characterized in that: In step S4, the material was collected by high-speed centrifugation at 8000 rpm for 5 minutes, and washed with tetrahydrofuran and ethanol for 3-5 times respectively to remove unreacted organic ligand molecules and soluble fragments to obtain a dark purple fluffy solid.

7. Use of the chiral porphyrin-based COF nanosheet as claimed in claim 1 in identifying enantiomers of 1,2-cyclohexanediamine.

8. The use of the chiral porphyrin-based COF nanosheet according to claim 7 in identifying enantiomers of 1,2-cyclohexanediamine, characterized in that: When an ethanol solution of (1S, 2S)-1,2-cyclohexanediamine or (1R, 2R)-1,2-cyclohexanediamine is added to the ethanol dispersion of the chiral porphyrin-based COF nanosheets, the fluorescence intensity of the system is enhanced to varying degrees.

Images