A novel photochromic metal-organic framework material and preparation method and use thereof

Abstract

The application discloses a novel photochromic metal-organic framework material and a preparation method and application thereof, and belongs to the technical field of inorganic-organic hybrid material synthesis. The chemical formula of the benzophenone metal-organic framework material is [Zn4(mu2-O)(mu3-O)(cdip)2(DMF)] n , the cell parameters are alpha=115.459(5)°, beta=93.033(4)° and gamma=91.808(4)°. The application further provides a preparation method of the benzophenone metal-organic framework material. The preparation method of the benzophenone metal-organic framework material is simple, and the material is responsive to ultraviolet light and X-ray irradiation; obvious color changes occur under ultraviolet light and X-ray irradiation. The printing and erasing process of the erasable inkless printing paper prepared based on the material is safe and pollution-free, and has good definition.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synthesis of inorganic-organic hybrid materials, and particularly relates to a benzophenone metal-organic framework material with dual response to ultraviolet light and X-rays and a preparation method thereof. TECHNICAL BACKGROUND

[0002] Stimuli-responsive metal-organic frameworks (MOFs) can produce reversible color changes under external stimuli (light, heat, pH), and are widely used in the fields of smart materials and renewable energy. Due to the advantages of remote controllability, instantaneity, safety and non-pollution of light, light-responsive MOFs have great advantages in applications such as sensing, advanced detection and inkless printing. (See D. Yan, Z.-F. Wang and Z.-J. Zhang, Acc. Chem. Res., 2022, 55, 1047-1058. L. E. Kreno, K. Leong, O. K. Farha, M. Allendorf, R. P. Van Duyne and J. T. Hupp, Chem. Rev., 2012, 112, 1105-1125. H.-Y. Li, S.-N. Zhao, S.-Q. Zang and J. Li, Chem. Soc. Rev., 2020, 49, 6364-6401.) One feasible method to construct photochromic MOFs is to introduce potential photochromic organic molecules into the framework. Although a large number of photochromic MOFs have emerged in recent years, the construction of them excessively relies on traditional photochromic organic molecules such as diarylethene, viologen and naphthalimide. Therefore, it is urgent to explore new active molecules to construct new photochromic MOFs and enrich the types of such materials. (See B. J. Furlong and M. J. Katz, J. Am. Chem. Soc., 2017, 139, 13280-13283. S.-L. L, M. Han, Y. Zhang, G.-P. Li, M. Li, G. He and X.-M. Zhang, J. Am. Chem. Soc., 2019, 141, 12663-12672. S. Guha, F. S. Goodson, S. Roy, L. J. Corson, C. A. Gravenmier and S. Saha, J. Am. Chem. Soc., 2011, 133, 15256-15259.) The benzophenone molecule (BP) can form a stable charge-separated state BP ·-It is a promising photoactive molecule.(See S.Y. Lee, T. Yasuda, Y.-S. Yang, Q. Zhang and C. Adachi, Angew. Chem. Int. Ed., 2014, 53, 6402-6406.) At the same time, the coordination framework has a modulation effect on the electron transfer process, so the introduction of BP units into MOFs can produce distinctive photochromic properties. SUMMARY

[0003] The purpose of the present application is to provide a novel photochromic metal-organic framework (MOF) material and a preparation method thereof. The erasable inkless printed paper prepared based on the material has good clarity.

[0004] The benzophenone-based photochromic MOF material in the present application has the chemical formula [Zn4(μ2-O)(μ3-O)(cdip)2(DMF)] n , wherein H2cdip is 5,5'-carbonyldiphthalic acid, cdip is obtained by losing two protons from H2cdip, and DMF is N,N'-dimethylformamide. The benzophenone-based photochromic MOF material in the present application is crystallized in a triclinic P1 space group, and the unit cell parameters are α = 115.459 (5) °, β = 93.033 (4) °, γ = 91.808 (4) °.

[0005] The crystal structure of the benzophenone-based photochromic MOF material in the present application is described as follows: the asymmetric unit contains two cdip 4- organic ligands, four Zn 2+ , one μ2-O (O10), one μ3-O (O11), and one coordinated DMF molecule. Among them, Zn 2+ adopts two different coordination modes, Zn1, Zn2, and Zn3 are respectively coordinated with four O atoms to form a tetrahedral geometry, and Zn4 is coordinated with six O atoms to form an octahedral geometry. μ2-O, μ3-O, and four bidentate bridging carboxylate groups connect Zn1, Zn2, Zn3, and Zn4 together to form a [Zn4O 15 ] secondary building unit (SBU). Each SBU is connected by eight cdip 4- organic ligands and extends along the a, b, and c axes to form a three-dimensional organic framework structure with a double-walled pore. The porosity estimated using PLATON software is 40.2%

[0006] The preparation method of the benzophenone-based photochromic MOF material and the inkless printed paper thereof in the present application mainly includes the following steps:

[0007] (1) Preparation of benzophenone-based photochromic MOF (abbreviated as 1): H4cdip, Zn(NO3)2.6H2O and 2,3,5,6-tetrafluoroterephthalic acid were added to a mixed solvent of DMF, ethanol and water. The mixture was placed in an oven at 85°C for constant temperature heating for 72h. After the reaction was completed, it was cooled to room temperature to obtain colorless block photochromic MOF crystal material. The material was washed with DMF and dichloromethane and then dried. The molar ratio of H4cdip to Zn(NO3)2.6H2O was 1:2:1, and the volume ratio of DMF, ethanol and water was 4:2:1.

[0008] (2) Obtaining MOF (abbreviated as 1-MeOH) after solvent exchange: the MOF material obtained in step (1) was transferred to anhydrous methanol solvent for soaking, and then activated at 80°C for 8h to obtain 1-MeOH, the molecular formula of which is [Zn4(μ2-O)(μ3-O)(cdip)2] n .

[0009] (3) Preparation of erasable inkless printed paper: filter paper was used as the bottom layer, and the photochromic MOF crystal material and hydroxyethyl cellulose were uniformly suction filtered onto the filter paper to obtain the erasable inkless printed paper.

[0010] The advantages of the present application are: the present application first synthesizes benzophenone-based MOF with photochromic properties; the benzophenone-based photochromic MOF material exhibits obvious color change under ultraviolet and X-ray irradiation, and has good reversibility; at the same time, the fluorescence intensity of the benzophenone-based MOF material can be regulated by ultraviolet light. The erasable inkless printed paper prepared based on the benzophenone-based photochromic MOF material has good clarity. The benzophenone-based photochromic MOF material provided by the present application not only enriches the types of photochromic materials, but also has important reference significance for constructing new photochromic MOF. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 、 2 is a crystal structure diagram of the benzophenone-based photochromic MOF material.

[0012] Figure 3 is a crystal structure diagram of 1-MeOH after removing the solvent from the benzophenone-based photochromic MOF material.

[0013] Figure 4 is a coloring diagram of the benzophenone-based photochromic MOF material under different light irradiation times and a fading diagram of the sample after color change under heating and dark conditions.

[0014] Figure 5is the color change graph of the benzophenone-based photochromic MOF material before and after X-ray irradiation.

[0015] Figure 6 is the UV-Vis absorption spectrum of the benzophenone-based photochromic MOF crystal under different light irradiation times.

[0016] Figure 7 is the UV-Vis absorption spectrum of the benzophenone-based photochromic MOF material after alternating UV irradiation and dark storage.

[0017] Figure 8 is the fluorescence spectrum of the benzophenone-based photochromic MOF material under different light irradiation times.

[0018] Figure 9 is the X-ray powder diffraction pattern (XRD) of the benzophenone-based photochromic MOF material before and after light irradiation.

[0019] Figure 10 is the field emission electron microscope image (SEM) of the benzophenone-based photochromic MOF material before and after light irradiation.

[0020] Figure 11 is the color change graph inside the crystal of the benzophenone-based photochromic MOF material before and after light irradiation.

[0021] Figure 12 is the electron paramagnetic resonance (EPR) spectrum of the benzophenone-based photochromic MOF material before and after light irradiation.

[0022] Figure 13 is the UV-Vis absorption spectrum of the benzophenone-based photochromic MOF crystal after removing the solvent and irradiating with UV light.

[0023] Figure 14 is the flowchart of preparing erasable inkless printed paper using the photochromic benzophenone-based photochromic MOF material.

[0024] Figure 15 is the printing and erasing process diagram of preparing erasable inkless printed paper using the photochromic benzophenone-based photochromic MOF material.

[0025] Figure 16 is the effect diagram of the erasable inkless printed paper prepared based on the benzophenone-based photochromic MOF material under different light irradiation times. DETAILED DESCRIPTION

[0026] Example 1:

[0027] (1) Synthesis of benzophenone-based photochromic MOF (1) material

[0028] 9.0 mg H4cdip, 18.6 mg Zn(NO3)2·6H2O, 6.0 mg 2,3,5,6-tetrafluoroterephthalic acid, 2 mL DMF, 1 mL ethanol, and 0.5 mL water were added to a 10 mL glass vial and mixed thoroughly. The vial was sealed and heated in an oven at 85 °C for 72 h. After the reaction was complete, the mixture was cooled to room temperature to obtain colorless blocky crystals. The obtained blocky crystals were washed with DMF and dichloromethane and then dried under vacuum to obtain the target product.

[0029] (2) Obtaining MOF(1-MeOH) after removing DMF

[0030] The above MOF material was transferred to anhydrous methanol solvent and immersed, with the methanol being replaced three times a day for three days. It was then activated at 80°C for 8 hours to obtain MOF(1-MeOH).

[0031] (3) Preparation of printing paper

[0032] The well-dispersed benzophenone-based photochromic MOF powder was evenly coated onto filter paper. After the paper dried, a layer of hydroxyethyl cellulose protective film was applied to the printing media layer.

[0033] The present invention uses the following instruments or methods to characterize and test the properties of materials.

[0034] The color changes of the benzophenone-based photochromic MOF material before and after ultraviolet light and X-ray irradiation, the ultraviolet-visible absorption and fluorescence intensity at different irradiation times, and the X-ray powder diffraction, field emission scanning electron microscopy, and electron paramagnetic resonance before and after irradiation were tested. The benzophenone-based photochromic MOF material prepared in this invention changed from colorless to yellow after 5 minutes of ultraviolet light irradiation. The color-changed MOF material could recover its initial color after heating at 100℃ for 20 minutes, and it could also return to colorless after being placed in the dark for 12 hours. Figure 4 The benzophenone-based photochromic MOF material prepared in this invention exhibits X-ray fluorescence (XRF) activity. After irradiation for 20 minutes, it changed from colorless to brown. Figure 5 The UV-Vis absorption spectra of the photochromic MOF material prepared in this invention were measured using a Shimadzu UV-2600 UV-Vis spectrophotometer. The UV-Vis absorption spectra under different illumination times are shown below. Figure 6The MOF material before irradiation has no obvious absorption of visible light, and after 10 seconds of ultraviolet irradiation, there is obvious absorption near 420 nm, and with the increase of irradiation time, the absorption value gradually increases, and after 20 minutes of irradiation, the absorption basically reaches saturation. The coloring-decoloring process of the photochromic MOF material prepared by the application can be at least cycled four times through irradiation-heating Figure 7 The fluorescence spectrum of the photochromic MOF material prepared by the application is tested by using a Hitachi F-7000 fluorescence spectrometer. The fluorescence spectra of different irradiation times are as shown in Figure 8 An intense fluorescence emission peak at 475 nm is shown (drawn by using Origin software), and after ultraviolet irradiation, the fluorescence emission peak intensity at 475 nm rapidly weakens, reaches saturation after 10 minutes, and a new absorption peak at 495 nm appears.

[0035] The powder X-ray diffraction (PXRD) pattern of the photochromic MOF material prepared by the application is collected on a Rigaku X-ray instrument, and Cu-Kα rays are used The X-ray diffraction pattern is as shown in Figure 9 The results show that the crystal structure does not change obviously before and after irradiation. The morphology of the photochromic MOF material prepared by the application is photographed by a field emission scanning electron microscope (JSM-7800F). As shown in Figure 10 The external morphology of the MOF material before and after irradiation does not change obviously. The internal color of the crystal of the photochromic MOF material prepared by the application after ultraviolet irradiation is as shown in Figure 11 The internal and external colors of the crystal are consistent, which excludes the surface reaction of photochromism. The electron paramagnetic resonance spectrum of the photochromic MOF material prepared by the application before and after irradiation is as shown in Figure 12 The electron paramagnetic resonance spectrum is collected by using a Bruker EMX-6 / 1 electron paramagnetic resonance spectrometer at an X-band of 9.854 GHZ magnetic field, and an obvious free radical signal peak appears at g=2.0012 after irradiation. It is proved that the photochromism of the MOF material is because the photo-induced electron transfer produces a ketone free radical anion. The single crystal X-ray (SCXRD) data of the MOF material prepared by the application and the MOF material after removing the solvent are collected on a Rigaku SuperNova CCD diffractometer, the temperature is 293K, Cu Kα radiation The multi-scan mode is adopted. The single crystal data of the MOF material show that the distance between the oxygen atom in the benzophenone unit and the nitrogen atom in the DMF is 4.440(8) (N1-O5) and 4.518(8) (N1-O16), which meets the electron transfer conditions of the UV and X-ray dual-responsive material. It is preliminarily proved that the nitrogen atom in DMF is the electron donor (A), and the oxygen atom in the benzophenone unit is the electron acceptor (D). To further prove the above reasoning, we obtained 1-MeOH after removing DMF. As shown in Figure 3 , no coordinated DMF appears in the 1-MeOH single crystal structure. The sample after removing DMF has no color change after irradiation under UV light for 20 minutes, and no additional absorption band is observed in the UV-Vis absorption spectrum (Fig. 2b, plotted using Origin software). The results verify the important role of DMF in the electron transfer process. Figure 13

[0036] The benzophenone-based MOF material changes color sensitively, reversibly and obviously under UV light irradiation, which is an ideal erasable inkless printing material. Figure 14 is a flow chart for preparing erasable inkless printing paper based on the benzophenone-based photochromic MOF material. The printing paper mainly consists of three layers. The uppermost layer is a protective layer, the main component of which is hydroxyethyl cellulose; the middle layer is a color-changing layer, the main component of which is a photochromic MOF material; and the lower layer is filter paper.

[0037] Figure 15 The printing-erasing effect diagram of the erasable inkless printing paper based on the benzophenone-based photochromic MOF material prepared by light-dark treatment is shown. Figure 16 The printing effect diagram of the erasable inkless printing paper based on the benzophenone-based photochromic MOF material prepared under different light irradiation times is shown.​

Claims

1. A photochromic metal-organic framework material, characterized in that: This material belongs to the metal-organic framework family, and its composition is represented by the chemical formula: [Zn4(μ2-O)(μ3-O)(cdip)2(DMF)] n H4cdip is 5,5′-carbonyl diisophthalic acid, cdip is obtained by losing four protons from H4cdip, DMF is N,N′-dimethylformamide, and the smallest asymmetric unit contains two cdip units. 4- Organic ligands, four Zn 2+ One μ2-O, one μ3-O, and one coordinated DMF molecule.

2. The photochromic metal-organic framework material as described in claim 1, characterized in that: The material is crystallized in the triclinic P1 space group with cell parameters a = 9.8670(5) Å, b = 12.0062(7) Å, c = 13.1276(6) Å, α = 115.459(5)°, β = 93.033(4)°, and γ = 91.808(4)°.

3. The photochromic metal-organic framework material as described in claim 1, characterized in that: Zn 2+ Two different coordination modes are adopted: Zn1, Zn2 and Zn3 coordinate with four O atoms to form a tetrahedral geometry with four coordination atoms, and Zn4 coordinates with six O atoms to form a octahedral geometry with six coordination atoms.

4. The photochromic metal-organic framework material as described in claim 1, characterized in that: μ2-O, μ3-O, and four bidentate bridging carboxylic acid groups link Zn1, Zn2, Zn3, and Zn4 together to form [Zn4O]. 15 Secondary building blocks (SBUs) consist of eight CDIPs. 4- Organic ligands are linked and extend along axes a, b, and c respectively to form a three-dimensional organic framework structure with double-walled pores and a porosity of 40.2%.

5. A method for preparing erasable inkless printing paper based on the photochromic metal-organic framework material according to any one of claims 1-4, comprising the following steps: (1) Preparation of benzophenone-based photochromic MOF, abbreviated as 1: H4cdip, Zn(NO3)2·6H2O and 2,3,5,6-tetrafluoroterephthalic acid were added to a mixed solvent of DMF, ethanol and water. The mixture was placed in an oven at 85 ℃ and heated at a constant temperature for 72 h. After the reaction was completed, it was cooled to room temperature to obtain a colorless blocky photochromic metal-organic framework crystal material. The material was washed with DMF and dichloromethane and then dried. The molar ratio of H4cdip, Zn(NO3)2·6H2O and 2,3,5,6-tetrafluoroterephthalic acid was 1:2:1; the volume ratio of DMF, ethanol and water was 4:2:

1. (2) Preparation of erasable inkless printing paper: Using filter paper as the bottom layer, benzophenone-based photochromic MOF and hydroxyethyl cellulose are uniformly filtered onto the filter paper to obtain erasable inkless printing paper.

6. The preparation method according to claim 5, characterized in that: The benzophenone-based photochromic MOF exhibits dual responses to ultraviolet light and X-rays. After 5 minutes of ultraviolet light irradiation, its color changes from colorless to yellow, and after 20 minutes of X-ray irradiation, it changes from colorless to brown. The color change process is reversible.

7. The use of the photochromic metal-organic framework material according to any one of claims 1-4, characterized in that: Photochromic metal-organic framework materials are used to prepare erasable inkless printing paper.

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