Dual-mode luminescent cd-eu-mof materials, methods of making and applications thereof

Abstract

This invention relates to luminescent metal-organic framework materials, and discloses a dual-mode luminescent Cd-Eu-MOF material, its preparation method, and its applications. The Cd-Eu-MOF material is prepared by a solvothermal reaction in a mixed solvent of N,N-dimethylformamide and water using cadmium salts and europium salts as metal sources and 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid as dual ligands. This material exhibits Eu emission under 365 nm ultraviolet light irradiation. 3+ It exhibits characteristic red fluorescence, which transforms into ligand-induced green phosphorescence upon cessation of illumination, thus providing a dual-mode optical signal with both color and temporal dimensions. The preparation process of this invention is simple and it can be used for information encryption and anti-counterfeiting.

Description

Technical Field

[0001] This invention relates to the field of luminescent metal-organic framework materials technology, specifically to a dual-mode luminescent Cd-Eu-MOF material, its preparation method, and its applications. Background Technology

[0002] The security of information during storage and transmission is receiving increasing attention. Traditional information encryption methods mainly rely on graphics, codes, or single optical signals. However, with the development of decoding and copying techniques, their security and anti-counterfeiting capabilities face challenges. Therefore, developing materials capable of outputting distinguishable optical signals under different excitation or time windows is of great significance for improving the level of information encryption.

[0003] Metal-organic frameworks (MOFs) are assembled from metal ions or metal clusters coordinated with organic ligands. Their composition and structure are tunable, making them a platform for constructing optically responsive materials. Lanthanides possess long emission lifetimes, large Stokes shifts, and characteristic narrow-band emission, among which Eu... 3+ They typically exhibit red emission characteristics; organic ligands can also generate an "antenna effect" by absorbing excitation energy and transferring it to the metal center.

[0004] However, the information dimensions that a single emission center or a single emission color can carry are limited. How to simultaneously accommodate the fluorescence signal during ultraviolet irradiation and the phosphorescence signal after irradiation stops in the same MOF material, and obtain a stable dual-mode response through a simple method, is a problem that still needs to be solved when existing luminescent MOFs are used for multi-level information encryption and anti-counterfeiting. Summary of the Invention

[0005] The purpose of this invention is to provide a dual-mode luminescent Cd-Eu-MOF material, its preparation method, and its application, in order to solve the problem that the existing luminescent MOFs have relatively single signal modes.

[0006] On one hand, the present invention provides a dual-mode luminescent Cd-Eu-MOF material, wherein the Cd-Eu-MOF material uses Cd 2+ and Eu 3+ It is a metallic component and contains 2,6-naphthalenedicarboxylic acid ligand and 2,6-pyridinedicarboxylic acid ligand; the Cd-Eu-MOF material emits red fluorescence under 365nm ultraviolet light irradiation and emits green phosphorescence after the ultraviolet light irradiation is stopped.

[0007] Furthermore, the Cd-Eu-MOF material is prepared by a solvothermal reaction of cadmium salt, europium salt, 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid, with a molar ratio of cadmium salt to europium salt of 1:(0.001~0.25) and a molar ratio of 2,6-naphthalenedicarboxylic acid to 2,6-pyridinedicarboxylic acid of 1:1.

[0008] Furthermore, under 365 nm excitation, the Cd-Eu-MOF material exhibits red fluorescence emission peaks at 598 nm, 620 nm, and 705 nm; after excitation is stopped, the Cd-Eu-MOF material exhibits a green phosphorescence emission peak at 515 nm, with a green phosphorescence lifetime of 0.403 s and a visually perceptible green afterglow duration of 1.5 s.

[0009] Secondly, the present invention provides a method for preparing a dual-mode luminescent Cd-Eu-MOF material, comprising the following steps: adding cadmium salt, europium salt, 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid to a mixed solvent composed of N,N-dimethylformamide and deionized water, and carrying out a solvothermal reaction after mixing; and performing solid-liquid separation, washing with anhydrous ethanol and drying the reaction product to obtain the Cd-Eu-MOF material.

[0010] Preferably, the cadmium salt is selected from at least one of cadmium nitrate tetrahydrate, cadmium acetate dihydrate, and cadmium chloride hemipentahydrate, and the europium salt is europium nitrate hexahydrate.

[0011] Preferably, the volume ratio of N,N-dimethylformamide to deionized water is 2:3, the molar ratio of cadmium salt to the total amount of the two organic ligands is 1:1, and the molar ratio of cadmium salt to europium salt is 1:(0.001~0.25).

[0012] Preferably, the mixture is stirred at room temperature for 30 min; the solvothermal reaction temperature is 140 °C and the time is 48–72 h; the reaction product is washed with anhydrous ethanol and then dried at 60 °C for 4 h.

[0013] Thirdly, this invention provides the application of dual-mode luminescent Cd-Eu-MOF materials in information encryption or anti-counterfeiting.

[0014] Fourthly, the present invention provides a method for information encryption using a dual-mode luminescent Cd-Eu-MOF material, comprising the following steps: dispersing the Cd-Eu-MOF material in a dispersion medium composed of ethanol, water and glycerol in a volume ratio of 1:2:2, and sequentially performing magnetic stirring for 30 min and ultrasonic treatment for 30 min to obtain luminescent ink; coating the luminescent ink to form an information pattern; irradiating the information pattern with 365 nm ultraviolet light to read red fluorescent information; stopping the ultraviolet light irradiation and reading green phosphorescent information.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces Cd into the same Cd-Eu-MOF system 2+ Eu 3+And dual ligands to achieve red fluorescence during ultraviolet light irradiation and green phosphorescence after irradiation stops, forming a dual-mode optical response with time and color dimensions.

[0016] (2) The present invention can complete the material preparation by one-step solvothermal method. The steps of raw material addition, solvothermal reaction, washing and drying are clear and the process is relatively simple.

[0017] (3) The Cd of the present invention 2+ As metallic nodes, they are beneficial for forming stable MOF structures and can enhance spin-orbit coupling and promote intersystem crossing through the heavy atom effect; Eu 3+ Provides characteristic red emission; the dual-ligand system provides ligand phosphorescence and Eu-directed emission. 3+ Energy transfer channels.

[0018] (4) The dual-mode signal of the present invention can be used to construct information patterns with different reading timing, and thus has the potential to be applied to multiple information encryption and anti-counterfeiting. Attached Figure Description

[0019] Figure 1 These are powder X-ray diffraction patterns of the Cd-MOF of the present invention at different synthesis times; Figure 2 The images show scanning electron microscope images and elemental distribution diagrams of the Cd-MOF of this invention. Figure 3 Scanning electron microscope image of Cd-1%Eu-MOF invented by Li and superimposed distribution map of Cd and Eu elements; Figure 4 This is a comparison of the fluorescence emission spectra of Cd-MOF and Cd-1%Eu-MOF of the present invention; Figure 5 This is a comparison of the phosphorescence emission spectra of Cd-MOF and Cd-1%Eu-MOF of the present invention; Figure 6 This is a comparison of the phosphorescence lifetime of the Cd-MOF and Cd-1%Eu-MOF of the present invention; Figure 7 This is a schematic diagram of the emission of Cd-MOF, Cd-Eu-MOF and Eu-MOF of the present invention after ultraviolet light is turned on and off; Figure 8 Information encryption patterns constructed using Cd-Eu-MOF and Eu-MOF of the present invention and their display diagrams under different reading conditions. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the invention. Unless otherwise specified, all reagents used are commercially available.

[0021] This invention uses 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid as dual ligands. Upon ultraviolet irradiation, the ligands absorb energy and enter the excited singlet state S1, then transfer to the triplet state T1 via intersystem crossing; part of the energy in the T1 state is released as green phosphorescence, and the other part is transferred to Eu. 3+ of 5 D0 energy level. Eu 3+ Depend on 5 The D0 energy level transitions to 7 A red characteristic emission is produced at the F2 energy level, with the emission at 615–620 nm. 5 D0→ 7 The F2 transition is relatively strong. Cd 2+ The material coordinates with ligands to form a MOF structure and promotes intersystem crossing through the heavy atom effect. As a result, the material emits red fluorescence under 365 nm ultraviolet light and green phosphorescence after the irradiation is stopped.

[0022] The general preparation steps are as follows: Cadmium salt, europium nitrate hexahydrate, 2,6-naphthalenedicarboxylic acid, and 2,6-pyridinedicarboxylic acid are weighed according to the set molar ratio and added to a mixed solvent of deionized water and DMF. The mixture is stirred at room temperature for 30 min. The reaction solution is transferred to a polytetrafluoroethylene-lined reactor and subjected to a solvothermal reaction at 140 °C. After the reaction, the mixture is allowed to cool naturally to room temperature, and solid-liquid separation is performed by centrifugation. The obtained solid is washed with anhydrous ethanol and then dried at 60 °C for 4 h to obtain Cd-Eu-MOF material. The Cd-MOF and Eu-MOF control samples are prepared using the same ligands, solvents, stirring, solvothermal reaction, washing, and drying conditions as the Cd-Eu-MOF material, except for the metal composition.

[0023] The general preparation steps are as follows: Weigh cadmium salt, europium nitrate hexahydrate, 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid according to the set molar ratio, add them to a mixed solvent of deionized water and DMF, and stir at room temperature for 30 min; transfer the resulting reaction solution to a polytetrafluoroethylene-lined reactor and carry out a solvothermal reaction at 140 °C; after the reaction is completed, cool naturally to room temperature, separate the solid and liquid by centrifugation, wash the obtained solid with anhydrous ethanol, and then dry at 60-80 °C to obtain Cd-Eu-MOF material. Cd-MOF and Eu-MOF are completely identical in all conditions except for the metal composition.

[0024] Example 1:

[0025] 0.4 mmol of cadmium nitrate tetrahydrate, 0.0004 mmol of europium nitrate hexahydrate, 0.2 mmol of 2,6-naphthalenedicarboxylic acid, and 0.2 mmol of 2,6-pyridinedicarboxylic acid were added to a mixed solvent consisting of 12 mL of deionized water and 8 mL of DMF, and stirred at room temperature for 30 min. The reaction solution was transferred to a polytetrafluoroethylene-lined reactor and reacted at 140 °C for 72 h. After cooling to room temperature, the resulting solid was washed with anhydrous ethanol and dried at 60 °C for 4 h.

[0026] Example 2:

[0027] Take 0.4 mmol of cadmium nitrate tetrahydrate, 0.02 mmol of europium nitrate hexahydrate, 0.2 mmol of 2,6-naphthalenedicarboxylic acid and 0.2 mmol of 2,6-pyridinedicarboxylic acid, and the remaining preparation steps and conditions are the same as in Example 1.

[0028] Example 3:

[0029] Take 0.4 mmol of cadmium acetate dihydrate, 0.004 mmol of europium nitrate hexahydrate, 0.2 mmol of 2,6-naphthalenedicarboxylic acid and 0.2 mmol of 2,6-pyridinedicarboxylic acid, and the remaining preparation steps and conditions are the same as in Example 1.

[0030] Example 4:

[0031] Take 0.4 mmol of cadmium chloride hemipentahydrate, 0.004 mmol of europium nitrate hexahydrate, 0.2 mmol of 2,6-naphthalenedicarboxylic acid and 0.2 mmol of 2,6-pyridinedicarboxylic acid, and the remaining preparation steps and conditions are the same as in Example 1.

[0032] Characterization and luminescence properties: Figure 1 Powder X-ray diffraction patterns of Cd-MOF at different synthesis times are shown. As the reaction time increases, the crystallinity of the product gradually increases; at synthesis times of 48 h and 72 h, the product shows characteristic diffraction peaks at 2θ of 23.4°, 30.3° and 36.4°.

[0033] Figure 2 and Figure 3 The microstructure and elemental distribution of Cd-MOF and Cd-1%Eu-MOF are shown respectively. Figure 2 Images at different magnifications show the particle morphology and elemental distribution of Cd-MOF; Figure 3 The superimposed distribution of Cd and Eu elements in the sample shows that Eu is distributed in the Cd-1%Eu-MOF particle region, which can serve as evidence of the morphology and elemental distribution of Eu introduced into the material system.

[0034] The emission spectra of the prepared materials were measured using an F-7000 fluorescence spectrometer. The excitation wavelength was 365 nm, and both the excitation and emission slits were 5 nm. The results are as follows: Figure 4 As shown. Compared with Cd-MOF, Cd-1%Eu-MOF exhibits Eu at 598 nm, 620 nm, and 705 nm. 3+ Characteristic emission peaks, respectively attributed to 5 D0→ 7 F1 5 D0→ 7 F2 and 5 D0→ 7 The F4 level transition indicates that Eu 3+ It has been introduced into the material system.

[0035] Figure 5 and Figure 6 The phosphorescence emission spectra and phosphorescence lifetimes of Cd-MOF and Cd-1%Eu-MOF are shown respectively. Figure 5 It can be seen that after excitation is stopped, both Cd-MOF and Cd-1%Eu-MOF exhibit a green phosphorescence emission peak at 515 nm, and the introduction of europium ions reduces the phosphorescence intensity. Figure 6 It can be seen that the phosphorescence lifetime decreased from 0.453 s for Cd-MOF to 0.403 s for Cd-1%Eu-MOF. This is because Eu... 3+ The introduction of the ligand T1 state energy shifts towards Eu 3+ The transfer reduces the energy released through ligand phosphorescence. Figure 7 It can be seen that the green afterglow, which can be seen with the naked eye, can last for 1.5 seconds after the ultraviolet light irradiation is stopped.

[0036] like Figure 7 As shown, Cd-Eu-MOF emits red light when ultraviolet light is on and a green afterglow when ultraviolet light is off. For information encryption, the Cd-Eu-MOF material is added to a dispersion medium of ethanol, water, and glycerol in a volume ratio of 1:2:2. The mixture is first magnetically stirred for 30 minutes, then ultrasonically treated for 30 minutes to obtain a uniformly dispersed luminescent ink. This luminescent ink is then coated to form an information pattern. Figure 8 The diagram illustrates an information pattern constructed using the different luminescence responses of Eu-MOF and Cd-5%Eu-MOF. This information pattern displays red fluorescence during 365 nm UV irradiation and green phosphorescence after UV irradiation is stopped, thus allowing different information to be obtained under different reading conditions or time windows.

[0037] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A dual-mode luminescent Cd-Eu-MOF material, characterized in that, Cd-Eu-MOF materials with Cd 2+ and Eu 3+ It is a metallic component and contains 2,6-naphthalenedicarboxylic acid ligand and 2,6-pyridinedicarboxylic acid ligand; the Cd-Eu-MOF material emits red fluorescence under 365 nm ultraviolet light irradiation and emits green phosphorescence after the ultraviolet light irradiation is stopped.

2. The dual-mode luminescent Cd-Eu-MOF material according to claim 1, characterized in that, Cd-Eu-MOF material is prepared by solvothermal reaction of cadmium salt, europium salt, 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid. The molar ratio of cadmium salt to europium salt is 1:(0.001~0.25), and the molar ratio of 2,6-naphthalenedicarboxylic acid to 2,6-pyridinedicarboxylic acid is 1:

1.

3. The dual-mode luminescent Cd-Eu-MOF material according to claim 1 or 2, characterized in that, Under 365 nm excitation, the Cd-Eu-MOF material exhibits red fluorescence emission peaks at 598 nm, 620 nm, and 705 nm; after excitation is stopped, the Cd-Eu-MOF material exhibits a green phosphorescence emission peak at 515 nm, with a green phosphorescence lifetime of 0.403 s and a visually perceptible green afterglow duration of 1.5 s.

4. A method for preparing a dual-mode luminescent Cd-Eu-MOF material according to any one of claims 1 to 3, characterized in that, The process includes the following steps: adding cadmium salt, europium salt, 2,6-naphthalenedicarboxylic acid and 2,6-pyridinedicarboxylic acid to a mixed solvent composed of N,N-dimethylformamide and deionized water, and then carrying out a solvothermal reaction; the reaction product is subjected to solid-liquid separation, washing with anhydrous ethanol and drying to obtain Cd-Eu-MOF material.

5. The method for preparing dual-mode luminescent Cd-Eu-MOF material according to claim 4, characterized in that, The cadmium salt is selected from at least one of cadmium nitrate tetrahydrate, cadmium acetate dihydrate, and cadmium chloride hemipentahydrate, and the europium salt is europium nitrate hexahydrate.

6. The method for preparing dual-mode luminescent Cd-Eu-MOF material according to claim 5, characterized in that, The volume ratio of N,N-dimethylformamide to deionized water is 2:3, the molar ratio of cadmium salt to the total amount of the two organic ligands is 1:1, and the molar ratio of cadmium salt to europium salt is 1:(0.001~0.25).

7. The method for preparing dual-mode luminescent Cd-Eu-MOF material according to claim 6, characterized in that, After mixing, the mixture was stirred at room temperature for 30 min; the solvothermal reaction was carried out at 140 °C for 48–72 h; the reaction product was washed with anhydrous ethanol and then dried at 60 °C for 4 h.

8. The application of a dual-mode luminescent Cd-Eu-MOF material as described in any one of claims 1 to 3 in information encryption or anti-counterfeiting.

9. A method for information encryption using the dual-mode luminescent Cd-Eu-MOF material according to any one of claims 1 to 3, characterized in that, It includes the following steps: Cd-Eu-MOF material was dispersed in a dispersion medium composed of ethanol, water and glycerol in a volume ratio of 1:2:2, and magnetic stirring and ultrasonic treatment were performed sequentially for 30 min and 30 min respectively to obtain luminescent ink; information pattern was formed by coating with luminescent ink; red fluorescence information was read by irradiating the information pattern with 365 nm ultraviolet light. Stop ultraviolet light irradiation and read green phosphorescence information.

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