A metal-organic framework material with room-temperature phosphorescence and thermally activated delayed fluorescence and a preparation method thereof

Abstract

The application belongs to the technical field of crystalline optical functional materials, and particularly relates to a metal-organic framework material with room-temperature phosphorescence and thermally activated delayed fluorescence and a preparation method thereof. 2+ The doping strategy combines thermally activated delayed fluorescence and phosphorescence in a single material, and the material has time-resolvable multicolor afterglow properties, the preparation method is simple, stable, and has high yield, is environmentally friendly, can be prepared into a light-emitting device and a security material for application, and has wide application value.

Description

Technical Field

[0001] This invention belongs to the field of crystalline optical functional materials technology, specifically relating to a metal-organic framework (MOF) material that combines room-temperature phosphorescence and thermally activated delayed fluorescence and its preparation method. Background Technology

[0002] Molecular-based long afterglow materials possess advantages such as strong structural designability and easy tunability of luminescence energy levels, showing broad application prospects in fields such as light-emitting diodes, sensors, bioimaging, and anti-counterfeiting technologies. Although the development of high-performance afterglow materials has made phased progress, most existing materials only exhibit a single emission mode, which greatly limits their application in fields such as multicolor smart displays and multi-channel information encryption. Simultaneously obtaining thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) in the same material holds promise for achieving multicolor afterglow emission, possessing significant fundamental and applied research value. The tunable lattice structure of metal-organic framework (MOF) materials provides a unique platform for controlling exciton dynamics through crystal engineering. For example, Chinese patent CN202310321831.8 discloses a cadmium metal-organic framework material with long afterglow characteristics, its preparation method and application. Its chemical formula is [Cd2(D-Cam)2(bidpe)2]·6H2O, where bidpe is 4,4'-bis(imidazol-1-yl)diphenyl ether and D-Cam is deprotonated D-camphoric acid. The preparation method is as follows: under solvothermal conditions, a mixed solvent of cadmium nitrate, 4,4'-bis(imidazol-1-yl)diphenyl ether, D-camphoric acid, N,N'-dimethylformamide and water is added to a reaction vessel with a polytetrafluoroethylene liner. The reaction is carried out at 120°C for 48 hours, followed by cooling, washing and drying. Under room temperature conditions and irradiation with a 365 nm ultraviolet lamp, it shows blue fluorescence emission. After the ultraviolet light is turned off, it shows a long green phosphorescence. Chinese patent CN202010025219.2 discloses a ligand compound, a functionalized MOF compound prepared therefrom, its preparation method, and its applications. First, the ligand compound is prepared. Carbazole reacts with 4-bromobenzaldehyde in an inert gas atmosphere via a Buchwald-Hartwig reaction to obtain intermediate 1. Intermediate 1, p-cyanoacetophenone, and an inorganic base are mixed and reacted in an alcoholic organic solvent. Ammonia is then added to the mixture, and after the reaction is complete, the product is separated to obtain intermediate 2. An N-methylpyrrolidone solution containing intermediate 2 is added to an aqueous sodium azide solution, and the mixture is refluxed at 120–150°C with stirring. After the reaction is complete, the product is separated to obtain the ligand compound. The ligand compound is then self-assembled with cadmium chloride to form a functionalized MOF compound, which exhibits high fluorescence quantum yield and long phosphorescence lifetime, with advantages such as high emission intensity and stable luminescence performance. Furthermore, it continues to emit light for a long time even after the excitation source is turned off under vacuum conditions.

[0003] While existing techniques have achieved long-lifetime room-temperature phosphorescence in MOF materials by utilizing the heavy atom effect and coordination bonds of metals to confine phosphorescent molecules, they are limited by the singlet-triplet energy level difference (…). Precise control of the α- and β-intersystem crossing (RISC) processes is still challenging in constructing MOF materials that combine long-lifetime delayed fluorescence and room-temperature phosphorescence. Therefore, it is necessary to develop a simple and effective strategy to construct MOF materials that combine long-lifetime delayed fluorescence and room-temperature phosphorescence in order to obtain multicolor afterglow with tunable excitation wavelength and time-resolved properties. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a metal-organic framework (MOF) material with both room-temperature phosphorescence and thermally activated delayed fluorescence, as well as its preparation method. 5-Methylisophthalic acid is selected as the organic ligand, and it reacts with Cd... 2+ A framework structure was formed through a self-assembly process, and trace amounts of Mn were introduced in situ into the synthetic system. 2+ ;Utilizing Mn 2+ with cd 2+ The ionic radius difference induces controllable shrinkage of the MOF lattice, aiming to achieve precise control of the singlet-triplet energy level difference and antisystem crossing process, and finally obtain a novel MOF material with dual emission characteristics of room temperature phosphorescence and thermally activated delayed fluorescence, as well as tunable excitation wavelength and time-resolved multicolor afterglow, providing new ideas and feasible solutions for the design and synthesis of novel multicolor long afterglow materials.

[0005] To achieve the above objectives, this invention provides a metal-organic framework material that exhibits both room-temperature phosphorescence and thermally activated delayed fluorescence, wherein 5-methylisophthalic acid is used as a functional ligand in combination with Cd... 2+ Self-assembly, with in-situ Mn doping 2+ Prepared from [material name].

[0006] This invention also provides a method for preparing a metal-organic framework material that exhibits both room-temperature phosphorescence and thermally activated delayed fluorescence. The specific preparation process is as follows:

[0007] (1) Add cadmium nitrate, 5-methylisophthalic acid, manganese nitrate and NaOH to a mixed solvent consisting of N,N'-dimethylformamide and deionized water, and then sonicate for 5-30 minutes until dissolved to obtain a homogeneous mixed solution;

[0008] (2) Seal the mixed solution obtained by ultrasound in step (1) in a high-temperature resistant glass bottle or reaction vessel, and heat it in an oven at 80-100°C for 12-24 hours to obtain colorless block crystals, which are metal-organic framework materials with both room temperature phosphorescence and thermally activated delayed fluorescence.

[0009] The ratio of cadmium nitrate, 5-methylisophthalic acid, manganese nitrate and NaOH used in this invention is (0.1-0.3) mmol:(0.1-0.2) mmol:(0.001-0.003) mmol:(0.03-0.08) mmol; the volume ratio of N,N'-dimethylformamide and deionized water is 3:2.

[0010] The ratio of cadmium nitrate, N,N'-dimethylformamide and deionized water is (0.1-0.3) mmol: 3 mL: 2 mL.

[0011] The present invention also provides a metal-organic framework material with both room temperature phosphorescence and thermally activated delayed fluorescence prepared by the above preparation method.

[0012] The Mn of the present invention 2+ The doped cadmium-based MOF material exhibits blue-white fluorescence emission under 365 nm UV light at room temperature. After the 365 nm UV light is turned off, the afterglow changes from deep blue to blue-white and then to yellow-green within 3 seconds. Under 254 nm UV light, it exhibits red fluorescence, and a green afterglow is observed after the UV light is removed. Under 310 nm UV light, it exhibits blue-white fluorescence, and a green afterglow is observed after the 310 nm UV light is turned off. Under 395 nm UV light, it exhibits blue fluorescence, and a deep blue afterglow is observed after the UV light is turned off. The Mn described in this invention... 2+ The doped cadmium-based MOF material exhibits both room-temperature phosphorescence and delayed fluorescence, and its afterglow is wavelength- and time-dependent.

[0013] The present invention also provides the application of the MOF material that combines room temperature phosphorescence and thermally activated delayed fluorescence, which can be used to prepare light-emitting devices or anti-counterfeiting materials.

[0014] Compared with the prior art, the advantages of the present invention are: using 5-methylisophthalic acid as a ligand, and reacting with Cd... 2+ and trace amounts of Mn 2+ A novel MOF material with tunable excitation wavelength and time-resolved afterglow was successfully constructed through self-assembly. (Cd) 2 + The coordination bonds between Cd and organic ligands create a rigid environment for organic molecules, effectively suppressing nonradiative transitions. 2+ The heavy atom effect of Mn can effectively enhance spin-orbit coupling, promote intersystem crossing, and thus obtain long-lifetime room-temperature phosphorescence. Furthermore, due to the heavy atom effect of Mn... 2+ Compared to Cd 2+ With a smaller ionic radius, Mn 2+Trace doping with Mn causes lattice shrinkage, leading to a decrease in singlet energy and a reduction in the singlet-triplet energy level difference, resulting in reverse intersystem crossing and thermally activated delayed fluorescence. Room-temperature phosphorescence and delayed fluorescence exhibit differences in excitation wavelength and decay rate, thus demonstrating tunable excitation wavelength and time-resolved afterglow emission, providing a feasible reference for the design and synthesis of novel multicolor afterglow materials. This invention utilizes Mn... 2+ The doping strategy achieves both thermally activated delayed fluorescence and phosphorescence in a single material, exhibiting multicolor afterglow properties with tunable excitation wavelength and time-resolved characteristics. The preparation method of this invention is simple, stable, and yields high efficiency, and is environmentally friendly. It can be used to prepare light-emitting devices and anti-counterfeiting materials, and has broad application value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the single-crystal X-ray diffraction results of the MOFs involved in this invention, wherein (a) is Mn prepared in Example 1. 2+ (a) is a schematic diagram of the structure of the doped cadmium-based MOF along the a-axis; (b) is a schematic diagram of the structure of the pure cadmium-based MOF along the a-axis.

[0016] Figure 2 This is a schematic diagram of the powder X-ray diffraction results of the MOFs involved in this invention, wherein (a) shows the simulation and experimental results of pure cadmium-based MOFs, and Mn 2+ Experimental results of doped cadmium-based MOFs; (b) is a magnified view of the diffraction angle of 5-15 degrees selected from Figure (a).

[0017] Figure 3 Images of the pure cadmium-based MOF crystal involved in this invention under different wavelengths of ultraviolet light irradiation and after the ultraviolet light is turned off.

[0018] Figure 4 The Mn involved in this invention 2+ Images of doped cadmium-based MOF crystals under different wavelengths of ultraviolet light and after the ultraviolet light is turned off.

[0019] Figure 5 The Mn involved in this invention 2+ Time-resolved emission spectra of doped cadmium-based MOFs (a) and corresponding emission spectra at different delay times (b).

[0020] Figure 6 The Mn involved in this invention 2+ Luminescence decay curves of the doped cadmium-based MOF monitored at 430 nm and 545 nm.

[0021] Figure 7 The Mn involved in this invention 2+ Temperature-delayed spectra of doped cadmium-based MOFs.

[0022] Figure 8 The Mn involved in this invention 2+ Fluorescence spectra of doped cadmium-based MOF and pure cadmium-based MOF under 365 nm excitation. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0024] Example 1

[0025] This embodiment relates to a method for preparing a metal-organic framework material that exhibits both room-temperature phosphorescence and thermally activated delayed fluorescence. The specific steps are as follows:

[0026] (1) Add cadmium nitrate (0.30 mmol), 5-methylisophthalic acid (0.20 mmol), manganese nitrate (0.003 mmol) and NaOH (0.08 mmol) to a mixed solvent consisting of 2 mL deionized water and 3 mL N,N'-dimethylformamide, and sonicate for 10 minutes until dissolved to obtain a homogeneous mixed solution;

[0027] (2) The mixed solution obtained by ultrasonication in step (1) was sealed in a high-temperature resistant glass bottle and reacted in an oven at 80°C for 24 hours. After filtration and separation, it was dried at room temperature. The resulting colorless blocky crystals were Mn. 2+ Doped cadmium-based MOF materials are MOF materials that possess both room-temperature phosphorescence and thermally activated delayed fluorescence.

[0028] The product was characterized by single-crystal X-ray diffraction and powder X-ray diffraction, with Mn-free... 2+ As a control, the results are as follows: Figure 1 and Figure 2 As shown.

[0029] No Mn 2+ The preparation method of doped pure cadmium-based MOFs differs from the above method in that manganese nitrate is not added, while the other steps are the same.

[0030] from Figure 1 Single-crystal X-ray diffraction results show that the pure cadmium-based MOF crystals are crystallized in the orthorhombic crystal system Pna21 space group, possessing a three-dimensional porous structure. 2+ It adopts an octahedral geometry and is coordinated with six oxygen atoms, five of which come from the carboxyl groups of four 5-methylisophthalic acid ligands, and one oxygen comes from an N,N'-dimethylformamide molecule. 2+ The crystal structure of the doped cadmium-based MOF is the same as that of the pure cadmium-based MOF.

[0031] Figure 2 Powder X-ray diffraction results show that Mn 2+ The structure of the doped cadmium-based MOF is consistent with that of the pure cadmium-based MOF, with only slight lattice shrinkage.

[0032] The Mn prepared in this embodiment 2+ Inductively coupled plasma optical emission spectroscopy (ICP-OES) was performed on the doped cadmium-based MOFs, and the results are shown in Table 1. 2+ Replace part of Cd 2+ It was successfully doped into the MOF lattice.

[0033] Table 1 ICP-OES Test Results

[0034]

[0035] Example 2

[0036] This embodiment relates to a method for preparing a metal-organic framework material that exhibits both room-temperature phosphorescence and thermally activated delayed fluorescence. The specific steps are as follows:

[0037] (1) Add cadmium nitrate (0.15 mmol), 5-methylisophthalic acid (0.10 mmol), manganese nitrate (0.001 mmol) and NaOH (0.05 mmol) to a mixed solvent consisting of 2 mL deionized water and 3 mL N,N'-dimethylformamide, and sonicate for 30 minutes until dissolved to obtain a homogeneous mixed solution;

[0038] (2) The mixed solution obtained by ultrasonication in step (1) was sealed in a high-temperature resistant glass bottle and reacted in an oven at 90°C for 18 hours. After filtration and separation, it was dried at room temperature. The resulting colorless blocky crystals were Mn. 2+ Doped cadmium-based MOF materials are MOF materials that possess both room-temperature phosphorescence and thermally activated delayed fluorescence.

[0039] Example 3

[0040] This embodiment relates to a method for preparing a MOF material that combines room-temperature phosphorescence and thermally activated delayed fluorescence. The specific steps are as follows:

[0041] (1) Add cadmium nitrate (0.1 mmol), 5-methylisophthalic acid (0.10 mmol), manganese nitrate (0.001 mmol) and NaOH (0.03 mmol) to a mixed solvent consisting of 2 mL deionized water and 3 mL N,N'-dimethylformamide, and sonicate for 5 minutes until dissolved to obtain a homogeneous mixed solution;

[0042] (2) The mixed solution obtained by ultrasonication in step (1) was sealed in a high-temperature resistant glass bottle and reacted in an oven at 100°C for 12 hours. After filtration and separation, it was dried at room temperature. The resulting colorless blocky crystals were Mn. 2+ Doped cadmium-based MOF materials exhibit both room-temperature phosphorescence and thermally activated delayed fluorescence.

[0043] Example 4

[0044] This embodiment is based on the Mn prepared in Example 1. 2+ Determination of photoluminescence properties of doped cadmium-based MOF materials.

[0045] 1. Emission and afterglow phenomenon under ultraviolet light irradiation of different wavelengths and after removal

[0046] (1) Emission under 365 nm wavelength ultraviolet lamp irradiation and afterglow phenomenon after ultraviolet lamp removal

[0047] Mn prepared in Example 1 2+ The doped cadmium-based MOF exhibits blue-white fluorescence under 365 nm ultraviolet light at room temperature. After the ultraviolet light is turned off, the afterglow changes from deep blue to blue-white and then to yellow-green within 3 seconds. Figure 4 As shown, this illustrates the Mn prepared according to the present invention. 2+ The doped cadmium-based MOFs exhibit time-dependent multicolor afterglow emission behavior.

[0048] Pure cadmium-based MOFs were used as a control. Pure cadmium-based MOFs exhibited blue emission under 365 nm UV light irradiation, and showed a yellow-green afterglow after the excitation source was removed, as shown in the following experiment. Figure 3 As shown.

[0049] (2) Emission under excitation by ultraviolet light of other wavelengths and afterglow phenomenon after removal of ultraviolet lamp

[0050] Mn prepared in Example 1 2+ The doped cadmium-based MOF material exhibits red fluorescence under 254 nm UV light at room temperature, followed by a 1.5-second green afterglow after the UV light is removed; it exhibits blue-white fluorescence under 310 nm UV light, followed by a 9-second green afterglow after the UV light is turned off; and it exhibits blue fluorescence under 395 nm UV light, followed by a 1.5-second deep blue afterglow after the UV light is turned off. Figure 4 As shown. It can be seen that Mn 2+ Doped cadmium-based MOF materials exhibit wavelength-dependent afterglow characteristics.

[0051] Using pure cadmium-based MOF as a control, such as Figure 3As shown, under UV light irradiation at 254 nm, it exhibits blue-white fluorescence, with a green afterglow after the UV light is turned off; under UV light irradiation at 310 nm, it exhibits blue fluorescence, with a green afterglow after the UV light is turned off; and under UV light irradiation at 395 nm, it exhibits blue fluorescence, with a yellow-green afterglow after the UV light is turned off. It is evident that the fluorescence color after irradiation with UV light of different wavelengths is blue, and the afterglow after the UV light is turned off is either green or yellow-green.

[0052] In summary, undoped pure cadmium-based MOF crystals exhibit only green or yellowish-green room-temperature phosphorescence, while Mn-doped MOF crystals... 2+ Subsequently, deep blue delayed fluorescence was generated. The coexistence of the two luminescence mechanisms induced excitation wavelength and time-dependent multicolor afterglow.

[0053] 2. Time-resolved emission spectrum under 365 nm ultraviolet light excitation

[0054] like Figure 5 As shown, the Mn prepared in Example 1 2+ Time-resolved emission spectra of doped cadmium-based MOFs after excitation with 365 nm ultraviolet light: 10 ms after the ultraviolet lamp is turned off, the main emission peak is located at 430 nm, corresponding to a deep blue afterglow; 500 ms after the ultraviolet lamp is turned off, the emission intensities at 430 and 545 nm are similar, corresponding to a bluish-white afterglow; 1000 ms after the ultraviolet lamp is turned off, the main emission peak is located at 545 nm, corresponding to a yellowish-green afterglow.

[0055] Therefore, Mn 2+ The thermally activated delayed fluorescence emission peak of the doped cadmium-based MOF is around 430 nm, while the room-temperature phosphorescence emission peak is around 545 nm. Due to the difference in intensity and decay rate between the two, delayed fluorescence is dominant initially, but phosphorescence emission becomes dominant over time.

[0056] 3. Life test

[0057] Figure 6 Mn in Example 1 2+ The long-lifetime emission decay curves of cadmium-doped MOFs under 365 nm UV excitation show a delayed fluorescence lifetime of 125.5 ms at 430 nm and a phosphorescence lifetime of 174.7 ms at 545 nm. The difference in decay rates between the two emission peaks endows the material with time-resolved afterglow emission characteristics.

[0058] 4. Research on luminescence mechanism

[0059] Figure 7 For Mn 2+The temperature-delayed spectrum of the doped cadmium-based MOF shows that the emission at 480 nm-600 nm is significantly enhanced during cooling, while the emission at 430 nm is significantly enhanced with increasing temperature in the range of 80-300 K, which correspond to the typical characteristics of phosphorescence and thermally activated delayed fluorescence, respectively.

[0060] Figure 8 For Mn 2+ Fluorescence spectra of doped cadmium-based MOFs and pure cadmium-based MOFs under 365 nm excitation. Due to Mn 2+ The ionic radius is smaller than that of Cd. 2+ This leads to lattice contraction, thus requiring the doping of trace amounts of Mn. 2+ The fluorescence emission peak is redshifted by approximately 25 nm. This redshift significantly reduces the energy level difference between the singlet and triplet states, allowing triplet excitons to be converted into singlet excitons via antisystem crossing, thereby generating thermally activated delayed fluorescence.

Claims

1. A method for preparing a metal-organic framework material exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence, characterized in that, The specific preparation process is as follows: (1) Add cadmium nitrate, 5-methylisophthalic acid, manganese nitrate and NaOH to a mixed solvent consisting of N,N'-dimethylformamide and deionized water, and then sonicate to dissolve to obtain a homogeneous mixed solution; (2) Seal the mixed solution obtained by ultrasound in step (1) in a high-temperature resistant glass bottle or reaction vessel, and heat it in an oven to obtain colorless block crystals, which are metal-organic framework materials with both room temperature phosphorescence and thermally activated delayed fluorescence.

2. The method for preparing a metal-organic framework material exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence according to claim 1, characterized in that, The ratio of cadmium nitrate, 5-methylisophthalic acid, manganese nitrate and NaOH is (0.1-0.3) mmol: (0.1-0.2) mmol: (0.001-0.003) mmol: (0.03-0.08) mmol.

3. The method for preparing a metal-organic framework material exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence according to claim 1, characterized in that, The volume ratio of N,N'-dimethylformamide to deionized water is 3:

2.

4. The method for preparing a metal-organic framework material exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence according to claim 1, characterized in that, The ultrasound time for step (1) is 5-30 minutes.

5. The method for preparing a metal-organic framework material exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence according to claim 1, characterized in that, Step (2) The heating time is 12-24 hours and the heating temperature is 80-100°C.

6. The metal-organic framework material with both room-temperature phosphorescence and thermally activated delayed fluorescence prepared by the preparation method according to any one of claims 1-5.

7. The metal-organic framework material of claim 6, exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence, characterized in that... The material exhibits both room-temperature phosphorescence and delayed fluorescence, with its afterglow exhibiting excitation wavelength and time dependence.

8. The metal-organic framework material of claim 6, possessing both room-temperature phosphorescence and thermally activated delayed fluorescence, characterized in that, The metal-organic framework material exhibiting both room-temperature phosphorescence and thermally activated delayed fluorescence displays blue-white fluorescence emission under 365 nm UV light at room temperature. After the 365 nm UV light is turned off, the afterglow changes from deep blue to blue-white and then to yellow-green. Under 254 nm UV light, it exhibits red fluorescence, and after the UV light is removed, it shows a green afterglow. Under 310 nm UV light, it exhibits blue-white fluorescence, and after the 310 nm UV light is turned off, it shows a green afterglow. Under 395 nm UV light, it exhibits blue fluorescence, and after the UV light is turned off, it shows a deep blue afterglow.

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