Thermal activation delayed fluorescence metal-organic framework material with pressure response and preparation method thereof

Abstract

The invention discloses a thermal activation delayed fluorescence metal-organic framework material with pressure response. The thermal activation delayed fluorescence metal-organic framework material is a compound prepared from an acceptor ligand, a donor ligand and metal ions in a molar ratio of (1-2): (1-2): 4, the receptor ligand is selected from polypyridyl ring compounds with different central N atom numbers and electron deficiency; the donor ligand is triphenylamine tricarboxylic acid (H3TCA); in the prepared compound, acceptor ligands and donor ligands are arranged in a face-to-face stacking manner. The high-purity crystalline MOFs material is constructed by selecting a donor ligand and an acceptor ligand with specific structures. Wherein the donor ligand and the acceptor ligand are arranged in a face-to-face stacking manner, a good space-crossing charge transfer effect is formed, the energy level difference delta EST is reduced by spatially separated HOMO and LUMO tracks, and effective thermal activation delayed fluorescence emission is realized.

Description

(1) Technical field:

[0001] The invention relates to a metal-organic framework material, in particular to a heat-activated delayed fluorescence metal-organic framework material with pressure response and a preparation method thereof. (2) Background technology:

[0002] Thermally activated delayed fluorescence (TADF) materials have been widely used in organic light-emitting diodes (OLEDs) due to their unique potential to achieve 100% exciton utilization efficiency. Efficient TADF emission requires triplet excitons (T1) to undergo a reverse intersystem crossing process (RISC) to transition to a singlet state (S1), where a small singlet-triplet energy level difference (ΔE ST ) is a prerequisite for efficient spin flip. In donor-acceptor (DA) systems, spatial separation of the highest occupied molecular orbital (HOMO, located on the donor) and the lowest unoccupied molecular orbital (LUMO, located on the acceptor) by twisting the donor-acceptor structure has been widely used to reduce ΔE ST However, the development of traditional through-bond charge transfer (TBCT)-TADF materials faces limitations due to the need for complex molecular design and time-consuming organic synthesis. In contrast, through-space charge transfer (TSCT)-TADF materials can not only achieve spatial separation of donors and acceptors to reduce HOMO-LUMO orbital overlap and small ΔE ST , and the unique spatial conformational advantages can be used to achieve stimulus-responsive regulation of TADF properties. Although TSCT-TADF materials have developed rapidly and small molecule-based material systems dominate this field, they are still plagued by synthetic complexity and limited precision in regulating photophysical properties. In addition, due to weak spatial DA coupling and severe non-radiative attenuation caused by molecular motion, traditional TSCT-TADF materials are often limited to low luminescence efficiency. In addition, most examples of TADF materials typically exhibit fixed emission wavelengths and single photophysical properties. For example, delayed lifetime and luminescence quantum yield.

[0003] Metal-organic frameworks (MOFs) have become promising candidates for realizing TSCT-TADF due to their crystalline properties, well-defined structures, and modular tunability. Compared with small-molecule TADF materials, TSCT-TADF-MOFs can be constructed through coordination assembly, avoiding complex organic chemical synthesis while ensuring good crystallinity and stability of the material. In addition, the rigid framework of MOFs helps to suppress molecular vibrations, thereby reducing non-radiative attenuation and improving luminescence efficiency. More importantly, the ligand components and metal nodes of MOFs can be flexibly controlled, providing an ideal platform for studying structure-property relationships and facilitating the regular regulation of material properties. In addition, the structure of MOFs is easily affected by conditions such as synthesis temperature, solvent, and pressure, thereby regulating the photophysical properties of the material. All of these contribute to the flexible regulation of the TADF properties of the material. (3) Summary of the invention:

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a pressure-responsive thermally activated delayed fluorescence metal-organic framework material and a preparation method thereof, and to design and construct a series of metal-organic framework materials with flexibly tunable thermally activated delayed fluorescence properties, wherein the emission characteristics of TADF are based on the cross-space charge transfer between the donor and acceptor ligands in the framework. During the synthesis process, different auxiliary solvents and acceptor ligands with adjustable components are used to change the structure and luminescence properties of the material. In addition, the introduction of electron-rich ligands with a flexible and flexible skeleton as donors can not only form a good space charge transfer with the acceptor ligands, but also give the material a stimulus-responsive property to pressure, providing a new solution to the problem that such materials are difficult to synthesize and their properties are difficult to flexibly adjust.

[0005] The technical solution of the present invention is a pressure-responsive thermally activated delayed fluorescence metal-organic framework material, which is a compound prepared from a receptor ligand, a donor ligand and a metal ion in a molar ratio of (1-2):(1-2):4; the receptor ligand is a polypyridyl ring compound with different numbers of central nitrogen atoms and electron deficiencies; the donor ligand is triphenylamine tricarboxylic acid (H3TCA); and in the prepared compound, the receptor ligand and the donor ligand form a face-to-face stacking arrangement.

[0006] The spatial separation of the donor and acceptor molecules is conducive to the realization of thermally activated delayed fluorescence. At the same time, the distance and arrangement between the donor and the acceptor can be flexibly adjusted under the influence of pressure, further flexibly regulating the luminescence properties dominated by the charge transfer effect between the donor and the acceptor.

[0007] The receptor ligands are selected from molecules with similar structures, different numbers of central N atoms and electron deficiencies, to achieve modular regulation of receptor components and further flexibly regulate the structure and optical properties of the material.

[0008] The receptor ligand is 2,4,6-tri-4-pyridyl-1,3,5-triazine (TPT) or 2,4,6-tri-4-pyridylpyrimidine (TPM) or 2,4,6-tri(4-pyridyl)pyridine (TPP) or 1,3,5-tri(4-pyridyl)benzene (TPB).

[0009] The donor ligand has a flexible skeleton, in which the three benzene ring components can rotate flexibly around the center of the N atom, which is conducive to achieving stimulation response to external factors, such as pressure response.

[0010] The metal ion is Cd 2+ .

[0011] The application of the pressure-responsive thermally activated delayed fluorescence metal-organic framework material is used as a luminescent material.

[0012] A method for preparing a pressure-responsive thermally activated delayed fluorescence metal-organic framework material comprises the following steps:

[0013] (1) Take the metal salt, donor ligand, and acceptor ligand and place them in a mixed solution of DMF (N,N-dimethylformamide) and EtOH (ethanol), or in a DMA (N,N-dimethylacetamide) solution, or in a mixed solution of DMA and H2O (water);

[0014] (2) After sealing, heat is applied to eventually generate crystals.

[0015] The molar ratio of the receptor ligand, the donor ligand and the metal ion in the step (1) is (1-2): (1-2): 4; the volume ratio of DMF:EtOH in the mixed solvent in the step (1) is 2:2, and the amount of the mixed solvent is 4 mL per 0.05 mmol of metal ion; the volume of DMA in the solvent in the step (1) is 2 mL per 0.05 mmol of metal ion; the volume ratio of DMA:H2O in the solvent in the step (1) is 2:2, and the amount of the mixed solvent is 4 mL per 0.05 mmol of metal ion.

[0016] In the step (2), the heating temperature range is 90-100° C., and the heating time range is 48-96 hours.

[0017] Advantages of the present invention: 1. The present invention selects donor ligands and acceptor ligands with specific structures to construct high-purity crystalline MOFs materials. The donor ligands and acceptor ligands are arranged face to face, forming a good cross-space charge transfer effect. The spatially separated H OMO and LUMO orbitals make the energy level difference ΔE ST 1. The ligand component of the MOFs material can be flexibly adjusted by regulating the number of N atoms in the center of the receptor molecule, thereby regularly adjusting the corresponding structure and photophysical properties of the material. 2. During the synthesis of the MOFs material, the addition of different auxiliary solvents will change the structure of the MOFs, regulate the distance, relative position and arrangement between the donor and the acceptor, and achieve effective enhancement and flexible tuning of the TADF properties. 3. The synthesized series of TADF-MOFs materials have emission wavelengths between 474-635nm, delayed lifetimes between 0.15-7.65μs, and quantum yields between 0.52-74.24%. Through a variety of regulatory methods, flexible regulation of the TADF properties of the material is achieved. 4. The synthesized MOFs material has a two-dimensional layered structure, and a stable three-dimensional supramolecular framework is formed by the stacking arrangement between the donor and the acceptor. In addition, the introduced donor ligand TCA has a flexible and flexible skeleton. These factors give the material the potential to respond to pressure stimuli. 6. The synthesized MOFs material not only has efficient TADF emission, but also can achieve dynamic and reversible regulation of a wide range of TADF emission wavelengths under high pressure. By utilizing pressure engineering, continuous tuning changes in the luminescence of a single material (from blue light to red light) can be achieved. (4) Description of the accompanying drawings:

[0018] Figure 1 This is the crystal structure diagram of the MOFs material in the example.

[0019] Figure 2 This is the emission spectrum of the MOFs material in the solid state in the example.

[0020] Figure 3 This is the fluorescence emission attenuation curve of the MOFs material in the solid state in the example.

[0021] Figure 4 In situ fluorescence images of Cd-TPB-DMA under different pressures.

[0022] Figure 5 High-pressure emission spectra of Cd-TPB-DMA at different pressures. (V) Specific implementation methods:

[0023] The present invention provides a pressure-responsive thermally activated delayed fluorescent metal-organic framework material and a method for preparing the same, which makes the objectives, technical solutions, and effects of the present invention more clear and specific. The present invention is described in further detail below. It should be understood that the specific embodiments described herein are merely illustrative of the present invention.

[0024] Example 1: A pressure-responsive thermally activated delayed fluorescence metal-organic framework material, which is a Cd-TPT-DMF[Cd3(TPT)(TCA)2(DMF)2] crystal, is prepared as follows: metal salt Cd(NO3)2·4H2O (0.04 mmol), receptor ligand TPT (0.01 mmol) and donor ligand TCA (0.02 mmol) are placed in a 20 mL glass vial containing a mixed solution of DMF (2 mL) and EtOH (2 mL); after sealing the vial, the vial is placed in a 92°C oven and heated for 48 hours to eventually generate red crystals.

[0025] Example 2: A pressure-responsive thermally activated delayed fluorescence metal-organic framework material, which is a Cd-TPM-DMF[Cd3(TPM)(TCA)2(DMF)2] crystal, is prepared as follows: metal salt Cd(NO3)2·4H2O (0.04 mmol), receptor ligand TPM (0.01 mmol) and donor ligand TCA (0.02 mmol) are placed in a 20 mL glass vial containing a mixed solution of DMF (2 mL) and EtOH (2 mL); the vial is sealed and placed in a 92°C oven for 48 hours to eventually generate orange crystals.

[0026] Example 3: Pressure-responsive thermally activated delayed fluorescence metal-organic framework material, which is Cd-TPP-NO3 - [Cd2(TPP)(TCA)(NO3 - )] crystals, which are prepared by the following method: taking metal salt Cd(NO3)2·4H2O (0.04 mmol), acceptor ligand TPP (0.01 mmol) and donor ligand TCA (0.02 mmol) and placing them into a 20 mL glass vial containing a mixed solution of DMF (2 mL) and EtOH (2 mL); sealing the vial and heating it in a 92°C oven for 48 hours to finally generate yellow crystals.

[0027] Example 4: Pressure-responsive thermally activated delayed fluorescence metal-organic framework material, which is Cd-TPB-NO3 - [Cd2(TPB)(TCA)(NO3 -)] crystals, which are prepared by the following method: taking metal salt Cd(NO3)2·4H2O (0.04 mmol), acceptor ligand TPB (0.01 mmol) and donor ligand TCA (0.02 mmol) and placing them into a 20 mL glass vial containing a mixed solution of DMF (2 mL) and EtOH (2 mL); sealing the vial and heating it in a 92°C oven for 48 hours, and finally generating light yellow crystals.

[0028] Example 5: A thermally activated delayed fluorescence metal-organic framework material with pressure response, which is a Cd-TPT-DMA[Cd3(TPT)(TCA)2(DMA)2] crystal. Its preparation method is as follows: take the metal salt Cd(NO3)2·4H2O (0.04mmol), the receptor ligand TPT (0.01mmol) and the donor ligand TCA (0.02mmol), and put them into a 20mL glass vial containing a mixed solution of DMA (2mL) and H2O (2mL); after sealing the vial, place it in a 92°C oven and heat it for 48 hours to finally generate red crystals.

[0029] Example 6: A thermally activated delayed fluorescence metal-organic framework material with pressure response, which is a Cd-TPM-DMA[Cd3(TPM)(TCA)2(DMA)2] crystal. Its preparation method is as follows: take the metal salt Cd(NO3)2·4H2O (0.04mmol), the receptor ligand TPM (0.01mmol) and the donor ligand TCA (0.02mmol), and put them into a 20mL glass vial containing a mixed solution of DMA (2mL) and H2O (2mL); after sealing the vial, place it in a 92°C oven and heat it for 48 hours to finally generate orange-red crystals.

[0030] Example 7: A thermally activated delayed fluorescence metal-organic framework material with pressure response, which is a Cd-TPP-DMA[Cd3(TPP)(TCA)2(DMA)2] crystal. Its preparation method is as follows: take the metal salt Cd(NO3)2·4H2O (0.04mmol), the receptor ligand TPP (0.01mmol) and the donor ligand TCA (0.02mmol), and put them into a 20mL glass vial filled with DMA (2mL) solution; after sealing the vial, put it into a 92°C oven and heat it for 72 hours to finally generate yellow crystals.

[0031] Example 8: A thermally activated delayed fluorescence metal-organic framework material with pressure response, which is a Cd-TPB-DMA[Cd3(TPB)(TCA)2(DMA)2] crystal. Its preparation method is as follows: take the metal salt Cd(NO3)2·4H2O (0.04mmol), the receptor ligand TPB (0.01mmol) and the donor ligand TCA (0.02mmol), and put them into a 20mL glass vial filled with DMA (2mL) solution; after sealing the vial, put it into a 92°C oven and heat it for 72 hours, and finally generate light yellow crystals.

[0032] like Figure 1 As shown, the MOFs materials in each example have similar two-dimensional layered structures, but different stacking patterns lead to different three-dimensional supramolecular frameworks. (Different layers are represented by different colors for easy distinction)

[0033] like Figure 2 As shown, in the emission spectrum test, the MOFs materials of each embodiment exhibited a photoluminescence emission peak position of 474nm-635nm, spanning the wavelength range of 161nm, realizing the flexible adjustment of the TADF emission wavelength.

[0034] like Figure 3 As shown, the fluorescence emission decay curves of the MOFs materials in each example show that the series of compounds have a significant component that delays the lifespan, demonstrating that the series of compounds have the properties of TADF. The emission decay curves of Cd-TPT-DMF and Cd-TPM-DMF materials are difficult to obtain due to their weak luminescence efficiency.

[0035] like Figure 4 As shown, taking Cd-TPB-DMA as an example, it was subjected to isotropic hydrostatic pressure treatment using a diamond anvil cell, and the fluorescence image of the crystal in situ was monitored. It can be seen intuitively that the emission color of the crystal shifted from blue to red.

[0036] like Figure 5 As shown in the figure, Cd-TPB-DMA was subjected to isotropic hydrostatic pressure treatment using a diamond anvil cell. The fluorescence emission spectrum of the crystal was monitored in situ, and the corresponding emission peak was observed to gradually red-shift from 474 nm to 590 nm. This demonstrates the flexible and tunable TADF emission of the compound under high pressure.

Claims

1. A pressure-responsive thermally activated delayed fluorescence metal-organic framework material characterized by The invention relates to a compound prepared from an acceptor ligand, a donor ligand and a metal ion in a molar ratio of (1-2): (1-2): 4; the acceptor ligand is a polypyridyl ring compound having different numbers of central nitrogen atoms and electron deficiencies; the donor ligand is triphenylaminetricarboxylic acid (H3TCA); and in the prepared compound, the acceptor ligand and the donor ligand form a face-to-face stacking arrangement.

2. The pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 1, characterized in that The receptor ligands are selected from molecules with similar structures, different numbers of central N atoms and electron deficiencies, to achieve modular regulation of receptor components and further flexibly regulate the structure and optical properties of the material.

3. The pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 1 or 2, characterized in that The receptor ligand is 2,4,6-tri-4-pyridyl-1,3,5-triazine (TPT) or 2,4,6-tri-4-pyridylpyrimidine (TPM) or 2,4,6-tri(4-pyridyl)pyridine (TPP) or 1,3,5-tri(4-pyridyl)benzene (TPB).

4. The pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 1, characterized in that The donor ligand has a flexible skeleton, in which the three benzene ring components can rotate flexibly around the center of the N atom, which is conducive to achieving stimulation response to external factors.

5. The pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 1, characterized in that The metal ion is Cd 2+ .

6. Use of the pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 1 as a luminescent material.

7. A method for preparing a pressure-responsive thermally activated delayed fluorescent metal-organic framework material, characterized in that The following steps are involved: (1) Take the metal salt, donor ligand, and acceptor ligand and place them in a mixed solution of DMF (N,N-dimethylformamide) and EtOH (ethanol), or in a DMA (N,N-dimethylacetamide) solution, or in a mixed solution of DMA and H2O (water); (2) After sealing, heat is applied to eventually generate crystals.

8. The method for preparing a pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 7, characterized in that The molar ratio of the receptor ligand, the donor ligand and the metal ion in the step (1) is (1-2): (1-2): 4; the volume ratio of DMF:EtOH in the mixed solvent in the step (1) is 2:2, and the amount of the mixed solvent is 4 mL per 0.05 mmol of metal ions; the volume of DMA in the solvent in the step (1) is 2 mL per 0.05 mmol of metal ions; the volume ratio of DMA:H2O in the solvent in the step (1) is 2:2, and the amount of the mixed solvent is 4 mL per 0.05 mmol of metal ions.

9. The method for preparing a pressure-responsive thermally activated delayed fluorescent metal-organic framework material according to claim 7, characterized in that In the step (2), the heating temperature range is 90-100° C., and the heating time range is 48-96 hours.

Images