Method for regulating luminescence of triphenylamine metal-organic framework material based on mixed ligand strategy

Abstract

This invention discloses a method for regulating the luminescence of triphenylamine-based metal-organic framework (MOF) materials based on a mixed-ligand strategy. Specifically, the method involves selecting an organic chromophore with two or more emission peaks, introducing a series of second ligands with similar or identical luminescence characteristics, and using the organic chromophore and any one of the second ligands as organic ligands to prepare MOF materials. By introducing the second ligands to alter the conformation of the organic chromophore, its local excited state and intramolecular charge transfer state can be regulated, achieving a wide range of tunable emission spectra for the MOF materials. The series of MOF materials of this invention exhibit a chromatographic range from cyan-green to orange under ultraviolet light irradiation. The preparation and synthesis process is simple, and the second ligands can also transfer energy to the organic chromophore, promoting improved quantum efficiency.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials, and more specifically to a method for regulating the luminescence of triphenylamine-based metal-organic framework materials based on a mixed ligand strategy. Background Technology

[0002] Luminescent materials, due to their unique optical properties, exhibit enormous application potential in numerous fields. In display technology and lighting, novel luminescent materials such as perovskites and quantum dots have attracted widespread attention due to their high quantum efficiency and wide color gamut. The application of luminescent materials has led to the gradual replacement of traditional light sources by more energy-efficient and environmentally friendly light-emitting diode (LED) lighting. In the biomedical field, luminescent materials provide new tools for in vivo imaging and treatment. With the development of wearable technology, luminescent materials can also be used for health monitoring, information display, and even treatment. From traditional lighting and display technologies to emerging biomedical and wearable devices, the versatility and high quantum efficiency of luminescent materials make them an indispensable part of modern technology.

[0003] It is worth noting that the color tunability of luminescent materials is a key characteristic for their applications in multiple fields. However, according to Kasha's rule, for multi-state molecules, photons can only be emitted from the lowest excited state. Achieving continuous tunability of emission color is a challenging task. Organic chromophores have unique advantages in luminescent materials due to their rich variety and wide emission range, and a large amount of research has been conducted to modulate their photophysical properties. For example, their luminescence properties can be modified through chemical synthesis, but the synthetic process is usually quite complex. Another common strategy is to introduce responsive groups to induce changes in molecular structure, but this suffers from poor reversibility and limited structural selectivity. Recently, changing the conformation of molecules has been considered a more promising and simpler method, attracting widespread attention.

[0004] Changes in molecular conformation can affect the electronic transition paths of excited states, thereby altering the luminescence properties of organic chromophores. However, two challenges remain in the preparation of organic crystalline materials with continuously tunable luminescence: (i) Conformational diversity is greatly limited in the solid state (especially in the crystalline phase), reducing the tunability of the luminescence color and limiting its application range. (ii) Traditional organic chromophores are affected by the aggregation-induced quenching (ACQ) effect, resulting in very low quantum efficiency.

[0005] The MOFs materials of this invention employ a mixed-ligand strategy, self-assembling from organic chromophores and dicarboxylic acids as second ligands, along with metal ions or metal clusters. Without altering the metal ions or organic chromophores, the conformation of the organic chromophore can be changed simply by modifying the second ligand, thereby controlling its local excited state and intramolecular charge transfer state, successfully achieving continuously tunable luminescence in the MOFs materials. Furthermore, the efficient and directional energy transfer from the second ligand to the organic chromophore effectively improves quantum efficiency. The one-step synthesis method allows for control and prediction of the synthesized products, facilitating the formation of highly interconnected three-dimensional infinite network structures. The synthesized series of MOFs materials exhibits good stability and high quantum efficiency, and can serve as continuously tunable luminescence materials with potential applications in sensing, bioimaging, display, and lighting fields. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a method for regulating the luminescence properties of triphenylamine-based metal-organic framework materials based on a hybrid ligand strategy, achieving rich color tunability. Furthermore, the stable rigid structure and energy transfer between luminescent functional units can effectively improve quantum efficiency.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for regulating the luminescence of triphenylamine-based metal-organic framework materials based on a mixed ligand strategy involves selecting an organic chromophore with two or more emission peaks, selecting a series of second ligands with the same or similar luminescence, and preparing MOF materials by combining any second ligand with the organic chromophore as organic ligands. The luminescence of the prepared MOF materials is regulated by changing the second ligand. The organic chromophore is a triphenylamine derivative, and the material is referred to as a triphenylamine-based metal-organic framework material.

[0009] Furthermore, the organic chromophore is tris(4-(pyridin-4-yl)phenyl)amine; the second ligand is specifically a second ligand that emits light in solution in the range of 334 nm to 371 nm.

[0010] Furthermore, the second ligand comprises: terephthalic acid with structural formula (a), 2-chloroterephthalic acid with structural formula (b), 2-bromoterephthalic acid with structural formula (c), 2-fluoroterephthalic acid with structural formula (d), 2,5-dichloroterephthalic acid with structural formula (e), 2,5-dibromoterephthalic acid with structural formula (f), 2,5-difluoroterephthalic acid with structural formula (g), isophthalic acid with structural formula (h), and 2-chloro-m-terephthalic acid with structural formula (i). Phthalic acid, 5-bromo-isophthalic acid with structural formula (g), 2-fluoro-isophthalic acid with structural formula (k), phthalic acid with structural formula (l), 4,4'-biphenyl dicarboxylic acid with structural formula (m), 2,2'-biphenyl dicarboxylic acid with structural formula (n), 4,4'-diphenyl ether dicarboxylic acid with structural formula (o), 2,5-furan dicarboxylic acid with structural formula (p), 2,6-pyridine-dicarboxylic acid with structural formula (q), and 3,5-pyridine-dicarboxylic acid with structural formula (r);

[0011]

[0012] Furthermore, the preparation method of the MOFs material includes the following:

[0013] The metal salt, any second ligand, and the organic chromophore are dissolved in a solvent, ultrasonically mixed, and then reacted at 85°C for 24–72 h. After natural cooling to room temperature, the mixture is washed, filtered, and dried to obtain MOF materials. The washing is performed using an organic solvent, specifically N,N-dimethylformamide or N,N-dimethylacetamide.

[0014] Furthermore, the ratio of the metal salt, the second ligand, the organic chromophore, and the solvent is (0.08–0.2 mmol): (0.08–0.2 mmol): (0.04–0.1 mmol): (4–16 ml).

[0015] Furthermore, the solvent is any one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, methanol, and deionized water in any proportion.

[0016] Furthermore, the metal salt is one of zinc nitrate, zinc acetate, cadmium nitrate, and cobalt chloride.

[0017] Furthermore, five MOF materials were combined to achieve tunable light emission covering a range of colors from cyan to yellow to orange. The combination order was Zn-IPA-TPPA, Zn-BPDC-TPPA, Zn-OBA-TPPA, Zn-BDC-TPPA, and Zn-FDA-TPPA.

[0018] Furthermore, the five MOF materials were prepared by using one of the five second ligands with tris(4-(pyridin-4-yl)phenyl)amine and zinc nitrate hexahydrate (Zn(NO3)2·6H2O);

[0019] The five second ligands are isophthalic acid (H2IPA), biphenyl dicarboxylic acid (H2BPDC), 4,4'-diphenyl ether dicarboxylic acid (H2OBA), terephthalic acid (H2BDC), and 2,5-furandicarboxylic acid (H2FDA).

[0020] A metal-organic framework material is prepared by using a metal salt, a second ligand, and an organic chromophore, wherein the metal salt is zinc nitrate hexahydrate (Zn(NO3)2·6H2O);

[0021] The second ligand is one of: 4,4'-diphenyl ether dicarboxylic acid (H2OBA), terephthalic acid (H2BDC), or 2,5-furan dicarboxylic acid (H2FDA);

[0022] The organic chromophore is tris(4-(pyridin-4-yl)phenyl)amine (TPPA).

[0023] The specific beneficial effects of this invention are as follows:

[0024] 1. The MOFs material used in this invention exhibits rich color tunability due to its specific structure and composition. In particular, when combined with organic chromophores with rich conformations, it further expands the chromatographic range of its luminescence. In addition, the stable rigid structure and energy transfer between luminescent functional units can effectively improve quantum efficiency.

[0025] 2. In this invention, the organic chromophore TPPA molecule, under different wavelength excitations, primarily emits at approximately 455 nm and 530 nm. This indicates that TPPA emission exists in two excited states: the former is a locally excited state, and the latter is an intramolecular charge-transfer state. This invention can alter the conformation of the organic chromophore simply by changing the second ligand, thereby controlling its locally excited state and intramolecular charge-transfer state, successfully achieving continuously tunable luminescence in MOF materials. Furthermore, the efficient and directional energy transfer from the second ligand to the organic chromophore can effectively improve quantum efficiency.

[0026] 3. The synthesis methods of the present invention all adopt a one-step synthesis method, the preparation process is simple, and the reaction can be carried out at 85°C without the need for a special environment of high temperature and high pressure.

[0027] 4. Compared with organic molecules, the MOFs materials of the present invention are a class of highly ordered crystalline materials. The present invention has obtained a series of highly connected crystal structures, such as a three-dimensional infinite network structure formed by zinc ions, organic ligand isophthalic acid, and organic chromophore tris(4-(pyridin-4-yl)phenyl)amine. The zinc ions are coordinated with the oxygen atoms of the two surrounding isophthalic acids and the nitrogen atoms of the two tris(4-(pyridin-4-yl)phenyl)amine.

[0028] 5. The series of MOFs materials synthesized in this invention are composed of metal ions or metal clusters and organic mixed ligands connected by coordination bonds. They have excellent thermal stability and can maintain structural stability in a nitrogen atmosphere at 300°C.

[0029] 6. Compared with organic molecules, the MOFs materials used in this invention have abundant luminescence sites, a wide range of emission wavelengths, and strong tunability of luminescence. In this invention, the absorption spectrum of the organic chromophore and the emission spectrum of the second ligand have good overlap, which can facilitate effective energy transfer and improve quantum efficiency, increasing it from 4.56% for organic chromophores to about 20% for MOFs materials.

[0030] 7. This invention introduces five second ligands to change the conformation of organic chromophores, thereby regulating their local excited state and intramolecular charge transfer state. After the five MOF materials are combined in sequence, the emission spectrum is continuously tunable from cyan-green to yellow and then to orange. Attached Figure Description

[0031] Figure 1 This is a powder X-ray diffraction pattern of a method for regulating the luminescence of triphenylamine metal-organic framework materials based on a mixed ligand strategy according to an embodiment of the present invention.

[0032] Figure 2 This invention relates to a method for regulating the luminescence of triphenylamine-based metal-organic framework materials using a hybrid ligand strategy, and describes the structure and solid-state fluorescence spectrum of the organic chromophore in one embodiment of the invention.

[0033] Figure 3 This is a schematic diagram of the structure of the dicarboxylic acid ligand in a method for regulating the luminescence of triphenylamine metal-organic framework materials based on a mixed ligand strategy according to an embodiment of the present invention;

[0034] Figure 4(a) shows the fluorescence spectrum of a method for regulating the luminescence of triphenylamine metal-organic framework materials based on a mixed ligand strategy according to an embodiment of the present invention. The luminescence of MOFs materials is continuously regulated by using five ligands.

[0035] Figure 4(b) shows a comparison of the fluorescence spectra of TPPA, dicarboxylic acid ligands, and MOFs crystals in one embodiment of the present invention. Detailed Implementation

[0036] The following examples will further illustrate the content of the present invention. However, these examples do not limit the scope of protection of the present invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0037] Example 1:

[0038] MOF materials were synthesized via a solvothermal method using zinc nitrate hexahydrate (Zn(NO3)2·6H2O), isophthalic acid (H2IPA), and tris(4-(pyridin-4-yl)phenyl)amine (TPPA). The specific synthetic route is as follows:

[0039] 16.6 mg of isophthalic acid, 48.0 mg of tris(4-(pyridin-4-yl)phenyl)amine (TPPA), and 29.7 mg of zinc nitrate hexahydrate were dissolved in 6 ml of N,N-dimethylformamide and 9 ml of deionized water. The solution was sonicated until clear and placed in a 20 ml sealed glass bottle. The mixture was then reacted in an oven at 85 °C for 72 h. After cooling to room temperature, the filtered solid was repeatedly washed with N,N-dimethylformamide and dried to obtain light yellow blocky crystals, namely Zn-IPA-TPPA.

[0040] The structure was determined using an Oxford Xcalibur Gemini Ultra single-crystal diffractometer. Test results showed that the space group of this material is C1 2 / c 1(15), belonging to the monoclinic crystal system, and the cell parameters are... β = 96.744° Z = 8. Experimental XRD and single-crystal XRD simulation images of Zn-IPA-TPPA are shown below. Figure 1 As shown in (a), this material is a three-dimensional infinite network structure formed by zinc ions, the organic ligand isophthalic acid, and the organic chromophore tris(4-(pyridin-4-yl)phenyl)amine. The zinc ions are coordinated with two surrounding oxygen atoms and two surrounding nitrogen atoms.

[0041] The obtained Zn-IPA-TPPA is a light yellow crystal in a blocky shape. The high bonding mode results in high chemical, light, and thermal stability. The quantum efficiency increased from 4.56% for organic chromophores to 12.39%.

[0042] Example 2:

[0043] MOF was synthesized via a solvothermal method using zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 4,4'-biphenyldicarboxylic acid (H2BPDC), and tris(4-(pyridin-4-yl)phenyl)amine (TPPA). The specific synthetic route is as follows:

[0044] Add 23.8 mg zinc nitrate hexahydrate, 38.1 mg tris(4-(pyridin-4-yl)phenyl)amine, 19.4 mg 4,4'-biphenyldicarboxylic acid, 8 ml N,N-dimethylacetamide, 4 ml acetonitrile, and 4 ml H2O to a 20 ml glass bottle. Sonicate until the solution is clear, heat to 85 °C and react for 72 h. Wash with N,N-dimethylacetamide and dry in air to obtain light yellow blocky crystals, namely Zn-BPDC-TPPA.

[0045] The structure was determined using an Oxford Xcalibur Gemini Ultra single-crystal diffractometer. Test results showed that the space group of this material is P1 21 / c 1(14), belonging to the monoclinic crystal system, and the cell parameters are... β = 97.857° Z = 4. Experimental XRD and single-crystal XRD simulation plots of Zn-BPDC-TPPA are shown below. Figure 1 As shown in (b), the material is a three-dimensional infinite network structure formed by zinc ions, the organic ligand 4,4'-biphenylcarboxylic acid, and the organic chromophore tris(4-(pyridin-4-yl)phenyl)amine. The zinc ions have two coordination modes: one is coordination with the two surrounding oxygen atoms and two nitrogen atoms, and the other is coordination via 4,4'-biphenylcarboxylic acid to form a metal cluster, with coordination to the eight oxygen atoms of the four carboxylic acids and the two nitrogen atoms of the two tris(4-(pyridin-4-yl)phenyl)amine atoms.

[0046] The obtained Zn-BPDC-TPPA is a light yellow crystal in a blocky shape. The high bonding mode results in high chemical, light, and thermal stability. The quantum efficiency increased from 4.56% for organic chromophores to 20.43%.

[0047] Example 3:

[0048] MOF materials were synthesized via a solvothermal method using zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 4,4'-diphenyl ether dicarboxylic acid (H2OBA), and tris(4-(pyridin-4-yl)phenyl)amine (TPPA). The specific synthetic route is as follows:

[0049] Add 29.7 mg zinc nitrate hexahydrate, 47.7 mg tris(4-(pyridin-4-yl)phenyl)amine, 25.8 mg 4,4'-diphenyl ether dicarboxylic acid, 10 ml N,N-dimethylformamide, and 5 ml H2O to a 20 ml glass bottle. Sonicate until the solution is clear, heat to 85 °C and react for 72 h. Wash with N,N-dimethylformamide and dry in air to obtain light yellow blocky crystals, namely Zn-OBA-TPPA.

[0050] The structure was determined using an Oxford Xcalibur Gemini Ultra single-crystal diffractometer. Test results showed that the space group of this material is P1 21 / c 1(14), belonging to the monoclinic crystal system, and the cell parameters are... β = 98.465° Z = 4. Experimental XRD and single-crystal XRD simulation images of Zn-OBA-TPPA are shown below. Figure 1 As shown in (c), this material is a three-dimensional infinite network structure formed by zinc ions, the organic ligand 4,4'-diphenyl ether dicarboxylic acid, and the organic chromophore tris(4-(pyridin-4-yl)phenyl)amine. The zinc ions are coordinated with two surrounding oxygen atoms and two surrounding nitrogen atoms.

[0051] The obtained Zn-OBA-TPPA is a light yellow crystal in a blocky shape. The high bonding mode results in high chemical stability, light stability, and thermal stability of the material.

[0052] Example 4:

[0053] MOF materials were synthesized via a solvothermal method using zinc nitrate hexahydrate (Zn(NO3)2·6H2O), terephthalic acid (H2BDC), and tris(4-(pyridin-4-yl)phenyl)amine (TPPA). The specific synthetic route is as follows:

[0054] 16.6 mg of terephthalic acid, 24.0 mg of tris(4-(pyridin-4-yl)phenyl)amine (TPPA), and 29.7 mg of zinc nitrate hexahydrate were dissolved in 5 ml of N,N-dimethylformamide. The solution was sonicated until clear and placed in a 20 ml sealed glass bottle. The mixture was then reacted in an oven at 85 °C for 24 h. After cooling to room temperature, the filtered solid was repeatedly washed with N,N-dimethylformamide and dried to obtain orange blocky crystals, namely Zn-BDC-TPPA.

[0055] The structure was determined using an Oxford Xcalibur Gemini Ultra single-crystal diffractometer. Test results showed that the space group of this material is P1 21 / n 1(14), belonging to the monoclinic crystal system, and the cell parameters are... β = 93.402° Z = 4. Experimental XRD and single-crystal XRD simulation images of Zn-BDC-TPPA are shown below. Figure 1As shown in (d), this material is a three-dimensional infinite network structure formed by zinc ions, the organic ligand terephthalic acid, and the organic chromophore tris(4-(pyridin-4-yl)phenyl)amine. The zinc ions have two coordination modes: one is coordination with three surrounding oxygen atoms and two nitrogen atoms, and the other is coordination with four surrounding oxygen atoms and one nitrogen atom. Two zinc ions are bridged by terephthalic acid.

[0056] The obtained Zn-BDC-TPPA is an orange crystal in a bulk shape. The high bonding mode results in high chemical, light, and thermal stability. The quantum efficiency increased from 4.56% for organic chromophores to 17.79%.

[0057] Example 5:

[0058] MOF materials were synthesized via a solvothermal method using zinc nitrate hexahydrate (Zn(NO3)2·6H2O), 2,5-furandicarboxylic acid (H2FDA), and tris(4-(pyridin-4-yl)phenyl)amine (TPPA). The specific synthetic route is as follows:

[0059] 15.6 mg of 2,5-furandicarboxylic acid, 23.8 mg of tris(4-(pyridin-4-yl)phenyl)amine (TPPA), and 29.7 mg of zinc nitrate hexahydrate were dissolved in 5 ml of N,N-dimethylformamide. The solution was sonicated until clear and placed in a 20 ml sealed glass bottle. The mixture was then reacted in an oven at 85 °C for 24 h. After cooling to room temperature, the filtered solid was repeatedly washed with N,N-dimethylformamide and dried to obtain orange blocky crystals, namely Zn-FDA-TPPA.

[0060] The structure was determined using an Oxford Xcalibur Gemini Ultra single-crystal diffractometer. Test results showed that the space group of this material is C1 2 / c 1(15), belonging to the monoclinic crystal system, and the cell parameters are... β = 111.331° Z = 8. Experimental XRD and single-crystal XRD simulation images of Zn-FDA-TPPA are shown below. Figure 1 As shown in (e), this material is a three-dimensional infinite network structure formed by zinc ions, the organic ligand 2,5-furandicarboxylic acid, and the organic chromophore tris(4-(pyridin-4-yl)phenyl)amine. The zinc ions have two coordination modes: one is coordination with the two surrounding oxygen atoms and two nitrogen atoms, and the other is coordination with the four oxygen atoms of 2,5-furandicarboxylic acid, one nitrogen atom of tris(4-(pyridin-4-yl)phenyl)amine, and an oxygen atom of N,N-dimethylformamide.

[0061] The obtained Zn-FDA-TPPA is an orange crystal in a blocky shape. The high bonding mode results in high chemical, light, and thermal stability. The quantum efficiency increased from 4.56% for organic chromophores to 10.78%.

[0062] In this invention, the solid-state fluorescence spectrum of the organic chromophore TPPA molecule is as follows: Figure 2 As shown, under different wavelength excitation, emission is predominantly around 455 nm and 530 nm, indicating that TPPA emission exists in two excited states: the former is a locally excited state, and the latter is an intramolecular charge transfer state. A mixed-ligand strategy was adopted, introducing a series of dicarboxylic acid ligands as second ligands to co-construct metal-organic framework materials with TPPA and metal ions. The structural schematic diagrams of five representative dicarboxylic acid ligands are shown below. Figure 3 As shown in Figure 4(a), the fluorescence spectrum of the constructed MOFs material extends from 478 nm to 600 nm, covering a range from cyan to yellow to orange. Figure 4(b) shows a significant redshift in the emission of MOFs crystals compared to the fluorescence spectra of TPPA, dicarboxylic acid ligands, and MOFs crystals.

[0063] In this invention, the conformation of the organic chromophore can be altered simply by changing the second ligand, thereby controlling the local excited state and intramolecular charge transfer state of the organic chromophore, thus achieving continuously tunable emission of the luminescent metal-organic framework material. Furthermore, the efficient and directional energy transfer from the second ligand to the organic chromophore effectively improves the quantum efficiency of the luminescent material.

[0064] The above specific embodiments are used to explain and illustrate the present invention, but the present invention should not be limited to the content disclosed in the embodiments and drawings. Therefore, any equivalents or modifications made without departing from the spirit of the present invention fall within the protection scope of the present invention.

Claims

1. A method for regulating the luminescence of triphenylamine-based metal-organic framework materials based on a mixed ligand strategy, characterized in that, Tris(4-(pyridin-4-yl)phenyl)amine (TPPA) was selected as the organic chromophore, zinc nitrate hexahydrate was selected as the metal salt, and five kinds of metal-organic framework materials were prepared by solvothermal reaction of TPPA and zinc nitrate hexahydrate with five kinds of second ligands. The luminescence of the prepared MOF materials was controlled by changing the second ligands. The second ligand is composed of isophthalic acid (H2IPA), biphenyl dicarboxylic acid (H2BPDC), 4,4'-diphenyl ether dicarboxylic acid (H2OBA), terephthalic acid (H2BDC), and 2,5-furan dicarboxylic acid (H2FDA), and the five second ligands emit wavelengths from 334 nm to 371 nm in solution; The five metal-organic framework materials are Zn-IPA-TPPA, Zn-BPDC-TPPA, Zn-OBA-TPPA, Zn-BDC-TPPA, and Zn-FDA-TPPA. Under ultraviolet light excitation, their emission wavelengths cover 478 nm to 600 nm, and their luminescence can be tunable from cyan to yellow to orange.

2. The method for regulating the luminescence of triphenylamine metal-organic framework materials based on a mixed ligand strategy according to claim 1, characterized in that, The preparation method of the MOF material includes the following: Zinc nitrate hexahydrate, along with any second ligand and the aforementioned organic chromophore, is dissolved in a solvent, ultrasonically mixed until homogeneous, and then reacted at 85 °C for 24–72 h. After natural cooling to room temperature, the mixture is washed, filtered, and dried to obtain MOF materials.

3. The method for regulating the luminescence of triphenylamine-based metal-organic framework materials based on a mixed ligand strategy according to claim 2, characterized in that, The ratio of zinc nitrate hexahydrate, the second ligand, the organic chromophore, and the solvent is (0.08 ~ 0.2 mmol): (0.08 ~ 0.2 mmol): (0.04 ~ 0.1 mmol): (4 ~ 16 ml).

4. The method for regulating the luminescence of triphenylamine metal-organic framework materials based on a mixed ligand strategy according to claim 2, characterized in that, The solvent is any one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, acetonitrile, methanol, and deionized water in any proportion.

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