Preparation of a complex with thermally activated delayed fluorescence property and scintillator application

Abstract

A preparation method of a complex with thermal activation delayed fluorescence property, comprising the following steps: (1) taking metal salt, auxiliary ligand, main ligand and guest molecules, and putting them into a mixed solution of DMF, EtOH and H2O; wherein the molar ratio of main ligand: auxiliary ligand: metal ion: guest molecule is 1: (2-3): (1-3): (1-10); (2) after sealing, put into heating, and finally generate crystals. The complex with thermal activation delayed fluorescence property is applied to X-ray detection. The complex with thermal activation delayed fluorescence property is used for preparing into a flexible film. The application provides a thermal activation delayed fluorescence crystal complex, which is formed by coordination of main ligand, auxiliary ligand and metal ion to form a complex acceptor framework, and the guest molecules are filled into the pores as donors to form luminescence based on space charge transfer. Through modification of R atoms of each component in the structure, the TADF property of the series of complexes is realized, and the regularity of the photophysical property of the complex is also completed.

Description

(I) Technical Field:

[0001] This invention relates to the field of coordination polymers, and in particular to a method for preparing crystalline coordination polymers with thermally activated delayed fluorescence properties and their scintillator applications. (II) Background Technology:

[0002] X-ray detection and imaging technology has important applications in many fields, including medical diagnosis, environmental monitoring, industrial flaw detection, nuclear technology, and radiation safety detection. Scintillator materials, which absorb X-rays and convert them into visible light, are key materials for X-ray detection. In the X-ray luminescence process of most scintillator materials, inner-shell electrons are excited through the photoelectric effect, followed by Compton scattering to generate high-energy electrons. These secondary electrons then fall into the excited state and emit photons through transitions to the ground state, thus emitting light. In this process, the ratio of triplet excitons to singlet excitons generated by radiation energy excitation is 3:1. In general systems, the triplet energy is lower than the singlet energy, and the energy level difference is large, making intersystem crossing between the triplet and singlet states difficult. This makes it difficult for triplet excited-state electrons to return to the ground state through singlet fluorescence emission. Furthermore, the process of triplet excited-state electrons returning to the ground state is subject to spin forbidden conditions, resulting in low phosphorescence intensity and long lifetime. This prevents the efficient conversion of excited-state energy into light emission, reducing the X-ray luminescence performance of the material. Materials exhibiting thermally activated delayed fluorescence (TADF) properties benefit from the small energy difference between the singlet and triplet states, which is conducive to ISC and RISC processes. This allows triplet excited-state electrons to fall back to the ground state via the singlet state, efficiently converting triplet energy into luminescence in the form of delayed fluorescence (microsecond-level lifetime), thus fully utilizing triplet exciton energy. Therefore, TADF luminescent materials hold promise for achieving breakthroughs in key indicators such as higher light yield and sensitivity in X-ray luminescence. However, due to the complex preparation process of organic TADFs and the low atomic number of small organic molecules, organic scintillator materials with good X-ray absorption and high light yield still require optimization and exploration. (III) Summary of the Invention:

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing crystalline coordination polymers with thermally activated delayed fluorescence (TADF) properties and their scintillator applications. First, the metal ions / metal clusters of coordination polymers have high atomic numbers, which can effectively absorb X-rays. The diversity of building blocks makes it easy to realize the TADF properties of the material. Combining the above, the aim is to construct novel coordination polymers and utilize the multi-level synergistic regulation of the "composition-structure-properties" of coordination polymers to realize crystalline scintillator materials with TADF properties. Finally, high spatial resolution X-ray imaging is achieved using sample thin films.

[0004] The technical solution of the present invention is as follows: a complex with thermally activated delayed fluorescence properties, which is prepared by a main ligand, an auxiliary ligand, a metal ion, and a guest molecule in a molar ratio of 1:(2-3):(1-3):(1-10); the main ligand acts as an acceptor and coordinates with the auxiliary ligand and the metal ion to form a triple interpenetrating hexagonal nested cage structure; the guest molecule acts as a donor.

[0005] The main ligand is pyridine triazine (TPT) or tripyridylpyridine (TPP);

[0006] The auxiliary ligand is selected from one of the following: terephthalic acid (PTA), 2-R-terephthalic acid (2-R-PTA), 2,5-diR-terephthalic acid (2,5-2R-PTA), 2,3,5,6-tetrar-R-terephthalic acid (2,3,5,6-4R-PTA), 1,4-cubicanedicarboxylic acid and its derivatives, 2,5-furandicarboxylic acid and its derivatives, 1,3-bicyclo[1.1.1]pentanedicarboxylic acid and its derivatives, 3,6-thieno[3,2-B]thienodicarboxylic acid and its derivatives, and derivative molecules in which two formic acids are para-substituted by an independent small group in the middle; wherein, the R group is a substituent.

[0007] The metal ions are transition metal ions, alkali metal ions, or alkaline earth metal ions.

[0008] The guest molecule is selected from one of the following: phenylcarbazole and its derivatives, phenyl acridine and its derivatives, planar polycyclic aromatic hydrocarbons, and dibenzofuran and its derivatives.

[0009] The phenylcarbazole and its derivatives include N-phenylcarbazole (Ph-Cz), 2-R-phenylcarbazole (Ph-Cz-R(2)), 2,7-diR-phenylcarbazole (Ph-Cz-2R(2,7)), 3-R-phenylcarbazole (Ph-Cz-R(3)), and 3,6-diR-phenylcarbazole (Ph-Cz-2R(3,6)).

[0010] The R group includes: F, Cl, Br, I, As, Se.

[0011] The derivatives formed by modifying different numbers of R atoms at different positions of the guest molecule serve as donors, making full use of the spin-orbit coupling effect of the R atoms themselves to promote intersystem crossing and reverse intersystem crossing, further optimizing the photophysical properties of the material and achieving higher triplet exciton utilization. Furthermore, in this structure, the face-to-face stacking and spatial separation of the donor and acceptor ensures effective charge transfer while also causing a small difference between singlet and triplet energy levels, ultimately achieving thermally activated delayed fluorescence emission.

[0012] The auxiliary ligand is modified with different numbers of R atoms at different positions to form derivatives, thereby achieving multi-angle and diversified heavy atom modification and maximizing the efficient utilization of triplet excitons.

[0013] A method for preparing a complex possessing thermally activated delayed fluorescence properties includes the following steps:

[0014] (1) Take metal salt, auxiliary ligand, main ligand and guest molecule and put them into a mixed solution of DMF, EtOH and H2O; wherein the molar ratio of main ligand: auxiliary ligand: metal ion: guest molecule is 1:(2-3):(1-3):(1-10);

[0015] (2) After sealing, it is placed in a heated environment to eventually form crystals.

[0016] The preferred molar ratio of main ligand: auxiliary ligand: metal ion: guest molecule is 1:2:2:1.

[0017] A complex with thermally activated delayed fluorescence (TADF) properties was applied to X-ray detection. Optionally, to ensure stable application in X-ray detection, the light yield of a series of coordination polymer materials under X-rays was first determined, as well as the changes in light yield under different X-ray powers. The switching stability of the light yield of the series of TADF materials under rated X-ray power was also tested. Secondly, the C3-3 sample with the optimal light yield under X-ray excitation was selected for film preparation, and the X-ray detection application of the C3-3 flexible film was completed.

[0018] A complex with thermally activated delayed fluorescence properties is used to prepare a flexible film. The specific method is as follows: high-purity complex crystals are selected, and the crystalline material is first uniformly ground to the micron level. The micron-sized sample powder of the complex is mixed with a polyacrylate solution at a ratio of 1:4 (g:ml). The air bubbles are driven to the surface of the mixture by ultrasonication and the two are fully mixed. After standing for 24 hours under normal temperature and pressure conditions, a flexible scintillator film is finally formed.

[0019] The technical effects of this invention are as follows: 1. The addition of heavy atoms to different components in this invention can effectively adjust the emission wavelength of the material. While ensuring efficient utilization of excitons, it can also achieve large-area emission domain control and coverage, providing favorable preconditions for realizing high-performance scintillator materials. 2. The thermally activated delayed fluorescence complex has metal ions with large atomic numbers participating in coordination, effectively increasing the absorption of radiation; and the material has excellent thermal stability, with a decomposition temperature of about 270 degrees Celsius. The thermally activated delayed fluorescence complex has an emission range of 510-590 nm, a wide wavelength control range; a quantum yield of 5.02-56.48%; and a delayed fluorescence lifetime of 0.3-2.3 μs, which can be used to prepare scintillator materials with high time resolution. 3. The method provided by this invention is simple to operate, easy to control, has a considerable material yield, and a concise synthesis step; it avoids the high-temperature and high-pressure synthesis process of traditional inorganic crystalline scintillator materials. This reduces resource waste during the synthesis process; and the material has good thermal processability, thus ensuring good film-forming stability, and is expected to produce novel TADF-based scintillator materials.

[0020] Advantages of this invention: 1. This invention provides a thermally activated delayed fluorescence (TADF) crystalline complex, which forms a complex acceptor framework with a host ligand, an auxiliary ligand, and metal ions coordinated together. Guest molecules, acting as donors, fill the pores, resulting in luminescence based on space charge transfer. 2. By modifying the R atoms of each component in the structure, this invention achieves both the TADF properties of the series of complexes and the regular regulation of their photophysical properties. 3. All of these complexes exhibit light emission under X-ray excitation; and through subsequent modification, the regular regulation of the X-ray response of the series of TADF complexes is achieved. 4. By selectively modifying the donor with R atoms, high photoluminescence quantum yield and short lifetime are achieved. 5. By introducing R atoms onto the auxiliary ligand, the photophysical properties of the complexes can be controlled by adjusting the number and position of the R atoms. 6. The multiple introduction of R atoms greatly enhances the TADF performance of the material, achieving a delayed fluorescence lifetime of nearly 1 μs during this modulation process. This is the optimal lifetime value for TADF luminescence, ensuring the stability of the excited state and demonstrating its potential for preparing high-performance X-ray detection scintillator materials with high exciton utilization and high light yield. 7. This invention achieves the introduction of heavy atoms and the enhancement of scintillator properties by replacing different types of components in the structure (including auxiliary ligands and guest molecules). (iv) Description of the attached drawings:

[0021] Figure 1 The UV-Vis absorption spectra of the complexes C1-C5 and C3-1 to C3-3 in the solid state of the series of examples are shown.

[0022] Figure 2 The emission spectra of the complexes C1-C5 and C3-1 to C3-3 in the solid state are shown in the series of examples.

[0023] Figure 3 The fluorescence emission decay curves of the complexes C1-C5 and C3-1 to C3-3 in the solid state are shown in the series of examples.

[0024] Figure 4 Thermogravimetric curves of the complexes C1-C5 and C3-1 to C3-3 in the solid state in the series of examples are shown.

[0025] Figure 5 The images show the radiative emission spectra of the complexes C1-C5 and C3-1 to C3-3 in the solid state of the series of examples.

[0026] Figure 6 Image of a C3-3 complex flexible thin film under X-ray excitation. (V) Specific Implementation Methods:

[0027] Example: A complex with thermally activated delayed fluorescence properties is prepared from a host ligand, an auxiliary ligand, a metal ion, and a guest molecule in a molar ratio of 1:2:2:1; the host ligand acts as an acceptor, coordinating with the auxiliary ligand and the metal ion to form a triple-interpenetrating hexagonal nested cage structure; the guest molecule acts as a donor.

[0028] A method for preparing a series of crystalline complex materials with thermally activated delayed fluorescence properties includes the following steps:

[0029] Preparation of C1[Cd4(TPT)2(PTA)3(H2O)4]·2(Ph-Cz) crystal: Take cadmium metal salt Cd(NO4)2(PPT)3(H2O)4]·2(Ph-Cz) crystal. 3)2 0.1 mmol of 4H₂O, 0.1 mmol of auxiliary ligand terephthalic acid, 0.05 mmol of pyridine triazine, and 0.05 mmol of guest Ph-Cz were placed in a 20 ml vial containing 12 ml of a mixed solution. The mixed solution contained 4 ml of DMF, 4 ml of EtOH, and 4 ml of H₂O. The vial was tightly capped and placed in a 100 °C oven and heated for 20 hours, eventually producing orange-colored Cl crystals.

[0030] Preparation of C2[Cd4(TPT)2(PTA)3(H2O)4]·2(Ph-Cz-Br(2)) crystals: According to the above synthesis method, pyridine triazine, terephthalic acid and cadmium ions were used in the same dosage. The guest molecule was replaced from Ph-Cz with 0.05 mmol of Ph-Cz-Br(2). The solution was placed in a 20 ml vial containing 12 ml of mixed solution. The mixed solution contained 4 ml of DMF, 4 ml of EtOH and 4 ml of H2O. The vial was tightly capped and placed in a 100℃ oven and heated for 20 hours. Orange crystals of C2 were finally generated.

[0031] Preparation of C3[Cd4(TPT)2(PTA)3(H2O)4]·2(Ph-Cz-2Br(2,7)) crystals: According to the above synthesis method, pyridine triazine, terephthalic acid and cadmium ions were used in the same dosage, and the guest molecule was 0.05 mmol of Ph-Cz-2Br(2,7). The mixture was placed in a 20 ml vial containing 12 ml of a mixed solution, which contained 4 ml of DMF, 4 ml of EtOH and 4 ml of H2O. The vial was tightly capped and placed in a 100 °C oven and heated for 20 hours, finally producing bright yellow C3 crystals.

[0032] Preparation of C4[Cd4(TPT)2(PTA)3(H2O)4]·2(Ph-Cz-Br(3)) crystals: According to the above synthesis method, pyridine triazine, terephthalic acid and cadmium ions were taken in the same dosage, and the guest molecule was Ph-Cz-Br(3) 0.05 mmol. It was placed in a 20 ml vial containing 12 ml of mixed solution. The mixed solution contained DMF: 4 ml, EtOH: 4 ml and H2O: 4 ml. The vial was tightly capped and placed in a 100℃ oven and heated for 20 hours. Orange C4 crystals were finally generated.

[0033] Preparation of C5[Cd4(TPT)2(PTA)3(H2O)4]·2(Ph-Cz-2Br(3,6)) crystals: According to the above synthesis method, pyridine triazine, terephthalic acid and cadmium ions were used in the same dosage, and the guest molecule was 0.05 mmol of Ph-Cz-2Br(3,6). The mixture was placed in a 20 ml vial containing 12 ml of a mixed solution, which contained 4 ml of DMF, 4 ml of EtOH and 4 ml of H2O. The vial was tightly capped and placed in a 100 °C oven and heated for 20 hours to finally produce orange C5 crystals.

[0034] Preparation of C3-1[Cd4(TPT)2(2-Br-PTA)3(H2O)4]·2(Ph-Cz-2Br(2,7)) crystals: Take cadmium metal salt Cd(NO3)4… 3)2· 4H2O 0.1mmol, auxiliary ligand 2-bromo-terephthalic acid: 0.1mmol, pyridine triazine 0.05mmol, guest Ph-Cz-2Br(2,7): 0.05mmol, were placed in a 20ml vial containing 12ml of the mixed solution. The mixed solution contained 4ml of DMF, 4ml of EtOH, and 4ml of H2O. The vial was tightly capped and heated in a 100℃ oven for 20 hours, eventually producing bright yellow crystals C3-1.

[0035] Preparation of C3-2[Cd4(TPT)2(2,5-2Br-PTA)3(H2O)4]·2(Ph-Cz-2Br(2,7)) crystals: Take cadmium metal salt Cd(NO3)2[Cd4(TPT)2(2,5-2Br-PTA)3(H2O)4]·2(Ph-Cz-2Br(2,7)) crystals. 3)2 · 4H2O 0.1mmol, auxiliary ligand 2,5-dibromo-terephthalic acid: 0.1mmol, pyridine triazine 0.05mmol, guest Ph-Cz-2Br(2,7): 0.05mmol, were placed in a 20ml vial containing 12ml of the mixed solution. The mixed solution contained 4ml of DMF, 4ml of EtOH, and 4ml of H2O. The vial was tightly capped and heated in a 100℃ oven for 20 hours, eventually producing bright yellow crystals C3-2.

[0036] Preparation of C3-3[Cd4(TPT)2(2,3,5,6-4Br-PTA)3(H2O)4]·2(Ph-Cz-2Br(2,7)) crystals: Take cadmium metal salt Cd(NO3)4… 3)2 · 4H2O 0.1mmol, auxiliary ligand 2,3,5,6-tetrabromo-terephthalic acid: 0.1mmol, pyridine triazine 0.05mmol, guest Ph-Cz-2Br(2,7): mg, 0.05mmol, were placed in a 20ml vial containing 12ml of the mixed solution. The mixed solution contained 4ml of DMF, 4ml of EtOH, and 4ml of H2O. The vial was tightly capped and placed in a 100℃ oven and heated for 20 hours, eventually producing light green crystals C3-3.

[0037] All the above synthetic methods employ quantitative feeding of components, i.e., the optimal feeding amount; the complexes can also be synthesized according to the optimal feeding ratio. In the optimal feeding ratio, the molar ratio between pyridine triazine and auxiliary ligands (including: terephthalic acid; 2-bromo-terephthalic acid; 2,5-dibromo-terephthalic acid; 2,3,5,6-tetrabromo-terephthalic acid), cadmium ions (including: cadmium nitrate tetrahydrate, cadmium chloride, cadmium oxide), and guest molecules is: pyridine triazine: auxiliary ligand: cadmium ion: guest = 1:2:2:1. Furthermore, the feeding amount of guest molecules in this system can also be changed. In summary, regardless of the optimal feeding ratio, the above complexes can be obtained with a pyridine triazine: auxiliary ligand: cadmium ion: guest ratio of 1:(2-3):(1-3):(1-10), the difference being the purity and yield of the synthesized sample.

[0038] A complex with thermally activated delayed fluorescence (TADF) properties was applied to X-ray detection. Optionally, to ensure stable application in X-ray detection, the light yield of a series of coordination polymer materials under X-rays was first determined, as well as the changes in light yield under different X-ray powers. The switching stability of the light yield of the series of TADF materials under rated X-ray power was also tested. Secondly, the C3-3 sample with the optimal light yield under X-ray excitation was selected for film preparation, and the X-ray detection application of the C3-3 flexible film was completed.

[0039] A complex with thermally activated delayed fluorescence properties is used to prepare a flexible film. The specific method is as follows: eight high-purity complex crystals are selected as samples. First, the crystalline materials are uniformly ground to the micron level. The micron-sized sample powders of the eight complexes are mixed with polyacrylate solution at a ratio of 1:4 (g:ml). The air bubbles are driven to the surface of the mixture by ultrasonication and the two are fully mixed. After standing for 24 hours under normal temperature and pressure conditions, a flexible scintillator film is finally formed.

[0040] like Figure 1 As shown, in the UV-Vis absorption spectroscopy tests, the series of complexes all exhibited strong charge transfer absorption peaks from 350 nm to 550 nm; in the emission spectroscopy tests, the excitation wavelength was 370 nm; the test results are as follows. Figure 2 As shown, C1 to C5 exhibit emission peaks at 592nm, 569nm, 543nm, 584nm, and 589nm. C3-1 and C3-3 exhibit emission peaks at 534nm and 509nm, respectively.

[0041] like Figure 3 The fluorescence emission decay curves shown clearly demonstrate the delayed fluorescence properties of this series of complexes; their fluorescence emission decay curves exhibit both short and long lifetimes. Furthermore, this series of complexes possesses a long lifetime of less than 3 μs, effectively reducing exciton roll-off based on TADF properties.

[0042] like Figure 4 The thermogravimetric analysis curves of the series of complexes shown indicate that the series of complexes have good thermal stability. For example... Figure 5 As shown, by using 5W X-rays to irradiate and excite a series of complexes, it was found that the irradiated light yield of the complexes increased dramatically with the increase of the number of heavy bromine atoms.

[0043] like Figure 6 As shown, the film prepared by mixing the complex and polyacrylate was subjected to object penetration imaging under 12W radiation. From the imaging results, the complex prepared into a film still has good light yield and good spatial resolution, and the contrast of the object is relatively clear, demonstrating the potential application of the complex in X-ray imaging.

Claims

1. A complex possessing thermally activated delayed fluorescence properties, characterized in that, The complex consists of pyridine triazine (TPT), 2,3,5,6-tetrabromoterephthalic acid (2,3,5,6-4Br-PTA), and Cd. 2+ It was prepared by reacting 2,7-dibromo-N-phenylcarbazole Ph-Cz-2Br(2,7) in a molar ratio of 1:2:2:1; the TPT was used as an acceptor in combination with the 2,3,5,6-4Br-PTA and Cd. 2+ Coordination forms a triple-interpenetrating hexagonal nested cage structure, with Ph-Cz-2Br(2,7) serving as the donor.

2. A method for preparing the complex according to claim 1, characterized in that, Includes the following steps: 0.1 mmol of Cd(NO3)2·4H2O, 0.1 mmol of 2,3,5,6-tetrabromoterephthalic acid, 0.05 mmol of pyridine triazine, and 0.05 mmol of Ph-Cz-2Br(2,7) were added to a mixed solvent containing 4 mL of DMF, 4 mL of EtOH, and 4 mL of H2O. The mixture was sealed and heated at 100 °C for 20 hours to obtain [Cd4(TPT)2(2,3,5,6-4Br-PTA)3(H2O)4]·2(Ph-Cz-2Br(2,7)) crystals.

3. The application of the complex according to claim 1, characterized in that, It is used in X-ray detection.

4. A method for preparing a flexible scintillator film containing the complex of claim 1, characterized in that, Includes the following steps: First, the crystals of the complex described in claim 1 are uniformly ground to the micron level. The micron-sized sample powder of the complex is then mixed with a polyacrylate solution at a ratio of 1g:4mL. Air bubbles are driven to the surface of the mixture using an ultrasonic method to ensure thorough mixing. Subsequently, the mixture is left to stand for 24 hours under normal temperature and pressure to form a flexible scintillator film.

5. The use of the flexible scintillator film prepared by the method according to claim 4, characterized in that, The resulting flexible scintillator film is used in X-ray imaging.

Images