A zero / negative thermal quenching near-infrared photoluminescent material and its preparation method and application

Abstract

The present invention belongs to the technical field of synthesis of special functional inorganic fluorescent materials, and relates to a zero / negative thermal quenching near-infrared photoluminescent material, a preparation method thereof and an application. The material is obtained by a solvothermal reaction of 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene obtained by reacting imidazole with α,α'-dichloro-o-xylene with cuprous iodide. The luminescence of this material is composed of metal-to-ligand charge transfer (MLCT) and cluster center triplet excited state ( 3 CC). This material (λ ex = 400 nm) exhibits a fluorescence thermal quenching effect at 295K - 385K and a fluorescence negative thermal quenching effect at 385K - 475K, and the fluorescence intensity is very stable in the high-temperature region. Its external quantum efficiency is as high as 22.07%, and it is a rare copper cluster that can emit light in the near-infrared region. It is a new type of high-efficiency OLED photoluminescent material with broad application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of special functional inorganic fluorescent material synthesis, and specifically relates to a zero / negative thermal quenching near-infrared photoluminescent material and a preparation method and application thereof. Background Art

[0002] Photoluminescent materials are widely used in LEDs, and the performance of photoluminescent materials is crucial to the performance of LEDs. Photoluminescent materials have potential application prospects in the fields of fluorescence, sensing, anti-counterfeiting, and can be used in the fields of biological labels, displays, and light-emitting diodes. However, the photoluminescent intensity of luminescent materials is affected by thermal quenching, that is, as the temperature increases, its luminescent intensity decreases and the emission spectrum red-shifts, which seriously hinders the application of photoluminescent materials.

[0003] In the prior art, their electronic and optical properties are usually optimized through molecular design, and the photoluminescence quantum yield is improved through ligand engineering. However, the organic ligands with conjugated structures in coordination polymers show various non-radiative internal relaxation pathways through various vibrational and electronic excited states. During the non-radiative relaxation process, thermal quenching behavior occurs, reducing the luminescence efficiency at ambient temperature. Another approach is to introduce organic molecules with thermal delayed fluorescence effect (TADF) and metal-free. The excited triplet energy level and the excited singlet energy level of such molecules are very close, so the energy can be efficiently inter-gap-crossed from the non-radiative triplet state to the radiative singlet state, thereby improving the efficiency of electroluminescence. However, most TADF-based materials still cannot avoid the quenching behavior caused by the non-radiative relaxation process, and cannot solve the technical problem of how to improve the luminescence efficiency at ambient temperature, which greatly limits the application of photoluminescent materials.

[0004] The integrated intensity of photoluminescence in solids, such as semiconductors and molecular crystals, usually decreases monotonically with increasing temperature. This phenomenon is called thermal quenching (TQ) because the non-radiative relaxation of excited electrons to the ground state increases rapidly with increasing temperature. This thermal quenching effect seriously affects the efficiency and performance of light-emitting diodes. Therefore, it is of great practical significance to develop photoluminescent materials that are resistant to thermal quenching. In some semiconductor nanostructures, such as ZnO and CdSe, the fluorescence intensity increases with increasing temperature. This abnormal phenomenon is called negative thermal quenching (NTQ) of fluorescence, and traditional semiconductor materials usually have such a property at very low temperatures (tens of Kelvin). However, thermally activated delayed fluorescence type emitters are often affected by thermal quenching (TQ) due to non-radiative deactivation. So far, the known examples of negative thermal quenching are quite limited.

[0005] In 2020, our research group reported a copper-organic framework material with delayed fluorescence properties (Chem. Commun., 2020, 56, 12057–12060). The complex was successfully synthesized under solvothermal conditions using the ligand 4,4′-bis(imidazol-1-yl)diphenylether(bidpe) and monovalent copper. 2 I 2 (biped)] n (CP1). The complex exhibits negative thermal quenching (NTQ) photoluminescence properties, which is driven by electronic fluctuations between the localized and delocalized forms of the imidazolyl group of its ligand, and the process is fully reversible during the cooling / heating cycle. In this work, it was found that the NTQ effect in the thermally activated delayed fluorescence (TADF) type Cu(I) iodine metal-organic layered framework can be precisely controlled by thermally driven transitions between two different electrons in the imidazolyl group in the ligand. This study has opened up a new path for exploring the electronically switchable NTQ effect in coordination networks and further developing light-emitting diodes based on the NTQ principle. Continuing this work, in 2021 our research group reported the continuation of this work (J.Phys.Chem.Lett.,2021,12,8237-8245), replacing the imidazolyl part in the ligand with triazole, synthesizing the ligand 4,4′-bis(1,2,4-triazole)diphenylether(btdpe), and successfully obtaining the complex [Cu] with monovalent copper under solvothermal conditions. 2 I 2 (btdpe)] n(CP2). The thermal quenching (TQ) effect was compared between CP1 and CP2. After the CP1 crystal was cooled in liquid nitrogen, its luminescence was almost completely quenched, fully recovered at 238K, and did not change until 318K. Therefore, the temperature-dependent emission spectrum shows that CP1 exhibits a negative thermal quenching (NTQ) effect in the low temperature range (77-238K). More interestingly, CP1 exhibits a zero thermal quenching (ZTQ) effect in a wider temperature range (238-318K). However, CP2 exhibits a significant TQ effect. Combining the temperature-dependent absorption spectrum and X-ray diffraction data analysis shows that the NTQ to TQ transition is driven by the electronic structure transition of the ligands around the cuprous center. CP1 exhibits a drastic NTQ effect in the TADF effect and partial charge localization range, and has a significant ZTQ effect near ambient temperature. Therefore, CP1 shows efficient luminescence with a PLQY of 46% at room temperature. By adopting a rational molecular design strategy, it is expected that luminescent metal-organic materials that exhibit NTQ or ZTQ performance at higher temperatures can be used as charge dynamic complexes. This study will help prepare highly emissive Cu(I)-organic frameworks and inspire the study of functional metal complexes.

[0006] The zero / negative thermal quenching near-infrared photoluminescent material provided by the present invention not only has an obvious zero / negative thermal quenching effect, but also has a zero thermal quenching (ZTQ) effect in the range of 295K-385K, and an obvious NTQ effect in the range of 385K-475K, and the fluorescence intensity is very stable in the high temperature region. It can also emit bright light in the near-infrared (NIR) region, with an emission center at 710nm. It is a very rare metal copper cluster that can photoluminesce in the near-infrared region. Compared with visible light and ultraviolet light, near-infrared light has the characteristics of being invisible, having strong penetration, having little background interference, and being harmless to organisms. It has important research value and broad application prospects in the fields of organic light-emitting diodes (OLEDs), night vision, biomedicine, communications, aerospace, information storage, and energy. However, synthesizing copper cluster materials that exhibit emission characteristics in the near-infrared (NIR) region is still a great challenge at this stage.

[0007] Near infrared (NIR) refers to electromagnetic waves with a wavelength range of 700–2500nm. About 50% of the spectrum from the sun to the earth is in the near infrared. Therefore, in the energy field, making full use of the energy in the near infrared region of sunlight can greatly improve the energy conversion efficiency of solar cells. In the biological field, the absorbance of proteins and water in organisms is the weakest in the near infrared region. If near infrared materials located in the optimal biological analysis window are used as biological dyes or probes, the background fluorescence interference of the organism itself can be avoided to achieve better labeling and treatment effects. However, photoluminescent materials that can emit light in the near infrared region are very rare. The cuprous complex with zero / negative thermal quenching near infrared photoluminescence provided by the present invention opens up new opportunities for the functional application of copper cluster materials. Summary of the invention

[0008] A zero / negative thermal quenching near-infrared photoluminescent material and its preparation method and application. The raw materials for the synthesis of the material are easily available, the synthesis method is simple, the yield is high, and the properties are stable. The complex not only exhibits excellent zero / negative thermal quenching photoluminescent performance, but also can emit bright light in the near-infrared (NIR) region, and its external quantum efficiency is as high as 22.07%. It is not only a rare copper cluster that can emit light in the near-infrared region, but also a material with a higher external quantum efficiency among the metal clusters that can emit light in the near-infrared region. It exhibits excellent luminescent properties and is a new and efficient photoluminescent material with broad application prospects in the fields of OLEDs, night vision, biomedicine, communications, aerospace, information storage and energy.

[0009] The present invention provides a zero / negative thermal quenching near-infrared photoluminescent material, the molecular formula of which is C 32 H 36 Cu 4 I 4 N 8 , the structural formula is as follows:

[0010]

[0011] The crystallographic data of a zero / negative thermal quenching near-infrared photoluminescent material (complex M-1) provided by the present invention are shown in the following table:

[0012]

[0013]

[0014] The zero / negative thermal quenching near-infrared photoluminescent material provided by the present invention is crystallized in the triclinic system, P2 1 / c space group. The unit cell parameters are α=90°, β=90.860(2)°, γ=90°, Z=4, The metal atom Cu coordinates with one N atom on the ligand 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene and one I atom on CuI to form a one-dimensional chain. Cu···Cu's distance is smaller than the van der Waals radius of copper atoms Therefore, this Cu 4 I 4 clusters with strong Cu···Cu interactions.

[0015] The invention provides a preparation method of the zero / negative thermal quenching near-infrared photoluminescent material. The reaction steps are as follows: a mixture of cuprous iodide, 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene, acetonitrile and water is sealed in a tetrafluoroethylene high-pressure reactor, reacted at 180±10°C for 3±0.2 days, then slowly cooled to room temperature, filtered to obtain light yellow crystals, repeatedly washed with distilled water and acetonitrile, and dried in air to obtain pure light yellow target crystals, namely the zero / negative thermal quenching near-infrared photoluminescent material.

[0016] Furthermore, the preparation method of the above 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene comprises: mixing 2-methylimidazole and α,α'-dichloro-o-xylene in a methanol solution under nitrogen protection or in air, heating and refluxing for reaction (further heating and refluxing for 20±4 hours at 80±5°C); cooling to room temperature after the reaction, rotary evaporating the solvent to obtain a thick yellow slurry containing 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene, and then dissolving it in an aqueous potassium carbonate solution. The obtained solution is allowed to stand to produce a large number of crystals, filtered, repeatedly washed with deionized water, and dried (preferably at 70°C) to obtain 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene.

[0017]

[0018] The compound synthesis reaction formula is as follows:

[0019] Furthermore, the reaction molar ratio of the reactants cuprous iodide and 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene is 5:2; and the volume ratio of the mixed solvent of water and acetonitrile is 6:2.

[0020] The present invention also provides the application of the zero / negative thermal quenching near-infrared photoluminescent material. The metal center of the complex is composed of four interconnected copper atoms, each copper ion is connected by μ 3-I bridge, the metal atom Cu is coordinated with one N atom on the ligand 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene and one I atom on CuI, forming a one-dimensional chain. Among them, Cu1-Cu2=2.654(3), Cu1-Cu3=2.556(3), Cu2-Cu4=2.555(3), Cu3-Cu4=2.737(4), and the distance between Cu···Cu is less than the van der Waals radius of the copper atom. , so this Cu 4 I 4 clusters, with strong Cu···Cu interactions. 4 I 4 clusters, with strong Cu···Cu interactions, which means that the cluster center triplet excited state ( 3 CC) is the main source of light emission from the zero / negative thermal quenching near-infrared photoluminescent material. The variable temperature fluorescence spectrum (λ ex =400nm) the maximum emission wavelength continues to blue shift with the increase of temperature, indicating that the luminescence of the zero / negative thermal quenching near-infrared photoluminescent material is caused by the charge transfer from metal to ligand (MLCT) and the triplet excited state of the cluster center ( 3 In addition, the zero / negative thermal quenching near-infrared photoluminescent material has an external quantum efficiency of up to 22.07%, is a rare copper cluster capable of emitting light in the near-infrared region, exhibits excellent luminescence performance, and is a highly efficient OLED photoluminescent material.

[0021] The application of the zero / negative thermal quenching near-infrared photoluminescent material in LED, the application method includes M-1 crystal packaging LED device, adding commercial blue powder BAM (BaMgAl 10 O 17 :Eu 2+ ) and commercial green powder (Ba, Sr) 2 SiO 4 :Eu 2+ Mixed solid powder encapsulation. The mass ratio of blue, green, and M-1 crystals is 3:1:6. ZWL8820 organic silica gel is used for encapsulation, and the total mass of all powders mixed with the mass ratio of organic silica gel is 1:0.8. 365nm ultraviolet chip is used for encapsulation; LED chip specifications: 1w, ~365nm.

[0022] The above zero / negative thermal quenching near-infrared photoluminescent material not only has zero / negative thermal quenching performance, but can also emit light in the near-infrared (NIR) region, and can be applied to the field of OLED light-emitting materials.

[0023] Compared with the prior art, the present invention has the following technical advantages: the zero / negative thermal quenching near-infrared photoluminescent material of the present invention has readily available raw materials for synthesis, a simple synthesis method, high yield and stable properties. ex =400nm) has zero thermal quenching effect in the range of 295K-385K, and obvious negative thermal quenching effect in the range of 385K-475K. The fluorescence intensity is very stable in the high temperature region, and the external quantum efficiency is as high as 22.07%. It is not only a rare copper cluster that can emit light in the near-infrared region, but also a material with high external quantum efficiency among the metal clusters that can emit light in the near-infrared region. It has excellent luminescence performance and is a new and efficient photoluminescent material with broad application prospects in OLEDs, night vision, biomedicine, communications, aerospace, information storage and energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the temperature-dependent fluorescence spectrum of M-1 measured by FS5-A2356-02 fluorescence spectrometer, with the maximum excitation wavelength of 400nm (λ ex =400nm). With the increase of temperature, the maximum emission wavelength continues to blue shift, indicating that the luminescence of M-1 is caused by the charge transfer from metal to ligand (MLCT) and the triplet excited state of the cluster center ( 3 CC) together.

[0025] Figure 2 is the curve of the integral of the excitation intensity of the M-1 crystal versus the temperature T, M-1(λ ex =400nm) has zero thermal quenching effect in the range of 295K–385K, and an obvious negative thermal quenching effect in the range of 385K–475K. The fluorescence intensity is very stable in the high temperature region. M-1 crystal is a new type of thermal quenching-resistant material.

[0026] Figure 3 is the emission spectrum of M-1 measured by FS5-A2356-02 fluorescence spectrometer, where λ ex represents the maximum excitation wavelength of fluorescence, λ em Indicates the maximum fluorescence emission wavelength. The maximum excitation wavelength of M-1 crystal is 400nm, and the maximum emission wavelength of the compound is 710nm. It is a rare monovalent copper complex that can emit light in the near-infrared region; the Stokes shift is 310nm.

[0027] Figure 4This is the quantum efficiency diagram of M-1 crystal measured by Quantaurus-QY Plus UV-NIR absolute quantum yield meter. The positions marked in the boxes are QY (internal quantum efficiency, i.e. fluorescence quantum efficiency) value and Abs (absorption rate) value. The product of the two is EQE (external quantum efficiency). The external quantum efficiency of the solid powder of M-1 crystal is as high as 22.07%, which is the material with higher external quantum efficiency among the metal clusters that can emit light in the near-infrared region.

[0028] Figure 5 This is the electroluminescence spectrum of the LED device assembled with M-1 crystal under the working current of 100-200mA flux, measured by the Rainbow Spectrum HP 9000 light and color tester.

[0029] Figure 6 This is the thermogravimetric diagram of M-1 crystal. The crystal structure begins to collapse at around 320°C and collapses completely at around 580°C. The thermal stability of M-1 crystal is very good.

[0030] Figure 7 This is the powder X-ray diffraction pattern of M-1. The experimental data is basically consistent with the computational simulation data, confirming that the test sample has a high purity and is consistent with the obtained crystal structure.

[0031] Figure 8 This is a diagram showing the lighting effect of an LED device obtained in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention is not limited to the following specific embodiments. A person skilled in the art can implement the present invention in various other specific embodiments according to the contents disclosed in the present invention, or any simple changes or modifications made to the design structure and ideas of the present invention fall within the protection scope of the present invention. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0033] The embodiment of the present invention provides a zero / negative thermal quenching near-infrared photoluminescent material, the molecular formula of which is C 32 H 36 Cu 4 I 4 N 8 , the structural formula is as follows:

[0034]

[0035] The crystallographic data of the above zero / negative thermal quenching near-infrared photoluminescent material are shown in Table 1.

[0036] Table 1 Crystallographic data of complex M-1

[0037]

[0038]

[0039] The zero / negative thermal quenching near-infrared photoluminescent material is crystallized in the triclinic system, P2 1 / c space group. The unit cell parameters are α=90°, β=90.860(2)°, γ=90°, Z=4, The metal atom Cu coordinates with one N atom on the ligand 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene and one I atom on CuI to form a one-dimensional chain. Cu···Cu's distance is smaller than the van der Waals radius of copper atoms Therefore, this Cu 4 I 4 clusters with strong Cu···Cu interactions.

[0040] The present invention further provides a preparation method and application method of the zero / negative thermal quenching near-infrared photoluminescent material. The present invention is further described in detail below in conjunction with the embodiments:

[0041] Example 1

[0042] Under nitrogen protection or in air, 2-methylimidazole (3.81g, 46.4mmol) and α,α'-dichloro-o-xylene (0.78g, 4.46mmol) were mixed in a methanol solution (50mL) and heated under reflux at 80°C for 20 hours. The reaction was stopped, cooled to room temperature, and the solvent was evaporated by rotary evaporation to obtain a thick yellow slurry, which was then dissolved in a potassium carbonate aqueous solution (80ml, 6.13g). The resulting solution was allowed to stand to produce a large amount of crystals, which were filtered, repeatedly washed with deionized water, and dried at 70°C to obtain a large amount of 1,2-bis((2-methyl-1H-imidazole-1-yl)methyl)benzene. A mixture of cuprous iodide (38 mg, 0.2 mmol), 1,2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene (21.3 mg, 0.08 mmol), acetonitrile (2 mL) and water (6 mL) was sealed in a 15 mL tetrafluoroethylene autoclave and reacted at 180°C for 3 days. After slowly cooling to room temperature, light yellow crystals were obtained by filtration, which were repeatedly washed with distilled water and acetonitrile, and dried in air to obtain pure light yellow target crystals.

[0043] Example 2

[0044] The LED device packaged in M-1 crystal is made of M-1 crystal with commercial blue powder BAM (BaMgAl 10 O 17 :Eu2+ ) and commercial green powder (Ba, Sr) 2 SiO 4 :Eu 2+ Mixed solid powder encapsulation. The mass ratio of blue, green, and M-1 crystals is approximately 3:1:6. ZWL8820 organic silica gel is used for encapsulation, and the powder-to-glue mass ratio is 1:0.8 (here refers to the total mass of all powders mixed). 365nm ultraviolet chip is used for encapsulation; LED chip specifications: 1w, ~365nm. The encapsulation environment temperature is 25℃ and the ambient humidity is 65%.

[0045] The device has the following electrical parameters: forward current: If = 100.00 mA, forward voltage: Vf = 3.49 V, reverse current: Ir = 0.00 uA, reverse voltage: Vr = 10.00 V; its chromaticity parameters: chromaticity coordinate: x =

[0046] 0.3514, y=0.3731, u=0.2075, v=0.3304, duv=0.0084; correlated color temperature: 4852K, dominant wavelength: 569.0nm, color purity: 17.4%, half width: 277.6nm; luminous flux color ratio: R=17.9%, G=78.4%, B=3.7%; peak wavelength: 525.7nm; photometric parameters: luminous flux: 5.8501m, luminous efficiency 16.81m / w, light radiation power: 25.4mw, radiation intensity: 0.0nw / sr, energy efficiency: 0.921, energy efficiency grade: E, photon number: 0.001umol / s; color rendering index: Ra=96.5, color rendering index is close to 100%, and color rendering is excellent.

[0047] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A zero / negative thermal quenching near-infrared photoluminescent material, characterized in that: The molecular formula is C 32 H 36 Cu4I4N8, structural formula: ； The unit cell parameters of the material are a = 8.9276 (2) Å, b = 14.0857(4) Å, c = 29.8293(8) Å, α = 90°, β = 90.860 (2)°, γ = 90°, Z = 4, V = 3750.66 (17) Å 3 ; The metal center of the material is composed of four interconnected copper atoms, each of which is bridged by μ3-I. The copper atoms are coordinated with one N atom on the ligand 1, 2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene and one I atom on CuI to form a one-dimensional chain.

2. The method for preparing the zero / negative thermal quenching near-infrared photoluminescent material according to claim 1, characterized in that: The following steps are involved: A mixture of cuprous iodide, 1, 2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene, acetonitrile and water was sealed in a tetrafluoroethylene high-pressure reactor, reacted at 180±10°C for 3±0.2 days, then slowly cooled to room temperature, filtered to obtain light yellow crystals, repeatedly washed with distilled water and acetonitrile, and dried in air to obtain pure light yellow target crystals, i.e. the above-mentioned zero / negative thermal quenching near-infrared photoluminescent material.

3. The method for preparing the zero / negative thermal quenching near-infrared photoluminescent material according to claim 2, characterized in that: The preparation method of 1, 2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene comprises: under nitrogen protection or in air, mixing 2-methylimidazole and α, α'-dichloro-o-xylene in a methanol solution and heating to reflux for reaction; cooling to room temperature after the reaction is completed; rotary evaporating the solvent to obtain a thick yellow slurry containing 1, 2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene; then dissolving the slurry in a potassium carbonate aqueous solution; standing the obtained solution for crystallization; suction filtering; repeatedly washing with deionized water; and drying to obtain 1, 2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene.

4. The method for preparing the zero / negative thermal quenching near-infrared photoluminescent material according to claim 3, characterized in that: The heating reflux reaction temperature is 80±5°C and the time is 20±4 hours.

5. The method for preparing the zero / negative thermal quenching near-infrared photoluminescent material according to claim 2, characterized in that: The reaction molar ratio of the reactants cuprous iodide and 1, 2-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene is 5:2; the volume ratio of the mixed solvent of water and acetonitrile is 6:

2.

6. The use of the zero / negative thermal quenching near-infrared photoluminescent material according to claim 1, characterized in that: Used as photoluminescent material in OLED devices.

7. The use of the zero / negative thermal quenching near-infrared photoluminescent material according to claim 1, characterized in that: For LED devices, LED device packaging includes: adding commercial blue powder BaMgAl to zero / negative thermal quenching near-infrared photoluminescent materials 10 O 17 : Eu 2+ and commercial green powder (Ba, Sr)2SiO4: Eu 2+ The mixed solid powder is encapsulated; the mass ratio of blue powder: green powder: zero / negative thermal quenching near-infrared photoluminescent material is 3:1:6; ZWL8820 organic silica gel is used for encapsulation, and the total mass ratio of blue powder, green powder and zero / negative thermal quenching near-infrared photoluminescent material to organic silica gel is 1:0.8; 365 nm ultraviolet chip is used for encapsulation; LED chip specifications: 1 W, ~365 nm.

8. The use of a zero / negative thermal quenching near-infrared photoluminescent material according to claim 7, characterized in that: The packaging environment temperature is 25°C and the environment humidity is 65%.

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