A tadf quaternary phosphonium salt scintillator material and a preparation method and application thereof

Abstract

The application belongs to the field of organic light-emitting materials, and discloses a thermally activated delayed fluorescence (TADF) quaternary phosphonium salt scintillator material, a preparation method and application thereof. The structure formula of the TADF quaternary phosphonium salt scintillator material is R-NMe2PTPP-X, R is an alkyl group or an aromatic substituent group, and X is halogen. The preparation method of the material is as follows: 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl and halogenated alkane or halogenated aromatic hydrocarbon are dissolved in a solvent to react, and the precipitated product is collected to obtain the material. The TADF quaternary phosphonium salt scintillator material is made into a thin film. The material can be applied to an X-ray detection imaging device, has strong X-ray absorption capacity and high exciton utilization rate, has excellent performance, low cost, simple synthesis steps, and does not need to use a noble metal catalyst, and is conducive to large-scale synthesis.

Description

Technical Field

[0001] This invention relates to the field of organic light-emitting materials, specifically to a TADF quaternary phosphonium salt scintillator material, its preparation method, and its application. Background Technology

[0002] Scintillator materials can convert high-energy particles (such as X-rays, gamma rays, beta particles, etc.) into ultraviolet or visible light, playing a vital role in fields such as medical imaging, security inspection, industrial flaw detection, and non-destructive testing.

[0003] Scintillators can be broadly classified into two categories: inorganic scintillators and organic scintillators. Most inorganic scintillators are bulk single crystals. Common commercially available inorganic scintillators include sodium iodide (NaI), cesium iodide (CsI), bismuth germanate (BGO), and Lu. 1.8 Y 0.2 SiO5, Ce(LYSO), etc. However, inorganic scintillators are mainly prepared via the Bridgman process, requiring high temperatures (>1000℃) and a high vacuum environment. Their single-crystal growth rate is slow, leading to high costs. Furthermore, inorganic scintillators have poor mechanical flexibility, making them difficult to process into desired shapes. In contrast, organic scintillators possess inherent advantages such as short radiation decay time, diverse structures, abundant elemental reserves, readily available raw materials, high mechanical flexibility, low-temperature synthesis, and ease of processing. However, the poor X-ray absorption capacity and low exciton utilization of organic scintillators result in their scintillating performance being far inferior to that of inorganic scintillators. For example, anthracene, currently the most widely used organic scintillator, has a light yield of only 12000 photons / MeV, far lower than that of inorganic scintillators.

[0004] Thermally activated delayed fluorescence (TADF) molecules have important applications in organic electroluminescent devices due to their high exciton utilization. The energy difference between the singlet and triplet states in TADF molecules is relatively small. Of the excitons generated by electrical excitation, 75% are triplet excitons. These triplet excitons can overcome the energy barriers between the triplet and singlet states, reaching the singlet state via antisystem crossing, and then radiating to generate TADF. The theoretical exciton utilization of TADF molecules is 100%. To ensure high triplet exciton utilization efficiency, the energy difference between the singlet and triplet states in the TADF molecule needs to be as small as possible. Quantum chemical calculations show that by designing the host-guest structure within the molecule, a small energy difference between the singlet and triplet states can be achieved, allowing the HOMO and LUMO orbitals to be localized on the donor and acceptor states of the molecule, respectively. Although various host-guest TADF molecules have been reported in domestic and international literature, and corresponding OLED devices have exhibited excellent performance, existing TADF molecules are purely organic materials containing only carbon and hydrogen, exhibiting poor X-ray absorption and thus unsuitable as scintillator materials. Furthermore, the synthesis of most host-guest structured organic molecules is complex, requiring multiple steps, resulting in low yields, high costs, and the reliance on expensive noble metal catalysts. Therefore, there is an urgent need to develop an organic scintillator material with superior performance, a simple and low-cost synthesis route, and the ability to be mass-produced commercially. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a TADF quaternary phosphonium salt scintillator material, its preparation method, and its application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a TADF quaternary phosphonate scintillator material, abbreviated as R-NMe2PTPP-X, the structural formula of which is:

[0008]

[0009] Wherein, R is an alkyl or aromatic substituent; and X is a halogen.

[0010] This invention uses quaternary phosphonium nuclei as electron acceptors and dimethylamine as electron donors. Through a one-step method, 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl is reacted with haloalkanes or haloaromatics in a solvent to obtain TADF quaternary phosphonium salt molecules with host-guest structures.

[0011] The quaternary phosphonium derivative (PR3) of the present invention +Positively charged, these components possess strong electron-accepting capabilities, making them suitable electron acceptors. Nitrogen and oxygen-containing functional groups act as suitable electron donors. Through reaction within the same molecule, quaternary phosphonium salt materials with intramolecular host-guest structures are obtained. The halogen components in quaternary phosphonium salts have high atomic numbers and strong X-ray absorption capabilities, effectively improving the material's X-ray attenuation ability. The 1 mm thick TADF quaternary phosphonium salt scintillator material of this invention can absorb 53.48% of X-rays, with a photoluminescence quantum efficiency approaching 100% and a light yield of 80817 photons / MeV, making it an organic scintillator material with excellent luminescent properties.

[0012] As a preferred embodiment of the TADF quaternary phosphonium salt scintillator material of the present invention, the alkyl group is any one of chain methyl, ethyl, propyl, butyl, pentyl, hexyl and their derivatives, and cyclic cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and their derivatives; the aromatic substituent is any one of benzyl, phenethyl, phenylpropyl, phenylbutyl, phenylpentyl, 9-(2-ethyl)carbazole and their derivatives; the halogen is any one of chlorine, bromine, and iodine.

[0013] Secondly, the present invention provides a method for preparing the TADF quaternary phosphonate scintillator material, comprising the following steps: reacting 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl and haloalkanes or haloaromatics in a solvent, and collecting the precipitated product.

[0014] In a preferred embodiment of the method for preparing the TADF quaternary phosphonate scintillator material of the present invention, the haloalkane is any one of chain halomethane, haloethane, halopropane, halobutane, halopentane, halohexane and their derivatives, and cyclic halocyclopropane, halocyclobutane, halocyclopentane, halocyclohexane and their derivatives; the haloaromatic hydrocarbon is any one of halobenzyl, halophenylethane, halophenylpropane, halophenylbutane, halophenylpentane, 9-(2-haloethyl)carbazole and their derivatives; preferably, the halogen is any one of chlorine, bromine and iodine.

[0015] In a preferred embodiment of the method for preparing TADF quaternary phosphonate scintillator material according to the present invention, the solvent is at least one selected from toluene, ethyl acetate, methanol, tetrahydrofuran, n-hexane, and N,N-dimethylformamide.

[0016] In a preferred embodiment of the method for preparing TADF quaternary phosphonate scintillator material according to the present invention, the reaction temperature is controlled to be between room temperature and 150°C.

[0017] Thirdly, the present invention provides a thin film comprising the TADF quaternary phosphonium salt scintillator material and a polymer; wherein the mass ratio of the TADF quaternary phosphonium salt scintillator material to the polymer is (0.1-2):1.

[0018] Fourthly, this invention provides a method for preparing the aforementioned thin film, comprising the following steps: mixing the TADF quaternary phosphonium salt scintillator material with a polymer, heating and melting the mixture, coating it onto a substrate, and cooling it to obtain the final product. The heating and melting temperature is higher than the melting temperature of the polymer; the substrate is a quartz, transparent glass, or similar material. The thin film prepared by this method, when used as an X-ray scintillation imaging screen, can image objects such as backpacks, peanuts, and shrimp, demonstrating its application potential in fields such as security inspection, non-destructive testing, and agricultural seed selection.

[0019] Fifthly, the present invention provides the application of the TADF quaternary phosphonium salt scintillator material and the thin film in organic light-emitting devices.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] The TADF quaternary phosphonate scintillator material of this invention exhibits very bright visible light emission under ultraviolet light excitation due to its thermally activated delayed fluorescence mechanism. It also demonstrates strong X-ray absorption and high exciton utilization. The synthesis route is very simple, with high yield, allowing for large-scale synthesis. Scintillator materials prepared based on this type of TADF quaternary phosphonate salt exhibit excellent optical properties and show great commercial application potential in organic light-emitting devices, such as X-ray detection imaging screens, light-emitting diodes, optical thermometers, luminescent anti-counterfeiting chips, upconversion luminescent materials, and solid-state lighting. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the reaction process of the present invention;

[0023] Figure 2 This is a single-crystal structure diagram of the product of Example 1 of the present invention;

[0024] Figure 3 The emission spectrum of the product of Example 1 of the present invention;

[0025] Figure 4 The images show the temperature-dependent steady-state emission spectrum (a) and temperature-dependent transient emission spectrum (b) of the product from Example 1 of this invention.

[0026] Figure 5 This is a single-crystal structure diagram of the product of Example 2 of the present invention;

[0027] Figure 6 The emission spectrum of the product of Example 2 of the present invention;

[0028] Figure 7 The above are a schematic diagram of the reaction process of the product of Example 3 of the present invention and a photograph under ultraviolet light irradiation;

[0029] Figure 8 This is a photograph of an experimental example of the present invention under X-ray excitation;

[0030] Figure 9 The X-ray attenuation efficiency curve (a) and the light energy yield test effect diagram (b) of the experimental example of the present invention are shown.

[0031] Figure 10 Photographs (a) and (b) of the product under ultraviolet light irradiation, which are examples of applications of the present invention. Detailed Implementation

[0032] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0033] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0034] Example 1: A TADF Quaternary Phosphor Salt Scintillator Material

[0035] 2-Diphenylphosphine-2'-(N,N-dimethylamino)biphenyl and iodobutane were added to toluene solvent, with the amount of toluene sufficient to completely dissolve the 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl, and the amount of iodobutane greater than or equal to the molar amount of 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. The reaction system was refluxed from room temperature to 150°C. As the reaction proceeded, a white precipitate gradually formed. The obtained white precipitate was filtered, the mother liquor was removed, and the product was washed repeatedly with toluene to obtain the butyl-substituted product (abbreviated as C4-NMe2PTPP-I). A schematic diagram of the reaction process is shown below. Figure 1 As shown.

[0036] The composition of the product was determined by nuclear magnetic resonance spectroscopy, elemental analysis, and high-resolution mass spectrometry, and the corresponding single-crystal structure was analyzed by X-ray single-crystal diffraction.

[0037] like Figure 2 As shown in the figure, the butyl group is attached to the phosphorus atom, forming a new PC bond, indicating that the tertiary phosphine has been successfully alkylated, and the iodide ions are distributed between the quaternary phosphine cations. From the structure of its smallest asymmetric unit, the dimethylamine, iodide ions, and one of the benzene rings connected to the quaternary phosphine nucleus form a sandwich-like sandwich structure, which facilitates the charge transfer of dimethylamine and iodide ions to the quaternary phosphine nucleus.

[0038] like Figure 3As shown, the luminescence efficiency was evaluated using the photoluminescence quantum efficiency testing system (C9920) produced by Hamamatsu Corporation. The synthesized C4-NMe2PTPP-I exhibited bright blue light emission under ultraviolet light excitation, with the emission peak located at 473 nm, and its photoluminescence quantum efficiency was close to 100%.

[0039] The temperature-dependent steady-state and temperature-dependent transient emission spectra of C4-NMe2PTPP-I were measured using an FLS1000 fluorescence spectrometer manufactured by Edinburgh Company. Liquid nitrogen was used to cool the samples. A xenon lamp was used as the excitation source for the steady-state emission spectrum, and a microsecond pulse flash lamp was used as the excitation source for the transient emission spectrum. Figure 4 As shown, as the sample temperature decreases from room temperature to 78K, the emission peak gradually redshifts from 473nm to 499nm, attributed to fluorescence and phosphorescence emission, respectively. The triplet state and triplet energy level difference ΔE are calculated accordingly. ST The value is 0.14 eV, and the material's ΔE is generally considered to be... ST At voltages below 0.2 eV, the TADF phenomenon can occur. Simultaneously, the transient spectral lifetime at low temperatures is significantly extended, consistent with the characteristics of the TADF luminescence mechanism.

[0040] Example 2: A TADF Quaternary Phosphor Salt Scintillator Material

[0041] 2-Diphenylphosphine-2'-(N,N-dimethylamino)biphenyl and iodopropane were added to toluene solvent, with the amount of toluene sufficient to completely dissolve the 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. The amount of iodopropane was greater than or equal to the molar amount of 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. The reaction system was refluxed from room temperature to 150°C. As the reaction proceeded, a white precipitate gradually formed. The obtained white precipitate was filtered, the mother liquor was removed, and the product was washed repeatedly with toluene to obtain the propyl-substituted product (abbreviated as C3-NMe2PTPP-I).

[0042] like Figure 5 As shown, its structure can be determined by single-crystal diffraction. The propyl group is attached to the phosphorus atom, forming a new PC bond, and the iodide ion is distributed between the quaternary phosphonium cations.

[0043] like Figure 6 As shown, C3-NMe2PTPP-I exhibits bright blue light emission under 365nm ultraviolet light irradiation, with its emission peak located at 470nm and its photoluminescence efficiency of 94.4%.

[0044] Example 3: Two TADF Quaternary Phosphor Salt Scintillator Materials

[0045] (1) Add 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl and benzyl chloride to toluene solvent. The amount of toluene should be sufficient to completely dissolve 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. The amount of benzyl chloride should be greater than or equal to the molar amount of 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. Reflux the above reaction system at room temperature to 150°C. As the reaction proceeds, a white precipitate gradually forms. Filter the obtained white precipitate, remove the mother liquor, and wash the product repeatedly with toluene to obtain the final product (abbreviated as Bz-NMe2PTPP-Cl).

[0046] (2) Add 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl and benzyl bromide to toluene solvent. The amount of toluene should be sufficient to completely dissolve 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. The amount of benzyl bromide should be greater than or equal to the molar amount of 2-diphenylphosphine-2'-(N,N-dimethylamino)biphenyl. Reflux the above reaction system at room temperature to 150°C. As the reaction proceeds, a white precipitate gradually forms. Filter the obtained white precipitate, remove the mother liquor, and wash the product repeatedly with toluene to obtain the final product (abbreviated as Bz-NMe2PTPP-Br).

[0047] like Figure 7 As shown, Bz-NMe2PTPP-Cl and Bz-NMe2PTPP-Br exhibit blue-green and blue light emission, respectively, under ultraviolet light irradiation.

[0048] Experimental Example: Scintillator Material Performance Testing

[0049] The organic scintillator anthracene (purchased from Shanghai Aladdin Reagent Co., Ltd.) and the inorganic scintillator bismuth germanate (BGO) (purchased from Shanghai Shuojie Crystal Co., Ltd.) were used as controls.

[0050] like Figure 8 As shown, when the product C4-NMe2PTPP-I from Example 1 was placed under X-rays along with the scintillator anthracene, it can be seen that C4-NMe2PTPP-I exhibited brighter luminescence compared to commercially available scintillator anthracene, demonstrating its application potential as an X-ray scintillator.

[0051] The X-ray scintillation performance and light energy yield of C4-NMe2PTPP-I were tested, such as... Figure 9 As shown in Figure a, a 1 mm thick layer of C4-NMe2PTPP-I can absorb 53.48% of X-rays, while anthracene can only absorb 4.33% of X-rays. Therefore, it can be concluded that the X-ray absorption capacity of C4-NMe2PTPP-I is significantly better than that of commercially available organic scintillator anthracene.

[0052] Using bismuth germanate scintillator as a reference, a miniature X-ray source (Mini-X2, Ag target) was used to irradiate the reference and the sample to be tested. An integrating sphere was used to collect and calculate the number of photons emitted by the reference and the sample (P). total ), then use P total Divide each photon by its respective attenuation efficiency to obtain the normalized photon number (P). norm ).like Figure 9 As shown in b, the attenuation efficiency of a 1 mm thick C4-NMe2PTPP-I layer is 53.48%. The P of the sample to be tested... norm Divided by the reference P norm Multiplying by the reference standard light yield, the light yield of C4-NMe2PTPP-I can be calculated to be 80817 photons / MeV (BGO's light yield is 8200 photons / MeV), while the calibrated light yield of anthracene is 11708 photons / MeV, close to its standard value of 12000 photons / MeV. Therefore, it can be concluded that the light yield of C4-NMe2PTPP-I is significantly better than that of commercially available scintillators bismuth germanate (BGO) and anthracene.

[0053] Application example:

[0054] The thin films prepared based on the TADF quaternary phosphonate salt scintillator material of this invention can be applied to X-ray scintillation imaging, such as... Figure 10 As shown, C4-NMe2PTPP-I powder was mixed with polycaprolactone at a mass ratio of 1:1. The mixture was heated to 210°C to obtain a uniform melt, which was then coated onto a quartz substrate. After cooling, a uniform film was obtained. Figure 10 a). For example Figure 10 As shown in b, the prepared thin film can be used as an X-ray scintillation imaging screen to image items such as schoolbags, peanuts, and shrimp, demonstrating its application potential in fields such as security inspection, non-destructive testing, and agricultural seed selection.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A TADF phosphonium salt scintillator material characterized in that, The structural formula of the material is: wherein R is an alkyl or an aromatic substituent; X is halogen; The alkyl is any one of linear methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclic cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl; The aromatic substituent is any one of benzyl, phenethyl, phenylpropyl, phenylbutyl, phenylpentyl, 9-(2-ethyl)carbazole; The halogen is any one of chlorine, bromine, iodine.

2. A method of producing the TADF phosphonium salt scintillator material of claim 1, characterized by, The method comprises the following steps: 2-diphenylphosphine-2'-(N,N-dimethylamino) biphenyl and halogenated alkane or halogenated aromatic hydrocarbon are dissolved in a solvent, reacted, and the precipitated product is collected to obtain the product; The halogenated alkane is any one of linear halogenated methane, halogenated ethane, halogenated propane, halogenated butane, halogenated pentane, halogenated hexane, cyclic halogenated cyclopropane, halogenated cyclobutane, halogenated cyclopentane, halogenated cyclohexane; The halogenated aromatic hydrocarbon is any one of halogenated benzyl, halogenated phenyl ethane, halogenated phenylpropane, halogenated phenylbutane, halogenated phenylpentane, 9-(2-haloethyl)carbazole.

3. The preparation method according to claim 2, characterized in that, The halogen is any one of chlorine, bromine, iodine.

4. The preparation method according to claim 2, characterized in that, The solvent is at least one of toluene, ethyl acetate, methanol, tetrahydrofuran, n-hexane, and N,N-dimethylformamide.

5. The preparation method according to claim 2, characterized in that, The reaction temperature is controlled to be room temperature to 150°C.

6. A film characterized by, The application comprises the TADF quaternary phosphonium salt scintillator material and a polymer according to claim 1, and the mass ratio of the TADF quaternary phosphonium salt scintillator material and the polymer is (0.1-2):

1.

7. A method of producing the film according to claim 6, characterized by, The method comprises the following steps: The TADF quaternary phosphonium salt scintillator material is mixed with the polymer, heated and melted, scraped onto a substrate, and cooled to obtain the product.

8. The application of the TADF quaternary phosphonium salt scintillator material according to claim 1 and the thin film according to claim 6 in an organic light-emitting device.

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