D-A-D 'asymmetrically decoupled organic X-ray scintillator, and synthetic method and application of D-A-D' asymmetrically decoupled organic X-ray scintillator

Abstract

The invention discloses a D-A-D'asymmetrically decoupled organic X-ray scintillator, and a synthesis method and application of the D-A-D 'asymmetrically decoupled organic X-ray scintillator. According to the invention, naphthalimide is used as an electron acceptor (A), a benzene bridge is connected with a donor (D) to realize self-selective orbital coupling, and a secondary donor (D ') and A are in linear face-to-face conjugation to construct a twisted illuminant. The configuration can independently regulate and control D and D'so as to balance a singlet-triplet energy gap (delta EST) and spin-orbit coupling (SOC), accelerate intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes, and realize phosphorescence dominated at low temperature and TADF dominated dual-mode temperature adaptive luminescence at room temperature and above; meanwhile, aggregation-induced emission quenching is inhibited, and high luminous efficiency is ensured. The N-CZ has photocatalytic performance and can be used for preparing a flexible X-ray film through photopolymerization. The invention provides a new design thought and preparation method for the next-generation high-performance organic X-ray scintillator.

Description

Technical Field

[0001] This invention belongs to the field of organic optoelectronic functional materials technology, specifically relating to a class of pure organic X-ray scintillators with a DA-D' asymmetric structure, their synthesis method, and their application in radiation detection and imaging. Background Technology

[0002] X-ray imaging technology is a core technology supporting key fields such as aerospace high-energy physics experiments, public safety inspections, industrial non-destructive testing, and modern medical diagnosis. Its performance improvement is closely related to the development of scintillator materials. As the core medium for converting X-rays to visible light, the scintillator directly determines the sensitivity, resolution, and application adaptability of the imaging system. Among existing scintillator materials, inorganic materials and organometallic complexes possess strong X-ray absorption capabilities, but their applications are severely limited by drawbacks such as the need for high-temperature synthesis, complex preparation processes, high production costs, and environmental pollution caused by heavy metal elements. Organic scintillators, on the other hand, have become an important development direction for scintillator materials due to their advantages such as readily available raw materials, low preparation costs, good mechanical flexibility, ease of processing, and large-area fabrication. However, traditional organic scintillators are based on fluorescent chromophores, and due to the spin-forbidden mechanism, the transition from singlet excitons (S1) to triplet excitons (T1) is hindered. Only about 25% of singlet excitons participate in luminescence, while the remaining 75% of triplet excitons dissipate energy through non-radiative relaxation, resulting in extremely low exciton utilization and restricting the performance improvement of organic scintillators. Thermally activated delayed fluorescence (TADF) materials benefit from a small singlet-triplet bandgap (ΔE). ST The potential for 100% exciton utilization and its properties provide a new approach to solving the exciton utilization problem; room-temperature phosphorescent (RTP) materials emit light through direct radiative transitions of triplet excitons, showing application potential in flexible X-ray imaging. However, both types of materials are highly sensitive to temperature changes, which not only limits their operating temperature range but also easily induces exciton quenching. How to improve thermal stability and achieve high-efficiency luminescence over a wide temperature range has become an urgent scientific problem to be solved. Studies have shown that achieving dual-mode temperature adaptive switching of low-temperature phosphorescence / high-temperature TADF requires the scintillator to simultaneously possess a small ΔE. STAnd the large spin orbital coupling parameter (SOC). Designing highly twisted donor-acceptor (DA) structures through bond charge transfer (TBCT) or space charge transfer (TSCT) mechanisms is an effective strategy for regulating ΔEST and SOC. However, no molecular configuration can currently achieve independent regulation of TBCT and TSCT in a synergistic manner, and the donor-acceptor combination is limited, making it difficult to balance small ΔEST and strong SOC. In summary, existing organic scintillators cannot maintain stable and efficient luminescence over a wide temperature range (e.g., from liquid nitrogen temperature to above room temperature), which severely restricts their application in complex environments (such as space exploration, polar scientific research, and certain industrial scenarios). Therefore, developing an organic scintillator that can adaptively adjust the luminescence mode over a wide temperature range while maintaining high exciton utilization is of great significance. Summary of the Invention To address the problems raised in the background art, the first objective of this invention is to provide a class of DA-D' asymmetric decoupled organic X-ray scintillators. These scintillators achieve compatibility between a small singlet-triplet bandgap (ΔEST) and strong spin-orbit coupling (SOC) through synergistic regulation of bond charge transfer (TBCT) and space charge transfer (TSCT) mechanisms. This allows for adaptive switching between low-temperature phosphorescence and room-temperature thermally activated delayed fluorescence (TADF) modes over a wide temperature range of 77 K to 400 K, significantly improving exciton utilization efficiency. Specifically, the following technical solution is provided: First, this invention discloses a type of DA-D' asymmetric decoupled organic X-ray scintillator, the structural formula of which is shown in general formula I:

[0003] I In general formula I: R1 is an electron donor at any position on the benzene ring, more preferably R1 is an electron-donating substituent at the 4-position of the benzene ring, selected from hydrogen, methyl, methoxy, One of N,N-dialkylamino and alkoxy, wherein n is selected from an integer from 1 to 12, representing an alkyl group having 1 to 12 carbons; further, n is preferably an integer from 1 to 6, representing an alkyl group having 1 to 6 carbons; Y is selected from O or S atoms; R2 is selected from a fused-ring aromatic group with electron-donating ability, preferably any one of the following substituents: .

[0004] For the technical solution described above, most preferably, R1 is N,N-diethylamino, R2 is 9-carbazole or 9-(9-anthrayl), and Y is O, i.e., the compound N-CZ in the examples.

[0005] For the technical solution described above, more preferably, the temperature response range of the DA-D' asymmetric decoupled organic X-ray scintillator is 70 K to 550 K; more preferably, the scintillator can achieve adaptive switching of emission modes in the temperature range of 77 K to 400 K.

[0006] For the technical solution described above, more preferably, the triplet quantum yield of the DA-D' asymmetric decoupled organic X-ray scintillator is between 10 and 80%, with a preferred range of 20 to 70%, which is significantly higher than that of traditional dyes.

[0007] A second objective of this invention is to provide a method for synthesizing a type of DA-D' asymmetric decoupled organic X-ray scintillator, comprising the following steps: (1) P-aniline with R1 substituent is mixed with 4-bromo-1,8-naphthalenedicarboxylic anhydride at a molar ratio of (1~10):1, and then the first organic solvent is added. The mixture is reacted at 80~130℃ to obtain intermediate 1. (2) Under a nitrogen atmosphere, intermediate 1 and R2-substituted borate ester, tetratriphenylphosphine palladium, and carbonate were added to toluene in a molar ratio of 1:(1~5):(0.01~0.5):(1~10) and mixed thoroughly. After the mixture was fully reacted at 70~120℃, it was cooled and the final product was obtained by column chromatography and recrystallization. For the technical solution described above, preferably, the molar ratio of the p-aniline modified by the R1 substituent in step (1) to 4-bromo-1,8-naphthalenedicarboxylic anhydride is (1~5):1, and most preferably (2~3):1.

[0008] For the technical solution described above, preferably, in step (1), the first organic solvent is selected from at least one of ethanol, acetonitrile, toluene, DMF, and acetic acid, with acetic acid being preferred.

[0009] For the technical solution described above, preferably, the reaction temperature in step (1) is 110~120℃.

[0010] For the technical solution described above, preferably, the molar ratio of the borate ester, tetratriphenylphosphine palladium, and carbonate in step (2) where intermediate 1 and R2 are replaced is 1:(1~3):(0.01~0.2):(1~4), more preferably 1:(2~3):(0.1~0.2):(3~4).

[0011] For the technical solution described above, preferably, the reaction temperature in step (2) is 100~120℃.

[0012] For the technical solution described above, preferably, the carbonate in step (3) is selected from at least one of sodium carbonate, potassium carbonate, cesium carbonate, sodium hydroxide, and potassium hydroxide, with potassium carbonate being preferred.

[0013] A third objective of this invention is to provide applications of a class of DA-D' asymmetric decoupled organic X-ray scintillators, including room-temperature X-ray imaging, variable-temperature imaging, and applications utilizing their excited-state properties to achieve photocatalytic polymerization for thin film preparation.

[0014] In a further preferred embodiment of the above-described technical solution, the organic X-ray scintillator, as an X-ray excited phosphorescent and thermally activated delayed fluorescence material and a photocatalyst for polymerization, can be used for X-ray imaging and scintillator thin film preparation.

[0015] In a further preferred embodiment of the above-described technical solution, the application involves dispersing the DA-D' asymmetric decoupled organic X-ray scintillator in a photocurable resin and then polymerizing it in situ by ultraviolet light irradiation to form a flexible X-ray scintillator film. The film emits blue light under X-ray irradiation and can be used for digital imaging in medical diagnosis, industrial non-destructive testing, or security inspection.

[0016] For the technical solution described above, a further preferred embodiment is that the DA-D' asymmetric decoupled organic X-ray scintillator is an N-CZ compound, and the thin film made from it has a minimum detection limit (LOD) of less than 10 μGy·s. - ¹, with a line-pair resolution greater than 14 lp / mm, and capable of adaptive luminescence imaging in a temperature range of 77 K to 400 K.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: In terms of exciton utilization, the TBCT and TSCT mechanisms are integrated through a DA-D' asymmetric decoupling configuration to precisely control ΔE. ST Compared with SOC, it significantly accelerates the triplet exciton ISC / RISC process, breaking through the traditional organic scintillator's 25% exciton utilization limit and potentially achieving nearly 100% exciton utilization. In terms of temperature adaptability, the innovative configuration endows the material with the dual-mode switching capability of low-temperature phosphorescence and TADF at room temperature and above, overcoming the temperature sensitivity of TADF / RTP materials, achieving a wide temperature range adaptive response from 77 K to 400 K, expanding the working temperature range of the scintillator, and alleviating the strong temperature dependence of traditional TADF / RTP materials. At the donor-acceptor selection level, the benzene bridge connection and the spatial arrangement design without π conjugation break the limitations of the traditional DA structure donor-acceptor combination, realize the independent design and collaborative adaptation of D and D', and significantly broaden the donor selection space. In terms of performance stability, the unique twisted molecular structure effectively suppresses aggregation-induced luminescence quenching in the solid state, ensuring the high luminescence efficiency and stability of the material in practical applications, laying the foundation for high-resolution imaging. In terms of functional diversity, the target product N-CZ has both X-ray scintillation properties and photocatalytic activity, and can be used to directly prepare flexible X-ray films through photopolymerization, which increases the functional dimensions and application scenario adaptability compared with existing technologies.

[0018] Through rational molecular design and simple synthesis process, the overall performance of this invention is greatly improved. The resulting thin film has a low LOD of 6.6 μGy / s and a resolution of >14 lp / mm, which meets the imaging requirements. It is also free of heavy metals, solution-processable, and has industrialization advantages such as low cost, environmental friendliness, and ease of large-area preparation. Attached Figure Description

[0019] Figure 1 Photoluminescence spectra of compounds N-CZ, N-9-AN, and N-Br at room temperature and low temperature.

[0020] Figure 2 Temperature-dependent photoluminescence spectrum of compound N-CZ.

[0021] Figure 3 : Temperature-dependent photoluminescence lifetime of compound N-CZ.

[0022] Figure 4 X-ray emission spectra of compounds N-CZ, N-9-AN, and N-Br at room temperature.

[0023] Figure 5 X-ray irradiation stability of compound N-CZ.

[0024] Figure 6 Irradiation and luminescence intensity curves of thin films made from compound N-CZ, and the calculated minimum detection limit.

[0025] Figure 7 Line pair resolution of thin films made from compound N-CZ.

[0026] Figure 8 X-ray imaging of a thin film made from the compound N-CZ. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise stated, the terms used herein have the following meanings.

[0029] The term "alkyl" as used in this application includes, but is not limited to, straight-chain alkyl and branched-chain alkyl.

[0030] The instruments and equipment used in the embodiments are as follows: In the column chromatography process of this invention, 200-300 mesh and 100-200 mesh silica gel for column chromatography purchased from Qingdao Meigao Group Co., Ltd., and 20-40 mesh analytical grade quartz sand purchased from Tianda Chemical Reagent Factory are used.

[0031] The photoluminescence spectrum and lifetime of the scintillator were measured using an FLS1000 from Edinburgh.

[0032] The X-ray emission spectrum and stability of the scintillator were measured using X-ray imaging equipment from Beijing Zhuoli Hanguang Company.

[0033] The "DA-D' asymmetric decoupling" described in this invention is structurally defined as follows: D and D' have different structures and different connection methods. Generally, DA uses bond connection or bridge connection, while AD' uses a spatial face-to-face or angled configuration. Based on these characteristics, bond charge transfer typically occurs in the DA structure, while space charge transfer occurs in A-D'.

[0034] Example 1 The synthesis method of N-CZ is as follows:

[0035] N-Br (127 mg, 0.30 mmol), 2-(carbazole-9-yl)phenylboronic acid (190 mg, 0.60 mmol), and K₂CO₃ (165 mg, 1.2 mmol) were dissolved in toluene (20 mL). Then, Pd₃(PPd₃)₄ (17 mg, 0.015 mmol) was added under N₂ atmosphere. The reaction mixture was heated to 110 °C and refluxed with stirring for 8 hours. After cooling to room temperature, the product was extracted with dichloromethane and water, and dried over anhydrous sodium sulfate. The solvent was removed by vacuum distillation. The crude product was purified by column chromatography (using silica gel and ethyl acetate:petroleum ether as eluent) to give a yellow product in 68% yield.

[0036] 1 H NMR (400 MHz, CDCl3) δ 8.48 (d, J = 7.2 Hz, 1H), 8.26 (d, J = 8.5 Hz, 1H), 8.17 (d, J = 7.6 Hz, 1H), 7.96 (d, J = 7.8 Hz, 1H), 7.91 – 7.84 (m, 1H), 7.80 – 7.66 (m, 4H), 7.53 (t, J = 7.9 Hz, 1H), 7.36 (d, J = 7.5 Hz, 2H), 7.25 –7.16 (m, 2H), 7.07 – 6.92 (m, 5H), 6.71 (d, J = 8.4 Hz, 2H), 3.36 (q, J = 7.1Hz, 4H), 1.17 (t, J = 7.1 Hz, 6H). Mass spectrum of N-CZ for [M + H] + :585.2416, found 585.16. [M + Na] + :585.2416, found 608.14. The obtained N-CZ compounds exhibit excellent temperature-adaptive luminescence properties, displaying significantly different photoluminescence behaviors under different temperature conditions (see...). Figure 1 and Figure 2 Furthermore, the X-ray emission spectrum of this compound at room temperature demonstrates its great potential as a highly efficient scintillator material (see [link]). Figure 4 ).

[0037] Comparative Example 1 The synthesis method of N-Br is as follows:

[0038] 4-Bromo-1,8-naphthalene anhydride (3.26 g, 11.78 mmol) was dissolved in 25 mL of acetic acid and stirred for 10 min. N,N-Diethyl-p-phenylenediamine (2.52 g, 15.5 mmol) was added to the mixture under a nitrogen atmosphere and stirred at 120 °C. o The mixture was stirred at C for 2 h. Then, it was cooled overnight, and a large number of needle-like crystals precipitated. The crystals were washed several times with anhydrous ethanol to give a brownish-red solid (yield = 93.6%).

[0039] 1 H NMR (400 MHz, CDCl3) δ 8.70 (dd, J = 7.3, 1.1 Hz, 1H), 8.61 (dd, J =8.5, 1.1 Hz, 1H), 8.46 (d, J = 7.8 Hz, 1H), 8.06 (d, J = 7.8 Hz, 1H), 7.87 (dd, J = 8.5, 7.3 Hz, 1H), 7.14 – 7.06 (m, 2H), 6.81 – 6.74 (m, 2H), 3.40 (q, J =7.1 Hz, 4H), 1.20 (t, J = 7.0 Hz, 6H). HRMS of N-Br (ESI, m / z): [M+H] + calcd for C 22 H 19 N₂O₂, 423.1390; found, 423.0703. The photoluminescence spectrum of N-Br compounds is as follows: Figure 1 .

[0040] Comparative Example 2 The synthesis method of N-9-AN is as follows:

[0041] N-Br (127 mg, 0.30 mmol), anthraquinone (74 mg, 0.60 mmol), and K₂CO₃ (165 mg, 1.2 mmol) were dissolved in toluene (20 mL). Then, Pd₃(PPd₃)₄ (17 mg, 0.015 mmol) was added under a nitrogen atmosphere. The reaction mixture was heated to 110 °C and refluxed with stirring for 8 hours. After cooling to room temperature, the product was extracted with dichloromethane and water, and dried over anhydrous sodium sulfate. The solvent was removed by vacuum distillation. The crude product was purified by column chromatography (using silica gel and ethyl acetate:petroleum ether as eluent) to give a yellow product in 54% yield.

[0042] 1 H NMR (600 MHz, CDCl3) δ 8.86 (d, J = 7.3 Hz, 1H), 8.69 – 8.64 (m,2H), 8.14 (d, J= 8.5 Hz, 2H), 7.85 (d, J = 7.3 Hz, 1H), 7.53 – 7.45 (m, 4H), 7.31 (d, J = 3.9 Hz, 4H), 7.19 (d, J = 8.3 Hz, 2H), 6.82 (d, J = 8.3 Hz, 2H), 3.43 (q, J = 7.2 Hz, 4H), 1.25 – 1.18 (m, 6H). Mass spectrum of N-9-AN for [M + H] + :521.2151, found 521.17. [M + Na] + :543.2151, Found 543.13. The X-ray emission spectrum of N-9-AN is shown in [reference needed]. Figure 4 .

[0043] Performance testing 1. Photoluminescence spectrum and light yield The prepared scintillator powder was placed in the sample chamber, and the fluorescence lifetime, TADF lifetime, phosphorescence emission spectrum and lifetime, and temperature-varying (77K-400K) spectrum and lifetime were measured using a transient steady-state fluorescence spectrometer FLS1000 (see [link to FLS1000]). Figure 2 and Figure 3 Time-resolved emission spectra were recorded using an Edinburgh FLS100 lifetime system with an excitation wavelength set to 350 nm.

[0044] 2. X-ray emission spectroscopy, minimum detection limit and stability X-ray emission spectra and intensities were measured under room temperature, variable temperature, normal oxygen, and vacuum conditions using an Edinburgh FLS1000 system and an Oxford Instruments Optistat DN with an X-ray tube. Linear curves of X-ray dose versus emission intensity were plotted, and sensitivity, limit of detection (LOD), and luminescence stability cycles were calculated (see [link to relevant documentation]). Figure 4 , Figure 5 and Figure 6 ).

[0045] 3. Large-scale preparation of flexible thin films Amorphous organic scintillators (ACOs) enable simpler solid solution treatment and large-area uniform luminescence, where luminescence performance is significantly influenced by a rigid environment. Ultraviolet (UV) curing was used to improve the X-ray luminescence performance of organic host-guest doped systems. A rigid environment created by UV curing was utilized to promote host-guest interactions, leading to the design of flexible thin-film materials with highly efficient scintillation properties. The fabricated N-CZ flexible thin film exhibited excellent spatial resolution in X-ray imaging, clearly resolving standard test cards with 10 line pairs / mm (see...). Figure 7 ).

[0046] Furthermore, X-ray imaging of printed circuit boards containing electronic components was performed using this thin film, yielding clear images with high contrast and low noise, thus validating its application potential in practical inspection (see...). Figure 8 ).

[0047] In summary, DA-D' asymmetric substituted N-CZ scintillators exhibit superior temperature-adaptive luminescence capabilities compared to other scintillator configurations.

[0048] Compared with existing technologies, the scintillator provided by this invention has: successfully developed a new scintillator structure and studied its photophysical properties; its temperature adaptability range is 77K~300K; it has high intersystem crossing efficiency and reverse intersystem crossing efficiency; it has a low detection limit and high resolution; thus, it can be better used in practical applications.

[0049] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A class of organic X-ray scintillators with DA-D' asymmetric decoupling, the structural formula of which is shown in general formula I: I in: R1 is an electron donor at any position on the benzene ring, selected from hydrogen, methyl, methoxy, ... One of N,N-dialkylamino and alkoxy; and n is an integer selected from 1 to 12; Y is selected from O or S atoms; R2 is selected from any of the following substituents: 。 2. The organic X-ray scintillator according to claim 1, characterized in that: Its temperature response is 70 K to 550 K; its triplet quantum yield is 10–80%.

3. The method for synthesizing the organic X-ray scintillator as described in claim 1, characterized in that: Includes the following steps: (1) P-aniline with R1 substituent is mixed with 4-bromo-1,8-naphthalenedicarboxylic anhydride at a molar ratio of (1~10):1, and then the first organic solvent is added. The mixture is reacted at 80~130℃ to obtain intermediate 1. (2) Under a nitrogen atmosphere, intermediate 1 and R2-substituted borate ester, tetra-triphenylphosphine palladium, and carbonate were added to toluene in a molar ratio of 1:(1~5):(0.01~0.5):(1~10) and mixed thoroughly. After the mixture was fully reacted at 70~120℃ and cooled, it was obtained by column chromatography and recrystallization.

4. The method according to claim 3, characterized in that: The molar ratio of the R1-substituted p-aniline to 4-bromo-1,8-naphthalenedicarboxylic anhydride in step (1) is (1~5):

1.

5. The method according to claim 3, characterized in that: In step (1), the first organic solvent is selected from at least one of ethanol, acetonitrile, toluene, DMF, and acetic acid.

6. The method according to claim 3, characterized in that: The molar ratio of the borate ester, tetratriphenylphosphine palladium, and carbonate substituted with intermediate 1 and R2 in step (2) is 1:(1~3):(0.01~0.2):(1~4).

7. The method according to claim 3, characterized in that: The carbonate mentioned in step (3) is selected from at least one of sodium carbonate, potassium carbonate, cesium carbonate, sodium hydroxide, and potassium hydroxide.

8. The application of the organic X-ray scintillator as described in claim 1, including applications in X-ray room temperature imaging, variable temperature imaging, and the preparation of thin films by photocatalytic polymerization utilizing its excited-state properties.

9. The application according to claim 8, characterized in that: The organic X-ray scintillator is dispersed in a photocurable resin and polymerized in situ by ultraviolet light irradiation to form a flexible X-ray scintillator film.

10. The application according to claim 9, characterized in that: The film has a minimum detection limit (LOD) of less than 6.6 μGy·s⁻¹, a line-pair resolution greater than 14 lp / mm, and can achieve adaptive luminescence imaging in a temperature range of 77 K to 400 K.

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