Synthesis and Imaging Applications of Thermoexciton Organic Scintillators

Abstract

The present invention discloses the synthesis and imaging application of a thermoexciton organic scintillator. Using MNI as the original raw material, MNI-PTZ is obtained through palladium-catalyzed Buchwald-Hartwig C-N coupling reaction. Under acidic conditions, an oxidation reaction is used to obtain a compound OMNI-PTZ with a thermoexciton luminescence mechanism. On this basis, an intramolecular interlocked compound D is obtained through intramolecular dehydration condensation. This compound has a high triplet exciton utilization rate, a single-exponential decay lifetime (13.8 ns), and excellent fluorescence quantum efficiency (0.41), and can be used in the application research fields of organic light-emitting devices and X-ray scintillators. It provides a feasible strategy for designing novel organic scintillators, and at the same time, this compound with a unique structure is expected to be applied to the field of X-ray circularly polarized luminescence.

Description

Technical Field

[0001] The present invention belongs to the field of design, synthesis and application of organic functional materials, and particularly relates to the synthesis and imaging application of a thermally excited organic scintillator. Background Art

[0002] Traditional flat panel X-ray detectors mainly consist of a scintillator material that can convert X-rays into visible light and a photodetector, and there are problems such as low spatial resolution caused by image overlap. In recent years, domestic and foreign researchers have used flexible X-ray detectors to construct high-resolution three-dimensional panoramic imaging technology, which can greatly improve its resolution, but intrinsically flexible scintillator materials are required. Currently, commercial inorganic single crystal scintillators do not have flexible characteristics and need to be used in combination with an organic polymer matrix, but there are problems such as difficulty in mixing evenly and easy agglomeration, which limit their further application. Therefore, it is imperative to develop intrinsically flexible high-performance scintillator materials.

[0003] Compared with inorganic scintillators, organic scintillators have received extensive attention in recent years due to their advantages such as large-area preparation, low growth temperature, good solubility, and low toxicity. In particular, it focuses on the development of organic scintillators with high light yield, low detection limit, fast response time, and high definition resolution, and in-depth exploration of their potential luminescence mechanisms. Currently, most organic fluorescent materials face the problem of being unable to efficiently utilize triplet excitons under X-ray excitation due to the spin-forbidden transition between singlet and triplet states. Although some researchers have used thermally activated delayed fluorescence materials (Nat. Mater. 2021, 21, 210-216) or phosphorescent materials (Nat. Photon. 2021, 15, 187-192) to solve the above problems, they have a long triplet exciton lifetime and are not suitable for high-resolution X-ray imaging. On the other hand, thermally excited fluorescent materials can solve the problems of triplet exciton quenching and long triplet exciton lifetime due to the reverse intersystem crossing between high-energy triplet and singlet states, and have been applied to the field of organic light-emitting diodes (Adv. Funct. Mater. 2014, 24, 1609-1614). In addition, it has been shown that the principle of X-ray luminescence is similar to that of electroluminescence. We speculate that fluorescent materials with a thermally excited luminescence mechanism can achieve efficient and fast-response X-ray luminescence.

[0004] Therefore, it is necessary to design new thermally excited organic fluorescent materials and apply them to X-ray imaging. This injects new vitality into the development of organic scintillators and inspires more researchers to invest in this field. Summary of the Invention

[0005] The object of the present invention is to provide the synthesis of a novel thermo-exciton organic scintillator aiming at the deficiencies of current organic scintillators and successfully apply it to X-ray imaging. The present invention provides a design and synthesis method of a novel thermo-exciton organic scintillator, which broadens the application of thermo-exciton organic fluorescent materials in X-ray imaging.

[0006] To achieve the above object of the invention, the following technical scheme is adopted by the present invention:

[0007] The novel thermo-exciton organic scintillator has a general structural formula of A or B:

[0008]

[0009] Wherein, R1, R2 and R3 are the same or different and are each independently selected from H, C1-C10 hydrocarbons, C1-C10 alkoxy groups, C6 aryl groups, C6-C10 aralkyl groups, and aryl groups substituted by substituents of single bonds, double bonds, triple bonds or combinations thereof. Further, R1, R2 and R3 are the same or different and are preferably H, methyl, ethyl, n-propyl, isopropyl, n-butyl, n-pentyl, 2,6-diisopropylphenyl, methoxy, ethoxy, propoxy. More preferably, R1 is preferably n-butyl or 2,6-diisopropylphenyl, R2 is preferably methoxy, and R3 is preferably methoxy or isopropyl.

[0010] Preferably, the novel thermo-exciton organic scintillators C and D have the following structural formulae:

[0011] .

[0012] A method for preparing the novel thermo-exciton organic scintillators C and D as described above includes the following steps:

[0013] 1) Mix 3-methoxy-4-bromo-1,8-naphthalimide derivative (MNI) with phenothiazine derivative (PTZ), dissolve in toluene, stir at room temperature, continue to add cesium carbonate anhydrous, then bubble to remove oxygen under an argon atmosphere, and finally add a palladium catalyst and a BINAP ligand. After heating under reflux for 12 - 72 h (preferably 24 - 36 hours), MNI-PTZ (4a, 4b, 5a, 5b) is obtained by rapid column chromatography separation, and its structural formula is:

[0014] ;

[0015] 2) Oxidize MNI-PTZ (4a, 4b, 5a, 5b) to OMNI-PTZ (1a, 1b, 2a, 2b): Add MNI-PTZ (4a, 4b, 5a, 5b) to a mixed solution of glacial acetic acid and hydrogen peroxide (30%), heat under reflux for 2 - 6 h (preferably 3 - 4 h), and separate OMNI-PTZ (1a, 1b, 2a, 2b) by column chromatography;

[0016] 3) Dissolve OMNI-PTZ (1a, 2a) in dichloromethane, add BBr3 dropwise under an ice bath, slowly warm up to room temperature and react for 24 - 72 h (preferably 30 - 36 h). After the reaction is completed, separate by column chromatography and rotary evaporate under reduced pressure at low temperature to obtain the demethoxylated product DMNI-PTZ (6a, 7a), and its structural formula is:

[0017]

[0018] 4) Dissolve DMNI-PTZ (6a, 7a) and anhydrous potassium carbonate in DMF solvent, heat under reflux for 36 h, rotary evaporate under reduced pressure at low temperature, and separate to obtain 3a, 3b by column chromatography.

[0019] In step 1), the 3-methoxy-4-bromo-1,8-naphthalimide derivative (MNI) is specifically N-butyl-3-methoxy-4-bromo-1,8-naphthalimide (MNI, CAS No.: 2380278-49-7); the phenothiazine derivative (PTZ) is 1-methoxy-10H-phenothiazine (CAS No.: 1576-70-1) or 1-isopropylphenothiazine (CAS No.: 83372-11-6).

[0020] In step 1), the molar ratio of MNI to PTZ is 1:1 - 5, preferably 1:1.3, and the heating reflux reaction temperature is 110 - 130 o °C, preferably the reaction temperature is 120 o °C. When separating by dry column chromatography, the eluent is a solvent composed of dichloromethane and petroleum ether, and the polarity gradually increases from a volume ratio of 1:10 to a volume ratio of 1:2.

[0021] In step 2), glacial acetic acid and hydrogen peroxide are mixed at a volume ratio of 3 - 5:1, preferably 5:1, and the hydrogen peroxide concentration is 30 wt%.

[0022] In step 3), the molar ratio of OMNI-PTZ (1a, 2a) to BBr3 is 1:2 - 10, preferably 1:10; the reaction temperature is 0 o °C to room temperature.

[0023] In step 4), during column chromatography separation, the eluent is a solvent composed of ethyl acetate and petroleum ether, and the polarity gradually increases from a volume ratio of 1:12 to a volume ratio of 1:8.

[0024] Furthermore, organic scintillator C first introduces bulky groups (methoxy and isopropyl) on the basis of the structure reported in the literature "ACS. Appl. Mater. Interfaces. 2020, 12, 51293 - 51301", and then realizes thermally activated delayed fluorescence (TADF) mechanism and highly efficient X-ray luminescence with short response time through oxidation.

[0025] Furthermore, organic scintillators C and D are obtained by first oxidizing and functionalizing on the basis of the structure reported in the literature "ACS. Appl. Mater. Interfaces. 2020, 12, 51293 - 51301" to obtain exciton organic scintillator C, and then obtaining thermally activated exciton organic scintillator D through intramolecular interlocking. Finally, organic scintillators C and D achieve highly efficient and short-response-time X-ray luminescence and are successfully applied to the field of X-ray imaging. Through oxidative functionalization, the intermolecular donor-acceptor interaction is weakened, the local molecular frontier orbital overlap is enhanced, resulting in a large oscillator strength and a small ground-state-excited-state molecular structure deformation, thus achieving a high luminescence quantum efficiency. Further, more efficient and short-lived X-ray luminescence is achieved through the intramolecular interlocking strategy.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1) By preparing novel thermally activated exciton organic scintillators C and D according to the method of the present invention, the synthesis steps are short, the yield is high, and the structure is novel. And for the first time, the interaction between intramolecular electron donors and acceptors is regulated by an oxidation strategy to achieve a thermally activated delayed fluorescence mechanism. In addition, the relationship between their structures and properties is deeply explored;

[0028] 2) Due to the fast reverse intersystem crossing of the high triplet-singlet energy levels, short triplet exciton lifetimes, and excellent fluorescence quantum yields of the novel thermally activated exciton organic scintillators C and D, the organic scintillators C and D can overcome the deficiencies of existing organic scintillators, providing a feasible strategy for realizing novel stable and efficient organic scintillators, and having broad application prospects in the fields of X-ray detection and imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 For the ultraviolet-visible absorption, steady-state and transient fluorescence emission spectra of compounds 1b and 4b in cyclohexane solution (10 -5 μM);

[0030] Figure 2Under X-ray irradiation (278 μGy s -1 ), the fluorescence emission spectra of compounds 1b, 4b, and the commercial product anthracene;

[0031] Figure 3 Schematic diagram of X-ray imaging of thermoexciton organic scintillators and an example of X-ray imaging of thermoexciton organic scintillator 1b. Detailed implementation manners

[0032] The technical solutions of the present invention will be further described below with specific examples, but the protection scope of the present invention is not limited thereto.

[0033] Example 1

[0034] Preparation of thermoexciton organic scintillators OMNI-PTZ (1a, 1b).

[0035] Using 3-methoxy-4-bromo-1,8-naphthalimide derivatives (MNI) and phenothiazine derivatives (PTZ) as starting materials, the intermediate MNI-PTZ (4a, 4b) is obtained through palladium-catalyzed Buchwald-Hartwig C-N coupling reaction. Then, MNI-PTZ (4a, 4b) is oxidized to OMNI-PTZ (1a, 1b) using hydrogen peroxide solution (30%) under acidic conditions.

[0036] The specific steps are as follows:

[0037] 1) Add N-butyl-3-methoxy-4-bromo-1,8-naphthalimide (MNI, CAS No.: 2380278-49-7) (0.938 g, 2.60 mmol), 1-methoxy-10H-phenothiazine (CAS No.: 1576-70-1) (0.458 g, 2.00 mmol) and cesium carbonate (3.258 g, 10.00 mmol) into a 50 mL two-necked round-bottom flask. Then add 20 mL of toluene solvent to the mixture and stir at room temperature for 10 mins. After degassing the reaction mixture under an argon atmosphere for 15 mins, add 2,2'-bis(diphenylphosphino)-1,1'-binaphthalene rac-BINAP (0.196 g, 0.31 mmol) and catalyst Pd2(dba)3 (0.281 g, 0.31 mmol) under an argon atmosphere. Heat under reflux for 24 h, and then detect the reaction progress using a thin-layer chromatography silica gel plate. When the reaction reaches the maximum extent, stop the reaction. First, filter off the catalyst with diatomaceous earth, collect the filtrate, evaporate toluene on a rotary evaporator, separate and purify by flash column chromatography. The eluent gradually increases the polarity from a volume ratio of CH2Cl2:PE = 1:8 to a volume ratio of CH2Cl2:PE = 1:2. After separation, collect the target component, and rotary evaporate to obtain a red solid 4a (0.632 g, 1.24 mmol), with a yield of 62%. 1 H NMR (400 MHz, CDCl3) δ 9.03 (d, 1H, J = 8.6 HZ), 8.51 (s, 1H, J = 8.6 HZ), 8.49 (d,1H, J = 8.6 HZ),7.77-7.73 (m,1H) 7.09-7.05 (m,1H), 6.94-6.82 (m,1H), 6.78 (d,1H, J = 7.76 HZ), 6.52 (d, 1H, J = 8.12 HZ), 4.25-4.21, (t, 1H, J = 7.52 HZ),4.15 (s, 3H), 3.18(s, 3H), 1.80-1.73 (m, 2H), 1.54-1.45 (m,2H), 1.04-1.00 (t,3H, J = 7.36 HZ). 1313C NMR (101 MHz, CDCl3) δ 164.35, 163.91, 157.27, 151.38,144.47, 135.73, 132.97,132.73, 131.28, 129.19, 127.82, 127.55, 127.05,126.56, 124.93, 124.71, 124.08, 123.80, 122.70, 122.62, 119.61, 118.90,117.39, 111.67, 56.76, 55.47, 40.34,30.28, 20.41, 13.87. HRMS (ESI)calculated for C 30 H 26 N2O4S, m / z 510.1613, found: [M+H] + , 510.1615;

[0038] 2) N-butyl-3-methoxy-4-bromo-1,8-naphthalimide (MNI) (0.938 g, 2.60 mmol), 1-isopropylphenothiazine (CAS No.: 83372-11-6) (0.426 g, 2.00 mmol) and cesium carbonate (3.258 g, 10.00 mmol) were added to a 50 mL two-necked round-bottom flask. Then 20 mL of toluene solvent was added to the mixture. The mixture was stirred at room temperature for 10 mins. After the reaction mixture was degassed for 15 mins under an argon atmosphere, 2,2'-bis(diphenylphosphino)-1,1'-binaphthalene rac-BINAP (0.196 g, 0.310 mmol) and catalyst Pd2(dba)3 (0.281 g, 0.310 mmol) were added under an argon atmosphere. The mixture was heated to reflux for 24 h. Then the reaction progress was detected by a thin-layer chromatography silica gel plate. When the reaction reached the maximum extent, the reaction was stopped. The catalyst was removed by filtration through diatomaceous earth. The filtrate was collected, and toluene was removed by rotary evaporation. The product was separated and purified by flash column chromatography. The eluent was gradually increased in polarity from a volume ratio of CH2Cl2:PE = 1:10 to a volume ratio of CH2Cl2:PE = 1:2. The target component was collected after separation and dried by rotary evaporation to obtain a red solid 4b (0.428 g, 0.82 mmol), with a yield of 41%. 11H NMR (400 MHz, CDCl3) δ 9.30 (d, 1H, J = 8.68 Hz), 8.54 (s, 1H), 8.46 (d, 1H, J = 7.20 Hz), 7.75 - 7.71 (t, 1H, J = 7.88 Hz), 7.53 (d, 1H, J = 8.08 Hz), 7.12 (d, 1H, J = 7.40 Hz), 7.06 (d, 1H, J = 7.24 Hz), 7.02 - 6.92 (m, 4H), 4.24 (s, 3H), 4.22 - 4.18 (m, 2H), 3.44 - 3.37 (m, 1H), 1.79 - 1.71 (m, 2H), 1.53 - 1.43 (m, 2H), 1.03 - 0.99 (t, 3H), 0.90 - 0.88 (d, 3H), 0.32 - 0.30 (d, 3H). 13 13C NMR (101 MHz, CDCl3) δ 164.17, 163.61, 156.83, 146.11, 142.82, 141.60, 138.19, 132.46, 131.19, 129.93, 129.48, 128.00, 127.16, 127.03, 126.53, 126.44, 125.13, 124.71, 124.70, 124.34, 122.91, 122.84, 120.87, 118.02, 56.54, 40.39, 30.22, 26.23, 20.39, 13.84. HRMS (ESI) calculated for C 32 H 31 N2O3S, m / z 523.2050, found: [M + H] + , 524.2051;

[0039] 3) Dissolve 4a (0.510 g, 1.00 mmol) in a mixed solution of glacial acetic acid (20 mL), dichloromethane (5 mL) and hydrogen peroxide (30 wt%, 4 mL). After the reaction mixture is degassed three times under an argon atmosphere, it is heated under reflux for 6 h. Then, the reaction progress is detected using a thin-layer chromatography silica gel plate. When the reaction reaches the maximum extent, the reaction is stopped. Pour the reaction mixture into 100 mL of ice water, extract with dichloromethane (3×50 mL), collect the organic phase, and then wash the organic phase with saturated sodium bisulfite solution (3×40 mL). After drying to remove water, dichloromethane is removed by rotary evaporation on a rotary evaporator. The product is separated and purified by flash column chromatography. The eluent is gradually increased in polarity from a volume ratio of CH2Cl2:PE = 1:12 to a volume ratio of CH2Cl2:PE = 1:1. After separation, the target component is collected and dried by evaporation to obtain a red solid 1a (0.499 g, 0.97 mmol), with a yield of 97%. 1 H NMR (400 MHz, CDCl3) δ 8.50(s, 1H), 8.46 (d, 1H, J = 7.16 HZ), 8.27 (d, 1H, J = 8.52 HZ), 8.16 (d,1H, J= 7.8 HZ), 7.87 (d, 1H, J = 7.92 HZ), 7.68-7.64 (t, 1H, J = 7.96 HZ), 7.37-7.33 (t, 1H, J = 7.4 HZ), 7.31-7.24 (m, 2H), 6.97-6.95 (t, 1H, J = 8.04HZ),6.79-6.77 (t, 1H, J = 8.64 HZ), 4.24-4.20 (t, 2H, J = 7.36 HZ), 4.05 (s, 1H),3.15 (s, 1H), 1.79-1.72 (m, 2H), 1.51-1.46 (m, 2H), 1.02-0.99 (m,3H). 1313C NMR (101 MHz, CDCl3) δ 164.02, 163.71, 155.80, 149.67, 141.06, 133.08, 131.73, 131.15, 131.11, 129.55, 129.31, 128.71, 127.13, 124.40, 124.09, 124.00, 123.72, 123.19, 123.07, 122.72, 118.12, 116.73, 116.25, 115.60, 56.73, 56.45, 40.49, 30.27, 20.41, 13.87. HRMS (ESI) calculated for C 30 H 26 N2O6S, m / z 542.1512, found: [M+H] + , 543.1516

[0040] 4) Dissolve 4b (1.108 g, 2.00 mmol) in a mixed solution of glacial acetic acid (20 mL), dichloromethane (5 mL) and hydrogen peroxide (30 wt%, 4 mL). After degassing the reaction mixture three times under an argon atmosphere, heat it under reflux for 6 h. Then, use a thin-layer chromatography silica gel plate to detect the reaction progress. When the reaction reaches the maximum extent, stop the reaction. Pour the reaction mixture into 100 mL of ice water, extract it with dichloromethane (3 × 50 mL), collect the organic phase, and then wash the organic phase with saturated sodium bisulfite solution (3 × 40 mL). After drying to remove water, rotary evaporate to remove dichloromethane on a rotary evaporator, and purify it by flash column chromatography. The eluent is PE:EA = 4:1 (volume ratio). After separation, collect the target component, and rotary evaporate to dryness to obtain a pale yellow solid 1b (1.019 g, 1.84 mmol), with a yield of 92%. 11H NMR (400 MHz, CDCl3) δ 8.53 (s, 1H), 8.49 (d, 1H, J = 6.80Hz), 8.41 (d, 1H, J = 8.60 Hz), 8.21 - 8.17 (m, 2H), 7.75 - 7.71 (t, 1H, J = 7.32Hz), 7.48 (d, 1H, J = 7.76 Hz), 7.43 - 7.39(m, 2H), 7.32 - 7.28 (m, 1H), 7.09 (d,1H, J = 8.64 Hz), 4.25 - 4.21 (t, 3H), 4.14 (s, 3H), 3.09 - 3.02 (m, 1H), 1.81 - 1.62 (m, 2H), 1.55 - 1.45 (m, 2H), 1.04 - 1.01(t, 3H), 0.82 (d, 3H), 0.35 (d,3H). 13 13C NMR (101 MHz, CDCl3) δ 163.77, 163.34, 155.87, 141.71, 140.35, 139.30,133.18, 133.10, 132.03,132.01, 129.90, 129.45, 129.17, 128.63, 125.33,124.79, 124.48, 124.22, 123.37, 123.30, 122.89, 121.78, 119.11, 116.73,56.57, 40.57, 30.21, 27.35, 24.26,23.64, 20.38, 13.84. HRMS (ESI) calculatedfor C 32 H 31 N2O5S, m / z 555.1948, found: [M+H] + , 555.1948.

[0041] Example 2

[0042] Preparation of thermally activated delayed fluorescence organic scintillator 3a

[0043] Using OMNI-PTZ (1a) as the raw material, the intermediate DMNI-PTZ (6a) was obtained through the cleavage reaction of the ether, and then DMNI-PTZ (6a) was dehydrated and condensed into OMNI-PTZ (3a) in anhydrous DMF and anhydrous potassium carbonate

[0044] The specific steps are as follows:

[0045] 1a (1.084 g, 2.00 mmol) was dissolved in 40 mL of dichloromethane. Under an ice-water bath, boron tribromide solution (1.8 mL, 20.00 mmol, DCM, 30 mL) was added via a constant-pressure dropping funnel. The reaction mixture was stirred under the ice-water bath and slowly warmed to room temperature. Then, the reaction progress was monitored using a thin-layer chromatography silica gel plate. When the reaction reached the maximum extent, the reaction was stopped. The reaction mixture was poured into 100 mL of ice water, and extracted with dichloromethane (3×50 mL). The organic phase was collected, dried over anhydrous sodium sulfate, filtered, and the dichloromethane was removed by rotary evaporation. The product was purified by flash column chromatography with an eluent of DCM:EA = 30:1 (v / v). The target fraction was collected and dried to obtain yellow solid 6a (0.945 g, 1.84 mmol), with a yield of 92%. 1 H NMR (400MHz, DMSO-d6) δ 11.15 (s, 1H), 10.02 (s, 1H), 8.30 (s, 1H), 8.26 (d, 1H, J =6.04 HZ), 8.09-8.07 (d, 1H, J = 7.16 HZ), 8.00-7.98 (d, 1H, J= 7.68 HZ), 7.66(m, 1H), 7.60-7.55 (m, 2H), 7.36 (m, 1H), 7.24 (m, 1H), 7.99 (d, 1H, J = 8.28HZ), 6.93 (d, 1H, J = 7 HZ), 4.08 (m, 2H), 1.64 (m, 2H), 1.39(m, 2H), 0.95(m, 3H). 13 C NMR (101 MHz, DMSO-d6) δ 163.85, 163.30, 155.56, 148.19, 140.93,134.16, 131.84, 129.48, 128.77, 128.07, 127.96, 127.67, 126.69, 124.61,123.81, 123.66,123.28, 123.00, 122.88, 122.56, 120.72, 118.48, 112.92, 40.39,30.09, 20.29, 14.19. HRMS (ESI) calculated for C 32 H 31 N2O5S, m / z 514.1199,found: [M+H] + , 515.1186.

[0046] Secondly, dissolve 6a (1.028 g, 2.00 mmol) in anhydrous DMF solvent (15 mL), then add anhydrous potassium carbonate (0.829 g, 6.00 mmol) to the reaction mixture. After degassing three times under an argon atmosphere, heat under reflux and monitor the reaction progress using a TLC silica gel plate. When the reaction reaches the maximum extent, stop the reaction. Pour the reaction mixture into 100 mL of ice water and extract it three times with ethyl acetate (3×50 mL). Collect the organic phase, dry it to remove water, and then rotary evaporate to remove ethyl acetate on a rotary evaporator. Purify it by flash column chromatography with an eluent of PE:EA = 4:1 (volume ratio). After separation, collect the target component, rotary evaporate to dryness to obtain a pale yellow solid 3a (1.019 g, 0.64 mmol), with a yield of 32%. 1 1H NMR (400 MHz, CDCl3) δ 8.50 (d, 1H, J = 6.96 HZ), 8.35 (s, 1H), 8.15 (d, 1H, J = 7.48 HZ), 7.69 (d, 1H, J = 7.6 HZ), 7.63 (d, 1H, J = 8.24 HZ), 7.55 - 7.51 (t, 1H, J = 7.36 HZ), 7.44 - 7.32 (m, 3H), 7.22 (d, 1H, J = 7.84 HZ), 6.89 (d, 1H, J = 8.16 HZ), 4.21 - 4.17 (t, 2H, J = 7.44 HZ), 1.77 - 1.69 (m, 2H), 1.51 - 1.41 (m, 2H), 1.01 - 0.98 (t, 3H, J = 7.32 HZ), 13 13C NMR (101 MHz, CDCl3) δ 163.62, 162.80, 148.58, 147.53, 141.21, 132.52, 132.25, 130.55, 129.06, 128.75, 128.27, 127.43, 126.71, 126.23, 124.65, 124.36, 123.79, 123.53, 121.92, 119.08, 118.19, 117.84, 40.47, 30.20, 20.38, 13.85. HRMS (ESI) calculated for C 32 H 31 N2O5S, m / z 496.1093, found: [M + H] + , 497.1121.

[0047] Figure 1 are the ultraviolet-visible absorption spectra and fluorescence emission spectra of compounds 1b and 4b in cyclohexane solvent. As can be seen from Figure 1 in (a), due to the strong donor-acceptor electronic interaction within the molecule, the unoxidized compound 4b exhibits an obvious intramolecular charge transfer absorption peak at 445 nm, resulting in a weak and broad fluorescence emission peak (631 nm). Compared with 4b, the oxidized compound 1b shows a significantly enhanced molar extinction coefficient and a blue-shifted absorption peak (378 nm), and exhibits a strong fluorescence emission at 462 nm. The results of the photophysical property study indicate that the electron-donating ability of the oxidized phenothiazine derivative is significantly weakened, which is beneficial to realizing the property of thermally activated exciton fluorescence emission. As can be seen from Figure 1 in (b) and (c), compound 1b shows a single-exponential fluorescence lifetime decay, which is in line with the characteristics of thermally activated exciton organic materials; secondly, compound 4b shows an obvious double-exponential fluorescence lifetime decay and has a delayed lifetime at the microsecond level, indicating that 4b has the property of thermally activated delayed fluorescence. Moreover, the X-ray radiation luminescence intensity of compound 4b is too low to be suitable for X-ray imaging.

[0048] Figure 2 are the X-ray luminescence spectra of compounds 1b, 4b, and the commercial scintillator anthracene. As can be seen from the figure, the radiation luminescence intensity of compound 1b is significantly stronger than that of compound 4b and the commercial scintillator anthracene, indicating that compound 1b has great potential in the fields of indirect X-ray detection and time-resolved X-ray imaging applications.

[0049] Figure 3 is a schematic diagram of X-ray imaging, as well as the items selected for imaging and the X-ray imaging diagram. The research results show that the organic scintillator designed in the present invention has been successfully applied to the field of X-ray imaging applications, further indicating that the thermally activated exciton scintillator has the potential to be used as a new type of triplet exciton capture and applied to the field of X-ray imaging.

[0050] The above are only the preferred embodiments of the present invention. Any equivalent structure or equivalent process transformation made using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A thermally excited organic scintillator, characterized in that: The structure of the thermally excited exciton organic scintillator is as follows: Among them, R1 is a n-butyl group, R2 is a methoxy group, and R3 is an isopropyl group.

2. The preparation method of the thermally excited exciton organic scintillator according to claim 1, characterized in that: The preparation method of the thermally excited exciton organic scintillator comprises the following steps: 1) Mix N-butyl-3-methoxy-4-bromo-1,8-naphthalimide MNI with 1-isopropylphenothiazine PTZ, add toluene for dissolution, stir at room temperature, then continue to add anhydrous cesium carbonate, and then bubble to remove oxygen under an argon atmosphere. Finally, add a palladium catalyst and a BINAP ligand, and heat under reflux for 12 - 72 hours. After that, separate by dry column chromatography to obtain MNI-PTZ; wherein, when separating by dry column chromatography, the eluent is a solvent composed of a mixture of dichloromethane and petroleum ether, and the polarity gradually increases from a volume ratio of 1:10 to a volume ratio of 1:2; 2) Add MNI-PTZ to a mixed solution of glacial acetic acid and hydrogen peroxide, heat under reflux for 2 - 6 hours, and separate by column chromatography to obtain the thermally excited exciton organic scintillator; wherein, the eluent is a solvent composed of a mixture of petroleum ether:ethyl acetate with a volume ratio of 4:1; The structure of the MNI-PTZ is as follows: Among them, R1 is a n-butyl group and R3 is an isopropyl group.

3. The preparation method according to claim 2, characterized in that: In step 1), the molar ratio of MNI to PTZ is 1:1 - 5, and the reaction temperature for heating under reflux is 110 - 130 o °C.

4. The preparation method according to claim 2, characterized in that: In step 2), glacial acetic acid and hydrogen peroxide are mixed at a volume ratio of 3 - 5:1, and the concentration of hydrogen peroxide is 30 wt%.

5. The application of a thermally excited exciton organic scintillator according to any one of claims 1 - 4 in X-ray imaging.

Images