
==== Front
Nat Commun
Nat Commun
Nature Communications
2041-1723
Nature Publishing Group UK London

39294138
51482
10.1038/s41467-024-51482-8
Article
Efficient metal free organic radical scintillators
Luo Ansheng 1
Zhang Jingru 1
Xiao Dongjie 1
http://orcid.org/0000-0003-1045-0884
Xie Gaozhan iamgzxie@njupt.edu.cn

1
Xu Xinqi 2
Zhao Qingxian 3
Sun Chengxi 1
Li Yanzhang 1
Zhang Zehua 1
Li Ping 1
Luo Shouhua 3
http://orcid.org/0000-0002-4830-1246
Xie Xiaoji 4
http://orcid.org/0000-0002-7558-3234
Peng Qiming 4
Li Huanhuan 1
http://orcid.org/0000-0003-0222-0296
Chen Runfeng 1
http://orcid.org/0000-0002-3039-2098
Chen Qiushui qchen@fzu.edu.cn

2
http://orcid.org/0000-0002-5080-2533
Tao Ye iamytao@njupt.edu.cn

15
http://orcid.org/0000-0001-7004-6408
Huang Wei vc@nwpu.edu.cn

146
1 https://ror.org/043bpky34 grid.453246.2 0000 0004 0369 3615 State Key Laboratory of Organic Electronics and Information Displays & Institute of Advanced Materials (IAM), Nanjing University of Posts & Telecommunications, Nanjing, China
2 https://ror.org/011xvna82 grid.411604.6 0000 0001 0130 6528 MOE Key Laboratory for Analytical Science of Food Safety and Biology, State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou, China
3 https://ror.org/04ct4d772 grid.263826.b 0000 0004 1761 0489 School of Biological Science & Medical Engineering, Southeast University, Nanjing, China
4 https://ror.org/03sd35x91 grid.412022.7 0000 0000 9389 5210 Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM) & School of Flexible Electronics (Future Technologies), Nanjing Tech University (Nanjing Tech), Nanjing, Jiangsu China
5 https://ror.org/020vtf184 grid.511002.7 Songshan Lake Materials Laboratory, Dongguan, Guangdong China
6 https://ror.org/01y0j0j86 grid.440588.5 0000 0001 0307 1240 Frontiers Science Center for Flexible Electronics (FSCFE), MIIT Key Laboratory of Flexible Electronics (KLoFE), Northwestern Polytechnical University, Xi’an, Shanxi China
18 9 2024
18 9 2024
2024
15 818112 3 2024
7 8 2024
© The Author(s) 2024
2024
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The development of high-performance metal-free organic X-ray scintillators (OXSTs), characterized by a synergistic combination of robust X-ray absorption, efficient exciton utilization, and short luminescence lifetimes, poses a considerable challenge. Here we present an effective strategy for achieving augmented X-ray scintillation through the utilization of halogenated open-shell organic radical scintillators. Our experimental results demonstrate that the synthesized scintillators exhibit strong X-ray absorption derived from halogen atoms, display efficacious X-ray stability, and theoretically achieve 100% exciton utilization efficiency with a short lifetime (∼18 ns) due to spin-allowed doublet transitions. The superior X-ray scintillation performance exhibited by these organic radicals is not only exploitable in X-ray radiography for contrast imaging of various objects but also applicable in a medical high-resolution micro-computer-tomography system for the clear visualization of fibrous veins within a bamboo stick. Our study substantiates the promise of organic radicals as prospective candidates for OXSTs, offering valuable insights and a roadmap for the development of advanced organic radical scintillators geared towards achieving high-quality X-ray radiography.

The development of metal-free organic X-ray scintillators combining X-ray absorption, efficient exciton utilization, and short luminescence lifetimes, remains challenging. Here, the authors present a strategy for achieving augmented X-ray scintillation through the utilization of halogenated open-shell organic radical scintillators.

Subject terms

Optical materials
Organic molecules in materials science
Single-molecule fluorescence
https://doi.org/10.13039/501100001809 National Natural Science Foundation of China (National Science Foundation of China) 62288102 Huang Wei issue-copyright-statement© Springer Nature Limited 2024
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pmcIntroduction

X-ray scintillators, capable of converting high-energy X-ray photons into visible light, have witnessed extensive applications in medical imaging, nondestructive inspection, and astronomical exploration1–5. The fundamental requisites for achieving high-efficiency radioluminescence (RL) in X-ray scintillators encompass robust X-ray absorption, high luminescence efficiency, and low self-absorption6–9. Moreover, a short luminescence lifetime is crucial for numerous applications, including quick-response real-time imaging and micro-computer tomography (micro-CT)10–12. Currently, most commercial X-ray scintillators are inorganic compounds like bismuth germanate (BGO) and CsI:Tl, which exhibit outstanding X-ray scintillation properties, but generally suffer from shortcomings such as harsh fabrication conditions, high costs, toxicity, and sensitivity to humidity and oxygen13–20. In contrast, metal-free organic X-ray scintillators (OXSTs) have garnered increasing attention due to their advantages of abundant source materials, ease of processing, low cost, and high mechanical flexibility21–23. Despite these inherent advantages, the X-ray scintillation performance of OXSTs currently lags behind their inorganic counterparts and requires further enhancement.

To attain distinguished OXSTs, a variety of materials employing different luminescence mechanisms have been developed, including conventional fluorophores11,24, thermally activated delayed fluorescence (TADF) emitters25–27, and room-temperature phosphorescence (RTP) materials21,28–30. Upon X-ray excitation, inner-shell electrons of the atoms, typically heavy atoms, are ejected through photoelectric effect and Compton effect (Fig. 1a)29. The ejected high-energy electrons further interact with atoms of the materials, generating numerous secondary electrons and producing electron–hole pairs for RL through radiative decay. According to spin statistics, the recombination of electron–hole pairs generates singlet and triplet excitons at a ratio of 1:331,32. In conventional fluorophores, 75% of triplet excitons are spin-forbidden to produce luminescence (Fig. 1b), resulting in low exciton utilization33. In contrast, TADF– and RTP–based OXSTs can theoretically achieve 100% exciton utilization efficiency34–36. TADF materials possess a small singlet–triplet splitting energy (ΔEST), allowing effective utilization of the 75% triplet excitons through an instant reverse intersystem crossing (RISC) process. Organic RTP materials typically incorporate heavy atoms or hetero atoms, which enhance spin-orbital coupling (SOC) for efficient intersystem crossing (ISC) and enable the emission of phosphorescence from originally transition-forbidden triplet excitons. However, the inherent sensitivity to oxygen and the extended microsecond/millisecond scale lifetime of triplet excitons render TADF and RTP materials vulnerable to the external environment, preventing them from practical applications.Fig. 1 Principle drawing of X-ray excited luminescence and exciton types for closed-shell and open-shell metal-free OXSTs.

a Schematic representation of the X-ray scintillation process for organic emitters. b, c The RL mechanisms for closed-shell OXSTs through radiative decay from singlet and/or triplet excitons (b) and open-shell OXSTs through radiative decay from doublet excitons (c) after the recombination of holes and electrons. Phos.: phosphorescence. d Chemical structures of TTM-1Cz and TTM-1CzBr.

Luminescent organic radicals have garnered significant attention in recent years due to their promising applications in organic electronics, especially in organic light-emitting diodes (OLEDs)37–40. Different from closed-shell organic emitters, luminescent organic radicals are a type of open-shell molecules with only one unpair electron in the singly occupied molecular orbital (SOMO). This unique feature enables a doublet spin configuration41,42, allowing for a spin-allowed radiative transition from the first excited doublet state (D1) to ground state (D0), thereby generating doublet emission with 100% exciton utilization efficiency (Fig. 1c). Additionally, doublet excitons are stable under ambient conditions and exhibit short luminescence lifetimes on the nanosecond scale. Considering these characteristics, we speculate that luminescent organic radicals are promising candidates for high-performance OXSTs.

Results

Material synthesis and characterization

To validate this concept, we synthesized a metal-free luminescent organic radical, namely (4-N-carbazolyl-2,6-dichlorophenyl)bis-(2,4,6-trichlorophenyl)methyl radical (TTM-1Cz) (Fig. 1d) using tri(2,4,6-trichlorophenyl)methyl radical (TTM) as electron acceptor and carbazole as electron donor. Since attenuation coefficient of X-ray absorption is proportional to the fourth power of the atomic number21, abundant chloride atoms in TTM are expected to enhance the X-ray absorption ability of TTM-1Cz. To further strengthen X-ray absorption ability, a bromide (Br) atom with a higher atomic number of 35 was incorporated into the TTM-1Cz molecular skeleton to synthesize another luminescent organic radical (TTM-1CzBr). The facile two-step synthetic route furnished the radicals of TTM-1Cz and TTM-1CzBr in gram-scale (Supplementary Fig. 1), demonstrating significant potential for upscaling the synthesis. Their chemical structures were confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), high-performance liquid chromatography (HPLC), and electron spin resonance (ESR) measurements (Supplementary Figs. 2-7).

Basic photophysical properties and theoretical calculations

TTM-1CzBr exhibits a strong absorption band peaking at 372 nm, attributed to a π–π* local transition of TTM unit, accompanied by two relatively weak absorption bands peaking at 542 and 585 nm derived from the intramolecular charge transfer (ICT) from the electron donor 2-bromocarbazole to the electron acceptor TTM (Fig. 2a). The steady-state photoluminescence (SSPL) spectrum of TTM-1CzBr peaks at 612 nm, which would generate bathochromic shift as the solvent polarity increases (Supplementary Fig. 8), indicating its ICT characteristic again. TTM-1Cz displays the similar absorption and SSPL spectra to TTM-1CzBr due to their analogous molecular skeletons, while the spectra of TTM-1CzBr are a little hypsochromically shifted than those of TTM-1Cz, which should be ascribed to the relatively weaker ICT since electronegative Br atom can reduce the electron-donating ability of carbazole43,44. The relatively weak electron-donating ability of 2-bromocarbazole is consistent with cyclic voltammetry (CV) experiments (Supplementary Fig. 9); the oxidation potential of TTM-1CzBr is 0.22 V higher than that of TTM-1Cz. In addition, TTM-1CzBr and TTM-1Cz shows a moderate photoluminescence quantum yield (PLQY) of 40% and 80% in n-hexane, respectively. The two radicals exhibit a fast decay time of ∼40 ns (Fig. 2b), which is several orders of magnitude shorter than those of commercial inorganic X-ray scintillators, TADF- and RTP-based OXSTs.Fig. 2 Photophysical properties and theoretical calculations of TTM-1Cz and TTM-1CzBr.

a, b UV–vis absorption (dashed lines), normalized SSPL spectra (solid lines), PLQYs (inset) (a), and lifetimes (b) in n-hexane at the concentration of 10-5 M under ambient conditions. c, d Calculated energy levels and wavefunctions for the frontier molecular orbitals of TTM-1Cz (c) and TTM-1CzBr (d). e Calculated molecular conformation variation of D0-D1. f Potential energy curves of D0 and D1 for TTM-1CzBr. Abs.: absorption; Fluo.: fluorescence. g Fluorescence stabilities of TTM-1Cz and TTM-1CzBr in PSF (doping concentration: 5 wt%) under the irradiation of a 376-nm pulsed laser at ambient conditions.

To further acquire insight into the structure-property relationship, quantum-chemical calculations of the radicals were performed. As shown in Fig. 2c, d, the highest doubly occupied molecular orbital (HOMO) and lowest singly unoccupied molecular orbital (SUMO) are mainly located on carbazole and TTM groups respectively for TTM-1Cz and TTM-1CzBr, while their SOMO is distributed over the whole molecular skeleton; the spin density calculations indicate the unpaired electrons of TTM-1Cz and TTM-1CzBr are confined to TTM group (Supplementary Fig. 10). Due to the electron-withdrawing effect of Br atom, the calculated HOMO, SOMO and SUMO energy levels of TTM-1CzBr are all lower-lying compared to those of TTM-1Cz. In consistent with experimental absorption results, the calculated D1 states are mainly attributed to a charge transfer transition from HOMO (β) to SUMO, showing weak absorption oscillator strengths of around 0.09. Additionally, TTM-1Cz and TTM-1CzBr display a significant molecular conformation variation between D1 and D0 states with large root of the mean of squared displacement (RMSD) values of 0.82 Å and 0.77 Å (Fig. 2e), respectively. Such large RMSD values would lead to a significant shift of atomic coordinates (ΔQi) between the ground state and excited state, resulting in an obvious Stokes shift of absorption and emission spectra (Fig. 2f). The large Stokes shift and weak absorption oscillator strengths are beneficial for the organic radicals to weaken reabsorption when functioned as OXSTs. Moreover, photostability is another key parameter for luminescent organic radicals. Both of TTM-1Cz and TTM-1CzBr doped in polysulfone (PSF) at a weight doping concentration of 5% (5 wt%) exhibit the excellent photostability with the almost unchanged SSPL intensity for one hour under the persistent irradiation of a 376-nm pulsed laser (Fig. 2g and Supplementary Fig. 11).

X-ray scintillation performance

The extraordinary luminescence characteristics forebode the promising X-ray scintillation performance for the developed radicals, thus their RL properties were systematically characterized. As shown in Fig. 3a, compared to TTM-1Cz (Zmax = 17, Kα = 2.8 keV), TTM-1CzBr (Zmax = 35, Kα = 13.8 keV) exhibits the enhanced X-ray absorption ability owing to the heavy-atom effect. Then the doped films of radical emitters in PSF at different doping concentrations were prepared for X-ray scintillation measurements. PSF was selected as the host matrix because its S = O bonds can form halogen bonds with the radicals, which improves the radicals’ solubility to yield homogeneous films45. The optimized weight ratio for TTM-1Cz/PSF and TTM-1CzBr/PSF films are 5 wt% and 8 wt% respectively (Supplementary Fig. 12). As the thickness of the doped film constantly increases, the RL intensity would increase to the highest value at 0.66 mm and then only show a slow decay at the higher thickness (Supplementary Fig. 13), indicating a weak reabsorption for the organic radicals. The RL spectra of 5 wt% TTM-1Cz/PSF and 8 wt% TTM-1CzBr/PSF films are almost the same with their corresponding SSPL excited at 399 nm (Fig. 3b and Supplementary Fig. 14), which originate from the doublet emission of the radical emitters. The 5 wt% TTM-1Cz/PSF film emits near-infrared RL with a peak wavelength of 725 nm, which is 30 nm red-shifted than that of 8 wt% TTM-1CzBr/PSF film, similar to the case in n-hexane. In addition, the lifetimes of TTM-1Cz and TTM-1CzBr in PSF are 20 and 18 ns respectively, shorter than their lifetimes in n-hexane (Supplementary Fig. 14 and Supplementary Table 1). Although the PLQY of 8 wt% TTM-1CzBr/PSF film is only 10% (Supplementary Table 1), lower than the 20% of 5 wt% TTM-1Cz/PSF film, the stronger X-ray absorption of TTM-1CzBr endows it with more intense RL than that of TTM-1Cz/PSF film (Fig. 3b). Benefiting from high doublet exciton utilization and weak reabsorption of the radical emitters, the X-ray scintillation properties of the two films are comparable to those films of the reported fluorescence46, TADF25,26, and inorganic scintillators46–48 (Fig. 3c and Supplementary Fig. 11). Notably, the RL intensity of the radicals is higher than that of the precursors, illustrating the doublet emission of the radicals plays an important role for the high X-ray scintillation performance (Supplementary Fig. 15). In addition, as the dosage of X-rays increases, their RL intensity would linearly enhance (Fig. 3d and Supplementary Fig. 16); the detection limit (DL) of 8 wt% TTM-1CzBr/PSF film is calculatedto be 4.25 μGy s–1, which is lower than the standard dosage for medical X-ray test (5.5 μGy s–1)49. Moreover, both TTM-1Cz/PSF and TTM-1CzBr/PSF films exhibit outstanding X-ray photostability with emission intensity being almost unchanged for 120 on-off excitation circles (Fig. 3e and Supplementary Fig. 17). After X-ray irradiation for 30 min, the 5 wt% TTM-1Cz/PSF experiences ∼10% RL intensity loss, whereas the RL intensity of 8 wt% TTM-1CzBr/PSF film remains the same, illustrating that introducing bromine atoms into radical emitters can strengthen their X-ray photostability. A possible reason might be that the heavy atoms absorb more X-ray to avoid the degradation of the molecular radical center. Therefore, the above-mentioned results forcefully prove that radical emitters are of great potential to serve as high-performance OXSTs, allowing the construction of flexible and large-area scintillation screen.Fig. 3 X-ray scintillation performance of the developed radical emitters.

a Simulated X-ray absorption spectra of TTM-1Cz and TTM-1CzBr. b RL spectra of 5 wt% TTM-1Cz/PSF and 8 wt% TTM-1CzBr/PSF films. c RL intensity comparison of a BGO single crystal film (1 mm thickness), and 2,3,5,6-tetrakis(3,6-di-t-butylcarbazol-9-yl)-1,4-dicyanobenzene (4CzTPN-Bu) (8 wt%), anthracene (8 wt%), TTM-1Cz (5 wt%), TTM-1CzBr (8 wt%) doped PSF films (∼0.1 mm thickness) under the same excitation conditions. d RL spectra of 8 wt% TTM-1CzBr/PSF film under different X-ray dose rates from 0.013 to 278 μGy s–1. Inset: linear behavior of RL intensity for 8 wt% TTM-1CzBr/PSF film as a function of excitation dose rates. e The X-ray photostability for 5 wt% TTM-1Cz/PSF and 8 wt% TTM-1CzBr/PSF films under continuous irradiation (top) and repeated on-off cycles (bottom) at a dose rate of 210 mGy s–1 under ambient conditions.

X-ray imaging applications

By virtue of the excellent X-ray scintillation performance of 8 wt% TTM-1CzBr/PSF film, we adopted it as the scintillation screen for X-ray imaging applications. The prepared doped film is uniform and highly flexible with sufficient light transmission (Fig. 4a, b). For the TTM-1CzBr/PSF scintillation screen, a high resolution of 12.0 lp mm-1 at a modulation transfer function (MTF) of 0.2 is achieved based on MTF calculation using the standard X-ray slanted-edge images (Fig. 4c)50. We then placed various objects between X-ray source and the scintillation screen for X-ray imaging. Under X-ray irradiation, the screw in capsule, the details of fishbone and USAF-1951 test chart can be captured by a commercial digital camera (Fig. 4d). Particularly, the maximum recognizable targets of the X-ray image of USAF-1951 test chart are located at group 4, element 1, which corresponds to a good resolution of 16.0 lp mm−1. Encouraged by the high X-ray imaging quality of the TTM-1CzBr/PSF film, we further applied it in a medical high-resolution micro-CT system equipped with an optical amplifying apparatus (Fig. 4e, f). Delightfully, the fibrous veins of a bamboo stick are visualized under X-ray excitation, illustrating that the doped film is highly homogeneous and the radical emitters have promising applications in commercial X-ray imaging.Fig. 4 X-ray imaging applications of TTM-1CzBr.

a Schematic diagram of the fabrication of thin scintillation screen. b Photographs of the fabricated scintillation screen. c MTF curve of the X-ray image of the screen. d Daylight photographs and X-ray images of a screw in capsule (top), a dried fish (middle) and a USAF-1951 test chart (bottom). e Schematic of a high-resolution micro-CT set-up. f Bright- (left) and dark-field (right) photographs of a bamboo stick. Note: there is a small iron ball on the top of the bamboo stick for positioning during X-ray imaging.

Discussion

In conclusion, we have demonstrated a simple yet highly effective approach to achieving high-performance X-ray scintillation through the use of metal-free organic radicals. Taking advantages of strong X-ray absorption and efficient exciton utilization, the developed organic radicals show comparable RL intensity but significantly shorter luminescence lifetimes compared to commercial inorganic scintillators and benchmark open-shell organic scintillators. The incorporation of heavy atoms into organic radicals not only enhances their X-ray absorption capacity but also improves X-ray photostability. Notably, the brominated organic radical maintains an unaltered scintillation intensity even after 30 min of X-ray irradiation at a high dose rate of 210 mGy s–1. Moreover, the successful application of a flexible and large-area doped film based on the organic radicals in a medical high-resolution micro-CT system demonstrates its capability to visualize the fibrous veins of a bamboo stick. This research provides insights into achieving efficient X-ray luminescence with organic radicals, establishing a foundation for the potential application of OXSTs in commercial radiography.

Methods

Materials and synthesis

All chemicals and solvents, unless otherwise stated, were purchased from commercial suppliers and used as received. Tetrabutylammonium hydroxide (99%), tetrachloro-p-quinone (98%), and 2-bromo-9H-carbazole (98%) were purchased from Energy Chemical. Manipulations involving air-sensitive reagents were performed in an atmosphere of dry argon (Ar). TTM and TTM-1Cz were synthesized according to a literature report40.

1H and 13C-nuclear magnetic resonance (NMR) spectra were recorded on Bruker Ultra Shield Plus 400 MHz instruments with CDCl3 as the solvent and tetramethylsilane (TMS) as the internal standard. The quoted chemical shifts and J values are expressed in ppm and Hz, respectively. The splitting patterns have been designed as follows: s (singlet), d (doublet), dd (doublet of doublets) and m (multiplet). High resolution mass spectrometry (HRMS) was performed on a Bruker autoflex speed MALDI-TOF instrument. HPLC was performed on Agilent 1260 Infinity I HPLC System. ESR was measured using a Bruker A300 instrument.

Synthesis of (2,6-dichloro-4-(2-bromo-N-carbazolyl)phenyl)bis(2,4,6-trichlorophenyl) methyl (HTTM-1CzBr): A mixture of TTM (0.30 g, 0.54 mmol, 1 eq.), 2-bromo-9H-carbazole (0.17 g, 0.70 mmol, 1.30 eq.), anhydrous Cs2CO3 (0.27 g, 0.83 mmol, 1.56 eq.), and DMF (20 mL) was stirred at 160°C for 17 h under Ar atmosphere in the dark. After cooling to room temperature, the resulting mixture was poured into (1 M) hydrochloric acid solution, and the precipitate was filtered. The precipitate was purified by silica gel column chromatography (n-hexane: dichloromethane = 5:1 v/v), obtaining the desired compound HTTM-1CzBr (0.156 g, 37%). 1H NMR (400 MHz, CDCl3, ppm): δ = 8.10-8.08 (d, J = 7.7 Hz, 1H), 7.98-7.96 (d, J = 8.3 Hz, 1H), 7.57-7.56 (d, J = 2.2 Hz, 1H), 7.53-7.52 (d, J = 1.4 Hz, 1H), 7.49-7.41 (m, 5H), 7.39-7.33 (dd, J = 15.5, 8.0 Hz, 2H), 7.32-7.31 (d, J = 2.1 Hz, 1H), 7.29-7.28 (d, J = 2.2 Hz, 1H), 6.86 (s, 1H). 13C NMR (100 MHz, CDCl3, ppm) δ = 140.90, 140.38, 138.70, 138.00, 137.84, 137.24, 134.65, 133.97, 133.91, 130.19, 130.11, 128.57, 128.26, 126.79, 126.65, 124.02, 123.10, 122.71, 121.69, 121.26, 120.50, 119.88, 50.09. HRMS (MALDI-TOF) calculated for C31H14NCl8Br: [M + H]+ m/z: 764.96, found: 764.59.

Synthesis of [2,6-dichloro-4-(2-bromo-N-carbazolyl)phenyl)bis(2,4,6-trichlorophenyl) methyl radical (TTM-1CzBr): The HTTM-1CzBr compound (1.00 g, 1.24 mmol, 1 eq.) was dissolved in 40 mL THF in argon. Then tetrabutylammonium hydroxide in methanol (2.5 mL, 1 M, 2 eq.) was added, which caused an immediate color change from brown to red. The solution was stirred under argon in the dark at room temperature for 2.5 h. Tetrachloro-p-quinone (1.53 g, 6.20 mmol, 5 eq.) was added subsequently and the solution was stirred for another 1 h. After the reaction was finished, the solvent was removed under reduced pressure. The crude product was purified by silica gel column chromatography (petroleum ether: dichloromethane = 10:1 v/v), obtaining the desired radical TTM-1CzBr (1.00 g, 61%). HRMS (MALDI-TOF) calculated for C31H13NCl8Br: [M + H]+ m/z: 763.96, found 763.76.

Photophysical property measurements

Ultraviolet-visible (UV-Vis) and fluorescence spectra were recorded on a Jasco V-750 spectrophotometer and Edinburgh FLS1000, respectively. PLQY was obtained using an Edinburgh FLS980 fluorescence spectrophotometer equipped with an integrating sphere. Fluorescence decay was measured using a picosecond pulse light emitting diode (EPLED-380, wavelength: 376 nm, pulse width: 947.7 ps). X-ray activated RL spectra and X-ray photostability were obtained from an Edinburgh FS1000 and FS5 fluorescence spectrophotometer equipped with a miniature X-ray source (AMPTEK, Inc.). X-ray imaging photographs were acquired with a digital camera (Canon, EOS R5 coupled with EF 100 mm f/2.8 L IS USM) in an all-manual mode.

Theoretical calculations

Density functional theory was used to optimize ground-state structures under UB3LYP/6-31 G(d) level calculated by Gaussian09 D.01 software. Vibrational frequency calculations were performed to verify the minimum nature of the optimized structures. In order to quantitatively measure the geometric changes of the molecule in the ground state, RMSD calculations were performed for the molecules. The spin density of TTM-1Cz and TTM-1CzBr were computed under UB3LYP/6-31 G(d) level.

Supplementary information

Supplementary Information

Peer Review File

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-024-51482-8.

Acknowledgements

This study was supported in part by the National Natural Science Foundation of China (22105104 awarded to G.X., 22322106 awarded to Y.T., 22075149 awarded to Y.T., 62075102 awarded to H.L., 22305126 awarded to H.L., and 62288102 awarded to W.H.), the Jiangsu Specially-Appointed Professor Plan, the China Postdoctoral Science Foundation (2023M731774 awarded to G.X.), the National Key Research & Development Program of China (2020YFA0709900 awarded to Q.C.), HuaLi Talents Program of Nanjing University of Posts and Telecommunications (awarded to Y.T.), the Open Research Fund of Songshan Lake Materials Laboratory (2022SLABFN16 awarded to Y.T.), the Project of State Key Laboratory of Organic Electronics and Information Displays, Nanjing University of Posts and Telecommunications (No. GZR2023010029 awarded to G.X.). Some image elements (atomic nucleus in Fig. 1a; hourglass in Fig. 1b; electromagnetic stirrer, dropper, beaker, and culture dish in Fig. 4a; X-ray source and camera in Fig. 4e) created with vectors were designed by Freepik.

Author contributions

A.L., G.X., Q.C., Y.T. and W.H. conceived the experiments and wrote the paper. A.L., J.Z., D.X., G.X., X.X. and Q.Z. were primarily responsible for the experiments. A.L., Y.L., Z.Z., X.X., Q.P., H.L. and R.C. measured and analyzed the photophysical properties. C.S. and P.L. performed the computational calculations. A.L., X.X., Q.Z. and S.L. fabricated the applications. All authors contributed to data analyses.

Peer review

Peer review information

Nature Communications thanks the anonymous, reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Data availability

Additional data are available from the corresponding author upon request.

Competing interests

The authors declare no competing interests.

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References

1. Yi L Hou B Zhao H Liu X X-ray-to-visible light-field detection through pixelated colour conversion Nature 2023 618 281 286 10.1038/s41586-023-05978-w 37165192
Yi, L., Hou, B., Zhao, H. & Liu, X. X-ray-to-visible light-field detection through pixelated colour conversion. Nature 618, 281–286 (2023).37165192
2. Hong Z Chen Z Chen Q Yang H Advancing X-ray luminescence for imaging, biosensing, and theragnostics Acc. Chem. Res. 2022 56 37 51 10.1021/acs.accounts.2c00517 36533853
Hong, Z., Chen, Z., Chen, Q. & Yang, H. Advancing X-ray luminescence for imaging, biosensing, and theragnostics. Acc. Chem. Res. 56, 37–51 (2022).36533853
3. Ou X High-resolution X-ray luminescence extension imaging Nature 2021 590 410 415 10.1038/s41586-021-03251-6 33597760
Ou, X. et al. High-resolution X-ray luminescence extension imaging. Nature 590, 410–415 (2021).33597760
4. Sakhatskyi K Stable perovskite single-crystal X-ray imaging detectors with single-photon sensitivity Nat. Photonics 2023 17 510 517 10.1038/s41566-023-01207-y
Sakhatskyi, K. et al. Stable perovskite single-crystal X-ray imaging detectors with single-photon sensitivity. Nat. Photonics 17, 510–517 (2023).
5. Hou B A swallowable X-ray dosimeter for the real-time monitoring of radiotherapy Nat. Biomed. Eng. 2023 7 1242 1251 10.1038/s41551-023-01024-2 37055542
Hou, B. et al. A swallowable X-ray dosimeter for the real-time monitoring of radiotherapy. Nat. Biomed. Eng. 7, 1242–1251 (2023).37055542
6. Liang L Controlling persistent luminescence in nanocrystalline phosphors Nat. Mater. 2023 22 289 304 10.1038/s41563-022-01468-y 36864164
Liang, L. et al. Controlling persistent luminescence in nanocrystalline phosphors. Nat. Mater. 22, 289–304 (2023).36864164
7. Hajagos TJ Liu C Cherepy NJ Pei Q High-Z sensitized plastic scintillators: a review Adv. Mater. 2018 30 1706956 10.1002/adma.201706956
Hajagos, T. J., Liu, C., Cherepy, N. J. & Pei, Q. High-Z sensitized plastic scintillators: a review. Adv. Mater. 30, 1706956 (2018).
8. Sun B Teo JY Wu J Zhang Y Light conversion nanomaterials for wireless phototherapy Acc. Chem. Res. 2023 56 1143 1155 10.1021/acs.accounts.2c00699 36897248
Sun, B., Teo, J. Y., Wu, J. & Zhang, Y. Light conversion nanomaterials for wireless phototherapy. Acc. Chem. Res. 56, 1143–1155 (2023).36897248
9. Chen Q All-inorganic perovskite nanocrystal scintillators Nature 2018 561 88 93 10.1038/s41586-018-0451-1 30150772
Chen, Q. et al. All-inorganic perovskite nanocrystal scintillators. Nature 561, 88–93 (2018).30150772
10. Gandini M Efficient, fast and reabsorption-free perovskite nanocrystal-based sensitized plastic scintillators Nat. Nanotechnol. 2020 15 462 468 10.1038/s41565-020-0683-8 32424340
Gandini, M. et al. Efficient, fast and reabsorption-free perovskite nanocrystal-based sensitized plastic scintillators. Nat. Nanotechnol. 15, 462–468 (2020).32424340
11. Chen M Organic semiconductor single crystals for X-ray imaging Adv. Mater. 2021 33 2104749 10.1002/adma.202104749
Chen, M. et al. Organic semiconductor single crystals for X-ray imaging. Adv. Mater. 33, 2104749 (2021).
12. Wang Y Efficient X-ray luminescence imaging with ultrastable and eco-friendly copper(I)-iodide cluster microcubes Light Sci. Appl. 2023 12 155 10.1038/s41377-023-01208-0 37357223
Wang, Y. et al. Efficient X-ray luminescence imaging with ultrastable and eco-friendly copper(I)-iodide cluster microcubes. Light Sci. Appl. 12, 155 (2023).37357223
13. Liang S Recent advances in synthesis, properties, and applications of metal halide perovskite nanocrystals/polymer nanocomposites Adv. Mater. 2021 33 2005888 10.1002/adma.202005888
Liang, S. et al. Recent advances in synthesis, properties, and applications of metal halide perovskite nanocrystals/polymer nanocomposites. Adv. Mater. 33, 2005888 (2021).
14. Yuan JW Highly efficient stable luminescent radical-based X-ray scintillator J. Am. Chem. Soc. 2023 145 27095 27102 10.1021/jacs.3c11027 38016919
Yuan, J. W. et al. Highly efficient stable luminescent radical-based X-ray scintillator. J. Am. Chem. Soc. 145, 27095–27102 (2023).38016919
15. Zhang Z-Z Large-area laminar TEA2MnI4 Single-crystal scintillator for X-ray imaging with impressive high resolution ACS Appl. Mater. Interfaces 2022 14 47913 47921 10.1021/acsami.2c14582 36223523
Zhang, Z.-Z. et al. Large-area laminar TEA2MnI4 Single-crystal scintillator for X-ray imaging with impressive high resolution. ACS Appl. Mater. Interfaces 14, 47913–47921 (2022).36223523
16. Liu X Lanthanide(III)-Cu4I4 organic framework scintillators sensitized by cluster-based antenna for high-resolution X-ray imaging Adv. Mater. 2023 35 e2206741 10.1002/adma.202206741 36303536
Liu, X. et al. Lanthanide(III)-Cu4I4 organic framework scintillators sensitized by cluster-based antenna for high-resolution X-ray imaging. Adv. Mater. 35, e2206741 (2023).36303536
17. Yao Q Achieving a record scintillation performance by micro-doping a heterovalent magnetic ion in Cs3Cu2I5 single-crystal Adv. Mater. 2023 35 2304938 10.1002/adma.202304938
Yao, Q. et al. Achieving a record scintillation performance by micro-doping a heterovalent magnetic ion in Cs3Cu2I5 single-crystal. Adv. Mater. 35, 2304938 (2023).
18. Xu L-J Lin X He Q Worku M Ma B Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide Nat. Commun. 2020 11 4329 10.1038/s41467-020-18119-y 32859920
Xu, L.-J., Lin, X., He, Q., Worku, M. & Ma, B. Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide. Nat. Commun. 11, 4329 (2020).32859920
19. Jana A Perovskite: scintillators, direct detectors, and X-ray imagers Mater. Today 2022 55 110 136 10.1016/j.mattod.2022.04.009
Jana, A. et al. Perovskite: scintillators, direct detectors, and X-ray imagers. Mater. Today 55, 110–136 (2022).
20. Zhou Y Chen J Bakr OM & Mohammed, O.F. Metal halide perovskites for X-ray imaging scintillators and detectors ACS Energy Lett. 2021 6 739 768 10.1021/acsenergylett.0c02430
Zhou, Y., Chen, J. & Bakr, O. M. & Mohammed, O.F. Metal halide perovskites for X-ray imaging scintillators and detectors. ACS Energy Lett. 6, 739–768 (2021).
21. Wang X Organic phosphors with bright triplet excitons for efficient X-ray-excited luminescence Nat. Photonics 2021 15 187 192 10.1038/s41566-020-00744-0
Wang, X. et al. Organic phosphors with bright triplet excitons for efficient X-ray-excited luminescence. Nat. Photonics 15, 187–192 (2021).
22. Koshimizu M Recent progress of organic scintillators Jpn. J. Appl. Phys. 2022 62 010503 10.35848/1347-4065/ac94fe
Koshimizu, M. Recent progress of organic scintillators. Jpn. J. Appl. Phys. 62, 010503 (2022).
23. Chen M Wang C Hu W Organic photoelectric materials for X-ray and gamma ray detection: mechanism, material preparation and application J. Mater. Chem. C. 2021 9 4709 4729 10.1039/D1TC00525A
Chen, M., Wang, C. & Hu, W. Organic photoelectric materials for X-ray and gamma ray detection: mechanism, material preparation and application. J. Mater. Chem. C. 9, 4709–4729 (2021).
24. Chen H Highly efficient, low-dose, and ultrafast carbazole X-ray scintillators Adv. Opt. Mater. 2023 11 2300365 10.1002/adom.202300365
Chen, H. et al. Highly efficient, low-dose, and ultrafast carbazole X-ray scintillators. Adv. Opt. Mater. 11, 2300365 (2023).
25. Ma W Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging Nat. Mater. 2022 21 210 216 10.1038/s41563-021-01132-x 34764429
Ma, W. et al. Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging. Nat. Mater. 21, 210–216 (2022).34764429
26. Wang J-X Heavy-atom engineering of thermally activated delayed fluorophores for high-performance X-ray imaging scintillators Nat. Photonics 2022 16 869 875 10.1038/s41566-022-01092-x
Wang, J.-X. et al. Heavy-atom engineering of thermally activated delayed fluorophores for high-performance X-ray imaging scintillators. Nat. Photonics 16, 869–875 (2022).
27. Wang X Halogenated thermally activated delayed fluorescence materials for efficient scintillation Research 2023 6 0090 10.34133/research.0090 37000186
Wang, X. et al. Halogenated thermally activated delayed fluorescence materials for efficient scintillation. Research 6, 0090 (2023).37000186
28. Wang X Organic phosphorescent nanoscintillator for low-dose X-ray-induced photodynamic therapy Nat. Commun. 2022 13 5091 10.1038/s41467-022-32054-0 36042210
Wang, X. et al. Organic phosphorescent nanoscintillator for low-dose X-ray-induced photodynamic therapy. Nat. Commun. 13, 5091 (2022).36042210
29. Dong C Influence of isomerism on radioluminescence of purely organic phosphorescence scintillators Angew. Chem. Int. Ed. 2021 60 27195 27200 10.1002/anie.202109802
Dong, C. et al. Influence of isomerism on radioluminescence of purely organic phosphorescence scintillators. Angew. Chem. Int. Ed. 60, 27195–27200 (2021).
30. Tang L X-ray excited ultralong room-temperature phosphorescence for organic afterglow scintillators Chem. Commun. 2020 56 13559 13562 10.1039/D0CC05389A
Tang, L. et al. X-ray excited ultralong room-temperature phosphorescence for organic afterglow scintillators. Chem. Commun. 56, 13559–13562 (2020).
31. Xie G Evaporation- and solution-process-feasible highly efficient thianthrene-9,9’,10,10’-tetraoxide-based thermally activated delayed fluorescence emitters with reduced efficiency roll-off Adv. Mater. 2016 28 181 187 10.1002/adma.201503225 26551788
Xie, G. et al. Evaporation- and solution-process-feasible highly efficient thianthrene-9,9’,10,10’-tetraoxide-based thermally activated delayed fluorescence emitters with reduced efficiency roll-off. Adv. Mater. 28, 181–187 (2016).26551788
32. Cai X Su SJ Marching toward highly efficient, pure-blue, and stable thermally activated delayed fluorescent organic light-emitting diodes Adv. Funct. Mater. 2018 28 1802558 10.1002/adfm.201802558
Cai, X. & Su, S. J. Marching toward highly efficient, pure-blue, and stable thermally activated delayed fluorescent organic light-emitting diodes. Adv. Funct. Mater. 28, 1802558 (2018).
33. Zhang Q Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence Nat. Photonics 2014 8 326 332 10.1038/nphoton.2014.12
Zhang, Q. et al. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence. Nat. Photonics 8, 326–332 (2014).
34. Tao Y Thermally activated delayed fluorescence materials towards the breakthrough of organoelectronics Adv. Mater. 2014 26 7931 7958 10.1002/adma.201402532 25230116
Tao, Y. et al. Thermally activated delayed fluorescence materials towards the breakthrough of organoelectronics. Adv. Mater. 26, 7931–7958 (2014).25230116
35. Xu S Chen R Zheng C Huang W Excited state modulation for organic afterglow: materials and applications Adv. Mater. 2016 28 9920 9940 10.1002/adma.201602604 27634285
Xu, S., Chen, R., Zheng, C. & Huang, W. Excited state modulation for organic afterglow: materials and applications. Adv. Mater. 28, 9920–9940 (2016).27634285
36. Qiu W A “flexible” purely organic molecule exhibiting strong spin-orbital coupling: toward nondoped room-temperature phosphorescence OLEDs J. Phys. Chem. Lett. 2022 13 4971 4980 10.1021/acs.jpclett.2c01205 35639995
Qiu, W. et al. A “flexible” purely organic molecule exhibiting strong spin-orbital coupling: toward nondoped room-temperature phosphorescence OLEDs. J. Phys. Chem. Lett. 13, 4971–4980 (2022).35639995
37. Ai X Efficient radical-based light-emitting diodes with doublet emission Nature 2018 563 536 540 10.1038/s41586-018-0695-9 30464267
Ai, X. et al. Efficient radical-based light-emitting diodes with doublet emission. Nature 563, 536–540 (2018).30464267
38. Guo H High stability and luminescence efficiency in donor-acceptor neutral radicals not following the Aufbau principle Nat. Mater. 2019 18 977 984 10.1038/s41563-019-0433-1 31332338
Guo, H. et al. High stability and luminescence efficiency in donor-acceptor neutral radicals not following the Aufbau principle. Nat. Mater. 18, 977–984 (2019).31332338
39. Abdurahman A Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes Nat. Mater. 2020 19 1224 1229 10.1038/s41563-020-0705-9 32541936
Abdurahman, A. et al. Understanding the luminescent nature of organic radicals for efficient doublet emitters and pure-red light-emitting diodes. Nat. Mater. 19, 1224–1229 (2020).32541936
40. Peng Q Obolda A Zhang M Li F Organic light-emitting diodes using a neutral pi radical as emitter: the emission from a doublet Angew. Chem. Int. Ed. 2015 54 7091 7095 10.1002/anie.201500242
Peng, Q., Obolda, A., Zhang, M. & Li, F. Organic light-emitting diodes using a neutral pi radical as emitter: the emission from a doublet. Angew. Chem. Int. Ed. 54, 7091–7095 (2015).
41. Cui Z Abdurahman A Ai X Li F Stable luminescent radicals and radical-based LEDs with doublet emission CCS Chem. 2020 2 1129 1145 10.31635/ccschem.020.202000210
Cui, Z., Abdurahman, A., Ai, X. & Li, F. Stable luminescent radicals and radical-based LEDs with doublet emission. CCS Chem. 2, 1129–1145 (2020).
42. Liu CH Hamzehpoor E Sakai-Otsuka Y Jadhav T Perepichka DF A pure-red doublet emission with 90% quantum yield: stable, colorless, iodinated triphenylmethane solid Angew. Chem. Int. Ed. 2020 59 23030 23034 10.1002/anie.202009867
Liu, C. H., Hamzehpoor, E., Sakai-Otsuka, Y., Jadhav, T. & Perepichka, D. F. A pure-red doublet emission with 90% quantum yield: stable, colorless, iodinated triphenylmethane solid. Angew. Chem. Int. Ed. 59, 23030–23034 (2020).
43. Reiss H Bromination improves the electron mobility of tetraazapentacene Angew. Chem. Int. Ed. 2018 57 9543 9547 10.1002/anie.201805728
Reiss, H. et al. Bromination improves the electron mobility of tetraazapentacene. Angew. Chem. Int. Ed. 57, 9543–9547 (2018).
44. Wang D Hu W Liu C Huang J Zhang X Electronic tuning of photoexcited dynamics in heteroleptic Cu(I) complex photosensitizers J. Phys. Chem. Lett. 2023 14 10137 10144 10.1021/acs.jpclett.3c02503 37922426
Wang, D., Hu, W., Liu, C., Huang, J. & Zhang, X. Electronic tuning of photoexcited dynamics in heteroleptic Cu(I) complex photosensitizers. J. Phys. Chem. Lett. 14, 10137–10144 (2023).37922426
45. Wang J-X Triplet-triplet energy-transfer-based transparent X-ray imaging scintillators Matter 2023 6 217 225 10.1016/j.matt.2022.09.031
Wang, J.-X. et al. Triplet-triplet energy-transfer-based transparent X-ray imaging scintillators. Matter 6, 217–225 (2023).
46. Du X Efficient and ultrafast organic scintillators by hot exciton manipulation Nat. Photonics 2024 18 162 169 10.1038/s41566-023-01358-y
Du, X. et al. Efficient and ultrafast organic scintillators by hot exciton manipulation. Nat. Photonics 18, 162–169 (2024).
47. Jomkaew T Electron and photon responses of CWO scintillation crystal Radiat. Phys. Chem. 2021 189 109749 10.1016/j.radphyschem.2021.109749
Jomkaew, T. et al. Electron and photon responses of CWO scintillation crystal. Radiat. Phys. Chem. 189, 109749 (2021).
48. Viererbl L YAP:Ce scintillator characteristics for neutron detection IEEE T. Nucl. Sci. 2016 63 1963 1966 10.1109/TNS.2016.2558680
Viererbl, L. et al. YAP:Ce scintillator characteristics for neutron detection. IEEE T. Nucl. Sci. 63, 1963–1966 (2016).
49. Wei H Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals Nat. Photonics 2016 10 333 339 10.1038/nphoton.2016.41
Wei, H. et al. Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals. Nat. Photonics 10, 333–339 (2016).
50. Wei J Organic room-temperature phosphorescent polymers for efficient X-ray scintillation and imaging Adv. Photonics 2022 4 035002 10.1117/1.AP.4.3.035002
Wei, J. et al. Organic room-temperature phosphorescent polymers for efficient X-ray scintillation and imaging. Adv. Photonics 4, 035002 (2022).
