【Angew.Chem.】福州大学林梅金等|空间分辨率高达 37 lp mm⁻¹！通过晶体结构可逆切换实现智能刺激响应三线态发射与X射线闪烁
文章标题：Stimuli‐Responsive Triplet Emission and X‐Ray Scintillation via Reversible Structural Switching in Pyromellitic Diimide Cocrystals
通讯作者：Hongming Chen, Mei-Jin Lin
文章概要
引言
开发具有可编程和可逆发射特性的智能刺激响应发光材料对于高级生物成像和信息安全防御具有重要意义。在各种设计策略中，利用三线态激子的有机材料因其对固态分子堆积和微环境变化的高度敏感性而备受青睐。然而，如何在保持高结晶度的前提下，实现可逆的固态结构转变并同步控制X射线激发发光（即闪烁响应）依然是该领域长期面临的巨大挑战。为了突破这一瓶颈，研究团队利用超分子共晶工程调控固态光物理行为，为构建动态可控的三线态发射有机固体提供了全新思路。
Chemical structures of the cocrystals and a schematic illustration of the scintillation mechanism under X-ray irradiation, including the distinct emission pathways in different cocrystals and the reversible polymorphic transformation.
主要实验及结论
研究团队以对称的均苯四甲酸二酰亚胺为受体核心，与卤代咔唑供体分子通过气相扩散法共同组装，成功构建了一系列供体-受体型卤键有机共晶材料。在溴代咔唑体系中，通过调控不同的溶剂结晶环境，成功制备出两种同质异形体，其中绿色的共晶表现出强烈的室温磷光和明亮的放射发光行为，而橙色的同质异形体在X射线照射下则几近不发光。令人兴奋的是，在温和的有机溶剂蒸气交替刺激下，该体系展现出高度可逆的、保持结晶度的有序到有序相转变，通过重新排列晶体内部的卤键和氢键等超分子作用网络，在固态下实现了数字化“开/关”控制的放射发光和光致发光切换。
(a) Schematic illustration of the reversible cocrystal transformation between Bu2PMDI-Br2Cz-G and Bu2PMDI-Br2Cz-O upon vapor fumigation, along with cocrystal structure and interaction analysis. The inset shows photographs of the corresponding powder samples under daylight. (b) PXRD patterns of Bu2PMDI-Br2Cz-O, transformed to Bu2PMDI-Br2Cz-G and subsequently restored, demonstrating the reversible cocrystal transformation. (c) Cocrystal structures of Bu2PMDI-I2Cz and interaction analysis.
(a) UV–vis absorption spectra, (b) Temperature-dependent lifetime decay profiles and (c) temperature-dependent steady-state emission spectra of all cocrystals. Steady-state photoluminescence spectra (solid lines) and delayed spectra (dashed lines) recorded at 280 K and 77 K for (d) Bu2PMDI-Br2Cz-G, (e) Bu2PMDI-Br2Cz-O, and (f) Bu2PMDI-I2Cz. (g) RL spectra under X-ray excitation at a dose rate of 278 µGy s−1 (50 kV, 79 µA), with the inset showcasing photographs of Bu2PMDI-Br2Cz-G and Bu2PMDI-I2Cz powders under X-ray irradiation. (h) The dose rate dependence of RL intensities across the range of 4.58 to 278 µGy s−1. (i) Enhanced RL of Bu2PMDI-Br2Cz-O after DCM fumigation, recorded under X-ray excitation at a dose rate of 278 µGy s−1. The inset shows the RL of Bu2PMDI-Br2Cz-O under identical conditions.
Independent gradient model based on the Hirshfeld partition (IGMH) analysis of the corresponding fragments from (a) Bu2PMDI-Br2Cz-G, (b) Bu2PMDI-Br2Cz-O, and (c)Bu2PMDI-I2Cz. Energy level diagrams and spin-orbit coupling matrix elements (ξ) of (d) Bu2PMDI-Br2Cz-G, (e) Bu2PMDI-Br2Cz-O, and (f) Bu2PMDI-I2Cz.
理论模拟与光谱动力学分析表明，该共晶体系截然不同的发光效率并非单纯取决于重原子身份，而是由卤键调控的自旋-轨道耦合、氢键辅助的晶格刚化以及激子电子耦合的协同效应共同决定的。凭借对三线态激子的高效捕获与利用，优化后的绿色共晶展现出高达 18667 photons MeV⁻¹ 的相对光产额和低至 39 nGy s⁻¹ 的检测极限，并被成功加工成均匀柔性的闪烁体薄膜。应用实验表明，该薄膜不仅实现了空间分辨率高达 37.0 lp mm⁻¹ 的高清静态X射线成像和无拖尾的 60 fps 实时动态成像，还基于双通道正交读取构建了可重写的多模态信息加密原型，实现了防伪领域的动态隐藏与读取。
(a) Photographs of the line-pair card under daylight and contrast images under X-ray irradiation, accompanied by pixel-intensity profiles along the indicated orange line. (b) X-ray contrast image of a tungsten sheet (inset) and the corresponding MTF versus actual line-pair spacing measured by the slanted-edge method under X-ray exposure. Photographs of (c) fish and (d) chip in daylight, alongside corresponding X-ray static images showing the internal structure. (e) Photographs of spring inside an opaque in daylight. (f) Real-time X-ray dynamic images of a spring inside an opaque capsule, showing two consecutive frames with a 16.67 ms interval.
(a) Photographs of Bu2PMDI-Br2Cz-G test papers under UV light at different pH values. (b) Photoluminescence intensity of Bu2PMDI-Br2Cz-G text paper under different pH. (c) Photoluminescence intensity of Bu2PMDI-Br2Cz-G text paper under cyclic EA/DCM vapor fumigation. (d) Schematic of the stimulus-responsive multimodal information encryption. (e) Initial images under daylight and UV light. (f) X-ray images after fumigation with DCM or EA.
总结及展望
这项研究成功为开发可编程有机闪烁体提供了一种强有力的超分子共晶工程策略。通过精细控制晶体内部非共价相互作用的动态平衡，实现了无损的固态结构切换与清晰的三线态能量操控。这种将晶体相转变与X射线响应无缝集成的全新设计思路，不仅在高性能超低辐射医学成像领域展现出广阔的应用前景，更为下一代多维智能自适应辐射材料和可重写高级光电安全系统的研发开辟了全新路径。