【Angew.Chem.】中科大张国庆联合北理工王涛|500K超高温下依然能发光！天然矿物启发的长寿命多色有机余辉新策略
文章标题：Nature-Inspired Organic–Inorganic Hybridization Enables High-Temperature and Multicolor Organic Phosphorescence
通讯作者：Tao Wang, Guoqing Zhang
文章概要
引言
具有长寿命和可调谐发光特性的有机室温磷光材料在信息存储和余辉显示等领域展现出巨大的应用潜力。然而，有机三线态激子极易受到分子振动、旋转及碰撞等非辐射失活通道的影响，导致大多数传统有机磷光材料的耐热性极差，余辉在环境温度升高时便会迅速熄灭。相比之下，天然矿物由于其稳固的无机晶格能够高效捕获电子，往往具备优异的天然余辉性能。受到这种天然矿物发光机制的启发，研究团队创新性地提出了一种通用的有机-无机杂化策略。通过将羧基化多环芳烃分子原位嵌入到具有密堆积六方结构的羟基磷灰石（HAP）晶格中，成功开发出一系列在高温下仍能保持高效、稳定发光的“人工矿物”磷光材料。
Design concept for triggering triplet-mediated RTP in inorganic minerals. (a) Photos showing RTP afterglows from representative calcium minerals and the schematic of the energy trap-assisted RTP mechanism of natural minerals. The trapped electrons can be released via thermal activation and the tunneling effect. (b) Schematic illustration of the HAP structure and its doping system. (c) Simplified Jablonski diagram depicting the triplet-mediated RTP mechanism in the organic–inorganic doping system with enhanced ISC and suppressed nonradiative transitions. GS: ground state; ES: excited state; Fl: fluorescence; IC: internal conversion.
主要实验及结论
研究人员采用了一种极其简便、高效的原位共沉淀法，在常温常压下仅需10分钟即可完成杂化材料的制备。实验中以羧基化三苯胺（TPA-3COOH）作为模型发光客体，使其在羟基磷灰石晶格生长过程中进行原位配位锁定。系统性的结构表征证实，客体分子在无机基质中达到了分子级别的均匀分散，且在低掺杂量下完全没有破坏羟基磷灰石固有的本体结晶度。光物理测试结果令人瞩目，优化后的杂化固体材料表现出明亮的蓝色余辉，其磷光量子效率高达31.1%，长寿命余辉持续时间超过10秒。更为震撼的是，由于无机晶格的强效刚性束缚，该材料在高达500 K（约227℃）的极强高温下依然能维持肉眼可见的有机延迟发光，且经历了10次加热-冷却循环后未见明显的发光疲劳，展现出极其优异的热稳定性。
Structural characterization of organic chromophore-modified HAP. (a) Schematic illustration of the sample preparation process of TPA-3COOH/HAP. (b) TEM image of 0.3 mol% TPA-3COOH/HAP. (c–e) EDS mapping images of the Ca, O, and N elements of 0.3 mol% TPA-3COOH/HAP. (f) Confocal fluorescence imaging of 0.3 mol% TPA-3COOH/HAP. The image color does not represent the real emission color, which only reflects the PL signal. (g) Powder XRD patterns of HAP and 0.3 mol% TPA-3COOH/HAP. (h) Transmission FTIR spectra of HAP, TPA-3COOH, and 0.3 mol% TPA-3COOH/HAP. (i) High-resolution XPS spectra of HAP and TPA-3COOH/HAP with different chromophore loadings.
Photophysical investigations of 0.3 mol% TPA-3COOH/HAP recorded in air. (a) Steady-state (top) and delayed (gated time: 1–50 ms; bottom) PL spectra recorded at 298 K (λexc = 365 nm). Insets: photos showing the formation of luminescent precipitates within 10 min (top) and RTP afterglow with UV off (bottom). (b) Phosphorescence decay profiles recorded at 470 nm at 298 K in air (λexc = 372 nm). Inset: high-resolution PL decay profiles used to extract prompt fluorescence and RTP QYs based on the TDC–TCSPC technique. (c) Temperature-dependent delayed PL spectra with associated spectra recorded at 298 and 500 K (λexc = 365 nm). Inset: photos showing phosphorescence afterglows at different temperatures. (d) RTP thermal resistance over 10 heating–cooling cycles. Inset: photos showing phosphorescence afterglow before heating and after 10-cycle thermal treatment.
为了阐明这种超常磷光背后的协同增强机制，研究团队通过超快瞬态吸收光谱、电子顺磁共振（EPR）以及理论计算进行了深度的物理机理挖掘。研究发现，发光分子与羟基磷灰石中的钙离子之间存在强烈的静电配位相互作用，这种作用在分子内部感应出了一个强大的局域内置电场，从而诱导电子密度发生不均匀分布，显著促进了单线态到三线态的系间窜越（ISC）速率。与此同时，羟基磷灰石本身固有的氧空位、羟基迁移等晶格缺陷形成了适度的能量陷阱，能够有效捕获光生电荷并延缓其复合过程，通过后续的空穴-电子重新复合源源不断地产生大量三线态激子。最终，无机晶格紧密的晶格空间限制最大程度地抑制了三线态激子的非辐射衰减，三大机制协同作用共同实现了超高温下的高效磷光发射。
Mechanistic elucidation of the enhanced RTP. (a–b) Transient absorption spectra of 0.3 mol% TPA-3COOH/HAP in the range of (a) 320–450 nm and (b) 500–900 nm as a function of delay time (λexc = 365 nm; pump power: 1 µJ/cm2 per pulse). (c) EPR spectra of HAP, TPA-3COOH and 0.3 mol% TPA-3COOH/HAP in the solid state before and after 365 nm UV light treatment for 90 s, respectively. (d) Calculated change in electron density distribution upon applying parallel and vertical electric fields (isovalue: 0.003). Blue and red denote the decrease and increase in electron density, respectively. (e-g) EFM phase images of 0.3 mol% TPA‑3COOH/HAP powder acquired under the applied biases of (e) 0 V, (f) 1 V, and (g) 2 V. White dotted lines indicate phase shift as a function of the lateral position for comparison (see Figure S44). (h-j) Calculated SOC constants between singlet and triplet excited states (h) without the electric field, (i) with the applied parallel electric field, and (j) with applied vertical electric field.
这种基于天然矿物启发的杂化设计策略具有极其强大的结构普适性。研究人员将该策略成功拓展至包括羧基化萘衍生物和1,3,5-三苯基苯在内的多种纯-共轭有机发光客体中，同样实现了寿命长达1191.6毫秒的高效室温磷光发射。通过精确调控不同发光客体的分子结构以及羟基磷灰石内部的局域内置电场，能够将余辉发射峰位从470纳米一路调整至565纳米，从而赋予了整个材料体系极具吸引力的多色余辉调控能力，甚至部分体系还观察到了由高阶三线态发射引起的独特双磷光现象。
Photophysical investigations of 0.3 mol% π-conjugated chromophores in HAP recorded at 298 K in air. (a) Steady-state (dashed line; λexc = 300 nm) and delayed (solid line; gated time: 1–50 ms; λexc = 254 nm) PL spectra recorded at 298 K in air. (b-c) Phosphorescence decay profiles and fitting values (λexc = 281 nm). (d) Photos showing RTP afterglows.
总结及展望
本研究成功构筑了一种兼具矿物晶格刚性与有机分子设计灵活性的高性能有机-无机杂化磷光平台。通过原位共沉淀策略，不仅实现了工业化放大生产的潜力，更在调谐发光颜色和提升热稳定性方面取得了突破性进展。基于这种独特的波长依赖性多色余辉特性，研究团队成功展示了其在紫外线波长智能可视化传感领域的应用潜力。此外，通过将该发光杂化矿物与聚丙烯酰胺水凝胶原位基质化结合，进一步制备出了具有良好可塑性和发光特性的矿化磷光水凝胶材料，鉴于羟基磷灰石优异的骨传导与生物相容性，该体系未来在骨修复与再生医学原位生物成像监测等医疗健康领域同样蕴含着广阔的应用前景。