Fluolab【Angew.Chem.】中山大学洪炜|255K至573K：超宽温域下的长寿命发光新策略
文章标题： Long-Lived Luminescence Over an Ultra-Broad Temperature Range via Sequential Exciplex and Chemiluminescence Pathways
通讯作者： Wei Hong
文章概要
引言
长余辉发光材料在防伪、光电子器件及化学传感等领域具有巨大的应用潜力。尽管近年来有机长余辉材料（如室温磷光和延迟荧光）取得了显著进展，但其在高温环境下的表现往往差强人意。传统的有机发光系统在超过400 K的高温下，通常会因为三线态激子的热猝灭、电荷复合加速以及聚合物基质氧渗透性增加而导致发光迅速消失。 面对这一挑战，研究团队提出了一种极具创意的“接力”策略。通过结合激基复合物（Exciplex）的长寿命发光特性与高温激发下的化学发光（CL）机制，成功实现了从255 K（-18°C）到573 K（300°C） 超宽温域内的持续发光，为极端环境下的光学应用开辟了新路径。
a) Molecular structures of the electron donors used and the PET acceptor. b) Schematic of the long-lived luminescence mechanisms (LPL and CL) in the HMDHA/PET system. c) Proposed mechanism for the LPL (CT: Charge Transfer; CS: Charge Separation; CR: Charge Recombination). d) Photographs of the HMDHA/PET film under UV irradiation (FL), and after turning off the UV lamp for 0.1 s (RTP) and 1 h (LPL) at room temperature, along with the photograph taken at 473 K (CL). Film thickness: 1 mm.
主要实验及结论
研究人员设计并合成了一种具有刚性结构的二氢吖啶衍生物（HMDHA）作为电子给体，并将其掺杂到具有优异电子抽取能力的聚乙烯对苯二甲酸酯（PET）基质中。实验发现，该系统表现出独特的三阶段发光演变：在紫外光激发下发出天蓝色荧光，关灯瞬间转为绿色余辉，最终演变为长达32小时的黄绿色余辉。这种超长余辉源于HMDHA与PET之间形成的激基复合物发生光诱导电荷分离，产生的自由基离子在基质中缓慢复合。在低温条件下，这种发光寿命甚至可以进一步延长，在255 K下持续时间超过360小时。
(a) Steady-state and time-delayed photoluminescence (PL) spectra of the HMDHA/PET film, measured with gate times of 10 ms and 1 h. (b) LPL spectra recorded at different delay times: 3 min, 1 h, 12 h, 24 h, and 32 h. (c) LPL decay curve of the HMDHA/PET film. (d) Photographs of the LPL from the HMDHA/PET film. Scale bar: 2.5 cm. (e) UV–vis spectra of the HMDHA/PET film before and after UV irradiation, alongside the spectra of HMDHA·+ and DMT·– in DCM. (f) Plots of lg(ILPL) vs. lg(∆Abs.) and time vs. lg(∆Abs.) after excitation, where ∆Abs. is the absorbance difference at 586 nm before and after excitation. (g) EPR spectra of the HMDHA/PET film acquired after different excitation durations. The dopant concentration in the HMDHA/PET film was 0.5 wt%. Excitation wavelength: 365 nm. Film thickness: 3 mm.
(a) Proposed mechanism for the LPL in the HMDHA/PET system. (b) Calculated hole and electron distribution in the S1 state of the system. (c) Charge transfer matrix of the HMDHA/PET system. (d) Independent gradient model based on Hirshfeld partition (IGMH) analysis, represented as a scatter plot of sign(λ2)ρ versus δg, depicting the interaction surface between HMDHA and PET. (e) sign(𝜆2)𝜌 colored IGMH isosurfaces (𝛿g = 0.00005) visualizing intermolecular interactions in HMDHA/PET system.
然而，该研究最核心的突破在于其高温下的“表现接力”。当环境温度升高至360 K以上时，传统的激基复合物发光由于热猝灭而减弱，但此时HMDHA分子中的异亚丙基桥结构开始与渗透进来的氧气发生热氧化反应，激发出强烈的蓝色化学发光。 这种化学发光表现出与温度正相关的特性，温度越高发光越强，甚至在PET基质已经熔融的573 K高温下依然清晰可见。更令人惊叹的是，这种化学发光的持久性极强，在400 K环境下连续发光一个月后，仍能保持一半以上的初始强度。通过理论计算与结构对比，研究证实了HMDHA分子中的多重异亚丙基桥既保证了低温下的结构刚性，又作为高温化学发光的“燃料”，是实现双模式发光切换的关键。
(a) Normalized LPL emission spectra for the different donor/PET systems. (b) Corresponding LPL decay curves. Film thickness: 3 mm. (c) Calculated HOMO and LUMO energy levels of the donors (TMTPA, HMDHA, DMDPA, DHA, ICz) and acceptors (DMT, PET). (d) Measured energy gaps of the donor/DMT systems by cyclic voltammetry (CV).
(a) Luminescence spectra of the HMDHA/PET film at different temperatures. (b) Temperature-dependent luminescence mapping of the film. (c) Photographs of the film at different temperatures. Scale bar: 2.5 cm. (d) LPL decay curves monitored at 510 nm at different temperatures. (e) LPL decay curves under triggered heating (monitored at 510 nm). The dopant concentration in the HMDHA/PET film was 0.5 wt%. Excitation wavelength: 365 nm. Film thickness: 3 mm.
基于这一特性，研究团队展示了该材料在柔性显示和视觉温度监控中的应用潜力。通过在PET薄膜上进行紫外光刻成像，可以实现信息的加密与读取。当温度升高时，原本绿色的长余辉图案会逐渐消失，取而代之的是均匀的蓝色化学发光背景，这种颜色切换过程可用于极端环境下的温度报警。此外，该材料还被成功应用于柔性电路板（FPC）的实时热成像监测，能够通过肉眼观察发光强度的变化精确识别出电路过热的毫秒级微小区域，其分辨率可与专业的红外热像仪相媲美。
(a) Luminescence spectra of the HMDHA/PET film measured at different temperatures without excitation. (b) Chemiluminescence (CL) spectra of HMDHA/PET films with different dopant concentrations (0.1, 0.5, 1, 2, and 4 wt%) at 480 K. (c) CL spectra of the film before and after air introduction. (d) CL spectra of the film after storage at 400 K for different time. (e) Photographs of the film at different temperatures without excitation. Scale bar: 2.5 cm. The dopant concentration was 0.5 wt% for all experiments except for (b). Film thickness: 3 mm.
(a) Photographs of LPL patterns based on HMDHA/PET and ICz/PET, and the time-dependent LPL color of a pattern from a co-doped (HMDHA:ICz=1:8) PET film. Scale bar: 3.0 cm. Film thickness: 3 mm. (b) Rewritable photolithographic patterning: cycles of pattern writing on an HMDHA/PET film and thermal erasure, showing the resulting LPL patterns. Scale bar: 1.0 cm. Film thickness: 1 mm. (c) Photolithographic patterning and high-temperature response of an HMDHA/PET label on a glass vial. Scale bar: 1.0 cm. Film thickness: 0.5 mm. (d) Temperature-dependent luminescence of an HMDHA/PET-based pattern from 298 to 573 K. Scale bar: 3.0 cm. Film thickness: 3 mm. (e and f) Application of an HMDHA/PET film for thermal probing on flexible printed circuits and the corresponding thermal camera images. Scale bar: 1.5 cm. LPL excitation wavelength: 365 nm. Film thickness: 0.5 mm.
总结及展望
该研究通过给体/受体激基复合物与化学发光的巧妙结合，打破了有机发光材料在高温环境下的性能瓶颈。这种基于HMDHA/PET的系统不仅实现了跨越318度的超宽工作温域，更在发光寿命上实现了从“小时级”到“月级”的飞跃。 这种材料凭借其高透明度、良好的柔韧性以及对温度和氧气的灵敏响应，在高端防伪、数据加密以及复杂环境下的视觉热传感器领域展现出巨大的商业化应用价值。未来，这种“接力发光”的设计思路有望激发更多兼具极端稳定性和多功能性的先进光学材料的诞生。