Fluolab【Adv.Mater.】中科院宁波材料技术与工程研究所路伟、陈涛|100°C下仍可发光30秒！首次制备出超长高温余辉水凝胶材料
文章标题：Post‐Salting‐Out Polymerization Enriching Dynamic Crosslinks for Ultralong High‐Temperature Phosphorescence Hydrogels
通讯作者：Tao Chen, Wei Lu
文章概要
引言
具有长寿命和大斯托克斯位移的室温磷光（RTP）聚合物水凝胶在3D打印、生物成像和信息加密等前沿光电领域展现出巨大的应用潜力。然而，水凝胶材料天然所具备的柔软、潮湿特性，内部包含的大量水分、溶解氧以及剧烈的聚合物分子链运动，与高效有机室温磷光发射所需的严格刚性基质限制相互矛盾。尽管近年来科学家们通过增强物理相互作用（如结晶、定向或缠结）在提升水凝胶室温磷光性能方面取得了卓越进展，但这些基质的局限性使得磷光寿命普遍难以突破1.2秒，且在100°C等高温环境下，物理相互作用会显著减弱，导致无法实现高温磷光发射。为了打破这一瓶颈，研究团队创新性地提出了一种后盐析聚合策略，通过构建多重、动态且高度有序的氢键网络，成功将有序的氢键有机框架结构与高效的水凝胶结晶基质融为一体，为发光体提供了极具刚性的紧凑微环境，率先实现了兼具超长室温和超长高温磷光性能的聚合物水凝胶材料。
Scheme 1 Post-freezing-salting-out polymerization enriching dynamic crosslinks for ultralong high-temperature phosphorescence hydrogels. (a) Schematic illustration of the fabrication of polymeric HTP hydrogels and the evolution of their dynamic hydrogen bonds. (b) Schematic illustration of polymeric HTP hydrogels at different temperatures and the corresponding evolution of dynamic hydrogen bonds. (c) Comparison of the RTP lifetime and afterglow time between this work and recently reported hydrogels (Ref 11, 13-15, 20, 21, 23, 42-49). (d) Our strategy for preparing HTP hydrogels is universal to various luminogens.
主要实验及结论
在材料制备方面，研究人员首先通过超分子多价组装将三苯基-2-硼酸与三聚氰胺、氰尿酸进行自组装，构建出具有高度刚性的TP@HOF微纳花簇结构。这种氢键有机框架结构能够将发光分子牢牢固定，极大地限制了其振动和旋转行为，从而有效抑制了非辐射跃迁。随后，将该发光体分散于聚乙烯醇（PVA）水溶液中进行反复冻融操作，并在含有引发剂的高浓度2-丙烯酰胺基-2-甲基丙烷磺酸钠（A-Na+） 单体溶液中进行长达48小时的常温后盐析处理。在盐析过程中，PVA分子链靠得更近并发生强烈聚集和结晶，最后的紫外光照引发聚合反应则进一步压实了整个网络。流变学和动态机械分析（DMA）测试结果表明，该水凝胶内部形成了发育完好的双网络交联结构，即使经历20°C至100°C的剧烈热扰动，其储能模量依然保持高位，展现出极其优异的热机械稳定性。
Figure 1 Schematic illustration of the formation of TP@HOF rosettes through supramolecular multivalent assembly. (a) The multivalent assembly of the luminogens, CA, and MA to form robust hydrogen-bonding rosettes. (b) SEM image of TP@HOF rosettes. (c) Delay luminescence spectra of TP@HOF rosettes at 25°C and 100°C. (d) Time-resolved emission-decay tests of the TP@HOF rosettes at 25°C and 100°C. (e) Photos of the TP@HOF rosettes captured during and after 365 nm UV irradiation at 25°C and 100°C.
Figure 2 Rheology tests and phosphorescence properties of the TP@HOF-PVA/PA–Na+ hydrogels. (a) Frequency sweep spectra of storage modulus G’ and loss modulus G” of the hydrogel. (b) DMA curve of the hydrogel from 20°C to 100°C. Delay luminescence spectra (c), Photos captured during and after 365 nm UV irradiation (d), and Time-resolved emission-decay tests (e) of TP@HOF-PVA/PA–Na+ hydrogel samples at 25 and 100°C. (f) Photos of the TP@HOF-PVA/PA–Na+ hydrogel retaining its phosphorescence performance during twisting, knotting, and bending at 25 and 100°C. (g) Excitation-phosphorescence mapping of the TP@HOF-PVA/PA–Na+ hydrogels.
在发光性能的研究中，这种独特的TP@HOF-PVA/PA-Na+水凝胶在365纳米紫外光激发下展现出显著的蓝色发光。当移除光源后，水凝胶在室温下表现出长达45秒的肉眼可见蓝色持久余辉，对应的室温磷光寿命达到了创纪录的3.3秒。令人惊叹的是，即使将该材料加热到100°C的高温环境下，其依然表现出明显的延迟发光，肉眼可见的高温余辉时间能够维持在30秒以上，高温磷光寿命高达1.3秒。变温延迟发光光谱证实，该发光行为随温度升高而强度渐次减弱，证明其属于纯粹的磷光发射而非热致延迟荧光。研究团队通过温度扰动红外光谱及二维相关红外光谱（2DCOS）深入探究了其热响应机理，发现升温首先引发羰基和氨基相关局部动态氢键的瞬态松弛，而核心的结晶结构与框架并未受到永久性破坏。随后的分子动力学（MD）模拟也完美印证了这一点，其展示了高分子链与框架之间在加热和冷却循环中具备极佳的动态解离与重新结合能力。
Figure 3 Phosphorescence mechanism of the TP@HOF-PVA/PA–Na+ hydrogels. (a) Delay luminescence spectra, (b) Time-resolved emission-decay tests, and (c) Photos captured during and after 365 nm UV irradiation of TP@HOF-PVA/PA–Na+ hydrogels with different salting-out time in A–Na+ solution. (d) WAXS, (e) SAXS, and (f) Estimated average distance between adjacent crystalline domains L and average crystalline domain size D of TP@HOF-PVA/PA–Na+ hydrogels with different salting-out time in A–Na+ solution. (g) FT-IR spectra of TP@HOF-PVA/PA–Na+ hydrogels with different salting out time in A–Na+ solution. (h) Crystallization ratio as a function of salting-out time. (i) RTP intensity and lifetime as a function of crystallization ratio. Crystallization ratio can be calculated from the ratio between the peak area centered at 1144 and 1094 cm−1.
Figure 4 HTP properties and mechanism of the TP@HOF-PVA/PA–Na+ hydrogel. (a) Photos of the hydrogel sample captured during and after the 365 nm UV irradiation at different temperatures. (b) Time-resolved emission-decay tests, (c) Delay luminescence spectra, and (d) Phosphorescence intensities and lifetimes of hydrogels at different temperatures. (e) The cyclic phosphorescence intensity and lifetime at 480 nm of the hydrogel under the alternation of heating at 100°C and cooling at 25°C. (f) Temperature-dependent FT-IR spectra and corresponding assignments of hydrogels (interval: 5°C). 2DCOS (g) synchronous, and (h) asynchronous spectra generated from (f).
为了进一步拓宽该水凝胶的应用场景并丰富其发光色彩，研究人员进一步引入了三线态-单线态福斯特共振能量转移（TS-FRET） 策略。通过在体系中掺杂微量的商业荧光染料（如荧光素钠、罗丹明6G和罗丹明B），利用水凝胶基质超长发光带与染料吸收光谱的重叠，成功将单一的蓝色余辉调节转化为绿色（535纳米）、黄色（575纳米）和红色（602纳米） 的多色长寿命余辉发射，且在掺杂比为0.05 wt.% 时，余辉时间均可维持在20秒左右。此外，该后盐析聚合策略表现出极其广泛的通用性，研究人员尝试用萘基苯硼酸、二苯基噻吩硼酸等其他四种芳香族硼酸发光体替代三苯基硼酸，均成功制备出了发光峰位各异、室温磷光寿命均超过0.2秒且高温下肉眼可见余辉的系列水凝胶材料。
Figure 5 MD simulations of the TP@HOF-PVA/PA–Na+ hydrogels. (a) The simulations modeled the network of the TP@HOF-PVA/PA–Na+ hydrogel during temperature cycling (25°C → 100°C → 25°C). (b) Dynamic dissociation and association of hydrogen bonds between polymers and TP@HOF. The number of H-bonds (c) between polymers and TP@HOF, (d) within TP@HOF, and (e) between polymer chains.
Figure 6 Multi-color afterglow is achieved via doping with various dyes and utilizing various luminogens. (a) Schematic illustration of FRET for achieving multi-color afterglow. (b) Delayed luminescence spectra showing the multi-color afterglow of TP@HOF-PVA/PA–Na+ hydrogels doped with various dyes. (c) Photos of the TP@HOF-PVA/PA–Na+ hydrogels captured during and after the 365 nm UV irradiation with different weight content dyes. (d) Normalized delayed luminescence spectra, and (e) Time-resolved emission-decay tests of the luminogen@HOF-PVA/PA–Na+ hydrogels with different luminogens. Photos of the luminogen@HOF-PVA/PA–Na+ hydrogels with different luminogens captured during and after the 365 nm UV irradiation at 25°C (f) and 100°C (g).
总结及展望
这项研究通过精妙的后盐析聚合策略，成功解决了水凝胶内部亲水软湿环境与高稳定性有机磷光发射之间的根本矛盾。通过有序氢键有机框架与致密聚合物结晶的协同效应，不仅创造了3.3秒的水凝胶室温磷光寿命新纪录，更填补了国际上在长寿命高温水凝胶磷光材料领域的空白，使其在100°C高温下展现出超过30秒的极限余辉。该研究不仅建立了一种通用的、可扩展的彩色高温磷光水凝胶材料设计范式，同时也为未来开发用于极端环境下的智能柔性光电器件、新型高温信息防伪编码以及多维度生物成像监控等领域奠定了坚实的科学基础。