Ministry of Education Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310058, China.
ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, Zhejiang 311215, China.
J Am Chem Soc. 2023 Feb 15;145(6):3763-3773. doi: 10.1021/jacs.2c13264. Epub 2023 Feb 7.
Conventional hydrogels such as polyacrylamide and polyacrylic acid ones seldom exhibit phosphorescences at ambient conditions, which limit their applications as optical materials. We propose and demonstrate here a facile strategy to afford these hydrogels with room-temperature phosphorescence by polymerization-induced crystallization of dopant molecules that results in segregation and confinement of the gel matrix with carbonyl groups and thus clusterization-induced phosphorescence. As a model system, crown ethers (CEs) are dissolved in an aqueous solution of concentrated acrylamide that greatly increases the solubility of CEs. During the polymerization process, CEs crystallize to form large spherulites in the polyacrylamide hydrogel. The crystallization arises from the drastically reduced solubility of CEs after the conversion of monomers to polymers during the gel synthesis. The resultant composite hydrogel with a water content of 67 wt % exhibits extraordinary phosphorescence behavior yet maintains good stretchability and resilience. We found that the partial gel matrix is squeezed and confined by in situ-formed crystals, leading to carbonyl clusters and thus phosphorescence emission. The composite gel shows green phosphorescence with an emission peak at 512 nm and a lifetime of 342 ms. The afterglow emission is detectable by the naked eye for several seconds. This strategy has good universality, as validated in other hydrogels with different polymeric matrices and dopant molecules. The development of hydrogels with good mechanical and phosphorescent properties should merit the design of multifunctional soft machines with applications in biomedical and engineering fields.
传统的水凝胶，如聚丙烯酰胺和聚丙烯酸水凝胶，在环境条件下很少表现出磷光，这限制了它们作为光学材料的应用。我们在这里提出并展示了一种简便的策略，通过聚合诱导掺杂分子的结晶来赋予这些水凝胶室温磷光，从而导致羰基基团的凝胶基质的分离和限制以及由此产生的聚集诱导磷光。作为一个模型体系，冠醚（CEs）溶解在浓缩丙烯酰胺的水溶液中，大大增加了 CEs 的溶解度。在聚合过程中，CEs 在聚丙烯酰胺水凝胶中结晶形成大球晶。结晶是由于单体转化为聚合物后 CEs 的溶解度急剧降低而产生的。所得的复合水凝胶含水量为 67wt%，具有非凡的磷光行为，但仍保持良好的拉伸性和弹性。我们发现，部分凝胶基质被原位形成的晶体挤压和限制，导致形成羰基簇，从而产生磷光发射。复合凝胶显示出绿色磷光，发射峰位于 512nm，寿命为 342ms。余辉发射可以用肉眼在几秒钟内检测到。这种策略具有很好的通用性，已经在具有不同聚合物基质和掺杂分子的其他水凝胶中得到验证。具有良好机械性能和磷光性能的水凝胶的开发应该值得设计用于生物医学和工程领域的多功能软机器。
