Programmable Multicolor Room‐Temperature Phosphorescence Hydrogels via the Synergy of Freeze‐Soaking and Salting‐Out

Room temperature phosphorescence (RTP) is rarely achieved in hydrogel systems, as water severely quenches their emission. Achieving multicolor RTP in hydrogels is even more challenging, despite its high potential in cutting-edge applications such as advanced anti-counterfeiting and camouflaging skins. Here, a universal strategy is presented to fabricate multicolor RTP hydrogels through the cascading freeze-soaking and salting-out process (F-S method). This method induces in situ polymer assembly around the phosphors, providing effective confinement and protection against quenching. As a result, RTP hydrogel (RTPgel) with strong phosphorescence (lifetime > 200 ms and afterglow >10 s), high water content (71 %), and excellent flexibility (stretchability > 3000%) is achieved in a modal system composed of polycyclic aromatic boronic acids (PABAs)-grafted polyvinyl alcohol (PVA). Since chain aggregation strongly correlates with the kosmotropic nature of the salt solution, the phosphorescence properties, including lifetime and intensity, are feasibly tunable by re-soaking the hydrogels in solution with different types of salts or concentrations, enabling programmable spatiotemporal emission patterns. Such a method is universal, adaptable for various luminophores and polymer matrices, allowing customizable emission colors across a wide spectrum. Moreover, it is compatible with scalable, high-precision fabrication techniques such as fiber spinning, direct ink writing (DIW), and digital light processing (DLP) 3D printing.