Freezing-Induced Spatial Confinement During Cryo-Polymerization Enables Stable Intrinsic Luminescence in Hydrogels.

Intrinsic luminescence in polymer hydrogels is highly desirable for soft optoelectronic and information-security applications, yet remains difficult to achieve under hydrated conditions, where clusterization-triggered emission (CTE) is easily quenched by water due to disrupted intermolecular interactions. Here, we establish a facile and general strategy to overcome this limitation via directional freezing-assisted cryo-polymerization. The anisotropic growth of ice crystals imposes spatial confinement during network formation, driving dense chain packing and stabilizing amide-based emissive clusters. Such structural confinement suppresses nonradiative decay and enables a robust CTE effect even at ultrahigh water content (∼90 wt%), effectively overcoming the long-standing challenge of hydration-induced quenching. The resulting polyacrylamide hydrogel exhibits stable blue emission, structural stability, excellent resistance to water-induced quenching, and mechanical softness with elasticity and shape programmability, enabling rewritable and multilevel information encryption. More broadly, this work demonstrates that stable intrinsic luminescence in water-rich soft materials can be achieved through structural confinement rather than molecular modification, providing a general design principle for CTE systems and opening new opportunities for integrating optical functionality with structural programmability in soft materials.