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

Abstract

ABSTRACT 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.