Fe 3+ /Zr 4+ Dual‐Responsive Distinct yet Reversible Fluorescence of Polymeric Hydrogels for Rewritable Information Encryption with Time‐Dependent Security

Abstract With the growing demand for information security, luminescent hydrogels with time dependence are highly required. However, the insufficient encryption sophistication and poor rewritability still hinder their application exploration in various scenarios. Herein, reversible multi‐responsive fluorescent hydrogels with time‐dependent information displays are successfully developed based on a dynamic coordinated interaction strategy. The fluorescent hydrogels are prepared by penetrating pyridine‐dihydrazone‐crosslinked oxidized dextran into poly(vinyl alcohol) networks. Fluorescent quenching and enhancement are achieved by dynamically controlling the coordination interaction of pyridine‐dihydrazone‐based ligands with Fe 3+ and Zr 4+ via the intramolecular charge transfer (ICT) and coordination effect (CE) mechanism, respectively. Notably, distinct time‐dependent fluorescent recoveries are found upon further treatment with H + , which is attributed to differential coordination energies of Fe 3+ and Zr 4+ with ligands. On the basis of multi‐responsive distinct yet reversible fluorescence behavior, the encoded information loaded by Fe 3+ /Zr 4+ can be sequentially decrypted until erased under the treatment of H + over time. Moreover, excellent rewritability can be realized by the alternation of metal ions and acid. Ultimately, rewritable 2D and 3D anti‐counterfeiting platforms with time dependence are established to improve the security level of information encryption. This work affords an inspiring approach to developing time‐dependent information encoding systems with enhanced security and rewritability.