Photogated Coordination Switching of Silver Nanoparticles for Reversible Coloration/Discoloration of Hydrogel

Abstract Hydrogels remain challenging for the reversible high‐resolution coloration/discoloration in response to external stimuli. Herein, a photogated coordination‐switching mechanism is proposed to alter the localized surface plasmon resonance of silver nanoparticles (AgNPs) inside a hydrogel network, which enables the reversible color change. The hydrogel is synthesized by free‐radical crosslinking of N,N'‐bisacrylylcystamine (BACA), sodium p‐styrenesulfonate (NASS), and acrylamide (Am) in the presence of AgNPs. Upon light irradiation at λ = 400 nm (300 mW cm⁻²), the AgNPs selectively coordinate with the disulfide bond of BACA to result in a reddish‐brown hydrogel in 30 s. In dark condition, this coordinating effect is replaced by the sulfonate of NASS and AgNPs, which brings the hydrogel into gray white. Such a photogated coordination‐switching mechanism is a physical process that enables the coloration/discoloration cycles without apparent reduction in the resolution. By means of a high‐precision mask, it allows writing, storing, and erasing of complicated information at the hydrogel surface, showing a great potential in informatics, cryptology, and security areas.