Nature-Inspired pH-Responsive Hydrogels with Rapid and High Contrast Changes in Color, Fluorescence, and Shape Simultaneously

To realize single-stimulus-induced simultaneous multi-behaviors in hydrogels is still quite challenging nowadays. Herein, an intelligent pH-responsive hydrogel (BP4VA/PAS) with rapid and high contrast changes in color, fluorescence, and shape simultaneously is reported. The BP4VA/PAS hydrogel is fabricated by incorporating styryl anthracene derivative (BP4VA) into copolymer networks (PAS) of acrylamide and sodium 4-styrene sulfonate. Under acid conditions, the protonation of BP4VA generates a rapid change with high color contrast from yellow to red and a fluorescence switch between bright green and weak red emission. At the same time, the electrostatic interactions between 2H-BP4VA²⁺ and sulfonate anions suspended on PAS trigger BP4VA/PAS hydrogels to shrink. Upon alkaline treatment, the 2H-BP4VA²⁺/PAS hydrogel deprotonates and recovers to its original color, fluorescence, and shape. Furthermore, utilizing rapid and remarkable pH-responsive properties of BP4VA/PAS hydrogels, we successfully demonstrated its applications in biomimicry, camouflage, and multistage information encryption. Collectively, this work provided an elegant strategy to develop intelligent hydrogels in applications of biomimetic smart materials and information encryption.