Ultraviolet‐Responsive Reversible Photochromic Hydrogel for Optical Information Storage and Ink‐Free Printing

ABSTRACT Photochromic materials can absorb specific wavelengths of light, thereby exhibiting photochromic effects. Among various photochromic materials, TiO 2 has garnered significant attention due to its abundance, eco‐friendliness, and non‐toxicity. However, most TiO 2 ‐based photochromic materials require doping or modification to achieve their photochromic properties, and the photochromic performance of pure TiO 2 is typically limited to solvents. To address this challenge, uniformly sized (~5 nm) and well‐crystallized TiO 2 NPs were prepared through a simple reflux method, followed by surface modification with butanol. The synthesized TiO 2 NPs were characterized using XRD, FTIR, and TEM. XRD and TEM confirmed their anatase phase composition, while FTIR results indicated the successful grafting of butanol groups onto the surface of TiO 2 NPs. Subsequently, the nanoparticles were dispersed in ethanol, demonstrating significant photoresponse under ultraviolet irradiation and rapid recovery to their initial color upon exposure to air. To overcome the limitation of solvent‐dependent color change, the nanoparticles were incorporated into P(HEA‐AM) hydrogel, which initially exhibited excellent optical transparency. The solvent molecules retained within the hydrogel synergistically enabled the photochromic performance of the TiO 2 NPs. The microstructure, photochromic properties, mechanical performance, and photochromic mechanism of the resulting photochromic hydrogel were systematically characterized and analyzed. UV–vis results revealed that the light transmittance of the hydrogel decreased from an initial 90% to 16%, demonstrating its excellent light modulation capability. Based on its superior photochromic performance, the feasibility of its practical applications, such as information storage, was explored. Under ultraviolet irradiation, P(HEA‐AM)‐TiO 2 could clearly display targeted printed content.