High‐Performance Photochromic Hydrogels for Rewritable Information Record

Rewritable information record materials usually demand not only reversibly stimuli‐responsive ability, but also strong mechanical properties. To achieve one photochromic hydrogel with super‐strong mechanical strength, hydrophobic molecule spiropyran (SP) has been introduced into a copolymer based on ion‐hybrid crosslink. The hydrogels exhibit both photoinduced reversible color changes and excellent mechanical properties, i.e., the tensile stress of 3.22 MPa, work of tension of 12.8 MJ m−3, and modulus of elasticity of 8.6 MPa. Moreover, the SP‐based Ca2+ crosslinked hydrogels can be enhanced further when exposed to UV‐light via ionic interaction coordination between Ca2+, merocyanine (MC) with polar copolymer chain. In particular, hydrogels have excellent reversible conversion behavior, which can be used to realize repeatable writing of optical information. Thus, the novel design is demonstrated to support future applications in writing repeatable optical information, optical displays, information storage, artificial intelligence systems, and flexible wearable devices. Ion‐hybrid crosslink approach enables mechanical enhancement of poly sodium acrylate‐co‐methyl acrylate‐co‐spiropyran hydrogels. The spiropyran (SP)‐based Ca2+ crosslink hydrogels can be enhanced further when exposed to UV‐light via ionic interaction coordination between Ca2+, zwitterionic merocyanine (MC), and polar polyacrylate (PSA) chain. Moreover, hydrogels have excellent reversible conversion behavior, which opens a window to realize repeatable writing of optical information.