Construction of a novel self-bleaching photochromic hydrogel embraced within the Zn-MOF@WO3 junction for assembling UV-irradiated smart rewritable device

Photochromic hydrogels, which are dynamic in response to external light stimuli, have aroused increasing attentions due to their potential applications in intelligent devices. However, achieving excellent photochromic activity with fast photoresponse and self-bleaching rates still remains a huge challenge. Herein, a novel photochromic junction of zinc-based metal–organic framework (Zn-MOF) and tungsten oxide (WO 3 ) was established as photochromic unit and embraced within hydrogel of poly(acrylic acid- co -polyethylene glycol) [P(AA/PEG)] via the interaction of ionic and hydrogen bonding (denoted as P(AA/PEG)-Zn-MOF@WO 3 ), following by exploiting as self-bleaching photochromic agent for assembling UV-irradiated smart rewritable device. The photoinduced electrons can be efficiently separated and migrated from Zn-MOF to WO 3 in the Zn-MOF@WO 3 junction after UV irradiation, thereby increasing the coloration degree. Due to the enhanced fast response to light stimuli, the P(AA/PEG)-Zn-MOF@WO 3 -3 hydrogel prepared using 200 mg Zn-MOF demonstrated the fast responsive photochromic behavior of 10 s under UV lamp illumination and the self-fading process could be easily performed in room condition (within 20 min). Moreover, the coloration degree of P(AA/PEG)-Zn-MOF@WO 3 -3 photochromic hydrogel was precisely controlled and repeated by changing the UV irradiation time. Consequently, the fast photochromic and self-fading properties of P(AA/PEG)-Zn-MOF@WO 3 -3 afforded rapid and easy ‘‘writing’’ and “erasing” abilities. The present work proposes a new way for the construction of the reversibly responsive photochromic hydrogel with smart optical materials, further broadening their applications in intelligence sensors, smart windows, and flexible memory devices.