Fast photochromic and fluorescent switchable organohydrogels based on photoinduced electron transfer for display and storage

The current research on viologen-based photochromic hydrogels is limited due to the significant hindrance of water on the photochromic behavior of viologens. However, there is considerable potential for applying viologen-based hydrogels that exhibit a rapid response to ultraviolet light in various applications. In this study, organohydrogels (OGHs) with excellent photochromic properties and fluorescence switchability were prepared by introducing zinc oxide (ZnO) and viologens into the PVA hydrogel system that used glycerol as a multifunctional co-solvent. Under the irradiation of a UV lamp (6 W, 365 nm), the photogenerated electrons efficiently transferred from ZnO to viologen dications, resulting in visible color change within 1 s. Meanwhile, the electron transfer achieved the quenching of yellow fluorescence from ZnO, enabling the fluorescence switchability of the OGHs. In addition, the fading process of the photochromic OGHs could be adjusted according to different temperature environments. Compared to traditional photochromic hydrogels, the OGHs demonstrated good freeze resistance and dry resistance, thus maintaining better photochromic repeatability and stability of initial fluorescence intensity under long-term storage conditions. These qualities give the OGHs high potential for applications in displays, optical information storage and anti-counterfeiting.