Rosin-based amphiphilic AIEgens with visualized solid-state molecular motion for injectable and thermostable supramolecular fluorescent hydrogels

Supramolecular hydrogels with aggregation-induced emission (AIE) activity are attracting significant attention due to their unique properties and promising application potential. However, using nonplanar conjugated molecules to self-assemble into ordered nanostructures remains a substantial challenge. In this study, a series of amphiphilic maleopimaric acid-derived Schiff bases (MPASA-R, R = H, 4Cl, 5Cl, 5Br, 5I, and 5-NO2) with AIE characteristics were easily synthesized from rosin. Changing the substituents significantly affected the molecular arrangement and the excited-state molecular motion, thereby altering the photophysical properties and photo- chromic behaviors of MPASA-R. Notably, MPASA-5Br in the solid state exhibited quick and obvious visualized photochromic behaviors and excellent fatigue resistance, making it an ideal material for encryption-decryption applications. Interestingly, the strong hydrophobic interactions and large geometrical restrictions of the rosin skeleton promoted MPASA-R to self-assemble into chiral nanofibers in alkaline conditions. AIE supramolecular hydrogels were further obtained, the fluorescence properties and mechanical strength of which could be regulated by changing substitutions or concentration. Furthermore, the obtained AIE supramolecular hydrogels exhibited excellent injectable ability and high temperature resistance, which could be shaped on demand and remain unchanged mechanical properties and intense fluorescence at 90 degrees C. The present work not only provides novel biobased encrypted materials but also proposes an effective strategy based on the strong aggregation of the rosin skeleton for preparing AIE supramolecular hydrogels.