Photoinduced Multimodal Motions and Reversible Fluorescence Switching in an Elasto-Plastic Crystal

Multi-stimuli-responsive materials have received widespread attention in the field of adaptive materials due to their ability to adapt to changes in the environment. However, fabricating multiple stimuli into a single component crystal still remains challenging. In this study, a polymorphic elasto-plastic Schiff-based crystal displaying morphology-dependent photomechanical motions is designed and investigated. Both Form I and Form II of it exhibit dual plasticity and elasto-plasticity along different facets, which is attributed to the slidable separating layers. Moreover, Form I retains its elastic bending ability even after being plastically twisted, owing to the well-maintained strong pi-pi interactions, whereas Form II can not twist without fractures. In addition, the photomechanical motions of Form I including jumping, twisting to bending are realized by adjusting the crystal morphologies, while Form II is lacking in response to ultraviolet light irradiation. Theoretical calculation analysis reveals that lattice deformation induced by photoisomerization of Form I is the driving forces for crystal motions. Furthermore, reversible luminescence switching behaviors are realized in Form I and Form II upon acid-base fumigation as well as heating. The synergistic multi-stimuli-responsive mode based on heat, acid, and solvent stimuli provides an alternative path for multi-mode information encryption. As two single crystals with elastoplastic traits, Form I and Form II of TBHP molecule exhibit different photomechanical motions and emission characteristics. The natural transition orbitals (NTOs) are applied to analyze the electron transition characters for absorption, which suggests the formation of pi-dimers in Form I induces its nonfluorescence. Furthermore, sequential stimuli of TFA and TEA trigger fluorescence switching in two forms. image