Fluorescence Turn-On and Visible-Light-Induced Photomechanical Response Driven via Polymorphism

Abstract

Polymorphism serves as an effective strategy for enriching and modulating the multistimuli-responsive behaviors of smart crystalline materials. In this work, we report a crystalline material, (Z)-3-(anthracen-9-yl)-2-(3,5-dibromophenyl)acrylonitrile (ADBA), in which two additional polymorphs (form-II and form-III) were discovered alongside its nonfluorescent bulk form-I. The two polymorphs enable fluorescence turn-on (form-II) and visible-light-driven photomechanical response (form-III), respectively, highlighting the critical role of crystal structure in determining the properties of crystalline materials. Subsequently, we investigated the active/passive dual-mode optical waveguide capability of form-II and observed a temperature-induced phase transition process. The visible-light-driven photomechanical bending behavior of form-III and its underlying mechanism were studied, revealing visible-light-induced Z/E isomerization through 1H NMR monitoring before and after irradiation. Meanwhile, the mechanism of achieving visible-light-driven response by modulating the crystal structure to red-shift the absorption band was elucidated. The findings of this work provide insights into the property regulation of smart crystalline materials and the design of visible-light-driven crystalline materials.