AIEgen based polymorphs with solvent regulated crystal-to-crystal switch properties†
Organic polymorphic materials have attracted considerable interest in recent years owing to their unique photophysical properties and application potential in fluorescent sensors and information storage. However, the preparation of organic polymorphs with crystal-to-crystal switch properties remains challenging, which hampers understanding the relationship between molecular stacking and emission properties. Herein, an AIEgen with tunable polymorphism-dependent emission and solvent regulated crystal-to-crystal switch properties is reported. Two polymorphs, an orange crystal (OC) and a red crystal (RC), of the AIEgen with different emission were obtained by slow evaporation in cultivation solvents (dichloromethane (DCM)/n-hexane) with different compositions. The polymorphs can be reversibly switched when exposed to different solvent vapors. Further investigation of the single crystal structures suggests that the molecular stacking mode of the crystal plays an important role in the emission properties. The real-time in situ monitoring of the polymorphs with fluorescence spectra and micrographs when exposed to solvent vapor reveals that the capture/release of DCM molecules induces molecular re-arrangements, and thus causes the switch. Such a conclusion is further supported by thermal recovery experiments. Our study on the crystal-to-crystal switch properties of AIEgen based polymorphs has provided insight into the relationship between molecular stacking and emission properties.