Polymorph-Dependent Multicolor-Switchable Mechanofluorochromism of 1-(9-Anthryl)Vinyl-3-(3-Pyridyl)Vinylbenzene: Molecular Conformation versus Intermolecular Interaction

The mechanism of most mechanofluorochromic (MFC) materials is related to a non-covalent change in aggregate packing. It is still a challenge to clarify the respective effects of molecular conformation and intermolecular interaction on the MFC performance. Herein, a new (9-anthryl)vinyl derivative APYB with polymorph-dependent multicolor-switchable MFC property is reported. APYB has only one torsion unit in the molecule configuration and could form four different crystal phases (APYB-a, APYB-b, APYB-c and APYB-d). Furthermore, all polymorphs are MFC-active. Therefore, it provides a rare and direct case to correlate the aggregate packing with MFC performance. The solid-state emission could be finely tuned from 465 to 500 nm by virtue of polymorphism. Crystal structure analyses and optical studies reveal that an increasing twist angle could result in a blue shift in the fluorescence spectra and a high-contrast MFC performance. In contrast, strong intermolecular interactions could lead to high emission effici...