Aggregation-induced emission and mechanofluorochromic materials based on the structural modification of 4,5,6-triaryl-4H-pyran skeleton

Abstract

Although aggregation-induced emission (AIE)-active molecules with twisted structures have become the mainstream of mechanofluorochromic (MFC) materials, twisted molecular conformations do not necessarily lead to MFC properties. There have been some examples of failure based on 4,5,6-triaryl-4H-pyran skeleton. Herein, a series of 4,5,6-triaryl-4H-pyran derivatives were designed and synthesized to obtain fluorescent materials with both AIE and MFC characteristics. The results reveal that the introduction of triphenylamine endows all these propeller-type compounds with typical AIE properties originating from the restriction of intramolecular rotation, while the introduction of halogen atoms and the imidization of amino group are both conducive to the generation of the MFC activity by reducing the crystallization ability of derivatives. Furthermore, the red-shifted MFC phenomena are demonstrated to be ascribed to the planarization of molecular conformation caused by the crystalline-to-amorphous transition upon external pressure. This work confirms that appropriate crystallinity is very important for the candidate AIE-active compounds to exhibit MFC activities, which can be achieved by precise structural modification.