Piezochromic luminescence of AIE-active molecular co-crystals: tunable multiple hydrogen bonding and molecular packing

Abstract

Prominent piezochromic materials play a vital role in the development of damage detection devices and smart sensors. However, compared to other external stimuli (such as light, pH and temperature), understanding of intermolecular interactions and piezochromic properties based on multicomponent molecular hybrid materials is still limited and examples are quite rare. Herein, we choose 4-bis(1-cyano-2-phenyl-ethenyl)benzene (DCSB, A) as the core chromophore to self-assemble with two small organic molecules (tetrafluorohydroquinone (B) and 2,3,5,6-tetrafluoro-4-hydroxy-benzoic (C)), for the sake of studying their relationship between solid-state molecular arrangement and piezochromic luminescence. The as-prepared samples (two new co-crystals: A-5B and A-2C) present tunable multiple hydrogen bonds, molecular packing, and photophysical properties (such as PL colors, lifetimes, PLQYs and aggregation-induced-emission (AIE) properties) compared to pristine DCSB. Moreover, these two co-crystals exhibit prominent piezochromic properties and fluorescence quenching phenomena towards specific environmental stimuli (applied pressure and vapor fumigation) due to collapse of inner supramolecular architectures. Furthermore, the mechanism of visible piezochromic behavior has been confirmed by in situ IR micro-spectroscopy. Therefore, this work not only illustrates the relationship between molecular configuration/packing and photophysical properties of new AIE-based co-crystals, but also develops potential applications in multiple optical sensors towards pressure and detrimental vapor (NH₃).