Mechanofluorochromic behaviours of functionalized carbazole-based difluoroboron compounds with different aryl substituents moieties.

To better understand the relationship between molecular structure and mechanofluorochromic characteristics, three carbazole-based N^O-chelated difluoroboron compounds (Cz-S-BF , Cz-PhNp-S-BF , and Cz-BNp-S-BF ) with different aryl substituents moieties were designed and synthesized. The mechanofluorochromic behaviours of Cz-S-BF (luminescence from bluish-green to yellowish-green, emission from 504 to 535 nm) without aryl substitution and Cz-PhNp-S-BF (luminescence from green and yellow, emission from 521 to 557 nm) with a phenyl-naphthalene group underwent reversible conversion using the grinding-fuming process. For Cz-BNp-S-BF this was not apparent due to the well coplanarity of the binaphthalene moiety. Mechanofluorochromic properties were demonstrated through XRD patterns measurement. We envisage that this study will provide a practicable reference to acquire organic molecules with mechanofluorochromic characteristics.