D-π-A type carbazole and triphenylamine derivatives with different π-conjugated units: Tunable aggregation-induced emission (AIE) and mechanofluorochromic properties

Abstract

Eight donor-π-acceptor (D-π-A) skeleton high brightness luminogens 1–8 with various π-conjugated units are designed, synthesized, and fully characterized. Among synthetic luminophores, 7 and 8 possess typical aggregation-induced emission properties, and these reported fluorophores display different fluorescence in the solid state. Meanwhile, their solid-state emission behaviors can be effectively regulated by mechanical grinding except for solids 5 and 7. More specifically, the solid-state fluorescence of D-π-A type compounds 1, 3, 4, and 6 can be reversibly switched by successive mechanical grinding and solvent fuming, while D-π-A type compounds 2 and 8 display irreversible mechanofluorochromism behaviors. Remarkably, when the pristine powders of these mechanical force-responsive fluorophores are ground, 1 and 2 exhibit an obvious blue-shift, while 3, 4, 6, and 8 show a red-shift. The powder X-ray diffraction measurements demonstrate that these observed diverse mechanoresponsive fluorescence phenomena are attributed to the different morphological interconersion between the crystalline and amorphous states.