Triphenylamine-based 1,3,4-thiadiazole derivative: Solvatochromism, aggregation-induced emission and reversible turn-on mechanofluorochromism

In this work, a new versatile AIE-active triphenylamine-based donor-acceptor fluorophore DPTA (N,N-diphenyl4-(5-phenyl-1,3,4-thiadiazol-2-yl)aniline) has been synthesized, whose photophysical properties in different solvents, aggregates emission behaviors and solid states were investigated systematically. It was found that DPTA exhibited well-defined ICT (intramolecular charge transfer) characteristics with remarkable positive solvatochromism. More importantly, DPTA exhibited reversible high-contrast turn-on mechanofluorochromism response to mechanical force with obviously increase of QY (the solid fluorescence quantum yield) from 6.4 % (pristine) to 31.8 % (being grinded), and the emitting wavelengths of DPTA were red-shifted from 469 nm to 496 nm upon grinding. The interesting mechanofluorochromic behaviors were rationalized to be caused by the reversible phase transition between ordered crystalline and amorphous states, which was proved by the measurement results of PXRD, DSC and FESEM. Single crystal X-ray diffraction analysis indicated the presence of twisted conformations and weak intermolecular hydrogen bonds, which are also responsible for the mechanofluorochromic behavior.