Effect of bridge units on the photophysical properties of tetraphenylethene-benzothiazole hybrid AIEgens with high-contrast mechanofluorochromic behaviour

Abstract

Tetraphenylethene-benzothiazole hybrid AIEgens (TP and TPM) with different bridge units (carbonyl and dicyanoethylene) are designed and synthesized to systematically investigate the effect of bridge units on their fluorescence properties. These molecules are demonstrated to have non-planar twisted structures and exhibit aggregation-induced emission (AIE) characteristics. Upon grinding, the pristine forms of TP and TPM show red-shifts of 24 nm and 74 nm, respectively, in their fluorescence spectra, revealing MFC characteristics. PXRD, SEM, crystal structure and DFT calculation studies provided further insights into the MFC behavior. The MFC behavior of TPM exhibits a large red-shift and obvious color change compared with TP (as the bridge unit changed from carbonyl to dicyanoethylene), indicating a better ICT and strong π stacking in the former. This work implies that the introduction of different bridge units to specific molecular structures might be useful as a feasible strategy for designing high-contrast MFC-active materials.