Mechano-responsive fluorescent AIE enantiomers with high contrast properties

Abstract

A pair of novel chiral AIE enantiomers (S-ETMPB and R-ETMPB) with entirely opposite mechanoluminescence activities were demonstrated here. R-ETMPB displayed reversible turn-on mechanofluorochromism with a significant increase in quantum yield (QY), whereas S-ETMPB exhibited reversible turn-off mechanofluorochromism. Notably, the processes of grinding-fumigation and heating can be repeated over multiple cycles, demonstrating good reversibility without signs of fatigue. The reversible physical transformation between the crystalline and amorphous phases has been shown to account for the distinct mechanofluorochromic behaviors. Furthermore, both enantiomers possess the characteristic property of aggregation-induced emission. As the water content increases, the fluorescence quantum yields of S-ETMPB and R-ETMPB can significantly rise from 0.56 % to 0.86 % to maximum values of 18.89 % and 23.61 %, resulting in AIE factors of approximately 33.7 for S-ETMPB and 27.5 for R-ETMPB, respectively.