Cyanostilben-based derivatives: mechanical stimuli-responsive luminophors with aggregation-induced emission enhancement

Cyanostilbene derivatives with the aggregation-induced emission enhancement (AIEE) activity are prepared by Knoevenagel and Suzuki reactions. Among them, the dye (Z)-2,3-bis(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)acrylonitrile (CNS-4) nanoparticle suspension shows the polarity-dependent characteristics of the fluorescence properties. By the fluorescence spectroscopy and transmission electron microscopy (TEM) analysis, the restriction of transfer from the local excited (LE) state to the intramolecular charge-transfer (ICT) state and crystal formation results in a blue-shift in emission and enhances the intensity in the aggregate state. Additionally, the luminophors CNS-3 and CNS-4 possess the AIEE effect as well as mechanochromic fluorescent properties. This mechanofluorochromic behavior originates from the change between the crystalline and the amorphous state.