Cyanostilben-based derivatives: mechanical stimuli-responsive luminophors with aggregation-induced emission enhancementElectronic supplementary information (ESI) available. See DOI: 10.1039/c2pp05404c

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. The cyanostilben-based derivatives ( CNS-4 ) nanoparticles prepared from the different solvent mixtures indicate the evident change of photophysical properties. Dyes CNS-3 and CNS-4 have mechanofluorochromism properties due to phase transition under the stimulus of external pressure.