D-π-A type dicyanoethylene derivatives modified by tetraphenylethylene exhibiting aggregation-induced emission and high-contrast mechanofluorochromism

Based on a rational design strategy by combining an electron-withdrawing dicyanoethylene unit and electron-donating tetraphenylethylene moiety, we successfully synthesized two π-conjugated molecules Ph-TPE-MMN and NA-TPE-MMN. According to the optical research and theoretical calculation results, they had highly distorted conformations, D-A type molecular structure and definite intramolecular charge transfer (ICT) properties. Moreover, two molecules Ph-TPE-MMN and NA-TPE-MMN showed aggregation-induced emission (AIE) properties in the THF/water mixture at higher fw (water fraction). Ph-TPE-MMN and NA-TPE-MMN also exhibited fluorescence response to external force. The emitting color of both had changed greatly before and after grinding. The maximum emission wavelengths of Ph-TPE-MMN and NA-TPE-MMN were redshifted by 46 nm and 33 nm, respectively, implying high-contrast mechanofluorochromism. Notably, mechanofluorochromic process also showed a good reversible. XRD experiments indicated that mechanofluorochromic mechanism originated from changes in molecular stacking in solid state.