Piezochromism, acidochromism, solvent-induced emission changes and cell imaging of D-π-A 1,4-dihydropyridine derivatives with aggregation-induced emission properties

Three D-π-A 1,4-dihydropyridine derivatives with aggregation-induced emission characteristics were synthesized. The molecules comprise of a 4-(dimethylamino)styryl group as the electron donor group and different end groups, dicyanomethylene, vinylcyanoacetate, and 2-methylene-1H-indene-1,3(2H)-dione, as the electron acceptor, respectively. These target compounds display different stimulus-responsive fluorescent properties in the solid state. The original samples with the dicyanomethylene and vinylcyanoacetate groups do not show fluorescence color changes in response to external force stimuli, whereas the compound containing the 2-methylene-1H-indene-1,3(2H)-dione unit exhibits reversible piezochromism and solvent-induced emission changes due to the transformation between the crystalline and amorphous states, which can be ascribed to their different molecular stacking mode in the solid state. Furthermore, these compounds show different acid/base-induced solid-state fluorescence switching properties due to the different sites of the protonation. Additionally, all of the derivatives can be fabricated into biocompatible fluorescent nanoparticles and used for MCF-7 cell imaging.