Two novel aggregation-induced emission active coumarin-based Schiff bases and their applications in cell imaging

Two new coumarin-based Schiff bases, 8,8′-((1 E ,1′ E )-hydrazine-1,2-diylidenebis(methanylylidene))bis(7-hydroxy-4-methyl-2 H -chromen-2-one), (CHC), and 7-hydroxy-8-(( E )-(( E )-((2-hydroxynaphthalen-1-yl)methylene)hydrazono)methyl)-4-methyl-2 H -chromen-2-one, (CHN), with excited-state intramolecular proton-transfer (ESIPT) properties, were synthesized and characterized. Both of the compounds displayed aggregation-induced emission (AIE) characteristics, of which CHC nanoparticles emitted a reddish orange fluorescence, while the CHN nanoparticles exhibited a saffron yellow fluorescence. The appearance of emission peaks in the long wave regions with large Stokes-shifts demonstrated the occurrence of the ESIPT process. Observations of the nanoparticles' morphologies were undertaken through a transmission electron microscope (TEM) method. Furthermore, due to the good biocompatibilities, high stabilities and the large Stokes-shifts, the two compounds were ideal candidates for cell staining.