A fluorescent pH switch probe for the 'turn-on' dual-channel discriminative detection of magnesium and zinc ions

A coumarin-based fluorescent probe, HL((E)-8-((benzo[d]thiazol-2-ylimino)methyl)-7-hydroxy-4-methyl-2H-chromen-2-one), is presented for the dual-channel "Turn-on " detection of Mg2+ (at 483 nm) and Zn2+ (at 560 nm) ions at two different wavelengths with large Stokes shifts. HL exhibits impressive detection limits and binding constants with both Mg2+ and Zn2+ ions. HL detected these ions by the inhibition of -C=N bond rotation and suppression of photoinduced electron transfer (PET) and excited state intramolecular proton transfer (ESIPT) while promoting chelation enhanced fluorescence (CHEF). For the detection of Mg2+ and Zn2+ ions, reversibility was achieved by using ATP. HL is not only sensitive and selective for the detection of Mg2+ and Zn2+ ions but also showed considerable reversible "Turn-on-Turn-off " fluorescent pH switch behavior. The DFT studies assisted in understanding the binding of Mg2+ and Zn2+ ions by the probe. HL was utilized to detect Mg2+ and Zn2+ ions in the human breast cancer cell line by fluorescence cell imaging studies while several low-cost detection methods were also illustrated.