A highly selective chromogenic sensor for Mn2+, turn-off fluorometric for Hg2+ ion, and turn-on fluorogenic sensor for F- ion with the practical application.

A colorimetric and fluorometric probe (E)-2-((8-hydroxy-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)methylene)hydrazinecarbothioamide based on thiosemicarbazide and julolidine moieties has been synthesised in pure crystalline form and characterized by 1H NMR, UV-vis, elemental analysis and single crystal XRD. The probe functioned as multitarget ion sensor, detect biologically important metal ions Hg2+ and Mn2+ in dual channel mode. Meanwhile, in mixed solvent media DMF/H2O [8:2], probe displayed selectivity for Hg2+ over other cations by the emission spectrum. Interestingly probe has been explored to recognize F- anion in DMF through ESIPT mechanism. The 1:1 binding stoichiometry of probe with Hg2+ and Mn2+ is confirmed by Job's plot through emission titration and UV-vis titration respectively. Probe is selective and sensitive to Hg2+ and Mn2+ with detection limit as low as 15μM and 0.2μM respectively. The sensing mechanism for selective ions was also scrutinized using 1H NMR experiments and computational studies.