A highly selective chromogenic sensor for Mn 2+ , turn-off fluorometric for Hg 2+ 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.