This study evaluated three isoniazid-based N-acylhydrazone derivatives (HL1, HL2, and HL3) varying their substituting groups (-H, -N(CH3)2, and -NO2) as potential chemosensors for Zn2+ ions. To this end, the absorption and emission properties of these derivatives were investigated in the presence of Zn2+ ions. Results point to the derivative HL2 as the best chemosensor for Zn2+ ions because of its comparatively higher sensitivity. The color of this derivative changed from colorless to strong yellow with zinc addition, as indicated by the shift in UV-vis spectrum. Moreover, HL2 was the only derivative to emit fluorescence in the presence of Zn2+ ions, attributable to PET inhibition and bond isomerization promoted by coordination with this metal. LOD, LOQ, and binding constant values for HL2 + Zn2+ were 0.43 μmol.l-1, 0.93 μmol.l-1, and 5.04 × 1012 l.mol-1, respectively. The fluorescence of HL2 with other metal ions (Fe3+, Mg2+, Na+, Cd2+, Cu2+, Co2+, Ni2+, Ca2+, and K+) was also investigated. Zn2+ yielded the best result without Cd2+ interferences. Job's Plot showed that the stoichiometric ratio of the complex formed by HL2 and Zn2+ ions is 2:1 (ligand:metal). The strip test with adsorbed HL2 indicated fluorescence in the presence of zinc ions under 365 nm UV irradiation.
Keywords: Chemosensor; Fluorescence; Isoniazid; N-acylhydrazone; Zinc(II).