A new azo–azomethine chemosensor, 2-((E)-(2-(1H-indol-3-yl)ethylimino)methyl)-4-((E)-(2- nitrophenyl)diazenyl)phenol, L, was synthesized and characterized by Infrared spectroscopy (IR), Ultraviolet–visible spectroscopy (UV-Visible) and Nuclear magnetic resonance spectroscopy (NMR) methods. The sensory properties of this Schiff base compound (L) were investigated in Dimethyl sulfoxide (DMSO)/H2O (9.5:0.5 v/v) solution. It was selectively sensitive to CN¯ and HCO3¯ and AcO¯ anions, and in the presence of them, the color of solution L through deprotonating mechanism changed from yellow to orange. This chemosensor also sensitive to Fe2+. Then, by using Job’s method and Benesi–Hildebrand equation, the binding stoichiometry of L with anions and binding constant (ka) were determined (CN−: 1:1, 3.47×10+5; HCO3−: 1:1, 2.44×10+5; AcO−: 1:1, 1.76×10+5), respectively. Also, the Limit of Detection (LOD) was calculated. Finally, the observed experimental results were confirmed by Density Functional Theory (DFT) calculations. ©
