A colorimetric and turn-on fluorescent sensor for rapid and selective detection of Fe3+ ion based on azo compound of 4-((4-(dimethylamino) phenyl)diazenyl)-N-(pyridin-2-yl)benzamide

•A new colorimetric and turn-on fluorescent sensor ligand based on azo was synthesized.•The optical sensing properties of the ligand toward different cations were studied.•It demonstrated a selective colorimetric sensing toward Fe3+ ion in acetonitrile. A new colorimetric and turn-on fluorescent sensor based on an azo compound of 4-((4-(dimethylamino) phenyl) diazenyl)-N-(pyridin-2-yl)benzamide dye (L) was designed, synthesized and investigated. The structure of L was characterized by FT-IR, 1HNMR, 13CNMR and elemental analysis. The binding structures and sensing mechanisms of L toward iron were investigated using the various spectroscopic studies and theoretical calculations. Sensor exhibited highly selective and sensitive detection toward Fe3+ in acetonitrile aqueous solution. Compared to other metal cations, in case of iron, the color change from yellow to red was visible by the naked eye and a selective enhancement of fluorescence as well. The Job's method confirmed the formation of complex between L and Fe3+ with 1:1 binding stoichiometry. Furthermore, the detection limit (1.3 nM) for Fe3+ was much lower than that recommended by EPA (Environmental Protection Agency) for drinking water (5.37 µM). The theoretical calculations confirmed the coordination between nitrogen atom of pyridine and the oxygen atom of the carbonyl (C=O) group of L with Fe3+.