Dual anion colorimetric and fluorometric sensing of arsenite and cyanide ions involving MLCT and CHEF pathways

Abstract

A newly designed quinoline acrylonitrile probe L was synthesized by reacting 6-methyl-2-oxo-1,2-dihydroquinoline-3-carbaldehyde with benzothiazole-2-acetonitrile and structurally characterized by various spectroscopic techniques. The sensing ability of probe L was studied with various anions by using visual, RGB tool, UV Visible, and spectrofluorometric methods. It shows a selective colorimetric response with AsO2− and turn-on emission fluorescent with CN− over other tested anions. The probe L exhibits a 1:1 complex formation with AsO2−and CN-. The probe L can work in the pH range of 2–10 and 3–8 with AsO2−and CN−respectively without interfering with other competing ions. The binding mechanism of L with AsO2− and CN− was characterized by using 1H NMR, ESI mass, and DFT analysis. It reveals that AsO2− and CN− ions are binding with L through metal-to-ligand charge transfer (MLCT) and chelation enhanced fluorescence (CHEF) respectively. The lowest detection limit (LOD) of AsO2− by using spectrophotometry and RGB color tool were found to be 24 ppb and 498 ppb respectively while CN− detection by spectrofluorimetry detected down to 1 ppb. Overall, probe L demonstrates a promising and potential for the detection of two toxic contaminates in the semi-aqueous phase.