A diquinone–imidazole ensemble for selective colorimetric sensing of cyanide in aqueous medium via anion induced NIR absorption

Abstract

A diquinone–imidazole ensemble (R) is rationally designed, synthesized and employed as a selective and sensitive colorimetric sensor for cyanide ions in DMSO : H₂O (1 : 4 v/v). ¹H NMR titration indicates that the mechanism of sensing involves the formation of a H-bond between CN⁻ and imidazole N–H. As rationalized, the R–CN⁻ complex exhibited intense NIR-absorption (913 nm; log ε 4.3) with a 428 nm red-shift from the absorbance maximum of free R. DFT calculations indicate that the R–CN⁻ complex is perfectly planar with a HOMO–LUMO energy gap of 0.9826 eV which is optimal for NIR-absorption.