Selective and sensitive fluorescence detection of Cr(III) or chromate by a simple derivative of a well-known dibenzodiaza-crown

A sensitive and selective fluorescence (FL) dual chemosensor (L) for the detection of CrO₄²⁻ or Cr(III) in the presence of background anions, and cations in ethanol: water (8:2, v/v) was synthesized, based on the appending a dibenzodiaza-crown ether macrocycle with two benzimidazole side arms and characterized by FT-IR, ¹H NMR, and ¹³C NMR, UV–visible, FL spectroscopy, X-ray, and elemental microanalyses. The FL emission band for L exhibited enhancement and quenching in the presence of Cr(III) and Cr(VI) (chromate anion) in ethanol: water (8:2, v/v) mixture, respectively, representing a unique property for the determination of these chromium species. In a series of anion competitive experiments, the FL chemosensing behavior of L toward different sodium salts of various anions was also examined, wherein L demonstrates a prompt and selective quenching for chromate anion. LOD values for the chromate anion and Cr(III) were calculated as 180 nM and 1.04 µM, respectively which denoted better LOD of L compared to some other chemosensors with complicated structures such as organometallic frameworks, coordination polymers, and metal clusters. By exploiting ¹H NMR titration, molecular electrostatic potential (MEP) map together with information obtained from UV–visible, and FL spectroscopy indicated the interaction of dichromate anion with the N–H of the benzimidazole moiety, however, the interaction of L with Cr(III) was shown through the N-donor groups of both the benzimidazole side arms and the macrocycle ring.