Controllable and reversible proton transfer for inorganic cyanide visual sensing based on the deprotonation of azo-phenolic hydroxyl group

Methods for optical detection of inorganic cyanide based on the single molecule sensor with high selectivity and sensitivity have attracted increasing interest recently due to the high toxicity of cyanide ions. In this work, a visual sensor (S1) containing both imidazole NH and azo-phenolic OH was synthesised and characterised. The spectral experimental data indicated that protic aqueous solution facilitated enhancing the selectivity of cyanide ions with the nanomolar-level detection limit in semi-aqueous solution. The visual sensing mechanism arising from the deprotonation of azo-phenolic OH and the enhancement of intramolecular charge transfer could be clearly demonstrated by titration experiments of ¹H NMR, HR MS and energy changes between the HOMO−LUMO band gaps. Furthermore, the reversibility and reusability of S1 upon alternating addition of CN⁻ and H⁺ were studied.

A visual sensor incorporated by imidazole NH and azo-phenolic OH was developed to detect inorganic CN⁻ via reversible proton transfer based on the deprotonation/protonation of azo-phenolic OH/O⁻ in aqueous solution.