Naked Eye Detection of Carbonate, Hydroxide, and Cyanide Ions with 1,4′‐Diazaflavonium Bromides: A Simple Spectrophotometric Method for Cyanide Determination

Anion sensor properties of N‐alkyl‐substituted 1,4′‐diazaflavonium bromides in methanol–water were evaluated by UV–vis spectrometry. Pronounced changes were observed in the absorption spectra of all compounds for only OH−, CO32−, and CN− among F−, Cl−, Br−, I−, OH−, CO32−, NO3−, PO43−, CN−, SO42−, HSO4−, HCO3−, SCN−, NO2−, and P2O72− ions. Two new absorption bands at 385 and 685 nm accompanying the distinct color change for OH−, CO32−, and CN− ions were observed in case of all compounds. The color changes were from pink to blue for CO32− and OH− ions and from pink to purple for CN− ion. Thanks to the distinct color change, the compounds can be used as selective colorimetric anion sensors. Linear changes of absorbance of N‐heptyl‐substituted compound at 385 nm as a function of the ion concentration were used to determine CN− ion in water samples. Detection and quantification limits of the proposed method were 0.94 and 2.82 mg/L, respectively.