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 − , CO 3 2− , and CN − among F − , Cl − , Br − , I − , OH − , CO 3 2− , NO 3 − , PO 4 3− , CN − , SO 4 2− , HSO 4 − , HCO 3 − , SCN − , NO 2 − , and P 2 O 7 2− ions. Two new absorption bands at 385 and 685 nm accompanying the distinct color change for OH − , CO 3 2− , and CN − ions were observed in case of all compounds. The color changes were from pink to blue for CO 3 2− 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.