Cyanide-Induced Decomplexation of Zn(II)-Dipyrrin Complexes Enables Selective Colorimetric Detection in Methanol

The cyanide ion (CN‐) is a highly toxic species that inhibits cellular respiration, and its release from natural and industrial sources poses significant environmental and health risks. This study investigates the colorimetric recognition of cyanide in liquid media using phenolic dipyrrin-metal complexes. Phenolic dipyrrin ligands were synthesized and coordinated with Zn(II) ions. Upon the addition of cyanide ions, dipyrrin complexes exhibited a pronounced color change from yellowish to red-magenta, readily visible to the naked eye and accompanied by characteristic shifts in their UV–Vis absorption spectra. In contrast, no significant spectral or visual changes were observed in the presence of competing anions, such as Cl‐ and F‐, demonstrating the selectivity for cyanide. The sensing behavior is attributed to cyanide-induced deprotonation of the phenolic moiety, followed by decomplexation of the metal center, leading to the formation of hemiquinone species in solution. These results highlight the cooperative roles of acid–base interactions and competitive coordination in governing cyanide recognition in liquid-phase systems, providing insights into the rational design of colorimetric sensors based on dipyrrin–metal complexes.