Rational design of aza-BODIPY derived near-infrared fluorescent probe for CN− in aqueous solutions

The lethal toxicity of cyanide ions has inspired the development of fluorescent probes for their recognition, but fluorescent probes that can selectively bind cyanide ions in aqueous solution have been a challenge. In this paper, the electron-donor/withdrawing groups were introduced to aza-BODIPY fluorophore to discover the optical properties and tune the addition reaction with CN−. The push-pull electron effect of the corresponding substituents in aza-BODIPY makes the spectral shifts, molar extinction coefficients and fluorescence quantum yields remarkably different. The introduction of the electron-withdrawing group (–CF3) to aza-BODIPY (CF3-BDP) resulted in the electron-deficient property of the CN double bond, and the ability of nucleophilic addition of CN− to CF3-BDP was enhanced in aqueous solutions. Due to the collapse of the conjugated structure after the addition, the fluorescence of CF3-BDP was rapidly quenched to realize the highly sensitive response to CN−. According to DFT calculation, the reaction site of controversial mechanism was verified to the CN band in the pyrrole of aza-BODIPY. Furthermore, CF3-BDP was proved to have the ability to detect cyanide in biological system.