A pyrenesulfonyl-imidazolium derivative as a selective cyanide ion sensor in aqueous media

In this work, N -imidazolylpropyl pyrenesulfonamide 1 and its diimidazolium salt 2 were synthesized to be tested as cyanide (CN − ) sensors. The probes were found to be selective and sensitive toward CN − in a PBS–EtOH solution. The sensing ability of the probes was examined by UV-Vis, fluorescence, and NMR spectroscopy. CN − sensing was characterized by the quenching of both the monomer and excimer emissions of probe 2 , owing to the unlocking of the π–π interaction; in the case of probe 1 , a small degree of quenching of the monomer emission intensity was observed. The selective sensing of CN − was associated with a color change and complete quenching of green fluorescence emission under 365 nm illumination. The degree of quenching of the emission intensity was driven by the presence of a positive charge, the number of positive charges (which lead to ionic interactions with anions), and hydrogen bonding. Probe 2 exhibited a large association constant with CN − ( K a = 2.32 × 10 5 M −1 ), with a 1 : 2 stoichiometry in a PBS–EtOH solution. The lowest detection limit for the estimation of CN − was determined to be 0.5 μM (13 ppb), which is lower than the permissible limit for drinking water established by the WHO.