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

Abstract

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 × 10⁵ 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.