A ratiometric chemosensor for fluorescent determination of Hg2+ based on a new porphyrin-quinoline dyad

Quinolin-8-ol p-[10′,15′,20′-triphenyl-5′-porphyrinyl]benzoate (1) was synthesized for the first time and developed as a ratiometric fluorescent chemosensor for recognition of Hg2+ ions in aqueous ethanol with high selectivity. The 1–Hg2+ complexation quenches the fluorescence of porphyrin at 646 nm and induces a new fluorescent enhancement at 603 nm. The fluorescent response of 1 towards Hg2+ seems to be caused by the binding of Hg2+ ion with the quinoline moiety, which was confirmed by the absorption spectra and 1H NMR spectrum. The fluorescence response fits a Hill coefficient of 1 (1.0308), indicating the formation of a 1:1 stoichiometry for the 1–Hg2+ complex. The analytical performance characteristics of the chemosensor were investigated. The sensor shows a linear response toward Hg2+ in the concentration range of 3 × 10−7 to 2 × 10−5 M with a limit of detection of 2.2 × 10−8 M. Chemosensor 1 shows excellent selectivity to Hg2+ over transition metal cations except Cu2+, which quenches the fluorescence of 1 to some extent when it exists at equal molar concentration. Moreover, the chemosensor are pH-independent in 5.0–9.0 and show excellent selectivity for Hg2+ over transition metal cations.