Mercuric ion-induced signaling by a dual turn-off/on switching of a quinoline-based fluorescent sensor

Abstract

Abstract Quinoline-based fluoroprobe, 3-isocyanatopropyl triethoxysilane grafted 3-aminoquinoline (AqI) has been designed and synthesized for detection of Hg2+ in aqueous solution. Fluorescent molecule, AqI was characterized by FTIR and NMR spectroscopy, and photophysical properties in solvents with different polarities were elucidated by UV–vis and fluorescence measurements. Quantum yield of AqI was calculated ( Φ F = 0.15 ) and acid dissociation constant ( p K a = 4.14 ± 0.15 ) was determined using data of integrated emission intensity versus pH. AqI shows emission quenching followed by fluorescence turn-on upon coordination-mediated complexation of Hg2+ ions. The fluorescence turn-on emission distinguishes Hg2+ ion from interfering metal ions and AqI is found to be selective for Hg2+ ion in buffered aqueous-ethanol solution (4:1, v/v) at pH 6.0. Equilibrium constant for the formation of complex between AqI and Hg2+ ions was calculated as K = 3.08 × 10 6 M − 2 / 3 applying by spectrofluorometric titration and stoichiometry of complex was determined as A q I 2 H g 3 2 + (2:3).