4-Phenyl-2-(2′-pyridyl) quinoline acts as a highly sensitive fluorescent probe for Fe2+ and Fe3+ ions and exhibits reversible photoelectric stimulation response

Abstract

4-Phenyl-2-(2′-pyridyl) quinoline (L1) was synthesized by a three-component reaction of aniline, phenylacetylene and pyridine-2-aldehyde catalyzed by trifluoromethanesulfonic acid (TfOH). Its structure was confirmed by FT-IR, MS, NMR and X-ray single crystal diffraction analysis. L1 was investigated as a probe for the detection of Fe3+ and Fe2+ ions, which displayed fluorescence enhancement by Fe3+ and fluorescence quenching by Fe2+. This unique fluorescence switching property of L1 was used to identify Fe2+ and Fe3+ with high selectivity and sensitivity. The detection limit of Fe2+ was 8.772 × 10−9 mol/L and that of Fe3+ was 1.912 × 10−9 mol/L. Mechanism investigation revealed that the fluorescence quenching of probe L1 was caused by ferrous-induced PET process and the fluorescence enhancement was due to the combinational effect of ferric-induced PCT enhancement and PET inhibition. In addition, the cyclic voltammetry curves demonstrated that both the Fe2+ complexes and the Fe3+ complexes displayed reversible redox process, indicating that the Fe2+ and Fe3+ complexes can be reversibly converted into each other upon electrical stimulation. The reversible “On” and “Off” of the fluorescence emission of iron complexes upon electrochemical stimulation could potentially be used in information recording and erasing.