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

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 Fe 3+ and Fe 2+ ions, which displayed fluorescence enhancement by Fe 3+ and fluorescence quenching by Fe 2+ . This unique fluorescence switching property of L1 was used to identify Fe 2+ and Fe 3+ with high selectivity and sensitivity. The detection limit of Fe 2+ was 8.772 × 10 −9 mol/L and that of Fe 3+ 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 Fe 2+ complexes and the Fe 3+ complexes displayed reversible redox process, indicating that the Fe 2+ and Fe 3+ 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.