A large-Stokes-shift fluorescence sensor for sensitive detection of iron ions: Rapid monitoring of Fe3+ in water samples, hydroponic fertilizers, and living cells via fluorescence visualization

Iron ions (Fe2+ and Fe3+) are physiologically essential for humans; however, an imbalance in intracellular iron ion levels can cause adverse health effects. Therefore, developing a method for monitoring iron ions in biological and environmental systems is necessary. In this study, a new fluorescence sensor derived from [5]helicene linked to 2‐methylene pyridine (M201P) was successfully synthesized. The sensor could detect iron ions with high sensitivity via fluorescence quenching with a large Stokes shift (175 nm). The total iron ion content in samples was determined via the simple oxidation of Fe2+ to Fe3+ using H2O2. The Fe3+‐sensing performance of the sensor efficiently tolerated interference from other metal ions, and the detection limit was found to be 0.51 μM (0.028 ppm). The sensor formed a complex with Fe3+ with a stoichiometric ratio of 2:1, as measured using a Job's plot. Its binding mode was further investigated via 1H NMR titration and molecular modeling. In addition, using ultraviolet irradiation, M201P was used to visualize and monitor Fe3+ in water samples, hydroponic fertilizers, and living cells.