A Fluorescent Chemosensor for Dihydrogen Phosphate Ion Based on 2‐[2‐Hydroxy‐4‐(diethylamino) phenyl]‐1 H ‐imidazo[4,5‐ b ]phenazine‐Fe 3+ Ensemble

A long wavelength emission fluorescent (612 nm) chemosensor with high selectivity for H 2 PO 4 − ions was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). The sensor can exist in two tautomeric forms ('keto' and 'enol') in the presence of Fe 3+ ion, Fe 3+ may bind with the 'keto' form of the sensor. Furthermore, the in situ generated GY‐Fe 3+ ensemble could recover the quenched fluorescence upon the addition of H 2 PO 4 − anion resulting in an off‐on‐type sensing with a detection limit of micromolar range in the same medium, and other anions, including F − , Cl − , Br − , I − , AcO − , HSO 4 − , ClO 4 − and CN − had nearly no influence on the probing behavior. The test strips based on 2‐[2‐hydroxy‐4‐(diethylamino) phenyl]‐1 H ‐imidazo[4,5‐ b ]phenazine and Fe 3+ metal complex ( GY‐Fe 3+ ) were fabricated, which could act as convenient and efficient H 2 PO 4 − test kits.