A ″On–Off″ Fluorescent Sensor Based on Coumarin-Furoic Hydrazide for Recognition of Fe3+: Drinking Water, Test Strip Applications and DFT Calculations

A coumarin based fluorescent probe (E)-N'-((7-hydroxy-2-oxo-2H-chromon-3-yl)methylene)furan-2-carbohydrazide (CFHZ) was synthesized for the detection of Fe³⁺ and its characterizations were carried out using spectroscopic methods such as FT-IR, mass spectrometry¹H-NMR, ¹³C-NMR. The novel probe CFHZ showed a highly selective and sensitive "turn-off" response to Fe³⁺ ion without any interference from other analytes. Strong fuorescence quenching phenomena of the CFHZ were observed in EtOH:H₂O (99/1, v/v) detection system (λ_em = 470 nm) upon the additions of Fe³⁺. The binding stoichiometry between CFHZ and Fe³⁺ was determined by Job's method, FT-IR and MALDI TOF-MS and found to be 2:1. Also, the binding constant was determined to be 1.82 × 10⁵ M^-1 and the limits of detection for the analysis of Fe³⁺ was measured as 25.7 nM. Besides, experimental applications were carried out for real-time monitoring of Fe³⁺ in water samples using developed sensor. Additionally, fluorescence imaging experiments for Fe³⁺ detection of CFHZ probe on test papers were successfully performed.