A Glycoluril‐Derived Fluorescent Molecular Clip for Highly Selective and Sensitive Detection of Fe ³⁺

Abstract The highly selective detection of Fe 3+ holds significant importance in environmental monitoring and biomedical applications. In this study, a novel “on–off” fluorescent molecular clip based on a glycoluril scaffold functionalized with 4‐(aminomethyl)benzoic acid groups (termed clip 1 ) was designed and synthesized via a straightforward two‐step procedure. Structural characterization was performed via single‐crystal X‐ray diffraction (XRD), whereas its optical properties were analyzed using ultraviolet–visible (UV–vis) absorption and fluorescence spectroscopy. Clip 1 exhibited strong fluorescence emission at 333 nm, which was specifically quenched upon Fe 3+ coordination, achieving a low detection limit of 0.52 µM (significantly below the WHO guideline of 5.36 µM for drinking water). Remarkably, it demonstrated exceptional selectivity and anti‐interference capability among 18 competing metal ions. Stern–Volmer analysis confirmed a 1:1 binding stoichiometry. Practical application in real water samples showed excellent recoveries (97.20%–101.9%) and reproducibility (RSD < 3.5%). Owing to its simple synthesis, high yield, excellent aqueous solubility, and superior sensitivity, this probe presents a promising tool for efficient Fe 3+ monitoring in aqueous environments.