A Rhodamine B Based Fe3+-Selective Colorimetric and Fluorescent Probe

A novel rhodamine B-based derivative 1, functionalized with an Ethylenediamine-N-Ethanolamine moiety, was rationally designed and synthesized as an “off-on” fluorescent probe for Fe3+ detection. This probe demonstrated outstanding selectivity and high sensitivity toward Fe3+ over other competing metal ions in aqueous media, achieving a remarkably low detection limit of 0.33 μM. The sensing mechanism was attributed to a Fe3+-triggered, reversible ring-opening process of the Rhodamine Spirolactam Unit(RSL), which switched the fluorescence from a non-emissive state to a strongly emissive form. Based on Job’s plot analysis and spectroscopic titrations, a 1:1 binding stoichiometry between probe 1 and Fe3+ was established. Importantly, the practical utility of this probe was successfully validated through its application in the fluorescence imaging of Fe³⁺ in living cells, highlighting its potential for biological and environmental monitoring.