<p>Leveraging an ICT-controlled turn-on mechanism, we developed a near-infrared fluorescent probe (<i>E</i>)-2-bromo-4-(2-(4-(dicyanomethylene)-<i>4H</i>-chromen-2-yl)vinyl)-<i>N</i>,<i>N</i>-dimethylaniline oxide, hereinafter denoted as DCMB, built on a propanedinitrile-benzopyran scaffold for the specific detection of ferrous ions (Fe²⁺). The probe exhibits a remarkable fluorescence enhancement upon exposure to Fe²⁺, achieving a detection limit of 5.6 µM and a rapid response within 90 s. Strategic incorporation of bromine substituents extends the operational pH window to 5.0–7.5, outperforming most conventional indicators and ensuring robust performance in both physiological milieus and acidic tumor microenvironments. In addition, DCMB displays exceptional selectivity for Fe²⁺ over abundant biological metal ions (Ca²⁺, Mg²⁺, etc.) and potential interfering substances in biological systems, showing no significant effect. It is well-suited for detecting Fe²⁺ in complex biological matrices and has been successfully&#xa0;applied for imaging in living cells and zebrafish employed for in vivo.</p> Graphical Abstract <p></p>