A Novel Boranil-Based Colorimetric and Fluorescence Quenching Probe for Selective Detection and Bioimaging of the Fe3+ ion

Abstract A novel, readily synthesizable boranil-based chemosensor, HSR, was structurally and spectroscopically characterized by single-crystal X-ray diffraction, IR spectroscopy, 1H, 13C, and 11B NMR spectroscopy, and high-resolution mass spectrometry (HRMS). HSR exhibited highly selective colorimetric and fluorescence responses toward the Fe3+ ion over a wide range of competing metal ions, including Na+, K+, Ba2+, Ca2+, Mg2+, Al3+, Zn2+, Ni2+, Cu2+, Co3+, Pb2+, Cd2+, Hg2+, and Fe2+. Upon Fe3+ addition, the solution color changes from pale yellow to red-brown, accompanied by pronounced quenching of fluorescence signals. Concentration-dependent Fe3+ ion titrations revealed significant modulation of the photoluminescence and UV–vis absorption profiles. The binding stoichiometry and association constant between HSR and the Fe3+ ion were determined by UV–vis and fluorescence titrations, Job’s plot analysis, and HRMS, confirming strong complex formation. Notably, no interference from biologically relevant or toxic metal ions was observed. The limit of detection (LOD), calculated using the 3σ method, was 7.5 × 10–6 M. The association constant (Ka), obtained from a Benesi–Hildebrand analysis, was 2.35 × 1015 M–1, indicating exceptionally strong Fe3+ ion binding. Furthermore, HSR displayed good solubility in mixed EtOH/H2O media and efficient cellular uptake with no cytotoxicity, highlighting its suitability for the detection of the Fe3+ ion and bioimaging applications.