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

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.