AIEE-driven highly sensitive fluorescent probe for Fe3+ sensing in aqueous and solid phases: application in interference-free biological media†

Herein, a novel fluorescein-based fluorescent probe FHP was systematically designed and synthesised, which exhibited aggregation-induced emission enhancement (AIEE) properties. FHP showed the maximum emission response at a wavelength (λ_max) of 516 nm. Using probe FHP, convenient and cost-effective sensing of Fe³⁺ in solution and solid states was accomplished with notable sensitivity and selectivity. Quenching of the FHP fluorescence intensity was observed owing to the chelation between the electron-rich probe and electron-deficient Fe³⁺, with a detection limit of 253 nM. The FHP–Fe³⁺ interaction was studied using UV-visible and fluorescence spectroscopies, dynamic light scattering (DLS), ¹H-NMR titration and density functional theory (DFT) calculations. Theoretical analysis was carried out using DFT to justify the non-covalent type of interaction in the FHP–Fe³⁺ complex and to study the electronic properties of probe FHP and FHP–Fe³⁺ complex. The practical application of the FHP probe in Fe³⁺ sensing was evaluated using biological samples.