A benzimidazole-based ‘turn-on’ fluorescent probe for highly sensitive detection of Fe3+/2+: synthesis, performance, DFT calculations and applications

Abstract

A turn-on fluorescent probe (E)-2-((4-(5-fluoro-1H-benzo[d]imidazol-2-yl)benzylidene)amino)phenol (probe FBBAP) for the detection of total iron was developed. The probe alone exhibited no fluorescence but rapidly emitted blue fluorescence in EtOH with increasing Fe^3+/2+ concentrations. It had better selectivity for Fe^3+/2+ than other ions on strips and displayed high sensitivity with a limit of 0.25 nM and the reaction achieved equilibrium within 1 min. It is the first reaction-type probe capable of detecting total iron content, with the fastest reaction time to date. The optimised structure and orbital energies of the probe FBBAP and its products were calculated by comparing three functional combinations with time-dependent density functional theory (TD-DFT) and the optimal functional and basis set [cam-b3lyp/6-311+g(d,p)]. The significant changes in the dihedral angle stemmed from the isomerisation and rotation of the CN bond. The probe FBBAP was successfully applied to monitor Fe^3+/2+ in wine using intelligent software and the rapid detection of Fe^3+/2+ using strips was also conducted.