A ‘off-on’ benzimidazole-based fluorescent probe ((E)-2-((4-(5-chloro-1H-benzo[d]imidazole-2-yl)benzylidene)amino)phenol) probe CBAP for the detection of Fe3+/2+ (probe CBAP) was developed. It didn't exhibit fluoresce at 450 nm in EtOH: H2O (v:v = 9:1), which was mainly attributed to the isomerization and rotation of the CN bond. The dihedral angle rotation hindered the charge transfer between benzimidazole and o-aminophenol. However, the CN in probe CBAP was cleaved to form compound 3 upon adding Fe3+/2+. Its electrons were transferred from the benzimidazole ring to the benzaldehyde portion upon excitation and showed blue-green fluorescence. Probe CBAP had high selectivity and sensitivity, with a detection limit as low as 1.12 nM, and didn't interfere with other analytes. In addition, the optimized structure and orbital energy levels of probe CBAP and compound 3 were calculated using time-varying density functional theory (TD-DFT) and PBE0 function. Moreover, the application of probe CBAP on mobile phones for rapid detection of Fe3+/2+ content in wine and confirmation of whether it exceeded the standard was explored.