Synthesis of Fluorescent Probe with D-π-A Structure and its Application in Dual-channel Recognition of Fe³

In this paper, a D-π-A fluorescent probe, (E)-2-(5,5-dimethyl-3-(2-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)vinyl)cyclohex-2-en-1-ylidene)malononitrile (DFP) was synthesized via the condensation of dicyanoisophorone and 9-formyljulolidine. The structure was characterized by NMR and ESI-HR-MS, and the structure optimization and energy level analysis were carried out by density functional theory (DFT) calculation. Additionally, its metal ion recognition performance was assessed by UV-vis absorption spectroscopy and fluorescence spectroscopy. The results showed that the probe could specifically recognize Fe³⁺ in CH₃OH/H₂O (1:1, v/v, pH = 7.2) buffer system. Upon the addition of Fe³⁺, the probe solution changed from blue-purple to colorless, accompanied by a significant fluorescence quenching of over 90%, exhibiting high selectivity without obvious interference from other metal ions. Job's plot and ESI-MS titration experiments revealed a 1:1 stoichiometry for the complex between the probe and Fe³⁺, with a binding constant of 1.4 × 10⁴ M^-1. Furthermore, the probe exhibited a low detection limit of 0.33 µM for Fe³⁺, and the optimal pH range for the response was 5-9. In terms of practicality, the probe has been successfully used for visual detection of test paper and imaging of Fe³⁺ in living cells.