| Summary: | Developing a fluorescent probe for UO<sub>2</sub><sup>2+</sup>, which is resistant to interference from other ions such as Cu<sup>2+</sup> and can be applied in acidic and high-water systems, has been a major challenge. In this study, a “turn-off” fluorescent probe for triamine-modified flavonoid derivatives, 2-triphenylamine-3-hydroxy-4H-chromen-4-one (abbreviated to HTPAF), was synthesized. In the solvent system of dimethyl sulfoxide:H<sub>2</sub>O (abbreviated to DMSO:H<sub>2</sub>O) (<i>v</i>/<i>v</i> = 5:95 pH = 4.5), the HTPAF solution was excited with 364 nm light and showed a strong fluorescence emission peak at 474 nm with a Stokes shift of 110 nm. After the addition of UO<sub>2</sub><sup>2+</sup>, the fluorescence at 474 nm was quenched. More importantly, there was no interference in the presence of metal ions (Pb<sup>2+</sup>, Cd<sup>2+</sup>, Cr<sup>3+</sup>, Fe<sup>3+</sup>, Co<sup>2+</sup>, Th<sup>4+</sup>, La<sup>3+</sup>, etc.), especially Cu<sup>2+</sup> and Al<sup>3+</sup>. It is worth noting that the theoretical model for the binding of UO<sub>2</sub><sup>2+</sup> to HTPAF was derived by more detailed density functional theory (DFT) calculations in this study, while the coordination mode was further verified using HRMS, FT-IR and <sup>1</sup>HNMR, demonstrating a coordination ratio of 1:2. In addition, the corresponding photo-induced electron transfer (PET) fluorescence quenching mechanism was also proposed.
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