An experimental and computational study on naphthylideneimine based pH sensitive fluorescence probe for zinc

Rational design chelating fluorescent sensors probing metal ions in biological system are continuously hot essays nowadays, especially for zinc detection. Herein, a naphthylideneimine based zinc fluorescence probe ( 3 ) was prepared and characterized in this work. Structural features and optical properties of 3 and its metallic complexes were characterized. Fluorescent experiment indicates 3 is extremely sensitive and selective for Zn 2+ with a strong fluorescence enhancement (∼34 folds) in aqueous buffer solution with a limit of detection (LOD) of 3.78 × 10 −7  mol L −1 . Formation constant (log K a ) of the chelating complex of 3 and Zn 2+ ion was determined to be 4.45. Theoretical studies were carried out to get deep insight into the response mechanism in the sensing process. Density functional theory (DFT) methods calculated formation Gibbs free energy (Δ r G m ө ) of the deprotonated complexes model ( 3 2−   ⊃   Zn ) is −2.9 kcal/mol, which is in good agreement with the experimental result. The calculation results show that the low excitation states can be ascribe to S0 → T2 and S0 → S1 at 390–430 nm and 310–330 nm, respectively, due to the π → π∗ transition. Finally, yeast cell imaging experiments indicate that 3 can monitor intracellular Zn 2+ as well. These findings would enable this fluorescent probe to be used as a Zinc sensor.