Pyrene Based Schiff Base for Cascade Fluorescent “On‐Off” Detection of Aluminium(III) and Fluoride Ions and its Applications in Live Cells Imaging

An easy-to-prepare pyrene-based Schiff base PNZ was synthesized by condensing equimolar amount of 1-pyrenebutyric hydrazide with 2-hydroxy-naphthaldehyde, and employed as a fluorescent chemosensor for in-situ cascade detection of aluminium (Al³⁺) and fluoride (F^-) ions. In DMSO:H₂O (1 : 1, v/v), the weakly emissive PNZ showed a significant fluorescence enhancement at 455 nm selectively upon the addition of Al³⁺ due to the complexation-induced formation of a pyrene excimer. Schiff base PNZ and Al³⁺ formed a complex in 2 : 1 binding ratio with the estimated binding constants of K_1:1=9826.01 M^-1 and K_2:1=3188.49 M^-1. The sensing mechanism was explored by performing quantum mechanical calculations and ¹H-NMR titration of PNZ with Al³⁺. The in-situ formed PNZ-Al³⁺ complex species enabled the fluorescent turn-off detection of F^-. Using PNZ and PNZ-Al³⁺, the concentrations of Al³⁺ and F^- ions can be detected down to 2.89×10^-7 M and 1.88×10^-7 M, respectively. The cytotoxicity of the PNZ and its ability to bioimage Al³⁺ and F^- ions was examined in the human cervical cancer cell line. Finally, the receptor PNZ was applied for the quantification of Al³⁺ and F^- ions in various real samples, such as tap water, river water, rainwater, mouthwash, and toothpaste.