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