'Turn-on' fluorescent chemosensors based on naphthaldehyde-2-pyridinehydrazone compounds for the detection of zinc ion in water at neutral pH

A series of naphthaldehyde-2-pyridinehydrazone derivatives were discovered to display interesting turn-on' fluorescence response to Zn2+ in 99% water/DMSO (v/v) at pH7.0. Mechanism study indicated that different substituent groups in the naphthaldehyde moiety exhibited significant influence on the detection of Zn2+. The electron rich group resulted in longer fluorescence wavelengths but smaller fluorescence enhancement for Zn2+. Among these compounds, 1 showed the highest fluorescence enhancement of 19-fold with the lowest detection limit of 0.17mol/L toward Zn2+. The corresponding linear range was at least from 0.6 to 6.0mol/L. Significantly, 1 showed an excellent selectivity toward Zn2+ over other metal ions including Cd2+.