Investigation of fluorescence properties of some onno type Schiff bases and their complexes with transition metals

In recent years, fluorescent chemosensors which is capable of selectively recognizing and effectively detecting cations have attracted significant interest because of their potential application in environmental and medicinal research. In this study, two simple Schiff base based on salicylaldehyde and 1,3 diaminopropane have been synthesized and evaluated for their fluorescent response towards metal ions. Chemosensor N-N'-bis(salicylidene)-1,3-diaminopropane (LH2) exhibited a highly selective fluorescence response in the presence of Zn2+ in ethanol–water mixture. However, no fluorescence emission was observed when the reduced derivative of this Schiff base, bis-N,N'-(2-hydroxybenzyl)-1,3-propanediamine (LHH2), was mixed with zinc or other metal ions. Optimization studies were then carried out on LH2-Zn complex in order to increase the fluorescence intensity of this molecule. Based on the obtained results, the highest fluorescence intensity was achieved at neutral pH, 10-4 M ligand concentration and in ethanol–water mixture. The effect of common metal ions on LH2 was also investigated and the results showed that this compound had a better selectivity for Zn2+ over other metal ions tested under the same conditions. Finally, the calibration curve was created and the method was tested with a Certified Reference Material (CRM).