ABSTRACT
Organic nanoparticles (ONPs) of N,N'-ethylenebis(salicylimine) (salen) were synthesized and applied for specific recognition of Zn(2+) and Al(3+) ions in an aqueous medium. The results show that fluorescence intensity rises with the increasing concentration of Zn(2+) in salen solution, proving that salen-ONPs detect Zn(2+) efficiently in the aqueous medium as chemo-sensor. Furthermore, the salen-ONPs/Zn(2+) system performs as an ON-OFF switch between pH 6.0 and 4.0. Amusingly, although salen-ONPs/Al(3+) does not show any significant effect in the fluorescence spectra, highest fluorescence intensity was observed when Al(3+) ion was added to salen-ONPs/Zn(2+) in a sequential order (addition of Zn(2+) to salen-ONPs, followed by Al(3+)). This system can be applied as a novel three inputs logic gate supported by the fluorescence for the detection of Zn(2+) and Al(3+) in biological and environmental samples. It appears that photo induced electron transfer (PET) occurs in the salen-ONPs when the fluorophore is excited. For salen/Zn(2+) system, the PET is being inhibited considerably by lowering the receptor HOMO energy due to the formation of a bond between the metal ion and ligand, enhancing the fluorescence emission. This is consistent with the theoretical study that the energy of HOMO of the ligand is lower than that of Zn(salen)(2+) complex.
