Fluorescent chemosensors for selective and sensitive detection of phosmet/chlorpyrifos with octahedral Ni2+ complexes

Abstract

The hexadentate ligands H2L1−L3 with mixed S, N, O donor sites and possessing substituents having either “no” or electronreleasing/withdrawing nature at terminal ends are synthesized. The ligands H2L1−L3 were tested for binding with library of metal ions, wherein maximum efficiency was observed with Ni2+, and it motivated us to prepare the Ni2+ complexes. The ligand H2L1 underwent deprotonation and formed binuclear complex when interacted with Ni2+ as evident from its crystal structure. The H2L2 and H2L3 having electron-withdrawing/electron releasing groups, respectively, were also deprotonated; however, they afforded mononuclear complexes with Ni2+ ion. This signifies the importance of steric parameters instead of electronic factors in these particular cases. Impressed by differential behavior of complexes of H2L1 and H2L2/H2L3 with Ni2+ and their photophysical and electrochemical properties, all the metal complexes were studied for their chemosensing ability. Nowadays with increased use of organophosphate, there is alarming increase of these agents in the environment, and thus we require efficient technique to estimate the level of these agents with high sensitivity and selectivity in aqueous medium. The Ni2+ complexes with hydrophobic nature were suspended into aqueous medium for testing them as sensor for organophosphate. The (L1)2.(Ni2+)2 could sense phosmet with detection limit of 44 nM, whereas L2.Ni2+ and L3.Ni2+ exhibited the detection limits of 62 and 71 nM, respectively, for chlorpyrifos.