Spectrophotometric and spectrofluorimetric studies on the selective sensing of fluoride ions by Co(II) and Ni(II) complexes of naphthoquinone derivative possessing enhanced H-bonding property

A novel colorimetric chemosensor based on aminonaphthoquinone (L) bearing an N–H receptor unit directly attached to quinone signaling unit has been designed, synthesized and demonstrated. The ligand showed a highly selective colorimetric response to fluoride ions based on H-bond formation with the receptor unit. The binding constants of the L and its square planar [Co(L)Cl2]·3H2O and [Ni(L)Cl2]·4H2O complexes, computed using fluorescent enhancement data, were found to be 0.6, 1.5 and 0.9 × 108 M−1, respectively, indicating enhancement of H-bond donor ability of the receptor unit, as a result of complexation with metal ions, towards fluoride ion sensing. Also, these sensors had high selectivity for fluoride ion detection over other common anions, such as Cl−, Br−, I−, AcO−, NO3−, H2PO4− and CN− in acetonitrile.

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► The developed sensor selectively detects fluoride ions in acetonitrile.
► The chemosensor is novel with sensing unit directly attached to the signaling unit for easy signaling.
► The mechanism of the colorimetric sensing is through H-bond formation between N–H moiety and fluoride ions.