Naphthazarin: Colorimetric detection of Cr³⁺ using highly selective F^- chemosensor

Naphthazarin(5,8-dihydroxy-1,4-naphthoquinone) exhibited high selectivity for F^-, as compared with CN^-, Cl^-, Br^-, HSO₄^-, H₂PO₄^-, ClO^- and NO₃^- in DMSO, which was attributed to the formation 1 : 1 complex. Interestingly, the blue color of the naphthazarin-F^- complex could be recovered after the addition of Cr³⁺. We have investigated the ability of complex formation based on the association constant, K_ass ; the binding ability for the complex formation of naphthazarin-F^- and Cr³⁺ is much greater in DMSO (K_ass =5.3 × 10⁴ M^-1) than that of the naphthazarin with F^- (K_ass =2.0 × 10³ M^-1).