Diamino malenonitrile-linked naphthalimide in selective sensing of F^-, CN^-, Hg²⁺ and Cu²⁺ under different experimental conditions

Diaminomalenonitrile-linked naphthalimide 1 has been designed and synthesised. It shows selective sensing of F⁻, CN⁻, Cu²⁺ and Hg²⁺ under different experimental conditions. While compound 1 in CH₃CN exhibits colour change from yellow to greenish blue or green in the presence of F⁻, AcO⁻, CN⁻ and H₂PO₄⁻, it shows a colour change from yellow to light green selectively in presence of CN⁻ in aqueous CH₃CN. The selectivity of 1 for F⁻ in pure CH₃CN is achieved by using Ca²⁺ ion as chelating agent. Besides anion sensing, the probe exhibits different colour attributes towards Hg²⁺ and Cu²⁺ ions in aqueous CH₃CN. While the yellowish solution of 1 is discharged to almost colourless in presence of Cu²⁺ ions, a light red colour is observed in the presence of Hg²⁺ ions. The interaction study has been performed by NMR, UV-vis, fluorescence and mass spectroscopic techniques. A theoretical study has been invoked to understand the deprotonation of 1 that occurs in presence of basic anions.