Naphthalimide-benzimidazole conjugate towards "Turn-on" recoginition of Hg2+ in pure aqueous medium.

[Display omitted] • Naphthalimide-benzimidazole conjugate was studied for selective detection of Hg2+ ions in aqueous medium. • Detection of limit was found to be 7.1 nM. • Mass spectrometry confirmed 2:1 stoichiometry between 9 and Hg2+ ions. • DFT calculations were found in good agreement with experimental results. A chemosensor, 6-(1-cyclohexyl-1 H -benzo[ d ]imidazol-5-yl)-2-(2-(diethylamino)ethyl)-1 H -benzo[ de ]isoquinoline-1,3(2 H)-dione (9), containing 1 H ,3 H -benzo[ de ]isochromene-1,3-dione and 1-cyclohexyl-1 H -benzo[ d ]imidazole moieties has been designed and found to be selective towards Hg2+ ions over-tested wide-range of metal ions. Compound 9 shows the absorption and emission peaks at 370 nm and 540 nm, respectively. The addition of Hg2+ ions to compound 9 (20 μM; H 2 O, p H = 7.4) prompted the formation of a 2:1 ligand–metal complex, 9 -Hg2+, which shows a significant blue-shifted emission enhancement to 495 nm, due to the mechanism of ligand to metal charge transfer. The formation of compound 9 and Hg2+ ions complex has also been confirmed through mass spectrometry and 1H NMR titrations. The photophysical properties of the compound and its complex corroborated with Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) calculations. [ABSTRACT FROM AUTHOR]