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

A chemosensor, 6-(1-cyclohexyl-1H-benzo[d]imidazol-5-yl)-2-(2-(diethylamino)ethyl)-1H-benzo[de]isoquino-line-1,3(2H)-dione (9), containing 1H,3H-benzo[de]isochromene-1,3-dione and 1-cyclohexyl-1H-benzo[d]imid-azole 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 & mu;M; H2O, pH = 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.