Selective “on–off–on” switchable chemosensor for metal ions detection and its complexes

An “on–off–on” switchable optical chemosensor namely: 5-(4-dimethylamino-phenyl)-1-pyridin-2-yl-penta-2,4-dien-1-one, DMAC and its metal complexes were synthesized and characterized. The optical studies of DMAC were presented, and reveal several interesting points when different metal ions such as Co(II), Ni(II) and Cu(II) were added. The results showed that the absorption and emission spectra are very sensitive to the used metal ions. Detectable cation-induced effects were observed on adding different concentrations of the used metal ions to DMAC, with instantaneous color change. The origin of the color change was attributed to modulation of the intramolecular charge transfer of chemosensor DMAC upon effective coordination with the used metal ions through nitrogen atoms of pyridine moiety along with oxygen of carbonyl group. Furthermore, ethylene diamine tetraacetic acid (EDTA) can selectively turn on the absorption and emission spectra of DMAC complex induced by the used metal ions (“on–off–on” type sensor). The stability constants, K, have been determined and confirming the formation of 1:1 complexes between DMAC and the used metal ions. Solid Co(II), Ni(II) and Cu(II) complexes were synthesized and characterized by a set of chemical and spectroscopic measurements using elemental analysis, electrical conductance, mass spectra, magnetic susceptibility and spectral techniques (FT-IR, UV–vis, 1H NMR). The structure of metal complexes has been also theoretically studied using molecular mechanics (MM+). The structures obtained were minimized with a semi-empirical (PM3) method. The synthesized DMAC and its complexes were screened for their biological activities.