Donor-π-acceptor (D-π-A) dyad for ratiometric detection of Hg2+ and PPi

A donor-pi-acceptor (D-pi-A) dyad 1 has been successfully synthesized by Linking phenanthrenequinone as an eLectron donor unit and anthraquinone as an eLectron acceptor unit through a phenyl ring. Dyad 1 exhibits intramolecular charge transfer and this is a key factor for the detection of Hg2+ and of the pyrophosphate ion (P2O74-, PPi) in a semi-aqueous medium. Dyad 1 exhibits absorption peaks at 430, 370, and 337 nm and an emission peak at 530 nm (lambda(ex) = 430 nm). Dyad 1 exhibits a new absorption peak at 390 nm ratiometrically along with emission quenching in the presence of Hg2+ ions while the presence of PPi results in drastic ratiometric changes in the absorption and emission spectra with new peaks at 495 nm and 620 nm, respectiveLy. The quantum yield of dyad 1 on complexation with PPi was also increased from 0.1 (free dyad) to 0.69 (dyad 1.PPi). The Lowest detection Limits for Hg2+ and PPi were found to be 31 nM and 46.5 nM, respectiveLy. DFT calculations have been performed to develop a mechanism for PPi and Hg2+ ion binding with dyad 1.