A donor–π–acceptor (D–π–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 (λ_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.