Pyrazinoquinoxaline-based building blocks were incorporated into both p-conjugated dendrimers and polymers. The dendrimers were synthesized using a convergent/divergent approach whereas the donor/acceptor copolymers were synthesized via Stille cross-coupling reactions. The structurally defined dendrimers and the p-conjugated polymers were investigated with respect to their optical and electronic properties as well as their performance in photovoltaic devices. Because of the presence of the electron-deficient pyrazinoquinoxaline moiety, the absorption spectra of the materials under investigation were red-shifted with respect to the all thiophene-containing materials. Power conversion efficiencies up to 1.7 and 0.8% were obtained from blends of second-generation dendrimers and polymers with PC71BM, respectively.