Synthesis of Pyrazinopyrazine-Fused Azaacenes through Direct Condensation Reactions between Quinoxalinediamine and Diketones

We report the synthesis of a new type of pyrazinopyrazine-fused azaacene molecules by a simple and versatile procedure. 6,9-Dihexyldithieno[3,2-f:2′,3′-h]quinoxaline-2,3-diamine was synthesized through the condensation between 2,7-dihexylbenzo[1,2-b:6,5-b′]dithiophene-4,5-diamine and bis(2,2,2-trifluoroethyl) oximidate. A series of derivatized molecules with extended two-dimensional aromatic fused-ring structures could be obtained by simple condensation reactions between the quinoxalinediamine intermediate and various diketones. The reaction was proved to be effective for the construction of tetrazaacene derivatives with extended heterocyclic aromatic ring systems. The molecules obtained exhibit low-lying LUMO levels that can be fine-tuned by modifying the molecular structure. Crystallographic results showed that in a solid state, the molecules form "brick wall" structures with a close π–π stacking mode. The stacking between the π-ring systems in the molecules could be further enhanced by expanding the large 2D planar-conjugated structure.