Synthesis of Polyazaacenes

Significance

This paper describes the synthesis of a series of polyazaacenes based on nucleophilic building blocks 1 and 5. Addition of bielectrophile 2 to the n-BuLi-treated amidine 1 at low temperature gave compound 3, which could be further transformed into an octaazanaphthacene 4 when it was molten with 2. Similarly, a simple heating of pyrazinopyrazine 5 with 2 afforded both polyazaacene 6 and 7. Interestingly, they found tetraazafulvalene 8 could be efficiently converted into an octaazahexacene 9, which gives strong red emission. This transformation was proposed to proceed with a dyotropic rearrangement of 8, leading to a pyrazinopyrazine, which undergoes twofold intramolecular [4+2] cycloaddition and aromatization.