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.

Comment

Acene derivatives have been extensively studied as channel materials for organic field effect transistors. Polyazaacenes, which are analogues of acenes with part of their CH groups replaced with aza nitrogens, have been found to be promising n-type organic semiconductors with high stability. In addition, polyazaacenes were proposed to be interesting sensor materials owing to the nitrogen functionality. The work described here demonstrated a novel synthetic method for the preparation of a family of polyazaacenes, some of which showed interesting redox and photophysical properties. These compounds have a great potential to be n-type semiconducting materials for organic electronics.