Azulene–Pyridine-Fused Heteroaromatics

Azulene, a nonbenzenoid bicyclic aromatic hydrocarbon with unique electronic structure, is a promising building block for constructing nonbenzenoid π-conjugated systems. However, azulene-fused (hetero)­aromatics remain rare as a result of limited synthetic methods. We report herein the unexpected synthesis of azulene- and pyridine-fused heteroaromatics Az-Py-1, a seven fused ring system with 30π electrons, by reductive cyclization of a 1-nitroazulene. The structure of Az-Py-1 was unambiguously confirmed by single-crystal X-ray analysis, and analogues Az-Py-2–Az-Py-6 were also synthesized, demonstrating that this is an effective method for constructing azulene- and pyridine-fused heteroaromatics. Theoretical calculations and photophysical and electrochemical studies of Az-Py-1–Az-Py-6 suggest their potential as semiconductors, and the single-crystal ribbons of Az-Py-1 show high hole mobilities up to 0.29 cm2 V–1 s–1.