Azulene–Pyridine-Fused Heteroaromatics

Abstract

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 <b>Az-Py-1</b>, a seven fused ring system with 30π electrons, by reductive cyclization of a 1-nitroazulene. The structure of <b>Az-Py-1</b> was unambiguously confirmed by single-crystal X-ray analysis, and analogues <b>Az-Py-2</b>-<b>Az-Py-6</b> 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 <b>Az-Py-1</b>-<b>Az-Py-6</b> suggest their potential as semiconductors, and the single-crystal ribbons of <b>Az-Py-1</b> show high hole mobilities up to 0.29 cm² V^-1 s^-1.