1,2,3-Triarylazulenes as precursors of azulene-embedded polycyclic aromatic hydrocarbons†‡

A series of 1,2,3-triarylazulenes was obtained using new synthetic methodology and subsequently subjected to Scholl-type oxidation aiming for conjugated azulene-embedded polycyclic aromatic hydrocarbons (PAHs). The oxidation yielded either unexpected azulen-1(8aH)-ones or desired purely hydrocarbon azulene-embedded PAHs, depending on the substitution pattern. Different reaction pathways were rationalized using DFT calculations, leading to the observation that 2-pyrenyl substituents facilitate formation of the desired conjugated molecules. The fully hydrocarbon azulene-embedded PAHs exhibit a relatively small electrochemical energy gap below 2 eV and optical absorption reaching the near-infrared (NIR) region. These properties are attributed to their non-alternant topology and retained azulene-like electronic structure.