Heptacyclic aromatic hydrocarbon isomers with two azulene units fused

Abstract

Azulene, known for its unique electronic properties and structural asymmetry, serves as a promising building block for the design of novel non-benzenoid polycyclic aromatic hydrocarbons (PAHs). Herein, we present the synthesis, characterization, and physical properties of three diazulene-fused heptacyclic aromatic hydrocarbons, 8,17-dioctyldiazuleno[2,1-a:2′,1′-h]anthracene (trans configuration), 16,18-dioctyldiazuleno[2,1-a:1′,2′-j]anthracene (cis configuration) and 3,18-dioctyldiazuleno[2,1-a:1′,2′-i]phenanthrene (zigzag configuration). Three compounds are configurational isomers with different fusing patterns of aromatic rings. All three isomers exhibit pronounced aromaticity, as revealed by nuclear magnetic resonance spectroscopy and theoretical calculations. They exhibit characteristics of both azulene and benzenoid PAHs and are much more stable than their all-benzene analogues. The optical and electrochemical properties of these three isomers were investigated through UV-vis absorption spectra and cyclic voltammetry, revealing distinct behaviors influenced by their molecular configurations. Furthermore, the isomer in trans configuration exhibits promising semiconducting properties with a hole mobility of up to 0.22 cm² V⁻¹ s⁻¹, indicating its potential in organic electronics applications.