AzUlene‐Fused Polycyclic Aromatic Hydrocarbons: Synthesis, Structural, Optical, and Electrochemical Properties of Azuleno[2,1‐a]phenalenones

The preparation of 2‐arylazulenes possessing 1‐naphthyl substructure is achieved via Suzuki–Miyaura coupling with various arylboronic acids. Intramolecular cyclization using Brønsted acids is examined, yielding azulene‐fused polycyclic aromatic hydrocarbons, that is, azuleno[2,1‐a]phenalenones, in high yields. The optical properties of azuleno[2,1‐a]phenalenones are characterized by UV/vis and fluorescence spectroscopy, revealing halochromic behavior and significant fluorescence under acidic conditions. Electrochemical properties are also assessed using voltammetry and spectroelectrochemical experiments, identifying compounds with remarkable electrochromic behavior.