Facile Synthesis of Dicyclohepta[ cd , fg ]‐ as ‐indacene and Confirmation of its Anti‐Kasha S 3 Emission

Interest in non‐benzenoid polycyclic aromatic hydrocarbons (PAHs) has rapidly increased due to their unique electronic configurations and physical properties, which differ significantly from those of their benzenoid counterparts. Herein, we report a novel strategy to synthesize a non‐benzenoid isomer of perylene, dicyclohepta[ cd , fg ]‐ as ‐indacene substituted with phenyl and methyl groups ( 1‐Ph‐Me ). The compound was synthesized via single‐electron reduction‐induced dimerization of 6‐methylazulene. The synthetic route to 1‐Ph‐Me (6 steps from 6‐methylazulene) is significantly shorter than the previously reported 12‐step synthesis of 1‐Ph from azulene. Compound 1‐Ph‐Me exhibits near‐infrared (NIR) absorption as well as weak anti‐Kasha emission. Spectroscopic analysis and theoretical calculations indicate that this emission originates from the third singlet excited state (S 3 → S 0 ), a phenomenon enabled by the fused biazulene framework. Our study paves the way for the synthesis and the comprehensive understanding of the electronic structures of non‐benzenoid PAHs incorporating multiple azulene units.