Constructing 1-Ethoxyphenanthro[9,10-]acephenanthrylene for the Synthesis of a Polyaromatic Hydrocarbon Containing a Formal Azulene Unit.

-Acenoacenes are attractive synthetic targets, but their non-benzenoid isomeric counterparts were unnoticed. 1-Ethoxyphenanthro[9,10-]acephenanthrylene was synthesized and converted to azulene-embedded , which is a tribenzo-fused non-alternant isomeric motif of -anthracenoanthracene. Aromaticity and single-crystal analyses suggested a formal azulene core for , which showed a smaller highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap with a charge-transfer absorption band and brighter fluorescence than (quantum yield (Φ): = 41.8%, = 8.9%). The reduction potentials of and were nearly identical, and the observations were further supported by density functional theory (DFT) calculations.