Construction of Polycyclic π‐Conjugated Systems Incorporating an Azulene Unit Following the Oxidation of 1,8‐Diphenyl‐9,10‐bis(phenylethynyl)phenanthrene.

Abstract: Polycyclic aromatic hydrocarbons (PAHs) that incorporate either heptagons or pentagons consist of non‐planar molecular structures with unusual optoelectronic properties, and the design of a relatively simple and efficient method to construct these highly fused π‐conjugated systems with odd‐membered rings is in high demand. This work describes the use of silver(I) cations to promote the efficient synthesis of azulene‐embedded PAH 2, which is a structural isomer of tribenzo[fg,ij,rst]pentaphene 3, via tandem oxidative transannulation between the phenyl and arylethynyl moieties. This method involves a carbophilic interaction of the silver(I) cation with the acetylene units, which facilitates an electron transfer in the initial step. The synthesized PAH 2 and the protonated cation 2 H⋅BF4 were fully characterized by X‐ray crystallographic analysis, electronic absorption, electrochemical measurement, and quantum chemical calculation. The azulene‐embedded PAH 2 exhibited a low‐energy absorption band and amphoteric redox events, which were characterized as non‐alternant characteristics originating from the azulene unit. [ABSTRACT FROM AUTHOR]