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⋅BF 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.

The synthesis and optical properties of 1,8-diphenyl-9,10-bis(arylethynyl)phenanthrenes, which are distorted phenanthrenes, are reported. The presence of the two phenyl groups at the 1,8-positions of phenanthrene significantly distorts the molecular geometries, as was evidenced by X-ray crystallography. The congested substitution pattern in the K region results in a distorted aromatic framework, which leads to a redshift in the emission spectrum. These observations are in stark contrast to 9,10-bis(phenylethynyl)phenanthrene with no phenyl groups at the 1,8-positions. A large Stokes shift suggested extensive structural relaxation between the phenyl and arylethynyl units in the excited state, which was supported by theoretical calculations.