Per‐Substituted [8]Circulene and Its Non‐Planar Fragments: Synthesis, Structural Analysis, and Properties

The syntheses, structures, and physical properties of a full series of benzannulated tetraphenylenes are reported. The palladium‐catalyzed annulation of tetraiodo‐substituted 2,3,6,7,10,11,14,15‐octamethyltetraphenylene with insufficient di(4‐anisyl)ethyne yielded a mixture of per‐substituted [8]circulene and its non‐planar fragments, including mono‐, para ‐di‐, ortho ‐di‐, and triannulated products. Their structures were unambiguously verified by X‐ray crystallography. Successive benzannulations significantly affect the molecular geometries, dynamic behaviors, and physical properties of the compounds. In this series of compounds, [8]circulene is the most strained one, as reflected by the significant deplanarization of the phenanthrene moieties (ca. 63° in the bay region) and the fact that it has the highest strain energy (120.6 kcal mol −1 ). The dynamic behaviors of these compounds were examined both experimentally and theoretically. The ring flipping of per‐substituted [8]circulene is confirmed to proceed through pseudorotation with a barrier of around 21 kcal mol −1 , whereas its non‐planar fragments require much more energy for the ring inversion. The photophysical and electrochemical properties of the investigated compounds depend strongly on the extent of efficient π conjugation. The successive benzannulations red‐shift both the absorption and the emission bands, and reduce the first oxidation potential.