2,11-Dibromo-13,14-dimesityl-5,8-dioxapentaphene: A Stable and Twisted Polycyclic System Containing the o-Quinodimethane Skeleton.

A stable o-quinodimethane (oQDM) derivative, 2,11-dibromo-13,14-dimesityl-5,8-dioxapentaphene (3) was synthesized, and its structure and properties were investigated. The X-ray structural analysis showed a significantly twisted π-framework and a clear bond-length alternation in the central oQDM skeleton. Owing to the quinoidal conjugation, 3 exhibited a broad absorption band in the visible region (up to 700 nm) and amphoteric redox behavior. Furthermore, radical cation 3(•+) was isolated, and its electronic structure was elucidated by spectroscopic measurements.