13. Trannulenes with “In-Plane” Aromaticity: Candidates for Harvesting Light Energy

Breaking with convention: In the textbook aromatic annulenes the p orbitals are oriented perpendicular to the ring plane. In trannulenes the p orbitals form a cyclic, conjugated π system within the ring plane (see scheme). This concept of “in-plane” aromaticity was first recognized in 1979, and now representative compounds have been synthesized. The all-trans configuration of the annulene ring is stabilized by a fullerene framework, and the novel physicochemical properties of trannulenes open new opportunities for the design of light-harvesting compounds.