Recent progress in chemistry of non-benzenoid carbohelicenes

Abstract

Helicenes fused by ortho-annulated benzene rings are one of interesting subset of chiral polycyclic aromatic hydrocarbons (PAHs). Helicenes containing non-benzenoid rings such as pentagonal and heptagonal rings have attracted increasing attentions because of their novel electronic properties, optical characteristics, dynamic behavior, and solid-state packing. Despite the disclosure of several beautiful examples in recent years, this field remains young and challenging due to the intrinsic difficulties of the formation of non-hexagonal rings. Herein an overview of non-benzenoid carbohelicenes with respect to structures, synthesis, optical properties, and stereochemical dynamics is provided. In this review, recent reports of helicenes with non-hexagons as chiral motif are surveyed with an emphasis on synthesis, molecular configurations and intriguing optical properties. Finally, a brief conclusion of non-benzenoid helicenes is achieved and an outlook for this field is provided according to these discussions.