'Clean Reaction' Strategy to Approach a Stable, Green Heptatwistacene Containing a Single Terminal Pyrene Unit

摘要

Acenes, first introduced by Clar to describe the family of hydrocarbons with linear annellation of benzene rings (Scheme 1), can be considered as one piece of carbon nanotube or graphene, and have received a lot of attention as active elements in organic semiconducting devices. Although polycyclic aromatic hydrocarbons (PAHs) can be found in heavy oil or be generated from petroleum asphaltenes, higher conjugated acenes are not observed owing to their high reactivity, such as easy oxidation and photodimerization. Natural rarity or non-existence of higher conjugated oligoacenes together with the theoretical interest (e.g. in the gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gap) and electronic properties) gave scientists more reasons to synthesize them. Unfortunately, the extreme instability, poor solubility, and tedious purification of higher conjugated oligoacenes make the synthetic work more challenging. Although several groups have reported the photo-spectroscopic characterization and the study of electronic structure of higher acenes (n>=7), there are only five examples of higher acenes (n >= 7) characterized by X-ray single-crystal structures.