A photochemical approach to extended corannulenes

Abstract

Graphene sheets with perfect atomic lattice show perfect electronic properties, but structural defects occur during the growth or processing of the material. Due to the inability to precisely control the length and the breadth of an atomically thin structure obtained by large-scale methods such as chemical vapor-deposition, tremendous effort has been invested into developing novel methods and strategies to access such unique architectures through rational (‘bottom-up’) synthetic approaches. We envisaged that taking corannulene, a molecule harboring an in-built defect in form of a central five-membered ring, and extending it would allow us to control where the defect will appear and thus control the properties of the extended carbon structures. Previously reported methods for the extension of corannulene scaffold, like flash vacuum pyrolysis and metal-catalyzed processes suffer from many disadvantages, like harsh conditions, low yields, use of expensive and environmentally unfriendly metal-based catalysts, etc. To overcome these disadvantages, we developed a new synthetic approach, which is mild, efficient, inexpensive, and with very good yields. In this approach, corannulene-based compounds that can undergo Wittig olefination or Heck coupling reactions are utilized to access diaryl-ethylene precursors. These compounds can then be subjected to a photochemically induced oxidative-cyclization process to yield a corannulene structure with extended π-framework. The generality of this method allows for the preparation of a myriad of polycyclic aromatic arenes as well as heteroarene structures.