Octafunctionalized biphenylenes: molecular precursors for isomeric graphene nanostructures.

A straightforward method for the octafunctionalization of biphenylene based on the [2+2]-cycloaddition of an aryne intermediate has been developed. This enabled a "North-South" extension of biphenylene towards isomeric graphene nanoribbons composed of four-, six-, and eight-membered rings. This procedure furthermore allowed an "East-West" expansion to [n]phenylenes with different lengths. For the fabrication of isomeric nanongraphenes, octaarylbiphenylenes decorated with phenyl, pyrenyl, and thieno substituents were prepared. The subsequent oxidative cyclodehydrogenation provided an expanded helicene as a model compound.