All-carbon scaffolds by rational design.

The search for new molecular and regular polymeric allotropes of carbon has greatly stimulated the preparation and investigation of pi-conjugated acetylenic macrocycles, which often represent substructures of proposed 2D carbon networks. Perethynylated dehydroannulenes, expanded radialenes, and radiaannulenes with large, multi-nanometer-sized all-carbon cores are potent electron acceptors, and their optoelectronic as well as stability and solubility properties are greatly enhanced by peripheral donor substitution. Acetylenic scaffolding into three dimensions has generated an expanded cubane with a C(56) core, the first representative of a new class of "platonic" objects. Exceptional chiroptical properties displayed by enantiomerically pure alleno-acetylenic, shape-persistent macrocycles promise fascinating perspectives for the development of molecular and supramolecular chiroptical materials.