The Bowl Depth of Corannulene

Ephrath Solel, The Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa, Israel
Ofer Reany, Department of Natural Sciences, The Open University of Israel, Ra'anana, Israel
Mark Botoshansky, The Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa, Israel
Amnon Stanger, The Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa, Israel
Ehud Keinan, The Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa, Israel

Corannulene is a polyaromatic molecule, which is the curvature-forming unit in fullerenes, nanotube caps and other curved graphene molecules. Its bowl shape is formed by a central five-membered ring that is surrounded by five aromatic rings. We studied the effect of different alkylthio substituents on the corannulene bowl depth using synthesis, X-ray crystallography and computational methods. The results indicate that the bowl depth is mainly determined by the substituents steric demands and electronic effects. Our theoretical calculations show that introducing 10 tert-butylthio substituents on the corannulene rim causes significant steric hindrance between the substituents, and that this strain is partially relieved by complete flattening of the corannulene core. These predictions were supported by experimental results with deca(tert-butylthio)corannulene, which was synthesized and characterized by X-ray crystallography, showing the first example of a completely flat corannulene derivative.