Expanded all-phenylene molecular spoked wheels: cutouts of graphenylene-3

Abstract

All-phenylene molecular spoked wheels, cutouts of graphenylene-3, have been synthesized by intramolecular Yamamoto coupling of the respective dodecabromides. The uneven number of aromatics at the sides of the wheels requires a non-D_6h symmetric precursor that is available via Vollhardt trimerization of an unsymmetrically substituted acetylene. The coupling gives a considerably lower yield. This is attributable to a supramolecular aggregation of the ring precursors during the coupling process that gives rise to an intermolecular dimer and oligomer formation. Larger side groups allow us to diminish this problem to a certain extent and increase the wheel yield. Scanning tunneling microscopy investigations clearly reveal the structures of the compounds with submolecular resolution and reflect the aggregation behavior. Time-resolved photoluminescence spectroscopy shows that there is no energy transfer from the rim to the spokes of the wheels due to an interruption of the conjugation at the center of the molecules.