Progress toward single-molecule electronics relies on a thorough understanding of the understanding of local physio-chemical processes anddevelopment of synthetic routines for controlled heterocoupling.We demonstrate a structurally unexpected ringclosure process for a homo-coupled 4,4'-bipicenyl, realizedin on-surface synthesis. An initial covalent C-C coupling of 4-bromopicene locks at lower temperatures the position andgeometrically shields part of 4,4'-bipicenyl. Employing thiseffect of shielding might offer a path toward controlled stepwise hetero-coupling. At higher temperatures, a thermallyactivated three-dimensional rotation upon hydrogen dissociation,a dehydrogenative roto-cyclization, lifts the surface dimensionality restriction, and leads to the formation of aperylene. Thereby, the shielded molecular part becomes accessibleagain.