Roto‐Cyclization of 4‐Bromopicene in On‐Surface Synthesis

Progress toward single‐molecule electronics relies on a thorough understanding of local physico‐chemical processes and development of synthetic routines for controlled hetero‐coupling. We demonstrate a structurally unexpected ring closure process for a homo‐coupled 4,4’‐bipicenyl, realized in on‐surface synthesis. An initial covalent C−C coupling of 4‐bromopicene locks at lower temperatures the position and geometrically shields part of 4,4’‐bipicenyl. Employing this effect of shielding might offer a path toward controlled stepwise hetero‐coupling. At higher temperatures, a thermally activated three‐dimensional rotation upon hydrogen dissociation, a dehydrogenative roto‐cyclization, lifts the surface‐dimensionality restriction, and leads to the formation of a perylene. Thereby, the shielded molecular part becomes accessible again.