On-surface synthesis and characterization of anti-aromatic cyclo12carbon and cyclo20carbon

Cycloncarbons have recently attracted significant attention owing to their geometric and electronic structures remaining largely unexplored in the condensed phase. In this work, we focus on two anti-aromatic cyclocarbons, namely C12 and C20. By designing two fully halogenated molecular precursors both including 4-numbered rings, we further extend the on-surface retro-Bergman ring-opening reaction, and successfully produce C12 and C20. The polyynic structures of C12 and C20 are unambiguously revealed by bond-resolved atomic force microscopy. More importantly, subtly positioning the C20 molecule into an atomic fence formed by Cl clusters allows us to experimentally probe its frontier molecular orbitals, yielding a transport gap of 3.8 eV measured from scanning tunneling spectroscopy. Our work may advance the field by easier synthesis of a series of cyclocarbons via on-surface retro-Bergman ring-opening strategy. Cycloncarbons have attracted significant attention owing to their geometric and electronic structures remaining largely unexplored in the condensed phase. Here, the authors extend the on-surface retro-Bergman ring-opening reaction and successfully produce two anti-aromatic cyclocarbons C12 and C20.