Experimental and Theoretical Investigations of Surface-Assisted Graphene Nanoribbon Synthesis Featuring Carbon–Fluorine Bond Cleavage

Edge-fluorinated
graphene nanoribbons are predicted to exhibit
attractive structural and electronic properties, which, however, still
need to be demonstrated experimentally. Hence, to provide further
experimental insights, an anthracene trimer comprising a partially
fluorinated central unit is explored as a precursor molecule, with
scanning tunneling microscopy and X-ray photoelectron spectroscopy
analyses, indicating the formation of partially edge-fluorinated polyanthrylenes via on-surface reactions after annealing at 350 °C
on Au(111) under ultrahigh-vacuum conditions. Further annealing at
400 °C leads to the cyclodehydrogenation of partially edge-fluorinated
polyanthrylenes to form graphene nanoribbons, resulting in carbon–fluorine
bond cleavage despite its high dissociation energy. Extensive theoretical
calculations reveal a defluorination-based reaction mechanism, showing
that a critical intermediate structure, obtained as a result of H
atom migration to the terminal carbon of a fluorinated anthracene
unit in polyanthrylene, plays a crucial role in significantly lowering
the activation energy of carbon–fluorine bond dissociation.
These results suggest the importance of transient structures in intermediate
states for synthesizing edge-fluorinated graphene nanoribbons.