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

Abstract

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.