Role of C-F Bonding on the Optical Properties of Fluorinated Graphene Oxide

Graphene oxide (GO) exhibits very poor photoluminescence (PL) characteristics because of the nonradiative recombination of electron-hole pairs. One of the crucial approaches for the enhancement of the optical features of GO is functionalization. In this study, we present a novel catalyst-free, rapid, one-step, aqueous-phase synthetic approach using SELECTFLUOR under mild conditions that provide access to highly photoluminescent fluorinated graphene oxide (FGO) emitting in the visible region. Time-resolved fluorescence spectroscopy and femtosecond transient absorption spectroscopy revealed that the enhanced PL is due to the increased pi* -> pi transition and weaker electron-phonon interactions in FGO. Most importantly, the structure and composition analyses using F-19 NMR and X-ray photoelectron spectroscopy suggest that the C-F bond on the basal plane neighboring to the aromatic rings is the key factor behind the enhancement of the fluorescence of FGO. Identification of the underlying C-F bonding features behind the emergence of strong orange fluorescence will contribute immensely to the fundamental understanding of the structure and optical property relationship of FGO. Moreover, strong orange fluorescence remains stable in a solid thin film of FGO, which offers a unique solution-processable route toward the integration of FGO in solid-state optoelectronic devices.