Tailoring electronic, optical, and reactive properties of Br- and F-doped graphene nanoflakes: A DFT-based study

The present study utilizes density functional theory (DFT) to methodically examine the geometric, electrical, and chemical characteristics of both pure and halogen doped graphene nanoflakes (GNFs). Geometric optimization indicates that the incorporation of bromine and fluorine atoms results in significant lattice distortions, elevated dipole moments, and heightened surface polarity, especially in multi-doped systems. A significant discovery is the adjustable modulation of the electronic band gap: pristine GNFs exhibit a broad band gap of 4.172 eV, whereas halogen doping substantially reduces this value resulting in 1.548 eV for BrF-GNFs, 1.580 eV for 2Br-GNFs, 1.676 eV for 2F-GNFs, 1.426 eV for Br₂F₂-GNFs, and as low as 1.194 eV for Br₃F₃-GNFs. This decrease is ascribed to the concentration of frontier molecular orbitals at dopant locations and the formation of mid-gap electronic states. Doping induces substantial alterations in the Fermi level and considerable enhancements in work function, reaching values as high as 4.364 eV in Br₂F₂-GNFs, which is beneficial for device applications. Chemical reactivity indices demonstrate that doped GNFs possess enhanced electrophilicity, softness, and a heightened tendency for electron transfer relative to virgin GNFs. These findings together indicate that halogen doping is a viable method for modifying the band gap and chemical reactivity of graphene nanoflakes, hence expanding their use in nanoelectronics, optoelectronics catalysis, and sensing technologies.