Giant enhancement of electronic polarizability and the first hyperpolarizability of fluoride-decorated graphene versus graphyne and graphdiyne: insights from ab initio calculations

Graphene (GE), graphyne (GY) and graphdiyne (GDY) have promising applications because of their unique structural features with largely delocalized π-conjugated frameworks. Based on the density functional theory calculations, we investigated the adsorption behavior of alkali-metal fluorides (M3F, M = Li, Na, and K) on graphene, graphyne and graphdiyne, including the adsorption configurations, charge transfer, binding energy, and electrical conductivity. The electronic properties including orbital interactions and density of states (DOS) were also discussed. The results revealed that alkali-metal fluorides favorably adsorb on the carbon surface, forming intramolecular electron donor–acceptor (D–π–A) pairs, and these complexes are rather stable against dissociation into fluorides, especially Li3F@GDY0/+ complexes. Moreover, the adsorption of the fluorides largely affects the electronic structures of the 2D carbon materials. More importantly, it is found that the static first hyperpolarizability (βtot) of these complexes not only depends on the M3F fluorides but also on their charge-states, and these cationic M3F@GDY+ complexes exhibit large βtot values in order to establish their strong nonlinear optical (NLO) response, e.g., as high as ∼1.63 × 105 a.u. for Li3F@GDY+. However, the K3F@GE complex possesses the largest βtot value (4.59 × 105 a.u.), which is even preferable to the cationic M3F@GDY+ (M = Li, Na, and K) complexes, and the largest βtot value can be further explained by the crucial electronic transitions from TDDFT calculations. This study not only provides an effective strategy to design new carbon-based NLO optoelectronic materials, but it will also inevitably stimulate future experimental investigation for synthesis.