Design of van der waals two-dimensional heterostructures from facially polarized janus all-cis 1,2,3,4,5,6-hexafluorocyclohexane (C₆H₆F₆)

The recently synthesized all-cis 1,2,3,4,5,6-hexafluorocyclohexane (1) has a large dipole moment (6.2 D) and uniaxial facial polarization. Based on density functional theory (DFT) calculations, it is shown that both the "positive" and "negative" surfaces of 1 can recognize flat aromatic molecules (X, X = benzene, pyrene, and coronene), 2D materials (graphene), and their fully hydrogenated analogues through attractive noncovalent interactions. 1 can be sandwiched between graphene and graphane layers, where the enhanced polarity of the axial C-H and C-F bonds leads to the formation of an unusual "triple-decker" complex. Upon adsorption with 1, the band gap of graphane reduces from 3.40 to 2.05 eV, which might be useful for visible-light energy-conversion applications. We demonstrate the controlled tuning of the structural and electronic properties in 1-benzene, 1-cyclohexane, and benzene-1-cyclohexane complexes by the application of an external electric field along the polarization axis. The extended analogue of 1, hydrofluorinated graphene (HFG), which has semiconducting properties (band gap ≈ 3.0 eV), can form strong C-H···F-C interlayer interactions with graphane to form a stable, metallic bilayer. Our calculations show that the two-dimensional HFG can be realized through the high-pressure topochemical condensation of monofluoroacetylene (C₂HF) for which the barrier of activation is 18.7 kcal/mol.