Analysis of intermolecular interactions of n -perfluoroalkanes with circumcoronene using dispersion-corrected DFT calculations: comparison with those of n -alkanes.

Understanding the interactions between the adsorbate and substrate is critical in basic and advanced scientific fields, including the formation of well-organised nanoarchitectures via self-assembly on surfaces. In this study, the interactions of n -alkanes and n -perfluoroalkanes with circumcoronene were studied using dispersion-corrected density functional theory calculations as models of their adsorption on graphite. The interactions of n -perfluoroalkanes with circumcoronene were significantly weaker than those of the corresponding n -alkanes, e.g. the calculated adsorption energies of n -perfluorohexane and n -hexane were -9.05 and -13.06 kcal mol -1 , respectively. The dispersion interactions were the major source of attraction between circumcoronene and the adsorbed molecules. Larger steric repulsion of n -perfluoroalkanes compared to those of n -alkanes increased their equilibrium distances from circumcoronene and decreased the dispersion interactions, resulting in weaker interactions. The interactions between two adsorbed n -perfluorohexane molecules and those of n -hexane molecules were -2.96 and -2.98 kcal mol -1 , respectively, which are not negligible in the stabilisation of adsorbed molecules. The geometries of adsorbed n -perfluoroalkane dimers revealed that the equilibrium distance between two n -perfluoroalkane molecules did not match the width of the six-membered rings in circumcoronene, in contrast to that between n -alkanes. The lattice mismatch also destabilised the adsorbed n -perfluoroalkane dimers. The difference in the adsorption energy between flat-on and edge-on orientations of n -perfluorohexane was smaller than that of corresponding n -hexane.