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.