Pauli Repulsion Versus van der Waals: Interaction of Indenocorannulene with a Cu(111) Surface

Abstract

Modification of metal electrode surfaces with functional organic molecules is an important step toward organic electronics. The interaction of the buckybowl indenocorannulene with a Cu(111) surface and the two-dimensional self-assembly on the same surface was studied by means of scanning tunneling microscopy and dispersion-enabled density functional theory. Based on the conjecture of maximizing van der Waals interaction with the surface one would expect the indeno group to be aligned parallel to the surface. Theoretical investigations predict a nonparallel arrangement with the benzo ring of the indeno group located higher above the surface than the bowl rim connected to the indeno group. This adsorbate geometry is due to strong electronic interaction between molecule and surface, including substantial Pauli repulsion. The long-range ordered monolayer shows differences for two molecules of the unit cell in scanning tunneling microscopy contrast, suggesting either different polar alignments, and therefore a different tilt of the indeno group, or occupation of different adsorption sites.

Fivefold Symmetry and 2D Crystallization: Self‐Assembly of the Buckybowl Pentaindenocorannulene on a Cu(100) Surface

“…A depletion in the molecule at 17 Å causes a mirror charge (accumulation) at 13 Å, for example (Figure b). Similar values have been reported (theoretically and experimentally) for 1 , pentamethyl‐ 1 , and 3 on Cu(111) . The polarization binding mechanism of adsorption has been described previously for benzene on coinage metals .…”

“…The D‐DFT calculations yield a strong binding of 5.7 eV for 2 , which is substantially larger than that calculated for 3 . D‐DFT calculations for 3 on Cu(111) also showed that the single indeno group was not perfectly parallel to the surface plane, indicating a binding to the surface at the bowl and not by maximal vdW contact to the surface through the benzene indeno tab …”

“…However, it has been shown for small aggregates (dimers, trimers, etc.) of fragment buckybowls of C 70 that intermolecular C−H⋅⋅⋅π and π⋅⋅⋅π bonding indeed come into effect on Cu(111) . As this packing motif is observed already at 50 % of the complete monolayer, the conclusion on the binding mechanism based on relative alignment seems valid.…”

“…Therefore, the overall contrast of a single molecule agrees better with the electron density map of a molecule adsorbing with two indeno groups proximal to the surface and one indeno group pointing up (Figure d). Note that 3 was found to align with its single indeno group parallel to the surface …”

“…Hence, lateral packing of the pentagonal shape determines the final packing pattern. For monoindenocorannulene (Figure c, C 20 H 14 , 3 ), the presence of a benzene tab at the rim of the bowl provides a deeper bowl and a biased side for tilting to maximize van der Waals (vdW) contact with the surface …”