Impact of Heterocirculene Molecular Symmetry Upon Two-Dimensional Crystallization

Supplementary Information

Impact of heterocirculene molecular symmetry upon two-dimensional crystallization

W.D. Xiao1,2*, Y.Y. Zhang2, L. Tao2, K. Aït-Mansour1,4, K.Y. Chernichenko5,6, V.G. Nenajdenko6, P. Ruffieux1, S.X. Du2, H.-J. Gao2, and R. Fasel1,3*

1 Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland

2 Institute of Physics, Chinese Academy of Sciences, 100190 Beijing, P.R. China

3 Department of Chemistry and Biochemistry, Universität Bern, Freiestrasse 3, 3012 Bern, Switzerland

4 ICMP, Ecole Polytechnique Fédérale de Lausanne, Station 3, 1015 Lausanne, Switzerland

5 Department of Chemistry, University of Helsinki, P.O. Box 55, 00014, Finland

6 Department of Chemistry, Moscow State University, Leninskiye Gory, 119992 Moscow, Russia

Contents

Interaction between heterocirculenesand Au(111)
Formation of a second layer of 1on Au(111) at a coverage of ~1.5 ML
Intermolecular interaction between heterocirculenes

*To whom correspondence should be addressed. Email: ; .

1.Interaction between heterocirculenesand Au(111)

The interactions between 1 and Au(111)arestudied using the vdW-DF method.1-8Periodic boundary conditions were appliedto model the adsorption of 1on Au(111).The calculation cells consisted of repeated p(5×5) four-layer Au(111) slabs separated by 18Åof vacuum. A single molecule of1was placed in each slab. The structures were relaxed until residual forces were less than 0.02 eV. Supplementary Figure 1 shows the optimized configuration of 1adsorbed on Au(111).

According to our vdW-DF calculations, the binding energy between 1 and Au(111)is 2.2 eV/molecule.This binding energy is comparable with that of 2.3 eV/molecule between coronene and Au(111) reported by Medeiros et al..6 The vertical distance between 1 and the toplayer of the substrate is 3.5 Å, also comparable to that of 3.3 Åbetween coronene and Au(111)reported by Medeiros et al..6Similar results are obtained for 2 adsorbed on Au(111). Thus, for the adsorption of both 1 and 2 on Au(111) we conclude that the molecule-substrate interaction mainly derives from aweak coupling between the molecular π-electrons and the metal, akin to the one of planar polycyclic aromatic hydrocarbon molecules on Au(111), and in contrast to the strong S-Au bonding widely reported for thiols adsorbed on gold substrates.9-11

Supplementary Figure 1 | Optimized configuration of 1 adsorbedon Au(111).

2.Formation of a second layer of 1 on Au(111) at a coverage of ~1.5 ML

Supplementary Figure 2 | STM images of 1.5 ML of 1 on Au(111). (a) Overview showing the formation of asecond layer on top of a completed first layer of 1. The first and second layers are labelled as I and II, respectively. (b) Close-up of the second layer exhibitingarectangular superlattice with a= 1.05±0.05nm and b= 1.89±0.05nm, respectively. Note that the molecules adopt tilted configurations, similar to thosewithin the (001) plane in the bulk crystal of 1.12,13

3.Intermolecular interaction between heterocirculenes

In plots of the electron localization function (ELF), which is often used to determine formation of bonds, we find no evidence for strong S-S interaction between adjacent molecules. Supplementary Figure 3 shows the iso-surface of ELF = 0.8 of 1 in the centered rectangular lattice. The iso-surface locates only at the molecule. We analyzed the electron density difference, which reflects the charge transfer between adjacent molecules (Supplementary Figure 3(b) and (c)). To get a significant iso-surface, iso-values have to be chosen as small as ±10-6 Å-3. This is clearly also within the regime of vdW interactions. For comparison, this value is around 10-3 Å-3 for FePc molecules adsorbed on Au(111).14

Supplementary Figure 3| Iso-surfaces of ELF and electron density difference of 1 in the centered rectangular lattice.(a) Iso-surface ofELF=0.8. (b, c) Iso-surface of electron density difference of Δρ=±10-6 Å-3 for positive (b) and for negative (c) values of Δρ.

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