Corannulene Derivatives DOI: 10.1002/anie.200805689 Self-Assembly of Fivefold-Symmetric Molecules on a Threefold- Symmetric Surface** Olivier Guillermet, Eeva Niemi, Samuthira Nagarajan, Xavier Bouju, David Martrou, AndrØ Gourdon, and SØbastien Gauthier* Fivefold rotational point-group symmetry plays a special role because of its incompatibility with translational symmetry. This symmetry mismatch has attracted interest for a long time, going back to Dürer [1] and Kepler, [2] who demonstrated that a wealth of unusual structures could be produced by tiling the plane with regular pentagons. These ideas have been used with great success in biology to understand the structure of virus capsids made from pentamers [3, 4] and in material science to clarify the nature of quasi-crystals. [5, 6] Transposed into the domain of surface science, they suggest that new and interesting patterns could be formed by depositing fivefold- symmetric molecules onto a substrate. [7] An example of this approach was reported recently. The adsorption on Cu(110) of corannulene, which is a C 60 fragment bowl with a fivefold symmetry axis (Figure 1 a), was studied by scanning tunneling microscopy (STM) and other techniques. [7] The molecules form a quasi-hexagonal superlattice whose structure is dominated by the vertical molecule–substrate interaction. The molecules occupy identical adsorption sites in one domain. But the large distance between these sites leads to a rather small contribution of the fivefold molecular symme- try to the intermolecular interaction, which appears not to be strong enough for the symmetry mismatch to significantly influence the resulting structure. To observe more pro- nounced effects, the strength of the intermolecular interac- tions must be increased to reach the onset of short-range repulsive interactions, at which point the fivefold shape of the molecule is expected to contribute in a much stronger way. On crystalline surfaces, where the molecules tend to stay at or near their preferred adsorption site, this requirement can be met if the size of the molecule fits adequately with the substrate (i.e. if it is “commensurate”) for neighboring molecules to approach closely or even to come in “contact”. We report herein on the adsorption of a corannulene derivative, penta-tert-butylcorannulene [8] (PTBC; Figure 1 b), on the high-symmetry Cu(111) surface studied by low- temperature STM (5 K) and structure calculations. Note that the synthesis of corannulene has been improved to achieve an overall yield of 32 % from 2,7-dimethylnaphtha- lene, compared to 13 % with standard methods (see the Supporting Information). The addition of five tert-butyl groups enhances the fivefold shape of the molecule relative to that of corannulene, as indicated qualitatively by the van der Waals surfaces displayed in Figure 1. Furthermore, the C À C s bonds connecting these lateral groups to the central part of the corannulene molecule are rather flexible, giving the molecule the possibility to adapt itself to the substrate surface structure and rendering the commensurability condition mentioned above less stringent. Note that the bowl-to-bowl inversion, which is known to happen easily at room temperature in corannulene, [9] is also likely to affect PTBC, but this process should be frozen at low temperature and for the adsorbed molecule. The PTBC molecule thus adopts two chiralities, as two equivalent sets of sites are available for the tert-butyl groups on the corannulene core. Deposition of PTBC on Cu(111) at room temperature and subsequent annealing at 100 8C for one hour leads to the formation of molecular islands, (STM image in Figure 2a), which coalesce to form a monolayer at higher coverage (see Supporting Information Figure S2). In this structure, individ- ual molecules appear as five lobes surrounding a central depression in a fivefold-symmetric pattern (Figure 2 b). As shown below, each of the five lobes marks the position of a Figure 1. Ball-and-stick representations and van der Waals surfaces of a) corannulene and b) PTBC (top and side views). The van der Waals surfaces were produced with Jmol. [10] [*] Dr. O. Guillermet, Dr. E. Niemi, Dr. S. Nagarajan, Dr. X. Bouju, Dr. D. Martrou, Dr. A. Gourdon, Dr. S. Gauthier CEMES-CNRS 29 rue J. Marvig, P.O. Box 94347, 31055 Toulouse (France) Fax: (+ 33) 5-6225-7999 E-mail: gauthier@cemes.fr [**] Partial support by the European Commission within the project PicoInside (Contract No. IST-015847) is gratefully acknowledged. E.N. thanks CNRS for a postdoctoral fellowship, Academy of Finland and Tekniikan edistämissäätiö. S.N. acknowledges the award of a BOYSCAST fellowship from the Department of Science and Technology of the Indian Government. Computational resour- ces at the Centre de Calcul Midi-PyrØnØes are gratefully acknowl- edged. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.200805689. Communications 1970  2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2009, 48, 1970 –1973