This journal is c The Royal Society of Chemistry 2011 Chem. Commun., 2011, 47, 7995–7997 7995 Cite this: Chem. Commun., 2011, 47, 7995–7997 Surface-assisted bowl-in-bowl stacking of nonplanar aromatic hydrocarbonswz Tobias Bauert, a Kim K. Baldridge,* b Jay S. Siegel* b and Karl-Heinz Ernst* ab Received 30th April 2011, Accepted 1st June 2011 DOI: 10.1039/c1cc12540k Bowl-in-bowl stacking of buckybowls on a copper surface is observed via scanning tunneling microscopy (STM) at low temperatures and characterized by density functional theory (DFT) calculations. Modification of surfaces with aromatic organic molecules is the key approach to new materials for organic photovoltaics (OPV), organic light-emitting devices (OLEDs), and molecular electronics such as organic field effect transistors (OFETs). 1 The interfaces between active layers and electrodes influence the electronic and optical properties as well as the device performance. 2 Furthermore, because the spatial extent of the molecular wavefunctions is rarely isotropic, the relative orientation of the molecules in the film, and thereby the degree of overlap of the frontier orbitals, will play an important role in determining film properties. 3 Bowl-shaped polynuclear hydrocarbons offer a special opportunity in this arena owing to their substantial dipole moment, large conjugated network and shape complementarity. Corannulene (C 20 H 10 , Fig. 1a, 1), a C 5n -symmetric, bowl- shaped fragment of C 60 is a polynuclear aromatic hydrocarbon with a surface area comparable to that of pyrene. The bowl shape of 1 suggests columnar aggregation, resembling stacked bowls in a cupboard; although derivatives can be engineered to obtain such stacking, the parent 1 packs in the crystal phase without displaying any columnar order. 4 The ability to induce columnar order in 1 combined with a large p surface area of interaction suggests that materials based on 1 should display exceptional photophysical and electro- chemical properties. 5 Indeed, the intense blue-light electro- luminescence, recently reported for 1, 6 and the excellent electron acceptor ability, shown by the formation of a quadruple anion of 1 complexed with lithium, 7 makes 1 and its derivatives promising candidates for applications such as OLEDs and high energy density carbon electrodes in Li batteries. Modification of metal surfaces with 1 and its derivatives has attracted interest previously with regard to fundamental stereochemical issues like symmetry-mismatch between substrate and molecules, 8 bicomponent packing, 9 2D packing strategies of fivefold-symmetric molecules, 10 and 2D phase transitions. 11 Previous work on Cu(110) shows that 1 acts as a host for C 60 , only after thermal activation. 12 Herein, two-dimensional (2D) arrays of 1 and of pentamethylcorannulene, C 20 H 5 (CH 3 ) 5 (2), 13 deposited on a Cu(111) surface, template bowl-in-bowl complexation at low temperatures and display densely packed second layers in that configuration. Compounds 1 and 2 were synthesized as described previously. 14,15 The copper(111) surface has been prepared in vacuo following standard procedures (see ESI for more experimental detailsz). 16 Fig. 1 presents two STM images of a half-filled 2nd layer of 1 on top of the low-temperature 2D (4 2, 0 7)y polymorph of 1 on Cu(111). 11 The lines in Fig. 1c reveal epitaxial growth, i.e., the molecules in the 2nd layer possess the same (4 2, 0 7) periodicity. In addition, they show that the individual 2nd layer molecules are located directly above the 1st layer molecules. The orientation of molecules of the yet uncovered 1st layer still show the original STM appearance, with a tilt of the molecule on the surface (see ESI-Fig. 1z). 11 DFT-GGA calculations predict that tilt comes from one of the five outer C-6 rings being oriented parallel to the surface and located either over a three-fold hollow hcp or fcc site. 11a,17 The orientation of 1st layer molecules covered by the 2nd layer remains the subject of Fig. 1 (a) Ball-and-stick models for 1. (b,c) STM images of a half- filled 2nd layer of 1 (28 nm  28 nm and 10 nm  10 nm, À1.74 V, 24 pA, 50 K). The yellow lines along high-symmetry directions of the ad-lattice reveal ‘‘on-top’’ ad-sites in the second layer with identical lattice periodicity. a Empa, Swiss Federal Laboratories for Materials Science and Technology, U ¨ berlandstrasse 129, CH-8600 Du ¨bendorf, Switzerland. E-mail: karl-heinz.ernst@empa.ch; Fax: +41 58 765 4034; Tel: +41 58 765 43 63 b Organic Chemistry Institute, University Zurich, CH-8057 Zu ¨rich, Switzerland. E-mail: jss@oci.uzh.ch, kimb@oci.uzh.ch; Fax: +41 44 635 6888; Tel: +41 44 635 4281 w This article is part of the ChemComm ‘Molecule-based surface chemistry’ web themed issue. z Electronic supplementary information (ESI) available: STM image of the (4 0, 2 7) structure, HOMO orbitals of the stacks and experimental and computational methodology. See DOI: 10.1039/c1cc12540k ChemComm Dynamic Article Links www.rsc.org/chemcomm COMMUNICATION Downloaded by University of Zurich on 13 October 2011 Published on 20 June 2011 on http://pubs.rsc.org | doi:10.1039/C1CC12540K View Online