Synthesis and Adsorption of Shape-Persistent Macrocycles Containing Polycyclic Aromatic Hydrocarbons in the Rigid Framework Xiaohong Cheng, †,# An Ver Heyen, ‡,# Wael Mamdouh, ‡,# Hiroshi Uji-i, ‡ Frans De Schryver, ‡ Sigurd Ho ¨ger,* ,§ and Steven De Feyter* ,‡ Institut fu ¨r Technische Chemie und Polymerchemie, Engesserstrasse 18, 76131 Karlsruhe, Germany, Department of Chemistry, Laboratory of Photochemistry and Spectroscopy, and INPACsInstitute of Nanoscale Physics and Chemistry, Katholieke UniVersiteit LeuVen, Celestijnenlaan 200-F, 3001 LeuVen, Belgium, and Kekule ´ -Institut fu ¨r Organische Chemie und Biochemie der UniVersita ¨t Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany ReceiVed August 9, 2006. In Final Form: October 31, 2006 Shape-persistent macrocycles with interiors in the nanometer regime were prepared by the oxidative cyclization of the appropriate bisacetylene precursors under high-dilution conditions. These compounds contain polycyclic aromatic hydrocarbons in the ring backbone and are decorated with extra annular oligoalkyl or silyl side groups. Interestingly, after depositing them on different surfaces and investigating the self-assembled structures by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), various nanostructures were observed. STM showed that these macrocycles are organized in two-dimensional (2D) layers, whereas AFM showed, in addition, the formation of 2D crystallites and one-dimensional fibrils. These results reveal the importance of the extra annular substitution of the macrocycles in creating patterned surfaces and nanoscale objects. Introduction During the past several years, the interest in rigid, well-defined structures with nanometer dimensions has continuously increased. In this context, cyclic structures play a special role. 1 On one hand, their lack of end groups makes them interesting candidates for the investigation of “end-group-free” oligomers. On the other hand, noncollapsible macrocycles contain an interior that is separated from the exterior, and, provided that they can be orthogonally modified, they are interesting molecular building blocks for constructing superstructures with a high degree of complexity. For example, nanotubular superstructures are ac- cessible by the one-dimensional (1D) organization of macrocycles when they are stacked on top of each other and the center-to- center offset is not too large. Therefore, the aggregation of macrocycles has been intensively investigated in the past few years. 2 Although several aspects of that issue are still not fully understood, basic principles for the structural design of mac- rocycles that aggregate are known. It is generally accepted that electron withdrawing substituents favor aggregation, whereas electron-donating as well as bulky substituents disfavor it. The aggregation is strongly solvent dependent and can be induced by solvophobic interactions. Additionally, the side groups of the macrocycle can increase the aggregation tendency. Nevertheless, the formation of discrete 1D aggregates from shape-persistent macrocycles without competing lateral aggregation is still challenging. 3 The organization of shape-persistent macrocycles in two dimensions has also been investigated for a limited number of systems. Sheet-like structures in the solid state are, in this connection, not representative since they display just a subunit of the bulk phase. 4 Pure two-dimensional (2D) organization is only found at an appropriate interface like the gas-liquid (especially air-water) or the liquid-solid interface. 5 Most of the investigations refer to the liquid-solid interface and highly oriented pyrolytic graphite (HOPG) in contact with an appropriate solvent that also contains the macrocycle. The investigation of the adsorbed molecules can then be performed by scanning tunneling microscopy (STM). Some STM images of shape- persistent macrocycles at the solvent-HOPG interface have been reported. 7 For a few examples, submolecular resolution allowed an exact determination of the orientation of the molecules relative to the HOPG layer underneath and even the visualization of different electronic states of the molecules. Recently, the use of * Corresponding author. Fax: (+49) 228-73-5662; e-mail: hoeger@ uni-bonn.de.(S.H.).Fax: ( +32)16-327-990;e-mail: Steven.DeFeyter@chem.kuleuven.be (S.D.). † Institut fu ¨r Technische Chemie und Polymerchemie. ‡ Katholieke Universiteit Leuven. § Kekule ´-Institut fu ¨r Organische Chemie und Biochemie der Universita ¨t Bonn. # These authors contributed equally to this work. (1) For recent reviews on shape-persistent macrocycles, see, e.g., (a) Moore, J. S. Acc. Chem. Res. 1997, 30, 402-413. (b) Ho ¨ger, S. J. Polym. Sci. Part A: Polym. Chem. 1999, 37, 2685-2698. (c) Haley, M. M.; Pak, J. J.; Brand, S. C. Top. Curr. Chem. 1999, 201, 81-130. (d) Grave, C.; Schlu ¨ ter, A. D. Eur. J. Org. Chem. 2002, 3075-3098. (e) Zhao, D.; Moore, J. S. Chem. Commun. 2003, 807-818. (f) Ho ¨ger, S. Chem.sEur. J. 2004, 10, 1320-1329. (g) Acetylene Chemistry, Diederich, F., Stang, P. J., Tykwinsky, R., Eds.; Wiley-VCH: Weinheim, Germany, 2005. 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