ORGN 332 |
| The design and synthesis of novel three-dimensional supramolecular materials based on the strategy of molecular tectonics have contributed to advances in the field of crystal engineering. The idea of using non-covalent interactions that are selective, well-oriented, and directional has been applied mostly in three dimensional structures. On surfaces, however, these concepts have not yet been fully exploited. In light of this fact, we have begun to probe the formation of two-dimensional (2D) supramolecular self-assembled molecular networks (SSAMNs) by scanning tunneling microscopy (STM). Nath et al. have recently demonstrated a cooperative adsorption process at the liquid-solid interface, involving self-assembly in which a three-fold hydrogen-bonding unit (trimesic acid, TMA) is directed into a linear tape pattern by non-covalent interaction with alcohols of varying lengths. Here we report on the formation and direct visualization of the self-assembly of 2D SSAMNs comprised of single-molecular tiles (tectons) in the liquid-solid interface by STM. Single molecules of pyrene-2,7-dicarboxylic acid were observed by time-elapsed STM to form a highly ordered, yet flexible 2D SSAMN, which is held together by hydrogen bonds and p-p interactions with the graphite surface. Further analyses of the network show layers and an intimate hydrogen-bonding interaction between four molecules of pyrene to form a tetramer, which exists within a disordered domain. These observations provide an understanding for the mechanism of crystal nucleation and crystal growth, which may help pave the way toward novel bottom-up strategies for the fabrication of supramolecular nanostructures.
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Molecular Recognition and Self-Assembly
1:00 PM-5:00 PM, Monday, 11 September 2006 Moscone Center -- Room 132, Oral
Division of Organic Chemistry |
