Stereochemical Effects in Supramolecular Self-Assembly at Surfaces: 1-D versus 2-D Enantiomorphic Ordering for PVBA and PEBA on Ag(111)

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• 作者：Johannes V. Barth ; Jens Weckesser ; Giancarlo Trimarchi ; Masha Vladimirova ; Alessandro De Vita ; Chengzhi Cai ; Harald Brune ; Peter Gü ; nter ; and Klaus Kern
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：July 10, 2002
• 年：2002
• 卷：124
• 期：27
• 页码：7991 - 8000
• 全文大小：538K
• 年卷期：v.124,no.27(July 10, 2002)
• ISSN：1520-5126

文摘

We present investigations on noncovalent bonding and supramolecular self-assembly of tworelated molecular building blocks at a noble metal surface: 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA)and 4-[(pyrid-4-yl-ethynyl)]benzoic acid (PEBA). These rigid, rodlike molecules comprising the samecomplementary moieties for hydrogen bond formation are comparable in shape and size. For PVBA, theethenylene moiety accounts for two-dimensional (2-D) chirality upon confinement to a surface; PEBA islinear and thus 2-D achiral. Molecular films were deposited on a Ag(111) surface by organic molecularbeam epitaxy and characterized by scanning tunneling microscopy. At low temperatures (around 150 K),both species form irregular networks of flat lying molecules linked via their endgroups in a diffusion-limitedaggregation process. In the absence of kinetic limitations (adsorption or annealing at room temperature),hydrogen-bonded supramolecular assemblies form which are markedly different. With PVBA, enantiomorphictwin chains in two mirror-symmetric species running along a high-symmetry direction of the substrate latticeform by diastereoselective self-assembly of one enantiomer. The chirality signature is strictly correlatedbetween neighboring twin chains. Enantiopure one-dimensional (1-D) supramolecular nanogratings withtunable periodicity evolve at intermediate coverages, reflecting chiral resolution in micrometer domains. Incontrast, PEBA assembles in 2-D hydrogen-bonded islands, which are enantiomorphic because of theorientation of the supramolecular arrangements along low-symmetry directions of the substrate. Thus, forPVBA, chiral molecules form 1-D enantiomorphic supramolecular structures because of mesoscopicresolution of a 2-D chiral species, whereas with PEBA, the packing of an achiral species causes 2-Denantiomorphic arrangements. Model simulations of supramolecular ordering provide a deeper understandingof the stability of these systems.