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Hydrogen Bonding Versus van der Waals Interactions: Competitive Influence of Noncovalent Interactions on 2D Self‐Assembly at the Liquid–Solid Interface
Author(s) -
Mali Kunal S.,
Lava Kathleen,
Binnemans Koen,
De Feyter Steven
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201001653
Subject(s) - van der waals force , hydrogen bond , supramolecular chemistry , chemistry , crystallography , alkyl , lamella (surface anatomy) , chemical physics , monolayer , non covalent interactions , intermolecular force , molecule , crystal structure , materials science , organic chemistry , biochemistry , composite material
The structures of the self‐assembled monolayers of various 4‐alkoxybenzoic acids physisorbed at the liquid–solid interface were established by employing scanning tunnelling microscopy (STM). This study has been essentially undertaken to explore the competitive influence of van der Waals and hydrogen‐bonding interactions on the process of two‐dimensional self‐assembly. These acid derivatives form hydrogen‐bonded dimers as expected; however, the dimers organise themselves in the form of relatively complex lamellae. The characteristic feature of these lamellae is the presence of regular discommensurations or kinks along the lamella propagation direction. The formation of kinked lamellae is discussed in light of the registry mechanism of the alkyl chains with the underlying graphite substrate. The location of the kinks along a lamella depends on the number (odd or even) of carbon atoms in the alkyl chain. This result indicates that concerted van der Waals interactions of the alkyl chain units introduce the odd/even chain‐length effect on the surface‐assembled supramolecular patterns. The odd/even effects are retained even upon complexation with a hydrogen‐bond acceptor. However, as the solvent is changed from 1‐phenyloctane to 1‐octanoic acid, the kinked lamellae as well as the odd/even effects disappear. This solvent‐induced convergence of supramolecular patterns is attained by means of co‐crystallisation of octanoic acid molecules in the 2D crystal lattice, which is evident from high‐resolution STM images. The solvent co‐adsorption phenomenon is discussed in terms of competing van der Waals and hydrogen‐bonding interactions.