Hydrogen Bonding Versus van der Waals Interactions: Competitive Influence of Noncovalent Interactions on 2D Self‐Assembly at the Liquid–Solid Interface

Abstract

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.

Two-dimensional self-assemblies of telechelic organic compounds: structure and surface host–guest chemistry

“…In addition, two-dimensional crystallization energy resulting from van der Waals forces between long alkyl chains can induce full interdigitation of alkyl chains and leads to the densely packed lamellar structures on surfaces [18]. Owing to the inherent conformation flexibility of alkyl chains, the interesting structural evolution of functional molecule homologues decorated with alkyl chains with different lengths has been observed in a number of systems [13][14][15][16].…”

“…Non-covalent bond interactions between molecules are mainly responsible for the formation of perfectly ordered supramolecular structures on surfaces [13][14][15]. Non-covalent bond interactions, for instance van der Waals forces [16][17][18][19][20], hydrogen bonds [21][22][23][24], π -π stacking interactions [25,26], dipole-dipole interactions [27][28][29] and electrostatic interactions [30,31] between functional groups in organic molecules, play an important role in the self-assembly process.…”

Cross-impact of surface and interaction anisotropy in the self-assembly of organic adsorption monolayers: a Monte Carlo and transfer-matrix study

“…This attractive interaction is negligible compared to the interaction between the functional groups. Examples of such systems include adsorption layers of alkoxybenzoic acids, 59 mono-functional derivatives of anthracene, 61 porphyrin and phthalocyanine. 12,19,20,[62][63][64][65] As seen in Fig.…”

“…The size of the functional groups and side substituents of the adsorbed molecule is either smaller than or commensurate with the size of their cores. Examples of such systems include the adsorption layers of amino acids, 7,23,58 alkoxybenzoic acids, 59 functional derivatives of benzene, 23 naphthalene and other bicyclic and more complicated organic molecules 22,23,60 such as anthracene, 61 porphyrin and phthalocyanine. 12,19,20,[62][63][64][65] It is important to stress that all the above mentioned molecules have a single functional group capable of forming a hydrogen bond.…”

Molecular self-assembly of substituted terephthalic acids at the liquid/solid interface: investigating the effect of solvent

“…10 In particular, by confining the selfassembly process on solid substrates, two-dimensional (2D) structures can be formed 11,12 by exploiting a number of different intermolecular forces: from metal coordination 13,14 to hydrogen bonding 14,15 , to weaker dispersion interactions. 16 While the nature of the interactions between the molecular units is typically the key factor in determining the resulting assembly, other more subtle influences have also been reported to affect the final supramolecular structures: the chemistry and symmetry of the substrate (even for inert surfaces such as highly ordered pyrolytic graphite (HOPG) and Au(111) 17 ), the temperature, [18][19][20] the ultra-high vacuum (UHV) or solution environment, 19,21,22 the nature of the solvent, 19,[23][24][25][26][27][28] the concentration of the solute (the self-assembling molecule), 18,[29][30][31][32][33][34][35] and any co-adsorption of solvent or guest molecules 24,25,34,36,37 . The possibility of controlling supramolecular polymorphism by weak intermolecular interactions, such as interactions with the solvent, is a new and fascinating approach to the ultimate goal of rationally programming molecular self-assembly.…”