Deposition-Temperature- and Solvent-Dependent 2D Supramolecular Assemblies of Trimesic Acid at the Liquid–Graphite Interface Revealed by Scanning Tunneling Microscopy

Abstract

We investigated the self-assembly of trimesic acid (TMA) at the solution–graphite interface by using scanning tunneling microscopy (STM). We show that the polymorphism of the adsorbate structures of TMA can be controlled by the substrate temperature during the deposition of the molecules out of the solution for various solvents of different polarity. TMA was dissolved in phenyloctane, octanoic acid, and undecanol. At elevated substrate temperatures, various periodic assemblies of TMA could be obtained. By increasing the temperature of the preheated substrate, the specific 2D supramolecular network structure and the corresponding packing density can be precisely tuned in each kind of the solvents studied. The results found by STM are explained by the increased concentration of the solution at the preheated substrate as well as the higher mobility of the solute molecules increasing the opportunity of interactions between the molecules, in particular different hydrogen bonding motifs. Our interpretation is supported by simulations for each structure using the semiempirical quantum-chemical method PM6-DH+.

Bias-induced conformational switching of supramolecular networks of trimesic acid at the solid-liquid interface

“…In nonanoic acid, only the chickenwire structure and the filled chickenwire structure were reported. In a subsequent study, Hietschold et al 34 observed the flower structure in octanoic acid only after the HOPG substrate was heated up to temperatures between 40 • and 70 • C.…”

“…Upon cooling down of the sample, the reverse phase transition was observed. For TMA, Hietschold et al 34 reported that annealing the chickenwire structure in octanoic acid solution at temperatures between 40 • and 70 • C resulted in the formation of the flower structure (images were acquired at positive sample bias, and thus, a bias effect can be ruled out). From the above discussion, we hypothesize for the present case that the chickenwire structure is stabilized by solvent molecules and the flower structure is preferred over the chickenwire one from a thermodynamical point of view.…”

“…1), a planar molecule with 3-fold a) Author to whom correspondence should be addressed: m.a.stohr@rug.nl symmetry, which consists of three carboxyl groups (-COOH) attached to a central benzene ring, has been widely investigated at the solid-liquid interface. [28][29][30][31][32][33][34][35]41 Previous STM experiments at the solid-liquid interface for TMA on highly oriented pyrolitic graphite (HOPG) showed that the type of TMA structure that forms can be controlled by the solvent choice, [30][31][32]34 by the concentration of TMA in solution, 33,36 and by the temperature. 34 Furthermore, it was shown that the structure of TMA networks can be changed by the addition of metal nitrites to the TMA solution.…”

Ester formation at the liquid–solid interface

“…With respect to most of the structural parameters, the patterns correspond (see Table 1 ) to that observed for sonication and stirring. This type of preparation procedure has been previously reported and leads also to an increased concentration in the deposited solution due to enforced evaporation as well as to an increased mobility of the molecules [ 35 ].…”

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.…”