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

Abstract

Self-assembly of three related molecules – terephthalic acid and its hydroxylated analogues – at liquid/solid interfaces (graphite/heptanoic acid and graphite/1-phenyloctane) has been studied using a combination of scanning tunnelling microscopy and molecular mechanics and molecular dynamics calculations. Brickwork-like patterns typical for terephthalic acid self-assembly have been observed for all three molecules. However, several differences became apparent: (i) formation or lack of adsorbed monolayers (self-assembled monolayers formed in all systems, with one notable exception of terephthalic acid at the graphite/1-phenyloctane interface where no adsorption was observed), (ii) the size of adsorbate islands (large islands at the interface with heptanoic acid and smaller ones at the interface with 1-phenyloctane), and (iii) polymorphism of the hydroxylated terephthalic acids’ monolayers, dependent on the molecular structure and/or solvent. To rationalise this behaviour, molecular mechanics and molecular dynamics calculations have been performed, to analyse the three key aspects of the energetics of self-assembly: intermolecular, substrate–adsorbate and solvent–solute interactions. These energetic characteristics of self-assembly were brought together in a Born–Haber cycle, to obtain the overall energy effects of formation of self-assembled monolayers at these liquid/solid interfaces.

Quantifying the “Subtle Interplay” between Intermolecular and Molecule–Substrate Interactions in Molecular Assembly on Surfaces

“…The high-resolution STM image in Figure b shows that the TPA hydrogen-bonded monolayer structure developed on Cu(111) exhibits marked differences to those reported previously on other weakly interacting surfaces. − Dark spots can be observed in the TPA/Cu(111) lattice, highlighted by the blue circle in Figure b, which are only located between the carboxyl moieties. These darker regions are the result of molecules presenting a larger separation from one another along the dimeric hydrogen bonding direction; the molecular separation across these spots is 10.4 ± 0.4 Å (measured as the distance between the centers of two consecutive phenyl rings within the TPA chain), compared to the ∼9.7 Å typically found in hydrogen-bonded TPA chains on other surfaces (a summary of previously reported intermolecular separations in hydrogen-bonded TPA structures on different surfaces can be found in ref , ). On Cu(111), approximately 15% of the intermolecular separations within the hydrogen-bonded chains are elongated in this manner.…”

Probing Molecular Nanostructures of Aromatic Terephthalic Acids Triggered by Intermolecular Hydrogen Bonds and Electrochemical Potential

“…The few reports of TPA study by electrochemical STM (EC-STM) could be possibly due to the fact that TPA is almost insoluble in aqueous solution, making the ordered assembly and structural study in aqueous solution challenging. This explains why many TPA studies were mostly performed either under ultrahigh vacuum (UHV) conditions, − where TPA molecules can be evaporated on a surface through a vacuum chamber instead of directly assembling it from its aqueous molecular solution, ,, or in an organic solvent environment or ambient condition so that TPA can be assembled to solvent–substrate or air–substrate interfaces from an organic solution. ,, Despite the difficulty, Itaya group has reported the self-assembly of TPA on Pt(111) in electrolyte solution by EC-STM . If the number of carboxyl groups are continuously reduced to one, the ACA molecule become 1-benzenemonocarboxylic acid (benzoic acid, BZA).…”

“…10 To create the well-defined nanostructures on a surface, different strategies have been applied, including the variation of substrate or electrode materials such as gold (Au), 11 platinum (Pt), 12 silver (Ag), 13 copper (Cu), 10 palladium (Pd), 8 TiO 2 , 14,15 and highly oriented pyrolytic graphite (HOPG). 16 Even for the same materials, if the surface morphology is changed, the formed surface structures can be distinctively different. 17,18 The structures of individual "building blocks", molecules, are also essential in determining the self-assembly processes and outcomes.…”

Fluorinated carboxylic acids as powerful building blocks for the formation of bimolecular monolayers

“…TPA is a prototypical molecule used to study hydrogen-bond-controlled self-assembly, and its ability to form ordered homomolecular monolayers is well known. [22][23][24][25][26][27][28][29][30][31][32][33] As the homomolecular self-assembly of TPA (Fig. S1 and Fig.…”

“…S1 and Fig. S2) has been extensively studied at the heptanoic acid/highly oriented pyrolytic graphite (HOPG) interface, [22][23][24][25] we decided to investigate the assembly of F4TPA at the same interface. However, despite multiple attempts performed with a range of different solution concentrations, we never observed any evidence for the homomolecular self-assembly of F4TPA (see ESI †).…”