Influence of Solvophobic Effects on Self-Assembly of Trimesic Acid at the Liquid-Solid Interface

Despite the multitude of surface supported monolayer structures already reported for trimesic acid (TMA), new self-assembled structures are still discovered, depending oil conditions and environment. This exemplifies the versatility of this archetypical supramolecular building block and justifies its role as a model system. At the interface between l-phenyloctane (PO), a highly nonpolar solvent, and graphite, a new densely packed and partly hydrogen-bonded TMA structure is observed by means of scanning tunnelling microscopy (STM). Normally, the TMA solubility in PO is too low to allow for self-assembly of interfacial monolayers. However, as verified by UV-vis spectroscopy, sonication of solutions with TMA sediment increases the amount of dissolved solute molecules. Consequently, the self-assembly of interfacial monolayers can be observed with these enriched solutions. In contrast to many other structures reported, the observed monolayers are densely packed and composed of partly hydrogen-bonded TMA molecules that form zigzag chains. The proposed structural model is derived from semiempirical quantum Chemistry methods, which also provide the basis for STM image simulations by means of it scattering formalism. Solvophobic effects are likely to account for both, low TMA solubility in PO and the high packing density of the interfacial monolayer.