Model systems are critical to our understanding of self-assembly processes. As such, we have studied the surface self-assembly of a small and simple molecule, indole-2-carboxylic acid (I2CA). We combine density functional theory gas-phase (DFT) calculations with scanning tunneling microscopy to reveal details of I2CA assembly in two different solvents at the solution/solid interface, and on Au(111) in ultrahigh vacuum (UHV). In UHV and at the trichlorobenzene/highly oriented pyrolytic graphite (HOPG) interface, I2CA forms epitaxial lamellar structures based on cyclic OH⋯O carboxylic dimers. The structure formed at the heptanoic acid/HOPG interface is different and can be interpreted in a model where heptanoic acid molecules co-adsorb on the substrate with the I2CA, forming a bicomponent commensurate unit cell. DFT calculations of dimer energetics elucidate the basic building blocks of these structures, whereas calculations of periodic two-dimensional assemblies reveal the epitaxial effects introduced by the different substrates.
Self-assembly of indole-2-carboxylic acid at graphite and gold surfaces
Present address: Central Analytical Research Facility (CARF), Institute for Future Environments, Queensland University of Technology, Brisbane, 4000 QLD, Australia.
Fabrizio De Marchi, Daling Cui, Josh Lipton-Duffin, Clara Santato, Jennifer M. MacLeod, Federico Rosei; Self-assembly of indole-2-carboxylic acid at graphite and gold surfaces. J. Chem. Phys. 14 March 2015; 142 (10): 101923. https://doi.org/10.1063/1.4908143
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