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Coplanar versus Noncoplanar Carboxyl Groups: The Influence of Sterically Enforced Noncoplanarity on the 2D Mixing Behavior of Benzene Tricarboxylic Acids

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journal contribution
posted on 29.10.2020, 17:38 by Robby Reynaerts, Andrea Minoia, Sai Manoj Gali, Lakshya Daukiya, Niels Van Velthoven, Dirk De Vos, Roberto Lazzaroni, Kunal S. Mali, Steven De Feyter
Hydrogen bonding is an indispensable tenet in the fabrication of surface-confined physisorbed supramolecular networks. On-surface supramolecular chemistry is dominated by aromatic carboxylic acids, which allow implementation of highly directional and robust design elements in the form of hydrogen bonds. In this article, we investigate the influence of sterically enforced noncoplanarity of the carboxyl groups on the hydrogen-bonding ability and the self-assembly behavior of iodinated benzene tricarboxylic acid at the solution/graphite interface. The carboxylic groups of this acid are noncoplanar with respect to the benzene ring because of the bulky iodine atoms substituted on the ring. The self-assembled networks formed at the solution–solid interface were characterized at submolecular resolution using scanning tunneling microscopy (STM). The assembly behavior was scrutinized further by employing detailed molecular modeling simulations that provide an insight into the energetics of the self-assembled network formation. The on-surface mixing behavior of the iodinated, and the noniodinated analogue, the widely studied trimesic acid, was investigated. STM reveals that deposition of the two compounds on the graphite surface leads to phase separation orthogonal to the substrate and yields a supramolecular heterostructure with a well-defined bilayer. The present results indicate that, while the noncoplanarity induced by steric factor is not detrimental to the assembly behavior, it certainly contributes to the peculiar mixing behavior observed at the solution–graphite interface.