Self-Assembly of Benzene-Dicarboxylic Acid Isomers at the Liquid Solid Interface: Steric Aspects of Hydrogen Bonding

We compare the self-assembly of the various isomers of benzene-dicarboxylic acids at the interface between solution and graphite substrate. In the case of planar benzene-dicarboxylic acids it was possible to observe long-range ordered monolayers by STM. However, no ordered adsorption was observed for the nonplanar 1,2-benzene-dicarboxylic acid. By means of a control experiment with 1,2,4,5-benzene-tetracarboxylic acid, it was possible to demonstrate that the nonplanar structure is not the decisive reason for the absence of selfassembly. In fact, the direct neighborhood of the two carboxylic groups in 1,2-benzene-dicarboxylic acid does not allow for extended hydrogen-bound aggregations. Thus, the stabilization due to intermolecular hydrogen bonding is too weak for STM investigations, at least at room temperature. It has been shown that a periodic, infinitely extendable hydrogen-bonding scheme is a requirement.