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 self-assembly. 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.