Hydrogen-Bond-Assisted Supramolecular Assembly of 1,3,5-Tris(5-carboxyamyloxy)Benzene at the Liquid–Solid Interface: An Scanning Tunneling Microscopy Study

The well-ordered self-assembled structure of 1,3,5-tris(5-carboxyamyloxy)benzene (TCAB) on Au(111) has been studied by electrochemical scanning tunneling microscopy (ECSTM) in HClO₄ solution. Close examination indicates that the complex supramolecular network is formed by the TCAB molecules with flat-lying adsorption geometry and mainly stabilized by the hydrogen bonding interactions between carboxyl groups, except for the molecule-substrate interactions. It is particularly noteworthy that two types of hydrogen bonds, the dimers and tetramers of carboxyl group, coexist at the interface to balance the molecule–molecule and molecule-substrate interactions as well as to minimize the surface energy. Interestingly, the propeller-like motifs in STM image are fabricated by the bent alkoxy chains from four neighboring molecules respectively, bonded together by the cyclic carboxyl group tetramers. Moreover, there are two propellers in one lattice of TCAB adlayer, rotating in the clockwise and counterclockwise directions, respectively. Careful inspection shows that two structure domains of the TCAB adlayer are mirror images of each other since the molecular self-organization breaks the reflection symmetry of the substrate underneath. Our results give a good example of the flexibility adopted by alkyl chains functionalized by carboxyl group for the supramolecular assemblies at the liquid–solid interface.