Supramolecular self-assemblies of hexahydroxybenzene on Au(111).

Supramolecular self-assemblies with varied basic building blocks can be designed to host tailored topological symmetries and exotic properties. The first step toward functional supramolecules is to reveal the self-assembly mechanism on surfaces. Here, we report the molecular self-assembly of one of the simplest functionalized benzene molecules, hexahydroxybenzene, on the Au(111) surface studied by low temperature scanning tunneling microscopy. Besides the normal hexagonal phase, we observe a new square lattice. The intact gold herringbone structure after adsorption indicates the weak molecule-substrate interaction. According to the shared domain boundary between such two phases, the detailed molecular orientation and lattice location with hydrogen bonding can be deduced. Subsequent annealing can then convert these phases into a new molecular striped phase with a much smaller lattice constant. Our study here shows the rich structures when the self-assembly formation occurs at surfaces.