Emergence of conformational diversity and complexity of supramolecular structure by the interaction of a simple molecule with a uniform surface.

The emergence of complexity during self-assembly of simple molecular building blocks is an important aspect in the synthesis of nanoarchitectures from supramolecular functional units. In particular, two-dimensional nanostructures are important from the point-of-view of technological applications. Here, a remarkably complex on surface network is observed to form spontaneously from a single molecular module (porphyrin) having multiple site-specific conformations. The interplay of different physicochemical interactions at the surface contributes to the site-specific symmetry breaking of the porphyrin conformation, and was investigated at different substrates. Molecular conformational flexure, relocation in the corrugated surface potential, interactions with surface state electrons, and last but not least mutual intermolecular binding by hydrogen bonding at different elevations above the substrate are critical elements. We discuss the possibility of surfaces and interfaces causing quasidegeneracy of molecular configurations in supramolecular self-assembly, and the adsorbate-adsorbent interface as the driver for this system to behave counterintuitively to equilibrium thermodynamics.