Kagome network from a single molecular building block

Kagome network from a single molecular building block
In the case of self-assembly on a silver surface, the analyzed porphyrin derivate is present in three different forms (represented by the three molecules at the bottom left). The formation of the complex Kagome network involves the orange and yellow conformations shown in the image. The hydrogen bonds vary depending on how the conformations bond to one another (as seen between two silver-colored hydrogen atoms in the magnified section). In the isolated molecules (pink), the side groups have a different configuration.

Complex structure produced by self-assembly of porphyrin derivate

Researchers from the Center of Photon Science at PSI and the Swiss Nanoscience Institute have shown that copies of a single molecular building block can spontaneously form a complex supramolecular structure on surfaces. The studied porphyrin derivate arranges itself as individual molecules, in short chains or as a complex Kagome network on a silver surface. In each of these three roles, the molecule adopts a different conformation. The results are an example of how self-assembled molecular structures can form complex structures from a single or few components at interfaces. Complexity emerging in the balance of different forces at surfaces and interfaces is a general phenomenon. In the primordial atmosphere for example, adaptable molecular structures with similarly flexible units may have contributed to the origin and emergence of biochemical processes and systems.

Self-assembly of molecules at surfaces and interfaces is one of the most fascinating phenomena occurring on the nanometer scale. With no outside intervention, various interactions cause different molecules to arrange themselves into specific patterns and structures. The molecules were designed “on the drawing board” in collaboration with Dr. Jonathan Hill before being synthesized by Hill at the National Institute of Materials Science in Tsukuba (Japan). The PSI and University of Basel Team has used scanning tunneling microscopy to investigate the self-assembly of a flexible porphyrin derivate (5,10,15,20-Tetrakis(3,4,5-trimethoxyphenyl)porphyrin, TTMPP). The researchers then identified three different conformations of the molecules existing alongside one another on a silver surface — isolated as a single molecule, in short chains and in the form of a complex Kagome network. This network featured an alternating pattern of triangles and hexagons made up of the molecules.

The Kagome structure occurs due to an interplay between many different interactions. Although the molecules are bound to one another by very weak hydrogen bonds, these bonds are strong enough as a whole to produce conformational changes in the molecules for the molecules to assume different roles in the network. Another key factor includes interactions between the molecule and the surface. TTMPP also assembles itself into complex patterns on gold, confirming that the molecular properties are responsible for the pattern's formation at interfaces.

Original Publication: 
S.F. Mousavi, A. Ahsan, T. A. Jung, J. Hill et al., Emergence of conformational diversity and complexity of supramolecular structure by the interaction of a simple molecule with a uniform surface Communications Chemistry (2025) https://doi.org/10.1038/s42004-025-01607-x

News Release of the Swiss Nanoscience Institute:

https://nanoscience.unibas.ch/en/news/details/kagome-netzwerk-aus-einze…