Symmetry-Directed Complex Tessellation of Irregular Polygons from a Single Molecular Precursor

Abstract

The construction of two-dimensional tessellations using irregular polygonal motifs remains a significant challenge in supramolecular chemistry, primarily due to the difficulty in achieving periodic ordering without intrinsic geometric regularity. Herein, we report the fabrication of molecular tessellations based on two irregular hexagons, highlighting the role of symmetry in the tiling of asymmetric building blocks. By precisely tuning the intramolecular hydrogen-transfer mediated reaction processes, three molecular superlattices are synthesized on a metallic substrate from a single fluorene-based precursor. Scanning tunneling microscopy (STM) measurements demonstrate that all three superlattices are assembled via Br-mediated hydrogen bonds, with building blocks adopting irregular hexagonal or decagonal geometries. Structural analysis indicates that one hexagon with mirror symmetry (Cs ) and one without intrinsic symmetry achieve tiling by dimerization (C2 symmetry) or hexamerization (C6 symmetry) under specific conditions. This work opens a route to constructing complex supramolecular architectures driven by geometric symmetry at the molecular scale.