Symmetry-directed complex tessellation of irregular polygons from a single molecular precursor

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Surface Chemistry

Background:

• Constructing 2D tessellations with irregular polygons is challenging due to difficulties in achieving periodic order.
• Achieving ordered supramolecular structures often relies on geometrically regular building blocks.

Purpose of the Study:

• To report the fabrication of molecular tessellations using irregular hexagonal motifs.
• To investigate the role of symmetry in the tiling of asymmetric molecular building blocks.
• To demonstrate a method for constructing complex supramolecular architectures at the molecular scale.

Main Methods:

• Synthesis of molecular superlattices from a single fluorene-based precursor using intramolecular hydrogen-transfer.
• Characterization using Scanning Tunneling Microscopy (STM).
• Analysis of molecular geometries and assembly mechanisms.

Main Results:

• Three distinct molecular superlattices were synthesized on a metallic substrate.
• Assemblies are mediated by Br-hydrogen bonds, with building blocks forming irregular hexagonal and decagonal shapes.
• Tiling is achieved through dimerization (C2 symmetry) or hexamerization (C6 symmetry) of building blocks, influenced by their intrinsic symmetry (Cs or lack thereof).

Conclusions:

• Geometric symmetry plays a crucial role in the self-assembly of irregular molecular building blocks into ordered 2D tessellations.
• Precise control over intramolecular reactions and intermolecular interactions enables the formation of complex supramolecular architectures.
• This study provides a new strategy for designing and constructing sophisticated molecular materials based on symmetry principles.