Square tiling by square macrocycles at the liquid/solid interface: co-crystallisation with one- or two-dimensional...

Area of Science:

• Supramolecular chemistry
• Surface science
• Materials science

Background:

• Macrocyclic compounds like pyridinophanes and cyclophanes are key in supramolecular chemistry.
• Understanding their self-assembly is crucial for designing advanced materials.
• Investigating bimolecular mixtures reveals complex interaction dynamics.

Purpose of the Study:

• To systematically investigate the self-assembly and mixing behavior of pyridinophane and cyclophane bimolecular mixtures.
• To elucidate the formation of ordered structures at liquid/graphite interfaces.
• To understand how molecular modifications influence co-crystal formation and dimensionality.

Main Methods:

• Scanning tunnelling microscopy (STM) was employed to visualize self-assembled monolayers.
• Tropylium ion was used as a marker for pyridinophanes.
• Analysis of seven distinct bimolecular mixtures with varying substituents.

Main Results:

• Formation of one- and two-dimensionally ordered square tilings through alternating macrocycle alignments.
• Observation of four distinct co-crystals with varying ordering dimensionality.
• Identification of attractive dipole-dipole and hydrogen-bonding interactions driving self-assembly.
• Demonstration that minor structural modifications drastically alter mixing behavior and co-crystal structures.

Conclusions:

• The study highlights the significant impact of subtle molecular structure changes on macrocycle self-assembly.
• Specific interactions between functional groups dictate the dimensionality and order of co-crystals.
• These findings provide insights for designing tailored supramolecular materials with predictable structures.