π-Enlargement in Porphyrin Macrocycles at Interfaces

Area of Science:

• Supramolecular Chemistry
• Surface Science
• Materials Science

Background:

• Porphyrins are vital macrocycles in biology and technology, with applications in sensing, catalysis, and energy.
• Current research focuses on modifying porphyrin structures in solution to tailor their properties.
• On-surface synthesis offers a unique platform for creating novel molecular architectures.

Purpose of the Study:

• To develop a pioneering strategy for tailoring porphyrin macrocycles at interfaces.
• To expand an 18-π porphyrin into a 20-π system using on-surface covalent synthesis.
• To investigate the properties and coordination behavior of the resulting expanded porphyrin.

Main Methods:

• Deposition of a functionalized porphyrin precursor onto a hot Ag(111) surface.
• Utilizing scanning probe microscopy and spectroscopy for characterization.
• Employing density-functional theory calculations for theoretical validation.

Main Results:

• Successful formation of a 20-π free-base expanded porphyrin at the interface.
• Observation of potential high antiaromaticity due to preserved planar conformation.
• Achieved a narrow bandgap of approximately 0.2 eV.
• Demonstrated cobalt coordination, forming a unique two-fold coordination node.

Conclusions:

• On-surface engineering enables the creation of expanded porphyrins with tailored electronic properties.
• The developed method allows for enhanced antiaromaticity and narrow bandgaps in porphyrin systems.
• This work highlights the potential of surface science in exploring novel macrocyclic architectures and coordination motifs.