Tailoring Bond Topologies in Open-Shell Graphene Nanostructures.

Area of Science:

• Materials Science
• Organic Chemistry
• Nanoscience

Background:

• Polycyclic aromatic hydrocarbons (PAHs) possess diverse physicochemical properties influenced by size, edge, and bond topology.
• Open-shell PAHs, featuring unpaired electron densities, are crucial for organic electronics, spintronics, and optoelectronics but are difficult to synthesize in solution.
• Understanding the impact of molecular structure, particularly bond topology, is key to designing novel carbon-based nanomaterials.

Purpose of the Study:

• To report the on-surface synthesis of two ultralow-gap open-shell molecules.
• To investigate the electronic properties of these molecules using scanning tunneling microscopy and spectroscopy.
• To elucidate how altered bond topologies affect molecular properties at the single-molecule level.

Main Methods:

• On-surface synthesis of polycyclic aromatic hydrocarbons.
• Scanning tunneling microscopy (STM) for atomic-scale imaging and manipulation.
• Scanning tunneling spectroscopy (STS) for probing electronic properties.

Main Results:

• Successful synthesis of peri-tetracene, a zigzag-edged benzenoid graphene fragment.
• Successful synthesis of a nonbenzenoid, nonalternant isomer of peri-tetracene containing azulene units.
• Characterization of the distinct electronic properties arising from different bond topologies in these open-shell molecules.

Conclusions:

• The study demonstrates the feasibility of on-surface synthesis for complex open-shell PAHs.
• Altered bond topologies significantly impact the electronic properties of molecules at the single-molecule scale.
• Provides a pathway for designing functionalities in carbon nanostructures through precise control of molecular topology.