A Stable Carbon-Centered Radical Showing Six Amphoteric Redox States

Area of Science:

• Organic Chemistry
• Materials Science
• Spectroscopy

Background:

• Development of novel polyaromatic hydrocarbons (PAHs) is crucial for advanced materials.
• Stable organic radicals offer unique electronic and magnetic properties.
• Cyclopenta-fused PAHs represent an underexplored class of aromatic compounds.

Purpose of the Study:

• To synthesize and characterize a novel air- and moisture-stable hydrocarbon radical.
• To investigate the electronic structure and properties of a cyclopenta-fused polyaromatic hydrocarbon (CP-PAH).
• To explore the potential of Suzuki couplings and S_EAr reactions in constructing complex fused systems.

Main Methods:

• Multi-step synthesis involving ortho fusion of diphenylfluorene derivatives.
• Suzuki couplings and cyclizing S_EAr reactions for constructing the fused ring system.
• Characterization using Electron Paramagnetic Resonance (EPR) and UV/Vis spectroscopy, cyclic voltammetry, and X-ray crystallography.
• Quantum chemical calculations for electronic structure and simulated spectra.

Main Results:

• Successful synthesis of a stable hydrocarbon radical with a unique heptacycle fused structure.
• Mesityl substituents confer stability to the radical.
• EPR and spectroscopic data confirm the radical's structure, with the unpaired electron localized in the outer five-membered rings.
• Quantum chemical calculations reveal significant antiaromatic character in the five-membered rings and provide insights into electronic properties.
• Triradical character was found to be negligible.

Conclusions:

• A novel, stable cyclopenta-fused polyaromatic hydrocarbon (CP-PAH) radical has been synthesized and fully characterized.
• The study demonstrates the utility of specific synthetic strategies for creating complex fused aromatic systems.
• The electronic properties, including significant antiaromaticity in the fused five-membered rings, offer avenues for future materials design.