Modulation of Koelsch Radical Stability and Aromaticity through Nonhexagonal Ring Fusion

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Koelsch radicals are known for their stability and redox properties.
• Engineering π-conjugated systems is crucial for developing functional organic materials.
• Incorporating non-planar or strained rings can significantly alter electronic properties.

Purpose of the Study:

• To synthesize and characterize a novel fused Koelsch radical derivative with a seven-membered ring.
• To investigate the impact of incorporating a heptagon on the molecule's redox behavior and aromaticity.
• To explore the potential for topology-based design of functional molecules with multiple persistent redox states.

Main Methods:

• Organic synthesis of the fused Koelsch radical derivative.
• Electrochemical characterization to determine redox potentials.
• Spectroscopic analysis (e.g., 1H NMR) and quantum chemical calculations to probe electronic structure and aromaticity.

Main Results:

• Successfully synthesized and characterized a Koelsch radical derivative with an integrated seven-membered ring.
• Generated and identified three persistent redox states: cation, neutral radical, and anion.
• The neutral radical exhibited lower stability compared to the parent Koelsch radical due to a lower oxidation potential.
• Tropylium-type 14π-aromatic stabilization in the seven-membered ring and tropylide-type 8π-antiaromaticity in the anion were confirmed.

Conclusions:

• The incorporation of a seven-membered ring into the Koelsch radical framework enables access to multiple stable redox states.
• Aromatic stabilization effects within the seven-membered ring play a critical role in tuning the redox potentials and stability.
• This study provides a foundation for designing novel functional molecules by controlling topology, conjugation, and charge delocalization.