Electronically Stabilized Nonplanar Phenalenyl Radical and Its Planar Isomer

Area of Science:

• Organic Chemistry
• Materials Science
• Molecular Electronics

Background:

• Stable phenalenyl radicals are crucial for molecular electronics.
• Synthesizing electronically stabilized phenalenyls without steric shielding is challenging.

Purpose of the Study:

• To synthesize and characterize novel phenalenyl-type cations and their corresponding radicals.
• To investigate the properties of planar and helical phenalenyl systems.
• To compare these new compounds with a known large polycyclic hydrocarbon.

Main Methods:

• Synthesis of benzo[i]naphtho[2,1,8-mna]xanthenium (8(+)) and benzo[a]naphtho[8,1,2-jkl]xanthenium (9(+)).
• Characterization using X-ray crystallography, NMR, EPR, electrochemistry, and electronic spectroscopy.
• Computational methods to analyze aromaticity and properties.

Main Results:

• Successful synthesis and characterization of water-soluble phenalenyl cations 8(+) and 9(+).
• Radical 9 is the first stable, helical phenalenyl radical not requiring steric protection.
• Radicals exhibit stability for weeks at room temperature under air.
• Crystal structure of benzo[5,6]naphthaceno[1,12,11,10-jklmna]xanthylium (5(+)) reported for the first time.

Conclusions:

• Novel phenalenyl radicals offer promising avenues for molecular electronics.
• The helical phenalenyl radical 9 demonstrates a new strategy for stability.
• Aromaticity plays a key role in the distinct properties of these polycyclic systems.