Charging OBO-Fused Double [5]Helicene with Electrons

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Helicenes are chiral aromatic hydrocarbons with unique electronic properties.
• OBO-fused double helicenes represent a specific class with potential applications in molecular electronics.
• Understanding their redox behavior is crucial for designing new functional materials.

Purpose of the Study:

• To investigate the chemical reduction of OBO-fused double[5]helicene using alkali metals.
• To characterize the resulting reduced species and their structural arrangements.
• To explore the electronic consequences of charge incorporation within the helicene core.

Main Methods:

• Chemical reduction using Group 1 metals (Na and K).
• Isolation and structural characterization of doubly-reduced products via single-crystal X-ray diffraction.
• Theoretical calculations (computational chemistry) to analyze charge distribution.
• NMR spectroscopy to corroborate structural findings.

Main Results:

• Two distinct doubly-reduced products were isolated: a solvent-separated ion triplet (SSIT) with Na+ and a contact ion pair (CIP) with K+.
• X-ray crystallography revealed the structural consequences of electron addition, including increased helicene core twisting.
• Theoretical calculations confirmed negative charge localization at the central core, consistent with experimental data.
• The two-electron reduction of OBO-fused double[5]helicene was found to be reversible.

Conclusions:

• The reduction of OBO-fused double[5]helicene with Na and K leads to different ion pairing motifs (SSIT vs. CIP).
• Electron addition induces significant structural changes, notably increased twisting of the helicene backbone.
• The observed charge localization and the reversibility of the reduction are key findings for potential applications.