Big, strong, neutral, twisted, and chiral π acids

Area of Science:

• Supramolecular Chemistry
• Materials Science

Background:

• Anion-π interactions are crucial for molecular recognition, translocation, and transformation.
• Developing π-acidic surfaces with high π acidity for strong anion-π interactions is challenging due to decreased substituent impact on larger surfaces.

Purpose of the Study:

• To establish a general synthetic route to expanded π-acidic surfaces with variable size, topology, chirality, and π acidity.
• To overcome limitations in achieving high π acidity in expanded π systems.

Main Methods:

• Synthesized expanded π-acidic surfaces by coupling perfluoroarenes and naphthalenediimides (NDIs) fragments using single-atom sulfide bridges.
• Modified π acidity through oxidation of sulfide bridges to sulfoxides and sulfones, and peripheral fluorine substitution.
• Separated stereoisomers using chiral High-Performance Liquid Chromatography (HPLC) and characterized structures via X-ray crystallography.

Main Results:

• Achieved a wide range of Lowest Unoccupied Molecular Orbital (LUMO) levels from -3.96 to -4.72 eV, indicating tunable π acidity.
• Introduced stereogenic centers and planar chirality through sulfoxide bridges, leading to diverse topologies like chairs and π boats.
• Synthesized a π superacid with two sulfone moieties, reaching -4.72 eV, near the limit of existence.

Conclusions:

• The developed synthetic strategy provides access to a diverse chemical space of π-acidic surfaces.
• These novel π-acidic surfaces are promising for anion-π interactions and as electron transporters in conductive materials.