Long-Lived C₆₀ Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Nanotechnology

Background:

• Fullerene C60 and its derivatives are crucial electron acceptors in molecular electronics, photovoltaics, and battery materials.
• The C60 radical anion (C60•⁻) is vital for these applications but suffers from a very short lifetime, limiting its study and use.
• Stabilizing reactive radical species is a significant challenge in chemistry and materials science.

Purpose of the Study:

• To dramatically stabilize the short-lived C60 radical anion (C60•⁻).
• To investigate the properties and potential applications of a stabilized C60•⁻ species.
• To develop a method for generating and detecting the stabilized C60•⁻ under ambient conditions.

Main Methods:

• Synthesis of a self-assembled M2L4 coordination cage using a triptycene-based ligand and Pd(II) cations.
• Encapsulation of C60 within the electron-deficient coordination cage.
• Photochemical one-electron reduction of encapsulated C60 using 1-benzyl-1,4-dihydronicotinamide.
• Characterization of the stabilized C60•⁻ using cyclic voltammetry, nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), UV-Vis-NIR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS).

Main Results:

• The coordination cage effectively binds C60, providing a complementary π-surface that stabilizes the fullerene.
• Cyclic voltammetry shows a positive potential shift for the reduction of encapsulated C60, indicating strong interaction with the cationic cage.
• Photochemical reduction successfully generated the C60 radical anion (C60•⁻) within the cage.
• The stabilized C60•⁻ exhibited an exceptionally long lifetime, detectable for over a month under an inert atmosphere.

Conclusions:

• A self-assembled coordination cage can dramatically stabilize the typically transient C60 radical anion (C60•⁻).
• The stabilized C60•⁻ demonstrates significantly enhanced longevity, opening avenues for its detailed investigation and practical application.
• This work presents a novel strategy for stabilizing radical anions within supramolecular structures for advanced materials.