Charge delocalization in self-assembled mixed-valence aromatic cation radicals

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Electrochemistry

Background:

• Aromatic molecules can form dimer cation radicals through spontaneous assembly with their neutral counterparts.
• These dimer cation radicals exhibit distinct spectral and electronic properties, including intervalence charge-resonance transitions and ESR signals.
• Understanding the charge delocalization and assembly behavior is crucial for developing novel electronic materials.

Purpose of the Study:

• To investigate the formation and properties of aromatic dimer cation radicals.
• To explore the relationship between molecular geometry and charge delocalization in these systems.
• To demonstrate the potential for creating higher-order assemblies for charge transport.

Main Methods:

• X-ray crystallography for structural analysis.
• Density Functional Theory (DFT) calculations for electronic structure.
• UV-Vis-NIR spectroscopy to characterize charge-resonance transitions.
• Electron Spin Resonance (ESR) spectroscopy.

Main Results:

• Confirmed complete delocalization of charge in representative dimer cation radicals.
• Established that monochromophoric cation radicals typically form 1D stacks.
• Demonstrated that polychromophoric cation radicals, like triptycene derivatives, can form 2D electronically coupled assemblies.
• Showed charge delocalization across all three rings in a triptycene cation radical.

Conclusions:

• Aromatic cation radicals can self-assemble into dimers with delocalized charges.
• Molecular design, particularly using polychromophoric systems, enables the formation of higher-dimensional assemblies.
• These findings pave the way for designing materials with tailored long-range charge transport properties.