Electron acceptors based on functionalizable cyclopenta[hi]aceanthrylenes and dicyclopenta[de,mn]tetracenes

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Polycyclic aromatic hydrocarbons (PAHs) are extensively studied for their unique electronic and optical properties.
• Developing novel PAHs with tailored functionalities is crucial for advanced materials applications.
• Externally fused PAHs offer unique structural and electronic characteristics compared to their internally fused counterparts.

Purpose of the Study:

• To synthesize and selectively functionalize novel externally fused cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs).
• To demonstrate the electron-accepting behavior of these synthesized CP-PAHs.
• To establish CP-PAHs as versatile building blocks for advanced organic electronic materials.

Main Methods:

• One-pot palladium-catalyzed cross-coupling reactions utilizing (trimethylsilyl)acetylene and dibrominated aromatic precursors.
• Selective bromination of trimethylsilyl-protected CP-PAHs using N-bromosuccinimide.
• Sonogashira cross-coupling reactions to introduce ethynyl substituents onto the CP-PAH core.
• Spectroscopic analysis (absorption spectra) and density functional theory (DFT) calculations to characterize electronic properties.
• Solution-phase fluorescence quenching experiments to assess electron-accepting capabilities.

Main Results:

• Successful synthesis of two novel CP-PAHs, 2,7-Bis(trimethylsilyl)cyclopenta[hi]aceanthrylene (1) and 2,8-bis(trimethylsilyl)dicyclopenta[de,mn]tetracene (4).
• Selective conversion of trimethylsilyl groups to bromides, yielding versatile cross-coupling partners (2 and 6).
• Sonogashira coupling produced highly conjugated ethynylated CP-PAHs (3 and 7) with significant bathochromic shifts.
• Ethynylated CP-PAHs 3 and 7 exhibited low optical bandgaps (1.52 and 1.51 eV) and demonstrated fullerene-like electron-accepting behavior.

Conclusions:

• Externally fused CP-PAHs can be effectively synthesized and selectively functionalized.
• The synthesized CP-PAHs possess tunable electronic properties, including low optical bandgaps.
• These CP-PAHs demonstrate promising electron-accepting capabilities, making them potential candidates for organic electronic applications.