Intramolecular Electron Transfer in Multi-Redox Systems Based on Cyclic [3]Spirobifluorenylene Compound

Area of Science:

• Organic Chemistry
• Materials Science
• Physical Chemistry

Background:

• Investigating electron transfer in π-conjugated systems is crucial for developing advanced molecular materials.
• Orthogonal π-conjugated chains present unique challenges and opportunities for charge transport.

Purpose of the Study:

• To design and synthesize a cyclic [3]spirobifluorenylene molecule with bulky alkyl groups.
• To investigate intramolecular electron transfer phenomena in a π-conjugated system with orthogonal chains.

Main Methods:

• Synthesis of cyclic [3]spirobifluorenylene (1).
• Characterization using absorption and fluorescence spectroscopy, electrochemical analysis, TD-DFT calculations, NTO calculations, and ESR spectroscopy.
• Chemical oxidation using SbCl5.

Main Results:

• Spiro-conjugation led to splitting of HOMO levels and a small SOMO-HOMO gap, facilitating intramolecular electron transfer.
• Electrochemical oxidation revealed interchain Coulombic repulsion.
• TD-DFT and NTO calculations visualized geometry-featured interchain electronic transitions.
• NIR absorption band exceeding 2000 nm attributed to intramolecular electron transfer.
• ESR experiments confirmed spin delocalization via hole hopping.

Conclusions:

• Spiro-conjugation is effective in bridging orthogonal π-conjugated units.
• This approach facilitates smooth intramolecular electron transfer, demonstrating potential for molecular wire applications.