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Thiophene-Based Double Helices: Syntheses, X-ray Structures, and Chiroptical Properties
Sheng Zhang1, Xinming Liu2, Chunli Li1
1Engineering Research Center for Nanomaterials, Henan University , Kaifeng 475004, China.
Journal of the American Chemical Society
|July 22, 2016
Summary
Researchers efficiently synthesized conjugated double helical ladder oligomers using cyclooctatetrathiophene building blocks. These novel structures exhibit high stability and strong chirooptical properties, surpassing those of similar compounds.
Area of Science:
- Organic Chemistry
- Supramolecular Chemistry
- Materials Science
Background:
- Conjugated organic molecules are crucial for advanced materials.
- Developing novel helical structures with tunable properties remains a challenge.
- Cyclooctatetrathiophene (COTh) offers a unique saddle-shaped scaffold for molecular design.
Purpose of the Study:
- To demonstrate a facile and efficient method for constructing conjugated double helical ladder oligomers.
- To synthesize and characterize novel oligomers based on COTh building blocks.
- To investigate the chirooptical properties and racemization barriers of these helical structures.
Main Methods:
- Deprotonation of tetra[3,4]thienylene (β,β-COTh) with n-BuLi for selective coupling.
- Diastereoselective coupling of racemic precursors to form double helical ladder oligomers (rac-DH-1, rac-DH-2, rac-DH-3).
- X-ray crystallography for structural elucidation, chiral High-Performance Liquid Chromatography (HPLC) for resolution, and chirooptical measurements (CD, optical rotation).
Main Results:
- Successful synthesis of three racemic double helical ladder oligomers with varying numbers of COTh units.
- X-ray crystallography confirmed the intertwined double helical scaffold structure.
- Resolved enantiomers of DH-1-D exhibited strong chirooptical properties (g = -0.039) and a high racemization barrier (ΔG‡ > 48 kcal mol⁻¹).
Conclusions:
- A robust synthetic route to conjugated double helical ladder oligomers from COTh is established.
- These oligomers possess significant structural rigidity and high enantiomeric stability.
- The enhanced chirooptical properties suggest potential applications in chiral materials and molecular recognition.
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