Cyclobishelicenes: Shape-Persistent Figure-Eight Aromatic Molecules with Promising Chiroptical Properties

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Chiroptical Spectroscopy

Background:

• Cyclobis[n]helicenes are chiral, D2-symmetric π-conjugated macrocycles.
• These molecules possess stable lemniscular (figure-eight) conformations.
• Understanding their conformational dynamics and chirality is crucial for molecular design.

Purpose of the Study:

• To investigate the conformational preferences of cyclobis[n]helicenes (n=3, 5).
• To determine the energy barriers for enantiomerization.
• To explore the chiroptical properties of resolved cyclobis[5]helicene enantiomers.

Main Methods:

• Computational conformational analysis of five cyclobis[n]helicene derivatives.
• High-Performance Liquid Chromatography (HPLC) for enantiomeric resolution.
• Characterization of chiroptical properties.

Main Results:

• Conformational analysis confirmed the exclusive existence of lemniscular conformers.
• High enantiomerization barriers (>200 kJ/mol) were determined, indicating conformational stability.
• Resolved cyclobis[5]helicene enantiomers exhibited unique chiroptical behavior.

Conclusions:

• Cyclobis[n]helicenes are conformationally locked in lemniscular forms.
• The inherent macrocyclic chirality dictates their observed chiroptical properties.
• These findings are significant for the development of chiral molecular architectures.