How do Nanohoops Exercise Their Strain in [5]Helicene Racemization?

Area of Science:

• Organic Chemistry
• Materials Science
• Physical Chemistry

Background:

• Strain in curved carbon nanohoops influences optoelectronic properties.
• The impact of strain on the dynamics and reactivity of nanohoops is under-explored.

Purpose of the Study:

• Investigate the effect of strain on the racemization of [5]helicene.
• Embed [5]helicene within cycloparaphenylenes of varying sizes (m=5-7) to study strain effects.

Main Methods:

• Synthesis and enantiomeric separation of strained helicene-paraphenylene macrocycles.
• Temperature-dependent racemization studies.
• Density Functional Theory (DFT) calculations.

Main Results:

• Configurational stability of [5]helicene increases with larger nanohoop size.
• Activation free energies for racemization ranged from 25 to 29 kcal mol⁻¹.
• A clear relationship between strain and racemization in helicene-embedded nanohoops was established.

Conclusions:

• Nanohoop size is a critical factor in controlling the configurational stability of embedded chiral molecules.
• Strain engineering in carbon nanohoops offers a pathway to tune molecular dynamics and reactivity.
• Experimental and computational methods successfully elucidated the strain-racemization relationship.