[5]Helicene-Embedded Cycloparaphenylene Nanohoops with Möbius Topology: Synthesis, Photophysical Properties, and...

Area of Science:

• Organic Chemistry
• Materials Science
• Theoretical Chemistry

Background:

• Möbius topology's relationship with aromaticity is poorly understood due to synthetic difficulties and limited examples.
• Existing Möbius systems lack diversity and quantity, hindering deeper investigation.

Purpose of the Study:

• To synthesize novel Möbius conjugated all-carbon nanohoops ([5]H-[7,8]CPPs) overcoming inherent strain.
• To investigate the photophysical and chiroptical properties of these new nanohoops.
• To explore the aromaticity of these systems under different electronic states.

Main Methods:

• Synthesis of [4n]Möbius conjugated all-carbon nanohoops using a [5]helicene unit.
• X-ray crystallography for structural elucidation.
• Photophysical and chiroptical spectroscopy (circular dichroism, circularly polarized luminescence).
• Theoretical calculations (DFT) to investigate electronic structure and aromaticity.

Main Results:

• Successful synthesis of [5]H-[7,8]CPPs exhibiting clear Möbius topology confirmed by X-ray analysis.
• [5]H-[7,8]CPPs show enhanced fluorescence quantum yields compared to parent compounds.
• Efficient chirality transfer from the [5]helicene moiety to the nanohoop was observed.
• Neutral [5]H-[7,8]CPPs display local Hückel aromaticity; dications exhibit global Hückel aromaticity, contradicting Heilbronner's prediction.

Conclusions:

• The study presents a new class of Möbius conjugated all-carbon nanohoops with tunable properties.
• The findings challenge established theories regarding Möbius topology and aromaticity, particularly in the context of 4n π-electron systems.
• This work provides a foundation for understanding the interplay between topology, chirality, and aromaticity in complex molecular architectures.