B,N-Embedded Helical Nanographenes Showing an Ion-Triggered Chiroptical Switching Function.

Area of Science:

• Organic Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Carbazole derivatives are versatile scaffolds for developing advanced organic materials.
• Helical nanographenes offer unique electronic and optical properties due to their extended π-systems and chirality.

Purpose of the Study:

• To synthesize novel B,N-embedded helical nanographenes.
• To investigate the anion-binding properties of these nanographenes, particularly for fluoride ions.
• To explore the potential for chiroptical sensing based on ion recognition.

Main Methods:

• Intramolecular oxidative aromatic coupling to form fused carbazole structures.
• Borylation to introduce boron and nitrogen into the nanographene framework.
• Spectroscopic and crystallographic analyses to characterize the synthesized compounds and their complexes.
• Binding studies to determine anion affinity and selectivity.

Main Results:

• Successful synthesis of bis(m-terphenyl)-fused and bis(quaterphenyl)-fused carbazoles.
• Formation of a B,N-embedded helical nanographene capable of binding fluoride anions.
• Observation of a structural transformation from three-coordinate to four-coordinate boron upon fluoride binding.
• High binding constant (Ka = 1×10^5 M⁻¹) for fluoride anions, with charge stabilization over the expanded π-framework.
• Reversibility of the binding with Ag⁺ and demonstration of a chiroptical switch.

Conclusions:

• The developed B,N-embedded helical nanographenes are effective fluoride anion sensors.
• The ion-induced structural change and subsequent spectral alterations enable selective and sensitive detection.
• This work presents a new platform for developing responsive supramolecular materials and chiral sensors.