Helicene-Azulene Conjugates: Synthesis, Photophysical Properties and Proton-Induced Chiroptical Switching.

Area of Science:

• Organic Chemistry
• Photophysics
• Supramolecular Chemistry

Background:

• Helicenes are chiral aromatic compounds with unique electronic properties.
• Azulene derivatives are known for their distinct optical and electronic characteristics.

Purpose of the Study:

• To synthesize novel 4,13-dimethoxy-carbo[6]helicene derivatives incorporating azulene units.
• To investigate the photophysical and chiroptical properties of these new helicene-azulene compounds.

Main Methods:

• Chemical synthesis of helicene-azulene conjugates.
• Spectroscopic analysis (UV-Vis, fluorescence).
• Chiroptical measurements (Circular Dichroism).
• Theoretical calculations (DFT).

Main Results:

• Successful synthesis of two helical constitutional isomers: H-2-azu and H-6-azu.
• Observation of strong electronic circular dichroic responses in the azulene absorption region.
• Demonstration of reversible chiroptical switching upon protonation/deprotonation.
• Detection of weak S1 emission, adhering to Kasha's rule, which is uncommon for azulenes.
• Confirmation of acid-base triggered chiroptical switching with a notable red shift upon protonation.

Conclusions:

• The synthesized helicene-azulene derivatives possess unique photophysical and chiroptical properties.
• These compounds exhibit efficient and reversible chiroptical switching, particularly in response to acid-base stimuli.
• The observed emission properties are noteworthy and supported by theoretical insights, suggesting potential applications in responsive materials.