Synthesis, Resolution, Configurational Stability, and Properties of Cationic Functionalized [5]Helicenes

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Cationic [5]helicenes are complex chiral molecules with potential applications in various fields.
• Developing efficient synthetic routes and understanding their properties are crucial for their advancement.

Purpose of the Study:

• To achieve a straightforward synthesis of two distinct series of cationic [5]helicenes.
• To investigate the impact of peripheral functionalization and scaffold modification on their photophysical properties.
• To study the racemization kinetics of these helical compounds.

Main Methods:

• Synthesis of dioxa and nitrogen-containing [5]helicene series.
• Photophysical studies including UV-Vis absorption and fluorescence spectroscopy.
• Chiral high-performance liquid chromatography (HPLC) and variable-temperature HPLC (VT-HPLC) for racemization kinetics analysis.

Main Results:

• Successful synthesis of functionalized cationic [5]helicenes.
• Aryl substituents at position 23 showed negligible impact on optical properties.
• Styryl substituents extended conjugation pathways.
• Nitrogen incorporation led to a red shift in optical properties and efficient red fluorescence.
• Racemization kinetics were determined with activation energy barriers (ΔG‡) ranging from 85.0 to 137.1 kJ·mol⁻¹.

Conclusions:

• A versatile synthetic strategy for cationic [5]helicenes was established.
• Photophysical properties can be tuned through scaffold modification, particularly with nitrogen incorporation.
• Detailed kinetic data on racemization provide insights into the stability of these helical structures.