Synthesis and Characterization of Carbazole-Containing Aza[7]helicenes.

Area of Science:

• Organic Chemistry
• Materials Science
• Chiroptical Spectroscopy

Background:

• Azahelicenes are recognized for their inherent axial chirality and tunable chiroptical and chiral recognition capabilities.
• Developing efficient synthetic routes for complex azahelicene architectures remains a significant challenge in organic chemistry.

Purpose of the Study:

• To establish an efficient synthetic pathway for novel aza[7]helicene scaffolds.
• To characterize the structural, chiroptical, and photophysical properties of the synthesized compounds.

Main Methods:

• Double Suzuki coupling to form a diamine precursor from carbazole.
• Double ortho fusion reactions, including diazotization with intramolecular azo coupling or Morgan-Walls cyclization.
• X-ray diffraction (XRD) measurements and quantum chemical calculations for structural confirmation.
• Chiral High-Performance Liquid Chromatography (HPLC) for enantiomeric separation and Electronic Circular Dichroism (ECD) spectroscopy.

Main Results:

• Successful synthesis of two distinct aza[7]helicene scaffolds: 9H-dicinnolino[3,4-c:4',3'-g]carbazole and 9H-pyrrolo[2,3-k:5,4-k']diphenanthridine.
• XRD and computational studies confirmed the unique, screw-shaped geometries of the synthesized azahelicenes.
• Separated enantiomers of the pyrrolodiphenanthridine exhibited distinct ECD spectra.
• Both compounds demonstrated strong acidochromic behavior with visible orange light emission (up to 614 nm).

Conclusions:

• The developed synthetic route provides efficient access to complex azahelicene structures.
• The synthesized azahelicenes possess unique geometries and exhibit significant acidochromic properties, suggesting potential in chiral sensing and optoelectronic devices.
• Calculated singlet-triplet energies for dicinnolinocarbazole indicate potential for singlet exciton fission (SEF) applications.