(Chiro)optical Properties of π-Extended Spiro-Double Carbo[7]helicene

Area of Science:

• Organic Chemistry
• Materials Science
• Nanotechnology

Background:

• Helical nanographenes are π-extended chiral nanocarbons with unique optoelectronic properties due to structural helicity.
• Chirality in carbon nanostructures is crucial for advanced electronic and optical applications.

Purpose of the Study:

• To synthesize and characterize a novel hexa-peri-hexabenzocoronene-based π-extended spiro-double carbo[7]helicene.
• To investigate the optoelectronic properties, including fluorescence and phosphorescence, of the synthesized molecule.
• To analyze the chiroptical properties and the origin of dissymmetry factors.

Main Methods:

• Synthesis of the π-extended spiro-double carbo[7]helicene.
• X-ray crystallography for structural confirmation.
• UV-Vis absorption, fluorescence, and phosphorescence spectroscopy.
• Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations.
• Chiral High-Performance Liquid Chromatography (HPLC) for enantiomer separation.

Main Results:

• Successful synthesis and X-ray crystallographic confirmation of the helical structure.
• Observation of thermally activated delayed fluorescence (TADF) at room temperature and phosphorescence at low temperatures.
• Resolution of enantiomers into three fractions (PP, MM, and meso forms) via chiral HPLC.
• Moderately high luminescence dissymmetry factor (g_lum) of 1.58 × 10⁻³ for pure enantiomers.

Conclusions:

• The synthesized spiro-double carbo[7]helicene possesses significant helical distortion and exhibits unique TADF and phosphorescence properties.
• The study provides insights into the relationship between molecular structure, chirality, and optoelectronic behavior in nanographenes.
• TD-DFT calculations successfully rationalized the observed dissymmetry factors by analyzing transition dipole moments.