Synthesis of a Hemispherical Geodesic Phenine Framework by a Polygon Assembling Strategy.

Area of Science:

• Supramolecular Chemistry
• Organic Synthesis
• Materials Science

Background:

• Phenine (1,3,5-trisubstituted benzene) units are fundamental building blocks for complex molecular architectures.
• Geodesic structures, inspired by carbon allotropes like C60, offer unique properties but are challenging to synthesize.
• Understanding structure-property relationships in large, discrete molecules is crucial for designing novel materials.

Purpose of the Study:

• To devise a synthetic strategy for constructing large, geodesic phenine-based molecular frameworks.
• To investigate the structural characteristics of the synthesized phenine molecule using spectroscopic and crystallographic methods.
• To elucidate the relationship between molecular dynamics and observed structural properties.

Main Methods:

• A convergent synthetic approach involving the assembly of phenine units around a central core.
• Nuclear Magnetic Resonance (NMR) spectroscopy for solution-phase structural characterization.
• X-ray crystallography for precise determination of the solid-state molecular structure.
• Theoretical calculations (e.g., density functional theory) to analyze molecular dynamics and conformational flexibility.

Main Results:

• Successful synthesis of a large C220H180 molecule with a phenine framework isoreticular to a segment of C60.
• Solution-phase NMR spectra suggested a hemispherical structure.
• Crystallographic analysis revealed an oval-like deformation of the molecule.
• Theoretical calculations indicated that dynamic fluctuations in biaryl torsion angles permit structural deformation and lead to a time-averaged hemispherical appearance in spectroscopy.

Conclusions:

• A novel synthetic route to complex geodesic phenine structures has been established.
• The synthesized molecule exhibits significant structural flexibility, deviating from a perfect hemisphere in the solid state.
• Dynamic conformational changes are responsible for the time-averaged hemispherical structure observed via NMR spectroscopy.
• This work highlights the importance of considering molecular dynamics when interpreting structural data of large, flexible molecules.