Fluctuating Carbonaceous Networks with a Persistent Molecular Shape: A Saddle-Shaped Geodesic Framework of 1,3,5-Trisubstituted Benzene (Phenine)

A saddle-shaped macromolecule has been synthesized. The molecule was designed as a geodesic saddle with 1,3,5-trisubstituted benzene (named phenine) as the fundamental unit. The phenines were woven into a polygonal framework that was composed of 168 sp(2)-hybridized carbon atoms. The saddle-shaped structure with unique symmetry showed atypical conformational changes. The biaryl linkages in this molecule had a small energy barrier for rotation, and these structural fluctuations resulted in seven H-1 NMR resonances representing 84 aromatic hydrogen atoms. Nevertheless, the overall saddle shape of the molecule was persistent, and the up and down orientations of phenine moieties circulated to give average H-1 resonances. The structural characteristics of this molecule, including the anomalous entropy-driven dimerization, may deepen our understanding of defect-rich graphitic sheets.