Differentiating π Interactions by Constructing Concave/Convex Surfaces Using a Bucky Bowl Molecule, Corannulene in Liquid Chromatography

Convex concave pi-conjugated surfaces in hemispherical bucky bowl such as corannulene (Cm) have shown increasing utility in constructing self-assembled new functional materials owing to its unique pi electrons and strong dipole. Here, we investigate these specific molecular recognitions on Cm by developing new silica-monolithic capillary columns modified with Cm and evaluating their performance in the separation of different aromatic compounds by liquid chromatography (LC). We synthesized two Cm derivatives and conjugated them onto the surface of a silica monolith. The first Cm derivative was edge functionalized, which can undergo free inversion of a convex-concave surface. The second Cm derivative was synthesized by modifying the spoke of Cm, which suppresses the convex-concave inversion. Results of LC suggest that each surface showed different shape recognition based on a pi interaction. Furthermore, the concave surface of Cm showed strong CH-pi interaction with a planar molecule, coronene, demonstrated by the shifts of the H-1 NMR signals of both Cm and coronene resulting from the multiple interactions between Cm and pi electrons in coronene. These results clearly demonstrated the presence of CH-pi interactions at multiple points, and the role of shape recognition.