Spherical Congeners of Polyaromatic Compounds Approaching C20- and C60-Fullerene-Type Structures.

A series of three symmetric, hollow spherical, and shape-persistent molecular organic cages analogous to C20 and C60 were examined by computational modeling, analyzing structural elements, strain indicators, and physical properties relevant for potential applications. The compounds are covalent aromatic cages based on 1,3,5-substituted benzene nodes linked by para-phenylene or para-pyrenylene-connectors, with diameters varying from 2.3 to 4.2 nm. The apertures in the cage interior are varied by virtue of the cage type (C20- or C60-type cage) and the linear connectors placed between the C6H3-units. NBO and MESP analyses indicate the presence of electrophilic and nucleophilic sites in the molecular skeleton. In the cages with the phenylene-connectors, the HOMO-LUMO gaps are close to 4.0 eV. In the cage coated with an enlarged polyaromatic spacer (pyrene-unit), the gap is reduced by approximately 0.4 eV.