The Roles of Molecular Concavities in the Hierarchical Self-Assembly of Giant Tetrahedra for CO2 Uptake

Giant tetrahedral molecules have sparked significant interest in the past decade due to their unique and diverse supramolecular nanostructures. The longer and bulkier peripheral substituents create deep molecular concavities and thus contribute to the different self-assembly behaviors compared to the conventional small tetrahedral molecules. In this study, a molecular giant tetrahedra, TetraNDI, was synthesized to investigate the important roles of the molecular concavities in the self-assembly mechanism. Single-crystal structural characterizations indicate that the TetraNDI takes its trigonal concavities to form 1D supramolecular columns, and its tetragonal concavities to reach close inter-columnar packing. The difficulty in occupying the concavities leads to the path-dependent phase behaviors of the giant tetrahedra. It is also found that the remaining molecular concavities in the supramolecular scaffolds affect the CO2 affinity of TetraNDI. With an understanding of the packing principles of molecular giant tetrahedra, the structure-property relationships could be better evaluated in the future and might broaden the horizon of porous materials.