Fractal Chiral Organic Molecular Cages

Abstract

Abstract Mimicking the intricate hierarchical superstructures of biological macromolecules in organisms, evolving organic molecular cages (OMCs) into higher-level chiral OMC with fractal superstructures presents an extremely challenging task. Herein, we utilized 2D tri-bladed propeller shaped triphenylbenzene (TPB) as building blocks to synthesize a racemic 3D tri-bladed propeller shaped helical molecular cage (TMC) that can be furthermore used as building blocks to construct a pair of higher-level 3D tri-bladed chiral helical molecular cages 4P-HTMC and 4M-HTMC with multilayer sandwich structures, and display elegant fractal characteristics with self-similarity in a discrete superstructure at different levels. During the evolutionary procession of the higher-level cages HTMC, the intramolecular self-shielding effect and exclusive chiral narcissistic self-sorting behaviors were observed. Moreover, the enantiomers 4P-HTMC and 4M-HTMC can be interconverted by introducing an excess of corresponding chiral cyclohexanediamine (CHDA). In solid state, 4P-HTMC and 4M-HTMC can also self-assemble into supermolecule architectures of L-helical or D-helical nanofibers. Therefore, the scale transformation of chiral characteristics from chiral atoms (chiral carbon atoms in CHDA) to microscopic (trihelical in advanced cages) and then to mesoscopic (spiral of nanofibers) has been realized.