All Are Aromatic: A 3D Globally Aromatic Cage Containing Five Types of 2D Aromatic Macrocycles

14 July 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The studies on three-dimensional (3D) aromaticity have been mainly focused on fullerenes, boron-based deltahedrons/clusters, metal clusters and polyhedral hydrocarbons, but there are very limited researches on the fundamental aromaticity rule for 3D fully π-conjugated molecules. Herein, we report a π-conjugated molecular cage in which two aromatic porphyrin units are bridged by four thiophene-based arms. Two-electron chemical oxidation leads to a 3D globally aromatic cage with a C2 symmetry according to X-ray diffraction, NMR, electronic absorption spectra, and theoretical calculations. Detailed magnetic shielding response analysis along different axes reveal that all the possible five types of two-dimensional (2D) macrocycles in the cage skeleton are aromatic and follow Hückel rule. The switch from localized aromaticity to global aromaticity upon chemical oxidation is also observed in a tricyclic model compound. The study indicates that to attain 3D global aromaticity in a molecular cage, all the formally available π-conjugated macrocycles should be 2D aromatic.


molecular cage
3D aromaticity
Huckel rule

Supplementary materials

Supplementary Information
The full experimental details, characterization data, and theoretical calculation results can be found in the Supplementary Information.


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