Aromaticity of Hückel and Möbius Topologies Involved in Conformation Conversion of Macrocyclic [32]Octaphyrin(1.0.1.0.1.0.1.0): Refined Evidence from Multiple Visual Criteria

A comprehensive investigation of the aromaticity control process of expanded porphyrins was carried out using a variety of visual criteria for the first time. The results show that the indicators based on magnetic property can be used to inspect the global aromaticity of [32]octaphyrins(1.0.1.0.1.0.1.0), whereas the methods according to electronic (de)localization are more suitable for the assessment of local aromaticity. The quasiplanar Hückel molecules with 32 π-electrons are shown to be distinctly antiaromatic, which follows the conventional 4n antiaromaticity Hückel's rule. The distortion of the molecular skeleton leads to weakening of π-conjugation in macrocycles, making the single-sided Möbius topologies with the same number of π-electron exhibit weak aromaticity. The seriously twisted figure-eight Hückel species are proved to be almost nonaromatic. These results agree well with our previous conclusions on aromaticity characteristic of the same system deduced from some numerical indexes. It is suggested necessary to extract evidence from multiple visual indicators for systematical analysis of the molecular aromaticity.