Global aromaticity at the nanoscale

Journal article

Aromaticity can be defined by the ability of a molecule to sustain a ring current when placed in a magnetic field. Hückel’s rule states that molecular rings with [4n + 2] π-electrons are aromatic, with an induced magnetization that opposes the external field inside the ring, whereas those with 4n π-electrons are antiaromatic, with the opposite magnetization. This rule reliably predicts the behaviour of small molecules, typically with fewer than 22 π-electrons (n = 5). It is not clear whether aromaticity has a size limit, or whether Hückel’s rule extends to much larger macrocycles. Here, we present evidence for global aromaticity in porphyrin nanorings with circuits of up to 162 π-electrons (n = 40); aromaticity is controlled by changing the constitution, oxidation state and conformation. Whenever a ring current is observed, its direction is correctly predicted by Hückel’s rule. The largest ring currents occur when the porphyrin units have fractional oxidation states.

Authors: Rickhaus, M; Jirasek, M; Tejerina, L; Gotfredsen, H; Peeks, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Springer Nature
• Journal: Nature Chemistry
• Publication date: 2020-01-20
• Acceptance date: 2019-11-20
• DOI: 10.1038/s41557-019-0398-3
• EISSN: 1755-4349
• ISSN: 1755-4330
• Language: English