Protonation of meso-aryl [28]hexaphyrins(1.1.1.1.1.1) triggered conformational changes. Whereas protonation with trifluoroacetic acid led to the formation of monoprotonated Möbius aromatic species, protonation with methanesulfonic acid led to the formation of diprotonated triangular antiaromatic species. A peripherally hexaphenylated [28]hexaphyrin was rationally designed and prepared to undergo diprotonation to favorably afford a triangular-shaped antiaromatic species. Protonation of [28]hexaphyrins(1.1.1.1. 1.1) triggers conformational changes. Whereas protonation with trifluoroacetic acid leads to the formation of monoprotonated Möbius aromatic species, protonation with methanesulfonic acid leads to the formation of diprotonated triangular antiaromatic species. A peripherally hexaphenylated [28]hexaphyrin was rationally designed to undergo diprotonation to afford a triangular-shaped antiaromatic species. © 2014 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.