Expanded Porphyrin with a Split Personality: A Hückel–Möbius Aromaticity Switch

Dual identity: It takes a single phenylene twist to reveal the dichotomous nature of a di-para-benzihexaphyrin (see picture; phenylene rings highlighted in red). This expanded porphyrinoid switches between Hückel and Möbius topologies in an unusual solvent- and temperature-dependent equilibrium. Each of the two incarnations of the macrocycle has its own unmistakable spectral signature.