A molecular Möbius strip that can flip between single-sided and double-sided modes has been synthesised by chemists in Poland without snapping the ring.
Lechoslaw Latos-Grazynski and his colleagues at the University of Wroclaw explain that for a molecule to be defined as aromatic it must exist as a near planar ring and have a pi electron system that allows for the free movement of electron pairs between alternating double and single bonds – the classic Hückel topology. Even rings that are twisted into a figure eight can have this topology. However, a molecule with a 180 degree twist has the Möbius topology and there is no distinction between the “upper and lower” pi electron cloud to give it the properties of aromaticity.
The team worked with an expanded porphyrin analogue – A,D-di-p-benzi[28]hexaphyrin(1.1.1.1.1.1) with a figure-of-eight shape having two phenylene six-membered carbon rings at the crossover point. Whether or not these rings are perpendicular or parallel dictates whether or not the molecule is Hückel or Möbius.
Finding molecules of this type are of fundamental importance to understanding molecular topology and aromaticity but the color change inherent in the flip might also allow the compound to be used as an indicator for the presence of other species in a solution, for instance.
You can read more about the study in the current issue of the SpectroscopyNOW.com ezine and see a blue-green morph of Prof Latos-Grazynski.