The CNB structural feature of irreducible inner and outer faces can be extended to aromatic molecules with the topology of a Möbius strip, which is the simplest example of a non-orientable surface (Fig. ). Möbius-type molecules are found in nature and have been of interest in synthetic organic chemistry, as demonstrated by the first successful preparation of a non-conjugated Möbius-type double-stranded molecule by Walba and co-workers in 1982 (Fig. , left) . Aromatic single-stranded molecules with Möbius aromaticity were realized by Harges and co-workers in 2003 , and Möbius aromaticity was further investigated by Grażyński 26 and Osuka .