C2- and C1-Symmetric Configurationally Stable Pyrene-Fused [5]Helicenes Connected via Hexagonal and Heptagonal Rings.

In this paper, we describe the stereospecific synthesis and functional properties of C2- and C1-symmetric pyrene-fused [5]helicene molecules 1 and 2 connected via hexagonal and heptagonal rings, respectively. Both molecules showed high configurational stability and distinct functional properties, which were attributed to the fusing mode of [5]helicene with the pyrene and molecular symmetry. The estimated Gibbs activation energy for enantiomerization of 2 is one of the highest reported values for any π-conjugated molecules incorporating [5]helicene moiety.