Aromatic Saddles Containing Two Heptagons

Soluble derivatives of C70H26 (1a,b) and C70H30 (2a,b), two new saddle-shaped
polycyclic arenes containing
two heptagons, were successfully synthesized from saddle-shaped diketones
(3a,b), whose carbonyl groups are the key
in the reactions to extend the polycyclic π-framework. As found
from the crystal structures, the polycyclic backbone of 1b has a deep saddle shape, while that of 2b is even more
distorted because of the existence of two [4]-helicene moieties. On
the basis of crystal structures, local aromaticity and nonplanarity
of individual rings in the saddle-shaped π-backbone were analyzed,
and were found to follow Clar’s rule in general. It was found
that 1b and 3b behaved as p-type semiconductors
in solution-processed thin film transistors while the amorphous films
of 2b appeared insulating.