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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.
Cheung et al. (Thu,) studied this question.