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Ph
Ph
Ph
Ph
Ph
113
Ph
Fig. 32 Structure of hexaphenyltetrabenzo[ a , c , l , n ]pentaacene 113 [ 97 ]
5.3 Highly Substituted Higher Acenes
Several highly substituted higher acenes with high degrees of end-to-end twists
have been reported. Octaphenyldibenzo[ a , c ]naphthalene 6 shows a 105 twist [ 14 ]
and hexaphenyltetrabenzo[ a , c , l , n ]pentaacene 113 (Fig. 32 ) has the largest twist
reported so far at 143.6 [ 97 ]. The enantiomers of 113 were resolved with very large
specific rotations of
150 ,
resembling those of helicenes. The activation barrier for racemization is
23.8 kcal/mol, which corresponds to a half-life of 9 h at room temperature.
] D 25
+7440
150
] D 25
7420
[
a
¼
and [
a
¼
6 Conclusions and Outlook
Synthetic methods have been developed to prepare twisted polyarenes with
diverse structural features. A large number of X-ray structures have been
reported, allowing direct measurements of the extent of distortion from planarity.
However, the use of these twisted compounds for synthetic applications remains
underdeveloped. While limited success has been achieved in using optically
active twisted polyarenes as catalysts for asymmetric induction, a systematic
study of this potentially fruitful area has not been undertaken. Molecular recogni-
tion is another area that is still in its infancy. Optical and electronic properties
have not been exploited. However, there isnoreasontobelievethatthechemistry
of twisted polyarenes will not be as fruitful in the future as has been observed over
the past 70 years. Because the future direction of the development of this
fascinating class of compounds can barely be imagined, success can come from
a wide variety of areas.
Acknowledgments The author thanks Professor Jeffrey L. Petersen for his assistance in
obtaining several X-ray structures and the structural information given in this chapter. The
financial support of the National Science Foundation (Grant CHE-0909613) is gratefully
acknowledged.
 
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