Synthesis, Structures, and Properties of Heptabenzo[7]circulene and Octabenzo[8]circulene

• Published in: Journal of the American Chemical Society 2019-06, Vol.141 (24), p.9680-9686
• Main Authors: Pun, Sai Ho, Wang, Yujing, Chu, Ming, Chan, Chi Kit, Li, Yuke, Liu, Zhifeng, Miao, Qian
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b03910

This study puts forth two new members of fully ortho-benzannulated [n]­circulenes, heptabenzo[7]­circulene and octabenzo[8]­circulene, which are new negatively curved nanographenes and also represent unprecedented structures of septuple [4]­helicene and octuple [4]­helicene, respectively. The successful synthesis of them through Scholl reaction in good to excellent yields takes advantage of the reactivity of naphthalene. Quantum chemistry calculations reveal that heptabenzo[7]­circulene and octabenzo[8]­circulene are both flexible π-molecules and adopt saddle-shaped geometry of C 2 and D 2d symmetry, respectively, at the global energy minimum in agreement with the single-crystal structures. A serendipitous discovery from this study is that tetra­(tert-butyl) octabenzo[8]­circulene in the single crystals self-assemble into a supramolecular nanosheet with an unprecedented motif of π–π stacking. Such a new molecular packing mode, in combination with the demonstrated semiconducting property of octabenzo[8]­circulene, suggests a new supramolecular two-dimensional material.