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.
This study presents a new type of negatively curved nanographene (C H ) that contains an unprecedented pattern of heptagons. A tert-butylated derivative of C H was successfully synthesized using tetrabenzodipleiadiene as a key building block. This synthesis involved a ring expansion reaction as a key step to form the seven-membered rings in the framework of tetrabenzodipleiadiene. The single-crystal structure reveals a saddle-shaped molecule with a highly bent naphthalene moiety at the center of the polycyclic backbone. As found from the DFT calculations, this aromatic saddle is flexible at room temperature and has a saddle-shaped geometry as the dominant conformation. The DFT calculations along with experimental results show that the attachment of t-butyl groups to the central tetrabenzodipleiadiene moiety of nanographene C H can stabilize the saddle conformation and make this nanographene less flexible.
Herein we report synthesis, structure and properties of a new type of twisted nanographene, which contains an [8]circulene moiety in a polycyclic framework of 96 sp carbon atoms. The key steps in this synthesis are the Diels-Alder reaction of a macrocyclic diyne and the subsequent Scholl reaction forming the [8]circulene moiety. Two incompletely cyclized products were isolated from the Scholl reaction, providing insight into the cyclization of the strained octagon. This nanographene is twisted along two directions with end-to-end twists of 142.4° and 140.2° as revealed by X-ray crystallography, and is flexible at room temperature as found from the computational and experimental studies.
Herein we report synthesis, structure and properties of a new type of twisted nanographene, which contains an [8]circulene moiety in a polycyclic framework of 96 sp2 carbon atoms. The key steps in this synthesis are the Diels–Alder reaction of a macrocyclic diyne and the subsequent Scholl reaction forming the [8]circulene moiety. Two incompletely cyclized products were isolated from the Scholl reaction, providing insight into the cyclization of the strained octagon. This nanographene is twisted along two directions with end‐to‐end twists of 142.4° and 140.2° as revealed by X‐ray crystallography, and is flexible at room temperature as found from the computational and experimental studies.
Synthesis of an unprecedented aromatic saddle consisting of 80 sp2 carbons is enabled by including naphthylene groups in the substrate of the Scholl reaction. The negatively curved polycyclic framework of this aromatic saddle is revealed by the single crystal X-ray crystallography, and its stereodynamics are studied with density functional theory calculations.
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