Chemistry Reference
In-Depth Information
Scheme 13 Preliminary studies towards peripentacene [
93
,
94
]
4
2D Nanographenes with Only Armchair Edges
2D graphene fragments with a fully armchair edge structure generally exhibit high
stability and a large band gap, as their chemical structures can be depicted in an all-
benzenoid manner with no additional isolated double bond existing. Among this
class of PAHs, hexa-
peri
-hexabenzocoronene (HBC) represents the most famous
and widely investigated 2D aromatic system. HBC can be viewed as
“superbenzene” due to its
D
6h
symmetry and more extended
-conjugation, and
in total seven sextet benzenoid rings can be drawn in this structure. The intrinsic
properties of HBC can be regarded as a “double-bladed sword” from two aspects:
(1) the all-benzoid feature renders a high stability; on the other hand the resulting
large band gap is unfavorable in many material applications; (2) the strong inter-
molecular
p
interaction and self-organization behavior makes HBC attractive in
organic electronic devices, but also leads to an extremely low solubility. Therefore,
rational design of the HBC derivatives with appropriate molecular size and func-
tional groups is highly desirable. Stimulated by the synthetic breakthroughs
achieved by M¨ llen's group, a boost was achieved in the last decade on
synthesizing HBC derivatives and seeking their applications as electronic materials,
and similar synthetic approaches are also applied as bottom-up methods to obtain
well-defined larger all-benzenoid graphene fragments. In the following section,
HBC derivatives and its higher homologue will be summarized and discussed.
Since two comprehensive reviews are available on this topic, only a brief overview
and selected examples will be given here [
96
,
97
].
p
-
p
