Chemistry Reference
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Fig. 2 Triangular fragments of graphene with open-shell structures
PAHs with only zigzag edges are promising in the field of spintronics and informa-
tion processing due to their unique magnetic properties, PAHs with both edge
structures are attractive as near-infrared (NIR) dyes and ambipolar semiconductors
due to their low bandgap and enhanced stability, while the self-assembly behavior
and controllable liquid crystal phase of PAHs with only armchair edge make them
suitable as electronic materials. In light of this background, we aim to provide
an overview of these three types of 2D nanographenes in terms of synthesis,
properties, and applications.
2
2D Nanographenes with Only Zigzag Edges
As mentioned above, if graphene is cut in a zigzag motif, or in a triangular shape, it
will lead to a series of non-Kekul
´
PAHs possessing one or more unpaired
electrons, which can be termed “open-shell graphene fragments” and are very
interesting from both theoretical and experimental aspects (Fig.
2
). The smallest
member in this family, phenalenyl radical 4, is composed of three benzene rings
fused in a triangular manner. It possesses one unpaired electron and spin multiplic-
ity 2
S
+1
-conjugation results in triangulene 1 with two
unpaired electrons and a triplet ground state, and further extension leads to larger
high spin system 5 (Fig.
2
). Apart from the open-shell and non-Kekul´ character,
these systems have a large delocalization of spin densities over the entire molecule,
although the largest coefficiency still resides on the edges of the molecule, which
are more exposed than the core.
Inspired by the promising potentialities and applications of these systems in the
field of electronics and spintronics [
4
], the synthesis and functionalization of
triangular shaped nanographenes have been intensively investigated for a long
time. However, the intrinsic low stability of these open-shell systems largely
impedes their isolation as well as application. Fueled by the development of modern
synthetic methods and deeper understanding of the decomposing pathways of those
radicals, such as dimerization, hydrogen abstraction, and oxidation, chemists have
¼
2. Extension of
p
