Chemistry Reference
In-Depth Information
4 2D Nanographenes with Only Armchair Edges ............................................ 231
4.1 Hexa-
Peri
-Hexabenzocoronene ....................................................... 232
4.2 All-Benzenoid PAHs Larger than HBC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
5 Conclusion and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Abbreviations
DDQ 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone
ESR Electron spin resonance
HBC Hexa-
peri
-hexabenzocoronene
HOMO Highest occupied molecular orbital
LUMO Lowest unoccupied molecular orbital
MALDI-TOF Matrix-assisted laser desorption time-of-flight
NIR
Near infrared
PDI
Perylene diimide
SOMO
Singly occupied molecular orbital
SQUID
Superconducting quantum interference device
TEMPO
(2,2,6,6-Tetramethylpiperidin-1-yl)oxyl
1
Introduction
Two-dimensional (2D) polyarenes represent one of the most widely studied organic
compounds and have attracted increasing attention due to their active role in
materials science. From a bottom-up point of view, 2D polyarenes can be viewed
as expanded networks by fusion of benzene rings in two-dimensions, which are
better described as benzenoid polycyclic aromatic hydrocarbons (PAHs). On the
other hand, from a top-down perspective they can be regarded as graphene
fragments formed by cutting infinite graphene sheet in different modes; thus they
are known as nanographenes. Both viewpoints will produce a series of structurally
well-defined molecules with two distinct edge structures - zigzag edge and arm-
chair edge. In this chapter the focus will be on three types of nanographenes divided
by the edge structures, i.e., those with zigzag edges only, those with armchair edges
only, and those possessing both (e.g., 1-3 in Fig.
1
).
Fusion of benzene rings in a triangular manner or cutting of graphene in a
triangular motif will lead to PAHs with only zigzag edges. No Kekul´ structure
or closed-shell structure can be drawn for this class of molecule, which inevitably
results in one or more unpaired electrons within the molecule. The number of
unpaired electrons, or radicals, increases with the size of the framework starting
from phenalenyl monoradical to high-spin polyradical systems. The high reactivity
derived from open-shell nature of these systems largely impedes their synthesis and
isolation, but still, continuous efforts have been made to synthesize and stabilize
them due to the desire to understand the interplay of the unpaired electrons and
