Chemistry Reference
In-Depth Information
3 Synthetic Methods for the Extension of Graphene-Type Structures . . . . . . . . . . . . . . . . . . . . . . 146
3.1 Polymerization Reactions . . . .......................................................... 147
3.2 Postfunctionalization of PAHs for the Extension to Graphene . . . . . . . . . . . . . . . . ...... 147
3.3 Direct Extension of PAHs by Diels-Alder Reaction . . . . . ........................... 148
4 Surface Assisted Methods for the Synthesis of Graphene-Type Structures . . . . . . . . . . . . . . . 149
5 Summary, Conclusions, and Outlook ....................................................... 150
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
1
Introduction
A material possessing no resistance, high stability, low weight, low toxicity, and
high abundance - is this just a dream? Graphene - a network of pure carbon atoms
just one atom thick - is the latest star in the sky of new materials [ 1 - 5 ]. The
preparation of graphene currently relies largely on physical methods, such as
micromechanical cleavage from highly ordered pyrolytic graphite, chemical vapor
deposition (CVD) [ 6 , 7 ], or chemical methods from graphene oxide [ 8 ]. Recently,
surface based methods have also been developed, relying on the self-assembly of a
mono-layer of molecules on a substrate followed by pyrolysis to form the graphene
layer [ 9 ]. On closer inspection, graphene consists of anullated benzene rings and
exhibits the structural characteristics of a polycyclic hydrocarbon (PAH). This class
of compounds was an early area of study in organic chemistry, not only from a
materials point of view but also in terms of the byproducts from combustion
processes (Fig. 1 ). With this background, organic synthetic methods should be and
have been applied to access defined graphene-type structures [ 10 - 13 ].
In this respect the application of organic synthetic methods to prepare graphene-
type structures is still in its infancy. Early endeavours in this direction have recently
been summarized [ 14 - 16 ]. Therefore this review aims mainly to give an overview
of exemplary organic synthetic methodologies capable of assembling large polycy-
clic aromatics as graphene-type structures. We do not claim completeness. We will
highlight the potential of the current status of organic chemistry in the light of
graphene. We concentrate on flat six-membered ring structures, as bowl-shaped
geometries are treated in a separate chapter in this topic. The focus is on
unsubstituted PAHs, only mentioning other examples in special cases.
2 Synthetic Methods to Assemble Graphene-Type
Structures
Aromatic chemistry is as old as organic chemistry itself. In the beginning most
aromatic compounds were isolated from coal tar and then further functionalized.
Early on there were methods developed to assemble aromatic molecules from
smaller precursors. The larger the compound the more difficult its synthesis. The
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