Abstract
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Nanographenes, which are defined as nanoscale (1–100 nm)
graphene cutouts, include quasi-one-dimensional graphene nanoribbons
(GNRs) and quasi-zero-dimensional graphene quantum dots (GQDs). Polycyclic
aromatic hydrocarbons (PAHs) larger than 1 nm can be viewed as GQDs
with atomically precise molecular structures and can thus be termed
nanographene molecules. As a result of quantum confinement, nanographenes
are promising for next-generation semiconductor applications with
finite band gaps, a significant advantage compared with gapless two-dimensional
graphene. Similar to the atomic doping strategy in inorganic semiconductors,
incorporation of heteroatoms into nanographenes is a viable way to
tune their optical, electronic, catalytic, and magnetic properties.
Such properties are highly dependent not only on the molecular size
and edge structure but also on the heteroatom type, doping position,
and concentration. Therefore, reliable synthetic methods are required
to precisely control these structural features. In this regard, bottom-up
organic synthesis provides an indispensable way to achieve structurally
well-defined heteroatom-doped nanographenes.
Polycyclic heteroaromatic
compounds have attracted great attention
of organic chemists for decades. Research in this direction has been
further promoted by modern interest in supramolecular chemistry and
organic electronics. The rise of graphene in the 21st century has
endowed large polycyclic heteroaromatic compounds with a new role
as model systems for heteroatom-doped graphene. Heteroatom-doped nanographene
molecules are in their own right promising materials for photonic,
optoelectronic, and spintronic applications because of the extended
π conjugation. Despite the significant advances in polycyclic
heteroaromatic compounds, heteroatom-doped nanographene molecules
with sizes of over 1 nm and their relevant GNRs are still scarce.
In this Account, we describe the synthesis and properties of large
heteroatom-doped nanographenes, mainly summarizing relevant advances
in our group in the past decade. We first present several examples
of heteroatom doping based on the prototypical nanographene molecule,
i.e., hexa-peri-hexabenzocoronene (HBC), including
nitrogen-doped HBC analogues by formal replacement of benzene with
other heterocycles (e.g., aromatic pyrimidine and pyrrole and antiaromatic
pyrazine) and sulfur-doped nanographene molecules via thiophene annulation.
We then introduce heteroatom-doped zigzag edges and a variety of zigzag-edged
nanographene molecules incorporating nitrogen, boron, and oxygen atoms.
We finally summarize heteroatom-doped GNRs based on the success in
the molecular cases. We hope that this Account will further stimulate
the synthesis and applications of heteroatom-doped nanographenes with
a combined effort from different disciplines.
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