Journal of the American Chemical Society
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Corresponding Author
The monolayer of 10 shows rectangular bright features
organized in a brick-wall type structure, where each bright
rectangle represents a single molecule of 10 (Figure 4a).
Close inspection of the STM image reveals that unit cell
vector ‘a’ is shorter than vector ‘b’. A molecular model based
on unit cell parameters (Figure 4b) indicates that iodine-
iodine interactions possibly contribute to the stabilization
of the monolayer along the ‘a’ vector of the unit cell. The
spacing of molecular rows along the other unit cell vector is
determined by the tert-butyl groups. Each molecule appears
as a group of four protrusions (inset Figure 4a), which ten-
tatively correspond to the location of tert-butyl groups. It
has been well documented that molecular orbitals corre-
sponding to the tert-butyl groups dominate the contrast in
STM images of aromatic molecules substituted with tert-
butyl.15
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xinliang.feng@tuꢀdresden.de
muellen@mpipꢀmainz.mpg.de
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
We are grateful for the financial support from the European
Research Council grant on NANOGRAPH and
NANOGRAPH@LSI (No. 340324), DFG Priority Program SPP
1459, Graphene Flagship (No. CNECTꢀICTꢀ604391), and Euroꢀ
pean Community through the FETꢀProactive Project “MoQuaS”
(No. 610449) and MarieꢀCurie projects ITN iSwitch (GA no.
642196). SDF, KM, and GM thank the Fund of Scientific Reꢀ
search−Flanders (FWO), KU Leuven (GOA 11/003), and Belꢀ
gian Federal Science Policy Office (IAPꢀ7/05).
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In summary, we achieved a synthesis of a new stable not-
fully benzenoid HBC derivative with four additional K-
regions, based on a precursor with two pre-fused benzo-
tetraphene units. Notably, experimental IR and Raman
spectra display remarkable agreement with theoretical ones,
elucidating specific peaks originating from the armchair
and zigzag peripheries. UV-Vis absorption analysis and
theoretical studies of 10 demonstrated significant red-shift
of the absorption and lowering of the HOMO–LUMO gap
compared to the parent HBC and its derivatives with one to
three K-regions. The DFT calculation on 10 revealed its
lowered HOMO-LUMO gap of 2.50 eV, which makes 10 an
interesting candidate for the optoelectronic applications
such as in photovoltaic cells. The synthetic design of 10
offers the opportunity for further functionalization utilizing
the four peripheral iodo groups as well as in the two re-
maining bay regions. Especially, addition of C2 units to
theremaining bay regions can lead to the long awaited “cir-
cumcoronene” that is fully surrounded by the zigzag edges.
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Figure 4. (a) STM image of a self-assembled monolayer of
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ASSOCIATED CONTENT
Supporting Information
Experimental details, NMR, MALDIꢀTOF MS, UV/Vis absorpꢀ
tion spectra. This material is available free of charge via the
AUTHOR INFORMATION
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