Lateral extension of π conjugation along the bay regions of bisanthene through a diels-alder cycloaddition reaction

Article abstract of DOI:10.1002/chem.201102120

Diels-Alder cycloaddition reactions at the bay regions of bisanthene (1) with dienophiles such as 1,4-naphthoquinone have been investigated. The products were submitted to nucleophilic addition followed by reductive aromatization reactions to afford the laterally extended bisanthene derivatives 2 and 3. Attempted synthesis of a larger expanded bisanthene 4 revealed an unexpected hydrogenation reaction at the last reductive aromatization step. Unusual Michael addition was observed on quinone 14, which was obtained by Diels-Alder reaction between 1 and 1,4-anthraquinone. Compounds 1-3 exhibited near-infrared (NIR) absorption and emission with high-to-moderate fluorescent quantum yields. Their structures and absorption spectra were studied by density function theory and non-planar twisted structures were calculated for 2 and 3. All compounds showed amphoteric redox behavior with multiple oxidation/reduction waves. Oxidative titration with SbCl₅ gave stable radical cations, and the process was followed by UV/Vis/NIR spectroscopic measurements. Their photostability was measured and correlated to their different geometries and electronic structures.

Full text of DOI:10.1002/chem.201102120

DOI: 10.1002/chem.201102120
Lateral Extension of p Conjugation along the Bay Regions of Bisanthene
through a Diels–Alder Cycloaddition Reaction
Jinling Li,[a] Chongjun Jiao,[a] Kuo-Wei Huang,[b] and Jishan Wu*[a]
Abstract: Diels–Alder cycloaddition
reactions at the bay regions of bisan-
thene (1) with dienophiles such as 1,4-
naphthoquinone have been investigat-
ed. The products were submitted to nu-
cleophilic addition followed by reduc-
tive aromatization reactions to afford
the laterally extended bisanthene de-
rivatives 2 and 3. Attempted synthesis
of a larger expanded bisanthene 4 re-
vealed an unexpected hydrogenation
reaction at the last reductive aromati-
zation step. Unusual Michael addition
was observed on quinone 14, which
was obtained by Diels–Alder reaction
density function theory and non-planar
twisted structures were calculated for 2
and 3. All compounds showed ampho-
teric redox behavior with multiple oxi-
dation/reduction waves. Oxidative titra-
tion with SbCl5 gave stable radical cat-
ions, and the process was followed by
UV/Vis/NIR spectroscopic measure-
ments. Their photostability was mea-
sured and correlated to their different
geometries and electronic structures.
between
1
and 1,4-anthraquinone.
Compounds 1–3 exhibited near-infra-
red (NIR) absorption and emission
with
high-to-moderate
fluorescent
quantum yields. Their structures and
absorption spectra were studied by
Keywords: cycloaddition · dyes/pig-
ments · hyperconjugation · Michael
addition · polycycles
Introduction
alkyne, or arylthio groups and/or electronegative halogen
atoms is required to obtain relatively stable hexacene,[7] hep-
tacene,[7d,8] and nonacene.[9] Alternative approaches to stabi-
lize oligoacenes and to extend p conjugation is benzannula-
tion around the acene framework, and various benzannulat-
ed pentacene and higher order homologues have been re-
ported.[10] Introduction of phenyl rings in these benzannulat-
ed acene fragments usually results in puckering of the
molecules, for example, twisting, and gives a family of con-
torted molecules termed “twistacenes”.[11] Another type of
interesting PAH molecule is rylene, in which two or more
naphthalene units are peri-condensed together in a top-on-
top mode. Similar to oligoacenes, rylene molecules show a
convergence of band gap with increasing numbers of naph-
thalene units from perylene to terrylene, quaterrylene, pen-
tarylene, and hexarylene.[12] Rylene derivatives have been
studied in detail because they are important dyes for many
practical applications.[13]
Polycyclic aromatic hydrocarbons (PAHs) with large, ex-
tended p conjugation and small band gaps have promising
applications as organic semiconductors[1] for electronic devi-
ces and as organic dyes[2] for solar cells and bio-imaging.
The physical properties and chemical reactivity of PAHs are
largely determined by the arrangement of the benzenoid
rings in the p system and by the extent of p conjugation.
Linear fusion of benzene rings leads to oligoacenes, among
which both the band gap and stability quickly decrease with
increasing numbers of benzene rings.[3] Anthracene,[4] tetra-
cene,[5] and pentacene derivatives[6] have been successfully
applied in organic field effect transistors (OFETs) and or-
ganic light-emitting diodes (OLEDs). Higher order acenes
(larger than pentacene) with low band gaps turned out to be
extremely unstable, and appropriate substitution by aryl,
The third type of interesting PAH molecules is called per-
iacene, in which two acene units (anthracene, tetracene, or
pentacene) are peri-condensed together in a similar mode to
that for perylene; the molecules are called bisanthene, peri-
tetracene, and peripentacene, respectively.[14] Periacene mol-
ecules have been predicted theoretically to have very small
band gaps with a significant singlet biradical character, and
they are expected to be highly reactive due to their high-
lying HOMO energy levels.[14] So far, syntheses of peritetra-
cene and peripentacene derivatives have never been success-
ful, although our group recently made some attempts.[15]
Even the smallest member of the periacene family (i.e., bi-
santhene) is very sensitive to oxygen and light.[16] We recent-
ly developed a number of approaches[17] to prepare a series
[a] J. Li, C. Jiao, Prof. J. Wu
Department of Chemistry
National University of Singapore
3 Science Drive 3, 117543 (Singapore)
Fax : (+65)6779-1691
E-mail: chmwuj@nus.edu.sg
[b] Prof. K.-W. Huang
KAUST Catalysis Center and
Division of Chemical and
Life Sciences and Engineering
4700 King Abdullah University
of Science and Technology
Thuwal 23955-6900 (Kingdom of Saudi Arabia)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102120.
14672
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14672 – 14680

FULL PAPER
of soluble and stable bisanthene-based near-infrared (NIR)
dyes with structural features that included: 1) substitution
by electron-withdrawing dicarboxylic imide groups at the
zig-zag edges; 2) quinoidization along the short-axis, and
3) substitution by aryl or alkyne groups at the most reactive
meso-positions. Similar to perylene, the bay regions of bisan-
thene have a diene character as shown in compound 1
vestigated, and attempts have been made to understand
their fundamental structure–property relationships.
Results and Discussion
Synthesis: The synthesis of 2 and 3 is depicted in Scheme 2.
The 3,5-di-tert-butylphenyl-substituted bisanthene 1 was first
prepared according to our previous report.[17c] Diels–Alder
reaction between 1 and a large excess of 1,4-naphthaqui-
none (20 equiv) in nitrobenzene heated to reflux (2408C) af-
forded the mono-addition product 6 and bis-addition prod-
uct 7; the ratio of 6/7 was dependent on the reaction time.
Compound 6 was obtained as a dominant product after
heating the reaction to reflux temperature for 24 h, but com-
pound 7 was generated as a major product after extending
the period of reflux to two days. The nitrobenzene served as
a high-boiling-point solvent as well as an oxidant to convert
the Diels–Alder product into the dehydrogenated final
products 6 and 7. Compound 6 reacted with the Grignard
reagent of 3,5-di-tert-butyl-1-bromobenzene in an anhydrous
mixture of tetrahydrofuran (THF) and toluene to give diol 8
in 52% yield, which was followed by dehydroxylation and
reductive aromatization with NaI/NaH2PO2 to afford the
target compound 2 in nearly quantitative yield. Subsequent
Scheme 1. Structures of compounds 1–5.
(Scheme 1) and this raises the opportunity to introduce fur-
ther functionalization through Diels–Alder cycloaddition re-
action at the bay positions of bisanthene. Clar et al. reported
that Diels–Alder cycloaddition of parent bisanthene with
maleic anhydride gave ovalene dianhydride, which was then
successfully converted into ovalene by decarboxylation.[18]
Liquid crystalline ovalene tetraesters were also prepared by
esterification of ovalene dianhydride.[19] Recently, Scott
et al. reported that nitroethylene could be used as a masked
acetylene, and this compound underwent Diels–Alder reac-
tion at the bay regions of bisanthene to give ovalene deriva-
tives.[20] This result implied that it was possible to synthesize
single-chirality carbon nanotubes by using a metal-free ap-
proach from a suitable cylindrical template. Diels–Alder re-
action between a diene and a dienophile such as 1,4-benzo-
quinone, 1,4-naphthoquinone, and 1,4-anthraquinone have
been frequently used to construct extended acenequinones
and higher order acenes.[3] In this work, we report the cyclo-
addition reactions between bisanthene and these quinones,
and subsequent synthesis of a series of aryl-annulated bisan-
thene compounds with laterally extended p conjugation
(e.g., compounds 2–5; Scheme 1). In all target molecules 2–
5, bulky 3,5-di-tert-butylphenyl groups are attached to the
zig-zag edges to increase their stability and solubility. These
molecules were expected to have a contorted structure due
to steric congestion induced by the phenyl substituents, and
can also be regarded as anthryl-annulated twistacenes.
Herein, the synthetic chemistry, structure, photophysical
properties, electrochemical properties, and photostability of
these laterally expanded bisanthene compounds are fully in-
Scheme 2. Synthesis of 2 and 3. Reagents and conditions: a) 1,4-naphtho-
quinone (20 equiv), nitrobenzene, reflux, 1 d (6 as major product) or 2 d
(7 as major product); b) 3,5-di-tert-butyl-phenyl magnesium bromide,
THF/toluene, RT; c) NaH2PO2·H2O, NaI, acetic acid, reflux, 2 h.
Chem. Eur. J. 2011, 17, 14672 – 14680
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14673

J. Wu et al.
Diels–Alder reaction of the latter with 1,4-naphthaquinone
(20 equiv) gave 10 in 85% yield, which underwent a similar
nucleophilic addition reaction with 3,5-di-tert-butyl-phenyl
magnesium bromide, dehydroxylation, and reductive aroma-
tization, to yield the target compound 3 in 76% yield. Alter-
natively, the latter compound could also be prepared from
quinone 7; thus, addition reaction of 3,5-di-tert-butyl-phenyl
magnesium bromide to 7 gave tetraol 9, and subsequent de-
hydroxylation/reductive aromatization afforded the final
compound 3 in moderate yield.
and afforded the intermediate compound 13. The resulting
diol 13 was used for subsequent dehydroxylation and reduc-
tive aromatization with the aim of preparing the target com-
pound 4. Surprisingly, a hydrogenated product 4-H2 was ob-
tained instead of 4, which was confirmed by high resolution
MALDI-TOF mass spectrometry. A peak at m/z=2685.6657
([M+]; calculated exact mass for C206H212: 2685.6589) was
observed, which is 2 Da higher than expected for 4 (calculat-
ed exact mass for C206H210: 2683.6433). The product 4-H2 is
red in color, with the longest absorption maximum at
595 nm (see Figure S1 in the Supporting Information),
which is much shorter than that for 2 and 3 (both at 700 nm,
see below) as well as 12 (674 nm, see Figure S1 in the Sup-
porting Information). This indicates that the p conjugation
in 4 was broken by dihydrogenation. This unexpected hydro-
genation may be caused by the greatly extended p delocali-
zation and strongly twisted structure of 4, which makes the
lateral acene fragment very reactive, leading to dihydroge-
nation under the reductive conditions (NaH2PO2/NaI, acetic
acid). However, the exact structure of 4-H2 was not con-
Scheme 3 outlines the synthetic route to the highly ex-
tended p-conjugated system of 4. Diels–Alder reaction took
place between compound 2 and an excess of 1,4-benzoqui-
1
firmed because of the complexity of the H NMR spectrum
and because of the lack of crystals suitable for crystallo-
graphic analysis.
To achieve further lateral extension of p conjugation
along the bisanthene core, a similar Diels–Alder cycloaddi-
tion reaction between compound 2 and a large excess of 1,4-
anthraquinone (20 equiv) was performed; under these con-
ditions, mono-addition-product 14 was obtained together
with a trace amount of 15 when the reaction was heated to
reflux for 1 day in nitrobenzene (Scheme 4). Extended reac-
tion time did not help to generate more 15, presumably due
to the relatively low reactivity and low solubility of 14 for
further Diels–Alder reaction. Nucleophilic addition of com-
pound 14 with excess Grignard reagent derived from 1-
bromo-3,5-di-tert-butylbenzene in anhydrous THF/toluene
was then tested. Interestingly, a diaryl-substituted compound
17 was obtained in 54% yield after standard acidification
Scheme 3. Synthetic route towards 4. Reagents and conditions: a) nitro-
benzene, reflux, 2 d; b) n-C4H9-CꢀC-MgBr, THF/toluene, 608C, over-
night; c) NaH2PO2·H2O, NaI, acetic acid, reflux, 2 h.
none in nitrobenzene at reflux temperature, to give 11 in
85% yield. A second Diels–Alder cycloaddition reaction be-
tween 2 and 11 produced quinone 12 in 40% yield. We also
attempted a one-step Diels–Alder reaction between two
equivalents of 2 and one equivalent of 1,4-benzoquinone,
however, no desired product 12 was formed. The nucleophil-
ic addition of 12 with triisopropylsilyl (TIPS) acetylene
Grignard reagent turned out to be challenging; there was no
addition product detected even under heating in THF, pre-
sumably due to the steric hindrance between the TIPS
groups and the core. Thus, the less bulky hexynyl group was
used; in this case, addition of 12 with hexynylmagnesium
bromide in anhydrous THF/toluene proceeded smoothly
Scheme 4. Reagents and conditions: a) 1,4-anthraquinone (20 equiv), ni-
trobenzene, reflux, 1 d; b) 3,5-di-tert-butyl-phenyl magnesium bromide,
THF/toluene, RT, 2 d; then quenched with water.
14674
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14672 – 14680

Extended p Conjugation of Bisanthene
FULL PAPER
workup and column chromatography in air, suggesting that
the aryl Grignard reagent attacked the benzene rings instead
of the carbonyl groups in 14. The structure of 17 was unam-
biguously confirmed by NMR spectroscopy and by high-res-
olution mass spectrometry (see the Supporting Information).
Such an unusual addition reaction is similar to the 1,4-Mi-
chael addition of a,b-unsaturated ketones.[21] Similar Mi-
chael addition reactions have been observed with a fused
bispentacenequinone, as recently reported in our group.[15b]
Herein, Michael addition reactions take place on the ben-
zene rings adjacent to the ketone groups and subsequent
acidification should give the intermediate compound 16,
which undergoes simultaneous dehydrogenation in air to
afford product 17 (Scheme 4). Only two, instead of four, hy-
drogen atoms were removed during the dehydrogenation
process, giving a partially dehydrogenated product. We also
attempted to perform further dehydrogenation of 17 with p-
chloranil in toluene heated to reflux, however, no reaction
took place.
Photophysical properties: The attachment of 3,5-di-tert-bu-
tylphenyl groups makes the final products and most inter-
mediate compounds readily soluble in common organic sol-
vents. The UV/Vis/NIR absorption and fluorescence spectra
of compounds 1, 2, and 3 recorded in toluene are shown in
Figure 1(a), and the data are collected in Table 1. The opti-
cal spectra of 2 and 3 in toluene show two major absorption
bands, one at 300–500 nm (b band) and a second at 550–
750 nm (p band). The absorp-
Figure 1. a) UV/Vis/NIR absorption, and b) fluorescence spectra of com-
pounds 1, 2, and 3 in dilute toluene solutions (concentration=1ꢂ10À5
for absorption spectra and 1ꢂ10À7 m for emission spectra).
m
tion maximum of 3 (409 nm)
Table 1. Photophysical and electrochemical data of compounds 1–3.[a]
displays a clear bathochromic
shift with respect to
Compd labs
[nm]
lem
QY E1ox
E2ox
[V]
E3ox
[V]
E1red
[V]
E2red
HOMO LUMO EEg C
EOg pt
2
[nm]
[V]
[V]
[eV]
[eV]
[eV] [eV]
(375 nm) as a result of annula-
tion of an additional naphtha-
lene unit at the bay regions.
The long-wavelength absorp-
tion bands of 1–3 have similar
shapes, and the maxima are lo-
cated at 687, 697, and 697 nm,
respectively. Such a small shift
of the absorption band can be
explained by Clarꢁs aromatic
rule.[22] Molecules 2 and 3, al-
though larger in size, possess
more Clarꢁs aromatic sextet
rings than 1 (i.e., three for 2,
1
582, 628, 701
687
0.81 À0.02 0.58
–
À1.68 À2.10 À4.71
À3.20
1.51 1.73
2
375, 427, 708, 778 0.45 À0.04 0.57
–
À1.72
–
À4.69
À3.14
1.55 1.72
1.62 1.72
453, 586,
637, 697
3
388, 409, 708, 778 0.38 À0.04 0.49 1.20 À1.80
–
À4.69
À3.07
451, 586,
637, 697
[a] The redox potentials are calibrated by Fc/Fc+. HOMO and LUMO energy levels were deduced from the
onset potentials of the first oxidation (E ) and the first reduction wave (E ), according to the following
onset
onset
red
ox
onset
onset
equations: HOMO=À(4.8+E ) and LUMO=À(4.8+E ), in which the potentials are calibrated to EFc+
ox
red
/Fc. EEg C as the electrochemical band gap deduced from the LUMOÀHOMO. EOg pt is optical band gap estimated
from the lowest energy absorption onset.
four for 3, and two for 1; labeled as circle rings in
Scheme 2). In addition, compounds 2 and 3 are expected to
show contorted structures (see below), and deviation from
planarity could also result in a blue shift of the absorption
spectrum. Compounds 2 and 3 show fluorescence, with the
emission maximum at 708 nm (Figure 1(b) and Table 1),
which is a 7 nm bathochromic shift with respect to com-
pound 1. The photoluminescence quantum yields (F) were
determined according to an optical dilute method (optical
density A<0.05) by using cardiogreen dye (labs (max)=
780 nm, F=0.13 in DMSO) as a standard.[23] The F values
of 0.45 and 0.38, obtained for 2 and 3, respectively, are
lower than for compound 1 (0.81) presumably due to the
twisted structures. The UV/Vis/NIR absorption spectra of
11, 12, 4-H2, and 17 were also recorded in toluene (see Fig-
ure S1 in the Supporting Information). Compounds 11, 12,
and 17 all showed typical intramolecular charge-transfer
bands at 684, 674, and 648 nm, respectively, due to the exis-
tence of electron-withdrawing quinone units. Compound 4-
H2 exhibits a p band at much shorter wavelength (450–
620 nm) because of interruption of p conjugation in 4.
Chem. Eur. J. 2011, 17, 14672 – 14680
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14675

J. Wu et al.
Theoretical calculations: The geometries and electronic
structures of molecules 2 and 3 were studied by density
function theory (DFT) calculations at the B3LYP/6-31G*
level. The optimized structures and the frontier molecular
orbital profiles of 2 and 3 are shown in Figure 2. As predict-
Figure 3. Cyclic voltammograms of a) 1, b) 2, and c) 3 in dichloromethane
(1 mm) with 0.1m Bu4NPF6 as supporting electrolyte, AgCl/Ag as refer-
ence electrode, Au disk as working electrode, Pt wire as counter elec-
trode, and a scan rate of 50 mVsÀ1
.
0.57 V for 2, whereas three oxidative waves were observed
for 3, with Enox at À0.04, 0.49, and 1.20 V (vs. Fc/Fc+). Com-
pound 1 also showed two quasi-reversible reduction waves
with the half-wave potential of the first reductive waves
(E1red) at À1.68 V, whereas compounds 2 and 3 exhibited one
reversible reduction wave with the half-wave potential (Er1ed
)
at À1.72 and À1.80 V, respectively. Such amphoteric redox
behavior suggests that compounds 1, 2, and 3 can be reversi-
bly oxidized to the respective cationic species (e.g., radical
cations and dications) and reduced to the corresponding
anionic species (e.g., radical anion and dianion), and the
charged species can be stabilized by the large delocalized p
system. The electrochemical properties of compounds 11
and 12 were also studied by CV in anhydrous dichlorome-
thane (see Figure S2 and Table S1 in the Supporting Infor-
mation). The cyclic voltammograms of 11 exhibited two re-
versible oxidation waves with half-wave potentials (Enox) at
0.25 and 0.71 V, whereas three oxidative waves were ob-
served for 12, with Enox at 0.22, 0.27, and 0.70 V (vs. Fc/Fc+).
Compound 11 also showed three quasi-reversible reduction
waves with the half-wave potential of the first reductive
waves (E1red) at À1.13 V, whereas compound 12 exhibited
four reversible reduction wave with the half-wave potential
of the first reductive wave (E1red) at À1.43 V.
Figure 2. Optimized geometric structure and frontier molecular orbital
profiles of 2–3. Hydrogen atoms are omitted for clarity.
ed, molecules 2 and 3 both have non-planar, twisted struc-
tures due to steric congestion, and the center-to-end distor-
tion angle is around 418 for both. In both cases, the HOMO
and LUMO are mainly delocalized in the bisanthene unit,
and are partially delocalized along the naphthalene units, al-
though there is significant twist between the bisanthene and
the naphthalene moieties. Time-dependent DFT (TD-DFT)
calculations also predict that both molecules have two major
absorption bands with maxima at 372 and 748 nm for 2, and
410 and 758 nm for 3 (see the Supporting Information).
These two bands can be correlated to the b band and p
band, respectively, and the redshift trend agrees well with
the experimental observations.
The HOMO and LUMO energy levels were deduced
onset
from the onset potentials of the first oxidation (E ) and
ox
onset
red
the first reduction wave (E ), according to the following
onset
ox
equations:
HOMO=À
(4.8+E
)
and
LUMO=
onset
À(4.8+E ), in which the potentials are calibrated to EFc+
red
[24]
.
/Fc
Compared with the precursor 1, compounds 2 and 3
have slightly higher HOMO and LUMO energy levels. In
agreement with the small optical band gap (EOg pt) deter-
mined from the absorption spectra, the electrochemical
band gaps are also small due to a convergence of the
HOMO and LUMO energy levels. Compounds 11 and 12
have similar HOMO energy levels, whereas a higher LUMO
energy level was observed for 12 than for 11.
Electrochemical properties: The electrochemical properties
of compounds 2 and 3 were investigated by cyclic voltamme-
try (CV) in anhydrous dichloromethane and compared to 1
(Figure 3 and Table 1). The cyclic voltammograms of 1 and
2 exhibited two reversible oxidation waves with half-wave
potentials (Enox) at À0.02 and 0.58 V for 1 and À0.04 and
Chemical oxidation titrations of 2 and 3 were conducted
in dichloromethane by using SbCl5 as an oxidant, and the
14676
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14672 – 14680

Extended p Conjugation of Bisanthene
FULL PAPER
process was followed by UV/Vis/NIR absorption spectrosco-
py. Like compound 1,[17c] these two compounds can be rever-
sibly oxidized by SbCl5 to generate stable radical cations,
with the appearance of two new characteristic absorption
bands at shorter and longer wavelength (Figure 4). Such a
The times required for 10% decomposition were approxi-
mately 244, 70, and 38 min for 1, 2, and 3, respectively; this
was determined by plotting the optical density at the longest
absorption lmax against the irradiation time (Figure 5). Upon
irradiation with a UV lamp (4 W), the decomposition pro-
cess became faster, and the compounds displayed times of
approximately 67, 9, and 24 min for 10% decomposition, re-
spectively (see Figure S3 in the Supporting Information).
These results revealed that the photostabilities of com-
pounds 2 and 3 are both lower than for compound 1, and
this difference can be explained by the strongly twisted
structures of 2 and 3 as well as by the slightly higher-lying
HOMO energy levels, which increases the sensitivity to-
wards light and oxygen. The structure of the obtained prod-
ucts after UV irradiation was investigated by MALDI-TOF
mass spectrometry, and the major components were found
to be addition products with one or two oxygen molecules,
which is common for many acene-related compounds.
Conclusion
We have investigated the synthesis of laterally expanded bi-
santhene compounds through Diels–Alder cycloaddition re-
action at the bay regions of bisanthene. The naphthalene-an-
nulated bisanthenes 2 and 3 have been successfully pre-
pared, but synthetic efforts towards the creation of more ex-
tended p systems, such as 4 and 5, met with unexpected hy-
drogenation or Michael addition reactions. Nevertheless,
compounds 2 and 3 represent new members of greatly ex-
tended PAHs with small band gaps and NIR absorption/
emission, which could be suitable for NIR OLEDs. Our de-
tailed studies on the geometric and electronic structures,
photophysical and electrochemical properties, and photosta-
bilities revealed that the twisted structures, the extent of p
conjugation, and the number of Clarꢁs sextet rings all played
important roles in the physical properties and chemical reac-
tivities. Synthesis of larger-sized, expanded bisanthenes with
planar geometry is underway in our laboratories; such com-
pounds could potentially be employed in organic electronic
devices such as OFETs.
Figure 4. UV/Vis/NIR absorption spectra of 2 and 3 during titration with
SbCl5 in anhydrous dichloromethane. The arrows show the changes of
the spectra during the titration.
phenomenon is common due to the redistribution of frontier
molecular orbital energy in the energy gap, and one-electron
transition at the higher energy and one-electron transition
at lower energy are allowed in the new energy diagram. The
longest absorption maximum for the radical cation exhibited
a
clear bathochromic shift from 1 2
(782 nm)[17c] to
(1276 nm) and 3 (1324 nm). The oxidized species can also be
reversibly reduced to the neutral state by adding Zn dust to
the solution containing oxidized species. Similar reversible
processes could be observed for 2 and 3 when iodine was
used as an oxidant and Zn as a reductant.
Experimental Section
General: All reagents and starting materials were obtained from com-
mercial suppliers and were used without further purification. THF and
toluene were purified by routine procedures and distilled over sodium
under nitrogen before use. Column chromatography was performed on
silica gel 60 (Merck 40–60 nm, 230–400 mesh). All NMR spectra were re-
corded with Bruker AMX500 or AMX300 spectrometers at RT. All
chemical shifts are quoted in ppm, relative to tetramethylsilane, by using
the residual solvent peak as a reference standard. MALDI-TOF MS
spectra were measured with a Bruker Autoflex MALDI-TOF instrument,
Photostability: In contrast to the very unstable parent bisan-
thene, solutions of 1–3 in toluene are relatively stable under
ambient conditions. The photostabilities of these three com-
pounds were also tested by irradiation with a white-light
bulb (60 W) and a UV lamp (254 nm, 4 W). Upon irradia-
tion with white light, the solutions gradually decomposed,
with a decrease of the optical intensity at the longest ab-
sorption band and the appearance of new absorption bands
at shorter wavelengths, as depicted by arrows in Figure 5.
with 1,8,9-trihydroxyanthracene as
a matrix. UV/Vis/NIR absorption
spectra were measured with a Shimadzu UV-1700 or a Lambda 750 spec-
trometer. Fluorescence spectra were recorded with a RF-5301 fluorome-
ter. Cyclic voltammetry measurements of compounds 2 and 3 in dichloro-
methane (1m) were performed with a CHI 620C electrochemical analyzer
Chem. Eur. J. 2011, 17, 14672 – 14680
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14677

J. Wu et al.
Synthesis of compound 8: Magnesium
(3 mg, 0.13 mmol) and
a piece of
iodine crystal were placed in anhy-
drous THF (1 mL). To the mixture, 1-
bromo-3,5-di-tert-butylbenzene
(305.5 mg, 1.13 mmol) in anhydrous
THF (4 mL) was added dropwise and
the mixture was stirred at RT for 2 h
to generate the Grignard reagent.
The prepared Grignard reagent was
transferred into a suspension of crude
compound 6 (100 mg) in anhydrous
toluene (20 mL) and the mixture was
stirred at RT for 2 d. The reaction
was quenched with water (100 mL)
and extracted with hexane. The or-
ganic layer was washed with water
and dried over anhydrous Na2SO4.
After removal of solvent, the residue
was further purified by column chro-
matography on silica gel (CHCl3/
hexane=2:1 v/v) to afford compound
8
(72 mg, 52%) as a black-purple
solid. 1H NMR (300 MHz, CDCl3):
d=1.11 (s, 36H; tBu), 1.41 (s, 18H;
tBu), 1.45 (s, 18H; tBu), 3.27 (s, 2H;
OH), 7.12 (s, 2H; Ph), 7.23 (dd, 3J=
6.09 Hz, 4J=3.3 Hz, 2H; Ph), 7.35 (s,
2H; Ph), 7.43 (s, 4H; Ph), 7.47 (s,
2H; Ph), 7.60 (m, 4H; Ar), 7.70 (m,
2H; Ar), 7.90 (t, J=8.0 Hz, 2H; Ar),
8.09 (d, J=8.4 Hz, 2H; Ar), 8.88 (d,
J=10.0 Hz, 2H; Ar), 9.02 ppm (d, J=
7.2 Hz, 2H; Ar). 13C NMR (75 MHz,
CDCl3): d=32.1, 32.3, 32.4, 35.5, 35.7,
35.8, 120.1, 120.9, 121.3, 121.8, 123.2,
124.5, 125.5, 125.8, 126.3, 126.6, 126.7,
127.3, 128.3, 128.7, 129.1, 129.2, 129.4,
132.3, 132.4, 135.5, 137.8, 138.6, 140.1,
149.8, 150.9 ppm. HRMS (FAB): m/z
calcd for C94H100O2: 1260.77178;
found: 1260.77196 [M+] (error=
0.14 ppm).
Synthesis of 2: In absence of light, a
mixture of 8 (100 mg, 0.079 mmol),
NaI
NaH2PO2·H2O
(119 mg,
0.79 mmol),
(152.8 mg,
1.185 mmol), and acetic acid (20 mL)
was heated to reflux for 2 h. After
cooling to RT, the precipitate was col-
lected by filtration, washed with
water, and purified by column chro-
matography with hexane as eluent to
afford 2 quantitatively as a deep-blue
Figure 5. Photostability test of compounds 1–3 in toluene upon irradiation with a 60 W white-light bulb. Left:
UV/Vis/NIR absorption spectra of a) 1, c) 2, and e) 3 in toluene recorded during the irradiation. The arrows
indicate the change in the spectra. Right: change of optical density of b) 1, d) 2, and f) 3 at the longest absorp-
tion maximum wavelength with the irradiation time. The original optical density before irradiation was nor-
malized at the absorption maximum.
solid. 1H NMR (300 MHz, CDCl3): d=1.29 (s, 36H; tBu), 1.42 (s, 36H;
tBu), 7.23 (m, 2H; Ar), 7.37 (d, J=1.65 Hz, 4H; Ph), 7.46 (d, J=1.62 Hz,
4H; Ph), 7.53 (s, 2H; Ph), 7.57 (s, 2H; Ar), 7.60 (m, 4H; Ar), 7.72 (m,
4H; Ar), 7.93 (m, J=8.55 Hz, 2H; Ar), 8.36 (m, 2H; Ar), 8.76 ppm (d,
J=7.41 Hz, 2H; Ar). 13C NMR (125 MHz, CDCl3): d=32.2, 32.3, 35.6,
35.8, 120.7, 121.37, 121.41, 123.9, 124.5, 125.7, 125.8, 126.0, 126.2, 126.8,
127.0, 127.3, 127.4, 127.5, 128.4, 128.8, 129.9, 130.0, 130.3, 132.4, 132.9,
136.5, 137.3, 138.6, 141.7, 151.4, 152.0 ppm. HRMS (FAB): m/z calcd for
C94H98: 1226.7663; found: 1226.7640 [M+] (error=À1.88 ppm).
Synthesis of 10: Compound 2 (100 mg, 0.08 mmol) was heated at reflux
for 2 d with 1,4-naphthoquinone (253 mg, 1.6 mmol) in deoxygenated ni-
trobenzene (30 mL); a slow color change from green to black-green was
observed. Nitrobenzene was distilled off under vacuum, and the remain-
ing green solid was washed with acetone and further purified by column
chromatography on silica gel (CHCl3/hexane=2:1 v/v) to afford 10
with a three-electrode cell, by using 0.1m Bu4NPF6 as supporting electro-
lyte, AgNO3/Ag as reference electrode, gold disk as working electrode,
Pt wire as counter electrode, and a scan rate of 50 mVsÀ1
.
Synthesis of compounds 6 and 7: Compound 1 (100 mg, 0.14 mmol) was
heated to reflux (2408C) with 1,4-naphthoquinone (435 mg, 2.75 mmol)
in deoxygenated nitrobenzene (50 mL); the color slowly changed from
deep-blue to black-brown. Methanol was added to the cooled solution
and the green precipitate was filtered off, washed with acetone, and dried
under vacuum to yield a mixture of compounds 6 and 7. When the reac-
tion time was 24 h, the major product was 6, together with a trace
amount of 7. When the reaction was conducted for 2 d, the major product
was 7 together with a trace amount of 6. The mixture was used directly
for the next step.
14678
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14672 – 14680

Extended p Conjugation of Bisanthene
FULL PAPER
(96 mg, 85%) as a black-green solid. 1H NMR (500 MHz, CDCl3): d=
1.29 (s, 36H; tBu), 1.52 (s, 36H; tBu), 7.56 (s, 4H; Ph), 7.61 (s, 2H; Ph),
7.62 (br, 2H; Ar), 7.67 (d, J=1.5 Hz, 4H; Ph), 7.72 (m, 2H; Ar), 7.75 (s,
2H; Ph), 8.18 (d, J=9.5 Hz, 2H; Ar), 8.20 (br, 2H; Ar), 8.48 (m, 2H;
Ar), 8.61 (d, J=9.5 Hz, 2H), 8.71 (d, J=9.5 Hz, 2H; Ar), 10.04 ppm (d,
J=10 Hz, 2H; Ar). 13C NMR (125 MHz, CDCl3): d=32.2, 32.4, 35.7,
35.9, 121.3, 121.7, 121.9, 122.8, 123.7, 124.4, 124.7, 126.5, 126.69, 126.73,
127.05, 127.14, 127.3, 127.6, 127.7, 128.6, 128.7, 128.9, 128.9, 129.5, 130.0,
130.7, 130.9, 133.5, 135.5, 137.3, 138.4, 138.6, 141.7, 151.5, 152.4,
188.1 ppm. HRMS (MALDI-TOF, positive): m/z calcd for C104H100O2:
1380.7718; found: 1380.7691 [M+] (error=À1.98 ppm).
Synthesis of 3: Magnesium (19.3 mg, 0.80 mmol) and a piece of iodine
crystal were placed in anhydrous THF (1 mL). To the mixture, 1-bromo-
3,5-di-tert-butylbenzene (194.7 mg, 0.72 mmol) in anhydrous THF (4 mL)
was added dropwise and the mixture was stirred at RT for 2 h to generate
the Grignard reagent. The prepared Grignard reagent was transferred
tive): m/z calcd for C194H192O2: 2553.4917; found: 2553.4978 [M+]
(error=2.39 ppm).
Synthesis of 4-H2: Ethylmagnesium bromide (3m in ether, 0.13 mL,
0.39 mmol) was added dropwise to
a solution of 1-hexyne (32 mg,
0.39 mmol) in anhydrous THF (1 mL) at RT with stirring, and this mix-
ture was maintained at 608C for 2 h. Compound 12 (100 mg, 0.039 mmol)
was dissolved under nitrogen in anhydrous toluene (10 mL) and then
added dropwise to the prepared Grignard reagent and the mixture was
stirred at 608C overnight. The reaction was quenched with water
(100 mL) and extracted with hexane. The organic layer was washed with
water and dried over anhydrous Na2SO4. The solvent was removed by
evaporation and the residue was dried under vacuum. In the absence of
light, a mixture of the crude diol 13 (62 mg, 0.39 mmol), NaI (105 mg,
0.7 mmol), NaH2PO2·H2O (68 mg, 0.78 mmol), and acetic acid (20 mL)
was heated to reflux for 2 h. After cooling to RT, the dark-purple precipi-
tate was collected by filtration, washed with water and acetone, and puri-
fied by column chromatography on silica gel (CHCl3/hexane=1:4 v/v) to
afford 4-H2 (a hydrogenated form of 4). HRMS (MALDI-TOF, positive):
into
a suspension of 10 (100 mg, 0.07 mmol) in anhydrous toluene
(20 mL) and the mixture was stirred at RT for 2 d. The reaction was
quenched with water (100 mL) and extracted with hexane. The organic
layer was washed with water and dried over anhydrous Na2SO4. The sol-
vent was removed by evaporation and the residue was dried under
vacuum. In the absence of light, a mixture of the crude product diol
(123 mg, 0.07 mmol), NaI (105 mg, 0.7 mmol), NaH2PO2·H2O (135.4 mg,
1.05 mmol), and acetic acid (20 mL) was heated to reflux for 2 h. After
cooling to RT, the deep-green precipitate was collected by filtration,
washed with water and acetone, and purified by column chromatography
on silica gel (CHCl3/hexane=1:5 v/v) to afford 3 (92 mg, 76%) as a
green solid. Alternatively, compound 3 can be prepared from qunione 7
m/z calcd for C206H212
:
2685.6584; found: 2685.6657 [M+] (error=
2.73 ppm).
Synthesis of 14: Compound 1 (100 mg, 0.14 mmol) was heated at reflux
for 2 d with 1,4-anthraquinone (573 mg, 2.75 mmol) in deoxygenated ni-
trobenzene (50 mL); a slow color change from deep-blue to black-brown
was observed. Methanol was added into the cooled solution, and the
green precipitate was filtered off, washed with acetone, and dried under
vacuum to yield 15 with a trace amount of 16 (as confirmed by MALDI-
TOF mass spectrometry). The mixture was used directly for the next
step.
1
by a similar approach via intermediate compound 9. H NMR (500 MHz,
Synthesis of 17: Magnesium (3 mg, 0.13 mmol) and a piece of iodine crys-
tal were placed in anhydrous THF (1 mL). To the mixture, 1-bromo-3,5-
di-tert-butylbenzene (305.5 mg, 1.13 mmol) in anhydrous THF (4 mL)
was added dropwise and the mixture was stirred at RT for 2 h to generate
the Grignard reagent. The prepared Grignard reagent was transferred
into a suspension of crude compound 14 (100 mg, 0.11 mmol) in anhy-
drous toluene (20 mL) and the mixture was stirred at RT for 2 d. The re-
action was quenched with water (100 mL) and extracted with hexane.
The organic layer was washed with water and dried over anhydrous
Na2SO4. After removal of solvent, the residue was further purified by
column chromatography on silica gel (CHCl3/hexane=1:8 v/v) to afford
17 (77 mg, 54%) as a black-purple solid. 1H NMR (300 MHz, CDCl3):
d=1.24 (s, 36H; tBu), 1.47 (s, 36H; tBu), 5.70 (s, 2H; CH), 7.13 (m, 2H;
Ar), 7.24 (m, 8H; Ar, Ph), 7.48 (m, 4H; Ph), 7.69 (t, J=2 Hz, 2H; Ph),
7.94 (d, J=10 Hz, 2H; Ar), 8.03 (t, J=7.5 Hz, 2H; Ar), 8.2 (d, J=
8.5 Hz, 2H; Ar), 9.04 (d, J=10 Hz, 2H; Ar), 9.16 ppm (d, J=7.5 Hz,
2H; Ar). 13C NMR (125 MHz, CDCl3): d=35.5, 35.8, 46.0, 121.1, 122.0,
122.2, 122.9, 123.9, 125.1, 125.5, 126.5, 126.7, 126.9, 127.2, 127.45, 127.53,
128.2, 129.2, 129.5, 130.0, 130.8, 132.2, 132.8, 137.1, 138.3, 139.6, 144.1,
147.0, 151.5, 151.7, 151.8, 189.7 ppm. HRMS (MALDI-TOF, positive): m/
[D6]benzene): d=1.27 (s, 72H; tBu), 1.54 (s, 36H; tBu), 7.45 (m, 4H;
Ar), 7.74 (s, 4H; Ph), 7.75 (s, 8H; Ph), 7.84 (s, 2H; Ph), 7.96 (s, 4H; Ph),
8.34 (d, J=9.5 Hz, 4H; Ar), 8.56 (d, J=9.5 Hz, 4H; Ar), 8.66 ppm (m,
4H; Ar). 13C NMR (125 MHz, [D6]benzene): d=32.3, 32.6, 35.7, 36.1,
121.5, 121.6, 124.3, 124.4, 125.7, 126.3, 126.5, 128.0, 128.1, 128.6, 129.0,
129.5, 129.8, 130.3, 131.3, 136.8, 137.1, 139.6, 142.9, 151.5, 152.6 ppm.
HRMS (MALDI-TOF, positive): m/z calcd for
found: 1727.1037 [M+] (error=À4.00 ppm).
C132H142: 1727.1106;
Synthesis of 11: Compound 2 (100 mg, 0.08 mmol) was heated at reflux
for 2 d with benzoquinone (173 mg, 1.6 mmol) in deoxygenated nitroben-
zene (30 mL); a slow color change from green to black-green was ob-
served. Nitrobenzene was distilled off under vacuum, and the remaining
green solid was washed with acetone and further purified by column
chromatography on silica gel (CHCl3/hexane=1:1 v/v) to afford 11
(90 mg, 85%) as a black-green solid. 1H NMR (500 MHz, CDCl3): d=
1.30 (s, 36H; tBu), 1.51 (s, 36H; tBu), 6.72 (s, 2H; quinone), 7.57 (d, J=
1 Hz, 4H; Ph), 7.62 (s, 2H; Ph), 7.65 (s, 4H; Ph), 7.72 (m, 2H; Ar), 7.74
(s, 2H; Ph), 8.17 (d, J=9.5 Hz, 2H; Ar), 8.48 (m, 2H; Ar), 8.61 (d, J=
9.5 Hz, 2H), 8.65 (d, J=9 Hz, 2H; Ar), 9.86 ppm (d, J=10 Hz, 2H; Ar).
13C NMR (125 MHz, CDCl3): d=32.2, 32.4, 35.7, 35.9, 121.2, 121.7, 122.0,
122.9, 123.7, 124.5, 124.7, 124.9, 126.2, 126.5, 126.6, 127.3, 127.5, 127.8,
128.5, 128.6, 128.9, 129.1, 129.6, 130.1, 131.1, 131.3, 137.5, 138.4, 138.9,
139.4, 141.7, 151.5, 152.5, 189.7 ppm. HRMS (FAB): m/z calcd for
z
calcd for C98H100O2: 1308.7668; found: 1308.7718 [M+] (error=
À3.81 ppm).
C
100H98O2: 1330.75613; found: 1330.75594 [M+] (error=À0.15 ppm).
Synthesis of 12: Compound 11 (100 mg, 0.07 mmol) was heated at reflux
for 2 d with
2 (184 mg, 0.15 mmol) in deoxygenated nitrobenzene
Acknowledgements
(30 mL); a slow color change from green to black-green was observed.
Nitrobenzene was distilled off under vacuum, and the remaining green
solid was washed with acetone and further purified by column chroma-
tography on silica gel (CHCl3/hexane=3:1 v/v) to afford 12 (142 mg,
40%) as a black-green solid. 1H NMR (500 MHz, CDCl3): d=1.29 (s,
72H; tBu), 1.54 (s, 72H; tBu), 7.56 (d, J=1.5 Hz, 8H; Ph), 7.61 (t, J=
2 Hz, 4H; Ph), 7.68 (d, J=2 Hz, 8H; Ph), 7.72 (m, 4H; Ar), 7.77 (t, J=
2 Hz, 4H; Ph), 8.19 (d, J=9.5 Hz, 4H; Ar), 8.49 (m, 4H; Ar), 8.62 (d,
J=9.5 Hz, 4H), 8.83 (d, J=9.5 Hz, 4H; Ar), 10.05 ppm (d, J=9.5 Hz,
4H; Ar). 13C NMR (125 MHz, CDCl3): d=32.2, 32.4, 35.7, 35.9, 121.7,
121.9, 122.0, 123.0, 123.9, 124.3, 124.8, 126.47, 126.49, 126.6, 127.1, 127.3,
127.5, 127.7, 128.8, 129.0, 129.1, 129.5, 130.0, 130.4, 130.8, 130.9, 137.2,
138.5, 138.6, 141.7, 151.6, 152.4, 193.4 ppm. HRMS (MALDI-TOF, posi-
J. W. acknowledges financial support from Singapore DSTA DIRP Proj-
ect (DSTA-NUS-DIRP/2008/03), the NRF Competitive Research Pro-
gram (R-143–000–360–281), and A*Star BMRC grant (No. 10/1/21/19/
642). K.-W. H. acknowledges financial support from KAUST.
[1] a) J. Wu, W. Pisula, K. Mꢃllen, Chem. Rev. 2007, 107, 718–747;
b) H. Dong, C. Wang, W. Hu, Chem. Commun. 2010, 46, 5211–
5222; c) Y. Wen, Y. Liu, Adv. Mater. 2010, 22, 1331–1345; d) J. E.
Anthony, A. Facchetti, M. Heeney, S. R. Marder, Adv. Mater. 2010,
22, 3876–3892.
Chem. Eur. J. 2011, 17, 14672 – 14680
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14679

J. Wu et al.
[2] a) J. Fabian, H. Nakanzumi, M. Matsuoka, Chem. Rev. 1992, 92,
1197–1226; b) G. Qian, Z. Wang, Chem. Asian J. 2010, 5, 1006–
1029; c) C. Jiao, J. Wu, Curr. Org. Chem. 2010, 14, 2145–2168.
[3] a) M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004, 104,
4891–4945; b) J. E. Anthony, Chem. Rev. 2006, 106, 5028–5048;
c) J. E. Anthony, Angew. Chem. 2008, 120, 460–492; Angew. Chem.
Int. Ed. 2008, 47, 452–483; d) F. Wꢃrthner, R. Schmidt, ChemPhys-
Chem 2006, 7, 793–797.
[4] a) K. Ito, T. Suzuki, Y. Sakamoto, D. Kubota, Y. Inoue, F. Sato, S.
Tokito, Angew. Chem. 2003, 115, 1191–1194; Angew. Chem. Int. Ed.
2003, 42, 1159–1162; b) H. Meng, F. Sun, M. B. Goldfinger, G. D.
Jaycox, Z. G. Li, W. J. Marshall, G. S. Blackman, J. Am. Chem. Soc.
2005, 127, 2406–2407; c) H. Meng, F. Sun, M. B. Goldfinger, F. Gao,
D. J. Londono, W. J. Marshall, G. S. Blackman, K. D. Dobbs, D. E.
Keys, J. Am. Chem. Soc. 2006, 128, 9304–9305.
[5] a) V. Podzorov, V. M. Pudalov, M. E. Gershenson, Appl. Phys. Lett.
2003, 82, 1739; b) A. Hepp, H. Heil, W. Weise, M. Ahles, R. Schme-
chel, H. von Seggern, Phys. Rev. Lett. 2003, 91, 157406; c) S. A.
Odom, S. R. Parkin, J. E. Anthony, Org. Lett. 2003, 5, 4245–4248;
d) V. C. Sundar, J. Zaumseil, V. Podzorov, E. Menard, R. L. Willett,
T. Someya, M. E. Gershenson, J. A. Rogers, Science 2004, 303,
1644–1646; e) H. Moon, R. Zeis, E.-J. Borkent, C. Besnard, A. J.
Lovinger, T. Siegrist, C. Kloc, Z. Bao, J. Am. Chem. Soc. 2004, 126,
15322–15323; f) D. A. da Silva Filho, E.-G. Kim, J.-L. Brꢄdas, Adv.
Mater. 2005, 17, 1072–1076.
[6] a) G. Horowitz, D. Fichou, X. Peng, F. Garnier, Synth. Met. 1991, 41,
1127–1130; b) Y. Y. Lin, D. J. Gundlach, S. Nelson, T. N. Jackson,
IEEE Trans. Electron Devices 1997, 44, 1325–1331; c) P. T. Herwig,
K. Mꢃllen, Adv. Mater. 1999, 11, 480–483; d) N. E. Gruhn, D. A. da
Silva Filho, T. G. Bill, M. Malagoli, V. Coropceanu, A. Kahn, J.-L.
Brꢄdas, J. Am. Chem. Soc. 2002, 124, 7918–7919; e) A. Afzali, C. D.
Dimitrakopoulos, T. L. Breen, J. Am. Chem. Soc. 2002, 124, 8812–
8813; f) Y. Sakamoto, T. Suzuki, M. Kobayashi, Y. Gao, Y. Fukai, Y.
Inoue, F. Sato, S. Tokito, J. Am. Chem. Soc. 2004, 126, 8138–8138;
g) S. K. Park, J. E. Anthony, D. A. Mourey, T. N. Jackson, Appl.
Phys. Lett. 2007, 91, 063514; h) D. Jurchescu, M. Popinciuc, B. J.
van Wees, T. T. M. Palstra, Adv. Mater. 2007, 19, 688–692.
[7] a) C. Marschalk, Bull. Soc. Chim. Fr. 1939, 6, 1112; b) E. Clar, Ber.
Dtsch. Chem. Ges. B 1939, 72, 2137; c) W. J. Bailey, C.-W. Liao, J.
Am. Chem. Soc. 1955, 77, 992–993; d) M. M. Payne, S. R. Parkin,
J. E. Anthony, J. Am. Chem. Soc. 2005, 127, 8028–8029.
[8] a) D. Chun, Y. Cheng, F. Wudl, Angew. Chem. 2008, 120, 8508–
8513; Angew. Chem. Int. Ed. 2008, 47, 8380–8385; b) I. Kaur, W.
Jia, R. P. Kopreski, S. Selvarasah, M. R. Dokmeci, C. Pramanik,
N. E. McGruer, G. P. Miller, J. Am. Chem. Soc. 2008, 130, 16274–
16275; c) I. Kaur, N. N. Stein, R. P. Kopreski, G. P. Miller, J. Am.
Chem. Soc. 2009, 131, 3424–3425; d) H. Qu, C. Chi, Org. Lett. 2010,
12, 3360–3363.
[9] a) C. Tçnshoff, H. F. Bettinger, Angew. Chem. 2010, 122, 4219–
4222; Angew. Chem. Int. Ed. 2010, 49, 4125–4128; b) I. Kaur, M.
Jazdzyk, N. N. Stein, P. Prusevich, G. P. Miller, J. Am. Chem. Soc.
2010, 132, 1261–1263; c) B. Purushothaman, M. Bruzek, S. R. Pakin,
A.-F. Miller, J. E. Anthony, Angew. Chem. 2011, 123, 7151–7155.
[10] a) E. Clar, Polycyclic Hydrocarbons, Vols. 1 and 2, Academic Press,
London, 1964; b) R. G. Harvey, Polycyclic Aromatic Hydrocarbons,
Wiley-VCH, New York, 1997.
[11] a) R. A. Pascal Jr., W. D. McMillan, V. D. Engen, R. G. Eason, J.
Am. Chem. Soc. 1987, 109, 4660–4665; b) N. Smyth, V. D. Engen,
R. A. Pascal, Jr., J. Org. Chem. 1990, 55, 1937–1940; c) X. Qiao,
D. M. Ho, R. A. Pascal, Jr., Angew. Chem. 1997, 109, 1588–1589;
Angew. Chem. Int. Ed. Engl. 1997, 36, 1531–1532; d) I. I. Schuster,
L. Cracium, D. M. Ho, R. A. Pascal, Jr., Tetrahedron 2002, 58, 8875–
8882; e) H. M. Duong, M. Bendikov, D. Steiger, Q. Zhang, G.
Sonmez, J. Yamada, F. Wudl, Org. Lett. 2003, 5, 4433–4436; f) Q.
Zhang, Y. Divayana, J. Xiao, Z. Wang, E, R, T. Tiekink, H. M.
Doung, H. Zhang, F. Boey, X. W. Sun, F. Wudl, Chem. Eur. J. 2010,
16, 7422–7426.
[12] N. G. Pschirer, C. Kohl, F. Nolde, J. Qu, K. Mꢃllen, Angew. Chem.
2006, 118, 1429–1432; Angew. Chem. Int. Ed. 2006, 45, 1401–1404.
[13] a) A. Herrmann, K. Mꢃllen, Chem. Lett. 2006, 35, 978–985; b) T.
Weil, T. Vosch, J. Hofkens, K. Peneva, K. Mꢃllen, Angew. Chem.
2010, 122, 9252–9278; Angew. Chem. Int. Ed. 2010, 49, 9068–9093;
c) X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A. Ratner, M. R.
Wasielewski, S. R. Marde, Adv. Mater. 2011, 23, 268–284.
[14] a) D.-E. Jiang, B. G. Sumpter, S. Dai, J. Chem. Phys. 2007, 127,
124703; b) D.-E. Jiang, S. Dai, Chem. Phys. Lett. 2008, 466, 72–75.
[15] a) X.-J. Zhang, X.-X. Jiang, J. Luo, C. Chi, H.-Z. Chen, J. Wu,
Chem. Eur. J. 2010, 16, 464–468; b) X. Zhang, J. Li, H. Qu, C. Chi,
J. Wu, Org. Lett. 2010, 12, 3946–3949; c) J. Yin, K. Zhang, C. Jiao, J.
Li, C. Chi, J. Wu, Tetrahedron Lett. 2010, 51, 6313–6315; d) Z. Sun,
J. Wu, Aust. J. Chem. 2011, 64, 519–528.
[16] a) E. Clar, Chem. Ber. 1948, 81, 52–63; b) H. Kuroda, J. Chem.
Phys. 1960, 1856–1857; c) S. M. Arabei, T. A. Pavich, J. Appl. Spec-
trosc. 2000, 67, 236–244.
[17] a) J. Yao, C. Chi, J. Wu, K.-P. Loh, Chem. Eur. J. 2009, 15, 9299–
9302; b) K. Zhang, K.-W. Huang, J. Li, C. Chi, J. Wu, Org. Lett.
2009, 11, 4854–4857; c) J. Li, K. Zhang, X. Zhang, K-W. Huang, C.
Chi, J. Wu, J. Org. Chem. 2010, 75, 856–863.
[18] E. Clar, Nature 1948, 161, 238–239.
[19] S. Saꢅdi-Besbes, ꢆ. Grelet, H. Bock, Angew. Chem. 2006, 118, 1815–
1818; Angew. Chem. Int. Ed. 2006, 45, 1783–1786.
[20] a) E. H. Fort, P. M. Donovan, L. T. Scott, J. Am. Chem. Soc. 2009,
131, 16006–16007; b) E. H. Fort, L. T. Scott, Angew. Chem. 2010,
122, 6776–6778; Angew. Chem. Int. Ed. 2010, 49, 6626–6628.
[21] a) C. F. H. Allen, A. Bell, J. Am. Chem. Soc. 1942, 64, 1253; b) M.
Ikawa, M. A. Stahmann, K. P. Link, J. Am. Chem. Soc. 1944, 66,
902; c) A. R. Lippert, J. Kaeobamrung, J. W. Bode, J. Am. Chem.
Soc. 2006, 128, 14738–14739.
[22] E. Clar, Aromatic Sextet, Wiley-Blackwell, London, 1972.
[23] K. Licha, B. Riefke, V. Ntziachristos, A. Becker, B. Chance, W.
Semmler, Photochem. Photobiol. 2000, 72, 392–398.
[24] a) J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bassler,
M. Porsch, J. Daub, Adv. Mater. 1995, 7, 551–554; b) C. Chi, G.
Wegner, Macromol. Rapid Commun. 2005, 26, 1532–1537.
Received: July 11, 2011
Published online: November 14, 2011
14680
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 14672 – 14680