meso-Substituted bisanthenes as soluble and stable near-infrared dyes

Article abstract of DOI:10.1021/jo902413h

(Chemical Equation Presented) Three meso-substituted bisanthenes, 4-6, were prepared in a short synthetic route from the bisanthenequinone. They exhibit largely improved stability and solubility in comparison to the parent bisanthene. All of these compoun

Full text of DOI:10.1021/jo902413h

pubs.acs.org/joc
meso-Substituted Bisanthenes as Soluble and Stable Near-infrared Dyes
Jinling Li,† Kai Zhang,† Xiaojie Zhang,† Kuo-Wei Huang,‡ Chunyan Chi,† and
Jishan Wu*,†
†Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 and
‡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
chmwuj@nus.edu.sg
Received November 11, 2009
Three meso-substituted bisanthenes, 4-6, were prepared in a short synthetic route from the
bisanthenequinone. They exhibit largely improved stability and solubility in comparison to the
parent bisanthene. All of these compounds also show near-infrared (NIR) absorption and emission
with high to moderate fluorescence quantum yields. Amphoteric redox behavior was observed for
4-6 by cyclic voltammetry, and these compounds can be reversibly oxidized and reduced into
respective cationic and anionic species by both electrochemical and chemical processes. In addition,
compound 5 adopts a herringbone π-stacking motif in the single crystal.
Introduction
However, many commercially available NIR dyes such as
cyanine dyes suffer from inevitable drawbacks due to their
insufficient photostability.8
Near infrared (NIR) dyes1 with absorption and/or emission
in the spectral range of 700-1400 nm are of importance for
many potential applications such as high-contrast bioimaging,2
optical recording,3 NIR laser filter,4 NIR photography,5 solar
cells,6 and optical limiting at telecommunications wavelength.7
Polycyclic aromatic hydrocarbons (PAHs) usually exhibit
excellent chemical stability and photostability with respect to
the traditional cyanine dyes, and one good example is rylene
(oligo-peri-naphthalene), which is a type of important stable
dye/pigment used in industry.9 For the design of PAH-based
NIR dyes, largely extended π-conjugation is usually required.
For example, the alkyl- or carboximide-substituted rylene
molecules show NIR absorption only when the mole-
cular length reaches four naphthalene units (quaterrylene).10
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Published on Web 01/07/2010
DOI: 10.1021/jo902413h
r
2010 American Chemical Society

Li et al.
JOCArticle
CHART 1. Molecular Structures of Bisanthene 1 and Its Deri-
vatives 2-6
FIGURE 1. Normalized UV-vis-NIR absorption and photolu-
minescence spectra of compounds 4, 5, and 6. The concentrations
for the absorption and emission spectroscopic measurements in
toluene are 10-5 and 10-6 M, respectively.
SCHEME 1. Synthetic Route to meso-Substituted Bisanthenes 4-6
Moreover, previous research disclosed that the band gap of a
PAH molecule depended on not only the molecular size but
also the edge structure.11 The arm-chair edged PAHs usually
exhibit high chemical stability but a large band gap. On the
other hand, theoretical calculations suggested that zigzag
edged PAH molecules with a smaller benzenoid component
would show low band gap with near-infrared absorption.12
Our recent interest is a type of zigzag edged, peri-fused
oligoacenes, namely, periacenes, which are expected to exhi-
bit NIR absorption and emission.12 As the smallest member
of the periacene family, bisanthene (1, Chart 1) was reported
to show far-red absorption with absorption maximum at
662 nm.13 However, the parent bisanthene is a very unstable
compound and decomposes quickly in solution under ambi-
ent air and light condition. This is mainly because of its high-
lying HOMO level, and it is ready to undergo addition
reaction with the singlet oxygen in air.13 Like the zigzag
edged pentacene compound,11b the reactive sites in bis-
anthene are the meso-positions of the zigzag edges. We
recently found that attachment of two electron-withdrawing
dicarboxylic imide groups at the zigzag edges of the bis-
anthene (compound 2 in Chart 1) not only largely improved
its stability but also significantly shifted the absorption to the
NIR spectral range with the absorption maximum at
830 nm.14 In addition, quinoidal bisanthene 3 (Chart 1) was
also prepared and exhibited good stability with NIR absorp-
tion.15 While these methods are successful, we are looking
for an alternative approach to prepare soluble and stable
bisanthene-basedNIR dyesbya short synthetic route. Herein,
we report that substitution at the active meso-positions of the
bisanthene with either aryl or alkyne group is also an efficient
way to achieve our target. In this work, two aryl-substituted
bisanthenes, 4 and 5, and one triisopropylsilylethynyl-substi-
tuted bisanthene, 6 (Chart 1), were prepared. The substi-
tuents are chosen on the basis of several considerations:
(a) Conjugation effect. The aryl and alkyne groups are supposed
to at least partially extend the π-conjugation with the central
bisanthene units so that the absorption and emission spectral
can shift into NIR spectral range. At the same time, the
extended π-conjugation can also improve the stability of the
electron-rich bisanthene unit by extended electron delocaliza-
tion. (b) Steric effect. The bulky substitution at the meso-
positions can prevent the oxidative addition of singlet oxygen
to the bisanthene core. Meanwhile, the solubility can be also
improved as a result of diminished intermolecular interactions
(especially for compound 4). (c) Electronic effect. To form
stable bisanthene derivatives, electron-withdrawing groups
should be attached. Herein, three substituents with different
electron-donating/-accepting capabilities are introduced; in
particular, the trifluoromethylphenyl in compound 5 and
the triisopropylsilylethynyl groups in 6 are both electron-
withdrawing groups that are expected to enhance the
stability of the electron rich bisanthene. The photophysical
properties and electrochemical behavior of compounds 4-6
were studied, and the effect of the different substituents on
their properties is discussed in detail. In addition, geometric
structure and molecular packing of one of these compounds
was studiedbycrystallographicanalysis, andtheirpotential as
semiconductors in a field effect transistor (FET) is also
discussed.
€
(11) (a) Wu, J.; Pisula, W.; Mullen, K. Chem. Rev. 2007, 107, 718–747. (b)
Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452–483.
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124703. (b) Jiang, D. E.; Dai, S. Chem. Phys. Lett. 2008, 466, 72–75. (c) Jiang,
D. E.; Dai, S. J. Phys. Chem. A 2008, 112, 332–335. (d) Chen, Z. F.; Jiang,
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D. E.; Lu, X.; Bettinger, H. F.; Dai, S.; von Rague, Schleyer, P.; Houk, K. N.
Org. Lett. 2007, 9, 5449–5452.
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(b) Kuroda, H. J. Chem. Soc. 1960, 1856–1857. (c) Clar, E. Chem. Ber. 1948,
81, 52–63.
Results and Discussions
(14) Yao, J.; Chi, C.; Wu, J.; Loh, K. Chem.;Eur. J. 2009, 15, 9299–9302.
(15) Zhang, K.; Huang, K. W.; Li, J. L.; Luo, J.; Chi, C. Y.; Wu, J. Org.
Lett. 2009, 11, 4854–4857.
Synthesis. The synthesis of compounds 4, 5, and 6 is
depicted in Scheme 1. Bisanthenequinone 7 was first
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TABLE 1. Summary of Photophysical and Electrochemical Properties of Compounds 4, 5, and 6a
εmax
λabs
(nm)
(M-1
λem
(nm)
QY
(nm)
Eox
(V)
Eox
(V)
Eox
(V)
Ered
(V)
Ered
(V)
HOMO
(eV)
LUMO
(eV)
Eg
(eV)
1
2
3
1
2
opt
compounds
cm-1
)
4
5
6
687
683
727
628
624
662
582
580
603
38 438
45 098
55 690
701
699
744
0.81
0.80
0.38
0.44
0.53
0.34
1.03
1.14
0.72
-1.21
-1.10
-0.92
-1.65
-1.53
-1.31
-4.71
-4.80
-4.57
-3.20
-3.31
-3.47
1.73
1.74
1.62
1.20
aEoxn and Eredn are half-wave potentials for respective redox waves with AgCl/Ag as reference. HOMO and LUMO energy levels were calculated from
the onset potentials of the first oxidation (Eoxonset) and the first reduction wave (Eredonset) according to the following equations: HOMO = -(4.8 þ
Eoxonset) and LUMO = -(4.8 þ Eredonset), where the potentials are referred to EFcþ/Fc
.
FIGURE 2. Optimized structure and frontier molecular orbital profiles of molecules 4-6 based on DFT (B3LYP/6-31G**) calculations.
prepared in gram scale according to literature procedure.13
The subsequent chemistry is similar to that of pentacenequi-
none.16 Compound 7 reacted with the Grignard reagent of
the respective arenes or the lithium reagent of triisopropylsi-
lylacetylene in anhydrous THF to give the respective
alcohols 8a-c in 50-60% yields. This was followed by
dehydroxylation and reductive aromatization with NaI/
NaH2PO2 to afford the target compounds 4, 5, and 6 in
good yields. Actually, this two-step reaction can also be done
in one pot without separation of the intermediate compound
8a-c. Thus this synthetic route is obviously simple and
straightforward, and the target compounds can be obtained
by simple column chromatography purification. Com-
pounds 4-6 have good solubility in normal organic solvents
such as chloroform and THF; in particular, the 3,5-di-tert-
butylphenyl-substituted bisanthene 4 shows the highest
solubility due to the very bulky substitution. All of the inter-
mediate compounds and the final products are well char-
acterized by NMR spectroscopy and high resolution mass
spectrometry (see Supporting Information).
respectively. Compared with the absorption spectra of
bisanthene,13 there is a red-shift of about 25, 21, and 65 nm
for 4, 5, and 6, respectively. The red-shift for all of these
compounds indicates that π-conjugation of the bisanthene
core is further extended by incorporation of the aryl and
triisopropylsilylethynyl moieties. DFT (B3LYP/6-31G**)
calculations of 4-6 were then conducted to further under-
stand their geometric and electronic structures. The opti-
mized structure and the frontier molecular orbital profiles of
4-6 are shown in Figure 2. The phenyl moieties in 4 and 5
are twisted about 80° with respect to the bisanthene
plane, and as a result, only weak electron delocalization
between the phenyl ring and the bisanthene units was
observed for 4 and 5. However, for 6, obvious electron
delocalization between the ethynyl moiety and the bisan-
thene unit was observed. Such a structural difference
accounts for the difference in their absorption spectra where
the largest red-shift was found for 6. In addition, time-
dependent DFT calculations also predict that the absorption
maxima for 4-6 are 716.3, 714.4, and 785.6 nm, respectively,
and such tendency also agrees well with our experimental
results.
Compounds 4-6 also show strong fluorescence with the
emission maximum at 701, 699, and 744 nm, respectively
(Figure 1 and Table 1). Their photoluminescence quantum
yields (Φ) were determined according to an optical dilute
method (optical density A < 0.05) by using cardiogreen dye
(λabs (max)=780 nm, Φ=0.13 in DMSO) as a standard.17
The Φ values of 0.81, 0.80, and 0.38 were obtained for 4, 5,
and 6, respectively. Such high to moderate quantum yields
for NIR dye are remarkable given that many NIR absorbing
Photophysical Properties and Theoretical Calculations.
The UV-vis-NIR absorption and fluorescence spectra of
4, 5, and 6 recorded in toluene are shown in Figure 1, and the
data are collected in Table 1. Solutions of 4-6 in toluene
display a blue color and well-resolved absorption bands
between 500 and 800 nm with the maximum peak at 687
(molar extinction coefficient ε=38 438 M-1 cm-1), 683 (ε=
45 098 M-1 cm-1), and 727 (ε = 55 690 M-1 cm-1) nm,
(16) (a) Allen, C. F. H.; Bell, A. J. Am. Chem. Soc. 1942, 64, 1253–1261.
(b) Funk, R. L.; Young, E. R. R.; Williams, R. M.; Flanagan, M. F.; Cecil,
T. L. J. Am. Chem. Soc. 1996, 118, 3291–3292. (c) Miller, G. P.; Mack, J.;
Briggs, J. Org. Lett. 2000, 2, 3983–3286. (d) Anthony, J. E.; Eaton, D. L.;
Parkin, S. R. Org. Lett. 2002, 4, 15–18. (e) Jiang, J. Y.; Kaafarani, B. R.;
Neckers, D. C. J. Org. Chem. 2006, 71, 2155–2158. (f) Wudl, F.; Perepichka,
D. F. Chem. Rev. 2004, 104, 4891–4945.
(17) Licha, K.; Riefke, B.; Ntziachristos, V.; Becker, A.; Chance, B.;
Semmler, W. Photochem. Photobiol. 2000, 72, 392–398.
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FIGURE 3. Photostability test of compounds 4-6 in toluene upon irradiation by 100 W white light bulb. (Left) UV-vis-IR absorption
spectra of 4 (a), 5 (c), and 6 (e) in toluene recorded during the irradiation. The arrows indicate the change in the spectra. (Right) Change of
optical density of 4 (b), 5 (d), and 6 (f) at the absorption maximum wavelength with the irradiation time. The original optical density before
irradiation was normalized at the absorption maximum.
dyes (including the bisanthenes 1-3) usually exhibit low
fluorescence quantum yields.
maximum with the irradiation time (Figure 3). Upon irra-
diation by UV lamp (4 W), the decomposition process
became faster, and the compounds displayed t1/2 of about
404, 452, and 586 min, respectively (Figure S1 in Supporting
Information). These results revealed that the photostability
of the bisanthene-based compounds followed the sequence
6 > 5 > 4 . 1 and also proved that introduction of phenyl or
triisopropylsilylethynyl groups at the meso-positions of the
bisanthene unit largely improved the stability of the chromo-
phore. The difference in the stability of the bisanthene 1
and its derivatives 4-6 can be explained by a combination of
the electronic effect, conjugation effect, and steric effect
of the substituents. Without any substituent, the parent
Photostability and Thermal Stability. In contrast to the
very unstable parent bisanthene, the air-saturated solutions
of 4, 5, and 6 in toluene are stable for weeks under ambient
conditions without significant change on their UV-vis-
NIR absorption spectra. Upon irradiation of white light
(100 W), the solutions gradually decomposed with a decrease
of the optical intensity at the major absorption band
(550-800 nm) and appearance of new absorption band in
the shorter wavelength (Figure 3). The half-times (t1/2) of
around 618, 674, and 870 min were estimated for 4, 5, and 6,
respectively, by plotting the optical density at the absorption
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Li et al.
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bisanthene 1 with a high lying HOMO energy level can be
easily oxidized by adding singlet oxygen to the core, and
eventually a more stable bisanthenequinone 7 is formed.13
However, after substitution by aryl and alkyne at the meso-
positions, the bulky substituents significantly prohibit the
intermolecular interaction between the oxygen and the
bisanthene core. Moreover, the extended π-conjugation
between the bisanthene and the aryl or alkyne moieties
further delocalizes the electron cloud and leads to a more
stable extended π-system; in particular, the electron delocali-
zation is more effective in 6 with respect to 4 and 5. More-
over, electron-withdrawing effect also plays an important
role in the stability of the bisanthene chromophore. For 5,
the electron-withdrawing trifluoromethyl group on the
phenyl ring reduces the electron density of the bisanthene
backbone, so it is less photo-oxidizable than 4. For 6, the
ethynyl group is fully conjugated to the bisanthene π-system
(resonance effect) and the sp-hybridized ethynyl carbons are
modestly more electronegative than sp2 -hybridized carbons
to which they are attached (inductive effect), so compound 6
is most stable. Such a trend is also in agreement with the
observation for meso-substituted pentacene derivatives.18
Thermogravimetric analysis (TGA) measurements reveal
that 4 and 5 are highly stable with a decomposition tempera-
ture of about 410 °C (5 wt % weight loss) in N2 atmosphere,
whereas for compound 6, its decomposition temperature is
about 334 °C, probably because of the relatively poor
thermal stability of CꢀC units (Figure S2 in Supporting
Information). For these three compounds, neither glass
transition nor crystal melting point or liquid crystalline-
isotropic transition was observed in the temperature range
of 25-300 °C by means of differential scanning calori-
metry (DSC). So we can conclude that after substitution
at the meso-positions of bisanthene, new soluble and
stable near-infrared absorbing and emitting dyes 4-6 are
obtained.
Electrochemical Properties and Chemical Oxidation
Titration. The electrochemical properties of compounds 4-6
were investigated by cyclic voltammetry (CV) in dry DCM
(Figure 4), and the data are collected in Table 1. The cyclic
voltammograms of 4 and 5 exhibit two reversible oxidation
waves with half-wave potentials (Eoxn) at 0.44 and 1.03 V for
4 and 0.53 and 1.14 V for 5, while three oxidative waves were
observed for 6, with Eoxn at 0.34, 0.72, and 1.20 V (vs AgCl/
Ag). Compounds 4, 5, and 6 also show two quasi-reversible
reduction waves with the half-wave potential of the first
reductive waves (Ered1) at -1.21, -1.10, and -0.92 V, respec-
tively. Such an amphoteric redox behavior suggests that all
of these compounds can be reversibly oxidized into respec-
tive cationic species (e.g., radical cations and dications) and
reduced into corresponding anionic species (e.g., radical
anion and dianion) and the charged species can be stabilized
by the largely delocalized π-system. The lowest first oxida-
tion potential observed for 6 can be explained by the most
effective π-conjugation between the bisanthene and the
ethynyl moieties as we discussed above. Moreover, more
detectable oxidation states can be determined for 6. The first
oxidation potential of 5 is higher than that for 4 as a result of
FIGURE 4. Cyclic voltammograms of 4 (a), 5 (b), and 6 (c) in
dichloromethane (1 mM) with 0.1 M Bu4NPF6 as supporting
electrolyte, AgCl/Ag as reference electrode, Au disk as working
electrode, Pt wire as counter electrode, and scan rate at 50 mV/s.
the electron-withdrawing effect of the trifluoromethyl
groups.
Chemical oxidation titrations of compounds 4-6 were
conducted in DCM by using either iodine or SbCl5 as
oxidant, and the process was followed by UV-vis-NIR
absorption spectroscopy. All of these compounds can be
reversibly oxidized by SbCl5 into stable radical cations with
the appearance of new characteristic absorption bands in the
shorter and longer wavelengths (Figure 5). Such a pheno-
menon is common due to the redistribution of frontier mole-
cular orbital energy level 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
oxidized species can also be reversibly reduced into the
neutral state by adding Zn dust to the solution containing
oxidized species (Figure 5). Similar reversible process can be
observed for 4 and 5 when iodine was used as oxidant.
However, chemical oxidization of 5 by iodine is irreversible
likely due to electrophilic addition of Iþ onto the CꢀC units
(Figure S4 in Supporting Information).
The HOMO and LUMO energy levels were deduced from
the onset potentials of the first oxidation (Eoxonset) and the
first reduction wave (Eredonset), according to the following
equations: HOMO=-(4.8 þ Eoxonset) and LUMO=-(4.8 þ
Eredonset), where the potentials are calibrated to EFcþ/Fc
19
.
Compared with the aryl-substituted bisanthenes (4 and 5),
compound 6 has a higher lying HOMO energy level (-4.57
eV). However, this compound is still more stable than 4 and 5
because of effective electron delocalization. In agreement
with the small optical band gap (Egopt) determined from the
absorption spectra, the electrochemcial band gaps are also
small due to a convergence of the HOMO and LUMO energy
levels. As a result, low band gap mateirals with NIR absorp-
tion and emission are obtained.
Single-Crystal Structure and Molecular Packing. Besides
the photophysical and electrochemical properties, molecular
structure and solid state packing of these molecules are also
of importance when considering of their potential applica-
tions as semiconductors in electronic devices such as
FET. Single crystal of 5 was successfully obtained by slow
(18) Kaur, I.; Jia, W.-L.; Kopreski, R.-P.; Selvarasah, S.; Dokmeci,
M.-R.; Pramanil, C.; McGruer, N.-E.; Miller, G.-P. J. Am. Chem. Soc.
2008, 130, 16274–16286.
(19) (a) Chi, C.; Wegner, G. Macromol. Rapid Commun. 2005, 26, 1532–
1537. (b) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler,
H.; Porsch, M.; Daub, J. Adv. Mater. 1995, 7, 551–554.
860 J. Org. Chem. Vol. 75, No. 3, 2010

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FIGURE 5. (Left) UV-vis-NIR absorption spectra of 4 (a), 5 (c), and 6 (e) during the titration with SbCl5 in dry DCM. The arrows show the
changes of the spectra during the titration. (Right) UV-vis-NIR absorption spectra of the oxidized pieces 4 (b), 5 (d), and 6 (f) during
reduction by Zn with different contact time. The arrows indicate the changes of the spectra with different contact time with Zn dust.
diffusion of methanol vapor to the chloroform solution. The
single-crystal structure and three-dimensional packing of 5
are shown in Figure 6.20 Compound 5 has a planar bisan-
thene unit, and the trifluoromethylphenyl groups are twisted
from the bisanthene plane by about 80° due to steric con-
gestion (Figure 6a). Such structure is similar to the phenyl-
meso-substituted pentacene.16 Interestingly, 5 adopts a layer-
like structure (Figure 6b), and in each layer a herringbone
π-stacking motif (Figure 6c) was observed. Two types of
π-π interactions can be distinguished: an offset π-overlap
between the bisanthene units with a close contact distance of
ꢀ
˚
3.301 A and an edge-to-face CH-π interaction with a close
ꢀ
˚
contact distance of 2.752 A. Such a close packing mode with
strong intermolecular π-interactions suggests that 5 could be
a good semiconductor for FET devices.
Conclusions
In summary, three meso-substituted bisanthenes 4-6 were
successfully prepared in a short synthetic route. Compared
with the parent bisanthene 1, compounds 4-6 exhibit largely
improved stability and solubility. The obtained materials
also show bathochromic shift of their absorption and emis-
sion spectra into the NIR spectral range with high to
moderate fluorescence quantum yields, qualifying them as
(20) Single crystal data for 5: C42H20F6, orthorhombic, space group Pbca.
˚
˚
˚
Unit cell parameters: a=10.9112(9) A, b=7.7032(7) A, c=34.108(3) A, R=
3
3
˚
90°, β=90°, γ=90°, volume=2866.8(4) A , Z=4, density=1.480 Mg/m , R1=
0.0775, wR2=0.1543.
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(1 mL). To the mixture was added dropwise 1-bromo-3,5-
di-tert-butylbenzene (707 mg, 2.62 mmol) in dry THF
(10 mL), and the mixture was stirred at room temperature for
2 h to generate Grignard reagent. The as-prepared Grignard
reagent was transferred into a suspension of bisanthenequinone
7 (100 mg, 0.26 mmol) in dry THF (20 mL), and the mixture was
stirred at room temperature overnight. The reaction was
quenched with water (100 mL) and extracted with diethyl ether.
The organic layer was washed by water and dried over anhy-
drous Na2SO4. After removal of solvent, the residue was further
purified by column chromatography on silica gel with DCM/
hexane=2:1 (v/v) as eluent to afford 8a (114 mg, 57%) as a light
yellow solid. Mp > 300 °C. 1H NMR (500 MHz, CDCl3) δ 1.04
(s, 36 H), 3.22 (s, 2 H), 7.02 (d, J=1.25 HZ, 4 H), 7.07 (t, J=1.9
Hz, 2 H), 7.56 (dd, J=7.86 Hz, 4 H), 7.89 (d, J=6.3 Hz, 4 H),
8.40 (d, J=7.55 Hz, 4 H). 13C NMR (125 MHz, CDCl3) δ 31.35,
34.68, 74.91, 119.25, 120.01, 120.14, 122.05, 123.81, 127.16,
127.36, 128.92, 141.36, 149.45, 149.93. EI MS: m/z = 760.6
([M]), calculated exact mass 760.4. HR EI MS: m/z=760.4257
([M]), calculated exact mass for C56H56O2 760.4280.
7,14-Bis(3,5-di-tert-butylphenyl)phenanthro[1,10,9,8-opqra]-
perylene (4). In absence of light, a mixture of 8a (200 mg,
0.26 mmol), NaI (394 mg, 2.62 mmol), NaH2PO2 H2O
3
(508 mg, 3.94 mmol), and acetic acid (50 mL) was heated to
reflux for 2 h. After cooling to room temperature, the deep blue
precipitate was collected by filtration, washed with water and
methanol, and purified by column chromatography on silica gel
with hexane/toluene=1:1 (v/v) as eluent to afford 4 (133 mg,
70%) as a deep blue solid. Mp > 300 °C. 1H NMR (500 MHz,
CDCl3) δ 1.41 (s, 36 H), 7.29 (d, J=1.9 Hz, 4 H), 7.34 (dd, J=8.2
Hz, 4 H), 7.42 (d, J=8.8 Hz, 4 H), 7.56 (t, J=1.58 Hz, 2 H), 8.25
(d, J=7.55 Hz, 4 H). 13C NMR (125 MHz, CDCl3) δ 31.62, 35.03,
120.18, 125.51, 126.39, 126.43, 127.10, 132.36, 132.39, 151.02. EI
MS: m/z=726.5 ([M]), calculated exact mass 726.4. HR EI MS:
m/z=726.4204 ([M]), calculated exact mass for C56H54 726.4226.
7,14-Bis(4-(trifluoromethyl)phenyl)-7,14-dihydrophenanthro-
[1,10,9,8-opqra]perylene-7,14-diol (8b). Magnesium (95 mg,
3.94 mmol) and a piece of iodine crystal were placed in dry
THF (1 mL). To the mixture was added dropwise 1-bromo-
4-(trifluoromethyl)benzene (591 mg, 2.62 mmol) in dry THF
(10 mL), and the mixture was stirred at room temperature
overnight to generate Grignard reagent. The as-prepared
Grignard reagent was transferred into a suspension of bisanthe-
nequinone 7 (100 mg, 0.26 mmol) in dry THF (20 mL) and the
mixture was stirred at room temperature overnight. The reac-
tion was quenched with water (100 mL) and extracted with
diethyl ether. The organic layer was washed by water and dried
over anhydrous Na2SO4. After removal of solvent, the residue
was purified by column chromatography on silica gel with
DCM/hexane=2:1 (v/v) as eluent to afford 8b (103 mg, 60%)
FIGURE 6. Single-crystal structure (a) of compound 5, its three-
dimensional layer-like packing (b), and the herringbone π-stacking
motif in each layer (c).
both NIR absorption and fluorescent dyes. These com-
pounds display amphoteric redox behavior with multistep
reversible redox processes, suggesting that they could be used
as both hole and electron transporting materials. In parti-
cular, the ordered herringbone π-stacking mode observed in
5 indicates that it can be used as potential semiconductor in
FETs in the future studies.
Experimental Section
General Experimental Methods. All reagents and starting
materials were obtained from commercial suppliers and used
without further purification. Anhydrous tetrahydrofuran
(THF) was purified by routine procedure and distilled over
sodium under nitrogen before using. The bisanthenequinone 7
was prepared according to literature.13 Photocyclization reac-
tion was carried out in a photochemical reactor with irradiation
of a 450 W mercury-vapor lamp. Column chromatography was
performed on silica gel. All chemical shifts in NMR spectra are
quoted in ppm, relative to tetramethylsilane, using the residual
solvent peak as a reference standard. High resolution mass
spectra were recorded with EI ionization source. UV-vis
absorption and fluorescence spectra were recorded in DCM
solution on a spectrometer and a fluorometer, respectively.
Cyclic voltammetry measurements of compounds 4-6 in
DCM (1 mM) was performed with a three-electrode cell, using
0.1 M Bu4NPF6 as supporting electrolyte, AgCl/Ag as reference
electrode, gold disk as working electrode, Pt wire as counter
electrode, and scan rate at 50 mV/s. Thermogravimetric analysis
(TGA) was carried out at a heating rate of 10 °C/min under
nitrogen flow. Differential scanning calorimetry (DSC) was
performed at a heating/cooling rate of 10 °C/min under nitrogen
flow.
1
as a light yellow solid. Mp > 300 °C. H NMR (500 MHz,
CDCl3) δ 3.26 (s, 2 H), 7.33 (br, 8 H), 7.59 (dd, J=7.58 Hz, 4 H),
7.83 (d, J=6.95 Hz, 4 H), 8.45 (d, J=7.55 Hz, 4 H). 13C NMR
(125 MHz, CDCl3) δ 74.09, 119.10, 122.68, 123.60, 124.87,
125.12, 125.15, 127.62, 127.77, 129.11, 140.28, 153.52. EI MS:
m/z=672.3 ([M]), calculated exact mass 672.2. HR EI MS: m/z=
672.1511 ([M]), calculated exact mass for C42H22F6O2 672.1524.
7,14-Bis(4-(trifluoromethyl)phenyl)phenanthro[1,10,9,8-opqra]-
perylene (5). In absence of light, a mixture of 8b (100 mg, 0.15
mmol), NaI (225 mg, 1.5 mmol), NaH2PO2 H2O (290 mg, 2.25
3
mmol), and acetic acid (25 mL) was heated to reflux for 2 h.
After cooling to room temperature, the deep blue precipitate
was collected by filtration, washed with water and methanol,
and purified by column chromatography on silica gel with
hexane/toluene=3:1 (v/v) as eluent to afford 5 (68 mg, 72%)
as a deep blue solid. Mp > 300 °C. 1H NMR (500 MHz, CDCl3)
δ 7.30 (d, J=8.85 Hz, 4 H), 7.39 (dd, J=7.88 Hz, 4 H), 7.40 (d,
J=8.3 Hz, 4 H), 7.92 (d, J=8.2 Hz, 4 H), 8.29 (d, J=7.6 Hz, 4 H).
7,14-Bis(3,5-di-tert-butylphenyl)-7,14-dihydrophenanthro[1,10,
9,8-opqra]perylene-7,14-diol (8a). Magnesium (82 mg, 3.42
mmol) and a piece of iodine crystal were placed in dry THF
862 J. Org. Chem. Vol. 75, No. 3, 2010

Li et al.
JOCArticle
13C NMR (75 MHz, CDCl3) δ 120.65, 125.85, 125.90, 126.37,
127.00, 131.77, 131.99, 132.27, 134.69, 142.90. EI MS: m/z =
638.2 ([M]), calculated exact mass 638.1. HR EI MS: m/z =
638.1469 ([M]), calculated exact mass for C42H20F6 638.1469.
7,14-Bis(triisopropylsilylethynyl)phenanthro[1,10,9,8-opqra]-
perylene (6). To a solution of triisopropylsilylacetylene (479 mg,
2.629 mmol) in anhydrous THF (30 mL) at 0 °C was added
dropwise n-BuLi (1.6 M in hexanes, 1.56 mL, 2.5 mmol). The
solution was allowed to stir for 30 min at 0 °C before bisanthe-
nequinone 7 (100 mg, 0.26 mmol) was added in one portion. The
mixture was warmed to room temperature, stirred overnight,
and then poured into a large amount of water. The mixture was
extracted with chloroform, and the organic layer was washed
with brine and dried over MgSO4. The solvent was removed by
evaporation and the residue was dried under vacuum. In
absence of light, a mixture of the crude product diol 8c (218
methanol, and purified by column chromatography on silica
gel with hexane/toluene=3:1 (v/v) as eluent to afford 6 (68 mg,
72%) as a deep green solid. Mp > 300 °C. 1H NMR (500 MHz,
CDCl3) δ 1.32 (br, 6 H, isopropyl), 1.33 (br, 36 H, isopropyl),
7.42 (br, 4 H), 7.95 (br, 4 H), 8.19 (br, 4 H). EI MS: m/z=710.5
([M]), calculated exact mass 710.4. HR EI MS: m/z=710.3756
([M]), calculated exact mass for C50H54Si2 710.3764.
Acknowledgment. This work was financially supported by
the NRF Competitive Research Program (R-143-000-360-
281) and NUS Young Investigator Award (R-143-000-356-
101).
Supporting Information Available: Original characteriza-
tion spectra of all new compounds, photostability test of 4-6
under irradiation of UV lamp, chemical oxidation titration
process of 4-6 by iodine, and DFT calculation details. This
material is available free of charge via the Internet at http://
pubs.acs.org.
mg, 0.26 mmol), NaI (394 mg, 2.62 mmol), NaH2PO2 H2O (406
3
mg, 3.15 mmol) and acetic acid (10 mL) was heated to reflux for
2 h. After cooling to room temperature, the deep green pre-
cipitate was collected by filtration, washed with water and
J. Org. Chem. Vol. 75, No. 3, 2010 863