Synthesis, characterization, and physical properties of a conjugated heteroacene: 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ)

Article abstract of DOI:10.1002/asia.201000659

We report the synthesis and characterization of a novel, stable and blue heteroacene, 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (BIQ 3). BIQ 3, with its relatively small π framework, has an absorption I_max at 620 nm, which is

Full text of DOI:10.1002/asia.201000659

FULL PAPERS
DOI: 10.1002/asia.201000659
Synthesis, Characterization, and Physical Properties of a Conjugated
Heteroacene: 2-Methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one
(BIQ)
Qichun Zhang,*[a] Jinchong Xiao,[a] Zongyou Yin,[a] Hieu M. Duong,[b] Fen Qiao,[a]
Freddy Boey,[a] Xiao Hu,[a] Hua Zhang,[a] and Fred Wudl*[b, c]
Abstract: We report the synthesis and
characterization of a novel, stable and
blue heteroacene, 2-methyl-1,4,6,7,8,9-
hexaphenylbenz(g)isoquinolin-3(2H)-
one (BIQ 3). BIQ 3, with its relatively
small p framework, has an absorption
lmax at 620 nm, which is larger than
that of pentacene (lmax =582 nm), but
BIQ 3 is more stable. The solutions of
BIQ 3 are observed without any no-
ticeable photobleaching on the order
of days. In the solid state, it is very
stable at ambient conditions and can
be stored indefinitely. Owing to its pyr-
idone end unit, BIQ 3 can display dif-
ferent resonance structures in different
solvents (aprotic and protic) or Lewis
acids to give different colors. The at-
tractive stability exhibited by BIQ 3 is
very desirable in organic semiconduc-
tor devices. Herein, we investigated a
simple heterojunction photovoltaic
device based on BIQ 3 as an electron
donor and [6,6]-phenyl-C61 butyric
methyl ester as an electron acceptor.
Our results show that this type of het-
eroacene could be a good candidate as
a charge-transport material in organic
semiconductor devices.
Keywords: absorption
·
hetero-
acenes · photovoltaics · semicon-
ductors · solvent effects
Introduction
cenes 1 (Scheme 1) and their derivatives have created a
great deal of interest not only in fundamental science but
also in potentially technological applications, such as organic
The pursuit of low-cost, mechanically flexible, and highly ef-
ficient organic semiconductor devices has strongly motivated
chemists to rationally design and synthesize novel small con-
jugated organic molecules and polymers.[1] As one family of
polycyclic aromatic hydrocarbons (PAHs),[2] linear oligoa-
Scheme 1. The structure of oligoacenes (1), isoquinolinones (2), and 2-
methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one (3).
[a] Prof. Q. Zhang, Dr. J. Xiao, Dr. Z. Yin, F. Qiao, Prof. F. Boey,
Prof. X. Hu, Prof. H. Zhang
School of Materials Science and Engineering
Nanyang Technological University
50 Nan yang Avenue, Singapore 639798 (Singapore)
Fax : (+65)67909081
E-mail: qczhang@ntu.edu.sg
light-emitting diodes (OLEDs), organic photovoltaic devi-
ces, organic photodetectors, and field-effect transistors
(FETs).[3] Their excellent electronic performance encourages
us to examine their similar analogues, heteroacenes,[4] the
conjugated frameworks of which have at least one heteroa-
tom, such as N, P, O, and S atoms. Currently, several types
of heteroacenes, such as thienobis(benzothiophenes),[5] an-
thradithiophene and its derivates,[6] pentathienopentacenes,[7]
carbazole-based heteroacenes,[8] and azapentacenes[9] have
been synthesized and applied in organic semiconductor devi-
ces. Their promising performance has stimulated us to look
[b] Dr. H. M. Duong, Prof. F. Wudl
Department of Chemistry and Biochemistry
University of California
Los Angeles, CA 90095 (USA)
[c] Prof. F. Wudl
Mitsubishi Chemical Center for Advanced Materials
Department of Chemistry and Biochemistry
and Center for Polymers and Organic Solids
University of California, Santa Barbara (USA)
E-mail: wudl@chem.ucsb.edu
856
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Chem. Asian J. 2011, 6, 856 – 862

at another class of heteroacenes, isoquinolinones
2
be used as p-type charge-transport materials in organic elec-
tronic devices.
(Scheme 1), the structures of which contain at least one
lactam unit. Although isoquinolinones 2 have attracted
some interest on account of their electronic properties and
sometimes unusual photophysics,[10] their applications in or-
ganic semiconductor devices remain largely undeveloped.
To enrich the family of organic semiconducting materials
and enhance the performance of organic electronic devices,
we are vigorously engaged in synthesizing a series of isoqui-
nolinones 2 and examining their performance in organic
semiconducting devices.
Generally, quinolinones and their derivatives contain
many biologically active alkaloids and can serve as bases in
nucleosides or building units in the synthesis of many alka-
loids.[11] Many methods, which are very important in synthet-
ic and medicinal chemistry, have been developed.[12] Howev-
er, in our research, isoquinolinones 2, which are different
from biologically active quinolinones, are a family of conju-
gated heterocyclic compounds. It is worth noting that the ni-
trogen atom in BIQ 2 is in the 2-position, not the 1-position
as reported in many papers. This feature makes the synthetic
work more challenging.
Results and Discussion
Although many synthetic routes have been reported in the
literature to prepare various types of isoquinolinones,[15]
a
quicker and more-practical way to approach a benzoisoqui-
nolinone, in which n=3, is through a [4+2] cycloaddition in-
volving in situ arynes as dienophiles and meso-ionic pyrimi-
dines 5[16] as dienes (Scheme 3). BIQ 3 was obtained in
In addition, isoquinolinones are very important building
blocks to challenge longer polyacenes through [4+2] cyclic
addition. However, it is well-known that longer polyacenes
(more than pentacene) become extremely insoluble and un-
stable. To overcome these problems, one possible way is to
increase more phenyl-substituted groups in these systems to
protect the conjugated system and increase the solubility.
Herein, we report a new method to synthesize a stable,
blue compound, 2-methyl-1,4,6,7,8,9-hexaphenylbenz(g)iso-
quinolin-3(2H)-one (BIQ 3, Scheme 1). Surprisingly, BIQ 3,
with its relatively small p framework, has an absorption lmax
at 620 nm, which is larger than that of pentacene (n=5 in 1,
Scheme 1, lmax =582 nm).[13] However, BIQ 3 is more stable
under atmospheric conditions. Interestingly, the structure of
BIQ 3 can be transformed into its resonant type—meso-ion
formation (Scheme 2)—with a significant color change if it
is dissolved in different solvents (aprotic and protic) or is
treated with Lewis acids.
Scheme 3. The synthetic route to BIQ 3.
quantitative yield from its precursor 1,4-dihydro-1,4,6,7,8,9-
hexaphenyl-2,12-dimethyl-1,4-(iminomethano)benz(g)isoqui-
noline-2,12-dione (4) through thermal elimination of lactam
bridges at 2208C. The precursor 4 was obtained in 65%
yield through slow addition of a suspension of 3-amino-
5,6,7,8-tetraphenylnaphthalene-2-carboxylic acid (6) in di-
chloroethane into a boiling solution of meso-ionic com-
pound 5 in the presence of isoamyl nitrite (Scheme 4).
Scheme 2. Resonance structures of BIQ 3.
Given that the molecular-electronic properties of penta-
cene have been shown to be desirable for electronic applica-
tions,[14] it is promising to envision similar functions for BIQ
3 as its electronic properties are quite similar, as reported
here. As a proof of concept, a heterojunction photovoltaic
device based on BIQ 3 and [6,6]-phenyl-C61 butyric methyl
ester (PCBM) (weight ratio 1:1) was fabricated, and our
preliminary results demonstrated that isoquinolinones can
Scheme 4. The synthetic route to 3-amino-5,6,7,8-tetraphenylnaphtha-
lene-2-carboxylic acid (6). DCE=1,2-dichloroethane.
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Q. Zhang, F. Wudl et al.
FULL PAPERS
The novel naphthalyne precursor 6 was synthesized by re-
acting a step-by-step bis-benzyne precursor 2-amino-5-nitro-
tetrephthalic acid 4-methyl ester (7) with tetraphenylcyclo-
pentadienone (8), followed by reduction and hydroxylation
(Scheme 4). The step-by-step bisACTHUNTGRNEUNG(benzyne) precursor 7 was
synthesized from a commercially available product, amino-
terephalic dimethyl ester, in four steps according to the re-
ported procedures.[17]
As we had difficulties in establishing a full 13C NMR spec-
trum of the precursor 4, light-yellow single crystals suitable
for X-ray diffraction analysis were grown from a mixed solu-
tion of dichloromethane/methanol (1:1) through slow evapo-
ration. Its structure with atomic labeling and crystal data
and structure refinement are shown in Figure 1 and Table 1.
The UV/Vis absorption spectrum of BIQ 3 was recorded
in THF at room temperature. As shown in Figure 2a, BIQ 3
Figure 2. a) UV/Vis spectrum of 3 in THF. b) Cyclic voltammogram of
10À5 m BIQ 3 in 0.1m TBAP/CH3CN (first three cycles vs. Ag/AgCl).
displays two broad absorption bands at around 300 and
620 nm. We were very surprised by the fact that BIQ 3, with
its relatively small p framework (three rings), has an absorp-
tion at 620 nm, with two shoulders at 582 and 670 nm. It is
worth noting that the absorption at 670 nm is longer than
that at the longest wavelength for pentacene (lmax =582 nm,
five rings).[13] When excited at 620 nm, it displays an emis-
sion peak at 710 nm (Figure 2b) with a low quantum yield
(Ff =0.3%, using 9,10-diphenylanthracene (ethanol solu-
tion, Ff =0.95) as a reference) at room temperature.[18]
Cyclic voltammetry (CV) of BIQ 3, recorded at room
temperature in dry CH3CN that contained 0.1m tetrabutyl-
ammonium perchlorate (TBAP), shows that the oxidation
and reduction processes are chemically and electrochemical-
ly reversible (Figure 4, discussed in more detail below). The
HOMO–LUMO gap calculated from the difference between
the half-wave redox potentials (Eo1 x =+0.15 eV and Er1ed
=
=
2
=
2
À1.80 eV) is 1.95 eV. This value is in good agreement with
the band gap, 2.0 eV, derived from the UV/Vis absorption
data. Like the UV/Vis data, the CV measurement collected
for BIQ 3 reinforces the similarity in electronic properties
to that of pentacene.
Figure 1. X-ray structure of 4.
The electronic states of BIQ 3 are strongly governed by
its pyridone end unit. There are two possible major contri-
buting resonance structures in BIQ 3 (Scheme 2). On the
left is the neutral polyene state and on the right is the
charge-separated state (meso-ion state). Either electronic
state can be readily favored through the choice of solvents.
In aprotic solvents, shown in Figure 3 with tetrahydrofuran
as well as other solvents (CH2Cl2, DMF, DMSO), the lon-
gest absorption maxima center is around 620 nm. In protic
solvents such as methanol, BIQ 3 is hydrogen-bonded to
clearly establish a different electronic species and the ab-
sorption has been blueshifted to 575 nm, whereas in strongly
acidic solvents such as trifluoroacetic acid (TFA), the ab-
sorption spectrum narrowed and the lmax is drastically blue-
shifted to 505 nm. In a relatively weaker acid such as acetic
acid (AcOH), the absorption spectrum falls between di-
chloromethane and trifluoroacetic acid at lmax =540 nm. In
contrast to the trifluoroacetic acid solution, in which BIQ is
completely protonated, the electronic spectrum of BIQ 3 in
AcOH suggested an acid–base equilibrium between proton-
ated BIQ 3 and the acetate anion. Based on the two acidic
media studied, the acidity of protonated BIQ 3 is roughly
Table 1. Crystal data and structure refinement for compound 4.
Compound 4
empirical formula
C52H38N2O2
Mr
722.84
crystal system
monoclinic
space group
P21/n
a [ꢁ]
11.9918(8)
b [ꢁ]
22.3878(16)
c [ꢁ]
14.3440(10)
a [8]
90
b [8]
92.1810(10)
g [8]
90
0.075
absorption coefficient [mmÀ1
]
F
(000)
1520
0.60ꢂ0.20ꢂ0.10
1.69 to 28.39
index ranges
reflns collected
independent reflns
À15ꢀhꢀ15,À29ꢀkꢀ29,À18ꢀlꢀ19
34476
9373
R
G
0.0696
completeness [%]
97.1
max/min transmission
final R indices (I>2s(I))
R indices (all data)
0.990/0.9550
R1=0.0556, wR2=0.1051
R1=0.1708, wR2=0.1368
858
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Chem. Asian J. 2011, 6, 856 – 862

Conjugated Heteroacene 2-Methyl-1,4,6,7,8,9-hexaphenylbenz(g)isoquinolin-3(2H)-one
The physical properties of BIQ 3 are equally noteworthy.
BIQ 3, as demonstrated in the solvent-dependent electronic
spectroscopy study, is readily soluble. In solution, it is sever-
al orders of magnitudes less sensitive than pentacene. Solu-
tions of BIQ 3 are observed without any noticeable photo-
bleaching on the order of days. In the solid state, it is very
stable at ambient conditions and can be stored indefinitely.
Given the very good performance of pentacene, but poor
stability in molecular electronics,[19] we were very interested
in replacing pentacene with BIQ 3 and examine its behavior
in semiconductor devices.
The structure and current density–voltage (J–V) charac-
teristic of a typical organic photovoltaic (OPV) is shown in
Figure 4. No current response in the dark was observed.
Figure 3. UV/Vis absorption spectra of BIQ 3 (3.0ꢂ10À5 m) in different
solvents: a) CH2Cl2, b) THF, c) CH3OH, d) DMF, e) DMSO,
f) CH3COOH, g) CF3COOH. The inset shows the color changes in differ-
ent solvents.
between AcOH and trifluoroacetic acid. The colors of these
solutions are also distinctly different (inset in Figure 3).
The dynamic structure of BIQ 3 from the solvent-depend-
ence studies demonstrated the importance of its amide bond
observed in the static structure. The drastic shift in the ab-
sorption spectrum clearly distinguishes the polyene and aro-
matic structure. In trifluoroacetic acid, the electronic spec-
À
trum of BIQ 3 is blueshifted due to the shortening of its N
CO bond through protonation, which locked the structure
into a lower-energy aromatic system. The same phenomenon
was also observed when BIQ 3 was treated with either
BF3·Et2O or methyl triflate. In both cases, the strong Lewis
or Brønsted acidity locked the structure into a charge-sepa-
rated state. This suggested that in aprotic solvents in which
BIQ 3 is not protonated, the electronic arrangement adopts
exclusively the higher-energy polyene resonance structure,
thereby reflecting a longer amide bond. Interestingly, in
methanol, the solution spectrum suggested an intermediate
bond length between the two structures since hydrogen
bonding is the only governing effect. This may be better elu-
cidated by the absorption exhibited in AcOH.
Figure 4. J–V characteristic of an ITO/PEDOT:PSS/BIQ:PCBM/Al OPV
device. Inset: schematic illustration of the solar-cell structure.
However, under simulated 100 mWcmÀ2 1.5 AM illumina-
tion, the results show that as-fabricated devices with an
open-circuit voltage (Voc) of 0.35 V, short-circuit current
density (Jsc) of 0.27 mAcmÀ2, and a fill factor (FF) of 0.24
were obtained. The Voc of this hybrid cell structure
(ꢁ0.4 V) is smaller than the difference (1.25 eV) in energy
between the LUMO of PCBM (3.7 eV)[20] and HOMO of
BIQ 3 (4.95 eV) on account of the barrier heights for elec-
trons going from Al (4.35 eV) into the LUMO level of
PCBM determined by investigation of the injection limited
electron current (ILC).[21] At present, a relatively low-power
conversion efficiency (ꢁ0.08%) is observed without optimi-
zation. However, a strong endeavor to improve the power
conversion efficiency through optimization of the fabrication
parameters is on the way.
The close resemblance in electronic properties between
BIQ and 5,7,12,14-tetraphenylpentacene (TPP)[17b] is demon-
strated in Table 2. The results obtained from UV/Vis and
CV for both molecules are strikingly similar. The UV/Vis
data of BIQ 3 and TPP show absorption maxima at approxi-
mately 620 nm (2.0 eV) and 622 nm (1.99 eV), respectively.
The DEHOMO–LUMO obtained from CV data for BIQ 3 and
TPP are 1.95 and 1.94 eV, respectively. These results are
highly suggestive that the electronic properties of BIQ 3 are
closely related to pentacene (DEHOMO–LUMO =2.1 eV).
In conclusion,
a stable, blue heteroacene 2-methyl-
1,4,6,7,8,9–hexaphenyl-benz(g) isoquinolin-3(2H)-one (BIQ
3) has been successfully synthesized and its optical property
and cyclic voltammetry have been studied. Interestingly,
BIQ 3 displays different colours in different solvents (aprot-
ic and protic) owing to its pyridone end unit, which can
have different resonance structures in various solvents.
Moreover, the fact that BIQ 3 has a low HOMO–LUMO
gap (1.95 eV), which is comparable to that of pentacene,
makes it a potential candidate for organic electronic applica-
tions. A heterojunction photovoltaic device based on BIQ 3
and PCBM has been fabricated. Our preliminary results
Table 2. Comparative electronic properties of BIQ 3 with TPP.
UV/Vis
lmax
Cyclic voltammetry
DE
[nm]
([eV])
(2.0)
(1.99)
[eV]
[nm]
(636.4)
(639)
BIQ 3
TPP
620
622
G
1.95
1.94
ACHTUNGTRENNUNG
R
ACHTUNGTRENNUNG
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859

Q. Zhang, F. Wudl et al.
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7.32–7.21 (m, 8H), 7.17 (s, 1H), 7.09–7.07 (m, 3H), 7.0 (m, 2H), 6.87–
6.79 (m,10H), 2.63 ppm (s, 6H); 13C NMR (CDCl3, 125 MHz): d=171.8,
140.08, 140.01, 139.96, 139.89, 139.08, 138.9, 138.7, 138.2, 136.0, 134.8,
131.4, 131.2, 131.0, 130.9, 130.7, 130.6, 129.9, 129.8, 128.6, 127.6, 127.4,
127.3, 127.2, 126.6, 126.58, 126.55, 126.3, 125.48, 125.44, 120.0, 80.8, 65.8,
33.7 ppm; IR (drift): n˜ =3054, 2979, 2973, 1687, 1603, 1492, 1444, 1198,
1008, 920, 886, 755, 703, 539 cmÀ1; MALDI-TOF: m/z: calcd: 722.29;
found: 723.3025 [M+H].
demonstrated a proof of concept that heteroacenes, such as
BIQ 3, can act as charge-transport materials in organic semi-
conductor devices. Further works such as enhancing the
power conversion efficiency through optimizing the photo-
voltaic devicesꢃ fabrication parameters, synthesizing highly-
conjugated heteroacenes with longer p-frameworks, and
their applications on organic semiconductor devices are
under investigation.
3 (Scheme 3): The corresponding precursor 4 was heated at 2208C for
6 h. Blue compound 3 was obtained in quantitative yield. m.p.>3008C;
1H NMR (CD2Cl2, 500 MHz): d=7.48 (d, 1H), 7.45–7.40 (m, 5H), 7.33–
7.21 (m, 6H), 7.15–6.98 (m, 10H), 6.86–6.82 (m, 10H), 1.58 ppm (s, 3H);
13C NMR (CD2Cl2, 125 MHz): d=158.0, 154.3, 140.78, 140.2, 140.1, 138.7,
138.6, 138.5, 137.2, 136.7, 136.5, 136.1, 135.6, 132.9, 131.0, 130.9, 130.7,
130.6, 130.1, 129.4, 128.67, 128.65, 127.66, 127.34, 127.1, 126.4, 126.3,
126.1, 126.08, 125.3, 125.2, 119.6, 117.0, 114.6, 36.8 ppm; IR (drift): n˜ =
3056, 3030, 1685, 1602, 1523, 1484, 1441, 1331, 1222, 1072, 1028, 887, 750,
698 cmÀ1; MALDI-TOF: m/z: calcd: 665.27; found: 666.2761 [M+H].
Experimental Section
All starting materials were used as received without further purification.
Compounds 5 and 7 were synthesized according to the reported proce-
dure.[16, 17]
9 (Scheme 4): Compound 7 (2.0 g, 8.4 mmol, precipitated in CH2ClCH2Cl
(30 mL)) was added dropwise to a boiling solution of tetraphenylcyclo-
pentadienone 8 (3.2 g, 8.4 mmol) and isoamyl nitrite (3.5 mL, 25.0 mmol)
in CH2ClCH2Cl (50 mL) under an Ar atmosphere. The reaction was
heated at reflux overnight. Then the solution was cooled down, and the
solvent was evaporated under vacuum. After passing through a silica
column using dichloromethane as a solvent, a pale yellow product was
obtained after washing with ether. Yield: 74%; m.p. 268–2708C;
1H NMR (CDCl3, 500 MHz): d=8.15 (s, 1H), 7.98 (s, 1H), 7.31–7.29 (m,
6H), 7.22–7.21 (m, 4H), 6.90–6.89 (m, 10H), 3.82 ppm (s, 3H); 13C NMR
(CDCl3, 125 MHz): d=165.8, 145.3, 143.1, 142.6, 140.0, 139.5, 139.4,
139.3, 137.7, 137.5, 132.5, 131.8, 130.86, 130.84, 130.71, 130.70, 130.25,
127.82, 127.76, 127.2, 127.1, 126.64, 126.62, 125.78, 125.77, 123.85, 123.42,
53.3 ppm; IR (drift): n˜ =3058, 3027, 2977, 2867, 1735, 1549, 1439, 1347,
1300, 1131, 1052, 913, 848, 748, 703, 531 cmÀ1; MALDI-TOF: m/z: calcd:
535.20; found: 535.14.
Cyclic Voltammetry (CV) Measurements
Cyclic voltammetry was performed with a three-electrode cell in a solu-
tion of acetonitrile and tetrabutylammonium perchlorate (0.1m, Bu4ClO4,
abbreviated as TBAP) at a scan rate of 100 mVsÀ1. A Pt wire was used
as a counter electrode, and glassy carbon was used as the working elec-
trode with an Ag/AgCl electrode used as reference electrode. Its poten-
tial was corrected to the saturated calomel electrode (SCE) by measuring
the ferrocene/ferrocenium couple in this system (0.44 V vs. SCE).[22]
X-Ray Crystal Structure
Single-crystal data was collected at 298 K with graphite-monochromat-
ized MoKa radiation (l=0.71073 ꢁ). The cell parameters were obtained
from the least squares refinement of the spots using the SMART pro-
gram. The structure was solved by direct methods using SHELXS-97,
which revealed the positions of all non-hydrogen atoms. This is followed
by several cycles of full-matrix least-squares refinements. Absorption cor-
rections were applied by using SADABS.[23] Hydrogen atoms were in-
cluded as fixed contributors to the final refinement cycles. The position
of hydrogen atoms were calculated on the basis of idealized geometry
and bond length. In the final refinement, all non-hydrogen atoms were
refined with anisotropic thermal coefficients.
10 (Scheme 4): A solution of compound 9 (6.0 g, 11.4 mmol) and Pd/C
(500 mg) in CH2Cl2/methanol (1:1) was stirred under hydrogen gas ad-
ministered with a balloon for 5 h. The inorganic residue was removed by
vacuum filtration and the filtrate was concentrated. The red residue was
purified by column chromatography over silica gel using chloroform to
afford amine (83.3%), then recrystallization from methanol/methylene
1
chloride (1:1) to give yellow powder. M.p: 293–2958C; H NMR (CDCl3,
CCDC 742124 (4) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
500 MHz): d=8.31 (s, 1H), 7.25–7.18 (m, 10H), 6.84–6.82 (m, 10H), 6.81
(s, 1H), 3.79 ppm (s, 3H); 13C NMR (CDCl3, 125 MHz): d=168.2, 141.5,
140.4, 140.3, 139.45, 139.38, 139.0, 136.0, 132.5, 131.4, 131.2, 131.1,
130.9,127.5, 127.4, 126.4, 126.3, 125.3, 125.1, 114.4, 51.8 ppm; IR (drift):
n˜ =3489, 3379, 3028, 2953, 2950, 1700, 1616, 1576, 1492, 1440, 1303, 1255,
1223, 1073, 749, 699, 568 cmÀ1; MALDI-TOF: m/z: calcd: 505.20; found:
505.2034.
Fabrication and Evaluation of Photovoltaic Devices
The photovoltaic devices were fabricated on indium tin oxide (ITO)-
coated glass substrates. The ITO glass was thoroughly cleaned by an ul-
trasonic treatment in acetone, ethanol, and deionized water sequentially
and dried before use. A layer of poly(3,4-ethylenedioxythiophene)/poly-
(styrenesulfonate) (PEDOT/PSS) was spin-coated at 3000 rps for 60 s on
the ITO substrate, followed by heating for 15 min at 1408C in an anneal-
ing oven. Afterwards, the active layer that contained a mixture of this
new material and PCBM (1:1 wt%) were spin-coated from o-dichloro-
benzene onto the substrates, respectively. Finally, the aluminum top elec-
trodes were evaporated by thermal evaporation in vacuum (2ꢂ10À4 Pa)
through a shadow mask. Post-device annealing was carried out at 1508C
for 15 min in a nitrogen-filled glovebox. The photovoltaic characteristics
of cells were determined by a SourceMeter (Keithley, model 2400) under
Xe-lamp illumination with a power density of 100 mWcmÀ2 (1.5 AM).
6 (Scheme 4): A solution of 10 (3.00 g, 5.94 mmol) and NaOH (2 g,
50 mol) in MeOH/isopropanol (20 mL, 1:1) was heated at reflux over-
night under an Ar atmosphere. Solvent was removed and the yellow resi-
due was taken up in water (20 mL). Concentrated HCl was added and
stirred at room temperature for 0.5 h. The participate was filtered and
dried to give compound
6 (92%) as a yellow solid. m.p.>3008C;
1H NMR (DMSO, 400 MHz): d=8.58 (br, 2H), 8.04 (s, 1H), 7.23–7.12
(m, 10H), 6.81–6.59 (m, 10H), 6.34 ppm (s, 1H); 13C NMR (DMSO,
125 MHz): d=168.9, 141.5, 140.5, 140.3, 140.2, 140.0, 139.3, 139.27, 139.0,
136.1, 135.8, 135.6, 132.4, 131.4, 131.15, 131.12, 130.9, 129.2, 128.5, 128.1,
127.9, 127.0, 126.9, 126.80, 126.78, 125.8, 125.7 ppm; IR (drift): n˜ =3492,
3384, 3057, 3042, 3300–2200 (br), 1700, 1618, 1584, 1494, 1426, 1314,
1266, 1217, 1087, 919, 701 cmÀ1; MALDI-TOF: m/z: calcd: 491.19; found:
491.1865.
4 (Scheme 3): The solution of meso-ionic compound 5 (292 mg, 1 mmol)
and the corresponding acid 6 (490 mg, 1 mmol) with isoamyl nitrite
(1 mL) in 1,2-dichloroethylene (DCE; 15 mL) was stirred at 908C over-
night. After DCE was removed, the residue was purified by column chro-
matography on silica gel using dichloromethane to give the correspond-
Acknowledgements
ing cycloadduct
4
(65%). m.p. 2108C (decomp); 1H NMR (CDCl3,
Q.Z. thanks the support from the NTU startup grant (SUG) and F.W.
thanks the NSF for support.
500 MHz): d=8.03 (d, 2H), 7.84 (s, 1H), 7.75 (m, 2H), 7.48 (m, 3H),
860
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