Functionalized organic dyes containing a phenanthroimidazole donor for dye-sensitized solar cell applications

Article abstract of DOI:10.1016/j.tet.2012.04.074

Five functionalized organic dyes (H6-10) containing a phenanthroimidazole unit as an electron donor were synthesized and characterized for use in dye-sensitized solar cell (DSSC) applications. Under standard global AM 1.5 solar conditions, the DSSCs based on dye H6 displayed the best performance, with an incident photon-to-current conversion efficiency (IPCE) exceeding 70% at wavelengths of 400-530 nm, a short-circuit photocurrent density of 10.98 mA cm^-2, an open-circuit voltage of 0.68 V, a fill factor of 0.69, and an overall conversion efficiency of 5.12%. This efficiency is ～94% of that for JK2 cells (5.46%) and ～72% of that for N719 cells (7.07%) under the same conditions.

Full text of DOI:10.1016/j.tet.2012.04.074

Tetrahedron 68 (2012) 5590e5598
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Functionalized organic dyes containing a phenanthroimidazole donor for
dye-sensitized solar cell applications
,
a,
Woochul Lee a, Youna Yang a, Nara Cho b, Jaejung Ko b , Jong-In Hong
*
*
a Department of Chemistry, Seoul National University, Seoul 151-747, Republic of Korea
b Department of New Material Chemistry, Korea University, Jochiwon, Chungnam 339-700, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Five functionalized organic dyes (H6-10) containing a phenanthroimidazole unit as an electron donor
were synthesized and characterized for use in dye-sensitized solar cell (DSSC) applications. Under
standard global AM 1.5 solar conditions, the DSSCs based on dye H6 displayed the best performance, with
an incident photon-to-current conversion efficiency (IPCE) exceeding 70% at wavelengths of
400e530 nm, a short-circuit photocurrent density of 10.98 mA cmꢀ2, an open-circuit voltage of 0.68 V,
a fill factor of 0.69, and an overall conversion efficiency of 5.12%. This efficiency is w94% of that for JK2
cells (5.46%) and w72% of that for N719 cells (7.07%) under the same conditions.
Received 30 November 2011
Received in revised form 16 April 2012
Accepted 20 April 2012
Available online 27 April 2012
Keywords:
Dye-sensitized solar cells (DSSCs)
Organic dyes
Ó 2012 Elsevier Ltd. All rights reserved.
Phenanthroimidazole
Squaraine dye
1. Introduction
a key factor in the fabrication of highly efficient solar cells, a dye
should possess several properties, including a wide absorption
In recent years, remarkable increases in energy consumption
have led to a focus on renewable natural energy sources. The
conversion of solar energy to electrical energy is very attractive, as
sunlight is a clean and readily available resource. Since the first
overlap with the solar spectrum for efficient light harvesting, ap-
propriate HOMO and LUMO energy levels for efficient electron in-
jection from the excited dye to the conduction band of TiO2, rapid
dye regeneration by electron injection into the oxidized dye from
the redox couple, and hydrophobicity to minimize charge
recombination.5
€
report in 1991 by Michael Gratzel et al., dye-sensitized solar cells
(DSSCs) have received much attention because of their low pro-
duction cost and relatively high energy conversion efficiency.1
Compared with traditional silicon-based solar cells, DSSCs offer
various advantages including cost effectiveness, tunability of the
absorption region, and effective performance under diffuse light.
Conventional DSSCs typically consist of a nanocrystalline titanium
oxide, a sensitizer, and an electrolyte. Among these three parts,
a suitable photosensitizer is essential in realizing highly efficient
DSSCs. To date, ruthenium-based dyes have achieved high power
conversion efficiencies of upto w11%.2 As an alternative to the
commonly used ruthenium dyes, organic dyes have a variety of
advantages, such as high molar extinction coefficients, easy modi-
fication of molecular structures, relatively low material costs and
environmental friendliness.3 Remarkable advances have been
achieved in metal-free organic dyes, and recently, an impressive
power conversion efficiency of over 10% has been reported.4 As
The general configuration of most reported organic dyes is a D-
p-A structure because of its effective photoinduced intramolecular
charge transfer (ICT) properties. The photophysical and electro-
chemical properties of such dyes can easily be tuned by in-
corporating a variety of donor, spacer, and acceptor moieties.6 The
most common donors used are arylamines, such as triphenylamine
and carbazole, which are well known for their strong electron-
donating and hole-transporting abilities.7 In
a recent study,
imidazole-based donors, such as phenanthroimidazole and pyr-
enoimidazole also exhibited good electron-donating abilities.8 The
p
-conjugated bridges often consist of thiophene or benzene units,
and the acceptor is usually a cyanoacrylate group.9
Herein, we report the synthesis and DSSC performance of five
functionalized organic dyes with D-
phenanthroimidazole as an electron donor and cyanoacetic acid as an
anchoring group, which are linked by -conjugated bridges, such as
p-A structures consisting of
p
phenylene and thiophenylene moieties. A systematic investigation
wasperformed todetermine the effectof thenumberof phenyleneon
* Corresponding authors. Tel.: þ82 2 880 6682; fax: þ82 2 889 1568 (J.-I.H.);
tel.: þ82 41 860 1337; fax: þ82 41 860 5396 (J.K.); e-mail addresses: jko@
korea.ac.kr (J. Ko), jihong@snu.ac.kr (J.-I. Hong).
p-conjugated bridges (H6, H7, and H8). Moreover, we studied an in-
fluence of the N-functionalized group in the phenanthroimidazole
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.074

W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
5591
moiety, such as a tri(ethylene oxide) chain and a squaraine unit (H9
and H10). A tri(ethylene oxide) chain that coordinates Liþ was in-
troduced instead of n-butyl to retard charge recombination.10 In an
effort to realize panchromatic dyes, we combined an additional
squaraine dye with the donor moiety to extend the absorption range
to the near-IR region.11 The overall conversion efficiencies of the de-
vices sensitized with H6, H7, H8, H9 and H10 were 5.12%, 4.15%, 3.49%,
4.22%, and 2.18%, respectively.
A more planar structure can be achieved in H6, which does not
have a biphenyl ring in the bridging unit, because the two adjacent
phenyl groups are rather twisted, not only with respect to each
other, but also with the adjacent phenanthroimidazole and thio-
phene moieties.13 Thus, intramolecular charge transfer in H6 dye is
more effective, leading to a bathochromic shift and the highest
molar extinction coefficient among these three dyes (H6e8). Thus,
the addition of phenyl rings did not contribute to extending the
conjugation length and did not improve light-harvesting ability. In
addition, H9 shows an absorption maximum (lmax) at 420 nm,
which is similar to that of H7 (lmax¼421 nm). However, the molar
2. Results and discussion
2.1. Synthesis
extinction coefficient of H9 (
3
¼46,655 Mꢀ1 cmꢀ1) is higher than
that of H7 (
3
¼34,090 Mꢀ1 cmꢀ1).
Squaraines are dyes well known for their strong absorption in
the near-IR region.14 Despite their intense absorption, their spectral
bands are located in a narrow region, limiting the efficiency of DSSC
devices sensitized with squaraine dyes.11,15 In recent years, squar-
aine units have been incorporated into the main conjugated back-
bone of dyes in efforts to extend their absorption range into the far-
red region for panchromatic absorption. H10 displays two absorp-
The molecular structures and the synthetic routes for the five
dyes are illustrated in Schemes 1 and 2, respectively. 4-(2-(2-(2-
methoxyethoxy)ethoxy)ethoxy)benzenamine 1012a and (E)-3-
hydroxy-4-((1,3,3-trimethylindolin-2-ylidene)methyl)cyclobut-
3-ene-1,2-dione 1412b and 50-(4-bromophenyl)-[2,20-bithio-
phene]-5-carbaldehyde 712c were synthesized as described in
previous reports. The phenanthroimidazole donor parts were
synthesized by the condensation of 9,10-phenanthrenequinone,
aldehydes and arylamines (4-butylaniline, 10, 16) in the presence
of ammonium acetate in acetic acid. The formylated compounds
3, 8, 9, 13, and 18 were then prepared by the palladium-
catalyzed Stille reaction and the Suzuki reaction. Finally, Knoe-
venagel condensation reactions between the formylated com-
pounds and cyanoacetic acid in the presence of piperidine
provided the dyes, H6eH10. The details are illustrated in the
experimental section.
tion maxima at 425 nm (
3
¼41,495 Mꢀ1 cmꢀ1) and 641 nm
(
3
¼91,030 Mꢀ1 cmꢀ1), which are assigned to the main conjugated
system and squaraine, respectively. Therefore, H10 seems to be
a promising dye because its absorption range extends into the near-
IR region.
The absorption spectra of dyes attached to the TiO2 films display
broader responses than those in solution (see Fig. 1b). The maxi-
mum absorption peaks of H6eH8, which all have a butylphenyl unit
in the phenanthroimidazole moiety, are red-shifted in TiO2 films,
whereas those of H9 and H10 in TiO2 films show slight blue-shifting
compared with their absorption spectra in DMF solution. We pre-
sumed that these shifts in absorption spectra were caused by dye
aggregation on the TiO2 films.16 It is worth noting that the broad-
ening of absorption bands and longer tailing upon dye adsorption
are advantageous for device performance.
2.3. Theoretical calculations
To achieve a better understanding of the molecular geometries
and electronic distributions of the dyes, we performed density
functional theory (DFT) calculations using the DFT B3LYP/6e31G(d)
basis set in the Gaussian 09 software package. The electronic dis-
tributions and optimized geometries of the dyes are shown in Figs.
2and 3 and S2. In the case of the H6eH9 dyes, a butyl group was
removed with ignorable effects on the molecular geometries and
electronic distributions of the dyes. For the H6eH8 dyes, the
HOMOs are mainly localized in the phenanthroimidazole unit and
extend to the
p-conjugated bridges and the LUMOs are located
mainly over the cyanoacrylic moiety and also extend to the
p
-
Scheme 1. Structures of dyes.
conjugated bridges. H6 has an almost planar conformation,
whereas the phenyl groups in H7 and H8 result in an overall non-
planar conformation. The calculated dihedral angles between
phenanthroimidazole and the adjacent phenyl ring are 26.88ꢁ and
23.57ꢁ for H7 and H8, respectively. Additionally, the adjacent
phenyl rings of H8 are more twisted, at 34.19ꢁ (Fig. 2). The torsion
angles between the phenyl rings and thiophene are 23.41ꢁ and
2.2. Photophysical properties
The UV-visible absorption spectra of the dyes in N,N-dime-
thylformamide (DMF) are shown in Fig. 1, and their photophysical
data are listed in Table 1. All dyes possess distinct absorption bands
in the visible region (350e500 nm) that are attributed to both the
17.87ꢁ for H7 and H8, respectively (Fig. 2). Therefore,
are more delocalized with fewer phenyl rings in the bridging part,
which results in more effective -conjugation. The twisted mo-
p-electrons
pe
p* transition of the conjugated system and an intramolecular
p
charge transfer (ICT) transition from the phenanthroimidazole
donor to the anchoring group. Interestingly, the absorption maxi-
mum peak of H6 (lmax¼432 nm) appears in the red-shifted region
compared with that of H8 (lmax¼369 nm), which has two phenyl
groups in the bridging unit (see Fig. 1). This phenomenon is in ac-
cord with the calculated geometric structure of the molecule (see
Fig. 2).
lecular geometries have negative effects on the light absorption
region and photoinduced charge transfer, which results in the de-
creased photocurrent. Unlike the other dyes, in the case of H10, the
HOMO is distributed over the squaraine unit, and HOMO-1 is
populated in the phenanthroimidazole unit (Fig. 3). Moreover, the
squaraine moiety is almost perpendicular to the phenan-
throimidazole unit (82.58ꢁ), which is reflected in two independent

5592
W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
Scheme 2. Synthetic routes of dyes.
Table 1
Photophysical and electrochemical parameters of the dyes
Dyes lmax
(
3
)a/nm
Eoxb/V E0e0c/V E0ꢂ ꢀ0d/V HOMOe/eV LUMOe/eV
H6
H7
H8
H9
H10
432 (38,625) 1.15
421 (34,090) 1.14
369 (24,275) 1.14
420 (46,655) 1.13
425 (41,495) 0.72
641 (91,030)
2.53
2.58
2.65
2.58
1.85
ꢀ1.38
ꢀ1.44
ꢀ1.51
ꢀ1.45
ꢀ1.13
5.31
5.30
5.30
5.29
4.88
2.78
2.72
2.65
2.71
3.03
a
Maximum absorption spectra of dyes in DMF solution (2.0ꢃ10ꢀ5 M).
b
Measured in DMF with 0.1 M TBAPF6. The oxidation potential was determined
from the onset of cyclic voltammograms with a scan rate of 100 mV sꢀ1. Potentials
are calibrated with the internal ferrocene/ferrocenium (Fc/Fcþ) standard.
c
E0e0 were derived from the 10% intensity of the absorption spectra.
Calculated by E0ꢂ ꢀ0¼Eox.ꢀE0e0
.
d
e
Calculated based on EHOMO(Fc/Fcþ)¼4.8 eV versus vacuum.
2.4. Electrochemical properties
Fig. 1. Absorption spectra of dyes in 0.02 mM DMF solution.
To confirm the successful operation of DSSCs using the novel
dyes H6eH10, the electrochemical properties of the dyes were
determined by cyclic voltammetry (CV) in DMF using tetrabuty-
lammonium hexafluorophosphate (TBAPF6) as a supporting elec-
trolyte; the data are summarized in Table 1. The first oxidation
potentials (Eox) of H6eH9 are in the range of 1.13e1.15 V versus the
normal hydrogen electrode (NHE), which indicates that these four
light absorption regions (Fig. 1). This molecular geometry has a di-
rect effect on cell performance, as discussed in the following sec-
tion. In all the dyes, the LUMO is located over the conjugated
bridges through cyanoacrylic acid. The apparent charge migration
from the HOMO to the LUMO reveals that intramolecular charge
transfer can occur except H10.

W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
5593
LUMO level because it has a narrow band gap owing to the presence
of the squaraine unit. The estimated LUMO levels of dyes are more
negative than the conduction band edge of TiO2 (ECB¼e0.5 V vs
NHE),17 indicating successful electron injection from the dyes into
TiO2. All the dyes have energetic configurations suitable for appli-
cation as DSSC sensitizers.
2.5. Photovoltaic performance
Devices with TiO2 layers of varying thicknesses were manufac-
tured to optimize cell performance, and the most effective thick-
ness was found to be 7 mm with a 4 mm scattering layer for all dyes.
The liquid electrolyte was composed of 0.6 M 1,2-dimethyl-n-pro-
pylimidazolium iodide (DMPImI), 0.1 M LiI, 0.05 M I2, and 0.5 M 4-
tert-butylpyridine (TBP) in acetonitrile. Current density-voltage
(IeV) characteristics and the incident photon-to-current conver-
sion efficiency (IPCE) spectra were measured with a black tape
mask under standard global AM 1.5 solar conditions (see Fig. 4 and
Table 2). The H6-sensitized cell showed the best performance, with
a short-circuit photocurrent density (Jsc) of 10.98 mA/cm2, an open-
circuit voltage (Voc) of 0.68 V, and a fill factor (FF) of 0.68, yielding
an overall cell efficiency (h) of 5.12% (see Table 2). For a precise
Fig. 2. Dihedral angles between aromatic rings of H dyes.
comparison, JK2- and N719-sensitized cells were also fabricated
under the same conditions; performance tests of these cells
resulted in the following respective values: Jsc, 13.28 and 13.64 mA/
cm2; Voc, 0.64 and 0.74 V; FF, 0.64 and 0.70; and
h, 5.46 and 7.07%.
The efficiency of the H6-based cell thus reached w94% of that of the
JK2 cell and w72% of the N719 cell, indicating that the phenan-
throimidazole unit is an efficient electron donor. The short-circuit
photocurrent density increased in the order H8<H7<H6 because
of the better light-harvesting ability of H6 than H7 and H8. The
Fig. 3. Frontier molecular orbitals of H10 dye.
dyes have very similar HOMO energy levels. Our calculations in-
dicated that the HOMOs of these dyes are mainly located in the
phenanthroimidazole unit. However, the first oxidation peak of H10
was measured at 0.72 V, which is more negative than the others.
This behavior corresponds to a different electronic distribution in
the HOMO level of H10. All the calculated HOMO levels are suffi-
ciently more positive than the Iꢀ/I3ꢀ redox potential (Eredox¼w0.4 V
vs NHE), indicating that the regeneration of oxidized dyes from
electrolytes is energetically favorable. The excited-state potentials
(E0ꢂ ꢀ0) were calculated from the equation (E0ꢂ ꢀ0¼Eox.ꢀE0e0), where
E0e0 is the zeroezero excitation energy derived from the wave-
length at an intensity of 10% of the normalized absorption spec-
trum. In contrast to the similar HOMO levels of H6eH9, the LUMO
energy values calculated from E0-0* differ depending on the con-
jugated components in their bridges. Thus, H7 and H9 have similar
HOMO and LUMO values because these two dyes have the same
main
p-conjugated system. However, H10 has the most positive
Fig. 4. IeV curve (top) and IPCE plot (bottom) of DSCs based on H dyes.

5594
W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
Table 2
generated by the squaraine unit into the TiO2 conduction band via
the anchoring group is unfavorable. Second, as shown in Fig. 4, H10
shows very low photon-to-current conversion efficiency below 20%
in the 400e600 nm region. We measured photoluminescence (PL)
spectra of a squaraine derivative (sq, Scheme S1), H7 and H10 dyes
in 1 mM DMF solution (see Fig. 5).14 H7 and sq exhibit maximum
emissions at 556 nm (ex. 450 nm) and 688 nm (both ex. 450 nm and
556 nm), respectively. When the main conjugated system of H10 is
excited at 450 nm, only one emission peak is observed, which
mostly comes from the squaraine moiety (lmax¼704 nm). This in-
Photovoltaic parameters of DSSCs based on the dyes in full sunlight (AM 1.5 G,
100 mW cmꢀ2
Dyesa
)
Voc (V)
Jsc (mA/cm2)
ff
h (%)
H6
H7
H8
H9
H10
JK2
N719
0.68
0.63
0.62
0.64
0.59
0.64
0.74
10.98
9.24
7.85
9.70
3.95
68.64
71.40
71.67
67.90
71.52
64.45
70.01
5.12
4.15
3.49
4.22
1.66
5.46
7.07
13.28
13.64
a
€
dicates that emission of H10 arises from the Forster resonance
Electrolyte composition : 0.6 M DMPImI, 0.1 M LiI, 0.05 M I2, and 0.5 M TBP in
acetonitrile.
energy transfer from the main conjugated system to the squaraine
moiety. To confirm the FRET in H10, we prepared a blending solu-
tion of H7 and sq (1:1) and measured its PL spectrum. As shown in
Fig. 5, the maximum PL of the blending solution was observed at
684 nm (ex. 450 nm). This emission profile is similar to that of H10.
Consequently, as H10 dye absorbs whole region from UVevis to
NIR, two processes are operative: intramolecular FRET from the
main conjugated system to the squaraine unit and inefficient
charge transfer to the TiO2 conduction band through the phenan-
throimidazole group, which induce the low photoconversion effi-
ciency. In contrast with H10, other H dyes possess IPCE spectra
ranging from 300 to 700 nm, exceeding 60% in the range of
400e500 nm. Especially, H9 exhibits a maximum value close to
80%, which is ascribed to its highest molar extinction coefficient.
This is because the perpendicular molecular geometry between
squaraine and phenanthroimidazole causes an unfavorable charge
transfer from the squaraine moiety to the phenanthroimidazole
unit (see Fig. 2), despite the improved light harvesting ability of
H10. This interpretation is supported by the incident photon-to-
current conversion efficiency (IPCE) spectra shown in Fig. 4.
relatively low efficiencies of H7 and H8 arise from their twisted
molecular structures, which inhibit efficient ICT. H9 exhibits better
photovoltaic performance than H7 because of the presence of
a tri(ethylene oxide) chain instead of a butyl group. It has been
clearly demonstrated that the tri(ethylene oxide) unit can co-
ordinate Liþ.10 The presence of lithium cations in the liquid elec-
trolyte leads to a positive shift in the TiO2 conduction band, causing
a reduction in Voc
18
.
Incorporating tri(ethylene oxide) into the
sensitizer thus enables the spatial separation of Liþ from the TiO2
surface as well as the high molecular extinction coefficient.
Therefore, the Liþ coordinating property of H9 positively affects
both Voc and Jsc. The device based on H10 showed a low efficiency of
1.66% because of its remarkable decrease in Jsc from that of H7 (3.95
vs 9.24 mA/cm2). To elucidate the functional role of the tri(ethylene
oxide) unit in the device performance of the H9-based cell, we
performed electrochemical impedance spectroscopy (EIS) ana-
lysis.12c This method is generally used to investigate electron life
time and charge recombination rate under open-circuit and dark
conditions.19 The second semicircle of the Nyquist plot (Fig. S4) is
related to the charge recombination process. As shown in Fig. S4,
the second semicircle radius decreases as going from H9 (10.8 U) to
H7 (4.49 U), indicating that H9 more inhibits electron re-
combination from injected electrons in TiO2 to electrolyte when
compared with H7. Moreover, in the Bode phase plot (Fig. S4), the
middle-frequency peak (in the 10e100 Hz range) is related to the
life time of injected electrons in TiO2 and is ultimately correlated
with Voc. The electron life time is obtained from the middle-
frequency peak in the Bode phase plot using equation (1), where f
is the frequency of the peak.
s
¼ 1=2
p
f
(1)
The electron life time of H9 (7.33 ms) is longer than H7
(3.29 ms). This result is correlated with the fact that H9, which
incorporates a tri(ethylene oxide) unit, has slightly higher Voc and
Jsc values than H7. Thus, the presence of the tri(ethylene oxide) in
the H9 dye as a functional unit suppress charge recombination,
which ultimately contributes to the positive effect on the photo-
conversion efficiency.
Although H10 showed the widest photo-active region from 350
to 700 nm, the device based on H10 exhibited the lowest photo-
current of 3.95 mA/cm2 as well as only w19% of the maximum IPCE.
There are two reasons for poor performance of the H10-based de-
vice: (1) inefficient charge transfer from the squaraine unit to the
Fig. 5. Photoluminescent spectra of sq, H7 and H10 in DMF solution.
3. Conclusion
€
main conjugated system and (2) Forster resonance energy transfer
We synthesized five functionalized organic dyes containing
a phenanthroimidazole donor for use in dye-sensitized solar cells.
The best performance was obtained with the H6 dye, yielding an
efficiency of 5.12%, which is comparable to the reference cell based
on JK-2 (5.46%), suggesting that phenanthroimidazole is a promis-
ing electron donor. The photovoltaic performance of dyes improved
with a decrease in the number of phenyl rings because the large
dihedral angle between aromatic rings in the bridges has a negative
effect on intramolecular charge transfer. The H9-sensitized DSSC
(FRET) from the main conjugated system to the squaraine unit.
First, the low efficiency of the H10-based cell arises from an un-
favorable charge transfer from the squaraine moiety to the phe-
nanthroimidazole unit, which is caused by the perpendicular
molecular geometry between squaraine and phenanthroimidazole
(see Fig. 2), despite the improved light-harvesting ability of H10.
This speculation is supported by low IPCE at>600 nm in the
squaraine absorption region (Fig. 4). The injection of electrons

W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
5595
exhibited slightly better photovoltaic performance than that of H7
because the tri(ethylene oxide) chain in H9 can coordinate with Liþ
and thus retard charge recombination. The H10 dye, containing an
extra squaraine moiety, was synthesized to extend the absorption
range into the near-IR region. Although H10 has an intense ab-
sorption band from 300 to 700 nm, low efficiency was observed
because of unfavorable electron transfer to the conduction band of
TiO2 and FRET from the main conjugated system to the squaraine
unit. Our results show that the coplanar geometry and suitable
energy levels should be carefully considered in designing new dyes.
It is very clear that photovoltaic dye performance is significantly
affected by the conjugated components and functionalized
moieties.
1036, 848, 781, 747, 719; MALDI-TOF MS, m/z: calcd for
29H23BrN2S: 510.077, found: 510.799 [M]þ.
C
4.2.2. 2-(4-Bromophenyl)-1-(4-butylphenyl)-1H-phenanthro[9,10-d]
imidazole (4). Compound 4 was prepared according to the syn-
thetic procedure for compound 1, using 4-bromobenzaldehyde
instead of 5-bromo-2-thiophenecarboxaldehyde (yield: 67%). Mp
168 ꢁC; 1H NMR (300 MHz, CDCl3):
d
(ppm) 8.89e8.86 (d, J¼7.8 Hz,
1H), 8.78e8.76 (d, J¼8.4 Hz, 1H), 8.72e8.70 (d, J¼8.3 Hz, 1H),
7.78e7.74 (t, J¼7.1 Hz,1H), 7.69e7.64 (t, J¼8.3 Hz,1H), 7.55e7.37 (m,
9H), 7.28e7.20 (m, 2H), 2.85e2.80 (t, J¼7.6 Hz, 2H), 1.79e1.74 (t,
J¼7.7 Hz, 2H), 1.50e1.43 (q, J¼7.5 Hz, 2H), 1.07e1.02 (t, J¼7.3 Hz,
3H); 13C NMR (75 MHz, CDCl3):
d (ppm) 149.7, 145.1, 137.4, 135.9,
131.4, 130.8, 130.2, 129.6, 129.3, 128.7, 128.4, 128.3, 127.3, 127.2,
126.3, 125.7, 124.9, 124.1, 123.3, 123.1, 123.0, 122.7, 120.9, 35.4, 33.3,
22.3, 14.0; ATR-FTIR (KBr, cmꢀ1): 3064, 2955, 2918, 2854, 1606,
1575, 1511, 1463, 1450, 1008, 829, 798, 752, 723; MALDI-TOF MS, m/
z: calcd for C31H25BrN2S: 504.120, found: 504.172 [M]þ.
4. Experimental
4.1. General information
All organic chemicals were purchased from Aldrich and TCI.
Column chromatography was performed on Merck silica gel 60
(70ꢀ230 mesh). All solvents and reagents were commercially
available and used without further purification unless otherwise
noted. Melting points were measured using Electrothermal 9100
from BARNSTEAD. 1H and 13C NMR spectra were recorded using
an Advance 300 or 500 MHz Bruker spectrometer. ATR-FTIR spectra
were obtained using Nicolet iS10 FTIR spectrometer from
ThermoFisher. UVevis spectra were recorded on a Beckman DU 650
spectrophotometer. Mass spectra were obtained using a Gas
Chromatography-Mass Spectrometer from JEOL, JMS-AX505WA,
HP 5890 Series II and a MALDI-TOF MS from Bruker. Cyclic vol-
tammetry (CV) was performed using a CH Instruments 660 Elec-
trochemical Analyzer (CH Instruments, Inc., Texas) with a 0.1 M
tetra-n-butylammonium hexafluorophosphate (Bu4NPF6) in DMF
solution as the supporting electrolyte at room temperature. The CV
was recorded using an Ag/Agþ reference electrode (0.1 M AgNO3 in
acetonitrile) with a platinum wire counterelectrode at a scan rate of
100 mV sꢀ1. The ferrocene/ferrocenium redox couple was calibrated
to a normal hydrogen electrode (NHE). The theoretical energy
levels of the dyes were obtained by density functional theory (DFT)
calculations at the B3LYP/6e31G(d) level with the Gaussian 09
program. The photovoltaic performances of the DSSCs were mea-
sured using a 1000-W xenon light source, with power calibration as
an AM 1.5 Oriel solar simulator using a KG5-filtered Si reference
solar cell. The IPCE spectra for the cells were measured on an IPCE
measuring system (PV Measurements).
4.2.3. 2-(4-Bromophenyl)-1-(4-(2-(2-(2-methoxyethoxy)ethoxy)eth-
oxy)phenyl)-1H-phenanthro[9,10-d]imidazole (11). Compound 11
was prepared according to the synthetic procedure for compound
4, using 1012a instead of 4-butylaniline. The crude product was
further purified by silica gel column chromatography using CH2Cl2/
EtOAC (10:1) as an eluent to give a pale brown solid (yield: 89%). Mp
119 ꢁC; 1H NMR (300 MHz, CDCl3):
d
(ppm) 8.86e8.83 (d, J¼8.1 Hz,
1H), 8.78e8.76 (d, J¼8.4 Hz, 1H), 8.72e8.69 (d, J¼8.1 Hz, 1H),
7.77e7.72 (t, J¼7.7 Hz, 1H), 7.68e7.63 (m, 1H), 7.56e7.43 (m, 5H),
7.41e7.38 (d, J¼8.8 Hz, 2H), 7.34e7.24 (m, 2H), 7.13e7.10 (d,
J¼8.8 Hz, 2H), 4.29e4.26 (t, J¼4.3 Hz, 2H), 3.99e3.96 (t, J¼4.8 Hz,
2H), 3.84e3.81 (m, 2H), 3.77e3.65 (m, 4H), 3.61e3.58 (m, 2H), 3.41
(s, 3H); 13C NMR (75 MHz, CDCl3): 159.6, 149.8, 137.2, 131.4, 131.0,
130.7, 129.8, 129.4, 129.2, 128.4, 128.2, 127.2, 127.1, 126.4, 125.6,
125.0, 124.0, 123.2, 123.1, 123.0, 122.6, 120.8, 115.9, 71.9, 70.9, 70.6,
70.6, 69.6, 67.8, 59.1; ATR-FTIR (KBr, cmꢀ1): 3037, 2985, 2880, 2861,
1608, 1508, 1449, 1247, 1107, 1062, 1007, 828, 757, 726; MALDI-TOF
MS, m/z: calcd for C34H31 BrN2O4: 610.147, found: 610.829 [M]þ.
4.2.4. (Z)-4-((5-(2-(4-bromophenyl)-1H-phenanthr-o[9,10-d]imida-
zol-1-yl)-1,3,3-trimethyl-3H-indolium-2-yl)methylene)-3-oxo-2-
((Z)-(1,3,3-trimethylindolin-2-ylidene)methyl)cyclobut-1-enolate
(17). Compound 17 was prepared according to the synthetic pro-
cedure for compound 4, using 16 instead of 4-butylaniline. The crude
product was further purified by silica gel column chromatography
using EtOAC/methanol (10:1) as an eluent to give a greenish-blue
solid (yield: 74%). Mp 279 ꢁC; 1H NMR (300 MHz, CDCl3):
d (ppm)
4.2. Synthetic procedures and characterizations
8.86e8.83 (d, J¼7.9 Hz, 1H), 8.80e8.77 (d, J¼8.5 Hz, 1H), 8.73e8.70
(d, J¼8.3 Hz, 1H), 7.78e7.73 (t, J¼7.1 Hz, 1H), 7.70e7.64 (t, J¼8.1 Hz,
1H), 7.55e7.19 (m,12H), 7.09e7.06 (d, J¼7.9 Hz, 2H), 6.01 (s, 2H), 3.64
(s, 3H), 3.59 (s, 3H), 1.84 (s, 6H), 1.80 (s, 6H); 13C NMR (75 MHz,
4.2.1. 2-(5-Bromothiophen-2-yl)-1-(4-butylphenyl)-1H-phenanthro
[9,10-d]imidazole (1). A mixture of 9,10-phenanthrenequinone (1 g,
4.8 mmol), 5-bromo-2-thiophenecarboxaldehyde (0.571 mL,
4.8 mmol), 4-butylaniline (3.79 mL, 24 mmol), ammonium acetate
(1.48 g, 19.2 mmol), and glacial acetic acid (40 mL) was refluxed for
3 h. After cooling to room temperature, water was added. The
precipitate was collected via filtration, and washed with water and
methanol to give a pale brown solid (yield: 1.061 g, 43%). Mp
CDCl3):
d (ppm) 182.2, 177.03, 173.2, 168.3, 149.2, 142.3, 142.0, 131.8,
131.6, 131.1, 129.5, 128.4, 128.0, 127.8, 127.7, 127.2, 126.6, 126.4, 125.7,
125.4, 124.8, 124.4, 124.2, 123.1, 123.0, 122.7, 122.3, 122.2, 120.8, 110.0,
109.8, 87.9, 87.7, 49.8, 48.5, 31.3, 30.7, 29.7, 27.2, 26.7; ATR-FTIR (KBr,
cmꢀ1): 3070, 2960, 2927, 1738, 1601, 1505, 1481, 1459, 1426, 1271,
1347, 1222, 1097, 1067, 965, 922, 806, 789, 754; MALDI-TOF MS, m/z:
calcd for C49H39BrN4O2: 794.226, found: 794.818 [M]þ.
166 ꢁC; 1H NMR (300 MHz, DMSO-d6):
d (ppm) 8.92e8.89 (d,
J¼8.4 Hz, 1H), 8.87e8.84 (d, J¼8.3 Hz, 1H), 8.62e8.60 (d, J¼7 Hz,
1H), 7.79e7.52 (m, 7H), 7.34e7.29 (t, J¼7.7 Hz, 1H), 7.14e7.13 (d,
J¼4 Hz, 1H), 7.10e7.07 (d, J¼8 Hz, 1H), 6.59e6.58 (d, J¼4 Hz, 1H),
2.87e2.82 (t, J¼7.4 Hz, 2H), 1.75e1.70 (t, J¼7.4 Hz, 2H), 1.43e1.36 (q,
J¼7.4 Hz, 2H), 1.00e0.95 (t, J¼7.3 Hz, 3H); 13C NMR (75 MHz,
4.2.5. 1-(4-Butylphenyl)-2-(5-(tributylstannyl)thiophen-2-yl)-1H-
phenanthro[9,10-d]imidazole (2). A solution of n-butyllithium
(0.656 mL, 2.5 M in hexane, 1.64 mmol) was added dropwise to
a cooled solution of 1 (0.7 g, 1.37 mmol) in dry THF (40 mL) at ꢀ78 ꢁC
under nitrogen. The reaction mixture was stirred at the same tem-
perature for 1 h and treated with tributyltin chloride (0.922 mL,
3.42 mmol). The resulting mixture was allowed to attain room
temperature and stirred overnight. After quenching with water, the
CDCl3):
d (ppm) 151.6, 146.0, 145.1, 137.4, 135.4, 134.7, 130.7, 130.2,
129.3, 128.9, 128.3, 128.3, 127.3, 126.9, 126.4, 125.7, 125.0, 124.1,
123.1, 122.8, 120.6, 114.8, 35.5, 33.4, 22.2, 14.0; ATR-FTIR (KBr,
cmꢀ1): 3032, 3053, 2952, 2929, 2867, 1612, 1516, 1473, 1453, 1235,

5596
W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
mixture was extracted with CH2Cl2. The organic layer was dried over
Na2SO4 and concentrated in vacuo. The crude product was purified
by silica gel column chromatography using CH2Cl2/hexane (1:5) as
an eluent to give a pale brown solid (yield: 0.493 g, 50%). Mp 117 ꢁC;
using 5 and 50-bromo-2,20-bithio-phene-5-carbaldehyde instead of
and 5-bromo-2-thiophenecarboxaldehyde, respectively. The
crude product was purified by silica gel column chromatography
2
using CH2Cl2 as an eluent to give an orange solid. (yield: 56%). Mp
1H NMR (500 MHz, CDCl3):
d
(ppm) 8.88e8.86 (m, 1H), 8.75e8.74 (d,
208 ꢁC; 1H NMR (300 MHz, DMSO-d6):
d (ppm) 9.89 (s, 1H),
J¼8.3 Hz, 1H), 8.69e8.68 (d, J¼8.4 Hz, 1H), 7.75e7.71 (m, 1H),
7.66e7.62 (m,1H), 7.51e7.47 (m, 5H), 7.24e7.23 (m, 1H), 7.18e7.16 (d,
J¼8.3 Hz, 1H), 6.97e6.93 (m, 2H), 2.88e2.84 (m, 2H) 1.82e1.76 (m,
2H), 1.68e1.62 (m, 2H), 1.56e1.47 (m, 6H), 1.37e1.28 (m, 8H),
1.11e1.08 (m, 4H), 1.05e1.02 (m, 3H), 0.94e0.88 (m, 9H); 13C NMR
8.94e8.92 (d, J¼8.4 Hz, 1H), 8.89e8.87 (d, J¼8.4 Hz, 1H), 8.72e8.70
(d, J¼7.8 Hz, 1H), 8.02e8.01 (d, J¼4 Hz, 1H), 7.79e7.61(m, 11H),
7.59e7.58 (d, J¼3.7 Hz, 1H), 7.56e7.50 (m, 2H), 7.34e7.29 (t,
J¼7.3 Hz, 1H), 7.11e7.08 (d, J¼8.3 Hz, 1H), 2.82e2.77 (t, J¼7 Hz, 2H),
1.72e1.67 (t, J¼6.8 Hz, 2H), 1.40e1.33 (q, J¼7.1 Hz, 2H), 0.98e0.93 (t,
(75 MHz, CDCl3):
d
(ppm) 146.5, 145.5, 140.2, 138.6, 137.6, 136.0,
J¼7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d (ppm) 182.4, 149.9,
135.6, 130.4, 129.1, 129.0, 128.2, 128.1, 127.8, 127.1, 126.5, 125.5, 124.7,
124.0, 123.0, 120.6, 35.5, 33.5, 28.9, 27.6, 22.3, 14.0, 13.7, 10.8; ATR-
FTIR (KBr, cmꢀ1): 3058, 2955, 2919, 1608, 1574, 1554, 1513, 1453,
1235, 1095, 838, 786, 751, 723; MALDI-TOF MS, m/z: calcd for
C41H50N2SSn: 722.272, found: 721.831 [M]þ.
146.9, 145.2, 145.0, 141.6, 137.4, 136.1, 135.4, 133.4,130.2, 130.1, 129.7,
129.6, 129.3, 128.7, 128.4, 128.3, 127.3, 127.1, 126.6, 126.2, 125.6,
125.3, 124.9, 124.6, 124.1, 123.1, 123.0, 122.7, 120.9, 35.4, 33.3, 22.2,
14.0; ATR-FTIR (KBr, cmꢀ1): 3058, 2988, 2891, 2856, 1642, 1514,
1450,1439,1247,1225,1113,1055, 794, 756, 723; MALDI-TOF MS, m/
z: calcd for C40H30N2OS2: 618.180, found: 619.314 [MþH]þ.
4.2.6. 4-(1-(4-Butylphenyl)-1H-phenanthro[9,10-d]-imidazol-2-yl)
phenylboronic acid (5). A solution of n-butyllithium (0.95 mL, 2.5 M
in hexane, 2.38 mmol) was added dropwise to a cooled solution of 4
(1 g, 1.98 mmol) in dry THF (50 mL) at -78 ꢁC under nitrogen. The
reaction mixture was stirred at the same temperature for 1 h and
treated with trimethylborate (0.331 mL, 2.97 mmol). The resulting
mixture was allowed to attain room temperature and was stirred
overnight. 1 N HCl solution was added, and the mixture was stirred
for 3 h and then extracted with CH2Cl2. The organic layer was dried
over Na2SO4 and concentrated in vacuo. The crude product was
purified by silica gel column chromatography using CH2Cl2/meth-
anol (1:10) as an eluent to give a white solid (yield: 0.466 g, 50%).
Mp 185 ꢁC; 1H NMR (300 MHz, DMSO-d6): 8.93e8.90 (d, J¼8.4 Hz,
1H), 8.88e8.85 (d, J¼8.3 Hz,1H), 8.70e8.68 (d, J¼7.4 Hz,1H), 8.14 (s,
2H), 7.82e7.65 (m, 4H), 7.59e7.47 (m, 7H), 7.33e7.28 (t, J¼7.7 Hz,
1H), 7.12e7.09 (t, J¼8.5 Hz, 1H), 2.79e2.75 (t, J¼7.5 Hz, 2H),
1.70e1.63 (t, J¼7.4 Hz, 2H),1.40e1.32 (q, J¼7.3 Hz, 2H), 0.98e0.93 (t,
4.2.9. 50-(40-(1-(4-Butylphenyl)-1H-phenanthro[9,1-d]imidazol-2-yl)
bi-phenyl-4-yl)-2,20-bithiophene-5 -carbaldehyde (9). Compound 9
was prepared according to the synthetic procedure for compound 8,
using 712c instead of 6. The crude product was purified by silica gel
column chromatography using CH2Cl2 as an eluent to give a yellow
solid (yield: 61%). Mp 212 ꢁC; 1H NMR (300 MHz, DMSO-d6):
d (ppm)
9.89 (s, 1H), 8.94e8.92 (d, J¼8.4 Hz, 1H), 8.89e8.87 (d, J¼8.3 Hz, 1H),
8.72e8.69 (d, J¼7.9 Hz, 1H), 8.02e8.01 (d, J¼4 Hz, 1H), 7.78e7.71 (t,
J¼7.5 Hz, 1H), 7.68e7.62 (m, 9H), 7.60e7.50 (m, 8H), 7.34e7.29 (d,
J¼7.3 Hz, 1H), 7.11e7.08 (d, J¼8.3 Hz, 1H), 2.82e2.77 (t, J¼8.8 Hz, 2H),
1.73e1.68 (t, J¼7.6 Hz, 2H), 1.41e1.34 (q, J¼7.4 Hz, 2H), 0.98e0.94 (t,
J¼7.3 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d (ppm) 182.4, 150.3, 145.5,
144.9, 141.5, 140.2, 140.1, 139.9, 137.3, 136.2, 132.6, 130.1, 129.7, 129.6,
129.2, 128.7, 128.3, 128.2, 127.5, 127.2, 127.2, 126.6, 126.5, 126.2, 126.1,
125.9, 125.6, 125.4, 124.8, 124.2, 124.0, 123.9, 123.1, 122.7, 120.9, 35.4,
33.3, 22.2, 14.0; ATR-FTIR (KBr, cmꢀ1): 3057, 2954, 2924, 2854, 1660,
1514, 1452, 1226, 1145, 1046, 794, 752, 723; MALDI-TOF MS, m/z:
calcd for C46H34N2OS2: 694.211, found: 695.405 [MþH]þ.
J¼7.2 Hz, 3H); 13C NMR (75 MHz, DMSO-d6):
d (ppm) 151.0, 145.0,
136.9, 126.2, 124.2, 132.1, 130.6, 129.3, 129.0, 128.4, 128.3, 128.1,
127.9, 127.2, 127.0, 126.2, 125.7, 124.9, 124.1, 123.0, 122.5, 122.4,
120.7, 34.9, 33.3, 22.0,14.3; ATR-FTIR (KBr, cmꢀ1): 3058, 2955, 2925,
2856, 1608, 1514, 1342, 1278, 1018, 844, 753, 723; MALDI-TOF MS,
m/z: calcd for C31H27BN2O2: 470.217, found: 471.245 [MþH]þ.
4.2.10. 50-(4-(1-(4-(2-(2-(2-Methoxyethoxy)ethoxy)-ethoxy)phenyl)-
1H-phenanthro[9,10-d]imidazol-2-y-l)phenyl)-2,20-bithiophene-5-
carbaldehyde (13). A mixture of 11 (0.556 g, 0.91 mmol), (50-(1,3-
dioxolan-2-yl)-2,20-bithiophen-5-yl)tributylstannane20a 12 (0.96 g,
1.82 mmol), and Pd(PPh3)4 (0.053 g, 0.045 mmol) in toluene (40 mL)
was refluxed overnight under nitrogen. After cooling to room tem-
perature, a 1 N HCl solution was added, and the mixture was stirred
for 3 h. The precipitate was collected via filtration to give the crude
product, which was purified by silica gel column chromatography
using CH2Cl2/EtOAC (5:1) as an eluent to give an orange solid (yield:
4.2.7. 50-(1-(4-Butylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-
2,20-bithiophene-5-carbaldehyde (3). A mixture of
2 (0.493 g,
0.68 mmol), 5-bromo-2-thiophenecarboxaldehyde (0.081 mL,
0.68 mmol), and Pd(PPh3)4 (0.039 g, 0.034 mmol) in toluene (40 mL)
was refluxed overnight under nitrogen. After cooling to room tem-
perature, the reaction mixture was extracted with CH2Cl2 and the
organic layer was dried over Na2SO4. The solvent was evaporated in
vacuo to give the crude product, which was purified by silica gel
column chromatography using CH2Cl2 as an eluent to give an orange
solid (yield: 0.17 g, 46%). Mp 196 ꢁC; 1H NMR (300 MHz, CDCl3):
0.515 g, 78%). Mp 176 ꢁC; 1H NMR (500 MHz, DMSO-d6):
d (ppm) 9.88
(s, 1H), 8.92e8.90 (d, J¼8.5 Hz, 1H), 8.87e8.85 (d, J¼8.5 Hz, 1H),
8.70e8.68 (d, J¼7.9 Hz, 1H), 8.01e7.99 (d, J¼4 Hz, 1H), 7.78e7.75 (t,
J¼7.1 Hz, 1H), 7.73e7.72 (d, J¼8.3 Hz, 2H), 7.69e7.63 (m, 7H),
7.57e7.54 (m, 2H), 7.40e7.37 (t, J¼7.9 Hz,1H), 7.25e7.23 (d, J¼8.7 Hz,
2H), 7.20e7.18 (d, J¼8.3 Hz, 1H), 4.24e4.23 (t, J¼4 Hz, 2H), 3.83e3.81
(t, J¼4.4 Hz, 2H), 3.64e3.62 (m, 2H), 3.57e3.55 (m, 2H), 3.54e3.52
(m, 2H), 3.44e3.42 (m, 2H), 3.22 (s, 3H); 13C NMR (75 MHz, CDCl3):
184.3, 159.8, 151.4, 150.3, 145.6, 144.4, 141.8, 139.6, 136.9, 135.3, 133.4,
131.1, 130.6, 130.0, 129.0, 128.8, 128.6, 128.1, 127.9, 127.2, 127.1, 126.5,
126.2, 125.7, 125.7, 125.6, 124.9, 123.0, 122.4, 120.7, 116.4, 110.4, 71.7,
70.5, 70.3, 70.1, 69.4, 68.1, 58.5; ATR-FTIR (KBr, cmꢀ1): 3056, 2923,
2892, 2853, 1642, 1514, 1451,1247, 1225, 1113, 1055, 839, 794, 756,
723; MALDI-TOF MS, m/z: calcd for C43H36N2O5S2: 724.207, found:
724.808 [M]þ.
d
(ppm) 9.87 (s, 1H), 8.86e8.83 (d, J¼7.4 Hz, 1H), 8.76e8.74 (d,
J¼8.4 Hz, 1H), 8.71e8.68 (d, J¼8.2 Hz, 1H), 7.78e7.65 (m, 3H),
7.54e7.49 (m, 5H), 7.30e7.18 (m, 3H), 7.14e7.12 (d, J¼4 Hz, 1H),
6.76e6.75 (d, J¼4 Hz, 1H), 2.93e2.88 (t, J¼7.5 Hz, 2H), 1.85e1.80 (t,
J¼7.7 Hz, 2H),1.55e1.47 (q, J¼7.5 Hz, 2H), 1.08e1.04 (t, J¼7.3 Hz, 3H);
13C NMR (75 MHz, CDCl3):
d (ppm) 182.4, 146.4, 146.0, 144.9, 141.8,
137.2, 137.0, 135.4, 134.5, 130.7, 129.3, 128.8, 128.3, 128.3, 127.6, 127.2,
126.7, 126.3, 126.3, 125.8, 125.1, 124.4, 124.0, 123.1, 122.8, 122.7, 120.6,
35.5, 33.4, 22.2, 14.0; ATR-FTIR (KBr, cmꢀ1): 3035, 2952, 2926, 2855,
1653,1575,1515,1451,1230,1051, 782, 746, 718; MALDI-TOF MS, m/z:
calcd for C34H26N2OS2: 542.149, found: 542.850 [M]þ.
4.2.8. 50-(4-(1-(4-Butylphenyl)-1H-phenanthro[9,10-d]imidazol-2-
yl)phenyl)-2,20-bithiophene-5-carbaldehyde (8). Compound 8 was
prepared according to the synthetic procedure for compound 3,
4.2.11. (Z)-4-((5-(2-(4-(50-Formyl-2,20-bithiophen-5-yl)phenyl)-1H-
phenanthro[9,10-d]imidazol-1-yl)-1,3,3-trimethyl-3H-indolium-2-yl)
methylene)-3-oxo-2-((Z)-(1,3,3-trimethylindolin-2-ylidene)methyl)

W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
5597
cyclobut-1-enolate (18). Compound 18 was prepared according to
the synthetic procedure for compound 13 using 17 instead of 11. The
crude product was purified by silica gel column chromatography
using EtOAC/methanol (20:1) as an eluent to give a greenish-blue
acetonitrile (20 mL) and THF (10 mL). The mixture was refluxed
overnight and then allowed to cool to room temperature. Water
was added, and the mixture was extracted with CH2Cl2, and dried
over Na2SO4. The solvent was evaporated in vacuo to afford the
crude product, which was purified by silica gel column chroma-
tography using CH2Cl2/methanol (5:1) and recrystallized with
CH2Cl2 and hexane to give a reddish-brown solid (yield: 0.13 g,
solid (yield: 37%). Mp 294 ꢁC; 1H NMR (500 MHz, CDCl3):
d (ppm)
9.86 (s,1H), 8.89e8.87 (d, J¼7.9 Hz,1H), 8.80e8.78 (d, J¼8.4 Hz,1H),
8.73e8.71 (d, J¼8.3 Hz,1H), 7.78e7.75 (t, J¼7.1 Hz,1H), 7.69e7.63 (m,
4H), 7.56e7.53 (m, 3H), 7.49 (s,1H), 7.42e7.34 (m, 3H), 7.32e7.29 (m,
4H), 7.25e7.24 (d, J¼3.9 Hz,1H), 7.23e7.20 (t, J¼7.5 Hz,1H), 7.11e7.10
(d, J¼8.2 Hz,1H), 7.08e7.07 (d, J¼7.9 Hz,1H), 6.0 (s, 2H), 3.65 (s, 3H),
3.61 (s, 3H),1.79 (s, 6H),1.78 (s, 6H); 13C NMR (75 MHz, CDCl3): 183.1,
182.4,178.3,172.9,168.5,150.1,146.8,145.0,144.1,144.0,142.6,142.0,
141.6,137.3,135.6,133.6,133.1,129.8,129.4,128.9,128.4,128.3,128.2,
128.0,127.4,127.1,126.9,126.3,125.8,125.3, 125.1,124.7,124.2,124.1,
123.1,122.8,122.3,120.7,109.8,109.5, 87.8, 87.5, 49.8, 48.6, 31.2, 30.6,
27.3, 27.2, 26.8; ATR-FTIR (KBr, cmꢀ1): 3068, 2972, 2933, 1735, 1650,
1601, 1504, 1481, 1459, 1426, 1271, 1347, 1223, 1097, 1067, 965, 923,
806, 789, 754, 725; MALDI-TOF MS, m/z: calcd for C58H44N4O3S2:
908.286, found: 908.843 [M]þ.
69%). Mp 234 ꢁC; 1H NMR (300 MHz, DMSO-d6):
d (ppm) 8.93e8.90
(d, J¼8.4 Hz, 1H), 8.88e8.85 (d, J¼8.5 Hz, 1H), 8.66e8.64 (d, J¼8 Hz,
1H), 8.03 (s, 1H), 7.80e7.62 (m, 8H), 7.58e7.53 (t, J¼7.5 Hz, 1H),
7.45e7.44 (d, J¼3.9 Hz, 1H), 7.34e7.30 (m, 2H), 7.13e7.10 (d, J¼8 Hz,
1H), 6.63e6.61 (d, J¼4 Hz, 1H), 2.88e2.84 (t, J¼7.4 Hz, 2H),
1.77e1.72 (t, J¼7.4 Hz, 2H), 1.45e1.38 (q, J¼7.4 Hz, 2H), 1.00e0.96 (t,
J¼7.3 Hz, 3H); 13C NMR (125 MHz, DMSO-d6):
d (ppm) 162.9, 145.6,
144.7, 144.6141.0, 137.0, 136.8, 136.7, 135.0, 132.7, 130.7, 128.7, 128.6,
128.0, 127.8, 127.5, 126.7, 126.2, 125.9, 125.8, 125.6, 125.0, 124.8,
124.5, 123.7, 122.1, 122.0, 120.0, 119.2, 118.0, 110.3, 34.5, 32.9, 21.5,
13.8; ATR-FTIR (KBr, cmꢀ1): 3460, 3035, 2955, 2930, 2861, 2206,
1627, 1578, 1517, 1435, 1302, 1233, 1136,939, 785, 748, 720; HRMS,
m/z: calcd for C37H27N3O2S2: 609.1545, found 610.1617 [MþH]þ.
4.2.12. (Z)-3-oxo-4-((1,3,3-Trimethyl-5-nitro-3H-indolium-2-yl)
methylene)-2-((Z)-(1,3,3-trimethylindolin-2-ylidene)methyl)cyclo-
but-1-enolate (15). (E)-3-Hydroxy-4-((1,3,3-trimethylindolin-2-yli-
dene)methyl)cyclobut-3-ene-1,2-dione 1412b (0.713 g, 2.65 mmol)
and 1,2,3,3-tetra methyl-5-nitro-3H-indolium iodide20b (1.21 g,
3.98 mmol) were dissolved in a mixture of benzene (10 mL) and n-
butanol (10 mL). The mixture was refluxed with a DeaneStark ap-
paratus for 20 h. The solvent was evaporated in vacuo to afford the
crude product, which was purified by silica gel column chromatog-
raphy using EtOAC/methanol (20:1) as an eluent to give a blue solid
4.2.15. (E)-3-(50-(4-(1-(4-Butylphenyl)-1H-phenanthro[9,10-d]imida-
zol-2-yl)phenyl)-2,20-bithiophen-5-yl)-2-cyanoacrylic acid (H7). H7
was prepared according to the synthetic procedure for H6, using 8
instead of 3. The crude product was purified by silica gel column
chromatography using CH2Cl2/methanol (10:1) as an eluent to give
an orange solid (yield: 71%). Mp 246 ꢁC; 1H NMR (300 MHz, DMSO-
d6):
d
(ppm) 9.07 (s, 2H), 8.93e8.90 (d, J¼8.5 Hz, 1H), 8.88e8.85 (d,
J¼8.4 Hz, 1H), 8.71e8.69 (d, J¼7.7 Hz, 1H), 8.13 (s, 1H), 7.79e7.74 (t,
J¼7.2 Hz, 1H), 7.71e7.57 (m, 8H), 7.54e7.48 (m, 5H), 7.32e7.27 (t,
J¼7.9 Hz, 1H), 7.10e7.07 (d, J¼8.2 Hz,1H), 2.81e2.76 (t, J¼7.3 Hz, 2H),
1.57e1.54 (t, J¼5.6 Hz, 2H), 1.40e1.33 (q, J¼7.4 Hz, 2H), 0.98e0.93 (t,
(yield: 0.768 g, 62%). Mp 234 ꢁC; 1H NMR (300 MHz, CDCl3):
d (ppm)
8.27e8.24 (d, J¼8.7 Hz, 1H), 8.16 (s, 1H), 7.44e7.30 (m, 3H), 7.17e7.14
(d, J¼7.9 Hz, 1H), 6.95e6.92 (d, J¼8.8 Hz,1H), 6.10 (s,1H), 5.97 (s, 1H),
3.73 (s, 3H), 3.51 (s, 3H), 1.83 (s, 6H), 1.80 (s, 6H); 13C NMR (75 MHz,
J¼7.2 Hz, 3H); 13C NMR (125 MHz, DMSO-d6):
d (ppm) 163.6, 149.7,
144.7, 142.8, 141.1, 140.4, 136.6, 136.5, 135.9, 135.7, 135.4, 133.2, 130.2,
129.6, 129.5, 128.8, 128.5, 128.0, 127.7, 127.4, 127.0, 126.6, 126.5, 125.9,
125.8, 125.2, 124.9, 124.7, 124.5, 123.5, 122.4, 122.0, 120.2, 119.0, 108.9,
34.4, 32.8, 22.1, 13.8; ATR-FTIR (KBr, cmꢀ1): 3566, 3057, 2953, 2929,
2859, 2213, 1602, 1515, 1435, 1379, 1226, 1158, 1096, 1049, 943, 842,
796, 742, 723; HRMS, m/z: calcd for C43H31N3O2S2: 685.1858, found
686.1945 [MþH]þ.
CDCl3):
d (ppm) 185.6, 176.6, 174.6, 166.7, 148.5, 142.9, 142.4, 142.3,
142.2,128.1,125.4,125.3,122.4,118.1,110.4,107.5, 89.1, 88.2, 50.3, 47.8,
31.6, 30.5, 27.3, 26.5; ATR-FTIR (KBr, cmꢀ1): 3023, 2965, 2924, 1602,
1500, 1476, 1261, 1214, 797, 744, 733; MALDI-TOF MS, m/z: calcd for
C28H27N3O4: 469.200, found: 469.543 [M]þ.
4.2.13. (Z)-4-((5-Amino-1,3,3-trimethyl-3H-indolium-2-yl)methy-
lene)-3-oxo-2-((Z)-(1,3,3-trimethylindolin-2-ylidene)methyl)cyclo-
but-1-enolate (16). A mixture of 15 (0.5 g, 1.06 mmol) and tin(II)
chloride dihydrate (1.674 g, 7.42 mmol) was refluxed in a mixture of
ethanol (15 mL) and concentrated HCl (2 mL) for 8 h. After cooling
to room temperature, the mixture was poured into cold water and
neutralized with 2 N NaOH. The mixture was extracted with CH2Cl2,
and the organic layer was dried over Na2SO4. The solvent was
evaporated to afford a crude solid, which was purified by silica gel
column chromatography using EtOAC/methanol (20:1) as an eluent
to give a blue solid (yield: 0.406 g, 87%). Mp 240 ꢁC; 1H NMR
4.2.16. (E)-3-(50-(40-(1-(4-butylphenyl)-1H-phenanthro[9,10-d]imi-
dazol-2-yl)biphenyl-4-yl)-2,20-bithiophen-5-yl)-2-cyanoacrylic acid
(H8). H8 was prepared according to the synthetic procedure for H6,
using 9 instead of 3. The crude product was purified by silica gel
column chromatography using CH2Cl2/methanol (10:1) as an eluent
to give a yellow solid (yield: 60%). Mp 258 ꢁC; 1H NMR (300 MHz,
DMSO-d6):
d
(ppm) 8.95e8.92 (d, J¼8.6 Hz, 1H), 8.90e8.87 (d,
J¼8.5 Hz, 1H), 8.72e8.70 (d, J¼7.8 Hz, 1H), 8.42 (s, 2H), 8.05 (s, 1H),
7.80e7.63 (m, 10H), 7.59e7.51 (m, 8H), 7.35e7.30 (t, J¼8.0 Hz, 1H),
7.12e7.09 (d, J¼8.2 Hz, 1H), 2.82e2.77 (t, J¼7.3 Hz, 2H), 1.57e1.54 (t,
J¼4.5 Hz, 2H), 1.41e1.33 (q, J¼7.2 Hz, 2H), 0.98e0.93 (t, J¼7.2 Hz,
(300 MHz, CDCl3):
d
(ppm) 7.33e7.28 (m, 2H), 7.12e7.07 (t, J¼7.4 Hz,
1H), 6.95e6.93 (d, J¼7.7 Hz,1H), 6.85e6.82 (d, J¼8.3 Hz,1H), 6.72 (s,
1H), 6.65e6.62 (d, J¼7.6 Hz, 1H), 5.86 (s, 2H), 3.84 (s, 2H), 3.57 (s,
3H), 3.47 (s, 3H), 1.78 (s, 6H), 1.74 (s, 6H); 13C NMR (75 MHz, CDCl3):
3H); 13C NMR (125 MHz, DMSO-d6):
d (ppm) 163.3, 150.0, 144.7,
143.6, 141.0, 139.3, 138.4, 136.5, 135.8, 135.0, 133.5, 132.4, 130.2,
129.5, 128.8, 128.5, 128.0, 127.7, 127.4, 127.3, 127.0, 126.7, 126.5,
126.2, 126.1, 125.9, 125.7, 125.5, 125.4, 125.2, 124.6, 124.5, 123.6,
122.5, 122.4, 122.0, 120.2, 110.1, 34.4, 32.8, 22.2, 13.8; ATR-FTIR (KBr,
cmꢀ1): 3566, 2948, 2928, 2854, 2211, 1608, 1592, 1514, 1465, 1452,
1380,1235,1145,1032, 947, 830, 795, 753, 729; HRMS, m/z: calcd for
C49H35N3O2S2: 761.2171, found 762.2251 [MþH]þ.
d
(ppm) 179.6, 176.2, 170.9, 168.8, 144.2, 143.7, 143.1, 141.8, 135.0,
127.6, 123.0, 122.1, 113.9, 110.4, 109.8, 108.5, 86.3, 49.6, 48.6, 31.2,
30.2, 29.7, 27.1, 26.8; ATR-FTIR (KBr, cmꢀ1): 3319, 3224, 2960, 2923,
2854, 1736, 1569, 1480, 1418, 1373, 1263, 1217, 1089, 1054, 1040, 932,
963, 789, 729; MALDI-TOF MS, m/z: calcd for C28H29N3O2: 439.226,
found: 440.008 [M]þ.
4.2.17. (E)-2-Cyano-3-(50-(4-(1-(4-(2-(2-(2-methoxyethoxy)ethoxy)
ethoxy)phenyl)-1H-phenanthro[9,1 0-d]imidazol-2-yl)phenyl)-2,20-
bithiophen-5-yl)ac-rylic acid (H9). H9 was prepared according to
the synthetic procedure for H6, using 13 instead of 3. The crude
product was purified by silica gel column chromatography using
4.2.14. 3-(50-(1-(4-Butylphenyl)-1H-phenanthro[9,1 0-d]imidazol-2-
yl)-2, 20-bithiophen-5-yl)-2-cyanoacrylic acid (H6). Piperidine
(0.092 mL, 0.93 mmol) was added to a mixture of 3 (0.17 g,
0.31 mmol) and cyanoacetic acid (0.053 g, 0.62 mmol) dissolved in

5598
W. Lee et al. / Tetrahedron 68 (2012) 5590e5598
CH2Cl2/methanol (10:1) as an eluent to give a red solid (yield:
0.145 g, 65%). Mp 214 ꢁC; 1H NMR (500 MHz, DMSO-d6):
(ppm)
acetonitrile) was injected though a hole in the counterelectrode and
driven into the cell by vacuum backfilling. Finally, the hole was sealed
using a hot-melt polymer film and a cover glass (0.1 mm thick).
d
8.91e8.90 (d, J¼8.5 Hz, 1H), 8.86e8.85 (d, J¼8.7 Hz, 1H), 8.70e8.68
(d, J¼8 Hz, 1H), 8.05 (s, 1H), 7.77e7.74 (t, J¼7.1 Hz, 1H), 7.72e7.68
(m, 2H), 7.67e7.62 (m, 8H), 7.56e7.53 (t, J¼7.1 Hz, 1H), 7.50e7.49 (d,
J¼3.8 Hz, 1H), 7.47e7.46 (d, J¼3.8 Hz, 1H), 7.40e7.36 (t, J¼7.3 Hz,
1H), 7.24e7.23 (d, J¼8.9 Hz, 2H), 7.19e7.18 (d, J¼8.4 Hz, 1H),
4.23e4.22 (t, J¼3 Hz, 2H), 3.83e3.81 (t, J¼4.4 Hz, 2H), 3.64e3.62
(m, 2H), 3.57e3.55 (m, 2H), 3.54e3.52 (m, 2H), 3.44e3.42 (m, 2H),
Acknowledgements
This work was supported by a grant for the Center for Next-
Generation Dye-Sensitized Solar Cells (No. 2012-0000591) from
the Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education,
Science and Technology (MEST) of Korea.
3.22 (s, 3H); 13C NMR (125 MHz, DMSO-d6):
d (ppm) 163.3, 159.4,
149.9, 142.8, 140.8, 140.1, 136.5, 136.2, 136.0, 135.4, 133.1, 130.6,
130.2, 129.6, 129.5, 128.5, 128.1, 127.7, 127.4, 126.9, 126.7, 125.9,
125.7, 125.2, 124.9, 124.6, 124.4, 123.6, 122.5, 122.0, 120.2, 119.2,
115.9, 109.6, 71.3, 70.0, 69.8, 69.6, 68.9, 67.6, 64.8, 58.0; ATR-FTIR
(KBr, cmꢀ1): 3566, 3036, 2939, 2925, 2870, 2210, 1738, 1606, 1511,
1450, 1373, 1296, 1248, 1108, 941, 840, 794, 755, 723; HRMS, m/z:
calcd for C46H37N3O6S2: 791.2124, found: 792.2207 [MþH]þ.
Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2012.04.074.
References and notes
4.2.18. (Z)-4-((5-(2-(4-(50-((Z)-2-Carboxy-2-cyano-vinyl)-2,20-bi-
thiophen-5-yl)phenyl)-1H-phenanthro-[9,10-d]imidazol-1-yl)-1,3,3-
trimethyl-3H-indoliu-m-2-yl)methylene)-3-oxo-2-((Z)-(1,3,3-
€
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uddin, M. K.; Zakeeruddin, S. M.; Humphry-Baker, R.; Jirousek, M.; Liska, P.;
was prepared according to the synthetic procedure for H6, using 18
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chromatography using CH2Cl2/methanol (10:1) as an eluent to give
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NMR (125 MHz, DMSO-d6):
d (ppm) 181.4, 181.1, 180.7, 180.3, 177.3,
175.1, 173.7, 171.4, 168.1, 165.1, 162.9, 149.9, 144.4, 144.0, 142.7, 142.6,
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(KBr, cmꢀ1): 3565, 2924, 2852, 2211, 1732, 1601, 1543, 1481, 1458,
1364, 1270, 1225, 1097, 1068, 923, 838, 791, 754, 723; HRMS, m/z:
calcd for C61H45N5O4S2: 975.2913, found: 976.2972 [MþH]þ.
€
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