Novel organic sensitizers with a quinoline unit for efficient dye-sensitized solar cells

Article abstract of DOI:10.5012/bkcs.2010.31.01.125

Three organic sensitizers,JK-128,JK-129,and JK-130 containing quinoline unit are designed and synthesized. Under standard global AM 1.5 solar condition,the JK-130 sensitized solar cell gave a short circuit photocurrent density of 11.52 mA cm^-2,an open circuit voltage of 0.70 V,and a fill factor of 0.75,corresponding to an overall conversion efficiency of 6.07%. We found that theη of JK-130 was higher than those of other two cells due to the higher photocurrent. The higher J_sc value is attributed to the broad and intense absorption spectrum of JK-130.

Full text of DOI:10.5012/bkcs.2010.31.01.125

Novel Organic Sensitizers with a Quinoline Unit
Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1 125
DOI 10.5012/bkcs.2010.31.01.125
Novel Organic Sensitizers with a Quinoline Unit
for Efficient Dye-sensitized Solar Cells
Hyeju Choi, Hyunbong Choi, Sanghyun Paek, Kihyung Song,† Moon-sung Kang,‡ and Jaejung Ko*
Department of Advanced Material Chemistry, Korea University, Jochiwon, Chungnam 339-700, Korea
*E-mail: jko@korea.ac.kr
†Department of Chemical Education, Korea National University of Education, Cheongwon, Chungbuk 363-791, Korea
‡Energy Lab, Samsung SDI Corporate R&D Center, Yongin, Gyeonggi-do 449-577, Korea
Received September 30, 2009, Accepted December 4, 2009
Three organic sensitizers, JK-128, JK-129, and JK-130 containing quinoline unit are designed and synthesized.
Under standard global AM 1.5 solar condition, the JK-130 sensitized solar cell gave a short circuit photocurrent
density of 11.52 mA cm-2, an open circuit voltage of 0.70 V, and a fill factor of 0.75, corresponding to an overall
conversion efficiency of 6.07%. We found that the η of JK-130 was higher than those of other two cells due to the
higher photocurrent. The higher Jsc value is attributed to the broad and intense absorption spectrum of JK-130.
Key Words: Quinoline, Dye, Bithiophene, Dye-sensitized solar cell
Introduction
Recently, a successful approach was introduced by incor-
porating a π-conjugation linker such as thiophene,6 thieno-
thiophene,7 3,4-ethylenedioxy-thiophene,8 benzo[1,2,5]-thia-
diazole9 and p-phenylene vinylene derivatives.10 As part of
our efforts to investigate the structural modifications that can
enhance the efficiency and stability, organic dyes containing
quinoline moiety have been synthesized for DSSCs (Fig. 1).
It is well documentated that molecules and polymers con-
taining quinoxaline,11 oxidiazole,12 and quinoline13 offer highly
efficient electron-transport material. Jenekle and co-workers14
reported that a new n-type conjugated copolymer containing
3,3'-dialkylthiophene and bis(phenylquinoline) moiety was
shown to be a good electron-transport material. One challenge
is to develop more efficient and robust electron-transport organic
sensitizers which can be utilized as an efficient dye-sensitized
solar cell. In this paper, we report three organic dyes containing
quinoline as bridged group. We also investigated the effect of
bridged structural modifications on the power conversion effi-
ciency.
Increasing energy demands and environmental issues such
as fossil fuel shortage and global warming have lead to the
need for clean renewable energy.1 Dye-sensitized solar cells are
attracting widespread interest for a renewable energy source
as a cost-effective alternative to conventional solid-state solar
cells.2 In this cell, the sensitizer is a crucial element in DSSCs,
exerting significant influence on the power conversion effi-
ciency as well as the stability of the devices. Some polypyridyl
ruthenium sensitizers have reached power conversion efficien-
cies over 11%.3 Due to their precious metal and limited quantity,
cheap metal-free organic sensitizers need to be developed for
commercial applications. Recently impressive photovoltaic per-
formance has been obtained with some organic indoline4 and
triarylamine dyes5 having efficiencies in the range of 8 ~ 9.7%.
The efficient organic dyes contained a donor and acceptor moiety
bridged by π-conjugation. In order to improve the photovoltaic
performance and stability of DSSCs, an important strategy on
organic sensitizers has been the structural modification of the
compounds. The absorption spectra of organic sensitizers have
to be red-shifted and broadened by expansion of the π-conju-
gation in the dyes. To obtain organic sensitizers with both red-
shift absorption and high stability, introduction of new π-con-
jugation units into organic framework is necessary.
Results and Discussion
The novel organic sensitizers JK-128, JK-129, and JK-130
were prepared by the synthetic protocol depicted in Scheme 1.
1-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)ethan-
HOOC
N
N
N
CN
COOH
N
HOOC
S
N
N
S
CN
S
CN
JK-130
JK-128
JK-129
JK-129
JK-128
JK-130
Figure 1. Structure of the dyes of JK‐128, JK‐129 and JK‐130.

126 Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1
Hyeju Choi et al.
(2-Amino-5-bromo-phenyl)phenyl-methanone
DPP
Acetic anhydride, SnCl4
O
N
N
N
m-cresol
CH2Cl2
N
Br
2
1
3
n-BuLi, DMF
NC
COOH
HOOC
N
N
CN
THF
Piperidine/CH3CN
N
CHO
N
4
JK-128
Pd(PPh3)4, K2CO3
THF
O
O
S
+
3
B
N
O
O
N
O
O
S
5
TFA
THF/ H2O
NC
COOH
N
N
COOH
CN
N
N
Piperidine/CH3CN
S
S
CHO
6
JK-129
O
Pd(PPh3)4, K2CO3
THF
B
3
+
O
O
S
O
S
N
N
O
O
S
S
7
TFA
THF/ H2O
NC COOH
Piperidine/CH3CN
N
N
N
HOOC
S
N
S
S
CN
S
CHO
8
JK-130
Scheme 1. Schematic diagram for the synthesis of JK-128, JK-129 and JK-130

Novel Organic Sensitizers with a Quinoline Unit
Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1 127
5
4
3
2
1
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
-1
-2
-3
-4
-5
0.0
400
500
600
700
800
-0.2
0.0 0.2 0.4 0.6
0.8
1.0
1.2
1.4
1.6
Wavelength (nm)
Voltage (V vs NHE)
Figure 2. Absorption and emission spectra of JK‐128 (black solid
line), JK‐129 (blue solid line) and JK‐130 (red solid line) in THF and
absorption spectra of JK‐128 (black dash line), JK‐129 (blue dash
line) and JK‐130 (red dash line) absorbed on TiO2 film.
Figure 3. Cyclic voltammograms of JK-128 (black solid line), JK-129
(blue solid line), and JK-130 (red solid line).
one (2) was readily synthesized via a Friedel-Craft acylation
reaction. The Friedlander condensation reaction15 of 2 with
(2-amino-5-bromo-phenyl)phenyl-methanone in the presence
of diphenyl phosphate yielded 3. Compound 4 was prepared
from 3 by a lithiation with 1.2 equiv of n-butyllithium and
subsequent quenching with DMF. The aldehyde 4, on reaction
with cyanoacetic acid in the presence of piperidine in CH3CN
gave the JK-128 dye. The JK-129 and JK-130 dyes were syn-
thesized by Suzuki coupling reaction16 of 6-bromo-phenylqui-
noline derivatives with 1.2 equiv of 2-(5-thiophen-2-yl)-1,3,2-
dioxaborolane or 2-(2,2'-bithiophen-5-yl)-1,3,2-dioxaborolane,
followed by dedioxanylation of 5 and 7 with trifluoroacetic
acid.
Fig. 2 shows the absorption and emission spectra of the
JK-128, JK-129, and JK-130 sensitizers measured in THF and
the data are listed in Table 1. The absorption spectrum of JK-128
displays two absorption maxima at 431 nm (ε = 22,500 dm3
mol-1cm-1) and 352 nm (ε = 27,500 dm3mol-1cm-1), which are
due to the π-π* transitions of the conjugated system. Under the
same conditions the JK-129 sensitizer that contains the thio-
phene unit exhibits absorption bands at 435 nm (ε = 28,100
dm3mol-1cm-1) and 367 nm (ε = 31,000 dm3mol-1cm-1) that are
red-shifted about 4 and 15 nm when compared with those of
JK-128. On the other hand, the introduction of bithiophene
unit, giving JK-130, causes a further red shift to 453 nm (ε =
51,000 dm3mol-1cm-1) compared to the JK-128 and JK-129
sensitizers.6 Such a high molar extinction coefficient and red
shift result from the extension of the π-conjugation in the
sensitizer due to the introduction of bithiophene unit in the
bridged framework. When the JK-128, JK-129, and JK-130
sensitizers were adsorbed on TiO2 electrode, a large red shift
of 44 ~ 72 nm was found due to the J-aggregation.17 The
absorption spectra of the three dyes on TiO2 are much broadened
due to an interaction between the dyes and TiO2.6 Such broaden-
ing and red shift of the absorption spectra are desirable for
harvesting the solar spectrum and lead to large photocurrent.
When the JK-128, JK-129, and JK-130 sensitizers are excited
within their π-π* bands in an air-equilibrated solution and at
298 K, they exhibit strong luminescence maxima at 556, 564,
and 594 nm, respectively.
Electrochemical properties of the dyes JK-128 ~ JK-130
were scrutinized by cyclovoltammetry in acetonitrile containing
0.1 M tetrabutyl ammonium hexafluoro-phosphate. TiO2 films
stained with the sensitizers were used as working electrodes.
The three organic dyes absorbed on TiO2 film show quasi-rever-
sible couples (Fig. 3). The oxidation potential of JK-128 was
measured to be 1.16 V versus NHE with a separation of 0.36 V
between anodic-to-cathodic peak. Under similar conditions the
JK-129 and JK-130 dyes exhibits the redox couples at 1.14 and
1.13 V versus NHE, respectively. The redox potentials of the
three dyes were calculated from the oxidation potential and the
E
0-0 determined from the intersection of absorption and emission
spectra (Table 1). The excited state oxidation potentials (EO*X)
of the sensitizers (JK-128: ‒1.33 V; JK-129: ‒1.38 V; JK-130:
Table 1. Optical, redox and DSSC performance parameters of dyes
‐1
‐1
‐2
Dye
λabsa/nm (ε/M cm )
Eredoxb/V
E
0‐0c/V
ELUMOd/V
Jsc (mAcm )
Voc (V)
FF
ηe (%)
JK‐128
JK‐129
JK‐130
352 (27 500), 431 (22 500)
367 (31 000), 435 (28 100)
320 (36 800), 453 (51 000)
1.16
1.14
1.13
2.49
2.52
2.48
‒1.33
‒1.38
‒1.35
7.568
8.289
0.7671
0.7059
0.6998
78.34
77.50
75.29
4.55
4.53
6.07
11.519
aAbsorption spectra measured in THF solution. bRedox potential of dyes on TiO2 were measured in CH3CN with 0.1 M (n-C4H9)4NPF6 with a scan rate
of 50 mVs-1 (vs. NHE). E0-0 was determined from intersection of absorption and emission spectra in THF. ELUMO was calculated by EOX ‒ E0-0
.
c
d
ePerformances of DSSCs were measured with 0.18 cm2 working area. Electrolyte 0.6 M DMOImI, 0.05 M I2, 0.1 M LiI, and 0.5 M tert-butylpyridine
in acetonitrile.

128 Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1
Hyeju Choi et al.
(a)
80
60
40
20
0
HOMO
LUMO
(b)
(c)
400
500
600
700
Wavelength (nm)
Figure 5. Spectra of incident photon‐to‐current conversion efficiencies
(IPCEs) for DSSC based on JK‐128 (black line), JK‐129 (blue line),
and JK‐130 (red line).
HOMO
HOMO
LUMO
LUMO
12
JK-128
JK-129
JK-130
10
8
6
Figure 4. Isodensity surface plots of the HOMO and LUMO of (a)
JK-128, (b) JK-129 and (c) JK-130.
4
2
0
‒1.35 V vs. NHE) are much negative than the conduction band
level of TiO2 at approximately ‒0.5 V versus NHE, indicating
that the electron injection should be thermodynamically favour-
able.18
-0.2
-0.4
0.0
0.2
0.4
0.6
0.8
Voc (V)
To gain insight into the characteristic features of the electronic
structure, molecular orbital calculations of three sensitizers
were performed with the TD-DFT on B3LYP/3-21G*. The
calculations indicate that the HOMO of three dyes is localized
over the fluorenylamino unit over phenyl and the LUMO of
JK-128 is localized over the cyanoacrylic unit through the exten-
sion of the quinoline unit (Fig. 4). On the other hand, the
LUMO of JK-129 and JK-130 is localized through the cyano-
acrylic and thiophene moieties. Examination of the HOMO
and LUMO of the three dyes indicates that the excitation of
the dyes moved the electron distribution from the amino unit
to the cyanoacrylic acid unit. Therefore the change in electron
distribution induced by photoexcitation results in an efficient
charge separation.
Fig. 5 shows action spectra of monochromatic incident-
to-current conversion efficiencies (IPCEs) for DSSCs based
on JK-128 ~ JK-130. The onset of IPCE spectra for DSSCs
based on JK-128 and JK-129 is 650 nm. On the other hand, the
onset of JK-130 tails off toward 690 nm, contributing to the
broad spectral light harvesting. Furthermore, the enhanced light
harvesting of JK-130 in the 550 ~ 650 nm due to the intro-
duction of bithiophene can be clearly seem from Figure 5. The
IPCE of JK-130 sensitizer exceeds 80% in the spectral region
from 400 to 550 nm, reaching its maximum of 85% at 435 nm.
Integrating the IPCE curve of JK-130 over the solar spectrum
results in a short circuit current of 11.31 mAcm-2 in agreement
with the measured device photocurrent. In addition, we find
Figure 6. J-V curve of JK-128 (black solid line), JK-129 (blue solid
line) and JK-130 (red solid line). Dark current-bias potential relation-
ship is shown as dotted curves.
that the device based on JK-130 exhibits a significant increase
in the short circuit current density (Jsc). This observation most
probably stems from the high molar extinction coefficient and
the red shift in the absorption spectrum of JK-130 relative to
JK-128 and JK-129. The J-V curve for the cells based on the
JK-128 ~ JK-130 is presented in Figure 6. Under standard
global AM 1.5 solar condition, the JK-128 and JK-129 sensi-
tized cell gave a short circuit photocurrent density (Jsc) of 7.57
and 8.29 mA cm-2, an open circuit voltage (Voc) of 0.77 and
0.71 V and a fill factor of 0.78 and 0.77, corresponding to an
overall conversion efficiency η of 4.55 and 4.53%, respectively.
Under the same condition, the JK-130 sensitized cell gave a
Jsc of 11.52 mA cm-2, Voc of 0.70 V and a fill factor of 0.75
corresponding to η of 6.07%. Of particular importance is the
3.23~3.95 mA cm-2 increase in Jsc of the JK-130 cell. In order
to explain the high photocurrent of JK-130, we have measured
the amount of dyes absorbed on TiO2 film. The absorbed amount
of 1.98 × 10-6 mmol cm-2 for JK-128, 2.64 × 10-6 mmol cm-2 for
JK-129, and 2.54 × 10-6 mmol cm-2 for JK-130 are observed.
Therefore, the large photocurrent in JK-130 is attributable to a
broad and intense absorption spectrum rather than their absorbed
amounts.

Novel Organic Sensitizers with a Quinoline Unit
Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1 129
trend to those of coumarin dyes.6b On the other hand, the τe
values show a significant gap among the dyes, resulting in the
increasing order of JK-128 > JK-129 > JK-130. The increase
in the number of thiophene unit enhances the light absorption
of long wavelength, and therefore the Jsc significantly increases
but the Voc decreases simultaneously as shown in Table 1. The
results of the electron lifetime are also well consistent with
those of the Voc.
(a)
JK-128
JK-128
JK-129
JK-129
JK-130
JK-130
1E-5
1E-6
1E-7
Fig. 8 shows the ac impedance spectra of the DSSCs mea-
sured under the illumination conditions. Under the illumination
(100 mW cm-2, open-circuit voltage (OCV) condition), the
radius of the intermediate-frequency semicircle in the Nyquist
plot decreased in the order of JK-128 (32.1 Ω) > JK-129 (17.7
Ω) > JK-130 (10.5 Ω), indicating the improved electron genera-
tion and transport. This result also well corresponds to that of
the overall efficiency.
0.01
0.1
1
Short-circuit current (mA cm-2)
10000
(b)
JK-128
JK-128
JK-12299
In summary, We have designed and synthesized three organic
sensitizers containing a quinoline unit. We obtained a maximum
solar energy to electricity conversion efficiency (η) of 6.07%
under AM 1.5 irradiation with a DSSC based on JK-130. Our
results suggest that the development of efficient sensitizers
comparable to ruthenium dyes can be possible through the
structural modifications of bridging units and these works are
now in progress.
JK-130
JK-130
1000
100
10
Experimental Section
0.5
0.55
0.6
0.65
Open-circuit voltage (V)
General methods. All reactions were carried out under argon
atmosphere. Solvents were distilled from appropriate reagents.
All reagents were purchased from Sigma-Aldrich and TCI.
9,9-Dimethyl-N-(9,9-dimethyl-9H-fluoren-7-yl)-N-phenyl-9
H-fluoren-2-amine10 and (2-amino-5-bromophenyl)phenyl-me-
thanone19 were synthesized using a modified procedure of
previous references. 1H and 13C NMR spectra were recorded
on a Varian Mercury 300 spectrometer. Elemental analyses were
recorded on a JEOL JMS-SX102A instruments CHNS-OEA
1108 analyzer. The absorption and photoluminescence spectra
were recorded on a Perkin-Elmer Lambda 2S UV-visible spec-
trometer and a Perkin LS fluorescence spectrometer, respec-
tively.
Figure 7. Electron diffusion coefficients (a) and lifetimes (b) of the
DSSCs employing JK-128, JK-129, and JK-130, respectively.
Illumination: 1 Sun; OCV
JK-128
30
20
10
0
JK-129
JK-130
Cyclovoltamogram:Cyclic voltammetry was carried out with
a BAS 100B (Bioanalytical Systems, Inc.). A three-electrode
system was used and consisted of a gold disk, working electrode,
a platinum wire electrode. Redox potential of dyes on TiO2
were measured in CH3CN with 0.1 M (n-C4H9)4N-PF6 with a
scan rate of 50 mV s-1 (vs. Fc/Fc+).
0
5
10
15
20
25
30
35 40
Z', Ohm
Figure 8. Electrochemical impedance spectra measured under the
‐2
Dye-sensitized solar cell Fabrication: FTO glass plates
(Pilkington TEC Glass-TEC 8, Solar 2.3 mm thickness) were
cleaned in a detergent solution using an ultrasonic bath for 30
min, rinsed with water and ethanol. The FTO glass plates were
immersed in 40 mM TiCl4 (aqueous) at 70 oC for 30 min and
washed with water and ethanol. Atransparent nanocrystalline
layer on the FTO glass plate was prepared by doctor blade
printing TiO2 paste (Solaronix, Ti-Nanoxide T/SP) and then
illumination (100 mW cm ) for the devices employing different
dyes (■ JK‐128, ● JK‐129, ▲ JK‐130).
To understand the electron injection property and the change
in Voc of JK-128, JK-129, and JK-130, we measured electron
diffusion coefficients and lifetimes in the photoelectrode. Fig. 7
shows the electron diffusion coefficients and lifetimes of the
DSSCs employing different dyes (i.e. JK-128, JK-129, and
JK-130) displayed as a function of the Jsc and Voc, respectively.
No significant differences among the De values were seen at the
identical short-circuit current conditions, showing the similar
o
dried for 2 h at 25 C. The TiO2 electrodes were gradually
heated under an air flow at 325 oC for 5 min, at 375 oC for 5
min, at 450 oC for 15 min, and at 500 oC for 15 min. The thick-
ness of the transparent layer was measured by using an Alpha-

130 Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1
Hyeju Choi et al.
step 250 surface profilometer (Tencor Instruments, San Jose,
CA), a paste for the scattering layer containing 400 nm sized
anatase particles (CCIC, PST-400C) was deposited by doctor
138.7, 135.8, 130.2, 130.0, 127.1, 125.2, 124.3, 122.8, 121.0,
120.3, 120.0, 47.1, 27.3, 27.0. MS: m/z 519 [M+]. Anal. Calc.
for C38H33NO: C, 87.83; H, 6.40. Found: C, 87.61; H, 6.19.
N-(4-(6-Bromo-4-phenylquinolin-2-yl)phenyl)-9,9-dime-
thyl-N-(9,9-dimethyl-9H-fluoren-7-yl)-9H-fluoren-2-amine
(3): Amixture of compound 2 (0.412 g, 0.79 mmol), diphenyl
phosphate (DPP, 0.422 g, 1.68 mmol) and (2-amino-5-bromo-
phenyl)phenyl-methanone (0.24 g, 0.87 mmol) in m-cresol (2
mL) was stirred at room temperature for 20 min and then reflux-
ed at 140 oC for 12 h. The solution was extracted with CH2Cl2,
and dried with MgSO4. The yellow product 3 was obtained by
silica gel column chromatography (eluent EA : Hx = 1 : 10).
1H NMR (CDCl3) δ 8.08 (t, J = 8.7 Hz, 3H), 8.02 (d, J = 1.5 Hz,
1H), 7.81 (s, 1H), 7.78 (d, J = 8.7 Hz, 1H), 7.72 (d, J = 1.8 Hz, 1H),
7.68-7.53 (m, 10H), 7.42 (d, J = 14.7 Hz, 2H), 7.37-7.28 (m, 6H),
7.16 (d, J = 8.1 Hz, 2H), 1.43 (s, 12H). 13C NMR (CDCl3) δ
156.9, 155.3, 153.7, 149.6, 148.3, 147.6, 147.0, 139.0, 137.9,
134.8, 133.1, 132.7, 131.8, 129.6, 129.4, 128.9, 128.8, 128.6,
126.9, 126.8, 123.9, 123.5, 122.7, 120.8, 120.1, 119.8, 119.6,
119.3, 47.0, 27.2. MS: m/z 758 [M+]. Anal. Calc. for C51H39BrN2:
C, 80.62; H, 5.17. Found: C, 80.41; H, 4.95.
o
blade printing and then dried for 2 h at 25 C. The TiO2
electrodes were gradually heated under an air flow at 325 oC
for 5 min, at 375 oC for 5 min, at 450 oC for 15 min, and at 500 oC
for 15 min. The resulting layer was composed of 20 µm thick-
ness of transparent layer and 4 µm thickness of scattering layer.
The TiO2 electrodes were treated again by TiCl4 at 70 oC for
30 min and sintered at 500 oC for 30 min. The TiO2 electrodes
were immersed into the JK-128, JK-129 and JK-130 (0.3 mM
in THF) containing 10 mM 3a,7a-dihydroxy-5b-cholic acid
(Cheno)) and kept at room temperature for 24 h. The FTO
plate (Pilkington TEC Glass-TEC 8, Solar 2.3 mm thickness)
for counter electrodes cleaned with ultrasonic bath in H2O, ace-
tone and 0.1 M HCl aq., subsequently. Counter electrodes were
prepared by coating with a drop of H2PtCl6 solution (2 mg of
Pt in 1 mLof ethanol) on a FTO plate and heating at 400 oC for
15 min. The dye adsorbed TiO2 electrode and Pt-counter elect-
rode were assembled into a sealed sandwich-type cell by heat-
ing at 80 oC with a hot-melt ionomer film (Surlyn SX 1170-25,
Solaronix) as a spacer between the electrodes. A drop of elect-
rolyte solution (electrolyte of 0.6 M 1-hexyl-2,3-dimethyl-
imidazolium iodide, 0.05 M iodine, 0.1 M LiI, and 0.5 M tert-
butylpyridine in acetonitrile) was placed on the drilled hole in
the counter electrode of the assembled cell and was driven into
the cell via vacuum backfilling. Finally, the hole was sealed
using additional Surlyn and a cover glass (0.1 mm thickness).
Electron transport measurements: The electron diffusion
coefficient (De) and lifetimes (τe) in TiO2 photoelectrode were
measured by the stepped light-induced transient measurements
of photocurrent and voltage (SLIM-PCV).20-24 The transients
were induced by a stepwise change in the laser intensity. A
diode laser (λ = 635 nm) as a light source was modulated using
a function generator. The initial laser intensity was a constant
90 mW cm-2 and was attenuated up to approximately 10 mW
cm-2 using a ND filter which was positioned at the front side of
the fabricated samples (TiO2 film thickness = ca. 10 µm; active
area = 0.04 cm2). The photocurrent and photovoltage transients
were monitored using a digital oscilloscope through an amplifier.
The De value was obtained by a time constant (τc) determined
by fitting a decay of the photocurrent transient with exp(-t/τc)
and the TiO2 film thickness (ω) using the equation, De = ω2/
(2.77 τc).17 The τe value was also determined by fitting a decay
of photovoltage transient with exp(-t/τe).17 All experiments
were conducted at room temperature.
3-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-4-
phenylquinoline-6-carbaldehyde (4): Under a nitrogen atmo-
sphere, n-BuLi (0.143 mL, 2.5 M solution in hexane) was
dropwise added into compound 3 (0.247 g, 0.33 mmol) solution
in dry tetrahydrofuran (THF) and the mixture was stirred at ‒10 oC
for 1 h. After dimethylformamide (0.027 mL, 0.34 mmol) was
added to the reaction mixture, the solution was then left under
stirring overnight at room temperature. After solvent was eva-
porated, the organic layer was separated and dried in MgSO4.
The product 4 was obtained by silica gel column chromato-
graphy (eluent EA : Hx = 1 : 5). 1H NMR (CDCl3) δ 10.10 (s,
1H), 8.38 (s, 1H), 8.30 (d, J = 8.7 Hz, 1H), 8.20 (t, J = 8.4 Hz,
3H), 7.90 (s, 1H), 7.69-7.25 (m, 19H), 7.17 (d, J = 8.1 Hz,
2H), 1.44 (s, 12H). 13C NMR (CDCl3) δ 191.8, 159.0, 155.3,
153.7, 151.9, 150.6, 150.1, 146.8, 138.9, 137.7, 136.2, 135.6,
135.1, 133.8, 133.2, 132.2, 132.1, 131.2, 129.6, 129.1, 128.9,
127.2, 126.8, 125.2, 124.0, 122.9, 122.6, 121.5, 120.8, 119.8,
119.7, 119.4, 48.2, 27.2. MS: m/z 708 [M+]. Anal. Calc. for
C52H40N2O: C, 88.10; H, 5.69. Found: C, 87.89; H, 5.48.
(Z)-3-(3-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phe-
nyl)-4-phenylquinolin-6-yl)-2-cyanoacrylic acid (JK-128): A
mixture of compound 4 (0.09 g, 0.13 mmol) and cyanoacetic
acid (0.02 g, 0.25 mmol) were added CH3CN (30 mL) and
piperidine (0.02 g, 0.23 mmol). The solution was refluxed for
6 h. After cooling the solution, the organic layer was removed
in vacuo. The crude product was extracted with CH2Cl2 and
water. The pure product JK-128 was obtained by silica gel
column chromatography (eluent MC : MeOH = 9 : 1). 1H NMR
(DMSO-d6) δ 8.30 (d, J = 15.3Hz), 8.23 (s, 1H), 8.17 (s, 1H),
8.06 (s, 1H), 7.97 (s, 1H), 7.79 (t, J = 10.8Hz, 4H), 7.68-7.28
(m, 14H), 7.19 (d, J = 6.3Hz, 2H), 7.11 (d, J = 7.8Hz, 2H), 1.40
(s, 12H). 13C NMR (DMSO-d6) δ 163.3, 162.7, 156.4, 154.9,
153.3, 149.2, 149.0, 148.9, 146.8, 146.2, 139.5, 138.2, 137.0,
134.5, 134.5, 131.4, 131.1, 130.3, 129.7, 129.4, 128.9, 127.2,
126.9, 125.7, 124.7, 123.7, 122.8, 121.9, 121.3, 119.8, 119.1,
114.5, 46.5, 26.7. MS: m/z 775 [M+]. Anal. Calc. for C55H41N3O2:
C, 85.13; H, 5.33. Found: C, 84.92; H, 5.12.
1-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-
ethanone (2): To a stirred solution of the compound 1 (0.615 g,
1.3 mmol) in CH2Cl2 was added a solution of acetic anhydride
in dry CH2Cl2 (1.1 equiv) and a solution of SnCl4 (1.1 equiv) in
dry CH3CN. The mixture was refluxed for 24 h and then poured
over ice containing glacial acetic acid. The organic layer was
separated and dried in MgSO4. The product 2 was obtained by
silica gel column chromatography (eluent EA: Hx = 1 : 3). 1H
NMR (CDCl3) δ 7.84 (d, J = 9.0 Hz, 2H), 7.66 (t, J = 7.2 Hz,
4H), 7.41 (d, J = 6.3 Hz, 2H), 7.31 (t, J = 5.7 Hz, 4H), 7.25 (d,
J = 2.1 Hz, 2H), 7.16-7.11 (m, 4H), 2.56 (s, 3H), 1.42 (s, 12H).
13C NMR (CDCl3) δ 196.7, 155.4 153.7, 152.5, 146.1, 141.9,

Novel Organic Sensitizers with a Quinoline Unit
Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1 131
9,9-Dimethyl-N-(4-(6-(5-(5,5-dimethyl-1,3-dioxan-2-yl)-
thiophen-2-yl)-4-phenylquinolin-2-yl)phenyl)-N-(9,9-dime-
thyl-9H-fluoren-7-yl)-9H-fluoren-2-amine (5): A mixture of
compound 3 (0.213 g, 0.28 mmol), 4,4,5,5-tetramethyl-2-(5-
(5,5-dimethyl-1,3-dioxan-2-yl)thiophen-2-yl)-1,3,2-dioxabo
rolane (0.11 g, 0.34 mmol), 2 M solution of K2CO3 (0.581 g,
4.2 mmol) in H2O (2.1 mL), and Pd(PPh3)4 (0.016 g, 0.014 mmol)
in dry THF was refluxed at 80 oC for 24 h. After cooling the
solution, the organic layer was removed in vacuo. The crude
product was extracted with CH2Cl2 and dried in MgSO4. The
product 5 was obtained by silica gel column chromatography
(eluent EA: Hx = 1 : 5). 1H NMR (CDCl3) δ 8.21 (d, J = 9.0 Hz,
1H), 8.13 (d, J = 8.4 Hz, 1H), 8.08 (d, J = 1.5 Hz, 1H), 7.98(d,
J = 9.0 Hz, 1H), 7.81 (s, 1H), 7.69-7.54 (m, 9H), 7.41 (d, J =
6.9 Hz, 2H), 7.36-7.23 (m, 10H), 7.17 (d, J = 8.1 Hz, 2H), 7.11
(d, J = 3.6 Hz, 1H), 5.36 (s, 1H), 3.72 (d, J = 11.1 Hz, 4H), 1.45
(s, 12H), 1.30 (s, 6H). 13C NMR (CDCl3) δ 156.4, 155.2, 153.7,
149.4, 149.1, 148.6, 147.1, 144.4, 141.3, 140.4, 139.0, 138.4,
137.7, 134.7, 133.1, 132.1, 129.6, 128.9, 128.6, 128.0, 127.1,
126.7, 126.3, 125.9, 123.7, 123.4, 122.6, 122.0, 120.8, 119.8,
119.6, 119.2, 98.4, 98.2, 77.6, 47.0, 30.4, 27.2, 23.0, 21.9. MS:
m/z 876 [M+]. Anal. Calc. for C61H52N2O2S: C, 83.53; H, 5.98.
Found: C, 83.32; H, 5.77.
46.6, 26.8. MS: m/z 857 [M+]. Anal. Calc. for C59H43N3 O2S:
C, 82.59; H, 5.05; Found: C, 82.38; H, 4.94.
9,9-Dimethyl-N-(4-(6-(5-(5-(5,5-dimethyl-1,3-dioxan-2-yl)-
thiophen-2-yl)thiophen-2-yl)-4-phenylquinolin-2-yl)phenyl)-
N-(9,9-dimethyl-9H-fluoren-7-yl)-9H-fluoren-2-amine (7):A
mixture of compound 3 (0.233 g, 0.31 mmol), 4,4,5,5-tetra-
methyl-2-(5-(5-(5,5-dimethyl-1,3-dioxan-2-yl)thiophen-2-yl)-
thiophen-2-yl)-1,3,2-dioxaborolane (0.15 g, 0.37 mmol), 2 M
solution of K2CO3 (0.638 g, 4.6 mmol) in H2O (2.3 mL), and
Pd(PPh3)4 (0.018 g, 0.015 mmol) in dry THF was refluxed at
80 oC for 24 h. After cooling the solution, the organic layer was
removed in vacuo. The crude product was extracted with CH2Cl2
and dried in MgSO4. The product 5 was obtained by silica gel
column chromatography (eluent EA : Hx = 1 : 3). 1H NMR
(CDCl3) δ 8.20 (d, J = 8.8 Hz, 1H), 8.12 (d, J = 8.7 Hz, 2H), 8.06
(d, J = 1.5 Hz, 1H), 7.90 (d, J = 8.8 Hz, 1H), 7.80 (s, 1H), 7.68-
7.57 (m, 8H), 7.40 (d, J = 7.8 Hz, 2H), 7.35-7.13 (m, 13H), 7.05
(d, J = 10.5 Hz, 2H), 5.62 (s, 1H), 3.70 (d, J = 11.1 Hz, 4H),
1.44 (s, 12H), 1.30 (s, 6H). 13C NMR (CDCl3) δ 156.4, 155.2,
153.7, 149.4, 149.0, 148.6, 147.0, 143.9, 140.4, 139.0, 138.3,
137.7, 137.4, 134.7, 133.1, 131.7, 130.5, 129.7, 128.9, 128.7,
128.6, 128.4, 127.7, 127.0, 126.3, 125.9, 125.6, 125.2, 124.9,
124.5, 123.6, 123.0, 122.7, 122.5, 121.6, 120.8, 119.6, 119.2,
98.2, 77.4, 47.0, 30.4, 27.2, 23.1, 21.9. MS: m/z 958 [M+]. Anal.
Calc. for C65H54N2O2S2: C, 81.38; H, 5.67; Found: C, 81.17;
H, 5.46.
5-(3-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-
4-phenylquinolin-6-yl)thiophene-2-carbaldehyde (6): To the
compound 5 (0.174 g, 0.2 mmol) in THF was added water.
Then trifluoroacetic acid (TFA, 1.075 mL) was added to the
solution. The mixture was refluxed for 2 h. The solution was
quenched with saturated aqueous sodium bicarbonate and ext-
racted with CH2Cl2 and dried with MgSO4. The product 6 was
obtained by silica gel column chromatography (eluent EA: Hx =
1 : 5). 1H NMR (CDCl3) δ 9.89 (s, 1H), 8.24 (d, J = 9.3 Hz, 1H),
8.19 (s, 1H), 8.13 (d, J = 8.1 Hz, 1H), 8.01 (d, J = 7.2 Hz, 1H),
7.85 (s, 1H), 7.74-7.59 (m, 9H), 7.40 (d, J = 7.2 Hz, 4H), 7.33-
7.31 (m, 9H), 7.17 (d, J = 7.8 Hz, 2H), 1.43 (s, 12H). 13C NMR
(CDCl3) δ 182.8, 157.2, 155.3, 153.9, 153.6, 149.7, 149.4, 149.3,
146.9, 142.8, 138.9, 138.0, 137.7, 137.4, 134.9, 132.6, 131.2,
130.9, 130.5, 129.7, 129.1, 128.5, 127.7, 127.5, 126.7, 125.8,
124.5, 123.9, 123.3, 122.6, 120.8, 120.1, 119.8, 119.5, 119.2,
118.7, 47.0, 27.1. MS: m/z 790 [M+]. Anal. Calc. for C56H42N2OS:
C, 85.03; H, 5.35; Found: C, 84.82; H, 5.14.
5'-(3-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)-
4-phenylquinolin-6-yl)-2,2'-bithiophene-5-carbaldehyde (8):
To the compound 7 (0.208 g, 0.217 mmol) in THF was added
water. Then TFA (4.5 mL) was added to the solution. The mix-
ture was refluxed for 2 h. The solution was quenched with satu-
rated aqueous sodium bicarbonate and extracted with CH2Cl2
and dried with MgSO4. The product 8 was obtained by silica
gel column chromatography (eluent EA : Hx = 1 : 3). 1H NMR
(CDCl3) δ 8.22 (d, J = 8.7 Hz, 1H), 8.13 (d, J = 9.0 Hz, 1H),
8.10 (d, J = 2.1 Hz, 1H), 7.97 (d, J = 9.0 Hz, 1H), 7.83 (s, 1H),
7.68-7.26 (m, 24H), 7.16 (d, J = 8.1 Hz, 2H), 1.44 (s, 12H).
13C NMR (CDCl3) δ 182.6, 174.5, 156.8, 155.3, 153.7, 149.6,
149.1, 148.8, 147.1, 147.0, 145.9, 141.8, 139.0, 138.3, 137.5,
135.8, 134.8, 132.9, 131.1, 130.9, 129.7, 128.9, 128.8, 127.6,
127.4, 127.1, 126.8, 126.2, 125.9, 125.0, 124.3, 123.8, 123.3,
122.7, 122.2, 120.8, 119.9, 119.6, 119.3, 48.2, 27.2. MS: m/z
872 [M+]. Anal. Calc. for C60H44N2OS2: C, 82.54; H, 5.08; Fo-
und: C, 82.32; H, 4.87.
(Z)-3-(5'-(3-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)-
phenyl)-4-phenylquinolin-6-yl)-2,2'-bithiophen-5-yl)-2-cya-
noacrylic acid(JK-130):Amixture of compound 8 (0.19 g, 0.21
mmol) and cyanoacetic acid (0.04 g, 0.42 mmol) were added
CH3CN (30 mL) and piperidine (0.04 g, 0.57 mmol). The solu-
tion was refluxed for 6 h. After cooling the solution, the organic
layer was removed in vacuo. The crude product was extracted
with CH2Cl2 and water. The pure product JK-130 was obtained
by silica gel column chromatography (eluent MC : MeOH = 9 :
1). 1H NMR (DMSO-d6) δ 8.30 (d, J = 7.8 Hz, 2H), 8.16 (s, 1H),
8.03 (t, J = 10.2 Hz, 3H), 7.82-7.28 (m, 22H), 7.20 (d, J = 8.1 Hz,
2H), 7.10 (d, J = 7.8 Hz, 2H), 1.20 (s, 12H). 13C NMR (DMSO-d6)
δ 165.1, 164.6, 163.2, 155.8, 155.3, 154.2, 153.9, 153.4, 150.1,
148.7, 148.4, 147.4, 146.5, 140.5, 140.0, 138.4, 137.5, 137.4,
(Z)-3-(5-(3-(4-(Bis(9,9-dimethyl-9H-fluoren-2-yl)amino)-
phenyl)-4-phenylquinolin-6-yl)thiophen-2-yl)-2-cyanoacrylic
acid (JK-129): A mixture of compound 6 (0.14 g, 0.2 mmol)
and cyanoacetic acid (0.034 g, 0.4 mmol) were added CH3CN
(30 mL) and piperidine (0.03 g, 0.35 mmol). The solution was
refluxed for 6 h. After cooling the solution, the organic layer
was removed in vacuo. The crude product was extracted with
CH2Cl2 and water. The pure product JK-129 was obtained by
silica gel column chromatography (eluent MC : MeOH = 9 : 1).
1H NMR (DMSO-d6) δ 8.32 (d, J = 8.7 Hz, 2H), 8.18 (s, 1H),
8.06 (t, J = 8.1 Hz, 3H), 7.82-7.62 (m, 12H), 7.52 (d, J = 6.9 Hz,
2H), 7.37-7.28 (m, 6H), 7.20 (d, J = 8.7 Hz, 2H), 7.12 (d, J =
7.8 Hz, 2H), 1.40 (s, 12H). 13C NMR (DMSO-d6) δ 164.2, 163.0,
155.6, 155.0, 153.9, 153.3, 149.1, 148.5, 148.2, 147.2, 146.3,
140.3, 139.8, 138.2, 137.3, 137.2, 136.2, 134.5, 131.6, 130.7,
129.7, 128.9, 127.8, 127.0, 126.8, 125.6, 125.1, 123.9, 123.6,
122.9, 122.7, 122.4, 122.2, 121.4, 119.8, 119.3, 112.0, 110.5,

132 Bull. Korean Chem. Soc. 2010, Vol. 31, No. 1
Hyeju Choi et al.
2006, 2792. (b) Wang, M.; Xu, M.; Shi, D.; Li, R.; Gao, F.; Zhang,
G.; Yi, Z.; Humphry-Baker, R.; Wang, P.; Zakeeruddin, S. M.;
Grätzel, M. Adv. Mater. 2008, 20, 4460.
136.8, 136.4, 134.9, 134.7, 131.8, 130.9, 129.9, 128.9, 128.0,
127.2, 127.0, 125.8, 125.3, 124.1, 123.8, 123.1, 122.9, 122.6,
122.4, 121.6, 120.0, 119.5, 112.5, 110.7, 46.7, 26.9. MS: m/z
939 [M+]. Anal. Calc. for C63H45N3O2S2: C, 80.48; H, 4.82;
Found: C, 80.27; H, 4.61.
8. (a) Liu, W.-H.; Wu, I.-C.; Lai, C.-H.; Chou, P.-T.; Li, Y.-T.; Chen,
C.-L.; Hsu, Y.-Y.; Chi, Y. Chem. Commun. 2008, 5152. (b) Choi,
H.; Lee, J. K.; Song, K. H.; Song, K.; Kang, S. O.; Ko, J. Tetra-
hedron 2007, 63, 1553. (c) Xu, M.; Wenger, S.; Bala, H.; Shi, D.;
Li, R.; Zhou, Y.; Zakeeruddin, S. M.; Grätzel, M.; Wang, P. J.
Phys. Chem. C 2009, 113, 2966.
Acknowledgments. We are grateful to the Korea University
Researh Program (2009).
9. (a) Kim, J.-J.; Choi, H.; Lee, J.-W.; Kang, M.-S.; Song, K.; Kang,
S. O.; Ko, J. J. Mater. Chem. 2008, 18, 5223. (b) Velusamy, M.;
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