Synthesis of conjugated organic dyes containing alkyl substituted thiophene for solar cell

Article abstract of DOI:10.1016/j.tet.2007.08.058

Three organic dyes, JK-41, JK-42, and JK-43 containing bis-dimethylfluoreneaniline and alkyl substituted thiophene unit are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-41 sensitized cell gave a short circuit photocurrent

Full text of DOI:10.1016/j.tet.2007.08.058

Tetrahedron 63 (2007) 11436–11443
Synthesis of conjugated organic dyes containing
alkyl substituted thiophene for solar cell
a
Sanghoon Kim, Hyunbong Choi, Chul Baik, Kihyung Song,
a
a
b
a,
Sang Ook Kang and Jaejung Ko
a,
*
*
a
Department of Chemistry, Korea University, Jochiwon, Seochang 208, Chungnam 339-700, Republic of Korea
Department of Chemistry, Korea National University of Education, Chongwon, Chungbuk 363-791, Republic of Korea
b
Received 5 July 2007; revised 16 August 2007; accepted 17 August 2007
Available online 22 August 2007
Abstract—Three organic dyes, JK-41, JK-42, and JK-43 containing bis-dimethylfluoreneaniline and alkyl substituted thiophene unit are
designed and synthesized. Under standard global AM 1.5 solar condition, the JK-41 sensitized cell gave a short circuit photocurrent density
ꢀ
Jsc) of 15.23 mA cm , open circuit voltage (V ) of 0.67 V, and a fill factor of 0.67, corresponding to an overall conversion efficiency h of
oc
2
(
7.69%. Molecular-orbital calculations of the three dyes suggest that the electron distribution moves from the aniline derivative to the cyano-
acrylic acid moiety. We found that the power conversion efficiency was shown to be quite sensitive to the structural variations of alkyl
substituted thiophene moiety.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
the dye not only rotates but also undergoes trans–cis isomer-
ization about the central methine bond (CH]CH). Such
1
0
Increasing energy demands and concerns over global warm-
ing have led to a greater focus on renewable energy sources
in recent years. The conversion of solar energy to electricity
trans–cis photoisomerization is one of the major nonradiative
deactivations for the excited singlet. Accordingly, a restric-
tion on the excited state makes the photoisomerization less
1
1
1
1
2
appears as one of the substitutes that can replace fossil fuels.
Dye-sensitized nanocrystalline TiO solar cells (DSSCs)
based on Ru complex photosensitizers have been inten-
feasible. One of the approaches for the rigid configuration
of the excited state would be to introduce the long alkyl chain
in order to prevent isomerization by the restriction of rotation
2
2
1
3
sively studied because of both their high performance as un-
conventional solar cells and the possibility for low-cost
production of such devices. Organic dyes have been also uti-
lized as photosensitizers in DSSCs. Recently, the solar cell
performance of DSSCs based on organic dye photosensi-
tizers has been remarkably improved and obtained efficien-
around the methine chain.
1
5
Recently, Sun and co-workers reported an efficient poly-
ene-diphenylaniline dye containing an extended p-conjuga-
tion with a methine chain. We envisioned that if the
thiophene unit conjugated with a methine unit has a long
alkyl group, we could make the photoisomerization less
efficient by the restriction of rotation, resulting in increasing
the power conversion efficiency h. In this article, we have
designed and synthesized the novel unsymmetrical organic
sensitizers JK-41, JK-42, and JK-43 (Fig. 1) that consist
of the bis-dimethylfluoreneaniline moiety acting as electron
donor and cyanoacrylic acid moiety acting as acceptor, the
two functions being connected by thiophene-ethylene unit.
We also investigated the effect of bridged structural modifi-
cations on the power conversion efficiency.
3
–8,13
cies in the range of 6–9%.
However, organic dyes have
several disadvantages as photosensitizers. First, organic sen-
sitizers have relatively sharp absorption bands in the visible
region. The absorption spectra of organic dyes must be
broadened and red shifted for harvesting the entire solar
spectrum. Second, the emission lifetimes of their excited
9
states are generally shorter than those of metal complexes.
One of the approaches to extend the absorption region of
dyes is to introduce the methine unit in order to increase
the p-conjugation. Such an extended p-conjugation with
a methine chain often results in instability of organic dyes
due to the possibility of isomer formation. In the excited state
2. Results and discussion
Keywords: Organic dye; Alkyl substituted thiophene; Solar cell.
*
The unsymmetrical organic sensitizers JK-41, JK-42, and
JK-43 were synthesized by the stepwise synthetic protocol
Corresponding authors. Tel.: +82 41 860 1337; fax: +82 41 867 5396;
e-mail: jko@korea.ac.kr
0
040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.08.058

S. Kim et al. / Tetrahedron 63 (2007) 11436–11443
11437
N
N
N
CN
COOH
CN
CN
COOH
S
S
S
COOH
JK-41
JK-42
JK-43
Figure 1. Structures of the dyes JK-41, JK-42, and JK-43.
illustrated in Scheme 1. Organic dye JK-41 is readily pre-
pared in four steps starting from the N,N-bis(9,9-dimethyl-
fluoren-2-yl)-4-bromoaniline.
between the phenyl and the methine unit and methine-
ꢁ
ꢁ
thienyl unit are 1.18 and 0.65 , respectively. Accordingly,
a red shift of JK-41 relative to JK-43 derives from more
delocalization over an entire conjugated system.
1
6
Carbaldehyde 2 was prepared from 1 by lithiation with
.2 equiv n-butyllithium and subsequent quenching with
1
When the JK-41, JK-42, and JK-43 sensitizers were ad-
sorbed on TiO electrode, a slight blue shift of 4–6 nm
dimethylformamide. Coupling reaction of carbaldehyde 2
with diethyl [5-(5,5-dimethyl-1,3-dioxan-2-yl)thiophen-2-
yl]methylphosphonate under Horner–Emmons–Wittig reac-
2
1
2
was found due to the H-aggregation (Fig. 2b). The absorp-
tion spectra of the three dyes on TiO are broadened. Such
a broadening of the absorption spectra is due to an inter-
2
1
7
tion led to intermediate 3. The thiophene derivative 3 was
converted into its corresponding thiophene aldehyde 4 by
dedioxanylation with trifluoroacetic acid (TFA). An aceto-
nitrile solution of 4 and cyanoacetic acid were refluxed in the
presence of piperidine for 6 h. Solvent removal followed
by purification using chromatography yielded JK-41. We
have also designed similar organic dyes to JK-41 with alkyl
substituted thiophene group. It is well established that intro-
duction of alkyl chain of thiophene unit probably prevents
photoisomerization by rather rigid configuration of the
1
8
action between the dyes and TiO2. This broadening of the
absorption spectrum is desirable for harvesting the solar
spectrum and leads to a large photocurrent. When the
JK-41, JK-42, and JK-43 sensitizers are excited within their
p–p* bands in an air-equilibrated solution and at 298 K,
they exhibit strong luminescence maxima at 582, 589,
587 nm, respectively. No emission signal was observed for
the three dyes on TiO films, suggesting that the interaction
2
of the excited electron from the excited dye to the TiO elec-
2
trodes is efficient.
1
3
excited state, improving the solar cell efficiency. The syn-
thetic strategy for the alkyl substituted dyes JK-42 and
JK-43 is quite different from that of JK-41. Coupling reaction
of carbaldehyde 2 with [(3-alkylthiophen-2-yl)methyl]-
triphenylphosphonium bromide under Horner–Emmons–
Wittig coupling condition led to 5/6. These were then
converted to the aldehydes 7/8, which yielded the dyes
JK-42 and JK-43 on treatment with cyanoacetic acid.
The electrochemical data for the dyes JK-41, JK-42, and
JK-43 are listed in Table 1. The cyclic voltammogram of
the three dyes on TiO measured in CH CN solvent contain-
2
3
ing 0.1 M tetrabutylammonium tetrafluoroborate shows
a quasi-reversible behavior. The oxidation potential of
JK-41 dye was measured to be 1.09 V versus NHE with a
separation of 0.13 V between anodic to cathodic peaks. Un-
der similar conditions the JK-42 and JK-43 dyes show the
redox couple at 1.08 Vand 1.07 V versus NHE, respectively.
The reduction potentials of the three dyes calculated from
the oxidation potentials and the E0–0 determined from the
intersection of absorption and emission spectra are listed
Figure 2 shows the absorption and emission spectra
of the JK-41, JK-42, and JK-43 sensitizers measured in
ethanol and the data are listed in Table 1. The absorption
spectrum of JK-41 displays two absorption maxima
3
ꢀ1
ꢀ1
at 461 nm (3¼55,890 dm mol cm ) and 368 nm (3¼
3
ꢀ1
ꢀ1
7
0,330 dm mol cm ), which are due to the p–p* transi-
in Table 1. The excited state oxidation potentials (E* ) of the
ox
tions of the conjugated system. Under the same condi-
tions the JK-42 sensitizer that contains the methyl
group on thiophene unit exhibits absorption peaks at
dyes (JK-41: ꢀ1.27 V vs NHE; JK-42: ꢀ1.27 V vs NHE;
JK-43: ꢀ1.29 V vs NHE) are all higher than the energy level
of TiO conduction band edge (ꢀ0.5 V vs NHE), showing
2
3
ꢀ1
ꢀ1
4
4
63 nm (3¼28,730 dm mol cm ) and 366 nm (3¼
that the energy injection should be possible thermodynami-
cally. A slight positive shift of the reduction potentials in
JK-41 and JK-42 is due to more delocalization of the p-
conjugation system, in keeping with the theoretical analysis
presented above.
3
ꢀ1
ꢀ1
0,960 dm mol cm ) that are almost the same as the
peaks of JK-41. On the other hand, the introduction of hexyl
group on thiophene unit in JK-41, giving JK-43, caused
a blue shift to 456 nm compared to the JK-41 and JK-42
sensitizers. A blue shift of JK-43 can be readily understood
from molecular modeling studies of the three dyes. The
To gain insight into the geometrical and electronic properties
of the JK-41, JK-42, and JK-43 sensitizers, we performed
DFT calculations on the three organic sensitizers using the
Gaussian 03 program package. In particular we used
B3LYP as exchange-correlation functional and 3-21G* as
ꢁ
ground state structure of JK-43 possesses an 8.15 twist
between N,N-bis(9,9-dimethylfluoren-2-yl)aniline and the
methine units (Fig. 3). The dihedral angle of the methine
ꢁ
and thienyl units is 7.35 . For JK-41, the dihedral angles

11438
S. Kim et al. / Tetrahedron 63 (2007) 11436–11443
O
O
O
P
S
O
O
n-BuLi, DMF
THF
N
Br
N
COH
N
t
K BuO, THF
S
O
O
1
2
3
HOOC
CN
piperidine
CH3CN
TFA
N
N
THF/H2O
CN
COOH
S
O
S
H
JK-41
4
R
Br-
+
Ph3 P
t
R
S
N
COH
N
POCl3
DMF
K BuO, THF
S
5: R= CH3
2
6: R= (CH2)5CH3
NC
piperidine
CH3CN
COOH
R
R
N
N
CN
S
S
COH
COOH
7
: R= CH3
JK-42: R= CH3
JK-43: R= (CH2)5CH3
8: R= (CH2)5CH3
Scheme 1. Schematic diagram for the synthesis of organic dyes JK-41, JK-42, and JK-43.
basis set. We optimized the molecular structure of JK-41,
JK-42, and JK-43 in the gas phase without any symmetry
constraints, obtaining the geometries shown in Figure 4.
The HOMO of the three organic dyes is delocalized over
the p-conjugated system via the aniline and the methine
units (Fig. 4) and the LUMO is delocalized over the cyano-
acrylic unit through thiophene. Molecular-orbital calculations
of these dyes strongly suggest that the electron distribution
moves from the aniline derivative to the cyanoacrylic acid
moiety by means of photoexcitation of the dye and is
carboxyl group. Therefore, the change in electron distribu-
tion induced by photoexcitation results in an efficient
separation.
The J–V curve for the DSSCs based on the JK-41, JK-42,
and JK-43 dyes is presented in Figure 5. Under standard
global AM 1.5 solar conditions, the JK-41, JK-42, and
JK-43 sensitized cells gave the short circuit photocurrent
ꢀ
2
density (J ) of 15.23, 12.72, and 10.56 mA cm , open cir-
sc
cuit voltage (V ) of 0.67, 0.64, and 0.66 Vand a fill factor of
oc
injected to the conduction band of TiO via the anchoring
2
75.8, 76.7, and 77.4, corresponding to an overall conversion

S. Kim et al. / Tetrahedron 63 (2007) 11436–11443
11439
(
a) 1.6
spectrum is red shifted by about 25 nm compared to
JK-43 as a result of extended p-conjugation, which is con-
sistent with the absorption spectrum of the JK-41 sensitizer.
JK - 41
JK - 42
JK - 43
1
1
1
0
0
0
0
0
.4
.2
.0
.8
.6
.4
.2
.0
From the above results, we have observed that the J and h
sc
of JK-41 were higher than those of JK-43. To understand
the high Jsc observed with JK-41, we calculated the light-
harvesting efficiency (LHE(l)) and the absorbed photon-
to-current conversion efficiency (APCE(l)) at 500 nm based
1
4a,b
on the following equation.
À Á
À Á
À Á
À Á
IPCE is the product of light-harvesting efficiency (LHE(l)),
À Á
IPCE ¼ LHE l ꢂ Finj l ꢂ h l ¼ LHE l ꢂ APCE l
c
3
00
400
500
600
Wavelength (nm)
700
800
900
the quantum yield of electron injection (F (l)), and the
inj
efficiency of collecting the injected charge (h (l)) at the back
c
ꢀ
ABS(l)
contact. The LHE(l) is defined as LHE(l)¼1–10
(b)
1
1
0
0
0
.6
.2
.8
.4
.0
where ABS(l) is absorbance of the dye adsorbed on nano-
JK - 41
JK - 42
JK - 43
1
4b
crystalline TiO2. It is noteworthy that the LHE for DSSCs
based on JK-41 (0.893) was higher than that for JK-43
(0.780) in the same condition (Table 2). Increased adsorbed
amount cannot be responsible for the increased IPCE com-
but this result indicated that the increased ad-
sorbed amount contributes to IPCE. To clarify the above
results, we have measured the amount of dyes adsorbed on
1
4a
pletely,
ꢀ
6
ꢀ2
TiO film. The adsorbed amounts of 2.66ꢂ10 mmol cm
2
ꢀ
6
ꢀ2
for JK-41, 2.38ꢂ10 mmol cm for JK-42, and 2.14ꢂ
ꢀ6 ꢀ2
10
mmol cm for JK-43 are observed. One of the main
reasons for the low efficiency of JK-43 with the hexyl group
was attributed to the difficulty of the dye absorption because
of the steric reason. It is also documented that the electron
injection process from the excited state of the dye to the
400
500
Wavelength (nm)
600
700
TiO electrode generally competes with other undesirable
2
Figure 2. (a) Absorption and emission spectra of JK-41 (solid line), JK-42
dashed line), and JK-43 (dot line) in ethanol solution. (b) Absorption spec-
tra of JK-41 (solid line), JK-42 (dashed line), and JK-43 (dot line) adsorbed
on TiO film.
processes and photoisomerization is one of the major decay
pathways for the nonradiative deactivation of the singlet
(
1
1
2
excited state. Initially, we expected that the solar conversion
efficiency of organic dyes with long alkyl chain is higher
than that of organic dyes without any alkyl chain because
the presence of long alkyl chain prevents isomerization by
the restriction of rotation. Therefore, the low efficiency of
JK-43 with a hexyl group demonstrates that the electron
efficiency h of 7.69, 6.23, and 5.42%, respectively. Figure 6
shows the incident monochromatic photon-to-current con-
version efficiency (IPCE) for the DSSCs based on the three
dyes. The IPCE data of JK-41 sensitizer in the maximum
region is about 77% at 496 nm. When the reflection and
absorption losses in the transparent conducting oxide
substrate are considered, the net photon-to-current conver-
sion efficiency exceeds 90%, indicating the highly efficient
performance of this solar cell. The JK-41 sensitizer IPCE
injection from the photo-excited state to TiO electrode is
2
more faster than nonradiative deactivation.
In summary, we have designed and synthesized three organic
dyes containing N,N-bis(9,9-dimethylfluoren-2-yl)aniline
unit bridged by three different methine thiophene units.
Table 1. Optical, redox, and DSSC performance data of JK-41, JK-42, and JK-43
a
3
ꢀ1
ꢀ1
a
b
c
d
ꢀ2
e
h, %
Dye
l
abs, nm (3, dm mol cm
)
l
em, nm
E
ox, V
E
0–0, V
E
LUMO, V
J
sc, mA cm
Voc, V
ff
JK-41
368 (70,330)
582
589
587
1.09
1.08
1.07
2.36
2.35
2.36
ꢀ1.27
ꢀ1.27
ꢀ1.29
15.23
12.72
10.56
0.67
0.64
0.66
75.8
7.69
6.23
5.42
4
61 (55,890)
366 (40,960)
63 (28,730)
368 (26,600)
56 (20,270)
JK-42
JK-43
76.7
77.4
4
4
3: Absorption coefficient; Eox: oxidation potential; E0–0: voltage of intersection point between absorption and emission spectra; Jsc: short circuit photocurrent
density; Voc: open circuit photovoltage; ff: fill factor; h: total power conversion efficiency.
Absorption spectra were measured in ethanol solution.
a
b
ꢀ1
Oxidation potential of dyes on TiO
E
2
was measured in CH CN with 0.1 M (n-C H ) NPF with a scan rate of 50 mV s (vs NHE).
3 4 9 4 6
c
d
e
0–0 was determined from intersection of absorption and emission spectra in ethanol.
E
LUMO was calculated by EoxꢀE0–0
.
2
Performances of DSSCs were measured with 0.18 cm working area.

11440
S. Kim et al. / Tetrahedron 63 (2007) 11436–11443
(a)
(b)
(c)
1.18°
2.07°
8.15°
0.65°
2.98°
7.35°
Figure 3. The optimized structure calculated with TD-DFT on B3LYP/3-21G* of (a) JK-41, (b) JK-42, and (c) JK-43.
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
400
500
600
Wavelength, nm
700
800
Figure 6. Spectra of monochromatic incident photon-to-current conversion
efficiencies (IPCEs) for DSSC based on spectra of JK-41 (solid line), JK-42
(
dashed line), and JK-43 (dotted line).
The power conversion efficiency of the DSSCs based on the
JK-41 sensitizer reaches 7.69%. The power conversion
efficiency was shown to be sensitive to the structural modifi-
cations of bridging thiophene groups. We believe that the de-
velopment of highly efficient organic dyes comparable to
ruthenium dyes is possible through more sophisticated struc-
tural modifications, and these works are now in progress.
Figure 4. Isodensity surface plots of the HOMO and LUMO of (a) JK-41,
b) JK-42, and (c) JK-43.
(
2
1
1
1
1
1
0
8
6
4
2
0
8
6
4
2
0
Table 2. IPCE, LHE, and APCE of JK-41, JK-42, and JK-43 at 500 nm
Dye
IPCE
LHE
APCE
JK-41
JK-42
JK-43
0.757
0.667
0.599
0.893
0.895
0.780
0.848
0.745
0.768
3. Experimental section
3.1. General methods
0.0
0.1
0.2
0.3
0.4
Voltage (V)
0.5
0.6
0.7
0.8
All reactions were carried out under an argon atmosphere.
Solvents were distilled from appropriate reagents. The H
and C NMR spectra were recorded on a Varian Gemini
Figure 5. A photocurrent–voltage curve obtained with a DSSC based on
JK-41 (solid line), JK-42 (dashed line), and JK-43 (dotted line) under
AM 1.5 radiation (100 mW cm ).
1
ꢀ2
13

S. Kim et al. / Tetrahedron 63 (2007) 11436–11443
11441
1
3
00 spectrometer operating at 300.00 and 75.44 MHz, respec-
yield. H NMR (CDCl , 300 MHz): d 9.84 (s, 1H), 7.73 (d,
3
tively. The IR spectra were recorded on a Biorad FTS-165
spectrometer. Mass spectra were recorded on a JEOL JMS-
SX102A instrument. Elemental analyses were performed
with a Carlo Erba Instruments CHNS-O EA 1108 analyzer.
The absorption and photoluminescence spectra were recorded
on a Perkin–Elmer Lambda 2S UV–visible spectrometer
and a Perkin LS fluorescence spectrometer, respectively.
J¼8.7 Hz, 2H), 7.68 (d, J¼7.5 Hz, 2H), 7.67 (d, J¼8.1 Hz,
2H), 7.42 (d, J¼8.1 Hz, 2H), 7.33 (d, J¼6.9 Hz, 2H), 7.32
(d, J¼6.6 Hz, 2H), 7.27 (s, 2H), 7.18 (d, J¼7.8 Hz, 2H),
1
3
1
7.17 (d, J¼7.8 Hz, 2H), 1.43 (s, 12H). C{ H} NMR
(CDCl , 75.44 MHz): d 190.5, 155.6, 153.8, 153.7, 145.8,
3
138.7, 136.3, 131.5, 129.4, 127.3, 127.2, 124.9, 122.7,
121.1, 120.5, 120.1, 119.9, 47.1, 27.1. MS: m/z 505.17
16
+
N,N-Bis(9,9-dimethylfluoren-2-yl)-4-bromoaniline, diethyl
5-(5,5-dimethyl-1,3-dioxan-2-yl)thiophen-2-yl]methylphos-
[M ]. Anal. Calcd for C H NO: C, 87.89; H, 6.18. Found:
3
7 31
[
C, 87.66; H, 6.11.
1
7
phonate weresynthesized according to procedures reported
in the literature.
3.5. 5-{4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
styrl}thiophene-2-carbaldehyde (4)
3
.2. Cyclic voltammogram
A mixture of 2 (0.30 g, 0.59 mmol), diethyl [5-(5,5-di-
methyl-1,3-dioxan-2-yl)thiophen-2-yl]methylphosphonate
(0.25 g, 0.71 mmol), and potassium tert-butoxide (0.09 g,
0.77 mmol) was vacuum-dried and THF (15 mL) was added.
The solution was refluxed for 6 h. THF was removed under
reduced pressure. The crude mixture was redissolved in
methylene chloride, washed with water, and dried with
MgSO . The organic layer was removed in vacuo. To the
4
compound 3 (0.34 g) in THF was added water. Then TFA
(2.1 mL) was added to the solution. The resulting reaction
Cyclic voltammetry was carried out with a BAS 100B
Bioanalytical System, Inc.). A three-electrode system was
(
used and consisted of a gold disk, working electrode, and
a platinum wire electrode. Redox potential of the dyes on
TiO was measured in CH CN with 0.1 M (n-C H ) NPF
6
2
3
4
9 4
ꢀ
1
with a scan rate of 50 mV s
.3. Fabrication and characterization of DSSC
For the preparation of DSSC, a washed FTO (Pilkington,
.
3
mixture was stirred for 2 h at room temperature. The solution
was quenched with saturated aqueous sodium bicarbonate
and extracted with methylene chloride. The combined meth-
ylene chloride phases were then washed with aqueous so-
ꢀ1
8
ous) at 70 C for 30 min and washed with water and ethanol.
U sq ) glass plate was immersed in 40 mM TiCl (aque-
4
ꢁ
The first TiO layer of 13 mm thickness was prepared by
2
screen printing TiO paste (Solaronix, 13 nm anatase), and
2
dium bicarbonate and dried with MgSO . The organic
4
the second scattering layer containing 400 nm sized anatase
particles (Catalysis & Chemicals Ind. Co. Ltd.) was coated.
The TiO electrodes were immersed into the JK-41, JK-42,
layer was removed in vacuo. The crude product was purified
by column chromatography using a mixture of ethyl acetate
and n-hexane (1:5) as an eluent (yield: 82%). H NMR
1
2
and JK-43 solutions (0.3 mM in ethanol containing 3a,7a-
dihydroxy-5b-cholic acid (10 mM)) and kept at room tem-
perature for 18 h. The stained TiO electrode and Pt-counter
2
electrode were assembled into a sealed sandwich cell by
heating with a hot-melt film (Surlyn 1702, 25 mm thickness)
as a spacer between the electrodes. The electrolyte was com-
posed of 0.6 M 3-hexyl-1,2-dimethyl imidazolium iodide,
(CDCl , 300 MHz): d 9.85 (s, 1H), 7.66 (d, J¼7.2 Hz,
3
2H), 7.62 (d, J¼8.1 Hz, 2H), 7.40 (d, J¼6.9 Hz, 2H), 7.38
(d, J¼7.5 Hz, 2H), 7.32 (d, J¼8.1 Hz, 2H), 7.28 (d,
J¼8.7 Hz, 2H), 7.24 (d, J¼8.1 Hz, 4H), 7.17 (d, J¼8.4 Hz,
1
3
1
2H), 7.14–7.11 (m, 4H), 1.42 (s, 12H). C{ H} NMR
(CDCl , 75.44 MHz): d 182.6, 155.3, 153.7, 153.3, 148.8,
3
146.8, 141.1, 138.9, 137.6, 134.9, 132.7, 129.6, 128.1,
127.2, 126.8, 126.1, 123.8, 123.1, 122.7, 120.8, 119.6,
119.3, 118.9, 47.0, 27.2. MS: m/z 613.19 [M ]. Anal. Calcd
0
.05 M iodine, 0.1 M LiI, and 0.5 M tert-butylpyridine in
+
acetonitrile. The cells were measured using 1000 W xenon
light source, whose power of an AM 1.5 Oirel solar simula-
tor was calibrated by using KG5 filtered Si reference solar
cell. The incident photon-to-current conversion efficiency
(IPCE) spectra for the cells were measured on an IPCE
measuring system (PV measurements).
for C H NO: C, 84.14; H, 5.75. Found: C, 83.82; H, 5.61.
37 31
3.6. 3-(5-{4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
styrl}thiophen-2-yl)-2-cyanoacrylic acid (JK-41)
The resulting thiophene aldehyde 4 (0.25 g, 0.40 mmol) and
cyanoacetic acid (0.06 g, 0.60 mmol) were allowed to react
in acetonitrile in the presence of piperidine (0.04 mL,
3.4. 4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
benzaldehyde (2)
0.40 mmol). The solution was refluxed for 6 h. After
N,N-Bis(9,9-dimethylfluoren-2-yl)-4-bromoaniline (2.23 g,
4
removal of acetonitrile in vacuo, the crude product was
extracted with methylene chloride and water. The crude
product was purified by column chromatography using
methanol as an eluent to give a red solid product JK-41
.0 mmol) dissolved in tetrahydrofuran (30 mL) was cooled
to ꢀ78 C under N . n-Butyllithium (3 mL, 1.6 M solution in
ꢁ
hexane, 4.8 mmol) was added dropwise with stirring. It was
2
ꢁ
ꢁ
1
warmed to 0 C and kept at this temperature for additional
ꢁ
(0.21 g, 0.31 mmol, yield: 78%). Mp: 201 C. H NMR
1
h. Again the solution was cooled to ꢀ78 C and dry dime-
(DMSO-d , 300 MHz): d 8.03 (s, 1H), 7.75 (d, J¼7.5 Hz,
6
thylformamide (0.93 mL, 12 mmol) was added. Stirring at
ambient temperature was continued for 2 h to complete the
reaction, and water (15 mL) was added. The solvents were re-
moved in vacuum, and the residue was taken up in methylene
chloride. The combined organic extract was dried over anhy-
2H), 7.72 (d, J¼6.6 Hz, 2H), 7.59 (d, J¼8.1 Hz, 2H), 7.56
(d, J¼8.7 Hz, 2H), 7.49 (d, J¼6.9 Hz, 2H), 7.39 (d,
J¼15.9 Hz, 1H), 7.32 (d, J¼7.2 Hz, 2H), 7.28 (m, 5H),
7.06 (d, J¼8.1 Hz, 2H), 7.03 (d, J¼7.5 Hz, 2H), 1.35 (s,
1
3
1
12H). C{ H} NMR (DMSO-d , 75.44 MHz): d 163.2,
6
drous MgSO and filtered. The pure product 2 was obtained
4
by silica gel chromatography (eluent EA/Hx¼1:5) in 73%
154.9, 153.2, 147.6, 147.5, 146.4, 139.9, 138.3, 135.9,
135.6, 134.2, 130.3, 129.9, 128.0, 127.2, 126.8, 126.6,

11442
S. Kim et al. / Tetrahedron 63 (2007) 11436–11443
1
4
23.4, 122.8, 121.3, 119.9, 119.7, 119.6, 119.5, 118.7, 109.7,
6.5, 26.7. MS: m/z 680.19 [M ]. Anal. Calcd for
(0.03 mL, 0.32 mmol). The solution was refluxed for 6 h.
After removal of acetonitrile in vacuo, the crude product
was extracted with methylene chloride and water. The crude
product was purified by column chromatography using
methanol as an eluent to give a red solid product JK-42
+
C H N O S: C, 81.15; H, 5.33. Found: C, 81.46; H, 5.28.
46 36 2 2
3.7. 5-{4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
styrl}-4-methylthiophene-2-carbaldehyde (7)
ꢁ
1
(0.16 g, 0.23 mmol, yield: 72%). Mp: 193 C. H NMR
(
DMSO-d , 300 MHz): d 7.95 (s, 1H), 7.75 (d, J¼7.8 Hz,
6
To a mixture of 2 (0.80 g, 1.58 mmol) and [(3-methylthio-
phen-2-yl)methyl] triphenylphosphonium bromide (0.79 g,
2H), 7.73 (d, J¼6.9 Hz, 2H), 7.62 (d, J¼8.7 Hz, 2H), 7.49
(d, J¼6.9 Hz, 2H), 7.43 (s, 1H), 7.36 (d, J¼8.4 Hz, 2H),
7.29 (d, J¼8.7 Hz, 2H), 7.28 (s, 1H), 7.25 (d, J¼7.2 Hz,
2H), 7.04 (d, J¼6.9 Hz, 2H), 7.03 (d, J¼6.9 Hz, 2H), 6.93
1
.74 mmol) in THF (30 mL) was added potassium tert-but-
ꢁ
oxide (0.25 g, 2.21 mmol) in THF (10 mL) dropwise at 0 C.
The mixture was stirred at room temperature for 20 h, and
then poured into distilled water (100 mL). The pH value
was adjusted to 7.0 by 0.1 M HCl. The product was extracted
twice with methylene chloride and the organic layer was
1
3
1
(d, J¼16.2 Hz, 1H), 2.29 (s, 3H), 1.36 (s, 12H). C{ H}
NMR (DMSO-d , 75.44 MHz): d 163.2, 154.9, 153.2,
6
147.3, 146.4, 141.7, 139.6, 138.2, 135.9, 135.7, 134.1,
133.7, 130.6, 129.4, 128.1, 127.1, 126.8, 123.3, 122.8,
122.7, 121.2, 119.6, 119.5, 118.6, 118.3, 109.7, 46.5, 30.7,
dried with MgSO . The organic layer was removed in vacuo.
4
+
To the compound 5 (0.82 g) in N,N-dimethylformamide
(
26.7. MS: m/z 694.88 [M ]. Anal. Calcd for C H N O S:
4
7 38 2 2
DMF) was added phosphorus oxychloride (0.15 mL,
ꢁ
C, 81.24; H, 5.51. Found: C, 81.19; H, 5.48.
1
.64 mmol) at 0 C. The solution was warmed to room tem-
perature and stirred for additional 2 h. After removal of
DMF in vacuo, the reaction mixture was neutralized with
sodium acetate and extracted with methylene chloride. The
crude product was purified by column chromatography
3.10. 3-(5-{4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
styrl}-4-hexylthiophen-2-yl)-2-cyanoacrylic acid
(JK-43)
using a mixture of ethyl acetate and n-hexane (1:5) as an
eluent (yield: 77%). H NMR (CDCl , 300 MHz): d 9.79 (s,
The resulting 4-hexylthiophene aldehyde
8
(0.2 g,
1
0.29 mmol) and cyanoacetic acid (0.04 g, 0.43 mmol) were
allowed to react in acetonitrile in the presence of piperidine
(0.03 mL, 0.29 mmol). The solution was refluxed for 6 h.
After removal of acetonitrile in vacuo, the crude product
was extracted with methylene chloride and water. The crude
product was purified by column chromatography using
methanol as an eluent to give a red solid product JK-43
3
1
(
7
H), 7.67 (d, J¼7.2 Hz, 2H), 7.62 (d, J¼8.1 Hz, 2H), 7.45
s, 1H), 7.42 (d, J¼8.7 Hz, 2H), 7.40 (d, J¼7.2 Hz, 2H),
.32 (d, J¼7.8 Hz, 2H), 7.28 (d, J¼7.5 Hz, 2H), 7.25 (d,
J¼6.9 Hz, 2H), 7.24 (d, J¼7.5 Hz, 1H), 7.17 (d, J¼8.4 Hz,
2
1
H), 7.12 (d, J¼8.1 Hz, 2H), 7.10 (s, 1H), 2.35 (s, 3H),
3
1
3
1
.43 (s, 12H).
C{ H} NMR (CDCl , 75.44 MHz):
ꢁ
1
d 182.5, 155.3, 153.7, 148.6, 147.8, 146.9, 139.9, 139.1,
1
(0.17 g, 0.22 mmol, yield: 76%). Mp: 197 C. H NMR
38.9, 135.9, 134.9, 132.2, 130.1, 128.0, 127.1, 126.8,
23.7, 123.2, 122.6, 120.8, 119.6, 119.2, 117.5, 47.0, 27.1,
4.1. MS: m/z 627.18 [M ]. Anal. Calcd for C H NOS:
(DMSO-d , 300 MHz): d 7.95 (s, 1H), 7.76 (d, J¼7.5 Hz,
6
1
1
2H), 7.74 (d, J¼6.9 Hz, 2H), 7.62 (d, J¼8.1 Hz, 2H), 7.50
(d, J¼7.2 Hz, 2H), 7.46 (s, 1H), 7.37 (d, J¼7.8 Hz, 2H),
7.33 (d, J¼8.1 Hz, 2H), 7.29 (s, 1H), 7.27 (d, J¼7.5 Hz,
+
4
4 37
C, 84.17; H, 5.94. Found: C, 84.04; H, 5.788.
2
H), 7.04 (d, J¼7.2 Hz, 2H), 7.03 (d, J¼6.9 Hz, 2H), 6.94
3.8. 5-{4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
styrl}-4-hexylthiophene-2-carbaldehyde (8)
(d, J¼16.2 Hz, 1H), 2.68 (t, 2H), 1.49 (q, 2H), 1.34 (s,
1
3
1
12H), 1.25 (m, 6H), 0.81 (t, 3H). C{ H} NMR (DMSO-
d6, 75.44 MHz): d 163.8, 154.9, 153.3, 146.4, 145.9,
142.0, 141.7, 138.1, 137.6, 135.0, 134.1, 133.8, 130.8,
130.2, 128.0, 127.1, 126.8, 123.3, 122.9, 122.7, 121.2,
119.7, 119.1, 118.6, 118.3, 109.6, 46.5, 31.0, 30.3, 28.2,
The product was synthesized according to the procedure as
described above for the synthesis of 7, in 69% yield. H
1
NMR (CDCl , 300 MHz): d 9.80 (s, 1H), 7.66 (d,
3
+
J¼7.2 Hz, 2H), 7.62 (d, J¼8.4 Hz, 2H), 7.52 (s, 1H), 7.41
26.7, 24.2, 22.1, 13.9. MS: m/z 764.31 [M ]. Anal. Calcd
for C H N O S: C, 81.64; H, 6.32. Found: C, 81.60; H,
6.29.
(
d, J¼8.4 Hz, 2H), 7.40 (d, J¼7.5 Hz, 2H), 7.31 (d,
5
2 48 2 2
J¼8.1 Hz, 2H), 7.28 (d, J¼7.5 Hz, 2H), 7.25 (d, J¼7.2 Hz,
2
(
1
H), 7.24 (d, J¼7.2 Hz, 1H), 7.17 (d, J¼8.1 Hz, 2H), 7.13
d, J¼7.8 Hz, 2H), 7.11 (s, 1H), 2.69 (t, 2H), 1.62 (q, 2H),
1
3
1
.42 (s, 12H), 1.33 (m, 6H), 0.88 (t, 3H). C{ H} NMR
Acknowledgements
(
CDCl , 75.44 MHz): d 182.6, 155.3, 153.7, 148.6, 147.6,
3
1
1
1
46.9, 141.5, 139.3, 139.1, 138.9, 134.9, 132.1, 130.1,
28.0, 127.2, 126.8, 123.7, 123.2, 122.7, 120.8, 119.6,
19.2, 117.4, 47.0, 31.8, 30.8, 29.1, 28.5, 27.2, 22.7, 14.2.
We are grateful to the KOSEF through National Research
Laboratory (No. M10500000034-06J0000-03410) program
and BK21 (2006).
+
MS: m/z 697.30 [M ]. Anal. Calcd for C H NOS: C,
4
9 47
8
4.32; H, 6.79. Found: C, 84.03; H, 6.57.
References and notes
3
.9. 3-(5-{4-[N,N-Bis(9,9-dimethylfluoren-2-yl)amino]-
styrl}-4-methylthiophen-2-yl)-2-cyanoacrylic acid
JK-42)
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