Synthesis and properties of seleno-analog MK-organic dye for photovoltaic cells prepared by CH functionalization reactions of selenophene derivatives

Article abstract of DOI:10.1246/cl.2011.922

CH arylation and homocoupling reactions of 2-formylselenophene were carried out with a palladium catalyst. By using these coupling reactions a seleno-analog of MK dye MK-49, which is an organic dye molecule of a dye-sensitized solar cell (DSSC), was synth

Full text of DOI:10.1246/cl.2011.922

doi:10.1246/cl.2011.922
922
Published on the web September 5, 2011
Synthesis and Properties of Seleno-analog MK-organic Dye for Photovoltaic Cells Prepared
by C-H Functionalization Reactions of Selenophene Derivatives
Shunsuke Tamba,1 Ryosuke Fujii,1 Atsunori Mori,*1 Kohjiro Hara,2 and Nagatoshi Koumura*2
1Department of Chemical Science and Engineering, Kobe University, Rokkodai, Nada, Kobe, Hyogo 657-8501
2Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST),
Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565
(Received April 6, 2011; CL-110287; E-mail: amori@kobe-u.ac.jp, n-koumura@aist.go.jp)
C-H arylation and homocoupling reactions of 2-formyl-
selenophene were carried out with a palladium catalyst. By using
these coupling reactions a seleno-analog of MK dye MK-49,
which is an organic dye molecule of a dye-sensitized solar cell
(DSSC), was synthesized. The performance of MK-49 as DSSC
was compared with the corresponding thiophene dye MK-48.
COOH
CN
Se
I
N
Se
N
H
CHO
MK-49 (1)
Se
Se
Properties of heterocyclic organic molecules as advanced
materials recently attract much attention particularly for sulfur-
containing five-membered heteroaromatic compounds such as
thiophenes and thiazoles.1 Introduction of a substituent into the
heterocyclic ring with transition-metal catalyst is a major
concern in organic synthesis.2 We have been engaged in the
functionalization of such thiophenes at their carbon-hydrogen
bonds by transition-metal catalysis and have shown that several
C-H coupling reactions take place.3
In contrast to a wide variety of cross-coupling reactions and
C-H functionalization with sulfur-containing heteroaromatics,
there are still few studies of the seleno-analog selenophenes.4
It is thus intriguing to investigate the reactivity of the C-H bond
of selenophene derivatives. Herein, we report C-H arylation
and homocoupling reactions of selenophene derivatives with a
palladium catalyst. In addition, synthesis and properties of a
selenophene-analog of MK-dye5 containing organic dye mole-
cules for dye-sensitized photovoltaic cells,6 are also described.
The dye molecule, which we envisaged to synthesize, is
MK-49 (1) bearing a biselenophene unit, a carbazole dye
moiety, and a cyanocarboxylate group. This compound would be
synthesized by homocoupling of selenophene, mono-deformy-
lation, C-H functionalization with halocarbazole and a follow-
ing Knoevenagel condensation with cyanoacetic acid as summa-
rized in Scheme 1.
OHC
CHO
H
CHO
Se
Se
Se
Scheme 1.
[PdCl2(NCPh)2] (5 mol%)
AgNO3/KF
(2.0 equiv. x 2)
OHC
H
Se
DMSO, 60 °C
2
OHC
CHO
Se
Se
3 (81%)
Scheme 2.
[RhCl(cod)]2
(0.5 equiv)
L (1.0 equiv)
H
CHO
OHC
CHO
Se
Se
Se
Se
xylene, 80 °C
4
3
40% (L=PPh3)
10% (L=Pt-Bu3)
48% (L=dppb)
Homocoupling of 2-formylselenophene (2) in the presence
of a palladium catalyst was first examined. We found that the
optimal conditions for the homocoupling of 2-formylthiophene
were available for the reaction of 2.3d When the reaction was
carried out with 2, 5 mol % of [PdCl2(NCPh)2], and AgNO3/KF
(2.0 equiv © 2) in DMSO at 60 °C, 81% of the corresponding
biselenophene 3 was obtained (Scheme 2).
Then, we performed mono-deformylation of diformylbi-
selenophene 3 in the presence of a rhodium complex [RhCl-
(cod)]2 in xylene at 80 °C as shown in Scheme 3. Several
phosphane ligands were added to rhodium. Among these, the use
of bidentate dppb exhibited superior performance to afford the
corresponding formylbiselenophene 4 in 48% yield while other
phosphanes resulted in lower yields.7,8
Scheme 3.
the reactivity of selenophene was found slightly inferior to the
corresponding thiophene.3b The reaction of ethyl 4-iodobenzoate
(5a) under similar conditions for the reaction of 2-formylthio-
phene to proceed smoothly in high yield resulted in giving the
corresponding coupling product 6 in 27% yield. The use of
increased amount of AgNO3/KF (2.50 equiv) at elevated
temperature (100 °C) improved the yield to 69%. Other aryl
iodides such as iodobenzene, 4-iodoanisole, and 4-iodobenzo-
trifluoride also underwent C-H arylation in 46 to 50% yields.
The C-H arylation reaction was employed for the reaction
of formylbiselenophene 4 with 9-ethyl-3-iodocarbazole (7) in
the presence of AgNO3/KF (Scheme 4). The corresponding
coupling product 8 was afforded in 52% yield. Then, the
formylbiselenophene was transformed into cyanocarboxylate
We next studied the C-H arylation reaction with formyl-
selenophene 2 toward several aryl iodides. As shown in Table 1,
Chem. Lett. 2011, 40, 922-924
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

923
Table 1. C-H arylation of 2-formylselenophene (2)a
Table 2. UV-vis absorption and photoluminescent spectra of
dyes MK-48 and MK-49
[PdCl2(PPh3)2]
(5 mol%)
+
COOH
Z
OHC
H
I
Aryl
OHC
Aryl
Se
AgNO3/KF
(2.5 equiv)
DMSO
Se
Z = S: MK-48
Z = Se: MK-49
Z
CN
N
2
5
6
AgNO3/KF
/equiv
Temp
/°C
Yieldb
/%
Solutiona
abs/nm (¾ © 10¹4/M¹1 cm
Film
I-Aryl
Dye
b/nm
-
abs/nm
¹1
-
)
-
em
(5a)
1.25
60
27
I
CO2Et
MK-48
MK-49
471 (3.49)
490 (3.34)
566
589
414
429
2.5
2.5
2.5
100
100
100
69
50
46
aAbsorption and emission data were obtained in 20%THF-
toluene solution. Excited at 480 nm.
I
I
H
(5b)
(5c)
b
OMe
I
CF3
(5d)
2.5
100
48
aThe reaction was carried out with 0.6 mmol of 2 and 0.5 mmol
b
of 4 in 2 mL of DMSO for 5 h. Isolated yield.
I
H
CHO
Se
+
N
Se
Se
7
4
[PdCl2(PPh3)2]
(5 mol%)
CHO
Figure 1. Photovoltaic performance for MK-48 and MK-49:
(a) current density-voltage characteristics and (b) IPCE spectra.
Se
8 52%
AgNO3/KF
DMSO
N
Table 3. DSSCs performance parameters of the dyesa
¹2
Dye
Jsc/mA cm
Voc/V
FF
©/%
CH2(CN)COOH
piperidine
MK-48
MK-49
11.24
11.92
0.636
0.599
0.757
0.763
5.41
5.44
MK-49 (1)
38%
aFor details: See refs. 5b and 11.
Scheme 4.
length toward that of MK-48 was shown in MK-49, however the
lower maximum IPCE of the DSSC in MK-49 was observed in
the range of 400-600 nm region.
(MK-49) with cyanoacetic acid in the presence of piperidine
(38% yield).
Studies on the properties of the obtained MK-49 as a dye-
sensitized photovoltaic cell were carried out comparing with the
corresponding thiophene analog MK-48. Table 2 summarizes
the results.9 Measurements of UV-vis absorption and photo-
luminescent spectra indicated that absorption and emission
maxima of MK-49 were approximately 20 nm higher than those
of the thiophene analog MK-48, whereas MK-48 and -49
showed similar ¾ values. However, these values were found to
be much higher than that of ruthenium-based N3 dye (ca. 16000
Table 3 summarizes the DSSC performance of MK-48
and -49. Under standard global AM 1.5G irradiation (100
mW cm¹2), the MK-49-sensitized solar cell gave superior
performance in Jsc (ca. 0.7 mA cm¹2), whereas the Voc value of
MK-49 was found to be slightly lower than that of MK-48
(0.04 V). The product of J and V values at the maximum power
point was also similar thus leading to little difference in fill
factor (FF) values. By these complimentary results, power
conversion efficiency © (%) values were mostly equal in MK-48
and -49 dyes, accordingly.
M
¹1 cm¹1).10 When these dyes were adsorbed onto transparent
TiO2 films, there were significant blue shifts of the absorption
peaks (ca. 60 nm). This is probably due to specific interaction
between the dyes or deprotonation of the dye on TiO2.
In summary, homocoupling and C-H arylation reactions of
selenophene were revealed to take place similarly to thiophene.
With the C-H functionalization protocols a short synthesis of
MK-49, which is a class of organic dye used in photovoltaic
cells, was performed and physical properties of MK-49 and the
corresponding thiophene analog MK-48 were compared.9
Figure 1a shows the photocurrent density-voltage charac-
teristics for dye-sensitized solar cell (DSSC) of MK-48, and
MK-49. The short-circuit photocurrent density (Jsc) was found to
¹2
be ca. 11-12 mA cm and the open-circuit photovoltage (Voc)
was ca. 0.6 V in both MK-48 and MK-49.
This work was partially supported by a Grant-in-Aid for
Scientific Research (B) by Japan Science Promotion Society.
The authors thank Nara Institute of Science and Technology,
As shown in Figure 1b,11 broadening of the incident photo-
to-current conversion efficiency (IPCE) spectra to longer wave-
Chem. Lett. 2011, 40, 922-924
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

924
Kyoto-Advanced Nanotechnology Network, supported by Min-
istry of Education, Culture, Sports, Science and Technology,
Japan for measurements of high-resolution mass spectra.
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11 DSC conditions: irradiated light: AM 1.5 (100 mW cm¹2);
photoelectrode: TiO2 (14 ¯m thickness and 0.2399 cm2 area);
electrolyte: 0.60 M 1,2-dimethyl-3-propylimidazolium io-
dide (DMPImI)/0.05 M iodine (I2)/0.10 M lithium iodide
(LiI)/0.50 M 4-tert-butylpyridine (TBP) in acetonitrile.
4
Chem. Lett. 2011, 40, 922-924
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/