Rapid Synthesis of D-A'-π-A Dyes through a One-Pot Three-Component Suzuki-Miyaura Coupling and an Evaluation of their Photovoltaic Properties for Use in Dye-Sensitized Solar Cells

Article abstract of DOI:10.1002/chem.201504277

Twenty-four D-A'-π-A dyes were rapidly synthesized through a one-pot three-component Suzuki-Miyaura coupling reaction, which was assisted by microwave irradiation. We measured the absorption spectra, electrochemical properties, and solar-cell performance

Full text of DOI:10.1002/chem.201504277

DOI: 10.1002/chem.201504277
Full Paper
&
Photochemistry
Rapid Synthesis of D-A’-p-A Dyes through a One-Pot Three-
Component Suzuki–Miyaura Coupling and an Evaluation of their
Photovoltaic Properties for Use in Dye-Sensitized Solar Cells**
Shunsuke Irie,[a] Shinichiro Fuse,*[a, b] Masato M. Maitani,[a] Yuji Wada,[a] Yuhei Ogomi,[c]
Shuzi Hayase,[c] Tatsuo Kaiho,[d] Hisashi Masui,[e] Hiroshi Tanaka,[a] and Takashi Takahashi[e]
Abstract: Twenty-four D-A’–p-A dyes were rapidly synthe-
sized through a one-pot three-component Suzuki–Miyaura
coupling reaction, which was assisted by microwave irradia-
tion. We measured the absorption spectra, electrochemical
properties, and solar-cell performance of all the synthesized
dyes. The D5pA4 dye contained our originally designed
rigid and nonplanar donor and exerted the highest efficiency
at 5.4%. The short-circuit current (Jsc) was the most impor-
tant parameter for the conversion efficiency (h) in the case
of the organic D-A’-p-A dyes. Optimal ranges for the D-A’-p-
A dyes were observed for high values of Jsc/lmax at l=560–
620 nm, an optical-absorption edge of l=690–790 nm, and
EHOMO and ELUMO values of <1.14 and À0.56 to À0.76 V, re-
spectively.
um–polypyridyl dyes.[3] However, one of the main drawbacks
of organic dyes is a poor light response in the red to near-in-
frared (NIR) region (l>600 nm).[3a,c] NIR dyes should have
narrow HOMO–LUMO gaps to enable sufficient photoabsorp-
tion in the NIR region. On the other hand, high HOMO and
low LUMO values of the NIR dyes decrease the driving force of
electron transfer at the TiO2/dye or dye/electrolyte interfaces.
Therefore, fine tuning of the HOMO and LUMO values is gener-
ally important for the development of high performance NIR
dyes. It is important to create templates of the NIR organic
dyes, and the HOMO and LUMO values can be readily tuned
by rapid structural modification.[4] In addition, NIR organic dyes
with sufficient chemical stability are highly desired, and al-
though many organic NIR dyes such as cyanines[5] and squar-
aines[6] have been reported, few can satisfy all the above crite-
ria (NIR-absorption, ready structural modification, and sufficient
chemical stability).
Introduction
Dye-sensitized solar cells (DSSCs) have garnered considerable
attention due to characteristics such as a high power-conver-
sion efficiency (PCE), simple fabrication procedures, and a low
production cost.[1] As sensitizers, dye molecules play a crucial
role in DSSCs.[2] The most common, readily available high-per-
forming dyes are the ruthenium-centered polypyridyls.[2] Metal-
free, organic dyes comprise a very important class of com-
pound owing to their large molar absorptivity, design flexibili-
ty, and lower potential production costs relative to the rutheni-
[a] S. Irie, Dr. S. Fuse, Dr. M. M. Maitani, Prof. Y. Wada, Dr. H. Tanaka
Department of Applied Chemistry
Tokyo Institute of Technology
2-12-1, Ookayama, Meguro-ku
Tokyo 152-8552 (Japan)
[b] Dr. S. Fuse
Present address: Chemical Resources Laboratory
Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku
Yokohama, 226-8503 (Japan)
We have developed a sequential/one-pot palladium-cata-
lyzed cross-coupling approach to the rapid synthesis of sys-
tematically modified p-conjugated molecules.[7] Based on the
developed synthetic methodology, we constructed a library of
UV/Vis-absorbing organic donor–p-acceptor (D–p-A) dyes for
DSSCs, evaluated their properties, and elucidated the struc-
ture–function relationships.[7a,d,e] Recently, Zhu and co-workers
reported organic D-A’-p-A dyes.[8] The electron-withdrawing
benzothiadiazole, benzotriazole, and quinoxaline structures
were used for the A’ moiety, and the absorption of the dyes
was redshifted. However, the PCE edges of these dyes usually
are as high as l=700 nm.[8b,9]
E-mail: sfuse@res.titech.ac.jp
[c] Dr. Y. Ogomi, Prof. S. Hayase
Graduate School of Life Science and Systems Engineering
Kyushu Institute of Technology
Fukuoka 808-0196 (Japan)
[d] Dr. T. Kaiho
Brine Resources Research & Development Division
Kanto Natural Gas Development Co., Ltd.
Chiba 297-8550 (Japan)
[e] Dr. H. Masui, Prof. T. Takahashi
Yokohama University of Pharmacy
601, Matano-cho, Totsuka-ku
Yokohama, 245-0066 (Japan)
Herein, we wish to report novel D-A’-p-A dyes with a strong
electron-withdrawing triazoloquinoxaline structure used for
the A’ moiety to enable power conversion in the NIR region.
The HOMO–LUMO level could be readily tuned by rapid struc-
[**] A=Acceptor, D=donor.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201504277.
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tural modification based on a microwave-assisted one-pot
three-component coupling approach. The D3pA4, D5pA2,
and D5pA4 dyes exerted good PCE in the UV–NIR regions (l<
900 nm). In addition, we disclose the optimal HOMO and
LUMO values of the NIR organic dyes that enable both suffi-
cient NIR absorption and smooth electron transfer at the inter-
faces in DSSCs.
Results and Discussion
We selected the highly electron-withdrawing triazoloquinoxa-
line[10] structure as the A’ moiety. The triazoloquinoxaline struc-
ture is reportedly an acceptor unit in low-bandgap D–A poly-
mers.[10] The use of the triazoloquinoxaline accepter allowed us
to introduce side chains to improve the solubility of the dyes.
We planned to couple donor block I with the aromatic scaffold
of II because the CÀBr bond of the first coupling product
would be less reactive relative to the corresponding CÀBr
bond of the aromatic scaffold II. Therefore, an undesirable
overreaction that afforded a D-A’-D compound would be sup-
pressed (Figure 1).[7b–d] A one-pot Suzuki–Miyaura (SM) cou-
Scheme 1. Synthesis of the triazoloquinoxaline block A’. Ac=acetyl,
Ph=phenyl.
duction of dinitro aryl 4 and the subsequent quinoxaline ring
formation afforded the desired dibromo triazoloquinoxaline A’
in an excellent yield.
The key SM coupling of triazoloquinoxaline block A’[13] with
the simple donor building block D1[14] was examined by using
a combination of Pd catalysts (Pd(OAc)2,[15] [Pd(PPh3)4],[16] and
[Pd2(dba)3],[17] phosphine ligands (PPh3, PCy3·BF4, 2-(di-tert-bu-
tylphosphino)biphenyl (JohnPhos),[18] XPhos,[19] [(tBu3P)H]BF,[20]
and 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xanto-
phos)),[21] bases (NaOH and Na2CO3), and solvents (THF/H2O,
toluene/EtOH/H2O, and toluene/H2O). As a result, the combina-
tion of Pd(OAc)2, Xantphos, and Na2CO3 in toluene/H2O at
608C for 8 hours afforded the best result (Table 1, entry 1). The
microwave-irradiation conditions shortened the reaction time
from 8 to 3 hours, and slightly improved the yield of the de-
sired product (Table 1, entry 2). The SM coupling of A’ with
D2[14] and D4, which contained our originally developed fused-
ring structure,[7d] was examined under microwave-irradiation
conditions (Table 1, entries 3 and 4). The use of D2 afforded
better results.
Figure 1. One-pot approach to the synthesis of D-A’-p-A dyes based on the
Suzuki–Miyaura (SM) coupling. B=(dihydroxy)boryl or (pinacolato)boryl.
pling[11] with III would afford the desired coupling product IV.
The subsequent removal of the tert-butyl group in block A
would afford the desired compound V. The NIR dyes and their
synthetic intermediates are usually highly planar molecules;
therefore, the isolation of the dyes from undesired planar
products tended to become tedious. The one-pot procedure
facilitates the laborious purification step. In addition, tuning of
the HOMO–LUMO values is particularly important in the devel-
opment of NIR dyes for DSSCs, which are usually influenced by
the donor and acceptor structures. Therefore, this approach
provides an opportunity to tune the HOMO–LUMO values by
rapidly altering the donor and acceptor structures. Moreover,
the designed dyes contained neither di- nor trisubstituted un-
stable acyclic alkenes, which are frequently found in conven-
tional NIR dyes, such as cyanines and squaraines. Thus, we an-
ticipated that the designed dyes would retain sufficient chemi-
cal stability.
A one-pot SM coupling was examined (Table 2). The D block,
A’ block, Na2CO3, Pd(OAc)2, and Xantphos were placed in an
argon atmosphere. Toluene and H2O were added, and the mix-
ture was degassed with argon. The reaction tube was
equipped with a rubber cap and placed in the microwave-syn-
thesis system that operated at 608C and 200 W for 3 hours.
After cooling to room temperature, the pA block, Na2CO3,
[Pd2(dba)3], [(tBu3P)H]BF, toluene, and H2O were added in suc-
cession, and the mixture was degassed with argon.[7d] The re-
sultant mixture was stirred at room temperature for 3–
The triazoloquinoxaline block A’ was synthesized in accord-
ance with a modified procedure.[10] The alkylation of 1,2,3-ben-
zotriazole (1) and the following dibromination afforded 3
(Scheme 1). A slightly modified nitration procedure[10c,d,12] af-
forded the desired dinitro product 4 in a good yield. The re-
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Table 1. The SM coupling reaction between donor blocks D1 and D2
with the triazoloquinoxaline block A’.
Table 2. One-pot SM coupling reaction assisted by microwave irradiation.
Entry
D
Heating conditions
DA’[a] [%]
DA’D[a] [%]
1
2
3
4
D1
D1
D2
D4
conventional, 608C, 8 h
MW=200 W, 608C, 3 h
MW=200 W, 608C, 3 h
MW=200 W, 608C, 3 h
25
31
49
39
trace
16
7
1
[a] Yield of the isolated products. BPin=(pinacolato)boryl, MW=micro-
wave, Xantphos=9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene.
19 hours (as monitored by TLC analysis). A standard workup
procedure afforded the desired coupling products.
Entry
D
pA
DpAÀtBu [%][a]
Treatment of the coupling products with TFA followed by
simple removal of the volatile TFA afforded the desired carbox-
ylic acids in good purity. The obtained carboxylic acids were
used to measure the absorption spectra and the electrochemi-
cal and photovoltaic properties without further purification.
All the synthesized dyes were soluble in DMF, CH2Cl2, and
CHCl3, but were not soluble in MeOH, MeCN, or acetone. As ex-
pected, the synthesized dyes were sufficiently stable under
a fluorescent lamp in air (>1 month) as solids or in solution
(i.e., CH2Cl2).
1
2
3
4
5
6
7
8
D1
D1
D1
D1
D2
D2
D2
D2
D3
D3
D3
D3
D4
D4
D4
D4
D5
D5
D5
D5
D6
D6
D6
D6
pA1
pA2
pA3
pA4
pA1
pA2
pA3
pA4
pA1
pA2
pA3
pA4
pA1
pA2
pA3
pA4
pA1
pA2
pA3
pA4
pA1
pA2
pA3
pA4
26
38
35
34
49
46
48
50
33
35
30
32
39
42
46
46
24
34
33
30
15
28
36
32
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
The absorption spectra and electrochemical properties of
the 24 dyes were measured (see Figure S1 in the Supporting
Information and Table 3). As expected, the absorption wave-
lengths of the D-A’-p-A dyes containing the strong electron-
withdrawing triazoloquinoxaline structure were redshifted (Dl
ꢀ200 nm) relative to our previously synthesized D–p-A dyes
1 and 2 (Figure 2).[7d]
As the donors influenced the EHOMO values of the dyes, the
EHOMO value became more positive on the order of D3<D5<
D6ꢀD4ꢁD1ꢁD2 (Figure 3a). On the other hand, the accept-
ors influenced the ELUMO value of the dyes; therefore, the
ELUMO value became more negative on the order of pA1<
pA3ꢁpA2ꢁpA4 (Figure 3d). The HOMO values of all the syn-
thesized dyes met the minimum requirement for a dye sensi-
tizer in DSSCs, and HOMO level had a more positive value than
the iodine/iodide redox potential (+0.4 V vs. the normal hy-
drogen electrode (NHE)). On the other hand, the ELUMO value of
7 dyes (i.e., D1pA1, D1pA2, D1pA3, D2pA1, D3pA1, D4pA1,
and D5pA1) was more positive than the conduction-band
edge of TiO2 (À0.5 V vs. NHE).
[a] Yield of the isolated products. dba=Dibenzylideneacetone, TFA =tri-
fluoroacetic acid, Xphos=2-dicyclohexylphosphino-2’,4’,6’-triisopropylbi-
phenyl.
Photovoltaic properties were evaluated for the solar cells
that were prepared by using the 24 synthesized dyes and
D149[22] (Table 4). Four dyes (i.e., D3pA4, D4pA2, D5pA2, and
D5pA4) exerted good PCEs (ꢂ4.5%). To our delight, the
D5pA4 dye, which contained our originally developed rigid
and nonplanar D5 unit, exerted the highest PCE at 5.4%.
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Table 3. Photophysical and electrochemical properties of the 24 dyes.
[b]
Entry Dye
lmax
[nm][a]
e [LmolÀ1 cmÀ1
]
Opt.
edge
[nm][c]
EHOMO [V][d] ELUMO [V][e]
(vs. NHE) (vs. NHE)
1
2
3
4
5
6
7
8
D1pA1 664
D1pA2 592
19600
14600
23800
25200
35100
12400
14900
13500
22200
27300
21900
25200
19600
12600
18200
13200
42800
38400
31100
14100
23100
18100
20500
17500
843
756
785
729
746
658
687
627
887
811
852
788
805
695
741
681
873
772
830
765
759
665
721
657
1.10
1.35
1.12
1.14
1.27
1.28
1.24
1.24
0.91
0.93
0.92
0.93
1.07
1.02
1.06
1.09
1.00
1.01
0.99
1.02
1.05
1.05
1.04
1.05
À0.37
À0.29
À0.46
À0.56
À0.39
À0.60
À0.57
À0.74
À0.49
À0.60
À0.54
À0.65
À0.47
À0.76
À0.62
À0.73
À0.42
À0.59
À0.51
À0.61
À0.58
À0.82
À0.68
À0.84
D1pA3 629
D1pA4 578
D2pA1 595
D2pA2 520
D2pA3 558
D2pA4 511
D3pA1 714
D3pA2 630
D3pA3 669
D3pA4 617
D4pA1 644
D4pA2 564
D4pA3 602
D4pA4 552
D5pA1 685
D5pA2 604
D5pA3 641
D5pA4 589
D6pA1 617
D6pA2 546
D6pA3 575
D6pA4 529
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Figure 2. Comparison of absorption spectra of D1A1 with our previously re-
ported dyes 1 and 2 without the triazoloquinoxaline structure in CH2Cl2.
[a] Absorption maxima in CH2Cl2. [b] Molar absorption coefficients in
CH2Cl2. [c] Optical-transmittance edge was defined by extrapolating the
leading edge of the optical-transmission spectra of the dyes on TiO2 (see
the Supporting Information) to the baseline. [d] The EHOMO value was de-
termined by means of cyclic voltammetry. [e] The EHOMOÀELUMO gap was
determined from the optical-transmittance edge; that is, the EHOMOÀELUMO
gap [eV] was calculated by using l=1240 [nm]/optical edge [nm] and
the ELUMO value was calculated by summation of the HOMO potential and
the EHOMOÀELUMO gap.
We previously reported that the short-circuit current (Jsc)
was the most important parameter for the conversion efficien-
cy (h) in the case of UV/Vis-absorbing D–p-A dyes.[7d] Similarly,
the Jsc value is strongly correlated with h (R2 =0.98; Figure 4c)
in the case of D-A’-p-A dyes, whereas no correlation was ob-
Figure 3. a) The average values for the EHOMO versus the NHE of dyes containing D1 (4 dyes), D2 (4 dyes), D3 (4 dyes), D4 (4 dyes), D5 (4 dyes), and D6
(4 dyes). b) The average values for the ELUMO versus the NHE of dyes containing D1 (4 dyes), D2 (4 dyes), D3 (4 dyes), D4 (4 dyes), D5 (4 dyes), and D6 (4 dyes).
c) The average values for the EHOMO versus the NHE of dyes containing pA1 (6 dyes), pA2 (6 dyes), pA3 (6 dyes), and pA4 (6 dyes). d) The average values for
the ELUMO versus the NHE of pA1 (6 dyes), pA2 (6 dyes), pA3 (6 dyes), and pA4 (6 dyes). The values are expressed as the meanÆstandard deviation (SD).
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Table 4. Photovoltaic properties of solar cells prepared by using the 24
dyes.
[a]
Entry
Dye
h[a] [%]
FF[a]
Voc [V]
Jsc[a] [mAcmÀ1
]
1
2
3
4
5
6
7
8
D149
6.1
1.4
2.6
2.6
4.4
4.2
2.2
3.4
3.3
0.3
2.7
1.2
4.8
2.8
4.8
4.4
4.1
0.7
4.5
3.2
5.4
3.1
2.0
4.1
3.9
0.69
0.66
0.59
0.62
0.68
0.71
0.52
0.72
0.68
0.54
0.69
0.68
0.62
0.69
0.67
0.70
0.67
0.69
0.66
0.67
0.64
0.70
0.71
0.66
0.66
0.71
0.52
0.61
0.58
0.61
0.59
0.64
0.60
0.64
0.44
0.57
0.53
0.61
0.55
0.61
0.61
0.63
0.48
0.56
0.55
0.63
0.56
0.63
0.61
0.64
12.3
4.0
7.1
D1pA1
D1pA2
D1pA3
D1pA4
D2pA1
D2pA2
D2pA3
D2pA4
D3pA1
D3pA2
D3pA3
D3pA4
D4pA1
D4pA2
D4pA3
D4pA4
D5pA1
D5pA2
D5pA3
D5pA4
D6pA1
D6pA2
D6pA3
D6pA4
7.3
10.5
10.1
6.5
7.9
7.6
1.2
6.8
3.4
12.5
7.5
11.5
10.4
9.7
2.1
11.6
8.6
13.3
7.9
4.4
10.2
9.2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
[a] Average values from two or three independent experiments.
served between the fill factor (FF) and h (R2 =0.058; Figure 4a)
and only a weak correlation was observed between the open-
circuit voltage (Voc) and h (R2 =0.24; Figure 4b).
To determine the important factors for a high Jsc value to be
obtained, correlations between the Jsc value and the absorp-
tion extinction coefficient (e), absorption maximum (lmax), opti-
Figure 4. Correlation between a) FF and h, b) Voc and h, and c) Jsc and h of
the 24 dyes studied herein.
cal-absorption edge, and the HOMO (EHOMO) and LUMO (ELUMO
)
energies were examined (Figure 5). In the case of UV/Vis-ab-
sorbing D–p-A dyes, no obvious correlations between e and
Jsc, lmax and Jsc, and the optical-absorption edge and Jsc were
observed, whereas the EHOMO and ELUMO values were critical for
high Jsc values.[7d] The UV/Vis dyes with more positive
EHOMO values and ELUMO <À0.80 V exerted higher Jsc values The
UV/Vis dyes that met the above criteria enabled smooth elec-
tron transfer at the TiO2/dye or dye/electrolyte interfaces be-
cause of a sufficient driving force; thus, they exerted higher
Jsc values.
when absorbing long-wavelength light tended to decrease
due to their high EHOMO and low ELUMO values (insufficient driv-
ing force of electron transfer at the TiO2/dye or dye/electrolyte
interfaces). Thus, it is conceivable that the optimal ranges of
the lmax value, optical-absorption edge, and EHOMO, and ELUMO
values for high Jsc values were observed in the case of the D-
A’-p-A dyes. In fact, the combinations of D4, D5, and D6 and
pA2 and pA4 that met the criteria of the EHOMO and ELUMO
values (<1.14 V and À0.56 to À0.76 V, respectively; Fig-
ure 3a,d) exerted high PCEs. Three of the four best PCE dyes
(i.e., D4pA2, D5pA2, and D5pA4) were found in these combi-
nations. It should be noted that as far as we could ascertain,
there have been no reports that describe the proper HOMO
and LUMO values of NIR organic dyes that will enable both
sufficient NIR absorption and smooth electron transfer at the
interfaces in DSSCs.
Interestingly, no obvious correlation was observed between
the e and Jsc values in the case of NIR-absorbing D-A’-p-A dyes,
whereas the optimal ranges for the lmax values (l=560–
620 nm), optical-absorption edge (l=690–790 nm), and the
EHOMO and ELUMO values of the dyes (<1.14 and À0.56 to
À0.76 V, respectively) for high Jsc values were observed (Fig-
ure 5b–e, boxes). Generally, the Jsc value is correlated with the
sensitizer-absorptive capability and the electron-injection effi-
ciency. The dyes that can absorb long-wavelength light (i.e.,
long lmax, a long optical-absorption edge, and high EHOMO, and
low ELUMO values) would have a good absorptive capability. On
the other hand, the electron-injection efficiency of the dyes
The photocurrent–voltage curves and the incident photon-
to-current conversion efficiency (IPCE) spectra of D3pA4,
D4pA2, D5pA2, and D5pA4 were compared with our previ-
ously reported best UV/Vis dye 3 (h=6.2%)[7d] and D149 as
a reference (Figure 6). As expected, the IPCE edges of the
high-performance dyes D3pA4, D5pA2, and D5pA4 exceeded
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Figure 6. Photocurrent–voltage curves obtained with DSSCs based on 3,
D149, D4pA2, D3pA4, D5pA2, and D5pA4 under a) solar conditions with
a standard air mass (AM) of 1.5 and b) incident photon-to-current conversion
efficiency (IPCE) spectra for DSSCs based on 3, D149, D4pA2, D3pA4,
D5pA2, and D5pA4.
l=800 nm. Relative to 3 and D149, the IPCEs for dyes D3pA4,
D5pA2, and D5pA4 were lower in the region l=400–600 nm
and higher in the region l=650–850 nm. Thus, dyes D3pA4,
D5pA2, and D5pA4 would be an attractive element in the
dye cocktails used in high-performance DSSCs.
Conclusion
We have achieved a rapid synthesis of 24 D-A’-p-A dyes by
using a one-pot, three-component Suzuki–Miyaura coupling re-
action assisted by microwave irradiation. The developed syn-
thetic approach has allowed us to readily modify the dye struc-
ture. We measured the absorption spectra, electrochemical
properties, and the cell performance of all the synthesized
dyes. As expected, the absorption wavelength of the synthe-
sized dyes was strongly redshifted (Dlꢀ200 nm) relative to
our previously synthesized D-p-A dyes due to the triazoloqui-
noxaline structure. The D5pA4 dye contained our originally
designed rigid nonplanar donor and exerted the highest effi-
Figure 5. Correlations between a) e and Jsc, b) lmax and Jsc, c) optical-absorp-
tion edge and Jsc, d) EHOMO and Jsc, and e) ELUMO and Jsc of the 24 dyes studied
herein.
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ter for efficiency h in the case of these organic D-A’-p-A yes.
The optimal ranges for high Jsc values of the D-A’-p-A dyes
were observed at lmax =560–620 nm, an optical-absorption
edge of l=690-790 nm, and EHOMO and ELUMO values of <1.14
and À0.56 À0.76 V, respectively. As far as we have been able
to ascertain, there have been no reports that describe the
proper HOMO and LUMO values of NIR organic dyes that
enable both sufficient NIR absorption and smooth electron
transfer at the interfaces in DSSCs. These results should be val-
uable in the design of high-performance D-A’-p-A dyes in the
future. It should be noted that the IPCEs of the D3pA4,
D5pA2, and D5pA4 dyes are complementary to those of dye
3 and the D149 dye. Thus, these dyes would be an attractive
element in the dye cocktails used for high-performance DSSCs.
Experimental Section
The experimental details are given in the Supporting Information,
including the synthetic, photophysical, and electrochemical proce-
dures and the characterization of the synthesized compounds.
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Acknowledgements
The authors thank Dr. Akimi Nishimura (Kyushu Institute of
Technology, Japan) for the preparation and evaluation of the
DSSCs. The authors also thank Mr. Kohei Kashibuchi and Mr.
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measuring the photophysical and electrochemical properties
of the dyes.
Keywords: combinatorial chemistry · cross-coupling · dyes/
pigments · solar cells · one-pot reactions
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Received: October 24, 2015
Published online on January 19, 2016
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim