Synthesis of specific solvatochromic D-π-A dyes with pyridinium ring as electron-withdrawing group for dye-sensitized solar cells

Article abstract of DOI:10.1002/ejoc.201300465

Specific solvatochromic D-π-A-type pyridinium dyes were designed and developed as photosensitizers for dye-sensitized solar cells (DSSCs). The dyes have N-sulfobutylpyridinium or N-(carboxybutyl)pyridinium bromide as an electron-withdrawing anchoring group. The two dyes show specific solvatochromism, leading to a large bathochromic shift of the absorption band in halogenated solvents. Moreover, a dye-adsorbed TiO₂ film immersed into halogenated solvents exhibits specific solvatochromism, as does a dye solution of halogenated solvents. DSSCs based on specific solvatochromic D-π-A-type pyridinium dyes and halogenated solvents as electrolyte solvent were prepared and their photovoltaic performance investigated. It was found that the appropriate combination of solvatochromic dyes with electrolyte solution and the effective interaction between solvatochromic dyes and TiO₂ surface can lead to not only an enhancement of light-harvesting efficiency (LHE), but also efficient electron injection from the dye to the conduction band (CB) of TiO₂. This work demonstrates that the solvatochromism of organic dyes is a key consideration for high-performance DSSCs based on organic dye sensitizers. Specific solvatochromic D-π-A dyes with a pyridinium ring as electron-withdrawing group, which can lead to a large bathochromic shift of absorption band in halogenated solvents, have been developed and applied as a photosensitizers to dye-sensitized solar cells. Copyright

Full text of DOI:10.1002/ejoc.201300465

Job/Unit: O30465
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Date: 11-06-13 17:32:08
Pages: 7
FULL PAPER
Donor-Acceptor Systems
Y. Ooyama,* Y. Oda, T. Mizumo,
Y. Harima, J. Ohshita* ..................... 1–7
Synthesis of Specific Solvatochromic D-π-
A Dyes with Pyridinium Ring as Electron-
Withdrawing Group for Dye-Sensitized So-
lar Cells
Keywords: Donor-acceptor systems / Solar
cells / Solvatochromism / Dyes/pigments /
Sensitizers
Specific solvatochromic D-π-A dyes with a
pyridinium ring as electron-withdrawing
group, which can lead to a large bathoch-
romic shift of absorption band in halo-
genated solvents, have been developed and
applied as a photosensitizers to dye-sensit-
ized solar cells.
0000, 0–0
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Pages: 7
Y. Ooyama, Y. Oda, T. Mizumo, Y. Harima, J. Ohshita
FULL PAPER
DOI: 10.1002/ejoc.201300465
Synthesis of Specific Solvatochromic D-π-A Dyes with Pyridinium Ring as
Electron-Withdrawing Group for Dye-Sensitized Solar Cells
Yousuke Ooyama,*[a] Yuichiro Oda,[a] Tomonobu Mizumo,[a] Yutaka Harima,[a] and
Joji Ohshita*[a]
Keywords: Donor-acceptor systems / Solar cells / Solvatochromism / Dyes/pigments / Sensitizers
Specific solvatochromic D-π-A-type pyridinium dyes were
designed and developed as photosensitizers for dye-sensi-
tized solar cells (DSSCs). The dyes have N-sulfobutylpyridin-
ium or N-(carboxybutyl)pyridinium bromide as an electron-
withdrawing anchoring group. The two dyes show specific
solvatochromism, leading to a large bathochromic shift of the
absorption band in halogenated solvents. Moreover, a dye-
adsorbed TiO2 film immersed into halogenated solvents exhi-
trolyte solvent were prepared and their photovoltaic perform-
ance investigated. It was found that the appropriate combi-
nation of solvatochromic dyes with electrolyte solution and
the effective interaction between solvatochromic dyes and
TiO2 surface can lead to not only an enhancement of light-
harvesting efficiency (LHE), but also efficient electron injec-
tion from the dye to the conduction band (CB) of TiO2. This
work demonstrates that the solvatochromism of organic dyes
bits specific solvatochromism, as does a dye solution of halo- is a key consideration for high-performance DSSCs based on
genated solvents. DSSCs based on specific solvatochromic D-
organic dye sensitizers.
π-A-type pyridinium dyes and halogenated solvents as elec-
the absorption band with increasing solvent polarity) or
negative solvatochromism (i.e., hypsochromic shift of ab-
sorption band with increasing solvent polarity).[7] Among
the various types of solvatochromic dyes, donor-π-acceptor
(D-π-A) type pyridinium dyes having a diphenyl- or dialk-
ylamino group as electron donor and a pyridinium ring as
electron acceptor linked by a π-conjugated bridge are well
known to show negative solvatochromism.[8–11] On the
other hand, we have mentioned the specific solvatochro-
mism of D-π-A-type pyridinium dyes, leading to a large ba-
thochromic shift of the absorption band in halogenated sol-
vents; the bathochromic shifts of the intramolecular charge-
transfer (ICT) absorption band in halogenated solvents are
larger than those in nonhalogenated solvents of similar sol-
vent polarity. We have demonstrated that the enhanced ICT
characteristics of the D-π-A pyridinium dye in halogenated
solvents are responsible for the large bathochromic shifts of
the ICT band in halogenated solvents.[11]
In this work, to utilize the solvatochromic characteristics
of a D-π-A-type pyridinium dye, we prepared DSSCs based
on newly synthesized D-π-A-type pyridinium dyes (OD5
and OD6) and electrolyte solutions of halogenated solvents
(Scheme 1). The dyes OD5 and OD6 have N-(sulfobutyl)-
pyridinium and N-(carboxybutyl)pyridinium bromide,
respectively, as an electron-withdrawing anchoring group.
It was found that dye-adsorbed TiO2 films immersed into
halogenated solvents exhibit specific solvatochromism, as
does a dye solution of halogenated solvents. Here, we report
the impact of specific solvatochromic characteristics of D-
π-A-type pyridinium dyes on the photovoltaic performance
Introduction
Dye-sensitized solar cells (DSSCs) based on dye-ad-
sorbed TiO2 electrodes have gained increasing attention
from chemists, physicists, and engineers because of enor-
mous scientific interest in not only their construction and
operational principles, but also in their high incident-solar-
light-to-electricity conversion efficiency and low cost of
production.[1–5] To develop high-performance DSSCs, many
kinds of ruthenium (Ru) complex dyes and organic dyes
have been designed and developed. Consequently, DSSCs
have achieved solar energy-to-electricity conversion yields
(η) of up to 12%.[6] To obtain further new and efficient dye
sensitizers for DSSCs, novel molecular designs are required
to fully utilize the photophysical and electrochemical char-
acteristics of the dyes themselves, and also form effective
interactions between dyes and TiO2 surface and between
dyes and electrolyte solution. For this purpose, we focused
on the solvatochromism of organic dyes. Some organic dyes
show positive solvatochromism (i.e., bathochromic shift of
[a] Department of Applied Chemistry, Graduate School of
Engineering,
Hiroshima University
Higashi-Hiroshima 739-8527, Japan
Fax: +81-82-424-5494
E-mail: yooyama@hiroshima-u.ac.jp
jo@hiroshima-u.ac.jp
Homepage: http://home.hiroshima-u.ac.jp/orgmtrls/Ohshita_G-
roup/Ohshita_
Group-Home.html
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300465.
2
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Solvatochromic D-π-A Dyes
Scheme 1. Synthesis of D-π-A-type pyridinium dyes OD5 and OD6.
of DSSCs and demonstrate that the solvatochromism of or- DBM. Moreover, as shown in Figure 1c and d, the ICT
ganic dyes is one of the most important factors for high- absorption bands in the mixed solvents of MeCN and halo-
performance DSSCs based on organic dye sensiti- genated solvent (CH2Cl2, DBM and DIM) are still red-
zers.
shifted compared with that in MeCN, although the ICT
Results and Discussion
Synthesis of D-π-A-Type Pyridinium Dyes OD5 and OD6
The D-π-A-type pyridinium dyes OD5 and OD6 were
synthesized from diphenyl{7-[5-(pyridin-4-yl)thiophen-2-
yl]-9H-carbazol-2-yl}amine (1)[12] and 1,4-butanesultone or
5-bromopentanoic acid (Scheme 1).
Photoabsorption Properties of OD5 and OD6 in Solution
The absorption spectra of OD5 and OD6 in various sol-
vents are shown in Figure 1, and their spectroscopic data
are summarized in Table 1. The two dyes show absorption
maxima at around 435–495 nm, which are assigned to the
ICT excitation from the electron-donor moiety (di-
phenylamino group) to the electron-acceptor moiety (pyrid-
inium ring). The ICT absorption bands of the two dyes ex-
hibit a general negative solvatochromism in nonhalo-
genated solvents (Figure 1a and b); with increasing solvent
polarity from 1,4-dioxane [dielectric constant (εr) = 2.22]
to acetonitrile (MeCN, εr = 36.64), for example, the ICT
absorption band of OD6 shows a hypsochromic shift from
470 to 440 nm. On the other hand, the two dyes showed
specific solvatochromism, leading to a large bathochromic
shift of the ICT absorption band in halogenated solvents;
although the εr value (εr = 7.77) of dibromomethane
(DBM) is very close to that of tetrahydrofuran (THF; εr =
7.52), the ICT absorption bands of OD5 and OD6 in DBM
show bathochromic shifts of 35 and 19 nm, respectively,
compared with those in THF. It is noteworthy that the ba-
thochromic shifts of the ICT band in diiodomethane (DIM)
Figure 1. Absorption spectra of (a) OD5 and (b) OD6 in various
solvents and absorption spectra of (c) OD5 and (d) OD6 in mixed
solvents of acetonitrile and halogenated solvent.
Table 1. Solvatochromic spectroscopic data of OD5 and OD6.
Solvent[a]
λmaxabs[nm] (ε [m–1 cm–1])
OD5
OD6
1,4-Dioxane
THF
MeCN
CH2Cl2
DBM
454 (–[b]
)
)
470 (–[b]
)
)
444 (–[b]
461 (–[b]
437 (27100)
471 (27000)
479 (27200)
440 (22700)
474 (19300)
480 (18100)
DIM
484 (–[b]
)
493 (–[b]
)
MeCN/CH2Cl2 (1:1)
MeCN/DBM (1:1)
MeCN/DIM (1:1)
454 (27900)
460 (28000)
454 (22900)
460 (21700)
463 (–[b]
)
463 (–[b]
)
[a] Acetonitrile (MeCN), dibromomethane (DBM) and diiodo-
are larger than those in dichloromethane (CH2Cl2) and methane (DIM). Solvent ratios given in v/v. [b] Poorly soluble.
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Y. Ooyama, Y. Oda, T. Mizumo, Y. Harima, J. Ohshita
FULL PAPER
absorption bands are blueshifted compared with those in in the electrolyte. The LUMO energy levels of the two dyes
pure halogenated solvents (Table 1).
were estimated from the E1/2ox and the onset of the absorp-
tion band in acetonitrile (530 nm; 2.34 eV for both OD5
and OD6). The LUMO energy levels for OD5 and OD6
were –1.25 and –1.21 V, respectively. Evidently, the LUMO
energy levels are higher than the energy level of the conduc-
tion band (CB) of TiO2 (–0.5 V), suggesting that an electron
injection to the CB of TiO2 is thermodynamically feasible.
Semiempirical MO Calculations (AM1, INDO/S)
The photophysical properties of OD5 and OD6 were an-
alyzed by using semiempirical molecular orbital (MO) cal-
culations. The molecular structures were optimized by using
the MOPAC/AM1 method,[13] and then the INDO/S
method.[14] The MO calculations reveal that the longest-
wavelength excitation bands are mainly attributable to the
transition from HOMO to LUMO, and for both OD5 and
OD6 the HOMO is mostly localized on the diphenylamino
group, whereas the LUMO is mostly localized on the pyrid-
inium ring (Figure 2a and b). The changes in the calculated
electron density accompanied by the first electron exci-
tations for the two dyes reveal a strong ICT nature from
the diphenylamino group to the pyridinium ring upon pho-
toexcitation (Figure 2c).
Figure 2. (a) HOMO and (b) LUMO of OD5 (above) and OD6 (be-
low). The red and blue lobes denote the positive and negative
phases, respectively, of the coefficients of the MOs. The size of each
lobe is proportional to the MO coefficient. (c) Calculated electron-
density changes accompanying the first electronic excitation of
OD5 (top) and OD6 (bottom). The black and white lobes signify
the decrease and increase in electron density accompanying the
electronic transition, respectively. Their areas indicate the magni-
tude of the electron-density change. Light-blue, green, blue, and
red spheres correspond to hydrogen, carbon, nitrogen, and oxygen
atoms, respectively.
Figure 3. Cyclic voltammograms of (a) OD5 and (b) OD6 in aceto-
nitrile containing 0.1 m Bu4NClO4 at a scan rate of 100 mVs–1. The
arrow denotes the direction of the potential scan.
Photoabsorption Properties of OD5 and OD6 Adsorbed on
TiO2 Nanoparticles
The absorption spectra of dye-adsorbed TiO2 films in air
(no solvent) and immersed in solvents are shown in Fig-
ure 4. For both OD5 and OD6, the absorption bands of the
dye-adsorbed TiO2 film in air and immersed in MeCN ap-
Electrochemical Properties of OD5 and OD6
The electrochemical properties of OD5 and OD6 were pear in almost the same wavelength region as those of the
determined by cyclic voltammetry (CV) in acetonitrile con- two dyes in MeCN, but are blueshifted by ca. 25 nm, com-
taining 0.1 m tetrabutylammonium perchlorate (Bu4N- pared with those of the two dyes in THF (Figure 1a and b).
ClO4). The potentials were referenced to internal ferrocene/ The blueshifts of the absorption bands for the dye-adsorbed
ferrocenium (Fc/Fc+) (Figure 3). The oxidation peaks for TiO2 films relative to dye solutions may be attributed to the
OD5 and OD6 were observed at 0.50 and 0.53 V vs. ferro- high polarity of the TiO2 surface. It was found that the dye-
cene/ferrocenium (Fc/Fc+), respectively. The corresponding adsorbed TiO2 films immersed in mixed solvents of MeCN
reduction peaks for OD5 and OD6 appeared at 0.42 and and halogenated solvent (CH2Cl2, DBM and DIM) exhibit
0.46 V, respectively, thus showing that the oxidized states of specific solvatochromism; the absorption bands of dye-ad-
the two dyes are stable. The HOMO energy levels of the sorbed TiO2 films in the mixed solvents are still redshifted
two dyes were evaluated from the half-wave potential for compared with those immersed in MeCN, as are the the
ox
oxidation (E1/2 = 0.46 and 0.50 V for OD5 and OD6, absorption spectra of the dye solutions (Figure 1). For the
respectively). The HOMO energy levels for OD5 and OD6 dye OD5 immersed in MeCN/DIM, the absorption maxi-
were 1.09 and 1.13 V vs. the normal hydrogen electrode mum was slightly redshifted compared with those of dyes
(NHE), respectively, thus indicating that the HOMO energy immersed in other mixed solvents. These results indicate
–
levels are more positive than the I3 /I– redox potential that the light-harvesting efficiency (LHE) of the dye-ad-
(0.4 V). This assures an efficient regeneration of the oxid- sorbed TiO2 film can be controlled by appropriate combi-
–
ized dyes by electron transfer from the I3 /I– redox couple nation of solvatochromic dyes and electrolyte solutions for
4
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Solvatochromic D-π-A Dyes
DSSCs; for example, positive solvatochromic dyes are ad- bidentate bridging linkages at Lewis acid sites on the TiO2
vantageous to the bathochromic shift of the absorption surface, whereas OD6 is adsorbed on the TiO2 surface
band of the dye-adsorbed TiO2 film, because the TiO2 sur- through bidentate bridging linkages at Brønsted acid sites.
face has a high polarity, as well as polar solvents such as
MeCN, which is usually used to dissolve the electrolyte
(iodine, lithium iodide, and imidazolium salt) for DSSCs.
Photovoltaic Performance of DSSCs Based on OD5 and
OD6
The DSSCs were prepared by using the dye-adsorbed
TiO2 electrode, Pt-coated glass as a counter electrode, and
a solution containing iodine (0.05 m), lithium iodide (0.1 m),
and 1,2-dimethyl-3-propylimidazolium iodide (0.6 m) as
electrolyte, in which MeCN or the mixed solvent of MeCN
and halogenated solvent (CH2Cl2, DBM and DIM) was
used to dissolve the electrolyte. The photocurrent–voltage
(I–V) characteristics were measured under simulated solar
light (AM 1.5, 100 mWcm–2). The incident-photon-to-cur-
Figure 4. Absorption spectra of (a) OD5 and (b) OD6 adsorbed on
rent conversion efficiency (IPCE) spectra and the I–V
TiO2 film (9 μm) in air (no solvent) and immersed in acetonitrile
curves are shown in Figures 6 and 7, respectively. The pho-
or mixed solvents of acetonitrile and halogenated solvent.
FTIR Spectra of OD5 and OD6 Adsorbed on TiO2
Nanoparticles
To elucidate the adsorption states of dyes OD5 and OD6
on TiO2 nanoparticles, we measured the FTIR spectra of
the dye powders and the dyes adsorbed on TiO2 nanopar-
ticles (Figure 5). For powders of OD5, the S=O stretching
vibrations of the sulfonate group were observed at 1170 and
1050 cm–1. On the other hand, for powders of OD6, the
C=O stretching vibration of the carboxy group was ob-
served at 1715 cm–1. When dye OD5 was adsorbed on the
TiO2 surface, the S=O stretching vibrations weakened sig-
nificantly; this suggests the formation of a bidentate bridg-
ing linkage between the sulfonate group of the dye and
Lewis acid sites (exposed Tin+ cations) on the TiO2 sur-
face.[15,16] On the other hand, when OD6 was adsorbed on
the TiO2 surface, the C=O stretching vibration of the car-
boxy group disappeared; this indicates the formation of a
bidentate bridging linkage between the carboxy group of
the dye and Brønsted acid sites (surface-bound hydroxy
groups, Ti–OH) on the TiO2 surface. These observations
Figure 6. IPCE spectra of DSSCs based on (a) OD5 and (b) OD6
indicate that OD5 is adsorbed on the TiO2 surface through employing various electrolyte solutions.
Figure 5. FTIR spectra of the dye powders and dyes adsorbed on TiO2 nanoparticles for (a) OD5 and (b) OD6.
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Y. Ooyama, Y. Oda, T. Mizumo, Y. Harima, J. Ohshita
FULL PAPER
tovoltaic performance parameters are collected in Table 2. of 410–515 nm, which is higher than those of DSSCs based
Overall, the maximum IPCE, the short-circuit photocurrent on the other electrolyte solutions (Figure 6a). The Jsc and
density (Jsc), and η for OD5 are higher than those for OD6. η values were 6.64 mAcm–2 and 2.21%, respectively (Fig-
The superior photovoltaic performance of OD5 may be at- ure 7a and Table 2). The higher photovoltaic performance
tributed to efficient electron injection by the formation of of DSSCs based on the electrolyte solution of halogenated
the bidentate bridging linkage between the sulfonate group solvents relative to commonly used MeCN are attributed to
of the dye and the Lewis acid sites on the TiO2 surface. For the enhanced ICT characteristics of the D-π-A pyridinium
both OD5 and OD6, it is worth mentioning that the IPCE dyes in halogenated solvents, leading to efficient electron
maxima for DSSCs based on the electrolyte solution of injection from the dye to the CB of TiO2.
MeCN/DIM are redshifted compared with those of the
other mixed solvents, which reflects the results of the ab-
sorption spectra of the dye-adsorbed TiO2 film immersed
in the mixed solvents, although the maximum IPCE, the
Conclusions
To assess the impact of solvatochromic characteristics of
dye sensitizers on the photovoltaic performance of DSSCs,
we have designed and synthesized the specific solvato-
chromic D-π-A-type dyes OD5 and OD6, which have N-
(sulfobutyl)pyridinium and N-(carboxybutyl)pyridinium
bromide, respectively, as an electron-withdrawing anchoring
group. The DSSCs based on specific solvatochromic D-π-
A-type pyridinium dyes and halogenated solvents as elec-
trolyte solvent were prepared and their photovoltaic per-
formances investigated. It was found that the appropriate
combination of solvatochromic dye with electrolyte solution
and the effective interaction between solvatochromic dye
and TiO2 surface can lead to not only an enhancement of
LHE, but also efficient electron injection from the dye to
the CB of TiO2. Thus, we demonstrate that the solvatochro-
mism of organic dyes is a key consideration for high-per-
formance DSSCs based on organic dye sensitizers. Further
studies on the design and development of efficient solva-
tochromic dyes for high-performance DSSCs are in pro-
gress, and we hope to gain greater insight into the impact
of solvatochromic characteristics of dye sensitizers on the
photovoltaic performance of DSSCs.
Jsc, and the η values are the lowest of the electrolyte solu-
tions used. Interestingly, the open-circuit photovoltage (Voc)
for DSSCs based on the electrolyte solution of MeCNe/
DBM is higher than those of the other mixed solvents. The
IPCE value of DSSC based on OD5 employing the electro-
lyte solution of MeCN/CH2Cl2 exceeds 80% in the range
Experimental Section
General: IR spectra were recorded with a Perkin–Elmer Spectrum
One FTIR spectrometer by using the ATR method. High-resolu-
tion mass spectrometric data were acquired with a Thermo Fisher
1
Figure 7. I–V curves of DSSCs based on (a) OD5 and (b) OD6
Scientific LTQ Orbitrap XL. H NMR spectra were recorded with
employing various electrolyte solutions.
a Varian-400 (400 MHz) FT NMR spectrometer. Absorption spec-
tra were recorded with a Hitachi U-2910 spectrophotometer. Cyclic
voltammetry (CV) curves were recorded in acetonitrile/Bu4NClO4
(0.1 m) solution with a three-electrode system consisting of Ag/Ag+
as reference electrode, Pt plate as working electrode, and Pt wire as
counter electrode, by using an AMETEK Versa STAT 4 potentio-
stat. The HOMO and LUMO energy levels of OD5 and OD6 were
evaluated from spectral analyses and the CV data. HOMO energy
levels were evaluated from E1/2ox. LUMO energy levels were esti-
Table 2. DSSC performance parameters of OD5 and OD6.[a]
Dye
Electrolyte[b]
Jsc
Voc
[mV]
ff
η [%]
[mAcm–2]
OD5
MeCN
5.52
6.64
6.08
4.26
4.54
5.20
5.16
4.20
552
528
660
464
468
488
625
433
0.63 1.93
0.63 2.21
0.59 2.36
0.59 1.17
0.66 1.41
0.61 1.56
0.59 1.90
0.60 1.09
[b]
MeCN/CH2Cl2
MeCN/DBM[b]
MeCN/DIM[b]
MeCN
ox
mated from E1/2 and an onset of the absorption band (530 nm;
OD6
2.34 eV for both OD5 and OD6).
[b]
MeCN/CH2Cl2
MeCN/DBM[b]
MeCN/DIM[b]
4-{4-[9-Butyl-7-(diphenylamino)-9H-carbazol-2-yl]pyridin-1-ium-1-
yl} Butane-1-sulfonate (OD5): A solution of 1[12] (0.35 g,
0.75 mmol) and 1,4-butanesultone (1.0 g, 7.3 mmol) in anhydrous
toluene (20 mL) was stirred at 100 °C for 4 d. The resultant precipi-
tate was washed with diethyl ether to give OD5 (0.16 g, 33%) as a
[a] The photovoltaic performance of DSSCs based on the adsorp-
tion amount per unit area of the TiO2 electrode is ca. 9.68–9.87 mo-
leculescm–2 under simulated solar light (AM 1.5, 100 mWcm–2).
[b] Ratio 1:1 (v/v).
yellow solid. IR (ATR): ν = 16214, 1177, 1035 cm–1. 1H NMR
˜
6
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Solvatochromic D-π-A Dyes
(400 MHz, [D6]DMSO): δ = 0.78 (t, J = 7.2 Hz, 3 H), 1.15–1.21 on the dye-adsorbed TiO2 film in the transmission mode with a
(m, 2 H), 1.59–1.68 (m, 4 H), 2.00–2.06 (m, 2 H), 3.2–3.4 (m, 2 H, calibrated integrating sphere system.
overlapping peak of dissolved water in [D6]DMSO), 4.35 (t, J =
7.2 Hz, 2 H), 4.59 (t, J = 6.8 Hz, 2 H), 6.88 (d, J = 6.8 Hz, 1 H),
7.05–7.09 (m, 6 H), 7.15 (s, 1 H), 7.31–7.35 (m, 4 H), 7.90 (d, J =
8.4 Hz, 1 H), 8.13 (d, J = 8.4 Hz, 1 H), 8.26 (d, J = 8.4 Hz, 1 H),
Supporting Information (see footnote on the first page of this arti-
cle): Copies of H NMR spectra for OD5 and OD6.
1
8.35 (s, 1 H), 8.66 (d, J = 6.8 Hz, 2 H), 9.07 (d, J = 6.8 Hz, 2 H)
Acknowledgments
ppm. HRMS (ESI): calcd. for C37H37N3O3SNa [M + Na+]
626.24478; found 626.24469.
This work was supported by Grants-in-Aid for Scientific Research
(B) (23350097) and (C) (24550225) from the Japan Society for the
Promotion of Science (JSPS), and by a research grant from the
JGC-S SCHOLARSHIP FOUNDATION.
4-[9-Butyl-7-(diphenylamino)-9H-carbazol-2-yl]-1-(4-carboxybutyl)-
pyridin-1-ium Bromide (OD6):
solution of 1[12] (0.10 g,
A
0.21 mmol) and 5-bromopentanoic acid (0.038 g, 0.21 mmol) in an-
hydrous DMF (20 mL) was stirred at 90 °C for 3 h. After concen-
trating under reduced pressure, the resulting residue was washed
with acetone and then toluene to give OD6 (0.012 g, 9%) as a yel-
[1] B. O’Regan, M. Grätzel, Nature 1991, 353, 737–740.
[2] A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo, H. Pettersson,
Chem. Rev. 2010, 110, 6595–6663.
low solid. IR (ATR): ν = 1715, 1620 cm–1. 1H NMR (400 MHz,
˜
[D6]DMSO): δ = 0.78 (t, J = 7.6 Hz, 3 H), 1.15–1.21 (m, 2 H),
1.51–1.55 (m, 2 H), 1.64–1.68 (m, 2 H), 1.94–1.99 (m, 2 H), 2.30
(t, J = 7.2 Hz, 2 H), 4.36 (t, J = 7.2 Hz, 2 H), 4.58 (t, J = 6.8 Hz,
2 H), 6.89 (dd, J = 2.0, 8.4 Hz, 1 H), 7.05–7.09 (m, 6 H), 7.15 (d,
J = 2.0 Hz, 1 H), 7.30–7.35 (m, 4 H), 7.91 (dd, J = 1.6, 8.4 Hz, 1
H), 8.14 (d, J = 8.8 Hz, 1 H), 8.26 (d, J = 8.0 Hz, 1 H), 8.35 (s, 1
H), 8.67 (d, J = 7.2 Hz, 2 H), 9.07 (d, J = 7.2 Hz, 2 H), 12.14 (s, 1
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H) ppm. HRMS (ESI): calcd. for C38H38N3O2 [M
568.29585; found 568.29596.
–
Br]+
Computational Methods: Semiempirical calculations were carried
out with the WinMOPAC (Ver. 3.9) package (Fujitsu, Chiba, Ja-
pan). Geometry calculations in the ground state were made by
using the AM1 method.[13] All geometries were completely opti-
mized (keyword PRECISE) by the eigenvector-following routine
(keyword EF). HOMO and LUMO of the compounds were evalu-
ated from INDO/S calculations.[14] All INDO/S calculations were
performed by using single excitation full SCF/CI (self-consistent
field/configuration interaction), which included the configuration
with one electron excited from any occupied orbital to any unoccu-
pied orbital, where 225 configurations were considered [keyword
CI (15 15)].
Fabrication of the Dye-Sensitized Solar Cells Based on Dyes OD5
and OD6: TiO2 paste (JGC Catalysts and Chemicals Ltd., PST-
18NR) was deposited on a fluorine-doped-tin-oxide (FTO) sub-
strate by doctor-blading, and sintered at 450 °C for 50 min. The
9 μm thick TiO2 electrode (0.5ϫ0.5 cm2 in photoactive area) was
immersed into a 0.05 mm dye solution in dichloromethane for suf-
ficient time to allow the electrode to adsorb the photosensitizer.
The DSSCs were fabricated by using the TiO2 electrode thus pre-
pared, Pt-coated glass as a counter electrode, and a solution of
0.05 m iodine, 0.1 m lithium iodide, and 0.6 m 1,2-dimethyl-3-prop-
ylimidazolium iodide in acetonitrile, dichloromethane/acetonitrile,
dibromomethane/acetonitrile, or diiodomethane/acetonitrile as
electrolyte. The photocurrent–voltage characteristics were mea-
sured by using a potentiostat under simulated solar light (AM 1.5,
100 mWcm–2). IPCE spectra were measured under monochromatic
irradiation with a tungsten-halogen lamp and a monochromator.
The amount of adsorbed dye on TiO2 nanoparticles was deter-
mined by absorption spectral measurement of the concentration
change of the dye solution before and after adsorption. Absorption
spectra of the dyes adsorbed on TiO2 nanoparticles were recorded
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Received: April 1, 2013
Published Online: ᭿
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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