Development of D-π-Cat fluorescent dyes with a catechol group for dye-sensitized solar cells based on dye-to-TiO2 charge transfer

Article abstract of DOI:10.1039/c4ta01286k

D-π-Cat fluorescent dyes YM-1 and YM-2 with a diphenylamine moiety as the electron-donating group, a catechol (Cat) unit as the anchoring group and fluorene or carbazole as the π-conjugated system were designed and developed as a photosensitizer for type-

Full text of DOI:10.1039/c4ta01286k

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Materials Chemistry A
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Development of D–p–Cat fluorescent dyes with a
catechol group for dye-sensitized solar cells based
on dye-to-TiO2 charge transfer
Cite this: J. Mater. Chem. A, 2014, 2,
8500
*
*
Yousuke Ooyama, Takehiro Yamada, Takuya Fujita, Yutaka Harima and Joji Ohshita
D–p–Cat fluorescent dyes YM-1 and YM-2 with a diphenylamine moiety as the electron-donating group, a
catechol (Cat) unit as the anchoring group and fluorene or carbazole as the p-conjugated system were
designed and developed as a photosensitizer for type-II dye-sensitized solar cells (DSSCs), which have a
direct electron-injection pathway from the dye to the conduction band (CB) of the TiO2 electrode by
photoexcitation of the dye-to-TiO2 charge transfer (DTCT) bands. Furthermore, not only to gain insight
into the influence of the molecular structure of D–p–Cat dyes on the appearance of a DTCT band and
the electron-injection mechanism, but also to investigate the impacts of the DTCT characteristics of D–
p–Cat dyes on the photovoltaic performances of DSSCs, a D–p–Cat fluorescent dye YM-3 with
carbazole–terthiophene as the p-conjugated system was also synthesized. It was found that the D–p–
Cat dyes possess a good light-harvesting efficiency (LHE) in the visible region due to a broad absorption
band corresponding to DTCT upon binding to a TiO2 film. The incident photon-to-current conversion
efficiency (IPCE) corresponding to the DTCT band for DSSCs based on YM-1 and YM-2 is higher than
that for YM-3. This work indicates that the stabilization of the LUMO level and the expansion of the
p-conjugated system by the introduction of a long p-bridge such as terthiophene on the Cat moiety
can lead to an increase in the intramolecular charge transfer (ICT) excitation based on p / p* transition
with a decrease in the DTCT characteristics, resulting in enhancement of an indirect electron-injection
pathway from the excited dye to the CB of TiO2 by photoexcitation of the local band of the adsorbed
dye on TiO2.
Received 15th March 2014
Accepted 26th March 2014
DOI: 10.1039/c4ta01286k
www.rsc.org/MaterialsA
TiO2 through carboxylic acid groups; a carboxylic acid group can
form a chelating linkage or a bidentate bridging linkage at
Introduction
Brønsted acid sites (surface-bound hydroxy groups, Ti–OH) of
the TiO2 surface. Ru complexes, porphyrin dyes, phthalocyanine
dyes, and organic dyes containing carboxylic acid groups have
Dye-sensitized solar cells (DSSCs) based on dye sensitizers
adsorbed on nanocrystalline TiO2 electrodes have received
considerable attention as a promising alternative to conven-
tional solar cells based on silicon because they have interesting
construction and operational principles, and colorful and
decorative nature,1–18 since Gratzel and co-workers have repor-
¨
ted high photovoltaic performances for DSSCs based on a Ru-
complex dye in 1991.19 TiO2-based DSSCs can be classied into
two types, I and II, depending on the electron-injection pathway
from the dye to the conduction band (CB) of the TiO2 (Fig. 1).6,7
The pathway for type-I DSSCs is photoexcitation of the local
band of the adsorbed dye on TiO2 followed by electron injection
from the excited dye to the CB of TiO2 (Fig. 1a: i.e., an electron is
excited from the HOMO to the LUMO level of the dye, followed
by injection into the CB of TiO2). This pathway can also be
called the “two-step” or “indirect” electron-injection pathway.
The dyes for type-I DSSCs are usually bound to the surface of
Fig. 1 Schematic representation of (a) type-I DSSC (i.e., an electron is
excited from the HOMO to the LUMO level of the dye, followed by
injection into the CB of the TiO2) and (b) type-II DSSC (i.e., an electron
is injected directly from the HOMO of the dye into the CB of the TiO2
upon photoexcitation).
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima
University, Higashi-Hiroshima 739-8527, Japan. E-mail: yooyama@hiroshima-u.ac.
jp; jo@hiroshima-u.ac.jp; Fax: +81-82-424-5494
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been known to inject electrons into TiO2, according to the type-I mechanism, the interfacial electron transfer dynamics of Cat
pathway.1–19 Thus, the dyes for type-I DSSCs must have at least dyes adsorbed on TiO2 nanoparticles have been carefully
one carboxylic acid group as an anchoring group for adsorption studied by transient absorption spectroscopy and density
onto the TiO2 surface. Among dye sensitizers used so far in type- functional theory (DFT) by some research groups. These
I DSSCs, donor–acceptor–p-conjugated (D–p–A) dyes possess- fundamental studies have revealed that the back-electron-
ing a diphenyl- or dialkylamino group as the electron donor (D) transfer (charge recombination) of electrons injected into TiO2
and a carboxylic acid group as the electron acceptor (A) and for the type-II pathway takes place in a subpicosecond time-
anchor linked by p-conjugated bridges, displaying broad and scale,38,45 which was signicantly faster than those (ms–ms) for
intense absorption spectral features, would be especially the type-I pathway. Thus, type-II Cat dyes have rarely been
expected to be one of the most promising classes of organic dye employed as sensitizers for DSSCs and there have been few
sensitizers for type-I DSSCs.4–10 The photoabsorption properties efforts to develop type-II dye sensitizers, compared with that of
of a D–p–A dye are associated with intramolecular charge type-I DSSCs. In an attempt to overcome this problem, Yoon and
transfer (ICT) excitation from the D to the A moiety of the dye, co-workers found that attaching electron-donating moieties,
resulting in efficient electron transfer from the excited dye such as (pyridin-4-yl)vinyl (v-P) and (quinolin-4-yl)vinyl (v-Q), to
through the acceptor moiety (carboxylic acid group) into the CB Cat led to 2- and 2.7-fold increases, respectively, in the h value,
of TiO2. D–p–A dyes can facilitate the ICT and subsequent driven by large increases in the short-circuit photocurrent
charge separation of the D and A moieties in the excited dye, density (Jsc).23 As a result, the h values obtained with Cat-v-P and
and rapidly inject electrons into the CB of TiO2 and effectively Cat-v-Q were 1.2 and 1.6%, respectively. They proposed that
retard charge recombination because the cationic charge on the both the consecutive charge shi from the secondary donor
D moiety of the excited dye is spatially separated by the (pyridine or quinoline unit) to a primary donor (4-vinylcatechol
p-conjugated bridge from the TiO2 surface with injected elec- unit), leading to retardation of the back-electron-transfer rate
trons. Therefore, much effort has been made on the develop- and a dramatic increase in electron-injection efficiency, and a
ment of various types of D–p–A organic dye sensitizers for type-I red-shi of the DTCT band caused by the increase in the donor
DSSCs and there has been a gradual accumulation of informa- strength of the dye through the attachment of a secondary
tion about the relationship between the chemical structures donor to the primary donor were responsible for the increase in
and photovoltaic performances of type-I DSSCs. Consequently, the h value. Thus, the application of the molecular design of
type-I DSSCs have achieved solar energy-to-electricity conver- D–p–Cat dye sensitizers with strong electron donors, such as
sion yields (h) of up to 12%.2
triphenylamine, indoline, and carbazole is one of the most
The pathway for type-II DSSCs, on the other hand, is a direct, promising strategies not only to inhibit back electron transfer,
“one-step” electron injection from the ground state of the dye to but also to enhance direct electron-injection efficiency in type-II
the CB of TiO2 by photoexcitation of the dye-to-TiO2 charge DSSCs based on Cat dyes.36,45h They also reported that DSSCs
transfer (DTCT) bands (Fig. 1b: i.e., an electron is injected based on Cat and dopamine as the sensitizers were typical type-
directly from the HOMO of the dye into the CB of TiO2 upon II DSSCs. On the other hand, for DSSCs based on bromopyr-
photoexcitation).6,7,20 Catechol (Cat) dyes, such as dopamine ogallol red, the photocurrent is generated not only by the type-I
and uorine, numerous natural pigments, such as bromopyr- pathway, but also by the type-II pathway in the visible region.
ogallol red, and anthocyanins containing Cat moieties show Therefore, the bromopyrogallol red-sensitized DSSC is a typical
strong new absorption bands corresponding to DTCT in the example in which both pathways operate over the whole spectral
visible region upon binding to TiO2.20–31 Cat dyes have been region. Two representative organic dye sensitizers for type-I and
known to bind to the TiO2 surface through bidentate mono- type-II DSSCs are alizarin and Cat, respectively. The appearance
nuclear chelating and/or bidentate binuclear bridging link- of DTCT characteristics and the electron-injection mechanism
ages.21–48 Thus, the advantages of type-II DSSCs over type-I for both dyes have been extensively studied from experimental
DSSCs are as follows: (1) type-II DSSCs have efficient light-har- and theoretical methods by Prezhdo and co-workers.46 More-
vesting capabilities over the wide spectral range of sunlight over, to study the electronic injection mechanism more in depth
because direct electron injection in type-II DSSCs can lead to the and to generalize the main differences between the type-I and
creation of a new DTCT band and ease of restrictions on the type-II pathways, Sanz and co-workers studied ve organic dyes
LUMO levels of the type-II dyes relative to type-I DSSCs with an of growing size, Cat, 2,3-naphthalenediol, alizarin, coumarin
indirect electron-injection pathway (for type-I DSSCs, to achieve C343 having a carboxylic acid group, and coumarin derivative
electron injection from the excited dye to the CB of TiO2, the NKX-2311 having a cyanoacrylic acid group, and the electronic
LUMO levels of the type-I dyes must be higher than those of the structures and optical response of the ve dyes attached to TiO2
CB of the TiO2 electrode). (2) Type-II dyes can inject electrons were analyzed and compared by using time-dependent density
into the CB of TiO2 through only the type-II pathway or through functional theory (TDDFT).47 From their analysis, NKX-2311 and
type-I and type-II pathways and the electron-injection efficiency Cat show purely indirect (type-I pathway) and direct (type-II
of the type-II pathway, in principle, should be unity. However, pathway) electron-injection behavior, respectively. Neverthe-
the photovoltaic performance of type-II DSSCs based on Cat less, intermediate ones are also possible. In the sequence from
dyes is signicantly lower than that of type-I DSSCs based on Cat to 2,3-naphthalenediol, C343, alizarin, and NKX-2311, the
organic dyes with a carboxylic acid group. To investigate the electron injection changes from a purely direct mechanism to a
appearance of DTCT characteristics and the electron-injection purely indirect mechanism. Alizarin and C343 represent
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diboron by Miyaura boronation reaction. Compound 9 was
prepared by Suzuki coupling of 1 with 2-([2,20:50,200-terthio-
phen]-5-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane followed by
bromination with N-bromosuccinimide (NBS). Compound 10
was prepared by Suzuki coupling of 9 with 7. Compound 10 was
hydrolyzed by treatment with acid to produce D–p–Cat dye
YM-3.
Optical properties of YM-1, YM-2 and YM-3 in solution
The absorption and uorescence spectra of YM-1, YM-2 and YM-
3 in THF are shown in Fig. 2 and their spectral data are
summarized in Table 1. The absorption and uorescence
spectra of YM-1 and YM-2 resemble each other very closely, but
are signicantly different from those of YM-3. The dye YM-3
shows a strong absorption band at around 430 nm, which is
assigned to the ICT excitation based on p / p* transition from
the electron donor moiety (carbazole–diphenylamine) to the Cat
unit through the terthiophene unit. Although the dyes YM-1 and
YM-2 also show the ICT band at around 360 nm, the absorption
maximum (lambasx) for the ICT band of YM-3 occurs at a longer
wavelength by ca. 70 nm than those of YM-1 and YM-2. More-
over, the molar extinction coefficient (3) for the ICT band of YM-
3 is 81 300 Mꢀ1 cmꢀ1, which is higher than those (ca. 33 000–
43 000 Mꢀ1 cmꢀ1) of YM-1 and YM-2. These results reveal that
the introduction of a terthiophene unit on the carbazole skel-
eton expands the p-conjugation in the dye, and thus results in
red-shi and broadening of the ICT band, and enhancement of
Scheme 1 Chemical structures of D–p–Cat dye sensitizers YM-1, YM-
2 and YM-3.
intermediate behavior in which both injection regimes are
present. This is related to the relative position of the LUMO
energy of the dye to the edge of the CB of TiO2.
In this work, to provide a direction in molecular design
toward creating efficient Cat dye sensitizers for type-II DSSCs,
we have designed and synthesized D–p–Cat uorescent dyes
YM-1 and YM-2 with a diphenylamine moiety as the electron-
donating group, a catechol (Cat) unit as the anchoring group,
and uorene or carbazole as the p-conjugated system (Scheme
1). Furthermore, not only to gain insight into the inuence of
the molecular structure of D–p–Cat dyes on the appearance of
DTCT bands and the electron-injection mechanism, but also to
investigate the impacts of the DTCT characteristics of D–p–Cat
dyes on the photovoltaic performances of DSSCs, D–p–Cat
the 3 value. The dye YM-3 shows a uorescence maximum (lm ax
)
at 478 nm, which occurs at a longer wavelength by ca. 80 nm
than those of YM-1 and YM-2. The dyes YM-1 (Ff ¼ 0.56) and
YM-2 (Ff ¼ 0.44) exhibit a higher uorescence quantum yield
(Ff) than YM-3 (Ff ¼ 0.27).
uorescent dye YM-3 with
a carbazole–terthiophene as
p-conjugated system was also synthesized. Here we reveal the
impacts of the molecular structure of D–p–Cat dyes on the
photovoltaic performances of type-II DSSCs, and demonstrate
that the stabilization of the LUMO level and the expansion of
the p-conjugated system by the introduction of terthiophene on
the Cat moiety can lead to an increase in the ICT excitation
based on p / p* transition with a decrease in the DTCT
characteristics, resulting in enhancement of an indirect elec-
tron-injection pathway from the excited dye to the CB of TiO2 by
photoexcitation of the local band of the adsorbed dye on TiO2.
Electrochemical properties of YM-1, YM-2 and YM-3
The electrochemical properties of YM-1, YM-2 and YM-3 were
determined by cyclic voltammetry (CV) in acetonitrile contain-
ing 0.1 M tetrabutylammonium perchlorate (Bu4NClO4). The
potentials were referenced to ferrocene/ferrocenium (Fc/Fc+) as
the internal reference. The CV curves of the three dyes are
shown in Fig. 3. For YM-3 the rst oxidation peak was clearly
observed at 0.41 V vs. Fc/Fc+, whereas for YM-1 and YM-2 the ill-
dened oxidation peak was observed at around 0.40 V. The
corresponding reduction peak appeared at 0.30 V for both YM-1
and YM-2, and 0.26 V for YM-3, respectively. On the other hand,
Results and discussion
Synthesis of D–p–Cat dyes YM-1, YM-2 and YM-3
D–p–Cat dyes YM-1, YM-2 and YM-3 were synthesized according the second oxidation peak appeared at 0.47 V for YM-1, 0.48 V
to the stepwise synthetic protocol illustrated in Scheme 2. For for YM-2, and 0.72 V for YM-3, respectively. The corresponding
YM-1, Suzuki coupling of 2,7-dibromo-9,9-dimethyl-9H-uorene reduction peak for YM-1 was observed at 0.42 V, whereas no
with 2 (ref. 49 and 50) gave compound 3. D–p–Cat dye YM-1 was reduction peak was observed for YM-2 and YM-3. The HOMO
prepared by Buchwald–Hartwig C–N coupling of 3 with diphe- energy levels of the dyes were estimated from the half-wave
ox
1/2
nylamine followed by treatment with acid. For YM-2 and YM-3, potential of oxidation (E ¼ 0.35 V for both YM-1 and YM-2 and
the starting material 5 was prepared from 2,7-dibromo-9-butyl- 0.34 V for YM-3). The HOMO energy levels of YM-1, YM-2 and
9H-carbazole and diphenylamine through Buchwald–Hartwig YM-3 were 0.98 V for both YM-1 and YM-2 and 0.97 V for YM-3
C–N coupling according to the literature.51 Compound 6 was vs. the normal hydrogen electrode (NHE), respectively, thus
prepared by Suzuki coupling of 5 with 2. Compound 6 is indicating that the three dyes have comparable HOMO energy
hydrolyzed by treatment with acid to produce D–p–Cat dye YM- levels (Table 1). This result shows that the HOMO energy levels
2. Compound 7 was prepared from 5 with bis(pinacolato) are more positive than the I3ꢀ/Iꢀ redox potential (0.4 V), and
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Scheme 2 Synthetic route to D–p–Cat dye sensitizers YM-1, YM-2 and YM-3.
for YM-2, and 478 nm; 2.59 eV for YM-3). The LUMO energy
levels were ꢀ2.27 for both YM-1 and YM-2 and ꢀ1.62 V for YM-3,
respectively. Therefore, it was revealed that the red-shi of the
ICT absorption band for YM-3 relative to YM-1 and YM-2 is
attributed to stabilization of the LUMO level by the introduction
of a terthiophene unit on the carbazole skeleton of the dye,
resulting in a decrease in the HOMO–LUMO band gap.
FTIR spectra of dye powders and dyes adsorbed on TiO2
nanoparticles
Fig. 2 (a) Absorption and (b) fluorescence spectra (lex ¼ 362, 364 and
429 nm for YM-1, YM-2 and YM-3, respectively) of YM-1, YM-2 and To elucidate the adsorption states of YM-1, YM-2 and YM-3 on
YM-3 in THF.
TiO2 nanoparticles, we measured the FTIR spectra of the dye
powders and the dyes adsorbed on TiO2 nanoparticles (Fig. 4).
For the powders of the dyes, the stretching vibrations of the
thus this ensures an efficient regeneration of the oxidized dyes phenolic group (C–OH) for the Cat unit was observed at 1272
by electron transfer from the I3ꢀ/Iꢀ redox couple in the elec- and 1256 cmꢀ1 for YM-1, 1271 and 1256 cmꢀ1 for YM-2 and 1264
trolyte. The LUMO energy levels of the three dyes were esti- and 1248 cmꢀ1 for YM-3, respectively. In the FTIR spectra of
ox
1/2
mated from the E
and an intersection of absorption and dyes adsorbed on TiO2 nanoparticles, the stretching vibrations
uorescence spectra (381 nm; 3.25 eV for YM-1, 382 nm; 3.25 eV merge to one prominent or loose their hyperne structure.
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Table 1 Optical and electrochemical data, HOMO and LUMO energy levels, and DSSC performance parameters of YM-1, YM-2 and YM-3
lambasxa/nm (3 Mꢀ1 cmꢀ1 lm axa/nm (Ff) Eo1/x2b/V HOMOc/V LUMOc/V Moleculesd cmꢀ2 Jsce/mA cmꢀ2 Voce/mV ffe he (%)
Dye
)
YM-1 362 (43 100)
YM-2 364 (33 800)
YM-3 429 (81 300)
398 (0.56)
397 (0.44)
478 (0.27)
0.35
0.35
0.34
0.98
0.98
0.97
ꢀ2.27
ꢀ2.27
ꢀ1.62
8.20 ꢁ 1016f
6.36 ꢁ 1016g
4.94 ꢁ 1016f
2.86 ꢁ 1016g
9.71 ꢁ 1016f
5.50 ꢁ 1016g
1.36
1.56
1.51
1.46
0.75
0.82
416
456
416
448
316
328
0.51 0.29
0.50 0.36
0.50 0.31
0.49 0.32
0.47 0.11
0.50 0.13
a
In THF, uorescence quantum yields (Ff) were determined by using a calibrated integrating sphere system (lex ¼ 362, 364 and 429 nm for YM-1,
YM-2 and YM-3, respectively). b Half-wave potential for the oxidation (E1o/x2) vs. Fc/Fc+ was recorded in acetonitrile/Bu4NClO4 (0.1 M) solution. c Vs.
normal hydrogen electrode (NHE). d Adsorption amount per unit area of the TiO2 electrode. e Under simulated solar light (AM 1.5, 100 mW cmꢀ2).
f
g
0.1 mM dye solution in THF. 0.1 mM dye and 5 mM CDCA solution in THF.
binuclear bridging linkage between the Cat unit of dye and TiO2
(Fig. 4d).40
Theoretical calculations
To examine the electronic structures of YM-1, YM-2 and YM-3
and their Ti–Cat chelate complexes (Ti–YM-1, Ti–YM-2 and Ti–
YM-3), the molecular orbitals of the three dyes were calculated
using density functional theory (DFT) at the B3LYP/6-31G(d,p)
level. The DFT calculations indicate that the HOMO is mostly
localized on the uorene–diphenylamine moiety for YM-1, the
carbazole–diphenylamine moiety for YM-2 and the carbazole–
diphenylamine moiety containing the terthiophene unit for YM-
3, and the LUMO is mostly localized on the uorene–Cat moiety
for YM-1, the carbazole–Cat moiety for YM-2 and the terthio-
phene–Cat moiety for YM-3 (Fig. 5). On the other hand, for the
Ti–Cat chelate complexes the LUMOs of Ti–YM-1, Ti–YM-2 and
Ti–YM-3 are mostly localized on the titanium of chelating
linkage, although the HOMOs are mostly localized on almost
the same moiety as those of YM-1, YM-2 and YM-3. Accordingly,
the DFT calculations reveal that when YM-1, YM-2 and YM-3
were adsorbed on the TiO2 surface, dye excitations upon light
irradiation induce an efficient direct electron injection from the
HOMO of the dye to the CB of TiO2, resulting in the appearance
of a DTCT band.
Fig. 3 Cyclic voltammograms of YM-1, YM-2 and YM-3 in acetonitrile
containing 0.1 M Bu4NClO4 at a scan rate of 50 mV sꢀ1. The arrow
denotes the direction of the potential scan.
Photoabsorption properties of YM-1, YM-2 and YM-3
adsorbed on the TiO2 lm
The absorption spectra of the dyes adsorbed on the TiO2 lm
are shown in Fig. 6a. In addition to the ICT band based on p
/ p* transition observed in THF, YM-1, YM-2 and YM-3
adsorbed on the TiO2 lm show the broad absorption band
corresponding to DTCT upon binding to the TiO2 lm, that is,
the DTCT band appears in the region of 450 to 650 nm for both
YM-1 and YM-2 and 550 to 800 nm for YM-3. Thus, the DTCT
band of YM-3 appears in a longer wavelength region than
those of YM-1 and YM-2. The red-shi of absorption peak
wavelengths for Cat dyes upon binding to the TiO2 lm can
attributed to the stabilization of the LUMO level of Ti–Cat dye
Fig. 4 FTIR spectra of the dye powders and the dyes adsorbed on TiO2
nanoparticles for (a) YM-1, (b)YM-2 and (c) YM-3. (d) Possible binding
modes for catechol on a TiO2 surface: a bidentate mononuclear
chelating linkage (left) and a bidentate dinuclear bridging linkage
(right).
Thus, these observations indicate that the three dyes are complexes. In fact, as shown in Fig. 5, the DFT calculations
adsorbed on the TiO2 surface through the formation of a reveal that the LUMO energy level of YM-3 is lower than those
bidentate mononuclear chelating linkage and/or a bidentate of YM-1 and YM-2, and the three dyes have comparable HOMO
energy levels, which are in good agreement with the
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Fig. 5 Energy level diagram and HOMO and LUMO of YM-1, YM-2 and YM-3 and their Ti–Cat chelate complexes Ti–YM-1, Ti–YM-2 and Ti–
YM-3.
Photovoltaic performances of DSSCs based on YM-1, YM-2
and YM-3
The DSSCs were prepared by using the dye-adsorbed TiO2
electrode, Pt-coated glass as a counter electrode, and an aceto-
nitrile solution with iodine (0.05 M), lithium iodide (0.1 M), and
1,2-dimethyl-3-propylimidazolium iodide (0.6 M) as an electro-
lyte. The photocurrent–voltage (I–V) characteristics were
measured under simulated solar light (AM 1.5, 100 mW cmꢀ2).
The incident photon-to-current conversion efficiency (IPCE)
spectra and the I–V curves are shown in Fig. 7. The photovoltaic
Fig. 6 (a) Absorption spectra of YM-1, YM-2 and YM-3 in THF (—) and
performance parameters are summarized in Table 1. It is worth
adsorbed on the TiO2 film (/). (b) Photographs of YM-1, YM-2 and
mentioning here that the adsorption amounts of YM-1, YM-2
and YM-3 adsorbed on the TiO2 electrode are 8.20 ꢁ 1016,
4.94 ꢁ 1016 and 9.71 ꢁ 1016 molecules per cm2, respectively,
which is comparable to that of conventional D–p–A dye sensi-
tizers with carboxyl groups. The IPCE spectra of YM-1 and YM-2
resemble each other very closely, and are in good agreement
with the observed absorption spectra on the TiO2 lm, that is,
the IPCE spectra coincide with the DTCT band (Fig. 7a). The
IPCE values of both YM-1 and YM-2 exceed 10% through the
YM-3 in THF and (c) YM-1, YM-2 and YM-3 adsorbed on the TiO2 film.
experimental results from the CV and the spectral analyses
(Fig. 2 and 3). On the other hand, the LUMO energy levels for
the surface-bound Ti–YM-1, Ti–YM-2 and Ti–YM-3 complexes
are lower than those of YM-1, YM-2 and YM-3, although the
HOMO energy levels for the Ti–Cat dye complexes are almost
the same energy levels as those of YM-1, YM-2 and YM-3. It is
worth mentioning here that the LUMO energy level of Ti–YM-3
is lower than those of Ti–YM-2 and Ti–YM-3. Thus, this result
clearly shows that the expansion of the p-conjugated system by
the introduction of the terthiophene unit on the Cat can lead
to the stabilization of the LUMO energy levels of the Ti–Cat dye
complexes, resulting in the red-shi of the DTCT band. As
shown in Fig. 6b and c, the colors of the Cat dyes in THF are
colorless for YM-1 and YM-2 and yellow for YM-3, respectively,
but the colors of the Cat dyes adsorbed on the TiO2 lm are
dark-orange for YM-1 and YM-2 and dark brown for YM-3,
respectively, which indicates a decrease in the transition
energy by the appearance of the DTCT band associated with
the formation of the surface-bound Ti–Cat complex.
Fig. 7 (a) IPCE spectra and (b) I–V curves of DSSCs based on YM-1,
YM-2 and YM-3 with (/) and without (—) CDCA as a coadsorbent.
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wavelength region of 580 nm. The onset of IPCE for both YM-1 and also produces the result that it can no longer form a
and YM-2 reached 700 nm. Therefore, it is clear that the compact blocking layer (larger surface coverage) to the
ꢀ
photocurrents for DSSCs based on YM-1 and YM-2 are mainly approach of I3 ions to the TiO2 surface, resulting in faster
generated by a direct electron-injection pathway from the Ti– charge recombination and a lower Voc value.4,10,52,53 When che-
Cat chelate complexes (Ti–YM-1 and Ti–YM-2) to the CB of the nodeoxycholic acid (CDCA) was employed as a coadsorbent to
TiO2. On the other hand, the IPCE corresponding to the DTCT prevent dye aggregation on the TiO2 surface, the Jsc, Voc and h
band for DSSCs based on YM-3 is below 10% in the wavelength values slightly increased (Fig. 7b). Under the adsorption
region over 500 nm, and is much lower than those of YM-1 and conditions of 0.1 mM dye and 5 mM CDCA, the Jsc, Voc and h
YM-2. However, it is worth mentioning here that the maximum values for DSSCs with CDCA are 1.56 mA cmꢀ2, 456 mV and
IPCE value of YM-3 reaches 20% at around 430 nm, which 0.36% for YM-1, 1.46 mA cmꢀ2, 448 mV and 0.32% for YM-2 and
corresponds to the p / p* transition based on the local band 0.82 mA cmꢀ2, 328 mV and 0.13% for YM-3, respectively
of the adsorbed dye on TiO2. Consequently, the photocurrent (Table 1).
for DSSCs based on YM-3 is mainly generated by an indirect
Thus, electrochemical impedance spectroscopy (EIS) anal-
electron-injection pathway from the excited dye to the CB of ysis was performed to study the electron recombination process
TiO2. Sanz and co-workers reported that whether the dye in DSSCs based on these three dyes under ꢀ0.6 V bias applied
sensitizers exhibit a purely indirect electron-injection behavior voltage in the dark. The Nyquist plots and Bode phase plots are
or a purely direct electron-injection behavior is related to the shown in Fig. 8. The small semicircle at around Z0 ¼ 20 ohm in
relative position of the LUMO energy of the dye to the edge of the Nyquist plot, which corresponds to the high-frequency
the CB of TiO2.47 Thus, this result indicates that the stabilization peaks in the Bode phase plots, represents the electron transfer
of the LUMO level and the expansion of the p-conjugated from the Pt counter-electrode to I3ꢀ ions in the electrolyte, that
system by the introduction of terthiophene on the Cat moiety is, the charge-transfer resistances at the Pt/electrolyte interface.
can lead to an increase in the ICT excitation based on p / p* The large semicircle in the Nyquist plot, which corresponds to
transition with a decrease in the DTCT characteristics,48 the midfrequency peaks in the Bode phase plots, represents the
resulting in enhancement of an indirect electron-injection chargeꢀrecombination between the injected electrons in TiO2
pathway from the excited dye to the CB of TiO2 by photoexci- and I3 ions in the electrolyte, that is, the charge-transfer
tation of the local band of the adsorbed dye on TiO2, that is, resistances at the TiO2/dye/electrolyte interface.54–57 The Nyquist
type-I DSSCs. In addition, the maximum IPCE value (20%) of plots (Fig. 8a) show the resistance value for the large semicircle
YM-3 is much lower than those of conventional D–p–A dyes to increase in the order of YM-3 (14.6 U) < YM-1 (37.0 U) z YM-2
having the carboxylic acid group. It is suggested that the elec-
tron-injection efficiency of D–p–Cat dyes through the type-I
pathway is lower than those of D–p–A dyes having the carboxylic
acid group through the type-I pathway. This may be attributed
to the difference in the binding mode onto the TiO2 surface
between D–p–Cat dyes and D–p–A dyes having the carboxylic
acid group. The I–V curves show that the Jsc and h values for YM-
1 (1.36 mA cmꢀ2 and 0.29%) and YM-2 (1.51 mA cmꢀ2 and
0.31%) are much higher than those for YM-3 (0.75 mA cmꢀ2 and
0.11%) (Fig. 7b). Thus, this shows that the expansion of the
p-conjugated system by the introduction of terthiophene on the
Cat moiety results in the facilitation of the back-electron-
transfer rate from electrons injected into TiO2 to the oxidized
dye, leading to a decrease in photovoltaic performances. On the
other hand, the open-circuit photovoltage (Voc) of Cat dye
Fig. 8 (a) Nyquist plots and (b) Bode phase plots of DSSCs based on
YM-1, YM-2 and YM-3 with and without CDCA as a coadsorbent.
sensitizers is lower than that of the conventional organic dye
sensitizers.32,36 It is assumed that the low Voc values (ca. 300–
400 mV) for YM-1, YM-2 and YM-3 are attributed to faster charge
recombination between the injected electrons in the CB of TiO2
ꢀ
and I3ꢀ ions in the electrolyte, arising from the approach of I3
ions to the TiO2 surface duꢀe to the electrostatic interactions
between the D–p–Cat and I3 ions due to the formation of Ti–
Cat chelate complexes, as with the case of catechol–thiophene
sensitizers by Burn and Meredith.32 Moreover, the Voc value (316
mV) for YM-3 with terthiophene is smaller than those (416 mV)
for YM-1 and YM-2. This is attributed to the fact that expansion
of the p-conjugated systems of dyes by introducing thiophene
ꢀ
units oen facilitates the approach of I3 ions to the TiO2
Fig. 9 Photovoltaic parameters (Jsc, Voc, ff, and h) for DSSCs based on
surface because of complexation between the dye and I3ꢀ ions, YM-2 during light soaking (AM 1.5, 100 mW cmꢀ2).
8506 | J. Mater. Chem. A, 2014, 2, 8500–8511
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(37.3 U), indicating that the electron recombination resistance recorded with a Hitachi U-2910 spectrophotometer and uo-
increases in the order of YM-3 < YM-1 z YM-2. The electron rescence spectra were recorded with a HORIBA FluoroMax-4
recombination lifetimes (se) expressing the electron recombi- spectrouorometer. The uorescence quantum yields in solu-
nation between the injected electrons in TiO2 and I3ꢀ ions in the tion were determined by using a HORIBA FluoroMax-4 spec-
electrolyte, extracted from the angular frequency (urec ¼ 2pf) at trouorometer with a calibrated integrating sphere system
the midfrequency peak in the Bode phase plot using se ¼ 1/urec
,
(lex ¼ 362, 364 and 429 nm for YM-1, YM-2 and YM-3, respec-
are 20.0 ms for YM-1, 15.9 ms for YM-2 and 6.3 ms for YM-3, tively). Cyclic voltammetry (CV) curves were recorded in an
respectively (Fig. 8b), which is consistent with the sequence of acetonitrile/Bu4NClO4 (0.1 M) solution with a three-electrode
Voc values in the DSSCs. When CDCA was employed as a coad- system consisting of Ag/Ag+ as the reference electrode, Pt plate
sorbent, the se values in the presence of CDCA slightly increased as the working electrode, and Pt wire as the counter electrode by
(se ¼ 25.2 ms for YM-1, 20.0 ms for YM-2, and 8.0 ms for YM-3), using a AMETEK Versa STAT 4 potentiostat. Electrochemical
compared with those in the absence of CDCA, that is, coad- impedance spectroscopy (EIS) for DSSCs in the dark under a
sorption of CDCA with D–p–Cat dyes can effectively retard forward bias of ꢀ0.60 V with a frequency range of 10 MHz to
charge recombination between the injected electrons in the CB 100 kHz was measured with an AMETEK Versa STAT 3.
ꢀ
of TiO2 and I3 ions. Moreover, we examined the durability of
the DSSCs based on D–p–Cat dyes to light soaking. As the result,
it was demonstrated that the DSSC based on the dye YM-2
Synthesis
shows a good light-soaking stability under simulated solar light:
there is little change in the Jsc, Voc, ff, and h values during 24 h of of iPr2NH (18.5 mL, 0.1 mol) in dry THF (30 mL) was added
4-Bromo-1,2-bis(methoxymethoxy)benzene (1).49 A solution
light soaking (Fig. 9).
slowly to a solution of 4-bromobenzene-1,2-diol (5.0 g,
26.5 mmol) in dry THF (88 mL) under an argon atmosphere. The
reaction mixture was stirred for 30 min at room temperature
and then chlorodimethyl ether (8.1 g, 0.1 mol) was added. The
Conclusions
In this work, to provide a direction in molecular design toward resulting mixture was stirred for 14 h at room temperature. Aer
creating efficient catechol (Cat) dye sensitizers for type-II concentrating under reduced pressure, the resulting residue
DSSCs, we have designed and synthesized D–p–Cat uorescent was dissolved in dichloromethane and washed with water. The
dyes YM-1 with uorene, YM-2 with carbazole, and YM-3 with dichloromethane extract was evaporated under reduced pres-
carbazole–terthiophene as a p-conjugated system. D–p–Cat sure. The residue was chromatographed on silica gel
dyes YM-1, YM-2 and YM-3 adsorbed on the TiO2 lm show the (dichloromethane as eluent) to give 1 (5.99 g, yield 82%) as a
broad absorption band corresponding to dye-to-TiO2 charge colorless viscous solid; 1H NMR (500 MHz, acetone-d6) d ¼ 3.51
transfer (DTCT) upon forming Ti–Cat chelate complexes (Ti– (s, 3H), 3.52 (s, 3H), 5.20 (s, 2H), 5.22 (s, 2H), 7.09 (d, J ¼ 8.7 Hz,
YM-1, Ti–YM-2 and Ti–YM-3). It was found that the photocur- 1H), 7.13 (dd, J ¼ 2.2 and 8.7 Hz, 1H), 7.30 (d, J ¼ 2.2 Hz, 1H)
rents for DSSCs based on YM-1 and YM-2 are mainly generated ppm; HRMS (ESI): m/z: (M + Na+) calcd for C10H13O4BrNa,
by a direct electron-injection pathway from the Ti–Cat chelate 298.98894; found 298.98907.
complexes (Ti–YM-1 and Ti–YM-2) to the CB of the TiO2, that is,
2-(3,4-Bis(methoxymethoxy)phenyl)-4,4,5,5-tetramethyl-
type-II DSSCs. On the other hand, the photocurrent for DSSC 1,3,2-dioxaborolane (2).50 A solution of 1 (12.3 g, 44.0 mmol),
based on YM-3 is mainly generated by an indirect electron- bis(pinacolato)diboron (13.2 g, 52.0 mmol), PdCl2(dppf) (1.1 g,
injection pathway from the excited dye to the CB of TiO2, that is, 1.3 mmol), and KOAc (10.2 g, 0.1 mol) in DMF (150 mL) was
type-I DSSCs. We demonstrate that the stabilization of the stirred for 15 h at 80 ꢂC. Aer concentrating under reduced
LUMO level and the expansion of the p-conjugated system by pressure, the resulting residue was dissolved in dichloro-
the introduction of a long p-bridge such as terthiophene on the methane and washed with water. The dichloromethane extract
Cat moiety can lead to an increase in the intramolecular charge was evaporated under reduced pressure. The residue was
transfer (ICT) excitation based on p / p* transition with a chromatographed on silica gel (hexane to remove bis(pinaco-
decrease in the DTCT characteristics, resulting in enhancement lato)diboron and then ethyl acetate–hexane ¼ 3 : 8 as eluent) to
of an indirect electron-injection pathway from the excited dye to give 2 (9.58 g, yield 67%) as a colorless solid; 1H NMR (400 MHz,
the CB of TiO2 by photoexcitation of the local band of the acetone-d6) d ¼ 1.32 (s, 12H), 3.46 (s, 3H), 3.58 (s, 3H), 5.20
adsorbed dye on TiO2.
(s, 2H), 5.24 (s, 2H), 7.14 (d, J ¼ 8.0 Hz, 1H), 7.38 (dd, J ¼ 1.6 and
8.0 Hz, 1H), 7.47 (d, J ¼ 1.6 Hz, 1H) ppm; HRMS (ESI): m/z: (M +
Na+) calcd for C16H25BO6Na, 347.16364; found 347.16409.
2-(3,4-Bis(methoxymethoxy)phenyl)-7-bromo-9,9-dimethyl-
Experimental
Melting points were measured with an MP model Yanaco micro 9H-uorene (3). To a mixture of 2,7-dibromo-9,9-dimethyl-9H-
melting point apparatus. IR spectra were recorded on a Perkin uorene (4.85 g, 13.78 mmol), 2 (2.23 g, 6.89 mmol), and
Elmer Spectrum One FT-IR spectrometer by using the ATR PdCl2(PPh3)2 (0.24 g, 0.34 mmol) under an argon atmosphere
method. High-resolution mass spectral data were acquired on a were added aqueous 1 M Na2CO3 (3 mL) and DMF (100 mL) and
Thermo Fisher Scientic LTQ Orbitrap XL. 1H NMR spectra stirred for 6 h at 100 ꢂC. Aer concentrating under reduced
were recorded on a Varian-400 (400 MHz) or Varian-500 pressure, the resulting residue was dissolved in dichloro-
(500 MHz) FT-NMR spectrometer. Absorption spectra were methane and washed with water. The dichloromethane extract
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7-Bromo-9-butyl-N,N-diphenyl-9H-carbazol-2-amine (5).51 To
a mixture of 2,7-dibromo-9-butyl-9H-carbazole (1.13 g, 2.96
mmol), diphenylamine (1.0 g, 5.92 mmol), Pd(dba)2 (0.081 g,
0.09 mmol), dppf (0.148 g, 0.27 mmol) and tBuONa (0.796 g,
8.28 mmol) under an argon atmosphere was added toluene (5
mL), and stirred for 6 h at 80 ꢂC. Aer concentrating under
reduced pressure, the resulting residue was dissolved in
dichloromethane and washed with water. The dichloromethane
extract was evaporated under reduced pressure. The residue was
chromatographed on silica gel (dichloromethane–hexane ¼
1 : 6 as eluent) to give 5 (1.02 g, yield 74%) as a white solid; 1H
NMR (400 MHz, acetone-d6, TMS) d ¼ 0.86 (t, J ¼ 7.4 Hz, 3H),
1.26–1.32 (m, 2H), 1.72–1.76 (m, 2H), 4.29 (t, J ¼ 7.0 Hz, 2H),
6.94 (dd, J ¼ 1.5 and 8.2 Hz, 1H), 7.03–7.07 (m, 2H), 7.10–7.13
(m, 4H), 7.23 (d, J ¼ 1.1 Hz, 1H), 7.28–7.33 (m, 5H), 7.23 (d, J ¼
1.3 Hz, 1H), 8.00 (d, J ¼ 8.2 Hz, 1H), 8.05 (d, J ¼ 8.5 Hz, 1H) ppm;
HRMS (APCI): m/z: (M + H+) calcd for C28H26N2Br, 469.12739;
found 469.12830.
was evaporated under reduced pressure. The residue was
chromatographed on silica gel (ethyl acetate–hexane ¼ 1 : 5 as
eluent) to give 3 (0.96 g, yield 30%) as a white solid; mp 128–129
1
ꢂC; IR (ATR): ~n ¼ 1514, 1455, 1246 cmꢀ1; H NMR (500 MHz,
acetone-d6) d ¼ 1.56 (s, 6H), 3.50 (s, 3H), 3.51 (s, 3H), 5.25 (s,
2H), 5.30 (s, 2H), 7.23 (d, J ¼ 8.5 Hz, 1H), 7.34 (dd, J ¼ 2.0 and 8.5
Hz, 1H), 7.49 (d, J ¼ 2.0 Hz, 1H), 7.53 (dd, J ¼ 1.5 and 8.0 Hz,
1H), 7.62 (dd, J ¼ 1.5 and 8.0 Hz, 1H), 7.74 (d, J ¼ 1.5 Hz, 1H),
7.78 (d, J ¼ 8.0 Hz, 1H), 7.80 (d, J ¼ 1.5 Hz, 1H), 7.88 (d, J ¼ 8.0
Hz, 1H) ppm; 13C NMR (125 MHz, acetone-d6) d ¼ 27.91, 48.0,
57.07, 57.16, 97.11, 97.3, 118.27, 119.57, 122.23, 122.25, 122.74,
122.77, 123.40, 127.69, 127.83, 131.82, 137.46, 138.57, 139.79,
142.13, 149.13, 149.64, 155.81, 158.0 ppm; HRMS (ESI): m/z: (M
+ Na+) calcd for C25H25O4BrNa, 491.08284; found 491.08301.
7-(3,4-Bis(methoxymethoxy)phenyl)-9,9-dimethyl-N,N-diphenyl-
9H-uoren-2-amine (4). To a mixture of 3 (0.96 g, 2.05 mmol),
diphenylamine (0.69 g, 4.10 mmol), Pd(OAc)2 (0.018 g, 0.08
mmol), and tBuONa (0.59 g, 0.08 mmol) under an argon
atmosphere were added (tBu)3P (10 wt% in hexane, 0.166 g,
0.082 mmol) and toluene (45 mL), and stirred for 19 h at 100 ꢂC.
Aer concentrating under reduced pressure, the resulting
residue was dissolved in dichloromethane and washed with
water. The dichloromethane extract was evaporated under
reduced pressure. The residue was chromatographed on silica
gel (ethyl acetate–hexane ¼ 3 : 10 as eluent) to give 4 (1.09 g,
yield 92%) as a white solid; mp 127–128 ꢂC; IR (ATR): ~n ¼ 1583,
7-(3,4-Bis(methoxymethoxy)phenyl)-9-butyl-N,N-diphenyl-
9H-carbazol-2-amine (6). To a mixture of 5 (0.69 g, 2.13 mmol), 2
(1.0 g, 2.13 mmol), and Pd(PPh3)4 (0.123 g, 0.107 mmol) under
an argon atmosphere were added aqueous 1 M Na2CO3 (2 mL)
ꢂ
and DMF (10 mL) and stirred for 10 h at 100 C. Aer concen-
trating under reduced pressure, the resulting residue was dis-
solved in dichloromethane and washed with water. The
dichloromethane extract was evaporated under reduced pres-
sure. The residue was chromatographed on silica gel (ethyl
acetate–hexane ¼ 2 : 1 as eluent) to give 6 (0.696 g, yield 56%) as
1
1485, 1463 cmꢀ1; H NMR (500 MHz, acetone-d6) d ¼ 1.47 (s,
6H), 3.50 (s, 3H), 3.52 (s, 3H), 5.25 (s, 2H), 5.30 (s, 2H), 7.02 (dd, J
¼ 2.0 and 8.2 Hz, 1H), 7.05–7.07 (m, 2H), 7.09–7.12 (m, 4H), 7.23
(d, J ¼ 8.5 Hz, 1H), 7.26 (d, J ¼ 2.0 Hz, 1H), 7.29–7.34 (m, 5H),
7.49 (d, J ¼ 2.2 Hz, 1H), 7.58 (dd, J ¼ 1.6 and 8.0 Hz, 1H), 7.73 (d,
J ¼ 8.2 Hz, 1H), 7.75 (d, J ¼ 1.6 Hz, 1H), 7.78 (d, J ¼ 8.0 Hz, 1H)
ppm; 13C NMR (100 MHz, acetone-d6) d ¼ 27.35, 47.62, 56.3,
56.39, 96.3, 96.45, 117.29, 118.77, 119.43, 120.69, 121.75,
121.82, 121.84, 123.7, 124.21, 124.85, 126.71, 130.24, 134.76,
136.9, 138.77, 140.04, 148.13, 148.33, 148.82, 148.93, 155.17,
156.33 ppm; HRMS (APCI): m/z: (M + H+) calcd for C37H36NO4,
558.26389; found 558.26361.
ꢂ
a light yellow solid; mp 107–110 C; IR (ATR): ~n ¼ 1583, 1515,
1491, 1462 cmꢀ1; 1H NMR (400 MHz, acetonitrile-d3) d ¼ 0.87 (t,
J ¼ 7.4 Hz, 3H), 1.28–1.34 (m, 2H), 1.77–1.81 (m, 2H), 3.51 (s,
3H), 3.53 (s, 3H), 4.36 (t, J ¼ 7.0 Hz, 2H), 5.26 (s, 2H), 5.31 (s,
2H), 6.93 (dd, J ¼ 1.8 and 8.4 Hz, 1H), 7.02–7.06 (m, 2H), 7.11–
7.14 (m, 4H), 7.24–7.33 (m, 6H), 7.39 (dd, J ¼ 2.2 and 8.4 Hz,
1H), 7.46 (dd, J ¼ 1.4 and 8.1 Hz, 1H), 7.55 (d, J ¼ 2.2 Hz, 1H),
7.74 (d, J ¼ 1.0 Hz, 1H), 8.06 (d, J ¼ 8.4 Hz, 1H), 8.11 (d, J ¼ 8.3
Hz, 1H) ppm; 13C NMR (125 MHz, acetonitrile-d3) d ¼ 13.95,
20.84, 31.52, 42.9, 56.42, 56.5, 96.17, 96.45, 106.06, 107.85,
117.62, 117.65, 118.52, 119.03, 119.14, 120.84, 121.74, 122.22,
122.55, 123.46, 124.58, 130.12, 137.32, 138.38, 142.26, 142.87,
147.09, 147.74, 148.42, 149.09 ppm; HRMS (APCI): m/z: (M + H+)
calcd for C38H39N2O4, 587.29043; found 587.29041.
4-(7-(Diphenylamino)-9,9-dimethyl-9H-uoren-2-yl)benzene-
1,2-diol (YM-1). To compound 4 (0.136 g, 0.29 mmol) were
added THF (2 mL) and 1N HCl (2 mL), and reuxed for 3 h. Aer
concentrating under reduced pressure, the resulting residue
was dissolved in dichloromethane and washed with water. The
dichloromethane extract was evaporated under reduced pres-
sure. The resulting residue was subjected to reprecipitation
from ethyl acetate–hexane to give YM-1 (0.106 g, yield 92%) as a
white powder; mp 107–108 ꢂC; IR (ATR): ~n ¼ 3385 (br), 1586,
4-(9-Butyl-7-(diphenylamino)-9H-carbazol-2-yl)benzene-1,2-
diol (YM-2). To compound 6 (0.102 g, 0.18 mmol) were added
THF (2 mL) and 1N HCl (2 mL), and reuxed for 3 h. Aer
concentrating under reduced pressure, the resulting residue
was dissolved in dichloromethane and washed with water. The
dichloromethane extract was evaporated under reduced pres-
sure. The resulting residue was subjected to reprecipitation
from ethyl acetate–hexane to give YM-2 (0.079 g, yield 89%) as a
white powder; mp 80–82 ꢂC; IR (ATR): ~n ¼ 3367 (br), 1593, 1488,
1
1489, 1465 cmꢀ1; H NMR (400 MHz, acetone-d6) d ¼ 1.46 (s,
6H), 6.92 (d, J ¼ 8.4 Hz, 1H), 7.01 (dd, J ¼ 2.0 and 8.4 Hz, 1H),
7.06–7.11 (m, 7H), 7.21 (d, J ¼ 2.4 Hz, 1H), 7.27 (d, J ¼ 2.0 Hz,
1H), 7.28–7.33 (m, 4H), 7.53 (dd, J ¼ 1.6 and 8.0 Hz, 1H), 7.69 (d,
J ¼ 1.6 Hz, 1H), 7.71 (d, J ¼ 8.4 Hz, 1H), 7.75 (d, J ¼ 8.0 Hz, 1H)
ppm; 13C NMR (100 MHz, acetone-d6) d ¼ 27.38, 47.57, 114.81,
116.53, 119.33, 119.56, 120.6, 121.48, 121.62, 123.64, 124.3,
124.78, 126.33, 130.22, 134.38, 134.99, 138.22, 140.63, 145.64,
146.3, 148.14, 148.96, 155.08, 156.27 ppm; HRMS (APCI): m/z:
(M + H+) calcd for C33H28NO2, 470.21146; found 470.21109.
1
1456 cmꢀ1; H NMR (400 MHz, acetone-d6) d ¼ 0.73 (t, J ¼ 7.4
Hz, 3H), 1.15–1.21 (m, 2H), 1.63–1.68 (m, 2H), 4.22 (t, J ¼ 7.0 Hz,
2H), 6.79 (dd, J ¼ 1.8 and 8.3 Hz, 1H), 6.80 (d, J ¼ 8.2 Hz, 1H),
6.88–6.92 (m, 2H), 6.97–7.00 (m, 4H), 7.02 (d, J ¼ 2.2 Hz, 1H),
7.10 (d, J ¼ 1.7 Hz, 1H), 7.14 (d, J ¼ 2.2 Hz, 1H), 7.15–7.19 (m,
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4H), 7.28 (dd, J ¼ 1.5 and 8.1 Hz, 1H), 7.54 (d, J ¼ 1.0 Hz, 1H), (0.53 g, yield 87%) as a yellow solid; mp 139–142 ꢂC; IR (ATR): ~n
7.90 (d, J ¼ 8.3 Hz, 1H), 7.94 (d, J ¼ 8.5 Hz, 1H) ppm; 13C NMR ¼ 1515, 1500 cmꢀ1; 1H NMR (400 MHz, acetone-d6) d ¼ 3.49 (s,
(100 MHz, acetone-d6) d ¼ 14.93, 21.77, 32.62, 43.7, 107.06, 3H), 3.52 (s, 3H), 5.25 (s, 2H), 5.29 (s, 2H), 7.13–7.21 (m, 3H),
108.21, 115.94, 117.25, 118.61, 119.73, 120.43, 120.46, 121.47, 7.24–7.31 (m, 4H), 7.35 (d, J ¼ 3.7 Hz, 1H), 7.45 (d, J ¼ 1.7 Hz,
122.42, 123.09, 124.07, 125.26, 130.85, 135.79, 140.14, 143.26, 1H) ppm; 13C NMR (100 MHz, CDCl3) d ¼ 56.41, 56.47, 95.51,
143.67, 146.26, 147.0, 147.64, 150.01 ppm; HRMS (APCI): m/z: 95.71, 111.14, 113.35, 117.01, 120.09, 123.57, 123.82, 124.16,
(M + H+) calcd for C34H31N2O2, 499.23800; found 499.23767.
9-Butyl-N,N-diphenyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxabor- 143.3, 147.18, 147.66; HRMS (APCI): m/z: (M + H+) calcd for
124.77, 124.83, 128.8, 130.84, 135.0, 135.69, 136.89, 138.74,
olan-2-yl)-9H-carbazol-2-amine (7). A solution of 5 (0.93 g, 1.97
mmol), bis(pinacolato)diboron (0.5 g, 1.97 mmol), PdCl2(dppf)
C
22H20O4S3Br, 522.97016; found 522.96979.
7-(500-(3,4-Bis(methoxymethoxy)phenyl)-[2,20:50,200-terthio-
(0.04 g, 0.05 mmol), and KOAc (0.39 g, 3.94 mmol) in DMF phen]-5-yl)-9-butyl-N,N-diphenyl-9H-carbazol-2-amine (10). To a
ꢂ
(4 mL) was stirred for 15 h at 80 C. Aer concentrating under mixture of 9 (0.22 g, 0.41 mmol), 7 (0.21 g, 0.41 mmol) and
reduced pressure, the resulting residue was dissolved in Pd(PPh3)4 (0.024 g, 0.02 mmol) under an argon atmosphere
dichloromethane, and washed with water. The dichloro- were added aqueous 1 M Na2CO3 (0.4 mL) and DMF (10 mL) and
methane extract was evaporated under reduced pressure. The stirred for 2 h at 90 ꢂC. Aer concentrating under reduced
residue was chromatographed on silica gel (hexane to remove pressure, the resulting residue was dissolved in dichloro-
bis(pinacolato)diboron and then ethyl acetate–hexane ¼ 1 : 1 as methane and washed with water. The dichloromethane extract
eluent) to give 7 (0.52 g, yield 51%) as a white solid; mp 60–63 was evaporated under reduced pressure. The residue was
1
ꢂC; IR (ATR): ~n ¼ 1625, 1587, 1492, 1433 cmꢀ1; H NMR (400 chromatographed on silica gel (ethyl acetate–hexane ¼ 1 : 2 as
MHz, acetone-d6) d ¼ 0.84 (t, J ¼ 7.3 Hz, 3H), 1.24–1.30 (m, 2H), eluent) to give 10 (0.23 g, yield 66%) as a yellow solid; mp 160–
1.38 (s, 12H), 1.72–1.78 (m, 2H), 4.29 (t, J ¼ 7.0 Hz, 2H), 6.92 (dd, 164 ꢂC; IR (ATR): ~n ¼ 1594, 1491, 1461 cmꢀ1; 1H NMR (400 MHz,
J ¼ 1.8 and 8.4 Hz, 1H), 7.02–7.06 (m, 2H), 7.10–7.13 (m, 4H), acetone-d6) d ¼ 0.88 (t, J ¼ 7.2 Hz, 3H), 1.28–1.35 (m, 2H), 1.77–
7.22 (d, J ¼ 1.8 Hz, 1H), 7.27–7.32 (m, 4H), 7.61 (d, J ¼ 7.8 Hz, 1.82 (m, 2H), 3.50 (s, 3H), 3.52 (s, 3H), 4.37 (t, J ¼ 6.8 Hz, 2H),
1H), 7.85 (s, 1H), 8.04–8.06 (m, 2H), 8.07 (d, J ¼ 8.3 Hz, 2H) ppm; 5.25 (s, 2H), 5.30 (s, 2H), 6.94 (dd, J ¼ 1.8 and 8.4 Hz, 1H), 7.04–
13C NMR (100 MHz, acetone-d6) d ¼ 14.89, 21.75, 26.0, 32.67, 7.07 (m, 2H), 7.11–7.14 (m, 4H), 7.19–7.23 (m, 2H), 7.29–7.36
43.72, 85.15, 106.64, 116.53, 118.36, 120.01, 120.51, 122.99, (m, 10H), 7.47 (d, J ¼ 1.8 Hz, 1H), 7.53–7.57 (m, 2H), 7.85 (s, 1H),
124.29, 125.51, 126.87, 127.0, 130.88, 141.93, 143.77, 148.5, 8.05 (d, J ¼ 8.4 Hz, 1H), 8.11 (d, J ¼ 8.1 Hz, 1H) ppm; 13C NMR
149.89 ppm (one aromatic carbon signal was not observed (100 MHz, acetone-d6) d ¼ 14.17, 21.00, 31.87, 56.34, 96.19,
owing to overlapping resonances); HRMS (APCI): m/z: (M + H+) 96.38, 106.02, 106.48, 115.66, 117.95, 118.03, 118.74, 119.4,
calcd for C34H38BN2O2, 517.30209; found 517.30328.
120.56, 121.15, 121.9, 123.55, 123.6, 124.68, 124.75, 124.78,
5-(3,4-Bis(methoxymethoxy)phenyl)-2,20:50,200-terthiophene 125.04, 125.35, 125.36, 125.44, 125.84, 125.95, 129.25, 130.16,
(8). To a mixture of 1 (0.37 g, 1.34 mmol), 2-([2,20:50,200-terthio- 131.61, 136.25, 136.3, 136.7, 136.88, 142.31, 143.26, 143.83,
phen]-5-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.5 g, 1.34 145.55, 147.48, 148.6, 148.91, 149.16 ppm; HRMS (APCI): m/z:
mmol) and Pd(PPh3)4 (0.077 g, 0.067 mmol) under an argon (M + H+) calcd for C50H45N2O4S3, 833.25360; found 833.25452.
atmosphere were added aqueous 1 M Na2CO3 (1.2 mL) and DMF
4-(500-(9-Butyl-7-(diphenylamino)-9H-carbazol-2-yl)-[2,20:50,200-
ꢂ
(5 mL) and stirred for 8 h at 100 C. Aer concentrating under terthiophen]-5-yl)benzene-1,2-diol (YM-3). To compound 10
reduced pressure, the resulting residue was dissolved in (0.09 g, 0.1 mmol) were added THF (5 mL) and 1 N HCl (2 mL),
dichloromethane and washed with water. The dichloromethane and reuxed for 8 h. Aer concentrating under reduced pres-
extract was evaporated under reduced pressure. The residue was sure, the resulting residue was dissolved in ethyl acetate and
chromatographed on silica gel (ethyl acetate–hexane ¼ 1 : 1 as washed with water. The dichloromethane extract was evapo-
eluent) to give 6 (0.27 g, yield 46%) as a yellow solid; mp 110–111 rated under reduced pressure. The organic extract was
ꢂC; IR (ATR): ~n ¼ 1514, 1495 cmꢀ1; 1H NMR (400 MHz, acetone- concentrated to afford YM-3 as a greenish yellow powder in
d6) d ¼ 3.49 (s, 3H), 3.52 (s, 3H), 5.25 (s, 2H), 5.30 (s, 2H), 7.11 quantitative yield; mp 260–263 ꢂC; IR (ATR): ~n ¼ 3369, 1593,
(dd, J ¼ 3.6 and 5.2 Hz, 1H), 7.20 (d, J ¼ 8.5 Hz, 1H), 7.24–7.27 1491, 1460 cmꢀ1; 1H NMR (400 MHz, acetone-d6) d ¼ 0.88 (t, J ¼
(m, 2H), 7.28–7.35 (m, 4H), 7.45–7.47 (m, 2H) ppm; 13C NMR 7.3 Hz, 3H), 1.29–1.33 (m, 2H), 1.77–1.83 (m, 2H), 4.36 (t, J ¼ 7.0
(100 MHz, acetone-d6) d ¼ 57.08, 57.16, 96.94, 97.13, 116.41, Hz, 2H), 6.86 (d, J ¼ 8.1 Hz, 1H), 6.93 (dd, J ¼ 1.8 and 8.4 Hz,
119.49, 121.3, 125.45, 125.62, 126.06, 126.27, 126.56, 126.71, 1H), 7.03–7.07 (m, 3H), 7.11–7.15 (m, 5H), 7.23–7.35 (m, 10H),
129.83, 130.0, 136.95, 137.53, 137.58, 138.25, 144.55, 149.34, 7.53–7.55 (m, 2H), 7.85 (s, 1H), 8.04 (d, J ¼ 8.4 Hz, 1H), 8.10 (d, J
149.66 ppm; HRMS (ESI): m/z: (M
C22H20O4NaS3, 467.04159; found 467.04163.
+
Na+) calcd for ¼ 8.1 Hz, 1H); 13C NMR (100 MHz, acetone-d6) d ¼ 14.15, 20.98,
31.85, 43.01, 106.03, 106.47, 113.53, 116.75, 117.95, 118.03,
5-(3,4-Bis(methoxymethoxy)phenyl)-500-bromo-2,20:50,200-ter- 118.38, 119.4, 121.14, 121.9, 123.55, 123.58, 123.67, 124.74,
thiophene (9). A solution of 8 (0.52 g, 1.16 mmol) and N-bro- 125.03, 125.16, 125.33, 125.79, 125.86, 126.92, 130.16, 131.63,
mosuccinimide (0.21 g, 1.16 mmol) in chloroform (100 mL) was 135.31, 136.37, 136.61, 136.95, 142.32, 143.26, 144.83, 145.45,
stirred for 2 h at 0 C. To a reaction mixture dichloromethane 146.43, 146.44, 147.47, 149.16 ppm; HRMS (ESI): m/z: (M + H+)
ꢂ
was added and washed with water. The dichloromethane extract calcd for C46H37N2O2S3, 745.20117; found 745.20020.
was evaporated under reduced pressure. The residue was
Preparation of DSSCs based on dyes YM-1, YM-2 and YM-3.
chromatographed on silica gel (chloroform as eluent) to give 9 The TiO2 paste (JGC Catalysts and Chemicals Ltd., PST-18NR)
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Journal of Materials Chemistry A
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was deposited on a uorine-doped-tin-oxide (FTO) substrate by
doctor-blading, and sintered for 50 min at 450 ꢂC. The 9 mm
thick TiO2 electrode (0.5 ꢁ 0.5 cm2 in photoactive area) was
immersed into a 0.1 mM dye solution in THF for a number of
hours to adsorb the photosensitizer. The DSSCs were fabricated
Chem.–Eur. J., 2011, 17, 14837; (c) Y. Ooyama,
N. Yamaguchi, I. Imae, K. Komaguchi, J. Ohshita and
Y. Harima, Chem. Commun., 2013, 49, 2548; (d) Y. Ooyama,
Y. Hagiwara, T. Mizumo, Y. Harima and J. Ohshita, New
J. Chem., 2013, 37, 2479.
by using the TiO2 electrode thus prepared, Pt-coated glass as a 15 D. Daphnomili, G. Landrou, P. Singh, A. Thomas,
counter electrode, and a solution of 0.05 M iodine, 0.1 M
lithium iodide, and 0.6 M 1,2-dimethyl-3-propylimidazolium
K. Yesudas, B. K. G. D. Sharma and A. G. Goutsolelos, RSC
Adv., 2012, 2, 12899.
iodide in acetonitrile as the electrolyte. The photocurrent– 16 M.-D. Zhang, H.-X. Xie, X.-H. Ju, L. Qin, Q.-X. Yang,
voltage characteristics were measured using a potentiostat
under simulated solar light (AM 1.5, 100 mW cmꢀ2). IPCE
H.-G. Zheng and X.-F. Zhou, Phys. Chem. Chem. Phys.,
2013, 15, 634.
spectra were recorded under monochromatic irradiation with a 17 H. He, A. Gurung and L. Si, Chem. Commun., 2012, 48, 5910.
tungsten–halogen lamp and a monochromator. The amount of 18 (a) Y. Ooyama, Y. Shimada, Y. Kagawa, I. Imae and
adsorbed dye on TiO2 nanoparticles was determined from the
calibration curve by absorption spectral measurement of the
concentration change of the dye solution before and aer
adsorption. Absorption spectra of the dyes adsorbed on TiO2
nanoparticles were recorded on the dye-adsorbed TiO2 lm
(thickness of 9 mm) in the transmission mode with a Shimadzu
Y. Harima, Org. Biomol. Chem., 2007, 5, 2046; (b)
Y. Ooyama, Y. Shimada, Y. Kagawa, Y. Yamada, I. Imae,
K. Komaguchi and Y. Harima, Tetrahedron Lett., 2007, 48,
9167; (c) Y. Ooyama, Y. Shimada, S. Inoue, T. Nagano,
Y. Fujikawa, K. Komaguchi, I. Imae and Y. Harima, New
J. Chem., 2011, 35, 111.
¨
UV-3150 spectrophotometer equipped with a calibrated inte- 19 B. O'Regan and M. Gratzel, Nature, 1991, 353, 737.
¨
grating sphere system.
20 P. Persson, R. Bergstrom and S. Lunell, J. Phys. Chem. B,
2000, 104, 10348.
21 Y. Liu, J. I. Dadap, D. Zimdars and K. B. Eisenthal, J. Phys.
Chem. B, 1999, 103, 2480.
Acknowledgements
This work was supported by Grants-in-Aid for Scientic 22 T. Rajh, J. M. Nedeljkovic, L. X. Chen, O. Poluektov and
Research from the Japan Society for the Promotion of Science
(JSPS) (24550225) and by the Tokuyama Science Foundation.
M. C. Thurnauer, J. Phys. Chem. B, 1999, 103, 3515.
23 E. Hao, N. A. Anderson, J. B. Asbury and T. Lianl, J. Phys.
Chem. B, 2002, 106, 10191.
24 Y. Wang, K. Hang, N. A. Anderson and T. Lian, J. Phys. Chem.
B, 2003, 107, 9434.
Notes and references
¨
1 A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson, 25 (a) H. Frei, D. J. Fitzmaurice and M. Gratzel, Langmuir, 1990,
Chem. Rev., 2010, 110, 6595.
6, 198; (b) J. Moser, S. Punchihewa, P. P. Infelta and
¨
M. Gratzel, Langmuir, 1991, 7, 3012; (c) N. J. Cherepy,
2 A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran,
M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh,
¨
G. P. Smestad, M. Gratzel and J. Z. Zhang, J. Phys. Chem. B,
¨
S. M. Zakeeruddin and M. Gratzel, Science, 2011, 334, 629.
1997, 101, 9342; (d) R. Huber, S. Spcrlein, J. E. Moser,
¨
3 L.-L. Li and E. W.-G. Diau, Chem. Soc. Rev., 2013, 42, 291.
4 Z. Ning and H. Tian, Chem. Commun., 2009, 5483.
M. Gratzel and J. Wachtveitl, J. Phys. Chem. B, 2000, 104,
8995.
¨
5 A. Mishra, M. K. R. Fischer and P. Bauerle, Angew. Chem., Int. 26 (a) K. Tennakone, A. R. Kumarasinghe, G. R. R. A. Kumara,
Ed., 2009, 48, 2474.
K. G. U. Wijayantha and P. M. Sirimanne, J. Photochem.
Photobiol., A, 1997, 108, 193; (b) K. Tennakone,
G. R. R. A. Kumara, I. R. M. Kottegoda, V. P. S. Perera and
P. S. R. S. Weerasundara, J. Photochem. Photobiol., A, 1998,
117, 137; (c) P. M. Jayaweera, A. R. Kumarasinghe and
T. Tennakone, J. Photochem. Photobiol., A, 1999, 126, 111.
27 (a) Q. Dai and J. Rabani, New J. Chem., 2002, 26, 421; (b)
Q. Dai and J. Rabani, J. Photochem. Photobiol., A, 2002, 148,
17.
6 Y. Ooyama and Y. Harima, Eur. J. Org. Chem., 2009, 2903.
7 Y. Ooyama and Y. Harima, ChemPhysChem, 2012, 13, 4032.
8 A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson,
Chem. Rev., 2010, 110, 6595.
9 T. Bessho, S. M. Zakeeruddin, C.-Y. Yeh, E. W.-G. Diau and
¨
M. Gratzel, Angew. Chem., Int. Ed., 2010, 49, 6646.
10 Z. Ning, Y. Fu and H. Tian, Energy Environ. Sci., 2010, 3, 1170.
11 J. Cong, X. Yang, J. Liu, J. Zhao, Y. Hao, Y. Wang and L. Sun,
Chem. Commun., 2012, 48, 6663.
28 E. L. Tae, S. H. Lee, J. K. Lee, S. S. Yoo, E. J. Kang and
K. B. Yoon, J. Phys. Chem. B, 2005, 109, 22513.
12 (a) J. Tang, S. Qu, J. Hu, W. Wu and J. Hua, Sol. Energy, 2012,
86, 2306; (b) Y. Ooyama, Y. Hagiwara, Y. Oda, T. Mizumo, 29 S. Hao, J. Wu, Y. Huang and J. Lin, Sol. Energy, 2006, 80, 209.
Y. Harima and J. Ohshita, New J. Chem., 2013, 37, 2336.
13 J. Mao, N. He, Z. Ning, Q. Zhang, F. Guo, L. Chen, W. Wu,
J. Hua and H. Tian, Angew. Chem., Int. Ed., 2012, 51, 9873.
30 G. R. A. Kumara, S. Kaneko, M. Okuya, B. Onwona-Agyeman,
A. Konno and K. Tennakone, Sol. Energy Mater. Sol. Cells,
2006, 90, 1220.
14 (a) Y. Ooyama, S. Inoue, T. Nagano, K. Kushimoto, 31 A. S. Polo and N. Y. M. Iha, Sol. Energy Mater. Sol. Cells, 2006,
J. Ohshita, I. Imae, K. Komaguchi and Y. Harima, Angew. 90, 1936.
Chem., Int. Ed., 2011, 50, 7429; (b) Y. Ooyama, T. Nagano, 32 B.-K. An, W. Hu, P. L. Burn and P. Meredith, J. Phys. Chem. C,
S. Inoue, I. Imae, K. Komaguchi, J. Ohshita and Y. Harima,
2010, 114, 17964.
8510 | J. Mater. Chem. A, 2014, 2, 8500–8511
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
33 S. A. Agarkar, R. R. Kulkarni, V. V. Dhas, A. A. Chinchansure,
P. Hazra, S. P. Joshi and S. B. Ogale, ACS Appl. Mater.
Interfaces, 2011, 3, 2440.
34 A. K. Sarker, M. G. Kang and J.-D. Hong, Dyes Pigm., 2012, 92,
1160.
35 M. R. Narayan, Renewable Sustainable Energy Rev., 2012, 16,
208.
36 S. Li, X. Yang, D. Qu, W. Wang, Y. Wang and L. Sun, Chin.
J. Chem., 2012, 30, 2315.
D. K. Palit and H. N. Ghosh, J. Phys. Chem. B, 2009, 113,
3593; (g) S. Verma, P. Kar, A. Das, D. K. Palit and
H. N. Ghosh, Chem.–Eur. J., 2010, 16, 611; (h) S. Verma,
P. Kar, A. Das and H. N. Ghosh, Chem.–Eur. J., 2011, 17, 1561.
46 (a) W. R. Duncan, W. M. Stier and O. V. Prezhdo, J. Am. Chem.
Soc., 2005, 127, 7941; (b) W. R. Duncan, W. M. Stier and
O. V. Prezhdo, J. Phys. Chem. B, 2005, 109, 365; (c)
W. R. Duncan, C. F. Craig and O. V. Prezhdo, J. Am. Chem.
Soc., 2007, 129, 8528.
´
´
37 (a) S.-C. Li, J.-G. Wang, P. Jacobson, X.-Q. Gong, A. Selloni 47 (a) R. Sanchez-de-Armas, J. O. Lopez, M. A. San-Miguel and
and U. Dieboldi, J. Am. Chem. Soc., 2009, 131, 980; (b)
L.-M. Liu, S.-C. Li, H. Cheng, U. Diebold and A. Selloni,
J. Am. Chem. Soc., 2011, 133, 7816.
J. F. Sanz, J. Chem. Theory Comput., 2010, 6, 2856; (b)
´
R. Sanchez-de-Armas, J. Oviedo, M. A. San-Miguel and
J. F. Sanz, J. Phys. Chem. C, 2011, 115, 11293; (c)
´
R. Sanchez-de-Armas, M. A. San-Miguel, J. Oviedo,
38 (a) L. G. C. ego and V. S. Batista, J. Am. Chem. Soc., 2003, 125,
7989; (b) S. G. Abusabara, L. G. C. Rego and V. S. Batista,
J. Am. Chem. Soc., 2005, 127, 18234; (c) S. G. Abuabara,
G. W. Cady, J. B. Baxter, C. A. Schmuttenmaer,
´
A. Marquez and J. F. Sanz, Phys. Chem. Chem. Phys., 2011,
´
13, 1506; (d) R. Sanchez-de-Armas, M. A. San-Miguel,
J. Oviedo and J. F. Sanz, Comput. Theor. Chem., 2011, 975, 99.
R. H. Crabtree, G. W. Brudvig and V. S. Batsista, J. Phys. 48 N. C. Jeong, J. S. Lee, E. L. Tae, Y. J. Lee and K. B. Yoon,
Chem. C, 2007, 111, 11982; (d) L. G. C. Rego, R. de Silva, Angew. Chem., Int. Ed., 2008, 47, 10128.
J. A. Freire, R. C. Snoeberger and V. S. Batsista, J. Phys. 49 (a) Y.-L. Zao, L. Liu, W. Zhang, C.-H. Sue, Q. Li, O. S. Miljanic,
´
Chem. C, 2010, 114, 1317.
O. M. Yaghi and J. F. Stoddart, Chem.–Eur. J., 2009, 15, 13356;
(b) D. W. Lin, T. Masuda, M. B. Biskup, J. S. Nelson and
P. S. Baran, J. Org. Chem., 2011, 76, 1013.
39 W. Macyk, K. Szaciłowski, G. Stochel, M. Buchalska,
J. Kuncewicz and P. Łabuz, Coord. Chem. Rev., 2010, 254,
2687.
50 N. Steinke, M. Jahr, M. Lehmann, A. Baro, W. Frey,
ˇ
ˇ
´
¨
40 I. A. Jankovic, Z. V. Saponjic, M. I. Comor and
S. Tussetschlager, S. Sauer and S. Laschat, J. Mater. Chem.,
J. M. Nedeljkovi&cacute, J. Phys. Chem. C, 2009, 113, 12645.
2009, 19, 645.
41 H. J. Nam, B. Kim, M. J. Ko, M. Jin, J. M. Kim and D.-Y. Jung, 51 A. Venkateswararao, K. R. J. Thomas, C.-P. Lee and K.-C. Ho,
Chem.–Eur. J., 2012, 18, 14000. Tetrahedron Lett., 2013, 54, 3985.
42 T. Lana-Villarreal, A. Rodes, J. M. Perez and R. Gomez, J. Am. 52 T. Marinado, K. Nonomura, J. Nissfolk, M. K. Karlsson,
´
´
Chem. Soc., 2005, 127, 12601.
43 C. Creutz and M. H. Chou, Inorg. Chem., 2008, 47, 3509.
D. P. Hagberg, L. Sun, S. Mori and A. Hagfeldt, Langmuir,
2010, 26, 2592.
´
´
44 M. Alvaro, E. Carbonell, P. Atienzar and H. Garcıa, 53 S.-H. Lin, Y.-C. Hsu, J. T. Lin, C.-K. Lin and J.-S. Yang, J. Org.
ChemPhysChem, 2006, 7, 1996.
Chem., 2010, 75, 7877.
45 (a) G. Ramakrishna and H. N. Ghosh, J. Phys. Chem. B, 2001, 54 (a) C. Teng, X. Yang, C. Yang, S. Li, M. Cheng, A. Hagfeldt
105, 7000; (b) G. Ramakrishna, H. N. Ghosh, A. K. Singh,
D. K. Palit and J. P. Mittal, J. Phys. Chem. B, 2001, 105,
12786; (c) G. Ramakrishna, S. A. Jose, D. K. Kumar, A. Das,
and L. Sun, J. Phys. Chem. C, 2010, 114, 9101; (b) H. Tian,
I. Bora, X. Jiang, E. Gabrielsson, K. M. Karlsson,
A. Hagfeldt and L. Sun, J. Mater. Chem., 2011, 21, 12462.
D. K. Palit and H. N. Ghosh, J. Phys. Chem. B, 2005, 109, 55 M. Lu, M. Liang, H.-Y. Han, Z. Sun and S. Xue, J. Phys. Chem.
15445; (d) G. Ramakrishna, S. Verma, D. A. Jose, C, 2011, 115, 274.
D. K. Kumar, A. Das, D. K. Palit and H. N. Ghosh, J. Phys. 56 Q.-Y. Yu, J.-Y. Liao, S.-M. Zhou, Y. Shen, J.-M. Liu,
Chem. B, 2006, 110, 9012; (e) S. Verma, P. Kar, A. Das, D. B. Kuang and C.-Y. Su, J. Phys. Chem. C, 2011, 115, 22002.
D. K. Palit and H. N. Ghosh, J. Phys. Chem. B, 2008, 112, 57 A. Baheti, P. Singh, C.-P. Lee, K. R. J. Thomas and K.-C. Ho,
2918; (f) S. Kaniyankandy, S. Verma, J. A. Mondal,
J. Org. Chem., 2011, 76, 4910.
This journal is © The Royal Society of Chemistry 2014
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