Molecular engineering of starburst triarylamine donor with selenophene containing π-linker for dye-sensitized solar cells

Article abstract of DOI:10.1039/c5tc03308j

A series of new D-π-A organic photosensitizers 7a-7d featuring a novel starburst electron donor unit and uncommon selenophene containing π-linker were synthesized, characterized, and applied for fabrication of dye-sensitized solar cells (DSSCs). Dyes 11d-

Full text of DOI:10.1039/c5tc03308j

Journal of
Materials Chemistry C
View Article Online
View Journal
PAPER
Molecular engineering of starburst triarylamine
donor with selenophene containing p-linker for
dye-sensitized solar cells†
Cite this:DOI: 10.1039/c5tc03308j
a
a
a
b
cd
Po-Yu Ho, Chi-Ho Siu, Wai-Hong Yu, Panwang Zhou, Tao Chen,*
ae
d
f
b
Cheuk-Lam Ho,* Lawrence Tien Lin Lee, Ying-Hsuan Feng, Jianyong Liu,
b
f
ae
Keli Han,* Yih Hsing Lo* and Wai-Yeung Wong*
A series of new D–p–A organic photosensitizers 7a–7d featuring a novel starburst electron donor unit
and uncommon selenophene containing p-linker were synthesized, characterized, and applied for
fabrication of dye-sensitized solar cells (DSSCs). Dyes 11d–13d with thiophene or phenyl ring as the
p-linker also were synthesized for comparison. The best power conversion efficiency (PCE) of 6.67% was
ꢀ
3ꢀ
attained for 11d with a relatively high open-circuit voltage (Voc) of 0.825 V using conventional I /I
redox electrolyte in DSSCs, and this value reaches about 84% of the device based on standard dye N719
(7.91%) under the same device fabrication conditions. Electrochemical impedance spectroscopy (EIS)
and open-circuit voltage decay (OCVD) were applied to verify the findings. All the results suggest that
Received 13th October 2015,
Accepted 3rd December 2015
2
starburst electron donor design strategy can be used to minimize dye aggregation on TiO and to slow
DOI: 10.1039/c5tc03308j
down the charge recombination kinetics in DSSCs to improve the photovoltaic performance. Effects of using
www.rsc.org/MaterialsC
selenophene as the p-linker building block on the photovoltaic parameters also were explored and evaluated.
of their high power conversion efficiency (PCE) of over 11% and
long-term stability. As alternatives to metal-containing dyes,
Introduction
5
,6
In the last decade, there has been great interest in the potential a number of organic photosensitizers also have been reported
7
8,9
of dye-sensitized solar cells (DSSCs), with their high performance of recently, such as coumarin dyes, indoline dyes, and triaryl-
1
0–12
energy conversion, simple device manufacture, and low production amine dyes.
Compared with the metal-containing complexes,
1
–4
cost,
modules. Among all of the DSSC photosensitizers being devel- lower production cost, and easier preparation and purification.
oped to date, the ruthenium complexes and zinc porphyrins are It is well known that the photosensitizer has a pivotal role in
to compete with conventional inorganic photovoltaic organic dyes have advantages of higher structural design flexibility,
13–19
the most outstanding candidates for commercialization because the performance of DSSCs. To boost the performance of organic
dyes, the chemical structures have to be modified to combat
against the narrow absorption band and dye aggregation on
a
9,20
Institute of Molecular Functional Materials, Department of Chemistry,
Partner State Key Laboratory of Environmental and Biological Analysis and
Institute of Advanced Materials, Hong Kong Baptist University, Waterloo Road,
Kowloon Tong, Hong Kong, P. R. China. E-mail: clamho@hkbu.edu.hk,
rwywong@hkbu.edu.hk
TiO
2
.
To achieve this goal effectively, the structure–property
relationship must be elucidated so that structural modification
can be accomplished in the correct direction. In general, most
organic dyes are featured in a rod shaped donor–p–acceptor
(D–p–A) framework, but this configuration favors formation of
b
c
State Key Laboratory of Molecular Reaction, Dynamics Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian 116012, P. R. China.
E-mail: klhan@dicp.ac.cn
2
aggregate on the surface of nanostructured TiO and inter-
21
molecular quenching of molecules is induced. It is reported
that simple phenothiazine-based dyes with a non-planar butterfly
conformation are able to inhibit the dye aggregation and the
formation of intermolecular excimers, hence phenothiazine-based
Department of Materials Science and Engineering, University of Science and
Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, P. R. China.
E-mail: tchenmse@ustc.edu.cn
d
e
f
Department of Physics, The Chinese University of Hong Kong, Shatin,
Hong Kong, P. R. China
21–24
dyes lead to some high performance DSSC devices (PCE 4 6%).
HKBU Institute of Research and Continuing Education,
Shenzhen Virtual University Park, Shenzhen, 518057, P. R. China
Department of Applied Physics and Chemistry, University of Taipei, Taipei 100,
Taiwan. E-mail: yhlo@utaipei.edu.tw
Also, the electron-donating property attributed by the electron-
rich sulfur and nitrogen atoms in the phenothiazine ring facilitates
25
the electron delocalization from donor to acceptor. However,
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c5tc03308j these simple phenothiazine-based dyes have relatively short
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
p-conjugation length and this limits the absorption coverage of
photovoltaic cells in the long wavelength region.
On the other hand, novel dianchoring A–p–D–p–A frame-
2
6–28
works
have been fully utilized in DSSCs. The dianchoring
dyes were able to increase the electron injection efficiency and
inhibit charge recombination simultaneously, so overall per-
formances were improved compared with the single anchoring
2
9,30
congeners.
Regarding this point, a simple molecular design
with a D–p–A framework, which can inhibit charge recombina-
tion and broaden light absorption coverage effectively at the
same time, is still required for further development.
The bulky starburst electron donor is a potential solution to
resolve such difficulty in molecular design. Several groups have Fig. 2 The chemical structures of 11d–13d.
reported that starburst donor-based organic dyes can increase
open-circuit voltage (Voc) by inhibiting charge recombination
on the dye layer interface, and increase the short-circuit current
Results and discussion
Synthesis and characterization
density ( Jsc) by expanding and strengthening the light absorp-
3
1–37
tion within the solar spectrum.
In this study, seven organic
dyes were synthesized with different donor and p-linker combi- The structures of new organic photosensitizers are shown in
nations, in particular with the new starburst triarylamine donor Fig. 1 and 2. Their corresponding synthetic routes are depicted
(
Fig. 1 and 2). For the electron donor units, disubstituted in Schemes 1 and 2 and Scheme S1 (ESI†). The key intermediate
triphenylamine donor with two 9-hexylcarbazole units at the 2,5-dibromoselenophene (2) was prepared by bromination of
-position was used for comparison with some other reported selenophene (1) with N-bromosuccinimide according to a pre-
3
4
0
donor building blocks. For the p-linker, selenophene was viously published method. Subsequently, compound 2 was
selected to further extend the p-conjugation because of its high reacted with 3-hexylthiophene-2-boronic acid under palladium-
electron donating effect and its uniqueness in DSSC studies.
Dyes with thiophene or phenyl ring as p-linker also were pound 3. Then, aldehyde precursor 4 was obtained by the
synthesized for comparison. Cyanoacrylic acid acts as the Vilsmeier–Haack reaction. Bromination of 4 with N-bromo-
electron acceptor to constitute the intramolecular charge transfer succinimide under acidic conditions yielded brominated 5.
3
8
catalyzed Suzuki coupling reaction conditions to yield com-
3
9
(
ICT) absorption band and to facilitate electron injection into the The organic dye precursors 6a–6d were prepared by a Suzuki
conduction band of titanium dioxide. This electron-deficient coupling reaction of 5 with the corresponding arylboronic
moiety also corresponds with the anchoring unit on the surface acids. Finally, Knoevenagel condensation using cyanoacetic
of TiO
2
. The synthetic procedures were straightforward, and all acid was performed to prepare organic photosensitizers 7a–7d
the products were purified easily by column chromatography. with high yields of around 90%. For 11d–13d, the key inter-
The photophysical and electrochemical properties of these mediates 11b–13b were obtained by either bromination using
organic photosensitizers were studied and the corresponding N-bromosuccinimide or iodination using potassium iodide
performances of DSSCs with traditional liquid electrolyte-based and potassium iodate of 11a–13a under acidic conditions.
device structure also were investigated.
Eventually, organic photosensitizers 11d–13d were prepared
Fig. 1 The chemical structures of 7a–7d.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
Scheme 1 Synthetic routes of 7a–7d.
by a Suzuki coupling reaction of 11b–13b with (9-hexylcarbazolyl)- of 300–600 nm. The molar extinction coefficients (10 000–
ꢀ1
ꢀ1
boronic acid and subsequent Knoevenagel condensation in high 70 000 mol cm ) of these photosensitizers are comparable
1
13
yield. All the organic precursors were characterized by H and
NMR spectroscopy. The singlet peak positioned at around literature,
d 10.0 ppm refers to the proton of aldehyde on the corresponding higher molar extinction coefficients than those of standard
C
with other D–p–A starburst donor-based dyes reported in the
3
1–36,41,42
and dyes 7a–7d, 11d and 12d possess much
4
3
organic aldehyde precursors. All the target organic dyes were ruthenium dyes. The absorption bands at short wavelength
soluble in common organic solvents, such as dichloromethane, (centered at 340–362 nm) are assigned to the localized aromatic
chloroform, tetrahydrofuran and dimethyl sulfoxide, and were p–p* transitions and the low-energy broad absorption bands
characterized by matrix-assisted laser desorption ionization time- (centered at 458–511 nm) refer to the intramolecular charge
of-flight (MALDI-TOF) mass spectrometry and H NMR spectro- transfer (ICT) from electron donor to electron acceptor. It is
scopy. In their H NMR spectra, the downfield singlet peaks evidenced that the replacement of terminal donor (7a–7d) or
1
1
positioned at around d 8.5 ppm are the specific peaks of the p-linker (7d, 11d–13d) in such a framework modulates the
proton on the carbon–carbon double bond of cyanoacrylic acid. absorption profiles of organic dyes, including the localized
Complete conversion of aldehyde precursors to the target organic p–p* transitions band and especially the ICT bands. The peak
dyes could be indicated by the disappearance of the singlet peak absorption wavelengths of ICT bands are red-shifted in the
positioned at around d 10.0 ppm and the presence of a new singlet order of 13d (458 nm) o 12d (478 nm) o 11d (480 nm) o 7d
peak positioned at d 8.5 ppm.
(511 nm). This is most probably correlated with the diminish-
ing electron donating strength of p-linkers in the order of
Photophysical properties
0
0
2
,5-bis(4-hexylthiophen-2-yl)selenophene 4 3,4 -dihexyl-2,2 -
The UV/Vis absorption spectra of all the organic photosensitizers bithiophene 4 3-hexylthiophene 4 phenyl ring. Importantly,
in CH Cl solution are depicted in Fig. 3, and the corresponding the adoption of starburst donor units in 7b–7d (with smaller
2
2
data are summarized in Table 1. All these organic dyes possess optical band gap values) allows us to broaden the absorption
two main structureless broad absorption bands in the range coverage and to enhance the absorption intensity compared
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
Scheme 2 Synthetic routes of 11d–13d.
Table 1 UV/Vis absorption data of 7a–7d and 11d–13d in CH
2
Cl
2
at 293 K
4
ꢀ1
ꢀ1
a
Dye
l
max (e/10 M cm )/nm
E
g,opt /eV
7
7
7
7
1
1
1
a
b
c
d
1d
2d
3d
352 (1.23)
344 (5.62)
362 (2.45)
345 (6.24)
346 (5.38)
341 (5.11)
340 (3.55)
507 (3.64)
510 (5.12)
503 (6.79)
511 (4.05)
480 (2.30)
478 (1.84)
458 (1.11)
2.10
2.07
2.09
2.04
2.15
2.16
2.26
a
Optical band gap was determined from the onset of absorption in
Cl
CH
2
2
.
the values and hence to examine the energy offsets of the dye
molecules between the semiconducting TiO film and the redox
2
electrolytes (Fig. S8 and S9, ESI†). If the conduction band edge
of TiO was significantly more negative than the energy level of
2
Fig. 3 UV/Vis absorption spectra of 7a–7d and 11d–13d in CH
2
Cl
2
at LUMO of the photosensitizers, this would favor the electron
injection process because of the larger driving force for charge
separation. If the redox potential of redox shuttle (iodide/triiodide
ions) in the electrolyte was considerably more positive than
the HOMO energy level of the dye, efficient dye regeneration
would occur. Both of these processes are necessary to afford charge
separation at the interface for energy conversion. CV was per-
formed with the corresponding photosensitizer films on the glassy
2
93 K.
with the non-starburst donor organic dye 7a bearing alkylated
carbazole.
Electrochemical properties
To identify high performance photosensitizers for DSSCs, the carbon electrode, platinum wire as the counter electrode, and
+
optimal energy levels of the highest occupied molecular orbital Ag/Ag as the reference electrode in acetonitrile containing 0.1 M
(
HOMO) and the lowest unoccupied molecular orbital (LUMO) tetrabutylammonium hexafluorophosphate at a scan rate of
ꢀ
1
must be attained. Cyclic voltammetry (CV) was used to calculate 100 mV s . The results of these organic dyes are shown in Table 2.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
Table 2 Electrochemical data and energy levels of 7a–7d and 11d–13d
ꢀ2.73 eV, respectively (Table S2, ESI†). The decrease in energy
level of LUMO for 7d can be attributed to the more extended
delocalization of electrons for the selenophene moiety in the
LUMO of 7d compared with 11d.
onset
a
onset
b
c
Dye
E
Ox (V) HOMO (eV)
E
Red (V) LUMO (eV)
Eg,ec (eV)
7
7
7
7
1
1
1
a
b
c
0.55
0.52
0.52
0.44
ꢀ5.28
ꢀ5.25
ꢀ5.25
ꢀ5.17
ꢀ5.16
ꢀ5.24
ꢀ5.20
ꢀ1.26
ꢀ1.25
ꢀ1.27
ꢀ1.27
ꢀ1.33
ꢀ1.28
ꢀ1.34
ꢀ3.47
ꢀ3.48
ꢀ3.46
ꢀ3.46
ꢀ3.40
ꢀ3.45
ꢀ3.39
1.81
1.77
1.79
1.71
1.76
1.79
1.81
d
Photovoltaic performance
1d 0.43
2d 0.51
3d 0.47
2
All the DSSCs with an effective area of 0.126 cm were prepared
according to conventional procedures, as described in the
a
c
onset
b
onset
Calculated from ꢀ(EOx + 4.73). Calculated from ꢀ(ERed + 4.73). Experimental section, and tested under standard conditions
Electrochemical band gap was obtained from the energy difference
ꢀ2
(
AM 1.5G, 100 mW cm ). The DSSCs were fabricated by
anchoring our new organic dyes and reference dye N719
accordingly onto nanocrystalline anatase TiO as the photo-
between HOMO and LUMO levels.
2
The first observed oxidation is ascribed to removal of an anode and the liquid electrolyte consisting of 0.1 M LiI, 0.6 M
electron from the electron-rich units in the molecule, and the 1,2-dimethyl-3-propylimidazolium iodide (DMPII), 0.05 M I in
2
reduction wave observed is an indication of electron gain to a mixture of acetonitrile and 4-tert-butylpyridine (volume ratio,
the electron-deficient moiety. The LUMO energy levels of all the 1 : 1). Their basic device performance parameters, such as PCE,
organic dyes (ranging from ꢀ3.39 to ꢀ3.48 eV) are more V , short-circuit current density ( J ), and fill factor (FF) are
oc
sc
positive than that of the energy level of the conduction band depicted in Table 3. Fig. 4 and 5 display the photocurrent
edge of titanium dioxide (ꢀ4.4 eV), thus ensuring a prompt density–voltage curves ( J–V curves) and incident-photon-to-
4
4
electron injection process. On the other hand, the redox current conversion efficiency (IPCE) spectra, respectively.
ꢀ
2
potential of iodide/triiodide ions (ꢀ4.95 eV) is more positive
The highest PCE of 6.67% ( Jsc = 11.22 mA cm , Voc = 0.825 V,
than the HOMO energy levels of all the organic dyes (ranging FF = 0.721) was obtained with dye 11d, attaining 84% of
from ꢀ5.28 to ꢀ5.16 eV), thereby facilitating efficient reduction the reference ruthenium dye N719-based cell (PCE = 7.91%)
4
5
of the oxidized dye. It was found that the electrochemical measured under the same conditions. The PCEs of DSSCs based
band gaps of 7a–7d and 11d–13d obtained in the film state on other organic dyes are in the range of 3.04–6.60%. The J , V ,
sc oc
ꢀ
2
conform to the trends of optical band gaps (7a 4 7c 4 7b 4 7d and FF values are in the range of 5.60–13.77 mA cm , 0.660–
and 13d 4 12d 4 11d 4 7d) obtained from their absorption 0.825 V, and 0.703–0.751, respectively. Impressively, the Voc of
spectra. This further confirms that replacement of terminal 11d exceeds the value of N719 (Voc = 0.701 V) by 0.124 V and this
donor and p-linker in the D–p–A framework controls the Voc value is remarkably high among the iodide/triiodide redox
3
9
magnitude of the HOMO–LUMO gap.
couple-based DSSCs. Notably, the Voc values of all starburst
donor-based dyes are higher than that of the non-starburst
donor-based dye 7a, and this implies that such starburst donor
molecular design can effectively improve the photovoltaic perfor-
Computational studies
The ground state geometries of all the dyes were optimized
using the DFT method (Fig. S1–S7, ESI†). From the results,
we observed that the triarylamine moiety in starburst shaped
dyes 7b, 7d, 11d–13d has a propeller geometry and the cyano-
acrylic acid is coplanar with the thienyl moiety or phenyl unit.
On the other hand, the electrons in the HOMO levels of the
compounds are distributed over the electron-donating moiety,
that is the triarylamine and/or carbazole fragment. Conversely,
the LUMO levels of the compounds showed that electrons are
distributed over the cyanoacrylic acid moiety of the dyes. Thus,
we anticipated that efficient photoinduced charge separation
and relatively stronger anchoring power would enhance the
mance of D–p–A dyes by elevating the V . Moreover, 7a–7d with
selenophene as the elongated p-linker unit present higher Jsc
values than do 11d–13d, implying that uncommon selenophene
oc
may be a useful p-linker building block to augment the Jsc
.
Meanwhile, the action response range of IPCE spectra among
the seven new organic photosensitizers is around 310–700 nm
and the IPCE curves conform well to the absorption profiles of
organic dyes after taking the common J-aggregate formation of
4
6
organic dyes into consideration. The IPCE values exceed 50%
from 400 to 550 nm for all the organic dyes, except for 13d. In
addition, the maximum IPCE value attained by 12d is larger than
degree of electron injection to the TiO
2
electrode. Furthermore,
we found that a p-conjugated linker, such as 2,5-bis(4-hexyl- Table 3 Photovoltaic performance of DSSCs with different photosensitizers
0
0
thiophen-2-yl)selenophene, 3,4 -dihexyl-2,2 -bithiophene, 3-hexyl- (7a–7d, 11d–13d and N719) under AM 1.5G sunlight illumination
thiophene and phenyl ring, as well as cyanoacrylic acid moieties,
are involved in the frontier molecular orbitals. It was also shown
that the energy levels of the LUMOs of the compounds are
dependent on the nature of the p-conjugated linker in the
compounds, whereas the energy levels of the HOMOs are not 7d
affected significantly by the identities of the p-conjugated
ꢀ2
Dye
J
sc (mA cm
)
V
oc (V)
FF
PCE (%)
7
7
7
a
b
c
13.77
12.89
13.13
13.21
11.22
10.66
5.60
0.660
0.701
0.692
0.706
0.825
0.824
0.770
0.701
0.706
0.705
0.724
0.703
0.721
0.751
0.704
0.713
6.41
6.37
6.57
6.53
6.67
6.60
3.04
7.91
1
1
1
1d
2d
3d
linker which are consistent with the CV results. For example,
the energy levels of the LUMO of 7d and 11d are ꢀ2.83 eV and N719
15.83
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
dyes (7b–7d and 11d–13d) are higher than that of the non-
starburst donor-based dye 7a, and this is ascribed to the
following. Firstly, the prolongation of rod-like D–p–A molecules
in 7a may facilitate the charge recombination of electrons to
ꢀ
I3 with the formation of dye-aggregates, thus reducing the
3
4,48,49
V
oc
.
Secondly, charge recombination may also occur
between electrolyte and the semiconducting TiO photoanode,
thus reducing the theoretical potential difference between the
2
5
0
electrolyte and TiO
2
.
To suppress these two unfavorable
processes, starburst structural design of donor was used to
prevent the p-stacked aggregation and to form a compact
ꢀ
ꢀ
hydrophobic layer between the hydrophilic I /I redox electrolyte
3
and the surface of TiO , which can block the backward electron
2
transfer for maintaining a high Voc value.
To assess the interfacial charge recombination process in
DSSCs, electrochemical impedance spectroscopy (EIS) was used
under dark conditions for 7a–7d and 11d–13d, with the corres-
ponding data shown in Table 4, and Fig. 6 and 7. In the EIS
Nyquist plot, seven semicircles for 7a–7d and 11d–13d were
recorded. This plot reveals the resistance of electron recombina-
tion (Rrec) at the interfaces between the redox couples/sensitizers/
Fig. 4 Photocurrent density–voltage (J–V) plots obtained with 7a–7d,
1
1d–13d, and N719.
51
TiO
rec will be calculated from the Nyquist plot, and this implies that
the recombination kinetics is faster. The Rrec values of 7b–7d and
1d–13d, which consist of starburst donor, are larger than that of
2
. If the radius of the semicircle is shorter, a smaller value of
R
1
non-starburst donor-based 7a, thereby suggesting that 7a suffers
from more serious charge recombination while 11d is most potent
to restrain the charge recombination. Simultaneously, these
results match the trend of their Voc values, and disubstituted
triphenylamine linked with two 9-hexylcarbazole units at the
3
-position as a novel starburst donor is potent to weaken the
dye aggregation on TiO and also the interaction between liquid
) and TiO in these D–p–A photosensitizers.
2
ꢀ
ꢀ
electrolyte (I /I
3
2
In addition to the EIS Nyquist plot, an EIS Bode plot
was used to extract the angular frequency (orec) at the mid-
frequency peak using the equation below, in which fmax
correlates to the peak frequency.
Fig. 5 Incident photon-to-current efficiency (IPCE) curves obtained with
a–7d, 11d–13d, and N719.
7
1
1
6
5% at 475 nm, but the corresponding IPCE curve rolls off
te ¼
¼
orec
2pfmax
sharply from 600 to 650 nm. And this explains the low Jsc value
attained compared with 7a–7d and 11d, which have more intense
action responses within 600–700 nm in the long wavelength
region. In other words, this accounts for the higher Jsc values
attained by 7a–7d.
From the equation, the electron lifetimes (t ) of DSSCs can
be estimated. The t estimation reflects the charge recombi-
nation rate at the interface of DSSCs.
values of dyes 7a–7d with selenophene as part of the p-linker
e
4
2
e
5
2,53
Interestingly, the
t
e
This result indicates that broadening the light harvesting
region by elongating p-conjugation length and placing p-linkers
with increasing electron donating power (phenyl ring o 3-hexyl- Table 4 Parameters obtained by fitting the EIS spectra of the DSSCs with
0
0
thiophene o 3,4 -dihexyl-2,2 -bithiophene o 2,5-bis(4-hexyl- dyes 7a–7d, 11d–13d and N719
thiophen-2-yl)selenophene) is an effective way to increase the
sc in the order 13d o 12d o 11d o 7d. This is in agreement
with most traditional D–p–A organic photosensitizers found
ꢀ1
Dye
R
rec (O cm
)
f
max (Hz)
t
e
(ms)
J
7
7
7
a
b
c
126.6
218.6
270.3
191.2
3270.5
3181.9
1790.7
93.5
39.36
26.80
16.43
19.37
1.48
4.0
5.9
9.7
8.2
4
7
in the literature. On the other hand, it is reasonable to expect
that the Jsc values of 7a–7d vary much less because of their 7d
1
1
1
1d
2d
3d
107.5
103.3
64.2
very similar absorption properties. Besides, the Voc values
measured in these dyes are highly dependent on the selection
1.54
2.48
4.54
of terminal donor. The Voc values of all starburst donor-based N719
35.1
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
Fig. 6 EIS Nyquist plots for DSSCs based on 7a–7d, 11d–13d, and N719
under darkness.
Fig. 8 Open-circuit voltage decay profiles of DSSCs based on 7a–7d,
1
1d–13d, and N719.
To further analyze the kinetics of charge recombination of
DSSC devices, open-circuit voltage decay (OCVD) was used to
illustrate the electron lifetime (t ), which is estimated from the
OCVD curve from a steady state to equilibrium in darkness.
n
5
5
The OCVD profiles of 7a–7d and 11d–13d are depicted in Fig. 8.
The equation shown below interprets the relationship between
tn and OCVD curves, where e, T, and kB denote the electron
5
6
charge, temperature, and Boltzmann constant, respectively.
ꢀ
ꢁꢀ
1
kBT dVoc
tn ¼ ꢀ
e
dt
The slope of the decay curve in the OCVD plot correlates the
tn value, and the less steep curve suggests the longer electron
lifetime accordingly. It is obvious that the curves of 7d and
Fig. 7 EIS Bode plots for DSSCs based on 7a–7d, 11d–13d, and N719
under darkness.
11d–13d with disubstituted triphenylamine linked with two
9-hexylcarbazole units at the 3-position as starburst donor are
less steep than those of 7a–7c and N719. This provides a strong
evidence to support the interfacial charge recombination
improvement by the novel starburst donor structure, thus
prolonging the electron lifetime (t ) and elevating the V value
in each of the organic photosensitizers. Again, weakening the
dye aggregation and formation of the protective, compact and
hydrophobic layer between hydrophilic redox couples and the
are much smaller than those of 11d–13d without selenophene
in their structures. Furthermore, the Rrec values of 11d–13d
are larger than those of 7a–7d by one order of magnitude and
this doubly confirms that selenophene plays a pivotal role in
determining the photovoltage by varying the charge recombi-
nation kinetics. This phenomenon indicates that the presence
of selenophene drives the decline of Voc regardless of the
structure of the terminal donor, hence some unknown inter-
actions induced by selenophene are expected to occur so as to
enhance the charge recombination process and hence lower the
n
oc
2
TiO photoanode using starburst donor molecular design might
best explain such variation in the photovoltaic performance.
Conclusions
V
oc. Recently, a similar result was reported using selenophene-
containing Ru complex photosensitizer, and the corresponding A series of new D–p–A organic photosensitizers based on
findings were ascribed to adduct formation between oxidized starburst triarylamine donor and selenophene-containing
5
4
iodide(s) and the selenophene moiety in the photosensitizer.
p-linker were designed and synthesized, with investigations
Spectroscopic studies identified that a 4-fold-larger and made of the effects of combinations of new or reported electron
second-order rate constant measured for the reaction between donors and p-linkers. All the photosensitizers were fully charac-
ꢀ
triiodide ions and TiO
2
(e ) accounted for this phenomenon, terized by spectroscopic studies. The PCEs of these organic
as compared with the use of thiophene as the p-conjugated dyes ranged from 3.04% to 6.67% under standard conditions
ꢀ
2
linker.
(AM 1.5G, 100 mV cm ). The best performance of the device is
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
6
0,61
achieved using the dye 11d with a novel starburst donor continuum
(PCM) model. Frequency calculations were then
structure, with PCE value attaining 84% of that of N719-based performed to confirm that each optimized structure was the
DSSC (7.91%) fabricated under the same conditions. The real minimum without imaginary vibration frequency. The
corresponding Voc achieved for 11d is 0.825 V and this is greater time-dependent DFT (TD-DFT) method was used to calculate
than that of N719 (0.710 V) by 0.124 V. All the photovoltaic vertically excited singlet-state energies. The 6-31G(d) basis set
performances were verified using IPCE curves, EIS, and OCVD was adopted. The absorption profiles were calculated using the
6
2
studies. The influences towards DSSCs driven by selenophene Multiwfn program as a sum of Gaussian-shaped bands with
as a p-linker unit were explored and evaluated. It is evident that the full width at half maximum (FWHM) equal to 0.667 eV.
the selection of starburst donor is essential to modulate both
Fabrication and characterization of DSSCs
light harnessing ability and the charge recombination process
at the interfaces, thus accounting for a clear improvement in All the anode films for the DSSCs were made using the same
device performance. Although the device performance obtained standard manner, and were composed of a 12 mm-thick trans-
is not as high as that of standard ruthenium complex photo- parent layer (TiO2 with diameter of 20 nm) and 6 mm-thick
sensitizer, elucidation of the structure–property relationship is scattering layer (TiO
worthwhile for future improvements towards better organic The doctor-blade technique was used to prepare photoanode
photosensitizers, particularly in the design of organic dyes with (TiO ) films. First, a layer of B6 mm TiO paste (20 nm) was
2
nanoparticles with a diameter of 200 nm).
2
2
high Voc. Synthesis of new starburst donor-based organic dyes doctor-bladed onto the FTO conducting glass and then relaxed
with broader light harvesting regions, and their DSSC fabrication, at room temperature for 3 min before heating at 150 1C for
is now ongoing in our group.
6 min; this procedure was repeated once to achieve a film
thickness of B12 mm and the resulting surface was finally
coated by a scattering layer (B6 mm) of TiO paste (200 nm).
2
Experimental
Materials and reagents
The electrodes were gradually heated under an air flow at
2
4
75 1C for 5 min, 325 1C for 5 min, 375 1C for 5 min, and
70 1C for 30 min to remove polymers and generate a three-
2
All reactions were performed under an inert N atmosphere
dimensional TiO
films were soaked with 0.02 M TiF
at 70 1C, washed with deionized water, and further annealed at
2
nanoparticle network. After that, the sintered
with the use of a Schlenk line. Glassware was dried in an oven
prior to use. Commercially available reagents were used without
purification unless otherwise stated. All the reagents for chemical
synthesis were purchased from Acros Organics, Sigma-Aldrich,
and Tokyo Chemical Industry Co., Ltd (TCI). Solvents were
purified by distillation over suitable drying agents. All the
reactions were monitored by thin-layer chromatography (TLC)
with Merck pre-coated aluminum plates. Products were purified
and separated by column chromatography with silica gel
4
aqueous solution for 45 min
4
50 1C for 30 min. After cooling down to B80 1C, the electrodes
ꢀ4
were immersed into a 5 ꢁ 10 M dye bath in acetonitrile/
tert-butyl alcohol (volume ratio, 1 : 1) for the dyes 7a–7d,
11d–13d and maintained in the dark for 12 h. Afterwards,
the electrodes were rinsed with ethanol to remove the non-
adsorbed dyes and dried in the air. Pt counter electrodes were
prepared by the sputtering method at 15 mA for 90 s at a power
of 150 W. Two holes (0.75 mm in diameter) were predrilled in
the FTO glass for introducing the electrolyte. The dye-adsorbed
(230–400 mesh) purchased from Merck.
Instrumentation
Proton and carbon NMR spectra were measured in CDCl or
TiO electrode and Pt-counter electrode were assembled into a
2
3
sandwich type cell and sealed with a hot-melt parafilm at about
6
DMSO-d on a Bruker Ultra-shield 400 MHz FT-NMR spectro-
1
00 1C. Liquid electrolyte consisting of 0.6 M 1,2-dimethyl-3-
propylimidazolium iodide (DMPII), 0.1 M LiI, 0.05 M I in a
mixture of acetonitrile and 4-tert-butylpyridine (volume ratio,
: 1) was introduced into the cell through the drilled holes at
meter, and tetramethylsilane (TMS) was used as an internal
standard for calibrating the chemical shift. Matrix-assisted
laser desorption ionization time-of-flight (MALDI-TOF) mass
spectra were performed on an Autoflex Bruker MALDI-TOF
system. Electrochemical measurements were conducted using
a Potentiostat/Galvanostat/EIS Analyzer model Parstat 4000 at a
scan rate of 100 mV s . UV/Vis absorption spectra were
performed on a Hewlett Packard 8453 spectrometer in CH
solution at 293 K.
2
1
the back of the counter electrode. The holes were sealed by
parafilm and covering glass (0.1 mm thickness) at elevated
temperature. The effective areas of all the TiO electrodes were
2
ꢀ
1
2
B0.126 cm . The current density–voltage ( J–V) characteristics
2 2
Cl
of the assembled DSSCs were measured using a semiconductor
characterization system (Keithley 236) at room temperature in
air under the spectral output from solar simulator (Newport)
Computational details
ꢀ2
using an AM 1.5G filter with a light power of 100 mW cm
.
All the calculations in this work were carried out using the IPCEs of DSSCs were recorded in the Solar Cell QE/IPCE
5
7
Gaussian 09 package. The ground state geometries of all the Measurement System (Zolix Solar Cell Scan 100) using dc mode.
dyes in dichloromethane (e = 8.93) were optimized using A CHI 660D electrochemical workstation was used to characterize
the density functional theory (DFT) method with hybrid func- the electrochemical properties of the DSSCs. Electrochemical
tional PBE0, and the solvation effects were included using the impedance spectroscopy (EIS) was recorded under dark condi-
5
8,59
5
integral equation formalism
(IEF) version of the polarizable tions over a frequency range of 0.1–10 Hz with an ac amplitude
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
of 10 mV, and the parameters were calculated from Z-View The organic extract was dried over anhydrous Na
2
4
SO and the
software (v2.1b, Scribner Associates, Inc.). For the open-circuit solvent was removed under reduced pressure to yield an orange
voltage decay (OCVD) measurements, the cell was first illuminated oil, which was purified by column chromatography on silica gel
for 20 s to achieve a steady voltage, and then the illumination was with hexane/CH Cl (1 : 1 v/v) as the eluent to give 5 as an
2
2
1
turned off for 90 s and the OCVD curve was obtained.
orange solid (0.627 g, 1.099 mmol). H NMR (400 MHz, CDCl ):
3
d = 9.98 (s, 1H, CHO), 7.38 (d, 1H, J = 4 Hz, Ar), 7.17 (d, 1H,
J = 4 Hz, Ar), 6.97 (s, 1H, Ar), 6.84 (s, 1H, Ar), 2.91 (t, 2H, J =
7.6 Hz, alkyl), 2.54 (t, 2H, J = 7.6 Hz, alkyl), 1.71–1.65 (m, 2H,
Synthetic procedures
4
0
2,5-Bis(3-hexylthiophenyl)selenophene (3). A mixture of 2
(
9
1.207 g, 4.179 mmol), 3-hexylthiophenyl-2-boronic acid (1.95 g, alkyl), 1.62–1.55 (m, 2H, alkyl), 1.40–1.30 (m, 12H, alkyl), 0.91–
.194 mmol), Pd(PPh ) (241 mg, 0.209 mmol) and 2 M aqueous 0.88 ppm (m, 6H, alkyl); C NMR (100 MHz, CDCl ): d = 181.55
3 4 3
1
3
solution of K CO (5 mL) in THF (40 mL) was heated to reflux (CHO), 153.94, 147.67, 143.34, 143.31, 139.58, 138.18, 136.02,
2
3
under a N atmosphere overnight. The reaction mixture was 128.98, 127.06, 126.52, 125.71, 109.10 (Ar), 31.61, 31.57, 31.38,
2
poured into water, followed by extraction using ethyl acetate. 29.64, 29.59, 29.00, 28.91, 28.57, 22.61, 22.56, 14.12, 14.08 ppm
The organic layer was dried over anhydrous Na SO and the (alkyl).
2 4
solvent was then removed under reduced pressure. The residue
was purified by column chromatography on silica gel using a
General synthetic procedures of 6a–6d
1
: 10 mixture of CH
2 2
Cl and hexane as eluent to afford com- A mixture of 5 (60 mg, 0.105 mmol), and each of the corres-
1
pound 3 (0.62 g, 1.337 mmol) as a pale yellow solid. H NMR ponding aromatic boronic acid (0.126 mmol), Pd(PPh
3
)
4
(6 mg,
(
400 MHz, CDCl ): d = 7.17 (s, 2H, Ar), 6.94 (s, 2H, Ar), 6.79 0.005 mmol), and 2 M aqueous solution of K CO (1 mL) in
3
2
3
(
1
s, 2H, Ar), 2.57 (t, 4H, J = 7.6 Hz, alkyl), 1.66–1.58 (m, 4H, alkyl), THF (20 mL) was heated to reflux under a N2 atmosphere
1
3
.37–1.32 (m, 12H, alkyl), 0.91–0.88 (t, 6H, J = 6.8 Hz, alkyl);
): d = 144.20, 141.17, 139.04, 126.00, by extraction using ethyl acetate. The organic layer was dried
25.62, 119.28 (Ar), 31.69, 30.53, 30.37, 29.01, 22.64, 14.14 ppm over anhydrous Na SO . Then, the solvent was removed under
alkyl). reduced pressure and the residue was purified by column
-Hexyl-5-(5-(3-hexylthiophen-2-yl)selenophenyl)thiophene- chromatography on silica gel using a 2: 1 mixture of CH Cl
C
overnight. The reaction mixture was poured into water, followed
NMR (100 MHz, CDCl
1
(
3
2
4
3
2
2
2
-carbaldehyde (4). The Vilsemier Haack reagent was first and hexane as eluent to yield 6a–6d as an orange red oil.
1
prepared in a two-necked round-bottom flask containing dry
Compound 6a. 72 mg (89% yield). H NMR (400 MHz,
DMF (0.489 g, 6.685 mmol). POCl (0.246 g, 1.604 mmol) was CDCl ): d = 10.01 (s, 1H, CHO), 8.19 (s, 1H, Ar), 8.14 (d, 1H,
3
3
added dropwise by syringe at 0 1C. A solution of 3 (0.62 g, J = 8 Hz, Ar), 7.58–7.51 (m, 2H, Ar), 7.47–7.43 (m, 3H, Ar), 7.31–
.337 mmol) in dry CH Cl (20 mL) was added dropwise to the 7.27 (m, 2H, Ar), 7.12 (s, 1H, Ar), 7.00 (s, 1H, Ar), 4.34 (t, 2H,
prepared Vilsmeier–Haack reagent under a N atmosphere. J = 7.2 Hz, alkyl), 2.94 (t, 2H, J = 7.6 Hz, alkyl), 2.73 (t, 2H, J =
The mixture was stirred for 15 minutes at 0 1C and then heated 8 Hz, alkyl), 1.96–1.89 (m, 2H, alkyl), 1.76–1.69 (m, 4H, alkyl),
1
2
2
2
1
3
overnight at 70 1C. After cooling, the reaction was poured into 1.44–1.30 (m, 22H, alkyl), 0.96–0.88 ppm (m, 9H, alkyl);
NaOH(aq) solution slowly in an ice bath with stirring for NMR (100 MHz, CDCl ): d = 180.39 (CHO), 152.94, 147.10,
0 minutes, then the resulting mixture was extracted with 143.74, 139.81, 138.86, 138.70, 138.17, 137.50, 134.93, 134.60,
CH Cl and H O. The organic fraction was dried over anhydrous 128.13, 126.47, 125.95, 125.70, 124.98, 124.77, 123.47, 121.96,
C
3
3
2
2
2
Na SO . The solvent was then removed under reduced pressure 121.61, 119.99, 119.40, 118.05 (Ar), 42.19, 30.76, 30.61, 30.53,
2
4
and an orange oil was obtained, which was purified by column 30.32, 29.96, 28.35, 28.17, 28.16, 27.97, 27.78, 27.51, 26.30,
chromatography on silica gel with hexane/CH Cl (1: 1 v/v) as the 21.58, 25.53, 13.05 ppm (alkyl).
eluent to give 4 as an orange solid (0.597 g, 1.214 mmol). H NMR
400 MHz, CDCl ): d = 10.00 (s, 1H, CHO), 7.42 (d, 1H, J = 4 Hz, CDCl
Ar), 7.25 (d, 1H, J = 4 Hz, Ar), 7.02 (s, 1H, Ar), 6.99 (s, 1H, Ar), 6.88 (d, 1H, J = 4 Hz, Ar), 7.32–7.30 (m, 2H, Ar), 7.21–7.18 (m, 5H,
s, 1H, Ar), 2.94 (t, 2H, J = 7.6 Hz, alkyl), 2.60 (t, 2H, J = 7.6 Hz, Ar), 7.16–7.14 (m, 2H, Ar), 7.02 (s, 1H, Ar), 6.97–6.93 (m, 5H, Ar),
alkyl), 1.75–1.61 (m, 4H, alkyl), 1.39–1.34 (m, 12H, alkyl), 0.93– 3.98 (t, 4H, J = 6.4 Hz, alkyl), 2.90 (t, 2H, J = 7.6 Hz, alkyl), 2.65
2
2
1
1
Compound 6b. 87 mg (76% yield). H NMR (400 MHz,
): d = 9.97 (s, 1H, CHO), 7.52–7.46 (m, 8H, Ar), 7.39
(
3
3
(
1
3
0
.90 ppm (m, 6H, alkyl); C NMR (100 MHz, CDCl ): d = 181.55 (t, 2H, J = 8 Hz, alkyl), 1.83–1.76 (m, 4H, alkyl), 1.72–1.60
3
(
1
CHO), 153.99, 148.01, 144.61, 144.47, 139.06, 138.42, 135.79, (m, 4H, alkyl), 1.49–1.26 (m, 24H, alkyl), 0.93–0.86 ppm
1
3
29.05, 126.90, 126.39, 126.24, 120.29 (Ar), 31.67, 31.57, 31.39, (m, 12H, alkyl); C NMR (100 MHz, CDCl
3
): d = 181.47
30.48, 30.37, 29.01, 28.99, 28.57, 22.63, 22.56, 14.13, 14.09 ppm (CHO), 158.55, 153.99, 148.08, 147.23, 146.00, 144.57, 139.41,
(alkyl).
138.77, 138.34, 136.03, 135.82, 135.74, 132.90, 129.79, 129.17,
5-(5-(5-Bromo-4-hexylthiophen-2-yl)selenophen-2-yl)-3-hexyl- 127.71, 127.51, 126.83, 126.00, 124.95, 123.02, 114.83 (Ar),
thiophene-2-carbaldehyde (5). NBS (0.214 g, 1.2 mmol) was 68.12, 31.67, 31.65, 31.59, 31.39, 30.94, 29.32, 29.23, 29.03,
slowly added to a solution of 4 (0.562 g, 1.143 mmol) in a 28.93, 28.59, 25.79, 22.66, 22.65, 22.59, 14.16, 14.10 ppm (alkyl).
1
mixture of CHCl (10 mL) and acetic acid (10 mL) at 0 1C under
Compound 6c. 40 mg (42% yield). H NMR (400 MHz,
3
3
darkness. After the mixture was stirred at room temperature CDCl ): d = 9.90 (s, 1H, CHO), 8.17 (d, 1H, J = 1.6 Hz, Ar), 8.1
overnight, the reaction was terminated by the addition of water. (d, 1H, J = 1.2 Hz, Ar), 7.62–7.60 (m, 1H, Ar), 7.55–7.53 (m, 2H,
The reaction mixture was then extracted with CH
2
Cl
2
and water. Ar), 7.46 (dd, 1H, J = 8.4, 2 Hz, Ar), 7.38–7.32 (m, 3H, Ar), 7.17
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
1
(d, 1H, J = 4 Hz, Ar), 7.01 (s, 1H, Ar), 6.94–6.92 (m, 2H, Ar), 6.89
3
H NMR (400 MHz, CDCl ): d = 9.82 (s, 1H, CHO), 7.57 (s, 1H, Ar),
(s, 1H, Ar), 4.23 (t, 2H, J = 7.2 Hz, alkyl), 3.94 (t, 2H, J = 6.4 Hz, 6.96 (s, 1H, alkyl), 2.74 (t, 2H, J = 7.6 Hz, alkyl), 2.57 (t, 2H, J =
alkyl), 2.83 (t, 2H, J = 7.6 Hz, alkyl), 2.63 (t, 2H, J = 8 Hz, alkyl), 7.6 Hz, alkyl), 1.69–1.56 (m, 4H, alkyl), 1.40–1.31 (m, 12H, alkyl),
1
3
1
(
(
1
1
1
1
3
2
.84–1.70 (m, 4H, alkyl), 1.65–1.56 (m, 4H, alkyl), 1.43–1.15 0.91–0.88 ppm (m, 6H, alkyl); C NMR (100 MHz, CDCl ): d =
3
1
3
m, 28H, alkyl), 0.86–0.74 ppm (m, 12H, alkyl); C NMR 182.62 (CHO), 142.99, 140.55, 140.42, 138.87, 134.33, 128.31,
100 MHz, CDCl ): d = 181.50 (CHO), 158.24,154.03, 148.19, 111.24 (Ar), 31.59, 30.30, 29.61, 29.49, 29.26, 29.11, 28.88, 22.59,
44.82, 140.36, 140.02, 139.75, 139.25, 138.57, 136.00, 135.67, 14.10, 14.07 ppm (alkyl).
3
34.40, 132.48, 129.21, 128.20, 127.56, 127.11, 126.89, 126.79,
26.38, 125.85, 125.35, 124.61, 123.20, 123.18, 121.10, 118.44,
General synthetic procedures of 11a–13a
14.87, 109.11, 108.84 (Ar), 68.16, 43.39, 31.84, 31.66, 31.60, A mixture of 10 (400 mg, 0.906 mmol) or 8 (400 mg, 1.453 mmol)
1.39, 31.02, 29.42, 29.35, 29.22, 29.10, 29.04, 28.88, 28.59, or 4-bromobenzaldehyde (600 mg, 3.243 mmol), (4-(diphenyl-
amino)phenyl)boronic acid (1.5 molar equivalents), Pd(PPh3)4
Compound 6d. 119 mg (92% yield). H NMR (400 MHz, (112 mg, 0.097 mmol), and 2 M aqueous solution of K CO3
7.38, 25.81, 22.67, 22.65, 22.59, 14.11 ppm (alkyl).
1
2
CDCl
(
(
3
): d = 10.01 (s, 1H, CHO), 8.36 (d, 2H, J = 1.6 Hz, Ar), 8.18 (2 mL) in THF (30 mL) was heated to reflux under N
d, 2H, J = 7.6 Hz, Ar), 7.76 (dd, 2H, J = 8.4, 1.6 Hz, Ar), 7.71 sphere overnight. The reaction mixture was poured into water,
d, 4H, J = 8.8 Hz, Ar), 7.54–7.35 (m, 12H, Ar), 7.30–7.26 (m, 6H, followed by extraction using ethyl acetate. The organic layer was
SO . The solvent was then removed
.94 (t, 2H, J = 7.6 Hz, alkyl), 2.72 (t, 2H, J = 7.6 Hz, alkyl), 1.97– under reduced pressure and the residue was purified by column
.89 (m, 4H, alkyl), 1.77–1.66 (m, 4H, alkyl), 1.45–1.30 (m, 24H, chromatography on silica gel using a 1 :1 mixture of CH Cl and
2
atmo-
Ar), 7.08 (s, 1H, Ar), 7.00 (s, 1H, Ar), 4.35 (t, 4H, J = 7.2 Hz, alkyl), dried over anhydrous Na
2
1
2
4
2
2
1
3
alkyl), 0.96–0.89 ppm (m, 12H, alkyl); C NMR (100 MHz, hexane as eluent to yield 11a–13a as an orange oil.
1
CDCl ): d = 181.47 (CHO), 153.98, 148.09, 147.37, 145.85,
Compound 11a. 173 mg (32% yield). H NMR (400 MHz,
3
1
1
1
1
3
2
44.57, 140.88, 139.79, 139.37, 138.69, 138.42, 137.16, 135.95, CDCl ): d = 9.70 (s, 1H, CHO), 7.51 (s, 1H, Ar), 7.19–7.13 (m, 6H,
3
35.68, 131.65, 129.77, 129.15, 128.07, 127.68, 127.52, 126.79, Ar), 7.16–7.14 (m, 5H, Ar), 7.11–7.04 (m, 4H, Ar), 2.82 (t, 2H, J =
25.96, 125.76, 125.11, 124.84, 123.33, 122.94, 122.86, 120.39, 7.6 Hz, alkyl), 2.67 (t, 2H, J = 8 Hz, alkyl), 1.73–1.60 (m, 4H,
18.85, 118.46, 108.91, 108.82 (Ar), 43.22, 31.66, 31.60, 31.56, alkyl), 1.43–1.27 (m, 12H, alkyl), 0.91–0.86 ppm (m, 6H, alkyl);
1
3
1.36, 30.94, 29.71, 29.22, 29.00, 28.91, 28.55, 27.00, 22.66,
2.63, 22.56, 14.14, 14.07, 14.03 ppm (alkyl).
3
C NMR (100 MHz, CDCl
3
): d = 182.58 (CHO), 147.55, 147.42,
141.95, 140.31, 139.88, 139.73, 139.24, 139.06, 132.26, 130.08,
,4 -Dihexyl-[2,2 -bithiophene]-5-carbaldehyde (9). A mixture 129.84, 129.40, 127.31, 124.84, 123.37, 122.83 (Ar), 31.65, 30.91,
0
0
of 8 (0.460 g, 1.671 mmol), 3-hexylthiophenyl-2-boronic acid 30.29, 29.44, 29.20, 29.16, 28.74, 22.63, 14.13 ppm (alkyl).
1
(
K
0.425 g, 2.005 mmol), Pd(PPh
3
)
4
(97 mg, 0.084 mmol), and 2 M
Compound 12a. 545 mg (85% yield). H NMR (400 MHz,
CDCl ): d = 9.82 (s, 1H, CHO), 7.59 (s, 1H, Ar), 7.31–7.27 (m, 6H,
2
CO (2 mL) in THF (30 mL) was heated to reflux under a N
3
2
3
atmosphere overnight. The reaction mixture was poured into Ar), 7.04–7.02 (m, 4H, Ar), 6.98–6.92 (m, 4H, Ar), 2.57 (t, 2H, J =
water, followed by extraction using ethyl acetate. The organic 8 Hz, alkyl), 1.56–1.48 (m, 2H, alkyl), 1.25–1.13 (m, 6H, alkyl),
1
3
2 4 3
layer was dried over anhydrous Na SO . Then, the solvent was 0.79–0.74 ppm (m, 3H, alkyl); C NMR (100 MHz, CDCl ): d =
removed under reduced pressure and the residue was purified 181.64 (CHO), 147.85, 147.32, 146.08, 139.33, 138.61, 137.81,
by column chromatography on silica gel using a 1 : 1 mixture of 128.75, 128.40, 125.47, 124.05, 123.37, 121.13 (Ar), 30.52, 29.65,
CH Cl and hexane as eluent to afford 9 (0.545 g, 1.504 mmol) 27.99, 27.65, 21.51, 13.05 ppm (alkyl).
2
2
1
1
as a pale yellow oil. H NMR (400 MHz, CDCl
CHO), 7.58 (s, 1H, Ar), 7.11 (d, 1H, J = 1.6 Hz, alkyl), 7.01 (d, 1H, CDCl
J = 1.2 Hz, alkyl), 2.79 (t, 2H, J = 7.6 Hz, alkyl), 2.62 (t, 2H, J = (d, 2H, J = 8 Hz, Ar), 7.41 (d, 2H, J = 8.8 Hz, Ar), 7.18 (t, 4H, J =
.6 Hz, alkyl), 1.70–1.60 (m, 4H, alkyl), 1.42–1.26 (m, 12H, 7.6 Hz, Ar), 7.07 (d, 6H, J = 8.4 Hz, Ar), 6.99 (t, 2H, J = 7.2 Hz, Ar);
3
): d = 9.82 (s, 1H,
Compound 13a. 953 mg (84% yield). H NMR (400 MHz,
3
): d = 9.88 (s, 1H, CHO), 7.79 (d, 2H, J = 8.4 Hz, Ar), 7.58
7
1
3
13
alkyl), 0.91–0.87 ppm (m, 6H, alkyl); C NMR (100 MHz,
3
C NMR (100 MHz, CDCl ): d = 191.68 (CHO), 148.54, 147.46,
CDCl ): d = 182.63 (CHO), 144.15, 141.82, 140.15, 140.08, 146.45, 134.87, 132.81, 130.50, 129.69, 128.25, 126.96, 125.05,
3
1
2
39.00, 134.58, 128.88, 122.19 (Ar), 31.66, 31.60, 30.38, 30.29, 123.73, 123.28 ppm (Ar).
0
0
0
9.28, 29.13, 28.96, 22.61, 22.60, 14.10, 14.07 ppm (alkyl).
5
5 -(4-(Bis(4-iodophenyl)amino)phenyl)-3,4 -dihexyl-[2,2 -
0
0
0
-Bromo-3,4 -dihexyl-[2,2 -bithiophene]-5-carbaldehyde (10). bithiophene]-5-carbaldehyde (11b). A mixture of 11a (0.403 g,
NBS (0.396 g, 2.227 mmol) was slowly added to a solution of 9 0.665 mmol), KI (166 mg, 0.998 mmol) and KIO (142 mg,
0.769 g, 2.121 mmol) in a mixture of CHCl (25 mL) and acetic 0.665 mmol) in acetic acid (20 mL) and water (2 mL) was stirred
acid (3 mL) at 0 1C under darkness. After the mixture was stirred overnight at 80 1C. After cooling, the reaction mixture was
at room temperature overnight, the reaction was terminated by washed with water and extracted with CHCl . Then, the solvent
3
(
3
3
the addition of water. The reaction mixture was then extracted was removed under reduced pressure and the crude compound
with CH Cl and water. The organic extract was dried over was purified by column chromatography on silica gel eluting
2
2
anhydrous Na SO and the solvent was removed under reduced with CH Cl /hexane (1 : 1, v/v) to give product 11b (0.406 g,
2
4
2
2
1
pressure to yield a yellow oil, which was purified by column 0.473 mmol). H NMR (400 MHz, CDCl
chromatography on silica gel with hexane/CH Cl (2: 1 v/v) as 7.57 (s, 1H, Ar), 7.55–7.52 (m, 4H, Ar), 7.33–7.31 (m, 2H, Ar),
the eluent to give 10 as a yellow oil (0.922 g, 2.088 mmol). 7.16 (s, 1H, Ar), 7.08 (d, 2H, J = 8.4 Hz, Ar), 6.88–6.85 (m, 4H, Ar),
3
): d = 9.79 (s, 1H, CHO),
2
2
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
2.82 (t, 2H, J = 8 Hz, alkyl), 2.66 (t, 2H, J = 8 Hz, alkyl), 1.72–1.60 (m, 4H, Ar), 7.26–7.22 (m, 4H, Ar), 7.17–7.14 (m, 4H, Ar), 7.09
(
m, 4H, alkyl), 1.43–1.26 (m, 12H, alkyl), 0.90–0.86 ppm (m, 6H, (s, 1H, Ar), 4.21 (t, 4H, J = 7.2 Hz, alkyl), 2.73 (t, 2H, J = 7.6 Hz,
13
alkyl); C NMR (100 MHz, CDCl ): d = 182.49 (CHO), 146.76, alkyl), 2.62 (t, 2H, J = 8 Hz, alkyl), 1.83–1.76 (m, 4H, alkyl), 1.61–
3
1
1
3
1
46.32, 141.66, 140.01, 139.92, 139.70, 139.36, 139.20, 138.50, 1.56 (m, 4H, alkyl), 1.33–1.18 (m, 24H, alkyl), 0.83–0.76 ppm
1
3
32.69, 130.16, 130.10, 128.82, 126.30, 123.88, 86.66 (Ar), 31.70, (m, 12H, alkyl); C NMR (100 MHz, CDCl ): d = 182.62 (CHO),
3
1.69, 30.94, 30.33, 29.49, 29.24, 29.20, 28.81, 22.74, 22.68, 14.26, 147.56, 145.86, 142.01, 140.91, 140.44, 139.88, 139.83, 139.69,
4.22 ppm (alkyl).
-(4-(Bis(4-bromophenyl)amino)phenyl)-4-hexylthiophene-2- 127.27, 125.82, 125.19, 124.89, 123.37, 122.97, 122.85, 120.44,
carbaldehyde (12b). NBS (0.441 g, 2.48 mmol) was slowly added 118.90, 118.51, 108.97, 108.87 (Ar), 43.25, 31.70, 31.65, 30.98,
to a solution of 12a (0.545 g, 1.24 mmol) in CHCl (25 mL) at 30.32, 29.48, 29.24, 29.05, 28.82, 27.05, 22.72, 22.67, 22.62,
1C under darkness. After the mixture was stirred at room 14.20, 14.17, 14.10 ppm (alkyl).
temperature overnight, the reaction was terminated by the Compound 12c. 161 mg (86% yield). H NMR (400 MHz,
addition of water. The reaction mixture was then extracted with CDCl ): d = 9.72 (s, 1H, CHO), 8.23 (d, 2H, J = 1.6 Hz, Ar), 8.04
139.29, 139.08, 137.24, 132.26, 131.67, 130.14, 129.92, 128.13,
5
3
0
1
3
CH
Na
2
Cl
SO
2
and water. The organic extract was dried over anhydrous (d, 2H, J = 7.6 Hz, Ar), 7.61 (dd, 2H, J = 8.8, 1.6 Hz, Ar), 7.59–7.57
and the solvent was removed under reduced pressure to (m, 4H, Ar), 7.51 (s, 1H, Ar), 7.40–7.35 (m, 3H, Ar), 7.33–7.32
2
4
yield a yellow oil, which was purified by column chromatography (m, 2H, Ar), 7.30–7.25 (m, 3H, Ar), 7.23–7.21 (m, 4H, Ar), 7.16–
on silica gel with hexane/CH Cl (2 :1 v/v) as the eluent to give 7.12 (m, 4H, Ar), 4.19 (t, 4H, J = 7.2 Hz, alkyl), 2.61 (t, 2H, J =
2b as a yellow oil (0.709 g, 1.187 mmol). H NMR (400 MHz, 7.6 Hz, alkyl), 1.82–1.74 (m, 4H, alkyl), 1.58–1.51 (m, 2H, alkyl),
2
2
1
1
1
3
CDCl ): d = 9.70 (s, 1H, CHO), 7.53 (s, 1H, Ar), 7.27–7.20 (m, 6H, 1.30–1.14 (m, 18H, alkyl), 0.82–0.76 ppm (m, 9H, alkyl);
C
3
Ar), 6.97–6.95 (m, 2H, Ar), 6.90–6.86 (m, 4H, Ar), 2.57 (t, 2H, J = NMR (100 MHz, CDCl ): d = 182.80 (CHO), 149.12, 148.45,
3
8
Hz, alkyl), 1.56–1.49 (m, 2H, alkyl), 1.26–1.15 (m, 6H, alkyl), 0.76 145.62, 140.94, 140.39, 139.89, 139.73, 138.93, 137.62, 131.62,
1
3
ppm (t, 3H, J = 6.8 Hz, alkyl); C NMR (100 MHz, CDCl
3
): d = 129.93, 128.21, 126.56, 125.85, 125.50, 124.90, 123.41, 122.99,
82.68 (CHO), 148.23, 147.40, 145.95, 140.78, 139.99, 138.80, 122.27, 120.44, 118.94, 118.54, 108.99, 108.89 (Ar), 43.26, 31.67,
32.67, 130.18, 127.94, 126.27, 123.12, 116.56 (Ar), 31.62, 30.76, 31.65, 30.79, 29.14, 29.05, 28.82, 27.05, 22.65, 22.62, 14.17,
9.09, 28.76, 22.62, 14.18 ppm (alkyl). 14.09 ppm (alkyl).
Compound 13c. 150 mg (51% yield). H NMR (400 MHz,
13b). A mixture of 13a (0.529 g, 1.514 mmol), KI (377 mg, CDCl ): d = 10.04 (s, 1H, CHO), 8.33 (d, 2H, J = 1.2 Hz, Ar), 8.15
1
1
2
0
0
-(Bis(4-iodophenyl)amino)-[1,1 -biphenyl]-4-carbaldehyde
1
4
(
3
2
.271 mmol) and KIO (324 mg, 1.514 mmol) in acetic acid (d, 2H, J = 7.6 Hz, Ar), 7.96–7.94 (m, 2H, Ar), 7.78–7.76 (m, 2H,
3
(
20 mL) and water (2 mL) was stirred overnight at 80 1C. After Ar), 7.73 (dd, 2H, J = 8.8, 1.6 Hz, Ar), 7.69–7.67 (m, 4H, Ar), 7.60–
cooling, the reaction mixture was washed with water and 7.58 (m, 2H, Ar), 7.48–7.42 (m, 6H, Ar), 7.34–7.29 (m, 6H, Ar),
extracted with CHCl . Then, the solvent was removed under 7.27–7.25 (m, 2H, Ar), 4.33 (t, 4H, J = 7.2 Hz, alkyl), 1.92–1.89
reduced pressure and the crude compound was purified by (m, 4H, alkyl), 1.44–1.26 (m, 12H, alkyl), 0.89–0.83 ppm (m, 6H,
3
1
3
column chromatography on silica gel eluting with CH
2
Cl
2
/
3
alkyl); C NMR (100 MHz, CDCl ): d = 191.91 (CHO), 148.45,
hexane (1 : 1, v/v) to give product 13b (0.210 g, 0.349 mmol) as 146.71, 145.78, 140.92, 139.85, 137.39, 134.68, 132.73, 131.64,
1
a yellow oil. H NMR (400 MHz, CDCl ): d = 10.04 (s, 1H, CHO), 130.38, 128.14, 128.11, 126.92, 125.80, 125.23, 124.86, 123.38,
3
7
.94 (d, 2H, J = 8.4 Hz, Ar), 7.72 (d, 2H, J = 8 Hz, Ar), 7.59–7.53 123.13, 122.96, 120.41, 118.89, 118.51, 108.94, 108.85 (Ar),
1
3
(
m, 6H, Ar), 7.15–7.13 (m, 2H, Ar), 6.89–6.87 (m, 4H, Ar);
C
43.26, 31.61, 29.01, 27.02, 22.57, 14.03 ppm (alkyl).
3
NMR (100 MHz, CDCl ): d = 191.84 (CHO), 147.21, 146.72,
1
1
46.28, 138.50, 134.96, 134.34, 130.37, 128.37, 127.09, 126.32,
24.15, 86.65 ppm (Ar).
General synthetic procedures of 7a–7d and 11d–13d
A mixture of each of the corresponding dye precursors 6a–6d
and 11c–13c and cyanoacetic acid (10 molar equivalents) in
General synthetic procedures of 11c–13c
A mixture of 11b (88 mg, 0.103 mmol) or 12b (120 mg, 0.200 mmol) acetic acid (8 mL) was refluxed in the presence of ammonium
or 13b (210 mg, 0.349 mmol), (9-hexylcarbazolyl)boronic acid acetate (25 mg) overnight under a N atmosphere. After cooling,
3 molar equivalents), Pd(PPh ) (10 mg, 0.008 mmol), and 2 M the reaction mixture was extracted with CHCl and water. Then,
(1 mL) in THF (20 mL) was heated to the solvent was removed under reduced pressure and the crude
atmosphere overnight. The reaction mixture was compound was purified by column chromatography on silica
poured into water, followed by extraction using ethyl acetate. The gel eluting with CHCl and then CHCl /MeOH (10 : 1, v/v) to
organic layer was dried over anhydrous Na SO
. Then, the solvent give the desired products 7a–7d and 11d–13d.
2
(
3
3
4
aqueous solution of K
2 3
CO
reflux under N
2
3
3
2
4
was removed under reduced pressure and the residue was purified
by column chromatography on silica gel using a 3 : 2 mixture of
CH Cl and hexane as eluent to yield 11c–13c as an orange oil.
Compound 7a. 75 mg (97% yield); dark purple solid.
H NMR (400 MHz, DMSO-d ): d = 8.29 (s, 1H, CQCH–),
8.25–8.22 (m, 2H, Ar), 7.71–7.64 (m, 3H, Ar), 7.55–7.46
1
6
2
2
1
Compound 11c. 95 mg (84% yield). H NMR (400 MHz, (m, 4H, Ar), 7.39 (s, 1H, Ar), 7.26–7.22 (m, 1H, Ar), 4.43 (t, 2H,
CDCl
): d = 9.71 (s, 1H, CHO), 8.23 (d, 2H, J = 1.6 Hz, Ar), 8.05 J = 6.8 Hz, alkyl), 2.79 (t, 2H, J = 7.6 Hz, alkyl), 2.69 (t, 2H, J =
d, 2H, J = 7.6 Hz, Ar), 7.62 (dd, 2H, J = 8.4, 1.6 Hz, Ar), 7.59–7.57 7.2 Hz, alkyl), 1.81–1.78 (m, 2H, alkyl), 1.65–1.60 (m, 4H, alkyl),
m, 4H, Ar), 7.46 (s, 1H, Ar), 7.41–7.35 (m, 4H, Ar), 7.33–7.27 1.31–1.19 (m, 22H, alkyl), 0.89–0.76 ppm (m, 9H, alkyl).
3
(
(
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
HRMS (MALDI-TOF, m/z): [M ] 836.2891; calcd for (C48
Journal of Materials Chemistry C
+
H
56
N
2
O
2
S
2
Se) 7.88 (d, 2H, J = 8.4 Hz, Ar), 7.79–7.73 (m, 8H, Ar), 7.63–7.59
836.2948.
(m, 4H, Ar), 7.48–7.44 (m, 2H, Ar), 7.25–7.15 (m, 8H, Ar), 4.38
Compound 7b. 81 mg (88% yield); dark purple solid. (t, 4H, J = 6.4 Hz, alkyl), 1.78–1.75 (m, 4H, alkyl), 1.27–1.18
1
H NMR (400 MHz, DMSO-d ): d = 8.26 (s, 1H, CQCH–), 7.65 (m, 12H, alkyl), 0.81–0.78 ppm (m, 6H, alkyl). HRMS (MALDI-
6
+
(
d, 1H, J = 3.6 Hz, Ar), 7.59–7.55 (m, 8H, Ar), 7.46 (s, 1H, Ar), TOF, m/z): [M ] 914.4616; calcd for (C H N O ) 914.4560.
6
4
58 4 2
7.42–7.36 (m, 3H, Ar), 7.34 (s, 1H, Ar), 7.13 (d, 4H, J = 8.4 Hz,
Ar), 7.08 (d, 2H, J = 8.4 Hz, Ar), 6.98 (d, 4H, J = 8.8 Hz, Ar),
Acknowledgements
3.98 (t, 4H, J = 6.4 Hz, alkyl), 2.77 (t, 2H, J = 7.2 Hz, alkyl), 2.62
(
(
(
t, 2H, J = 7.2 Hz, alkyl), 1.75–1.68 (m, 4H, alkyl), 1.60–1.58
P.-Y. Ho and C.-H. Siu contributed equally to this work. We are
grateful for the financial support from the Areas of Excellence
Scheme, University Grants Committee of HKSAR (Project No.
AoE/P-03/08), Hong Kong Research Grants Council (HKBU203011),
Hong Kong Baptist University (FRG2/13-14/083 and FRG2/13-14/
m, 4H, alkyl), 1.42–1.24 (m, 24H, alkyl), 0.90–0.82 ppm
+
m, 12H, alkyl). HRMS (MALDI-TOF, m/z): [M ] 1154.3167; calcd
for (C H N O S Se) 1154.4568.
7
0
78 2 4 2
Compound 7c. 40 mg (92% yield); dark purple solid.
H NMR (400 MHz, CDCl ): d = 8.39 (s, 1H, CQCH–), 8.27
1
3
078) and the Science, Technology and Innovation Committee
(d, 1H, J = 1.2 Hz, Ar), 8.19 (d, 1H, J = 1.6 Hz, Ar), 7.72–7.70
(m, 1H, Ar), 7.66–7.64 (m, 2H, Ar), 7.56–7.54 (m, 1H, Ar), 7.51
(d, 1H, J = 4 Hz, Ar), 7.47–7.42 (m, 2H, Ar), 7.28–7.27 (m, 1H, Ar),
of Shenzhen Municipality (JCYJ20120829154440583 and
JCYJ20140818163041143). The work was also supported by
Partner State Key Laboratory of Environmental and Biological
Analysis (SKLP-14-15-P011) and Strategic Development Fund of
HKBU. K. L. Han thanks the National Basic Research Program
of China (2013CB834604) and NSFC (21533010). T. Chen thanks
the RGC Theme-based Research Scheme (Project No. T23-407/
7
.11 (s, 1H, Ar), 7.05–7.02 (m, 3H, Ar), 4.33 (t, 2H, J = 6.8 Hz,
alkyl), 4.04 (t, 2H, J = 6.8 Hz, alkyl), 2.80 (t, 2H, J = 7.6 Hz, alkyl),
.72 (t, 2H, J = 8 Hz, alkyl), 1.96–1.85 (m, 4H, alkyl), 1.69–1.64
2
(
(
m, 4H, alkyl), 1.54–1.26 (m, 28H, alkyl), 0.96–0.85 ppm
m, 12H, alkyl). HRMS (MALDI-TOF, m/z): [M ] 1012.3496; calcd
+
1
3-N) for the financial support. Y. H. Lo gratefully acknowledges
the financial support from the National Science Council of Taiwan
NSC 102-2113-M-845-001) and the project of the specific research
for (C60
Compound 7d. 101 mg (80% yield); dark purple solid.
H NMR (400 MHz, CDCl ): d = 8.31 (s, 1H, CQCH–), 8.29
72 2 3 2
H N O S Se) 1012.4150.
(
1
3
fields in the University of Taipei, Taiwan.
(d, 2H, J = 1.6 Hz, Ar), 8.11 (d, 2H, J = 7.6 Hz, Ar), 7.68–7.62
(m, 6H, Ar), 7.48–7.44 (m, 2H, Ar), 7.41–7.38 (m, 4H, Ar), 7.28–
7
.13 (m, 12H, Ar), 6.98 (s, 1H, Ar), 6.94 (s, 1H, Ar), 4.26 (t, 4H,
Notes and references
J = 7.2 Hz, alkyl), 2.77 (t, 2H, J = 7.2 Hz, alkyl), 2.62 (t, 2H, J =
7
1
.6 Hz, alkyl), 1.89–1.82 (m, 4H, alkyl), 1.66–1.59 (m, 4H, alkyl),
1 B. O’Regan and M. Gr ¨a tzel, Nature, 1991, 353, 737–740.
2 Y. Ooyama and Y. Harima, Eur. J. Org. Chem., 2009, 2903–2934.
3 L. Wang, H. Zhang, C. Wang and T. Ma, ACS Sustainable
Chem. Eng., 2013, 1, 205–208.
4 S. I. Cha, Y. Kim, K. H. Hwang, Y.-J. Shin, S. H. Seo and
D. Y. Lee, Energy Environ. Sci., 2012, 5, 6071–6075.
5 M. K. Nazeeruddin, F. D. Angelis, S. Fantacci, A. Selloni,
G. Viscardi, P. Liska, S. Ito, B. Takeru and M. Gr ¨a tzel, J. Am.
Chem. Soc., 2005, 127, 16835–16847.
.42–1.25 (m, 24H, alkyl), 0.94–0.84 ppm (m, 12H, alkyl).
+
HRMS (MALDI-TOF, m/z): [(M + H) ] 1301.5270; calcd for
(
C
82
H
85
N
4
O
2
S
2
Se) 1301.5274.
Compound 11d. 99 mg (89% yield); dark red solid. H NMR
400 MHz, DMSO-d ): d = 8.50 (d, 2H, J = 1.6 Hz, Ar), 8.40 (s, 1H,
1
(
6
CQCH–), 8.26 (d, 2H, J = 7.6 Hz, Ar), 7.91 (s, 1H, Ar), 7.82–7.77
m, 6H, Ar), 7.68 (d, 2H, J = 8.4 Hz, Ar), 7.63 (d, 2H, J = 8.4 Hz,
Ar), 7.50–7.46 (m, 4H, Ar), 7.36 (s, 1H, Ar), 7.28 (d, 4H, J =
(
8
2
.8 Hz, Ar), 7.25–7.17 (m, 4H, Ar), 4.43 (t, 4H, J = 7.2 Hz, alkyl),
.82 (t, 2H, J = 7.6 Hz, alkyl), 2.74–2.70 (m, 2H, alkyl), 1.82–1.77
6 A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran,
M. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M.
Zakeeruddin and M. Gr ¨a tzel, Science, 2011, 334, 629–634.
7 Z. S. Wang, Y. Cui, K. Hara, Y. Dan-oh, C. Kasada and
A. Shinpo, Adv. Mater., 2007, 19, 1138–1141.
(m, 4H, alkyl), 1.66–1.61 (m, 4H, alkyl), 1.34–1.22 (m, 24H,
alkyl), 0.88–0.81 ppm (m, 12H, alkyl). HRMS (MALDI-TOF, m/z):
+
[M ] 1170.6682; calcd for (C H N O S ) 1170.5879.
78 82 4 2 2
1
Compound 12d. 166 mg (95% yield); dark red solid. H NMR
8 T. Horiuchi, H. Miura and S. Uchida, Chem. Commun., 2003,
3036–3037.
(400 MHz, DMSO-d ): d = 8.48 (d, 2H, J = 1.6 Hz, Ar), 8.38 (s, 1H,
6
CQCH–), 8.24 (d, 2H, J = 7.6 Hz, Ar), 7.90 (s, 1H, Ar), 7.81–7.76
9 T. Horiuchi, H. Miura, K. Sumioka and S. Uchida, J. Am.
Chem. Soc., 2004, 126, 12218–12219.
(m, 6H, Ar), 7.66 (d, 2H, J = 8.8 Hz, Ar), 7.61 (d, 2H, J = 8 Hz, Ar),
7
.49–7.45 (m, 4H, Ar), 7.28 (d, 4H, J = 8.4 Hz, Ar), 7.23–7.16 10 M. Liang, W. Xu, F. S. Cai, P. Q. Chen, B. Peng, J. Chen and
Z. M. Li, J. Phys. Chem. C, 2007, 111, 4465–4472.
alkyl), 1.82–1.75 (m, 4H, alkyl), 1.61–1.56 (m, 2H, alkyl), 1.32– 11 M.-D. Zhang, H. Pan, X.-H. Ju, Y.-J. Ji, L. Qin, H.-G. Zheng
(m, 4H, Ar), 4.41 (t, 4H, J = 6.8 Hz, alkyl), 2.71 (t, 2H, J = 7.6 Hz,
1
.20 (m, 18H, alkyl), 0.86–0.79 ppm (m, 9H, alkyl). HRMS
and X.-F. Zhou, Phys. Chem. Chem. Phys., 2012, 14,
2809–2815.
+
(MALDI-TOF, m/z): [(M + H) ] 1005.5955; calcd for (C H N O S)
6
8
69
4 2
1
005.5136.
12 S. Ko, H. Choi, M.-S. Kang, H. Hwang, H. Ji, J. Kim, J. Ko and
Y. Kang, J. Mater. Chem., 2010, 20, 2391–2399.
1
Compound 13d. 132 mg (80% yield); dark red solid. H NMR
6
(400 MHz, DMSO-d ): d = 8.48 (d, 2H, J = 0.8 Hz, Ar), 8.33 (s, 1H, 13 Y.-S. Yen, H.-H. Chou, Y.-C. Chen, C.-Y. Hsu and J. T. Lin,
CQCH–), 8.24 (d, 2H, J = 7.6 Hz, Ar), 8.11 (d, 2H, J = 8.4 Hz, Ar),
J. Mater. Chem., 2012, 22, 8734–8747.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015

View Article Online
Journal of Materials Chemistry C
Paper
1
1
1
1
1
4 A. Mishra, M. K. R. Fischer and P. B ¨a uerle, Angew. Chem., 38 K. H. Hendriks, W. Li, M. M. Wienk and R. A. J. Janssen,
Int. Ed., 2009, 48, 2474–2499. J. Am. Chem. Soc., 2014, 136, 12130–12136.
5 K. Hara, K. Miyamoto, Y. Abe and M. Yanagida, J. Phys. 39 M. Liang and J. Chen, Chem. Soc. Rev., 2013, 42, 3453–3488.
Chem. B, 2005, 109, 23776–23778.
6 K. Sayama, K. Hara, Y. Ohga, A. Shinpou, S. Suga and
H. Arakawa, New J. Chem., 2001, 25, 200–202.
7 C. L. Mai, W. K. Huang, H. P. Lu, C. W. Lee, Y. R. Liang, E. W. G.
Diau and C. Y. Yeh, Chem. Commun., 2010, 46, 809–811.
8 L. Y. Lin, C. H. Tsai, K. T. Wong, T. W. Huang, L. Hsieh,
S. H. Liu, H. W. Lin, C. C. Wu, S. H. Chou, S. H. Chen and
A. I. Tsai, J. Org. Chem., 2010, 75, 4778–4785.
40 S. Haid, A. Mishra, C. Uhrich, M. Pfeiffer and P. B ¨a uerle,
Chem. Mater., 2011, 23, 4435–4444.
41 S.-H. Lin, Y.-C. Hsu, J. T. Lin, C.-K. Lin and J.-S. Yang, J. Org.
Chem., 2010, 75, 7877–7886.
42 Y. Hua, B. Jin, H. Wang, X. Zhu, W. Wu, M.-S. Cheung,
Z. Lin, W.-Y. Wong and W.-K. Wong, J. Power Sources, 2013,
237, 195–203.
43 C.-Y. Chen, M. Wang, J.-Y. Li, N. Pootrakulchote, L. Alibabaei,
C. Ngoc-le, J.-D. Decoppet, J.-H. Tsai, C. Gr ¨a tzel, C.-G. Wu, S. M.
Zakeeruddin and M. Gr ¨a tzel, ACS Nano, 2009, 3, 3103–3109.
1
2
2
9 Q. H. Yao, F. S. Meng, F. Y. Li, H. Tian and C. H. Huang,
J. Mater. Chem., 2003, 13, 1048–1053.
0 G. Li, M. Liang, H. Wang, Z. Sun, L. Wang, Z. Wang and 44 T. Bessho, E. Yoneda, J.-H. Yum, M. Guglielmi, I. Tavernelli,
S. Xue, Chem. Mater., 2013, 25, 1713–1722.
H. Imai, U. Rothlisberger, M. K. Nazeeruddin and
1 Y. Hua, S. Chang, D. Huang, X. Zhou, X. Zhu, J. Zhao,
M. Gr ¨a tzel, J. Am. Chem. Soc., 2009, 131, 5930–5934.
T. Chen, W.-Y. Wong and W.-K. Wong, Chem. Mater., 2013, 45 S. A. Haque, E. Palomares, B. M. Cho, A. N. M. Green,
2
5, 2146–2153.
N. Hirata, D. R. Klug and J. R. Durrant, J. Am. Chem. Soc.,
2005, 127, 3456–3462.
46 Z. Chai, M. Wu, M. Fang, S. Wan, T. Xu, R. Tang, Y. Xie,
A. Mei, H. Han, Q. Li and Z. Li, Adv. Energy Mater., 2015,
5, 1500846.
2
2
2 C.-J. Yang, Y. J. Chang, M. Watanabe, Y.-S. Hon and
T. J. Chow, J. Mater. Chem., 2012, 22, 4040–4049.
3 Y. J. Chang, P.-T. Chou, Y.-Z. Lin, M. Watanabe, C.-J. Yang,
T.-M. Chin and T. J. Chow, J. Mater. Chem., 2012, 22,
2
1704–21712.
47 P. Gao, H. N. Tsao, C. Yi, M. Gr ¨a tzel and M. K. Nazeeruddin,
Adv. Energy Mater., 2014, 4, 1301485.
Y. Zhang, S. Liu and J. Xu, J. Mater. Chem., 2012, 22, 8994–9005. 48 D. P. Hagberg, T. Marinado, K. M. Karlsson, K. Nonomura,
2
2
4 C. Chen, J.-Y. Liao, Z. Chi, B. Xu, X. Zhang, D.-B. Kuang,
5 S. H. Kim, H. W. Kim, C. Sakong, J. Namgoong, S. W. Park,
M. J. Ko, C. H. Lee, W. I. Lee and J. P. Kim, Org. Lett., 2011,
P. Qin, G. Boschloo, T. Brinck, A. Hagfeldt and L. Sun, J. Org.
Chem., 2007, 72, 9550–9556.
1
3, 5784–5787.
49 J. Tang, W. Wu, J. Hua, J. Li, X. Li and H. Tian, Energy
Environ. Sci., 2009, 2, 982–990.
2
2
6 W.-I. Hung, Y.-Y. Liao, C.-Y. Hsu, H.-H. Chou, T.-H. Lee,
W.-S. Kao and J. T. Lin, Chem. – Asian J., 2014, 9, 357–366. 50 B.-G. Kim, K. Chung and H. Kim, Chem. – Eur. J., 2013, 19,
7 C.-H. Siu, L. T. L. Lee, P.-Y. Ho, P. Majumdar, C.-L. Ho, 5220–5230.
T. Chen, J. Zhao, H. Li and W.-Y. Wong, J. Mater. Chem. C, 51 J. Bisquert, Phys. Chem. Chem. Phys., 2003, 5, 5360–5364.
2
014, 2, 7086–7095.
52 M. Adachi, M. Sakamoto, J. Jiu, Y. Ogata and S. Isoda,
J. Phys. Chem. B, 2006, 110, 13872–13880.
53 Q. Wang, J.-E. Moser and M. Gr ¨a tzel, J. Phys. Chem. B, 2005,
109, 14945–14953.
2
8 Q. Li, J. Shi, H. Li, S. Li, C. Zhong, F. Guo, M. Peng, J. Hua,
J. Qin and Z. Li, J. Mater. Chem., 2012, 22, 6689–6696.
9 R. Y.-Y. Lin, F.-L. Wu, C.-H. Chang, H.-H. Chou, T.-M.
2
Chuang, T.-C. Chu, C.-Y. Hsu, P.-W. Chen, K.-C. Ho, Y.-L. 54 K. Hu, H. A. Severin, B. D. Koivisto, K. C. D. Robson, E. Schott,
Lo and J. T. Lin, J. Mater. Chem. A, 2014, 2, 3092–3101.
0 S. Jiang, S. Fan, X. Lu, G. Zhou and Z.-S. Wang, J. Mater.
Chem. A, 2014, 2, 17153–17164.
1 Z. Ning, Q. Zhang, W. Wu, H. Pei, B. Liu and H. Tian,
J. Org. Chem., 2008, 73, 3791–3797.
R. Arratic-Perez, G. J. Meyer and C. P. Berlinguette, J. Phys.
Chem. C, 2014, 118, 17079–17089.
55 A. Zaban, M. Greenshtein and J. Bisquert, ChemPhysChem,
2003, 5, 859–864.
56 J. Bisquert, A. Zaban, M. Greenshtein and I. Mora-Ser o´ ,
J. Am. Chem. Soc., 2004, 126, 13550–13559.
3
3
3
2 D. P. Hagberg, J.-H. Yum, H. Lee, F. D. Angelis, T. Marinado,
K. M. Karlsson, R. Humphry-Baker, L. Sun, A. Hagfeldt, 57 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. Gr ¨a tzel and Md. K. Nazeeruddin, J. Am. Chem. Soc., 2008,
30, 6259–6266.
3 Z. Ning and H. Tian, Chem. Commun., 2009, 5483–5495.
4 J. Tang, J. Hua, W. Wu, J. Li, Z. Jin, Y. Long and H. Tian,
Energy Environ. Sci., 2010, 3, 1736–1745.
5 M. Lu, M. Liang, H.-Y. Han, Z. Sun and S. Xue, J. Phys. Chem.
C, 2011, 115, 274–281.
6 L.-L. Tan, J.-F. Huang, Y. Shen, L.-M. Xiao, J.-M. Liu, D.-B.
Kuang and C.-Y. Su, J. Mater. Chem. A, 2014, 2, 8988–8994.
7 Q. Li, L. Lu, C. Zhong, J. Huang, Q. Huang, J. Shi, X. Jin,
T. Peng, J. Qin and Z. Li, Chem. – Eur. J., 2009, 15,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N.
Kudin, V. N. Staroverov, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo,
R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi,
1
3
3
3
3
3
9664–9668.
This journal is ©The Royal Society of Chemistry 2015
J. Mater. Chem. C

View Article Online
Paper
Journal of Materials Chemistry C
C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, 59 E. Canc `e s, B. Mennucci and J. Tomasi, J. Chem. Phys., 1997,
V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, 107, 3032–3041.
¨
ˇ
S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, 60 S. Miertus, E. Scrocco and J. Tomasi, J. Chem. Phys., 1981,
J. Cioslowski and D. J. Fox, Gaussian 09, Revision D.01, Gaussian,
Inc., Wallingford CT, 2009.
8 B. Mennucci, E. Canc `e s and J. Tomasi, J. Phys. Chem. B,
55, 117–129.
61 R. Cammi and J. Tomasi, J. Comput. Chem., 1995, 16,
1449–1458.
5
1997, 101, 10506–10517.
62 T. Lu and F. Chen, J. Comput. Chem., 2012, 33, 580–592.
J. Mater. Chem. C
This journal is ©The Royal Society of Chemistry 2015