Fluorenylvinylenes bridged triphenylamine-based dyes with enhanced performance in dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tet.2011.09.008

We have synthesized a series of new dipolar organic dyes Bn (n=0, 1, 2) employing triarylamine as the electron-donor, 2-cyanoacrylic acid as the electron-acceptor, and fluorenevinylene as the conjugated bridge, which were used as sensitizers in dye-sensitized solar cells. It is found that the solar-energy-to-electricity conversion efficiencies of the prepared DSSCs are in the range of 2.79-5.56%, which reach 35-70% of a standard device based on N719 fabricated and measured under the same conditions. The DSSC sensitized with B1 with balanced length of conjugated bridge shows the highest photo-to-electrical energy conversion efficiency and the open-circuit photovoltage (V_oc) of 0.86 V.

Full text of DOI:10.1016/j.tet.2011.09.008

Tetrahedron 67 (2011) 8477e8483
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Tetrahedron
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Fluorenylvinylenes bridged triphenylamine-based dyes with enhanced
performance in dye-sensitized solar cells
Huipeng Zhou a, Pengchong Xue a, Yuan Zhang b, Xin Zhao a, Junhui Jia a, Xiaofei Zhang a, Xingliang Liu a,
,
Ran Lu a
*
a State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, PR China
b College of Chemistry, Beijing Normal University, Beijing 100875, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 June 2011
Received in revised form 26 August 2011
Accepted 6 September 2011
Available online 8 September 2011
We have synthesized a series of new dipolar organic dyes Bn (n¼0, 1, 2) employing triarylamine as the
electron-donor, 2-cyanoacrylic acid as the electron-acceptor, and fluorenevinylene as the conjugated
bridge, which were used as sensitizers in dye-sensitized solar cells. It is found that the solar-energy-to-
electricity conversion efficiencies of the prepared DSSCs are in the range of 2.79e5.56%, which reach
35e70% of a standard device based on N719 fabricated and measured under the same conditions. The
DSSC sensitized with B1 with balanced length of conjugated bridge shows the highest photo-to-electrical
energy conversion efficiency and the open-circuit photovoltage (Voc) of 0.86 V.
Keywords:
Dye-sensitized solar cells (DSSCs)
Triphenylamine
Ó 2011 Elsevier Ltd. All rights reserved.
Fluorenylvinylene
1. Introduction
hemicyanine,14 merocyanine,15 perylene,16 thiophene,17 fluo-
rene,18 and triarylamine,19 as the sensitizers have yielded good
In recent years, energy demands and global warming have
aroused intense attention in clean renewable solar energy sources.
In this context, dye-sensitized solar cells (DSSCs) have attracted
considerable attention as they offer the possibility of low-cost
conversion of photovoltaic energy.1 Although the conventional
ruthenium-based sensitizers (such as N3/N719)2,3 and the black
dye4 hold the record of the solar-energy-to-electricity conversion
efficiencies of 11% under AM 1.5 irradiation, they are expensive and
hard to purify relative to metal-free organic sensitizers. Thus, or-
ganic sensitizers have emerged as competitive alternatives to the
Ru-based counterparts because various organic chromophores
with high molar extinction coefficients can be facilely synthesized.5
Thus, considerable progress has been made on the design of
organic dyes, which favor high performance in DSSCs.6,7 Recently,
Wang and co-workers reported an impressive high conversion ef-
conversion efficiencies. It has been found that most of the efficient
organic dyes employed in DSSCs generally contain donor and ac-
ceptor bridged by a
p-conjugated linker (DepeA), and tuning of
the length and torsion angle of the conjugated linker is important
in increasing the molar extinction coefficient and realizing pan-
chromatic light-harvesting. For example, the linker of styrene,20
furan,21 vinyl,22 thiophene23 or thienothiophene24 incorporated
into the triarylamine-based organic framework could enhance the
efficiency. As a well-known conjugated unit, fluorenylvinylene has
been extensively studied in functional organic materials (including
emitting, nonlinear optical and liquid crystal materials, etc.),25
however, it has not been used as a spacer in triphenylamine-
based dyes employed in DSSCs. Herein, we synthesized
triphenylamine-based dyes bridged by 9,9-di-n-octylfluorene-2-
vinylene with different conjugation degree to link to the acceptor
of cyanoacrylic acid (Bn, Chart 1) in order to reveal the relationship
between the molecular structures and the performance of DSSCs. It
has been found that the total solar-to-energy conversion efficiency
of the devices sensitized with B0, B1, and B2 are 2.79%, 5.56%, and
4.49%, respectively. It was clear that the cell based on B1 with
balanced conjugated spacer showed a better performance than the
one based on B2. The reason might be that the electron re-
combination process from the conduction of TiO2 to the redox
electrolyte was retarded in B1-based cell. Therefore, the organic
dye with balanced conjugation is important in improving the per-
formance of DSSCs.
ficiency of 9.8% for a DSSC based on a DepeA chromophore in
which 3,4-ethylenedioxythiophene was used as a spacer linked
to dihexyloxy-substituted triphenylamine electron-donor (D)
and cyanoacrylic acid electron-acceptor (A).8 In addition, many
reported DSSCs that utilize organic dyes, such as the derivatives
of carbazole,9 phenothiazine,10 coumarin,11 indoline,12 cyanine,13
* Corresponding author. Tel.: þ86 431 88499179; fax: þ86 431 88923907; e-mail
address: luran@mail.jlu.edu.cn (R. Lu).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.09.008

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H. Zhou et al. / Tetrahedron 67 (2011) 8477e8483
2. Results and discussion
2.1. Syntheses of Bn
The synthetic routes for triphenylamine-based dyes (Bn, n¼0, 1,
2) are sketched in Scheme 1. The compounds of 4-(N,N-dipheny-
lamino)benzaldehyde (1) and 3-(4-diphenylaminophenyl)-2-
cyanoacrylic acid (B0) were synthesized according to the reported
procedures.26,22 The precursors of compounds 4 and 6 were pre-
pared by alternate Heck and Wittig reaction.23a For example,
N-phenyl-N-(4-vinylphenyl)benzenamine (3) was obtained via
Wittig reaction between methyltriphenylphosphoniumiodine and
compound 1 in a yield of 89%. Then, compound 4 was readily
synthesized from compound 3 and 2-bromo-7-formyl-9,9-di-n-
octylfluorene (2), which was an important intermediate for the
whole synthetic process and prepared in accordance with the lit-
erature,27,28 via Heck reaction catalyzed by Pd(OAC)2 at 110 ꢀC for
10 h in a yield of 72%. The Wittig reaction between compound 4 and
methyltriphenylphosphoniumiodine afforded compound
5 in
a yield of 87%. Accordingly, we gained compound 6 from com-
pounds 5 and 2 following the general procedure for compound 4 in
a yield of 73%. Finally, the dyes of B1 and B2 were prepared by
Knoevenagel reaction between cyanoacetic acid and compound 4
or 6, respectively, in a yield of 90% and 92%. All the intermediates
and the final products were purified by column chromatography
followed by recrystallization, and the new compounds were char-
acterized with FT-IR, 1H NMR, 13C NMR, elemental analysis, and
MALDI/TOF mass spectroscopy. The compounds 4, 5, 6, B1, and B2
exhibited vibration absorption bands around 960 cmꢁ1 arising from
the wagging vibration of the trans-double bond (C]C) in the IR
Chart 1. The molecular structures of triphenylamine-based dyes Bn.
Scheme 1. Syntheses of fluorenylvinylenes bridged triphenylamine-based dyes Bn.

H. Zhou et al. / Tetrahedron 67 (2011) 8477e8483
8479
spectrum.29 In addition, the 1H NMR spectra of B1 and B2 also
confirmed that all the ethenyl groups adopted the trans-confor-
mation on account of the absence of the signal at w6.5 ppm
assigned to the protons in cis-double bonds (CH]CH).28,29 The dyes
B0, B1, and B2 are highly soluble in aromatic solvents (i.e., toluene,
benzene, and o-dichlorobenzene) and other common organic sol-
vents (such as, CH2Cl2, THF, CHCl3, DMF, and DMSO).
which could be ascribed to the electronic interactions between the
dyes and the semiconductor surface.24b,31 The maximal fluores-
cence emission bands of B0, B1, and B2 in CH2Cl2 appeared at 531,
612, and 561 nm, respectively, excited at their absorption maxi-
mum (Fig. S1). Such large Stokes shifts between the absorption and
the emission bands (6804e7641 cmꢁ1) of Bn further confirmed the
ICT emission.21
It should be noted that the absorption bands of B1 and B2 would
blue-shift with increasing the polarity of the solvents as shown in
Fig. 2. In other words, a negative solvatochromism was observed for
the charge transfer transition band, indicating that the dyes possess
smaller dipole moments in the excited state than in the ground
state. The reason might be that in polar solvents the electron-
withdrawing ability of the carboxylic acid group would be de-
2.2. Photophysical properties
The UVevis absorption spectra of triphenylamine-based dyes
Bn (n¼0, 1, 2) in dichloromethane and on TiO2 film are shown in
Fig. 1, and the photophysical data are listed in Table S1. As shown in
Fig. 1a, we can find two distinct absorption at ca. 300 nm and
Fig. 1. UVevis absorption spectra of Bn (a) in dichloromethane (2.0ꢂ10ꢁ5 M), (b) in dichloromethane (2.0ꢂ10ꢁ5 M) upon addition of TBAOH, (c) on TiO2 film (normalized).
430 nm in CH2Cl2, and the former one is assigned to
p
e
p
* transi-
creased because of its partial deprotonation in the excited state,21,32
which could be supported by the blue-shift (ca. 20 nm) of the CT
bands for B1 and B2 in deprotonated forms (cyanoacrylic acid salts)
compared with those in protonated forms (cyanoacrylic acid) in
THF and toluene (Fig. 2).
tion, while the later one originates from the intramolecular charge
transfer (ICT) transition.23c However, we can not find that the ab-
sorption bands red-shift with increasing the molecular conjuga-
tion, which might be due to different degree of protonation of Bn in
Fig. 2. UV-vis absorption spectra of B1 (left) and B2 (right) in different solvents before and after addition of TBAOH.
dichloromethane.17,30 Moreover, in order to confirm the above
conclusion, the UVevis absorption spectra of the deprotonated Bn
are given in Fig. 1b. The deprotonation of Bn was achieved by
adding TBAOH (tetrabutylammonium hydroxide) to the corre-
sponding solutions. It was clear that the absorption maximum red-
shifted obviously with increasing the number of fluorenevinylene
unit in Bn. For instance, the maximal absorption bands for B0, B1,
and B2 were located at 378, 406, and 417 nm, respectively. In ad-
dition, the absorption spectra of Bn adsorbed on transparent TiO2
2.3. Molecular orbital calculations
Density functional theory (DFT) calculations method was per-
formed to analyze the electron distribution of the frontier orbitals
of dyes B1 and B2. As shown in Fig. 3, the electron density of the
highest occupied molecular orbitals (HOMOs) of the both mole-
cules is mainly located at the triphenylamine moieties, whereas
electron density of the lowest unoccupied molecular orbital
(LUMO) is primarily located at the cyanoacrylic acid acceptor and
the neighboring fluorene ring. Therefore, the strong electron den-
sity relocation between HOMO and LUMO is present and supports
an intramolecular charge transfer (ICT) transition.7 Furthermore,
films (2
mm in thickness) are shown in Fig. 1c. The absorption
maximum for B0, B1, and B2 appeared at 412, 418, and 422 nm,
respectively, giving blue-shift compared with those in CH2Cl2,

8480
H. Zhou et al. / Tetrahedron 67 (2011) 8477e8483
hence, an effective electron transfer from the excited dye to the
TiO2 is ensured.
2.5. Photovoltaic properties of DSSCs
Fig. 5 shows the photocurrent densityephotovoltage (IeV)
curves of DSSCs based on the as-synthesized dyes, and the detailed
parameters, including short-circuit photocurrent density (Jsc),
open-circuit photovoltage (Voc), fill factor (ff), and conversion effi-
Fig. 3. The frontier orbital plots of the HOMO and LUMO of Bn.
the calculated electron distribution illustrates favorable di-
rectionality for injection of photoexcited electrons from the donor
group to TiO2 film via the bridge of fluorenylvinylenes and an-
choring group.
Fig. 5. Current densityevoltage curves under full sunlight (real) (AM 1.5 G,
100 mW cmꢁ2) and in the dark (dashed) of devices sensitized with Bn and N719 using
a volatile electrolyte.
2.4. Electrochemical properties
To estimate the HOMO level of the dyes, cyclic voltammetry was
employed using a three-electrode cell and an electrochemistry
workstation (CHI 604). The cyclic voltammetry (CV) diagrams of
dyes Bn (n¼0, 1, 2) in methylene chloride (DCM) in the presence of
Bu4NBF4 as the supporting electrolyte are shown in Fig. 4, and the
corresponding data are listed in Table S2. It is shown that the first
oxidation potentials (Eox) corresponding to the HOMO levels of the
dyes (B0: 1.21 eV, B1: 0.91 eV, B2: 0.93eV) are sufficiently more
positive than the Iꢁ/I3ꢁ redox potential value (0.4 V vs NHE), in-
dicating that the oxidized dyes formed after electron injection into
the conduction band of TiO2 could accept electrons from Iꢁ ther-
modynamically. The LUMO levels of these dyes (calculated by
EoxꢁE0e0, see Table S2) are more negative than Ecb (conduction-
band-edge energy level) of the TiO2 electrode (ꢁ0.5 V vs NHE),1
ciency (h), are summarized in Table 1. The DSSC based on dye B1
shows the best performance with an open-circuit voltage of 0.86 V,
a short-circuit photocurrent density of 11.33 mA cmꢁ2, and a fill
factor of 0.57 under AM 1.5 irradiation (100 mW cmꢁ2). And the
corresponding overall conversion efficiency (h) is 5.56%, which
reaches w70% of a N719-based DSSC (8.04%) fabricated and mea-
Table 1
Photovoltaic parameters of devices with sensitizers B0, B1, and B2 at full sunlight
(AM 1.5 G, 100 mW cmꢁ2
)
Dye
Dye loada (10ꢁ7 mol cmꢁ2
)
Voc (V)
Jsc (mA cmꢁ2
)
ff
h (%)
B0
B1
B2
N719
3.28
3.03
3.13
0.64
0.86
0.81
0.71
6.88
11.33
9.22
0.63
0.57
0.60
0.49
2.79
5.56
4.49
8.04
22.88
a
Amount of the dyes absorbed on TiO2 film.
sured under the same conditions. The spectra of monochromatic
incident-photon-to-current conversion efficiency (IPCE) of the de-
vices are shown in Fig. 6, and the characteristics of the spectral
response of the photocurrent is comparable to the absorption
spectra of the dyes. The IPCE curve of the cell based on dye B1
shows the highest plateau from 404 to 496 nm, with a maximum of
81% at 468 nm. However, the lower IPCE response for the device
sensitized by B2 with long conjugation of the bridge of fluo-
renylvinylenes compared with that of B1 might originate from the
poor injection efficiency.24
In addition, the difference of the IPCE spectra of Bn-based cell
(Fig. 6) could explain why Jsc values of the device are in the order of
JscB0<JscB2<JscB1. The high Voc value of B1 indicates that the electron
recombination process is retarded more effectively in comparison
to that in the device of B0 and B2. In order to confirm this judg-
ment, a dark current test was performed (Fig. 5). By extrapolating
Fig. 4. The cyclic voltammograms of dyes Bn, scan rate¼50 mV sꢁ1, versus Fcþ/Fc.

H. Zhou et al. / Tetrahedron 67 (2011) 8477e8483
8481
versus Ag/AgCl (saturated) as a reference electrode. The scan rate
was maintained at 50 mV sꢁ1. The thickness of the film was
measured using Veeco Dektak 150 Surface Profiler. Ether and
tetrahydrofuran (THF) were distilled over sodium and benzo-
phenone. DMF was distilled from phosphorous pentoxide, and
other chemicals were used as received without further
purification.
4.2. Synthetic procedures and characterizations
4.2.1. 3-(4-(Diphenylamino)phenyl)-2-cyanoacrylic acid (B0). Com-
pound B0 was synthesized according to the corresponding litera-
ture procedures.22 Mp: 195.0e197.0 ꢀC. 1H NMR (500 MHz, CDCl3)
d
¼8.14 (s, 1H), 7.88 (d, J¼9.0 Hz, 2H), 7.31e7.39 (m, 4H), 7.14e7.24
(m, 6H), 6.97 (d, J¼9.0 Hz, 2H). IR (KBr, cmꢁ1): 3062, 3036, 2961,
2931, 2873, 2211, 1672, 1585, 958, 826, 761. Elemental analysis
calculated for C22H16N2O2: C, 77.63; H, 4.74; N, 8.23. Found: C, 77.72,
H, 4.56, N, 8.27.
Fig. 6. Incident-photo-to-current conversion efficiency (IPCE) curves of DSSCs sensi-
tized with Bn and N719.
4.2.2. N-Phenyl-N-(4-vinylphenyl)benzenamine (3). Potassium tert-
butoxide 2.60 g (23.2 mmol) was added to a solution of 11.6 g
(28.6 mmol) triphenylmethylphosphonium iodine in 50 mL dry
THF at 0 ꢀC. After the mixture was stirred for 15 min at room
temperature, 6.50 g (24.0 mmol) 4-(N,N-diphenylamino)benzal-
dehyde (1) was added at 0 ꢀC. And the mixture was stirred at room
temperature for another 3 h, it was then poured into 400 mL water.
The solid was collected by filtration. The crude product was
recrystallized in ethyl alcohol to give a white solid in a yield of 89%.
the high potential region of the IeV curves to I¼0, the onset po-
tentials of dark currents for the three dyes are estimated as 0.57 V,
0.96 V, and 0.91 V for B0, B1, and B2, respectively. This result
suggests that B1 showed a large dark current and thus suppressed
the electron recombination between TiO2 and Iꢁ/I3ꢁ redox couple in
the electrolyte compared with B2.23,33
Mp: 91.0e92.0 ꢀC. 1H NMR (500 MHz, CDCl3)
d
¼7.28 (d, J¼8.5 Hz,
3. Conclusion
2H), 7.23e7.26 (m, 4H), 7.09 (d, J¼8.0 Hz, 4H), 6.98e7.03 (m, 4H),
6.63e6.69 (m, 1H), 6.63 (d, J¼16.5 Hz, 1H), 5.15 (d, J¼8.5 Hz, 1H). IR
(KBr, cmꢁ1): 3085, 3061, 3033, 3003, 2976, 1625, 1592, 992, 841,
760. Elemental analysis calculated for C20H17N: C, 88.52; H, 6.31; N,
5.16. Found: C, 88.49, H, 6.43, N, 5.17. MS (MALDI-TOF), m/z: calcd:
271.4, found: 270.6 (see Fig. S2).
New fluorenylvinylenes bridged triphenylamine-based dyes Bn
have been synthesized and employed in organic dye-sensitized
solar cell. Although a longer conjugation length of the linker may
give the increased molar extinction coefficients, the recombination
of the photo-induced electrons and triiodide was increased, leading
to a lower IPCE response of B2-based cell compared with that of B1.
The maximum photo-to-electrical energy conversion efficiency of
5.56% was achieved in the DSSC based on B1 under AM 1.5 irradi-
ation (100 mW cmꢁ2). As a result, the introduction of the 9,9-di-n-
octylfluorene-2-vinylene conjugated spacer can improve the per-
formance of DSSCs efficiently, and the balanced conjugation length
4.2.3. (E)-7-(4-(Diphenylamino)styryl)-9,9-dioctyl-9H-fluorene-2-
carbaldehyde (4). A mixture of 2.71 g (10.0 mmol) N-phenyl-N-(4-
vinylphenyl)benzenamine (3), 4.97 g (10.00 mmol) 2-bromo-7-
formyl-9,9-di-n-octylfluorene (2), 2.76 g (20.00 mmol) anhy-
drous potassium carbonate, 3.22
g (10.00 mmol) tetrabuty-
lammonium bromide, and 20 mg (0.089 mmol) Pd(OAc)2 was
added into 15 mL anhydrous DMF under N2 atmosphere. The
resulting mixture was stirred at 110 ꢀC for 12 h, and then was
cooled to room temperature, followed by poured into 400 mL
water with stirring. The mixture was extracted with CH2Cl2
(3ꢂ50 mL), the organic liquid was combined and washed with
brine. After dried with anhydrous MgSO4, the solvent was re-
moved. The crude product was purified by column chromatogram
(silica gel) with petroleum ether/dichloromethane (4:1) as eluent,
and then recrystallized in petroleum ether to give a green solid in
a yield of 72%. Mp: 90.0e92.0 ꢀC. 1H NMR (500 MHz, CDCl3)
of the linker in DepeA type dyes is of importance in the perfor-
mance of DSSCs.
4. Experimental section
4.1. Materials and measurements
1H NMR spectra were recorded on a Mercury plus 500 MHz
using CDCl3 as solvent in all cases. 13C NMR spectra were recor-
ded on a Mercury plus 125 MHz using CDCl3 as solvent in all
cases. UVevis absorption spectra were determined on a Shi-
madzu UV-1601PC spectrophotometer. Photoluminescence (PL)
spectra were carried out on a Shimadzu RF-5301 luminescence
spectrometer. IR spectra were measured using a Germany bruker
vertex 80v FT-IR spectrometer by incorporating samples in KBr
disks. Mass spectra were performed on Agilent 1100 MS series
and AXIMA CFR MALDI/TOF (Matrix assisted laser desorption
ionization/Time-of-flight) MS (COMPACT). C, H, and N elemental
analyses were taken on a PerkineElmer 240C elemental analyzer.
Cyclic voltammetry (CV) was performed using CHI 604B elec-
trochemical working station in DCM containing 0.1 M Bu4NBF4 as
a supporting electrolyte at room temperature. Platinum button
and platinum wire were used as a working electrode and
a counter electrode, respectively. The potentials were recorded
d
10.05 (s, 1H), 7.86e7.84 (m, 2H), 7.80 (d, J¼7.8 Hz, 1H), 7.74 (d,
J¼7.9 Hz, 1H), 7.53e7.51 (m, 1H), 7.47 (s, 1H), 7.44e7.41 (m, 2H),
7.30e7.26 (m, 5H), 7.15e7.09 (m, 5H), 7.08e7.02 (m, 4H), 2.10e1.95
(m, 4H), 1.21e0.99 (m, 20H), 0.82e0.78 (m, 6H), 0.70e0.51 (m, 4H)
(see Fig. S3). IR (KBr, cmꢁ1): 3057, 3024, 2952, 2926, 2854, 1698,
1602, 1591, 966, 821, 755. Elemental analysis calculated for
C50H57NO: C, 87.29; H, 8.35; N, 2.04. Found: C, 87.41, H, 8.23, N,
2.17. MS, m/z: calcd: 688.0, found: 687.8 (see Fig. S4).
4.2.4. (E)-4-(2-(9,9-Dioctyl-7-vinyl-9H-fluoren-2-yl)vinyl)-N,N-di-
phenylaniline (5). According to the synthetic procedure of com-
pound 3, compound 5 was prepared from 4 and triphenyl-
methylphosphonium iodine in a yield of 87% as a light blue solid.
Mp: 108.0e110.0 ꢀC. 1H NMR (500 MHz, CDCl3)
d
7.63 (t, J¼8.0 Hz,

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H. Zhou et al. / Tetrahedron 67 (2011) 8477e8483
2H), 7.47 (d, J¼8.9 Hz, 1H), 7.45e7.34 (m, 5H), 7.30e7.26 (m, 4H),
7.14e7.10 (m, 6H), 7.09e7.01 (m, 4H), 6.84e6.78 (m, 1H), 5.80 (d,
J¼17.5 Hz, 1H), 5.26 (d, J¼10.9 Hz, 1H), 2.0e1.97 (m, 4H), 1.22e1.02
(m, 20H), 0.83e0.78 (m, 6H), 0.70e0.62 (m, 4H) (see Fig. S5). IR
(KBr, cmꢁ1): 3062, 3029, 2955, 2927, 2852, 1628, 1593, 961, 825,
751. Elemental analysis calculated for C51H59N: C, 89.29; H, 8.67; N,
2.04. Found: C, 89.17, H, 8.80, N, 2.11. MS, m/z: calcd: 686.02, found:
685.4 (see Fig. S6).
Fig. S13). IR (KBr, cmꢁ1): 3059, 3027, 2952, 2926, 2852, 2217, 1625,
1589, 961, 823, 752. Elemental analysis calculated for C84H100N2O2:
C, 86.25; H, 8.62; N, 2.39. Found: C, 86.32, H, 8.76, N, 2.27. MS, m/z:
calcd: 1169.7, found: 1169.9 (see Fig. S14).
4.3. Theoretical calculation methods
The geometrical structures of Bn were optimized by employing
the density functional theory at the B3LYP/6-31 level with the
Gaussian 03W program package.34 Molecular orbitals were visu-
alized using Gaussview.
4.2.5. 7-((E)-2-(7-(4-(Diphenylamino)styryl)-9,9-dioctyl-9H-fluo-
ren-2-yl)vinyl)-9,9-dioctyl-9H-fluorene-2-carbaldehyde
(6). According to the synthetic procedure of compound 4, com-
pound 6 was prepared from compound 5 and 2-bromo-7-formyl-
9,9-di-n-octylfluorene (2) in a yield of 73% as a light green solid.
4.4. Preparation of Bn-absorbed TiO2 films
Mp: 50.0e52.0 ꢀC. 1H NMR (500 MHz, CDCl3)
d
10.03 (s, 1H),
FTO glasses (Solar 2.2 mm thickness, 15 U
/cm2, Nippon Sheet
7.85e7.82 (m, 2H), 7.79 (d, J¼7.7 Hz, 1H), 7.74 (d, J¼7.9 Hz, 1H),
7.66e7.62 (m, 2H), 7.57e7.55 (m, 1H), 7.53e7.48 (m, 3H), 7.46e7.44
(m, 1H), 7.43e7.37 (m, 3H), 7.27e7.23 (m, 6H), 7.13e7.06 (m, 6H),
7.06e6.99 (m, 4H), 2.07e1.98 (m, 8H), 1.18e1.00 (m, 40H),
0.79e0.75 (m, 12H), 0.68e0.53 (m, 8H) (see Fig. S7). IR (KBr, cmꢁ1):
3058, 3025, 2953, 2927, 2852, 1693, 1602, 1591, 963, 823, 751. Ele-
mental analysis calculated for C81H99NO: C, 88.23; H, 9.05; N, 1.27.
Found: C, 88.19, H, 8.86, N, 1.41. MS, m/z: calcd: 1102.6, found:
1102.7 (see Fig. S8).
Glass) were first cleaned in a detergent solution using an ultrasonic
bath for 10 min, and then rinsed with distilled water and ethanol.
After UVeO3 irradiation for 18 min, the TiO2 paste, which consists
of 16.2% of P25 (NanoTiO2) and 4.5% of ethyl cellulose in terpineol,
was printed on a conducting glass using a screen printing technique
and the electrode was kept in a clean box for a few minutes fol-
lowed by dried for 6 min at 125 ꢀC. This screen-printing procedure
with the nanocrystalline-TiO2 paste was repeated until the thick-
ness reaches 7 m
m. The area of the TiO2 film was 0.24 cm2 (0.55 cm
of diameter). The film was further dried in air at 100 ꢀC for 15 min
followed by another 15 min at 150 ꢀC. Then, the film was calcined at
350 ꢀC for 10 min. Finally, the film was treated at 450 ꢀC for 30 min
under oxygen atmosphere. The TiO2 electrodes were immerged in
the aqueous of TiCl4 (40 mM) for 30 min at 70 ꢀC, and then sintered
at 500 ꢀC for 30 min. When the temperature was decreased to
100 ꢀC, the electrodes were immersed into the solution of the dye in
dry CH2Cl2 (0.2 mM) and kept at room temperature for 12 h.
To prepare a counter electrode, a small hole was drilled in an
4.2.6. (Z)-2-Cyano-3-(7-(4-(diphenylamino)styryl)-9,9-dioctyl-9H-
fluoren-2-yl)acrylic acid (B1). A mixture of compound 4 (0.7 g,
1.02 mmol), cyanoacetic acid (2.13 g, 2.50 mmol), ammonium ac-
etate (200 mg, 2.60 mmol) in glacial acetic acid (30 mL) was heated
at 135 ꢀC for 24 h. After cooling to room temperature, the mixture
was poured into ice water. The resulting precipitate was filtered off
and washed with water. The solid was dissolved in EtOAc and
washed with brine. The organic phase was dried by anhydrous
MgSO4, and the solvent was removed. The crude product was pu-
rified by column chromatogram (silica gel) with methyl alcohol/
dichloromethane (1:10) as eluent to give a yellow solid (690 mg,
FTO glass (Solar 2.2 mm thickness, 15
U
/cm2, Nippon Sheet Glass).
The perforated plate was rinsed with distilled water and ethanol,
followed by ultrasonic treatment in 0.1 M HCl solution in iso-
propanol for 5 min to remove an iron contamination source. The
FTO glass was washed by distilled water and ethanol, and then was
treated with ultrasound in acetone for 10 min. After the FTO glass
was dried by N2 flow, H2PtCl6 paste was printed on a conducting
glass using a screen printing technique and the electrode was kept
in a clean box overnight, and then was calcined at 400 ꢀC for 10 min
to obtain the counter Pt electrode.
A sandwich cell was prepared by using the dye-anchored TiO2
film as a working electrode and a counter Pt electrode, which were
assembled with a hot-melt-ionomer film of Surlyn polymer gasket.
The electrodes were tightly held and heated at 120 ꢀC for 25 s to
seal the two electrodes in seal machine (DHS-ES2). The aperture of
the Surlyn frame was 2 mm larger than that of the area of TiO2 film
and its width was 1 mm. The hole in the counter electrode was
sealed by a film of Surlyn. A hole was then made in the film of
Surlyn covered on the hole by a needle. A drop of an electrolyte was
put on the hole in the back of the counter electrode. It was in-
troduced into the cell via vacuum backfilling. Finally, the hole was
sealed using Surlyn film and a cover glass (0.13e0.17 mm of
thickness). The edge of the FTO outside of the cell was roughened
with sandpaper. An electrolyte solution used was 0.6 M DMPII (1,2-
dimetyl-3-methylimidazolium iodide), 0.1 M LiI, 0.05 M I2, 0.5 M
TBP (4-tert-butylpyridine) and 0.05 mM GUSCN (Guanidine Thio-
cyanate) in acetonitrile.
90%) as. Mp: 68.0e70.0 ꢀC. 1H NMR (500 MHz, DMSO)
d 8.00 (d,
J¼23.1 Hz, 2H), 7.89e7.82 (m, 3H), 7.69 (s, 1H), 7.57e7.53 (m, 3H),
7.35e7.29 (m, 5H), 7.20 (d, J¼16.3 Hz, 1H), 7.09e7.04 (m, 6H), 6.97
(d, J¼8.7 Hz, 2H), 2.08e1.92 (m, 4H), 1.16e0.97 (m, 20H), 0.75 (t,
J¼7.1 Hz, 6H), 0.61e0.47 (m, 4H) (see Fig. S9). 13C NMR (125 MHz,
CDCl3) d 155.63, 153.14, 152.15, 151.37, 147.90, 147.36, 139.46, 138.69,
131.77, 130.82, 129.71, 128.92, 127.82, 127.68, 126.03, 125.72, 125.00,
123.86, 123.53, 121.48, 121.17, 120.49, 97.40, 55.71, 40.74, 30.36,
30.12, 30.00, 29.61, 24.27, 22.99, 14.49 (see Fig. S10). IR (KBr, cmꢁ1):
3063, 3031, 2952, 2925, 2853, 2217, 1624, 1591, 962, 825, 752. El-
emental analysis calculated for C53H58N2O2: C, 84.31; H, 7.74; N,
3.71. Found: C, 84.44, H, 7.65, N, 3.81. MS, m/z: calcd: 755.0, found:
755.0 (see Fig. S11).
4.2.7. 2-Cyano-3-(7-((E)-2-(7-(4-(diphenylamino)-styryl)-9,9-
dioctyl-9H-fluoren-2-yl)vinyl)-9,9-dioctyl-9H-fluoren-2-yl)acrylic
acid (B2). According to the synthetic procedure of compound B1,
compound B2 was prepared from compound 6 and cyanoacetic
acid in a yield of 92% as a yellow solid. Mp: 104.0e106.0 ꢀC. 1H NMR
(500 MHz, DMSO)
d
7.96 (d, J¼17.4 Hz, 2H), 7.90e7.83 (m, 3H),
7.81e7.76 (m, 3H), 7.72 (s, 1H), 7.66 (s, 1H), 7.63e7.59 (m, 2H), 7.55
(d, J¼8.7 Hz, 3H), 7.48e7.40 (m, 2H), 7.36e7.32 (m, 4H), 7.29 (d,
J¼16.5 Hz, 1H), 7.21 (d, J¼16.3 Hz, 1H), 7.10e7.04 (m, 6H), 6.98 (d,
J¼8.7 Hz, 2H), 2.10e1.98 (m, 8H), 1.14e1.00 (m, 40H), 0.76e0.71 (m,
12H), 0.61e0.51 (m, 8H) (see Fig. S12). 13C NMR (125 MHz, CDCl3)
d
154.77, 153.09, 152.10, 151.97, 147.99, 147.66, 145.88, 144.32, 141.31,
4.5. Photovoltaic characterization of DSSCs
140.74, 139.85, 138.47, 137.09, 136.58, 132.17, 131.30, 129.98, 129.70,
128.58, 128.13, 127.91, 127.70, 126.27, 125.88, 125.45, 124.91, 124.04,
123.43, 121.43, 121.22, 121.04, 120.46, 120.32, 98.22, 55.75, 55.41,
41.00, 40.69, 32.19, 30.47, 30.12, 29.64, 24.27, 24.18, 23.00, 14.47 (see
Photoelectrochemical data were measured using a 150 W xenon
light source that was focused to give 100 mW cmꢁ2, the equivalentof
one sun at AM 1.5, at the surface of the test cell. The spectral output of

H. Zhou et al. / Tetrahedron 67 (2011) 8477e8483
8483
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onto the photovoltaic cell under test. The IPCE values were de-
termined at 2 nm intervals.4 The solar-energy-to-electricity con-
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Acknowledgements
20. Hwang, S.; Lee, J. H.; Park, C.; Lee, H.; Kim, C.; Park, C.; Lee, M. H.; Lee, A.; Park,
This work is financially supported by the National Natural Sci-
ence Foundation of China (20874034 and 51073068), 973 Program
(2009CB939701), and Open Project of State Key Laboratory of Su-
pramolecular Structure and Materials (SKLSSM201102).
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2011.09.008.
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