Synthesis of sensitizers containing donor cascade of triarylamine and dimethylarylamine moieties for dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tet.2010.02.095

Four triarylamine derivatives (XS6-9) containing N,N-dimethylaryl amine units as secondary electron-donating groups are designed and synthesized. These dyes were applied into nanocrystalline TiO₂ dye-sensitized solar cells through standard operations. For a typical device the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach 93%, with a short-circuit photocurrent density (J_sc) 10.8 mA cm^-2, an open-circuit photovoltage (V_oc) 690 mV, and fill factor (FF) 0.61, which corresponds to an overall conversion efficiency of 4.54%.

Full text of DOI:10.1016/j.tet.2010.02.095

Tetrahedron 66 (2010) 3318–3325
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of sensitizers containing donor cascade of triarylamine and
dimethylarylamine moieties for dye-sensitized solar cells
*
Lu Zhang, Yongkang Liu, Zhongyuan Wang, Mao Liang, Zhe Sun, Song Xue
Department of Applied Chemistry, Tianjin University of Technology, Tianjin 300384, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 January 2010
Received in revised form 22 February 2010
Accepted 26 February 2010
Available online 6 March 2010
Four triarylamine derivatives (XS6–9) containing N,N-dimethylaryl amine units as secondary electron-
donating groups are designed and synthesized. These dyes were applied into nanocrystalline TiO2
dye-sensitized solar cells through standard operations. For a typical device the maximal monochromatic
incident photon-to-current conversion efficiency (IPCE) can reach 93%, with a short-circuit photocurrent
density (Jsc) 10.8 mA cmꢀ2, an open-circuit photovoltage (Voc) 690 mV, and fill factor (FF) 0.61, which
corresponds to an overall conversion efficiency of 4.54%.
Keywords:
Dye-sensitized solar cell
Photovoltaic
Ó 2010 Elsevier Ltd. All rights reserved.
Donor cascade
Triarylamine
Dimethylarylamine
1. Introduction
design of organic dyes is the changes in the electron-donating
nature and amine unit for the donor moiety. Various amines,
For the past two decades, more and more attentions from both
academia and industry have been paid to the development of dye-
sensitized solar cells (DSSCs) because of their simple structure, low
incident-light-angle, and potential for low-cost manufacturing.1,2
The ruthenium complexes used as sensitizers for cells have
achieved power conversion efficiencies above 11%.3 In comparison
with ruthenium complexes, the DSSCs based on organic dyes have
also been remarkably improved due to their organic structural
variation, high molar extinction coefficients, and low-cost prepa-
ration.4 Recently, the highest overall photoelectric conversion
efficiency of solar cells using organic dyes as sensitizers has reached
9%, which indicated the promising perspective of organic dyes for
cells. Great effort has been made on the design of new organic dyes
in order to obtain excellent sensitizers with high power conversion
efficiency and long-term stability.5–8
such as coumarin,10 indoline,11 oligoene,12 hemicyanine, and cya-
nine13 have been used and exhibited good performances of DSSCs.
Organic dyes derived from triphenylamine (TPA) with TPA as the
electron donor and 2-cyanoacrylic acid as the electron acceptor
afforded a 3.3% of power conversion efficiency.14 Its analogy dyes
based on diphenylvinyl triarylamine improved the power conver-
sion efficiency to 5.47%,15 which showed that expansion of
p-
electron systems conjugated with phenyl ring of TPA had obvious
effect on the performance of DSSCs and gave high power conver-
sion efficiency. On the other hand, organic dyes with D–D-p-A
structure based on triphenylamine and carbazole are reported by
several groups.16 Their studies suggested that great performance of
organic dyes with D–D–p-A structure over the simple D–p-A
configuration can be achieved by molecular design. Furthermore,
introducing a secondary electron donor into the dye molecule can
increase electron-density of donor and enhance molar extinction
coefficient, which resulted in high overall conversion effi-
ciency.12c,17 Based on these strategies, we designed and synthesized
four new triarylamine derivatives XS6–9 containing N,N-dimethyl-
aryl amine moieties as secondary electron-donating groups. Both
Most organic dyes contain a structure of donor-p-acceptor
moieties. 2-Cyanoacrylic acid or rhodanine moiety acts as the
electron acceptor while amines act as the electron donor. These two
parts are connected by
thiophene unit, thereby forming a D–
has been made through variation of functionalized thiophene units
for the
-conjugated systems.9 Another important approach on the
p-conjugated systems, such as methene or
p
-A structure. Great progress
triarylamine and N,N-dimethylaryl amine constructed a D–D–p-A
p
structure with electron donor cascade in dyes. We are especially
interested in the strong electron donor of N,N-dimethylaryl amine,
which may be possible to induce efficient light-induced charge
separation. Here, we wish to report the synthesis, characterization,
and photovoltaic properties of these new organic dyes (Scheme 1).
* Corresponding author. Tel.: þ86 22 60214250; fax: þ86 22 60214252; e-mail
address: xuesong@ustc.edu.cn.
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.02.095

L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
3319
HOOC
HOOC
HOOC
NC
N
CN
COOH
NC
S
NC
N
S
N
N
S
N
S
N
N
N
N
N
N
N
XS9
XS6
XS8
XS7
Scheme 1. Structure of dyes (XS6–9).
2. Results and discussion
broaden the absorption spectrum and to red-shifted. When the
dyes were excited within respective * bands in an air-
p–p
The synthetic routes of four organic dyes XS6–9 are shown in
Scheme 2. Phosphonate 1 was used as starting material to react
with 4-bromobenzaldehyde in the presence of ButOK to give
intermediate 2. Treatment of the intermediate 2 with n-BuLi and
trimethyl borate afforded a key intermediate 4-(2,2-bis(4-(di-
methylamino)phenyl)vinyl)phenylboronic acid (3). 4-((4-Bromo-
phenyl)(phenyl)amino)benzaldehyde (5) was prepared from
triphenylamine via bromonation reaction with NBS and Vilsmeier–
Haack reaction with POCl3 in DMF according to literature pro-
cedure.18 Treatment of the boronic acid 3 with the aldehyde 5
through Suzuki coupling reaction gave an important intermediate
aldehyde 6. Then the target dye XS6 was obtained via Knoevenagel
condensation reaction of the aldehyde 6 with cyanoacetic acid in
the presence of a catalytic amount of piperidine. The dyes XS7–9
were obtained according to the similar procedures of XS6, and their
synthesis routes are summarized in Scheme 2. These dyes
containing thiophene unit were desired to induce a red shift of the
equilibrated chloroform solution at 298 K, they exhibited strong
luminescence maximum of 522–575 nm.
Electrochemical properties of the dyes XS6–9 are listed in
Table 1. The redox potentials of these dyes were obtained by cyclic
voltammetric (CV) curve with 0.1 M tetrabutylammonium hexa-
fluorophosphate in acetonitrile solution. The dyes absorbed on TiO2
films showed quasi-reversible couples. The oxidation potentials
(Eox) of XS6–9 on nanocrystalline TiO2 electrodes are 1.09, 1.14, 1.46,
and 0.97 V versus NHE, respectively. These Eox value are more
positive than the Iꢀ3 /Iꢀ redox potential (w0.4 V vs NHE), and in-
dicate that the oxidized dyes formed from respective electrons
injection into the conduction band of TiO2 will favorably accept
electrons from Iꢀ ions in thermodynamic property. The reduction
potentials (Ered) of the dyes are calculated from the oxidation
potentials and the E0–0 determined from the intersection of
absorption and emission spectra. The excited-state oxidation
potentials of the four dyes are calculated to be ꢀ1.32, ꢀ1.28, ꢀ0.97,
and ꢀ1.41 V, respectively. They are much more negative than the
conduction band of TiO2 at approximately ꢀ0.5 V versus NHE.19
Therefore, the four dyes used as sensitizers will have sufficient
driving force for electron transfer from the excited dye molecules to
the conduction band of TiO2 electrode.
absorption spectrum by expansion of
p-electron systems conju-
gated with phenyl ring of TPA. All the intermediates and target dyes
(XS6–9) were characterized by standard spectroscopic methods.
The UV–vis and emission spectra of organic dyes in chloroform
solution are displayed in Figure 1, together with the spectra of the
corresponding sensitizers absorbed on TiO2 film. The four dyes
show strong absorption bands at around 350–450 nm. XS6 and XS9
display two visible bands, appearing at 387/432 nm and
384/463 nm, respectively. The second absorption peak (463 nm) for
XS9 is red-shifted in comparison with that of XS6, which is due to
the introduction of thiophene moiety, manifesting the effect of
thiophene unit in increasing conjugation. For XS7, one of the
corresponding absorptions is red-shifted to 416 nm, which is
ascribed to the thiophene unit between triarylamine and N,N-di-
The photovoltaic performance was measured at 100 mW cmꢀ2
under AM 1.5 conditions. The incident monochromatic photon-
to-current conversion efficiency (IPCE) was obtained with
a sandwich cell using 0.6 M 1,2-dimethyl-3-n-propylimidazolium
iodide (DMPImI), 0.1 M LiI, 0.05 M I2, and 0.5 M tertbutylpyridine
in acetonitrile solution. The IPCE data of dyes XS6–9 plotted as
a function of wavelength are shown in Figure 2. The four dyes as
sensitizers produced a strikingly high maximum IPCE value. The
IPCE value for XS6 reached 86% at 460 nm, and the dyes XS7–9
reached 88%, 90%, and 93%, respectively. The high maximum IPCE
value for these four dyes may be tentatively ascribed to high
electron injection efficiency and charge separation efficiency
methylaryl amine moieties, extending the
p-conjugation system.
The other absorption is appearing as a shoulder peak at around
432 nm. When bi-thiophene units are introduced to form XS8, the
corresponding absorption peak is further red-shifted and overlaps
the other peak, therefore look like one peak. It is notable that the
because of the D–D–p-A structure with strongly electron donor
unit of N,N-dimethylaryl amine. Unfortunately, the IPCE spectrum
for the four dyes was responded at about 400–550 nm in wave-
length, which is consistent with the absorption spectra on the
TiO2 film. Their lack of broad absorption in the visible spectrum
will result in low power conversion efficiency.
molar extinction coefficients (3) of these four dyes XS6–9 are
124,800, 194,000, 263,700, and 90,100 Mꢀ1 cmꢀ1, respectively,
which are very high in comparison with ruthenium complexes. The
dyes containing thiophene unit between triarylamine and N,N-
dimethylaryl amine, such as XS7–8, gave much higher molar
extinction coefficient than that of dyes XS6 and XS9. The greater
absorption coefficient of organic dyes indicates a good ability of
light harvesting and allows for a thinner nanocrystalline film.
Adsorption of the dyes XS6–9 onto a TiO2 electrode was observed to
The corresponding photocurrent–voltage curves are shown in
Figure 3, and the overall conversion efficiencies (h) for these DSSCs
are listed in Table 2. The performance of XS6 in DSSCs showed
a shortcircuit current (Jsc) of 7.8 mA cmꢀ2, an open-circuit voltage
(Voc) of 680 mV, and an overall conversion efficiency (h) of 3.29%.

3320
L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
OH
B
Br
OH
CHO
PO(OEt)2
n-BuLi
Br
ButOK THF
B(OCH3)3
N
N
N
N
N
N
1
2
3
COOH
CHO
NC
CHO
NC
COOH
N
N
3, Pd(Ph3P)4
1) NBS, CCl4
piperidine, CH3CN
N
N
2) DMF, POCl3
Br
5
4
N
N
N
N
6
XS6
HOOC
NC
OHC
CHO
N
N
CHO
N
N
OH
S
NC
COOH
5, Pd(Ph3P)4
NBS, DMF
S
3, Pd(Ph3P)4
B
OH
S
N
piperidine, CH3CN
S
N
S
Br
7
8
N
N
9
XS7
OHC
HOOC
N
N
CN
CHO
CHO
OH
S
8, Pd(Ph3P)4
NBS, DMF
3, Pd(Ph3P)4
NC
COOH
B
S
S
S
N
OH
N
piperidine, CH3CN
S
N
S
S
S
Br
S
10
11
N
N
N
12
XS8
HOOC
OHC
NC
S
S
OHC
Br
S
OHC
OH
S
NC
COOH
B
3, Pd(Ph3P)4
OH
N
N
piperidine, CH3CN
N
Pd(Ph3P)4
N
Br
Br
13
14
N
N
N
N
15
XS9
Scheme 2. Synthesis of organic dyes (XS6–9).

L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
3321
12
XS6
XS7
XS8
XS9
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
XS6
XS7
XS8
XS9
10
8
(a)
6
4
2
300
350
400
450
Wavelength/nm
500
550
600
650
700
0
0
100
200
300
400
500
600
700
1.4
1.2
1.0
0.8
0.6
0.4
0.2
XS6
Voltage [mV]
XS7
XS8
XS9
Figure 3. Current–potential (I–V) curves for the dyes XS6–9.
(b)
Table 2
Photovoltaic performance of DSSCs sensitized with the four dyesa
Dye
Jsc/mA cmꢀ2
Voc/mV
FF
h/%
XS6
XS6
XS7
XS8
XS9
N719
9.1
7.8
8.2
9.5
10.8
14.2
693
680
644
658
690
714
0.64
0.62
0.65
0.64
0.61
0.63
4.04
3.29b
3.43
4.00
4.54
6.39a
400
450
500
Wavelength/nm
550
600
a
Photovoltaic performances of DSSCs were measured under irradiation of AM
1.5 G simulated solar light (100 mW cmꢀ2) at room temperature with a 0.16 cm2
working area. The thickness of the TiO2 film was 9 mm.
Figure 1. Absorption and emission spectra of dyes XS6–9 in chloroform (1ꢁ10ꢀ5 M) (a)
and on TiO2 film (b).
b
Chenodeoxycholic acid was not employed as co-adsorbate.
When CDCA was employed as a co-adsorbate, the overall conver-
Table 1
Optical properties and electrochemical properties of four dyes
sion efficiency was improved into 4.04% with higher Jsc and Voc
value. The DSSCs based on XS7 showed relatively lower Jsc and Voc
,
a
Dye lmax
,
nm (
3
, Mꢀ1 cmꢀ1
)
E0–0/eVb Eox/V versus Ered/V versus
NHEc
NHEd
resulting in a lower value of 3.43%. The dye XS9 shows the highest
h
overall conversion efficiency of 4.54% among the four dyes, which
resulted from the largest shortcircuit current and high open-circuit
voltage. The high efficiency of XS9 dye is mainly attributed to more
sufficient driving force for the photo-induced electron transfer
from the excited dye molecules to the conduction band of TiO2
electrode and broader absorption in visible spectrum. These results
suggest that a suitable structure of XS9 with thiophene located
between TPA donor and cyanoacrylic acceptor is responsible for its
prominent solar-to-electrical conversion efficiency. With this
structure, the XS9 exhibited broadening light response, leading to
broad IPCE response and high photovoltaic performance. A slightly
higher Voc value of XS6 and XS9 compared to XS7–8 may be
ascribed to the lower Eox value, which might be beneficial for
retarding the electron transfer from TiO2 to the oxidized dye or
electrolyte, resulting in enhancing open-circuit voltage.20 For a fair
comparison, the N719-sensitized TiO2 solar cell showed an
efficiency of 6.39%, with a Jsc of 14.2 mA cmꢀ2, a Voc of 714 mV, and
a fill factor (FF) of 0.63.
To get further insight into the molecular structure and elec-
tron distribution of XS9, density functional theory (DFT) calcu-
lations were made on a B3LYP/6-31 G level with Gaussian 03.21
Figure 4 shows the electron distribution of the HOMO and
LUMO of XS9. It is obviously that, the HOMO of XS9 is localized
over the diphenylvinyl unit and the LUMO is localized over the
cyanoacrylic unit through thiophene, indicating that the HOMO–
LUMO excitation moves the electron distribution from the
diphenylvinyl unit to the cyanoacrylic acid moiety, thus allowing
an efficient photo-induced electron transfer from the dye to the
TiO2 electrode under light irradiation.
XS6 387 (120,400), 432 (124,800) 2.41
1.09
1.14
1.46
0.97
ꢀ1.32
ꢀ1.28
ꢀ0.97
ꢀ1.41
XS7 416 (199,900), 432(194,000)
XS8 434 (263,700)
XS9 384 (134,800), 463 (90,100)
2.42
2.43
2.38
a
Absorption and emission spectra were measured in chloroform.
E0–0 values were calculated from intersect of the normalized absorption and the
b
emission spectra (lint): E0–0¼1240/lint
.
c
The oxidation potentials (vs NHE) of dyes were measured in CH3CN with tet-
rabutylammonium perchlorate (TBAP, 0.1 M) as supporting electrolyte.
d
Ered was calculated from EoxꢀE0–0
.
100
80
60
40
20
0
XS6
XS7
XS8
XS9
400
450
500
Wavelength/nm
550
600
650
Figure 2. IPCE spectra for DSSCs based on the dyes XS6–9.

3322
L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
Figure 4. The frontier molecular orbitals of the HOMO and LUMO calculated at B3LYP/6-31þG (D) level of XS9.
In summary, we have designed and synthesized four organic
Ag/Agþ (nonaqueous) electrode as reference electrode with a scan
rate of 50 mV/s. Tetrabutylammonium perchlorate (TBAP, 0.1 mol/
L) and acetonitrile were used as supporting electrolyte and solvent,
respectively. The measurements were calibrated using ferrocene as
standard. The redox potential of ferrocene internal reference was
taken as 0.63 V versus NHE. The solutions were purged with argon
and stirred for 15 min before the measurements.
sensitizers containing donor cascade of triarylamine and N,N-
dimethylaryl amine moieties. The dyes gave high molar extinction
coefficient and high maximum IPCE value (93%). These results
imply that synthesis of sensitizer containing a secondary electron-
donating group is a possible alternative to produce excellent IPCE
value with high electron injection efficiency and charge separa-
tion efficiency. The power conversion efficiency of the DSSCs
based on the XS9 reached 4.54%. The lower efficiency of these four
3.3. Fabrication of DSSCs
dyes compared to literature reports (
the lack of broad absorption in the visible spectrum. It is possible
to develop highly efficient organic sensitizers through expansion
h
¼9%) is mainly ascribed to
TiO2 colloid was prepared according to the literature,23 which
was used for the preparation of the nanocrystalline films. The TiO2
paste consisting of 18 wt % TiO2, 9 wt % ethyl cellulose and 73 wt %
terpineol was firstly prepared, which was printed on a conducting
glass using a screen printing technique. The thickness of the TiO2
film was controlled by selection of screen mesh size and repetition
of printing. A second layer of commercial TiO2 (P25) anatase par-
ticles was applied. The film was dried in air at 120 ꢂC for 30 min and
calcined at 500 ꢂC for 30 min under flowing oxygen before cooling
to room temperature. The heated electrodes were impregnated
with a 0.05 M titanium tetrachloride solution in a water-saturated
desiccator at 70 ꢂC for 30 min and then recalcined at 500 ꢂC for
30 min. The as-prepared TiO2 electrode was stained by immersing
of
p-electron systems between TPA donor and acceptor to
broaden spectral response. The more conjugated organic dyes by
functionalized thiophene units were desired to induce broader
absorption in the visible spectrum, and these works are now in
progress.
3. Experimental section
3.1. Materials and instruments
The FTO conducting glass (fluorine doped SnO2, sheet resistance
10
U
/square, transmission >90% in the visible) was obtained from
it into a dye solution containing 300 mM dye sensitizers and 2 mM
Nippon Sheet Glass, Hyogo, Japan, and cleaned by a standard
procedure. All reactions and manipulations were carried out under
argon atmosphere with the use of Schlenk techniques. Diethyl ether
and THF were distilled from Na/benzophenone under nitrogen
atmosphere. Dichloromethane and chloroform were distilled from
calcium hydride under nitrogen atmosphere. Titanium (IV)
isopropoxide and tertbutylpyridine were purchased from Aldrich.
Lithium iodide was purchased from Alfa. The starting materials
diethyl bis(4-(dimethylamino)phenyl)methylphosphonate (1) and
4-bromo-N-(4-bromophenyl)-N-phenylbenzenamine (13) were
synthesized following the known procedure.11,22
chenodeoxycholic acid (CDCA) in a mixture of chloroform and
methanol (volume ratio 10/1) for 24 h. The CDCA was employed as
a co-adsorbate to prevent dye aggregations on the TiO2 surface. Pt
catalyst was deposited on the FTO glass by coating with a drop of
H2PtCl6 solution (40 mM in ethanol) with the heat treatment at
395 ꢂC for 15 min to give photoanode. The photocathode (the dye-
deposited TiO2 film) was placed on top of the counter electrode and
was tightly clipped together to form a cell. Electrolyte was then
injected into the seam between two electrodes. The electrolyte
employed was a solution of 0.6 M 1,2-dimethyl-3-n-propylimid-
azolium iodide (DMPImI), 0.1 M LiI, 0.05 M I2, and 0.5 M tertbu-
tylpyridine in acetonitrile.
1H NMR and 13C NMR spectra were recorded on a Bruker AM-
300 or AM-400 spectrometer. Mass spectra were recorded on
a LCQ AD (Thermofinnigan, USA) mass spectrometer. The melting
point was taken on a RY-1 thermometer and temperatures were
uncorrected.
3.4. Characterization of DSSCs
The photocurrent–voltage (I–V) characteristics of solar cells
were carried out using a Keithley 2400 digital source meter con-
trolled by a computer and a standard AM 1.5 solar simulator-Oriel
91160–1000 (300 W) SOLAR SIMULATOR 2ꢁ2 BEAM. The active
electrode area was 0.16 cm2. The action spectra of monochromatic
incident photon-to-current conversion efficiency (IPCE) for solar
cells were performed by using a commercial setup (QTest Station
2000 IPCE Measurement System, CROWNTECH, USA).
3.2. Photophysical and electrochemical measurements
The absorption spectra of the dyes either in solution or on the
adsorbed TiO2 films was measured by HITACHI U-3310 spectro-
photometer. Adsorption of the dye on the TiO2 surface was done by
soaking the TiO2 electrode in a dry chloroform solution of the dye
(standard concentration 3ꢁ10ꢀ4 M) at room temperature for 24 h.
Fluorescence measurement was carried with a HITACHI F-4500
fluorescence spectrophotometer. FT-IR spectra were obtained with
a Bio-Rad FTS 135 FT-IR instrument.
3.5. The detailed experimental procedures and
characterization data
Electrochemical measurements were performed at room tem-
perature under Ar atmosphere on a Voltammetric Analyzer (Met-
3.5.1. 4,40-(2-(4-Bromophenyl)ethane-1,1-diyl)bis(N,N-dimethylani-
line) (2). To a suspension of diethyl bis(4-(dimethylamino) phenyl)
methylphosphonate (1) (1.5 g, 3.6 mmol) in 20 mL dry THF at 0 ꢂC
under N2, ButOK (0.6 g, 5.4 mmol) was added and the mixture
rohm,
mAutolab III) with polymer coated ITO glass as the working
electrode, and platinum (Pt) plate as the counter electrode, using

L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
3323
turned yellow. The mixture was stirred at this temperature for 1 h
before 4-bromobenzaldehyde (0.686 g, 3 mmol) dissolved in 10 ml
dry THF was added dropwise. The mixture was stirred at 0 ꢂC for 1 h
and moved into room temperature for another 12 h. Saturated
NH4Cl was added and the resulting mixture was extracted with
EtOAc (3ꢁ20 mL). The combined extracts were washed with water
and dried over MgSO4. After filtration and removal of the solvent
under vacuum, the crude product was recrystallized from petro-
leum to give a yellow product (0.909 g, 60%). Mp: 162–163 ꢂC. IR
filtered. Afterremovingthesolvent, theresultingsolidwaspurifiedby
column chromatography on silica gel (petroleum/ethyl acetate¼10:1
as eluent) as a yellow powder (45%). Mp: 128–129 ꢂC. IR (KBr): 3449,
3030, 2886, 2799,1689,1608 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d 9.82
(s,1H), 7.70 (d, J¼8.7 Hz, 2H), 7.53 (d, J¼7.6 Hz, 2H), 7.39–7.33 (m, 4H),
7.28–7.25 (m, 2H), 7.21–7.05 (m, 11H), 6.78 (s,1H), 6.72–6.67 (m, 4H),
3.00 (s, 6H), 2.98 (s, 6H). 13C NMR (75 MHz, CDCl3):
d 190.5, 153.3,
150.1, 149.8, 146.2, 145.1, 143.2, 138.0, 137.5, 137.1, 132.4, 131.4, 129.8,
129.4, 128.8, 128.6, 127.9, 126.4, 126.3, 126.2, 125.2, 123.3, 119.7, 112.4,
112.1, 40.6, 40.5. HRMS (ESI) calcd for C43H40N3O (MþHþ): 613.3093,
found: 613.3090.
(KBr): 2992, 2888, 2804, 1888, 1606 cmꢀ1 1H NMR (300 MHz,
.
CDCl3):
d
7.45 (d, J¼8.4 Hz, 2H), 7.26–7.22 (m, 4H), 6.93 (d, J¼8.4 Hz,
2H), 6.67 (d, J¼8.4 Hz, 5H), 2.98 (s, 6H), 2.96 (s, 6H). 13C NMR
(75 MHz, CDCl3):
d
150.2, 149.9, 143.8, 137.8, 132.1, 130.9, 130.8,
3.5.5. 3-(4-((40-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)biphenyl-4-
yl)(phenyl)amino)phenyl)-2-cyanoacrylic acid (XS6). To a solution of
compound 6 (0.184 g, 0.3 mmol) and cyanoacetic acid (0.042 g,
0.5 mmol) in acetonitrile (10 mL) was added dichlormethane (5 mL)
128.8, 128.1, 122.4, 119.2, 112.3, 112.0, 40.6, 40.5. HRMS (ESI) calcd
for C24H25N2Br (Mþ): 420.1201, found: 420.1196.
3.5.2. 4-(2,2-Bis(4-(dimethylamino)phenyl)vinyl) phenylboronic acid
(3). A solution of compound 2 (0.421 g, 1.0 mmol) in dry THF
(10 mL) was cooled to ꢀ78 ꢂC. To this solution n-BuLi (0.42 mL,
2.7 M in hexane, 1.134 mmol) was added dropwise through
a dropping funnel. The mixture was stirred at this temperature for
3 h before 7.8 g of trimethyl borate (0.28 mL, 2.5 mmol) dissolved in
20 mL of dry THF was added in a dropwise manner. The solution
was allowed to warm to room temperature and stirred for 12 h. The
reaction was quenched with saturated NH4Cl, extracted with
chloroform and dried over MgSO4. After filtration and removal of
the solvent under vacuum, the product was purified by a silica gel
column (petroleum/ethyl acetate¼3:1 as eluent) to give a kelly
powder (0.27 g, 70% yield). Mp: 67–69 ꢂC. IR (KBr): 3479, 3416,
and piperidine (50 mL). The solution was refluxed for 24 h. After
cooling the solution, the solvent was removed in vacuo. The pure
product was obtained by silica gel chromatography (CH2Cl2/
MeOH¼10:1 as eluent) as an orange powder in 92% yield. Mp: 176–
179 ꢂC. IR (KBr): 3434, 2210, 1592 cmꢀ1. 1H NMR (300 MHz, DMSO-
d6):
d
7.87–7.85 (m, 3H), 7.79 (d, J¼8.7 Hz, 2H), 7.62 (d, J¼8.4 Hz, 2H),
7.43 (d, J¼8.4 Hz, 2H), 7.37 (d, J¼7.5 Hz, 2H), 7.20–7.07 (m, 9H), 6.93
(d, J¼7.5 Hz, 2H), 6.76 (s,1H), 6.71 (d, J¼8.7 Hz, 2H), 6.66 (d, J¼8.7 Hz,
2H), 2.92 (s, 6H), 2.90 (s, 6H). 13C NMR (75 MHz, DMSO-d6):
d 165.1,
150.8, 150.6, 150.5, 148.6, 146.8, 146.1, 143.5, 138.3, 137.2, 136.4, 132.2,
132.1, 132.0, 131.6, 130.8, 130.4, 129.2, 128.4, 128.3, 126.7, 126.6, 126.4,
125.9, 123.2, 121.2, 120.2, 113.2, 112.8, 44.4. HRMS (EI) calcd for
C45H40N4 ([MꢀCO2]þ): 636.3253, found: 636.3259.
3242, 1610, 1519 cmꢀ1. 1H NMR (400 MHz, CDCl3):
4H), 7.14–7.10 (m, 5H), 6.73–6.70 (m, 4H), 3.03(s, 3H), 3.00 (s, 3H),
2.99 (s, 3H), 2.98 (s, 3H). 13C NMR (100 MHz, CDCl3):
149.6, 149.3,
d 7.32–7.27 (m,
3.5.6. 4-(Phenyl(4-(thiophen-2-yl)phenyl)amino) benzaldehyde (7). A
mixture of compound 5 (3.52 g, 10 mmol), thiophen-2-ylboronic
acid (1.408 g, 11 mmol), Pd(PPh3)4 (300 mg, 0.255 mmol), aqueous
1 M Na2CO3 (25 mL), and 45 mL DME was refluxed for 18 h under N2.
Ethyl acetate (20 mL) was added before cooling down to room
temperature. The organic layer was separated and washed three
times with water, dried over anhydrous MgSO4, and filtered. After
removing the solvent, the resulting solid was purified by column
chromatography on silica gel (petroleum/ethyl acetate¼5:1 as elu-
ent) to give a yellow powder (2.84 g, 86% yield). Mp: 126–127 ꢂC. IR
d
131.4, 130.6, 130.0, 129.3, 128.9, 128.5, 127.9, 115.0, 112.9, 112.3,
112.2, 112.1, 40.9, 40.7, 40.68, 40.60. HRMS (ESI) calcd for
C24H27BN2O2 (MþHþ): 387.2244, found: 387.2257.
3.5.3. 4-((4-Bromophenyl)(phenyl)amino) benzaldehyde (5)22b. A
mixture of N-bromosuccinimide (5.34 g, 30 mmol), triphenylamine
(4) (7.65 g, 30 mmol), and 80 mL of CCl4 was refluxed for 4 h. After
cooling to room temperature, the precipitate was filtered off and
recrystallized from EtOH to give 4-bromo-N,N-diphenylaniline as
a buff powder (8.747 g, 89.9% yield). To a solution of 4-bromo-N,N-
diphenylaniline (3.849 g, 11.87 mmol) in anhydrous DMF (12 mL,
152 mmol) at 0 ꢂC under N2 atmosphere was added POCl3 (4.33 mL,
29 mmol) dropwise and stirred for 1 h. Subsequently, the mixture
was heated at 50 ꢂC for 12 h. The mixture was cooled and poured
into an ice-water with vigorous stirring. After neutralization with
NaOH, the mixture was further stirred at 70 ꢂC for 1 h. After cooling
and extraction with ethyl acetate, the organic fractions were
combined and dried over MgSO4. The resulting solid was purified
by column chromatography on silica gel (petroleum/ethyl
acetate¼5:1 as eluent) to give a buff powder (4.157 g, 99.4% yield).
(KBr): 2739, 1685, 1585 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d 9.82 (s,
1H), 7.70 (d, J¼7.4 Hz, 2H), 7.57 (d, J¼6.7 Hz, 2H), 7.38–7.33 (m, 2H),
7.28–7.15 (m, 7H), 7.14–7.06(m, 3H). 13C NMR (75 MHz, CDCl3):
d
190.6, 153.3, 146.2, 145.7, 143.9, 131.5, 131.3, 130.0, 129.8, 128.3,
127.4, 126.6, 126.4, 125.5, 125.0, 123.2, 120.1. HRMS (ESI) calcd for
C23H18NOS (MþHþ): 356.1104, found: 356.1109.
3.5.7. 4-((4-(5-Bromothiophen-2-yl)phenyl) (phenyl)amino)benzalde-
hyde (8). Compound 7 (6.606 g, 9.379 mmol) and NBS (1.669 g,
9.379 mmol) were dissolved in DMF (100 mL) and stirred at room
temperature for 24 h. The mixture was poured into water (100 mL)
and leading to a precipitate yellow solid. The precipitate was filtered
and purified by chromatography on silica gel (petroleum/ethyl
acetate¼5:1 as eluent) to give a yellow solid (4.01 g, 98% yield). Mp:
IR (KBr): 1686, 1604, 1588, 1576, 1505, 1487, 818 cmꢀ1
(400 MHz, CDCl3):
9.85 (s, 1H), 7.71 (d, J¼8.0 Hz, 2H), 7.47 (d,
J¼8.0 Hz, 2H), 7.39–7.35 (m, 2H), 7.23–7.16 (m, 3H), 7.07–7.03 (m,
4H). 13C NMR (100 MHz, CDCl3):
190.4, 152.9, 145.9, 145.4, 132.8,
.
1H NMR
d
107–109 ꢂC. IR (KBr): 2803, 1695, 459 cmꢀ1 1H NMR (300 MHz,
.
d
CDCl3):
7.39–7.34 (m, 2H), 7.22–7.06 (m, 7H), 7.05–7.00 (m, 2H). 13C NMR
(75 MHz, CDCl3): 190.6, 153.2, 146.1, 145.3, 133.1, 131.5, 131.2, 130.3,
d
9.83 (s, 1H), 7.72 (d, J¼6.9 Hz, 2H), 7.46 (d, J¼6.7 Hz, 2H),
131.4, 130.2, 129.9, 127.4, 126.3, 125.4, 120.0, 117.7.
d
3.5.4. 4-((40-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)biphenyl-4-
yl)(phenyl)amino) benzaldehyde (6). A mixture of compound 5
(0.352 g, 1 mmol), 4-(2,2-bis(4-(dimethy lamino)phenyl)vinyl)ph-
enylboronic acid (3) (0.425 g, 1.1 mmol), Pd(PPh3)4 (50 mg,
0.042 mmol), aqueous 1 M Na2CO3 (3 mL), and 10 mL DME was
refluxed for 18 h under N2. Ethyl acetate was added before cooling
down to room temperature. The organic layer was separated and
washed three times with water, dried over anhydrous MgSO4, and
129.9, 127.7, 127.0, 126.6, 126.2, 125.6, 123.3, 120.3, 111.5. HRMS (ESI)
calcd for C23H17NOSBr (MþHþ): 434.0209, found: 434.0197.
3.5.8. 4-((4-(5-(4-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)phenyl)-
thiophen-2-yl)phenyl)(phenyl) amino)benzaldehyde (9). The prod-
uct was synthesized according to the procedure for synthesis of
compound 6, giving an orange powder of the product in 84% yield.
Mp: 126–128 ꢂC. IR (KBr): 2795,1748, 1508 cmꢀ1. 1H NMR (300 MHz,

3324
L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
CDCl3):
d
9.82 (s, 1H), 7.70 (d, J¼6.9 Hz, 2H), 7.55 (d, J¼6.7 Hz, 2H),
124.6, 124.0, 123.5, 123.4, 120.2, 112.6, 112.2, 40.7. HRMS (ESI) calcd
7.40–7.33 (m, 4H), 7.27–7.20 (m, 5H), 7.18–7.11 (m, 5H), 7.07 (d,
for C51H44N3OS2 (MþHþ): 778.2920, found: 778.2918.
J¼4.4 Hz, 5H), 6.74–6.65 (m, 5H), 2.99 (s, 6H), 2.97 (s, 6H). 13C NMR
(75 MHz, CDCl3):
d
190.6, 153.3, 150.3, 150.0, 146.2, 142.3, 138.5, 132.5,
3.5.13. 3-(4-((4-(50-(4-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)ph-
enyl)-2,20-bithiophen-5-yl)phenyl) (phenyl)amino)phenyl)-2-cyano-
acrylic acid (XS8). The product was synthesized according to the
procedure for synthesis of XS6, giving a salmon pink powder of the
product in 68% yield. Mp: 233–234 ꢂC. IR (KBr): 3649, 3446, 2215,1653,
131.6, 131.2, 130.1, 130.0, 129.7, 129.0, 128.7, 126.9, 126.6, 126.4, 125.5,
125.1,124.2,123.8,123.4,120.1,112.6,112.2, 40.7. HRMS (ESI) calcd for
C47H42N3OS (MþHþ): 696.3043, found: 696.3018.
3.5.9. 3-(4-((4-(5-(4-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)phenyl)-
thiophen-2-yl)(phenyl) amino)phenyl))-2-cyanoacrylic acid (XS7). The
product was synthesized according to the procedure for synthesis of
XS6, giving an orange powder of the product in 92% yield. Mp: 17ꢀ41–
1608 cmꢀ1. 1H NMR (300 MHz, CDCl3):
2H), 7.28–7.25 (m, 2H), 7.16–7.08 (m, 7H), 6.95–6.88 (m, 13H), 6.58–
6.49(m, 6H), 2.82 (s, 6H), 2.80 (s, 6H).13CNMR(75 MHz,CDCl3):
161.5,
d 7.93 (br s, 1H), 7.59–7.57 (m,
d
151.7, 150.6, 149.9, 149.6, 145.6, 143.0, 141.8, 138.0, 136.5, 135.8, 132.3,
132.1, 131.2, 130.9, 130.1, 129.6, 128.6, 126.5, 126.1, 125.6, 125.1, 124.7,
124.4, 124.3, 123.6, 123.2, 120.3, 118.7, 112.7, 112.3, 112.0, 41.2. HRMS
(ESI) calcd for C54H45N4O2S2 (MþHþ): 845.2978, found: 845.2976.
175 ꢂC. IR (KBr): 3565, 3446, 1791, 1772, 1749, 1700, 1683, 1653 cm
.
1H NMR (400 MHz, CDCl3):
(d, J¼7.6 Hz, 2H), 7.41–7.36 (m, 5H), 7.28–7.02 (m, 15H), 6.79–6.76 (m,
4H), 3.02 (s, 6H), 3.00 (s, 6H). 13C NMR (100 MHz, CDCl3):
167.4,
d
8.15 (s, 1H), 7.87 (d, J¼7.6 Hz, 2H), 7.55
d
154.2, 152.1, 149.8, 149.6, 145.6, 144.9, 143.9, 143.0, 142.1, 138.1, 133.2,
131.4, 129.9, 129.8, 129.6, 129.1, 128.8, 126.7, 126.5, 126.2, 126.0, 125.6,
124.9, 124.0, 123.6, 119.7, 112.9, 112.6, 79.1, 40.8. HRMS (ESI) calcd for
C50H43N4O2S (MþHþ): 763.3101, found: 763.3090.
3.5.14. 5-(4-((4-Bromophenyl)(phenyl)amino) phenyl)thiophene-2-
carbaldehyde (14). A mixture of 4-bromo-N-(4-bromophenyl)-N-
phenylbenzenamine (13) (0.806 g, 2 mmol), Pd(PPh3)4 (60 mg,
0.050 mmol), 5-formylthiophen-2-ylboronic acid (0.343 g, 2.2 mmol),
aqueous 1 M Na2CO3 (6 mL), and 20 mL DME was refluxed for 18 h
under N2. Ethyl acetate (10 mL) was added before cooling down to
room temperature. The organic layer was separated and washed three
times with water, dried over anhydrous MgSO4, and filtered. After
removing the solvent, the resulting solid was purified by column
chromatography on silica gel (petroleum/ethyl acetate¼10:1 as elu-
ent) to give a yellow powder (0.342 g, 39.4% yield). Mp: 132–134 ꢂC. IR
3.5.10. 4-((4-(2,20-Bithiophen-5-yl)phenyl) (phenyl)amino)benzalde-
hyde (10). A mixture of compound
8 (2.118 g, 4.88 mmol),
Pd(PPh3)4 (150 mg, 0.127 mmol), thiophen-2-ylboronic acid
(0.687 g, 5.37 mmol), aqueous 1 M Na2CO3 (15 mL), and 25 mL DME
was refluxed for 18 h under N2. Ethyl acetate (10 mL) was added
before cooling down to room temperature. The organic layer was
separated and washed three times with water, dried over anhy-
drous MgSO4, and filtered. After removing the solvent, the resulting
solid was purified by column chromatography on silica gel (petro-
leum/ethyl acetate¼5:1 as eluent) to give a yellow powder (1.489 g,
(KBr): 2796,1663,1591 cmꢀ1.1H NMR (400 MHz, CDCl3):
d 9.88(s,1H),
7.74 (d, J¼4.0 Hz,1H), 7.55 (dd, J¼6.8,1.6 Hz, 2H), 7.41 (d, J¼6.4 Hz, 2H),
7.40–7.18 (m, 3H), 7.15–7.07 (m, 5H), 7.02 (d, J¼6.4 Hz, 2H). 13C NMR
(100 MHz, CDCl3): d 182.6, 154.2,148.6, 146.6, 141.6,137.7, 132.7, 129.7,
70%). Mp: 170–172 ꢂC. IR (KBr): 3742, 3687, 2816, 1506 cmꢀ1
.
1H
9.83 (s, 1H), 7.72 (d, J¼6.6 Hz, 2H), 7.55 (d,
J¼6.9 Hz, 2H), 7.39–7.33 (m, 2H), 7.26–7.12 (m, 9H), 7.10–7.02 (m,
3H). 13C NMR (75 MHz, CDCl3):
190.6, 153.2, 146.2, 145.8, 142.5,
127.4, 126.8, 126.3, 125.3, 125.2, 124.3, 123.9, 122.9, 116.2. HRMS (ESI)
NMR (300 MHz, CDCl3):
d
calcd for C23H17NOSBr (MþHþ): 434.0209, found: 434.0201.
d
3.5.15. 5-(4-((40-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)biphenyl-
4-yl)(phenyl)amino)phenyl) thiophen-2-carbaldehyde (15). The
product was synthesized according to the procedure for synthesis
of compound 6, giving a yellow powder of the product in 42% yield.
Mp: 204–205 ꢂC. IR (KBr): 1654,1608, 815 cmꢀ1. 1H NMR (300 MHz,
137.6,136.9,131.6,130.8,130.1,129.8,128.1,127.0,126.6,126.3,125.6,
124.9, 124.7, 123.9, 123.8, 120.2. HRMS (ESI) calcd for C27H20NOS2
(MþHþ): 438.0981, found: 438.0973.
3.5.11. 4-((4-(50-Bromo-2,20-bithiophen-5-yl)phenyl)(phenyl)ami-
no)benzaldehyde (11). Compound 10 (2.149 g, 4.919 mmol) and
NBS (0.876 g, 4.919 mmol) were dissolved in DMF (50 mL) and
stirred at room temperature for 24 h. The mixture was poured into
water (50 mL) and leading to precipitate yellow solid. The pre-
cipitate was filtered and purified by chromatography on silica gel
(petroleum/ethyl acetate¼5:1 as eluent) to give a yellow solid
(2.371 g, 93%). Mp: 144–146 ꢂC. IR (KBr): 3528, 3419, 1792, 1749,
CDCl3):
d
9.83 (s, 1H), 7.69 (d, J¼3.9 Hz,1H), 7.52–7.45 (m, 4H), 7.36–
7.31 (m, 2H), 7.29–7.23 (m, 6H), 7.16–7.06 (m, 10H), 6.75 (s, 1H),
6.69–6.65 (m, 4H), 2.98 (s, 6H), 2.94 (s, 6H). 13C NMR (75 MHz,
CDCl3):
d 182.0, 154.3, 149.9, 148.9, 145.8, 137.7, 137.5, 136.2, 132.5,
131.4,129.7,129.5,128.8,127.6,127.3,126.0,125.3,125.1,124.1,123.4,
123.0, 122.7, 112.5, 112.2, 41.3. HRMS (ESI) calcd for C47H42N3OS
(MþHþ): 696.3043, found: 696.3049.
1717, 1653, 1604 cmꢀ1
.
1H NMR (300 MHz, CDCl3):
d
9.83 (s, 1H),
3.5.16. 3-(5-(4-((40-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)-
biphenyl-4-yl)(phenyl)amino) phenyl)thiophen-2-yl)-2-cyanoacrylic
acid (XS9). The product was synthesized according to the pro-
cedure for synthesis of XS6, giving an orange powder of the product
in 42.4% yield. Mp: >300 ꢂC. IR (KBr): 2942, 2211, 1595, 1561, 1518,
7.72 (d, J¼7.2 Hz, 2H), 7.52 (d, J¼6.6 Hz, 2H), 7.39–7.34 (m, 2H),
7.26–7.11 (m, 6H), 7.10–7.05 (m, 3H), 6.99 (d, J¼3.9 Hz, 1H), 6.93 (d,
J¼3.6 Hz, 1H). 13C NMR (75 MHz, CDCl3):
d 190.6, 153.2, 146.1, 146.0,
143.1, 135.8, 131.5, 130.9, 130.5, 130.1, 129.9, 127.0, 126.6, 126.2,
125.6, 125.1, 123.9, 123.8, 120.3. HRMS (ESI) calcd for C27H19NOS2Br
(MþHþ): 516.0086, found: 516.0071.
1491 cmꢀ1. 1H NMR (300 MHz, CDCl3):
d 8.27 (br s, 1H), 7.49 (s, 1H),
7.31–7.28 (m, 2H), 7.24–7.13 (m, 8H), 7.07–7.02 (m, 5H), 6.99–6.96
(m, 5H), 6.89–6.87 (m, 2H), 6.73 (s, 1H), 6.65 (d, J¼6.9 Hz, 4H), 2.93
3.5.12. 4-((4-(50-(4-(2,2-Bis(4-(dimethylamino) phenyl)vinyl)phenyl)-
2,20-bithiophen-5-yl) phenyl)(phenyl)amino)benzaldehyde (12). The
product was synthesized according to the procedure for synthesis of
compound 6, giving a salmon pink powder of the proꢀd1uct in 52%
(s, 6H), 2.86 (s, 6H). 13C NMR (75 MHz, CDCl3):
d 169.5, 152.3, 149.8,
149.5, 148.1, 146.6, 145.6, 145.2, 142.7, 138.1, 137.4, 137.1, 135.7, 134.6,
132.5, 131.3, 129.7, 129.4, 128.7, 127.4, 127.1, 126.4, 125.9, 125.2,
124.8, 123.9, 123.5, 123.1, 122.5, 118.6, 112.7, 112.4, 41.3, 41.2. HRMS
(ESI) calcd for C50H43N4O2S (MþHþ): 763.3101, found: 763.3101.
yield. Mp: 201–202 ꢂC. IR (KBr): 2803, 1756, 1506 cm
.
1H NMR
(300 MHz, CDCl3):
d
9.82 (s,1H), 7.70 (dd, J¼6.8, 2.0 Hz, 2H), 7.53 (dd,
J¼6.5, 2.0 Hz, 2H), 7.38–7.33 (m, 4H), 7.27–7.22 (m, 2H), 7.20–7.11 (m,
Acknowledgements
11H), 7.07 (d, J¼7.5 Hz, 4H), 6.73–6.65 (m, 5H), 2.99 (s, 6H), 2.96 (s,
6H). 13C NMR (75 MHz, CDCl3):
d
190.7, 153.2, 150.3, 150.0, 146.2,
We are grateful to the National 863 Program (2009AA05Z421)
and the Tianjin Natural Science Foundation (09JCZDJC24400) for
financial supports.
145.7, 143.7, 143.6, 142.3, 138.6, 137.1, 136.2, 132.4, 131.6, 131.2, 130.8,
130.1, 130.0, 129.8, 129.0, 128.7, 126.9, 126.6, 126.3, 125.6, 125.2, 124.8,

L. Zhang et al. / Tetrahedron 66 (2010) 3318–3325
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