Organic dye bearing asymmetric double donor-π-Acceptor chains for dye-sensitized solar cells

Article abstract of DOI:10.1021/jo201057b

A novel efficient metal free sensitizer containing asymmetric double donor-π-acceptor chains (DC) was synthesized for dye-sensitized solar cells (DSSCs). Comparing to 3.80%, 4.40% and 4.64% for the DSSCs based on the dyes with single chain (SC1, SC2) and

Full text of DOI:10.1021/jo201057b

NOTE
pubs.acs.org/joc
Organic Dye Bearing Asymmetric Double Donor-π-Acceptor Chains
for Dye-Sensitized Solar Cells
||
Yanping Hong,†, Jin-Yun Liao,‡ Derong Cao,*,†,§ Xufeng Zang,† Dai-Bin Kuang,*,‡ Lingyun Wang,†
Herbert Meier,^ and Cheng-Yong Su‡
†School of Chemistry and Chemical Engineering and §State Key Laboratory of Luminescent Materials and Devices,
South China University of Technology, Guangzhou 510640, China
‡MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, KLGHEI of Environment and Energy Chemistry, State Key Laboratory
of Optoelectronic Materials and Technologies, School of Chemistry and Chemical Engineering, Sun Yat-sen University,
Guangzhou 510275, China
College of Food Science and Engineering, Jiangxi Agricultural University, Nanchang 330045, China
^Institute of Organic Chemistry, University of Mainz, 55099 Mainz, Germany
S Supporting Information
b
ABSTRACT: A novel efficient metal free sensitizer containing asym-
metric double donor-π-acceptor chains (DC) was synthesized for dye-
sensitized solar cells (DSSCs). Comparing to 3.80%, 4.40% and 4.64%
for the DSSCs based on the dyes with single chain (SC1, SC2) and
cosensitizers (SC1 + SC2), the overall conversion efficiency reaches
6.06% for DC-sensitized solar cells as a result of its longer electron
lifetime and higher incident monochromatic photon-to-current con-
version efficiency.
ye-sensitized solar cells (DSSCs) as one of the most
promising alternatives to crystalline Si-based photovoltaics
As is well-known, organic dyes bearing a single D-π-A system
often afford only one absorption peak in the visible region.
Hence, there will be much interest to design and synthesize novel
dyes containing two different D-π-A systems, which show two
different absorption bands in the visible light range.
D
for converting clean, inexhaustible sunlight to electricity have
received significant research interest due to their low fabrication
cost and relatively high power conversion efficiency (η) since
the first cell reported by Gr€atzel et al. in 1991.1 As a critical
component in DSSCs, the sensitizer plays a vital role in the light-
harvesting efficiency, providing electron injection into the con-
duction band of an oxide semiconductor (e.g., TiO2) upon light
excitation. Nowadays, the photoelectric conversion efficiency of
DSSCs sensitized by Ru-complex dyes has achieved maximum
power conversion efficiencies of more than 11%.2À4 In recent
years, metal-free organic dyes have been investigated intensely as
an alternative to noble Ru-complexes owing to their advantages
of high molar extinction coefficients, flexibility in structure
tailoring, low-cost preparation process, and compliance with
environmental issues.5 Many efficient metal-free dyes have been
explored for DSSCs showing good performance.6À20
Organic dyes possessing a rod-like configuration with donor
and acceptor moieties bridged by a π-conjugated unit (called
D-π-A structure) are considered as one of the most promising
classes of organic sensitizers. It is found that the photoinduced
intramolecule electron transfer takes place easily and the photo-
physical properties can be easily tuned by varying donor, spacer,
and acceptor moieties in these dyes.21À23 DSSCs with these dyes
show a better perfomance.24,25
In our previous work, it was demonstrated that organic dyes
containing two symmetric D-π-A chains (DB) could increase η
of DSSCs compared to the corresponding single D-π-A dye
because one molecule of DB contained two light-harvesting
units.26 However, DB did not broaden the absorption range
because the two chains are the same and absorb in the same range
of the sunlight. In this work, in order to increase the light-
harvesting units and broaden the absorption range of organic
dyes, we designed a novel organic dye containing two asymmetric
D-π-A chains that are linked by a nonconjugated n-hexane chain.
The resulting DC has two separate light-harvesting systems. In
one D-π-A chain, diphenylamine (DPA) was introduced as the
donor, and it would form the starburst structure similar to
triphenylamine (TPA), which could contribute to depress the
aggregation of dyes on the TiO2 surface. In the other D-π-A
chain, phenoxazine (POZ) was introduced as donor because of
its good light-havesting property in the visible region.27,28 Owing
to two different light-harvesting units in one dye molecule, DC
Received: June 3, 2011
Published: August 22, 2011
r
2011 American Chemical Society
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NOTE
Scheme 1. Synthesis of Dyes DC, SC1, and SC2
might be expected to exhibit a stronger and broader absorption
range, resulting in higher conversion efficiency of DSSC com-
pared to the reference dyes SC1 and SC2 with a single D-π-A
unit each.
The synthesis of the dyes SC1, SC2 and DC is shown in
Scheme 1. Well-known organic reactions including alkylation,
Vilsmeier and Knoevenagel reactions were used for this purpose.
The absorption spectra of the dyes in MeOH/CH2Cl2 (1:1)
solutions are shown in Figure 1, and the photophysical data are
collected in Table 1. All of these dyes have a relatively broad
and strong absorption in the ultraviolet and visible region. The
absorption bands at 220À400 nm are ascribed to the πÀπ*
transitions of the conjugated systems, while the bands in the
range of 400À650 nm are assigned to the intramolecular charge
transfer (ICT) between donor and acceptor. The major absorp-
tion peaks for SC1, SC2, and DC are at 463/343 nm, 513/
376 nm and 511/437/373 nm, respectively. In comparison to
SC1 and SC2, DC possesses a broader and more intensive
absorption in the ultraviolet and visible region, which could
produce a higher short-circuit current in the DSSCs. The molar
absorption coefficient (ε) of DC is much higher (εmax > 18043
MÀ1 cmÀ1) than those of SC1 and SC2 in the range of
400À553 nm, indicating that DC has a good light-harvesting
ability. It is worthy to note that the DC dye has two absorption
bands compared to the one absorption band of the SC1 and SC2
dyes between 400À600 nm. The absorption of DC is not just the
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The Journal of Organic Chemistry
NOTE
sum of the absorption bands of SC1 and SC2 (Figure 1). The
distinctive and stronger absorption of DC may be attributed to
the absorption overlap of the two independent D-π-A units.
Cyclic voltammetry (CV) was employed to estimate the first
oxidation potential (Eox) corresponding to the HOMO level of
the dyes (Table 1). The HOMO energy levels of the three dyes
are more positive than the IÀ/I3À redox couple (0.4 V vs NHE),
ensuring regeneration of the oxidized dyes by IÀ after electron
injection. The LUMO levels of the three dyes (calculated by
Eox À E0À0, Table 1) are sufficiently more negative than the fermi
level of TiO2 (À0.5 V vs NHE),29 and provided that an energy
gap of 0.2 eV is necessary for efficient electron injection.30,31
Hence the electron injection process is energetically favorable.
The JÀV curves and all essential photovoltaic properties of
DSSCs based on these dyes are demonstrated in Figure 2 and
summarized in Table 2, respectively. As shown in Figure 2 and
Figure 3 shows the IPCE as a function of the wavelength for
the DSSCs based on the three new dyes as sensitizers. There are
two characteristic peaks at 470 and 550 nm that were clearly
observed in the IPCE spectrum of the cosensitized cell, which
proved that the two organic dyes (SC1 + SC2) were efficiently
coadsorbed to the surface of TiO2, resulting in increase of the
photocurrent density compared to the single dye (Table 2).
Moreover, the IPCE of DC based DSSC exceeds 50% in a broad
spectral region from 350 to 630 nm and reaches its maximum of
72% at 450 nm. In contrast, the IPCE of cosensitizers (SC1 +
SC2)- and SC1-based DSSCs also exceed 50% in a narrow range
of 400À580 nm and 440À530 nm and give relatively low values
with maxima of 65% and 58% at 470 nm, respectively. The higher
and broader spectra response of the DC-based cell within the
whole visible region might contribute to a higher photocurrent,
Table 2, under the standard AM 1.5 G (100 mW cmÀ2
)
irradiation, the cosensitized (SC1 + SC2) solar cell shows
a higher photocurrent than the cells with individual dyes SC1
and SC2. A higher power conversion efficiency is due to a
better utilization of sunlight. Furthermore, the DC-sensitized
cell exhibits an overall conversion efficiency (η) of 6.06%
accompanied a short circuit photocurrent density (Jsc) of
12.75 mA cmÀ2, an open-circuit photovoltage (Voc) of 691 mV
and a fill factor (FF) of 0.69. The η value is much higher than
those of DSSCs based on SC1 (3.80%), SC2 (4.40%), and
cosensitizers (SC1 + SC2, 4.64%) because of its relatively higher
Jsc and Voc.
Figure 2. JÀV curves of DSSCs sensitized by SC1, SC2, cosensitizers
(SC1 + SC2) and DC.
Table 2. Photovoltaic Performance of DSSCs Based on the
Dyes SC1, SC2, Cosensitizers (SC1 + SC2) and DC
dye
Jsc (mA cmÀ2
)
Voc (mV)
FF
η (%)
SC1
8.20
9.13
655
679
674
691
0.71
0.71
0.69
0.69
3.80
4.40
4.64
6.06
SC2
SC1 + SC2
DC
10.02
12.75
Figure 1. Absorption spectra of the dyes in CH2Cl2/MeOH.
Table 1. Absorption, Emission, and Electrochemical Properties of Dyes SC1, SC2, and DC
absorption
emission
oxidation potential data
b
λmax in
ε
Eox
E0À0
Eox À E0À0
Egap
EHOMO/
ELUMOc (eV)
dye
CH2Cl2/MeOH (nm)
(MÀ1 cmÀ1
)
λmax (nm)
(V, vs NHE)
(V)a
(V, vs NHE)
(V, vs NHE)
1.08
SC1
343
463
376
513
373
437
511
22633
20311
8374
599 (463)
0.73
0.62
0.66
2.31
À1.58
À1.47
À1.63
À5.33/À2.75
SC2
DC
676 (513)
568 (511)
2.09
2.29
0.97
1.13
À5.12/À2.91
12667
31371
44976
26103
À5.44/À2.75d
À5.31/À2.94e
a E0À0 were estimated from the intersection of the normalized absorption and emission spectra (see Supporting Information). b Egap is the energy gap
c
between the Eox À E0À0 of the dye and the conductive band level of TiO2 (À0.5 V vs NHE). Calculated at the B3LYP-31G(d) level in vacuum.
d Calculated for the SC1 side of DC. e Calculated for the SC2 side of DC.
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which can be confirmed by the amount of dyes adsorbed on TiO2
films (1.72 Â 10À7 mol cmÀ2 for SC1, 1.23 Â 10À7 mol cmÀ2 for
SC2, (0.95 Â 10À7 + 0.52 Â 10À7 mol cmÀ2) for cosensitizers
(SC1 + SC2), and 1.56 Â 10À7 mol cmÀ2 for DC) according to
the UVÀvis absorption measurement. Compared to the cells
based on SC1 and SC2, the cosensitizers (SC1 + SC2)-based cell
exhibits the higher IPCE due to the broader absorption range
initiated from the two dyes coadsorbed on the TiO2 film. The
IPCE of the DC-based cell is higher than that of the cosensitizers
(SC1 + SC2)-based cell because the adsorbed amount of the
dyes in the former cell is higher, which results in a higher short-
circuit current density.
To further elucidate the photovoltaic results and display more
dynamic information of interfacial charge transfer process in
DSSCs sensitized by SC1, SC2, cosensitizers (SC1 + SC2), and
DC, electrochemical impedance spectroscopy (EIS) was also
performed in dark under a forward bias of 0.65 V. The Nyquist
plots and Bode phase plots for SC1, SC2, cosensitized (SC1 +
SC2), and DC sensitized cells are shown in Figure 4a and b,
respectively. Two semicircles, including a small one at higher fre-
quency (103À105 Hz) and a large semicircle at lower frequency
(1À102 Hz), are observed in the Nyquist plots. Usually, the
smaller semicircle corresponds to the high-frequency peaks of
Bode plots, which represents mainly the electron transfer process
from the Pt counter electrode to the oxidized species in the
electrolyte. The larger semicircle corresponding to the low
frequency peaks of Bode plots is ascribed to the recombination
resistance and chemical capacitance across the TiO2/redox
electrolyte interface. The recombination resistance of the DC-
based cell is smaller than those of other cells obtained from the
Z-view software (Supporting Information). However, the largest
chemical capacitance will result in the longest lifetime for the cell
based on DC. The electron lifetime values derived from the
Nyquist curves for the cells of SC1, SC2, cosensitizers (SC1 +
SC2), and DC are 52.7, 61.2, 53.8, and 61.7 ms, respectively (see
Supporting Information). The longer electron lifetime observed
for DC indicates a more effective suppression of the back
reaction of the injected electron with the I3À in the electrolyte,
reflecting in the improvement of the photocurrent and photo-
voltage yielding a substantially enhanced overall conversion
efficiency. The Bode phase plots (Figure 4b) likewise support
the differences in the electron lifetime (fitting from Nyquist
plots) for TiO2 films based on these dyes. The middle-frequency
peak of the DSSC based on DC shifts to lower frequency relative
to SC1, SC2, and cosensitizers (SC1 + SC2), indicating a longer
lifetime for the former dye.
Density functional theory (DFT) calculations were performed
on a B3LYP/6-31+G(d) level with Gaussian 03.27 The electron
distribution of the HOMO and LUMO of the dyes are shown in
the Supporting Information. The HOMOs of the dyes are
localized in the DPA and POZ units and the LUMOs are
localized in the cyanoacrylic unit and thiophene. The results
indicated that the HOMOÀLUMO excitation induced by
light moved the high electron density from the DPA and POZ
units to the cyanoacrylic acid moieties, thus allowing an efficient
photoinduced electron transfer from the dye to the TiO2
electrode.
In summary, a new efficient organic dye (DC) with double
asymmetric D-π-A chains and two corresponding reference dyes
containing single D-π-A chains [SC1, SC2, and cosensitizers
(SC1 + SC2)] were investigated. It was found that not only did
the dye with double D-π-A chains exhibit a broader and more
intense absorption than the reference dyes, but the incident
monochromatic photon-to-electron conversion efficiency
(IPCE), short-circuit current density, open-circuit voltage, and
overall conversion efficiency (η) of the DSSCs based on DC
were superior to the other dyes systems. The electron lifetime of
DC was the longest among these dyes. These results confirm that
the dyes containing two asymmetric D-π-A chains with different
donors might enhance significantly the photoelectrical perfor-
mance of DSSCs.
Figure 3. IPCE spectra of DSSCs based on the dyes.
Figure 4. Electrochemical impedance spectra for DSSCs sensitized by SC1, SC2, cosensitizers (SC1 + SC2) and DC, respectively: (a) Nyquist plots
and (b) Bode phase plots.
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’ EXPERIMENTAL SECTION
mixture was extracted three times with CH2Cl2. The combined organic
fractions were washed with brine and dried over anhydrous Na2SO4.
The solvent was removed under reduced pressure, and the residue was
purified by column chromatography with CH2Cl2/petroleum ether (v/v
= 5/1) as the eluent to give 3 (1.38 g, 70.6% yield) as a yellow solid, mp
48À49 ꢀC. 1H NMR (400 MHz, CDCl3) δ 1.45 (m, 4H), 1.66 (m, 2H),
1.75 (m, 2H), 3.50 (t, 2H,), 3.75 (t, 2H), 6.45 (m, 1H), 6.48 (m, 1H),
6.64 (m, 1H), 6.69 (m, 2H), 6.73 (m, 1H), 6.79 (m, 1H), 7.06 (m, 1H),
7.21 (m, 2H), 7.29 (m, 2H), 7.44 (m, 2H), 7.65 (m, 2H), 9.65 (s, 1H),
9.73 (s, 1H); 13C NMR (100 MHz, CDCl3) δ 25.1, 26.6, 26.8, 27.3, 44.0,
52.5, 110.4, 112.0, 113.3, 114.3, 115.8, 122.6, 123.9, 126.5, 126.5, 127.5,
128.6, 129.9, 130.2, 131.3, 131.8, 139.2, 144.7, 145.1, 145.7, 153.3, 189.6,
190.2; MS (m/z, ESI) calcd for C30H30N2O 490.2, found 513.2 [M +
Na]+. Anal. Calcd for C32H30N2O3: C, 78.34; H, 6.16; N, 5.71. Found:
C, 78.32; H, 6.18; N, 5.73.
(E)-3-[4-({6-[3-((E)-2-Cyano-2-thiophen-2-yl-vinyl)pheno-
xazin-10-yl]hexyl}phenyl-amino)phenyl]-2-thiophen-2-yl-
acrylonitrile (4). To a stirred solution of t-BuOK (0.112 g, 1.0 mmol)
and 2-thiopheneacetonitrile (0.985 g, 8.0 mmol) in THF (20 mL) was
added 3 (0.98 g, 2.0 mmol) at room temperature under nitrogen. The
reaction mixture was refluxed for 1 h and cooled to room temperature,
and then the mixture was concentrated under reduced pressure. The
resulting residue was purified by column chromatography with ethyl
acetate/petroleum ether (v/v = 1/10) as the eluent to give 4 (0.866 g,
61.8%) as a scarlet solid, mp 68À69 ꢀC. 1H NMR (400 MHz, CDCl3) δ
1.42 (m, 4H), 1.64 (m, 2H), 1.73 (m, 2H), 3.43 (t, 2H,), 3.73 (t, 2H),
6.38 (m, 1H), 6.44 (m, 1H), 6.62 (m, 1H), 6.67 (m, 1H), 6.74 (m, 2H),
6.78 (m, 1H), 6.84 (s, 2H), 7.01 (m, 2H), 7.04 (s, 1H), 7.21 (m, 8H),
7.40 (m, 2H), 7.71 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 25.1, 26.7,
26.8, 27.5, 43.9, 52.3, 100.4, 101.8, 110.9, 111.7, 114.7, 114.8, 115.7,
117.6, 118.1, 122.0, 122.9, 123.9, 124.8, 125.3, 125.5, 125.6, 126.0, 126.1,
126.7, 126.9, 128.0, 130.0, 130.9, 131.7, 135.6, 138.6, 139.9, 140.3, 144.7,
146.2, 150.1, 153.8; MS (m/z, ESI) calcd for C44H36N4OS2 700.2, found
723.4 [M + Na]+. Anal. Calcd for C44H36N4OS2: C, 75.40; H, 5.18; N,
7.99; S, 9.15. Found: C, 75.49; H, 5.20; N, 8.01; S, 9.14.
General. All reactions were carried out under an inert gas atmo-
sphere (nitrogen or argon). All solvents and chemicals were reagent
grade, and the solvents were dried by standard procedures. The column
chromatography was performed with 200À300 mesh silica gel as
1
stationary phase. The H and 13C NMR spectra were measured by
using a 400 MHz spectrometer. The absorption, emission spectra were
measured in CH2Cl2/MeOH solution (2 Â 10À5 M) at room tempera-
ture. The electrochemical impedance spectra of the DSSCs were
measured at a forward bias voltage of 0.65 V in the dark between
10 mHz and 1 MHz with an alternate current (AC) amplitude of 10 mV.
The Eox was measured in dry acetonitrile containing 0.1 M tetrabuty-
lammonium hexafluorophosphate (TBAPF6) as electrolyte (work elec-
trolyte FTO/TiO2/dye; reference electrode Ag/Ag+; calibrated with
ferrocenium/ferrocene (Fc/Fc+) as an external reference and converted
to NHE by addition of 0.65 mV; counter electrode Pt). DSSCs were
constructed by building a sandwich configuration with an electrolyte
composed of 0.6 M 1-methyl-3-propylimidazolium iodide (PMII),
0.10 M guanidinium thiocyanate (GuSCN), 0.03 M I2, 0.5 M tert-
butylpyridine in acetonitrile and valeronitrile (85:15).
(6-Bromohexyl)-diphenyl-amine (1). A solution of diphenyla-
mine (5.07 g, 30 mmol), NaH (1.8 g, 45 mmol) in MeO(CH2)2OMe
(30 mL) was stirred at room temperature for 0.5 h under argon. Then
1,6-dibromohexane (8.79 g, 36 mmol) was poured into the mixture and
heated at 85 ꢀC for 2 h. After cooling, the reaction mixture was filtered,
and the solvent was evaporated under reduced pressure. The residue was
purified by column chromatography with petroleum ether as eluent to
give 1 (4.16 g, 41.7% yield) as a colorless liquid. 1H NMR (400 MHz,
CDCl3) δ 1.35 (m, 2H), 1.44 (m, 2H), 1.67 (m, 2H), 1.83 (m, 2H), 3.37
(t, 2H), 3.68 (t, 2H), 6.95 (m, 6H), 7.25 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 26.2, 27.3, 27.9, 32.6, 33.7, 52.1, 120.8, 121.1, 129.2, 148.0;
MS (m/z, ESI) calcd for C18H22BrN 331.1, found 330.3 [M À H]+.
Anal. Calcd for C18H22BrN: C, 65.06; H, 6.67; N, 4.22. Found: C, 65.12;
H, 6.69; N, 4.21.
Hexyl-diphenyl-amine (6). Prepared as colorless liquid (5.64 g,
74.2% yield) from diphenylamine by using the method established for 1.
1H NMR (400 MHz, CDCl3) δ 0.87 (t, 3H), 1.29 (m, 6H), 1.65
(m, 2H), 3.67 (t, 2H), 6.92 (m, 2H), 6.97 (m, 4H), 7.24 (m, 4H); 13C
NMR (100 MHz, CDCl3) δ 14.1, 22.7, 26.8, 27.5, 31.7, 52.4, 120.9,
121.1, 129.3, 148.2.
(E)-3-{4-[(6-{3-[(E)-2-Cyano-2-(5-formylthiophen-2-yl)-
vinyl]phenoxazin-10-yl}-hexyl)phenylamino]phenyl}-2-(5-
formylthiophen-2-yl)acrylonitrile (5). To a solution of 4 (0.841 g,
1.2 mmol) and dry DMF (0.53 g, 7.2 mmol) in 1,2-dichloroethane
(15 mL) was slowly added phosphorus oxychloride (1.11 g, 7.2 mmol)
at 0 ꢀC in an iceÀwater bath. Then the bath was heated to 90 ꢀC and
maintained for 2 h. A aqueous solution of dilute sodium hydroxide was
added, and the mixture was extracted three times with CH2Cl2. The
combined organic phases were washed with brine and dried over
anhydrous Na2SO4. The solvent was removed under reduced pressure,
and the residue was purified by column chromatography with acetone/
petroleum ether (v/v = 1/10) as the eluent to give 5 (0.556 g, 61.1%) as a
red-black solid, mp 63À65 ꢀC. 1H NMR (400 MHz, CDCl3) δ 1.46 (m,
4H), 1.66 (m, 2H), 1.76 (m, 2H), 3.48 (t, 2H), 3.84 (t, 2H), 6.41
(m, 1H), 6.47 (m, 1H), 6.64 (m, 1H), 6.71 (m, 1H), 6.79 (m, 1H), 6.99
(m, 2H), 7.07 (m, 1H), 7.22 (m, 4H), 7.29 (m, 1H), 7.32 (s, 1H), 7.34
(m, 2H), 7.65 (m, 1H), 7.74 (m, 2H), 7.86 (m, 2H), 9.81 (s, 1H,), 9.82
(s, 1H); 13C NMR (100 MHz, CDCl3) δ 25.2, 26.6, 26.8, 27.5, 43.9,
52.3, 100.5, 104.8, 110.9, 111.9, 115.0, 115.9, 116.8, 117.1, 117.3, 122.5,
123.9, 124.1, 125.4, 126.1, 126.3, 127.0, 128.2, 128.3, 128.8, 129.2, 130.8,
131.2, 131.7, 136.9, 137.1, 138.5, 139.3, 141.8, 142.2, 144.6, 144.8, 147.9,
149.3, 152.3, 182.4, 190.3; MS (m/z, ESI) calcd for C46H36N4O3S2 756.2,
found 779.7 [M + Na]+. Anal. Calcd for C46H36N4O3S2: C, 72.99; H, 4.79;
N, 7.40; S, 8.47. Found: C, 72.94; H, 4.81; N, 7.42; S, 8.46.
(6-Phenoxazin-10-yl-hexyl)diphenyl-amine (2). Phenoxa-
zine (0.915 g, 5.0 mmol) was added to a suspension of potassium
hydroxide (0.336 g, 6.0 mmol) in DMSO (12 mL) under nitrogen. The
mixture was stirred for 30 min after which time 1 (1.83 g, 5.5 mmol) was
added. The reaction was stirred for 3 h at room temperature. Water
(30 mL) was added, the mixture was extracted with dichloromethane
(3 Â 30 mL), and the organic fraction was then washed with brine, dried
with anhydrous sodium sulfate, and evaporated. The residue was purified
by column chromatography with CH2Cl2/petroleum ether (v/v = 1/7)
as the eluent to give 2 (1.95 g, 89.7%) as a colorless solid, mp 87À88 ꢀC.
1H NMR (400 MHz, CDCl3) δ 1.41 (m, 4H), 1.63 (m, 2H), 1.70 (m,
2H), 3.42 (t, 2H,), 3.69 (t, 2H), 6.41 (m, 2H), 6.62 (m, 4H), 6.75 (m,
2H), 6.93 (m, 2H), 6.97 (m, 4H), 7.25 (m, 4H); 13C NMR (100 MHz,
CDCl3) δ 24.9, 26.8, 26.9, 27.6, 43.9, 52.2, 111.3, 115.4, 120.7, 120.9,
121.2, 123.6, 129.3, 133.4, 145.0, 148.1; MS (m/z, ESI) calcd for C30-
H30N2O 434.2, found 457.3 [M + Na]+. Anal. Calcd for C30H30N2O: C,
82.91; H, 6.96; N, 6.45. Found: C, 83.03; H, 7.01; N, 6.46.
10-{6-[(4-Formyl-phenyl)-phenyl-amino]-hexyl}-10H-phe-
noxazin-3-carbaldehyde (3). To a solution of 2 (1.74 g, 4 mmol)
and dry DMF (1.76 g, 24 mmol) in 1,2-dichloroethane (20 mL)
phosphorus oxychloride (3.69 g, 24 mmol) was added slowly at 0 ꢀC
in an iceÀwater bath. Then the bath was heated to 90 ꢀC and maintained
for 5 h. Dilute aqueous solution of sodium hydroxide was added, and the
4-(Hexyl-phenyl-amino)-benzaldehyde (7). Prepared as light
yellow liquid (0.875 g, 77.8% yield) from 6 by using the method
1
established for 3. H NMR (400 MHz, CDCl3) δ 0.87 (t, 3H), 1.31
(m, 6H), 1.69 (m, 2H), 3.71 (t, 2H), 6.69 (m, 2H), 7.20 (m, 2H),
7.27 (m, 1H), 7.42 (m, 2H), 7.65 (m, 2H), 9.72 (s, 1H); 13C NMR
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NOTE
(100 MHz, CDCl3) δ 13.9, 22.5, 26.4, 27.2, 31.4, 52.5, 113.1, 126.2,
126.3, 127.4, 130.0, 131.6, 145.6, 153.2, 190.0; MS (m/z, ESI) calcd for
C19H23NO 281.2, found 282.1 [M + H]+. Anal. Calcd for C19H23NO:
C, 81.10; H, 8.24; N, 4.98. Found: C, 80.93; H, 8.27; N, 4.99.
10-Hexyl-phenoxazine (10). Prepared as colorless liquid (1.21 g,
90.8% yield) from phenoxazine by using the method established for 2.
1H NMR (400 MHz, CDCl3) δ 0.93 (t, 3H), 1.42 (m, 6H), 1.67
(m, 2H), 3.47 (t, 2H), 6.47 (m, 2H), 6.63 (br. s, 4H), 6.80 (m, 2H); 13C
NMR (100 MHz, CDCl3) δ14.1, 22.7, 24.9, 26.6, 31.6, 44.1, 111.3,
115.3, 120.7, 123.6, 133.5, 145.0.
(E)-3-[4-(Hexyl-phenyl-amino)-phenyl]-2-thiophen-2-yl-
acrylonitrile (8). Prepared as yellow liquid (0.678 g, 87.8% yield) from
7 by using the method established for 4. 1H NMR (400 MHz, CDCl3) δ
0.79 (t, 3H), 1.21 (m, 6H), 1.59 (m, 2H), 3.61 (t, 2H), 6.65 (m, 2H),
6.92 (m, 1H), 7.11 (m, 5H), 7.16 (m, 1H), 7.30 (m, 2H), 7.62 (m, 2H);
13C NMR (100 MHz, CDCl3) δ 14.1, 22.7, 26.8, 27.4, 31.7, 52.6, 100.3,
114.7, 118.1, 122.8, 124.8, 125.5, 125.6, 126.8, 128.0, 130.0, 130.9, 140.1,
140.5, 146.3, 150.3; MS (m/z, ESI) calcd for C25H26N2S 386.2, found
387.1 [M + H]+. Anal. Calcd for C25H26N2S: C, 77.68; H, 6.78; N, 7.25;
S, 8.30. Found: C, 77.58; H, 6.80; N, 7.26; S, 8.29.
(E)-3-{5-[(E)-2-(4-{[6-(3-{(E)-2-[5-((E)-2-Carboxy-2-cyanovi-
nyl)thiophen-2-yl]-2-cyanovinyl}phenoxazin-10-yl)-hexyl]-
phenylamino}phenyl)-1-cyanovinyl]thiophen-2-yl}-2-cya-
noacrylic Acid (DC). A solution of 5 (0.493 g, 0,65 mmol) in CHCl3
(15 mL) was condensed with 2-cyanoacetic acid (0.552 g, 6.5 mmol) in
the presence of piperidine (0.35 mL, 3.55 mmol). The mixture was refluxed
for 2 h under nitrogen. After cooling to room temperature, the mixture was
poured into a mixture of CH2Cl2 and 2 M aqueous HCl. The organic layer
was separated and dried over anhydrous Na2SO4. After removal of the
solvent at reduced pressure, the crude product was purified by column
chromatography with CH2Cl2/methanol/acetic acid (v/v = 100/10/1) as
the eluent to give DC (0.398 g, 68.7%) as a black solid, mp 182À184 ꢀC. 1H
NMR (400 MHz, DMSO-d6) δ1.41 (br. s, 4H), 1.52 (br. s, 2H), 1.63 (br. s,
2H), 3.54 (br. s, 2H,), 3.87 (br. s, 2H), 6.76 (m, 5H), 7.08 (m, 2H), 7.15 (s,
1H), 7.38 (m, 6H), 7.62 (m, 2H), 7.69 (s, 1H), 7.88 (m, 5H), 8.08 (s, 1H),
8.28 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ 24.4, 25.6, 25.9, 27.0,
42.9, 51.4, 99.0, 102.7, 111.8, 112.7, 113.6, 115.3, 117.2, 117.3, 117.5, 117.8,
122.3, 123.3, 123.4, 124.3, 125.3, 125.3, 126.3, 127.4, 128.4, 129.2, 130.7,
130.9, 132.7, 135.7, 136.2, 138.6, 138.8, 139.3, 141.6, 143.4, 143.8, 146.3,
147.4, 150.4, 152.0, 163.3, 164.3. MS (m/z, ESI) calcd for C52H38N6O5S2
890.2; found 889.3 [M À H]+. Anal. Calcd for C52H38N6O5S2: C, 70.09; H,
4.30; N, 9.43; S, 7.20. Found: C, 70.04; H, 4.29; N, 9.41; S, 7.19.
(E)-2-Cyano-3-(5-{(E)-1-cyano-2-[4-(hexyl-phenyl-amino)-
phenyl]vinyl}thiophen-2-yl)acrylic Acid (SC1). Prepared as
black solid (0.247 g, 79.2% yield) from 9 by using the method established
for DC, mp 73À74 ꢀC. 1H NMR (400 MHz, DMSO-d6) δ 0.82 (t, 3H),
1.23 (m, 4H), 1.30 (m, 2H), 1.58 (m, 2H), 3.75 (t, 2H), 6.77 (m, 2H),
7.27 (m, 2H), 7.30 (m, 1H), 7.49 (m, 3H), 7.79 (s, 1H), 7.84 (m, 2H),
7.93 (m, 1H), 8.42 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ 13.9,
22.1, 25.9, 26.9, 31.1, 51.8, 96.8, 99.1, 114.0, 116.7, 117.7, 121.6, 125.2,
126.3, 127.0, 130.2, 132.0, 134.4, 140.9, 143.6, 145.2, 145.9, 148.9, 151.1,
163.6. MS (m/z, ESI) calcd for C29H27N3O2S 481.1, found 435.7
[M À COOH]+. Anal. Calcd for C29H27N3O2S: C, 72.32; H, 5.65; N,
8.72; S, 6.66. Found: C, 72.39; H, 5.67; N, 8.73; S, 6.65.
(E)-2-(5-Formyl-thiophen-2-yl)-3-[4-(hexyl-phenyl-amino)-
phenyl]acrylonitrile (9). Prepared as red liquid (0.394 g, 79.4% yield)
1
from 8 by using the method established for 5. H NMR (400 MHz,
CDCl3) δ 0.80 (t, 3H), 1.18 (m, 6H), 1.63 (m, 2H), 3.65 (t, 2H), 6.64
(m, 2H), 7.14 (m, 2H), 7.22 (m, 2H), 7.32 (s, 1H); 7.36 (m, 2H), 7.60
(m, 1H), 7.70 (m, 2H), 9.77 (s, 1H); 13C NMR (100 MHz, CDCl3) δ
14.0, 22.6, 26.7, 27.3, 31.6, 52.7, 98.4, 114.1, 117.4, 121.7, 125.6, 126.4,
127.3, 130.1, 131.9, 137.2, 141.6, 143.3, 145.7, 150.3, 151.3, 182.4; MS
(m/z, ESI) calcd for C26H26N2OS 414.2, found 415.2 [M + H]+. Anal.
Calcd for C26H26N2OS: C, 75.33; H, 6.32; N, 6.76; S, 7.73. Found: C,
75.31; H, 6.34; N, 6.77; S, 7.74.
10-Hexyl-phenoxazine-3-carbaldehyde (11). Prepared as
yellow liquid (1.03 g, 87.5% yield) from 10 by using the method
1
established for 3. H NMR (400 MHz, CDCl3) δ 0.92 (t, 3H), 1.36
(E)-2-Cyano-3-{5-[(E)-1-cyano-2-(10-hexyl-10H-phenoxa-
zin-3-yl)vinyl]thiophen-2-yl}acrylic Acid (SC2). Prepared as
black solid (0.261 g, 81.1% yield) from 13 by using the method
(m, 6H), 1.64 (m, 2H), 3.46 (t, 2H), 6.45 (m, 1H), 6.49 (m, 1H), 6.60
(m, 1H), 6.69 (m, 1H), 6.79 (m, 1H), 7.02 (m, 1H), 7.25 (m, 1H), 9.61
(s, 1H); 13C NMR (100 MHz, CDCl3) δ 14.1, 22.7, 25.0, 26.6, 31.6,
44.4, 110.5, 112.1, 114.1, 115.7, 122.5, 124.0, 128.8, 129.8, 131.4, 139.3,
144.7, 145.1, 189.6; MS (m/z, ESI) calcd for C19H21NO2 295.2, found
318.2 [M + Na]+. Anal. Calcd for C19H21NO2: C, 77.26; H, 7.17; N,
4.74. Found: C, 77.19; H, 7.20; N, 4.73.
(E)-3-(10-Hexyl-10H-phenoxazin-3-yl)-2-thiophen-2-yl-
acrylonitrile (12). Prepared as red liquid (0.651 g, 81.3% yield) from
11 by using the method established for 4. 1H NMR (400 MHz, CDCl3):
δ 0.82 (t, 3H), 1.26 (m, 6H), 1.51 (m, 2H), 3.31 (t, 2H), 6.28 (m, 1H),
6.34 (m, 1H), 6.50 (m, 1H), 6.55 (m, 1H), 6.66 (m, 1H), 6.90 (m, 2H),
7.06 (m, 1H), 7.10 (m, 2H), 7.14 (m, 1H); 13C NMR (100 MHz,
CDCl3) δ 14.1, 22.7, 25.0, 26.6, 31.6, 44.1, 101.6, 110.9, 111.7, 114.7,
115.6, 117.6, 121.9, 123.8, 125.2, 125.9, 126.9, 128.0, 131.8, 135.7, 138.6,
140.0, 144.7; MS (m/z, ESI) calcd for C25H24NO2S 400.2, found 401.1
[M + H]+. Anal. Calcd for C25H24N2OS: C, 74.97; H, 6.04; N, 6.99; S,
8.01. Found: C, 74.94; H, 6.05; N, 7.00; S, 7.99.
(E)-2-(5-Formyl-thiophen-2-yl)-3-(10-hexyl-10H-phenoxa-
zin-3-yl)acrylonitrile (13). Prepared as red-black solid (0.380 g,
73.9% yield) from 12 by using the method established for 5, mp
143À144 ꢀC. 1H NMR (400 MHz, CDCl3): δ 0.93 (t, 3H), 1.39
(m, 6H), 1.66 (m, 2H), 3.49 (t, 2H), 6.45 (m, 1H), 6.50 (m, 1H), 6.64 (m,
1H), 6.70 (m, 1H), 6.81 (m, 1H), 7.22 (s, 1H), 7.27 (m, 1H), 7.29
(m, 1H), 7.34 (m, 1H), 7.66 (m, 1H), 9.83 (s, 1H); 13C NMR (100 MHz,
CDCl3) δ 14.1, 22.8, 25.2, 26.6, 31.6, 44.3, 100.3, 111.0, 112.1, 114.9,
115.8, 116.9, 122.5, 124.0, 125.3, 126.3, 128.6, 131.4, 137.1, 141.9, 142.1,
144.7, 144.8, 149.5, 182.4; MS (m/z, ESI) calcd for C26H24N2O2S 428.2,
found 451.3 [M + Na]+. Anal. Calcd for C26H24N2O2S: C, 72.87; H, 5.64;
N, 6.54; S, 7.48. Found: C, 72.81; H, 5.65; N, 6.53; S, 7.46.
1
established for DC, mp 248À249 ꢀC. H NMR (400 MHz, C5H5N-
d5) δ 0.84 (t, 3H), 1.21 (m, 4H), 1.29 (m, 2H), 1.53 (m, 2H), 3.46
(t, 2H), 6.67 (m, 1H), 6.70 (m, 1H), 6.79 (m, 2H), 6.89 (m, 1H), 7.41
(m, 1H), 7.50 (m, 1H), 7.52 (d, 1H), 7.58 (s, 1H), 7.61 (m, 1H), 7.73
(m, 1H); 13C NMR (100 MHz, C5H5N-d5) δ 14.2, 22.9, 25.3, 26.6, 31.7,
44.1, 100.6, 102.6, 111.9, 112.9, 115.1, 116.0, 117.6, 117.8, 122.8, 124.6,
126.2, 126.7, 129.2, 131.9, 136.1, 136.2, 137.2, 138.9, 142.1, 145.0, 145.2,
148.4, 165.5. MS (m/z, ESI) calcd for C29H25N3O3S 495.1, found 449.7
[M À COOH]+. Anal. Calcd for C29H25N3O3S: C, 70.28; H, 5.08; N,
8.48; S, 6.47. Found: C, 70.32; H, 5.10; N, 8.49; S, 6.46.
’ ASSOCIATED CONTENT
S
Supporting Information. NMR spectra, normalized ab-
b
sorption and emission spectra, frontier molecular orbitals, and
the calculated electron lifetime of all of the dyes. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: drcao@scut.edu.cn, kuangdb@mail.sysu.edu.cn.
’ ACKNOWLEDGMENT
We thank the National Natural Science Foundation of China
(20872038, 20873183, 21072064), Jiangxi Province Natural
8020
dx.doi.org/10.1021/jo201057b |J. Org. Chem. 2011, 76, 8015–8021

The Journal of Organic Chemistry
NOTE
Science Foundation of China (2009GQC0055), and the Natural
Science Foundation of Guangdong Province, China (10351064-
101000000) for financial support.
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