Dithienothiophene (DTT)-based dyes for dye-sensitized solar cells: Synthesis of 2,6-dibromo-DTT

Article abstract of DOI:10.1021/jo2001484

A one-pot synthesis of 2,6-dibromodithieno[3,2-b;2′,3′-d] thiophene (dibromo-DTT, 4) was developed. A key step was bromodecarboxylation of DTT-2,6-dicarboxylic acid, obtained by saponification of the diester 1. The donor-acceptor dye DAHTDTT (13), based o

Full text of DOI:10.1021/jo2001484

NOTE
pubs.acs.org/joc
Dithienothiophene (DTT)-Based Dyes for Dye-Sensitized
Solar Cells: Synthesis of 2,6-Dibromo-DTT
Tae-Hyuk Kwon,† Vanessa Armel,‡ Andrew Nattestad,‡ Douglas R. MacFarlane,*,‡ Udo Bach,*,‡
Samuel J. Lind,§ Keith C. Gordon,§ Weihua Tang,† David J. Jones,† and Andrew B. Holmes*,†
†School of Chemistry, Bio21 Institute, University of Melbourne, Parkville, Vic 3010, Australia
‡ARC Centre of Excellence for Electromaterials Science, Monash University, Clayton, Vic 3800, Australia
§MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry, University of Otago, Dunedin,
New Zealand
S Supporting Information
b
ABSTRACT: A one-pot synthesis of 2,6-dibromodithieno[3,2-b;20,
30-d]thiophene (dibromo-DTT, 4) was developed. A key step was bromo-
decarboxylation of DTT-2,6-dicarboxylic acid, obtained by saponification
of the diester 1. The donorꢀacceptor dye DAHTDTT (13), based on a
central 2,6-bis[20-(30-hexylthienyl)]dithieno[3,2-b;20,30-d]thiophene core
(9), was prepared and incorporated in a dye-sensitized solar cell (DSC),
which exhibited an energy conversion efficiency of 7.3% with Voc of 697 mV,
Jsc of 14.4 mA/cm2, and ff of 0.73 at 1 sun.
ecently, organic dye-sensitized solar cells (DSCs) have re-
ceived considerable attention owing to their wide variety,
Recently thiophene-based dyes have been used for light-
harvesting in DSCs.4ꢀ6 However, as DTT-based dyes may not
exhibit a broad absorption region,6 modification of the structure
through additional double conjugation by introduction of 3-hex-
ylthiophene units can improve this situation. An additional
benefit is the inhibition of electron recombination from the
TiO2 nanoparticle to the radical cation of the dye owing to
the presence of the hexyl substituents. The final components
of the light-harvesting dye, 2-cyano-3-[5-(6-{5-[2-(4-(dipheny
lamino)phenyl)vinyl][20-(30hexylthienyl)]}dithieno[3,2-b;20,30-d]
thien-2-yl)-4-hexylthien-2-yl]acrylic acid, DAHTDTT 13, are
the nonplanar triphenyl amine (TPA) donor unit (D) and an
R-cyanoacrylic acid group as the electron acceptor (A) to form a
D-π-A structure.
The synthesis of the dye DAHTDTT 13 is shown in Scheme 2.
2,6-Dibromo-DTT 4 can be prepared by bromination of DTT 3,
itself obtained by decarboxylation of the diacid 2 (overall yield
40% for three steps).23,24 However, this classical method,
although it gave a good yield, still required a three-step process
and included the harsh preliminary decarboxylation step as
outlined in Scheme 1. We now report an improved synthesis of
the dibromo-DTT 4 by a one-pot bromo-decarboxylation of the
DTT-2,6-diacid 5 (Scheme 1).27ꢀ31 Conventional saponification
R
high molar extinction coefficients of dyes, and potentially low
cost of fabrication compared with those based on ruthenium dye
sensitizers.1ꢀ17 Some organic dyes exhibit impressive photovol-
taic performances with high efficiency and good stability. Most
organic sensitizers consist of a donor fragment (D), a π-conjugated
linking segment, and an acceptor fragment (A) to achieve broad
and intense absorption within the visible to near-IR spectrum.
When designing dyes for high-efficiency DSCs, it is preferable
to (i) employ a nonplanar structure to prevent self-aggregation,
(ii) incorporate appropriate conjugation length for a broad absorp-
tion, (iii) use long alkyl chain substituents to minimize electron
recombination, and (iv) aim for chemical and structural stability.
In this study, we employ a 2,6-bis[20-(30-hexylthienyl)]dithieno-
[3,2-b;20,30-d]thiophene core unit 9 for the π-conjugated linking
segment. This is due to the relatively high hole mobility exhibited by
the fused thiophene core18 in a variety of electronic and optical
applications,4ꢀ7,19 such as organic thin film transistors18,20ꢀ22 and
polymer solar cells.21 Owing to the various useful applications of
dithieno[3,2-b;20,30-d]thiophene (DTT) in the optoelectronic field,
the synthesis of DTT derivatives has received much attention.23ꢀ25
However, many approaches still require multiple steps and harsh
conditions.23,24 For the purpose of a convenient synthesis and scale
up of the DTT unit, we developed a synthesis of 2,6-dibromo-DTT 4
by a modification of the Hunsdiecker-type reaction (Scheme 1).26
Received: January 24, 2011
Published: April 12, 2011
r
2011 American Chemical Society
4088
dx.doi.org/10.1021/jo2001484 J. Org. Chem. 2011, 76, 4088–4093
|

The Journal of Organic Chemistry
NOTE
Scheme 1. Routes to Dibromo-DTT 4 from the Diester 1
Scheme 2. Synthesis of the Dye 13
of the diester 1 (heat to reflux in THF containing aqueous LiOH
solution) followed by dilution of the cooled resulting slurry
produced a solution of the dicarboxylate lithium salt. Treatment
of this solution with an excess of solid NBS (>6 mol equiv)
followed by stirring of the reaction mixture overnight at room
temperature and extraction with dichloromethane gave the
dibromo-DTT 4 in excess of 80% yield.
Without column purification, the dibromo-compound 4 was
coupled under Suzuki conditions with 3-hexylthiophene-2-pina-
colylboronate 8 in the presence of Pd2(dba)3, (tert-butyl)3-
the resulting aldehyde 12 with cyanoacetic acid (>20 equiv) in a
microwave reactor gave the required dye 13 in 87% yield after
purification by column chromatography.
The UV/vis absorption spectrum of the dye DAHTDTT 13 in
CH2Cl2 (0.02 mM) showed a strong broad absorption maximum
around 490 nm (εmax > 30 000), with the PL emission maximum
at 613 nm as shown in Figure 1.
Cyclic voltammetry measurements of the dye 13 in CH2Cl2
solutions (0.5 mM) with 0.1 M tetra-n-butylammonium hexa-
fluorophosphate (TBAPF6) as the supporting electrolyte are
summarized in Table 1. Also included are the observed UV/vis
and PL emission spectra and the DFT-calculated HOMO and
LUMO energies.
P HBF4, and 2 M K3PO4, to afford bis(3-hexylthiophenyl)-
3
DTT 9 in 79% yield. Vilsmeier formylation gave the dialdehyde
10, which underwent a mono-WittigꢀHorner chain extension in
53% yield with the ylide derived from the known triarylamine-
based phosphonium salt 11.6 Knoevenagel-type condensation of
The oxidation potential of the dye 13 (0.98 V versus NHE) is
sufficiently positive compared with the reduction potential of
4089
dx.doi.org/10.1021/jo2001484 |J. Org. Chem. 2011, 76, 4088–4093

The Journal of Organic Chemistry
NOTE
iodine/iodide (0.4 V versus NHE) that the photooxidized dye
could be expected to be reduced efficiently by the iodine/iodide
redox couple. The reduction potential of the dye (ꢀ1.29 V vs
NHE) was calculated from Eox ꢀ E0ꢀ0 (V). As this is a more
negative value than the level of the TiO2 conduction band (CB)
edge (ꢀ0.5 V vs NHE), we can expect that the photoexcited state
of the dye 13 can effectively inject electrons into the conduction
band (CB) of TiO2.
Optimized Density Functional Theory (DFT) calculations
were carried out utilizing Gaussian09 at the B3LYP/6-31G(d)
level of theory.32 The electron densities in the HOMO and
LUMO of the dye are well separated (see ESI). The HOMO is
generally located on the triphenyl amine unit while the LUMO is
on the cyanoacetic acid group; this is a desirable feature for the
required charge separation in dye-sensitized solar cells.
DSCs were constructed by using a sandwich configuration with
an electrolyte composed of 0.6 M 1,2-dimethyl-3-propylimidazo-
lium iodide, 0.025 M lithium iodide, 0.04 M iodine, 0.05 M
guanidinium thiocyanate (GuSCN), and 0.28 M tert-butylpyr-
idine (TBP) in a dry acetonitrile/valeronitrile solvent mixture
(v/v = 85/15).6 For the titanium oxide different film thicknesses
of the transparent and scattering layer were used as follows: 6 μm
(6), 6 þ 6 scattering layer μm (6 þ 6s), and 12 þ 6 scattering
layer μm (12 þ 6s) were studied with the coadsorbent (DCA =
3R,7R-dihydroxy-5β-cholic acid).
The device performances are summarized in Table 2, with
optimal results shown in Figures 2 and 3. The dye 13 was
adsorbed onto the titania from different solvents. The choice of
solvent is crucial, and the device performance varied significantly
according to the solvent system chosen. The difference in
performance could be due to the interaction of the dye with
the solvent, which can affect the photophysical and chemical
properties of the dye on the TiO2 surface.6 The binding mode
and the number of dye molecules adsorbed onto the TiO2
depend on the solvents. Adsorption of the dye 13 in CHCl3
and EtOH solvent mixtures (1:1) yielded the highest device
efficiency compared with CHCl3, CH2Cl2, CH2Cl2/EtOH,
chlorobenzene, and chlorobenzene/EtOH (see ESI). Optimum
devices were obtained by using the dye (0.2 mM) in CHCl3/
EtOH (1/1) solutions with overnight soaking on titania. Thus all
devices were prepared in 0.2 mM CHCl3/EtOH (1/1) solutions
after overnight soaking.
Using a 6 μm titania film with 10 mM DCA as coadsorbent, a
device fabricated with dye 13 gave a short-circuit photocurrent
density (Jsc) of 12.2 mA/cm2, an open-circuit voltage (Voc) of
718 mV, and a fill factor (ff) of 0.74, corresponding to an overall
conversion efficiency (η) of 6.5%. With a 6 μm scattering layer
(6 þ 6s), an increase in Jsc from 12.2 to 12.6 mA/cm2 was
obtained. However, with a concomitant decrease in the fill factor
from 0.74 to 0.71, the device efficiency with a 6 þ 6s film (6.4%)
was not significantly different from that of a 6 μm film (6.5%).
Using a 12 μm transparent film with a 6 μm scattering layer, 12 þ
6s, Jsc significantly increased to 14.7 mA/cm2 while Voc slightly
decreased to 698 mV and the fill factor was 0.70, leading to device
efficiency improving to 7.1%. The Jsc of devices made with the
dye 13 is slightly higher than that achieved for N719 (14.5 mA/
cm2) under the same conditions. Through further optimization,
via an increase of coadsorbent (20 mM), the performance of the
cell increased to 7.3% with Voc of 697 mV, Jsc of 14.4 mA/cm2,
and fill factor of 0.73.
Compared with the previously reported device performance
(η = 2.76%) of a similar dithienothiophene-based dye (E)-
2-cyano-3-{6-[2-(4-(diphenylamino)phenyl)vinyl]dithieno[3,2-
b;20,30-d]thiophen-2-ylacrylic acid TTC2,6 the efficiency of de-
vice made with dye 13 increases by a factor of ca. 2.6 under similar
electrolyte composition and film thickness. Moreover, this
efficiency reached 88% of the efficiency of devices made with
N719 dye (η = 8.3%). Figure 2 shows the detailed current density
versus voltage (IꢀV) curve at different light intensity: 10.3%,
38.5%, and 100% sunlight, respectively. Under 10.3% and 38.5%
sunlight, the device efficiency reached 7.0% and 7.3%, respec-
tively. The increase of short circuit current density with different
film thickness is confirmed by using the incident photon-to-
current conversion efficiency (IPCE) spectrum; the spectrum
becomes broader in the sequence 6 < 6 þ 6s < 12 < 12 þ 6s. The
IPCE spectrum of a device using dye 13 with 12 þ 6s exhibits the
broad absorption range starting from 800 nm and a higher
plateau at 67% (λ = 495 nm) (Figure 3).
In summary, we have developed a simple one-step synthesis of
dibromo DTT (4) from diester DTT (1) in over 80% yield using
a modified Hunsdiecker reaction for the DSC dye core unit. The
organic DSC dye DAHTDTT (13) consisted of TPA and DTT
coupled with hexylthiophene showing high efficiency of 7.3%
with Voc of 697 mV, Jsc of 14.4 mA/cm2, and ff of 0.73.
Figure 1. UV/vis and PL spectra of dye 13 in CH2Cl2 (0.02 mM).
Table 1. DFT-Calculated HOMO and LUMO Energy Levels, the Experimentally Determined Values from the Electrochemically
Measured Oxidation Potential and the Optical Bandgap, and UV/Vis Absorption and PL Emission Maxima in Dichloromethane Solution
HOMOcal
(exptl)a
LUMOcal
(exptl)a
abs
PLb
E0ꢀ0 (V)
Eox ꢀ E0ꢀ0 (V)
b
entry
(nm)(ε ꢁ 104 cmꢀ1 molꢀ1
)
(λmax
)
Eox (V) vs NHEc
vs (abs/Em)d
vs NHE
dye 13
ꢀ4.67 (ꢀ5.15)
ꢀ2.75 (ꢀ2.88)
301 (2.0), 423 (3.0), 489 (3.0)
613 nm
0.98
2.27
ꢀ1.29
a HOMO = ꢀ(Eonset vs Fcþ/Fc ꢀ 4.8 eV), LUMO = HOMO þ E0ꢀ0. b 0.02 mM CH2Cl2 solution at 298 K. c Cyclic voltammetry measurement of the
onset point of oxidation Eox of the dye was measured in dry CH2Cl2 containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as
supporting electrolyte, Ag/AgCl as a reference electrode, and glassy carbon as working electrode. Potentials calibrated with Fcþ/Fc were converted to
normal hydrogen electrode (NHE) by addition of þ0.63 V.6 d The E0ꢀ0 transition energy was estimated from the intersection of the absorption and
emission spectra.
4090
dx.doi.org/10.1021/jo2001484 |J. Org. Chem. 2011, 76, 4088–4093

The Journal of Organic Chemistry
NOTE
Table 2. Photovoltaic Performance of Cells Fabricated with
Use of the Dye 13
thickness
coads.
(mM)a (mV)
Voc
eff
no.
(μm)
Jsc(mA/cm2)
ff
(%)
1
2
3
4
6
10
10
10
20
718
720
698
697
780
12.2
12.6
14.7
14.4
14.5
0.74
0.71
0.70
0.73
0.73
6.5
6.4
7.1
7.3
8.3
6 þ 6sb
12 þ 6s
12 þ 6s
12 þ 6s
N719c
a Coadsorbent is 3R,7R-dihydroxy-5β-cholic acid. b 6s is 6 μm scattering layer.
c Electrolyte for N719:0.6 M 1-butyl-3-methyl imidazolium iodide, 0.03 M I2,
0.10 M guanidinium thiocyanate (GuSCN), and 0.50 M tert-butylpyridine
(TBP) in the dry acetonitrile/valeronitrile (v/v = 85/15).
Figure 3. IPCE spectrum of devices fabricated with use of the dye 13
according to the film thickness of titania.
2,6-Bis[20-(30-hexylthienyl)]dithieno[3,2-b;20,30-d]thioph-
ene (9). To a degassed solution of dibromo DTT 4 (4.3 g, 12.0 mmol),
2-(3-hexyl-2-thienyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (8), and
HP(tert-butyl)3BF4 (0.72 mmol, 0.06 equiv, 208 mg) in THF (100 mL)
was added Pd2(dba)3 (0.36 mmol, 0.03 equiv, 329 mg), then the mixture
was stirred at 60 °C overnight. After being cooled to room temperature,
the reaction mixture was extracted with ethyl acetate. The combined
organic layers were washed with water and brine, then dried with
MgSO4. After the solvent was removed via rotary evaporator, the residue
was purified by column chromatography on silica gel eluting with
petroleum spirits 40ꢀ60 °C to give compound 9 (5.0 g, 79% yield) as
an orange solid after drying under high vacuum, Rf 0.50 (petroleum
spirits 40ꢀ60 °C), whose spectroscopic data were identical with the
reported values.23 1H NMR (500 MHz, CDCl3) δ 0.89 (6H, t, J = 6.5 Hz),
1.30ꢀ1.33 (8H, m), 1.39ꢀ1.41 (4H, m), 1.68 (4H, q, J = 7.5 Hz), 2.82
(4H, q, J = 8.0 Hz), 6.98 (2H, d, J = 5.0 Hz), 7.24 (2H, d, J = 5.0 Hz), 7.30
(2H, s); 13C NMR (125 MHz, CDCl3) δ 14.1, 22.6, 29.2, 29.3, 30.7,
31.7, 119.3, 119.3, 124.4, 130.1, 130.6, 130.6, 136.9, 140.4, 140.9; m/z
(ESI) 528.6 [Mþ], calcd for C28H32S5 528.1
Figure 2. The IꢀV curve of a DSC device, using thetitania layers 12 þ 6s
and standard electrolyte under various solar simulated light intensities.
’ EXPERIMENTAL SECTION
2,6-Bis[20-(30-hexyl-50-formylthienyl)]dithieno[3,2-b;20,30-
d]thiophene (10). To a solution of 9 (400 mg, 0.75 mmol) in dry
DMF (30 mL) at 0 °C was added dropwise POCl3 (0.4 mL, 4.6 mmol).
The reaction was stirred at this temperature for 30 min, and then the
temperature was raised to 70 °C and the mixture was stirred for 12 h.
The reaction mixture was poured into cold water and neutralized with
NaOH (1 N), followed by extraction with CHCl3. The combined
organic layers were washed with water and brine, then dried with
MgSO4. After the solvent was removed via rotary evaporator, the residue
was purified by column chromatography with petroleum spirits
40ꢀ60 °C and CHCl3 (v/v = 4/1 to 1/4) to give the dialdehyde
compound 10 (350 mg, 80% yield) as an orange crystalline solid after
trituration with petroleum spirits 40ꢀ60 °C and CH2Cl2, mp 133 °C, Rf
0.28 (1:2 petroleum spirits 40ꢀ60 °C/CH2Cl2). 1H NMR (500 MHz,
CDCl3) δ 0.90 (6 H, t, J = 7.0 Hz), 1.32ꢀ1.35 (8 H, br m), 1.41ꢀ1.44
(4H, br m), 1.69ꢀ1.75 (4H, m), 2.86 (4 H, t, J = 7.5 Hz), 7.48 (2 H, s),
7.63 (2 H, s), 9.86 (2 H, s); 13C NMR (125 MHz, CDCl3) δ 14.3, 22.8,
29.4, 29.7, 30.6, 31.8, 114.8, 121.0, 131.9, 136.5, 139.1, 140.9, 141.2, 142.5,
182.7; m/z (EI) [rel intensity] 584.1 [100, (M)þ], 585.1 [95, (M þ H)þ],
586.1 [40, (M þ 2H)þ]; m/z (EI) 584.1002 [Mþ], calcd for
C30H32O2S5 584.1006; FT-IR (neat cmꢀ1): 3822, 3676, 2931, 1658,
1431, 1244, 1154.
All reactions were performed with anhydrous solvent under an inert
atmosphere (nitrogen or argon) unless stated otherwise. Silica gel was
used for flash chromatography. Thin layer chromatography was per-
formed on silica gel on glass (0.25 mm thick). 1H and 13C NMR
spectroscopy were carried out with a 500 MHz instrument. All high-
resolution mass spectrometry experiments were conducted with use of a
commercially available hybrid linear ion trap and Fourier-transform ion
cyclotron resonance mass spectrometer, equipped with ESI. The
microwave reaction was performed with a Biotage (Initiator EXP EU).
The syntheses of the intermediates 1, 8, and 11 were carried out as
previously reported.6,23,33
One-Pot Bromo-Decarboxylation of Dithieno[3,2-b;20,30-
d]thiophene-2,6-dicarboxylic Acid Diethyl Ester (1) To Pre-
pare the 2,6-Dibromodithieno[3,2-b;20,30-d]thiophene (4).
To a suspension of DTT-diester 1 (3.4 g, 10 mmol) in the THF (40 mL)
was added 40 mL of 1 M LiOH. After the reaction mixture had been
heated under reflux for 3 h, water was added to give a clear brownish
yellow solution. Excess solid N-bromosuccinimide (10.7 g, 60 mmol)
was then added and the reaction mixture was stirred overnight at room
temperature. The reaction mixture was extracted with CH2Cl2. The
combined organic layers were washed with saturated NaHCO3 (aq), water,
and brine, then dried with MgSO4. Afterthesolvent wasremovedviarotary
evaporator, the residue was precipitated with EtOH and then filtered to
give the known dibromo-DTT 4 (3.1 g, 89% yield) as a white solid, mp
165 °C (lit.23 mp162ꢀ163 °C), whose spectroscopic data were identical
with the reported values.23 1H NMR (500 MHz, CDCl3) δ 7.28 (2H, s).
5-(6-{5-[2-(4-(Diphenylamino)phenyl)vinyl][20-(30-hexylt-
hienyl)]}dithieno[3,2-b;20,30-d]thien-2-yl)-4-hexylthiene-2-
carbaldehyde (12). To a suspension of a solution of compound 10
(186 mg, 0.32 mmol) in DMF (10 mL) containing anhydrous K2CO3
(88 mg, 0.64 mmol) and 18-crown-6 (7 mg, 0.025 mmol) at a
4091
dx.doi.org/10.1021/jo2001484 |J. Org. Chem. 2011, 76, 4088–4093

The Journal of Organic Chemistry
NOTE
temperature of 70 °C was added dropwise a solution of phosphonium salt
11 (210 mg, 0.35 mmol) in DMF (10 mL) over 3 h. The reaction mixture
was stirred for a further 3 h. It was then cooled and extracted with CH2Cl2.
The combined organic layers were washed with water and brine solution.
The organic phase was dried over MgSO4, then purified by column
chromatography on silica gel eluting with petroleum spirits 40ꢀ60 °C/
dichloromethane (v/v 4/1 to 1/4) to give alkene 12 (140 mg, 53%) as a red
solid, mp 50 °C, Rf 0.40 (2:1 petroleum spirits 40ꢀ60 °C/CH2Cl2). 1H
NMR (500 MHz, CDCl3) δ 0.83 (6 H, br t), 1.26 (8 H, br m), 1.36 (4H, br
m), 1.60ꢀ1.66 (4 H, br m), 2.71 (2 H, t, J = 8.0 Hz), 2.79 (2 H, t,
J= 8.0 Hz), 6.78 (1 H, d, J=16Hz), 6.82(1H, s), 6.94ꢀ6.98 (5 H, m), 7.04
(4 H, d, J = 8.5 Hz), 7.18ꢀ7.21 (5 H, m), 7.23 (1 H, s), 7.25 (1 H, s), 7.39
(1 H, s), 7.54 (1 H, s), 9.77 (1 H, s); 13C NMR (125 MHz, acetone-d6)
δ 15.3, 31.9, 32.0, 33.3, 34.4, 120.8, 121.1, 121.6, 123.3, 124.9, 125.3, 126.5,
126.6, 127.1, 127.9, 128.3, 129.3, 130.3, 131.3, 131.6, 131.7, 132.9, 133.3,
137.2, 140.0, 141.6, 143.0, 143.1, 143.9, 144.8, 149.4, 184.6; m/z (EI)
[rel intensity] 825.2 [100, (M)þ], 826.2 [55, (M þ H)þ], 827.2 [20 (M þ
2H)þ], 828.2 [10 (M þ 2H)þ]; m/z (EI) 825.2258 [Mþ], calcd for
C49H47NOS5 825.2261; FT-IR (neat cmꢀ1) 2926, 2853, 1664, 1590, 1506,
1492, 1422, 1328, 1281, 1241, 1154, 821, 752, 696.
Government DPI (SERD) and DBI (VSA SPF) Program VICOSC
for financial support. We thank Drs. Joseph Frey and Michael
Armitage (University of Cambridge) for their early observations
on the bromodecarboxylation reactions of DTT-carboxylic acids.
’ REFERENCES
(1) Mishra, A.; Fischer, M. K. R.; B€auerle, P. Angew. Chem., Int. Ed.
2009, 48, 2474.
(2) Oyama, Y.; Harima, Y. Eur. J. Org. Chem. 2009, 2903.
(3) Ning, Z. J.; Tian, H. Chem. Commun. 2009, 5483.
(4) Qin, H.; Wenger, S.; Xu, M.; Gao, F.; Jing, X.; Wang, P.;
Zakeeruddin, S. M.; Gr€atzel, M. J. Am. Chem. Soc. 2008, 130, 9202.
(5) Yang, H. Y.; Yen, Y. S.; Hsu, Y. C.; Chou, H. H.; Lin, J. T. Org.
Lett. 2010, 12, 16.
(6) Tian, H. N.; Yang, X. C.; Chen, R. K.; Zhang, R.; Hagfeldt, A.;
Sunt, L. C. J. Phys. Chem. C 2008, 112, 11023.
(7) Wang, Z. S.; Cui, Y.; Dan-Oh, Y.; Kasada, C.; Shinpo, A.; Hara, K.
J. Phys. Chem. C 2007, 111, 7224.
(8) Neale, N. R.; Kopidakis, N.; van de Lagemaat, J.; Gr€atzel, M.;
Frank, A. J. J. Phys. Chem. B 2005, 109, 23183.
2-Cyano-3-[5-(6-{5-[2-(4-(diphenylamino)phenyl)vinyl]-
[20-(30-hexylthienyl)]dithieno[3,2-b;20,30-d]thien-2-yl)-4-hex-
ylthien-2-yl]acrylic Acid DAHTDTT (13). A solution of aldehyde
12 (80 mg, 0.09 mmol) in a mixture of acetonitrile (10 mL) and CHCl3
(10 mL) with an excess of cyanoacetic acid (153 mg, 1.8 mmol) and
piperidine (0.1 mL) was heated to 100 °C in a microwave reactor for
20 min. The reaction mixture was extracted with CH2Cl2 and the
combined organic extracts were washed with 1 N HCl, water, and brine
solution. The organic layer was dried over MgSO4. After removal of the
solvent, the residue was purified by column chromatography on silica gel
eluting with dichloromethane/methanol/acetic acid (in the volume
proportions 10/1/0 to 10/1/0.1) to give the organic dye 13 (70 mg,
87% yield) as a dark solid, mp 144 °C, Rf 0.56 (10:1:0.1 CH2Cl2/
MeOH/Acetic acid) after trituration with petroleum spirits 40ꢀ60 °C
and CH2Cl2. 1H NMR (500 MHz, DMSO-d6) δ 0.84 (6 H, t, J = 7.0 Hz),
1.28 (8 H, br m), 1.37 (4H, br m), 1.62ꢀ1.67 (4 H, br m), 2.75 (2 H, t,
J = 7.5 Hz), 2.83 (2 H, t, J = 7.5 Hz), 6.88ꢀ6.93 (3 H, m), 7.02ꢀ7.07
(6 H, m), 7.11 (1 H, s), 7.24 (1 H, d, J = 16 Hz), 7.32 (4 H, t, J = 7.5 Hz),
7.47 (4 H, d, J = 8.5 Hz), 7.66 (1 H, s), 7.89 (1 H, s), 7.90 (1 H, s), 8.36
(1 H, s); 13C NMR (125 MHz, DMSO-d6 at 50 °C) δ 14.6, 22.7, 29.1,
29.2 29.3, 29.6, 30.1, 30.4, 31.7, 31.8, 117.5, 120.2, 120.4, 122.6, 123.3,
124.1, 125.0, 128.3, 128.8, 128.9, 129.7, 130.3, 130.7, 131.2, 131.7, 134.0,
135.2, 138.1, 141.0, 141.3, 142.0, 142.8, 142.9, 143.0, 143.7, 147.5, 147.6,
147.6, 164.0; m/z (EI) [rel intensity] 892.2 [100, (M)þ], 893.2 [60,
(M þ H)þ], 894.2 [20 (M þ 2H)þ]; m/z (EI) 892.2310 [Mþ], calcd
for C52H48N2O2S5 892.2319; FT-IR (neat cmꢀ1) 2921, 1684, 1569,
1507, 1492, 1391, 1276, 1173, 696.
(9) Zeng, W. D.; Cao, Y. M.; Bai, Y.; Wang, Y. H.; Shi, Y. S.; Zhang,
M.; Wang, F. F.; Pan, C. Y.; Wang, P. Chem. Mater. 2010, 22, 1915.
(10) Bessho, T.; Zakeeruddin, S. M.; Yeh, C.-Y.; Diau, E. W.-G.;
Gr€atzel, M. Angew. Chem., Int. Ed. 2010, 49, 6646.
(11) Paek, S.; Choi, H.; Lee, C. W.; Kang, M. S.; Song, K.;
Nazeeruddin, M. K.; Ko, J. J. Phys. Chem. C 2010, 114, 14646.
(12) Ko, S.; Choi, H.; Kang, M. S.; Hwang, H.; Ji, H.; Kim, J.; Ko, J.;
Kang, Y. J. Mater. Chem. 2010, 20, 2391.
(13) Lin, L. Y.; Tsai, C. H.; Wong, K. T.; Huang, T. W.; Hsieh, L.;
Liu, S. H.; Lin, H. W.; Wu, C. C.; Chou, S. H.; Chen, S. H.; Tsai, A. I.
J. Org. Chem. 2010, 75, 4778.
(14) Li, R. Z.; Liu, J. Y.; Cai, N.; Zhang, M.; Wang, P. J. Phys. Chem. B
2010, 114, 4461.
(15) Fischer, M. K. R.; Wenger, S.; Wang, M. K.; Mishra, A.;
Zakeeruddin, S. M.; Gr€atzel, M.; B€auerle, P. Chem. Mater. 2010,
22, 1836.
(16) Zhang, G. L.; Bala, H.; Cheng, Y. M.; Shi, D.; Lv, X. J.; Yu, Q. J.;
Wang, P. Chem. Commun. 2009, 2198.
(17) Daeneke, T.; Kwon, T.-H.; Holmes, A. B.; Duffy, N. W.; Bach,
U.; Spiccia, L. Nat. Chem. 2011, 3, 211.
(18) Li, X. C.; Sirringhaus, H.; Garnier, F.; Holmes, A. B.; Moratti,
S. C.; Feeder, N.; Clegg, W.; Teat, S. J.; Friend, R. H. J. Am. Chem. Soc.
1998, 120, 2206.
(19) Wang, L.; Chen, Q.; Pan, G. B.; Wan, L. J.; Zhang, S. M.; Zhan,
X. W.; Northrop, B. H.; Stang, P. J. J. Am. Chem. Soc. 2008, 130, 13433.
(20) Zhang, L.; Tan, L.; Wang, Z. H.; Hu, W. P.; Zhu, D. B. Chem.
Mater. 2009, 21, 1993.
(21) Zhan, X. W.; Tan, Z. A.; Zhou, E. J.; Li, Y. F.; Misra, R.; Grant,
A.; Domercq, B.; Zhang, X. H.; An, Z. S.; Zhang, X.; Barlow, S.; Kippelen,
B.; Marder, S. R. J. Mater. Chem. 2009, 19, 5794.
’ ASSOCIATED CONTENT
(22) He, M. Q.; Li, J. F.; Sorensen, M. L.; Zhang, F. X.; Hancock,
R. R.; Fong, H. H.; Pozdin, V. A.; Smilgies, D. M.; Malliaras, G. G. J. Am.
Chem. Soc. 2009, 131, 11930.
(23) Frey, J.; Bond, A. D.; Holmes, A. B. Chem. Commun. 2002,
2424.
S
Supporting Information. Spectra of 5, 10, 12, and 13,
b
device fabrication, and DFT calculations. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
(24) We thanks Drs. J. Frey, S. Proemmel, and M. Armitage for first
developing this method in the synthesis of DTT. See; Frey, J.;
Proemmel, S.; Armitage, M. A.; Holmes, A. B. Org. Synth. 2006, 83, 209.
(25) Chen, M. C.; Chiang, Y. J.; Kim, C.; Guo, Y. J.; Chen, S. Y.;
Liang, Y. J.; Huang, Y. W.; Hu, T. S.; Lee, G. H.; Facchetti, A.; Marks,
T. J. Chem. Commun. 2009, 1846.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: aholmes@unimelb.edu.au (A.B.H.), douglas.macfarlane@
monash.edu (D.R.M.), and udo.bach@sci.monash.edu.au (U.B.).
(26) A reviewer has drawn our attention to the electrophilic variation
of the Hunsdiecker reaction of electron-rich aromatic and heteroaro-
matic carboxylic acids.27ꢀ31 This process suffers the limitation of further
electrophilic substitution reactions in the aromatic ring.
(27) Janz, K.; Kaila, N. J. Org. Chem. 2009, 74, 8874.
’ ACKNOWLEDGMENT
We thank the Australian Research Council, the Australian
Government [DIISR ISL (CG10059)], and the Victorian State
4092
dx.doi.org/10.1021/jo2001484 |J. Org. Chem. 2011, 76, 4088–4093

The Journal of Organic Chemistry
NOTE
(28) Camps, P.; Lukach, A. E.; Pujol, X.; Vazquez, S. Tetrahedron
2000, 56, 2703.
(29) Grovenstein, E.; Henderson, U. V. J. Am. Chem. Soc. 1956,
78, 569.
(30) Johnson, R. G.; Ingham, R. K. Chem. Rev. 1956, 56, 219.
(31) Koo, B. S.; Kim, E. H.; Lee, K. J. Synth. Commun. 2002, 32, 2275.
(32) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian09; Gaussian, Inc., Pittsburgh, PA, 2003.
(33) Kong, H.; Lee, D. H.; Kang, I. N.; Lim, E.; Jung, Y. K.; Park,
J. H.; Ahn, T.; Yi, M. H.; Park, C. E.; Shim, H. K. J. Mater. Chem. 2008,
18, 1895.
4093
dx.doi.org/10.1021/jo2001484 |J. Org. Chem. 2011, 76, 4088–4093