Synthesis and photovoltaic properties of efficient organic dyes containing the benzo[b]furan moiety for solar cells

Article abstract of DOI:10.1021/jo0625150

(Graph Presented) New organic dyes composed of the benzo[b]furan donor, thiophene-conjugated bridge, and cyano acrylic acid acceptor have been newly synthesized through the one-pot coupling cyclization key step. Nanocrystalline TiO₂ dye-sensiti

Full text of DOI:10.1021/jo0625150

Synthesis and Photovoltaic Properties of Efficient Organic Dyes
Containing the Benzo[b]furan Moiety for Solar Cells
Il Jung,† Jae Kwan Lee,† Kyu Ho Song,† Kihyung Song,‡ Sang Ook Kang,*,† and
Jaejung Ko*,†
Department of Chemistry, Korea UniVersity, Jochiwon, Chungnam 339-700, Korea, and Department of
Chemistry, Korea National UniVersity of Education, Chongwon, Chungbuk 363-791, Korea
jko@korea.ac.kr
ReceiVed December 8, 2006
New organic dyes composed of the benzo[b]furan donor, thiophene-conjugated bridge, and cyano acrylic
acid acceptor have been newly synthesized through the one-pot coupling cyclization key step.
Nanocrystalline TiO2 dye-sensitized solar cell was fabricated using this dye. A solar-to-electric conversion
efficiency of 6.65% and 4.70% is achieved with 1 and 2, respectively.
Introduction
coumarin,3 indoline,4 oligoene,5 merocyanine,6 and hemicyanine
dyes7 having efficiencies in the range of 5-9%. Nevertheless,
Dye-sensitized solar cells (DSSCs) are currently attracting
widespread interest as low-cost alternatives to conventional
solid-state photovoltaic devices.1 Until now only three polypy-
ridyl ruthenium(II) complexes have achieved power conversion
efficiencies over 10% in standard air mass 1.5 sunlight.2
Although the metal-complexed dyes exibited high effieciency
and stability, they are quite expensive and hard to purify
compared to the metal-free organic dyes. Recently, impressive
photovoltaic performance has been obtained with some organic
(2) (a) Nazeeruddin, M. K.; De Angelis, F.; Fantacci, S.; Selloni, A.;
Viscardi, G.; Liska, P.; Ito, S.; Takeru.B.; Gra¨tzel, M. J. Am. Chem. Soc.
2005, 127, 16835. (b) Nazeeruddin, M. K.; Pe´chy, P.; Renouard, T.;
Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.;
Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Gra¨tzel,
M. J. Am. Chem. Soc. 2001, 123, 1613.
(3) (a) Hara, K.; Sato, T.; Katoh, R.; Furube, A.; Ohga, Y.; Shinpo, A.;
Suga, S.; Sayama, K.; Sugihara, H.; Arakawa, H. J. Phys. Chem. B 2003,
107, 597. (b) Hara, K.; Kurashige, M.; Dan-oh, Y.; Kasada, C.; Shinpo,
A.; Suga, S.; Sayama, K.; Arakawa, H. New J. Chem. 2003, 27, 783. (c)
Hara, K.; Sayama, K.; Ohga, Y.; Shinpo, A.; Suga, S.; Arakawa, H. Chem.
Commun. 2001, 569.
(4) (a) Horiuchi, T.; Miura, H.; Uchida, S. Chem. Commun. 2003, 3036.
(b) Horiuchi, T.; Miura, H.; Sumioka, K.; Uchida, S. J. Am. Chem. Soc.
2004, 126, 12218. (c) Schmidt-Mende, L.; Bach, U.; Humphry-Baker, R.;
Horiuchi, T.; Miura, H.; Ito, S.; Uchida, S.; Gra¨tzel, M. AdV. Mater. 2005,
17, 813. (d) Ito, S.; Zakeeruddin, S. M.; Humphry-Baker, R.; Liska, P.;
Charvet, R.; Comte, P.; Nazeeruddin, M. K.; Pe´chy, P.; Takada, M.; Miura,
H.; Uchida, S.; Gra¨tzel, M. AdV. Mater. 2006, 18, 1202.
* Corresponding author. Phone: 82-41-860-1337. Fax: 82-41-867-5396.
† Korea University.
‡ Korea National University of Education.
(1) (a) O’Regan, B.; Gra¨tzel, M. Nature 1991, 353, 737. (b) Gra¨tzel,
M.; Nature 2001, 414, 338. (c) Yanagida, M.; Yamaguchi, T.; Kurashige,
M.; Hara, K.; Katoh, R.; Sugihara, H.; Arakawa, H. Inorg. Chem. 2003,
42, 7921. (d) Wang, P.; Klein, C.; Humphry-Baker, R.; Zakeeruddin,
S. M.; Gra¨tzel, M. J. Am. Chem. Soc. 2005, 127, 808. (e) Jang, S.-R.; Lee,
C.; Ko, J.; Lee, J.; Vittal, R.; Kim, K.-J. Chem. Mater. 2006, 18, 5604.
10.1021/jo0625150 CCC: $37.00 © 2007 American Chemical Society
Published on Web 03/30/2007
3652
J. Org. Chem. 2007, 72, 3652-3658

DSSC Containing Benzo[b]furan
many organic dyes have often presented low conversion
efficiency and low operation stability compared to metal-
complexed dyes. The major factor for the low conversion
efficiency of many organic dyes in the DSSCs is due to the
formation of dye aggregates on the semiconductor surface. The
low stability of organic dyes is due to the formation of unstable
radical species during redox reaction cycles.
aldehyde 2,2-dimethylpropane-1,3-diyl acetal12 followed by
reduction of the nitro group in 4 using Raney Ni13 and
N-arylation under Ullmann conditions.14 Subsequent cleavage
of the 1,3-dioxalane protecting group in aqueous acid produced
the free aldehyde 7. The aldehyde, upon reaction with cy-
anoacetic acid in the presence of a catalytic amount of piperidine
in CH3CN, produced the 1 dye. Organic dye 2 was prepared by
alkylation of 8 with bromoacetaldehyde diethyl acetal followed
by ring closure reaction of 915 and coupling reaction of aldehyde
10 with phosphonate under Horner-Emmons-Wittig coupling
conditions using potassium tert-butoxide in THF.16 The thiophene
derivative 11 was converted into thiophene-aldehyde 12 which
produced the organic dye 2 upon treatment with cyanoacetic
acid.
Thus, we became interested in the development of efficient
new organic dyes, which are not aggregated and stable. The
highly efficient organic dyes have an almost push-pull structure
such as nonlinear optical molecules, which are composed of a
donor, conjugated bridge, and acceptor, and many researchers
have attempted to create organic dyes through the structural
modification of each donor,3a,4a,5a conjugated bridge,3c,4a,5b,8 or
acceptor unit.3a Among these approaches, we are especially
interested in the structural modification of the organic dye’s
donor unit and concerned about their structures and related
efficiencies for DSSC.
Figure 1 shows the UV/vis spectrum of the 1 sensitizer
measured in ethanol solution, and the data is collected in Table
1. The absorption spectrum of the 1 sensitizer shows two
absorption maxima of 463 nm (ꢀ ) 25 300 dm3 mol-1 cm-1
)
and 358 nm (ꢀ ) 36 700 dm3 mol-1 cm-1) which are due to
the π-π* transitions of the conjugated molecule. Under similar
conditions, the 2 sensitizer exhibits absorption bands at 479 nm
(ꢀ ) 33 300 dm3 mol-1 cm-1) and 367 nm (ꢀ ) 40 600 dm3
mol-1 cm-1) that are red-shifted compared to the 1 sensitizer.
When the 1 sensitizer was absorbed to TiO2 electrode, a slight
red shift from 463 to 468 nm was found due to the interaction
of the anchoring group with the surface titanium anions. The
absorption spectrum of the 1 on the TiO2 electrode is broadened.
Similar broadening and red shift have been reported in several
organic dyes on TiO2 electrodes.6,16 When the 1 sensitizer is
excited within its π-π* bands in an air-equilibrated solution
at 298 K, it exhibits strong luminescence maximum at 627 nm.
To thermodynamically evaluate the possibility of electron
transfer from the excited-state of the dye to the conduction band
of the TiO2 electrode, a cyclic voltammogram was carried out
to determine the redox potentials (Table 1). The redox potentials
of two organic dyes on TiO2 films were measured in MeCN
with 0.1 M tetra-n-butylammonium hexafluorophosphate (TBA-
PF6). The reference electrode was a silver wire calibrated with
Fc/Fc+ as an internal reference. The two organic dyes absorbed
on TiO2 films showed quasireversible behaviors. The oxidation
potential of 1 dye was measured to be 0.60 V vs Fc/Fc+, an
oxidation potential energetically favorable for iodide oxidation.
The reduction potential of 1 dye calculated from the oxidation
potential and the E0-0 determined from the intersection of
absorption and emission spectra is listed in Table 1. The excited-
state oxidation potential (EOX*) of the dyes (1: -1.70 V vs
Fc/Fc+, -1.07 V vs NHE; 2: -1.67 V vs Fc/Fc+, -1.04 V vs
NHE) are much more negative than the conduction band level
of TiO2 at approximately -0.5 V vs NHE.
Very recently, we reported highly efficient and stable organic
dyes that have a bis-dimethylfluorenyl amino phenyl donor unit.9
The bis-dimethylfluorenyl moiety was introduced to prevent
aggregation Via molecular stacking by the bulky nonplanar
structure and to ensure greater resistance to degradation when
exposed to light and high-temperature.10
In this article, as part of our efforts to develop more efficient
organic dyes, we report new organic dyes containing [bis(9,9-
dimethylfluoren-2-yl)amino]benzofuran as the electron donor
and cyanoacrylic acid as the electron acceptor bridged by a
thiophene unit. Although many structural frameworks such as
coumarin, aniline, and indoline have been employed as good
electron donor units, an organic dye containing the benzo[b]-
furan structural motif has never been explored for DSSCs.
Results and Discussion
Scheme 1 illustrates the synthetic procedures of organic dyes
1 and 2 starting from 2-iodo-5-nitrophenol acetate 3and 4-[bis-
(9,9-dimethylfluoren-2-yl)amino]-2- hydroxybenzaldehyde 811
The key step in the synthesis of 1 and 2 relies on the cyclization
of 3 and 9. Organic dye 1 was prepared by one-pot coupling
cyclization of 3 and 2-trimethylsilylacetyl-5-thiophene-carboxy-
(5) (a) Hara, K.; Kurashige, M.; Ito, S.; Shinpo, A.; Suga, S.; Sayama,
K.; Arakawa, H.; Chem. Commun. 2003, 252. (b) Kitamura, T.; Ikeda, M.;
Shigaki, K.; Inoue, T.; Anderson, N. A.; Ai, X.; Lian, T.; Yanagida, S.;
Chem. Mater. 2004, 16, 1806. (c) Hara, K.; Sato, T.; Katoh, R.; Furube,
A.; Yoshihara, T.; Murai, M.; Kurashige, M.; Ito, S.; Shinpo, A.; Suga, S.;
Arakawa, H. AdV. Funct. Mater. 2005, 15, 246.
(6) (a) Sayama, K.; Tsukagoshi, S.; Hara, K.; Ohga, Y.; Shinpou, A.;
Abe, Y.; Suga, S.; Arakawa, H. J. Phys. Chem. B. 2002, 106, 1363. (b)
Sayama, K.; Hara, K.; Mori, N.; Satsuki, M.; Suga, S.; Tsukagoshi, S.;
Abe, Y.; Sugihara, H.; Arakawa, H. Chem. Commun. 2000, 1173.
(7) (a) Yao, Q.-H.; Shan, L.; Li, F.-Y.; Yin, D.-D.; Huang, C.-H. New
J. Chem. 2003, 27, 1277. (b) Wang, Z.-S.; Li, F.-Y.; Huang, C.-H. Chem.
Commun. 2000, 2063
In order to obtain the geometrical configuration and charac-
teristic features of the electronic structure, molecular orbital
(12) (a) Osuka, A.; Fujikane, D.; Shinmori, H.; Kobatake, S.; Irie, M.
J. Org. Chem. 2001, 66, 3913. (b) Shultz, D. A.; Gwaltney, K. P.; Lee, H.
J. Org. Chem. 1998, 63, 4034.
(13) Ple´, P. A.; Green, T. P.; Hennequin, L. F.; Curwen, J.; Fennell, M.;
Allen, J.; Lambert van der Brempt, C.; Costello, G. J. Med. Chem. 2004,
47, 871.
(8) (a) Li, S. L.; Jiang, K. J.; Shao, K. F.; Yang, L. M. Chem. Commun.
2006, 2792. (b) Koumura, N.; Wang, Z. X. S.; Mori, S.; Miyashita, M.;
Suzuki, E.; Hara, K. J. Am. Chem. Soc. 2006, 128, 14256. (c) Hagberg,
D. P.; Edvinsson, T.; Marinado, T.; Boschloo, G.; Hagfeldt, A.; Sun, L.
Chem. Commun. 2006, 2245.
(9) Kim, S.; Lee, J. K.; Kang, S. O.; Ko, J.; Yum, J.-H.; Fantacci, S.;
De Angelis, F.; Di Censo, D.; Nazeeruddin, Md. K.; Gra¨tzel, M. J. Am.
Chem. Soc. 2006, 128, 16701.
(10) (a) Shirota, Y.; Kinoshita, M.; Noda, T.; Okumoto, K.; Ohara, T.
J. Am. Chem. Soc. 2000, 122, 11021. (b) Kim, S.; Song, K.-H.; Kang, S.
O.; Ko, J. Chem. Commun. 2004, 68.
(14) Bushby, R. J.; McGill, D. R.; Ng, K. M.; Taylor, N. J. Mater. Chem.
1997, 7, 2343.
(15) Yoshimura, H.; Yoshimura, H.; Kikuchi, K.; Hibi, S.; Tagami, K.;
Satoh, T.; Yamauchi, T.; Ishibahi, A.; Tai, K.; Hida, T.; Tokuhara, N.; Nagai,
M. J. Med. Chem. 2000, 43, 2929.
(16) Zhang, C.; Harper, A. W.; Dalton, L. R. Synth. Commun. 2001, 31,
1361.
(11) Dai, W.-M.; Lai, K. W. Tetrahedron Lett. 2002, 43, 9377.
J. Org. Chem, Vol. 72, No. 10, 2007 3653

Jung et al.
SCHEME 1. Schematic Diagram for the Synthesis of Organic Dyes 1 and 2
calculation of 1 was performed with B3LYP/3-21G*. The
HOMO is delocalized over the π-conjugated system via the
amino unit through benzo[b]furan moiety. Examination of the
HOMO and LUMO of 1 indicates that HOMO-LUMO
excitation moved the electron distribution from the bisdimeth-
ylfluorenyl amino framework to the cyanoacrylic acid group
(Figure 2). Therefore, the change in electron distribution induced
by photoexcitation results in an efficient charge separation. The
2 dye showed similar configuration geometry to 1.
screen printing TiO2 paste (13 nm anatase) and was sintered at
450 °C for 30 min. Then, a paste for the transparent layer was
coated with a scattering layer (HWP-400) and was again sintered
at 450 °C for 30 min. The resulting layer was composed of a
13 µm thick transparent layer and 10 µm thick scattering layer.
The TiO2 electrodes were treated again by NbCl5 followed by
oxidation at 500 °C for 30 min. The TiO2 electrode was
immersed into the 1 solution (0.3 mM dye in ethanol containing
10 mM 3a,7a-dihydroxy-5b-cholic acid (Cheno)) and kept at
room temperature for 18 h. The chenodeoxycholic acid was
added to the dye solution to enhance the cell efficiency of dye
on the TiO2 electrode.19 A counter electrode was coated with a
drop of H2PtCl6 solution (2 mg Pt in 1 mL ethanol) on a FTO
plate and heated at 400 °C for 15 min. The dye-adsorbed TiO2
electrode and Pt counter electrode were assembled into a sealed
sandwich type cell by heating with a Surlyn film (25 µm
thickness) as a spacer between the electrode. The electrolyte
was then introduced into the cell, which was composed of 0.6
For the preparation of DSSC, the washed FTO (8 Ωsq-1
,
2.3 mm thickness) glass plate was immersed in 40 mM TiCl4
of aqueous solution at 60 °C for 30 min and washed with water
and ethanol as reported by the Gra¨tzel group.18 A transparent
nanocrystalline layer on the FTO glass plate was prepared by
(17) (a) Nu¨esch, F.; Moser, J. E.; Shklover, V.; Gra¨tzel, M. J. Am. Chem.
Soc. 1996, 118, 5420. (b) Li, S.-L.; Jiang, K.-J.; Shao, K.-F.; Yang, L.-M.
Chem. Commun. 2006, 2792.
(18) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.;
Mu¨ller, E.; Liska, P.; Vlachopoulos, N.; Gra¨tzel, M. J. Am. Chem. Soc.
1993, 115, 6382.
(19) Kay, A. Gra¨tzel, M. J. Phys. Chem. 1993, 97, 6272.
3654 J. Org. Chem., Vol. 72, No. 10, 2007

DSSC Containing Benzo[b]furan
FIGURE 1. Absorption and emission spectra of the 1 (blue line) dye and 2 (red line) in EtOH compared with the absorption spectrum of the dye
anchored to TiO2 (dashed line). The emission spectra (dotted line) were obtained by exciting the same solution at 450 nm at 298 K. The concentration
for the solution was 10-5 M.
TABLE 1. Optical, Redox, and DSSC Performance Parameters of Dyes
dye
λ
abs,a nm (ꢀ/dm3 M-1cm-1
)
Eox,b (∆Ep)/V
E0-0,c eV
ELUMO,d V
Jsc (mA cm-2
)
Voc (V)
FF
ηe (%)
1
2
463 (25300)
479 (33300)
0.60 (0.36)
0.52 (0.28)
2.30
2.19
-1.70
-1.67
14.39 ( 0.25
11.43 ( 0.22
0.70 ( 0.01
0.67 ( 0.01
0.66 ( 0.01
0.62 ( 0.02
6.65 ( 0.20
4.70 ( 0.15
a Absorption spectra were measured in ethanol solution. b Oxidation potential of dyes on TiO2 was measured in CH3CN with 0.1 M (n-C4H9)4NPF6 with
c
d
a scan rate of 50 mVs-1 (vs Fc/Fc+). E0-0 was determined from the intersection of absorption and emission spectra in ethanol. ELUMO was calculated by
Eox - E0-0
e Performances of DSSCs were measured with 0.18 cm2 working area. ꢀ: absorption coefficient; Eox: oxidation potential; ∆Ep: Epa - Epc;
0-0: voltage of intersection point between absorption and emission spectra; Jsc: short-circuit photocurrent density; Voc: open-circuit photovoltage; FF: fill
.
E
factor; η: total power conversion.
FIGURE 2. Isodensity surface plots of the HOMO and LUMO of 1 (a) and 2 (b).
M 3-hexyl-1,2-dimethylimidazolium iodide, 0.04 M iodine,
0.025 M LiI, 0.05 M guanidium thiocyanate, and 0.28 M tert-
butylpyridine in acetonitrile. The photovoltaic measurements
were recorded under the simulated AM 1.5 irradiation (1000
W xenon light).
2 dyes are presented and compared with N719 dye in Figure 3.
Under standard global AM 1.5 solar conditions, the 1 and 2
sensitized cell gave the short circuit photocurrent density (Jsc)
of 14.39 ( 0.25 and 11.43 ( 0.22 mA cm-2, open circuit
voltage (Voc) of 0.70 ( 0.01 and 0.67 ( 0.01 V and a fill factor
of 0.66 ( 0.01 and 0.62 ( 0.02, corresponding to an overall
conversion efficiency η, derived from the equation: η ) JscVoc-
The J-V curve and incident mono-chromatic photon-to-current
conversion efficiency (IPCE) for the DSSCs based on the 1 and
J. Org. Chem, Vol. 72, No. 10, 2007 3655

Jung et al.
2-Trimethylsilylethynyl-5-(5,5-dimethyl-1,3-dioxan-2-yl)th-
iophene. A mixture of 2-bromo-5-thiophenecarboxyaldehyde 2,2-
dimethylpropane-1,3-diyl acetal (1.40 g, 5.1 mmol), trimethylsily-
lacetylene (0.78 mL, 5.6 mmol), Pd(PPh3)4 (5 mol %), and CuI (5
mol %) were dissolved in degassed triethylamine (30 mL). The
solution was refluxed for 8 h. After the solution was cooled, H2O
(30 mL) and dichloromethane (50 mL) were added to the solution.
The organic layer was separated and dried with MgSO4. The organic
layer was removed in Vacuo. The pure product was obtained brown
oil by silica gel chromatography (eluent MC:Hx ) 1:1, Rf ) 0.4)
1
to afford acetal (1.38 g) in 92% yield. H NMR (CDCl3): δ 7.09
(d, J ) 3.90 Hz, 1H), 6.95 (d, J ) 3.90 Hz, 1H), 5.56 (s, 1H), 3.73
(d, J ) 11.10 Hz, 2H), 3.60 (d, J ) 11.10 Hz, 2H), 1.25 (s, 3H),
0.79 (s, 3H), 0.24 (s, 9H). 13C{1H} NMR (CDCl3): δ 143.1, 132.2,
124.8, 123.6, 99.1, 97.9, 97.7, 77.6, 30.3, 23.0, 21.9, 0.0. MS: m/z
294 [M+]. Anal. Calcd. for C15H22SSiO2: C, 61.18; H, 7.53.
Found: C, 61.02; H, 7.44.
2-(5-(5,5-Dimethyl-1,3-dioxan-2-yl)thiophene-2-yl)-6-nitroben-
zofuran (4). A mixture of 3 (1.00 g, 3.8 mmol), 2-trimethylsilyl-
ethynyl-(5-(5,5-dimethyl-1,3-dioxan-2-yl)thiophene (1.11 g, 3.8
mmol), K2CO3 (1.05 g, 7.6 mmol), Pd(PPh3)4 (5 mol %), and CuI
(5 mol %) were dissolved in degassed diethylamine (10 mL) and
acetonitrile (50 mL). The solution was refluxed for 8 h. After the
solution was cooled, H2O (30 mL) and dichloromethane (50 mL)
were added to the solution. The organic layer was separated and
dried with MgSO4. The organic layer was removed in Vacuo. The
pure product 4 was obtained by silica gel chromatography (eluent
MC:Hx ) 1:1, Rf ) 0.4) to afford 4 (0.12 g) in 44% yield. Mp:
142 °C. 1H NMR (CDCl3)): δ 8.37 (s, 1H), 8.17 (d, J ) 8.70 Hz,
1H), 7.60 (d, J ) 8.70 Hz, 1H), 7.48 (d, J ) 3.90 Hz, 1H), 7.16
(d, J ) 3.90 Hz, 1H), 6.92 (s, 1H), 5.67 (s, 1H) 3.79 (d, J ) 11.40
Hz, 2H), 3.67 (d, J ) 11.40 Hz, 2H), 1.30 (s, 3H), 0.82 (s, 3H).
13C{1H} NMR (CDCl3): δ 156.6, 144.3, 143.5, 135.4, 134.3, 131.9,
126.2, 120.4, 119.3, 116.2, 107.6, 101.2, 97.9, 77.7, 30.4, 23.1,
21.9. MS: m/z 359 [M+]. Anal. Calcd. for C18H17NO5S: C, 60.15;
H, 4.77. Found: C, 59.87; H, 4.68.
2-(5-(5,5-Dimethyl-1,3-dioxan-2-yl)thiophene-2-yl)-6-aminoben-
zofuran (5). Methanol (30 mL), Raney nickel (0.020 g), and
hydrazine hydrate (0.097 mL, 2 mmol) were warmed to 55-
60 °C, and 4 (0.18 g, 0.5 mmol) was added portionwise. The
reaction mixture was then heated to reflux for 5 h. The catalyst
was removed by filtration, the solvent evaporated, and the residue
dissolved in water and extracted with dichloromethane. The organic
phase was dried over magnesium sulfate and the solvent evaporated.
The pure product 5 was obtained by silica gel chromatography
(eluent MC, Rf ) 0.5) to afford 5 (0.064 g) in 39% yield. Mp:
160 °C. 1H NMR (CDCl3)): δ 7.28 (d, J ) 8.10 Hz, 1H), 7.25 (d,
J ) 3.60 Hz, 1H), 7.08 (d, J ) 3.60 Hz, 1H), 6.79 (s, 1H), 6.72 (s,
1H), 6.59 (d, J ) 8.10 Hz, 1H), 5.64 (s, 1H), 3.77 (d, J ) 11.40
Hz, 2H), 3.65 (d, J ) 11.40 Hz, 2H), 1.30 (s, 3H), 0.80 (s, 3H).
13C{1H} NMR (CDCl3): δ 156.2, 149.3, 144.7, 140.6, 134.1, 125.8,
122.8, 121.2, 121.0, 112.5, 101.5, 98.2, 97.3, 77.6, 30.3, 23.0, 21.9.
MS: m/z 329 [M+]. Anal. Calcd. for C18H19NO3S: C, 65.63; H,
5.81. Found: C, 65.39; H, 5.68.
FIGURE 3. J-V curves of DSSCs prepared with film of N719 (s), 1
(----), and 2 (····). The inset shows IPCE spectra of DSSCs containing
1 and 2. Light intensity was 100 mW/cm2.
FF/light intensity, of 6.65 ( 0.20 and 4.70 ( 0.15%, respec-
tively. In the same condition, the N719 sensitized cell gave a
Jsc of 18.44 ( 0.40 mA cm-2, Voc of 0.75 ( 0.01 V and a fill
factor of 0.67 ( 0.01, corresponding to η of 9.16 ( 0.25%.
The IPCE data of 1 and 2 sensitizer plotted as a function of
excitation wavelength exhibits a high plateau at 77% and 66%,
respectively.
From these results, we have observed that the Voc and Jsc of
dye 1 were higher than that of dye 2 even though dye 2 exhibited
a similar LUMO level and greater absorption strength. The 2
had a more enhanced optical data than the 1 dye. To explain
these results clearly, we investigated the amounts of 1 and 2
adsorbed on TiO2 film. However, we cannot explain the
differences of their adsorbed amounts because they were very
similar. On the other hand, we believed that because the more
conjugated organic dyes with a vinyl bridge unit are more
flexible on TiO2 surface than that of short conjugated dye or
rigid conjugated dyes, the flexible conjugated organic dyes can
lie on the neighboring TiO2 surface and can affect the electronic
state of the band potential of the TiO2 conduction band, and
these effects can reduce the electron injection efficiency from
dye to TiO2. Thus, the Jsc and Voc of dye 2 may be lower than
that of dye 1 due to these reasons. Now, we are working on
finding evidence to support these explanations.
Conclusion
This work has demonstrated that the two organic dyes, 1 and
2 containing bis-dimethylfluorenyl amino benzo[b]furan moiety
are very efficient dyes for dye-sensitized solar cells. And that
dye 1 was newly synthesized through the one-pot coupling
cyclization key step. We believe that the development of
alternative highly efficient organic dyes to ruthenium complexes
is possible through more sophisticated structural modifications,
and these works are now in progress.
2-(5-(5,5-Dimethyl-1,3-dioxan-2-yl)thiophene-2-yl)-6-N,N-bis-
(9,9-dimethylfluoren-2-yl)aminobenzofuran (6). A stirred mixture
of 5 (0.2 g, 0.6 mmol), 2-iodo-9,9-dimethylfluorene (0.42 g, 1.3
mmol), powdered anhydrous potassium carbonate (0.36 g, 2.7
mmol), copper bronze (0.13 g, 0.2 mmol), 18-crown-6 (0.02 g, 0.07
mmol), and 1,2-dichlorobenzene (40 mL) was refluxed for 48 h.
After cooling, the insoluble inorganic material was filtered off under
suction and the dark brown filtrate collected. The insoluble material
was washed with dichloromethane (3 × 30 mL). The combined
filtrate and organic phase was washed with dilute aqueous ammonia
and water and dried with magnesium sulfate. The solvent was
removed under reduced pressure. The pure product 6 was obtained
by silica gel chromatography (eluent MC:Hx ) 1:1, Rf ) 0.5) to
Experimental Section
Cyclovoltagram. A three-electrode system was used and con-
sisted of a gold disk, working electrode, and a platinum wire
electrode. Redox potential of dyes on TiO2 were measured in CH3-
CN with 0.1M (n-C4H9)4N-PF6 a scan rate between 50 mVs-1 (vs
Fc/Fc+).
1
afford 6 (0.22 g) in 51% yield. Mp: 193 °C. H NMR (CDCl3)):
δ 7.70 (s, 1H), 7.65 (d, J ) 6.90 Hz, 2H), 7.59 (d, J ) 7.80 Hz,
3656 J. Org. Chem., Vol. 72, No. 10, 2007

DSSC Containing Benzo[b]furan
2H), 7.42 (d, J ) 8.10 Hz, 1H), 7.39 (d, J ) 6.90 Hz, 2H), 7.35
(d, J ) 7.80 Hz, 2H), 7.35 (t, J ) 7.80 Hz, 2H), 7.32 (t, J ) 7.80
Hz, 2H), 7.31 (d, J ) 7.80 Hz, 2H), 7.28 (s, 2H), 7.15-7.05 (m,
3H), 6.82 (s, 1H), 5.64 (s, 1H) 3.77 (d, J ) 11.10 Hz, 2H), 3.65
(d, J ) 11.10 Hz, 2H), 1.42 (s, 12H), 1.39 (s, 3H), 0.81 (s, 3H).
13C{1H} NMR (CDCl3): δ 166.8, 156.4, 155.2, 153.7, 139.3, 134.4,
132.2, 127.1, 126.5, 126.0, 125.1, 122.6, 120.8, 119.6, 118.4, 117.4,
112.5, 111.6, 107.3, 105.8, 101.5, 101.0, 98.2, 95.7, 93.0, 72.0,
47.0, 30.3, 27.2, 23.1, 21.9. MS: m/z 713 [M+]. Anal. Calcd. for
C48H43NO3S: C, 80.75; H, 6.07. Found: C, 80.42; H, 5.97.
2-(5-Formylthiophene-2-yl)-6-bis(9,9-dimethylfluoren-2-yl)-
aminobenzofuran (7): THF (30 mL) and water (10 mL) were
added to a flask containing 6 (0.1 g, 0.14 mmol). Then, TFA (2
mL) was added to the solution. The resulting reaction mixture was
stirred for 2 h at room temperature, quenched with saturated aqueous
sodium bicarbonate, and extracted with dichloromethane. The
combined dichloromethane phases were then washed with aqueous
sodium bicarbonate and dried MgSO4. The organic layer was
removed in Vacuo. The pure product 7 was obtained by silica gel
chromatography (eluent EA:Hx ) 1:2, Rf ) 0.5) to afford 7 (0.06
127.1, 126.6, 123.4, 122.6, 120.7, 119.5, 118.8, 116.5, 109.6, 108.5,
55.3, 46.9, 27.2. MS: m/z 507 [M+]. Anal. Calcd. for C37H33NO:
C, 87.54; H, 6.55. Found: C, 87.30; H, 6.43.
3-(N,N-Bis(9,9-dimethylfluoren-2-yl)aminophenol. 3-(N,N-Bis-
(9,9-dimethylfluoren-2-yl)aminoanisole (0.13 g, 0.26 mmol) was
dissolved in CH2Cl2 (50 mL). BBr3 (0.05 mL, 0.52 mol) was added
dropwise into the solution at-78 °C. The mixture was further stirred
for 8 h at room temperature. Saturated aqueous Na2CO3 (30 mL)
was added to quench the reaction. The organic layer was separated.
The aqueous layer was extracted with dichloromethane (2 × 50
mL). The combined extracts were washed with water and dried
with MgSO4. The organic layer was removed in Vacuo. The pure
product phenol was obtained by silica gel chromatography (eluent
1
MC:Hx ) 1:1, Rf ) 0.1), 66% yield (0.085 g). Mp: 221 °C. H
NMR (CDCl3): δ 7.65 (d, J ) 7.80, 2H), 7.60 (d, J ) 8.10 Hz,
2H), 7.40 (d, J ) 7.80 Hz, 2H), 7.32 (t, J ) 8.10 Hz, 2H), 7.29 (t,
J ) 8.10 Hz, 2H), 7.23 (s, 2H), 7.13 (t, J ) 7.80 Hz, 1H), 7.10 (d,
J ) 8.10 Hz, 2H), 6.77 (d, J ) 7.80 Hz, 1H), 6.66 (s, 1H), 6.51 (d,
J ) 7.80 Hz, 1H), 1.41 (s, 12H). 13C{1H} NMR (CDCl3): δ 156.5,
155.2, 153.7, 149.6, 147.4, 139.1, 134.4, 130.2, 127.1, 126.6, 123.5,
122.6, 120.7, 119.6, 119.0, 116.5, 110.8, 119.6, 47.0, 27.2. MS:
m/z 493 [M+]. Anal. Calcd. for C36H31NO: C, 87.59; H, 6.33.
Found: C, 87.36; H, 6.19.
1
g) in 70% yield. Mp: 188 °C. H NMR (CDCl3): δ 9.90 (s, 1H),
7.71 (d, J ) 3.60 Hz, 1H), 7.63 (d, J ) 6.90 Hz, 2H), 7.59 (d, J )
7.80 Hz, 2H), 7.46 (s, 1H), 7.45 (d, J ) 3.60 Hz, 1H), 7.40 (d,
J ) 6.90 Hz, 2H), 7.33 (t, J ) 7.80 Hz, 2H), 7.32 (t, J ) 7.80 Hz,
2H), 7.28 (d, J ) 8.10 Hz, 1H), 7.24 (s, 2H), 7.16 (d, J ) 8.10 Hz,
1H), 7.12 (d, J ) 7.80 Hz, 2H), 7.06 (s, 1H), 1.42 (s, 12H). 13C-
{1H} NMR (CDCl3): δ 182.6, 156.8, 155.4, 153.7, 149.7, 147.5,
147.1, 142.5, 139.1, 137.1, 134.6, 127.2, 126.8, 124.3, 124.0, 123.5,
122.7, 121.6, 121.2, 120.8, 119.6, 118.9, 112.3, 106.7, 105.1, 47.0,
27.2. MS: m/z 627 [M+]. Anal. Calcd. for C43H33NO2S: C, 82.27;
H, 5.30. Found: C, 82.09; H, 5.22.
4-(Bis(9,9-dimethylfluoren-2-yl)amino)-2-hydroxybenzalde-
hyde (8). A mixture of POCl3 (1.05 g, 10.9 mmol) in DMF (10
mL) was cooled at 0 °C. 3-(N,N-Bis(9,9-dimethylfluoren-2-yl)-
aminophenol (2.7 g, 5.47 mmol) was dissolved in DMF (20 mL).
The POCl3 solution was then added dropwise into 3-(N,N-bis(9,9-
dimethylfluoren-2-yl)aminophenol at 0 °C. The reaction mixture
was reacted for 2 h and then hydrolyzed with water (40 mL) for 6
h. The crude product was extracted with CH2Cl2 (3 × 50 mL).
The combined extracts were washed with water and dried with
MgSO4. The organic layer was removed in Vacuo. The pure product
8 was obtained by silica gel chromatography (eluent MC:Hx )
(E)-3-(5-(6-(Bis(9,9-dimethylfluoren-2-yl)amino)benzofuran-
2-yl)thiophene-2-yl)-2-cyanoacrylic Acid (1): A mixture of 7
(0.03 g, 0.05 mmol) and cyanoacetic acid (0.01 g, 0.1 mmol) were
vacuum-dried and added MeCN (60 mL) and piperidine (0.003 mL).
The solution was refluxed for 6 h. After the solution was cooled,
the organic layer was removed in Vacuo. The pure product 1 was
obtained by silica gel chromatography (eluent EA:MeOH ) 10:1,
1
1:1, Rf ) 0.1) to afford 8 (1.97 g) in 69% yield. Mp: 196 °C. H
NMR (CDCl3): δ 11.43 (s, 1H), 9.63 (s, 1H), 7.69 (d, J ) 8.10
Hz, 4H), 7.42 (d, J ) 8.10 Hz, 2H), 7.35 (t, J ) 8.10 Hz, 2H),
7.33 (t, J ) 11.10 Hz, 2H), 7.31 (d, J ) 8.40 Hz, 1H), 7.25 (s,
2H), 7.2 (d, J ) 8.10 Hz, 2H), 6.62 (d, J ) 8.40 Hz, 1H), 6.50 (s,
1H), 1.43 (s, 12H). 13C{1H} NMR (CDCl3): δ 192.5, 163.8, 155.8,
155.6, 153.9, 145.1, 138.6, 136.9, 134.8, 127.4, 127,3, 125.7, 122.8,
121.1, 120.3, 114.7, 113.0, 111.6, 105.5, 47.1, 27.2. MS: m/z 521
[M+]. Anal. Calcd. for C37H31NO2: C, 85.19; H, 5.99. Found: C,
84.92; H, 5.78.
1
Rf ) 0.1) to afford 1 (0.016 g) in 47% yield. Mp: 229 °C. H
NMR (DMSO): δ 8.03 (s, 1H), 7.75 (d, J ) 8.10 Hz, 2H), 7.74
(d, J ) 7.50 Hz, 2H), 7.69 (d, J ) 3.60 Hz, 1H), 7.63 (d, J ) 3.60
Hz, 1H), 7.60 (d, J ) 8.40 Hz, 1H), 7.50 (d, J ) 7.50 Hz, 2H),
7.40 (s, 1H), 7.32 (t, J ) 8.10 Hz, 2H), 7.30-7.26 (m, 4H), 7.10
(s. 1H), 7.05 (d, J ) 8.40 Hz, 1H), 7.04 (d, J ) 8.10 Hz, 2H), 1.37
(s, 12H). 13C{1H} NMR (DMSO): δ 158.2, 155.2, 154.8, 153.2,
146.9, 145.7, 138.3, 137.4, 136.6, 133.8, 127.9, 127.5, 127.1, 125.0,
124.3, 123.1, 122.8, 121.2, 119.6, 118.1, 117.6, 116.9, 114.2, 109.0,
107.2, 104.6, 104.0, 99.6, 46.5, 26.7. MS: m/z 694 [M+]. Anal.
Calcd. for C46H34N2O3S: C, 79.51; H, 4.93. Found: C, 79.48; H,
4.90.
4-(Bis(9,9-dimethylfluoren-2-yl)amino)-2-(2,2-diethoxyethoxy)-
benzaldehyde (9). A solution of 8 (0.47 g, 0.92 mmol), K2CO3
(0.25 g, 1.84 mmol), and bromoacetaldhyde diethylacetal (0.14 mL,
0.92 mmol) in DMF (50 mL) was refluxed for 6 h. DMF was
removed under reduced pressure. The crude mixture was redissolved
in ethyl acetate (100 mL). The organic layer was washed with water
(100 mL) and collected. The aqueous layer was extracted with ethyl
acetate (2 × 50 mL). The combined extracts were dried with
MgSO4. The organic layer was removed in Vacuo. The pure product
9 was obtained by silica gel chromatography (eluent EA:Hx ) 1:5,
Rf ) 0.5) to afford 9 (1.08 g) in 72% yield. Mp: 131 °C. 1H NMR
(CDCl3): δ 10.41 (s, 1H), 7.80 (d, J ) 8.40 Hz, 1H), 7.71 (d, J )
7.80 Hz, 4H), 7.44 (d, J ) 7.80 Hz, 2H), 7.38 (s, 2H), 7.31 (t, J )
7.80 Hz, 4H), 7.23 (d, J ) 7.80 Hz, 2H), 6.77 (d, J ) 8.40 Hz,
1H), 6.74 (s, 1H), 4.85 (t, J ) 5.10 Hz, 1H), 3.92 (d, J ) 5.10 Hz,
2H), 3.75 (m, 2H), 3.61 (m, 2H), 1.48 (s, 12H), 1.22 (t, J ) 6.60
Hz, 6H),. 13C{1H} NMR (CDCl3): δ 187.4, 162.2, 155.2, 154.8,
153.5, 145.4, 138.4, 136.2, 129.4, 127.1, 124.9, 122.5, 120.9, 120.4,
119.7, 118.5, 113.2, 103.2, 100.2, 68.9, 62.9, 62.3, 46.8, 26.9, 15.2.
MS: m/z 637 [M+]. Anal. Calcd. for C43H43NO4: C, 80.97; H,
6.80. Found: C, 80.68; H, 6.66.
3-(N,N-Bis(9,9-dimethylfluoren-2-yl)aminoanisole. A stirred
mixture of m-aminoanisole (1.04 mL, 9.23 mmol), 2-iodo-9,9-
dimethylfluorene (6.5 g, 20.3 mmol), powdered anhydrous potas-
sium carbonate (5.62 g, 40.6 mmol), copper bronze (1.93 g, 30.5
mmol), 18-crown-6 (0.29 g, 1.11 mmol), and 1,2-dichlorobenzene
(70 mL) was refluxed for 48 h. After cooling, the insoluble
inorganic material was filtered off and the dark brown filtrate was
collected. The insoluble material was washed with dichloromethane
(3 × 50 mL). The combined filtrate and organic phase was washed
with dilute aqueous ammonia and water and dried with magnesium
sulfate. The solvent was removed under reduced pressure. The pure
product was obtained by silica gel chromatography (eluent MC:
Hx ) 1:2, Rf ) 0.4) in 41% yield (1.92 g). Mp: 243 °C. 1H NMR
(CDCl3): δ 7.66 (d, J ) 7.50, 2H), 7.60 (d, J ) 8.40 Hz, 2H),
7.40 (d, J ) 7.50 Hz, 2H), 7.32 (t, J ) 8.40 Hz, 2H), 7.30 (t, J )
8.40 Hz, 2H), 7.25 (s, 2H), 7.18 (t, J ) 8.10 Hz, 1H), 7.10 (d, J )
8.40 Hz, 2H), 6.78 (d, J ) 8.10 Hz, 2H), 6.76 (s, 1H), 6.61 (d,
J ) 8.10 Hz, 1H), 3.72 (s, 3H), 1.42 (s, 12H). 13C{1H} NMR
(CDCl3): δ 160.6, 155.1, 153.7, 149.4, 147.5, 139.1, 134.3, 129.9,
6-(Bis(9,9-dimethylfluoren-2-yl)amino)-2-formylbenzofuran
(10). A solution of 9 (0.13 g, 0.20 mmol) in acetic acid (50 mL)
was refluxed for 6 h. Saturated aqueous NaHCO3 (50 mL) and
dichloromethane were added to quench the reaction. The organic
J. Org. Chem, Vol. 72, No. 10, 2007 3657

Jung et al.
layer was separated. The aqueous layer was extracted with
dichloromethane (2 × 50 mL). The combined extracts were dried
with MgSO4. The organic layer was removed in Vacuo. The pure
product 10 was obtained by silica gel chromatography (eluent MC:
Hx ) 1:1, Rf ) 0.3) to afford 10 (0.033 g) in 30% yield. Mp:
(E)-2-(5-Formylthiopheneyl)vinyl-6-N,N-bis(9,9-dimethylfluo-
ren-2-yl)aminobenzofuran (12). THF (30 mL) and water (10 mL)
were added to a flask containing 11 (0.1 g, 0.13 mmol). Then, TFA
(2 mL) was added to the solution. The resulting reaction mixture
was stirred for 2 h at room temperature, quenched with saturated
aqueous sodium bicarbonate, and extracted with dichloromethane.
The combined dichloromethane phases were then washed with
aqueous sodium bicarbonate and dried with MgSO4. The organic
layer was removed in Vacuo. The pure product 12 was obtained by
silica gel chromatography (eluent EA:Hx ) 1:2, Rf ) 0.4) to afford
12 (0.06 g) in 72% yield. Mp: 180 °C. 1H NMR (CDCl3): δ 9.85
(s, 1H), 7.66 (d, J ) 6.90 Hz, 2H), 7.65 (d, J ) 3.90 Hz, 1H), 7.61
(d, J ) 8.10 Hz, 2H), 7.42 (d, J ) 8.10 Hz, 1H), 7.39 (d, J ) 6.90
Hz, 2H), 7.32 (t, J ) 8.10 Hz, 2H), 7.32-7.26 (m, 4H), 7.25 (s,
2H), 7.14 (d, J ) 3.90 Hz, 1H), 7.11 (d, J ) 8.10 Hz, 2H), 7.10
(d, J ) 8.10 Hz, 1H), 6.99 (d, J ) 15.90 Hz, 1H), 6.75 (s, 1H),
1.42 (s, 12H). 13C{1H} NMR (CDCl3): δ 174.7, 165.5, 165.1, 163.1,
158.4, 156.5, 155.2, 154.5, 153.7, 153.1, 151.0, 150.0, 147.6, 141.7,
139.1, 134.4, 129.2, 128.5, 128.2, 127.3, 124.0, 122.6, 121.0, 119.6,
118.8, 117.5, 96.3, 47.0, 25.8. MS: m/z 653 [M+]. Anal. Calcd.
for C45H35NO2S: C, 82.66; H, 5.40. Found: C, 82.35; H, 5.27.
1
184 °C. H NMR (CDCl3): δ 9.75 (s, 1H), 7.68 (d, J ) 7.50 Hz,
2H), 7.65 (d, J ) 8.10 Hz, 2H), 7.57 (d, J ) 8.40 Hz, 1H), 7.49 (s,
1H), 7.42 (d, J ) 7.50 Hz, 2H), 7.35 (t, J ) 8.10 Hz, 2H), 7.32 (s,
1H), 7.28 (s, 2H), 7.27 (t, J ) 8.10 Hz, 2H), 7.19 (d, J ) 8.40 Hz,
1H), 7.16 (d, J ) 8.10 Hz, 2H), 1.43 (s, 12H). 13C{1H} NMR
(CDCl3): δ 178.8, 158.1, 155.5, 153.7, 152.8, 150.3, 146.7, 138.8,
135.5, 127.2, 127.0, 124.2, 123.8, 122.7, 121.2, 121.0, 120.7, 120.0,
119.7, 118.7, 105.0, 47.0, 27.2. MS: m/z 545 [M+]. Anal. Calcd.
for C39H31NO2: C, 85.84; H, 5.73. Found: C, 85.68; H, 5.58.
Diethyl (5-(5,5-Dimethyl-1,3-dioxan-2-yl)thiophene-2-yl)m-
ethylphosphonate. A mixture of 2-methylphosphonate-5-formylth-
iophene (10.5 g, 40.0 mmol), neopentylglycol (5.0 g, 48.0 mmol),
and p-toluenesulfonic acid (0.76 g) were dissolved in benzene (80
mL). The reaction mixture was refluxed for 3 h and then cooled
and washed with aqueous sodium bicarbonate (100 mL). The
combined benzene layers were then dried with MgSO4, filtered,
and evaporated in Vacuo to yield acetal as a yellow oil (13.2 g,
95%). 1H NMR (CDCl3): δ 6.98 (d, J ) 3.60 Hz, 1H), 6.87 (d, J
) 3.60 Hz, 1H),5.57 (s, 1H), 4.07 (m, 4H), 3.74 (d, J ) 11.10 Hz,
2H), 3.62 (d, J ) 11.10 Hz, 2H), 3.32 (d, J ) 21.60 Hz, 2H), 1.29
(t, J ) 7.20 Hz, 6H), 1.26 (s, 3H), 0.79 (s, 3H). 13C{1H} NMR
(CDCl3): δ 140.4, 132.7, 128.0, 126.4, 124.7, 97.9, 76.5, 62.1, 29.9,
22.7, 21.5, 16.1. MS: m/z 348 [M+]. Anal. Calcd. for C15H25-
SO2P: C, 51.71; H, 7.23. Found: C, 51.46; H, 7.16.
(E)-2-(5-(5,5-Dimethyl-1,3-dioxan-2-yl)thiophene-2-yl)vinyl-
6-N,N-bis(9,9-dimethylfluoren-2-yl)aminobenzofuran (11). A
mixture of 10 (0.15 g, 0.28 mmol), diethyl (5-(5,5-dimethyl-1,3-
dioxan-2-yl)thiophene-2-yl)methylphosphonate (0.12 g, 0.33 mmol),
and potassium tert-butoxide (0.04 g, 0.33 mmol) was vacuum-dried
and THF (30 mL) was added. The solution was refluxed for 6 h.
THF was removed under reduced pressure. The crude mixture was
redissolved in dichloromethane, washed with water, and dried with
MgSO4. The organic layer was removed in Vacuo. The pure product
11 was obtained by silica gel chromatography (eluent MC:Hx )
1:1, Rf ) 0.4) to afford 11 (0.12 g) in 58% yield. Mp: 201 °C. 1H
NMR (CDCl3): δ 7.66 (d, J ) 7.20 Hz, 2H), 7.60 (d, J ) 8.10
Hz, 2H), 7.39 (d, J ) 7.20 Hz, 2H), 7.38 (s, 1H), 7.33 (t, J ) 8.10
Hz, 2H), 7.31 (d, J ) 16.50 Hz, 1H), 7.30 (t, J ) 8.10 Hz, 2H),
7.25 (s, 2H), 7.25 (d, J ) 8.40 Hz, 1H), 7.11 (d, J ) 8.10 Hz, 2H),
7.10 (d, J ) 8.40 Hz, 1H), 7.02 (d, J ) 3.30 Hz, 1H), 6.97 (d, J )
3.30 Hz, 1H), 6.77 (d, J ) 16.50 Hz, 1H), 6.60 (s, 1H), 5.61 (s,
1H), 3.77 (d, J ) 11.10 Hz, 2H), 3.64 (d, J ) 11.10 Hz, 2H), 1.42
(s, 12H), 1.29 (s, 3H), 0.81 (s, 3H). 13C{1H} NMR (CDCl3): δ
156.1, 155.2, 154.7, 153.7, 147.8, 147.1, 145.9, 144.1, 142.7, 140.7,
139.2, 134.2, 128.9, 127.1, 126.5, 124.9, 123.1, 122.6, 121.1, 120.7,
119.5, 118.5, 117.1, 116.1, 110.3, 105.8, 98.3, 77.4, 47.0, 30.4,
27.2, 23.1, 22.0. MS: m/z 739 [M+]. Anal. Calcd. for C50H45SO3:
C, 81.16; H, 6.13. Found: C, 81.09; H, 6.10.
(Z)-3-(5-((E)-2-(6-(Bis(9,9-dimethylfluoren-2-yl)amino)benzo-
furan-2-yl)vinyl)thiophene-2-yl)-2-cyanoacrylic Acid (2). A mix-
ture of 12 (0.11 g, 0.17 mmol) and cyanoacetic acid (0.03 g, 0.34
mmol) were vacuum-dried, and MeCN (60 mL) and piperidine
(0.005 mL) were added. The solution was refluxed for 6 h. After
the solution was cooled, the organic layer was removed in Vacuo.
The pure product 2 was obtained by silica gel chromatography
(eluent EA:MeOH ) 10:1, Rf ) 0.1) to afford 2 (0.061 g) in 51%
1
yield. Mp: 239 °C. H NMR (DMSO): δ 8.12 (s, 1H), 7.70 (d,
J ) 8.10 Hz, 4H), 7.62 (d, J ) 3.30 Hz, 1H), 7.50 (d, J ) 8.40
Hz, 1H), 7.46 (d, J ) 8.10 Hz, 2H), 7.32 (t, J ) 8.10 Hz, 2H),
7.31 (d, J ) 15.60 Hz, 1H), 7.29 (d, J ) 3.30 Hz, 1H), 7.28 (s,
2H), 7.27 (t, J ) 8.10 Hz, 2H), 7.22 (d, J ) 8.40 Hz, 1H), 7.17 (s,
1H), 7.09 (d, J ) 15.60 Hz, 1H), 7.02 (s, 1H), 7.01 (d, J ) 8.10
Hz, 2H), 1.32 (s, 12H). 13C{1H} NMR (DMSO): δ 163.7, 159.7,
155.4, 154.8, 153.9, 153.1, 151.8, 146.9, 146.5, 145.6, 143.3, 142.6,
138.3, 136.4, 136.2, 133.8, 128.1, 127.1, 126.7, 124.4, 122.7, 121.8,
121.1, 120.5, 119.5, 119.1, 118.1, 117.8, 109.2, 107.5, 46.4, 26.7.
MS: m/z 720 [M+]. Anal. Calcd. for C48H36N2O3S: C, 79.97; H,
5.03. Found: C, 79.72; H, 4.91.
Acknowledgment. We are grateful to the KOSEF through
National Research Laboratory (NRL 2005) program and BK21
(2006).
Supporting Information Available: General experimental,
cyclovoltamogram, geometrical configuration, and 1H and 13C NMR
spectra for the new compounds described in this paper. This material
is available free of charge via the Internet at http://pubs.acs.org.
JO0625150
3658 J. Org. Chem., Vol. 72, No. 10, 2007