A R T I C L E S
Gao et al.
Synthesis of 4,4′-Bis(5-hexylfuran-2-yl)-2,2′-bipyridine (L2). 2-Hex-
ylfuran (2.20 g, 14.45 mmol) was dissolved in 40 mL of anhydrous
THF and cooled to -78 °C. After addition of n-butyllithium (6.90
mL, 2.5 M in hexane, 17.34 mmol), the solution was stirred under
Ar at -78 °C for 1 h. The mixture was stirred for 3 h at 20 °C and
then cooled to -78 °C. Tributylstannyl chloride (6.12 g, 18.80
mmol) in 10 mL of anhydrous THF was added dropwise via a
syringe and stirred for 2 h at -78 °C. The mixture was stirred
overnight at room temperature. The reaction mixture was quenched
with aqueous NH4Cl and extracted with CH2Cl2. The combined
organic layers were dried over MgSO4. After the removal of solvent,
the unpurified 2-hexyl-5-tributylstannylfuran (4.22 g, 9.55 mmol)
and 4,4′-dibromo-2,2′-bipyridine (1.00 g, 3.18 mmol) were dissolved
in 120 mL of DMF. A catalytic amount of Pd(PPh3)2 Cl2 (0.13 g,
0.16 mmol) was added and the reaction mixture was stirred at 85
°C under Ar overnight. After the removal of DMF, the resulting
solid was passed through a silica gel column using CHCl3 as eluent
to afford L2 (1.12 g, 77% yield) as yellowish solid. 1H NMR (600
MHz, CDCl3, δH): 8.66 (dd, J ) 5.2 Hz, J ) 0.6 Hz, 2H), 8.61 (s,
2H), 7.54 (dd, J ) 5.2 Hz, J ) 1.6 Hz, 2H), 6.93 (d, J ) 2.8 Hz,
2H), 6.13 (d, J ) 3.2 Hz, 2H), 2.72 (t, J ) 7.6 Hz, 4H), 1.75-1.67
(m, 4H), 1.44-1.31 (m, 12H), 0.90 (t, J ) 7.0 Hz, 6H). MS (EI)
m/z calcd for (C30H36N2O2), 456.62; found, 456.
with B3LYP/3-21G* functional and basis set.13 In both C101 and
C102 complexes, the central ruthenium (II) atom adopts a low spin
4d65s0 electronic configuration in the quasi-octahedral symmetrical
ligand field.14 Based on such a model, we optimized their
geometrical structures and further calculated the lowest 60
singlet-singlet transitions. Without any symmetry constraints, the
geometry was optimized in vacuo and solvent effects of acetontrile
were included in TDDFT calculation by means of the Polarizable
Continuum Model.15 On the basis of TDDFT results, we calculated
tion profile as a sum of Gaussian band using the following
equation16
fI
(ω - ωI)2
ε(ω) ) 2.174 × 109
exp -2.773
(1)
∑
2
1⁄2,I
(
)
∆
1⁄2,I
∆
I
where ε is the molar extinction coefficient given in units of M-1
cm-1, the energy ω of all allowed transitions included in eq 1 is
expressed in cm-1, fI denotes the oscillator strength, and the half-
bandwidths, ∆1/2, are assumed to be 3000 cm-1
.
UV-Vis, Emission, and Voltammetric Measurements. Elec-
tronic absorption spectra were performed on a Cary 5 spectropho-
tometer. Emission spectra were recorded with a Spex Fluorolog
112 spectrofluorometer. The emitted light was detected with a
Hamamatsu R2658 photomultiplier operated in a single-photon
counting mode. The emission spectra were photometrically cor-
rected with a calibrated 200 W tungsten lamp as reference source.
A computer controlled CHI 660C electrochemical workstation was
used for square-wave voltammetric measurements in combination
with a mini electrochemical cell equipped with a 5 µm radius Pt
ultramicroelectrode as the working electrode. A Pt wire and a silver
wire were used as counter- and quasi-reference electrodes, respec-
tively. The redox potential values versus the ferrocene internal
reference were converted to those versus NHE (normal hydrogen
electrode).
ATR-FTIR Measurements. ATR-FTIR spectra were measured
using a FTS 7000 FTIR spectrometer (Digilab, USA). The data
reported here were taken with the “Golden Gate” diamond anvil
ATR accessory. Spectra were derived from 64 scans at a resolution
of 2 cm-1. The samples were measured under the same mechanical
force pushing the samples in contact with the diamond window.
No ATR correction has been applied to the data. It also has to be
appreciated that this ATR technique probes at most 1 µm of sample
depth and that this depends on the sample refractive index, porosity
etc. Some of the spectra show artifacts due to attenuation of light
by the diamond window in the 2000 to 2350 cm-1 region. Dye-
coated films were rinsed in acetonitrile and dried prior to measuring
the spectra.
Device Fabrication. A screen-printed double layer film of
interconnected TiO2 particles was used as mesoporous negative
electrode. A 7 µm thick film of 20 nm sized TiO2 particles was
first printed on the fluorine-doped SnO2 conducting glass electrode
and further coated by a 5 µm thick second layer of 400-nm-sized
light scattering anatase particles. The detailed preparation procedures
of TiO2 nanocrystals, pastes for screen-printing, and double-layer
nanostructured TiO2 film have been reported in our previous
paper.17 Unless otherwise stated with cheno as coadsorbent, a TiO2
electrode was stained by immersing it into a dye solution containing
300 µM of C101 or C102 sensitizer in the mixture of acetonitrile
and tert-butanol (volume ratio: 1/1) overnight. After washing with
Synthesis of NaRu(4,4′-bis(5-hexylthiophen-2-yl)-2,2′-bipyridine)(4-
carboxylic acid-4′-carboxylate-2,2′-bipyridine)(NCS)2 (C101). Dichlo-
ro(p-cymene)ruthenium(II) dimmer (0.32 mmol) and L1 (0.64
mmol) were dissolved in DMF. The reaction mixture was stirred
at 80 °C for 4 h under Ar in the dark. Subsequently, 4,4′-
dicarboxylic acid-2,2′-bipyridine (0.64 mmol) was added into the
flask and the reaction mixture was stirred at 140 °C for 4 h. At
last, an excess of NH4NCS (26.50 mmol) was added to the resulting
dark solution and the reaction continued for another 4 h at the same
temperature. Then the reaction mixture was cooled down to room
temperature and the solvent was removed on a rotary evaporator
under vacuum. Water was added to get the precipitate. The solid
was collected on a sintered glass crucible by suction filtration,
washed with water and Et2O, and dried under vacuum. The crude
complex was dissolved in basic methanol (NaOH) and purified on
a Sephadex LH-20 column with methanol as eluent. The collected
main band was concentrated and slowly dropped with an acidic
methanol solution (HNO3) to pH 5.9. Yield with column purification
(4×): 63%. The precipitate was collected on a sintered glass crucible
by suction filtration and dried in air. 1H NMR (200 MHz,
CD3OD+NaOD, δH): 9.65 (d, 1H), 9.10 (d, 1H), 9.00 (s, 1H), 8.85
(s, 1H), 8.40 (s, 1H), 8.35 (d, 1H), 8.25 (s, 1H), 8.10 (d, 1H), 7.95
(d, 1H), 7.65 (d, 1H), 7.55 (d, 1H), 7.45 (d, 1H), 7.10-7.20 (m,
3H), 6.85 (d, 1H), 3.05 (t, 2H), 2.95 (t, 2H), 1.80 (m, 4H), 1.50
(m, 12H), 1.00 (m, 6H). Anal. Calcd for NaRuC44H43N6O4S4 ·2H2O:
C, 52.42; H, 4.70; N, 8.34%. Found: C, 52.53; H, 4.68; N, 8.19%.
Synthesis of NaRu(4,4′-bis(5-hexylfuran-2-yl)-2,2′-bipyridine)(4-
carboxylic acid-4′-carboxylate-2,2′-bipyridine)(NCS)2 (C102). The
synthesis and column purification were done with the same
procedures described above for C101. After collecting the main
band and rotary evaporating the solvent, the resultant solid was
redissolved in water. Lowering the pH to 4.8 by titration with dilute
nitric acid afforded a precipitate. The precipitate was collected on
a sintered glass crucible by suction filtration and dried in air. Yield
with column purification (4×): 60%. 1H NMR (200 MHz,
CD3OD+NaOD, δH): 9.65 (d, 1H), 9.05 (d, 1H), 9.00 (s, 1H), 8.80
(s, 1H), 8.35 (d, 1H), 8.15 (s, 1H), 8.00 (s, 1H), 7.60-7.50 (m,
4H), 7.40 (d, 1H), 7.00 (d, 1H), 6.80 (d, 1H), 6.50 (d, 1H), 6.40
(d, 1H), 3.05 (t, 2H), 2.85 (t, 2H), 1.80 (m, 4H), 1.50 (m, 12H),
1.05 (m, 6H). Anal. Calcd for NaRuC44H43N6O6S2 ·4H2O: C, 52.22;
H, 5.08; N, 8.30%. Found: C, 52.50; H, 4.97; N, 8.09%.
(13) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
W.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(14) Pourtois, G.; Beljonne, D.; Moucheron, C.; Schumm, S.; Mesmaeker,
A. K.; Lazzaroni, R.; Bre´das, J. L. J. Am. Chem. Soc. 2004, 126, 683.
(15) Foresman, J. B.; Keith, T. A.; Wiberg, K. B.; Snoonian, J.; Frisch,
M. J. J. Phys. Chem. 1996, 100, 16098.
Calculation Methods. To get insight on the geometric structures
and electronic transition properties of the C101 and C102 sensitizers
viewed from the molecular orbital level, we performed density
functional theory (DFT) and time dependent density functional
theory (TDDFT) calculations in the Gaussian03 program package,
(16) Hay, P. J.; Wadt, W. R. J. J. Chem. Phys. 1985, 82, 270.
(17) Wang, P.; Zakeeruddin, S. M.; Comte, P.; Charvet, R.; Humphry-
Baker, R.; Gra¨tzel, M. J. Phys. Chem. B 2003, 107, 14336.
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10722 J. AM. CHEM. SOC. VOL. 130, NO. 32, 2008