C. Wang et al. / Tetrahedron xxx (2014) 1e8
7
13C NMR spectra were recorded on Brucker AM-400 MHz in-
struments with tetramethylsilane as internal standard. HRMS were
performed using a Waters LCT Premier XE spectrometer.
chromatography on silica (DCM/methanol¼20/1, v/v) to yield
a red solid, ISB-4 (108 mg, 0.19 mmol, 68.7%). 1H NMR (400 MHz,
DMSO,
d
): 8.39 (s, 1H), 8.22e8.12 (m, 4H), 7.97 (d, J¼7.5 Hz, 1H), 7.74
(d, J¼7.5 Hz, 1H), 7.69 (d, J¼8.7 Hz, 2H), 7.65e7.55 (m, 6H), 7.47 (t,
4.2. Photophysical and electrochemical measurements
J¼7.2 Hz, 2H), 6.97 (s, 2H), 6.27 (d, J¼8.8 Hz, 2H). 13C NMR
(100 MHz, DMSO, d): 163.31, 153.39, 153.28, 153.13, 148.77, 141.96,
The absorption spectra of the dyes in solution and adsorbed on
TiO2 films were measured with a Varian Cary 500 spectropho-
tometer. Emission spectra of sensitized dyes in solution were
measured with Varian Cary Eclipse. The oxidation potentials of dyes
adsorbed on TiO2 films were measured in a normal three-electrode
electrochemical cell. TiO2 films stained with sensitizer were used as
the working electrode, a platinum wire was the counter electrode,
and a regular calomel electrode in saturated KCl solution was the
reference electrode. The measurements were performed using
a potentiostat/galvanostat model K0264 (Princeton Applied Re-
search). The supporting electrolyte was 0.1 M TBAPF6 (tetra-n-
butylammoniumhexafluorophosphate) in acetonitrile as the sol-
vent. The ferrocenium/ferrocene (Fc/Fcþ) redox couple was used as
an external potential reference. The potentials versus NHE were
calibrated by addition of 630 mV to the potentials versus Fc/Fcþ.3
141.11, 135.79, 133.33, 130.97, 130.74, 130.55, 130.39, 130.11,
129.98, 129.64, 129.46, 129.20, 129.03, 127.56, 126.15, 116.34, 111.29.
HRMS (ESI, m/z): [MꢀH]ꢀ calcd for C36H21N4O2S, 573.1385; found,
573.1380.
4.4.3. Synthesis of ISB-5. The synthesis method resembles that of
compound ISB-3 and the crude compound was purified by column
chromatography on silica (DCM/methanol¼10/1, v/v) to yield a deep
red solid, ISB-5 (93 mg, 0.15 mmol, 60.3%). 1H NMR (400 MHz,
DMSO,
d
): 8.21 (d, J¼3.9 Hz,1H), 8.16e8.08 (m, 2H), 7.85 (d, J¼7.6 Hz,
1H), 7.80 (d, J¼3.9 Hz, 1H), 7.67e7.55 (m, 6H), 7.48 (t, J¼7.3 Hz, 2H),
7.30 (d, J¼8.7 Hz, 2H), 6.98 (s, 2H), 6.21 (d, J¼8.7 Hz, 2H). 13C NMR
(100 MHz, DMSO, d): 154.25, 150.92, 149.16, 141.45, 139.05, 135.55,
134.85, 132.52, 132.17, 130.56, 130.31, 130.23, 129.71, 128.19, 127.72,
126.37, 125.16, 115.83, 111.48, 110.39, 97.92, 84.70. HRMS (ESI, m/z):
[MꢀH]ꢀ calcd for C36H19N4O2S2, 603.0949; found, 603.0947.
4.3. Photovoltaic performance measurements
4.4.4. Synthesis of ISB-6. The synthesis method resembles that of
compound ISB-3 and the crude compound was purified by column
chromatography on silica (DCM/methanol¼10/1, v/v) to yield a red
Photovoltaic measurements employed an AM 1.5 solar simulator
equipped with a 300 W xenon lamp (Model No. 91160, Oriel). The
power of the simulated light was calibrated to 100 mW cmꢀ2 by
a Newport Oriel PV reference cell system (Model 91150V). JeV
curves were obtained by applying an external bias to the cell and
measuring the generated photocurrent with a Keithley model 2400
digital source meter. The voltage step and delay time of photocur-
rent were 10 mV and 40 ms, respectively. The photocurrent action
spectra were measured with an IPCE test system consists of a Model
SR830 DSP Lock-In Amplifier and a Model SR540 Optical Chopper
(Stanford Research Corporation, USA), a 7IL/PX150 xenon lamp and
power supply, and a 7ISW301 Spectrometer. The electrochemical
impedance spectroscopy (EIS) measurements of all the DSSCs were
performed using a Zahner IM6e Impedance Analyzer (ZAHNER-
Elektrik GmbH & CoKG, Kronach, Germany). The frequency range is
0.1 Hze100 kHz. The applied voltage bias is ꢀ0.60 V. The magnitude
of the alternative signal is 10 mV.
solid, ISB-6 (85 mg, 0.14 mmol, 58.4%).1H NMR (400 MHz, DMSO,
d):
8.15 (d, J¼8.5 Hz, 2H), 8.08e8.00 (m, 3H), 7.95 (d, J¼7.5 Hz, 1H), 7.91
(d, J¼7.4 Hz, 1H), 7.68e7.55 (m, 6H), 7.52e7.43 (m, 2H), 7.31 (d,
J¼8.9 Hz, 2H), 6.98 (s, 2H), 6.21 (d, J¼8.9 Hz, 2H).13C NMR (100 MHz,
DMSO,
d): 163.37, 154.47, 152.27, 149.11, 147.31, 141.49, 138.49,
135.56, 133.09, 132.48, 132.14, 131.50, 130.55, 130.30, 130.21, 129.70,
129.56, 129.39, 128.24, 127.69, 118.95, 116.09, 113.18, 111.49, 110.48,
97.25, 84.47. HRMS (ESI, m/z): [MꢀH]ꢀ calcd for C38H21N4O2S,
597.1385; found, 597.1390.
4.5. Preparation of photovoltaic devices
A screen-printed double layer of TiO2 particles was used as
photoelectrode. A 7-
Nanoxide T/SP) was first printed on the FTO conducting glass and
further coated by a 6- m thick second layer of 400-nm light-
mm thick film of 13-nm-sized TiO2 particles (Ti-
m
4.4. Synthesis
scattering anatase particles (TieNanoxide 300). Sintering was car-
ried out at 450 ꢁC for 30 min. Before immersion in the dye solution,
these films were immersed into a 40 mM aqueous TiCl4 solution at
70 ꢁC for 30 min and washed with water and ethanol. Then the films
were heated again at 450 ꢁC for 30 min followed by cooling to 80 ꢁC
and dipping into a 3ꢂ10ꢀ4 M solution of dye in acetonitrile for 12 h
at room temperature. To prepare the counter electrode, the Pt cat-
alyst was deposited on the cleaned FTO glass by coating with a drop
of H2PtCl6 solution (20 mM 2-propanol solution) with the heat
treatment at 400 ꢁC for15 min. A hole (0.6 mm diameter) was drilled
on the counter electrode by a drill press. The perforated sheet was
cleaned by ultrasound in an ethanol bath for 10 min. About the
assemblage of DSSCs, the dye-covered TiO2 electrode and Pt-
counter electrode were assembled into a sandwich type cell and
All sensitizers were synthesized quite straightforward with the
traditional Knoevenagel reaction in relatively high yield. The syn-
thetic routes as well as detailed synthesis of intermediates are list
in Scheme 1 (Supplementary data).
4.4.1. Synthesis of ISB-3. A mixture of compound 3 (159 mg,
0.31 mmol), 2-cyanoacetic acid (29 mg, 0.34 mmol), piperidine
(0.5 mL) and THF (15 mL) was heated to reflux under nitrogen at-
mosphere for 6 h. Solvent was removed by rotary evaporation and
the residue was purified by column chromatography on silica (DCM/
methanol¼20/1, v/v) to yield a deep red solid, ISB-3 (120 mg,
0.21 mmol, 72.8%). 1H NMR (400 MHz, DMSO,
d): 8.33 (s, 1H),
8.26e8.14 (m, 2H), 7.94 (d, J¼3.8 Hz, 1H), 7.73 (t, J¼8.6 Hz, 3H),
sealed with a hot-melt gasket of 25 mm thickness made of the ion-
7.68e7.55 (m, 6H), 7.54e7.44 (m, 2H), 6.98 (s, 2H), 6.28 (d, J¼8.8 Hz,
omer Surlyn 1702 (DuPont). The electrolyte was introduced into the
cell via vacuum backfilling. Finally, the hole was sealed with a self-
adhesive silver film.
2H). 13C NMR (100 MHz, DMSO,
d): 163.87, 152.82, 151.72, 148.83,
145.62, 143.51, 141.89, 137.40, 136.96, 135.74, 133.21, 130.53, 130.37,
130.10, 129.92, 129.60, 127.57, 127.41, 127.27, 125.95, 125.88, 122.60,
117.85, 111.29. HRMS (ESI, m/z): [MꢀH]ꢀ calcd for C34H19N4O2S2,
579.0949; found, 579.0952.
Acknowledgements
This work was supported by NSFC/China (91233207, 21302055),
the Fundamental Research Funds for the Central Universities, and
the Scientific Committee of Shanghai (12ZR1407100).
4.4.2. Synthesis of ISB-4. The synthesis method resembles that of
compound ISB-3 and the crude compound was purified by column