A fluorene-modified porphyrin for efficient dye-sensitized solar cells

Article abstract of DOI:10.1039/c2cc30892d

Porphyrins bearing a polyaromatic or a heterocyclic group are prepared to study their fundamental and photovoltaic properties. Solar cells sensitized with a fluorene-modified porphyrin outperform other dyes in the series, reaching ～90% efficiency of N719

Full text of DOI:10.1039/c2cc30892d

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Electronic Supplementary Information
Fluorene-Modified Porphyrin for
Efficient Dye-Sensitized Solar Cell
Cheng-Hua Wu,a Tsung-Yu Pan,b Shang-Hao Hong,a Chin-Li Wang,a Hshin-Hui
Kuo,a Yang-Yun Chu,a Eric Wei-Guang Diau*,b and Ching-Yao Lin*a
a Department of Applied Chemistry, National Chi Nan University, Puli, Nantou Hsien
54561, Taiwan. Fax: +886-49-2917956; Tel: +886-49-2910960 ext. 4152; E-mail:
cyl@ncnu.edu.tw
b Department of Applied Chemistry and Institute of Molecular Science, National
Chiao Tung University, Hsinchu 30010, Taiwan. Fax: +886-3-5723764; Tel:
+886-3-5131524; E-mail: diau@mail.nctu.edu.tw
* To whom correspondence should be addressed.

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Experimental Section
Materials. Air-sensitive solids were handled in a glove box (MBraun Uni-lab). A
vacuum line and standard Schlenk techniques were employed to process air-sensitive
solutions. Solvents for the synthesis (ACS Grade) were CH2Cl2 and CHCl3
(Mallinckrodt Baker, KE USA), hexanes (Haltermann, Hamburg Germany) and THF
(Merck, Darmstadt Germany). These solvents were used as received unless otherwise
stated. Other chemicals were obtained commercially (Acros Organics, NJ, USA).
THF for cross-coupling reactions was purified and dried with a solvent purification
system (Asiawong SD-500, Taipei, Taiwan); H2O about 50 ppm was found in the
resulting THF. For electrochemical measurements, THF was distilled over sodium
under N2. Pd(PPh3)4 catalyst (Strem, MA, USA) and Pd2(dba)3 (Acros Organics, NJ,
USA) were used as received. For chromatographic purification, we used silica gel 60
(230-400 mesh, Merck, Germany).
Instruments. NMR spectra (Bruker Avance II 300 MHz NMR Spectrometer at
National Chi Nan University or Varian Inova 600 NMR Spectrometer at NSC
Instrumentation Center in National Chung Hsing University), elemental analyses
(Elementar Vario EL III at NSC Instrumentation Center in NCHU), mass spectra
(Microflex MALDI-TOF MS, Bruker Daltonics), electrochemical measurements (CH
Instrument Electrochemical Workstation 611A), absorption spectra (Agilent 8453
UV-Visible spectrophotometer) and fluorescence spectra (Varian Cary Eclipse
fluorescence spectrometer) were recorded with the indicated instruments.
Compound Synthesis and Characterization. As shown in Scheme S1, the LD2x
dyes were readily prepared in two steps based on the Sonogashira cross-coupling
method.S1,S2 The typical procedure involves of mixing 100 mg of di-brominated
porphyrin 1, ~1.0 eq. of a suitable 4-ethynyl polyaromatic or heterocyclic substituent,
70 ml THF and 5 ml triethylamine. The solutions were then degassed by 3 cycles of
freeze-pump-thaw technique, followed by the addition of 15 mol. % of Pd(PPh3)4 and
CuI under an inert atmosphere in a glovebox. The reaction was stirred at 40 oC for
20 – 24 hours. The completion of the reaction was monitored by TLC. After
chromatographic separation on silica gel with suitable eluents (THF/Hex = 1/9 for
LD21 – LD23, THF/Hex = 1/5 for LD24, and THF/Hex = 1/2 for LD25) and
crystalization (THF/Hex), intermediate porphyrin 2's were collected (yields: for LD21,
30%; for LD22, 23%; for LD23, 33%; for LD24, 20%; and for LD25, 17%). For the
second step of cross-coupling reactions, 40 mg of intermediate porphyrin 2 were
usually mixed with ~3eq. of 4-Ethynyl benzoic acid, 70 ml THF and 5 ml
triethylamine. After 3 cycles of freeze-pump-thaw, 15 mol. % of Pd(PPh3)4 and CuI
were added to the solution under N2 in a glovebox. The reaction was stirred at 40 oC
for 60 – 72 hours. The completion of the reaction was monitored by TLC. After

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chromatographic separation on silica gel (MeOH/CH2Cl2 = 1/9) and crystalization
(THF/Hex), 74%, 78%, 78%, 85%, and 60% of LD21, LD22, LD23, LD24 and LD25
were collected, respectively.
LD21
OH
R
H
H
LD22
LD23
O
Pd(PPh3)4, CuI
Et3N, THF, 40oC
Pd(PPh3)4, CuI
Et3N, THF, 40oC
N
N
N
N
N
N
N
N
N
N
N
N
O
Zn
Zn
Zn
Br
Br
R
Br
R
R =
OH
N
N
LD24
LD25
N
N
1
2
LD2x
Scheme S1 General synthetic procedure of LD porphyrins
Characterization data:
1
LD21: H NMR (300 MHz, THF-d8 at 1.73 ppm, 3.58 ppm): δ/ppm, porphyrin,
9.80 (two overlapped doublets, J = 4.5 Hz, 4H), 8.94 (two overlapped doublets, J =
4.5 Hz, 4H), 8.14 (d, J = 1.5 Hz, 4H), 7.91 (t, J = 1.5 Hz, 2H), 1.60 (s, 36H);
biphenylethynyl: 8.17 (d, overlapped, 2H), 7.90 (d, overlapped, 2H), 7.80 (d, J = 7.8
Hz, 2H), 7.50 (t, J = 7.6 Hz, 2H), 7.38 (t, J = 7.4 Hz, 1H); benzoic acid: 8.25 (d, J =
8.2 Hz, 2H), 8.17 (d, overlapped, 2H). Elemental Analysis: C71H64N4O2Zn.
THF.0.5H2O, calc'd C 78.21%, H 6.39%, N 4.86%; found: C 78.56%, H 6.10%, N
4.53%. MS (M+): calc'd 1068.43, found 1068.60.
1
LD22: H NMR (300 MHz, THF-d8 at 1.73 ppm, 3.58 ppm): δ/ppm, porphyrin,
9.82 (d, J = 4.6 Hz, 2H), 9.78 (d, J = 4.6 Hz, 2H), 8.94 (d, J = 4.6 Hz, 2H), 8.93 (d, J
= 4.6 Hz, 2H), 8.15 (d, J = 1.5 Hz, 4H), 7.93 (t, J = 1.5 Hz, 2H), 1.60 (s, 36H);
fluorenylethynyl: 8.29 (s, 1H), 8.10 (d, overlapped, 1H), 8.05 (d, J = 7.9 Hz, 1H),
7.95 (d, overlapped, 1H), 7.63 (d, J = 7.5 Hz, 1H), 7.42 (t, J = 7.3 Hz, 1H), 7.35 (t, J =
7.3 Hz, 1H), 4.10 (s, 2H); benzoic acid: 8.25 (d, J = 8.1 Hz, 2H), 8.18 (d, overlapped,
2H). Elemental Analysis: C72H64N4O2Zn.0.5H2O, calc'd C 79.21%, H 6.00%, N
5.13%; found: C 79.06%, H 5.73%, N 4.79%. MS (M+): calc'd 1080.43, found
1080.57.
1
LD23: H NMR (300 MHz, THF-d8 at 1.73 ppm, 3.58 ppm): δ/ppm, porphyrin,
9.90 (d, J = 4.6 Hz, 2H), 9.78 (d, J = 4.6 Hz, 2H), 8.94 (two overlapped doublets, 4H),
8.14 (d, J = 1.5 Hz, 4H), 7.93 (t, J = 1.5 Hz, 2H), 1.60 (s, 36H);
acenaphthenylethyuyl: 8.58 (d, J = 8.2 Hz, 1H), 8.25 (d, overlapped, 1H), 7.75 (t, J =
7.5 Hz, 1H), 7.50 (d, J = 7.2 Hz, 1H), 7.45 (d, J = 6.9 Hz, 1H), 3.52 (s, 4H); benzoic
acid: 8.25 (d, overlapped, 2H), 8.15 (d, overlapped, 2H). Elemental Analysis:
C71H64N4O2Zn.H2O, calc'd C 78.33%, H 6.11%, N 5.15%; found: C 78.55%, H 5.73%,
N 4.79%. MS (M+) calc'd 1068.43, found 1068.95.

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LD24: 1H NMR (300 MHz, DMSO-d6 at 2.50 ppm): δ/ppm, porphyrin, 9.85 (d,
J = 4.6 Hz, 2H), 9.80 (d, J = 4.5 Hz, 2H), 8.87 (two overlapped doublets, 4H), 8.06 (d,
J = 1.5 Hz, 4H), 7.89 (t, J = 1.5 Hz, 2H), 1.56 (s, 36H); 5-pyrimidylethyuyl: 9.61 (s,
2H), 9.33 (s, 1H); benzoic acid: δ 8.26 (d, J = 8.2 Hz, 2H), 8.17 (d, J = 8.2 Hz, 2H).
Elemental Analysis: C63H58N6O2Zn.1.5THF.1.5H2O, calc'd C 73.23%, H 6.50%, N
7.43%; found: C 73.29%, H 6.66%, N 7.54%. MS (M+) calc'd 994.39, found 994.04.
LD25: 1H NMR (300 MHz, DMSO-d6 at 2.50 ppm): δ/ppm, porphyrin, 9.82 (d, J =
4.6 Hz, 2H), 9.71 (d, J = 4.5 Hz, 2H), 8.92 (d, J = 4.5 Hz, 2H), 8.87 (d, J = 4.6 Hz,
2H), 8.06 (d, J = 1.5 Hz, 4H), 7.89 (t, J = 1.5 Hz, 2H), 1.56 (s, 36H);
2-pyrimidylethyuyl: 9.07 (d, J = 4.9 Hz, 2H), 7.66 (t, J = 5.0 Hz, 1H); benzoic
acid: 8.27 (d, J = 8.0 Hz, 2H), 8.17 (d, J = 8.1 Hz, 2H). Elemental Analysis:
C63H58N6O2Zn.0.5THF.0.5H2O, calc'd C 74.95%, H 6.10%, N 8.07%; found: C
75.09%, H 5.98%, N 8.07%. MS (M+) calc'd 994.39, found 994.19.
Cell Fabrication and Characterization of Performance. The porphyrin-sensitized
solar cells devices were fabricated with a working electrode based on TiO2
nanoparticles (NP) and a Pt-coated counter electrode reported elsewhere.S3 For the
working electrode, a paste composed of TiO2 NP (particle size ~25 nm) prepared with
a sol-gel methodS4 for the transparent nanocrystalline layer was coated on a
TiCl4-treated FTO glass substrate (TEC 7, Hartford, USA) to obtain the required
thickness on repetitive screen printing. To improve the performance of the PSSC, an
additional scattering layer (particle size ~ 300 nm) was screen-printed on the
transparent active layer. The electrode was then immersed in a dye solution (0.15 mM
in THF) at 25 °C for 1.5 h for dye loading onto the TiO2 film. The electrolyte solution
containing LiI (0.05 M), I2 (0.05 M), DMPII (1.0 M), 4-tert-butylpyridine (0.5 M) in a
mixture of acetonitrile and valeronitrile (volume ratio 85 : 15) was introduced into the
space between the two electrodes, so completing the fabrication of these PSSC
devices. The performance of a PSSC device was assessed through measurement of an
I–V curve with an AM-1.5 G solar simulator (XES-502S, SAN-EI), calibrated with a
Si-based reference cell (S1133, Hamamatsu). The incident monochromatic
efficiencies for conversion from photons to current (IPCE) spectra of the
corresponding devices were measured with a system comprising a Xe lamp (PTi
A-1010, 150 W), monochromator (PTi, 1200 gr mm-1 blazed at 500 nm), and source
meter (Keithley 2400, computer controlled). A standard Si photodiode (Hamamatsu
S1337-1012BQ) served as a reference to calibrate the power density of the light
source at each wavelength.

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Fig. S1 Cyclic voltammograms of LD2x porphyrins in THF/TBAP. Experimental conditions: 0.5 mM of LD2x
porphyrins in THF/0.1M TBAP/N2.; Pt working and counter electrodes; SCE; scan rate = 100 mV/s.
Fig. S2 MO patterns of LD2x porphyrins (DFT, B3LYP/LanL2DZ). LD22 and LD23 show more MO pattern
localization at the HOMO and LUMO levels, suggesting that the push-pull effects may occur upon dye excitation.
References:
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S2. S. Takahashi, Y. Kuroyama, K. Sonogashira, Synthesis, 1980, 627-630.
S3. Y.-C. Chang, C.-L. Wang, T.-Y. Pan, S.-H. Hong, C.-M. Lan, H.-H. Kuo, C.-F. Lo, H.-Y. Hsu,
C.-Y. Lin, E. W.-G. Diau, Chem. Commun., 2011, 47, 8910-8912.
S4. (a) S. Ito, P. Chen, P. Comte, M. K. Nazeeruddin, P. Liska, P. Péchy, M. Grätzel, Prog. Photovolt:
Res. Appl., 2007, 15, 603. (b) S. Ito, T. N. Murakami, P. Comte, P. Liska, C. Grätzel, M. K.
Nazeeruddin, M. Grätzel, Thin Solid Films, 2008, 516, 4613. (c) J. Joo, S. G. Kwon, T. Yu, M.
Cho, J. Lee, J. Yoon, T. Hyeon, J. Phys. Chem. B, 2005, 109, 15297–15302.