Electrochemistry and spectroelectrochemistry of carboxyphenylethynyl porphyrins

Article abstract of DOI:10.1142/S1088424612501313

Zinc 5-(4-carboxy-phenylethynyl)-10,20-biphenylporphines bearing various substituents on the 10,20-phenyl rings are studied for their electrochemical and spectroelectrochemical properties. Cyclic voltammetry and optically transparent thin-layer electroche

Full text of DOI:10.1142/S1088424612501313

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2013; 17: 92–98
DOI: 10.1142/S1088424612501313
Published at http://www.worldscinet.com/jpp/
Electrochemistry and spectroelectrochemistry
of carboxyphenylethynyl porphyrins
Pei-Shang Chao, Ming-Yu Kuo, Chen-Fu Lo, Min-Hsu Hsieh,Yu-Hsiang Cheng,
Chin-Li Wang, Hsiu-Yu Lu, Hshin-Hui Kuo,Yen-Ni Hsiao, Chieh-Ming Wang and
Ching-Yao Lin*
Department of Applied Chemistry, National Chi Nan University, No. 302 University Road, Puli,
Nantou Hsien 54561, Taiwan
Received 23 July 2012
Accepted 1 October 2012
ABSTRACT: Zinc 5-(4-carboxy-phenylethynyl)-10,20-biphenylporphines bearing various substituents
on the 10,20-phenyl rings are studied for their electrochemical and spectroelectrochemical properties.
Cyclic voltammetry and optically transparent thin-layer electrochemical measurements suggest that the
first reductions of these porphyrins should be the reduction reaction of the carboxylic protons. For the
porphyrin ring reactions, our study shows that the redox properties can be significantly affected by the
alkoxyl chains on the 10,20-phenyl rings.
KEYWORDS: porphyrin, electrochemistry, spectroelectrochemistry, carboxyphenylethyne.
past [14–19], three of which showed overall efficiencies
INTRODUCTION
greater than 10% with the use of classic DSSC setup.
Dye-sensitized solar cells (DSSC) have drawn much
It is worth noting that 4-carboxy-phenylethyne is often
attention because of the relatively high efficiencies,
used as the anchoring group for the porphyrin dyes [8a,
simple device design, and lower production cost [1–3].
Overall efficiencies (h) greater than 11% have been
11, 13–19], including many highly efficient ones [11,
17, 18]. However, only very basic electrochemistry of
demonstrated with ruthenium dyes [4–6]. In recent
these porphyrins, such as the redox potentials, has been
years, other types of sensitizers have also been intensely
reported.
studied. Among the dyes under investigation, porphyrins
In this work, we aim to reveal more detailed
are considered as one of the more efficient sensitizers for
electrochemical properties of zinc porphyrins modified
DSSC applications because of the vital roles of porphyrin
with a 4-carboxy-phenylethynyl anchoring group. The
derivatives in photosynthesis, the strong UV-visible light
porphyrins under investigation are denoted as PE1,
absorption, and the ease of modifying their chemical
PE1-OR6, and PE1-OR4 and their structures are shown in
structures [7–19]. In the development of porphyrin dyes,
Chart 1. As shown in the chart, these porphyrins employ
Officer and co-workers reported the overall efficiency
of porphyrin-sensitized solar cells (PSSC) above 7%
zinc biphenylporphine (ZnBPP) as the core chromophore
and
a 4-carboxy-phenylethyne as the anchoring
by using a side-anchoring, fully conjugated dye [10].
With the use of cobalt-based electrolyte and an organic
co-sensitizer, the PCE of the PSSC device reached 12%
recently [11a]. Independently, our systematic studies
have yielded several highly efficient porphyrin dyes in the
substituent for DSSC applications. The differences in
the structures of these porphyrins are the substituents
on the 10,20-phenyl rings. For PE1, the phenyl groups
are not further modified. For PE1-OR6, six dodecoxyl
chains are added to the para- and meta-positions of the
two phenyl rings. For PE1-OR4, four dodecoxyl chains
are attached to the ortho-positions of the two phenyl
groups. The dodecoxyl chains are introduced to increase
the solubility of the porphyrin in the organic solvents.
*Correspondence to: Ching-Yao Lin, email: cyl@ncnu.edu.tw,
tel: +886 49-2910960 ext. 4152, fax: +886 49-2917956
Copyright © 2013 World Scientific Publishing Company

ELECTROCHEMISTRY AND SPECTROELECTROCHEMISTRY OF CARBOXYPHENYLETHYNYL PORPHYRINS
93
OC12H25
C12H25
O
OC12H25
C12H25
O
OC12H25
N
N
N
N
N
N
N
N
N
N
N
N
O
O
O
Zn
Zn
Zn
OH
OH
OH
C12H25
O
OC12H25
C12H25
O
OC12H25
OC12H25
PE1
PE1-OR6
PE1-OR4
Chart 1. Structural diagram of the PE1 porphyrins under investigation
As we have recently reported, the positions of these long
alkoxyl groups play a significant role in improving the
photovoltaic performance of the PSSC [17]. Likewise, the
positions of the long alkoxyl groups were also observed
to significantly affect the electrochemical behaviors of
the porphyrins.
found C 79.23%, H 9.31%, N 3.82%. Mass [MH]+ calcd.
1342.94, found 1343.83.
Instrumentation
Absorption spectra were recorded on an Agilent 8453
UV-visible spectrophotometry system. A CH Instruments
ElectrochemicalWorkstation611Awasusedtoperformed
cyclic voltammograms and thin-layer electrolysis.
Cyclic voltammetry was carried out with a standard
three-electrode cell. The reference electrode (SCE) was
isolated from the main compartment by a junction tipped
with a platinum wire. Spectroelectrochemical results
were measured with an air-tight, optically transparent
thin-layer electrochemical (OTTLE) cell [21]. The cell
is made of quartz with 1-mm in light path. The working
electrode, constructed with a 100 mesh platinum gauze,
was placed inside the cell, while the reference and
counter electrodes were individually separated from
the main compartment by a layer of fine glass frit. The
electrochemical cells were all assembled in a glovebox
equipped with a drytrain to exclude moisture and oxygen.
EXPERIMENTAL
Materials
Air-sensitive solids were handled in an MBraun Uni-
lab glove box. A vacuum line and standard Schlenk
techniques were employed to process air-sensitive
solutions. Tetrahydrofuran (THF) was obtained from
Merck (Darmstadt, Germany). Other chemicals were
ordered from Acros Organics (New Jersey, U.S.A.).
THF and tetrabutylammonium perchlorate (TBAP)
were were purified according to the literature methods
[20]. The synthesis of PE1, PE1-OR6 and PE1-OR4 has
been previously reported [14, 17]. Free-base PE1-OR4
was prepared by demetallating PE1-OR4 in CHCl3 with
HCl(aq). 100 mg PE1-OR4 was usually dissolved in 100
mL of CHCl3 for the process.After adding 10 mL of 12 M
HCl(aq), the solution was stirred at room temperature for
4 hours. The completion of the reaction was monitored
by UV-visible spectrscopy and TLC techniques. Upon
completion, the organic solution was first neutralized
by three washes of K2CO3(aq) followed by three washes
of NH4Cl(aq). After chromatographic separation on
silica gel (with CH2Cl2/MeOH = 9/1) and crystalization
from CH2Cl2/MeOH, 71% of free-base PE1-OR4 was
Molecular simulation
The molecular dynamics (MD) simulations of the
porphyrins were carried out with the use of Materials
Studio software package. Details of the simulation
procedure have been previously published [17b]. To
simplify the calculation, free-base porphyrins were used
in these simulations.
RESULTS AND DISCUSSION
1
collected. Characterization data: H NMR (300 MHz
Figure 1 collects the cyclic voltammograms (CVs) of
PE1 porphyrin, ZnBPP, 4-carboxy-phenylethyne (PE),
and the blank solution (THF/0.1 M TBAP) under the same
experimental conditions. The redox potentials are listed
in Table 1. First of all, the reduction reaction of ZnBPP
occurs at -1.40 V vs SCE as a quasi-reversible reaction
(Fig. 1b). This potential is consistent with the formation
CDCl3 at 7.26 ppm): , ppm 10.02 (s, 1H), 9.69 (d, J =
4.5 Hz, 2H), 9.16 (d, J = 4.8Hz, 2H), 8.92 (d, J = 4.5 Hz,
2H), 8.86 (d, J = 4.5 Hz, 2H), 8.30 (d, J = 8.0 Hz, 2H),
8.11 (d, J = 8.0, 2H), 7.71 (t, J = 8.4 Hz, 2H), 7.01 (d, J =
8.4 Hz, 4H), 3.85 (t, J = 6.5 Hz, 8H), 1.30–0.75 (m, 64H),
0.75–0.35 (m, 34H), -2.43 (s, 2H). Elemental analysis:
C89H122N4O6, calcd. C 79.54%, H 9.15%, N 4.17%;
Copyright © 2013 World Scientific Publishing Company
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94
P.-S. CHAO ET AL.
4-carboxy-phenylethyne, under the same
conditions (Fig. 1c). In contrast, the second
reduction potential of PE1 porphyrin is not
sensitive to the introduction of H2O. Half-
wave potential of ZnPE1’s second reduction
was observed at -1.24V vs SCE. This value is
consistent with the formation of a porphyrin
anion radical. This potential is positively
shifted from that of ZnBPP (-1.40 V)
due to the more extended p-conjugation
system of PE1 porphyrin [14]. As such, by
comparing the CVs of PE1 with those of
ZnBPP and 4-carboxy-phenylethyne, Fig. 1
indicates that the first reduction reaction
of PE1 porphyrin should localize at the
anchoring 4-carboxy-phenylethynyl group
and the second reduction should occur at the
porphine ring.
To further our understanding to the
reduction reactions of PE1 porphyrin,
spectroelectrochemical measurements were
carried out with the use of an OTTLE cell
in THF/TBAP under N2. Figure 2 collects
the UV-visible spectrum changes of PE1
porphyrin upon (a) the first reduction at
-1.10 V vs SCE, (b) the second reduction
at -1.40 V vs SCE, and (c) the acid-
base titration by TBAOH. Coulometric
titration (Fig. 2a and 2b insets) indicates
that two reductions of PE1 are both
one-electron transfer reactions. Upon
the first reduction, the absorption bands
of PE1 are slightly red-shifted and the
absorption bands remain relatively sharp
(Fig. 2a). Isosbestic points observed in
this figure suggest that no intermediates
were observed during the electrolysis.
Intriguingly, these spectral changes are
nearly identical to those of PE1 being
Fig. 1. Cyclic voltammograms of 1.0 mM (a) PE1, (b) ZnBPP, (c) 4-carboxy-
phenylethyne (PE) in 8 mL THF/0.1 M TBAP solutions, and (d) the blank
solutions (THF/0.1 M TBAP). The dotted lines represent the dried solutions,
thin solid lines: added 0.02 mL H2O (2.5%), and bold lines: added 0.06 mL
H2O (7.5%). This figure qualitatively demonstrates the effect of H2O on the
potential of PE1’s first reduction reaction
Table 1. Reduction potentials of PE1, ZnBPP, and 4-carboxy-phenylethyne (PE)a
Entry
THF/0.1 M TBAP Added H2O (2.5%) Added H2O (7.5%)
PE1 (Red 1)
PE1 (Red 2)
ZnBPP
-0.86 V (450 mV)
-1.24 V (160 mV)
-1.40 V (190 mV)
-0.91 V (570 mV)
-0.83 V (390 mV)
-1.24 V (140 mV)
-1.39 V (170 mV)
-0.84 V (36 mV)
-0.78 V (300 mV)
-1.24 V (130 mV)
-1.40 V (200 mV)
-0.78 V (250 mV)
PE
a Reaction conditions: 1.0 mM of the compound in 8 mL THF/0.1 M TBAP; Pt
working and counter electrodes; SCE reference electrode; scan rate = 100 mV/s.
For Fc+/0 in the same condition, E1/2 = +0.49 V vs SCE. Peak-to-peak separations
(mV) are put in the parentheses for the quasi-reversible reactions.
titrated by TBAOH (Fig. 2c). Therefore, this figure
strongly suggests that the first reduction of PE1 in
THF/TBAP should involve deprotonation reaction of
the 4-carboxy-phenylethynyl substituent, generating a
localized anion at the anchoring group. This phenomenon
is similar to changing a substituent at the porphyrin meso-
position and observing slightly shifted sharp absorption
bands. Upon the second reduction, the absorption bands
of PE1 became very broadened and largely red-shifted
at -1.40 V vs SCE (Fig. 2b). These spectrum changes
are consistent with the formation of a porphyrin anion
radical, i.e. a one-electron reduction at the porphine core
[22].
of a zinc porphyrin anion radical [22]. For PE1 porphyrin,
two waves of reversible reductions were observed at
-0.86 and -1.24 V vs SCE (Fig. 1a). Bulk electrolysis
indicates that there are two electrons involved in these
reduction reactions. In other words, there are two one-
electron reduction reactions observed for PE1 porphyrin.
Coulometric titration with the use of an OTTLE cell [21]
agrees well with this suggestion (titration curves shown
as insets in Fig. 2a and 2b). The first reduction of PE1
porphyrin is an ill-shaped, quasi-reversible reaction.
Interestingly, the potential of this reaction is susceptible
to the presence of H2O in the system. As shown in
Fig. 1a and Table 1, the redox potential of PE1’s first
reduction reaction is positively shifted from -0.86 V to
-0.78 V vs SCE by increasing water content in the THF
solution to 7.5% (v/v). A nearly identical phenomenon
was also observed for the anchoring substituent,
It has been reported that benzoic acid undergoes one-
electronreductionreactioninsolutions,generatingbenzoate
anion and hydrogen [23]. Based on this mechanism, we
suggest that the carboxylic substituent of PE1 porphyrin
loses one proton upon the first one-electron reduction
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ELECTROCHEMISTRY AND SPECTROELECTROCHEMISTRY OF CARBOXYPHENYLETHYNYL PORPHYRINS
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around -0.86 V vs SCE, yielding a carboxylate group and
hydrogen. At -1.24 V vs SCE, the porphine core receives
an additional electron and becomes a porphyrin anion
radical. Scheme 1 illustrates this proposed mechanism. It
is worth mentioning that it would be of great interests if the
first reduction reaction of PE1 porphyrin were catalytical.
That would translate to a possibility of continuous H2
generation. Unfortunately, we did not observe catalytical
generation of hydrogen at this time.
Figure 3 collects the CVs of PE1, PE1-OR6, and
PE1-OR4 in THF/TBAP. The redox potentials are listed
in Table 2. As shown in the figure and table, PE1 and
PE1-OR6 behaves very similarly. The first porphine ring
reductions are both quasi-reversible for PE1 (-1.24 V
vs SCE) and PE1-OR6 (-1.27 V vs SCE). However, the
first porphine ring oxidations appear to be irreversible
reactions for PE1 (+1.04 V vs SCE) and PE1-OR6 (+1.08
V vs SCE). As for PE1-OR4, the first porphine ring
reduction was observed at -1.47 V vs SCE as a quasi-
reversible reaction. Interestingly, the first oxidation of
PE1-OR4 was observed as a quasi-reversible reaction
at +0.85 V vs SCE, in sharp contrast to the irreversible
oxidation waves of PE1 and PE1-OR6 under the same
condition. This phenomenon strongly suggests that six
alkoxyl chains at the meta- and para-positions of the
phenyl groups should have very limited influence to the
porphyrin redox behaviors. On the contrary, four alkoxyl
chains at the ortho-positions of the phenyl groups have
a significant impact to the potentials as well as the
reversibility of the redox reactions. These differences
may be attributed to two possibilities. (a) The four
alkoxyl chains at the ortho-positions of the PE1-OR4
phenyl groups are in the positions to have more electron-
donating influence than are the six alkoxyl chains at the
meta- and para-positions of the PE1-OR6 phenyl rings.
(b) The spacial arrangement of PE1-OR4’s four alkoxyl
chains are in a shape of wrapping around the porphyrin
core structure in the solution whereas PE1-OR6’s six
alkoxyl chains extend into the solution (see below).
In order to further our understanding to the differences
in the electrochemical behaviors mentioned above, we
performed molecular simulations on PE1-OR6 and
PE1-OR4 by using Materials Studio software package
[24]. Because of the long alkoxyl chains, obtaining
crystal structures of the porphyrins is not feasible. More
importantly, simulation results provide the opportunity of
visualizing the alkoxyl chains in the solutions. To simplify
Fig. 2. Absorption spectrum changes of PE1 porphyrin in
THF/0.5 M TBAP upon (a) the first one-electron reduction, (b)
the second one-electron reduction, and (c) TBAOH titration.
The insets show the coulometric titration curves
-
.
N
N
N
N
N
N
N
N
N
N
N
N
E1/2 = -0.86 V
E1/2 = -1.40 V
O
O
O
.
Zn
H
+
Zn
Zn
OH
O-
O-
Scheme 1. Proposed mechanism of PE1 porphyrin reduction reactions. This suggested mechanism is based on reference [23]
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P.-S. CHAO ET AL.
Fig. 3. Cyclic voltammograms of 1.0 mM of PE1 (grey lines), PE1-OR4 (bold dotted lines), and PE1-OR6 (thin solid lines) in
THF/0.1 M TBAP (thin dotted lines) solutions
Table 2. Redox potentials of PE1, PE1-OR6, and PE1-OR4 porphine
solution. As mentioned above, the redox potentials
of the first porphine reduction and oxidation of
PE1-OR4 are both negatively shifted from those of
PE1 and PE1-OR6. In addition, the first oxidation
of PE1-OR4 is much more reversible than those
of PE1 and PE1-OR6. Therefore, in addition
to the electro-donating influence of the alkoxyl
groups, we suggest that PE1-OR4’s negatively
shifted redox potentials as well as the reversible
oxidation may also be attributed to the wrapping
alkoxyl chains. This suggestion agrees well with
the results observed for PE1-OR6. Because the
PE1-OR6 simulation did not suggest the wrapping
phenomenon, it is reasonable to observe that the
electrochemical behaviors of PE1-OR6 remain
ring reactionsa
PE1
Reduction -1.24 (100) -1.27 (140)
Oxidation +1.08 (Epa)
PE1-OR6
PE1-OR4
H2PE1-OR4
-1.47 (130)
-1.22 (140)
+1.11b
+1.04 (Epa) +0.85 (150)
a
Reaction conditions: 1.0 mM of the porphyrin in THF/0.1 M TBAP;
Pt working and counter electrodes; SCE reference electrode; scan rate =
100 mV/s. For Fc+/0 in the same condition, E1/2 = +0.49 V vs SCE. Peak-
to-peak separations (mV) are put in the parentheses for quasi-reversible
b
reactions. This value is determined by differential pulse voltammetry
because the reaction is too close to the detection limit to have a correct
reading.
similar to those of PE1 porphyrin.
Because of free-base porphyrins were used in the
simulations, it is of interest to observe the effect of
the cental metal. Figure 4 compares the CVs of (zinc)
PE1-OR4 and free-base PE1-OR4. The redox potentials of
free-base PE1-OR4 are listed in Table 2. As shown in the
figure and the table, removing the central metal ion from
PE1-OR4 seem only to shift the redox potential positively.
For the first porphyrin-ring reductions, the reactions are
qusai-reversible for the zinc and the free-base porphyrins.
The potentials, however, shift from PE1-OR4’s -1.47 V to
free-base PE1-OR4’s -1.22 V. For the first porphyrin-ring
oxidations, the reaction is qusai-reversible for PE1-OR4.
Unfortunately, reversibility of free-base PE1-OR4’s first
oxidation is difficult to determine because the reaction is
very close to the detection limit of the solvent system.
Consequently, we determine the oxidation potential by
differential pulse voltammetry. Nevertheless, a similar
positive shift is also observed. The oxidation potentials
shift from PE1-OR4’s +0.85 V to free-base PE1-OR4’s
+1.11V. This phenomenon is consistent with the literature
reports [25]. As for the carboxylic acid reduction, the
redox couples do not seem to be sensitive to the removal
of the central metal ion.
Scheme 2. Simulated molecular structures of (a) PE1-OR4 and
(b) PE1-OR6 in solutions. The alkoxyl and alkyl chains are
highlighted. Note that this scheme is to visualize the orientations
of the long alkoxyl chains in the solutions
the calculation, free-base porphyrins were used in these
simulations. The results are compared in Scheme 2. As
shown in the scheme, the phenyl groups at the macrocyclic
meso-positions are fairly perpendicular to the porphyrin
macrocylic planes due to the steric hindrance between
the porphine ring and the phenyl rings. As for the alkoxyl
chains, thefourdodecoxylchainsofPE1-OR4aresimulated
to wrap around the porphine core whereas the six alkoxyl
chains of PE1-OR6 are simulated to extend into the bulk
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Fig. 4. Cyclic voltammograms of 1.0 mM of PE1-OR4 (bold dotted lines), and free-base PE1-OR4 (dash lines) in THF/0.1 M TBAP
(thin dotted lines) solutions. The arrows indicate the potential differences between the zinc and the free-base porphyrins
Finally, it is worth mentioning that changing the
lengths of the alkoxyl chains would not have a significant
impact on the redox properties of alkoxyl-wrapped
porphyrins. We have recently reported that shortening
the alkoxyl groups from 12 carbons to 8 and to 4 carbons
did not generate any sifnificant changes in the UV-visible
absorptions, fluorescent emissions, and the redox
behaviors of the LD14 porphyrins, a push-pull version of
PE1-OR4 [17b]. Molecular simulations were carried out
in the said report and the results suggested that, despite
the alkoxyl chains becoming shorter, the tendency to
wrap around the porphyrin core remained the same for
all versions of the LD14 porphyrins.
4. Nazeeruddin MK, De Angelis F, Fantacci S, Selloni
A, Viscardi G, Liska P, Ito S, Takeru B and Grätzel
M. J. Am. Chem. Soc. 2005; 127: 16835–16847.
5. Grätzel M. Inorg. Chem. 2005; 44: 6841–6851.
6. a) Chen CY, Wang M, Li JY, Pootrakulchote N,
Alibabaei L, Ngocle CH, Decoppet JD, Tsai JH,
Grätzel C, Wu CG, Zakeeruddin SM and Grätzel
M. ACS Nano. 2009; 3: 3103–3109. b) Kuang D,
Klein C, Snaith H J, Moser JE, Humphry-Baker R,
Comte P, Zakeeruddin SM and Grätzel M. Nano
Lett. 2006; 6: 769–773.
7. a) Imahori H, Umeyama T, Ito S. Acc. Chem. Res.
2009; 42: 1809–1818. b) Martinez-Diaz MV, de la
Torrea G and Torres T. Chem. Commun. 2010; 46:
7090–7108.
8. a) Mathew S, Iijima H, Toude Y, Umeyama T,
Matano Y, Ito S, Tkachenko NV, Lemmetyinen
H and Imahori H, J. Phys. Chem. C. 2011; 115:
14415–14424. b) Kira A, Matsubara Y, Iijima H,
Umeyama T, MatanoY, Ito S, Niemi M, Tkachenko
NV, Lemmetyinen H and Imahori H. J. Phys. Chem.
C. 2010; 114: 11293–11304.
CONCLUSION
We demonstrated that the first reduction reaction
of PE1 porphyrins is actually the reduction of the
anchoring carboxylic proton. We also showed that the
electrochemical behaviors of a zinc porphyrin can be
significantly affected by wrapping the porphine core
structure with long alkyl chains.
9. a) Lee CH, Chitre K and Galoppini E. J. Chin.
Chem. Soc. 2010; 57: 1103–1110. b) Lee CH and
Galoppini E. J. Org. Chem. 2010; 75: 3692–3704.
10. Campbell WM, Jolley KW, Wagner P, Wagner
K, Walsh PJ, Gordon KC, Schmidt-Mende L,
Nazeeruddin MK, Wang Q, Grätzel M and Officer
DL. J. Phys. Chem. C. 2007; 111: 11760–11762.
11. a)Yella A, Lee HW, Tsao HN, Yi C, Chandiran AK,
Nazeeruddin MK, Diau EWG,Yeh CY, Zakeeruddin
SM and Grätzel M. Science, 2011; 334: 629–634.
b) Bessho T, Zakeeruddin SM, Yeh CY, Diau EWG
and Grätzel M. Angew. Chem. Int. Ed. 2010; 49:
6646–6649.
Acknowledgements
This work was supported by the National Science
Council of Taiwan.
REFERENCES
1. a)GrätzelM. Nature. 2001;414:338–344. b)O’Regan
B and Gratzel M. Nature. 1991; 353: 737–740.
2. Nazeeruddin MK, Zakeeruddin SM, Humphry-
Baker R, Jirousek M, Liska P, Vlachopoulos N,
Shklove VR, Fischer CH and Grätzel M. Inorg.
Chem. 1999; 38: 6298–6305.
3. Hamann TW, Jensen RA, Martinson ABF,
Ryswykac HV and Hupp JT. Energy Environ. Sci.
2008; 1: 66–78.
12. a) Park SW, Hwang DS, Kim DY, Kim D. J. Chin.
Chem. Soc. 2010; 57: 1111–1118. b) Ishida M, Park
SW, Hwang D, Koo YB, Sessler JL, Kim DY and
Kim D. J. Phys. Chem. C. 2011; 115: 19343–19354.
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 97–98

98
P.-S. CHAO ET AL.
13. Biroli AO, Tessore F, Pizzotti M, Biaggi C, Ugo R,
Caramori S, Aliprandi A, Bignozzi CA, De Angelis
F, Giorgi G, Licandro E and Longhi E. J. Phys.
Chem. C. 2011; 115: 23170–23182.
14. a) Lin CY, Lo CF, Luo L, Lu HP, Hung CS and Diau
EWG. J. Phys. Chem. C. 2009; 113: 755–764. b)
Lo CF, Luo L, Diau EWG, Chang IJ and Lin CY.
Chem. Commun. 2006: 1430–1432.
19. Wu CH, Hong SH, Kuo HH, Chu YY, Diau EWG
and Lin CY, Chem. Commun. 2012; 48: 4329–4331.
20. Purification of laboratory chemicals, 3rd ed., Perrin
DD and Armarego WLF. (Eds.) Pergamon Press:
Oxford, 1988.
21. Lin CY, McGlashen ML, Hu S, Shim YK, Smith
KM and Spiro TG. Inorg. Chim. Acta. 1996; 252:
179–184.
15. Lin CY, Wang YC, Hsu SJ, Lo CF and Diau EWG.
J. Phys. Chem. C. 2010; 114: 687–693.
16. Lo CF, Hsu SJ, Wang CL, Cheng YH, Lu HP, Diau
EWG and Lin CY. J. Phys. Chem. C. 2010; 114:
12018–12023.
22. Hu S, Lin CY, Blackwood Jr. ME, Mukherjee A and
Spiro TG. J. Phys. Chem. 1995; 99: 9694–9701.
23. Silvester DS, He W, Aldous L, Hardacre C
and Richard GC, J. Phys. Chem. C. 2008; 112:
12966–12973.
17. a) Chang YC, Wang CL, Pan TY, Hong SH, Lan
CM, Kuo HH, Lo CF, Hsu HY, Lin CY and Diau
EWG. Chem. Commun. 2011; 47: 8910–8912. b)
Wang CL, Lan CM, Hong SH, Wang YF, Pan TY,
Chang CW, Kuo HH, Kuo MY, Diau EWG and Lin
CY. Energy Environ. Sci. 2012; 5: 6933–6940. c)
Lan CM, Wu HP, Pan TY, Chang CW, Chen CT,
Wang CL, Lin CY and Diau EWG. Energy Environ.
Sci. 2012; 5: 6460–6464.
24. Materials Studio. Accelrys Materials Studio, v 4.2,
Accelrys Inc: San Diego, CA, 2006.
25. a) For the reviews: Kadish KM, Caemelbecke
EV and Royal G. In The Porphyrin Handbook,
Vol. 8, Kadish KM, Smith KM and Guilard G.
(Eds.) Academic Press: New York, 2000. b)
For the database of porphyrins redox potentials
in nonaqueous media: Kadish KM, Royal G,
Caemelbecke EV and Gueletti L. In The Porphyrin
Handbook, Vol. 9, Kadish KM, Smith KM and
Guilard G. (Eds.) Academic Press: New York,
2000.
18. Wang CL, Chang YC, Lan CM, Lo CF, Diau
EWG and Lin CY. Energy Environ. Sci., 2011; 4:
1788–1795.
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