Cyclometalated ruthenium(ii) complexes with bis(benzimidazolyl)benzene for dye-sensitized solar cells

Article abstract of DOI:10.1039/c5ra20294a

A series of cyclometalated ruthenium complexes with bis(benzimidazolyl)benzene ligands were prepared and their applications in dye-sensitized solar cells are presented. The Ru(iii/ii) redox process of these complexes occurs at +0.71 V vs. Ag/AgCl. All complexes show broad absorptions extending into the near-infrared (NIR) region. The length of alkyl chains on the benzimidazole rings were found critical to the device performance. Sensitizer 4b with octyl substituents exhibits the best cell performance under the standard air mass 1.5 sunlight (η = 3.7%, J_sc = 9.85 mA cm^-2, V_oc = 555 mV, FF = 0.67). The device exhibits appreciable action in the NIR region between 700 and 850 nm.

Full text of DOI:10.1039/c5ra20294a

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ARTICLE
Cyclometalated Ruthenium(II) Complexes with
Bis(benzimidazolyl)benzene for Dye-Sensitized Solar Cells
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a
a
Jiang-Yang Shao, Nianqing Fu, Wen-Wen Yang, Chun-Yu Zhang, Yu-Wu Zhong,* Yuan Lin* and
a
Jiannian Yao
DOI: 10.1039/x0xx00000x
A series of cyclometalated ruthenium complexes with the bis(benzimidazolyl)benzene ligand were prepared and their
applications in dyeꢀsensitized solar cells are presented. The Ru(III/II) redox process of these complexes occurs at +0.71 V vs
Ag/AgCl. All complexes show broad absorptions extending into the nearꢀinfrared (NIR) region. The length of alkyl chains
on the benzimidazole rings were found critical to the device performance. Sensitizer 4b with octyl substituents exhibits the
www.rsc.org/ra
2
best cell performance under the standard air mass 1.5 sunlight (η = 3.7%, Jsc = 9.85 mA/cm , Voc = 555 mV, FF = 0.67). The
device exhibits appreciable action in the NIR region between 700 and 850 nm.
1
0
efficiency of 6.04% has been achieved. It should be noted that
most thiocyanateꢀfree ruthenium complexes exhibit insufficient
light harvesting in the nearꢀinfrared (NIR) region. Dyes that
absorb in the NIR region are believed critical to further improve
the cell efficiency, because NIR light accounts for a significant
Introduction
1
Since the pioneering work by O’Regan and Grätzel in 1991,
dyeꢀsensitized solar cells (DSSCs) have been extensively
studied due to their low cost, easy fabrication, and high power
conversion efficiency (
1
1
2
percentage of solar energy.
Cyclometalated ruthenium complexes contain a RuꢀC bond
η
). Recently, the record efficiency has
3
been boosted to 13%. Photosensitizers such as ruthenium
complexes, zinc porphyrins, and metalꢀfree organic dyes have
been developed to serve as efficient light harvesters for
1
2
between the metal center and a supporting ligand. Because of
the presence of the carbon anionic ligand, the metal center of
cyclometalated ruthenium complexes is much more electronꢀ
rich with respect to that of conventional trisbipyridine or
bisterpyridine ruthenium complexes. The highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) levels of cyclometalated ruthenium complexes
can be largely modulated by changing the electronic nature of
the cyclometalating ligand and noncyclometalating ligand,
respectively. Recently, cyclometalated ruthenium(II) complexes
4
DSSCs. In spite of these efforts, new dyes have continued to
be designed to broaden their light absorption wavelength range,
increase molar absorptivity and improve the longꢀterm stability
5
of solar cells.
Ruthenium(II) polypyridyl complexes are promising
sensitizers for DSSCs. They display rich metalꢀtoꢀligand charge
transfer (MLCT) absorptions in the visible region. Many
6
ruthenium sensitizers are known to achieve efficiencies higher
1
3
7
have been shown to act as efficient sensitizers in DSSCs. The
elevated HOMO level of cyclometalated ruthenium complexes
relative to trisbipyridine or bisterpyridine ruthenium complexes
lead to a bathochromic shift of the absorption spectrum. On the
other hand, the HOMO level of cyclometalated ruthenium
than 10%
， such as N3, N719, Z907, and black dyes.
However, the thiocyanateꢀcontaining ruthenium(II) complexes
are questioned by the stability problems because the
thiocyanate ligands are labile under thermal stress and longꢀ
term light soaking. This may hinder the commercialization
prospect of DSSCs. In this context, many attempts have been
made to replace the thiocyanate ligands in ruthenium dyes. For
instance, Singh and coꢀworkers reported a thiocyanteꢀfree
ruthenium dye SPSꢀG3 containing the tridentate 2,6ꢀbis(Nꢀ
methylbenzimidazolꢀ2ꢀyl)pyridine ligand, with which an
complexes is still below the I2• /I level, which ensures efficient
dye regeneration. In addition, replacing the thiocyanate ligands
of common ruthenium dyes with chelating cyclometalating
ligands provides the opportunity to enhance the dye stability.
The first example of a cyclometalated ruthenium sensitizer on
− −
8
9
TiO
modest
of 10.1% with a cyclometalated dye YE05. Following these
works, many new cyclometalated ruthenium dyes have been
2
was reported by van Koten and coꢀworkers to produce a
1
4
η
of 2.1%. In 2009, Grätzel and coꢀworkers reported a
a.
15
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of
Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing
η
1
00190, China. *Email: zhongyuwu@iccas.ac.cn (Y.-W.Z.); linyuan@iccas.ac.cn
Y.L.).
Electronic Supplementary Information (ESI) available: CVs and DPVs of 1a 3a – 5a,
1
6
synthesized and studied. However, cyclometalated ruthenium
dyes that display efficient NIR absorptions are still limited.
(
,
photocurrent density-voltage characteristic of the device with N3, NMR and mass
spectra of new compounds, and Cartesian coordinates for the DFT-optimized
structure of 2a . See DOI: 10.1039/x0xx00000x
+
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COOH
R
R
H
H
NH
2
2
N
N
N
N
L3: R = n-C H , 53%
4
9
PPA
NaH, DMF
+
L4: R = n-C
8
H
17, 48%
N
N
N
N
alkyl bromide
L5: R = n-C12
H25, 49%
NH
COOH
MeOOC
L1
COOMe
COOH
(
PF
6
)
(PF6)
MeOOC
COOMe
HOOC
COOH
N
N
N
Cl
N
N
N
N
N
1
2
. AgOTf
NEt3
2
DMF/H O
MeOOC
N
Ru Cl
Cl
Ru
N
Ru
N
. L1 - L5
N
N
N
N
N
N
R
R
R
R
MeOOC
Ru(Me
1
a: R = H, 23%
1b: R = H, 70%
2b: R = CH , 81%
3b: R = n-C H , 78%
4 9
4b: R = n-C H17, 81%
2
3
4
5
a: R = CH , 58%
3
[
3
tctpy)Cl
3
]
3
a: R = n-C
a: R = n-C
a: R = n-C12
4
H
9
, 32%
17, 33%
25, 47%
8
H
8
H
5b: R = n-C12H25, 67%
Scheme 1 Synthesis of Compounds 1b – 5b
by column chromatography on silica gel with 5 mM
tetrabutylammonium hydroxide (TBAOH) in methanol/water
(1:1, v/v) as the eluent. The isolated solid was obtained as the
TBA salt at this stage. This salt was then dissolved in water,
followed the addition of 1 M aqueous HCl. The resulting
We report herein the synthesis and characterization of five
cyclometalated ruthenium(II) dyes (1b 5b) with the
bis(benzimidazolyl)benzene ligand (Scheme 1). Proton or
alkyl chains of various lengths are placed on the
benzimidazole rings. All complexes show broad absorptions
extending into the NIR region. The DSSC performances of
ꢀ
precipitate was isolated to afford complexes 1b
– 5b in
acceptable yield. The identity of cyclometalated ruthenium
−
these complexes on TiO
2
and the effect of the length of alkyl
complexes with one PF
microanalysis data.
6
counteranion is supported by
differs from [RuN ]ꢀtype
chains on the device performance are presented. It should be
noted that although the effect alkyl chains on DSSC
This
6
noncyclometalated ruthenium complexes which needs the presence
of two counteranions.
7
i,7j
performance has been reported,
this effect has not been
examined on cyclometalated ruthenium dyes.
Single crystal of 2a suitable for Xꢀray analysis was
obtained by diffusion of petroleum ether into the solution of
2 2
the complex in CH Cl . The thermal ellipsoid plot of the Xꢀ
Results and discussion
Synthesis
ray structure is shown in Fig. 1. The ruthenium ion has an
expected octahedral configuration with one NNNꢀ and one
NCNꢀtype tridentate ligand. The RuꢀC bond has a distance of
Ruthenium dyes 1b
Scheme 1. Ligands 1,3ꢀbis(2ꢀbenzimidazolyl)benzene (L1),
,3ꢀbis(Nꢀmethylbenzimidazolyl)benzene (L2) and 1,3ꢀbis(Nꢀ
butylbenzimidazolyl)benzene L3 were synthesized
according to literature procedures. The reaction of
– 5b were synthesized as outlined in
2
.009(6) Å.
1
(
)
1
7
isophthalic acid with 1,2ꢀdiaminobenzene or Nꢀmethylꢀ1,2ꢀ
benzenediamine dihydrochloride in polyphosphoric acid
(PPA) afforded L1 and L2, respectively. The Nꢀalkylated
derivatives
octylbenzimidazolyl)benzene
dodecylbenzimidazolyl)benzene
of
L1
,
namely
L4),
L3
and
,
1,3ꢀbis(Nꢀ
1,3ꢀbis(Nꢀ
(
(
L5), were prepared by
deprotonation of L1 with NaH, followed by subsequent
alkylation with 1ꢀbromobutane, 1ꢀbromooctane and 1ꢀ
bromododecane, respectively. Cyclometalated ruthenium
Fig. 1 Thermal ellipsoid plot of the singleꢀcrystal Xꢀray
ꢀ
complexes 1a
Ru(Me tctpy)Cl
tricarboxylateꢀ2,2':6',2''ꢀterpyridine) with ligands L1
respectively, in the presence of AgOTf, followed by anion
exchange using KPF . These complexes were purified through
flash column chromatography on silica gel and obtained as
–
5a were prepared by the reaction of
(Me tctpy trimethylꢀ4,4',4''ꢀ
L5
structure of 2a at 30% probability. Solvents and anion (PF )
6
[
3
3
]
3
=
are omitted for clarity.
–
6
Electrochemical Studies and Density Functional Theory
(
DFT) Calculation
The electronic properties of 1a
voltammetric (CV) studies. The anodic CV of 1a
benchꢀstable compounds. The reaction of 1a
–
5a with
–
5a were examined by cyclic
5a in
triethylamine in a mixed solvent of DMF and H
2
O gave the
–
ruthenium complexes 1b
– 5b. These products were purified
CH CN are shown in Fig. 2a. All complexes exhibit a
3
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chemically reversible redox couple at +0.71 V vs Ag/AgCl
observed in the DFT results of cyclometalated ruthenium
2
0
(
+0.26 V vs the ferrocene/ferrocenium redox couple). These
complexes. This suggests that the first oxidation event of 2a
is mostly associated with the ruthenium ion and the metalating
phenyl ring as has been mentioned above. The HOMOꢀ1 and
HOMOꢀ2 of 2a are dominated by the ruthenium ion. The
LUMO, LUMO+1 and LUMO+2 are associated with the
noncyclometalating ligand, which suggests that the terpyridine
III/II
waves are ascribed to the Ru
process with some possible
involvement of the oxidation of the cyclometalating ring. Note
III/II
that the Ru
potential of [RuN
6
]ꢀtype noncyclometalated
vs
5a is estimated
to be +0.91 V with respect to a normal hydrogen electrode
NHE) and the dyes 1b 5b on TiO are believed to have
similar HOMO energy levels. This suggests that the dye can
ruthenium complexes generally occurs around +1.3
V
1
2d
Ag/AgCl. The HOMO energy level of 1a
–
ligand is mostly involved in the first reduction event of 2a
.
(
–
2
−
•− −
be efficiently regenerated by I (
E
(I
2
/I ) = +0.79 V vs NHE
0
LUMO+7
1
8
in CH
around +1.60 V vs Ag/AgCl are ascribed to the Ru
3
CN). The second oxidation waves of complexes 1a
–
IV/III
-1
5a
-2
-3
-4
-5
-6
-7
process (Fig. 2b and S1 – S4 in the Supporting Information,
SI). Taking complex 2a as an example (Fig. 2b), two
LUMO
LUMO+1
LUMO+2
LUMO
HOMO
chemically reversible cathodic waves are observed at
and 1.45 vs Ag/AgCl 1.55 and 1.90
−
V
1.10
vs
−
V
(
−
−
ferrocene/ferrocenium). These waves are assigned to the
reductions of the noncyclometalating ligand (Me tctpy). A
previously reported cyclometalated ruthenium complex
Ru(Me tctpy)(dpb)](PF ) (dpb = 1,3ꢀdi(pyridꢀ2ꢀyl)benzene)
also shows two cathodic waves at −1.10 and −1.45 V vs
HOMO-6
3
HOMO
HOMO-1
HOMO-2
[
3
6
Fig. 3 Isodensity plots of selected frontier orbitals of 2a along with the
energy level label.
1
9,20
Ag/AgCl.
Electronic Absorption Spectra and Time-Dependent DFT
(
TDDFT) Calculations
The electronic absorption spectra of complexes 1a
shown in Fig. 4, together with that of N3 for comparison.
Complexes 1a 5a exhibit very similar absorption patterns
and molar absorptivity. The absorptions in the ultraviolet
UV) region are due to intraligand transitions from both
(
a)
1
2
3a
a
a
1
2
8
4
0
4
8
– 5a are
4a
–
5a
(
I
-
-
cyclometalating and auxiliary ligands. In the visible (vis) to
NIR region, three main absorption bands are distinguished
(
350 ~ 500 nm; 500 ~ 650 nm; 650 ~ 900 nm), which are
-
12
largely ascribed to the MLCT transitions. In addition, these
complexes display distinct absorptions in the wavelength
range of 700 ~ 900 nm. This feature is not observed for N3
and the previously reported ruthenium dye with the
noncyclometalating
yl)pyridine ligand SPSꢀG3.
recorded for these complexes at room temperature.
Cyclometalated ruthenium complexes are known to be nonꢀ or
very weakly emissive.
0
.0 0.2 0.4 0.6 0.8 1.0 1.2
E
/ V vs Ag/AgCl
(
b)
3
0
5
0
1
2,6ꢀbis(
N
ꢀmethylbenzimidazolꢀ2ꢀ
1
0
No distinct emission was
>
I
1
6k
-
15
N3
1a
0
0
0
.6
.5
.4
-30
-1.6 -1.2 -0.8 -0.4 0.0 0.4 0.8 1.2 1.6
2a
3a
4a
5a
E
/ V vs Ag/AgCl
n
Fig. 2 (a) CVs of 1a
3 4 4
– 5a in CH CN containing 0.1 M Bu NClO as the
supporting electrolyte at a scan rate of 100 mV/s. The working electrode is
a glassy carbon and the counter electrode is a platinum wire. The reference
electrode is Ag/AgCl in saturated aqueous NaCl solution. (b) CV of 2a in
0.3
3
CH CN in a wide potential window.
0
0
.2
.1
ε
DFT calculations were performed on 2a on the level of
theory of B3LYP/6ꢀ31G*/LANL2DZ. Fig. 3 shows the
isodensity plots of selected frontier orbitals of 2a along with
the energy level label. The HOMO of 2a exhibits a high
electron delocalization between ruthenium and the
cyclometalating ligand. This phenomenon is commonly
0.0
3
00 400 500 600 700 800 900 1000
/ nm
λ
Fig. 4 UV/vis absorption spectra of 1a – 5a and N3.
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In order to assist the detailed interpretations of the
absorption bands of these complexes, TDDFT calculations
were performed on complex 2a on the basis of the above
DFTꢀoptimized structure. The predicted main lowꢀenergy
Journal Name
typical photocurrent density–voltage (JꢀV) characteristics are
shown in Fig. 6 and Table 2.
Among the five cyclometalated ruthenium dyes studied, 4b
shows the best photovoltaic performance, which exhibits an openꢀ
excitations are shown in Fig. 5
summarized in Table 1. TDDFT results suggest that the
absorption bands between 650 and 900 nm are mainly
,
and related results are
circuit photovoltage (Voc) of 555 mV, a shortꢀcircuit photocurrent
2
density (Jsc) of 9.85 mA/cm , a fillꢀfactor (FF) of 0.67, and
η
of
3.7%, respectively. Under similar conditions, the N3ꢀsensitized
2
associated with the HOMOꢀ1
excitation). The predicted and
ꢀ
LUMO transition (
S
2
device gave a Voc of 625 mV, Jsc of 12.56 mA/cm , FF of 0.69, and
S
5
S
6
excitations of complex 2a
η of 5.4% (Fig. S5). The length of alkyl chains is critical for the
at 519 and 493 nm are responsible for the experimentally
observed absorptions between 500 and 650 nm. These two
performance of the cells using 1b – 5b. The short circuit current
density increases with increasing length of alkyl chains from 1b
through 4b. These alkyl chains form a molecular layer with high
excitations are associated with the excitation of HOMOꢀ2
LUMO+1 and HOMOꢀ2 LUMO, respectively. A series of
excitations in 350 ~ 500 nm region with appreciable oscillator
strengths are predicted (from S to S20 excitations). These
ꢀ
ꢀ
2
hydrophobicity between the mesoporous TiO surface and the
electrolyte, which is beneficial for reducing the electronꢀhole
22
9
recombination. However, the cell with the dodecylꢀsubstituted
2
excitations are associated with the charge transfer from the
HOMO, HOMOꢀ1, HOMOꢀ2, and HOMOꢀ3 orbitals of
dye 5b shows a reduced Jsc of 8.56 mA/cm with respect to the
octylꢀsubstituted dye 4b. In this case, the dye regeneration may be
retarded due to the thick alkyl layer, leading to the reduced device
performance. The openꢀcircuit photovoltage consistently increases
with increasing length of alkyl chains from 1b through 5b. The
power conversion efficiency of 1b, 2b, 3b, and 5b is 0.8%, 1.5%,
complex 2a
.
0
0
0
0
0
0
.5
.4
.3
.2
.1
.0
2
.3%, and 3.3%, respectively.
S12
12
4b
S9
S
6S
5
9
6
3
0
5b
3b
S20
S2
3
00 400 500 600 700 800 900 1000
/ nm
λ
Fig. 5 UV/vis absorption spectrum (black curve) and TDDFTꢀpredicted
excitations (vertical red lines) of 2a
2b
1b
.
Table 1 Calculated Excitation Energy (E), Oscillator Strength (f), Dominant
Contributing Transitions and Associated Percent Contribution of 2a
0
200
400
Voltage / mV
600
S
n
E /
eV
λ
/
f
dominant transitions
Fig.
6 Photocurrent densityꢀvoltage characteristic of devices using
nm
cyclometalated ruthenium sensitizers.
2
1.85 671 0.0297
2.39 519 0.0736
2.51 493 0.0978
2.89 430 0.0929
2.89 429 0.0129
2.94 421 0.0495
3.01 411 0.2166
3.09 401 0.1215
3.10 400 0.0495
3.23 383 0.0306
HOMOꢀ1 ꢀ LUMO (95%)
HOMOꢀ2 ꢀ LUMO+1 (97%)
HOMOꢀ2 ꢀ LUMO (50%)
HOMOꢀ1 ꢀ LUMO+2 (69%)
HOMO ꢀ LUMO+3 (83%)
HOMOꢀ3 ꢀ LUMO (78%)
HOMO ꢀ LUMO+4 (94%)
HOMOꢀ2 ꢀ LUMO+2 (42%)
HOMOꢀ2 ꢀ LUMO+3 (75%)
HOMOꢀ3 ꢀ LUMO+1 (78%)
5
6
9
1
Table 2 Photovoltaic properties of DSSCs.
0
2
Dye
N3
J (mA/cm ) Voc (mV)
η
(%)
FF
0.69
0.70
0.69
0.68
0.67
0.66
sc
1
1
1
1
1
2
2
4
5
0
12.56
2.47
4.19
625
435
510
530
555
575
5.4
0.8
1.5
2.3
3.7
3.3
1
b
2b
3
4
5
b
b
b
6.39
Photovoltaic Performance
In order to evaluate the performance of ruthenium(II) complexes in
the DSSCs, commercially available test cells with transparent TiO
9.85
8.56
2
anodes stained with the standard N3 dye or the cyclometalated
ruthenium dyes 1b – 5b were assembled according to standard
2
1
literature procedures. The photovoltaic properties were measured
using the liquid electrolyte containing 0.5 M LiI, 0.05 M I , 0.6 M
ꢀtertꢀbutylpyridine (TBP), and 0.6 1ꢀmethylꢀ3ꢀ
2
4
M
hexylimidazolium iodide (HMII) in 3ꢀmethoxypropionitrile (MPN)
2
under AM 1.5 full sunlight (100 mW/cm ) illumination. Their
4
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effective core potential LANL2DZ basis set for ruthenium and 6ꢀ
1
00
24
3
1G* for other atoms. In all calculations, solvation effects in
1
2
3
4
5
b
b
b
b
b
N3
CH CN are included, and the conductorꢀlike polarizable continuum
3
80
60
40
20
0
2
5
model (CPCM) was employed. All orbitals have been computed
at an isovalue of 0.02 e/bohr .
3
4b
N3
Fabrication of DSSCs. The solar cells were fabricated and
26
measured according to known procedures. TiO was fabricated on
2
2
the FTO substrates (fluorineꢀdoped SnO , 15 ꢁ/sq) using a doctorꢀ
blade method and the electrodes were heated at 450 °C for 30 min.
After this sintering, the temperature was cooled to 90 °C. The
ꢀ4
electrodes were then immersed in a dye bath (3 × 10 M) in ethanol
for 24 h. The redox electrolyte is a mixture of 0.5 M LiI, 0.05 M I
.6 M TBP, and 0.6 M HMII in MPN. The counter electrode is Ptꢀ
400
500
600
/ nm
Fig. 7 The IPCE characteristics of DSSCs with 1b
700
800
2
,
λ
0
–
5b and N3.
coated FTO. The sandwiched solar cells were assembled using the
dyeꢀsensitized TiO2 photoelectrode and the Pt counter electrode
with the liquid electrolyte between them.
The incident photonꢀtoꢀcurrent conversion efficiency (IPCE)
characteristics of the devices using the above ruthenium dyes and
N3 are shown in Fig. 7. The maximum IPCE of 4b occur around
Photovoltaic Measurements. The photocurrent densityꢀvoltage (Jꢀ
V) measurements were tested using a Keithley 2611 Source Meter.
The light source is an AM 1.5 solar simulator (91160A, Newport
530 nm (48.0%). All devices exhibit appreciable actions in the
region between 700 and 850 nm. The device with 4b shows an
IPCE of 15.5% at 700 nm. In contrast, the device with N3 shows no
photo action in this region. We believe that the absorption of these
cyclometalated ruthenium dyes can be further extended into longerꢀ
wavelength region by structural modifications.
2
Co.). The incident light intensity is 100 mW/cm calibrated with a
standard Si solar cell. The tested solar cells have a working area of
2
0
.2 cm .
X-ray Crystallography. The Xꢀray diffraction data were collected
using a Rigaku Saturn 724 diffractometer on a rotating anode (Moꢀ
K radiation, 0.71073 Å) at 173 K. The structure was solved by the
Conclusions
2
7
direct method using SHELXSꢀ97 and refined with SHELXTꢀ
To summarize, five cyclometalated ruthenium(II) complexes
based on the bis(benzimidazolyl)benzene ligand with varying
alkyl chains were prepared. These complexes show
absorptions in a wide range of wavelength extending into the
NIR region. The dyeꢀsensitized solar cells with these
28
29
2
(
014 in conjugation with Olex2. Crystallographic data for 2a
CCDC 1428503): C43 PRu⋅3.5(CH Cl ), M = 1288.05,
triclinic, space group Pꢀ1, a = 12.163(3), b = 13.716(3), c =
H
34
F
6
N
7
O
6
2
2
1
2
8.215(4) Ǻ,
α
= 105.644(2)º,
β = 94.048(2)º, γ = 115.759(2)º, U =
3
572.8(9) Ǻ , T = 173 K, Z = 2, 31799 reflections measured,
complexes on TiO
2
were investigated. The best power
radiation type MoK\a, radiation wavelength 0.71073 Ǻ, final R
indices R1 = 0.0688, wR2 = 0.1717, R indices (all data) R1 =
conversion efficiencies of 3.7% was achieved with the dye
with octyl substituents. This result indicates that dyes with
appropriate length of alkyl chains are critical for the
optimization of device performance. Cyclometalated
ruthenium complexes are potential dyes for harvesting the
NIR light, which is important for further improvement of the
power conversion efficiency of DSSC.
0
.0736, wR2 = 0.1754.
Synthesis. NMR spectra were recorded in the designated solvent
on Bruker Avance 300 or 400 MHz spectrometer. Spectra are
reported in ppm values from residual protons of deuterated solvent.
Mass data were obtained with a Bruker Daltonics Inc. Apex II FTꢀ
ICR or Autoflex III MALDIꢀTOF mass spectrometer. The matrix
for MALDIꢀTOF measurement is αꢀcyanoꢀ4ꢀhydroxycinnamic acid.
Microanalysis was carried out using Flash EA 1112 or Carlo Erba
1106 analyzer at the Institute of Chemistry, Chinese Academy of
Sciences. Ligands L1, L2 and L3 were prepared according to the
Experimental
Spectroscopic and Electrochemical Measurements. All optical
ultraviolet/visible (UV/vis) absorption spectra were obtained using
17
a
TUꢀ1810DSPC spectrometer of Beijing Purkinje General
previously reported procedure.
Synthesis of L4. To a solution of 1,3ꢀbis(benzimidazolyl)benzene
100 mg, 0.32 mmol) and NaH (17 mg, 0.7 mmol) in 10 mL DMF
Instrument Co. Ltd. at room temperature in denoted solvents, with
a conventional 1.0 cm quartz cell. All cyclic voltammograms were
taken using a CHI 620D or 660D potentiostat. All measurements
were carried out in 0.1 M of Bu NClO /CH CN at a scan rate of
(
was added 1ꢀbromooctane (0.15 mL, 0.7 mmol). The resulting
o
4
4
3
mixture was stirred at 100 C for overnight under a nitrogen
100 mV/s with a Ag/AgCl reference electrode. The working
atmosphere. The solvent was removed in vacuum. The residue was
electrode was glassy carbon, and a platinum coil was used as the
counter electrode.
dissolved in 10 mL CH
2
Cl
2
, followed by washing with water (3 ×
. After filtration and
3
0 mL) and drying over anhydrous MgSO
4
Computational Methods. DFT calculations were carried out using
removal of the solvent, the residue was purified by column
chromatography on silica gel using petroleum ether/ethyl acetate
2
3
the B3LYP exchange correlation functional and implemented in
the Gaussian 09 package. The electronic structures of complexes
were determined using a general basis set with the Los Alamos
(4/1, v/v) as the eluent to give 82 mg of L4 as a yellow oil in 48%
1
yield. H NMR (400 MHz, CDCl
3
): δ 0.82 (t, J = 7.0 Hz, 6H), 1.17ꢀ
This journal is © The Royal Society of Chemistry 2015
J. Name., 2013, 00, 1-3 | 5
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DOI: 10.1039/C5RA20294A
ARTICLE
Journal Name
1
1
7
7
.22 (m, 20H), 1.81 (t, J = 6.6 Hz, 4H), 4.26 (t, J = 7.6 Hz, 4H),
0.055 mmol) and L3 (30 mg, 0.07 mmol) in 32% yield. H NMR
.26ꢀ7.31 (m, 4H), 7.40ꢀ7.43 (m, 2H), 7.69 (t, J = 7.6 Hz, 1H),
3
(400 MHz, CD CN): δ 0.96 (t, J = 7.4 Hz, 6H), 1.41ꢀ1.48 (m, 4H),
13
.81ꢀ7.84 (m, 2H), 7.88 (d, J = 7.6 Hz, 2H), 8.05 (s, 1H). C NMR
): δ 8.17, 16.68, 20.83, 23.17, 23.97, 25.77, 39.04,
0.90, 71.21, 71.53, 104.4, 114.2, 116.6, 117.0, 123.4, 124.2, 124.7,
1.96ꢀ2.04 (m, 4H), 3.83 (s, 6H), 4.23 (s, 3H), 4.73 (t, J = 7.6 Hz,
4H), 5.60 (d, J = 8.0 Hz, 2H), 6.74 (t, J = 7.8 Hz, 2H), 7.05 (t, J =
7.6 Hz, 2H), 7.39ꢀ7.44 (m, 6H), 7.67 (t, J = 7.6 Hz, 1H), 8.35 (d, J
(100 MHz, CDCl
3
7
1
5
25.5, 129.7, 137.3, 146.9. HRMS (EI) calcd for C36
34.3722. Found: 534.3716.
H
46
N
4
:
= 7.6 Hz, 2H), 8.92 (s, 2H), 9.46 (s, 2H). MALDIꢀTOF: 930.2 for
+
[M – PF
6
] . Anal. Calcd for C49
H
46
F
6
N
7
O
6
PRu·H
2
O: C, 53.85; H,
4
.43; N, 8.97. Found: C, 53.44; H, 4.27; N, 9.15.
Synthesis of Complex 4a. According to the synthetic procedure for
1a, complex 4a was prepared from [Ru(Me tctpy)Cl ] (57 mg,
0.092 mmol) and L4 (54 mg, 0.1 mmol) in 33% yield. H NMR
(400 MHz, CD CN): δ 0.80 (t, J = 6.8 Hz, 6H), 1.16ꢀ1.27 (m, 20H),
Synthesis of L5. According to the synthetic procedure for L4,
compound L5 was prepared from 1,3ꢀbis(benzimidazolyl)benzene
(
103 mg, 0.32 mmol) and 1ꢀbromododecane (0.16 mL, 0.7 mmol)
3
3
1
1
in 49% yield. H NMR (400 MHz, CDCl
H), 1.17ꢀ1.22 (m, 36H), 1.81 (t, J = 6.4 Hz, 4H), 4.26 (t, J = 7.6
Hz, 4H), 7.29ꢀ7.33 (m, 4H), 7.43ꢀ7.44 (m, 2H), 7.69 (t, J = 7.6 Hz,
3
): δ 0.86 (t, J = 6.8 Hz,
6
3
1.35ꢀ1.41 (m, 4H), 3.83 (s, 6H), 4.24 (s, 3H), 4.73 (t, J = 7.0 Hz,
4H), 5.59 (d, J = 8.0 Hz, 2H), 6.73 (t, J = 7.6 Hz, 2H), 7.05 (t, J =
7.4 Hz, 2H), 7.38ꢀ7.42 (m, 6H), 7.65 (t, J = 7.2 Hz, 1H), 8.35 (d, J
= 7.6 Hz, 2H), 8.92 (s, 2H), 9.46 (s, 2H). C NMR (100 MHz,
CD CN): δ 13.91, 22.84, 26.92, 29.40, 29.45, 30.03, 31.94, 45.48,
53.13, 53.46, 111.5, 114.2, 122.5, 122.9, 123.6, 123.7, 125.2, 126.3,
1
3
1
H), 7.82ꢀ7.84 (m, 2H), 7.88 (d, J = 7.6 Hz, 2H), 8.05 (s, 1H). C
3
NMR (100 MHz, CDCl ): δ 8.26, 16.81, 20.84, 23.19, 23.45, 23.54,
1
3
2
3.58, 23.70, 23.97, 26.02, 39.03, 70.91, 71.23, 71.55, 104.4, 114.2,
16.6, 117.0, 123.4, 124.2, 124.7, 125.5, 129.7 137.3, 146.9.
: 646.4974. Found: 646.4982.
Synthesis of Complex 1a. To 10 mL dry acetone were added
Ru(Me tctpy)Cl ] (34 mg, 0.055 mmol) and AgOTf (58 mg, 0.23
1
3
62 4
HRMS (EI) calcd for C44H N
1
1
C
32.6, 134.1, 135.2, 135.8, 141.8, 155.0, 155.9, 160.3, 160.7, 164.5,
+
65.9, 219.6. MALDIꢀTOF: 1042.3 for [M – PF
PRu·H O: C, 56.80; H, 5.35; N, 8.14. Found: C,
6.99; H, 5.26; N, 8.21.
Synthesis of Complex 5a. According to the synthetic procedure for
1a, complex 5a was prepared from [Ru(Me tctpy)Cl ] (32 mg,
0.052 mmol) and L5 (35 mg, 0.054 mmol) in 47% yield. H NMR
(400 MHz, CD CN): δ 0.86 (t, J = 7.2 Hz, 6H), 1.10ꢀ1.28 (m, 36H),
6
] . Anal. Calcd for
[
3
3
57
H
62
F
6
N
7
O
6
2
mmol). The mixture was refluxed for 2 h before cooling to room
temperature. The precipitate was removed by filtration, and the
filtrate was concentrated to dryness. To the residue were added L1
5
(17 mg, 0.055 mmol), DMF (10 mL), and tꢀBuOH (10 mL). The
3
3
1
mixture was then refluxed for 24 h. After cooling to room
temperature, the solvent was removed under reduced pressure, and
the residue was dissolved in proper amount of methanol. After
3
1.33ꢀ1.41 (m, 4H), 3.83 (s, 6H), 4.24 (s, 3H), 4.73 (t, J = 7.2 Hz,
4H), 5.59 (d, J = 8.4 Hz, 2H), 6.73 (t, J = 7.6 Hz, 2H), 7.05 (t, J =
7.6 Hz, 2H), 7.38ꢀ7.42 (m, 6H), 7.65 (t, J = 8.0 Hz, 1H), 8.34 (d, J
= 8.0 Hz, 2H), 8.92 (s, 2H), 9.46 (s, 2H). C NMR (100 MHz,
CD CN): δ 13.61, 22.60, 26.44, 29.00, 29.22, 29.42, 29.48, 29.54,
31.83, 45.10, 52.75, 53.07, 54.52, 111.2, 113.8, 122.2, 122.5,
123.3, 124.9, 125.9, 132.2, 133.7, 134.9, 135.4, 141.4, 154.7,
155.6, 159.9, 160.3, 164.1, 165.5, 219.2. MALDIꢀTOF: 1154.4 for
addition of an excess of KPF
collected by filtration and washing with water and Et
obtained solid was subjected to flash column chromatography on
silica gel (eluent: CH Cl /ethyl acetate, 10/1) to give 11.3 mg
complex 1a as a black solid in 23% yield. H NMR (400 MHz,
CD CN): δ 3.83 (s, 6H), 4.24 (s, 3H), 5.64 (d, J = 8.0 Hz, 2H), 6.72
t, J = 7.6 Hz, 2H), 7.01 (t, J = 7.8 Hz, 2H), 7.36 (d, J = 8.4 Hz,
6
, the resulting precipitate was
2
O. The
1
3
2
2
3
1
3
(
+
2
8
5
1
1
H), 7.43 (s, 4H), 7.64 (t, J = 7.8 Hz, 1H), 8.24 (d, J = 7.6 Hz, 2H),
[M – PF
6
] . Anal. Calcd for C65
H
78
F
6
N
7
O
6
PRu·H
2
O: C, 59.26; H,
1
3
.92 (s, 2H), 9.45 (s, 2H). C NMR (100 MHz, CD
3
CN): δ 52.73,
6.12; N, 7.44. Found: C, 59.13; H, 6.12; N, 7.43.
Synthesis of Complex 1b. A solution of 1a (15 mg, 0.016 mmol),
O (5 mL), and NEt (5 mL) in 20 mL DMF was refluxed for 24 h.
3.06, 112.5, 113.8, 122.1, 122.4, 123.1, 123.5, 123.6, 125.9,
32.2, 132.9, 133.2, 135.5, 142.1, 154.9, 155.7, 160.1, 161.5,
H
2
3
+
64.2, 165.6, 216.4. MALDIꢀTOF: 818.0 for [M – PF
6
] . Anal.
After cooling to room temperature, the solvent was removed under
reduced pressure. The residue was dissolved in a minimal amount
of 0.1
Calcd for C41
0.95; H, 3.60; N, 9.79.
Synthesis of Complex 2a. According to the synthetic procedure for
30 6 7 6
H F N O PRu: C, 51.15; H, 3.14; N, 10.18. Found: C,
5
M
tetrabutylammonium hydroxide (TBAOH) in
methanol/H
2
O (1:1, v/v). The product was purified by column
1
0
a, complex 2a was prepared from [Ru(Me
.06 mmol) and L2 (24.6 mg, 0.07 mmol) in 58% yield. H NMR
CN): δ 3.83 (s, 6H), 4.24 (s, 3H), 4.30 (s, 6H), 5.60
d, J = 8.0 Hz, 2H), 6.73 (t, J = 8.0 Hz, 2H), 7.06 (t, J = 8.0 Hz,
3
tctpy)Cl
3
] (37.4 mg,
chromatography on silica gel with
5
mM TBAOH in
1
methanol/water (1:1, v/v) as the eluent. The isolated solid was
dissolved in proper amount water followed by the addition of 0.1 M
aqueous HCl. The resulting precipitate was filtrated, and washed
with water to give 10 mg complex 1b in 70% yield. H NMR (400
3
MHz, CD OD): δ 5.73 (d, J = 8.4 Hz, 2H), 6.69 (t, J = 7.8 Hz, 2H),
(400 MHz, CD
3
(
1
2H), 7.37 (d, J = 8.4 Hz, 2H), 7.44 (s, 4H), 7.64 (t, J = 8.0 Hz, 1H),
13
8
.45 (d, J = 8.0 Hz, 2H), 8.91 (s, 2H), 9.46 (s, 2H). C NMR (100
CN): δ 32.02, 52.73, 53.06, 54.51, 110.9, 113.7, 122.1,
22.4, 123.1, 123.2, 125.0, 125.8, 132.1, 134.1, 135.2, 135.4,
41.4, 154.7, 155.8, 160.0, 161.1, 164.2, 165.6, 218.9. MALDIꢀ
MHz, CD
1
1
3
6.97 (t, J = 7.6 Hz, 2H), 7.23 (d, J = 6.0 Hz, 2H), 7.31 (t, J = 7.2
Hz, 4H), 7.54 (t, J = 7.6 Hz, 1H), 8.20 (d, J = 7.6 Hz, 2H), 8.86 (s,
+
2H), 9.40 (s, 2H). MALDIꢀTOF: 775.9 for [M – PF
for C38
6
] . Anal. Calcd
+
TOF: 846.6 for [M – PF
2.13; H, 3.46; N, 9.90. Found: C, 51.64; H, 3.44; N, 9.51.
Synthesis of Complex 3a. According to the synthetic procedure for
6
] . Anal. Calcd for C43
H
34
F
6
N
7
O
6
PRu: C,
H
24
F
6
N
7
O
6
PRu: C, 49.57; H, 2.63; N, 10.65. Found: C,
5
50.01; H, 3.20; N, 10.95.
Synthesis of Complex 2b. According to the synthetic procedure
1
a, complex 3a was prepared from [Ru(Me
3
tctpy)Cl
3
] (34 mg,
for 1b, complex 2b was prepared from 2a (13.3 mg, 0.013 mmol) in
6
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5RA20294A
Journal Name
ARTICLE
1
8
=
7
1% yield. H NMR (400 MHz, CD
3
OD): δ 4.38 (s, 6H), 5.73 (d, J
4 (a) Q. Yu, Y. Wang, Z. Yi, N. Zu, J. Zhang, M. Zhang and P.
Wang, ACS Nano, 2010, 4, 6032; (b) A. Yella, H. W. Lee, H. N.
Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin, E. W. G.
Diau, C. Y. Yeh, S. M. Zakeeruddin and M. Grätzel, Science,
2011, 334, 629; (c) A. Yella, R. HumphryꢀBaker, B. F. E.
Curchod, N. AshariꢀAstani, J. Teuscher, L. E. Polander, S.
Mathew, J.ꢀE. Moser, I. Tavernelli, U. Rothlisberger, M. Grätzel,
Md. K. Nazeeruddin and J. Frey, Chem. Mater., 2013, 25, 2733;
8.0 Hz, 2H), 6.73 (t, J = 7.6 Hz, 2H), 7.04 (t, J = 7.4 Hz, 2H),
.21 (d, J = 6.0 Hz, 2H), 7.28 (d, J = 6.4 Hz, 2H), 7.39 (d, J = 8.4
Hz, 2H), 7.61 (t, J = 7.8 Hz, 1H), 8.48 (d, J = 8.0 Hz, 2H), 8.84 (s,
+
2
H), 9.39 (s, 2H). MALDIꢀTOF: 804.2 for [M – PF
for C40 PRu·H O: C, 49.70; H, 3.13; N, 10.14. Found: C,
9.13; H, 3.66; N, 10.51.
6
] . Anal. Calcd
H
28
F
6
N
7
O
6
2
4
Synthesis of Complex 3b. According to the synthetic procedure
(
d) P. G. Bomben, B. D. Koivisto and C. P. Berlinguette, Inorg.
for 1b, complex 3b was prepared from 3a (15 mg, 0.014 mmol) in
1
Chem., 2010, 49, 4960.
7
6
=
7
8% yield. H NMR (400 MHz, d
6
ꢀDMSO): δ 0.88 (t, J = 7.2 Hz,
5
(a) S.ꢀW. Wang, K.ꢀL. Wu, E. Ghadiri, M. G. Lobello, S.ꢀT. Ho,
Y. Chi, J.ꢀE. Moser, F. De Angelis, M. Grätzel and M. K.
Nazeeruddin, Chem. Sci., 2013, 4, 2423; (b) T. Moehl, H. N.
Tsao, K.ꢀL. Wu, H.ꢀC. Hsu, Y. Chi, E. Ronca, F. De Angelis, M.
K. Nazeeruddin and M. Grätzel, Chem. Mater., 2013, 25, 4497;
H), 1.34ꢀ1.40 (m, 4H), 1.90ꢀ1.93 (m, 4H), 4.84 (s, 4H), 5.53 (d, J
8.4 Hz, 2H), 6.80 (t, J = 7.8 Hz, 2H), 7.07 (t, J = 7.4 Hz, 2H),
.31 (d, J = 5.6 Hz, 2H), 7.53 (d, J = 5.6 Hz, 2H), 7.61 (d, J = 8.0
Hz, 2H), 7.68 (t, J = 7.8 Hz, 1H), 8.42 (d, J = 7.6 Hz, 2H), 9.14 (s,
+
2
H), 9.69 (s, 2H). MALDIꢀTOF: 887.8 for [M – PF
for C46 PRu·H O: C, 52.57; H, 4.03; N, 9.33. Found: C,
2.63; H, 4.52; N, 9.13.
6
] . Anal. Calcd
(c) J. Zheng, T.ꢀL. Zhang, X.ꢀF. Zang, D.ꢀB. Kuang, H. Meier
H
40
F
6
N
7
O
6
2
and D.ꢀR. Cao, Sci. China Chem., 2013, 56, 505; (d) C.ꢀC. Chou,
F.ꢀC. Hu, H.ꢀH. Yeh, H.ꢀP. Wu, Y. Chi, J. N. Clifford, E.
Palomares, S.ꢀH. Liu, P.ꢀT. Chou and G.ꢀH. Lee, Angew. Chem.
Int. Ed., 2014, 53, 178; (e) K. Kanaizuka, S. Yagyu, A.
Kajikawa, T. Kakuta, H. Kon, T. Togashi, K. Uruma, M.
Ishizaki, M. Sakamoto and M. Kurihara, Chem. Lett., 2013, 42,
5
Synthesis of Complex 4b. According to the synthetic procedure
for 1b, complex 4b was prepared from 4a (15 mg, 0.013 mmol) in
1
8
6
=
7
8
9
1% yield. H NMR (400 MHz, d
6
ꢀDMSO): δ 0.73 (t, J = 8.8 Hz,
H), 1.05ꢀ1.23 (m, 20H), 1.93ꢀ1.96 (m, 4H), 4.85 (s, 4H), 5.52 (d, J
10.4 Hz, 2H), 6.79 (t, J = 10.2 Hz, 2H), 7.06 (t, J = 9.6 Hz, 2H),
.31 (d, J = 7.6 Hz, 2H), 7.50 (d, J = 7.6 Hz, 2H), 7.63 (m, 3H),
.42 (d, J = 7.6 Hz, 2H), 9.14 (s, 2H), 9.69 (s, 2H). MALDIꢀTOF:
99.9 for [M – PF
669. (f) L.ꢀJ. Wang, K. Zhang, F.ꢀY. Cheng and J. Chen, Sci.
China Chem., 2014, 57, 1559.
6
(a) J.ꢀF. Yin, M. Velayudham, D. Bhattacharya, H.ꢀC. Lin and
K.ꢀL. Lu, Coord. Chem. Rev., 2012, 256, 3008; (b) A. Juris, V.
Balzani, F. Barigelletti, S. Campagna, P. Belser and A. von
Zelewsky, Coord. Chem. Rev., 1988, 84, 85; (c) G. C.
Vougioukalakis, A. I. Philippopoulous, T. Stergiopoulos and P.
Falaras, Coord. Chem. Rev., 2011, 255, 2602; (d) H. Ozawa, K.
Fukushima, T. Sugiura, A. Urayama and H. Arakawa, Dalton.
Trans., 2014, 43, 13208; (e) B.ꢀB. Ma, Y.ꢀX. Peng, T. Tao and
W. Huang, Dalton. Trans., 2014, 43, 16601; (f) H. Ozawa, T.
Kuroda, S. Harada and H. Arakawa, Eur. J. Inorg. Chem., 2014,
4734; (g) C.ꢀC. Chou, F.ꢀC. Hu, K.ꢀL. Wu, T. Duan, Y. Chi, S.ꢀ
H. Liu, G.ꢀH. Lee and P.ꢀT. Chou, Inorg. Chem., 2014, 53, 8593;
+
6
] . Anal. Calcd for C54
H
56
F
6
N
7
O
6
PRu: C, 56.64;
H, 4.93; N, 8.56. Found: C, 56.80; H, 5.26; N, 8.21.
Synthesis of Complex 5b. According to the synthetic procedure
for 1b, complex 5b was prepared from 5a (15 mg, 0.012 mmol) in
1
6
6
=
7
8
1
5
7% yield. H NMR (400 MHz, d
6
ꢀDMSO): δ 0.95 (t, J = 8.6 Hz,
H), 1.04ꢀ1.28 (m, 36H), 1.92ꢀ19.5 (m, 4H), 4.85 (s, 4H), 5.52 (d, J
8.0 Hz, 2H), 6.78 (t, J = 7.6 Hz, 2H), 7.06 (t, J = 7.6 Hz, 2H),
.31 (d, J = 5.6 Hz, 2H), 7.50 (d, J = 7.6 Hz, 2H), 7.64 (m, 3H),
.42 (d, J = 8.0 Hz, 2H), 9.14 (s, 2H), 9.69 (s, 2H). MALDIꢀTOF:
112.3 for [M – PF
+
6
] . Anal. Calcd for C62
H
72
F
6
N
7
6
O PRu·H
2
O: C,
8.39; H, 5.85; N, 7.69. Found: C, 58.08; H, 5.66; N, 7.17.
(
h) C. Dragonetti, A. Colombo, M. Magni, P. Mussini, F. Nisic,
D. Roberto, R. Ugo, A. Valore, A. Valsecchi, P. Salvatori, M. G.
Lobello and F. D. Angelis, Inorg. Chem., 2013, 52, 10723.
Acknowledgements.
7
(a) M. K. Nazeeruddin, F. De Angelis, S. Fantacci, A. Selloni, G.
Viscardi, P. Liska, S. Ito, B. Takeru and M. Grätzel, J. Am.
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We thank the National Natural Science Foundation of China
grants 21501183, 91227104, 21271176, 21472196, and
1221002), the Ministry of Science and Technology of China
grant 2012YQ120060), the Strategic Priority Research
Program of the Chinese Academy of Sciences (grant XDB
2010400), and Institute of Chemistry, Chinese Academy of
(
2
(
1
Sciences (grant PYꢀ201524) for funding support.
1993, 115, 6382; (e) M. Y. A. Rahman, A. A. Umar, R. Taslim
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Journal Name
ARTICLE
Title/Authours/Abstract/Figure for Table of
contents
Cyclometalated Ruthenium(II)
Complexes with
Bis(benzimidazolyl)benzene for
Dye-Sensitized Solar Cells
Jiang-Yang Shao, Nianqing Fu, Wen-Wen Yang,
Chun-Yu Zhang, Yu-Wu Zhong,* Yuan Lin* and
Jiannian Yao
The length of alkyl chains on the benzimidazole rings of
cyclometalated ruthenium dyes is critical to the DSSC
performance.
R = C H
17
(
PF )
6
8
R
R
9
6
3
0
N
N
R = C12H25
N
N
N
N
R = C H9
Ru
N
4
R = CH3
J
HOOC
COOH
R = H
0
200
400
/ mV
600
COOH
V
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