The effect of: Cis - Trans configurational difference on the performance of pyridylimine-based ruthenium sensitizers

Article abstract of DOI:10.1039/c8dt01131a

New heteroleptic Ru(ii) complexes consisting of pyridylimine as an ancillary ligand were synthesized and characterized for applications in dye sensitized solar cells. Complexes with cis and trans configurations around the central ruthenium metal were obtained using simple synthetic protocols by varying the substituents on the pyridylimine ligands. The geometries of these complexes were confirmed by single crystal X-ray analysis. The effect of the difference in the configurations of these complexes on their device performances was studied and the sensitizer with a trans arrangement around the metal showed a higher overall conversion efficiency (η) of 7.27% than that of the cis configured complex (η = 2.04%).

Full text of DOI:10.1039/c8dt01131a

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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Effect of Cis-trans Configurational Difference on the Performance
of Pyridylimine-based Ruthenium Sensitizers
Yogesh S. Tingare, ‡a Suri Babu Akula, ‡a Ming-Tai Shen,a Chaochin Su,*b Shih-Yu Ho,b Sheng-Han
Tsai,b Ya-Fen Lin,a and Wen-Ren Li,*a
Received 00th October 20xx,
Accepted 00th October 20xx
DOI: 10.1039/x0xx00000x
New heteroleptic Ru(II) complexes consisting pyridylimine as ancillary ligands were synthesized and characterized for
applications in dye sensitized solar cells. Complexes with cis and trans configurations around the central ruthenium metal
were obtained using simple synthetic protocols by varying the substituents on the pyridylimine ligands. The geometries of
these complexes were confirmed by single crystal X-ray analysis. The effect of difference in the configurations of these
complexes on their device performances was studied and the sensitizer with the trans arrangement around the metal
showed higher overall conversion efficiency (η) of 7.27 % than that of the cis configured complex (η = 2.04%).
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through developing different kinds of heterocyclic rings like
fused pyridine, pyrimidine, pyrazine, and N-heterocyclic
carbene as ancillary ligands which showed good conversion
Introduction
Energy consumption has been increasing due to the
modernization of society and fast development of technology.
Finding inexpensive, renewable, and environment friendly
energy resources has become a well-focused academic and
industrial research topic.1 After the first report of Grätzel and
O’Regan,2 the dye-sensitized solar cell (DSSC) technology has
emerged as a resourceful alternative to the fossil fuel energy.
The design is relatively simple and is composed of five
components; semiconducting photoanode, dye sensitizer,
redox mediator, counter electrode, and conducting glass
substrate.3-5 Among these constituents, the sensitizing dye is
considered one of the most important parts in the DSSC.6 Till
date, numerous sensitizers such as ruthenium complexes, non-
ruthenium organometallic dyes, and metal-free organic
sensitizers were designed and their photophysical properties
and device performances are reported.7-21 Mostly, the
efficiencies.27, 36-41 In these templates, both the donor nitrogen
atoms in the ancillary ligand are part of the heterocyclic ring.
Another example of the ruthenium sensitizer using
a
conjugated dipyridylamine ligand as an ancillary group is
reported to show that an extra nitrogen atom outside the
heterocycle which is not chelated to central metal atom, can
lift up the highest occupied molecular orbital (HOMO).42
Moreover, the studies employing pyridylimine units as
ancillary ligands of ruthenium complexes have not yet been
explored. Also, the effect of cis and trans configurations of
pyridylimine-based ruthenium dyes on their device
performance is worthy to be investigated.
Herein, we report two first heteroleptic ruthenium(II)
complexes
(IP102 and IP104) with pyridylimine ancillary
ligands (Fig. 1). Our interest in the ruthenium pyridylimine
complexes is particularly important due to two reasons. First,
the metal−pyridylimine ligands combination are commonly
ruthenium(II) dyes such as N3 22, 23 N719 18, 24 black dye,25, 26
,
,
and other ruthenium complexes27 utilizing mainly bipyridyl
ligands, are known to be the efficient heterogeneous charge
transfer sensitizers and successful dye designs. Advancements
in these molecular developments have been focused in
enhancing the light harvesting properties to improve the
photoelectric conversion efficiencies.28-35
served as active catalyst precursors and have widespread
applications.43,
44
These ligands are easy to prepare and
possess similar properties to the extensively explored
bipyridine ligands.45
OH
H
OH
Optimization of Ru(II) sensitizers has been carried out
O
O
N
O
O
N
N
N
N
N
N
N
N
Ru
Ru
C
S
OH
OH
IP102
IP104
Fig. 1 Molecular structures of IP102 and IP104.
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Alike the ruthenium N719 dye, one of the most efficient was reacted with [RuCl2(p-cymene)]2 in CH2Cl2 and then with 4,
sensitizers, the metal−pyridylimine ligand complexes shows 4′-bis(methoxycarbonyl)-2, 2′-bipyridine to yield a ruthenium-
low lying
π
orbitals46 which usually could be account into good chloride complex which was treated with KSCN in a mixture of
charge transfer spectra. Being composed of rich redox and H2O and DMF at 85oC to afford the ruthenium-thiocyanide
optical properties, these pyridylimine ligands are expected to complex 5a. Hydrolysis of the ester 5a under basic conditions
act as excellent ancillary ligands.47 Second, the design of of LiOH in H2O/DMF produced the desired sensitizer IP102. As
pyridylimine ligands can be fine-tuned with varying shown in Scheme 2, the ligand 4b was synthesized by
substitution which will allow structural engineering at a condensing 2-benzoylpyridine (2b) with compound
3 in the
molecular level. With some appropriate structural presence of p-toluenesulfonic acid (PTSA) in toluene. The
modifications by inducing steric effect, one can manipulate the complex IP104 which has an additional phenyl substitution on
possibilities to obtain either cis- or trans-ruthenium complexes the imine bond was synthesized from the ligand 4b using a
exclusively.
method similar to that described for the preparation of IP102.
X-ray Crystallography
Results and discussion
The dye IP102 with unsubstituted imine ligand acquired cis
configuration around the ruthenium metal, confirmed by the
single-crystal X-ray structural analysis (Fig. 2a and Table S1†).
All the Ru–N bond lengths range from 2.011 to 2.034 A˚, which
are in the range that has been reported for typical
bis(bipyridyl) ruthenium complexes. The N(pyridine) atom of
the ancillary ligand [Ru–N3, 2.034 A˚] is positioned trans to the
Ru–N(pyridine) bond of the anchoring ligand [Ru–N6, 2.026 A˚]
Synthesis
The syntheses of new pyridylimine dyes IP102 and IP104
were accomplished in simple synthetic routes depicted in
Schemes 1 and 2, respectively. The condensation reaction
between picolinaldehyde (2a) and 2, 6-dimethylaniline (3) in
the presence of ethanol and catalytic amount of formic acid
afforded ligand 4a. The ester complex 5a was obtained from
the resulting ligand 4a in three consecutive steps. Imine ligand
4a
a)
Scheme 1 Synthesis of sensitizer IP102
.
NH2
1. [RuCl2(p-cymene)]2
3
CH2Cl2
N
N
O
formic acid
ethanol, 60 o
2. 4,4'-bis(methoxycarbonyl)-
2,2'-bipyridine, ClCH2CH2Cl
3. KSCN, DMF/H2O
N
C
2a
4a
OMe
OH
H
N
H
N
O
O
O
O
N
N
N
N
N
N
N
LiOH
Ru
Ru
b)
DMF/H2O
C
C
S
N
S
OMe
OH
5a
IP102
Scheme 2 Synthesis of sensitizer IP104
.
1. [RuCl2(p-cymene)]2
NH2
CH2Cl2
3
N
2. 4,4'-bis(methoxycarbonyl)-
2,2'-bipyridine, ClCH2CH2Cl
3. KSCN, DMF/H2O
PTSA
toluene
O
N
N
2b
4b
OMe
OH
O
O
O
O
Fig. 2 Perspective view of IP102 ester (5a) and IP104 ester (5b) with thermal ellipsoids
N
N
N
N
N
LiOH
drawn at the 50% probability level. Hydrogen atoms and solvent (dichloromethane)
Ru
Ru
have
been
omitted
for
the
sake
of
clarity.
DMF/H2O
N
N
N
OMe
OH
5b
IP104
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whereas, the N(imine) atom [Ru–N4, 2.011 A˚] is located trans
to the NCS (2) ligand. Therefore, for the complex IP102, the
majority of the electron donation might be contributed from
the pyridine ring of ancillary ligand and one of the NCS ligands.
In the case of IP104, the dye having phenyl substituted imine
ligand developed trans configured molecular arrangement
around the ruthenium metal with Ru–N bond lengths range
from 2.035–2.105 A˚ (Fig. 2b and Table S2†) which are longer
than those of the IP102. Especially, the Ru–N(imine) bond
length of IP104 (Ru–N4, 2.105 A˚) is higher than that of the
IP102 (Ru–N4, 2.011 A˚), due to steric strain induced from the
additional phenyl ring of the imine ligand. Similar to the dye
IP102, the N(pyridine) atom of the ancillary ligand in IP104 is
located trans to the Ru–N(pyridine) bond [Ru–N6, 2.072 A˚] of
the anchoring ligand. However, the N(imine) atom of IP104
dye is placed trans to the other Ru–N(pyridine) bond [Ru–N5,
2.070 A˚] of the anchoring ligand, not to the NCS ligand as in
the case of the sensitizer IP102, which might be beneficial for
charge separation.
4
Fig. 3 Absorption spectra of 3×10− M solutions of IP102, IP104, and N719 in CH3CN/t-
BuOH
Electrochemical properties
Optical properties
In order for a dye to be utilized as sensitizer, it is essential to
have sufficiently lower HOMO energy level than the redox
potential of electrolyte and appropriately higher LUMO energy
level than the conduction band of TiO2, for effective dye
regeneration and efficient electron injection, respectively. The
HOMO and LUMO energy levels of the pyridylimine-based dyes
were measured by cyclic voltammetry (CV) in DMF solutions
and UV-vis absorption spectra (Fig. 3). From Table 1, the
HOMO and LUMO energy levels of the dye IP104 were lifted
up when compared to those of IP102, which are closer to
those of N719. The HOMO energy levels of these new dyes are
sufficiently lower than that of the electrolyte (I−/I3−) redox
couple for efficient dye regeneration of the photooxidized dye
and the LUMO energy levels are appropriately higher than that
of the TiO2 conduction band for facile electron injection into
the semiconductor. Furthermore, the LUMO+1 energy level of
IP104 (Fig. S1†) was delocalized between the anchoring and
the ancillary pyridyl-imine ligands which might favor the
effective charge injection into TiO2 conduction band.
The electronic absorption spectra of IP102, IP104, and
N719 in CH3CN/t-BuOH solutions are shown in Fig. 3 and the
corresponding spectroscopic data are listed in Table 1. The
absorption spectrum of the sensitizer IP102 showed two bands
centred around 394 nm and 545 nm which are attributed to
intraligand π-π* with some contribution from metal-to-ligand
charge-transfer (MLCT) band and MLCT transition,
respectively. The absorption bands in the dye IP102 are red
shifted relative to the standard N719 dye (381 nm and 528
nm). Surprisingly, the absorption spectrum of IP104 showed
slight red shift in the higher energy band (402 nm) while the
MLCT band was blue shifted with lower molar extinction
1
coefficient (
ε
) (520 nm,
ε
compared to IP102 sensitizer (545 nm,
= 0.588
×
ε
104 M− cm−1), when
1
1
= 1.15×
104 M− cm− ).
The MLCT blue shift in the lower energy region of IP104 might
be due to the decreased π back-donation from the metal Ru to
bipyridine π* orbitals associated with the destabilization of
ligand based LUMO (lowest unoccupied molecular orbital).48
Table 1 Optical and electrochemical data of the dyes
[c]
[d]
[d]
Eox[b] of RuIII/II
[V vs. Fc/Fc+]
EHOMO
ELUMO
E0-0
λmax[nm][a]
1
1
ε[104 M− cm−
]
Dye
[eV]
[eV]
[eV]
0.70, 1.15
0.40, 0.52
1.00, 0.52
IP102
IP104
N719
394, 545
402, 520
381, 528
0.48
0.36
0.30
5.28
5.16
5.10
3.64
3.49
3.45
1.64
1.67
1.65
[a] Absorption spectra were measured in CH3CN/t-BuOH solution. [b] The Ag/AgNO3 reference electrode was calibrated with a ferrocene/ferrocinium (Fc/Fc+) redox
couple. The same value for Eox of RuIII/II was obtained when the electrochemical experiments were performed using 0.1 m [nBu4N]PF6 in DMF. [c] EHOMO = Eox − EFc/Fc+
4.8 eV. [d] ELUMO EHOMO E0–0 The band gap E0–0 was estimated from the onset of the absorption spectrum measured in CH3CN/t-BuOH
+
=
−
.
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a)
Journal Name
Table 2 Photovoltaic performance of DSSCs based on IP102, IP104 and N719 sensitizers
Sensitizer
IP102
JSC
VOC
FF
η
(mA cm-2)
(mV)
(%)
4.75
16.50
18.44
610
700
740
0.706
0.630
0.646
2.04
7.27
8.81
IP104
N719
Jsc, whilst retardation in recombination dynamics should
increase Voc. Device based on IP104 showed much higher Jsc
than IP102 cell which indicated that the former device has
better charge separation. Such variation could be due to their
different structural arrangement around the ruthenium metal
(trans over cis configuration). Also, in dye IP102 the electron
donation occurs mainly from pyridine group of ancillary ligand
and one of the NCS ligand. Whereas, in IP104 the electron
pushing is contributed from the pyridine as well as the imine
groups of the ancillary ligand (as the two NSC ligand are trans
to each other) resulting in better current density. The higher
Jsc value in IP104 could also be accounted to its two trans NCS
ligands which might be placed appropriately for their readily
b)
−
interaction with the I−/I3 redox couple, thus speeding the
regeneration process of the photooxidized dye.49 The dye
IP104 with trans geometry also showed higher Voc value than
that of cis configured IP102, revealing that there is a major
difference in their recombination dynamics. The incident
photon-to-current conversion efficiencies (IPCE) of the DSSCs
based on IP102, IP104 and N719 are depicted in Fig. 4b. The
IPCE spectrum of the DSSC based on IP102 sensitizer exhibited
inferior performance compared to that of standard N719 and
Fig. 4 a) Monochromatic IPCE spectra of the photovoltaic devices (TiO2 thickness: 16
µm; cell active area tested with
a
mask: 0.16 cm2). b) Current density–voltage
IP104 dyes with value limiting to 20% in the range of 450−800
characteristics of photovoltaic devices incorporating IP102, IP104, and N719 as
nm. The IPCE spectrum of the IP104 cell exhibited
photocurrent generation near to that of N719 device and
reaching a maximum value of 68% at 520 nm.
sensitizers under illumination with AM 1.5 simulated sunlight (100 mWcm-2).
Photovoltaic performance of DSSCs
The DSSCs were fabricated using the new pyridylimine based
ruthenium sensitizers and the corresponding data are
presented in Table 2. The performance parameters of DSSC
devices were recorded under simulated AM 1.5 illumination at
IP102
20
IP104
N719
2
100 mW cm− . For comparison, a device based on N719 was
also studied under the same conditions. As shown in Fig. 4a,
10
the DSSC sensitized by IP102 exhibited
2
a
short-circuit
photocurrent (Jsc) of 4.75 mA cm−
, an open-circuit
photovoltage (Voc) of 610 mV, and a fill factor (FF) of 0.70
corresponding to an overall conversion efficiency (η) of 2.04%.
The device based on dye IP104 showed superior power
conversion efficiency of 7.27% with a Jsc of 16.50 mA cm−2, a
Voc of 700 mV, and a FF of 0.63 compared to the complex
IP102. The higher efficiency of the IP104-sensitized cell
(relative to that of the IP102 cell) arose from its higher Jsc
value. However, the overall performance of IP104 cell was
slightly lower than that of the standard N719 dye (η = 8.81%;
Jsc = 18.44 mA cm−2; a Voc = 740 mV and a FF = 0.64). The
improvements in charge separation result in an increase in
0
20
30
40
50
60
70
80
90
Z' (ohm)
Fig. 5 ESI (Nyquist plots) of DSSCs measured under AM 1.5 illumination.
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Table 3 Parameters determined by fitting the EIS experimental data of the devices to the equivalent circuit
Sensitizer
Rk
Rw
L
keff
τ
Ln
Deff
(x10-5 cm2/s)
(Ω)
(Ω)
(μm)
(ms-1)
(μm)
IP102
IP104
N719
20.7
9.4
17.7
4.3
15
15
15
12.82
17.12
14.83
78
16
22
31
3.37
8.42
14.5
123
201
7.8
1.8.
tunable pyridylimine with extended conjugation as an ancillary
ligand could be a promising alternative component to engineer
the ruthenium complexes to increase the conversion efficiency
of DSSCs.
Electrochemical impedance spectroscopy (EIS)
In order to rationalize the difference in Jsc of pyridylimine
sensitizers in detail, we performed electrochemical impedance
spectroscopy under standard AM 1.5 illumination and the
corresponding Nyquist plots are presented in Fig. 5. The fitted
EIS data, the charge transfer resistance related to the
recombination of electron at the interface (Rk), the electron
transport resistance in the photoanode (Rw), the effective rate
constant for recombination (keff), electron lifetime in
photoanode (τ), the effective electron diffusion coefficient
(Deff), and electron diffusion length (Ln) are compiled in Table
3. The radius of the semicircles in the intermediate frequency
regime of Nyquist diagram denotes the interfacial charge
transfer resistances at TiO2/dyes/electrolyte. A smaller radius
of the medium-frequency semicircle implies an improved rate
of electron generation and transport. The significant difference
in the radii of the semicircles in the EIS spectra of the DSSCs
based on IP102 and IP104 reveals that the interfacial charge
transfer mechanism of both the dyes is strongly influenced by
their geometrical arrangement around the central ruthenium
metal. As shown in Fig. 5, the device IP104 exhibited a lower
electron transport resistance (Rw = 4.3 Ω) than that of the
IP102 cell (Rw = 17.7 Ω), resulting in higher photocurrent
density. Also, from the Table 3, the longer electron lifetime (τ =
123 ms) observed for IP104 compared to IP102, indicates an
effective suppression of the back reaction of the electron with
Experimental
General methods
All the reagents and starting materials were purchased from
commercial sources such as Sigma–Aldrich, Fluka, Merck, and Alfa
Aesar etc., and used without further purification. Solvents like THF,
CH2Cl2, and DMF were dried using VAC purifier (VAC 103991,
Vacuum Atmospheres). All the other solvents were of HPLC grade.
The N719 dye was procured from Solaronix. All the intermediates
and sensitizers were characterised by 1H and 13C NMR spectra using
a Bruker 300 or 500 MHz spectrometer. UV−vis spectra have been
recorded on Shimadzu UV3600 UV-vis-NIR spectrophotometer.
Electrospray ionization mass spectrometry measurements were
performed using a JMS-700 HRMS spectrometer.
Synthesis and characterization of dyes IP102 and IP104
Synthesis of ligand 4a: To
a
solution of 2-
pyridinecarboxaldehyde (2a) (1.00 g, 9.29 mmol) and 2,6-
dimethylaniline (1.13 g, 9.29 mmol) in ethanol (19.34 mL) were
added a few drops of formic acid at room temperature. The
reaction mixture was stirred at 60°C for 5h, and then the
solvent was evaporated under reduced pressure. The yellow
crystalline solids (4a) were collected by recrystallization from
hexane in 82% yield (1.60 g). 1H NMR (300 MHz, CDCl3) δ:
(ppm) 8.72 (d, 6.4 Hz, 1H), 8.34 (s, 1H), 8.29 (dt, J =7.9,1.1
Hz,1H), 7.84 (td, J = 7.7, 1.7 Hz, 1H), 7.41 (ddd, J = 7.5, 4.8, 1.3
Hz, 1H), 7.09 (d, J = 7.5 Hz, 2H), 6.98 (dd, J = 8.3, 6.6 Hz, 1H),
2.17 (s, 6H). 13C NMR (75 MHz, CDCl3) δ: 163.3, 154.3, 150.2,
149.5, 136.6, 128.0, 126.7, 125.2, 124.0, 121.1, 18.2.
−
the I3 in the electrolyte, reflected in the improvement of the
photovoltage. Moreover, the trend of the Voc of IP dyes and
N719 was further elucidated by measuring EIS under dark
condiꢀons (Fig. S2†). Despite its inferior absorption properties,
the EIS results support the higher efficiency of the IP104 cell
which might be influenced by the trans geometry around the
central ruthenium metal leading to better charge separation.
Synthesis of Ru(II) complex 5a: To a round-bottom flask
charged with 4a (0.200 g, 0.95 mmol) and [RuCl2(p-cymene)]2 (0.305
g, 0.47 mmol) was added CH2Cl2 (47.5 mL) and the reaction mixture
was stirred at room temperature. After 8 h, the solvent was
removed under vacuum and the resulting crude product was
Conclusions
Two new ruthenium sensitizers consisting pyridylimine
ancillary ligands were designed, synthesized, and evaluated for
their application in DSSCs for the first time. The pyridylimine
ligands were fine-tuned by inducing steric effect to obtain two combined with 4,4’-dimethoxycarbonyl-2,2’-bipridine (0.258 g, 0.95
sensitizers with cis and trans geometry around the ruthenium
metal and the effects of the configuration of these dyes on the
device performance were scrutinized. The cell based on IP104
sensitizer with trans arrangement achieved overall power
conversion efficiency of 7.27% and outperformed the cell with
cis configured dye IP102. To the best of our knowledge, the
IP104 cell exhibited the highest efficiency reported for the
pyridylimine-based Ru(II) complexes. Overall, the easily
mmol) in 1,2-dichloroethane (47.5 mL). The resulting mixture was
o
stirred at 80 C for 6 h. After evaporating the solvent, the crude
product was dried and added to a suspension of potassium
thiocyanate (0.923 g, 9.50 mmol) in H2O/DMF (47.5 mL, 1:9). The
reaction mixture was heated to 85 oC and stirred for 16 h. The
solvent was evaporated under reduced pressure. The residue was
diluted with CH2Cl2 (50 mL), washed with H2O (3×35 mL), dried
(Na2SO4), and concentrated. The crude compound was purified by
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column chromatography using ethyl acetate/dichloromethane (1:9, HRMS (m/z): [M+H]+ calcd. for (C36H31O4N6RuS2): 777.0886; found,
v/v) as eluent and then recrystallized (ether/CH2Cl2) to afford the 777.0887.
ester complex 5a as deep-purple crystals (0.199 g, 30 %). 1H NMR
Synthesis of pyridylimine dye IP104: The complex IP104 was
(500 MHz, DMSO-d6) δ: (ppm) 9.27 (d, J = 5.35 Hz, 1H), 9.13 (d, J =
prepared from compound 5b using a method similar to that
5.85 Hz, 1H), 8.97-8.96 (m, 2H), 8.81 (s, 1H), 8.38 (d, J = 7.50 Hz,
described for the synthesis of IP102. Yield: 85%; as a dark-purple
1
1H), 8.33 (td, J = 1.25, 7.73 Hz, 1H), 8.17 (d, J = 5.95 Hz, 1H), 8.14-
solid. H NMR (500 MHz, DMSO-d6) δ: (ppm) 9.47 (s, 2H), 9.05 (s,
8.11 (m, 1H) 7.99 (dd, J = 1.60, 2.91 Hz, 1H), 7.82 (dd, J = 1.70, 5.92
1H), 8.99 (s, 1H), 8.17-8.23 (m, 2H), 7.99 (s, 1H), 7.61 (d, J = 6.15 Hz,
Hz, 1H), 6.80 (m, 2H), 6.59 (d, J = 7.00 Hz, 1H), 3.97 (s, 3H), 3.95 (s,
1H), 7.52-7.42 (m, 3H), 7.41-7.38 (m, 1H), 7.36-7.24 (m, 4H) 7.21-
3H), 2.22 (s, 3H), 0.65 (s, 3H). 13C NMR (125 MHz, DMSO-d6) δ:
7.12 (m, 2H), 7.17 (d, J = 6.15 Hz, 2H), 2.08 (s, 6H). 13C NMR (125
171.9, 164.0, 163.9, 159.2, 156.9, 156.8, 154.3, 153.3, 152.2, 146.8,
MHz, DMSO-d6) δ: 176.5, 165.0, 164.8, 159.2, 158.9, 158.5, 155.1,
137.1, 136.6, 136.0, 135.4, 129.4, 128.6, 128.3, 127.6, 127.4, 126.3,
154.7, 152.8, 147.0, 137.7, 132.9, 132.7, 130.9, 130.3, 129.14,
125.3, 124.8, 122.3, 121.8, 53.2, 18.3, 15.4. HRMS (m/z): [M+Na]+
128.8, 128.4, 127.7, 127.3, 127.0, 124.9, 18.8 HRMS (m/z): [M]+
calcd. for (C30H26O4N6NaRuS2): 723.0393; found, 723.0418.
calcd. for (C34H26N6O4RuS2): 748.0495; found, 748.0480.
Synthesis of pyridylimine dye IP102: To a solution of compound
5a (40.0 mg, 0.057 mmol) in DMF (2.86 mL) was added 0.5 M Electrochemical measurement
o
LiOH(aq) (0.313 mL, 0.157 mmol) at 0 C, and the reaction mixture
Cyclic voltammetry (CV) analyses were performed using a CHI 627 C
was stirred for 2 h. After the hydrolysis was completed, the solvent
electrochemical analyzer (CH Instruments) and a conventional
was evaporated. The residue was dissolved in water (2.86 mL), and
single-compartment, three-electrode cell. A glassy carbon electrode
then 0.1 M HCl(aq) was added to precipitate the product. The solid
and a silver wire (Ag/AgNO3 in acetonitrile) were served as the
was filtered, washed with water (3×6 mL), and dried under vacuum
working electrode and the reference electrode, respectively while a
to afford IP102 as a dark-purple solid (36.48 mg, 95%). 1H NMR (500
Pt wire was utilized as a counter-electrode. Dye solutions were
3
MHz, DMSO-d6) δ: (ppm) 9.28 (d, J = 5.15 Hz, 1H), 9.08 (d, J = 5.75
prepared with 1 x 10− M concentrations in DMF and a 0.1 M
Hz, 1H), 8.97 (s, 1H), 8.86 (s, 1H), 8.70 (s, 1H), 8.37 (d, J = 7.60 Hz,
solution of tetrabutylammonium hexafluorophosphate was used as
1H), 8.31 (t, J = 7.60 Hz, 1H), 8.12-8.09 (m, 2H), 7.95-7.94 (m, 1H),
the supporting electrolyte. Ferrocene was utilized as the internal
7.80-7.78 (m, 1H), 6.81-6.78 (m, 2H) 6.60 (d, J = 7.00 Hz, 1H), 2.22
(s, 3H), 0.65 (s, 3H). 13C NMR (125 MHz, DMSO-d6) δ: 172.1, 165.5,
reference for calibration of the obtained redox potentials. The cyclic
voltammograms of IP102, IP104 and N719 were record at a typical
scan rate of 50 mV s-1.
165.4, 159.5, 157.3, 157.2, 154.4, 153.4, 152.7, 147.4, 139.3, 138.4,
137.4, 136.1, 135.4, 136.1, 135.8, 129.8, 129.7, 128.9, 128.7, 128.0,
127.9, 126.7, 126.7, 126.0, 125.4, 122.8, 122.3, 18.7, 15.8. HRMS
Preparation of TiO2 electrodes and DSSC devices
(m/z): [M-H]- calcd. for (C28H21N6O4RuS2): 803.3233; found,
The preparation of the TiO2 nanoparticles was carried out by
803.3241.
hydrothermal process as follows. The starting precursor Ti(O-Bu)4
Synthesis of ligand 4b: A mixture of 2-Benzoylpyridine (2b)
(22.0 g) was dissolved into 2.0 M CH3COOH(aq) (108.4 mL) and then
(1.09 g, 5.95 mmol), 2, 6-dimethylaniline (3) (0.721 g, 5.95 mmol),
stirred vigorously for 5 days. The resulting homogeneous solution
and p-toluenesulfonic acid (0.134 g, 0.704 mmol) in toluene (50 mL)
was subjected to the hydrothermal treatment in an autoclave at
o
was taken into a round bottom flask equipped with a Dean−Stark
trap. The reaction mixture was refluxed under nitrogen atmosphere
200 C for 5 h, and then the obtained TiO2 colloidal solution was
centrifuged twice with ethanol. The residue was dissolved into
for 48 h. After the reaction was completed, the solvent was
absolute ethanol (60 mL) and the mixture was stirred vigorously
evaporated and the residue was suspended in diethyl ether (50 mL).
followed by ultra-sonication. The resulting solution was mixed with
The undissolved white solid was filtered and the filtrate was
α-Terpineol (38.94 g) and a mixture of ethyl cellulose (10 cps 2.73 g
evaporated under vacuum to afford a crude compound which was
and 45 cps 2.10 g) in anhydrous ethanol (43.5 mL) and then
purified
by
column
chromatography
using
ethyl
sonicated repeatedly. The solvent was evaporated under reduced
pressure of 70 mbar and the a-TiO2 was finalized after grinding. For
the preparation of the TiO2 scattering layer, in a round bottom flask,
2.0 g of QF-1125 TiO2 powder of particle size around 200~300 nm
acetate/dichloromethane (2:8, v/v) as eluent to get the desired
product 4b as an yellow solid (0.85 g, 50 %) HRMS (m/z): [M+H]+
calcd. for (C20H19N2): 287.1543; found, 287.1547.
Synthesis of Ru(II) complex 5b: The ester 5b was prepared from was suspended in 80 mL anhydrous ethanol. After sonication for 2
compound 4b using a method similar to that described for the min., the above solution was combined with α-Terpineol (12.98 g)
1
synthesis of the ester 5a. Deep-green crystals with 15 % yield. H and a solution of ethyl cellulose (10 cps 0.90 g and 45 cps 0.70 g) in
NMR (500 MHz, CDCl3) δ: (ppm) 9.29 (d, J = 5.75 Hz, 1H), 9.18 (d, J = anhydrous ethanol (14.4 mL). The mixture was then subjected to
5.00 Hz, 1H), 8.72 (s, 1H), 8.64 (s, 1H), 8.14 (dd, J = 2.84, 1.60 Hz, repeated sonication. Finally, the dispersed solution was
o
1H), 7.92 (td, J = 7.80, 1.35 Hz, 1H), 7.69 (t, J = 5.95 Hz, 1H), 7.57 (d, concentrated by evaporator at 40 C with 70 mbar. The QF-1125
J = 7.5 Hz, 1H), 7.46 (d, J = 5.85 Hz, 1H), 7.41-7.34 (m, 4H), 7.28 (d, J paste was finalized after grinding by three-roller-miller grinder.
= 7.28 Hz, 2H), 7.17 (t, J = 7.58 Hz, 1H), 7.06 (d, J = 7.45 Hz, 2H), 4.09
The TiO2 electrode was prepared by spreading the TiO2 paste
(s, 3H), 4.01 (s, 3H), 2.18 (s, 6H). 13C NMR (125 MHz, CDCl3) δ:
onto fluorine-doped SnO2 conducting glass (FTO, Hartford Glass;
176.8, 164.1, 164.0, 160.2, 159.8, 159.5, 154.9, 154.4, 154.1, 147.3,
sheet resistance: 8Ω/□; transmiꢁance ≥ 80%; HAZE 5%).
Subsequently, the TiO2 electrodes were dried in air and heated at
138.4, 137.5, 136.9, 133.5, 132.9, 131.9, 130.6, 129.2, 129.1, 128.6,
128.2, 127.6, 126.2, 124.4, 123.2, 121.7, 121.3, 53.6, 53.7, 19.5.
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o
o
100 C for 15 min, followed by annealing at 450 C for 30 min. The
TiO2 scattering layer was also coated followed by the above
procedure using the QF-1125F TiO2 paste. The average thickness of
the TiO2 film was 15 ꢀm, measured using a Force EZstep profiler.
The resulting TiO2 electrode was scraped to an active area of 0.25
Notes and references
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3
4
5
o
cm2 (0.5 cm x 0.5 cm), followed by heat treatment at 80 C. Dye
solutions of N719, IP102, and IP104 with 3 x 10-4 M concentration in
1:1 CH3CN/t-BuOH (v/v) were prepared and then the electrodes
were soaked for 36 h. The Pt counter electrodes were prepared by
sputter-deposition of 20-nm-thick Pt layers onto FTO substrates
using a Hitachi E-1045 ion sputter. Prior to assembling of the DSSCs,
two holes were drilled on the counter electrodes. The Pt electrodes
were then placed over the dye-adsorbed TiO2 electrodes. The edges
of the cells were sealed with Surlyn 1702 (Dupont; thickness: 125
mm) spacer at 100 oC. To complete the DSSC fabrication, the
electrolyte was injected into the intervening space between the
TiO2 and Pt electrodes through the two holes, which were then
covered with a microscope slide and sealed with Surlyn spacer. The
electrolyte solution comprised of 0.5 M Lithium Iodide, 0.05 M
Iodide, 0.5 M 1,2-dimethyl-3- propylimidazolium iodide, and 0.5 M
tert-butylpyridine in acetonitrile was employed as the redox
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DSSC performance measurements
Photovoltaic parameters were measured utilizing a Keithley model
2400 source unit equipped with an A-class solar simulator of 300-W
Xenon light source (Oriel, No. 91160) with an AM 1.5 filter (Oriel,
No. 81094). The power of the output light at the cell measuring
2
position was calibrated to 100 mW cm− using a certified reference
14
15
S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, F. E.
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photon-to current conversion efficiencies (IPCEs), an equipment,
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monochromator (Oriel CornerstoneTM 130) and Keithley model
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16
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EIS measurements
The electrochemical impedance spectroscopy (EIS) was studied
using an impedance analyzer (IM6ex, Zahner, Germany) under
illumination condition of 100 mW/cm-2 with an ac amplitude of 10
mV and frequency range of 10-1-105 Hz. The Z-View software was
utilized for modeling and fitting the EIS data of DSSCs to obtain the
electron transport parameters of cells. The equivalent circuit (Fig.
S2†) and calculations of EIS parameters are provided in the
supporting information.
19
20
21
Conflicts of interest
The authors declare no competing financial interest.
22
23
Acknowledgements
24
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M. K. Nazeeruddin, R. Splivallo, P. Liska, P. Comte and M.
Grätzel, Chem. Commun., 2003, DOI: 10.1039/B302566G,
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M. K. Nazeeruddin, P. Péchy, T. Renouard, S. M.
Zakeeruddin, R. Humphry-Baker, P. Comte, P. Liska, L.
We thank the National Science Council, ROC, for financial
support (grants: MOST 103-2113M-008-008-MY3 and MOST
104-2113M-027-005- MY3).
This journal is © The Royal Society of Chemistry 20xx
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Table of Contents
Effect of Cis-trans Configurational Difference on the Performance of
Pyridylimine-based Ruthenium Sensitizers
Yogesh S. Tingare, ‡a Suri Babu Akula, ‡a Ming-Tai Shen,a Chaochin Su,*b Shih-Yu Ho,b
Sheng-Han Tsai,b Ya-Fen Lin,a and Wen-Ren Li,*a
IP102
IP104
15
OH
H
OH
O
O
N
O
O
N
N
N
N
N
N
N
N
Ru
Ru
C
S
10
5
OH
OH
IP104
IP102
cis-configuration
trans-configuration
0
0.0
0.2
0.4
0.6
Voltage (V)
The effect of configurational difference on DSSC performance was studied with
pyridylimine-based ruthenium dyes. The device with the trans configured sensitizer
showed higher overall conversion efficiency (η) of 7.27 % than that of the cis
configured complex (η = 2.04%)