New ruthenium sensitizers containing styryl and antenna fragments

Article abstract of DOI:10.1016/j.ica.2007.04.050

Amphiphilic ligands 4′-((4-(5-pyridin-4-yloxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L1), 4,4′-bis((E)-4-(5-(pyridin-4-yloxy)pentyloxy)styryl)-2,2′-bipyridine (L2), 4′-(4-(5-(4′-cyano-4-biphenoxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L3), and 4′-(4-(5-(zinc tetrakis-5,10,15-tritolyl-20-(4-hydroxyphenyl)porphyrin)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L4) and their heteroleptic ruthenium(II) complexes of the types [Ru(L1)(L)(NCS)₂] (D20), [Ru(L2)(L)(NCS)₂] (D21), [Ru(L3)(L)(NCS)₂] (D22), and [Ru(L4)(L)(NCS)₂] (D23) (where L = 4,4′-bis(carboxylic acid)-2,2′-bipyridine) have been synthesized, as photosensitizers for nanocrystalline dye-sensitized solar cells. All complexes D20-D23 exhibit a broad MLCT band around 520-530 nm in DMF and an emission band around 740-790 nm in DMF. We have studied photovoltaic performances based on the newly synthesized dyes. Under standard AM 1.5 sunlight, the dye D20 gave a short-circuit photocurrent density of 13.31 mA/cm², an open-circuit voltage of 0.64 V, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 5.81%.

Full text of DOI:10.1016/j.ica.2007.04.050

Inorganica Chimica Acta 360 (2007) 3518–3524
www.elsevier.com/locate/ica
New ruthenium sensitizers containing styryl and antenna fragments
*
*
Il Jung, Hyunbong Choi, Jae Kwan Lee, Kyu Ho Song, Sang Ook Kang , Jaejung Ko
Department of Chemistry, Korea University, Jochiwon, Chungnam 339-700, Republic of Korea
Received 23 November 2006; received in revised form 13 April 2007; accepted 17 April 2007
Available online 13 May 2007
Abstract
Amphiphilic ligands 40-((4-(5-pyridin-4-yloxy)pentyloxy)styryl)-4-methyl-2,20-bipyridine (L1), 4,40-bis((E)-4-(5-(pyridin-4-yloxy)pen-
tyloxy)styryl)-2,20-bipyridine (L2), 40-(4-(5-(40-cyano-4-biphenoxy)pentyloxy)styryl)-4-methyl-2,20-bipyridine (L3), and 40-(4-(5-(zinc
tetrakis-5,10,15-tritolyl-20-(4-hydroxyphenyl)porphyrin)pentyloxy)styryl)-4-methyl-2,20-bipyridine (L4) and their heteroleptic ruthe-
nium(II) complexes of the types [Ru(L1)(L)(NCS)2] (D20), [Ru(L2)(L)(NCS)2] (D21), [Ru(L3)(L)(NCS)2] (D22), and [Ru(L4)(L)
(NCS)2] (D23) (where L = 4,40-bis(carboxylic acid)-2,20-bipyridine) have been synthesized, as photosensitizers for nanocrystalline
dye-sensitized solar cells. All complexes D20–D23 exhibit a broad MLCT band around 520–530 nm in DMF and an emission band
around 740–790 nm in DMF. We have studied photovoltaic performances based on the newly synthesized dyes. Under standard
AM 1.5 sunlight, the dye D20 gave a short-circuit photocurrent density of 13.31 mA/cm2, an open-circuit voltage of 0.64 V, and
a fill factor of 0.68, corresponding to an overall conversion efficiency of 5.81%.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Ru; Dye-sensitized; Alkoxy-pyridine unit; Porphyrin; Solar cell; Amphiphilic
1. Introduction
ful synthetic method has been to replace one of the 2,20-
bipyridyl-4,40-dicarboxylate groups in the N3 dye by a sty-
ryl-substituted bipyridine [5] or by an antenna fragment.
This not only increases the extinction coefficient of the sen-
sitizer but also its hydrophobicity, stabilizing device perfor-
mance under long-term light soaking.
Dye-sensitized solar cells are attracting widespread
interest for the conversion of sunlight into electricity
because of their low cost and high efficiency [1]. In these
cells, the dye is one of the key elements for high-power con-
version efficiencies. Several Ru(II) complexes such as
([Ru(dcbpyH2)2(NCS)2]) (N3) and ((Bu4N)2[Ru(dcb-
pyH)2(NCS )2]) (N719) have been used in DSSCs as effi-
cient sensitizers [2]. Considerable attention has been
focussed on understanding the factors that control cell per-
formance to improve the conversion efficiency and stability
of DSSCs. Thus the quest for new dyes that efficiently har-
vest solar light and meet the stability criteria continues to
be an important goal. The enhanced absorption is expected
by extending the conjugated system of the hydrophobic
spectator ligand [3] or by substituting the sensitizer mole-
cule with a sensitizer–antenna molecular unit [4]. A success-
A recent work by Gra¨tzel’s group [6] has revealed that
the use of K-19 as amphiphilic bipyridyl ruthenium com-
plex is promising. The dye has an alkoxy styryl group in
its ligand and this ligand was reported to enhance the har-
vesting of solar light as well as to retain the stability.
Recently, we [7] reported the oligophenylenevinylene-func-
tionalized Ru(II)-bipyridine sensitizers for efficient dye-
sensitized nanocrystalline TiO2 solar cells relative to that
of a cell using N3 dye. Polynuclear complexes exhibiting
an antenna effect were also investigated as sensitizers for
DSSCs, in which only one metal complex is directly
attached to TiO2 film through its anchoring ligand [8].
Kim and co-workers [9] reported that the linking of N3
with another TiO2-attached N3 through trans-1,2-bis(4-
pyridyl)ethylene rendered an enhanced short-circuit photo-
current and thereby conversion efficiency for the pertinent
*
Corresponding authors. Tel.: +82 41 860 1337; fax: +82 41 867 5396
(J. Ko).
E-mail address: jko@korea.ac.kr (J. Ko).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.04.050

I. Jung et al. / Inorganica Chimica Acta 360 (2007) 3518–3524
3519
N
DSSC due to an antenna effect. Sugihara [10] also reported
N
5
5
O
O
that addition of heterocycles such as pyridine and quino-
line in electrolyte for the pertinent DSSC rendered an
enhanced conversion efficiency with increasing open-circuit
voltage due to an intermolecular charge interaction with
iodine electrolyte.
O
O
N
O
5
O
We envisioned that the introduction of pyridyl, cyanobi-
phenyl [11] or porphyrin [12] unit in the peripheral position
of bipyridyl ruthenium complex shows an enhanced con-
version efficiency because the antenna unit has the role of
absorbing the incident light and transferring the electronic
energy to the sensitizer fragment. In line with the continu-
ation of the efforts in this direction for improving the solar
energy conversion efficiency, we synthesized new type of
ruthenium sensitizers, consisting of both styryl and
antenna fragment as light harvester. These extended conju-
gation dyes were successfully employed in DSSCs.
N
N
SCN
SCN
N
N
Ru
N
Ru
SCN
SCN
N
N
N
OH
OH
O
O
O
O
OH
OH
D21
D20
N
CN
2. Results and discussion
N
Zn
N
N
5
O
5
O
2.1. Synthesis of dyes
O
O
The novel ruthenium dyes D20–D23 were synthesized by
the stepwise synthetic protocol illustrated in Scheme 1.
Ligands L1–L4 were synthesized in two steps using
O-alkylation and Wittig coupling reaction. The reaction
of [Ru(p-cymene)Cl2]2 complex with L1–L4 in DMF under
nitrogen resulted in a mononuclear complex. The hetero-
leptic dichloro complexes were synthesized by reaction of
the mononuclear complex with 4,40-dicarboxyl-2,20-bipyri-
dine. The chloro complexes were reacted with a large excess
of ammonium thiocyanate ligand to afford the ruthenium
dyes D20–D23 (Scheme 1). The complexes D20–D23 were
spectroscopically characterized, and all data are consistent
with the formulated structures (Fig. 1).
N
N
N
SCN
SCN
N
Ru
SCN
Ru
N
N
SCN
N
N
OH
OH
O
O
O
OH
O
OH
D23
D22
Fig. 1. Structures of complexes D20–D23.
tionship of the MLCT band among D20–D22 is similar
to that of cis-[Ru(H2dcbpy)2X2] (X = Cl or SCN) [13].
The molar extinction coefficient of the lowest energy
MLCT band in D22 is slightly higher than those of two
dyes D20 and D21 due to the introduction of cyanobiphe-
nyl as light harvester. However, the molar extinction coef-
ficient of the MLCT band in D22 is lower about 15%
compared to that of cis-dithio-cyanato(4,40-dicarboxylic
acid-2,20-bipyridine)ruthenium(II) complex [14].
2.2. Optical and electrochemical properties of dyes
Fig. 2a shows the UV/Vis spectra of the dyes D21 and
D22 measured in DMF solution and the data are collected
in Table 1. The strong absorption band of D20–D22
around 300 nm is due to p–p* transition. Two absorption
maxima at 360–370 nm and 522–532 nm, which are due
to the metal-to-ligand charge-transfer (MLCT) bands in
DMF, are observed in the spectra of D20–D22. The rela-
R
R
R
R'
R'
HOOC
COOH
R'
N
SCN
N
NH4NCS
DMF
N
N
N
N
Ru
N
[RuCl2(p-cymene)]2
SCN
N
DMF
80 c
DMF
160
c
130 c
˚
˚
˚
OH
O
O
OH
= L1 - L4
N
N
Scheme 1. Synthetic protocol for the preparation of D20–D23.

3520
I. Jung et al. / Inorganica Chimica Acta 360 (2007) 3518–3524
face titanium anions [16]. The absorption intensity of D23
a
10
8
10
8
on the TiO2 film is lower than those of D20–D22, indicat-
ing that D23 is less efficiently absorbed on the TiO2 surface
than D20–D22.
The emission maxima of D20–D22, which were obtained
at room temperature by excitation within their MLCT
bands at 530 nm in an air-equilibrated DMF solution,
are summarized in Table 1. Fig. 2a shows representative
emission spectra of D21 and D22. They exhibit strong
luminescence maxima at 789 and 746 nm, respectively, stee-
ply rising at 650 nm. From the intersection of the lowest
energy absorption and its emission band, one derives for
the E0ꢀ0 transition energy of D21–D22 a value of 2.02
and 2.03 eV [17].
6
6
4
4
2
2
0
0
900
300
400
500
600
700
800
Wavelength (nm)
To thermodynamically evaluate the possibility of elec-
tron transfer from the excited state of the dye to the con-
duction band of TiO2 electrode, cyclic voltammogram
was carried out to determine the redox potential (Table
1). The redox potentials of four ruthenium dyes D20–
D23 on TiO2 films were measured in CH3CN with 0.1 M
tetrabutylammonium hexafluorophosphate (n-C4H9)4-
NPF6. The oxidation potential of D20 shows a quasi-
reversible behavior at 0.31 V (versus Fc/Fc+) with a peak
separation of 0.09 V, which is attributed to the RuIII/II
redox couple and is in good agreement with the reported
value of 0.38–0.40 V (versus Fc/Fc+) for a similar type of
complex and N3 [18]. The separation between the cathodic
and the anodic wave at a scan rate of 50 mV sꢀ1 is 250 mV.
Dyes D21, D22, and D23 show a quasi-reversible couple at
0.32, 0.41, and 0.23 V, respectively, assigned to the metal-
centered oxidation process. The RuIII/II oxidation potential
of dye D22 is more positive than those of dyes D20, D21,
and D22. This implies the increased electron donating
properties of ligands L1, L2, and L4, compared to that
of L3. The reduction potentials of D20–D23 calculated
from the oxidation potential and the E0ꢀ0 determined from
the intersection of absorption and emission spectra are
listed in Table 1. The excited state oxidation potential
(Eꢁox) of the dyes (D20: ꢀ1.96 V versus Fc/Fc+, ꢀ1.29 V
versus NHE; D21: ꢀ1.70 V versus Fc/Fc+, ꢀ1.03 V versus
NHE; D22: ꢀ1.62 V versus Fc/Fc+, ꢀ0.95 V versus NHE;
D23: ꢀ1.67 V versus Fc/Fc+, ꢀ1.02 V versus NHE) is
much negative than the conduction band level of TiO2 at
b
5
4
3
2
1
0
1
0
500
600
700
800
400
500
600
Wavelength (nm)
700
800
Fig. 2. (a) Absorption and emission spectra of dyes D21 (
(----). (b) Absorption spectra of D23 in DMF (
TiO2 film ( ). The inset shows the expanded absorption spectra.
) and D22
) and adsorbed on
The UV/Vis spectrum of the dye D23 exhibits an intense
soret or B-band around 425 nm, assigned to a p–p* transi-
tion to the second electronic excited state, and two Q-bands
at 562 and 604 nm, corresponding to p–p* transition to the
first electronic excited state [15]. In addition to that, the dye
D23 shows a broad visible band at 518 nm due to MLCT
transition. When the dye D23 was absorbed to TiO2 elec-
trode, a slight red shift from 518 to 521 nm was found
due to the interaction of the anchoring group with the sur-
Table 1
Optical, redox and DSSC performance parameters of dyes
kabsa/nm (e/dm3 Mꢀ1 cmꢀ1
)
Eoxb(DEp) (V)
E0–0 (V)
ELUMO (V)
ELUMO (V) vs. NHE
Jsc (mA cmꢀ2
)
Voc (V)
ff
ge (%)
c
d
Dye
D20
D21
D22
D23
N3
522 (10400)
532 (9820)
527 (11400)
518 (5840)
530 (14100)
0.31 (0.25)
0.32 (0.14)
0.41 (0.14)
0.23 (0.19)
0.38 (0.05)
2.27
2.02
2.03
1.92
2.03
ꢀ1.96
ꢀ1.70
ꢀ1.62
ꢀ1.69
ꢀ1.65
ꢀ1.29
ꢀ1.03
ꢀ0.95
ꢀ1.02
ꢀ0.98
13.31
9.32
8.79
6.45
13.13
0.64
0.65
0.67
0.63
0.73
0.68
0.73
0.69
0.73
0.66
5.81
4.40
4.09
2.98
6.32
a
Absorption spectra were measured in DMF solution.
b
c
Redox potential of dyes on TiO2 was measured in CH3CN with 0.1 M (n-C4H9)4N-PF6 with a scan rate of 50 mV sꢀ1 (vs. Fc/Fc+).
E0ꢀ0 was determined from intersection of absorption and emission spectra in DMF.
d
e
ELUMO was calculated by Eox ꢀ E0ꢀ0
.
Performances of DSSCs were measured with 0.18 cm2 working area.

I. Jung et al. / Inorganica Chimica Acta 360 (2007) 3518–3524
3521
approximately ꢀ0.5 V versus NHE [18]. Therefore, the
LUMO levels of these dyes D20–D23 are sufficiently nega-
tive to inject electrons into the conduction band of TiO2.
D20–D23 is ineffective for inducing self-organization near
the surfaces of their TiO2 nanoparticles, in a fashion facil-
itating the Voc increase. It was well documented that the
open-circuit photovoltage (Voc) of solar cells sensitized
with ruthenium dyes increased when 4-tert-butylpyridine
was added into an electrolyte because TBP is regarded as
2.3. Photovoltaic performance
Fig. 3 shows the typical photocurrent–voltage (J–V)
curves of five DSSCs fabricated with TiO2 films, which
are anchored with N3, and D20–D23. The photovoltaic
performances of the devices are listed in Table 1. Under
standard global AM 1.5 solar condition, an overall conver-
sion efficiency (g) of 5.81% was attained from the D20 sen-
sitized cell with Jsc of 13.31 mA/cm2, Voc at 0.64 V, and ff
of 0.68. Under the same conditions, we obtained g of 6.32%
for the Ru(dcbpy)2(NCS)2/TiO2 solar cell (short-circuit
photocurrent density, Jsc = 13.13 mA/cm2; open-circuit
photovoltage, Voc = 0.73 V; fill factor, ff = 0.66), indicat-
ing that g for the D20/TiO2 solar cell is about0.5% inferior
to that of the N3/TiO2 solar cell.
a blocking agent of reverse electron transfer and
shifts the Ecb value more negatively [19]. We anticipated
that the presence of pyridine moiety in D20–D21 increased
the open-circuit voltage due to the suppression of the dark
current at the semiconductor electrolyte injection. How-
ever, the open-circuit voltages of the dyes D20–D21 rela-
tive to those of D22–D23 were not increased. It
demonstrates that the long alkyl chains with pyridine moi-
ety in D20–D21 could not form hydrophobic layers around
their corresponding TiO2 particles. The formation of such
a layer can reduce the back electron transfer from the con-
ꢀ
duction band of TiO2 to the I3 ions in the electrolyte solu-
tion and thereby increase the Voc [18d,20].
By contrast, the D23 sensitized cell gave an overall effi-
ciency (g) of 2.98% with low Jsc of 6.45 mA/cm2. The low
performance of the D23/TiO2 solar cell is due at least to
the inefficient absorption of the dye. The Jsc enhancement
of D20 relative to D23 can be correlated with the increased
amount of dye molecules on TiO2. The amount of
adsorbed dyes D20–D23 was determined by desorbing
the dyes from the TiO2 surfaces from the KOH
(3.5 · 10ꢀ5 M) in ethanol. With use of molar absorptivities
in Table 1, the moles of D20–D23 absorbed to their TiO2
films of 0.5 cm · 0.5 cm · 10 lm are found to be
2.3 · 10ꢀ8, 1.7 · 10ꢀ8, 1.6 · 10ꢀ8, and 1.1 · 10ꢀ8 mol,
respectively. The low absorption of D23 can be interpreted
to be due to the presence of a bulky porphyrin group. The
bulky sensitizers require more space on the TiO2 surface
and penetrate less easily in the small cavities of the nano-
crystalline TiO2 than the sterically less hindered complexes.
Contrary to a big chance of Jsc in the dyes D20–D23, the
invariance of Voc of the cells with the four sensitizers
The incident monochromatic photon-to-current con-
version efficiencies (IPCEs) for the DSSCs based on the
five dyes are presented in Fig. 4. The IPCE data of D20
sensitizer plotted as a function of excitation wavelength
exhibit a high plateau at 58%. The decline of the IPCE
above 600 nm toward the red is caused by the decrease
in the extinction coefficient of D20. In contrast, the DSSC
based on D22 shows a relatively low IPCE with the max-
imum of 46% at 535 nm. The IPCE spectrum of D20 is
red shifted by about 20 nm compared to the D22 as a
result of increased amount of dye molecules on TiO2.
Therefore, the increased absorption coefficient of D22 rel-
ative to D20 does not necessarily lead to an enhanced
light absorption on the TiO2 electrode because of the
reduced surface concentration of the bulkier dye on the
nanoporous TiO2.
In summary, we have synthesized new efficient dyes
D20–D23 containing the chromophores such as cyanobi-
phenyl or porphyrin unit. The photovoltaic performance
70
60
50
40
30
20
10
0
400
500
600
700
800
Wavelength (nm)
Fig. 3. Photocurrent–voltage characteristics of representative TiO2 elec-
Fig. 4. Typical action spectra of incident photon-to-current conversion
efficiencies (IPCE) obtained for nanocrystalline TiO2 solar cells sensitized
trodes sensitized with dyes: N3 (—), D20 (
), D23 ( ).
), D21 (
), D22
(
by N3 (—), D20 (
), D21 (
), D22 (
), D23 (
).

3522
I. Jung et al. / Inorganica Chimica Acta 360 (2007) 3518–3524
of the solar cells sensitized with D20–D23 was compared
with that of the N3-sensitized cell. A solar-to-electricity
conversion efficiency of 5.81% in D20 is comparable to
g of 6.32% for the N3/TiO2 solar cell. However, the D23
sensitized cell gave an overall efficiency (g) of 2.98%. The
low efficiency of D23 is correlated with lower absorption
coefficient of this dye due to the decreased amount of dye
molecules on TiO2. Analysis of the absorption spectra of
the dye-coated TiO2 films and the desorbed dyes in an
aqueous KOH solution indicates that D23 sensitizer was
less absorbed to its TiO2 films due to the presence of a
bulky porphyrin group. By modulating the substituted
group, we can design more efficient dyes for photovoltaic
performance.
[M+]. Anal. Calc. for C29H29N3O2: C, 77.13; H, 6.47.
Found: C, 76.86; H, 6.35%.
3.2. 4,40-Bis((E)-4-(5-(pyridin-4-yloxy)pentyloxy)styryl)-
2,20-bipyridine (L2)
A mixture of 4-(5-(pyridin-4-yloxy)pentyloxy)benzalde-
hyde (0.48 g, 2.2 mmol), 4,40-bis(diethylphosphonom-
ethyl)-2,20-bipyridine (0.45 g, 1.0 mmol), and potassium
tert-butoxide (0.48 g, 4.2 mmol) was vacuum-dried and
added to THF (60 mL). The solution was refluxed for
12 h. After cooling the solution, H2O (50 mL) and methy-
lene chloride (50 mL) were added. The organic layer was
separated and dried with MgSO4. The organic layer was
removed in vacuo. The pure product L2 was obtained by
silica gel chromatography (eluent; acetone, Rf = 0.1) to
afford L2 (0.21 g) in 30% yield. Mp: 174 ꢁC. 1H NMR
(CDCl3): d 8.64 (d, 2H, J = 5.4 Hz), 8.52 (s, 2H), 8.42 (d,
4H, J = 4.8 Hz), 7.50 (d, 4H, J = 7.8 Hz), 7.41 (d, 2H,
J = 16.2 Hz) 7.36 (d, 2H, J = 5.4 Hz), 6.99 (d, 2H,
J = 16.2 Hz), 6.91 (d, 4H, J = 7.8 Hz), 6.79 (d, 4H,
J = 4.8 Hz), 4.04 (m, 8H), 1.88 (m, 8H), 1.67 (m, 4H).
13C{1H} NMR (CDCl3): d 165.1, 159.7, 156.6, 151.1,
149.6, 146.2, 133.0, 129.1, 128.5, 124.0, 121.0, 118.1,
114.9, 110.4, 67.8, 67.7, 29.0, 28.8, 22.8. MS: m/z 718
[M+]. Anal. Calc. for C46H46N4O4: C, 76.85; H, 6.45.
Found: C, 76.59; H, 6.32%.
3. Experimental section
All reactions were carried out under an argon atmo-
sphere. Solvents were distilled from appropriate
reagents. 2,20-Bipyridyl-4,40-dicarboxylic acid was pur-
chased from Strem. 40-Hydroxy-4-biphenylcarbonitrile and
4-hydroxypyridine were purchased form Sigma–Aldrich.
4-(5-Bromopentyloxy)benzaldehyde [21], 4-(diethylphospho-
nomethyl)-40-methyl-2,20-bipyridine [22], 4,40-bis(diet-
hylphosphnomethyl)-2,20-bipyridine [22] and zinc tetrakis-5,
10,15-tritolyl-20-(4-hydroxyphenyl)porphyrin [23] were syn-
thesized using a modified procedure of previous references.
1H and 13C NMR spectra were recorded on a Varian Mer-
cury 300 spectrometer. The absorption and photolumines-
cence spectra were recorded on a Perkin–Elmer Lambda
2S UV–Vis spectrometer and a Perkin LS fluorescence spec-
trometer, respectively.
3.3. 40-(4-(5-(40-Cyano-4-biphenoxy)pentyloxy)styryl)-4-
methyl-2, 20-bipyridine (L3)
Potassium tert-butoxide (0.20 g, 1.8 mmol) was added to
a solution of 4-(5-(40-cyano-4-biphenoxy)pentyloxy)benzal-
dehyde (0.5 g, 1.29 mmol) and 4-(diethylphosphonom-
ethyl)-40-methyl-2,20-bipyridine (0.41 g, 1.29 mmol) in
THF (30 mL). The reaction mixture was stirred for 10 h
at room temperature. After addition of water (10 mL),
THF was removed under reduced pressure, and the aque-
ous residue was extracted with CH2Cl2 (50 mL). The col-
lected organic layer was washed with water (50 mL),
dried over magnesium sulfate, and filtered. The solvent
was removed in vacuo. The pure product L3 was obtained
by chromatographic work-up (eluent; EA, Rf = 0.3) as a
3.1. 40-(4-(5-(Pyridin-4-yloxy)pentyloxy)styryl)-4-methyl-
2,20-bipyridine (L1)
A mixture of 4-(5-(pyridin-4-yloxy)pentyloxy)benzalde-
hyde (0.3 g, 1.1 mmol), 4-(diethylphosphonomethyl)-40-
methyl-2,20-bipyridine (0.3 g, 1.0 mmol), and potassium
tert-butoxide (0.24 g, 2.1 mmol) was vacuum-dried and
added to THF (40 mL). The solution was refluxed for
12 h. After cooling the solution, H2O (50 mL) and methy-
lene chloride (50 mL) were added. The organic layer was
separated and dried with MgSO4. The organic layer was
removed in vacuo. The pure product L1 was obtained by
silica gel chromatography (eluent; EA, Rf = 0.1) to afford
1
yellow solid in 70% yield. Mp: 117 ꢁC. H NMR (CDCl3):
d 8.60 (d, J = 5.1 Hz, 1H), 8.56 (d, J = 5.1 Hz, 1H), 8.48 (s,
1H), 8.26 (s, 1H), 7.66 (d, J = 8.4 Hz, 2H), 7.61 (d, J =
8.1 Hz, 2H), 7.51 (d, J = 8.7 Hz, 2H), 7.48 (d, J = 8.4 Hz,
2H), 7.39 (d, J = 16.2 Hz, 1H), 7.32 (d, J = 4.8 Hz, 1H),
7.14 (d, J = 4.8 Hz, 1H), 6.98 (d, J = 8.1 Hz, 2H), 6.96
(d, J = 16.2 Hz, 1H), 6.91 (d, J = 8.7 Hz, 2H), 4.03 (m,
4H), 2.43 (s, 3H), 1.89 (m, 2H), 1.70 (m, 2H), 1.24 (m,
2H). 13C{1H} NMR (CDCl3): d 191.0, 164.2, 159.8,
157.0, 156.3, 149.5, 148.7, 146.5, 145.3, 132.7, 132.1,
131.5, 128.6, 128.4, 127.1, 125.0, 123.7, 122.5, 121.6,
121.1, 119.2, 116.2, 114.8, 110.1, 68.2, 67.9, 29.0, 27.2,
24.9, 22.8. MS: m/z 551 [M+]. Anal. Calc. for
C37H33N3O2: C, 80.55; H, 6.03. Found: C, 80.12; H, 5.98%.
1
L1 (0.13 g) in 32% yield. Mp: 169 ꢁC. H NMR (CDCl3):
d 8.61 (d, 1H, J = 5.4 Hz), 8.57 (d, 1H, J = 5.4 Hz), 8.49
(s, 1H), 8.42 (d, 2H, J = 6.6 Hz), 8.27 (s, 1H), 7.50 (d,
2H, J = 8.4 Hz), 7.41 (d, 1H, J = 16.2 Hz) 7.35 (d, 1H,
J = 4.8 Hz), 7.16 (d, 1H, J = 4.8 Hz), 6.99 (d, 2H,
J = 16.2 Hz) 6.92 (d, 2H, J = 8.4 Hz), 6.80 (d, 2H,
J = 6.6 Hz), 4.04 (m, 4H), 2.45 (s, 3H), 1.89 (m, 4H),
1.67 (m, 2H). 13C{1H} NMR (CDCl3): d 165.1, 159.6,
156.7, 156.1, 151.2, 149.6, 149.1, 148.3, 146.2, 132.9,
129.1, 128.6, 124.9, 124.0, 122.1, 120.9, 118.1, 114.9,
110.4, 67.8, 67.7, 29.0, 28.8, 22.8, 21.3. MS: m/z 451

I. Jung et al. / Inorganica Chimica Acta 360 (2007) 3518–3524
3523
3.4. 40-(4-(5-(Zinc tetrakis-5,10,15-tritolyl-20-(4-
hydroxyphenyl)porphyrin) pentyloxy)styryl)-4-methyl-2,20-
bipyridine (L4)
1H),d 8.69 (d, 1H, J = 5.4 Hz), 8.60 (d, 1H, J = 5.4 Hz),
8.54 (s, 1H), 8.43 (d, 2H, J = 6.6 Hz), 8.36 (d, 2H), 8.27
(s, 1H), 7.58 (d, 2H, J = 8.4 Hz), 7.40 (d, 1H,
J = 16.2 Hz) 7.36 (dd, 1H), 7.13 (dd, 1H), 7.06 (d, 2H,
J = 16.2 Hz) 6.99 (d, 2H, J = 8.4 Hz), 6.90 (d, 2H,
J = 6.6 Hz), 4.07 (m, 4H), 2.49 (s, 3H), 1.80 (m, 4H),
1.57 (m, 2H). MS: m/z 913 [M+]. Anal. Calc. for
C43H37N7O6RuS2: C, 56.57; H, 4.08; N, 10.74. Found: C,
56.39; H, 4.01; N, 10.50%.
A mixture of 4-(5-(zinc tetrakis-5,10,15-tritolyl-20-(4-
hydroxyphenyl)porphyrin)pentyloxy)benzaldehyde (0.26 g,
0.28 mmol), 4-(diethylphosphonomethyl)-40-methyl-2,20-
bipyridine (0.1 g, 0.31 mmol), and potassium tert--butoxide
(0.04 g, 0.31 mmol) was vacuum-dried and added to THF
(30 mL). The solution was refluxed for 12 h. After cooling
the solution, H2O (50 mL) and methylene chloride (50 mL)
were added. The organic layer was separated and dried
with MgSO4. The organic layer was removed in vacuo.
The pure product L4 was obtained by silica gel chromatog-
raphy (eluent; EA, Rf = 0.1) to afford L4 (0.1 g) in 33%
yield. Mp: 193 ꢁC. 1H NMR (CDCl3): d 8.99 (s, 8H),
8.53 (d, 1H, J = 4.80 Hz), 8.48 (d, 1H, J = 4.80 Hz), 8.39
(s, 1H), 8.19 (s, 1H), 8.11 (d, 8H, J = 7.80 Hz), 7.55 (d,
6H, J = 7.80 Hz), 7. 48 (d, 2H, J = 8.70 Hz), 7.37 (d, 1H,
J = 16.2 Hz) 7.27 (d, 1H, J = 4.80 Hz), 7. 25 (d, 2H,
J = 7.80 Hz), 7.11 (d, 1H, J = 4.80 Hz), 6.93 (d, 1H, J =
16.2 Hz), 6.92 (d, 2H, J = 8.70 Hz), 4.25 (t, 2H), 4.07 (t,
2H), 2.71 (s, 9H), 2.43 (s, 3H), 2.00 (m, 4H), 1.82 (m,
2H). 13C{1H} NMR (CDCl3): d 159.77, 158.77, 156.62,
155.89, 150.61, 150.41, 149.54, 148.97, 148.03, 146.05,
140.10, 137.17, 135.57, 135.36, 134.52, 133.14, 132.02,
129.05, 128.57, 127.41, 124.82, 123.88, 122.17, 121.19,
120.92, 118.10, 115.01, 112.70, 68.11, 68.06, 29.36, 29.19,
23.03, 21.68, 21.34. MS: m/z 1090 [M+]. Anal. Calc. for
C71H58N6O2Zn: C, 78.05; H, 5.35. Found: C, 77.87; H,
5.26%.
3.6. Synthesis of [Ru(L2)(L)(NCS)2] (D21)
Complex D21 was synthesized by a procedure similar to
D20 except that L2 (0.3 g, 0.417 mmol) was used in place of
L1. Yield = 0.106 g, 43%. 1H NMR (DMSO): d 9.43
(d, 1H), 9.14 (d, 1H), 8.98 (s, 1H), 8.92 (s, 1H), 8.85
(d, 1H), 8.64 (d, 2H, J = 5.4 Hz), 8.56 (s, 2H), 8.47 (d,
4H, J = 4.8 Hz), 7.59 (d, 4H, J = 7.8 Hz), 7.50 (d, 2H,
J = 16.2 Hz) 7.40 (d, 2H, J = 5.4 Hz), 7.01 (d, 2H,
J = 16.2 Hz), 6.90 (d, 4H, J = 7.8 Hz), 6.77 (d, 4H,
J = 4.8 Hz), 4.08 (m, 8H), 1.78 (m, 8H), 1.54 (m, 4H).
MS: m/z 1180 [M+]. Anal. Calc. for C60H54N8O8RuS2: C,
61.05; H, 4.01; N, 9.49. Found: C, 60.98; H, 3.96; N, 9.28%.
3.7. Synthesis of [Ru(L3)(L)(NCS)2] (D22)
Complex D22 was synthesized by a procedure similar to
D20 except that L3 (0.15 g, 0.27 mmol) was used in place
of L1. Yield = 0.071 g, 54%. 1H NMR (DMSO): d 9.28 (d,
1H), 9.20 (d, 1H), 8.81 (s, 1H), 8.72 (s, 1H), 8.67 (d,
J = 5.1 Hz, 1H), 8.60 (d, J = 5.1 Hz, 1H), 8.52 (s, 1H), 8.34
(s, 1H), 8.24 (d, 1H), 8.13 (d, 1H), 7.78 (d, J = 4.2 Hz, 1H),
7.69 (d, J = 4.8 Hz, 1H), 7.66 (d, J = 8.4 Hz, 2H), 7.61 (d,
J = 8.1 Hz, 2H), 7.51 (d, J = 8.7 Hz, 2H), 7.48 (d, J =
8.7 Hz, 2H), 7.39 (d, J = 16.2 Hz, 1H), 6.98 (d, J = 8.1 Hz,
2H), 6.96 (d, J = 16.2 Hz, 1H), 6.91 (d, J = 8.7 Hz, 2H),
4.06 (m, 4H), 2.41 (s, 3H), 1.83 (m, 2H), 1.65 (m, 2H), 1.24
(m, 2H). MS: m/z 1013 [M+]. Anal. Calc. for
C51H41N7O6RuS2: C, 60.46; H, 4.08; N, 9.68. Found: C,
60.12; H, 4.00; N, 9.47%.
3.5. Synthesis of [Ru(L1)(L)(NCS)2] (D20)
A mixture of [{RuCl2(p-cymene)}2] (0.095 g, 0.16 mmol)
and L1 (0.14 g, 0.31 mmol) was vacuum-dried and added
to DMF (30 mL). The reaction mixture was heated at
80 ꢁC under nitrogen for 4 h and then, 2,20-bipyridyl-4,40-
dicarboxylic acid (L) (0.075 g, 0.31 mmol) was added to
the solution. The reaction mixture was refluxed at 160 ꢁC
for another 4 h under dark condition to avoid light induced
cis to trans isomerisation. Then an excess of NH4NCS
(1.86 mmol) was added to the reaction mixture and heated
at 130 ꢁC for further 5 h. The solvent was removed using a
rotary-evaporator under vacuum. Water was added to the
resulting semisolid to remove excess NH4NCS. The water-
insoluble product was collected on a sintered glass crucible
by suction filtration and washed with distilled water, fol-
lowed by diethyl ether and dried. The crude complex was
dissolved in a solution of tetrabutyl ammonium hydroxide
(0.4 g) in methanol (4 mL). The concentrated solution was
charged onto a Sephadex LH-20 (2 · 30 cm) column and
eluted with methanol. The main red band was collected
and concentrated to 3 mL. The pure complex was isolated
3.8. Synthesis of [Ru(L4)(L)(NCS)2] (D23)
Complex D23 was synthesized by a procedure similar to
D20 except that L4 (0.18 g, 0.165 mmol) was used in place
of L1. Yield = 0.072 g, 56%. 1H NMR (DMSO): d 9.42 (d,
1H), 9.12 (d, 1H), 8.96 (s, 1H), 8.83 (s, 1H), 8.82 (d, 1H),
8.76 (s, 8H), 8.60 (d, 1H, J = 4.8 Hz), 8.53 (d, 1H,
J = 4.8 Hz), 8.38 (d, 1H), 8.36 (s, 1H), 8.21 (s, 1H), 8.05 (d,
8H, J = 7.8 Hz), 7.75 (d, 1H), 7.59 (d, 6H, J = 7.8 Hz),
7.50 (d, 2H, J = 8.7 Hz), 7.34 (d, 1H, J = 16.2 Hz) 7.26 (d,
1H, J = 4.8 Hz), 7.20 (d, 2H, J = 7.8 Hz), 7.09 (d, 1H,
J = 4.8 Hz), 6.91 (d, 1H, J = 16.2 Hz), 6.85 (d, 2H,
J = 8.7 Hz), 4.28 (t, 2H), 4.04 (t, 2H), 2.66 (s, 9H), 2.40 (s,
3H), 1.74 (m, 2H), 1.57 (m, 2H). MS: m/z 1552 [M+]. Anal.
Calc. for C85H66N10O6Ru S2Zn: C, 65.69; H, 4.28; N, 9.01.
Found: C, 65.39; H, 4.19; N, 8.83%.
upon addition of
a few drops of 0.01 M HNO3.
Yield = 0.073 g (52%). 1H NMR (DMSO): d 9.43 (d,
1H), 9.16 (d, 1H), 8.99 (s, 1H), 8.91 (d, 1H), 8.85 (s,

3524
I. Jung et al. / Inorganica Chimica Acta 360 (2007) 3518–3524
[5] (a) V. Balzani, F. Scandola, Supramolecular Photochemistry, Ellis
Horwood, Chichester, 1990;
3.9. Fabrication of sandwich type cells
(b) R. Amadelli, R. Argazzi, C.A. Bignozzi, F. Scandola, J. Am.
Chem. Soc. 112 (1990) 7099.
[6] (a) P. Wang, C. Klein, R. Humphry-Baker, S.M. Zakeeruddin, M.
Gra¨tzel, J. Am. Chem. Soc. 127 (2005) 808;
For the preparation of DSSC, the washed FTO (Pilking-
ton, 8 X sqꢀ1, 2.3 mm thickness) glass plate was immersed
in 40 mM TiCl4 aqueous solution at 60 ꢁC for 30 min and
washed with water and ethanol as reported by the Gra¨tzel
group [14]. A transparent nanocrystalline layer on the FTO
glass plate was prepared by screen printing TiO2 paste
(Solaronix, 13 nm anatase) and was sintered at 450 ꢁC for
30 min. And then, a paste for the scattering layer (Solaro-
nix, 300 nm, anatase) was coated on the transparent layer
and was again sintered at 450 ꢁC for 30 min. The resulted
layer was composed of 15 lm thickness of transparent
layer and 5 lm thickness of scattering layer. The TiO2 elec-
trode was immersed into the dye solution (0.3 mM dye in
ethanol containing 10 mM) and kept at room temperature
for 18 h. Counter electrode was prepared by coating with a
drop of H2PtCl6 solution (2 mg Pt in 1 mL ethanol) on a
FTO plate and heated at 400 ꢁC for 15 min. The dye
adsorbed TiO2 electrode and Pt-counter electrode were
assembled into a sealed sandwich type cell by heating with
a Surlyn film (25 lm thickness, Du-Pont) as a spacer
between the electrode. The electrolyte was then introduced
into the cell, which was composed of 0.6 M 3-hexyl-1,2-
dimethyl imidazolium iodide, 0.04 M iodine, 0.025 M LiI,
0.05 M guanidium thiocyanate and 0.28 M tert-butylpyri-
dine in acetonitrile. The DSSCs were characterized for their
photoelectrochemical characteristics using a Keithley 2400
source measure unit. A 300 W solar simulator (Model:
69920, Newport-Oriel Instruments, Stratford, CT, USA)
was used as a light source. The light intensity was adjusted
using a Si solar cell. IPCE values were measured using a
system by PV Measurement, Inc.
(b) P. Wang, C. Klein, R. Humphry-Baker, S.M. Zakeeruddin, M.
Gra¨tzel, Appl. Phys. Lett. 86 (2005) 123508;
(c) D. Kuang, S. Ito, B. Wenger, C. Klein, J.-E. Moser, R. Humphry-
Baker, S.M. Zakeeruddin, M. Gra¨tzel, J. Am. Chem. Soc. 128 (2006)
4146.
[7] S.-R. Jang, C. Lee, H. Choi, J. Ko, J. Lee, R. Vittal, K.-J. Kim,
Chem. Mater. 18 (2006) 5604.
[8] A.F. Nogueira, S.H. Toma, M. Vidotti, A.L.B. Formiga, S.I.C. De
Torresi, H.E. Toma, New J. Chem. 29 (2005) 320.
[9] S.-R. Jang, R. Vittal, J. Lee, N. Jeong, K.-J. Kim, Chem. Commun.
(2006) 103.
[10] H. Kusama, H. Sugihara, J. Comput. Chem. 26 (2005) 1372.
[11] (a) M. Frigoli, G.H. Mehl, Chem. Commun. (2004) 818;
(b) S.H. Chen, H.M.P. Chen, Y. Geng, S.D. Jacobs, K.L. Marshall,
Adv. Mater. 15 (2003) 1061;
(c) T. Cardinaels, K. Driesen, T.N. Parac-Vogt, B. Heinrich, C.
Bourgogne, D. Guillon, B. Donnio, K. Binnemans, Chem. Mater. 17
(2005) 6589.
[12] (a) Q. Wang, W.M. Campbell, E.E. Bonfantani, K.W. Jolley, D.L.
Officer, P.J. Walsh, K. Gordon, R. Humphry-Baker, M.K. Nazee-
ruddin, M. Gra¨tzel, J. Phys. Chem. B 109 (2005) 15397;
´
(b) F. Odobel, E. Blart, M. Lagree, M. Villieras, H. Boujtita, N.E.
Murr, S. Caramori, C.A. Bignozzi, J. Mater. Chem. 13 (2003) 502.
[13] (a) R. Argazzi, C.A. Bignozzi, T.A. Heimer, F.N. Castellano, G.J.
Meyer, Inorg. Chem. 33 (1994) 5741;
(b) M.K. Nazeeruddin, S.M. Zakeeruddin, R. Humphry-Baker, M.
Jirousek, P. Liska, N. Vlachopoulos, V. Shklover, C.-H. Fischer, M.
Gra¨tzel, Inorg. Chem. 38 (1999) 6298.
[14] M.K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E.
Muller, P. Liska, N. Vlachopoulos, M. Gra¨tzel, J. Am. Chem. Soc.
¨
115 (1993) 6382.
[15] K. Kalyanasundaram, Photochemistry of Polypyridine and Porphy-
rin Complexes, Academic Press, New York, 1992.
[16] C. Klein, M.K. Nazeeruddin, D.D. Censo, P. Liska, M. Gra¨tzel,
Inorg. Chem. 43 (2004) 4216.
[17] (a) A. Islam, H. Sugihara, H. Arakawa, J. Photochem. Photobiol. A
158 (2003) 131;
Acknowledgements
(b) E.M. Kober, J.V. Caspar, R.S. Lumpkin, T.J. Meyer, J. Phys.
Chem. 90 (1986) 3722.
[18] (a) A. Hagfeldt, M. Gra¨tzel, Chem. Rev. 95 (1995) 49;
(b) K. Kalyanasundaram, M. Gra¨tzel, Coord. Chem. Rev. 177 (1998)
347;
We are grateful to the KOSEF through National Re-
search Laboratory (No. M10500000034-06J0000-03410)
program and BK21 (2006).
(c) A.M. Bond, G.B. Deacon, J. Howitt, D.R. MacFarlane, L.
Spiccia, G. Wolfbauer, J. Electrochem. Soc. 146 (1999) 648;
(d) P. Wang, S.M. Zakeeruddin, J.-E. Moser, M. Gra¨tzel, J. Phys.
Chem. B 107 (2003) 13280.
References
[1] (a) B. O’Regan, M. Gra¨tzel, Nature 353 (1991) 737;
(b) A. Hagfeldt, M. Gra¨tzel, Acc. Chem. Res. 33 (2000) 269.
[2] (a) M.K. Nazeeruddin, P. Pechy, T. Renouard, S.M. Zakeeruddin, R.
[19] (a) S.Y. Huang, G. Schlichtho¨rl, A.J. Nozik, M. Gra¨tzel, A.J. Frank,
J. Phys. Chem. B 101 (1997) 2576;
´
Humphry-Baker, P. Comte, P. Liska, L. Cevey, E. Costa, V.
Shklover, L. Spiccia, G.B. Deacon, C.A. Bignozzi, M. Gra¨tzel, J.
Am. Chem. Soc. 123 (2001) 1613;
(b) Z.-S. Wang, T. Yamaguchi, H. Sugihara, H. Arakawa, Langmuir
21 (2005) 4272;
(c) P. Wang, S.M. Zakeeruddin, J.E. Moser, R. Humphry-Baker, P.
Comte, V. Aranyos, A. Hagfeldt, M.K. Nazeeruddin, M. Gra¨tzel,
Adv. Mater. 16 (2004) 1806.
(b) G. Schlichtho¨rl, S.Y. Huang, J. Sprague, A.J. Frank, J. Phys.
Chem. B 101 (1997) 8141.
[20] J.-J. Lagref, M.K. Nazeeruddin, M. Gra¨tzel, Synth. Met. 138 (2003)
333.
[21] C.-H. Huang, N.D. McClenaghan, A. Kuhn, G. Bravic, D.M.
Bassani, Tetrahedron (2006) 2050.
´ ´
´
[22] (a) O. Maury, L. Viau, K. Senechal, B. Corre, J.P. Guegan, T.
Renouard, I. Ledoux, J. Zyss, H. Le Bozec, Chem. Eur. J. 10 (2004)
4454;
[3] (a) C. Klein, M.K. Nazeeruddin, P. Liska, D.D. Censo, N. Hirata, E.
Palomares, J.R. Durrant, M. Gra¨tzel, Inorg. Chem. 44 (2005) 178;
(b) K.-J. Jiang, N. Masaki, J.-B. Xia, S. Noda, S. Yanagida, Chem.
Commun. (2006) 2460.
[4] N. Hirata, J.-J. Lagref, E.J. Palomares, J.R. Durrant, M.K. Nazee-
ruddin, M. Gra¨tzel, D.D. Censo, Chem. Eur. J. 10 (2004) 595.
(b) S. Gould, G.F. Strouse, T.J. Meye, B.P. Sullivan, Inorg. Chem. 30
(1991) 2942;
(c) G.F. Strouse, J.R. Schoonover, R. Duesing, S. Boyde, W.E. Jones
Jr., T.J. Meyer, Inorg. Chem. 34 (1995) 473.
[23] L. Giribabu, T.A. Rao, B.G. Maiya, Inorg. Chem. 38 (1999) 4971.