A heteroleptic bis(tridentate) ruthenium(II) platform featuring an anionic 1,2,3-triazolate-based ligand for application in the dye-sensitized solar cell

Article abstract of DOI:10.1021/ic402701v

A series of bis(tridentate) ruthenium(II) complexes featuring new anionic 1,2,3-triazolate-based tridentate ligands and 2,2′:6′, 2′′-terpyridine is presented. For a complex equipped with carboxy anchoring groups, the performance in a dye-sensitized solar cell is evaluated. The title complexes are readily synthesized and can be decorated with alkyl chains utilizing azide-alkyne cycloaddition methods, in order to improve the device stability and allow the use of alternative electrolytes. On account of the strong electron donation from the 1,2,3-triazolates, the complexes exhibit a broad metal-to-ligand charge-transfer absorption (up to 700 nm), leading to an electron transfer toward the anchoring ligand. The lifetimes of the charge-separated excited states are in the range of 50 to 80 ns. In addition, the ground- and excited-state redox potentials are appropriate for the application in dye-sensitized solar cells, as demonstrated by power conversion efficiencies of up to 4.9% (vs 6.1% for N749).

Full text of DOI:10.1021/ic402701v

Article
pubs.acs.org/IC
A Heteroleptic Bis(tridentate) Ruthenium(II) Platform Featuring an
Anionic 1,2,3-Triazolate-Based Ligand for Application in the Dye-
Sensitized Solar Cell
Stephan Sinn,†,‡,△ Benjamin Schulze,†,‡,△ Christian Friebe,†,‡ Douglas G. Brown,§ Michael Jager,†,‡
̈
Joachim Kubel,⊥,∇ Benjamin Dietzek,⊥,∇,‡,* Curtis P. Berlinguette,§,∥,* and Ulrich S. Schubert†,‡,*
̈
†Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstr. 10, 07743 Jena,
Germany
‡Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743 Jena, Germany
§Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, Canada T2N 1N4
∥Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
⊥Institute of Physical Chemistry (IPC) and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743
Jena, Germany
∇Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Str. 9, 07745 Jena, Germany
S
* Supporting Information
ABSTRACT: A series of bis(tridentate) ruthenium(II) com-
plexes featuring new anionic 1,2,3-triazolate-based tridentate
ligands and 2,2′:6′,2′′-terpyridine is presented. For a complex
equipped with carboxy anchoring groups, the performance in a
dye-sensitized solar cell is evaluated. The title complexes are
readily synthesized and can be decorated with alkyl chains
utilizing azide−alkyne cycloaddition methods, in order to
improve the device stability and allow the use of alternative
electrolytes. On account of the strong electron donation from the
1,2,3-triazolates, the complexes exhibit a broad metal-to-ligand charge-transfer absorption (up to 700 nm), leading to an electron
transfer toward the anchoring ligand. The lifetimes of the charge-separated excited states are in the range of 50 to 80 ns. In
addition, the ground- and excited-state redox potentials are appropriate for the application in dye-sensitized solar cells, as
demonstrated by power conversion efficiencies of up to 4.9% (vs 6.1% for N749).
long-term stability and similar or higher PCEs compared to
thiocyanate-based benchmark dyes.24 Moreover, these chelating
ligands enable the introduction of hydrophobic alkyl chains and
additional chromophores to further improve the DSSC life
span18,25−27 and the light-harvesting capability, respectively.24
Chou and co-workers presented ruthenium(II) dyes
featuring functionalized dianionic 2,6-bis(5-pyrazolyl)pyridine
ligands (Figure 1), which achieved remarkable PCEs of 9.1%
(TF-1) and 10.7% (TF-2, vs 9.2% for N749) in the DSSC.23
Building on these promising results, we present herein a series
of heteroleptic bis(tridentate) ruthenium(II) complexes con-
taining anionic 1,2,3-triazolates as thiocyanate surrogates
(Figure 1). This approach benefits from a very simple ligand
synthesis via azide−alkyne cycloaddition, which also allows the
ready installation of alkyl chains. In comparison to the parent,
charge-neutral 1,2,3-triazoles,28−30 the σ lone pair and the π
system of anionic triazolates are raised in energy, resulting in an
enhanced σ- and π-donor strength. Furthermore, the use of
INTRODUCTION
■
Dye-sensitized solar cells (DSSCs) rely on the sensitization of a
wide-band-gap semiconductor such as TiO2 with dye
molecules. The sensitizer needs to be photo- and redox-stable,
absorb as much light as possible, and feature excited- and
ground-state redox potentials that allow for efficient electron
injection into the conduction band of the semiconductor and
subsequent regeneration by the electrolyte, respectively.1,2
Meanwhile, power conversion efficiencies (PCEs) of up to
12.3% have been achieved with molecular dyes3 and
ruthenium(II) polypyridyl complexes featuring thiocyanato
ligands, such as (NBu4)3[Ru(Htctpy)(NCS)3] (N749 or
black dye; Htctpy = 2,2′:6′,2″-terpyridine-4′-carboxylic acid-
4,4″-dicarboxylate) (Figure 1), are among the most efficient
sensitizers, with PCEs up to 11.4%.4−7 However, the
monodentate thiocyanato ligands preclude further optimization
via ligand functionalization and limit the lifetime of DSSCs, as
they can decoordinate easily.8,9 Consequently, the thiocyanate
ligands have been replaced by anionic multidentate ligands
including anionic phenyl rings,10−16 tetrazolates,17 1,2,4-
triazolates,18−20 and pyrazolates,20−23 enabling an improved
Received: October 27, 2013
Published: January 21, 2014
© 2014 American Chemical Society
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Scheme 1. Schematic Representation of the Synthesis of
Complexes 1 and 2a−2c, and the Numbering Scheme of the
a
Studied Complexes
Figure 1. Schematic representation of the ruthenium(II) complexes 1
and 2a−2c and related literature examples.4,23
1,2,3-triazolates circumvents the formation of coordination
isomers, which plague analogous 1,2,4-triazolate-based
ruthenium(II) complexes (Figure 2),31 and, in contrast to
related pyrazolate complexes,23 no electron-withdrawing groups
need to be installed to raise the Ru(III)/Ru(II) redox potential,
due to the higher degree of aza substitution of the 1,2,3-
triazolate.
a
Conditions: (a) HCHOaq, AcOH, NaN3, CuSO4, sodium ascorbate,
dioxane, rt, 24 h. (b) NaOH, MeOH/H2O, rt, 24 h. (c) Azidomethyl
pivalate, 100 °C, 72 h. (d) [RuII(tpy)(MeCN)3](PF6)2 or
[RuII(tcmtpy)(MeCN)3](PF6)2, alcohol, or triethylene glycol dimethyl
ether, 150 °C, 30 min, microwave irradiation. (e) DMF/NEt3/H2O
(3:1:1 v/v/v).
The solubilities of the charge-neutral complexes are expectedly
low; however, the introduction of the alkyl chains (2a−2c)
improves the solubility, allowing the investigation of the
photophysical and electrochemical properties (vide infra).
Computational Methods. To enable a deeper under-
standing of the electronic properties of the new ruthenium(II)
complexes, density functional theory (DFT) calculations have
been performed for 2a−2c (note that the hexyl chains have
been replaced by methyl groups to shorten the computing
time). Additionally, the electronic properties of the fully
deprotonated form of 2c (2c′) were calculated, while the
electronic excitations for 2c were computed with the help of
time-dependent (TD) DFT.23 The calculations revealed that
the highest occupied molecular orbital (HOMO) of the
complexes is composed of a metal d orbital and π orbitals
located on the triazolate rings, which is expected in view of the
electron-rich π system of the anionic ring.18,22,24 As a result of
the electron repulsion between the anionic ligand and the metal
center, the HOMO is strongly destabilized in comparison to
polypyridyl complexes such as [Ru(tpy)2](PF6)2. For 2a−2c,
the lowest unoccupied molecular orbital (LUMO) is mainly
composed of π* orbitals of the terpyridine ligand (Table S2).
Relative to 2a, the HOMO and, in particular, the LUMO of 2b
are stabilized due to the electron-withdrawing −COOMe
groups, resulting in a significantly smaller HOMO−LUMO gap.
The −COOH anchoring groups of 2c have a similar effect on
the frontier orbitals energies. In contrast, when compared to 2a,
the HOMO and LUMO of the fully deprotonated complex 2c′
are destabilized and the HOMO−LUMO gap is slightly larger
Figure 2. Schematic illustration of the formation of isomeric
ruthenium(II) complexes with tridentate ligands based on 1,2,4-
triazolates.
RESULTS AND DISCUSSION
■
Synthesis. The 2,6-bis(1,2,3-triazol-4-yl)pyridine ligands
were synthesized either via Cu(I)-catalyzed azide−alkyne
cycloaddition, using in situ generated hydroxymethyl azide,32
followed by a base-induced cleavage of formaldehyde, or, in the
case of the internal alkyne (see Scheme 1 and the Supporting
Information (SI)), via a thermal azide−alkyne cycloaddition
with azidomethyl pivalate.33 For the latter, the cycloadduct is
obtained as a statistically distributed mixture; however, after
cleavage in basic media and subsequent reprotonation, the free
NH-triazole is obtained, which undergoes rapid tautomeriza-
tion.30 The corresponding ruthenium(II) complexes were
obtained in good yields utilizing [RuII(tpy)(MeCN)3](PF6)2
(tpy = 2,2′:6′,2″-terpyridine) or [RuII(tcmtpy)(MeCN)3]-
(PF6)2 (tcmtpy = 4,4′,4″-tricarboxymethyl-2,2′:6′,2″-terpyri-
dine; see Scheme 1 and the SI) as precursor.34 The subsequent
saponification of 2b was achieved as described previously.12
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(Figure S11), which is attributed to the electron-donating effect
of the −COO− groups. The most relevant electronic transitions
of 2c are displayed in Figure 3 along with the corresponding
anchoring tctpy ligand in each case, 2c features an excited-state
electronic structure suitable for electron injection into TiO2.36
To allow the estimation of the “hole distribution” resulting after
photo-oxidation, the spin-density distribution was calculated for
the oxidized complex. As a result, the hole is shared by the
metal and the anionic ligand, which is believed to facilitate the
sensitizer regeneration.37,38
Photophysics and Electrochemistry. The photophysical
and electrochemical properties of the complexes are in line with
the computational results. The increased σ- and π-donor
strength of the anionic 1,2,3-triazolates relative to the neutral
1,2,3-triazoles31,34,39 causes a destabilization of the metal d
orbitals, resulting in a cathodically shifted Ru(III)/Ru(II) redox
couple as well as bathochromically shifted MLCT transitions
(Table 1). Consequently, a weak, plateau-like absorption band
that extends to very long wavelengths is observed (Figures 4
and 5), which is typical for bis(tridentate) ruthenium(II)
complexes featuring azolate donors.21,23,31,40
As the 1,2,3-triazolate rings of the ruthenium(II) complexes
feature additional nitrogen donors, the complexes can be
protonated (Figure 4) with the properties of the resulting
complexes reflecting those of analogous 1,2,3-triazole
ruthenium(II) complexes.34,39 The protonation was inves-
tigated in more detail by UV−vis acid−base titration of 1
(Figures S1−S3). Within the studied pH range from 0 to 12,
only one spectral change around pH 4 to 5 occurs; no
isosbestic points are present, which indicates that there are
more than two species involved. The first and second
protonation of the triazolate ligand of 1 occur most likely
both within the narrow pH window of 4 to 5, and thus, only a
single pKa value of about 4.7 could be determined (Figures S1
and S2). Furthermore, a weak emission appears upon
increasing the pH value, which can be attributed to an
increased destabilization of the deactivating triplet metal-
centered (3MC) excited states relative to the 3MLCT
state.31,40,41 Accordingly, the excited-state lifetimes of 2a (54
ns, Table 1) and 2c (83 ns) are significantly prolonged relative
to those of the related [Ru(tpy)2](PF6)2 complex (0.21 ns)42
and sufficiently long (>10 ns) to enable efficient electron
injection into TiO2 given that injection occurs on the
picosecond time scale.43 Comparison with analogous hetero-
leptic bis(tridentate) ruthenium(II) complexes featuring 1,2,4-
triazolates or tetrazolates shows that 1 is less basic than the
1,2,4-triazolate complex but more basic than the tetrazolate
counterpart.31 Apparently, the cumulative arrangement of the
nitrogen atoms within the 1,2,3-triazolate lowers the base
strength relative to the 1,2,4-triazolate.44 The corresponding
excited-state lifetimes are slightly prolonged with increasing
azolate donor strength.31 Furthermore, in view of the similar
excited-state lifetimes that are observed with related tris-
(bidentate) ruthenium(II) complexes featuring imidazolates,45
the excited-state decay of the deprotonated complexes appears
to be governed by the energy-gap law.46
Figure 3. Top: Experimental UV−vis absorption spectrum of 2c
adsorbed on TiO2 (12 μm thick, transparent film, active area of 0.88
cm2) and calculated vertical singlet−singlet transitions of 2c. Bottom:
Corresponding EDDM plots (blue and yellow represent depletion and
accumulation, respectively, of electron density upon electronic
excitation, isovalue = 0.001) and spin-density plot of the oxidized
ground state (bottom right, isovalue = 0.004) of 2c. Color code:
carbon, gray; hydrogen, white; oxygen, red; nitrogen, blue; ruthenium,
cyan. Note that the tpy ligand is functionalized with carboxy groups,
which are known to electronically resemble Ti(IV)-coordinated
carboxylates.35
As mentioned above, the −COOMe groups cause a LUMO
stabilization and, by increasing the π acidity of the tpy ligand,
also a minor stabilization of the HOMO of 2b. In the case of
2c, the tctpy ligand (tctpy = 2,2′:6′,2′′-terpyridine-4,4′,4′′-
tricarboxylic acid) features three successive deprotonation steps
with corresponding pKa values of approximately 1.2, 3.1, and
5.5.4,34 In view of the above-mentioned pKa values for the first
and second protonation steps of the triazolate ligand of 1
(about 4.7), complex 2c is expected to form a zwitterion in
solution with two protons of the three carboxylic acid groups
electron-density difference maps (EDDM). The computed
electronic excitations are in good agreement with the
experimental UV−vis absorption spectrum (vide infra). The
lowest-energy absorption (population of S1) is a pure HOMO−
LUMO transition, which can thus be assigned to a metal-to-
ligand charge transfer (MLCT) with some ligand-to-ligand
charge-transfer (LLCT) character. Also the other electronic
transitions in the visible-light region are of MLCT character
with varying LLCT contribution (Figure 3, population of S3, S6,
S7, and S8). As the electron transfer is directed toward the
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Table 1. Photophysical and Electrochemical Data of Selected Ruthenium(II) Complexes
E1/2,ox/V vs Fc+/Fc
ES*/V vs Fc+/Fc
a
b
c
d
e
complex
λAbs/nm (ε /103 M−1 cm−1
)
λEm (λEx)/nm
Φ
PL/%
τ/ns
(vs NHE)
(vs NHE)
E0−0/eV
f
1
661s (0.3), 600s (0.8), 482 (5.2), 370 (5.2),
316 (29.9)
705 (490)
0.55
g
g
g
1.85
f
2a
662 (0.7), 608 (0.9), 487 (5.6), 389 (4.4), 319 (30.5) 719 (490)
0.35
54
0.20 (0.83)
0.46 (1.09)
−1.60 (−0.97)
1.80
f
2b
742 (2.3), 673 (2.7), 507 (8.9), 448 (10.7),
397 (13.7), 323 (28.7)
h
h
h
ij
ij
83 ,
k
l
j
2c
651(1.2), 602(2.1), 479(11.0), 388 (10.9),
698 (480) ,
0.23 (0.86)
0.16 (0.85)
−1.63 (−1.00)
1.86
i j
320 (40.9) ,
l
l
m
N749 620(6.5), 585(6.0), 420(10.5), 329(18.5)
820
30
−1.40 (−0.71)
b
1.58
Determined using [Ru(dqp)2](PF6)2 (in MeOH/EtOH 1:4, ΦPL = 2.0%)48 as reference; solutions were purged with N2. Air-equilibrated solution.
a
c
Unless stated otherwise, redox half-wave potentials were determined by cyclic voltammetry using Bu4NPF6 as the supporting electrolyte and Fc+/Fc
as the internal standard; conversion to NHE scale by addition of 0.63 V49 and 0.69 V50 when the measurement was done in MeCN and DMF/
d
2 e
MeOH (4:1 v/v), respectively. Calculated using ES* = E1/2,ox − E0−0
. Determined at the intersection of the absorption and emission spectra with
f g
the latter being normalized with respect to the lowest-energy absorption. Measured in MeCN containing 0.5 M NEt3. Not measured due to low
h
i
j
solubility. Not observed with the used instrumental setup. Measured in MeOH containing 0.5 M NEt3. Fully deprotonated species, see text.
k
Determined by square-wave voltammetry with the complex-anchored TiO2 anode as the working electrode immersed in MeCN containing 0.5 M
l
m
pyridine and 0.1 M Bu4NPF6 as the supporting electrolyte. Measured in DMF/MeOH (4:1 v/v). Measured in EtOH, taken from ref 4.
the onset of the incident photon-to-current efficiency (IPCE)
spectrum (vide infra), which occurs at 700 nm; that is, the E0−0
value for 2c featuring TiO2-coordinated carboxylates is at least
1.77 eV.
Importantly, due to the presence of 0.5 M 4-tert-
butylpyridine (tBP) in the DSSC electrolyte (vide infra), the
two triazolates of 2c are deprotonated under working
conditions. This assessment is corroborated by the measure-
ment of the Ru(III)/Ru(II) redox potential of 2c by square-
wave voltammetry in acetonitrile containing 0.5 M pyridine
with a 2c-anchored TiO2 anode as the working electrode. The
measured value of 0.86 V vs NHE is between the redox
potentials of 2a and 2b and considerably less positive than that
for the analogous complex featuring charge-neutral 1,2,3-
triazoles (1.61 V vs NHE),34,39which supports the presence
Figure 4. UV−vis absorption (solid) and room-temperature emission
(dashed) spectra of 1 in the presence of NEt3 and HPF6 in MeCN.
of two anionic triazolates. Notably, the redox potential of 2c is
sufficiently high to ensure efficient regeneration by the relevant
I2•−/I− redox couple (0.79 V vs NHE).47 Despite the above-
mentioned difficulties to accurately determine the E0−0 value, a
lower limit of the excited-state redox potential of 2c can be
determined from the ground-state redox potential and the
minimum E0−0 value, which corresponds to the onset in the
IPCE spectrum (750 nm or 1.65 eV). On this basis, the excited-
state redox potential is at least −0.79 V vs NHE, which is
sufficiently more negative than the conduction band edge of
TiO2 (ca. −0.7 V vs NHE)43 and should enable efficient
electron injection into the semiconductor.
Dye-Sensitized Solar Cells. To investigate the perform-
ance of 2c in the DSSC, commercially available test cells were
assembled according to literature procedures (vide infra)51 and
an electrolyte composition typically used for N749 was
chosen.5 The obtained parameters are reported in Table 2.
Under identical conditions, the PCEs of 2c and N749 are 4.0%
and 6.1%, respectively. The lower VOC and JSC achieved with 2c
(Figure 6) were expected in view of the higher degree of
protonation, which lowers the TiO2 conduction-band energy,35
and the lower light-harvesting capability. However, the IPCE
spectrum not only reflects the inferior light harvesting at longer
wavelengths but also reveals a lower IPCE maximum (Figure
7). When coadsorbed with chenodeoxycholic acid (cheno), 2c
allows a slightly higher VOC and a significantly improved JSC, in
line with much higher IPCE values, resulting in a promising
PCE of 4.9%. The significant enhancement of the photocurrent
in the presence of cheno suggests that the relatively low IPCE
Figure 5. UV−vis absorption spectra of 1, 2a, 2b (in MeCN + 0.5 M
NEt3), and 2c (in MeOH + 0.5 M NEt3).
being transferred to the triazolate rings. Thus, to provide a
defined protonation state, the photophysical properties were
determined in MeOH solution containing 0.5 M NEt3 in order
to ensure the complete deprotonation of the 1,2,3-triazolates.
The UV−vis absorption and emission maxima are slightly
hypsochromically shifted relative to 2a, which is attributed to
the LUMO destabilization by the three carboxylates. Notably,
the E0−0 value determined for 2c in solution (1.86 eV, Table 1)
is therefore overestimated, which becomes obvious in view of
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by the lowered recombination tendency (cf. Table 2) as the
TiO2 surface passivation is improved by cheno. Accordingly,
the Voc is slightly enhanced by cheno. As a further result of the
lowered Rt and the increased Rct, the injected electrons can be
collected much more efficiently, which is reflected by a
normalized diffusion length well above 153 if 2c is coadsorbed
with cheno (Figure S8), which is in line with a higher Jsc.
Without cheno, N749 allows a higher Rct than 2c, which leads
to an intermediate normalized diffusion length when compared
to 2c with and without cheno (Figure S8). The slightly higher
recombination tendency for the sensitizer 2c suggests a less
effective surface coverage than for N749 and/or interactions
between iodine and 2c. Nonetheless, 2c is not expected to leave
larger voids on the TiO2 surface, since, even in the absence of
cheno, a promising performance (Jsc = 6.2 mA cm−2, Voc = 0.70
V, FF = 0.58, PCE = 2.7%) was achieved in an initial attempt
using a [CoIII(bpy)3](PF6)3/[CoII(bpy)3](PF6)2-containing
electrolyte14,58 (see SI). This is attributed to the decoration
of 2c with hexyl chains allowing a more effective protection of
the TiO2 surface from the bulky redox mediator and, thus, a
diminution of recombination reactions, which are typically
observed when using thiocyanate-based benchmark dyes and
the same Co(III)/Co(II)-based redox shuttle.14,59
Table 2. Selected DSSC Data for the Ruthenium(II)
Complexes Measured under AM1.5 Light Conditions
a
dye
2c
cheno
Voc/V
Jsc/ mA cm−2
FF
PCE/%
no
yes
no
0.61
0.62
0.69
8.9
11.8
12.7
0.70
0.63
0.66
4.0
4.9
6.1
2c
N749
a
Conditions: TiO2 layer thickness of 12 μm (20 nm particles) + 3 μm
(400 nm particles), active area of 0.28 cm2; acetonitrile-based
electrolyte containing 0.6 M 1,3-dimethylimidazolium iodide, 0.06 M
I2, 0.1 M LiI, 0.5 M tBP, and 0.1 M guanidinium thiocyanate.
CONCLUSION
■
The new heteroleptic bis(tridentate) ruthenium(II) complex
featuring 1,2,3-triazolates was accessed by a facile and modular
synthesis and possesses photophysical and electrochemical
properties suitable for DSSC application. In comparison to
ruthenium(II) polypyridyl complexes ([Ru(tpy)2](PF6)2), the
presented compounds exhibit prolonged excited-state lifetimes
and room-temperature emission. A promising DSSC perform-
ance was achieved with different types of electrolytes.
Prospectively, the thiocyanate-free, bis(tridenate) sensitizer
platform should enable an extended DSSC life span18 and
offers the potential to optimize the light-harvesting capability
via attachment of additional chromophores at the central
pyridine ring of the anionic ligand.12,23
Figure 6. Selected J−V curves of 2c and N749 (see Table 2 for
conditions).
EXPERIMENTAL SECTION
■
[RuII(tpy)(MeCN)3](PF6)2,34 [RuII(tcmtpy)(MeCN)3](PF6)2,34 2,6-
diethynylpyridine,60 and azidomethyl pivalate33 were synthesized
according to literature procedures. Dry toluene was obtained from a
Pure Solv MD-4-EN solvent purification system (Innovative
Technologies Inc.). Triethylamine was dried over KOH. Methanol
was dried by distillation over magnesium and kept under nitrogen
using standard Schlenk techniques. Tcmtpy was purchased from
hetcat. [Ru(Htctpy)(NCS)3](NBu4)3 was purchased from Solaronix.
All other chemicals were purchased from commercial suppliers and
used as received. All reactions were performed in oven-dried flasks and
were monitored by thin-layer chromatography (TLC) (silica gel on
aluminum sheets with fluorescent dye F254, Merck KGaA). Micro-
wave reactions were carried out using a Biotage Initiator Microwave
synthesizer. NMR spectra have been recorded on a Bruker AVANCE
250 MHz, AVANCE 300 MHz or AVANCE 400 MHz instrument in
deuterated solvents (euriso-top) at 25 °C. 1H and 13C resonances were
assigned using appropriate 2D correlation spectra. Chemical shifts are
reported in ppm using the solvent as internal standard. Matrix-assisted
laser desorption-ionization time-of-flight (MALDI-TOF) mass spectra
were obtained using an Ultraflex III TOF/TOF mass spectrometer
with dithranol as matrix in reflector mode. High-resolution electro-
spray-ionization time-of-flight mass spectrometry (ESI-Q-TOF MS)
was performed on an ESI-(Q)-TOF-MS microTOF II (Bruker
Daltonics) mass spectrometer. UV−vis absorption spectra were
recorded on a Perkin-Elmer Lambda 750 UV/vis spectrophotometer,
Figure 7. Photocurrent action spectra of 2c and N749.
values observed in the absence of cheno are not caused by
inefficient regeneration or injection but rather by more
pronounced recombination reactions (vide infra). Similarly, it
was reported that the PCE achieved with N749 could be
increased from 4.3 to 4.7% by coadsorption with cheno,
although the higher PCE is mostly a result of an increased
voltage.52
To better understand the effect of cheno, electrochemical
impedance spectroscopy was performed (Figure S8).16,51,53−56
A secondary effect is the lowering of the transport resistance
(Rt), which is usually caused by a lowered TiO2 conduction-
band energy.53 This effect may be ascribed to a reduced
accessibility of the TiO2 surface for the tBP electrolyte
additive,16 which is known to raise the conduction band.57
The expected concomitant lowering of the recombination or
charge-transfer resistance (Rct) is apparently overcompensated
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and emission spectra on a Jasco FP6500. Measurements were carried
out using 10−6 M solutions of respective solvents (spectroscopy grade)
in 1 cm quartz cuvettes or on dye-loaded, transparent TiO2 anodes (12
μm thick, 0.88 cm2 active area, see the Cell Fabrication) at room
temperature. Acid−base titration was carried out in aqueous solution
containing Britton−Robinson buffer (0.04 M phosphoric acid, 0.04 M
acetic acid, 0.04 M boronic acid).61 The pH value was adjusted using 2
M aqueous solutions of hydrochloric acid and sodium hydroxide. The
resulting spectral behavior was monitored recording UV−vis
absorption and emission spectra at distinct pH values. The variation
of absorbance and emission intensity was analyzed for selected
wavelengths by fitting a sigmoidal Boltzmann function to the
experimental data; the obtained turning points represent the pKa
values. Emission lifetimes are mostly obtained by time-correlated
single-photon counting. Here, a Titan:Sapphire laser (Tsunami,
Newport Spectra-Physics GmbH) is used as the light source. The
repetition rate is reduced to 400 kHz by a pulse selector (model 3980,
Newport Spectra-Physics GmbH). Afterwards, the fundamental beam
of the Ti-Sapphire oscillator is frequency doubled in a second
harmonic generator (Newport Spectra-Physics GmbH) to create the
500-nm pump beam. The emission is detected by a Becker & Hickel
PMC-100-4 photon-counting module. For these measurements the
instrumental response function was on the order of several
nanoseconds due to filter fluorescence. Thus, for lifetime determi-
nation the first 10−15 ns after excitation were consequently ignored.
In most cases a monoexponential fitting was carried out with the rest
of the data points. However, both models yield the same numerical
data for the respective longer lifetime being the subject of the
discussion. Since the lifetimes reported are significantly longer than the
instrumental response, we claim our results with a typical uncertainty
of 10%. For some measurements, excitation was carried out at 390 nm
and emission was detected by a Hamamatsu HPDTA streak camera via
a suitable spectrograph. Here, the decay curves were obtained as the
spectral integral, as no spectral relaxation was observed. Samples are
prepared to yield an optical density of 0.1 at the excitation wavelength.
Cyclic voltammetry measurements were performed on a Metrohm
Autolab PGSTAT30 potentiostat with a standard three-electrode
configuration using a graphite-disk working electrode, a platinum-rod
auxiliary electrode, and a Ag/AgCl reference electrode; scan rates from
50 to 500 mV·s−1 were applied. The experiments were carried out in
degassed solvents (spectroscopy grade) containing 0.1 M Bu4NPF6
salt (dried previously by heating at 110 °C and storing under vacuum).
At the end of each measurement, ferrocene was added as an internal
standard. All calculations are based on density functional theory
(DFT). The geometries of the singlet ground state and the singly
oxidized ground state have been optimized for all the ruthenium(II)
complexes, presented herein. The hybrid functional B3LYP62,63 has
been selected in combination with the 6-31G* basis set for all atoms.
To reproduce the measured absorption UV−vis spectrum, the lowest-
lying 75 vertical singlet electronic excitation energies were calculated
using time-dependent DFT (TD-DFT) at the S0 optimized geometry.
The TD-DFT calculations were performed in solution using
acetonitrile as solvent with the polarization continuum model and
with the same functional and basis set as in the optimizations.64,65 All
these calculations were performed with the Gaussian09 program
package.66 The analysis of the EDDM calculations were performed by
GaussSum2.2.67 Electron-density difference maps (density isovalue =
0.001), Kohn−Sham orbitals (MO isovalue = 0.04), and spin-density
calculations (density isovalue = 0.004) were visualized by Gauss-
View5.0.8.66
containing the dyes 2c and N749, respectively. The stained films were
rinsed copiously with the solvent they were dipped in and
subsequently dried. The cells were fabricated using a Pt-coated
counter electrode (FTO TEC-15 (15 Ω cm−2)) that was heated to 450
°C for 15 min under ambient atmosphere and allowed to cool to room
temperature prior to the assembling. Both electrodes were sandwiched
with a 30 μm Surlyn (Dupont) gasket by resistive heating. An
acetonitrile electrolyte solution, El 1 (0.6 M 1,3-dimethylimidazolium
iodide (DMII), 0.06 M I2, 0.1 M LiI, 0.5 M 4-tert-butylpyridine (tBP),
and 0.1 M guanidinium thiocyanate (GuSCN)), El 2 (0.21 M
[Co(bpy)3](PF6)2, 0.033 M [Co(bpy)3](PF6)3, 0.1 M LiClO4, 0.5 M
tBP), was introduced to the void via vacuum backfilling through a hole
in the counter electrode. The hole was sealed with an aluminum-
backed Bynel foil (Dyesol). After sealing, silver bus bars were added to
all cells.51,14
Cell Characterization. Photovoltaic measurements were recorded
with a Newport Oriel solar simulator (model 9225A1) equipped with a
class A 150 W xenon light source powered by a Newport power supply
(model 69907). The light output (area = 5 cm × 5 cm) was calibrated
to AM 1.5 using a Newport Oriel correction filter to reduce the
spectral mismatch in the region of 350−700 nm to less than 1.5%. The
power output of the lamp was measured to 1 Sun (100 mW cm−2)
using a certified Si reference cell. The current−voltage (I−V)
characteristic of each cell was obtained by applying an external
potential bias to the cell and measuring the generated photocurrent
with a Keithley digital source meter (model 2400). All cells were
measured without a mask. IPCE measurements were performed on a
QEX7 Solar Cell Spectral Response Measurement System from PV
Instruments, Inc. The system was calibrated with a photodiode that
was calibrated against NIST standard I755 with transfer uncertainty
less than 0.5% between 400 and 1,000 nm and less than 1% at all other
wavelengths. All measurements were carried out in AC mode at 4 Hz
chopping frequency under a bias light between 0.01 and 0.1 sun. The
system was calibrated and operated in Beam Power mode. Electro-
chemical impedance spectroscopy (EIS) was performed on a Gamry
EIS300 potentiostat. All EIS experiments were performed in the dark
and scanned the frequency range from 100 kHz to 0.5 Hz with a 10
mV voltage modulation applied to the bias.51
Synthesis of L1. According to the literature,32,33 a mixture of
aqueous HCHO (37%, 1.2 mL, 13.6 mmol), concentrated AcOH
(96%, 0.14 mL, 2.1 mmol), and 1,4-dioxane (1.2 mL) was stirred at
room temperature for 15 min. After the addition of sodium azide
(153.3 mg, 2.36 mmol) and 2,6-diethynylpyridine (100 mg, 0.79
mmol), the mixture was stirred at room temperature for additional 10
min. Subsequently, concentrated aqueous solutions, first of sodium
ascorbate (63 mg, 0.32 mmol) and then of CuSO4 (13 mg, 0.08
mmol), were added and the resulting mixture was stirred at room
temperature for 24 h. After the complete conversion of the alkyne was
confirmed by TLC, EDTA was added (30 mg, 0.1 mmol), and stirring
was maintained for 2h. After addition of an excess of water, the
resulting suspension was filtered and washed with a minimal amount
of water, and the obtained solid was kept. Additionally, the filtrate was
extracted 3 times with ethyl acetate, and the organic solvent was
removed in vacuo. The obtained solids were combined, MeOH/H2O
(1:1, 6 mL), solid NaOH (140 mg, 3.5 mmol) was added, and the
mixture was stirred at room temperature for 24 h. After neutralization
with 1 M HCl (3.5 mL) and addition of H2O (30 mL), the formed
precipitate was filtered, washed with water, and dried in vacuo to yield
128 mg (0.6 mmol, 76%) of a white solid. 1H NMR (400 MHz,
DMSO-d6, ppm) δ = 15.37 (s, 2H, NH), 8.53 (s, 2H, Ntrz−H), 8.29−
7.67 (m, 3H, H3a′,4a′,5a′). 13C NMR (100 MHz, DMSO-d6, ppm) δ =
149.37, 145.43, 138.27, 128.43, 118.98 MS (MALDI-TOF, dithranol):
calcd for C22H29N ([M + H]+): m/z = 214.0834; found: m/z =
214.0640.
Cell Fabrication. Photoanodes were prefabricated by Dyesol, Inc.
(Australia) with a screen-printable TiO2 paste (18-NRT, Dyesol). The
active area of the TiO2 electrode is 0.28 cm2 with a thickness of 12 μm
(18-NRT) and 3 μm (WER4-O) on fluorine-doped tin-oxide (FTO;
TEC15 (15 Ω cm−2)). TiO2 substrates were treated with TiCl4(aq)
(0.05 M) at 70 °C for 30 min and subsequently rinsed with H2O and
EtOH and dried prior to heating. The electrodes were heated to 450
°C for 20 min under ambient atmosphere and allowed to cool to 80
°C before dipping into the dye solution. The anode was soaked
overnight for 16 h in a methanol and ethanol solution (∼0.25 mM)
Synthesis of 2,6-Di(oct-1-yn-1-yl)pyridine. Under a nitrogen
atmosphere, 2,6-dibromopyridine (2.34 g, 9.87 mmol), Pd(PPh3)4
(583 mg, 0.51 mmol, 5 mol-%), and CuI (101.2 mg, 0.53 mmol, 5
mol-%) were suspended in deaerated toluene/triethylamine (4:1, v/v
53 mL). The resulting suspension was additionally purged with
nitrogen. Subsequently, 1-octyne (4.15 mL, 27.87 mmol, 2.8 equiv)
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Inorganic Chemistry
Article
3
4
was added dropwise at room temperature to the stirred suspension.
The reaction mixture was heated to 55 °C with an oil bath, and the
reaction was monitored by GC-MS. After 72 h, the reaction mixture
was allowed to cool to room temperature and filtered, and the
remaining solid was washed with toluene. The filtrate was evaporated
in vacuo, and the obtained solid was dissolved in CH2Cl2 and extracted
with aqueous NH4Cl to remove Cu(I). The organic phase was dried
over Na2SO4, concentrated in vacuo, and purified by column
chromatography (silica, CH2Cl2/n-hexane 1:1; Rf = 0.4). The solvents
were evaporated in vacuo to yield 2.07 g (7.00 mmol, 71%) of a yellow
H3a′,4a′,5a′, 4′, 3,3″), 7.91 (td, J = 7.9 Hz, J = 1.5 Hz, 2H, H4,4″), 7.29
(d, 3J = 4.9 Hz, 2H, H6,6″), 7.18 (ddd, 3J = 7.5, 5.5 Hz, 4J = 1.2 Hz, 2H,
H5,5″); MS (MALDI-TOF, dithranol): calcd for C36H41N10Ru ([M +
H]+): m/z = 547.0691; found: m/z = 547.0840.
Note: Under the reaction conditions, a partial triazole N-
alkylation,68 presumably due to the formation of a carbenium ion
from the alcohol solvent under the acidic reaction conditions was
observed; however, the minor side product was easily removed by
trituration of the reaction mixture with MeOH/NEt3 (9:1, v/v).
Nonetheless, TEGDME was chosen as solvent in case of 2b (vide
infra) in order to circumvent this side reaction.
Synthesis of 2a. A 20 mL microwave vial was charged with L2
(160 mg, 0.419 mmol), [Ru(tpy)(MeCN)3](PF6)2 (313 mg, 0.419
mmol), and EtOH (17 mL). The vial was capped and the suspension
purged with nitrogen for 10 min. Subsequently, the mixture was
heated to 160 °C for 30 min in the microwave reactor. The full
conversion of the precursor was proven by TLC (silica, MeCN/H2O/
aq KNO3 40:4:1). NEt3 was added to the crude product mixture to
ensure complete deprotonation. Afterwards, the black solid was filtered
and thoroughly washed with EtOH/NEt3 (9:1, v/v). The solid was
dried and suspended in MeOH/NEt3 (9:1, v/v), filtered, washed again
with MeOH/NEt3 (9:1, v/v), and dried to yield 215 mg (0.301 mmol,
72%) of a black solid. Due to the low solubility of the charge-neutral
1
3
oil. H NMR (250 MHz, CD2Cl2, ppm) δ = 7.53 (t, J = 7.8 Hz, 1H,
H4a′), 7.23 (d, 3J = 7.8 Hz, 2H, H3a′,5a′), 2.42 (t, 3J = 7.0 Hz, 4H, CC−
CH2−CH2−), 1.71−1.53 (m, 4H, CC−CH2−CH2−), 1.53−1.19 (m,
3
12H, −CH2−), 0.90 (t, J = 6.6 Hz, 6H, CH3); 13C NMR (63 MHz,
CD2Cl2, ppm) δ = 144.3, 136.5, 125.7, 91.3, 80.5, 31.8, 29.1, 28.8, 22.9,
19.6, 14.2 ppm; MS (HR ESI-Q-TOF): calcd for C22H29N ([M +
H]+): m/z = 296.2371; found: m/z = 296.2460.
Synthesis of PL2. A 20 mL microwave vial was charged with 2,6-
di(oct-1-yn-1-yl)pyridine (1.27 g, 4.29 mmol) and azidomethyl
pivalate (1.67 g, 10.65 mmol, 2.5 equiv). The vial was capped and
heated to 100 °C in an oil bath for 72 h. The completion of the
reaction was confirmed by TLC (alumina, CH2Cl2) and GC-MS. All
volatiles were removed in vacuo, and the remaining solid was subjected
to column chromatography (alumina, CH2Cl2/n-hexane, 3:1). All
product fractions (irrespective of the regioisomer) were combined to
yield 1.99 g (3.27 mmol, 76%) of a brown oil. For the NMR analysis,
the asymmetric product (see Scheme 1) was used exemplarily. 1H
1
complex, TFA was added for NMR analysis. H NMR (400 MHz,
CD2Cl2 + CF3COOH, ppm) δ = 8.45 (d, J = 8.1 Hz, 2H, H3′,5′),
3
8.32−8.19 (m, 4H, H3,3″,4′,4a′), 8.04 (d, 3J = 8.1 Hz, 2H, H3a′,5a′), 7.87
(t, 3J = 7.8 Hz, 2H, H4,4″), 7.26 (d, 3J = 5.1 Hz, 2H, H6, 6″), 7.15 (d, 3J
= 6.4 Hz, 2H, H5, 5″), 3.23−3.04 (m, 4H, C5a,5a″−CH2−), 1.86−1.64
(m, 4H, C5a,5a″−CH2−CH2−), 1.48−1.17 (m, 12H, −CH2−), 1.04−
0.77 (m, 6H, −CH3); 13C NMR (100 MHz, CD2Cl2 + CF3COOH,
ppm) δ = 159.0, 156.7, 152.0, 151.2, 144.1, 141.1, 138.1, 137.1, 135.8,
127.6, 124.1, 122.7, 118.6, 31.5, 29.1, 28.6, 24.0, 22.8, 14.0; MS (HR
ESI-Q-TOF): calcd for C36H41N10Ru ([M + H]+): m/z = 715.2550;
found: m/z = 715.2328.
3
NMR (250 MHz, CD2Cl2, ppm) δ = 8.28 (d, J = 8.0 Hz, 1H, H3a′),
7.94 (t, 3J = 7.9 Hz, 1H, H4a′), 7.38 (d, 3J = 7.6 Hz, 1H, H5a′), 6.44 (s,
2H, N−CH2−O), 6.27 (s, 2H, Ntrz−CH2−O), 3.33−2.99 (m, 2H,
C5a−CH2−CH2), 2.88−2.67 (m, 2H, C5a″−CH2−CH2), 1.79−1.45
(m, 4H, C5a,5a″−CH2−CH2), 1.35−1.07 (m, 21H, CH2, Htert‑butyl), 0.96
(s, 9H, −CH3), 0.92−0.59 (m, 6H, Htert‑butyl); 13C NMR (63 MHz,
CD2Cl2, ppm) δ = 177.1, 176.7, 152.9, 147.2, 147.1, 143.0, 138.4,
138.0, 133.5, 123.4, 121.5, 70.3, 69.1, 39.1, 38.9, 31.8, 31.7, 29.6, 29.4,
29.2, 29.2, 27.0, 26.8, 25.5, 23.5, 22.9, 22.8, 14.2, 14.1; MS (HR ESI-Q-
TOF): calcd for C33H52N7O4 ([M + H]+): m/z = 610.4081; found: m/
z = 610.4084.
Synthesis of 2b. A 10 mL microwave vial was loaded with
[Ru(tcmtpy)(MeCN)3](PF6)2 (80 mg, 0.086 mmol), L2 (33 mg,
0.086 mmol), and TEGDME (4.8 mL) The vial was capped, and the
solution was purged with nitrogen for 10 min. Subsequently, the
reaction mixture was heated to 150 °C for 30 min in the microwave
reactor. After the full conversion of [Ru(tcmtpy)(MeCN)3](PF6)2 was
confirmed by TLC (silica, MeCN/H2O/aq KNO3 40:4:1), the
reaction mixture was dropped into H2O and the precipitate was
filtered, washed with H2O, rinsed with MeCN, and subjected to
column chromatography (silica, MeCN/MeOH 9:1). Subsequently,
the product was precipitated in H2O from a concentrated MeCN
solution, additionally washed with H2O, and rinsed with MeCN. After
evaporation of the solvent in vacuo, 44 mg (0.049 mmol, 58%) of a red
Synthesis of L2. According to the literature,33 PL2 (1.4 g, 2.29
mmol) and NaOH (210 mg, 5.25 mmol, 4.4 equiv) were dissolved in
MeOH/H2O (1:1, v/v 30 mL) and the mixture was stirred at room
temperature. The full conversion of the educt was determined by TLC
(alumina, CH2Cl2). After 24 h, the reaction mixture was dropped into
HClaq (0.175 M) and, subsequently, neutralized with NaHCO3. The
precipitated product was filtered, washed with water, and dried in
vacuo to yield 650 mg (1.71 mmol, 74%) of a colorless solid. 1H NMR
(250 MHz, DMSO-d6, ppm) δ = 15.20 (s, 1H, N−H), 14.80 (s, 1H,
N−H), 7.93 (m, 3H, H3a′,4a′5a′), 3.26−2.88 (m, 4H, C5a,5a″−CH2−),
1.80−1.43 (m, 4H, C5a,5a″−CH2−CH2−), 1.38−1.04 (m, 12H,
−CH2−), 0.85−0.63 (m, 6H, −CH3). 13C NMR (63 MHz, DMSO-
d6, ppm) δ = 151.6, 151.1, 145.2, 142.7, 141.1, 137.6, 135.9, 120.4,
112.0, 119.7, 119.3, 31.0, 30.9, 28.2, 25.2, 22.8, 21.9, 13.8; MS (HR
ESI-Q-TOF): calcd for C21H31N7Na ([M + Na]+): m/z = 404.2538;
found: m/z = 404.2513. Elem. anal. calcd for C21H31N7 (381.52): C,
66.11%; H, 8.19%; N, 25.70%; found: C, 64.93%; H, 8.78%, N,
25.82%.
Synthesis of 1. A 10 mL microwave vial was charged with L1 (50
mg, 0.23 mmol), [Ru(tpy)(MeCN)3](PF6)2 (175 mg, 0.23 mmol),
and EtOH (8 mL). The vial was capped and the suspension was
purged with nitrogen for 10 min. Subsequently, the mixture was
heated to 150 °C for 30 min in the microwave reactor. NEt3 (1 mL)
was added to the reaction mixture to complete the precipitation. The
dark precipitate was filtered and washed thoroughly with MeOH/NEt3
(9:1, v/v) and, subsequently, with CH2Cl2. The obtained solid was
allowed to dry upon standing, yielding 99 mg (0.18 mmol, 77%) of a
dark brown solid. Due to the low solubility of the charge-neutral
complex, some drops of trifluoroacetic acid (TFA) were added for the
NMR analysis. A 13C NMR spectrum could not be recorded, owing to
the low solubility. 1H NMR (400 MHz, CD2Cl2 + CF3COOH, ppm) δ
= 8.68 (s, 2H, H5a,5a″), 8.48 (d, 3J = 8.1, 2H, H3′,5′), 8.40−8.21 (m, 6H,
1
solid were obtained. H NMR (400 MHz, CD2Cl2, ppm) δ = 9.08 (s,
2H, H3′,5′), 8.85 (s, 2H, H3,3″), 8.04 (t, J = 7.9 Hz, 1H, H4a′), 7.71 (d, J
= 8.0 Hz, 2H, H3a′,5a′), 7.62 (d, J = 4.3 Hz, 2H, H5,5″), 7.58 (d, J = 5.8
Hz, 2H, H6,6″), 4.16 (s, 3H, −COOCH3′), 3.95 (s, 6H, −COOCH3),
2.94 (t, 4H, C5a,5a″−CH2−), 1.75−1.62 (m, 4H, C5a,5a″−CH2−CH2−),
1.34 (m, 12H, −CH2−), 0.87 (d, J = 6.5 Hz, 6H, −CH3); 13C NMR
(100 MHz, CD2Cl2, ppm) δ = 165.1, 164.2, 159.6, 157.3, 152.4, 152.0,
146.8, 141.0, 137.2, 136.8, 132.4, 126.3, 122.2, 121.5, 114.7, 53.5, 53.4,
32.0, 29.8, 29.6, 26.9, 23.0, 14.2; MS (HR ESI-Q-TOF): calcd for
C42H47N10O6Ru ([M + H]+): m/z = 889.2730; found: m/z =
889.2861.
Synthesis of 2c. According to the literature,12,69 2b (30 mg, 0.03
mmol) was suspended in DMF/NEt3/H2O (3:1:1, v/v 3 mL) and
heated to reflux under a nitrogen atmosphere. After 36 h, the full
conversion was confirmed with MS (MALDI ToF) and the solvents
were evaporated in vacuo. The resultant solid was suspended in
CH2Cl2 and collected by centrifugation. The solvent was decanted,
and this procedure was repeated twice with CH2Cl2 and once with
MeOH. The remaining solid was dried in vacuo to obtain 16 mg (0.02
mmol, 56%) of a brown solid. 1H NMR (400 MHz, MeOD, ppm) δ =
9.23 (s, 2H, H3′,5′), 9.02 (s, 2H, H3,3″), 8.36 (t, J = 7.9 Hz, 1H, H4a′),
8.22 (d, J = 8.1 Hz, 2H, H3a′,5a′), 7.70 (d, J = 5.7 Hz, 2H, H5,5″), 7.58
(d, J = 5.5 Hz, 2H, H6,6″), 3.19−3.10 (m, 4H, C5a,5a″−CH2−), 1.84−
1643
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1.72 (m, 4H, C5a,5a″−CH2−CH2−), 1.48−1.25 (m, 12H, −CH2−),
0.88 (t, J = 7.0 Hz, 6H, −CH3); MS (MALDI-TOF, dithranol): calcd
for C39H40N10O6Ru ([M + H]+): m/z = 847.2780; found: m/z =
847.2221.
(17) Dragonetti, C.; Colombo, A.; Magni, M.; Mussini, P.; Nisic, F.;
Roberto, D.; Ugo, R.; Valore, A.; Valsecchi, A.; Salvatori, P.; Lobello,
M. G.; De Angelis, F. Inorg. Chem. 2013, 52, 10723.
(18) Hsu, C.-W.; Ho, S.-T.; Wu, K.-L.; Chi, Y.; Liu, S.-H.; Chou, P.-
T. Energy Environ. Sci. 2012, 5, 7549.
(19) Yeh, H.-H.; Ho, S.-T.; Chi, Y.; Clifford, J. N.; Palomares, E.; Liu,
S.-H.; Chou, P.-T. J. Mater. Chem. A 2013, 1, 7681.
(20) Wang, S.-W.; Wu, K.-L.; Ghadiri, E.; Lobello, M. G.; Ho, S.-T.;
Chi, Y.; Moser, J.-E.; De Angelis, F.; Gratzel, M.; Nazeeruddin, M. K.
ASSOCIATED CONTENT
* Supporting Information
Additional computational, photophysical, electrochemical, and
EIS data as well as NMR and MS spectra. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
̈
Chem. Sci. 2013, 4, 2423.
(21) Wu, K.-L.; Li, C.-H.; Chi, Y.; Clifford, J. N.; Cabau, L.;
Palomares, E.; Cheng, Y.-M.; Pan, H.-A.; Chou, P.-T. J. Am. Chem. Soc.
2012, 134, 7488.
(22) Wu, K.-L.; Hsu, H.-C.; Chen, K.; Chi, Y.; Chung, M.-W.; Liu,
W.-H.; Chou, P.-T. Chem. Commun. 2010, 46, 5124.
(23) Chou, C.-C.; Wu, K.-L.; Chi, Y.; Hu, W.-P.; Yu, S. J.; Lee, G.-H.;
Lin, C.-L.; Chou, P.-T. Angew. Chem., Int. Ed. 2011, 50, 2054.
(24) Bomben, P. G.; Robson, K. C. D.; Koivisto, B. D.; Berlinguette,
C. P. Coord. Chem. Rev. 2012, 256, 1438.
AUTHOR INFORMATION
Corresponding Author
*E-mail: benjamin.dietzek@uni-jena.de (B.D.), cberling@
chem.ubc.ca (C.P.B.), ulrich.schubert@uni-jena.de (U.S.S.).
■
Author Contributions
△S.S. and B.S. contributed equally to this work.
Notes
(25) Wang, M.; Moon, S.-J.; Zhou, D.; Le Formal, F.; Cevey-Ha, N.-
The authors declare no competing financial interests.
L.; Humphry-Baker, R.; Gratzel, C.; Wang, P.; Zakeeruddin, S. M.;
̈
Gratzel, M. Adv. Funct. Mater. 2010, 20, 1821.
̈
ACKNOWLEDGMENTS
■
(26) Wang, P.; Zakeeruddin, S. M.; Moser, J. E.; Nazeeruddin, M. K.;
B.S. and C.F. are grateful to the Fonds der Chemischen
Industrie for Ph.D. scholarships. B.D. thanks the Fonds der
Chemischen Industrie for financial support. M.J. is grateful to
the Carl Zeiss foundation for financial support. D.G.B. and
C.P.B. are grateful to the Canadian Natural Science and
Engineering Research Council, the Canadian Foundation for
Innovation, Alberta Ingenuity, and the Alfred P. Sloan
Foundation for support.
Sekiguchi, T.; Gratzel, M. Nat. Mater. 2003, 2, 402.
̈
(27) Zakeeruddin, S. M.; Nazeeruddin, M. K.; Humphry-Baker, R.;
́
Pechy, P.; Quagliotto, P.; Barolo, C.; Viscardi, G.; Gratzel, M.
̈
Langmuir 2002, 18, 952.
(28) Crowley, J. D.; McMorran, D. A. In Topics in Heterocyclic
Chemistry: Click Triazoles; Kosm
Heidelberg, 2012; Vol. 28, p 31.
(29) Struthers, H.; Mindt, T. L.; Schibli, R. Dalton Trans. 2010, 39,
675.
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rlj, J., Ed.; Springer: Berlin
(30) Schulze, B.; Schubert, U. S. Chem. Soc. Rev., in press, DOI:
10.1039/c3cs60386e.
(31) Duati, M.; Tasca, S.; Lynch, F. C.; Bohlen, H.; Vos, J. G.; Stagni,
S.; Ward, M. D. Inorg. Chem. 2003, 42, 8377.
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