Ferrocenylethenyl-substituted oxadiazoles with phenolic and nitro anchors as sensitizers in dye sensitized solar cells

Article abstract of DOI:10.1039/c8nj06242k

Three new ferrocenyl oxadiazoles, viz. (E)-2-(4-hydroxyphenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole (D2), (E)-2-(4-nitrophenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole (D3) and (E)-3-(4-nitrophenyl)-5-[5-(2-ferroceneylethen-1-yl)-1,3,4-oxadia

Full text of DOI:10.1039/c8nj06242k

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2019, DOI: 10.1039/C8NJ06242K.
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DOI: 10.1039/C8NJ06242K
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Ferrocenylethenyl-substituted oxadiazoles with phenolic and nitro
anchors as sensitizers in dye sensitized solar cells
a
b
c
d
a
Amita Singh, Gabriele Kociok-Köhn, Manoj Trivedi, Ratna Chauhan, * Abhinav Kumar, * Suresh
Received 00th January 20xx,
Accepted 00th January 20xx
e
f
f
W. Gosavi , Chiaki Terashima and Akira Fujishima
DOI: 10.1039/x0xx00000x
Three new ferrocenyl oxadiazoles viz. (E)-2-(4-hydroxyphenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole (D2), (E)-2-(4-
nitrophenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole (D3) and (E)-3-(4-nitrophenyl)-5-[5-(2-ferroceneylethen-1-yl)-
1,3,4-oxadiazol-2-yl]-1,2,4-oxadiazole (D4) derived from (E)-3-ferrocenylacrylic acid (D1) having phenolic or nitro anchors
have been synthesized and characterized using microanalyses and relevant spectroscopic techniques. UV-Vis spectroscopic
studies indicate that with respect to ferrocene the electronic absorption bands new compounds are bathochromically
shifted up to 600 nm with concomitant enhancement in their intensities. All four compounds have been used as
www.rsc.org/
photosensitizers in TiO -based dye-sensitized solar cells (DSSCs). The photovoltaic performances and charge transport
2
properties (EIS spectra) of these compounds were studied to appraise their dye performance. All four compounds displayed
good photovoltaic performances. However, compounds D2 and D4 displayed superior performance which might be due to
the better electronic communication between the ferrocenyl moiety and the six membered aromatic ring with their –
OH/NO
2
anchors through five membered oxadiazole spacers, as well as the high dye loading of these compounds on the TiO
2
surface, which suppresses charge recombination, prolongs electron lifetime, and decreases the total resistance of DSSCs.
The assembly fabricated using D4 performed superior with an overall conversion efficiency η of 4.70%, Jsc of 10.33 mA.cm-2
and Voc of -0.712 V.
9
porphyrins and pervoskites have shown remarkable power
Introduction
During the past two decades dye-sensitized solar cells (DSSCs),
conversion efficiency (PCE). However, their high cost especially
the Ru-based dyes limit their practical implementation.
To resolve this issue, several organic dyes possessing
versatile structures have been employed as sensitizers in DSSCs.
Organic dyes comprising of triphenylamine (TPA) donors and
different π-conjugated linkers such as aromatic and
heteroaromatic moieties with cyanoacrylic acid as
anchoring/acceptor group were best suited to enhance the
photovoltaic performances of DSSCs.10
have been attracting enormous attention amongst the scientific
community1,
2
as they offer edge over the conventional
photovoltaic devices such as they are light weight, colored and
flexible and have established power conversion efficiency
3
4
reported from 11.4% to 14.3%. The key component in DSSCs
are sensitizers which play crucial role in DSSCs as they control
the light harvesting and charge separation properties.1
Additionally, the structure of sensitizers can be modified to
enhance the molar extinction coefficient as well as the solar light
harvesting capacity. This objective can be accomplished by
modifications in the chromophore and anchoring group which
therefore can improve the photocurrent and efficiency of
DSSC.5-7 Several metal based sensitizer viz. Ru-based dyes, Zn
During recent years we have been continuously working to
develop ferrocene and its derivatives as possible photo-
sensitizers that can be used in DSSC. In our pursuit to develop
potential ferrocene based sensitizers we have reported the light
harvesting properties of the homo- and heteroleptic complexes
of ferrocenyl dithiocarbamates,11-14 and their organomercury(II)
derivatives.15,16 We also worked on ferrocene dithiocarbamate
and dithiocarbonate as anchors in DSSCs.17 In addition to these
sulphur derivatives π-conjugated derivatives of ferrocene and
biferrocene with different anchors have been reported by our
8
a.Department of Chemistry, Faculty of Science, University of Lucknow, Lucknow
226007, India, Email: abhinavmarshal@gmail.com
Materials and Chemical Characterisation Facility (MC ), University of Bath, Bath,
b.
2
group.18-21
Recently,
we
deployed
1,1'-
BA2 7AY, UK.
c.
bis(diphenylphosphino)ferrocene appended Ni(II) ditihiolates as
sensitizers22 but they displayed modest photovoltaic efficiencies
due to an unfavourable charge transfer direction.22 Mishra et. al
reported ferrocenyl substituted triphenylamine based donor–
acceptor dyes for dye sensitized solar cells.23 Sirbu et al. found
that DSSCs fabricated using a trisubstituted ferrocene-based
Department of Chemistry, University of Delhi, Delhi, India
Centre for Materials for Electronics Technology, Pune, India Email:
ratnasingh.bhu@gmail.com
Department of Physics, University of Pune, Pune
Photocatalysis International Research Center, Research Institute for Science &
Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510,
Japan
d.
e.
f.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
2
+
3+
porphyrin derivative with a Co /Co electrolyte, resulted in
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NH
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only modest conversion efficiency . Cariello and co-workers
designed some ferrocenyl based dyes and investigated the role of O2N
π-conjugation on the conversion efficiency.25 The choice of
using ferrocene derivatives as sensitizers is down to the well-
defined reversible one-electron redox process26-28 and electron
donating properties.26,29,30 The formal reduction potential of the
ferrocenyl group depends on the nature of the substituents on the
cyclopentadienyl ring. The redox potential can be tuned to obtain
the desired potential for a specific application.26,30,31
In continuation to our development program for
photosensitizers comprising of ferrocene, we found that
oxadiazole derivatives which exist in four regioisomeric forms
View Article Online
(
i)
CN
O N
2
DOI: 10.1039/C8NJ06242K
N
OH
(ii)
N
N
O
O N
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OC H
2
5
O
(iiI)
(
two 1,2,4-isomers, if asymmetrically substituted, a 1,3,4-
N
O
isomer, and a 1,2,5-isomer) have been used as luminescent
materials32 as well as sensitizers in DSSCs.33 Their electron
withdrawing effects have been utilized to develop charge-
transfer species.34 In addition to common oxadiazoles connected
with aromatic rings, the ferrocenyl derivatives of oxadiazoles
have been reported.35 These ferrocenyl oxadiazoles have been
investigated for DNA binding assay35a and antimicrobial
activity.35c Although, the biological properties associated with
ferrocenyl based oxadiazoles are reported but to the best of our
knowledge the applications of ferrocenyl oxadiazoles as
sensitizers in DSSCs have not been reported. In the expedition
of new ferrocene based sensitizers we have synthesized three
new ferrocenylethynyl-substituted oxadiazoles and tested their
ability as sensitizers in DSSCs. The results of these
investigations are presented herewith.
O N
2
H
N
N
NH2
O
N
N
O
O N
2
H
N
NH2
O
O
Et N (5 equiv)
3
OH
TBTU (1.1)
dichloromethane ,TsCl (3 equiv
)
Fe
N
N
O
N
O
NO
2
O
Fe
C
OH
O
O
O
N
H
Piperidine
Pyridine
Reflux 6.5 h
Fe
+
Fe
Scheme 2. Synthetic routes for the sensitizer D4
HO
OH
Conditions: i) NH OH.HCl, NaOH; EtOH, H
2
h. iii) NH NH ·H O; EtOH, r.t.; 1h.
2
2 2 2
O, r.t. 15h. ii) Et O CCOCl, DIPEA; THF, reflux,
O
2
2
2
OH
Results and discussion
Fe
The ferrocenecarboxaldehyde was condensed with malonic acid
in refluxing pyridine/piperidine following the Knoevenagel-
D1
Doebner reaction procedure to produce (
acid (D1) in moderate yield (Scheme 1). The condensation of
)-3-ferrecenylacrylic acid with aromatic acid hydrazides
yielded the desired ferrocenyl 1,3,4-oxadiaoles viz. )-2-(4-
hydroxyphenyl)-5-(2-ferrocenyl-ethen-1-yl)-1,3,4-oxadiazole
D2 and )-2-(4-nitrophenyl)-5-(2-ferrocenyl-ethen-1-yl)-
,3,4-oxadiazole (D3) (Scheme 1). In order to obtain ( )-3-(4-
E)-3-ferrecenylacrylic
O
Et N (5 equiv)
TBTU (1.1)
dichloromethane ,TsCl (3 equiv)
3
R
(E
HN
NH
2
(E
N
N
(
1
)
(E
E
O
nitrophenyl)-5-[5-(2-ferroceneylethen-1-yl)-1,3,4-oxadiazol-2-
yl]-1,2,4-oxadiazole (D4), the hydrazide was prepared using a
three step process, starting with the synthesis of amidoxime by
treating 4-nitro benzene nitrile with hydroxylamine
hydrochloride and aqueous sodium hydroxide ethanol at room
temperature for 15 h. Thereafter amidoxime was condensed with
ethyl oxalyl chloride, employing DIPEA as base, in
tetrahydrofuran at 0 ºC and the reaction mixture was refluxed for
Fe
R
R = OH (D2); R = NO (D3)
2
Scheme 1. Synthetic routes for the sensitizers D1, D2 and D3.
~
2 h, giving the corresponding 1,2,4-oxadiazole. Hydrazinolysis
2
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of the ester in ethanol by action of aqueous hydrazine at room excellent electronic communication between feVrrieowcAernticylelOanlninde
temperature for 1 h yielded 3-(4-nitrophenyl)-1,2,4-oxadiazole- nitro-aromatic entity. Further the coDmOIp: o10s.i1t0io3n9/C8oNfJ06th24e2sKe
5
-carbohydrazide. The obtained final product was condensed sensitizers had been confirmed with the aid of HRMS
with ( )-3-ferrecenylacrylic acid similar to and to get (
)-3- experiments (vide infra).
4-nitrophenyl)-5-[5-(2-ferroceneylethen-1-yl)-1,3,4-oxadiazol-
E
2
3
E
(
2
-yl]-1,2,4-oxadiazole (4) (Scheme 2).
Spectroscopy and X-ray structure description
The sensitizers were characterized using FTIR, H and 13C NMR
spectroscopy as well as high resolution mass spectrometry. The
purity and composition of all sensitizers were assessed with H
NMR spectroscopy which display well resolved signals that
integrated well to the corresponding hydrogens (vide infra). In
the 13C NMR spectra for the dyes D2
0
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1
1
-
D4 the resonances lying in
the region ~
δ 140-165 ppm correspond to oxadiazole ring. The
-
IR spectra of the four dyes show the bands arising at ~3070 cm
1
can which be assigned to the νC-H. The dye D1 displays a band
-
1
near 1668 cm which corresponds to νCOOH. In D2 the band at
3
-
1
490 cm can be ascribed to νOH. The bands arising at 1610 (D1),
-
1
1
604 (D2), 1631 (D3) and 1641 cm (D4) are because of νC=C
bands at 1519 and 1523 cm-1 corresponds to the
)asymm for D3 and D4, respectively, while bands
appearing at 1338 and 1350 cm-1 can be attributed to
ν(NO )symm for D3 and D4, respectively. Also, in all the dyes
bands at ~1450-1490 cm-1 and ~1260 cm-1 correspond to the
.
Fig. 2 Electronic absorption spectra for sensitizers recorded in 10-4 M dichloromethane
solution.
In D3 and D4
ν(NO
,
2
The electronic absorption spectra for the sensitizers were
recorded in dichloromethane solution (Fig. 2) which display
absorption maxima in the visible region ranging between 470 to
500 nm. This band is arising due to the d →d transition (assigned
to 1E1g ← A1g).36 In comparison to D1 which is the base unit of
2
-
1
presence of oxadiazole ring. Additionally band at ~490 cm may
be arising because of the stretching vibration from the Fe-Cp
ring.
1
the sensitizers the band is red shifted in dyes D2, D3 and D4. The
bathochromic shifting may be accredited to extensive
conjugation between the ferrocenyl moiety to the six membered
aromatic ring with anchoring groups via the olefinic moiety and
the oxadiazole linkage. This leads to a strong electronic
communication between ferrocene to the aromatic fragment to
which the anchors are attached. This spectral feature prompted
us to deploy these molecules as potential sensitizers in DSSC.
Fig. 1 Perspective views of the sensitizers D1 (above) and D4 (below).
The perspective view of the dyes D1 and D4 are presented in Fig.
1. The X-ray structures for both the sensitizers indicate that the
exo-cyclic double bond lying in vicinity to ferrocenyl moiety
acquires
E configuration. In the case of D1 the dihedral angle
between the plane formed by five membered Cp ring and olefinic
carbon center is 3.38º. In the case of D4 the two oxadiazole ring
are exactly planar while the dihedral angle between the 1,2,4- Fig. 3 Electronic absorption spectra of dyes adsorbed at TiO
oxadiazole ring and the six membered ring is 1.93º. The dihedral
angle between the Cp ring and 1,3,4-oxadizaole unit is 6.13º.
2
nanoparticulate.
This indicates that the D4 is highly planar molecule and can offer
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The electronic absorption spectra of the dyes recorded on a TiO
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Based on the DOS plot, the minimum inter-banVideweAxrticclietaOtniloinne
DOI: 10.1039/C8NJ06242K
2
film (Fig. 3) shows slight broadening in the maxima range with energy lie in the range of 0.7-1.0 eV for dye@(TiO )30 systems.
minor bathochromic shifts which may arise because of The results of DOS indicates significant electronic coupling
aggregation of the dyes37 or electronic coupling of the dyes on between the LUMO of dyes and the CB of TiO
, which facilitates
the TiO
surface.38 Also, the IR spectra of the dyes after the electron injection from photo-excited dyes in the conduction
adsorption on TiO film displayed perceptible shifting of band of TiO nanoparticle.
ν(C=O)asymm. from 1668 cm to ~ 1637 cm in D1. In D2, band
2
2
2
2
-
1
-1
-
1
Electrochemical properties
at 3490 cm corresponding to νOH disappeared and a new band
0
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-
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ascends at ~3392 cm . While slight shifting of ν(NO
2
)
asymm. from Further evaluation of thermodynamic feasibility of dye
-
1
-1
-1
1
519 cm to 1502 cm and ν(NO
cm in the case of D3 and shifting of ν(NO
to 1506 cm-1 and ν(NO
2
)
symm. from 1338 cm to 1314 regeneration and electron transfer process from photo-excited
-
1
-
2
)
asymm. from 1523 cm dye to conduction band of TiO
2
the position of HOMO and
1
symm. from 1350 cm-1 to 1320 cm in LUMO energy levels have been estimated electrochemically
-1
2
)
the case of D4 have been observed. These results indicate using cyclic voltammetry (Fig 6). From cyclic voltammetry it
binding of dyes by –COOH, –OH and –NO
on TiO
film.21
2
groups, respectively was inferred that the dyes D1 to D4 were highly active towards
photoredox processes. Cyclic voltammetry experiments were
carried out in a three-electrode cell on an electrochemical
workstation using a Pt disc as working electrode and Ag/Ag+ (in
acetonitrile) as reference electrode in dichloromethane
containing 0.1 M tetra-n-butylammonium perchlorate. The
electrochemical parameters for the dyes are summarized in Table
2
1.
Fig. 4 Density of states plots for (TiO
2
)
30 nanocluster and dyes D1 to D4.
Electron injection
To assess whether electrons can be injected by dyes D1-D4 in
the conduction band of TiO nanoparticulte, we have performed
density of states (DOS) calculations on (TiO 30, dyes D1
well as dye+(TiO 30 systems. The results of these calculations
are presented in Figs. 4 and 5. Figure 4 reveals that in comparison
to the DOS of (TiO 30 cluster, the DOS of the dyes shows clearly
localized states, which are all occupied (Fig. 4). In the case of
dye+(TiO 30, the DOS plot clearly indicates core states, valence
band (VB), and conduction band (CB). The fundamental valence
band in (TiO 30 is located at the energy levels roughly between
10.0 eV and –8.2 eV, and the conduction band is located
starting from –4.6 eV. The DOS plot for the (TiO 30 cluster
2
2
)
-
2 2 30
D4 as Fig. 5 Density of states plots for (TiO )30 nanocluster and dyes@(TiO ) .
2
)
2
)
2
)
2
)
–
2
)
displayed a clear separation between VB and CB without any gap
states (Fig. 4). The adsorption of the dyes onto the nanoparticle
surface introduces occupied states at the lower part of the
nanoparticle band gap and extending the valence states from
around –8.2 eV to –5.6, –5.3, –5.5 and -5.5 eV for D1@(TiO
D2@(TiO D3@(TiO 30 and D4@(TiO 30, respectively
Fig. 5). Based on the DOS plots (Fig. 5), it can be inferred that
2 30
) ,
2
)
30
,
2
)
2
)
(
lower energy electrons are excited from VB energy levels
approximately between –8.2 and –5.6 to –5.3 eV for
dye@(TiO )
2
30 and then transferred to CB states above –4.6 eV. Fig 6 Cyclic voltammogram for the dyes recorded in 10-3 M dichloromethane solution
4
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Table 1. Electrochemical parameters of the dyes (D-1 to D-4) calculated from cyclic Photovoltaic measurements
voltammogram
View Article Online
DOI: 10.1039/C8NJ06242K
To study the photovoltaic properties of the DSSCs fabricated
with the D1 to D4 dyes, the J-V curves were recorded (Fig. 8).
The DSSCs Parameters such as Voc, short-circuit current density
Eo (V)
Δ E
= Ep,a- Ep,c
(V)
+0.210
+0.240
+0.435
+0.216
o
Dyes
E
p,a (V)
E
p,c (V)
= (Ep,a
+
E.S= E + hν
E
p,c)/2
(Jsc), fill factor (FF), η and the maximum values of IPCE are
D-1
D-2
D-3
D-4
+0.650
+0.704
+0.686
+0.568
+0.440
+0.464
+0.252
+0.352
+0.545
+0.584
+0.469
+0.460
-1.96
-1.98
-2.06
-2.16
summarized in 2. The highest cell efficiency η (4.7%) was found
in the case of the D4 dye, although the incorporation of two
oxadiazole units serving as π-bridging group in D4 caused a
slight decrease in the VOC (0.712 V) than D3 comprising of only
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
one oxadiazole unit VOC (0.736 V). The
J
SC was observed to
-2
increase significantly from 7.85 to 10.33ꢀmA·cm for D3 to D4
on incorporation of an additional oxadiazole unit leading to
higher efficiency in D4 probably resulting from better electron
separation. The dye D2 shows the second highest efficiency
among all dyes due to the –OH group which offers better
2
anchorage on the TiO surface thereby leading to a maximum
photon absorption for current conversion (Table 2).
Table 2: Photovoltaic parameters for the dyes D-1 to D-4
Dye
Dyes
J
sc
Max.
IPCE
(%)
Loading
amount
(mmol.
-
(mAcm
2
Voc (V)
FF
(%)
)
-
2
cm )
Fig. 7 Energy level diagram for the cell assembly fabricated by sensitizers D1 to D4.
N719
D-1
D-2
D-3
D-4
13.62
-0.77
0.73
7.70
55
3.78×10-7
-
7
6.35
9.05
7.85
-0.696
-0.711
-0.736
-0.712
0.61
0.64
0.61
0.64
2.71
4.11
3.52
4.70
51
55
53
58
2.79×10
-
7
2.94×10
From Table 1 it is apparent that the excited-state of the dyes are
sufficiently negative (–2.16 to –1.96 V vs. Ag/Ag+ in ACN) than
the conduction band edge of TiO
which ensures an energetically favourable electron injection
from the photo-excited dye to TiO and that the ground states of
the dyes are more positive (+0.545 to +0.460 V vs. Ag/Ag+ in
acetonitrile) which suggests a thermodynamically sufficient
driving force for the regeneration of the dyes (Fig. 7).
Furthermore, the energy level diagram (Fig 7) for the four dyes
shows favourable excited-state oxidation potential with respect
-7
2.81×10
2.95×10
-7
10.33
2
(–0.75 V vs. Ag/Ag+ in ACN),
2
2
to the TiO conduction band. This would ensure better electron
transfer, electron collection which results in higher photocurrent,
and better cell efficiency while favourable ground-state
reduction potential ensures the dye regeneration capability.
Fig. 9 IPCE plots for the dyes D1 to D4.
Figure 9 presents the IPCE spectra of the DSSCs
photosensitized by dyes D1 D4 which are recorded in the region
-
of 400–700 nm. The results of the IPCE measurements are
consistent with the results of current-potential curves. The close
resemblance were observed between the electronic absorption
spectra of dyes with their respective IPCE spectra, except for a
minor red shift by ca. 3–4 nm. This confirms the sensitization of
-
Fig. 8 J–V curves for DSSCs based on dyes D1 to D4 sensitized photoelectrodes
the photocurrent by dye. The strong blue light absorption by I
3
-
/I redox couples present in electrolyte have been considered to
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decrease the IPCE value at shorter wavelength region, resulting region up to 600 nm. The presented results are encVoieuwraArgtiicnlegOanlninde
in the slight red shift in the bands in IPCE spectrum. The DSSC clearly indicates that the photovoltaic paDraOmI:e1t0e.1r0s3o9f/Cf8eNrrJo0c62e4n2yKl
assembly with dye D4 showed maximum IPCE value of 58% at oxadiazoles as photosensitizers are akin to the state-of-the-art
5
00 nm. The trend of IPCE maxima in decreasing order is N719 dye and these ferrocenyl oxadiazole dyes with some fine
D4>D2>D3>D1, which is in good agreement with photocurrent tuning may become promising candidates for the realization
of respective dyes.
DSSC assembly with good- cell performance.
0
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0
Fig. 11 The (a) electron life time and (b) transport time for dye D-1 to D-4 as
photosensitizers with TiO in DSSCs as a function of open-circuit voltage
-
2
Fig. 10 Electrochemical impedance spectra of DSSCs measured at Voc, 100 mWcm : (a)
Nyquist plots and (b) Bode plots.
2
EIS Measurements
Previously in our quest for the synthesis of ferrocene based dyes
to be used as sensitizers in DSSCs, we have synthesized
ferrocenyl dithiolate complexes with no specific anchoring
groups. These dyes acted as photosensitizers through remote
sensing or physical adsorption on the TiO
spectral response in the range of 400-440 nm.11, 12, 14, 15 Our
recent investigation with phenylmercury(II)
methylferrocenyldithiocarbamates with –OH linker16 enhances
the photovoltaic performance. To overcome the anchoring
problem we designed -extended ferrocenes with a variety of
anchoring groups which provided better anchorage than the
previous dyes and gave better results,17-21 which enabled us to
enhance the spectral response in the visible region beyond 450
nm. With the ferrocenyl oxadiazoles reported herein we
succeeded in extending the spectral response into the visible
Electrical impedance spectroscopy (EIS) is a useful analytical
tool to investigate the electron transport properties at DSSC
interfaces and its correlation with the performance at their open
-
2
5
circuit potential (OCP) over a frequency range of 10 –10 Hz
under 1.5 AM.
2
surface and have
There are different processes that occur in the cell under
illumination: The transfers of electrons from dyes to the
conduction band of TiO
2
, electrons are transported through the
3
-
-
TiO system and react with I . At the same time I is oxidized to
2
I3- (dye regeneration) at the counter electrode. The Nyquist and
Bode plots for the dye (D1 to D4) sensitized cells are shown in
Figure 10a and b, respectively. The presence of two semicircles
in the Nyquist plots can be attributed to charge transfer reactions
at interfaces as the appearance of the first smaller semicircle is
ascribed to charge transfer at the Pt/electrolyte interface. The
6
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second larger semicircle in the middle frequency region stand for spacer units which result in efficient charge separatiVoienw aArntidcleloOwnliener
the charge transfer processes at the TiO
2
/dye/electrolyte recombination rate. Therefore the cell performance can be
DOI: 10.1039/C8NJ06242K
interface at the bias applied voltage. The semicircle diameter for enhanced by introducing suitable linker and π acceptor group
TiO
/dye/electrolyte interface decreases as the charge transfer which facilitate the lowering of the energy barrier and
resistance decreases upon illumination of cell.
recombination rate which thereby stimulate superior electron
2
The decrease in charge transport resistance in the middle transport as well as high charge collection efficiency.43
frequency region is D4>D2>D3>D1, which follows the same
trend as photocurrent results obtained from the ferrocene Conclusions
0
1
2
3
4
5
6
7
8
9
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1
2
3
4
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9
0
oxadiazole based DSSCs. The decreasing trend of recombination
The presented investigation shows that ferrocenyl oxadizole
rates are D1>D3>D2>D4, which supports the higher Voc values
dyes with phenolic and nitro anchoring groups can be utilized as
donor type sensitizers. By using these dyes, the spectral response
of a wide band gap TiO electrode can be extended well into the
2
visible region (up to 600 nm wavelength). The photo-action
spectra for the DSSCs fabricated using these compounds provide
for D2
obtained to determine the effective lifetime (teff) which explains
further the higher oc values of dyes by electron lifetime. The
value of the frequency for dyes D1 D2 D3 and D4 is 47.32,
2.65, 39.23 and 23.06 Hz, respectively, with effective life times
, D3 and D4. The Bode phase plots (Fig. 10b) have been
V
,
,
3
strong evidence for their sensitization effect on the TiO
2
of 3.36, 4.87, 4.05 and 6.90 ms, respectively. These results have
been obtained using the following equation.40
photoanode. We have succeeded to achieve a maximum of ~61%
of cell efficiency compared to the N719 dye using these
ferrocenyl oxadiazole dyes. Looking into the techno-economic
aspects of these ferrocen oxadiazole based dyes could be a
serious alternative for the N719 dye. We have also shown that
incorporation of an extra oxadiazole spacer between the six
membered aromatic ring with anchoring group and the
ferrocenyl moiety improved the electronic communication
operating from the ferrocenyl fragment to the six membered
aromatic ring, which in turn improved the photovoltaic
parameters of the device. Broadening and enhancement in the
spectral response into the visible region, down to a suitable
anchoring group and electron communication properties
associated with the ferrocenyl oxadiazole systems makes them
an attractive candidate for enhancing the cell efficiency in
DSSCs.
t
eff = 1/2πf
where the frequency ( f ) corresponds to the maximum frequency
of the mid-frequency peak in the Bode phase plot. The lowest
electron lifetime in the case of D1 in comparison to other dyes
could explain the lowest
highest performance of the D4 based cell is due to the presence
of two oxadiazole spacer as π-linker which provides better
electronic communication to inject electrons efficiently in the
Voc value for D1 sensitized cell. The
conduction band of TiO
resistance value, which acts as a driving force for the highest
and oc for D4
2
as well as the lowest electron transport
J
sc
V
.
IMVS and IMPS study
Intensity modulation photovoltage spectroscopy (IMVS) and
intensity modulation photocurrent spectroscopy (IMPS) studies
in DSSCs are important tools to determine the electron lifetimes
n d n d
(τ ) and electron transit times (τ and τ
).41, 42 The parameters τ
Experimental
are important as they imply recombination lifetime of electrons
in the electrolyte and transport lifetime of the photo-generated
electrons within the photoanode film. Figure 11 displays the
results of IMVS and IMPS investigations for D1 to D4 based
cell. The IMVS study indicates that the back reaction between
Materials and Methods
All chemicals and reagents were commercially available and
used without further purification. Ferrocene carboxaldehyde,
malonic
acid,
TBTU,
4-hydroxybenzhydrazide,
4-nitrobenzonitrile,
4-
N,N'-
nitrobenzhydrazide,
the electrons in the TiO
2
conduction band and I3- in the
diisopropylethylamine, ethyl oxalyl chloride, hydrazine hydrate
were purchased from Sigma-Aldrich while the remaining
chemicals were from TCI chemicals.
electrolyte is mainly responsible for charge recombination in
DSSCs thereby resulting in decline in electron lifetime as well as
poor device performance. The IMVS and IMPS results shows the
Physical measurements. Elemental analyses were performed on
a Perkin-Elmer 240 C, H, N analyzer. Infrared spectra were
n
lower electron lifetime (τ ) and higher transport time for D1
based cell in comparison to rest of the three dyes with the
oxadiazole spacers. These results are in agreement with the
results of EIS measurements. This is probably happening due to
the strong aggregation of D1 dye on the TiO
its large dipole moment. The dyes D2 D3 and D4 based cells
show lower recombination than the D1 based cell. The reason is
that these dyes possess auxiliary acceptor unit (oxadiazole unit)
into the D-π-A skeleton, which is responsible for improved
electron lifetime in the devices. This leads to the enhanced
charge separation and electron injection from the dyes to the
1
recorded as KBr pellets on a Shimadzu IRAffinity-1S. H and
13C NMR spectra were recorded on a BRUKER Avance III
FTNMR spectrophotometer. Chemical shifts were reported in
parts per million using TMS as internal standard. The electronic
absorption spectra in dichloromethane solution were recorded
using a SPECORD 210 PLUS BU UV-Vis spectrophotometer.
Electrochemistry was carried out using a Pt working electrode,
Pt rod counter electrode and Ag/AgCl as a working electrode.
All electrochemical experiments were carried out in
dichloromethane. In all cases TBAP (0.1 M) was used as
supporting electrolyte. After each experiment the reference
electrode was calibrated against the ferrocene/ferrocenium
couple which was found to be at 0.55 V. The
2
surface owing to
,
2
conduction band of TiO . Amongst the three ferrocenyl
oxadiazole based dyes, the D4 based assembly shows highest
photocurrent and cell efficiency as it contains two oxadiazole
This journal is © The Royal Society of Chemistry 20xx
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photoelectrochemical performance, including the short-circuit modulated light containing 10% of the DC compVoienweAnrtti.cleIMOnPlinSe
2
DOI: 10.1039/C8NJ06242K
current (
FF), and overall energy conversion efficiency (
determined from the curve obtained by using a digital
Jsc, mA/cm ), open-circuit voltage (V
oc, V), fill factor and IMVS were measured at different bias light intensities.
(
η) were
Preparation of TiO
electrode
2
electrode (photoanode) and counter
J–V
Keithley 236 mm under an irradiation of white light from a 1000
W/HS Xenon arc lamp with a 100 mW/cm light intensity with The TiO
2
2
photoanodes were prepared using highly transparent
paste (Titanium-HT, Dyesol) by spreading on conducting
1
.5 AM. The maximum output power (
choosing a point on J-V curve corresponding to which the glass plate (15 Ω/cm , Pillkington, USA) by using doctor’s blade
product of current ( max) and voltage ( max) is maximum. The technique. The prepared thin films were annealed at 450 °C for
power conversion efficiency ( ) and fill factor (FF) were half an hour in air with the heating rate of 4 °C/min. The dyes
P
max) was obtained by TiO
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
J
V
η
evaluated using the following relations:
were adsorbed onto the TiO
2
surface by immersing the
TiO photoanode in dichloromethane solution of dyes for 12 h.
2
ꢃ
퐽ꢀꢁꢂ(A⁄cm ) × 푉ꢄꢅꢆ(V)
Thereafter, un-adsorbed dyes were washed out using
dichloromethane and then with anhydrous ethanol. Platinum
counter electrode was prepared by deposition of Pt catalyst PT1
paste (purchased from Dyesol) on another conducting glass and
annealed at 400°C for half an hour in air with heating rate of 4
퐹퐹 =
ꢃ
퐽ꢇꢈ(A⁄cm ) × 푉ꢉꢈ(V)
ꢊꢋꢌ ×ꢍꢎꢌ×ꢏꢏ
ꢐꢑꢒꢓ (ꢔ/ꢕꢀꢖ)
휂(%) =
× 100
°
C/min.
sc
Here J , Voc and Iinc are short-circuit photocurrent, open-circuit
potential and intensity of incident light respectively.
DSSC assembly
The sandwich type DSSCs were assembled by placing the
platinum catalyst-coated counter electrode on the dye coated
To avoid spurious light reflections and refractions a black mask
was used for the cell on the illuminated side and also used to
cover the side area of the cell, which largely contributed to the
cell response and lead to erroneous interpretation. The
reproducibility and reliability of the results was confirmed by
creating three cells of each sensitized photoanode and keeping
all structural and photovoltaic characterization identical. The
active area of the cells was 0.25 cm2.
The incident photon-to-electron conversion efficiency (IPCE
was measured by using a 300 W Xe lamp light source joined to
a monochromator (Oriel). A reference Si photodiode calibrated
for spectral response was used for the monochromatic power-
density calibration. From the values of
corresponding monochromatic light (
TiO
sealed by three sides by using spacer SX1170-60, 50μm
Solaronix) by leaving the one side open for the injection of
electrolyte solution. The iodide electrolyte solution (electrolyte
was composed of 0.05 m iodine, 0.5 m LiI, and 0.5 m 4-tert
2
film in face to face manner and then the assembly was
(
-
butypyridine in acetonitrile) was placed at the edges of the plates.
The liquid was drawn into the space between the electrodes by
capillary action. After filling electrolyte, the open side of the cell
assembly was sealed with the help of araldite and the contacts
were made by copper wire by using silver paste followed by
araldite for sealing the contacts.
)
J
I
sc and the intensity of the
inc), the incident photon-
Syntheses
to-current conversion efficiency (IPCE) was calculated at each
excitation wavelength (λ) using the following relation:
(E)-3-ferrocenylacrylic acid (D1)
ꢗꢃꢘꢙ ꢊꢚꢓ(ꢛ⁄ꢕ ꢖ)
ꢡ
Compound ( )-3-ferrocenylacrylic acid (D1) was prepared in
accordance with the previously reported procedure.44 Ferrocene
carboxyaldehyde (0.512 g, 2 mmol) and malonic acid (0.311 g,
.99 mmol) were added and dissolved in 2 mL of freshly distilled
pyridine followed by addition of 1-2 drops of piperidine. The
resulting solution was refluxed at 108 ˚C with stirring for 6 hours
E
퐼푃퐶퐸 (%) =
× 100

(ꢜꢄ)×ꢐꢝꢞꢟꢠꢓꢢꢖꢣ
2
The electrochemical impedance spectroscopy (EIS) was
performed on a CH 660C electrochemical analyzer (CH
Instruments, Shanghai, China) in a two electrode configuration.
The photoanode was used as a working electrode and the Pt
electrode as a counter electrode. The electron transport properties
under nitrogen atmosphere during which the evolution of CO
2
stopped. The obtained reaction mixture was cooled slowly to
room temperature followed by washing with 2N HCl and
thereafter extracted with 5% NaOH 3-4 time. The sodium
hydroxide extracts were combined and was acidified with 6N
HCl. A brick-red precipitate was formed upon complete
acidification, which was collected by filtration and washed with
distilled water thoroughly to remove traces of acid and finally
the residue was dried under vacuum.
were
investigated
using
electrochemical
impedance
spectroscopy (EIS) with 10 mV alternative signal in the
frequency range of 10-2 – 105 Hz. Electron transport time and
electron lifetimes were measured by intensity-modulated
photocurrent spectroscopy (IMPS) and intensity-modulated
photovoltage spectroscopy (IMVS) with same electrochemical
workstation (CH 660C electrochemical analyzer). The
electrochemical workstation is equipped with a red LED source
(635 nm) which is used as light source for the above studies.
Photovoltage response of the cells were studied in the frequency
range of 1 Hz to 1 kHz. The cell was illuminated with sinusoidal
Yield: 0.354g, 69.14% (red solid). m. p. 193˚C. 1H NMR
(
6
DMSO-d6, 300MHz):
.07 (d, 1H), 4.66 (2H, FcCH2), 4.44 (2H, FcCH2), 3.86 (s, 5H,
Fc); 13C NMR (DMSO-d6, 75.50 MHz):
168.0 (-COOH),
45.0 (C-COOH), 116.0 (C=C), 79.0 (Fc-CH), 71.0 (4C, Fc),
δ 12.05 (s, 1H, COOH), 7.42 (d, 1H),
δ
1
8
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1
1
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2
2
2
2
2
2
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6
-
1
6
1
6
9.8 (5C, Fc). FT-IR (KBr, cm ): ν 3070 (C-H), 1668 (COOH), mL). The resulting solution was stirred under VnieitwroArgticelne Oanlninde
610 (C=C), 487 (Fe-Cp ring); Calcd. For C13
0.97, H 4.72. Found C 61.02, H 4.82.
DOI: 10.1039/C8NJ06242K
Fe (%): C NaHCO
H O (0.336 g, 4 mmol) dissolved in 4.6 mL water was added
12 2 3
dropwise to the stirring solution. The obtained yellow coloured
solution was stirred at room temperature for 24 h and the reaction
)-2-(4-hydroxyphenyl)-5-(2-ferrocenyl-ethen-1- was monitored using TLC. Thereafter the solvent vacuum
evaporated. The compound was extracted with ethyl acetate and
Synthesis of (
yl)-1,3,4-oxadiazole (D2)
E
D1 (0.064 g, 0.25 mmol) and triethylamine (0.175g, 0.25 mmol) water. The obtained fluorescent yellow solution was kept in
were dissolved in dichloromethane (3.5 mL) and the resulting anhydrous sodium sulfate and filtered, the solvent was removed
solution was stirred for 10 minutes followed by addition of by rotary evaporation and product was vacuum dried.
dichloromethane suspension of 4-hydroxybenzhydrazide (0.038 Yield: 0.325 g, 98.0% m. p. 180˚C. H NMR (DMSO-
g, 0.25 mmol) and TBTU (1.1 equiv, 0.26 mmol) under nitrogen MHz,
atmosphere. The resulting mixture was stirred 20 h at room 2H, C
temperature. Thereafter triethylamine (0.051, 0.5 mmol) was MHz,
added, followed by addition of 4-methylbenzenesulfonyl C6H4), 137.3 (2C, C
chloride (0.143 g, 0.75 mmol). The obtained reaction mixture
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
d
6
, 300
), 7.95 (dd,
); 13C NMR (DMSO-
, 75.50
): 166.7 (C=N-OH), 150.4 (C-NH2), 140.4 (C-NO
δ
): 10.15 (s, 1H, N-OH), 8.24 (dd, 2H, C
6 4
H
6
H
4
), 6.08 (br, 2H, NH
2
d
6
δ
2
,
6 4 6 4 2
H ), 129.3 (2C, C H ), 123.9 (C-NH ).
Synthesis of Ethyl 3-aryl-1,2,4-oxadiazole-5-carboxylate
was stirred for another 12 hour and after that the reaction was
quenched by adding 14% aqueous ammonia solution. The N,N'-diisopropylethylamine (0.480 g, 3.6 mmol) was added
stirring was continued for an additional 45 minutes. The product dropwise to the stirring THF solution of amidoxime (0.303 g,
was extracted with dichloromethane: water. To remove traces of 1.8 mmol) in an ice bath (5 °C) under nitrogen. Ethyl oxalyl
4
-methylbenzenesulfonamide, the organic layer was treated with chloride (2.16 ml, 1.8 mmol) was added to the mixture and this
a 2N NaOH solution. The obtained organic layer was washed was stirred for 10 minutes. The temperature of the reaction
with water and kept in anhydrous sodium sulfate for 4 h, filtered mixture was brought upto room temperature and then the
and vacuum evaporated to dryness and finally the product was reaction mixture was refluxed for 150 min under nitrogen
washed with diethyl ether.
Yield: 0.170 g, 47.3 % (dark red solid), m. p. 220°C (d). H was cooled on ice-bath and 2N HCl (1.8 mL) was added
NMR (CDCl , 300 MHz) : 8.08 (d, 1H), 7.97 (d, 1H), 7.64 ((d, dropwise to it. Thereafter, the product was extracted with ethyl
H, C ), 7.42 (d, 2H, C ), 4.65 (2H, Fc), 4.33 (2H, Fc), 4.15 acetate (4×25 mL) and water (100 mL). The obtained dark
s, 5H, Fc). 13C NMR (CDCl
, 75.50 MHz) : 150.4 (C-OH, yellow organic layer was washed with aqueous sodium
), 148.1 (C=N-N=C), 139.1 (C-O-), 129.17 (-C=C-), 128.3 bicarbonate and dried over anhydrous sodium sulfate. The
CH-C ), 69.0 (Fc-C), 68.8 (Fc-4C), 67.1 (Fc, 5C). FTIR solvent was removed under reduced pressure and the crude
KBr, cm ):
C=N-N=C, oxadiazole), 1261, (C-O-C, oxadiazole), 486 (Fe- 120), using hexane:ethyl acetate (88:12, V/V).
Fe (372.0561) (%): C 64.54, H 4.33, Yield: 0.892 g, 97%, m.p. 120˚C. 1H NMR (CDCl
N 7.53. Found C 65.02, H 4.76, N 8.12. HRMS (ESI): m/z ): 8.30 (dd, 2H, C -NO ), 7.76 (dd, 2H, C ), 4.56 (q, 2H,
CH ), (1.58, t, 3H, CH , 75.50 MHz, ):
); 13C NMR (CDCl
66.8 (COO), 152.7 (C=N, oxadiazole), 148.8 (C-NO ), 132.4 (-
)-2-(4-nitrophenyl)-5-(2-ferrocenyl-ethen-1-yl)- C- oxadiazole), 127.7 (2C, C ), 123.2 (2C, C ), 63.2 (CH ),
13.0 (CH ).
atmosphere. After completion of reaction, the reaction mixture
1
3
δ
H
6 4
2
6
H
5
(
3
δ
6 5
C H
(
(
(
6 4
H
-
1
ν
6 4
3490 (OH-C H ), 2962 (C-H), 1604 (C=C), 1490 product was purified using column chromatography (silica 60-
Cp). Calcd. For C20
H
16
O
2
N
2
3
, 300 MHz,
=
δ
6
H
4
2
6 4
H
3
73.0620 [M+H]+.
2
3
3
δ
1
2
Synthesis of (
E
6
H
4
6
H
4
2
1
,3,4-oxadiazole (D3
)
3
A similar procedure was adopted to synthesize D3 except that Synthesis of aryl oxadiazole-5-carbohydazide
instead of 4-hydroxybenzhydrazide, 4-nitrobenzhydrazide
Hydrazine monohydrate (0.212 g, 4.24 mmol) was added in the
ethanol solution (5.3 ml) of ethyl aryl carboxylate (0.558 g, 2.12
mmol). A cream-yellow precipitate of hydrazide was readily
formed. The mixture was stirred for 2 h at room temperature. The
(
0.046 g, 0.25 mmol) was taken.
Yield: 0.199 g, 50% (dark red solid), m. p. 212 °C (d). H NMR
CDCl , 300 MHz) : 8.36 (d, 1H), 8.22 (d, 1H), 7.51 (d, 2H,
), 7.45 (d, 2H, C ), 4.52 (2H, Fc), 4.42 (2H, Fc), 4.16
5H, Fc). 13C NMR (CDCl
, 7.50 MHz) : 165.5 (C-NO ), 163.8
C=N-N=C), 149.8 (C-O), 129.5, 128.5, 127.6 (C=C, C ), 71.7
C-CH, Fc), 70.0 (2C, Fc), 69.1 (2C, Fc), 68.3 (5C, Fc). FTIR
1
(
C
3
δ
6
H
4
6 4
H
obtained precipitate was filtered and washed with cold ethanol.
(
(
(
(
3
δ
2
1
Yield: 0.558 g, 99%, m.p. 197˚C (d). H NMR (DMSO-
d
6
, 300
), 8.31 (d, 2H, C ),
): 180.2
) ,
6 4
H
MHz,
4
(
1
δ
): 10.95 (s, N-H), 8.45 (d, 2H, C
6
H
4
6 4
H
); 13C NMR (DMSO-
.97 (br, 2H, NH
2
d
6
, 75.50 MHz, δ
-
1
KBr, cm )
431 (C=N-N=C, oxadiazole), 1338 (symm NO
oxadiazole), 482 (Fe-Cp). Calcd. For C20
%): C 59.87, H 3.77, N 10.47. Found C 60.73, H 4.01, N 10.84.
HRMS (ESI): m/z = 402.0520 [M+H]+.
ν
: 2962 (C-H), 1631 (C=C), 1519 (asymm NO
), 1259 (C-O-C,
(401.0463)
2
),
CONH), 170.0 (C-O-N=C), 167.1 (C=N-), 151.8 (C-NO
31.8 (C-oxadiazole), 129.0 (2C, C ), 125.0 (2C, C ).
2
1
2
6
H
4
6 4
H
H
3 3
15FeN O
(
Synthesis of (E)-3-(4-nitrophenyl)-5-[5-(2-ferroceneylethen-1-yl)-
,3,4-oxadiazol-2-yl]-1,2,4-oxadiazole (D4)
1
A similar procedure was adopted to synthesize D4 as used for the
syntheses of D2 and D3 except that instead of 4-
Synthesis of (
Z)-N'-hydroxyimidamide
4
-Nitrobenzonitrile (0.297 g, 2 mmol) and hydroxylamine
hydrochloride (0.129 g, 4 mmol) were dissolved in ethanol (5
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9
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Pl eNa es we dJ oo u nr no at l ao df jCu hs et mm i as tr rgy ins
Page 10 of 13
ARTICLE
Journal Name
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
hydroxybenzhydrazide, aryl oxadiazole-5-carbohydazide (0.046 31G** basis set for other atoms were used fVoierw AgrteicolemOentlirnye
DOI: 10.1039/C8NJ06242K
optimization. All the calculations were performed using
g, 0.25 mmol) was taken.
Yield: 0.118 g, 50% (Red solid) m.p. 280˚C (d). HNMR (CDCl
00MHz): 8.36 (d, 1H), 8.28 (d, 1H), 7.73 (2H, d, C ), 6.68 system was optimized by using 3-21G* basis set and initial
2 30
2H, C ), 4.55 (2H, Fc), 4.48 (2H, Fc), 4.15 (s, 5H, geometry were taken from the relaxed geometry of (TiO )
1
Gaussian 09 programme.49 The TiO
3
,
cluster(TiO ) +D1-D4
2 2 30
3
δ
6 4
H
(
6
H
4
1
3
Fc). CNMR (CDCl
3
, 75.50 MHz):
δ
127.6 (C=C, C
H ), 70.5 (CH-Fc), 68.7 (2C, Fc), 67.4 (2C, Fc), 64.7
2962 (C-H), 1641 (C=C), 1523 Conflicts of interest
2
), 1450 (C=N-N=C, oxadiazole), 1350 (symmNO ),
6
H
4
), 123.1 cluster and D1-D4
.
(
(
(
C=C, C
5C, Fc).FT-IR (KBr, cm ):
aymmNO
6 4
-
1
ν
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
There are no conflicts to declare.
1
261 (C-O-C, oxadiazole), 489 (Fe-Cp). Calcd. For
22 5 4
C H15FeN O (469.0473) (%): C 56.31, H 3.22, N 14.93. Found
C 57.03, H 3.45, N 15.01. HRMS (ESI): m/z = 470.0529 [M+H]+.
Acknowledgements
X-ray Crystallography
RC is grateful to Department of Science and Technology for the
Intensity data for D1 were collected at 150(2) K on a Rigaku INSPIRE fellowship IFA-12CH-34. AK is grateful to Council of
Xcalibur, EosS2 single crystal diffractometer using graphite Scientific and Industrial Research, New Delhi for the financial
monochromated Mo-Kα radiation (λ = 0.71073 Å). For D4 on a assistance in the form of project no. 01(2899)/17/EMR-II.
Rigaku Supernova Dual, EosS2 system using monochromated
Cu-Kα radiation (λ = 1.54184 Å). Unit cell determination, data
collection and data reduction were performed using the
CrysAlisPro software.45 An empirical absorption correction ‡ Footnotes relating to the main text should appear here. These
using spherical harmonics was employed. The structures were
solved with SHELXT and refined by a full-matrix least-squares
procedure based on F2 (SHELXL-2018/3).46 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed
onto calculated positions and refined using a riding model.
Notes and references
might include comments relevant to but not central to the matter
under discussion, limited experimental and spectral data, and
crystallographic data.
4
6
1
2
B. O’Regan, M. Grätzel, Nature, 1991, 353, 737–740.
(a) A. Hagfeldt, G. Boschloo, L. C. Sun, L. Kloo and H. Pettersson,
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Constable and C. E. Housecroft, Coord. Chem. Rev., 2013, 257, 3089;
(c) M. K. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E.
Crystal Data D1
a = 8.6991(3) Å, b = 11.5638(4) Å, c = 11.4461(4) Å,
13 2
. C H12FeO , M = 256.08, Monoclinic, P21/n,

=
-3
3
1
10.945(4)° V = 1075.34(7) Å , Z = 4, Dcalc = 1.582 mg m ,
F(000) = 528, crystal size 0.600 × 0.400 × 0.200 mm, reflections
collected 9009, independent reflections 2797 [R(int) = 0.0258],
Meller, P. Liska, N. Vlachopoulos and M. Grätzel, J. Am. Chem. Soc.
,
1993, 115, 6382; (d) M. K. Nazeeruddin, S. M. Zakeeruddin, R.
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Final indices [I> 2σ(I)] R
data) R = 0.0408, wR = 0.0806, gof 1.036, Largest difference
peak and hole 0.884 and -0.266 e Å . CCDC No. 1882088
Crystal Data D4 15FeN , M = 469.24, Monoclinic,
P21/n, a = 5.9928(3) Å, b = 8.5610(5) Å, c = 37.157(3) Å,
1 2
= 0.0349, wR = 0.0770, R indices (all
1
2

3
.
.
C
22
H
5 4
O
Viscardi, P. Liska, S. Ito, B. Takeru and M. Grätzel, J. Am. Chem. Soc.
,

2005, 127, 16835; (f) M. Grätzel, J. Photochem. Photobiol. A, 2004,
164, 3; (g) M. K. Nazeeruddin, P. Pechy, T. Renouard, S. M.
Zakeeruddin, R. Humphry-Baker, P. Comte, P. Liska, L. Cevey, E.
Costa, V. Shklover, L. Spiccia, G. B. Deacon, C. A. Bignozzi and M.
Grätzel, J. Am. Chem. Soc., 2001, 123, 1613; (h) G. Boschloo and A.
Hagfeldt, Acc. Chem. Res., 2009, 42, 1819-1826.
3
-
=
3,
91.337(5)° V = 1905.80(19) Å , Z = 4, Dcalc
F(000) = 960, crystal size 0.12 × 0.05 × 0.04 mm, reflections
= 1.635 mg m
collected 19880, independent reflections 19880 [R(int) = ?], Final
indices [I> 2σ(I)] R = 0.0939, wR = 0.2041, R indices (all data)
= 0.1297, wR = 0.2280, gof 1.104, Largest difference peak
and hole 0.734 and -0.484 e Å . CCDC No. 1882089
Note: the entire molecule is disordered over two sites in the ratio
:1. Due to the proximity of the two parts which overlap in most
1
2
R
1
2

3
.
3
L. Y. Han, A. Islam, H. Chen, C. Malapaka, B. Chiranjeevi, S. F.
Zhang, X. D. Yang and M. Yanagida, Energy Environ. Sci. 2012, 5,
1
6057−6060.
cases ADP restraints had to be applied for all atoms and
geometric constraints for the C-ring atoms. The crystal did not
diffract well to high angles which lead to weak high angle data
which explains the high R-value. Additionally, the structure was
refined as a 2-component twin 180.0° rotation about 6. 0. -1
reciprocal lattice direction.
4
5
K. Kakiage, Y. Aoyama, T. Yano, K. Oya, J. Fujisawa and M. Hanaya,
Chem. Commun. 2015, 51, 15894−15897.
B. O’Regan, K. Walley, M. Juozapavicius, A. Anderson, F. Matar, T.
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Soc., 2009, 131, 3541–3548.
6
7
F. Gao, Y. Wang, D. Shi, J. Zhang, M. Wang, X. Jing, R. Humphry-
Baker, P. Wang, S. M. Zakeeruddin and M. Grätzel, J. Am. Chem. Soc.
2008, 130, 10720–10728.
,
Computational details
In order to ascertain the nature of electronic transition in the
ferrocenyl oxadiazole, compounds density functional theory
D. Kuang, S. Ito, B. Wenger, C. Klein, J. E. Moser, R. Humphry-
Baker, S. M. Zakeeruddin and M. Grätzel, J. Am. Chem. Soc., 2006,
128, 4146–4154.
(
DFT) calculations were performed. Optimized molecular
geometries were calculated using the B3LYP exchange-
correlation functional.47, 48 The MDF10 basis set for Fe and 6-
1
0 | J. Name., 2012, 00, 1-3
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Pl eNa es we dJ oo u nr no at l ao df jCu hs et mm i as tr rgy ins
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ARTICLE
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Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
View Article Online
DOI: 10.1039/C8NJ06242K
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X.
Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R.
Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G.
A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S.
Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A.
D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A.
G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P.
M. W. Gill, B. Johnson, W. Chen, W. M. Wong, C. Gonzalez, J. A.
Pople, Gaussian 09 (Gaussian, Inc., Wallingford CT, revision B.01
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New Journal of Chemistry
View Article Online
DOI: 10.1039/C8NJ06242K
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Ferrocenylethenyl-substituted
oxadiazoles
with phenolic and nitro anchors synthesized
and used as sensitizers in dye sensitized solar
cells (DSSCs)
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