Content uploaded by Gangala Sivakumar
Author content
All content in this area was uploaded by Gangala Sivakumar on Jun 30, 2015
Content may be subject to copyright.
Metal-free organic dyes containing thiadiazole unit
for dye-sensitized solar cells: a combined
experimental and theoretical study†
Gangala Siva Kumar,
ab
Kola Srinivas,
ab
Balaiah Shanigaram,
b
Dyaga Bharath,
a
Surya Prakash Singh,*
be
K. Bhanuprakash,*
b
V. Jayathirtha Rao,*
ace
Ashraful Islam
d
and Liyuan Han
d
We have designed and synthesized four new metal free D–A–p–A type dyes (9–12) with variations in their
acceptor/anchor groups. The four dyes carry tert-butyl substituted triphenylamine as donor, thiadiazole as
acceptor and bithiophene as p-spacer. Cyanoacetic acid, rhodanine-3-acetic acid, 2-(4-methoxyphenyl)-
acetic acid and 2-phenylacetic acid are used as acceptor/anchor groups, respectively in the dyes 9–12. The
acceptor/anchor effect on their photophysical, electrochemical and photovoltaic properties was
investigated. The dyes exhibited good power conversion efficiency ranging from 1.95–4.12%. Among the
four dyes, 9showed the best photovoltaic performance: short-circuit current density (J
sc
) of 8.50 mA
cm
2
, open-circuit voltage (V
oc
) of 645 mV and fill factor (FF) of 0.75, corresponding to an overall
conversion efficiency of 4.12% under standard global AM 1.5 solar light conditions.
Introduction
Due to the increasing global energy demands and decline of
natural energy resources, much attention has been focused by
researchers to harness solar energy in recent years. Among
several solar energy technologies, dye-sensitized solar cells have
attracted immense attention owing to their energy conversion,
low production cost compared to the conventional inorganic Si-
based solar cells.
1
To date, over 11% efficiency has been
reported for the DSSCs with Ru based complexes as dyes.
2
Metal
free organic dyes have received much attention because of their
high molar extinction co-efficient, synthetic exibility, low cost
and compliance with environmental issues. Several metal free
organic dyes have been reported with the efficiency ranging
from 5–10.3%.
3,4
Metal free organic dyes with D–p–A architec-
ture
5
are promising due to their long range absorption, ease in
tuning their photo-physical, electrochemical and photovoltaic
properties by varying donor, p-bridge and acceptor moieties.
Various entities like triphenylamine,
6–8
carbazole,
9
indoline,
10,11
coumarin,
12,13
uorene,
14–16
and phenothiazine,
17
are used as
donor motifs. Moieties like methine,
18
benzene,
19,20
and thio-
phene
21
are employed as p-spacers and electron decient
groups like cyanoacetic acid
5,22,23
or rhodanine-3-acetic acid
24
acts as acceptor/anchor.
Metal free organic dyes with molecular architecture D–A–p–
A, containing an additional acceptor group compared to the
dyes with D–p–A architecture have been recently reported.
25
The
additional acceptor acts as an electron trap and facilitates
electron transfer from donor to the end group acceptor/anchor.
The D–A–p–A dyes have advantages like improved photo and
thermal stability, high open circuit voltage and red-shied
absorption.
26
Several electron withdrawing groups such as
benzothiadiazole,
27–29
benzotriazole,
30,31
quinoxaline,
32
diketo-
pyrrolopyrrole,
33,34
thienopyrazine,
35
thiazole,
36
and bithiazole,
37
have been used as additional acceptor units. The DSSCs with D–
A–p–A dyes have exhibited 9% power conversion efficiency,
under AM 1.5 G irradiation.
38
As a part of our research efforts
39–42
to study the dependence
of photovoltaic performance of DSSC on structural modica-
tions of organic dyes, herein we report the synthesis of four new
D–A–p–A type dyes (9–12; Scheme 1) with variations in the
acceptor/anchor groups. Their photophysical, electrochemical
and photovoltaic properties are also explored. The four dyes
consist of tert-butyl substituted triphenylamine as donor, thia-
diazole as acceptor and bithiophene as p-spacer. Cyanoacetic
acid, rhodanine-3-acetic acid, 2-(4-methoxyphenyl)acetic acid
and 2-phenylacetic acid are used as acceptor/anchor groups,
respectively in the dyes 9–12. The tert-butyl groups on triphe-
nylamine hinder the intermolecular aggregation. To the best of
a
Crop Protection Chemicals Division, Uppal Road Tarnaka, Hyderabad 500007, India.
E-mail: jrao@iict.res.in
b
Inorganic and Physical Chemistry Division, Uppal Road Tarnaka, Hyderabad 500007,
India
c
Academy of Scientic & Innovative Research-IICT, CSIR-Indian Institute of Chemical
Technology, Uppal Road Tarnaka, Hyderabad 500007, India
d
Photovoltaic Materials Unit, National Institute for Materials Science, 1-2-1 Sengen,
Tsukuba, Ibaraki 305-0047, Japan
e
National Institute for Solar Energy, New Delhi, India
†Electronic supplementary information (ESI) available: Absorption, uorescence
and computational details of dyes 9–12. See DOI: 10.1039/c3ra47330a
Cite this: RSC Adv.,2014,4,13172
Received 5th December 2013
Accepted 24th February 2014
DOI: 10.1039/c3ra47330a
www.rsc.org/advances
13172 |RSC Adv.,2014,4,13172–13181 This journal is © The Royal Society of Chemistry 2014
RSC Advances
PAPER
our knowledge this is the rst report on thiadiazole containing
DSSCs.
Results and discussion
Synthesis
All the dyes (9–12) were synthesized in multi-step synthetic
pathway as shown in Scheme 2. 4-Aminobenzoic acid was ester-
ied and then N-arylation conducted using bromo-4-tert-butyl-
benzene under modied Ullman conditions to get triarylamine
derivative 3. Hydrazine hydrate was reacted with triarylamine
ester 3to make N0-4-(bis(4-tert-butylphenyl)amino)benzohy-
drazide (4). Compound 4further converted, by reacting with
thiophene-2-carbonyl chloride to N0-(4-(bis(4-tert-butylphenyl)-
amino)benzoyl)thiophene-2-carbohydrazide (5). The compound
5was treated with Lawesson's reagent to produce thiadiazole
derivative 6, later it was converted into tributyl stannane deriva-
tive 7. The tributyl stannane derivative 7was coupled with
5-bromothiophene-2-carbaldehyde using standard Stille protocol
to afford 50-(5-(4-(bis(4-tert-butylphenyl)amino)phenyl)-1,3,4-
thiadiazol-2-yl)-2,20-bithiophene-5-carbaldehyde (8). The bithio-
phene-5-carbaldehyde derivative 8was subjected to Knoevenagel
condensation to produce the target dyes 9–12 in good yields.
Absorption and emission characteristics
The UV-Vis absorption spectra of the dyes 9–12 (1 10
5
M)
were recorded in CHCl
3
(Fig. 1a) and the results are summa-
rized in Table 1. All the four dyes display their absorption
maxima in the visible region (400–490 nm). The observed visible
region absorption is attributed to the intramolecular charge
transfer between donor (triphenylamine) and acceptor (acid)
groups. The dyes 11 and 12 show nearly equal absorption
maxima, 444 nm and 443 nm respectively, whereas, the dyes 9
and 10 show red shied absorption maxima 453 nm and 487
nm compared to 11 and 12. The observed higher molar
extinction coefficients of the dyes could result in the improved
light harvesting capacity. Fluorescence emission spectra of the
dyes 9–12 (1 10
5
M) were recorded in CHCl
3
solution
(Fig. S1†) and the results are summarized in Table 1. All these
dyes exhibit maximum emission wavelength in the range of
537–564 nm. The absorption and emission characteristics of the
synthesized dyes were also measured in 1 10
5
M acetoni-
trile–tert-butyl alcohol (1 : 1) solvent mixture (Fig. S3†) and the
results are summarized in Table S3.†In compare to spectra
recorded in chloroform, all the molecules showed about 10 nm
blue shiof absorption maxima (443–487 nm); 9,10, and 11
showed red shiof 61, 12, and 20 nm respectively in maximum
emission wavelength.
The absorption spectra of the dyes adsorbed on TiO
2
are
shown in Fig. 1b. The absorption bands of dyes are broadened
aer their adsorption on TiO
2
surface compared to their solution
spectra. This broad range of absorption can improve the light
harvesting ability, photo current response region and short
circuit current density (J
sc
) of the solar cells. The absorption
spectrum of the dyes are either blue or red shied
42,43
compared
to solution phase. The maximum red shi(40 nm) observed with
9, may be attributed to J-aggregation of the dye on TiO
2
surface.
43
The dyes 10 and 12 displayed only a minimal shis (1 and 4 nm
in their absorption maxima) upon binding to TiO
2
and this
indicates that the bulky phenyl group hindered their aggrega-
tion. The observed blue shi(8 nm) in the case of 11 might be
attributed to the H-aggregation of dye on TiO
2
surface.
44
Electrochemical properties
Electrochemical properties of the synthesized dyes were investi-
gated using cyclic voltammetry (Fig. 2). All the dyes displayed
nearly equal oxidation potentials (E
OX
) ranging from 0.93–0.96 V
and reduction potentials (E
red
)rangingfrom0.85 to 0.98 V
(Table 1). The oxidation of TPA moiety is responsible for the
observed oxidation potentials. Excited state oxidation potentials of
Scheme 1 Molecular structures of dyes 9–12.
This journal is © The Royal Society of Chemistry 2014 RSC Adv.,2014,4,13172–13181 | 13173
Paper RSC Advances
Scheme 2 Outline of synthetic scheme for 9–12: (i) SOCl
2
, EtOH, reflux, 6 h (ii) 1-bromo-4-tert-butylbenzene, 10 mol% 1,10-phenthroline, 20
mol% CuI, 2.5 eq. K
2
CO
3
, DMF, reflux, 48 h (iii) NH
2
NH
2
$H
2
O, EtOH, reflux, 17 h (iv) thiophene-2-carbonyl chloride, Et
3
N, dry THF, RT, 16 h (v)
Lawesson's reagent, dry THF, reflux, 5 h (vi) n-BuLi, Bu
3
SnCl, dry THF, 6 h (vii) 5-bromothiophene-2-carbaldehyde, Pd(PPh
3
)
2
Cl
2
, toluene, reflux,
14 h (viii) NH
4
OAc, AcOH, reflux, 6 h.
Fig. 1 The UV-visible spectra of the dyes in (a) solution (1 10
5
M in chloroform) and (b) thin film (adsorbed on TiO
2
) state.
13174 |RSC Adv.,2014,4,13172–13181 This journal is © The Royal Society of Chemistry 2014
RSC Advances Paper
the dyes (E
*
OX
), which correspond to LUMO, are obtained by sub-
tracting their oxidation potentials from optical band gap, which
was derived from the intersection point of excitation and emission
spectra. The ground state oxidation potentials (E
OX
)ofthedyesare
more positive than I
/I
3
(0.2 V vs. SCE),
45
the electrolyte used in
DSSCs, whereas, the calculated excited state oxidation potentials of
the dyes (E
*
OX
)(1.42 to 1.52) are more negative compared to
TiO
2
conduction band (0.8 V vs. SCE).
46
These results conrm the
feasibility of dye regeneration and electron injection processes.
Computational studies
The molecular orbital analysis was carried out for all four dyes in
the gas phase at B3LYP/6-311G(d,p) level of theory. The electron
density distribution for the HOMO, HOMO1 and LUMO of 9–12
dyes are shown in Fig. 3. HOMO of all the four dyes is localized on
the donor (TPA) moiety, whereas the LUMO it is localized on the
A–p–A moiety. LUMO of 9,11 and 12 is localized on the carboxylic
acid anchoring group, whereas in case of 10,ithasalarger
contribution of the sulfur atom of rhodanine ring. The observed
electron density distribution of the dyes on the bridging units in
both HOMO and LUMO levels suggest effective photo-driven
charge transfer excitation. The well separated electron density
distribution of HOMO and LUMO levels indicated that the tran-
sition between these levels could be considered as a charge
transfer excitation. TDDFT is used to study the excited states and
the results show that the dyes have their absorption in the visible
region. Of the functionals used M06-2X and CAM-B3LYP results
are in good agreement with experimental data. The rst two low
energy transitions with high oscillator strengths and ground state
dipole moments are listed in Table S1 and S2.†The low energy
transition corresponds to an excitation from HOMO to LUMO as
the major component and HOMO1 to LUMO as a minor
component. This mixing of HOMO1 into the lowest energy
transition decreases the charge transfer tendency.
Adsorption of dye on TiO
2
surface
To investigate the DSSC properties of the synthesized dyes, Ti
16
O
32
nanocluster model is considered for TiO
2
as electron acceptor.
47,48
Table 1 Photophysical and electrochemical properties of the synthesized dyes 9–12
Dye l
maxa
/nm (M
1
cm
1
)l
maxb
/nm l
maxc
/nm E
OXd
/V (vs. SCE) E
redd
/V (vs. SCE) E
0–0e
/eV E
*
OXf
/V (vs. SCE)
Dye-loading amount
(10
7
mol cm
2
)
9453 (54 679) 493 537 0.95 0.85 2.47 1.52 1.93
10 487 (34 299) 488 564 0.96 0.95 2.38 1.42 1.66
11 444 (49 617) 436 544 0.94 0.96 2.45 1.51 1.74
12 443 (63 304) 447 545 0.93 0.98 2.45 1.52 1.68
a
Absorption maxima in CHCl
3
solution.
b
Absorption maxima on TiO
2
lm.
c
Fluorescence emission maxima in CHCl
3
.
d
Measured in CH
2
Cl
2
with
0.1 M tetrabutylammonium hexauorophosphate (TBAPF
6
) as the electrolyte (working electrode: glassy carbon; reference electrode: SCE; calibrated
with ferrocene/ferrocenium (Fc/Fc
+
) as an external reference. Counter electrode: Pt wire).
e
E
0–0
was estimated from the intersection between the
absorption and emission spectra.
f
E
*
OX
estimated by E
*
OX
¼E
OX
E
00
.
Fig. 2 Cyclic voltammograms of the dyes (5 10
4
M) in CH
2
Cl
2
.
Fig. 3 Frontier molecular orbitals of dyes 9–10 obtained at B3LYP/6-
31G(d,p) level.
This journal is © The Royal Society of Chemistry 2014 RSC Adv.,2014,4,13172–13181 | 13175
Paper RSC Advances
For the present work we considered the dye adsorbed on TiO
2
model in which the dye is attached to TiO
2
via bidentate bridging
mode and the proton of the deprotonated acid group of the dye is
attached to adjacent oxygen atom on TiO
2
surface as shown in
Fig. 4. The dye molecule can anchor on to TiO
2
nanocluster surface
through the acid group in various modes of adsorption, such as
mono dentate, bidentate chelating and bidentate bridging mode.
We considered only the bidentate bridging mode in this study as it
is the strongest adsorption mode reported in the literature.
40,41,49,50
To validate the TiO
2
nanocluster model we calculated the
adsorption energies for the molecules 9 and 12 using the formula
(E
ads
¼E
molecule
+E
TiO
2
E
molecule+TiO
2
).
40,41
These are found to be
14.1 kcal mol
1
and 20.0 kcal mol
1
which are in the same range
of the adsorption energies of molecules with similar anchoring
groups using larger TiO
2
clusters.
51
To understand the electron density in the molecules, density of
states (DOS) is calculated for Ti
16
O
32
aloneandthedyeadsorbed
Ti
16
O
32
and the results are depicted in Fig. S2.†The results show
that DOS of Ti
16
O
32
alone has very broad surface and the valence
and conduction bands are separated by wide band gap. Whereas in
dye adsorbed Ti
16
O
32
, the valence and conduction band gap is
decreased due to the introduction of dye occupied molecular
energy levels. The DOS analysis reveals that all the dyes exhibited a
strong overlap of the valence and conduction bands over a broad
range of energies. From frontier molecular orbital analysis of the
dye adsorbed on to TiO
2
surface (Fig. 5) it is clear that on excitation
electrondensityistransferredfrom HOMO of dye to its LUMO and
from there to LUMO of the semiconductor, indicating the efficient
interfacial electron injection from excited dye to semiconductor.
Photovoltaic performance of DSSCs
The IPCE action spectrum of the dye is shown in Fig. 6 and the
results indicate that all the dyes can efficiently convert the light
to photocurrent in the region from 300 to 650 nm. The onsets of
the IPCE spectra (640, 660, 580 and 585 nm, respectively for 9,
10, 11 and 12) are signicantly broadened compared to their
UV-Vis absorption spectra on the TiO
2
lm. The photocurrents
measured at wavelengths less than 400 nm may have contri-
butions from the direct excitation of TiO
2
and competitive light
absorption triiodide (I
3
) in the electrolyte solution; however,
those at longer wavelengths are reasonably attributed to sensi-
tization by the indicated sensitizer. The DSSC in which 9 is used
as dye, showed more than 60% IPCE in the range 350–550 nm
and it is the highest among the four. This might be due to the
Fig. 4 Optimized bidentate bridging mode of the (a) Ti
16
O
32
, (b) Ti
16
O
32
-9(b), and (c) Ti
16
O
32
-12.
Fig. 5 Frontier molecular orbitals of dyes 9and 12 adsorbed on
Ti
16
O
32
obtained at PBE0/TZVP level.
13176 |RSC Adv.,2014,4,13172–13181 This journal is © The Royal Society of Chemistry 2014
RSC Advances Paper
wide range of absorption of 9 adsorbed on TiO
2
lm. The IPCE
values of the DSSCs based on 11 and 12 dyes displayed more
than 60% in the range of 420–510 nm and 380–520 nm,
respectively. The strong dip in the IPCE spectrum around 380
nm for compound 11 is induced by the competitive light
absorption between sensitizer and triiodide. Interestingly, the
DSSC with 10 dye portrayed low IPCE value, even though it has a
broader range of absorption. The reason behind the observed
low IPCE value at wavelengths higher than 400 nm for
compound 10 is explained using computational experiments.
The energetically stable conformer of 10 showed that its LUMO
was located on rhodanine sulfur atom instead of carboxylic acid
moiety, which reduced the electron transfer from the dye to the
TiO
2
conduction band and hence minimized the IPCE. The high
photocurrents measured in the range of 300–380 nm may have
contributions from the direct excitation of TiO
2
and hot elec-
tron injection from higher excited state of the sensitizer.
The photocurrent density–photovoltage (J–V) curves of the
DSSCs with 9–12 dyes, under simulated AM 1.5 solar irradiation
(100 mW cm
2
) is shown in Fig. 7 and their photovoltaic
properties are summarized in Table 2.
Among all, the DSSC with dye 9showed highest efficiency
(h¼4.12%), with short-circuit current density (J
sc
) of 8.50 mA
cm
2
, open-circuit voltage (V
oc
) of 645 mV and ll factor (FF) of
0.75. Whereas, the DSSC with 10 dye displayed the lowest effi-
ciency h¼1.95% due to its low short-circuit current density
(J
sc
¼4.00 mA cm
2
). The observed low J
sc
might be due to the
poor electron injection nature of 10 to the TiO
2
conduction
band. The DSSCs with 11 and 12 dyes exhibited comparable
efficiencies (h¼2.74 and 3.10%, respectively for 11 and 12).
Experimental
Materials and instruments
All the materials for synthesis were purchased from commercial
suppliers and used without further purication. Dry DMF (dried
over molecular sieves) and freshly distilled THF (distilled over
sodium/benzophenone) were used in all experiments. NMR
spectra were recorded using Bruker Avance (300 MHz) or Varian
Inova (500 MHz) spectrometers. ESI MS spectra were obtained
on a Thermonngan Mass Spectrometer. Absorption spectra
were recorded on a Jasco V-550 UV-visible spectrophotometer.
Fluorescence measurements were performed on a Fluorolog-3
uorescence spectrophotometer. Cyclic voltammetric
measurements were performed on a PC-controlled CHI 620C
electrochemical analyzer using 0.5 mM dye solution in
dichloromethane (CH
2
Cl
2
) at a scan rate of 100 mV s
1
. Tetra-
butylammonium hexauorophosphate (0.1 M) was used as
supporting electrolyte. The glassy carbon, standard calomel
electrode (SCE) and platinum wire were used as working,
reference and counter electrodes, respectively. The potential of
reference electrode was calibrated using ferrocene internal
standard. All the potentials were reported against SCE. All
measurements were carried out at room temperature.
DSSC characterization
Screen printing method was used to prepare a nanocrystalline
TiO
2
(thickness 25 nm, area: 0.25 cm
2
) as described earlier.
52
The dye solution (3 10
4
M) was prepared in acetonitrile–tert-
butyl alcohol (1 : 1 v/v) and to prevent aggregation of the dye
molecules, deoxycholic acid (DCA) (20 mM) was used as a co-
adsorbent. The TiO
2
lms were dipped into the dye solution and
kept at 25 C for 24 h. Acetonitrile solution, contained 0.6 M
dimethylpropyl-imidazolium iodide (DMPII), I
2
(0.05 M), LiI (0.1
M) and 0.5 M tert-butylpyridine (TBP) was used as electrolyte. A
Surlyn spacer with 40 mm thickness was used to separate the
counter electrode and dye-deposited TiO
2
lm, sealed with
polymer frame. The photocurrent density–voltage (I–V) charac-
teristics of the sealed solar cells were measured under AM 1.5 G
simulated solar light with light intensity of 100 mW cm
2
and a
Fig. 6 IPCE action spectra of DSSCs based on 9–12 dyes.
Fig. 7 J–Vcharacteristics of DSSCs fabricated using 9–12 as dyes
under AM 1.5 solar irradiation.
Table 2 Photovoltaic performance of DSSCs fabricated using 9–12
Dye J
sc
(mA cm
2
)V
oc
[V] FF PCE (%)
98.50 0.645 0.75 4.12
10 4.0 0.654 0.74 1.95
11 5.59 0.650 0.75 2.74
12 6.27 0.658 0.75 3.10
This journal is © The Royal Society of Chemistry 2014 RSC Adv.,2014,4,13172–13181 | 13177
Paper RSC Advances
metal mask of 0.25 cm
2
. These I–Vcharacteristics were used to
estimate the photovoltaic parameters.
Measurement of dye-loading
The adsorption amount of dyes on the surface of TiO
2
lms,
that were prepared under the same conditions as those fabri-
cated into cells, was estimated as follows: TiO
2
lms sensitized
with dyes were immersed into 0.1 M NaOH in THF–H
2
O (1/1,
v/v) for desorption of the dyes. The amount of adsorbed dye was
estimated from the absorption peak of each resulting solution.
Four pieces of TiO
2
lm for one cell were tested and an average
value was adopted.
Computational studies
Ground state geometry of all the four dyes (9to 12) were opti-
mized using density functional theory B3LYP/6-311G(d,p)
method. Vibrational analysis was carried out to check the
geometries optimized to be local minima. TD-DFT calculations
were performed on the optimized geometries for the rst singlet
excited states to estimate the rst excitation energy for the dyes
using various functionals like M06-2X, CAM-B3LYP, LC-BLYP,
LC-WPBE, and WB97XD with 6-311+G(d,p) basis set in solvent
chloroform phase using SCRF(PCM) method.
53
The ground
state geometry of Ti
16
O
32
nanocluster alone and dye absorbed
Ti
16
O
32
nanocluster was optimized using PBE0 functional
54
and
TZVP
55
basis set. Density of states was analyzed using Gauss-
Sum2.2 program.
56
All the calculations were performed using
G09 soware.
57
Synthesis
Ethyl 4-(bis(4-tert-butylphenyl)amino)benzoate (3). To the
mixture of 1-bromo-4-tert-butylbenzene (17.0 g, 80 mmol) and
ethyl 4-aminobenzoate
58
(6.0 g, 36 mmol) in 50 mL of DMF,
crushed K
2
CO
3
(12.5 g, 90.7 mmol) and CuI (1.38 g, 7.2 mmol)
were added, sonicated under nitrogen atmosphere. Aer for 20
minutes, 1,10-phenathroline (0.67 g, 3.6 mmol) was added to
the reaction mixture and it was reuxed under nitrogen atmo-
sphere for 48 h. Aer completion of the reaction monitored
using TLC, the reaction mixture was cooled, concentrated under
reduced pressure. Ethyl acetate (100 mL) was added and the
solution was ltered through a small pad of silica gel. The
ltrate was concentrated and puried by column chromatog-
raphy (silica gel 60–120 mesh and 2 : 98 ethyl acetate–petro-
leum ether as eluent) to afford desired product as white solid
(isolated yield: 60%, 9.3 g):
1
H NMR (CDCl
3
, 300 MHz): d7.79 (d,
J¼9.06 Hz, 2H), 7.26 (d, J¼8.30 Hz, 4H), 7.02 (d, J¼8.30 Hz,
4H), 6.92 (d, J¼9.06 Hz, 2H), 4.31 (q, J¼6.79 Hz, 2H), 1.36 (t, J
¼6.79 Hz, 3H), 1.32 (s, 18H).
13
C NMR (CDCl
3
, 75 MHz): d
166.41, 152.17, 147.24, 143.84, 130.65, 126.27, 125.61, 121.61,
119.06, 60.29, 34.35, 31.36, 14.39. ESI-MS: m/z430 ([M + H]
+
).
HRMS (ESI+) calcd for C
29
H
36
O
2
N[M+H]
+
430.2740 found
430.2738.
4-(Bis(4-tert-butylphenyl)amino)benzohydrazide (4). To the
solution of hydrazine monohydrate (3.0 g, 60 mmol) in ethanol
(50 mL), 3(5.0 g, 11.6 mmol) was added portion wise and the
mixture was reuxed for 17 h. Aer completion of the reaction
as monitored using TLC, ethanol was removed under reduced
pressure and added water to the residue resulted in the
formation of white solid. The solid was ltered and re-crystal-
lized from ethanol to afford pure product as white solid (iso-
lated yield: 3.8 g, 80%).
1
H NMR (CDCl
3
, 300 MHz): d7.55 (d, J¼
8.68 Hz, 2H), 7.24 (d, J¼8.68 Hz, 4H), 7.0 (d, J¼8.68 Hz, 4H),
6.94 (d, J¼8.68 Hz, 2H), 4.79 (brs, NH
2
, 2H), 1.31 (s, 18H).
13
C
NMR (CDCl
3
, 75 MHz): d168.42, 151.41, 147.09, 143.83, 127.88,
126.27, 125.16, 123.51, 119.63, 34.33, 31.34. ESI-MS: m/z416 ([M
+H]
+
). HRMS (ESI+) calcd for C
27
H
34
ON
3
[M + H]
+
416.2696
found 416.2693.
N0-(4-(Bis(4-tert-butylphenyl)amino)benzoyl)thiophene-2-
carbohydrazide (5). To the mixture of 4(7.0 g, 16.8 mmol) and
triethylamine (5.09 g, 50.4 mmol) in dry THF at 0 C, thienyl
chloride (2.4 g, 16.8 mmol) was added drop wise. Aer the
addition, the reaction mixture was allowed to stir at room
temperature for 16 h. Aer the complete consumption of 4,
water (20 mL) followed by a saturated solution of sodium
bicarbonate (20 mL) was added to the reaction mixture. The
water phase was extracted with ethyl acetate (3 25 mL) and the
combined organic fractions were washed with brine (25 mL),
dried over anhydrous sodium sulfate. The solvent was removed
in vacuo and re-crystallized from ethanol to yield the desired
product as a white solid (isolated yield: 7.7 g, 87%).
1
H NMR
(CDCl
3
+ DMSO-d
6
, 300 MHz): d10.33 (s, 1H), 10.15 (s, 1H), 7.89
(d, J¼3.77 Hz, 1H), 7.78 (d, J¼8.68 Hz, 2H), 7.60 (d, J¼5.09 Hz,
1H), 7.29 (d, J¼8.68 Hz, 4H), 7.12 (dd, J¼5.09 Hz, 3.77), 7.03 (d,
J¼8.68 Hz, 4H), 6.95 (d, J¼8.68 Hz, 2H), 1.32 (s, 18H).
13
C NMR
(CDCl
3
, 75 MHz): d170.69, 166.39, 156.23, 152.23, 149.14,
138.84, 134.24, 133.48, 131.95, 130.66, 124.31, 39.67, 36.72. ESI-
MS: m/z526 ([M]
+
). HRMS (ESI+) calcd for C
32
H
35
N
3
O
2
S[M+H]
+
525.2450 found 526.2520.
4-tert-Butyl-N-(4-tert-butylphenyl)-N-(4-(5-(thiophen-2-yl)-
1,3,4-thiadiazol-2-yl)phenyl)aniline (6). Lawesson's reagent (2.3
g, 5.7 mmol) was added to 5(3.0 g, 5.7 mmol) in dry THF (30 mL)
and the mixture was stirred under reux at 80 Cfor5h.Aer
completion of the reaction as monitored by TLC, the crude
product was chromatographed on silica gel (60–120 mesh)
using ethyl acetate–hexane (3 : 97; v/v) as eluent to afford the
product in pure form as yellow solid (isolated yield: 2.3 g, 80%).
1
H NMR (CDCl
3
, 500 MHz): d7.77 (d, J¼9.16 Hz, 2H), 7.54 (d, J
¼3.66 Hz, 1H), 7.45 (d, J¼5.49 Hz, 1H), 7.30 (d, J¼8.24 Hz,
4H), 7.11 (dd, J¼3.66 Hz, 5.49, 1H), 7.07 (d, J¼8.24 Hz, 4H),
7.05 (d, J¼9.16 Hz, 2H), 1.35 (s, 18H).
13
C NMR (CDCl
3
,75
MHz): d167.39, 160.47, 150.81, 147.16, 143.83, 132.74, 129.10,
128.85, 128.72, 127.84, 126.31, 125.16, 121.54, 120.39, 34.36,
31.37. ESI-MS: m/z524 ([M]
+
). HRMS (ESI+) calcd for C
32
H
34
N
3
S
2
[M + H]
+
524.2188 found 524.2190.
50-(5-(4-(Bis(4-tert-butylphenyl)amino)phenyl)-1,3,4-thiadia-
zol-2-yl)-2,20-bithiophene-5-carbaldehyde (8). Under argon
atmosphere, n-butyllithium (1.6 M, 1.24 mL, 2.0 mmol) was
added drop wise to 6(1.0 g, 1.9 mmol) in 15 mL of anhydrous
THF at 78 C. Aer stirring for 1 h at 78 C, tributylstannyl
chloride (0.78 g, 2.4 mmol) was added and temperature
was raised to room temperature, stirred for 6 h. Aer
complete consumption of the starting material, the reaction
was terminated with water. The mixture was extracted with
13178 |RSC Adv.,2014,4,13172–13181 This journal is © The Royal Society of Chemistry 2014
RSC Advances Paper
dichloromethane, dried over anhydrous sodium sulfate, ltered
and concentrated under reduced pressure to obtain 7as brown
oil and it was used as it is for further reaction. To the mixture of
7(1.0 g, 1.2 mmol) and Pd(PPh
3
)
2
Cl
2
(0.13 g, 0.19 mmol) in
toluene (20 mL), 5-bromothiophene-2-carbaldehyde (0.38 g, 2.0
mmol) was added and the mixture was reuxed for 14 h at
110 C under argon atmosphere. Aer completion of the reac-
tion, the mixture was partitioned between ethyl acetate and
water, ethyl acetate layer was collected, washed with brine and
dried over anhydrous sodium sulfate. Aer removing solvent
under reduced pressure, the residue was puried by column
chromatography (silica gel 60–120 mesh and 1 : 10 ethyl
acetate–petroleum ether as eluent) on to yield the product as red
solid (isolated yield: 0.68 g, 90%).
1
H NMR (CDCl
3
, 500 MHz): d
9.87 (s, 1H), 7.75 (d, J¼8.65 Hz, 2H), 7.66 (d, J¼3.84 Hz, 1H),
7.44 (d, J¼4.81 Hz, 1H), 7.33 (dd, J¼3.84 Hz, 4.81, 1H), 7.28 (d,
J¼8.65 Hz, 4H), 7.25 (s, 2H), 7.07 (s, 2H), 7.06 (d, J¼8.65 Hz,
4H), 7.02 (s, 1H) 1.33 (s, 18H).
13
C NMR (CDCl
3
, 75 MHz): d
182.65, 167.95, 159.87, 151.01, 147.31, 145.65, 144.80, 143.75,
142.50, 139.43, 138.77, 137.33, 133.76, 132.20, 129.93, 128.82,
126.48, 125.29, 121.30, 120.17, 34.40, 31.37. ESI-MS: m/z634
([M]
+
). HRMS (ESI+) calcd for C
37
H
39
O
2
N
3
S
3
[M + H]
+
634.20044
found 634.2033.
General procedure for synthesis of 9–12
To the solution of carbaldehyde 8(1 g, 1.5 mmol) and ammo-
nium acetate (5.7 mg, 0.07 mmol) in acetic acid (20 mL), 4.5
mmol of 2-cyanoacetic acid (0.38 g), rhodanine-3-acetic acid
(0.86 g, 4.5 mmol), 2-(4-methoxyphenyl)acetic acid (0.74 g, 4.5
mmol) or 2-phenylacetic acid (0.61 g, 4.5 mmol) was added. The
resultant mixture was reuxed for 4 h and the progress of the
reaction was monitored using TLC. Aer completion, the reac-
tion mixture was cooled and the precipitate formed was ltered,
washed sequentially with water, cold methanol and with
hexane–diethylether (1 : 1) mixture. Further, the precipitate was
re-crystallized from toluene-methanol mixture to afford the
target compounds 9–11 or 12 in pure form.
3-(50-(5-(4-(Bis(4-tert-butylphenyl)amino)phenyl)-1,3,4-thia-
diazol-2-yl)-2,20-bithiophen-5-yl)-2-cyanoacrylic acid (9). Red
solid (isolated yield: 0.63 g, 60%).
1
H NMR (DMSO-d
6
, 300 MHz):
d8.42 (s, 1H), 8.11 (s, 1H), 7.91 (d, J¼4.15 Hz, 1H), 7.75 (d, J¼
8.68 Hz, 2H), 7.67 (d, J¼3.96 Hz, 1H), 7.58 (m, 1H), 7.33 (d, J¼
8.68 Hz, 4H), 7.06 (d, J¼8.68 Hz, 4H), 6.98 (d, J¼8.68 Hz, 2H),
1.32 (s, 18H).
13
C NMR (CDCl
3
, 75 MHz): d167.41, 163.43,
159.08, 154.18, 150.49, 146.88, 145.50, 144.19, 143.14, 139.53,
138.01, 135.08, 132.82, 130.61, 129.17, 128.59, 127.95, 126.74,
125.54, 124.06, 121.05, 116.05, 33.99, 31.03. ESI-MS: m/z699 ([M
H]
). HRMS (ESI+) calcd for C
40
H
37
O
2
N
4
S
3
701.2073 [M + H]
+
found 701.2092.
2-(5-((50-(5-(4-(Bis(4-tert-butylphenyl)amino)phenyl)-1,3,4-
thiadiazol-2-yl)-2,20-bithiophen-5-yl)methylene)-4-oxo-2-thio-
xothiazolidin-3-yl)acetic (10). Red solid (isolated yield: 0.7 g,
58%).
1
H NMR (DMSO-d
6
, 300 MHz): d8.17 (s, 1H), 7.85–7.80
(m, 4H), 7.74 (d, J¼3.96 Hz, 1H), 7.70 (d, J¼3.96 Hz, 1H), 7.42
(d, J¼8.49 Hz, 4H), 7.09 (d, J¼8.49 Hz, 4H), 6.91 (d, J¼8.87 Hz,
2H), 4.72 (s, 2H), 1.29 (s, 18H). ESI-MS: m/z805 ([M H]
).
HRMS (ESI+) calcd for C
44
H
39
O
3
N
4
S
5
[M + H]
+
807.1627 found
807.1639.
3-(50-(5-(4-(Bis(4-tert-butylphenyl)amino)phenyl)-1,3,4-thia-
diazol-2-yl)-2,20-bithiophen-5-yl)-2-(4-methoxyphenyl)acrylic
acid (11). Orange-red solid (isolated yield: 065 g, 56%)
1
H NMR
(CDCl
3
, 300 MHz): d8.04 (s, 1H), 7.77–7.73 (m, 2H), 7.36 (d, J¼
4.53 Hz, 1H), 7.34–7.30 (m, 4H), 7.22 (d, J¼8.30 Hz, 2H), 7.20–
7.16 (m, 2H), 7.13 (d, J¼4.53 Hz, 1H), 7.08 (d, J¼8.30 Hz, 4H),
7.05–7.01 (m, 4H), 3.90 (s, 3H) 1.32 (s, 18H).
13
C NMR (CDCl
3
,75
MHz): d172.30, 167.54, 160.13, 159.91, 150.89, 147.24, 143.76,
141.37, 139.81, 138.49, 135.25, 132.01, 131.17, 129.80, 128.77,
128.28, 126.15, 125.21, 125.01, 124.29, 121.28, 120.25, 114.76,
113.88, 55.33, 34.39, 31.37. ESI-MS: m/z780 ([M H]
). HRMS
(ESI+) calcd for C
46
H
43
O
3
N
3
S
3
[M + H]
+
782.2515 found
782.2545.
3-(50-(5-(4-(Bis(4-tert-butylphenyl)amino)phenyl)-1,3,4-thia-
diazol-2-yl)-2,20-bithiophen-5-yl)-2-phenylacrylic acid (12).
Orange-red solid (isolated yield: 0.63 g, 56%).
1
H NMR (CDCl
3
,
300 MHz): d8.06 (s, 1H), 7.74 (d, J¼8.30, 2H), 7.52–7.49 (m,
3H), 7.36–7.28 (m, 7H), 7.17–7.12 (m, 2H), 7.10–7.02 (m, 5H),
7.02–6.98 (m, 2H) 1.32 (s, 18H).
13
C NMR (CDCl
3
, 75 MHz): d
171.72, 160.05, 159.89, 150.90, 147.25, 143.76, 141.58, 139.75,
138.26, 135.36, 135.28, 134.23, 132.07, 129.81, 129.38, 129.08,
128.77, 128.59, 128.46, 127.70, 126.36, 125.21, 124.92, 124.23,
121.28, 120.26, 34.40, 31.37. ESI-MS: m/z751 ([M H]
). HRMS
(ESI+) calcd for C
46
H
43
O
2
N
3
S
3
[M + H]
+
752.2469 found
752.2439.
Conclusions
Four new D–A–p–A type organic dyes with different acceptor/
anchor groups were synthesized, characterized, their photo-
physical, electrochemical and photovoltaic properties were
explored. All the dyes showed their absorption in the visible
region and exhibited good light harvesting capacity. The
oxidation potentials of the dyes are more positive than I
/I
3
(0.2 V vs. SCE) and the calculated excited state oxidation
potentials are more negative compared to TiO
2
conduction
band (0.8 V vs. SCE). The importance of the localization of the
LUMO electron density on the acid/anchor group for better
interfacial electron injection from excited state dye to semi-
conductor is also explored by DFT and TDDFT calculations and
all the dyes exhibited efficient interfacial electron transfer.
Under AM 1.5 irradiation, all the dyes showed moderate to good
efficiencies. Among all, the DSSC with 9dye showed highest
efficiency (h¼4.12%), with short-circuit current density (J
sc
)of
8.504 mA cm
2
, open-circuit voltage (V
oc
) of 645 mV and ll
factor (FF) of 0.75. The structural modication of 9is in prog-
ress for further improvement in its photophysical and photo-
voltaic properties.
Acknowledgements
We thank the Director CSIR-IICT for the encouragement. We
acknowledge funding from NWP-0054 project. GSK, KS, BS and
DB thank CSIR for fellowships.
This journal is © The Royal Society of Chemistry 2014 RSC Adv.,2014,4,13172–13181 | 13179
Paper RSC Advances
References
1 B. O'Regan and M. Gratzel, Nature, 1991, 353, 737.
2 Y. Numata, S. P. Singh, A. Islam, M. Iwamura, A. Imai,
K. Nozaki and L. Han, Adv. Funct. Mater., 2013, 23, 1817.
3 W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang,
C. Pan and P. Wang, Chem. Mater., 2010, 22, 1915.
4 Y. S. Yen, H. H. Chou, Y. C. Chen, C. Y. Hsu and J. T. Lin,
J. Mater. Chem., 2012, 22, 8734.
5 A. Mishra, M. K. R. Fischer and P. B¨
auerle, Angew. Chem., Int.
Ed., 2009, 48, 2474.
6 Y. Liang, B. Peng, J. Liang, Z. Tao and J. Chen, Org. Lett.,
2010, 12, 1204.
7 J. H. Yum, D. P. Hagberg, S. J. Moon, K. M. Karlsson,
T. Marinado, L. C. Sun, A. Hagfeldt, M. K. Nazeeruddin
and M. Gratzel, Angew. Chem., Int. Ed., 2009, 48, 1576.
8 D. P. Hagberg, J. H. Yum, H. Lee, F. De Angelis, T. Marinado,
K. M. Karlsson, R. Humphry-Baker, L. C. Sun, A. Hagfeldt,
M. Gratzel and M. K. Nazeeruddin, J. Am. Chem. Soc., 2008,
130, 6259.
9 N. Koumura, Z. S. Wang, S. Mori, M. Miyashita, E. Suzuki
and K. Hara, J. Am. Chem. Soc., 2006, 128, 14256.
10 D. Kuang, S. Uchida, R. H. Baker, S. M. Zakeeruddin and
M. Gr¨
atzel, Angew. Chem., Int. Ed., 2008, 47, 1923.
11 Y. Wu, M. Marszalek, S. M. Zakeeruddin, Q. Zhang, H. Tian,
M. Gratzel and W. Zhu, Energy Environ. Sci., 2012, 5, 8261.
12 K. Hara, M. Kurashige, Y. Dan-oh, C. Kasada, A. Shinpo,
S. Suga, K. Sayama and H. Arakawa, New J. Chem., 2003, 27,
783.
13 K. Hara, K. Sayama, Y. Ohga, A. Shinpo, S. Suga and
H. Arakawa, Chem. Commun., 2001, 569.
14 P. J. Skabara, R. Berridge, I. M. Serebryakov,
A. L. Kanibolotsky, L. Kanibolotskaya, S. Gordeyev,
I. F. Perepichka, N. S. Saricici and C. Winder, J. Mater.
Chem., 2007, 17, 1055.
15 H. Qin, S. Wenger, M. F. Xu, F. F. Gao, X. Y. Jing, P. Wang,
S. M. Zakeeruddin and M. Gratzel, J. Am. Chem. Soc., 2008,
130, 9202.
16 J. Zhang, H. B. Li, S. L. Sun, Y. Geng, Y. Wu and Z. M. Su,
J. Mater. Chem., 2012, 22, 568.
17 H. Tian, X. Yang, R. Chen, Y. Pan, L. Li, A. Hagfeldt and
L. Sun, Chem. Commun., 2007, 3741.
18 K. Hara, T. Sato, R. Katoh, A. Furube, T. Yoshihara,
M. Murai, M. Kurashige, S. Ito, A. Shinpo, S. Suga and
H. Arakawa, Adv. Funct. Mater., 2005, 15, 246.
19 D. P. Hagberg, T. Edvinsson, T. Marinado, G. Boschloo,
A. Hagfeldt and L. C. Sun, Chem. Commun., 2006, 2245.
20 S. Hwang, J. H. Lee, C. Park, H. Lee, C. Kim, C. Park,
M. H. Lee, W. Lee, J. Park, K. Kim, N. G. Park and C. Kim,
Chem. Commun., 2007, 4887.
21 H.Choi,C.Baik,S.O.Kang,J.Ko,M.S.Kang,M.K.Nazeeruddin
and M. Gratzel, Angew. Chem., Int. Ed., 2008, 47, 327.
22 K. R. J. Thomas, Y.-C. Hsu, J. T. Lin, K.-M. Lee, K.-C. Ho, C.-H. Lai,
Y.-M. Cheng and P.-T. Chou, Chem. Mater., 2008, 20, 1830.
23 Q. Feng, X. Lu, G. Zhou and Z.-S. Wang, Phys. Chem. Chem.
Phys., 2012, 14, 7993.
24 H. N. Tian, X. C. Yang, R. K. Chen, R. Zhang, A. Hagfeldt and
L. Sun, J. Phys. Chem. C, 2008, 112, 11023.
25 Y. Z. Wu and W. H. Zhu, Chem. Soc. Rev., 2013, 42, 2039.
26 W. H. Zhu, Y. Z. Wu, S. T. Wang, W. Q. Li, X. Li, J. Chen,
Z. S. Wang and H. Tian, Adv. Funct. Mater., 2011, 21, 756.
27 S. Haid, M. Marszalek, A. Mishra, M. Wielopolski,
J. Teuscher, J. Moser, R. Humphry-Baker,
S. M. Zakeeruddin, M. Gratzel and P. Bauerle, Adv. Funct.
Mater., 2012, 22, 1291.
28 J. Kim, H. Choi, J. Lee, M. Kang, K. Song, S. O. Kang and
J. Ko, J. Mater. Chem., 2008, 18, 5223.
29 Y. Z. Wu, X. Zhang, W. Q. Li, Z. S. Wang, H. Tian and
W. H. Zhu, Adv. Energy Mater., 2012, 2, 149.
30 Y. Cui, Y. Z. Wu, X. F. Lu, X. Zhang, G. Zhou, F. B. Miapeh,
W. H. Zhu and Z. S. Wang, Chem. Mater., 2011, 23,
4394.
31 J. Y. Mao, F. L. Guo, W. J. Ying, W. J. Wu, J. Li and J. L. Hua,
Chem.–Asian J., 2012, 7, 982.
32 K. Pei, Y. Z. Wu, W. J. Wu, Q. Zhang, B. Q. Chen, H. Tian and
W. H. Zhu, Chem.–Eur. J., 2012, 18, 8190.
33 S. Y. Qu, W. J. Wu, J. L. Hua, C. Kong, Y. T. Long and H. Tian,
J. Phys. Chem. C, 2010, 114, 1343.
34 S. Y. Qu, C. J. Qin, A. Islam, Y. Z. Wu, W. H. Zhu, J. L. Hua,
H. Tian and L. Y. Han, Chem. Commun., 2012, 48, 6972.
35 X. F. Lu, G. Zhou, H. Wang, Q. Y. Feng and Z. S. Wang, Phys.
Chem. Chem. Phys., 2012, 14, 4802.
36 C. Chen, Y. Hsu, H. Chou, K. R. J. Thomas, J. T. Lin and
C. Hsu, Chem.–Eur. J., 2010, 16, 3184.
37 J. X. He, W. J. Wu, J. L. Hua, Y. H. Jiang, S. Y. Qu, J. Li,
Y. T. Long and H. Tian, J. Mater. Chem., 2011, 21, 6054.
38 Y. Z. Wu, M. Marszalek, S. M. Zakeeruddin, Q. Zhang,
H. Tian, M. Gratzel and W. H. Zhu, Energy Environ. Sci.,
2012, 5, 8261.
39 K. Srinivas, K. Yesudas, K. Bhanuprakash, V. Jayathirtha Rao
and L. Giribabau, J. Phys. Chem. C, 2009, 113, 20117.
40 K. Srinivas, Ch. R. Kumar, M. Ananth Reddy,
K. Bhanuprakash, V. Jayathirtha Rao and L. Giribabu,
Synth. Met., 2010, 161, 96.
41 K. Srinivas, G. Sivakumar, Ch. R. Kumar, M. Ananth Reddy,
K. Bhanuprakash, V. Jayathirtha Rao, C. W. Chenc,
Y. C. Hsuc and J. T. Lin, Synth. Met., 2011, 161, 1671.
42 S. G. Bairu, E. Mghanga, J. A. Hasan, S. Kola,
K. Bhanuprakash, V. Jayathirtha Rao, L. Giribabu,
G. P. Wiederrecht, R. da Silva, L. G. C. Rego and
G. Ramakrishna, J. Phys. Chem. C, 2013, 117, 4824.
43 M. Guo, P. Y Diao, J. Ren, F. S. Meng and H. Tian, Sol. Energy
Mater. Sol. Cells, 2005, 88, 23.
44 S. L. Li, K. J. Jiang, K. F. Shao and L. M. Yang, Chem.
Commun., 2006, 2792.
45 A. Hagfeldt and M. Gratzel, Chem. Rev., 1995, 95, 49.
46 K. Hara, M. Kurashige, Y. Dan-oh, C. Kasada, A. Shinpo,
S. Suga, K. Sayama and H. Arakawa, New J. Chem., 2003,
27, 783.
47 M. Nilsing, P. Persson and L. Ojamae, Chem. Phys. Lett.,
2005, 415, 375.
48 M. Guo, R. He, Y. Dai, W. Shen, M. Li, C. Zhu and S. H. Lin, J.
Phys. Chem. C, 2012, 116, 9166.
13180 |RSC Adv.,2014,4,13172–13181 This journal is © The Royal Society of Chemistry 2014
RSC Advances Paper
49 K. Hara, T. Sato, R. Katoh, A. Furube, T. Yoshihara,
M. Murai, M. Kurashige, S. Ito, A. Shinpo, S. Suga and
H. Arakawa, Adv. Funct. Mater., 2005, 15, 246.
50 Q. Wang, W. M. Campbell, E. E. Bonfanatani, K. W. Jolley,
D. L. Officer, P. J. Walsh, K. Gordon, R. H. Baker,
M. K. Nazeeruddin and M. Gratzel, J. Phys. Chem. B, 2005,
109, 15397.
51 S. Jungsuttiwong, T. Yakhanthip, S. Jungsuttiwong,
T. Yakhanthip, Y. Surakhot, J. Khunchalee, T. Sudyoadsuk,
V. Promarak, N. Kungwan and S. Namuangruket,
J. Comput. Chem., 2012, 33, 1517.
52 L. Han, N. Koide, Y. Chiba, A. Islam, R. Komiya, N. Fuke,
A. Fukui and R. Yamanaka, Appl. Phys. Lett., 2005, 86, 213501.
53 J. Tomasi, B. Mennucci and R. Cammi, Chem. Rev., 2005,
105, 2999.
54 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865.
55 A. Schaefer, C. Huber and R. Ahlrichs, J. Chem. Phys., 1994,
100, 5829.
56 N. M. O'Boyle, A. L. Tenderholt and K. M. Langner,
J. Comput. Chem., 2008, 29, 839.
57 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li,; H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr,
J. E. Peralta, F. Ogliaro, M. Bearpark,; J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, N. J. Millam,
M. Klene, J. E. Knox, 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,
R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth,
P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and
D. J. Fox, Gaussian 09, Revision B.01, Gaussian, Inc.,
Wallingford CT, 2010.
58 D. H. Bhaskar and H. D. Rajesh, Tetrahedron Lett., 1996, 37,
6375.
This journal is © The Royal Society of Chemistry 2014 RSC Adv.,2014,4,13172–13181 | 13181
Paper RSC Advances
