Introducing rigid π-conjugated peripheral substituents in phthalocyanines for DSSCs

Article abstract of DOI:10.1142/S1088424616501121

A new carboxy-Zn(II)phthalocyanine bearing rigid 2,6-diarylphenyl peripheral substituents linked to the macrocycle through alkynyl spacers has been prepared by a convergent approach, which implies a triple Sonogashira coupling between the formyltriiodoZnP

Full text of DOI:10.1142/S1088424616501121

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2016; 20: 1–7
DOI: 10.1142/S1088424616501121
Published at http://www.worldscinet.com/jpp/
Introducing rigid p-conjugated peripheral substituents
in phthalocyanines for DSSCs
Lara Tejerinaa◊◊, Esmeralda Caballeroa, M. Victoria Martínez-Díaz*a,
Mohammad Khaja Nazeeruddin*b, Michael Grätzelc and Tomas Torres*a,d◊
a Departamento de Química Orgánica, Facultad de Ciencias, C/ Francisco Tomás y Valiente 7, Universidad
Autónoma de Madrid, 28049 Madrid, Spain
b Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering,
École Polytechnique Fédérale de Lausanne (EPFL), Rue de l’Industrie 17, 1951 Sion, Switzerland
c Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique
Fédérale de Lausanne (EPFL), Station 6, 1015 Lausanne, Switzerland
d IMDEA-Nanociencia, C/Faraday 9, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain
Dedicated to Professor Tomás Torres on the occasion of his 65th birthday
Received 21 March 2016
Accepted 18 May 2016
ABSTRACT:. A new carboxy-Zn(II)phthalocyanine bearing rigid 2,6-diarylphenyl peripheral substi-
tuents linked to the macrocycle through alkynyl spacers has been prepared by a convergent approach,
which implies a triple Sonogashira coupling between the formyltriiodoZnPc and the corresponding
terminal alkyne. Indeed, the introduction of this type of p-conjugated peripheral substituents accounts for
a remarkable red shift of the phthalocyanine Q-band until ca. 700 nm. However, aggregation phenomena
could not be supressed and may explain the moderate overall efficiencies achieved with these devices.
KEYWORDS: phthalocyanines, solar cells, p-conjugated systems, near IR dyes
semiconductor. Not only the presence of bulky groups is
paramount for obtaining good efficiencies in ZnPc-based
DSSCs, but also the anchoring group that should be close
and p-conjugated to the macrocycle ZnPc core. The results
shown in Table 1 point to the effectiveness of the alkynyl
bridge as a connecting group. Thus, TT40 [2] largely
INTRODUCTION
During the last years, a number of unsymmetrically
substituted phthalocyanines (A3B type) have emerged as
efficient red absorbing molecules for Dye Sensitized Solar
Cells (DSSCs), reaching power conversion efficiencies
(PCE) of up to 6% [1] when used as a single sensitizer.
outperforms the efficiency of PcS6 [3] which presents a
Commun structural requirements, such as incorporation
phenylene bridge betweeen the anchoring carboxy group
of peripheral bulky donor substituents (typically tert-butyl
and the macrocycle. Moreover, TT40 leads to a slightly
and 2,6-diphenylphenoxy substituents), have resulted
higher efficiency than that for TT58 [2b] with the COOH
crucial in order to both minimize aggregation of the dye
group directly linked to the macrocycle.
on the TiO2 surface and achieve a directional excited
Our work consists of exploring new bulky peripheral
state to facilitate efficient injection of electrons onto the
substituents to further improve the possibilities of phtha-
locyanines as sensitizers for DSSCs. Taking all the above
◊ SPP full and ◊◊ student member in good standing
requirements into consideration, we have designed
new unsymmetrical A3B-type carboxy-ZnPc for
a
*Correspondence to: M. Victoria Martínez-Díaz, email:
victoria.martinez@uam.es; Mohammad Khaja Nazeeruddin,
email: mdkhaja.nazeeruddin@epfl.ch; Tomas Torres, email:
tomas.torres@uam.es
DSSCs, TT65, in which the bulky and rigid peripheral
substituents are linked to the macrocycle through a
p-conjugated bridge (Chart 1). As mentioned earlier,
Copyright © 2016 World Scientific Publishing Company

2
L. TEJERINA ET AL.
Table 1. Efficiency values of TT40, TT58 and PcS6
substituents at the periphery of the macrocycle, and to
take advantage of the red-shift induced in the absorption
properties of the new Pc dye because of the extended
p-conjugated system.
under 1 sun irradiation (100 mW.cm-2)
Dye
Structure
PCE
TT40
RO
OR
RO
RO
OR
RESULTS AND DISCUSSION
N
N
Ph
Ph
N
N
R =
N
Zn
N
6.0%
N
Synthesis
N
COOH
In view of our previous experience on the functi-
onalization of iodoZnPcs by Pd-mediated reactions
[4,6], we planned the preparation of target TT65
by a convergent synthetic strategy which implies
the macrocyclization of two phthalonitriles, one
bearing a precursor of the anchoring group, and
the other bearing the iodo-substitution which will
suffer the subsequent functionalization. Thus, a 4:1
molar ratio mixture of 4-iodophthalonitrile (1) and
4-hydroxymethylphthalonitrile (2) was reacted at
reflux in DMAE in the presence of Zn(OAc)2. The
desired A3B ZnPc 3 was obtained in 24% yield after
isolation by column chromatography (Scheme 1).
ZnPc 3 was then oxidized under mild conditions with
periodinane derivative IBX in DMSO to yield the
formyl derivative ZnPc 4 in 90% yield (Scheme 1).
Given the good solubility of 4 in organic solvents, the
subsequent triple Sonogashira coupling was performed
on this compound, employing the arylethynyl 8 and
standard conditions, giving rise to a regioisomeric
mixture of b-triarylalkynyl-substituted ZnPc 9 in 70%
yield (Scheme 1) which has three pretty bulky aromatic
groups linked to the macrocycle via sp carbon–aromatic
sp2 carbon bonds. By using sodium hypochlorite in the
presence of sulfamic acid, ZnPc 9 was converted to ZnPc
TT65 in 90% yield (Scheme 1) after a final purification
by gel permeation chromatography (GPC).
RO
RO
OR
RO
OR
N
Ph
N
N
N
N
R =
N
Zn
N
N
TT58
5.6%
Ph
COOH
RO
RO
RO
OR
RO
OR
N
Ph
N
N
N
N
R =
N
Zn
N
N
PcS6
4.6%
Ph
RO
COOH
RO
Ph
Ph
N
Ph
Ph
N
N
The synthesis of the bulky substituents was addressed
by reacting the comercially available 2,6-dibromo-4-
methylaniline in a Sandmeyer reaction to obtain product 5
in61%yield.Thus,thearomaticaminogroupwasdisplaced
with iodide anion via preparation of its diazonium salt
catalized by copper(I) salts. Derivative 5 was subjected to
a Sonogashira coupling reaction with a propargyl alcohol
giving rise to compound 6 in 64% yield. This reaction
resulted highly selective and none competitive reaction
of the bromine atoms was detected. Afterthat, the double
Suzuki–Miyaura cross-coupling reaction was performed
on derivative 6, employing 4-biphenylboronic acid and
standard conditions, giving rise to the bulky derivative 7 in
65% yield, which was subjected to a elimination reaction
in the presence of NaOH to obtain the ethynylarene 8 in
71% yield (Scheme 2).
Ph
N
N
N
Zn
N
N
COOH
Ph
Chart 1. ZnPc TT65
alkynyl bridges are considered the most efficient groups
to electronically connect the Pc core and the anchoring
COOH group, but they have never been used as units to
link the bulky peripheral groups and the ZnPc core. Using
this new approach we sought both being able to avoid dye
aggregation by the introduction of bulky and rigid donor
The structures of all new compounds were confirmed
by mass spectrometry and IR, UV-vis, and NMR spectro-
1
scopies (see the Supporting information). The H NMR
spectrum in d8-THF of final carboxyZnPc TT65 showed
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 2–7

INTRODUCING RIGID p-CONJUGATED PERIPHERAL SUBSTITUENTS IN PHTHALOCYANINES FOR DSSCs
3
I
I
I
I
CN
CN
N
N
I
N
N
N
N
N
N
N
N
Zn(OAc)2
IBX
1
+
N
N
Zn
Zn
N
N
DMAE
reflux, 20 h
DMSO
rt, 20 h
CN
CN
N
N
24%
90%
OH
HO
CHO
I
I
2
3
4
8
PdCl2(PPh3)2, CuI
THF/NEt3
70%
35 °C, 20 h
R
R
Ph
Ph
N
N
N
N
NaClO2, H3NSO3
R =
ZnPc TT65
N
Zn
N
THF/H2O
N
0 °C - rt, 3 h
90%
N
CHO
R
9
Scheme 1. Convergent synthesis of b-triarylalkynyl-substituted ZnPc 9 by triple Sonogashira coupling reaction on triiodo ZnPc 4
and final oxidation to obtain the target TT65
OH
OH
OH
Ph
Ph
B(OH)2
Ph
Ph
NH2
I
i) NaNO2
HCl/AcOH
Br
Br
Br
Br PdCl2(PPh3)2, CuI
Br
Br
Pd(PPh3)4, Na2CO3
NaOH
ii) KI
61%
THF/NEt3
50 °C, 20 h
DME
Toluene
80 °C, 20 h
reflux, 20 h
64%
65%
71%
5
6
7
8
Scheme 2. Synthesis of the bulky peripheral substituents
bad resolution due to both mixture of regioisomers and
strong aggregation due to p–p stacking induced by the
peripheral large aromatic substituents.
Optical and electrochemical properties
The normalized UV-vis absorption spectra for 3, 4, 9
and TT65 in THF are shown in Fig. 1. Molecules 9
and TT65 show nearly superimposable spectra with
a maximum absorbance in the near-infrared region at
696 nm. Moreover, an overall 23 nm red-shift was
achieved in the Q-band of the Pcs due to the peripheral
incorporation of p-conjugated groups. The electro-
chemical measurements were performed at room temper-
ature in CH2Cl2 containing [TBA]PF6 (0.1 M) as
supporting electrolyte and using Ag/AgCl electrode as
internal reference. The results of Table 2 allowed us to
determine the HOMO–LUMO levels energy of TT65.
Thus, the energies of the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) are related to the ground-state redox
Fig. 1. UV-visible spectra of 3, 4, 9 and TT65 in THF (5 ×
10 M-1)
potentials (EHOMO = Eox1 vs. NHE; ELUMO = Ered1 vs. NHE).
Potentials measured vs. Fc/Fc+ (Table 2) were converted
to normal hydrogen electrode (NHE) by addition of
+0.64 V [7]. Therefore, EHOMO = 0.901 V and ELUMO
=
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 3–7

4
L. TEJERINA ET AL.
Table 3 shows the short-circuit photocurrent density
(Jsc), open-circuit photovoltage (V ), fill factor (FF) and
oc
PCE obtained under 1 sun irradiation for TT65 devices,
either prepared with the coadsorption of chenodeoxy-
cholic acid (CDCA) or without any co-adsorbent. The
latter exhibits a Jsc of 4.2 mA.cm-2, a V of 508 mV, a FF
oc
of 0.72, yielding a PCE of 1.5%. The coadsorption of
CDCA can hinder the formation of dye aggregates and
improve electron injection yield, and thus Jsc. Therefore,
the photovoltaic performance of TT65 in the presence
of CDCA increases in comparison with the absence of
it. In such a way, in the presence of 0.05 mM of CDCA,
the cell exhibits a Jsc of 4.4 mA.cm-2, a V of 500 mV,
oc
a FF of 0.73, yielding a PCE of 1.6%. Moreover, the
maximum PCE value of 1.7% was achieved in the
presence of 0.10 mM of CDCA into the dye solution,
Fig. 2. J–V curves for DSSC based on TT65/CDCA at several
light intensities
besides exhibiting a Jsc of 4.8 mA.cm-2, a V of 491 mV
oc
and a FF of 0.72. Figure 2 shows the photocurrent
density–voltage (J–V) curves at several light intensities
of DSSCs based on TT65 and 10 mM CDCA .The IPCE
for this cell, plotted in Fig. 3 as a function of excitation
wavelength, reaches 30% at the maximum absorption
of the Q-band (700 nm), and shows a remarkable
broadening due to the aggregates formation on TiO2
surface. When adding more co-adsorbent into the dye
solution, i.e. 0.15 mM of CDCA, the efficiency value of
the device does not increase anymore owing to the loss of
dye loaded. Thus, the cell exhibits a Jsc of 4.2 mA.cm-2, a
Table 2. Electrochemical data of TT65 determined by
Square-Wave Voltammetry (SWV)
Ered1a, V
-1.511
Eox1a, V
0.261
E0-0b, nm (eV)
701 (1.769)
E0–0*c, V
-1.508
a Potentials are reported vs. the ferrocene/ferrocenium (Fc/
Fc+) couple as external reference. bThe zero-zero excitation
energy (E0–0) is obtained from the intersection between the
normalized absorption and emission spectra. Converted to
eV according to the relation E0–0 (eV) = 1240/E0–0 (nm).
cThe excited-state oxidation potential (E0–0*) reported vs.
V of 514 mV and a FF of 0.74, yielding a PCE of 1.6%.
oc
Fc/Fc+ is calculated from E0–0* = Eox1–E0–0
.
EXPERIMENTAL
-0.871 V, being the latter more negative than the TiO2
conduction band (ca. -0.5 V vs. NHE), consequently
making the electron injection from the excited state of
TT65 into the TiO2 termodinamically feasible.
General
Chemicals employed were purchased from Aldrich
Chemical Co. and used without further purification. Dry
solvents were obtained from a Solvent Drying System
(SPS). The monitoring of the reactions was carried out by
TLC employing aluminum sheets coated with silica gel
60 F254 purchased from Merck. Purification of compounds
Dye-sensitized solar cells
Table 3. Photovoltaic performance of DSSCsa based on TT65, with and without
co-adsorbent, under 1 sun irradiation (100 mW.cm-2)
CDCA, mM
—
V , mV
Jsc, mA.cm-2
FF
PCEb, %
1.5
PCEc, %
1.3 0.2
1.6 0.0
1.6 0.1
1.5 0.1
oc
508
500
491
514
4.2
4.4
4.8
4.2
0.72
0.73
0.72
0.74
0.05
1.6
0.10
1.7
0.15
1.6
b
a Two devices were made for each configuration. Efficiency values of the best cells are
presented. cAverage efficiency values of the devices presented with the standard deviation.
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 4–7

INTRODUCING RIGID p-CONJUGATED PERIPHERAL SUBSTITUENTS IN PHTHALOCYANINES FOR DSSCs
5
obtained. Yield 0.34 g (64%), mp 123°C. 1H NMR (300
MHz, CDCl3): d, ppm 7.35 (s, 2H), 2.30 (s, 3H), 2.20 (s,
1H), 1.66 (s, 6H). 13C NMR (75 MHz, CDCl3): d, ppm
141.0, 132.3, 126.3, 123.9, 102.5, 80.7, 66.2, 31.5, 21.1.
IR (KBr): n, cm-1 3242, 2981, 2923, 1733, 1594, 1530,
1455, 1381, 1360, 1275, 1192, 1166, 1143, 1062, 1035,
1007, 965, 916, 883, 849, 788, 742, 712, 623, 586, 570.
HR-MS (EI): m/z 329.9262 [M]+, calcd. for C12H12Br2O:
329.9255.
Preparation of 4-(2,6-bis-(4-biphenyl)-4-methyl-
phenyl)-2-methylbut-3-yn-2-ol (7). A Na2CO3 1 M solu-
tion (1 mL) was added to a mixture of compound 6
(0.34 g, 1.0 mmol), Pd(PPh3)4 (0.12 g, 0.1 mmol) and
4-biphenylboronic acid (0.55 g, 2.8 mmol) in DME
(5 mL). The mixture was degassed and fluxed with argon
Fig. 3. IPCE spectrum for DSSC based on TT65/CDCA
for 10 min. The reaction mixture was heated at 80°C
for 20 h. The crude was poured onto an NH4Cl 1 M
was performed by column chromatography using silica
gel Merck-60 (40–63 mm) and Bio-Beads S-X1 Support
from Bio-Rad (200–400 mesh) for gel permeation
chromatography (GPC). Solvents were purchased from
Carlo Erba Reagents and Scharlab in a synthesis grade.
NMR spectra were recorded by using Bruker AV-300
or Bruker DRX-500 spectrometers. Deuterated solvent
employed is indicated in brackets for each case. UV-vis
spectra were recorded in solution using solvents in
spectroscopic grade on a Jasco V-660 spectrophotometer.
The logarithm of the absorption coefficient (e) is
indicated in brackets for each maximum. Mass Spectro-
metry (Electron Impact and Matrix-Assisted Laser
Desorption Ionization Time-Of-Flight) as well as
HR-MS were performed in a VG-AutoSpec and Bruker-
ULTRAFLEX-III apparatus respectively, the latter with a
Nd:YAG laser operating at 355 nm. DCTB, and PEGNa
2000 poly(ethylenglycol)-2000 were used as matrix and
internal reference, respectively.
solution (100 mL), and extracted with ethyl acetate (3 ×
30 mL). The organic phases were collected and washed
with brine and dried over anhydrous MgSO4. After
filtration, the solvent was removed under vacuum. The
solid was purified by column chromatography on silica
gel (eluent: hexane/ethyl acetate 5:1) and recrystallized
from methanol. A white solid was obtained. Yield 0.32 g
1
(65%). H NMR (300 MHz, CDCl3): d, ppm 7.69 (m,
12H), 7.43 (m, 8H), 2.47 (s, 3H), 1.31 (s, 6H). 13C NMR
(75 MHz, CDCl3): d, ppm 144.9, 141.2, 140.5, 140.4,
138.6, 130.2, 129.6, 129.1, 127.6, 127.4, 126.7, 117.1,
100.0, 81.7, 65.8, 31.2, 21.8. IR (KBr): n, cm-1 3575,
3442, 3060, 3031, 2972, 2924, 2864, 2854, 2366, 2340,
1954, 1929, 1636, 1598, 1561, 1521, 1487, 1452, 1398,
1383, 1359, 1314, 1264, 1158, 1107, 1076, 1036, 1006,
952, 918, 876, 846, 759, 729, 692, 633, 608, 581. HR-MS
(EI): m/z 478.2280 [M]+, calcd. for C36H30O: 478.2297.
Preparation of 1,3-bis-(4-biphenyl)-2-ethynyl-5-
methylbenzene (8). Compound 7 (0.32 g, 0.67 mmol)
and powdered NaOH (0.029 g, 0.74 mmol) were
dissolved in dry toluene (19 mL) under argon atmosphere.
The reaction mixture was heated to reflux for 20 h. The
solvent was eliminated under reduced pressure and the
solid dissolved in CH2Cl2. The organic phase was washed
with brine and dried over anhydrous MgSO4. After
filtration, the solvent was removed under vacuum and the
solid recrystallized from isopropanol. A white solid was
obtained. Yield 0.20 g (71%). mp 184°C. 1H NMR (300
MHz, CDCl3): d, ppm 7.71 (m, 12H), 7.43 (m, 8H), 2.99
(s, 1H), 2.47 (s, 3H). 13C NMR (75 MHz, CDCl3): d, ppm
145.6, 141.0, 140.3, 140.0, 138.8, 130.1, 129.7, 128.9,
127.4, 127.3, 126.7, 116.2, 83.8, 82.3, 21.6. IR (KBr):
n, cm-1 3313, 3290, 3278, 3051, 3031, 2914, 2852, 2098,
1922, 1598, 1581, 1561, 1519, 1487, 1451, 1395, 1159,
1114, 1077, 1039, 1006, 914, 873, 841, 775, 759, 732,
695, 651, 624, 608. HR-MS (EI): m/z 420.1894 [M]+,
calcd. for C33H24: 420.1878.
Synthesis
Phthalocyanines 3 and 4 were prepared according to
procedures reported by us [4]. 2,6-Dibromo-4-methylio-
dobenzene 5 was used after its preparation following the
literature [5].
Preparation of 4-(2,6-Dibromo-4-methylphenyl)-2-
methylbut-3-yn-2-ol(6).Compound5(0.61g,1.6mmol),
PdCl2(PPh3)2 (0.0112 g, 1 mol%) and CuI (0.0015 g,
0.5 mol%) were dissolved in a mixture of dry THF and
distilled NEt3 (2:1, 6 mL). The mixture was degassed
and fluxed with argon for 10 min. Then the 2-methylbut-
3-yn-2-ol (0.19 mL, 1.9 mmol) was added dropwise.
The reaction mixture was heated at 50°C for 20 h. The
solvent was eliminated under reduced pressure and the
solid dissolved in CH2Cl2. The organic phase was washed
with brine and dried over anhydrous MgSO4. After
filtration, the solvent was removed under vacuum. The
solid was purified by column chromatography on silica
gel (eluent: hexane/THF 10:1). A light yellow solid was
Preparation of b-triarylalkynyl-substituted formyl-
phthalocyanine (9) (mixture of regioisomers). Phthalo-
cyanine 4(0.074 g, 0.075 mmol), terminal alkyne 8(0.12 g,
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 5–7

6
L. TEJERINA ET AL.
0.28 mmol), PdCl2(PPh3)2 (0.0053 g, 10 mol%) and CuI
(0.0014 g, 10 mol%) were dissolved in a mixture of dry
THF and distilled NEt3 (8:1, 15 mL). The mixture was
degassed and fluxed with argon for 10 min. The reaction
mixture was heated at 35°C for 20 h. The solvent was
eliminated under reduced pressure and the solid dissolved
in CHCl3. The organic phase was washed with brine and
dried over anhydrous MgSO4. After filtration, the solvent
was removed under vacuum. The solid was purified by gel
permeation chromatography (eluent: THF). A dark green
solid was obtained. Yield 0.098 g (70%), mp > 250°C. 1H
NMR (500 MHz, THF-d8): d, ppm 10.39–10.04 (m, 1H),
9.10–8.61 (br m, 8H), 8.06–7.32 (br m, 64H), 2.58–2.45
(br m, 9H). UV-vis (THF): lmax, nm (log e) 696 (4.25),
626 (3.56), 359 (3.83), 284 (4.15). IR (KBr): n, cm-1
3055, 3029, 2958, 2922, 2852, 2597, 2554, 2201, 1912,
1695, 1608, 1486, 1447, 1391, 1363, 1339, 1311, 1276,
1250, 1200, 1159, 1141, 1088, 1047, 1006, 934, 897, 870,
837, 757, 745, 730, 697, 671. HR-MS (MALDI-TOF,
DCTB+PEGNa 2000): m/z 1858.5937 [M]+, calcd. for
C132H82N8OZn: 1858.5898.
chenodeoxycholic acid (CDCA) as co-adsorbent when
indicating. The electrodes were dipped into the dye
solutions for 5 h at room temperature. The dye-coated
electrodes were rinsed quickly with ethanol to remove
the loosely bounded dye molecules and used as such
for photovoltaic measurements. The electrolyte was
composed of 0.86 M 1,3-dimethylimidazolium iodide,
0.4 M LiI, 0.04 M I2, 0.29 M 4-tert-butylpyridine and
0.05 M guanidine thiocyanate in acetonitrile. The dye-
adsorbed TiO2 electrode and thermally platinized counter
electrode were assembled into a sealed sandwich-type
cell with a gap of a hot-melt ionomer film (25 mm)
(SurlynTM, DuPont, USA).
For photovoltaic measurements of the DSSCs, the
irradiation source was a 450 W xenon light source (Oriel,
USA) equipped with a Schott K113 Tempax sunlight filter
(Präzisions Glas & Optik GmbH, Germany) to match the
emission spectra to the AM1.5G standard in the region of
350–750 nm. The current–voltage characteristics of the
devices were obtained by applying external potential bias
to the cell while recording the generated photocurrent
using a Keithley (Model 2400) digital source meter
(Keithley, USA). The J–V curves of all devices were
measured by fixing the active area with a metal mask of
0.16 cm2. The measurement of incident photon-to-current
conversion efficiency (IPCE) was plotted as a function of
excitation wavelength by using the incident light from a
300 W xenon lamp (ILC Technology, USA), which was
focused through a Gemini-180 double monochromator
(Jobin Yvon Ltd., U.K.).
Preparationofb-triarylalkynyl-substitutedcarboxy-
phthalocyanine (TT65) (mixture of regioisomers).
Phthalocyanine 9 (0.071 g, 0.038 mmol) was dissolved
in dry THF (7 mL). An aqueous solution of sulfamic
acid (0.15 mmol in 1 mL of miliQ water) was added.
The reaction was cooled down to 0°C and an aqueous
solution of NaClO2 (0.095 mmol in 0.5 mL of miliQ
water) was added dropwise. The reaction was stirred at
0°C for half an hour, and then at room temperature for
two and a half hours. Then, it was poured over HCl 1 M
(50 mL). The solution was extracted with ethyl acetate
(3 × 25 mL), the organic phases washed with brine and
dried over anhydrous MgSO4. After filtration, the solvent
was removed under reduced pressure. The solid was
purified by gel permeation chromatography (eluent: THF).
A dark green solid was obtained. Yield 0.064 g (90%),
CONCLUSION
We have prepared a new family of carboxy-phthalo-
cyanines for DSSCs showing a strong absorption at ca.
700 nm by linking rigid and p-conjugated peripheral aryl
substituents to the macrocycle through alkynyl spacers.
Aggregation phenomena may explain the moderate overall
efficiencies achieved with these devices, as in previously
reported Pc-sensitized solars cells incorporating three
peripheral bisthiophene substituents [4]. We are currently
exploring new molecular designs wherein aggregation
through the peripheral substituents is suppressed.
1
mp > 250°C. H NMR (500 MHz, THF-d8): d, ppm
10.18–9.83 (m, 1H), 9.16–8.59 (br m, 8H), 8.04–7.28 (br
m, 64H), 2.58–2.48 (br m, 9H). UV-vis (THF): lmax, nm
(log e) 696 (4.35), 625 (3.55), 346 (3.85), 284 (4.20). IR
(KBr): n, cm-1 3634, 3423, 3058, 3028, 2957, 2919, 2851,
2205, 1721, 1690, 1669, 1644, 1600, 1485, 1460, 1434,
1391, 1363, 1338, 1308, 1246, 1234, 1142, 1092, 1047,
1008, 935, 881, 838, 771, 757, 744, 698, 577. HR-MS
(MALDI-TOF, DCTB+PEGNa 2000): m/z 1874.5849
[M]+, calcd. for C132H82N8O2Zn: 1874.5847.
Acknowledgements
The authors thank Prof. M. Graetzel for allowing us
to use his facilities. Financial support from the European
Union (FP7-ENERGY-2012-1 framework, GLOBASOL
project, Proposal No. 309194-2), from the Spanish
MINECO (CTQ2014-52869-P), Comunidad de Madrid
(FOTOCARBON S2013/MIT-2841), and MECD (FPU
fellowship to LT) is gratefully acknowledged. LT and
MVMD acknowlege Prof Torres on the occasion of this
65th anniversary introducing us in the fascinating topic
of Phthalocyanines for Photovoltaic Applications.
Dye-sensitized solar cells
The TiO2 film composed of ca. 8 mm (transparent
layer) and ca. 4 mm (scattering layer) was prepared
by screen-printing and treated with a 0.04 M titanium
tetrachloride solution for 30 min at 70°C. The film
was heated to 500°C in air for 30 min before use. Dye
solutions were prepared in a concentration of 0.05 mM
in a 4/1 (v/v) mixture of ethanol and THF containing
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 6–7

INTRODUCING RIGID p-CONJUGATED PERIPHERAL SUBSTITUENTS IN PHTHALOCYANINES FOR DSSCs
7
Supporting information
de la Torre G, Grätzel M, Nazeeruddin MK and
Torres T. ChemPhysChem 2014; 15: 1033–1036.
3. Mori S, Nagata M, Nakahata Y, Yasuta K, Goto R,
Kimura M and Taya M. J. Am. Chem. Soc. 2010;
132: 4054–4055.
Figures S1–S8 are given in the supplementary material.
This material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
4. Ince M, Cardinali F, Yum JH, Martínez-Díaz MV,
Nazeeruddin MK, Grätzel M and Torres T. Chem.
Eur. J. 2012; 18: 6343–6348.
5. Shah S, Burdette SC, Swavey S, Urbach FL and
Protasiewicz JD. Organometallics 1997; 16:
3395–3400.
6. Tejerina L, Martínez-Díaz MV and Torres T. Org.
Lett. 2015; 17: 552–555.
7. Cardona CM, Li W, Kaifer AE, Stockdale D and
Bazan GC. Adv. Mater. 2011; 23: 2367–2371.
8. Tejerina L, Martínez-Díaz MV, Nazeeruddin MK
and Torres T. Chem. Eur. J. 2016; 22: 4369–4373.
REFERENCES
1. (a) Ragoussi ME, Ince M and Torres T. Eur. J.
Org. Chem. 2013; 6475–6489. (b) Singh VK,
Kanaparthi RK and Giribabu L. RSC Adv. 2014; 4:
6970–6984. (c) Martín-Gomis L, Fernández-Lázaro
F and Sastre-Santos A. J. Mater. Chem. A 2014; 2:
15672–15682.
2. (a) Ragoussi ME, Cid JJ, Yum JH, de la Torre G, Di
Censo D, Grätzel M, Nazeeruddin MK and Torres
T. Angew. Chem. Int. Ed. 2012; 51: 4375–4378.
(b) Ragoussi ME, Yum JH, Chandiran AK, Ince M,
Copyright © 2016 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2016; 20: 7–7