Synthesis, characterization, oxygen electrocatalysis and OFET properties of novel mono- and ball-type metallophthalocyanines

Article abstract of DOI:10.1039/c3dt51955d

Novel mono- and ball-type Co(ii), Zn(ii) and Cu(ii) metallophthalocyanines (MPcs) were synthesized from 1,1′-p-anisylidenbis(2- naphthoxyphthalonitrile). The MPcs have been characterized by elemental analysis, UV/Vis, IR and ¹H-NMR spectroscopy and MALDI-TOF mass spectrometry. The performances of organic field effect transistors (OFETs) of the dinuclear ball-type MPcs have been compared to those of mononuclear counterparts. The ball-type MPc based OFETs showed a p-channel and typical ambipolar transport properties. On the other hand, it was not possible to measure the full transfer characteristics of the mononuclear MPc based devices. The best results were obtained in the case of dinuclear Cu₂Pc ₂. In this case, the mobility value is μ = 4.4 × 10 ^-2 cm² V^-1 s^-1 and the threshold voltage is 27.6 volts. The reduction and oxidation characteristics of the mono-nuclear and ball-type MPcs have been compared by cyclic voltammetry, square wave voltammetry and controlled potential coulometry on platinum in nonaqueous media. The comparison suggested that the ball-type complexes form ring-based and/or metal-based mixed-valence species as a result of the remarkable interaction between the two Pc rings and/or metal centers. The stability of these species was confirmed by the mixed-valence splitting values for the complexes. The electrocatalytic performances of the mononuclear and dinuclear complexes for the oxygen reduction reaction were also studied. The compounds involving Co(ii) at the phthalocyanine core, especially the ball-type one, showed much higher catalytic performances towards oxygen reduction than those of the other ones.

Full text of DOI:10.1039/c3dt51955d

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Synthesis, characterization, oxygen
electrocatalysis and OFET properties of novel
mono- and ball-type metallophthalocyanines†
Cite this: Dalton Trans., 2014, 43,
5858
Ali Sadi Başak,a Ali Rıza Özkaya,*a Ahmet Altındal,*b Bekir Salih,c
Abdurrahman Şengüld and Özer Bekaroğlu*e
Novel mono- and ball-type Co(II), Zn(II) and Cu(II) metallophthalocyanines (MPcs) were synthesized from
1,1’-p-anisylidenbis(2-naphthoxyphthalonitrile). The MPcs have been characterized by elemental analysis,
1
UV/Vis, IR and H-NMR spectroscopy and MALDI-TOF mass spectrometry. The performances of organic
field effect transistors (OFETs) of the dinuclear ball-type MPcs have been compared to those of mono-
nuclear counterparts. The ball-type MPc based OFETs showed a p-channel and typical ambipolar trans-
port properties. On the other hand, it was not possible to measure the full transfer characteristics of the
mononuclear MPc based devices. The best results were obtained in the case of dinuclear Cu2Pc2. In this
case, the mobility value is μ = 4.4 × 10−2 cm2 V−1 s−1 and the threshold voltage is 27.6 volts. The reduction
and oxidation characteristics of the mono-nuclear and ball-type MPcs have been compared by cyclic
voltammetry, square wave voltammetry and controlled potential coulometry on platinum in nonaqueous
media. The comparison suggested that the ball-type complexes form ring-based and/or metal-based
mixed-valence species as a result of the remarkable interaction between the two Pc rings and/or metal
centers. The stability of these species was confirmed by the mixed-valence splitting values for the
complexes. The electrocatalytic performances of the mononuclear and dinuclear complexes for the
oxygen reduction reaction were also studied. The compounds involving Co(II) at the phthalocyanine core,
especially the ball-type one, showed much higher catalytic performances towards oxygen reduction than
those of the other ones.
Received 3rd October 2013,
Accepted 30th January 2014
DOI: 10.1039/c3dt51955d
www.rsc.org/dalton
coworkers.4 This new type of Pcs has four bridged substituents
on the peripheral positions of each benzene ring of the two Pc
1. Introduction
Different types of phthalocyanine (Pc) dimers have been inten- monomers which are arranged cofacially.5 Recent studies
sively studied in recent years, for example, clamshell dimers,1 suggested that these compounds exhibit very interesting gas
cofacial sandwich type lanthanide complexes2 and double- sensing,6 electrical,7 nonlinear, optical8 and electrochemical9
decker lanthanide(III) complexes.3 Also the synthesis of a new properties depending on the wide range of interactions
class of Pc dimers, dinuclear ball-type metallophthalocyanines between the face to face Pc rings and/or the two metal centers.
(MPcs), was reported for the first time by Zefirov and Thus, dinuclear ball-type MPcs have attracted increasing tech-
nological interest in various fields. For instance, ball-type
cobalt Pcs displayed high catalytic activity toward dioxygen
reduction which has vital importance in fuel cell appli-
cations.10,11 Since bridging units with bulky substituents at the
periphery may lead to changes in ball-type Pc characteristics,
our studies to synthesize new examples of this type of com-
pounds are still continuing and will be presented in forth-
coming reports.
The large conjugated π-system, excellent photoelectric
characteristics, intriguing and unique optical properties, high
thermal and chemical stability, molecular tolerability via
chemical modification and compatibility with the flexible sub-
strates of Pcs render them ideal organic semiconductor
materials as active layers for organic field effect transistors
aDepartment of Chemistry, Marmara University, 34722 Göztepe-Istanbul, Turkey.
E-mail: asbasak@marmara.edu.tr, aliozkaya@marmara.edu.tr;
Fax: +90 216 3478783; Tel: +90 216 3479641
bDepartment of Physics, Yildiz Technical University, Davutpaşa Caddesi, 34220,
Esenler, Istanbul, Turkey. E-mail: altindal@yildiz.edu.tr; Fax: +90 212 383 42 34;
Tel: +90 212 383 42 31
cDepartment of Chemistry, Hacettepe University, 06800, Beytepe, Ankara, Turkey.
E-mail: bekir@hacettepe.edu.tr; Fax: +90 312 288 2163; Tel: +90 312 297 7975
dDepartment of Chemistry, Bulent Ecevit University, 34469 Zonguldak, Turkey.
E-mail: sengul@karaelmas.edu.tr; Fax: +90 372 257 41 81; Tel: +90 372 257 20 70
eDepartment of Chemistry, Technical University of Istanbul, 34469 Maslak-Istanbul,
Turkey. E-mail: obek@itu.edu.tr; Fax: +90 216 3860824; Tel: +90 216 3479641
†Electronic supplementary information (ESI) available. See DOI:
10.1039/c3dt51955d
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(OFETs). Examples of reported Pc-based OFETs have good carried out with a combination of methods including elemen-
field-effect properties with field-effect mobilities ranging from tal analyses, FT-IR, 1H-NMR and UV/Vis spectroscopy, and
9 × 10−6 cm2 V−1 s−1 to 10 cm2 V−1 s−1 12,13
,
the values depend- MALDI-TOF mass spectrometry.
ing upon the central metal atom, gate dielectric and the depo- Elemental analysis, FT-IR, MALDI-TOF mass and UV/Vis
sition techniques and parameters. It is well known that to be spectra confirmed the proposed structures of the compounds.
used as an active layer in OFET, the Pc materials are always FT-IR spectra indicated the formation of 4, 5 and 6 clearly with
prepared in thin film form. However, Pc compounds that carry the appearance of a sharp band at 2230 cm−1 (–CuN),
no substituent on the ring system are essentially insoluble in and additional bands at 1240–1245 cm−1 (Ar–O–Ar),
organic solvents and are therefore not amenable to solution 1590–1670 cm−1 (–CvC–), 1715–1730 cm−1 (CvN) and
processing for deposition as thin films.
3050–3060 cm−1 (aromatic CH). The main indicator of the for-
As compared to their parent monomers, ball-type Pcs mation of M2Pc2 complexes 7, 8 and 9 was the disappearance
display different and interesting electrochemical properties of the sharp intense –CN stretching band at 2230 cm−1 in the
due to the wide range of interactions between the face-to-face IR spectra. The IR-spectra of the CoPc 4, the ZnPc 5 and the
Pc rings and/or two metal centres. The high catalytic activity of CoPc 6 were very similar, as also IR-spectra of homo-dinuclear
the ball-type cobalt Pcs toward dioxygen reduction has vital ball-type Pcs 7, 8 and 9.
importance in fuel cell applications.14 It is known that electron
The UV-Vis spectra of 4, 5 and 6 in DMSO (2 × 10−5 M)
cloud overlap is important for strong interactions, mainly (Fig. 2) showed characteristic absorptions between 600 and
depending on the nature of the metal centres, bridging links 700 nm in the Q-band region. The Q-band observed for the
and the presence or absence of axial ligands. The intermole- compounds was attributed to the π→π* transition from the
cular and/or intramolecular interactions between the Pc rings highest occupied molecular orbital (HOMO) to the lowest
and/or metal centers in dinuclear MPcs may be detected by unoccupied molecular orbital (LUMO) of the Pc ring. The
spectroscopic and electrochemical measurements.10,11–15
observed B bands within the range of 280–360 nm were due to
In the present work, starting from a bulky electron donor the transitions from the deeper π levels to the LUMO. The
1,1′-p-anisylidenbis(2-naphthol) 1, mono- and ball-type dinuc- comparison of UV-Vis spectra of mononuclear Pc compounds
lear Co(II), Zn(II), Cu(II) Pcs have been reported. The charge 4, 5, 6 with those of dinuclear ball-type ones 7, 8, 9 in DMSO
transport characteristics of Pc films have been investigated by (2 × 10−5 M) (Fig. 2) implies that both groups of compounds
preparing OFETs in which the active semiconductor layers display H-type aggregation, characterized by broadening of the
were the spin-coated films of 7–9. In addition, the redox and Q-band absorptions for 4, 5, 7, 8 and splitting of the Q-band
electrocatalytic properties of the novel mono-nuclear Pcs (4, 5 absorptions for 6 and 9. H-aggregation of mononuclear com-
and 6) and dinuclear ball-type Pcs (7, 8 and 9) have been inves- pounds 4, 5 and 6 resulted from intermolecular π–π stacking
tigated and compared.
interactions while the broadening or splitting of the Q-band
absorptions for 7, 8 and 9 is probably due to intramolecular
interactions between the two MPc units in these compounds.
This interpretation is compatible with the theoretically deter-
mined highly planar structure of the molecule of 8 and the
considerably small distance between the two MPc units in the
2. Results and discussion
2.1. Synthesis
Our key material 1,1′-p-anisylidenbis(2-naphthoxyphthalo- molecule (Fig. 1). The fully optimized minimum energy struc-
nitrile) 3 was synthesized by the reaction of 1 and 2, in dry di- ture in Fig. 1 was refined by performing an optimized geome-
methylformamide (DMF) in the presence of K2CO3, with a try calculation in MOPAC using PM3 parameters.16 This
yield 92%. The novel cobalt 4, zinc 5 and copper 6 Pcs were structure reflects very small geometrical constraints due to
prepared by the cyclotetramerization reaction of compound 3 connectivity of the bulky substituents at the peripheral posi-
with Co(OAc)2·4H2O, Zn(OAc)2·2H2O and Cu(OAc)2·4H2O tions in comparison with that of a previously reported dinuc-
respectively in anhydrous DMF at 180 °C under a nitrogen lear ball-type M2Pc2 model compound.15e In order to compare
atmosphere (Scheme 1). The conversion of 4, 5 and 6 Pcs to the bond distances and angles in the optimized structure, a
the ball-type dinuclear Co2Pc2 (7), Zn2Pc2 (8) and Cu2Pc2 (9) 3D structure visualization software, Mercury 3.1, was also
complexes was accomplished in anhydrous DMF and in the used.17 In the present case, the distance between the two
presence of excessive amounts of appropriate metal salts at metal centers is 5.884 Å, comparatively shorter than that of
180 °C (Scheme 1). The yields were moderate and depended 11.06 Å determined previously for the analogous molecule by
upon the metal ion.
the same method.15e The closest contact between the two rings
Our novel MPcs are soluble in various solvents such as is about 5.14 Å. These values reflect high planarity of the ring
tetrahydrofuran (THF), acetone, dichloromethane (DCM), systems in the molecule. Furthermore, the N–Zn–N angles are
methanol, dimethylsulfoxide (DMSO), chloroform (CHCl3) and also very close to 90°, which provides strong support for high
DMF. The intense solubility of these new MPcs in most of the planarity of the molecule. (ESI, Fig. S1†). The bulky naphthyl
organic solvents is probably due to methoxy (–OCH3) groups substituents are inclined at 66.69°, whereas the angle between
on the para-position of the benzene ring of the bulky starting these rings and the methoxyphenyl ring is about 75.81°. The
compound. Characterization of the new Pc complexes was bending of peripheral substituents causes the molecule to be
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Scheme 1 (i) K2CO3, DMF, 80 °C; (ii) 4, Co(OAc)2·4H2O, 180 °C, 12 h; 5, Zn(OAc)2·2H2O, 180 °C, 12 h; 6, Co(OAc)2·4H2O, 180 °C, 12 h; (iii) 7,
Co(OAc)2·4H2O, 180 °C, 12 h; 8, Zn(OAc)2·2H2O, 180 °C, 12 h; 9, Co(OAc)2·4H2O, 180 °C, 12 h.
puckered as reflected by the
Niso–Zn–Niso angles of
171.2–172.2°. It is expected that the bending of peripheral sub-
stituents hinders strong intermolecular interactions between
M2Pc2-type molecules. Thus, the foregoing attribution of the
broadening or splitting of the Q-bands of dinuclear ball-type
compounds to intramolecular interactions rather than inter-
molecular interactions is consistent with the bended peri-
pheral substituents in the optimized structure.
In the 1H-NMR spectra of 3 in CHCl3, the phenyl protons
bearing nitrile groups appeared at 7.26 ppm (s), 7.01 ppm (d),
6.81 ppm (d) and the phenyl protons with methoxy groups at
6.62 ppm (br s), 6.53 ppm (br s), naphthalene protons at
7.85 ppm (d), 7.80 ppm (d), 7.66 ppm (d), 7.50 ppm (t) and
7.44 ppm (t), 6.50 ppm (d), aliphatic proton at 6.91 ppm (s),
and a characteristic signal for –OCH3 protons at 3.59 ppm
(ESI, Fig. S2–S4†). In the 1H NMR spectra of 8, the aromatic
protons appeared at 8.95–6.11 ppm (m), Ar–OCH3 peaks at
3.65–2.60 ppm and Ar–CH peaks at 2.89–2.77 ppm (ESI,
Fig. 1 The space-filling presentation of the molecular structure of the
ball-type homo-dinuclear zinc phthalocyanine (8). The structure was
refined by performing an optimized geometry calculation in MOPAC
using PM3 parameters.16
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active layer (semiconductor) through an insulating layer, and
the source and drain electrodes are connected with the semi-
conductor. For a given drain–source voltage, VDS, the current
flowing through the organic semiconductor shows a strong
correlation with the applied gate–source voltage, VGS. In order
to estimate the field effect mobility in 4–9 based OFETs, the
drain–source current (IDS) was measured as a function of the
VDS by varying the applied VGS. It was observed that it was not
possible to measure the full transfer characteristics of 4–6
based devices. Within the experimental range of VDS, a rather
good linear relation was observed in 4–6 based devices includ-
ing with a zero VGS voltage. Therefore, we focused on 7–9
based OFETs.
Information concerning the performance of an organic
field-effect transistor is provided by the most important para-
meters of these devices, namely the charge carrier mobility
and the threshold voltage. Their value can be determined from
the two typical characteristics obtained when characterizing
these devices electrically, i.e. the output and transfer character-
istics. To compare the effect of the active layer on the perform-
Fig. 2 UV/Vis spectra of mono (A) and ball-type (B) Pcs in DMSO.
ance of an OFET device, a typical set of the output (IDS − VDS
)
characteristics of the produced OFETs based on 7–9 for fixed
gate voltage (VGS = −50 V) applied to the ITO electrode is
shown in Fig. 3. The characteristics of the 7–9 based device
exhibit an ideal IDS − VDS relationship in which the curves can
be divided into two regions: a linear region and a saturated
region. The curves match the behaviour of the traditional Pc
based field-effect-transistor. On the application of a negative
bias to the gate electrode, a typical hole accumulation (p-type)
behaviour was observed for all devices. The maximum drain–
source currents, IDS = 0.64 μA, at gate–source bias VGS = −50 V
was observed for sample 9, while the maximum drain–source
currents for sample 7 and for sample 8 were 0.41 μA and
0.53 μA for the same gate–source bias (VGS = −50 V), respecti-
vely. A close investigation of these characteristics also shows
that at low drain–source voltages VDS, the current IDS follows
Ohm’s law, and is proportional to VDS. As VDS approaches the
gate voltage VG, the drain–gate voltage approaches zero. This
results in the so-called pinch-off of the channel. Therefore it
Fig. S5†). MALDI-TOF mass spectra of the starting compound
3 and all MPcs 4–9 are shown in ESI (Fig. S6–S12†). For 4, the
mass spectrum was obtained in high resolution mode showing
only protonated molecular ions and also one and two water
adducts to the protonated molecular ion. Although a proto-
nated molecular ion peak was not observed in the case of 7, it
was observed for the other complexes. Furthermore, the peaks
characterizing matrix clusters and some fragmentations at
different masses within the range of 670–780 Da were observed
for all Pc complexes 4–9. These signals were found to have
almost similar intensities, and the masses of the fragment
ions were found to be identical. Additional water adduct peaks
up to three were also observed for 8. For compound 7, the
signals for the species of only sodiated at high intensity and
potassiated and also water adduct were observed dominantly in
the MALDI-TOF mass spectrum. This is because of the low pro-
ton affinity of the complex. When isotopic mass distributions of
the experimental and theoretical four sodium adducts of the
complex peaks were compared, it was noticed that the peaks
overlapped each other perfectly. Also monoisotopic peak masses
for the experimental and the theoretical values were found to be
very close to each other. The comparison of the experimental
and theoretical isotopic mass distributions of the protonated
ions of 8 and 9 suggested that the peaks overlapped each other
perfectly as 7. This showed the mass accuracy between the
theoretical and experimental monoisotopic masses. In the mass
range between 500 and 3500 Da, no signal representing impurity
was observed during MALDI-TOF mass spectrometry measure-
ments of the complexes.
2.2. Characteristics of OFETs
It is well known that an OFET is a three-terminal device in
Fig. 3 OFET characteristics of the films of 7–9 measured under
which the gate electrode is electrically insulated from the ambient conditions.
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can be said that the observed saturation in IDS is due to pinch-
off of the channel.
The gate–source voltage dependence of the output charac-
teristics of the produced OFETs was also investigated. In
Fig. 4, the drain–source current IDS is plotted as a function of
the drain–source voltage VDS by varying the applied gate–
source voltage VGS for the 9 based OFET device. It is clear that
the drain–source current IDS increases with increasing the
gate–source voltage VGS negatively and the IDS current is also
effectively modulated by gate–source voltage. This shows that
the 9 based OFET typically works in a p-channel operational
mode. The same types of output characteristics were observed
for 7 and 8 based devices. The observed p-type channel oper-
ation indicates that an injection of holes from the metal elec-
trode into the organic material takes place and there is a close
match between the Fermi level (EF) of the metal electrode
(source and drain electrode) and the HOMO energy level of the
ball-type Pcs.
Fig. 5 Transfer characteristics of 9 based OFET.
The most important parameter of the OFET is the field- and summarized in Table 1. As can be seen from Table 1, the
effect mobility which indicates how easily the charge carriers mobility value of the 9 based OFET transistor is higher than
can drift under the influence of the electric field. The relation that of the mobilities of 7 and 8. It was also observed that the
between the IDS and the VGS in the saturation regions is given obtained mobility value of the studied Pc based OFET transis-
by eqn (1).18
tor is higher than that of the mobilities of CuPc based FET
with the mobility of 2.2 × 10−4 cm2 V−1 s−1 using PVA as a gate
insulator19 and CuPc organic thin film transistors (OTFTs)
with the mobility of 0.2 × 10−4 cm2 V−1 s−1 using a polymethyl
methacrylate (PMMA) dielectric layer.20 It seems that both the
molecular shape and the central metal atom are important for
OFET performance. It is well established that good match of
energy level between the organic semiconductor and electrode
for charge-carrier injection, large π-orbit overlap and short
intermolecular distance are necessary for semiconductor
materials in order to achieve high-performance OTFTs. It is
also shown that the molecular orientation of the Pc molecules
in the solid state is of great interest because it is thought to
strongly affect the carrier mobility in electronic devices.21
Therefore it is not easy to decide which mechanism is respon-
sible for the observed higher mobility value in the case of 9.
On the other hand the performance of OFETs is closely related
to the packing mode of organic molecules in thin solid films.
Several reports elucidated that π–π stacking is a favored
packing mode for OFET applications.22 The π–π stacking
affords strong interactions between neighbouring molecules.
Though the relationship between the mobility and film struc-
ture is not yet fully understood, we believe that the contri-
bution from Pc ring stacking to the observed high mobility in
the case of 9 might be significant.
W
2L
2
IDS
¼
CiμFðVGS ꢀ VtÞ
ð1Þ
where μF is the field-effect mobility, W and L are the channel
width and length, respectively, Ci is the insulator capacitance
per unit area, and Vt is the threshold voltage. The mobility of
the transistors can be obtained in different ways. In this work,
the values of the mobility for all devices were extracted from a
plot of the square root of the drain–source current versus VGS
by fitting data to eqn (1).
Fig. 5 shows the typical transfer characteristics (√IDS vs. VGS
and IDS vs. VGS) of 9 OFET with PVA gate insulators at a fixed
VDS of −50 V. With the aid of eqn (1), from the slope of the
linear portion of Fig. 5 the μF and Vt values were determined
Table 1 Summary of the electrical characteristics of the OFETs
Complex
μF (cm2 V−1 s−1
)
Vt (V)
7
8
9
5.2 × 10−3
6.7 × 10–3
4.4 × 10−2
−2.5
−4.0
−27.6
Fig. 4 Output characteristics (IDS-VDS) of 9 based FET prepared on
200 nm thick PVA.
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Table 2 The electrochemical dataa for 4–9 in TBAP/DMSO
Complex
Redox processes
E1/2 (V)
ΔEp (V)
ΔE1/2 (V)
ΔEs (V)
4
[Co(III)Pc(-2)]+/Co(II)Pc(-2)
(O1)
(R1)
(R2)
(O1)
(R1)
(R2)
(R3)
(R4)
(O1)
(R1)
(R2)
(R3)
(R4)
(O1)
(R1)
(R2)
(R3)
(R4)
(O1)
(R1)
(R2)
(R3)
(R4)
(O1)
(R1)
(R2)
(R3)
(R4)
0.40
−0.33
−1.37
0.61
−0.87
−1.20
−1.56
−1.65
0.71
−0.80
−1.10
−1.50
−1.70
0.38
−0.40
−0.64
−1.01
−1.41
0.70
−0.50
−0.85
−1.11
−1.50
0.65
−0.48
−0.80
−1.04
−1.45
0.08
0.10
0.06
0.73
Co(II)Pc(-2)/[Co(I)Pc(-2)]−
[Co(I)Pc(-2)]−/[Co(I)Pc(-3)]2−
[Zn(II)Pc(-1)]+/Zn(II)Pc(-2)
5
6
7
8
9
0.080
0.060
0.060
rev
0.080
0.060
0.080
0.080
Rev
0.080
0.080
0.080
0.080
0.120
0.06
1.48
1.51
0.78
1.20
1.13
Zn(II)Pc(-2)/[Zn(II)Pc(-3)]−
[Zn(II)Pc(-3)]− /[Zn(II)Pc(-4)]2−
[Zn(II)Pc(-4)]2−/[Zn(II)Pc(-5)]3−
Reduction of nitrile substituents
[Cu(II)Pc(-1)]+/Cu(II)Pc(-2)
Cu(II)Pc(-2)/[Cu(II)Pc(-3)]−
[Cu(II)Pc(-3)]−/[Cu(II)Pc(-4)]2−
[Cu(II)Pc(-4)]2−/[Cu(II)Pc(-5)]3−
Reduction of nitrile substituents
[Co(II)Pc(-2)·Co(II)Pc(-1)]+/[Co(II)Pc(-2)]2
[Co(II)Pc(-2)]2/[Co(II)Pc(-2)·Co(I)Pc(-2)]−
0.24
0.40
[Co(II)Pc(-2)·Co(I)Pc(-2)]− /[Co(I)Pc(-2)]2
[Co(I)Pc(-2)]22−/[Co(I)Pc(-2)·Co(I)Pc(-3)]3−
2−
[Co(I)Pc(-2)·Co(I)Pc(-3)]3−/[Co(I)Pc(-3)]2
4−
[Zn(II)Pc(-1)]22+/[Zn(II)Pc(-2)]2
0.060
2−
b
[Zn(II)Pc(-2)]2/[Zn(II)Pc(-3)]2
—
0.35
0.39
4−
b
[Zn(II)Pc(-3)]22−/[Zn(II)Pc(-4)]2
—
6−
b
[Zn(II)Pc(-4)]24− /[Zn(II)Pc(-5)]2
—
8−
b
[Zn(II)Pc(-5)]26−/[Zn(II)Pc(-6)]2
—
[Cu(II)Pc(-1)]22+/[Cu(II)Pc(-2)]2
0.060
2−
b
[Cu(II)Pc(-2)]2/[Cu(II)Pc(-3)]2
—
0.32
0.41
[Cu(II)Pc(-3)]22−/[Cu(II)Pc(-4)]26−
—
4−
b
b
[Cu(II)Pc(-4)]24−/[Cu(II)Pc(-5)]28−
[Cu(II)Pc(-5)]26−/[Cu(II)Pc(-6)]2
—
b
—
a Potentials are reported with respect to the SCE. E1/2 values were measured by cyclic voltammetry [E1/2 = (Epa + Epc)/2] and/or differential pulse
voltammetry. The peak separation values (ΔEp = Epa − Epc) are reported at 0.050 V s−1. ΔE1/2 is the potential difference between the first oxidation
and first reduction potentials. It represents the HOMO–LUMO gap for 5, 6, 8 and 9, but the charge transfer transition for 4 and 7 involving redox-
active metal centers. ΔEs indicates mixed-valence splitting energy for the relevant split redox couple. b The peak separation values could not be
monitored due to ill-defined cyclic voltammetry signals, but square wave voltammograms indicated the reversible or quasi-reversible nature of
these redox processes.
2.3. Electrochemistry
The cyclic voltammetry, square wave voltammetry and con-
trolled-potential coulometry (CPC) measurements of 4–9 were
carried out on platinum in DMSO using tetrabutylammonium
perchlorate as a supporting electrolyte. The relevant data are
presented in Table 2. It was concluded from the CPC measure-
ments and well-known electrochemical behaviour of mono-
nuclear phthalocyanine complexes23 that compounds 4–6 gave
ring and/or central metal-based stepwise one-electron
reduction processes (except the last reduction process for 5
and 6) and a one-electron oxidation processes. The anodic to
cathodic peak separations of these redox processes were within
the range of 0.060–0.100 V which showed the reversible or
quasi-reversible nature of these electron transfer processes.24
Fig. 6 Cyclic and square wave voltammograms of 5 on Pt in TBAP/
DMSO.
For both 5 and 6, the difference between the half-peak poten-
tials (E1/2) of the first oxidation and the first reduction pro-
cesses (ΔE1/2) is about 1.50 V, which is closely related to the
energy difference between the highest occupied molecular couple are much higher than those of the other reduction
orbital (HOMO) and the lowest unoccupied molecular orbital couples, probably due to the fact that the last reduction
(LUMO).25 Fig. 6 shows cyclic and square wave voltammograms couples for 5 and 6 result from the reduction of nitrile substi-
of 5 in TBAP/DMSO as an example. Approximate ΔE1/2 values tuents which are redox-active in this type of mononuclear
of 5 and 6 strongly suggest that the redox processes of these phthalocyanine compounds.26 On the other hand, both the
complexes are phthalocyanine ring-based.23 However, it first reduction and the first oxidation of 4 occur more easily
should be noted that the peak currents for the last reduction than those of 5 and 6, and thus the ΔE1/2 value of this complex
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is 0.73 V (Table 2 and Fig. 7). This redox behaviour suggests
that the first reduction and the first oxidation processes of 4
are metal-based.
Compound 8 displayed four reductions and a single oxi-
dation within the potential limits of DMSO/TBAP medium
(Table 2). The CPC studies showed that each redox process
involves the transfer of one electron. Typical voltammograms
for 8 are shown in Fig. 8. The transfer of one electron in each
step, instead of two, indicates that the redox process of each
ZnPc unit in 8 occurs at different potentials as a result of the
interactions between the two ZnPc units and thus the splitting
of the molecular orbitals. The strong interaction between the
molecular orbitals of two ZnPc units in 8 causes remarkable
changes in redox potentials, compared with the corresponding
mononuclear phthalocyanine 5. It appears that the first
reduction process of 8 shifts to less negative potentials and
thus, the ΔE1/2 value becomes smaller in comparison with 5.
All redox processes of 8 are Pc ring-based since ZnII is redox-
inactive in MPcs.23 Similarly, the redox processes of mono-
nuclear complexes 4 and 6 are split into two waves in 7 and 9,
due to the interactions between the two MPc units (Table 2).
Fig. 9 shows cyclic and square wave voltammograms of 7 in
TBAP/DMSO as examples. The mixed-valence splitting, ΔEs,
Fig. 9 Cyclic and square wave voltammograms of 7 at 0.050 V s−1 scan
rate on Pt in TBAP/DMSO.
values in V for the redox processes of 7–9 are presented in
Table 2. These values give evidence of the delocalization of
charge among the cofacial MPc units, and thus the formation
of electrochemically stable oxidized and reduced mixed-
valence species.
In recent years, it was shown by our group that ball-type
dinuclear metal phthalocyanines with various bridging units
such as cyclopentyldisilanoxy-polyhedral oligomeric silses-
quioxanes,10 perfluorodecyl,15a pentaerythritol,11 1,1′-methylene-
dinaphthalen-2-ol15b and dithioerythritol15c show high
catalytic activity towards oxygen reduction reaction (ORR),
which is important for fuel cell applications. These bridging
units link two metal phthalocyanine units cofacially at two
sides with four arms. The relevant previous studies showed
that the length of the bridging units, the main factor deter-
mining the suitable distance between the two metal centers
for high catalytic activity, has vital importance. Thus, the elec-
trocatalytic performance of each Pc complex towards ORR was
tested in O2-saturated 0.5 M H2SO4 aqueous electrolyte solu-
tion (Fig. 10A). These measurements were performed by RRDE
voltammetry with a glassy carbon disk electrode and a plati-
num ring electrode, and the glassy carbon electrode was modi-
fied by a mixture of the relevant Pc complex with carbon
powder, Vulcan XC-72 (VC) and Nafion (Nf). The onset poten-
tial (Eo) where the current begins to increase, the limiting
diffusion disk current density (JL) and the half-wave potential
(E1/2) for ORR were taken as the measure of catalytic perform-
ance. The disk potential at which the current density reaches
0.100 mA cm−2 was taken as Eo. The electrocatalytic perform-
ances of the Pc-based catalysts are summarized in Table 3. The
7 (Co2Pc2)-based catalyst displayed the best catalytic activity
with the most positive onset potential (0.44 V vs. SCE), the
highest JL value (3.10 mA cm−2 at 2500 rpm) and the most
positive E1/2 value for ORR (0.06 V vs. SCE) (Table 3 and
Fig. 10A). Complex 7 displays two reduction waves. The first
wave probably produces water as the main product and some
hydrogen peroxide as the side product. The second wave,
appearing at considerably negative potentials presumably cor-
responds to the reduction of hydrogen peroxide to water. The
Fig. 7 Cyclic and square wave voltammograms of 4 at 0.050 V s−1 scan
rate on Pt in TBAP/DMSO.
Fig. 8 Cyclic and square wave voltammograms of 8 on Pt in TBAP/
DMSO.
5864 | Dalton Trans., 2014, 43, 5858–5870
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Fig. 10 (A) RRDE polarization curves for the electrocatalytic ORR at 0.005 V s−1 on VC/Nf/metallophthalocyanine modified rotating (2500 rpm)
glassy carbon disk electrodes in O2-saturated 0.5 M H2SO4, (B) the number of total electrons exchanged, (C) %H2O and (D) %H2O2 produced in ORR
as a function of disk potential (Ering = 0.95 V vs. SCE) for VC/Nf/metallophthalocyanine modified electrodes.
absolute ring current decreases simultaneously while the disk
Table 3 Electrocatalytic performances of 4–9 for ORR, and the com-
current increases during the appearance of the second wave
(Fig. 10A), which confirms that hydrogen peroxide produced at
the first step as the side product is further reduced to water
during the second wave. The 4(CoPc)-based catalyst also dis-
played much higher performance than those of the other
phthalocyanine-based catalysts (Table 3 and Fig. 10A). ORR
occurs at much more positive potentials at the VC/Nf/7 and
VC/Nf/4 modified GCEs than that at the other Pc-based electro-
des. In addition, the limit current densities for the VC/Nf/7
and VC/Nf/4 modified GCEs are much higher than those for
the other Pc-based electrodes. These findings clearly indicate
the higher catalytic activity of the formers relatively. Electro-
catalytic reduction of oxygen on metallophthalocyanines takes
place through a redox-catalysis type of process where oxygen
binding ability and the redox potential of the central metal
ions play a critical role.27 The metal ion in the center of the Pc
ring is oxidized by an oxygen molecule during its adsorption
and thus reduces it. Therefore, the distinctive catalytic per-
formance of 4- and 7-based catalysts can be attributed to the
redox-active behavior of the Co(II) metal center. It appears that,
in the case of a redox-active metal center, the interaction
between the metal center and the O2 molecule is enhanced.
The catalytic performance of the 7(Co2Pc2)-based catalyst is
better than that of the 4(CoPc)-based one (Table 3 and
Fig. 10A). The better catalytic activity of the 7(Co2Pc2)-based
catalyst, compared to the 4(CoPc)-based one, should also be
parison with previously reported dinuclear metal phthalocyani-
nes10,11,15a,c–f
Eo a for
ORR/V
JL b for
E1/2 for
ORR/V
Complex
CoPc
ORR/mA cm−2
Ref.
twc
4
0.23
2.78
0.40
—
−0.06
−0.29
—
—
0.06
−0.30
−0.30
−0.04
−0.34
−0.30
−0.07
0.35
−0.20
−0.15
−0.14
0.41
ZnPc
CuPc
Co2Pc2
5
6
7
−0.11
0.04
0.44
twc
twc
twc
—
3.10
0.73
2.45
0.50
1.95
1.06
2.54
2.63
0.92
4.66
3.30
4.27
2.17
4.50
4.84
Zn2Pc2
Cu2Pc2
8
9
0.07
0.03
twc
twc
d
Zn2Pc2 d
2
3
−0.15
0.06
0.45
15f
15f
15d
Co2Pc2 e
Co2Pc2
f
Co2Pc2 g
0.11
0.10
0.68
15e
15c
10
Co2Pc2 h
Co2Pc2
−0.19
−0.09
0.05
i
Co2Pc2
Co2Pc2
0.25
0.61
15a
11
j
a The potential at which the current density reaches 0.100 mA cm−2
was taken as the onset potential. b The limiting diffusion current
density at 2500 rpm. c This work. d Octa substituted phenoxy-bridged.
e Dicumarol
ylidene)bisphenyl
bridged.
f 4,4′-(Octahydro-4,7-methano-5H-inden-5-
bridged.
g Dithioerythritol-bridged.
h Cyclopentyldisilanoxy-polyhedral
oligomeric
silasesquioxanes
bridged. i Pentaerythritol-bridged. j Pentaerythritol-bridged with
heptadecafluorodecyl substituents.
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related to its ability to bind a dioxygen molecule through limiting diffusion current plateau, leading to the production
peroxo species, Co–O–O–Co, the promotion of the O–O bond of water as the main product. The detection of hydrogen per-
breakage and thus, the increase in the tendency of reduction oxide suggests that the first step of the series path, i.e., oxygen
directly to water via the four-electron path. It is known from reduction to hydrogen peroxide, is certainly operative.
the literature that even mononuclear metal Pcs with redox- However, a direct path, i.e., oxygen reduction to water via a
active metal centers have the ability to form peroxo species as four-electron process without the formation of hydrogen per-
a result of the interaction between the metal center and O2.28 oxide as an intermediate, is the main reaction to occur.
However, it appears that the presence of two redox-active face-
to-face metal centers in 7 further promotes the formation of
Co–O–O–Co species through the interaction of the two Co(II)
centers with the O2 molecule. In terms of onset and half-wave
potentials, and the limiting diffusion current densities for
3. Experimental
3.1. Materials
The starting material 2 was synthesized by methods described
ORR, the catalytic performance of 7 is comparable to that of
previously in the literature.29 Compounds 1, Zn(OAc)2·2H2O,
Co(OAc)2·4H2O and Cu(OAc)2·4H2O, were obtained from com-
mercial suppliers. All reactions were carried out under a nitro-
gen atmosphere. The Pc compounds were purified by column
chromatography and washed with acetic acid, water, and
ethanol. The purity of the products was tested in each step by
TLC (SiO2). Chromatography was performed on silica gel 60.
the recently reported dinuclear dicumarol-bridged15d cobalt
phthalocyanine and better than those of previously reported
dinuclear pentaerythritol-,15a dithioerythritol-,15c 4,4′-(octa-
hydro-4,7-methano-5H-inden-5-ylidene)bisphenyl-15e and octa
substituted phenoxy-bridged15f cobalt phthalocyanines while it
is lower than those of cyclopentyldisilanoxy-polyhedral oligo-
meric silsesquioxane-bridged dinuclear cobalt phthalo-
cyanine10 and dinuclear cobalt phthalocyanine including
pentaerythritol bridging units with heptadecafluorodecyl
substituents.11
3.2. Equipment
UV-vis spectra were recorded on a Shimadzu UV-1601 UV-vis
spectrometer. IR spectra were recorded on
a Shimadzu
ORR in acidic medium can be reduced to water via a four-
electron process or hydrogen peroxide through a two-electron
reduction. A complete reduction directly to water via a four-
electron transfer mechanism is desirable. However, it is poss-
ible in the case of low catalytic activity that oxygen gets
reduced to hydrogen peroxide via a two-electron process, but
the peroxide can still get reduced further via another two-elec-
tron process to form water. The number of electrons trans-
ferred, nt, and the amount of generated hydrogen peroxide and
thus water selectivity were determined by using the following
equations.
FTIR-8300 spectrophotometer as KBr pellets. Elemental ana-
lyses were performed by the Instrumental Analysis Laboratory
of Tubitak–Ankara. Nuclear magnetic resonance (NMR)
spectra were recorded on a Bruker Avance DPX-400 MHz
spectrometer. Mass spectra were acquired on a Voyager-DE™
PRO MALDI-TOF mass spectrometer (Applied Biosystems,
USA) equipped with a nitrogen UV-laser operating at 337 nm.
Spectra were recorded in reflectron mode with the average of
100 shots. In MALDI matrix, 2,5-dihydroxybenzoic acid was
prepared in a THF–H2O mixture in a 1 : 1, v/v, ratio at a con-
centration of 20 mg mL−1 and acidified with trifluoroacetic
acid (0.1%). MALDI samples were prepared by mixing sample
solutions (2 mg mL−1 in a THF–H2O mixture in a 1 : 1, v/v,
ratio containing 0.1% trifluoroacetic acid) with the matrix solu-
tion (1 : 10, v/v) in a 0.5 mL Eppendorf® micro tube. Finally
1.0 μL of this mixture was deposited on the sample plate, dried
at room temperature and then analyzed. MALDI-TOF mass
spectra of all synthesized Pc complexes were recorded in 2,5-
dihydroxybenzoic acid with a better intensity than the other
conventional MALDI matrices and the MALDI-TOF mass
spectra are given in ESI, Fig. S6–S12.†
nt ¼ 4ID ½ID þ ðIR=NÞꢁ
% H2O2 ¼ 100ð4 ꢀ ntÞ
ð2Þ
ð3Þ
Here, N, ID, and IR are the collection efficiency, VC/Nf/phthalo-
cyanine modified glassy carbon disk current and platinum
ring (polarized at 0.95
V vs. SCE) current, respectively
(Fig. 10B–10D). Reduction directly to water via a four-electron
process occurs nearly in the case of all catalysts, together with
reduction to hydrogen peroxide via a two-electron process.
However, except the ones driven by VC/Nf/7 and VC/Nf/4 modi-
fied GCEs, all other ORRs occur at considerably negative
potentials with high overpotential and usually produce higher
amounts of water than that of hydrogen peroxide, i.e., the
3.3. Synthesis
3.3.1. [1,1′-p-Anisylidenbis(2-naphthoxyphthalonitrile)] 3.
numbers of exchanged electrons at different potentials on A mixture of 1 (0.69 g, 4 mmol) and 2 (0.90 g, 2 mmol) in
ORR waves are lower than 3 which corresponds to the for- 20 mL DMF was stirred at room temperature under argon.
mation of equal amounts of water and hydrogen peroxide. On K2CO3 (0.828 g, 6 mmol) was added into the mixture over a
the other hand, ORRs catalyzed by VC/Nf/4 and especially VC/ period of 2 h. After stirring the reaction mixture at 80 °C for a
Nf/7 modified GCEs produce a higher amount of water than week, the undissolved salt was removed by filtration. The reac-
that of hydrogen peroxide (nt is higher than 3). With the VC/ tion mixture was poured into water (100 mL). The precipitate
Nf/7 modified electrode, the nt value increases with increasing was filtered, washed with water and dried in vacuo (55 °C). The
overvoltage and becomes 3.64 (82% H2O and 18% H2O2) at the residue was fractionated on a silica gel column eluting with
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CHCl3. Yield: 1.1 g (92%). Compound 3 is soluble in CHCl3, (0.263 g, 0.4 mmol), Cu(OAc)2·4H2O (0.020 g, 0.1 mmol) and
THF, acetone, DMSO, DMF, methanol, DCM and toluene. Mp: anhydrous DMF (3 mL) was heated and stirred at 180 °C in a
248 °C. Anal. calc. for C44H26N4O3, calculated C, 80.23; H, sealed glass tube for 12 hours under a dry N2 atmosphere.
3.98; N, 8.51; found C, 80.41; H, 3.67; N, 8.23%; MS (MALDI- After cooling to room temperature, the reaction mixture was
TOF): m/z 681.6 [M + Na]+, m/z 697.7 [M + K]+; IR (KBr pellet) ν, precipitated by adding acetic acid. The dark-green product was
cm−1: 521, 752, 821, 964, 1032, 1089, 1171, 1213, 1279, 1293, filtered. Then, the crude product was washed with acetic acid,
1308, 1392, 1422, 1463, 1483, 1508, 1565, 1590, 2015, 2225, ethanol and water for 12 hours respectively in the Soxhlet
1
2833, 2899, 3070; H NMR (CHCl3) δ 7.85 (d, J = 7.10 Hz, 2H), apparatus. The residue was coarsely fractionated on a silica gel
7.80 (d, J = 7.75 Hz, 2H), 7.66 (d, J = 6.85 Hz, 2H), 7.50 (t, 2H), column eluting with CHCl3 and a gradient of CHCl3–THF up
7.44 (t, 2H), 7.26 (s, 2H), 7.01 (d, J = 8.65 Hz, 2H), 6.91 (s, 1H), to 100% THF. Yield: 189 mg (72%). This compound is soluble
6.81 (d, J = 8.70 Hz, 2H), 6.62 (br s, 2H), 6.53 (br s, 2H), 6.50 in acetone, CHCl3, DCM, THF, DMF and DMSO. Mp >300 °C.
(d, J = 7.35 Hz, 2H), 3.59 (s, 3H) ppm.
Anal calc. for C176H104CuN16O12: C, 78.28; H, 3.96; N, 8.30;
3.3.2. [{2,10,16,24-Tetrakis-1,1′-p-anisylidenbis(2-naphthoxy- found: C, 78.08; H, 3.75; N, 8.47%; MS (MALDI-TOF): m/z
phthalonitrile)} phthalocyaninatocobalt (II)] 4. A mixture of 3 2698.76[M + H]+, IR (KBr pellet), cm−1: 385, 398, 422, 440, 521,
(0.263 g, 0.4 mmol), Co(OAc)2·4H2O (0.025 g, 0.1 mmol) and 539, 650, 747, 817, 863, 972, 1053, 1091, 1118, 1177, 1313,
anhydrous DMF (3 mL) was mixed in a glass tube which was 1341, 1400, 1460, 1509, 1593, 1737, 1772, 2231, 2939, 3061;
sealed under N2. The reaction mixture was stirred at 180 °C for UV/Vis (DMSO), nm(log ε): 686(4.52), 634(4.40), 338 (4.51).
12 h. After cooling to room temperature, the dark blue mixture
3.3.5. [{2′,10′,16′,24′-Tetrakis(1,1′-p-anisylidenbis-2-naphth-
was diluted with acetic acid (10 mL) to precipitate the product oxy)}phthalocyaninatodicobalt(II)] 7. The mixture of com-
and it was filtered. After it was washed successively with hot pound 4 (0.119 g, 0.043 mmol) and Co(OAc)2·4H2O (0.25 g,
acetic acid (3 × 20 mL), hot ethanol (3 × 20 mL) and hot water 1 mmol) was powdered in a quartz crucible and transferred
to remove the unreacted organic materials, it was dried into a reaction tube. 1 mL of DMF was added to this reaction
in vacuo (60 °C). The crude product was purified by column mixture and the reaction mixture was heated in a sealed glass
chromatography with silica gel eluting with CHCl3. Yield: tube for 12 h under a dry N2 atmosphere at 180 °C. After
171 mg (65%). This compound is soluble in CHCl3, methanol, cooling to room temperature, the reaction mixture was precipi-
acetone, toluene, DMSO, DCM, THF, and DMF. Mp >300 °C. tated by adding acetic acid. The precipitate was filtered and
Anal calc. for C176H104CoN16O12: C, 78.42; H, 3.96; N, 8.31%; washed with acetic acid, ethanol and water for 24 h respect-
found: C, 78.62; H, 3.76; N, 8.26%. MS (MALDI-TOF): m/z ively in the Soxhlet apparatus. The crude product was purified
2694.75[M + H]+, IR (KBr pellet) ν, cm−1: 384, 443, 522, 649, by column chromatography with silica gel eluting with CHCl3
750, 818, 864, 968, 1032, 1059, 1091, 119, 1177, 1244, 1309, and a gradient of CHCl3–THF up to 5% THF. This compound
1407, 1461, 1509, 1591, 1671, 1733, 2023, 2163, 2230, 2834, is soluble in CHCl3, DMF, DMSO and THF. Yield: 71 mg (60%).
2931, 3059; UV/Vis (DMSO), nm (log ε): 671(4.60), 618(4.22), Mp >300 °C. Anal. calc. for C176H104Co2N16O12: C, 76.79; H,
312 (4.76).
3.3.3. [2,10,16,24-Tetrakis{1,1′-p-anisylidenbis(2-naphthoxy- (MALDI-TOF): m/z 2839.67[M − 3H + 4Na]+; IR (KBr pellet) ν,
phthalonitrile)}phthalocyaninatozinc(II)] 5. A mixture of
cm−1: 397, 422, 520, 644, 744, 813, 861, 969, 1032, 1089, 1117,
3.81; N, 8.14%; found: C, 76.89; H, 3.91; N, 8.20%; MS
3
(0.263 g, 0.4 mmol), Zn(OAc)2·2H2O (0.022 g, 0.1 mmol) and 1176, 1312, 1393, 1458, 1508, 1594, 1713, 1770, 2160, 2826,
anhydrous DMF (3 mL) was mixed in a glass tube which was 2951, 3055, 3391; UV/Vis (DMSO), nm(log ε): 678(4.55), 623
sealed under nitrogen. The reaction mixture was stirred at (4.24), 318 (4.66).
180 °C for 12 h. After cooling to room temperature, the dark
3.3.6. [{2′,10′,16′,24′-Tetrakis(1,1′-p-anisylidenbis-2-naphth-
blue–greenish mixture was diluted with acetic acid (10 mL) to oxy)}phthalocyaninatodizinc(II)] 8. The mixture of 5 (0.123 g,
precipitate the product and it was filtered. The residue was 0.044 mmol), Zn(OAc)2·2H2O (0.22 g, 1 mmol) and DMF(1 mL)
washed successively first with hot acetic acid and then with was mixed in a glass tube which was sealed under nitrogen.
hot ethanol and hot water before drying it in vacuo (60 °C). The mixture was heated at 180 °C for 12 h. After cooling to
The residue was coarsely fractionated on a silica gel column room temperature,
a blue-green reaction product was
eluting with CHCl3 and a gradient of CHCl3–methanol up to obtained, isolated and purified using the same procedure as
5% methanol. Yield: 176 mg (67%). This compound is soluble explained above for 7. This compound is soluble in CHCl3,
in CHCl3, acetone, DMSO, DCM, THF, and DMF. Mp >300 °C. DMF, DMSO and THF. Yield: 60 mg (49%). Mp >300 °C. Anal.
Anal calc. for C176H104N16O12Zn: C, 78.23; H, 3.95; N, 8.29%; calc. for C176H104N16O12Zn2: C, 76.43; H, 3.79; N, 8.10%;
found: C, 78.03; H, 3.75; N, 8.17%; MS (MALDI-TOF): m/z found: C, 76.28; H, 3.88; N, 8.01%; MS (MALDI-TOF): m/z
2699.75[M + H]+, IR (KBr pellet) ν, cm−1: 386, 422, 440, 521, 2761.66[M + H]+, IR (KBr pellet) ν, cm−1: 388, 396, 421,
540, 648, 744, 815, 862, 966, 1043, 1087, 1115, 1143, 1176, 443, 520, 646, 744, 815, 861, 969, 1044, 1087, 1116, 1176,
1311, 1334, 1391, 1459, 1482, 1509, 1592, 1718, 1770, 2027, 1312, 1334, 1392, 1459, 1509, 1595, 1610, 1715, 1771, 2169,
2230, 2833, 3055; UV/Vis (DMSO), nm (log ε): 689(4.65), 629 2830, 2927, 3059; UV/Vis (DMSO), nm(log ε): 689(4.66),
(4.13), 355(4.41).
626(4.12), 354(4.44); 1H NMR (CHCl3): δ, ppm 8.95–6.11 (m,
3.3.4. [2,10,16,24-Tetrakis{1,1′-p-anisylidenbis(2-naphthoxy- 88H, arom.), 3.65–2.60(m, 12H, Ar–OCH3), 2.89–2.77 ppm (m,
phthalonitrile)}phthalocyaninatocopper(II)] 6. The mixture of 3 4H, Ar–CH).
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3.3.7. [{2′,10′,16′,24′-Tetrakis(1,1′-p-anisylidenbis-2-naphth- solution at least 20 min prior to each run and to maintain a
oxy)}phthalocyaninatodicopper(II)] 9. The mixture of com- nitrogen blanket during the measurements. For controlled-
pound 6 (0.132 g, 0.047 mmol), Zn(OAc)2·2H2O (0.20 g, potential Coulometry studies, a Pt gauze as a working elec-
1 mmol) and DMF (1 mL) was heated and stirred at 180 °C in trode (10.5 cm2 surface area), a Pt wire as a counter electrode
a sealed glass tube for 12 h under N2. After cooling to room separated by a glass bridge, and SCE as a reference electrode
temperature, a dark green reaction product was obtained, iso- were used.
lated and purified using the same procedure as explained
Ultra-pure water and sulfuric acid were used to prepare the
above for 7. This compound is soluble in CHCl3, DMF, DMSO electrolyte solution in electrocatalytic measurements. Vulcan
and THF. Yield: 69 mg (52%). Mp >300 °C. Anal. calc. for XC-72 (VC) (Cabot Co), 5% Nafion (Nf) solution (Aldrich), extra
C176H106Cu2N16O12: C, 76.54; H, 3.80; N, 8.11%; found: C, pure ethyl alcohol (Merck), and the Pc compounds were used
76.39; H, 3.89; N, 8.05%; MS (MALDI-TOF): m/z 2759.68 in catalyst preparation. A glassy carbon disk electrode, a plati-
[M + H]+, IR (KBr pellet) ν, cm−1: 385, 439, 519, 645, 744, 814, num ring-glassy carbon disk electrode and a polishing kit for
861, 970, 1048, 1088, 1116, 1143, 1176, 1313, 1396, 1458, 1508, these electrodes were purchased from Pine Instruments. Two
1594, 1715, 1770, 2161, 2834, 2927, 3056; UV/Vis (DMSO), Gamry Ref. 600 potentiostats were connected as a bipotentio-
nm(log ε): 688(4.49), 639(4.25), 333(4.47).
stat to control the ring and disk potentials and to collect the
respective currents during rotating ring-disk electrode (RRDE)
experiments. A Pine Instrument Company AFMSRCE modu-
3.3. OFET fabrication
The field effect transistors were prepared using indium tin lator speed rotator was employed in RRDE experiments. A Pine
oxide (ITO) coated glass substrate as the gate electrode. The Instrument Company AFMSRCE modulator speed rotator was
OFET devices were fabricated with the bottom-gate and top employed in RDE RRDE experiments. RRDE measurements
source–drain contact geometry configuration. Before using, were performed with a glassy carbon disk (5 mm dia.) in O2
the ITO coated substrates were cleaned by ultrasonic treatment saturated 0.5 M H2SO4 aqueous solution under quasi-station-
in acetone, isopropyl alcohol, and deionised water in that ary conditions (0.005 V s−1 sweep rate) at 25 °C. For RRDE
order. The gate insulator layer was PVA, obtained commercially experiments, the working electrode was a glassy carbon disk
and used as received. The PVA gate insulating film was spin- (5.61 mm dia.) and a platinum ring leading to a collection
coated from a solution of PVA in distilled water at 2500 rpm efficiency, N = 37%. These experiments were carried out at
for 45 s. After drying the PVA film in a vacuum oven at 90 °C 2500 rpm in oxygen saturated 0.5 M H2SO4 aqueous electrolyte
for 15 min to evaporate the solvent remaining in the film, a solution at 25 °C. The disk potential was swept at 0.005 V s−1
solution of Pcs in chloroform, with a concentration of 5 × 10−3 whereas the ring potential was held at 0.95 V vs. SCE. In order
M, was spun on top of the PVA film rotating at 3500 rpm. Sub- to disperse the catalysts on a carbon support for RRDE exper-
sequently, the deposited films were thermally annealed at iments, a mixture of the Pc compound, VC and 5 wt% Nf solu-
120 °C for 45 min to evaporate the solvent. The ellipsometric tion in absolute ethanol was prepared and ultrasonically
technique was used to measure the thickness of the dielectric homogenized for half an hour. A micropipette was used to
layer and the Pc films. The source and drain electrodes were load a suitable amount of the catalyst ink onto a freshly
deposited onto the semiconducting layer with a shadow mask polished glassy carbon electrode. The amount of Nf in the ink
to produce top contact OFETs. Au was used for the source– was adjusted so that the catalyst film was sufficiently thin, and
drain contact metal, at a thickness of 100 nm. The channel thus its diffusion resistance was negligible. In order to obtain
length and width of the OFETs were 80 μm and 4 mm, respect- a total coverage of the glassy carbon surface, the deposited
ively. The electrical characteristics of these devices were drop of ink was dried with pulsed air at ambient temperature
measured in air. For electrical measurements a Keithley 617 to evaporate the solvent quickly. Each voltammogram was
programmable electrometer and a Keithley 2400 source-meter recorded with a freshly prepared electrode due to the possible
were used.
catalyst degradation in acidic medium. The counter electrode
was a Pt spiral and the reference electrode was a SCE.
3.4. Electrochemical measurements
Electrochemical and in situ spectroelectrochemical measure-
ments were achieved by a Gamry Ref. 600 potentiostat com-
4. Conclusions
bined
with
an
Ocean
Optics
HR2000
UV/vis
spectrophotometer. A Pt disc, a Pt spiral wire and a saturated The novel mono-nuclear 4, 5 and 6, and ball-type 7, 8 and 9
calomel electrode (SCE) were employed as the working, have been synthesized from 3. The complexes were character-
counter and reference electrodes, respectively, for cyclic vol- ized by elemental analysis, UV-vis, IR, 1H NMR and MALDI-
tammetry and square voltammetry measurements. Ferrocene TOF mass spectroscopies.
was used as an internal reference, but all potentials were pre-
By choosing an appropriate metal electrode (drain and
sented as the ones vs. SCE. Electrochemical grade tetrabutyl- source electrode), high field effect mobility in OFETs consist-
ammonium perchlorate (TBAP) in extra pure DMSO was ing of spin coated 7–9 film was successfully demonstrated and
employed as the supporting electrolyte at a concentration of characterized. It was observed that the field-effect mobility and
0.20 mol dm−3. High purity N2 was used for deoxygenating the the threshold voltage, which are the main OFET performance
5868 | Dalton Trans., 2014, 43, 5858–5870
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parameters, using spin coated film of 9 as organic channels
are much higher than the values of the respective devices
using 7 and 8. One of the reasons why, unlike the ball-type Pc
based OFETs, the mono-nuclear based OFETs are incapable of
exhibiting a satisfactory saturation area of the drain current–
drain voltage curves, is that in the film during the spin
coating, stacking structures are rapidly formed. The results
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materials for the fabrication of OFETs with low threshold
voltage and high mobility.
9
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dioxygen molecule through peroxo species, Co–O–O–Co, the
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Acknowledgements
We thank the Turkish Academy of Sciences (TUBA) and the
Marmara University Scientific Research Commission (project
numbers FEN-A-090512-0165 and FEN-A-150513-0164) for their
financial support. We also thank Assoc. Prof. Dr Z. Odabaş,
Assoc. Prof. Dr M. Özer and Ö. Kurt for their valuable help
during the preparation of the manuscript.
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