Synthesis, electrochemistry, spectroelectrochemistry and electropolymerization of metal-free and metallophthalocyanines

Article abstract of DOI:10.1016/j.poly.2014.07.009

Metal-free 4 and metallophthalocyanine complexes 5-7 (MPcs, M = Ni, Co, Cu) substituted with the electropolymerizable (2-{2-[3-(dimethylamino)phenoxy] ethoxy}ethoxy) group have been synthesized and their structure have been identified by IR, ¹H and ¹³C NMR, mass and UV-Vis spectroscopy techniques. The electrochemical characterization of the phthalocyanines sustained the submitted structures of the complexes, since the half wave peak potentials of the redox processes are in harmony with the common electrochemical behavior of MPcs. CoPc gives a metal based reduction process in addition to the ligand based electron transfer processes, which enrich the possible usage of the complex in various electrochemical technologies. All the complexes were coated on the working electrode with an oxidative electopolymerization process during the anodic potential scans.

Full text of DOI:10.1016/j.poly.2014.07.009

Polyhedron 81 (2014) 525–533
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, electrochemistry, spectroelectrochemistry and
electropolymerization of metal-free and metallophthalocyanines
a
b
Volkan Çakır a, Halit Kantekin a, , Zekeriya Bıyıklıog˘lu , Atıf Koca
⇑
a Department of Chemistry, Faculty of Science, Karadeniz Technical University, 61080 Trabzon, Turkey
Department of Chemical Engineering, Engineering Faculty, Marmara University, Göztepe 34722, Istanbul, Turkey
b
_
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal-free 4 and metallophthalocyanine complexes 5–7 (MPcs, M = Ni, Co, Cu) substituted with the
electropolymerizable (2-{2-[3-(dimethylamino)phenoxy]ethoxy}ethoxy) group have been synthesized
and their structure have been identified by IR, 1H and 13C NMR, mass and UV–Vis spectroscopy tech-
niques. The electrochemical characterization of the phthalocyanines sustained the submitted structures
of the complexes, since the half wave peak potentials of the redox processes are in harmony with the
common electrochemical behavior of MPcs. CoPc gives a metal based reduction process in addition to
the ligand based electron transfer processes, which enrich the possible usage of the complex in various
electrochemical technologies. All the complexes were coated on the working electrode with an oxidative
electopolymerization process during the anodic potential scans.
Received 2 April 2014
Accepted 2 July 2014
Available online 16 July 2014
Keywords:
Phthalocyanine
Cobalt
Synthesis
Electropolymerization
Electrochemistry
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
extend our previous research and to find possible application fields
for these complexes.
Phthalocyanine (Pc) and its derivatives have received increasing
attention due to their unique physical, chemical, biological and
spectral properties [1]. They have been used for a wide range of
applications in various areas, such as liquid crystals, electronic
devices, gas and chemical sensors, electrochromic and electrolumi-
nescent displays, non-linear optics, photovoltaics, semiconductors,
catalysis and photodynamic therapy (PDT) [2–11]. As a new class
of phthalocyanine, electropolymerizable phthalocyanines have
been studied in recent years.
In our previous papers, we studied the electrochemical charac-
terization and electrochemical application of various MPcs bearing
different metal centers and substituent environments [12–16]. Our
studies indicated that incorporating redox active and/or functional
substituents to the Pcs extend the redox richness and application
possibilities of MPcs. Thus, in the last few years, we have narrowed
our research to MPcs bearing a redox active metal center and
substituents, such as quinoline [17], thiophene [18,19] and amino
groups. Nowadays, we are interested in the electrochemistry of
MPcs carrying amino containing substituents because of the elec-
tropolymerization of MPcs with the assistance of the amino groups.
In this paper, we have investigated the electrochemistry and elec-
tropolymerization of MPcs bearing dimethylamino substituents to
2. Experimental
2.1. Materials
2-{2-[3-(Dimethylamino)phenoxy]ethoxy}ethanol (1) [20], 4-
nitrophthalonitrile (2) [21], 4-(2-{2-[3-(dimethylamino)phenoxy]
ethoxy}ethoxy)phthalonitrile (3) [22] and cobalt(II) phthalocya-
nine (6) [23] were prepared according to the literature procedures.
All reagents and solvents were of reagent grade quality and were
obtained from commercial suppliers. All solvents were dried and
purified as described by Perrin and Armarego [24].
2.2. Equipment
The IR spectra were recorded on a Perkin Elmer 1600 FT-IR
spectrophotometer, using KBr pellets. 1H and 13C NMR spectra
were recorded on a Varian Mercury 300 MHz spectrometer in
CDCl3, and chemical shifts were reported (d) relative to Me4Si as
an internal standard. Mass spectra were measured on a Micromass
Quatro LC/ULTIMA LC–MS/MS spectrometer. MALDI-MS of com-
plexes were obtained in dihydroxybenzoic acid as the MALDI
matrix, using a nitrogen laser accumulating 50 laser shots, with a
Bruker Microflex LT MALDI-TOF mass spectrometer. Optical spec-
tra in the UV–Vis region were recorded with a Perkin Elmer
⇑
Corresponding author. Tel.: +90 462 377 25 89; fax: +90 462 325 31 96.
E-mail address: halit@ktu.edu.tr (H. Kantekin).
http://dx.doi.org/10.1016/j.poly.2014.07.009
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

526
V. Çakır et al. / Polyhedron 81 (2014) 525–533
O2N
CN
CN
N
O
O
1
OH
2
dry DMF
K2CO3
50 °C
CN
CN
N
O
O
O
3
N
n-pentanol
DBU
160 °C
N
O
O
O
O
O
O
N
N
HN
N
N
N
NH
N
O
O
4
O
O
O
O
N
N
Fig. 1. The synthetic route for the metal-free phthalocyanine.
Lambda 25 spectrophotometer. Melting points were measured on
an electrothermal apparatus and are uncorrected.
2.4. Synthesis
2.4.1. 2(3),9(10),16(17),23(24)-Tetrakis-(2-{2-[3-(dimethylamino)
phenoxy]ethoxy}ethoxy) phthalocyanine (4)
2.3. Electrochemical and spectroelectrochemical measurements
A solution of compound 3 (0.3 g, 0.00085 mol) in dry n-pentanol
(3 ꢀ 10ꢁ3 L) and 1,8-diazabycyclo[5.4.0]undec-7-ene (DBU) (4
drops) were heated and stirred in a glass sealed tube at 160 °C
for 24 h under a N2 atmosphere. After cooling to room tempera-
ture, a green product was precipitated by adding ethanol. The
green solid product was filtered and then washed with hot ethanol,
diethyl ether and dried in a vacuum. Finally, the pure metal-free
phthalocyanine 4 was obtained by column chromatography, using
aluminium oxide with CHCl3 as the solvent system. Yield: 0.15 g
All the electrochemical measurements were carried out with
Gamry Reference 600 potentiostat/galvanostat controlled by the
following procedure. The working electrode was a Pt disc with a
surface area of 0.071 cm2. A Pt wire served as the counter elec-
trode. A saturated calomel electrode (SCE) was employed as the
reference electrode. Electrochemical grade tetrabuthylammonium
perchlorate (TBAP) in dichloromethane (DCM) was employed as
the supporting electrolyte. An OceanOptics QE65000 diode array
spectrophotometer was used for UV–Vis absorption spectra and
chromaticity diagram measurements. In situ spectroelectrochemi-
cal measurements were carried out by utilizing a three-electrode
configuration of thin-layer quartz thin-layer spectroelectrochemi-
cal cell, consisting of a Pt tulle working electrode, a Pt wire counter
electrode and a SCE reference electrode.
(50%). IR (KBr tablet,
m
max/cmꢁ1): 3292 (N–H), 3074 (Ar–H),
2921–2800 (Aliph. C–H), 1606, 1572, 1499, 1482, 1447, 1346,
1322, 1283, 1233, 1116, 1095, 1058, 998, 951, 820, 746, 685. 1H
NMR (CDCl3, d/ppm): 8.15–7.96 (m, 4H, Ar–H), 7.26–7.09 (m,
12H, Ar–H), 6.45–6.38 (m, 12H, Ar–H), 4.31–4.11 (m, 32H,
CH2–O), 2.93 (s, 24H, CH3–N). 13C NMR (CDCl3, d/ppm): 160.23,

V. Çakır et al. / Polyhedron 81 (2014) 525–533
527
N
N
O
O
O
O
O
O
N
CN
i
N
N
N
N
N
O
N
M
N
N
O
O
CN
3
O
O
O
O
O
O
6
Compound
M
5
7
N
Cu
Ni
Co
N
Fig. 2. The synthetic route for the nickel, cobalt and copper phthalocyanines. Reagents and conditions: (i) n-pentanol, DBU, 160 °C, NiCl2, CoCl2, CuCl2.
1,2
H2Pc
NiPc
CoPc
CuPc
1
0,8
0,6
0,4
0,2
0
Fig. 3. UV–Vis spectra of 4–7 in chloroform.
159.95, 152.25, 130.05, 129.91, 106.27, 106.20, 106.17, 102.42,
102.38, 102.14, 100.21, 100.09, 100.06, 70.50, 67.64, 40.95. UV–
Vis (chloroform, kmax/nm (loge)): 704 (4.97), 667 (4.90), 645
a N2 atmosphere. After the reaction mixture was cooled, the
product was precipitated by adding ethanol. The crude solid prod-
uct was filtered and then washed with hot ethanol, diethyl ether
and dried in a vacuum. Finally, the pure nickel(II) phthalocyanine
5 was obtained by column chromatography, using aluminium
oxide with CHCl3:CH3OH (100:2) as the solvent system. Yield:
(4.57), 607 (4.39), 378 (4.50), 340 (4.79). MALDI-TOF-MS m/z:
1407 [M]+.
2.4.2. 2(3),9(10),16(17),23(24)-Tetrakis-(2-{2-[3-(dimethylamino)
phenoxy]ethoxy}ethoxy) phthalocyaninato nickel(II) (5)
0.18 g (70%). IR (KBr tablet, m
max/cmꢁ1): 3072 (Ar–H), 2919–2798
(Aliph. C–H), 1719, 1607, 1572, 1499, 1447, 1416, 1348, 1275,
1233, 1118, 1091, 1062, 997, 1021, 988, 962, 818, 749, 685. 1H
NMR. (CDCl3, d/ppm): 7.69–7.53 (m, 4H, Ar–H), 7.26–7.19
(m, 12H, Ar–H), 6.40–6.39 (m, 12H, Ar–H), 4.25–4.04 (m, 32H,
CH2–O), 2.91 (s, 24H, CH3-N). 13C NMR. (CDCl3, d /ppm): 152.29,
152.21, 130.06, 130.03, 123.39, 109.98, 106.22, 106.20, 106.14,
A mixture of 4-(2-{2-[3-(dimethylamino)phenoxy]ethoxy}eth-
oxy)phthalonitrile (3) (0.25 g 0.00071 mol), anhydrous NiCl2
(0.045 g, 0.00035 mol), dry n-pentanol (3 ꢀ 10ꢁ3 L) and 1,8-dia-
zabycyclo[5.4.0]undec-7-ene (DBU) (3 drops) were heated in a
sealed tube with efficient stirring at 160 °C for about 24 h under

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V. Çakır et al. / Polyhedron 81 (2014) 525–533
Table 1
Voltammetric data of the complexes. All voltammetric data were given vs. SCE.
Complex
Electropolymerization
MII/MI
Ring reductions
CoPc
aE1/2
0.97d (0.60)e
–
–
ꢁ0.37 (ꢁ0.72)
120
0.93
ꢁ1.47
112
0.89
–
–
–
bDEp (mV)
cIp,a/Ip,c
H2Pc
aE1/2
0.97d (0.57)e
–
–
–
–
–
ꢁ0.70
160
0.94
ꢁ1.02
175
0.93
bDEp (mV)
cIp,a/Ip,c
CuPc
NiPc
aE1/2
0.90d (0.61)e
–
–
–
–
–
–
–
ꢁ0.85
150
0.96
ꢁ0.87
80
ꢁ1.15
120
0.91
ꢁ1.19
70
bDEp (mV)
cIp,a/Ip,c
aE1/2
–
0.88d (0.64)e
bDEp (mV)
cIp,a/Ip,c
–
–
0.96
0.91
a
b
c
E1/2 values ((Epa + Epc)/2) were given vs. SCE at 0.100 V sꢁ1 scan rate.
D
Ep = Epa ꢁ Epc
.
Ip,a/Ip,c for reduction, Ip,c/Ip,a for oxidation processes.
d
e
Anodic peak of the electropolymerization reaction recorded during first CV cycle.
Cathodic peak of the electropolymerization reaction recorded during first CV cycle.
102.36, 102.33, 100.21, 100.20, 100.18, 70.44, 67.57, 40.83. UV–Vis
(DBU) (3 drops). The pure cobalt(II) phthalocyanine 6 was
(chloroform kmax/nm (log
e
)): 673 (5.07), 624 (4.66), 379 (4.61), 327
obtained by column chromatography, using aluminium oxide
with CHCl3:CH3OH (100:2) as the solvent system. Yield: 0.094 g
(36%). IR (KBr tablet,
(4.78). MALDI-TOF-MS m/z: 1465 [M+H]+.
m
max/cmꢁ1): 3088 (Ar–H), 2919–2802
(Aliph. C–H), 1714, 1607, 1572, 1481, 1447, 1410, 1382, 1349,
1280, 1233, 1122, 1093, 1063, 998, 961, 819, 751, 686. UV–Vis
2.4.3. 2(3),9(10),16(17),23(24)-Tetrakis-(2-{2-[3-(dimethylamino)
phenoxy]ethoxy}ethoxy) phthalocyaninato cobalt(II) (6)
A similar preparation method to that of complex 5 was used to
obtain cobalt(II) phthalocyanine 6, using a mixture of compound 3
(0.25 g 0.00071 mol), anhydrous CoCl2 (0.046 g, 0.00035 mol), dry
n-pentanol (3 ꢀ 10ꢁ3 L) and 1,8-diazabycyclo[5.4.0]undec-7-ene
(chloroform, kmax/nm (loge)): 675 (4.99), 618 (4.60), 448 (4.46),
387 (4.69). MS (ESI) m/z: 1464 [M]+.
2.4.4. 2(3),9(10),16(17),23(24)-Tetrakis-(2-{2-[3-(dimethylamino)ph
enoxy]ethoxy}ethoxy) phthalocyaninato copper(II) (7)
A similar preparation method to that of complex 5 was used to
obtain the copper(II) phthalocyanine 7, using
a
mixture of
compound
3
(0.25 g 0.00071 mol), anhydrous CuCl2 (0.047 g,
0.00035 mol), dry n-pentanol (3 ꢀ 10ꢁ3 L) and 1,8-diazabycy-
clo[5.4.0]undec-7-ene (DBU) (3 drops). The pure copper(II) phtha-
locyanine 7 was obtained by column chromatography, using
aluminium oxide with CHCl3:CH3OH (100:2) as the solvent system.
Yield: 0.080 g (30%). IR (KBr tablet,
m
max/cmꢁ1): 3074 (Ar–H),
2921–2800 (Aliph. C–H), 1719, 1606, 1501, 1447, 1403, 1343,
1280, 1234, 1118, 1094, 1061, 998, 959, 819, 745, 685. UV–Vis
(chloroform, kmax/nm (loge)): 682 (5.03), 616 (4.61), 379 (4.53),
338 (4.83). MALDI-TOF-MS m/z: 1470 [M+H]+.
Fig. 4. (a) CV and SWV of CoPc recorded at various scan rates on a Pt working
electrode in DCM/TBAP (b) SWV of CoPc.
Fig. 5. Repetitive CVs of CoPc recorded between 0.0 and 1.70 V in the DCM/TBAP
electrolyte system at 0.100 V sꢁ1 scan rate on a Pt working electrode.

V. Çakır et al. / Polyhedron 81 (2014) 525–533
529
Fig. 6. (a) CVs of H2Pc, CuPc, NiPc and CoPc recorded at cathodic potentials at
0.100 V sꢁ1 scan rate on a Pt working electrode in DCM/TBAP and (b) SWV of the
complexes recorded with SWV parameters: step size = 5 mV; pulse size = 100 mV;
Frequency = 25 Hz.
Fig. 7. Repetitive CVs of (a) H2Pc, (b) CuPc, and (c) NiPc recorded between 0.0 and
1.70 V in the DCM/TBAP electrolyte system at 0.100 V sꢁ1 scan rate on a Pt working
electrode.
3. Results and discussion
3.1. Synthesis and characterization
m/z = 1407 [M]+ and this result is in good accord with the sug-
gested structure.
The synthesis of substituted metal-free and metallophthalocya-
nines starts generally with the preparation of the corresponding
phthalonitrile precursors. The syntheses of the target metal-free
4 and metallophthalocyanines 5–7 undertaken in this work are
shown in Figs. 1 and 2.
According to the IR spectrum of compound 4, the signals for the
CN groups at 2233 cmꢁ1 for compound 3 disappeared and new
peaks appeared at 3292 and 1606 cmꢁ1, that are dedicated to the
N–H group in the phthalocyanine core of 4. In the 1H NMR spec-
trum of 4, the typical shielding of the inner core protons could
not be observed due to the probable strong aggregation of the mol-
ecules [25]. The 1H NMR spectrum of compound 4 exhibited the
aromatic protons, integrating to a total of 7 protons, at 8.15–
7.96, 7.26–7.09 and 6.45–6.38 ppm. Also the CH2-O and CH2-N
In the IR spectra of the metallophthalocyanines 5–7, the cyclo-
tetramerization of 3 was confirmed by the disappearance of the
sharp CN stretching vibration at 2233 cmꢁ1. The IR spectra of NiPc,
CoPc and CuPc are also very similar to that of the precursor H2Pc,
except for the disappearance of the N–H vibration of the phthalo-
cyanine core. The 1H NMR spectrum of 5 exhibited signals at
d = 7.69–7.53 (m, 4H, Ar–H), 7.26–7.19 (m, 12H, Ar–H), 6.40–6.39
(m, 12H, Ar–H), 4.25–4.04 (m, 32H, CH2–O) and 2.91 (s, 24H,
CH2–N), belonging to aromatic and aliphatic protons. The 13C
NMR spectrum of 5 indicated carbon atoms at d = 152.29, 152.21,
130.06, 130.03, 123.39, 109.98, 106.22, 106.20, 106.14, 102.36,
102.33, 100.21, 100.20, 100.18, 70.44, 67.57 and 40.83. 1H NMR
measurements of the cobalt(II) and copper(II) phthalocyanines 6
and 7 were precluded due to their paramagnetic nature [26]. The
UV–Vis absorption spectra of the metal-free and metallophthalo-
cyanines 4–7 in chloroform at room temperature are shown in
Fig. 3. The electronic spectra of metallophthalocyanines 5–7 in
chloroform show an intense Q absorption at kmax = 673, 675 and
682 nm, with a weaker absorption at 624, 618 and 616 nm, respec-
tively. The single Q bands in metallo derivatives 5, 6 and 7 are
characteristic. B band absorptions of compounds 5, 6 and 7 were
observed at kmax = (387, 448), (327, 379) and (338, 379) nm as
expected, respectively. In the mass spectra of compounds 5, 6
and 7, the presence of molecular ion peaks at m/z = 1465 [M+H]+,
protons of metal-free
4 were observed between 4.31 and
2.93 ppm, which integrated to 14 protons. The 1H NMR spectrum
of compound 4 is in agreement with the proposed structure. The
13C NMR data of 4 confirm the results of the 1H NMR spectrum.
The UV–Vis spectrum of the phthalocyanine core is dominated
by two intense bands, the Q band, at around 600–710 nm, and
the B band in the near UV region, at about 300–400 nm, both cor-
related with
p–
p⁄ transitions. In the electronic spectrum of 4 in
chloroform, intense Q absorption bands were observed at 667
and 704 nm, respectively. B absorption bands of the metal-free
phthalocyanine 4 were observed at 340 and 378 nm, respectively.
The MALDI-TOF mass spectrum of compound 4 was measured as

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V. Çakır et al. / Polyhedron 81 (2014) 525–533
at different scan rates and they were analyzed with respect to the
half-wave peak potentials (E1/2), anodic to cathodic peak potential
separation ( Ep), peak width (
D
D
Ep ꢁ Ep/2) and the anodic to catho-
dic peak current ratio (Ipa/Ipc). The analyses of the redox processes
indicate the presence of a chemical reaction succeeding the R1
process. This chemical reaction is most probably an aggregation–
disaggregation equilibria. Observation of R01 supports the presence
of aggregated CoPc species. Voltammetric analyses performed with
different concentrations at different scan rates support the aggre-
gation assignment of the R01 wave. Large
DEp values of the reduc-
tion reactions (higher than 100 mV at even very slow scan rates)
indicate that both of the reduction processes R1 and R2 have elec-
trochemically quasi-reversible character.
While CoPc illustrates common metal and Pc ring based reduc-
tion reactions during the cathodic potential scans, it gives extraor-
dinary redox responses during the anodic potential scans. Fig. 5
represents repetitive CVs of CoPc recorded during anodic CV cycles.
CoPc gives a huge anodic wave at 0.97 V and its reverse cathodic
couple at 0.60 V during the first anodic CV scan. This CV behavior
indicates the oxidation of the amino groups on the substituents
of the complex. Oxidation of amino groups triggers an oxidative
electropolymerization process and the complex was coated on
the working electrode as a polymeric film as a result of the elec-
tropolymerization reaction. Electropolymerization of the complex
was well reflected by the consecutive CV responses of the system.
During the consecutive second CV cycle, a new anodic wave was
recorded at 0.87 V, assigned to the polymerized complex. This
new wave decreases in current intensity with a positive potential
shift, as a result of consecutive CV cycles. Similarly the cathodic
wave at 0.60 V decreases with current intensity, while a small
wave is observed at around 0.20 V. These CV changes illustrate
coating of the complex on the working electrode with an electrop-
olymerization process. The film on the electrode surface was seen
easily with the naked eye, as shown in the photograph of the film
in Fig. 5. IR analysis of the CoPc film has been recorded, as given
below and in the Supplementary material file as Fig. S3. The peaks
at around 3000 cmꢁ1 are characteristic aromatic hydrogen peaks of
the Pc ring. The disappearance of the peaks of the groups on the
substituent indicated that the electropolymerization of the com-
plexes significantly affected the behavior of the substituents.
The CoPc film on the electrode surface was characterized by CV
and UV–Vis measurements (Fig. S4 in the Supplementary file). The
ITO/CoPc film gave two quasi-reversible oxidation reactions and
the characters of these peaks are completely different than those
of monomeric CoPc. Both the ITO/CoPc film and monomeric CoPc
gave a Q band at the same wavelength, 675 nm, which indicates
that the electropolymerization reaction did not significantly affect
the electronic behavior of the Pc ring. It is well known that elec-
tropolymerization reactions occur from the cationic polymeriza-
tion of amino groups. Except the amino groups, there is no
polymerization side for these complexes.
Fig. 8. In situ UV–Vis spectral changes of NiPc in DCM/TBAP. (a) Eapp = ꢁ1.00 V. (b)
Eapp = 1.30 V. (c) Chromaticity diagram (each symbol represents the color of the
ꢁ1
electro-generated species; h: [NiIIPcꢁ2], s:[NiIIPcꢁ3
]
,
: polymer. (Color online.)
1464 [M]+ and 1470 [M+H]+, respectively, confirmed the proposed
structures.
3.2. Voltammetric measurements
The electrochemical features of MPcs were examined to derive
basic electrochemical parameters for the complexes, which are
need to decide their usage in different electrochemical technolo-
gies. For this purpose, the electrochemical properties of the com-
plexes were determined in solution with CV and SWV techniques
and then the voltammetric responses of the complexes were ana-
lyzed. The derived electrochemical parameters of the complexes,
presented in Table 1, are in agreements with similar complexes
in the literature [27–30]. As shown in Table 1, while CoPc gives a
metal based redox process in addition to the Pc based redox reac-
tions, H2Pc, CuPc and NiPc show common Pc based reduction reac-
tions. All the complexes studied electropolymerized during the
anodic potential scans.
Fig. 4 represents the CV responses of CoPc recorded on the
cathodic potential side of the TBAP/DCM electrolyte system on a
Pt working electrode. CoPc gives a metal based reduction couple
R1 at ꢁ0.37 V, a wave R01 assigned to aggregated CoPc species at
ꢁ0.72 V and a Pc based reduction couple R2 at ꢁ91.47 V during
the cathodic potential scans. These redox processes were recorded
The effects of the metal ions in the Pc cores of the complexes are
well reflected with the CVs of the complexes. As shown in Fig. 6,
H2Pc, CuPc, and NiPc give very similar reduction processes during
the cathodic potential scans. All of these complexes give two
reversible reduction couples. The only difference between the CV
and SWV of the complexes is the peak potentials of the redox pro-
cesses. The reduction reactions shift to negative potentials with
respect to the decreasing effective nuclear charge of the central
ions. The order of the easy of reduction is observed as: H2Pc (E1/2
of R1: ꢁ90.87 V) > NiPc (E1/2 of R1: ꢁ0.90 V) > CuPc (E1/2 of R1:
ꢁ0.93 V). For the analyses of the complexes, the CVs of the com-
plexes were recorded at different scan rates and the results are
given in the Supplementary file. The
DEp and Ipa/Ipc values of the
redox couples indicate electrochemical and chemical reversibility
of all the reduction processes of the complexes [31].

V. Çakır et al. / Polyhedron 81 (2014) 525–533
531
Fig. 9. In situ UV–Vis spectral changes of H2Pc in DCM/TBAP. (a) Eapp = ꢁ0.80 V. (b) Eapp = ꢁ1.30 V. (c) Eapp = 1.50 V. (d) Chromaticity diagram (each symbol represents the
ꢁ2
color of the electro-generated species; h: [H2Pcꢁ2], s:[ H2Pcꢁ3
]
ꢁ1, 4: [H2Pcꢁ4
]
,
: polymer. (Color online.)
Like CoPc, the compound H2Pc, CuPc and NiPc were also elec-
tropolymerized on the working electrode in similar manners. How-
ever, when central ion of the Pc core changed, the CV responses of
the electropolymerization processes also changed. Generally the
peak potentials of the polymers, peak current changes and/or shift-
ing trends of the peaks differed when the metal centers were chan-
ged. Fig. 7 represents the repetitive CVs of H2Pc, CuPc and NiPc
recorded during the anodic CV cycles. As shown in Fig. 7, while
the peak current of the electropolymerization reaction starts to
decrease after the third CV cycle for H2Pc, it increases until the
12th CV cycle for NiPc and it continuously increases for CuPc. Thus
CuPc can form a more electroactive and thicker polymeric film
than the other complexes. When we compared the peak potential
of the electropolymerization waves of the complexes, we can list
the complexes with respect to the ease of oxidation as: H2Pc
(Epa: 0.97 V) > CuPc (Epa: 0.90 V) > NiPc (Epa: 0.88 V). Modification
of the working electrodes on electropolymerization of these com-
plexes is a desired factor for the usage of an active species in differ-
ent electrochemical application fields. It is possible to control all
the parameters of a modified electrode by controlling the potential,
concentration and or CV cycle numbers of the electropolymeriza-
tion reactions [32–36].
without a shift and observation of new bands at ligand to metal
charge transfer (LMCT) and/or metal to ligand charge transfer
(MLCT) regions. The complexes H2Pc and CuPc gave similar
spectral changes to similar complexes reported in the literature
[37–41]. However NiPc gives different spectral changes than those
reported in the literature [42,43]. As shown in Fig. 8, NiPc also
gives Pc based electron transfer processes, but the spectral changes
are different from those recorded for the Pc based reduction reac-
tions. In the neutral state, NiPc gives a Q band at 670 nm with a
shoulder at 623 nm. The shoulder is assigned to the aggregated
NiPc species. When ꢁ0.90 V was applied, the Q band decreases in
intensity and a new sharp band is recorded at 580 nm (Fig. 8a).
These spectral changes are inconsistent with the spectral changes
of a Pc based reduction reaction. However under ꢁ0.90 V applica-
tion, different spectral changes are also observed. During this pro-
cess, a new sharp band is also observed at 932 nm and the band at
623 nm shifts to 637 nm, in addition to the Pc reduction based
spectral changes. These different spectral responses also alter the
color of the neutral and anionic forms of the complex, as shown
in Fig. 8b. During the oxidation reaction at 1.40 V, first of all the
intensity of all the bands decreases and then small bands start to
increase in LMCT regions (at around 470 and 800 nm). Finally all
the bands increase in intensity. These spectral changes support
the electropolymerization process. Due to the electropolymeriza-
tion, the concentration of the monomeric species decreases, which
diminishes the intensity of the bands of the monomeric NiPc. The
electropolymerized film then starts to plug the pores of the Pt
gauze working electrode, which prevents penetrating light and
causes an increase of the band intensities.
3.3. Spectroelectrochemistry
The in situ spectroelectrochemical measurements of MPcs
having a redox inactive Pc core are well characterized from our
previous studies. For this type of complex, general UV–Vis spectral
changes during redox reactions are a decrease of the Q band

532
V. Çakır et al. / Polyhedron 81 (2014) 525–533
Fig. 10. In situ UV–Vis spectral changes of CoPc in DCM/TBAP. (a) Eapp = ꢁ0.50 V. (b) Eapp = ꢁ1.50 V. (c) Eapp = 1.50 V. (d) Chromaticity diagram (each symbol represents the
ꢁ1
ꢁ2
color of the electro-generated species; h: [CoIIPcꢁ2], s:[CoIPcꢁ2
]
4: [CoIPcꢁ3
]
,
: polymer. (Color online.)
The general trend in the spectral changes of H2Pc is different
from those of the MPc complexes. H2Pc gives a characteristic split
Q band at 666 and 702 nm. Due to the aggregation, a band as a
shoulder of the Q band is observed at 640 nm (Fig. 9a). This spec-
tral response is in harmony with the metal free Pc complexes
reported in the literature [44–47]. During the first reduction reac-
tion, the split Q band turns into a sharp single band at 676 nm
(Fig. 9a), which is the characteristic spectral change of the Pc based
reduction of metal free Pc complexes. During the second reduction
reaction, the Q band at 676 nm decreases in intensity without a
shift, which indicates the formation of dianionic H2Pc species
(Fig. 9b). When 0.0 V was applied to the working electrode after
the reduction reactions, approximately the same spectrum of
H2Pc was obtained, which indicates the chemical reversibility of
the reduction reactions. Spectral changes of H2Pc recorded during
the oxidation reaction support electropolymerization of the com-
plex, since while the bands of the monomer immediately decrease
in intensity, new bands of the polymeric species are observed at
460 and 730 nm (Fig. 9c). The colors of the neutral anionic and
polymeric H2Pc are represented in the chromaticity diagram of
the complex (Fig. 9d).
CoPc shows different in situ spectroelectrochemical responses to
the other complexes, due to the redox activity of the CoII center of
the complex. Whilst all the reduction processes of H2Pc, NiPc and
CuPc are Pc based reduction reactions, the first reduction reaction
of CoPc is a metal based electron transfer process. This different
behavior of the complex is well reflected by the in situ spectroelect-
rochemical measurements. While the Q band of NiPc and CuPc
change without a shift, the Q band of CoPc shifts from 674 to
704 nm. At the same time, a new band is recorded at 468 nm
(Fig. 10a). Shifting of the Q band and the observation of a new band
between 450 and 500 nm characterize a metal based electron trans-
fer reaction. The spectral changes represented in Fig. 10a show that
the first reduction reaction of CoPc is a metal based process and is
assigned to the [CoIIPcꢁ2]/[CoIPcꢁ2 1ꢁ
reaction [48–54]. The bluish
]
green color (x = 0.3034 and y = 0.3567) of the complex changes to
light orange (x = 0.343 and y = 0.3711) after the first reduction reac-
tion, as shown in Fig. 10d. Fig. 10b shows the spectral changes
recorded during the second reduction reaction of CoPc. During this
process, while the Q band at 704 nm decreases without a shift, a
new broad band is observed at 550 nm. These spectral changes indi-
cate the reduction of [CoIPcꢁ2 1ꢁ to [CoIPcꢁ3 2ꢁ
] during the R2 redox
]
reaction. An orange color (x = 0.3524 and y = 0.352) is obtained after
the second reduction reaction, as shown in Fig. 10d. During the oxi-
dation reaction, CoPc gives similar spectral changes to H2Pc, NiPc
and CuPc due to the electropolymerization of the complex. During
this process, the band of monomeric CoPc immediately decreases
and then the intensity of all the bands increase due to coating of
the electrode surface with the polymer. Fig. 10c shows the spectral
changes recorded during the oxidation reaction of CoPc. A decrease
of the Q band and the observation of new bands at 530 and 745 nm
are characteristic changes for the Pc oxidation reaction of CoPc dur-
ing the R1 redox reaction. A light orange color is recorded for the
cationic species of CoPc, obtained after the oxidation reaction
(x = 0.3484 and y = 0.3506).
4. Conclusion
In this study, the syntheses, spectral and electrochemical
properties of soluble peripheral substituted metal-free, nickel(II),

V. Çakır et al. / Polyhedron 81 (2014) 525–533
533
[13] F. Demir, A. Erdog˘mußs, A. Koca, J. Electroanal. Chem. 703 (2013) 117.
cobalt(II) and copper(II) phthalocyanines (4–7) are discussed. The
target symmetrical phthalocyanines were separated by column
chromatography, using aluminium oxide. All the compounds were
characterized by standard methods (UV–Vis, IR, 1H NMR, 13C NMR
and MS spectroscopic data). Electrochemical responses of the com-
plexes support the proposed structures of the complexes. The pres-
ence of alkyl amino groups on the substituents of the complexes
causes the coating of the complexes on the working electrode with
an oxidative electropolymerization process. Modification of the
working electrode with thin films upon electropolymerization
increases the usage potential of the complexes in various electro-
chemical devices, such as electrocatalytic, electrochromic and
electrosensing applications. The more distinctive color changes
during the redox reactions of CoPc most probably result from the
redox active character of the metal center. Thus metal based redox
reactions alter the spectrum of the complex more than those of the
Pc based electron transfer reactions. The distinct color changes of
CoPc illustrate its possible usage as an electrochromic material.
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Acknowledgements
This study was supported by the Research Fund of Karadeniz
Technical University, (Project No. 8660) and the Scientific and
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