Synthesis, characterization, electrochemical and spectroelectrochemical properties of metal-free and metallophthalocyanines bearing electropolymerizable dimethylamine groups

Article abstract of DOI:10.1016/j.dyepig.2013.03.021

The synthesis and characterization of novel peripherally-tetra substituted metal-free 4 and metallophthalocyanines 5-7 are described for the first time in this study. All the new compounds are characterized by a combination of IR, ¹H and ¹³C NMR, mass and UV-vis spectroscopy techniques. Electrochemical and spectroelectrochemical properties of metal-free, nickel(II), cobalt(II) and copper(II) phthalocyanines were investigated by using cyclic voltammetry and square wave voltammetry techniques. While all complexes give common reduction processes, they electropolymerized on the working electrode. Applied potentials and type of the metal center of the complexes affect the electropolymerization mechanism. Spectroelectrochemical and electrocolorimetric measurements exhibit that electrogenerated anionic species of the complexes have distinct color differences which are desire factors for electrochromic application of the complexes.

Full text of DOI:10.1016/j.dyepig.2013.03.021

Dyes and Pigments 98 (2013) 414e421
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, characterization, electrochemical and
spectroelectrochemical properties of metal-free and
metallophthalocyanines bearing electropolymerizable
dimethylamine groups
a
b
a
,
b
,
a
*
**
ꢀ
Volkan Çakır , Faruk Demir , Zekeriya Bıyıklıoglu , Atıf Koca
, Halit Kantekin
a Department of Chemistry, Faculty of Science, Karadeniz Technical University, 61080 Trabzon, Turkey
b Department of Chemical Engineering, Engineering Faculty, Marmara University, 34722 Göztepe, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and characterization of novel peripherally-tetra substituted metal-free 4 and metal-
lophthalocyanines 5e7 are described for the first time in this study. All the new compounds are char-
acterized by a combination of IR, 1H and 13C NMR, mass and UVevis spectroscopy techniques.
Electrochemical and spectroelectrochemical properties of metal-free, nickel(II), cobalt(II) and copper(II)
phthalocyanines were investigated by using cyclic voltammetry and square wave voltammetry tech-
niques. While all complexes give common reduction processes, they electropolymerized on the working
electrode. Applied potentials and type of the metal center of the complexes affect the electro-
polymerization mechanism. Spectroelectrochemical and electrocolorimetric measurements exhibit that
electrogenerated anionic species of the complexes have distinct color differences which are desire factors
for electrochromic application of the complexes.
Received 12 February 2013
Received in revised form
1 March 2013
Accepted 25 March 2013
Available online 9 April 2013
Keywords:
Phthalocyanine
Cobalt
Synthesis
Ó 2013 Elsevier Ltd. All rights reserved.
Electropolymerization
Electrochemistry
Spectroelectrochemistry
1. Introduction
center and types, number and position of substituents. MPcs have
proven to be functional species as electrocatalyst, sensors, and
Metal-free and metallophthalocyanines have found a great
number of important technological applications for example gas
sensors [1], non-linear optical devices [2], electrochromism [3],
photochromic materials [4,5], catalysis [6], liquid crystal [7],
photodynamic therapy and nanotechnology [8e10]. Metal-free and
metallophthalocyanines don’t usually soluble in common organic
solvents and their insolubility causes difficulties for many appli-
cations [11]. When functional groups such as crown ethers, alkyl,
alkoxy, alkylthio, tertiary butyl groups and amide groups bound in
the peripheral benzene rings of the Pc structure, solubility of
phthalocyanines can exceedingly improve in protic or non-protic
solvents [12e20].
electrochromic devices because of their rich redox behavior. It is
well documented that functional materials should be coated on a
substrate for their practical applications [25e27]. Thus in this pa-
per, we have aimed to synthesize a new class of phthalocyanines
bearing electropolimerizable dimethylamine groups on the sub-
stituents and to coat these newly synthesized MPcs on the elec-
trodes with electropolymerization to open a way for their possible
applications. For this purpose, we have investigated electro-
chemical and spectroelectrochemical properties and also tried to
electropolymerize and investigate the electropolymerization
mechanisms of the complexes with voltammetric and in-situ
spectroelectrochemical measurements.
Metallophthalocyanines (MPcs) are profoundly studied due to
their interesting electrochemical properties [21e24]. Their elec-
trochemical properties are easily arranged by changing the metal
2. Experimental
2.1. Materials
* Corresponding author. Tel.: þ90 462 377 36 64; fax: þ90 462 325 31 96.
4-nitrophthalonitrile (2) was prepared according to the litera-
ture [28]. 3-dimethylaminophenol and 2-chloroethanol were pur-
chased from Aldrich. All reagents and solvents were of reagent
** Corresponding author. Tel.: þ90 216 348 02 92; fax: þ90 216 348 02 93.
ꢀ
E-mail
addresses:
zekeriya_61@yahoo.com
(Z.
Bıyıklıoglu),
akoca@
marmara.edu.tr (A. Koca).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.03.021

V. Çakır et al. / Dyes and Pigments 98 (2013) 414e421
415
grade quality and were obtained from commercial suppliers. All
solvents were dried and purified as described by Perrin and
Armarego [29].
(CDCl3), (
4.09 (t, 2H, CH2eO), 3.97 (m, 2H, CH2eO), 2.95 (s, 6H, CH3), 2.35
(bs, 1H, OH). 13C NMR (CDCl3), (
:ppm): 159.57, 151.79, 129.65,
d:ppm): 7.16 (m, 1H, AreH), 6.41e6.32 (m, 3H, AreH),
d
106.005, 101.97, 99.64, 68.88, 61.34, 40.51. MS (ESI), (m/z): 182
2.2. Equipment
[M þ H]þ.
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 200 MHz spectrometer in
2.5.2. Synthesis of 4-{2-[3-(dimethylamino)phenoxy]ethoxy}
phthalonitrile (3)
4-Nitrophthalonitrile (1.24 g, 7.20 ꢂ 10ꢁ3 mol) was dissolved in
anhydrous DMF (0.015 L) under nitrogen and 2-[3-(dimethylamino)
phenoxy]ethanol (1) (1.3 g, 7.2 ꢂ 10ꢁ3 mol) was added. After stir-
ring for 10 min, finely ground anhydrous K2CO3 (4 g,
28.8 ꢂ 10ꢁ3 mol) was added in portions over 2 h with stirring. The
reaction mixture was stirred at 50 ꢀC for 96 h under nitrogen. Then
water (0.1 L) was added and the aqueous phase was extracted with
chloroform (3 ꢂ 0.050 L). The combined extracts were treated with
water and dried over anhydrous MgSO4 and then filtered. Solvent
was evaporated and the product was crystallized from ethanol.
CDCl3, and chemical shifts were reported (d) relative to Me4Si as
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 MALDI matrix
using nitrogen laser accumulating 50 laser shots using Bruker
Microflex LT MALDI-TOF mass spectrometer. Optical spectra in the
UVevis region were recorded with a Perkin Elmer Lambda 25
spectrophotometer. Melting points were measured on an electro-
thermal apparatus and are uncorrected.
Yield: 1.1 g (50%), mp: 93e94 ꢀC. IR (KBr Tablet), /cmꢁ1: 3074 (Are
n
2.3. Electrochemical measurements
H), 2926e2804 (Alif. CeH), 2232 (C^N), 1614, 1597, 1573, 1503,
1448, 1412, 1375, 1359, 1306, 1246, 1178, 1151, 1099, 1080, 1000, 968,
All electrochemical measurements were carried out with Gamry
Reference 600 potentiostat/galvanostat utilizing a three-electrode
configuration at 25 ꢀC. The working electrode was a Pt disc with a
surface area of 0.071 cm2. A Pt wire was served as the counter
electrode and saturated calomel electrode (SCE) was employed as
the reference electrode and separated from the bulk of the solution
by a double bridge. Electrochemical grade TBAP in extra pure DCM
was employed as the supporting electrolyte at a concentration of
893, 869, 842, 826, 764, 689, 524. 1H NMR (CDCl3), (
d:ppm): 7.73 (d,
1H, AreH), 7.34 (s, 1H, AreH), 7.20e7.12 (m, 2H, AreH), 6.42 (d, 1H,
AreH), 6.26 (s, 2H, AreH), 4.38 (m, 4H, CH2eO), 2.93 (s, 6H, CH3).
13C NMR (CDCl3), (
d:ppm): 162.10, 159.47, 152.23, 135.50, 130.15,
120.06, 119.87, 117.56, 116.02, 115.58, 107.69, 106.61, 101.76, 99.83,
68.07, 66.00, 40.80. MS (ESI), (m/z): 308 [M þ H]þ.
2.5.3. Synthesis of metal-free phthalocyanine (4)
0.10 mol dmꢁ3
.
A mixture of4-{2-[3-(dimethylamino)phenoxy]ethoxy}phtha-
lonitrile (3) (0.40 g, 1.3 ꢂ 10ꢁ3 mol) and 5 drops of 1.8-diazabicyclo
[5.4.0]undec-7-ene (DBU) in 0.004 L of dry n-pentanol was heated
and stirred at 160 ꢀC for 12 h under N2. After cooling to room
temperature, the green suspension was precipitated with ethanol
and then dried in vacuo. Finally, pure metal-free phthalocyanine
was obtained by column chromatography which is placed
aluminium oxide using CHCl3:CH3OH (100:1.5) as solvent system.
Yield: 0.17 g (43%). IR (KBr tablet) nmax/cmꢁ1: 3289 (NeH), 3073
(AreH), 2922e2869 (Aliph. CeH), 1610, 1572, 1500, 1481, 1447,
1345, 1233, 1151, 1063, 999, 951, 820, 745, 684. 1H NMR. (CDCl3),
2.4. In-situ spectroelectrochemical and in-situ electrocolorimetric
measurements
An OceanOptics QE65000 diode array spectrophotometer was
used for UVevis absorption spectra and chromaticity diagram
measurements. In-situ spectroelectrochemical measurements were
carried out by utilizing a three-electrode configuration of thin-layer
quartz thin-layer spectroelectrochemical cell consisting a Pt tulle
working electrode, a Pt wire counter electrode, and a SCE reference
electrode. In-situ electrocolorimetric measurements, under poten-
tiostatic control, were obtained using an OceanOptics QE65000
diode array spectrophotometer at color measurement mode by
utilizing a three-electrode configuration of thin-layer quartz spec-
troelectrochemical cell.
(d:ppm): 7.30e7.21 (m, 12H, AreH), 6.51e6.44 (m, 16H, AreH), 4.23
(m, 16H, CH2eO), 2.96 (s, 24H, eCH3), ꢁ6,51 (s, 2H, NeH). 13C NMR.
(CDCl3), (d:ppm): 160.21, 152.31, 145.53, 136.10, 131.31, 130.12,
127.88, 122.68, 122.00, 119.48, 117.21, 106.31, 102.45, 100.08, 66.44,
63.15, 40.93. UVevis (chloroform): lmax, nm (log ε): 337 (4.92), 608
(4.55), 643 (4.71), 667 (4.93), 704 (4.96). MS (ESI), (m/z): 1232
[M þ H]þ.
2.5. Synthesis
2.5.1. Synthesis of 2-[3-(dimethylamino)phenoxy]ethanol (1)
2.5.4. General procedures for metallophthalocyanine derivatives
(5e7)
3-dimethylaminophenol (5.00 g, 30.5 ꢂ 10ꢁ3 mol) was added
to ethanol (0.041 L) and nitrogen gas was bubbled through this
mixture for 10 min. NaOH (1.82 g, 45.6 ꢂ 10ꢁ3 mol) was then
added and dissolved by stirring at 50 ꢀC for 1.5 h. 2-chloroethanol
(3.67 g, 45.6 ꢂ 10ꢁ3 mol) in 0.0028 L ethanol was added dropwise
to this solution with stirring for 30 min. The reaction mixture was
refluxed under nitrogen for 20 h. After the mixture was cooled, the
solvent was removed under vacuum, and resulting crude product
was dissolved in chloroform (0.1 L). The mixture was washed with
%10 NaOH and with water. The organic phase was dried over
MgSO4, filtered and rotary evaporated. The obtained oily crude
product was purified by using column chromatography with basic
alumina as column material and CHCl3/MeOH (100:4) solvent
A mixture of 4-{2-[3-(dimethylamino)phenoxy]ethoxy}phtha-
lonitrile (3) (0.30 g, 0.97 ꢂ 10ꢁ3 mol), 4 drops of 1.8-diazabicyclo
[5.4.0]undec-7-ene (DBU) in 0.003 L of n-pentanol and anhydrous
metal salts [NiCl2 (0.063 g), CoCl2 (0.063 g), CuCl2 (0.065 g)] were
heated and stirred at 160 ꢀC for 12 h under N2. After the
reaction mixture was cooled, the product was precipitated by
adding ethanol. The precipitated green solid product was filtered
off, and then dried in vacuo over P2O5. Finally, pure metal-
lophthalocyanines were obtained by column chromatography
which is placed aluminium oxide using CHCl3:CH3OH (100:2) as
solvent system.
system. Yield: 3.89 g (59%). IR (KBr Tablet),
n
/cmꢁ1: 3390 (OeH),
2.5.5. Nickel(II) phthalocyanine (5)
3087 (AreH), 2926e2874 (Alif. CeH), 1614, 1574, 1505, 1447, 1353,
Yield: 0.203 g (65%). IR (KBr tablet) nmax/cmꢁ1: 3076 (AreH),
2922e2875 (Aliph. CeH), 1610, 1574, 1500, 1448, 1351, 1236, 1126,
1302, 1240, 1171, 1152, 1058, 998, 924, 896, 826, 754, 687. 1H NMR

416
V. Çakır et al. / Dyes and Pigments 98 (2013) 414e421
2.5.6. Cobalt(II) phthalocyanine (6)
N
Yield: 0.160 g (51%). IR (KBr tablet) vmax/cmꢁ1: 3068 (AreH),
2922e2870 (Aliph. CeH), 1610, 1573, 1500, 1480, 1447, 1349, 1280,
1233, 1127, 1095, 1065, 998, 822, 751, 685. UVevis (chloroform):
lmax, nm (log ε): 616 (4.82), 672 (4.96). MS (ESI), (m/z): 1168 [Me
C6H4eN(CH3)2]þ.
O2N
CN
CN
i
OH
OH
N
+
OH
1
O
N
Cl
2
ii
CN
CN
2.5.7. Copper(II) phthalocyanine (7)
Yield: 0.112 g (36%). IR (KBr tablet) nmax/cmꢁ1: 3079 (AreH),
2923e2857 (Aliph. CeH), 1609, 1575, 1502, 1481, 1447, 1400, 1343,
O
O
3
1235, 1122, 1095, 1065, 998, 824, 746. UVevis (chloroform): lmax
,
nm (log ε): 336 (5.04), 618 (4.86), 679 (5.01). MALDI-TOF-MS m/z:
1292 [M]þ.
iii
3. Results and discussion
N
N
3.1. Synthesis and characterization
O
O
The synthesis of the metal-free and metallophthalocyanines
containing {2-[3-(dimethylamino)phenoxy]ethoxy} groups are
shown in Figs. 1 and 2. 4-{2-[3-(dimethylamino)phenoxy]ethoxy}
phthalonitrile 3 was synthesized by K2CO3 base catalyzed nucleo-
philic aromatic nitro displacement of 2-[3-(dimethylamino)phe-
noxy]ethanol 1 with 4-nitrophthalonitrile 2 in DMF. The novel
metal-free, nickel(II), cobalt(II) and copper(II) phthalocyanines
were prepared by the templated cyclotetramerization reaction
O
O
N
N
HN
N
N
N
NH
N
O
O
O
from 4-{2-[3-(dimethylamino)phenoxy]ethoxy}phthalonitrile
3
4
O
and metal salts (NiCl2, CoCl2, CuCl2) in n-pentanol and DBU at
160 ꢀC. Metal-free and metallophthalocyanines were purified by
column chromatography. The structures of the target compounds
were confirmed using UVevis, IR, 1H NMR, 13C NMR, MS spectro-
scopic data. The analyses are consistent with the predicted struc-
tures as shown in the experimental section.
N
N
Fig. 1. The synthetic route of the metal-free phthalocyanine. Reagents and conditions:
(i) EtOH, NaOH, 90 ꢀC; (ii) dry DMF, K2CO3, 50 ꢀC, 96 h; (ii) n-pentanol, DBU, 160 ꢀC.
In the IR spectra, the formation of compound 1 was clearly
confirmed by the disappearance of the OH band and appearance of
1096, 1069, 999, 964, 821, 750, 685. 1H NMR. (CDCl3), (
7.28e7.20 (m, 12H, AreH), 6.50e6.40 (m, 16H, AreH), 4.34e4.23
(m, 16H, CH2eO), 2.93 (s, 24H, eCH3). 13C NMR. (CDCl3), (
:ppm):
161.40, 151.22, 146.33, 135.51, 132.30, 131.60, 128.43, 122.62, 122.04,
118.56, 117.34, 107.40, 101.46, 100.18, 67.23, 64.25, 40.84. UVevis
(chloroform): lmax, nm (log ε): 326 (4.86), 617 (4.73), 672 (4.93).
MALDI-TOF-MS m/z: 1288 [M]þ.
d:ppm):
the eCH2eOH, aliph. CeH bands at 3390 and 2926-2874 cmꢁ1
,
respectively. In the 1H NMR spectrum of 1, OH group of 3-
d
dimethylaminophenol disappeared as expected and a new signal
appeared at
d
¼ 2.35 ppm belonging to OH group. 1H NMR spectrum
of 1 showed new signals at
d
¼ 4.09 (CH2eO), 3.97 (CH2eO), 2.95
(CH3) ppm belonging to aliphatic protons. 13C NMR spectrum of 1
indicated the aliphatic carbon atoms at
d
¼ 99.64, 68.88, 61.34,
N
N
O
O
O
O
N
N
N
N
N
CN
iv
N
M
N
N
N
O
CN
O
3
O
O
O
O
N
N
Compound
M
5
6
7
Co Cu
Ni
Fig. 2. The synthetic route of the nickel, cobalt and copper phthalocyanines. Reagents and conditions: (iv) n-pentanol, DBU, 160 ꢀC, NiCl2, CoCl2, CuCl2.

V. Çakır et al. / Dyes and Pigments 98 (2013) 414e421
417
Fig. 3. The MALDI-TOF MS spectrum of nickel(II) phthalocyanine 5.
40.51 ppm. The ESI-mass spectrum of compound 1 shows a peak at
m/z ¼ 182 [M þ H]þ.
attributed to the NeH resonances [30]. The IR spectrum of the
nickel(II), cobalt(II) and copper(II) phthalocyanines 5e7 clearly
indicated the cyclotetramerization of the phthalonitrile derivative 3
with the disappearance of the C^N peak at 2232 cmꢁ1. The 1H NMR
spectrum of nickel(II) phthalocyanine 5 indicated the aromatic
protons at 7.28e7.20, 6.50e6.40 ppm and aliphatic protons at
4.34e4.23, 2.93 ppm. The 1H NMR spectrum of cobalt and copper
phthalocyanine 6, 7 could not be taken due to the paramagnetic
cobalt(II) and copper(II) centers [31]. The mass spectra of tetra-
substituted phthalocyanines 4, 5, 6 and 7 confirmed the proposed
structure, with the molecular ion being easily identified at 1232
[M þ H]þ, 1288 [M]þ (Fig. 3), 1168 [MeC6H4eN(CH3)2]þ, 1292 [M]þ
(Fig. 4), respectively.
According to the IR spectral data, the observation of a new
vibrational peak at 2232 cmꢁ1 clearly proved the existence of nitrile
groups in the structure of compound 3. In the 1H NMR spectra of
compound 3 the aromatic protons appeared at 7.73 (d), 7.34 sm),
7.20e7.12 (m), 6.42 (d), 6.26 (s) ppm and aliphatic protons appeared
at 4.38 (m), 2.93 (s) ppm. The 13C NMR spectra of compound 3
indicated carbon atoms between at 162.10e40.80 ppm. In the 13C
NMR spectrum of 3, the new peaks at 116.02 and 115.58 ppm,
belonging to nitrile carbons, provided evidence for the substitution.
In the mass spectra of compound 3, the presence of molecular ion
peak at m/z ¼ 308 [M þ H]þ confirmed the proposed structures.
In the IR spectrum of metal-free phthalocyanine 4, the peak at
3289 cmꢁ1 is characteristic peak for the metal-free phthalocyanine
NeH stretching vibration band. The 1H NMR spectrum of metal-
free phthalocyanine exhibited the typical shielding of inner core
The metal-free and metallophthalocyanines display typical
electronic spectra with two strong absorption regions, one of them
in the UV region at about 300e350 nm (B band) and the other one
in the visible region at 600e700 nm (Q band). The electronic ab-
sorption spectra of the metal-free and metallophthalocyanines 4, 5,
protons as a broad signal at around
d
¼ ꢁ6.51 ppm, which could be
Fig. 4. The MALDI-TOF MS spectrum of copper(II) phthalocyanine 7.

418
V. Çakır et al. / Dyes and Pigments 98 (2013) 414e421
concentration, and scan rate affected the peak characters which
4
5
6
7
supported the aggregation behaviors of the complexes. During the
oxidation processes, all complexes are electropolymerized on the
working electrode. Applied potential ranges and metal center
of the complexes affect the polymerization mechanism. Electro-
polymerization processes are desired factors for preparing com-
posite electrodes for the possible usage of the complexes in different
areas. Since for practical applications, a functional species should be
coated on a substrate. It is well documented that electrode modifi-
cation with electropolymerization process is of the most preferred
method for the electrode coating processes. It is a very easy way to
control the film thickness, film type, and morphology on an elec-
trode [37e39].
1,4
1,2
1
0,8
0,6
0,4
0,2
0
300
400
500
600
700
800
H2Pc, CuPc and NiPc complexes illustrate very similar electro-
chemical responses, thus the CV and SWV responses of CuPc are
represented in Fig. 6. CuPc displays two reduction couples (R1
at ꢁ0.84 V and R2 at ꢁ1.12 V). SWVs clearly show these redox
Wavelength (nm)
Fig. 5. UVevis spectrum of 4, 5, 6 and 7 in chloroform.
processes (Fig. 6b).
respectively at 0.10 V sꢁ1 scan rate.
ples are bigger than that of reversible ferrocene, whose
D
Ep’s of these couples are 100 and 90 mV
Ep values of these redox cou-
Ep is
6 and 7, in chloroform at room temperature are shown in Fig. 5. In
the UVevis spectra of metal-free derivative 4 (in CHCl3), split Q
bands appears at 704, 667, 643, 608 nm, while the B band is
recorded at 337 nm. UVevis spectra of metallophthalocyanines 5e
7 (in CHCl3) exhibit intense single Q band absorption of
transitions at around 672e679 nm and the B bands in the UV region
at around 326e336 nm.
D
D
70 mV at 0.10 V sꢁ1 scan rate. Thus these couples have electro-
chemical quasi-reversible character. Moreover reversibility of these
couples can be concluded with respect to symmetry and peak
current ratios of the waves recorded during the forward and
reverse SWV scans (Fig. 6b) [40]. During the anodic scans, CuPc is
electropolymerized on the working electrode. Fig. 7a illustrates the
repetitive CV scans with in the whole potential windows of DCM/
TBAP (between ꢁ1.70 and þ1.60 V). During the first anodic scan, an
anodic wave and its reverse couple are recorded at 0.78 and 0.64 V
respectively. During the continuous CV scans, anodic wave in-
creases in current intensity with positive potential shift up to 1.02 V
until the 10. CV scan. However the cathodic couple increases in
current intensity with negative shift from 0.64 V to 0.57 V until the
5. scan. A new wave is recorded at 0.23 V between the 5. and 10.
scans. After this point, these couples start to decrease in current
intensity with the same potential shifts. These voltammetric be-
haviors indicate the electropolymerization of the complex on the
working electrode. Polymerization process of the complex changes
when only anodic potentials are scanned (from 0.0 V to 1.70 V). As
shown in Fig. 7b, an anodic wave is recorded at 0.77 V and its
reverse couple is recorded at 0.64 V during the first CV cycle. The
anodic wave increases during the second CV cycle, however it
immediately shifts to 1.00 V during the third CV cycle and increases
in current intensity until the 5. cycle. After this point, it decreases in
p /
p*
3.2. Voltammetric measurements
To propose possible application of the complexes in the elec-
trochemical technologies, redox behaviors of the complexes were
performed in DCM/TBAP electrolyte system on a Pt working elec-
trode. Results of the voltammetric analysis are tabulated on Table 1.
As shown in Table 1, E1/2 and DE1/2 values of the complexes are in
agreements with the similar complexes in the literature [32e36].
While H2Pc, CuPc and NiPc complexes generally give two common
ring-based reduction processes, CoPc gives a metal-based and a ring
based reduction processes during the cathodic potential scans.
Common similarities of the complexes are the aggregation of the
complexes. Due to the aggregation of the complexes, the first
reduction couples are complicated with a chemical reaction, ag-
gregationedisaggregation equilibrium. Due to the aggregation, the
peak current of the first couples of the complexes are usually smaller
than those of the second reduction couples. All redox couples are far
from the reversible character due to the aggregation. Altering the
Table 1
Voltammetric data of the complexes. All voltammetric data were given versus SCE.
Complex
Ring oxidations
M
III/MII
MII/MI
Ring reductions
dDE1/2
H2Pc
aE1/2
e
0.81e (0.59)f
e
e
e
e
e
e
e
e
e
e
e
ꢁ0.83
89
0.95
ꢁ0.97
110
0.92
ꢁ0.92
100
0.96
ꢁ1.44
83
ꢁ1.13
86
0.96
ꢁ1.26
96
0.97
ꢁ1.22
110
0.91
e
e
e
e
e
e
e
e
e
e
e
e
e
1.17
bDEp (mV)
cIp,a/Ip,c
aE1/2
e
e
e
e
e
NiPc
CuPc
CoPc
e
0.75e (0.65)f
e
1.00
0.98
0.77
bDEp (mV)
cIp,a/Ip,c
aE1/2
e
e
e
e
e
e
e
0.78e (0.64)f
e
bDEp (mV)
cIp,a/Ip,c
aE1/2
e
e
e
e
e
e
1.44
e
0.87e (0.60)f
0.41
64
0.93
ꢁ0.20
95
0.73
bDEp (mV)
cIp,a/Ip,c
e
e
e
e
0.96
e
a
E1/2 values ((Epa þ Epc)/2) were given versus SCE and Fc/Fcþ (in parenthesis) at 0.100 V sꢁ1 scan rate.
b
c
d
e
f
DEp ¼ Epa ꢁ Epc
.
Ip,a/Ip,c for reduction, Ip,c/Ip,a for oxidation processes.
D
E1/2 ¼ E1/2 (first oxidation)- E1/2 (first reduction).
Epa of the polymerization process recorded during the first CV cycle.
Epc of the polymerization process recorded during the first CV cycle. tw: This work.

V. Çakır et al. / Dyes and Pigments 98 (2013) 414e421
419
responses of CoPc are also performed and compared with those of
CuPc. Fig. 8 illustrates the CV and SWV responses of CoPc in DCM/
TBAP electrolyte system. CoPc gives two common reduction pro-
cesses, first one is a metal based reduction at ꢁ0.20 V and the
second one is a Pc ring based reduction at ꢁ1.30 V during the
cathodic scan. CoPc is also electropolymerized on the working
electrode during the anodic potential scans. During the first CV
measurement, it gives an anodic peak at 0.87 V and its reverse
cathodic couple at 0.60 V and these waves increase in current in-
tensity until the 4. CV cycle. Moreover a small anodic wave is also
recorded at 1.45 V during the first CV cycle and it disappeared just
after the second CV cycle. In addition to the previous wave, an
anodic wave is recorded at 0.50 V during the second CV cycle, and
then it shifts to the positive potentials and mixes with the wave at
0.87 V during the consecutive CV cycles. It is clearly shown in Figs. 7
and 8 that CV responses of CoPc is completely different than those
of CuPc, which indicates that changing the metal center of MPcs
alters the electropolymerization process.
3.3. Spectroelectrochemistry
In situ spectroelectrochemical studies were employed to
perform assignments of the electron transfer reactions recorded
with CV and SWV measurements. It is well documented that H2Pc,
CuPc and NiPc complexes have redox inactive metal centers, thus
these complexes show spectral changes assigned to the electron
transfer of Pc rings during the reduction reactions. Spectral changes
of these types of complexes are investigated in detail in our pre-
vious papers [41e43]. Spectral changes, decreasing the Q bands in
intensity without shift and observation of new bands in the LMCT
regions, are characteristic changes for the MPcs having redox
inactive metal centers. During the oxidation reactions, all bands
of these complexes decreased in intensity, which support the
electropolymerization of the complexes. Because concentration of
MPcs decreases due to the polymerization, thus the bands decrease
in intensity. CoPc has redox active metal center thus its spectral
Fig. 6. (a) CVs of CuPc recorded at cathodic potentials at various scan rates on a Pt
working electrode in DCM/TBAP and (b) SWV of CuPc recorded with SWV parameters:
Step size ¼ 5 mV; pulse size ¼ 100 mV; frequency ¼ 25 Hz.
current intensity until the 20. cycle. In addition to the changes on
the anodic waves, the cathodic wave increases until the 5. cycle and
decreases until the 20. cycle. As we compare the CV responses given
in Fig. 7a with Fig. 7b, it is clearly shown that changing the potential
range of CV cycles alters the polymerization process considerable.
To analyze the effects of redox active metal center to the elec-
tropolymerization and reduction processes of MPcs, CV and SWV
Fig. 7. (a) Repetetive CVs of CuPc recorded with in the whole potential windows of
DCM/TBAP electrolyte system at 0.100 V sꢁ1 scan rate on a Pt working electrode (b)
Repetetive CVs of CuPc recorded at anodic potential windows of DCM/TBAP electrolyte
system at 0.100 V sꢁ1 scan rate on a Pt working electrode.
Fig. 8. (a) CV and SWV of CoPc recorded at 0.100 V sꢁ1 scan rate on a Pt working
electrode in DCM/TBAP (b) repetetive CVs of CoPc recorded with in the whole potential
windows of DCM/TBAP electrolyte system at 0.100 V sꢁ1 scan rate on a Pt working
electrode.

420
V. Çakır et al. / Dyes and Pigments 98 (2013) 414e421
Fig. 9. In-situ UVevis spectral changes of CoPc in DCM/TBAP. a) Eapp ¼ ꢁ0.50 V b) Eapp ¼ ¼ ꢁ1.50 V b) Eapp ¼ ¼ 1.50 V d) chromaticity diagram (each symbol represents the color of
O
ꢁ1
electro-generated species; ,: [CoIIPcꢁ2], B: [CoIPcꢁ2
]
: [CoIPcꢁ3 ꢁ2. (For interpretation of the references to color in this figure legend, the reader is referred to the web
]
version of this article.)
changes are different than those of Pcs having redox inactive metal
center. Fig. 9 represents in situ UVevis spectral changes and in situ
recorded chromaticity diagram of CoPc in DCM/TBAP during the
electron transfer processes. Shifting of the Q band and observation
of a new band at 450 nm during the first reduction reaction in-
The target symmetrical phthalocyanines were separated by column
chromatography which is placed aluminium oxide and character-
ized by a combination of IR, 1H NMR, 13C NMR, UVevis and MS
spectral data. Electrochemical and spectroelectrochemical mea-
surement indicates that substitution of the complexes with dime-
thylamine groups supply electropolymerization of the complexes
on the working electrode. Coating of the complexes on a substrate
(e.g an electrode) with electropolymerization is a desired property
for preparation of composite electrode, which has potentials for the
usage in different electrochemical technologies such as, electro-
catalytic, electrochromic and electrosensing applications. Since a
functional material should be coated on a substrate with tech-
niques (e.g. electropolymerization), with which film thickness,
morphology and conductivity could be controlled easily.
dicates reduction of [CoIIPcꢁ2] to [CoIPcꢁ2 1ꢁ
(Fig. 9a) [44e47]. Well
]
defined isosbestic points at 382, 575, and 700 nm and a color
changes from bluish green (x ¼ 0.270 and y ¼ 0.351) to light green
(x ¼ 0.3368 and y ¼ 0.4108) are recorded during the first reduction
reaction (Fig. 9d). Spectral changes given in Fig. 9b indicate the
ring-based reduction character of the second reduction reaction.
Since while the Q band at 706 nm and its shoulder at 674 nm
decrease, a new broad band is recorded at 537 nm. All bands de-
creases in intensity due to the electropolymerization of the com-
plexes during the oxidation reaction at 1.10 V potential application
(Fig. 9c from red to pink spectrum). However, when more positive
potential is applied, absorption intensity of the MLCT (ligand to
metal charge transfer) regions (around 600 nm and 800 nm) in-
creases, while the intensity of the Q band and its shoulder decreases
in intensity (Fig. 9c from pink to blue spectrum). These spectral
changes indicate a ring based oxidation process of the complex.
Acknowledgments
We thank to TUBITAK and TUBA for their financial support
(Project No: 111T963 and 2010-01-02-GEP03).
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