Synthesis, electrochemical, in-situ spectroelectrochemical and in-situ electrocolorimetric characterization of non-peripheral tetrasubstituted metal-free and metallophthalocyanines

Article abstract of DOI:10.1016/j.dyepig.2010.09.002

The synthesis of new metal-free, nickel, zinc, cobalt and copper phthalocyanines with four 6-oxyquinoline groups on the non-peripheral position were prepared by cyclotetramerization of a novel 3-(quinolin-6-yloxy) phthalonitrile. All new compounds were ch

Full text of DOI:10.1016/j.dyepig.2010.09.002

Dyes and Pigments 89 (2011) 49e55
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, electrochemical, in-situ spectroelectrochemical and in-situ
electrocolorimetric characterization of non-peripheral tetrasubstituted
metal-free and metallophthalocyanines
a
b
c
b,
*
ꢀ
Zekeriya Bıyıklıoglu , Volkan Çakır , Atıf Koca , Halit Kantekin
a Macka Vocational School, Karadeniz Technical University, 61750, Macka, Trabzon, Turkey
b Department of Chemistry, Faculty of Arts & Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey
c
_
Department of Chemical Engineering, Faculty of Engineering, Marmara University, Göztepe 34722, 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 of new metal-free, nickel, zinc, cobalt and copper phthalocyanines with four 6-
oxyquinoline groups on the non-peripheral position were prepared by cyclotetramerization of a novel 3-
Received 20 June 2010
Received in revised form
5 September 2010
Accepted 8 September 2010
Available online 17 September 2010
(quinolin-6-yloxy)phthalonitrile. All new compounds were characterized by the ways of IR, 1H NMR, 13
C
NMR and MS spectral data, all of which were compatible with the proposed structures. Electrochemical
properties of metal-free, Ni(II) and Zn(II) phthalocyanines were investigated by using cyclic voltammetry
and differential pulse voltammetry techniques. The metal-free phthalocyanine exhibits two reversible Pc
ring-based one-electron reduction couples. The Ni(II) and Zn(II) phthalocyanines give very similar vol-
tammetric responses with slightly potential shift due to the different metal center.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
6-Hydroxyquinoline
Phthalocyanine
Synthesis
Non-peripheral
Cyclic voltammetry
Differantial pulse voltammetry
1. Introduction
The range of solubility in phthalocyanines becomes very
important for these applications, since many phthalocyanines are
Metallophthalocyanines (MPcs) have a attracted a lot of atten-
tion for many years since their discovery in the early 1900s. Their
remarkable properties that include flexibility, chemical and thermal
stabilities, semiconductivity and photoconductivity [1] have been of
great interest in research. Phthalocyanines, which are of enormous
technological importance for the manufacture of green and blue
pigments [2] and are of considerable interest owing to their fasci-
nating electronic and optical properties [3], don’t occur in nature [4].
In many fields, phthalocyanines have been remarkably used because
of their magnificently versatile properties to illustrate photody-
namic reagents for cancer therapy [5,6], and other medical appli-
cations [7], for optical read-write discs [8], in chemical sensors, in
photocopying machines [9,10], LangmuireBlodgett films [11], solar
cells, electrochromism, high energy batteries [12], fibrous assem-
blies [13], coloring for plastics and metal surfaces and dyestuffs for
clothing [8].
poorly soluble in organic solvents and water. The solubility of
phthalocyanins can be enhanced by adding different kinds of
substituents such as bulky or long chain alkyl, alkylthio or alkoxy
groups at the periphery axial positions of the phthalocyanine ring
[14e17]. The most extensively investigated soluble substituted
phthalocyanines are the tetra- and octasubstituted derivatives and
tetrasubstituted ones exhibit usually a higher solubility [18,19].
Microwaves have been previously used for the synthesis of
phthalocyanines and include a wider range of references on the
topic [20e27]. In this paper, we describe the synthesis and char-
acterization of metal-free and metallophthalocyanines (MPc; M=Zn
(II), Ni(II) and Co(II)) substituted with 3-(quinolin-6-yloxy) groups
by microwave irradiation.
The phthalocyanine ring often can be reduced to the mono-, di-,
tri-, and tetraanionic states or oxidized to the mono- and dicationic
states. In addition, Pc’s with redox-active metal ions or substituents
typically show additional metal-based or substituent based redox
couples [28]. In this study we perform electrochemical character-
ization of newly synthesized Pc complexes bearing 2Hþ (H2Pc, 4),
Ni2þ (NiPc, 5), and Zn2þ (ZnPc, 6) Pc ring centers. Voltammetric
responses of the complexes were analyzed to support the proposed
* Corresponding author. Tel.: þ90 462 377 25 89; fax: þ90 462 325 31 96.
E-mail address: halit@ktu.edu.tr (H. Kantekin).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.09.002

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Z. Bıyıklıoglu et al. / Dyes and Pigments 89 (2011) 49e55
50
structures by comparing with each other and with the similar MPc
in the literature [28e33]. In-situ spectroelectrochemical and elec-
trocolorimetric measurements were performed to assign the redox
processes and to determine the spectral and color states of the
electro-generated anionic and cationic form of the complexes.
2923, 2862, 2229 (C^N), 1621, 1598, 1581, 1501, 1455, 1375, 1327,
1279, 1149, 1113, 996, 888, 835, 805, 731, 697, 614. 1H NMR. (CDCl3),
(d
:ppm): 8.96 (br s, 1H, AreH), 8.23e8.11 (m, 2H, AreH), 7.65e7.51
(m, 5H, AreH), 7.17 (d, 1H, AreH). 13C NMR. (CDCl3), (
d:ppm):
160.59, 151.95, 150.86, 146.35, 135.94, 134.94, 132.74, 129.23, 127.87,
123.42, 122.42, 121.34, 117.63, 116.96, 115.30, 112.86, 106.75. MS
(ESþ), (m/z): 271 [M]þ. Anal. Calcd for C17H9N3O: C, 75.34; H, 3.34;
N, 15.50. Found: C, 75.23; H, 3.37; N, 15.48.
2. Experimental
2.1. Materials
2.3.2. Synthesis of metal-free phthalocyanine (4)
3-Nitrophthalonitrile (2) [34] was prepared according to the
literature. 6-Hydroxyquinoline was purchased from Aldrich. 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 [35].
A mixture of 3-(quinolin-6-yloxy)phthalonitrile 3 (0.25 g,
0.92 ꢂ 10ꢁ3 mol) and 0.9 ꢂ 10ꢁ3 mol of 1.8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (0.0005 L) in 0.0025 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 diethyl
ether and then dried in vacuo. Finally, pure metal-free phthalocy-
anine was obtained by column chromatography which is placed
aluminium oxide using CHCl3 as solvent. Yield: 0.1 g (40%),
mp > 300 ꢀC. IR (KBr tablet) nmax/cmꢁ1: 3291 (NeH), 3032 (AreH),
2929, 2851, 1622, 1591, 1499, 1487, 1463, 1375, 1322, 1257, 1219,
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 200 MHz spectrometer in CDCl3, and
1148,1136,1106,1027, 968, 941, 866, 834. 1H NMR. (CDCl3), (
d:ppm):
chemical shifts were reported (
d
) relative to Me4Si as internal
8.68e8.56 (m, 4H, AreH), 7.97e7.72 (m, 4H, AreH), 7.58e7.47 (m,
4H, AreH), 7.26e6.95 (m, 16H, AreH), 6.89e6.80 (m, 4H, AreH),
6.60e6.51 (m, 4H, AreH), ꢁ3, 22 (s, 2H, NeH). 13C NMR. (CDCl3),
standard. Mass spectra were measured on a Micromass Quatro LC/
ULTIMA LC-MS/MS spectrometer. Melting points were measured on
an electrothermal apparatus and are uncorrected. The elemental
analyses were performed on a Costech ECS 4010 instrument. The
cyclic voltammetry (CV) and square wave voltammetry (SWV)
measurements were carried out with Gamry Reference 600
potentiostat/galvanostat controlled by an external PC and 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 served as the
counter electrode. 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 0.10 mol dmꢁ3. UVeVis absorption spectra and
chromaticity diagrams were measured by an OceanOptics QE65000
diode array spectrophotometer. In-situ electrocolorimetric
measurements, under potentiostatic control, were obtained using
an OceanOptics QE65000 diode array spectrophotometer at color
measurement mode by utilizing a three-electrode configuration of
thin-layer quartz spectroelectrochemical cell. The standard illu-
minant A with 2 degree observer at constant temperature in a light
booth designed to exclude external light was used. Prior to each set
of measurements, background color coordinates (x, y, and z values)
were taken at open-circuit, using the electrolyte solution without
the complexes under study. During the measurements, readings
were taken as a function of time under kinetic control, however
only the color coordinates at the beginning and final of each redox
processes were reported.
(d:ppm): 156.85, 153.73, 153.50, 148.83, 148.40, 144.30, 137.95,
134.65, 130.70, 129.81, 128.68, 124.82, 123.45, 122.14, 118.65, 117.36,
110.20. UVevis (chloroform): lmax, nm (log 3): 331 (4.94), 625
(4.59), 659 (4.73), 689 (5.18), 721 (5.24). MS (ESþ), (m/z): 1108
[M þ Na ꢁ 2H]þ.
2.3.3. General procedures for metallophthalocyanine
derivatives (5e8)
A
mixture of 3-(quinolin-6-yloxy)phthalonitrile 1 (0.25 g,
0.92 ꢂ 10ꢁ3 mol), anhydrous metal salts [NiCl2 (0.059 g), Zn
(CH3COO)2 (0.084 g), CoCl2 (0.059 g), CuCl2 (0.062 g)] and 2-
(dimethylamino)ethanol (0.0025 L) was irradiated in a microwave
oven at 175 ꢀC, 350 W for 8 min. After cooling to room temperature
the reaction mixture was refluxed with ethanol to precipitate the
product which was filtered off and dried in vacuo over P2O5. Finally,
pure metallophthalocyanines were obtained by column chroma-
tography which is placed aluminium oxide using CHCl3:CH3OH
(10:0.5) as solvent system.
2.3.4. Nickel(II) phthalocyanine (5)
Yield: 0.126 g (48%). IR (KBr tablet) nmax/cmꢁ1: 3054, 3027
(AreH), 2956, 2926, 1621, 1593, 1530, 1499, 1479, 1463, 1375, 1331,
1257, 1217, 1166, 1135, 1113, 1090, 1011, 987, 956, 913, 834, 797, 747.
1H NMR. (CDCl3), (
d:ppm): 8.70e8.50 (m, 8H, AreH), 7.76 (m, 4H,
AreH), 7.57e7.44 (m, 4H, AreH), 7.19e6.88 (m, 12H, AreH),
6.89e6.80 (m, 4H, AreH), 6.51e6.35 (m, 4H, AreH). 13C NMR.
(CDCl3), (d:ppm): 157.21, 154.25, 153.68, 149.47, 148.60, 144.58,
2.3. Synthesis
138.73, 137.97, 134.87, 131.50, 128.83, 128.41, 124.43, 122.90, 121.42,
116.26, 110.31. UVevis (chloroform): lmax, nm (log 3): 299 (4.68),
2.3.1. Synthesis of 3-(quinolin-6-yloxy)phthalonitrile (3)
331 (4.64), 625 (4.50), 693 (5.24). MS (ESþ), (m/z): 1143 [M]þ. Anal.
Calcd for C68H36N12O4Ni: C, 71.40; H, 3.17; N, 14.69. Found: C, 71.46;
H, 3.22; N, 14.72.
6-Hydroxyquinoline 1 (2 g, 13.8 ꢂ 10ꢁ3 mol) was dissolved in
dry DMF (0.02 L) under N2 atmosphere and 3-nitrophthalonitrile 2
(2.4 g, 13.8 ꢂ 10ꢁ3 mol) was added to the solution. After stirring
10 min, finely ground anhydrous K2CO3 (5 g, 36 ꢂ 10ꢁ3 mol) was
added portionwise within 2 h with efficient stirring. The reaction
mixture was stirred under N2 at 50 ꢀC for 2 days. Then the solution
was poured into ice-water (0.2 L). The precipitate formed was
filtered off, washed first with water until the filtrate was neutral
and then diethyl ether and dried in vacuo over P2O5. The crude
product was crystallized from ethanol. Yield: 1.56 g (42%), mp:
196e198 ꢀC. IR (KBr tablet) nmax/cmꢁ1: 3164, 3070, 3019 (AreH),
2.3.5. Zinc(II) phthalocyanine (6)
Yield: 0.135 g (51%). IR (KBr tablet) nmax/cmꢁ1: 3076, 3021
(AreH), 2924, 2854, 1729, 1662, 1621, 1604, 1586, 1503, 1482, 1463,
1377, 1330, 1245, 1114, 1079, 976, 878, 833, 748. 1H NMR. (CDCl3),
(d
:ppm): 8.91 (br s, 4H, AreH), 8.25 (br s, 4H, AreH), 7.92 (s, 4H,
AreH), 7.71 (m, 8H, AreH), 7.53 (m, 4H, AreH), 6.90e6.79 (m, 12H,
AreH). 13C NMR. (CDCl3), (
:ppm): 170.39, 167.77, 157.19, 155.17,
150.19, 135.71, 135.06, 133.12, 132.34, 130.88, 129.13, 128.75, 123.59,
d

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51
N
122.78, 121.32, 114.64, 114.04. UVevis (chloroform): lmax, nm (log
3
): 329 (4.72), 631 (4.53), 699 (5.30). MS (ESþ), (m/z): 1150 [M]þ.
N
O
Anal. Calcd for C68H36N12O4Zn: C, 70.90; H, 3.15; N, 14.60. Found: C,
70.95; H, 3.21; N, 14.59.
CN
CN
O
3
2.3.6. Cobalt(II) phthalocyanine (7)
N
Yield: 0.155 g (59%). IR (KBr tablet) nmax/cmꢁ1: 3054, 2924
(AreH), 2851, 1728, 1594, 1500, 1475, 1459, 1374, 1324, 1247, 1215,
O
N
N
N
N
M
N
N
N
1114, 987, 834, 750. UVevis (chloroform): lmax, nm (log 3): 321
N
N
(5.22), 623 (4.64), 689 (5.26). MS (ESþ), (m/z): 1144 [M]þ. Anal.
Calcd for C68H36N12O4Co: C, 71.39; H, 3.17; N, 14.69. Found: C, 71.39;
H, 3.19; N, 14.69.
O
O
2.3.7. Copper(II) phthalocyanine (8)
Yield: 0.161 g (61%). IR (KBr tablet) nmax/cmꢁ1: 3043 (AreH),
2923, 2862, 1764, 1725, 1706, 1618, 1593, 1500, 1473, 1459, 1380,
1316, 1242, 1152, 1119, 1050, 976, 875, 828, 801, 749. UVevis (DMF):
Compound
M
5
6
7 8
Cu
N
Ni Zn Co
Fig. 2. The synthesis of the metallophthalocyanines.
lmax, nm (log 3
): 315 (5.23), 629 (4.39), 695 (4.83). MS (ESþ), (m/z):
1147 [M ꢁ H]þ. Anal. Calcd for C68H36N12O4Cu: C, 71.10; H, 3.15; N,
15.46. Found: C, 71.40; H, 3.10; N, 14.65.
[NiCl2, Zn(CH3COO)2, CoCl2 and CuCl2] in 2-(dimethylamino)
ethanol by microwave irradiation. The structures of the target
compounds were confirmed using IR, 1H NMR, 13C NMR and MS
spectral data. All the results were consistent with the predicted
structures as shown in the Experimental section.
3. Results and discussion
3.1. Synthesis and characterization
The IR spectra of the phthalonitrile compound 3 clearly indicate
the presence of C^N group by the intense stretching bands at
2229 cmꢁ1. The 1H NMR spectra of phthalonitrile compound 3 were
recorded in CDCl3. In the 1H NMR spectrum of compound 3, OH
group of 6-hydroxyquinoline disappeared as expected. In the 1H
NMR spectrum of 3 the aromatic protons appear at 8.96 (br s),
8.23e8.11 (m), 7.65e7.51 (m), 7.17 (d) ppm. In the 13C NMR spec-
trum of compound 3 indicated the presence of nitrile carbon atom
Starting from 6-hydroxyquinoline 1 and 3-nitrophthalonitrile 2,
the general synthetic route for the synthesis of new metal-free and
metallophthalocyanines are given in Figs. 1 and 2. The synthesis of
non-peripheral substituted phthalonitrile derivative 3 is based on
the reaction of 6-hydroxyquinoline with 3-nitrophthalonitrile (in
dry DMF and in the presence of dry K2CO3 as base, at 50 ꢀC in 48 h).
Cyclotetramerization of the phthalonitrile derivative 3 to the
metal-free phthalocyanine 4 was accomplished in n-pentanol in
the presence of a few drops of 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) as a strong base at 160 ꢀC in sealed tube. The metal-
lophthalocyanines 5e8 were obtained by the anhydrous metal salts
at
d
¼ 116.96, 115.30 ppm. In the mass spectra of phthalonitrile
compound 3, the molecular ion peak was observed at m/z 271 [M]þ.
Cyclotetramerization of the dinitriles 3 to the phthalocyanine
4e8 was confirmed by the disappearance of the sharp C^N
vibration at 2229 cmꢁ1. IR bands characteristic of the metal-free
phthalocyanine ring is an NeH stretching at 3291 cmꢁ1. The IR
spectra of metal-free 4 and metallophthalocyanines 5e8 are very
NO2
N
N
CN
CN
dry K2CO3
dry DMF,
similar, except these
core in the metal-free molecule. These protons are also very well
characterized by the 1H NMR spectrum which shows a peak at
-electron system of the phtha-
y (NH) vibrations of the inner phthalocyanine
50 ºC
OH
O
1
d
:
2
CN
CN
ꢁ3.22 ppm, as a result of the 18
p
locyanine ring. The 1H NMR spectra of 4 indicated characteristic
aromatic protons at 8.68e8.56 (m, 4H, AreH), 7.97e7.72 (m, 4H,
AreH), 7.58e7.47 (m, 4H, AreH), 7.26e6.95 (m, 16H, AreH),
6.89e6.80 (m, 4H, AreH), 6.60e6.51 (m, 4H, AreH) ppm. The 13C
NMR spectra of 4 indicated characteristic aromatic carbon atoms
between at 156.85e110.20 ppm. The mass spectrum of 4 displayed
the [M þ Na ꢁ 2H]þ parent ion peak at m/z ¼ 1108, which confirms
the same structure.
3
DBU
160 o
C
N
n-pentanol
O
In the IR spectra of the metallophthalocyanines (5e8) cyclo-
tetramerization of 3 was confirmed by the disappearance of the
sharp C^N stretching vibration at 2229 cmꢁ1. The IR spectra of
NiPc, ZnPc, CoPc and CuPc are also very similar to that of the
precursor H2Pc. The 1H NMR spectra of these compound were
almost identical to those of H2Pc 4. 1H NMR spectra of compounds
5, 6 were the broad signals encountered in the case of compound 5,
6 as a result of the aggregation of phthlocyanine cores at the
considerable high concentration used for the NMR measurements
[36]. 1H NMR measurements of the cobalt(II) and copper(II)
phthalocyanine 7, 8 were precluded due to its paramagnetic nature.
In the mass spectrum of compounds 5, 6, 7 and 8 the presence of
molecular ion peaks at m/z ¼ 1143 [M]þ, 1150 [M]þ, 1144 [M]þ and
1147 [M ꢁ H]þ respectively, confirmed the proposed structures.
N
O
N
HN
N
N
N
N
N
NH
O
N
O
N
4
Fig. 1. The synthesis of the metal-free phthalocyanine.

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52
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) [37]. The best indi-
cations for phthalocyanine systems are given by their UVeVis
spectra in solution (Fig. 3). UVeVis spectra of metal-free derivative
4 (in CHCl3) split Q bands appeared at 721, 689, 659, 625 nm, while
the B band remained at 331 nm. UVeVis spectra of metallo
phthalocyanines 5e8 (in CHCl3) exhibited an intense single Q band
absorption of
p /
p* transitions around 699e689 nm and B bands
in the UV region around 329e299 nm [38,39].
3.2. Electrochemical measurements
Fig. 4a and b illustrates CVs and SWVs of 4 (H2Pc) in DCM/TBAP
electrolyte on a Pt working electrode. Complex 4 exhibits two
reversible Pc ring-based one-electron reduction couples with
respect to
D
Ep values, which are easily assigned to [H2Pcꢁ2]/
[H2Pcꢁ3 ꢁ
]
at ꢁ0.67 V ( Ep ¼ 58 mV and Ip,a/Ip,c ¼ 0.40 at
D
0.100 mV sꢁ1 scan rate) and [H2Pcꢁ3]ꢁ/[H2Pcꢁ4 2ꢁ
]
at ꢁ1.07 V
(
D
Ep ¼ 62 mV and Ip,a/Ip,c ¼ 0.95 at 0.100 mV sꢁ1 scan rate) and one
quasi-reversible Pc ring-based one-electron oxidation couple
Fig. 4. a) CVs of 4 (1.0 10ꢁ4 mol dmꢁ3) at various scan rates on a Pt working electrode
in DCM/TBAP (inset CV of 4 (5.0 10ꢁ4 mol dmꢁ3) recorded with different switching
potential at 0.100 V sꢁ1scan rate). b) SWV of 4 recorded with SWV parameters: step
size ¼ 5 mV; pulse size ¼ 100 mV; Frequency ¼ 25 Hz.
assigned to [H2Pcꢁ2]/[H2Pcꢁ]þ at 1.05 V (
D
Ep ¼ 165 mV and Ip,c
/
Ip,a ¼ 0.90 at 0.100 mV sꢁ1 scan rate). Although
DEp values of the
first reduction couple is in reversible range, the values of Ipa/Ipc are
less than unity at all scan rates suggesting existence of a fast irre-
versible chemical reaction succeeding the second reduction reac-
tion [40]. The following chemical reaction is dominant when the
solution is concentrated. As shown in Fig. 4a inset, as the potential
Ip,c ¼ 0.75 at 0.100 mV sꢁ1 scan rate). When compared with the
redox potentials of the compound 4, these couples shift to negative
potentials ca. 0.15 V due to the effective nuclear charge differences
of the central ions. However oxidation behavior of 5 and 6 are
completely different than the compound 4. Both complexes poly-
merize on the working electrode electrochemically during the
anodic potential scans. As shown in Fig. 5a, the complex 5 gives ill-
defined oxidation waves and peak current of these processes
is switched just after the first reduction reaction, the values of Ipa
/
Ipc is almost unity however, when the switching potentials go to
negative potentials, a third irreversible reduction reaction is
recorded at ꢁ1.23 V, which may due to the reduction of the
chemical reaction’s product. When the switching potential passes
the second reduction reaction, the reverse couples of the first and
second reduction reactions, and consequently Ipa/Ipc values get
smaller. These data support the proposed chemical reaction.
Replacement of the 2Hþ with Ni2þ (NiPc), and Zn2þ (ZnPc)
significantly affect the redox behavior of the complexes. The
complexes 5 and 6 give very similar voltammetric responses with
slightly potential shift due to the different metal center, thus the CV
and SWV responses of the complex 5 are given in Fig. 5a and b as
a representative of these complexes. In the cathodic scan, the
complex 5 exhibits two quasi-reversible one-electron reduction
couples, which are easily assigned to [NiIIPcꢁ2]/[NiIIPcꢁ3 ꢁ
at
]
ꢁ0.67 V (
D
Ep ¼ 58 mV and Ip,a/Ip,c ¼ 0.90 at 0.100 mV sꢁ1 scan rate)
and [NiIIPcꢁ3]ꢁ/[NiIIPcꢁ4 2ꢁ
]
at ꢁ1.07 V (
D
Ep ¼ 62 mV and Ip,a
/
2
1.5
1
0.5
0
Fig. 5. a) SWVs and CVs of 5 (5.0 10ꢁ4 mol dmꢁ3) at various scan rates in cathodic side
and repetitive CVs in the anodic side at 0.100 V sꢁ1 scan rate on a Pt working electrode
in DMSO/TBAP. b) Repetitive CVs of 5 (5.0 10ꢁ4 mol dmꢁ3) recorded in the whole
potential window of the DMSO/TBAP electrolyte system at 0.100 Vsꢁ1 scan rate on a Pt
working electrode.
200
300
400
500
600
( nm )
700
800
900
Fig. 3. UVevis spectra of compounds 4 (d), 5 ( ) and 6 (—) in chloroform.
z

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53
increases continuously during the repetitive cycles. Switching
potential affects the polymerization mechanism significantly.
When whole potential window of the electrolyte system is scanned
instead of the positive potentials, the peak currents of the oxidation
processes do not increase, but a new wave is recorded at ꢁ0.37 V,
which increases with negative shifting with repetitive CV cycles
(Fig. 5b). These voltammetric data indicate the polymerization of
the complexes with different mechanism as a function of the
switching potentials.
observed at 617 nm, which demonstrates that the reduction
proceeds cleanly in deoxygenated DCM to give a single, reduced
species. Rollmann and Iwamoto [11] and Koca et al. [30,42] also
reported similar spectroscopic chances for one-electron reduction
of H2Pc complexes. It was mentioned that there might be
a symmetry change from D2h to D4h because of the substitution of
central hydrogens by cations of supporting electrolyte. It was
shown that the pair of excited states which usually give rise to the Q
band doubling in the [H2Pc3ꢁ 1ꢁ
species, is still present but the
]
states are too close together to be resolved. During the potential
application at ꢁ1.20 V versus SCE, [H2Pc3ꢁ 1ꢁ
]
is one-electron
3.3. Spectroelectrochemical studies
reduced to form the [H2Pc4ꢁ 2ꢁ
dianion (Fig. 6b). Spectroscopic
]
changes show that while the band at 547 nm increases in intensity
with shifting to 552 nm, the Q bands decrease. At the same time
a new band is recorded at 582 nm. Clear isosbestic points are
recorded at 620 and 809 nm in the spectra. During the oxidation of
H2Pc at 1.20 V applied potential, intensity of the Q bands decrease
in intensity while the region between 450e550 nm and the NIR
region increase (Fig. 6c). The isosbestic points at 410, 575 and
750 nm vibrates continuously during the oxidation process which
indicates decomposition of the complex during the oxidation
process.
Spectroelectrochemical studies were employed to confirm the
assignments in the CVs of the complexes. The complexes 4e6 have
all redox inactive centers. Therefore, in-situ UVeVis spectral
changes of them indicate the Pc ring-based redox characters.
To represent the in-situ spectroelectrochemical response of the
metal-free phthalocyanines, spectral chances of 4 during the
controlled potential application at the redox potentials are given in
Fig. 6. For the metal-free phthalocyanines, the symmetry is D2h and
therefore there are two sharp bands (split Q band) at 683 and
702 nm [28,33,41,42]. Due to the presence of aggregation and/or
may due to performing of the measurements with high concen-
tration, splitting of the Q band is shadowy. When the working
electrode is polarized at ꢁ0.80 V versus SCE, [H2Pc2ꢁ] is one-
The color change of the solution of the complexes during the
redox processes were recorded using in-situ colorimetric
measurements. Fig. 6d gives the chromaticity diagram of the
electron reduced to form the [H2Pc3ꢁ 1ꢁ
anion. During the reduc-
]
complex
4 recorded simultaneously during the spectroelec-
tion of [H2Pc2ꢁ] at constant potential application, the split Q band
decreases in intensity while a new band is recorded at 547 nm
(Fig. 6a). During this process, a well-defined isosbestic point is
trochemical measurements. Without any potential application, the
solution of 4 is green (x ¼ 0.269 and y ¼ 0.387). As the potential is
stepped from 0 to ꢁ0.80 V, color of neutral 4 starts to change and
Fig. 6. In-situ UVeVis spectral changes of 4. a) Eapp ¼ ꢁ0.80 V. b) Eapp ¼ ꢁ1.20 V. c) Eapp ¼ 1.20 V. d) Chromaticity diagram (each symbol represents the color of electro-generated
q
species; ,: H2Pcꢁ2, B: H2Pcꢁ3
,
6
: H2Pcꢁ4
,
: H2Pcꢁ1
.

ꢀ
Z. Bıyıklıoglu et al. / Dyes and Pigments 89 (2011) 49e55
54
Fig. 7. In-situ UVeVis spectral changes of 5. a) Eapp ¼ ꢁ0.80 V. b) Eapp ¼ ꢁ1.40 V. c) Eapp ¼ 1.20 V. d) Chromaticity diagram (each symbol represents the color of electro-generated
q
species; ,: NiIIPcꢁ2, B: NiIIPcꢁ3
,
6
: NiIIPcꢁ4
,
: NiIIPcꢁ1
.
blue color (x ¼ 0.282 and y ¼ 0.263) of monoanionic form of 4 was
obtained at the end of the first reduction. Similarly color of the
dianionic species was recorded as deep blue (x ¼ 0.261 and
y ¼ 0.203) and monocationic species has yellowish green color
(x ¼ 0.345 and y ¼ 0.367). Measurement of the xyz coordinates
allows quantification of each color of redox species that is very
important to decide their possible electrochromic application.
Fig. 7 shows the in-situ UVeVis spectral changes of 5 under the
controlled potential application. During the potential application at
ꢁ0.80 V, the Q band shifts from 680 nm to 673 nm with decreasing
and new bands in the LMCT region at 590 and 935 nm are observed
(Fig. 7a). Although the band in the LMCT region and decreasing of
the Q band are characteristics of the ring-based redox processes
[29,43e46], differently shifting of the Q band is not a common
spectral change for the MPc having redox inactive metal center.
This unusual change may due to the conformational changes of the
complex during reduction process. A band observed at 648 nm may
also due to this conformational change. While the process gives
clear isosbestic point at 760 nm in the spectra, isosbestic point at
662 nm tremble which indicate the formation more than one
product during the process, which support the conformational
change. Then at the ꢁ1.40 V potential application, while the bands
at 648 and 673 nm decrease in intensity, new bands are recorded at
465 and 817 nm. At the same time the band at 935 nm increases in
intensity. These spectroscopic changes are easily assigned to the
complexes having redox inactive metal center (like the complex 5),
all bands of the complex 5 increase in intensity which cause to the
broadening of the Q band especially. These spectroscopic changes
support the polymerization of the complex on the electrode during
the anodic CV scans. It is well known that MPcs coated on an
electrode have the Q band which is broader than those in solution
[47,48]. The color change of the solution of the complex during the
redox processes were recorded using in-situ colorimetric
measurements. Fig. 7d gives the chromaticity diagrams of the
complex
5 recorded simultaneously during the spectroelec-
trochemical measurements. Without any potential application, the
solution of 5 is greenish blue (x ¼ 0.247 and y ¼ 0.342). As the
potential is stepped from 0 to ꢁ1.50 V color of neutral 5 gets deep
blue (x ¼ 0.202 and y ¼ 0.226) and then blue (x ¼ 0.238 and
y ¼ 0.254) for the anionic forms of 5 respectively.
4. Conclusion
In this study, the syntheses, spectral and electrochemical prop-
erties of soluble non-peripheral 6-oxyquinoline substituted metal-
free, nickel, zinc, cobalt and copper phthalocyanines (4, 5, 6, 7 and 8)
are discussed. The target symmetrical phthalocyanines were sepa-
rated by column chromatography which is placed aluminium oxide
and characterized by a combination of IR, 1H NMR, 13C NMR,
elemental analysis and MS spectral data. This study content elec-
trochemical and spectroelectrochemical characterization of H2Pc (4),
Ni(II)Pc (5), Zn(II)Pc (6). Complex 4 exhibits two reversible Pc ring-
reduction of the monomeric species, [NiIIPcꢁ3 ꢁ1
to [NiIIPcꢁ4 ꢁ2
]
]
dianionic species (Fig. 7b) [29,43e46]. Spectroscopic changes given
in Fig. 7c are not characteristics of the oxidation of [MIIPcꢁ2]. Since
while the Q band decreases in intensity with a new band in the
LMCT region during the Pc ring-based oxidation processes of MPc
based one-electron reduction couples with respect to
which are easily assigned to [H2Pcꢁ2]/[H2Pcꢁ3 ꢁ and [H2Pcꢁ3]ꢁ/
[H2Pcꢁ4 2ꢁ
and one quasi-reversible Pc ring-based one-electron
DEp values,
]
]

ꢀ
Z. Bıyıklıoglu et al. / Dyes and Pigments 89 (2011) 49e55
55
oxidation couple assigned to [H2Pcꢁ2]/[H2Pcꢁ]þ. The complexes 5
and 6 give very similar voltammetric responses with slightly poten-
tial shift due to the different metal center. The complex 5 exhibit two
quasi-reversible one-electron reduction couples, which are easily
ꢀ
[23] Bıyıklıoglu Z, Kantekin H. The synthesis, using microwave irradiation and
characterization of novel, organosoluble metal-free and metal-
lophthalocyanines substituted with flexible crown ether moieties. Dyes and
Pigments 2009;80:17e21.
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[24] Bıyıklıoglu Z, Kantekin H. New long-chain substituted polymeric metal-free
assigned to [NiIIPcꢁ2]/[NiIIPcꢁ3 ꢁ and [NiIIPcꢁ3]ꢁ/[NiIIPcꢁ4 2ꢁ
] ] . When
and metallophthalocyanines by microwave irradiaton: synthesis and charac-
terization. Polyhedron 2008;27:1650e4.
compared with the redox potentials of the compound 4, these
couples shift to negative potentials ca. 0.15 V due to the effective
nuclear charge differences of the central ions. However oxidation
behavior of 5 and 6 are completely different than the compound 4.
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[25] Degirmencioglu I, Bayrak R, Er M, Serbest K. The microwave-assisted synthesis
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Acknowledgement
_
ꢀ
ꢀ
This study was supported by the Research Fund of Karadeniz
Technical University.
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