Novel alpha-7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituted metal-free, Co(II) and Zn(II) phthalocyanines: Photochemistry, photophysics, conductance and electrochemistry

Article abstract of DOI:10.1016/j.dyepig.2012.05.021

Novel alpha-substituted metal-free, Co(II) and Zn(II) phthalocyanines, bearing four 7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin moieties were synthesized. The compounds were characterized by elemental analysis, IR, UV-vis, ¹H NMR, ¹³C NMR and MALDI-TOF mass spectroscopies. The Zn(II) phthalocyanine compound showed J-type aggregation in non-coordinating solvents. The photophysical and photochemical properties of these compounds were described in different solvents. Direct current conductivity measurements of the films of Co(II) and Zn(II) phthalocyanines as a function of temperature showed that these compounds are semiconductors with the activation energies within the range of 0.40-0.84 eV. The variation of alternating current conductivity of the films with frequency was found to be represented by the function σ_AC = Aω^s. The results indicated that charge transport mechanism of the films can be explained by hopping. The redox properties of the compounds were also examined in dimethylsulfoxide and dichloromethane by voltammetry and in situ spectroelectrochemistry. The compounds displayed metal and/or phthalocyanine ring-based reduction and oxidation processes. The electrochemistry of a phthalocyanine compound forming a J-aggregated species has been investigated. It was found that some redox couples of the Zn(II) compound in dichloromethane is split due to the equilibrium between its aggregated and non-aggregated species.

Full text of DOI:10.1016/j.dyepig.2012.05.021

Dyes and Pigments 95 (2012) 540e552
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Novel alpha-7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituted
metal-free, Co(II) and Zn(II) phthalocyanines: Photochemistry,
photophysics, conductance and electrochemistry
a
a
b
a,
*
ꢀ c
Zafer Odabas¸ , Efe Baturhan Orman , Mahmut Durmus¸ , Fatih Dumludag , Ali Rıza Özkaya
,
Mustafa Bulut a
,
*
a Department of Chemistry, Marmara University, Kadıköy, 34722 Göztepe-Istanbul, Turkey
b Department of Chemistry, Gebze Institute of Technology, P.O. Box 141, Gebze 41400, Kocaeli, Turkey
c Department of Physics, Marmara University, Kadıköy 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:
Novel alpha-substituted metal-free, Co(II) and Zn(II) phthalocyanines, bearing four 7-oxy-4-(4-
methoxyphenyl)-8-methylcoumarin moieties were synthesized. The compounds were characterized
by elemental analysis, IR, UVevis, 1H NMR, 13C NMR and MALDI-TOF mass spectroscopies. The Zn(II)
phthalocyanine compound showed J-type aggregation in non-coordinating solvents. The photophysical
and photochemical properties of these compounds were described in different solvents. Direct current
conductivity measurements of the films of Co(II) and Zn(II) phthalocyanines as a function of temper-
ature showed that these compounds are semiconductors with the activation energies within the range
of 0.40e0.84 eV. The variation of alternating current conductivity of the films with frequency was found
Received 2 April 2012
Received in revised form
21 May 2012
Accepted 22 May 2012
Available online 7 June 2012
Keywords:
Phthalocyanine
Electrochemistry
J-aggregation
Photophysics
Semiconductor
Photochemistry
to be represented by the function sAC ¼ A
u
s. The results indicated that charge transport mechanism of
the films can be explained by hopping. The redox properties of the compounds were also examined in
dimethylsulfoxide and dichloromethane by voltammetry and in situ spectroelectrochemistry. The
compounds displayed metal and/or phthalocyanine ring-based reduction and oxidation processes. The
electrochemistry of a phthalocyanine compound forming a J-aggregated species has been investigated.
It was found that some redox couples of the Zn(II) compound in dichloromethane is split due to the
equilibrium between its aggregated and non-aggregated species.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the type, number, and positions of the substituents on the
macrocycle.
Phthalocyanines (Pcs) are composed of four iminoisoindoline
units where the pyrrole groups are conjugated to benzene rings and
bridged by azanitrogens. Pcs have highly coloured, planar and 18p-
Supramolecular self-assembly is a very useful technique to
fabricate molecular materials and molecular machines to perform
specific functions such as chemical sensing, electrical conductivity,
and mechanical movements. In the case of Pcs, self-aggregation
that forms dimers and high order aggregates has been exten-
sively investigated. The driving force for such aggregation involves
electron heterocyclic aromatic systems [1]. A great number of
unique properties arise from this electronic delocalization that
makes these compounds valuable in different fields of technology
as pigments, dyes, sensors, photodynamic therapy of cancer, optical
recording and non-linear optical materials, electronic device
components photovoltaics, catalysts and electrochromism [1e4]. It
is well known that nearly all technologically important properties
of Pc derivatives can be tuned by varying the central metal atom,
ligand-metal coordination,
p-stacking, hydrogen bonding and
donoreacceptor interactions. It has been established that Pcs can
form H-and J-aggregates depending on the orientation of the
induced transition dipoles of their constituent monomers. In H-
aggregates, the component monomers are arranged into a face-to-
face conformation, and transition dipoles are perpendicular to the
line connecting their centers. In contrast, in J-aggregates, the
component monomers adopt a side-by-side conformation, and
their transition dipoles are parallel to the line connecting their
centers. Except for a few examples, usually, H-aggregates of Pcs
have been observed [5]. The high H-aggregation tendency of Pc
changing the size of the
p-conjugated system, or alternating
* Corresponding authors. Tel.: þ90 216 347 96 41; fax: þ90 216 347 87 83.
E-mail addresses: aliozkaya@marmara.edu.tr (A.R. Özkaya), mbulut@
marmara.edu.tr (M. Bulut).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.05.021

Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
541
compounds, especially
b
-substituted ones, through the intermo-
functional groups into a single hybrid compound via synthetic
methodology and characterize its metal-free and metallo deriva-
tives, which may also exhibit high solubility in various solvents and
intriguing physicochemical properties.
The synthesis and characterization of Pc compounds including
different oxy-coumarin substituents have been studied previously
[16e18]. Contrary to the previously reported studies, in the present
work, the designed compounds formed J-aggregates and their
electrochemical properties in different solvents has been discussed.
Although there have been many reports on the electrochemical
properties of various H-aggregated metallo Pcs [19e21], to the best
of our knowledge, this is the first report investigating the redox and
in situ spectroelectrochemical behavior of a J-aggregated metallo
lecular interactions between their rings usually causes these
compounds to be insoluble or have limited solubility in many
solvents [6] and thus, complicate the detection of their physico-
chemical properties [7]. Furthermore, the intermolecular interac-
tions resulting from this phenomenon can dramatically affect their
photophysical [8], photochemical [9], electrical [10] and electro-
chemical [11]properties. For instance, H-aggregation has been
found to cause decrease in their light absorption and induce a large
reduction in their fluorescence quantum yield [8]. On the other
hand,
aggregation and thus various physicochemical properties, in
comparison with corresponding -substituted ones [12]. These
a-substituted Pcs differ significantly in their solubility,
b
compounds do not form H-aggregated species, due to their
Pc. Novel
a-tetra substituted metal free, cobalt and zinc Pcs have
conformation deviating from planarity, and thus fluoresce.
been prepared from 3-[4-(4-methoxyphenyl)-8-methylcoumarin-
7-oxy]phthalonitrile (Scheme 1) and characterized by elemental
analyses, UVevis, IR, 1H NMR, 13C NMR and matrix assisted laser
desorption/ionization-time of flight (MALDI-TOF) mass spectros-
copies. The aggregation behavior of newly synthesized compounds
was investigated by UVevis spectroscopy in different solvents such
as toluene, chloroform, DCM and dimethylsulfoxide (DMSO). Pho-
tophysical (fluorescence lifetime and quantum yields) and photo-
chemical (singlet oxygen and photodegradation quantum yields)
properties were investigated in different solvents. Direct current
(DC) and alternating current (AC) conductivity and impedance
spectroscopy measurements of their thin films were also per-
formed as functions of temperature and frequency under vacuum
(w2 ꢀ 10ꢁ3 mbar) in dark with the aim of identifying the charge
transport mechanism.
However,
a-substituted Pcs can form J-type aggregates in non-
coordinating solvents such as chloroform, dichloromethane
(DCM) or toluene. J-aggregates are highly desirable to maximize the
optical properties of the organic dyes [13].
Coumarin
(2H-1-benzopyran-2-one,
2H-chromen-2-one)
derivatives are biologically active compounds with numerous
metabolites and widespread in nature [14]. These compounds
possess a significant organic fluorophore and are widely used in
some applications such as synthesizing laser dyes, chemosensors
for metal detections, pH sensors, liquid crystals and organic non-
linear optical materials, due to their characteristics of high emis-
sion yield, excellent photostability and extended spectral range
[15]. In view of the versatile importance of both coumarins and
alpha-substituted Pcs it is worthwhile to combine these two
Scheme 1. Synthesis of 3, 4, 5 and 6. Reagents and conditions: i. K2CO3, N2, dimethylsulfoxide, 50 ꢂC, 24 h; ii a) 2-N,N-dimethylaminoethanol, N2 160 ꢂC, 48 h, b) Co(OAc)2.4H2O or
c) Zn(OAc)2.2H2O, N2, 320 ꢂC, 20 min, respectively.

542
Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
2. Experimental section
acid, ethanol and acetonitrile for 12 h respectively in the soxhlet
apparatus. The product was further purified by column chroma-
tography with silica-gel eluting with CHCl3 a gradient of CHCl3-THF
up to 5% THF.
2.1. Synthesis of 3-[4-(4-methoxyphenyl)-8-methylcoumarin-7-
oxy]phthalonitrile (3)
5: Mp>300 ꢂC. Yield: 80.00 mg (77.20%). Anal calculated for
C100H64CoN8O16: C, 70.96%; H, 3.81%; N, 6.62%; found C, 70.85%; H,
3.94%; N, 6.71%. IR (KBr pellet) nmax/cmꢁ1: 528, 566, 601, 747, 832,
957, 979, 1084, 1175, 1243, 1330, 1366, 1421, 1483, 1511, 1584, 1604,
1724, 2837, 2933, 3066. MALDI-TOF-MS: m/z 1677.57 (M ꢁ CH3)þ,
1691.59 (M)þ and 1714.56 (M þ Na)þ.UVevis (DCM): lmax(nm),
(log ε): 317 (5.759), 618 (5.210), 685 (5.838).
3-Nitrophthalonitrile (1) (0.86 g, 5 mmol) and 7-hydroxy-4-(4-
methoxyphenyl)-8-methylcoumarin (2) (1.41 g, 5 mmol) were
dissolved in anhydrous DMSO (20 mL). After stirring for 10 min;
finely ground anhydrous K2CO3 (2.07 g, 15 mmol) was added by
stirring. The reaction mixture was stirred at 50 ꢂC for 24 h under N2
atmosphere. The mixture was poured into ice water and the
obtained precipitate was filtered off, washed by using water and
dried in vacuum at 50 ꢂC. Then it was also purified by column
chromatography with silica gel eluting with CHCl3 a gradient of
CHCl3-tetrahydrofuran (THF) up to 5% THF.
6: Mp>300 ꢂC. Yield: 75.00 mg (72.20%). Anal calculated for
C100H64ZnN8O16: C, 70.69%; H, 3.80%; N, 6.60%; found C, 70.82%; H,
3.65%; N, 6.46%. IR (KBr pellet) nmax/cmꢁ1: 529, 558, 602, 741, 831,
866, 955, 1045, 1083, 1175, 1244, 1332, 1366, 1422, 1478, 1511, 1579,
Compound 3 is soluble in DCM, CHCl3, THF, dimethylformamide
(DMF), DMSO and acetic acid. Mp: 214e215 ꢂC Yield: 1.86 g
(91.18%). Anal calculated for C25H16N2O4 C, 73.52%; H, 3.95%; N,
1602, 1722, 2827, 2929, 3066. 1H NMR (500 MHz, CDCl3)
d
ppm
8.06e6.72 (m, 40H), 3.90 (s, 12H), 2.12 (s, 12H). 13C NMR (125 MHz,
CDCl3):d ppm 163.88e109.97 (92C), 55.32 (4C), 9.07 (4C). MALDI-
6.86%; found C, 73.41%; H, 4.08%; N, 6.72%. IR (KBr pellet) nmax
/
TOF-MS: m/z 1696.61 (M)þ, 1803.44 (Mþ2Na þ CH3COOH)þ and
3393.19 (M2)þ.UVevis(DCM): lmax(nm), (log ε): 317 (5.537), 624
(4.984), 665 (4.988), 693 (5.739), 741 (4.788).
cmꢁ1: 597, 798, 895, 950, 1027, 1087, 1174, 1249, 1283, 1366, 1422,
1461, 1487, 1512, 1572, 1603, 1732, 2228, 2854, 2922, 3066. 1H NMR
(500 MHz, CDCl3): d, ppm 2.42 (s, 3H), 3.87 (s, 3H), 6.38 (s, 1H), 6.89
(d, J ¼ 8.98 Hz, 1H), 7.02 (dd, J ¼ 8.99 Hz, J ¼ 1.95 Hz, 1H), 7.06 (dd,
J ¼ 8.59 Hz, J ¼ 1.95 Hz, 2H), 7.41 (dd, J ¼ 8.98 Hz, J ¼ 1.95 Hz, 2H),
7.49 (d, J ¼ 8.98 Hz, 1H), 7.54 (dd, J ¼ 8.59 Hz, J ¼ 1.95 Hz, 1H), 9.76
(t, 1H).
3. Results and discussion
3.1. Syntheses and characterization
The starting material, 3-[4-(4-methoxyphenyl)-8-methyl-
coumarin-7-oxy]phthalonitrile (3), was synthesized by K2CO3 base
catalyzed nucleophilic aromatic nitro displacement of 3-
nitrophthalonitrile (1) with 7-hydroxy-4-(4-methoxyphenyl)-8-
methylcoumarin (2) in DMSO. The novel CoPc (5) and ZnPc (6)
were prepared by the templated cycloetetramerization reaction
from compound 3 and metal salts [Co(OAc)2.4H2O and Zn(OA-
c)2.2H2O] in DMF (0.3 mL) at 320 ꢂC. Metal-free Pc (4) was also
synthesized by heating compound 3 in 2-N,N-dimethylaminoe-
thanol at 160 ꢂC under N2 atmosphere (Scheme 1). Compounds 4e6
were purified by washing with acetic acid, hot water, ethanol and
acetonitrile, respectively in the soxhlet apparatus and by column
chromatography. The yields were considerably high (approxi-
mately 38% for 4, 77% for 5 and 72% for 6). These novel Pcs are
soluble in common solvents such as toluene, chloroform, DCM, THF,
DMSO and DMF.
2.2. Synthesisof1(4),8(11),15(18),22(25)-tetra[4-(4-methoxyphenyl)-
8-methylcoumarin-7-oxy]phthalocyanine (4)
Compound 3 (0.10 g, 0.25 mmol) was heated in dry 2-N,N-
dimethylaminoethanol (2 mL) in a sealed tube. The mixture was
held at 160 ꢂC for 48 h under N2 atmosphere. After cooling to room
temperature, the reaction mixture was treated with dilute HCl and
the mixture was filtered and washed with water until the filtrate
became neutral. The raw green product was taken in the soxhlet
apparatus then purified by washing with hot water, acetic acid,
ethanol and acetonitrile for 12 h, respectively. The product was
further purified by column chromatography with silica gel eluting
with CHCl3 a gradient of CHCl3-THF up to 5% THF.
The metal free Pc 4 is soluble in CHCl3, DCM, toluene, THF, DMF
and DMSO. Mp>300 ꢂC. Yield: 38.0 mg (38.0%). Anal calculated for
C100H66N8O16: C, 73.43%; H, 4.07%; N, 6.85%; found C, 73.26%; H,
3.96%; N, 7.03%. IR (KBr pellet) nmax/cmꢁ1: 529, 748, 831, 937, 1021,
1083, 1175, 1243, 1332, 1366, 1478, 1511, 1581, 1603, 1722, 2837,
The characterization of the new products involved a combina-
tion of methods including elemental analyses, IR, UVevis, 1H NMR,
13C NMR and MALDI-TOF mass spectroscopies. Elemental analysis
results and the spectral data of the newly synthesized compounds
3e6 are consistent with the proposed structures.
2924, 3066, 3283.1H NMR (500 MHz, CDCl3):
d ppm 8.08e6.75 (m,
40H), 3.70 (s, 12H), 2.09 (s, 12H), ꢁ1.58 (s, 2H). 13C NMR (125 MHz,
CDCl3):
d
ppm 161.92e110.84 (92C), 55.28 (4C), 9.69 (4C). MALDI-
The FT-IR absorption spectrum of 3 exhibited two strong bands
TOF-MS: m/z 1634.67 (M)þ and 1657.65 (M þ Na)þ, 1673.63
(M þ K)þ.UVevis (DCM): lmax(nm), (log ε): 319 (5.800), 621 (5.290),
653 (5.417), 684 (5.860), 715 (5.922).
at 1732 and 1603 cmꢁ1, which may be assigned to coumarin
carbonyl (lactone, ꢁC]O) and
a
,b
-unsaturated eC]Cꢁ double
bond (or aromatic rings eC]Cꢁ), respectively. The bands at
3066 cmꢁ1 indicated Ar-H stretching frequencies. The formation of
3 was confirmed by the appearance of a new absorption band at
2228 cmꢁ1 (ꢁC^N) and additional bands at 1249 cmꢁ1 (AreOeAr)
in the FT-IR spectrum. The IR spectra of 4, 5 and 6 were very similar,
but compound 4 showed an extra weak NꢁH stretching band at
3283 cmꢁ1 due to the inner core.
2.3. Synthesisof1(4),8(11),15(18),22(25)-tetra[4-(4-methoxyphenyl)-
8-methylcoumarin-7-oxy]phthalocyaninatocobalt(II) and zinc(II)
(5 and 6)
A mixture of compound 3 (0.10 g, 0.25 mmol) and metal salt
(either 0.063 g, 0.25 mmol Co(OAc)2.4H2O or 0.064 g, 0.25 mmol
Zn(OAc)2.2H2O) was powdered in a quartz crucible and transferred
in a reaction tube. 0.30 mL of DMF was added to this reaction
mixture and the mixture was heated in a sealed glass tube for
20 min under dry N2 atmosphere at 320 ꢂC. After cooling to room
temperature, DMF (3 mL) was also added to the residue to solve the
product. The reaction mixture was precipitated by adding acetic
acid. The precipitate was filtered and washed with hot water, acetic
The molecular ion peaks [M]þ of the Pc compounds 4, 5 and 6
were identified easily with
a-cyano-4-hydroxycinnamic acid
(ACCA) MALDI matrix in the reflectron mode by using MALDI-TOF
mass spectrometry. The molecular ion peak of 4 was observed at
1634.67 [M]þ. Beside the molecular ion peak of the complexes,
sodium and potassium adducts were observed at 1657.85 and
1673.63 respectively (Supplementary material, Fig. S1). The
molecular ion peak of 5 was observed at 1691.59 Da. Two intense

Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
543
peaks were also observed at 1677.57 [M ꢁ CH3]þ and 1714.56 Da
[M þ Na]þ (Supplementary material, Fig. S2). The molecular ion
peak of 6 was observed at 1696.61 Da. The extra aggregate dimer
peak was also observed at 3393.19 [M2]þ (Fig. 1). The molecular ion
peaks of the complexes overlapped with the theoretical calculated
mass values of the complexes.
strong Q band absorption corresponding to the monomeric species,
meanwhile a new, broader and blue-shifted band is seen to increase
in intensity. Therefore, the narrow and sharp Q-bands in the elec-
tronic spectra of 4 and 5 in toluene, DCM and chloroform are typical
of non-aggregated species. The electronic spectra of 6 in DMSO and
DMF also display monomeric behavior (Fig. 2). However, in addition
to the normal Q band, an unusual red-shifted sharp band at 740 nm
is observed in DCM, chloroform and toluene.
The 1H NMR spectrum of 3 exhibited characteristic signals for
methyl (-CH3) and eOCH3 protons at
respectively, each as a singlet. The peaks at
6.89e9.76 ppm indicated the presence of protons at lactone ring
d
2.42 and
d 3.87 ppm,
d
6.38 and between
This band should be due to the presence of J-aggregated species
since it is well known from literature that zinc Pc complexes
involving ether oxygen atoms usually display J-aggregation
behavior [5,8,24]. Complementary coordination of the linking
oxygen atoms in one molecule of 6 (etheric oxygens and/or lactone
oxygens) with the core Zn(II) ion of its another molecule should be
responsible for the formation of J-aggregates [5]. The J-aggregation
behavior of 6 was also supported by the appearance of a peak at
3393.19 Da in its MALDI-TOF mass spectrum (Fig. 1). The reason for
the formation of J-aggregates of only 6 may be stronger coordi-
nating ability of zinc atom than hydrogen and cobalt atoms. The
gradual addition of DMSO to the solution of 6 in chloroform caused
an increase in the absorption of the monomer band at 693 nm and
a decrease in that of the J-band at 740 nm followed by its disap-
pearance (Supplementary material, Fig. S10). These spectral
changes suggested clearly that the addition of a coordinating
solvent caused disaggregation of the J-aggregated species as
a result of the competitive coordination of the solvent molecules to
central zinc atoms. Monomer and J-aggregated dimer films of 6
were also obtained by spraying their solutions on glass. The
evidence for the formation of J-type network structures of 6 in non-
coordinating solvents based on electronic absorption spectroscopy
as well as MALDI-TOF mass spectroscopy were further strength-
ened by a scanning electron microscopy (SEM) study. Fig. 3 shows
the SEM images of the sprayed film prepared from aggregated
solution of 6 with a stick-like morphology with long and thin fibrils
(around 80 nm thick) forming one dimensional bundle. This
morphology was not observed with the film of 6, prepared from its
solution involving monomer species.
d
and the aromatic protons, respectively (Supplementary material,
Fig. S3). In the 1H NMR spectra of 4 and 6, the aromatic, eOCH3,
eCH3 and eNH protons of 4 appeared between 8.08 and 6.75 ppm
(m), and at 3.70 ppm (s), 2.09 ppm (s) and ꢁ1.58 ppm (bs),
respectively and the aromatic, eOCH3 and eCH3 protons of the
compound 6 were observed between 8.06 and 6.72 ppm (m), at
3.90 ppm (s) and at 2.12 ppm (s), respectively (Supplementary
material, Figs. S4 and S5).
In the 13C NMR spectra of 4 and 6, the aromatic, eOCH3, and
eCH3 carbon atoms of
55.28 ppm, and 9.69 ppm, respectively, whereas the aromatic,
eOCH3 and eCH3 carbon atoms of were observed at
4 appeared at 161.92e110.84 ppm,
6
163.88e109.97 ppm, 55.32 ppm and 9.07 ppm, respectively
(Supplementary material, Figs. S6 and S7).
Electronic absorption behavior of 4e6 has been examined by
UVevis spectroscopy in different solvents. The split Q band of 4 in
toluene, DCM and chloroform is characteristic for the D2h symmetry
of monomeric metal-free Pcs (Supplementary material, Fig. S8).
There is also a set of weaker vibronic satellite bands at shorter
wavelengths. The split Q band converted to single band in DMF and
DMSO, suggesting that deprotonation of the inner pyrrolic H atoms
in the Pc core and thus, symmetry change from D2h to D4h occurs
due to basicity of these solvents [22e24]. Compound 5 gave elec-
tronic spectra involving a single narrow and non-split Q band,
typical of metal Pc complexes (Supplementary material, Fig. S9) in
DMSO, DMF, toluene, DCM and chloroform. The presence of Pc
aggregates can be observed in the Q-band region of the electronic
absorption spectrum since upon formation of higher order
complexes, the coupling between the electronic states of individual
monomeric Pc units causes significant spectral perturbations. It has
been established that Pcs usually form H-aggregates with the
arrangement of the component monomers into a face-to-face
conformation [5,25]. This results in a decrease in intensity of
3.2. Photophysical and photochemical properties
The fluorescence behavior of 4 and 6 was studied in different
solvents (toluene, chloroform, DCM and DMSO). Complex 5 is not
fluorescence due to paramagnetic properties of central cobalt atom.
Fig. 4 shows the absorption, fluorescence emission and excitation
Fig. 1. Positive ion and reflectron mode MALDI-TOF-MS spectrum of 6 in a-cyano-4-
hydroxycinnamic acid MALDI matrix using nitrogen laser (at 337 nm wavelength)
accumulating 50 laser shots.
Fig. 2. Absorption spectra of 8.0 ꢀ 10ꢁ6 M 6 in different solvents.

544
Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
Fig. 3. SEM images of the sprayed film (gold-stained) of 6 on glass.
lifetime (s0) by the Strickler-Berg equation (Supplementary mate-
rial, Eq.(2)). A good correlation was found between experimentally
and the theoretically determined lifetimes for the Pc molecules, as
reported in a literature example [27]. Generally, the sF values are
within the range reported for MPc complexes [26]. sF values are
longer for 4 when compared to 6 in all studied solvents (Table 2).
The natural radiative lifetimes (
rescence (kF) values of 4 and 6 in different solvents are also given in
Table 2. 0 values of 4 and 6 are longest in DMSO. There was no clear
s0) and the rate constants for fluo-
s
trend for the natural radiative lifetimes (s0) and rate constants for
fluorescence (kF) values of 4 and 6.
The singlet oxygen quantum yield, (FD) values of 4, 5 and 6 were
determined in DMSO and toluene using a chemical method. These
values could not be investigated in chloroform and DCM due to the
lack of a standard in these solvents. There was no decrease in the Q
band or formation of new bands during FD determinations, as
shown in Fig. 5 for 6 in toluene as an example. This indicates that
the Pcs are not degradated during singlet oxygen studies. It is
believed that during photosensitization, the Pc is firstly excited to
the singlet state and through intersystem crossing reaches the
Fig. 4. Absorption, fluorescence emission and excitation spectra of 6 in toluene.
spectra of 6 in toluene, as an example. The shapes of the excitation
spectra were similar to absorption spectra for 4 (Supplementary
material, Fig. S11) and 6 (Fig. 4) in all studied solvents suggesting
that the molecules did not show any degradation during excitation.
Fluorescence emission and excitation peaks in different solvents
are listed in Table 1. While the observed Stokes shifts of 6 are
similar, Stokes shifts of 4 are lower than Pc derivatives having
different substituents on the Pc ring in the literature [26]. The
Stokes shifts of the substituted 6 are higher than those of 4 in all
studied solvents (Table 1).
triplet state, then it transfers energy to ground state oxygen,
P
O2(3 g), and converts itself into its excited state (singlet oxygen),
O2(1Dg). This singlet oxygen is the chief cytotoxic species, which
subsequently oxidizes the surrounding substrates: this oxidation is
the key of the Type II mechanism [28]. The FD values of 6 are higher
when compared to 4 and 5 in both toluene and DMSO. The FD
values of 5 are very low due to paramagnetic properties of the
central cobalt atom (Table 2).
The spectral changes observed for all Pcs (4, 5 and 6) during
irradiation are as shown in Fig. 6 (using complex 4 in chloroform as
an example). For all substituted Pcs in all studied solvents, the
collapse of the absorption spectra without any distortion of the
The fluorescence quantum yields (FF) of 4 and 6 are typical of Pc
complexes in all studied solvents. Compound 4 shows larger FF
values than 6 in all studies solvents (Table 2). Lifetimes of fluores-
cence (sF, Table 2) were calculated using the natural radiative
Table 1
Spectral data for Pcs 4e6 in various solvents at 3.0 ꢀ 10ꢁ6 M.
Solvent
Pcs
Q band, lmax/nm
Log ε
B-band, lmax/nm
Log ε
Excitation
Emission
Stokes shift
lEx, (nm)
lEm, (nm)
DStokes, (nm)
Toluene
CHCl3
DCM
DMSO
Toluene
CHCl3
DCM
DMSO
Toluene
CHCl3
DCM
4
4
4
4
5
5
5
5
6
6
6
6
716, 685, 653, 621
718, 685, 653, 620
715, 685, 653, 621
689, 658, 631
685, 617
684, 617
685, 618
676, 613
740, 693, 664, 624
740, 694, 663, 626
741, 693, 665, 624
695, 662, 626
5.970, 5.906, 5.397, 5.270
5.841, 5.764, 5.237, 5.067
5.922, 5.860, 5.417, 5.290
5.681, 5.354, 5.268
5.819, 5.171
5.907, 5.248
5.838, 5.210
5.744, 5.208
4.727, 6.003, 5.204, 5.230
5.408, 5.758, 5.127, 5.011
4.788, 5.739, 4.988, 4.984
5.755, 4.988, 5.006
314
322
319
318
289
318
317
319
315
316
317
325
5.763
5.637
5.800
5.724
5.988
5.806
5.759
5.766
5.732
5.549
5.537
5.540
685, 717
686, 718
685, 716
695, 722
e
722
723
721
726
e
5
5
5
4
e
e
e
e
8
10
10
10
e
e
e
e
e
e
694
694
694
697
702
704
703
707
DMSO

Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
545
Table 2
Photophysical and photochemical data for Pcs 4e6 in various solvents.
a
Solvent Pcs FF
sF (ns) s0 (ns)
kF (sꢁ1) (ꢀ108) Fd (ꢀ10ꢁ5
)
FD
Toluene
CHCl3
DCM
DMSO
Toluene
CHCl3
DCM
DMSO
Toluene
CHCl3
DCM
4
4
4
4
5
5
5
5
6
6
6
6
0.18 0.91
5.03
8.15
4.96
9.06
e
1.99
1.16
1.76
1.18
2.75
1.67
9.29
3.12
1.07
0.97
0.020
0.015
1.47
0.31
e
0.23 1.87
0.21 1.04
0.19 1.72
1.22
2.01
1.10
e
e
0.21
0.0064
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
0.012
0.57
e
0.16 0.84
0.16 0.73
0.15 0.73
0.16 1.32
5.27
4.57
4.85
8.26
1.89
2.18
2.06
1.21
e
DMSO
0.78
a
kF is the rate constant for fluorescence. The values were calculated using kF
¼
FF/
sF
.
Fig. 6. Absorption spectral changes of Pc complex 4 in chloroform under light irra-
diation showing the disappearance of the Q band at 10 min intervals.
shape confirms photodegradation which is not associated with
phototransformation. The photodegradation quantum yield (Fd
)
values of 4, 5 and 6 in different solvents are given in Table 2. All the
complexes showed about the same stability with Fd of the order of
10ꢁ5. It was reported in literature that stable Pc molecules show Fd
values as low as 10ꢁ6 and unstable ones show Fd values of the order
of 10ꢁ3 [26]. The Fd values, found in this study, are similar with zinc
Pc derivatives having different substituents on the Pc ring in the
literature [26]; except those of 6 in both chloroform and DCM
suggesting that complex 6 forms J-aggregated species in these
solvents.
The value of 3.16 ꢀ 10ꢁ10 S/cm for the film of 6 at room temperature
is also higher than the reported [30] value (2.6 ꢀ 10ꢁ11 S/cm) for an
ortho-chloranil doped non-substituted zinc Pc and nearly in equal
order with that reported for non-substituted zinc Pc [31].
The higher conductivity values of 5 and 6 may arise from alpha-7-
oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituents in the
complexes. In general, DC conductivity values of the films of 5 and 6
were observed to increase with increasing temperature, suggesting
that the compounds are semiconductor in nature (Fig. 7).
Conductivity behavior of 5 and 6 can be analyzed in two different
temperature regions, low temperature region (T ꢃ 438 K for 5 and
T ꢃ 458 K for 6) and high temperature region (T > 438 K for 5 and
T > 458 K for 6). Each region corresponds to a different activation
energy with a different slope. This type of behavior can be inter-
preted as a transition from extrinsic to intrinsic conduction due to
the introduced acceptor level within the band gap by impurities
such as adsorbed O2 molecules during the deposition of the films.
Activation energy, EA1, for the low temperature region is associated
with a short lived charge transfer between impurity and complex.
Activation energy, EA2, for the higher temperature region, is asso-
ciated with the resonant energy involved in the short lived excited
state. EA1 and EA2 correspond to impurity conduction and an
intrinsic generation process, respectively. A similar behavior was
reported by Ceyhan et al. [32]. Linear behavior between the DC
conductivity and temperature can be represented by the well-
known expression (Arrhenius plot) for conductivity [33],
3.3. Electrical properties
3.3.1. DC properties
DC conductivity studies were performed on the films of 5 and 6
at different temperatures during heating from 295 K to 523 K under
vacuum (w2 ꢀ 10ꢁ3 mbar) in the dark. Current values passing
through the films were recorded versus (vs.) applied voltages. DC
conductivity values were determined using the IeV curves and
found to be 1.58 ꢀ 10ꢁ10 S/cm for the film of 5 and 3.16 ꢀ 10ꢁ10 S/cm
for the film of 6 at 295 K, respectively. These values increased to the
values of 5.86 ꢀ 10ꢁ5 S/cm and 3.70 ꢀ 10ꢁ5 S/cm at 523 K, for the
films of 5 and 6, respectively. The value for the film of 5
(1.58 ꢀ 10ꢁ10 S/cm) at room temperature is greater than that
(3.84 ꢀ 10ꢁ12 S/cm) reported [29] for the unsubstituted cobalt Pc.
Fig. 5. Absorption spectral changes during the determination of singlet oxygen
quantum yield of 6 in toluene at a concentration of 1 ꢀ 10ꢁ5 M.
Fig. 7. The variation of DC conductivity with temperature for the films of 5 and 6.

546
Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
Fig. 8. The variation of AC conductivity with frequency at different temperatures for
the film of 6.
Fig. 9. The variation of s with temperature for three different frequency regions for the
film of 6 (inset for the film of 5).
ꢀ
ꢁ
ꢁEA
sdc
¼
s0exp
(1)
kT
seen from this figure, s values should be analyzed in three different
frequency regions, low frequency region (
frequency region (103 Hz< < 104 Hz) and high frequency region
(104 Hz< < 105 Hz). In all frequency regions, temperature
u
< 103 Hz), middle
where EA is activation energy, T is temperature, k is Boltzman’s
constant and s0 is a proportionality constant. The EA1 and EA2
activation energies, determined from the slope of the ln sDC-1/T
graph, were found to be 0.84 eV (T ꢃ 438 K) and 0.48 eV (T > 438 K)
for 5 and 0.80 eV (T ꢃ 458 K) and 0.40 eV (T > 458 K) for 6,
respectively. These values are consistent with other reports in
different Pc films [34].
u
u
dependence of the s values showed decreasing behavior with
temperature. Derived values of s for the film of 5 take place within
the ranges of 0.687e0.006, 0.866e0.003 and 0.908e0.086 for the
low, middle and high frequency regions, respectively. The values for
the film of 6 are within the ranges of 0.440e0.001, 0.860e0.012 and
0.940e0.178 for the low, middle and high frequency regions,
respectively. One important point is the values of s at the temper-
atures 458, 478, 498 and 523 K for the films of 5 and 6. At these
temperatures s values are quite low and the values take place in the
range of 0.016 (458 K)e0.006 (523 K) and 0.019 (458 K)e0.001
(523 K) for the films of 5 and 6, respectively.
3.3.2. AC properties
Alternating current (AC) and impedance measurements were
carried out on the films of 5 and 6 as a function of frequency in the
range of 40 Hze100 kHz at different temperatures (295 K-523 K) in
vacuum ambient (w2 ꢀ 10ꢁ3 mbar) in dark. The AC conductivity of
6 was found to increase with increasing temperature and frequency
(Fig. 8). While as frequency increases from 40 Hz to 105 Hz, AC
conductivity of 6 increases from 5.00 ꢀ 10ꢁ9 S/cm (at 1600 Hz) to
2.55 ꢀ 10ꢁ7 S/cm at room temperature, the values increase from
7.45 ꢀ 10ꢁ6 S/cm (at 40 Hz) to 1.12 ꢀ 10ꢁ5 S/cm at 523 K in the
measurement frequency range. As in the case of the film 6, as
frequency increases from 40 Hz to 105 Hz, while AC conductivity of
5 increases from 5.00 ꢀ 10ꢁ9 S/cm (at 1000 Hz) to 3.35 ꢀ 10ꢁ7 S/cm
at room temperature, the values increases from 1.98 ꢀ 10ꢁ5 S/cm
(at 40 Hz) to 2.45 ꢀ 10ꢁ5 S/cm at 523 K. In general, sAC values of 5
were higher than those of 6 at all measurement frequency range
and temperatures. The temperature dependence of AC conductivity
of the film 6 can also be analyzed in two parts, low temperature
region (T < 438 K) and high temperature region (T > 438 K). At the
temperatures T < 438 K, its conductivity increases with increasing
frequency. At the temperatures T > 438 K, frequency dependence of
The Hopping model predicts
a frequency dependent AC
conductivity, which increases with the increasing frequency under
the condition that, the frequency exponent s ꢃ 1 [37]. The Hopping
model, which was developed by Elliot [37], assumes that charge
carriers hop between sites over the potential barrier separating
them. The model gives AC conductivity which can be expressed to
a first order approximation given by (for single electron hopping),
p
3N2εεo
u
24
sac
ð
u
; TÞ ¼
Ru6
(3)
where ε is the dielectric constant of the material, εo that of free
space, N is the spatial density of defect states and Ru is the hopping
distance. This model predicts a temperature-dependent s value
which is given by,
6kBT
Wm
AC conductivity of the film decreases. The sAC vs
similar to those in Fig. 8.
u curves of 5 were
s ¼ 1 ꢁ
b
¼ 1 ꢁ
(4)
At all temperatures frequency dependence of the measured AC
conductivity of the films of 5 and 6 follows a universal power law
given by Eq. (2) [35,36],
where kB is Boltzmann’s constant and Wm is the binding energy. In
this model s values decreases with increasing temperature. It is
observed that variation of s values shows a general tendency to
decrease with increasing temperature all over the measured
frequency range.
sac ¼ Aus
(2)
where
u
is the angular frequency, A and s are material depended
According to the Band theory, the AC conductivity should be
frequency independent and drops at sufficiently high frequency. In
the Quantum-Mechanical Tunneling (QMT) model [38], the
component s is almost equal to 0.8 and increases slightly as
temperature increases or is independent of temperature. In this
constants. To determine the charge transport mechanism involved,
the variation of the exponent s with temperature were examined. S
values were calculated from slope of straight portions of the AC
conductivity vs. frequency plot. The variation of s values with
temperature for the films of 5 (inset) and 6 were given in Fig. 9. As
model, s is given by s ¼ 1þ(4/lnuso) where,
u is the angular

Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
547
frequency and
s
o the relaxation time of the carrier. So, QMT model
rather than a single-relaxation time [40]. The depressed semicircles
with different radii indicate deviation from Debye dispersion
relation. Therefore, the equivalent circuit is modified to include
a constant phase element (CPE). The series resistance in the
equivalent circuit represents the ohmic losses in the test fixture and
electrode sheet resistance. The parallel resistance is of the coating
material in parallel with that of the substrate. The intercepts of the
semicircular arcs with real axis give us an estimate of the bulk
resistance of the material. It is observed that bulk resistance
decreases with increasing temperature indicating semiconductor
property. The existence of the CPE represents a slight distribution of
relaxation times instead of a discrete relaxation time. This inter-
is not applicable to our results. According to the Overlapping-Large
Polaron Tunneling (QLPT) model [39], the component s is both
frequency and temperature dependent and decreases with
increasing temperature to a minimum value at a certain tempera-
ture, then it increases with increasing temperature. This model is
also not applicable to our results. According to the Small Polaron
Quantum Mechanical Tunneling (SP) model, the component s is an
increasing function of temperature [37]. It is also well known that
the low values of s indicate multi-hopping process, while high
values of s indicate single-hopping process.
By comparing the models with our results, charge transport
mechanism of the films of 5 and 6 can be interpreted in two parts
depending on both temperature and frequency. In the low
temperature region (T < 458 K), dominant conduction mechanism
can be modeled by single hopping all over the measured frequency
range. In the high temperature region (T ꢄ 458 K) conduction
mechanism can be modeled depending on frequency region, i) low
pretation was consistence with Z versus
u plot (Bode plot). The
Bode plots for the films of 5 and 6 (inset) are shown in Fig. 11.
As temperature increases from 295 K to 418 K, the slope of log Z
versus log w curves varies from ꢁ0.989 to ꢁ0.921. It appears that
the film exhibits capacitive behavior between the temperatures of
295e418 K. The slope of the curves in the frequency range of
104e105 Hz takes the values ꢁ0.678, ꢁ0.478 and ꢁ0.250 at the
temperatures 478, 498 and 523 K, respectively. The results also
indicate the existence of a CPE [32]. Similar results of the Bode plot
were found for the film of 6 (inset in Fig. 11). The complex
impedance spectrum of 6 was also similar to those in Fig. 10.
frequency region (
u < 1000 Hz) and ii) high frequency region
(
u
ꢄ 1000 Hz). In the low frequency region, dominant conduction
mechanism can be modeled by multi-hopping and in the high
frequency region by single hopping.
The impedance data for the films of 5 and 6 were plotted in
complex plane (ColeeCole plot). The complex impedance, Z(
u) can
be represented as a function of frequency as,
3.4. Electrochemical and in situ spectroelectrochemical
measurements
Zð
u
Þ ¼ Z0ð
u
Þ þ jZ00ð
Þ
u
(5)
where Z0( ) and Z00(
u u) are the real and imaginary parts of imped-
The electrochemical behavior of
a-tetra substituted coumar-
ance. Variation of Z00(
u
) with ꢁZ0(
u) (Nyquist plot) for the film of 5
inoxy Pcs 4e6 was investigated by cyclic voltammetry, differential
pulse voltammetry and in situ spectroelectrochemistry in DMSO
and DCM involving tetrabutylammonium perchlorate (TBAP) as
supporting electrolyte. The voltammetric data of the complexes,
including the half-wave redox potential value (E1/2), anodic-to-
at different temperatures in the temperature range of 295e523 K
were given in Fig. 10. The impedance spectra of the film of 5
consist of a quasi-vertical line up to 438 K. The existence of
a semicircular shaped curve in the Nyquist plot means that the
impedance becomes capacitive even at relatively high frequency.
The curves can be modeled a resistor parallel with a capacitor in
series with another resistor [32]. The impedance spectra consist of
depressed semicircles with a different radius at the temperatures
438, 458, 478, 498 and 523 K. The temperature effect on impedance
spectra can be seen from Fig. 10. The radius of the semicircle
decreases with increasing temperature. An ideal semicircle in
complex plane only appears in Debye dispersion relations for
a single-relaxation time process. Most of the materials show
a pronounced deviation from Debye treatment as in our case. In this
case, the relaxation time is considered as a distribution of values,
cathodic peak potential separation
(
DEp) and the difference
between the first oxidation and reduction potential (
D
E1/2) are
summarized in Table 3. The peak currents for the redox couples of
the complexes were usually found to be directly proportional to the
square root of scan rate, suggesting their diffusion-controlled
nature.
Compound 4 displayed three reduction couples (R1eR3) and an
oxidation couple (O1) in DMSO/TBAP (Supplementary material,
Fig. S12). These processes are clearly Pc ring-based, except the third
reduction process (R3) which could be monitored only by differ-
ential pulse voltammetry. The R3 process occurs at remarkably
negative potentials and probably corresponds to the reduction of 7-
oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituents since
these groups, less conjugated as compared with the Pc ring, are
Fig. 10. The Nyquist plot at temperatures T ꢄ 458 K for the film of 5 (inset for
295K ꢃ T < 458 K).
Fig. 11. The variation of impedance with frequency for the film of 5 at different
temperatures (inset for the film of 6).

548
Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
Table 3
Voltammetric data for
a
-tetra-7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituted Pcs 4e6.
Complex
Ring Oxidations
M
II /MIII
MII /MI
Ring reductions
fDE1/2
a
d,e
4 (H2Pc) in DMSO
E1/2 (V)
0.49
0.070
ꢁ0.48
0.060
ꢁ1.23
0.100
ꢁ1.29
0.100
ꢁ0.68
0.080
ꢁ0.86
ꢁ1.64
0.97
bDEp (V)
0.080
d rev
a
d
5 (CoPc) in DMSO
5 (CoPc) in DCM
6 (ZnPc) in DMSO
6 (ZnPc) in DCM
E1/2 (V)
0.49
0.080
1.09
ꢁ0.29
0.100
ꢁ0.20
0.080
ꢁ1.65
0.78
0.85
1.53
1.08
bDEp (V)
drev
a
E1/2 (V)
0.65
0.060
0.85
0.100
0.88
0.080
bDEp (V)
0.060
a
e
E1/2 (V)
ꢁ0.96
ꢁ1.31
ꢁ1.64
0.140
bDEp (V)
aE1/2 (V)
bDEp (V)
0.120
e
c
c
c
e
ꢁ0.20 (ꢁ0.64)
ꢁ0.96
ꢁ1.30
ꢁ1.50
crev (rev)
c rev
c rev
rev
c
a
E1/2 ¼ (Epa þ Epc)/2 at 0.025 V s-1.
b
c
D
Ep ¼ Epa þ Epc at 0.025 V s-1.
E1/2 and
DEp could not be determined due to ill-defined cyclic voltammetry waves, associated with aggregation-deaggregation equilibria, however, the shape of the
differential pulse voltammograms implied reversible electron transfer.
d
E1/2 could be determined only by differential pulse voltammetry. The shape of the differential pulse voltammogram confirmed the reversibility of electron transfer process.
It corresponds probably to the reduction of coumarin substituent.
e
f
DE1/2 ¼ E1/2 (first oxidation) e E1/2 (first reduction). This value corresponds to the HOMOeLUMO gap for metal-free and metallophthalocyanines having electro-inactive
metal center, but it represents metal to ligand (MLCT) or ligand to metal (LMCT) charge transfer transition gap for metallophthalocyanines having redox active metal center.
expected to be reduced at relatively more negative potentials. The
cathodic to anodic peak current ratio of the first reduction process
was observed to increase with increasing potential scan rate,
indicating that electrochemically produced radical cations are not
stable electrochemically. Fig. 12A shows the cyclic voltammograms
of 5.00 ꢀ 10ꢁ4 M 6 at different scan rates in DMSO/TBAP. It shows
four reduction processes (R1-R4) and an oxidation couple (O1). The
redox-inactive nature of metal center in zinc Pcs is very clear from
previous literature [41]. R1eR3 and O1 processes can be attributed
to successive addition of electrons to, and removal of an electron
from the macrocycle orbitals, respectively [42]. The process R4,
appearing at high negative potentials at the end of solvent-limited
cathodic potential range, probably corresponds to the reduction of
7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituents since
the currents for this process occurring at the same potential are
much higher than those of the other Pc-based one-electron ones. In
fact, the current for this process is expected to be four times higher
than that of the other Pc-based one-electron ones. However, it was
not possible to check this proportionality exactly, due to the ill-
defined process appearing at high negative potentials. The
comparison of the two groups of cyclic voltammograms at different
scan rates in Fig. 12A suggests that the shape of the O1 couple is
strongly affected by the switching potential at the cathodic side.
The Pc-based redox processes of oxy-coumarin substituted 6 in
DMSO/TBAP occur at remarkably more positive potentials than
those of various unsubstituted [42] and RO-substituted zinc(II) Pcs
[43e46] due to the electron-withdrawing character of 7-oxy-4-(4-
methoxyphenyl)-8-methylcoumarin moieties. In situ spectroelec-
trochemical measurements were also carried out during the
controlled-potential electrolysis of 6 in DMSO at a suitable potential
corresponding to its first reduction process since this type of
measurements do not only have a vital importance in determining
the nature of the redox processes, but also provide support for the
evaluation of the aggregation effect on the redox processes. The
spectral changes during the first reduction process of 6 at ꢁ0.85 V
vs. SCE are shown in Fig. 12B. As shown in this figure, the associa-
tion of electron transfer process with aggregation is excluded by
a sharp Q absorption band in the spectrum of 6 in DMSO/TBAP at
the beginning of electrolysis. During the controlled-potential
electrolysis at ꢁ0.85 V vs. SCE, a decrease in the absorptions of
the Q band centered at 695 nm and the vibrational band at 625 nm
is observed without shift. At the same time, the absorption of the B
band at 320 nm decreases without shift and a new band appears at
556 nm. Well-defined isosbestic points are observed at 282, 428,
604 and 726 nm. These spectral changes, especially the formation
of a new band at 556 nm, are typical for Pc ring reduction, and thus,
the formation of [Zn(II)Pc(-3)]ꢁ species [47,48]. Therefore, the first
reduction process of 6 is assigned to Pc(-2)/Pc(-3) electron transfer
process which is not associated by aggregation-deaggregation
equilibrium.
Fig. 12. Cyclic voltammograms (A) and in situ UVevis spectral changes during the first
reduction (B) of 6.

Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
549
Fig. 13A shows the cyclic and differential pulse (inset) voltam-
mograms of 5.00 ꢀ 10ꢁ4 mol dmꢁ3 6 in a non-coordinating solvent
medium, DCM/TBAP. It also shows four reduction processes
(R1eR4) and an oxidation couple (O1) in DCM/TBAP. However, the
first reduction process is split into two reduction couples (R1’ and
R1’’). Thus, it occurs at less negative potentials than those in DMSO/
TBAP. The first oxidation process in DCM/TBAP is observed at
similar potentials to those in DMSO/TBAP. It appears that the non-
coordinating solvent DCM makes the first reduction process of 6
easier, probably as a result of the increasing interaction between
the metal center of a Pc molecule and the oxygen atoms in another
Pc molecule, and thus remarkable stabilization of the LUMO energy
level. It appears that the mentioned interactions between the ZnPc
molecules lead to the establishment of equilibrium between
monomer and J-aggregated species. In the light of this evaluation,
the R1’ and R1’’ processes can be attributed to the reduction of J-
aggregated and monomeric species, respectively. The presence of
equilibrium between monomer and J-aggregated species of 6 in
DCM/TBAP was confirmed clearly by the split Q band in its elec-
tronic absorption spectrum (Fig. 13B). Fig. 13B shows the former
spectral changes during the application of ꢁ0.80 V vs. SCE. The
absorption of the J-band at 741 nm decreases without shift and
finally disappears while the absorption of the Q band at 692 nm
increases. The first group of spectral changes is followed by
decrease in the absorptions of the bands at 692, 622, 400 and
316 nm without shift and increase in the absorption between 500
and 600 nm (Fig. 13C). This second group of spectral changes are
typical for a Pc(-2)/Pc(-3) reduction process. The two groups of
spectral changes in Fig. 13B and C suggest clearly that in DCM/TBAP,
J-aggregated species of 6 deaggregates before the first reduction
process. The spectral changes during the second reduction process
of 6 at ꢁ1.00 V vs. SCE are shown in Fig.13D. As shown in this figure,
the absorptions of the bands at 692, 662, 622 and 589 nm decrease
without shift whereas the intensity of the band at 587 nm increases
also without shift. These spectral changes are characteristic for
a Pc(-3)/Pc(-4) reduction process. On the basis of the well-known
electrochemical behavior of metal Pcs involving redox-inactive
metal center [42], the R3 couple corresponds to the third reduc-
tion process of Pc(-4)/Pc(-5). Although the peak currents of R4
couple appearing at remarkably negative potentials at the end of
solvent-limited cathodic potential range are comparable to those of
other Pc-based couples, the remarkably higher peak currents of R4
in the differential pulse voltammogram in the inset in Fig. 13A
implies that it can be attributed to the four-electron reduction of
four substituents at the same potential.
Fig. 14A shows the cyclic and differential pulse (inset) voltam-
mograms of 5 (CoPc) in DMSO/TBAP. The complex 5 undergoes
three reductions (R1, R2 and R3) and an oxidation (O1) within the
available potential range. As shown in the inset, the R3 couple could
be monitored only by differential pulse voltammetry. Co(II) center
in 5 may have accessible d orbital levels lying between the HOMO
and LUMO gap of the Pc ligand, depending on whether there are
any available coordinating species that would stabilize it, and thus,
can be oxidized and reduced before the ring-based redox processes.
For this reason, spectroelectrochemical measurements were also
carried out to assign the redox processes of 5, especially the first
reduction and the first oxidation. The complex 5 does not aggregate
in TBAP/DMSO as evidenced from the narrow Q band at 677 nm in
Fig. 13. Cyclic and differential pulse (inset) voltammograms of 6 (A) and in situ UVevis spectral changes during the electrolysis of 6 at various constant potentials (BeD).

550
Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
Fig. 14. Cyclic and differential pulse (inset) voltammograms of 5 (A) and in situ UVevis spectral changes during the redox processes of 5 at various constant potentials (BeD) in
DMSO/TBAP.
its original absorption spectra in Fig. 14B which also shows the
spectroscopic changes observed across the first reduction of 5 in
DMSO/TBAP. With the progress of electrolysis, the Q band nearly
fades away and a new Q band, which has approximately half the
intensity of the original Q band, develops at longer wavelength,
accompanied by formation of a new band at 476 nm in the region
between the Q and Soret bands. A set of isosbestic points was
detected at four wavelengths. These are similar to the changes
observed to date for many CoPc derivatives when Co(II) was
reduced to Co(I), and the band developed between the Q and Soret
bands has been assigned to an metal-to-ligand charge transfer
(MLCT) process from cobalt eg to ligand b1u and b2u orbitals under
D4h symmetry [49e51]. Thus, it is very clear that the first reduction
is occurring at cobalt. During the second reduction, the Q bands at
686 and 718 nm decreased without shift (Fig. 14C) while the
absorption between 500 and 600 nm increased and a new weak
band at 564 nm appeared. These spectral changes at the potential of
the couple R2 are characteristic for a ring-based reduction in Co(II)
Pc complex, [Co(I)Pc(-2)]ꢁ/[Co(I)Pc(-3)]2ꢁ. The subsequent third
reduction is also expected to be on the ring in comparison with
literature [42]. Fig. 14D displays the spectral changes during the
first oxidation process. The Q band at 677 nm increases in intensity
with red shift to 683 nm. The increase of the Q band with red shift is
typical of a metal-based oxidation in CoPc complexes, and thus,
indicates clearly that the O1 couple of 5 corresponds to Co(II)Pc(-2)/
[Co(III)Pc(-2)]þ process [52e54].
couples in DCM/TBAP while it shows only one oxidation couple in
DMSO/TBAP within the available potential ranges. The first oxida-
tion process of 5 in DCM/TBAP occurs at more positive potentials
than that in DMSO/TBAP. Contrary to that in DMSO/TBAP, the first
oxidation couple in DCM/TBAP is probably ring-based whereas the
second oxidation process of 5 in DCM/TBAP should correspond to
Co(II)/Co(III) couple [42]. Fig. 15B displays the UVevis spectrum of 5
in DCM/TBAP and in situ spectral changes during its first reduction
at ꢁ0.60 V vs. SCE. As shown in this figure, the solution of complex 5
in DCM/TBAP does not involve H- or J-aggregated species as
understood clearly from the narrow and non-split Q band at
683 nm. The absorption of the Q band at 683 nm decreases and
a new Q band develops at longer wavelength. These spectral
changes at ꢁ0.60 V vs. SCE are accompanied by the formation of
a new band at 471 nm which is assigned to an MLCT process from
cobalt eg to ligand b1u and b2u orbitals under D4h symmetry when
Co(II) is reduced to Co(I) [49e51]. During the second reduction, the
Q bands at 649, 686 and 712 nm decreases without shift while the
absorption between 500 and 600 nm increases, and a new band at
this region appears (Fig. 15C). These spectral changes at the
potential of the couple R2 are characteristic for a ring-based
reduction in Co(II)Pc complex, [Co(I)Pc(-2)]ꢁ/[Co(I)Pc(-3)]2-
.
Fig. 15D displays in situ UVevis spectral changes during the first
oxidation process of 5 at 0.85 V vs. SCE in DCM/TBAP. The absorp-
tion of the Q band at 683 nm decreases without shift and a new
band forms at 538 nm. These spectral changes are characteristic
for a Pc-based oxidation and thus, lead to the formation of [Co(II)
Pc(-1)]þ species [47,48]. Unfortunately, the controlled-potential
The reduction behavior of 5 in DMSO/TBAP and DCM/TBAP is
very similar (Figs. 14A and 15A). However, it displays two oxidation

Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
551
Fig. 15. Cyclic voltammograms of 5 (A) and in situ UVevis spectral changes during the redox processes of 5 at various constant potentials (BeD) in DCM/TBAP.
electrolysis of 5 at the potentials more positive than 1.20 V vs. SCE
in DCM/TBAP resulted in decomposition of the complex under the
conditions of constant-potential electrolysis, as evidenced from
decrease in the absorption of all peaks. However, the previous
studies on the redox behavior of Co(II) Pcs suggest that the second
oxidation of 5 in DCM is metal-based and thus, can be assigned to
[Co(II)Pc(-1)]þ/[Co(III)Pc(-1)]2þ redox couple [42].
In general, DC conductivity of the films of 5 and 6 was observed
to increase with increasing temperature and display Arrhenius
behavior with activation energies varying within the range of
0.40e0.84 eV depending on temperature regions. The evaluation of
the AC conductivity measurements suggested that the charge
transport mechanism in their films can be explained by a hopping
model.
Electrochemical and in situ spectroelectrochemical measure-
ments of the complexes showed that 4 and 6 display Pc ring-based
redox processes whereas 5 display both metal and Pc ring-based
processes. In DMSO, the oxidation of the Co(II) center in 5 occurs
before that of Pc ring, probably as a result of its coordination at axial
positions by the solvent molecules while the order of the oxidation
processes changes in DCM which is non-coordinating. In DCM, the
first reduction and oxidation couples of 6 are split due to the
presence of J-aggregates and the equilibrium between monomeric
and aggregated species.
4. Conclusion
The novel
(5) and zinc(II) Pc (6) have been synthesized from 3-[4-(4-
methoxyphenyl)-8-methylcoumarin-7-oxy]phthalonitrile (3).
a-tetra substituted metal free Pc (4), cobalt(II) Pc
The complexes were characterized by elemental analysis,
UVevis, IR, 1H NMR, 13C NMR and MALDI-TOF mass spectros-
copies. It was concluded from the investigation of the spectro-
scopic behavior of these novel compounds in various solvents
that complex 6 forms J-aggregates in non-coordinating solvents
Acknowledgment
such as chloroform, DCM and toluene, as
a result of the
complementary coordination of the oxygen atoms in the mac-
rocycle of one molecule to the core zinc atom of another mole-
cule. The observed J-aggregates were broken up by the addition
of a coordinating solvent such as DMSO.
We are thankful to The Foundation of Marmara University and
The Commission of Scientific Research (BAPKO) (Project No: FEN-A-
090909-0302).
The photophysical and photochemical properties of metal-free
(4), cobalt (5) and zinc (6) Pc complexes were described in
different solvents (toluene, chloroform, DCM and DMSO) for
comparison. Complex 6 showed good singlet oxygen generation
which gives an indication of its potential usability as photosensi-
tizer in photocatalytic applications such as photodynamic therapy.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.dyepig.2012.05.
021.

552
Z. Odabas¸ et al. / Dyes and Pigments 95 (2012) 540e552
[27] Maree MD, Nyokong T, Suhling K, Phillips D. Effects of axial ligands on the
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