Synthesis, characterization and electrochemical properties of novel β 7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituted metal-free, Zn(II) and Co(II) phthalocyanines

Article abstract of DOI:10.1016/j.poly.2012.03.036

Novel metal-free (4), Co(II) (5) and Zn(II) (6) phthalocyanines bearing four 7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituents at peripheral (β) positions have been prepared by cyclotetramerization of 4-(4-(4-methoxyphenyl)-8-methylcoumarin-7-oxy)phthalonitrile. The compounds have been characterized by elemental analysis and IR, UV-Vis and MALDI-TOF mass spectroscopies. H-aggregation behaviour of the compounds has been investigated in different solvent media. Furthermore, the redox properties of the complexes were examined in dimethylsulfoxide and dichloromethane by voltammetry and in situ spectroelectrochemistry. In general, compounds 4 and 6 displayed ligand-based one-electron redox processes, while compound 5 showed both ligand- and metal-based processes, in addition to a couple corresponding to the reduction of the 7-hydroxy-4-(4-methoxyphenyl)-8-methylcoumarin substituents. Both electrochemical and in situ spectroelectrochemical data showed that the redox processes of these complexes are complicated by their high aggregation tendency.

Full text of DOI:10.1016/j.poly.2012.03.036

Polyhedron 39 (2012) 38–47
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and electrochemical properties of novel
b 7-oxy-4-(4-methoxyphenyl)-8-methylcoumarin substituted metal-free,
Zn(II) and Co(II) phthalocyanines
⇑
⇑
Zafer Odabasß, Hatice Kara, Ali Rıza Özkaya , Mustafa Bulut
Department of Chemistry, Marmara University, 34722 Göztepe, Kadıköy, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel metal-free (4), Co(II) (5) and Zn(II) (6) phthalocyanines bearing four 7-oxy-4-(4-methoxyphenyl)-
8-methylcoumarin substituents at peripheral (b) positions have been prepared by cyclotetramerization of
4-(4-(4-methoxyphenyl)-8-methylcoumarin-7-oxy)phthalonitrile. The compounds have been character-
ized by elemental analysis and IR, UV–Vis and MALDI-TOF mass spectroscopies. H-aggregation behaviour
of the compounds has been investigated in different solvent media. Furthermore, the redox properties of
the complexes were examined in dimethylsulfoxide and dichloromethane by voltammetry and in situ
spectroelectrochemistry. In general, compounds 4 and 6 displayed ligand-based one-electron redox pro-
cesses, while compound 5 showed both ligand- and metal-based processes, in addition to a couple cor-
responding to the reduction of the 7-hydroxy-4-(4-methoxyphenyl)-8-methylcoumarin substituents.
Both electrochemical and in situ spectroelectrochemical data showed that the redox processes of these
complexes are complicated by their high aggregation tendency.
Received 2 February 2012
Accepted 8 March 2012
Available online 2 April 2012
Keywords:
Coumarin
Phthalocyanine
Synthesis
Aggregation
Electrochemistry
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
oxygen heterocyclics with a d-lactone ring and comprise a very
large class of compounds found throughout the plant kingdom
Phthalocyanines (Pcs) have attracted much attention for many
decades because they can be used in catalysts [1], chemical sensors
[2], solar cells [3], colour filters for liquid crystal display devices,
ink jet inks, data storage, infrared ray absorbents, electrophoto-
graphic photoreceptors, non-linear optical devices, deodorizers
and photosensitizers used for photodynamic therapy [4,5]. The sol-
ubility of Pcs is very important for the investigation of their chem-
ical and physical characteristics. Their properties are influenced
not only by the nature of the substituents (i.e., their electron
donating or electron withdrawing properties) on the ligand, but
also by that of the metal ion in the core of the ligand. Thus, the sol-
ubility can be improved by introducing different kinds of solubil-
ity-enhancing substituents, such as alkyl, alkoxyl, phenoxyl and
macrocyclic groups, into the peripheral of the Pc ring [6].
Numerous studies have been performed to modify Pcs with the
goal of tuning their properties and optimizing the efficiency in
their various applications. For the medical applications, Pcs conju-
gated with biological molecules are rare and only a few examples
containing monosaccharides [7], amino acids [8], antibodies [9]
and coumarins [10–12] have been described. Coumarins (2H-chro-
men-2-ones, 2H-1-benzopyran-2-ones) are among the best known
[13]. When the lactone ring at the coumarin has been opened in
strong alkaline media, water-soluble species occur. If alkyl groups
are introduced into the coumarin compounds, the groups will in-
duce the Pc solubility in organic solvents [14,15]. Therefore, we
have combined coumarin and Pc materials into a single compound
via a synthetic methodology to obtain novel Pcs.
The electrochemistry of Pcs has received considerable interest
in recent years since there is a strong relationship between their
redox properties and most of their industrial applications, such as
semiconductors, photovoltaic cells, electrochromic displays and
catalysts [16]. Small modifications in Pc molecules may remark-
ably influence their redox properties since these properties de-
pend on various factors, such as the type of the central metal,
solvent, axial ligands, substituents and aggregation [16–18]. It is
well known that Pcs may dimerize and even form larger and
more complex aggregates, owing to the extended
p system [19–
21]. In most cases, the aggregation phenomenon is deleterious
to the desired electrical [22], spectroscopic [23], photophysical
[24] and electrochemical [25] properties of these compounds.
On the other hand, the formation of well-defined Pc dimers
and/or aggregates is useful in materials and catalytic applications
where the self-assembly of Pc cores in close proximity is benefi-
cial [26–28].
⇑
Corresponding authors. Tel.: +90 216 347 96 41; fax: +90 216 347 87 83.
E-mail addresses: aliozkaya@marmara.edu.tr (A.R. Özkaya), mbulut@marmara.
Voltammetry is the most widely used electrochemical method
to determine the redox properties of Pcs compounds. However,
edu.tr (M. Bulut).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.03.036

Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
39
in most cases, the nature of their redox processes cannot be distin-
guished thoroughly by voltammetric methods alone. A combina-
tion of spectroscopic and electrochemical techniques, i.e., in situ
spectroelectrochemical measurements, allows us to determine
whether the redox processes occur in the Pc ring or at the metal
centre [29]. In addition, this technique makes the identification
of the effect of aggregation phenomena on the redox processes
possible since the aggregation processes can be probed using elec-
tronic spectroscopy.
In the present work, novel b-tetra substituted metal free, cobalt
and zinc Pcs have been prepared from 4-(4-(4-methoxyphenyl)-
8-methylcoumarin-7-oxy)phthalonitrile (Scheme 1) and character-
ized by elemental analyses, UV–Vis, IR and matrix assisted laser
desorption/ionization-time of flight (MALDI-TOF) mass spectrosco-
pies. The aggregation behaviour of the newly synthesized com-
pounds was investigated by UV–Vis spectroscopy in different
solvents, such as toluene, chloroform, dichloromethane (DCM)
and dimethylsulfoxide (DMSO). Moreover, the redox and aggrega-
tion behaviours of 4–6, and the effect of aggregation phenomena
on their redox behaviours have been examined by voltammetry
and in situ spectroelectrochemistry.
sively by washing with acetic acid, water, ethanol and acetonitrile
in a soxhlet apparatus and by column chromatography. The melt-
ing points of the Pc compounds were found to be higher than
300 °C. The purity of the products was tested in each step by TLC
(SiO2). Chromatography was performed on silica gel 60. UV–Vis
spectra were recorded on
a
Shimadzu UV-1601 UV–Vis
spectrometer. IR spectra (KBr pellets) were recorded on a Shima-
dzu FT-IR-8300 spectrometer. 1H NMR spectra were recorded on
a Varian UNITY INOVA 500 MHz spectrometer. Elemental analyses
were performed by the Instrumental Analysis Laboratory of the
TUBITAK Marmara Research Centre. Mass spectra were acquired
on an Autoflex III MALDI-TOF mass spectrometer (Bruker Dalton-
ics, Germany) equipped with a nitrogen UV-Laser operating at
337 nm and spectra were recorded in the reflectron mode with
an average of 50 shots.
The electrochemical and in situ spectroelectrochemical mea-
surements were monitored using a Gamry Reference 600 poten-
tiostat/galvanostat controlled by an external PC and utilizing a
three electrode configuration at 25 °C. UV–Vis absorption spectra
were recorded by an Agilent 8453 diode array spectrophotometer
equipped with a potentiostat/galvanostat. The electrochemical
measurements were carried out in extra pure DMSO containing
electrochemical grade tetrabutylammonium perchlorate (TBAP)
as the supporting electrolyte at a concentration of 0.10 mol dmÀ3
.
2. Experimental
For cyclic voltammetry (CV) and differential pulse voltammetry
(DPV) measurements, the working electrode was a Pt plate with
a surface area of 0.10 cm2. A Pt spiral wire served as the counter
electrode. A saturated calomel electrode (SCE) was employed as
the reference electrode and separated from the bulk of the solu-
tion by a double bridge. High purity N2 was used for deoxygenat-
ing the solution at least 20 min prior to each run and to maintain
a nitrogen blanket during the measurements. Ferrocene was used
as an internal reference, but the potentials were presented as the
ones versus SCE. In situ spectroelectrochemical measurements
were carried out by utilizing a three-electrode configuration of
2.1. Materials and methods
Our starting compounds 7-hydroxy-4-(4-methoxyphenyl)-8-
methylcoumarin 1 and 4-nitrophthalonitrile 2 were prepared
according to the reported procedures [30,31]. Zn(OAc)2Á2H2O and
Co(OAc)2Á4H2O were purchased from Aldrich Chemical Co., and
were used as received. All reactions were carried out under a nitro-
gen atmosphere. All solvents were purified, dried and stored over
molecular sieves (4 Å). The Pc compounds were purified succes-
a
thin-layer quartz spectroelectrochemical cell at 25 °C. The
working electrode was a transparent Pt gauze. A Pt wire counter
electrode separated by a glass bridge and a SCE reference elec-
trode separated from the bulk of the solution by a double bridge
were used.
2.2. Sample and matrix preparation
The matrix, a-cyano-4-hydroxycinnamic acid, was prepared in
tetrahydrofuran (THF) at a concentration of 10 mg/mL as the ma-
trix. The MALDI samples were prepared by mixing sample solu-
tions (2 mg/mL in chloroform) and the matrix solution (1:10 v/v)
in a 0.5 mL eppendorfÒ micro tube. Finally, 0.5
lL of this mixture
was deposited on the sample plate, dried at room temperature
and then analyzed.
2.3. Syntheses
2.3.1. 4-(4-(4-Methoxyphenyl)-8-methylcoumarin-7-
oxy)phthalonitrile (3)
7-Hydroxy-4-(4-methoxyphenyl)-8-methylcoumarin 1 (1.41 g,
5 mmol) and 4-nitrophthalonitrile 2 (0.86 g, 5 mmol) were dis-
solved in 20 mL anhydrous DMSO. 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 °C for 24 h under a N2
atmosphere. After the K2CO3 salt was filtered off, the mixture
was poured into ice water and the obtained precipitate was filtered
off, washed with water and dried in a vacuum at 50 °C. The crude
product was purified by column chromatography with silica gel
eluting with chloroform, with a gradient of chloroform–THF from
0% to 5% THF.
Scheme 1. Synthesis of 3, 4, 5 and 6. Reagents and conditions: i. K2CO3, N2, DMSO,
50 °C, 24 h; ii. (a) 2-N,N-dimethylaminoethanol, N2 160 °C, 48 h, (b) Co(OAc)2Á4H2O,
N2, 320 °C, 20 min, (c) Zn(OAc)2Á2H2O, N2, 320 °C, 20 min.

40
Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
Compound 3 is soluble in DCM, CHCl3, THF, dimethylformamide
3. Results and discussion
(DMF) and DMSO. Mp: 205–208 °C. Yield: 1.86 g (91.18%). Anal.
Calc. for C25H16N2O4: C, 73.52; H, 3.95; N, 6.86. Found: C, 73.41;
H, 4.12; N, 7.03%. IR (KBr pellet) mmax (cmÀ1): 524, 609, 825, 960,
1017, 1071, 1093, 1180, 1247, 1365, 1419, 1485, 1513, 1587,
1606, 1730, 2234, 2847, 2964, 3045, 3079. 1H NMR (CDCl3) d,
ppm: 2.30 (s, 3H), 3.80 (s, 3H), 6.35 (s, 1H), 6.82 (d, J = 8.98 Hz,
1H), 6.98 (dd, J = 8.99 Hz, J = 2.73 Hz, 2H), 7.18 (dd, J = 8.20 Hz,
J = 2.35 Hz, 1H), 7.22 (s, 1H), 7.34 (dd, J = 8.98 Hz, J = 2.74 Hz, 2H),
7.42 (d, J = 8.59 Hz, 1H), 7.69 (dd, J = 8.20 Hz, J = 2.35 Hz, 1H).
MALDI-TOF mass m/z: 393 (MÀCH3)+, 409 (M+H)+, 431 (M+Na)+,
447 (M+K)+.
3.1. Syntheses and characterization
The starting material, 4-(4-(4-methoxyphenyl)-8-methylcoum-
arin-7-oxy)phthalonitrile 3, was synthesized by the K2CO3-
catalyzed nucleophilic aromatic nitro displacement of 4-nitropht-
halonitrile
2 with 7-hydroxy-4-(4-methoxyphenyl)-8-methyl-
coumarin 1 [31–33]. The novel cobalt Pc 5 and zinc Pc 6 were
prepared by a templated cyclotetramerization reaction from 4-(4-
(4-methoxyphenyl)-8-methylcoumarin-7-oxy)phthalonitrile
3
and the metal salts [anhydrous Co(OAc)2Á4H2O or Zn(OAC)2Á2H2O]
in a little DMF (gel media) at 320 °C. The metal-free Pc 4 was
synthesized by using the same starting material 3 in 2-N,N-dimeth-
ylaminoethanol at 160 °C under a N2 atmosphere (Scheme 1). The
b-tetra-[4-(4-methoxyphenyl)-8-methylcoumarin-7-oxy]-substi-
tuted Pcs 4–6 were washed with water, acetic acid, ethanol and
acetonitrile, respectively, in a soxhlet apparatus, and then purified
by column chromatography. These novel Pcs are soluble in various
solvents, such as toluene, chloroform, DCM, THF, DMSO and DMF.
The characterization of the new products involved a combination
of methods including elemental analyses, IR, UV–Vis and MALDI-
TOF mass spectroscopy. Elemental analysis results and the spectral
data of the newly synthesized compounds 3, 4, 5 and 6 are consis-
tent with the proposed structures.
2.3.2. 3,10,17,24-Tetra(4-(4-methoxyphenyl)-8-methylcoumarin-7-
oxy)phthalocyanine (4)
Compound 3 (0.20 g, 0.5 mmol) was heated with 2 mL dry 2-
N,N-dimethylaminoethanol in a sealed tube. The mixture was
held at 160 °C for 48 h under a N2 atmosphere. After cooling
to room temperature, the reaction mixture was treated with di-
lute HCl and the mixture was filtered and washed with water
until the filtrate became neutral. The raw green product was ta-
ken in a soxhlet apparatus then purified by washing with acetic
acid, water, ethanol and acetonitrile for 12 h, respectively. The
crude product was purified by column chromatography with sil-
ica gel, eluting with chloroform, with a gradient of chloroform–
THF from 0% to 5% THF. The metal-free Pc 4 is soluble in chloro-
form, DCM, THF, DMF and DMSO. Mp >300 °C. Yield: 138.2 mg
(67.70%). Anal. Calc. for C100H66N8O16: C, 73.43; H, 4.07; N,
6.85. Found: C, 73.31; H, 3.95; N, 6.99%. IR (KBr pellet) mmax
(cmÀ1): 531, 743, 834, 1019, 1083, 1175, 1248, 1366, 1470,
1511, 1596, 1728, 2837, 2916, 2963, 3064, 3287. MALDI-TOF
mass m/z: 1632 (M+), 1655 (M+Na)+. UV–Vis (DCM): kmax (nm),
The FT-IR absorption spectrum of 3 exhibited a –C@C– double
bond at 1606 cmÀ1
, coumarin carbonyl (lactone, –C@O) at
1730 cmÀ1, –CH3 at 2847 and 2964 cmÀ1, and stretching frequen-
cies for Ar–H at 3106 and 3079 cmÀ1. The FT-IR spectrum clearly
showed the formation of 3 with the appearance of a new absorp-
tion band at 2230 cmÀ1 (–C„N) and additional bands at
1247 cmÀ1 (Ar–O–Ar). The IR-spectra of the metal-free Pc 4, the co-
balt Pc 5 and the zinc Pc 6 are very similar, with the exception of 4
showing an N–H weak stretching band due to the inner core at
(loge): 289 (5.532), 336 (5.586), 608 (5.149), 639 (5.307), 664
(5.550), 698 (5.585).
3287 cmÀ1
.
The molecular ion peaks [M]+ of the ligand 3 and Pc compounds
4–6 were identified easily by using MALDI-TOF mass spectroscopy.
For ligand 3, the protonated molecular ion peak was observed at
409 Da. Besides the protonated molecular ion peak of the com-
pound, three intense peaks were observed, one at 394 Da with a
15 Da mass difference (for the leaving CH3 group) from the proton-
ated molecular ion peak, the sodium adduct at 431 [M+Na]+ Da and
the potassium adduct at 447 [M+K]+ Da. The molecular ion peaks of
4, 5 and 6 were observed at 1632, 1691 and 1697 [M]+ Da, respec-
tively. The sodium adducts were also observed at 1655, 1714 and
1720 [M+Na]+ Da. The experimental mass values for the molecular
ions of 3–6 overlapped with the theoretical or calculated ones. The
MALDI-TOF mass spectrum of 5 is shown as an example in Fig. 1.
The 1H NMR spectra of 3 exhibited characteristic signals for
methyl (–CH3) and –OCH3 protons at d 2.30 and 3.80 ppm, respec-
tively, each as a singlet. The peaks at d 6.35 and 6.82–7.69 ppm
indicate the presence of the proton at the lactone ring and the aro-
matic protons respectively.
2.3.3. 3,10,17,24-Tetra(4-(4-methoxyphenyl)-8-methylcoumarin-7-
oxy)phthalocyaninatozinc (II) and cobalt(II) (5 and 6)
A mixture of compound 3 (0.20 g, 0.5 mmol) and the metal
salts [0.13 g, 0.5 mmol Co(OAc)2Á4H2O or 0.13 g, 0.5 mmol
Zn(OAc)2Á2H2O] was powdered in a quartz crucible and trans-
ferred to a reaction tube. DMF (0.30 mL) was added to this reac-
tion mixture, and then the mixture was heated in the sealed
glass tube for 20 min under dry N2 atmosphere at 320 °C. After
cooling to room temperature, 3 mL of DMF was also added to
the residue to dissolve the product. The reaction mixture was
precipitated by adding acetic acid. The precipitate was filtered
and washed with acetic acid, water, ethanol and acetonitrile
for 12 h respectively in a soxhlet apparatus. The crude product
was purified by column chromatography with silica gel, eluting
with chloroform, with a gradient of chloroform–THF from 0%
to 5% THF.
Cobalt Pc 5 is soluble in chloroform, DCM, THF, DMF and DMSO.
Mp >300 °C. Yield: 101.6 mg (49.03%). Anal. Calc. for C100H64Co-
N8O16: C, 70.96; H, 3.81; N, 6.62. Found: C, 70.75; H, 3.99; N,
6.74%. IR (KBr pellet) mmax (cmÀ1): 436, 752, 831, 959, 1084,
1176, 1249, 1367, 1411, 1469, 1512, 1595, 1726, 2837, 2932,
3072. MALDI-TOF mass: m/z 1691 (M+), 1714 (M+Na)+. UV–Vis
3.2. Electronic absorption properties
(DCM): kmax (nm), (log
Zinc Pc 6 is soluble in chloroform, DCM, THF, DMF and DMSO.
Mp >300 °C. Yield: 114.6 mg (55.10%). Anal. Calc. for
e
): 313 (5.934), 614 (5.116), 672 (5.332).
The propensity of Pcs to self-aggregate through the coplanar
association of the Pc rings to form dimers and higher order aggre-
gates is well known [34,35]. In general, Pc aggregation is thought
to reflect coplanar interactions involving the macrocycle ring. These
C
100H64ZnN8O16: C, 70.69; H, 3.80; N, 6.60. Found: C, 70.87; H,
3.64; N, 6.48%. IR (KBr pellet) mmax (cmÀ1): 532, 565, 616, 696,
742, 761, 833, 863, 885, 960, 990, 1026, 1081, 1176, 1242, 1366,
1390, 1428, 1487, 1512, 1596, 1728, 2836, 2934, 3068. MALDI-
TOF mass m/z: 1697 (M+), 1720 (M+Na)+. UV–Vis (DCM) kmax
interactions occur as a result of favourable van der Waals forces, p-
stacking interactions and solvent effects. The aggregation process of
Pcs can be easily probed using electronic spectroscopy. Upon for-
mation of higher order complexes, the coupling between the elec-
tronic states of individual monomeric Pc units causes significant
(nm), (loge): 288 (5.558), 347 (5.604), 613 (5.167), 680 (5.907).

Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
41
at 617 nm with a relatively higher intensity (Fig. 2A). The B-band
is observed at 321 nm as a single peak in DMSO. The presence of
higher order Pc systems due to aggregation can be observed in
the Q-band region of the electronic absorption spectrum. Typically,
Pc aggregation results in a decrease in intensity of the components
of the Q-band corresponding to the monomeric species, meanwhile
a new, broader and blue-shifted band is usually seen to increase in
intensity. This shift to lower wavelengths corresponds to H-type
aggregates. Thus, the broad band at 617 nm can be assigned to H-
type aggregates. The reason for the non-split broad main Q-band
of 4 should also be aggregation. Aggregation behaviour of 4 in
DMSO was also examined by the spectra monitored at different
concentrations within the range between 3.0 Â 10À6 and
0.38 Â 10À6 mol dmÀ3 (Fig. 3A). At
a
concentration of
3.0 Â 10À6 mol dmÀ3, the band with the higher energy at 617 nm
is much stronger than the one with lower energy at 678 nm. How-
ever, as the concentration of 4 is decreased, the decrease in the
absorption is more pronounced for the band at 617 nm, and thus
their intensities become approximately equal when compound 4
is diluted to a concentration of 0.38 Â 10À6. This observation pro-
vides strong evidence for the assignment of the band at 617 nm
to the H-type aggregates.
Fig. 1. Positive ion in reflectron mode MALDI-TOF-MS spectrum of 5 obtained in a-
cyano-4-hydroxycinnamic acid. Inset spectrum shows the expanded molecular ion
and the sodium ion adducts mass region of the complex.
spectral perturbations [36]. Different solvents and the concentra-
tion have a great influence on the aggregation behaviour of Pcs.
Therefore, in this study, the effects of solvent and concentration
on the aggregation behaviour and thus on the electronic absorption
properties of the novel Pcs have been investigated. The relevant Q-
band and B-band absorption data of the compounds in toluene,
CHCl3, DCM and DMSO are summarized in Table 1. The variations
in kmax in Table 1 reveal how the central ions and the solvents pro-
vide a means of tuning the wavelength of the Q-band absorption.
The UV–Vis spectrum of the metal-free Pc 4 exhibits a sharply split
Q-band absorption at 701 and 666 nm in toluene, at 697 and
664 nm in chloroform, and at 698 and 664 nm in DCM (Fig. 2A).
Monomeric Pcs exhibit strong absorption bands in the 300 and
700 nm spectral regions, corresponding to the electronic transitions
The cobalt Pc 5 shows only a single broad Q-band absorption for
the
p
p⁄ transitions within the range 672–660 nm, with a weak
À
vibrational band as a shoulder at around 605 nm in different sol-
vents (Fig. 2B). While H-aggregation of metal-free Pc 4 in DMSO
is observed by the appearance of a strong and broad band at the
blue side of the main non-split Q-band, that of cobalt Pc 5 in the
same solvent is observed by the remarkable broadening in its main
Q-band absorption (Fig. 2B). A broad Q-band due to H-type aggre-
gation is also observed in the spectra of 5 in chloroform and DCM.
H-type aggregates in toluene, evidenced by a very weak band
around 640 nm, appear to be very little. As shown in Fig. 3B, when
the concentration of
5
is decreased from 3.00 Â 10À6 to
0.38 Â 10À6, its aggregated species is still present, as evidenced
from
p
to p⁄ orbitals, termed the B- and Q-bands, respectively.
by the continuing broadness of the Q-band absorption.
Similar to the situation for 4, the electronic spectrum of the zinc
Pc 6 involves a strong band at 632 nm at the blue side of the main Q-
band absorption at 673 nm, due to the presence of its H-aggregated
species in DMSO (Fig. 2C). As shown in Fig 3C, as the concentration
of 6 in DMSO is increased, the increase in the absorption is pro-
nounced for the band at 632 nm. This observation confirms that
the band at 632 nm results from the presence of aggregated species.
It is clear from the sharp Q-band absorption that compound 6 does
not form aggregated species in chloroform, while very weak peaks
in its electronic spectra around 650 nm in DCM and toluene indi-
cate that nearly all the molecules of 6 are in the form of monomeric
species in these solvents, though a very small amount of aggregated
species is present in the solution.
However, for metal-free Pcs, the symmetry is usually D2h and there-
fore the main Q-band absorption is split. Thus, the split Q-band
absorptions of 4 in toluene, chloroform and DCM are attributed to
p
to p⁄ electronic transitions of its monomeric species, but not to
the aggregated species. There are also vibrational absorptions as
two shoulders at 638 and 606 nm in toluene, at 635 and 604 nm
in CHCl3 and at 639 and 608 nm in DCM. A partly split B-band of
4 also appears in the UV region at 337 and 291 nm, at 338 and
290 nm, and at 336 and 289 nm in toluene, CHCl3 and DCM, respec-
tively. Contrary to the situation in toluene, CHCl3 and DCM, the UV–
Vis spectrum of 4 in DMSO involves a broad Q-band between 650
and 725 nm, with maximum absorption at 678 nm, in addition to
a very broad band at the higher energy side of the main Q-band
Table 1
UV–Vis spectral data for Pcs 4, 5 and 6 in various solvents at a concentration of 3.0 Â 10À6 mol dmÀ3
.
Solvent
Pcs
Q-band, kmax (nm)
log
e
B-band, kmax (nm)
loge
Toluen
CHCl3
DCM
4
4
4
4
701, 666, 638, 606
697, 664, 635, 604
698, 664, 639, 608
678, 617
5.611, 5.551, 5.212, 5.035
5.574, 5.548, 5.296, 5.511
5.585, 5.551, 5.307, 5.149
5.231, 5.381
337, 291
338, 290
336, 289
321
5.463, 5.460
5.561, 5.524
5.586, 5.532
5.733
DMSO
Toluen
CHCl3
DCM
5
5
5
5
670, 606
662, 600
672, 614
660, 600
5.332, 5.116
5.432, 4.885
5.332, 5.116
5.504, 5.169
311
328
313
320
5.884
5.512
5.934
5.746
DMSO
Toluen
CHCl3
DCM
6
6
6
6
680, 650, 612
682, 616
680, 613
5.892, 5.068, 5.113
5.702, 5.009
5.907, 5.167
350
5.461
343, 312
347, 288
344, 287
5.476, 5.468
5.604, 5.558
5.837, 5.754
DMSO
673, 632
5.672, 5.646

42
Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
Fig. 2. The UV–Vis spectra of (A) 4, (B) 5 and (C) 6 in various solvents with a concentration of 3.0 Â 10À6 mol dmÀ3
.
Finally, the UV–Vis spectral changes were monitored during the
potentials of the first oxidation and reduction processes (DE1/2).
gradual addition of trifluoroacetic acid (TFA) into a 3.5 Â 10À6
M
The number of electrons transferred is usually unity for the redox
processes, except the last reduction couples of 5 and 6. Typically Pc
compounds undergo successive one-electron reduction and one-
electron oxidation to yield the anion and cation radicals, and mul-
ti-electron processes occurring in one-step are not common.
Fig. 5 shows the cyclic and differential pulse voltammograms of
metal-free Pc 4. Compound 4 gives two one-electron reduction
processes. These redox processes are ring-based since compound
4 is a metal-free Pc. The separation between the first and second
ring reductions was found to be approximately 0.32 V. This peak
separation value is in agreement with the reported ones for redox
processes in metal-free Pcs [37]. A comparison of the redox poten-
tials of 4 in DMSO with those of the relevant unsubstituted Pcs in a
similar coordinating solvent, DMF, in the literature [37] shows
clearly that the redox potentials of the former shifts to relatively
solution of each Pc compound in chloroform. On the contrary to
their behaviour in the above mentioned solvents, the Pc com-
pounds exhibit protonated species in chloroform, as evidenced by
the appearance of a red-shifted band at 740 nm for 4, 720 nm for
5 and 721 nm for 6. The UV–Vis spectral changes of 6 are shown
as an example in Fig. 4.
3.3. Electrochemical and in situ spectroelectrochemical measurements
Redox properties of the Pc compounds 4–6 in solution were
studied by CV and DPV on a platinum working electrode in
DMSO/TBAP. Table 2 lists the voltammetric data of the complexes,
which include the half-peak potentials (E1/2), the peak to peak po-
tential separations (DEp) and the difference between the half-peak

Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
43
Fig. 3. The UV–Vis spectra of (A) 4, (B) 5 and (C) 6 in DMSO at different concentrations.
more positive potentials, probably due to the 7-hydroxy-4-(4-
methoxyphenyl)-8-methylcoumarin substituents, suggesting that
the redox potentials and thus the efficiency of the Pcs in various
applications can be changed remarkably by the peripheral substit-
uents. For instance, the efficiency of MPcs in electrocatalytic appli-
cations is closely related to their redox potentials. The first
oxidation process of 4 is out of the available potential range of
the DMSO/TBAP medium, probably as a result of the shifting the re-
dox potentials towards more positive potentials by the 7-hydroxy-
4-(4-methoxyphenyl)-8-methylcoumarin substituents. However,
both waves of the first reduction couple (R1) are somewhat
rounded, which implies the presence of aggregated species in solu-
tion. The peaks of the second reduction couple (R2) are also
rounded. The broadness of the redox peaks of 4 is probably due
to the presence of its aggregated species and an equilibrium be-
tween monomeric and aggregated species. The aggregation of Pc
molecules is usually by coplanar association, which results mainly
from the p– p electron clouds of adja-
p⁄ interactions between the
cent Pc macrocycles. The presence of both aggregated and non-
aggregated Pc species in equilibrium results generally in a broad-
ening of the redox signals or their splitting, due to the differences
in the redox potentials of these species. The presence of aggregated
species in solution in the case of b-substitution should be due to its
peripheral nature, leading to planarity of the complex.
Fig. 6A shows cyclic and differential pulse voltammograms of 6.
It undergoes five reductions and two oxidations (inset B). The oxi-
dation processes could be identified only by DPV, due to their high
positive potentials within the available potential range (inset B in

44
Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
Fig. 5. Cyclic and differential pulse (inset) voltammograms of 5.0 Â 10À4 mol dmÀ3
4 in TBAP/DMSO.
Fig. 4. UV–Vis spectral changes observed during the addition of TFA into
2.50 Â 10À6 mol dmÀ3 solution of 6 in CHCl3.
a
ing to aggregated species, decreases while that of the main Q-band
at 675 nm increases with a red shift to 683 nm. On the other hand,
the Q-band decreases without shift and a new band at 574 nm ap-
pears during the second group of spectral changes, which is accom-
panied by a decrease in the B-band absorption at 343 nm (Fig. 6C).
These spectral changes indicate clearly that the aggregation equi-
librium shifts towards the monomer species before the ligand-
based first reduction process.
Fig. 6A). It is clear that all redox processes of 6, except the last
reduction couple, are ligand-based since the Zn(II) ion is redox-
inactive in zinc Pcs. The peak currents of the last reduction couple
are much higher than those of the other redox couples, suggesting
that it corresponds to the reduction of the four coumarin substitu-
ents. In general, zinc Pcs display a maximum of two or three li-
gand-based reductions within the available potential range in a
coordinating solvent such as DMSO or DMF [37]. The appearance
of five reductions for 6 strongly implies that the splitting of the re-
dox processes of 6 occurs due to the presence of aggregated species
and reduction of aggregated species at different potentials com-
pared to that of the monomer species. For this reason, in situ spec-
troelectrochemical measurements during the controlled-potential
electrolysis of the complex at À0.75 V versus SCE were also carried
out to provide additional support for the identification of possible
aggregation effects. The two groups of in situ spectroelectrochem-
ical changes during the controlled-potential electrolysis of 6 at
À0.75 V versus SCE are shown in Fig. 6B and C. As shown in
Fig. 6B, the Q-band absorption in the spectrum at the start of the
electrolysis is split, although the spectroelectrochemical measure-
ments were carried out at relatively low concentrations
(5.00 Â 10À5 mol dmÀ3) as compared to that in the voltammetric
measurements (5.00 Â 10À5 mol dmÀ3). It is clear that there is still
an equilibrium between the aggregated and monomer species
since aggregation in MPc complexes is typified by a broadened or
split Q-band, with the high energy band being due to the aggregate
and the low energy band due to the monomer. As shown by the
first group of spectral changes in Fig. 6B at À0.75 V versus SCE,
upon reduction, the absorption of the band at 636 nm, correspond-
Fig. 7A shows the cyclic voltammogram of 5. It undergoes a one-
electron oxidation and two one-electron reductions, in addition to
a further reduction involving the transfer of more than one elec-
tron. The
DEp parameter of the phthalocyanine-based redox cou-
ples takes values within the range 0.060–0.100 V at 0.050 V sÀ1
scan rate, indicating reversible or quasi-reversible character of
the electron transfer processes (Table 2). The
DE1/2 value of 5 is
0.66 V, which is much lower in comparison with those of 6 and
4, although the first oxidation couple of 4 is out of the available sol-
vent-limited potential range. Thus, it is reduced and oxidized more
easily than the other products. This distinctive behaviour of 5 can
be attributed to the fact that the Co(II) centre has accessible d orbi-
tal levels lying between the HOMO and the LUMO gap of the Pc
species. In that case, metal centre can be oxidized and reduced be-
fore the ring-based redox processes. This type of Pc complexes can
vary their electrochemical behaviour according to their environ-
ment, depending on whether there are any available coordinating
species that would stabilize the Co(II) centre. The main difference
lies in whether the metal or the ring is oxidized first. Donor sol-
vents strongly favour Co(III)Pc(À2) by coordinating along the axis
to form six coordinate species. If such solvents are absent, then oxi-
dation to Co(III) is inhibited and ring oxidation occurs first. Thus,
Table 2
Voltammetric data on Pt in TBAP/DMSO for 4–6.
d
Complex
Ring oxidations
MII/MIII
MII/MI
Ring reductions
Substituent reduction
DE1/2
b
4 (H2Pc)
E1/2 (V)
D
À0.56
À0.88
c
Ep (V)
0.090
0.080
b
5 (CoPc)
6a (ZnPc)
E1/2 (V)
0.35
0.060
À0.31
À1.24
À1.63
0.220
À1.65
0.200
0.66
1.51
c
D
Ep (V)
0.060
0.100
b
E1/2 (V)
1.06
0.96
À0.55 (À0.70)
À0.81 (À1.07)
c
D
Ep (V)
0.060
0.200 (0.18)
a
The redox behaviour of 6 was complicated by aggregation phenomenon and thus its redox couples were split in general. Phthalocyanine redox potentials were
determined by differential pulse voltammetry.
b
E1/2 = (Epa + Epc)/2 at 0.050 V sÀ1
.
c
D
Ep = Epa + Epc at 0.050 V sÀ1
E1/2 = E1/2 (first oxidation) À E1/2 (first reduction).
.
d

Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
45
the second reduction process is ring-based [37]. The peak currents
of the last reduction couple are much higher than those of the
other redox couples, as also observed for 6. This behaviour implies
that it corresponds to the reduction of the four coumarin substitu-
ents. Spectroelectrochemical measurements were also carried out
to assign especially the first reduction and the first oxidation pro-
cesses of 5 with certainly. Fig. 7B shows the in situ UV–Vis spectral
changes during the first reduction of 5 at À0.75 V versus SCE, cor-
responding to the redox process labelled R1 in Fig. 7A. The consid-
erably broad Q-band absorption in the UV–Vis spectrum of 5 in
DMSO/TBAP indicates the presence of aggregated species, although
the cyclic voltammogram of 5 does not show any evidence for
these species. Upon the first reduction, the broad shoulder on the
Q-band at 616 nm, corresponding to aggregated species, nearly
disappears, while the main Q-band at 669 nm shifts to 705 nm
and a new band appears at 475 nm with a shoulder around
437 nm. The spectral changes have well-defined isosbestic points
at 411 and 550 nm. However, these changes form various isos-
bestic points at different wavelengths within the ranges 678–694
and 725–733 nm, rather than ones at specific wavelengths, due
to the formation of different reduced species produced from the
reduction of aggregated and monomer species of 5. It is probable
that the reduction of aggregated species is followed by the disag-
gregation of the reduction product, giving the same species as
those produced from the monomer reduction. The band at
475 nm and the shifting of the Q-band indicate the formation of
[Co(I)Pc(À2)]À species, confirming the CV assignment of the couple
R1 to the Co(II)Pc(À2)/[Co(I)Pc(À2)]À process [31,38–40]. During
the second reduction at À1.40 V versus SCE, the Q-band at
705 nm decreases without shift and the absorption at 475 nm in-
creases slightly in intensity with a red shift to 482 nm, while the
absorption between 500 and 600 nm increases (Fig. 7C). These
spectral changes at the potential of the couple R2 are characteristic
for a ring-based reduction in Co(II)Pc complexes and confirm our
voltammetric assignment of this process to [Co(I)Pc(À2)]À/
[Co(I)Pc(À3)]2À
.
Fig. 7D displays the in situ UV–Vis spectral changes during the
first oxidation process at 0.60 V versus SCE. The Q-band at
669 nm increases in intensity with a red shift to 678 nm. The in-
crease of the Q-band with a red shift is typical of a metal-based
oxidation in CoPc complexes and thus, confirms the CV assignment
of Co(II)Pc(À2)/[Co(III)Pc(À2)]+ for the couple O1 of 5 in Fig. 7A
[31,38–40].
4. Conclusions
The novel metal free Pc 4 and metallo Pcs 5 and 6 have been
synthesized from 4-(4-(4-methoxyphenyl)-8-methylcoumarin-7-
oxy)phthalonitrile 3. The complexes were characterized by ele-
mental analysis, UV–Vis, IR and MALDI-TOF mass spectroscopies.
The effect of solvent and concentration on the aggregation behav-
iour of the novel Pcs and thus on their spectroscopic properties
were investigated. H-aggregation behaviours of the compounds
suggested that the formation of their aggregated species can be
controlled by changing the solvent medium. It was observed in
the UV–Vis spectra of the Pcs that they exhibit protonated species
in acidic medium in chloroform.
The compounds 4–6 displayed redox processes located at the
ring and/or metal centre. A general trend for the compounds was
their aggregation character, implied by splitting or broadening of
the redox waves. In some cases, it was not possible to identify
the nature of the redox processes and also to understand the pos-
sible aggregation effects on these processes with great detail on the
basis of electrochemical measurements alone. In situ spectroelect-
rochemical measurements during controlled-potential electrolysis
Fig. 6. (A) Cyclic and differential pulse (insets) voltammograms of
5.0 Â 10À4 mol dmÀ3 6 in TBAP/DMSO. (B) The first and (C) the second groups of
in situ UV–Vis spectral changes during the controlled potential electrolysis of 6 at
À0.75 V vs. SCE in TBAP/DMSO.
the first oxidation and the first reduction processes of 5 are prob-
ably metal-based and correspond to Co(II)Pc(À2)/[Co(III)Pc(À2)]+
and Co(II)Pc(À2)/[Co(I)Pc(À2)]À redox couples, respectively, since
the voltammetric measurements were carried out in DMSO/TBAP.
On the other hand, it is also well known from the literature that

46
Z. Odabaßs et al. / Polyhedron 39 (2012) 38–47
Fig. 7. (A) Cyclic voltammogram of 5.0 Â 10À4 mol dmÀ3 5 in TBAP/DMSO. In situ UV–Vis spectral changes during the controlled potential electrolysis of 5 (B) at À0.75 V (C) at
À1.40 V and (D) at 0.60 V vs. SCE in TBAP/DMSO.
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of the complexes at suitable potentials allowed us to provide addi-
identify the aggregation effects.
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Acknowledgments
We are thankful to The Foundation of Marmara University, The
Commission of Scientific Research (BAPKO) (Project No: FEN-C-
YLP-040112-0004).
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