Synthesis, photophysical and photochemical properties of quinoline substituted zinc (II) phthalocyanines and their quaternized derivatives

Article abstract of DOI:10.1016/j.jphotochem.2010.01.018

The new tetrakis-(6-oxyquinoline)phthalocyaninato zinc (II) (5), octakis-(6-oxyquinoline)phthalocyaninato zinc (II) (6) and their quaternized derivatives (5a and 6a) have been synthesized and characterized. Photophysical and photochemical properties of 6-oxyquinoline appended zinc (II) phthalocyanines are investigated in dimethylsulfoxide (DMSO) for both the non-ionic (5 and 6) and quaternized ionic (5a and 6a) complexes and in phosphate buffered solution (PBS) for quaternized ionic complexes. General trends are described for photodegradation quantum yields, fluorescence quantum yields and fluorescence lifetimes as well as singlet oxygen quantum yields of these compounds. In this study, the effects of the position and number of the substituents, and quaternization of the substituents on the photophysical and photochemical parameters of the zinc (II) phthalocyanines are also reported. A spectroscopic investigation of the binding of the quaternized ionic zinc (II) phthalocyanine complexes to bovine serum albumin (BSA) is also presented in this work.

Full text of DOI:10.1016/j.jphotochem.2010.01.018

Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Synthesis, photophysical and photochemical properties of quinoline substituted
zinc (II) phthalocyanines and their quaternized derivatives
Zekeriya Bıyıklıog˘lua, Mahmut Durmus¸ b,∗, Halit Kantekina
a Department of Chemistry, Faculty of Arts and Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey
b Gebze Institute of Technology, Department of Chemistry, PO Box 141, Gebze 41400, Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The new tetrakis-(6-oxyquinoline)phthalocyaninato zinc (II) (5), octakis-(6-oxyquinoline)
phthalocyaninato zinc (II) (6) and their quaternized derivatives (5a and 6a) have been synthe-
sized and characterized. Photophysical and photochemical properties of 6-oxyquinoline appended zinc
(II) phthalocyanines are investigated in dimethylsulfoxide (DMSO) for both the non-ionic (5 and 6) and
quaternized ionic (5a and 6a) complexes and in phosphate buffered solution (PBS) for quaternized ionic
complexes. General trends are described for photodegradation quantum yields, fluorescence quantum
yields and fluorescence lifetimes as well as singlet oxygen quantum yields of these compounds. In this
study, the effects of the position and number of the substituents, and quaternization of the substituents
on the photophysical and photochemical parameters of the zinc (II) phthalocyanines are also reported.
A spectroscopic investigation of the binding of the quaternized ionic zinc (II) phthalocyanine complexes
to bovine serum albumin (BSA) is also presented in this work.
Received 23 November 2009
Received in revised form 20 January 2010
Accepted 25 January 2010
Available online 2 February 2010
Keywords:
Phthalocyanine
Microwave
Water soluble
Zinc
Quantum yield
Fluorescence
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
oxygen to generate reactive oxidative species (ROS) such as singlet
oxygen as well as other ROS to kill tumor cells [10].
Phthalocyanines (Pcs), a family of aromatic macrocycles based
on an extensive delocalized 18 ␲ electron system, have been exten-
sively studied due to their unique optical, electronic, catalytic and
structural properties. Particularly, they have been studied as dyes
and pigments, light emitting diodes, in optical limiting devices, in
molecular electronics, for non-linear optical applications, as liq-
uid crystals, gas sensors, semiconductor materials, in photovoltaic
cells, photodynamic therapy (PDT) of cancer and for electrochromic
displays [1–3].
PDT is an effective single modality treatment for several medical
indications, including cancer, age-related maculopathy, periodon-
titis, malignant and pre-malignant skin disorders [4–6]. PDT
involves the uptake of the photosensitizing compound (photosen-
sitizer) by cancerous tissues or other sites of therapeutic interest
(e.g. neovascular regions), followed by selective irradiation with
visible or IR light of an appropriate wavelength that is absorbed by
the photosensitizer [7–9]. Three fundamental requirements for PDT
are oxygen, light source, and photosensitizer. Each factor is harm-
less by itself, but their combination can produce cytotoxic agents.
In PDT, the photosensitizer preferentially localizes in rapidly grow-
ing cells and gets activated by the exposure of light in presence of
The first photosensitizers are hematoporphyrin derivatives and
have already been described in detail in several articles [11,12].
Second generation photosensitizers such as phthalocyanines have
also been introduced for PDT in research and clinical trials [13]. Sev-
eral phthalocyanine systems such as the silicon (IV) phthalocyanine
Pc4 and a liposomal preparation of zinc (II) phthalocyanine have
been in clinical trials. Photosens®, which is a mixture of sulfonated
aluminium (III) phthalocyanines, is clinically used in Russia for the
treatment of a range of cancers [14]. Due to their high molar absorp-
tion coefficient in the red part of the spectrum, photostability and
long lifetimes of the photoexcited triplet states, Pcs are known to be
useful photosensitizers [15–18]. Especially, ZnPcs have been exten-
sively studied since the d10 configuration of the central Zn2+ ion
results in optical spectra that are not complicated by additional
bands, as in transition-metal complexes. ZnPcs have intensive red-
visible region absorption and high singlet and triplet yields, which
make them valuable photosensitizer for PDT applications.
Some previous papers reported that ZnPc derivatives func-
tionalized with substituents such as polyoxyethylene, pyridyloxy,
4-pyridylmethyloxy and crown ether groups in peripheral and
non-peripheral positions on the phthalocyanine ring which have
compounds offered PDT properties due to their interesting photo-
physical properties [19–25].
One of the most important characteristic of a photosensitiz-
ing drug is the perfect balance between its hydrophobic and
∗
Corresponding author. Tel.: +90 262 6053108; fax: +90 262 6053101.
E-mail address: durmus@gyte.edu.tr (M. Durmus¸ ).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.01.018

Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
33
hydrophilic properties. Phthalocyanine skeletons are essentially
hydrophobic due to intermolecular interactions between the
macrocyles. The solubility of phthalocyanines can be improved
by introduction of substituents on the periphery of the molecule,
which increase the ␲-electron density and make solvation easier
[18]. Some water-soluble phthalocyanine compounds have poten-
tial for use as photosensitizers in PDT since they can be injected
directly into the bloodstream. The water solubility of these pho-
tosensitizers is an additional advantage despite the fact that the
aggregation tendency in such polar medium, in particular, is very
high [26]. Hydrophilic phthalocyanines are therefore important
and potentially useful materials. A substantial number of water-
soluble tetra- and octa-substituted phthalocyanines have been
reported. The hydrophilic moieties which have been incorporated
on the substituted by periphery of phthalocyanine ring include
sulfonates [27], carboxylates [28], phosphanates [29], and qua-
ternarized amino groups [30–32]. Another type of water-soluble
phthalocyanines contains hydrophilic groups as axial ligands coor-
dinated to the central metal ion [33].
In this work, the synthesis, characterization and spectro-
scopic behaviour as well as photophysical (fluorescence quantum
yields and lifetimes) and photochemical (singlet oxygen and
photodegradation quantum yields) properties of new tetra- and
octa-6-oxyquinoline substituted non-ionic (5 and 6) and quater-
nized ionic (5a and 6a) zinc (II) phthalocyanine complexes (Fig. 1)
are presented. The aim of our ongoing research is to synthesize
water-soluble zinc (II) phthalocyanines to be used as potential PDT
agents, since zinc (II) phthalocyanine complexes show good pho-
tophysical and photochemical properties for PDT studies.
Photo-irradiations were done using a General Electric quartz
line lamp (300 W). A 600 nm glass cut off filter (Schott) and a
water filter were used to filter off ultraviolet and infrared radia-
tions, respectively. An interference filter (Intor, 670 nm with a band
width of 40 nm) was additionally placed in the light path before the
sample. Light intensities were measured with a POWER MAX5100
(Molelectron detector incorporated) power meter.
2.3. Photophysical parameters
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (˚F) are determined by the com-
parative method (Eq. (1)) [39,40],
F AStd n2
FStd A n2Std
˚
F
= ˚F(Std)
(1)
where F and FStd are the areas under the fluorescence emission
curves of the samples (5, 5a, 6 and 6a) and the standard, respec-
tively. A and AStd are the respective absorbances of the samples and
standard at the excitation wavelengths, respectively. n2 and nS2td
are the refractive indices of solvents used for the sample and stan-
dard, respectively. Unsubstituted ZnPc (in DMSO) (˚F = 0.20) [41]
was employed as the standard. The absorbance of the solutions at
the excitation wavelength ranged between 0.04 and 0.05.
Natural radiative life times (ꢀ0) are determined using Pho-
tochemCAD program which uses the Strickler–Berg equation [42].
The fluorescence lifetimes (ꢀF) are evaluated using Eq. (2).
ꢀF
BSA and human serum albumin (HSA) are major plasma pro-
teins, which contribute significantly to physiological functions and
display effective drug delivery roles [34,35], hence the investiga-
tion of binding of drugs with albumin is of interest. A spectroscopic
investigation of the binding of the water-soluble zinc (II) phthalo-
cyanine complexes (5a and 6a) to BSA is also presented in this
work.
˚
=
(2)
F
ꢀ0
2.4. Photochemical parameters
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield (˚ꢁ) determinations are carried
out using the experimental set-up described in literature [27]. Typ-
ically, a 3 mL portion of the respective unsubstituted, tetra- and
octa-substituted zinc (II) phthalocyanine (5, 5a, 6 and 6a) solu-
tions (absorbance ∼1.0 at the irradiation wavelength) containing
the singlet oxygen quencher was irradiated in the Q band region
with the photo-irradiation set-up described in references [27]. ˚ꢁ
values were determined in air using the relative method with ZnPc
(in DMSO) or ZnPcSmix (in aqueous media) as references. DPBF
and ADMA were used as chemical quenchers for singlet oxygen
in DMSO and aqueous media, respectively. Eq. (3) was employed
for the calculations:
2. Experimental
2.1. Materials
All reagents and solvents were of reagent grade quality and
were obtained from commercial suppliers. 6-Hydroxyquinoline
was purchased from Aldrich. 9,10-Antracenediyl-bis(methylene)
dimalonoic acid (ADMA) and 1,3-diphenylisobenzofuran (DPBF)
were purchased from Fluka. All solvents were dried and purified
as described by Perrin and Armarego [36]. 4-Nitrophthalonitrile
[37], 1,2-dichlorophthalonitrile [38] were synthesized and purified
according to well known literature.
Std
R I
abs
˚
= ˚Std
(3)
ꢁ
ꢁ
RStd Iabs
where ˚Sꢁtd is the singlet oxygen quantum yields for the stan-
2.2. Equipment
dard ZnPc (˚ꢁStd = 0.67 in DMSO) [43] and ZnPcSmix (˚Sꢁtd = 0.45
in aqueous media) [27], R and RStd are the DPBF (or ADMA) pho-
The IR spectra were recorded on a Perkin Elmer 1600 FT-IR
spectrophotometer using KBr pellets. 1H- and 13C NMR spectra
were recorded on a Varian Mercury 200 MHz spectrometer in CDCl3
and DMSO-d6. Chemical shifts were reported (ı) relative to Me4Si
as internal standard. Mass spectra were measured on a Micro-
mass Quatro LC/ULTIMA LC–MS/MS spectrometer. The elemental
analyses were performed on a Costech ECS 4010 instrument. Melt-
ing points were measured on an electrothermal apparatus and
were uncorrected. Absorption spectra in the UV–vis region were
recorded with a Shimadzu 2001 UV spectrophotometer. Fluores-
cence excitation and emission spectra were recorded on a Varian
Eclipse spectrofluorometer using 1 cm pathlength cuvettes at room
temperature.
tobleaching rates in the presence of the respective samples (5, 5a,
Std
abs
6 and 6a) and standards, respectively. Iabs and I
are the rates
of light absorption by the samples and standards, respectively. To
avoid chain reactions induced by quenchers (DPBF or ADMA) in the
presence of singlet oxygen [44], the concentration of quenchers
(DPBF or ADMA) was lowered to ∼3 × 10−5 M. Solutions of sen-
sitizer (absorbance = 1 at the irradiation wavelength) containing
quencher (DPBF or ADMA) were prepared in the dark and irradi-
ated in the Q band region using the setup described above. DPBF
degradation at 417 nm and ADMA degradation at 380 nm were
monitored. The light intensity 6.21 × 1015 photons s−1 cm−2 was
used for ˚ꢁ determinations.

34
Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
Fig. 1. Synthetic pathway for preparation of phthalocyanine complexes (5, 5a, 6 and 6a). (i) K2CO3, N2, DMF, 50 ◦C, 48 h. (ii) Zn(CH3COO)2, DMAE, 175 ◦C, 350 W. (iii) CHCl3,
CH3I, 5 h for compound 5a, 8 h for compound 6a.

Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
35
2.4.2. Photodegradation quantum yields
microwave reaction oven at 175 ◦C, 350 W for 10 min. After cooling
to room temperature, ethanol (60 mL) was added. The precipitated
green solid product was filtered off, and then dried. The obtained
green product was purified by the column chromatography over
aluminium oxide using chloroform:methanol (100:2) as solvent
system. Yield: 0.112 g (53%). IR (KBr pellet) ꢂmax/cm−1: 3083
(Ar–H), 1607, 1593, 1499, 1462, 1376, 1322, 1259, 1223, 1089, 1045,
963, 833, 748. 1H NMR. (DMSO-d6), (ı ppm): 8.87 (m, 4H, Ar–H),
8.29 (d, 4H, Ar–H), 8.09–7.86 (m, 8H, Ar–H), 7.69–7.36 (m, 20H,
Ar–H). Calc. for C68H36N12O4Zn: C 70.99, H 3.15, N 14.61; Found:
C 71.43, H 3.34, N 14.16. MS (ES+), m/z: Calc. 1150; Found: 1151
[M+H]+.
Photodegradation quantum yield (˚d) determinations are car-
ried out using the experimental set-up described in literature [27].
Photodegradation quantum yields were determined using Eq. (4),
(C0 − Ct) V NA
˚
=
(4)
d
Iabs S t
where C0 and Ct are the samples (5, 5a, 6 and 6a) concentrations
before and after irradiation respectively, V is the reaction volume,
NA the Avogadro’s constant, S the irradiated cell area and t the
irradiation time, Iabs is the overlap integral of the radiation source
light intensity and the absorption of the samples. A light intensity
of 2.17 × 1016 photons s−1 cm−2 was employed for ˚d determina-
tions.
2.5.3. Synthesis of quaternized 2,9(10),16(17),23(24)-tetrakis-
(quinolin-6-yloxy) phthalocyaninato zinc (II) (5a)
Compound 5 (0.050 g, 0.043 mmol) was dissolved in chloroform
(4 mL) and methyl iodide (0.030 g, 0.21 mmol) was added to this
solution. The reaction mixture was stirred under reflux for 5 h. After
cooling to room temperature, the green precipitate was filtered off,
washed with ethanol, acetone, diethyl ether, chloroform, and then
dried. Yield: 0.048 g (65%). IR (KBr pellet) ꢂmax/cm−1: 3010 (Ar–H),
2923–2851 (Aliph. C–H), 1597, 1526, 1481, 1464, 1389, 1332, 1266,
1240, 1088, 1045, 965, 941, 746. Calc. for C72H48I4N12O4Zn: C 50.33,
H 2.82, N 9.78; Found: C 49.38, H 2.95, N 9.47. MS (ES+), m/z: Calc.
1718; Found: 1658 [M-4CH3]+.
2.4.3. Binding of quaternized zinc (II) phthalocyanine derivatives
to BSA
The binding of the quaternized zinc (II) phthalocyanine deriva-
tives (5a and 6a) to BSA was studied by spectrofluorometry at
room temperature. A PBS solution of BSA (fixed concentration) was
titrated with varying concentrations of the respective quaternized
zinc (II) phthalocyanine solutions. BSA was excited at 280 nm and
fluorescence recorded between 290 and 500 nm. The changes in
BSA fluorescence intensity were related to quaternized phthalo-
cyanine concentrations by the Stern–Volmer relationship (Eq. (5)):
F0BSA
FBSA
2.5.4. Synthesis of 4,5-bis-(quinolin-6-yloxy)phthalonitrile (4)
4,5-Dichlorophthalonitrile (2) (1.36 g, 6.89 mmol) and 6-
hydroxyquinoline (2.00 g, 13.79 mmol) were dissolved in dry DMF
(10 mL) at 50 ◦C under N2 atmosphere. Potassium carbonate (2.85 g,
20.67 mmol) was added to the reaction solution in 8 portions
every 15 min. The reaction mixture was heated for 48 h, then
cooled to room temperature, and poured into ice-water (80 mL).
After filtration under vacuum, the crude product was crystallized
from ethanol. Yield: 1.22 g (43%), mp: 152–153 ◦C. IR (KBr pel-
let), ꢂmax/cm−1: 3084–3025 (Ar–H), 2235 (C N), 1648, 1620, 1597,
1562, 1499, 1462, 1396, 1324, 1295, 1211, 1151, 1136, 1070, 958,
877, 835, 799. 1H NMR. (DMSO-d6), (ı ppm): 8.83 (d, 2H, Ar–H), 8.28
(d, 2H, Ar–H), 8.11 (s, 2H, Ar–H), 8.03 (d, 2H, Ar–H), 7.62–7.49 (m,
6H, Ar–H). 13C NMR. (DMSO-d6), (ı ppm): 152.72, 150.73, 149.73,
144.96, 135.36, 131.34, 128.55, 126.31, 122.15, 121.91, 115.16,
113.89, 111.50. MS (ES+), (m/z): 415 [M+H]+.
= 1 + KSBVSA[Pc]
(5)
BSA
SV
and k
is given by Eq. (6):
BSA
K
= kqꢀF(BSA)
(6)
SV
where F0BSA and FBSA are the fluorescence intensities of BSA in the
absence and presence of quaternized phthalocyanines (5a and 6a),
respectively; KSBVSA, the Stern–Volmer quenching constant; kq, the
bimolecular quenching constant; and ꢀF (BSA), the fluorescence
lifetime of BSA. ꢀF (BSA) is known to be 10 ns [45–47], thus from
the values of KSBVSA obtained from the plots of F0BSA/FBSA versus [Pc],
the value of kq may be determined (Eq. (6)).
2.5. Synthesis
2.5.1. Synthesis of 4-(quinolin-6-yloxy)phthalonitrile (3)
4-Nitrophthalonitrile (1) (1.19 g, 6.90 mmol) and 6-
hydroxyquinoline (1.00 g, 6.90 mmol) were dissolved in dry
dimethylformamide (DMF) (10 mL) at 50 ◦C under N2 atmosphere.
Potassium carbonate (2.38 g, 17.25 mmol) was added to the reac-
tion solution in 8 portions every 15 min. The reaction mixture was
heated for 48 h, then cooled to room temperature, and poured
into ice-water (100 mL). After filtration under vacuum, the crude
product was crystallized from ethanol. Yield: 1.14 g (61%), mp:
147–148 ◦C. IR (KBr pellet), ꢂmax/cm−1: 3077–3038 (Ar–H), 2232
(C N), 1624, 1594, 1565, 1498, 1487, 1324, 1280, 1249, 1213,
1166, 1138, 1088, 968, 880, 836, 756. 1H NMR. (CDCl3), (ı ppm):
8.97 (d, 1H, Ar–H), 8.20 (m, 2H, Ar–H), 7.79 (d, 1H, Ar–H), 7.52–7.44
(m, 3H, Ar–H), 7.37–7.32 (m, 2H, Ar–H). 13C NMR. (CDCl3), (ı ppm):
163.32, 153.54, 152.70, 149.28, 137.54, 134.80, 131.07, 125.29,
124.18, 123.98, 123.77, 119.90, 118.59, 117.20, 116.77, 111.55,
107.46. MS (ES+), (m/z): 272 [M+H]+.
2.5.5. Synthesis of 2,3,9,10,16,17,23,24-octakis-(quinolin-6-
yloxy) phthalocyaninato zinc (II) (6)
4,5-Bis-(quinolin-6-yloxy)phthalonitrile (4) (0.50 g, 1.20 mmol)
and anhydrous Zn(CH3COO)2 (0.056 g, 0.30 mmol) were ground
together in a microwave oven and DMAE (3 mL) was added. The
reaction mixture was irradiated in microwave reaction oven at
175 ◦C, 350 W for 12 min. After cooling to room temperature,
ethanol (80 mL) was added. The precipitated green solid product
was filtered off, and then dried. The green product was purified by
the column chromatography over aluminium oxide using chloro-
form:methanol (100:3) as solvent system. Yield: 0.310 g (60%). IR
(KBr pellet) ꢂmax/cm−1: 3054 (Ar–H), 1621, 1598, 1500, 1446, 1401,
1377, 1323, 1271, 1214, 1177, 1145, 1114, 1088, 1027, 961, 920,
832, 746. 1H NMR. (CDCl3), (ı ppm): 8.82 (m, 8H, Ar–H), 8.06 (m,
16H, Ar–H), 7.48–7.36 (m, 32H, Ar–H). Calc. for C104H56N16O8Zn: C
72.49, H 3.28, N 13.01; Found: C 72.88, H 3.57, N 12.79. MS (ES+),
m/z: Calc. 1723; Found: 1746 [M+Na]+.
2.5.2. Synthesis of 2,9(10),16(17),23(24)-tetrakis-(quinolin-6-
yloxy)phthalocyaninato zinc (II) (5)
4-(Quinolin-6-yloxy)phthalonitrile (3) (0.400 g, 1.47 mmol)
and anhydrous Zn(CH3COO)2 (0.068 g, 0.37 mmol) were ground
together in a microwave oven and 2-(dimethylamino)ethanol
(DMAE) (3 mL) was added. The reaction mixture was irradiated in
2.5.6. Synthesis of quaternized 2,3,9,10,16,17,23,24-octakis-
(quinolin-6-yloxy) phthalocyaninato zinc (II) (6a)
Compound 6 (0.10 g, 0.058 mmol) was dissolved in chloroform
(6 mL) and methyl iodide (0.081 g, 0.58 mmol) was added to this
solution. The reaction mixture was stirred under reflux for 8 h. After

36
Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
Fig. 2. Mass spectrum of complex 5a.
cooling to room temperature, the green precipitate was filtered off,
washed with ethanol, acetone, diethyl ether and chloroform, and
then dried. Yield: 0.119 g (72%). IR (KBr pellet) ꢂmax/cm−1: 3076
(Ar–H), 2923–2851 (Aliph. C–H), 1621, 1596, 1522, 1445, 1385,
1270, 1231, 1083, 1028, 960. Calc. for C112H80I8N16O8Zn: C 47.06,
H 2.82, N 7.84; Found: C 46.74, H 2.99, N 7.70. MS (ES+), m/z: Calc.
2858; Found: 2859 [M+H]+.
pounds 3 and 4 the aromatic protons appeared at 8.97 (d), 8.20 (m),
7.79 (d), 7.52–7.44 (m), 7.37–7.32 (m) ppm for compound 3 and
8.83 (d), 8.28 (d), 8.11 (s), 8.03 (d), 7.62-7.49 (m) ppm for compound
4. The 13C NMR spectra of compounds 3 and 4 indicated aromatic
carbon atoms between at 163.32–107.46 and 152.72–111.50 ppm,
respectively. Also nitrile carbon atoms for compounds 3 and 4 were
observed 116.77, 111.55 and 113.89 ppm, respectively. In the mass
spectra of compounds 3 and 4 the presence of molecular ion peaks
at m/z = 272 [M+H]+ and 415 [M+H]+ respectively, confirmed the
proposed structures.
3. Results and discussion
Cyclotetramerization of the dinitrile derivatives (3 and 4) to the
zinc (II) phthalocyanines (5 and 6) were confirmed by the dis-
3.1. Synthesis and characterization
appearance of the sharp C N vibration of 2232 and 2235 cm−1
,
The synthetic procedure of the phthalocyanine complexes (5
and 6) and their quaternized derivatives (5a and 6a) is given in
Fig. 1. 6-Oxyquinoline substituted phthalonitrile derivatives (3 and
4) were synthesized through base-catalyzed aromatic displace-
ment of 4-nitrophthalonitrile (1) and 4,5-dichlorophthalonitrile (2)
with 6-hydroxyquinoline using K2CO3 as the base in dry DMF.
The reactions were carried out at 50 ◦C under N2 atmosphere
for 48 h. Cyclotetramerization of the phthalonitrile derivatives (3
and 4) to the tetra- and octa-substituted zinc (II) phthalocya-
nines (5 and 6) were accomplished in the presence of anhydrous
Zn(CH3COO)2 in DMAE by using microwave irradiation and the
crude product was purified column chromatography using alumina
filled column. Tetra- and octa-cationic zinc (II) phthalocyanines
(5a and 6a) were obtained from the reaction of corresponding
zinc phthalocyanines (5 and 6) with methyl iodide in chloroform.
The structures of the target compounds were confirmed using IR,
1H NMR, 13C NMR spectroscopy and mass spectra. The analyses
are consistent with the predicted structures as shown in Section
2.
respectively. The 1H NMR spectra of tetra- and octa-substituted
zinc (II) phthalocyanines (5 and 6) were obtained as expected.
The 1H NMR spectrum of tetra-substituted zinc (II) phthalocya-
nine (5) indicated the aromatic protons at 8.87, 8.29, 8.09–7.86,
7.69–7.36 ppm. Also, the 1H NMR spectrum of octa-substituted zinc
(II) phthalocyanine (6) indicated the aromatic protons at 8.82, 8.06,
7.48–7.36 ppm. The mass spectra of phthalocyanine compounds
showed molecular ion peaks at m/z = 1151 [M+H]+ for 5, 1746
[M+Na]+ for 6 support the proposed formula for these compounds.
Quaternized tetra- and octa-substituted zinc phthalocyanines
(5a and 6a) are soluble in water, DMF and DMSO. No major change
in the IR spectra was found after quaternization. The mass spectra
of quaternized tetra- and octa-substituted zinc (II) phthalocyanines
(5a and 6a) confirmed the proposed structure, with the molecular
ion being easily identified at 1658 [M-4CH3]+ for 5a, 2859 [M+H]+
for 6a (Fig. 2 for complex 5a as an example).
3.2. Ground state electronic absorption and fluorescence spectra
The IR spectra clearly indicated the formation of compounds
(3) and (4) with the appearance of absorption bands at 2232 cm−1
(C N), 1624 cm−1 (C N) for compound (3) and 2235 cm−1 (C N),
1620 cm−1 (C N) for compound (4). In the 1H NMR spectra of com-
The electronic spectra of the studied zinc (II) phthalocyanine
complexes showed characteristic absorption in the Q band region
at around 680 nm in DMSO, Table 1. The B-bands were observed at

Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
37
Table 1
Absorption, excitation, emission, photophysical and photochemical data for unsubstituted, tetra- and octa-substituted zinc (II) phthalocyanine complexes in DMSO and PBS.
a
Comp. Solvent Q band, ꢃmax (nm) Log ε
Excitation, ꢃEx
(nm)
Emission, ꢃEm
(nm)
Stokes shift,
ꢁStokes (nm)
˚
F
ꢀF (ns) ꢀ0 (ns) kF (s−1) (×108)
˚
d
(×10−5
)
˚
ꢁ
5
DMSO
680
5.24
680
691
11
0.15 1.37
0.02 0.13
7.74
1.29
0.68
0.56
DMSO
PBS
678
687, 640
5.20
4.62, 4.69
678
–
688
–
10
–
6.57
–
1.52
–
0.54
3.64
0.13
0.07
5a
6
–
–
DMSO
680
5.16
680
689
9
0.17 1.64
9.67
1.03
1.75
0.69
DMSO
PBS
681
665, 636
5.27
4.74, 4.58
680
–
690
–
9
–
0.003 0.018
6.12
–
1.63
–
0.27
2.05
0.07
0.03
6a
–
–
ZnPcb DMSO
672
5.14
672
682
10
0.20c 1.22
6.80
1.47
2.61
0.67
a
kF is the rate constant for fluorescence. Values calculated using kF = ˚F/ꢀF.
Ref. [19].
Ref. [41].
b
c
show aggregation in DMSO. Beer–Lambert law was obeyed for all
of these compounds in DMSO for the concentrations ranging from
1.4 × 10−5 to 4 × 10−6 M.
Fig. 6 shows fluorescence emission, absorption and excitation
spectra of zinc (II) phthalocyanine complexes (Fig. 6a for complex 6
and Fig. 6b for complex 6a in DMSO as examples). All non-ionic zinc
(II) phthalocyanine complexes (5 and 6) showed similar fluores-
cence behaviour in DMSO (Fig. 6a for complex 6 as an example). For
ionic zinc (II) complexes (5a and 6a), the quaternization of the zinc
(II) phthalocyanine complexes caused decreasing for fluorescence
emission of the studied zinc (II) phthalocyanine complexes (Fig. 6b
for complex 6a as an example). Fluorescence emission peaks were
Fig. 3. Absorption spectra of tetra- and octa-substituted zinc (II) phthalocyanines
complexes (5, 5a, 6 and 6a) in DMSO. Concentration = 1 × 10−5 M.
around 350 nm (Fig. 3). The spectra showed monomeric behaviour
evidenced by a single (narrow) Q band, typical of metallated
phthalocyanine complexes in DMSO [48]. In DMSO, the Q bands
were observed at: 680 (5), 678 (5a), 680 (6) and 681 (6a), Table 1.
The red-shifts were observed for zinc (II) phthalocyanine com-
plexes following substitution (the Q band for the unsubstituted
ZnPc was 672 nm). The B-bands are broad due to the superim-
position of the B1 and B2 bands in the 350 nm region. In PBS, the
absorption spectra of quaternized complexes (5a and 6a) showed
co-facial aggregation, as evidenced by the presence of two non-
vibrational peaks in the Q band region, Fig. 4a and b. The lower
energy (red-shifted) bands at 687 nm for 5a and 665 nm for 6a
were due to the monomeric species, while the higher energy (blue
shifted) bands at 640 nm for 5a, and 636 nm for 6a were due to the
aggregated species.
Aggregation is usually depicted as a coplanar association of
rings progressing from monomer to dimer and higher order com-
plexes. It is dependent on the concentration, nature of the solvent,
nature of the substituents, complexed metal ions and tempera-
ture [49]. In the aggregated state the electronic structure of the
complexed phthalocyanine rings are perturbed resulting in alter-
nation of the ground and excited state electronic structures [50].
In this study, the aggregation behaviour of the zinc (II) phthalo-
cyanine complexes (5, 5a, 6 and 6a) was investigated at different
concentrations in DMSO (Fig. 5, for complex 6a as an example). As
the concentration was increased, intensity of absorption for the
Q band also increased and there were no new bands (normally
blue shifted) observed due to the aggregated species. The stud-
ied zinc (II) phthalocyanine complexes (5, 5a, 6 and 6a) did not
Fig. 4. Absorption spectra of: (a) tetra-substituted quaternized zinc (II) phthalo-
cyanine (5a) and (b) octa-substituted quaternized zinc (II) phthalocyanine (6a) in
DMSO and PBS. Concentration = 1 × 10−5 M.

38
Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
3.3. Fluorescence lifetimes and quantum yields
The fluorescence quantum yields (˚F) for non-ionic (5 and 6)
and for quaternized ionic zinc (II) phthalocyanine complexes (5a
and 6a) in DMSO were given in Table 1. The ˚F values of studied
non-ionic zinc (II) phthalocyanine complexes are typical of zinc (II)
phthalocyanine complexes [19,20,51,52].
The ˚F values of the substituted non-ionic zinc (II) phthalo-
cyanine complexes (5 and 6) were slightly lower as compared
to unsubstituted zinc (II) phthalocyanine complex in DMSO. The
˚
F
values of the quaternized ionic zinc (II) phthalocyanine com-
plexes (5a and 6a) were lower than that of unsubstituted zinc (II)
phthalocyanine complex in DMSO, which implied that the quater-
nization of the zinc (II) phthalocyanine complexes certainly results
in fluorescence quenching. Quaternized cationic complexes (5a and
6a) showed lower ˚F values with respect to the corresponding
non-ionic complexes (5 and 6) in DMSO. The lower values for quat-
ernized zinc phthalocyanine complexes (5a and 6a) were ascribed
to the phenomenon of Photoinduced Electron Transfer (PET). Mask-
ing of the nitrogen lone pair electrons (as in 5a and 6a) prevents the
nitrogen lone pair from participating in PET, and causes a quench
the fluorescence of the ZnPc moiety.
Fluorescence lifetime (ꢀF) refers to the average time a molecule
stays in its excited state before fluorescing, and its value is directly
related to that of ˚F; i.e. the longer the lifetime, the higher the
quantum yield of fluorescence. Any factor that shortens the fluores-
cence lifetime of a fluorophore indirectly reduces the value of ˚F.
Such factors include internal conversion and intersystem crossing.
As a result, the nature and the environment of a fluorophore deter-
mine its fluorescence lifetime. ꢀF values (Table 1) were calculated
using the Strickler–Berg equation. The ꢀF values of the substituted
non-ionic zinc (II) phthalocyanine complexes (5 and 6) were higher
to unsubstituted zinc (II) phthalocyanine complex in DMSO. The
ꢀF values of the substituted quaternized ionic zinc (II) phthalocya-
nine complexes (5a and 6a) were lower to unsubstituted zinc (II)
phthalocyanine complex in DMSO, suggesting more quenching by
quaternization of the zinc (II) phthalocyanine complexes. However
the ꢀF values were typical for non-ionic zinc (II) phthalocyanine
complexes in DMSO [19,20,51,52].
Fig. 5. Aggregation behaviour of 6a in DMSO at different concentrations: 14 × 10−6
(A), 12 × 10−6 (B), 10 × 10−6 (C), 8 × 10−6 (D), 6 × 10−6 (E), 4 × 10−6 (F) M (inset: plot
of absorbance versus concentration).
observed at 691 nm for 5, 688 nm for 5a, 689 nm for 6 and 690 nm
for 6a in DMSO (Table 1). The studied quaternized zinc (II) phthalo-
cyanine complexes did not show fluorescence emission in PBS. The
observed Stokes shifts (Table 1) were typical of MPc complexes. The
excitation spectra were similar to absorption spectra and both had
mirror images of the fluorescent spectra for all zinc (II) phthalocya-
nine complexes in DMSO (Fig. 6). The proximity of the wavelength
of each component of the Q band absorption to the Q band maxima
of the excitation spectra for all zinc (II) phthalocyanine complexes
suggested that the nuclear configurations of the ground and excited
states were similar and not affected by excitation in DMSO.
The natural radiative lifetime (ꢀ0) and the rate constants for flu-
orescence (kF) values were also shown in Table 1. The ꢀ0 values
of the substituted non-ionic zinc (II) phthalocyanine complexes (5
and 6) were also higher to substituted quaternized ionic zinc (II)
phthalocyanine complexes (5a and 6a) in DMSO. The kF values of
the substituted non-ionic zinc (II) phthalocyanine complexes (5 and
6) were lower to substituted quaternized ionic zinc (II) phthalocya-
nine complexes (5a and 6a) in DMSO.
3.4. Singlet oxygen quantum yields
Energy transfer between the triplet state of photosensitizers and
ground state molecular oxygen leads to the production of singlet
oxygen. There is a necessity of high efficiency of transfer of energy
between excited triplet state of MPc and ground state of oxygen to
generate large amounts of singlet oxygen, essential for PDT.
The ˚ꢁ values were determined using a chemical method (DPBF
in DMSO and ADMA in aqueous solution). The disappearance of
quenchers (DPBF or ADMA) was monitored using UV–vis spec-
trophotometer (Fig. 7 using DPBF for complex 5 in DMSO as an
example). Many factors are responsible for the magnitude of the
determined quantum yield of singlet oxygen including; triplet
excited state energy, ability of substituents and solvents to quench
the singlet oxygen, the triplet excited state lifetime and the effi-
ciency of the energy transfer between the triplet excited state
and the ground state of oxygen. There was no change in the Q
bandintensityduringthe ˚ꢁ determinations, confirming that com-
Fig. 6. Absorption, excitation and emission spectra of: (a) 6 in DMSO and (b) 6a in
DMSO. Excitation wavelengths: 650 nm.

Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
39
Fig. 8. The photodegradation of 6 in DMSO showing the disappearance of the Q band
at 10 min intervals (inset: plot of Q band absorbance versus time).
Fig. 7. A typical spectrum for the determination of singlet oxygen quantum yield
of 5 in DMSO using DPBF as a singlet oxygen quencher. Concentration = 4 × 10−6
M
(inset: plots of DPBF absorbance versus time).
plexes were not degraded during singlet oxygen studies (Fig. 7 as an
example for complex 5). Table 1 showed that the values of ˚ꢁ were
higher for substituted non-ionic zinc (II) phthalocyanine complexes
(5 and 6) when compared to respective substituted quaternized
ionic zinc (II) phthalocyanine complexes (5a and 6a) in DMSO. The
quaternization of the zinc (II) phthalocyanine complexes caused
the decreasing of the ˚ꢁ values in DMSO.
Table 1 shows that lower ˚ꢁ values were observed in PBS
(which is mainly water) solutions as compared to in DMSO. The
low ˚ꢁ in water compared to other solvents such as deuter-
ated water and DMSO was explained [41] by the fact that singlet
oxygen absorbs at 1270 nm, and water, which absorbs around
this wavelength has a great effect on singlet oxygen lifetime,
while DMSO which exhibits little absorption in this region has
longer singlet oxygen lifetimes than water, resulting in large
Fig. 9. Fluorescence emission spectral changes of BSA on addition of varying con-
centrations of 5a in PBS. [BSA] = 3.00 × 10−5 M, [5a] varies from 0 to 8.30 × 10−6 M.
Excitation wavelength = 280 nm.
˚
values in DMSO. Low singlet oxygen values of quaternized
ꢁ
phthalocyanine complexes (5a and 6a) in PBS could also be due to
aggregation.
3.6. Interaction of quaternized ionic Zn (II) phthalocyanine
complexes with BSA
3.5. Photodegradation studies
Fig. 9 shows the fluorescence emission spectra of BSA in the
presence of different concentrations of 5a in PBS as an example.
The BSA fluorescence at 348 nm is mainly attributable to tryp-
tophan residues in the macromolecule. BSA and the respective
quaternized ionic phthalocyanine complexes exhibited recipro-
cated fluorescence quenching on one another; hence it was
possible to determine Stern–Volmer quenching constants (KSV).
The slope of the plots shown at Fig. 10 gave KSV values and
listed in Table 2, suggested that BSA fluorescence quenching
was more effective for quaternized octa-substituted zinc (II)
phthalocyanine complex (6a) than quaternized tetra-substituted
phthalocyanine complex (5a) in PBS. Using the approximate fluo-
rescence lifetime of BSA (10 ns) [43,44], the bimolecular quenching
constant (kq) was determined (Eq. (6)). These values were of
Degradation of the molecules under irradiation can be used
to study their stability and this is especially important for those
molecules intended for use in photocatalysis. The collapse of the
absorption spectra without any distortion of the shape confirms
clean photodegradation not associated with phototransformation
into different forms of MPc absorbing in the visible region. The spec-
tral changes observed for all the studied complexes (5, 5a, 6 and 6a)
during confirmed photodegradation occurred without phototrans-
formation (Fig. 8 as an example for complex 6).
Allthe studiedzinc (II)phthalocyaninecomplexesshowedabout
the same stability with ˚d of the order of 10−5 in DMSO, Table 1.
Stable zinc phthalocyanine complexes show ˚d values as low as
10−6 and for unstable molecules, values of the order of 10−3 have
been reported [53]. Studied zinc (II) phthalocyanine complexes
seemed to show similar ˚d values and stability with other zinc
(II) phthalocyanine complexes. Table 1 shows that the lower ˚d
values were observed for the studied quaternized ionic zinc (II)
phthalocyanine complexes as compared to for the studied non-
ionic zinc (II) phthalocyanine complexes. The quaternization of the
zinc (II) complexes caused the increasing of the stability of the zinc
(II) phthalocyanine complexes in DMSO. The ˚d values for quater-
nized ionic zinc (II) phthalocyanine complexes were higher in PBS
solution than in DMSO. These complexes were more stable in DMSO
than in PBS.
the order of 1013
M
−1 s−1, which exceeded the proposed value
of 1010 M−1 s−1 for diffusion-controlled (dynamic) quenching
(according to the Einstein–Smoluchowski approximation at room
Table 2
Binding and fluorescence quenching data for interaction of BSA with quaternized
zinc (II) phthalocyanine complexes (5a and 6a) in PBS.
BSA
SV
Compound
K
(×105 M−1
)
kq (×1013 s−1
)
5a
6a
2.14
2.98
2.14
2.99

40
Z. Bıyıklıog˘lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 211 (2010) 32–41
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4. Conclusion
˙
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quaternized ionic zinc (II) phthalocyanine complexes. The effect
of quaternization on these properties was presented. It was
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phthalocyanine complexes. Solvent effect (DMSO or PBS) on the
photophysical and photochemical properties of the quaternized
derivative was determined. The non-ionic and ionic zinc (II)
phthalocyanine complexes were found to be monomeric in DMSO.
The ionic complexes showed aggregation in PBS. The studied non-
ionic zinc (II) phthalocyanine complexes (5 and 6) showed similar
fluorescence behaviour with MPcs. The ionic Zn (II) phthalocyanine
complexes showed less fluorescence emission in DMSO and they
were not fluorescence in PBS. The ˚F values of the non-ionic zinc
(II) phthalocyanine complexes (5 and 6) were higher than that of
ionic zinc (II) phthalocyanine complexes (5a and 6a) in DMSO. The
chemical properties of substituted zinc phthalocyanines, Dalton Trans. (2007)
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˚
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complexes (5 and 6) than ionic zinc (II) phthalocyanine complexes
(5a and 6a) in DMSO. The ˚ꢁ values were higher in DMSO than that
of ionic zinc (II) phthalocyanine complexes (5a and 6a) in PBS. This
study reveals that the water-soluble derivatives bind strongly to
serum albumin; hence they can easily be transported in the blood.
After injection into the blood stream, these molecules will have to
encounter serum albumin, which presents a justification for their
BSA binding study.
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Acknowledgement
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This study was supported by the Research Fund of Karadeniz
Technical University (project no: 2006.111.002.1).
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