New water soluble cationic zinc phthalocyanines as potential for photodynamic therapy of cancer

Article abstract of DOI:10.1016/j.jorganchem.2013.08.025

The novel phthalonitrile derivatives (2 and 3) bearing 2-[3-(dimethylamino) phenoxy]ethanol substituents on the 3 and 4 positions have been synthesized. The novel peripherally and non-peripherally tetra-{2-[3-(dimethylamino)phenoxy]} substituted zinc phth

Full text of DOI:10.1016/j.jorganchem.2013.08.025

Journal of Organometallic Chemistry 745-746 (2013) 423e431
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New water soluble cationic zinc phthalocyanines as potential for
photodynamic therapy of cancer
a
a
a
,
b
a
*
ꢀ
Dilek Çakır , Volkan Çakır , Zekeriya Bıyıklıoglu , Mahmut Durmus¸ , Halit Kantekin
a Department of Chemistry, Faculty of 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 novel phthalonitrile derivatives (2 and 3) bearing 2-[3-(dimethylamino)phenoxy]ethanol sub-
stituents on the 3 and 4 positions have been synthesized. The novel peripherally and non-peripherally
tetra-{2-[3-(dimethylamino)phenoxy]} substituted zinc phthalocyanines (2a and 3a) were also synthe-
sized by cyclotetramerization of phthalonitrile derivatives (2 and 3). The obtained new zinc phthalo-
cyanines (2a and 3a) were converted into water-soluble quaternized products (2b and 3b). The new
compounds have been characterized by combination of spectroscopic data including UVeVis, IR, 1H NMR,
13C NMR, MS spectroscopic data and elemental analysis as well. The photophysical and photochemical
properties of newly synthesized zinc phthalocyanines were investigated in DMSO for non-ionic and in
both DMSO and phosphate buffer solution (PBS) for ionic compounds. The obtained ionic complexes (2b,
3b) show excellent solubility in both organic and aqueous solutions which is very useful for the treat-
ment of cancer by photodynamic therapy (PDT).
Received 28 May 2013
Received in revised form
10 August 2013
Accepted 13 August 2013
Keywords:
Phthalocyanine
Water soluble
Zinc
Singlet oxygen
Photodynamic therapy
Photosensitizer
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
injected into the patient’s blood stream and because the blood itself
is a hydrophilic system, water solubility becomes crucial for a po-
Metal-free and metallophthalocyanines are one of the impor-
tant tetrapyrrole derivatives. Phthalocyanines are a family of aro-
tential photosensitizer for PDT [17].
The target of our ongoing research is to synthesis water-soluble
zinc phthalocyanines as potential PDT agents. In this work, the
synthesis, characterization, photophysical (fluorescence quantum
yields and lifetimes) and photochemical (singlet oxygen and pho-
todegradation quantum yields) properties of peripherally and non-
peripherally tetra-substituted non-ionic (2a and 3a) and ionic (2b
and 3b) zinc phthalocyanines were reported for the first time. The
photophysical and photochemical properties were studied in
DMSO for non-ionic and in both DMSO and PBS solutions for ionic
zinc phthalocyanines. The binding properties of ionic phthalocya-
nines (2b and 3b) with bovine serum albumin(BSA) which is one of
the blood proteins were also investigated in PBS solution.
matic macrocycles based on an extensive delocalized 18
p electron
system. As a consequence of their dark green-blue colour, phtha-
locyanines are an important class of chemicals for commercial use
in dyestuff for textiles and colorants for metals and plastics [1,2]. In
addition to this application, some recent focuses have been put on
their application as chemical sensors [3], solar cells [4], catalyst [5],
optical recording materials [6], photovoltaics [7].
The range of solubility in phthalocyanines becomes very
important for their applications, since many phthalocyanines are
poorly soluble in organic solvents and water. The solubility of
phthalocyanines can be enhanced by adding different kinds of
substituents such as long chain alkyl, crown ether, alkylthio or
alkoxy groups in common organic solvents, while anionic or
cationic (e.g. sulfo, carboxy, ammonium) groups in water at the
peripheral positions of the phthalocyanine ring [8e14].
2. Experimental
2.1. Materials and equipments
Zinc(II) phthalocyanine complexes have taken an interest in the
photodynamic therapy (PDT) of certain types of cancers due to their
long triplet lifetimes [15,16]. In PDT applications, the drug is
4-Nitrophthalonitrile [18], 3-nitrophthalonitrile [19], 2-[3-
(dimethylamino)phenoxy]ethanol (1) [20], 4-{2-[3-(dimethyla-
mino)phenoxy]ethoxy}phthalonitrile 2 [20] were prepared ac-
cording to the literature. All reagents and solvents were of reagent
grade quality and were obtained from commercial suppliers. All
* Corresponding author. Tel.: þ90 462 377 76 39; fax: þ90 462 325 31 96.
ꢀ
E-mail address: zekeriya_61@yahoo.com (Z. Bıyıklıoglu).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.08.025

424
D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
solvents were dried and purified as described by Perrin and
Armarego [21]. 9,10-Antracenediyl-bis(methylene) dimalonoic
acid (ADMA) and 1,3-diphenylisobenzofuran (DPBF) were pur-
chased from Fluka. The IR spectra were recorded on a Perkin
to room temperature, the reaction mixture was precipitated by
adding it drop-wise into ethanol. The crude product was collected
by filtration and washed with water, ethanol and ether and then
dried. Purification was achieved using column chromatography
with basic alumina as column material and CHCl3 as eluent. Yield:
Elmer 1600 FT-IR spectrophotometer using KBr pellets. 1H and 13
C
NMR spectra were recorded on a Varian Mercury 200 and
400 MHz spectrometer in CDCl3, and chemical shifts were re-
0.132 g (42%). IR (KBr Tablet), n
/cmꢁ1 : 3089 (AreH), 2919e2850
(Aliphatic CeH), 1608, 1575, 1490, 1449, 1395, 1339, 1235, 1170,
ported (
d
) relative to Me4Si as internal standard. Mass spectra
1152, 1124, 1093, 1069, 1000, 960, 825, 768, 746. 1H NMR (CDCl3),
were measured on a Micromass Quatro LC/ULTIMA LC-MS/MS
spectrometer and MALDI-MS of complexes were obtained in
dihydroxybenzoic acid as MALDI matrix using nitrogen laser
accumulating 50 laser shots using Bruker Microflex LT MALDI-TOF
mass spectrometer. The elemental analyses were performed on a
Costech ECS 4010 instrument. Electronic absorption spectra in the
UVevis region were recorded with Shimadzu 2101 UVeVis spec-
trophotometer operating in the range 300e800 nm. Fluorescence
excitation and emission spectra of the phthalocyanines were
recorded on a Varian Eclipse spectrofluorometer. Electronic ab-
sorption and fluorescence spectra were recorded at the room
temperature using 1 cm path length with quartz cuvette. General
Electric quartz line lamp (300 W) was used for photo-irradiation
studies. A 600 nm glass cut off filter (Intor) and a water filter
were used to filter off ultraviolet and infrared radiations, respec-
tively. An interference filter (Intor, 670 nm) for zinc phthalocya-
nines (2aeb and 3aeb) was additionally placed in the light path
before the sample. A POWER MAX5100 (Molelectron detector
incorporated) power meter was used for the measurements of
light intensities.
(
d
:ppm): 7.73e7.25 (m, 8H, AreH), 6.86 (bs, 4H, AreH), 6.21 (m,
16H, AreH), 4.24 (m, 16H, CH2eO), 2.23 (m, 24H, CH3). 13C NMR
(CDCl3), ( :ppm): 159.69, 151.49, 139.55, 131.22, 130.64, 129.82,
129.11, 123.39, 117.66, 106.15, 105.00, 102.76, 99.93, 72.06, 66.49,
d
40.58. UVeVis (DMSO), lmax(log )nm: 359 (4.77), 615 (4.06), 683
3
(5.07). MS (ESI), (m/z): 1295.76 [M þ H]þ, calcd for C72H68N12O8Zn:
1294.77. Found: C 66.30, H 5.05, N 12.90%, requires C 66.79, H 5.29,
N 12.98%.
2.2.3. 1(4),8(11),15(18),22(25)-Tetrakis-{2-[3-(dimethylamino)
phenoxy]ethoxy}phthalocyaninato zinc (II) (3a)
Synthesis and purification were as outlined for compound 2a
except 3-{2-[3-(dimethylamino)phenoxy]ethoxy}phthalonitrile (3)
was employed instead of 4-{2-[3-(dimethylamino)phenoxy]
ethoxy}phthalonitrile (2). The amounts of the reagents employed
were: 3-{2-[3-(dimethylamino)phenoxy]ethoxy}phthalonitrile (3)
(0.3 g, 0.97 ꢀ 10ꢁ3 mol), anhydrous Zn(CH3COO)2 (0.09 g,
0.48 ꢀ 10ꢁ3 mol), DBU (0.6 ꢀ 10ꢁ3 L, 0.48 ꢀ 10ꢁ3 mol) in n-pentanol
(0.003 L). Yield: 0.101 g (32%). IR (KBr Tablet),
2924e2868 (Aliphatic CeH), 1610, 1585, 1488, 1447, 1336, 1235,
1152, 1082, 1000, 889, 801, 743, 686. 1H NMR (CDCl3), (
:ppm): 8.71
n
/cmꢁ1 : 3076 (AreH),
The photophysical and photochemical formulas and parameters
were given as Supplementary information.
d
(m, 4H, AreH), 7.79e7.53 (m, 8H, AreH), 7.34 (m, 4H, AreH), 6.60e
6.33 (m, 12H, AreH), 5.23 (m, 8H, CH2eO), 4.76 (m, 8H, CH2eO),
2.2. Synthesis
2.72 (bs, 24H, CH3). 13C NMR (CDCl3), (
d:ppm): 159.89, 155.45,
153.08, 152.06, 141.30, 130.17, 129.83, 125.17, 117.63, 112.77, 106.09,
2.2.1. 3-{2-[3-(Dimethylamino)phenoxy]ethoxy}phthalonitrile (3)
3-Nitrophthalonitrile (1.24 g, 7.2 ꢀ 10ꢁ3 mol) was dissolved in
anhydrous DMF (0.015 L) under nitrogen atmosphere and 2-[3-
(dimethylamino)phenoxy]ethanol (1) (1.3 g, 7.2 ꢀ 10ꢁ3 mol) was
added to this solution. After stirring for 10 min, finely ground
anhydrous K2CO3 (4 g, 28.8 ꢀ 10ꢁ3 mol) was added in portionwise
over 2 h with stirring. The reaction mixture was stirred at 50 ꢂC
for 96 h under nitrogen atmosphere. Then 0.1 L water was added
and the aqueous phase extracted with chloroform (3 ꢀ 0.05 L).
The combined extracts were dried over anhydrous MgSO4 and
then filtered. Solvent was evaporated and the product was crys-
tallized from ethanol. Yield: 0.99 g (45%), mp: 135e136 ꢂC. IR (KBr
103.60, 102.56, 100.51, 67.93, 67.17, 40.83. UVeVis (DMSO), lmax(log
3
)nm : 366 (4.62), 633 (4.24), 702 (5.32). MS (ESI), (m/z): 1295.76
[M þ H]þ, calcd for C72H68N12O8Zn: 1294.77. Found: C 67.04, H 5.01,
N 12.40%, requires C 66.79, H 5.29, N 12.98%.
2.2.4. 2(3),9(10),16(17),23(24)-Tetrakis-{2-[3-(trimethylamino)
phenoxy]ethoxy}phthalocyaninato zinc (II)iodide (2b)
Zinc(II) phthalocyanine 2a (0.035 g, 0.03 ꢀ 10ꢁ3 mol) was dis-
solved in 0.003 L of chloroform and 0.0015 L methyl iodide was
added to this solution. The reaction mixture was stirred at room
temperature for 48 h. The green precipitate was filtered off, washed
with chloroform, acetone and diethyl ether. Finally, water-soluble
quaternized zinc phthalocyanines were dried in vacuo. Yield:
Tablet), n
/cmꢁ1 : 3089 (AreH), 2917e2889 (Aliphatic CeH), 2229
(C^N), 1614, 1583, 1566, 1504, 1466, 1450, 1361, 1324, 1295, 1250,
0.039 g (78%). IR (KBr Tablet),
(Aliphatic CeH), 1606, 1488, 1451, 1394, 1334, 1225, 1092, 1058, 963,
n
/cmꢁ1: 3010 (AreH), 2926e2862
1174, 1158, 1071, 995, 870, 823, 788, 752, 726, 685. 1H NMR
(CDCl3), (
d
:ppm): 7.66 (t, 1H, AreH), 7.38 (d, 2H, AreH), 7.14 (t, 1H,
746, 687. UVeVis (DMSO), lmax(log )nm: 360 (4.86), 614 (4.48),
3
AreH), 6.40 (d, 1H, AreH), 6.25 (s, 2H, AreH), 4.49 (m, 2H, CH2e
683 (5.16). MALDI-TOF-MS m/z: 339 [M ꢁ 4I þ 1]þ4, calcd for
O), 4.38 (m, 2H, CH2eO), 2.93 (s, 6H, CH3). 13C NMR (CDCl3),
C76H80N12O8ZnI4: 1862.53. Found: C 49.35, H 4.06, N 9.48%, requires
(
d
:ppm): 161.38, 159.47, 152.22, 134.88, 130.14, 125.76, 117.49,
C 49.01, H 4.33, N 9.02%.
117.19, 115.66, 113.31, 106.58, 105.32, 102.08, 99.86, 68.56, 66.56,
40.80. MS (ESI), (m/z): 308.40 [M þ H]þ, calcd for C18H17N3O2:
307.35. Found: C 70.61, H 5.13, N 13.12%, requires C 70.34, H 5.58,
N 13.67%.
2.2.5. 1(4),8(11),15(18),22(25)-Tetrakis-{2-[3-(trimethylamino)
phenoxy]ethoxy}phthalocyaninato zinc (II)iodide (3b)
Synthesis and purification were as outlined for compound 2b
except compound 3a was employed instead of compound 2a. The
amounts of the reagents employed were: Zinc(II) phthalocyanine
3a (0.035 g, 0.03 ꢀ 10ꢁ3 mol), methyl iodide (0.0015 L) in chloro-
2.2.2. 2(3),9(10),16(17),23(24)-Tetrakis-{2-[3-(dimethylamino)
phenoxy]ethoxy}phthalocyaninato zinc (II) (2a)
4-{2-[3-(Dimethylamino)phenoxy]ethoxy}phthalonitrile
(2)
form (0.003 L). Yield: 0.045 g (90%). IR (KBr Tablet), n
/cmꢁ1: 3010
(0.3 g, 0.97 ꢀ 10ꢁ3 mol), anhydrous Zn(CH3COO)2 (0.09 g,
0.48 ꢀ 10ꢁ3 mol) and 0.003 L of n-pentanol were placed in a
standard Schlenk tube in the presence of 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (0.6 ꢀ 10ꢁ3 L, 0.48 ꢀ 10ꢁ3 mol) under a nitrogen
atmosphere and held at reflux temperature for 24 h. After cooling
(AreH), 2923e2862 (Aliphatic CeH), 1604, 1589, 1488, 1454, 1333,
1229, 1082, 745. UVeVis (DMSO), lmax(log )nm: 382 (4.35), 630
3
(3.94), 701 (5.08). MALDI-TOF-MS m/z: 340 [M ꢁ 4I þ 2]þ4, calcd for
C76H80N12O8ZnI4: 1862.53. Found: C 49.39, H 4.02, N 9.58%, requires
C 49.01, H 4.33, N 9.02%.

D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
425
3. Results and discussion
and D2h. In this study, synthesized peripherally and non-
peripherally substituted zinc phthalocyanine complexes are ob-
tained as isomer mixtures as expected. No attempt was made to
separate the isomers of complexes due to the difficulties of the
separation.
In the IR spectra of phthalonitrile compound 3 indicated CN
group by the presence of an intense band at 2229 cmꢁ1. In the
1H NMR spectrum of compound 3, the aromatic protons were
appeared at 7.66 (t), 7.38 (d), 7.14 (t), 6.40 (d), 6.25 (s) ppm. Also
nitrile carbon atoms were observed 117.49 and 113.31 ppm in the
13C NMR spectrum of the compound 3. In the mass spectrum of
compound 3, the presence of molecular ion peak at m/z ¼ 308.40
[M þ H]þ confirmed the proposed structure.
3.1. Synthesis and characterization
Peripherally and non-peripherally tetra-substituted zinc phtha-
locyanines carrying four {2-[3-(dimethylamino)phenoxy]ethoxy}
substituents and their quaternized derivatives were prepared ac-
cording to the route shown in Schemes 1 and 2. The first step in the
synthetic procedure was to obtain 2-[3-(dimethylamino)phenoxy]
ethanol (1). This compound was synthesized by treating 3-
dimethylaminophenol with 2-chloroethanol in ethanol at reflux
temperature using NaOH as the base. Then, substituted phthaloni-
trile derivatives 2 and 3 were synthesized by reaction of 2-[3-
(dimethylamino)phenoxy]ethanol (1) with 4-nitrophthalonitrile
and 3-nitrophthalonitrile, respectively, in the presence of K2CO3 as
the base in dry DMF at 50 ꢂC for 96 h. The self-condensation of the
phthalonitrile derivatives 2 and 3 in a high-boiling solvent (n-pen-
tanol) in the presence of a few drops DBU as a strong base and
anhydrous Zn(CH3COO)2 at reflux temperature under a nitrogen
atmosphere afforded the zinc phthalocyanines (2a and 3a). The dark
green products are extremely soluble in polar and apolar organic
solvents such as CHCl3, CH2Cl2, THF, DMF and DMSO. Water soluble
tetra-cationic zinc phthalocyanines (2b and 3b) were obtained from
the reaction of corresponding zinc phthalocyanine complexes (2a
and 3a) with methyl iodide as quaternization agent in chloroform.
After reaction with methyl iodide, the quaternized zinc phthalocy-
anine complexes (2b and 3b) are very soluble in water. All new
compounds were characterized by the combination of UVeVis, IR,
1H NMR, 13C NMR, MS spectral data and elemental analysis and all of
which were supported the proposed structures. The four probable
isomers can be designed by their molecular symmetry as C4h, C2v, Cs
The cyclotetramerization of the 2-[3-(dimethylamino)phenoxy]
substituted phthalonitrile derivatives (2 and 3) to the zinc (II)
phthalocyanine counterparts (2a and 3a) can be seen clearly by the
disappearance of the C^N peaks (at 2232 cmꢁ1 for phthalonitrile 2
and 2229 cmꢁ1 for phthalonitrile 3) in the IR spectra of phthalo-
nitrile derivatives. The IR spectra of peripherally (2a) and non-
peripherally (3a) substituted zinc phthalocyanines showed
similar characteristics. The 1H NMR spectra of peripherally and
non-peripherally tetra-substituted zinc (II) phthalocyanines (2a
and 3a) were almost identical with that of the starting phthaloni-
trile compounds (2 and 3) except for broadening and small shifts in
the positions of some signals. The mass spectra of phthalocyanine
compounds 2a and 3a, which showed a peak at m/z ¼ 1295.76
[M þ H]þ support the proposed formula for these compounds.
Peripherally and non-peripherally tetra-substituted cationic
zinc phthalocyanines (2b and 3b) are soluble in polar organic sol-
vents such as DMF or DMSO and water as expected. These water
soluble ionic zinc phthalocyanines (2b and 3b) were obtained from
OH
i
N
N
+
Cl
OH
1
OH
O
NO2
CN
O2N
CN
CN
ii
ii
CN
CN
N
O
CN
CN
N
CN
O
O
3
O
2
iii
iii
RO
RO
OR
N
N
N
N
N
N
RO
N
N
N
N
R =
Zn
N
N
N
Zn
N
N
N
O
N
OR
RO
2a
OR
3a
OR
Scheme 1. Synthetic pathway for preparation of peripherally and non-peripherally tetra-substituted zinc(II) phthalocyanine complexes. (i) EtOH, NaOH. (ii) K2CO3, N2, DMF.
(iii) Zn(CH3COO)2, n-pentanol, DBU, 160 ꢂC.

426
D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
4+
RO
OR
R'O
OR'
N
R =
N
N
N
N
N
O
N
N
N
CH3-I
N
N
Zn
4I-
N
N
Zn
N
CHCl3, rt
N
N
N
R' =
N
O
RO
2a
OR
R'O
OR'
2b
4+
RO
R'O
N
R =
N
N
RO
R'O
O
N
N
N
N
N
N
N
CH3-I
CHCl3, rt
4I-
N
Zn
N
N
N
Zn
N
N
N
OR
OR'
N
R' =
O
OR
OR'
3a
3b
Scheme 2. The synthesis of the quaternized ionic zinc phthalocyanine complexes.
the reaction of corresponding non-ionic zinc phthalocyanines (2a
and 3a) with methyl iodide which is a quaternization agent in
chloroform. No major change in the IR spectra was observed after
quaternization. In the mass spectra of ionic zinc phthalocyanine
compounds (2b and 3b) the molecular ion peaks were observed at
m/z ¼ 339 [M ꢁ 4I þ 1]þ4, 340 [M ꢁ 4I þ 2]þ4 respectively,
confirmed the proposed structures.
peripherally substituted counterparts. This changes on the wave-
length of Q bands between peripheral and non-peripheral substi-
tution attribute linear combinations of the atomic orbitals (LCAO)
coefficients at the non-peripheral positions of the highest occupied
molecular orbital (HOMO) being greater than those at the periph-
eral positions [22].
Generally, phthalocyanines exhibit characteristic bands in the
electronic spectra at ultraviolet and visible region. Two principle
3.2. Aggregation studies
p
/
p
* transitions are seen for phthalocyanines: One of them is
called as Q band and another is called Soret or B band. Q band
which is a * transition from the highest occupied molecular
Phthalocyanine compounds form high aggregation tendency
due to the interactions between their 18
p-electron systems and
p
/ p
aggregation is decrease the solubility of these compounds in many
organic solvents and water as well. It also affects seriously their
spectroscopic, photophysical, photochemical and electrochemical
properties. Generally, aggregation is highly depends on concen-
tration, temperature, nature of the substituents, nature of solvents
and complexed metal ions [23,24]. Phthalocyanine molecules can
form two types aggregates in solution called H-and J-type
depending on the nature and position of the substituents. Gener-
ally, phthalocyanine molecules form H-type aggregates in solution.
J-type aggregation is observed rarely among the phthalocyanine
molecules. Although, the H-type aggregates are not photoactive,
orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO)
of the complexes. While the Q bands are observed at 650e750 nm
region, the B bands are observed at 300e350 nm region in the
electronic spectrum. The ground state electronic spectra of the
studied peripherally and non-peripherally tetra-substituted zinc
phthalocyanines showed characteristic absorptions in the Q band
region at 683 nm for compound 2a, 702 nm for compound 3a, 683
for compound 2b and 701 nm for compound 3b in DMSO, Table 1. B
band absorptions of these complexes were observed at 359, 366,
360, 382 nm, respectively.
The Q bands of the non-peripherally substituted zinc phthalo-
cyanines were red-shifted approximately 20 nm compared to
1.2
1
Table 1
DMSO
DMF
THF
Electronic absorption and fluorescence data of studied zinc phthalocyanines in
DMSO (for all compounds), PBS and PBS þ triton X-100 (for quaternized compounds)
solutions.
0.8
Chloroform
0.6
0.4
0.2
0
Dichloromethane
Toluene
Compound Solvent Q band
lmax, (nm)
(log
3
)
Excitation Emission Stokes
lEx, (nm) lEm, (nm) shift DStokes
(nm)
,
2a
2b
DMSO
DMSO
PBS
683
683
5.07
5.16
685
685
692
692
e
7
7
e
6
7
4
e
6
625, 683 4.34, 4.11 e
PBS þ TX 683
4.87
5.32
5.08
687
705
704
693
712
708
e
300
400
500
600
700
800
3a
3b
DMSO
DMSO
PBS
702
701
Wavelength (nm)
651, 697 4.56, 4.60 e
5.10 704
Fig. 1. Electronic absorption spectra of compound 3a in different solvents.
(Concentration w 2.0 ꢀ 10ꢁ6 M).
PBS þ TX 702
710

D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
427
0.4
Chloroform+K CO
0.3
0.2
2b
3b
Chloroform
0.1
0
300
400
500 600
Wavelength (nm)
700
800
800
Wavelength (nm)
Fig. 4. Electronic absorption spectra of compounds 2b and 3b in PBS.
(Concentration w 1.0 ꢀ 10ꢁ5 M).
Fig. 2. Electronic absorption spectra of compound 3a in chloroform and
chloroform þ K2CO3. (Concentration w 2.0 ꢀ 10ꢁ6 M).
can be formation of J-type aggregates with the adaptation of Pc
molecules into a side-by-side conformation [28e30,36e41]. The
splitting Q band in the electronic spectra of the phthalocyanines
can be interpreted two reasons. One of them can be protonation of
the inner nitrogen atoms due to the some acidic impurities such as
HCl in chloroform or dichloromethane. The protonation of the ni-
trogen atoms on the phthalocyanine occurs aggregation among the
phthalocyanine molecules in non-coordinating solvents such as
chloroform, dichloromethane or toluene. In this study, the possi-
bility of J-aggregation may be ruled out by the fact that the red-
shifted Q band of compound 3a was observed only in chloroform
and dichloromethane (as a shoulder). This band did not observed in
toluene which is also a non-coordinating solvent, which implies
that the presence of acid as impurity in the chloroform (or
dichloromethane) causes protonation of the pyrollic nitrogens of
the phthalocyanine ring and the observed band at 745 nm is due to
the protonation not J-aggregation. Another evidence for the for-
mation of the extra red shifted band due to the protonation is
treatment of the using chloroform with a base before dissolving
compound 3a. The extra red shifted band did not observe when the
chloroform dealing with K2CO3 before use, Fig. 2.
the J-type aggregates are photoactive for phthalocyanine molecules
because the molecules form bigger aggregates for H-type (generally
bulky species) than J-type (generally dimer species) aggregation.
Generally, two types of J-aggregates could be formed among the
phthalocyanine molecules. One of them, J-aggregates occurred by
utilizing the coordination of the linker oxygen atoms of side sub-
stituent on non-peripheral position from one phthalocyanine
molecule to the zinc (II) ion in a neighbor phthalocyanine molecule
[25e28]. For another type formation, J-aggregates occurred by
utilizing the coordination of nitrogen atoms on the substituents
from one phthalocyanine molecule to the zinc (II) ion in a neighbor
phthalocyanine molecule [29,30].
The aggregation behavior of the studied peripherally and non-
peripherally non-ionic tetra-substituted zinc phthalocyanines (2a
and 3a) were investigated in different solvents (DMSO, DMF, THF,
CHCl3, CH2Cl2 and toluene), Fig. 1 as an example for compound 3a.
Both non-ionic phthalocyanines (2a and 3a) showed single (nar-
row) Q bands in all studied solvents except for non-peripherally
substituted phthalocyanine (3a) in chloroform, Fig. 1. This is indi-
cated that studied non-ionic phthalocyanines showed monomeric
behavior in these solvents except for chloroform. The non-
peripherally substituted zinc phthalocyanine (3a) showed an ex-
tra peak at 745 nm in chloroform. This peak was also observed in
dichloromethane as a small shoulder. Generally, the observation of
this extra red shifted band compare to Q band cause lowering of the
symmetry of the molecules. The Q bands of the protonated
phthalocyanines observe as splitted peak [31e35]. Another reason
The aggregation behavior of the studied peripherally and non-
peripherally ionic tetra-substituted zinc phthalocyanines (2b and
3b) were also investigated in different solvents (DMSO, DMF,
MeOH, PBS and water). These phthalocyanines did not show any
aggregation in DMSO, DMF and MeOH, but they formed H-type
aggregates in aqueous solutions, Fig. 3 as an example for compound
3b. These compounds formed more aggregated species in PBS than
0.5
1.2
0.4
1
DMSO
DMF
MeOH
PBS
PBS
PBS+TX
0.8
0.6
0.4
0.2
0
0.3
0.2
0.1
0
Water
800
300
400
500 600
Wavelength (nm)
700
800
Wavelength (nm)
Fig. 3. Electronic absorption spectra of compound 3b in different solvents.
(Concentration w 2.0 ꢀ 10ꢁ6 M).
Fig. 5. Electronic absorption spectra of compound 3b in PBS and PBS þ triton X-100.
(Concentration w 4.0 ꢀ 10ꢁ6 M).

428
D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
Table 2
Photophysical and photochemical results of studied zinc phthalocyanines in DMSO
(for all compounds), PBS and PBS þ triton X-100 (for quaternized compounds)
solutions.
Compound
Solvent
FF
sF (ns)
Fd ꢀ 10ꢁ3
FD
2a
2b
DMSO
DMSO
PBS
PBS þ TX
DMSO
DMSO
PBS
0.22
0.25
e
2.27
2.89
e
0.030
0.046
3.151
11.188
0.066
0.127
3.221
2.845
0.49
0.56
0.054
0.52
0.39
0.80
0.042
0.56
0.12
0.11
0.17
e
1.84
0.82
1.81
e
3a
3b
PBS þ TX
0.17
2.20
Wavelength (nm)
Fig. 6. Electronic absorption spectra of compound 3b in PBS
þ
triton X-100 at
intensities in DMSO, Fig. 7A as an example for compound 2b. While
the ionic zinc phthalocyanines were fluorescent in organic solution,
these compounds were not fluorescent in aqueous solution because
of the aggregation of these compounds in aqueous solutions. Ag-
gregation is known to reduce fluoresce of the molecules due to the
formation of the aggregates instead of monomer molecules. The
best evidence for the effect of the aggregation on the fluorescence
properties of the studied phthalocyanines was measurement of the
fluorescence after addition of the triton X-100. Both the studied
ionic zinc phthalocyanines showed intense fluorescence emission
rising after addition of TX to the PBS solutions, Fig. 7B as an
example for compound 2b. The shapes of the absorption and
fluorescence excitation spectra were similar and both mirror image
of the emission spectra in DMSO, Fig. 7A. It is indicated that the
nuclear configurations of the ground and excited states of the
molecules are similar and not affected by using light for excitation
during the fluorescence studies. The fluorescence emission and
excitation maxima of the studied zinc phthalocyanines in DMSO
and PBS þ TX were listed in Table 1. The observed Stokes shifts are
typical for zinc phthalocyanines.
different concentration. (A ¼ 12 ꢀ 10ꢁ6, B ¼ 10 ꢀ 10ꢁ6, C ¼ 8.0 ꢀ 10ꢁ6, D ¼ 6.0 ꢀ 10ꢁ6
,
E ¼ 4.0 ꢀ 10ꢁ6 and F ¼ 2.0 ꢀ 10ꢁ6 M).
in water according to the proportion between the monomeric (low
energy) and aggregated (high energy) bands, Fig. 3. The non-
peripherally substituted phthalocyanine showed lower aggrega-
tion than peripherally substituted phthalocyanine in PBS (Fig. 4)
suggesting that more sterically crowded substitution on the non-
peripheral positions of phthalocyanine ring. The formed aggre-
gates for ionic phthalocyanine molecules in the PBS were trans-
formed into monomeric species by the addition of triton X-100 in
the PBS solution since the Q band significantly became sharp, Fig. 5
as an example for compound 3b. Triton X-100 (TX) which is a
surfactant molecules penetrate among the phthalocyanine mole-
cules and these molecules away from each other. As a result, the
addition of TX to the PBS solution inhibited aggregation of the
phthalocyanine molecules in PBS solution.
The aggregation behavior of substituted zinc phthalocyanines
(2aeb, 3aeb) were also studied at different concentration in DMSO
for determination of the aggregation depends on concentration.
The studied zinc phthalocyanines (2aeb, 3aeb) did not show any
aggregation concentration ranges between 2 ꢀ 10ꢁ6 M and
12 ꢀ 10ꢁ6 M in DMSO, Fig. 6 as an example for compound 3b.
3.4. Photophysical studies
An ideal photosensitizer should be exhibiting some fluorescence
behavior for imaging of these molecules in the body. Therefore, the
determination of the fluorescence properties such as fluorescence
3.3. Fluorescence studies
quantum yield (FF) and fluorescence lifetime (
photosensitizers is very important for PDT studies. The fluores-
cence quantum yields (FF) and lifetimes ( F) of the non-ionic zinc
phthalocyanines were determined in DMSO whereas these values
were determined in DMSO and PBS þ TX solutions for ionic zinc
phthalocyanines and the values were given in Table 2. These values
did not measure in PBS solutions because the ionic zinc phthalo-
cyanines did not exhibited any fluorescence due to the strong ag-
gregation in this solution. Thanks to TX because these values could
sF) values of the
The fluorescence emission and excitation behavior of the
peripherally and non-peripherally substituted zinc phthalocya-
nines (2aeb, 3aeb) were studied in three different solutions.
DMSO, PBS and PBS þ TX solutions were used for the measure-
ments in order to determination of aggregation effect on the fluo-
rescence properties of studied phthalocyanines. All studied
phthalocyanines (2aeb, 3aeb) exhibited similar fluorescence
s
(B)
(A)
2b in PBS+Triton X-100
Emission
Excitation
2b in PBS
Absorption
500
600
700
800
670
690
710
730
750
770
790
Wavelength (nm)
Wavelength (nm)
Fig. 7. (A) Electronic absorption, fluorescence emission and excitation spectra of compound 2b in DMSO, (B) fluorescence emission and excitation spectra of compound 2b in both
PBS and PBS þ triton X-100. (Excitation wavelength ¼ 660 nm).

D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
429
0.8
0.6
0.4
0.2
0
(B)
(A)
300
400
500
600
700
800 300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 8. Electronic absorption spectral changes during the singlet oxygen determination for compound 3b (A) in DMSO using DPBF at 5 s intervals and (B) in PBS þ Triton X-100 using
ADMA at 5 min intervals.
be obtained by the addition of the TX to the PBS solutions due to the
inhibiting of the aggregation. The calculated FF and sF values are
typical for zinc phthalocyanines. For example the FF value of the
unsubstituted zinc phthalocyanine which use as standard for
fluorescence measurements is 0.20 in DMSO [42]. The sF value of
this complex is 1.22 ns in same solvent [43]. These values are also
convenient in PBS solution after addition of TX for imaging of the
molecules. The FF values of the peripherally substituted zinc
phthalocyanines are higher than non-peripherally substituted
counterparts in DMSO. The FF values of the 2-[3-(dimethylamino)
phenoxy] substituted zinc phthalocyanines increased when the
quaternization of the dimethylamino groups on the substituents.
The sF values of the non-peripheral substituted zinc phthalocya-
nines are longer than peripheral substituted phthalocyanines in
DMSO. The quaternized ionic zinc phthalocyanines stay longer time
than non-ionic phthalocyanines at the excited state.
triton X-100 to PBS solution of ionic zinc phthalocyanines affected
the singlet oxygen generation capability of these phthalocyanines.
The addition of the triton X-100 increased the production of singlet
oxygen for studied ionic zinc phthalocyanines because the FD
values of these complexes also increased by the addition of triton X-
100 (Table 2). This is attributed to the decrease in aggregation
behavior of these ionic phthalocyanines by the addition of triton X-
100.
The photostability determination of the photosensitizers under
light irradiation is also important for photocatalitic reactions such
as PDT. The photosensitizer molecules should be decomposed after
injection in the blood at an optimum time. They must be spent
sufficient time in the cell during the photodynamic activity
and they also must be easily thrown out of the body after
completion of PDT activity. The degradation of the molecules under
light irradiation is generally defined as photodegradation quantum
yield
(Fd). The degradation of the peripherally and non-
peripherally substituted zinc phthalocyanines under light irradia-
tion were investigated in DMSO for non-ionic phthalocyanines and
in aqueous solutions (PBS and PBS þ TX) for ionic phthalocyanines
and the obtained results were given in Table 2. The Fd values of the
peripheral substituted zinc phthalocyanines are lower than non-
peripheral substituted ones so the peripherally substitution more
stable than non-peripheral substitution in DMSO. The obtained Fd
values of the studied zinc phthalocyanines are lower in DMSO than
in aqueous solutions. The solubility of the studied compounds in
the aqueous solutions decrease the stability of them. The quater-
nization of the dimethylamino groups on the substituents reduced
3.5. Photochemical studies
The determination of the formed singlet oxygen by photosen-
sitizers during the photochemical reactions is immense important
before cell studies for PDT applications. An efficient photosensitizer
must be generated high singlet oxygen which is quantified as
singlet oxygen quantum yield (FD) under light irradiation. The
chemical method was used for determination of the produced
singlet oxygen by studied zinc phthalocyanines using 1,3-
diphenylisobenzofuran (DPBF) in organic solution and 9,10-antra-
cenediyl-bis(methylene) dimalonoic acid (ADMA) in aqueous so-
lution as singlet oxygen quenchers. A diminution was observed to
the absorbance of the quenchers at 417 nm for DPBF (Fig. 8A as an
example for compound 3b in DMSO) and 380 nm for ADMA (Fig. 8B
as an example for compound 3b in PBS þ TX solution) under using
light irradiation (30 V). The intensities or shapes of the Q bands for
studied zinc phthalocyanines did not show any changes and this is
indicating that the substituted phthalocyanine photosensitizers did
not expose any degradation during the singlet oxygen studies by
the light irradiation. The FD values of the non-ionic zinc phthalo-
cyanines were determined in organic solution (DMSO) whereas
these values were determined in DMSO and aqueous solutions (PBS
and PBS þ TX) for ionic zinc phthalocyanines and the calculated
values were given in Table 2. The quaternization of the zinc
phthalocyanines resulted higher FD values in DMSO especially non-
peripherally substituted compound produced two times singlet
oxygen when quaternized. The amount of the generated singlet
oxygen is higher in DMSO than in PBS due to the aggregation of
studied zinc phthalocyanines in latter solvent. The addition of the
600
400
200
0
290
310
330
350
370
390
410
430
450
Wavelength (nm)
Fig. 9. Emission changes of BSA (C ¼ 3.00 ꢀ 10ꢁ5 M) by the addition of varying
amounts of 2b in PBS. [2b]: 0, 1.66 ꢀ 10ꢁ6, 3.33 ꢀ 10ꢁ6, 5.00 ꢀ 10ꢁ6, 6.66 ꢀ 10ꢁ6
8.33 ꢀ 10ꢁ6 M and saturated with 2b.
,

430
D. Çakır et al. / Journal of Organometallic Chemistry 745-746 (2013) 423e431
0.2
2b
(B)
0
-0.2
-0.4
-0.6
-0.8
-1
2b
3b
1.9
1.6
1.3
1
(A)
3b
-1.2
-5.9
-5.8
-5.7
-5.6
-5.5
-5.4
-5.3
-5.2
-5.1
-5
0
0.000002
0.000004
0.000006
0.000008
0.00001
log[Pc]
[Pc]
Fig. 10. (A) SterneVolmer plots of compounds 2b and 3b quenching of BSA in PBS. (B) Determination of binding constants and number of binding sites on BSA for compounds 2b
and 3b. [BSA] ¼ 3.00 ꢀ 10ꢁ5 M and [Pc] ¼ 0, 1.66 ꢀ 10ꢁ6, 3.33 ꢀ 10ꢁ6, 5.00 ꢀ 10ꢁ6, 6.66 ꢀ 10ꢁ6, 8.33 ꢀ 10ꢁ6 M in PBS.
the stability of the studied zinc phthalocyanines against the used
light.
4. Conclusion
In this study, the binding properties of the studied peripherally
and non-peripherally substituted zinc phthalocyanines to blood
proteins such as BSA were also examined by spectroscopic inves-
tigation in PBS solutions. The binding studies give an idea about
the transportation of the photosensitizers in blood via complexa-
tion of photosensitizer molecules with BSA. Fluorescence emission
of the BSA at 348 nm is generally due to its tryptophane moieties
and it is intensity decreased when the protein is bound to zinc
phthalocyanine photosensitizer molecules. Fig. 9 offers decreasing
of the fluorescence emission spectra of BSA by the addition of
different concentrations of 2b in PBS as an example. The observed
fluorescence reciprocated quenching between BSA and the ionic
zinc phthalocyanines can be determine SterneVolmer quenching
constants (KSV). The slopes of the plots in Fig. 10A gave KSV values
and these values were listed in Table 3. The KSV value of the
peripherally substituted zinc phthalocyanine is two times higher
than non-peripherally substituted analogue. It is suggesting that
peripherally substitution is more effective than non-peripherally
substitution to the binding BSA in PBS. Using the approximate
fluorescence lifetime of BSA as 10 ns [44,45], the bimolecular
quenching constant (kq) can be determined. These values are of the
In the presented work, the synthesis a range of new non-ionic zinc
phthalocyanines (2a and 3a) carrying four 2-[3-(dimethylamino)
phenoxy] functionalities and their quaternized ionic derivatives (2b
and 3b) were described. The obtained zinc phthalocyanines were
fully characterized by elemental analysis, UVeVis, IR, 1H NMR, 13C
NMR and mass spectral data. The non-ionic zinc phthalocyanines are
soluble in most of organic solvents whereas their quaternized ionic
analogues are soluble in aqueous solutions as well which makes them
convenient candidates as photosensitizers for treatment of cancer by
using PDT. For this purpose, the photophysical and photochemical
properties of these zinc phthalocyanine photosensitizers were
investigated in both organic and aqueous solutions. DMSO was
selected as an organic solvent which is not toxic at higher doses for
cells, PBS was also selected for aqueous solutionwhich is more proper
than water to physiological fluid. The studied zinc phthalocyanines
showed moderate fluorescence properties in DMSO and PBS þ TX
solutions whereas they did not exhibit any fluorescence in alone PBS.
The newly synthesized zinc phthalocyanines (especially non-
peripherally substituted ones) produced relatively higher singlet
oxygen in both DMSO and PBS þ TX solutions which is most impor-
tant factor for PDT of cancer. The binding properties of zinc phtha-
locyanines to BSA proteinwere also studied in this study to determine
whether to transport these photosensitizer molecules into the blood.
order of 1013 Mꢁ1
s
ꢁ1, which exceed the proposed value of
1010 Mꢁ1 sꢁ1 for diffusion-controlled (dynamic) quenching ac-
cording to the EinsteineSmoluchowski approximation at room
temperature [46]. This indicates that the mechanism of BSA
quenching by ionic zinc phthalocyanines is not diffusion-
controlled and that the quenching is static, not dynamic. The
number of binding sites (n) and binding constants (Kb) on BSA
were determined from slopes of the plots of Fig. 10B and intercepts
of these plots, respectively and the results are shown in Table 3.
The Kb and n values are typical for phthalocyanine-BSA in-
teractions in aqueous solutions [47,48]. n-Values of near unity
suggest that zinc phthalocyanine photosensitizers form 1:1 con-
jugates with BSA. The decrease in the intrinsic fluorescence in-
tensity of BSA with by the increasing of ionic zinc phthalocyanine
concentration indicates that studied zinc phthalocyanines readily
bind to BSA, which implies that the phthalocyanine photosensi-
tizers reach the subdomains where tryptophan residues are
located in BSA.
Acknowledgements
This study was supported by The Scientific & Technological
_
Research Council of Turkey (TÜBITAK, project no: 111T963).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.08.025.
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