Water-soluble quaternized mercaptopyridine-substituted zinc- phthalocyanines: Synthesis, photophysical, photochemical and bovine serum albumin binding properties

Article abstract of DOI:10.1016/j.dyepig.2011.02.007

The synthesis and characterization of the new zinc phthalocyanine derivatives, tetra- (non-peripheral, 5) and octa-(peripheral, 6) substituted with 2-mercaptopyridine and their respective quaternized derivatives (8 and 9) are reported. Photochemical and p

Full text of DOI:10.1016/j.dyepig.2011.02.007

Dyes and Pigments 91 (2011) 153e163
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Water-soluble quaternized mercaptopyridine-substituted
zinc-phthalocyanines: Synthesis, photophysical, photochemical
and bovine serum albumin binding properties
a
,
a
a
a,
Mahmut Durmus¸ , Hanifi Yaman , Cem Göl , Vefa Ahsen b, Tebello Nyokong c
*
a Gebze Institute of Technology, Department of Chemistry, PO Box 141, Gebze, 41400 Kocaeli, Turkey
b TUBITAK-Marmara Research Center, Materials Institute, PO Box 21, Gebze, 41470 Kocaeli, Turkey
c Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and characterization of the new zinc phthalocyanine derivatives, tetra- (non-peripheral, 5)
and octa-(peripheral, 6) substituted with 2-mercaptopyridine and their respective quaternized deriva-
tives (8 and 9) are reported. Photochemical and photophysical properties of the new complexes are
compared with those of the previously reported peripherally tetra-substituted complexes 7 and 10. The
quaternized compounds exhibit excellent solubility in water, making them potential photosensitizers for
use in photodynamic therapy (PDT) of cancer. Spectroscopic, aggregation, photophysical and photo-
chemical properties of these complexes are also investigated and compared. Photophysical (fluorescence
quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yield)
properties of these phthalocyanine photosensitizers are very important for the assessment of these
complexes as PDT agents. In this study, the effects of the position of the substituents and quaternization
of the substituents on the photophysical and photochemical parameters of the zinc phthalocyanines are
also reported. This study also showed that the water-soluble quaternized zinc phthalocyanines strongly
bind to blood plasma proteins such as bovine serum albumin (BSA).
Received 3 January 2011
Received in revised form
4 February 2011
Accepted 7 February 2011
Available online 8 March 2011
Keywords:
Phthalocyanine
Quaternization
Water soluble
Photosensitizer
Bovine serum albumin
Photodynamic therapy
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
properties of the Pc dyes are strongly influenced by the presence
and nature of the central metal ion. MPcs containing transition
Phthalocyanines (Pcs) are remarkable macrocyclic compounds
having magnificent physical and chemical properties [1]. Metal-
lophthalocyanines (MPc) have been investigated in detail for many
years due to their wide applications in many fields, mostly in terms
of their uses as blue-green dyes and catalysts [2,3]. They have also
found different applications in many fields ranging from industrial
[4], technological [5,6] to medical [7,8]. Most metal ions can be
engaged in the Pc macrocyle’s cavity; therefore, a large number of
different MPc complexes have been synthesized. When the central
metal is diamagnetic and non-transitional, MPc derivatives are
photoactive and may be employed in photosensitization [9,10]. In
this regard, it is worth emphasizing the Pcs’ application as photo-
sensitizers in the photodynamic therapy (PDT) of tumours. High
triplet state quantum yields and long triplet lifetimes are required
for efficient sensitization by MPc complexes. The photophysical
metals give short triplet lifetimes. Closed shell and diamagnetic
ions, for example Zn2þ, Ga3þ and Si4þ, give Pc complexes excellent
properties such as high triplet yields and long lifetimes [11e13].
ZnPcs in particular have been extensively studied because of d10
configuration of the central Zn2þ ion results in optical spectra that
are not complicated by additional bands, as in transition-metal Pc
complexes. ZnPcs have intensive red-visible region absorption and
high singlet and triplet yields, making them valuable photosensi-
tizers for PDT applications.
In PDT applications, the drug is injected into the patient’s blood
stream, and since the blood itself is a hydrophilic system, water
solubility plays a very important role for a potential photosensitizer
in PDT [14e17]. The advantages of MPcs bearing cationic substitu-
ents over those with neutral and anionic substituents are numerous
[18], for examples: (i) they are able to improve water solubility and
prevent aggregation [19]; aggregation seriously compromises the
PDT value of the photosensitizer, (ii) they are more efficient as PDT
agents [20] and also improve cell uptake [21], (iii) they are selec-
tively localized in the cell mitochondria and cause apoptosis [22].
* Corresponding author. Tel.: þ90 262 6053075; fax: þ90 262 6053101.
E-mail address: durmus@gyte.edu.tr (M. Durmus¸ ).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.02.007

154
M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
Thiol-substituted MPc complexes are known to absorb light at
positions with a 2-mercaptopyridine group (Scheme 1) and their
quaternized (8 for tetra-non-peripheral, and 9 for octa-peripheral
position) complexes (Scheme 2). The photophysical and photo-
chemical properties of these complexes are compared with those of
the previously reported tetra substituted complexes 7 and 10.
Bovine serum albumin (BSA) and human serum albumin (HSA)
are major plasma proteins, which contribute significantly to phys-
iological functions and display effective drug delivery roles [27,28],
hence the investigation of binding of drugs with albumin is of
interest. A spectroscopic investigation of the binding of the water-
soluble zinc Pc complexes (8, 9 and 10) to BSA is also presented in
this work.
longer wavelengths (>700 nm) [23e26] and to exhibit good
spectroscopic and photochemical properties. Therefore these
complexes have a very useful feature for applications in optoelec-
tronics, near-IR devices and PDT.
The aim of our ongoing research is to synthesise water-soluble
zinc Pc complexes as potential PDT agents. Herein, we report on the
synthesis, characterization and spectroscopic behavior as well as
photophysical (fluorescence quantum yields and lifetimes) and
photochemical (singlet oxygen and photodegradation quantum
yields) properties of zinc Pc complexes tetra-substituted at the
non-peripheral (5), and octasubstituted at the peripheral (6)
RS
SR
N
N
N
N
N
CN
CN
RSH, DMF
K CO , RT
Zn(OAc) , n-pentanol
2
Zn
N
N
CN
2
3
reflux, 18 hrs
CN
NO
N
SR
2
SR
1
3
SR
5
RS
SR
N
N
N
N
N
Cl
Cl
CN
CN
RS
RS
CN
CN
RSH, DMF
K CO , RT
SR
SR
Zn(OAc) , n-pentanol
RS
RS
2
Zn
N
N
2
3
reflux, 18 hrs
N
4
2
RS
SR
6
SR
R
=
N
N
N
N
N
N
SR
Zn
N
N
RS
N
SR
7
Scheme 1. Synthesis of tetra- and octa-2-mercaptopyridine substituted zinc phthalocyanine complexes. The synthesis of complex 7 has been reported before [33].

M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
155
4+
RS
R'S
SR'
SR
N
N
N
N
N
N
Dimethylsulphate, DMF
N
2-
N
N
Zn
N
N
2SO4
Zn
N
N
120OC, 12h
N
N
N
SR
SR'
SR
SR'
5
8
R'S
SR'
RS
SR
8+
N
N
N
N
N
N
N
N
N
N
SR'
SR'
SR
SR
R'S
R'S
RS
RS
Dimethylsulphate, DMF
120OC, 12h
2-
Zn
N
N
Zn
N
4SO4
N
N
N
R'S
SR'
RS
SR
9
6
SR'
4+
R
=
N
N
N
N
N
N
2-
SR'
Zn
N
N
2SO4
R'S
R'
=
N
N
+
CH
3
SR'
10
Scheme 2. Synthesis of quaternized tetra- and octa-2-mercaptopyridine substituted zinc phthalocyanine complexes. The synthesis of complex 10 has been reported before [33].
2. Experimental section
literature procedures. ZnPcSmix containing a mixture of differently
sulfonated derivatives was synthesized as reported before [34].
2.1. Materials
2.2. Equipment
Quinoline, dimethylsulphoxide (DMSO), methanol, n-hexane,
chloroform (CHCl3), dichloromethane (DCM), tetrahydrofuran
(THF), acetone, ethanol and dimethylformamide (DMF) were dried
as described in Perrin and Armarego [29] before use. Unsubstituted
zinc phthalocyanine, zinc (II) acetate, K2CO3, dimethylsulphate
(DMS) were purchased from Aldrich. 2-Mercaptopyridine was
purchased from Fluka. 3-Nitrophthalonitrile (1) [30], 4,5-dichlor-
ophthalonitrile (2) [31], 3-(2-mercaptopyridine)phthalonitrile (3)
[32], 2,(3)-tetra-(2-mercaptopyridine) phthalocyaninatozinc (II) (7)
[33] and quaternized 2,(3)-tetra-(2-mercaptopyridine)phthalocya-
ninato zinc (II) (10) [33] were synthesized and purified according to
Absorption spectra in the UVevisible region were recorded with
a Shimadzu 2001 UV spectrophotometer. Fluorescence excitation
and emission spectra were recorded on a Varian Eclipse spectro-
fluorometer using 1 cm pathlength cuvettes at room temperature.
IR spectra (KBr pellets) were recorded on a Bio-Rad FTS 175C FTIR
spectrometer. The mass spectra were acquired on a Bruker Dal-
tonics (Bremen, Germany) MicrOTOF mass spectrometer equipped
with an electronspray ionization (ESI) source. The instrument was
operated in positive ion mode using a m/z range of 50e3000. The
capillary voltage of the ion source was set at 6000 V and the

156
M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
capillary exit at 190 V. The nebulizer gas flow was 1 bar and drying
gas flow 8 cm3/min. The drying temperature was set at 200 ꢀC for
non-ionized complexes (5e7) and positive ion and linear mode
MALDI-MS spectrum of quaternized complex (8) was obtained in
3,5-dimethoxy-4-hydroxycinnamic acid as MALDI matrix using
nitrogen laser accumulating 50 laser shots using by Bruker Micro-
flex LT MALDI-TOF mass spectrometer. 1H spectra were recorded in
CDCl3 for phthalonitrile (4) and DMSO-d6 solutions for phthalocy-
anine complexes (5,6,8,9) on a Varian 500 MHz spectrometer.
Elemental analyses were obtained with a Thermo Finnigan Flash
1112 Instrument.
Photo-irradiations were done using a General Electric quartz
line lamp (300W). A 600 nm glass cut off filter (Schott) and a water
filter were used to filter off ultraviolet and infrared radiations
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.
aqueous media) [42]. R and RStd are the DPBF (or ADMA) photo-
bleaching rates in the presence of the ZnPc derivatives and stan-
dards, respectively. Iabs and ISabtds are the rates of light absorption by
ZnPc derivatives and standards, respectively. To avoid chain reac-
tions induced by DPBF (or ADMA) in the presence of singlet oxygen
[43], the concentration of quenchers (DPBF or ADMA) was lowered
to ∼3 ꢁ 10ꢂ5 M. Solutions of sensitizer containing DPBF (or ADMA)
were prepared in the dark and irradiated in the Q band region using
the set-up described above. DPBF degradation at 417 nm (in DMSO)
and ADMA degradation at 380 nm (in water) were monitored. The
light intensity 6.72 ꢁ 1015 photons sꢂ1 cmꢂ2 was used for FD
determinations.
2.4.2. Photodegradation quantum yields
Photodegradation quantum yield (Fd) determinations were carried out
using the experimental set-up described in literature [34,39,40]. Photo-
degradation quantum yields were determined using Eq. (4),
ðC0 ꢂ CtÞ : V : NA
Fd
¼
(4)
Iabs : S : t
2.3. Photophysical parameters
where C0 and Ct are the samples (5e7 and 8e10) concentrations
before and after irradiation respectively, V is the reaction volume,
NA is the Avogadro’s constant, S is the irradiated cell area, t is the
irradiation time and Iabs is the overlap integral of the radiation
source light intensity and the absorption of the samples (5e7 and
8e10). A light intensity of 2.24 ꢁ 1016 photons sꢂ1 cmꢂ2 was
employed for Fd determinations.
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (FF) were determined by the
comparative method (Eq. (1)) [35,36],
F : AStd : n2
FF
¼
FFðStdÞ
(1)
FStd : A : n2Std
where F and FStd are the areas under the fluorescence emission
curves of the samples (5,6 and 8,9) and the standard, respectively. A
and AStd are the respective absorbances of the samples and stan-
dard at the excitation wavelengths, respectively. n and nStd are the
refractive indices of solvents used for the sample and standard,
respectively. Unsubstituted ZnPc (in DMSO) (FF ¼ 0.20) [37] was
employed as the standard. The absorbance of the solutions at the
excitation wavelength ranged between 0.04 and 0.05.
2.4.3. Binding studies of quaternized zinc phthalocyanine
complexes to BSA
The binding properties of the water-soluble quaternized
phthalocyanine complexes (8e10) to BSA were studied by spec-
trofluorometry at room temperature. An aqueous solution of BSA
(fixed concentration) was titrated with varying concentrations of
the respective samples (8e10) solutions in water. BSA was excited
at 280 nm and fluorescence recorded between 290 and 500 nm.
The steady diminution in BSA fluorescence with increase in qua-
ternized cationic zinc Pc concentrations was noted and used in the
determination of the binding constants and the number of binding
sites on BSA, according to Eq. (5) [44e46].
Natural radiative (s0) lifetimes were determined using Photo-
chemCAD program which uses the StricklereBerg equation [38].
The fluorescence lifetimes (sF) were evaluated using Eq. (2).
sF
s0
FF
¼
(2)
Á
ꢀ
ꢁ
ðF0 ꢂ F
Á
log
¼ logKb þ nlog½Pcꢃ
(5)
ðF ꢂ FN
2.4. Photochemical parameters
where F0 and F are the fluorescence intensities of BSA in the
absence and presence of quaternized cationic Pc complexes (8e10)
respectively; FN, the fluorescence intensity of BSA saturated
with quaternized cationic Pc complexes; Kb, the binding constant;
n, the number of binding sites on a BSA molecule; and [Pc] the
concentration of quaternized cationic Pc complexes. Plots of
log ðF0 ꢂ FÞ=ðF ꢂ FNÞ against log [Pc] would provide the values of
n (from the slope) and Kb (from the intercept). The changes in BSA
fluorescence intensity were related to quaternized cationic Pc
concentrations by the SterneVolmer relationship (Eq. (6)):
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield (FD) determinations were carried
out using the experimental set-up described in literature
[34,39,40]. Typically, a 3 cm3 portion of the respective non-
peripherally tetra- (5, 8) and peripherally octa- (6,9) substituted
zinc (II) phthalocyanine derivatives, (absorbance w 1 at the irra-
diation wavelength) containing the singlet oxygen quencher was
irradiated in the Q band region with the photo-irradiation set-up
described in references [34,39,40]. Singlet oxygen quantum yields
Â
Ã
(
FD) were determined in air using the relative method with ZnPc
FB0SA
FBSA
Â
Ã
(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:
BSA
SV
¼ 1 þ K
Pc
(6)
BSA
and K
is given by Eq. (7):
SV
Std
R : I
RStd: Iabs
FD
¼
FSDtd
(3)
abs
BSA
K
¼ kqsFðBSAÞ
(7)
SV
where FB0SA and FBSA are the fluorescence intensities of BSA in the
absence and presence of quaternized cationic Pc complexes (8e10),
where FSDtd is the singlet oxygen quantum yields for the standard
ZnPc (FSDtd ¼ 0.67 in DMSO) [41] and ZnPcSmix
(
FSDtd ¼ 0.45 in

M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
157
BSA
SV
respectively. K
is the SterneVolmer quenching constant; kq is
F(BSA) is the fluorescence
F(BSA) is known to be 10 ns [47e49], thus from the
obtained from the plots of FB0SA=FBSA versus [Pc], the
2.5.4. Quaternized 1,(4)-tetrakis-[(2-mercaptopyridine)
phthalocyaninato] zinc (II) (8, Scheme 2)
the bimolecular quenching constant and
s
lifetime of BSA.
s
Compound 5 (0.18 g, 0.177 mmol) was heated to 120 ꢀC in freshly
distilled DMF (5 cm3) and excess dimethylsulphate (0.168 cm3) was
added dropwise. The mixture was stirred at 120 ꢀC for 12h. After this
time, the mixture was cooled to room temperature and the product
was precipitated with hot acetone and collected by filtration. The
green solid product was washed successively with hot ethyl acetate,
chloroform, n-hexane, CCl4 and diethyl ether. The resulting hygro-
scopic product was dried over phosphorous pentoxide.
BSA
values of K
SV
value of kq may be determined from Eq. (7).
2.5. Synthesis
2.5.1. 4,5-Bis-(2-mercaptopyridine)phthalonitrile (4, Scheme 1)
In a stream of nitrogen, 2-mercaptopyridine (6.74 g, 60.8 mmol)
and 4,5-dichlorophthalonitrile (2) (6.00 g, 30.4 mmol) were dis-
solved in DMF (100 cm3) and the mixture stirred at room temper-
ature for 30 min. Thereafter, finely ground K2CO3 (15 g, 108 mmol)
was added portion-wise over a period of 4 h and the reaction
mixture left to stir for a further 12 h at room temperature. The
mixture was added to water (100 cm3) and stirred for 30 min. The
resulting precipitate was filtered off, thoroughly washed with
water, dried and recrystallised from chloroform/ethanol (1/4). M.p.:
220 ꢀC Yield: 5.79 g (55%). IR [(KBr) nmax/cmꢂ1]: 3037(AreCH),
M.p. > 240 ꢀC. Yield: 0.17 g (77%). UV/Vis (DMSO): lmax nm (log
e) 327
(4.62), 627 (4.38), 691(5.02). IR [(KBr) nmax/cmꢂ1]: 3041(AreCH),
2955 (CH), 1563(C]C), 1485, 1439, 1227(S]O), 1107(S]O),
586(SeO). 1H NMR (DMSO-d6):
d, ppm 9.74e6.91 (m, 28H, Pc-H and
Pyridyl-H), 4.33 (d,12H, CH3). Calc. forC56H50N12O13S6Zn(þ5H2O): C
49.57, H 3.71, N 12.39; Found: C 50.13, H 3.27, N 12.87. MALDI-TOF-
MS m/z: Calc. for C56H40N12O8S6Zn, 1266; Found 1167 [M ꢂ SO4]þ,
1073.6 [M-2SO4]þ 1042.1, [Me2SO4e2CH3]þ.
2.5.5. Quaternized 2,3-octakis-[(2-mercaptopyridine)
phthalocyaninato] zinc (II) (9, Scheme 2)
2230 (C^N), 1574 (C]C). 1H NMR (CDCl3):
d, ppm 8.55 (d, 2H,
Pyridyl-H), 7.83 (s, 2H, Pc-H), 7.70 (t, 2H, Pyridyl-H), 7.38 (d, 2H,
Pyridyl-H), 7.28 (t, 2H, Pyridyl-H). Calc. for C18H10N4S2: C 62.41, H
2.91, N 16.17; Found: C 62.20, H 2.80, N 16.17. MS (ESI-MS) m/z: Calc.
346; Found: 347.1 [M þ H]þ.
Synthesis and purification was as outlined for
8 except
compound 6 instead compound 5 was employed. The amounts of
the reagents employed were: 6 (0.18 g, 0.124 mmol), excess dime-
thylsulphate (0.118 cm3, 1.24 mmol) in DMF (5 cm3). M.p. > 240 ꢀC.
Yield: 0.19 g (79%). UV/Vis (DMSO): lmax nm (log e) 377 (4.79), 639
(4.44), 704(4.90). IR [(KBr) nmax/cmꢂ1]: 3056(AreCH), 2953 (CH),
2.5.2. 1,(4)-Tetrakis-(2-mercaptopyridine)phthalocyaninatozinc (II)
(5, Scheme 1)
1566(C]C), 1489, 1223(S]O), 1115(S]O), 586(SeO). 1H NMR
(DMSO-d6): d, ppm 10.13 (br, 4H, Pyridyl-H), 9.14 (s, 8H, Pc-H), 8.25
A mixture of anhydrous zinc (II) acetate (0.77 g, 4.22 mmol), 3-
(2-mercaptopyridine)phthalonitrile (3) (1.0 g, 4.22 mmol), DBU
(0.97 cm3, 0.65 mmol) and 10 cm3 dried n-hexanol was stirred at
160 ꢀC for 12 h under nitrogen atmosphere. After cooling, the
solution was dropped in the n-hexane. The green solid product
was precipitated and collected by filtration and washed with n-
hexane. The crude product was dissolved in chloroform and
precipitated again by dropping in n-hexane. The green solid
product was collected by filtration and washed with n-hexane. The
green crude product was purified by passing through an alumina
column with firstly ethyl acetate and then ethyl acetate/MeOH
(5:1) elution. M.p. > 2400C Yield: 0.13 g (12%). UV/Vis (DMSO):
(br, 12H, Pyridyl-H), 7.91e7.88 (m, 16H, Pyridyl-H), 4.51 (s, 24H,
CH3). Calc. for C80H74N16O21S12Zn (þ5H2O): C 46.97, H 3.65, N 10.95;
Found: C 47.34, H 3.98, N 11.42.
3. Results and discussion
3.1. Synthesis and characterization
Generally, substituted phthalocyanines are prepared by cyclo-
tetramerization of substituted phthalonitriles or 1,3-diimino-
1H-isoindoles. 2(3),9(10),16(17),23(24)-Tetra-substituted phthalocy-
anines can be synthesized from 4-substituted phthalonitriles while
lmax nm (log
cmꢂ1]: 3045(AreCH), 1570(C]C), 1451, 1416, 1316, 1103, 895, 756,
741. 1H NMR (DMSO-d6):
, ppm 9.32e9.10 (m, 4H, Pyridyl-H),
e) 342 (4.81), 631 (4.58), 700 (5.29). IR [(KBr) nmax/
1(4),8(11),15(18),22(25)-tetra-substituted
phthalocyanines
are
d
obtained from 3-substituted analogues [50]. 2,3,9,10,16,17,23,24-
Octa-substituted phthalocyanines can be synthesized from 4,5-
disubstituted phthalonitriles. For tetra-substituted derivatives,
a mixture of four possible structural isomers is obtained. In this
study, synthesized tetra-substituted phthalocyanine compounds are
obtained as isomer mixtures as expected. No attempt was made to
separate the isomers of 5 and 8.
The preparation of phthalocyanine complexes from the
aromatic nitriles occurs under different reaction conditions. The
synthesis of zinc phthalocyanine complexes (5,6) were achieved by
treatment of phthalonitriles 3 and 4 with anhydrous zinc(II) acetate
in dried n-hexanol (Scheme 1). Column chromatography with
neutral alumina was employed to obtain the pure products from
the reaction mixtures.
8.68e8.50 (m, 4H, Pyridyl-H), 8.11e7.68 (m, 16H, Pc-H and Pyridyl-
H), 7.33e7.25 (m, 4H, Pyridyl-H). Calc. for C52H28N12S4Zn: C 61.56,
H 2.78, N 16.57; Found: C 61.40, H 2.70 N 16.45. ESI-MS m/z: Calc.
1012; Found: 1013.2 [M þ H]þ.
2.5.3. 2,3-Octakis-(2-mercaptopyridine)phthalocyaninato zinc (II)
(6, Scheme 1)
Synthesis and purification was as outlined for 5 except 4,5-
bis-(2-mercaptopyridine)phthalonitrile (4) instead of 3-(2-mer-
captopyridine)phthalonitrile (3) was employed. The amounts of
the reagents employed were: 4 (1.00 g, 2.9 mmol), anhydrous
zinc (II) acetate (0.53 g, 2.9 mmol), DBU (0.67 cm3, 0.45 mmol)
in n-hexanol (5 cm3). Yield: 0.11 g (10%). M.p. > 2400C. Yield:
0.13 g (12%). UV/Vis (DMSO): lmax nm (log
e
) 373 (4.78), 638
Quaternization of the zinc phthalocyanine complexes was ach-
ieved by reaction with excess dimethylsulphate (DMS) as quater-
nization agent in DMF at 120 ꢀC. The yields of the products were
77% for 8 and 79% for 9. After reaction with DMS, quaternized
complexes are very soluble in water (Scheme 2).
Generally, phthalocyanine complexes are insoluble in most
organic solvents; however introduction of substituents on the ring
increases the solubility. All complexes (5e7 and 8e10) exhibited
(4.80), 667 (4.75), 707 (5.24). IR [(KBr) nmax/cmꢂ1]:
3045(AreCH), 1574(C]C), 1451, 1416, 1281, 1119, 945, 760. 1H
NMR (DMSO-d6): d, ppm 9.12 (br, 8H, Pyridyl-H), 8.93 (br, 8H,
Pc-H), 7.66 (br, 8H, Pyridyl-H), 7.30 (br, 8H, Pyridyl-H), 7.15 (br,
8H, Pyridyl-H), Calc. for C72H40N16S8Zn: C 59.59, H 2.78, N 15.44;
Found: C 59.41, H 2.72 N 15.34. ESI-MS m/z: Calc. 1450; Found:
1451.2 [M þ H]þ.

158
M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
excellent solubility in DMF and DMSO. Quaternized complexes
(8e10) are soluble in water as well. The new compounds (5,6,8 and
9) were characterized by UVevis, IR and NMR spectroscopies, mass
spectra and elemental analysis. The analyses are consistent with
the predicted structures as shown in the experimental section. The
sharp peak in the IR spectra for the C^N vibrations of phthaloni-
triles 3 and 4 at ∼2230 cmꢂ1 disappeared after conversion into zinc
phthalocyanines, indicative of metallophthalocyanine formation.
The characteristic vibrations corresponding to C]C groups at
∼1570 cmꢂ1, and aromatic CH stretching at 3041e3056 cmꢂ1 were
observed for all complexes. Aliphatic CH stretches were observed at
∼2950 cmꢂ1 for quaternized complexes. S]O stretching at ∼1220
and ∼1110 cmꢂ1, SeO stretching at 586 cmꢂ1 for quaternized
complexes are indicative of quaternization formation.
absorption in the Q band region at around 685e707 for complexes
5e7 and 685e704 nm for complexes 8e10 in DMSO, Table 1. The B
bands were observed at around 320e370 nm in DMSO (Fig. 1a and
b). The spectra showed monomeric behavior evidenced by a single
(narrow) Q band which is typical of metallated phthalocyanine
complexes in DMSO [52]. The Q bands of the non-peripherally
substituted complexes (5 and 8) are red-shifted when compared to
the corresponding peripherally substituted complexes (7 and 10) in
DMSO (Fig. 1a and b). The red-shifts are observed 15 nm between 5
and 7, and 6 nm between 8 and 10. The observed red spectral shifts
are typical of Pcs with substituents at the non-peripheral positions
and have been explained in the literature [53,54]. The red-shift was
observed for octa-peripherally substituted complex (6) compared
to tetra-peripherally substituted complex (7) due to increase in the
number of 2-mercaptopyridine groups which increase the electron
donation due to sulfur atoms on the phthalocyanine framework for
octa substitution. In water, the absorption spectra of quaternized
complexes (8e10) showed cofacial aggregation, as evidenced by the
presence of two non-vibrational peaks in the Q band region, Fig. 1c
and d, Table 1. The lower energy (red-shifted) bands at 666 for 8,
694 for 9 and 665 nm for 10 are due to the monomeric specie, while
the higher energy (blue-shifted) bands at 636 for 8, 656 for 9 and
630 nm for 10 are due to aggregated specie.
Aggregation is usually depicted as a coplanar association of rings
progressing from monomer to dimer and higher order complexes. It
is dependent on the concentration, nature of the solvent, nature of
the substituents, complexed metal ions and temperature [55]. In
the aggregated state the electronic structure of the complexed
phthalocyanine rings are perturbed resulting in alternation of the
ground and excited state electronic structures [56]. In this study,
the aggregation behavior of the Pc complexes (5e7 and 8e10) was
investigated at different concentrations in DMSO (Fig. 2, for
complex 9 as an example). The BeereLambert law was obeyed for
all of these complexes at concentrations ranging from 1.2 ꢁ 10ꢂ5 to
4 ꢁ 10ꢂ6 M. The studied zinc Pc complexes (5e7 and 8e10) did not
show aggregation in DMSO.
1
The H NMR spectra of tetra-substituted phthalocyanine deriv-
atives (5 and 8) show complex patterns due to the mixed isomer
character of these compounds. The octasubstituted complexes (6
and 9) show more resolved patterns due to presence of just one
isomer. The complexes were found to be pure by 1H NMR with all
the substituents and ring protons observed in their respective
regions. The resonances were observed as multiplets between 9.32
and 9.10 ppm, 8.68 and 8.50 ppm, 8.11 and 7.68 ppm, and 7.33 and
7.25 ppm integrating for 4, 4, 16, 4 protons each, making a total of
28 protons expected for both phthalocyanine ring and mercapto-
pyridine protons for 5. For complex 6, the resonances were
observed as broad peaks at 9.12 ppm, 7.66 ppm, 7.30 ppm and
7.15 ppm integrating for 8, 8, 8, 8 protons each, making a total of 32
protons expected for mercaptopyridine protons and a singlet for
phthalocyanine ring at 8.93 ppm intergrading for 8 protons.
The NMR spectra of the quaternized tetra-substituted phthalo-
cyanine complex (8) showed more unresolved patterns compared to
non-quaternized derivative. This complex showed the phthalocya-
nine ring protons and mercaptopyridine group protons as unresolved
multiplets integrating for a total of 28 protons. Phthalocyanine ring
and mercaptopyridine protons were observed between 9.74 and
6.91 ppm as multiplets. The methyl protons which integrated for 12
protons were observed at 4.33 ppm for complex 8 as a doublet due to
the mixture of isomers. The NMR spectra of the quaternized octa-
substituted phthalocyanine complex (9) showed more resolved
patterns compared to quaternized tetra-substituted derivative (8).
This complex (9) showed phthalocyanine ring protons at 9.14 ppm as
a singlet integrating for 8 protons. Broad peaks at 10.13 ppm and
8.25 ppm, and a multiplet between 7.91 and 7.88 ppm, integrating for
4, 12, 16 protons each, making a total of 32 protons, belong to mer-
captopyridine protons for 9. The methyl protons which integrated for
24 protons were observed as a singlet at 4.51 ppm for complex 9.
Inadditiontothe elementalanalysis results, themassspectraldata
for the newly synthesized tetra- and octasubstituted zinc phthalo-
cyanines (5,6 and 8,9) were consistent with the assigned formula-
tions. The mass spectra of compounds were obtained by Electron
Spray Ionization (ESI) technique for non-ionic complexes (5,6) and
MALDI-TOF-MS for quaternized complexes (8,9). The molecular ion
peaksofnon-quaternizedcomplexesshowingparentionswerefound
Fig. 3 shows fluorescence emission, absorption and excitation
spectra of complex 5 in DMSO as example of the studied zinc Pc
complexes. Fluorescence emission peaks are listed in Table 1. The
observed Stokes shifts were within the region (∼10e20 nm)
observed for zinc Pc complexes. All studied zinc Pc complexes
(5e10) showed similar fluorescence behavior in DMSO. The exci-
tation spectra were similar to absorption spectra and both were
mirror images of the fluorescent spectra for all zinc Pc complexes in
DMSO. 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 Pc complexes suggested that the nuclear configurations
of the ground and excited states are similar and not affected by
Table 1
Absorption, excitation and emission spectral data for unsubstituted, tetra- and
octasubstituted zinc phthalocyanine complexes in DMSO and water.
Compound Solvent Q band
lmax, (nm)
DMSO 700
(log
e
)
Excitation Emission Stokes shift
lEx, (nm) lEm, (nm) DStokes, (nm)
þ
þ
at m/z 1013.2 [M þ H] for complex 5 and 1451.2 [M þ H] for
complex6. Themolecularionpeaksofquaternizedcomplex8showed
parent ions at m/z 1167 [MꢂSO4]þ, 1073.6 [Me2SO4]þ 1042.1,
[Me2SO4e2CH3]þ. MALDI-TOF-MS spectra of quaternized phthalo-
cyanine complex (8) show thebasepeakcleavageofanion and methyl
groups, as it is often observed for this type of compounds [51]. The
molecular ion peaks for quaternized complex 9 was not observed.
5
6
7
8
5.21
5.14
5.38
5.03
701
710
686a
692
e
717
721
698a
707
e
17
14
12a
16
e
DMSO 707
DMSO 685a
DMSO 691
H2O
DMSO 704
H2O
DMSO 685a
H2O
630, 665a 4.50, 4.51
DMSO 672b
5.38
636, 666 4.67, 4.68
9
5.22
706
716
707
698a
e
12
13
11a
e
656, 694 4.48, 4.32 695
10
4.96
687a
e
672b
3.2. Ground state electronic absorption and fluorescence spectra
ZnPc
681b
9b
a
The electronic spectra of the studied non-ionic (5e7) and qua-
ternized ionic (8e10) zinc Pc complexes showed characteristic
Data from reference [33].
Data from reference [70].
b

M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
159
2
2.5
9
7
a
b
2
1.5
5
8
1.5
1
6
10
1
0.5
0.5
0
300
0
300
400
500
600
700
800
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
1.5
0.8
0.6
0.4
0.2
0
c
d
8 in DMSO
8
1
0.5
0
10
8 in water
9
300
400
500
600
700
800
300
400
500
600
700
800
Wavelength (nm)
Wavelength (nm)
Fig. 1. Absorption spectra of: (a) substituted non-ionic zinc Pc complexes (5e7) in DMSO, (b) substituted quaternized ionic zinc Pc complexes (8e10) in DMSO and (c) water,
(d) substituted quaternized ionic zinc Pc complex 8 in DMSO and water. Concentration ¼ 1 ꢁ 10ꢂ5 M.
excitation. In aqueous media, the water-soluble quaternized zinc Pc
complexes (8e10) are not fluorescent. Aggregated MPc complexes
are not known to fluorescence [57] since aggregation lowers the
photoactivity of molecules through dissipation of energy.
of the studied zinc Pc complexes (5e7 and 8e10) are slightly lower
than unsubstituted zinc Pc in DMSO, suggesting that more
quenching of substitution of the 2-mercaptopyridine groups on the
Pc framework. The FF values of non-ionic zinc Pc complexes are
similar and typical MPc complexes in DMSO [57]. The peripherally
tetra-substituted complex (7) shows largest FF value in DMSO
compared to the others complexes, Table 2. The non-ionic zinc Pc
complexes (5e7) show larger FF values compared to the corre-
sponding quaternarized ionic zinc Pc complexes (8e10) in DMSO.
Comparing DMSO and water, while the quaternarized ionic zinc Pc
complexes (8e10) are fluorescent in DMSO, these complexes are
3.3. Fluorescence quantum yields and lifetimes
The fluorescence quantum yields (FF) for non-ionic zinc Pc
complexes (5e7) in DMSO and for quaternized ionic complexes
(8e10) in both DMSO and water are given in Table 2. The FF values
2
A
1000
800
600
400
200
0
2
A
B
1.5
C
D
E
1.5
1
1
E
Emission
Absorption
0.5
0.5
Excitation
0
0
800
300
400
500
600
700
800
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 2. Aggregation behavior of 9 in DMSO at different concentrations: 12 ꢁ 10ꢂ6 (A),
10 ꢁ 10ꢂ6 (B), 8 ꢁ 10ꢂ6 (C), 6 ꢁ 10ꢂ6 (D), 4 ꢁ 10ꢂ6 (E) M. (Inset: Plot of absorbance
versus concentration).
Fig. 3. Absorption, excitation and emission spectra of 5 in DMSO. Excitation wave-
length: 665 nm.

160
M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
Table 2
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
singlet oxygen quantum yields (FD), give an indication of the
potential of the complexes as photosensitizers in applications
where singlet oxygen is required, (e.g. for Type II mechanism). The
FD values were determined using a chemical method (using DPBF
in DMSO and ADMA in water as quenchers). The disappearance of
DPBF or ADMA was monitored using UVevis spectrophotometer
(Fig. 4a using DPBF in DMSO and Fig. 4b using ADMA in water for
complex 9). 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 decrease in the Q band of
formation of the ZnPc derivatives during FD determinations (Fig. 4).
Table 2 shows that while the FD values are higher for periph-
erally tetra-substituted zinc Pc complexes (7 and 10) in DMSO, the
FD values of the non-peripherally tetra-(5 and 8) and peripherally
octa-(6 and 9) substituted zinc Pc derivatives are lower when
compared to respective unsubstituted zinc Pc. The peripherally
tetra-substituted complexes (7 and 10) showed higher FD values
when compared to the non-peripherally tetra-(5 and 8) and
peripherally octa-(6 and 9) substituted zinc Pc complexes in DMSO.
Quaternarized ionic zinc Pc complexes (8e10) showed lower FD
values when compared to corresponding non-ionic complexes
(5e7) in DMSO, suggesting that the quaternization of the zinc Pc
complexes caused the decrease in the FD values. Table 2 shows that
lower FD values are observed in aqueous solutions compared to in
DMSO. The low FD in water compared to other solvents such as
deuterated water and DMSO was explained [37] by the fact that
singlet oxygen absorbs at 1270 nm, and water, which absorbs
around this wavelength has a great effect on singlet oxygen life-
time, while DMSO which exhibits little absorption in this region has
longer singlet oxygen lifetimes than water, resulting in larger FD
values in DMSO. The quaternized peripherally tetra-substituted
zinc Pc complex (10) showed highest FD value than other studied
quaternized zinc Pc complexes in water.
Photophysical and photochemical parameters of unsubstituted, tetra- and octa-
substituted zinc phthalocyanine complexes in DMSO and water.
Compound Solvent FF
sF (ns) kF (sꢂ1
)
s0 (ns) Fd
FD
(ꢁ 108)a
(ꢁ 10ꢂ5
)
5
6
7
8
DMSO
DMSO
DMSO
DMSO
H2O
DMSO
H2O
DMSO
H2O
0.12
0.11
0.17
0.01
e
0.92
1.10
1.20
0.19
e
1.31
1.00
1.58
0.75
e
7.65
10.00
6.34
13.35
e
1.87
2.19
0.66
2.64
2.30
10.58
3.61
6.74
2.04
2.61d
0.57
0.51
0.86b
0.45
0.19
0.63
0.10
0.82b
0.45b
0.67d
9
0.03
e
0.17
e
1.70
e
5.88
e
10
0.02b 0.20b
0.66
e
1.47d
15.18
e
e
e
ZnPc
DMSO
0.20c 1.22d
6.80d
a
kF is the rate constant for fluorescence. Values calculated using kF
Data from reference [33].
Data from reference [37].
¼
FF/sF.
b
c
d
Data from reference [70].
not fluorescent in water. This is attributed to aggregation as dis-
cussed above.
Fluorescence lifetime (sF) refers to the average time a molecule
stays in its excited state before emission, and its value is directly
related to that of FF; i.e. the longer the lifetime, the higher the
quantum yield of fluorescence. Any factor that shortens the fluo-
rescence lifetime of a fluorophore indirectly reduces the value of FF
.
Such factors include internal conversion and intersystem crossing.
As a result, the nature and the environment of a fluorophore
determine its fluorescence lifetime. Lifetimes of fluorescence were
calculated using the StricklereBerg equation. Using this equation,
a good correlation has been found [36] between experimentally and
the theoretically determined lifetimes for the unaggregated mole-
cules as is the case for DMSO in this work. The sF value is higher for
peripherally tetra-substituted zinc complex (7) when compared to
non-peripherally tetra-substituted (5) and peripherally octasub-
stituted complex (6) in DMSO. For the quaternarized ionic
complexes, the
compared to 9, but the value for 10 is similar to the one for 8, Table 2.
The natural radiative lifetime ( 0) and the rate constants for fluo-
rescence (kF) values are also given in Table 2. But there was no clear
trend found for 0 and kF values among the studied zinc Pc complexes.
sF value is higher for peripheral complex (10) when
s
Singlet oxygen quantum yield (FD) values of all employed
mercaptopyridine substituted zinc Pc complexes were higher
(ranging from 0.51e0.86 in DMSO), than those of their corre-
sponding pyridyloxy substituted zinc Pc complexes in literature
that ranged from 0.06e0.46 [51,58]. The FD values, found in this
study, are similar to those of Cd(II), Hg(II), Ga(III), In(III), Si(IV) and
s
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
Fig. 4. A typical spectrum for the determination of singlet oxygen quantum yield of: (a) 9 in DMSO using DPBF as a singlet oxygen quencher and (b) 9 in water using ADMA as
a singlet oxygen quencher. Concentration ¼ 1 ꢁ 10ꢂ5 M (Inset: Plots of DPBF or ADMA absorbance versus time).

M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
161
1.2
0.9
0.6
0.3
0
2
8
1.75
1.5
1.25
1
10
9
0 sec
300 sec
600 sec
900 sec
1200 sec
1500 sec
300
400
500
600
700
800
0.00E+00 1.00E-06 2.00E-06 3.00E-06 4.00E-06 5.00E-06 6.00E-06 7.00E-06 8.00E-06 9.00E-06
Wavelength (nm)
[Pc]
Fig. 5. The photodegradation of 8 in DMSO showing the disappearance of the Q band
at 5 min intervals. (Inset: Plot of Q band absorbance versus time).
Fig. 7. SterneVolmer plots of 2-mercaptopyridine substituted zinc phthalocyanines
quenching of BSA in water. [BSA] ¼ 3.00 ꢁ 10ꢂ5 M in water. [Pc] ¼ 0, 1.66 ꢁ 10ꢂ6
,
3.33 ꢁ 10ꢂ6, 5.00 ꢁ 10ꢂ6, 6.66 ꢁ 10ꢂ6, 8.33 ꢁ 10ꢂ6 M.
Sn(IV) Pc complexes having pyridyloxy or mercaptopyridine groups
on the phthalocyanine ring reported in literature [16,51,58e64].
The peripheral tetra-2-mercaptopyridine substituted zinc Pc
complexes (7 and 10), studied in this work gave highest FD values
(0.86 for complex 7 in DMSO and 0.45 for complex 10 in water),
compared to 2-mercaptopyridine substituted Pc complexes in
literature [60,62]. A value of FD ¼ 0.86 is the highest ever reported
for a ZnPc derivative.
unstable molecules, values of the order of 10ꢂ3 have been reported
[57]. The non-ionic zinc Pc complexes (5e7) showed lower Fd
values when compared to the unsubstituted ZnPc in DMSO,
whereas, the ionic zinc Pc complexes (8e10) showed higher Fd
values (compared to 5e7), suggesting that the substitution of the 2-
mercaptopyridine groups on the phthalocyanine framework
increasing the stability of the zinc Pc complexes, but the quater-
nization of these groups resulted in the decrease in the stability of
the ionic zinc Pc complexes.
3.5. Photodegradation studies
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
spectral changes observed for all the complexes (5e7 and 8e10)
during confirmed photodegradation occurred without photo-
transformation (Fig. 5 as an example for complex 8 in DMSO).
All the studied zinc Pc complexes showed about the same
stability with Fd of the order of 10ꢂ5. The Fd values, found in this
study, are similar with zinc Pc complexes having different substit-
uents on the phthalocyanine ring in the literature [57]. Stable zinc
phthalocyanine complexes show Fd values as low as 10ꢂ6 and for
3.6. Binding of quaternized zinc phthalocyanine complexes to BSA
Fig. 6 shows the changes in the fluorescence emission spectra of
BSA in the presence of different concentrations of 8 (as an example)
in water. The quaternized ionic zinc Pc complexes are mixtures of
aggregated and unaggregated species. The total concentrations of
the complexes are mixture of the monomer and aggregated species.
We calculated the percentage aggregation (% Agg) of these
complexes using the equation described in the literature [65,66].
The aggregation percentages are 3.7% for 8, 28.3% for 10 and 6.4%
for 9 in water. The non-peripherally substituted Pc complex showed
lowest percentage aggregation value, probably due to reduced
aggregation tendencies when substitution is at the non-peripheral
position of the Pc skeleton [67]. The BSA fluorescence at 348 nm is
mainly attributable to tryptophan residues in the macromolecule.
BSA and the respective quaternized ionic Pc complexes exhibit
reciprocated fluorescence quenching on one another; hence it was
possible to determine SterneVolmer quenching constants (KSV).
The slope of the plots shown at Fig. 7 gave KSV values which are
listed in Table 3. These values suggest that BSA fluorescence
quenching is more effective for quaternized non-peripherally
substituted Pc complex (8) than quaternized peripherally
substituted Pc complex (10) and octasubstituted Pc complex (9) in
water. Using the approximate fluorescence lifetime of BSA [48,49],
A
B
C
[Pc]=0
D
E
F
[Pc]=saturated
Table 3
G
Binding and fluorescence quenching data for interaction of BSA with quaternized
ionic zinc phthalocyanine complexes in water.
290
340
390
Wavelength (nm)
440
490
BSA
Compound
K
/105 (Mꢂ1
)
kq/1013 (Mꢂ1 sꢂ1
)
Kb/10ꢂ6 (Mꢂ1
)
n
SV
8
9
10
1.16
0.55
0.65
1.16
0.55
0.65
8.13
15.14
10.96
1.56
1.48
1.58
Fig. 6. Fluorescence emission spectral changes of BSA (C ¼ 3.00 ꢁ 10ꢂ5 M) on addition
of varying concentrations of 8 in water [8].: A ¼ 0, B ¼ 1.66 ꢁ 10ꢂ6, C ¼ 3.33 ꢁ 10ꢂ6
D ¼ 5.00 ꢁ 10ꢂ6, E ¼ 6.66 ꢁ 10ꢂ6, F ¼ 8.33 ꢁ 10ꢂ6 M, G ¼ saturated with 8.
,

162
M. Durmus¸ et al. / Dyes and Pigments 91 (2011) 153e163
0.6
0.3
water are still good enough for PDT applications. These complexes
gave good FD values. In particular, quaternarized peripheral zinc Pc
complex (10) has high FD value (0.45) in water. Thus, these
complexes exhibit potential as Type II photosensitizers for PDT of
cancer. This work will certainly enrich the hitherto scanty literature
on the potentials of cationic zinc phthalocyanines as photosensi-
tizers in PDT. This study reveals that the water-soluble complexes
bind strongly to serum albumin; hence they can easily be trans-
ported in the blood.
8
0
10
9
-0.3
-0.6
-0.9
-1.2
-1.5
Acknowledgements
This work was supported by the Department of Science and
Technology (DST) and National Research Foundation (NRF), South
Africa through DST/NRF South African Research Chairs Initiative for
Professor of Medicinal Chemistry and Nanotechnology as well as
Rhodes University and Medical Research Council of South Africa
and Scientific Research Project of Gebze Institute of Technology
(BAP-2007-A-01).
-5.9
-5.8
-5.7
-5.6
-5.5
-5.4
-5.3
-5.2
-5.1
-5.0
log[Pc]
Fig. 8. Determination of 2-mercaptopyridine substituted zinc phthalocyanine-BSA
binding constant (and number of binding sites on BSA). [BSA] ¼ 3.00 ꢁ 10ꢂ5 M and
[Pc] ¼ 0, 1.66 ꢁ 10ꢂ6, 3.33 ꢁ 10ꢂ6, 5.00 ꢁ 10ꢂ6, 6.66 ꢁ 10ꢂ6, 8.33 ꢁ 10ꢂ6 M in water.
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the bimolecular quenching constant (kq) was determined using
equation (7). These values are of the order of 1013 Mꢂ1 ꢂ1, which
s
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4. Conclusion
electrochemical and spectroelectrochemical properties of a novel, cationic,
water-soluble Zn phthalocyanine with extended conjugation. Dyes and
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The synthesis and characterization of non-peripherally tetra-(5)
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quaternized derivatives (8 and 9) have been undertaken. The
spectral, photophysical and photochemical properties of non-
peripherally tetra-, peripherally tetra- and peripherally octa-2-
mercaptopyridine substituted non-ionic (5-7) and quaternized
ionic (8e10) zinc Pc complexes are compared. The effects of the
number and position of the substituents, quaternization of the 2-
mercaptopyridine groups and the solvents (DMSO or water for
ionic complexes) on the properties of the zinc Pc complexes are also
presented. All studied zinc Pc complexes did not show aggregation
in DMSO. The quaternized complexes exhibited excellent solubility
in water, but they showed aggregation in this solvent. Although, the
photophysical and photochemical properties relevant for photo-
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