Synthesis, characterization, photophysical and photochemical properties of tetra-2-[2-(benzothiazolylthio)]ethoxy substituted phthalocyanine derivatives

Article abstract of DOI:10.1016/j.jorganchem.2012.09.002

The metal-free and zinc (II) phthalocyanine compounds tetra substituted with 2-(2-benzothiazolylthio)ethoxy groups have been synthesized for the first time in this study for comparison central metal effect on photophysical and photochemical properties. Th

Full text of DOI:10.1016/j.jorganchem.2012.09.002

Journal of Organometallic Chemistry 723 (2013) 1e9
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization, photophysical and photochemical properties of
tetra-2-[2-(benzothiazolylthio)]ethoxy substituted phthalocyanine derivatives
a
a
b
b
a
a,
*
ꢀ
ꢀ
Ece Tugba Saka , Nagihan Ersoy , Cem Göl , Mahmut Durmus¸ , Zekeriya Bıyıklıoglu , Halit Kantekin
a Department of Chemistry, 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 metal-free and zinc (II) phthalocyanine compounds tetra substituted with 2-(2-benzothiazolylthio)
ethoxy groups have been synthesized for the first time in this study for comparison central metal effect
on photophysical and photochemical properties. The new compounds have been characterized by IR, 1H
NMR, 13C NMR and MS spectra data. These compounds showed excellent solubility in most common
organic solvents. The photophysical and photochemical properties of metal-free and zinc (II) phthalo-
cyanine compounds have been studied in DMF and toluene in order to investigate of polar and non-polar
solvent effect on these properties. The fluorescence quenching behaviour of the studied compounds by
1,4-benzoquinone (BQ) have also been studied in DMF and toluene.
Received 13 June 2012
Received in revised form
4 September 2012
Accepted 10 September 2012
Keywords:
Phthalocyanine
Metal-free
Ó 2012 Elsevier B.V. All rights reserved.
Zinc
Fluorescence
Quantum yield
Singlet oxygen
1. Introduction
a useful way of tuning the wavelength of the visible region
absorption band [9e16].
Metal-free and metallophthalocyanines (MPcs) are one of the
major types of tetrapyrrole derivatives showing a wide range of
applications in various areas such as semiconductors, nonlinear
optics, electro-chromic display devices and liquid crystals [1]. The
exceptional chemical and physical properties of phthalocyanines
are derived from various substituents on the phenyl rings [2]. Over
70 elements can be included into the phthalocyanine core, and its
chemical versatility allows the introduction of many different
substituents at peripheral positions on phthalocyanine framework
[3,4]. The usual purification methods such as crystallization and
chromatographic separation cannot be used in most phthalocya-
nines because of their extreme insolubility [5].
Their utility derives, in part from the ease with which their
properties (solubility, electronic absorption, fluorescence etc.) can
be modified through synthetic manipulation. Specificity in the
applications of phthalocyanines can be introduced by modification
of the benzenoid substituents or variation in the central metal ion
[6e8]. Substituents provide the prime means of solubilizing the
ring system in either aqueous media or in organic solvents and offer
MPcs have also attracted sizeable curiosity in recent years as
photosensitizers in photodynamic therapy (PDT). They show
intense absorption towards the red end of the visible spectrum,
which allows for deeper penetration into biological tissues.
However, not all MPc derivatives are applicable in PDT; in principle,
only Pcs containing diamagnetic metal ions [17] are ideal for this
purpose as their triplet properties (quantum yield and lifetime) are
high, resulting in efficient generation of singlet oxygen, O2(1Dg), the
key mediator in tumour destruction. The triplet states of para-
magnetic central metal ions, on the other hand, are very short lived,
limiting their use in PDT. Accordingly, MPc derivatives incorpo-
rating non-transition metal (or metalloid) ions like Al3þ, Zn2þ, Si4þ
,
Ge4þ and Sn4þ have been studied [18e20] due to their potential
applicability in PDT.
The aim of our ongoing research is to synthesis soluble metal-
free and metallophthalocyanine complexes to be used in some
application areas. Recently, we reported that metal-free and met-
allophthalocyanine derivatives functionalized with substituents
such as 2-[2-(1-naphthyloxy)ethoxy]ethanol, 2-[2-(2-naphthyloxy)
ethoxy]ethanol [21,22], 2-[2-(dimethylamino)ethoxy]ethanol [23]
groups in peripheral and non-peripheral positions on the phtha-
locyanine ring, compounds offered PDT and electrochemical
properties due to their interesting properties. Our previous studies
* Corresponding author. Tel.: þ90 462 377 2589; fax: þ90 462 325 3196.
E-mail address: halit@ktu.edu.tr (H. Kantekin).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.09.002

2
E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
regarding synthesis, photophysical and photochemical properties
of various substituted phthalocyanines have already been reported
[24e31]. These phthalocyanine complexes show interesting pho-
tophysical and photochemical properties especially high singlet
oxygen quantum yields which are very important for PDT of cancer.
In this work, 2-(2-benzothiazolylthio)ethoxy tetra-substituted
metal free (4) and zinc (II) (5) phthalocyanines have been synthe-
sized as potential PDT agents. Furthermore, to determine PDT
activity of photosensitizers, the photophysical and photochemical
properties of studied phthalocyanine compounds 4 and 5 has been
examined in both DMF and toluene.
Natural radiative lifetimes (
chemCAD program [38] which uses the StricklereBerg equation.
s0) were determined using Photo-
The fluorescence lifetimes (
s
F) were evaluated using equation (2).
sF
s0
FF
¼
(2)
2.4. Photochemical parameters
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield
(FD) determinations were
carried out by using the experimental set-up described in the
literature [19,39,40]. Typically, a 3 mL portion of the respective
unsubstituted (Std-ZnPc), metal-free 4 and zinc 5 phthalocyanine
solutions (C ¼ 1 ꢀ 10ꢁ5 M) containing the singlet oxygen
quencher was irradiated in the Q band region with the photo-
irradiation set-up described in references [19,39,40]. Singlet
oxygen quantum yields (FD) were determined in DMF and
toluene using the relative method with unsubstituted ZnPc (Std-
ZnPc) as reference. DPBF was used as chemical quencher for
singlet oxygen in DMF and toluene. Equation (3) was employed
for the calculations:
2. Experimental
2.1. Materials
2-(2-Benzothiazolylthio)ethanol 1 [32], 4-nitrophthalonitrile 2
[33]
were
synthesized
according
to
literature. 1,3-
Diphenylisobenzofuran (DPBF) and unsubstituted zinc phthalocy-
anine (Std-ZnPc) were purchased from Aldrich. All chemicals,
solvents, and reagents were of reagent grade quality and were used
as purchased from commercial sources. All solvents were dried and
purified as described by Perrin and Armarego [34].
Std
R$I
FSDtd
(3)
abs
FD
¼
RStd$Iabs
2.2. Equipment
where FSDtd is the singlet oxygen quantum yield for the standard
unsubstituted ZnPc (Std-ZnPc) (FSDtd ¼ 0:56 in DMF [41] and 0.58
in toluene [42]). R and RStd are the DPBF photobleaching rates in the
FT-IR spectra were obtained on a Perkin Elmer 1600 FTIR
spectrophotometer with the samples prepared as KBr pellets.
NMR spectra were recorded on a Varian Mercury 200 MHz
presence of the samples 4 and 5 and standard, respectively. Iabs and
spectrometer in CDCl3 and chemical shifts were reported (
d)
Std
abs
I
are the rates of light absorption by the samples 4 and 5 and
relative to TMS as an internal standard. Mass spectra were
recorded on a Micromass Quattro LC/ULTIMA LCeMS/MS spec-
trometer. Melting points were measured on an electrothermal
apparatus. Domestic microwave oven was used for synthesis of
zinc (II) phthalocyanine compound. Absorption spectra in the
UVevis region were recorded with a Shimadzu 2101 UV spec-
trophotometer. Fluorescence excitation and emission spectra
were recorded on a Varian Eclipse spectrofluorometer using 1 cm
pathlength cuvettes at room temperature. 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 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 (Mollectron
detector incorporated) power metre.
standard, respectively. To avoid chain reactions induced by DPBF in
the presence of singlet oxygen, the concentration of quencher
(DPBF) was lowered to w3 ꢀ 10ꢁ5 mol dmꢁ3 [41]. Solutions of
sensitizers (C ¼ 1 ꢀ 10ꢁ5 M) containing DPBF were prepared in the
dark and irradiated in the Q band region using the photoirradiation
setup. DPBF degradation at 417 nm was monitored. The light
intensity 6.48
determinations.
ꢀ
1015 photons sꢁ1 cmꢁ2 was used for FD
2.4.2. Photodegradation quantum yields
Photodegradation quantum yield (Fd) determinations were
carried out using the experimental set-up described in the litera-
ture [19,39,40]. Photodegradation quantum yields were deter-
mined using equation (4),
ðC0 ꢁ CtÞ$V$NA
Fd
¼
(4)
I
abs$S$t
2.3. Photophysical parameters
where C0 and Ct are the samples 4 and 5 concentrations before and
after irradiation respectively, V is the reaction volume, NA is the
Avogadro’s constant, S is the irradiated cell area and t is the irra-
diation time. Iabs is the overlap integral of the radiation source light
intensity and the absorption of the samples (4 and 5). A light
intensity of 2.16 ꢀ 1016 photons sꢁ1 cmꢁ2 was employed for Fd
determinations.
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (FF) were determined in DMF and
toluene by the comparative method using equation (1) [35,36]
F$AStd$n2
FF
¼
FFðStdÞ
(1)
F
Std$A$n2Std
where F and FStd are the areas under the fluorescence emission
curves of the samples 4 and 5 and the standard, respectively. 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 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. Fluorescence quenching by 1,4-benzoquinone (BQ)
Fluorescence quenching experiments on the metal-free 4 and
zinc (II) 5 Pc compounds were carried out by the addition of
different concentrations of BQ to a fixed concentration of the
compounds, and the concentrations of BQ in the resulting mixtures
were 0, 0.008, 0.016, 0.024, 0.032 and 0.040 mol dmꢁ3. The fluo-
rescence spectra of the substituted metal-free 4 and zinc (II) 5 Pc
compounds at each BQ concentration were recorded, and the

E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
3
changes in fluorescence intensity related to BQ concentration by
the SterneVolmer (SV) equation [43] using equation (5):
product was also refluxed in EtOH (50 mL) for 6 h. The obtained
dark-green product was filtered off, washed with hot EtOHeMeOH
and then dried in vacuo over P2O5. After cooling to room temper-
ature, the reaction mixture was precipitated in hot ethanol (40 mL),
then the product was filtered off. The green solid product was
purified through alumina column using CHCl3:MeOH (90:10) as
eluting solvent system. The light-green solid product is soluble in
CHCl3, CH2Cl2, DMSO, DMF, THF, pyridine. Yield: 0.282 g (45%),
mp > 300 ꢃC. IR (KBr tablet) nmax/cmꢁ1: 3085 (AreH), 2933e2867
I0
I
¼ 1 þ KSV½BQꢂ
(5)
where I0 and I are the fluorescence intensities of samples in the
absence and presence of BQ, respectively. KSV is the SterneVolmer
constant; and this is the product of the bimolecular quenching
constant (kq) and the fluorescence lifetime sF (equation (6)):
(Aliph. CeH), 1738, 1642, 1092, 915, 846, 793. 1H NMR (CDCl3) (
d:
ppm): 7.74 (m, 12H, ArH), 7.30 (m, 16H, ArH), 4.55 (m, 8H, CH2eO),
KSV ¼ kqsF
(6)
3.73 (m, 8H, CH2eS). MS (ESþ), m/z: Calc. for C68H44N12S8O4Zn:
1415.09; Found: 1438 [M þ Na]þ. UV/vis:
l, nm (log ε): in DMF; 678
The ratios I0/I were calculated and plotted against [BQ] accord-
ing to equation (5), and KSV was determined from the slope.
(5.26), 611 (4.56), 355 (4.93), in toluene; 682 (5.26), 615 (4.66), 360
(4.94).
2.5. Synthesis
3. Results and discussion
2.5.1. 2-(2-Benzothiazolylthio)ethoxy phthalonitrile (3)
2-(2-Benzothiazolylthio)ethanol (1) (2 g, 9.52 mmol) was dis-
solved in dry DMF (40 mL) under N2 atmosphere and 4-
nitrophthalonitrile (2) (1.90 g, 9.52 mmol) was added to the solu-
tion. The solution was stirred up to 10 min and finely ground
anhydrous K2CO3 (4.14 g, 28.56 mmol) was added portion wise
within 2 h with efficient stirring. Stirred the reaction mixture under
inert atmosphere at 50 ꢃC for 3 days. Solution was then poured into
ice-water (100 mL). The resultant precipitates were filtered off,
washed with water (for neutralization), diethyl ether and dried in
vacuum over P2O5. The crude product was crystallized from
3.1. Synthesis and characterization
The general route for the syntheses of new metal-free (4) and
zinc (II) (5) phthalocyanine compounds is given in Scheme 1. The
synthesis of the phthalonitrile compound 3 was based on the
reaction of 4-nitrophthalonitrile (2) with 2-(2-benzothiazolylthio)
ethanol (1) in the presence of dry K2CO3 as a base in dry DMF at
50 ꢃC. The self-condensation of the phthalonitrile compound 3 in
a high-boiling solvent in the presence of a few drops of 1,8-
diazabicyclo[5.4.0] undec-7-ene (DBU) as a strong base at reflux
temperature under a nitrogen atmosphere afforded the metal-free
phthalocyanine (4) in 41% yield as a dark green solid after purifi-
cation by column chromatography which is placed aluminium
oxide using CHCl3:CH3OH (9:1) as solvent system. Zinc (II) phtha-
locyanine (5) was obtained in the presence of the anhydrous
Zn(CH3COO)2 in 2-(dimethylamino)ethanol as solvent using
microwave irradiation.
ethanol. Yield: 2.50 g (78%), mp: 134e135 ꢃC. IR (KBr tablet) nmax
/
cmꢁ1: 3077 (AreH), 2948e2852 (Aliph. CeH), 2227 (C^N), 1594,
1500, 1458, 1428, 1318, 1256, 1171, 1093, 1020, 994, 835, 767, 727,
523. 1H NMR (CDCl3), (
d
: ppm): 7.95 (d, 1H, J ¼ 8.2 Hz, ArH), 7.75 (t,
2H, J ¼ 10.9 Hz, ArH), 7.46 (m, 2H, ArH), 7.31 (m, 2H, AreH), 4.51 (t,
2H, J ¼ 6.6 Hz, CH2eO), 3.74 (t, 2H, J ¼ 7.0 Hz, CH2eS). 13C NMR
(CDCl3), (d: ppm): 165.02, 161.33, 152.66, 135.15, 126.25, 124.61,
121.48, 121.08, 119.66, 119.51, 117.38, 115.58, 115.22, 107.54, 67.13,
30.71. MS (ESþ), m/z: Calc. for C17H11N3S2O: 337.43; Found: 338
[M þ H]þ.
In the IR spectra, the formation of compound 3 was clearly
confirmed by the disappearance of the eOH and eNO2 bands and
appearance of eC^N band at 2227 cmꢁ1. In the 1H NMR spectra of
3, the proton signals corresponding to OH group for compound 1
appeared as expected. 1H NMR spectrum of 3 showed new signals
2.5.2. Synthesis of metal-free phthalocyanine (4)
The mixture of 2-(2-benzothiazolylthio)ethoxy phthalonitrile
(3) (0.6 g, 1.78 mmol), n-pentanol (3 mL) and 12 drops of 1.8-
diazabicyclo[5,4,0]undec-7-ene (DBU) was placed in Schlenk tube
at 160 ꢃC, for 24 h. After cooling to room temperature the reaction
mixture was refluxed with ethanol (45 mL) in order to precipitate
the product which was filtered off. The green solid product was
washed with hot ethanol, diethyl ether and dried in vacuo. After
that the crude product was purified by column chromatography
which is placed silicagel using chloroform as eluent. Yield: 103 mg
(41%). mp > 300 ꢃC. IR (KBr tablet) nmax/cmꢁ1: 3292 (NeH), 3063
(AreH), 2923e2852 (Aliph. CeH), 1603, 1541,1486, 1457, 1427, 1312,
at
d
¼ 7.95, 7.75, 7.46 and 7.31 ppm for aromatic protons. The 1H
NMR signals belong to aliphatic protons were observed at
d
¼ 4.51,
3.74 ppm. The 13C NMR spectra of 3 showed signals for carbon
atoms at
¼ 165.02, 161.33, 152.66, 135.15, 126.25, 124.61, 121.48,
d
121.08, 119.66, 119.51, 117.38, 115.58, 115.22, 107.54, 67.13, 30.71. The
MS spectrum of compound 3 showed a molecular ion peak at m/
z ¼ 338 [M þ H]þ support the proposed formula for this compound.
The sharp peak in the IR spectra for the C^N vibration of
phthalonitrile compound (3) at 2227 cmꢁ1 disappeared after
conversion into metal-free phthalocyanine, indicative of metal-free
phthalocyanine formation. The characteristic NeH stretching for
the metal-free phthalocyanine ring was observed at 3292 cmꢁ1. The
IR spectra of metal-free (4) and zinc (II) (5) phthalocyanines are
1281, 1238, 1117, 1018, 996, 833, 756, 726. 1H NMR (CDCl3) (
d: ppm):
7.96 (d, J ¼ 7.8 Hz, 4H, ArH), 7.72 (m, 8H, ArH), 7.40 (m, 8H, ArH),
7.30 (m, 8H, AreH), 4.47 (m, 8H, CH2eO), 3.72 (m, 8H, CH2eS). MS
(ESþ), m/z: Calc. for C68H46N12S8O4: 1351.72; Found: 1374
very similar, except these
cyanine core in the metal-free molecule. In the 1H NMR spectrum of
compound 4, aromatic protons were observed at
¼ 7.96, 7.72, 7.40
and 7.30 ppm. The aliphatic protons were observed at
¼ 4.47 and
n (NH) vibrations of the inner phthalo-
[M þ Na]þ. UV/vis:
l
, nm (log ε): in DMF; 702 (4.31), 670 (4.40), 639
d
(4.26), 335 (4.56), in toluene; 704 (4.76), 666 (4.72), 641 (4.51), 340
(4.67).
d
3.72 ppm. The NH protons of compound 4 could not be observed
owing to the probable strong aggregation of the molecules [44]. In
the mass spectrum of compound 4, the presence of the character-
istic molecular ion peak at m/z ¼ 1374 [M þ Na]þ confirmed the
proposed structure.
2.5.3. Synthesis of zinc (II) phthalocyanine (5)
A mixture of compound 3 (0.6 g, 1.78 mmol), Zn(CH3COO)2
(0.080 g, 0.44 mmol) and 2-(dimethylamino)ethanol (6 mL) was
irradiated in a microwave oven at 175 ꢃC, 350 W for 10 min. After
the mixture was cooled to the room temperature, it was stirred in
EtOH (30 mL) addition for overnight and filtered off. The crude
In the IR spectrum of zinc (II) phthalocyanine, the sharp vibra-
tion for the eC^N groups in the IR spectra of phthalonitrile
compound 3 at 2227 cmꢁ1, disappeared after conversion into zinc

4
E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
CN
N
S
OH
S
O2N
CN
2
1
i
CN
CN
N
S
O
S
3
ii
iii
RO
RO
OR
OR
N
N
N
HN
N
N
N
N
N
Zn
N
N
N
NH
N
N
N
4
OR
5
RO
OR
RO
N
R =
S
S
Scheme 1. The synthetic route of the phthalonitrile and its metal-free and zinc phthalocyanine derivatives. Reagents and conditions: (i) dry DMF, K2CO3, 50 ꢃC, 72 h; (ii) n-pentanol,
DBU, 160 ꢃC, (iii) Zn(CH3COO)2, DMAE, 175 ꢃC, 350 W.
Fig. 1. Absorption spectra of compound 4 and 5 (a) in toluene and (b) in DMF.

E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
5
Table 1
Aggregation behaviour of these compounds was also studied at
different concentrations in DMF and toluene. The compound 5 did
not show any aggregation in all these solvents while the compound
4 showed a little aggregation in DMSO. BeereLambert law could be
obeyed for studied phthalocyanine complexes in the concentra-
tions ranging from 1.2 ꢀ 10ꢁ5 to 2 ꢀ 10ꢁ6 M (Fig. 2).
Absorption, excitation and emission spectral data for substituted metal-free (4) zinc
(5) and unsubstituted zinc (Std-ZnPc) phthalocyanine compounds in DMF and
toluene.
Compound Solvent Q band
lmax, (nm)
log ε
Excitation Emission Stokes shift
lEx, (nm) lEm, (nm) DStokes, (nm)
4
DMF
670, 702 4.40, 4.31 673, 704 711
Toluene 666, 704 4.72, 4.76 668, 705 710
9
6
The fluorescence behaviour of the studied phthalocyanine
complexes was examined in DMF and toluene. Fig. 3 shows fluo-
rescence emission, absorption and excitation spectra of compound
4 in toluene (Fig. 3a) and compound 5 in DMF (Fig. 3b) as examples.
The observed Stokes shifts (w5e15 nm) were within the region
observed for Pc complexes. Metal-free 4 and zinc 5 phthalocyanine
compounds showed similar fluorescence behaviour in DMF and
toluene. The excitation spectra were similar to absorption spectra
and both were mirror images of the fluorescent spectra for both
compounds 4 and 5 in both DMF and toluene. The proximity of the
wavelength of the Q-band absorption and the Q band maxima of
the excitation spectra for all studied compound suggested that the
nuclear configurations of the ground and excited states are similar
and not affected by excitation.
5
DMF
Toluene 682
678
5.26
680
690
12
12
5.26
686
694
Std-ZnPc DMF
670a
5.37a
5.14b
670a
672c
676a
676d
6a
Toluene 672b
6d
a
b
c
Data from reference [52].
Data from reference [29].
Data from reference [30].
Data from reference [53].
d
(II) phthalocyanine. In the 1H NMR spectrum of zinc (II) phthalo-
cyanine, the aromatic ring protons were observed at
¼ 7.74 ppm
as multiplet and aromatic protons on the substituents were also
observed at
observed at
d
d
¼ 7.30 ppm as multiplet. The aliphatic protons were
d
¼ 4.55 and3.73 ppm. In the mass spectrum of
Fluorescence emission and excitation peaks in DMF and toluene
are listed in Table 1. The observed Stokes shifts of substituted
metal-free 4 and zinc 5 phthalocyanine compounds are higher than
standard ZnPc in both DMF and toluene (Table 1). The observed
Stokes shift of the substituted zinc phthalocyanine complex 5 is
higher than substituted metal-free 4 phthalocyanine compound in
both DMF and toluene (Table 1).
compound 5, the presence of molecular ion peaks at m/z ¼ 1438
[M þ Na]þ, confirmed the proposed structures.
3.2. Ground state electronic absorption spectra and fluorescence
spectra
UVevis spectroscopy is one of the best indicator to confirm the
formation of phthalocyanines in their dilute solutions. The UVevis
spectra of the studied metal-free 4 and zinc (II) 5 phthalocyanine
compounds in DMF and toluene were given in Fig. 1. The Q band of
the metal-free phthalocyanine was observed as split two bands due
to D2h symmetry [45] in both studied solvents. The splitting Q band
was observed at lmax 702 and 670 nm in DMF and at lmax 704 and
666 nm in toluene (Table 1), indicating the structure with non-
degenerate D2h symmetry [45]. The ground state electronic
absorption spectrum of zinc (II) phthalocyanine compound 5
showed monomeric behaviour evidenced by a single (narrow) Q
band, typical of metallated phthalocyanine complexes, Fig. 1 [46].
The Q band of this complex was observed at 678 nm in DMF and
682 in toluene, Table 1. The B bands of studied phthalocyanine
compounds 4 and 5 were observed at around 340e360 nm in
DMSO (Fig. 1).
3.3. Photophysical properties
3.3.1. Fluorescence quantum yields and lifetimes
The fluorescence quantum yield (FF) values of metal-free 4 and
zinc (II) 5 phthalocyanine compounds in DMF and toluene are given
in Table 2. The FF values of the studied phthalocyanine compound 4
and 5 are higher than unsubstituted zinc Pc (Std-ZnPc) in both DMF
and toluene. Especially, the FF values of substituted phthalocyanine
compounds are quite higher than unsubstituted zinc Pc (Std-ZnPc)
in toluene. The increasing in the FF values for substituted phtha-
locyanine complexes in the presence of the ring substituents
suggests that the substituents less quench the excited singlet state
than the fluorescence. The substituted metal-free Pc (4) complex
shows larger FF values in both studied solvents. Fluorescence
quantum yield (FF) values of studied phthalocyanines complexes (4
and 5) are almost similar values compared to metal free and zinc
phthalocyanine derivatives studied in the literature [49].
Aggregation is highly depends on a number of parameters such
as concentration, temperature, nature of the substituents, nature of
solvents and complex metal ions [47,48]. Aggregation behaviour of
metal-free 4 and zinc 5 phthalocyanine compounds were investi-
gated in different solvents (DMSO, THF and chloroform).
Fluorescence lifetime (sF), directly related to FF value, refers to
the average time a molecule stays in its excited state before emis-
sion. The value of FF could be indirectly reduced by such factors
Fig. 2. Absorption spectra: (a) for compound 4 in toluene and (b) for compound 5 in DMF at different concentrations. (Inset: Plot of absorbance versus concentration).

6
E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
Fig. 3. Absorption, excitation and emission spectra of (a) compound 4 in toluene and (b) compound 5 in DMF. Excitation wavelength: 640 for compound 4 and 650 nm for
compound 5.
shortening the fluorescence lifetime of a fluorophore, including
internal conversion and intersystem crossing. Lifetimes of fluores-
cence were calculated using the StricklereBerg equation. Using this
equation, a good correlation has been found [36] between experi-
mentally and the theoretically determined lifetimes for the unag-
gregated molecules as is the case in this work. Generally, the sF
values are within the range reported for MPc complexes [50]. The sF
values of metal-free 4 and zinc (II) 5 phthalocyanine compounds
are higher than unsubstituted zinc Pc (Std-ZnPc). Among the
photosensitizer. Energy transfer from the triplet state of a photo-
sensitizer to ground state molecular oxygen leads to the produc-
tion of singlet oxygen. There is a necessity of high efficiency of
transfer of energy between excited triplet state of photosensitizer
and ground state of oxygen to generate large amounts of singlet
oxygen, essential for PDT. The singlet oxygen quantum yield (FD
)
value gives the amount of the singlet oxygen generation and this
value is an indication of potential of the complexes as photosen-
sitizers in applications where singlet oxygen is required. The FD
values were determined using a chemical method (in DMF and
toluene using DPBF as quenchers). The disappearance of DPBF was
monitored using UVevis spectrophotometer (Fig. 4 as examples:
(a) for compound 4 in toluene and (b) for compound 5 in DMF)
Many factors are responsible for the magnitude of the determined
quantum yield of singlet oxygen including such as triplet excited
state energy, nature of substituents and solvents, the triplet
excited state lifetime and the efficiency 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 studied
metal-free 4 and zinc (II) 5 phthalocyanine derivatives during FD
determinations.
Table 2 gives the FD values of substituted metal-free 4,
substituted zinc (II) 5 phthalocyanines and unsubstituted zinc
phthalocyanine (Std-ZnPc) which is used as standard for singlet
oxygen studies of phthalocyanine compounds for comparison.
While the FD values of substituted zinc (II) phthalocyanine
compound 5 are higher, the FD values of substituted metal-free 4
phthalocyanine compound are lower than unsubstituted zinc (II)
phthalocyanine in both DMF and toluene. The FD values of
substituted zinc (II) phthalocyanine compound 5 are higher than
substituted phthalocyanine compounds, the
compound 4 are higher than zinc phthalocyanine compound 5 in
both studied solvents. Fluorescence lifetime ( F) values of employed
sF values of metal-free
s
phthalocyanines complexes (4 and 5) are almost similar values
compared to metal free and zinc phthalocyanine derivatives
studied in the literature [49].
The natural radiative lifetime (
fluorescence (kF) values are also given in Table 2. The
s
0) and the rate constants for
0 values of
s
metal-free 4 and zinc 5 phthalocyanine compounds are higher
than unsubstituted ZnPc (Std-ZnPc) in DMF but the s0 values of
these compounds are lower than unsubstituted ZnPc (Std-ZnPc)
in toluene. The kF values of these compounds (4 and 5) are
higher than unsubstituted ZnPc (Std-ZnPc) in both DMF and
toluene.
3.4. Photochemical properties
3.4.1. Singlet oxygen quantum yields
In PDT applications, it is worth saying that the most important
parameter is the efficiency in singlet oxygen generation of the
the FD values of substituted metal-free
4 phthalocyanine
compound in both DMF and toluene. The singlet oxygen quantum
yield (FD) values of employed phthalocyanines complexes (4 and 5)
are almost similar values compared to metal free and zinc phtha-
locyanine derivatives studied in the literature [49]. In general, zinc
phthalocyanine compounds which could be generated highly
singlet oxygen possess high triplet yields duo to the d10 configu-
ration of the central Zn2þ ion, giving an excellent candidate as
a photosensitizers for PDT applications.
Table 2
Photophysical and photochemical parameters of substituted metal-free (4), zinc (5)
and unsubstituted zinc (Std-ZnPc) phthalocyanine compounds in DMF and toluene.
Compound Solvent
FF
s
F (ns) s0 (ns) kF (sꢁ1
)
Fd
FD
(ꢀ107)a (ꢀ10ꢁ5
)
4
DMF
0.31
7.58
3.02
1.71
1.16
24.21
12.95
7.57
4.13
7.72
13.20
17.87
1.65b
7.70d
0.52
9.65
0.21
6.72
2.3b
0.26
0.36
0.73
0.61
0.56b
0.58c
Toluene 0.23
DMF 0.23
Toluene 0.21
DMF
Toluene 0.07c 0.90d
5
5.60
Std-ZnPc
0.17b 1.03b
6.05b
12.97d
3.4.2. Photodegradation studies
6.19e
Degradation of the compounds under light irradiation can be
used to study their stability and this is especially important for
those compounds intended for use in photocatalysis. The collapse
of the absorption spectra without any distortion of the
shape confirms photodegradation not associated with
a
kF is the rate constant for fluorescence. Values calculated using kF
Data from reference [52].
Data from reference [53].
Data from reference [30].
Data from reference [28].
¼
FF/sF.
b
c
d
e

E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
7
Fig. 4. Absorbance changes during the determination of singlet oxygen quantum yield: (a) for compound 4 in toluene and (b) for compound 5 in DMF at a concentration of
1.0 ꢀ 10ꢁ5 M. (Inset: Plots of DPBF absorbance versus time).
phototransformation into different forms of photosensitizers
absorbing light in the visible region. The spectral changes observed
for metal-free 4 and zinc (II) 5 Pc complexes during confirmed
photodegradation occurred without phototransformation (Fig. 5 as
examples: (a) for compound 4 in DMF and (b) for compound 5 in
toluene).
3.4.3. Fluorescence quenching studies by 1,4-benzoquinone [BQ]
The fluorescence quenching of metal-free 4 and zinc 5 phtha-
locyanine compounds by BQ was found to obey SterneVolmer
kinetics, which is consistent with diffusion-controlled bimolec-
ular reactions in both DMF and toluene. Fig. 6 shows the quenching
of metal-free (4) (Fig. 6a) and zinc (II) (5) (Fig. 6b) Pc compounds by
BQ in toluene and DMF, respectively. The slopes of the plots were
given as insets in Fig. 6a and b. These plots gave SterneVolmer
constants (KSV) values of studied phthalocyanine compounds 4
and 5 and listed in Table 3. The linearity of these plots indicates that
fluorescence quenching is reasonably described by a collisional
quenching mechanism. The KSV values of the substituted phthalo-
cyanine complexes 4 and 5 are lower than unsubstituted ZnPc (Std-
ZnPc) in DMF and toluene. The KSV values of zinc phthalocyanine
compound 5 are slightly lower than metal-free phthalocyanine
compound 4 in both DMF and toluene. These two compounds
compared in terms of solvent effect, KSV values are higher in
toluene than in DMF. The bimolecular quenching rate constant (kq)
values of the substituted phthalocyanine complexes 4 and 5 are
also lower than unsubstituted ZnPc (Std-ZnPc) in DMF and toluene,
thus substitution of phthalocyanine framework with 2-(2-
benzothiazolylthio)ethoxy groups seems to decrease the kq values
of the compounds in both DMF and toluene. Moreover, studied zinc
(II) 5 phthalocyanine has higher kq value than metal-free 4 Pc
The photodegradation quantum yield (Fd) values of metal-free 4
and zinc 5 phthalocyanine compounds as well as unsubstituted
zinc (II) phthalocyanine (Std-ZnPc) in DMF and toluene are given in
Table 2. All the studied complexes showed about the same stability
with Fd of the order of 10ꢁ5. The Fd values, found in this study, are
similar with zinc Pc complexes having different substituents on the
phthalocyanine ring in literature [50]. The Fd values have been
reported as low as 10ꢁ6 for stable zinc phthalocyanine complexes
and the Fd values of the order of 10ꢁ3 for unstable zinc phthalo-
cyanine complexes [49]. The metal-free 4 and zinc 5 phthalocya-
nine compounds showed lower Fd values when compared to the
unsubstituted ZnPc (Std-ZnPc) in DMF but studied compounds
showed slightly higher in Fd values toluene. The substitution of the
phthalocyanine framework with 2-(2-benzothiazolylthio)ethoxy
groups slightly increased the stability of studies phthalocyanine
compounds in DMF but slightly decreased in toluene. However,
studied Pc complexes could be classified as stable compounds. The
photodegradation quantum yield (Fd) values of studied phthalo-
cyanines complexes (4 and 5) are almost similar values compared
to metal free and zinc phthalocyanine derivatives studied in the
literature [49].
complex in both solvents. The kq values are near 1010
M
ꢁ1 sꢁ1 and in
agreement with the theoretical SmoluchowskieStokeseEinstein
approximation at 298 K [51].
Fig. 5. Absorbance changes during the photodegradation study: (a) for compound 4 in DMF and (b) for compound 5 in toluene showing the disappearance of the Q-band at 5 and
2.5 min intervals, respectively. (Inset: Plot of Q band absorbance versus time).

8
E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
Fig. 6. Fluorescence emission spectral changes of: (a) compound 4 and (b) compound 5 (C ¼ 1.00 ꢀ 10ꢁ5 M) on addition of different concentrations of BQ in toluene and DMF
respectively. [BQ] ¼ 0, 0.008, 0.016, 0.024, 0.032, 0.040 M and saturated with BQ. (Insets: SterneVolmer plots for benzoquinone (BQ) quenching of compounds 4 and 5 in DMF and
toluene).
Table 3
toluene. The substituted phthalocyanine compounds 4 and 5
showed slightly lower KSV values in toluene but showed quite lower
values in DMF when compared to unsubstituted ZnPc (Std-ZnPc)
according to the results of fluorescence quenching studies.
Fluorescence quenching data for substituted metal-free (4), zinc (5) and unsub-
stituted zinc (Std-ZnPc) phthalocyanine compounds in DMF and toluene.
Compound
Solvent
KSBVQ /(Mꢁ1
)
kq/1010 (Mꢁ1 sꢁ1
)
4
DMF
Toluene
DMF
36.79
61.40
32.02
60.57
57.60
61.53
0.49
2.03
1.87
5.22
5.59
6.83
Acknowledgement
5
Toluene
DMFa
This study was supported by the Research Fund of Karadeniz
Technical University, Project no: 2010.111.002.5 (Trabzon-Turkey).
Std-ZnPc
Tolueneb
a
Data from reference [52].
Data from reference [28].
b
References
[1] J. Simon, T. Toupance, in: D.N. Reinhoudt (Ed.), Comprehensive Supramolec-
ular Chemistry, vol. 10, Pergamon Press, Exeter, 1996.
[2] A. Bilgin, B. Ertem, Y. Gok, Polyhedron 24 (2005) 1117e1124.
[3] S.J. Lange, J.W. Sibert, A.G.M. Barrett, B.M. Hoffman, Tetrahedron 56 (2000)
7371e7377.
4. Conclusion
The novel metal-free 4 and zinc (II) 5 phthalocyanines bearing
four 2-(2-benzothiazolylthio)ethoxy groups at peripheral position
have been synthesized for the first time in this study. The studied
compounds were characterized by elemental analysis, UVevis, FT-
IR, 1H NMR and ESI mass spectroscopies. Both studied Pc complexes
are very soluble in most organic solvents such as chloroform,
dichloromethane, toluene, THF etc. The photophysical and photo-
chemical properties of studied metal-free 4 and zinc 5 phthalocy-
anines compounds have also been described in both DMF and
toluene for comparison of solvent effect. In solution, the absorption
spectra showed monomeric behaviour evidenced by a single
(narrow) Q band for the zinc phthalocyanine compound 5 due to
D4h symmetry of this compound. But the metal-free phthalocya-
nine compound 4 showed a doublet Q band in different solvents
due to D2h symmetry of this compound. The substitution of the 2-
(2-benzothiazolylthio)ethoxy substituents on the phthalocyanine
ring increased the wavelength of the Q band. In both DMF and
toluene, the fluorescence behaviour of the phthalocyanine
complexes indicated that the metal-free 4 and zinc 5 Pc complex
are more fluorescent than unsubstituted ZnPc (Std-ZnPc). The
substituted zinc Pc 5 complex has good singlet oxygen quantum
yields (FD) in compared to the metal free 4 Pc complex and
unsubstituted ZnPc (Std-ZnPc) in both solvents. The value of FD
ranged from 0.26 (for complex 4 in DMF) to 0.73 (for complex 5 in
DMF) indicates that there is a considerable potential of these
compounds as photosensitizers in PDT applications. The substitu-
tion of the phthalocyanine framework with 2-(2-benzothiazo-
lylthio)ethoxy groups slightly increased the stability of studies
phthalocyanine compounds in DMF but slightly decreased in
ꢀ
[4] O. Bekaroglu, J. Porphyr. Phthalocyanines 4 (2000) 465e473.
ꢀ
[5] O. Bekaroglu, Appl. Organomet. Chem. 10 (1996) 605e622.
[6] S. Marakov, C. Litwinski, E.A. Ermilov, O. Suvorova, B. Röder, D. Wöhrle, Chem.
A Eur. J. 12 (2006) 1468e1474.
[7] I. Özçes¸ meci, A.I. Okur, A. Gül, Dyes Pigm. 75 (2007) 761e765.
[8] A.W. Snow, J.S. Shirk, R.G.S. Pong, J. Porphyr. Phthalocyanines 4 (2000) 518e524.
[9] H.A. Dinçer, A. Gül, M.B. Koçak, J. Porphyr. Phthalocyanines 8 (2004) 1204e1208.
[10] M.J. Cook, J. Mater. Chem. 6 (1996) 677e689.
ꢀ
[11] E. Hamuryudan, Ö. Bekaroglu, J. Chem. Res. S 11 (1993) 460e461.
ꢀ
[12] Y.Arslanoglu,A.M. Sevim,E.Hamuryudan,A.Gül, DyesPigm.68(2006)129e132.
[13] M. Brewis, N.B. Mc Keown, Chem. A Eur. J. 4 (1998) 1633e1640.
[14] M. Hanack, A. Beck, H. Lehmann, Synthesis 8 (1987) 703e705.
[15] J.V. Bakboord, M.J. Cook, E. Hamuryudan, J. Porphyr. Phthalocyanines 4 (2000)
510e517.
[16] E. Hamuryudan, S. Merey, Z.A. Bayır, Dyes Pigm. 59 (2003) 263e268.
[17] L.R. Milgrom, Colours of Life, Oxford University Press, Oxford, 1997.
[18] A. Ogunsipe, T. Nyokong, J. Porphyr. Phthalocyanines 9 (2005) 121e129.
[19] A. Ogunsipe, T. Nyokong, J. Photochem. Photobiol. A Chem. 173 (2005) 211e220.
[20] A. Ogunsipe, T. Nyokong, Photochem. Photobiol. Sci. 4 (2005) 510e516.
_
_
ꢀ
ꢀ
[21] I. Acar, Z. Bıyıklıoglu, A. Koca, H. Kantekin, Polyhedron 29 (2010) 1475e1484.
[22] I. Acar, Z. Bıyıklıoglu, M. Durmus¸ , H. Kantekin, J. Organomet. Chem. 708e709
(2012) 65e74.
ꢀ
[23] Z. Bıyıklıoglu, Synth. Met. 162 (2012) 26e34.
[24] M. Durmus¸ , A. Erdogmus¸ , A. Ogunsipe, T. Nyokong, Dyes Pigm. 82 (2009)
ꢀ
244e250.
[25] I. Gürol, M. Durmus¸ , V. Ahsen, T. Nyokong, Dalton Trans. 34 (2007) 3782e3791.
[26] D. Atilla, N. Saydan, M. Durmus¸ , A.G. Gürek, T. Khan, A. Rück, H. Walt,
T. Nyokong, V. Ahsen, J. Photochem. Photobiol. A Chem. 186 (2007) 298e307.
[27] M. Durmus¸ , V. Ahsen, J. Inorg. Biochem. 104 (2010) 297e309.
[28] M. Durmus¸ , T. Nyokong, Spectrochim. Acta Part A 69 (2008) 1170e1177.
[29] A. Ogunsipe, M. Durmus¸ , D. Atilla, A.G. Gürek, V. Ahsen, T. Nyokong, Synth.
Met. 158 (2008) 839e847.
[30] E.T. Saka, M. Durmus¸ , H. Kantekin, J. Organomet. Chem. 696 (2011) 913e924.
[31] M. Durmus¸ , H. Yaman, C. Göl, V. Ahsen, T. Nyokong, Dyes Pigm. 91 (2011)
153e163.
[32] C.M. Petersen, J. Vine, J. Ashley, R.L. Nation, J. Pharm. Sci. 70 (1981) 1139e1143.

E.T. Saka et al. / Journal of Organometallic Chemistry 723 (2013) 1e9
9
[33] J.G. Young, W. Onyebuagu, J. Org. Chem. 55 (1990) 2155e2159.
[34] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemicals, second ed.,
Pergamon Press, New York, 1985.
[35] S. Fery-Forgues, D. Lavabre, J. Chem. Ed. 76 (1999) 1260e1264.
[36] D. Maree, T. Nyokong, K. Suhling, D. Phillips, J. Porphyr. Phthalocyanines 6
(2002) 373e376.
[44] C.F. Van Nostrum, S.J. Picken, A.J. Schouten, R.J.M. Nolte, J. Am. Chem. Soc. 117
(1995) 9957e9965.
[45] J. Mack, M.J. Stillman, J. Am. Chem. Soc. 116 (1994) 1292e1304.
[46] M.J. Stillman, T. Nyokong, in: C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocya-
nines: Properties and Applications, vol. 1, VCH Publishers, NewYork, 1989,
pp. 202e228.
[37] A. Ogunsipe, J.-Y. Chen, T. Nyokong, New J. Chem. 28 (2004) 822e827.
[38] H. Du, R.A. Fuh, J. Li, A. Corkan, J.S. Lindsey, Photochem. Photobiol. 68 (1998)
141e142.
[47] H. Enkelkamp, R.J.M. Nolte, J. Porphyr. Phthalocyanines 4 (2000) 454e459.
[48] D.D. Dominguez, A.W. Snow, J.S. Shirk, R.S. Pong, J. Porphyr. Phthalocyanines 5
(2001) 582e592.
[39] H. Brannon, D. Madge, J. Am. Chem. Soc. 102 (1980) 62e65.
[40] I. Seotsanyana-Mokhosi, N. Kuznetsova, T. Nyokong, J. Photochem. Photobiol.
A Chem. 140 (2001) 215e222.
[41] W. Spiller, H. Kliesch, D. Wöhrle, S. Hackbarth, B. Roder, G. Schnurpfeil,
J. Porphyr. Phthalocyanines 2 (1998) 145e158.
[42] L. Kaestner, M. Cesson, K. Kassab, T. Christensen, P.D. Edminson, M.J. Cook,
I. Chambrier, G. Jori, Photochem. Photobiol. Sci. 2 (2003) 660e667.
[43] J. Rose, Advanced Physico-chemical Experiments, Sir Isaac Pitman & Sons Ltd,
London, 1964, p. 257.
[49] T. Nyokong, V. Ahsen, Photosensitizers in Medicine, Environment, and Secu-
rity, in: M. Durmus¸ (Ed.), Photochemical and Photophysical Characterization,
Springer Science þ Business Media, London, 2012, pp. 135e266.
[50] T. Nyokong, Coord. Chem. Rev. 251 (2007) 1707e1722.
[51] S.L. Murov, I. Carmichael, G.L. Hug, Handbook of Photochemistry, second ed.,
Marcel Decker, New York, 1993, p. 207.
[52] Y. Zorlu, F. Dumoulin, M. Durmus¸ , V. Ahsen, Tetrahedron 66 (2010)
3248e3258.
[53] A. Ogunsipe, D. Maree, T. Nyokong, J. Mol. Struct. 650 (2003) 131e140.