Synthesis of zinc phthalocyanine derivatives with improved photophysicochemical properties in aqueous media

Article abstract of DOI:10.1016/j.molstruc.2010.04.048

The synthesis, photophysical and photochemical properties of new peripherally (β) tetra-substituted thioquinoline Zn(II) (2) and quaternized thioquinoline Zn(II) phthalocyanines (3) and quaternized fluoro functional thiopyridine Zn(II) (5) are described for the first time. These complexes (2, 3 and 5) have been synthesized and characterized by elemental analysis, IR, ¹H NMR spectroscopy and electronic spectroscopy. Complexes 2, 4 and 6 have good solubility in organic solvents such as CHCl₃, DCM, DMSO, DMF, THF and toluene and are not aggregated in all solvents (except for 2 in DMSO) within a wide concentration range. Complexes 3 and 5 showed very good solubility in water as well as DMSO and DMF. General trends are described for singlet oxygen, photodegradation, fluorescence quantum yields, triplet quantum yields and triplet life times of these complexes in DMSO (2, 4 and 6) and water (3 and 5). Complex 3 gave a very large triplet quantum yield in aqueous media (Φ_T = 0.8 in water plus Triton X-100) and a reasonable triplet lifetime of 110 μs. Photophysical and photochemical properties of the phthalocyanines complexes 2-6 are very useful for PDT.

Full text of DOI:10.1016/j.molstruc.2010.04.048

Journal of Molecular Structure 977 (2010) 26–38
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis of zinc phthalocyanine derivatives with improved
photophysicochemical properties in aqueous media
Ali Erdog˘mußs a,b, Tebello Nyokong a,
*
a Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
b Department of Chemistry, Yildiz Technical University, 34210 Esenler, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 March 2010
Received in revised form 30 April 2010
Accepted 30 April 2010
Available online 11 May 2010
The synthesis, photophysical and photochemical properties of new peripherally (b) tetra-substituted
thioquinoline Zn(II) (2) and quaternized thioquinoline Zn(II) phthalocyanines (3) and quaternized fluoro
functional thiopyridine Zn(II) (5) are described for the first time. These complexes (2, 3 and 5) have been
synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy and electronic spectros-
copy. Complexes 2, 4 and 6 have good solubility in organic solvents such as CHCl3, DCM, DMSO, DMF,
THF and toluene and are not aggregated in all solvents (except for 2 in DMSO) within a wide concentra-
tion range. Complexes 3 and 5 showed very good solubility in water as well as DMSO and DMF. General
trends are described for singlet oxygen, photodegradation, fluorescence quantum yields, triplet quantum
yields and triplet life times of these complexes in DMSO (2, 4 and 6) and water (3 and 5). Complex 3 gave
a very large triplet quantum yield in aqueous media (UT = 0.8 in water plus Triton X-100) and a reason-
Keywords:
Zinc phthalocyanines
Water soluble
Triplet quantum yield
Fluorescence quantum yield
Singlet oxygen
able triplet lifetime of 110
ls. Photophysical and photochemical properties of the phthalocyanines com-
Photodynamic therapy
plexes 2–6 are very useful for PDT.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
stituents over those with neutral and anionic substituents are
numerous [12–15] and include the following: (i) they have been
shown to be more efficient as PDT agents [14] improve cell uptake
[15] and (ii) are selectively localized in the cell mitochondria,
which induces apoptosis [16].
Metallophthalocyanines (MPcs) have been known to have very
interesting properties coupled with excellent stability to heat, light
and strong chemical environments. Their optical and electronic
properties have been exploited in various applications including
as pigments, in infrared security devices, information storage and
computer disk writing and in photodynamic therapy of cancer
(PDT) [1–4]. For PDT applications, it is important that MPcs exhibit
MPcs which are substituted with aryl thio groups have been re-
ported [17,18]. MPcs substituted with thiopyridine groups and
their quaternized derivatives have also been reported [19,20].
The use of thioquinoline followed by quaternization is reported
here for the first time. Although phthalocyanines bearing elec-
tron-donating substituents have frequently been studied, those
bearing electron-withdrawing ones have not been extensively
studied, especially those containing fluorine atoms [21,22]. There-
fore we report the synthesis, characterization and photophysical
and photochemical properties of new organo-soluble and water
soluble Zn phthalocyanines bearing fluoro-functionalised pyridine
and thiopyridine substituents. The effect of the extension of the
ring substituents (compared to thiopyridine) on the photophysical
properties will be discussed.
This work investigates the photosensitizing tendencies of some
Zn2+ tetra substituted phthalocyanines (Scheme 1a) and their quat-
ernized derivatives (Scheme 1b). The effect of the substituent and
solvent on the photophysical and photochemical properties of the
new complexes will be discussed. The solvents employed are:
dimethylsulfoxide (DMSO) and water (for 3 and 5). The combina-
tion of fluorine substituents and quaternization results in
high absorption coefficients (e
> 105 Mꢀ1 cmꢀ1) in the visible re-
gion of the spectrum, mainly in the phototherapeutic window
(600–800 nm) and a long lifetime of triplet excited state in order
to produce singlet molecular oxygen, O2(1
Dg) efficiently.
Applications of phthalocyanines are restricted due to their
insolubility in common solvents and water [5]. The solubility of
phthalocyanines can be improved by introducing different kinds
of bulky substituents, such as crown ethers, alkyl, alkoxy and alkyl-
thio; electron-withdrawing substituents (AF, ACl, ABr, ANO2, etc.)
and donor atoms such as N and O at the periphery of the phthalo-
cyanines [6–10]. For PDT applications, the drug is injected into the
patient‘s blood stream, and since the blood itself is a hydrophilic
system, water solubility becomes crucial for a potential photosen-
sitizer for PDT [11]. The advantages of MPcs bearing cationic sub-
* Corresponding author. Tel.: +27 46 603 8260; fax: +27 46 622 5109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.04.048

A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
27
a
CN
CN
O2N
OH
SH
N
N
F3C
(i)
SH
(i)
(i)
N
F3C
O
CN
CN
N
N
F3C
CN
CN
S
Reported [23]
1
S
CN
CN
(ii)
N
(ii)
F3C
Reported [23]
OR1
SR3
(ii)
N
N
N
Zn
N
N
N
N
N
R1O
N
N
OR1
R3S
N
Zn
N
SR3
SR2
N
N
N
N
N
N
N
Zn
N
OR1
SR3
R2S
N
N
SR2
2
6
N
N
Reported [23]
SR2
4
Reported [23]
N
R3
=
N
N
R1
=
CF3
R2
=
CF3
Scheme 1. (a) Synthetic route of phthalonitrile. (1), and its zinc phthalocyanine. (i) Anhydrous Zn(Ac)2, 1-pentanol, 12 h, argon atm. References in brackets. (b) Synthetic
route of quaternized zinc phthalocyanines (3 and 5), (i) DMS, dry DMF, 10 h, argon atm.
molecules which are water soluble and with enhanced intersystem
crossing, hence large triplet quantum yield in aqueous media.
acetate were purchased from Aldrich. The synthesis and
characterization of 4-(tetra-5-(trifluoromethyl)-2-thiopyridineph-
thalocyaninato) zinc(II) (4) and 4-(tetra-5-(trifluoromethyl) pyrid-
inephthalocyaninato) zinc(II) (6) have been reported before [23].
2. Experimental
2.1. Materials
2.2. Equipment
Dimethyl sulfoxide (DMSO), N,N0-dimethylformamide (DMF),
chloroform, tetrahydrofuran (THF), methanol (MeOH), dichloro-
methane (DCM), 1-pentanol, n-hexane, acetone and toluene were
purchased from SAARCHEM; zinc phthalocyanine (ZnPc) 1,2-diph-
FT-IR spectra (KBr pellets) were recorded on a Perkin–Elmer
spectrum 2000 FT-IR spectrometer. UV/Vis spectra were recorded
on a Cary 500 UV/Vis/NIR spectrophotometer. 1H NMR spectra
were obtained in DMSO-d6, CDCl3, D2O using a Bruker EMX 400
NMR spectrometer. Elemental analyses were done on Vario Ele-
mentar EL III. Fluorescence spectra were recorded on the Varian
Eclipse spectrofluorimeter. Triplet absorption and decay kinetics
were recorded on a laser flash photolysis system, the excitation
pulses were produced by a Nd: YAG laser (Quanta-Ray, 1.5 J/
90 ns) pumping a dye laser (Lambda Physic FL 3002, Pyridin 1 in
enyisobenzofuran
(DPBF),
9,10-antracenediyl-bis(methylene)
dimalonoic acid (ADMA), 4-nitrophthalonitrile, 2-quinolinethiol,
5-(trifluoromethyl)-2-thiopyridine, 2-hydroxy-5-(trifluoromethyl)
pyridine, 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU), potassium
carbonate, dimethylsulphate (DMS), zinc acetate (Zn(OAc)2), zinc
phthalocyanine, tetrasulphonated zinc phthalocyanine and zinc

28
A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
b
CF
3
S
S
N
N
N
N
N
N
N
N
Zn
N
N
N
N
N
F C
3
s
s
S
Zn
N
N
N
S
CF
3
N
N
N
N
N
N
s
4 Reported [23]
S
N
2
N
CF
3
i
i
+4
+4
S
CF
3
+
S
N
+
N
H C
3
H C
CH
3
3
CH
3
+
N
N
N
N
N
Zn
N
N
N
+
N
N
F C
3
N
S
CF
N
Zn
N
3
N
S
s
s
+
2-
4
N
2-
2SO
N
N
2SO
4
N
N
+
H C
3
N
H C
3
H3C
s
S
+
H C
3
N
+
N
CF
3
5
3
Scheme 1 (continued)
methanol). The analyzing beam source was from a Thermo Oriel
xenon arc lamp, and a photomultiplier tube was used as detector.
Signals were recorded with a two-channel digital real-time oscillo-
scope (Tektronix TDS 360); the kinetic curves were averaged over
256 laser pulses. 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 20 nm) was additionally placed in
the light path before the sample. Light intensities were measured
with a POWER MAX 5100 (Molelectron detector incorporated)
power meter.
anhydrous potassium carbonate (2.17 g, 15.80 mmol) was added in
portions during 2 h with efficient stirring. The reaction mixture
was stirred under argon atmosphere at room temperature for a to-
tal of 24 h. Then the mixture was poured into 200 ml iced water,
and the precipitate was filtered off, washed with water and meth-
anol and then dried. The crude product was recrystallized from
methanol–ethanol mixture. Finally the pure product was dried in
vacuum. Yield: 1.25 g (69%). IR spectrum (cmꢀ1): 3072, 3052
(ArACH), 2229 (C„N), 1579 (C@C), 1560 (C@N), 1474, 1421,
1385, 1288, 1096, 1037, 966, 778, 664 (CASAC). 1H NMR (CDCl3):
d = 8.14 (d, J = 8.63 Hz, 2H, ArAH), 7.95 (2H, s, ArAH), 7.86–7.82
(3H, m, ArAH), 7.59 (1H, s, ArAH), 7.38 (d, J = 8.54 Hz, 1H, ArAH).
Calcd for C17H9N3S: C, 71.06; H, 3.16; N, 14.62; S, 11.16%. Found: C,
71.10; H, 3.12; N, 14.59; S, 11.20%.
2.3. Synthesis
2.3.1. 4-[2-Thioquinoine]-phthalonitrile (1)
2.3.2. (4)-Tetra[2-thioquinoline]phthalocyaninato zinc(II) (2)
4-Nitrophthalonitrile (1.10 g, 6.30 mmol) was dissolved in DMF
(15 ml) under argon and 2-quinolinethiol (1.00 g, 6.30 mmol) was
added. After stirring for 30 min at room temperature, finely ground
Compound 1 (0.50 g, 1.74 mmol), anhydrous zinc acetate
(Zn(OAc)2, 0.38 g, 1.74 mmol) and 3 ml of dry 1-pentanol were
placed in a standard Schlenk tube in the presence of 1,8-diazabicyclo

A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
29
F ꢁ AStd ꢁ n2
[5.4.0] undec-7-ene (DBU) (0.39 ml, 0.25 mmol) under an argon
atmosphere and held at reflux temperature for 12 h. After cooling
to room temperature, the reaction mixture was precipitated by add-
ing it drop-wise into n-hexane. The crude product was precipitated,
collected by filtration and washed with hot hexane, ethanol and
methanol. The crude green product was further purified by chroma-
tography over a silica gel column using THF and a mixture of THF and
CH2Cl2 (1:25 by volume), as eluents respectively. Yield 0.27 g (51%).
UF
¼
UF ðStdÞ
ð1Þ
FStd ꢁ A ꢁ n2Std
where F and FStd are the areas under the fluorescence curves of 2, 3
or 5, and the standard respectively. A and AStd are the respective
absorbances of the sample and standard at the excitation wave-
lengths (which was ꢂ0.05 in all solvents used), and n and nStd are
the refractive indices of solvents used for the sample and standard,
respectively. ZnPc in DMSO (UF = 0.20) [27], was employed as the
standard.
UV–Vis (DMSO): kmax nm (log
688 (5.11), (Toluene): kmax nm (log
(5.44), (DMF): kmax nm (log ) 368 (4.88), 616 (4.63), 684 (5.37). IR
e
) 356 (4.90), 619 (4.68), 645 (5.07),
e
) 365 (4.89), 617 (4.70), 689
e
spectrum (cmꢀ1): 3057 (ArACH), 1588, (C@C), 1554 (C@N), 1491,
1419, 1386, 1218, 1097, 942, 816, 745, 686 (CASAC). 1H NMR
(CDCl3): d = 9.47–8.42 (10H, m, ArAH), 8.46–8.00 (12H, m, PcAH),
7.79 (4H, s, ArAH), 7.64–7.52 (7H, m, ArAH), 7.45–7.38 (3H, m,
ArAH). Calcd for C68H36N12 S4Zn: C, 67.23; H, 2.99; N, 13.84; S,
10.56%. Found: C, 66.36; H, 3.22; N, 13.34; S, 9.79%.
2.4.2. Triplet quantum yields and lifetimes
The solutions for triplet quantum yields and lifetimes were
introduced into a 1.0 mm pathlength UV/Vis spectrophotometric
cell, deaerated using nitrogen and irradiated at the Q band max-
ima. Triplet state quantum yields (UT) of 2, 3 or 5, were determined
by the triplet absorption method [28], using zinc phthalocyanine
(ZnPc) as a standard, Eq. (2):
2.3.3. Quaternized (4)-tetra[2-thioquinoline]phthalocyaninato zinc(II)
(3)
D
D
AT ꢁ eSTtd
UT
¼
USTtd
ꢁ
ð2Þ
ASTtd are the changes in the triplet state absor-
ASTtd
ꢁ
eT
This complex was prepared according to the method previously
reported by Smith et al. [24]. Compound 2 (50 mg, 0.041 mmol)
was heated to 120 °C in freshly distilled 2 ml DMF and excess dim-
ethylsulphate (0.1 ml) was added drop-wise using a micro syringe.
The mixture was stirred at 120 °C for 10 h. After this time, the mix-
ture was cooled to room temperature and the product was precip-
itated with hot acetone and collected by filtration. The green solid
product was washed successively with acetone, ethanol, ethyl ace-
tate, DCM, THF, chloroform, n-hexane and diethylether. The result-
ing hygroscopic product was dried over phosphorous pentoxide.
where
D
AT and
D
bances of 2, 3 or 5, and the standard, respectively. eT and eSTtd are
the triplet state molar extinction coefficients for 2, 3 or 5, and the
standard, respectively. USTtd is the triplet quantum yield for the stan-
dard, ZnPc (UT = 0.65 in DMSO [29] and ZnPcS4 (in H2O; UT = 0.56
[30]). eT and eSTtd were determined from the molar extinction
coefficients of the respective ground singlet state (eS and eSStd) and
the changes in absorbances of the ground singlet states (
D
AS and
D
ASStd), according to Eq. (3):
Yield: 50 mg (85%). UV–Vis (DMSO): kmax nm (log
621 (4.60), 689 (5.24), (DMF): kmax nm (log ) 360 (4.93), 635
(4.45), 692 (5.13), (Water + Triton X-100): kmax nm (log ) 360
e) 364 (4.99),
D
D
AT
AS
e
eT
¼
eS
ꢁ
ð3Þ
e
(4.94), 645 (4.74), 687 (5.12). IR spectrum (cmꢀ1): 3060 (ArACH),
2960 (CAH), 1637, 1572 (C@C), 1559 (C@N), 1503, 1486, 1456,
1231 (S@O), 1141 (S@O), 743, 682 (CASAC), 617 (SAO). 1H NMR
(D2O): d = 9.21–7.48 ppm (36H, m, PcAH and ArAH), 3.78 (12H,
s, CH3). Calcd for C72H48N12O8S6Zn (+6H2O): C, 54.90; H, 3.84; N,
10.67%. Found: C, 55.86; H, 3.76; N, 10.79.
Quantum yields of internal conversion (UIC) were obtained
from Eq. (4), which assumes that only three processes (fluores-
cence, intersystem crossing and internal conversion), jointly deac-
tivate the excited singlet state of the 2, 3 or 5.
UIC ¼ 1 ꢀ ðUF
þ
UT
Þ
ð4Þ
2.5. Photochemical studies
2.3.4. Quaternized (4)-(tetra-5-(trifluoromethyl)-2-thiopyridi-
nephthalocyaninato) zinc(II) (5)
2.5.1. Singlet oxygen quantum yields
This complex was prepared according to the method previously
reported by Smith et al. [24]. Compound 3 (60 mg, 0.047 mmol)
was heated to 120 °C in freshly distilled 2 ml DMF and excess dim-
ethylsulfate (0.1 ml) was added drop-wise using a micro syringe.
The mixture was stirred at 120 °C for 12 h. After this time, the mix-
ture was cooled to room temperature and the product was precip-
itated with acetone and collected by filtration. The green solid
product was washed successively with ethyl acetate, DCM, THF,
chloroform, n-hexane and diethylether. The resulting hygroscopic
product was dried over phosphorous pentoxide. Yield: 47 mg
Quantum yields of singlet oxygen photogeneration were deter-
mined in air (no oxygen bubbled) using the relative method with
ZnPc (in DMSO and DMF) and ZnPcS4 (in water) as reference and
DPBF (in DMSO and DMF) and ADMA (in water) as chemical
quenchers for singlet oxygen, using Eq. (5):
RDPBFIStd
abs
UD
¼
USDtd
ð5Þ
Std
R
Iabs
DPBF
where USDtd is the singlet oxygen quantum yield for the standard,
ZnPc (UD = 0.67 in DMSO [31]) and ZnPcS4 UD = 0.30 in aqueous
solution in the presence of Triton X-100 [32]). RDPBF and R
(65%). UV–Vis (DMSO): kmax nm (log e) 355 (4.64), 641 (4.01),
(
690 (4.98). IR spectrum (cmꢀ1): 3051 (ArACH), 2944 (CAH),
1636, 1598 (C@C), 1503, 1486, 1334 (CAF), 1259 (S@O), 1174
(S@O), 743, 682 (CASAC), 614 (SAO). 1H NMR(D2O): d = 8.33–
8.01 ppm (24H, m, PcAH and pyridylAH), 3.79 (12H, s, CH3). Calcd
for C60H36F12N12O8S6Zn (7H2O): C, 43.28; H, 3.03; N, 10.10%.
Found: C, 43.24; H, 3.03; N, 9.85%.
Std
DPBF
are
the DPBF and ADMA photobleaching rates in the presence of 2, 3
or 5, and the standard respectively. Iabs and IStd are the rates of light
abs
absorption by 2, 3 or 5, and the standard respectively. To avoid
chain reactions induced by DPBF in the presence of singlet oxygen
[33], the concentrations of DPBF and ADMA were lowered to
ꢂ3 ꢃ 10ꢀ5 mol lꢀ1. Solutions of sensitizer (absorbance = 0.2 at the
irradiation wavelength) containing DPBF or ADMA were prepared
in the dark and irradiated in the Q-band region using the setup de-
scribed above. DPBF degradation was monitored at 417 nm. ADMA
degradation was monitored at 381 nm. The light intensity for sin-
glet oxygen studies was 2 ꢃ 1015 photons sꢀ1 cmꢀ2. The error in
2.4. Photophysical studies
2.4.1. Fluorescence quantum yields
Fluorescence quantum yields (UF) were determined by the
comparative method) [25,26], (Eq. (1)):

30
A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
The compounds were found to be pure by 1H NMR with both
the substituents and ring protons observed in their respective re-
gions. The 1H NMR spectra of tetrasubstituted phthalocyanine (2)
and quaternized derivative (3) were almost identical with starting
compound 1 except for broadening and a small shift. 1H NMR spec-
tra of 2, 3 and 5 showed complex patterns due to the mixed isomer
character of these compounds. In the 1H NMR spectra of 2 and 3
the aromatic and Pc protons appear between 7.38 and 9.47 ppm
and 7.48 and 9.21, respectively. The methyl protons which inte-
grated for 12 protons were observed at 3.78 ppm for 3 as a singlet.
Quaternization of 4 [23] was done by reaction with excess dimeth-
ylsulfate (DMS) as quaternization agent in DMF at 120 °C. Other
quaternizing agents such as methyl iodide did not work. However,
quaternization of 6 failed. The NMR spectra of the quaternized
phthalocyanine complex (5) showed unresolved patterns between
8.33 and 8.01 ppm integrating for a total of 24 protons. The methyl
protons which integrated for 12 protons were observed 3.79 ppm
for 5 as a singlet.
the determination of UD was ꢂ10% (determined from several UD
values).
2.5.2. Photodegradation quantum yields
For determination of photodegradation quantum yields, the
usual Eq. (6) was employed [34]:
ðC0 ꢀ CtÞVNA
UPd
¼
ð6Þ
IabsSt
where C0 and Ct in mol dmꢀ3 are the concentrations of 2, 3 or 5, be-
fore and after irradiation respectively; V is the reaction volume; S,
the irradiated cell area (2.0 cm2); t, the irradiation time; NA, the
Avogadro’s number and Iabs, the overlap integral of the radiation
source intensity and the absorption of 2, 3 or 5, (the action
spectrum) in the region of the interference filter transmittance.
The light intensity for photodegradation studies was 2.97 ꢃ 1016
photons sꢀ1 cmꢀ2
.
Elemental analysis results were also consistent with the pro-
posed structures of 2, 3 and 5 as shown in Section 2, with the per-
cent carbon values differing by less than 2% from the calculated
values. Quaternized phthalocyanines are very hygroscopic com-
pounds, so elemental analysis include some water.
3. Results and discussion
3.1. Synthesis and characterization
The synthetic procedure for novel phthalocyanines 2, 3 and 5 is as
outlined in Scheme 1. Complex 2 was prepared by the template
cyclotetramerization of 4-[2-thioquinoline]-phthalonitrile (1), and
anhydrous Zn(OAc)2 in 1-pentanol (reflux temperature and under
Ar atmosphere) and in the presence of DBU as a strong base. The
new zinc phthalocyanine (2) was purified by column chromatogra-
phy and a high yield (51%) was obtained. Complex 2 was also char-
acterized by elemental analysis together with spectral data (1H
NMR, FT-IR and UV–Vis). Quaternized zinc phthalocyanines (3 and
5) were synthesized by reactions of 2 or 4 with excess dimethylsul-
phate (DMS) as quaternization agent in DMF at 120 °C. The yield of
the quaternized complex 3 was 85%, for 5, the yield was 65%. The
compounds are very soluble in water, after reaction with DMS.
Generally, phthalocyanines derivatives are insoluble in com-
mon organic solvents and water, however introduction of substit-
uents on the ring can increase the solubility. Complexes 2, 4 and 6
showed high solubility in DMF, DMSO, THF, CHCl3, DCM, toluene
and acetone. Quaternized complexes 3 and 5 have good solubility
in water as well as DMSO and DMF. Both complexes are insoluble
in acetone and are slightly soluble in ethanol.
3.2. Ground state electronic absorption spectra
The UV–Vis spectra of complex 2 in different solvents (Fig. 1)
showed characteristic absorptions ranging from 685 to 690 nm in
the Q-band region (only results in DMSO and aqueous media are
shown in Table 1). When aggregation occurs, a band in the region
of 630–645 nm is observed in the electronic absorption spectrum
of MPcs as a result of the intramolecular interactions between
the Pc units [35–37]. Thus, the band at around 640 nm in DMSO
for 2 can be attributed to aggregation. Normally, DMSO is known
to prevent aggregation since it is strong coordinating solvent. How-
ever, it has been observed before that aggregation occurs in DMSO
for some MPc derivatives [17]. The aggregates in this case were
attributed to the rare J aggregates which are not usually observed
in aqueous media [17]. For complex 2 in DMSO, evidence of aggre-
gation was judged by the faster decrease of the high energy band
(due to H aggregates), Fig. 2a. Also addition of Triton X-100 to solu-
tions 2 in DMSO resulted in the decrease in the high energy band
due to the aggregates and the increase in the low energy band
In this study, complex 2 was isolated as a mixture of isomers, as
expected. The presence of isomers might be verified by the slight
broadening encountered in the UV–Vis absorption bands and
broadening in the 1H NMR. No attempt was made to separate the
isomers of 2, 3 and 5.
The characteristic vibrations corresponding to CN and thio-
ethers groups (CASAC) at 2229 cmꢀ1 and 664 cmꢀ1 were observed
for 1 in the FT-IR spectra. Aromatic CAH peaks were observed at
3072 and 3052 cmꢀ1 for the phthalonitrile (1). The 1H NMR spec-
trum of compound 1 showed signals with d ranging from 7.38 to
8.14, belonging to aromatic protons integrating for nine protons
as expected.
After conversion into zinc phthalocyanine derivations, the
characteristic CN stretch at 2229 cmꢀ1 of the phthalonitrile 1 dis-
appeared in the FT-IR spectrum, indicative of metallophthalo-
cyanine formation. The characteristic vibrations corresponding to
ether groups (CASAC) were observed at 686 (for 2), 682 cmꢀ1(for
3), 682 cmꢀ1 (for 5) and aromatic CAH stretching at ca.
3050 cmꢀ1 for the complexes 2, 3 and 5. Aliphatic CAH stretching
at ca. 2960 cmꢀ1 (for 3), 2944 cmꢀ1 (for 5), S@O stretching at 1231
and 1141 cmꢀ1 (for 3), 1259 and 1174 cmꢀ1 (for 5) and SAO
stretching at 617 cmꢀ1 (for 3), 614 cmꢀ1 (for 5) for complexes 3
and 5 are indicative of quaternization.
Fig. 1. UV–Vis absorption spectra of complex 2 in different solvents (concentration
ꢂ4 ꢃ 10ꢀ6 mol dmꢀ3).

A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
31
Table 1
Spectral parameters of 2–6 in DMSO and aqueous media.
Complex
Solvent
Q band kmax, (nm)
Log
e
Excitation kEx, (nm)
Emission kEm, (nm)
Stokes shift DStokes, (nm)
2
3
3
4
5
5
6
DMSO
688
689
687
685b
690
683
678b
5.11
5.24
5.12
5.21b
4.98
4.73
5.28b
688
688
686
686
689
684
677
701
704
700
698
704
702
689
13
15
13
13
14
19
11
DMSO
Water (Triton Xa)
DMSOb
DMSO
Water (Triton Xa)
DMSOb
a
Triton X = Triton X-100.
Values from Ref. [23].
b
a
1,60
1,40
1,20
1,00
0,80
0,60
0,40
0,20
0,00
E
A
400
450
500
550
600
650
700
750
800
Wavelength
b
Wavelength (nm)
Fig. 2. Absorption spectra of 2 in ((a) DMSO at different concentrations: (A) 2 ꢃ 10ꢀ6, (B) 4 ꢃ 10ꢀ6, (C) 6 ꢃ 10ꢀ6, (D) 8 ꢃ 10ꢀ6, (E) 10 ꢃ 10ꢀ6 mol dmꢀ3, (b) in DMSO and DMSO
containing Triton X-100 and (c) in toluene at different concentrations: (A) 2 ꢃ 10ꢀ6, (B) 4 ꢃ 10ꢀ6, (C) 6 ꢃ 10ꢀ6, (D) 8 ꢃ 10ꢀ6, (E) 10 ꢃ 10ꢀ6 mol dmꢀ3
.
due to the monomer, Fig. 2b. Surfactants such as Triton X-100
breaks up the aggregates. For 2 in other solvents (other than
DMSO), as concentration increased, the intensity of the Q band also
increased and there were no new bands due to the aggregated spe-
cies, Fig. 2c [38]. Lambert–Beer law was obeyed for these com-
pounds in the concentrations ranging from 2.0 ꢃ 10ꢀ6 to
1.0 ꢃ 10ꢀ5 mol dmꢀ3 as shown for 2 in toluene as an example,
Fig. 2c.

32
A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
c
3
2.5
2
E
3
2.5
2
1.5
1
0.5
0
y = 275000x + 0.023
R² = 0.9977
1.5
1
0
0.000005
0.00001
0.000015
Concentration
0.5
0
A
400
450
500
550
600
650
700
750
800
Wavelength (nm)
Fig. 2 (continued)
Aggregation behavior of Pc is depicted as a coplanar association
not affected by excitation, Table 1 [39]. Fluorescence emission
peaks were observed at: 701 nm for 2, 704 nm for 3 and 704 nm
for 5 in DMSO (Table 1). The Stokes’ shifts range from 11 to
15 nm, which is usual for ZnPc derivatives [40].
of rings progressing from monomer to dimer and higher order
complexes and it is dependent on concentration, nature of solvent
and substituents, metal ions and temperature [37]. Aggregation is
not desired in MPc complexes since aggregates are generally
photoinactive. Aggregation is more enhanced for peripherally
substituted MPc complexes when compared to non-peripherally
substituted ones.
The UV–Vis spectrum of the quaternized metallophthalocya-
nines (3 and 5) show extensive aggregation in water with the pres-
ence of two main bands one at 680 nm (weak) and due to
monomeric species and the other at 640 nm due to aggregated spe-
cies. Surfactants are known to decrease aggregation. Addition of a
drop of Triton X-100 to an aqueous solution of 3 and 5 brought
about increase in intensity of the low energy side of the Q band
(687 nm for 3, Fig. 3a and 683 nm for 5, Fig. 3b). However, some
aggregation of 3 and 5 still remained in solution even after addition
of Triton X-100, as shown in Fig. 3a and b. Complexes 3 and 5
exhibited lower aggregation properties in DMSO than in water plus
Triton X-100 (Fig. 3c).
The fluorescence quantum yields (UF) of 2, 3 and 5 are given in
Table 2. Fluorescence quantum yield (UF) values for 2, 3 and 5 in
DMSO are lower than those for unsubstituted ZnPc (UF = 0.20,
[40]) and are also lower than those of the ZnPc derivatives substi-
tuted with quaternized thiopyridine group in aqueous media con-
taining small amounts of pyridine for monomerization [19]. This
implies that the presence of quinoxalinyl and arylthio substituents
caused some fluorescence quenching of the parent ZnPc. Complex
2 has higher fluorescence quantum yield (UF) values than complex
3 in DMSO. While quaternized complex (3) has high UF value in
water (plus Triton X-100) compared to in DMSO due to aggregation
in the latter solvent. Quaternized complex (5) showed similar UF
value in DMSO compared to in water (plus Triton X-100) (Table
2). For complexes 4 and 6 the UF values are typical of MPc com-
plexes as discussed in the literature [23].
3.4. Triplet quantum, yields and lifetimes
3.3. Fluorescence spectra, and quantum yields
Triplet quantum yield (UT) is the fraction of absorbing mole-
cules that undergo intersystem crossing to the metastable triplet
excited state. Therefore, factors which induce spin–orbit coupling
will certainly populate the triplet excited state. Transient spectrum
for complex 6 in DMSO is shown in Fig. 5, and shows a maximum
at 490 nm, hence triplet lifetimes and yields were determined at
this wavelength for complex. All complexes showed triplet absorp-
tion in the same region (490–500 nm). Fig. 6 displays the triplet
decay curves of the complexes (using complexes 3 and 5 in water
The absorption and fluorescence emission and excitation spec-
tra of 2 and 3 are similar in DMSO and water (plus Triton X-100)
for 3. Fig. 4 shows the absorption, fluorescence excitation and
emission spectra of 2, 3 and 5 in DMSO (and in water for 3). Note
that at the low concentrations employed for fluorescence, there is
reduced aggregation in DMSO compared to Fig. 1. The excitation
spectrum was not exactly similar to absorption spectrum due to
aggregation in complex 2. The excitation spectrum was a mirror
image of the fluorescent spectra for 2. For complexes 3 and 5 in
DMSO and in water (plus Triton X-100), there was a clear narrow-
ing of the excitation spectra compared to absorption spectra due to
aggregation evident in the latter. The proximity of the wavelength
of each component of the Q band absorption to the Q band maxima
of the excitation spectra for both complexes suggest that the nucle-
ar configurations of the ground and excited states are similar and
as examples). Complex 2 has longer triplet life times (
plex 3 in DMSO and DMF. The triplet life time for complex 2
(171 s), 3 (31 s) and 60 s (for 5) in DMSO are lower than for
unsubstituted ZnPc (350 s) in DMSO [22] suggesting that the sub-
stituents quench the triplet state. In water (plus Triton X-100) the
triplet lifetime of 5 was 12 s, a value which is lower than the one
determined in DMSO, due to aggregation since even in the
sT) than com-
l
l
l
l
l

A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
33
a
Complex 5
b
Wavelength (nm)
Fig. 3. UV–Vis absorption spectra (a) 3 in water and in water containing Triton X-100 and (b) 5 in water and in water containing Triton X-100 (c) 2–6 in DMSO.
presence of Triton X-100, aggregation still exists for 5 in water
(Fig. 3b). The sT values value for complex 3 in aqueous media is
higher than that of thiopyridine substituted ZnPc [19], though dif-
ferent monomerizing agents were employed.
containing fluorinated substituents has a large triplet quantum
yield due to the combination of enhanced intersystem crossing
by the fluorines. Halogens are known to increase intersystem
crossing [41].
The triplet quantum yields (UT) for substituted complex 2 in
DMSO (UT = 0.79) are high compared to complex 3 (UT = 0.75),
complex 5 (UT = 0.45) and ZnPc standard in DMSO (UT = 0.65 for
ZnPc in DMSO). While water soluble compound (3) bearing thio-
quinoline substituent showed high triplet quantum yield value in
water (plus Triton X-100) (UT = 0.80), the other water soluble com-
plex (5) bearing fluoro functional thiopyridine has low triplet
quantum yield value (UT = 0.32) in the same solvent mixture. A
low UT value (=0.43) was obtained for the thiopyridine substituted
ZnPc [19]. Triplet quantum yields and life times for complexes 4
and 6 in DMSO were discussed in the literature [23]. Complex 3
3.5. Photochemical properties
3.5.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield UD is a measure of singlet oxygen
generation and the UD values were obtained using Eq. (5). Singlet
oxygen quantum yields were studied in DMSO and water (for 3 and
5) using a chemical method (DPBF and ADMA). Fig. 7 shows spec-
tral changes observed during photolysis of complex 2 in DMSO in
the presence of DPBF. The disappearance of DPBF was monitored
using UV–Vis spectral changes. There were no changes in the Q

34
A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
c
1,2
1
DMSO
Complex 2
Complex 3
Complex 4
Complex 5
Complex 6
0,8
0,6
0,4
0,2
0
400
450
500
550
600
650
700
750
800
Wavelength (nm)
Fig. 3 (continued)
Fig. 4. Absorption (i), excitation (ii) and emission (iii) spectra of the compounds 2 (a) and 3 (b) in DMSO, (c) 3 in water containing Triton X-100 and (d) 5 in DMSO. Excitation
wavelength = 688 nm for (2), 688 nm for (3) and 689 for (5) in DMSO and 686 nm for (3) in water containing Triton X-100.

A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
35
c
Complex 3 in Water plus Triton X-100
1,2
1
0,8
0,6
0,4
0,2
0
600
620
640
660
680
700
720
740
760
780
800
Wavelength (nm)
Complex 5 in DMSO
d
1.2
1
0.8
0.6
0.4
0.2
0
(iii)
(ii)
(i)
600 620 640 660 680 700 720 740 760 780 800
Wavelength (nm)
Fig. 4 (continued)
Table 2
Photophysical and photochemical properties of 2–6 in DMSO and aqueous media.
Complex
Solvent
UF ( 0.02)
sT
(l
s)
UT ( 0.03)
UIC
Ud (ꢃ10ꢀ5
)
UD ( 0.01)
S
D
2
3
3
4
5
5
6
DMSO
DMSO
0.10
0.03
0.08
0.10b
0.01
0.02
0.13b
171
31
110
140b
60
0.79
0.75
0.80
0.86b
0.45
0.32
0.74b
0.11
0.22
0.12
0.04
0.53
0.67
0.13
3.98
11
0.56
0.52
0.34
0.68
0.41
0.24
0.63
0.71
0.69
0.43
0.79
0.91
0.75
0.85
Water (Triton Xa)
DMSO
18.7
3.57
0.24
7.05
0.74
DMSO
Water (Triton Xa)
DMSO
12
210b
a
Triton X = Triton X-100.
Values from Ref. [23].
b
band intensities during the UD determinations, confirming that
complexes are not degraded during singlet oxygen studies. The
complexes (4 and 6) in this work were selected because they bore
similar substituents, however they differed in their ether (CAOAC)
and thio (CASAC) bond linkages. We investigated the effect of this
difference on the photophysicochemical properties. The UD values
are: 2 (UD = 0.56), 3 (UD = 0.52), 4 (UD = 0.68), 5 (UD = 0.41) and 6
(Table 2), corresponding to UT values. As was the case for UT values,
the presence of sulfur atom may promote ISC, thus leading to higher
singlet oxygen quantum yield for [42] 4. The UD values of complexes
3 and 5 in DMSO are higher than in water plus Triton X-100.
The magnitude of the S (=UD/UT) represents the efficiency of
D
quenching of the triplet excited state by singlet oxygen. Compound
2 displayed S near unity in DMSO. However, complex 3 showed
D
(UD = 0.63) in DMSO and for 3 (UD = 0.34), 5 (UD = 0.24) in water
lower values of S suggesting less efficient transfer of energy to
D
plus Triton X-100. The UD values of complex 4 were higher than all
complexes 3–6 in DMSO, Table 2. The UD values for 2, 4 and 6 are
lower or almost equal when compared to unsubstituted ZnPc in
DMSO (0.67 [30]). UD values of the arylthio-substituted complex
4 was larger than that of the aryloxy-substituted complex 6
the ground state oxygen, Table 2. This resulted in a lower singlet
oxygen quantum yield even though complex
3
had
a high
(UT = 0.80) triplet quantum yield. Compounds 4, 5 and 6 displayed
S
D
of near unity in DMSO implying efficient quenching of the trip-
let states by singlet oxygen (Table 2).

36
A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
0.2
-0.3
-0.8
-1.3
-1.8
-2.3
used. Stable ZnPc molecules show values as low as 10ꢀ6 and for
unstable molecules, values of the order 10ꢀ3 have been reported
[43]. Photobleaching quantum yield value of complex 2 is lower
than complex 3 in both DMSO, hence complex 2 are more stable
than complex 3 in same solvent. Stability of complex 3 in water
is lower than in DMSO, while complex 5 is more stable in DMSO
than in water. In both cases, the observation contradicts what is
expected in terms of singlet oxygen quantum yields, where high
UD values should result is higher degradation, since it is believed
that photodegradation is a singlet oxygen mediated process [33].
The arylthio-substituted complex 4 is less stable than the corre-
sponding aryloxy-substituted complex 6 in DMSO. The electronic
effect of the substituents could explain the slight variation in the
Ud values, i.e. the arylthio groups are more electron-donating than
their corresponding aryloxy groups and thus tend to enhance the
probability of the photobleaching process [44]. While the most sta-
ble complex among the all complexes in DMSO is 5, complex 3 is
the least stable complex in the solvent.
400
500
600
700
800
Wavelength (nm)
Fig. 5. Transient difference spectrum of complex 6 in DMSO.
3.5.2. Photodegradation quantum yields
Photodegradation is a process where a phthalocyanine is de-
graded under light irradiation. It can be used to determinate MPcs
stability and this is especially important for those molecules in-
tended for use as photocatalysts. The photobleaching stabilities
of complexes 2–6 were determined in DMSO and in water for 3
and 5 by monitoring the decrease in the intensity of the Q band un-
der irradiation with increasing time. The spectral changes observed
for the complexes 2–6 during irradiation are shown in Fig. 8 (using
complex 2 as an example in DMSO). There was no phototransfor-
mation into products which absorb in the visible region. The pho-
todegradation quantum yield (Ud) values for the complexes are
shown in Table 2 and are of the order of 10ꢀ5–10ꢀ4. These values
show that the molecules are of moderate stability in all solvents
4. Conclusion
In this study, we have described the syntheses, spectral and
photophysicochemical properties of soluble peripheral tetrakis
[2-thioquinoine]-substituted zinc phthalocyanines (2) and its
quaternized derivative (3) and quaternized 4-(tetra-5-(trifluoro-
methyl)-2-thiopyridinephthalocyaninato) zinc(II) (5). While com-
plex 2 has good solubility in common organic solvents and is
monomeric in solution (except in DMSO), complexes 3 and 5 are
highly soluble in water as well as DMSO and DMF. It is important
to mention here that for high-technological applications the
a
0.20
0.16
0.12
0.08
0.04
0.0001
0.0002
0.0003
0.0004
0.0005
Time (s)
b
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.0001
0.0002
0.0003
0.0004
0.0005
Time (s)
Fig. 6. Mono-exponential triplet decay profile for complex 3 (a) and complex 5 (b) in water.

A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
37
Complex 2 in DMSO
0 sec
1,4
1,2
1
50 sec
0,8
0,6
0,4
0,2
0
350
400
450
500
550
600
650
700
750
800
Wavelength (nm)
Fig. 7. A typical spectra for the determination of singlet oxygen quantum yield. This figure was for complex 2 in DMSO at a concentration of 6 ꢃ 10ꢀ6 mol dmꢀ3
.
1
Complex 2
0 min.
0.8
1.8E-09
1.6E-09
1.4E-09
25 min.
1.2E-09
1E-09
0.6
8E-10
y = 1.72E-4
6E-10
R² = 0.989
4E-10
2E-10
2E-25
0.4
-2E-10
0
0.000005
0.00001
0.000015
0.00002
time, s
0.2
0
350
400
450
500
550
600
650
700
750
800
Wavelength (nm)
Fig. 8. The photodegradation of compound 2 in DMSO showing the disappearance of the Q band at 5 min intervals.
solubility of phthalocyanines is important. The introduction of [2-
thioquinoine] and with-drawing fluoro-functional groups with thio
and oxo linkages on the ring results in high triplet quantum yields
(ranging from 0.32 to 0.86 in DMSO and water (for 3 and 5)) and
high singlet oxygen quantum yields (0.56 for 2, 0.68 for 4 and
0.63 for 6 in DMSO). Quaternized complex 5 showed lower triplet
quantum and singlet oxygen quantum yields values than unquat-
ernized 4 and 6 in DMSO (UT = 0.45, UD = 0.41 for 5) and water
complexes show potential as Type II. Photophysical and photo-
chemical properties of the phthalocyanines complexes 2–6 are
very useful for PDT. Complexes 3 and 5 are even more appropriate
due to water solubility.
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.
(UT = 0.32, UD = 0.24, for 5) due to aggregation. Singlet oxygen
quantum yields, which give indication of the potential of the com-
plexes as photosensitizers in applications where singlet oxygen is
required (Type II mechanism) ranged from 0.34 to 0.68. Thus, these

38
A. Erdog˘mußs, T. Nyokong / Journal of Molecular Structure 977 (2010) 26–38
[23] A. Erdog˘mußs, S. Moeno, C. Litwinski, T. Nyokong, Photochem. Photobiol. A:
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