Novel, soluble, FluXoro functional substituted zinc phthalocyanines; synthesis, characterization and photophysicochemical properties

Article abstract of DOI:10.1016/j.dyepig.2010.01.001

Three novel phthalonitriles and the respective, peripheral tetrakis zinc phthalocyanines were synthesized and characterized using elemental analysis, IR, ¹H NMR, mass spectra and electronic spectroscopy. The phthalocyanines displayed good solubility in organic solvents such as CHCl₃, DCM, DMSO, DMF, THF and toluene. The presence of a long chain fluorine substitituent was found to result in reduced aggregation. The singlet oxygen, photodegradation, fluorescence quantum yield, triplet quantum yield and triplet life time of the complexes in toluene were determined. The effect of fluoro-functional groups on the photophysical and photochemical parameters of the zinc(II) phthalocyanines are also reported. Fluorescence quantum yields for the complexes ranged from 0.021 to?0.041.

Full text of DOI:10.1016/j.dyepig.2010.01.001

Dyes and Pigments 86 (2010) 174e181
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Novel, soluble, FluXoro functional substituted zinc phthalocyanines; synthesis,
characterization and photophysicochemical properties
a
,
,
Ali Erdogmus¸ 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:
Three novel phthalonitriles and the respective, peripheral tetrakis zinc phthalocyanines were synthe-
sized and characterized using elemental analysis, IR, 1H NMR, mass spectra and electronic spectroscopy.
The phthalocyanines displayed good solubility in organic solvents such as CHCl3, DCM, DMSO, DMF, THF
and toluene. The presence of a long chain fluorine substitituent was found to result in reduced aggre-
gation. The singlet oxygen, photodegradation, fluorescence quantum yield, triplet quantum yield and
triplet life time of the complexes in toluene were determined. The effect of fluoro-functional groups on
the photophysical and photochemical parameters of the zinc(II) phthalocyanines are also reported.
Fluorescence quantum yields for the complexes ranged from 0.021 to 0.041
Received 16 November 2009
Received in revised form
6 January 2010
Accepted 8 January 2010
Available online 18 January 2010
Keywords:
Zinc phthalocyanines
Triplet quantum yield
Fluorescence quantum yield
Singlet oxygen
Ó 2010 Elsevier Ltd. All rights reserved.
Photodynamic therapy
1. Introduction
peripheral of the Pc ring enhances solubility [17,18]. Recently,
fluorinated MPcs are receiving a great deal of attention [19e23].
Metallophthalocyanines (MPcs) have potential applications in
many areas such as in medicinal and material science [1e3]. MPcs
enjoy usage in printing inks, catalysis, display devices, data
storage, chemical sensors, gas sensors, solar cells, organic light
emitting devices (OLED) and photonic devices [4e6]. Owing to
their strong and long-wavelength absorption, highly efficient
reactive oxygen specie generation (ROS) and ease of chemical
modification, phthalocyanines have emerged as a promising class
of second-generation photosensitizers for photodynamic therapy
(PDT), [7e16]. Over the last decade, a substantial number of
phthalocyanine-based photosensitizers have been prepared and
evaluated for their photodynamic activity, with the focus being on
silicon, zinc and aluminium analogues as a result of their desirable
photophysical properties.
Fluorinated phthalocyanines have been reported to show
improved photosensitizer activity for PDT compared to non-
fluorinated derivatives [24,25]. However, the study of photochem-
ical and photophysical properties of fluorinated MPc complexes is
still very limited. Our previous papers have described synthesis,
photophysical and photochemical properties of zinc phthalocya-
nines carrying various substituents [26e28]. In this work, we
describe the photophysical and photochemical properties of the
three novel zinc-phtalocyanines peripherally tetra substituted
with fluoro groups (Scheme 1, complexes 4e6), which show
good solubility in common organic solvents such as chloroform,
dichloromethane, tetrahydrofuran (THF), dimethylformamide
(DMF) and toluene. The effect of different fluoro groups on the
photophysical and photochemical properties of ZnPc will be eval-
uated in toluene. Fluorine substituted MPc complexes are of
interest since conjugation (or its lack) with the Pc ring influences
photophysical properties [29] therby enabling the design of MPc
complexes with optimal photophysical properties. The novel zinc
phthalocyanines described herein displayed good photophysical
and photochemical properties with high singlet oxygen quantum
yield in toluene. The presence of sulfur in the complexes is expected
to result in red shifting of the Q band.
Unsubstituted phthalocyanines are generally insoluble in
organic solvents. The introduction of different types of substituents
such as alkyl, alkoxyl, phenoxyl and macrocyclic groups into the
* Corresponding author. Tel.: þ27 46 6038260; fax: þ27 46 6225109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.01.001

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A. Erdogmus¸, T. Nyokong / Dyes and Pigments 86 (2010) 174e181
175
CN
CN
O2N
SH
N
OH
F3C
F3C(F2C)7H2C
S
(i)
(i)
(i)
CF3
N
F3C
O
CN
CN
S
CN
CN
N
SH
F3C(F2C)7H2C
S
N
1
3
F3C
N
S
CN
CN
(ii)
(ii)
N
2
OR1
SR3
(ii)
N
N
N
N
Zn
N
N
N
N
N
N
R1O
OR1
N
R3S
Zn
N
SR3
SR2
N
N
N
N
N
N
N
N
N
Zn
N
OR1
SR3
R2S
N
SR2
6
4
N
SR2
5
R
=
3
N
N
R
=
1
R
=
S
2
CH2(CF2)7CF3
N
CF3
CF3
Scheme 1. Synthetic route of three phthalonitriles (1, 2 and 3), (i) DMF, K2CO3, 24h; and their zinc phthalocyanines derivatives (4, 5 and 6) (ii) anhydrous Zn(Ac)2, pentanol, 15h,
DBU, argon atm.
2. Experimental
potassium carbonate, and zinc acetate were purchased from
Aldrich.
2.1. Materials and equipment
FTIR spectra (KBr pellets) were recorded on a PerkineElmer
spectrum 2000 FTIR spectrometer. UV/Vis spectra were recorded
on a Cary 500 UV/Vis/NIR spectrophotometer. 1H and spectra were
obtained in CDCl3 using a Bruker EMX 400 NMR spectrometer.
Elemental analyses were done on Vario Elementar EL III. Fluores-
cence spectra were recorded on the Varian Eclipse spectro-
fluoremeter. 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 methanol).
Dimethyl sulfoxide (DMSO), N,N0-dimethylformamide (DMF),
chloroform (CHCl3), tetrahydrofuran (THF), methanol (MeOH),
dicholoromethane (DCM), 1-pentanol, n-hexane, acetone and
toluene were purchased from SAARCHEM; zinc phthalocyanine
(ZnPc), 1,2-diphenyisobenzofuran (DPBF), 4-nitrophthalonitrile,
7-(trifluoromethyl)quinoline-4-thiol, 4-(trifluoromethyl)pyrimi-
dine-2-thiol, 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-
decylthio)phenol, 1,8-diazabicyclo[5.4.0] undec-7-ene (DBU),

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A. Erdogmus¸, T. Nyokong / Dyes and Pigments 86 (2010) 174e181
176
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 oscilloscope
(Tektronix TDS 360); the kinetic curves were averaged over 256
laser pulses. 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 radia-
tions 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. MALDI-TOF
mass spectra were recorded using an Applied Biosystems Voyager-
DE STR at the University of Stellenbosch in Cape Town, with
2,5-dihydroxy benzoic acid as matrix. The mass spectra for phtha-
lonitriles (1e3) were acquired on a Bruker Daltonics, MicrOTOF
mass spectrometer equipped with an electronspray ionization (ESI)
source.
carbonate, 1.52 g (11.00 mmol). Yied: 0.60 g (38%). IR spectrum
(cmꢀ1): 3090, 3047 (Ar-CH), 2235 (C^N), 1582 (C]C), 1454, 1353
(CeF), 1288, 1065, 974, 884, 778, 679 (CeSeC). 1H NMR (CDCl3):
d
¼ 9.03e8.89 (m, 1H, Ar-H), 8.69-8-53 (m, 2H, Ar-H), 8.43e8.11 (m,
2H, Ar-H), 7.85e7.53 (m, 3H, Ar-H). Calcd for C18H8F3N3S C, 60.84; H,
2.27; N, 11.83; S, 9.02%. Found: C, 60.91; H, 2.32; N, 11.78; S, 8.95%.
MS (ESI-MS) m/z: Calc. 355.3; Found: 378.1 [M þ Na]þ.
2.2.4. (4)-tetra[(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
heptadecafluorodecylthio)phenoxy]-phthalocyaninato zinc(II) (4)
Compound 1 (0.50 g, 0.72 mmol), anhydrous zinc acetate
(0.16 g, 0.72 mmol) and 2 mL of dry 1-pentanol were placed in
a standard Schlenk tube in the presence of 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (0.45 mL, 0.29 mmol) under a nitrogen
atmosphere and held at reflux temperature for 15 h. After cooling
to room temperature, the reaction mixture was precipitated by
adding it drop-wise into water. The crude product was precipi-
tated, collected by filtration and washed with water, hexane,
ethanol and methanol and then dried. The crude green product
was further purified by chromatography over a silica gel column
using THF, CHCl3 and a mixture of THF and CH2Cl2 (1:50 by
volume), as eluent respectively. Yield: 45 mg (10%). UVeVis
2.2. Synthesis
2.2.1. 4-[(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
heptadecafluorodecylthio)phenoxy]-phthalonitrile (1)
4-Nitrophthalonitrile (0.30 g 1.75 mmol) was dissolved in dry
DMF (15 mL) under argon and 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
heptadecafluorodecylthio)phenol (1.00 g 1.75 mmol) was added.
After stirring for 30 min at room temperature, finely ground
anhydrous potassium carbonate (0.73 g 5.25 mmol) was added in
portions during 2 h with efficient stirring. The reaction mixture was
stirred under argon atmosphere at room temperature for 24 h after
which time, the ensuing mixture was poured into 100 mL iced water
and the precipitate filtered off, washed with water and methanol
and then dried. The crude product was chromatographed over
a silica gel column using a mixture of CHCl3:MeOH (100:5 (v:v)) as
eluent, giving a powder of 4-[(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
heptadecafluorodecylthio)phenoxy]-phthalonitrile (1). Finally, the
pure powder was dried in a vacuum. Yield: 0.78 g (65%). IR spectrum
(cmꢀ1): 3075 (Ar-CH), 2234 (C^N), 1602 (C]C), 1584, 1486, 1370
(CeF), 1314, 1249, 1083 (CeOeC), 1036, 954, 778, 664 (CeSeC). 1H
(toluene): lmax nm (log 3) 355 (4.66), 613 (4.39), 679 (5.11). IR
spectrum (cmꢀ1): 3073 (Ar-CH), 2935, 2856 (CH), 1589 (C]C),
1487, 1398, 1334 (CeF), 1237, 1088 (CeOeC), 952, 815, 745, 731,
617 (CeSeC). 1H NMR (CDCl3):
d
¼ 8.42e7.26 (28H, m, Ar-H),
3.32e3.21 (m, 8H, CH2), 2.61e2.49 (m, 8H, CH2). Calcd for
C96H44F68N8O4S4Zn: C, 41.33; H, 1.85; N, 3.92; S, 4.49%. Found: C,
42.39; H, 2.00; N, 4.09; S, 4.37%. MS (ESþ), (m/z): Calc. 2858;
Found: 2849 [M ꢀ 9H].
2.2.5. (4)-tetra-[4-(Trifluoromethyl)pyrimidine-2-thio]
phthalocyaninato zinc(II) (5)
The synthesis and purification of 5 was as outlined for 4, except
compound 2 (0.30 g, 0.10 mmol) was employed instead of complex
1. The amounts of the other reagents were anhydrous zinc acetate
(0.21 g, 0.10 mmol), dry 1-pentanol (2 mL) and DBU (0.23 mL,
0.15 mmol). Yield: 35 mg (12%). UVeVis (toluene): lmax nm (log 3)
NMR (CDCl3):
d
¼ 7.77 (d, J ¼ 8.70 Hz, 1H, Ar-H), 7.50 (d, J ¼ 8.76 Hz,
368 (4.70), 622 (4.42), 684 (5.12). IR spectrum (cmꢀ1): 3066 (Ar-
2H, Ar-H), 7.34e7.10(m, 4H, Ar-H), 3.18 (t, 2H, CH2), 2.54e2.40 (m,
2H, CH2). Calcd for C24H11F17N2OS: C, 41.21; H,1.73; N, 4.01; S, 4.58%.
Found: C, 41.34; H, 1.79; N, 3.97; S, 4.65%. MS (ESI-MS) m/z: Calc.
698.4; Found: 721.1 [M þ Na]þ.
CH), 1618 (C]C), 1431, 1392, 1363 (C-F), 1231, 1026, 930, 862, 812,
772, 619 (CeSeC). 1H NMR (CDCl3):
Calcd for C52H20F12N16S4Zn: C, 48.40; H, 1.56; N, 17.37; S, 9.94%.
Found: C, 49.15; H, 1.67; N, 17.79; S, 10.32%. MS (ESþ), (m/z): Calc.
1290.5; Found: 1291.6 [MHþ].
d
¼ 8.79e7.11 (20H, m, Ar-H).
2.2.2. 4 [4-(Trifluoromethyl)pyrimidine-2-thio]-phthalonitrile (2)
The synthesis of 2 was similar to that of 1, except 4-(trifluoro-
methyl)pyrimidine-2-thiol (1.00 g 5.55 mmol) was employed
instead of -(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorode-
cylthio) phenol. The amounts of the other reagents were: 4-nitro-
phthalonitrile, 0.96 g (5.55 mmol) and anhydrous potassium
carbonate, 1.92 g (13.88 mmol).
2.2.6. (4)-tetra-[7-(trifluoromethyl)quinoline-4-thio]
phthalocyaninato zinc(II) (6)
The synthesis and purification of 6 was as outlined for 4, except
compound 3 (0.50 g, 1.41 mmol) was employed instead of complex
1. The amounts of the other reagents were anhydrous zinc acetate
(0.30 g, 1.41 mmol), dry 1-pentanol (3 mL) and DBU (0.45 mL,
Yied: 0.40 g (23%). IR spectrum (cmꢀ1): 3081, 3021 (Ar-CH),
2227 (C^N), 1572 (C]C), 14 377, 1386 (CeF), 1232, 1034, 990, 866,
0.29 mmol). Yield: 35 g (7%). UVeVis (toluene): lmax nm (log 3) 360
(4.76), 619 (4.49), 689 (5.17). IR spectrum (cmꢀ1): 3079 (Ar-CH),
799, 719, 661 (CeSeC). 1H NMR (CDCl3):
d
¼ 8.41 (s, 1H, Ar-H), 7.76
1617 (C]C), 1463, 1385, 1364 (CeF), 1233, 1069, 980, 907, 853, 833,
(d, J ¼ 4.83 Hz, 1H, Ar-H), 7.49e7.06 (m, 3H, Ar-H). Calcd for
C13F3H5N4S: C, 50.98; H, 1.65; N,18.29; S, 10.47%. Found: C, 50.93; H,
1.71; N, 18.23; S, 10.53%. MS (ESI-MS) m/z: Calc. 306.3; Found: 329.1
[M þ Na]þ.
741, 618 (CeSeC). 1H NMR (CDCl3):
Calcd for C72H32F12N12S4Zn: C, 58.16; H, 2.17; N, 11.31; S, 8.63%.
Found: C, 59.11; H, 2.32; N, 12.04; S, 8.79%. MS (ESþ), (m/z): Calc.
1468.8; Found: 1489.6 [MHþ].
d
¼ 8.92e7.18 (32H, m, Ar-H).
2.2.3. 4-[7-(Trifluoromethyl)quinoline-4-thio]-phthalonitrile (3)
The synthesis of 3 was similar to that of 1, except 7-(tri-
fluoromethyl)quinoline-4-thiol (1.00 g 4.40 mmol) was employed
instead of 4-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-
decylthio) phenol. The amounts of the other reagents were: 4-
nitrophthalonitrile, 0.76 g (5.55 mmol) and anhydrous potassium
2.3. Photophysical studies
2.3.1. Fluorescence quantum yields
Fluorescence quantum yields (FF) were determined by the
comparative method [30,31], (Eq. (1)):

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A. Erdogmus¸, T. Nyokong / Dyes and Pigments 86 (2010) 174e181
177
F$AStd$n2
F
2.4.2. Photodegradation quantum yields
For determination of photodegradation quantum yields, Eq. (6)
was employed [32,35e37]:
FF
¼
FFðStdÞ
(1)
Std$A$n2Std
where F and FStd are the areas under the fluorescence emission
curves of 4 to 6 and the standard, respectively. A and AStd are the
respective absorbances of the sample and standard at the excitation
wavelengths (which was w0.05 in the solvent used), and n and nStd
are the refractive indices of solvents used for the sample and
standard, respectively. Unsubstituted ZnPc in toluene (FF ¼ 0.07)
[32], was employed as the standard.
ðC0 ꢀ CtÞ V NA
FPd
¼
(6)
Iabs S t
where C0 and Ct in mol dmꢀ3 are the concentrations of 4 to 6 before
and after irradiation respectively; V is the reaction volume; S, the
irradiated cell area (2.0 cm2); t, the irradiation time; NA, the Avo-
gadro's number and Iabs, the overlap integral of the radiation source
intensity and the absorption of 4 to 6 (the action spectrum) in the
region of the interference filter transmittance. The light intensity
2.3.2. Triplet quantum yields and lifetimes
for photodegradation studies was 5 ꢁ 1016 photons sꢀ1 cmꢀ2
.
The solutions for triplet quantum yields and lifetimes were
introduced into a 1.0 mm pathlength UV/visible spectrophoto-
metric cell, deaerated using nitrogen and irradiated at the Q band
maxima. Triplet state quantum yields (FT) of 4 to 6 were deter-
mined by the triplet absorption method [33], using zinc phthalo-
cyanine (ZnPc) as a standard, Eq. (2):
3. Results and discussion
3.1. Syntheses and characterization
The synthetic routes to novel phthalocyanines (4 to 6) are
showed in Scheme 1. These complexes were prepared by the
template cyclotetramerization of 4-[(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,
10-heptadecafluorodecylthio)phenooxy]-phthalonitrile (1), 4-[4-
(trifluoromethyl)pyrimidine-2-thio]-phthalonitrile (2), 4-[7-(tri-
fluoromethyl)quinoline-4-thio]-phthalonitrile (3) and anhydrous
Zn(OAc)2 in the presence of 1-pentanol and DBU (as a strong base)
at reflux temperature under argon atmosphere. 2(3),9(10),16(17),23
(24)-Tetra-substituted phthalocyanines can be synthesized from 4-
substituted phthalonitriles [1]. A mixture of four possible structural
isomers is obtained. The four probable isomers can be designed
by their molecular symmetry as C4h, C2v, Cs and D2h. The 2(3)-
substituted compounds always occur in the expected statistical
mixture of 12.5% C4hꢀ, 25%C2vꢀ, 50%Csꢀ and 12.5%D2hꢀ isomer [39].
In this study, synthesized tetra-(triethyleneoxythia) substituted
phthalocyanine compounds are obtained as isomer mixtures as
expected. No attempt was made to separate the isomers of
complexes 4 to 6. All of these new zinc phthalocyanines were
purified by column chromatography. They were obtained in a low
yield (10% for 4, 12% for 5, and 7% for 6) and were characterized by
elemental analysis together with the spectral data (1H NMR, FTIR,
mass and UVevisible spectroscopies). The characterization data of
the new compounds are consistent with the assigned formula.
Generally, phthalocyanine complexes are insoluble in most
organic solvents; however introduction of substituents on the ring
increases the solubility. All phthalocyanine complexes (4 to 6)
exhibited excellent solubility in organic solvents such as dichloro-
methane, chloroform, THF, toluene, DMF, DMSO. Complex 4, in
particular, showed high solubility in these solvents (except DMSO)
due to long fluoro chain.
D
D
AT$3STtd
FT
¼
FSTtd
$
(2)
Std
3
$
T
AT
where
D
AT and
D
ASTtd are the changes in the triplet state absor-
bances of 4 to 6 and the standard, respectively. 3T and 3STtd are the
triplet state molar extinction coefficients for 4 to 6 and the stan-
dard, respectively. FSTtd is the triplet quantum yield for the standard,
ZnPc (FT ¼ 0.65 in toluene [34]). 3T and 3STtd were determined from
the molar extinction coefficients of their respective ground singlet
state (3S and 3SStd) and the changes in absorbances of the ground
singlet states (DAS and
D
ASStd), according to Eq. (3):
D
D
AT
AS
3T
¼
3S
$
(3)
Quantum yields of internal conversion (FIC) were obtained from
Eq. (4), which assumes that only three processes (fluorescence,
intersystem crossing and internal conversion), jointly deactivate
the excited singlet state of the 4 to 6 molecules.
FIC ¼ 1 ꢀ ðFF
þ
FT
Þ
(4)
2.4. Photochemical studies
2.4.1. Singlet oxygen quantum yields
Quantum yields of singlet oxygen photogeneration were deter-
mined as previously explained in detail [32,35e37] in air (no
oxygen bubbled) using the relative method with ZnPc as reference
and DPBF as chemical quencher for singlet oxygen, using Eq. (5):
RDPBFISabtds
The characteristic vibrations corresponding to CN were
observed at 2234, 2227 and 2235 cmꢀ1 for 1, 2 and 3 respectively.
The CeOeC vibration for 1 was observed at 1083cmꢀ1, the thio
ethers (CeSeC) for 1, 2 and 3 at 664 and, 661, 679 cmꢀ1, respec-
tively. Aromatic CeH peaks occurred above 3050 cmꢀ1 for all the
phthalonitriles. The 1H NMR spectrum of the compounds 1, 2 and 3
FD
¼
FSDtd
$
(5)
Std
R
Iabs
DPBF
where FSDtd is the singlet oxygen quantum yield for the standard,
Std
ZnPc (FD ¼ 0.58 in toluene [32]). RDPBF and R
are the DPBF
DPBF
photobleaching rates in the presence of 4 to 6 and the standard
respectively. Iabs and ISabtds are the rates of light absorption by 4 to 6
and the standard respectively. To avoid chain reactions induced by
DPBF in the presence of singlet oxygen [38], the concentration of
showed signals with
d ranging from 7.06 to 9.03, belonging to
aromatic protons and 2.40e3.18 ppm belonging to aliphatic H for
just compound 1 integrating for a total of 11 protons for 1, 5 protons
for 2, and 8 protons for 3 as expected.
In the mass spectra of phthalonitriles obtained by the relatively
soft ESI-MS technique, the molecular ion peaks were observed at m/
z 721.1 [M þ Na]þ for 1, 329.1 [M þ Na]þ for 2 and 378.1 [M þ Na]þ
for 3 with Na ion.
DPBF was w3
ꢁ
10ꢀ5 mol Lꢀ1
. Solutions of sensitizer
(absorbance ¼ 1.1 at the irradiation wavelength) containing DPBF
were prepared in the dark and irradiated in the Q band region using
the setup described above. DPBF degradation at 417 nm was
monitored. The light intensity used for singlet oxygen studies was
2 ꢁ 1015 photons sꢀ1 cmꢀ2. The error in the determination of FD
was w10% (determined from several FD values).
After conversion into zinc phthalocyanine derivations, the
characteristic CN stretch at w2230 cmꢀ1 of phthalonitriles 1, 2 and

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A. Erdogmus¸, T. Nyokong / Dyes and Pigments 86 (2010) 174e181
178
3
disappeared in the FTIR spectra, indicative of metal-
lophthalocyanine formation. The characteristic vibrations corre-
sponding to CeOeC group were observed at 1088 (for 4). Thio ether
groups (CeSeC) were observed at 617 cmꢀ1 (for 4), 619 cmꢀ1 (for 5)
and 618 cmꢀ1 (for 6).
The ZnPc derivatives were found to be pure by 1H NMR with
both the substituents and ring protons observed in their respective
regions. The 1H NMR spectra of tetra substituted phthalocyanine
derivatives (4 to 6) were almost identical with that of the starting
compounds 1, 2 and 3 except for broadening and small shift. It is
likely that broadness is due to both chemical exchange caused by
aggregationedisaggregation equilibrium in CDCl3 and the fact that
the product obtained in this reaction is a mixture of four positional
isomers which are expected to show chemical shifts which slightly
differ from each other. In the 1H NMR spectrum of 4 to 6 the
aromatic and Pc protons appear between 7.26 and 8.42 ppm (for 4,
integrating for 28H), 7.11 and 8.79 ppm (for 5, integrating for 20H),
and 7.18 and 8.92 ppm (for 6, integrating for 32H). For complex 4
aliphatic protons, were observed between at 2.49 and 3.32 ppm,
integrating for a total of 16 protons. In the mass spectrum of Zn
phthalocyanines (4e6), the presence of molecular ion peaks at m/z
2849 [M ꢀ 9H], 1291.6 [MH]þ and 1489.6 [MH]þ respectively,
confirmed the proposed structures. MPc complexes have been
observed to degrade with molecular ion peaks [M]þ, [M þ nH]þ or
[MꢀnH]þ (n ¼ 1e3) [40]. The matrix employed in this work is 2,5-
dihydroxy benzoic acid, which is known [40] to intensify the
fragmentation process hence the observed patterns, hence the
observed mass spectral data.
Elemental analysis results also were consistent with the
proposed structures of all compounds 1 to 6.
3.2. Ground state electronic absorption spectra
Fig. 1. UVevis absorption spectra of 4,
5
and
6
in toluene (a),
The UVeVis spectra of the phthalocyanine complexes exhibit
concentration ¼ 1 ꢁ 10ꢀ5 mol dmꢀ3; THF (b), concentration ¼ 6 ꢁ 10ꢀ6 mol dmꢀ3 for 4
characteristic Q and B bands. Two principle
p
ep
* transitions are
* transition
and 5, 8 ꢁ 10ꢀ6 mol dmꢀ3 for 6.
seen for phthalocyanines: a Q-band which is a
pep
from the highest occupied molecular orbital (HOMO, a1u) to the
lowest unoccupied molecular orbital (LUMO, eg) of the complexes.
The B bands (B1 and B2), were observed in the 300e350 nm region
[41,42]. The Q band absorptions in the UVeVis absorption spectra of
the phthalocyanines (4, 5 and 6) were observed as a single high
Aggregation behavior of Pc is depicted as a coplanar association
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 [43]. In this study, the
aggregation behavior of the ZnPc derivatives (4, 5 and 6) were
investigated in toluene at different concentrations. For all
complexes, as the concentration was increased, the intensity of the
Q band also increased and there was no new bands due to the
aggregated species [44] observed, Fig. 2. LamberteBeer law was
obeyed for all complexes in the concentrations ranging from
2.0 ꢁ 10ꢀ6 to 1.2 ꢁ 10ꢀ5 mol dmꢀ3 as given for 4 in toluene as an
example, Fig. 2, showing that the complexes are not significantly
aggregated within this concentration range.
intensity band due to a pep* transition at 679, 684 and 689 nm in
toluene. Table 1 and Fig. 1. The Q band maxima are red shifted
compared to ZnPc in toluene alone, 670 nm [32], showing the
electron donating effects of the presence of sulfur. Complex 4
showed less red shifting, this is consistent with the notion that
aromatic fluorine groups in complexes 5 and 6 are part of the
phthalocyanine
p system while aliphatic fluorine groups in
complex 4 are not conjugated with the phthalocyanine
p system,
hence less red shifted for the latter [29].
The Q bands for complex 5 and 6 are broader compared to that
of 4, suggesting some aggregation, Fig. 1a. This was also observed in
THF, Fig. 1b. Some aggregation for 5 and 6 was also observed in
other solvents (DMSO and DMF). The fact that there is less aggre-
gation in 4, suggests that the long chain group is more effective at
preventing the stacking of the Pc rings.
3.3. Fluorescence spectra and quantum yields
Fig. 3 shows the absorption, fluorescence excitation and emis-
sion spectra of 4, 5 and 6 in toluene. For complex 4, the excitation
spectra showed broadening compared to absorption spectra,
suggesting slight change in symmetry upon excitation. For
complexes 5 and 6, the excitation spectra show less absorption in
the region between 500 and 600 nm. Absorbance in this area is due
to aggregation and aggregates do not fluorescence.
The fluorescence spectra were mirror images of the excitation
spectra for 4 to 6. The proximity of the wavelength of each
component of the Q band absorption to the Q band maxima of the
excitation spectra for all complexes suggest that the nuclear
Table 1
Spectral parameters of 4, 5 and 6 in toluene.
Compound Q band, lmax (log
3) Excitation,
Emission,
Stokes shift,
(nm)
lmax (nm)
lmax (nm)
dStokes (nm)
4
5
6
679
684
689
5.11 679
5.12 683
5.17 686
689
695
704
10
12
18

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A. Erdogmus¸, T. Nyokong / Dyes and Pigments 86 (2010) 174e181
179
Table 2
Complex 4
Photophysical and photochemical properties of 4, 5 and 6 in toluene.
Compound Solvent FF sT FT FIC
Fd (106) Fd
Toluene 0.041 110 0.65 0.31 8.11
1.8
1.6
1.4
1.2
1
2
1.5
1
Sd
F
4
5
6
0.52 0.80
0.60 0.87
0.56 0.79
Toluene 0.035 90 0.69 0.28 1.39
Toluene 0.021 100 0.71 0.27 4.22
y=130100x -0.0182
R²= 0.9997
0.5
0
0.00E+00 5.00E-06 1.00E-05 1.50E-05
Concentration
fluorine groups in complex 4 are not conjugated with the phtha-
locyanine system, resulting in larger fluorescence quantum yield
0.8
0.6
0.4
0.2
0
p
compared to 5 and 6. The decrease for all complexes compared to
ZnPc alone is due to the heavy atom effect of the halogen. The lower
FF values for 5 and 6 (compared to 4) may also be explained by the
aggregation tendencies of these molecules in this solvent. Aggre-
gation reduces the likelihood of radiative deactivation (fluores-
cence) through dissipation of energy by the aggregates. Complex 4
showed larger quantum yield for internal conversion (FIC, Table 2)
in toluene when compared to complexes 5 and 6.
A
400
450
500
550
600
650
700
750
800
Wavelength (nm)
3.4. Triplet quantum, yields and lifetimes
Fig. 2. Absorption spectra of 4 in toluene at different concentration: (A) 2 ꢁ 10ꢀ6, (B)
4 ꢁ 10ꢀ6, (C) 6 ꢁ 10ꢀ6, (D) 8 ꢁ 10ꢀ6, (E) 10 ꢁ 10ꢀ6, (F) 12 ꢁ 10ꢀ6 mol dmꢀ3
.
Triplet quantum yield (FT) represents the fraction of absorbing
molecules that undergo intersystem crossing to the metastable
triplet excited state. Therefore, factors which induce spin-orbit
coupling will certainly populate the triplet excited state. Fig. 4
displays the triplet decay curves of the complexes (using complex 6
configurations of the ground and excited states are similar and not
affected by excitation in toluene [45]. Fluorescence emission peaks
were observed at: 689 nm for 4, 695 nm for 5, 704 nm for 6 in
toluene (Table 1). The Stokes' shifts range from 10 to 18 nm, which
is usual for ZnPc derivatives [46]. As has been observed before [29],
there is a decrease FF on going from ZnPc (FF ¼ 0.07 [32] in
toluene) to fluorinated derivatives (FF ¼ 0.041 (4), ¼ 0.035 (5) and
0.021 (6)) with complex 4 showing the largest value. This obser-
vation is again consistent with the fact that aromatic fluorine
in toluene as an example). The triplet life time for 4 (110
(90 s) and 6 (100 s) in toluene are lower than for unsubstituted
ZnPc (330 s) in toluene [46]. This suggests that the fluoro-func-
ms), 5
m
m
m
tional substituents quench the triplet state.
The triplet quantum yields (FT) for substituted complexes (4, 5
and 6) in toluene are higher or comparable to ZnPc standard in
toluene (FT ¼ 0.65 for ZnPc). The high values of FT values suggest
more efficient intersystem crossing (ISC) in the presence of the
groups in complexes 5 and 6 are part of the phthalocyanine
p
system and thus increase the intersystem crossing. Aliphatic
Fig. 3. Absorption (i), excitation (ii) and emission (iii) spectra of the compounds 4(a), 5(b), and 6(c) in toluene. Excitation wavelength ¼ 679nm for (4) 683 nm for (5) and 686 nm for
(6) in toluene.

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A. Erdogmus¸, T. Nyokong / Dyes and Pigments 86 (2010) 174e181
180
0.30
0.25
0.20
0.15
0.10
0.05
0.00
important for those molecules intended for use as photocatalysts.
The photobleaching stabilities of complexes 4, 5 and 6 were
determined in toluene by monitoring the decrease in the intensity
of the Q band under irradiation with increasing time. The photo-
degradation quantum yield (Fd) values for the complexes are listed
in Table 2 are of the order of 10ꢀ6. These values show that the
molecules are of high stability in the solvent used. Stable ZnPc
molecules show values as low as 10ꢀ6 and for unstable molecules,
values of the order 10ꢀ3 have been reported [48]. The order of
stability among the substituted complexes was 5 > 6 > 4 in toluene.
0.00000
0.00004
0.00008
0.00012
4. Conclusion
Time (s)
In this study, the syntheses, spectral and photophysicochemical
properties of soluble peripheral fluoro-functional substituted zinc
phthalocyanines (4, 5 and 6) are discussed. The complexes have
good solubility and are mainly monomeric in solution. The intro-
duction of different fluoro-functional groups on the ring results in
high triplet quantum yields (ranging from 0.65 to 0.71 in toluene).
All complexes showed similar and typical fluorescence quantum
yields for MPcs in the solvent used. While Complex 4 has the lowest
triplet quantum yield (0.65) and singlet quantum yield values
(0.52), complexes 5 and 6 have higher triplet quantum yields and
singlet quantum yield values in toluene. The singlet oxygen
quantum yields, which give indication of the potential of the
complexes as photosensitizers in applications where singlet oxygen
is required (Type II mechanism) ranged from 0.52 to 0.60. Thus,
these complexes show potential as Type II photosensitizers and can
be used in photodynamic therapy.
Fig. 4. Mono-exponential triplet decay profile for complex 6 in toluene. Excitation
wavelength ¼ 689 nm.
fluorine substituents for substituted complexes 5 (FT ¼ 0.69) and 6
(FT ¼ 0.71), corresponding to low FF values discussed above.
3.5. Photochemical properties
3.5.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield FD is a measure of singlet oxygen
generation and the FD values were obtained using eq. (5). Singlet
oxygen quantum yields were studied in toluene using a chemical
method (1,3-diphenylisobenzofuran, DPBF). Fig. 5 shows spectral
changes observed during photolysis of complex 4 in toluene in
the presence of DPBF. The disappearance of DPBF was monitored
using UVevis spectroscopy. There were no changes in the Q band
intensities during the FD determinations, confirming that
complexes are not degraded during singlet oxygen studies [47]. The
FD values of three complexes are high in toluene, corresponding to
high FT values in this solvent. The FD values for 4 and 6 (FD ¼ 0.52
and 0.56 in toluene, respectively) are lower and for 5 (FD ¼ 0.60) is
higher when compared to unsubstituted ZnPc in toluene (0.58
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.
[32]). The magnitude of the SD ¼ (FD
/FT) represents the efficiency
of quenching of the triplet excited state by singlet oxygen.
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