The synthesis and photophysical properties of water soluble tetrasulfonated, octacarboxylated and quaternised 2,(3)-tetra-(2 pyridiloxy) Ga phthalocyanines

Article abstract of DOI:10.1016/j.dyepig.2009.09.011

The photophysical behaviour of chlorogallium 2,(3)-tetra-(2 pyridiloxy) phthalocyanine (ClGaT-2-PyPc) and its quaternised derivative were compared with that of the water soluble anionic tetrasulfonated gallium phthalocyanine ((OH)GaTSPc) and hydoxy galliu

Full text of DOI:10.1016/j.dyepig.2009.09.011

Dyes and Pigments 84 (2010) 242–248
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The synthesis and photophysical properties of water soluble tetrasulfonated,
octacarboxylated and quaternised 2,(3)-tetra-(2 pyridiloxy) Ga phthalocyanines
*
Nkosiphile Masilela, Tebello Nyokong
Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2009
Received in revised form
22 September 2009
Accepted 24 September 2009
Available online 30 September 2009
The photophysical behaviour of chlorogallium 2,(3)-tetra-(2 pyridiloxy) phthalocyanine (ClGaT-2-PyPc)
and its quaternised derivative were compared with that of the water soluble anionic tetrasulfonated
gallium phthalocyanine ((OH)GaTSPc) and hydoxy gallium octacarboxy phthalocyanine ((OH)GaOCPc).
Although both the quaternised compound and the tetrasulfonated gallium phthalocyanine aggregated in
aq. solution at pH 11, resulting in low fluorescence and triplet yields, the presence of the surfactant
Cremophore EL improved yields. Triplet quantum yields ranged from 0.52 to 0.70 and fluorescence
quantum yields ranged from <0.01 to 0.21. The nature of substituent (sulfonate, carboxy and pyridiloxy)
did not influence photophysical properties. Chlorogallium 2,(3)-tetra-(2 pyridiloxy) phthalocyanine and
its quaternised derivative displayed longer triplet lifetime than both the tetrasulfonated gallium
phthalocyanine ((OH)GaTSPc) and hydroxy gallium octacarboxy phthalocyanine in DMSO and in aq.
media in both the presence and absence of surfactant.
Keywords:
Gallium phthalocyanine
Sulfo phthalocyanine
Carboxy phthalocyanines quaternised
phthalocyanines
Triplet yields and triplet lifetimes
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
This work concerns the synthesis of novel, cationic as well as
anionic, gallium phthalocyanines tetrasubstituted at peripheral
The synthesis of novel metallophthalocyanine (MPc) derivatives
has become very important in recent years owing to their appli-
cations in various scientific, medicinal and nanotechnological areas.
This family of aromatic macrocycles are important because of their
positions with 2-pyridiloxy groups and octasubstituted with car-
boxy groups, respectively. The complexes in question are chlor-
ogallium 2,(3)-tetra-(2 pyridiloxy) phthalocyanine (ClGaT-2-PyPc),
its quaternised derivative (QClGaT-2-PyPc) and hydoxy gallium
octacarboxy phthalocyanine ((OH)GaOCPc), the latter two
compounds being water soluble. The current authors have recently
reported the synthesis and photophysical behaviour of chlor-
ogallium 2,(3)-tetra-(3 pyridiloxy) phthalocyanine (ClGaT-3-PyPc),
which differ in terms of the placement of the nitrogen of the
pyridine group, and its quaternised (hence water soluble) deriva-
tive (QClGaT-3-PyPc) [24,25]. In this work the photophysical
behaviour of the novel complexes ClGaT-2-PyPc and QClGaT-2-PyPc
are compared with those of ClGaT-3-PyPc, QClGaT-3-PyPc.
Although the synthesis of water soluble anionic tetrasulfonated
gallium phthalocyanine ((OH)GaTSPc) has been previously repor-
ted [26,27], its photophysical properties are not known; similarly,
whilst (OH)GaOCPc is also known [28] its photophysical behaviour
is not.
extensive delocalized 18
p electron system and high stability and
have been extensively studied [1] as nonlinear optical (NLO)
devices [2], photosensitizers for dye sensitised solar cells (DSSC)
[3,4], liquid crystals, Langmuir–Blodgett films, electrochromic
devices [5–11] and in fields such as photodynamic therapy of
cancer (PDT) [12–14]. Water soluble phthalocyanines exist as
loosely associated aggregates that are not chemically bound in
aqueous solution and which can be dissociated by surfactants or by
non-aqueous solvents [15–17]. Aggregation occurs as a result of
solvent effects that alter the chemical properties of the MPc
complexes leading to co-planar association of the aromatic rings
[18–23]. MPc complexes that contain central metals (e.g. Ga(III))
and axial ligands may display reduced aggregation as the axial
ligands act as spacers between the rings. Although the aggregation
tendency of Pcs in aqueous medium is problematic, water solubility
is an additional advantage for application in, for example, PDT, since
they can be injected directly into the bloodstream.
2. Experimental and method
2.1. Materials
Cremophore EL (CEL), pyromellitic dianhydride, 4-sulfophthalic
acid,1,8-diazabicyclo [5.4.0]undec-7-ene (DBU), urea, ammonium
* Corresponding author. Tel.: þ27 46 6038260; fax: þ27 46 6225109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.09.011

N. Masilela, T. Nyokong / Dyes and Pigments 84 (2010) 242–248
243
chloride and ammonium molybdate were obtained from Aldrich.
Quinoline, dimethylsulphoxide (DMSO), methanol, n-hexane,
chloroform (CHCl3), dichloromethane (DCM), tetrahydrofuran
(THF), acetone, ethanol and dimethylformamide (DMF) were dried
according to reported procedures [29] before use. 2-Tydroxypyr-
idine, deuterated D2O, DMSO-d6, potassium carbonate (K2CO3),
gallium(III) chloride, and dimethyl sulphate (DMS) were also
obtained from Aldrich. Phosphate-buffered saline (PBS) solution pH
11 was prepared using appropriate amounts of Na2HPO4
(0.005 mol) and NaOH (8.2 ꢀ 10ꢁ4 mol) in 100 mL distilled water.
All other reagents were obtained from commercial supplies and
used as received. Zn tetrasulfo phthalocyanine (ZnTSPc) was
synthesized according to well known procedures [30]. Zinc
phthalocyanine was purchased from Aldrich.
(0.2 ml) was added drop-wise. The mixture was stirred at 120 ꢂC for
12 h. After this time, the mixture was cooled to room temperature
and the product was precipitated with hot acetone and collected by
centrifugation. The green solid product was washed successively
with hot ethanol, ethyl acetate, THF, chloroform, n-hexane and
diethylether under Soxhlet extraction. The resulting hygroscopic
product was dried over phosphorous pentoxide.
Yield: (75%). IR (KBr, cmꢁ1): 3132(C–H), 1569(C]C), 1501, 1474,
1403, 1384, 1276(S]O), 1097(S]O), 1061(C–O–C), 1007, 749,
668,617. 1H NMR (D2O):
d
, ppm 8.84–9.46 (28H, m, Pc-H and Pyr-
idyl-H), 3.95–4.31 (12H, m, CH3): UV/Vis (pH 11/CEL) lmax (nm)
(log ): 350 (4.10), 679(4.81): Calc. for C56H46ClN12O14S2Ga (4H2O):
3
C 50.93, H 3.48, N 12.73; Found: C 50.46, H 2.97, N 13.66. MALDI-
TOF MS m/z: Calcd: 1014.4 amu. Found: (M ꢁ Cl) 1015.3 amu.
2.2. Equipment
2.3.3. Hydoxy gallium octacarboxy phthalocyanine
(Scheme 2, (OH)GaOCPc, 6)
Fluorescence excitation and emission spectra were recorded on
a Varian Eclipse spectrofluoremeter. UV–visible spectra were
recorded on a Varian 500 UV–Vis/NIR spectrophotometer. IR
spectra (KBr pellets) were recorded on a Perkin–Elmer spectrum
2000 FTIR spectrometer. 1H NMR spectra were recorded using
a Bruker EMX 400 MHz NMR spectrometer. Laser flash photolysis
experiments were performed with light pulses produced by
a Quanta-Ray Nd: YAG laser providing 400 mJ, 90 ns pulses of laser
light at 10 Hz, pumping a Lambda -Physik FL3002 dye (Pyridin 1 dye
in methanol). Single pulse energy ranged from 2 to 7 mJ. The
analyzing beam source was from a Thermo Oriel xenon arc lamp,
and a photomultiplier tube was used as a detector. Signals were
recorded with a digital real-time oscilloscope (Tektronix TDS 360).
The triplet lifetimes were then determined by exponential fitting of
the kinetic curves using the program OriginPro 7.5. Maldi-TOF mass
spectrometry was carried out at the University of Stellenbosch
using an ABI Voyager DE-STR Maldi-TOF instrument.
(OH)GaOCPc was synthesized, purified and characterized
according to the established literature methods for similar
complexes [33]. Benzene-1,2,4,5-tetracarboxylic dianhydride
(pyromellitic dianhydride (4); (caution: flammable, hazardous)
2.50 g 11.5 mmol), urea (13.0 g, 0.22 mol), GaCl3 (0.72 g,4.1 mmol)
and DBU (0.1 g, 0.7 mmol) were heated to 250 ꢂC in a flask until the
reaction mixture was fused. The reaction products were washed
with water, acetone and 6 M hydrochloric acid (HCl), forming the
solid product 5, which was not purified any further following
literature [33]. To form the final product 6, complex 5 was dried and
hydrolyzed in 20% H2SO4 for a period of 72 h. Then the product was
purified as explained in literature [33].
Yield: (34%). IR (KBr, cmꢁ1): 3423(OH), 3029 (C–H), 2781,
1724(C]O), 1466, 1398, 1399, 1283, 1186(C–O or O–H) 1054,772,
536. 1H NMR (D2O): 8.73–8.78 (8H, s, Pc-H), 4.81–4.86 (8H, s,
Carboxylic-H). UV/Vis (pH 11): lmax (nm) (log
3) 360 (3.41),
688(4.52) nm. Calc. for C40H17N8O17Ga (18H2O): C 37.67, H 4.16, N
8.79; Found: C 37.03, H 3.71, N 8.55. MALDI-TOF MS m/z: Calcd:
951.2 amu. Found: (M þ 1) 952.4 amu.
2.3. Synthesis
The synthesis of 4-(2-pyridyloxy)phthalonitrile (2a) has been
reported before [31].
2.3.4. Hydroxy gallium tetrasulfo phthalocyanine
(Scheme 3, (OH)GaTSPc, 8)
The (OH)GaTSPc was synthesized and purified according to the
2.3.1. 2,(3)-(Tetra-2-pyridyloxyphthalocyaninato) gallium (III)
chloride (Scheme 1, (ClGaT-2-PyPc, 3a))
microwave procedure for SnTSPc [34]. Briefly, a mixture of
commercially available 50% aqueous 4-sulfophthalic acid solution
(7) (4 g, 8.12 mmol), urea (1.95 g, 32 mmol), and GaCl3 (0.72 g,
4.1 mmol) in the presence of ammonium chloride (1.56 g, 29 mmol)
and ammonium molybdate (0.17 g, 0.14 mmol) as catalysts, was
irradiated in a microwave oven at 560 W for 15 min. The mixture
was then added to aqueous sodium hydroxide solution (100 ml,
10 wt.%), heated until it boiled, and cooled to the room tempera-
ture. The solution was then poured into methanol (50 ml), and then
i-propyl alcohol (100 ml) was added to precipitate the product. The
complex was purified by following literature methods [34] in
addition to Soxhlet extraction of impurities using methanol and
ethanol.
A mixture of anhydrous gallium (III) chloride (0.60 g, 3.4 mmol),
2-pyridyloxyphthalonitrile (2a) (1.50 g, 6.8 mmol) and quinoline
(5 mL, doubly distilled over CaH2) was stirred at 180 ꢂC for 7 h
under nitrogen atmosphere. The solution was then cooled and
dropped in n-hexane. The green solid product was precipitated and
collected by centrifugation and washed with n-hexane. The crude
product was dissolved in DMF. After concentrating, the dark green
waxy product was precipitated with hot ethanol and washed
according to reported procedure [31] with ethanol, acetone, THF,
CHCl3, n-hexane and diethylether in a Soxhlet extraction apparatus.
Yield: (64%). IR (KBr, cmꢁ1): 3439(O–H), 3102(C–H), 1564(C]C),
1474, 1235, 1092(C–O–C), 843, 748. 1H NMR (DMSO-d6):
d
, ppm
Yield: (47%). IR (KBr, cmꢁ1): 3432(OH), 2046, 1669, 1631(C]C),
1401, 1195, 1136(S]O), 904, 686, 584. 1H NMR (D2O): 8.31–8.33(4H,
s, Pc-H), 8.01–8.06 (8H, d, Pc-H), 6.60–6.63(1H s-br,O–H). UV/Vis
8.95–9.14 (4H, m, Pc-H), 9.25–9.38 (4H, d, Pc-H), 9.64–9.67 (4H, m,
Pc-H), 8.21–8.29 (4H, br, Pyridyl-H), 8.10–8.14 (8H, m, Pyridyl-H),
7.83–7.95 (4H, br, Pyridyl-H). UV/Vis (DMF) lmax nm (log
3): 340
lmax(nm) (log 3) (pH 11/CEL): 380 (3.74), 678 (4.96) nm. Calc. for
(3.20), 686 (4.43). Calc. for C52H28ClN12O4Ga: C 63.08, H 2.83, N
16.98; Found: C 62.61, H 2.53 N 16.81.
C32H13N8O13S4Na8Ga (2H2O): C 33.85, H 1.50, N 9.87; Found: C
34.13, H 2.06, N 9.68. MALDI-TOF MS m/z: Calcd: 898.4 amu. Found:
(M ꢁ OH) 898.9 amu.
2.3.2. Quaternarized 2,(3)-(tetra-pyridyloxyphthalocyaninato)
gallium (III) chloride (Scheme 1, QClGaT-2-PyPc, 3b)
2.4. Flourescence and photophysical studies
This molecule was synthesized according to the reported liter-
ature procedure [32]. Complex 3a (100 mg, 0.1 mmol) was heated
to 120 ꢂC in freshly distilled DMF (0.5 ml) and dimethyl sulphate
Fluorescence quantum yields
comparative method [35] (Equation (1)),
(FF) were determined by

244
N. Masilela, T. Nyokong / Dyes and Pigments 84 (2010) 242–248
Cl
R O
OR
N
O N
2
CN
CN
CN
CN
R O
N
N
N
N
GaCl , quinoline
3
ROH, DMF
K CO , RT
N
Ga
N
N
0
DBU, 180 C, 7 h
2
3
OR
1
R O
2a
3a
Cl
4+
Cl
OR
R O
OR
R O
N
N
N
N
N
Dimethylsulphate, DMF
N
N
N
N
N
N
Ga
N
Ga
N
N
0
120 C, 12 h
N
N
OR
OR
CH
2-
R O
2SO
R O
4
3a
3b
3
+
N
a
N
R
R
b
Scheme 1. Synthesis of 2,(3)-(tetra-pyridyloxyphthalocyaninato) gallium (III), (ClQGaT-2-PyPc) (3a) and water soluble quaternised 2,(3)-(tetra-pyridyloxyphthalocyaninato)gallium
(III), QClGaT-2-PyPc (3b).
H
N
O
O
HO
N
N
O
O
O
O
O
O
O
O
N
urea, DBU, metal salt
reflux for 20 mins
Ga
N
N
HN
NH
O
N
O
N
N
4
O
O
N
H
HOOC
COOH
H S O
2
20%
4
5
reflux
72 h
HO
N
N
N
HOOC
HOOC
COOH
Ga
N
N
COOH
N
N
N
COOH
HOOC
6
Scheme 2. Synthesis of gallium octacarboxy phthalocyanine, ((OH)GaOCPc) (6).

N. Masilela, T. Nyokong / Dyes and Pigments 84 (2010) 242–248
245
NaO S
3
OH
SO Na
3
N
HO S
3
COOH
COOH
N
N
N
urea, metal source, catalyst.
NaOH
Ga
N
N
microwave (560 W, 11 mins)
N
N
7
SO Na
3
SO Na
3
8
Scheme 3. Microwave synthesis of gallium tetrasulfonated phthalocyanine, ((OH)GaTSPc) (8).
F$AStd$n2
metallophthalocyanines (Scheme 1) were obtained in the presence
of metal salts and substituted phthalonitriles. Complex 3b was
obtained by methylation of 3a in DMF in the presence of dime-
thylsulfate and good yields were obtained. The non-ionic complex
3a in this study was soluble in organic solvents such as DCM, DMF
and DMSO and the ionic complex 3b was highly soluble in polar
solvents like water, methanol and DMSO. Octacarboxy phthalocy-
anine ((OH)GaOCPc) Scheme 2 was highly soluble and monomeric
in alkaline medium and gave similar spectroscopic results to the
previously reported metalloctacarboxy complexes [39]. The
synthesis of tetrasulfonated gallium phthalocyanines Scheme 3 has
been reported before as stated previously and gave satisfactory
spectroscopic results. The OH axial ligand for (OH)GaOCPc and
(OH)GaTSPc is a result of work-up procedure. The complexes were
characterized by various spectroscopic methods: IR, UV–vis, 1H
NMR and elemental analysis and are consistent with predicted
structures. The characteristic of a nitrile stretch at w2225 cmꢁ1 (2a)
disappears upon formation of the phthalocyanine (3a), Scheme 1.
The 1H NMR spectra of all the complexes showed aromatic ring
protons between 8 and 10 ppm. The presence of isomers as well as
phthalocyanine aggregation at the concentrations used for the 1H
NMR measurements leads to broadening of the aromatic signals
[40]. However, the peaks integrated correctly giving the expected
total number of protons for each complex, confirming the relative
purity of the complexes. Mass spectral data was additionally
employed to characterise the water soluble complexes, and the data
was consistent with the structure of the complexes.
FF
¼
FFðStdÞ
$
(1)
F
Std$A$n2Std
where F and FStd are the areas under the fluorescence curves of the
MPc derivatives and the used standard. A and AStd are the absor-
bances of the sample and reference at the excitation wavelength,
and n and nStd are the refractive indices of solvents used for the
sample and standard, respectively. ZnPc in DMSO was used as
a standard, FF ¼ 0.2 [36]. For each study at least two independent
experiments were performed for the quantum yield determina-
tions. Both the sample and the standard were excited at the same
relevant wavelength.
Triplet quantum yields were determined using a comparative
method based on triplet decay, using Equation (2):
StdDASample3Std
FSTample
¼
FT
(2)
D
AStd3Sample
where ATSample andASTtd are the changes in the triplet state absor-
bance of the sample and the standard, respectively. 3STampleand 3TStd
are the triplet state extinction coefficients for the sample and
standard, respectively. FSTtdis the triplet state quantum yield for the
standard. ZnTSPc in aqueous solution, FSTtd ¼ 0.56 [37], unsub-
stituted ZnPc in DMSO, FSTtd ¼ 0.65 [37] and unsubstituted ZnPc in
DMF FSTtd ¼ 0.58 [38] were used as standards. Quantum yields of
internal conversion were obtained from Equation (3) which
assumes that only three processes (fluorescence, intersystem
crossing and internal conversion), jointly deactivate the excited
singlet states of the complexes.
3.2. Ground state electronic absorption and fluorescence spectra
FIC ¼ 1 ꢁ ðFF
þ
FT
Þ
(3)
The ground state electronic spectra of the QClGaT-2-PyPc Fig. 1a
shows that this complex is aggregated in aqueous solution (pH 11),
with the presence of two main bands one at w678 nm due to the
monomeric species and the other at w645 nm due to the aggre-
gated species. This pH was chosen to allow for the solubility of both
QClGaT-2-PyPc, (OH)GaTSPc and (OH)GaOCPc. The latter is only
soluble is highly basic media. Addition of a surfactant, CEL, resulted
in a decrease in the intensity of the band due to the aggregates with
a slight increase in the intensity and narrowing of the band due to
the monomeric species, which confirms that the complexes were
aggregated in aqueous solution of pH 11. There was incomplete
disaggregation of QClGaT-2-PyPc even after the addition of CEL, as
judged by the observation of some broadening in the 640 nm region
after addition of CEL in Fig. 1a. In contrast, (OH)GaTSPc was weakly
aggregated, Fig. 1b, as judged by less pronounced absorption in the
640 nm region. There was a decrease in absorption in the 640 nm
region on addition of CEL, Fig. 1b. There was also a 4 nm red shift of
the Q band of the (OH)GaTSPc after addition of CEL, Fig. 1b, Table 1,
probably due to change in media.
3. Results and discussion
3.1. Synthesis and characterisation
Schemes 1–3 show the synthetic pathways for the compounds
used in this work. Substituted phthalocyanines are normally
prepared by cyclotetramerization of substituted phthalonitriles.
4-Tetra-substituted phthalocyanines can be synthesized from
4-substituted phthalonitriles (2a) Scheme 1 or from commercially
available starting materials (7) Scheme 3. Octacarboxy phthalocy-
anines can be synthesized from commercially available pyromellitic
dianhydride (4) as shown Scheme 2. Sulfonated phthalocyanines
can also be obtained from commercially available 4-sulfophthalic
acid through microwave synthesis as shown in Scheme 3. The
syntheses of all these complexes gave satisfactory spectroscopic
analyses. The 2-pyridiloxy substituents on complex 3a Scheme 1
are suitable for conversion into quaternary ammonium groups and
this results in solubility in water. Unquaternised and quaternised

246
N. Masilela, T. Nyokong / Dyes and Pigments 84 (2010) 242–248
Table 1
Ground state absorption, fluorescence emission and excitation spectral parameters
for various MPc complexes.
Complex
Solvent
Q band
Excitation Emission Stokes
labs (nm) lex (nm)
lem (nm) shift Dstokes
OHGaOCPc
OHGaTSPc
OHGaTSPc
pH 11
pH 11
pH 11 þ CEL
688 687
674 674
678 675
699
679
681
683
682
700
701
702
694
17
5
6
3
7
17
12
15
13
QClGaT-2-PyPc pH 11
645, 678 680
678 675
QClGaT-2-PyPc pH 11 þ CEL
ClGaT-2-PyPc
ClGaT-2-PyPc
aClGaT-3-PyPc
DMF
DMSO
DMSO
686 683
690 689
687 686
681 681
aQClGaT-3-PyPc Water
a
Values from Ref. [25].
Fig. 2 shows that as the concentration was increased for
(OH)GaOCPc in pH 11, the intensity of the absorption of the Q band
also increased and there were no new bands normally blue shifted
due to the aggregated species. Same trend was also observed with
the ClGaT-2-PyPc derivatives which did not show aggregation in
DMF. Beer–Lambert’s law was obeyed for both of these compounds
in the concentrations ranging from 2 ꢀ 10ꢁ6 to 12 ꢀ 10ꢁ6 mol dmꢁ3
.
Fluorescence excitation spectra of (OH)GaTSPc complexes
showed a lack of agreement between the absorbance and excitation
spectra as shown in Fig. 3a. The band around 640 nm, associated
with the dimer is not seen in the fluorescence excitation spectrum
since only the monomer fluoresces but there was improvement
upon addition of CEL, Fig. 3b. It has been documented before in
literature that dimers are non-photoactive [15]. However the
absorption spectra was mirror image of the emission spectra for the
ClGaT-2-PyPc in (DMF and DMSO) and of the (OH)GaOCPc in pH 11
which is usual for MPc complexes. The Stokes’ shifts shown in
Table 1 ranged from 3 nm to 17 nm, typical of MPc complexes.
3.3. Photophysical parameters
Fig. 4 shows the transient absorption spectrum of (OH)GaOCPc
in pH 11. The absorption of the triplet state is at w460–550 nm. The
triplet absorption curve of (OH)GaOCPc in pH 11 is shown in Fig. 4
(inset), and it obeyed second order kinetics. This is typical of MPc
complexes at high concentrations [41] due to triplet–triplet
recombination.
Triplet quantum yield FT is the measure of the fraction of
absorbing molecules that undergo intersystem crossing (isc) to the
Fig. 1. Ground state electronic absorption spectra of (a) QClGaT-2-PyPc and
(b) ClGaTSPc in the absence (i) and presence of (ii) CEL, both in pH 11. (c) ground state
electronic absorption spectra of ClGaT-2-PyPc in DMF (i) and (OH)GaOCPc in pH 11
buffer (ii).
Unlike the tetrasulfonated and the quaternised complexes,
the ground state electronic absorption spectra (Fig. 1c, ii) of
(OH)GaOCPc in pH 11 was monomeric w688 nm which was evident
by a single narrow Q band typical of metallated phthalocyanine
complexes [16] in aqueous solution. The spectrum of ClGaT-2-PyPc
(Fig.1c, i) in DMF shows characteristic monomeric absorption in the
Q band region at 686 nm. The absorption spectra of the monomers
in pH 11 (with CEL where needed) varied from 674 for (OH)GaTSPc
to 688 nm for (OH)GaOCPc, showing red shifting for the latter.
In DMSO, QClGaT-2-PyPc showed blue shifting compared to
ClGaT-2-PyPc due to the lowering of the electron donating ability of
the nitrogen groups on quaternization as was the case for the
corresponding QClGaT-3-PyPc and ClGaT-3-PyPc complexes [24].
Fig. 2. Ground state absorption spectra of (OH)GaOCPc at various concentrations:
(i) ¼ 2 ꢀ 10ꢁ6, (ii) ¼ 4 ꢀ 10ꢁ6, (iii) ¼ 6 ꢀ 10ꢁ6, (iv) ¼ 8 ꢀ 10ꢁ6, (v) ¼ 10 ꢀ 10ꢁ6, and
(vi) ¼ 12 ꢀ 10ꢁ6 mol dmꢁ3
.

N. Masilela, T. Nyokong / Dyes and Pigments 84 (2010) 242–248
247
0.4
Wavelength (nm)
600 700
0.0
400
500
800
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
-0.4
-0.8
-1.2
-1.6
0.0000 0.0002 0.0004 0.0006 0.0008 0.0010
Time (s)
Fig. 4. Transient differential curve for (OH)GaOCPc in pH 11, excitation
wavelength ¼ 687 nm and triplet decay curve insert.
and ClGa-2-PyPc in DMSO gave the same lifetime as QClGa-2-PyPc
in the presence of CEL. The triplet lifetimes are highly influenced by
the presence of oxygen, however in the work the solutions for
triplet lifetimes determinations were deaerated sufficiently before
recording of flash photolysis traces. The sT values for ClGaT-2-PyPc
reported in this work in DMSO were marginally higher than those
reported for the corresponding ClGaT-3-PyPc [25], Table 2. Simi-
larly for QClGaT-2-PyPc, sT values are slightly higher than the
corresponding QClGaT-3-PyPc in aqueous media [25]. As stated
above, pH 11 is employed in this work in order to ensure solubility
of all complexes (MOCPc complexes in particular are soluble in
basic media). The reported data [25] for QClGaT-3-PyPc were in
non-buffered water. Lifetimes were longer in the presence of CEL
compared to pH 11 alone for the aggregated complexes
((OH)GaTSPc and QClGaT-2-PyPc), which may be due to the
reduction in the exposure of the phthalocyanine in the aqueous
medium because of the presence of the CEL and due to
monomerization.
Fig. 3. Absorption, fluorescence emission and excitation spectra of (OH)GaTSPc in pH
11 (a) and in pH 11 þ CEL (b), excitation wavelength ¼ 630 nm.
triplet state. The efficiency of a phthalocyanine as a photosensitizer
is determined by its triplet state quantum yield (FT) and lifetime
The fluorescence quantum yields FF of the complexes are also
listed in Table 2. The aggregated ((OH)GaTSPc and QClGaT-2-PyPc)
complexes showed relatively low yields of fluorescence in pH 11, but
there was an improvementon addition of CEL. Aggregation is known
to dissipate the electronic energy of the excited singlet state, thereby
lowering fluorescence. Thus monomerization of the aggregates
enhances fluorescence and this is noticed in the FF of the complexes
in the presence of CEL. Some of the FF values are however low
compared to MPcs in general [44]. FF values were relatively higher
for the (OH)GaOCPc and ClGaT-2-PyPc probably due to their
monomeric nature. The values of intersystem quantum yields were
highest for ClGaT-2-PyPc in pH 11 buffer, Table 2. FF values in DMSO
are almost the same for ClGaT-3-PyPc and ClGaT-2-PyPc.
(sT). All the complexes showed relatively high triplet yields
(Table 2). It has been documented in literature that gallium
phthalocyanines give good photochemical and photophysical
properties that make them useful for PDT [42]. Unquaternised
ClGaT-2-PyPc showed the highest triplet yield in DMSO followed by
the (OH)GaOCPc in pH 11 and QClGaT-2-PyPc in pH 11 þ CEL. All
the three complexes are monomeric in their respective solutions,
and monomers have greater tendencies to undergo intersystem
crossing because less energy is lost through internal conversion
[43]. (OH)GaTSPc, in pH 11 without CEL, showed the lowest triplet
yield followed by QClGaT-2-PyPc in pH 11 (without CEL) due to
aggregation, but there was a high improvement after addition of
CEL for both complexes. The FT value for QClGaT-2-PyPc is lower
than that reported for QClGaT-3-PyPc in aqueous media [25],
Table 2. However the effect of different pH cannot be ignored. The
reported data [25] for QClGaT-3-PyPc were in non-buffered water.
The determination of triplet yield and lifetime values for QClGaT-2-
PyPc in unbuffered water did not make much difference in the
values. The FT value of unquaternised ClGaT-2-PyPc in DMSO is
larger than that of the corresponding ClGaT-3-PyPc [25], Table 2.
Since for these complexes, the same media was employed, the
differences do suggest that the position of the nitrogen atom on the
substituents affects the photophysical behaviour of the complexes.
Table 2
Photophysical parameters for various excited state deactivation processes of the MPc
complexes.
Complex
Solvent
FT
sT
(
m
s)
FF
0.21
FIC
(OH)GaOCPc
(OH)GaTSPc
(OH)GaTSPc
QClGaT-2-PyPc
aQClGaT-3-PyPc
QClGaT-2-PyPc
ClGaT-2-PyPc
ClGaT-2-PyPc
aClGaT-3-PyPc
pH 11
pH 11
0.67
0.52
0.63
0.55
0.61
0.68
0.59
0.70
0.57
80
60
80
60
50
170
120
170
160
0.12
0.39
0.22
0.45
0.27
0.28
0.25
0.10
0.24
0.09
0.15
<0.01
0.12
0.04
0.16
0.20
0.19
pH 11 þ CEL
pH 11
Water
pH 11 þ CEL
The triplet lifetime, sT values range from 60 to 170
ms, for
DMF
DMSO
DMSO
complexes under discussion in this work, which is a usual range for
MPc complexes containing heavy metals. (OH)GaOCPc in pH 11
alone gave the same lifetime as (OH)GaTSPc in the presence of CEL,
a
Values from Ref. [25].

248
N. Masilela, T. Nyokong / Dyes and Pigments 84 (2010) 242–248
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New peripherally tetrasubstituted unquaternised gallium
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(QClGaT-2-PyPc), have been synthesized and characterized. Their
photophysical properties have been studied and compared with
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Acknowledgements
This work was supported by the Department of Science and
Technology (DST)/Nanotechnology (NIC) and National Research
Foundation (NRF) of South Africa through DST/NRF South African
Research Chairs Initiative for Professor of Medicinal Chemistry and
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