The synthesis and fluorescence behaviour of new unsymmetrically mono-functionalized carboxy Ge, Ti and Sn phthalocynines

Article abstract of DOI:10.1016/j.dyepig.2011.03.026

This work reports on the synthesis and fluorescence behaviour of novel unsymmetrically substituted monocarboxy germanium ((OH)₂GeMCPc, 3), titanium (OTiMCPc 4) and tin ((ac)₂SnMCPc, 5) phthalocyanines. The fluorescence quantum yields

Full text of DOI:10.1016/j.dyepig.2011.03.026

Dyes and Pigments 91 (2011) 164e169
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Dyes and Pigments
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The synthesis and fluorescence behaviour of new unsymmetrically
mono-functionalized carboxy Ge, Ti and Sn phthalocynines
*
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:
This work reports on the synthesis and fluorescence behaviour of novel unsymmetrically substituted
monocarboxy germanium ((OH)2GeMCPc, 3), titanium (OTiMCPc 4) and tin ((ac)2SnMCPc, 5) phthalo-
cyanines. The fluorescence quantum yields ranged from 0.09 to 0.14. The fluorescence lifetimes were
found to be higher for the complex with higher fluorescence quantum yield value. Higher fluorescence
quantum yields and lifetimes were obtained for the (ac)2SnMCPc complex (5), followed by OTiMCPc
complex (4), and the lowest fluorescence quantum yield and lifetime were observed for (OH)2GeMCPc (3).
Ó 2011 Elsevier Ltd. All rights reserved.
Received 2 February 2011
Received in revised form
24 March 2011
Accepted 26 March 2011
Available online 2 April 2011
Keywords:
Low symmetry phthalocyanines
Monocarboxy phthalocyanines
Germanium
Titanium
Tin
Fluorescence quantum yields and lifetimes
1. Introduction
many carboxylic acid groups available for attachment on ZnO.
The complexes also showed aggregation when they were bound to
Metallophthalocyanines (MPcs) show promise for many appli-
cations including in: photocatalysis [1e4], photo-electrocatalysis [5]
and photodynamic therapy of cancer [6e10]. Mono-functionalized
MPc complexes are of great interest since they can be coupled to
various substrates by chemically binding one reactive substituent of
the Pc, with the other binding sides being blocked with non reactive
substituents [11,12]. It is also believed that low symmetry phthalo-
cyanines have less tendencies to form aggregates compared
to symmetrically tetrasubstituted Pcs which is a very useful and
attractive property for these Pcs for their application as photosen-
sitizers. For a good photosensitizer a molecule is required to be
in its monomeric state for successful photo-induced energy and
electron transfer [13e15]. Low symmetry bisthienylethene phtha-
locyanines with photochromic properties have been reported
[16,17]. The complexes showed potential for applications in photo-
switching devices [17]. Recently our group has reported on selective
coupling of a monocarboxy phthalocyanine complex on zinc oxide
substrates for solar cells applications [15]. The photo-electro-
chemical studies of a series of symmetrically carboxy phthalocya-
nines displayed a lack of selective binding due to the presence of
ZnO substrate, which lead to low power efficiencies compared
to unsymmetrically monosubstituted carboxy Pc [15]. Other studies
in our group have shown successful linking of nano particles such as
quantum dots to low symmetry amino phthalocyanines for the
improvement of Förster resonance energy transfer (FRET) as
compared to symmetrically substituted carboxy Pcs [18]. However
the disadvantage of working with low symmetry phthalocyanine
complexes is the low yield that is obtained during the synthesis of
the complexes [19]. The statistical condensation method of making
low symmetry phthalocyanines results in a mixture of different
compounds depending on the ratio of the two starting material
used [20e23]. Separation of the various compounds formed during
the synthesis to get the desired mono-functionalized Pc complex is
a major and a crucial step during the purification of these complexes,
resulting in low yields of the desired product due to loss during the
separation. Herein we report on the synthesis and characterization
of germanium, titanium and tin phthalocyanine complexes with
only one reactive carboxy group as an electrophile. We investigate
the fluorescence properties of these compounds in solution. Most
low symmetry MPc complexes contain the common central metals
such as Zn. In this work we use Ti, Ge and Sn as central metals, the
use of the carboxy group is to allow coordination of biological
molecules containing amino groups at a later state, the dieth-
ylaminoethanethiol substituents were chosen to enhance solubility
* 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 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.03.026

N. Masilela, T. Nyokong / Dyes and Pigments 91 (2011) 164e169
165
as well as red shifting of the spectra, which are requirements for
photosensitizers.
Mass spectral data were collected with a Bruker AutoFLEX III
Smartbeam TOF/TOF Mass spectrometer. The instrument was
operated in positive ion mode using an m/z range of 400e3000. The
voltage of the ion sources were set at 19 and 16.7 kV for ion sources
1 and 2 respectively, while the lens was set at 8.50 kV. The reflector
1 and 2 voltages were set at 21 and 9.7 kV respectively. The spectra
were acquired using dithranol as the MALDI matrix, using a 355 nm
nitrogen laser.
2. Experimental and method
2.1. Materials
Potassium carbonate (K2CO3), D2O, DMSO-d6, germanium (IV)
chloride, titanium (IV) butoxide, tin (IV) acetate, 2-(dieth-
ylaminoethanethiol) hydrochloride, 1,8-diazabicyclo[5.4.0]undec-
7-ene (DBU), zinc phthalocyanine and aluminum oxide (WN-3:
neutral) for column chromatography were purchased from Sig-
maeAldrich. Pentanol was purchased from Saarchem. Dime-
thylformamide (DMF), dichloromethane (DCM) and dimethyl
sulphoxide (DMSO), methanol (MeOH), n-hexane, chloroform
(CHCl3), dichloromethane (DCM), tetrahydrofuran (THF), acetone,
and ethanol were obtained from Merck and were dried according to
reported procedures [24] before use. 4-Carboxyphthalonitrile (2)
was synthesized in a similar method reported in literature using
trimellitic anhydride (Aldrich) as the starting material [4,25]. 4-
Nitrophthalonitrile was synthesized as reported in literature [26].
2.3. Synthesis
The synthesis of 4-carboxyphthalonitrile (2) has been reported
before [25].
4-(2-Diethylaminoethanethiol) phthalonitrile (1) was synthe-
sized according to the literature method [28]. Briefly 4-nitro-
phthalonitrile (3.05 g, 17.6 mmol) was dissolved in anhydrous DMF
(150 ml) under argon and 2-diethylaminoethanethiol hydrochlo-
ride (9 g, 53.0 mmol) was slowly added. The mixture was left stir-
ring at room temperature, and after 20 min finely ground
anhydrous K2CO3 (29.3 g, 212.0 mmol) was added in portions over
a period of 2 h with stirring. The reaction mixture was constantly
stirred at room temperature for a period of 48 h under argon. Then
the solution was poured into ice (900 g) for precipitation. The
precipitate was filtered off, washed with water, until the filtrate was
neutral. The pure product was then dried in air. Yield: (82.30%). IR
(KBr) mmax/cmꢀ1: 3098 (AreCeH), 2956 (CH2), 2234 (CN), 742
2.2. Equipment
UVevisible spectra were recorded on a Varian 500 UVeVis/NIR
spectrophotometer. 1H-NMR spectra were recorded using a Bruker
EMX 400 MHz NMR spectrometer. Fluorescence excitation and
emission spectra were recorded on a Varian Eclipse spectro-
fluoremeter. IR spectra (KBr pellets) were recorded on a Per-
kineElmer spectrum 2000 FTIR spectrometer.
(CeSeC), 714, 624, 550. 1H-NMR (CDCl3)
d :7.74e7.62 (m, 3H,
AreH), 3.21e3.04 (t, 2H, SCH2), 2.84e2.73 (t, 2H, NCH2), 2.37e2.18
(qnt, 4H, CH2C), 1.16e1.08 (t, 6H, CH3) ppm.
Fluorescence lifetimes were measured using a time correlated
single photon counting setup (TCSPC) (FluoTime 200, Picoquant
GmbH) with a diode laser (LDH-P-670 with PDL 800-B, Picoquant
GmbH, 670 nm, 20 MHz repetition rate, 44 ps pulse width). Fluo-
rescence was detected under the magic angle with a peltier cooled
photomultiplier tube (PMT) (PMA-C 192-N-M, Picoquant) and
integrated electronics (PicoHarp 300 E, Picoquant GmbH).
A monochromator with a spectral width of about 8 nm was used to
select the required emission wavelength band. The response
function of the system, which was measured with a scattering
Ludox solution (DuPont), had a full width at half-maximum
(FWHM) of 300 ps. All luminescence decay curves were measured
at the maximum of the emission peak and lifetimes were obtained
by deconvolution of the decay curves using the FLUOFIT software
program (PicoQuant GmbH, Germany). The support plane approach
[27] was used to estimate the errors of the decay times.
2.3.1. Tris {9 (10), 16 (17), 23 (24)-4-(2-diethylaminoethanethiol)-
2-(4-carboxyphthalonitrile) phthalocyaninato} germanium (IV)
dihydroxy (Scheme 1, (GeMCPc (3)))
A mixture of 4-carboxyphthalonitrile (2) (0.22 g, 1.3 mmol) and
4-(2-diethylaminoethanethiol) phthalonitrile (1) (0.99 g, 3.9 mmol)
was firstly finely ground and homogenized and placed in a round
bottom flask that contained pre-heated pentanol. The mixture was
then stirred under reflux at 160 ꢁC for 26 h in an argon atmosphere
in the presence of excess germanium (IV) chloride as a metal salt
and DBU as a catalyst. Thereafter, the mixture was cooled to room
temperature and dropped in n-hexane to precipitate. The green
solid product precipitated and was collected by centrifugation and
washed with n-hexane and dried in air. Purification was achieved
using column chromatography with neutral alumina as column
material and DCM:MeOH:THF (10:3:3) as eluent, followed by
drying. The desired product was further washed with ethanol,
Scheme 1. Schematic representation of the statistical synthetic route used for the synthesis of low symmetry monocarboxy phthalocyanine complexes: (OH)2GeMCPc (3), OTiMCPc
(4) and (ac)2SnMCPc (5). ac ¼ acetate.

166
N. Masilela, T. Nyokong / Dyes and Pigments 91 (2011) 164e169
acetone, n-hexane and diethylether in a Soxhlet extraction appa-
ratus. Yield: (10.44%). IR (KBr, cmꢀ1): 3447(OeH), 3123(CeH),
2854e2969 (carboxylic acid OH), 1559(C]C), 1447, 1348, 1128, 843,
3. Results and discussion
3.1. Synthesis and characterization
748 (CeSeC), 701(GeeO), 610, 543. 1H-NMR (DMSO-d6):
d, ppm
9.17e9.19 (9H, m, Pc-H), 8.27e8.29 (3H, br, Pc-H), 4.73e4.78 (2H, br,
OH) 3.37 (12H, m, SeCH2), 2.13e2.24 (12H, q, NeCH2), 1.67e1.74
(18H, dd, CH3). UV/Vis (DMF) lmax nm (log 3): 350 (3.26), 695 (4.87).
Calc. for C51 N11H57O4S3Ge: C 57.98, N 14.59, H 5.39, S 9.11; Found: C
56.32, N 13.17.H 5.39, S 10.47. MALDI TOF MS m/z: Calcd: 1055.59.
Found: [M ꢀ 3H]þ 1053.18.
Scheme 1 shows the synthetic route employed for the mono-
functionalized carboxy Ge (3), Ti (4) and Sn (5) phthalocyanines.
The most common strategy for synthesizing the low symmetry Pc’s
is statistical condensation reactions using two different precursors.
Thus in this work, phthalonitrile 1 (A) and 2 (B), Scheme 1 were
employed to form an expected mixture of compounds with AAAA,
AAAB, AABB, ABAB, ABBB, and BBBB structures as previously
2.3.2. Tris {9 (10), 16 (17), 23 (24)-4-(2-diethylaminoethanethiol)-
2-(4-carboxyphthalonitrile) phthalocyaninato} titanium (IV) oxide
(Scheme 1, (TiMCPc (4)))
described in literature [20e23,31,32]. Phthalonitrile 1 was
substituted with bulky groups to enhance the solubility of the low
symmetry phthalocyanines which improves the separation of the
various compounds formed. However the separation of the
different structures formed was extremely challenging since it
required different solvent ratios with various polarity to elute each
compound. In forming the desired mono-functionalized carboxy
phthalocyanine (AAAB type), the synthetic method was optimized
in statistical terms by adjusting the ratio to 3:1 mol equivalence of
the phthalonitrile (1 and 2) precursors. Chromatographic separa-
tion of the desired product from the other products was then
undertaken successfully. The AAAB will also contain structural
isomers.
The desired mono-functionalized carboxy complexes were
obtained in relatively low yields, with complex (3) having a slightly
higher yield of 10.44% and complexes 4 and 5 with a yield of 8.15
and 8.21%, respectively. The structural analyses of all the three
(complex 3, 4 and 5) newly synthesized compounds were consis-
tent with the predicted structures as shown in the experimental
section. The complexes were successfully characterized with
spectroscopic techniques such as the UVevis, MaldieTOF MS, IR,
proton NMR and by elemental analyses. The formation of phtha-
locyanine complexes (3e5) was characterized by the disappearance
CN vibration in the 2200e2250 cmꢀ1 region. The 1H-NMR spectra
of all the complexes showed aromatic Pc ring protons between 8
and 10 ppm. Phthalocyanine aggregation at the concentrations
used for the 1H-NMR measurements leads to broadening of the
aromatic signals [33], all the proton NMR peaks integrated correctly
giving the expected total number of protons for each complex (3, 4
and 5), confirming the relative purity of the complexes as shown in
the experimental section.
The synthesis and purification of the low symmetry titanium
(IV) phthalocyanine complex (4) was as outlined for the low
symmetry germanium (IV) phthalocyanine complex (3), except that
0.8 mL titanium (IV) butoxide was employed as a metal source
instead of germanium (IV) chloride. Purification procedure and the
amounts of the rest of the reagent were as outlined for (3).
Yield: (8.15%). IR (KBr, cmꢀ1): 3439(OeH), 3213(CeH),
2850e3000 (carboxylic acid OH), 1491(C]C), 1353, 1238, 987(Ti]
O), 962, 742 (CeSeC), 572. 1H-NMR (DMSO-d6):
d, ppm 8.91e8.99
(9H, m, Pc-H), 8.57e8.62 (3H, br, Pc-H), 3.58e3.60 (12H, m, SeCH2),
2.96e3.01 (12H, m, NeCH2), 1.98e2.01 (18H, dd, CH3). UV/Vis
(DMF) lmax nm (log
3): 340 (3.31), 734 (4.91). Calc. for
C51N11H55O3S3Ti þ H2O: C 59.32, N 15.20, H 5.52, S 9.32; Found: C
58.69, N 14.43, H 4.29, S 8.73. MALDI TOF MS m/z: Calcd:
1012.88 Da. Found: [M þ H]þ 1013.58 Da.
2.3.3. Tris {9 (10), 16 (17), 23 (24)-4-(2-diethylaminoethanethiol)-
2-(4-carboxyphthalonitrile) phthalocyaninato} tin (IV) acetate
(Scheme 1, (SnMCPc (5)))
The synthesis and purification of the low symmetry tin (IV)
phthalocyanine complex (5) was as outlined for the low symmetry
germanium (IV) phthalocyanine complex (3), except that excess tin
(IV) acetate was employed as a metal salt instead of germanium (IV)
chloride. Purification procedure and the amounts of the rest of the
reagent were as outlined for (3).
Yield: (8.21%). IR (KBr, cmꢀ1): 3439(OeH), 3213(CeH),
2824e2897 (carboxylic acid OH), 1587(C]C), 1326, 1335 (CeO),
1265, 829, 758 (CeSeC), 673, 559 (SneO). 1H-NMR (DMSO-d6):
d,
ppm 9.10e9.19 (9H, m, Pc-H), 8.64e8.67 (3H, br, Pc-H), 4.15e4.22
(6H, m, ac-CH3) 3.81e3.88 (12H, m, SeCH2), 3.14e3.20 (12H, q,
All the other characterization techniques confirmed the struc-
tures for each compound as presented in the experimental section.
NeCH2), 2.10e2.16 (18H, dd, CH3). UV/Vis (DMF) lmax nm (log 3):
330 (3.47), 720 (4.90). Calc. for C51N11H55O2S3Sn: C 57.52, N 14.43, H
5.51, S 9.01; Found: C 57.74, N 13.55.H 6.39, S 8.52. MALDI TOF
MS m/z: Calcd: 1185.71. Found: [M ꢀ 1H]þ 1184.80.
3.2. Ground state UVevisible spectral characterization
The ground state absorption spectra for complexes 3e5 are
shown in Fig. 1a. The broadening of the Q band in symmetrical Pcs
is usually associated with aggregation [34e36], however for
unsymmetrically substituted phthalocynines, loss of symmetry will
also result in broadening or splitting of spectra. A clear splitting of
the Q band was observed for SnPc derivative (5), the TiPc derivative
(4) did not show splitting but the spectrum was broadened. Less
broadening was seen for the GePc derivative (3). Fig. 2 shows that
as the concentration was increased for complex (4), the intensity of
the absorption of the Q band maxima also increased and there were
no new bands normally blue shifted due to the aggregated species.
Same trend was also observed with complex which did not show
aggregation in DMF. BeereLambert’s law was obeyed for all of these
complexes in the concentrations ranging from 2 ꢂ 10ꢀ6 to
14 ꢂ 10ꢀ6 mol dmꢀ3. These studies confirm that the broadness is
not due to aggregation, but most likely due to the low symmetry
nature of the complexes especially for complexes 4 and 5. OTiPc
complexes are known to have a slightly square pyramidal structure
2.4. Fluorescence behaviour
The fluorescence quantum yields
comparative method [29] using Equation (1)
(
FF
)
were obtained by
(1)
F$AStd$n2
FF
¼
FFðStdÞ
$
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 absorbances
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
[30]. For each study at least two independent experiments were
performed for the quantum yield determinations. Both the sample
and the standard were excited at the same relevant wavelength.

N. Masilela, T. Nyokong / Dyes and Pigments 91 (2011) 164e169
167
The Q band absorption maxima in DMF (Fig. 1a) of the various
monocarboxy Pc’s were observed at completely different wave-
lengths. As shown in Table 1, complex 4 (Q band at 734 nm) and
complex 5 (Q band at 720 nm) were red shifted relative to complex
3 (Q band at 695 nm). The shift in spectra has been explained in
terms of conformational distortion caused by the stress of the
substituents in MPc complexes [40]. And have also been attributed
to coordination of certain ligands to the central metals leading to
enlargement of the
p-system of the Pc [37,41]. However certain
central metals such as Ti and Sn are known to result in red shift of
the Q band [42]. In this work, the red shifting of the Q band of these
low symmetry phthalocyanine complexes was strongly influenced
by the electron donating nature of the diethylaminoethanethiol
substituents.
Charge transfer bands were observed for all the three complexes
in a region from 400 to 500 nm, with complex (3) showing the most
prominent charge transfer band compared to complex (4 and 5) in
DMF.
3.3. Fluorescence spectra and properties
Shown in Fig. 3, are the absorption, fluorescence excitation and
emission spectra of the complexes 3e5 in DMF. The fluorescence
excitation of GeMCPc (complex 3, Fig. 3a) was observed as mirror
image of both the absorption and the excitation spectra, and hence
the excitation was similar to the absorption spectra typical of MPcs.
However there was a disagreement of the absorption, fluorescence
excitation and emission of complexes 4 and 5 (Fig. 3b and c). The
deviation of the spectra could be due to size of the central metal in
particular for SnMCPc (4) which showed a more pronounced
splitting upon excitation, due to loss of symmetry. The loss of
symmetry or disagreement of the spectral properties has been
documented before (i.e on InPc [43] and SnPc [44] derivatives) and
it was found to be due to the fact that Sn and In are metals with
large atomic numbers that can be easily displaced from the core of
the Pc ring on excitation, hence resulting into a loss of symmetry.
For TiMCPc, the excitation spectrum was red shifted and nar-
rower compared to absorption spectrum, and the emission spec-
trum was a mirror image of the excitation spectrum, Fig. 3b. The red
shift and narrowing in the excitation spectrum compared to
absorption spectrum for complex 4 suggests aggregation with only
the monomer fluorescing. This confirms that in Fig. 1, the observed
broadening in the absorption spectrum includes contribution from
the aggregate even though Beer’s law was obeyed in the concen-
tration range of Fig. 2. Stokes shifts for complexes 4 and 5 were
larger than is typical of MPc complexes [45,46]. For symmetrically
substituted OTiOCPc, the absorption and excitation spectra were
similar and mirror images of emission spectrum due to lack of
aggregation [36].
Fig. 1. Ground state electronic absorption spectra of (a) GeMCPc (3), TiMCPc (4) and
SnMCPc (5) in DMF and (b) OTiOCPc in pH 10 buffer.
[37], hence do not fit perfectly into the center of the ring. Sn is
a large metal hence it also does not fit into the Pc ring. This may
explain why both TiPc and SnPc derivatives show more broadening
in the spectra due to the effects of both the central metal and the
unsymmetric nature of the substituents. The corresponding
symmetrical octacarboxy phthalocyanines (MOCPc) did not show
the broadening in spectra (see for example Fig. 1b for OTiOCPc)
[36,38] observed for complexes 4 and 5, hence exhibited no
aggregation as is typical of MOCPc complexes. These complexes are
not aggregated even in aqueous media where in general phthalo-
cyanines are aggregated. Phthalocyanines containing dieth-
ylaminoethanethiol substituents also show a narrow Q band typical
of phthalocyanines [39].
Fig. 4 shows the time-resolved florescence decay curve for
SnMCPc (5) in DMF, indicaticating a mono-exponential decay. A
mono-exponential decay was observed for all the complexes (3, 4
and 5) in DMF suggesting only one fluorescing species present in
each solution. The fluorescence lifetimes (Table 1) were obtained
Table 1
Fluorescence and UVevisible spectral data for (OH)2GeMCPc, (ac)2SnMCPc and
OTiMCPc in DMF.
Compound
Q-band
Emission
Fluorescence Fluorescence
quantum
wavelength wavelength Life time
(nm)
(OH)2GeMCPc (3) 695
(nm)
(
s
F) (ns)
yield (FF)
700
765
748
1.61
1.84
2.35
0.09
0.11
0.14
Fig. 2. Ground state electronic absorption spectra of TiMCPc at various concentrations:
(i) 2 ꢂ 10ꢀ6, (ii) 4 ꢂ 10ꢀ6, (iii) 6 ꢂ 10ꢀ6, (iv) 8 ꢂ 10ꢀ6, (v) 10 ꢂ 10ꢀ6, (vi) 12 ꢂ 10ꢀ6 and
14 ꢂ 10ꢀ6 mol dmꢀ3 in DMF.
OTiMCPc (4)
734
720
(ac)2SnMCPc (5)

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N. Masilela, T. Nyokong / Dyes and Pigments 91 (2011) 164e169
from the photoluminescence decay curves and all the lifetimes
showed an increase with the increase in fluorescence quantum
yield. Complex (3) showed the lowest fluorescence quantum yield
(FF) and lifetime of 0.09 and 1.61 ns in DMF, followed by complex
(4) with 0.11 fluorescence quantum yield and a life time of 1.84 ns
and complex 5 showed the highest yield and lifetime of 0.14 and
2.35 ns respectively. The fluorescence quantum yield values were
within a range reported for MPcs in general [45,46]. The FF value
for symmetrically substituted (OH)2GeOCPc of 0.19 in DMSO has
been reported [38]. In aqueous media a FF ¼ 0.07 for OTiOCPc was
reported [36] with a fluorescence lifetimes of 1.59 ns. Thus in terms
of the fluorescence parameters, the unsymmetrically substituted
complexes reported in this work do not differ much from their
symmetrical counterparts.
4. Conclusions
The synthesis and characterization of novel low symmetrically
substituted carboxy phthalocyanines was successfully achieved.
Spectral changes upon excitationwere observed for complex 4 and 5
due to their sizes and the nature of the axial ligands. The fluores-
cence behaviour of the complexes was successful investigated, and
an increase in fluorescence lifetimes was observed with increase in
fluorescence quantum yield. The trend of the fluorescence behav-
iour (lifetimes and quantum yields) of all the compounds can be
summarized in the form of an increasing order as follows;
(OH)2GeMCPc < OTiMCPc < (ac)2SnMCPc respectively. The pres-
ence of one carboxy group makes these molecules ideal for coor-
dination to biological molecules and quantum dots since a more
defined coordination is achieved. Thus the use of these molecules in
applications such as photodynamic therapy when coordinated to
cancer specific molecules will be explored in the future in
comparison with their symmetrically substituted counterparts.
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
Nanotechnology and Rhodes University. NM thanks DAAD for
funding.
Fig. 3. UVevis absorption (i), fluorescence emission (ii) and excitation (ii) spectra of (a)
GeMCPc (3), (b) TiMCPc (4) and (c) SnMCPc (5) in DMF.
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