The syntheses and photophysical properties of 4,4′- isopropylidendioxydiphenyl substituted ball-type dinuclear Mg(II) and Zn(II) phthalocyanines

Article abstract of DOI:10.1016/j.poly.2011.10.024

The syntheses of ball-type dinuclear Zn(II) and Mg(II) phthalocyanines containing four 4,4′-isopropylidendioxydiphenyl substituents at the peripheral and non-peripheral positions are presented. The structures of the synthesized compounds were characterize

Full text of DOI:10.1016/j.poly.2011.10.024

Polyhedron 31 (2012) 704–709
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Polyhedron
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The syntheses and photophysical properties of 4,40-isopropylidendioxydiphenyl
substituted ball-type dinuclear Mg(II) and Zn(II) phthalocyanines
Mevlüde Canlıca a,b, Tebello Nyokong b,
⇑
a Yildiz Technical University, Chemistry Department, Inorganic Chemistry Division, Davutpasa Campus, 34220 Esenler, Istanbul, Turkey
b Rhodes University, Chemistry Department, P.O. Box 6140, Grahamstown, South Africa
a r t i c l e i n f o
a b s t r a c t
The syntheses of ball-type dinuclear Zn(II) and Mg(II) phthalocyanines containing four 4,40-isopro-
pylidendioxydiphenyl substituents at the peripheral and non-peripheral positions are presented. The
structures of the synthesized compounds were characterized using elemental analyses, and UV–Vis,
FT-IR, 1H NMR and mass spectroscopies. The UF values were 0.14, 0.11, 0.22, 0.15 and UT values were
0.84, 0.88, 0.62, 0.74, for 6–9, respectively. The largest triplet yields were observed for the non-peripher-
ally substituted complexes 6 and 7, showing that non-peripheral substitution favors increased population
of the triplet state. All complexes showed reasonably long triplet lifetimes with sT 510, 310, 910 and
Article history:
Received 3 April 2011
Accepted 24 October 2011
Available online 2 November 2011
Keywords:
Mg ball-type phthalocyanine
Zn ball-type phthalocyanine
Photodynamic therapy
Non-peripheral phthalocyanine
Triplet quantum yield
350 ls in DMSO, respectively.
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
properties of ball-type Pcs can change dramatically depending on
the bridging compounds or the central metal. The distance be-
tween the two Pc units affect the degree of interactions between
the rings. In this paper, we describe the syntheses and photophys-
ical properties of new symmetrically substituted ball-type MgPc
and ZnPc complexes containing substituents at the non-peripheral
Metallophthalocyanines (MPcs) have been studied as materials
for many applications including in electronics [1], non-linear optics
[2], liquid crystals [3], gas sensors [4], photosensitizers [5,6], elect-
rocatalysis [7], semiconductors [8] and photovoltaic cells [9]. There
is considerable interest in MPc complexes containing non-transi-
tion metals for use as photosensitizers in the relatively new meth-
od of cancer treatment called photodynamic therapy (PDT)
[5,6,10–14]. The mode of operation in PDT is based on visible light
excitation of a tumor-localized photosensitizer. After excitation,
energy is transferred from the photosensitizer (in its triplet excited
state) to ground state oxygen (3O2), forming excited singlet state
oxygen (1O2). High triplet state quantum yields and long triplet
lifetimes are required for efficient photosensitization. Syntheses,
electrochemical and spectroelectrochemical behavior of ball-type
Pc derivatives have been extensively studied since the complexes
were published in the literature for the first time in 2002 [15,16].
Ball-type phthalocyanine derivatives show spectroscopic and elec-
trochemical properties which differ significantly from the parent
monomer [17–19]. However, the studies on non-peripherally
substituted ball-type MPc derivatives are still limited and the
photophysical behavior of ball-type molecules in general have also
not received much attention. Our interest in ball-type complexes is
due to the possibilities of intramolecular interactions between the
Pc rings and/or metal centers of these compounds. The electronic
(a) and peripheral (b) positions, Scheme 1.
2. Experimental
2.1. Materials
Anhydrous magnesium(II) chloride and zinc(II) acetate were
purchased from Sigma-Aldrich. All solvents for example dimethyl-
sulfoxide (DMSO) and chloroform were from Saarchem. Silica gel
for column chromatography was purchased from MERCK. All other
reagents were obtained from suppliers and used as received.
2.2. Equipment
UV–Vis absorption spectra were obtained using the Varian Cary
500 UV–Vis/NIR spectrometer. Fluorescence excitation and emis-
sion spectra were recorded with Varian Eclipse spectrophotometer.
FT-IR data were recorded using the Perkin-Elmer spectrum 2000
FTIR spectrometer. 1H NMR spectra were obtained using a Bruker
EMX 400 MHz spectrometer. Elemental analyses were done on a
Vario-Elementar Microcube EL III. Mass spectral data were col-
lected with a Bruker AutoFLEX III Smartbeam MALDITOF/TOF Mass
spectrometer. The instrument was operated in positive ion mode
⇑
Corresponding author. Tel.: +27 46 6038260; fax: +27 46 6225109.
E-mail address: t.nyokong@ru.ac.za (T. Nyokong).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.10.024

M. Canlıca, T. Nyokong / Polyhedron 31 (2012) 704–709
705
O
O
O
H3
H3
C
C
CH
3
N
O
CN
N
N
N
M
N
CH3
H3
C
N
N
O
CN
CN
O2N
N
CN
CN
ii
H3
C
O
O
N
OH
H3C
CH3
N
N
(2)
N
M
N
i
i
N
N
O
CN
H3
C
CH3
H3C
H3C
N
(5)
O
O
(8) M=Mg
(9) M=Zn
O
CH3
O
NO2
H3C
H3C
OH
O
N
(3)
CH3
CN
N
N
N
M
N
N
H3
C
O
O
N
N
NC
CN
ii
N
O
CN
H3
C
(1)
NC
CN
O
O
CH3
CH3
N
H3C
H3C
N
N
N
M
O
N
N
N
(4)
O
(6) M=Mg
(7) M=Zn
Scheme 1. Non-peripherally and peripherally substituted ball-type metallophthalocyanines. i: DMSO, rt, 5 days. ii: MgCl2, 450 °C, 15 min for 6,8 and Zn(CH3COO)2, 300 °C,
12 min for 7,9.
using an m/z range of 400–3000. 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 and a 354 nm nitrogen laser.
Triplet absorption and decay kinetics were recorded on a laser flash
photolysis system, the excitation pulses were produced by a Quan-
ta-Ray Nd: YAG laser providing 400 mJ, 9 ns pulses of laser light at
10 Hz, pumping a Lambda-Physic FL 3002, dye (Pyridin 1 in meth-
anol). The analyzing beam source was from a Thermo Oriel xenon
arc lamp, and a photomultiplier tube was used as a detector. Sig-
nals were recorded with a two-channel 300 MHz digital real-time
oscilloscope (Tektronix TDS 3032C); kinetic curves were averaged
over 256 laser pulses. The triplet lifetimes were determined by
exponential fitting of the kinetic curves using the OriginPro 7.1.
potassium carbonate (2.4 g, 17.3 mmol) was added. After 4 h of
stirring at room temperature, further potassium carbonate
(0.58 g, 4.3 mmol) was added and this same amount was added
again after 24 h of stirring. After a total of 5 days of stirring, the
reaction mixture was poured into water (200 mL) resulting in the
formation of a white precipitate. The crude product was centri-
fuged and was further purified by chromatography over a silica
gel column using a CHCl3 as eluent. This process was repeated
once. Finally, the pure product was dried using P2O5 for one week.
Yield: 2.9 g. IR(KBr) (l
max/cmꢀ1): 3078 (Ar–CH), 2228 (C„N), 1573
(C@C), 1256 (C–O–C). 1H NMR (DMSO-d6): d, ppm 7.83 (2H, d,
J = 7.6 Hz, Ar–H), 7.37 (2H, d, J = 8.8 Hz, Ar–H), 7.29 (6H, d,
J = 7.2 Hz, Ar–H), 7.18 (4H, d, J = 8.4 Hz, Ar–H), 1.69 (6H, s, –CH3).
Anal. Calc. for C31H20N4O2: C, 77.49; H, 4.20; N, 11.66%. Found: C,
77.37; H, 3.68; N, 12.03%.
General procedure for 6–8: A mixture of complex 4 or 5 (0.10 g,
0.21 mmol) and magnesium(II) chloride (0.3 g, 0.31 mmol) for 6
and 8 or zinc(II) acetate (0.104 g, 0.313 mmol) for 7 (using 4)
was ground in a quartz crucible and heated in sealed glass tube
for 15 min under argon atmosphere at 450 °C for MgPcs 6 and 8
and for 12 min under argon atmosphere at 300 °C for ZnPc 7,
respectively. After cooling to room temperature, the green reaction
products were washed with hot methanol and hot water. The prod-
ucts were separated by column chromatography on silica gel using
chloroform and a gradient of chloroform-methanol up to 50%. And
then, the products were washed with methanol, ethanol, acetoni-
trile and acetone for 24 h, consecutively in the Soxhlet apparatus.
Finally, the green products were obtained by column chromatogra-
phy on silica gel using chloroform as eluting solvent. All of the
compounds are soluble in common solvents such as CHCl3, dichlo-
romethane, dimethylformamide, and DMSO, and had Mp >350 °C.
2.3. Syntheses
3-Nitrophthalonitrile 1 and 4-nitrophthalonitrile 2 were syn-
thesized according to literature [20]. 4,40-Isopropylidendioxydi-
phenyl
3
was obtained from commercial suppliers. The
syntheses of compounds 5 and 9 has been reported in literature
[21]. All solvents were dried and purified as described by Perrin
and Armarego [22]. Commercial CHCl3 was dried with P2O5 then
distilled. The distilled CHCl3 was stored on activated molecular
sieves. Purification of commercial DMSO was achieved by drying
overnight with chromatographic grade alumina. It are then re-
fluxed for 4 h over CaO, dried over CaH2, and then fractionally
distilled at low pressure. It was then stored over molecular sieves.
Both solvents purified freshly before use. Target precursor 4
was prepared by a nucleophilic aromatic substitution reaction
between compound 1 and 4,40-isopropylidendioxydiphenyl 3 in
DMSO, Scheme 1.
2.3.2. 10,110,150,250-[Tetrakis(4,40-isopropylidenedioxydiphenyl)]bis-
phthalocyaninato dimagnesium(II) (6)
2.3.1. 3,30-[4,40-(Propane-2,2-diyl) bis(4,1-phenylene)]bis(oxy)
diphthalonitrile (4)
Compound 3 (2.0 g, 8.67 mmol) was dissolved in dry DMSO
(15 mL) and compound 1 (3 g, 17.34 mmol) was added under inert
atmosphere. To this reaction mixture finely ground anhydrous
Dark green color. Yield: 0.010 g (10%). UV–Vis (CHCl3) kmax/nm
(log
e
/dmꢀ3 molꢀ1 cmꢀ1): 742 (3.72), 700 (4.70), 671 (4.01), 632
(3.97), 320 (4.52). IR[(KBr) l
max/cmꢀ1]: 3085 (Ar–CH), 1577 (C@C),
1256 (C–O–C). 1H NMR (DMSO-d6): d, ppm 7.85–7.02 (56H, m,
Ar–H), 1.72 (24H, m. –CH3). Anal. Calc. For C124H80N16O8Mg2: C,

706
M. Canlıca, T. Nyokong / Polyhedron 31 (2012) 704–709
USTtd is the triplet quantum yield for the standard, ZnPc (UT = 0.65 in
DMSO) [27].
T and eSTtd were determined from the molar extinction
coefficients of their respective ground singlet state (
S and eSStd) and
AS and
75.57; H, 4.09; N, 11.37. Found: C, 76.01; H, 4.15; N, 11.45%. MALDI-
TOF-MS m/z Calculated: 1970.67. Found [M]+: 1970.82.
e
e
2.3.3. 10,110,150,250-[Tetrakis(4,40-isopropylidenedioxydiphenyl)]bis-
phthalocyaninato dizinc(II) (7)
the changes in absorbances of the ground singlet states (
D
D
ASStd), and excited triplet states (
DAT and
D
ASTtd) according to Eq. (3):
Green color. Yield: 0.012 g (11%). UV–Vis (CHCl3) kmax/nm (log
e/
D
D
AT
AS
dmꢀ3 molꢀ1 cmꢀ1): 743 (3.92), 699 (4.56), 669 (3.93), 630 (3.87),
eT
¼
eS
ꢁ
ð3Þ
320 (4.64). IR[(KBr)
l
max/cmꢀ1]: 3078 (Ar–CH), 1579 (C@C), 1245
(C–O–C). 1H NMR (DMSO-d6): d, ppm 7.85–7.01 (56H, m, Ar–H),
1.70 (24H, m, –CH3). Anal. Calc. For C124H80N16O8Zn2: C, 72.55; H,
3.93; N, 10.92. Found: C, 71.92; H, 3.88; N, 10.93%. MALDI-TOF-
MS m/z Calculated: 2052.88. Found [Mꢀ4H]+: 2048.49.
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 6–9 molecules.
UIC ¼ 1 ꢀ ðUF
þ
UT
Þ
ð4Þ
2.3.4. 20,100,160,240-[Tetrakis(4,40-isopropylidenedioxydiphenyl)]bis-
phthalocyaninato dimagnesium(II) (8)
Dark green color. Yield: 0.012 g (12%). UV–Vis (CHCl3) kmax/nm
3. Results and discussion
(log
(4.36). IR[(KBr)
e
/dmꢀ3 molꢀ1 cmꢀ1): 685 (4.33), 670 (3.97), 619 (3.71), 350
l
max/cmꢀ1]: 3064 (Ar–CH), 1587 (C@C), 1238 (C–
3.1. Syntheses and characterization
O–C). 1H NMR (DMSO-d6): d, ppm 7.76–6.95 (56H, m, Ar–H), 1.70
(24H, m, –CH3). Anal. Calc. For C124H80N16O8Mg2: C, 75.57; H,
4.09; N, 11.37. Found: C, 75.68; H, 4.37; N, 11.39%. MALDI-TOF-
MS m/z Calculated: 1970.67. Found [M]+: 1969.996.
The syntheses of bisphthalodinitriles 4 and 5 is based on the
reaction of 3 with excess of compound 1 or 2 in dry DMSO in the
presence of K2CO3 as a base, at room temperature in good yields.
The ball-type binuclear Mg(II)Pc and Zn(II)Pc complexes 6–8 were
prepared as a mixture of isomers by the reaction of compound 4 or
5 with MgCl2 or Zn(CH3COO)2. Complex 9 was synthesized as re-
ported before [21]. Cyclotetramerization of the phthalonitrile
derivative 4 or 5 to the MPc derivatives 6–8 was accomplished
without a solvent in the presence of metal salts at 300 °C for 7
and 450 °C for 6 and 8. Column chromatography on silica gel using
CHCI3 as mobile phase was used twice to purify the complexes. The
structure and purity of the MgPc and ZnPc derivatives was con-
firmed by UV–Vis, 1H NMR, IR and mass spectral data and elemen-
tal analyses.
The IR spectrum of 4 clearly indicates the absence of OH groups
of 3. A diagnostic feature of the formation of 6–8 from the phtha-
lodinitrile derivatives 4 and 5, is the disappearance of the sharp CN
vibration of the latter at 2228 and 2232 cmꢀ1, respectively.
The 1H NMR spectra of 4 shows the aromatic protons between
7.87 and 7.26 ppm, integrating for a total of 20 for protons. In the
1H NMR spectrum of 4, a sharp singlet signal was observed at
1.69 ppm belonging to CH3. The 1H NMR spectra of Pcs 6–8, were re-
corded in DMSO, and were similar to each other. The aromatic pro-
tons appeared at 7.85–7.02, 7.85–7.01 and 7.76–6.95 ppm as well
as CH3 groups at 1.72, 1.70 and 1.70 ppm, respectively and integrat-
ing for a total of 80 for 6–8. Elemental analysis results also were
consistent with the proposed structures of 6–8. The purified phthal-
ocyanines were further characterized by mass spectra. The ex-
pected mass values corresponded with the found values for all
complexes using dithranol as the matrix. The results were repeated
twice to give the observed molecular peaks. Molecular ion peak for
MgPcs and deprotonated molecular ion peak ZnPcs were found. The
ion peaks of complexes 6-8 were observed at 1970.82, 2048.49 and
2.4. Photophysical studies
2.4.1. Fluorescence quantum yields
Fluorescence quantum yields (UF) were determined by the
comparative method [23,24], Eq. (1):
F ꢁ AStd ꢁ n2
UF
¼
UFðStdÞ
ð1Þ
FStd ꢁ A ꢁ n2Std
where F and FStd are the areas under the fluorescence curves of 6–9
and the standard, respectively. A and AStd are the respective absor-
bances of the sample and standard at the excitation wavelengths
(which was ꢂ0.05 in all solvents used), and n and nStd are the refrac-
tive indices of solvents used for the sample and standard, respec-
tively. ZnPc (UF ¼ 0:20) was employed as the standard [25].
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–Visible spectrophotome-
try cell, deaerated using nitrogen and irradiated at the Q-band
maxima. Triplet state quantum yields (UT) of 6–9 were determined
by the triplet absorption method [26] using zinc phthalocyanine
(ZnPc) as a standard; Eq. (2):
D
D
AT ꢁ eSTtd
ASTtd
UT
¼
USTtd
ꢁ
ð2Þ
ꢁ
eT
where
D
AT and D
ASTtd are the changes in the triplet state absorbances
of 6–9 and the standard, respectively. eT and eSTtd are the triplet state
molar extinction coefficients for 6–9 and the standard, respectively.
Fig. 1. Absorption spectra of complexes 6–9 in CHCl3 at concentration 5 ꢃ 10ꢀ5 mol dmꢀ3
.

M. Canlıca, T. Nyokong / Polyhedron 31 (2012) 704–709
707
1969.996 amu, respectively. MPc complexes have been observed to
degrade with molecular ion peaks [M]+, [M+nH]+ or [MꢀnH]+ (with
n being variable) [28] in some matrices as observed in this work.
The UV–Vis spectra in CHCl3 shown in Fig. 1 for 6–9 are in ac-
cord with the expected structure. The band maxima are listed in
Table 1. The phthalocyanines show typical electronic spectra with
Table 1
UV–Vis absorption (Q-band), emission and excitation spectral data, and photophysical data for the phthalocyanines.
Solvent
kmax/nm (log
CHCl3
e
/dmꢀ3 molꢀ1 cmꢀ1
)
DMSO
kAbs
kAbs
kEms
kExc
D
kStokes
UF
UT
UIC
sT (ls)
Complex
6
7
8
9
700(4.70)
699(4.59)
685(4.33)
682(4.56)
698
697
682
680
709
707
692
691
699
698
683
682
11
10
10
11
0.14
0.11
0.22
0.15
0.84
0.88
0.62
0.74
0.02
0.01
0.16
0.11
510
310
910
350
Fig. 2. Absorbance (a), excitation (b), emission (c) spectra of complexes 6–9 in DMSO, Excitation kmax = 614, 620, 622, 613 nm, respectively.

708
M. Canlıca, T. Nyokong / Polyhedron 31 (2012) 704–709
two absorption regions, one in the UV region at about 300–400 nm
(B-band) and the other in the visible region at 600–700 nm (Q-
band). Aggregation behavior of Pc is a result of 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 [29]. Aggregation in
MPcs is observed as a broadened or split Q-band, with the high en-
ergy band being due to the aggregate and the low energy band due
to the monomer. Complexes 6 and 7 show Q-band absorptions at
698 nm, 697 nm whereas complexes 8 and 9 show Q-bands
absorption at 682 nm, 680 nm in DMSO, Table 1. In CHCl3, com-
plexes 6 and 7 show Q-band absorption at 700 and 699 nm,
whereas complexes 8 and 9 show Q-band absorption at 685 and
682 nm, respectively, Table 1 and Fig. 1. This red shift in complexes
6 and 7 is due to substitution at non-peripheral position. It is well
Fig. 3. Triplet state decay curve of complex 7 in DMSO.
monomeric phthalocyanines, showing the interaction between
the two rings is minimal.
known that
a substitution results in red shifting of the spectra
[30,31]. Complexes 6–9 show B-bands from 320 to 337 nm. How-
ever, complexes 6 and 7 in CHCl3 has an extra band near 742 and
743 nm, which could be associated with a loss of symmetry often
observed in chlorinated solvents [32]. The observation of the extra
band in chloroform is due to protonation since this solvent may
contain small amounts of acid as observed before [33]. This extra
band is not observed in DMSO. The broad shoulder observed at
632, 630, 619, 613 nm for 6–9, respectively, in chloroform has been
reported to indicate aggregation of complexes of ball-type struc-
ture [17–19].
3.3. Triplet quantum yields and lifetimes
The triplet quantum yields (UT) and lifetimes of the complexes
are listed in Table 1 and Fig. 3 shows the triplet decay curve for the
complex 7 (in DMSO) which obeyed second order kinetics. Triplet
quantum yields represent the fraction of absorbing molecules that
undergo intersystem crossing to the metastable triplet excited
state.
A well defined band near 620 nm in ball-type phthalocyanines
is due to exciton coupling between the two Pc rings [17]. The spec-
tra of complexes 6 to 9 in DMSO shows bands in this region, which
may be attributed to intermolecular interactions between the rings
in agreement with literature. However, there is more broadening
for 8 and 9 which are peripherally substituted, due to aggregation.
Non-peripheral substitution prevents aggregation to a larger ex-
tent compared to peripheral substitution. Thus it is clear that there
is more aggregation for complexes 8 and 9 which are peripherally
substituted compared to non-peripherally substituted 6 and 7, as is
typical of phthalocyanines [31].
High UT values and correspondingly low UF values are observed
for ZnPc derivatives compared to MgPc counterparts substituted at
same positions, due to a more efficient intersystem crossing (ISC),
for the former complexes. The UT values for 6–9 are 0.84, 0.88, 0.62
and 0.74, respectively. The UT values are higher for the non-periph-
erally substituted derivatives 6 and 7 compared to their peripher-
ally substituted derivatives 8 and 9, due to reduced aggregation in
the former.
Complexes 6–9 have low UIC values, which may be explained by
strong intramolecular interactions between the Pc rings, probably
due to the cofacial structure. All complexes showed reasonably
long triplet lifetimes with sT ranging from 310 to 910
ls. MgPc
derivatives 6 and 8 show longer T when compared to ZnPc deriv-
s
3.2. Fluorescence spectra and quantum yields
atives 7 and 9, due to the heavy atom effect of Zn. Non-peripheral
substitution in 7 shows slightly shorter sT values compared to
peripheral substitution in 9 for ZnPc derivatives, hence showing
a small effect of position of the substituent on the triplet lifetime
values. However, comparing MgPc complexes 8 with 6 shows a
large effect of peripheral substitution on triplet lifetimes. The sT
values are much longer for peripheral (8) compared to non-periph-
eral (6) substitution in MgPc derivatives.
The absorption, fluorescence excitation and emission spectra of
complex 6–9 in DMSO are shown in Fig. 2. The excitation, absorp-
tion and emission spectral data are listed in Table 1. The absorption
and excitation spectra show the same Q-band maxima, however,
the absorption spectra are broadened in the 600–650 nm region
for 8 and 9 compared to the emission and excitation spectra, due
to aggregation. The proximity of the wavelength of each compo-
nent of the Q-band absorption to the Q-band maxima of the exci-
tation spectra for all complexes suggests that the nuclear
configurations of the ground and excited states are similar and
not affected by excitation. The emission spectra are mirror images
of the excitation spectra. Stokes shifts were 10 or 11 nm, typical of
ZnPc complexes [32]. The effect of point of substitution is not clear
from the nature of excitation and emission spectra.
The fluorescence quantum yield (UF) values are typical of MPc
complexes for MgPc and ZnPc derivatives (6–9). The UF values ran-
ged from 0.11 to 0.22 in DMSO. The UF values were lower for ZnPc
derivatives than for MgPc derivatives. This is attributed to the cen-
tral Zn metal which is heavier than Mg and hence encourages
intersystem crossing to the triplet state as will be confirmed below.
Face-to-face interaction of the two monomers in dimers is
expected to decrease the energy gap between the singlet state
and the triplet state and enhance the formation of triplet state
(i.e. intersystem crossing increases) decreasing fluorescence [34].
However, in this work the UF values are similar to those of
4. Conclusions
The syntheses of the ball-type Mg(II)Pc and Zn(II)Pc complexes
6–8 and photophysical properties of complexes 6–9 are presented.
MgPc derivatives 6 and 8 show longer sT when compared to corre-
sponding ZnPc derivatives 7 and 9. The largest triplet yields were
observed for the non-peripherally substituted complexes 6 and 7,
showing that non-peripheral substitution favors increased popula-
tion of the triplet state. All complexes show reasonably high triplet
state quantum yields and long triplet life which are required for
efficient photosensitization.
Acknowledgments
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

M. Canlıca, T. Nyokong / Polyhedron 31 (2012) 704–709
709
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[16] A.Y. Tolbin, A.V. Ivanov, L.G. Tomilova, N.S. Zefirov, J. Porphyrins
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[17] O. Bekaroglu, in: J. Jiang (Ed.), Functional Phthalocyanine Molecular Materials,
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