Synthesis and investigation on photophysical and photochemical properties of 7-oxy-3-methyl-4-phenylcoumarin bearing zinc phthalocyanines

Article abstract of DOI:10.1016/j.saa.2012.06.029

The synthesis of peripherally and non-peripherally tetrakis-(7-oxy-3- methyl-4-phenylcoumarin) and peripherally octakis-[tetrachlorotetra-(7-oxy-3- methyl-4-phenyl coumarin)] substituted zinc(II) phthalocyanines are performed and characterized for the fir

Full text of DOI:10.1016/j.saa.2012.06.029

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Synthesis and investigation on photophysical and photochemical properties of
7-oxy-3-methyl-4-phenylcoumarin bearing zinc phthalocyanines
Mehmet Pisßkin a, Mahmut Durmusß b, Mustafa Bulut a,
⇑
a Marmara University, Faculty of Art and Science, Department of Chemistry, 34722 Kadikoy-Istanbul, Turkey
b Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze 41400, Kocaeli, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
The synthesis of peripherally and non-peripherally tetrakis(7-oxy-3-methyl-4-phenylcoumarin) and
peripherally octakis[tetrachloro-tetra(7-oxy-3- methyl-4-phenylcoumarin)] substituted zinc(II) phthalo-
cyanine complexes are performed and characterized for the first time in this study. The photophysical
and photochemical properties of phthalocyanine complexes are also investigated in dimethylformamide.
"
"
"
"
The synthesis of novel coumarin
substituted zinc(II) phthalocyanines
are reported.
The studied complexes exhibited
excellent solubility in general
organic solvents.
Photophysical and photochemical
properties of new compounds are
studied in DMF.
Non-peripheral or peripheral
position effect for tetra substitution
is determined.
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of peripherally and non-peripherally tetrakis-(7-oxy-3-methyl-4-phenylcoumarin) and
peripherally octakis-[tetrachlorotetra-(7-oxy-3-methyl-4-phenyl coumarin)] substituted zinc(II) phthal-
ocyanines are performed and characterized for the first time in this study. The new compounds show
excellent solubility in organic solvents, which makes them candidates for use in different applications.
Photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen genera-
tion and photodegradation under light irradiation) properties of these novel coumarino phthalocyanines
are investigated in dimethylformamide (DMF). The effects of the positions (peripheral or nonperipheral)
of the substituents on the photophysical and photochemical parameters of the coumarino zinc(II) phthal-
ocyanines are reported. The fluorescence quenching behavior of the studied zinc(II) phthalocyanines by
addition of 1,4-benzoquinone (BQ) are also described.
Received 26 December 2011
Received in revised form 12 June 2012
Accepted 23 June 2012
Available online 29 June 2012
Keywords:
Zinc(II) phthalocyanine
Coumarin (2H-chromen-2-one)
Photophysical
Photochemical
Ó 2012 Elsevier B.V. All rights reserved.
Singlet oxygen
Introduction
[1–3]. Several bioactivities of coumarins such as antibacterial,
anticancer, inhibitory of platelet aggregation, steroid 5a-reductase,
Coumarins (2H-chromen-2-ones) are one of the most important
compounds of natural products. They have been used largely in
pharmaceuticals, perfumery and agrochemical industries as start-
ing or intermediate material. They are also used as fluorescent
brightener, efficient laser dye and as additives in food and cosmetics
and HIV-1 protease, have also been reported [1,4–6]. Coumarins
also belong to an important class of fluorescent compounds having
interesting photophysical properties and a wide range of applica-
tions as laser dyes [7], photosensitizers [8], pesticides [9], etc.
The coumarin compounds with an aryl- or heteroaryl substituent
at 3-position exhibit excellent fluorescence properties but the
studied coumarin in this work; the delocalization stopped at the
3-position of the coumarin moiety because of the substitution with
⇑
Corresponding author. Tel.: +90 216 3479641/1370; fax: +90 216 3478783.
E-mail address: mbulut@marmara.edu.tr (M. Bulut).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.06.029

M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
503
methyl groups at 3-position and with phenyl groups at 4-position,
so the molecule showed very low fluorescence properties [10–12].
Phthalocyanines (Pcs) are multi faceted grade of synthetic
organic dyes, electron-rich planar aromatic macrocycles. Pcs
exhibit a wide variety of applications in materials science, indus-
tries, and science of medicine [13,14]. The chemical and physical
characteristics of these compounds have been affected by the cen-
tral metal ion, peripheral substituents and organic molecule at-
tached to the central metal atom as axial ligand [13]. The wide
planar organic surface of the Pc molecule causes aggregation of
the complexes both in solution and in solid state [15,16]. The
aggregation of the Pc molecules affects solubility of Pcs. A major
O
O
O
O
O
N
O
N
N
N
N
Zn
N
O
O
O
i
N
N
N
N
O
O
O
1
O
4
O
O
O
O
O
O
O
O
N
Zn
N
N
N
O
O
O
N
N
N
N
i
N
N
O
O
O
O
2
5
O
O
O
O
Cl
O
O
O
O
Cl
N
N
N
O
O
O
Cl
N
N
N
N
i
Zn
N
N
N
O
Cl
O
O
O
Cl
3
6
O
O
Scheme 1. Synthesis of (7-oxy-3-methyl-4-phenylcoumarin)-substituted zinc(II) phthalocyanine compounds (4–6) (i) DMAE, Zn(OAc)2ꢀ2H2O, reflux.

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M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
disadvantage of Pcs and MPcs is their low solubility in organic sol-
vents or in water. Substituted Pcs have become more soluble in
common solvents. Depending on the polarity of the substituents,
Pcs become more soluble in apolar or polar solvents [17,18].
Water-soluble Pcs are among the most promising photosensitizers
to date, a number of Pcs bearing hydrophilic moieties, such as car-
boxylates, sulfonates, glucose, phosphonates, amino, and carbora-
nyl groups have been reported. The introduction of either long
chains or bulky substituents onto the periphery of the macrocycle
hinders the aggregation in organic solvents, but has almost no con-
tribution to enhance solubility in aqueous medium; similarly, an
ionic substituent such as sulfonate, carboxylate or ammonium
leads to products extensively soluble in aqueous media [19].
In recent years, metallophthalocyanines (MPcs) have been
extensively studied in non-linear optic applications, chemical
sensors, catalysis, liquid crystals, photovoltaic cells, semiconduc-
tive materials and photodynamic therapy (PDT) [20–23]. PDT is
the novel treatment in cancer therapy and this technique based
on a photochemical reaction, which is initiated by light activation
of a photosensitizing drug causing tumor cell death. Pcs are use-
ful photosensitizers due to their intense absorption in red region
of the visible light [24]. Especially zinc Pc complexes are often
used due to their long triplet lifetimes [25]. Such long lifetimes
constitute a great advantage since the number of diffusional
encounters between the triplets excited state and the ground
state molecular oxygen increases with the lifetime of the excited
state [26].
Equipment
Absorption spectra in the UV–vis region were recorded with a
Shimadzu 2001 UV–vis spectrophotometer. Fluorescence excita-
tion and emission spectra were recorded on a Varian Eclipse
spectrofluorometer using 1 cm path length cuvettes at room tem-
perature. IR spectra (KBr pellets) were recorded on a Bio-Rad FTS
175C FTIR spectrometer. Elemental analyses carried out using a
LECO CHN 932 was performed by the Instrumental Analysis
Laboratory of TUBITAK Ankara Test and Analysis Laboratory. Mass
spectra were performed on a Bruker Autoflex III MALDI–TOF spec-
trometer using 2,5-dihydroxybenzoic acid (DHB, 20 mg/mL in THF)
as matrix. MALDI samples were prepared by mixing the compound
(2 mg/mL in THF) with the matrix solution (1:10 v/v) in a 0.5 mL
Eppendorf micro tube. Finally, 1 lL of this mixture was deposited
on the sample plate, dried at room temperature and then analyzed.
1H-NMR spectra were recorded in CDCl3 for Pc compounds (4–6)
on a Varian 500 MHz spectrometer.
General Electric quartz line lamp (300 W) was used for photo-
irradiations studies. 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 (Into, 670 nm with a
band width of 40 nm) was additionally placed in the light path
before the sample. Light intensities were measured with
a
POWER MAX5100 (Molelectron detector incorporated) power
meter.
The aim of our ongoing research is to synthesize 7-oxy-3-
methyl-4-phenylcoumarin substituted zinc Pcs as potential PDT
agents. In view of the biological importance of both coumarins
and Pcs it is worthwhile to combine these two functional mole-
cules into a single compound. In this work, the synthesis, charac-
terization and spectroscopic behavior as well as photophysical
(fluorescence quantum yields and lifetimes) and photochemical
(singlet oxygen generation and photodegradation quantum yields)
properties of non-peripherally (4) and peripherally tetrakis(7-oxy-
3-methyl-4-phenylcoumarin) (5) and peripherally octakis[tetra-
chloro-tetra(7-oxy-3-methyl-4-phenylcoumarin)] substituted zin-
c(II) Pcs (6) (Scheme 1) are presented. These compounds show
good solubility in common organic solvents. The effects of the
number of the substituents, substitution positions and aggregation
on the photophysical and photochemical properties of novel
compounds were investigated. The effects of the number of sub-
stituents and their position on the fluorescence quenching of
coumarino zinc Pcs were also explored by using 1,4-benzoquinone
(BQ). The compounds 4, 5 and 6 might be a potential candidate for
the application of PDT.
Photophysical parameters
Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (UF) were determined by the
comparative method using Eq. (1) [32],
F:AStd:n2
F
UF
¼
UF ðStdÞ
ð1Þ
Std:A:n2Std
where F and FStd are the areas under the fluorescence emission
curves of the samples (4–6) and the standard, respectively. A and
AStd are the respective absorbances of the samples and standard
at the excitation wavelengths, respectively. n and nstd are the refrac-
tive indices of solvents used for the sample and standard, respec-
tively. Unsubstituted ZnPc (UF = 0.20) [33] was employed as the
standard in DMSO. The absorbance of the solutions at the excitation
wavelength ranged between 0.04 and 0.05.
Natural radiative lifetimes (
chemCAD program [34] which uses the Strickler–Berg equation.
The fluorescence lifetimes (sF) were evaluated using Eq. (2).
s0) were determined using Photo-
sF
s0
UF
¼
ð2Þ
Experimental
Photochemical parameters
Singlet oxygen quantum yields
Materials
All reagents and solvents were of reagent grade quality and
were obtained from commercial suppliers. All solvents were puri-
fied as described in Perrin and Armarego before use [27]. Zinc(II)
acetate dihydrate, K2CO3 and unsubstituted zinc Pc were pur-
chased from the Aldrich Chemical Company. 1,3-Diph-
enylisobenzofuran (DPBF) and silica gel (70–230 mesh) were
purchased from Merck. 3-(3-methyl-2-oxo-4-phenyl-2H-chro-
men-7-yloxy)phthalonitrile (1) [28], 4-(3-methyl-2-oxo-4-phe-
nyl-2H-chromen-7-yloxy)phthalonitrile (2) [28], 4-chloro-5-(3-
methyl-4-phenyl-2H-chromen-7-yloxy)phthalonitrile (3) [28],
4-nitrophthalonitrile [29], 3-nitrophthalonitrile [30] and 4,5-dichlor-
ophthalonitrile [31] were synthesized and purified according to
well known literature.
Singlet oxygen quantum yield (UD) determinations were car-
ried out using the experimental set-up described in literature
[35–37], in DMF. Typically, a 3 mL portion of the respective substi-
tuted zinc(II) Pc (4–6) solutions (C = 1 ꢁ 10ꢂ5 M) containing the
singlet oxygen quencher was irradiated in the Q band region with
the photo-irradiation set-up described in references [35–37]. Sin-
glet oxygen quantum yields (UD) were determined in air using
the relative method with unsubstituted ZnPc (in DMF) as reference.
DPBF was used as chemical quenchers for singlet oxygen in DMF.
Eq. (3) was employed for the calculations:
Std
R:I
USDtd
ð3Þ
abs
UD
¼
RStd:Iabs

M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
505
where USDtd is the singlet oxygen quantum yield for the standard
Yield: 0.17 g (32%). UV–vis kmax (nm) (log
645 (4.57), 690 (4.75). FT–IR [(KBr)
e
) (DMF): 319 (4.51),
unsubstituted ZnPc (UDStd = 0.56 in DMF) [38]. R and RStd are the
m
max/cmꢂ1]: 3061 (Ar–CH),
DPBF photobleaching rates in the presence of the respective sam-
2957–2926 (aliphatic CH), 1721 (C@O, lactone), 1609–1582
(Ar–C@C), 1276 (Ar–O–Ar). 1H NMR (CDCl3): d, ppm: Aromatic pro-
tons, at 7.75–7.20 (m, 44H) and alkyl protons at 1.57 (s, 12H). MS
(MALDI–TOF) m/z: Calculated, 1578.93; Found: 1578.85 [M]+ and
1601.45 [M + Na]+. Anal. Calc. for C96H56N8O12Zn (1578.93): C,
73.03; H, 3.57; N, 7.10; Found: C 72.88, H 3.41, and N 7.28%.
ples (4–6) and standards, respectively. Iabs and IStd are the rates of
abs
light absorption by the samples (4–6) and standards, respectively.
To avoid chain reactions induced by DPBF in the presence of singlet
oxygen [39], the concentration of quenchers was lowered to
ꢃ3 ꢁ 10ꢂ5 M. Solutions of sensitizer (1 ꢁ 10ꢂ5 M) containing DPBF
was prepared in the dark and irradiated in the Q band region using
the setup described above. DPBF degradation at 417 nm was moni-
tored. The light intensity 6.60 ꢁ 1015 photons sꢂ1 cmꢂ2 was used for
UD determinations.
2(3),9(10),16(17),23(24)-Tetrakis(7-oxy-3-methyl-4-
phenylcoumarin) phthalocyaninato zinc(II) (5)
The compound 2 (0.5 g, 1.32 mmol), zinc(II)acetate dihydrate
(0.29 g, 0.65 mmol) and dried N,N-dimethylaminoethanol (2 mL)
were refluxed with stirring under argon atmosphere for 24 h. After
cooling to room temperature, the solution was dropped in the hot
methanol and then filtered off. The green solid product was precip-
itated and collected by filtration and washed with several times
with hot methanol, ethanol, ethyl acetate, acetonitrile, acetone,
diethyl ether and dried. The green product was purified by passing
through a silica gel column using chloroform as the eluting solvent.
The compound (5) is soluble in chloroform, dichloromethane, tet-
rahydrofuran, dimethylformamide and dimethylsulfoxide.
Photodegradation quantum yields
Photodegradation quantum yield (Ud) determinations were car-
ried out using the experimental set-up described in literature [35–
37]. Photodegradation quantum yields were determined using Eq.
(4),
ðC0 ꢂ CtÞ:V:NA
Ud
¼
ð4Þ
I
abs:S:t
where C0 and Ct are the samples (4–6) concentrations before and
after irradiation respectively, V is the reaction volume, NA is the
Avogadro’s constant, S is the irradiated cell area, t is the irradiation
time and Iabs is the overlap integral of the radiation source light
intensity and the absorption of the samples (4–6). A light intensity
Yield: 0.16 g (30%). UV–vis kmax (nm) (log
e) (DMF): 324 (4.74),
653 (4.66), 677 (5.04). FT–IR [(KBr)
m
max/cmꢂ1]: 3045 (Ar–H),
2922–2852 (aliphatic CH), 1714 cmꢂ1 (C@O, lactone) 1656 cmꢂ1
(Ar–C@C), 1237 (Ar–O–Ar). 1H NMR (CDCl3): d, ppm: Aromatic pro-
tons, at 8.04–7.02 (m, 44H) and alkyl protons at 1.52 (s, 12H). MS
(MALDI–TOF) m/z: Calculated, 1578.93; Found 1578.152 [M]+.
Anal. Calc. for C96H56N8O12Zn (1578.93) C, 73.03; H, 3.57; N,
7.10; Found: C 72.76, H 3.43, and N 7.24%.
of
2.20 ꢁ 1016 photons sꢂ1 cmꢂ2
was
employed for Ud
determinations.
Fluorescence quenching studies by 1,4-benzoquinone (BQ)
Fluorescence quenching experiments on the substituted zinc(II)
Pc compounds (4–6) were carried out by the addition of different
concentrations of BQ to a fixed concentration of the compounds,
and the concentrations of BQ in the resulting mixtures were 0,
0.008, 0.016, 0.024 and 0.032 M. The fluorescence spectra of substi-
tuted zinc(II) Pc compounds (4–6) at each BQ concentration were
recorded, and the changes in fluorescence intensity related to BQ
concentration by the Stern–Volmer (SV) equation [40] (Eq. (5)):
Octakis[2,9,16,23-(7-oxy-3-methyl-4-phenylcoumarin)-3,10,17,24-
chloro] phthalocyaninato zinc(II) (6)
The compound 3 (0.5 g, 1.21 mmol), zinc(II)acetate dihydrate
(0.27 g, 1.21 mmol) and dried N,N-dimethylamino ethanol (2 mL)
were refluxed with stirring under argon atmosphere for 24 h. After
cooling to room temperature, the solution was dropped in the hot
methanol and then filtered off. The green solid product was precip-
itated and collected by filtration and washed with several times
with hot methanol, ethanol, ethyl acetate, acetonitrile, acetone,
diethyl ether and dried. The green product was purified by passing
through a silica gel column using chloroform as the eluting solvent.
The compound (6) is soluble in chloroform, dichloromethane, tet-
rahydrofuran, dimethylformamide and dimethylsulfoxide.
I0
I
¼ 1 þ KSV ½BQꢄ
ð5Þ
where I0 and I are the fluorescence intensities of fluorophore in the
absence and presence of quencher, respectively. KSV is the Stern–
Volmer constant; and this is the product of the bimolecular quench-
ing constant (kq) and the fluorescence lifetime sF (Eq. (6)):
Yield: 0.18 g (34%). UV–vis kmax (nm) (log
e) (DMF): 328 (4.47),
629 (4.48), 679 (4.80). FT–IR [(KBr)
m
max/cmꢂ1]: 3060 (Ar–H),
KSV ¼ kqsF
ð6Þ
2919–2850 (aliphatic CH), 1715 (C@O, lactone), 1600 (Ar–C@C),
1272–1242 (Ar–O–Ar). 1H NMR (CDCl3): d, ppm: Aromatic protons,
at 7.70–7.35 (m, 40H) and alkyl protons at 1.54 (s, 12H). MS (MAL-
DI–TOF) m/z: Calculated, 1715.5; Found: 1715.26 [M]+, 1755.33
[M + K]+. Anal. Calc. for C96H52Cl4N8O12Zn (1715.5): C, 67.17; H,
3.05; N, 6.53; Found: C 66.94, H 2.93, and N 6.84%.
The ratios I0/I were calculated and plotted against [BQ] according to
Eq. (5), and KSV determined from the slope.
Synthesis
1(4),8(11),15(18),22(25)-Tetrakis(7-oxy-3-methyl-4-phenylcoumarin)
phthalocyaninato zinc(II) (4)
The compound 1 (0.5 g, 1.32 mmol), zinc(II)acetate dihydrate
(0.29 g, 0.65 mmol) and dried N,N-dimethylamino ethanol (2 mL)
were refluxed with stirring under argon atmosphere for 24 h. After
cooling to room temperature, the solution was dropped in the hot
methanol and then filtered off. The green solid product was precip-
itated and collected by filtration and washed with several times
with hot methanol, ethanol, ethyl acetate, acetonitrile, acetone,
diethyl ether and dried. The green product was purified by passing
through a silica gel column using chloroform as the eluting solvent.
The compound (4) is soluble in chloroform, dichloromethane, tet-
rahydrofuran, dimethylformamide and dimethylsulfoxide.
Results and discussion
Synthesis and characterization
Tetra- and octa-substituted zinc(II) Pc compounds (4–6) were
prepared by cyclotetramerization of 7-oxy-3-methyl-4-phenyl-
coumarin substituted phthalonitrile derivatives (1–3). In both
cases, a mixture of four possible structural isomers is obtained
for tetra-substituted zinc(II) Pcs. The four probable isomers can
be designed by their molecular symmetry as C4h, C2v, Cs and D2h
In this study, compounds 4 and 5 are obtained as isomer mixtures
.

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M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
as expected. No attempt was made to separate the isomers
mixture.
The preparation of substituted phthalonitriles from 3-nitropht-
halonitrile, 4-nitrophthalonitrile, and 4,5-dichlorophthalonitrile
were used to prepare compounds 1, 2 and 3 respectively, through
base catalyzed nucleophilic aromatic displacement [28].
protons observed in their respective regions. In the 1H NMR spectra
of Pcs (4–6), the aromatic protons were observed at between 7.75–
7.20 ppm for compound 4, 8.04–7.02 ppm for compound 5 and
7.70–7.35 ppm for compound 6 integrating totally 44, 44, 40, pro-
tons for each Pcs respectively. The aliphatic methyl protons were
observed at 1.57, 1.52, 1.54 ppm for all Pcs respectively integrating
12 protons for each Pcs (4, 5 and 6).
The syntheses of zinc(II) Pc compounds (4–6) were achieved by
treatment of 7-oxy-3-methyl-4-phenyl-2H-chromen-2-one substi-
tuted phthalonitriles (1–3) with zinc(II) acetate in N,N-dimethyl-
aminoethanol (DMAE) (Scheme 1). The compounds 4, 5 and 6
were washed several times with different organic solvents and
dried then purified by column chromatography with silica gel
using chloroform as eluenting solvent. Generally, Pc compounds
are insoluble in most organic solvents; however introduction of
substituents on the ring increases the solubility. All studied zinc(II)
Pc compounds (4–6) exhibited excellent solubility in organic sol-
vents such as dichloromethane, chloroform, THF, DMF and DMSO.
The combination of phthalocyanine and coumarin compounds
into a single molecule was studied in our earlier work [41]. In this
work, 7-oxy-3-methyl-4-phenylcoumarin group was connected as
substituent on the phthalocyanine framework. We have been also
investigated the position effect of coumarin groups. Moreover, the
effect of chlorine atom on the phthalocyanine framework on pho-
tochemical and photophysical properties of coumarin substituted
phthalocyanine complexes was also investigated in this study.
The synthesis, photophysical and photochemical properties of
indium(III) acetate counterparts of 7-oxy-3-methyl-4-phenyl-
coumarin substituted zinc(II) phthalocyanine complexes were
reported by our earlier work [28]. When compared to 7-oxy-3-
methyl-4-phenylcoumarin substituted zinc(II) and indium(II)
phthalocyanine complexes, while the singlet oxygen generation
of 7-oxy-3-methyl-4-phenylcoumarin substituted indium(III) ace-
tate phthalocyanines are higher than zinc(II) phthalocyanine deriv-
atives containing same substituents, the stability of indium (III)
acetate complexes are lower than zinc(II) phthalocyanine com-
plexes which investigated in this study approximately 10 times.
The photostability of compounds during photosensitized reactions
are immense importance. The fluorescence quenching properties of
7-oxy-3-methyl-4-phenylcoumarin substituted zinc(II) phthalocy-
anine complexes by 1,4-benzoquinone were also examined in this
work. The effective fluorescence quenching of the complexes by BQ
suggests that systems that are composite of complexes and qui-
nones could well serve as good light harvesters and energy
transducers.
In the mass spectra of Pcs obtained by the MALDI–TOF tech-
nique, the molecular ion peaks were observed at m/z: 1578.85
for 4, 1578.15 for 5, 1715.26 for 6 as M+ ion peaks (Fig. 1). The
melting points of the new synthesized compounds (4, 5 and 6)
are higher than 300 °C.
Ground state electronic absorption spectra
The electronic spectra of the compounds 4, 5 and 6 showed
characteristic absorption in the Q band region at around 677–
690 nm in DMF, Table 1. The B bands were observed at around
318–338 nm (Fig. 2). The spectra showed monomeric behavior
for tetra-substituted zinc Pc compounds (4 and 5) evidenced by a
single (narrow) Q band, typical of metallated Pc compounds [42].
The peripherally tetra-substituted zinc Pc compound (5) exhibited
unusual absorption band at 660 nm in the absorption spectrum.
This unusual band did not observed at low concentration
(C = 8.4 ꢁ 10ꢂ7 M) in DMF suggesting that this band could be due
to the dimer formation of this compound at higher concentration
in DMF. The octa-substituted zinc Pc compound (6) showed mini-
mal aggregation in DMF (Fig. 2). It could be due to the effect of
chlorine atoms on the Pc framework suggesting that the chlorine
atom is an electronegative atom; it attracts electrons in the phtha-
locyanine ring. Therefore, chlorine atom provides aggregation due
to the weak intermolecular interactions. In DMF, the Q bands were
observed at: 690 nm for 4, 677 nm for 5 and 679 nm for 6, Table 1.
The red-shifts were observed for zinc(II) Pc compounds following
substitution. The Q band of the non-peripheral substituted com-
pound (4) is red-shifted when compared to the corresponding
peripheral tetra-(5) and octa-(6) substituted compounds in DMF
(Fig. 2). The red-shifts are 13 nm between compounds 4 and 5,
11 nm between compounds 4 and 6. The observed red spectral
shifts are typical of Pcs with substituents at the non-peripheral
positions and have been explained in the literature [43] due to lin-
ear combination of the atomic orbitals (LCAO) coefficients at the
non-peripheral positions of the highest occupied molecular orbital
(HOMO) being greater than those at the peripheral positions. As a
result, the HOMO level is more destabilized upon non-peripherally
substitution than peripherally substitution. Essentially, the energy
The new compounds were characterized by UV–vis, FT–IR and
NMR spectroscopies, MALDI–TOF mass spectra and elemental
analysis. The analyses are consistent with the predicted structures
as shown in the experimental section. In the IR spectra of Pc com-
pounds (4–6), vibration bands were observed at: 3061–3045 cmꢂ1
for aromatic C–H stretching, 2957–2850 cmꢂ1 for aliphatic C–H
stretching, 1721–1714 cmꢂ1 for C@O vibration of the ester groups,
1600–1582 cmꢂ1 for C@C stretching and 1276–1237 cmꢂ1 for
Ar–O–Ar stretching. The C@O and C@C bands for zinc(II) Pc
compounds (4–6) in IR spectra were broader and shorter than
those of dinitrile compounds (1–3) because of the H-type aggrega-
tion of coumarin moiety.
gap (DE) between the HOMO and lowest unoccupied molecular
orbital (LUMO) becomes smaller, resulting in a ꢃ20 nm bathochro-
mic shift. The B-bands are broad due to the superimposition of the
B1 and B2 bands in the ꢃ320–330 nm regions.
Fluorescence spectra
Fig. 3 shows fluorescence emission, absorption and excitation
spectra of compound 4 in DMF as an example for studied zinc(II)
Pc compounds. Fluorescence emission peaks were listed in Table 1.
The observed Stokes shifts were within the region observed for zin-
c(II) Pc compounds. All zinc(II) Pc compounds (4–6) showed simi-
lar fluorescence behavior in DMF (Fig. 3 as an example for
compound 4). The excitation spectra were similar to absorption
spectra and both were mirror images of the emission spectra for
tetra-substituted zinc(II) Pc compounds (4 and 5) in DMF. The
proximity of the wavelength of each component of the Q-band
absorption to the Q band maxima of the excitation spectra for
tetra-substituted zinc(II) Pc compounds (4 and 5) suggest that
the nuclear configurations of the ground and excited states are
The 1H NMR spectra of Pcs (4–6) were recorded in CDCl3. The 1H
NMR spectra of substituted Pc compounds (4–6) have broad
absorptions when compared with that of corresponding phthalo-
nitrile derivatives (1–3). It is likely that broadness is due to both
chemical exchange caused by aggregation–disaggregation equilib-
rium in CDCl3 and the fact that the product obtained in this reac-
tion is a mixture of four positional isomers (for tetra-substituted
compounds) which are expected to show chemical shifts which
slightly differ from each other. The compounds 4, 5 and 6 were
found to be pure by 1H NMR with all the substituents and ring

M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
507
Fig. 1. Mass spectra of the studied phthalocyanine compounds (4–6).
similar and not affected by excitation. The chloro-octa substituted
compound (6) showed broad absorption at Q band region in its
electronic spectrum due to aggregation of this complex in DMF.
However, the fluorescence spectrum of this complex showed sharp

508
M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
Table 1
studied zinc Pc compounds are lower than unsubstituted zinc Pc
in DMF. For comparison among the studied zinc(II) Pc compounds,
the UF value of the compound 6 is the lowest among the studied
zinc(II) Pc compounds because only the monomer species (not
aggregated species) are fluorescent for this complex in DMF. The
electronegative chlorine atoms on the phthalocyanine framework
could be enhanced aggregation behavior of this complex due to
increasing of intermolecular interactions.
Absorption, excitation and emission spectral data for unsubstituted and substituted
zinc(II) phthalocyanine compounds in DMF.
Compound Q band
kmax, (nm)
log
e
Excitation
kEx, (nm)
Emission
kEm, (nm)
Stokes shift
DStokes, (nm)
4
5
6
690
4.81 687
5.03 676
4.79 677
5.37 670
695
685
686
676
8
9
9
6
677
679
670
ZnPca
Fluorescence lifetime (sF) values of the tetra-substituted zinc(II)
a
Data from Ref. [44].
Pc compounds (4 and 5) are higher compared to unsubstituted zin-
c(II) Pc compound in DMF, suggesting less quenching by substitu-
tion. The sF value of the compound 6 is lower than unsubstituted
zinc(II) Pc compound due to the aggregation behavior of this com-
pound in DMF again. sF value is higher for non-peripherally tetra-
substituted zinc(II) Pc compound (4) when compared to peripher-
ally tetra-substituted (5) and peripherally octa-substituted (6) zin-
c(II) Pc compounds, Table 2, suggesting more quenching by
peripherally-tetra and octa-substitution compared to non-periph-
erally substitution. However, the sF values are typical for zinc(II)
Pc compounds [44–47].
band at Q band region. It is suggesting that only the monomer spe-
cies are fluorescent for this complex in DMF. The fluorescence
emission of the non-peripherally substituted zinc(II) Pc compound
(4) is more intense than other studied zinc(II) Pc compounds (5 and
6) in DMF suggesting that less quenching of the 7-oxy-3-methyl-4-
phenylcoumarin groups on the non-peripheral position.
Fluorescence quantum yields and lifetimes
The natural radiative lifetime (s0) and the rate constants for
fluorescence (kF) values are also given in Table 2. The s0 values of
The fluorescence quantum yields (UF) of the studied zinc Pc
compounds (4, 5 and 6) are given in Table 2. The UF values of
0.8
0.6
0.4
0.2
0
4
5
6
300
400
500
600
700
800
Wavelength (nm)
Fig. 2. Absorption spectra of substituted zinc(II) phthalocyanine compounds (4–6) in DMF. Concentration = 1 ꢁ 10ꢂ5 M.
600
500
400
300
200
100
0
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Emission
Excitation
Absorption
500
600
700
800
Wavelength (nm)
Fig. 3. Absorption, excitation and emission spectra of the compound 4 in DMF. (Excitation wavelength = 630 nm).

M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
509
Table 2
There was no change in the Q band intensity during the UD
determinations, confirming that compounds were not degraded
during singlet oxygen studies for the studied zinc(II) Pc com-
pounds. The UD values of the substituted zinc(II) Pc compounds
(4, 5 and 6) are given in Table 2. All substituted zinc(II) Pc com-
pounds showed lower UD values than unsubstituted zinc(II) Pc
compound in DMF. The peripherally tetra-substituted zinc(II) Pc
compound (5) showed the highest UD value among the studied
zinc(II) Pc compounds (Table 2). The UD value of chloro-octa
substituted compound (6) is lower than other substituted zinc(II)
Pc compounds (4 and 5) in DMF due to the minimal aggregation
behavior of this compound in DMF.
Photophysical and photochemical data of unsubstituted and substituted zinc(II)
phthalocyanine compounds in DMF.
Compound UF
sF (ns) s0 (ns) akF (sꢂ1) (ꢁ107) Ud (ꢁ10ꢂ5
)
UD
4
5
6
0.084 2.35
0.15 1.78
0.038 0.75
0.17 1.03
27.99
11.87
19.75
6.05
3.57
8.42
5.06
1.65
15.61
8.89
5.71
2.3
0.37
0.42
0.24
0.56
ZnPcb
a
kF is the rate constant for fluorescence. Values calculated using kF
Data from Ref. [44].
=
UF/sF.
b
the substituted zinc(II) Pc compounds (4–6) are higher than unsub-
stituted zinc(II) Pc compound in DMF. The non-peripherally tetra-
substituted zinc(II) Pc compound (4) showed the highest s0 value
among the studied zinc(II) Pc compounds in DMF (Table 2). This
could be due to the position effect. The rate constants for fluores-
cence (kF) of substituted zinc(II) Pc compounds (4–6) are higher
than unsubstituted zinc(II) Pc compound in DMF. The kF value of
compound 5 is the highest among the studied zinc Pc compounds.
Photodegradation studies
Degradation of the molecules under light irradiation can be
used to study their stability and this is especially important for
those molecules intended for use in photocatalytic reactions. The
collapse of the absorption spectra without any distortion of the
shape confirms photodegradation not associated with phototrans-
formation into different forms of MPc absorbing in the visible
region.
Singlet oxygen quantum yields
The quantity of the singlet oxygen quantum yield (UD) is a sign of
the capability of the compounds as photosensitizers in photocata-
lytic applications for instance PDT. The UD values were determined
in DMF using a chemical method and DPBF used as a scavenger. A
reducing of DPBF absorbance at 417 nm was monitored using UV–
vis spectrophotometer.
Many factors can be responsible for the magnitude of the deter-
mined singlet oxygen quantum yield including; triplet excited
state energy, ability of substituents and solvents to quench the sin-
glet oxygen, the triplet excited state lifetime and the efficiency of
the energy transfer between the triplet excited state and the
ground state of oxygen. It is believed that during photosensitiza-
tion, the photosensitizer molecule is first excited to the singlet
The spectral changes observed for all the compounds (4–6) dur-
ing light irradiation are as shown in Fig. 4 (using compound 5 as an
example in DMF) and hence confirm photodegradation occurred
without phototransformation. The Ud values, found in this study,
are similar Pc derivatives having different metals and substituents
on the Pc ring in literature [48]. Stable zinc Pc molecules show Ud
values as low as 10ꢂ6 and for unstable molecules, values of the or-
der of 10ꢂ3 have been reported [48].
Table 2 shows that all substituted compounds (4, 5 and 6) were
less stable to degradation under light irradiation compared to
unsubstituted ZnPc in DMF. Thus, the substitution of ZnPc with
7-oxy-3-methyl-4-phenylcoumarin groups seems to decrease the
stability of the compounds in DMF. The non-peripherally substi-
tuted zinc(II) Pc compound (4) was less stable when compared to
the other substituted compounds (5 and 6). The chloro-octa substi-
tuted compound (6) is the most stable than the other compounds
could be related to the aggregated nature of this compound in
DMF. It seems zinc(II) metal and 7-oxy-3-methyl-4-phenylcouma-
state and through intersystem crossing forms the triplet state,
P
and then transfers the energy to ground state oxygen, O2(3 g),
generating excited singlet state oxygen, O2(1Dg), by Type II mech-
anism. Singlet oxygen is the chief cytotoxic species and subse-
quently degradate the substrate.
1.4
1.2
1.4
y = -0.0003x + 1.2611
2 = 0.9784
1.2
1
R
0.8
0.6
0.4
0.2
0
1
0.8
0.6
0.4
0.2
0
0 sec
600 sec
0
500
1000
1500
Time (sec)
2000
2500
3000
1200 sec
1800 sec
2400 sec
3000 sec
300
400
500
600
700
800
Wavelength (nm)
Fig. 4. Absorption changes during the photodegradation studies of compound 5 in DMF showing the disappearance of the Q-band at ten minutes intervals. (Inset: Plot of
absorbance vs time).

510
M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
250
200
150
100
50
[BQ]=0
[BQ]=saturated
0
650
700
750
800
Wavelength (nm)
Fig. 5. Fluorescence emission spectral changes of 6 (1.00 ꢁ 10ꢂ5 M) on addition of different concentrations of BQ in DMF. [BQ] = 0, 0.008, 0.016, 0.024, 0.032 M.
2
5
1.8
4
6
1.6
1.4
1.2
1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
[BQ]
Fig. 6. Stern–Volmer plots for BQ quenching of coumarin substituted zinc(II) phthalocyanines (4–6). [MPc] ꢃ1.00 ꢁ 10ꢂ5 M in DMF. [BQ] = 0, 0.008, 0.016, 0.024, 0.032 M.
rin groups increases the Ud values and decreases the stability of
compounds due to electron-donating ability of these groups [49].
seems to decrease the KSV values of the compounds in DMF. The
bimolecular quenching constant (kq) values of the substituted zinc
Pc compounds (4, 5 and 6) are also lower than unsubstituted ZnPc
in DMF, thus substitution with 7-oxy-3-methyl-4-phenylcoumarin
group seems to decrease the kq values of the compounds. The order
Fluorescence quenching studies by 1,4-benzoquinone [BQ]
The fluorescence quenching of zinc Pc compounds by BQ in DMF
was found to obey Stern–Volmer kinetics, which is consistent with
Table 3
diffusion-controlled bimolecular reactions. Fig.
5 shows the
Fluorescence quenching data for unsubstituted and substituted zinc(II) phthalocya-
nine compounds in DMF.
quenching of compound 6 by BQ in DMF as an example. The slope
of the plots shown at Fig. 6 gave KSV values and listed in Table 3.
The KSV values of the substituted zinc Pc compounds (4, 5 and 6)
are lower than unsubstituted ZnPc in DMF. The peripherally substi-
tuted zinc(II) Pc compound (5) has highest KSV value, while chloro-
octa substituted compound (6) has the lowest KSV in DMF could be
related to the aggregated nature of this compound in DMF. The
substitution with 7-oxy-3-methyl-4-phenylcoumarin groups
Compound
KSV (Mꢂ1
)
kq/1010 (dm3 molꢂ1 sꢂ1
)
4
5
6
22.19
27.88
19.76
57.60
0.94
1.56
2.63
5.59
ZnPca
a
Data from Ref. [44].

M. Pißskin et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 502–511
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Conclusions
In the presented work, the syntheses of novel zinc(II) Pc com-
pounds (4–6) were described and they were characterized by
elemental analysis, 1H-NMR, MALDI–TOF, IR, UV–vis and fluores-
cence spectral data. All the studied zinc(II) Pc compounds show
excellent solubility in general organic solvents (such as chloroform,
dichloromethane, THF, DMF and DMSO). The photophysical and
photo-chemical properties of these zinc(II) Pc compounds were
also described in DMF for comparison of the effects of the position
of substituents on the Pc framework and aggregation behavior as
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aggregation, but the octa substituted compound (6) showed aggre-
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Acknowledgement
We are thankful to the Research Foundation of Marmara Uni-
versity, Commission of Scientific Research Project (BAPKO) [FEN-
C-DRP-110908-0232 and FEN-A-090909-0302].
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