Coumarino-12-crown-4 bearing phthalocyanine photosensitizers for singlet oxygen production

Article abstract of DOI:10.1016/j.jphotochem.2011.06.007

The synthesis, characterization, photophysical and photochemical properties of the new metal-free and zinc (II) phthalocyanines tetra-substituted at the peripheral (complexes 3a and 3b) and non-peripheral (complexes 4a and 4b) positions with 7,8-(12-crown

Full text of DOI:10.1016/j.jphotochem.2011.06.007

Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Coumarino-12-crown-4 bearing phthalocyanine photosensitizers for singlet
oxygen production
Meryem C¸ amura, Mahmut Durmus¸ b, Mustafa Bulutc,∗
a Kırklareli University, Department of Chemistry, 39100 Kırklareli, Turkey
b Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, 41400 Gebze, Turkey
c Marmara University, Department of Chemistry, 34722 Goztepe-Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis, characterization, photophysical and photochemical properties of the new metal-free and
zinc (II) phthalocyanines tetra-substituted at the peripheral (complexes 3a and 3b) and non-peripheral
(complexes 4a and 4b) positions with 7,8-(12-crown-4)-3-(4-oxyphenyl)coumarin groups are reported
for the first time. The new compounds have been characterized by elemental analysis, FT-IR, 1H NMR,
electronic spectroscopy and mass spectra. General trends are described for photodegradation, singlet
oxygen and fluorescence quantum yields, and fluorescence lifetimes of these compounds in dimethyl-
sulphoxide (DMSO). Photophysical and photochemical properties of phthalocyanine complexes are very
useful for photodynamic therapy (PDT) applications. The singlet oxygen quantum yields (˚ꢀ) ranged
from 0.11 to 0.80 are indicating the potential of the complexes as photosensitizers in applications of PDT.
Received 19 March 2011
Received in revised form 29 May 2011
Accepted 9 June 2011
Available online 16 June 2011
Keywords:
Phthalocyanine
Coumarin
Crown ether
Singlet oxygen
Fluorescence
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
biological activity [18]. A combination of these three potentially
promising units (i.e. phthalocyanines, crown ethers and coumarins)
Phthalocyanines (Pcs) are a family of an aromatic macrocycles
depends on delocalized 18␲- electron system [1]. There has been a
growing interest in the use of Pcs in a variety of new technological
fields such as semiconductor devices [2], electrochromic display
devices [3], liquid crystals [4], Langmuir–Blodgett films [5,6], and
as photosensitizers in photodynamic therapy of cancer (PDT) [7,8].
Crown ethers are heteromacrocycles in which the framework
is typically comprised of repeating ethyleneoxy [–(CH2CH2O)n–]
units [9–11]. Crown ethers have found wide applications in molec-
ular electronic devices due to their remarkable recognition and
metal binding properties [12]. The first effort was the prepara-
tion of crown ether-substituted phthalocyaninato copper complex,
Cu[Pc(15C5)4], reported in 1986 [13–15]. From that time, signif-
icant efforts have been paid in introducing different species of
crown-ether substituents onto the Pc ring [16].
for the purpose of constructing novel supramolecular structures
with novel multi-functional properties has attracted research inter-
ests. Attachment of crown ether and coumarin groups to the Pc
ring significantly increases the solubility of Pcs in many organic
solvents, leading to significant advances in research such as bio-
logical modeling, homogeneous catalysis, alkaline or earth alkaline
and lanthanide metal extractions [19,20]. The main feature of the
crown ether groups is that they can hold the alkali cations within
their cavity [21].
Over the last decade,
a substantial number of Pc-based
photosensitizers have been prepared and evaluated for their pho-
todynamic activity, with the focus on silicon, zinc and aluminum
analogues as a result of their desirable photophysical properties
[22]. The first photosensitizers were hematoporphyrin derivatives
and have already been described in detail in several articles [23,24].
Second generation photosensitizers such as Pcs have also been
introduced for PDT in research and clinical trials [25]. Due to their
high molar absorption coefficient in the red part of the spectrum,
photostability and long lifetimes of the photoexicited triplet states,
Pcs are known to be useful photosensitizers [26–29].
The aim of our ongoing research is to synthesize crown ether
bearing coumarin substituted metal-free and zinc (II) Pcs as poten-
tial PDT agents. In this work, we report on the effects of the
crown ether bearing coumarin groups as substituent and the posi-
tion of the substituent on the photophysical and photochemical
parameters. Aggregation behaviour, photophysical (fluorescence
Coumarins (2H-1-benzopyran-2-one) are a group of compounds
that have important roles as food constituents; as anti-oxidants,
stabilizers, and immunomodulatory substances; as fluorescent
markers for use in analysis, in lasers and in clinical use [17]. The
coumarin compounds exist in a variety of forms, due to the various
substitutions possible in their basic structure, which modulate their
∗
Corresponding author. Tel.: +90 216 3479641/1370; fax: +90 216 3478783.
E-mail addresses: mbulut@marmara.edu.tr, mustafabulut50@gmail.com
(M. Bulut).
1010-6030/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2011.06.007

M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
267
lifetime and quantum yields) and photochemical (singlet oxygen
2. Experimental
and photodegradation quantum yields) properties are investigated.
This work also explores the effects of ring substitutions and posi-
tion on the fluorescence quenching of metal-free and zinc (II)
Pcs by 1,4-benzoquinone (BQ) using the Stern–Volmer relation-
ship. Since PDT activity is mainly based on singlet oxygen, its
production is determined by the dye-sensitized photooxidation of
1,3-diphenylisobenzofuran (DPBF), a specific scavenger of this toxic
species [30]. We report herein on the synthesis, spectroscopic, pho-
tophysical and photochemical properties of metal-free and zinc
(II) Pcs tetra-substituted at the peripheral (complexes 3a and 3b)
and non-peripheral (complexes 4a and 4b) positions with 7,8-(12-
crown-4)-3-(4-oxyphenyl)coumarin groups (Scheme 1).
2.1. Materials and equipment
Unsubstituted zinc (II) phthalocyanine (ZnPc), 1,3-
diphenylisobenzofuran (DPBF), 2,3,4-trihydroxybenzaldehyde,
tetrabutylammonium hydroxide (TBAOH) and trifluoroacetic
acid (TFA) were purchased from Aldrich. Zinc (II) acetate,
sodium carbonate (Na2CO3), sodium acetate (NaOAc) and tri-
ethylene glycol ditosylate were purchased from Fluka. Basic
aluminum oxide (Al2O3) was purchased from Aldrich. All solvents
were dried as described by Perrin and Armarego [31] before
use. p-(2,3-Dicyanophenoxy)phenylacetic acid [32] and 7,8-
CN
O
NC
O
NC
NC
COOH
p-(2,3-Dicyanophenoxy)phenylacetic acid
COOH
p-(3,4-Dicyanophenoxy)phenylacetic acid
OH
HO
OH
CHO
2,3,4-Trihydroxybenzaldehyde
1. AcONa, Ac2O
160-170oC
2. MeOH / HCl
60oC
HO
HO
HO
HO
O
O
O
O
CN
(2)
(1)
O
CN
O
CN
CN
TsOCH 2(CH2OCH2)2CH2OTs
CH3CN, Na2CO3
O
O
O
O
O
O
O
O
O
O
O
O
CN
(4)
(3)
O
CN
O
CN
CN
2-Dimethylaminoethanol, 150oC, 48 h (for 3a and 4a)
2-Dimethylaminoethanol, Zn(AcO)2, 150oC, 24 h (for 3b and 4b)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
N
M
N
O
O
O
O
N
N
O
O
N
O
O
O
N
O
O
N
O
O
O
O
O
O
O
O
N M
N
O
O
O
O
N
N
O
O
O
N
N
N
M= 2H (3a)
M= Zn (3b)
M= 2H (4a)
M= Zn (4b)
O
O
O
O
O
O
O
O
O
O
O
O
O
Scheme 1. Synthesis route of new phthalonitriles (2, 3 and 4), metal-free (3a and 4a) and zinc (II) Pcs (3b and 4b).

268
M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
dihydroxy-3-[p-(3ꢀ,4ꢀ-dicyanophenoxy)phenyl]coumarin (1) [33]
were synthesized and purified according to literature procedures.
Infrared (IR) spectra were recorded on a Shimadzu FTIR-8300
Fourier Transform Infrared Spectrophotometer using KBr pellets,
electronic spectra were recorded on a Shimadzu UV-2450 and Shi-
madzu UV-2001 UV–vis spectrophotometers. Elemental analyses
were performed by the Instrumental Analysis Laboratory of the
TUBITAK Marmara Research Centre. 1H NMR spectra were recorded
on a Varian Unity Inova 500 MHz spectrometer using TMS as an
internal standard. Mass spectra were performed on a Bruker Aut-
oflex III MALDI-TOF spectrometer using 2,5-dihydroxybenzoic acid
(DHB, 0.02 g cm−3 in THF) as matrix. MALDI samples were pre-
pared by mixing the complex (0.02 g cm−3 in DMF) with the matrix
solution (1:10 v/v) in a 0.5 cm3 Eppendorf micro tube. Finally,
1 × 10−3 cm3 of this mixture was deposited on the sample plate,
dried at room temperature and then analyzed. Photo-irradiations
were done using a General Electric quartz line lamp (300 W). A
600 nm glass cut off filter (Schott) and a water filter were used
to filter off ultraviolet and infrared radiations, respectively. An
interference filter (Intor, 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.
(Ar–O–Ar), 1176–1109 (Ar–O–C). 1H NMR (CDCl3, 500 MHz): 7.85
(s, 1H, coumarin 4-H), 7.83 (bd, 2H, Ar-H), 7.78 (d, J = 8 Hz, 1H,
Ar-H), 7.38 (bd, 1H, Ar-H), 7.35 (dd, J = 8 and 2 Hz, 1H, Ar-H), 7.30
(d, J = 2 Hz, 1H, Ar-H), 7.18 (dd, J = 8 and 2 Hz, 2H, Ar-H), 6.94 (d,
J = 8 Hz, 1H, Ar-H), 4.46 (t, J = 6 Hz, 2H, –OCH2), 4.29 (t, J = 6 Hz, 2H,
–OCH2), 4.03 (t, J = 6 Hz, 2H, –OCCH2), 3.90 (t, J = 6 Hz, 2H, –OCCH2),
3.87–3.70 (m, 4H, –OCCO(CH2)2). UV–vis (CHCl3) ꢂmax (nm) (log
ε): 341 (4.82). MS (MALDI-TOF): m/z 533 [M+Na]+. Anal. Calc. for
C29H22N2O7: C, 68.23; H, 4.34; N, 5.49. Found: C, 68.25; H, 4.31; N,
5.45%.
2.2.3. 2(3),9(10),16(17),23(24)-Tetra[7,8-(12-crown-4)-
3-(4-oxyphenyl)coumarin]-phthalocyanine (3a)
A
solution of
3
(0.100 g, 0.196 mmol) in dry 2-
dimethylaminoethanol (DMAE) (1.5 ml) was refluxed with
stirring for 48 h under nitrogen atmosphere. After cooling to
room temperature, methanol (5 ml) was added to precipitate the
product. The green product was filtered and washed with water,
methanol, ethanol, acetonitrile, ethyl acetate, aceton, acetic acid
and diethyl ether. The crude product was purified by column chro-
matography on silica gel with CHCl3 as eluent. Yield: 0.038 g (38%).
M.p. > 300 ◦C. FT-IR (KBr), ꢁmax/(cm−1): 3292 (NH), 3082–3046
(Ar–CH), 2928–2864 (aliphatic CH), 1719 (C O, lactone), 1604
(C C), 1510–1464 (Ar C C), 1296–1238 (Ar–O–Ar), 1124–1080
(Ar–O–C). 1H NMR (CDCl3, 500 MHz): 7.66–7.32 (m, 40H, Ar-H),
4.37–3.62 (m, 48H, –OCH2). UV–vis ꢂmax (CHCl3) (nm) (log ε):
341 (4.89), 599 (shoulder, 4.15), 633 (shoulder, 4.33), 665 (4.63),
700 (4.65). MS (MALDI-TOF, DHB as matrix): m/z 2042 [M]+, 2043
[M+H]+, 2044 [M+2H]+, 2045 [M+3H]+, 2065 [M+Na]+. Anal. Calc.
for C116H90N8O28: C, 68.17; H, 4.41; N, 5.49. Found: C, 68.20; H,
4.45; N, 5.45%.
2.2. Synthesis
2.2.1. 7,8-Dihydroxy-3-[p-(2ꢀ,3ꢀ-dicyanophenoxy)phenyl]
coumarin (2)
A mixture of p-(2,3-dicyanophenoxy)phenylacetic acid (2.71 g,
9.74 mmol), 2,3,4-trihydroxybenzaldehyde (1.50 g, 9.74 mmol),
anhydrous NaOAc (3.99 g, 48.70 mmol) and anhydrous acetic
anhydride (15 ml) was heated with stirring at 160–170 ◦C
in
a sealed glass tube for 8 h under nitrogen. After cool-
2.2.4. 2(3),9(10),16(17),23(24)-Tetra[7,8-(12-crown-4)-
ing to room temperature, water was added and the mixture
stirred overnight. The resulting solid was filtered, washed with
water and dried. The crude product 7,8-diacetoxy-3-[p-(2ꢀ,3ꢀ-
dicyanophenoxy)phenyl]coumarin was suspended in methanol.
A 10% aqueous HCl solution was added to adjust the pH to
3 and the ensuing mixture was heated and stirred at 60 ◦C
for 18 h under nitrogen. The resulting solid (7,8-dihydroxy-3-
[p-(2ꢀ,3ꢀ-dicyanophenoxy)phenyl]coumarin) was filtered, washed
with water and dried. The crude product was purified by recrystalli-
sation from ethanol. Yield: 3.180 g (82%). M.p. > 300 ◦C. FT-IR (KBr),
3-(4-oxyphenyl)coumarin]-phthalocyaninato zinc (II) (3b)
Compound
3 (0.050 g, 0.098 mmol), Zn(AcO)2 (0.0045 g,
0.0245 mmol) and dried DMAE (1.5 ml) were refluxed with stirring
under nitrogen atmosphere for 24 h. After cooling to room tem-
perature the solution was treated with methanol (5 ml) and the
product was filtered off and washed with water, methanol, ethanol,
acetonitrile, ethyl acetate, aceton, acetic acid and diethyl ether. The
crude product was purified by column chromatography on silica
gel with CHCl3 as eluent. Yield: 0.035 g (68%). M.p. > 300 ◦C. FT-IR
(KBr), ꢁmax/(cm−1): 3059–3042 (Ar–CH), 2914–2860 (aliphatic
CH), 1717 (C O, lactone), 1602 (C C), 1508–1464 (Ar C C),
1294–1234 (Ar–O–Ar), 1122–1080 (Ar–O–C). 1H NMR (CDCl3,
500 MHz): 7.60–7.43 (m, 40H, Ar-H), 4.42–3.71 (m, 48H, –OCH2).
UV–vis ꢂmax (CHCl3) (nm) (log ε): 342 (5.05), 599 (shoulder, 4.15),
607 (shoulder, 4.17), 675 (4.79). MS (MALDI-TOF, DHB as matrix):
m/z 2105 [M]+, 2106 [M+H]+, 2107 [M+2H]+, 2108 [M+3H]+, 2128
[M+Na]+. Anal. Calc. for C116H88N8O28Zn: C, 66.13; H, 4.18; N, 5.32.
Found: C, 66.18; H, 4.14; N, 5.36%.
ꢁ
max/(cm−1): 3320 (OH), 3092–3054 (Ar–CH), 2229 (C N), 1686
(C O, lactone), 1606 (C C), 1586–1463 (Ar C C), 1298 (Ar–O–Ar).
1H NMR (DMSO-d6, 500 MHz): 10.15 (bs, 1H, –OH), 9.45 (bs, 1H,
–OH), 8.22 (s, 1H, coumarin 4-H), 7.92–7.89 (m, 4H, Ar-H), 7.41 (d,
J = 8 Hz, 1H, Ar-H), 7.35 (d, J = 8 Hz, 2H, Ar-H), 7.16 (d, J = 8 Hz, 1H,
Ar-H), 6.89 (d, J = 8 Hz, 1H, Ar-H). UV–vis (THF) ꢂmax (nm) (log ε):
346 (4.13). MS (MALDI-TOF): m/z 396 [M]+, 419 [M+Na]+. Anal. Calc.
for C23H12N2O5: C, 69.70; H, 3.05; N, 7.07. Found: C, 69.75; H, 3.65;
N, 7.01%.
2.2.5. 7,8-(12-Crown-4)-3-[p-(2ꢀ,3ꢀ-dicyanophenoxy)phenyl]
2.2.2. 7,8-(12-Crown-4)-3-[p-(3ꢀ,4ꢀ-dicyanophenoxy)phenyl]
coumarin (4)
coumarin (3)
A
mixture of 7,8-dihydroxy-3-[p-(2ꢀ,3ꢀ-dicyanophenoxy)
A
mixture of 7,8-dihydroxy-3-[p-(3ꢀ,4ꢀ-dicyanophenoxy)
phenyl]coumarin (2) (1.00 g, 2.52 mmol), triethylene glycol dito-
sylate (1.158 g, 2.52 mmol) and anhydrous Na2CO3 (0.535 g,
5.05 mmol) in acetonitrile (100 ml) was heated to reflux for 3
days under nitrogen atmosphere. After the removal of solution
by distillation, the precipitate was dissolved in CHCl3, washed
with water and dried on Na2SO4. The crude product was purified
by column chromatography on silica gel with CHCl3 as eluent.
Yield: 0.140 g (11%). M.p.: 202–204 ◦C. FT-IR (KBr), ꢁmax/(cm−1):
3076–3052 (Ar–CH), 2913–2861 (aliphatic –CH), 2232 (C N), 1716
(C O, lactone), 1606 (C C), 1509–1458 (Ar C C), 1281 (Ar–O–Ar),
1118–1074 (Ar–O–C). 1H NMR (CDCl3, 500 MHz): 7.83 (s, 1H,
phenyl]coumarin (1) (1.00 g, 2.52 mmol), triethylene glycol dito-
sylate (1.158 g, 2.52 mmol) and anhydrous Na2CO3 (0.535 g,
5.05 mmol) in acetonitrile (CH3CN) (100 ml) was heated to reflux
for 3 days under nitrogen atmosphere. After the removal of solution
by distillation, the precipitate was dissolved in chloroform (CHCl3),
washed with water and dried on Na2SO4. The crude product was
purified by column chromatography on silica gel with CHCl3 as
eluent. Yield: 0.228 g (18%). M.p.: 208 ◦C. FT-IR (KBr), ꢁmax/(cm−1):
3070–3055 (Ar–CH), 2955–2870 (Aliphatic –CH), 2227 (C N),
1728 (C O, lactone), 1600 (C C), 1576–1454 (Ar C C), 1298–1246

M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
269
coumarin 4-H), 7.81 (bd, 2H, Ar-H), 7.64 (t, J = 6 Hz, 1H, Ar-H),
2.4. Photochemical parameters
7.53 (d, J = 8 Hz, 1H, Ar-H), 7.30 (bd, 1H, Ar-H), 7.23 (d, J = 8 Hz, 1H,
Ar-H), 7.19 (dd, J = 8 and 2 Hz, 2H, Ar-H), 6.94 (d, J = 8 Hz, 1H, Ar-H),
4.46 (t, J = 6 Hz, 2H, –OCH2), 4.29 (t, J = 6 Hz, 2H, –OCH2), 4.03 (t,
J = 6 Hz, 2H, –OCCH2), 3.90 (t, J = 6 Hz, 2H, –OCCH2), 3.87–3.75 (m,
4H, –OCCO(CH2)2). UV–vis (CHCl3) ꢂmax (nm) (log ε): 339 (4.09).
MS (MALDI-TOF): m/z 533 [M+Na]+. Anal. Calc. for C29H22N2O7: C,
68.23; H, 4.34; N, 5.49. Found: C, 68.27; H, 4.36; N, 5.52%.
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yields (˚ꢀ) of the samples (3a, 3b, 4a
and 4b) were determined as previously explained in detail [38–40].
Typically, 2 cm3 portion of the samples (3a, 3b, 4a and 4b) solu-
tions (concentration = 1 × 10−5 M) containing the singlet oxygen
quencher was irradiated in the Q band region with the photo-
irradiation set-up described in references [38–40]. Singlet oxygen
quantum yields (˚ꢀ) were determined in air using the relative
method with unsubstituted ZnPc (in DMSO) as reference; and DPBF
as chemical quencher for singlet oxygen, using Eq. (3):
2.2.6. 1(4),8(11),15(18),22(25)-Tetra[7,8-(12-crown-4)-
3-(4-oxyphenyl)coumarin]-phthalocyanine (4a)
Compound 4a was prepared and purified according to the
procedure described for 3a, starting from 0.100 g (0.196 mmol)
4 and DMAE (1.5 ml). Yield: 0.023 g (23%). M.p. > 300 ◦C. FT-IR
(KBr), ꢁmax/(cm−1): 3288 (NH), 3053–3046 (Ar–CH), 2924–2861
(aliphatic CH), 1715 (C O, lactone), 1603 (C C), 1507–1452 (Ar
Std
RI
abs
˚
= ˚Std
(3)
ꢀ
ꢀ
RStdIabs
where ˚Sꢀtd is the singlet oxygen quantum yield for the standard
(˚Sꢀtd = 0.67 for unsubstituted ZnPc in DMSO) [41]; R and RStd are
the DPBF photobleaching rates in the presence of the samples (3a,
3b, 4a and 4b) and standard, respectively; Iabs and IaSbtds are the rates
of light absorption by the samples (3a, 3b, 4a and 4b) and stan-
dard, respectively. To avoid chain reactions induced by DPBF in
the presence of singlet oxygen [42], the concentration of quencher
(DPBF) was lowered to ∼3 × 10−5 M. Solutions of sensitizer contain-
ing the quencher (DPBF) were prepared in the dark and irradiated
in the Q band region using the photoirradiation setup. DPBF degra-
dation at 417 nm was monitored. The light intensity 7.33 × 1015
photons s−1 cm−2 was used for ˚ꢀ determinations. The error in
the determination of ˚ꢀ was ∼10% (determined from several ˚ꢀ
values).
C
C), 1294–1246 (Ar–O–Ar), 1122–1074 (Ar–O–C). 1H NMR (CDCl3,
500 MHz): 7.63–7.38 (m, 40H, Ar-H), 4.34–3.65 (m, 48H, –OCH2).
UV–vis ꢂmax (CHCl3) (nm) (log ε): 339 (4.99), 614 (shoulder, 3.83),
648 (shoulder, 4.10), 684 (4.65), 717 (4.72). MS (MALDI-TOF, DHB
as matrix): m/z 2042 [M]+, 2043 [M+H]+, 2044 [M+2H]+, 2045
[M+3H]+, 2065 [M+Na]+. Anal. Calc. for C116H90N8O28: C, 68.17; H,
4.41; N, 5.49. Found: C, 68.13; H, 4.38; N, 5.46%.
2.2.7. 1(4),8(11),15(18),22(25)-Tetra[7,8-(12-crown-4)-
3-(4-oxyphenyl)coumarin]-phthalocyaninato zinc (II) (4b)
Compound 4b was prepared and purified according to the
procedure described for 3b, starting from 0.104 g (0.204 mmol)
4, Zn(AcO)2 (0.0093 g, 0.051 mmol) and DMAE (1.5 ml). Yield:
0.064 g (60%). M.p. > 300 ◦C. FT-IR (KBr), ꢁmax/(cm−1): 3048–3016
(Ar–CH), 2913–2859 (aliphatic CH), 1717 (C O, lactone), 1603
(C C), 1505–1479 (Ar C C), 1294–1242 (Ar–O–Ar), 1120–1077
(Ar–O–C). 1H NMR (CDCl3, 500 MHz): 7.68–7.45 (m, 40H, Ar-H),
4.45–3.78 (m, 48H, –OCH2). UV–vis ꢂmax (CHCl3) (nm) (log ε): 337
(4.90), 620 (shoulder, 4.11), 658 (shoulder, 4.26), 692 (4.79), 736 (J
band, 4.45). MS (MALDI-TOF, DHB as matrix): m/z 2105 [M]+, 2106
[M+H]+, 2107 [M+2H]+, 2108 [M+3H]+, 2128 [M+Na]+. Anal. Calc.
for C116H88N8O28Zn: C, 66.13; H, 4.18; N, 5.32. Found: C, 66.09; H,
4.22; N, 5.26%.
2.4.2. Photodegradation quantum yields
Photodegradation quantum yield (˚d) determinations were car-
ried out using the experimental set-up described in literature
[38–40]. For determination of photodegradation quantum yields
(˚d), the usual Eq. (4) was employed:
(C0 − Ct)VNA
˚
=
(4)
d
Iabc St
where C0 and Ct are the samples (3a, 3b, 4a and 4b) concentra-
tions before and after irradiation, respectively. V is the reaction
volume; S is the irradiated cell area (2.0 cm2); t is the irradiation
time; NA is Avogadro’s number and Iabs is the overlap integral of the
radiation source intensity and the absorption of the Pc (the action
spectrum) in the region of the interference filter transmittance. A
light intensity of 2.20 × 1016 photons s−1 cm−2 was employed for
2.3. Photophysical parameters
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (˚F) were determined by the com-
parative method using Eq. (1) [34,35]:
˚
determinations.
d
2.4.3. Fluorescence quenching by 1,4-benzoquinone (BQ)
FAStdn2
FStdAn2Std
˚
= ˚F (Std)
(1)
Fluorescence quenching experiments of Pc complexes (3a, 3b,
4a and 4b) were carried out by the addition of different concentra-
tions of BQ to a fixed concentration of the Pc complexes, and the
concentrations of BQ in the resulting mixtures were 0, 0.008, 0.016,
0.024, 0.032 and 0.040 M. The fluorescence spectra of Pc complexes
(3a, 3b, 4a and 4b) at each BQ concentration were recorded, and
the changes in fluorescence intensity related to BQ concentration
by the Stern–Volmer (SV) Eq. (5) [43]:
F
where F and FStd are the areas under the fluorescence emission
curves of the samples (3a, 3b, 4a and 4b) and the standard, respec-
tively. A and AStd are the relative absorbance of the samples and
standard at the excitation wavelength, respectively. n and nStd
are the refractive indices of solvents for the sample and stan-
dard, respectively. Unsubstituted ZnPc (˚F = 0.20 in DMSO) [36]
was employed as the standard. Both the sample and standard were
excited at the same wavelength. The absorbance of the solutions
was ranged between 0.04 and 0.05 at the excitation wavelength.
Natural radiative lifetimes (ꢃ0) were determined using Pho-
tochem CAD program which uses the Strickler–Berg equation [37].
The fluorescence lifetimes (ꢃF) were evaluated using Eq. (2).
I0
= 1 + KSV[BQ]
(5)
I
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 bimolecu-
lar quenching constant (kq) and the fluorescence lifetime ꢃF (Eq.
(6)):
ꢃF
˚
F
=
(2)
KSV = kqꢃF
(6)
ꢃ0

270
M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
200
150
100
50
80
60
40
20
0
2030
2040
2050
2060
2070
2080
m/z
0
0
250
500
750
1000
1250
m/z
1500
1750
2000
2250
Fig. 1. MALDI-TOFF mass spectra of complex 3a.
The ratios I0/I were calculated and plotted against [BQ] accord-
ing to Eq. (5), and KSV determined from the slope.
3. Results and discussion
3.1. Synthesis and characterization
The general synthetic routes for the synthesis of new phthaloni-
triles (2, 3 and 4), metal-free (3a and 4a) and zinc (II) Pcs (3b and
4b) are given in Scheme 1. 7,8-Dihydroxy-3-[p-(3ꢀ,4ꢀ-dicyano-
phenoxy)phenyl]coumarin (1) and 7,8-dihydroxy-3-[p-(2ꢀ,3ꢀ-
dicyanophenoxy)phenyl]coumarin (2) were prepared by
the condensation of 2,3,4-trihydroxybenzaldehyde with
p-(3,4-dicyanophenoxy)phenylacetic acid (for 1) or p-(2,3-
dicyanophenoxy)phenylacetic acid (for 2) in the presence of
sodium acetate and acetic anhydride at 160 ◦C. The crude products
(1 and 2) purified by crystallization from ethanol. Compounds 1
and 2 reacted with triethylene glycol ditosylate to give the crown
ethers (3 and 4) in the presence of Na2CO3 in CH3CN. The crude
products (3 and 4) were purified by column chromatography on
silica gel with CHCl3 as eluent. Cyclotetramerization of the 3 and
4 to the metal-free Pcs (3a and 4a) was accomplished in DMAE at
150 ◦C under nitrogen atmosphere. The zinc (II) Pcs (3b and 4b)
were obtained from the dicyano derivatives (3 and 4) and anhy-
drous Zn(AcO)2 in DMAE at 150 ◦C under nitrogen atmosphere. The
novel compounds have been characterized by elemental analysis,
FT-IR, 1H NMR and MALDI-TOFF mass spectroscopy. The results
were in accord with the proposed structures.
The FT-IR spectrum of 2 exhibits the intense absorption band
at 2229 cm−1 corresponding to the C N stretching, and charac-
teristic frequencies at 3320 (–OH), 3092–3054 (Ar–CH) and 1686
(C O, lactone) cm−1. The 1H NMR spectrum of 2, the –OH protons
appeared at 10.15 and 9.45 ppm as broad singlets, the aromatic
protons appeared at 7.92–6.89 ppm as doublets and the proton of
coumarin at 4 position appeared at 8.22 ppm as a singlet. The mass
spectra of 2 which showed peaks at m/z = 396 [M]+ and 419 [M+Na]+
support the proposed formula for this compound.
The FT-IR spectra of
3 and 4 showed vibration peaks
for their aliphatic CH stretching frequency at 2870–2955 and
2861–2913 cm−1, respectively. The characteristic vibration peaks
of the nitrile (C N) and carbonyl groups (C O, lactone) appeared
at 2227, 2232 cm−1 and 1728, 1716 cm−1, respectively. The 1H
NMR spectra of 3 and 4 in CDCl3 showed characteristic signals
Fig. 2. Absorption spectra of substituted metal-free and zinc (II) Pc complexes: (A)
3a and 3b, (B) 4a and 4b in CHCl3 (concentrations: 1 × 10−5 M).

M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
271
Fig. 3. Aggregation behaviour of 3b in DMSO at different concentrations: 12 × 10−6 (A), 10 × 10−6 (B), 8 × 10−6 (C), 6 × 10−6 (D), 4 × 10−6 (E), 2 × 10−6 (F) M (inset: Plot of
absorbance versus concentration).
for etheric (–OCH2CH2O–) protons at ı 4.46–3.70 ppm for 3 and
4.46–3.75 ppm for 4 each a triplet. The singlets at ı 7.85 ppm
for 3 and 7.83 ppm for 4 indicated the presence the proton of
coumarin at position 4. In addition the chemical shifts of the aro-
matic protons are observed at ı 7.83–6.94 ppm for compound 3 and
7.81–6.94 ppm for compound 4. Molecular ion peaks were easily
identified at m/z = 533 [M+Na]+ for 3 and 4.
peripherally metal-free (3a) and zinc (II) (3b) Pc complexes in
CHCl3 (Fig. 2). The observed red spectral shifts are typical of Pcs
with substituents at the non-peripheral positions and have been
explained [44,45] due to linear 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 gap (ꢀE) between the HOMO
and lowest unoccupied molecular orbital (LUMO) becomes smaller,
resulting in a ∼20 nm bathochromic shift. The B (Soret) bands of
these complexes exist at 341 nm for 3a, 342 nm for 3b, 339 nm for
4a and 337 nm for 4b.
The aggregation behaviour of the Pc complexes (3a–b, 4a–b) was
investigated at different concentrations in DMSO (Fig. 3 for com-
plex 3b). In DMSO, as the concentration was increased, the intensity
of absorption of the Q band also increased and there were no new
bands due to the aggregated species for zinc (II) Pc complexes (3b
and 4b). Beer–Lambert law was obeyed for all Pc complexes in
the concentrations ranging from 1.2 × 10−5 to 2 × 10−6 M. While
metal-free Pc complexes (3a and 4a) showed doublet Q bands
in CHCl3, they showed a Q band around 665 nm together with a
The sharp vibration for the C N groups in the FT-IR spectra of
phthalonitriles 3 and 4 at 2227 and 2232 cm−1, respectively, dis-
appeared after conversion into metal-free (3a and 4a) and zinc (II)
(3b and 4b) Pcs. Characteristic NH stretching band of the metal-
free Pcs (3a and 4a) appeared at 3292 cm−1 for 3a and 3288 cm−1
for 4a. The FT-IR spectra of the metal-free (3a and 4a) and zinc (II)
(3b and 4b) Pcs are very similar, except the ꢄ(NH) vibrations of the
inner Pc core in the metal-free molecule. The 1H NMR spectra of
complexes showed ring protons between 7.66 and 7.32 ppm for 3a,
7.60 and 7.43 ppm for 3b, 7.63 and 7.38 ppm for 4a and 7.68 and
7.45 ppm for 4b as multiplets. The NH protons of complexes 3a and
4a could not be observed owing to the probable strong aggregation
of the molecules. Etheric (–OCH2CH2O–) protons were observed
between 4.37 and 3.62 ppm for 3a, 4.42 and 3.71 ppm for 3b, 4.34
and 3.65 ppm for 4a and 4.45 and 3.78 ppm for 4b as multiplets.
The MALDI-TOF mass spectra of Pcs (3a–b and 4a–b) confirmed
the proposed structures; molecular ions were easily identified at
m/z: 2042 [M]+, 2065 [M+Na]+ for 3a (Fig. 1) and 4a, at m/z: 2105
[M]+, 2065 [M+Na]+ for 3b and 4b. The elemental analyses for com-
plexes 3a–b and 4a–b gave satisfactory results that were close to
calculated values.
3.2. Electronic absorption spectra
The electronic spectra of the peripherally and non-peripherally
tetra-substituted Pc complexes (3a–b, 4a–b) showed characteristic
Q band absorptions in CHCl3. The ␲–␲* transitions for Q band
absorptions were observed at 665, 700 (3a), 675 (3b), 684, 717
(4a) and 692, 736 nm (4b) (Fig. 2) in CHCl3. The substitution of the
crown ether and coumarin substituents on the Pc ring increased
the wavelength of the Q band compared to unsubstituted zinc
(II) Pc. The Q bands of the non-peripherally metal-free (4a) and
zinc (II) (4b) Pc complexes were red-shifted 19, 17 nm (between
3a and 4a) and 17 nm (between 3b and 4b) compared to the
Fig. 4. Absorption spectra of 3a in CHCl3, DMSO, the addition of TBAOH in CHCl3
solution and the addition of TFA in DMSO solution (concentration: 12 × 10−6 M).

272
M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
blue shifted band around 600 nm in DMSO (Fig. 4 for complex 3a).
Firstly, we thought that this corruption could be due to the aggre-
gation of the Pc molecules. Triton X-100, which is a surfactant for
reducing of aggregation, was added to the metal-free Pc solutions,
but any changes were not observed after addition of triton X-100.
Metal-free Pcs contain four pyrolle nitrogen atoms, all of which
theoretically capable of undergoing protonation/deprotonation
reactions [46]. We thought that this modification could be due to
the deprotonation of the pyrolle nitrogens in the Pc core due to
basic nature of using solvent (DMSO, solvent basicity: 0.647 [47]).
TBAOH which is an organic base was also used for proving of the
deprotonation phenomenon. The metal-free Pcs showed Q band
around 665 nm together with a blue shifted band around 600 nm
after addition of TBAOH in CHCl3 solution, resulting completely
deprotonation of the pyrolle nitrogens in the Pc core (Fig. 4 for com-
plex 3a). The protonation of the pyrolle nitrogens in the Pc core by
the addition of the TFA caused doublet Q bands in DMSO (Fig. 4 for
complex 3a).
Fig. 6. Absorption spectra of 4b in CHCl3, CHCl3 treated with basic Al2O3 and the
addition of TBAOH in CHCl3 solution (concentration: 1 × 10−5 M).
Generally in metallo Pc complexes, the peak due to aggrega-
tion is blue shifted with respect to the monomer (called H-type
aggregation). However, a less common type of aggregation in solu-
tion (called J-type aggregation) results in a red-shifted peak [48].
While complex 4b showed a single Q band in DMSO and THF, it
showed a new peak at 736 nm in CHCl3 and CH2Cl2 (Fig. 5). The
peak at 736 nm is not due to aggregation. We suggest that this new
peak is a result of the splitting in the Q band due to lowering in
symmetry observed [49] because of the protonation. In solvents
which contain small amounts of acid such as dichloromethane and
chloroform (which contain small amount of HCl), protonation of
the inner nitrogen atoms may occur forming protonated metallo
Pc derivatives which are of lower symmetry than the parent met-
allo Pc molecule, hence the Q band is split [50,51]. The split is not
observed in DMSO which is basic and THF which is neither acidic
nor basic. 4b showed a single Q band after addition of TBAOH in
CHCl3 solution, resulting completely deprotonation of the nitrogen
atoms in the Pc core (Fig. 6). 4b also showed a single Q band in CHCl3
which is neutralized with basic Al2O3 (Fig. 6). Complex 4b contains
electron donating groups at the alpha position, hence close to the
nitrogen atoms, making the latter more basic than for 3b, so proto-
nation occurs in 4b but not in 3b. There is no change in the electronic
spectra of the metal-free Pcs (3a and 4a) in CHCl3. The strong coor-
dinating ability of zinc atom to the inner nitrogen atoms causes
the outer nitrogen atoms more basic than inner nitrogen atoms. So
protonation occurs easily in CHCl3 for non-peripherally substituted
zinc (II) Pc (4b).
3.3. Fluorescence spectra, fluorescence quantum yields and
lifetimes
Fig. 7 (as an example for complex 4a) shows the fluorescence
emission and excitation spectra for the metal-free Pc complexes in
DMSO and CHCl3 (concentration = 2 × 10−6 M). While the excitation
spectra of 3a and 4a showed splitting Q band in CHCl3 (Fig. 7A), they
showed non-splitting Q band in DMSO (Fig. 7B) due to the depro-
tonation of inner nitrogen protons on the phthalocyanine core in
DMSO. Fluorescence emission peaks were observed at 709 nm for
3a and 719 nm for 4a (Table 1). Zinc (II) Pc complexes (3b and 4b)
showed excitation spectra in DMSO which were similar to absorp-
Fig. 5. Absorption spectra of 4b in CHCl3, CH2Cl2, THF and DMSO (concentration:
1 × 10−5 M).
Fig. 7. Excitation and emission spectra of complex 4a: (A) in CHCl3 and (B) in DMSO
(concentration: 2 × 10−6 M). Excitation wavelength = 657 nm.

M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
273
Table 1
Absorption, excitation and emission spectral data for peripherally and non-peripherally substituted metal-free and zinc (II) Pcs in DMSO.
Compound
Q band ꢂmax (nm)
log ε
Excitation ꢂEx (nm)
Emission ꢂEm (nm)
Stokes shift ꢀStokes (nm)
3a
3b
4a
674, 702
681
693, 716
697
4.11, 4.11
5.05
4.63, 4.67
5.15
674, 703
682
694, 717
698
709
692
719
709
682
7
11
3
12
10
4b
ZnPca
672
5.14
672
a
Data from Ref. [52].
eral Pc complexes (1.53 for 3a and 1.78 for 3b) when compared to
unsubstituted zinc (II) Pc (1.22) in DMSO. The ꢃF values of the zinc
(II) Pc complexes (3b and 4b) were longer than for metal-free Pc
complexes (3a and 4a). The natural radiative lifetime (ꢃ0) values of
all substituted Pc complexes (3a, 3b, 4a and 4b) were longer when
compared to unsubstituted zinc (II) Pc in DMSO. The ꢃ0 values of
metal-free Pc complexes (3a and 4a) were also longer when com-
pared to zinc (II) Pc complexes (3b and 4b) in DMSO and complex
3a showed highest natural radiative lifetime. Also the peripheral
Pc complexes (3a and 3b) show higher natural radiative lifetime
(ꢃ0) values compared to the non-peripheral Pc complexes (4a and
4b). The rate constant for fluorescence (kF) value for complex 4b
showed highest and kF values for all substituted Pc complexes (3a,
3b, 4a and 4b) were lower than unsubstituted zinc (II) Pc in DMSO.
3.4. Singlet oxygen quantum yields
Singlet oxygen quantum yields (˚ꢀ) were determined in DMSO
using a chemical method using DPBF as a quencher. The dis-
appearance of DPBF absorption was monitored using UV–vis
spectrophotometer. Many factors are responsible for the magni-
tude of the determined quantum yield of singlet oxygen including;
triplet excited state energy, ability of substituents and solvents to
quench the singlet oxygen, the triplet excited state lifetime and
the efficiency of the energy transfer between the triplet excited
state and the ground state of oxygen. There was no change in the
Q band intensity during the ˚ꢀ determinations, confirming that
complexes were not degraded during singlet oxygen studies (Fig. 9
as an example for complex 4b). The ˚ꢀ value of non-peripheral
zinc (II) complex (0.80, 4b) was higher when compared to unsub-
stituted zinc (II) Pc (0.67) in DMSO. The ˚ꢀ values of zinc (II) Pc
complexes (3b and 4b) were higher when compared to metal-free
Pc complexes (3a and 4a) in DMSO, suggesting that closed shell
d10 configuration and the heavy atom effect of the zinc as central
metal in the Pc complexes. Zinc (II) Pcs (3b and 4b) gave good singlet
oxygen quantum yields (˚ꢀ) (0.51 for 3b and 0.80 for 4b, respec-
tively, Table 2) which are indicating the potential of the complexes
as photosensitizers in applications of PDT.
Fig. 8. Absorption, excitation and emission spectra of complex 4b in DMSO (con-
centration: 2 × 10−6 M). Excitation wavelength = 674 nm.
tion spectra with both being mirror images of emission (Fig. 8 as an
example for complex 4b). The proximity of the wavelength of each
component of the Q band absorption to the Q band maxima of the
excitation spectra for all complexes suggests that the nuclear con-
figurations of the ground and excited states were similar and not
affected by excitation in DMSO. Fluorescence emission peaks were
observed at 692 nm for 3b and 709 nm for 4b in DMSO (Table 1).
The observed Stokes shifts (Table 1) are typical of Pc complexes in
DMSO.
The fluorescence quantum yield (˚F) values for the complexes
were found to range from 0.09 to 0.15, with complex 3b having the
highest quantum yield, Table 2. The ˚F values of all studied Pc com-
plexes are lower than unsubstituted zinc (II) Pc in DMSO. The ˚F
values of the zinc (II) Pc complexes (3b and 4b) are higher than for
metal-free Pc complexes (3a and 6a). The error in the determination
of ˚F was ∼10% (determined from several ˚F values).
Lifetimes of fluorescence (ꢃF) were calculated using the
Strickler–Berg equation. Using this equation, a good correlation has
been [35] found for the experimentally and theoretically deter-
mined fluorescence lifetimes in this work for Pc complexes in
DMSO. Thus, we suggest that the values which were obtained using
this equation are a good measure of fluorescence lifetimes. Com-
plexes 3a and 3b showed highest lifetime of fluorescence among
the studied Pc complexes, Table 2. ꢃF values were longer for periph-
3.5. Photodegradation studies
Degradation of the molecules under irradiation can be used
to study their stability and this is especially important for those
molecules intended for use as photocatalysts. The collapse of the
absorption spectra without any distortion of the shape confirms
Table 2
Photophysical and photochemical parameters of peripherally and non-peripherally substituted metal-free and zinc (II) Pcs in DMSO.
a
Compound
˚
F
ꢃF (ns)
ꢃ0 (ns)
kF (ns)
˚
d
(×10−5
)
˚
ꢀ
KSV (M−1
)
kq/1010 (M−1 s−1
)
3a
3b
4a
0.09
0.15
0.08
0.12
0.20
1.53
1.78
0.93
1.19
1.22
17.00
11.87
11.46
10.53
6.80
0.06
0.08
0.09
0.10
14.70
0.7
1.0
0.8
1.0
2.6
0.18
0.51
0.11
0.80
0.67
16.11
18.32
15.27
19.46
31.90
1.05
1.03
1.65
1.64
2.61
4b
ZnPcb
a
kF is the rate constant for fluorescence. Values calculated using kF = ˚F/ꢃF.
Data from Ref. [52].
b

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M. C¸ amur et al. / Journal of Photochemistry and Photobiology A: Chemistry 222 (2011) 266–275
Fig. 11. Stern–Volmer plots for 1,4-benzoquinone (BQ) quenching of metal-free and
zinc (II) Pc complexes (3a, 3b, 4a and 4b). [MPc]: 1 × 10−5 M, [BQ] = 0, 0.008, 0.016,
0.024, 0.032, 0.040 M in DMSO.
Fig. 11 gave KSV values, listed in Table 2. The KSV values of the
substituted Pc complexes (3a, 3b, 4a and 4b) were lower than
unsubstituted zinc (II) Pc in DMSO. The KSV values of zinc (II) Pc
complexes (3b and 4b) were higher when compared to metal-free
Pc complexes (3a and 4a). The substitution with crown ether
bearing coumarin groups seems to decrease the KSV values of
the complexes in DMSO suggesting that the steric effect of the
substituents. The bimolecular quenching constant (kq) values of
the substituted Pc complexes (3a, 3b, 4a and 4b) were lower than
for unsubstituted zinc (II) Pc in DMSO, thus substitution with
crown ether bearing coumarin groups seems to decrease the kq
values of the complexes. Also the non-peripheral Pc complexes
(4a and 4b) showed higher kq values compared to the peripheral
Pc complexes (3a and 3b).
Fig. 9. A typical spectra for the determination of singlet oxygen quantum yield.
This determination was for complex 4b in DMSO at a concentration of 1 × 10−5
M
(inset: Plot of DPBF absorbance versus time).
clean photodegradation not associated with phototransformation.
The spectral changes observed for all the studied Pc complexes
(3a, 3b, 4a and 4b) during confirmed photodegradation occurred
without phototransformation.
The photodegradation quantum yield (˚d) values of the Pc com-
plexes (3a, 3b, 4a and 4b) in DMSO are given in Table 2. Table 2
shows that all substituted complexes (3a, 3b, 4a and 4b) were
more stable to degradation compared to unsubstituted zinc (II) Pc
in DMSO. Thus, the substitution of Pc with crown ether bearing
coumarin groups seems to increase the stability of the complexes
in DMSO.
4. Conclusion
In conclusion, we have prepared and characterized new metal-
free and zinc (II) Pcs tetra-substituted at the peripheral (complexes
3a and 3b) and non-peripheral (complexes 4a and 4b) posi-
tions with 7,8-(12-crown-4)-3-(4-oxyphenyl)coumarin groups.
The spectroscopic, photophysical and photochemical properties
of Pc complexes (3a–b, 4a–b) were also described. While metal-
free Pc complexes (3a and 4a) showed doublet Q bands in CHCl3,
they showed no splitting Q band due to the deprotonation of the
pyrolle nitrogens in the Pc core due to basic nature of DMSO. On the
other hand, while the absorption spectra of 4b showed monomeric
behaviour evidenced by a single (narrow) Q band in DMSO and THF,
it showed a new peak at 736 nm in CHCl3 and CH2Cl2. The red-
shifted and split Q band of 4b in CHCl3 and CH2Cl2 due to lowering
in symmetry observed because of the protonation. The singlet oxy-
gen quantum yields, which give indication of the potential of the
complexes as photosensitizers in applications where singlet oxy-
gen is required (Type II mechanism) ranged from 0.11 to 0.80. Thus,
these complexes show potential as Type II photosensitizers and can
be used in photodynamic therapy. Substitution of Pc complexes
with crown ether bearing coumarin groups seems to increase the
stability of the complexes in DMSO. The fluorescences of the substi-
tuted Pc complexes are effectively quenched by 1,4-benzoquinone
(BQ). The substituted complexes showed lower KSV values when
compared to the unsubstituted zinc (II) Pc in DMSO.
3.6. Fluorescence quenching studies by 1,4- benzoquinone [BQ]
The fluorescence quenching of Pc complexes by 1,4-
benzoquinone (BQ) in DMSO was found to obey Stern–Volmer
kinetics, which is consistent with diffusion-controlled bimolecular
reactions. Fig. 10 shows the quenching of zinc (II) Pc complex (4b)
by BQ in DMSO as an example. The slope of the plots shown in
Acknowledgement
We are thankful to the Research Foundation of Marmara
University, Commission of Scientific Research Project (BAPKO)
[FEN-A-090909-0302] for supporting this study.
Fig. 10. Fluorescence emission spectral changes of 4b (concentration: 1 × 10−5 M)
on addition of different concentrations of BQ in DMSO. [BQ] = 0, 0.008, 0.016, 0.024,
0.032, 0.040 M.

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275
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