Synthesis, characterization and comparative studies on the photophysical and photochemical properties of metal-free and zinc(II) phthalocyanines with phenyloxyacetic acid functionalities

Article abstract of DOI:10.1016/j.poly.2011.04.044

The synthesis and characterization of new peripherally and non-peripherally tetra-substituted metal-free and zinc(II) phthalocyanines with 2-, 3- and 4-phenyloxyacetic acid functionalities are described for the first time in this study. The new compounds

Full text of DOI:10.1016/j.poly.2011.04.044

Polyhedron 30 (2011) 1935–1944
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Polyhedron
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Synthesis, characterization and comparative studies on the photophysical
and photochemical properties of metal-free and zinc(II) phthalocyanines with
phenyloxyacetic acid functionalities
Meryem Çamur a, Mahmut Durmusß b, Mustafa Bulut c,
⇑
a Kırklareli University, Department of Chemistry, 39100 Kırklareli, Turkey
b Gebze Institute of Technology, Department of Chemistry, P.O. Box 141, Gebze 41400, 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 and characterization of new peripherally and non-peripherally tetra-substituted metal-free
and zinc(II) phthalocyanines with 2-, 3- and 4-phenyloxyacetic acid functionalities are described for the
first time in this study. The new compounds have been characterized by elemental analysis, FT-IR, UV–
Vis, MALDI-TOF and 1H-NMR spectra. Photodegradation, singlet oxygen and fluorescence quantum yields,
and fluorescence lifetimes of these compounds are studied in dimethylformamide (DMF). The influence
of the substituent position on the phthalocyanine framework (non-peripherally or peripherally), central
metal ion (metal-free or zinc) and the position of the COOH group (2-, 3- or 4-position on the phenyloxy-
acetic acid) on the spectroscopic, photophysical and photochemical properties have been investigated.
Non-peripherally zinc(II) phthalocyanines (1b and 2b) and peripherally zinc(II) phthalocyanine (4b) gave
good singlet oxygen quantum yields (UD) (0.37, 0.39 and 0.38, respectively) which indicate the potential
of the complexes as photosensitizers in applications of PDT.
Received 3 February 2011
Accepted 13 April 2011
Available online 1 May 2011
Keywords:
Phthalocyanine
Phenyloxyacetic acid
Fluorescence
Singlet oxygen
Quantum yields
Photodegradation
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
oxyacetic acid functionalities (Scheme 1) are reported in this work.
Phenylacetic acid (PA) and hydroxylated derivatives of PA are pro-
Phthalocyanines (Pcs) are tetrabenzo[5,10,15,20]tetraazapor-
phyrins that have traditionally found applications as dyes and
photoconducting agents in photocopying devices [1], chemical
sensors [2–4], electrochromism agents [5,6], non-linear optics
[7,8] and liquid crystals [9,10]. They have also found importance
in a number of applications including photodynamic therapy
(PDT) [11,12]. In the last few years, particularly the aluminum
and zinc Pc derivatives have been intensively studied as second-
generation photosensitizers for PDT [13,14]. Interest in improving
the photophysical properties of the Pc ring system continues
[15–19]. The Pcs with different functional groups situated at
peripheral positions may enhance the spectral properties and
applications.
duced as catabolic intermediates by both bacteria and fungi growing
on a wide variety of different naturally occurring aromatic com-
pounds such as aromatic amino acids or lignin as well as varioussyn-
theticaromaticcompounds[20–22]. In thispaperwehavecombined
two functional materials (phthalocyanines and phenylacetic acid)
into a single compound via a synthetic methodology. The investiga-
tion of the photophysical and photochemical properties of the Pcs
areveryusefulforphotocatalyticapplicationssuchasPDT. Theeffect
of peripherallyand non-peripherally substitution and theposition of
carboxylic acid functionalities of metal-free and zinc(II) Pcs on their
photophysical and photochemical properties are evaluated in
dimethylformamide (DMF).
The aim of this research is to synthesize new phthalocyanine
complexes as potential candidates for PDT treatment. The synthesis,
characterization and spectroscopic behavior as well as photophysi-
cal (fluorescence quantum yields and lifetimes) and photochemical
(singletoxygenand photodegradationquantumyields)propertiesof
the new oxygen containing tetra-substituted (peripherally and non-
peripherally) metal-free and zinc(II) Pcs with 2-, 3- and 4-phenyl-
2. Experimental
2.1. Materials and equipment
Zinc(II) phthalocyanine (ZnPc) and 1,3-diphenylisobenzofuran
(DPBF) were purchased from Aldrich. Zinc(II) acetate, potassium
carbonate, lithium metal, 2-hydroxyphenylacetic acid, 3-hydroxy-
phenylacetic acid and 4-hydroxyphenylacetic acid were purchased
from Fluka. All solvents were dried as described by Perrin and
Armarego [23] before use. 4-Nitrophthalonitrile [24], 3-nitropht-
⇑
Corresponding author. Tel.: +90 216 3479641/1370; fax: +90 216 3478783.
E-mail addresses: mustafabulut50@gmail.com, mbulut@marmara.edu.tr (M.
Bulut).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.04.044

1936
M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
X
Z
Y
Y
Y
Z
X
1) 1,2-Dichlorobenzene,
Pentanol, Lithium
170ºC, 3h
2) HCl
(for M=2H)
Z
X
O
NO2
Z
O
1) K2CO3, DMF
50 C, N2
O
N
N
N
NC
NC
HO
Y
X
NC
NC
º
N
M
N
N
N
2) HCl
Zn(AcO)2, DMF
155ºC, 24h
(for M=Zn)
O
Z
N
3-Nitrophthalonitrile
1: X=-CH2COOH, Y=Z=H
2: Y=-CH2COOH, X=Z=H
3: Z=-CH2COOH, X=Y=H
Z
O
X
Y
Y
X
1a: M=2H, 1b:M=Zn
2a: M=2H, 2b:M=Zn
3a: M=2H, 3b:M=Zn
Y
Z
X
O
1) 1,2-Dichlorobenzene,
Pentanol, Lithium
170ºC, 3h
X
Z
2) HCl
(for M=2H)
Z
1) K2CO3, DMF
Z
Y
N
N
N
N
N
M
N
NC
NC
NO2
NC
O
Y
X
HO
Y
X
O
50ºC, N2
Y
X
N
Z
O
N
2) HCl
NC
Zn(AcO)2, DMF
155
º
C, 24h
(
for M=Zn)
4: X=-CH2COOH, Y=Z=H
5: Y=-CH2COOH, X=Z=H
6: Z=-CH2COOH, X=Y=H
4-Nitrophthalonitrile
4a: M=2H, 4b:M=Zn
5a: M=2H, 5b:M=Zn
6a: M=2H, 6b:M=Zn
O
Z
X
Y
Scheme 1. Synthesis of phenyloxyphenylacetic acid substituted metal-free and zinc(II) phthalocyanine complexes (1a–6a, 1b–6b).
halonitrile [25], 4-(2,3-dicyanophenoxy)phenylacetic acid (1) [26],
4-(3,4-dicyanophenoxy)phenylacetic acid (4) and its metal-free,
zinc(II) Pc complexes (4a and 4b) [27] were synthesized and puri-
fied according to the literature procedures.
1.00 g (5.78 mmol) phthalonitrile compound (3-nitrophthalonitrile
or 4-nitrophthalonitrile) were dissolved in dry DMF (10 cm3) under
nitrogen atmosphere and 1.60 g (11.56 mmol) anhydrous K2CO3
was added. After stirring for 3 days at 50 °C, the reaction mixture
was treated with diluted HCl (2 M) under ice cooling. The obtained
precipitate was filtered, washed with water to neutralize, and
dried. The crude product was purified by column chromatography
on silica gel with chloroform as the eluting solvent.
Infrared spectra (IR) were recorded on a Shimadzu FTIR-8300
Fourier Transform Infrared spectrophotometer using KBr pellets,
electronic spectra were recorded on 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 re-
corded on a Varian Mercury-VX 400 MHz spectrometer using
TMS as an internal standard. Mass spectra were performed on a
Bruker Autoflex III MALDI-TOF spectrometer using 2,5-dihydroxy-
benzoic acid (DHB, 0.02 g/cm3 in THF) as the matrix. MALDI sam-
ples were prepared by mixing the complex (0.02 g/cm3 in DMF)
with the matrix solution (1:10 v/v) in a 0.5 cm3 eppendorf micro
tube. Finally, 1 ꢀ 10ꢁ3 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 cutoff filter (Schott) and a water fil-
ter 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.
2.2.1.1. 3-(2,3-Dicyanophenoxy)phenylacetic acid (2). Yield: 0.78 g
(48.5%). M.p. 171–173 °C. FT-IR (KBr), m
max/(cmꢁ1): 3416 (carbox-
ylic acid OH), 3085–3025 (Ar-CH), 2951–2908 (aliphatic CH),
2232 (C„N), 1702 (C@O), 1574–1466 (Ar C@C), 1283 (Ar-O-Ar).
1H-NMR (DMSO-d6, 400 MHz): 12.30 (s, 1H, COOH), 7.85 (t,
J = 6 Hz, 1H, Ar-H), 7.58 (d, J = 8 Hz, 1H, Ar-H), 7.50 (d, J = 8 Hz,
1H, Ar-H), 7.22 (t, J = 6 Hz, 1H, Ar-H), 7.12 (bd, 1H, Ar-H), 6.90 (d,
J = 8 Hz, 2H, Ar-H), 3.65 (s, 2H, CH2). MS (MALDI-TOF); calc. for
C
C
16H10N2O3: m/z 278 [M]+, found: m/z 278.44 [M]+. Anal. Calc. for
16H10N2O3: C, 69.06; H, 3.60; N, 10.07. Found: C, 69.08; H, 3.61;
N, 10.01%.
2.2.1.2. 2-(2,3-Dicyanophenoxy)phenylacetic acid (3). Yield: 0.65 g
(40.4%). M.p. 190–192 °C. FT-IR (KBr), m
max/(cmꢁ1): 3432 (carbox-
ylic acid OH), 3075–3028 (Ar-CH), 2941–2924 (aliphatic CH),
2232 (C„), 1705 (C@O), 1584–1464 (Ar C@C), 1275 (Ar-O-Ar).
1H-NMR (DMSO-d6, 400 MHz): 12.35 (s, 1H, COOH), 7.87 (t,
J = 6 Hz, 1H, Ar-H), 7.63 (d, J = 8 Hz, 1H, Ar-H), 7.54 (d, J = 8 Hz,
1H, Ar-H), 7.20 (t, J = 6 Hz, 2H, Ar-H), 7.13 (d, J = 8 Hz, 2H, Ar-H),
3.68 (s, 2H, CH2). MS (MALDI-TOF); calc. for C16H10N2O3: m/z 278
[M]+, found: m/z 278.69 [M]+, 143.33 [M-C8H7O2]+. Anal. Calc. for
2.2. Synthesis
2.2.1. General procedure for the dicyanophenoxyphenylacetic acid
derivatives (2, 3, 5 and 6)
0.88 g (5.78 mmol) Hydroxyphenylacetic acid compound (3-
hydroxyphenylacetic acid or 2-hydroxyphenylacetic acid) and
C
16H10N2O3: C, 69.06; H, 3.60; N, 10.07. Found: C, 69.07; H, 3.63;
N, 10.04%.

M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
1937
2.2.1.3. 3-(3,4-Dicyanophenoxy)phenylacetic acid (5). Yield: 0.85 g
(52.8%). M.p. 135–137 °C. FT-IR (KBr),
max/(cmꢁ1): 3415 (carbox-
2.2.2.3. 1(4),8(11),15(18),22(25)-Tetra(2-phenyloxyacetic acid)phtha-
m
locyanine (3a). Yield: 0.015 g (15%). M.p. > 300 °C. FT-IR (KBr),
ylic acid OH), 3081–3042 (Ar-CH), 2930–2857 (aliphatic CH),
2239 (C„), 1715 (C@O), 1602–1487 (Ar C@C), 1285 (Ar-O-Ar).
1H-NMR (DMSO-d6, 400 MHz): 12.40 (s, 1H, COOH), 8.15 (d,
J = 8 Hz, 1H, Ar-H), 7.95 (d, J = 3 Hz, 1H, Ar-H), 7.45 (d, J = 3 and
8 Hz, 1H, Ar-H), 7.30 (t, J = 6 Hz, 1H, Ar-H), 7.16 (bd, 1H, Ar-H),
6.95 (d, J = 8 Hz, 2H, Ar-H), 3.69 (s, 2H, CH2). MS (MALDI-TOF); calc.
for C16H10N2O3: m/z 278 [M]+, found: m/z 278.59 [M]+, 143.25
[MꢁC8H7O2]+. Anal. Calc. for C16H10N2O3: C, 69.06; H, 3.60; N,
10.07. Found: C, 69.08; H, 3.64; N, 10.04%.
m
max/(cmꢁ1): 3438 (carboxylic acid OH), 3286 (NH), 3069 (Ar-
CH), 2932–2853 (aliphatic CH), 1717 (C@O), 1586–1495 (Ar
C@C), 1255 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 321
(4.65), 709 (4.66), 725 (4.68). 1H-NMR (DMSO-d6, 400 MHz):
12.40 (br s, 4H, COOH), 7.78–6.15 (m, 28H, Ar-H), 3.93 (s, 8H,
CH2), ꢁ3.81 (br s, 2H, NH). MS (MALDI-TOF); calc. for
C
64H42N8O12: m/z 1114 [M]+, found: m/z 1114.39 [M]+, 1186.26
[M+4H2O]+. Anal. Calc. for C64H42N8O12: C, 68.94; H, 3.77; N,
10.05. Found: C, 69.08; H, 3.85; N, 10.09%.
2.2.2.4. 2(3),9(10),16(17),23(24)-Tetra(3-phenyloxyacetic acid)phtha-
2.2.1.4. 2-(3,4-Dicyanophenoxy)phenylacetic acid (6). Yield: 0.75 g
(46.6%). M.p. 217–219 °C. FT-IR (KBr), m
max/(cmꢁ1): 3427 (carbox-
locyanine (5a). Yield: 0.064 g (64%). M.p. > 300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3425 (carboxylic acid OH), 3283 (NH), 3064 (Ar-
ylic acid OH), 3081–3034 (Ar-CH), 2973–2912 (aliphatic CH),
2234 (C„N), 1715 (C@O), 1601–1487 (Ar C@C), 1282 (Ar-O-Ar).
1H-NMR (DMSO-d6, 400 MHz): 12.38 (s, 1H, COOH), 8.05 (d,
J = 8 Hz, 1H, Ar-H), 7.90 (d, J = 3 Hz, 1H, Ar-H), 7.40 (dd, J = 3 and
8 Hz, 1H, Ar-H), 7.15 (t, J = 6 Hz, 2H, Ar-H), 7.09 (d, J = 8 Hz, 2H,
Ar-H), 3.70 (s, 2H, CH2). MS (MALDI-TOF); calc. for C16H10N2O3:
m/z 278 [M]+, found: m/z 278.32 [M]+, 143.31 [MꢁC8H7O2]+. Anal.
Calc. for C16H10N2O3: C, 69.06; H, 3.60; N, 10.07. Found: C, 69.05;
H, 3.61; N, 10.05%.
CH), 2929–2863 (aliphatic CH), 1714 (C@O), 1609–1474 (Ar
C@C), 1248 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 342
(4.77), 667 (4.73), 699 (4.68). 1H-NMR (DMSO-d6, 400 MHz):
12.45 (br s, 4H, COOH), 7.93–6.37 (m, 28H, Ar-H), 3.90 (s, 8H,
CH2), ꢁ3.75 (br s, 2H, NH). MS (MALDI-TOF); calc. for
C
64H42N8O12: m/z 1114 [M]+, found: m/z 1114.67 [M]+, 1115.26
[M+H]+, 1116.63 [M+2H]+. Anal. Calc. for C64H42N8O12: C, 68.94;
H, 3.77; N, 10.05. Found: C, 68.83; H, 3.68; N, 9.87%.
2.2.2.5. 2(3),9(10),16(17),23(24)-Tetra(2-phenyloxyacetic acid)phtha-
2.2.2. General procedure for the metal-free phthalocyanine complexes
(1a, 2a, 3a, 5a and 6a)
locyanine (6a). Yield: 0.048 g (48%). M.p. > 300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3432 (carboxylic acid OH), 3294 (NH), 3064 (Ar-
A mixture of the dicyanophenoxyphenylacetic acid compound
[1, 2, 3, 5 or 6] (0.10 g, 0.36 mmol) and lithium metal (0.05 g,
7.19 mmol) was heated and stirred at 170 °C for 3 h under a N2
atmosphere in a mixture of 1,2-dichlorobenzene (1.5 cm3) and
pentanol (1.5 cm3). After cooling to room temperature the green
mixture was treated with acetone to precipitate the product com-
pletely. The green precipitate was collected by centrifuging and
then it was washed with acetone. It was dissolved in a small
amount of methanol and precipitated by diluted HCl (2 M). In this
mixture, the Li2Pc formed was converted into H2Pc. The green pre-
cipitate was centrifuged and washed several times with water, hot
ethanol, hot methanol, ethyl acetate, acetone and diethyl ether,
and then dried in vacuum. This product was then further purified
by preparative thin layer chromatography (silica gel) using a
THF:MeOH (10:1) solvent mixture as the eluting system.
CH), 2953–2868 (aliphatic CH), 1718 (C@O), 1611–1472 (Ar
C@C), 1234 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 343
(4.59), 670 (4.49), 698 (4.48). 1H-NMR (DMSO-d6, 400 MHz):
12.48 (br s, 4H, COOH), 7.95–6.24 (m, 28H, Ar-H), 3.98 (s, 8H,
CH2), ꢁ3.70 (br s, 2H, NH). MS (MALDI-TOF); calc. for
C
64H42N8O12: m/z 1114 [M]+, found: m/z 1114.42 [M]+, 1186.11
[M+4H2O]+. Anal. Calc. for C64H42N8O12: C, 68.94; H, 3.77; N,
10.05. Found: C, 69.04; H, 3.81; N, 10.17%.
2.2.3. General procedure for the zinc(II) phthalocyanine complexes (1b,
2b, 3b, 5b and 6b)
The dicyanophenoxyphenylacetic acid compound [1, 2, 3, 5 or
6] (0.20 g, 0.72 mmol) was dissolved in dry DMF (1.5 cm3) and
Zn(AcO)2 (0.033 g, 0.18 mmol) was added, and the mixture was
heated under stirring for 24 h at 155 °C under a N2 atmosphere
in a sealed glass tube. After cooling to room temperature, the reac-
tion mixture was treated with diluted HCl (2 M) to precipitate the
product. The green solid was centrifuged and washed several times
successively with water, hot methanol, hot ethanol, ethyl acetate,
acetone and diethyl ether, and then dried in vacuum. This product
was then further purified by preparative thin layer chromatogra-
phy (silica gel) using a THF:MeOH (10:1) solvent mixture as the
eluting system.
2.2.2.1. 1(4),8(11),15(18),22(25)-Tetra(4-phenyloxyacetic acid)phtha-
locyanine (1a). Yield: 0.036 g (36%). M.p. > 300 °C. FT-IR (KBr),
m
max/(cmꢁ1): 3438 (carboxylic acid OH), 3287 (NH), 3047 (Ar-
CH), 2941–2857 (aliphatic CH), 1715 (C@O), 1586–1503 (Ar
C@C), 1253 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 330
(4.69), 693 (4.93), 717 (4.89). 1H-NMR (DMSO-d6, 400 MHz):
12.45 (br s, 4H, COOH), 7.47–6.31 (m, 28H, Ar-H), 3.97 (s, 8H,
CH2), ꢁ3.70 (br s, 2H, NH). MS (MALDI-TOF); calc. for
C
64H42N8O12: m/z 1114 [M]+, found: m/z 1114.27 [M]+, 1115.12
2.2.3.1. 1(4),8(11),15(18),22(25)-Tetra(4-phenyloxyacetic acid)phtha-
[M+H]+, 1116.28 [M+2H]+. Anal. Calc. for C64H42N8O12: C, 68.94;
locyaninato zinc(II) (1b). Yield: 0.181 g (85.5%). M.p. > 300 °C. FT-IR
(KBr),
2875 (aliphatic CH), 1720 (C@O), 1583–1479 (Ar C@C), 1245 (Ar-O-
Ar). UV–Vis kmax (nm) (log ) in DMF: 338 (4.56), 633 (4.33), 696
m
max/(cmꢁ1): 3370 (carboxylic acid OH), 3064 (Ar-CH), 2924–
H, 3.77; N, 10.05. Found: C, 68.58; H, 3.71; N, 10.21%.
2.2.2.2. 1(4),8(11),15(18),22(25)-Tetra(3-phenyloxyacetic acid)phtha-
e
locyanine (2a). Yield: 0.025 g (25%). M.p. > 300 °C. FT-IR (KBr),
(5.02). 1H-NMR (DMSO-d6, 400 MHz): 12.40 (br s, 4H, COOH),
8.00–6.24 (m, 28H, Ar-H), 3.31 (s, 8H, CH2). MS (MALDI-TOF); calc.
for C64H40N8O12Zn: m/z 1177 [M]+, found: m/z 1177.21 [M]+,
1178.14 [M+H]+, 1179.31 [M+2H]+, 1180.03 [M+3H]+, 1249.24
[M+4H2O]+. Anal. Calc. for C64H40N8O12Zn: C, 65.25; H, 3.40; N,
9.52. Found: C, 65.36; H, 3.51; N, 9.58%.
m
max/(cmꢁ1): 3454 (carboxylic acid OH), 3289 (NH), 3076 (Ar-
CH), 2930–2851 (aliphatic CH), 1718 (C@O), 1578–1483 (Ar
C@C), 1254 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 334
(4.63), 689 (4.84), 713 (4.85). 1H-NMR (DMSO-d6, 400 MHz):
12.40 (br s, 4H, COOH), 7.81–6.28 (m, 28H, Ar-H), 3.90 (s, 8H,
CH2), ꢁ3.63 (br s, 2H, NH). MS (MALDI-TOF); calc. for
C
64H42N8O12: m/z 1114 [M]+, found: m/z 1114.52 [M]+, 1115.51
2.2.3.2. 1(4),8(11),15(18),22(25)-Tetra(3-phenyloxyacetic acid)phtha-
[M+H]+, 1116.43 [M+2H]+. Anal. Calc. for C64H42N8O12: C, 68.94;
locyaninato zinc(II) (2b). Yield: 0.121 g (57%). M.p. > 300 °C. FT-IR
H, 3.77; N, 10.05. Found: C, 68.75; H, 3.69; N, 10.12%.
(KBr), m
max/(cmꢁ1): 3342 (carboxylic acid OH), 3070 (Ar–CH),

1938
M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
sF
s0
2936–2864 (aliphatic CH), 1729 (C@O), 1611–1478 (Ar C@C), 1253
UF
¼
ð2Þ
(Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 330 (4.66), 628 (4.25),
693 (4.71). 1H-NMR (DMSO-d6, 400 MHz): 12.40 (br s, 4H, COOH),
8.15–6.30 (m, 28H, Ar–H), 3.40 (s, 8H, CH2). MS (MALDI-TOF); calc.
for C64H40N8O12Zn: m/z 1177 [M]+, found: m/z 1177.34 [M]+. Anal.
Calc. for C64H40N8O12Zn: C, 65.25; H, 3.40; N, 9.52. Found: C, 65.31;
H, 3.35; N, 9.61%.
2.4. Photochemical parameters
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yields of the samples (1a–6a, 1b–6b)
were determined as previously explained in detail [32–34]. Typi-
cally, a 2 cm3 portion of the samples (1a–6a, 1b–6b) solutions
(concentration = 1 ꢀ 10ꢁ5 M) containing the singlet oxygen
quencher was irradiated in the Q band region with the photo-irra-
diation set-up described in the references [32–34]. Singlet oxygen
quantum yields (UD) were determined in air using the relative
method with unsubstituted ZnPc (in DMF) as a reference; and DPBF
as a chemical quencher for singlet oxygen, using the following
equation:
2.2.3.3. 1(4),8(11),15(18),22(25)-Tetra(2-phenyloxyacetic acid)phtha-
locyaninato zinc(II) (3b). Yield: 0.115 g (54%). M.p. > 300 °C. FT-IR
(KBr),
m
max/(cmꢁ1): 3358 (carboxylic acid OH), 3067 (Ar-CH),
2941–2873 (aliphatic CH), 1728 (C@O), 1603–1473 (Ar C@C),
1246 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 332 (4.45), 620
(4.01), 700 (4.32). 1H-NMR (DMSO-d6, 400 MHz): 12.43 (br s, 4H,
COOH), 8.02–6.20 (m, 28H, Ar-H), 3.37 (s, 8H, CH2). MS (MALDI-
TOF); calc. for
C
64H40N8O12Zn: m/z 1177 [M]+, found: m/z
1177.40 [M]+, 1178.65 [M+H]+, 1179.73 [M+2H]+, 1180.54
[M+3H]+, 1249.36 [M+4H2O]+. Anal. Calc. for C64H40N8O12Zn: C,
65.25; H, 3.40; N, 9.52. Found: C, 65.39; H, 3.48; N, 9.61%.
Std
abs
RStd ꢂ Iabs
R ꢂ I
UD
¼
USDtd
ð3Þ
where USDtd is the singlet oxygen quantum yield for the standard
(
2.2.3.4. 2(3),9(10),16(17),23(24)-Tetra(3-phenyloxyacetic acid)phtha-
USDtd ¼ 0:56 for unsubstituted ZnPc in DMF) [30]; R and RStd are
locyaninato zinc(II) (5b). Yield: 0.189 g (89%). M.p. > 300 °C. FT-IR
(KBr),
m
max/(cmꢁ1): 3365 (carboxylic acid OH), 3053 (Ar-CH),
the DPBF photobleaching rates in the presence of the samples
(1a–6a, 1b–6b) and the standard, respectively; Iabs and IStd are the
2926–2886 (aliphatic CH), 1715 (C@O), 1602–1475 (Ar C@C),
abs
rates of light absorption by the samples (1a-6a, 1b-6b) and the
standard, respectively. To avoid chain reactions induced by DPBF
in the presence of singlet oxygen [35], the concentration of quench-
er (DPBF) was lowered to ꢃ3 ꢀ 10ꢁ5 M. Solutions of the sensitizer
containing quencher (DPBF) were prepared in the dark and irradi-
ated in the Q band region using the photo-irradiation setup. DPBF
degradation at 417 nm was monitored. The light intensity
7.47 ꢀ 1015 photons sꢁ1 cmꢁ2 was used for the UD determinations.
1237 (Ar-O-Ar). UV–Vis kmax (nm) (log e) in DMF: 357 (4.97), 617
(4.49), 681 (5.09). 1H-NMR (DMSO-d6, 400 MHz): 12.48 (br s, 4H,
COOH), 8.07–6.23 (m, 28H, Ar-H), 3.40 (s, 8H, CH2). MS (MALDI-
TOF); calc. for
C
64H40N8O12Zn: m/z 1177 [M]+, found: m/z
1177.62 [M]+, 1178.86 [M+H]+, 1179.42 [M+2H]+, 1180.19
[M+3H]+, 1249.20 [M + 4H2O]+. Anal. Calc. for C64H40N8O12Zn: C,
65.25; H, 3.40; N, 9.52. Found: C, 65.35; H, 3.44; N, 9.60%.
2.2.3.5. 2(3),9(10),16(17),23(24)-Tetra(2-phenyloxyacetic acid)phtha-
2.4.2. Photodegradation quantum yields
locyaninato zinc(II) (6b). Yield: 0.103 g (48.7%). M.p. > 300 °C. FT-IR
(KBr),
2914 (aliphatic CH), 1719 (C@O), 1608–1484 (Ar C@C), 1233 (Ar-O-
Ar). UV–Vis kmax (nm) (log ) in DMF: 357 (4.59), 620 (4.11), 684
m
max/(cmꢁ1): 3386 (carboxylic acid OH), 3059 (Ar-CH), 2936–
Photodegradation quantum yield (Ud) determinations were car-
ried out using the experimental set-up described in the literature
[32–34]. For determination of the photodegradation quantum
yields (Ud), the usual Eq. (4) was employed:
e
(4.64). 1H-NMR (DMSO-d6, 400 MHz): 12.40 (br s, 4H, COOH),
8.10–6.30 (m, 28H, Ar-H), 3.35 (s, 8H, CH2). MS (MALDI-TOF); calc.
for C64H40N8O12Zn: m/z 1177 [M]+, found: m/z 1177.56 [M]+,
1178.19 [M+H]+, 1179.18 [M+2H]+, 1249.59 [M+4H2O]+. Anal. Calc.
for C64H40N8O12Zn: C, 65.25; H, 3.40; N, 9.52. Found: C, 65.29; H,
3.48; N, 9.55%.
ðC0 ꢁ CtÞ ꢂ V ꢂ NA
Ud
ð4Þ
Iabs ꢂ S ꢂ t
where C0 and Ct are the sample (1a–6a, 1b–6b) concentrations be-
fore and after irradiation respectively, V, the reaction volume; S, the
irradiated cell area (2.0 cm2); t, the irradiation time; NA, Avogadro’s
number and Iabs, the overlap integral of the radiation source inten-
sity and the absorption of the Pc (the action spectrum) in the region
2.3. Photophysical parameters
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (UF) were determined by the
comparative method using the following equation [28,29]:
of the interference filter transmittance.
A light intensity of
2.24 ꢀ 1016 photons sꢁ1 cmꢁ2 was employed for Ud determinations.
F ꢂ AStd ꢂ n2
2.4.3. Fluorescence quenching by 1,4-benzoquinone (BQ)
UF
¼
UFðStdÞ
ð1Þ
FStd ꢂ A ꢂ n2Std
Fluorescence quenching experiments of the Pc complexes (1a–
6a, 1b–6b) were carried out by the addition of different concentra-
tions of BQ to a fixed concentration of the complex, and the con-
centrations of BQ in the resulting mixtures were 0, 0.008, 0.016,
0.024, 0.032 and 0.040 M. The fluorescence spectra of the Pc com-
plexes (1a–6a, 1b–6b) at each BQ concentration were recorded,
and the changes in fluorescence intensity were related to the BQ
concentration by the Stern–Volmer (SV) equation (5) [36]:
where F and FStd are the areas under the fluorescence emission
curves of the samples (1a–6a, 1b–6b) and the standard, respec-
tively. A and AStd are the relative absorbance of the sample and stan-
dard at the excitation wavelength, respectively. n and nstd are the
refractive indices of the solvents for the sample and standard,
respectively. Unsubstituted ZnPc (in DMSO) (UF = 0.20) [30] was
employed as the standard. Both the sample and standard were ex-
cited at the same wavelength. The absorbance of the solutions ran-
ged between 0.04 and 0.05 at the excitation wavelength.
I0
I
¼ 1 þ KSV½BQꢄ
ð5Þ
Natural radiative lifetimes (
tochem CAD program which uses the Strickler–Berg equation [31].
s
0) were determined using the Pho-
where I0 and I are the fluorescence intensities of the fluorophore in
the absence and presence of quencher, respectively. KSV is the
Stern–Volmer constant; and this is the product of the bimolecular
quenching constant (kq) and the fluorescence lifetime sF (Eq. (6)):
The fluorescence lifetimes (
equation
sF) were evaluated using following

M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
1939
the molecular ions were easily identified at m/z: 1114 [M]+ for
the metal-free Pcs (1a, 2a, 3a, 5a and 6a, Figs. 1, 3, 5, 7 and 9 in
Supplementary data) and at m/z: 1177 [M]+ for the zinc(II) Pcs
(1b, 2b, 3b, 5b and 6b; Figs. 2, 4, 6, 8 and 10 in the Supplementary
data).
KSV ¼ kqsF
ð6Þ
The ratios I0/I were calculated and plotted against [BQ] according to
Eq. (5), and KSV was determined from the slope.
3. Results and discussion
3.2. Electronic absorption spectra
3.1. Synthesis and characterization
The electronic spectra of the non-peripherally and peripherally
tetra-substituted Pc complexes (1a–6a, 1b–6b) showed character-
istic Q band absorptions in DMF (see Fig. 1 for examples of com-
Scheme 1 shows the synthetic procedures used to obtain the
dicyanophenoxyphenylacetic acid derivatives (1–6). The base cata-
lyzed nucleophilic substitution of the nitro group with a phenolic –
OH group was performed in dry DMF at 50 °C under an inert nitro-
gen atmosphere. Good yields were obtained for all reactions. Con-
version of the dicyanophenoxyphenylacetic acid derivatives (1–6)
into the metal-free Pcs (1a–6a) was accomplished in a mixture of
1,2-dichlorobenzene and pentanol in the presence of lithium.
Dilithium Pc complexes can be labile towards water and acid,
and can easily be converted to the metal-free Pcs. The zinc(II) Pcs
(1b–6b) were prepared from the corresponding dicyanophenoxy-
phenylacetic acid derivatives (1–6) and Zn(AcO)2 as a metal salt
in DMF (Scheme 1). The Pcs are only soluble in DMSO and DMF.
Characterization of the products involved a combination of meth-
ods including elemental analysis, FT-IR, UV–Vis (for Pcs), MALDI-
TOF and 1H-NMR spectra. The spectroscopic data of the new com-
pounds were in accordance with the structures.
plexes 1a, 4a and 1b, 4b). The
p
–p⁄ transitions for the Q band
absorptions were observed at 693, 717 (1a), 696 (1b), 689, 713
(2a), 693 (2b), 709, 725 (3a), 700 (3b), 667, 699 (4a), 680 (4b),
667, 699 (5a), 681 (5b), 670, 698 (6a) and 684 nm (6b), Table 1.
The Q bands of the metal-free or zinc(II) Pcs substituted with 2-,
3- and 4-phenyloxyacetic acid functionalities were similar, but
the Q bands of the non-peripherally metal-free (1a–3a) and zinc
(1b–3b) Pc complexes were red-shifted 26, 18 nm (between 1a
and 4a), 16 nm (between 1b and 4b), 22, 14 nm (between 2a and
5a), 12 nm (between 2b and 5b), 39, 27 nm (between 3a and 6a)
and 16 nm (between 3b and 6b) compared to the peripherally me-
tal-free (4a–6a) and zinc (4b–6b) Pc complexes in DMF (Fig. 1
shows examples for complexes 1a, 4a and 1b, 4b). The observed
red spectral shifts are typical of Pcs with substituents at the non-
peripheral positions and have been explained [37,38] as being
due to a linear combination of the atomic orbital (LCAO) coeffi-
cients at the non-peripheral positions of the highest occupied
molecular orbital (HOMO) being greater than those at the periph-
eral positions. As a result, the HOMO level is more destabilized
In the IR spectra of the dicyanophenoxyphenylacetic acid deriv-
atives (1–6), the peaks around 1705–1715 cmꢁ1 indicate the pres-
ence of
a
C@O group and the peaks at 3416–3432 cmꢁ1
corresponds to –OH of the –COOH group. In addition, the charac-
teristic vibrations of the C„N group appeared at around 2230–
2240 cmꢁ1. After conversion of the dicyanophenoxyphenylacetic
acid derivatives (1–6) into Pc complexes (1a–6a, 1b–6b), the sharp
peak for the C„N vibrations disappeared. The NH group of the me-
tal-free Pcs (1a–6a) in the inner core gave a weak absorption peak
at around 3283–3294 cmꢁ1. The IR spectra of the metal-free Pcs
(1a–6a) and zinc(II) Pcs (1b–6b) were similar, except the m(NH)
vibrations of the inner Pc core in the metal-free molecules. In the
1H-NMR analysis of the dicyanophenoxyphenylacetic acid deriva-
tives (2, 3, 5 and 6) in deuterated DMSO, the carboxylic acid proton
appeared at around d 12.35 ppm as a singlet, the aromatic protons
appeared between d 8.15 and 6.90 ppm as a triplet, doublet or dou-
blet of doublets. The aliphatic protons (–CH2) adjacent to the car-
boxylic acid group appeared at around d 3.65 ppm as a singlet. A
preliminary investigation of the 1H-NMR spectra of the Pc com-
plexes (1a–6a, 1b–6b) was carried out in deuterated DMSO. The
1H-NMR spectra of the metal-free Pcs (1a, 2a, 3a, 5a and 6a) indi-
cate the carboxylic acid protons (COOH) at around d 12.40 ppm as a
broad singlet, aromatic protons at around d 7.95–6.15 ppm as a
broad peak and aliphatic protons (CH2) at around d 3.97 ppm as
a singlet. The 1H-NMR spectra of the metal-free Pcs (1a, 2a, 3a,
5a and 6a) showed the inner core NH protons at around d
ꢁ3.75 ppm. The only difference between the 1H-NMR spectra of
the metal-free Pcs (1a, 2a, 3a, 5a and 6a) and the zinc(II) Pcs (1b,
2b, 3b, 5b and 6b) is the lack of broad chemical shifts of the inner
core NH protons. The 1H NMR spectra of the phthalocyanines are
rather broad, probably owing to the aggregation of the phthalocy-
anines, which is frequently encountered at the concentrations used
for NMR spectroscopy [1].
The MALDI-TOF mass spectra of the phthalonitrile compounds
(2, 3, 5 and 6) showed an intense peak at m/z = 278 [M]+, support-
ing the proposed formula for this compound. In the mass spectra of
compounds 3, 5 and 6, in addition to the [M]+ peak, a fragment ion
corresponding to the loss of phenylacetic acid was easily identified
at m/z: 143 [MꢁC8H7O2]+. The MALDI-TOF mass spectra of the Pc
complexes (1a–6a, 1b–6b) confirmed the proposed structures;
Fig. 1. Absorption spectra of (A) complexes 1a, 4a and (B) complexes 1b, 4b in DMF.
Concentrations: 1 ꢀ 10ꢁ5 M.

1940
M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
Table 1
Absorption, excitation and emission spectral data for peripherally and non-periph-
erally substituted metal-free and zinc(II) Pcs in DMF.
Compound Q band
kmax (nm)
log
e
Excitation Emission Stokes Shift
kEx (nm) kEm (nm) DStokes, (nm)
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
693, 717
696
689, 713
693
709, 725
700
667, 699
680
667, 699
681
670, 698
684
670
4.93, 4.89 698, 716
5.02 697
4.84, 4.85 691, 714
4.71 693
4.66, 4.68 710, 716
4.32 698
4.77, 4.72 667, 699
5.03 678
4.73, 4.68 668, 695
5.09 678
4.49, 4.48 670, 698
726
709
725
704
730
706
706
690
707
690
706
692
676
9
13
12
11
5
6
7
10
8
9
8
8
6b
4.64
5.37
680
670
ZnPca
6
a
Data from Ref. [43].
upon non-peripheral substitution than peripheral substitution.
Essentially, the energy gap ( E) between the HOMO and lowest
D
unoccupied molecular orbital (LUMO) becomes smaller, resulting
in a ꢃ20 nm bathochromic shift. The B-bands are broad due to
the superimposition of the B1 and B2 bands in the 300–350 nm
regions.
3.3. Aggregation behavior
Aggregation is usually depicted as a coplanar association of
rings progressing from monomer to dimer and higher order com-
plexes. It is dependent on the concentration, nature of the solvent,
nature of the substituents, complexed metal ions and temperature
[39,40]. The peripherally substituted metal-free Pc complexes (4a–
6a) gave doublet Q bands in DMF as a result of the D2h symmetry
[41] (see Fig. 1a as an example for complexes 1a and 4a). The
ground state electronic absorption spectra showed monomeric
behavior evidenced by a single (narrow) Q band for all the studied
zinc Pc complexes and they are typical of metallated phthalocya-
nine complexes in DMF (see Fig. 1b as an example for complexes
1b and 4b).
The non-peripherally substituted metal-free complexes (1a–3a)
showed different electronic spectra from their peripherally substi-
tuted analogues. Firstly, we thought that this corruption can be due
to the aggregation of the Pc molecules. Triton X-100, which is a
surfactant for reducing of aggregation, was added to the non-
peripherally substituted metal-free Pc solutions, but no change
was observed after addition of Triton X-100. Later, we thought that
this modification could be due to the deprotonation of the pyrrole
nitrogens in the Pc core due to basic nature of the solvent used
(DMF). The deprotonation increased on lowering of the Pc concen-
tration suggesting that more inner H atoms are removed from the
Pc core on increasing the number of basic DMF molecules (see
Fig. 2a as an example for complex 2a). Tetrabutylammonium
hydroxide (TBAOH), which is an organic base, was also used for
proving the deprotonation phenomenon. The non-peripherally
substituted metal-free Pcs showed a single narrow Q band after
addition of TBAOH, resulting in complete deprotonation of the pyr-
role nitrogens in the Pc core (see Fig. 2b as an example for complex
2a). The absorption spectra showed only one narrow peak in the Q
band region due to the changing symmetry of the molecules from
D2h to D4h. The effect of the COOH position on the deprotonation of
the pyrrole nitrogens for non-peripherally substituted metal-free
Pc complexes was also compared. The position of the carboxylic
acid groups (2-, 3- and 4-phenyloxyacetic acid) affected the elec-
tronic spectra. The order of the number of deprotonated H atoms
Fig. 2. Absorption spectra of (A) complex 2a in DMF at different concentrations:
12 ꢀ 10ꢁ6 (A), 10 ꢀ 10ꢁ6 (B), 8 ꢀ 10ꢁ6 (C), 6 ꢀ 10ꢁ6 (D), 4 ꢀ 10ꢁ6 (E), 2 ꢀ 10ꢁ6 (F) M
and (B) the change of absorption spectra of complex 2a with addition of TBAOH
(concentration: 12 ꢀ 10ꢁ6 M).
with the position of the COOH group was as follows: 2-position
(3a) > 3-position (2a) > 4-position (1a), suggesting that closeness
of the COOH group to the Pc core is preferential for deprotonation.
The 2-position is situated at the closest position to the Pc core and
the electron withdrawing COOH groups at the 2-position had the
most activated inner H atoms on the pyrrole nitrogens for deproto-
nation. The Q bands of 3a were red shifted compared to 1a and 2a
for this phenomenon (Fig. 3).
The aggregation behavior of the studied Pc complexes was
investigated at different concentrations in DMF (see Fig. 4 as exam-
ples for complexes 5a and 5b). Carboxylic acid groups can interact
with each other between Pc molecules to keep the chromophores
close enough to cause exciton coupling. The band at about
625 nm is due to the interaction between adjacent Pc molecules.
Except for this type of aggregation, no new bands were observed
for the zinc(II) (1b–6b) and peripherally metal-free (4a–6a) Pc
complexes, signifying no aggregation behavior at these concentra-
tions. (see Fig. 4a for complex 5b). The non-peripherally substi-
tuted metal-free Pc complexes (1a–3a) showed deprotonation of
the pyrrole nitrogens in the Pc core as explain above.
3.4. Fluorescence spectra
Fig. 5 (for complexes 5a and 5b as examples) shows the absorp-
tion, fluorescence emission and excitation spectra for the Pc com-
plexes in DMF (concentration = 2 ꢀ 10ꢁ6 M). The excitation spectra
for the metal-free Pc complexes (1a–6a) were similar to the

M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
1941
Fig. 3. Absorption spectra of non-peripherally substituted metal-free Pcs (1a–3a) in
DMF. Concentrations: 1 ꢀ 10ꢁ5 M.
Fig. 5. Absorption, excitation and emission spectra of: (A) complex 5a and (B)
complex 5b in DMF (2 ꢀ 10ꢁ6 M). Excitation wavelength = 640 nm.
5a. Fluorescence emission peaks were observed at 726 nm for 1a,
725 nm for 2a, 730 nm for 3a, 706 nm for 4a, 707 nm for 5a and
706 nm for 6a in DMF (Table 1). Also the Zn(II) Pc complexes
(1b–6b) showed excitation spectra which were similar to absorp-
tion spectra, with both being mirror images of the emission spectra
(see Fig. 5b as an example for complex 5b). Fluorescence emission
peaks were observed at 709 nm for 1b, 704 nm for 2b, 706 nm for
3b, 690 nm for 4b, 690 nm for 5b and 692 nm for 6b in DMF (Ta-
ble 1). The observed Stokes shifts (Table 1) are typical of Pc com-
plexes in DMF.
3.5. Fluorescence quantum yields and lifetimes
The fluorescence quantum yield (UF) values for the complexes
were found to range from 0.03 to 0.11, with complex 3b having
the highest quantum yield, Table 2. The UF values of all the studied
Pc complexes are lower than unsubstituted ZnPc in DMF, which
implies that the presence of the phenylacetic acid substituents cer-
tainly results in fluorescence quenching. The UF values of the Zn(II)
Pc complexes (1b–6b) are higher than for the metal-free Pc com-
plexes (1a–6a). Also the non-peripheral Pc complexes (1a–3b)
show higher UF values compared to the peripheral Pc complexes
(4a–6b).
Fig. 4. Aggregation behavior of (A) complex 5b and (B) complex 5a in DMF at
different concentrations: 12 ꢀ 10ꢁ6 (A), 10 ꢀ 10ꢁ6 (B), 8 ꢀ 10ꢁ6 (C), 6 ꢀ 10ꢁ6 (D),
4 ꢀ 10ꢁ6 (E), 2 ꢀ 10ꢁ6 (F) M. (Inset: plot of absorbance vs. concentration.)
corresponding absorption spectra in that there was no change in
the Q band positions, but the relative intensities of the split pair
were different, suggesting a slight change in symmetry upon
absorption due to deprotonation (see Fig. 5a as an example for
complex 5a). Low symmetry Pc complexes, such as that of the me-
tal-free Pcs [42], show fluorescence with only one main peak that
is assigned as the 0–0 transition of the fluorescence, hence the
observation of a single main emission peak in Fig. 5a for complex
Lifetimes of fluorescence (sF) were calculated using the Stric-
kler–Berg equation. Using this equation, a good correlation has
been [29] found for the experimentally and theoretically deter-
mined fluorescence lifetimes for the non-aggregated molecules,
as is the case in this work for the Pc complexes in DMF. Thus we
suggest that the values which were obtained using this equation

1942
M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
Table 2
Photophysical and photochemical parameters of peripherally and non-peripherally substituted metal-free and zinc(II) Pcs in DMF.
kF (sꢁ1) (ꢀ108)a
Ud (ꢀ10ꢁ4
)
UD
BQ
SV
kBqQ (ꢀ108 sꢁ1
)
K
(Mꢁ1
)
Compound
UF
sF (ns)
s0 (ns)
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
0.08
0.09
0.06
0.10
0.07
0.11
0.05
0.07
0.05
0.06
0.03
0.04
0.17
0.87
0.96
0.79
2.88
1.34
4.00
0.62
0.76
0.77
0.53
0.65
0.67
1.03
9.61
11.88
12.73
29.08
18.64
35.75
12.69
11.62
13.77
8.91
1.04
0.84
0.79
0.34
0.54
0.28
0.79
0.86
0.73
1.12
0.54
0.51
0.17
7.66
13.38
7.05
15.29
5.27
42.29
2.22
6.62
3.50
15.20
3.68
17.07
0.23
0.12
0.37
0.13
0.39
0.05
0.14
0.12
0.38
0.12
0.29
0.08
0.21
0.56
9.61
18.57
12.60
20.32
18.48
19.80
10.08
16.03
15.02
23.61
11.20
17.03
57.60
1.11
1.93
1.60
0.71
1.38
0.49
1.62
2.11
1.95
5.10
1.74
2.54
5.59
18.42
19.74
6.05
6b
ZnPcb
a
kF is the rate constant for fluorescence. Values calculated using kF = UF/sF.
Data from Ref. [43].
b
are a good measure of the fluorescence lifetimes. Complex 3b
showed the highest lifetime of fluorescence among the studied
Pc complexes, Table 2. The sF values were longer for the substi-
tuted Pc complexes (4.00 for 3b, 2.88 for 2b and 1.34 for 3a) when
compared to the unsubstituted Zn(II) Pc (1.03) in DMF. The sF val-
ues of the Zn(II) Pc complexes (1b–6b) were longer than for the
metal-free Pc complexes (1a–6a), except for complex 5b. The nat-
ural radiative lifetime (s0) values of all the substituted Pc com-
plexes (1–6) were also longer when compared to unsubstituted
Zn(II) Pc in DMF. The s0 values of the Zn(II) Pc complexes (1b–
6b) were also longer when compared to the metal-free Pc com-
plexes (1a–6a) in DMF, and complex 3b showed the highest natu-
ral radiative lifetime. The natural radiative lifetime (s0) values
decreased as follows: 2-phenyloxyacetic acid > 3-phenyloxyacetic
acid > 4-phenyloxyacetic acid functionalities, except for complex
5b. The rate constant for the fluorescence (kF) for complex 5b
showed the highest value, and the rate constants for fluorescence
(kF) decreased as follows: 4-phenyloxyacetic acid > 3-phenyloxy-
acetic acid > 2-phenyloxyacetic acid functionalities, except for
complex 5b. The kF values for all the substituted Pc complexes
(1a–6a, 1b–6b) were higher than the unsubstituted Zn(II) Pc in
DMF.
Fig. 6. A typical spectrum for the determination of singlet oxygen quantum yield.
This determination was for complex 4b in DMF at a concentration of 1 ꢀ 10ꢁ5 M.
(Inset: plot of DPBF absorbance vs. time.)
0.39 and 0.38, respectively, Table 2) which indicate the potential
of the complexes as photosensitizers in PDT applications.
3.7. Photodegradation studies
3.6. Singlet oxygen quantum yields
Degradation of the molecules under irradiation can be used to
study their stability, and this is especially important for those mol-
ecules intended for use as photocatalysts. The collapse of the
absorption spectra without any distortion of the shape confirms
Singlet oxygen quantum yields (UD) were determined in DMF
using a chemical method using DPBF as a quencher. The disappear-
ance of the DPBF spectra was monitored using a UV–Vis spectro-
photometer. Many factors are responsible for the magnitude of
the determined quantum yield of singlet oxygen, including the
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 ex-
cited state and the ground state of oxygen. There was a noteworthy
change in the Q band intensity during the UD determinations, con-
firming that the complexes were not degraded during the singlet
oxygen studies (see Fig. 6 as an example for complex 4b), and this
indicates that the Pcs were not damaged by the generated singlet
oxygen. The UD values of the Pc complexes (1a–6a, 1b–6b) were
lower when compared to unsubstituted Zn(II) Pc in DMF. The UD
values of the Zn(II) Pc complexes (1b–6b) were higher when com-
pared to the metal-free Pc complexes (1a–6a) in DMF, suggesting a
closed shell d10 configuration of zinc as the central metal in the Pc
complexes. The non-peripherally substituted zinc(II) phthalocya-
nines (1b and 2b) and peripherally substituted zinc(II) phthalocy-
anine (4b) gave good singlet oxygen quantum yields (UD) (0.37,
Fig. 7. The photodegradation of compound 5b in DMF showing the disappearance
of the Q band at 30 s intervals. (Inset: plot of absorbance vs. time.)

M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
1943
clean photodegradation not associated with phototransformation.
The spectral changes observed for all the Pc complexes (1a–6a,
1b–6b) during the confirmed photodegradation occurred without
phototransformation (see Fig. 7 as an example for complex 5b).
The photodegradation quantum yield (Ud) values of the Pc com-
plexes (1a–6a, 1b–6b) in DMF are given in Table 2. Stable Pc mol-
ecules show Ud values as low as 10ꢁ6, and for unstable molecules
values of the order of 10ꢁ3 have been reported [15]. The substi-
tuted Pc complexes (1a–6a, 1b–6b) have an intermediate photo-
stability. This is especially required for PDT applications: very
unstable photosensitizer molecules degrade before having time
to undergo PDT activation, but on the other hand, highly stable
photosensitizer molecules are not easily eliminated by cell media
[43].
3.8. Fluorescence quenching studies by 1,4-benzoquinone [BQ]
The fluorescence quenching of the complexes by 1,4-benzoqui-
none (BQ) in DMF was found to obey Stern–Volmer kinetics, which
is consistent with diffusion-controlled bimolecular reactions. Fig. 8
shows the quenching of the zinc(II) Pc complex (2b) by BQ in DMF
as an example. The slope of the plots shown in Fig. 9 gave the KSV
values listed in Table 2. The KSV values of the substituted Pc com-
plexes (1a–6a, 1b–6b) were lower than unsubstituted Zn(II) Pc in
DMF. The KSV values of the Zn(II) Pc complexes (1b–6b) were high-
er when compared to the metal-free Pc complexes (1a–6a) in DMF.
When the substituted complexes were compared, 5b showed the
highest KSV value in DMF, while complex 1a showed the lowest
KSV value. The bimolecular quenching constant (kq) values of the
substituted Pc complexes (1a–6a, 1b–6b) were also lower than
for unsubstituted Zn(II) Pc in DMF, thus substitution with the phe-
nyloxyacetic acid group seems to decrease the kq values of the
complexes. Also the peripheral Pc complexes (4a–6b) showed
higher kq values compared to the non-peripheral Pc complexes
(1a–3b).
4. Conclusion
Fig. 8. Fluorescence emission spectral changes of 2b (1 ꢀ 10ꢁ5 M) on addition of
In the presented work, the syntheses of new tetra-substituted
(peripherally and non-peripherally) metal-free and zinc(II) Pcs
with 2-, 3- and 4-phenyloxyacetic acid functionalities were de-
scribed and the compounds characterized by elemental analysis,
FT-IR, UV–Vis (for Pcs), MALDI-TOF and 1H-NMR spectra. The
photophysical (fluorescence quantum yields and lifetimes) and
photochemical (singlet oxygen and photodegradation quantum
yields) properties of these Pc complexes were also described in
DMF for comparison. In DMF, the absorption spectra showed
monomeric behavior, as evidenced by a single (narrow) Q band
for the Zn(II) Pcs typical of a metallated Pc, and a doublet Q band
for metal-free Pcs. Substitution of the phenyloxyacetic acid group
at a non-peripheral position for the metal-free Pcs (1a-3a) showed
deprotonation of the pyrrole nitrogens in the Pc core, and 2-phe-
nyloxyacetic acid substitution showed more deprotonation be-
cause the carboxylic acid group is situated at the closest position
to the Pc ring. The fluorescence behavior of the Pc complexes
was studied in DMF. All the studied Pc complexes showed lower
UF values than unsubstituted Zn(II) Pc, and the UF values of the
Zn(II) Pc complexes (1b–6b) showed larger values than for the me-
tal-free Pc complexes (1a–6a). Also the non-peripheral Pc com-
plexes (1a–3a, 1b–3b) showed larger UF values compared to the
peripheral Pc complexes (4a–6a, 4b–6b). The singlet oxygen quan-
tum yields (UD) give an indication of the potential of the com-
plexes as photosensitizers in PDT applications. These values for
the Pc complexes (1a–6a, 1b–6b) were lower when compared to
unsubstituted Zn(II) Pc in DMF, but they are still high enough for
PDT applications. The substituted Pc complexes (1a–6a, 1b–6b)
showed an intermediate photostability. The Stern–Volmer con-
stant (KSV) and bimolecular quenching constant (kq) values of the
substituted Pc complexes (1a–6a, 1b–6b) were lower than unsub-
stituted Zn(II) Pc in DMF.
different concentrations of BQ in DMF. [BQ] = 0, 0.008, 0.016, 0.024, 0.032, 0.040 M.
Acknowledgement
We are thankful to the Research Foundation of Marmara Uni-
versity, Commission of Scientific Research Project (BAPKO) [FEN-
A-090909-0302] for supporting this study.
Fig. 9. Stern–Volmer plots for 1,4-benzoquinone (BQ) quenching of (A) metal-free
Pcs (1a–6a) and (B) zinc(II) Pcs (1b–6b). [MPc]: 1 ꢀ 10ꢁ5 M, [BQ] = 0, 0.008, 0.016,
0.024, 0.032, 0.040 M in DMF.

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M. Çamur et al. / Polyhedron 30 (2011) 1935–1944
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