Synthesis, characterization and comparative studies on the photophysical and photochemical properties of peripherally and non-peripherally tetra-substituted zinc(II) phthalocyanines

Article abstract of DOI:10.1016/j.jorganchem.2012.02.028

In this study, the novel peripherally and non-peripherally tetra-substituted zinc(II) phthalocyanines were synthesized for the first time by cyclotetramerization reactions of corresponding four different phthalonitriles. All of these new zinc phthalocyani

Full text of DOI:10.1016/j.jorganchem.2012.02.028

Journal of Organometallic Chemistry 708-709 (2012) 65e74
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and comparative studies on the photophysical and
photochemical properties of peripherally and non-peripherally tetra-substituted
zinc(II) phthalocyanines
a
b,
c
b
_
*
ꢀ
Irfan Acar , Zekeriya Bıyıklıoglu , Mahmut Durmus¸ , Halit Kantekin
a Department of Woodworking Industry Engineering, of Faculty of Technology, Karadeniz Technical University, 61830 Trabzon, Turkey
b Department of Chemistry, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey
c Gebze Institute of Technology, Department of Chemistry, PO Box 141, Gebze, 41400 Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, the novel peripherally and non-peripherally tetra-substituted zinc(II) phthalocyanines were
Received 19 January 2012
Received in revised form
18 February 2012
synthesized for the first time by cyclotetramerization reactions of corresponding four different phtha-
lonitriles. All of these new zinc phthalocyanines were characterized by the spectral data (IR, 1H NMR, 13
C
NMR, UVeVis and mass spectroscopies) as well as elemental analysis. These new zinc(II) phthalocya-
nines showed excellent solubility in many organic solvents. Surprisingly, the non-peripherally
substituted zinc (II) phthalocyanine complexes (9 and 10) formed J-aggregates in non-coordinating
solvents such as chloroform, dichloromethane and toluene. The formation of the J-aggregation was
proved by UVeVis and MALDI-TOF mass spectra of these complexes. The photophysical and photo-
chemical properties of zinc phthalocyanine complexes were also investigated in DMSO. The investigation
of the photophysical and photochemical properties of photosensitizers is very useful for photodynamic
therapy (PDT) applications.
Accepted 21 February 2012
Keywords:
Phthalocyanine
Zinc
Singlet oxygen
J-aggregation
Photodynamic therapy
Photosensitizer
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
high molar absorption coefficient in the red part of the spectrum,
photostability and long lifetimes of the photoexicited triplet states
Phthalocyanines (Pcs), a family of aromatic macrocycles based
on an extensive delocalized 18 -electron system, have been
[21e23]. Especially, ZnPcs have been extensively studied because of
d10 configuration of the central Zn2þ ion results in optical spectra
that are not complicated by additional bands, as in transition-metal
Pc complexes. ZnPcs have intensive red-visible region absorption
and high singlet and triplet yields, which make them valuable
photosensitizer for PDT applications.
The aggregation behavior of phthalocyanine compounds has
been extensively investigated [24,25]. The aggregation formation
among the phthalocyanine molecules involves ligandemetal coor-
p
extensively studied due to their unique optical, electronic, catalytic
and structural properties. They have been used in very different
areas of technology and medical applications, i.e., gas sensor [1e3],
solar cell [4,5], liquid crystal [6], catalyst [7], electrochromic display
[8], photodynamic therapy (PDT) of cancer [9e11]. They have also
found different applications in many fields ranging from industrial
[12], technological [13,14], to medical [15,16].
Applications of phthalocyanines are restricted owing to their
insolubility in common organic solvents and water. It has been
found that suitable functional groups on the peripheral benzene
rings of the phthalocyanine structure can improve the solubility in
protic or non-protic solvents [17,18].
Metallophthalocyanine derivatives are photoactive and may be
employed in photosensitization [19,20]. In this regard, it is worth
emphasizing the Pcs’ application as photosensitizers in the PDT of
tumors. Pcs are known to be useful photosensitizers due to their
dination [26,27], p-stacking [28,29], hydrogen bonding [27] and
donoreacceptor [30] interactions. The phthalocyanine compounds
have two types of aggregations which affect on electronic and
optical properties of these compounds. One of them namely face-to-
face H-aggregation and another one is side-to-side J-aggregation
[1,31].
In H-aggregates, the phthalocyanine molecules are arranged
into
a face-to-face conformation, and transition dipoles are
perpendicular to the line connecting their centers. In contrast, in
J-aggregates, the phthalocyanine molecules adopt a side-by-side
conformation, and their transition dipoles are parallel to the line
connecting their centers. In general, J-aggregates are highly desir-
able to maximize the optical properties of the phthalocyanines.
* Corresponding author. Tel.: þ90 462 512 76 39; fax: þ90 462 325 31 96.
ꢀ
E-mail address: zekeriya_61@yahoo.com (Z. Bıyıklıoglu).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.02.028

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
Typically, phthalocyanine aggregation results in a decrease in
intensity of the Q band corresponding to the monomeric species,
meanwhile a new, broader and blue-shifted band is seen to increase
in intensity. This shift to lower wavelengths indicates to H-type
aggregation among the phthalocyanine molecules. Rare cases red-
shifted bands have been observed corresponding to J-type aggre-
gation of the phthalocyanine molecules. Generally, J-aggregates of
Pc molecules occurred by utilizing the coordination of the side
substituent from one Pc molecule to the central metal ion in
a neighbor molecule [32e36]. The substituted zinc Pcs in non-
coordinated organic solvents, e.g. chloroform and dichloro-
methane exhibit J-aggregation [37,38]. The addition of coordinating
solvents such as methanol or pyridine caused dissociation of the
dimers, which implies that the absence of coordinating solvents is
essential for J-aggregation of Pc compounds [39]. UVevis and
MALDI-TOF-MS spectra could be used for determination presence
of J-aggregation for Pc compounds [40].
accumulating 50 laser shots using Bruker Microflex LT MALDI-TOF
mass spectrometer. The elemental analyses were performed on
a Costech ECS 4010 instrument. Melting points were measured on an
electrothermal apparatusand are uncorrected. Absorption spectra in
the UVevis region were recorded with a Shimadzu 2001 UV spec-
trophotometer. Fluorescence excitation and emission spectra were
recorded on a Varian Eclipse spectrofluorometer using 1 cm path-
length cuvettes at room temperature. Photoirradiations 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.
2.3. Photophysical parameters
Recently, we reported that ZnPc derivatives functionalized with
substituents such as 4-(quinolin-6-yloxy) and crown ether groups in
peripheral and non-peripheral positions on the phthalocyanine
ring, compounds offered PDT properties due to their interesting
photophysical properties [41,42]. Herein, we reporton the synthesis,
characterization and spectroscopic behavior as well as photo-
physical (fluorescence quantum yields and lifetimes) and photo-
chemical (singlet oxygen and photodegradation quantum yields)
properties of zinc phthalocyanine complexes substituted with four
2-[2-(1-naphthyloxy)ethoxy]ethanol and 2-[2-(2-naphthyloxy)
ethoxy]ethanol groups (Schemes 1 and 2). The aggregation behavior
of the synthesized zinc (II) phthalocyanine complexes are investi-
gated in different solvents. The non-peripherally substituted
complexes (9 and 10) showed J-type aggregation in non-
coordinating solvents such as chloroform, dichloromethane and
toluene. The formation of J-aggregation among the phthalocyanine
molecules was determined using by UVeVis spectra of these
complexes in non-coordinating solvents as well as MALDI-TOF
spectra.
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (FF) were determined in DMSO by
the comparative method using equation (1) [48,49].
F$AStd$n2
FF
¼
FFðStdÞ
(1)
F
Std$A$n2Std
where F and FStd are the areas under the fluorescence emission
curves of the samples (4, 5, 9 and 10) and the standard, respectively.
A and AStd are the respective absorbances of the samples and
standard at the excitation wavelengths, respectively. n2 and nS2td are
the refractive indices of solvents used for the sample and standard,
respectively. Unsubstituted ZnPc (in DMSO) (FF ¼ 0.20) [50] was
employed as the standard. The absorbance of the solutions at the
excitation wavelength ranged between 0.04 and 0.05.
Natural radiative lifetimes (s0) were determined using Photo-
chemCAD program [51] which uses the StricklereBerg equation.
The fluorescence lifetimes (
sF) were evaluated using equation (2).
sF
s0
2. Experimental
FF
¼
(2)
2.1. Materials
2.4. Photochemical parameters
All reagents and solvents were of reagent grade quality and
were obtained from commercial suppliers. All solvents were dried
and purified as described by Perrin and Armarego [43]. 1,3-
diphenylisobenzofuran (DPBF) and 1,8-diazabicyclo[5.4.0]undec-7-
ene (DBU) were purchased from Fluka. Unsubstituted zinc (II)
phthalocyanine was purchased from Aldrich. 2-[2-(1-naphthyloxy)
ethoxy]ethanol (1) [44], 2-[2-(2-naphthyloxy)ethoxy]ethanol (6)
[44], 3-nitrophthalonitrile [45], 4-nitrophthalonitrile [46], 4-{2-[2-
(1-naphthyloxy)ethoxy]ethoxy}phthalonitrile (2) [47]and 2(3),9(10),
16(17),23(24)-tetrakis {2-[2-(1-naphthyloxy)ethoxy]ethoxy} phtha-
locyaninato zinc (II) (4) [47] were synthesized and purified according
to well known literature.
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield (FD) determinations were carried
out using the experimental set-up described in the literature
[52,53]. Singlet oxygen quantum yields (FD) were determined in
DMSO using the relative method with unsubstituted ZnPc as
reference. DPBF was used as chemical quencher for singlet oxygen
in DMSO. Typically, a 3 ml portion of the respective unsubstituted
zinc phthalocyanine (ZnPc) and substituted zinc phthalocyanine
(4, 5, 9 and 10) solutions (C ¼ 1 ꢀ 10ꢁ5 M) containing the singlet
oxygen quencher were irradiated in the Q band region with the
photo-irradiation set-up described in references [52,53]. Equation
(3) was employed for the calculations:
2.2. Equipment
Std
R$I
FD
¼
FSDtd
(3)
abs
The IR spectra were recorded on a Perkin Elmer 1600 FT-IR
spectrophotometer using KBr pellets. 1H-and 13C NMR spectra
were recorded on a Varian Mercury 200 MHz spectrometer in CDCl3.
RStd$Iabs
where FSDtd is the singlet oxygen quantum yield for the standard
unsubstituted ZnPc (FDStd ¼ 0.67 in DMSO) [54]. R and RStd are the
DPBF photobleaching rates in the presence of the samples (4, 5, 9
Chemical shifts were reported (d) relative to Me4Si as internal
standard. Mass spectra were measured on a Micromass Quatro LC/
ULTIMA LC-MS/MS spectrometer. The formation of J-aggregation for
non-peripherally substituted zinc (II) Pc complexes (9 and 10) were
determined by positive ion and linear mode MALDI-MS in dihy-
droxybenzoic acid as MALDI matrix using nitrogen laser
Std
abs
and 10) and standard, respectively. Iabs and I are the rates of light
absorption by the samples (4, 5, 9 and 10) and standard, respec-
tively. To avoid chain reactions induced by DPBF in the presence of
singlet oxygen, the concentration of quencher (DPBF) was lowered

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
67
O2N
CN
CN
O
O
OH
O
OH
O
i
i
1
6
O
O
CN
CN
O
O
O
O
CN
CN
2
3
ii
ii
RO
RO
OR
OR
N
N
N
N
N
N
N
N
N
Zn
N
N
Zn
N
N
N
N
N
5
RO
R=
OR
4
RO
OR
O
O
R=
O
O
Scheme 1. Synthetic pathway for preparation of peripherally tetra-substituted zinc(II) phthalocyanine complexes. (i) K2CO3, N2, DMF. (ii) Zn(CH3COO)2, DMAE, 175 ꢂC, 350 W.
to w3
ꢀ
10ꢁ5 mol dmꢁ3 [55]. Solutions of sensitizer
To this reaction mixture finely ground anhydrous potassium
carbonate (1.78 g, 12.93 ꢀ 10ꢁ3 mol) was added in 8 portions every
15 min. The reaction mixture was stirred under N2 at 50 ꢂC for 4
days. Then the solution was poured into iceewater (0.1 L) and the
aqueous phase was extracted with chloroform (3 ꢀ 0.05 L). The
combined extracts were dried over anhydrous sodium sulfate. The
crude product was crystallized from ethanol. Yield: 0.96 g (62%),
mp: 95e96 ꢂC. IR (KBr pellet), nmax/cmꢁ1: 3057 (AreH), 2926e2873
(Aliph. CeH), 2229 (C^N), 1628, 1599, 1562, 1509, 1470, 1389, 1356,
1320, 1256, 1217, 1183, 1119, 1049, 969, 840, 750. 1H NMR. (CDCl3),
(C ¼ 1 ꢀ 10ꢁ5 M) containing DPBF were prepared in the dark and
irradiated in the Q band region using the photoirradiation set-up.
DPBF degradation at 417 nm was monitored. The light intensity
6.57 ꢀ 1015 photons sꢁ1 cmꢁ2 was used for FD determinations.
2.4.2. Photodegradation quantum yields
Photodegradation quantum yield (Fd) determinations were
carried out using the experimental set-up described in the litera-
ture [52,53]. Photodegradation quantum yields were determined
using equation. (4),
(d
:ppm): 7.76e7.61 (m, 4H, AreH), 7.45 (d, 1H, AreH), 7.38 (d, 1H,
AreH), 7.25 (s, 1H, AreH), 7.19e7.12 (m, 3H, AreH), 4.25 (t, 4H,
CH2eO), 3.98 (t, 4H, CH2eO). 13C NMR. (CDCl3), (
:ppm): 162.18,
ðC0 ꢁ CtÞ$V$NA
d
Fd
¼
(4)
I
abs$S$t
157.75, 135.55, 135.12, 129.32, 128.68, 128.323, 127.68, 126.47,
125.92, 123.46, 119.55, 117.75, 116.18, 115.49, 112.38, 108.63, 105.35,
70.83, 69.43, 68.66, 67.34. MS (ESþ), (m/z): 358 [M]þ. C22H18N2O3:
calcd. C 73.73, H 5.06, N 7.82%; found: C 73.82, H 5.24, N 7.99.
where C0 and Ct are the samples (4, 5, 9 and 10) concentrations
before and after irradiation respectively, V is the reaction volume,
NA is the Avogadro’s constant, S is the irradiated cell area and t is the
irradiation time. Iabs is the overlap integral of the radiation source
light intensity and the absorption of the samples (4, 5, 9 and 10). A
light intensity of 2.19 ꢀ 1016 photons sꢁ1 cmꢁ2 was employed for Fd
determinations.
2.5.2. 2(3),9(10),16(17),23(24)-Tetrakis{2-[2-(2-naphthyloxy)
ethoxy] ethoxy} phthalocyaninato zinc (II) (5)
4-{2-[2-(2-naphthyloxy)ethoxy]ethoxy}phthalonitrile (3) (0.3 g,
0.84 ꢀ 10ꢁ3 mol) and anhydrous Zn(CH3COO)2 (76 ꢀ 10ꢁ3 g,
0.42 ꢀ 10ꢁ3 mol) were added in 2-(dimethylamino)ethanol (DMAE)
(0.003 L). Then the mixture was irradiated by microwave oven at
175 ꢂC, 350 W for 8 min. After cooling to room temperature the
reaction mixture was refluxed with ethanol (0.05 L) to precipitate
the product which was filtered off. The green solid product was
washed with hot ethanol, diethyl ether and dried in vacuo. The
green solid product was chromatographed on preparative silicagel
2.5. Synthesis
2.5.1. 4-{2-[2-(2-Naphthyloxy)ethoxy]ethoxy}phthalonitrile (3)
2-[2-(2-naphthyloxy)ethoxy]ethanol (6) (1 g, 4.31 ꢀ 10ꢁ3 mol)
was dissolved in dry DMF (0.015 L) and 4-nitrophthalonitrile
(0.74 g, 4.31 ꢀ 10ꢁ3 mol) was added under nitrogen atmosphere.

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
NO2
CN
CN
O
O
OH
O
OH
O
i
i
1
6
O
O
ii
O
O
O
O
CN
CN
CN
7
8
CN
ii
RO
RO
N
N
RO
RO
N
N
N
N
N
N
N
N
N
Zn
N
N
N
Zn
N
N
OR
OR
10
OR
9
OR
O
O
R=
R=
O
O
Scheme 2. Synthetic pathway for preparation of non-peripherally tetra-substituted zinc(II)phthalocyanine complexes. (i) K2CO3, N2, DMF. (ii) Zn(CH3COO)2, DMAE, 175 ꢂC, 350 W.
plate with chloroform:methanol (100:3) as eluents. Yield: 0.192 g
(61%). IR (KBr pellet) nmax/cmꢁ1: 3054 (AreH), 2925e2873 (Aliph.
CeH), 1628, 1601, 1509, 1488, 1391, 1338, 1218, 1183, 1118, 1060, 970,
4.06 (t, 4H, CH2eO). 13C NMR. (CDCl3), (
d:ppm): 161.19, 154.28,
134.34, 134.16, 127.38, 126.37, 125.83, 125.45, 125.14, 121.91, 120.44,
119.85, 117.19, 116.58, 115.35, 113.09, 107.44, 104.85, 70.31, 69.67,
69.55, 67.81. MS (ESþ), (m/z): 397 [M þ K]þ. C22H18N2O3: calcd. C
73.73, H 5.06, N 7.82%; found: C 73.88, H 5.20, N 7.90.
839, 745. 1H NMR. (CDCl3), (
d:ppm): 7.69e7.55 (m, 20H, AreH),
7.35e7.28 (m, 8H, AreH), 7.15e7.03 (m, 12H, AreH), 4.16 (m, 16H,
CH2eO), 3.90 (m, 16H, CH2eO). MS (ESþ), (m/z): 1498 [M]þ.
C88H72N8O12Zn: calcd. C 70.51, H 4.84, N 7.48%; found: C 70.28, H
4.95 N 7.40.
2.5.4. 3-{2-[2-(2-Naphthyloxy)ethoxy]ethoxy}phthalonitrile (8)
2-[2-(2-naphthyloxy)ethoxy]ethanol (6) (1 g, 4.31 ꢀ 10ꢁ3 mol)
was dissolved in dry DMF (0.015 L) and 3-nitrophthalonitrile
(0.74 g, 4.31 ꢀ 10ꢁ3 mol) was added under nitrogen atmosphere.
To this reaction mixture finely ground anhydrous potassium
carbonate (1.78 g, 12.93 ꢀ 10ꢁ3 mol) was added in 8 portions every
15 min. The reaction mixture was stirred under N2 at 50 ꢂC for 3
days. Then the solution was poured into iceewater (0.1 L) and the
aqueous phase was extracted with chloroform (3 ꢀ 0.05 L). The
combined extracts were dried over anhydrous sodium sulfate. The
crude product was crystallized from ethanol. Yield: 0.89 g (58%),
2.5.3. 3-{2-[2-(1-Naphthyloxy)ethoxy]ethoxy}phthalonitrile (7)
2-[2-(1-naphthyloxy)ethoxy]ethanol (1) (1 g, 4.31 ꢀ 10ꢁ3 mol)
was dissolved in dry DMF (0.015 L) and 3-nitrophthalonitrile
(0.74 g, 4.31 ꢀ 10ꢁ3 mol) was added under nitrogen atmosphere.
To this reaction mixture finely ground anhydrous potassium
carbonate (1.78 g, 12.93 ꢀ 10ꢁ3 mol) was added in 8 portions every
15 min. The reaction mixture was stirred under N2 at 50 ꢂC for 3
days. Then the solution was poured into iceewater (0.1 L) and the
aqueous phase was extracted with chloroform (3 ꢀ 0.05 L). The
combined extracts were dried over anhydrous sodium sulfate. The
crude product was crystallized from ethanol. Yield: 0.78 g (51%),
mp: 91e93 ꢂC. IR (KBr pellet), nmax/cmꢁ1: 3055 (AreH), 2943e2884
(Aliph. CeH), 2225 (C^N), 1581, 1509, 1470, 1447, 1398, 1286, 1271,
1242, 1182, 1156, 1127, 1105, 1070, 863, 790, 767. 1H NMR. (CDCl3),
mp: 118e120 ꢂC. IR (KBr pellet), nmax/cmꢁ1
: 3085 (AreH),
2928e2878 (Aliph. CeH), 2227 (C^N), 1627, 1600, 1584, 1509,
1475, 1463, 1396, 1258, 1220, 1183, 1135, 1068, 1039, 827, 798, 748.
1H NMR. (CDCl3), (
d
:ppm): 7.74e7.70 (m, 3H, AreH), 7.55e7.40 (m,
2H, AreH), 7.33e7.24 (m, 3H, AreH), 7.16e7.13 (m, 2H, AreH), 4.30
(t, 4H, CH2eO), 4.02 (t, 4H, CH2eO). 13C NMR. (CDCl3), (
:ppm):
d
(
d
:ppm): 8.23 (d, 1H, AreH), 7.78 (d, 1H, AreH), 7.45e7.32 (m, 5H,
168.03, 161.29,156.52, 155.89, 144.94, 134.47, 129.64,129.42, 128.98,
127.60, 126.77, 126.42, 125.32, 123.74, 118.85, 117.22, 115.33, 106.72,
AreH), 7.21 (m, 2H, AreH), 6.82 (d, 1H, AreH), 4.29 (t, 4H, CH2eO),

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
69
70.37, 69.74, 69.45, 67.40. MS (ESþ), (m/z): 397 [M þ K]þ.
C22H18N2O3: calcd. C 73.73, H 5.06, N 7.82%; found: C 73.93, H 5.28,
N 7.96.
spectra of the substituted phthalonitrile compounds (2, 3, 7 and 8)
showed signals with ranging from 6.82 to 8.23, belonging to
d
aromatic protons and 4.30e3.98 ppm belonging to aliphatic
protons for compounds 3, 7 and 8 integrating for a total of 18
protons as expected. In the 13C NMR spectra of studied phthaloni-
trile compounds indicated the presence of nitrile carbon atoms at
115.49 and 112.38 ppm for compound 3, 115.35 and 113.09 ppm for
compound 7 and 117.22 and 115.33 ppm for compound 8. In the
mass spectra of studied phthalonitrile compounds, the molecular
ion peaks were observed at m/z 358 [M]þ for 3, 397 [M þ K]þ for 7
and 397 [M þ K]þ for 8.
2.5.5. 1(4),8(11),15(18),22(25)-Tetrakis {2-[2-(1-naphthyloxy)
ethoxy]ethoxy} phthalocyaninato zinc (II) (9)
3-{2-[2-(1-naphthyloxy)ethoxy]ethoxy}phthalonitrile (7) (0.3 g,
0.84 ꢀ 10ꢁ3 mol) and anhydrous Zn(CH3COO)2 (76 ꢀ 10ꢁ3 g,
0.42 ꢀ 10ꢁ3 mol) were added in DMAE (0.003 L). Then the mixture
was irradiated by microwave oven at 175 ꢂC, 350 W for 8 min. After
cooling to room temperature the reaction mixture was refluxed
with ethanol (0.05 L) to precipitate the product which was filtered
off. The green solid product was washed with hot ethanol, diethyl
ether and dried in vacuo. The green solid product was chromato-
graphed on preparative silicagel plate with chloroform:methanol
After conversion into zinc phthalocyanine derivatives, the
characteristic C^N stretch at around 2225 cmꢁ1 for substituted
phthalonitrile derivatives disappeared in the IR spectra, indicative
of phthalocyanine formation. The characteristic vibrations corre-
sponding to aromatic CeH groups were observed at around
3050 cmꢁ1 for all zinc phthalocyanine complexes. The 1H NMR
spectra of zinc phthalocyanine complexes (5, 9 and 10) were almost
identical with that of the starting phthalonitrile compounds (3, 7
and 8) except for broadening and small shift. In the 1H NMR spectra
of studied zinc (II) phthalocyanine complexes (5, 9 and 10) the
aromatic and Pc protons appear between 7.69 and 7.03 ppm (for 5),
8.21e6.83 ppm (for 9), 7.95e6.92 ppm (for 10). In the mass spectra
of studied zinc phthalocyanines (5, 9 and 10), the molecular ion
peaks were observed at m/z 1498 [M]þ, 1499 [M þ H]þ and 1498
[M]þ respectively, confirmed the proposed structures.
(100:4) as eluents. Yield: 0.157 g (50%). IR (KBr pellet) nmax/cmꢁ1
:
3054 (AreH), 2925e2868 (Aliph. CeH), 1591, 1580, 1506, 1488,
1455, 1397, 1333, 1269, 1239, 1128, 1100, 1072, 792, 771, 745. 1H
NMR. (CDCl3), (d:ppm): 8.21 (m, 4H, AreH), 7.95e7.74 (m, 12H,
AreH), 7.64e7.50 (m, 16H, AreH), 6.99e6.83 (m, 8H, AreH), 4.44
(m, 16H, CH2eO), 4.01 (m, 16H, CH2eO). MS (ESþ), (m/z): 1499
[M þ H]þ. C88H72N8O12Zn: calcd. C 70.51, H 4.84, N 7.48%; found: C
70.33, H 4.97 N 7.37.
2.5.6. 1(4),8(11),15(18),22(25)-Tetrakis {2-[2-(2-naphthyloxy)
ethoxy]ethoxy} phthalocyaninato zinc (II) (10)
3-{2-[2-(2-naphthyloxy)ethoxy]ethoxy}phthalonitrile (8) (0.3 g,
0.84 ꢀ 10ꢁ3 mol) and anhydrous Zn(CH3COO)2 (76 ꢀ 10ꢁ3 g,
0.42 ꢀ 10ꢁ3 mol) were added in DMAE (0.003 L). Then the mixture
was irradiated by microwave oven at 175 ꢂC, 350 W for 8 min. After
cooling to room temperature the reaction mixture was refluxed
with ethanol (0.05 L) to precipitate the product which was filtered
off. The green solid product was washed with hot ethanol, diethyl
ether and dried in vacuo. The green solid product was chromato-
graphed on preparative silicagel plate with chloroform:methanol
3.2. Ground state electronic absorption spectra
Phthalocyanine compounds exhibit typical UV/Vis electronic
spectra with two significant absorption bands, one of them in the
visible region at about 614e707 nm corresponding to the Q band,
and the other in the UV region, approximately at 300 nm. The Q
band was attributed to
p /
p* transition from the highest occupied
molecular orbital (HOMO) to the lowest unoccupied molecular
orbital (LUMO) of the Pc ring. The other bands (B) in the UV region
at 275e389 nm are observed due to the transitions from the deeper
(100:4) as eluents. Yield: 0.151 g (48%). IR (KBr pellet) nmax/cmꢁ1
:
3054 (AreH), 2923e2846 (Aliph. CeH), 1628, 1599, 1506, 1488,
1390, 1333, 1259, 1218, 1182, 1118, 1069, 965, 840, 745. 1H NMR.
p
levels to the LUMO [56].
(CDCl3), (
d:ppm): 7.95 (m, 4H, AreH), 7.70e7.51 (m, 20H, AreH),
The UVeVis spectra of the studied zinc (II) phthalocyanine
7.36e7.30 (m, 8H, AreH), 7.13e6.92 (m, 8H, AreH), 4.30 (m, 16H,
CH2eO), 3.97 (m, 16H, CH2eO). MS (ESþ), (m/z): 1498 [M]þ.
C88H72N8O12Zn: calcd. C 70.51, H 4.84, N 7.48%; found: C 70.41, H
4.98 N 7.31.
compounds (4, 5, 9 and 10) in DMSO were given in Fig. 1. The
ground state electronic absorption spectra of zinc (II) phthalocya-
nine complexes (4, 5, 9 and 10) showed monomeric behavior evi-
denced by
a single (narrow) Q band, typical of metalated
phthalocyanine complexes, Fig. 1 [56]. The Q bands were observed
at around 680 nm for peripherally substituted zinc (II)
3. Results and discussion
3.1. Syntheses and characterization
2
The synthetic routes to novel zinc phthalocyanines (4, 5, 9 and
10) are showed in Scheme 1 and Scheme 2. The substituted
phthalonitrile compounds (2, 3, 7 and 8) were obtained via a based-
catalyzed (K2CO3) nucleophilic aromatic substitution reaction.
Cyclotetramerization of substituted phthalonitrile compounds (2,
3, 7 and 8) occurred in the presence of Zn(CH3COO)2 to form the
desired zinc (II) phthalocyanine complexes (4, 5, 9 and 10). All of
these new zinc phthalocyanines were purified by preparative thin
layer chromatograph. They were obtained in a yield (66% for 4, 61%
for 5, 50% for 9 and 48% for 10) and were characterized by the
spectral data (IR, 1H NMR, UVeVis and mass spectroscopies) as well
as elemental analysis. The characterization data of the new
compounds are consistent with the assigned formula.
1,6
4
5
1,2
9
10
0,8
0,4
0
300
400
500
600
700
800
The characteristic vibrations corresponding to C^N were
observed at 2229 cmꢁ1 for compound 3, 2225 cmꢁ1 for compound 7
and 2227 cmꢁ1 for compound 8. Aromatic CeH peaks occurred
around 3050 cmꢁ1 for all the studied phthalonitriles. The 1H NMR
Wavelength (nm)
Fig. 1. Absorption spectra of substituted zinc (II) phthalocyanine complexes (4, 5, 9 and
10) in DMSO. Concentration ¼ 1 ꢀ 10ꢁ5 M.

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
phthalocyanine complexes (4 and 5) and at around 700 nm for non-
peripherally substituted zinc (II) phthalocyanine complexes (9 and
10) in DMSO, Table 1. The Q bands of the non-peripherally tetra-
substituted zinc (II) complexes (9 and 10) are red-shifted by 21 nm,
when compared to the respective peripherally tetra-substituted
complexes (4 and 5) in DMSO (Table 1). The observed red spectral
shifts are typical of phthalocyanines with substituents at the non-
peripheral positions and have been explained to be due to linear
combinations of the atomic orbitals (LCAO) coefficients at the non-
peripheral positions of the HOMO being greater than those at the
peripheral positions [57,58]. As a result, the HOMO level is desta-
bilized more at the non-peripheral position that it is at the
peripheral position. Essentially, the energy gap (DE) between the
HOMO and LUMO becomes smaller, resulting in a bathochromic
shift. The B-bands are broad due to the superimposition of the B1
and B2 bands in the 340e380 nm region.
3.3. Aggregation studies
Aggregation behavior of studied zinc (II) phthalocyanine
complexes (4, 5, 9 and 10) were investigated in different solvents
(chloroform, dichloromethane, toluene, DMF and DMSO) (Fig. 2a as
an example for compound 10). Phthalocyanine compounds
generate high aggregation tendency due to the interactions
between their 18
p-electron systems and aggregation is decrease
the solubility of these compounds in many solvents. It also affects
seriously their spectroscopic, photophysical, photochemical and
electrochemical properties. Generally, aggregation is depends on
concentration, temperature, nature of the substituents, nature of
solvents and complexed metal ions [59,60]. Phthalocyanine
molecules can form two types aggregates in solution called H-and
J-type depending on the nature and position of the substituents.
Generally, phthalocyanine molecules form H-type aggregates in
solution. J-type aggregation was rarely observed for the phthalo-
cyanine molecules. The formation of the J-type aggregates among
the phthalocyanine molecules is very important since while the H-
type aggregates are not photoactive, the J-type aggregates are
photoactive. Generally, two types of J-aggregates could be formed
among the phthalocyanine molecules. One of them, J-aggregates
occurred by utilizing the coordination of the linker oxygen atoms
of side substituent on non-peripheral position from one phthalo-
cyanine molecule to the zinc (II) ion in a neighbor phthalocyanine
molecule [35,40,61,62]. For another type formation, J-aggregates
occurred by utilizing the coordination of nitrogen atoms on the
substituents from one phthalocyanine molecule to the zinc (II) ion
in a neighbor phthalocyanine molecule [32,33]. In this study, the
peripherally substituted zinc (II) phthalocyanine complexes (4 and
5) did not show any aggregation in all studied solvents. On the
other hand, while the non-peripherally zinc (II) complexes (9 and
10) did not show aggregation in DMSO and DMF, these complexes
Fig. 2. Absorption spectra of: (a) complex 10 in different solvents and (b) substituted zinc
(II) phthalocyanine complexes (4,5,9 and 10) in chloroform. Concentration ¼ 4 ꢀ 10ꢁ6 M.
10). This red-shifted band showed only non-peripherally
substituted zinc (II) phthalocyanine complexes (Fig. 2b as an
example in chloroform). The formation of this new band at non-
peripherally substituted complexes could be due to two reasons.
One of them can be lowering in symmetry of molecules observed
because of the protonation of phthalocyanine molecules [63]. In
solvents such as chloroform and dichloromethane which contain
small amounts of acid (such as HCl), protonation of the nitrogen
atoms may occur forming protonated metallo Pc complexes which
are of lower symmetry than the parent metallo Pc molecule, hence
the Q band is split [64,65]. Another reason about the formation of
this new band can be formation of J-aggregates among the
phthalocyanine molecules [35,40,61,62]. It is suggesting that; the
observed new red-shifted absorption band at 745 nm for studied
non-peripherally substituted zinc (II) phthalocyanine complexes (9
and 10) occurred due to formation of J-aggregates among the
phthalocyanine molecules instead of lowering of symmetry due to
protonation of nitrogen atoms on the phthalocyanine framework.
This red-shifted peak was appeared when the using chloroform
treated with NaHCO3 or basic alumina before use. If this red-
shifted peak could be due to protonation, it should be dis-
appeared after treatment of chloroform by NaHCO3 or basic
alumina. The formation of J-type aggregation among the non-
peripherally substituted zinc (II) phthalocyanine molecules
instead of protonation was also confirmed by the appearance of
dimer and trimer peaks in their MALDI-TOF mass spectra (Fig. 3 as
an example for complex 10) at 1408.195 Da for monomer,
2996.622 Da for dimer formation and 4494.645 Da for trimer
formation of the molecules.
showed
a new absorption band at 745 nm in chloroform,
dichloromethane and toluene (Fig. 2a as an example for compound
Table 1
Absorption, excitation and emission spectral data for unsubstituted and substituted
zinc(II) phthalocyanines in DMSO.
Compound
Q band lmax
,
Log
3
Excitation
Emission
Stokes shift
(nm)
lEx, (nm)
lEm, (nm)
DStokes, (nm)
4
5
9
682
683
703
704
672
5.18
5.11
5.32
5.35
5.14
683
684
704
705
672
694
694
714
715
682
12
11
11
11
10
In this study, J-aggregates could be occurred by utilizing the
coordination of the linker oxygen atoms of side substituent on non-
peripheral position from one phthalocyanine molecule to the zinc
(II) ion in a neighbor phthalocyanine molecule in non-coordinating
10
ZnPca
a
Data from reference [68].

_
I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
71
2
1.6
1.2
0.8
0.4
0
A
B
C
D
E
F
300
400
500
600
700
800
Wavelength (nm)
Fig. 5. Aggregation behavior of 5 in DMSO at different concentrations: 14 ꢀ 10ꢁ6 (A),
12 ꢀ 10ꢁ6 (B), 10 ꢀ 10ꢁ6 (C), 8 ꢀ 10ꢁ6 (D), 6 ꢀ 10ꢁ6 (E), 4 ꢀ 10ꢁ6 (F) M. (Inset: Plot of
absorbance versus concentration).
Fig. 3. MALDI-TOF mass spectrum of complex 10 using dihydoxybenzoic acid as
matrix.
solvents. On the other hand, only monomer band at 712 nm
appeared and J-aggregation band at 745 nm disappeared by the
addition of methanol to the J-aggregated solutions of non-
peripherally substituted zinc phthalocyanines (9 and 10) in chlo-
roform (Fig. 4 as an example for complex 10). Thus, the addition of
a coordinating solvent breaks J-aggregation completely as a result
of the competitive coordination of MeOH molecules to central Zn
atoms [35,40,66].
excitation spectra for all studied complexes suggested that the
nuclear configurations of the ground and excited states are similar
and not affected by excitation. The observed Stokes shifts were
within the region (w10 nm) observed for zinc (II) phthalocyanine
complexes (Table 1).
3.5. Fluorescence quantum yields and lifetimes
Aggregation behavior of the studied zinc (II) phthalocyanine
complexes (4,5,9 and 10) were also investigated in DMSO at
different concentration. BeereLambert law could be obeyed for
studied peripherally (4 and 5) and non-peripherally (9 and 10)
substituted zinc (II) phthalocyanine complexes in the concentra-
tions ranging from 1.4 ꢀ 10ꢁ5 to 4 ꢀ 10ꢁ6 M in DMSO (Fig. 5 for
compound 5 as an example).
The fluorescence quantum yields (FF) of substituted zinc (II)
phthalocyanine complexes (4,5,9 and 10) in DMSO are given in
Table 2. The FF values of all these phthalocyanine complexes are
typical of zinc (II) Pc complexes [67]. The FF values of the
substituted zinc (II) phthalocyanine complexes (4,5,9 and 10) are
lower than unsubstituted zinc (II) phthalocyanine in DMSO. The
decreasing in the FF values for substituted zinc (II) phthalocyanine
complexes in the presence of the ring substituents suggests that the
substituents more quench the excited singlet state then the fluo-
rescence. The FF values of peripherally substituted complexes (4
and 5) are marginally larger than non-peripherally substituted
complexes (9 and 10) suggesting less quenching of the excited
singlet state by peripheral substitution compared to non-
peripheral substitution.
3.4. Fluorescence studies
The fluorescence behavior of the substituted zinc (II) phthalo-
cyanine complexes (4,5,9 and 10) were studied in DMSO. Fig. 6
shows absorption, fluorescence emission and excitation spectra of
these complexes (4,5,9 and 10). All studied zinc (II) phthalocyanine
complexes (4,5,9 and 10) showed similar fluorescence behavior in
DMSO. The excitation spectra were similar to absorption spectra
and both were mirror images of the fluorescence emission spectra
for all studied complexes. The proximity of the wavelength of each
component of the Q band absorption to the Q band maxima of the
Fluorescence lifetime (sF) refers to the average time a molecule
stays in its excited state before emission. Such factors include
internal conversion and intersystem crossing shortens the fluo-
rescence lifetime of a fluorophore. As a result, the nature and the
environment of a fluorophore determine its fluorescence lifetime.
Lifetimes of fluorescence were calculated using the StricklereBerg
equation. Using this equation, a good correlation has been found
[49] between experimentally and the theoretically determined
lifetimes for the unaggregated molecules as is the case for DMSO in
this work. While the sF values of peripherally substituted zinc (II)
phthalocyanine complexes (4 and 5) are higher, the non-
peripherally substituted complexes (9 and 10) are lower than
unsubstituted zinc Pc in DMSO. The sF values of peripherally
substituted complexes (4 and 5) are larger than non-peripherally
substituted complexes (9 and 10) suggesting less quenching of
the substituents on peripheral position than non-peripheral
position.
0.8
10 in chloroform+MeOH
0.6
0.4
10 in chloroform
0.2
The natural radiative lifetime (
fluorescence (kF) values are also given in Table 2. The
s
0) and the rate constants for
0
300
400
500
600
700
800
s
0 values of all
Wavelength (nm)
studied zinc (II) Pc complexes (4,5,9 and 10) are higher while the kF
values of these complexes (4,5,9 and 10) are lower than unsub-
stituted zinc Pc complex in DMSO.
Fig. 4. Absorption spectra of complex 10 in chloroform and changing by addition of
methanol.

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
Fig. 6. Absorption, excitation and emission spectra of the compounds: 4 (a), 5 (b), 9 (c) and 10 (d) in DMSO. Excitation wavelength ¼ 650 nm for 4 and 5; 675 nm for 9 and 10.
3.6. Singlet oxygen quantum yields
phthalocyanine complexes did not show any decomposition during
singlet oxygen studies.
Transfer of energy from the triplet state of a photosensitizer
such as phthalocyanine to ground state molecular oxygen leads to
the production of singlet oxygen. There is a necessity of high effi-
ciency of energy transfer between excited triplet state of photo-
sensitizer and ground state of oxygen to generate large amounts of
singlet oxygen, essential for PDT applications. The singlet oxygen
quantum yield (FD) value give the amount of the generated singlet
oxygen and this value is an indication of the potential of the
compounds as photosensitizers in applications where singlet
oxygen is required. The FD values were determined using a chem-
ical method (using DPBF as a quencher in DMSO). The disappear-
ance of DPBF was monitored using UVeVis spectrophotometer.
Many factors can be responsible for the magnitude of the deter-
mined singlet oxygen quantum yield including such as triplet
excited state energy, ability of substituents and solvents to quench
the singlet oxygen, the triplet excited state lifetime and the effi-
ciency of the energy transfer between the triplet excited state and
the ground state of oxygen. There was no decrease in the Q band of
formation of the all studied zinc (II) phthalocyanine complexes
(4,5,9 and 10) during FD studies suggesting that all studied zinc
The FD values of substituted (4,5,9 and 10) and unsubstituted
(ZnPc) zinc (II) phthalocyanines are given in Table 2. Unsubstituted
zinc phthalocyanine is used as standard for singlet oxygen studies
of phthalocyanine compounds. While the FD values of peripherally
substituted zinc (II) phthalocyanine complexes (4 and 5) are lower,
the FD value of non-peripherally substituted zinc (II) phthalocya-
nine complexes (9 and 10) are higher than unsubstitued zinc (II)
phthalocyanine in DMSO. The substitution of the groups on the
non-peripheral position of phthalocyanine framework resulted in
the higher singlet oxygen generation than substitution on periph-
eral position.
3.7. Photodegradation studies
The photodegradation of the compounds 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 phototransformation
into different forms of phthalocyanines absorbing light in the visible
region. The spectral changes observed for substituted zinc (II)
phthalocyanine complexes (4,5,9 and 10) during photodegradation
studies occurred without phototransformation.
Table 2
Photophysical and photochemical data of unsubstituted and substituted zinc(II)
phthalocyanines in DMSO.
The photodegradation behavior of substituted zinc (II) phtha-
locyanine complexes (4,5,9 and 10) were studied in DMSO. The
photodegradation quantum yield (Fd) values of these complexes
(4,5,9 and 10) as well as unsubstituted zinc (II) phthalocyanine
complex (ZnPc) in DMSO are given in Table 2. All the studied
complexes showed about the same stability with Fd of the order of
10ꢁ5. The Fd values, found in this study, are similar with zinc Pc
complexes having different substituents on the phthalocyanine
framework in literature [67]. All studied zinc (II) phthalocyanine
Compound
FF
sF (ns)
s
0 (ns)
kF (sꢁ1
)
Fd (ꢀ10ꢁ5
)
FD
(ꢀ108)a
4
5
9
0.18
0.19
0.14
0.13
0.20
1.45
1.81
1.13
0.96
1.22
8.07
9.51
8.06
7.35
6.80
1.24
1.05
1.24
1.36
1.47
0.86
1.50
2.13
2.16
2.61
0.52
0.59
0.82
0.84
0.67
10
ZnPcb
a
kF is the rate constant for fluorescence. Values calculated using kF
Data from reference [68].
¼
FF/sF.
b

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I. Acar et al. / Journal of Organometallic Chemistry 708-709 (2012) 65e74
73
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to the unsubstituted ZnPc in DMSO. The substitution of the
phthalocyanine framework with substituted groups slightly
increased the stability of studies phthalocyanine complexes. The Fd
values of peripheral substituted zinc (II) phthalocyanine complexes
(4 and 5) are lower than non-peripherally substituted counterparts
(9 and 10). So the substitution of phthalocyanine framework with
studied substituents on peripheral position results more stable
phthalocyanine complexes compared to substitution on non-
peripheral position. High degradation of non-peripherally
substituted zinc (II) phthalocyanine complexes (9 and 10) is due
to larger singlet oxygen quantum yields of these compounds.
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The novel phthalonitrile derivatives substituted with 2-[2-(1-
naphthyloxy)ethoxy]ethanol (compound 7) and 2-[2-(2-naph-
thyloxy)ethoxy]ethanol (compounds 3 and 8) groups and their
peripherally (complex 5) and non-peripherally (complexes 9 and 10)
zinc (II) phthalocyanine complexes have been synthesized for the
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(II) phthalocyanine complex 4 have been synthesized according to
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phthalocyanine complexes have been characterized by elemental
analysis, UVevis (for phthalocyanine complexes), IR, 1H NMR, 13C
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solubility in many organic solvents such as chloroform, dichloro-
methane, toluene, THF, DMF and DMSO. It was concluded from the
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compounds in various solvents that the non-peripherally
substituted zinc (II) phthalocyanine complexes (9 and 10) formed
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TOF spectroscopic techniques. The J-aggregates among the zinc (II)
Pc molecules were broken up by the addition of a coordinating
solvent such as methanol. The photophysical (fluorescence quantum
yields and lifetimes) and photochemical properties (singlet oxygen
and photodegradation quantum yields) of substituted zinc phtha-
locyanine complexes (4,5,9 and 10) were investigated in DMSO and
compared with unsubstituted zinc (II) phthalocyanine complex. The
production of singlet oxygen is very important for PDT application.
The substituted zinc (II) phthalocyanine complexes (4,5,9 and 10)
showed good singlet oxygen generation, especially non-peripheral
complexes showed higher than unsubstituted zinc (II) phthalocya-
nine complex, gives an indication of the potential of these complexes
as photosensitizer in photocatalytic applications such as PDT of
cancer. The substituted zinc (II) phthalocyanine complexes showed
approximately same stability degradation to light irradiation.
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This study was supported by the Research Fund of Karadeniz
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