Synthesis of non-peripherally and peripherally substituted zinc (II) phthalocyanines bearing pyrene groups via different routes and their photophysical properties

Article abstract of DOI:10.1016/j.dyepig.2013.07.027

This work reports on photophysical properties of the non-peripherally and peripherally substituted zinc phthalocyanines (Pcs) prepared by two different synthetic routes. Tetra-substituted non-peripheral (5) and peripheral (6) zinc phthalocyanines containi

Full text of DOI:10.1016/j.dyepig.2013.07.027

Accepted Manuscript
Synthesis of non-peripherally and peripherally substituted zinc (II) phthalocyanines
bearing pyrene groups via different routes and their photophysical properties
Serdar Sürgün, Yasin Arslanoğlu, Esin Hamuryudan
PII:
S0143-7208(13)00286-6
10.1016/j.dyepig.2013.07.027
DYPI 4035
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 13 June 2013
Revised Date: 11 July 2013
Accepted Date: 19 July 2013
Please cite this article as: Sürgün S, Arslanoğlu Y, Hamuryudan E, Synthesis of non-peripherally and
peripherally substituted zinc (II) phthalocyanines bearing pyrene groups via different routes and their
photophysical properties, Dyes and Pigments (2013), doi: 10.1016/j.dyepig.2013.07.027.
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ACCEPTED MANUSCRIPT
Synthesis of non-peripherally and
peripherally substituted zinc (II)
phthalocyanines bearing pyrene
groups via different routes and their
photophysical properties
Serdar Sürgün, Yasin Arslanoğlu and
Esin Hamuryudan
The synthesis, characterization and
photophysical properties of the non-
peripherally and peripherally substituted
zinc phthalocyanines (Pcs) bearing
mercaptophenol groups and their pyrene
containing analogues prepared by two
different synthetic routes for the first
time in this study.
Photophysical and photochemical studies
were carried out in order to determine the
potential
of
the
complexes
as
photosensitizers for use in photodynamic
therapy.

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Synthesis of non-peripherally and peripherally substituted zinc
(II) phthalocyanines bearing pyrene groups via different routes
and their photophysical properties
Serdar Sürgüna, Yasin Arslanoğlub, Esin Hamuryudana*
aDepartment of Chemistry, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
bMaritime Faculty, Istanbul Technical University, 34940 Tuzla, Turkey
Abstract
This work reports on photophysical properties of the non-peripherally and peripherally
substituted zinc phthalocyanines (Pcs) prepared by two different synthetic routes. Tetra-
substituted non-peripheral (5) and peripheral (6) zinc phthalocyanines containing 4-
mercaptophenol groups were synthesized from novel phthalonitrile derivatives for the first time.
Pyrene-containing phthalocyanine derivatives (7-8) were obtained by the reaction of compounds
5-6 with 1-bromoacetylpyrene. In the second route, compounds 7-8 were prepared by
cyclotetramerization of pyrene-containing phthalonitrile derivatives (3a or 4a). The synthesized
compounds were characterized by elemental analysis, FT-IR, UV-Vis, NMR spectroscopy and
mass spectra. General trends were described for electronic absorption, fluorescence quantum
yields, lifetimes, and fluorescence quenching by benzoquinone of these compounds. The effects
of position of substituent on photophysical properties of the tetra-substituted zinc Pcs were also
investigated.
__________________________________________________________________
Keywords: Zinc phthalocyanines, nucleophilic substitution, pyrene dyads, non-peripheral and
peripheral substitution, fluorescence quantum yield, fluorescence quenching.
*Corresponding author. Tel: + 90 212 2856826; Fax: + 90 212 2856386.
E-mail: esin@itu.edu.tr (E. Hamuryudan)
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1. Introduction
Phthalocyanines are one of the important classes of tetrapyrrole derivatives showing a wide
range of applications such as liquid crystals, electronic devices, gas and chemical sensors,
electrochromic and electroluminescent displays, non-linear optics, photovoltaic and
semiconductors in addition to their traditional use as dyes and pigments [1-6]. In view of these
important applications, there is a need for optimization of chemical, physical, absorption and
electronic properties of phthalocyanines such as solubility, optical and electrochemical
potentials. It is well known that these properties of Pc derivatives can be modified by changing
the central metal ion and\or number, position and character of substituents on the macrocycle [7-
9].
Intermolecular interaction of Pc molecules results in a disadvantageous outcome as known
aggregation that minimizes their technological applications. The nature and position of
substituents are very important in terms of solubility, the state of aggregation in solution and also
physical and photophysical properties of phthalocyanines [10]. Complexation of Pcs with
transition metals give dyes with short lifetimes, zinc phthalocyanine complexes have attracted
much interest because of their appreciably long triplet lifetimes [11-13].
On the other hand, pyrene (Py) and its derivatives are alternant flat polycyclic aromatic
hydrocarbon systems. In the last decades, researchers’ interests have focused on pyrene to
perform specific functions such as electrochemical and photophysical attributes resulting in its
utilization in a variety of scientific areas [14]. Pyrene is the most popular moiety among the
fluorescent chromophores used for photochemical applications. Its derivatives are also
considered to be valuable molecular probes via fluorescence spectroscopy, thus having a high
quantum yield and lifetime (0.65 and 410 nanoseconds, respectively, in ethanol at 293 K). Its
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fluorescence emission spectrum is very sensitive to the polarity of the solvent used, so pyrene
moiety has been used as a probe to determine solvent environments [15].
Phthalocyanines and pyrene moieties appear to be promising candidates. Although both
molecules have been comprehensively studied, reports on the combination of these two
functionalities have been sparse [16-18]. They could be used as valuable molecular probes for
fluorescence spectroscopy due to their high quantum yield and lifetime properties [19].
For the preparation of light-harvesting antennae, we were interested in the synthesis of new
phthalocyanines with their outer parts decorated with pyrene units to build up light-harvesting
systems based on the fluorescence properties of pyrene [20, 21]. Moreover, photosensitizing
properties of phthalocyanines is affected by aggregation [22]. Side-chain pyrene functional
phthalocyanines through 4-mercaptophenol moieties were chosen in this study to improve
fluorescence properties and also to prevent aggregation of phthalocyanines.
Our previous papers have essentially focused on the synthesis, characterization and
electrochemical measurement of new Pcs with various functional groups. Among these we made
site O- and S- functionalities such as crown ether, alkyl, benzyloxyphenoxy, fluorophenyl,
etc.[23-28].
The introduction of a sulfur donor on the periphery of the Pcs show excellent spectroscopic and
photochemical properties such as wavelengths absorption over 700 nm [29-34]. This is important
in applications in many devices such as semi-conductor lasers, optoelectronics, PDT and near-IR
devices.
The aim of the present work is to synthesize peripheral (p-) and non-peripheral (np-) side-chain
pyrene functionalized tetra-substituted new zinc phthalocyanines compounds by two different
routes. Aggregation behaviors, photophysical properties of these complexes were investigated as
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well as the effects of the position of substituents on the photophysical properties of zinc (II)
phthalocyanine derivatives in DMSO.
2. Experimental
2.1 Equipment and materials
All reagents and solvents purchased from commercial sources without further purification. All
solvents were dried using standard techniques as described by Perrin and Armarego before use
[35]. Chromatography was performed on silica gel 60 (0.04–0.063 mm). 3-Nitrophthalonitrile (1)
was purchased from Sigma-Aldrich and 4-nitrophthalonitrile (2) was prepared according to a
procedure as previously described in literature [36]. IR spectra were recorded on a Perkin Elmer
Spectrum One FT-IR spectrophotometer, UV-Vis spectra were recorded on Scinco Neosys-2000
double-beam ultraviolet visible (UV-Vis) spectrophotometer using 1 cm path length cuvettes at
room temperature. Elemental analyses were performed by the Instrumental Analysis Laboratory
1
of the TUBITAK Marmara Research Center. H and 13C NMR spectra were recorded using
Varian 500 MHz spectrometer using TMS as internal reference. Mass spectra were performed on
Bruker Micro TOF-ESI/MS and Bruker microflex LT MALDI-TOF MS spectrometer.
Fluorescence excitation and emission spectra were recorded by using Varian Cary Eclipse
Fluorescence Spectrophotometer.
2.2 Synthesis
2.2.1. 3-(4-hydroxyphenylthio)phthalonitrile (3)
The synthetic procedure was adopted from Mayukh et al with some modifications [37]. A
mixture of 4-mercaptophenol (1.26 g, 0.01 mol) and K2CO3 (4.15 g, 0.03 mol) in dry
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dimethylformamide (DMF) (25 mL) was stirred vigorously in nitrogen atmosphere for 30 min
and then 3-nitrophthalonitrile (1.75 g, 0.01 mol) was added into the reaction mixture followed by
a stirring for 16 h at 90 °C. The reaction mixture was allowed to cool room temperature and
poured into 1M HCl and the precipitate formed was filtered off and washed with water until the
filtrate was neutral and dried in vacuum. The precipitate was extracted with ethyl acetate. The
combined organic phases were treated with distilled water, dried with anhydrous sodium sulfate
and solvent removed under reduced pressure to obtain solid orange colored powder. The product
was further purified by chromatography over a silica gel column using Ethyl acetate and hexane
(3:1) mixture as eluent. Yield: 1.73 g, (68%); m.p. 162-164˚C. FT-IR νmax/ cm-1; 3403 (Ar-
1
OH), 3077-2923 (Ar-H), 2241 (C≡N). H NMR (DMSO-d6) δ/ppm: 10.18 (s, 1H, Ar-OH), 7.84
(d, 1H, Ar-H), 7.68 (t, 1H Ar-H), 7.42 (d, 2H, Ar-H), 7.09 (d, 1H, Ar-H), 6.91 ppm (d, 2H, Ar-
H); 13C NMR (DMSO-d6) δ/ppm: 160.21 (aromatic C–O), 147.51, 137.76, 134.51, 130.96,
117.97, 116.40 (C≡N), 114.57, 110.27. Anal. Calcd. for C14H8N2OS (252.291 g/mol); C 66.65, H
3.20, N 11.10; Found: C 66.56, H 3.09, N 11.08. MS (GC/MS): m/z: 252 [M]+.
2.2.2. 4-(4-hydroxyphenylthio)phthalonitrile (4)
Compound 4 was prepared according to procedure described for 3, from 4-nitrophthalonitrile
(1.75 g, 0.01 mmol). The crude product was isolated as a yellow-brown powder. Yield: 1.60 g,
1
(63%); m.p. 165-167˚C. FT-IR νmax/ cm-1; 3369 (Ar-OH), 3105-3027 (Ar-H), 2240 (C≡N). H
NMR (DMSO-d6) δ/ppm: 10.09 ppm (s, 1H, Ar-OH), 7.86 (d, 1H, Ar-H), 7.70 (t, 1H Ar-H), 7.43
(d, 2H, Ar-H), 7.10 (d, 1H, Ar-H), 6.91ppm (d, 2H, Ar-H); 13C NMR (DMSO-d6) δ/ppm: 160.13
(aromatic C–O), 149.37, 137.83, 134.72, 129.85, 117.98, 116.46(C≡N), 115.59, 110.36 Anal.
Calcd. for C14H8N2OS (252.291 g/mol); C 66.65, H 3.20, N 11.10; Found: C 66.60, H 3.13, N
11.02. MS (GC/MS): m/z: 252 [M]+.
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2.2.3. 3-(4-(2-oxo-2-(pyren-1-yl)ethoxy)phenylthio)phthalonitrile (3a)
Compound 3 (0.5 g, 1.98 mmol) and 1-bromoacetylpyrene (0.80 g, 2.48 mmol) were added with
stirring to dry acetone (30 mL). Anhydrous K2CO3 (0.82 g, 5.95 mmol) was then added
portionwise and the mixture was refluxed for 4h. After evaporation of the solvent, the residue
was dissolved in chloroform. The chloroform solution was washed with water and dried on
MgSO4 and then the solvent was evaporated. The residue was purified by column
chromatography on silica gel, using 3:1 CHCl3 and ethyl acetate as the eluting solvent to afford
compound 3a. The crude product was isolated as a yellow powder. Yield: 0.62 g (63%); mp.
183-185 °C; FT-IR νmax/cm-1; 3069-2899(Ar-H), 2846 (alkyl-CH), 2225 (C ≡ N), 1691 (C=O),
1
1251 (C-O-C). H NMR (CDCl3) δ/ppm: 9.03 (d, 1H, Ar-H), 8.41 (d, 1H, Ar-H), 8.26-8.11 (m,
7H, Ar-H), 7.47-7.24 (m, 4H , Ar-H), 7.08 (d, 1H, Ar-H), 6.93 (d, 2H, Ar-H), 5.54 ppm (s, 2H, -
13
O=CCH2). C NMR (DMSO-d6) δ/ppm: 197.65 (O=C), 159.86–119.86, 116.69 (C≡N), 72.12
(O=CCH2). Anal. Calcd. for C32H18N2O2S (494.563 g/mol); C 77.71, H 3.67, N 5.66; Found: C
77.43, H 3.62, N 5.54. MS (ESI-MS): m/z: 495.732 [M+H]+.
2.2.4. 4-(4-(2-oxo-2-(pyren-1-yl)ethoxy)phenylthio)phthalonitrile (4a)
Compound 4a was prepared according to procedure described for 3a, from 4 (0.5 g, 1.98 mmol).
The crude product was isolated as a yellow powder. Yield: 0.56g (57%) ; mp. 181-183 °C; FT-IR
1
νmax/cm1; 3097-3062 (Ar-H), 2915 (alkyl-CH), 2226 (C≡N), 1685 (C=O). 1252 (C-O-C). H
NMR (CDCl3) δ/ppm: 9.04 (d, 1H, Ar-H), 8.42 (d, 1H, Ar-H), 8.30-8.08 (m, 7H, Ar-H), 7.44 (d,
2H, Ar-H), 7.36 (d, 1H , Ar-H), 7.29 (d, 1H, Ar-H), 7.26 (s, 1H, Ar-H), 7.09 (d, 2H, Ar-H), 5.55
13
ppm (s, 2H, -O=CCH2). C NMR (DMSO-d6) δ/ppm: 197.67 (O=C), 160.04–123.93, 116.84
(C≡N), 72.16 (O=CCH2). Anal. Calcd. for C32H18N2O2S (494.563 g/mol); C 77.71, H 3.67, N
5.66; Found: C 77.51, H 3.58, N 5.61. MS (ESI-MS): m/z 495.821 [M+H]+.
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2.2.5. (3)-Tetra(4-hydroxyphenyltio)phthalocyaninatozinc (II) (5)
A mixture of phthalonitrile 3 (0.2 g, 0.8 mmol) and anhydrous Zn(OAc)2 (0.036 g, 0.2 mmol)
with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) (3 drops) in dry DMF (2 mL) was heated at 140
°C for 16h under N2 in sealed tube. Intense colored solution was cooled to room temperature
and the suspension was poured into ice-water mixture. The precipitated solid was then filtered
off and the precipitate was washed with ethyl acetate. The crude product was purified by column
chromatography on silica gel using CHCl2 and CH3OH as eluent, respectively. Yield: 0.045 g
(21%); m.p. >200˚C. FT-IR νmax/ cm-1; 3287 (Ar-OH), 2971, 2928 (alkyl-CH). UV/Vis λmax
1
(nm) (log ε) in DMF: 713 (4.90), 337 (4.47). H NMR (DMSO-d6) δ/ppm: 10.10 (s, 4H, Ar-
OH), 9.21-6.96 (br, 28H, Ar-H). Anal. Calcd. for C56H32N8O4S4Zn (1074.55 g/mol); C 62.59, H
3.00, N 10.43; Found: C 62.43, H 2.94, N 10.37. MS (MALDI-MS): m/z 1075.396 [M+H]+.
2.2.6. (4)-Tetra(4-hydroxyphenyltio)phthalocyaninatozinc (II) (6)
Compound 6 was prepared according to procedure described for 5, from phthalonitrile 4 (0.200
g, 0.8 mmol), anhydrous Zn(OAc)2 (0.036 g, 0.2 mmol), DBU (3 drop) and dry DMF (2 mL).
Purification of the product was accomplished by column chromatography on silica gel first with
CHCl2 then with THF as the eluent. Yield: 0.056 g (26%); m.p. >200˚C. FT-IR νmax/ cm-1; 3160
1
(Ar-OH), 2926, 2849 (alkyl-CH). UV/Vis λmax (nm) (log ε) in DMF: 692 (4.85), 364 (4.42). H
NMR (DMSO-d6) δ/ppm: 10.07 (s, 4H, Ar-OH), 9.46-6.91 (br, 28H, Ar-H). Anal. Calcd. for
C56H32N8O4S4Zn (1074.55 g/mol); C 62.59, H 3.00, N 10.43; Found: C 62.35, H 2.93, N 10.23.
MS (MALDI-MS): m/z 1075.487 [M+H]+.
2.2.7. (3)-Tetra(4-(2-oxo-2-(pyren-1-yl)ethoxy)phenylthio)phthalocyaninatozinc (II) (7)
Method I (Direct functionalization of phthalocyanine macrocycle). A mixture of phthalocyanine
5 (0.05 g, 0.047 mmol), K2CO3 (0.104 g, 0.23 mmol) and 1-bromoacetylpyrene (0.09 g, 0.28
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mmol) in dry DMF (5 mL) was stirred vigorously in nitrogen atmosphere for 6 h at 80 °C under
N2 in sealed tube. Then the solution was cooled to room temperature and the suspension was
poured into ice-water mixture. The resulting precipitate was filtered, washed several times with
water, chloroform and dichloromethane to remove any traces of unreacted materials and dried in
vacuum. Yield: 0.047 g (% 49).
Method II (Cyclotetramerization of the precursor ligand). A mixture of phthalonitrile 3a (0.2 g,
0.4 mmol) and anhydrous Zn(OAc)2 (0.019 g, 0.10 mmol) with DBU (3 drops) in dry DMF (2
mL) was heated at 140 °C for 18 h. After this time, intensely colored solution was cooled to
room temperature and the suspension was poured into ice-water mixture. The precipitated solid
was then filtered and washed with chloroform and DCM then dried in vacuum. The crude
product was purified by column chromatography on silica gel using methanol as eluent. Yield:
0.032 g (16%); m.p. >200˚C.
FT-IR νmax/cm1; 3038 (Ar-H), 2925, 2853 (alkyl-CH), 1661(C=O), 1215 (C-O-C). UV/Vis λmax
(nm) (log ε) in DMF: 711 (5.0), 350 (5.08), 281 (5.19). 1H NMR (DMSO-d6) δ/ppm: 8.63-7.14
(br, 64H, Ar-H), 5.77 (s, 8H, -O=CCH2). Anal. Calcd. for: C128H72N8O8S4Zn (2043.64 g/mol); C
75.23, H 3.55, N 5.48; Found: C 75.06, H 3.34, N 5.32. MS (MALDI-MS): m/z 2041.85 [M]+.
2.2.8. (4)-Tetra(4-(2-oxo-2-(pyren-1-yl)ethoxy)phenylthio)phthalocyaninatozinc (II) (8)
Method I (Direct functionalization of phthalocyanine macrocycle). Compound 8 was prepared
according to procedure described for 7, from 6 (0.05 g, 0.047 mmol), K2CO3 (0.03g, 0.23 mmol)
and 1-bromoacetylpyrene (0.09 g, 0.28 mmol) in dry DMF (3 mL). Yield: 0.053 g (56%).
Method II (Cyclotetramerization of the precursor ligand). Compound 8 was prepared according
to procedure described for 7, from phthalonitrile 4a (0.2 g, 0.4 mmol) and anhydrous Zn(OAc)2
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(0.019 g, 0.1 mmol) with DBU (3 drop) in dry DMF (2 mL), after column chromatography (SiO2,
THF as eluent). Yield: 0.039 g (19%); m.p. >200˚C.
FT-IR νmax/cm1; 3055(Ar-H), 2924, 2849 (alkyl-CH), 1645 (C=O), 1263 (C-O-C). UV/Vis λmax
(nm) (log ε) in DMF: 688 (4.94), 349 (4.89), 279 (4.97). 1H NMR (DMSO-d6) δ/ppm: 8.52-7.05
(br, 64H, Ar-H), 5.73 (s, 8H, -O=CCH2). Anal. Calcd. for C128H72N8O8S4Zn (2043.64 g/mol); C
75.23, H 3.55, N 5.48; Found: C 75.11, H 3.46, N 5.39. MS (MALDI-MS): m/z 2041.47 [M]+.
2.3. Photophysical parameters
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (
Φ
F) were determined by the comparative method (Eq. 1) [38]
(1)
where F and FStd are the areas under the fluorescence curves of the complex (5-8) and the
standard respectively, A and AStd are the respective absorbances of the sample and standard at
the excitation wavelengths, and
and
are the refractive indices of solvents used for the
sample and standard, respectively. Both the sample and reference were excited at the same
wavelength. Unsubstituted zinc phthalocyanine (ZnPc) in DMSO (ΦF = 0.18) [39] was employed
as the standard.
Natural radiative lifetimes (τ0) were determined using Photochem Cad Software which uses the
Strickler-Berg equation [40]. The fluorescence lifetimes (τF) were evaluated Eq. (2).
(2)
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2.3.2. Fluorescence quenching by benzoquinone (BQ)
Fluorescence quenching experiments on the various MPc complexes were carried out by the
addition of increasing concentrations of BQ to a fixed concentration of the complex, and the
concentrations of BQ in the resulting mixtures were 0, 0.008, 0.016, 0.024, 0.032 and 0.04 mol
dm−3. In order to establish the quenching mechanism, the fluorescence quenching data
were analyzed using Stern–Volmer equation (Equation 3.) [41]:
(3)
where I0 and I denotes the fluorescence intensity before and after the quencher (BQ) addition,
[Q] is the quencher concentration and KSV is the Stern-Volmer constant, defining the
quenching efficiency, which is the product of the bimolecular quenching constant (kq) and
the
and is expressed in Eq. (4).
(4)
The ratios I0/I were calculated and plotted against [BQ] according to Eq. (3), and KSV was
determined from the slope.
3. Results & Discussions
3.1 Synthesis and characterization
Scheme 1-2 summarizes the synthesis of zinc (II) phthalocyanines and corresponding
phthalocyanine-pyrene (ZnPc-Py) derivatives. Phthalonitriles 3 and 4 were synthesized by
nucleophilic substitution on 3-nitrophthalonitrile (1) and 4-nitrophthalonitrile (2), with 4-
mercaptophenol. Due to the higher nucleophilicity of sulfur relative to oxygen atom, the S-
arylation isomer was obtained exclusively [37]. The reaction was carried out at 90ºC in
dimethylformamide with K2CO3 as the base and the yield was reasonable (% 68 (3) to % 63 (4)).
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Non-peripherally (5) and peripherally (6) substituted zinc (II) phthalocyanines were prepared by
cyclotetramerization of mercaptophenoxy-substituted phthalonitriles (3, 4). Phthalocyanine-
pyrene complexes (7, 8) were synthesized by two different routes. In the first route, starting from
the symmetrically substituted peripheral and non-peripheral Pcs (5,6) bearing a
mercaptophenoxy moiety, base-catalyzed (K2CO3) nucleophilic aromatic displacement reaction
was carried out with 1-bromoacetylpyrene in dry DMF to synthesize corresponding
phthalocyanine-pyrene complexes (7, 8). In the second route, compounds 7 and 8 were prepared
directly from phthalonitriles bearing pyrene groups (3a, 4a) which were synthesized from
mercaptophenoxy-substituted phthalonitriles (3,4) (Scheme 1-2).
Two synthetic methods were used to select the better way for obtaining compounds with high
yields and mild conditions. The overall yields in both methods are very close to one another in
both peripherally and non-peripherally substituted phthalocyanines. The analytical and spectral
data confirm that the products are identical and independent to the route taken.
In order to verify that all the phenoxy groups in 5 are converted to pyrenemethylether, a simple
practical test was used. For this purpose, we compared the UV-Vis spectra of compound 7 with
those of mixtures containing compound 5 and 1-bromoacetylpyrene in 1:0, 1:1, 1:2, 1:3 and 1:4
mole ratios as shown in Fig. 1. Here it is clear that there is no shift in Q band absorption for 5
and 7. The absorptions due to pyrene group at around 350 nm in compound 7 is about the same
intensity when 5/1-bromoacetylpyrene ratio is 1:4. It confirms that the isolated product 7 by
direct aryl alkylation method has four pyrene units for each molecule.
An advantage of carrying out the cyclotetramerization reaction beforehand at hydroxyphenylthio
phthalonitrile steps is the isolation of intermediate phthalocyanines with hydroxyphenyltio
substituents (5, 6), so their properties might be compared with pyrene condensed ones (7, 8).
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As is well documented, mono-substituted phthalonitriles give a mixture of four constitutional
isomers of tetrasubstituted phthalocyanines (D2h, C2v, C4h, Cs) [42], in the present case we expect
that the C4h symmetry should be predominant in non-peripherally substituted complexes due to
the steric effect of bulky pyrene substituents. However, successful isolation of one of these
isomers is very challenging and needs more complicated separation techniques than ordinary
column chromatography. For this reason, it was not attempted to separate or investigate the
constitutional isomers of the complexes, as it has not been in the scope of this work to reach a
pure isomer. The structure of the synthesized compounds was characterized by FT-IR, 1H NMR,
13C NMR, UV-Vis and MS (MALDI-TOF, GC-MS, ESI-MS) spectroscopic methods, as well as
by elemental analysis. All the analytical and spectral data suggest sufficient purity of the
structures synthesized in this study.
In FT-IR spectra of phthalonitrile derivatives, the characteristic vibrations corresponding to C≡N
were observed at around 2240 cm−1 (3, 4) and around 2225 cm−1 (3a, 4a). These sharp peaks
disappeared after conversion of phthalocyanine formation. In the IR spectra of 3a and 4a, the
characteristic vibrations of C-O-C were observed at around 1250 cm-1 and aromatic -OH peaks
-1
disappeared at around 3400 cm . The synthesized phthalocyanine complexes 5, 6 showed the
characteristic vibrations of Ar-OH groups at 3287 and 3160 cm-1 respectively. The ZnPc-Py
phthalocyanine complexes (7, 8) showed characteristic vibrations belonging to carbonyl (C=O)
and aromatic C–O–C groups at around 1650 and 1250 cm-1 respectively, the broad stretching
vibrations of Ar-OH groups were disappeared.
The 1H NMR spectrum of 3 and 4 exhibited aromatic protons at around δ =7.86 - 6.90 ppm and
the aromatic O-H protons as singlet at δ = 10.18 and 10.09 ppm while 3a and 4a showed
aliphatic -O=CCH2 protons at 5.55 ppm whereas O-H peak disappears. In the 13C NMR spectrum
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of 3a and 4a revealed around δ = 197.0 (O=C-), 116.84 (C≡N) and 72.10 (-O=CCH2) ppm.
Compounds 3 and 4 have a C-O peak around δ = 160 ppm besides C≡N peak.
1
The H NMR spectra of phthalocyanine complexes are somewhat broader than corresponding
signals in the starting nitrile derivatives due to presence of phthalocyanine isomers aggregation.
1H NMR spectra of 5 and 6 exhibited the aromatic O-H protons as a singlet around δ = 10.00
ppm and the aromatic protons as a broad peaks at around δ = 8.88-6.91 ppm, while complexes 7
and 8 showed substituent and ring protons between δ = 8.73–6.83 ppm and methylene protons
observed at around ~5.70 ppm and the aromatic -OH protons disappeared.
3.2. Ground state electronic absorption and fluorescence spectra
The electronic absorption spectra of the complexes 5-8 showed typical Soret band between 325 -
364 nm and strong Q-band in the near infrared between 692-712 nm in DMF (Fig. 1). The single
(narrow) Q bands indicate the monomeric nature of these complexes in this solvent. The
difference in maxima reflect a ~20 nm red shift of the α-substitution relative to the β-substitution
at the phthalocyanine periphery due to greater destabilization of the a1u orbital (HOMO) [43].
The spectrum of pyrene in dilute solution showed two major absorption bands with maximum
absorption wavelength at about 280 and 360 nm. After conversion phthalocyanine derivative
Soret band of substituted complexes (7 and 8) overlap with the absorption of Py unit at around
~350 nm (Fig. 2).
Aggregation behavior of complexes (5-8) has been studied by concentration-dependent UV-Vis
spectra measurements in DMSO. The intensity of the Q band absorption increased in parallel
with the concentration without observed any new bands (normally blue shifted) associated with
the aggregated species for complexes 5-8 (Fig. 3 for complex 5 and 7). The bands strictly
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followed the Lambert-Beer law, which is characteristic of non-aggregated Pcs, in concentration
range from 1.4 × 10-5 to 2 × 10-6 mol dm- 3 (Fig. 3 inset plot).
Fluorescence measurements have been studied under identical conditions in DMSO at room
temperature. The fluorescence emission spectra of all complexes show emission bands that are
typical for phthalocyanines with Stokes’ shifts (λEm –λAbs) ranging from 7 to 12 nm. Fig. 4 shows
the fluorescence emission, absorption and excitation spectra of the complexes (5-8) and the
related records were summarized in Table 1. Identical excitation and absorption spectra of these
complexes (5-8) suggest that the nuclear configurations of the ground and excited states are not
affected by excitation [44].
3.3. Photophysical and photochemical properties
3.3.1. Fluorescence quantum yields and fluorescence lifetimes
The determination of fluorescence quantum yields (
using ZnPc as the reference was
accomplished in DMSO. The compounds have fluorescence quantum yields in the range 0.08-
0.15 (Table 2). The lower quantum yield values of the tetra substituted ZnPc complexes (5-8)
compared to unsubstituted ZnPc shows that the presence of mercaptophenol and pyrenyl
substituents caused some fluorescence quenching of the parent ZnPc. The
values were found
to be slightly higher in the p-substituted complexes (6 and 8) compared to the corresponding np-
substituted (5 and 7) ones (Table 2). This suggest that the extent of quenching is greater in the np
substitution due to substituents are closer to the point of fusion to the ring [45].
Lifetimes of fluorescence ( ) were calculated from experimentally measured quantum yield
of fluorescence and natural radiative lifetime (
derived from the Strickler-Berg equation.
Using this equation, a good correlation has been found for the experimentally and theoretically
determined fluorescence lifetimes for the unaggregated molecules [46]. As stated above the
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aggregation was not observed in all studied compounds in DMSO, so the values obtained using
this equation are a good measure of fluorescence lifetimes in this study. The values are lower
for complexes 5-8 when compared to unsubstituted ZnPc in DMSO (Table 2).
The natural radiative lifetime ( ) and rate constants for fluorescence (kF) values of the
substituted complexes (5-8) are also given in Table 2. The kF values of the peripheral substituted
phthalocyanines (5 and 7) are higher than non-peripheral derivatives (6 and 8) in DMSO.
3.3.2. Fluorescence quenching studies by benzoquinone [BQ]
Fluorescence quenching is an important method to study the energetics of excited states. The
fluorescence quenching process of ZnPc (5-8) by benzoquinone (BQ) in DMSO was described
by the Stern-Volmer equation which allows the determination of quenching constants. Fig. 5
shows the emission spectra of p-ZnPc-Py during quenching by benzoquinone (BQ) as an
example. The linearity of Stern-Volmer plot (I0/I) versus the quencher concentration ([Q])
indicates generally that one type of quenching mechanism is predominating (Fig. 6.). It can be
seen that the fluorescence intensity of ZnPc decreased strongly and no change in the λ max of
ZnPc emission occurred hence the quenching mechanism can be said to be dynamic [47]. The
slope of the plots shown at Fig. 5 gave KSV values (Table 3).
The KSV values of the tetra-substituted peripheral and non-peripheral phthalocyanines (5-8) are
lower than those of unsubstituted ZnPc. The substitution with Schiff base Zn(II) complex group
seems to decrease the KSV values of the complexes. The KSV values among the substituted
complexes decreased as follows: p-ZnPc-Py > np-ZnPc-Py > p-ZnPc > np-ZnPc.
The bimolecular quenching constant (kq) values of the substituted phthalocyanines are also lower
than those of unsubstituted ZnPc. The kq values were found to be close to the diffusion-
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controlled limits, ~1010 M-1 s-1 [48, 49]. The kq values for the substituted complexes decreased as
follows: np-ZnPc > np-ZnPc-Py > p-ZnPc > p-ZnPc-Py in DMSO (Table 3).
4. Conclusion
In this work we described the synthesis, characterization, spectral and photophysical properties
of new peripheral and non-peripheral tetra-substituted zinc (II) phthalocyanine complexes with
pendant pyrene groups. We accomplished the prepare the pyrene substituted phthalocyanines (7,
8) by introduction of pyrene group in either phthalonitrile or phthalocyanine steps The effects of
substitution position on aggregation and fluorescence properties of tetra substituted
phthalocyanine complexes (5-8) have been studied. All phthalocyanine complexes are
monomeric form in DMSO solution.
The photophysics of phthalocyanines (5–8) have been extensively investigated and compared
with each other. All these complexes showed similar and typical fluorescence behavior in
DMSO. The fluorescence behavior of the complexes showed that fluorescence lifetimes
increased with fluorescence quantum yields. Complexes bearing pyrene groups (6, 8) have
higher fluorescence quantum yields. Highest fluorescence results found for compound 8 due to
pyrene groups at the peripheral positions. The fluorescence of the substituted zinc (II)
phthalocyanines is effectively quenched by 1,4-benzoquinone in DMSO.
Acknowledgements
This work was supported by Istanbul Technical University (Project No: 36441)
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Table captions:
Table 1. Absorption, excitation and emission spectral data for substituted zinc phthalocyanine
complexes in DMSO
Table 2. Photophysical and photochemical parameters of substituted zinc phthalocyanine
complexes in DMSO
Table 3. Fluorescence quenching data of substituted zinc phthalocyanine complexes in DMSO
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Figure Captions
Fig. 1. UV-Vis spectra of compound 7 with those of mixtures containing compound 5 and 1-
bromoacetylpyrene in 1:0, 1:1, 1:2, 1:3 and 1:4 molar ratios. [MPcs]: 1.00 x 10 -6, [Py]: 0.00, 1.0
x 10−5, 2.0 x 10−5, 3.0 x 10−5, 4.0 x 10−5 mol dm−3 in DMSO.
Fig. 2. UV/Vis spectra of np-ZnPc (5), p-ZnPc (6), np-ZnPc-Py (7) and p-ZnPc-Py (8) in DMF.
The absorption spectra were normalized with respect to the absorption maxima.
Fig 3. Absorption spectral changes of 5 (a) and 7 (b) in DMSO at different concentrations:
14x10-6 (A), 12x10-6 (B), 10x10-6 (C), 8.0x10-6 (D), 6.0x10-6 (E), 4.0x10-6 (F), 2.0x10-6 (G) mol
dm-3 (Inset: Plot of absorbance versus concentration).
Fig. 4. Absorption, excitation and emission spectra of (a) 5 (λEx= 647 nm), (b) 6 (λEx= 632 nm),
(c) 7 (λEx= 647 nm ), and (d) 8 (λEx= 628 nm ) in DMSO. [M]: 1x 10 -6 mol dm-3.
Fig. 5. Fluorescence emission spectral changes of p-ZnPc-Py on addition of different
concentrations of BQ in DMSO. [MPc] ~ 1.00 x 10-6 mol dm-3. [BQ] = 0.008, 0.016, 0.024,
0.032, 0.040 mol dm-3.
Fig. 6. Stern–Volmer plots for benzoquinone (BQ) quenching of MPc in DMSO. (a) p-ZnPc and
p-ZnPc-Py, (b) n-ZnPc and n-ZnPc-Py. (~ 1.00 x 10-6 mol dm-3). [BQ] = 0, 0.008, 0.016, 0.024,
0.032, 0.040 mol dm-3.
23

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Scheme Captions
Scheme 1. Preparation of corresponding non-peripheral substituted phthalonitriles and
phthalocyanine derivatives. Reagents and conditions, (i) K2CO3, DMF, 90°C, 16h; (ii)
(Zn(OAc)2, DBU, DMF, 140°C, 16h; (iii) K2CO3, DMF, reflux, 4h; (iv) (Zn(OAc)2, DBU,
DMF, 140°C, 18h; (v) 1-bromoacetylpyrene, K2CO3, DMF, 80°C, 6h.
Scheme 2. Preparation of corresponding peripheral substituted phthalonitriles and
phthalocyanine derivatives. Reagents and conditions, (i) K2CO3, DMF, 90°C, 16h; (ii)
(Zn(OAc)2, DBU, DMF, 140°C, 16h; (iii) K2CO3, DMF, reflux, 4h; (iv) (Zn(OAc)2, DBU,
DMF, 140°C, 18h; (v) 1-bromoacetylpyrene, K2CO3, DMF, 80°C, 6h.
24

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Table 1: Absorption, excitation and emission spectral data for substituted zinc phthalocyanine
complexes in DMSO
Q band
Excitation Emission
Stokes shift
Stokes, (nm)
log (ɛ)
Complex
∆
λmax, (nm)
λEx, (nm)
λEm, (nm)
5
718
698
717
698
672 a
4.86
4.80
4.97
4.92
5.14 a
717
695
716
696
672 a
729
705
729
709
682 a
11
6
07
7
12
8
11
ZnPc
10 a
a Ref. [39].

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Table 2: Photophysical and photochemical parameters of substituted zinc phthalocyanine
complexes (5-8) in DMSO
kf (s-1) ( x 108) a
Complex
(ns)
5
0.08
0.13
0.11
0.15
0.18b
0.52
0.71
0.62
0.82
1.22b
6.51
5.47
5.60
5.50
6.80b
1.54
1.83
1.78
1.82
1.47b
6
7
8
ZnPc
a kF is the rate constant for fluorescence. Values calculated using
b Ref [39].

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Table 3: Fluorescence quenching data of substituted zinc phthalocyanine complexes in DMSO
Complex
K
SV (M-1)
kq/ (1.00x1010 s-1)
5
18.751
20.073
22.138
22.323
31.90 a
3.60
2.82
3.57
2.72
2.61 a
6
7
8
ZnPc
a Ref. [39].

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Fig. 1. UV-Vis spectra of compound 7 with those of mixtures containing compound 5 and 1-
-5
bromoacetylpyrene in 1:0, 1:1, 1:2, 1:3 and 1:4 molar ratios. [MPcs]: 1.00 x 10 , [Py in 5]:
0.00, 1.0 x 10−5, 2.0 x 10−5, 3.0 x 10−5, 4.0 x 10−5 mol dm−3 in DMSO.