Synthesis, photophysical and photochemical properties of highly soluble phthalocyanines substituted with four 3,5-dimethylpyrazole-1-methoxy groups

Article abstract of DOI:10.1016/j.jorganchem.2011.09.002

The synthesis and characterization of new peripherally tetra-3,5- dimethylpyrazole-1-methoxy substituted metal-free (4), zinc (5), nickel (6), cobalt (7), copper (8) and lead (9) phthalocyanines are described for the first time in this study. The photophy

Full text of DOI:10.1016/j.jorganchem.2011.09.002

Journal of Organometallic Chemistry 696 (2011) 3807e3815
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, photophysical and photochemical properties of highly soluble
phthalocyanines substituted with four 3,5-dimethylpyrazole-1-methoxy groups
,
a
Rıza Bayraka, Hakkı Türker Akçayb, Mahmut Durmus¸ c , Ismail Degirmencioglu
_
*
ꢀ
ꢀ
a Department of Chemistry, Faculty of Sciences, Karadeniz Technical University, 61080 Trabzon, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Rize University, 53050 Rize, Turkey
c Gebze Institute of Technology, Department of Chemistry, P.O.Box 141, 41400, Gebze, Kocaeli, 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 tetra-3,5-dimethylpyrazole-1-methoxy
substituted metal-free (4), zinc (5), nickel (6), cobalt (7), copper (8) and lead (9) phthalocyanines are
described for the first time in this study. The photophysical (fluorescence quantum yields and fluores-
cence lifetimes) and photochemical (photodegradation and singlet oxygen quantum yields) properties of
metal-free (4), zinc (5) and lead (9) phthalocyanines are studied in dimethylsulfoxide (DMSO). Nickel (6),
cobalt (7) and copper (8) phthalocyanines (6e8) did not evaluate for this purpose due to transition metal
and paramagnetic behavior of central metals in the phthalocyanine cavity. The fluorescence quenching
behavior of metal-free (4), zinc (5) and lead (9) phthalocyanines are also investigated. The fluorescence
emissions of these phthalocyanines are effectively quenched by 1,4-benzoquinone in DMSO.
Ó 2011 Elsevier B.V. All rights reserved.
Received 12 July 2011
Received in revised form
28 August 2011
Accepted 1 September 2011
Keywords:
Phthalocyanine
Pyrazole
Photophysical
Photochemical
Quenching
1. Introduction
short triplet lifetimes. Closed shell or diamagnetic ions, such as Zn2þ
,
Al3þ and Si4þ, give phthalocyanine complexes both high triplet
yields and singlet oxygen generation [9]. Zinc phthalocyanines
(ZnPcs) in particular 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, high
singlet and triplet quantum yields. These properties make them
important candidates as photosensitizers for PDT applications.
Heterocyclic compounds have so far been synthesized mainly
due to the wide range of biological activities. Pyrazoles are one of the
most important classes of heterocyclic compounds and they are very
significant for medicinal chemistry [10]. Pyrazoles exhibit antiar-
rhythmic [11], antipyretic [12], analgesic and anti-inflammatory [13],
neuroleptic [14], sedative-hypnotic effect [15] and antimicrobial
activity [16]. They are inhibitors and deactivators of liver alcohol
dehydrogenase [17]. The 3,5-substituted pyrazoles show hypogly-
cemic activity [13] in glucose primed and diabetic rats. Heterocyclic
compounds are also used as intermediaries in the industry of the
dyes [18].
Phthalocyanines (Pcs) have been actively explored for various
technological applications since their discovery [1]. Substituted
phthalocyanine derivatives have been used in areas such as catalysis
[1], chemical sensors [2], liquid crystals [3], semiconductors [4],
non-linear optics [5] and photodynamic therapy (PDT) of cancer [6].
The solubility of phthalocyanine derivatives is very important for
these applications, because many phthalocyanines are not soluble in
organic solvents and aqueous medium. The substitution improves
the useful properties of phthalocyanines and usually enhances their
solubility. Generally, tetra-substituted phthalocyanines are more
soluble than the corresponding octa-substituted phthalocyanines
due to the formation of constitutional isomer mixture [7,8].
Phthalocyanine derivatives have proved to be highly promising
as photosensitizers for PDT due to their intense absorption in the
long wavelength region of the visible light, high triplet state
quantum yields and long triplet lifetime values which are required
for an efficient sensitization. The photophysical properties of the
phthalocyanine dyes are strongly influenced by the presence and
nature of the central metal ion. Complexation of phthalocyanine
molecules with transition metals or paramagnetic ions gives dyes
There is no research in literature about the PDT activities of
pyrazole substituted phthalocyanines and investigation of these
properties is compulsory due to the wide range of biological
activities of the 3,5-substituted pyrazoles [10e18]. Therefore in this
study, 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methoxy]phthalonitrile
and its corresponding metal-free and metallophthalocyanine (zinc,
* Corresponding author. Tel.: þ90 262 6053075; fax: þ90 262 6053101.
E-mail address: durmus@gyte.edu.tr (M. Durmus¸ ).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.09.002

3808
R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
nickel, cobalt, copper and lead) derivatives synthesized with high
yield. The structures of the new compounds were characterized by
IR, 1H and 13C NMR, UVeVis, mass spectroscopies and elemental
analysis. Metal-free and metallophthalocyanines show excellent
solubility in variety of solvents, which improves the possible
applications (such as PDT) of these compounds.
A mixture of phthalocyanine and quinone should be a good
mimicker of the natural photosynthetic systems; with the phtha-
locyanine being the light harvester, and the quinone, the energy
transducer. An investigation into the light-harvesting and energy-
transducing tendencies of metal-free (4), zinc (5) and lead (9)
phthalocyanine-benzoquinone systems is presented in this work.
Quinones are known to quench the excited singlet states of
phthalocyanines under red light excitation. This work also explores
the effects of substituents and nature of the central metal ions on
the fluorescence properties of the phthalocyanines and on the
quenching of the phthalocyanines by 1,4-benzoquinone (BQ) using
the SterneVolmer relationship.
where F and FStd are the areas under the fluorescence emission
curves of the samples (4, 5 and 9) and the standard, respectively. A
and AStd are the relative absorbance of the samples (4, 5 and 9) and
standard at the excitation wavelength, respectively. n and nstd are
the refractive indices of solvents for the sample and standard,
respectively. Unsubstituted ZnPc (FF ¼ 0.20) [24] was employed as
the standard in DMSO. The concentrations of the samples and
standard were arranged at 1 ꢀ10ꢁ6 M in DMSO.
Natural radiative (
s0) lifetimes were determined using Photo-
chem CAD program using StricklereBerg equation [25]. The fluo-
rescence lifetimes (sF) were evaluated using equation (2).
sF
s0
FF
¼
(2)
2.4. Photochemical parameters
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield (FD) determinations were carried
out by using the experimental set-up described in literatures
[26e28]. Typically, 3 cm3 portion of the respective metal-free (4),
zinc (5) or lead (9) phthalocyanine solutions (C ¼ 1 ꢀ10ꢁ5 M)
containing the DPBF which singlet oxygen quencher was irradiated
in the Q band region with the photoirradiation set-up described in
references [26e28]. FD was determined in air using the relative
method with unsubstituted ZnPc as a reference in DMSO. Equation
(3) was employed for the calculations of FD values:
2. Experimental
2.1. Materials
All reactions were carried out under nitrogen atmosphere using
standard Schlenk techniques. All solvents were dried and purified
as described by Perrin and Armarego [19]. 1,3-diphenyliso-
benzofuran (DPBF) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
were purchased from Fluka. (3,5-dimethyl-1H-pyrazol-1-yl)meth-
anol (1) [20] and 4-nitrophthalonitrile (2) [21] were prepared
according to the literature procedures.
Std
R$I
FSDtd
(3)
abs
FD
¼
RStd$Iabs
2.2. Equipment
where FSDtd is the singlet oxygen quantum yield for the standard
unsubstituted ZnPc (FDStd ¼ 0.67 in DMSO) [29]. R and RStd are the
DPBF photobleaching rates in the presence of the respective
samples (4, 5 and 9) and standard, respectively. Iabs and IStd are the
rates of light absorption by the samples (4, 5 and 9) andabsstandard,
respectively. To avoid chain reactions induced by DPBF in the
presence of singlet oxygen, the concentration of quencher was
lowered to w3 ꢀ10ꢁ5 M [30]. Solutions of sensitizers 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 was 6.54 ꢀ1015 photons sꢁ1 cmꢁ2 for
FD determinations.
1H NMR and 13C NMR spectra were recorded on a Varian XL-200
NMR spectrophotometer in CDCl3, and chemical shifts were re-
ported (d) relative to Me4Si as internal standard. IR spectra were
recorded on a PerkineElmer Spectrum FT-IR spectrometer using KBr
pellets. The mass spectra were measured with a Micromass Quattro
LC/ULTIMA LC-MS/MS spectrometer using chloroformemethanol
solvent system. All experiments were performed in the positive ion
mode. Elemental analyses were performed on a Costech ECS 4010
instrument and the obtained values agreed with the calculated ones.
UVeVis spectra were recorded by Unicam UV2-100 and Shimadzu
2001 spectrophotometers using 1 cm pathlength cuvettes at room
temperature. Fluorescence excitation and emission spectra were
recorded on a Varian Eclipse spectrofluorometer using 1 cm path-
length cuvettes at room temperature. Melting points were
measured on an electrothermal apparatus and are uncorrected.
Photo-irradiations were done using a General Electric quartz
line lamp (300 W) for metal-free (4), zinc (5) and lead (9) phtha-
locyanine derivatives. A 600 nm glass cut off filter (Schott) and
a water filter were used to filter off ultraviolet and infrared radia-
tions respectively. An interference filter (Intor, 670 nm with a band
width of 40 nm) was additionally placed in the light path before the
sample solution. Light intensities were measured using a POWER
MAX5100 (Molelectron detector incorporated) power meter.
2.4.2. Photodegradation quantum yields
Determination of photodegradation quantum yields (Fd) of Pc
derivatives were carried out as described in the literatures [26e28].
Fd values were determined using equation (4),
ðC0 ꢁ CtÞ$V$NA
Fd
¼
(4)
I
abs$S$t
where C0 and Ct are the samples (4, 5 and 9) concentrations before
and after irradiation, respectively. V is reaction volume, NA is the
Avogadro’s constant, S is irradiated cell area, t is irradiation time
and Iabs is the overlap integral of the radiation source light intensity.
A light intensity of 2.18 ꢀ 1016 photons sꢁ1 cmꢁ2 was employed for
Fd determinations.
2.3. Photophysical parameters
2.3.1. Fluorescence quantum yields and lifetimes
2.4.3. Fluorescence quenching by 1,4-benzoquinone (BQ)
Fluorescence quantum yields (FF) were determined by the
comparative method using equation (1) [22,23].
Fluorescence quenching experiments on the substituted
phthalocyanine compounds (4, 5 and 9) were carried out by the
addition of different concentrations of BQ to a fixed concentration
of the samples. The concentrations of BQ solutions in the resulting
mixtures were 0, 0.008, 0.016, 0.024, 0.032 and 0.040 M. The
F$AStd$n2
FF
¼
FFðStdÞ
(1)
F
Std$A$n2Std

R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
3809
fluorescence emission spectra of substituted phthalocyanine
derivatives (4, 5 and 9) at each BQ concentration were recorded,
and the changes in fluorescence intensity related to BQ concen-
tration by the SterneVolmer (SeV) equation [31] was shown in
equation (5):
ppm): 161.35, 148.21, 147.45, 145.11, 143.17, 133.34, 121.78, 119.45,
118.36, 106.55, 102.71 (CHpyrazole), 77.21 (CH2), 12.85 (CH3(a)), 12.02
(CH3(b)). UV/Vis (chloroform): lmax nm (log ε) 700 (5.21), 662
(5.13), 636 (4.83), 600 (4.59), 338 (5.03). MS (ESI), (m/z): Calculated:
1010.42; Found: 1011.58 [M þ H]þ.
I0
I
2.5.3. The general procedure for synthesis of
metallophthalocyanines (5e8)
¼ 1 þ KSV½BQꢂ
(5)
The solution of 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methoxy]
phthalonitrile (3) (0.20 g, 0.790 mmol) and anhydrous metal salts
[Zn(Ac)2 (0.036 g, 0.198 mmol), Ni(Ac)2 (0.035 g, 0.198 mmol), CoCl2
(0.025 g, 0.198 mmol), CuCl2 (0.027 g, 0.198 mmol) and Pb(Ac)2
(0.075 g, 0.198 mmol)] in dry n-hexanol (4 cm3) heated to 90 ꢃC in
a glass tube and DBU (0.44 cm3, 0.8 mmol) was added to this
solution. Then the temperature of the mixture was increased to
160 ꢃC and stirred at this temperature for 24 h. Then the mixture
was cooled to room temperature and diluted with n-hexane (ca.
30 cm3) and stirred for 12 h. The precipitated product was filtered
and then washed with methanol, hot ethanol, diethyl ether and
dried in vacuum over P2O5. Finally pure metallophthalocyanines
were obtained by column chromatography on silica gel with chlo-
roform/methanol (20:0.5) for compound 5, (25:0.5) for compound
6, (23:0.5) for compound 7, (18:0.5) for compound 8, and (22:0.5)
for compound 9 solvent system as eluents.
where I0 and I are the fluorescence intensities of fluorophore
(phthalocyanines in this study) in the absence and presence of
quencher, respectively. [BQ] is the concentration of the quencher
and KSV is the SterneVolmer constant which is the product of the
bimolecular quenching constant (kq) and the
s
F. KSV is expressed in
equation (6).
KSV ¼ kq$sF
(6)
The ratios of Io/I were calculated and plotted against [BQ]
according to equation (5), and KSV is determined from the slope.
2.5. Synthesis
2.5.1. 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methoxy]phthalonitrile (3)
3,5-dimethylpyrazole-1-methanol (1) (2.52 g, 0.02 mol) was
added to a solution of 4-nitrophthalonitrile (2) (3.46 g, 0.02 mol) in
dry DMF (50 cm3), and the mixture was stirred at 55e60 ꢃC.
Powdered K2CO3 (2.76 g, 0.02 mol) was added to this solution in
eight equal portions at 15 min intervals with efficient stirring and
the reaction system was stirred at the same temperature for 5 days.
Then the solution poured into ice-water (150 cm3). The precipitate
was filtered off, washed with water until the filtrate neutral, then
diethyl ether and dried in vacuum over P2O5. The crude product
crystallized from ethyl acetate/petroleum ether (1:1) solvent
system to give light brown crystalline powder. Yield: 3.34 g, (66%),
mp: 134e136 ꢃC. Anal. Calc. for C14H12N4O: C 66.65, H 4.79, N 22.21;
Found: C 66.52, H 4.68, N 22.17. IR [(KBr) nmax/cmꢁ1]: 3091
2.5.3.1. Zn(II) phthalocyanine (5). Yield: 0.067 g, (32%), mp
>300 ꢃC. Anal. Calc. for C56H48N16O4Zn: C 62.60, H 4.50, N 20.86;
Found: C 62.41, H 4.33, N 20.67. IR [(KBr) nmax/cmꢁ1]: 3073
y
y
d
(AreCH), 2942e2862
(CH]N), 1252e1217
(CeOeC), 972
(CH). 1H NMR (CDCl3), (
y
(Aliph. CH), 1735e1601
(CeOeC)/(CeN), 1130 (CeN), 1099e1005
: ppm): 7.72e7.69 (d,
y(C]C), 1572
y
d
d
d
J ¼ 7.4 Hz, 4H/AreH), 7.54e7.39 (d, J ¼ 8.2 Hz, 8H/AreH), 5.93 (s,
8H/CH2), 5.88 (s, 4H/CHpyrazole), 2.31 (s, 12H/CH3(a)), 2.21 (s, 12H/
CH3(b)). 13C NMR (CDCl3), (
d: ppm): 160.41, 146.78, 145.87, 145.08,
142.15, 131.52, 120.98, 118.78, 116.63, 105.84, 101.32 (CHpyrazole),
76.41 (CH2), 12.53 (CH3(a)), 11.05 (CH3(b)). UV/Vis (chloroform):
lmax nm (log ε) 682 (5.17), 618 (4.46), 356 (4.92). MS (ESI), (m/z):
Calculated: 1072.33; Found: 1072.45 [M]þ.
y
(AreCH), 2923e2875
C), 1567e1550 (CH]N), 1277e1253
(CeN), 1095e1010 (CeOeC), 991 d:
(CH). 1H NMR (CDCl3), (
y
(Aliph. CH), 2231 (C^N), 1624e1601
y(C]
y
y(CeOeC)/(CeN), 1140
d
d
d
ppm): 7.74e7.70 (d, J ¼ 8.2 Hz, 1H/Ar-H), 7.61e7.57 (d, J ¼ 8.1 Hz,
2.5.3.2. Ni(II) phthalocyanine (6). Yield: 0.055 g, (26%), mp >300 ꢃC.
Anal. Calc. for C56H48N16O4Ni: C 62.99, H 4.53, N 20.99; Found: C
2H/AreH), 5.96 (s, 2H/CH2), 5.83 (s, 1H/CHpyrazole), 2.34 (s, 3H/
CH3(a)), 2.21 (s, 3H/CH3(b)). 13C NMR (CDCl3), (
d
: ppm): 163.34,
62.83, H 4.39, N 20.86. IR [(KBr) nmax/cmꢁ1]: 3088
y
(AreCH),
(CH]N),
(CeOeC), 985
: ppm): 7.72 (bs, 4H/AreH), 7.55e7.37 (d,
J ¼ 7.2 Hz, 8H/AreH), 5.90 (bs,12H/CH2 þ CHpyrazole), 2.29 (s,12H/
CH3(a)), 2.20 (s, 12H/CH3(b)). 13C NMR (CDCl3), (
: ppm): 163.32,
148.86, 144.28, 135.44, 123.14, 120.54, 117.65, 115.48 (C^N), 112.79,
105.14, 101.80 (CHpyrazole), 79.67 (CH2), 13.23 (CH3(a)), 11.45
(CH3(b)). MS (ESI), (m/z): Calculated: 252.10; Found: 252.75 [M]þ.
2917e2867
1245 (CeOeC)/(CeN), 1125
(CH). 1H NMR (CDCl3), (
y
(Aliph. CH), 1630e1617
y(C]C), 1585e1547 y
y
d
(CeN), 1085e1015 d
d
d
2.5.2. Synthesis of metal-free phthalocyanine (4)
d
The solution of 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methoxy]
phthalonitrile (3) (0.20 g, 0.79 mmol) in dry n-hexanol (4 cm3) was
heated to 90 ꢃC in a glass tube and DBU (0.44 cm3, 0.80 mmol) was
added to this solution at this temperature. The mixture was heated
to 160 ꢃC for 24 h. Then it was cooled to room temperature and
diluted with n-hexane (ca. 30 cm3) and stirred for 12 h. The
precipitated product was filtered and then washed with methanol,
hot ethanol, and diethyl ether and dried in vacuum over P2O5. The
solid product was purified with column chromatography on silica
gel with chloroform/methanol (50:0.5) solvent system as eluent to
give dark green product. Yield: 0.05 g, (25%), mp >300 ꢃC. Anal.
Calc. for C56H50N16O4: C 66.52, H 4.98, N 22.16; Found: C 66.34, H
147.14, 144.28, 144.08, 141.56, 130.96, 121.46, 119.62, 116.54, 104.25,
102.03 (CHpyrazole), 76.79 (CH2),11.59 (CH3(a)),10.23 (CH3(b)). UV/
Vis (chloroform): lmax nm (log ε) 673 (5.15), 606 (4.38), 334 (4.67).
MS (ESI), (m/z): Calculated: 1066.34; Found: 1067.96 [M þ H]þ.
2.5.3.3. Co(II) phthalocyanine (7). Yield: 0.068 g, (32%), mp >300 ꢃC.
Anal. Calc. for C56H48N16O4Co: C 62.98, H 4.53, N 20.98; Found: C
62.77, H 4.35, N 20.77. IR [(KBr) nmax/cmꢁ1]: 3086
y
(AreCH),
(Aliph. CH), 1622e1615 (CH]N),
(CeN), 1074e1010 d(CeOeC), 992
2913e2869
1251 (CeOeC)/(CeN), 1147
y
y(C]C), 1587e1553 y
y
d
d
(CH). UV/Vis (chloroform): lmax nm (log ε) 676 (5.21), 608 (4.43), 350
(4.82). MS (ESI), (m/z): Calculated: 1067.34; Found: 1068.63 [M þ H]þ.
4.77, N 22.25. IR [(KBr) nmax/cmꢁ1]: 3294 (eNH), 3092
y
(AreCH),
(CH]N),
(CeOeC),
: ppm): 7.70 (bs, 4H/AreH), 7.56e7.48
(d, J ¼ 7.7 Hz, 8H/AreH), 6.08 (s, 8H/CH2), 5.95 (s, 4H/CHpyrazole),
2.35 (s, 12H/CH3(a)), 2.23 (s, 12H/CH3(b)). 13C NMR (CDCl3), (
2925e2871
1264e1251
y
(Aliph. CH), 1721e1614
y
(C]C), 1565
y
2.5.3.4. Cu(II) phthalocyanine (8). Yield: 0.038 g, (18%), mp
>300 ꢃC. Anal. Calc. for C56H48N16O4Cu: C 62.71, H 4.51, N 20.89;
Found: C 62.61, H 4.38, N 20.75. IR [(KBr) nmax/cmꢁ1]: 3094
y
(CeOeC)/(CeN), 1135 (CeN), 1091e1001 d
d
982 d d
(CH). 1H NMR (CDCl3), (
y(AreCH), 2923e2884
y(Aliph. CH), 1615e1605
y(C]C), 1575e1541
d:
y
(CH]N), 1248 (CeOeC)/(CeN), 1132
y
d(CeN), 1064e1018

3810
R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
d
(CeOeC), 978
d
(CH). UV/Vis (chloroform): lmax nm (log ε) 678
metallophthalocyanines (5, 6, 7, 8 and 9) is shown in Scheme 1. The
structures of novel compounds have been characterized by a combi-
nation of 1H and 13C NMR, IR, UV-Vis spectroscopy, elemental analysis
and mass spectral data.
(5.19), 610 (4.52), 338 (4.81). MS (ESI), (m/z): Calculated: 1071.33;
Found: 1071.85 [M]þ.
2.5.3.5. Pb(II) phthalocyanine (9). Yield: 0.055 g, (23%), mp
>300 ꢃC. Anal. Calc. for C56H48N16O4Pb: C 55.30, H 3.98, N 18.43,
Found: C 55.15, H 3.30, N 18.52. IR [(KBr) nmax/cmꢁ1]: 3065
3.1.1. Synthesis of 3,5-dimethylpyrazole-1-methoxy substituted
phthalonitrile (3)
y
y
d
(AreCH), 2950e2851
(CH]N), 1273 (CeOeC)/(CeN), 1126
(CeOeC), 976 : ppm): 7.78e7.64 (m, 4H/
(CH). 1H NMR (CDCl3), (
y
(Aliph. CH), 1662e1614
y
(C]C), 1565e1471
The preparation of phthalonitrile derivative 3 was achieved
from the reaction of 3,5-dimethylpyrazole-1-methanol (1) and 4-
nitrophthalonitrile (2) in the presence of anhydrous K2CO3 as
base in DMF under N2 atmosphere at 60 ꢃC for 5 days. This is
accomplished by base catalyzed nucleophilic aromatic nitro
displacement of 4-nitrophthalonitrile with compound 1 [32e35].
The structure of the target compound was confirmed by spectral
investigation. In the IR spectrum (KBr pellets) the formation of
compound 3 clearly indicated by the disappearance of eOH
stretching/deformation of compound 1 at 3349/1331 cmꢁ1 and NO2
stretching of compound 2 at 1519, 1333 cmꢁ1 and by the appear-
ance of C^N absorption band at 2231 cmꢁ1. Its 1H NMR spectrum
(in CDCl3) was also in good agreement with the structure of the
synthesized compound. Phenolic (D2O exchangeable) eOH at
7.81 ppm disappeared after condensation. In addition, compound 1
have no aromatic groups and of course have no aromatic signals,
y
d(CeN), 1082e1049
d
d
AreH), 7.55e7.37 (d, J ¼ 7.8 Hz, 8H/AreH), 5.96 (s, 8H/CH2), 5.90 (s,
4H/CHpyrazole), 2.34 (s, 12H/CH3(a)), 2.21 (s, 12H/CH3(b)). 13C NMR
(CDCl3), (d: ppm): 164.42, 148.55, 143.45, 142.26, 142.03, 131.75,
122.64, 120.19, 116.38, 104.82, 101.45 (CHpyrazole), 75.19 (CH2), 10.98
(CH3(a)), 10.02 (CH3(b)). UV/Vis (chloroform): lmax nm (log ε) 712
(5.13), 643 (4.47), 359 (4.70). MS (ESI), (m/z): Calculated: 1216.38;
Found: 1216.76 [M]þ.
3. Results and discussion
3.1. Outlook of the synthesized compounds
The synthesis route of 3,5-dimethylpyrazole-1-methoxy
but after the condensation two doublets at ca.
d
¼ 7.74e7.70 and
substituted phthalonitrile (3), its target metal-free (4) and
Scheme 1. Synthetic route of novel phthalocyanine compounds.

R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
3811
7.61e7.57 appeared in the spectrum. Additionally, the 1H NMR
spectrum of 3 showed two singlet peaks at
¼ 5.96 (-CH2), 5.83
d
(HCpyrazole) as expected. Also two methyl groups (a and b) on the
pyrazole moiety of compound 3 are not identical because of the
electronegative oxygen and phthalonitrile group. So the signal of
the methyl group a showed more downfield shift (2.34 ppm) than
methyl group b (2.21 ppm). The proton-decoupled 13C NMR spec-
trum indicated the presence of nitrile carbon atoms for compound
3 at 115.48 ppm. In addition, the mass spectrum of 3 showed
a molecular ion peak at m/z ¼ 252.75 [M]þ, supporting the
proposed formula for this compound.
3.1.2. Syntheses of 3,5-dimethylpyrazole-1-methoxy substituted
metal-free (4) and metallophthalocyanines (5e8)
The peripherally tetra-substituted metal-free phthalocyanine
(4) was obtained by cyclotetramerization of compound 3 in n-
hexanol in the presence of DBU under reflux for 24 h. Also, cyclo-
tetramerization of substituted phthalonitrile compound (3) in the
presence of the metal salts [Zn(CH3COO)2, Ni(CH3COO)2, CoCl2,
CuCl2 and Pb(CH3COO)2] and DBU in dry n-hexanol at 160 ꢃC for
24 h gave the tetra-substituted metallophthalocyanines (5, 6, 7, 8
and 9), respectively.
The spectroscopic characterization of the novel phthalocyanine
compounds includes 1H NMR, IR, UV/Vis and mass spectral investi-
gations, and the results are in accordance with the proposed struc-
tures. Cyclotetramerization of phthalonitrile compound (3) to metal-
free Pc (4) was confirmed by the disappearance of the sharp C^N
vibration at 2231 cmꢁ1 in their own IR spectra. The IR spectrum of the
metal-free phthalocyanine (4) showed usual inner core eNH
absorption at 3294 cmꢁ1, that is characteristic for metal-free phtha-
locyanines. The restof the spectrumof 4 wassimilar tothatof3. Inthe
1H NMR spectrum of compound 4 shielded inner core eNH protons
could not be observed due to the probable strong aggregation. The
signals belong to aromatic and aliphatic protons of 4 represent the
significant absorbance characteristics of the proposed structure.
Furthermore, the ESI mass spectrum of compound 4 showed
a molecular ion peak at m/z ¼ 1011.58 [M]þ, supporting the proposed
formula for this compound. In addition, elemental analysis values
were also satisfactory.
The disappearance of the C^N vibration of phthalonitrile
compound (3) at 2231 cmꢁ1 in the IR spectra of metal-
lophthalocyanines (5e9) proves the formation of these phthalo-
cyanine compounds. The 1H NMR spectra of 7 and 8 could not be
determined because of the presence of paramagnetic cobalt and
copper atoms [36] in the phthalocyanine core. The 1H NMR spectra
of the compounds 5 and 6 were almost similar to those of the
metal-free phthalocyanine 4. In the mass spectra of compounds
5e9, the parent molecular ion peaks were observed at m/
z ¼ 1072.45 [M]þ for 5, 1067.96 [M þ 1]þ for 6, 1068.63 [M þ 1]þ for
7,1071.85 [M]þ for 8 and 1216.76 [M]þ for 9 confirmed the proposed
structures.
Fig. 1. Absorption spectra of compounds 4, 5 and 9 in CHCl3 at 1 ꢀ10ꢁ5 M.
splitting Q band was observed at lmax 700 and 662 nm, indicating
the structure with non-degenerate D2h symmetry [39e41].
The UVeVis absorption spectra of metallophthalocyanines
(5e9) (Figs. 1 and 2) showed strong Q absorption bands between
673 and 712 nm with shoulders at 606e643 nm -sign of the
degenerate D4h symmetry- and B bands at ca. 340 nm [42] in
chloroform. The sharp bands in Figs. 1 and 2 are evidence of the
presence of non-aggregated species at measured concentration. It
has been well established that non-aggregated Pcs are extremely
important for their various applications [43]. The Q band of the
lead phthalocyanine complex (9) was red-shifted when compared
to the corresponding other studied phthalocyanine complexes
(4e8), suggesting that the non-planar effect of the bigger lead as
central atom.
Aggregation is usually depicted as a coplanar association of rings
progressing from monomer to dimer and higher order complexes. It
is dependent on the concentration, nature of the solvent, nature of
the substituents, type of the complexed metal ions and tempera-
ture. In this study, the aggregation behavior of the studied phtha-
locyanine compounds (4e9) was investigated at different
concentrations in DMSO. In DMSO, as the concentration was
increased, the intensity of absorption of the Q band also increased
and there were no new bands (normally blue shifted) due to the
aggregated species for the studied phthalocyanine compounds
(4e9), (Fig. 3 as an example for compound 9). BeereLambert law
was obeyed for these compounds in the concentrations ranging
from 1.2 ꢀ 10ꢁ5 to 2 x 10ꢁ6 M in DMSO.
3.1.3. UVeVis absorption spectra
The metal-free (4) and metallophthalocyanines (5e9) exhibit
typical electronic spectra with two strong absorption regions, one
around ca. 300 nm is called as the ‘‘B’’ or Soret band because of
electronic transitions from deeper
levels, while the other one at 600e750 nm is called as the ‘‘Q’’ band,
due to electronic transitions from -HOMO to *-LUMO energy
p-HOMO to n*-LUMO energy
p
p
levels [37]. One of the best indicators of the formation of phtha-
locyanines is their UVeVis spectra in dilute solution (Figs. 1 and 2).
The Q band of the metal-free phthalocyanine was observed as
splitted two bands due to D2h symmetry, as Qx and Qy bands
[38,39]. The electronic absorption spectrum of compound 4 in
chloroform solution at room temperature is shown in Fig. 1. The
Fig. 2. Absorption spectra of compounds 6, 7 and 8 in CHCl3 at 1 ꢀ10ꢁ5 M.

3812
1.8
R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
1.8
1.6
1.4
1.2
1
1.6
1.4
1.2
1
y = 141033x
2
R
= 0.993
0.8
0.6
0.4
0.2
0
A
B
C
0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-05 1.20E-05
Concentration (M)
D
E
F
0.8
0.6
0.4
0.2
0
300
400
500
600
700
800
Wavelength (nm)
Fig. 3. Absorption spectra changes of compound 9 in DMSO at different concentra-
tions: 12 ꢀ 10ꢁ6 (A),10 ꢀ 10ꢁ6 (B), 8 ꢀ 10ꢁ6 (C), 6 ꢀ 10ꢁ6 (D), 4 ꢀ 10ꢁ6 (E), 2 ꢀ 10ꢁ6 (F)
M. (Inset: Plot of absorbance versus concentration).
3.1.4. Fluorescence spectra
The fluorescence behavior of the metal-free (4), zinc (5) and lead
(9) phthalocyanines were studied in DMSO. Fig. 4 shows the
absorption, fluorescence emission and excitation spectra of these
complexes in DMSO. The shapes of the excitation spectra were
similar to absorption spectra for the metal-free (4) and zinc
phthalocyanine (5) compounds (Fig. 4a and b) suggesting that the
proximity of the wavelength of each component of the Q band
absorption to the Q band maxima of the excitation spectra for
phthalocyanine derivatives 4 and 5 suggests that the nuclear
configurations of the ground and excited states are similar and not
affected by excitation. However, for the lead phthalocyanine
compound (9), the shape of excitation spectra was different from
the absorption spectra in that the Q band of the former showed two
peaks in the Q band region, Fig. 4c, unlike the narrow Q band of the
latter. This attribute that there are changes in the molecule
following excitation most likely due to the larger lead metal being
out of the plane of the phthalocyanine ring.
Fluorescence emission and excitation peaks for compounds 4, 5
and 9 in DMSO are listed in Table 1. Fluorescence emission peaks
were observed at 710 nm for 4, 692 nm for 5 and 710 nm for 9 in
DMSO. While the observed Stokes shift of the substituted zinc
phthalocyanine complex (5) is higher, the metal-free (4) and lead
(9) phthalocyanine compounds are lower than unsubstituted ZnPc
(Std-ZnPc), (Table 1). The nickel (6), cobalt (7) and copper (8)
phthalocyanine compounds did not show fluorescence in DMSO.
Fig. 4. Absorption, fluorescence, emission and excitation spectra for: (a) compound 4,
(b) compound 5 and (c) compound 9 in DMSO. Excitation wavelengths ¼ 640 nm for 4,
650 nm for 5 and 670 nm for 9.
quenching. Thus the decrease in the FF values for substituted
phthalocyanine compounds in the presence of the ring substituents
suggests that the substituents more quench the excited singlet state.
The substituted metal-free complex (4) shows higher FF values than
other studied Pc compounds in DMSO (Table 2).
3.2. Photophysical properties of metal-free (4), zinc (5) and lead (9)
phthalocyanines
Fluorescence lifetime (sF) is the average time a molecule stays in
its excited state before fluorescence, and its value is directly related
3.2.1. Fluorescence quantum yields and lifetimes
The fluorescence quantum yields (FF) of metal-free (4), zinc (5)
and lead (9) phthalocyanine compounds are typical of Pc compounds
in DMSO, but the FF values of lead phthalocyanine compound (9) is
lower than for other studied phthalocyanine compounds (4 and 5) in
DMSO (Table 2) suggesting that there are more changes in the
molecule following excitation in DMSO most likely due to the larger
lead metal being out of the plane of the phthalocyanine ring. While
the FF values of the substituted metal-free and lead phthalocyanine
compounds are lower than unsubstituted ZnPc (Std-ZnPc), the FF
value of zinc phthalocyanine complex is similar with experimental
error. A decrease in fluorescence intensity (hence yield) may occur in
the presenceofsubstituted groupswhich increaseof the fluorescence
Table 1
Absorption, excitation and emission spectral data for unsubstituted and substituted
phthalocyanines in DMSO.
Compound Q band
lmax, (nm)
671, 702
(log ε)
Excitation Emission
lEx, (nm) lEm, (nm) DStokes, (nm)
4.55, 4.58 671, 703
Stokes shift
4
5
9
710
692
710
682
8
12
2
680
708
672
4.72
5.10
5.14
681
671, 705
672
Std-ZnPca
10
a
Data from Ref. [50].

R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
3813
Table 2
1.2
1.2
1
0 sec
Photophysical and photochemical parameters of unsubstituted and substituted
phthalocyanines in DMSO.
5 sec
1
0.8
0.6
0.4
0.2
0
10 sec
15 sec
20 sec
25 sec
30 sec
0.8
0.6
0.4
0.2
0
Compound
FF
s
F (ns)
s
0 (ns)
kF (sꢁ1
)
Fd
FD
(x107)a
(x 10ꢁ5
)
4
5
9
0.19
0.17
0.13
0.20
3.95
2.99
1.07
1.22
20.79
17.63
8.21
4.81
5.68
12.14
1.47
8.08
6.76
36.24
2.61
0.17
0.78
0.22
0.67
15
0
5
10
20
25
30
Std-ZnPcb
6.80
Time (sec)
a
kF is the rate constant for fluorescence. Values calculated using kF
Data from Ref. [50].
¼
FF/sF.
b
to that of FF. The longer the lifetime means the higher the fluo-
rescence quantum yield. Any factor that shortens the fluorescence
lifetime of a fluorophore (phthalocyanine in this study) indirectly
reduces the value of FF. Such factors include internal conversion
and intersystem crossing. As a result, the nature and the environ-
ment of a fluorophore determine its fluorescence lifetime. Lifetimes
300
400
500
600
700
800
Wavelength (nm)
Fig. 5. A typical spectrum for the determination of singlet oxygen quantum yield. This
determination was for compound 5 in DMSO at a concentration of 1.0 ꢀ 10ꢁ5 M (Inset:
Plots of DPBF absorbance versus time).
of fluorescence (sF, Table 2) were calculated using the Stricklere-
Berg equation. Using this equation, a good correlation has been
found between experimentally and the theoretically determined
lifetimes for the unaggregated molecules [23]. Thus we suggest that
the sF values obtained using this equation are an appropriate
measure of fluorescence lifetimes. Generally, the sF values of the
studied phthalocyanine compounds (4, 5 and 9) are within the
range reported for Pc compounds [44]. While the sF values are
higher for substituted metal-free (4) and zinc (5) phthalocyanine
compounds, the sF value of lead phthalocyanine compound (9) is
lower when compared to unsubstituted ZnPc (Std-ZnPc) (Table 2).
For the substituted complexes, longer sF value is obtained for the
metal-free (4) phthalocyanine compound compared to other
studied phthalocyanine complexes (5 and 9).
the ground state of oxygen. There was no change in the Q band
intensity of studied phthalocyanine compounds (4, 5 and 9) during
the FD determination, confirming that complexes were not
decompose during singlet oxygen studies. It is believed that during
photosensitization, the phthalocyanine is firstly excited to the
singlet excited state and through intersystem crossing reaches the
triplet state, then transfers its energy to ground state oxygen,
P
O2(3 g), converted into its excited state (singlet oxygen), O2(1Dg).
This singlet oxygen is the chief cytotoxic species, which subse-
quently oxidizes the surrounding substrates. This oxidation is the
key of the Type II mechanism for PDT.
The value of FD is higher for studied zinc phthalocyanine
compound (5) when compared to respective Std-ZnPc complex in
DMSO. But, the FD values of studied metal-free (4) and lead (9)
phthalocyanine compounds are lower than Std-ZnPc in DMSO
(Table 2). When compared to the FD values among the studied
phthalocyanine compounds (4, 5 and 9), substituted zinc phthalo-
cyanine compound (5) shows highest FD values in all studied
compounds.
The natural radiative lifetime (s0) and the rate constants for
fluorescence (kF) values are also given in Table 2. s0 values of the
studied phthalocyanine compounds (4, 5 and 9) are longer than
Std-ZnPc in DMSO. The substituted metal-free phthalocyanine
compound (4) showed the longest s0 values when compared to
other substituted complexes (5 and 9) in DMSO. The rate constants
for fluorescence (kF) values of studied phthalocyanine compounds
(4, 5 and 9) are also higher than Std-ZnPc in DMSO. The kF value of
substituted lead phthalocyanine compound (9) is highest among
the studied phthalocyanine compounds in DMSO.
3.3.2. Photodegradation study
Photodegradation of the molecules under light irradiation can
be used to study their stability and this is important for their
application as photocatalytic reactions (such as photosensitization).
Photodegradation is an oxidative degradation of a photosensitizer
molecule with time into lower molecular weight fragments under
3.3. Photochemical properties of metal-free (4), zinc (5) and lead
(9) phthalocyanines
3.3.1. Singlet oxygen quantum yields
An effective photosensitizer must be very productive in gener-
ating singlet oxygen for photocatalytic reactions such as PDT.
Energy transfer between the triplet state of a photosensitizer (such
as phthalocyanine) and the ground state of molecular oxygen leads
to the production of singlet oxygen and must be highly efficient to
generate large amounts of singlet oxygen. This is quantified by the
singlet oxygen quantum yield (FD) and this parameter can be give
an indication of the potential of compounds to be used as photo-
sensitizers in PDT applications. In this study, singlet oxygen
quantum yields (FD) of the studied phthalocyanine compounds (4,
5 and 9) were determined in DMSO via chemical method using
DPBF as a quencher. The disappearance of DPBF absorption was
monitored using UVevis spectrophotometer (Fig. 5 as an example
for compound 5). Many factors are responsible for the magnitude of
the determined quantum yield of singlet oxygen 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
Fig. 6. The photodegradation of compound 5 in DMSO showing the disappearance of
the Q band at 10 min intervals. (Inset: Plot of Q band absorbance versus time).

3814
500
R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
Table 3
Fluorescence quenching data for unsubstituted and substituted phthalocyanines in
DMSO.
[BQ]=0
400
300
200
100
0
Compound
KSV (Mꢁ1
)
kq/1010(dm3 molꢁ1 sꢁ1
)
4
5
9
24.69
22.33
20.11
31.90
0.62
0.75
1.88
2.61
Std-ZnPca
[BQ]=saturated
a
Data from Ref. [50].
transfer with ease such as phthalocyanine-quinone systems have
proved to be favored candidates for understanding of energy
transfer process [27,45]. The fluorescence quenching of studied
phthalocyanine compounds (4, 5 and 9) by BQ in DMSO was found
to obey SterneVolmer kinetics. Fig. 7 shows the quenching of
compound 4 by BQ in DMSO as an example. The slope of the plots
shown at Fig. 8 gave KSV values of the studied phthalocyanine
compounds. The SterneVolmer plots for all studied phthalocyanine
compounds (4, 5 and 9) gave straight lines, depicting diffusion-
controlled quenching mechanisms. Quinones have high electron
affinities and their involvement in electron transfer processes is
well documented [46]. The energy of the lowest excited state for
quinones is greater than the energy of the excited singlet state of
phthalocyanine compounds [47]. Therefore, energy transfer from
the excited phthalocyanine molecule to BQ is not likely to occur.
Moreover, phthalocyanine compounds are known to be easily
reduced. Therefore, fluorescence quenching of phthalocyanine
compounds by BQ is via excited state electron transfer from the
phthalocyanine to the BQ [48]. The KSV and bimolecular quenching
constant (kq) values for the BQ quenching of phthalocyanine
compounds in DMSO are listed in Table 3. The KSV values of the
substituted phthalocyanine compounds (4, 5 and 9) are lower than
Std-ZnPc in DMSO. When compared the substituted complexes,
compound 4 showed the highest KSV values, while compound 9
showed the lowest KSV values in DMSO. The substitution of the
phthalocyanine framework with 3,5-dimethylpyrazole-1-methoxy
groups seems to decrease the KSV values of the phthalocyanine
compounds. The bimolecular quenching constant (kq) values of the
studied phthalocyanine compounds (4, 5 and 9) were also lower
than for Std-ZnPc in DMSO, thus substitution with 3,5-
dimethylpyrazole-1-methoxy groups seems to decrease the kq
values of the complexes. The kq values of the studied phthalocya-
nine compounds (4, 5 and 9) were found to be close to the
650
700
750
800
850
Wavelength (nm)
Fig. 7. Fluorescence emission spectral changes of compound 4 (1.00 ꢀ 10ꢁ5 M) on
addition of different concentrations of BQ in DMSO. [BQ] ¼ 0, 0.008, 0.016, 0.024, 0.032,
0.040 M and saturated with BQ.
light. Photodegradation generally depends on the structure of the
molecule, concentration, solvent and light intensity [30].
The spectral changes observed for all the studied phthalocya-
nine compounds (4, 5 and 9) during light irradiation are as shown
in Fig. 6 (using complex 5 in DMSO as an example). The collapse of
the absorption spectra without any distortion of the shape confirms
photodegradation not associated with phototransformation for
studies phthalocyanine compounds (4, 5 and 9).
The photodegradation quantum yield (Fd) values of the studied
phthalocyanine compounds (4, 5 and 9) in DMSO are given in Table 2.
Stable phthalocyanine molecules show the Fd values as low as 10ꢁ6
[44]. All studied phthalocyanine compounds(4, 5 and 9) areless stable
to degradation compared to Std-ZnPc in DMSO (Table 2) because the
Fd values of all studied phthalocyanine compounds (4, 5 and 9) are
higher than Std-ZnPc in DMSO (Table 2). Thus the substitution of
phthalocyanine compounds with 3,5-dimethylpyrazole-1-methoxy
groups seems to decrease the stability of these complex in DMSO.
The substituted lead phthalocyanine compound (9) is the lowest
stable derivative among the studied phthalocyanine compounds
suggesting that heavy atom effect of the lead atom.
3.4. Fluorescence quenching studies of metal-free (4), zinc (5) and
lead (9) phthalocyanines by 1,4-benzoquinone (BQ)
diffusion-controlled limits, w 1010 Mꢁ1 ꢁ1, which is in agreement
s
with the EinsteineSmoluchowski approximation at room temper-
ature for diffusion-controlled bimolecular interactions [49].
Phthalocyanine complexes may also be used as photosynthetic
mimickers. An essential requirement for an effective photosyn-
thetic mimicker is the ability to undergo excited state charge
4. Conclusion
4
In this paper, the synthesis of new highly soluble tetrakis-3,5-
dimethylpyrazole-1-methoxy substituted metal-free (4), zinc (5),
nickel (6), cobalt (7), copper (8) and lead (9) phthalocyanines have
been reported. The new compounds have been characterized by IR,
UVeVis, 1H and 13C NMR, mass spectroscopy and elemental analysis.
The photophysical and photochemical properties of metal-free (4),
zinc (5) and lead (9) phthalocyanine compounds have also been
investigated in DMSO for comparison of the central metal effect on
these properties. All the compounds show excellent solubility in
most solvents such as chloroform, toluene, DMF, DMSO etc. In the
UVeVis spectra, while the metal-free complex (4) shows splitting Q
band, the metallophthalocyanines (5e9) exhibit single narrow Q
bands as expected and support the formation of phthalocyanine
complexes. The substitution of the 3,5-dimethylpyrazole-1-methoxy
substituents on the phthalocyanine ring increased the wavelength of
5
1.9
9
1.6
1.3
1
0
0.005
0.01
0.015
0.02
0.025
[BQ]
0.03
0.035
0.04
0.045
Fig. 8. SterneVolmer plots for BQ quenching of 4,
5
and 9 in DMSO. [MPc]
w1.00 ꢀ 10ꢁ5 M [BQ] ¼ 0, 0.008, 0.016, 0.024, 0.032, 0.040 M.

R. Bayrak et al. / Journal of Organometallic Chemistry 696 (2011) 3807e3815
3815
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_
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zon/Turkey).
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