Lipophilic phthalocyanines for their potential interest in photodynamic therapy: Synthesis and photo-physical properties

Article abstract of DOI:10.1016/j.tet.2013.09.035

Several phthalocyanines with different peripheral substituents were prepared and characterized by MALDI-TOF, ¹H NMR, UV-vis, fluorescence, and singlet oxygen quantum yields and retention time in HPLC normal phase. Zinc was used as a central metal ion to increase the photodynamic therapy efficiency. Phthalonitrile or 4-nitro phthalonitriles were used as starting materials. The influence of lipophilicity on the photophysical and photochemical properties was evaluated.

Full text of DOI:10.1016/j.tet.2013.09.035

Tetrahedron 69 (2013) 10116e10122
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Lipophilic phthalocyanines for their potential interest in
photodynamic therapy: synthesis and photo-physical properties
,
,
b
c,d,
Albert Moussaron a b, Philippe Arnoux a , Regis Vanderesse e, Estelle Sibille f,
ꢀ
f
a,b,e,
*
ꢀ
Patrick Chaimbault , Celine Frochot
a
ꢀ
ꢀ
ꢀ
ꢀ ꢀ
Universite de Lorraine, Laboratoire Reactions et Genie des Procedes (LRGP), UMR 7274, Nancy F-54000, France
b CNRS, LRGP, UMR 7274, Nancy F-54000, France
c
ꢀ
ꢀ
Universite de Lorraine, Laboratoire de Chimie Physique Macromoleculaire (LCPM), FRE CNRS 3564, Nancy F-54000, France
d CNRS, LCPM, FRE CNRS 3564, Nancy F-54000, France
e
ꢀ
ꢀ
GDR CNRS 3049 “Medicaments Photoactivables-Photochimiotherapie (PHOTOMED)”, France
Laboratoire de Chimie et Physique Approche Multiechelle des Milieux Complexes LCP-A2MC (EA 4632) ICPM, Universite de Lorraine, 1 Boulevard Arago,
f
ꢀ
ꢀ
57078 Metz Cedex 3, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 April 2013
Received in revised form 9 September 2013
Accepted 11 September 2013
Available online 19 September 2013
Several phthalocyanines with different peripheral substituents were prepared and characterized by
MALDI-TOF, 1H NMR, UVevis, fluorescence, and singlet oxygen quantum yields and retention time in
HPLC normal phase. Zinc was used as a central metal ion to increase the photodynamic therapy effi-
ciency. Phthalonitrile or 4-nitro phthalonitriles were used as starting materials. The influence of lip-
ophilicity on the photophysical and photochemical properties was evaluated.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Synthesis
Phthalocyanines
Photodynamic therapy
Lipophylic
Bathochromic
1. Introduction
energy from the excited matter can be transferred to surrounding
molecules. Thus, a photosensitizer is classically defined as a chem-
Phthalocyanines (Pcs) are synthetic porphyrin (Por) analogs
(tetrabenzo[5,10,15,20]tetra-azaporphyrin) and planar aromatic
macrocycles consisting of four indol units linked together by ni-
trogen atoms. Because of the two-dimensional delocalization of
ical entity that, upon absorption of light, induces a chemical or
physical alteration of another chemical entity. This allows the
generation of reactive oxygen species (ROS) including singlet oxy-
gen (1O2), which is believed to be the major cytotoxic agent.8,9 Thus,
the delivery of a photosensitizer into cancer-associated cells means
that a tumor can be specifically destroyed.
The successful achievement of any PDT concept depends cru-
cially on the nature of the photosensitizer.10 Early preparations of
photosensitizers for PDT were based on a complex mixture of
porphyrins called haematoporphyrin derivative (HpD). Today,
PhotofrinÒ, a purified HpD derivative, is the most frequently used
clinically. Another PDT compound is temoporfin (meta-tetra(hy-
droxyphenyl)chlorine, m-THPC, FoscanÒ). Temoporfin is effective
for the palliative treatment of head and neck cancers and it was
approved in Europe for such treatment in 2001. The benzopor-
phyrin derivative verteporfin (VisudyneÒ) was also recently ap-
proved for use in man, but it has only been developed for the
treatment of age-related macular degeneration, and is not indicated
for therapy against cancer.11 Concerning photosensitizers for
their 18p-electron, Pcs have unique physical and optical properties.
Their qualities have led to numerous interests in many fields, such
as pigments or dyestuffs, organic electronic devices,1 thin-film for
gas detection2 and electro-chromic devices,3 solar photovoltaic
cells,4 nonlinear optical materials5 and photodynamic therapy
(PDT). PDT is an emerging non-invasive technique for the treatment
of a variety of cancerous tumors. It involves the light activation of
a photo-responsive molecule called a photosensitizer, in the pres-
ence of oxygen.6,7 After light irradiation of the photosensitizer, the
* Corresponding author. Tel.: þ33 3 83 17 51 15; fax: þ33 3 83 37 81 20; e-mail
addresses: albert.moussaron@insa-lyon.fr (A. Moussaron), celine.frochot@uni-
v-lorraine.fr (C. Frochot).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.09.035

A. Moussaron et al. / Tetrahedron 69 (2013) 10116e10122
10117
topical application to treat skin lesions, proto-porphyrin IX (PpIX)
can be produced in nucleated cells after local application of either
aminolevulinic acid (ALA) or methyl aminolevulinate (mALA) at the
site of a skin cancer or pre-cancerous lesion. This finding led to the
approval of ALA in the USA, and of mALA in Europe for use in man.12
The limiting factor of all the drugs mentioned above is their low
absorbance in the optical window for photosensitizer excitation,
which reduces their efficiency in terms of 1O2 production. To
overcome this problem, Por isomers, such as the porphycenes,13e15
expanded Por,16 such as the texaphyrins,17,18 and Pcs have been
developed and are currently being tested for PDT applications.19,20
Pcs are among the most promising second-generation photo-
sensitizers. Because of their low solubility in water, different strate-
gies are used to modify their chemical structure or to encapsulate the
Pcs in nanocarriers.22e25 The latter approach allows the enhance-
ment of the therapeutic effect by increasing both the biodisponibility
and the bioavailability of the drug. Furthermore, treatment is focused
to the desired site and the comfort of the patient simultaneously
improved, by reducing side effects, such as photo-damage or pho-
tosensitivity. Some carriers have been previously described, in-
cluding liposomes, Cremophor EL based emulsions, micelles,26
nanoparticles, and recently novel lipid nanoparticles (LNP) com-
posed of a hydrophobic inner core surrounded by a hydrophilic shell.
These LNP present an outstanding colloidal stability even in bi-
ological media and are suitable for the encapsulation of highly li-
pophilic compounds, such as photosensitizers.27,28
bioavailability and stability, and deliver photosensitizers to the
target tissues.22
In this paper, we describe the synthesis of different hydrophobic
Pcs to encapsulate them in the near future into LNP with lipophilic
oil cores (in progress). Different manufacturing schemas were de-
veloped to obtain the best yield for each Pc.
As shown in Scheme 1, different Pcs have been synthesized by
different routes starting from phthalonitrile for non-substituted Pc
and from 4-nitrophthalonitrile for the substituted ones (Table 1).
The aim of this study was to develop new Pcs that could be
encapsulated or covalently coupled to nanoparticles with the
highest PDT efficiency in terms of photo-physical properties (high
epsilon and high 1O2 formation). Six Pcs with different substituents
were synthesized. Their manufacture was optimized to obtain good
yields, and their photo-physical properties were studied.
Scheme 1. Synthesis routes for zinc Pcs (a) K2CO3, DMSO, (b) 1. Li, 1-pentanol; 2.
CH3COOH; 3. Zn(CH3COO)2, DMF, (c) Zn(CH3COO)2, DBU, 1-pentanol, (d) Zn(CH3COO)2,
DMAE.
2. Results and discussion
2.1. Synthetic strategy and characterization
Among the different kinds of Pcs, zinc Pcs are of particular in-
terest and have been studied in vitro and in vivo. The presence of
the diamagnetic central Zn2þ metal in the Pc nucleus is known to
improve the triplet state lifetime as well as the yield of 1O2.19
Therefore, we decided to use zinc as the central ion in our Pcs. To
that end, anhydride zinc acetate was used as the metal salt during
synthesis.
Pcs were first synthesized in 1907 by Braun and Tcherniac29
during the fabrication of o-cyanobenzamide from phthalimide
and phthalic acid. Since their discovery much information con-
cerning their synthesis, photochemical, and photophysical prop-
erties have emerged.21 In the 1930s, Lindstead and Robertson
determined the structure of metal-free unsubstituted Pcs using X-
ray diffraction analyses.30e34 Pcs have been used as blue-green dyes
and pigments for long time. For over twenty years, Pcs and their
derivatives have been used as photosensitizers for PDT against
cancer.19,35,36 Pcs and PDT are also used for other treatments, such
as against intimal hyperplasia37 and some mycotic infections, in
particular Candida albicans.38 In addition, it has been shown that
aluminum Pc has a bactericidal effect against Escherichia coli39 and
virucidal activity on herpes simplex virus type 1 (HSV-1).40 Pho-
tosensÒ, a mixture of aluminum chloride Pcs with 1 to 4 sulfonated
side-groups with an average sulfonation value of 3 was developed
at the general Physics Institute of the Russian Academy of Sciences
and is commercialized in Russia by NIOPIK. Clinical trials have been
performed that included 47 patients with pre-cancerous lesions of
the cervix or non-invasive cervical lesions. The results are very
promising.41,42
Unsubstituted Pcs undergo aggregation caused by
pep in-
teractions of the planar macrocyclic molecules. This aggregation is
undesirable because the absorbed energy is dissipated by internal
conversion to the ground state rather than through triplet forma-
tion followed by a possible 1O2 production. In order to prevent the
stacking of planar molecules and to decrease aggregation, we in-
troduced peripheral substituents, such as long alkyl chains or bulky
substituents.44e46 Different substituents were chosen to increase
the hydrophobicity of the compounds. First we synthesized the
unsubstituted Pc well-known as CGP55847Ò, which is undergoing
phase I and phase II clinical trials against squamous cell carcinomas
of the upper aerodigestive tract,47 as a reference and then some
substituted Pcs to evaluate the effect of peripheral substituents on
the hydrophobicity and the photo-physical properties of the com-
pounds. We chose as peripheral substituents 4-phenoxybenzoic
acid, 4-isopropoxy and dodecylsulfanyl. 4-Phenoxybenzoic acid
could allow binding of the Pcs to nanocarriers via an amide bond.
Sulfide substituents are thought to induce a bathochromic shift
effect on the maximum absorption of Pcs and then a near-infrared
(NIR) shifted absorption.48,49
Many potent Pc photosensitizers are hydrophobic and poorly
water-soluble, which limits their therapeutic applications. As a re-
sult, advanced delivery systems and different strategies are studied
to improve the effectiveness of PDT. Thus, many teams are working
on the synthesis of water-soluble Pcs.43
Results have proven that using nanoparticles as carriers of
photosensitizers is a very promising route. Nanoparticles have the
potential to increase photosensitizer aqueous solubility,
For the starting phthalonitrile, we used a base catalyzed reaction
in DMSO with 4-nitrophthalonitrile. K2CO3 was used as the base for
nucleophilic aromatic displacement.50,51 4-isopropoxyphthaloni
trile (1) and 3-(3,4-dicyano-phenoxy)-benzoic acid (2) were

10118
A. Moussaron et al. / Tetrahedron 69 (2013) 10116e10122
Table 1
Phthalocyanine formulas
Compound
Phthalocyanine
X1
X2
4
5
ZnPc
ZnPceCOOH
H
H
H
HOOC
O
O
O
6
ZnPc(Oipr)4
7
8
9
ZnPc(SC12H25)
4
S
S
O
ZnPc[(Oipr)3eCOOH]
HOOC
HOOC
O
O
ZnPc[(SC12H25)3eCOOH]
S
synthesized, respectively, using the procedures of Leznoff et al.52
and Chidawanyika et al.53 Pcs were obtained through the usual
direct cyclotetramerization reaction of phthalonitriles in the pres-
ence of a reducing agent, such as lithium for the free-metal Pcs (the
first step of the synthesis of ZnPceCOOH)50 or a metal salt, such as
zinc acetate for the metal Pc. For ZnPceCOOH (5), the procedure
described by Kliesch et al. was used for the fabrication of the zinc Pc
in two steps. First, we synthesized the metal-free Pc in 1-pentanol
in the presence of lithium. Then, zinc was inserted using zinc ace-
tate in DMF.50 For the other Pcs, known procedures exist for direct
cyclotetramerization in 1-pentanol as the solvent and DBU as the
base43,54e56 or in N,N-dimethylethanolamine as both solvent and
base.43,57e60
Although we used known procedures to synthesize zinc Pcs, we
developed and optimized the purifications strategies and some
yields compared to previously described methods. ZnPc was syn-
thesized via a novel route known for the fabrication of other Pcs.
The yield of this method was 48%. This value is approximately the
same as that described by Luzyanin et al. and Kluson et al.61,62 Bayo
et al. obtained a higher yield (82%) but the purification of the
compounds was a longer process.63 ZnPc(Oipr)4 was obtained at
44% yield. This value is higher than that obtained by Leznoff et al.52
and approximately the double of that obtained by Liu et al.59
Fig. 1. Absorbance of phthalocyanines in ethanol.
Fluorescence emission and 1O2 production of the different Pcs
were recorded (Fig. 3). The introduction of a substituent increases
the maximum of absorption and fluorescence emission wave-
lengths and this depends on hydrophobicity (Figs. 1 and 2). As
expected, the highest absorption and emission wavelength is for
ZnPc(SC12H25)4 was synthesized with a similar yield to that re-
ZnPc(SC12H25 4. This is in accordance with reports that sulfanyl
)
ported in the literature using a manufacture procedure in DMAE as
both the solvent and base in the place of quinoline.64 Also, we
synthesized two new Pcs, ZnPc[(S12C12)3eCOOH] and ZnPc
[(Oipr)3eCOOH] using the procedure of DMAE. Yields of those
molecules were respectively 43 and 20%.
substituents have a bathochromic shift effect on the maximum
absorption of Pcs and then an NIR shifted absorption.48,49
If we compare the fluorescence and 1O2 quantum yields, the
most interesting compounds seem to be ZnPc and ZnPc(OiPr)4 that
both present an excellent 1O2 quantum yield of around 0.70. While
ZnPc shows good fluorescent properties (ØF¼0.27), the fluores-
cence of ZnPc(Oipr)4 is totally quenched. In terms of PDT agents,
depending on the applications envisaged, all these new compounds
are potentially good candidates except for ZnPc[(Oipr)3eCOOH]
that has a low 1O2 quantum yield.
2.2. Photo-physical properties
As shown in Fig. 1, whatever the substituents, no significant
change was observed in the shape of ZnPc and its derivatives: the
UVevisible spectrum remained unchanged with a maximum be-
tween 666 nm and 688 nm in ethanol depending on the
substituents.
2.3. Physicalechemical properties
Epsilons have been estimated at the maximal absorbance
wavelengths, and are given and compared in Fig. 2. The highest
log ε is calculated for ZnPc and ZnPc(Oipr)4, respectively, as 5.32 and
5.29, whereas the lowest are for the S-substituted Pcs (4 for
To compare the hydrophobicity of our molecules, we attempted
to determine the partition coefficient (log P) in octanol and water.
Unfortunately, because of the high hydrophobicity, we did not
manage to determine properly the concentration of our molecules
in water. This approach does not seem to be the most appropriate
one to evaluate the hydrophobicity of these Pcs. Instead, we chose
another technique. We determined the retention time of each
ZnPc(SC12H25)4 and 3.2 for ZnPc(SC12H25)3eCOOH). Thus, against
high maximal absorbance wavelength in NIR, sulfide Pcs are less
interesting candidates than other substituted Pcs for PDT because
of their lower log ε.

A. Moussaron et al. / Tetrahedron 69 (2013) 10116e10122
10119
Fig. 2. Comparison of the characteristics of phthalocyanines.
and 5.41 min for ZnPc(Oipr)4) and the most hydrophobic is
ZnPc(SC12H25)4. This is due to the long alkyl chain C12. The com-
parison of retention times and hydrophobicities is described in
Fig. 2.
3. Conclusion
Six hydrophobic Pcs were synthesized by different routes in
good yields. They all presented high hydrophobicity when com-
pared by normal phase HPLC. By changing the substituents it is
possible to modulate the hydrophilic/hydrophobic balance. Physi-
cal, chemical, and photo-physical properties of these Pcs were
evaluated. Some of them, especially ZnPc and ZnPc(Oipr)4, present
good to excellent photo-physical properties, such as good 1O2
quantum yield and high wavelength of excitation. These molecules
could be very good candidates for PDT applications. ZnPc and
ZnPc(Oipr)4 have indeed the highest quantum yield of singlet ox-
ygen. ZnPc is already undergoing clinical trials phase I and phase II
against squamous cell carcinomas of the upper aerodigestive
tract.47 ZnPc(Oipr)4 presents an advantage: its maximum absorp-
tion wavelength is higher than ZnPc leading to a potential better
penetration of light into the tissues. So, the next step will be the
encapsulation of these compounds into LNPs followed by in vitro
and in vivo studies.
Fig. 3. Fluorescence spectra of phthalocyanines in ethanol (lexc¼357 nm) DO¼0.2.
molecule in normal phase HPLC using n-hexane:ethyl acetate as
the eluting solvents. A high retention time indicates a low hy-
drophobicity and vice versa. When retention times were com-
pared, as expected, all the compounds with
a hydrophilic
carboxylic group present higher retention times than the
same compounds without carboxylic groups (5.52 min for
ZnPc and respectively 14.60 min, 14.60 min, and 16.41 for
ZnPc(SC12H25)3eCOOH, ZnPc(OiPr)3eCOOH and ZnPceCOOH). The
introduction of 4 substituents decreases the retention time com-
pared to the unsubstituted Pc (2.05 min for ZnPc(SC12H25 4
)

10120
A. Moussaron et al. / Tetrahedron 69 (2013) 10116e10122
4. Experimental details
At this wavelength, the absorbance of the samples was set to
around 0.2. Rose Bengal was chosen as a reference solution be-
4.1. General
cause of its high 1O2 quantum yield production in ethanol
(
length (357 nm) of both the reference and the sample solutions
were set to around 0.2.
FD(ref)¼0.68).66 The absorbance value at the excitation wave-
4.1.1. Materials. Unless otherwise stated, reagents were purchased
from chemical companies and used without further purification.
Reagent grade solvents were used as received. Thin-layer chro-
matography (TLC) was carried out on Merck silica gel 60 F254 plates
(Merck Chimie S.A.S., Fontenay Sous Bois, France) and eluted with
the appropriate solvent mixtures. The TLC spots were visualized by
UV light. Chromatography columns were using Merck silica gel
Analytic HPLC were performed on a SHIMADZU CTO-20A/
ꢀ
Prominence column oven (Shimadzu, Marne la vallee, France),
with LC Solution program Release 1.23 SP1 on a Varian Chromspher
5
m
m Si 250ꢃ100 mm column and using a linear gradient of ethyl
acetate in n-hexane (10%d20 min/100%d10 min/100%d
5 min/10%) with 3.5 mL/min flow. The detection was performed
at two wavelengths (350 and 690 nm) using a SHIMADZU SPD-
20AV/Prominence UV/VIS detector.
(40e63 mm; 230e400 mesh ASTM).
4.1.2. Equipment. 1H NMR and 13C (300 MHz) spectra
were recorded on a Bruker Advance 300 machine (Bruker, Wis-
senburg, Germany). Multiplicities are reported as follows:
s¼singlet, t¼triplet, q¼quadruplet, m¼multiplet. Chemical shifts
are reported in parts per million relative to the solvent peak
or TMS. Absorption spectra were recorded on a PerkineElmer
UVevisible spectrophotometer (Lambda 2, Courtabœuf, France).
ES Mass spectra were recorded on a Shimadzu LCMS 2010 EV
4.1.3. Synthesis
4.1.3.1. 4-Dodecylsulfanyl-phthalonitrile (3). Dodecylmercapto
thiol (3 g, 15 mmol) and 4-nitrophthalonitrile (2 g, 11 mmol)
were dissolved in 20 mL DMSO and stirred at room temperature
for 20 min under dry nitrogen. Then 5 g potassium carbonate
was added portion wise over 2 h. The reaction was left for 12 h
with stirring. Then it was monitored by TLC using diethyl
ether/petroleum ether (ratio 2:3; v:v) as the eluting solvent. The
crude product was precipitated out from the reaction mixture by
adding water, washed with water and oven-dried. The product
was purified using silica gel column chromatography with
diethyl ether/petroleum ether (ratio 2:3; v:v). The yield was 60%.
TLC Rf 0.8 2:3 diethyl ether:petroleum ether. The MS calculated
for C20H28N2S [MþH]þ m/z was 329.5 and the experimental
value found was 329.4. 1H NMR (300 MHz, chloroform-d6)
ꢀ
apparatus (Marne la Vallee, France).
MALDIeTOFMS analyses were carried out on a Bruker Reflex IV
time-of-flight mass spectrometer (Bruker Daltonic, Bremen, Ger-
many) equipped with the SCOUT 384 probe ion source fitted with
a nitrogen pulsed laser (337 nm, VSD-337ND model, Laser Science
Inc., Boston, MA). The laser output energy was 400 mJ/pulse. The
reflector voltage was 23 kV. Positives ions were accelerated with
a 200 ns extraction delay. Mass spectra were manually acquired
using Flex-control software (Bruker Daltonic, Bremen, Germany)
by accumulating four series of 100 laser shots. A 1 M solution of
2,5-dihydroxybenzoic acid (DHB) (Sigma Aldrich, Saint Quentin
Fallavier, France) in 50% acetonitrile, 0.1% trifluoroacetic acid (TFA)
(Merck, Darmstadt, Germany) matrix was used for MALDI analy-
ses. All deposits were performed using the dried-droplet method
d
(ppm) 0.87 (t, 3H, eCH3), 1.25 (m, 16H, eCH2), 1.45 (m, 2H,
eCH2), 1.69 (m, 2H, eCH2), 3.02 (t, 2H, eCH2, J1¼J2¼7.3 Hz),
7.48e7.52 (dd, 1H, benzyl), 7.55e7.56 (d, 1H, benzyl), 7.64e7.66
(d, 1H, benzyl).
with 1 m
L of both analyte and matrix. 10ꢀ4 M master solutions of
4.1.3.2. Zinc phthalocyanine (4). 1,8-Diazabicyclo[5.4.0]undec-
7-ene (1.2 mL, 8 mmol) was added to a mixture of phthalonitrile
(500 mg, 4 mmol) and zinc acetate (183 mg, 1 mmol) in 1-
pentanol (5 mL). The reaction mixture was stirred upon reflux
under dry nitrogen for 12 h. It was then cooled to room tem-
perature and poured into water. A few millilitre of ethanol were
added until the mixture became a homogeneous liquid solution.
Then the precipitate was filtered off and washed with five 5 mL
portions of methanol and five 5 mL portions of acetone. The yield
was 48%. 1H NMR (DMSO-d6): 8.28e8.31 (m, 8H, Ar), 9.45e9.48
(m, 8H, Ar). MALDIeTOF: C32H16N8Zn-calculated was 577.91 g/
mol and the experimental value found (Mþ) was 577 g/mol. Re-
tention time: 5.52 min. UVevis, lmax nm (log ε): ethanol, 666
(5.32).
analytes were used for analyses. The analyte was diluted 10-fold
when the MS signal obtained with the master solution was too
high.
External calibration was carried out using DHB matrix peaks and
a mixture of standard peptides (Bruker Daltonic, Bremen). The
following monoisotopic peaks were used: m/z 155.034
([DHBþH]þ), m/z 757.400 (bradikynin), m/z 1046.542 (human an-
giotensin II) and m/z 1533.860 (P14R). The calibration was consid-
ered successful if the rms error was in the range of ꢁ10e15 ppm for
TOFMS.
Absorption spectra were recorded on
a PerkineElmer
(Lambda EZ 210) double beam UVevisible spectrophotometer.
Fluorescence spectra were recorded on a Horiba Jobin Yvon
Fluorolog-3 (FL3-222) spectrofluorimeter equipped with a 450 W
Xenon lamp, a thermostated cell compartment (25 ꢂC), a R928
(HAMAMATSU Japan) UVevisible photomultiplier and a liquid
nitrogen-cooled InGaAs infrared detector (DSS-16A020L Electro-
Optical System Inc, Phoenixville, PA, USA). The excitation spec-
trometer is a SPEX double grating monochromator (1200 grating/
mm blazed 330 nm). The fluorescence was measured by the
UVevisible detector through a SPEX double grating mono-
chromator (1200 grating/mm blazed 500 nm). 1O2 production
was measured by the IR detector through a SPEX double grating
4.1.3.3. Zinc tetrakis (isopropoxy) phthalocyanine (6). 1,8-
Diazabicyclo[5.4.0]undec-7-ene (1.2 mL, 8 mmol) was added to
a mixture of 4-isopropoxyphthalonitrile (745 mg, 4 mmol) and zinc
acetate (183 mg, 1 mmol) in 1-pentanol (5 mL). As described above
for Zinc Pc, the reaction mixture was stirred upon reflux under dry
nitrogen for 12 h and then cooled to room temperature and poured
into water. A few millilitre of ethanol were added until the mixture
became a homogeneous liquid solution. Then the precipitate was
filtered off and washed with five 5 mL portions of water. The
product was purified using silica gel column chromatography with
diethyl etherepetroleum ether (ratio 7:3). The yield was 44%. 1H
NMR (DMSO-d6): 1.60e1.65 (m, 24H, eCH3), 5.22e5.29 (m, 4H,
eCH), 7.62e7.70 (m, 4H, Ar), 8.62e8.72 (m, 4H, Ar), 8.96e9.09 (m,
4H, Ar). MALDIeTOF: C44H40N8O4Zn gave a calculated value of
810.23 g/mol and that found experimentally (Mþ) was 809 g/mol.
monochromator (600 grating/mm blazed 1 mm). All spectra were
recorded using four optical faces quartz cells. Fluorescence
quantum yields (FF) were determined using a tetraphenyl por-
phyrin (TPP) solution in toluene as a fluorescence standard
(
FF(std)¼0.11).65 All molecules were dissolved in ethanol
(n¼1.36) and the fluorescence standard in toluene (nstd¼1.4968).
The excitation wavelength of Pcs and the standard was 357 nm.

A. Moussaron et al. / Tetrahedron 69 (2013) 10116e10122
10121
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Retention time: 5.41 min. UVevis, lmax nm (log ε): ethanol, 679
(5.29).
4.1.3.4. Zinc tetrakis (dodecylthio) phthalocyanine (7). A mixture
of 4-dodecylsulfanyl-phthalonitrile (1500 mg, 4.5 mmol) and zinc
acetate (275 mg, 1.5 mmol) in 2-dimethylaminoethanol (10 mL)
was stirred upon reflux under dry nitrogen for 12 h. Then the re-
action mixture was allowed to cool to room temperature and excess
water was added. The crude product was extracted with chloro-
form and the solvent was then evaporated. The crude product was
purified using silica gel column chromatography with chlor-
oformeTHF (ratio 3:1) as the eluting solvent. Afterward, the
resulting product was re-dissolved in chloroform and poured into
a mixture of watereacetone (ratio 5:1) and the precipitate was
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MALDIeTOF:
C80H112N8S4Zn-calculated value was 1379.45 g/
mol that found experimentally (Mþ) was 1380 g/mol. Retention
time: 2.05 min. UVevis, lmax nm (log ε): ethanol, 688 (4).
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4.1.3.5. Zinc (4-carboxyphenoxy)tris(isopropoxy) phthalocyanine
(8). Zinc acetate (2000 mg, 11 mmol) was added to a mixture of 4-
isopropoxyphthalonitrile (2200 mg, 12 mmol) and 4-(3,4-dicyano-
phenoxy)-benzoic acid (1000 mg, 4 mmol) in 2-dimethylamino
ethanol (25 mL) and the resulting combination was stirred upon
reflux for 12 h. Once cooled to 25 ꢂC, water (250 mL) was added and
the crude product was filtered off and oven-dried. The crude
product was dissolved in the minimum volume of DMF and was
purified by column chromatography on silica, starting with an el-
uent of diethyl ethereDMF (ratio: 98:2). Once the first fraction,
tetra-iso-propyl phthalocyanine, had come off, the eluent was very
slowly changed to pure DMF. The next fraction to come off was ZnPc
[(Oipr)3eCOOH] with a yield of 43%. 1H NMR (DMSO-d6): 1.22e1.31
(m, 18H, eCH3), 5.25e5.30 (m, 3H, eCH), 7.35e7.47 (m, 4H, Ar),
7.65e7.76 (m, 4H, Ar), 8.80e8.91 (m, 4H, Ar), 9.21e9.29 (m, 4H, Ar),
11.2 (s, 1H, eCOOH). MALDIeTOF: C48H38N8O6Zn-calculated value
was 888.26 g/mol and that found experimentally (Mþ) 887.2 g/mol.
Retention time: 14.6 min. UVevis, lmax nm (log ε): ethanol, 679
(4.4).
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4.1.3.6. Zinc (4-carboxyphenoxy)tris(dodecylthio) phthalocyanine
(9). The procedure for the synthesis of ZnPc[(SC12H25)3eCOOH]
was similar to that used for ZnPc[(Oipr)3eCOOH], except 4-
dodecylsulfanyl-phthalonitrile (1300 mg, 4 mmol) was used in-
stead of 4-isopropoxyphthalonitrile and the eluting solvent for
column chromatography was chloroformeTHF (ratio 2:1) for the
first fraction, which contained ZnPc(SC12H25)4 and then pure THF to
obtain the desired Pc. The yield was 20%. 1H NMR (DMSO-d6): 0.86
(t, 9H, eCH3), 1.22 (m, 60H, eCH2), 3.10e3.15 (t, 6H, eCH2),
7.01e8.31 (m, 16H, Ar), 11.2 (s, 1H, eCOOH). MALDIeTOF:
C
75H92N8O3S3Zn-calculated value of 1315.17 g/mol and that found
experimentally (Mþ) was 1314.7 g/mol. Retention time: 14.6 min.
UVevis, lmax nm (log ε): ethanol, 679 (3.2).
Supplementary data
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Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2013.09.035.
These data include MOL files and InChiKeys of the most important
compounds described in this article.
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