Efficient diborane-mediated synthesis of phthalocyanines carrying amino groups near the macrocycle

Article abstract of DOI:10.1016/j.poly.2012.07.089

N-(3,4-dicyanophenyl)piperidine-2,6-dione (2) and 4- phthalimidophthalonitrile (3) were synthesized in 24% and 74% yield respectively, using 4-aminophthalonitrile as the starting material. Treatment of 2 and 3 with zinc acetate in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene gave respectively phthalocyanines 4 and 5, whose reduction with diborane afforded dyes 6 and 7. Quaternization of 6 and 7 with iodomethane gave cationic zinc(II) phthalocyanines 8 and 9 respectively. A bathochromic shift was observed in the absorption spectra when amino and ammonium groups were present near the macrocycle in comparison with those dyes carrying alkylamino and quaternary alkyl ammonium salts as peripheral substituents.

Full text of DOI:10.1016/j.poly.2012.07.089

Polyhedron 46 (2012) 90–94
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Efficient diborane-mediated synthesis of phthalocyanines carrying amino
groups near the macrocycle
Gabriela A. Gauna a, Diego Cobice b, Josefina Awruch a,
⇑
a Departamento de Química Orgánica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina
b Queen’s Medical Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH16 4TJ, Scotland, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
N-(3,4-dicyanophenyl)piperidine-2,6-dione (2) and 4-phthalimidophthalonitrile (3) were synthesized in
24% and 74% yield respectively, using 4-aminophthalonitrile as the starting material. Treatment of 2 and
3 with zinc acetate in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene gave respectively phthalocya-
nines 4 and 5, whose reduction with diborane afforded dyes 6 and 7. Quaternization of 6 and 7 with iodo-
methane gave cationic zinc(II) phthalocyanines 8 and 9 respectively. A bathochromic shift was observed
in the absorption spectra when amino and ammonium groups were present near the macrocycle in com-
parison with those dyes carrying alkylamino and quaternary alkyl ammonium salts as peripheral
substituents.
Received 8 March 2012
Accepted 30 July 2012
Available online 4 August 2012
Keywords:
Zinc(II) phthalocyanines
4-Aminophthalonitrile
Reduction
Ó 2012 Elsevier Ltd. All rights reserved.
Diborane
Photophysical properties
1. Introduction
The uptake and cell killing efficacy of cationic phthalocyanines
with different lipophilicity have been studied by different
Photodynamic therapy (PDT) is currently used for the treatment
of several types of cancer, including skin, mouth, esophageal, lung
and bladder tumors [1–9]. PDT requires photosensitizers and visi-
ble light to produce reactive oxygen species which selectively de-
stroy malignant cells [10,11].
researchers [15,20–22]. The interest in the development of phthal-
ocyanines as potential mitochondrial targets has led us to investi-
gate the synthesis and spectroscopic parameters of zinc(II)
complexes, which are herein reported.
Mitochondria play a major role in photodynamic cell death [12].
Cationic photosensitizers accumulate in the mitochondria along
membrane potential gradients. The accumulation of the cationic
photosensitizers is dependent on their degree of lipophilicity and
the extent of their delocalized charge [13]. Also, it has been re-
ported that more lipophilic cationic phthalocyanines enter mito-
chondria more readily than less lipophilic ones [14]. On the other
hand, it has been postulated that the biological efficacy of cationic
zinc pyridyloxy phthalocyanines could be modulated upon the
introduction of alkyl chains of different length on the pyridyloxy
groups [15,16].
In a recent study, we found that the reduction of N-substituted
phthalimides by means of diborane is a useful method to produce
N-substituted isoindolines in excellent yields [17]. We also showed
that zinc(II) phthalocyanines derivatives carrying amido substitu-
ents on the macrocycle can be effectively reduced by diborane un-
der relatively mild conditions to give the corresponding amino
phthalocyanines in good yields [18,19].
2. Material and methods
Melting points were determined on an Electrothermal 9100
capillary melting point apparatus. 1H NMR was recorded on a Bru-
ker MSL 300 spectrometer. The 1H NMR of phthalocyanines 4–9
were recorded on a Bruker AM 500. Mass spectra of 2, 3 were ob-
tained with a TRIO 2 (electronic ionization 70 eV) spectrometer. An
ZQ Single Quad mass spectrometer equipped with API multi-probe
ESI/APCI (Micromass, Manchester, UK) was adapted to cold spray
ionization mass spectroscopy (CSI-MS) for phthalocyanines 4–5,
7. Phthalocyanines 6, 8 and 9 mass spectra were obtained with a
12T MALDI-FTCIR-MS instrument. Electronic absorption spectra
were determined with a Shimadzu UV-3101 PC spectrophotome-
ter. Fluorescence spectra were monitored with a QuantaMaster
Model QM-1 PTI spectrofluorometer. Infrared spectra were ob-
tained with a Perkin Elmer Spectrum One FT-IR spectrometer.
Microanalyses were carried out by using a Carlo Erba EA 1108 ele-
mental analyzer. Chromatography columns were prepared with tlc
0
Kiesegel (Merck). N,N-dimethylformamide was dried over 3 ÅA
molecular sieves for 72 h, then filtered and freshly distilled before
use [23]. All reagents were from Sigma Aldrich.
⇑
Corresponding author. Tel.: +54 11 4964 8252; fax: +54 11 4508 3645.
E-mail address: jawruch@ffyb.uba.ar (J. Awruch).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.07.089

G.A. Gauna et al. / Polyhedron 46 (2012) 90–94
91
2.1. Synthesis
2.1.5. 2,9(10),16(17),23(24)-Tetrakis-
piperidinophthalocyaninatozinc(II) (6)
2.1.1. N-(3,4-dicyanophenyl)piperidine-2,6-dione (2)
BF3ꢁEt2O (18 mL) was dropped into a suspension of NaBH4
(5.4 g) in diglyme (18 mL) and the resulting B2H6 was bubbled
for 45 min through a solution of 4 (0.07 g, 0.07 mmol) in anhyd.
THF. The mixture was poured into hexane, and then centrifuged.
The green residue was dried and then applied to a silica-gel column
that had been packed and pre-washed with CH2Cl2. The title com-
pound was eluted with CH2Cl2–MeOH (9:1); after evaporation of
the solvent an amorphous green residue was obtained. Yield:
0.04 g (65%). IR (KBr): 2940, 1648, 1440, 1175, 1053, 1008, 980,
A mixture of 4-aminophthalonitrile (1) (0.200 g, 1.4 mmol) and
glutaric anhydride (0.638 g, 5.6 mmol) was heated at 136 °C for
24 h. After cooling the solid was dissolved in a small volume of
CH2Cl2–MeOH (9.7:0.3) and filtered through a silica-gel column
that had been packed and pre-washed with the same solvent. After
evaporation of the solvent, the solid residue was recrystallized
from CH2Cl2-hexane. Yield: 0.080 g (24%); mp 197–200 °C. IR
(KBr): 3412, 3096, 2957, 2923, 2852, 1667, 1590, 1530, 1476,
1406, 1384, 1302, 1261, 1127, 1027, 877, 821, 667, 618, 581,
945, 887, 833, 748 cmꢀ1 1H NMR (500 MHz, DMSO-d6): d = 1.43
.
480 cmꢀ1
.
1H NMR (300 MHz, CDCl3): d = 2.14 (m, 2H, CH2), 2.9
(m, 8H, CH2), 2.51 (m, 16H, CH2), 7.7 (m, 12H, Ar). MALDI-FTCIR-
MS: m/z [M+] calc. for C52H52N12Zn: 908.3729; Found: [M+]
908.3722.
(t, 4H, CH2CO), 5.5 (d, 1H, Ar), 7.6 (s, 1H, Ar), 7.9 (d, 1H, Ar). MS
(EI, 70 eV): m/z (%) = 239 (33.76) [M+], 240 (6.49) [M++1], 241
(0.87) [M++2], 211 (100), 210 (46.01). Anal. Calc. for C13H9N3O2:
C, 65.27; H, 3.79; N, 17.56. Found: C, 65.50; H, 3.81; N, 17.48.
2.1.6. 2,9(10),16(17),23(24)-Tetrakis-
isoindolinophthalocyaninatozinc(II) (7)
2.1.2. 4-phthalimidophthalonitrile (3)
BF3ꢁEt2O (18 mL) was dropped into a suspensionof NaBH4
(5.4 g) in diglyme (18 mL) and the resulting B2H6 was bubbled
through a solution of 5 (0.06 g, 0.07 mmol) in anhyd. MeOH. The
mixture was refluxed for 48 h, cooled, and poured into hexane.
The blue–green precipitate was separated by centrifugation, dried,
and then applied to a silica-gel column that had been packed and
pre-washed with CH2Cl2. The title compound was eluted with
MeOH, evaporated in vacuo. The green residue was dissolved in a
small volume of MeOH; after the addition of hexane, the amor-
phous solid was isolated by centrifugation. Yield: 0.037 g (57%).
IR (KBr): 2924, 2852, 1790, 1730, 1715, 1583, 1566, 1561, 1493,
A mixture of 4-aminophthalonitrile (1) (0.200 g, 1.4 mmol) and
phthalic anhydride (0.207 g, 1.4 mmol) was heated at 170 °C for
1 h. After cooling, the solid was dissolved in a small volume of CH2-
Cl2–MeOH (9.7:0.3) and filtered through a silica-gel column that
had been packed and pre-washed with the same solvent. After
evaporation of the solvent, the solid residue was recrystallized
from CH2Cl2-hexane. Yield: 0.280 g (74%); mp 243–244 °C. IR
(KBr): 3468, 3377, 3084, 2924, 2853, 2720, 2596, 2429, 2344,
2301, 2237, 2007, 1959, 1868, 1786, 1773, 1725, 1657, 1600,
1564, 1498, 1469, 1429, 1417, 1375, 1291, 1282, 1261, 1235,
1184, 1176, 1126, 1095, 1073, 970, 935, 898, 878, 851, 791, 780,
1465, 1384, 1262, 1081 cmꢀ1 1H NMR (500 MHz, DMSO-d6):
.
725, 714, 685, 628, 614, 524 cmꢀ1 1H NMR (300 MHz, CDCl3):
.
d = 4.54 (s, 16H, CH2), 7.2-7.9 (m, 28H, Ar). CSI-MS: m/z [M+] calc.
for C64H44N12Zn: 1046.3; Found: [M+] 1046.4 and [M+Na]+ 1069.4.
d = 7.82-8.00 (m, 4H, phthalimide), 7.87–8.39 (m, 3H, Ar). MS (EI,
70 eV): m/z (%) = 273 (66.17) [M+], 272 (1.15) [M+ꢀ1], 274
(12.48) [M++1], 229 (65.77), 76 (100). Anal. Calc. for C16H7N3O2:
C, 70.33; H, 2.58; N, 15.38. Found: C, 70.05; H, 2.59; N, 15.46.
2.1.7. 2,9(10),16(17),23(24)-Tetrakis-[N-methylpiperidinium]
phthalocyaninatozinc(II) tetraiodide (8)
MeI (17 mL, 0.27 mmol) was added to a solution of phthalocya-
nine 6 (0.6 g, 0.066 mmol) in DMF (10 mL) and the solution was
stirred for 48 h at 60 °C. After cooling at r.t., CH2Cl2 (5 mL) was
added and the blue–green powder was centrifuged, suspended in
CH2Cl2 (5 mL), and centrifuged again. Yield: 0.19 g (20%). IR
(KBr): 2938, 2875, 2363, 1740, 1663, 1540, 1447, 1384, 1262,
2.1.3. 2,9(10),16(17),23(24)-Tetrakis(2,6-dioxopiperidino)
phthalocyaninatozinc(II) (4)
A mixture of 2 (0.022 g, 0.092 mmol), anhyd. Zn(OAc)2 (0.023 g,
0.125 mmol), and 0.022 mL (0.147 mmol) DBU in anhyd. BuOH
(5 mL) was stirred and heated at reflux for 1.5 h under Ar. After
evaporation in vacuo, the residue was treated with CH2Cl2 (5 mL
and centrifuged to eliminate the excess of Zn(OAc)2. The organic
solution was evaporated in vacuo leaving a blue–green solid, which
was then dissolved in CH2Cl2 and filtered through a silica-gel col-
umn that had been packed and pre-washed with the same solvent.
The title compound was eluted with CH2Cl2–MeOH (1:1). After
evaporation, an amorphous dye was obtained. Yield: 0.020 g
(85%). IR (KBr): 3435, 3066, 2929, 2856, 2326, 1941, 1867, 1732,
1624, 1551, 1492, 1446, 1383, 1354, 1261, 1199, 1085, 979,
1225, 1174, 1053, 1009, 979, 946, 887, 801, 740, 700 cmꢀ1 1H
.
NMR (500 MHz, DMSO-d6): d = 1.43 (m, 8H, CH2), 2.51 (m, 16H,
CH2), 2.26 (br, 12H, CH3), 4.38 (m, 16H, CH2), 7.9 (m, 12H, Ar). MAL-
DI-FTCIR-MS: m/z [M+] calc. for C56H64N12ZnI4: 1476.08472;
Found: [M+] 1476.08385.
2.1.8. 2,9(10),16(17),23(24)-Tetrakis-[N-methylisoindolinium]
phthalocyaninatozinc(II) (9)
804 cmꢀ1 1H NMR (500 MHz, DMSO-d6): d = 1.55 (m, 8H, CH2),
.
MeI (28 mL, 0.45 mmol) was added to a solution of phthalocya-
nine 7 (0.6 g, 0.066 mmol) in DMF (10 mL) and the solution was
stirred for 48 h at 60 °C. Isolation of the title dye was performed
as described for compound 8. Yield: 0.028 g (16%). IR (KBr):
3432, 2960, 2924, 2853, 2363, 2344, 1726, 1617, 1490, 1457,
2.51 (m, 16H, CH2), 7.7 (m, 12H, Ar). CSI-MS: m/z [M+] calc. for C52-
H36N12O8Zn: 1022.3; Found: [M+] 1022.3.
2.1.4. 2,9(10),16(17),23(24)-Tetrakis-
phthalimidophthalocyaninatozinc(II) (5) [24]
1384, 1261, 1098, 1025, 802 cmꢀ1 1H NMR (500 MHz, DMSO-d6):
.
d = 0.87 (m, 12H, CH3), 2.51 (m,16H, CH2), 7.66–7.73 (m, 28H,
Ar). MALDI-FTCIR-MS: m/z [M+] calc. for C68H56N12ZnI4:
1612.02212; Found: [M+] 1612.02117.
A mixture of 3 (0.057 g, 0.21 mmol), anhyd. Zn(OAc)2 (0.058 g,
0.316 mmol), and 0.057 mL (0.38 mmol) DBU in anhyd. BuOH
(5 mL) was reacted by applying the same procedure described for
4. The dye was purified by filtering through a silica-gel column,
which had been packed and pre-washed with CH2Cl2–MeOH
(1:1). Yield: 0.046 g (77%). IR (KBr): 3035, 2989, 1700, 1651,
1567, 1562, 1415, 1326, 1122, 1079, 1020, 930, 889, 842, 722,
2.2. Photophysical and photochemical parameters
2.2.1. Spectroscopic studies
655, 525 cmꢀ1
.
1H NMR (500 MHz, DMSO-d6): d = 6.9–8.5 (m,
Absorption and emission spectra were recorded at different
concentrations by using a 10 ꢂ 10 mm quartz cuvette. All experi-
ments were performed at room temperature.
28H, phthalimide and Ar). CSI-MS: m/z [M+] calc. for C64H28N12O8-
Zn: 1158.4; Found: [M+] 1158.1 and [M+Na]+ 1181.4.

92
G.A. Gauna et al. / Polyhedron 46 (2012) 90–94
The emission spectra of 4–9 were collected at an excitation
wavelength of 610 nm (Q-band) and recorded between 630 and
800 nm.
for 1 h to achieve 4-phthalimidophthalonitrile (3) in 74% yield.
Phthalocyanine 4 was readily prepared by cyclotetramerization
of phthalonitrile
2
in the presence of 1,8-diazabicy-
clo[5.4.0]undec-7-ene (DBU) in butanol and zinc acetate (85%
yield) [18,29]. Phthalocyanine 5 was obtained using the same pro-
cedure described for 4, affording 77% yield. Recently, the synthesis
of compound 5 by the reaction of tetraamino-substituted phthalo-
cyanine with phthalic anhydride in 81% yield has been reported
[24]. Phthalocyanines 6 and 7 were synthesized in 65% and 57%
yields respectively by the reduction with diborane. The stability
of phthalocyanine 6 and 7 under the reaction conditions showed
the usefulness of the reduction with diborane of the peripheral
macrocyclic amido-groups of phthalocyanines 4 and 5. Treatment
of phthalocyanines 6 and 7 with iodomethane at 60 °C gave cat-
ionic phthalocyanines 8 and 9 respectively.
Intermediates 2–3 and dyes 4–9 were characterized by IR and
1H NMR spectroscopy. The 1HNMR spectra of phthalocyanines
showed broadening of signals due to the presence of several regioi-
somers as well as phthalocyanine aggregation at the concentra-
tions used for spectra measurements. Integration of signals
agreed with the expected number of protons.
2.2.2. Fluorescence quantum yields
Fluorescence quantum yields (UF) were determined by compar-
ison with those of tetrakis 2,3,9,10,16,17,23,24-octakis [N,N-dim-
ethylaminoethylsulfanyl)]phthalocyaninatozinc(II)
tetrahydrofuran and N,N-dimethylformamide) [25] as reference
(UF = 0.26 in
at kexc = 610 nm for 4–9. Calculations were performed by Eq. (1).
R
ꢀ
ꢁ
2
ISð1 ꢀ 10ꢀA
Þ
Þ
nS
nR
UFS
¼
UFR
ð1Þ
S
IRð1 ꢀ 10ꢀA
where R and S superscripts refer to the reference and the sample
respectively; I is the integrated area under the emission spectrum;
A is the absorbance of solutions at the excitation wavelength and
(ns/nR)2 stands for the refractive index correction.
2.2.3. Quantum yield of singlet oxygen production
Standard chemical monitor bleaching rates were used to calcu-
late the quantum yield of singlet oxygen generation (UD) [26]. For
UD studies, 1,3-diphenylisobenzofuran (DPBF) was used as a sin-
glet oxygen chemical quencher. To avoid chain reactions induced
by DPBF in the presence of singlet oxygen, the absorbance of DPBF
was under 1.9 using a 10 ꢂ 10 mm quartz cuvette. DPBF decay at
410 nm was monitored. Polychromatic irradiation was performed
using a projector lamp (Philips 7748SEHJ, 24 V–250 W), and a
cut-off filter at 610 nm (Schott, RG 610) and a water filter were
used to prevent ultraviolet and infrared radiation. Samples 4–9
and reference (tetrakis[N,N-dimethylaminoethylsulfanyl)]phtha-
locyaninatozinc(II): UD = 0.69 in tetrahydrofuran and N,N-dimeth-
ylformamide) [25,27] were irradiated within the same wavelength
interval k1–k2, and UD was calculated according to Eq. (2).
EI-MS spectroscopy at 70 eV was performed for the character-
ization of phthalonitriles 2–3. Cold-spray ionization mass spectros-
copy (CSI-MS) was used for the successful characterization of
phthalocyaninates 4–5 and 7. The molecular-ion signal of 6 and
cationic phthalocyanines 8–9 was observed only by Fourier trans-
form ion cyclotron resonance mass spectrometry (FTICR-MS)
[30,31].
3.2. Photophysical parameters
Table 1 shows the photophysical parameters obtained for
phthalocyanines 4–9. These parameters were measured in tetrahy-
drofuran for phthalocyanines 4 and 6, and N,N-dimethylformamide
for phthalocyanines 5 and 7–9. A bathochromic shift was observed
in the absorption spectra when amino and ammonium groups
were present near the macrocycle in comparison with those dyes
carrying alkylamino and quaternary alkyl ammonium salts as
peripheral substituents [19,32,33]. Such bathochromic shift into
the therapeutic window could be useful for biomedical applica-
tions such as photodynamic therapy [21,22]. The low extinction
coefficients and the non-linearity of the Lambert–Beer law ob-
tained evidence that dyes 4–9 remain aggregated even at low con-
centrations (i.e. 1 ꢂ 10ꢀ7 M).
R
ꢀAR
k2
k1
IoðkÞð1 ꢀ 10 ðkÞÞdk
rS
rR
UDS
¼
UDR
ð2Þ
R
S
k2
k1
IoðkÞð1 ꢀ 10ꢀA ðkÞÞdk
where r is the singlet oxygen photogeneration rate and the super-
scripts S and R stand for the sample and reference respectively, A
is the absorbance at the irradiation wavelength and Io(k) is the inci-
dent spectral photon flow (mol sꢀ1 nmꢀ1). When the irradiation
wavelength range is narrow, the incident intensity varies smoothly
with wavelength and the sample and reference have overlapping
spectra, Io may be approximated by a constant value which may
be drawn out of the integrals and cancelled.
The emission spectra of 4–9 were collected at an excitation
wavelength of 610 nm (Q-band) and recorded between 630 and
800 nm.
3. Results and discussion
Fluorescence quantum yields are similar for compounds 4–6,
showing higher UF values than dyes 7–9 (Table 1). It has been re-
ported that UF becomes smaller with a decreasing energy gap be-
tween the HOMOs and LUMOs, thus suggesting that excited states
become unstable in systems showing a Q-band at lower energy,
plausibly due to the ease of electron transfer [34].
The UD values in tetrahydrofuran obtained for the dyes 4 and 6
are listed in Table 1. Sample absorbances were kept as low as pos-
sible in order to minimize aggregation, but high enough to obtain
measurable values of quantum yield of singlet oxygen production.
The UD values for 4 and 6 were 0.53 and 0.45 respectively. Dyes 5
and 7–9 were highly soluble in N,N-dimethylformamide. The low
UD values obtained for these compounds evidenced that they re-
mained strong aggregated even at low concentrations (Table 1).
Cationic phthalocyanines 8 and 9 showed the lowest values of
UD in comparison with 4–7. However, as previously described
[20,22,35–38], phthalocyanines with similar UD values show a
phototoxic effect against different cell lines. Thus, it could be
3.1. Synthesis
Tetrasubstituted phthalocyanines 4–9 were designed and syn-
thesized as depicted in Scheme 1. The sequence begins with the
reaction of the commercially available 4-aminophtalonitrile (1)
with the corresponding anhydrides to achieve precursors 2 and
3. Thus, the reaction of 1 with four moles of glutaric anhydride
at 136 °C for 24 h gave the best yield of N-(3,4-dicyano-
phenyl)piperidine-2,6-dione (2), 24%. Attempts to obtain 2 by the
reaction of 3,4-dichloronitrobenzene with glutaric acid in the pres-
ence of two equivalents of red phosphorus and 0.04 equivalents of
iodine as described elsewhere [28] afforded N-(3,4-dichloro-
phenyl)piperidine-2,6-dione in 34% yield. The nucleophilic substi-
tution of the above mentioned compound with copper(I) cyanide
in 1-methylpyrrolidin-2-one (NMP) or N,N-dimethylformamide
(DMF) as a solvent yielded only 9% of compound 2. Compound 3
was prepared by reaction of 1 with phthalic anhydride at 170 °C

G.A. Gauna et al. / Polyhedron 46 (2012) 90–94
93
Scheme 1. Reagents and conditions: (a) glutaric anhyd., 136 °C, 24 h, 2 24%, or phthalic anhyd., 170 °C, 1 h, 3 74%; (b) Zn (AcO)2, DBU, BuOH, 136 °C, 1.5 h, 4 85%, 5 77%; (c) 6
B2H6, THF, r.t., 48 h, 65%, 7 B2H6, MeOH, reflux, 48 h, 57%; (d) MeI, DMF, 60 °C, 48 h, 8 20%, 9 16%.
Table 1
Photophysical parameters obtained for phthalocyanines 4, 6 in THF and 5, 7–9 in DMF.
Compound
kmax, Q-band (nm)
kmax, emission (nm)
emax (Mꢀ1 cmꢀ1
)
UF
UD
4
5
6
7
8
9
689.5
699
723
700
738.5
690.5
693.5
700
733
704.5
750
696
(1.4 0.2) ꢂ 104
(1.7 0.1) ꢂ 104
(5.0 0.1) ꢂ 103
(2.6 0.1) ꢂ 104
(1.0 0.1) ꢂ 103
(1.0 0.1) ꢂ 103
0.34 0.01
0.29 0.01
0.29 0.01
0.09 0.01
0.10 0.01
0.07 0.01
0.53 0.01
0.23 0.02
0.45 0.01
0.37 0.02
0.10 0.01
0.05 ‘0.01
expected that 8 and 9 will behave as efficient photosensitizers for
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Acknowledgments
This work was supported by grants from the Universidad de
Buenos Aires, Consejo Nacional de Investigaciones Científicas y
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