Photophysical studies of tetratolylporphyrin photosensitizers for potential medical applications

Article abstract of DOI:10.1016/j.molstruc.2005.12.052

A group of meso-substituted synthetic tetratolylporphyrins was investigated by the methods of absorption and fluorescence spectroscopies as well as steady-state and time-resolved photothermal spectroscopies. The experiments were carried out in the air, oxygen or nitrogen atmospheres, at two temperatures. The details concerning the fast and slow deactivation processes of excitation energy of the dyes were studied. The estimated quantum yield of fluorescence and the efficiency of (S₁-T₁) intersystem crossing process give a possibility to evaluate the population yield and quenching rate of the triplet state, important for the therapeutic application, mostly mediated by the T₁-state. For tetrapyrrole with the carboxyphenyl group substituted in meso-position, the triplet state yield was the highest, of 0.86-0.94, whereas the porphyrin with aminophenyl group seemed to be efficient singlet oxygen generators (0.81-0.99) with a high rate constant of its excited triplet state quenching by molecular oxygen.

Full text of DOI:10.1016/j.molstruc.2005.12.052

Journal of Molecular Structure 792–793 (2006) 93–98
www.elsevier.com/locate/molstruc
Photophysical studies of tetratolylporphyrin photosensitizers
for potential medical applications
a
b
Alina Dudkowiak a, , Ewa Teslak , Jan Habdas
*
´
a
´ ´
Faculty of Technical Physics, Poznan University of Technology, Nieszawska 13A, 60 965 Poznan, Poland
b Institute of Chemistry, University of Silesia, Szkolna 9, 40 006 Katowice, Poland
Received 15 September 2005; received in revised form 23 December 2005; accepted 23 December 2005
Available online 27 March 2006
Abstract
A group of meso-substituted synthetic tetratolylporphyrins was investigated by the methods of absorption and fluorescence spectroscopies as
well as steady-state and time-resolved photothermal spectroscopies. The experiments were carried out in the air, oxygen or nitrogen atmospheres,
at two temperatures. The details concerning the fast and slow deactivation processes of excitation energy of the dyes were studied. The estimated
quantum yield of fluorescence and the efficiency of (S1–T1) intersystem crossing process give a possibility to evaluate the population yield and
quenching rate of the triplet state, important for the therapeutic application, mostly mediated by the T1-state. For tetrapyrrole with the
carboxyphenyl group substituted in meso-position, the triplet state yield was the highest, of 0.86–0.94, whereas the porphyrin with aminophenyl
group seemed to be efficient singlet oxygen generators (0.81–0.99) with a high rate constant of its excited triplet state quenching by molecular
oxygen.
q 2006 Elsevier B.V. All rights reserved.
Keywords: Photodynamic therapy; Photothermal spectroscopy; Porphyrin; Singlet oxygen; Triplet state
1. Introduction
their properties on the molecular level, that is to study possible
aggregation effects, radiative (fluorescence) and non-radiative
(internal conversion, intersystem crossing) processes as well as
triplet state generation, which are essential or influence the
photodynamic treatment and diagnostic efficiency. It is known
that dyes characterized by significant intersystem crossing
transitions, long-lived triplet states and sufficient excitation
Recently, there has been considerable interest in the
synthesis and application of tetrapyrrolic photosensitizers
such as porphyrinoids: porphyrins, chlorines, bacteriochlorins,
phtalocyanines [1–8]. Their photophysical properties can be
modified by introducing metal ion at the center of the pyrrole
rings and/or by attaching side groups to their skeleton. By these
means it is possible to control the influence of the dye
molecular structure on dye capability of photodynamic
activity. At the first step, the new tetrapyrrole-based
photosensitizers are subjected to photophysical and photo-
chemical studies in model systems, which permits the choice of
proper ones and their optimization. It is interesting to analyse
the properties of dyes in solutions so that to be able to control
1
energy transfer of their triplets to promote O2 formation are
able to induce photodynamic reactions leading to the
phototherapeutic killing of malignant tumours.
In search for new second-generation photosensitizers or
photomarkers useful for medical applications, a group of meso-
substituted synthetic tetratolylporphyrins (TTP) has been
studied by means of optical and photothermal techniques.
The meso-derivatives of tolylporphyrin have been widely
applied in various model systems (e.g. for study of
photosynthesis, oxygen transport, etc.). They have been chosen
for our photophysical study for several reasons: (i) they are
relatively easily synthesised in the laboratory, (ii) the
introduction of desired functional can be achieved by the
Adler–Longo method (or it modifications) with yields varying
from a few to about 20% of the total yield (there is a timely
separation process of a desired derivative, which makes the
yield of a particular derivative about 1–5%, depending on
Abbreviations: A, absorbance; BCP, bromocresol purple; LIOAS, laser
induced optoacoustic spectroscopy; PAS, photoacoustic; PDT, photodynamic
therapy; TD, thermal deactivation; TPP, tetraphenylporphyrin; TTP,
tetratolylporphyrin.
*
Corresponding author. Tel.: C48 61 665 3181; fax: C48 61 665 3178.
E-mail address: alina.dudkowiak@phys.put.poznan.pl (A. Dudkowiak).
0022-2860/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2005.12.052

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A. Dudkowiak et al. / Journal of Molecular Structure 792–793 (2006) 93–98
the type of substituents applied), (iii) the presence of an
acetamide, amine and carboxylic group allows a study of the
effect of weakly (–NHCOCH3) or strongly (–NH2) activating
groups and deactivating (–COOH) groups on the porphyrin
photophysical properties, and (iv) the presence of an amine or
carboxylic groups allow to link, e.g. amino acids, which may
influence the dye sensitizing properties (e.g. transport into the
cell).
The information on the dye singlet states is obtained from
the absorption and fluorescence spectra recorded for dyes in
solutions. On the basis of these experiments, the photophysical
properties and spectral parameters of dyes, essential for the
further analysis of the laser induced optoacoustic spectroscopy
(LIOAS) results, were estimated. The time-resolved LIOAS
and steady-state photoacoustic (PAS) techniques [4,9–11]
detect the fate of the energy absorbed by dyes and its loss
through non-radiative channels. The LIOAS signal analysis
methods proposed by Marti et al. [12] and Small et al. [13]
were applied. The experiments were performed in the air,
oxygen or nitrogen atmosphere, at two temperatures. The
obtained results give an opportunity to get insight into the
mechanisms responsible for molecular processes occurring in
dyes upon light illumination. LIOAS results provide the
information about the dye triplet state properties, its population
and quenching, whereas PAS signals give the global thermal
energy release by the dyes.
Fig. 1. Molecular structure of porphyrin under investigation.
ranged from about 10K6 to 10K3 M. The organic solvent
used in the measurements was of spectroscopic grade.
Electronic absorption spectra were recorded on a Varian
Cary 4000 spectrophotometer. The emission spectra were
recorded by means of a Hitachi F4500 spectrofluorimeter. The
steady-state photoacoustic (PAS) signal measurements were
made on a one-beam spectrometer described elsewhere [11].
On the basis of the absorption, fluorescence and PAS spectra,
the spectral parameters (position of main bands, extinction
coefficient, thermal deactivation (TD) parameter determined as
intensity of PAS signal divided by absorbance), the quantum
yield of fluorescence (FF) and the natural lifetime (tN) of the
studied dyes were obtained (Table 1). The FF values were
estimated according to the method described in [16] using
bacteriochlorophyll c in acetone as a reference [17].
The aim of our study was to check and to compare the
influence of the meso-substituents on the porphyrin photo-
physical parameters. It was of interest to investigate by means
of LIOAS method, the substitution influence on excited
porphyrin triplet population and quenching. This study was
also supposed to help establish if the time-resolved photo-
thermal method was sensitive enough to differentiate between
the porphyrins differing only in the meso-substituted groups.
We also wished to find possible correlations between the
molecular structure of the dyes and their spectroscopic
properties. The estimated properties of the dye-sensitizer can
be helpful to determine its photochemical activity, which is of
great importance for its successful application for medical
purposes such as photodynamic therapy (PDT).
Time-resolved photothermal signal was recorded by means
of the LIOAS setup [4,9,10,18] in the time range up to 5 ms
(limited by the setup used). Before the LIOAS experiments,
some of the samples were deaerated (or oxygenated) by
bubbling nitrogen (or oxygen). For the LIOAS measurements,
at the laser flash wavelengths used (llas) the absorption
intensities of the investigated and the reference samples were
adjusted the same. The bromocresol purple (BCP), whose total
excitation energy is promptly thermally deactivated (in time
shorter than 0.5 ms - the estimated time resolution of the
experimental setup [4,18]), was used as a reference in the
LIOAS performed measurements. The LIOAS signal analysis
method proposed by Marti et al. [12] was applied, based on a
comparison of the first maximum of the signal (Hmax, Eq. (1))
measured for the sample and the reference (Fig. 2). According
to [12], the part of the energy exchanged promptly into heat,
i.e. in a time shorter than 0.5 ms, is denoted as a (Fig. 3). It can
be obtained from the equation:
2. Experimental
Meso-substituted tetratolylporphyrins (TTP) (e.g. 5-(4-
carboxyphenyl)-10,15,20-tritolylporphyrin, 5-(40-acetamido-
phenyl)-10,15,20-tritolylporphyrin, 5-(40-aminophenyl)-
10,15,20-tritolylporphyrin, the so-called Co-TTP, Ac-TTP
and Am-TTP, respectively) were studied. Fig. 1 presents
molecular structures of the dyes under investigation. Co- and
Ac-TTP were synthesized according to the Adler–Longo
method, by refluxing in propionic acid, two aromatic aldehydes
with pyrrole at the molar ratio of 1:3:4 or 2:2:4, to obtain
monosubstituted derivatives. Am-TTP was prepared from
5-(40-acetamidophenyl)-10,15,20-tritolylporphyrin by heating
it in a mixture of trifluoric acid/hydrochloric acid at 80 8C for
20 h [14,15]. Substituted porphyrins were dissolved in toluene
and for spectroscopic measurements their concentrations
Hmax Z KaElasð1K10KA
Þ
(1)
where Hmax, the amplitude of the first maximum of the LIOAS
signal; A, the sample absorbance at llas; Elas, the average laser
pulse energy; K, the coefficient related to the optical geometry,

A. Dudkowiak et al. / Journal of Molecular Structure 792–793 (2006) 93–98
95
Table 1
Comparative spectroscopic properties of porphyrins under investigation in toluene
lAmax (nm)
lFmax (nm)
Qx(0,0)
TTP
3!104 (MK1 cmK1
)
tN (ns)
TD (a.u.)
Soret
Soret
Qx(0,0)
Soret
Qx(0,0)
Qx(0,0)
Co-
Ac-
Am-
421
421
423
648
646
652
26.76
57.03
31.93
1.30
0.92
0.90
650
652
655
17.04
11.61
17.54
0.43
0.43
0.77
0.71
0.31
0.40
lAmax; lFmax, absorption and fluorescence wavelength at maximum; 3, molar absorption coefficient; TD, thermal deactivation parameter; tN, natural lifetime;
Ð
ð1=tNÞZð8pn2=c2Þð2303=N0Þ 3ðnÞdn, where 3(n), the molar extinction coefficient as a function of the absorption frequency n; c, the speed of light; N0, the Avogadro
n
number.
electronic impedance and thermoelastic properties of the
sample solution.
Hence, the values of k1 and a obtained by deconvolution [13]
and Marti et al. [12] methods, respectively, should be similar
for a given dye. The contributions from slow thermal
deactivation processes occurring in the time range from 0.5
to 5 ms are represented by k2 and t2 values (Fig. 3).
Assuming that, in N2-saturated samples, the photochemical
reactions and other non- or thermal paths of energy
deactivation are not realised, the approximate value of the
yield of triplet state generation (FT) can be obtained from the
equation:
3. Results and discussion
ð1KaÞEhn KFFEF
It is known that the porphyrin skeleton is essentially
hydrophobic, which facilitates the dye-photosensitizer
inclusion into the transformed cells, but it limits they solubility
in solutions and physiological liquids. Synthesized meso-
substituted TTP can be dissolved only in a few organic
solvents. For our investigation toluene was chosen. All studied
meso-substituted compounds show typical spectroscopic
characteristics of free-base porphyrins (intense Soret band in
the violet range of the visible region and four wide Q bands in
the 500–680 nm region) (Fig. 4(a), Table 1). As seen from
Table 1 the absorption and fluorescence regions for synthetic
porphyrins are similar, it means that meso-substituents do not
cause significant changes in the positions of the energy bands.
It was also established that TTP independently of the groups
FT Z
(2)
ET
For the calculation, the energy of the dye triplet state (ET)
was taken from literature [6,19], Ehn, the molar energy of the
incident photons; EF, the energy of singlet state and FF, the
fluorescence yield of dye were estimated as described above.
The method of LIOAS signal analysis proposed by Small
et al. [13] consists in deconvolution of both sample and
reference signals, where the sample thermal signal (H) is based
on the formula
ꢀ
ꢁ
X
ꢀt
H w
ki exp
(3)
ti
i
where ti, the lifetime of the i-th transient; and ki, a pre-
exponential factor (the fraction of thermal energy released in
i-th lifetime) [13]. In this procedure one can assume that the k1
value is related to the decay time t1%0.5 ms (below the setup
time resolution) and describes the fast non-radiative processes.
Fig. 3. Schematic diagram of energy levels and photoinduced processes in
pigment and oxygen molecules; using LIOAS analysis methods (a, ki,
ti - parameters) [12,13], the radiationless processes are described by three
sequential exponentials: (i) formation of the triplet state (ISC (FT), Eq. (2)) and
internal conversion to the ground state (TDF), followed by (ii) decay of the
triplet (tTZ1/kT) by intersystem crossing (TDS) or energy transfer to oxygen
(ISC(FD)) and, finally (iii) the decay of singlet oxygen (TDS, tD); Ehn, the
molar energy of the incident photons; EF, ET, the energy of singlet and triplet
state, respectively; F, fluorescence; FF, fluorescence quantum yield; P,
phosphorescence.
Fig. 2. LIOAS signals of porphyrin (Ac-TTP) and reference (BCP) sample
recorded in aerated toluene at room temperature.

96
A. Dudkowiak et al. / Journal of Molecular Structure 792–793 (2006) 93–98
concentration range (Table 1). The relative intensity of the Q
bands indicates an etio-type spectrum.
The steady-state fluorescence emission spectra of all
compounds present two maxima assigned to the Q(0,0) and
Q(0,1) transitions (Table 1, Fig. 4(a)). The fluorescence spectra
of TTP are roughly the mirror images of the long-wavelength
region of the absorption spectra. The FF values of the
porphyrins studied were 0.05–0.10 (Table 2) and are typical
of porphyrins [6]. The calculated FF values do not depend
significantly on the experimental conditions applied (different
atmospheres and/or temperatures), i.e. they vary only in the
range of accuracy. This suggests no aggregate formation and
supports the idea that because of the short lifetime (0.85–
1.23 ns, calculated using FF, tN from Tables 1 and 2), the
quenching of fluorescence by molecular oxygen is not a crucial
factor in aerated solutions of these porphyrins. The estimated
lifetimes are of an order of nanoseconds as expected. For
example Ac-TTP is characterized by the shortest tN and by the
largest value of FF from among the synthetic porphyrin under
investigation (Tables 1 and 2). In general, the spectral
parameters of Co-, Ac-, Am-TTP are in good agreement
with the available literature data for tetraphenylporphyrin
(TPP) and corresponding derivatives [3,6,18]. Furthermore,
photophysical parameters of substituted TTP (e.g. FF, tN) are
comparable with those reported in literature [1,3,6] for TPP and
other porphyrin derivatives.
Fig. 4. Exemplary of absorption (A) and fluorescence (F) (lexcZ421 nm)
spectra of Am-TTP (a) and PAS spectra for all TTP dyes studied (b), the
frequency of light modulation, nZ15 Hz.
The nanoseconds time range of tN for porphyrins
(Table 1) could indicate an intensive intersystem crossing
transition, which may lead to high population of the their
triplet states. To get a deeper insight into this problem we
performed steady-state PAS (it gives information on the
global TD processes with singlet and triplet states partici-
pation) (Fig. 4(b)) and time-resolved LIOAS experiments
(give insight into triplet state population) (Fig. 2). The latter
was also expected to answer the question about a possibility
of triplet state contribution in the photodynamic reaction.
The part of the energy absorbed converted into heat is
estimated by TD parameters collected in Table 1. For
example, Co- and Am-TTP loose much energy in thermal
relaxation processes when compared to Ac-TTP, which
substituted (Co-, Ac- or Am-) did not show aggregate
formation in the concentration range 10K6–10K3 M. Aggrega-
tion of tetrapyrrolic sensitizers plays a remarkable role in
determination of their photophysical properties (e.g. absorption
parameters, lifetimes of excited states as well as fluorescence
(FF), intersystem crossing (FT) and singlet oxygen (FD)
quantum yields, etc.). The spectra of the second derivative of
absorption and fluorescence signals (not shown) have indicated
that at the concentrations used the dyes were in non-
aggregated, monomeric forms. The absorption coefficient of
the Soret and Q bands (3%104 MK1 cmK1) was obtained from
the Beer–Lambert law using solutions in the 10K6 M
Table 2
Results of LIOAS signals analysis of the porphyrin in toluene at 20 and 4 8C (results in parentheses), llasZ421 nm, EhnZ283.9 kJ molK1
TTP
FF
a (N2)
a (air/O2)
k2
t2 (ms)
FT
FD
SD
kT!109
(MK1 sK1
)
Co-
Ac-
Am-
0.05
0.10
0.07
0.55 (0.51)
0.61 (0.58)
0.58 (0.52)
0.59
0.63
0.67
0.73
0.78
0.85
0.24
0.06
0.11
0.53
0.76
0.47
0.86 (0.94)
0.66 (0.73)
0.78 (0.90)
0.54 (0.66)
0.79 (0.74)
0.81 (0.99)
0.63 (0.70)
1.19 (1.01)
1.04 (1.10)
0.96
0.73
1.18
FF, fluorescence yield; FF ZFRðI=IRÞðODR=ODÞðn2=nR2 Þ [16], where FR, the fluorescence quantum yield of the reference; I, IR, and OD, ODR and n, nR, the areas
under the fluorescence curves, the absorption intensities, refractive indices of the sample and reference, respectively; a, a fraction of excitation energy exchange into
heat promptly (in shorter time than time resolution of apparatus) estimated based on Eq. (1), k1, pre-exponential factor for t1%0.5 ms, k2 and t2, pre-exponential
factor and decay time, for time range: 0.5–5.0 ms; FT, yield of triplet state formation - Eq. (2); FD, yield of singlet molecular oxygen production; FD ZðFTET K
Ehnk2Þ=ED [19] where EDZ94 kJ molK1; SD, the fraction of triplet states quenched by oxygen, SDZFD/FT, kT, the rate constant of triplet state quenching by
molecular oxygen, estimated taking [O2]Z1.81!10K3 M in toluene at room temperature.

A. Dudkowiak et al. / Journal of Molecular Structure 792–793 (2006) 93–98
97
deactivated efficiently its absorbed energy in radiative
processes (the high FF value). It means that for porphyrins
with acetamidophenyl group there is a competition between
the fast TD processes (described as a in Table 2) and
fluorescence. For all porphyrins under study, the linear
correlation coefficient, estimated on the basis of the
experimental dependence of the PAS value signals on light
modulation frequency and predicted on the basis of
Rosencwaig–Gersho theory [20], does not reach unity (not
shown). It indicates that not only prompt internal conversion
transitions but also slow relaxation processes, with triplet
state participation, are involved.
molecular oxygen (kT) and singlet oxygen production were
higher for Am- than for Ac-TTP. As follows from the FD
results in Table 2, this efficiency depends strongly on the
character of the substituents and does not show a simple
correlation with the FT values, as it is confirmed by SD-
parameters. The lowest FD and SD values were obtained for
Co-TTP and the highest for Am-TTP. The FD and kT values
imply that a strong quenching of triplets for TTP with
aminophenyl-substituted group is observed. But on the other
hand, the results indicate that the triplet of Co-TTP is not
completely depopulated be energy transfer to O2 in toluene
at ambient and low temperature. The somewhat high values
of FD estimated at 4 8C are probably due to two effects: the
higher FT value and the higher viscosity of toluene, resulting
in a lower diffusion coefficient of oxygen in chilled (4 8C)
than ambient (20 8C) temperature. It should be also noted
here that the change in temperature has not a very strong
effect on the yield of (S1–T1) transition leading to a slight
increase in FT values, which is well correlated with the
decrease in a-values at low temperature.
For the therapeutic application, the yield of dye triplet state
and its interactions with molecular oxygen are the most
important photophysical properties because the photodynamic
activity is mostly mediated by the T1-state. On the basis of the
LIOAS experiments it is possible conclude about the
population and quenching efficiency of dye triplet state as
well as about singlet oxygen production yield. As follows from
Table 2 and LIOAS measurements performed, for all
porphyrins a decrease in the O2 presence in the solution causes
an increase in the yield of the slow thermal deactivation. This
increase is due to the decrease in quenching of the triplet state
by oxygen. For a photochemically stable dye, the FT value can
be estimated from the measurement of the slow component of
TD of the excitation energy. To evaluate FT for the new
compounds the value of ET was taken the same as for TPP
(138 kJ molK1) [6].
Our results strongly confirm that incorporation of the
electron donor amino group (NH2) in the meso-position of
the porphyrin molecule causes an increase in the FD and also
kT values, whereas the electron acceptor group (COOH)
reduces the singlet oxygen generation quantum yields
similarly as it was reported in [6]. So, it seems that the
introduction of Co-, Ac- and Am-groups at the meso-position
of the phenyl rings does not markedly influence the
p-electronic system of the main chromophore and does not
cause a significant change in the intersystem crossing
probabilities, but it influences the efficiency of the triplet
generation and quenching. The LIOAS results in nitrogen
atmosphere are not affected by oxygen quenching of the dye
triplet state, therefore they give the possibility to calculate
FT values, which can be comparable with the data reported
by other authors. To the best of our knowledge, the following
literature data are available: for unsubstituted TPP in toluene,
FT is 0.67–0.83 and FD is 0.65–0.68 [6,21,22,24]. The
values of FT (0.66–0.86) estimated for meso-substituted TTP
dyes are in agreement with that for TPP, while FD estimated
for Co-TTP is similar as that of TPP.
For Ac-TTP the values of FF and a are quite high
indicating that a significant fraction of absorbed energy is
dissipated in the fast deactivating processes, which is in
agreement with the low FT value, while for the other two
dyes Co- and Am-TTP the situation is the reverse (Table 2).
The latter dyes convert into heat more energy in slow
processes taking place above 0.5 ms. For Co- and Am-TTP
the obtained FT values are quite high and can be explained
by the high probability of intersystem crossing (S1–T1)
transition. The high yield of the intersystem crossing (S1–T1)
explains the low value of a related to the fast TD processes
(taking place in the time scale up to 5 ms).
Excitation energy transfer between porphyrin derivatives
and singlet oxygen has been, in principle, a well-known
phenomenon [6,21–23]. Porphyrin in their lowest triplet
excited state can transfer their excitation energy to oxygen,
resulting in its triplet-singlet transition. Therefore, further
analysis by the deconvolution method [13] was made for the
LIOAS results recorded in the air. Assuming that the second
(exponential) component of the LIOAS signal obtained by
the method of Small et al. [13], represents the two possible
pathways of the triplet state deactivation involving almost
complete energy transfer from this state of porphyrin to the
oxygen or radiationless decay to the ground state, the
deconvolution implies that the parameters k2 and t2 (Table 2)
can be correlated with the dye triplet state quenching by
molecular oxygen and generation of singlet oxygen. The
values FD were determined at two temperatures. As follows
from Table 2, the rate constant of triplet state depletion by
4. Conclusions
The triplet state generation yield and the photosensitising
potential of porphyrins investigated have been estimated on the
basis of a study of radiation and thermal depopulation
processes of their excited states. The correlation of TTP
photophysical parameters and meso-substituted groups has also
been examined. The differences in the molecular structure of
the dyes lead to distinctly different spectroscopic properties,
e.g. the triplets of various dyes are differently populated and
quenched by oxygen.
On the basis of the results presented, the following
conclusions on the possibility of the dye studied applications
in photodynamic therapy or diagnostics of cancerous tissues,
can be drawn:

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A. Dudkowiak et al. / Journal of Molecular Structure 792–793 (2006) 93–98
(1) Co-TTP studied exhibits high efficiency of triplet states
generation (0.86–0.94) in solution, and it seems that it will
also able to trigger directly the photodynamic reaction in
biological systems because of their triplet is incompletely
depopulated in an access amount of molecular oxygen.
(2) Photophysical properties of meso-substituted TTP dyes
depend strongly on the nature of substituents, and only
compound with aminophenyl group combines both high
yield of triplet (0.78–0.90) and of singlet molecular oxygen
production (0.81–0.99), hence it could be used in
photodynamic cancer treatment, which involves tumor
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Acknowledgements
The paper was financially supported from KBN Grant 1
P03B 155 29 (2005-2007).
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