The synthesis of new potential photosensitizers [1-3]. Part 4. Photophysical properties of some monophenyltripyridyl-porphyrin derivatives

Article abstract of DOI:10.1142/S1088424615501047

Six monophenyltripyridylporphyrin derivatives were synthesized and characterized by spectroscopy in order to demonstrate their potential usefulness as photosensitizers for anticancer therapy purposes. Compounds 1 and 3-5 are amphiphilic, thus they may be

Full text of DOI:10.1142/S1088424615501047

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2015; 19: 1204–1211
DOI: 10.1142/S1088424615501047
Published at http://www.worldscinet.com/jpp/
The synthesis of new potential photosensitizers [1–3].
Part 4. Photophysical properties of some
monophenyltripyridyl-porphyrin derivatives
Piotr Kus´*a◊, Anna Pasewicz-Sokółb, Alicja Ratusznab,c and Marcin Rojkiewicza
a Department of Chemistry, University of Silesia, 9, Szkolna Street, 40-006 Katowice, Poland
b A. Chełkowski Institute of Physics, University of Silesia, 4, Uniwersytecka Street, 40-007 Katowice, Poland
c Silesian Center for Education and Interdisciplinary Research, 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland
Received 18 October 2015
Accepted 9 November 2015
ABSTRACT: Six monophenyltripyridylporphyrin derivatives were synthesized and characterized
by spectroscopy in order to demonstrate their potential usefulness as photosensitizers for anticancer
therapy purposes. Compounds 1 and 3–5 are amphiphilic, thus they may be suitable for transfer inside
cells. Photochemical parameters such as fluorescence yield and singlet oxygen yield were determined.
The former parameter does not exceed 10% which makes them unsuitable for photodynamic diagnosis
(PDD). However, singlet oxygen yields are high and sufficient for these compounds to be considered as
potential photodynamic therapy (PDT) photosensitizers.
KEYWORDS: photosensitizers, porphyrins, fluorescence, UV-vis, singlet oxygen, tetrapyrroles.
Compounds 1 and 2, shown in Scheme 1, were earlier
INTRODUCTION
reported by us and had been characterized biologically as
We have been particularly interested by tetrapyrrole
well as using crystallography and synchrotron radiation
compounds suitable for PDD or PDT [1–3]. In particular,
[19, 20].
of interest to us have been their photochemical properties,
Compound 1 demonstrated photodynamic activity
including yield of singlet oxygen. The latter is generated
causing cell death upon intracellular transfer and
during irradiation of the photosensitizer in the presence
subsequent irradiation. Responsible for cell death was
of triplet oxygen. This phenomenon, if occurring inside a
most likely singlet oxygen formed during the process.
cell or on a cell membrane, might result in cell death; as
This phenomenon occurs for all porphyrins that can be
such it has been taken advantage of in anticancer therapy.
transferred to the cell inside. Responsible for this process
Photofrin or Foscan, tetrapyrrole derivatives, are two
is the central porphyrin ring of the molecule. Substituents
well-known photosensitizers used for years in PDT.
generally make introduction of porphyrin entity into
The following derivatives: tripyridylmonohydroxy-
biological material easier (or more difficult). A real
phenyl [4–6], tripyridylmonocarboxyphenyl [7–10] and
challenge for synthesizing these compounds is such their
tripyridylmonoaminophenylporphyrin [11–18] have been
modification that would allow them to be delivered only
frequently reported and suggested as potentially photo-
to cancer cells owing to their hydrophobic-hydrophilic
cytotoxic to cancer cells [5, 6, 9, 12]; as chemical
nature or, perhaps, by using suitable carriers which they
shift reagents [7]; as multimodal agents for molecular
couldbelinkedinvariouscombinations.Ourownattempts
imaging [10]; as biocatalysts [14, 16] and as compounds
to obtain suitable porphyrin derivatives are geared
selectively binding to DNA [17, 18].
towards use of liposomal carriers in which they could be
“anchored.” One of the features of a good photosensitizer
is its easy procurement, i.e. simple synthetic procedure
and uncomplicated structure. They ought to be very
◊ SPP full member in good standing
*Correspondence to: Piotr Kuś, email: pkus@ich.us.edu.pl
thoroughly characterized physico-chemically.
Copyright © 2015 World Scientific Publishing Company

THE SYNTHESIS OF NEW POTENTIAL PHOTOSENSITIZERS [1–3] 1205
N
Synthesis
1 OC16H33
2 COOCH3
R =
5-(4-Hexadecyloxyphenyl)-10,15,20-tri(4-pyridyl)
porphyrin (1). 4-Hexadecyloxybenzaldehyde (3.46 g,
0.01 mol), 4-pyridylaldehyde (3.21 g, 0.03 mol) were
NH
N
N
3 COOC16H33
4 COOC18H37
5 NHCOC15H31
R
N
dissolved in 300 mL of propionic acid and heated to
reflux. Pyrrole (2.68 g, 0.04 mol) was added and the
resulting mixture was heated under reflux for 2 h. 250 mL
of propionic acid was removed by distillation. Rest of
propionic acid was neutralized by saturated solution of
sodium carbonate and the resulting mixture was extracted
by dichloromethane. Organic layer was washed with
water (5 × 100 mL) and dried with anhydrous MgSO4.
Dichloromethane was evaporated and the residue was
chromatographed on silica gel with chloroform-ethyl
acetate (2:1, v/v) mixture as eluent. Yield 0.21 g (2.5%).
Anal. calcd. for. C57H59N7O: C, 79.78; H, 6.93; N, 11.43.
Found C, 79.49, H, 6.95, N, 11.20. 1H NMR (400 MHz,
CDCl3): dH, ppm 9.02, 8.14 (dd, 12H, J = 5.4 Hz), 8.94,
8.78 (dd, 4H), 8.82 (bs, 4H), 8.07, 7.27 (dd, 4H, J = 8.4
Hz), 4.23 (t, 2H), 1.96 (q, 2H), 1.45 (q, 2H), 1.40–1.20
(m, 22H), 0.76 (t, 3H), -2.88 (bs, 2H). 13C NMR (CDCl3):
dC, ppm 14.2, 22.7, 26.3, 29.4, 29.6, 29.7, 29.8, 31.9, 68.4,
112.9, 116.8, 117.4, 121.9, 129.4, 133.5, 135.7, 148.2,
150.2, 159.3. MS (ESI): m/z 858.7 (calcd. for [M + H]+
858.5). HRMS (ESI+): m/z calcd. for [M + H]+ 858.4853,
found 858.4746.
HN
N
1-5
N
NH
N
N
O
N
O
N
HN
HN
N
6
Fig 1. Structures of 1–6
5-(4-Methoxycarbonylphenyl)-10,15,20-tri(4-pyri-
dyl)porphyrin (2). 4-Methoxycarbonylbenzaldehyde
(3.28 g, 0.02 mol), 4-pyridylaldehyde (6.43 g, 0.06 mol)
were dissolved in 300 mL of propionic acid and heated
to reflux. Pyrrole (5.37 g, 0.08 mol) was added and the
resulting mixture was heated under reflux for 2 h. 250 mL
of propionic acid was removed by distillation. Rest of
propionic acid was neutralized by saturated solution of
sodium carbonate and the resulting mixture was extracted
by dichloromethane. Organic layer was washed with
water (5 × 100 mL) and dried with anhydrous MgSO4.
Dichloromethane was evaporated and the residue was
chromatographed on silica gel with chloroform-methanol
(3:1, v/v) mixture as eluent. Yield 0.64 g (4.7%). Anal.
calcd. for. C43H29N7O2: C, 76.43; H, 4.33; N, 14.51. Found
C, 76.08, H, 4.25, N, 14.80. 1H NMR (400 MHz, CDCl3):
dH, ppm 9.07, 8.20 (dd, 12H, J = 5.4 Hz), 8.86–8.83 (m,
8H), 8.30, 8.20 (dd, 4H, J = 10 Hz), 4.1 (s, 3H), -2.89 (bs,
2H). MS (ESI): m/z 676.4 (calcd. for [M + H]+ 676).
5-(4-Hexadecyloxycarbonylphenyl)-10,15,20-tri(4-
pyridyl)porphyrin (3). 5-(4-Carboxyphenyl)-10,15,20-
tri(4-pyridyl)porphyrin was obtained by hydrolysis of 2
in the solution of KOH in DMF in 85%. 5-(4-Carboxy-
phenyl)-10,15,20-tri(4-pyridyl)porphyrin (0.01 g, 0.015
mmol), 4-(dimethylamino)pyridine (DMAP) (0.0035 g,
ca 0.03 mmol) and 1.5 mL of 0.01 M dicyclohexyl
carbodiimide (DCC) solution (0.015 mmol) dissolved in
5 mL of dichloromethane were refrigerated for 2 days.
After that haxadecan-1-ol (0.004 g, ~0.015 mmol) dis-
solved in 5 mL of dichloromethane was added and
EXPERIMENTAL
General
All chemical reagents were purchased from Aldrich
or Acros and were used without further purification.
NMR spectra were recorded in CDCl3 using a Brucker
spectrometer (400 MHz). The peaks were referenced
to the residual CHCl3 resonances in H and 13C NMR
1
(7.26 and 77.16 ppm, respectively). IR spectra were
recorded on Bio-Rad FTS-600. UV-vis spectra were
recorded in dichloromethane solutions using a Genesys
6 (ThermoSpectronic) spectrophotometer. Fluorescence
spectra of the samples were taken on Varian Eclipse
Cary — fluorescence spectrophotometer. ESI MS
spectra were acquired using a LCQ DUO FINNINGAN
THERMOQUEST spectrometer. The compounds to be
studied were dissolved in a dichloromethane-methanol or
acetone solutions and introduced into the source through
a capillary at the rate of 20 mL.min-1. The evaporation was
assisted by an outflow of nitrogen heated at 200°C. The
ESI voltage 4.5 kV, current 58–60 mA, capillary voltage
was 10.5 V, capillary temperature — 200°C, collision
gas — helium. For all compounds full-scan positive ion
mass spectra were acquired. High resolution mass spectra
were recorded on Bruker AD-604 spectrometer using
electrosprey technique.
Copyright © 2015 World Scientific Publishing Company
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´
1206 P. K U S ET AL.
the resulting mixture was refrigerated for next 4 days.
Finally the mixture was stirred at room temperature
for 2 days. 10 mL of dichloromethane was added to
the mixture and the resulting solution was washed
with water (2 × 20 mL) and dried with anhydrous
MgSO4. Dichloromethane was evaporated and the
residue was separated on preparative silica gel plates
with chloroform-methanol (200:3, v/v) as eluent. Yield
140.4, 147.6, 149.9, 171.9. MS (ESI): m/z 871 (calcd. for
[M + H]+ 871). HRMS (ESI+): m/z calcd. for [M + H]+
871.4806, found 871.4706.
N-[5-(4-Carbonylphenyl)-10,15,20-tri(4-pyridyl)
porphyrin]-N,N′-dicyclohexylurea (6). This compound
was isolated (ca. 20% yield) during preparative
1
chromatographic separation of compounds 3 and 4. H
NMR (400 MHz, CDCl3): dH, ppm 9.06, 8.17 (dd, 12H,
J = 6 Hz), 8.88–8.84 (m, 8H), 8.30, 8.02 (dd, 4H, J =
10.05 Hz), 6.27 (m, 1H), 4.43 (m, 1H), 3.75 (m, 1H),
2.20–1.20 (m, 20H), -2.87 (bs, 2H). 13C NMR (CDCl3):
dC, ppm 24.7, 25.4, 25.5, 26.4, 29.7, 30.9, 32.7, 50.0,
57.3, 117.4, 117.6, 120.1, 125.6, 129.4, 134.6, 136.8,
144.1, 148.2, 150.0, 150.1, 154.4, 170.7. MS ESI: m/z
868 (calcd. for [M + H]+ 868). HRMS (ESI+): m/z calcd.
for [M + H]+ 868.4081, found 868.3965. Anal. calcd. for
C55H49N9O2:C, 76.10; H, 5.69; N, 14.52. Found C, 76.02,
H, 5.80, N, 14.76.
1
0.006 g (40%). H NMR (400 MHz, CDCl3): dH, ppm
9.04, 8.18 (dd, 12H, J = 5.5 Hz), 8.89–8.85 (m, 8H),
8.50, 8.32 (dd, 4H, J = 8 Hz), 4.54 (t, 2H), 1.94 (q, 2H),
1.61 (q, 2H), 1.48 (q, 2H), 1.35–1.21 (m, 22H), 0.87 (t,
3H), -2.88 (bs, 2H). 13C NMR (CDCl3): dC, ppm 14.2,
22.7, 24.9, 26.2, 29.6, 29.7, 29.8, 31.2, 65.7, 117.2,
117.4, 120.6, 128.1, 129.6, 130.5, 132.4, 134.5, 145.9,
147.6, 149.9, 150.8, 166.7. MS (ESI): m/z 886 (calcd. for
[M + H]+ 886). HRMS (ESI+): m/z calcd. for [M + H]+
886.4803, found 886.4706.
5-(4-Octadecyloxycarbonylphenyl)-10,15,20-tri(4-
pyridyl)porphyrin (4). This compound was obtained
similar to 3, using octadecan-1-ol instead of hexadecane-
1-ol. Product was chromatographed on silica gel with
chloroform-methanol (200:3, v/v) mixture as eluent.
5,10,15,20-Tetra(9-phenanthrenyl)porphyrin (7).
This compound was synthesized according to [26]. H
1
NMR (400 MHz, CDCl3): dH, ppm 8.96 (t, 8H), 8.64 (bs,
8H), 8.60 (d, 4H), 8.05 (d, 4H), 7.85 (t, 4H), 7.76 (t, 4H),
7.63 (t, 4H), 7.40–7.20 (m, 8H), -2.1 (bs, 2H). 13C NMR
(CDCl3): dC, ppm 117.7, 122.5, 122.8, 126.3, 126.7,
127.3, 127.4, 129.0, 129.6, 130.0, 130.1, 130.7, 130.8,
133.5, 133.6, 133.8, 136.2, 137.5, 137.6. MS (ESI): m/z
1015 (calcd. for [M + H]+ 1015). HRMS (ESI+): m/z
calcd. for [M + H]+ 1015.3795, found 1015.3678.
1
Yield 47%. H NMR (400 MHz, CDCl3): dH, ppm 9.09,
8.18 (dd, 12H, J = 5.5 Hz), 8.90-8.85 (m, 8H), 8.50, 8.30
(dd, 4H, J = 10.05), 4.54 (t, 2H), 1.95 (q, 2H), 1.61 (q,
2H), 1.38–1.21 (m, 28H), 0.87 (t, 3H), -2.86 (bs, 2H).
13C NMR (CDCl3): dC, ppm 14.1, 22.7, 26.2, 28.9, 29.1,
29.3, 29.4, 29.6, 29.7, 31.9, 65.6, 117.4, 117.6, 120.2,
128.0, 129.3, 130.4, 131.3, 134.5, 146.1, 148.3, 149.9,
166.9. MS (ESI): m/z 914 (calcd. for [M + H]+ 914).
HRMS (ESI+): m/z calcd. for [M + H]+ 914.5116, found
914.5026.
RESULTS AND DISCUSSION
Synthesis
5-(4-Hexadecanamidophenyl)-10,15,20-tri(4-
pyridyl)porphyrin (5) was synthesized according to
Compounds 1–5 were obtained in a series of reactions
shown in Schemes 1–3. All of them display asymmetry
and have three pyridine substituents and a phenyl one
substituted in para-position. Derivatives of this kind
are obtained in reactions of mixed aldehydes with
pyrrole (yields of these reactions are most frequently
very low since six various porphyrin derivatives
are obtained) or by modifying functional groups or
1
[21]. H NMR (400 MHz, CDCl3): dH, ppm 9.08–9.04
(m, 6H), 8.87 (bs, 4H), 8.98, 8.83 (dd, 4H), 8.20–8.14
(m, 8H), 8.00 (d, 2H), 7.81 (s, 1H), 2.6 (t, 2H), 1.91 (q,
2H), 1.41–1.28 (m, 24H), 0.89 (t, 3H), -2.86 (bs, 2H).
13C NMR (CDCl3): dC, ppm 14.1, 22.7, 25.4, 25.6, 25.8,
29.4, 29.5, 29.6, 29.7, 31.9, 34.5, 38.1, 117.3, 118.1,
127.4, 128.2, 129.6, 131.0, 132.4, 135.2, 137.9, 138.3,
N
CHO
N
CHO
NH
N
N
CH3CH2COOH
OC16H33
3
+
+ 4
N
HN
N
H
OC16H33
1
N
Scheme 1. Synthesis of compound 1
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 1206–1211

THE SYNTHESIS OF NEW POTENTIAL PHOTOSENSITIZERS [1–3] 1207
N
CHO
N
CHO
NH
N
N
CH3CH2COOH
COOCH3
3
+
+ 4
N
N
HN
H
COOCH3
2
N
N
N
NH
NH
N
N
N
KOH/DMF
COOCH3
COOH
N
N
HN
HN
N
2
N
N
N
N
NH
N
NH
N
N
N
ROH/DCC/DMAP
CH2Cl2
COOH
COOR
N
N
HN
HN
3
4
R = C16H33
R = C18H37
N
N
Scheme 2. Synthesis of compounds 2, 3 and 4
porphyrin-type compounds (in these cases yields
are higher since one of the substrates is porphyrin).
Compound 1 was obtained directly in the reaction of
mixed aldehydes (4-hexadecyloxybenzaldehyde and
4-pyridylaldehyde) with a yield of 2.5%. Likewise,
compound 2 was obtained (from 4-pyridylaldehyde
and 4-methoxycarbonylbenzaldehyde) with ca. 5%
yield. Compound 2 was the starting point for obtaining
5-(4-carboxyphenyl)-10,15,20-tri(4-pyridyl)porphyrin
via hydrolysis of ester moiety. The carboxylic derivative
was transformed by esterification, into compounds 3 and 4
with ca. 40% yield. Compound 5 was obtained in a three-
stage procedure reported in [21] and shown in Scheme 3.
Compound 6 was obtained (accidentally) with a
good yield (ca. 20% with respect to the main product)
during preparation of a mixture of carboxyporphyrin
and DCC. In the case of carboxylic derivatives of
tetraphenylporphyrin greater yield is obtained for stable
N-acylurea species than for O-acylurea [22]. This type of
reaction when making esters or amides is not favorable
since it lowers total yield of the reaction. This compound
is a stable product with defined structure. We therefore
decided to check its physicochemical and photooptical
properties.
UV-vis spectra
All porphyrin conjugates show typical electronic
spectra. A Soret band appears near 420 nm and four less
intense Q-bands are present at 513, 548, 589 and 645 nm
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J. Porphyrins Phthalocyanines 2015; 19: 1207–1211

´
1208 P. K U S ET AL.
N
CHO
N
CHO
NH
N
N
CH3CH2COOH
NHCOCH3
3
+
+ 4
N
HN
N
H
NHCOCH3
N
N
N
NH
N
N
NH
N
N
CF3COOH/HCl
NHCOCH3
NH2
N
N
HN
HN
N
N
N
N
NH
N
N
NH
N
N
C15H33COCl/Et3N
CHCl3
NH2
NHCOC15H33
N
N
HN
HN
5
N
N
Scheme 3. Synthesis of compound 5
with an ethio outline. For all the examined compounds
there is little difference in extinction coefficients. The
UV-vis data are shown in Table 1.
3315–3331 cm-1 range which corresponds to vibration
values for N–H groups present in the porphyrin ring. In
the case of compounds 5 and 6 with additional amide
groups, there are additional vibrations of N–H groups
at 3349 and 3442 cm-1, respectively. In spectra of all
compounds with pyridine substituents, characteristic
strong stretching vibrations nCpyr-Cpyr are seen in a very
narrow range (1590–1609 cm-1).
IR spectra
Porphyrin compounds show very strong absorption
in the infrared range. The best solution to obtain
high-quality spectra is to use ATR (Attenuated Total
Reflection) technique. Our spectra were recorded for
powdered sample using Bio-Rad FTS-600 spectrometer
equipped with ATR Miracle accessory and KRS5
lenses. All samples showed presence of vibrations in the
Fluorescence and singlet oxygen
Fluorescence spectra of the investigated compounds,
as well as tetraphenylporphyrin (TPP) are shown in
Copyright © 2015 World Scientific Publishing Company
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THE SYNTHESIS OF NEW POTENTIAL PHOTOSENSITIZERS [1–3] 1209
Table 1. UV-vis spectra of compounds 1–7 [lnm (log e)] in chloroform solutions
Derivatives
lSoret
Qy(1–0)
Qy(0–0)
Qx(1–0)
Qx(0–0)
1
2
3
4
5
6
7
420 (5.33)
419 (6.94)
417 (5.51)
419 (5.73)
420 (5.61)
419 (5.38)
427 (5.74)
514 (4.26)
513 (4.24)
513 (4.10)
513 (4.28)
514 (4.17)
513 (4.18)
516 (4.35)
549 (3.86)
547 (3.76)
548 (3.62)
546 (3.86)
549 (3.75)
547 (3.72)
550 (3.65)
591 (3.74)
588 (3.72)
588 (3.61)
589 (3.80)
589 (3.63)
589 (3.66)
591 (3.81)
648 (3.46)
645 (3.36)
643 (3.23)
645 (3.46)
647 (3.32)
646 (3.36)
648 (3.18)
NH
N
NH
N
N
HN
HN
N
7
TPP
Fig 2. Structures of tetrakis-5,10,15,20-phenylporphyrin (TPP) and tetrakis-5,10,15,20-(9 phenanthrenyl)porphyrin (7)
Table 2. Selected IR data for compounds 1–7 (cm-1)
1
2
3
4
5
6
7
nN-H
3315
2853
2924
—
3320
—
3324
2851
2918
1720
1609
3331
2851
2915
1719
1590
3320
2851
2921
1716
1592
3315
2863
2930
1724
1591
3315
—
n
symCH2
asymCH2
n
—
—
nC=O
1721
1592
—
nCpyrCpyr
1593
—
Table 3. Emission bands for all the compounds occur at
650 2 and 717 2 nm. Fluorescence yields of these
compounds, determined by a comparative method (with
TPP used as a reference) did not exceed a 10% threshold.
Such values preclude use of these compounds in
photodynamic diagnostics; at the same time it suggests
that they can generate greater amounts of singlet oxygen
since there is a greater probability of intercombinatory
transitions responsible for this process.
measurement of characteristic emission of singlet
oxygen at ca. 1280 nm. This is a relative value and
in our case we made use of a previously determined
singlet oxygen quantum yield for TPP (FD = 0.62) [23]
as a reference value. Samples of compounds in toluene
with absorbance of ~0.35 [Soret band] were subjected
to oxygen saturation for ca. 2 min and then they were
excited with a laser flash of l = 355 nm. Emission
spectrum of samples was recorded in the 1245–1320 nm
range. Measurements were repeated 30–50 times. Values
of relative effectiveness of generating singlet oxygen for
all the compounds are comparable and average ca. 60%.
Singlet oxygen quantum yield was determined in an
identical manner as described in part 2 of our publication.
To this purpose we used laser flash photolysis and
Copyright © 2015 World Scientific Publishing Company
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´
1210 P. K U S ET AL.
Table 3. Fluorescence emission maximums, wavelengths (Lmax), fluorescence quantum
yields (DF), Stokes shifts (nm) between the Q(0–0) and Qx(0–0) band and quantum
yield of singlet oxygen FD for compound 1–7 and tetraphenylporphyrine (TPP)
Photosensitizers
Q(0–0)
Q(0–1)
FF (420 nm)
FD
Stokes shift
1
651
648
651
651
651
650
651
651
718
716
717
716
717
717
719
719
0.09
0.10
0.08
0.08
0.08
0.10
0.100
0.09
0.61
0.60
0.61
0.61
0.59
0.62
0.62
0.63
3
3
2
3
8
4
6
5
4
6
4
TPP
7
—
3
This value indicates that they may be potentially useful
in PDT.
CONCLUSION
Porphyrins obtained by us with three pyridine
substituents and one substituent of hydrophobic nature
showsimilarphotochemicalproperties.Thesecompounds
might be used as potential photosensitizers in PDT since
they show great capacity to form singlet oxygen which is
one of the most important factors mediating targeted cell
death. Low fluorescence quantum yield suggests that they
are not suitable for PDD. The hydrophobic-hydrophilic
nature of the obtained compounds, on the other hand,
makes feasible using liposomes as their carrier for in
vivo applications. Our observations suggest that these
compounds are stable solids and their solutions in neutral
solvents do not show changes in UV spectra after storage
for several days at room temperature.
For compound 1 oxygen quantum yield was earlier
determined by us using a different method and 1-H-
phenalen-1-one as a reference [19]. The value of FD
determined with this method was 0.66, so it does not differ
substantiallyfromthevaluedeterminedandcitedinthispaper.
Both determined values are higher than that of Photofrin
(FD = 0.32 [19]). Oxygen quantum yield determined in the
same way for tetra-phenanthrenylporphyrin (7) has a similar
value to those of the remaining compounds discussed in
this paper, to TPP reference (FD = 0.66, determined acc.
to [24]), and to tetra-a-naphthylporphyrin (FD = 0.97,
determined acc. to [25]). Both FD values were measured by
a photoacoustic method.
Stokes shift, which characterizes magnitude of the
shift between Q (0–0) band of the fluorescence spectrum
and Qx (0–0) band of the absorbance spectrum is for
our compounds small. This can reflect small structural
changes occurring in porphyrin molecules during
excitation process.
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Mass spectra
The ESI mass spectra were recorded using LCQ
DUO FINNINGAN THERMOQUEST spectrometer.
The compounds to be studied were dissolved in
dichloromethane/methanol or acetone solutions and
introduced into the source through a capillary at the
rate of 20 mL.min-1. Only positive mode electrospray
ionization method could be used in analysis of
porphyrins 1–7. The base peaks corresponding to [M +
H]+ ions for all compounds were observed (data are in
the Experimental section accompanying description of
particular compounds). No presence of fragmentary ions
was detected. Peaks corresponding to the formation of
ion clusters were not observed.
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