42
Z. Katona et al./Journal of Molecular Structure 450 (1998) 41–45
5,10,15,20-tetrakis(methoxyphenyl)porphyrins (I)1
which are the synthetic precursors of the appropriate
hydroxy derivatives applied in PDT [4]. Although the
triplet state properties investigated by photolysis tech-
niques can be used in the preliminary evaluation of the
photosensitizing activity of compounds designed for
PDT, these data for (I) and related porphyrins have
not been reported previously.
carried out by bubbling helium through the solution.
The analyzing light from a xenon lamp (150 W) was
set perpendicular to the excitation beam on the sample
cell, and focused on a monochromator (Applied
Photophysics Ltd. The signal was detected by a photo-
multiplier tube (RCA, 1P28) and digitized by a PC
data acquisition board (Sonix STR*832). A shutter
used to protect the sample from the analyzing light,
as well as data acquisition and processing were con-
trolled by computer. Porphyrin concentrations were
between 5 and 10 mM, the optical path length was
1.00 cm, the energy of the laser flashes was 0.3–
1.3 mJ and absorbances in the range 0.02–0.08 were
measured at 532 nm.
Determination of triplet lifetime in the presence of
oxygen and of triplet quantum yield were carried out on
a similar laser instrument based on a Quanta-Ray DCR-
1 Nd:YAG laser, a xenon lamp (450 W) and a Tektro-
nix TDS-684A digital oscilloscope (1 GHz bandwidth,
5 GS s−1 sampling rate). This setup allowed measure-
ments with a time resolution of the order of 10 ns and
of absorbances of the order of 0.001 [7].
For the determination of singlet oxygen quantum
yield (FD) the emission at 1.27 mm following laser
excitation was monitored by a liquid nitrogen-cooled
germanium photodiode (EO-817P, North Coast
Scientific Co.). The excitation source was the Surelite
Nd:YAG laser mentioned above. Two interference
filters (centered at 1.27 m, FWHM 40 nm) were
placed between the sample and the detector. The
absorbances of the reference solution (Rose Bengal
sensitizer (Fluka) in ethanol, FD = 0.80, or meso-
tetraphenylporphyrin (I, R1 = R2 = R3 = H) in
benzene, FD = 0.66 [8]) and the sample solution (at
532 nm) were set equal (between 0.30 and 0.67) by
dilution.
The measurements were carried out at room tem-
perature (298 K) in benzene (spectroscopic grade) and
ethanol (analytical grade). Naphthacene used in triplet
quantum yield measurements was purchased from
Fluka. meso-Tetraphenylporphyrin was synthesized
as described in Ref. [5], and its purity was checked.
2. Experimental
Compounds (I) were synthesized from the corre-
sponding aromatic aldehydes and pyrrole with an
improved version of the Rothemund–Adler method
[5].
The absorption spectra were recorded on a
HP8452A diode array spectrophotometer. Porphyrin
concentration was 1 or 5 mM, the optical path length
was 1.00 cm.
A laser flash photolysis setup [6] based on a Q-
switched frequency-doubled Nd:YAG laser excitation
source (Continuum, Surelite I-10, 4–6 ns pulses at
532 nm) was used for the triplet absorption measure-
ments in the range 370–500 nm. Pulse energy was
measured by an energy meter (Rj 7100, Laser Preci-
sion Corporation). Deoxygenation of the samples was
1 The compounds (I) will be abbreviated as follows: 3-TMPP
(5,10,15,20-tetrakis(3-methoxyphenyl)porphyrin (R1 = OCH3, R2
= R3 = H)), 3,4-TDMPP (5,10,15,20-tetrakis(3,4-dimethoxyphe-
3. Results and discussion
nyl)porphyrin (R1
=
R2
=
OCH3, R3
=
H)), 3,5-TDMPP
(5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin (R1 = R3
OCH3, R2
H)), 3,4,5-TTMPP (5,10,15,20-tetrakis(3,4,5-tri-
methoxyphenyl)porphyrin (R1 = R2 = R3 = OCH3)).
=
The absorption characteristics of compounds (I) are
shown in Table 1. It is clearly seen that the number
=