Synthesis of vinylated 5,10,15,20-tetraphenylporphyrins via heck-type coupling reaction and their photophysical properties

Article abstract of DOI:10.1039/b203910a

The direct coupling reaction between substituted olefins and 5,10,15,20-tetrakis(4-bromophenyl)porphyrin, via a Heck-type reaction, constitutes a versatile method for the vinylation of 5,10,15,20-tetrakis(4-bromophenyl)porphyrin to yield new vinylated tetraphenylporphyrins quantitatively. Another strategy for the vinylporphyrin synthesis has been developed. A phosphapalladacycle has been used as catalyst for the coupling reaction between 4-bromoaryl aldehydes and olefins to yield vinyl aldehydes quantitatively. These aldehydes have been condensed with pyrrole, by the one-step nitrobenzene method, to give the corresponding vinylated tetraphenylporphyrins. Photophysical studies of these new porphyrins are also reported.

Full text of DOI:10.1039/b203910a

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Synthesis of vinylated 5,10,15,20-tetraphenylporphyrins via
Heck-type coupling reaction and their photophysical properties
a
b
b
a
Mariette M. Pereira,* Guillermo Muller, Juan Ignacio Ordinas, M. Emília Azenha and
Luís G. Arnaut
a
2
a
Rua Larga, Departamento de Química, Universidade de Coimbra, 3049 Coimbra, Portugal.
E-mail: mmp@ci.uc.pt
Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 647, 08028,
Barcelona, Spain
b
Received (in Cambridge, UK) 22nd April 2002, Accepted 18th June 2002
First published as an Advance Article on the web 10th July 2002
The direct coupling reaction between substituted olefins and 5,10,15,20-tetrakis(4-bromophenyl)porphyrin, via a
Heck-type reaction, constitutes a versatile method for the vinylation of 5,10,15,20-tetrakis(4-bromophenyl)porphyrin
to yield new vinylated tetraphenylporphyrins quantitatively. Another strategy for the vinylporphyrin synthesis has
been developed. A phosphapalladacycle has been used as catalyst for the coupling reaction between 4-bromoaryl
aldehydes and olefins to yield vinyl aldehydes quantitatively. These aldehydes have been condensed with pyrrole, by
the one-step nitrobenzene method, to give the corresponding vinylated tetraphenylporphyrins. Photophysical studies
of these new porphyrins are also reported.
Introduction
phenyl)porphyrin 2, via Heck reaction and also by the con-
densation reaction between vinyl aldehydes 3 and 4 with
pyrrole. Comparative studies of the catalytic efficiency of the
palladacycles 5 and the classic catalytic system palladium()
acetate–triphenylphosphine are discussed. Fluorescence, phos-
phorescence, flash photolysis and photoacoustic calorimetry
were employed to characterise the photophysics of the new
porphyrins 6–8.
The development of new strategies to improve the synthesis
of functionalized meso-arylporphyrins has been extensively
studied in recent years due to the multiple applications of
porphyrins and metalloporphyrins in various areas such as
photodynamic therapy, molecular electronics, sensors and
1
2–4
5
6
7–9
oxidation catalysis. meso-Arylporphyrins have been the com-
pounds of choice in the great majority of these applications
mainly due to their ease of synthesis. Extension of the one-pot
10
11
Rothemund synthesis by Adler et al. using propionic acid
Experimental
Reagents were used as received: 4-bromobenzaldehyde
12,13
instead of pyridine, and by Gonsalves and Pereira
using
acetic acid–nitrobenzene opened the way for large scale syn-
thesis of several meso-arylporphyrins. The attachment of
unusual organic groups to such porphyrins is of considerable
interest, since slight changes in the substituents can significantly
change the fundamental properties of the macrocycle.
The application of the Heck reaction to promote the
coupling of halogenated aromatic compounds with several sub-
stituted olefins is an established method reckoned as a powerful
(
(
(
(
(
Aldrich), 4-methoxystyrene (Janssen Chimica), butyl acrylate
Fluka), methyl vinyl ketone (Fluka), cinnamyl acetate
Aldrich), 2-methylbut-3-en-1-ol (Aldrich), vinyl acetate
Fluka), dimethylformamide (Fluka), 4-bromobenzaldehyde
Aldrich), pyrrole (Aldrich).
All solvents and reagents were purified and dried using
standard procedures. Except where noted, all the solutions were
carefully de-aerated with N -saturated in toluene before the
14,15
2
synthetic strategy to functionalize aromatic compounds.
The usual catalyst for the classic Heck reaction is palladium
acetate, palladium chloride or preformed (triarylphosphine)-
photophysical measurements were made. In order to obtain an
appropriate glass, at liquid nitrogen temperature, the toluene
solutions were frozen very quickly.
16
palladium complexes. Recently, other catalytic systems have
been explored, using different palladium ligands namely,
1
7
18,19
20
diphosphine, phosphite,
active phosphapalladacycles.
1s–u23lfur–phosphine and the very
Instrumentation
H NMR spectra were recorded on a 300 MHz Bruker AMX
2
1
Palladium-catalysed coupling reactions have often been
employed to functionalize the porphyrin periphery and have
recently been reviewed. In previously described methods only
the coupling of β-halogenated porphyrins with the desired
unsaturated compounds has been studied.
Furthermore, the coupling of 5,15-diiodo-10,20-diphenyl-
porphyrins with alkynes and aromatic iodides with the vinyl
group of protoporphyrin-IX, via Heck reaction, has also been
described.
spectrometer. Mass spectra were obtained through the MS
services of the University of Swansea. Elemental analysis was
carried out using Fisons Instruments EA1108-CHNS-0 appar-
atus. Absorption and luminescence spectra were recorded with
Shimadzu UV-2100 and SPEX Fluorolog 3.22 spectrophoto-
meters, respectively. Low-temperature phosphorescence spectra
and lifetimes were obtained with the same SPEX Fluorolog
24
25–29
3
0
3
1
3
.22 with 1934D phosphorimeter.
To the best of our knowledge the Heck-type reaction has
never been used in direct functionalization of meso-substituted
halogenated phenylporphyrins. In this paper we report the
synthesis of new meso-vinylphenylporphyrins by direct coupling
of substituted olefins 1a–f and 5,10,15,20-tetrakis(4-bromo-
Methods
Luminescence measurements. Fluorescence measurements
were made in 1 cm quartz cuvettes on toluene solutions, care-
fully deaerated with N . Fluorescence quantum yields (Φ ) were
2
F
DOI: 10.1039/b203910a
J. Chem. Soc., Perkin Trans. 2, 2002, 1583–1588
1583
This journal is © The Royal Society of Chemistry 2002

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measured with carefully diluted solutions of the desired
porphyrin in deaerated toluene, with absorbance 0.02 at an
formamide (15 ml), also under a nitrogen atmosphere. Both
solutions were heated to 120 ЊC, and then the catalyst solution
was transferred by cannula to the Schlenk tube containing the
reagents. After 16 hours the reaction was stopped, and the mix-
ture was cooled to room temperature and quenched by adding
10 ml of HCl (5%). The crude product was purified by extrac-
tion with dichloromethane and water. The organic phase was
dried with Na SO and concentrated to dryness.
excitation wavelength of 417 nm. Using Φ = 0.10 for tetra-
F
32
phenylporphyrin (TPP) as reference, the ΦF values for the
33
new porphyrins were obtained as previously described. The
phosphorescence studies were carried out in toluene solution at
liquid nitrogen temperature with excitation at the maximum of
the Soret band. Fluorescence excitation spectra for all the por-
phyrins are in agreement with the corresponding absorption
spectra, confirming the purity of the samples.
2
4
(E )-4-(2-Butoxycarbonylethenyl)benzaldehyde (3)
.20 g of (E)-4-(2-butoxycarbonylethenyl)benzaldehyde were
5
Flash photolysis measurements. Flash photolysis employed an
Applied Photophysics LKS.60 spectrometer, with a Spectra-
Physics Quanta-Ray GCR-130 Nd–YAG laser and a Hewlett-
1
obtained as a yellow oil (yield: 83%). H NMR (CDCl3,
50 MHz) δ 0.91 (t, J = 7.3 Hz, 3H), 1.37 (m, 2H), 1.63 (m, 2H),
4.17 (d, J = 6.6 Hz, 2H), 6.48 (d, J = 16.0 Hz, 1H), 7.61 (d, J =
2
Ϫ1
Packard Infinium Oscilloscope (1 GS s ; GS = Giga Sample);
8
9
3
1
.3 Hz, 2H), 7.64 (d, J = 16.0 Hz, 1H), 7.84 (d, J = 8.3 Hz, 2H),
the samples were irradiated with the third harmonic of the laser
13
.97 (s, 1H). C NMR (CDCl , 62.9 MHz) δ 13.56, 19.01,
3
(
355 nm), the monitoring light was produced by a 150 W pulsed
Xe lamp and the detection of the transient spectra in the 300–
00 nm range was made with Hamamatsu 1P28 and R928
0.56, 64.54, 121.33, 128.33, 129.96, 136.91, 139.96, 142.60,
ϩ
66.22, 191.22. MS-EI m/z = 232 (M ).
9
photomultipliers. Experiments were carried out both in aerated
(
E )-4-[2-(4-Methoxyphenyl)ethenyl]benzaldehyde (4)
.27 of (E)-4-[2-(4-methoxyphenyl)ethenyl]benzaldehyde
were obtained as a yellow powder (yield: 89%). H NMR
CDCl , 200 MHz) δ 3.85 (s, 3H, Me), 6.93 (d, J = 8.2 Hz, 2H,
and N -saturated toluene solutions.
2
1
g
Time-resolved photoacoustic measurements. Time-resolved
1
photoacoustic (PAC) measurements were carried out with a
(
3
34
front-face cell using a dielectric mirror. This PAC apparatus
and the procedure employed in the measurements was recently
ortho MeO), 7.50 (d, J = 8.2 Hz, 2H, meta MeO), 7.63 (d, J =
8
7
9
.6 Hz, 2H, ortho CHO), 7.86 (d, J = 8.6 Hz, 2H, meta CHO),
.01 (d, J = 16.4 Hz, 1H, vinyl), 7.23 (d, J = 16.4 Hz, 1H, vinyl),
35,36
described in detail.
In short, the sample and reference sol-
13
utions, and the solvent were allowed to flow separately at a rate
.98 (s, 1H, CHO). C NMR (CDCl , 50.3 MHz) δ 53.35
3
Ϫ1
of 1 ml min (SSI chromatographic pump) through a 0.11 mm
(
1
OMe), 114.20 (ortho OMe), 125.07 (vinyl), 126.52, 128.17,
29.23 (para OMe), 130.19, 131.70 (vinyl), 134.87 (ipso CHO),
thick cell. They were irradiated at 421 nm with an unfocused
PTI dye laser (model PL2300), pumped by an N laser working
2
143.75 (para CHO), 159.87 (ipso OMe), 191.51 (CHO). MS-EI
m/z = 238 (M ).
ϩ
at a frequency of 2 Hz. A small fraction of the laser beam was
reflected on to a photodiode that was used to trigger the tran-
Ϫ1
sient recorder (Tektronix DSA 601, 1 GS s ). The photoacous-
General conditions for porphyrin synthesis via Heck reaction
tic waves, detected with a 2.25 MHz Panametrics transducer
Ϫ3
5
1
,10,15,20-Tetrakis(4-bromophenyl)porphyrin 2 (0.1 × 10 g,
(
model 5676) and captured by the transient recorder, were
Ϫ4
.07 × 10 mol) was dissolved in dimethylformamide (15 ml)
transferred to a PC for data analysis. In a typical PAC experi-
ment 100 waves of the sample, reference and pure solvent are
recorded and averaged under the same experimental conditions.
Four sets of averaged sample, reference and solvent waves were
used for the data analysis at a given laser intensity, and four
laser intensities were employed in each experiment. The dif-
ferent laser intensities were obtained by interposing neutral
density filters with transmissions between 25 and 100%. All the
measurements were made in toluene using all-trans-β-carotene
as the photoacoustic reference.
under a nitrogen atmosphere. The desired olefin (7.00 ×
1
phosphapalladacycle 5 (5.5 × 10 g, 6.05 × 10 mol) or
palladium acetate (2.80 × 10 g, 1.25 × 10 mol) and tri-
Ϫ3
Ϫ3
Ϫ4
0
mol), sodium acetate (45.0 × 10 g, 5.50 × 10 mol) and
Ϫ3 Ϫ6
Ϫ3
Ϫ5
Ϫ3
Ϫ5
phenylphosphine (10.0 × 10 g, 3.80 × 10 mol) were then
added. The temperature was raised to 120 ЊC for the desired
time. The evolution of the reaction was followed by TLC using
hexane–dichloromethane (1 : 1) as eluent. The crude product
was extracted with dichloromethane and washed with water.
After standard work-up and evaporation of the solvents the
residue was washed with methanol to remove the triphenyl-
phosphine oxide. The product was purified by silica gel column
chromatography using hexane–dichloromethane (1 : 1) as
eluent.
Synthesis
Synthesis of anti-[Pd(ꢀ-Ac){(2-C H CH )PBzPh}] (5). To a
6
4
2
2
Ϫ3
solution of palladium acetate (1.50 g, 6.7 × 10 mol) in toluene
150 ml) was added dibenzylphenylphosphine (2.55 g, 8.8 ×
(
1
Ϫ3
0
mol); the resulting mixture was stirred for 16 hours at
(
all-E )-5,10,15,20-Tetrakis[4-(2-butoxycarbonylethenyl)phenyl]-
5
0 ЊC. Then, the solution was cooled to room temperature and
porphyrin (6)
concentrated. Addition of hexane caused the precipitation of 5
1
as a yellow solid that was filtered off and dried under vacuum.
Isolated yield: 80 mg (67%). H NMR (CDCl
δ Ϫ2.79 (2H, br s, NH), 1.01 (12H, t, CH , J = 7.3 Hz), 1.54
(8H, m, CH ), 1.77 (8H, m, CH ), 4.30 (8H, t, CH , J = 6.6 Hz),
6.73 (4H, d, vinyl, J = 16.0 Hz), 7.91 (8H, d, meta, J = 8.1 Hz),
8.00 (4H, d, vinyl, J = 16.0 Hz), 8.22 (8H, d, ortho, J = 8.1 Hz),
8.84 (8H, s, Hβ). MS-FAB m/z 1118 (M ). Anal. calcd. for
C H N O : C, 77.28; H, 6.26; N, 5.0; found: C, 76.93; H, 6.50;
N, 4.97%.
, 200 MHz)
3
1
Yield: 2.59 g (85%). H NMR (250 MHz, CDCl ) δ 2.23 (s, 6H,
3
3
CH ), 2.60–3.20 (m, 8H, CH ), 6.00–7.70 (m, 28H, aromatics);
2
2
2
3
2
31
1
P{ H} NMR (101.26 MHz, CDCl ) δ 53.45 (s), 44.98 (d,
J = 4.2 Hz); C{ H} NMR (62.86 MHz, CDCl ) δ 24.5
3
13
1
3
ϩ
(
s, CH ), 33.6–37.2 (m, CH ), 180 (s, COO). Anal. calcd. for
3
2
C H O P Pd : C, 58.10; H, 4.65; found: C, 57.61; H, 4.54%.
72 70 4 8
4
4
42
4
2
2
Ϫ1
IR (KBr) 1559, 1409, 1096, 698 cm .
General catalytic conditions for the synthesis of aldehydes
(all-E )-5,10,15,20-Tetrakis[4-(3-oxobut-1-enyl)phenyl]porphyrin
7)
(
Ϫ5
Complex 5 (10.0 mg, 1 × 10 mol) was dissolved in dimethyl-
1
formamide (5 ml) under a nitrogen atmosphere in a Schlenk
tube. In another Schlenk tube, 4-bromobenzaldehyde (27.0 ×
Isolated yield: 76 mg (80%). H NMR (CDCl , 200 MHz)
3
δ Ϫ2.77 (2H, br s, NH), 2.54 (12H, s, CH ), 7.04 (4H, d, vinyl,
3
Ϫ3
Ϫ3
1
0
mol), the desired olefin (35.1 × 10 mol) and sodium
J = 16.3 Hz), 7.87 (4H, d, vinyl, J = 16.3 Hz), 7.96 (8H, d, meta,
J = 8.0 Hz), 8.27 (8H, d, ortho, J = 8.0 Hz), 8.87 (8H, s, Hβ).
Ϫ3
acetate (2.50 g, 30.5 × 10 mol) were dissolved in dimethyl-
1
584
J. Chem. Soc., Perkin Trans. 2, 2002, 1583–1588

View Article Online
ϩ
MS-FAB m/z 887 (M ). Anal. calcd. for C H O N : C, 81.26;
Table 1 Comparative studies of the coupling reaction between bromin-
60
46
4
4
ated porphyrin, 2, and different olefins, using the palladacycle, 5, or
H, 5.19; N, 6.32; found: C, 81.71; H, 4.96; N, 6.10%.
palladium acetate–triphenylphosphine as catalyst
General porphyrin synthesis via the nitrobenzene method
a
Entry Substrate Catalyst
Time
Conversion (%)
Ϫ3
The desired vinyl aldehyde, 3 or 4 (0.40 × 10 mol), was dis-
b
solved in a mixture of glacial acetic acid (140 ml, 2.45 mol) and
nitrobenzene (70.0 ml, 0.68 mol), and the temperature was
1
2
3
4
5
6
7
1a
1b
1c
1a
1d
1e
1f
5
5
5
7 days
7 days
10 days
24 hours
24 hours
7 days
70
—
—
c
c
Ϫ3
raised to 120 ЊC. Pyrrole (0.40 × 10 mol) was then added. The
Pd(OAc) –PPh
100
100
80
2
3
3
3
3
evolution of the reaction was followed by UV–visible absorp-
tion spectroscopy until the Soret band reached its maximum.
The reaction was left at room temperature during 12 hours. If
the porphyrin crystallized directly from the reaction medium, it
was filtered off. If it did not precipitate, the solvent was evapor-
ated and the crude product was purified by column chrom-
atography. The purple fraction was collected and porphyrins
were recrystallized from dichloromethane–methanol.
Pd(OAc) –PPh
Pd(OAc) –PPh
Pd(OAc) –PPh
2
b
2
c
7 days
—
2
a
1
Conversion obtained by H NMR by comparison between the new
olefinic protons and the aromatic porphyrin signals. Mixture of
mono-, di-, tri- and tetra-substituted vinylporphyrins. Only signals due
b
c
to the starting material were observed.
(
all-E )-5,10,15,20-Tetrakis[4-(2-butoxycarbonylethenyl)phenyl]-
porphyrin (6)
Isolated yield: 7%. The porphyrin exhibits the same spectro-
scopic and analytic data as those described above.
(
all-E )-5,10,15,20-Tetrakis{4-[2-(4-methoxyphenyl)ethenyl]-
phenyl}porphyrin (8)
The required porphyrin was obtained from 200 mg (5.40 ×
Ϫ3
1
0
mol) of (E)-4-[2-(4-methoxyphenyl)ethenyl]benzaldehyde
Ϫ3
and pyrrole (0.35 ml, 5.40 × 10 mol). Isolated yield: 18.1 mg
7.5%). H NMR (CDCl , 300 MHz) δ Ϫ2.7 (2H, br s, NH),
1
(
3
3
.89 (12H, s, OCH ), 7.01 (8H, d, J = 9 Hz, phenyl), 7.35 (4H,
3
d, J = 12 Hz, H-vinyl), 8.19–8.26 (20H, 16-phenyl-porphyrin,
4
H-vinyl), 7.88 (8H, d, J = 9 Hz, phenyl), 8.92 (8H, s, H );
β
ϩ
MS-FAB m/z 1143 (M ). Anal. calcd. for C H N O ؒ4 H O:
80
62
4
4
2
C, 79.07, H, 5.76, N, 4.61; found: C, 79.09, H, 5.08, N, 4.67%.
5
,10,15,20-Tetrakis(4-bromophenyl)porphyrin (2)
The required porphyrin was obtained from 4-bromobenz-
Ϫ3
Scheme 1
aldehyde (1.2 × 10 mol) and an equivalent amount of pyrrole.
1
Isolated yield: 93 mg (25%). H NMR δ Ϫ1.8 (2H, br s, NH),
7
8
.89 (8H, d, meta, J = 9.0 Hz), 8.05 (8H, d, ortho, J = 9.0 Hz),
.8 (8H, s, Hβ). MS-FAB m/z 930 (M ). Anal. calcd. for
ϩ
C H N Br : C, 56.79; H, 2.79; N, 6.02; found: C, 56.81; H,
4
4
26
4
4
2
.90; N, 5.91%.
Results and discussion
Palladacyclic complexes are structurally defined catalysts for
the Heck vinylation of haloaromatic compounds, and are easy
21
to handle and thermally more stable than conventional ones.
A new phosphapalladacycle has been synthesized by reaction
between palladium acetate and the appropriate phosphine to
give 5 (Scheme 1).
Fig. 1 Structures of the olefins studied.
The halo derivative 5,10,15,20-tetrakis(4-bromophenyl)-
12
porphyrin 2 was prepared using the nitrobenzene method by
mixing equimolar amounts of pyrrole and 4-bromobenz-
aldehyde in a mixture of acetic acid–nitrobenzene (2 : 1) at
1
evaluated by H NMR. The results are presented in Table 1. A
great excess of olefin is used to force the coupling reaction with
the four porphyrin bromine groups. This catalytic system is not
very active (entries 1–3), and showed a significant dependence
on the structure of the olefin. Only with the activated terminal
electron-poor olefin 1a was an overall yield of 70% obtained,
after 7 days, but as a complicated mixture of substituted
vinylated porphyrins. The porphyrins from the reaction mixture
were isolated by preparative thin layer chromatography giving
mainly porphyrins with four, and two olefin groups, as shown
by NMR and FAB mass spectra, with peaks centered at 1118
and 1025, respectively. With the electron-rich, disubstituted
deactivated olefins 1b,c no reaction was observed after 7 days.
In order to compare the palladacycle 5 with conventional
1
20 ЊC during 1 hour. The pure compound, without any chlorin
contamination, was obtained in 25% yield by direct filtration of
the crystals from the reaction medium.
In order to study the effect of the olefin in the Heck reaction,
the reaction of brominated porphyrin 2 with olefins 1a–f (Fig. 1)
in the presence of palladacycle 5 and with the classic Heck
catalytic system, palladium acetate–triphenylphosphine, were
investigated.
In the catalytic coupling reaction, porphyrin 2 was dissolved
in dimethylformamide and the olefin 1a–c, sodium acetate, and
the palladium complex 5 were subsequently added and the
reaction mixture maintained at 120 ЊC. The evolution of the
reaction was monitored by TLC and the final conversions were
14
catalysts the coupling of olefins 1a, 1d–f with 2, in the
J. Chem. Soc., Perkin Trans. 2, 2002, 1583–1588 1585

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Scheme 2
presence of Pd(OAc) –PPh and sodium acetate was attempted
of the nitrobenzene and purification of the product by silica gel
2
3
(
Scheme 2). The results are collected in Table 1 (entries 4–7).
In the coupling reactions using electron-poor olefins 1a and
d, complete transformation of the porphyrin 2 to the corre-
column chromatography using chloroform as eluent, the purple
fraction was collected, yielding 7 and 7.5% of the correspond-
ing porphyrins 6 and 8 (Scheme 4) without any contamination
from the corresponding chlorin.
1
sponding tetravinylporphyrins was observed after 24 hours,
while with electron-rich olefins either no reaction or a complex
mixture of products was observed after 7 days. It is noteworthy
that vinylation gave only the (E)-isomer with 100% regio-
selectivity for the terminal olefinic carbon. We were surprised
to find that the catalytic activity for the palladacycle 5 was
significantly lower, even for the activated olefin 1a.
The catalytic system using the palladacycle 5 allows the trans-
formation of brominated aldehydes into the corresponding
vinyl ketones, using either electron-rich or electron-poor olefins
which are good precursors for the synthesis of the correspond-
ing meso-p-vinylphenylporphyrins, using the simple one-step
12,13
nitrobenzene methodology.
In light of the results presented in Table 1, it is likely that the
standard Heck catalytic system is efficient for the vinylation
of 5,10,15,20-tetrakis(4-bromophenyl)porphyrin with electron-
withdrawing olefins, but the catalyst palladacycle 5 only permits
very specific applications.
Another approach to the synthesis of the desired vinyl-
porphyrins is prior functionalization of the aldehyde, via Heck
reaction, followed by condensation with pyrrole. The pallada-
cycle 5 was able to catalyse the coupling reaction of the
activated 4-bromobenzaldehyde with the olefins 1a and 1e to
give (E)-4-(2-butoxycarbonylethenyl)benzaldehyde 3 (83%) in
Photophysical results
The photophysical properties of the three new porphyrins 6–8
studied in this work are presented in Table 2. The UV–visible
absorption spectra were interpreted in terms of the nomen-
37–39
clature of the four-orbital model of Gouterman
for the D2h
symmetry expected for these free-base porphyrins. The absorp-
tion and fluorescence features shown in Fig. 2 closely resemble
those of TPP, also included in the Table 2 for comparison. The
excitation and absorption spectra are in excellent agreement,
also confirming the purity of the compounds.
1
6 hours and (E)-4-[2-(4-methoxyphenyl)ethenyl]benzaldehyde
4
(89%) in 16 hours (Scheme 3).
Scheme 3
Then, the one-step porphyrin synthesis using the direct
condensation–cyclization reaction between the new aldehydes 3
or 4 and an equivalent amount of pyrrole was carried out in a
mixture of glacial acetic acid–nitrobenzene. After evaporation
Fig. 2 Absorption, fluorescence, and excitation spectra of porphyrin 6
12
Ϫ7
(5.7 × 10 M), in toluene solution at room temperature.
1
586 J. Chem. Soc., Perkin Trans. 2, 2002, 1583–1588

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Table 2 Absorption and luminescence data of the porphyrins in toluene solution
Fluorescence
λmax/nm (RT)
Ϫ1
Ϫ1
Absorption λmax/nm (ε/M cm
)
E /kJ
S
Ϫ1
Porphyrin Q (0–0) Q (1–0)
Q (0–0)
y
Q (1–0)
y
B(0–0)
Q(0–0) Q(0–1) mol
Φ (N )
x
x
F
2
3
3
3
4
5
6
7
8
651.0 (3.8 × 10 ) 594.0 (4.1 × 10 ) 554.5 (9.3 × 10 ) 518.0 (1.3 × 10 ) 426.5 (3.3 × 10 ) 657
720
719
722
719
182.9
183.0
182.3
183.9
0.17
0.15
0.27
0.11
3
3
3
4
5
651.0 (2.8 × 10 ) 594.0 (3.2 × 10 ) 555.0 (7.4 × 10 ) 518.5 (1.0 × 10 ) 427.0 (3.1 × 10 ) 656
3
3
4
4
5
654.0 (9.6 × 10 ) 597.0 (8.2 × 10 ) 558.0 (2.2 × 10 ) 520.0 (2.4 × 10 ) 431.0 (5.6 × 10 ) 659
a
3
4
4
4
5
H TPP
2
649.8 (9.6 × 10 ) 592.0 (1.0 × 10 ) 548.0 (1.2 × 10 ) 514.6 (1.8 × 10 ) 418.0 (2.7 × 10 ) 652
a
Refs. 33 and 40.
Scheme 4
However, quite unexpectedly, phosphorescence was observed
with bands at 691–697 and 764–773 nm, with a lifetime of
ca. 1.4 ms. The phosphorescence of free-base porphyrins is
much more difficult to detect, occurs at much lower energy and
40
is longer lived.
The palladium complex of porphyrin 6 was synthesised by
refluxing porphyrin 6 in dimethylformamide with an excess of
palladium() acetate and phosphorescence studies were carried
out. The position of the phosphorescence bands and lifetimes
are, within experimental error, identical to those observed for
the vinylporphyrins. This strongly suggests that the observed
phosphorescence originates from the residual palladium that
remains in the materials even after repeated purification.
The singlet state energies (E ) were obtained from the
S
intersection of the normalised absorption and fluorescence
spectra (Fig. 2).
We further investigated the nature of the triplet state of the
porphyrins 6–8 using flash photolysis and PAC. The transient
spectrum observed in flash photolysis is typical of tetraphenyl-
Ϫ6
Fig. 3 Laser flash photolysis of porphyrin 8 (6 × 10 M), in toluene
solution at room temperature. Triplet–triplet absorption spectrum.
porphyrins (Fig. 3). The lifetime in N -saturated toluene
2
solutions measured at all wavelengths (350, 460, and 650 nm)
is ca. 70 µs, which is comparable with the lifetimes measured
for tetraphenylporphyrins subjected to the deoxygenation pro-
cedure followed. The isosbestic points at 403 and 443 nm,
associated with the bleaching of the ground state, indicate that
the triplet state decays directly to the ground state. The emissive
triplet state is not observed in room-temperature flash
photolysis.
ation. The transient heat released may be due to internal
conversion, intersystem crossing, energy transfer or some other
photoinduced reaction. The experimental conditions employed
in this work, associated with the deconvolution of reference and
sample waves, allow us to distinguish sequential heat releases
that occur in the 10 ns to 5 µs time range. All the heat released in
less than 10 ns appears as prompt heat (a faster process that
includes the internal conversion from higher excited states, the
intersystem crossing to the triplet manifold and the relaxation
PAC measures the fraction of light energy released as heat in
each of the radiationless processes following electronic excit-
J. Chem. Soc., Perkin Trans. 2, 2002, 1583–1588
1587

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of the spectroscopically formed ground state species). Processes
occurring with lifetimes longer than 5 µs are not detected and
the sum of their enthalpies is the fraction of energy not released
in the PAC experiment.
References
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K. M. Kadish and R. Guilard, The Porphyrin Handbook, Academic
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T. J. Dougherty, Photochemistry in the Treatment of Cancer, Wiley &
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The fraction of heat released in the formation of an inter-
mediate is the product of the quantum yield and the enthalpy
of its formation. We cannot determine Φ because E is not
3 H. Honigsmann, G. Jori and A. R. Young, The Fundamental Bases
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T
T
4
R. Bonnett, Chemical Aspects of Photodynamic Therapy, Gordon
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accurately known for the porphyrins 6–8. Thus, we focussed
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Deconvolution of the photoacoustic waves of porphyrin 8 in
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1
quantum yield, the formation of singlet oxygen with a quantum
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33
yield Φ , and the radiationless decay to the ground state,
∆
J. T. Groves, J. Porphyrins Phthalocyanines, 2000, 4, 350.
E Φ = (E Ϫ E ) ϩ (E Ϫ E )Φ ϩ E Φ
S1 ic
(1)
10 P. Rothemund, J. Am. Chem. Soc., 1935, 57, 2010.
hν
1
hν
S1
S1
∆
∆
1
1
1
1 A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour
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where E = 94 kJ mol is the electronic energy of singlet oxygen.
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∆
This equation neglects the relaxation of the ground state
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F
∆
ic
that all the triplet states quantitatively transfer their energy to
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1
1
1
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3
F
S1
Ϫ1
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∆
It is interesting to note that this porphyrin has a much larger
ΦF and a significantly lower Φ∆ than TPP. The deactivation
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2
0 M. Casey, J. Lawless and C. Shirran, Polyhedron, 2000, 19,
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5
2
1 W. A. Herrmann, C. Brossmer, K. Ofele, C.-P. Reisinger, T.
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1
995, 34, 1844.
This paper describes the application of a new phosphapallada-
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tetrakis(4-bromophenyl)porphyrin 2 or 4-substituted aldehydes
as substrates. However, in the direct vinylation of 5,10,15,20-
etrakis(4-bromophenyl)porphyrin 2 the standard Heck catalytic
system proved to be more active.
This is the first time that the standard Heck coupling reaction
has been conducted successfully with a tetra-halogenated por-
phyrin to give new tetravinylporphyrins with yields up of to
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0%. In this work we present an almost general method for the
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2
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3
3
5
The luminescent properties of the new extended conjugated
meso-phenylvinylporphyrins have been studied. They have
proved to be more fluorescent than TPP and their efficiency in
singlet-oxygen sensitisation is lower.
The synthesis of new free-base porphyrins with other vinyl
groups is currently being developed.
33 M. Pineiro, A. L. Carvalho, M. M. Pereira, A. M. d’ A. Rocha
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Acknowledgements
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We are grateful to FCT, project POCTI/QUI/42536/2001,
and Ministerio de Ciencia y Tecnología (BQU2001-3358) for
financial support.
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J. Chem. Soc., Perkin Trans. 2, 2002, 1583–1588