Synthesis and spectral properties of N4, N3S, and N2S2 porphyrins containing one, two, three, and four meso-furyl groups

Article abstract of DOI:10.1016/j.tet.2007.05.099

Porphyrins with N₄, N₃S, and N₂S₂ cores having one, two, three, and four furyl groups at the meso-positions were synthesized by following various methodologies and characterized by using mass spectrometry, NMR s

Full text of DOI:10.1016/j.tet.2007.05.099

Tetrahedron 63 (2007) 7833–7844
Synthesis and spectral properties of N4, N3S, and N2S2 porphyrins
containing one, two, three, and four meso-furyl groups
*
G. Santosh and M. Ravikanth
Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400076, India
Received 8 March 2007; revised 11 May 2007; accepted 24 May 2007
Available online 2 June 2007
Abstract—Porphyrins with N4, N3S, and N2S2 cores having one, two, three, and four furyl groups at the meso-positions were synthesized by
following various methodologies and characterized by using mass spectrometry, NMR spectroscopy, elemental analysis, absorption, and fluo-
rescence spectroscopic techniques. NMR studies indicated that by replacing the meso-aryl groups with meso-furyl groups, the b-pyrrole and
b-thiophene protons of porphyrins experienced considerable downfield shifts, supporting the alteration of p-delocalization of porphyrins on
the introduction of meso-furyl groups. The absorption and emission bands of porphyrins experienced red shifts on the introduction of meso-
furyl groups and the magnitude of red shifts vary linearly with the number of meso-furyl groups. Thus, the spectral studies supported a sys-
tematic alteration in spectral properties on successive introduction of meso-furyl groups.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
continuing our studies on meso-furylporphyrins, we synthe-
sized a series of meso-furylporphyrins with N4, N3S, and
N2S2 porphyrin cores 1–13 by replacing one, two, three,
and four six-membered meso-aryl groups with five-mem-
bered furyl groups (Chart 1). It is observed that by replacing
the meso-aryl groups with meso-furyl groups successively,
the electronic properties are varied systematically and these
effects appear to be additive in nature. To the best of our
knowledge, this kind of systematic changes in the electronic
properties of porphyrin is not observed earlier by replace-
ment of meso-aryl groups with any other six-membered
aryl groups.
Porphyrin macrocycles are not only important for under-
standing various biological processes but also have applica-
tions in divergent fields including catalysis of organic
reactions and the photodynamic therapy of cancer.1 These
properties arise from their synthetic flexibility and the ease
by which their properties can be modified for a particular ap-
plication by introducing substituents selectively at the b- or
meso-position, or by incorporating a required metal in the
porphyrin cavity. meso-Tetraarylporphyrins offer attractive
features in this context and have been used for a wide variety
of applications owing to their ease of synthesis and facile
functionalization.2 Recently we found that the replacement
of the four six-membered aryl groups with five-membered
furyl groups at the meso-positions alter the electronic prop-
erties drastically, suggesting that the meso-furylporphyrins
can be tested in place of meso-arylporphyrins for various ap-
plications.3 For example, the introduction of furyl groups at
the meso-positions in place of six-membered aryl groups
shifts the Q1 band of porphyrin by 20–40 nm bathochromi-
cally, indicating that the meso-furylporphyrins are energeti-
cally low as compared to meso-arylporphyrins, hence can act
as energy acceptors. This has been shown recently by the
synthesis of a series of covalently linked porphyrin dyads
containing meso-arylporphyrin and meso-furylporphyrin
subunits, and the demonstration of an efficient energy trans-
fer from meso-arylporphyrin to meso-furylporphyrin on
selective excitation of the meso-arylporphyrin subunit.4 In
2. Results and discussion
2.1. Synthesis of one, two, three, and four meso-furyl
groups with N4 porphyrin core 1–4
To synthesize meso-furylporphyrins with the N4 core having
one, two, three, and four meso-furyl groups, we adopted the
mixed condensation approach. Condensation of 3 equiv of
furan-2-carboxaldehyde, 1 equiv of p-tolualdehyde, and
4 equiv of pyrrole in CH2Cl2 in the presence of a catalytic
amount of BF3$OEt2 at room temperature for 1 h, followed
by oxidation with DDQ for an additional hour was expected
to yield six porphyrins.5 However, the TLC analysis of the
crude porphyrin mixture after column chromatography
showed three unresolved spots. Hence we metalated the
crude porphyrin mixture by heating it with Zn(OAc)2 in
CH2Cl2/CH3OH at reflux. The TLC analysis of the meta-
lated porphyrin mixture showed five clear spots indicating
* Corresponding author. Tel.: +91 22 25767176; fax: +91 22 25723480;
e-mail: ravikanth@chem.iitb.ac.in
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.05.099

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G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
R1
R1 = R2 = R3 = R4
=
: H2TTP
: 1
4-tolyl
R1 = R2 = R3
=
R4
=
=
=
4-tolyl;
2-furyl
2-furyl
2-furyl
NH
N
N
R1 = R3
R1
R1 = R2 = R3 = R4
=
R2 = R4
4-tolyl;
: 2
: 3
: 4
R2
R4
HN
=
4-tolyl; R2 = R3 = R4
=
2-furyl
R3
R1
R
1 = R2 = R3 = R4
=
4-tolyl
: STTPH
: 5
R4
R2 = R3
2 = R3
=
=
=
R1 = R2 = R3
=
4-tolyl;
2-furyl
2-furyl
4-tolyl
S
N
N
R
1 = R4
1 = R4
=
=
4-tolyl;
2-furyl;
: 6
R2
R4
R
R
: 7
HN
R1
=
4-tolyl;
R2 = R3 = R4
=
2-furyl
: 8
: 9
R1 = R2 = R3 = R4
=
2-furyl
R3
R1
: S2TTP
R1 = R2 = R3 = R4
=
4-tolyl
R4
=
2-furyl
: 10
: 11
R
1 = R2 = R3 = 4-tolyl;
S
N
N
S
R1 = R4
=
R2 = R3 = 2-furyl
R2 = R3 = R4 = 2-furyl
R2
4-tolyl;
R4
: 12
: 13
R1
=
4-tolyl;
R1 = R2 = R3 = R4
=
2-furyl
R3
Chart 1. Structures of meso-furylporphyrins.
that the cis and trans forms of meso-difurylporphyrins are
not resolved. The crude porphyrin mixture was subjected
to silica gel column chromatography using petroleum ether/
CH2Cl2, and the fast moving Zn(__) tetratolylporphyrin was
collected first, followed by the desired compounds as Zn2+
derivatives in reasonable yields. The demetallation was
carried out by treating the Zn2+ derivatives with 6 M HCl
in CH2Cl2 followed by standard work-up. Since we did not
get meso-difurylporphyrin in a pure form, we attempted to
synthesize trans meso-difurylporphyrin by condensing
1 equiv of meso-5-tolyldipyrromethane6 19 with 1 equiv of
furan-2-carboxaldehyde under similar porphyrin forming
conditions. Although the TLC analysis showed the
formation of other meso-furylporphyrins as very minor com-
pounds due to scrambling, the required trans meso-furylpor-
phyrin was formed in major amount and collected in 2.1%
yield after simple column chromatographic purification.
The meso-furylporphyrins 1–4 were characterized by mass
spectrometry, NMR spectroscopy, elemental analysis, ab-
sorption and emission spectroscopic techniques. The M+
ion peak in ESMS mass spectra confirmed the identities of
the compounds. In the 1H NMR, it is observed that the pro-
tons, which are closer to the meso-furyl group(s) experi-
enced downfield shifts due to alteration of ring current on
introduction of meso-furyl groups in place of the six-mem-
bered meso-aryl groups. In mono meso-furylporphyrin 1,
the eight b-pyrrole protons appeared as three sets of signals,
two doublets and one singlet at d 9.12, 8.91, and 8.84 ppm,
respectively, due to the unsymmetrical nature of the com-
pound. The pyrrole protons of 1 experienced downfield
shifts compared to 5,10,15,20-tetrakis(p-tolyl)-porphyrin
(H2TTP),7 which showed a singlet at d 8.72 ppm for the eight
b-pyrrole protons (Table 1). The two b-pyrrole protons,
which were adjacent to the meso-furyl group appeared
more downfield compared to the other pyrrole protons of
the porphyrin macrocycle. The inner NH proton also
exhibited a downfield shift compared to H2TTP, due to
alteration of p-delocalization of the porphyrin ring on
introduction of the meso-furyl group in place of the six-
membered aryl group (Table 1). The trans meso-furylpor-
phyrin 2 showed two sets of multiplets for the b-pyrrole
protons, each corresponding to four protons, which were
downfield shifted as compared to H2TTP (Table 1). The pyr-
role protons, which were adjacent to the meso-furyl groups
were more downfield shifted as compared to the pyrrole pro-
tons, which were adjacent to the meso-tolyl groups (Table 1).
For meso-furylporphyrin 3, the eight pyrrole protons
appeared as one multiplet corresponding to four protons
and two doublets, each corresponding to two protons. The
two inner NH protons appeared as a sharp singlet at
d ꢀ2.63 ppm. The pyrrole and inner NH protons of 3 were
downfield shifted compared to H2TTP, supporting the alter-
ation of p-delocalization in 3 on the introduction of furyl
groups in place of the six-membered aryl groups in meso-
positions. In tetra meso-furylporphyrin 4, the eight pyrrole
protons and two inner NH protons appeared as singlets.
The change in the ring current effects in 4 was clearly
seen in the downfield shifts of pyrrole and inner NH protons
compared to H2TTP (Table 1).
2.2. Synthesis of one, two, three, and four meso-furyl
groups with N3S porphyrin core 5–9
The meso-furylporphyrins with an N3S core were synthe-
sized by following different methods as outlined in Schemes
1 and 2. To synthesize these porphyrins, 2-(hydroxy(2-

G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
7835
Table 1. 1H NMR chemical shifts (d in ppm) of selected protons of meso-furylporphyrins 1–13 recorded in CDCl3
Porphyrin
Thiophene
Pyrrole
NH
H2TTP
1
2
—
—
—
—
8.72 (s)
ꢀ2.79 (s)
ꢀ2.76 (s)
ꢀ2.73 (s)
ꢀ2.63 (s)
ꢀ2.59 (s)
ꢀ2.66 (s)
ꢀ2.51 (s)
ꢀ2.75 (s)
ꢀ2.32 (s)
ꢀ2.59 (s)
ꢀ2.41 (s)
—
9.12 (d), 8.91 (d), 8.84 (s)
9.13 (br s), 8.90 (br s)
9.18 (m), 9.12, (d), 8.90 (d)
9.16 (s)
8.88 (s), 8.72 (d), 8.61 (d)
8.99 (d), 8.90 (d), 8.59 (d), 8.63 (d), 8.67 (d)
9.30 (d), 8.88 (d), 8.73 (d)
8.97 (d), 8.86 (d), 8.60 (d)
9.26 (m), 9.04 (d), 8.85 (m), 8.72 (d)
9.22 (d), 9.01 (d), 8.85 (d)
8.67 (d)
3
4
STTPH
5
6
7
—
9.81 (s)
10.15 (d), 9.79 (d)
9.75 (s)
10.19 (s)
10.17 (d), 9.80 (d)
10.21 (s)
9.68 (s)
10.13 (m), 9.76 (m)
10.11 (s), 9.63 (s)
10.08 (m), 10.01 (d), 9.66 (d)
10.05 (s)
8
9
S2TTP
10
11
12
13
9.05 (m), 8.74 (m)
8.97 (d), 8.68 (d)
8.97 (m), 8.66 (d)
8.97 (s)
—
—
—
—
furyl)methyl)-5-[hydroxyl(p-tolyl)methyl]thiophene 14 and
2,5-bis(2-furyl hydroxy methyl) thiophene 15 were required
as precursors. The unsymmetrical thiophene diol 14 was
synthesized in two steps starting from thiophene.8 In the first
step, the thiophene mono-ol, 2-(p-tolylhydroxymethyl) thio-
phene 16 was prepared by treating thiophene with 1.2 equiv
of n-BuLi followed by 1.2 equivs of p-tolualdehyde in THF
at 0 ꢁC and purified by column chromatography. The diol 14
was prepared by treating thiophene mono-ol 16 with 2 equiv
of n-BuLi followed by 1.2 equiv of furan-2-carboxaldehyde
in THF at 0 ꢁC and purified by column chromatography. The
symmetrical thiophene diol, 2,5-bis(2-furylhydroxymethyl)
thiophene 15 was prepared by following our earlier proce-
dure.3a The diols 14 and 15 were confirmed by mass spec-
trometry, NMR spectroscopy, and elemental analysis,
which were in agreement with the composition.
current effects due to the meso-furyl group compared to
the protons, which are far from the meso-furyl group.
In the case of meso-difuryl-21-thiaporphyrins, we synthe-
sized two different types of porphyrins 6 and 7. In 7, the
meso-furyl groups are flanking the thiophene and in 6, the
furyl groups are flanking one of the pyrroles. The meso-
difuryl-21-thiaporphyrin 7 was prepared by condensing
1 equiv of 2,5-bis (2-furylhydroxymethyl) thiophene 153a
with 2 equiv of p-tolualdehyde and 3 equiv of pyrrole under
mild porphyrin forming conditions. The condensation re-
sulted in the formation of a mixture of three porphyrins
and the desired compound was separated from other two
by column chromatography. Similarly, porphyrin 6 was
prepared by condensing 1 equiv of 2,5-bis (p-tolylhydroxy-
methyl) thiophene9 16 with 2 equiv of furan-2-carboxalde-
hyde and 3 equiv of pyrrole under the same reaction
conditions and purified by column chromatography. The
porphyrins 6 and 7 were confirmed by a molecular ion
peak in the mass spectra, matching elemental analysis, and
The mono meso-furyl-21-thiaporphyrin 5 was synthesized by
condensing 1 equiv of diol 14 with 2 equiv of p-tolualdehyde
and 3 equiv of pyrrole under Lindsey’s mild porphyrin form-
ing conditions.5 The TLC analysis of crude porphyrin after
filtration column showed the desired compound and some
amount of H2TTP, which were separated by column chroma-
tography. The porphyrin was confirmed by a molecular ion
peak in the mass spectrum, as well as a matching elemental
analysis, and clean 1H NMR spectrum. In the 1H NMR spec-
trum, the two b-thiophene protons appeared as two doublets
at d 9.79 and 10.15 ppm unlike 5,10,15,20-tetra(p-tolyl)-21-
thiaporphyrin7(STTPH), which showed a singlet, indicating
the unsymmetrical nature of porphyrin 5.
1
1
clean H NMR spectrum. In the H NMR spectrum of 7,
the b-thiophene protons, which were flanked by meso-furyl
groups appeared as singlet and were downfield shifted by
d 0.38 ppm compared to STTPH7 (Table 1). The six b-pyr-
role protons appeared as three sets of signals with negligible
shifts compared to STTPH. The inner NH proton appeared
as a singlet with a downfield shift compared to STTPH. In
porphyrin 6, the two b-thiophene protons, which were
flanked by meso-tolyl groups appeared as singlets with no
shifts compared to STTPH. The six b-pyrrole protons
appeared as three sets of doublets.
The b-thiophene proton, which is adjacent to meso-furyl
group experienced downfield shift (at d 10.15 ppm) and the
other b-thiophene proton, which is adjacent to the meso-tolyl
group experienced a negligible shift (at d 9.79 ppm) com-
pared to STTPH (at d 9.81 ppm) (Table 1).
The two b-pyrrole protons, which were flanked by meso-
furyl groups showed downfield shifts, whereas the other
four b-pyrrole protons did not show any shift compared to
STTPH.
The six b-pyrrole protons of 5 appeared as five sets of sig-
nals. The b-pyrrole proton, which is adjacent to the meso-
furyl group was downfield shifted compared to the other
five b-pyrrole protons. The NH signal was also downfield
shifted compared to STTPH (Table 1). All these observa-
tions indicate that the protons, which are in the near vicinity
of the meso-furyl group have experienced alteration of ring
The meso-tri-furyl-21-thiaporphyrin 8 was synthesized by
condensing 1 equiv of unsymmetrical diol 14 with 2 equiv
of furan-2-carboxaldehyde and 3 equiv of pyrrole under
mild acidic conditions and purified by column chromat-
ography. The identity of the porphyrin was established
by a molecular ion peak in mass spectrum and elemental
analysis, which was in agreement with the expected

7836
G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
S
N
O
pyrrole, p-tolualdehyde
.
CH2Cl2, BF3 OEt2
N
HN
DDQ
5
S
N
pyrrole, 2-furylaldehyde
O
.
CH2Cl2, BF3 OEt2
O
HN
N
DDQ
O
8
O
S
S
HO
OH
HN
S
NH
N
O
17
14
.
S
N
BF3 OEt2, CH2Cl2
DDQ
10
O
O
S
S
N
O
HN
NH
18
O
N
S
.
BF3 OEt2, CH2Cl2
DDQ
12
O
Scheme 1. Synthesis of mono meso-furyl and tri meso-furylporphyrins with N3S and N2S2 cores.
1
composition of the porphyrin 8. In the H NMR spectrum,
the two b-thiophene protons appeared as two sets of dou-
blets and the proton, which was adjacent to the meso-furyl
group was downfield shifted. The other b-thiophene proton
did not show any shift compared to STTPH. The six b-
pyrrole protons appeared as four sets of signals and the
b-pyrrole protons, which were adjacent to the meso-furyl
groups were downfield shifted. The inner NH proton of
8 appeared as a singlet and was downfield shifted com-
pared to STTPH.
The symmetrical meso-tetrafuryl-21-thiaporphyrin 9 was pre-
pared as reported previously3a by condensing 1 equiv of diol
15, 2 equiv of furan-2-carboxaldehyde and 3 equiv of pyrrole
under porphyrin forming conditions. Compound 9 was ob-
tained and its structure confirmed by mass spectrometry, ele-
mental analysis, and 1H NMR spectroscopy. In the 1H NMR
spectrum, the b-thiophene, b-pyrrole, and inner NH protons
of 9 were downfield shifted compared to STTPH supporting
the alteration of p-delocalization on introduction of meso-
furyl groups in place of the six-membered meso-aryl groups.

G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
7837
O
S
N
pyrrole, p-tolualdehyde
.
CH2Cl2, BF3 OEt2
O
HN
N
DDQ
7
O
pyrrole, 2-furylaldehyde
S
N
O
.
CH2Cl2, BF3 OEt2
DDQ
O
HN
N
O
9
O
O
S
HO
OH
S
15
HN
NH
17
S
N
O
.
BF3 OEt2, CH2Cl2
S
N
DDQ
O
11
O
S
N
O
.
pyrrole, CH2Cl2, BF3 OEt2
O
S
N
DDQ
13
O
Scheme 2. Synthesis of di meso-furyl and tetra meso-furylporphyrins with N3S and N2S2 cores.
2.3. Synthesis of one, two, three, and four meso-furyl
groups with a N2S2 porphyrin core
spectrum, the two b-thiophene protons appeared as two
sets of multiplets (Fig. 1). The b-thiophene proton, which
was adjacent to the meso-furyl group was downfield shifted
and the other b-thiophene proton did not experience any shift
compared to 5,10,15,20-tetrakis(p-tolyl)-21,23-dithiapor-
phyrin7 (S2TTP). The four b-pyrrole protons appeared as
two sets of multiplets corresponding to one and three b-pyr-
role protons. The b-pyrrole proton, which was adjacent
to the meso-furyl group was downfield shifted whereas
the other three b-pyrrole protons, having an adjacent
meso-aryl group, did not experience so much difference in
chemical shifts compared to S2TTP.
The mono meso-furylporphyrin with a N2S2 porphyrin core
was synthesized by condensing 1 equiv of unsymmetrical
diol 14 with 1 equiv of 5,10-di(p-tolyl)-16-thia-15,17-dihy-
drotripyrrin10 17 under standard porphyrin forming condi-
tions. The condensation resulted in the formation of mono
meso-furylporphyrin 10 as a single product, suggesting
that no scrambling occurred during the reaction. The
porphyrin 10 was confirmed by mass spectrometry, NMR
spectroscopy, and elemental analysis. In the 1H NMR

7838
G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
-thiophene
-pyrrole
S TTP
2
10
11
12
13
ppm
10.40
10.20
10.00
9.80
9.60
9.40
9.20
9.00
8.80
8.60
Figure 1. Comparison of 1H NMR spectra of meso-furyl N2S2 porphyrins 10, 11, 12 and 13 with S2TTP recorded in CDCl3 (only the b-thiophene and b-pyrrole
region is shown).
The meso-difurylporphyrin with an N2S2 porphyrin core 11
was synthesized by condensing symmetrical diol 15 with
symmetrical tripyrrane 17 under similar porphyrin condi-
tions and was obtained as the sole product. The porphyrin
formation was confirmed by mass spectrometry, elemental
analysis, and NMR spectroscopy. In this porphyrin, one thio-
phene ring was flanked by two meso-furyl groups and the
other thiophene ring was flanked by meso-tolyl groups, giv-
ing a symmetrical environment for b-thiophene protons.
b-thiophene and b-pyrrole protons and showed that the
meso-furyl groups alter the porphyrin ring current effect.
2.4. Absorption and fluorescence studies
The absorption and fluorescence studies of one, two, three,
and four meso-furylporphyrins with N4, N3S, and N2S2
porphyrin cores were studied in toluene, and the data are
presented in Tables 2 and 3, respectively. For comparison
purpose, the data of the corresponding meso-tetratolyl por-
phyrins7 (H2TTP, STPPH, and S2TTP) and meso-tetra
thienyl porphyrins11 (H2TThP, STThPH, and S2TThP) are
also included in the table. Figure 2 shows the comparison
of the Soret band absorption spectra of one, two, three,
and four meso-furylporphyrins with N4 (1–4) and N2S2
(10–13) cores along with H2TTP and S2TTP, respectively.
An inspection of Figure 2 and Table 2 reveals the following:
(1) The number of Q-bands, which is generally four in the
case of tetraarylporphyrins, is reduced to two or three bands
as we increase the number of meso-furyl groups from one to
four. (2) With the increase in the number of meso-furyl
groups, the Soret and Q-bands were red shifted and broad-
ened systematically compared to their tetraarylporphyrins,
and the maximum shifts were observed for tetrafurylpor-
phyrins. (3) The extinction coefficients of the meso-furylpor-
phyrins were lower than meso-tetraarylporphyrins. (4) The
maximum red shifts in absorption bands among the meso-
furylporphyrin reported here were noted for the meso-
tetrafurylporphyrin with a N2S2 core. Thus, the absorption
studies clearly showed that by replacing the six-membered
aryl groups with five-membered furyl groups at the meso-po-
sitions, the electronic properties of the porphyrin alter consid-
erably. It has been shown recently that the meso-tetra thienyl
porphyrins11 also exhibit similar characteristic features, but
the magnitude of effects were relatively smaller compared
to the meso-tetra furylporphyrins (Table 2). Furthermore,
the plots of absorption band maxima versus the number of
meso-furyl groups shown as an inset for Soret and Q1 bands
of N4 and N2S2 meso-furylporphyrins are linear, indicating
1
These effects were clearly noted in the H NMR spectrum,
which showed two singlets for four b-thiophene protons.
The b-thiophene protons having adjacent meso-furyl groups
showed downfield shifts and the b-thiophene protons having
meso-tolyl groups did not show much shifts compared to
S2TTP. The b-pyrrole protons, which were adjacent to the
meso-furyl groups showed similar downfield shifts com-
pared to S2TTP.
The meso-tri-furyl-21,23-dithiaporphyrin 12 was synthe-
sized by condensing unsymmetrical diol 14 and symmetri-
cal tripyrrane 18 under the same mild acid catalyzed
conditions and purified by column chromatography. The
molecular ion peak in the mass spectrum and matching el-
1
emental analysis confirmed the compound. In the H NMR
spectrum, the three b-thiophene protons, which are adjacent
to the meso-furyl groups were downfield shifted and the
only b-thiophene proton, which is adjacent to the meso-tol-
yl group did not show any shift compared to S2TTP. Simi-
larly the three b-pyrrole protons, which were adjacent to
meso-furyl groups experienced downfield shifts compared
to S2TTP.
The meso-tetra furyl-21,23-dithiaporphyrin 13 was synthe-
sized as reported previously3a by condensing symmetrical
diol 15 with pyrrole under mild acidic conditions and puri-
fied by column chromatography. In the 1H NMR spectrum,
the thiophene and pyrrole protons appeared as singlets and
were downfield shifted compared to S2TTP. Thus, the NMR
studies clearly differentiated the chemical environment of

G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
Table 2. Absorption data of meso-furylporphyrins 1–13 in toluene
7839
Porphyrin
Soret band, l [nm] (log 3)
Q-bands, l [nm] (log 3)
IV
III
II
I
H2TTPa
1
2
3
417 (5.72)
423 (5.45)
426 (5.25)
430 (4.92)
433 (4.92)
426 (5.59)
428 (5.56)
436 (5.45)
435 (5.21)
442 (5.20)
442 (5.35)
448 (5.00)
440 (5.53)
435 (5.40)
442 (4.96)
448 (5.25)
452 (5.25)
458 (4.92)
447 (5.23)
514 (4.36)
518 (4.36)
520 (3.94)
523 (3.84)
526 (3.88)
523 (4.25)
514 (4.47)
520 (4.43)
519 (4.11)
524 (4.10)
526 (4.23)
530 (3.83)
523 (4.36)
514 (4.41)
521 (3.90)
525 (4.20)
529 (4.21)
536 (sh)
548 (4.03)
555 (4.12)
559 (3.82)
562 (3.70)
571 (3.84)
558 (3.70)
550 (4.04)
559 (4.21)
558 (3.83)
566 (4.03)
568 (4.16)
575 (3.88)
562 (4.06)
547 (3.85)
559 (3.64)
566 (4.12)
574 (4.23)
585 (3.79)
563 (4.08)
590 (3.90)
595 (3.95)
595 (3.54)
599 (3.57)
605 (sh)
594 (3.48)
618 (3.62)
617 (3.85)
623 (3.46)
618 (sh)
647 (3.86)
651 (3.83)
657 (3.45)
659 (3.23)
670 (3.20)
661 (3.40)
675 (3.69)
685 (3.81)
687 (3.45)
691 (3.58)
699 (3.77)
705 (3.36)
692 (3.56)
696 (3.65)
705 (3.33)
715 (3.67)
722 (3.87)
740 (3.15)
713 (3.52)
4
H2TThPb
STTPHa
5
6
7
8
630 (3.69)
632 (sh)
9
STThPHc
S2TTPa
10
627 (3.58)
633 (3.34)
644 (2.69)
643 (3.49)
654 (3.64)
—
11
12
13
S2TThPc
525 (4.28)
642 (3.26)
a
Data taken from Ref. 7.
Data taken from Ref. 11a.
Data taken taken from Ref. 11d.
b
c
Table 3. Emission data of meso-furylporphyrins 1–13 in toluene
properties of the porphyrin, and effects were dependent
linearly on the number of meso-furyl groups.
Porphyrin
lem (nm)
Q(0,0) Q(0,1)
Stokes shift (cmꢀ1
)
ff
The fluorescence properties, studied for all these porphyrins
were in line with the absorption studies. Comparison of the
fluorescence spectra of one, two, three, and four meso-furyl-
porphyrins with N4 (1–4) and N2S2 (10–13) cores along with
H2TTP and S2TTP, respectively, shown in Figure 3 and the
data in Table 3 indicate the following: (1) Unlike the meso-
tetraarylporphyrins, which show two fluorescence bands,
the number of fluorescence bands in the meso-furylporphyr-
ins was reduced to one with the increase in the number of
meso-furyl groups. (2) The fluorescence band was very broad
and red shifted in the meso-furylporphyrins compared to the
meso-tetraarylporphyrins. (3) The magnitude of the red shifts
in the fluorescence band was dependent on the number of
meso-furyl groups, and increases linearly with the increase
in the number of meso-furyl groups. (4) The quantum yields
of meso-furylporphyrins were decreased as compared to
meso-tetraarylporphyrins and the decrease in quantum yields
were dependent on the number of meso-furyl groups. (5)
Among the meso-furylporphyrins, maximum red shifts and
broadening of fluorescence band with reduction in fluores-
cence intensities are observed for porphyrins with the N2S2
core. Similar observations were noted recently for meso-tetra
thienyl porphyrins,11 but the magnitude of the effects were
relatively less in meso-tetra thienyl porphyrins compared to
meso-tetra furylporphyrins. Thus, the absorption and fluores-
cence studies indicatethat with the replacement of one to four
meso-aryl groups with meso-furyl groups, the electronic
properties of the porphyrins are altered in a systematic fash-
ion, and the changes in the electronic properties were maxi-
mum for meso-tetrafurylporphyrins.
H2TTPa
1
2
3
652
659
670
680
697
670
678
698
702
717
718
729
709
706
720
737
747
773
738
718
721
728
—
118
186
296
469
578
203
66
272
311
525
378
467
346
243
295
417
463
577
475
0.11
0.045
0.038
0.019
0.011
0.0046
0.017
0.0041
0.004
0.0037
0.0037
0.0021
0.0012
0.0076
0.0022
0.0019
0.0017
0.0017
0.0022
4
—
H2TThPb
727 (sh)
760
—
—
—
—
—
—
781
—
—
—
—
—
STTPHa
5
6
7
8
9
STThPHc
S2TTPa
10
11
12
13
S2TThPc
a
Data taken from Ref. 7.
Data taken from Ref. 11a.
Data taken taken from Ref. 11d.
b
c
that the porphyrin absorption bands are shifted toward red
systematically with the increase in the number of meso-furyl
groups from one to four. It is also noted that in the case of
meso-difurylporphyrins with N3S core 6 and 7, the porphyrin
having two meso-furyl groups adjacent to thiophene 7
showed more red shifts compared to porphyrin having the
two meso-furyl groups adjacent to pyrrole. These observa-
tions were in line with the 1H NMR studies, which showed
that the b-thiophene protons flanked by two meso-furyl
groups were more downfield shifted as compared to b-thio-
phene protons adjacent to meso-aryl groups.
The changes in the absorption and emission properties can
be explained using the four orbital model developed by Gou-
terman.12 This model focuses on transitions from the highest
occupied molecular orbitals (HOMOs) to the lowest unoccu-
pied molecular orbitals (LUMOs). The absorption and
Thus, the replacement of six-membered meso-aryl groups
systematically with meso-furyl groups alters the electronic

7840
G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
Q1
Soret
(a)
0.9
0.6
0.3
20
H2TTP
1
2
3
4
10
0
1
2
3
4
Number of furyls
0.0
0.9
(b)
S2TTP
Q1
Soret
40
10
11
12
13
20
0
0.6
0.3
1
2
3
4
Number of furyls
400
440
Wavelength (nm)
480
Figure 2. Comparison of Soret absorption spectra of: (a) N4 meso-furylporphyrins 1–4 with H2TTP and (b) N2S2 meso-furylporphyrins 10–13 with S2TPP
recorded in toluene. The inset shows the plot of change of labs versus the number of furyl groups for Q1 and Soret bands.
fluorescence studies of meso-furylporphyrins indicate that
the presence of furyl groups at the meso-positions alters
the energy levels of HOMOs and LUMOs, and reduces the
energy gap between them, resulting in significant changes
in ground and excited state properties. The Stokes shift
data presented in Table 3 indicate that the Stokes shift in-
creases with the increase in the number of meso-furyl
groups, and the maximum were observed with tetrafurylpor-
phyrins compared to tetraarylporphyrins. The large Stokes
shift observed for the meso-furylporphyrins suggests that
the structure of the porphyrin in the excited state is different
from that in the ground state and may be undergoing struc-
tural reorganization in the excited state.13 Furthermore, the
meso-furylporphyrins are weakly fluorescent compared to
their corresponding meso-tetraarylporphyrins. The weak
fluorescence behavior of the meso-furylporphyrins may be
due to the orientation of the meso-furyl groups with respect
to the porphyrin plane, and the decay of the singlet excited
state through internal conversion. Thus, absorption and
steady state fluorescence studies indicated that the replace-
ment of meso-aryl groups with meso-furyl groups dramati-
cally alter the electronic properties. We are presently
exploring the time-resolved fluorescence and electrochemi-
cal studies of these porphyrins.
porphyrin cores such as N4, N3S, N2S2 and compared the
spectral properties with their corresponding meso-tetraaryl-
porphyrins. The spectral studies clearly indicate that with the
replacement of one to four meso groups with furyl groups,
the electronic properties have been altered in a systematic
way and this kind of systematic trend in alteration of spectral
properties observed for meso-furylporphyrins are quite
unique.
4. Experimental
4.1. General
1H and 13C NMR spectra were recorded with a Varian
400 MHz instrument using tetramethylsilane as an internal
standard. Absorption and steady state fluorescence spectra
were obtained with Perkin–Elmer Lambda-35 and
Lambda-55 instruments, respectively. ESMS spectra were
recorded with a Q-Tof micromass spectrometer. The time-
resolved fluorescence decay measurements were carried
out at magic angle using a picosecond diode laser based
time correlated single photon counting (TCSPC) fluores-
cence spectrometer from IBH, UK. All the decay curves
were fitted to single exponential functions using IBH soft-
ware. All general chemicals and solvents were procured
from S.D. Fine chemicals, India. Column chromatography
was performed using 60–120 mesh silica obtained from
Sisco Research Laboratories, India.
3. Conclusions
In conclusion, we have synthesized porphyrins having one,
two, three, and four meso-furyl groups with three different

G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
7841
(a)
40
0.9
0.6
0.3
0.0
H2TTP
1
2
3
4
20
0
1
2
3
4
Number of furyls
640
680
720
760
800
Wavelength (nm)
(b)
60
40
20
0
0.9
0.6
0.3
0.0
S2TTP
10
11
12
13
1
2
3
4
Number of furyls
680
720
760
Wavelength (nm)
800
840
Figure 3. Comparison of steady state fluorescence spectra of: (a) N4 meso-furylporphyrins 1–4 with H2TTP and (b) N2S2 meso-furylporphyrins 10–13 with
S2TPP recorded in toluene. The inset shows the plot of change of lem versus the number of furyl groups.
4.1.1. 2-(Hydroxy(2-furyl)methyl)-5-[hydroxy(p-tolyl)-
methyl]thiophene (14). N,N,N0,N0-Tetramethyl ethylene-
diamine (1.90 mL, 12.25 mmol) and n-BuLi (7.70 mL of
1.6 M solution in hexane, 12.25 mmol) were added to a
solution of mono-ol 16 (1.000 g, 4.9 mmol) in diethyl ether
(50 mL) and kept stirring at 0 ꢁC for 1 h. An ice cold solution
of furan-2-carboxaldehyde (0.49 mL, 5.88 mmol) in dry
THF (30 mL) was added and kept stirring for an additional
hour. Saturated aqueous NH4Cl solution was added to the
reaction mixture and it was extracted with diethyl ether
(3ꢂ50 mL). The organic layers were combined, washed
with saturated brine, and dried over Na2SO4. The crude
product was concentrated in vacuo and purified by silica
gel column chromatography using petroleum ether/ethyl
acetate (75:25) as an eluent to give a yellow oily compound
(0.630 g) in 43% yield. IR (neat, cmꢀ1): n¼3411, 2348,
(M+23)+, 283.19 (Mꢀ17)+. Analysis: Found: C, 68.01; H,
5.33; S, 10.64. C17H16O3S requires C, 67.98; H, 5.37; S,
10.68.
4.1.2. General procedure for synthesizing meso-furyl
substituted normal porphyrins. Furan-2-carboxaldehyde
(1.00 mL, 12.1 mmol), p-tolualdehyde (0.48 mL, 4 mmol),
and pyrrole (1.11 mL, 16.0 mmol) were dissolved in di-
chloromethane (300 mL) in a 500-mL one necked round bot-
tomed flask fitted with a nitrogen bubbler. After purging the
solution with nitrogen for 10 min, the condensation was ini-
tiated by adding a catalytic amount of BF3$OEt2 (120 mL of
2.5 M solution). The reaction mixture was stirred at room
temperature for 1 h. DDQ (2.750 g, 12.0 mmol) was added
and the reaction mixture was stirred in air for an additional
hour. The solvent was removed under reduced pressure
and the crude compound containing the mixture of porphy-
rins was passed quickly through a silica gel column to
remove non-porphyrin impurities using dichloromethane
as an eluent. The resulting mixture was dissolved in chloro-
form (50 mL) and refluxed with an excess of Zn(OAc)2 in
methanol (20 mL). The reaction progress was monitored
by TLC, which showed distinct separable spots, which was
not previously possible with the mixture of the unmetalated
1
1644, 1261, 1015, 750. H NMR (400 MHz, CDCl3, d in
ppm): 2.34 (s, 3H, tolyl CH3), 5.95 (s, 2H, CH), 6.28 (m,
1H, furyl), 6.33 (m, 1H, furyl), 6.73 (m, 1H, thiophene),
6.83 (m, 1H, thiophene), 7.16 (d, J¼7.93 Hz, 2H, tolyl), 7.31
(d, J¼7.93 Hz, 2H, tolyl), 7.39 (br s, 1H, furyl). 13C NMR
(CDCl3, d in ppm): 21.3, 66.5, 72.5, 107.5, 110.5, 124.9,
126.4, 129.4, 137.9, 140.1, 142.7, 148.8, 154.9. ESMS:
C17H16O3S av calcd mass: 300.08: found m/z¼323.20

7842
G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
porphyrins. The reaction mixture was washed with water
several times to remove excess Zn(OAc)2 and dried over
Na2SO4. The metalated porphyrins were separated by silica
gel column chromatography using dichloromethane/petro-
leum ether as an eluent. The separated zinc porphyrins
were demetalated by stirring a solution of the porphyrin in
dichloromethane (50 mL) with 6 M HCl (20 mL) for 2 h.
The reaction mixture was neutralized by saturated NaHCO3
and the demetalated porphyrin was purified by silica gel col-
umn chromatography using dichloromethane/petroleum
ether as an eluent.
8.10 (br s, 2H, furyl), 8.10 (br s, 4H, tolyl), 8.90 (br s, 4H,
pyrrole), 9.13 (br s, 4H, pyrrole). ESMS: C42H30N4O2 av
calcd mass: 622.24: found m/z¼623.25. Analysis: Found:
C, 81.04; H, 4.89; N, 8.96. C42H30N4O2 requires C, 81.01;
H, 4.86; N, 9.00. UV–visible (toluene) nm (log 3): 426
(5.25), 520 (3.94), 559 (3.82), 595 (3.54), 657 (3.45). Fluo-
rescence: lmax: 670 and 728 nm (sh). ff¼0.082.
4.1.2.4. 5-(2-Furyl)-10,15,20-tri(p-tolyl)-21-thiapor-
phyrin (5). A solution of the diol 14 (0.200 g, 0.67 mmol),
pyrrole (0.14 mL, 2.0 mmol), and p-tolualdehyde
(0.16 mL, 1.34 mmol) in dichloromethane (200 mL) was
purged with N2 for 10 min. Then BF3$OEt2 (40 mL of
2.5 M stock solution) was added. The mixture was allowed
to stir at room temperature for 1 h under N2 atmosphere.
DDQ (0.304 g, 1.34 mmol) was added to the reaction mix-
ture and kept stirring in air for another 1 h. Triethylamine
(0.2 mL) was added and the solvent was removed under re-
duced pressure. TLC and absorption spectral analysis
showed the formation of N4 tetratolyl porphyrin along
with the desired porphyrin. The product was separated and
purified from the black solid by silica gel column chromato-
graphy with petroleum ether/dichloromethane (70:30) elu-
ent to afford 5 in 5.4% yield (0.024 g). Mp >300 ꢁC. IR
(KBr, cmꢀ1): n¼3428, 3055, 2923, 2346, 1651, 1421,
4.1.2.1.
5-(2-Furyl)-10,15,20-tri(p-tolyl)-porphyrin
(1). Porphyrin 1 was separated on silica gel column with
60:40 petroleum ether/dichloromethane mixture as the sec-
ond band, eluting after ZnTTP. Yield 0.056 g (2.2%). Mp
>300 ꢁC. IR (KBr, cmꢀ1): n¼3434, 3055, 2923, 2340,
1
1648, 1418, 1266, 1020, 740. H NMR (400 MHz, CDCl3,
d in ppm): ꢀ2.76 (s, 2H, NH), 2.69 (s, 9H, tolyl CH3),
6.98 (m, 1H, furyl), 7.27 (m, 1H, furyl), 7.54 (m, 6H, tolyl),
8.07 (m, 6H, tolyl), 8.10 (m, 1H, furyl), 8.84 (s, 4H, pyrrole),
8.91 (m, 2H, pyrrole), 9.12 (m, 2H, pyrrole). ESMS:
C45H34N4O av calcd mass: 646.27: found m/z¼647.29.
Analysis: Found: C, 83.51; H, 5.34; N, 8.69. C45H34N4O re-
quires C, 83.57; H, 5.30; N, 8.66. UV–visible (toluene) nm
(log 3): 423 (5.45), 518 (4.36), 555 (4.12), 595 (3.95), 651
(3.83). Fluorescence: lmax: 659 and 717 nm. ff¼0.045.
1
1266, 1017, 742. H NMR (400 MHz, CDCl3, d in ppm):
ꢀ2.51 (s, 1H, NH), 2.71 (s, 9H, tolyl CH3), 7.03 (m, 1H,
furyl), 7.37 (m, 1H, furyl), 7.53–7.64 (m, 6H, tolyl), 8.05–
8.15 (m, 6H, tolyl), 8.16 (m, 1H, furyl), 8.59 (d,
J¼4.89 Hz, 1H, pyrrole), 8.63 (d, J¼4.28 Hz, 1H, pyrrole),
8.67 (d, J¼4.28 Hz, 1H, pyrrole), 8.90 (d, J¼1.83 Hz, 2H,
pyrrole), 8.99 (d, J¼4.28 Hz, 1H, pyrrole), 9.79 (d,
J¼4.89 Hz, 1H, thiophene), 10.15 (d, J¼4.89 Hz, 1H, thio-
phene). ESMS: C45H33N3OS av calcd mass: 663.23: found
m/z¼664.30. Analysis: Found: C, 81.45; H, 5.03; N, 6.30;
S, 4.80. C45H33N3OS requires C, 81.42; H, 5.01; N, 6.33;
S, 4.83; UV–visible (toluene) nm (log 3): 436 (5.45), 520
(4.43), 559 (4.21), 617 (3.85), 685 (3.81). Fluorescence:
lmax: 698 nm. ff¼0.0041.
4.1.2.2.
5,10,15-Tri(2-furyl)-20-(p-tolyl)-porphyrin
(3). Porphyrin 3 was separated on silica gel column with
40:60 petroleum ether/dichloromethane mixture as the
fourth band. Yield 0.077 g (3.2%). Mp >300 ꢁC. IR (KBr,
cmꢀ1): n¼3437, 3050, 2923, 2307, 1650, 1421, 1261,
1
1026, 750. H NMR (400 MHz, CDCl3, d in ppm): ꢀ2.63
(s, 2H, NH), 2.72 (s, 3H, tolyl CH3), 7.02 (m, 3H, furyl),
7.31 (m, 3H, furyl), 7.58 (m, 2H, tolyl), 8.10 (m, 3H, furyl),
8.12 (m, 2H, tolyl), 8.90 (d, J¼4.89 Hz, 2H, pyrrole), 9.12
(d, J¼4.89 Hz, 2H, pyrrole), 9.18 (m, 4H, pyrrole). ESMS:
C39H26N4O3 av calcd mass: 598.20: found m/z¼599.21.
Analysis: Found: C, 78.28; H, 4.34; N, 9.32; O, 8.08.
C39H26N4O3 requires C, 78.25; H, 4.38; N, 9.36; O, 8.02.
UV–visible (toluene) nm (log 3): 430 (4.92), 523 (3.84),
4.1.2.5. 5,10,15-Tri(2-furyl)-20-(p-tolyl)-21-thiapor-
phyrin (8). A solution of the diol 14 (0.200 g, 0.67 mmol),
pyrrole (0.14 mL, 2.0 mmol), and furan-2-carboxaldehyde
(0.11 mL, 1.34 mmol) in dichloromethane (200 mL) was
purged with N2 for 10 min. Then BF3$OEt2 (40 mL of
2.5 M stock solution) was added. The mixture was allowed
to stir at room temperature for 1 h under N2 atmosphere.
DDQ (0.304 g, 1.34 mmol) was added to the reaction mix-
ture and kept stirring in air for another 1 h. Triethylamine
(0.2 mL) was added and the solvent was removed under
reduced pressure. TLC and absorption spectral analysis
showed the formation of N4 tetrafurylporphyrin along with
the desired porphyrin. The product was separated and puri-
fied from the black solid by silica gel column chromato-
graphy with petroleum ether/dichloromethane (40:60)
eluent to afford 8 in 7.3% yield (0.030 g). Mp >300 ꢁC.
IR (KBr, cmꢀ1): n¼3435, 3055, 2923, 2675, 2339, 1648,
562 (3.7), 599 (3.57), 659 (3.23). Fluorescence: lmax
680 nm. ff¼0.0019.
:
4.1.2.3. 5,15-Di(2-furyl)-10,20-di(p-tolyl)-porphyrin
(2). Dipyrromethane 19 (0.100 g, 0.43 mmol) and furan-2-
carboxaldehyde (0.035 mL, 0.43 mmol) were dissolved in
dichloromethane (100 mL) in a 250-mL one necked round
bottomed flask fitted with a nitrogen bubbler. After purging
the solution with nitrogen for 10 min, the condensation was
initiated by adding a catalytic amount of BF3$OEt2 (20 mL
of 2.5 M solution). The reaction mixture was stirred at
room temperature for 1 h. DDQ (0.195 g, 0.86 mmol) was
added and the reaction mixture was stirred in air for an addi-
tional hour. The solvent was removed under reduced pres-
sure and the porphyrin 2 was purified by silica gel column
chromatography eluting with 50:50 petroleum ether/di-
chloromethane mixture as an eluent. Yield 0.006 g (2.1%).
Mp >300 ꢁC. IR (KBr, cmꢀ1): n¼3435, 3049, 2989, 2306,
1
1418, 1266, 1020, 740. H NMR (400 MHz, CDCl3, d in
ppm): ꢀ2.59 (s, 1H, NH), 2.71 (s, 3H, tolyl CH3), 7.01 (m,
3H, furyl), 7.27–7.39 (m, 3H, furyl), 7.62 (m, 2H, tolyl),
8.08–8.17 (m, 3H, furyl), 8.12 (m, 2H, tolyl), 8.72
(d, J¼4.28 Hz, 1H, pyrrole), 8.85 (m, 2H, pyrrole), 9.04
(d, J¼4.28 Hz, 1H, pyrrole), 9.26 (m, 2H, pyrrole), 9.80
1
1650, 1422, 1266, 1017, 748. H NMR (400 MHz, CDCl3,
d in ppm): ꢀ2.73 (s, 2H, NH), 2.72 (s, 6H, tolyl CH3), 7.0
(br s, 2H, furyl), 7.28 (br s, 2H, furyl), 7.57 (m, 4H, tolyl),

G. Santosh, M. Ravikanth / Tetrahedron 63 (2007) 7833–7844
7843
(d, J¼4.89 Hz, 1H, thiophene), 10.17 (d, J¼4.89 Hz, 1H,
thiophene). ESMS: C39H25N3O3S av calcd mass: 615.16:
found m/z¼616.23. Analysis: Found: C, 76.12; H, 4.02; N,
6.86; S, 5.23. C39H25N3O3S requires C, 76.08; H, 4.09; N,
6.82; S, 5.21. UV–visible (toluene) nm (log 3): 442 (5.35),
526 (4.23), 568 (4.16), 630 (3.69), 699 (3.77). Fluorescence:
lmax: 718 nm. ff¼0.0037.
0.67 mmol) and 16-thia tripyrrane 18 (0.251 g, 0.67 mmol)
in dichloromethane (200 mL) was purged with N2 for
10 min. Then BF3$OEt2 (40 mL of 2.5 M stock solution)
was added. The mixture was allowed to stir at room temper-
ature for 1 h under N2 atmosphere. DDQ (0.304 g,
1.34 mmol) was added to the reaction mixture and kept stir-
ring in air for another 1 h. Triethylamine (0.2 mL) was added
and the solvent was removed under reduced pressure. The
product was separated and purified from the black solid by
silica gel column chromatography with petroleum ether/
CH2Cl2 (60:40) eluent to afford 11 in 8.7% yield
(0.037 g). Mp >300 ꢁC. IR (KBr, cmꢀ1): n¼3436, 2929,
4.1.2.6. 5-(2-Furyl)-10,15,20-tri(p-tolyl)-21,23-dithia-
porphyrin (10). A solution of the diol 14 (0.200 g,
0.67 mmol) and 16-thia tripyrrane 17 (0.283 g, 0.67 mmol)
in dichloromethane (200 mL) was purged with N2 for
10 min. Then BF3$OEt2 (40 mL of 2.5 M stock solution)
was added. The mixture was allowed to stir at room temper-
ature for 1 h under N2 atmosphere. DDQ (0.304 g,
1.34 mmol) was added to the reaction mixture and kept stir-
ring in air for another 1 h. Triethylamine (0.2 mL) was added
and the solvent was removed under reduced pressure. The
product was separated and purified from the black solid by
silica gel column chromatography with petroleum ether/di-
chloromethane (40:60) eluent to afford 10 in 7% yield
(0.032 g). Mp >300 ꢁC. IR (KBr, cmꢀ1): n¼3436, 3054,
2986, 2681, 2305, 1421, 1266, 896, 745. 1H NMR
(400 MHz, CDCl3, d in ppm): 2.74 (s, 9H, tolyl CH3), 7.05
(m, 1H, furyl), 7.43 (m, 1H, furyl), 7.64 (m, 6H, tolyl),
8.17 (m, 6H+1H, tolyl+furyl), 8.74 (m, 3H, pyrrole), 9.05
(m, 1H, pyrrole), 9.63 (m, 3H, thiophene), 10.13 (m, 1H,
thiophene). ESMS: C45H32N2OS2 av calcd mass: 680.20:
found m/z¼681.41. Analysis: Found: C, 79.42; H, 4.70; N,
4.06; S, 9.48. C45H32N2OS2 requires C, 79.38; H, 4.74; N,
4.11; S, 9.42. UV–visible (toluene) nm (log 3): 442 (4.96),
521 (3.90), 559 (3.64), 644 (2.69), 705 (3.33). Fluorescence:
lmax: 720 nm. ff¼0.0022.
1
2462, 1643, 1273, 1021, 750. H NMR (400 MHz, CDCl3,
d in ppm): 2.71 (s, 3H, tolyl CH3), 7.04 (m, 3H, furyl),
7.40 (m, 3H, furyl), 7.66 (d, J¼7.69 Hz, 2H, tolyl), 8.12
(d, J¼7.69 Hz, 2H, tolyl), 8.18 (m, 3H, furyl), 8.66 (d,
J¼4.58 Hz, 1H, pyrrole), 8.97 (m, 3H, pyrrole), 9.66
(d, J¼4.89 Hz, 1H, thiophene), 10.01 (d, J¼4.89 Hz,
1H, thiophene), 10.08 (m, 2H, thiophene). ESMS:
C39H24N2O3S2 av calcd mass: 632.12: found m/z¼633.37.
Analysis: Found: C, 74.07; H, 3.78; N, 4.38; S, 10.12.
C39H24N2O3S2 requires C, 74.03; H, 3.82; N, 4.43; S,
10.14. UV–visible (toluene) nm (log 3): 452 (5.25), 529
(4.23), 574 (4.23), 654 (3.64), 722 (3.87). Fluorescence:
lmax: 747 nm. ff¼0.0017.
Acknowledgements
G.S. thanks CSIR for fellowship. This research was sup-
ported by Department of Science and Technology and
Department of Atomic Energy, Govt. of India, New Delhi.
NMR and mass spectra were obtained at Department of
Chemistry, IIT-Bombay.
4.1.2.7.
10,15-Di(2-furyl)-5,20-di(p-tolyl)-21,23-di-
thiaporphyrin (11). A solution of the diol 15 (0.131 g,
0.47 mmol) and 16-thia tripyrrane 17 (0.200 g, 0.47 mmol)
in dichloromethane (200 mL) was purged with N2 for
10 min. Then BF3$OEt2 (40 mL of 2.5 M stock solution)
was added. The mixture was allowed to stir at room temper-
ature for 1 h under N2 atmosphere. DDQ (0.214 g,
0.94 mmol) was added to the reaction mixture and kept stir-
ring in air for another 1 h. Triethylamine (0.2 mL) was added
and the solvent was removed under reduced pressure. The
product was separated and purified from the black solid by
silica gel column chromatography with petroleum ether/
CH2Cl2 (50:50) eluent to afford 11 in 12% yield (0.040 g).
Mp >300 ꢁC. IR (KBr, cmꢀ1): n¼3430, 3054, 2987, 2522,
References and notes
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1
1655, 1422, 1266, 742. H NMR (400 MHz, CDCl3, d in
ppm): 2.71 (s, 6H, tolyl CH3), 7.12 (m, 2H, furyl), 7.38
(m, 2H, furyl), 7.62 (d, J¼7.69 Hz, 4H, tolyl), 8.12 (d,
J¼7.69 Hz, 4H, tolyl), 8.19 (s, 2H, furyl), 8.66 (d,
J¼4.12 Hz, 2H, pyrrole), 8.97 (d, J¼4.12 Hz, 2H, pyrrole),
9.63 (s, 2H, thiophene), 10.11 (s, 2H, thiophene). ESMS:
C42H28N2O2S2 av calcd mass: 656.81: found m/z¼656.90.
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9.76. UV–visible (toluene) nm (log 3): 448 (5.25), 525
(4.20), 566 (4.12), 643 (3.49), 715 (3.67). Fluorescence:
lmax: 737 nm. ff¼0.0019.
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€
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