Synthesis and studies of covalently linked porphyrin-expanded heteroporphyrin dyads

Article abstract of DOI:10.1002/ejoc.201001482

Mono-functionalized core-modified sapphyrin (with a N₂S ₃ core) and smaragdyrin (with a N₄O core) containing a meso-iodophenyl functional group were synthesized by following a [3+2] condensation approach using appropriate

Full text of DOI:10.1002/ejoc.201001482

FULL PAPER
DOI: 10.1002/ejoc.201001482
Synthesis and Studies of Covalently Linked Porphyrin-Expanded
Heteroporphyrin Dyads
M. Rajeswara Rao[a] and M. Ravikanth*[a]
Keywords: Porphyrinoids / Anions / Sensors / Energy transfer / Fluorescence
Mono-functionalized core-modified sapphyrin (with a N2S3
core) and smaragdyrin (with a N4O core) containing a meso-
iodophenyl functional group were synthesized by following
a [3+2] condensation approach using appropriate precursors.
The mono-functionalized sapphyrin and smaragdyrin build-
ing blocks were used to synthesize the first examples of di-
phenyl ethyne bridged porphyrin–sapphyrin and porphyrin/
ZnIIporphyrin–smaragdyrin dyads under mild Pd0-coupling
conditions. The dyads are freely soluble in common organic
solvents and were characterized by various spectroscopic
techniques. Photophysical studies indicated the possibility of
energy transfer from the porphyrin/ZnII porphyrin sub-unit
to the smaragdyrin sub-unit in porphyrin/ZnIIporphyrin–sma-
ragdyrin dyads. The potential of these dyads as fluorescent
sensors for anions was explored. The studies indicated that
the porphyrin–sapphyrin dyad cannot be used as fluorescent
sensors, whereas the porphyrin–smaragdyrin dyad was suit-
able.
Introduction
phyrin–sapphyrin dyad that was assembled through salt-
bridge formation between a carboxyl-containing porphyrin
and a monoprotonated sapphyrin. In this novel dyad, por-
phyrin acts as an energy donor and sapphyrin acts as an
energy acceptor, and an efficient singlet–singlet energy
transfer from porphyrin to the sapphyrin sub-unit was
found on selective excitation of the porphyrin sub-unit. Re-
cently, Inokuma and Osuka[6c] synthesized meso-por-
phyrinyl-substituted expanded porphyrins and tentatively
assigned the low fluorescence yields of porphyrins to the
intramolecular excitation energy transfer from porphyrin
units to the expanded porphyrin, or to electron transfer
from the porphyrin units to the easily accessed oxidized or
reduced state of the expanded porphyrin. Except for these
reports, to the best of our knowledge, no other studies are
available on either covalently or noncovalently linked ex-
panded porphyrin–porphyrin assemblies. Chandrashekar
and co-workers recently synthesized several core-modified
expanded porphyrins[7] and expanded corroles[8] by replac-
ing one or more pyrrole nitrogen atoms with other hetero-
atoms such as oxygen, sulfur, and selenium. The core-modi-
fication resulted in significant changes to the electronic,
photochemical, and optical properties. Furthermore, Chan-
drashekar and co-workers showed that the core-modified
expanded porphyrins are good complexing agents for met-
als as well as for anions, and are potential materials for
non-linear optics and medical applications.[7,8] The same
authors also recently synthesized a meso–meso linked core-
modified 22π smaragdyrin–smaragdyrin dyad[9] and studied
the unusual absorption properties. Except for the limited
number of studies mentioned above, to the best of our
knowledge, there is no other report on porphyrin-expanded
porphyrin dyads or higher oligomers. Although the ex-
Expanded porphyrins and expanded corroles are syn-
thetic analogues of the porphyrins and corroles, respec-
tively, containing more than 18 π-electrons in the conju-
gated system either due to an increased number of heterocy-
clic rings or due to multiple meso carbon bridges.[1] Thus,
compared to porphyrins and corroles, the expanded por-
phyrins and expanded corroles have large cavities, more π-
electrons in conjugation and an increased number of hetero-
atoms. Because of these additional features, the expanded
porphyrins and expanded corroles have the potential to ex-
hibit diverse chemistry, such as the ability to coordinate
anions and cations,[2] to act as sensitizers for photodynamic
therapy PDT,[3] to act as magnetic resonance imaging
(MRI) contrasting agents,[4] and to be used as materials for
non-linear optics (NLO) applications.[5] The most interest-
ing feature of expanded porphyrins/corroles is that they ab-
sorb in the red region and that their singlet state lies at
lower energy than the corresponding porphyrins and cor-
roles. Hence, an assembly of expanded macrocycle and nor-
mal porphyrin/corrole would offer an opportunity of creat-
ing interesting electronic interactions between two macro-
cycles both in the ground and excited states; such interac-
tions may be tuned further by appropriate metalation either
at one or at both macrocycles. Interestingly, there are very
few reports on covalently or noncovalently linked, ex-
panded porphyrin–porphyrin dyads[6] or higher oligomers.
Sessler and co-workers[6a,6b] created a noncovalent por-
[a] Department of Chemistry, Indian Institute of Technology,
Bombay, Powai, Mumbai 400076, India
E-mail: ravikanth@chem.iitb.ac.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201001482.
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M. Rajeswara Rao, M. Ravikanth
FULL PAPER
panded porphyrins have been shown to be good receptors sired compound, along with spots corresponding to the un-
for anions, these systems have never been used as fluores- reacted starting materials, which could be separated by sil-
cent anion sensors. In this paper, we report the synthesis of ica gel column chromatography using petroleum ether/ethyl
the mono-functionalized N2S3 sapphyrin and N4O sma- acetate to afford pure functionalized unsymmetrical bithio-
ragdyrin building blocks containing a meso-iodophenyl phene diol 5 as a white solid in 49% yield. The diol 5 was
1
group and used these expanded porphyrin building blocks characterized by melting point, ES-MS, H and 13C NMR
to synthesize the first examples of weakly coupled diphenyl and elemental analyses. Diol 5 showed a [M+ – OH] peak
ethyne bridged porphyrin–N2S3 sapphyrin dyad 1 and por- in the mass spectrum, and elemental analysis confirmed the
1
phyrin/ZnIIporphyrin–N4O smaragdyrin dyad 2/Zn2 using identity of diol 5. In the H NMR spectrum, the two CH
mild copper-free Pd0 coupling conditions. The studies indi- protons appeared as a singlet at δ = 5.32 ppm and the four
cate that dyad 2 can be used for singlet–singlet energy trans- thiophene protons appeared as sets of three signals in the
fer, and as an fluorescent anion sensor, whereas dyad 1 was region δ = 6.0–7.0 ppm (see Supporting Information). The
not suitable for this purpose.
other two known precursors, 16-thiatripyrrin 9 and 16-oxa-
tripyrrin 10, were synthesized by following the literature
methods.[12]
Results and Discussion
The mono-functionalized N2S3 sapphyrin 3 and N4O
smaragdyarin 4 were synthesized by following the synthetic
strategies presented in Schemes 1 and 2, respectively. The
N2S3 sapphyrin can be prepared by [3+2] condensation[7] of
bithiophene diol and 16-thiatripyrrane, and N4O sma-
ragdyrin can be prepared by [3+2] condensation[8] of meso-
aryl dipyrromethane and 16-oxatripyrrane under mild acid-
catalyzed conditions. To synthesize the mono-function-
alized N2S3 sapphyrin 3 and N4O samaragdyrin 4 building
blocks, access to unsymmetrical bithiophene diol 5-[hy-
droxy(4-iodophenyl)methyl]-5Ј-(hydroxy(p-tolyl)methyl)-
2,2Ј-bithiophene (5) and meso-iodophenyl dipyrromethane
6, respectively, were required. The precursor 6 was synthe-
sized by following the literature procedure,[10] and com-
pound 5 was synthesized in two steps by Ulman’s method[11]
starting with bithiophene 7. In the first step, the bithio-
phene mono-ol, 5-[hydroxy(p-tolyl)methyl]bithiophene (8)
Scheme 1. Synthesis of N2S3 sapphyrin building block 3.
Scheme 2. Synthesis of N4O smaragdyrin building block 4.
The mono-functionalized sapphyrin 3 was synthesized by
was synthesized by treating the bithiophene 7 with acid-catalyzed condensation of bithiophene diol 5 with 16-
1.2 equivalents of nBuLi followed by 1.2 equiv. of p-tolylal- thiatripyrrane 9. The sapphyrin building block 3, contain-
dehyde in tetrahydrofuran (THF) at 0 °C. The crude com- ing a functionalized meso-aryl group at the bithiophene
pound was purified by silica gel column chromatography to side, was synthesized by condensing one equivalent of un-
afford 8 as a white solid in 77% yield. In the second step, symmetrical bithiophene diol 5 with one equivalent of sym-
the bithiophene mono-ol 8 was then treated with 2.5 equiv. metrical 16-thiatripyrrane 9 in CH2Cl2 in the presence of
nBuLi followed by 1.2 equiv. of 4-iodobenzaldehyde in one equivalent of trifluoroacetic acid (TFA) at room tem-
THF at 0 °C (Scheme 1). After work up, TLC analysis of perature for 1 h under an inert atmosphere and oxidized
the crude mixture showed a spot corresponding to the de- with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in
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Porphyrin-Expanded Heteroporphyrin Dyads
open air for an additional 1 h. TLC analysis indicated for-
The smaragdyrin building block, 19-(4-iodophenyl)-5,10-
mation of the required mono-functionalized sapphyrin 3 ditolyl-25-oxasmaragdyrin (4) was synthesized by condens-
along with 5,10,15,20-tetratolyl-21,23-dithiaporphyrin ing one equivalent of meso-(iodophenyl)dipyrromethane (6)
(S2TPP) and functionalized N2S4 rubyrin. The crude mate- with one equivalent of 16-oxatripyrrane[12] (10) in dichloro-
rial was subjected to silica gel column chromatographic pu- methane in the presence of 0.1 equiv. of trifluoroacetic acid
rification to afford the desired sapphyrin building block 3 at room temperature under a nitrogen atmosphere, followed
in 14% yield. No attempt was made to characterize the by oxidation with DDQ in air. TLC analysis of the crude
functionalized N2S4 rubyrin, which was collected as the last reaction mixture showed the formation of the required sma-
band to be eluted from the silica gel column in very trace ragdyrin building block 4 and very trace amounts of an
1
amounts. In the H NMR spectrum of sapphyrin building uncharacterized pink compound (Ͻ1%). The crude mate-
block 3, the four bithiophene protons appeared as three sets rial was subjected to column chromatography to afford pure
of signals in the region δ = 9.71–10.17 ppm due to unsym- oxasmaragdyrin building block 4 as a green solid in 26%
metrical substitution around the bithiophene group, unlike yield. The molecular ion peak in the ES-MS and the match-
the symmetrically substituted sapphyrin, 5,10,15,20-tet- ing CHN analysis confirmed the identity of oxasmaragd-
1
ratolyl-25,27,29-trithiasapphyrin (TTSP), which exhibits yrin building block 4. In the H NMR spectrum of 4, the
two sets of doublets for the four bithiophene protons. It has eight β-pyrrole protons appeared as sets of four doublets at
been shown[7a] that, in symmetrically substituted sapphyrin, δ = 8.48, 8.88, 9.38, and 9.48 ppm, and two β-furan protons
the thiophene opposite to the bithiophene group is inverted appeared as a singlet at δ = 8.81 ppm (see the Supporting
and appears at δ = –0.73 ppm due to ring current effects. Information). The absorption spectrum of 3 showed one
However in compound 3, the two thiophene protons of in- strong Soret band at 444 nm and four Q-bands at 555, 595,
verted thiophene showed a singlet at δ = –0.90 ppm. The 636, and 700 nm; the peak positions were identical with the
absorption spectra of sapphyrin building block 3 showed reported oxasmaragdyrin, 5,10,19-triphenyl-25-oxasmarag-
one strong Soret band at 512 nm and five Q-bands in the dyrin.[8a]
575–900 nm region; the peak maxima matched those of the
symmetrical sapphyrin TTSP.
The synthesis of porphyrin–sapphyrin dyad 1 and por-
phyrin–smaragdyrin dyads 2 and Zn2 is shown in Scheme 3.
Scheme 3. Synthesis of covalently linked porphyrin–sapphyrin dyad 1 and porphyrin–smaragdyrin dyads 2 and Zn2.
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M. Rajeswara Rao, M. Ravikanth
FULL PAPER
The other required porphyrin building block, 20-(4-ethyn- dyads 1, 2, and Zn2 in detail. The resonances of the dyads
ylphenyl)-5,10,15-tri(p-tolyl)porphyrin (11) was synthesized were assigned on the basis of the spectra observed for the
by following a literature procedure.[13] The covalently linked corresponding two monomers taken independently. A com-
porphyrin-N2S3 sapphyrin dyad 1 was synthesized using parison of 1H NMR spectra of dyad 1 with the correspond-
Lindsey’s modified Pd0-mediated coupling conditions[14] by ing monomers is presented in Figure 1. It is clear that the
coupling of N2S3 sapphyrin building block 3 and porphyrin 1H NMR spectrum of dyad 1 was composed of a superim-
building block 11 in toluene/triethylamine at 50 °C in the position of the spectra of the corresponding monomers. For
presence of [Pd2(dba)3] and AsPh3. TLC analysis after 12 h instance, in dyad 1, the four bithiophene protons of the sap-
showed two minor spots corresponding to unreacted start- phyrin sub-unit appeared as sets of three signals in the δ
ing materials and one major spot corresponding to the re- = 9.5–10.5 ppm region; the two protons of the inverted β-
quired porphyrin–sapphyrin dyad 1. The crude mixture was thiophene ring of the sapphyrin sub-unit appeared as an
subjected to silica gel column chromatography twice using upfield singlet (δ = –0.84 ppm) due to strong ring current
petroleum ether/dichloromethane, and the pure dyad 1 was effects. The four β-pyrrole protons of the sapphyrin sub-
collected as a brown solid in 62% yield. Similarly, the coval- unit appeared as four doublets in the δ = 8.5–8.8 ppm re-
ently linked porphyrin–oxasmaragdyrin dyad 2 was synthe- gion, and the eight β-pyrrole protons of the porphyrin ring
sized by coupling[14] of porphyrin building block 11 and appeared as a multiplet in the δ = 8.8–9.1 ppm region; the
oxasmaragdyrin building block 4 under similar Pd0-medi- two inner NH protons of the porphyrin sub-unit appeared
ated coupling conditions (Scheme 3). The progress of the as a broad singlet at δ = –2.85 ppm. Thus, dyad 1, contain-
reaction was monitored by TLC analysis. The reaction was ing the N4 porphyrin and the N2S3 sapphyrin, showed the
1
stopped after the disappearance of significant amounts of combined H NMR spectral features of its corresponding
starting materials and appearance of a spot corresponding monomers. Similarly, dyad 2, containing the N4 porphyrin
to the required dyad 2. The crude compound was subjected and the N4O smaragdyrin, exhibited NMR spectral features
to basic alumina column chromatography using petroleum of both ring systems, with negligible changes in their chemi-
ether/dichloromethane, and the pure dyad 2 was obtained cal shifts compared to the constituent monomers, suggest-
as a light-green solid in 70% yield. The ZnII derivative of 2 ing that the porphyrin and smaragdyrin sub-units in dyad
(Zn2) was prepared by treating 2 in dichloromethane with 2 interact very weakly (see the Supporting Information).
1
methanolic Zn(OAc)2 at reflux temperature for 4 h. The The Zn2 compound showed the same H NMR spectral
ZnII ion formed a complex only with porphyrin sub-unit of features as dyad 2, except for the absence of a signal at δ =
dyad 2. The crude compound was purified by basic alumina –2.90 ppm, corresponding to the two inner NH protons of
column to afford pure Zn2 in 90% yield. The dyads 1, 2, the porphyrin sub-unit due to complexation with the Zn2+
1
and Zn2 were freely soluble in all common organic solvents, ion. The H NMR studies therefore indicate that the por-
and all showed molecular ion peaks in mass spectra con- phyrin and the expanded porphyrin sub-units in dyads 1,
1
firming their identity (see the Supporting Information). H 2, and Zn2 interact very weakly and retain most of their
1
NMR spectroscopic analysis was used to characterize the individual H NMR spectral features.
1
Figure 1. Comparison of the partial H NMR spectra of porphyrin–sapphyrin dyad 1 with monomers 3 and 11 recorded in CDCl3.
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Porphyrin-Expanded Heteroporphyrin Dyads
Absorption, Electrochemical and Fluorescence Properties
The absorption spectra of dyads 1, 2, and Zn2, along
with their corresponding porphyrin monomers, were re-
corded in toluene and the data are presented in Table 1.
The absorption spectra of the dyads were essentially a linear
combination of the absorption spectra of both monomers.
For example, the absorption spectrum of dyad 1 showed
eight bands at 422, 513, 593, 626, 651, 682, 781, and 882 nm
(Figure 2, a). In this dyad, the bands at 422, 593, and
651 nm were exclusively due to the porphyrin sub-unit and
the bands at 626, 682, 781, and 882 nm were mainly due to
the sapphyrin sub-unit.[7a] The band at 513 nm, which is
similar to the Soret band of the sapphyrin unit, masks the
absorption bands of the porphyrin sub-unit present at 517
and 551 nm. Overall, the absorption bands of dyad 1
showed the absorption features of both macrocycles, with
slight alterations in peak maxima and absorption coeffi-
cients, supporting the proposed weak interaction between
the two macrocycles in dyad 1. The porphyrin–smaragdyrin
dyad 2 showed similar absorption features; the absorption
spectrum recorded in toluene is shown in Figure 2 (b). The
dyad 2 also showed six Q-bands at 516, 553, 595, 637 (sh),
650, and 703 nm and two Soret bands at 421 and 451 nm
(Figure 2, b), indicating a weak ground state interaction be-
tween the sub-units. The dyad Zn2 showed two Soret bands
at 424 and 452 nm and four Q-bands at 552, 593, 638, and
702 nm, which are composed of the absorption bands of
the ZnII porphyrin and the smaragdyrin[8a] unit.
Figure 2. The absorption spectra of (a) porphyrin–sapphyrin dyad
1 and (b) porphyrin-smaragdyrin dyad 2 recorded in toluene. The
inset shows the expansion of Q-band region.
–1.51 V. Among these reductions, the first reduction
(–0.84 V) was exclusively due to reduction of the sapphyrin
sub-unit because this moiety is easier to reduce than the
porphyrin. The other three reductions (–1.09, –1.18, and
–1.51 V) were due to reduction of both the porphyrin and
sapphyrin sub-units. The other two dyads, 2 and Zn2, ex-
hibited similar redox features and their oxidation and re-
Table 1. Absorption data of dyads 1, 2, and Zn2 along with their
corresponding monomers recorded in toluene.
Soret band λ [nm]
Q-bands λ [nm]
[log(ε/mol–1 dm3 cm–1)]
[log(ε/mol–1 dm3 cm–1)]
H2TTP 421 (6.4)
517 (5.0), 551 (4.4), 594 (4.2), 652
(4.0)
ZnTTP 423 (6.2)
550 (5.9), 590 (4.3)
626 (4.2), 682 (4.6), 782 (3.2), 884
(4.0)
3
511 (5.5)
4
448 (6.7)
554 (5.6), 595 (5.5), 637 (5.4), 700
(5.5)
1
422 (5.6), 513 (5.4)
422 (6.3), 452 (5.9)
424 (5.9), 452 (5.5)
593 (4.2), 626 (4.2), 651 (4.3), 682
(4.5), 781 (3.5), 882 (4.0)
516 (5.1), 553 (5.1), 595 (4.9), 637
(sh), 650 (4.9), 703 (4.8)
552 (4.8), 593 (4.4), 638 (4.3), 702
(4.4)
2
Zn2
The redox properties of dyads 1, 2, and Zn2, along with
their corresponding porphyrin monomers, were studied by
cyclic voltammetry at a scan rate of 50 mV/s and by
differential pulse voltammetry (DPV) using tetrabutylam-
monium perchlorate as supporting electrolyte (0.1 m) in
dichloromethane. A comparison of the reduction waves of
porphyrin–sapphyrin dyad 1 with the corresponding mono-
mers is shown in Figure 3, and the data is presented in
Table 2. The dyads exhibited features of both of the mono-
mers, and the peak potentials of the dyads were assigned
on the basis of their corresponding monomers. For in-
stance, dyad 1, containing porphyrin and sapphyrin sub-
Figure 3. Comparison of cyclic voltammogram reduction waves of
dyad 1 with their monomers 3 and 11 in dichloromethane contain-
ing 0.1 m TBAP as supporting electrolyte recorded at 50 mV s–1
units, showed four reductions at –0.84, –1.09, –1.18, and scan speed.
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M. Rajeswara Rao, M. Ravikanth
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duction peak potentials were in the same range as the corre-
sponding monomers. Thus, the electrochemical studies sup-
ported the proposal that the two macrocycles retain their
individual characteristic features in the dyads.
Table 2. Electrochemical redox data (V) of porphyrin dyads 1, 2,
and Zn2, and their corresponding monomers.[a]
Oxidation
Reduction
E1/2/V vs. SCE
E1/2/V vs. SCE
H2TTP
3
4
1
–
–
–
1.03 1.30 –
–
–
–1.23 –1.55
–
–
0.74 1.03 1.35 1.55 –0.82 –1.06
–
–1.50
–
0.36 0.69 –
–
–
–
–
–
–1.31
–1.63
–
0.78 1.00 1.35 1.43 –0.84 –1.09 –1.18 –1.51
2
0.33 0.58 1.00 1.43 –
–
–
–
–
–
–1.16 –1.49 –1.67
–1.25 –1.67
–1.16 –1.49 –1.67
ZnTTP
Zn2
–
0.80 1.09 –
–
–
–
0.37 0.78 1.09 –
–0.83
[a] Recorded in dichloromethane containing 0.1 m TBAP as sup-
porting electrolyte using a scan rate of 50 mV/sec. E1/2 values re-
ported are relative to SCE.
The steady-state fluorescence properties of dyads 1, 2,
and Zn2, along with 1:1 mixtures of the corresponding
monomers in toluene at room temperature, are presented in
Figure 4; the relevant photophysical data is given in Table 3.
For dyad 1, containing the porphyrin and sapphyrin sub-
units, the sapphyrin sub-unit was nonfluorescent, and emis-
sion was noted only from the porphyrin sub-unit on exci-
tation at 420 nm Ϫ a frequency at which the porphyrin sub-
unit absorbs strongly. A comparison of the steady-state
emission spectra of dyad 1 and a corresponding 1:1 mixture
of monomers 3 and 11 recorded at 420 nm is shown in part
a of Figure 4. It was clear that emission from the porphyrin
sub-unit in dyad 1 was quenched by 96% (Figure 4, a) com-
pared to the corresponding 1:1 mixture of monomers. This
observation indicates that in dyad 1, upon excitation at
420 nm, the singlet state energy of the porphyrin sub-unit
can be transferred to the sapphyrin unit, the singlet state
energy level of which is lower than for the porphyrin, and
the singlet state of the sapphyrin unit decays nonradiatively,
resulting in a reduction of the quantum yield of the por-
phyrin sub-unit. Interestingly, for dyads 2 and Zn2, both
porphyrin and smaragdyrin sub-units are fluorescent and
their singlet state energy levels are arranged in a favorable
manner to transfer the singlet state energy of the porphyrin
sub-unit to the smaragdyrin sub-unit. Thus, excitation of
dyad 2 (420 nm) results in quenching of the porphyrin fluo-
rescence by 89% and strong emission from the oxasmarag-
dyrin sub-unit was observed (Figure 4, b). However, when
a 1:1 mixture of porphyrin building block 11 and N4O sma-
ragdyrin building block 4 was excited at the same frequency,
Figure 4. Comparison of steady-state emission spectra of (a) dyad
1 (Ϫ) and a 1:1 mixture of 3 and 11 (----); (b) dyad 2 (Ϫ) and a 1:1
mixture of 4 and 11 (----) in toluene; the excitation wavelength used
was 420 nm. (c) Comparison of steady-state emission spectra of
dyad Zn2 (Ϫ) and a 1:1 mixture of ZnTTP and 4 (----). The exci-
tation wavelength used was 550 nm.
Table 3. Emission data of dyads 1, 2, and Zn2 and monomers re-
corded in toluene.
λex
–
φ
Quenching [%]
H2TTP
420
550
450
420
420
450
550
450
–
–
–
0.110
0.033
0.065
0.003
0.007
0.042
0.003
0.027
–
–
–
96
89
–
92
–
ZnTTP
4
1
2
N4em
N4em
N4Oem
ZnN4em
N4Oem
Zn2
The steady-state fluorescence studies of Zn2, together
strong emission was noted from the porphyrin building with the corresponding 1:1 mixture of monomers, were also
block 11 (Figure 4, b). The excitation spectrum of dyad 2 carried out in toluene using an excitation wavelength of
recorded at 720 nm, which is the emission peak maxima 550 nm. When Zn2 was excited at this frequency (at which
of the oxasmaragdyrin sub-unit, showed absorption bands ZnII porphyrin absorbs strongly), the fluorescence of the
corresponding to both the porphyrin and smaragdyrin sub- ZnII porphyrin was quenched by 92%, and strong emission
units, and closely matched its absorption spectrum. These from the oxasmaragdyrin unit was observed. This was in
results support the involvement of an efficient singlet–sing- marked contrast to the emission spectrum observed for the
let energy transfer from the porphyrin sub-unit to the sma- corresponding 1:1 mixture of ZnII porphyrin and sma-
ragdyrin sub-unit in dyad 2.
ragdyrin monomers, which exhibited emission mainly from
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Porphyrin-Expanded Heteroporphyrin Dyads
the ZnII porphyrin alone (Figure 4, c). These observations
also support the idea of singlet–singlet energy transfer from
the ZnII porphyrin sub-unit to the oxasmaragdyrin sub-unit
in dyad Zn1. Thus, the steady-state fluorescence studies
with dyads 2 and Zn2 indicated the possibility of energy
transfer from the porphyrin/ZnII porphyrin to the sma-
ragdyrin in the singlet excited state. Although we attributed
the fluorescence quenching of the donor porphyrin unit in
dyads 1, 2, and Zn2 to only energy transfer, we cannot ruled
out the possibility of some contribution from electron
transfer between the two macrocycles in these dyads. How-
ever, detailed time-resolved studies are required to quantify
the energy transfer dynamics of these porphyrin-expanded
porphyrin dyads.
Figure 5. Absorption spectra of 1 (1 μm) with increasing amounts
of trifluoroacetic acid recorded in toluene. The acid concentrations
used were: 0, 40, 60, 80, 100, 120, 140, 160, 180, and 200 μm. The
inset shows an expansion of the absorption spectra in the 350–
550 nm region.
Anion Binding Studies
It is well-established that acyclic and cyclic polypyrrole
systems can act as anion sensors.[15] Although porphyrins
are known to bind only cations, the expanded porphyrins
Ϫ by virtue of their bigger core size Ϫ are known for their
strong ability to coordinate anions in their protonated
forms.[1] Protonation of expanded porphyrins leads to the
formation of cations, which bind to anions through electro-
static interactions. Chandrashekar and co-workers[3a,4a]
demonstrated that core-modified expanded porphyrins,
such as sapphyrin with N2S3 core and smaragdyrin with
N4O core, can bind anions in the protonated form, al-
though the binding is less effective compared to their aza
analogues.[1b] However, these compounds were never inves-
tigated as fluorescent sensors for anions. We carried out
protonation studies for dyads 1 and 2 to test their potential
as fluorescent sensors. We assumed that selective proton-
Figure 6. Absorption spectra of 2 (1 μm) with increasing amounts
of trifluoroacetic acid recorded in toluene. The acid concentrations
used were 0, 20, 40, 60, 70, and 80 μm. The inset shows the com-
ation of the expanded porphyrin sub-unit, such as the sap- parison of 2 (Ϫ) and 2·H+ (- - -) in the Q-band region.
phyrin sub-unit in dyad 1 or the smaragdyrin sub-unit in
dyad 2, would help bind anions at the protonated expanded
porphyrin site. The extent of this anion binding would then However, in dyad 2, on addition of increasing amounts of
be measured by following the changes in the fluorescence trifluoroacetic acid, the smaragdyrin sub-unit was proton-
of the porphyrin sub-unit, thus the dyads could be used as ated first, indicating that the smaragdyrin group is more
fluorescent sensors. Initially, we systematically carried out basic than the porphyrin (Figure 6). On addition of tri-
protonation studies on dyads 1 and 2 by titrating the dyads fluoroacetic acid to dyad 2, the absorption bands at 422,
with trifluoroacetic acid in toluene; the results are presented 516, 552, 595, and 650 nm, corresponding to the porphyrin
in Figures 5 and 6, respectively. For dyad 1, on addition of sub-unit, remain unaltered and the absorption bands at
increasing amounts of trifluoroacetic acid, the porphyrin 452, 637, and 703 nm, which mainly correspond to the sma-
sub-unit was first protonated, indicating that the porphyrin ragdyrin sub-unit, experience redshifts and appear at 457,
moiety is more basic than the sapphyrin sub-unit, as clearly 669, and 735 nm, respectively. Furthermore, from fluores-
evident in Figure 5. Protonation of the porphyrin sub-unit cence studies, it was noted that upon protonation of the
in dyad 1 leads to clear changes in the absorption spectral smaragdyrin sub-unit of dyad 2, the fluorescence of the por-
bands corresponding to the porphyrin sub-unit without any phyrin sub-unit remained almost the same, but the strong
alteration in the sapphyrin absorption bands. The absorp- fluorescence from the smaragdyrin sub-unit was completely
tion bands at 422, 593, and 651 nm, corresponding to the quenched (see the Supporting Information). Thus, proton-
porphyrin sub-unit, experienced redshifts and appeared at ation studies on dyads 1 and 2 indicated that dyad 1, in
446, 614, and 672 nm, respectively, whereas the absorption which the porphyrin was protonated first, cannot be used
bands at 513, 682, 781, and 882 nm, corresponding to the as a fluorescent sensor, whereas dyad 2, in which the sma-
sapphyrin sub-unit, remained unaltered, supporting the ragdyrin sub-unit was protonated, can be used as fluores-
idea of protonation of the porphyrin sub-unit in dyad 1. cent sensor.
Eur. J. Org. Chem. 2011, 1335–1345
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1341

M. Rajeswara Rao, M. Ravikanth
FULL PAPER
We carried out the anion-sensing experiments by adding addition of anion were clear, they were minimal, as ex-
increasing amounts of various tetrabutylammonium an- pected because the porphyrin acts as a remote site. Further
ionic salts to the protonated dyad 2·H+, in which the sma- verification of anion binding at the protonated smaragdyrin
ragdyrin unit was selectively protonated, and the fluores- site in dyad 2 was obtained from mass spectral analysis,
cence of the porphyrin sub-unit was monitored at 650 nm which showed a clear mass peak corresponding to phos-
upon excitation at a wavelength of 410 nm. The effect of phate-bound protonated dyad 2·H+ (Figure 8). The appar-
adding increasing amounts of tetrabutylammonium fluo- ent association constants for the formation of anion-bound
ride salt on the fluorescence spectra of selectively proton- protonated dyad for various anions were calculated by
ated dyad 2 is shown in Figure 7. Addition of increasing using the Benesi–Hildebrand equation; the binding con-
amounts of tetrabutylammonium fluoride, bromide, iodide, stants for various anions are shown in Scheme 4. Thus, al-
sulfate, and phosphate salts in toluene resulted in a gradual though a more detailed study is needed, these preliminary
enhancement of the intensity of the porphyrin emission investigations indicate that the porphyrin–oxasmaragdyrin
band at 650 nm, suggesting that the anions were bound at dyad 2 can be used as a fluorescent anion sensor.
the protonated smaragdyrin sub-unit site in dyad 2·H+.
Thus, in dyad 2, binding of anions at the smaragdyrin site
was measured by observing changes in the fluorescence in-
tensity of the porphyrin sub-unit, suggesting that the por-
phyrin–smaragdyrin dyad 2 should be suitable as a fluores-
cent sensor. However, although the changes in the fluores-
cence intensity of the porphyrin sub-unit in dyad 2·H+ on
Figure 7. Fluorescence emission changes (λex = 410 nm) of dyad
2·H+ (1 μm) upon the addition of tetrabutylammonium fluoride in
toluene. The F– concentrations were 0, 4, 8, 12, 10, 16, 26, 46, and
Figure 8. ES-MS spectrum of hydrogen phosphate bound proton-
66 μm. The inset shows the plot of 1/[A–] vs. 1/(I – I0).
ated dyad 2 (2·H+–HPO42–).
Scheme 4.
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Eur. J. Org. Chem. 2011, 1335–1345

Porphyrin-Expanded Heteroporphyrin Dyads
Conclusions
(1)
A synthesis of mono-functionalized sapphyrin (with
N2S3 core) and smaragdyrin (with N4O core) building
blocks using readily available precursors has been devel-
oped. The mono-functionalized, expanded-core-modified
porphyrin building blocks were used to synthesize the first
Where I0 is the intensity of 2·H+ before addition of anions, I is the
intensity in the presence of A–, I1 is the intensity upon saturation
with A–, and Ka is the association constant of the complex
examples of covalently linked porphyrin-expanded por- formed.
phyrin dyads. Steady-state fluorescence studies indicated the
5-[Hydroxy(p-tolyl)methyl]bithiophene (8): Anhydrous, distilled
ether (40 mL) was added to a 250 mL three-necked, round-bottom
flask fitted with a rubber septum and gas inlet tube. The flask was
possibility of efficient energy transfer in the singlet state
from the porphyrin sub-unit to the smaragdyrin sub-unit
upon selective excitation of the porphyrin sub-unit in the flushed with argon for 10 min then tetramethylethylenediamine
(TMEDA; 2.16 mL, 14.4 mmol) and n-butyllithium (ca. 1.6 m in
hexane, 9 mL) were added to the stirred solution and the reaction
temperature was maintained at 0 °C in an ice bath. Bithiophene 7
(2.0 g, 12 mmol) was added and the solution was stirred for 1 h.
As the reaction progressed, a white turbid solution formed, indicat-
ing the formation of the 5-lithiated salt of bithiophene. An ice-
cold solution of p-tolualdehyde (1.69 mL, 14.4 mmol) in anhydrous
THF (40 mL) was then added and the reaction was stirred for an
additional 15 min at 0 °C. The reaction mixture was brought to
room temperature and quenched by the addition of ice-cold satd.
porphyrin–smaragdyrin dyad, and a significant decrease in
the fluorescence yield of the porphyrin sub-unit in por-
phyrin–sapphyrin dyad was observed. Protonation studies
indicated that the porphyrin becomes protonated in the
porphyrin–sapphyrin dyad, and smaragdyrin becomes pro-
tonated in the porphyrin–smaragdyrin dyad, indicating that
only the porphyrin–smaragdyrin dyad in the protonated
form can be used as a fluorescent sensor. Preliminary
anion-binding studies indicated that the smaragdyrin sub-
unit in the protonated form binds anions; the extent of this aqueous NH4Cl solution (50 mL). The organic layer was diluted
with diethyl ether and washed several times with water and brine
and dried with anhydrous Na2SO4. The solvent was removed in a
rotary evaporator under reduced pressure to afford the crude com-
pound. TLC analysis showed three spots; the first two spots corre-
sponded to unreacted bithiophene 7 and tolualdehyde, respectively,
and the last major spot corresponded to the mono-ol 8. The crude
compound was subjected to silica gel column chromatography and
the desired mono-ol 8 was collected as the third band (petroleum
ether/ethyl acetate, 95:5). The solvent was removed on a rotary
evaporator under vacuo to afford pure 8 as a white solid (2.5 g,
binding can be sensed by changes in the fluorescence inten-
sity of porphyrin sub-unit, thus the porphyrin–smaragdyrin
dyad has the potential to be used as a fluorescent sensor
for anions. Detailed anion-binding studies with these dyads
are under investigation in our laboratory.
Experimental Section
1
General: H NMR spectra were recorded with a Varian VXR 300
1
spectrometer operating at the appropriate frequencies using TMS
as internal reference or referred to the residual proton signal of
CDCl3 (δ = 7.26 ppm). Absorption and steady-state fluorescence
spectra were obtained with a Perkin–Elmer Lambda-35 and PC1
photon-counting spectrofluorometer manufactured by ISS and
USA instruments, respectively. The ES-MS spectra were recorded
with a Q-Tof micro mass spectrometer. MALDI-TOF spectra were
obtained with an Axima-CFR instrument manufactured by Kratos
analyticals. THF and chloroform were dried with sodium benzo-
phenone ketyl and distilled prior to use. BF3·Et2O, 2,3-dichloro-
5,6-dicyano-1,4-benzoquinone (DDQ), and N,N,NЈ,N-tetramethyl-
ethylenediamine (TMEDA), were used as obtained. All other
chemicals were reagent grade unless otherwise specified. Column
chromatography was performed on silica gel (60–120 mesh).
77% yield); m.p. 59–60 °C. H NMR (400 MHz, CDCl3): δ = 2.35
(s, 3 H), 5.98 (s, 1 H), 6.78 (d, 3JH,H = 3.6 Hz, 1 H), 6.99 (m, 2 H),
3
7.10 (m, 1 H), 7.18 (m, 3 H), 7.34 (d, JH,H = 7.8 Hz, 2 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 21.3, 72.5, 123.3, 123.7, 124.5,
125.5, 125.9, 126.4, 127.9, 129.4, 137.5, 138.1, 140.0 and
147.4 ppm. ES-MS (C16H14OS2): m/z
C16H14OS2: calcd. C 68.95, H 4.66; found C 68.58, H4.61.
= – OH].
268.1 [M+
5-[Hydroxy(4-iodophenyl)methyl]-5Ј-(hydroxytolylmethyl)-2,2Ј-
bithiophene (5): Freshly distilled anhydrous diethyl ether (30 mL)
was added to a 250 mL three-necked round-bottomed flask
equipped with rubber septum, gas inlet and gas outlet tube. After
purging with N2 gas for 5 min, TMEDA (1.3 mL, 8.5 mmol) and
nBuLi (ca. 1.6 m in hexane, 5.5 mL) were added, followed by the
mono-ol 8 (1 g, 3.4 mmol) and the solution was stirred for 1 h at
0 °C. An ice-cold solution of p-iodobenzaldehyde (0.96 g,
4.1 mmol) in anhydrous THF (40 mL) was then added to the stirred
solution and the reaction was stirred at 0 °C for 15 min. An ice-cold
satd. aqueous solution of NH4Cl (50 mL) was added to quench the
excess of nBuLi. The organic layer was separated and the aqueous
layer was extracted several times with ether. The combined organic
layers were washed with water and brine, and dried with anhydrous
Na2SO4. The solvent was removed with a rotary evaporator under
reduced pressure to afford the crude compound. TLC analysis
showed three major spots corresponding to the unreacted 4-iodo-
benzaldehyde, unreacted mono-ol, and the desired diol 5. The alde-
hyde and the mono-ol were removed by silica gel column
chromatography (petroleum ether/ethyl acetate, 95:5) and the diol
5 was collected (petroleum ether/ethyl acetate, 80:20). The solvent
was removed on a rotary evaporator under reduced pressure to
afford the pure diol 5 as a white solid (900 mg, 49%); m.p.
Solution Studies: All the anion salts used for the titrations were
applied as their tetrabutylammonium salts. Solvents used were of
analytical grade and were purified and dried by routine procedures
immediately before use.
Fluorescence Studies: Stock solutions containing the anions
(10 mm) were prepared in methanol and a stock solution of 2
(1 mm) was prepared in toluene. For fluorescence measurements,
the stock solution of 2 was diluted to 1 μm with toluene and dilute
trifluoroacetic acid (80 equiv.) was used to selectively generate pro-
tonated dyad 2·H+. Titration experiments were performed by plac-
ing a solution 2·H+ (1 μm, 2.5 mL) in a quartz cuvette of 1 cm path
length, and various amounts of anions were added incrementally
by means of a micro-pipette. Excitation was provided at 410 nm,
and emission was collected from 630–800 nm. The association con-
stant of the anion complex formed in the solution was estimated
using the standard Benesi–Hildebrand, see Equation (1).
Eur. J. Org. Chem. 2011, 1335–1345
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1343

M. Rajeswara Rao, M. Ravikanth
FULL PAPER
1
Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = 2.35 (s, 3 H), 5.93 (s, 0.011 mmol) and 5-(4-ethynylphenyl)-10,15,20-tri(p-tolyl)porphyrin
3
1 H), 5.95 (s, 1 H), 6.75 (d, JH,H = 3.3 Hz, 2 H), 6.92–6.94 (m, 2
H), 7.20–7.23 (m, 4 H), 7.34–7.36 (m, 2 H), 7.70 (d, 3JH,H = 8.5 Hz,
2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 21.4, 71.8, 72.6, 122.3,
122.5, 123.1, 123.3, 125.7, 125.8, 126.4, 127.2, 127.4, 128.1, 128.6,
129.4, 131.8, 135.7, 135.9, 138.0, 140.6, 142.0, 142.7, 145.2, 146.7,
150.2 ppm. ES-MS (C23H19IO2S2): m/z = 501.2 [M+ – OH], 420.2
[M+ – I]. C23H19IO2S2: calcd. C 53.29, H 3.69; found C 53.58, H
3.61.
(11; 7.5 mg, 0.02 mmol) were dissolved in anhydrous toluene/trieth-
ylamine (5:1, 30 mL) in a 50 mL round-bottomed flask fitted with
a reflux condenser, gas inlet, and gas outlet tubes for nitrogen purg-
ing. The reaction vessel was placed in an oil bath preheated to
50 °C. After purging with nitrogen for 15 min, AsPh3 (4.0 mg,
0.013 mmol) followed by [Pd2(dba)3] (2.1 mg, 0.0016 mmol) were
added and the reaction mixture was stirred under nitrogen at 50 °C
for 12 h. TLC analysis of the reaction mixture showed the disap-
pearance of spots corresponding to the starting materials and the
appearance of a new spot corresponding to dyad 1. After removal
of the solvent, the crude compound was purified by silica gel col-
umn chromatography (petroleum ether/dichloromethane, 65:35) to
afford the desired dyad 1 as a brown solid (10 mg, 62%); m.p.
5-(4-Iodophenyl)-10,15,20-tritolyl-25,27,29-trithiasapphyrin (3): In a
250 mL one-necked round-bottomed flask fitted with a nitrogen
bubbler, diol 5 (200 mg, 0.42 mmol) and 16-thiatripyrrane 9
(179 mg, 0.42 mmol) were dissolved in CH2Cl2 (200 mL). After
purging with nitrogen for 10 min, the condensation of diol 5 with
tripyrrane 9 was initiated by adding TFA (0.032 mL, 0.42 mmol).
The reaction mixture was stirred at room temperature for 1 h then
DDQ (95 mg, 0.42 mmol) was added and the reaction mixture was
stirred in air for additional 1 h. TLC analysis indicated the forma-
tion of a three-component mixture containing 21,23-dithiapor-
phyrin, the desired N2S3 sapphyrin 3, and N2S4 rubyrin. The crude
mixture was subjected to silica gel column chromatography and the
desired N2S3 sapphyrin 3 was obtained as the second band (petro-
leum ether/dichloromethane, 60:40). The solvent was removed in
vacuo to afford 3 as a green solid (57 mg, 14%). 1H NMR
(400 MHz, CDCl3): δ = –0.90 (s, 2 H), 2.62 (s, 9 H), 7.57–7.67 (m,
6 H), 8.00–8.02 (m, 2 H), 8.17–8.28 (m, 8 H), 8.59–8.61 (m, 3 H),
1
Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = –2.75 (s, 2 H), –0.84
(s, 2 H), 2.71 (s, 18 H), 7.50–7.73 (m, 16 H), 8.07–8.40 (m, 16 H),
3
3
8.60 (d, JH,H = 4.5 Hz, 1 H), 8.62 (d, JH,H = 4.5 Hz, 1 H), 8.64
3
3
(d, JH,H = 4.5 Hz, 1 H), 8.70 (d, JH,H = 4.5 Hz, 1 H), 8.74 (d,
3JH,H = 4.5 Hz, 1 H), 8.80–8.90 (m, 8 H), 9.75–9.77 (m, 1 H), 9.81
3
3
(d, JH,H = 4.0 Hz, 1 H), 10.20 (d, JH,H = 4.5 Hz, 2 H) ppm.
MALDI-TOF (C100H70N6S3): m/z = 1451.9 [M + 1]+. UV/Vis (tol-
uene): λmax [log(ε/mol–1 dm3 cm–1)] = 421 (17.2), 512 (8.2), 593
(5.5), 652 (7.4), 683 (1.0), 882 (0.2) nm. C100H70N6S3: calcd. C
82.73, H 4.86, N 5.79; found C 82.46, H 5.08, N 5.78.
Porphyrin-N4O Smaragdyrin Dyad (2): A solution of 19-(4-iodo-
phenyl)-5,10-bis(tolyl)-25-oxasmaragdyrin (4; 20.0 mg, 26.8 μmol)
and 20-(ethynylphenyl)-5,10,15-tri(p-tolyl)porphyrin (11; 18.2 mg,
26.8 μmol) in anhydrous toluene/triethylamine (3:1, 20 mL) were
coupled in the presence of catalytic amounts of AsPh3 (9.8 mg,
32.0 μmol) and [Pd2(dba)3] (3.6 mg, 4.0 μmol) at 50 °C for 12 h.
The formation of the dyad was confirmed by the appearance of a
new spot on TLC, as well as the characteristic absorption bands
observed in the UV/Vis spectra. The crude compound was purified
by basic alumina column chromatography (petroleum ether/dichlo-
romethane, 60:40), and the pure dyad 2 was collected as a light-
green solid (24 mg, 70%); m.p. Ͼ300 °C. 1H NMR (400 MHz,
CDCl3): δ = –2.78 (s, 2 H), 2.73 (s, 15 H), 7.53–7.62 (m, 12 H),
3
3
8.68 (d, JH,H = 4.4 Hz, 1 H), 9.69 (d, JH,H = 4.1 Hz, 1 H), 9.78
(d, JH,H = 4.1 Hz, 1 H), 10.17 (d, JH,H = 4.1 Hz, 2 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 21.2, 21.6, 22.7, 123.1, 125.4, 128.3,
128.7, 128.9, 129.3, 129.5, 129.7, 129.8, 130.1, 131.0, 131.1, 131.3,
131.7, 132.2, 132.6, 133.0, 133.5, 133.7, 133.9, 134.0, 134.4, 134.5,
134.7, 135.6, 136.7, 137.0, 137.6, 137.6, 138.2, 138.4, 139.6, 140.4,
144.4, 144.7, 153.8, 154.4, 155.1, 155.5, 157.6, 167.9, 173.5 ppm.
ES-MS (C51H35IN2S3): m/z = 899.9 [M + 1]+. UV/Vis (toluene):
λmax [log(ε/mol–1 dm3 cm–1)] = 511 (5.4), 623 (5.7), 679 (9.2), 779
(1.2), 880 (1.9) nm. C51H35IN2S3: calcd. C 68.14, H 3.92, N 3.12;
found C 67.83, H 4.08, N 3.42.
3
3
3
19-(4-Iodophenyl)-5,10-ditolyl-25-oxasmaragdyrin (4): Samples of
meso-(iodophenyl)dipyrromethane (6; 250 mg, 0.71 mmol) and 16-
oxatripyrrane 10 (312 mg, 0.71 mmol) were dissolved in anhydrous
dichloromethane (500 mL) and stirred under a nitrogen atmo-
sphere for 5 min. The reaction was initiated by adding TFA (5.5 μL,
0.07 mmol) and stirring was continued for 90 min. DDQ (506 mg,
2.21 mmol) was then added and the reaction mixture was stirred in
open air for an additional 90 min. The solvent was removed with
a rotary evaporator under vacuum and the crude material was sub-
jected to basic alumina column chromatographic purification. A
trace amount of an uncharacterized pink fraction (petroleum ether/
dichloromethane, 5:1) was removed and the required product was
collected as a green band (petroleum ether/dichloromethane, 4:1).
The solvent was removed with a rotary evaporator under vacuum
to afford the mono-functionalized 25-oxasmaragdyrin building
block 4 as a green compound (144 mg, 26%); m.p. Ͼ300 °C. 1H
NMR (400 MHz, CDCl3): δ = 2.73 (s, 6 H), 7.62 (d, 3JH,H = 7.9 Hz,
8.03–8.13 (m, 14 H), 8.32 (d, JH,H = 7.94 Hz, 2 H), 8.47–8.50 (m,
3
2 H), 8.79 (s, 2 H), 8.85–8.93 (m, 8 H), 9.05 (d, JH,H = 3.98 Hz, 2
3
3
H), 9.45 (d, JH,H = 3.97 Hz, 2 H), 9.51 (d, JH,H = 3.97 Hz, 2
H) ppm. MALDI-TOF (C92H66N8O): m/z = 1301.9 [M + 1]+. UV/
Vis (toluene): λmax [log(ε/mol–1 dm3 cm–1)] = 421 (6.3), 452 (5.95),
516 (5.1), 553 (5.1), 595 (4.9), 637 (4.8), 650 (4.9), 703 (4.8) nm.
C92H66N8O: calcd: C 85.03, H 5.12, N 8.62; found C 84.82, H 5.23,
N 8.56.
ZnII-Porphyrin–Smaragdyrin Dyad (Zn2): A solution of 2 (10 mg,
0.0024 mmol) and an excess of Zn(OAc)2 in dichloromethane/
methanol (3:1, 30 mL) was refluxed for 4 h. The crude compound
was purified by basic alumina column chromatography (dichloro-
methane) to afford Zn2 as a green solid in 90% yield; m.p.
1
Ͼ300 °C. H NMR (400 MHz, CDCl3): δ = 2.73 (s, 15 H), 7.53–
3
7.62 (m, 12 H), 8.03–8.13 (m, 14 H), 8.32 (d, JH,H = 7.94 Hz, 2
H), 8.47–8.50 (m, 2 H), 8.79 (s, 2 H), 8.85–8.93 (m, 8 H), 9.05 (d,
3
3JH,H = 3.98 Hz, 2 H), 9.45 (d, JH,H = 3.97 Hz, 2 H), 9.51 (d,
3
3
4 H), 8.10 (m, 6 H), 8.20 (d, JH,H = 8.2 Hz, 2 H), 8.47 (d, JH,H
3JH,H = 3.97 Hz, 2 H] ppm. ES-MS (C92H64N8OZn): m/z = 1363.1
[M + 1]+. UV/Vis (toluene): λmax [log(ε/mol–1 dm3 cm–1)] = 424
(5.9), 452 (5.54), 552 (4.8), 593 (4.5), 638 (4.3), 702 (4.4) nm.
C92H64N8OZn: calcd. C 81.07, H 4.73, N 8.22; found C 81.32, H
4.71, N 8.36.
3
= 4.28 Hz, 2 H), 8.81 (s, 2 H), 8.93 (d, JH,H = 4.28 Hz, 2 H), 9.39
3
3
(d, JH,H = 4.28 Hz, 2 H), 9.48 (d, JH,H = 4.28 Hz, 2 H), ES-MS
(C43H31IN4O): m/z = 747.9 [M + 1]+. UV/Vis (toluene): λmax [log(ε/
mol–1 dm3 cm–1)] = 448 (6.7), 554 (5.6), 595 (5.5), 637 (5.4), 700
(5.5) nm. C43H31IN4O: calcd. C 69.17, H 4.18, N 7.50; found C
69.43, H 4.08, N 7.42.
Supporting Information (see footnote on the first page of this arti-
Porphyrin-N2S3 Sapphyrin Dyad (1): A solution of 5-(4-iodo- cle): Complete spectroscopic data for all new compounds and
phenyl)-10,15,20-tritolyl-25,27,29-trithiasapphyrin (3; 10 mg, anion binding studies.
1344
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1335–1345

Porphyrin-Expanded Heteroporphyrin Dyads
V. G. Anand, S. J. P. Narayanan, S. K. Pushpan, M. Raviku-
mar, T. K. Chandrashekar, K.-I. Sugiura, Y. Sakata, J. Org.
Chem. 1999, 64, 8693–8697; e) S. J. P. Narayanan, B. Sridevi,
T. K. Chandrashekar, R. Roy, A. Vij, J. Am. Chem. Soc. 1999,
121, 9053–9068; f) R. Misra, R. Kumar, T. K. Chandrashekar,
B. S. Joshi, J. Org. Chem. 2007, 72, 1153–1160; g) H. Rath,
V. G. Anand, J. Sankar, S. Venkatraman, T. K. Chandrashekar,
B. S. Joshi, C. L. Khetrapal, U. Schilde, M. O. Senge, Org. Lett.
2003, 5, 3531–3533; h) V. G. Anand, S. K. Pushpan, S. Venka-
traman, A. Dey, T. K. Chandrashekar, B. S. Joshi, R. Roy, W.
Teng, K. R. Senge, J. Am. Chem. Soc. 2001, 123, 8620–8621; i)
V. G. Anand, S. K. Pushpan, A. Srinivasan, S. J. Narayanan,
B. Sridevi, T. K. Chandrashekar, R. Roy, B. S. Joshi, Org. Lett.
2000, 2, 3829–3832; j) V. G. Anand, S. K. Pushpan, S. Venka-
traman, S. J. Narayanan, A. Dey, T. K. Chandrashekar, R. Roy,
B. S. Joshi, S. Deepa, G. N. Sastry, J. Org. Chem. 2002, 67,
6309–6319; k) S. Gokulnath, T. K. Chandrashekar, Org. Lett.
2008, 10, 637–640; l) S. Gokulnath, V. Prabhuraja, T. K. Chan-
drashekar, Org. Lett. 2007, 9, 3355–3357; m) R. Kumar, R.
Misra, T. K. Chandrashekar, Org. Lett. 2006, 8, 4847–4850.
[8] a) S. J. P. Narayanan, B. Sridevi, T. K. Chandrashekar, Org.
Lett. 1999, 1, 587–590; b) B. Sridevi, S. J. Narayanan, R. Rao,
T. K. Chandrashekar, Inorg. Chem. 2000, 39, 3669–3677; c) S.
Venkataraman, R. Kumar, J. Sankar, T. K. Chandrashekar, K.
Sendhil, C. Vijayan, A. Kelling, M. O. Senge, Chem. Eur. J.
2004, 10, 1423–1432; d) R. Misra, R. Kumar, T. K. Chandra-
shekar, A. Nag, D. Goswami, Org. Lett. 2006, 8, 629–631; e)
R. Misra, R. Kumar, T. K. Chandrashekar, C. H. Suresh, A.
Nag, D. Goswami, J. Am. Chem. Soc. 2006, 128, 16083–16091;
f) S. Gokulnath, V. Prabhuraja, J. Sankar, T. K. Chandra-
shekar, Eur. J. Org. Chem. 2007, 191–200.
Acknowledgments
We thank the Council of Scientific and Industrial Research (CSIR),
New Delhi and the Department of Science and Technology (DST)
for financial support. M. R. R. thanks the CSIR for a fellowship.
[1] a) J. L. Sessler, S. J. Weghorn, Expanded, Contracted & Isomeric
Porphyrins, Tetrahedron Organic Chemistry Series, vol. 15, Per-
gamon, New York, 1997; b) J. L. Sessler, D. Seidel, Angew.
Chem. 2003, 115, 5292; Angew. Chem. Int. Ed. 2003, 42, 5134–
5175; c) T. K. Chandrashekar, S. Venkatraman, Acc. Chem.
Res. 2003, 36, 676–691.
[2] a) J. L. Sessler, E. Tomat, T. D. Mody, V. M. Lynch, J. M.
Veauthier, U. Mirsaidov, J. T. Markert, Inorg. Chem. 2005, 44,
2125–2127; b) J. L. Sessler, E. Tomat, Acc. Chem. Res. 2007,
40, 371–379; c) S. Shimizu, A. Osuka, Eur. J. Inorg. Chem.
2006, 1319–1335; d) S. Mori, A. Osuka, J. Am. Chem. Soc.
2005, 127, 8030–8031; e) T. Koide, G. Kashiwazaki, K. Furu-
kawa, A. Osuka, Inorg. Chem. 2009, 48, 4595–4597; f) M.
Shionoya, H. Furuta, V. Lynch, A. Harriman, J. L. Sessler, J.
Am. Chem. Soc. 1992, 114, 5714–5722; g) J. L. Sessler, J. M.
Davis, Acc. Chem. Res. 2001, 34, 989–997; h) J. L. Sessler, A.
Andrievsky, J. W. Genge, Adv. Supramol. Chem. 1997, 4, 97–
142; i) J. L. Sessler, A. K. Burrell, H. Furuta, G. W. Hemmi,
B. L. Iverson, V. Kral, D. J. Magda, T. D. Mody, K. Shreder,
D. Smith, S. J. Weghorn, Transition Met. Supramol. Chem.
1994, 391–408; j) J. L. Sessler, P. I. Sansom, A. Andrievsky, V.
Kral, in: Supramolecular Chemistry of Anions (Eds.: A. Bianchi,
K. B. James, E. G. Espana), Wiley-VCH, New York, 1997, pp.
355–419; k) M. Shionoya, H. Furuta, V. Lynch, A. Harriman,
J. L. Sessler, J. Am. Chem. Soc. 1992, 114, 5714–5722; l) J. L.
Sessler, M. C. Hoehner, A. Gebauer, A. Andrievsky, V. Lynch,
J. Org. Chem. 1997, 62, 9251–9260.
[3] a) J. L. Sessler, R. A. Miller, Biochem. Pharmacol. 2000, 59,
733–739; b) J. L. Sessler, G. Hemmi, T. D. Mody, T. Murai, A.
Burrell, S. W. Young, Acc. Chem. Res. 1994, 27, 43–50.
[4] a) S. W. Young, F. Qing, A. Harriman, J. L. Sessler, W. C. Dow,
T. D. Mody, G. W. Hemmi, Y. P. Hao, R. A. Miller, Proc. Natl.
Acad. Sci. USA 1996, 93, 6610–6615; b) J. L. Sessler, T. D.
Mody, G. Hemmi, V. Lynch, S. W. Young, R. A. Miller, J. Am.
Chem. Soc. 1993, 115, 10368–10369.
[5] H. Rath, J. Sankar, V. Prabhu Raja, T. K. Chandrashekar, A.
Nag, D. Goswami, J. Am. Chem. Soc. 2005, 127, 11608–11609.
[6] a) S. L. Springs, D. Gosztola, M. R. Wasielewski, V. Kral, A.
Andrievsky, J. S. Sessler, J. Am. Chem. Soc. 1999, 121, 2281–
2289; b) V. Kral, S. L. Springs, J. L. Sessler, J. Am. Chem. Soc.
1995, 117, 8881–8882; c) Y. Inokuma, A. Osuka, Org. Lett.
2004, 6, 3663–3666.
[9] R. Misra, R. Kumar, T. K. Chandrashekar, C. H. Suresh,
Chem. Commun. 2006, 4584–4586.
[10] C. H. Lee, J. S. Lindsey, Tetrahedron 1994, 50, 11427–11440.
[11] A. Ulman, J. Manassen, F. Frolow, D. Rabinovich, J. Am.
Chem. Soc. 1979, 101, 7055–7059.
[12] a) B. Sridevi, S. J. Narayanan, A. Srinivasan, M. V. Reddy,
T. K. Chandrashekar, J. Porphyrins Phthalocyanines 1998, 2,
69–78; b) P.-Y. Heo, C.-H. Lee, Bull. Korean Chem. Soc. 1996,
17, 515–520.
[13] J. S. Lindsey, S. Prathapan, J. S. Johnson, R. W. Wagner, Tetra-
hedron 1994, 50, 8941–8968.
[14] R. W. Wagner, T. E. Johnson, F. Li, J. S. Lindsey, J. Org. Chem.
1995, 60, 5266–5273.
[15] a) J. L. Sessler, S. Camiolo, P. A. Gale, Coord. Chem. Rev. 2003,
240, 17–55; b) P. A. Gale, Acc. Chem. Res. 2006, 39, 465–475;
c) P. A. Gale, J. L. Sessler, S. Camiolo, in: Encyclopedia of Sup-
ramolecular Chemistry (Eds.: J. L. Atwood, J. W. Steed), Marcel
Dekker, New York, 2004, pp. 1176–1185; d) P. A. Gale, in: En-
cyclopedia of Supramolecular Chemistry (Eds.: J. L. Atwood,
J. W. Steed), Marcel Dekker, New York, 2004, pp. 31–41; e)
E. A. Katayev, Y. A. Ustynyuk, J. L. Sessler, Coord. Chem. Rev.
2006, 250, 3004–3037; f) P. A. Gale, P. Anzenbacher Jr., J. L.
Sessler, Coord. Chem. Rev. 2001, 222, 57–102; g) J. L. Sessler,
J. M. Davis, Acc. Chem. Res. 2001, 34, 989–997.
[7] a) A. Srinivasan, S. K. Pushpan, M. Ravi Kumar, S. Mahajan,
T. K. Chandrashekar, R. Roy, P. Ramamurthy, J. Chem. Soc.
Perkin Trans. 2 1999, 961–968; b) S. J. P. Narayanan, B. Sridevi,
T. K. Chandrashekar, A. Vij, R. Roy, Angew. Chem. 1998, 110,
3582; Angew. Chem. Int. Ed. 1998, 37, 3394–3397; c) S. J. P.
Narayanan, B. Sridevi, A. Srinivasan, T. K. Chandrashekar, R.
Roy, Tetrahedron Lett. 1998, 39, 7389–7392; d) A. Srinivasan,
Received: November 2, 2010
Published Online: January 26, 2011
Eur. J. Org. Chem. 2011, 1335–1345
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