Linear conjuncted porphyrin trimer synthesis via click reaction

Article abstract of DOI:10.1142/S1088424613500636

Two isomers of porphyrin trimer with 1,4-diaryltriazole linkers have been synthesized using click methodology and characterized by MS, NMR and UV-vis spectroscopy. The porphyrin compounds were shown to exhibit photostability and high solubility. Photophys

Full text of DOI:10.1142/S1088424613500636

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2013; 17: 1–15
DOI: 10.1142/S1088424613500636
Published at http://www.worldscinet.com/jpp/
Linear conjuncted porphyrin trimer synthesis
via “click” reaction
Yulia P. Polevayaa, Vladimir S.Tyurina and Irina P. Beletskaya*a,b
a Frumkin Institute of Physical Chemistry and Electrochemistry, Leninskiy prospekt, 31-4, Moscow 119071,
Russian Federation
b Lomonosov Moscow State University, Chemistry Department, Leninskie Gory, 1-3, Moscow 119992,
Russian Federation
Dedicated to Professor Aslan Tsivadze on the occasion of his 70th birthday
Received 7 February 2013
Accepted 15 April 2013
ABSTRACT: Two isomers of porphyrin trimer with 1,4-diaryltriazole linkers have been synthesized
using “click” methodology and characterized by MS, NMR and UV-vis spectroscopy. The porphyrin
compounds were shown to exhibit photostability and high solubility. Photophysical data were compared
with corresponding ones of synthesized triazole-bridged dimer with the same electronic surrounding and
known linear dimer and trimer with diarylethyne linkers. Obtained data revealed weak inter-chromophore
electronic communication in the ground state but significant exciton coupling whereas the properties of
the individual chromophores are mainly retained for triazole-bridged dimer and trimers.
KEYWORDS: porphyrins, click chemistry, triazoles, building blocks approach, triad.
together, but the number of interesting conformational
INTRODUCTION
and supramolecular features can arise from triazole-rich
From the moment of discovery by Sharpless and
compounds [12]. Thus triazole-bridged oligoporphyrins
coworkers [1] of copper(I)-catalyzed 1,3-dipolar cyclo-
can be promising for the construction of self-organized
addition of azides and alkynes leading to 1,4-substituted
supramolecular ensembles. The organization of chromo-
1,2,3-triazoles which received a name “click” reaction,
phores on the nanoscale level as it is achieved in natural
Huisgen’s 1,3-diploar cycloaddition has got a new
photosynthetic centers is necessary for the directional
breath [2, 3]. The simple and efficient reaction became
flow of photonic energy which is an ultimate goal in
a paramount methodology of linking two organic
the design of efficient artificial phototransforming
fragments by triazole bridge. The reaction has gained
devices [13, 14]. It is known that the synthesis of multi-
wide applications in various fields of organic chemistry
porphyrin systems is of interest for further construction
and, especially in obtaining macromolecules and diverse
of electron devices, sensors, solar cells [15–18, 19–21],
functional materials [4]. This reaction plays an important
catalysts [19, 22], adsorbents [23], NLO materials [24,
role in porphyrin chemistry allowing modification of
25] and for applications in photodynamic therapy (PDT)
the porphyrin ring, forming conjugates with fullerenes
[26]. In such covalently bonded porphyrins acetylene or
[5], pharmacophore fragments [6–8], dendrimers with
porphyrin core [9, 10], immobilization of porphyrin on
solid support [11] including polypeptides [7]. Triazole
phenylene linkers were mostly used, as these systems
are easy to synthesize via the recently well-developed
catalytic cross-coupling methodology such as Suzuki
heterocycle is not only the simple, “non-interfering”
and Sonogashira reactions [13, 20, 21, 27–29]. The
linker for connection of independent molecular species
diarylethyne linked multiporphyrin arrays are weakly
coupled electronically because of the orthogonal orien-
tation of phenyl substituents of porphyrin. The rapid and
efficient excited singlet-state energy transfer was found
*Correspondence to: Irina P. Beletskaya, email: beletska@org.
chem.msu.ru
Copyright © 2013 World Scientific Publishing Company

2
Y.P. POLEVAYA ET AL.
to occur in such systems [20, 21, 30]. The nature of the
bridge linking porphyrin cores exerts a strong influence
on the energy transfer processes. At present time only
a few porphyrin dimers with 1,2,3-triazole bridge have
been synthesized. Thus Odobel and coworkers obtained
both meso–meso triazole bridged and also 1,4-diphenyl-
1,2,3-triazole bridged dimers of meso-triarylporphyrin
[31]. The former dimer was also asymmetrical with
different metals in each porphyrin core. Chen et al.
prepared asymmetrical b-meso-triazole linked dimer of
nickel complexes of tetraphenyl- and diphenylporphyrins
[32]. And finally Ravikanth and Shetti have synthesized
a series of diphenyltriazole-bridged unsymmetrical
porphyrin dimers containing two different porphyrin
subunits where one subunit is a normal porphyrin core
(N4) and another is a thia- or oxaporphyrin analog (N3S,
N2SO, N2S2) [33].
trans–meso-bis(4-azidophenyl)porphyrin (A2B2-
azidoP) III.
5-(4′-tert-butylphenyl)dipyrromethane 1 [35], 5-(4′-
nitrophenyl)dipyrromethane 2 [36] and 5-mesityldi-
pyrromethane 3 [37] were easily obtained in high yields
by published procedures. The [2+2] condensation of 1
and 2 with 4-nitrobenzaldehyde and 4-tert-butylbenzal-
dehyde, respectively yielded
a
hardly separable
mixture of desired trans-A2B2-porphyrin with side cis-
A2B2-, AB3-, A3B-, A4- and B4- porphyrins, where A is
4-nitrophenyl substituent and B is 4-tert-butylphenyl
substituent. The scrambling by-products are typically
observed in MacDonald’s condensations because of
reversible character of reactions involved [34, 36b].
Much better result was obtained in the condensation of
5-mesityldipyrromethane 3 and 4-nitrobezaldehyde in
CH2Cl2 catalyzed by TFA at room temperature affording
porphyrin 4 in 25% yield. The reduction of nitro group
was carried out in CHCl3/AcOH by SnCl2/HCl procedure
to give the 4-aminophenyl substituted porphyrin 5 in 85%
yield. Diazotization of 5 with TFA/NaNO2, followed
by one-pot reaction with NaN3 furnished meso-bis(4-
azidophenyl)porphyrin which was further converted by
reaction with zinc acetate to the desired zinc porphyrin 6
having two azide functionalities (building block III) with
80% yield over two stages (Fig. 3).
The same [2+2] approach was used for condensation
5-mesityldipyrromethane 3 and 4-(TMS-ethynyl)benzal-
dehyde (TMS = trimethylsilyl), followed by deprotection
of acetylene groups with TBAF and metallation by
Zn(OAc)2 to give zinc meso-bis(4-acetylenylphenyl)-
porphyrin 7 (building block I) in overall 28% yield
(Fig. 4). Thus 5-mesityldipyrromethane 3 proved to
be the most convenient precursor for the synthesis of
A2B2-type porphyrins via [2+2] condensation with
arylaldehydes. These data conform to investigations
that reactions of sterically hindered dipyrromethanes
RESULTS AND DISCUSSION
In the present work we have for the first time
performed the synthesis of porphyrin trimers using the
“click” chemistry. Two trimers were constructed from
two sets of building blocks. In the first case the central
porphyrin building block I of the future trimer has two
4-alkynylphenyl groups in opposite meso-positions and
reacts with meso-(4-azidophenyl)porphyrin II. In the
second case the central porphyrin III has two opposite
meso-4-azidophenyl groups reacting with meso-(4-
acetylenylphenyl)porphyrin IV (Fig. 1).
The reaction of dipyrromethane with an aldehyde
via the MacDonald type [2+2] condensation [34] is a
convenient way to trans–meso-A2B2-substituted porphy-
rins I and III. Three 5-substituted dipyrromethanes (Fig. 2)
were used in the synthesis of meso-bis-(p-nitrophenyl)-
porphyrin which is a precursor for the corresponding
R
R
N
N
N
N
N
N
N
Zn
N3
Zn
tBu
N
II
I
R
R
R
R
N
N
N
N
N
N
N
N
N3
Zn
N3
Zn
R
tBu
IV
III
R
R
=
Fig. 1. Two ways of construction of porphyrin trimers by “click” methodology
Copyright © 2013 World Scientific Publishing Company
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LINEAR CONJUNCTED PORPHYRIN TRIMER SYNTHESIS VIA “CLICK” REACTION
3
NO2
with aldehydes give no scrambling by-products to afford
pure A2B2-porphyrins [34, 38].
tBu
Lindsey procedure [39] of mixed aldehydes-pyrrole
condensation with BF3 etherate catalyst, followed by
DDQ oxidation was used to obtain A3B-porphyrins
(building blocks II and IV) (Fig. 5). Pyrrole, 4-tert-
butylbenzaldehyde and 4-nitrobenzaldehyde in the ratio
NH
NH
HN
NH
HN
HN
4/3/1/ reacted in CH2Cl2 at room temperature for 80 min
yielding a mixture of trans- and cis-A2B2-, AB3-, A3B-,
A4- and B4- porphyrins where A is 4-nitrophenyl substi-
3
2
1
tuent and B is 4-tert-butylphenyl substituent. After flash
chromatography purification from tar the reduction of
Fig. 2. Dipyrromethanes involved in [2+2] condensation with
aldehydes
NO2
CH2Cl2, N2, TFA,
rt, 30 min, 25%
NH
N
N
+
NO2
O2N
HN
NH
O
HN
4
HCl, SnCl2X2,
CH3Cl/HOAc (1:2)
70 °C, 80 min, 85%
1. NaNO2, NaN3, TFA, 0 °C
2. Zn(OAc)2, 80%
N
N
NH
N
N
N
N
N3
NH2
Zn
N3
H2N
HN
5
6
Fig. 3. Synthesis of the zinc porphyrin with two azide functionalities (building block III)
TMS
1. CH2Cl2, N2, TFA,
rt, 30 min, 30%
2. TBAF
N
N
N
N
3. Zn(OAc)2 95%
+
Zn
NH
HN
O
7
Fig. 4. Synthesis of the zinc porphyrin with two alkyne functionalities (building block I)
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Y.P. POLEVAYA ET AL.
tBu
tBu
NO2
1. BF3 X Et2O, CH2Cl2,
N2, rt, 80 min
NH
N
N
tBu
3
4
1
+
H2N
+
2. HCl, SnCl2 X 2 H2O,
CHCl3/HOAc, 70 °C, 80 min
HN
N
H
O
O
tBu
8
tBu
N
N
N
tBu
N3
Zn
N
9
tBu
tBu
TMS
tBu
1. BF3 X Et2O, CH2Cl2,
N2, rt, 80 min
N
N
N
N
tBu
1
3
Zn
4
+
+
2. Zn(OAc)2
3.TBAF
NH
O
O
10
tBu
Fig. 5. Synthesis of A3B-porphyrins-building blocks II and IV through mixed aldehydes-pyrrole condensation
nitro derivatives was performed without separation with
subsequent easy isolation of meso-(4-aminophenyl)
porphyrin 8. Azidoporphyrin 9 was obtained using the
same procedures for 6 in overall 8% yield. Analogously,
the condensation of pyrrole, 4-tert-butylbenzaldehyde
and 4-(TMS-ethynyl)benzaldehyde in ratio 4/3/1 gave a
mixture of substituted porphyrins which was metalated
without isolation, TMS deprotected and then porphyrin
10 was chromatographically isolated with 13% yield.
Mixed aldehyde and pyrrole condensation method
yielded mixture of six differently substituted porphyrin
products and required difficult separation. Therefore we
used another approach to mono-azido functionalized
porphyrin, the condensation of dipyrromethane with two
differentaldehydesleadingtoA2BC-porphyrin.Thereaction
of 5-mesityldipyrromethane with 4-nitrobenzaldehyde and
4-tert-butylbenzaldehyde furnished the novel nitrophenyl
functionalized porphyrin 11 in 28% yield (Fig. 6). The
presence of tert-butyl group serves to improve porphyrin
solubility and mesityl substituent suppresses scrambling
and cofacial aggregation. Earlier reported meso-substituted
porphyrins bearing single nitro- or acetamidophenyl group
as azide precursors were obtained in lower yields in a
range 10–18% [31, 40, 41a, 41b, 42].
A similar condensation of 5-mesityldipyrromethane,
4-(TMS-ethynyl)benzaldehyde and 4-tert-butylbenzal-
dehyde produced, after deprotection and metalation, zinc
porphyrin 14 in overall 22% yield (Fig. 7).
Thus, the condensation of dipyrromethane with
two different aldehydes is a more attractive method
for the synthesis of asymmetrical meso-functionalized
porphyrins, giving higher yields and fewer amounts of
byproducts, allowing feasible isolation of the desired
product [43].
With all I–IV building blocks, porphyrins 6, 7, 13, 14
in hands we pursued two methods of their connection via
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LINEAR CONJUNCTED PORPHYRIN TRIMER SYNTHESIS VIA “CLICK” REACTION
5
tBu
NO2
BF3 X Et2O, CH2Cl2,
N2, rt, 80 min, 28%
NH
N
N
tBu
1
2
O2N
+ 1
+
HN
NH
HN
O
O
11
HCl, SnCl2X2,
CH3Cl/HOAc (1:2)
70 °C, 80 min, 80%
1. NaNO2, NaN3, TFA, 0 °C
2. Zn(OAc)2, 78%
N
NH
N
N
N
N
tBu
tBu
Zn
N3
H2N
HN
N
12
13
Fig. 6. Synthesis of building block III-A2BC-porphyrin via dipyrromethane-mixed aldehydes condensation
TMS
1. BF3XEt2O, CH2Cl2, N2,
rt, 80 min, 23%
2. TBAF
tBu
N
N
N
N
3. Zn (OAc)2 , 95%
1
tBu
1
2
+
Zn
+
NH
HN
O
O
14
Fig. 7. Synthesis of building block IV-A2BC-porphyrin via dipyrromethane-mixed aldehydes condensation
the “click” reaction. There are various reported reaction
conditions, for the CuI-catalyzed Huisgen’s 1,3-dipolar
cycloaddition, which unpredictably give range of yields
from zero to satisfactory [44]. We investigated “click”-
coupling of ethynyl functionalized zinc porphyrin 7 and
azido functionalized porphyrin 13 in order to find the
optimized reaction conditions. First we tried those copper-
based catalysts and conditions, which were reported by
others to be satisfactory with the porphyrin substrates [41,
45, 31–33] (Table 1). The conditions [41f] using copper
sulfate with sodium ascorbate in dichloromethane-water
mixture gave only traces of product (entry 1). But the
same reagents in DMF led to success (entry 2) (Fig. 8).
The noticeable product spot in TLC appeared at 20 min
after start. After 2 h the reaction was complete and the
desired trimer 15 was easily isolated after workup by silica
gel flash chromatography as a dark-purple solid in 60%
yield. The copper complex with carbene ligand SIMes
(N,N′-bis(2,4,6-trimethylphenyl)-4,5-dihydro-imidazole-
2-ylidene)) (SIMes)CuBr was recently reported to be
the best catalyst for reaction of water insoluble meso-(p-
azidophenyl)- and meso-(p-ethynylphenyl)- porphyrins
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6
Y.P. POLEVAYA ET AL.
Table 1. The Huisgen’s 1,3-dipolar cycloaddition reaction of porphyrins 7 and 13 under various
conditions
Entry
Reaction conditions
Yield, %
1
2
3
4
5
6
7
CuSO4·5H2O, sodium ascorbate, CH2Cl2/H2O (3:1), 12 h, rt, vigorously stirring
CuSO4·5H2O, sodium ascorbate, DMF, 100 °C, 2 h;
iPrCuBr[a], THF/H2O (3:1), 45 °C, 12 h
traces
60
nd
CuBF4(CH3CN)4, THF/H2O (3:1), 45 °C, 12 h
CuI, DIPEA[b], THF/MeCN (1:1), rt, 12 h
nd
traces
68
CuI, DIPEA, THF/MeCN (5:1), 60 °C, 3 h
CuI, DIPEA, toluene, 100 °C, 3 h
traces
a iPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). b DIPEA = diisopropylethylamine.
N
N
N
N
N
N
N
N
N3
Zn
tBu
Zn
1 eq.
2 eq.
a) CuI/DIPEA in THF/MeCN, 68%
b) CuSO4 x 5H2O, sodium ascorbate,
DMF, 60%
7
13
tBu
tBu
N
N
N
Zn
N
N
Zn
N
N
N
N
N
N
N
N
N
N
N
Zn
N
N
15
Fig. 8. Synthesis of the trimer 15
[31]. Since the complex (SIMes)CuBr was not readily
available, we used a similar complex of copper bromide
with carbene ligand N,N′-bis(2,6-diisopropyl-phenyl)-
imidazol-2-ylidene in the same reaction conditions in
THF/H2O (3:1), at 45 °C, for 12 h, however this catalyst
failed to give detectable amount of product (entry 3).
Reaction with CuBF4(CH3CN)4 catalyst also failed to
give the desired product (entry 4). Copper iodide with
DIPEA in THF/MeCN (1:1) utilized by Ravikhanth and
coworkers [33, 45a] for triazole-bridged porphyrin dimers
was also explored, but only traces of trimer 15 were
detected after 10 h (entry 5). Probably these conditions
were unsuccessful because substrates 7 and 13 are poorly
soluble in the solvent mixture used, as compared to
meso-(p-tolyl)substituted porphyrins used by Ravikhanth
[33, 45a]. We modified reaction conditions by diluting
the mixture with THF and heating at 60 °C for 3 h,
hereupon trimer 15 was isolated in 68% yield (entry 6)
(Fig. 8). Use of the same catalyst in toluene at 100 °C
gave only traces of product (entry 7).
Reaction conditions utilized in entry 6 proved to be
the best for reaction for the porphyrin 7 and 13: simple
work-up allowed easy purification of the product by flash
chromatography on silica, the catalyst is readily available
CuI with DIPEA. The yield of porphyrin trimer is higher
than that of reported analogous porphyrin dimers [31, 33,
45a] except the directly linked b-meso-triazole-bridged
dimer [32]. Using the optimized “click” reaction conditions
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LINEAR CONJUNCTED PORPHYRIN TRIMER SYNTHESIS VIA “CLICK” REACTION
7
N
N
N
N
N
N
N
N
N3
Zn
tBu
Zn
1 eq.
6
2 eq.
14
CuI/DIPEA in THF/MeCN, 70%
tBu
tBu
N
N
N
Zn
N
N
Zn
N
N
N
N
N
N
N
N
N
N
N
Zn
N
N
16
Fig. 9. Synthesis of the trimer 16
N
N
N
N
N
N
tBu
Zn
Zn
tBu
N3
N
N
1 eq.
13
1 eq.
14
CuI/DIPEA in THF/MeCN, 60%
tBu
tBu
N
N
N
N
Zn
Zn
N
N
N
N
N
N
N
17
Fig. 10. Synthesis of the dimer 17
the cycloaddition of 6 to 14 was carried out furnishing the
trimer of the second type 16 in 70% yield (Fig. 9).
Firstly, we have compared NMR and absorption charact-
eristics of novel trimers with the corresponding dimers
with the same linker, structural rigidity and electronic
surrounding. Triazole-bridged zinc porphyrin dimer 17
was obtained under the same conditions as for trimer from
equimolar amounts of 14 and 13 in 60% yield (Fig. 10).
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Y.P. POLEVAYA ET AL.
1
compounds [41a, 33]. H NMR spectra shows the typical
singlet of the 1,2,3-triazole unit at d = 8.79 ppm for 15 and
at 8.73 ppm for 16 and singlet 3.33 ppm of the alkynyl
protons of starting porphyrins 7 and 14 disappeared. The
2,6-protons (g) of meso-phenyl group connected to the
position 1 of the triazole ring were shifted downfield by 0.9
ppm compared to that resonance in starting azidoporphyrins
6 and 13 (Fig. 12).
The nature of linker, structural rigidity and degree
of interchromophore electronic coupling have been
reported to influence intramolecular porphyrin-porphyrin
electronic communication [46b, 46c, 47]. In order to
understand the effect of triazole linker we have undertaken
the measurement of absorption and emission spectra of
the new porphyrin arrays.
The photophysical data of porphyrin dimer Zn2U and
trimer Zn3L joined via diphenylethyne linkers (Fig. 13)
were published [41g, 46b]. For unsymmetrical porphyrin
dyads an increased energy transfer efficiency between
subunits was noted on changing the rigid diphenylethyne
“linker” to more flexible triazole one [45a].
Sufficient solubility of the porphyrins and their dimers
and trimers is essential for synthesis and characterization.
Starting porphyrins, their zinc derivatives and compounds
15,16,17aresolubleinarangeofsolvents:CH2Cl2,CHCl3,
toluene and particularly well in THF. Consequently THF
became the solvent of choice for spectroscopic studies.
According to reported data for Zn porphyrin arrays their
absorption and fluorescence properties hardly change
with solvent polarity [46a, 46b].
The UV-visible absorption spectra were measured
at room temperature. As a reference, the spectra of
the starting Zn-monomers (6, 7, 14, 13) contain the
intense near-UV Soret band at 425–426 nm and the
weaker visible bands corresponding to the transitions
from the ground state to the lowest excited singlet state
(S0-S1); Q-band at 596–598 nm and more intense Q
vibronic band at 558–559 nm. The dimer and trimers
spectra exhibit Q-bands region (500–600 nm) which
is very near to the spectra of the starting monomers
(Fig. 14).
On the other hand Soret bands display broadening for
dimer and red shift and splitting for trimers (Fig. 14).
These changes of Soret bands caused by point-dipole
excitation coupling [48] and reported as characteristic for
meso–meso linked porphyrins [49].
The geometry optimization performed with molecular
mechanics MM+ method predicts the center to center
distance between the neighboring porphyrin units in
trimer at ca. 18 Å (Fig. 15).
According to the excitation coupling theory [50],
Equation 1 predicts the relationship of the splitting
energy of the neighboring porphyrin units, DE0, where M
is the transition dipole moment, R is the center to center
chromophore distance, a is the angle between polarization
axes for the component absorbing units and q is the angle
made by the polarization axes of the unit molecule with
Fig. 11. MALDI-TOF mass spectra of triazole-bridged trimers
15 (a), 16 (b) and dimer 17 (c)
The trimers 15, 16 and dimer 17 were characterized
by MS, NMR, UV-visible spectroscopy. During mass-
spectral analysis, the fragmentation of these compounds
occurs readily with loss of nitrogen molecules. Thus
MALDI-TOF spectra shows the following isotopic ion
clusters: molecular ion of the trimer/dimer and ions
resulted from the loss of N2 molecules from triazole
bridges (Fig. 11).
The 1H NMR resonance signals of 15 and 16 were assig-
ned by comparison with the spectra of starting porphyrin
monomers, and the reported data for porphyrin-triazole
Copyright © 2013 World Scientific Publishing Company
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LINEAR CONJUNCTED PORPHYRIN TRIMER SYNTHESIS VIA “CLICK” REACTION
9
Fig. 12. 1H NMR spectra of trimers 15 (a) and 16 (b)
the line of molecular centres. The splitting energy (DE)
extinction coefficients of the Soret and Q-bands of
trimers 15 and 16 are increased relative to that of dimer
and monomers (Table 2). Thus the porphyrin subunits in
trimers mainly retain their static absorption properties
but manifesting weak interchromophore interaction in
the ground electronic state and clear exciton coupling
in the excited state. The static absorption properties of
triazole-bridged trimers do not differ appreciably from
those of the ethyne-bridged trimer [41g, 46b]. Diaryl-
triazole linker provides sufficiently weak inter-porphyrin
coupling (at ca. 18 Å center-to-center separation) as
opposed to direct meso–meso linkers that gives very
for larger arrays is described by Equation 2 [32].
2M2
R3
(1)
(2)
DE0 =
(cosa + 3cos2q)
DE = DE0 cos[p /(N + 1)].
Approximate calculation using Equations 1 and 2 gives
values of Soret splitting ~5.6 nm which is consistent
with the observed absorption data for trimers. The molar
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10
Y.P. POLEVAYA ET AL.
N
N
N
N
Zn
Si(CH3)3
ZnU
N
N
N
N
N
N
N
N
Zn
Zn
Zn2U
N
N
N
N
N
N
N
N
N
N
N
N
Zn
Zn
Zn
Zn3L
Fig. 13. Porphyrin dimer and trimer joined via diarylethyne linkers. The quantum yield is referred to that of ZnU, Ff = 0.035 [46b]
of multichromophoric arrays for light-harvesting
applications [41g]. Recently triazole-linker was utilized
in porphyrin-b-carboline conjugate which exhibited
remarkable phototoxicity [53]. New physicochemical
aspects of metalloporphyrins associated with axial
ligation of halides were reported for porphyrin-based
host compound containing four triazole groups. Receptor
design can be proposed based on a combination of
multiple binding motifs [54, 55].
EXPERIMENTAL
1H NMR spectra (400 MHz and 600 MHz) were
recorded with a Bruker AM-400 and Avance 600 (IPCE
RAS) spectrometers. Chemical shifts are reported in d
(ppm), referred to 1H (of residual proton, d 7.28) signal of
Fig. 14. Absorption spectra of compounds in THF (spectra
in the 470–720 nm region are multiplied by the factor of 5).
CDCl3. MALDI-TOF mass spectra were recorded on an
Ultraflex mass spectrometer Bruker Daltonics, (positive-
Absorption and fluorescence characteristics were measured at
room temperature, samples concentration 2.5 × 10-6 M
ion mode, voltage 20 mV), 1,8,9-trihydroxyanthracene
matrix was used for dimer and trimers. Photophysical
studies were performed in Institute of Problems of
Chemical Physics RAS 142432 Chernogolovka,
Moscow region, Russia. Electronic absorption spectra
were obtained with Shimadzu UV-3101PC UV-vis NIR.
Fluorescence spectra were recorded at 25 °C in a 1 cm
strong interactions between porphyrin units and involves
radical changes in photophysical characteristics [48a, 49,
51, 52]. Thus diaryltriazole linker could be successfully
applied for one of two basic approaches in the design
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 10–15

LINEAR CONJUNCTED PORPHYRIN TRIMER SYNTHESIS VIA “CLICK” REACTION
11
Columnchromatographywascarried
out on MN-Kieselgel 60 (0.04–
0.063 mm mesh size). All other
chemicals used for the synthesis
were reagent grade unless otherwise
specified.
Syntheses of porphyrins 4, 7, 11,
14 were carried out via MacDonald
type [2+2] condensation [34] with
5-mesitydipyrromethane.
5,15-Bis(4-nitrophenyl)-10,
20-dimesitylporphyrin (4).
Condensation of 5-mesityldipyr-
romethane (0.66 g, 2.5 mmol) and
p-nitrobenzaldehyde (0.42 mL, 2.5
mmol) in CH2Cl2 (250 mL) with
TFA (0.34 mL, 4.45 mmol) was
carried out at room temperature
for 30 min, following the described
procedure [34] of oxidation with
DDQ. Product isolation: the solvent
was removed under vacuum to
give black solid which was placed
on the top of column prepacked
with silica gel and CH2Cl2 for
Fig. 15. Molecular model of trimers 15 (a) and 16 (b) calculated using MM+ method
chromatography separation. First
fraction was eluted with CH2Cl2
to remove pale brown layer of
byproduct; main product was eluted
Table 2. Absorption and fluorescence characteristics
with CH2Cl2 and 5% EtOAc. Removal of the solvent
under vacuum gave a brown solid 4. Yield 493 mg
Compound
(Ff)[b]
Soret band, lmax
Q-bands, lmax
(e × 10-5, M-1 cm-1) (e × 10-4, M-1 cm-1)
1
(25%). H NMR (400 MHz, CDCl3): dH ppm -2.78
7
0.049 426 (5.4)
0.015 425 (3.2)
0.017 426 (2.8)
0.034 425 (5.3)
0.047 426 (3.5)
558 (3.2), 598 (1.9)
559 (3.4), 598 (2.6)
559 (3.3), 596 (2.6)
558 (3.9), 597 (2.7)
558 (3.2), 598 (2.3)
550 (4.3), 588 (0.72)
(2H, br s), 1.84 (12H, s), 2.62 (6H, s), 7.27 (4H, s),
3
3
8.41 (4H, d, J = 8.5 Hz) 8.60 (4H, d, J = 8.7 Hz),
8.71 (4H, d, 3J = 4.7 Hz), 8.75 (4H, d, 3J =
4.7 Hz). MS (MALDI-TOF): m/z 788.38 (calcd. for
[C50H40N6O4]+ 788.89).
13
6
14
17 dimer
Zn2U[a] dimer 0.043 426 (6.8)
5,15-Bis(4-aminophenyl)-10,20-dimesityl-
porphyrin (5). To a solution of 4 (450 mg, 0.57
mmol) in 1:2 CHCl3/HOAc (30 mL) a solution of
SnCl2·2H2O (903.6 mg, 4 mmol) in concentrated
HCl (10 mL) was added. The mixture was vigorously
stirred in a preheated oil bath (65–70 °C) for 30 min,
refluxed for 7 h, and then neutralized with ammonia
solution (25%) to pH 8–9. Chloroform (100 mL)
was added, and the mixture was stirred for 1 h. The
organic phase was separated, and the water phase was
extracted with CHCl3 (2 × 100 mL). The combined
organic layers were washed once with dilute
ammonia solution, three times with water, and then
concentrated to dryness. The residue was purified by
column chromatography (silica gel, chloroform with
5% EtOAc) to give 5. Yield 353 mg (85%). 1H NMR
(400 MHz, CDCl3): dH ppm -2.56 (2H, br s), 1.87 (12H,
s), 2.66 (6H, s), 3.91 (2H, br s, NH2), 7.07 (4H, d, 3J = 8.2
Hz), 7.31 (4H, s), 8.02 (4H, d, 3J = 8.2 Hz), 8.80 (4H, d,
3J = 4.7 Hz), 8.88 (4H, d, 3J = 4.7 Hz).
15 trimer
16 trimer
0.053 425 (6.9), 431 (6.5) 558 (6.1), 599 (3.9)
0.051 425 (5.8), 431 (5.9) 558 (4.9), 599 (2.9)
Zn3L[a] trimer 0.058 423 (8.9), 431 (8.9) 550 (6.9), 590 (1.4)
Solvent THF; a Compound with diarylethyne linker in toluene
[41g, 46b]. Absorption and fluorescence characteristics were
measured at room temperature, samples concentration 2.5 × 10-6
M. b Fluorescence yields were obtained using relative method. The
emission spectra were integrated from 570 to 780 nm, lex = 400 nm.
The quantum yield is referred to that of ZnU, Ff = 0.035 [46b] with
correction for the difference in solvent refractive index.
quartz fluorescence cuvette on Perkin-Elmer LS 55
luminescence spectrometer. The course of the reactions
was monitored and the purity of the reaction products was
checked by TLC (thin-layer chromatographic plates were
coated with MN-Kieselgel, Machery-Nagel GmbH & Co).
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 11–15

12
Y.P. POLEVAYA ET AL.
Zinc(II) 5,15-bis(4-azidophenyl)-10,20-dimesityl-
porphyrin (6). Porphyrin 5 (300 mg, 0.41 mmol) was
dissolved in 13.2 mL TFA and cooled to 0 °C in an
ice bath. Sodium nitrite (108.4 mg, 1.56 mmol) was
dissolved in 3 mL of water and added to the mixture,
which was then stirred for 30 min at 0 °C. Sodium
azide (152.8 mg, 2.35 mmol) was dissolved in 3 mL
of water and added to the reaction mixture. After the
reaction was stirred on ice for 1 h, cold water was
added to the flask. The crude mixture was extracted
with CH2Cl2, and the green organic layer was washed
with water until it turned purple. The organic phase
was dried over Na2SO4, filtered, and concentrated under
vacuum to about 200 mL. Zinc acetate (2 g, 9.12 mmol)
was dissolved in ~25 mL of MeOH and added to the
porphyrin solution. The reaction was heated at reflux
for 1 h, and the crude mixture was washed with water
three times. The organic layer was dried over Na2SO4
and filtered. Flash column chromatography with silica
gel was used to purify the crude material using CH2Cl2
as the eluent, and the desired product was eluted with
(250 mL) with TFA (0.34 mL, 4.45 mmol) during 80 min
following the procedure described for 4. Solvent was
removed under vacuum and black solid was poured onto
a pad of silica and eluted with CH2Cl2 without products
separation; reduction of nitro groups was performed
following the procedure described for synthesis of 5.
Chromatography separation: elution with CH2Cl2:PE=2:1
gavefirstpurplelayerof5,15,10,20-tetramesitylporphyrin
(as byproduct); product 12 was eluted in second fraction,
after solvent evaporation gave purple solid with overall
22% yield after two steps. 1H NMR (400 MHz, CDCl3):
dH ppm -2.55 (2H, s), 1.63 (9H, s), 1.85 (12H, s), 2.66
(6H, s), 7.08 (2H, d, J = 8.2 Hz) 7.31 (4H, s), 7.77 (2H, d,
J = 8.2 Hz), 8.03 (2H, d, J = 8.2 Hz), 8.17 (2H, d, J = 8.2
Hz), 8.70 (4H, d, J = 4.6 Hz), 8.86 (2H, d, J = 4.6 Hz),
8.91 (2H, d, J = 4.6 Hz).
Zinc(II) 5-(4-tert-butylphenyl)-15-(4-azidophenyl)-
10,20-dimesitylporphyrin (13). 13 was obtained from 12
1
following the procedure described for synthesis of 6. H
NMR(400MHz,CDCl3):dH ppm1.63(s,9H),1.85(12H,s),
2.66 (6H, s), 7.31 (4H, s), 7.40 (2H, d, J = 8.1 Hz), 7.77
(2H, d, J = 8.1 Hz), 8.17 (2H, d, J = 8.1 Hz), 8.23 (2H, d,
J = 8.1 Hz), 8.80 (4H, m), 8.88 (2H, d, J = 4.6 Hz), 8.96
(4H, d, J = 4.6 Hz). UV-vis: lmax, nm (e × 10-5, M-1.cm-1)
425 (3.2), 559 (0.34), 598 (0.26). MS (MALDI-TOF): m/z
831.31 (calcd. 831.38 [C54H47N7Zn - N2]+).
1
the solvent front. The yield for two steps was ~80%, H
NMR (400 MHz, CDCl3): dH ppm 1.85 (12H, s), 2.66
(6H,s), 7.31 (4H, s), 7.42 (4H, d, 3J = 8.4 Hz), 8.23 (4H,
d, 3J = 8.4 Hz), 8.80 (4H, d, 3J = 4.7 Hz), 8.88 (4H, d, 3J =
4.7 Hz). UV-vis: lmax, nm (e × 10-5, M-1.cm-1) 426 (2.8),
559 (0.33), 596 (0.26).
Zinc(II) 5-(4-tert-butylphenyl)-15-(4-ethynyl-
phenyl)-10,20-dimesitylporphyrin (14). Condensation
of 5-mesityldipyrromethane (0.66 g, 2.5 mmol) with
4-((trimethylsilyl)ethynyl)benzaldehyde (0.25 g,
1.25 mmol) and 4-tert-butylbenzaldehyde (1.25, 0.42 mL)
in CH2Cl2 (250 mL) withTFA (0.34 mL, 4.45 mmol) during
80 min following the procedure described for 4. Metalation
and TMS deprotection was performed according to
Zinc(II) 5,15-bis(4-ethynylphenyl)-10,20-dimesityl-
porphyrin(7).Condensationof5-mesityldipyrromethane
(0.66 g, 2.5 mmol) and 4-((trimethylsilyl)ethynyl)benz-
aldehyde (0.51 g, 2.5 mmol) in CH2Cl2 (250 mL)
with TFA (0.34 mL, 4.45 mmol) following the procedure
described for 4 gave a dark purple solid of 5,15-
bis(4-((trimethylsilyl)ethynyl)phenyl)-10,20-dimesityl-
porphyrin (668.5 mg, 30%). Product was dissolved in
50 mL CH2Cl2 and metalated by adding of excess of
Zn(OAc)2·2H2O (1 g) in MeOH (10 mL) and heating
at reflux for 1 h. Solvent was evaporated and the
product was dissolved in CHCl3/THF (1:1, 100 mL).
Tetrabutylammonium fluoride (TBAF) (1.0 M solution
in THF, 3 mL) was added and the solution was stirred
at rt for 1 h. Glacial acetic acid (2.5 mL) was added and
the product was washed over a silica funnel with CHCl3.
Solvent removal gave product 7. The yield for two steps
was 635 mg, 95%, 1H NMR (400 MHz, CDCl3): dH ppm
1.85 (12H, s), 2.66 (6H, s), 3.33 (2H, s), 7.31 (4H, s), 7.90
(4H, d, 3J = 7.7 Hz) 8.22 (4H, d, 3J = 7.7 Hz), 8.80 (4H, d,
3J = 4.6 Hz), 8.87 (4H, d, 3J = 4.6 Hz). UV-vis: lmax, nm
(e × 10-5, M-1.cm-1) 426 (5.4), 558 (0.32), 598 (0.19). MS
(MALDI-TOF): m/z 810.11 (calcd. for [C54H40N4Zn]+
810.31).
1
procedure described for 7. H NMR (400 MHz, CDCl3):
dH ppm 1.63 (9H, s), 1.85 (12H, s), 2.66 (6H, s), 3.33 (1H,
s,), 7.31 (4H, s,), 7.77 (2H, d, 3J = 8.2 Hz), 7.90 (2H, d, 3J =
7.8 Hz), 8.18 (2H, d, 3J = 8.2 Hz), 8.23 (2H, d, 3J = 7.8 Hz),
8.72–8.97 (8H, m, b-H). UV-vis: lmax, nm (e × 10-5, M-1.
cm-1) 425 (5.3), 558 (0.39), 597 (0.27).
A3B-Porphyrins 8, 10 were obtained following
general procedure [39] for the pyrrole condensation with
mixed aldehydes. The reactant concentrations were 7.5
mM aldehyde A, 2.5 mM aldehyde B, 10 mM pyrrole, 3
mM BF3·O(Et)2, and 7.5 mM DDQ. After the addition of
DDQ, the mixture was allowed to stir overnight. Solvent
was removed under reduced pressure and the residue
was chromatographed over silica. First chromatography
affords a mixture of porphyrins, which then was separated
on a second column chromatography.
5-(4-Aminophenyl)-10,15,20-tris(4-tert-butyl-
phenyl)porphyrin (8). The spectroscopic data were in
accordance with previously described [40].
Zinc(II) 5-(4-azidophenyl)-10,15,20-tris(4-tert-
butylphenyl)porphyrin (9). Synthesis was carried out
using the general method of diazotization with TFA/
NaNO2, followed by one-pot reaction with NaN3 and
5-(4-Tert-butylphenyl)-15-(4-nitrophenyl)-10,20-
dimesitylporphyrin(11);5-(4-tert-butylphenyl)-15-(4-
aminophenyl)-10,20-dimesitylporphyrin (12).
Condensation of 5-mesityldipyrromethane (0.66 g, 2.5
mmol) with p-nitrobenzaldehyde (0.21 mL, 1.25 mmol)
and 4-tert-butylbenzaldehyde (2.5, 0.42 mL) in CH2Cl2
Copyright © 2013 World Scientific Publishing Company
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LINEAR CONJUNCTED PORPHYRIN TRIMER SYNTHESIS VIA “CLICK” REACTION
13
preparation of zinc derivative as described above for 6.
Trimer 15. 1H NMR (400 MHz, CDCl3): dH ppm 1.64
(18H, s), 1.88 (24H, s), 1.91 (12H, s,), 2.67 (18H, s,), 7.33
(12H, s, broad), 7.78 (4H, d, broad), 8.19 (4H, d, broad),
8.32 (4H, d, broad), 8.38–8.44 (8H, broad), 8.51 (4H. d,
broad), 8.73 (2H, s, triazole), 8.79–9.04 (24H, m, b-H).
UV-vis: lmax, nm (e × 10-5, M-1.cm-1) 425 (6.9), 431 (6.5),
558 (0.61), 599 (0.39). MS (MALDI-TOF): m/z 2528.84
[C162H134N18Zn3]+, 2500.89 [M+ - N2], 2473.43 [M+ - 2N2].
1H NMR (400 MHz, CDCl3): dH ppm 1.63 (27H, s), 7.40
(2H, d, 3J = 8.3 Hz), 7.77 (6H, d, 3J = 8.1 Hz), 8.17 (6H,
d, 3J = 8.1 Hz), 8.23 (2H, d, 3J = 8.1 Hz), 8.82 (2H, d, 3J =
4.6 Hz), 8.91 (6H, broad).
Zinc(II) 5-(4-ethynylphenyl)-10,15,20-tris(4-tert-
butylphenyl)porphyrin (10). After the addition of DDQ,
the mixture was allowed to stir for night. Triethylamine
(1.5 mmol, 0.21 mL) was added to neutralize the
solution which was then filtered through a pad of silica
using CH2Cl2 as eluent. The solution was concentrated
and the porphyrin was then metalated by adding an
excess of Zn(OAc)2·2H2O (2 g) in MeOH (10 mL) and
heating at reflux for 1 h. Solvent was evaporated and
the product was dissolved in CHCl3/THF (1:1, 100 mL).
Tetrabutylammonium fluoride (TBAF) (1.0 M solution
in THF, 20 mL) was added and the solution was stirred
at rt for 1 h. Glacial acetic acid (6 mL) was added and
the product was washed over a silica funnel with CHCl3.
Following chromatography separation of a mixture
of substituted porphyrins (silica gel, PE/CH2Cl2, 1:2)
1
Trimer 16. H NMR (400 MHz, CDCl3): dH ppm 1.64
(18H, s), 1.88 (24H, s), 1.91 (12H, s), 2.67 (18H, s), 7.33
(12H, s, broad), 7.78 (4H, d, broad), 8.19 (4H, d, broad), 8.32
(4H,d, broad), 8.38–8.44 (8H, broad), 8.53 (4H, d, broad),
8.73 (2H, s, triazole), 8.79–9.04 (24H, m, b-H). UV-vis:
l
max, nm (e × 10-5, M-1.cm-1) 425 (5.8), 431 (5.9), 558 (0.49),
599 (0.29). MS (MALDI-TOF): m/z 2473.42 [M+ - 2N2].
Dimer 17. 1H NMR (400 MHz, CDCl3): dH ppm 1.64
(18H, s), 1.88 (24H, s), 2.67 (12H, s), 7.33 (6H, s), 7.78
(2H, d, 3J = 6.8 Hz), 8.19 (4H, d, 3J = 8.1 Hz), 8.32 (2H,
3
d, J = 8.5 Hz), 8.38–8.44 (4H, s, broad), 8.53 (2H, d,
3J = 8.5 Hz), 8.74 (1H, s, triazole), 8.80–9.03 (16H, m,
b-H). UV-vis: lmax, nm (e × 10-5, M-1.cm-1) 426 (3.5),
558 (0.32), 598 (0.23). MS (MALDI-TOF): m/z 1702.15
[C110H95N11Zn2]+, 1674.93 [M+ - N2].
1
yielded 43.5 mg, 13% of product. H NMR (400 MHz,
CDCl3): dH ppm 1.64 (27H, s), 3.3 (1H, s, alkyne-H),
3
3
7.78 (6H, d, J = 7.5), 7.91 (2H, d, J = 7.8), 8.17 (6H,
d), 8.22 (2H, d, 3J = 7.8), 8.92–8.96 (2H, m), 9.00–9.03
(6H, m). MS (MALDI-TOF): m/z 870.10 (calcd. 870.45
[C55H52N4Zn]+).
Supporting information
<< To be completed by authors >> Figures S1–S13
are given in the supplementary material. This material is
available free of charge via the Internet at http://www.
worldscinet.com/jpp/jpp.shtml.
General procedures of Cu(I)-catalyzed 1,3-dipolar
cycloaddition for synthesis of zinc triazole-bridged
porphyrins (15–17)
CONCLUSION
(A) A small round-bottomed flask was charged with
azidoporphyrin, alkynylporphyrin, CuSO4·5H2O (0.25
equiv. per functionality) stock solution 10 mg per 0.3 mL
of water, sodium ascorbate (1 equiv. per functionality)
in DMF. The reaction mixture was stirred at 100 °C for
60 °C. The progress of reaction was monitored by TLC.
After cooling, the product was extracted using CH2Cl2.
The resulting organic layer was dried with Na2SO4 and
evaporated to dryness, a colored solid was obtained.
Product was isolated via column chromatography:
unreacted starting materials were eluted with first fraction
in CH2Cl2:PE 1:1, target trimer/dimer product was eluted
as second fraction with 1% MeOH in CH2Cl2.
(B) A small round-bottomed flask was charged with
azidoporphyrin,alkynylporphyrin,diisopropylethylamine
(0.5 equiv. per functionality), CuI (0.1 equiv. per
functionality) in a solvent mixture THF/MeCN 5/1. The
flask was flushed with argon repeatedly. The reaction
mixture was stirred at 60 °C for 3 h. The progress of
reaction was monitored by TLC. After removal of the
solvent in vacuo a colored solid was obtained. Product
isolation with column chromatography: unreacted
starting materials were eluted with first fraction in
CH2Cl2:PE, 1:1, desired trimer/dimer product eluted as
second fraction in CH2Cl2 with 1% MeOH.
Synthesis of novel 1,4-diaryl-1,2,3-triazole-linked
porphyrin trimers was achieved based on “click”
chemistry approach. The two symmetric isomers of
trimer with both possible orientations of the triazole
linker between porphyrins were obtained. For this
purpose the synthesis of a set of four starting porphyrin
building blocks for “click” reaction was elaborated.
Optimized conditions of the copper catalyzed 1,3-dipolar
cycloaddtion led to the successful yields of the porphyrin
trimers up to 70%. The analogous porphyrin dimer was
also obtained for comparison. Static absorption properties
of triazole-bridged trimers revealed weak inter-porphyrin
electronic communication in the ground electronic state
with the increasing tendency from dimer to trimer.
Photophysical data were compared with corresponding
ones of known linear trimer with diarylethyne linkers.
More photophysical investigations are required to study
interchromophore interactions and energy flow and this
work is in progress.
Acknowledgements
This work was supported by Russian Foundation for
Basic Research (grant No. 11-03-12160-ofi-m-2011),
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 13–15

14
Y.P. POLEVAYA ET AL.
Russian Academy of Sciences (Program of Division
of Chemistry and Material Science N6 “Chemistry
and Physical Chemistry of Supramolecular Systems
and Atomic Clusters”) and the Ministry of Education
and Science of Russia, project 8433. We would like to
thank Professor Razumov V.F. and Gak V.Yu (Institute
of Problems of Chemical Physics RAS) for help with
photophysical studies.
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