Synthesis and properties of porphyrin-expanded porphyrin click dyads

Article abstract of DOI:10.1016/j.tet.2013.07.013

Abstract Six covalently linked 1,2,3-triazole bridged porphyrin-expanded porphyrin dyads containing Zn(II) porphyrin as energy donor and thiarubyrin, oxasmaragdyrin and BF₂-oxasmaragdyrin as energy acceptors were synthesized under click reaction conditions. The click dyads were synthesized by coupling of azido Zn(II) porphyrin with ethynyl functionalized expanded porphyrins under Cu(I) catalyzed mild reaction conditions. Both rigid and flexible triazole bridges were used to understand the interaction between the Zn(II) porphyrin and expanded porphyrin units in dyads. The dyads were characterized by mass, NMR, absorption, fluorescence and electrochemical studies. The NMR, absorption and electrochemical studies indicated that the Zn(II) porphyrin and expanded porphyrin units in dyads interact weakly and maintain their independent characteristic features. The fluorescence studies indicated a possibility of energy transfer from donor Zn(II) porphyrin unit to expanded porphyrin unit such as oxasmaragdyrin and BF₂-oxasmaragdyrin units in both flexible and rigid porphyrin-expanded porphyrin dyads.

Full text of DOI:10.1016/j.tet.2013.07.013

Tetrahedron 69 (2013) 7943e7949
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and properties of porphyrin-expanded porphyrin click
dyads
*
Yogita Pareek, Mangalampalli Ravikanth
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Six covalently linked 1,2,3-triazole bridged porphyrin-expanded porphyrin dyads containing Zn(II)
porphyrin as energy donor and thiarubyrin, oxasmaragdyrin and BF2eoxasmaragdyrin as energy ac-
ceptors were synthesized under click reaction conditions. The click dyads were synthesized by coupling
of azido Zn(II) porphyrin with ethynyl functionalized expanded porphyrins under Cu(I) catalyzed mild
reaction conditions. Both rigid and flexible triazole bridges were used to understand the interaction
between the Zn(II) porphyrin and expanded porphyrin units in dyads. The dyads were characterized by
mass, NMR, absorption, fluorescence and electrochemical studies. The NMR, absorption and electro-
chemical studies indicated that the Zn(II) porphyrin and expanded porphyrin units in dyads interact
weakly and maintain their independent characteristic features. The fluorescence studies indicated
a possibility of energy transfer from donor Zn(II) porphyrin unit to expanded porphyrin unit such as
oxasmaragdyrin and BF2eoxasmaragdyrin units in both flexible and rigid porphyrin-expanded porphyrin
dyads.
Received 29 May 2013
Received in revised form 1 July 2013
Accepted 4 July 2013
Available online 12 July 2013
Keywords:
Expanded porphyrins
BF2eoxasmaragdyrin
Click reaction
Energy transfer
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
science.6,7 A perusal of literature revealed that there are very few
reports on covalently or non-covalently linked porphyrin-expanded
Expanded porphyrins are synthetic analogues of the porphyrins
containing more than 18 electrons in the conjugated pathway ei-
ther due to an increased number of heterocycle rings or due to
multiple meso-carbon bridges.1e5 The expanded porphyrins, which
are aromatic show the typical characteristic features of porphyrins
with enhancement in their properties such as optical features due to
porphyrin arrays.8e14 Sessler and co-workers8,9 synthesized non-
covalently linked porphyrinesapphyrin conjugates and showed
a possibility of excitation energy transfer from porphyrin to sap-
phyrin. Inokuma and Osuka10 developed a simple one-pot route for
the synthesis of a series of meso-porphyrinyl substituted expanded
porphyrins. Thus, the chemistry of expanded porphyrin based mo-
lecular arrays is not well developed either because of inaccessibility
of appropriate expanded porphyrin building blocks or their poor
photophysical properties. Chandrashekar and co-workers15 in 1999
reported the synthesis of oxasmaragdyrin, which absorbs and emits
>700 nm and the macrocycle is decently fluorescent. Subsequently,
we prepared BF2-complex of oxasmaragdyrin,16 which is three times
more fluorescent and exhibits interesting optical properties com-
pared to free base oxasmaragdyrin. Since the emission bands of
oxasmaragdyrin and BF2eoxasmaragdyrin are far red shifted from
Zn(II) porphyrin emission bands without any overlap, it is very
convenient to follow the quenching of fluorescence of energy donor
Zn(II) porphyrin due to its energy transfer to oxasmaragdyrin/
BF2eoxasmaragdyrin unit in covalently linked Zn(II)porphyr-
ineoxasmaragdyrin/BF2eoxasmaragdyrin dyads. With this idea in
mind, we previously synthesized diphenyl ethyne bridged Zn(II)
p
increase in the p-delocalization compared to porphyrins. Thus, ar-
omatic expanded porphyrins absorb and emit at higher wave-
lengths and possess low lying singlet state energy levels compared
to porphyrins. This suggests that the expanded porphyrins can be
used as energy acceptors when connected to porphyrins/metal-
loporphyrins covalently or non-covalently, which act as energy
donors to study energy transfer at singlet state from porphyrin/
metalloporphyrin to expanded porphyrin. Interestingly, most of the
expanded porphyrins available in the literature are not sufficiently
fluorescent and in general, the reports on the detail photophysical
studies on expanded porphyrins are scarce.1e5 The focus of research
on expanded porphyrins is always limited to their ability to bind
anions and cations, and their applications in medicine and material
porphyrineoxasmaragdyrin11
and
Zn(II)
porphyrineBF2e
oxasmaragdyrin14 dyads and studied their singletesinglet energy
* Corresponding author. Tel.: þ91 (0)22 2576 7176; e-mail address: ravikanth@
transfer properties. Although the diphenyl ethyne bridged dyads
chem.iitb.ac.in (M. Ravikanth).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.013

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Y. Pareek, M. Ravikanth / Tetrahedron 69 (2013) 7943e7949
showed an efficient energy transfer, our earlier studies on triazole
bridged porphyrin dyads17 indicated that triazole ring is better
linker for energy transfer from donor unit to acceptor unit com-
pared to ethyne linker. In this paper, we attempted to synthesize
a series of 1,2,3-triazole bridged porphyrin-expanded porphyrin
dyads under click reaction conditions.18 The Cu(I) catalyzed cyclo-
addition reaction is versatile and extensively used but the reports on
the applications of this methodology to porphyrin chemistry are
rather limited.17,19e23 There are some reports on triazole appended
porphyrin systems19,20 and triazole bridged porphyrin dyads,17,21e23
which were synthesized under click reaction conditions but to the
best of our knowledge, there is no report on expanded porphyrins
where click conditions are employed to synthesize any expanded
porphyrin based systems. Here, we report the first synthesis of six
1,2,3-triazole bridged dyads 1e6 containing Zn(II) porphyrin as
energy donor unit and thiarubyrin, oxasmaragdyrin and BF2e
oxasmaragdyrin units as energy acceptors by coupling of azido
Zn(II) porphyrin with ethynyl expanded porphyrin under click re-
action conditions. Although thiarubyrin is non-fluorescent macro-
cycle24e27 but we synthesized Zn(II) porphyrinethiarubyrin dyads
to highlight the importance of oxasmaragdyrin and BF2e
oxasmaragdyrin units as energy acceptors in their corresponding
dyads. We used rigid as well as flexible triazole linkers to un-
derstand the interaction between the two macrocycles. The 1H
NMR, absorption and electrochemical studies supported weak in-
teraction between porphyrin and expanded porphyrin units in
dyads 1e6. The steady state fluorescence studies indicated a possi-
bility of an efficient singlet state energy transfer from Zn(II) por-
phyrin unit to expanded porphyrin unit in dyads 1e6 and our
preliminary studies concluded that BF2eoxasmaragdyrin is a better
energy acceptor than free base oxasmaragdyrin.14
2. Results and discussion
2.1. Synthesis and characterization
The required mono-functionalized porphyrin and expanded
porphyrin building blocks such as 5-(4-azidophenyl)-10,15,20-tri(p-
tolyl)zinc(II)porphyrin23 7, 5-[4-(3-azido)-n-propyloxyphenyl]-10,
15,20-tri(p-tolyl)zinc(II)porphyrin17 8, 5-(4-ethynylphenyl)-10,19,
24-tris(4-tolyl)-29,30,32,33-tetrathiarubyrin13 9, 5,10-(diphenyl)-
19-(4-ethynylphenyl)-25-oxasmaragdyrin13 10 and BF2-complex
of 5,10-(diphenyl)-19-(4-ethynylphenyl)-25-oxasmaragdyrin13 11
were prepared by following the reported procedures. The triazole
bridged dyads 1e6 were synthesized by coupling of Zn(II) porphyrin
building block containing azidophenyl group 7/8 with expanded
porphyrin building blocks containing ethynylphenyl group 9e11 in
THF/CH3CN in the presence of CuI/DIPEA at room temperature for
7e10 h as shown in Schemes 1 and 2. The progress of the reaction
was monitored by TLC analysis and the reaction was stopped after
complete disappearance of spots corresponding to starting mac-
rocycles and appearance of major spot corresponding to the for-
mation of the desired click dyad. Column chromatographic
purification on alumina afforded dyads 1e6 in 60e70% yield. The
click porphyrin-expanded porphyrin dyads 1e6 are freely soluble
in common organic solvents and confirmed their identities by
mass and NMR techniques. The molecular ion peak in ES-MS mass
spectra confirmed the molecular structure of dyads 1e6. NMR
spectroscopy has been used to characterize the dyads 1e6 in detail
and the comparison of 1H NMR spectra of dyad 4 along with its
corresponding monomers 8 and 9 is shown in Fig. 1. The close
inspection of Fig. 1 indicated that the dyad 4 exhibited overlapping
features of its constituted monomers 8 and 9 and the signals were
Scheme 1. Synthesis of rigid triazole bridged porphyrin-expanded porphyrin dyads 1e3.

Y. Pareek, M. Ravikanth / Tetrahedron 69 (2013) 7943e7949
7945
Scheme 2. Synthesis of flexible triazole bridged porphyrin-expanded porphyrin dyads 4e6.
at 8.30 ppm. Furthermore, more number of meso-aryl signals were
observed in dyad 4 compared to its corresponding monomers 8
and 9 due to eight protons of bridging aryl groups, which
appeared as four sets of doublets at 8.63, 8.49, 8.22 and 7.74 ppm.
The alkoxy protons appeared as three sets of signals at 2.72, 4.46
and 5.02 ppm, which experienced slight downfield shifts com-
pared to the corresponding Zn(II) porphyrin monomer 8. Thus, the
dyad 4 showed the NMR features of both the constituted mono-
mers with slight changes in their chemical shifts indicating a weak
interaction between the two macrocycles in dyad 4. The compar-
ison of 1H NMR spectra of dyad 3 with rigid linker and dyad 6 with
flexible linker is presented in Fig. 2. Although both types of dyads
showed the features of the constituted monomers, the resonances
of various protons of both constituted macrocycles experienced
slightly more downfield in rigid dyad 3 compared to flexible dyad
6. For example, the eight pyrrole protons of oxasmaragdyrin unit
appeared at 10.12, 9.53, 9.01 and 8.99 ppm in flexible dyad 6 ex-
perienced slight downfield shifts in rigid dyad 3 and appeared at
10.36, 10.25, 9.71 and 9.08 ppm. Similarly the two furan protons of
dyad 6 were also shifted from 9.40 to 9.45 ppm in dyad 3. These
observations indicate that the two macrocycles in rigid dyads in-
teract relatively more strongly compared to flexible dyads
(Scheme 2).
Fig. 1. Comparison of 1H NMR of (i) click dyad 4 with its corresponding monomers (ii)
9 and (iii) 8 recorded in CDCl3.
2.2. Absorption, electrochemical and fluorescence properties
assigned on the basis of spectra observed for the two monomers
The absorption spectra of dyads 1e6 and the appropriate
monomers 7e11 were recorded in toluene and data are presented
in Table 1. The comparison of absorption spectra of dyad 3 along
with its corresponding monomers 7 and 11 is shown in Fig. 3a and
the comparison of absorption spectra of rigid dyad 3 and flexible
dyad 6 is shown in Fig. 3b. The absorption spectra of dyads showed
taken independently. For example, in dyad 4, the eight
phene protons of thiarubyrin unit appeared as 4 sets of signals in
11.60e10.42 ppm region; the 12 -pyrrole protons of both Zn(II)
b-thio-
b
porphyrin and thiarubyrin units appeared as multiplet in
8.90e9.10 ppm region and the triazole proton appeared as singlet

7946
Y. Pareek, M. Ravikanth / Tetrahedron 69 (2013) 7943e7949
Fig. 2. Comparison of partial 1H NMR spectrum of (i) flexible dyad 6 with (ii) rigid dyad 3.
Table 1
Absorption data for dyads 1e6 along with their corresponding monomers recorded in toluene
Compd. no.
Soret band
l
[nm] (log
3 )
Q bands l [nm] (log 3 )
7
8
9
10
11
425 (6.09)
425 (6.21)
527 (5.97)
450 (5.69)
450 (5.32)
474 (5.26)
425 (5.62)
527 (5.55)
425 (5.89)
450 (5.33)
425 (5.50)
450 (5.41)
476 (4.98)
425 (5.89)
528 (5.77)
424 (5.66)
450 (5.33)
425 (5.63)
450 (5.53)
476 (5.17)
550 (4.85)
550 (4.51
d
591 (4.32)
591 (3.89)
662 (4.03)
596 (3.89)
593 (3.97)
616 (4.18)
d
d
d
d
d
721 (4.53)
637 (3.83)
631 (4.11)
843 (3.45)
700 (3.83)
649 (4.19)
958 (3.94)
556 (3.94)
577 (3.85)
705 (4.52)
959 (3.55)
1
2
3
550 (3.89)
552 (4.54)
551 (4.20)
662 (4.08)
592 (4.26)
591 (4.08)
721 (4.59)
637 (4.11)
630 (4.11)
843 (3.40)
699 (4.77)
647 (4.15)
705 (4.48)
4
5
6
d
664 (4.17)
592 (4.02)
591 (4.18)
721 (4.67)
637 (3.86)
629 (4.21)
844 (3.48)
670 (3.86)
647 (4.21)
959 (3.63)
d
557 (4.32)
552 (4.25)
705 (4.59)
features corresponding to both the constituted macrocycles. For
example, the Zn(II)porphyrineBF2eoxasmaragdyrin dyad
monomers was followed by cyclic voltammetry at scan rate of
50 mV/s and differential pulse voltammetry (DPV) using tetrabu-
tylammonium perchlorate as supporting electrolyte (0.1 M) in
dichloromethane. The representative oxidation waves of dyad 3
along with its monomers 7 and 11 are presented in Fig. 4 and redox
data for dyads 1e6 are presented in Table 2. In general dyads 1e6
showed 3e4 oxidations and 3e4 reductions and peak potentials
were assigned on the basis of their corresponding meso-ethynyl
expanded porphyrin and meso-azidophenyl Zn(II)porphyrin build-
ing blocks. For instance, the dyad 3 containing ZnN4 porphyrin and
BF2eoxasmaragdyrin units showed three oxidations at 0.66, 0.83
and 1.10 and three reductions at ꢀ0.69, ꢀ1.30 and ꢀ1.69 V. The first
oxidation at 0.66 V was due to BF2eoxasmaragdyrin unit and the
second oxidation at 0.83 V was due to ZnN4 porphyrin unit. The
oxidation at 1.10 V was assigned to the oxidation of both ZnN4
porphyrin and BF2eoxasmaragdyrin units. Similarly, the first re-
duction at ꢀ0.69 V was due to reduction of BF2eoxasmaragdyrin
3
exhibited three Soret bands at 425, 450 and 476 nm and five Q-
bands at 551, 591, 630, 647 and 705 nm. In this, the bands at 450,
476, 630, 647 and 705 nm were mainly due to BF2eoxasmaragdyrin
unit and the bands at 425 and 550 nm were corresponding to Zn(II)
porphyrin and the band at 590 nm is due to both macrocycles in
dyad 3. The comparison of rigid dyad 3 with flexible dyad 6 con-
taining two same macrocycles showed identical absorption fea-
tures with slight changes in the extinction coefficients. All other
click dyads showed similar overlapping absorption features of their
constituted macrocycles. Thus, absorption studies of dyads 1e6
showed sum of the absorption bands of their corresponding
monomers and support that the two macrocycles retain their in-
dividual characteristic features in the dyads.
The redox chemistry of triazole-bridged dyads containing two
different macrocycles 1e6 along with their corresponding

Y. Pareek, M. Ravikanth / Tetrahedron 69 (2013) 7943e7949
7947
Table 2
Redox data for dyads 1e6 along with their corresponding monomers recorded in
dichloromethane using tetrabutylammonium perchlorate as supporting electrolyte
(0.1 M)
Compd. no.
Oxidation
Reduction
E1/2/V versus SCE
E1/2/V versus SCE
ZnTTP
9
10
11
1
2
3
4
5
d
0.80
d
1.09
1.12
d
d
d
d
ꢀ1.25
d
ꢀ1.67
ꢀ1.61
ꢀ1.63
d
d
1.32
d
ꢀ0.73
d
ꢀ0.96
d
0.36
0.67
d
0.69
d
ꢀ1.31
ꢀ1.33
ꢀ1.28
ꢀ1.31
ꢀ1.30
ꢀ1.29
ꢀ1.32
ꢀ1.30
1.13
1.14
1.10
1.10
1.11
1.08
1.10
d
ꢀ0.68
ꢀ0.75
d
d
0.77
0.78
0.83
0.75
0.76
0.83
1.31
d
ꢀ0.97
d
ꢀ1.70
ꢀ1.63
ꢀ1.69
ꢀ1.69
ꢀ1.64
ꢀ1.69
0.39
0.66
d
d
ꢀ0.69
ꢀ0.76
d
d
1.30
d
ꢀ0.99
d
0.37
0.66
6
d
ꢀ0.69
d
there is a possibility of energy transfer from Zn(II) porphyrin unit,
which acts as energy donor to expanded porphyrin unit, which acts
as energy acceptor in these dyads. The energy transfer phenome-
non from Zn(II) porphyrin to expanded porphyrin in dyads 1e6 can
be monitored by steady state fluorescence studies provided that the
acceptor expanded porphyrin unit is sufficiently fluorescent. As
mentioned above, the oxasmaragdyrin and BF2eoxasmaragdyrin
macrocycles are sufficiently fluorescent with decent quantum
yields16 but the thiarubyrin macrocycle is non-fluorescent.24e27 We
studied the steady state fluorescence properties of dyads 1e6 using
excitation wavelength of 550 nm where the donor Zn(II) porphyrin
unit absorbs strongly as well as at 450 nm where the acceptor
oxasmaragdyrin and BF2eoxasmaragdyrin units absorbs strongly in
dyads 2, 3, 5 and 6. When dyads 2, 3, 5 and 6 were excited at the
peak maxima of acceptor unit (450 nm) such as oxasmaragdyrin or
BF2eoxasmaragdyrin unit, we noted a strong emission from ac-
ceptor unit (w710 nm) with quantum yield (w0.06e0.09) match-
ing closely with the corresponding acceptor monomeric unit.
However, when dyads 1e6 were excited at 550 nm where donor
Zn(II) porphyrin absorbs strongly, the emission properties of dyads
were quite different from their 1:1 mixture of corresponding
monomers. The comparison of fluorescence spectra of dyads 1, 2
and 3 with their corresponding 1:1 mixture of monomers recorded
under excitation wavelength of 550 nm is shown in Fig. 5 and
photophysical data for dyads 1e6 is presented in Table 3. As clear
from Fig. 5, on excitation of 1:1 mixtures of monomers of corre-
sponding dyads 1e3 at 550 nm, the emission was noted at 600 and
650 nm corresponding to Zn(II) porphyrin unit and no emission
was noted from the expanded porphyrin unit. However, in dyads 2
and 3, on excitation at 550 nm, the emission from Zn(II) porphyrin
unit was significantly quenched and strong emission was noted
from the corresponding acceptor unit. In compound 1, on excitation
at 550 nm, the emission from Zn(II) porphyrin unit was quenched
by 90% but no emission was noted from acceptor thiarubyrin unit
since thiarubyrin is non-fluorescent macrocycle. The excitation
Fig. 3. (a) Comparison of absorption spectra of dyad 3 (solid line) along with its cor-
responding monomers 7 (dotted line) and 11 (dot-dashed line); (b) comparison of
absorption spectra of rigid dyad 3 (solid line) with flexible dyad 6 (dotted line).
Fig. 4. Comparison of oxidation wave of cyclic voltammogram (solid line) and differ-
ential pulse voltammogram (dotted line) of (a) dyad 3 with its corresponding mono-
mers (b) 7 and (c) 11.
spectrum recorded for dyad
3 by sitting at the emission
peak maxima (720 nm) of acceptor BF2eoxasmaragdyrin unit
showed absorption features of both the constituted macrocycles as
shown in Fig. 6. All these observations indicated that there is
a possibility of energy transfer at singlet state from Zn(II) porphyrin
unit to acceptor expanded porphyrin unit, which is clearly evident
when oxasmaragdyrin or BF2eoxasmsaragdyrin unit is the
energy acceptor macrocycle. The energy transfer efficiencies28 for
dyads 3 and 6 were found to be more than our earlier reported
diphenyl ethyne bridged Zn(II) porphyrineoxasmsragdyrin/
BF2eoxasmaragdyrin dyads14 (Supplementary data Fig. S21) which
supports that the triazole is the better linker compared to ethyne
linker. A detail time-resolved study is required to quantify these
observations.
unit; the last reduction at ꢀ1.69 V was due to ZnN4 porphyrin unit
and reduction at ꢀ1.30 V was due to reduction of both ZnN4 por-
phyrin and BF2eoxasmaragdyrin units. Similarly, the other dyads
also exhibited oxidation and reduction waves, and the peak po-
tentials were in the same range of their corresponding porphyrin
and expanded porphyrin monomers. Thus, the electrochemical
studies also indicated that the porphyrin and expanded porphyrin
sub-units in dyads 1e6 interact very weakly.
In dyads 1e6, the Zn(II) porphyrin unit absorbs at higher energy
and the expanded porphyrin unit absorbs at lower energy. Thus,

7948
Y. Pareek, M. Ravikanth / Tetrahedron 69 (2013) 7943e7949
3. Conclusions
In conclusion, we synthesized three flexible and three rigid
triazole bridged porphyrin-expanded porphyrin dyads by coupling
of azido Zn(II) porphyrins and ethynyl expanded porphyrins under
mild click reaction conditions. The reactions worked smoothly and
dyads were freely soluble in all common organic solvents. The
Zn(II) porphyrin and expanded porphyrin units in dyads interact
weakly and retain their individual characteristic features as verified
by NMR, absorption and electrochemical studies. In these dyads,
the Zn(II) porphyrin absorb at higher energy and act as energy
donor and the expanded porphyrin such as oxasmaragdyrin and
BF2eoxasmaragdyrin absorbs at lower energy and act as energy
acceptor. The fluorescence studies supported an efficient energy
transfer from Zn(II) porphyrin to oxasmaragdyrin/BF2eoxasmarag-
dyrin unit in corresponding dyads.
4. Experimental section
4.1. Chemicals
All general chemicals and solvents were procured from S.D. Fine
chemicals, India. Column chromatography was performed using
silica gel and basic alumina obtained from Sisco Research Labora-
tories, India. All the solvents used were of analytical grade and were
purified and dried by routine procedures immediately before use.
4.2. Instrumentation
1H NMR spectra were recorded with Bruker 400 MHz in-
strument using trimethylsilane (TMS) as an internal standard. All
NMR measurements were carried out at room temperature in
deuterochloroform (CDCl3). Absorption and steady state fluores-
cence spectra were obtained with PerkineElmer Lambda-35 and
Varian Cary-Eclipse, respectively. The fluorescence quantum yields
Fig. 5. Emission spectra of dyads (solid line) (a) 1, (b) 2 and (c) 3 along with 1:1
mixture (dotted line) of their corresponding monomers.
(
Ff) were estimated from the emission and absorption spectra by
Table 3
comparative method.29 Elemental analysis was performed with
PerkineElmer 240C elemental analyser. ES-MS mass spectra were
recorded with a Q-Tof Micromass spectrometer. Cyclic voltam-
metric (CV) and differential pulse voltammetric (DPV) studies
were carried out with BAS electrochemical system utilizing the
Photophysical data of dyads 1e6
Compound no.
lex (nm)
FD
FA
% Donor
FENT
ZnTTP
550
450
450
550
550
450
550
450
550
550
450
550
450
0.033
d
d
d
d
d
90
95
d
97
d
83
85
d
91
d
d
d
d
d
98
d
99
d
d
92
d
97
d
11
10
1
0.094
0.065
d
d
three electrode configuration consisting of
(working electrode), platinum wire (auxiliary electrode) and sat-
urated calomel (reference electrode) electrodes in dry dichloro-
methane using 0.1
supporting electrolyte.
a glassy carbon
0.0032
0.0017
d
2
0.048
0.061
0.082
0.11
d
3
0.001
d
M tetrabutylammonium perchlorate as
4
5
0.0056
0.005
d
0.056
0.045
0.056
0.085
4.3. General synthesis of click porphyrin dyads 1e6
6
0.003
d
Samples of 1 equiv of meso-azidophenylporphyrin 7 or 8 and
1 equiv of corresponding ethynyl expanded porphyrin 9, 10 or 11
were dissolved in 1:1 mixture of THF/CH3CN under nitrogen at-
mosphere with stirring at room temperature. To this solution,
1 equiv of diisopropylethylamine (DIPEA) was added followed by
the addition of CuI (0.1 equiv) and continued stirring for 7e10 h.
Progress of the reaction was monitored by periodic TLC analysis and
after completion of the reaction solvent was removed under re-
duced pressure and the crude mixture was subjected to basic alu-
mina flash column chromatography. The small amounts of
unreacted precursors were removed with dichloromethane/petro-
leum ether (30:70) and the desired fraction of click porphyrin
dyads 1e6 was eluted with 1e2% methanol in dichloromethane and
the resulting compound was recrystallized from dichloromethane/
pet ether to give the desired products as brownish red solid in
60e70% yield.
Fig. 6. Excitation spectrum for dyad 3 (solid line) along with emission spectra of dyad
3 (dotted line) and its 1:1 mixture of corresponding monomers 7 and 11 (dashed line).

Y. Pareek, M. Ravikanth / Tetrahedron 69 (2013) 7943e7949
7949
4.3.1. Zn(II) porphyrinethiarubyrin click dyad (1). Yield: 70%; mp
>300 ꢁC; Rf (CH2Cl2/1% CH3OH) 0.33; 1H NMR (400 MHz, CDCl3):
MS: C93H67N11O2Zn (M)þ calcd av mass 1436.0, obsd m/z 1436.9
(Mþ). Elemental analysis calcd (%): C 77.78, H 4.70, N 10.73. Found:
C 77.73, H 4.67, N 10.69.
d¼2.72 (s, 3H, CH3), 2.74 (s, 6H, CH3), 2.86 (s, 6H, CH3), 2.87 (s, 3H,
CH3), 7.58 (m, 6H, Ar), 7.81 (m, 6H, Ar), 8.14 (m, 6H, Ar), 8.34 (d,
J¼8.2 Hz, 2H Ar), 8.47 (m, 8H, Ar), 8.60 (d, J¼7.8 Hz, 2H, Ar), 8.70 (d,
4.3.6. Zn(II) porphyrineBF2eoxasmaragdyrin (CH2)3 bridged click
dyad (6). Yield 63%; mp >300 ꢁC; Rf (CH2Cl2/1% CH3OH) 0.66; 1H
J¼7.8 Hz, 2H, Ar), 8.85 (s, 1H, triazole), 9.00 (s, 4H,
b-pyrrole), 9.01
(d, J¼4.7 Hz, 2H,
J¼4.6 Hz, 1H, -pyrrole), 9.15 (d, J¼4.6 Hz, 1H,
3H, -thiophene), 11.60 (m, 3H,
-thiophene), 10.57 (d, J¼5.0 Hz,1H,
-thiophene) ppm; ES-MS:
b
-pyrrole), 9.05 (d, J¼3.4 Hz, 4H,
b
-pyrrole), 9.10 (d,
NMR (400 MHz, CDCl3):
d
¼ꢀ3.78 (t, 2H, inner NH), 2.62 (s, 6H, CH3),
b
b
-pyrrole), 10.51 (m,
2.66 (br s, 2H, CH2), 2.71 (s, 3H, CH3), 4.45 (t, 2H, CH2), 4.50 (t, 2H,
CH2), 7.48 (d, J¼8.0 Hz, 4H, Ar), 7.55 (m, 6H, Ar), 7.90 (m, 6H, Ar),
8.03 (d, J¼7.8 Hz, 2H, Ar), 8.08 (d, J¼7.8 Hz, 2H, Ar), 8.22 (d, J¼8.7 Hz,
2H, Ar), 8.26 (s, 1H, triazole), 8.40 (m, 4H, Ar), 8.50 (d, J¼8.5 Hz, 2H,
b
b
b
-thiophene), 11.63 (d, J¼5.0 Hz, 1H,
b
C104H71N9S4Zn (M)þ calcd av mass 1640.4, obsd m/z 1642.9
(Mþþ2). Elemental analysis calcd (%): C 76.15, H 4.36, N 7.68. Found:
C 76.18, H 4.40, N 7.69.
Ar), 8.67 (d, J¼8.7 Hz, 2H, Ar), 8.90 (m, 8H,
b
-pyrrole), 8.99 (d,
-pyrrole) 9.40 (s,
-pyrrole),10.12 (d, J¼4.5 Hz, 2H,
J¼4.6 Hz, 2H,
b
-pyrrole), 9.01 (d, J¼4.6 Hz, 2H,
b
2H,
b
-furan), 9.53 (d, J¼4.4 Hz, 2H,
b
4.3.2. Zn(II) porphyrineoxasmaragdyrin click dyad (2). Yield 65%;
mp >300 ꢁC; Rf (CH2Cl2/0.5% CH3OH) 0.46; 1H NMR (400 MHz,
b
-pyrrole) ppm; ES-MS: C93H66BF2N11O2Zn (M)þ calcd av mass
1483.8, obsd m/z 1483.0 (Mþ). Elemental analysis calcd (%): C 75.28,
CDCl3):
(m, 6H, Ar), 8.24 (m, 4H Ar), 8.35 (d, J¼7.95 Hz, 2H, Ar), 8.50 (m, 6H,
Ar), 8.56 (m, 2H, -pyrrole), 9.00
-pyrrole), 8.78 (m, 3H, triazoleþ
(m, 6H, -pyrrole), 9.05 (m, 4H, -pyrrole), 9.45 (br s, 2H,
-furanþ
d
¼2.72 (s, 9H, CH3), 7.58 (m, 6H, Ar), 7.82 (m, 6H, Ar), 8.12
H 4.48, N 10.38. Found: C 75.29, H 4.51, N 10.41.
b
b
Acknowledgements
b
b
b
b
-pyrrole), 9.50 (br s, 2H, b-pyrrole) ppm; ES-MS: C90H61N11OZn
M.R. thanks Department of Science and Technology (DST) for
financial support. Y.P. thanks Council of Scientific and Industrial
Research (CSIR) for senior research fellowship.
calcd av mass 1377.9 (M)þ obsd m/z 1377.8 (Mþ). Elemental analysis
calcd (%): C 78.45, H 4.46, N 11.18. Found: C 78.49, H 4.50, N 11.19.
4.3.3. Zn(II) porphyrineBF2eoxasmaragdyrin click dyad (3). Yield
62%; mp >300 ꢁC; Rf (CH2Cl2/0.5% CH3OH) 0.53; 1H NMR (400 MHz,
Supplementary data
The characterization data including mass, 1H NMR for all the
compounds. Supplementary data associated with this article can be
found in the online version, at http://dx.doi.org/10.1016/
j.tet.2013.07.013.
CDCl3):
d
¼ꢀ3.70 (t, 2H, inner NH), 2.73 (s, 9H, CH3), 7.60 (m, 6H, Ar),
7.90 (m, 6H, Ar), 8.15 (m, 6H, Ar), 8.35 (d, J¼8.4 Hz, 2H, Ar), 8.43 (m,
4H, Ar), 8.51 (d, J¼8.4 Hz, 2H, Ar), 8.64 (d, J¼8.2 Hz, 2H, Ar), 8.79 (d,
J¼8.32 Hz, 2H, Ar), 8.85 (s, 1H, triazole), 9.03 (s, 6H,
b
-pyrrole), 9.06
-pyrrole), 9.45 (s,
-pyrrole),10.25 (d, J¼4.5 Hz, 2H,
-pyrrole); ES-MS:
(d, J¼4.6 Hz, 2H,
b
-pyrrole), 9.08 (d, J¼4.6 Hz, 2H,
b
2H,
b
-furan), 9.71 (d, J¼4.5 Hz, 2H,
b
References and notes
b
-pyrrole), 10.36 (d, J¼4.5 Hz, 2H,
b
C90H60BF2N11OZn (M)þ calcd av mass 1425.7, obsd m/z 1425.8
(Mþ). Elemental analysis calcd (%): C 75.82, H 4.24, N 10.81. Found:
C 75.88, H 4.30, N 10.89.
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4.3.4. Zn(II) porphyrinethiarubyrin (CH2)3 bridged click dyad
(4). Yield 70%; mp >300 ꢁC; Rf (CH2Cl2/1% CH3OH) 0.60; 1H NMR
(400 MHz, CDCl3):
d
¼2.50 (s, 6H, CH3), 2.70 (s, 3H, CH3), 2.72 (br s,
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2H, CH2), 2.80 (s, 3H, CH3), 2.90 (s, 6H, CH3), 4.46 (t, 2H, CH2), 5.02
(t, 2H, CH2), 7.44 (d, J¼7.6 Hz, 6H, Ar), 7.52 (d, J¼8.4 Hz, 4H, Ar), 7.74
(d, J¼7.6 Hz, 2H, Ar), 7.78 (d, J¼7.0 Hz, 4H, Ar), 8.05 (m, 6H, Ar), 8.22
(d, J¼8.5 Hz, 2H Ar), 8.30 (s, 1H, triazole), 8.43 (m, 4H, Ar), 8.49 (d,
11. Rao, M. R.; Ravikanth, M. Eur. J. Org. Chem. 2011, 1335e1345.
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J¼7.9 Hz, 2H, Ar), 8.63 (d, J¼7.9 Hz, 2H, Ar), 8.90 (m, 12H,
b-pyrrole)
10.42 (d, J¼4.9 Hz, 1H,
thiophene), 10.50 (m, 2H,
thiophene), 11.46 (d, J¼5.0 Hz, 1H,
b
-thiophene), 10.46 (d, J¼4.9 Hz, 1H,
b
b
-
-
b
-thiophene), 11.43 (d, J¼5.0 Hz, 1H,
b-thiophene), 11.60 (d, J¼5.0 Hz,
2H, b
-thiophene) ppm; ES-MS: C107H77N9OS4Zn (M)þ calcd av mass
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549e552.
1698.5, obsd m/z 1699.2 (Mþþ1). Elemental analysis calcd (%): C
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75.66, H 4.57, N 7.42. Found: C 75.62, H 4.49, N 7.38.
4.3.5. Zn(II) porphyrineoxasmaragdyrin (CH2)3 bridged click dyad
(5). Yield 60%; mp >300 ꢁC; Rf (CH2Cl2/1% CH3OH) 0.64; 1H NMR
(400 MHz, CDCl3):
d
¼2.65 (s, 3H, CH3), 2.75 (s, 3H, CH3), 2.79 (q, 2H,
CH2), 2.89 (s, 3H, CH3), 4.45 (t, 2H, CH2), 4.98 (t, 2H, CH2), 7.36 (d,
J¼7.8 Hz, 2H, Ar), 7.47 (d, J¼7.7 Hz, 4H, Ar), 7.55 (d, J¼8.0 Hz, 4H, Ar),
7.80 (m, 4H, Ar), 8.05 (m, 7H, triazoleþAr), 8.21 (m, 6H, Ar) 8.36 (d,
J¼7.8 Hz, 2H, Ar), 8.42 (d, J¼4.1 Hz, 2H,
b
-pyrrole), 8.47 (d, J¼7.8 Hz,
2H, Ar), 8.74 (s, 2H,
b
-furan), 8.90 (m, 6H,
-pyrrole), 9.01 (d, J¼4.6 Hz, 2H,
-pyrrole), 9.41 (d, J¼4.1 Hz, 2H,
b
-pyrrole), 8.98 (d,
J¼4.6 Hz, 2H,
b
b
b-pyrrole), 9.28 (d,
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29. Gupta, I.; Ravikanth, M. Inorg. Chim. Acta 2007, 360, 1731e1742.
J¼4.0 Hz, 2H,
b-pyrrole) ppm; ES-