Supramolecular array of imizazolylethynyl-zinc-porphyrin

Article abstract of DOI:10.1016/j.jorganchem.2006.08.041

Novel imidazolylethynyl-zinc-porphyrin 1a and its meso,meso-linked bisporphyrin 5M were synthesized effectively by the reaction of the corresponding bromoporphyrins and 2-imidazolylethyne in the presence of palladium-arsenic catalyst. The complementary coordination of monomer 1a into dimer 2a was observed by ¹H NMR and UV-Vis spectroscopy. Self-association constant of 1a to 2a in CHCl₃ (including 0.5% ethanol) was determined as 1.84 × 10⁷ M^-1 by UV-Vis titration of 2a with N-methylimidazole. UV-Vis absorption and fluorescence spectra of 1a, 2a, monomer 5M, and its polymer 5P were compared.

Full text of DOI:10.1016/j.jorganchem.2006.08.041

Journal of Organometallic Chemistry 692 (2007) 635–644
www.elsevier.com/locate/jorganchem
Supramolecular array of imizazolylethynyl-zinc-porphyrin
*
Akiharu Satake, Osami Shoji, Yoshiaki Kobuke
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
Received 27 February 2006; received in revised form 24 March 2006; accepted 3 April 2006
Available online 30 August 2006
Abstract
Novel imidazolylethynyl-zinc-porphyrin 1a and its meso,meso-linked bisporphyrin 5M were synthesized effectively by the reaction of
the corresponding bromoporphyrins and 2-imidazolylethyne in the presence of palladium-arsenic catalyst. The complementary coordi-
nation of monomer 1a into dimer 2a was observed by 1H NMR and UV–Vis spectroscopy. Self-association constant of 1a to 2a in CHCl3
(including 0.5% ethanol) was determined as 1.84 · 107 Mꢀ1 by UV–Vis titration of 2a with N-methylimidazole. UV–Vis absorption and
fluorescence spectra of 1a, 2a, monomer 5M, and its polymer 5P were compared.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Supramolecular; Porphyrin
1. Introduction
ous imidazolyl-zinc-porphyrin dimer 4. Inter zinc-to-zinc
˚
˚
distances are estimated as 8.4 A for 2 and 6.2 A for 4. For-
mation of dimer 2 from 1 and absorption and fluorescence
spectra are examined in view of the effect of insertion
of the ethynyl unit. Further, meso,meso-linked bis(imi-
dazolylethynylporphyrin) 5M was prepared by the similar
coupling reaction and its linear array formation (5P) are
described. Comparison of UV–Vis spectra between 5 and
6 is also discussed.
Supramolecular porphyrin arrays are interesting mate-
rial for light-harvesting antenna and non-linear optical
device [1]. Characteristic organizations, especially, into
face-to-face and slipped cofacial arrangements of porphy-
rins have been achieved by use of several non-covalent
interactions, such as coordination bonding [2], hydrogen
bonding [3], p–p interaction [4], and electrostatic interac-
tion [5]. We have examined supramolecular organization
using imidazolyl-zinc-porphyrin motif, in which a large
self-association constant was achieved by complementary
coordination [6]. By use of this unique motif, supramolec-
ular light-harvesting antenna [7], special pair complex in
photosynthetic reaction center [8] and non-linear optical
materials [9] have been constructed.
We will report here a novel complementary coordina-
tion dimer 2 of imidazolylethynyl-zinc-porphyrin 1 as
another supramolecular motif. Introduction of the ethynyl
unit allows effective synthesis of the motif by Sonogashira
coupling. The supramolecular structure of complementary
dimer 2 is generated by molecular mechanics calculation on
Cerius2ꢁ and illustrated in Fig. 1 in reference to the previ-
2. Results and discussion
Free base imidazolylethynylporphyrin 9 was prepared
from porphyrin 7 by monobromination and Sonogashira
coupling [10] as shown in Scheme 1. Porphyrin 7 obtained
by the reported procedure [11] was brominated with N-
bromosuccinimide in the presence of pyridine at ꢀ40 ꢂC
to give monobromoporphyrin 8 (48%) along with meso-
dibromoporphyrin (35%). Bromide 8 was isolated by chro-
matography and coupled with 1-methyl-2-imidazolylethyne
in the presence of Pd2(dba)3CHCl3 and AsPh3 as catalyst
to afford 9 in 84% yield. Treatment of Zn(OAc)2 with 9
gave the corresponding zinc porphyrin 1a, which was orga-
nized spontaneously into 2a in non-coordinating solvents.
Free base and zinc porphyrins 9 and 1a (2a) were identified
by NMR spectroscopy and mass spectrometry.
*
Corresponding author. Tel.: +81 743 72 6110; fax: +81 743 72 6119.
E-mail address: kobuke@ms.naist.jp (Y. Kobuke).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.08.041

636
A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
Fig. 1. Upper left: Structures of imidazolylethynyl-zinc-porphyrin 1 and imidazolyl-zinc-porphyrin 3, and their respective coordination dimers 2 and 4.
Upper right: molecular models constructed by molecular mechanics calculation. (A) Top and (B) side views of 2. (C) Top and (D) side views of 4. Lower:
Structures of 5M and 6M.
CO2Et
Ar2
Ar1
CO2Et
Pd2(dba)3CHCl3
AsPh3, Et3N
THF
Zn(OAc)2
94%
NH
N
N
NH
N
N
N
Im5
Im4
meso
X
N
N
N
HN
HN
β1
β4
β2
β3
NBS
9
7 X = H
8 X = Br
pyridine
CHCl3
-40 oC
84%
CO2Et
CO2Et
Ar
48%
(dibromo 35%)
Ar
N
N
N
Im5
Im4
N
N
N
N
Zn
meso
Zn
Ar
N
N
N
N
N
Ar
β1
1/2
β4
Ar
N
N
N
N
β3
β2
Zn
CO2Et
N
N
Ar2
Ar1
1a
Ar =
Ar
2a
Scheme 1. Synthesis of 1a.
Proton NMR spectra of 9 and 2a (10 mM as a monomer
1a in (CDCl2)2) are shown in Fig. 2. Each signal was
assigned from HH-COSY and HMQC correlation spectra.
One set of proton signals and characteristically shielded
imidazolyl peaks indicate the formation of complementary
dimer 2a. Thus, Im4 (1.67), Im5 (5.28), and N-Me
(2.63 ppm) signals are shifted to upper-fields due to the
shielding effect of porphyrin coordinated by the imidazole.
The relative upper-field shifts are similar to those on the
formation of dimeric imidazolyl-zinc-porphyrin 4 [2a].
The upper-field shift of proton b1 in 2a, however, is small
as ca. 1 ppm, whereas upper-field shift of ca. 4 ppm is
observed in 4 [12]. The smaller shift value is consistent with
the dimeric structure of 2a having a larger center-to-center
distance (see Fig. 1).
UV–Vis spectra of 2a (Fig. 3) were concentration depen-
dent. The peak maximum of Soret band at 434 nm
(4 · 10ꢀ6 M in CHCl3) was gradually sharpened and red-
shifted to 436 nm (8 · 10ꢀ8 Mꢀ1) on dilution, suggesting
dissociation of 2a into 1a at the lower concentration limit.
The shift of the peak maximum to a longer wavelength side
on the structural change of dimer to monomer may corre-
spond to the increase of p-conjugation through all planar
conformation in 1a. In the higher concentration range
between 1 · 10ꢀ6 and 4 · 10ꢀ6 M in CHCl3, the spectra
have a similar shape and follow the Beer’s law (data not

A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
637
Fig. 2. 1H NMR spectra (600 MHz) of 9 in CDCl3 (A) and 2a in (CDCl2)2 (B).
ethanol which competes the imidazolyl/zinc coordination
bond in 2. The coordinated structure is maintained under
more diluted conditions in other solvents free from coordi-
nating stabilizer, such as CH2Cl2. The self-association con-
stant of 1a into 2a in CHCl3 was determined by UV–Vis
titration of 2a and phenylethynylporphyrin 11 with use of
N-methylimidazole. (Fig. 3, inset). Absorption spectrum
of dimer 2a (4 · 10ꢀ6 M in CHCl3) shows broad Soret band
at 434 nm due to weak excitonic coupling between two por-
phyrins. The Soret band was red-shifted and sharpened by
the addition of N-methylimidazole. From curve fitting anal-
ysis, the equilibrium constant for ligand substitution of 2a
with N-methylimidazole was obtained as K1 = 21.7 Mꢀ1
.
As the reference, the association constant of 11 with
N-methylimidazole was determined as K02 ¼ 2:0 ꢁ 104 Mꢀ1
in CHCl3. Therefore, the self-association constant of 1a to
2a was obtained as K3 = 1.84 · 107 Mꢀ1 according to Eq.
(4) (Fig. 4). This value is four orders of magnitudes smaller
than the self-association constant of imidazolyl-zinc-
porphyrin 4. At the same time, the value is three orders of
magnitudes larger than the stability constant of N-methy-
limidazole coordination to zinc porphyrins [13]. It is strong
enough to keep the dimer structure almost completely
above tens micromolar concentration. Following consider-
ations may be important for understanding the molecular
behavior. Before coordination, imidazolyl p-orbitals are
conjugated with those of the porphyrin. All planar confor-
mation is energetically favorable, but molecular rotation
around the ethynyl bond is allowed. Imidazolyl coordina-
tion induces the orientation perpendicular to porphyrin
and disrupts the p-conjugation and further loses its rota-
tional freedom. The free energy loss from these contributions
may lower the self-association constant. Another factor may
arise from the small overlap of porphyrin p-planes due to the
presence of acetylenyl linker. Despite these unfavorable
Fig. 3. UV–Vis (upper) and fluorescence (lower) spectra of dimer 2a (solid
line) and monomer 1a (dotted line) in CHCl3. 2a (4 · 10ꢀ6 M). 1a was
prepared by the addition of pyridine (4 · 10ꢀ2 M) to 2a solution.
Fluorescence spectra were measured by excitation at 573 nm (Abs. 0.13
for both 2a and 1a). (Upper inset) UV–Vis spectral change of 2a
(2.06 · 10ꢀ6 M in CHCl3) to 1a/Im by the addition of N-methylimidazole
(0, 80, 160, 320, 480, 640, 800, 960, 1110, 1420, 1570, 3150, 6300, 12600,
25200 eq.) The inset spectra were corrected to eliminate the dilution factor.
shown), indicating that dimer structure looks maintained at
concentrations higher than 1 · 10ꢀ6 M in CHCl3. It is noted
that the chloroform used here contains a stabilizer of 0.5%

638
A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
factors, complementarity is effective to increase dramatically
the association constant of imidazolyl coordination.
The imidazolylethynyl-zinc-porphyrin motif was applied
to a bidirectional system to produce linear polymer.
meso,meso-Linked bis(imidazolylethynylporphyrin) 16 was
synthesized from 12 according to the route shown in
Scheme 2. meso,meso-Linked porphyrin 13 was prepared
by oxidative coupling of 12 [15]. Bromination of 13 fol-
lowed by demetalation and palladium-catalyzed coupling
with imidazolylethyne gave 16 in 47% yield (3 steps). Zinc
ion was then introduced into 16 to afford 5P. Proton
NMR spectra of 16 and 5P (2.5 mM as a monomer) are
shown in Fig. 5. Well-resolved sharp signals were observed
in 16, whereas all of the signals except residual CHCl3
appeared broad in 5P. This peak broadening indicates the
formation of polymeric structure of 5M. Imidazolyl protons
Im5 and N-methyl were upper-field shifted characteristically
to appear at 5.78 and 3.01 ppm, respectively, with disap-
pearance of non-coordinating imidazolyl protons around
at 7.3 ppm. These chemical shifts are close to 5.28 and
2.63 ppm, respectively, observed for dimer 2a. Considering
the fact that these protons are deshielded by another por-
phyrin plane attached to the coordinating one, most of
the imidazolyl parts are participating to the coordination
to zinc porphyrin. In other words, the linear array should
have a large mean molecular weight. If we assume that
the self-association constant of the imidazolylethynyl-
zinc-porphyrin part in 5M is the same as that of 1a
(1.8 · 107 Mꢀ1), the mean number of porphyrins in the
2
½1a=Imꢂ
K1 ¼
;
ð1Þ
2
½2aꢂ½Imꢂ
½1a=Imꢂ
½1aꢂ½Imꢂ
½11=Imꢂ
½11ꢂ½Imꢂ
½2aꢂ
K2 ¼
K02 ¼
K3 ¼
;
ð2Þ
ð3Þ
ð4Þ
;
K22 K022
’
¼
:
2
K1 K1
½1aꢂ
Fluorescence spectra of dimer 2a and monomer 1a (as a
pyridine adduct) are shown in Fig. 3b. Fluorescence quan-
tum yields of 1a (UF = 0.053) and 2a (UF = 0.043) were
obtained from the fluorescence spectra as a reference with
that of ZnTPP (UF = 0.033 in benzene) [14]. It has been
established that the fluorescence is not quenched by com-
plementary coordination [7a,7b,7d]. For the decrease of
the fluorescence quantum yield by 19% from monomer 1a
to dimer 2a, the loss of conjugation on coordination with
the imidazolyl group may be taken into account. The fluo-
rescence decrease is not fatal and 2a is more fluorescent
than ZnTPP by a factor of 130%. The imidazolylethynyl-
zinc-porphyrin motif can be used as a light-harvesting
antenna unit even better than imidazolyl-zinc-porphyrin.
N
Ar
N
Ar
N
N
N
N
N
K1
Zn
N
N
N
N
N
+
N
2
2
Zn
Ar
N
N
N
N
CO2Et
Ar
N
N
N
Im
Zn
Ar =
Ar
N
N
1a/Im
Ar
2a
N
N
Ar
Ar
Zn
Ar
K2
N
N
N
N
N
N
N
N
N
+
Zn
N
N
N
N
N
Im
1a
1a/Im
Ar
N
Ar
Zn
Ar
N
Ar
N
K2'
N
N
N
+
N
N
N
N
Zn
Ar
N
N
Im
11
11/Im
Ar
Ar
N
N
N
N
N
N
Zn
N
N
K3
2
N
Zn
Ar
N
N
Ar
N
CO2Et
Ar
N
N
N
N
Ar =
Zn
Ar
N
N
1a
2a
Fig. 4. Coordination equilibria of 1a, 2a, and 11 with N-methylimidazole (Im).

A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
639
Ar
Ar
Ar
Ar
M
Ar
N
N
N
N
NBS
N
N
N
N
N
N
N
N
AgPF6
N
N
N
N
N
N
N
N
Br
Br
M
Zn
Ar
Zn
Zn
Ar
pyridine
CHCl3
CHCl3
15%
Ar
Ar
98%
Ar
tBu
tBu
12
M = Zn
M = 2H
14
15
6N HCl
CHCl3
84%
13
Ar =
Ar
M
Ar
N
N
N
N
N
N
N
N
N
N
N
M
N
N
N
Pd2(dba)3CHCl3
AsPh3, Et3N
THF
Ar
16
Ar
M = 2H
M = Zn
Zn(OAc)2
83%
57%
5M
Ar
Ar
N
N
N
N
N
N
N
N
N
N
Ar
N
5M
Zn
Zn
N
N
Ar
N
N
N
Ar
N
N
N
N
Zn
Zn
Ar
N
N
N
N
Ar
Ar
5P
n
Scheme 2. Synthesis of 5.
array is estimated as ca. 400 mer at 2.5 mM, indicating that
only 0.5% of non-coordinating imidazole exists.
UV–Vis spectra of polymeric form of 5 (hereafter 5P)
(5.8 · 10ꢀ5 M in CHCl3, 1 mm cell) [16] and monomeric
form of 5 (5M) (5.3 · 10ꢀ7 M in CHCl3/MeOH, 95/5,
v/v) [17], normalized at the lower energy Soret band,
are shown in Fig. 6A. In order to examine the effect of ethy-
nyl moiety, UV–Vis spectra of polymeric and monomeric
forms of 6 (meso,meso)-linked bis(imidazoly-zinc-porphyrin)
reported previously [7a] are shown in Fig. 6B. The split
Soret bands in the both monomeric states (dotted lines)
are explained by the simple exciton coupling theory [18].
Fig. 5. 1H NMR (600 MHz, CDCl3) spectra of 16 (upper) and 5P (lower).

640
A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
Fig. 6. UV–Vis spectra in CHCl3 of 5 (upper, plain: polymer 5P 6 · 10ꢀ6 M, dotted: monomer 5M 6 · 10ꢀ7 M + MeOH) (A) and 6 (plain: 6P 10ꢀ6 M,
dotted: 6M 10ꢀ6 M + MeOH) (B). Absorption ( ) and Fluorescence ($) spectra of 5 (Ex. 479 nm for 5M (dotted), Ex. 590 nm for 5P (plain)) (C).
*
Thus, the transition dipoles of two porphyrins along the
meso,meso-linkage bond (Bx) interact each other in a
head-to-tail manner to give the lower energy Soret band.
The other Soret band originates in the other transition
dipoles (By and Bz). If two porphyrins connected at the
meso position are of an orthogonal conformation, the
higher energy Soret band should appear as a sum of two
unperturbed degenerated transitions By and Bz. When
two porphyrin planes rotate to allow the exciton interac-
tion, the higher energy Soret band should contain a blue-
shifted band due to the parallel interaction of two transi-
tion dipoles at each rotational angle. The resulting effect
on the shape of the spectrum may broaden the higher-
energy Soret band. This was eventually observed in the
spectrum 5M, in which the absorbance at 444 nm is
decreased by broadening with appearance of a shoulder
peak at the higher-energy (424 nm). A similar UV–Vis
spectral pattern was observed by Osuka et al. in
meso,meso-linked phenylethynyl-zinc-porphyrin [19]. The
spectral difference between 5M and 6M indicates that the
orthogonal conformation is predominant in 6M, whereas
rotational freedom is allowed to some extent in 5M. When
polymeric structures are formed by complementary coordi-
nation, similar spectral changes are observed in both 5P
and 6P. (Fig. 6A and B, plain lines) Thus, the higher-
energy Soret band is blue-shifted, whereas the lower energy
Soret band and Q-bands are red-shifted. These spectral
changes are explained on the basis of the Kasha’s theory
as reported in our previous paper [7a]. It is noted that
the higher-energy Soret band of 5P shows an absorbance
similar to the lower-energy Soret band. Therefore, two
spectral patterns of 5P and 6P become similar. The result
indicates that the orthogonal conformation is predominant
in the polymeric state of 5P. It means that the relatively
flexible structure of monomeric form of 5M was converted
to a rigid one by the complementary coordination.
The increase in molecular rigidity on coordination
polymer formation is observed in the excited state, too.
Absorption and fluorescence spectra of monomeric and
polymeric forms of 5 are illustrated by normalized inten-
sity as a function of wavenumber (cmꢀ1) for the qualita-
tive comparison. The fluorescence spectrum of 5M is very
broad. The (0.1) fluorescence band is not a mirror image
to the (0.1) absorption band. The broader fluorescence
spectrum indicates that more conformational isomers exist
in the excited state. On the other hand, (0.1) bands of
absorption and fluorescence spectra are more symmetric
for 5P, indicating that the structure becomes rigid by
the formation of coordination polymer. The increasing
rigidity is probably coming from increased moment of
inertia of the rotamer by formation of polymer. Rate of
rotation of meso–meso bond of 5P may decrease in the
excited state.
3. Conclusion
Novel imidazolylethynyl-zinc-porphyrin 1a and its
meso,meso-linked bisporphyrin 5 were synthesized by facial
coupling reactions of bromoporphyrins with ethynylimidaz-
ole. The complementary coordination of 1a was observed
1
by H NMR and UV–Vis spectroscopy. Self-association
constant of 1a to 2a was determined as 1.84 · 107 Mꢀ1
,
which is larger enough to maintain the complementary
coordination structure. A linear polymeric array of porphy-
rins is obtainable by successive complementary coordina-
tion of 5a. Excitonic coupling between the porphyrins in

A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
641
2a is very small, whereas that in polymeric species from its
meso,meso-linked dimer 5 is much larger due to the large
transition dipole along the linking bond. UV–Vis and fluo-
rescence spectra of 5 indicated that rigid structure of orthog-
onal orientation formed in the polymeric state.
J < 1 Hz, Im), 6.68 (d, 1H, J = <1 Hz, Im), 3.52 (s, 3H,
N-Me), 0.07 (s, 9H, TMS). To a solution of 2-trimethylsily-
lethynylimidazole (70 mg, 0.393 lmol) in CHCl3 (10 mL), n-
Bu4NF (1 M in THF, 1.18 mL, 1.18 lmol) was added at RT
for 40 min. Water was added to the mixture, and the
organic layer was extracted with CHCl3 and dried over
anhydrous Na2SO4. After evaporation, the residue was
purified by SiO2 column chromatography (hexane/
EtOAc = 2/1 to 1/1) to give 1-methyl-2-ethynylimidazole
(24 mg, 60%). (This material gradually decomposes even
in freezer, so that it should be used for the next coupling
reaction as soon as possible.) 1H NMR (270 MHz, CDCl3)
d 7.04 (d, 1H, J < 1 Hz, Im), 6.90 (d, 1H, J < 1 Hz, Im), 3.74
(s, 3H, N–Me), 3.31 (s, 1H, acetylene).
4. Experimental
4.1. General procedures
1H NMR spectra were recorded on JEOL EX-270
(270 MHz) or ECP-600 (600 MHz) spectrometer using
TMS (0 ppm) or the residual proton resonance ((CHCl2)2
5.95 ppm) of the solvent as the internal standard.
MALDI-TOF mass spectra were obtained with Perseptive
Biosystems Voyager DE-STR with dithranol (Aldrich) as
a matrix. UV–Vis spectra were obtained with a Shimadzu
UV-3100PC spectrometer. Fluorescence spectra were
obtained with a Hitachi F-4500 spectrometer. Column
chromatography was performed with silica gel (63–
210 lm, KANTO chemical Co., Inc.). THF was distilled
over sodium-benzophenone ketyl radical. Triethylamine
was distilled over calcium hydride. All other chemicals
obtained from commercial sources were used without fur-
ther purification, unless otherwise mentioned. 2-Ethynyl-
1-methylimidazole [20] was synthesized according to the lit-
erature [21].
4.3. 5,15-Bis(ethoxycarbonylphenyl)porphyrin (7)
Dipyrromethane (146 mg, 1 mmol) and 4-ethoxycar-
bonylbenzaldehyde (178 mg, 1 mmol) were dissolved in
CHCl3 (200 mL). Nitrogen gas was passed through the
mixture for 10 min to remove dissolved oxygen. Trifluoro-
acetic acid (TFA, 77 lL, 1 mmol) was added dropwise.
The mixture was stirred for 20 h in the dark. Triethyl-
amine (139 mL, 3.1 mmol) and p-chloranil (738 mg,
3 mmol) were added to the mixture, and refluxed for
1.5 h. The crude mixture was directly mounted onto
SiO2 column chromatography and eluted with CHCl3 to
give 7 (107 mg, 35%) as a purple solid. 1H NMR
(270 MHz, CDCl3) d 10.34 (s, 2H, meso), 9.41 (d, 4H,
J = 4.6 Hz, b), 9.04 (d, 4H, J = 4.6 Hz, b), 8.51 (d, 4H,
J = 8.1 Hz), 8.36 (d, 4H, J = 8.1 Hz), 4.61 (q, 4H,
J = 7.3 Hz, CH2CH3), 1.56 (t, 6H, J = 7.3 Hz, CH2CH3),
ꢀ3.1 (br, NH). MALDI TOF-Mass (Dithranol) m/z =
607.2 [M+H]+; Calc. for C38H30N4O4 = 606.2.
4.2. 2-Ethynyl-1-methylimidazole
To a solution of 1-methylimidazole (3.0 g, 36.5 mmol) in
THF (100 mL), n-BuLi (1.58 M in hexane, 30 mL,
47.5 mmol) was added dropwise slowly during 1 h at
ꢀ80 ꢂC. The mixture was stirred for 2 h, and the tempera-
ture was raised to ꢀ60 ꢂC. Iodine (11.12 g, 43.8 mmol) in
dry THF (40 mL) was added dropwise. The temperature
was raised at RT and the mixture was stirred for 16 h.
The mixture was washed with a sodium thiosulfate solution.
Organic layer was extracted with CHCl3, washed with
brine, dried over anhydrous Na2SO4. After evaporation,
the residue was purified by SiO2 column chromatography
(CHCl3/MeOH = 10/1) to give 2-iodo-1-methylimidazole
4.4. 5,15-Bis(ethoxycarbonylphenyl)-10-bromoporphyrin
(8)
To a mixture of 7 (126 mg, 0.208 mmol) and pyridine
(170 lL, 2 mmol) in CHCl3 (20 mL), N-bromosuccini-
mide (NBS, 37 mg, 0.208 mmol) in CHCl3 (4 mL) was
added at ꢀ40 ꢂC. The reaction progress was monitored
by TLC (eluent: CHCl3/hexane = 1/4), and three spots
corresponding to dibrominated compound, 8, and 7 were
observed. Additional NBS (7 mg, 0.04 mmol) was added
to the mixture until monobrominated compounds
became a major component. Acetone was added to
quench the reaction, and the temperature was raised to
RT. Water was added to the mixture, and the organic
layer was extracted with CHCl3. The organic layer was
dried over anhydrous Na2SO4, and evaporated. The res-
idue was purified by SiO2 column chromatography. Mon-
obrominated compound 8 (68 mg, 48%) was eluted after
elution of dibromoporphyrin (55 mg, 35%). 1H NMR
(270 MHz, CDCl3) d 10.17 (s, 1H, meso), 9.74 (d, 2H,
J = 4.8 Hz, b), 9.28 (d, 2H, J = 4.8 Hz, b), 8.89 (d, 2H,
J = 4.8 Hz, b), 8.88 (d, 2H, J = 4.8 Hz, b), 8.47 (d, 4H,
1
(6.0 g, 79%). H NMR (270 MHz, CDCl3) d 7.07 (s, 1H,
Im), 7.03 (s, 1H, Im), 3.62 (s, 3H, N-Me). In a Schlenk tube,
Pd(PPh3)2Cl2 (14 mg, 19 lmol), CuI (0.9 mg, 4.8 lmol),
and 2-iodo-1-methylimidazole (100 mg, 0.48 mmol) were
dissolved in triethylamine (20 mL). Trimethylsilyl acetylene
was added to the mixture, and the mixture was stirred at
70 ꢂC for 1.5 h. Solvent was removed under reduced pres-
sure. Water was added to the mixture, and organic layer
was extracted with CHCl3. The organic layer was washed
with a saturated NH4Cl solution, brine, and water. After
drying over anhydrous Na2SO4 and concentration under
reduced pressure, the residue was purified by SiO2 column
chromatography (hexane/EtOAc = 4/1 to 1/1) to give 1-
methyl-2-trimethylsilylethynylimidazole (70 mg, 82%) as a
1
yellow oil. H NMR (270 MHz, CDCl3) d 6.81 (d, 1H,

642
A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
J = 8.1 Hz), 8.28 (d, 4H, J = 8.1 Hz), 4.60 (q, 4H,
J = 7.3 Hz, CH2CH3), 1.56 (t, 6H, J = 7.3 Hz, CH2CH3),
ꢀ3.0 (br, 2H, NH). MALDI TOF-Mass (Dithranol) m/
z = 685.1 [M+H]+; Calc. for C38H29BrN4O4 = 684.1.
anhydrous Na2SO4, and purified by SiO2 column chroma-
tography (eluent: CHCl3) to give 10 (40 mg, 92%). 1H
NMR (600 MHz, (CDCl2)2) d 8.81 (s, 1H, meso), 8.43 (d,
2H, b, J = 4.8 Hz), 7.98 (d, 2H, b, J = 4.8 Hz), 7.61 (d,
2H, b, J = 4.8 Hz), 7.59 (d, 2H, b, J = 4.8 Hz), 7.04 (d,
4H, Ar, J = 7,2 Hz), 6.92 (d, 4H, Ar, J = 7,2 Hz), 3.14
(q, 4H, J = 7.2 Hz, CH2CH3), 0.19 (t, 4H, J = 7.2 Hz,
CH2CH3). MALDI TOF-Mass (Dithranol) m/z = 747.1
[M+H]+; Calc. for C38H27BrN4O4Zn = 746.1.
4.5. 5,15-Bis(ethoxycarbonylphenyl)-10-(10-methyl-20-
imidazolyl)(ethynyl)porphyrin (9)
To a solution of bromoporphyrin 8 (62 mg, 90.4 lmol)
in dry THF (15 mL), a mixture of THF:Et3N (5:1, 3 mL),
Pd2(dba)3CHCl3 (15 mg, 14.5 lmol) and AsPh3 (33 mg,
109 lmol) was added. 2-Ethynyl-1-methylimidazole
(29 mg, 270 lmol) in THF (3 mL) was added to the mix-
ture, and the mixture was stirred at 45 ꢂC under Ar. Disap-
pearance of 8 was monitored by TLC after 20 min. The
solvent was removed under reduced pressure and the resi-
due was purified by SiO2 column chromatography (CHCl3)
and reprecipitation from CHCl3/hexane to give 9 (54 mg,
4.8. 5,15-Bis(ethoxycarbonylphenyl)-10-
phenylethynylporphyrinatozinc (11)
To
a
solution of bromoporphyrin 10 (25 mg,
33.4 lmol) in dry THF (7 mL), a mixture of THF:Et3N
(5:1, 1.4 mL), Pd2(dba)3CHCl3 (5.5 mg, 5.34 lmol) and
AsPh3 (12 mg, 40 lmol) was added. Phenylacetylene
(10 mg, 100 lmol) in THF (1 mL) was added to the mix-
ture, and the mixture was stirred at 50 ꢂC under Ar.
After 30 min, solvent was removed under reduced pres-
sure and the residue was purified by SiO2 column chro-
matography (CHCl3) twice to give 11 (16.5 mg, 64%).
1H NMR (600 MHz, CDCl3) d 10.19 (s, 1H, meso),
9.88 (d, 2H, J = 4.2 Hz, b), 9.34 (d, 2H, J = 4.2 Hz, b),
8.99 (d, 2H, J = 4.2 Hz, b), 8.98 (d, 2H, J = 4.2 Hz, b),
8.47 (d, 4H, J = 8.1 Hz), 8.31 (d, 4H, J = 8.1 Hz), 8.04
(d, 2H, J = 7.8 Hz, Ph), 7.58 (t, 2H, , J = 7.8 Hz, Ph),
7.50 (tt, 2H, , J = 1.8, 7.8 Hz, Ph), 4.58 (q, 4H,
J = 7.2 Hz, CH2CH3), 4,23 (s, 3H, N–Me), 1.53 (t, 6H,
J = 7.2 Hz, CH2CH3). MALDI TOF-Mass (Dithranol)
m/z = 768.2 [M]+; Calc. for C46H32N6O4Zn = 768.2.
1
84%). H NMR (600 MHz, CDCl3) d 10.21 (s, 1H, meso),
9.82 (d, 2H, J = 4.7 Hz, b), 9.30 (d, 2H, J = 4.7 Hz, b),
8.93 (d, 2H, J = 4.7 Hz, b), 8.91 (d, 2H, J = 4.7 Hz, b),
8.49 (d, 4H, J = 8.0 Hz), 8.31 (d, 4H, J = 8.0 Hz), 7.33
(d, 1H, J = 1.0 Hz, Im), 7.18 (d, 1H, J = 1.0 Hz, Im),
4.61 (q, 4H, J = 7.2 Hz, CH2CH3), 4,23 (s, 3H, N–Me),
1.57 (t, 6H, J = 7.2 Hz, CH2CH3), ꢀ2.61 (s, 2H, NH).
MALDI TOF-Mass (Dithranol) m/z = 710.3 [M]+; Calc.
for C44H34N6O4 = 710.3.
4.6. 5,15-Bis(ethoxycarbonylphenyl)-10-(10-methyl-20-
imidazolyl)(ethynyl)porphyrinatozinc (1a, 2a)
To a solution of free base 9 (25 mg, 35.2 lmol) in CHCl3
(30 mL), zinc acetate dihydrate (232 mg, 1.06 mmol) in
MeOH (3 mL) was added at RT, and the mixture was stir-
red for 2 h. A saturated NaHCO3 solution (10 mL) was
added. Organic layer was extracted with CHCl3, dried over
anhydrous Na2SO4, and evaporated to give 1a (25.6 mg,
94%). 1a forms dimer 2a spontaneously in non-coordinat-
ing solvents such as CHCl3 and tetrachroloethane. 1H
NMR (600 MHz, (CDCl2)2) of 2a d 10.30 (s, 1H, meso),
9.38 (d, 2H, J = 4.2 Hz, b), 8.92 (d, 2H, J = 4.2 Hz, b),
8.91 (d, 2H, J = 4.1 Hz, b), 8.60 (d, 4H, J = 7.2 Hz), 8.58
(d, 4H, J = 7.2 Hz), 8.49 (d, 2H, J = 4.2 Hz, b), 8.44 (d,
4H, J = 7.2 Hz), 8.25 (d, 4H, J = 7.2 Hz), 5.28 (s, 1H,
Im), 4.63 (q, 4H, J = 7.2 Hz, CH2CH3), 2.63 (s, 3H, N–
Me), 1.67 (s, 1H, Im), 1.62 (t, 6H, J = 7.2 Hz, CH2CH3).
MALDI TOF-Mass (Dithranol) m/z = 772.0 [M]+; Calc.
for C44H32N6O4Zn = 772.2.
4.9. meso,meso-Linked diporphyrinatozinc (13) [15]
According to the reported procedure, 13 (15 mg, 15%)
was prepared from porphyrin 12 (100 mg, 134 lmol) by
oxidative coupling and GPC separation. 1H NMR
(600 MHz, CDCl3) d 10.39 (s, 1H, meso), 9.49 (d, 2H,
J = 10.2 Hz, b), 9.19 (d, 2H, J = 10.2 Hz, b), 8.75 (d,
2H, J = 10.2 Hz, b), 8.13 (d, 2H, J = 10.2 Hz, b), 8.114
(s, 4H, Ph), 8.107 (s, 4H, Ph), 7.71 (t, 2H, J = 3.6 Hz,
Ph), 1.45 (s, 72H, tBu). MALDI TOF-Mass (Dithranol)
m/z = 1496.3 [M+H]+; Calc. for C96H102N8Zn2 = 1494.7.
4.10. meso,meso0-Dibrominated meso,meso-linked
diporphyrinatozinc (14) [19]
According to the reported procedure, 14 (15 mg, 98%)
was prepared from porphyrin 13 (14 mg, 9.34 lmol) by
bromination with NBS. 1H NMR (270 MHz, CDCl3) d
9.86 (d, 4H, J = 4.8 Hz, b), 9.08 (d, 4H, J = 4.8 Hz,
b), 8.65 (d, 4H, J = 4.8 Hz, b), 8.07 (d, 4H,
J = 4.8 Hz, b), 8.05 (d, 8H, J = 1.6 Hz, Ar), 7.71 (t,
4H, J = 1.6 Hz, Ar), 1.44 (s, 72H, tBu). MALDI TOF-
Mass (Dithranol) m/z = 1530.2 [M+H]+; Calc. for
C96H104Br2N8 = 1529.7.
4.7. 5,15-Bis(ethoxycarbonylphenyl)-10-
bromoporphyrinatozinc (10)
To a solution of free base 8 (40 mg, 58.3 lmol) in CHCl3
(20 mL), zinc acetate dihydrate (384 mg, 1.75 mmol) in
MeOH (5 mL) was added at RT, and the mixture was stir-
red for 30 min. A saturated NaHCO3 solution (10 mL) was
added. Organic layer was extracted with CHCl3, dried over

A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
643
4.11. meso,meso0-Dibrominated meso,meso-linked
diporphyrin (15)
imidazole was added as a chloroform solution initially,
and then, directly to avoid the volume increase. The mix-
ture was stirred for 2 min at rt and UV–Vis spectra of
the solution was measured. The change of absorbance at
443.5 nm was plotted as a function of added N-methylimi-
dazole. The curve fitting analysis was carried out by refer-
ring to the literature [22].
A solution of zinc porphyrin 14 (9 mg, 5.43 lmol) in
CHCl3 (10 mL) was added to a 6M HCl aqueous solution.
The mixture was stirred under N2 for 1 h at RT. The mix-
ture was adjusted to pH 8 with a saturated NaHCO3 solu-
tion. The organic layer was extracted with CHCl3, dried
over anhydrous Na2SO4, and evaporated. The residue
was purified by SiO2 column chromatography (eluent:
CHCl3) to give 15 (7 mg, 84%). 1H NMR (270 MHz,
CDCl3) d 9.76 (d, 4H, J = 4.8 Hz, b), 8.97 (br. d, 4H,
J = 4.8 Hz, b), 8.65 (d, 4H, J = 4.8 Hz, b), 8.07 (d, 4H,
J = 4.8 Hz, b), 8.05 (d, 8H, J = 1.6 Hz, Ar), 7.71 (t, 4H,
J = 1.6 Hz, Ar), 1.44 (s, 72H, t-Bu), ꢀ2.15 (br. s, NH).
MALDI TOF-Mass (Dithranol) m/z = 1530.2 [M+H]+;
Calc. for C96H104Br2N8 = 1529.7.
6. Molecular modeling
Molecular mechanics calculation was performed on
Cerius2ꢁ (Accelrys Software Inc.) using Universal force
field.
7. Estimation of molecular length of 5P
Aggregation numbers of 5P are estimated from Eqs.
(5) and (6) on the basis that the association constant
of the zinc porphyrin unit (imidazolylethynyl-zinc-por-
phyrin moiety) in 5P is same as that in 2 (K =
1.8 · 107 Mꢀ1).
4.12. meso,meso0-Bis(10-methyl-20-imidazolyl)(ethynyl)-
substituted meso,meso-linked diporphyrin (16)
To a solution of bromoporphyrin 15 (2.5 mg, 23.5 lmol)
in dry THF (5 mL), a mixture of THF:Et3N (5:1, 1 mL),
Pd2(dba)3CHCl3 (1.3 mg, 1.25 lmol) and AsPh3 (2.9
mg, 9.4 lmol) was added. 2-Ethynyl-1-methylimidazole
(2.5 mg, 23.5 lmol) in THF (1 mL) was added to the mix-
ture, and the mixture was stirred at 45 ꢂC under Ar. Disap-
pearance of 15 was monitored by TLC after 40 min. The
solvent was removed under reduced pressure and the residue
was purified by SiO2 column chromatography (CHCl3) to
Zt ¼ 2½ZDꢂ þ ½ZMꢂ;
½ZDꢂ
ð5Þ
ð6Þ
K ¼
:
2
½ZMꢂ
Here [Zt], [ZD], and [ZM] are concentrations of total, di-
meric, and monomeric zinc porphyrin units, respectively.
A mean aggregation number is calculated when an appro-
priate [Zt] is defined as the initial concentration of the zinc
porphyrin.
1
give 16 (3.5 mg, 57%). H NMR (600 MHz, CDCl3) d 9.83
(d, 4H, J = 4.8 Hz, b), 9.00 (br. d, 4H, J = 4.8 Hz, b), 8.55
(d, 4H, J = 4.8 Hz, b), 8.05 (d, 8H, J = 1.6 Hz, Ar), 8.02
(d, 4H, J = 4.8 Hz, b), 7.72 (br. s, 4H, Ar), 7.36 (s, 2H,
Im), 7.20 (s, 2H, Im), 4.29 (s, 6H, N-Me), 1.44 (s, 72H,
tBu), ꢀ1.77 (br. S, NH). MALDI TOF-Mass (Dithranol)
m/z = 1581.5 [M+H]+; Calc. for C108H114N12 = 1579.9.
8. Deconvolution of Soret bands in 5M
Peak analysis of Soret band of 5M was performed by
using ORIGINꢁ Pro ver.7 program (Origin Lab Co.).
The original spectrum was translated into wavenumber
and divided into three components predicted by head-to-
tail interaction along Bx–Bx transition, unperturbed By
and Bz transitions, and parallel interaction of the transition
dipoles due to rotation along the meso–meso bond. The
deconvoluted peak maxima (half band widths) are
21045 cmꢀ1 (475 nm, 971 cmꢀ1), 22533 cmꢀ1 (444 nm,
1562 cmꢀ1), and 23575 cmꢀ1 (424 nm, 2575 cmꢀ1). In the
case of 6M, Soret band can be deconvoluted by two com-
ponents, 21536 cmꢀ1 (464 nm, 1559 cmꢀ1) and 23960 cmꢀ1
(417 nm, 2109 cmꢀ1).
4.13. meso,meso0-Bis(10-methyl-20-imidazolyl)(ethynyl)-
substituted meso,meso-linked diporphyrinatozinc 5
To a solution of free base 16 (1 mg, 0.633 lmol) in
CHCl3 (5 mL), zinc acetate dihydrate (4 mg, 19 lmol)
in MeOH (0.5 mL) was added at RT, and the mixture
was stirred for 1 h. A saturated NaHCO3 solution
(10 mL) was added. The organic layer was extracted with
CHCl3, dried over anhydrous Na2SO4, and evaporated to
give 5 (0.9 mg, 83%). MALDI TOF-Mass (Dithranol) m/
z = 1704.9 [M+H]+; Calc. for C108H110N12Zn2 = 1703.8.
1H NMR (600 MHz, (CDCl2)2) of 5P are shown in
Fig. 5.
Acknowledgments
This work was supported by Grant-in-Aids for Scientific
Research (A) (Y.K.), Young Scientists (B) (A.S.), and Sci-
entific Research on Priority Areas (No. 15036248), Reac-
tion Control of Dynamic Complexes (Y.K.) from the
Ministry of Education, Culture, Sports, Science and Tech-
nology, Japan and JSPS (Japan Society for the Promotion
of Science).
5. UV–Vis titration
UV–Vis titration shown in Fig. 3 inset was carried out in
a Pyrexꢁ glass cuvette (band path 1 cm) filled with a sample
solution (4 · 10ꢀ6 M, 3 mL) in chloroform. N-Methyl

644
A. Satake et al. / Journal of Organometallic Chemistry 692 (2007) 635–644
[8] H. Ozeki, A. Nomoto, K. Ogawa, Y. Kobuke, M. Murakami, K.
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