Synthesis and characterization of a β-fused tetraporphyrin-phthalocyanine star-shaped array

Article abstract of DOI:10.1142/S1088424616500978

A star-shaped array, consisting in four tetraphenylporphyrin fused to a phthalocyanine central unit by pyrazine groups, is constructed via the condensation reaction of a dicyanoquinoxaline annulated to a porphyrin ring. The nature of the annulated group is critical for the success of the reaction; in the case of smaller linkers, such as a dicyanopyrazine unit, a nucleophilic substitution occurred, giving the corresponding alcoxy derivative in alcoholic solvents. The visible spectrum of the array shows the typical absorptions of the macrocyclic sub units. The synthetic pathway here presented opens the way to the preparation of β-fused porphyrin-phthalocyanine arrays.

Full text of DOI:10.1142/S1088424616500978

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2016; 20: 1–8
DOI: 10.1142/S1088424616500978
Published at http://www.worldscinet.com/jpp/
Synthesis and characterization of a b-fused tetraporphyrin-
phthalocyanine star-shaped array
Federica Mandoja, Giuseppe Pomaricoa◊, Frank R. Fronczekb, Kevin M. Smithb◊
and Roberto Paolesse*a◊
a Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata, via della Ricerca Scientifica 1,
00133 Rome, Italy
b Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA
Dedicated to Professor Tomás Torres on the occasion of his 65th birthday
Received 16 February 2016
Accepted 13 April 2016
ABSTRACT: A star-shaped array, consisting in four tetraphenylporphyrin fused to a phthalocyanine
central unit by pyrazine groups, is constructed via the condensation reaction of a dicyanoquinoxaline
annulated to a porphyrin ring. The nature of the annulated group is critical for the success of the reaction;
in the case of smaller linkers, such as a dicyanopyrazine unit, a nucleophilic substitution occurred, giving
the corresponding alcoxy derivative in alcoholic solvents. The visible spectrum of the array shows the
typical absorptions of the macrocyclic sub units. The synthetic pathway here presented opens the way to
the preparation of b-fused porphyrin-phthalocyanine arrays.
KEYWORDS: porphyrins, phthalocyanines, chromophores.
Even if the skeletal differences are relative small,
with four aza moieties replacing, in the phthalocyanines,
the meso methine bridges of porphyrins, they produce
INTRODUCTION
Porphyrin derivatives have been called the Pigments
of Life [1], since their ubiquitous presence in biological
dramatic changes in the chemical and physical behavior
materials imparts the color of the living systems. The
of these macrocycles, with the optical properties being
impressive optical properties of porphyrins have led to
the most evident example.
an intense effort aimed to prepare synthetic mimics of
Due to their expanded conjugated systems, all these
the natural chromophores, with the aim to use them for
compounds show intense absorptions in the visible
applications in different fields, ranging from medicine to
region, but while porphyrins exhibit a strong Soret band
materials science [2]. Looking at the examples furnished
around 410–450 nm, together with four weaker Q-bands
by Nature, where even simple skeletal modifications
around 500–600 nm, the aza-derivatives show lower
induce important variations in the macrocycle properties,
absorptions at around 320–360 nm and quite intense ones
a cornucopia of different porphyrin analogs, i.e.
at 600–700 nm. The photophysical as well as the redox
macrocycles having framework modification to respect
properties of these classes of macrocycles are also very
the parent porphyrin, have been prepared [3, 4]. Among
different, despite their structural similarity.
them, phthalocyanines have a special role, rivalling that
These differences, however, have also aroused the
of porphyrins as the most famous and exploited pyrrolic
interest for the preparation of dyads or even arrays of
macrocycles [5].
macrocycles where these species are linked together
throughboththeirmeso-andb-pyrrolicpositions[6]. Most
of the hybrids are linked either in a covalent manner or
◊ SPP full member in good standing
through a large metal center or even through electrostatic
interactions, axial coordination, and other supramolecular
interactions. The resulting hybrids can display the
*Correspondence to: Roberto Paolesse, email: roberto.
paolesse@uniroma2.it, tel: +39 067-259-4752, fax: +39 067-
259-4328
Copyright © 2016 World Scientific Publishing Company

2
F. MANDOJ ET AL.
complementary absorptions of individual chromophores,
covering a large part of the visible spectrum; moreover, it
ispossibletoexploittheinteraction, whenpresent, through
photo-induced electron and/or energy transfer pathways.
These systems are interesting in view of their unique
photoelectronic properties and potential applications as
mimics of light-harvesting systems in photosynthesis, as
electron energy transfer moieties in molecular wires, as
sensing materials and PDT [7–16].
Examples of porphyrin-phthalocyanine arrays have
been reported in the literature, with different bridging
units [17, 18]. In this field, we have been interested
in the establishment of synthetic routes where two or
more porphyrin units are annulated at their b-pyrrolic
positions. In these compounds, the p-aromatic system is
extended all over the molecules, resulting in significant
changes in the UV-visible spectra, with new absorption
bands featuring red shifts reaching the NIR region. In
this pathway, we have reported the preparation of a star-
shaped planar array, where four porphyrins were fused
onto a central tetrabenzoporphyrin unit [19].
0.11 mmol) and a catalytic amount of DBU were added.
The mixture was heated to reflux, under N2, for 24 h,
following the progress of the reaction by TLC analysis
and UV-visible spectroscopy. After evaporation of the
solvent, the crude product was purified on a silica gel
chromatography column, eluting with dichloromethane.
Only one fraction was isolated, collected and crystallized
from dichloromethane/methanol, affording 2 (13 mg,
0.015 mmol; 21%); mp >300°C. UV-vis (CH2Cl2):
lmax, nm (log e) 406 (4.39), 440 (5.01), 565 (4.21), 604
(4.09). 1H NMR (300 MHz, CDCl3): d, ppm 8.95 (m, 5 H,
b-pyrroles), 8.83 (d, J = 4.77, 1 H, b-pyrroles), 8.22
(m, 4 H, phenyls), 8.09 (m, 4 H, phenyls), 7.79 (m, 4 H,
phenyls), 4.10 (m, 2 H, –O–CH2(CH2)3CH3), 3.20 (m, 4 H,
–O–CH2(CH2)3CH3), 1.79 (m, 2 H, –O–CH2(CH2)3CH3),
1.03 (m, 3 H, –O–CH2(CH2)3CH3). MS (FAB): m/z 841
[M]+. Anal. calcd. for C52H37N7OZn: C, 74.24; H, 4.43;
N, 11.65. Found C, 74.47; H, 4.61; N, 11.10%.
Preparation of cyanopyrazinoporphyrin deriva-
tives (compounds 4 and 5). Zn-dioxo-porphyrin complex
3 (80 mg; 0.11 mmol) was dissolved in a solution of
dichloromethane/ethanol/acetic acid (5:5:1) (22 mL)
and an excess of 4,5-diaminophthalonitrile (190 mg;
1.19 mmol) was added. The resulting solution was
refluxed for 3 h, following the progress of the reaction
by TLC analysis and UV-visible spectroscopy. After
evaporation of the solvent, the crude product was purified
on a silica gel chromatography column, eluting with
dichloromethane. Two fractions were collected and
crystallized from dichloromethane/methanol affording,
in order of elution, porphyrin 5 (16 mg, 0.018 mmol;
16%) and 4 (56 mg, 0.068 mmol; 60%). 4. mp > 300°C.
UV-vis (CH2Cl2): lmax, nm (log e) 426 (5.41), 484 (4.63),
We have been interested to investigate the preparation of
a similar system, where the central unit is a phthalocyanine
ring. In this paper, we report a general method for the
synthesis of dicyano porphyrinoid derivatives, and their
potential application as precursors for the preparation of a
more sophisticated architecture endowed with an extended
aromatic system, based on a fused phthalocyanine-
porphyrins oligomer.
EXPERIMENTAL
1
596 (4.07), 644 (3.92). H NMR (300 MHz, CDCl3): d,
General
ppm 8.97 (s, 4 H, b-pyrroles), 8.88 (s, 2 H, b-pyrroles),
8.48 (s, 2 H, quinoxaline), 8.22 (4 H, phenyls), 8.12 (4 H,
phenyls), 7.96 (m, 2 H, phenyls), 7.80 (m, 10 H, phenyls).
MS (FAB): m/z 884 [M]+. Anal. calcd. for C52H28N8Zn:
C, 75.23; H, 3.40; N, 13.50. Found C, 75.45; H, 3.61;
N, 12.10%. 5. mp > 300°C. UV-vis (CH2Cl2): lmax, nm
(log e) 419 (5.57), 469 (4.85), 583 (4.27), 630 (4.19).
1H NMR (300 MHz, CDCl3): d, ppm 8.95 (m, 4 H,
b-pyrroles), 8.87 (s, 2 H, b-pyrroles), 8.38 (s, 1 H,
quinoxaline), 8.28 (s, 1 H, quinoxaline), 8.22 (4 H,
phenyls), 8.11 (4 H, phenyls), 7.93 (m, 2 H, phenyls),
7.80 (m, 10 H, phenyls). MS (FAB): m/z 831 [M]+. Anal.
calcd. for C51H28BrN7Zn: C, 69.28; H, 3.19; N, 11.09.
Found C, 68.91; H, 3.16; N, 11.73%.
Preparation of tetraporphyrinphthalocyanine 6. A
suspension of magnesium turnings (175 mg, 7.2 mmol) in
n-butanol (50 mL) was heated to reflux, under N2, for 4 h
using small crystal of iodine to initiate the reaction. Once
cooled, this suspension was poured, under an atmosphere
of nitrogen, into a flask containing the dicyanopirazino
derivative 4 (40 mg, 0.057 mmol) and an excess of zinc
acetate, and the mixture was heated again; finally, a
catalytic amount of DBU was added and the mixture was
Silica gel 60 (70–230 mesh, SigmaAldich) was used for
column chromatography. Reagents and solvents (Aldrich,
Merck or Fluka) were of the highest grade available
1
and were used without further purification. H NMR
spectra were recorded on a Bruker AV300 (300 MHz)
spectrometer. Chemical shifts are given in ppm relative
to residual CHCl3 (7.25 ppm). UV-visible spectra were
measured on a Cary 50 spectrophotometer. Mass spectra
wererecordedonaVGQuattrospectrometerinthepositive-
ion mode, using m-nitrobenzyl alcohol (NBA, Aldrich) as
a matrix (FAB), or on a Voyager DE STR Biospectrometry
workstation in the positive mode, using a-cyano-4-
hydroxycinnamic acid as a matrix (MALDI). Elemental
analysis (C, H, N) were obtained at the Microanalytical
Laboratory of the University of Padova, Italy.
Synthesis
Condensation reaction of Zn-dicyano porphyrin
complex 1. Zn-dicyano porphyrin complex 1 (60 mg;
0.08 mmol) was dissolved in anhydrous pentanol,
bubbled with nitrogen, and anhydrous ZnCl2 (15 mg;
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SYNTHESIS AND CHARACTERIZATION OF A b-FUSED TETRAPORPHYRIN-PHTHALOCYANINE STAR-SHAPED ARRAY
3
left to reflux, under nitrogen, for 24 h. The progress of the
reaction was followed by TLC analysis and UV-visible
spectroscopy. After evaporation of the solvent, the crude
product was purified on a short column of silica gel eluting
with tetrahydrofuran. The first fraction was isolated and
characterized as the porphyrin 5 (9 mg, 0.0027 mmol;
5%). mp > 300°C. UV-vis (CHCl3): lmax, nm (log e) 425
(5.36), 584 (4.18), 622 (4.09), 833 (4.15). MS (MALDI):
m/z 3385 [M]+. Anal. calcd. for C208H112N32Zn5: C, 73.77;
H, 3.33; N, 13.24. Found C, 74.25; H, 3.06; N, 12.94%.
35,319 data was collected at to q = 26.7°, R = 0.093 for
11,316 data with I>2s(I) of 18,189 unique data and
1137 refined parameters, CCDC 1453163.
For 4. C53H32N8OZn. CHCl3, triclinic space group
P-1, a = 11.980(2), b = 13.447(3), c = 15.607(3) Å,
a = 66.441(12), b = 72.978(13), g = 82.031(11)°, Z = 2,
T = 90 K, Dcalcd = 1.480 g.cm-3, m(MoKa) = 0.79 mm-1.
A total of 30,184 data was collected at to q = 25.7°, R =
0.054 for 5322 data with I>2s(I) of 8382 unique data
and 608 refined parameters, CCDC 1453164.
For 5. C52H32BrN7OZn, monoclinic space group
P2/n, a = 21.1727(7), b = 10.9397(4), c = 21.7399(7) Å,
b = 112.345(2)°, Z = 4, T = 90 K, Dcalcd = 1.300 g.cm-3,
m(CuKa) = 2.01 mm-1. A total of 36,080 data was
collected at to q = 61.4°, R = 0.074 for 5580 data with
I>2s(I) of 7180 unique data and 588 refined parameters,
CCDC 1453165.
X-ray crystallographic data
Diffraction data for 2 and 4 were collected at low
temperature on a Nonius KappaCCD diffractometer
with MoKa radiation and those for 5 on a Bruker Kappa
Apex-II diffractometer equipped with CuKa radiation.
Refinement was by full-matrix least squares using
SHELXL, with H atoms in idealized positions, except for
the OH hydrogen in 4, for which coordinates were refined.
4 was the chloroform solvate, and 5 had disordered
solvent of unknown identity, which was removed using
SQUEEZE. 5 was also a two-component nonmerohedral
twin and had substitutional disorder on adjacent C atoms
in which CN and Br substituents overlap. Refinement
of CN and Br occupancies summing to unity on each C
led to values close to 50:50, consistent with mono CN
monobromo formulation.
RESULTS AND DISCUSSION
The synthetic pathway for the preparation of the
target phthalocyanine-porphyrins array should start from
a porphyrin bearing two vicinal cyanide groups in the
peripheral positions. In the past, we have reported the
preparation of a 2,3-dicyano-tetraphenylporphyrin, but all
our attempts to obtain the corresponding phthalocyanine
failed, probably due to the steric hindrance of the vicinal
phenyl groups. To avoid this problem, we decided to
prepare the dicyano porphyrin moiety 1, as substrate in the
self-condensation reaction leading to a heteroporphyrin-
porphyrazine like structure (Scheme 1).
Crystallographic data. For 2. C53H41N7O2Zn, mono-
clinic space group P21/n, a = 15.979(2), b = 20.040(4),
c = 27.025(3) Å, b = 94.499(10)°, Z = 8, T = 90 K,
Dcalcd = 1.345 g.cm-3, m(MoKa) = 0.62 mm-1. A total of
R
R
N
N
N
N
N
N
N
N
Zn
R
R
R
Zn
R
R
R
CN
N
N
CN
N
N
N
N
N
N
ZnCl2, DBU
N
N
N
N
N
N
N
N
Pentanol, ∆
Zn
Zn
N
N
N
R
R
Zn
R
N
N
R
N
R
1
N
N
N
N
CN
N
N
N
N
R
Zn
R
R
N
O
N
N
N
N
N
Zn
R =
2
Scheme 1. Self-condensation reaction of 1
Copyright © 2016 World Scientific Publishing Company
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4
F. MANDOJ ET AL.
porphyrin structure suggested that reaction occurred
on the peripheral pyrazine ring; the characterization of
the compound highlighted the formation of the mono
CN mono pentyloxyporphyrin 2, confirmed by X-ray
crystallography (Fig. 1).
The crystal of 2 has two independent molecules, one
of which is shown. In both, the Zn is square pyramidal
with a coordinated methanol in the axial position, mean
Zn–O distance 2.174 Å, and the Zn lies 0.242 Å out of the
plane of the four N atoms. The porphyrin cores exhibit a
very slight saddle distortion, with the beta C atoms lying
0.024–0.269 Å (mean 0.112 Å) out of the N4 plane.
The formation of 2 again indicated that the pyrazine
ring is ineffective in avoiding the steric hindrance that
can prevent the cyclization reaction leading to the
porphyrazine ring; in this case the reactivity of the
pyrazine ring toward nucleophilic aromatic substitution
drives the reaction to the formation of 2.
We next modified the reaction conditions, changing
various parameters such as solvent, salt, catalyst or
reaction time, as reported in Table 1. In all cases the
reaction was not successful; in alcoholic media 1 always
underwent the CN nucleophilic substitution, while in
non-nucleophilic aromatic solvent, such as TCB or
xylene, we observed no reaction, observing only the
decomposition of the starting material.
These results strongly support the hypothesis that the
steric hindrance problem was not resolved, even in 1,
thus preventing the formation of the porphyrazine ring.
For this reason, we followed a similar approach,
but modifying the reaction scheme starting from 3,
as illustrated in Scheme 2. In 4 the annulated ring is a
quinoxaline, which allowed us to solve the two potential
obstacles observed with 2: the cyano groups are now
substituents on a bezene ring, so more distant from the
porphyrin ring and less activated toward the nucleophilic
substitution.
Fig. 1. X-ray crystal structure of 2 with 50% ellipsoids
The porphyrin 1 has been prepared by a condensation
reactionoftheZndioxoporphyrinwiththediaminomaleo-
nitrile, the synthesis of which was recently optimized
in our laboratories [20]. This compound was reacted
following a common procedure used for phthalocyanine
preparation, by dissolving 1 in anhydrous pentanol, in
presence of ZnCl2 and DBU, and refluxing the mixture
for 24 h. Chromatographic separation of the crude
reaction mixture allowed the isolation of a reaction
product. The UV-visible spectrum of this compound was
quite similar to that of the starting material, showing
the absence of the expected porphyrazine absorption,
over 650 nm. This result indicated the failure to obtain
the porphyrazine, while the retention of a single
Also in this case we obtained 4 by reaction of the dioxo
porphyrinzinccomplex3,with1,2-diamminophthalonitrile,
Table 1. The products obtained from the reaction of the porphyrin 1 in different conditions
Starting material
Solvent
Salt
Cat.
DBU
Reaction time
24 h
Product
1
1
1
1
1
1
1
pentanol anhydrous
hexanol anhydrous
hexanol anhydrous
Mg/I2 butanol
Zn(OAc)2
Zn(OAc)2
ZnCl2
2
DBU
24 h
mono-substituted
DBU
24 h
mono-substituted
Zn(OAc)2
DBU
24 h
mono-substituted
1,2,4-trichlorobenzene Zn(OAc)2
DBU
48 h
—
—
—
DMF
ZnCl2
HMDS
HMDS
48 h
Xylene
Zn(OAc)2
48 h
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SYNTHESIS AND CHARACTERIZATION OF A b-FUSED TETRAPORPHYRIN-PHTHALOCYANINE STAR-SHAPED ARRAY
5
CN
CN
CN
R
X
R
Zn
R
O
R
Zn
R
R
Zn
R
N
N
N
R
N
R
O
R
N
N
N
N
N
N
N
N
N
N
H2N
H2N
CN
CN
N
N
CH2Cl2/EtOH/HOAc
+
+
R
R
∆
3
4
5
R =
X = Br
Scheme 2. The formation of 4 and 5 from the reaction of porphyrin 3
in a EtOH/CH2Cl2/CH3CO2H solvent mixture, refluxing for
3 h. Once TLC showed the disappearance of the starting
material, the solvent was removed and the residue was
purified by column chromatography on silica gel, eluting
with CH2Cl2; in this case we obtained two fractions, in 60%
and 16% yield, respectively (Scheme 2).
Theformationof5wasquitesurprising,sincenobromine
sourceshavebeenemployedinpreparationoftheporphyrin
derivative. For this reason we turned our attention toward
the commercial 4,5-diaminophthalonitrile used as starting
material. The synthetic route for the preparation of the
4,5-diaminophthalonitrile uses dibromo-diaminobenzene
as intermediate and a mono Br-mono CN diamino benzene
was present as an impurity in the commercial reagent
used, as confirmed by HPLC separation and mass analysis
of the reagent. Probably this impurity is more reactive than
the corresponding 4,5-diaminophthalonitrile, and only
the excess of phthalonitrile led to the formation of 5 in
appreciable amount.
The desired dicyano-porphyrin 4 was then reacted,
following the synthetic route based on the preliminary
preparation of Mg(OBu)2, in refluxing butanol, with
Mg and I2. After 4 h, the solvent was poured in a flask
containing 4 and Zn(OAc)2 and a catalytic amount of
DBU was added. The mixture was heated to reflux,
under nitrogen, for 24 h. The progress of the reaction was
monitored by TLC and UV-visible spectroscopy; in this
case the UV-visible spectrum showed a significant peak
around 840 nm, together with some modifications of the
starting porphyrin absorptions, suggesting the formation
of a phthalocyanine like structure 6 (Scheme 3), further
supported by the red-shift of the peak.
The work up of the reaction was particularly difficult,
since the low solubility showed by 6 in several organic
solvents made it difficult to purify the crude reaction
product; furthermore, the reaction yields were quite low,
making more difficult the separation of the pure product.
The strong tendency of the compound to aggregate led
also to a very broad 1H NMR spectrum.
The identification of the compound was also supported
by the MALDI mass spectrum, which was in agreement
with the structure of 6.
The UV-visible spectrum of 6 is presented in Fig. 5;
it is worth mentioning that the spectrum seems to be the
sum of the characteristic absorbances of both porphyrins
and phthalocyanine, and only a broadening and red shift
can be observed. This feature seems to indicate minimal
Although their UV-visible spectra were very similar,
1
slightly shifted by only a few nanometers, the H NMR
analysis revealed a different substitution pattern for the
porphyrin derivatives. The second fraction, identified as
the desired product 4, shows a singlet around 8.5 ppm,
integrating for 2 H, which correspond to the residual
protons of the quinoxaline ring. The presence of only
one signal corroborated the formation of the expected
symmetric derivative. Lower symmetry was observed in
the 1H NMR spectrum of the first fraction. In detail, the
signal corresponding to quinoxaline protons splitted into
two (1 H each) resonances, and also the signals of the
b-pyrroles signals increased in number.
Both these features suggested that a substitution
occurred in the peripheral quinoxalino group, as
suggested also by the corresponding mass spectra.
Forbothcompoundswehavebeenabletoobtaincrystals
suitable for X-ray crystallographic characterization,
which allowed us to unambiguously identify the products.
Compound 4 (Fig. 3) was the expected compound, while
the additional product 5 was a similar quinoxalino fused-
porphyrin, where one cyano group and a bromine atom
were present at the peripheral positions (Fig. 4).
The structure of 4 is quite similar to that of 2, with the
Znlying0.241ÅoutoftheN4 planeandtheZn–O(MeOH)
distance 2.146 Å. The saddle distortion is slightly more
pronounced than in 2, with beta C atoms 0.099–0.276
(mean 0.182) Å out of the N4 plane. The structure of 5
has disorder in which the adjacent Br and CN positions
are swapped. The Zn coordination is similar to that seen
in 2 and 4, with the Zn lying 0.226 Å out of the N4 plane
and the Zn–O distance 2.189 Å. The porphyrin core is
somethat more planar than those 2 and 4, with the 24
atoms lying a mean of 0.053 Å from coplanarity and the
maximum deviation of a beta C atom 0.123 Å.
Copyright © 2016 World Scientific Publishing Company
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F. MANDOJ ET AL.
Fig. 2. 1H NMR spectra of compounds 4 and 5 in CDCl3. The asterisk indicates the residual solvent peak
Fig. 3. X-ray crystal structure of 4 with 50% ellipsoids
Fig. 4. X-ray crystal structure of 5 with 50% ellipsoids,
illustrating the disorder of the Br and CN substituents
interactions between the aromatic systems of the five
tetrapyrrolic subunits. It is interesting to note that the
UV-visible spectrum of 6 was significantly influenced
by the solvent used. In Fig. 5a we show the spectrum
obtained in CHCl3, which confirms the strong tendency
of 6 to aggregate. The addition of pyridine, in fact,
induced a modification of the spectrum, as indicated
in Fig. 5a, with a better resolution of the bands. In this
case, the coordination of pyridine can in fact reduce
intermolecular aggregation. This effect is even more
evident when the spectrum is measured in a coordinating
solvent, such as the THF (Fig. 5b).
In conclusion, we have established a suitable
synthetic procedure for the preparation of b-fused
porphyrin-phthalocyanine array. The star shaped array
6 shows a strong tendency toward aggregation, which
is a serious drawback for a complete characterization
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SYNTHESIS AND CHARACTERIZATION OF A b-FUSED TETRAPORPHYRIN-PHTHALOCYANINE STAR-SHAPED ARRAY
7
N
N
N
N
N
N
N
N
Zn
Zn
N
N
N
N
N
Zn
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Zn
Zn
6
Scheme 3. Structure of 6
Fig. 5. UV-visible spectra of 6 in (a) CHCl3 (full line), CHCl3 + pyridine (dotted line) and (b) THF
of the properties of the compound. However it should
material. This material is available free of charge via the
be noted that this problem can be significantly reduced
by a judicious choice of the meso-aryl groups of the
porphyrin subunits, and these studies are now ongoing
in our laboratories.
Internet at http://www.worldscinet.com/jpp/jpp.shtml.
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Center (CCDC) under
numbers CCDC-1453163, CCDC-1453164, CCDC-
1453165. Copies can be obtained on request, free of
charge, via www.ccdc.cam.ac.uk/data_request/cif or from
the Cambridge Crystallographic Data Center, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: +44 1223-336-033
or email: data_request@ccdc.cam.ac.uk).
Supporting information
1H NMR spectra for 2, 4 and 5 and mass spectra of 2,
4, 5 and 6 (Figs S1–S7) are given in the supplementary
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F. MANDOJ ET AL.
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