Phosphoniumyl cationic porphyrins Self-aggregation origin from π-π and cation-π interactions

Article abstract of DOI:10.1039/a703965d

The electrospectroscopic properties of four cationic porphyrins possessing phosphoniums residues in the periphery of the porphyrin plane are investigated in aqueous and organic solvent phases. The electronic spectra of the phosphoniumyl porphyrins in pure

Full text of DOI:10.1039/a703965d

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Phosphoniumyl cationic porphyrins
Self-aggregation origin from p–p and cation–p interactions
Ren-Hua Jin,* Shinya Aoki and Kensuke Shima
Department of Materials Science, Faculty of Engineering, Miyazaki University, Miyazaki 889-21,
Japan
The electrospectroscopic properties of four cationic porphyrins possessing phosphoniums residues in the periphery of the porphy-
rin plane are investigated in aqueous and organic solvent phases. The electronic spectra of the phosphoniumyl porphyrins in pure
water and in the presence of inorganic and organic electrolytes are compared, and it is proposed that self-aggregation of the
phosphoniumyl porphyrins arises from pÈp interaction forming H-aggregates and that this geometry can be transformed into
J-aggregates by cationÈp interaction between the porphyrin plane and the peripheral phosphonium cations on addition of NaCl.
1
H NMR spectra provide evidence that the highly polarizable phosphonium cation interacts strongly with the highly polarizable
porphyrin p-surface.
For this purpose, a derivative of tetra(phenyl)porphyrin
bearing active chloromethyl groups in the para-position of the
meso-phenyl ring was synthesized,6 so that the chloromethyl
group could be reacted with amines, pyridines, phosphines
and sulÐdes as well as many nucleophiles in order to yield the
corresponding cationic porphyrins or other derivatives. In this
paper, we report the solution chemistry of a new cationic
porphyrin family containing phosphonium units in both
aqueous and organic media.
Introduction
Water soluble cationic porphyrins are currently of interest
because of their possible wide applications, such as in supra-
molecular architecture, in photochemical cleavage of DNA, in
water splitting reactions and as mimics of energy transfer
systems.1 Most attention has focused on the tetrakis(methyl-
pyridiniumyl)porphyrins (TPyPs), and the fundamental
research about TPyPs in the area of solution chemistry has
concluded some inconsistent results from various independent
groups.2 Compared with organic solvent soluble porphyrin
systems, where a large number of well-deÐned porphyrins
have signiÐcant roles in chemistry,3 water soluble cationic
porphyrins have not been systematically documented, prob-
ably because not much e†ort has been made towards their
synthesis. Many of the reports concerning water soluble
cationic porphyrins have argued that the peripheral structures
of the porphyrin plane play an important role in their incorp-
oration of guest molecules and also their self-assembly proper-
ties.4 In the cationic porphyrin systems, our interest is mainly
aimed at the following ideas. First, the macrocyclic p-plane of
the cationic porphyrin not only has a strong hydrophobic
feature but is also highly polarizable. Thus, porphyrins dis-
solved in water do not allow many water molecules to lie over
the p-plane. Second, the p-surface of the porphyrin is elec-
tronically negative due to the quadrupole moment of the
quadrupole moment of the p-plane and this makes it possible
to promote the cationÈp interaction between the face of the
porphyrin and the cation. In view of the recent progress in
molecular recognition and biomimetic systems, one of the
most interesting events is the cationÈp interaction;5 this inter-
action plays an extremely important role in water soluble
molecular systems, such as in the structure and function of
proteins, and in ion channels and in molecular recognition
hosts.
Results
Synthesis
As shown in Scheme 1, the cationic porphyrins PorÈPPh,
PorÈPBu,
ZnPorÈPPh,
ZnPorÈPBu,
ZnPorÈDABCO
(DABCO \ diazabicyclo[2.2.2]octane) were conveniently
obtained from the reaction of tetrakis(p-chloromethylphenyl)
porphyrin (CMPP) or ZnCMPP with the corresponding
phosphine or amine (DABCO). In particular, the reaction
between ZnCMPP and DABCO was very facile and yielded
quantitatively the corresponding cationic porphyrin
(possessing DABCO residues) within 2 h. This result is signiÐ-
cantly di†erent to those for trialkylamines, such as N(C H )
2 5 3
and N(C H ) , which required long reaction times6 (data not
4 9 3
listed). All the cationic porphyrins gave satisfactory structures
as determined by 1H NMR.
Soret bands and the environment
The phosphoniumyl porphyrins, PorÈPPh, PorÈPBu, ZnPorÈ
PPh, ZnPorÈPBu, have four positive charges in the periphery
of the p-plane of the porphyrins. The cationic sites are separ-
ated within the TPP framework by methylene bridges. Thus,
these tetra-cationic porphyrins are distinguishable from pre-
vious cationic porphyrins, such as TPyPs and tetra(trimethyl-
ammoniumylphenyl)porphyrin (whose cationic centres can
inÑuence the electronic density of the meso-phenyl or pyridyl
rings by an inductive e†ect). For TPyPs, the positive charge
on the pyridinium nitrogen atoms may be delocalized over the
porphyrin plane through resonance structures.2f Because the
above porphyrins prevent the delocalization of the positive
charges of the cations, there will be less of a bonding e†ect
from the cations on the electronic properties of the porphyrin
With regard to their structural character, the cationic
porphyrins are a family bearing onium units, such as ammon-
ium (or pyridinium), phosphonium and sulfonium. However,
the cationic porphyrins researched so far are almost limited to
the nitrogen cationic centre, including ammonium and pyri-
dinium. Our interest is the introduction of nitrogen, phos-
phorus and sulfur atoms into the periphery of the porphyrin.
J. Chem. Soc., Faraday T rans., 1997, 93(22), 3945È3953
3945

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width at half-height peak (W ) are listed. The wavelength for
1
@2
PorÈPPh remained constant at 416 nm without any concen-
tration dependence, but the Soret band for PorÈPBu was
shifted to 415 nm from 422 nm as the concentration was
increased from 0.1 to 10 lM. It is very interesting that when
the concentration of PorÈPBu was adjusted to 2.0 lM, two
peaks from Soret bands at 420.0 and 415.0 nm with absorb-
ances of 0.588 and 0.576 (see Fig. 1) appeared. At this concen-
tration
W
also increased signiÐcantly. Above this
1@2
concentration, the Soret bands became one peak at a blue-
shifted wavelength of 414.8 nm. By using water as solvent
instead of methanol in this experiment, we observed a di†erent
tendency. In water, the band-width was signiÐcantly increased
as the concentration was increased although the wavelength
for the Soret band of PorÈPPh did not change. For PorÈPBu
in water the Soret band appeared at a relatively short wave-
length (414 nm) even over a wide concentration range, and the
band width only increased at higher concentration (10 lM).
For both ZnPorÈPPh and ZnPorÈPBu in aqueous medium,
the concentration of porphyrins signiÐcantly inÑuenced the
Soret band peak (see Table 2). j
appeared above 430 nm at
max
extremely dilute concentrations (e.g. 0.1È0.5 lM); over this
concentration the Soret band was greatly blue-shifted (by 8È10
nm). However, with MeOH the Soret band appeared at 422È
424 nm with both high and lower concentrations of zinc phos-
phoniumyl porphyrins.
Soret band and NaCl e†ect. Many reports about water
soluble cationic or anionic porphyrins demonstrate that
aggregation of porphyrins takes place as electrolytes are
Scheme 1
plane. In other words, the electronic properties of the Ñat p-
surfaces of the non-cationic CMPP and the cationic porphy-
rins must be identical. With this in mind, we made a detailed
investigation of the Soret bands of these porphyrins in
aqueous and organic solutions.
added. In general, addition of electrolytes, such as KNO ,
3
NaCl and KCl, makes the Soret band red-shift.2b,7 Compared
with the Soret bands for the aggregates caused by the concen-
tration of porphyrins, the aggregates induced by addition of
electrolytes have signiÐcantly di†erent Soret bands.
As summarized in Table 3, the phosphoniumyl porphyrins
exhibited a unique change in response to the concentration of
NaCl. PorÈPPh (5 lM) in water showed a very broad Soret
band at 415.8 nm. Addition of 0.1 M NaCl to an aqueous solu-
tion of PorÈPPh caused a red-shift (427.5 nm) of the Soret
band and a lower absorbance. When the concentration of
NaCl increased to 0.3 M the Soret band split into three peaks,
appearing at 407, 427 and 441 nm (see Table 3 and Fig. 2).
Solvent and wavelength. Table 1 shows the wavelength of the
Soret bands for the cationic and neutral porphyrins in several
organic solvents and/or in water. The wavelength of CMPP
(
which is insoluble in water) shifted in the range 413.5È419.2
nm with di†erent solvents; the wavelength shift is related to
the solvent polarizability (discussed below). The other cationic
porphyrins also displayed similar responses, although the
cationic substituents are di†erent each other. Apparently, the
Soret bands for the cationic porphyrins appeared at longer
wavelengths in DMSO but were blue-shifted in MeOH. It
should be noted that the cationic porphyrins are freely soluble
in both DMSO and MeOH, but the behavior of the porphy-
rins are opposite in these two solvents.
E†ect of concentration. By using water and methanol as sol-
vents, we determined the relationship between concentration
and the Soret band. The details are summarized in Table 2,
where wavelength (jmax), absorbance (A) at jmax and band-
Table 1 Soret bands of porphyrins in various solventsa
jmax/nm
solvent
a/Ó3
TTPb
CMPP
PorÈPPh
PorÈPBu
H O
2
MeCN
acetone
DMF
CHCl
DMSO
1.47
3.28
4.86
6.33
7.31
8.34
8.87
415.7
415.2
416.0
416.6
419.2
420.6
420.0
413.6
414.8
415.3
416.1
418.8
420.1
420.0
MeOH
413.4
414.3
414.7
417.9
419.2
419.2
413.5
414.0
414.7
418.1
419.2
419.2
3
Fig. 1 Plot of j
for the Soret band versus the concentrations of
PorÈPBu in methanol. Insert: proÐles of UVÈVIS spectra at di†erent
concentrations of PorÈPBu.
max
a Concentration of the porphyrins was ca. 5 lM. b TTP \ 5, 10, 15,
0-tetra-p-tolylporphyrin.
2
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Table 2 Soret bands of tetracationic porphyrins in methanol and water
MeOH
H O
2
conc./lM
jmax/nm
W1@2/nm
A
jmax/nm
W1@2/nm
A
PorÈPPh
PorÈPBu
0.1
415.9
415.4
415.6
415.2
415.2
415.5
416.0
12.5
12.6
12.6
12.6
15.0
16.3
18.8
0.026
0.151
0.401
0.789
1.922
2.254
2.372
0
1
2
5
7
0
.5
.0
.0
.0
.0
415.6
416.0
416.0
416.4
416.4
416.4
16.3
21.3
24.5
27.0
28.8
29.5
0.071
0.143
0.337
1.087
1.46
1
1
1
1
1.83
0.1
422.3
422.3
422.0
10
12
13.8
17.5
17.5
17.5
18.8
0.027
0.182
0.376
0
1
2
5
7
0
.5
.0
.0
.0
.0
413.5
414.0
414.0
413.6
413.5
413.9
12.5
12.5
12.5
13.5
14.8
17.5
0.038
0.245
0.491
1.528
1.896
2.237
420.0/415.0
414.8
0.588/0.576
1.523
414.7
415.2
2.013
2.292
ZnPorÈPPh
ZnPorÈPBu
0.1
423.9
424.0
424.0
424.0
424.0
423.4
423.9
10
0.048
0.292
0.596
1.195
2.138
2.210
2.243
432.9
431.8
426.0
424.0
423.1
423.5
424.1
25
25
25
22
22
23
25
0.024
0.070
0.138
0.410
1.321
1.793
2.172
0
1
2
5
7
0
.5
.0
.0
.0
.0
9.5
9.8
9.5
11.8
14.3
17
0.1
422.5
423.0
422.9
422.7
422.5
421.5
419.7
9.0
10
10
0.022
0.269
0.550
1.105
2.067
2.150
2.195
430.7
431.6
422.0
422.0
421.6
421.6
420.1
27.7
27.7
13.8
12.3
14.3
15.8
21.8
0.026
0.045
0.206
0.547
1.614
2.075
2.273
0
1
2
5
7
0
.5
.0
.0
.0
.0
9.3
11.8
13.8
16.8
Further increase in the concentration of NaCl, to 1.0 M, did
not change this pattern. At a concentration of NaCl of 2.0 M,
the bands formed one band at 427 nm. A similar result was
also observed for PorÈPBu. The Soret band of PorÈPBu was
abruptly red-shifted from 413.8 nm (in the absence of NaCl) to
425.7 nm (in the presence of NaCl) and the absorbance was
markedly decreased. The Soret band at 425 nm was split into
three peaks when the concentration of NaCl was increased to
1.0 M. A longer wavelength peak appeared at 439 nm and a
shorter wavelength peak was seen at 409 nm (Fig. 2).
However, for ammoniumyl cationic porphyrins with triethyl-
or tributyl-ammonium residues splitting of the Soret band and
large red-shifts were not observed (data not shown) even when
NaCl was added over a wide concentration range. The addi-
tion of NaCl to the solutions of zinc phosphoniumyl porphy-
rins, ZnPorÈPPh and ZnPorÈPBu, gave di†erent results. The
Soret band for ZnPorÈPPh was signiÐcantly red-shifted to
448 nm, but the half-width remained at 33 nm. For ZnPorÈ
PBu the Soret band red-shifted with a dramatic decrease in
absorption, the half-width also increased signiÐcantly as the
concentration of NaCl increased; the largest wavelength shift
was 9 nm (Table 4).
Fig. 2 Absorption spectra of (a) PorÈPBu and (b) PorÈPPh at di†er-
ent concentrations of NaCl. Porphyrin concentration \ 5 lM. Split
band: (a) 409.3, 423.0 and 438.9 nm (1.0 M NaCl); (b) 407.4, 426.9 and
4
41.1 nm (0.3 M NaCl).
Table 3 E†ect of concentration of NaCl on the Soret band of phosphoniumyl porphyrinsa
PorÈPPh
PorÈPBu
[NaCl]/M
A(jmax/nm)
A(jmax/nm)
0
0
0
0
0
1
2
.0
.1
.3
.5
.7
.0
.0
1.116(415.8)
0.838(427.5)
0.553(426.9)
0.598(426.9)
0.593(425.9)
0.530(425.9)
0.526(425.9)
1.488(413.8)
0.978(425.7)
0.937(425.1)
0.875(425.1)
0.690(425.0)
0.546(424.2)
0.571(423.0)
0.329(407.4)
0.364(407.9)
0.359(407.3)
0.334(407.4)
0.589(441.1)
0.606(440.7)
0.577(440.3)
0.492(440.3)
0.459(439.1)
0.420(439.2)
0.481(438.9)
0.424(409.3)
a Concentration of porphyrins in H is 5 lM.
2
J. Chem. Soc., Faraday T rans., 1997, V ol. 93
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Table 4 E†ect of concentration of NaCl on the Soret band of zinc phosphoniumyl porphyrinsa
ZnPorÈPPh ZnPorÈPBu
[NaCl]/M
A(jmax/nm)b
W1@2/nm
A(jmax/nm)c
W1@2/nm
0
0
0
0
0
1
2
.0
.1
.3
.5
.7
.0
.0
1.190(424.4)
0.980(431.8)
23.0
24.5
35.8
33.0
33.0
33.8
34.3
1.614(422.0)
12.5
23.3
24.5
26.5
26.8
35.5
49.5
1.023(435.9)
0.726(440.0)
1.168(424.2)
1.100(425.9)
1.020(425.4)
0.819(424.9)
0.341(426.9)
1.161(427.6)
1.100(428.0)
1.008(428.4)
0.770(430.9)
0.743(448.3)
0.858(448.1)
0.831(448.4)
0.763(447.6)
0.781(448.4)
È
È
0.45(broad peak 430È450)
a Concentration of porphyrins in H O is 5 lM. b Peak with shoulder at longer wavelength appeared. c Peak with shoulder at shorter wavelength
2
appeared when NaCl was added.
The results above indicate that the aggregation of cationic
porphyrins is strongly inÑuenced by the addition of electro-
lyte; the aggregation behaviors di†ered depending on the
cationic center, the substituents and the central metal.
tion. Hence, we believe that interpretation of these results will
be very important in establishing the interaction mechanism
that relates to the formation of monomeric, dimeric, and poly-
meric cationic porphyrins. As with many other spectroscopic
techniques,9 such as Ñuorescence spectrometry, NMR, EPR,
Raman spectrometry and dynamic photolysis, UVÈVIS spec-
troscopy is a very prominent and simple tool to aid research
into the ground-state chemistry of porphyrins and informa-
tion obtained from UV-VIS spectroscopy is also valid for use
in gaining an understanding of the geometry of the aggre-
gates.10 We found that the Soret bands of the cationic
porphyrins used here were very sensitive to several factors,
such as the solvent, the concentration of the porphyrins and
the addition of electrolytes, whereas the Q-bands are far less
a†ected by these factors.
The e†ect of concentration on the Soret band showed that
for a deÐned concentration of PorÈPBu two Soret bands
appeared at 420 and 415 nm; below this deÐned concentration
one Soret band was observable at longer wavelength and
above this concentration a single Soret band appeared at
shorter wavelength. Such a “critical concentrationÏ (CC) was
also observable for the zinc forms of the phosphoniumyl
cationic porphyrins. This phenomenon strongly suggests that
these porphyrins exist mainly as monomers below the CC but
as dimers over the CC. The dimers should contribute to the
formation of face-to-face geometry because of the blue-shift of
the Soret band.4a,10d,11 In the relations between the Soret
band absorbance and the concentrations in both water and
methanol, we did not Ðnd that BeerÏs law was obeyed for the
cationic porphyrins. In particular, PorÈPPh exhibited an
extremely broad band with a shoulder (at shorter wavelength)
in water. However, in DMSO solution, it was found that a
plot of the absorbance of the Soret band (at 420 nm) versus
the concentration of PorÈPPh (to 5 lM) gave a linear relation,
with a constant band-width (see Table 6) of 15 nm. The e†ect
of solvent is also evident from the 1H NMR spectra for
PorÈPPh (Fig. 3). The b-protons give a sharp single peak in
E†ect of anionic aromatic electrolyte. Anionic or cationic
aromatic compounds are usually used with cationic and
anionic porphyrin systems in order to establish interaction
models
for
porphyrins
with
substrates.7a,8
Here,
anthraquinone-2,6-disulfonic acid disodium salt (DSAQ) was
selected as the anionic aromatic electrolyte, and its e†ects on
the Soret band of the cationic porphyrins were investigated.
Compared with the e†ects of NaCl on the Soret bands, the
inÑuence of DSAQ started at very low concentrations, e.g.,
micromolar ranges. Setting the porphyrin concentration at 5
lM, we varied the concentrations of DSAQ from 5 to 100 lM.
For PorÈPPh, the addition of an equimolar amount of DSAQ
made the Soret band red-shift from 416 nm (without DSAQ)
to 426 nm and resulted in a decrease in absorbance (see Table
5). As the DSAQ concentration was increased to twice equi-
molar, the Soret band was split into three peaks (similar to the
case when adding NaCl). When the molar ratio of DSAQ to
porphyrin was [14, the three bands recombined into one
band, which is also seen with NaCl. Hence, it can be said that
aggregates having the same geometry resulted from both inor-
ganic and aromatic sodium salts. The Soret band for ZnPorÈ
PPh was only red-shifted to 434 nm, even when the
concentration of DSAQ was increased signiÐcantly. On the
other hand, the free-base form of the butyl-substituted phos-
phoniumyl porphyrin, PorÈPBu, did not show the Soret band
splitting under the same experimental conditions (see Table 5),
although it did split in the presence of NaCl. As the ratio of
porphyrin to DSAQ was increased, the Soret band for
PorÈPBu gradually red-shifted from 413 nm to 423 nm, the
band-width increased dramatically accompanied by
reduction in absorption.
a
[
2H ]DMSO that broadens in [2H ]methanol. In D O, the
Discussion
6
4
2
total signal becomes complex with other new peaks appearing.
From these results, it could be concluded that PorÈPPh is
favored to exist as a monomer in DMSO. We can see from
All the results described above are very interesting with regard
to the investigation of the structureÈmediumÈaggregate rela-
Table 5 E†ect of concentration of DSAQ on the Soret band of phosphoniumyl porphyrinsa
PorÈPPh
PorÈPBu
ZnPorÈPPh
[DSAQ]/[Por]
A(jmax/nm)
A(jmax/nm)
W1@2/nm
A(jmax/nm)
W1@2/nm
0
1.116(415.8)
0.613(426.0)
0.614(427.2)
0.348(429.2)
0.248(429.0)
0.214(429.9)
0.198(429.9)
0.483(429.2)
1.488(413.8)
0.725(419.2)
0.726(420.4)
0.703(420.2)
0.616(421.5)
0.476(422.0)
0.459(421.6)
0.476(423.1)
13.3
27.5
31.3
30.5
35.0
39.5
40.0
40.5
1.280(423.1)
0.982(427.9)
0.836(431.0)
0.585(432.7)
0.699(433.8)
0.645(434.7)
0.592(436.0)
0.614(434.4)
20.8
27.0
27.0
26.8
28.8
30.0
30.0
30.0
1
1
2
6
0
4
0
.0
.4
.0
.0
0.146(409.0)
0.131(409.0)
0.115(409.0)
0.109(409.0)
0.304(440.3)
0.242(441.5)
0.204(441.1)
0.187(441.6)
1
1
2
a Concentration of porphyrins in H O is 5 lM.
2
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neutral CMPP exist as monomers because DMSO has a rela-
tively high polarizability. DMSO inhibits the interaction
between the p-surfaces of the porphyrins, even for a porphyrin
dimer linked covalently face-to-face.16 The cationic porphy-
rins are less soluble in chloroform. The Soret band appeared
at 420 nm indicating that the cationic porphyrins exist as
monomers due to the high polarizability of chloroform. DMF
also inhibits self-aggregation of the porphyrins. Previous
reports about anionic and/or cationic porphyrins describe
self-dimerization with a face-to-face model in which the per-
ipheral octa-ionic charges take a cross-arranged geometry8b to
overcome charge repulsion. The dimeric form has octa-
cationic charges but the area of its hydrophobic surface is the
same as that of a monomer, so that the hydrophility of the
dimer can become larger than that of monomers.
As described above (Table 5 and Fig. 2), addition of electro-
lytes (inorganic and aromatic) to the dimeric (or polymeric)
porphyrins in aqueous solution induced a red-shift of the
Soret bands. However, the extent and pattern of the red-shift
are di†erent for each cationic porphyrin. Por-PPh (5 lM) in
water shows a Soret band at 416 nm, which red-shifted by 10
nm at a deÐned concentration of NaCl or DSAQ. A further
increase in the concentration of the electrolytes induced a split
of the band at 427 nm and two extra peaks appeared (one at a
higher and one at a lower wavelength). This indicates that the
species absorbing at 427 nm were transformed into di†erent
species. Two problems now attract our attention: (i) why do
the inorganic sodium salt and the aromatic sodium salt lead
to the same spectra and (ii) what species are formed after addi-
tion of the electrolytes. Inorganic electrolytes that induce
aggregation of ionic porphyrins have been reported pre-
viously.2b,7 It is generally believed that neutralization of the
positively or negatively charged porphyrins by the inorganic
electrolytes reduces the electrostatic repulsion between the
ionic charges on the periphery of the porphyrins so that
aggregation takes place more easily. For PorÈPPh, the split of
the Soret band appeared only at a concentration of 10 lM
DSAQ where the molar ratio of the positive (porphyrin) to
negative charges (DSAQ) is just 1; the e†ect of adding 10 lM
DSAQ is equal to that of adding 0.3 M NaCl. The identical
UVÈVIS spectral pattern for PorÈPPh in the presence of
NaCl and the aromatic electrolyte (DSAQ) provides unam-
biguous evidence that the “productsÏ have the same structures.
In other words, the spectra of the aggregates do not relate to a
pÈp stacked complex beween the p-plane of the porphyrin and
the p-plane of DSAQ. In our opinion, the neutralization
hypothesis is inadequate for our system. In practice, PorÈPPh
as well as other cationic porphyrins also exist as aggregates in
which the face-to-face geometry (H-aggregate) is dominant in
the absence of electrolytes. This means that formation of H-
aggregates does not need neutralization of the cationic
charges. Addition of electrolytes causes a large red-shift, which
suggests the formation of J-aggregates.10d,17 The aggregates
have split Soret bands that return to the state before splitting
upon large increases in the concentration of electrolytes.
Therefore, we conclude that the morphology of the aggregates
of PorÈPPh, as induced by the addition of electrolytes, can be
controlled precisely by the concentration of the electrolytes.
Fig. 3 1H NMR proÐles of PorÈPPh in di†erent deuterated solvents.
For D O, 10% v/v deuterated methanol was included to dissolve the
2
PorÈPPh completely.
Table 1 that j
evidently blue-shifts with decreasing solvent
max
polarizability, this is because of the high polarizability (60.97
Ó3 for the p-plane) of porphyrin,12,13 i.e., a highly polarizable
solvent interacts e†ectively with the highly polarizable p-plane
of the porphyrin. Therefore, the p-plane of the porphyrin can
be sufficiently isolated in the solvent “clusterÏ, and the solvated
p-face hardly aggregates together. Water and methanol have
high cohesive interactions even though their molecular polari-
zabilities are very low. This feature often promotes the hydro-
phobic and/or van der Waals interactions between the apolar
solutes dissolved in water and leads to aggregation.14 This is
also possible with the cationic porphyrin used in this work;
little of the water lies on the highly polarizable and largely
hydrophobic15 porphyrin plane. Hence, we think that an
interaction between the p-surface and the low polarizability
solvent is unfavorable. It is probable that for this reason the
porphyrin stacks in water and in MeOH give face-to-face
aggregates. For PorÈPPh in aqueous solution, the extremely
wide band-width probably means that there are some other
species present, including dimers and oligomers (the 1H NMR
proÐle in D O also supports this possibility). However, in
2
methanol,thedimermustbethemajoraggregatingspecies.Other
cationic porphyrins, e.g. PorÈPBu, and zinc forms also exist as
dimers in water. In DMSO the cationic porphyrins and
Table 6 Absorbance and wavelength of PorÈPPh in DMSO
[PorÈPPh]/lM
A(jmax/nm)
W1@2/nm
0
0
1
2
5
7
0
.1
.5
.0
.0
.0
.0
0.034(421.6)
0.173(420.2)
0.348(420.7)
0.712(420.2)
1.786(420.0)
2.444(419.5)
2.526(419.0)
È
È
È
È
È
È
È
È
14.3
14.3
13.8
13.8
14.3
17.0
18.0
0.029(513.7)
0.043(514.1)
0.094(514.1)
0.133(515.1)
0.172(515.3)
0.023(551.7)
0.031(551.5)
0.057(550.4)
0.079(549.6)
0.100(551.4)
0.019(591.6)
0.024(591.0)
0.040(590.2)
0.052(591.1)
0.066(590.7)
0.019(645.8)
0.021(645.8)
0.033(645.7)
0.043(645.6)
0.052(645.6)
1
J. Chem. Soc., Faraday T rans., 1997, V ol. 93
3949

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be induced (discussed below). Mauzerall15 compared the e†ect
When the e†ect on aggregation of adding electrolytes was
measured at 80 ¡C, spectral patterns were observed that were
the same as those obtained at room temperature. This means
that the transformation of the H-aggregate into the J-form is
not a†ected by temperature. Di†erent from the free base form,
ZnPorÈPPh (5 lM) was red-shifted by 24 nm in the presence of
a deÐnite amount of NaCl, but by only 10 nm in the presence
of over 10 lM of DSAQ. From these shifted patterns, it can be
said that the addition of NaCl to ZnPorÈPPh solution
induced the transformation10d,18 of H-aggregates into J-
aggregates, whereas addition of DSAQ to the solution
resulted in monomeric porphyrins with deaggregation of the
H-form. It is probable that the zinc metal plays a role in
strengthening the interaction between ZnPorÈPPh and
DSAQ.
In the H-aggregates of PorÈPPh, ZnPorÈPPh and PorÈ
PBu, the pÈp stacking is probably a loose interaction because
of the bulky cationic sites so that the H-form transforms into
the J-form when NaCl is added. What is the role of electro-
lytes in this transformation? If neutralization of the charges
on the porphyrin causes the transformation, we should not
need such high concentrations (molar range) of NaCl to neu-
tralize the micromolar positive charges. Before considering
these problems, it should be emphasized that the aromatic
p-face has two negatively charged p-electron clouds that sand-
wich a positively charged r-framework.5,19 This is the case for
the porphyrin p-plane. Therefore, we propose the following
mechanism for the transformation of aggregate geometry
of the size of cation on the electronic spectra of uroporphyrin
III in aqueous solution and proposed that large cations,
including quaternary ammoniums, pyridiniums and Cs`, are
more likely to interact with uroporphyrin than are small
cations, such as Li`, Na` and K`. In our study, the ammon-
iumyl porphyrins did not exhibit J-aggregation spectral pat-
terns in the presence of NaCl (data not listed).6 Considering
the fact that the solvents having high polarizability prefer to
interact with the highly polarizable porphyrin plane, the
ability of phosphoniumyl porphyrins to form J-aggregates
would be contributed to by the large atomic polarizability21
of phosphorus (24.5 Ó3), which is larger than nitrogen (7.4 Ó3).
We think that the geometry of the aggregates of the phos-
phoniumyl porphyrins depends upon both the nature of the
interaction and the structure of phosphonium. The van der
Waals attractive force and/or hydrophobic interactions result
in face-to-face geometry, but the electrostatic attractive force
(cationÈp interaction) gives o†set J-geometry. On the basis of
the extent of the red-shift, it can be said that the strength of
the interactions between phosphonium and the p-surface of
porphyrin would be larger for the [P`Ph cation than for
3
[P`Bu cation; the polarizability of the phosphoniumyl resi-
3
dues is 40.20 and 33.63 Ó3, respectively.12 The transformation
of H- into J-aggregates for PorÈPPh that accompanies the
addition of a small amount of DSAQ can also be ascribed to
the fact that DSAQ weakens the van der Waals force between
the p-surfaces of the dimeric porphyrins, which results in
(
Scheme 2).
cationÈp interactions betweeen the peripheral [P`Ph and
3
Addition of a large amount of NaCl to water results in sol-
the porphyrin plane. As a consequence, we suggest that the
vated Na`. Hence, the water-shelled Na` attracts the p-
surface of porphyrin by electrostatic interaction even over a
long distance. This driving force weakens the van der Waals/
hydrophobic interactions between the p-surfaces leading to
deformation of the face-to-face geometry. As a response to the
driving force from the Na`, the two p-surfaces in face-to-face
dimer slide20 to give an o†set stacking19 where a new close
contact caused by cationÈp interactions between the periph-
eral phsophoniumyl charge and the p-plane of porphyrin can
cationÈp interactions between the large peripheral phos-
phonium cation and the large p-plane for phosphoniumyl
porphyrins are promoted by the inorganic and aromatic salts.
In order to conÐrm the existence of the interactions
between the phosphonium and the p-plane of porphyrins, we
examined the e†ect of benzyltriphenylphosphonium chloride
(BTPP), which has the same structural cationic residue as the
triphenylphosphoniumyl porphyrins, on aggregates of
PorÈPPh and ZnPorÈPPh. The Soret band was slightly red-
shifted and the band-width narrowed as the concentration of
BTPP increased (see Table 7). On the other hand, the absorp-
tion intensity returned to its initial level when the amount of
BTPP was further increased. As a result, monomeric porphy-
rin formed completely in the presence of 100-fold BTPP; the
spectral pattern was similar to that in DMSO solution, i.e.,
cationic porphyrins in water aggregate only slightly as highly
polarizable phosphonium salt is added. It became apparent
that H-aggregates deaggregated on addition of BTPP to a
solution of the above two porphyrins, and that the deaggrega-
tion procedure depended on the concentration of BTPP. This
deaggregation can be explained by BTPP interacting strongly
with the surface of the porphyrins. It can be concluded that
Scheme 2
Table 7 E†ect of BTPP on the absorption spectra of PorÈPPh and ZnPorÈPPha
[BTPP]/10~3 M
A(jmax/nm)
W
(Soret bands)
1@2
PorÈPPh
0
0
0
1
5
0
1.116(415.8)
1.051(416.4)
0.806(417.1)
0.720(418.4)
0.736(421.6)
1.032(422.7)
0.064(517.6)
0.070(519.7)
0.076(520.7)
0.077(520.5)
0.071(519.9)
0.067(518.8)
0.044(554.7)
0.052(555.5)
0.062(556.0)
0.064(557.0)
0.057(557.0)
0.049(544.8)
0.027(585.5)
0.034(587.6)
0.046(591.4)
0.049(591.9)
0.044(590.0)
0.034(590.8)
0.022(643.2)
0.031(643.1)
0.041(644.4)
0.044(644.7)
0.041(645.6)
0.031(643.3)
28
.1
.5
.0
.0
28.8
27.5
28.8
20.5
16.8
1
ZnPorÈPPh
0
0
0
1
5
0
1.699(420.7)
1.740(420.7)
1.726(421.1)
1.618(420.9)
1.596(422.7)
1.432(424.2)
0.064(554.9)
0.066(555.7)
0.067(556.0)
0.066(555.9)
0.072(556.9)
0.064(557.0)
0.029(595.5)
0.029(595.5)
0.030(594.6)
0.031(596.3)
0.034(596.5)
0.031(596.8)
10.8
10.8
11.3
11.3
12.5
12.5
.1
.5
.0
.0
1
a Concentration of the porphyrins was 5 lM.
950 J. Chem. Soc., Faraday T rans., 1997, V ol. 93
3

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It can be seen from Fig. 4 that the protons on the periphery of
the porphyrin, such as p-CH , CH CH (on DABCO), o-H,
the phosphonium chloride added prevents the cationÈp aggre-
gation of phosphoniumyl porphyrins, whereas NaCl induces a
cationÈp interaction between the peripheral phosphonium and
the p-plane of phosphoniumyl porphyrins. By using ZnPorÈ
DABCO, which is freely soluble in water, we investigated the
interactions between ZnPorÈDABCO and BTPP in aqueous
solution using 1H NMR. Fig. 4 shows the NMR spectra for
BTPP, ZnPorÈDABCO and a mixture of BTPPÈ(ZnPorÈ
DABCO) (2 ] 1). The peaks were identiÐed by homo-
decoupling. All of the signals, including one benzyl and three
phenyl groups for BTPP, were apparently shifted upÐeld
2
2
2
m-H (on the meso-phenyl ring) and the b-protons of ZnPorÈ
DABCO, were shifted downÐeld; the downÐeld shifts for the
b-protons and o-H, which are near the porphyrin plane, were
very slight. Perhaps the interaction of BTPP with the p-
surface of the porphyrin slightly increases the deshielding
power of the porphyrin to the peripheral residues. We found
that when the mixture of BTPP and ZnPorÈDABCO was
heated to 80 ¡C from 27 ¡C the upÐeld pattern for the protons
of BTPP was not changed. This means, at least, that the inter-
action between the phosphonium and the porphyrin plane is
very strong (a quantitative study of the interactions between
the phosphoniums and porphyrins is in progress and will be
published elsewhere).
We also performed a JobÏs plot for the mixture of BTPP
and ZnPorÈDABCO in aqueous solution (total concentration,
10 lM). Fig. 5 shows the results. Absorbences at di†erent
wavelengths, 421, 427 and 430 nm, were taken for this plot,
each peak maximum, for the three wavelengths, appeared at
nearly 0.5 molar composition, indicating that the porphyrin
complexes with BTPP at a ratio of 1 : 1.
(
without free BTPP peaks) when ZnPorÈDABCO was added
to the BTPP solution. The most signiÐcant upÐeld shift ([1.6
ppm) is seen for the CH peak with broadening. The order of
2
upÐeld shift for the benzyl group is as follows: CH [ o-H [
2
m-H [ p-H. For the phenyl protons, the upÐeld order is also
o-H, m-H [ p-H. These upÐeld shifts must arise from the
BTPP lying on the porphyrin plane where it is shielded by the
strong p-current e†ect of porphyrin.22 This result provides
unambiguous evidence that cationic BTPP strongly interacts
with the p-surface of porphyrin to form a cationicÈp complex.
We know from the above discussion that the behavior of
PorÈPBu in NaCl is similar to that of PorÈPPh, but the
response of PorÈPBu to DSAQ apparently di†ered to that of
PorÈPPh. No split of the Soret band appeared on adding
DSAQ to this porphyrin. JobÏs plots for PorÈPPh and
PorÈPBu with DSAQ were also examined. As shown in Fig. 6,
the JobÏs plot for the (PorÈPBu)ÈDSAQ mixture showed a
maximum for X (mol fraction of porphyrin) of 0.67 at 414 nm
p
and of 0.5 at 422 nm, indicating that the complexes between
PorÈPBu and DSAQ existed not only in the ratio of 2 : 1
(Por : DSAQ), but also 1 : 1. For the (PorÈPPh)ÈDSAQ
mixture, however, no information about the stochiometry
between PorÈPPh and DSAQ was observed.
For the typical cationic porphyrins, such as tetrakis(methyl-
pyridiniumyl)porphyrin and tetrakis(trimethylammoniumyl-
phenyl)porphyrin, the cationic centre is located at a Ðxed
position. Compared with this, the cationic sits on our cationic
porphyrins are quite “fruitfulÏ as the cationic atoms freely
rotate in relation to the methylene carbon. This rotational
feature must be important in the construction of the geometry
of the J-aggregates. We propose that the splitting of the Soret
band might be related to T-shape-like geometry (Scheme 2).
As reported by Maruyama and co-workers in their covalently
linked porphyrin dimer or polymer system, the Soret band
split appears as the two p-surfaces adopt a geometry having a
dihedral angle.23 That non-covalent porphyrin aggregates
Fig. 4 1H NMR proÐles of (a) BTPP (8 ] 10~3 M), (b) ZnPorÈ
DABCO (4 ] 10~3 M) and (c) a mixture containing BTPP (8 ] 10~3
M) and ZnPorÈDABCO (4 ] 10~3 M) in deuterated water. Upper: ali-
phatic proton region, 2.5È5.5 ppm. Bottom: aromatic proton region,
Fig. 5 JobÏs plot for (ZnPorÈDABCO)ÈBTPP in H O at di†erent
2
6
.2È9.2 ppm. Temperature \ 27 ¡C.
wavelengths. Total concentration \ 1 ] 10~5 M.
J. Chem. Soc., Faraday T rans., 1997, V ol. 93
3951

View Online
without further puriÐcation. Chloranil, boron triÑuorideÈ
diethyl ether, triethylamine, NaCl and DSAQ were purchased
from Wako Pure Chemical Co. and used without further puri-
Ðcation. DMF was used as the reaction solvent after drying
over 4 Ó molecular sieve. The solvents (DMSO, MeOH,
DMF, acetonitrile, acetone and chloroform) used in the
UVÈVIS analysis were a special grade of Wako Pure Chemi-
cal Co. Deionized water was used after distillation. BTPP was
synthesized by reaction of triphenylphosphine and benzyl
chloride, and the product was recrystalysed three times from
ether. TTP was obtained from Aldrich and puriÐed by column
chromatography using chloroform as eluent. p-Chloromethyl-
benzaldehyde, CMPP and the cationic porphyrins were syn-
thesized according to a previously reported method.6
CMPP. To a three-neck round bottomed Ñask equipped
with a condenser, a three-way stop-cock and a gas-bubbling
tube, p-chloromethylbenzaldehyde (0.31 g, 2.0 mmol), pyrrole
(0.14 g, 2.0 mmol) and chloroform (200 ml, dried over 4 Ó
molecular sieves) were added. The mixture was stirred with
bubbling by Ar for 10 min and boron triÑuorideÈdiethyl ether
Fig. 6 JobÏs plot for (PorÈPBu)ÈDSAQ in H O at di†erent wave-
2
lengths. Total concentration \ 1 ] 10~5 M.
result in such apparent Soret band splits indicates that the
aggregates have a highly speciÐc geometry with a stable dihe-
dral angle supported by a strong attractive force.
(
0.01 ml, 0.025 mmol) was added. Then the mixture was stirred
at room temperature for 1 h. Then, triethylamine (0.113 ml,
.51 mmol) and chloranil (0.37 g, 1.50 mmol) were added and
1
the mixture was reÑuxed for 1 h. The solvent was then
removed under reduced pressure. The residue was dissolved in
dichloromethane and any non-soluble impurities Ðltered o†.
The Ðltrate was concentrated to 30 ml, and 45 ml of methanol
was added. This solution was concentrated until the total
volume was reduced to 10 ml. The mixture was then Ðltered
and the Ðltrate evaporated o†. The solid residue was passed
through a silica column using chloroform as eluent. Yield, 0.19
Conclusions
Water soluble cationic porphyrins bearing phosphonium resi-
dues have a very strong self-aggregation power exhibiting pÈp
stacking geometry in pure water and in low polarizability sol-
vents. This aggregation depends upon the concentration of the
porphyrins. In particular, face-to-face aggregation takes place
below concentrations of 1 lM. Addition of NaCl or organic
salt (DSAQ) to aqueous solutions of the porphyrins can
induce transformation of the geometry from H- (face-to-face)
to J-aggregates. However, the formation and structure of the
J-aggregates are very sensitive to the structure of cationic resi-
dues. In the cationic porphyrin systems used here the Ñat p-
surface of the porphyrin is not altered structurally by the
peripheral cationic sites because the cationic centre is linked
to the meso-phenyl ring by a methylene bridge. Therefore, we
conclude that self-aggregation of the cationic porphyrins in
water is determined by the structure of the cationic site, and
that the cationÈp interaction between the peripheral cations
and the porphyrin plane also plays an important role in the
self-aggregation. Our work provides an important example in
investigating the relations between the self-assembly proper-
ties of cationic porphyrins and the peripheral cationic struc-
tures. We believe that the concept of cationÈp interaction
between the porphyrin face and the phosphoniumyl cation has
high potential utility in the building up of supramolecular
systems in aqueous solution. Further related work is in
progress.
g (47.5%). 1H NMR (250 MHz, in CDCl , TMS as internal
3
standard) d [2.8 (s, 2 H), 5.0 (s, 8 H), 7.7È7.8 (d, 8 H), 8.1È8.2
(
5
d, 8 H), 8.8 (s, 8 H). UVÈVIS (in CHCl ) j /nm 418.9, 515.4,
3
max
41.7, 590.0, and 648.4. SIMS (m/z) 808.
ZnCMPP. This was obtained according to a standard
method by reaction of free base CMPP with Zn(OAc) in
MeOHÈCHCl solution. The yield isolated by silica column
3
chromatography (CHCl as eluent) was 85%. 1H NMR (250
3
MHz, in CDCl , TMS as internal standard) d 5.0 (s, 8 H),
7.6È7.8 (d, 8 H), 8.1È8.3 (d, 8 H), 8.9 (s, 8 H). UVÈVIS (in
3
CHCl ) j /nm 423.0, 548.6 and 594.6. SIMS (m/z) 870.
3
max
Cationic porphyrins. The tetra-cationic porphyrins were pre-
pared according to the previous method6 from the reactions
of CMPP (or ZnCMPP) with excess (10 equiv. per ClCH
group) of the corresponding phosphines (or amines) in DMF
2
at 80 ¡C for 2 d (but 2 h for DABCO) under argon. Within
this reaction time, the ClCH groups completely reacted with
2
the phosphines (or amines) as conÐrmed by 1H NMR. The
DMF was then removed under reduced pressure and the resi-
dues dissolved in a small amount of methanol. This mixture
was then poured into ether to precipitate the cationic porphy-
rin. The solid obtained was reprecipitated twice in the same
manner. The method yielded quantitative amounts of the
cationic porphyrins.
Experimental
General
1
H NMR (250 MHz) spectra were recorded on a Bruker AC
250P spectrometer relative to an internal standard of TMS in
deuterated organic solvent or an internal standard of H O
2
(
4.83 ppm) in deuterated water. Stock solutions of cationic
Por–PBu. 1H NMR (250 MHz, in [2H ]DMSO, TMS as
porphyrins were prepared as 1 ] 10~3 M and used in dilution.
Absorption spectra were recorded in 1.0 cm pathlength quartz
cells at room temperature on a Hitachi 150-20 spectropho-
tometer using the solvents as references.
6
internal standard) d [2.9 (s, 2 H), 0.9È1.1 (t, 36 H), 1.5È1.6
(
m, 48 H), 2.5 (m, 24 H), 4.2È4.3 (d, 8 H), 7.8È7.9 (d, 8 H),
8
4
.2È8.3 (d, 8 H), 8.8 (s, 8 H). UVÈVIS (in MeOH) j /nm
max
14.8, 512.0, 550.7, 592.3 and 644.0. FABMS (m/z) 1545,
1
546 (M4` ] 2Cl~ [ H`)`, 1508, 1509, 1510, 1511
Reagents and solvents
(
M4` ] Cl~ [ H`), 1270.8, 1271.8 (M4` [ PBu ` [ 2H`)`,
3
Triphenylphosphine, tri-n-butylphosphine, pyrrole and
DABCO were purchased from Tokyo Kassei Co. and used
1069.6, 1070.6 (M4` [ 2PBu ` [ H`)`, 868.5, 869.5 (M4`
3
[ 3PBu `)`,
1472,
1473
(M4` [ 2H`)2`,
736.5
3
3952
J. Chem. Soc., Faraday T rans., 1997, V ol. 93

View Online
Koyama, T. Ema, A. Nomura, T. Yoshita and H. Ogoshi, Chem.
L ett., 1995, 941; (d) H. J. Schneider and M. Wang, J. Org. Chem.,
1994, 59, 7473.
D. A. Dougherty, Science, 1996, 271, 163.
R-H. Jin, S. Aoki and K. Shima, Chem. Commun., 1996, 1939.
(a) K. Kano, T. Nakajima and S. Hashimoto, J. Phys. Chem.,
1987, 91, 6614; (b) N. C. Maiti, M. Ravikanth, S. Mazumdar and
N. Periasamy, J. Phys. Chem., 1995, 99, 17192.
(a) K. Kano, T. Sato, S. Yamada and T. Ogawa, J. Phys. Chem.,
1983, 87, 566; (b) J. A. Shelnutt, Inorg. Chem., 1983, 22, 2535; (c)
K. Kano, M. Takei and S. Hashimoto, J. Phys. Chem., 1990, 94,
[
(M4` [ 2H`)2`/2], 636.0 [(M4` [ PBu ` [ H`)2`/2];
3
calc. 1476.1 for M4` (C
H
N P ).
9
6 142 4 4
Por–PPh. 1H NMR (250 MHz, in [2H ]DMSO, TMS as
5
6
7
6
internal standard) d [3.1 (s, 2 H), 5.6È5.7 (d, 8 H), 7.3È8.0
(
m, 76 H), 8.76 (s, 8, H). UVÈVIS (in MeOH) j /nm 414.8,
max
5
19.2, 555.6, 585.2 and 642.8. FABMS (m/z) 1711.8, 1712.8
(
1
M4` [ 3H`)`, 1449.6, 1450.6 (M4` [ PPh ` [ 2H`)`,
8
9
3
188.7, 1189.6 (M4` [ 2PPh ` [ H`)`, 927.4, 928.4 (M4`
3
[
[
3PPh `)`, 1713, 1714 (M4` [ 2H`)2`, 856.5, 857.0
3
2
181.
(M4` [ 2H4)2`/2]; calc. 1716.7 for M4` (C
H N P ).
1
20 96 4 4
D. L. Akins, H-R. Zhu and C. Guo, J. Phys. Chem., 1996, 100,
5420; K. M. Kadish, B. G. Maiya and C. Araullo-McAdams, J.
Phys. Chem., 1991, 95, 427; K. Kemnitz and T. Sakaguchi, Chem.
Phys. L ett., 1992, 196, 497.
ZnPor–PPh. 1H NMR (250 MHz, in [2H ]methanol, TMS
4
as internal standard) d 5.2È5.3 (d, 8 H), 7.3È7.4 (d, 8 H), 7.6È
8
5
.0 (m, 68 H), 8.7 (s, 8 H). UVÈVIS (in MeOH) j /nm 423.5,
max
10 (a) E. S. Enerson, M. A. Conlin, A. E. Roseno†, K. S. Norland, H.
Rodriguez, D. Chin and G. R. Bird, J. Phys. Chem., 1967, 71,
2396; (b) L. L. Shipman, J. R. Norris and J. J. Katz, J. Phys.
Chem., 1976, 80, 877; (c) W. W. Parson and A. Warshel, J. Am.
Chem. Soc., 1987, 109, 6152; (d) O. Q. Munro and H. M.
Marques, Inorg. Chem., 1996, 35, 3768.
11 T. Shimidzu and T. Iyoda, Chem. L ett., 1981, 853; V. Thanabal
and V. Krishnan, J. Am. Chem. Soc., 1982, 104, 3643; A. C.
Bookser and T. C. Bruice, J. Am. Chem. Soc., 1991, 113, 4208.
12 The molecular polarizabilities are cited from the literature and
57.3 and 596.7; (in CHCl ) 426.9, 558.2 and 603.5.
3
ZnPor–PBu. 1H NMR (250 MHz, in [2H ]methanol, TMS
4
as internal standard) d 1.1È1.3 (t, 36 H), 1.5È1.7 (m, 48 H),
2
8
.4È2.5 (m, 24 H), 4.0È4.1 (d, 8 H), 7.7È7.8 (d, 8 H), 8.2È8.3 (d,
H), 8.7 (s, 8 H). UVÈVIS (in MeOH) j
max/nm 422.5, 557.0
and 596.0
ZnPor–DABCO. 1H NMR (250 MHz, in [2H ]DMSO,
6
TMS as internal standard) d 3.2È3.4 (t, 24 H), 3.5È3.7 (t, 24 H),
4
UVÈVIS (in MeOH) j /nm 421.0, 555.3 and 595.4
are calculated according to the equation a/Ó3 \ (4/N)[& q ]2,
.9 (s, 8 H), 7.9È8.0 (d, 8 H), 8.3È8.4 (d, 8 H), 8.9 (s, 8 H).
A A
where N is the number of electrons in the molecules and q are
A
the atomic components for atoms in particular hybrid conÐgu-
max
rations. See K. J. Miller and A. Savchik, J. Am. Chem. Soc., 1979,
We give great thanks to N. Morisaki (University of Tokyo) for
the FABMS measurement. We also appreciate the practical
assistance of K. Tanabe and K. Kaigake for the NMR and
SIMS measurements.
101, 7206.
13 K. Kano, T. Hayakawa and S. Hashimoto, Bull. Chem. Soc. Jpn.,
1991, 64, 778.
1
4 D. B. Smithrud and F. Diederich, J. Am. Chem. Soc., 1990, 112,
3
39.
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