Novel functional groups with fine-controlled metal assembling function

Article abstract of DOI:10.1246/bcsj.78.349

Half-substituted dendritic phenylazomethine dendrimers with various substituents (Half-DPA-X Gn, where n is the generation number) were synthesized in order to elucidate the electron gradients in the dendrons by complexation with metal ions. Along with th

Full text of DOI:10.1246/bcsj.78.349

Ó 2005 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 78, 349–355 (2005)
349
Novel Functional Groups with Fine-Controlled Metal
Assembling Function
ꢀ
Kimihisa Yamamoto, Masayoshi Higuchi, Atsushi Kimoto, Takane Imaoka, and Kiriko Masachika
Department of Chemistry, Faculty of Science & Technology, Keio University, Yokohama 223-8522
Received July 2, 2004; E-mail: yamamoto@chem.keio.ac.jp
Half-substituted dendritic phenylazomethine dendrimers with various substituents (Half-DPA-X Gn, where n is
the generation number) were synthesized in order to elucidate the electron gradients in the dendrons by complexation
with metal ions. Along with the change in the UV–vis spectra, the isosbestic point shifted about 11 nm from 371 to
360 nm. The number of added equivalents of SnCl2 required to induce a shift was in agreement with the number of
the imine sites present in each layer of Half-DPA-H G4. The degree of the electron gradient in the phenylazomethine
monodendrons, Half-DPAs, was estimated via titration with trifluoroacetic acid. We found drastic differences in the ba-
sicity of the imine sites; the basicity of the core imines is higher than that of the more peripheral imines. The stepwise
complexation behavior is thermodynamically controlled from the core to terminal imines in Half-DPA-H. Furthermore,
Half-DPA G4 with various substituents possesses the same electron gradients in the dendron, so the complexation be-
havior with metal ions is the same.
1
Dendrimers are nanosized macromolecules with a regular
tree-like array of units, providing gradients in the branch den-
sity from the interior to the exterior which direct the transfer of
charge and energy from the dendrimer periphery to its core.2
We can move to the next stage of advanced molecular design
by utilizing these molecular funnels in electric and/or optic
applications, such as a photovoltaic cell and an electrolumines-
found a unique behavior in which a metal ion is stepwise
assembled during each generation of the dendron.
Results and Discussion
Synthesis of the DPA Dendrons and Half-DPAs. Den-
dritic phenylazomethine (DPA) dendrons Gn (n ¼ 1{4) were
synthesized via dehydration of aromatic ketones with aromatic
amines in the presence of titanium tetrachloride, and then iso-
3
cence device. These electro-optical devices possess the se-
8
quential HOMO/LUMO energy gradients of a fixed vector
within a device with the multi-layered structure and lower en-
ergy barriers. Another important aspect of a dendritic structure
with some peripheral units is an energy harvesting, resulting in
a highly efficient emission. We have recently synthesized the
phenylazomethine (phenyliminomethane) dendrimer, and
found that the tin ions, Sn2 , are coordinated on the imine
lated by silica gel column chromatography. Half-DPA-H G1,
G2, G3, and G4 (Fig. 1) were obtained by the dehydration of
8
benzophenone, dendrons G2, G3, and G4 (ketones) with ani-
line, and isolated in 92, 90, 89, and 80% yields, respectively.
This dehydration efficiently proceeded, and the yields are sig-
nificantly higher than those reported in the dehydration of DPA
4
þ
5
dendrons and p-phenylenediamine, because aniline deriva-
tives can be added in excess with a lower steric hindrance at
5
groups in a stepwise fashion. This complexation behavior
was supported by UV–vis spectroscopy, 1H NMR measure-
ments and TEM, confirming the expansion of the molecular
size due to complexation. This behavior reflects a gradient in
the electron density associated with the imine groups, and it
should be possible to control the number and location of the
metal ions incorporated into the dendrimer structures. This
unique complexation might find use in creating tailored cata-
lysts or building blocks for advanced materials.
the last step. The isolated Half-DPAs were identified by H
1
1
3
and C NMR spectroscopies, elemental analysis, and matrix-
assisted laser desorption/ionization time-of-flight mass spec-
troscopy (MALDI-TOF MS).
UV–Visible Spectra of Half-DPAs with SnCl2.9
The
spectra of Half-DPA-H G4 gradually changed (Fig. 2a), with
an isosbestic point at 371 nm up to the addition of 1 equivalent
(molar amount) of SnCl2. The isosbestic point then shifted
upon the further addition of SnCl2, and appeared at 368 nm be-
tween 1 and 3 equivalents. With the addition of between 3 and
7 equivalents of SnCl2, an isosbestic point appeared at 363 nm,
moving to 360 nm when between 7 and 15 equivalents were
added (Fig. 2b). Overall, the isosbestic point shifted about
11 nm from 371 to 360 nm, and the number of added equiva-
lents of SnCl2 required to induce a shift was in agreement with
the number of imine sites present in each layer of Half-DPA-
H G4. From a kinetic standpoint, complexation of the terminal
imines of the dendrimer is expected to occur first. However,
the titration results suggest that, on the time scale of our obser-
For our next strategy, the dendron, which is a dendrimer
compound, should be employed in order to overcome any syn-
thetic difficulties. Moreover, the dendrons expand the possibil-
ities for advanced materials, for example, dendronized poly-
mer, surface modification of electrode or metal cluster.7
Half-substituted dendritic phenylazomethine dendrimers with
various substituents (Half-DPA-X Gn, where n is the genera-
tion number) were synthesized in order to elucidate the elec-
tron gradients in the dendrons by complexation with metal
ions. We estimated the basicity within the phenylazomethine
dendron by profiling the change in the UV–vis spectra. We
6
Published on the web February 11, 2005; DOI 10.1246/bcsj.78.349

3
50 Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
Fine-Controlled Metal Assembling Group
N
N
N
N
N
N
N
N
N
N
N
X
X
n=1
X
n=2
n=3
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Layer
D
C
B
A
X
n=4
Fig. 1. Chemical structures of the Half-DPA-X Gn (n ¼ 1{4) and four imine layers.
vations, the process is thermodynamically controlled and pro-
ceeds in a stepwise fashion from the core imines to the termi-
nal imines of Half-DPA-H G4 (Fig. 2c). A similar stepwise
complexation was previously reported in phenylazomethine
dendrimers, and was also observed in Half-DPA-H G2
(352 and 349 nm for 0–1 and 1–3 equivalents of SnCl2, respec-
quantitative evaluation of the degree of the electron gradient
present in the Half-DPAs.
Basicity of the Imine Units in Each Generation of the
Half-DPAs. For the quantitative evaluation, we have to know
how much difference between neighboring complexation con-
stants K is required for the stepwise complexation. To answer
this question, we first tried to make a theoretical model of the
multi-equilibrium system. For the first assumption, the elec-
tronic effect of preceding complexation at the other free imines
were neglected. This is justified because the stepwise complex-
ation from the core side was clearly observed. If the effect was
not negligible, the coordinating metals should be dispersed, be-
cause one complexation lowered the constants of neighboring
imines through bond electron withdrawing. Therefore, we can
use the simplest four-equilibrium model expressed below.
5
tively) and in Half-DPA-H G3 (362, 358, and 351 nm upon
adding 0–1, 1–3, and 3–7 equivalents).10 These results further
supported the idea that metal ions are incorporated in a step-
wise fashion, first filling the shells close to the dendrimer core
and then progressively filling the more peripheral shells. The
spectral changes accompanying the addition of SnCl2 to the
linear phenylazomethine dimer and trimer5a resulted in the ap-
pearance of only one isosbestic point in each case. This behav-
ior shows that the complexation between SnCl2 molecules and
the imine sites is random. Therefore, these observations sug-
gest that the stepwise complexation behavior in DPAs does
not reflect changes in the basicity of the imine groups induced
by complexation at the neighboring imine groups. If that were
the case, we would also expect to see stepwise complexation
when titrating the linear oligomers. Also, this stepwise behav-
ior has been supported by several other measurements such as
þ
þ
[
A] þ [H ] ꢀ [AH ]: Ka
ð1Þ
ð2Þ
ð3Þ
ð4Þ
þ
þ
[B] þ [H ] ꢀ [BH ]: Kb
þ
þ
[C] þ [H ] ꢀ [CH ]: K
c
þ
þ
[
D] þ [H ] ꢀ [DH ]: Kd:
þ
In these equations, protonations by H are assumed instead of
complexations by SnCl2. The complexation reactions by SnCl2
1
H NMR measurement and direct observation of the molecular
a,d
size by TEM.5
can also treated by the same procedures. [A]–[D] and [AH ]–
þ
þ
Drastic differences in the basicity of the imines results in the
stepwise complexation behavior of the Half-DPA-H G4. The
experimental observations suggest that the basicity of the core
imine is higher than that of the more peripheral imines. These
conclusions are further supported by determination of the com-
plexation constants K of each generation using UV–visible
spectroscopy. However, the K values obtained from the SnCl2
titration are enormous, so the method is unsuitable for the
[DH ] represent the unit concentrations of free base imines
and coordinated imines in four layers (here we assumed that
‘‘A’’ is the first layer nearest to the focal point), respectively.
The calculation method described in the experimental section
can predict the shift of the isosbestic point on the addition of
þ
H , if each coordination constant (Ka–Kd) and the maximum
0
absorption wavelengths (ꢀ ) of each chromophore (A–D and
AH –DH ) are given.
þ
þ

K. Yamamoto et al.
Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
351
(a)
a)
2
80
[
AH+]
[BH+]
1
.5
6
4
2
0
0
0
[
[
CH+]
DH+]
1
0.5
0
250
300
350
400
450
500
550
Wavelength / nm
0
b)
c)
0
100
200
300
3
71 nm
368 nm
363 nm
360 nm
+
Initial Concentration of H / µM
(b)
0-1 equiv.
1-3 equiv.
3-7 equiv.
7-15 equiv.
8
6
0
0
1
SnCl2
4
3
2
1
4 3 2 1
2
SnCl2
4 SnCl2
40
4
3 2 1
20
8
SnCl2
4
3
2
1
4 3 2 1
0
Fig. 2. a) UV–vis spectral changes in Half-DPA-H G4
upon the stepwise addition of SnCl2 to CH3CN=
CH2Cl2 ¼ 1=1, b) enlargements showing isosbestic points
during complexation with SnCl2, and c) schematic repre-
sentation of stepwise radial complexation of Half-DPA-
H G4 with SnCl2.
0
100
200
300
+
Initial Concentration of H / µM
Fig. 3. Calculated concentration profiles of protonated
þ
imines upon addition of H when KN are the values
ꢂ5
ꢂ5
in Table 1, [A]0 ¼ 2:0 ꢁ 10 M, [B]0 ¼ 4:0 ꢁ 10 M,
ꢂ5
ꢂ4
[
C]0 ¼ 8:0 ꢁ 10 M, [D]0 ¼ 1:6 ꢁ 10 M.
Table 1. Equilibrium Constants of Protonations to Each
Imine Site
Table 2. Assumed Peak Wavelength for the Simulation of
Isosbestic Point
ꢂ1
KN/M
(a)
(b)
(c)
Ka
Kb
Kc
Kd
1010
108
106
104
107
106
105
104
107
107
107
107
0
0
N
ꢀ
N/nm
ꢀ
NH/nm
406
403
398
395
A
B
C
D
336
333
328
325
Secondly, we tried to apply the defined model to three ex-
ample cases. For each case, the concentration of the dendrimer
ꢂ5
(
here we assume Half-DPA-G4) was set to 2 ꢁ 10 M, so
clearly show that at least 100 times difference between neigh-
boring complexation constants is required to observe the step-
wise shift of isosbestic point. If the difference is set to 10
times, the shift would be continuous. Therefore, in any exper-
imental case, the complexation constant of inner imines should
be 100 times larger than that of the neighboring outer imines.
To apply these methods to the experiment, we have to de-
that the initial unit concentrations of imines (defined as [A]0,
ꢂ5
ꢂ5
ꢂ5
[
B]0, [C]0, and [D]0) become 2 ꢁ 10 , 4 ꢁ 10 , 8 ꢁ 10
,
ꢂ5
and 16 ꢁ 10 M, respectively. When the complexation con-
stants KN (N ¼ A{D) are the values listed in Table 1 (a, b
and c), the concentration profiles are calculated as shown in
0
Fig. 3. If the ꢀ values are given as in Table 2, the variation
0
0
of the isosbestic point ꢀiso can be calculated as shown in
Fig. 4 from the concentration profiles in Fig. 3a. The results
cide ꢀ values experimentally. The ꢀ values could be practi-
cally obtained from the differential spectra of the UV–vis ab-

3
52 Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
Fine-Controlled Metal Assembling Group
ꢂ1
3
3
3
3
3
70
66
62
58
54
Table 3. Basicity [M ] of the Imine Units for Each Gener-
ation of Half-DPA-H Gn
a
b
c
n
A
B
C
D
3
4
7
7
1
2
3
4
1:1 ꢁ 10
7:0 ꢁ 10
1:3 ꢁ 10
1:5 ꢁ 10
2
5
5
9:0 ꢁ 10
2:0 ꢁ 10
3:0 ꢁ 10
3
4
1:0 ꢁ 10
1:4 ꢁ 10
3
1:2 ꢁ 10
0
5
10
15
8
6
4
2
0
[
SnCl ] / [Half-DPA-H G4]
2
Fig. 4. The variation in the isosbestic point calculated from
the peak wavelengths in Table 3 (a, b, and c) and concen-
tration profiles in Fig. 3.
a) isosbestic points
3
3
3
3
3
70
60
50
40
30
4
3
n
2
A
1
B
Lay
C
er [N]
D
n=2
n=3
n=4
n=2
n=3
n=4
simulated
observed
Fig. 6. Schematic representation of basicity within each
layer of Half-DPA Gn (n ¼ 1{4).
0
is attributed to the ꢀ A (maximum wavelength of free base
chromophore), and the positive peak is attributed to the
ꢀ AH (maximum wavelength of coordinated chromophore), re-
spectively. Similar analyses were performed on the next three
0
0
5
10
15
20
25
30
+
[
H ] / [Half-DPA-H Gn]
0
0
0
0
generations to obtain ꢀ B ꢃ ꢀ D and ꢀ BH ꢃ ꢀ DH. The ex-
b) titration curve
pected isosbestic points are calculated for every equivalent
þ
1
1
0
0
0
0
.2
.0
.8
.6
.4
.2
of added H using these parameters.
The systematic changes in the UV spectra were also record-
ed in dichloromethane with the addition of various concentra-
tions of trifluoroacetic acid to Half-DPA solutions, instead of
using SnCl2, whereas the complexation constant K of that acid
to the imines is relatively small. The values of KN represent the
complexation constant of the imines in each generation and are
estimated by the curve fitting of two simulated curves; i.e., iso-
sbestic point change and absorption change (Fig. 5). The basic-
ity of the four imine units in each generation obtained from the
simulation are listed in Table 3 and shown in Fig. 6. Here, the
complexation constant K for the Half-DPAs indicates a down-
ward electron gradient structure from the core to terminal
phenylazomethines. In Half-DPA-H G3 and G4, the basicity
n=2
n=3
n=4
n=2
n=3
n=4
simulated
observed
0
0
5
10
15
20
25
30
+
[
H ] / [Half-DPA-H Gn]
7
Fig. 5. Results of the simulations, a) isosbestic points and
b) titration curve.
of the core imine proved to be extraordinarily large (ꢃ10
ꢂ1
M
). These values of the terminal branch imines are roughly
3
ꢂ1
of the same order (ꢃ10 M ) as those of Half-DPA-H G1
for all generations. From these simulations, the complexation
constant should be larger than the outer phenylazomethines
for the spectral changes with the stepwise isosbestic point. If
the difference is about ten times, only a continuous change
in the isosbestic points could be observed (Fig. 4). Indeed, this
result calculated from the UV–vis spectral change proved that
sorption when the KN (N ¼ A{D) values are different enough
to discriminate the basicity of each imine by the proton titra-
þ
tion. The spectral change during the addition of H up to 1
molar amount reflects the chromophore of the free base and
coordinated imine at the root nearest to the focal point. The
wavelength of the negative valley in the differential spectrum

K. Yamamoto et al.
Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
353
the inner complexation constant for Half-DPA-H is over ten
times larger than the values of the neighboring outer imines.
We found drastic differences of the basicity in the phenylazo-
methine moiety; the basicity of the core imines is higher than
those of the more peripheral imines.11 This stepwise complex-
ation process is thermodynamically controlled from the core to
terminal imines in Half-DPA-H.
a)
2
.5
2
1.5
The complex formation constant K of SnCl2 with Half-
1
4
ꢂ1
DPA-H G1 was determined to be 9:5 ꢁ 10 M in dichloro-
methane. The K value is 100 times greater than that of a pro-
ton. On the basis of this result, the formation constants of
SnCl2 with Half-DPA-H G4 for each generation are postulat-
ed to be two orders of magnitudes greater than that of a proton.
Synthesis of the Half DPAs with Various Substituents.
We also changed the core phenyl ring of Half-DPA G4 to
three other substituents: methoxyphenyl (X ¼ MeO, Fig. 1),
an electron-donating group, by dehydration of the G4 dendron
with methoxyaniline; chlorophenyl, an electron-drawing
group, by dehydration of the G4 dendron with chloroaniline
0.5
0
2
50
300
350
400
450
500
550
Wavelength / nm
b)
c)
3
71 nm
365 nm
363 nm
0
-1 equiv.
1-3 equiv.
3-15 equiv.
(
X ¼ Cl, Fig. 1); and trifluoromethylphenyl, a strong elec-
tron-withdrawing group, by dehydration of the G4 dendron
with trifluoromethylaniline (X ¼ CF3, Fig. 1).
1 SnCl2
2 SnCl2
When SnCl2 was added to the Half-DPA G4 carrying a me-
thoxyphenyl core (Half-DPA-MeO G4), four isosbestic points
appeared at 373, 366, 361, and 360 nm upon adding 0–1, 1–3,
4
3
2 1
4 3 2 1
3
–7, and 7–15 equivalents of SnCl2, respectively. When SnCl2
was added to the Half-DPA G4 carrying a chlorophenyl, a
weak electron-drawing core (Half-DPA-Cl G4), four isosbes-
tic points are observed in the same manner. These stepwise
complexation behaviors resulted from the original electron
gradients that did not change in these dendrons.
On the other hand, when SnCl2 was added to the Half-DPA
G4 having a trifluoromethylphenyl core (Half-DPA-CF3 G4),
three isosbestic points appeared at 371, 365, and 363 nm upon
adding 0–1, 1–3, and 3–15 equivalents of SnCl2, respectively.
This behavior suggested that the electron gradient between the
third and fourth layers (C and D, Fig. 1) is cancelled by the
strong electron-withdrawing substituent (Fig. 7).
12 SnCl2
4
3
2 1
4 3 2 1
Fig. 7. a) UV–vis spectral changes in Half-DPA-CF3
G4 upon the stepwise addition of SnCl2 to CH3CN=
CH2Cl2 ¼ 1=1, b) enlargements showing isosbestic points
during complexation with SnCl2, and c) schematic repre-
sentation of stepwise radial complexation of Half-DPA-
CF3 G4 with SnCl2.
obtained using a Shimadzu/Kratos KOMPACT MALDI mass
spectrometer (Positive mode, Matrix: Dithranol). The UV–vis
spectra were recorded using a Shimadzu UV-3100PC spectrome-
ter with a sealed quartz cell (optical path length: 1 cm). All chem-
icals were purchased from Aldrich, Tokyo Kasei Co., Ltd., and
Kantoh Kagaku Co., Inc. (reagent grade) and were used without
further purification.
General Procedure for the Synthesis of Half-DPA-X Gn.
TiCl4 was dropwise added to a mixture of the aniline derivatives,
the corresponding phenylazomethine dendron and DABCO in
chlorobenzene. The addition funnel was then rinsed with chloro-
benzene. The reaction mixture was heated in an oil bath at 125
Conclusion
In conclusion, the degree of the electron gradient in the
phenylazomethine dendron, Half-DPAs, was estimated via ti-
tration with trifluoroacetic acid. We found drastic differences
in the basicity of the imine sites; the basicity of the core imines
is higher than that of the more peripheral imines. The stepwise
complexation behavior is thermodynamically controlled from
the core to terminal imines in Half-DPA-H. Furthermore,
Half-DPA G4 with various substituents possesses the same
electron gradients in the dendron and shows the same com-
plexation behavior with metal ions. We found a unique behav-
ior in which a metal ion is stepwise assembled in each gener-
ation of the dendron on the basis of the dendron gradients. The
electron gradients in the dendrons were able to be controlled
by the introduction of various substituents.
ꢄ
C for 30 min under N2. The precipitate was removed by filtration.
The filtrate was concentrated, and the pure product was isolated by
silica gel column chromatography.
Half-DPA-H G1: The previous procedure was followed using
0
.55 mL (6.0 mmol) of aniline, 0.91 g (5.0 mmol) of benzophe-
none (n ¼ 1), 0.84 g (7.5 mmol) of DABCO, and 3.3 mL (30
mmol) of TiCl . The product was isolated by silica gel column
4
chromatography using 7:1 hexane/ethyl acetate with 2% Et N
3
1
as the eluent, yielding 1.18 g (92%). H NMR (400 MHz, CDCl3,
ꢄ
Experimental
TMS standard, 20 C, ppm) ꢁ 7.67 (t, J ¼ 7:6 Hz, 1H), 7.31 (d,
General. The NMR spectra were recorded using a JEOL
JMN400 FT-NMR spectrometer (400 MHz) in CDCl3 + TMS
J ¼ 7:6 Hz, 2H), 7.26 (t, J ¼ 7:6 Hz, 1H), 7.18 (dd, J ¼ 7:6,
7.6 Hz, 2H), 7.14 (dd, J ¼ 7:6, 7.6 Hz, 2H), 7.13–7.06 (m, 5H),
13
(
internal standard) solution. The MALDI-TOF-Mass spectra were
6.53 (d, J ¼ 7:6 Hz, 2H); C NMR (100 MHz, CDCl3, TMS

3
54 Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
Fine-Controlled Metal Assembling Group
ꢄ
ꢄ
standard, 20 C, ppm) ꢁ 168.06, 151.08, 139.54, 136.08, 130.58,
ard, 20 C, ppm) ꢁ 168.02, 167.05, 167.56, 153.08, 153.01,
151.57, 145.12, 139.04, 138.93, 138.74, 137.43, 135.65, 135.42,
134.14, 132.28, 132.05, 130.69, 130.16, 130.22, 129.96, 129.81,
129.26, 128.70, 128.22, 128.01, 127.69, 127.67, 120.62, 120.10,
1
29.39, 129.19, 128.43, 128.34, 128.07, 127.76, 123.02, 120.83;
þ
MALDI-TOF-Mass: 257.3 ([M] Calcd for C19H15N: 257.1);
Anal. Calcd for C19H15N: C, 88.68; H, 5.88; N, 5.44%. Found:
C, 88.67, H, 5.59; N, 5.45%.
þ
120.11, 119.87, 119.63; MALDI-TOF-Mass: 2795.00 ([M]
Half-DPA-H G2: The previous procedure was followed using
.08 mL (9.25 mmol) of aniline, 0.050 g (0.93 mmol) of the G2
Calcd for C202H143N15: 2794.16); Anal. Calcd for C202H143N15O:
C, 86.76; H, 5.15; N, 7.51%. Found: C, 86.69; H, 5.18; N, 7.52%.
Half-DPA-Cl G4: The previous procedure was followed us-
ing 0.024 g (0.19 mmol) of chloroaniline, 0.05 g (0.02 mmol) of
the G4 dendron, 0.014 g (0.12 mmol) of DABCO, and 0.05 mL
(0.5 mmol) of TiCl4. The product was isolated by silica gel col-
umn chromatography using from 6:1:6 to 3:1:3 hexane/ethyl ace-
tate/chloroform with 2% Et3N as the eluent, yielding 0.044 g
0
dendron, 0.16 g (1.4 mmol) of DABCO, and 0.6 mL (5.6 mmol)
of TiCl4. The product was isolated by silica gel column chroma-
tography using from 7:1:1 to 4:1:1 hexane/ethyl acetate/chloro-
form with 2% Et3N as the eluent, yielding 0.514 g (90%).
1
ꢄ
H NMR (400 MHz, CDCl3, TMS standard, 20 C, ppm) ꢁ 7.73
(
6
2
t, J ¼ 7:1 Hz, 4H), 7.50 (d, J ¼ 8:3 Hz, 2H), 7.47–7.38 (m,
1
ꢄ
H), 7.30–7.13 (m, 10H), 7.02–6.92 (m, 2H), 6.90–6.85 (m,
H), 6.72 (d, J ¼ 8.0 Hz, 2H), 6.56 (d, J ¼ 2:4 Hz, 2H), 6.54
(79%). H NMR (400 MHz, CDCl3, TMS standard, 20 C, ppm)
ꢁ 7.74–6.43 (m, 140H); 13C NMR (100 MHz, CDCl3, TMS stand-
13
ꢄ
(
d, J ¼ 8:1 Hz, 2H); C NMR (100 MHz, CDCl3, TMS standard,
ard, 20 C, ppm) ꢁ 168.92, 168.55, 168.21, 154.63, 153.92,
ꢄ
2
1
1
0 C, ppm) ꢁ 168.73, 168.33, 167.74, 139.28, 135.78, 135.64,
151.68, 146.42, 139.06, 138.23, 138.88, 137.19, 135.44, 135.40,
134.14, 132.18, 132.11, 130.75, 130.41, 130.00, 129.97, 129.89,
129.17, 128.67, 128.28, 128.06, 127.77, 127.41, 120.71, 120.39,
34.59, 132.32, 130.83, 130.06, 129.97, 129.89, 129.37, 129.32,
29.25, 128.76, 128.58, 128.29, 127.73, 120.44; MALDI-TOF-
þ
þ
Mass: 615.0 ([M] Calcd for C45H33N3: 615.3); Anal. Calcd for
C45H33N3: C, 87.77; H, 5.40; N, 6.82%. Found: C, 87.70; H,
120.06, 119.61, 119.49; MALDI-TOF-Mass: 2799.02 ([M]
Calcd for C201H140ClN15: 2798.11); Anal. Calcd for
C201H140ClN15: C, 86.19; H, 5.04; N, 7.50%. Found: C, 86.57;
H, 5.08; N, 7.56%.
Half-DPA-CF3 G4: The previous procedure was followed us-
ing 0.031 g (0.19 mmol) of 2-(trifluoromethyl)aniline, 0.05 g (0.02
mmol) of the G4 dendron, 0.014 g (0.12 mmol) of DABCO, and
0.05 mL (0.5 mmol) of TiCl4. The product was isolated by silica
gel column chromatography using from 6:1:6 to 3:1:3 hexane/eth-
yl acetate/chloroform with 2% Et3N as the eluent, yielding 0.044
5
.42; N, 6.81%.
Half-DPA-H G3: The previous procedure was followed using
.07 mL (0.80 mmol) of aniline, 0.10 g (0.08 mmol) of the G3
dendron, 0.014 g (0.12 mmol) of DABCO, and 0.05 mL (0.5
mmol) of TiCl4. The product was isolated by silica gel column
chromatography using from 12:2:3 to 3:1:1 hexane/ethyl ace-
tate/chloroform with 2% Et3N as the eluent, yielding 0.095 g
0
1
ꢄ
(
ꢁ
(
1
1
1
1
1
1
89%). H NMR (400 MHz, CDCl3, TMS standard, 20 C, ppm)
7.72 (s, 8H), 7.54–7.12 (m, 37H), 7.03–6.49 (m, 24H); C NMR
1
3
1
ꢄ
g (78%). H NMR (400 MHz, CDCl3, TMS standard, 20 C, ppm)
ꢁ 7.82–6.42 (m, 140H); 13C NMR (100 MHz, CDCl3, TMS stand-
ꢄ
100 MHz, CDCl3, TMS standard, 20 C, ppm) ꢁ 168.91, 168.78,
ꢄ
68.41, 168.17, 168.11, 167.63, 153.91, 153.63, 151.83, 151.71,
51.53, 139.23, 139.08, 135.75, 135.61, 135.55, 134.26, 134.12,
32.33, 130.88, 130.80, 130.60, 130.53, 130.37, 130.22, 130.05,
29.94, 129.78, 129.62, 129.35, 129.09, 128.72, 128.38, 128.16,
27.98, 127.83, 127.76, 122.78, 121.26, 120.79, 120.73, 120.48,
ard, 20 C, ppm) ꢁ 169.80, 169.35, 168.76, 154.01, 153.42,
151.67, 146.61, 139.10, 138.83, 138.66, 137.38, 135.65, 135.41,
134.14, 132.28, 132.05, 130.70, 130.42, 130.22, 129.97, 129.89,
129.17, 128.69, 128.29, 128.02, 127.89, 127.73, 120.71, 120.33,
þ
120.18, 119.86, 119.66; MALDI-TOF-Mass: 2833.10 ([M]
Calcd for C202H140F3N15: 2763.76).
þ
20.24, 120.09; MALDI-TOF-Mass: 1331.1 ([M] Calcd for
C97H70N7: 1331.6); Anal. Calcd for C97H69N7: C, 87.42; H,
Calculation of the Equilibrium and Isosbestic Point in UV–
Vis Spectra. The equilibrium constants of the coordination (Eqs.
1–4) are defined as Ka–Kd for imines in each generation. The val-
ues of KN are given by layers:
5
.22; N, 7.36%. Found: C, 87.49; H, 5.21; N, 7.35%.
Half-DPA-H G4: The previous procedure was followed using
.02 mL (0.19 mmol) of aniline, 0.05 g (0.02 mmol) of the G4
0
dendron, 0.014 g (0.12 mmol) of DABCO, and 0.05 mL (0.5
mmol) of TiCl4. The product was isolated by silica gel column
chromatography using from 6:1:6 to 3:1:3 hexane/ethyl acetate/
chloroform with 2% Et3N as the eluent, yielding 0.044 g (80%).
þ
[
NH ]
þ
KN ¼ [
:
ðN ¼ A{DÞ:
ð5Þ
N][H ]
Equation 5 leads to
1
ꢄ
H NMR (400 MHz, CDCl3, TMS standard, 20 C, ppm) ꢁ
1
3
[N]0
7
.76–6.37 (m, 141H); C NMR (100 MHz, CDCl3, TMS stand-
ꢄ
[
N] ¼
ð6Þ
þ
K [H ] þ 1
N
ard, 20 C, ppm) ꢁ 168.80, 168.35, 168.06, 154.03, 153.62,
1
1
1
1
51.77, 146.62, 139.14, 138.93, 138.79, 137.39, 135.65, 135.44,
34.24, 132.38, 132.25, 130.79, 130.46, 130.23, 129.97, 129.89,
29.27, 128.71, 128.28, 128.07, 127.89, 127.73, 120.72, 120.40,
þ
using the relation of [N] + [NH ] = [N]0 (N ¼ A, B, C, and D)
where [A]0, [B]0, [C]0, and [D]0, represent the initial concentra-
þ
tions of A, B, C, and D, respectively. [H ] is represented by using
the concentration of the unprotonated imines ([A], [B], [C], and
þ
20.16, 119.88, 119.67; MALDI-TOF-Mass: 2763.92 ([M]
Calcd for C201H141N15: 2764.15); Anal. Calcd for C201H141N15:
C, 87.27; H, 5.14; N, 7.59%. Found: C, 87.22; H, 5.18; N, 7.51%.
Half-DPA-MeO G4: The previous procedure was followed
using 0.023 g (0.19 mmol) of methoxyaniline, 0.05 g (0.02 mmol)
of the G4 dendron, 0.014 g (0.12 mmol) of DABCO, and 0.05 mL
[
D]): and their initial concentrations:
þ
þ
þ
þ
þ
þ
[
H ] ¼ [H ]0 ꢂ [AH ] ꢂ [BH ] ꢂ [CH ] ꢂ [DH ]
þ
¼ [H ] ꢂ ð[A] ꢂ [A]Þ ꢂ ð[B] ꢂ [B]Þ
0
0
0
ꢂ ð[C]0 ꢂ [C]Þ ꢂ ð[D]0 ꢂ [D]Þ:
ð7Þ
(0.5 mmol) of TiCl4. The product was isolated by silica gel col-
umn chromatography using from 6:1:6 to 3:1:3 hexane/ethyl ace-
þ
Substituting (6) into (7) yields the equation for [H ], KN, and
[N]0. We can calculate the concentrations of each chemical spe-
cies ([H ], [N], and [NH ] for N ¼ A{D) after the equilibrium
on the basis of (6) and (7) by four given (or assumed) KN values,
tate/chloroform with 2% Et3N as the eluent, yielding 0.045 g
ꢄ
1
þ
þ
(
ꢁ
81%). H NMR (400 MHz, CDCl3, TMS standard, 20 C, ppm)
1
3
7.76–6.40 (m, 143H); C NMR (100 MHz, CDCl3, TMS stand-

K. Yamamoto et al.
Bull. Chem. Soc. Jpn., 78, No. 2 (2005)
355
þ
because the initial concentrations [H ]0 and [N]0 are known
constants.
To determine accurate constants of the complexation, we have
the 21st COE program (KEIO-LCC) from the Ministry of
Education, Culture, Sports, Science and Technology.
þ
to know the concentration profiles on the addition of H . In gen-
References
eral, it is impossible to determine the discrete information about
concentrations from a titration curve (absorption changes vs molar
amounts) in a multi-equilibrium system. If the absorption spectra
changes corresponding to each equilibrium reaction are well-sep-
arated, we can determine by the titration curve fitting at some dif-
ferent wavelengths. However, in our case, it is impossible because
the spectral difference between complexations at each layer of
Half-DPA is very small. Thus, we tried to analyze the isosbestic
points during the titration.
1
For reviews, see: a) J. M. J. Fr e´ chet and D. A. Tomalia,
‘Dendrimers and Other Dendritic Polymers,’’ J. Wiley and Sons,
New York (2001). b) G. R. Newkome, C. N. Moorefield, and F.
V o¨ gtle, ‘‘Dendritic Molecules: Concept, Synthesis, Perspectives,’’
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‘
2
a) C. Devadoss, P. Bharathi, and J. S. Moore, J. Am. Chem.
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54 (1997). c) T. D. Selby and S. C. Blackstock, J. Am. Chem.
Soc., 120, 12155 (1998).
4
The UV–vis absorption coefficient is expressed as a function of
the Gaussian type for the wavenumber. Therefore, the function for
the wavelength is given by:
3 a) C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 51,
13 (1987). b) U. Bach, D. Lupo, P. Comte, J. E. Moser, F.
9
(
)
Weiss o¨ rtel, J. Salbeck, H. Spreitzer, and M. Gr a¨ tzel, Nature,
395, 583 (1998).
0
2
ꢂꢁð1=ꢀ ꢂ 1=ꢀÞ
kT
0
"
ðꢀÞ ¼ " exp
ð8Þ
4
a) P. Furuta, J. Brooks, M. E. Thompson, and J. M. J.
Fr e´ chet, J. Am. Chem. Soc., 125, 13165 (2003). b) B. Li, J. Li,
Y. Fu, and Z. Bo, J. Am. Chem. Soc., 126, 3430 (2004).
0
0
where ꢀ is the wavelength of maximum absorption, " is the mo-
lar absorption coefficient for ꢀ , and ꢁ is the thermal vibration pa-
rameter of the chromophore. Here, we assume the ꢁ value to be
0
5
a) K. Yamamoto, M. Higuchi, S. Shiki, M. Tsuruta, and H.
Chiba, Nature, 415, 509 (2002). b) T. Imaoka, H. Horiguchi, and
K. Yamamoto, J. Am. Chem. Soc., 125, 340 (2003). c) N. Sato,
J.-S. Cho, M. Higuchi, and K. Yamamoto, J. Am. Chem. Soc.,
7
2
constant ((kT=ꢁ) to be 10 nm ) for each chromophore because
the influence to the wavelength of the isosbestic point is very
small. In this case, these chromophores are at each imine site
and are influenced by the protonation. The overall absorption
can be expressed as the summation of Eq. 8 for each chromophore
1
25, 8104 (2003). d) M. Higuchi, M. Tsuruta, H. Chiba, S. Shiki,
and K. Yamamoto, J. Am. Chem. Soc., 125, 9988 (2003).
a) B. Karakaya, W. Claussen, K. Gessler, W. Saenger, and
6
þ þ
(
action is present between neighboring chromophores.
A–D and AH –DH ) based on the approximation that no inter-
A. D. Schl u¨ ter, J. Am. Chem. Soc., 119, 3296 (1997). b) T. Sato,
D.-L. Jiang, and T. Aida, J. Am. Chem. Soc., 121, 10658 (1999). c)
S. Setayesh, A. C. Grimsdale, T. Weil, V. Enkelmann, K. M u¨ llen,
F. Meghdadi, E. J. W. List, and G. Leising, J. Am. Chem. Soc.,
(
)
A!D
0
N
2
X
ꢂꢁNð1=ꢀ ꢂ 1=ꢀÞ
kT
þ
0
N
Absðꢀ; [H ]Þ ¼
[N]" exp
N
1
23, 946 (2001). d) A. Kimoto, K. Masachika, J.-S. Cho, M.
(
)
0
2
ꢂꢁNHð1=ꢀ ꢂ 1=ꢀÞ
kT
Higuchi, and K. Yamamoto, Org. Lett., 6, 1179 (2004). e) A.
Kimoto, K. Masachika, J.-S. Cho, M. Higuchi, and K. Yamamoto,
Chem. Mater., 16, 5706 (2004).
0
NH
þ [NH]" exp
:
ð9Þ
NH
The wavelength of the isosbestic point, ꢀiso, is a solution of the
following equation for ꢀ, because the ꢀiso is defined as the wave-
length where the absorbance does not change upon titration.
7
a) W. Guo, J. J. Li, Y. A. Wang, and X. Peng, J. Am. Chem.
Soc., 125, 3901 (2003). b) F. Le Derf, E. Levillain, G. Trippe, A.
Gorgues, M. Salle, R. M. Sebastian, A. M. Caminade, and J. P.
Majoral, Angew. Chem., Int. Ed., 40, 224 (2001). c) H. C. Yoon
and H. S. Kim, Anal. Chem., 72, 922 (2000).
þ
þ
þ
Absðꢀiso; [H ] þ ꢀ[H ]Þ ꢂ Absðꢀiso; [H ]Þ ¼ 0:
The variation of isosbestic points for the concentration of added
ð10Þ
8
a) M. Higuchi, S. Shiki, and K. Yamamoto, Org. Lett., 2,
079 (2000). b) M. Higuchi, S. Shiki, K. Ariga, and K.
Yamamoto, J. Am. Chem. Soc., 123, 4414 (2001).
Complexation of SnCl2 with imines, see: J. M. Van den
Berg, Acta Crystallogr., 15, 1051 (1962).
These complexation behaviors were the same as the di-sub-
þ
þ
H
([H ]0) can be calculated by solving Eq. 10 when the various
0
, " , and KN values are defined. The ꢀ and " are obtained
from the differential spectra during the titration experiment. In
3
0
0
0
ꢀ
9
principle, the KN values were estimated by fitting the theoretical
ꢀ
iso profiles into the experiment. However, this procedure was
1
0
not sufficient to obtain the absolute values of KN, although the rel-
ative values among the Ka–Kd could be estimated. The absorbance
profiles during the titration should be employed with analysis of
the isosbestic point to calculate the exact coordination constants.
They are also expressed as Eq. 9.
stituted phenylazomethine dendrimers (previous study) based on
the same chemical shifts attributed to the imine carbon for each
generation. These results suggested that, for these dendrimers,
there is no steric influence on the morphology of the dendrimers
substituted by one and two dendrons, complexing with SnCl2.
These methods are not only applicable for the protonation, but
also the 1:1 complexation of a Lewis acid (e.g., SnCl2) to the
imines.
1
1
These differences are based on their unique dendritic layers
and the structural vectors of the imine bond. From outer layers,
imine nitrogen acts as electron-donating substituents, whereas
from inner layers, imine carbon acts as electron-withdrawing ones.
As a result of the summation of electronic donation/acceptance,
the stepwise sequence of the basicity on the phenylazomethine
dendron could be realized.
This work was partially supported by CREST from the
Japan Science and Technology Agency, Grants-in-Aid for Sci-
entific Research (Nos. 15036262, 15655019, 15350073) and