Organogels of 8-quinolinol/metal(II)-chelate derivatives that show electron- and light-emitting properties

Article abstract of DOI:10.1002/chem.200601813

8-Quinolinol/copper(II)-, palladium(II)-, and platinum(II)-chelate-based organogelators (IM) and their nongelling reference compounds (2M) were synthesized. Complexes IM could gelate various organic solvents at very low concentrations. Electron microscope

Full text of DOI:10.1002/chem.200601813

FULL PAPER
DOI: 10.1002/chem.200601813
Organogels of 8-Quinolinol/Metal(II)–Chelate Derivatives That Show
Electron- and Light-Emitting Properties
Michihiro Shirakawa,[a] Norifumi Fujita,[a] Takahiro Tani,[a] Kenji Kaneko,[b]
Masayoshi Ojima,[c] Akihiko Fujii,[c] Masanori Ozaki,[c] and Seiji Shinkai*[a, d]
Abstract: 8-Quinolinol/copper(II)-, pal-
ladium(II)-, and platinum(II)-chelate-
based organogelators (1M) and their
nongelling reference compounds (2M)
were synthesized. Complexes 1M could
gelate various organic solvents at very
low concentrations. Electron micro-
scope measurements gave visual
images of well-developed fibrous struc-
tures characteristic of low-molecular-
weight organogels. UV/Vis and FTIR
spectroscopy revealed that the good
gelation ability of 1M arises from the
p–p interactions of the chelate moieties
and the hydrogen-bond interactions
among the amide groups. Very interest-
ingly, field emission performances of
the nanofibers prepared from the 1M
gels are evidently different depending
on the electronic states of the three
kinds of central metals. In addition, the
1Pt gel shows unique thermo- and sol-
vatochromism of visible and phosphor-
escent color in response to a sol–gel
phase transition. Furthermore, the 1Pt
gel possesses an attractive ability to in-
hibit dioxygen quenching of excited
triplet states, which increases the phos-
phorescence quantum yield of this gel.
This effect is attributed to the isolation
effect of the phosphorescent chelate
moiety from the dioxygen-containing
solution phase.
Keywords: chelates · field emission ·
gels
·
phosphorescence
·
self-assembly
Introduction
but also as well-defined nanostructured assemblies.[1] In par-
ticular, p-block-based low-molecular-weight gels have re-
ceived much attention, because they have great potential in
applications for nanoscale molecular electronics.[2,3]
Spontaneous, but programmed self-assembly of low-molecu-
lar-weight compounds is an essential concept to construct
distinct supramolecules for nanotechnology by the bottom-
up method. Among various supramolecular architectures de-
veloped thus far, low-molecular-weight gel systems have
become a topic of growing interest because they are expect-
ed to be useful not only as novel functional soft materials,
In the last several years, low-molecular-weight organogels
with metal–chelate moieties, namely metallogels, have been
widely investigated to explore advanced soft and nanomate-
rials.[4] Metal chelates are favorable from a viewpoint of gel
functionality because they have not only various electronic
states arising from inorganic metal elements, but also limit-
less possibilities of molecular design arising from organic li-
gands. Until now, metallogels with various features of metal
chelates have been reported to show unusual functional
properties such as redox responsiveness,[5] catalytic action,[6]
phosphorescence behavior,[7] spin-crossover phenomena,[8]
conductivities,[9] and so on.[10] Among the numerous metal
chelates, 8-quinolinol/metal–chelate derivatives are known
to possess attractive electronic and luminescent properties.
For instance, tri(8-quinolinol)aluminum (Alq3) has become
one of the most efficient electron transport and emitting
materials for organic light-emitting diode devices.[11] Fur-
thermore, Alq3 nanowires and nanobelts are utilized as field
emission materials.[12]
[a] Dr. M. Shirakawa, Dr. N. Fujita, T. Tani, Prof. S. Shinkai
Department of Chemistry & Biochemistry
Graduate School of Engineering
Kyushu University
744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan)
Fax : (+81)92-802-2820
E-mail: seijitcm@mbox.nc.kyushu-u.ac.jp
[b] Prof. K. Kaneko
HVEM Laboratory, Kyushu University
744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan)
[c] M. Ojima, Prof. A. Fujii, Prof. M. Ozaki
Division of Electrical, Electronic, and Information Engineering,
Graduate School of Engineering
Osaka University Suita
Osaka 565-0871 (Japan)
[d] Prof. S. Shinkai
Here, we report on gel formation and electron- and light-
emitting properties of 8-quinolinol copper(II)–, palladi-
Center for Future Chemistry, Kyushu University
744 Moto-oka, Nishi-ku, Fukuoka 819-0395 (Japan)
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Table 1. Gelation properties of 1M at 258C.[a,b]
Entry
Solvent
1Cu
1Pd
1Pt
1
2
3
4
5
6
7
8
hexane
octane
decane
cyclohexane
methylcyclohexane
decalin
benzene
toluene
p-xylene
pyridine
anisole
methanol
ethanol
2-propanol
1-butanol
acetone
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
S
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (10)
G (1)
P
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
G (1)
S
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
um(II)–, and platinum(II)–chelate derivatives (1M) bearing
G (1)
P
G (1)
P
P
3,4,5-tris(n-dodecyloxy)benzoylamide substituents.[13] We ex-
pected that their square-planar chelate structures would be
of great advantage to gel formation because of their strong
p–p interactions, which are one of the main driving forces
for gelation.[14] In addition, it is known that introduction of
G (1)
G (10)
G (1)
G (1)
G (10)
P
G (1)
G (1)
P
P
G (10)
G (1)
G (1)
G (2)
P
G (1)
G (1)
G (10)
P
G (10)
G (1)
G (1)
G (5)
P
G (1)
G (1)
G (5)
P
THF
3,4,5-tris(alkoxy)phenyl substituents into a p-conjugated
G
acetonitrile
ethyl acetate
1,4-dioxane
DMF
planar molecule is favorable for self-assembly into a colum-
nar-stacking structure to give highly ordered structures such
as liquid crystals and gels.[15] It is considered that the gel
fiber formed should be applicable as an effective electron-
and light-emitting nanomaterial, because of exciton delocali-
zation along the fiber network.[16] Furthermore, we can
expect that the three kinds of gelators designed would give
similarly shaped nanofibers because their coordination ge-
ometry is the same, whereas the properties of these fibrous
structures could be controlled by choosing the central metal
(Figure 1). To clarify the gelation effect, we also designed
nongelling reference compounds 2M, which have 2-ethyl-
hexyl moieties as solubilizing substituents.
DMSO
P
dichloromethane
chloroform
TCE
G(10)
S
S
G(10)
S
S
G(10)
S
S
[a] G: gel; P: precipitate; and S: solution. [b] The critical gelation con-
centrations [mgmLꢀ1] of gelators are shown in the parentheses.
tion ability of 1M arises from the cooperative action of
three different intermolecular interactions, that is, the p–p
interaction among the chelate moieties, the hydrogen-bond-
ing interaction among the amide groups, and the van der
Waals interaction among the long alkyl chains, that princi-
pally exert their power in different environments.
Electron microscope measurements: The morphology of the
1M gel fibers was investigated by using a scanning electron
microscope (SEM) and a transmission electron microscope
(TEM). As shown in Figure 2, we could observe well-devel-
oped networkstructures characteristic of low-molecular-
weight organogels, the approximate diameters and the
length of the fibrous aggregate of the 1M+p-xylene gels
being 10–50 nm and several mm, respectively. We also con-
firmed the creation of similar fibrous structures in gels pre-
pared from other gelling solvents. It is worth mentioning
that the morphology of the fibers prepared from the three
gelators, which have different central metal atoms, is almost
the same. This result implies that it is possible to create
nanomaterials that have the same shape: in other words, the
different properties, if they exist, are attributable to the dif-
ference in the central metals. This subject is discussed in
more detail in a later section.
Figure 1. Schematic representation of the 1M nanofibers that have differ-
ent electronic states depending on the central metals.
Results and Discussion
Gelation properties of 1M: The gelation properties of the 8-
quinolinol/metal(II)–chelate derivatives 1M were evaluated
in various organic solvents by the “stable to inversion of a
test tube” method. It is seen from Table 1 that 1Cu, 1Pd,
and 1Pt can gelate 18, 19, and 18 solvents, among 25 candi-
dates, respectively, such as, benzene, hexane, 1-butanol, 1,4-
dioxane, and so on. Additionally, 1M derivatives show a
very low critical gelation concentration (CGC), 1.0 mgmLꢀ1
(ca. 0.5 mm). These results indicate that 1M derivatives act
as versatile gelators for polar solvents, as well as, for nonpo-
lar ones. It is considered, therefore, that such a good gela-
UV/Vis absorption and FTIR spectroscopic analyses: To
obtain insight into the aggregation mode of the chelate moi-
eties and the amide groups in the gel tissue, we measured
UV/Vis absorption spectra and FTIR spectra comparing the
1M+p-xylene gels with the 1M+1,1,2,2-tetrachloroethane
(TCE) solutions. 8-Quinolinol/metal(II)–chelate derivatives
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FULL PAPER
Figure 3. UV/Vis absorption spectra of the 1M+p-xylene gels (b) and
the 1M+TCE solutions (c): [1M]=10 mgmLꢀ1; a) [1Cu], b) [1Pd],
and c) 1Pt. Photographs show the 1M+p-xylene gels and their heated
solutions.
Figure 2. SEM (left) and TEM (right) images of the 1Cu (top), 1Pd
(middle), and 1Pt+p-xylene (bottom) gels: a–c) [1M]=5 mgmLꢀ1; d–f),
[1M]=1 mgmLꢀ1. The scale bar length is 2 mm.
shorter wavenumbers by 7–10 cmꢀ1 compared to those
bands appearing in the solution phase, supporting the for-
mation of the intermolecular hydrogen bonds (Figure 4).
From these results, 8-quinolinol/metal(II)–chelate-based ge-
lators 1M self-assemble not only by the van der Waals inter-
action among the dense long alkyl chains, but also by the p–
p interaction among the chelate moieties and hydrogen-
bond interaction among the amide groups.
have two characteristic absorption bands in the UV/Vis
region. One is a ligand-centered p–p transition, which is ob-
served around 350 nm, and the other is a singlet intraligand
charge-transfer (1ILCT) transition, which is observed be-
tween 380 and 500 nm depending on the central metal. As
shown in Figure 3, these two peaks of 1M are shifted to
longer wavelengths in the gel phase compared to those in
the solution phase (1Cu: lmax =346!352 (p–p) and 392!
413 nm (1ILCT), 1Pd: lmax =349!358 (p–p) and 417!
455 nm (1ILCT), 1Pt: lmax =352!363 (p–p) and 460!
491 nm (1ILCT)). These shifts indicate that 8-quinolinol/
metal(II)–chelate moieties in the 1M+p-xylene gel tissues
tend to adopt a J-aggregation mode.[17] Furthermore, these J
aggregates cause the unique thermochromism in relation to
a sol–gel transition phenomenon, especially in the case of
1Pt (Figure 3c). The color of a heated solution was yellow,
whilst that of a cooled gel was orange. We also measured
UV/Vis absorption spectra of the 1M+n-decane, 1,4-diox-
ane, and 1-butanol gels. The spectral patterns were almost
the same as that of the p-xylene gel, indicating that the ag-
gregation mode of 1M in the gel phase is scarcely affected
by solvents. Meanwhile, formation of the hydrogen bonds
among the amide groups is easily discussed by the data ob-
tained from the FTIR measurements. The C=O stretching
bands appearing in the gel phase were observed to shift to
Powder X-ray diffraction: We performed powder X-ray dif-
fraction (XRD) analysis to determine the packing structure
of the gelators in detail. Powder XRD analysis of the xero-
gel prepared from the 1Pt+benzene gel shows two strong
peaks at 2q=2.18 (42 Š) and 3.48 (26 Š), which should be
assigned to the (100) diffraction and the (010) diffraction
peaks, respectively (Figure 5). Taking a typical stacking dis-
tance of hꢁ4.5 Š between two closely packed 3,4,5-tris-
A
1=1.3 gcmꢀ3 into consideration,[18] we could calculate Z=2,
that is, two molecules per unit cell. Therefore, a packing
structure shown in Figure 6b is proposed as the most likely
aggregation model. The distance of the intercolumnar sepa-
ration (42 Š) is shorter than the molecular length of 1M
(ca. 52 Š). This result implies that the molecules in the gel
tissue are stacked in a tilted fashion along the c axis (Fig-
ure 6c). As clearly seen in Figure 6d, these p–p stacked
structures along the c axis were visually confirmed by high-
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4157

S. Shinkai et al.
resolution TEM (HRTEM) as strong stripe contrasts paral-
lel to the axis along the length of the fiber.
Differential pulse voltammetry (DPV)measurements : To
compare the electronic state of each metal–chelate deriva-
tive, we estimated the electrochemical potential, which is
one of the most essential parameters to determine the per-
formance of materials composed of metal–chelate deriva-
tives, by measuring solutions of the nongelling reference
compounds 2M in benzonitrile by DPV analysis (tetrabutyl-
A
Ag+; counter electrode: Pt wire; scan rate: 50 mVsꢀ1). The
voltammograms obtained for 2M apparently show different
reduction and oxidation potentials depending on the central
metals (Figure 7): 2Cu has a relatively low oxidation poten-
Figure 4. FTIR spectra of the 1M+p-xylene gels (b) and the 1M+
TCE solutions (c): [1M]=5 mgmLꢀ1; a) [1Cu], b) [1Pd], and c) 1Pt.
Figure 7. DPV diagrams of the 2M+benzonitrile solutions; [2M]=
~
&
*
10 mm, 2Cu ( ), 2Pd ( ), and 2Pt ( ); a) Oxidations and b) Reductions.
Figure 5. A powder XRD diagram of the xerogel prepared from the
1Pt+benzene gel: [1Pt]=200 mgmLꢀ1
.
tial (990 mV versus Ag/Ag+) and a high reduction potential
(ꢀ980 mV versus Ag/Ag+), 2Pd has a relatively high oxida-
tion potential (1190 mV versus Ag/Ag+) and a low reduc-
tion potential (ꢀ1720 mV versus Ag/Ag+), and 2Pt has rela-
tively low oxidation (1000 mV versus Ag/Ag+) and reduc-
tion potentials (ꢀ1800 mV versus Ag/Ag+). Taking the idea
into consideration that these differences in the redox poten-
tials should be reflected in the electronic properties of each
1M gel fiber, we carried out the following experiments.
Field-emission properties of the 1M gel fibers: Field emis-
sion of inorganic nanostructures and carbon nanotubes has
been reported for many years.[19,20] Meanwhile, it has been
confirmed in the last five years that several organic nano-
[21]
structures also workas effective field-emission materials.
As a field emitter, a needle-like shape and semiconducting
properties are required. Considering that the 1M gel fibers
can fulfil both requirements, we expect that they would
show field-emission properties. Field-emission measure-
Figure 6. a) Molecular scales of 1M; b) proposed packing model of 1M
in the gel tissues; c) tilted arrangement of 1M along the c axis, and d) an
HRTEM image of the 1Pt+p-xylene gel: [1Pt]=2.0 mgmLꢀ1. The scale
bar length is 20 nm.
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Organogels
FULL PAPER
ments were carried out with the cast-film of the 1M gel
fiber on an ITO (indium titanium oxide) electrode. Figure 8
shows typical plots of the field-emission current density J
versus the applied electric field E of the 1M cast-films. The
*
Figure 8. Field-emission J–E curves of the 1M nanofibers, 1Cu ( ), 1Pd
~
&
( ), and 1Pt ( ).
Figure 9. a) Phosphorescence spectra of the 1Pt+p-xylene gel (b) and
the 1Pt+TCE solution (c): [1Pt]=2.0 mgmLꢀ1, excited at 490 nm for
the gel and at 460 nm for the solution. b) A photograph of the 1Pt gel
and solution under UV light (365 nm). c) A CLSM image of the 1Pt+p-
1Cu, 1Pd, and 1Pt cast-films exhibit turn-on field values of
approximately 90, 125, and 40 Vmmꢀ1, respectively. Al-
though these values are higher than those of other inorganic
and organic field-emission materials reported earlier,[12,19–21]
the gel fibers have the advantage over other materials in
that they are easily prepared by a spontaneous self-assem-
bling process in solution. Furthermore, the turn-on field
values of 1M are clearly different depending on the central
metals. As confirmed above, the shapes of the gel fibers pre-
pared from 1M are almost the same, because their self-as-
sembling properties are mainly dominated by the organic
ligand moieties and the three kinds of central metals have
the same coordination geometry. The above-mentioned re-
sults therefore imply that the field-emission performances of
nanofibers with the same shape are easily controlled by
changing the central metals. Generally speaking, it is very
difficult, especially in the nanoscale region, to control the
turn-on field value by molecular design. In this context, the
present metallogel system has a unique character.
xylene gel: [1Pt]=2.0 mgmLꢀ1
.
luminescence and high luminescence quantum yield for vari-
ous applications such as electroluminescent displays,[23] sen-
sors,[24] photovoltaic devices,[25] and photocatalysts.[26] Con-
sidering the practical utilization of phosphorescent materi-
als, the most essential, but difficult, problem is how to avoid
the dioxygen quenching of their excited triplet states. One
of the successful methods in aqueous solution is to utilize
micellar functions in which the collisional deactivation of ex-
cited triplet states can be minimized by solute partitioning
to the micellar phase.[27] Meanwhile, low-molecular-weight
gel tissues are produced by microphase (or nanophase) sep-
aration of gelator molecules and solvent molecules, in which
the gelator phase is well segregated from the solvent phase
that contains dioxygen. In addition, the gelator assemblies
have a crystal-like nature favorable to segregation, being
different from the dynamic nature characteristic of the mi-
cellar systems. Considering that the phosphorescent chelate
moieties are located inside the 1Pt gel fibers, deactivation
of excited triplet states by collision with dioxygen molecules
could be effectively inhibited. To estimate the inhibition ef-
Phosphorescence spectra of 1Pt: Next, we focus upon the
influence of the gel formation on phosphorescence proper-
ties of 1Pt. It is known that 8-quinolinol/platinum(II)–che-
late derivatives show red phosphorescence around 600–
650 nm, which is emitted from the triplet ligand-centered
transitions (3p–p or 3ILCT).[22] We observed light orange
phosphorescence appearing at 620 nm from the 1Pt+TCE
solution, whereas red phosphorescence appeared at 650 nm
from the 1Pt+p-xylene gel under UV light (Figure 9). This
color change originates from J aggregation of the chelate
moieties as confirmed by the UV/Vis absorption spectra and
the powder XRD analysis. Moreover, this red phosphores-
cence is emitted from a nanoscale fibrous structure, which is
directly observable by confocal laser scanning microscopy
(CLSM) (Figure 9c).
ficiency of dioxygen quenching (Evs.O ) we conducted the fol-
2
lowing experiments. Phosphorescence spectra of 1Pt and
2Pt were measured under an argon atmosphere or a dioxy-
gen-saturated atmosphere in the gel phase or in the solution
phase,[28] for which we defined Evs.O as PIdioxygen/PIargon ”100
2
under each measurement condition.[29] The experimental re-
sults are summarized in Figure 10. We found that the Evs.O
2
values of 1Pt are larger than those of 2Pt in all gelling sol-
vents, such as p-xylene, 1,4-dioxane, and 1-butanol. On the
other hand, the Evs.O values of 1Pt and 2Pt are almost the
2
same in the nongelling solvent TCE. These results support
Inhibition efficiency of dioxygen quenching: Phosphorescent
materials composed of metal–chelate derivatives have
gained much interest due to their advantages of long-lived
the view that the increase of the Evs.O is not due to the dif-
ference in the peripheral substituent structure, but due to
the molecular assembling effect in the gel phase. In other
2
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4159

S. Shinkai et al.
phosphorescence spectra were recorded by using a Shimadzu UV-2500PC
spectrometer and a Perkin–Elmer LS 55 luminescence spectrometer, re-
spectively. DPV measurements were performed by using a BAS 100B/W
(CV-50W) instrument.
Gelation test: The gelator and the solvent were put in a septum-capped
test tube and heated until the solid was dissolved. The sample vial was
cooled in air to 258C, then left for 1 h at this temperature. The state of
the materials was evaluated by the “stable to inversion of a test tube”
method.
SEM and TEM measurements: For SEM observations, a piece of the gel
was placed on a carbon-coated copper grid and was dried in vacuo for
12 h at RT. Then, the obtained sample was shielded by Pt and was exam-
ined with a Hitachi S-5000 scanning electron microscope. The accelerat-
ing voltage was 25 kV. For TEM observations, a carbon-coated copper
grid was immersed in the gel and dried for 12 h under reduced pressure.
The grid was examined with a Hitachi H-600 transmission electron mi-
croscope, operating at 120 kV.
Figure 10. Evs. values of 1Pt (white) and 2Pt (black) for four kinds of
solvents: [1Pt]=[2Pt]=1 mm.
O2
words, one can regard that the gel phase is capable of pro-
tecting the chromophore moiety from dioxygen quenching.
Powder X-ray diffraction: The gel was prepared in a sample tube and
was frozen by using liquid nitrogen. The frozen specimen was evaporated
by using a vacuum pump for 1 day at RT. The obtained xerogel was put
in a capillary (F=2.0 mm). An X-ray diffraction pattern was recorded
on an imaging plate by using Cu radiation (l=1.54178 Š).
Conclusion
We have demonstrated that 3,4,5-tris(n-dodecyloxy)benzoyl-
A
Confocal laser scanning microscopy (CLSM)measurements : The 1Pt+
p-xylene gel was placed on a glass plate and was observed with a BIO-
RAD Radiance 2000 AGR3 microscope. The excitation wavelength was
514 nm (argon laser with reflector turret).
1M act as highly efficient gelators for various organic sol-
vents. This gelation capability is attributed to the strong p–p
interactions of chelate moieties as well as the hydrogen-
bond interactions among the amide groups. As confirmed by
the field-emission measurements, the electronic properties
of the three kinds of gel fibers obtained are evidently differ-
ent depending on the central metals although their shapes
are almost the same. In the case of 1Pt, the p–p interaction
of the chelate moiety results in thermo- and solvatochrom-
ism of visible color and a color change in the phosphores-
cence emission in response to a sol–gel phase transition.
Furthermore, it was shown that dioxygen quenching of the
excited triplet states is efficiently inhibited in the gel phase.
These findings consistently indicate that introduction of
metal chelates into the low-
Field-emission measurements: Field-emission measurements were carried
out in a high-vacuum chamber under about 10ꢀ7 Torr pressure. We used a
tungsten probe with a diameter of 500 mm as an anode.[30] The cross-sec-
tional area of the anode was 1.96”10ꢀ7 m2. Field-emission current density
and electric field characteristics were measured for a constant distance
(10 mm) between the anode and the 1M nanofibers.
Syntheses of 8-quinolinol/metal(II)-chelate-based gelators and nongelling
reference compounds: Compounds 1M and 2M were synthesized accord-
ing to Scheme 1 and identified by MALDI-TOF mass spectrometry,
1H NMR, FTIR, and UV/Vis absorption spectra, and elemental analysis.
Compound 5 was prepared as described earlier.[13] 3,4,5-Trihydroxybenzo-
ic acid methyl ester was converted into its ether (3) by the reaction with
1-bromododecane. Subsequent hydrolysis of the ester groups with NaOH
yielded 4. The coupling reaction of 4 with ethylenediamine gave 5.
molecular-weight gel system is
one of the most effective strat-
egies to obtain a wide variety
of photo- and electrochemical
nanomaterials.
Experimental Section
All starting materials and solvents
were purchased from Aldrich, TCI,
Kishida Chemical, or Wako, and were
used as received. 1H NMR spectra
were recorded by using Bruker AC-
250 PC and DMX 600 spectrometers.
Chemical shifts are reported in ppm
downfield from tetramethylsilane
(TMS) as the internal standard. FTIR
spectra were obtained by using
a
Perkin–Elmer instrument Spectru-
m One FTIR spectrometer. Mass
spectral data were obtained by using
Scheme 1. Syntheses of 1M and 2M: a) n-C12H25Br, K2CO3, DMF, 608C; b) NaOH, 1,4-dioxane, H2O, reflux;
c) Ethylenediamine, BOP reagent, THF, reflux; d) 8-Quinolinol-7-carboxylic acid, BOP reagent, TEA, THF,
a
Perseptive Voyager RP MALDI-
reflux; e) Cu
G
N
TOF mass spectrometer. UV/Vis and
2Pd; K2PtCl4, NaOH, H2O, 2-propanol, reflux, for 1Pt and 2Pt.
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Organogels
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Preparation of 1: Compound 5 (2.0 g, 4.1 mmol) was dissolved in THF
(30 mL). BOP reagent (1.9 g, 4.2 mmol), triethylamine (430 mg,
4.2 mmol), and 8-hydroxyquinoline-7-carboxylic acid (790 mg, 4.2 mmol)
were added to the solution and the resultant mixture was refluxed for
3 h. After cooling the mixture to RT, the solution was concentrated
under reduced pressure. The resultant residue was dissolved in CHCl3
and was washed with brine three times. The organic layer was dried over
anhydrous Na2CO3 and concentrated under reduced pressure. The resul-
tant residue was subjected to column chromatography (silica gel, CHCl3/
MeOH 20:1 (v/v)) to give 1 in 84% (2.1 g) yield as a white solid.
1H NMR (250 MHz, CDCl3, TMS, RT): d=0.84–0.88 (m, 9H), 1.20–1.60
(m, 54H), 1.67–1.88 (m, 6H), 3.67–3.79 (m, 2H), 3.79–3.91 (m, 2H), 3.97
(t, J=6.5 Hz, 2H), 4.04 (t, J=6.5 Hz, 4H), 7.07 (s, 2H), 7.37 (d, J=
8.7 Hz, 1H), 7.50–7.60 (m, 2H), 8.14 (d, J=9.0 Hz, 1H), 8.18 (m, 1H),
8.42–8.48 (m, 1H), 8.86 ppm (m, 1H); MALDI-TOF MS (dithranol): m/z
calcd for [M+H]+: 888.68; found: 888.61; elemental analysis calcd (%)
for C55H89N3O6: C 74.36, H 10.10, N 4.73; found: C 74.26, H 10.06, N
4.73.
(v/v)) to give 2 in 80% (670 mg) yield as a white solid; 1H NMR
(250 MHz, CDCl3, TMS, RT): d=0.87–0.98 (m, 6H), 1.20–1.50 (m, 8H),
1.60–1.70 (m, 1H), 3.50 (t, J=5.3 Hz, 2H), 7.34 (d, J=8.9 Hz, 1H), 7.48
(dd, J=8.2, 4.2 Hz, 1H), 7.99 (br, 1H), 8.13–8.18 (m, 2H), 8.83 ppm (d,
J=3.3 Hz, 1H); MALDI-TOF MS (dithranol): m/z calcd for [M+H]+:
301.18; found: 303.84; elemental analysis calcd (%) for C18H24N2O2: C
71.97, H 8.05, N 9.33; found: C 71.76, H 8.04, N 9.26.
Preparation of 2Cu: This compound was prepared by a procedure similar
to that for the synthesis of compound 1Cu from 2 and Cu
A
2Cu was obtained as an greenish solid (yield 85%). IR (NaCl): n˜ =3299,
2930, 1638, 1547, 1499, 1385 cmꢀ1
; UV/Vis (TCE): lmax =331, 345,
398 nm; MALDI-TOF MS (dithranol): m/z calcd for [M+Na]+: 682.3;
found: 684.3; elemental analysis calcd (%) for C36H46CuN4O4: C 65.28, H
7.00, N 8.46; found: C 65.35, H 6.96, N 8.41.
Preparation of 2Pd: This compound was prepared by a procedure similar
to that for the synthesis of compound 1Cu from 2 and Pd(OAc)2, and
U
2Pd was obtained as a yellow solid (yield 72%). 1H NMR (600 MHz,
[D4]TCE, TMS, 808C): d=0.89 (t, J=6.9 Hz, 6H), 1.00 (t, J=7.0 Hz,
6H), 1.31–1.34 (m, 4H), 1.40–1.45 (m, 8H), 1.50–1.53 (m, 4H), 1.62–1.65
(m, 2H), 3.50 (m, 4H), 7.07 (d, J=8.4 Hz, 2H), 7.45 (m, 2H), 8.31 (d, J=
8.3 Hz, 2H), 8.34–36 (m, 4H), 9.04 ppm (br, 2H); IR (NaCl): n˜ =3686,
2929, 1637, 1603, 1546, 1501, 1448, 1374 cmꢀ1; UV/Vis (TCE): lmax =334,
349, 425 nm; MALDI-TOF MS (dithranol): m/z calcd for [M+H]+:
703.2; found: 703.9; elemental analysis calcd (%) for C36H46N4O4Pd: C
61.31, H 6.57, N 7.94; found: C 61.29, H 6.58, N 7.90.
Preparation of 1Cu: A suspension of Cu(OAc)2 (10.0 mg, 0.055 mmol) in
N
methanol (2 mL) was added to a solution of compound 1 (100 mg,
0.11 mmol) in chloroform (10 mL), and the mixture was stirred at RT for
20 min. The reaction mixture was poured into methanol (100 mL), and
the resultant precipitate was collected. The obtained solid was further pu-
rified by the recrystallization from the mixed solvent of methanol and
ethyl acetate to give 1Cu in 70% yield (72 mg) as a greenish solid. IR
(NaCl): n˜ =3284, 2928, 2855, 1639, 1582, 1544, 1499, 1450, 1386 cmꢀ1
;
Preparation of 2Pt: This compound was prepared by a procedure similar
to that for the synthesis of compound 1Pt from 2 and K2PtCl4, and 2Pt
was obtained as an orange solid (yield 4%). 1H NMR (600 MHz,
[D4]TCE, TMS, 808C): d=0.90 (t, J=7.1 Hz, 6H), 1.01 (t, J=7.3 Hz,
6H), 1.20–1.80 (m, 18H), 3.53 (m, 4H), 7.10 (d, J=8.5 Hz, 2H), 7.45 (m,
2H), 8.29 (d, J=8.4 Hz, 2H), 8.39 (d, J=8.3 Hz, 2H), 8.64 (m, 2H),
8.90 ppm (m, 2H); IR (NaCl): n˜ =3686, 3341, 2929, 1639, 1603, 1547,
1502, 1449, 1375 cmꢀ1; UV/Vis (TCE): lmax =342, 351, 464 nm; MALDI-
TOF MS (dithranol): m/z calcd for [M+H]+: 794.32; found: 793.36; ele-
mental analysis calcd (%) for C36H46N4O4Pt: C 54.47, H 5.84, N 7.06;
found: C 54.29, H 5.84, N 7.06.
UV/Vis (TCE): lmax =332, 346, 393 nm; MALDI-TOF MS (dithranol):
m/z calcd for [M+H]+: 1837.3; found: 1836.1; elemental analysis calcd
(%) for C110H176CuN6O12·H2O: C 71.18, H 9.67, N 4.53; found: C 71.21,
H 9.53, N 4.50.
Preparation of 1Pd: This compound was prepared by a procedure similar
to that for the synthesis of compound 1Cu from 1 and Pd(OAc)2 and
U
1Pd was obtained as a yellow solid (yield 76%). 1H NMR (600 MHz,
[D4]TCE, TMS, 808C): d=0.85–0.87 (m, 18H), 1.24–1.28 (m, 96H), 1.41–
1.43 (m, 12H), 1.67 (m, 4H), 1.74 (m, 8H), 3.71 (m, 4H), 3.83 (m, 4H),
3.89 (t, J=6.5 Hz, 4H), 3.96 (t, J=6.4 Hz, 8H), 7.02 (s, 4H), 7.07 (d, J=
8.5 Hz, 2H), 7.27 (br, 2H), 7.53 (m, 2H), 8.25 (d, J=8.5 Hz, 2H), 8.29
(m, 4H), 9.44 ppm (t, J=5.8 Hz, 2H); IR (NaCl): n˜ =3303, 2928, 2855,
1639, 1582, 1544, 1500, 1448, 1375 cmꢀ1; UV/Vis (TCE): lmax =334, 349,
418 nm; MALDI-TOF MS (dithranol): m/z calcd for [M+H]+: 1880.2;
found: 1879.5; elemental analysis calcd (%) for C110H176N6O12Pd·H2O: C
69.57, H 9.45, N 4.43; found: C 69.33, H 9.15, N 4.46.
Acknowledgements
Preparation of 1Pt: A solution of K2PtCl4 (23 mg, 55 mmol) in aqueous
NaOH (pH 10, 1 mL) was added to a suspension of compound 1 (100 mg,
0.11 mmol) in 2-propanol (30 mL). The reaction mixture was refluxed for
20 h. After cooling the mixture to RT, the solution was concentrated
under reduced pressure. The resultant residue was subjected to column
chromatography (silica gel, CHCl3/MeOH 20:1 (v/v)) to give 1Pt in 40%
(44 mg) yield as an orange solid. 1H NMR (600 MHz, [D4]TCE, TMS,
808C): d=0.86–0.88 (m, 18H), 1.25–1.28 (m, 96H), 1.39–1.43 (m, 12H),
1.66 (m, 4H), 1.73 (m, 8H), 3.74 (m, 4H), 3.87 (m, 4H), 3.89 (t, J=
6.5 Hz, 4H), 3.95 (t, J=6.5 Hz, 8H), 7.01 (s, 4H), 7.06 (d, J=8.5 Hz,
2H), 7.22 (br, 2H), 7.55 (dd, J=8.3, 5.0 Hz, 2H), 8.24 (d, J=8.5 Hz, 2H),
8.33 (d, J=8.3 Hz, 2H), 8.62 (d, J=4.8 Hz, 2H), 9.36 ppm (t, J=5.9 Hz,
This workwas partially supported by the Ministry of Education, Culture,
Sports, Science, and Technology (Japan) through Grants-in-Aid (No.
16750122, 15105004,and 18033040) and through the 21st Century COE
Program, “Functional Innovation of Molecular Informatics”. A JSPS fel-
lowship for M.S. is also acknowledged.
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Received: December 18, 2006
Published online: April 3, 2007
4162
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Chem. Eur. J. 2007, 13, 4155 – 4162