Chiral amplification in one-dimensional helical nanostructures self-organized from phenylethynyl thiophene with elaborated long-chain dicarboxamides

Article abstract of DOI:10.1021/jo200573y

A bis-phenylethynyl thiophene derivative functionalized with long-chain pyridyl biscarboxamides displayed unique helical morphology in the xerogel form via nicely complementary intermolecular interactions. The helical nanostructures visualized by TEM and AFM remarkably matched well with the computational results. Supramolecular chirality can be amplified by coassembly of a chiral conductor to bias the helical arrangement.

Full text of DOI:10.1021/jo200573y

ARTICLE
pubs.acs.org/joc
Chiral Amplification in One-Dimensional Helical Nanostructures
Self-Organized from Phenylethynyl Thiophene with Elaborated
Long-Chain Dicarboxamides
Chun-Hsian Li,†,‡ Kai-Chi Chang,† Chia-Chen Tsou,† Yikang Lan,§ Hsiao-Ching Yang,*,§ and
Shih-Sheng Sun*,†
†Institute of Chemistry, Academia Sinica, Taipei, 115, Taiwan, Republic of China
‡Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan, Republic of China
§Department of Chemistry, Fu-Jen Catholic University, Taipei County, Taiwan, Republic of China
S Supporting Information
b
ABSTRACT: A bis-phenylethynyl thiophene derivative functionalized
with long-chain pyridyl biscarboxamides displayed unique helical mor-
phology in the xerogel form via nicely complementary intermolecular
interactions. The helical nanostructures visualized by TEM and AFM
remarkably matched well with the computational results. Supramolecular
chirality can be amplified by coassembly of a chiral conductor to bias the
helical arrangement.
’ INTRODUCTION
and the supramolecular chirality of such assemblies can be further
biased by coassembly of chiral and achiral gelators through the
“sergeants-and-soldiers” approach.7
Chirality plays a fundamental role in biological processes and
has a profound influence on the chemistry and molecular interac-
tions of living organisms.1 Particular attention has been devoted to
realization of the artificial hierarchical assemblies inspired from
those intriguing self-organization of biological molecules into highly
functional supramolecular chiral assemblies through noncovalent
interactions.2 Remarkable control of supramolecular chirality in
nonbiological systems has been demonstrated with well-designed
complementary building blocks by cooperative noncovalent inter-
actions. Manipulation of chiral amplification is also important for
many applications such as enantioselective catalysis, chiral separa-
tion, and sensing.3
Self-assembly of small molecules into one-dimensional nano-
structures offers a number of potential applications in electron-
ically and biologically active materials.4 In this context, organogels
represent promising candidates for creating such unique nanoscopic
structures due to their ability of self-organization into highly ordered
hierarchical nanomorphology.5 Recently, we reported a unique
building block featuring elaborated long-chain dicarboxamides,
which easily turns the molecules incorporating such moieties into
organogelators capable of effectively immobilizing a variety of
organic solvents.6 The perfectly matched intermolecular hydro-
gen-bonding and π-stacking interactions have been attributed to the
highly efficient gelation ability of such rigid π-conjugated gelators.
Herein, we report an interesting example of gelation-assisted
preferential growth of one-dimensional helical nanostructures,
’ RESULTS AND DISCUSSION
Three organogelators shown in Figure 1 were prepared by
published methods and fully characterized.6 TM12 was synthe-
sized as a model compound to assess the photophysical proper-
ties of these organogelators. The different chain length in the
gelators is expected to have little influence on the opticalties. The
gelation ability is superior in somesolvents withminimum gelation
concentration as low as 0.5 mg/mL (see Table S1, Supporting
Information). The solꢀgel interconversion is fully thermorever-
sible by several cycles of heating and cooling. The organogels are
remarkably stable, which can be stored for months except for gels
based on PM-chiral, which slowly “melted” to viscous solution,
and precipitation appeared in a few days. The longer alkyl chains in
PM18 seem to provide stronger intermolecular interactions
between the gelator molecules and the surrounding solvent
molecules than its shorter congener PM-chiral, which resulted
in their differences in terms of thermodynamic stability.
Temperature-dependent 1H NMR spectra were recorded for
all three gelators (Figures S1ꢀS3, Supporting Information). In
general, the carboxamide NꢀH proton signal resonances in all
Received: January 6, 2011
Published: May 27, 2011
r
2011 American Chemical Society
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Figure 1. Structure of organogelators.
Figure 2. TEM images of helical fibers of PM18 (5.0 ꢁ 10ꢀ5 M) self-assembly from a solution of toluene. The image at the right is a magnification of the
image at the left side.
three gelators shifted to the upfield position, whereas the
β proton resonances of pyridine and proton resonances of
thiophene shifted to the downfield position with the temperature
being raised from 298 to 338 K. The upfield shift of the
carboxamide NꢀH proton signal and the downfield shift of
the aromatic proton signals with increasing temperature suggest
the weakening of intermolecular hydrogen-bonding and aromatic
πꢀπ interactions. The two doublet signal resonances from
phenyl rings in PM18 and PM-chiral also showed minor down-
field shifts when temperature was raised from 298 to 338 K, also
evidence of the weakening of aromatic πꢀπ interactions. These
results clearly demonstrated that the primary interactions respon-
sible for molecular aggregation are due to the intermolecular
hydrogen-bonding and favorable aromatic πꢀπ interactions
between the gelator molecules.
The absorption and fluorescence data along with fluorescence
quantum yields of three gelators in optically dilute solution are
summarized in Tables S2 and S3, Supporting Information. All
three gelators display a series of absorption bands in the UV
region and tailed into the near UV region (Figure S4, Supporting
Information). The high-energy absorption band at ca. 334 nm for
these compounds is assigned to a πꢀπ* transition mainly
localized on the ethynylpyridine biscarboxamide moieties,
whereas the low-energy absorption band at ca. 385 nm, which
is absent in the spectrum of TM12, is assigned to the πꢀπ*
transition mainly localized on the bisphenylethynyl thiophene.
All compounds show fairly weak fluorescence at room tempera-
ture solution with quantum yields less than 0.42% with typical
fluorescence lifetimes in the subnanosecond scale.
The fluorescence intensities of these gelators are enhanced
from solution to gel state (Figure S5, Supporting Information).
The radiative rate constants in dilute solution and in the gel form
are comparable for both PM18 and PM-chiral, whereas the
nonradiative rate constants display a 2-fold decrease in the gel
form compared to the solution state (see Tables S2 and S3,
Supporting Information). Upon formation of gel, the resulting
ordered aggregates not only bathochromatically shifted the
absorption to a longer wavelength compared to its molecularly
dissolved counterparts but also expect to greatly reduce the
conformational flexibility and, thus, slow down the nonradiative
decay processes with enhanced fluorescence quantum yields.6b,8
TEM images for three gelators display interconnected net-
works of fibers with a diameter on the order of 20ꢀ50 nm and a
length of several micrometers. The aspect ratios of the fibril
assemblies are estimated to be ∼2000. Careful scrutiny of the
image of gelator PM18 from a dilute solution of toluene (5.0 ꢁ
10ꢀ5 M) in Figure 2 (see also Figure S9, Supporting Information,
for a larger image of Figure 2) reveals an intriguing one-
dimensional helical morphology with an average helical pitch
of ∼11 nm. The diameters of these helical stacks are estimated to
be 10.4 nm, which is slightly longer than the extended molecular
length calculated by molecular modeling (vide infra).
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Figure 3. AFM images of helical fibers of PM18 from a solution of toluene: (left) 5.0 ꢁ 10ꢀ5 and (right) 6.0 ꢁ 10ꢀ4 M (image size 2.0 μm ꢁ 2.0 μm).
Figure 4. Schematic representation of the self-assembled organogelators into helical nanostructures, and effect of doping PM-chiral on the energy
disparity of the enantiomeric helical formation.
The helical fibers observed in TEM for xerogels of PM18
prepared from toluene solution are even more prominent under
AFM studies. Figure 3 shows AFM images of the xerogels of
PM18 prepared from toluene on silicon oxide (see also Figures
S10ꢀS13, Supporting Information). The AFM images clearly
display formation of entangled left-handed helical and right-
handed helical fibers. The pitch distribution of these helical fibers
ranges from ∼11 to 120 nm depending on the gelator concen-
tration. At a concentration of 5.0 ꢁ 10ꢀ5 M, the thinnest helical
pitch and diameter are estimated to be ∼11 and 12 nm,
respectively, with a typical length of 1.5 μm. Longer and thicker
helical fibers of PM18 were observed in the AFM image at a
concentration of 6.0 ꢁ 10ꢀ4 M. Attempts to acquire AFM images
at 1.0 ꢁ 10ꢀ3 M or higher concentration were not successful but
produced very blurry images. It is interesting to note that the
AFM images of PM-chiral showed scattered helical fibers out of
normal linear fibers (Figures S14 and S15, Supporting In-
formation). The lack of a majority of helical fibers in the xerogel
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of PM-chiral is likely due to the nature of the thermodynamic
instability of PM-chiral aggregates during the solvent evaporation
process when preparing the xerogels for AFM measurements.
To unveil the nature of noncovalent interactions and supra-
molecular aggregation at these gelator systems, molecular me-
chanics and dynamics simulations were carried out using a
Dreiding force field.9 By taking advantage of the intramolecular
hydrogen-bonding interactions between the amide NꢀHs and
the pyridine N atom, the pyridyl bis-carboxamide moiety adopts
a rigid planar conformation and affords the corresponding
twisted structures of an enantiomeric pair in PM18 (Figure
S16, Supporting Information). This stereorequirement develops
extraordinary features, leading to the enantiomeric stacking
arrangements between the neighboring gelators with slightly
clockwise- and counter-clockwise-oriented stackings. The opti-
mized stackings are stabilized by the strong intermolecular
hydrogen-bonding interactions of the amide NꢀHs with the
next adjacent amide carbonyl O atoms and πꢀπ interactions.
The optimized spacing and offset angle between the two adjacent
gelator molecules are found to be 3.7 Å and 11°, respectively. As
anticipated, the XRD patterns of toluene films of PM18 and PM-
chiral exhibit a diffuse reflection at d = 3.6 and 3.7 Å, respectively,
indicative of noticeable πꢀπ interactions in the gel state (see
Figure S18, Supporting Information).
Figure 5. CD spectra of PM18 in toluene (1 ꢁ 10ꢀ3 M) at 25 °C with
different amounts of coassembled PM-chiral.
Figure 4 gives the nanocoil aggregate structures of PM18 in
which the relevant structural parameters are closely matched with
the TEM and AFM images with a diameter of around 10 nm and
a pitch length of 11 nm consisting of 33 aggregated gelator
molecules. Molecular dynamics simulations show that an equi-
librium mixture exists between the left-handed and right-handed
sense of PM18 assembly. It is interesting to note that a slight
counter-clockwise-oriented stacking of the coassembly would be
relatively more stable than the clockwise one by 8.5 and 14.5 kcal
molꢀ1 at a doping of 50% and 100% PM-chiral, respectively. The
XRD pattern of PM18 showed a reflection peak corresponding
to a d spacing of the aggregate of 32.2 Å (see Figure S18,
Supporting Information), which is on the order of the calculated
interdigitated alkoxyl chains with 31.9 Å. Both XRD patterns of
PM18 and PM-chiral at the low-angle region displayed a peak at
∼20 Å, which is attributed to the molecular dimension along the
2,5-bis-phenylethynyl thiophene framework.
PM-chiral showed no circular dichroism (CD) responses
until the concentration was higher than 7.5 ꢁ 10ꢀ5 M with
three negative CD bands appearing at 360, 412, and 438 nm
(Figure S20, Supporting Information). The contribution of
linear dichroism (LD) to the observed spectra is considered to
be small because the recorded LD signals from the same samples
were very weak and the intensities of CD bands were intact to the
rotation of the sample by 90° in a plane normal to the incident
light.10 As expected, achiral PM18 was CD silent, which indicates
no net macromolecular chirality presented in these achiral
supramolecular aggregates. Nonetheless, it is possible to bias
the helicity of achiral units in the presence of chiral handles and
strong noncovalent interactions between the monomeric units
with an intrinsic conformational chirality of the assembly and
careful matching of secondary interactions to obtain a well-
defined chiral conformation in the aggregation process.1 Indeed,
the appearance of the CD signal of PM18 with a negative value
was observed upon doping of PM-chiral over 5 mol %, which is
indicative of formation of left-handed chiral helical aggregates
(Figure 5).5a,11 The negative and positive Cotton bands at a
doping of PM-chiral over 20 mol % appeared at 362 and 338 nm,
Figure 6. Temperature dependence of the UVꢀvis (top) and CD
(bottom) spectra of a toluene solution of PM18 (1 ꢁ 10ꢀ3 M) and PM-
chiral (5 mol %) coassembly at different temperatures.
respectively, with a zero crossing at 348 and 330 nm, which is
close to the πꢀπ* transition of the thiophene ethynylpyridyl
dicarboxamide chromophore in the gel state. Thus, the observed
CD spectra suggest that the left-handed helical arrangement is
circularly polarized along the transition moments of the thio-
phene ethynylpyridyl dicarboxamide chromophores. The CD
intensities at 362 nm are plotted against the doping concentra-
tion of PM-chiral (Figure S21, Supporting Information), show-
ing a steady increase of CD signal upon increasing the amount of
PM-chiral. The LD spectra were separately recorded under the
same experimental conditions (Figure S22, Supporting In-
formation). The optical densities of the LD signals from these
gel samples were very weak (<0.001), and thus, their contribu-
tions to the observed CD spectra were considered to be
negligible.10 The CD signals increased with doping amount of
PM-chiral up to 30 mol % in the supramolecular assemblies with
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Scheme 1
Scheme 2
anisotropy factor g values of ꢀ1.9 ꢁ 10ꢀ3 and 2.3 ꢁ 10ꢀ4 at 362
and 338 nm, respectively.7b A similar pattern but weaker intensity
of CD responses of PM18 upon coassembling various amounts
of PM-chiral was observed when the concentration of PM18 was
lowered to 1 ꢁ 10ꢀ4 M (Figure S23, Supporting Information).
Variable-temperature absorption spectra of coassembled
PM18 (1 ꢁ 10ꢀ3 M) and PM-chiral (5 mol %) showed a clear
transition from the molecularly isolated molecules to the self-assembly
nanostructures upon decreasing temperature (Figure 6).12 The
temperature at Ragg = 0.5 is estimated to be 35 °C on the basis of
temperature-dependent UVꢀvis absorption spectra of coassembled
PM18 (1 ꢁ 10ꢀ3 M) and PM-chiral (5 mol %) (Figure S24,
Supporting Information).5e The CD signal did not appear until the
temperature was lower than 45 °C, which is slightly higher than the
critical gelation temperature of 36 °C. The CD intensity increased
with decreasing temperature due to the enhanced intermolecular
interactions between gelator molecules with decreasing temperature.
Heating the sample again resulted in a gradual disappearing of the CD
signal, whereas the CD signal can be restored by cooling the sample,
demonstrating the highly dynamic nature during the chiral conversion
process.
the molecular level by microscopic techniques. The supramole-
cular chirality can be induced by coassembly of a chiral conductor
PM-chiral and PM18 to bias the helical arrangement via the
“sergeant and soldiers” principle, which was confirmed by chiral
amplification of CD Cotton signals. The degree of chiral
amplification strongly depends on temperature. The intermole-
cular interactions are enhanced between the gelators with
decreasing temperature and resulted in a favorable chiral ampli-
fication effect.
’ EXPERIMENTAL SECTION
Materials and Methods. All chemicals are commercially available
unless mentioned elsewhere. All reactions and manipulations were
carried out under N2 with the use of standard inert atmosphere and
Schlenk techniques. Solvents used for synthesis were dried by standard
procedures and stored under nitrogen atmosphere. Reactions were
monitored by TLC using aluminum plates precoated with a 0.25 mm
layer of silica gel containing a fluorescent indicator. Starting materials,
3,4-diethynyl-2,5-bis(phenylethynyl)thiophene (4),6a 4-bromo-N2,N6-
bis(4-(dodecyloxy)phenyl)pyridine-2,6-dicarboxamide (7),6a and 3,4-
diethynylthiophene (17)13 were synthesized according to published
methods. The synthetic procedures are outlined in Schemes 1 and 2.
Compound 8. To a 500-mL flask containing 4-(octadecyloxy)aniline
(1.66 g, 4.6 mmol) and 4-bromo-pyridine-2,6-dicarbonyl dichloride
(0.59 g, 2.1 mmol) was added CH2Cl2 (60 mL) and NEt3 (1.0 mL),
and the resulting mixture was stirred at room temperature for 12 h. The
solution was washed with water (100 mL ꢁ 3). The organic layer was
collected and dried over MgSO4. The resulting residue was redissolved
in THF and slowly precipitated with MeOH in a freezer to afford a white
’ CONCLUSION
In summary, the xerogel of PM18 displayed unique helical
morphology via nicely complementary intermolecular hydrogen-
bonding and aromatic πꢀπ stacking interactions. The helical
nanostructures visualized by TEM and AFM matched with the
theoretically calculated helical pitches and diameters. Thus, the
hierarchical assembly of supramolecular helices can be realized at
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solid (1.53 g, 78%). 1H NMR (400 MHz, CDCl3) δ 9.29 (s, 2H), 8.58 (s,
2H), 7.60 (d, 4H, J = 8 Hz), 6.91 (d, 4H, J = 8 Hz), 3.94 (t, 4H, J = 6 Hz),
1.87ꢀ1.79 (m, 4H), 1.53ꢀ1.18 (m, 60H), 0.86 (t, 6H, J = 6.8 Hz). 13C
NMR (100 MHz, CDCl3) δ 159.9, 156.7, 150.0, 136.8, 129.7, 128.7,
122.0, 114.9, 68.4, 31.9, 29.7, 29.6, 29.3, 26.0, 22.7, 14.1. HRFABMS m/z
932.5878 (calcd m/z 932.5880 for [M + H]+). Anal. Calcd for
with 17 (0.10 g, 0.76 mmol), 7 (1.21 g, 1.59 mmol), Pd(PPh3)4 (53 mg,
0.10 mmol), CuI (7.7 mg, 0.10 mmol), iPr2NH (20 mL), and THF
(30 mL). The mixture was stirred at 50 °C for 48 h. After reaction, the
volatile solvent was removed under reduced pressure. Subsequently,
water (100 mL) was added and the brown suspension was extracted with
CH2Cl2 (100 mL ꢁ 3). The organic layer was collected, dried over
MgSO4, filtered through a short neutral alumina column, and then
evaporated to dryness. The resulting residue was redissolved in THF and
slowly precipitated with CH3CN in a freezer to afford a yellow solid
(0.40 g, 35%). 1H NMR (400 MHz, CDCl3) δ 9.56 (s, 4H), 8.17 (s, 4H),
7.65ꢀ7.47 (m, 10H), 6.59 (d, 8H, J = 8.4 Hz), 3.79 (t, 8H, J = 6.6 Hz),
1.84ꢀ1.62 (m, 8H), 1.49ꢀ1.02 (m, 72H), 0.87 (t, 12H, J = 6.6 Hz). 13C
NMR (100 MHz, CDCl3) δ 160.6, 155.9, 149.1, 133.7, 130.6, 130.0,
126.6, 123.7, 121.6, 114.3, 89.0, 88.9, 68.3, 67.9, 31.9, 30.9, 29.7, 29.6,
29.5, 29.4, 26.1, 25.6, 22.7, 14.1. HR-MALDI MS m/z 1499.9445 (calcd
C55H86N3O4Br H2O: C, 69.45; H, 9.32; N, 4.42. Found: C, 69.13;
3
H, 9.21; N, 4.33.
Compound S-9. To a 500-mL flask containing (S)-4-(2-methylbu-
toxy)aniline (0.88 g, 4.9 mmol) and 4-bromo-pyridine-2,6-dicarbonyl
dichloride (0.62 g, 2.2 mmol) was added CH2Cl2 (60 mL) and NEt3
(1.0 mL), and the resulting mixture was stirred at room temperature for
12 h. The solution was washed with water (100 mL ꢁ 3). The organic
layer was collected and dried over MgSO4. The resulting residue was
redissolved in THF and slowly precipitated with MeOH in a freezer to
afford a white solid (0.98 g, 78%). 1H NMR (400 MHz, CDCl3) δ 9.28
(s, 2H), 8.59 (s, 2H), 7.61 (d, 4H, J = 7 Hz), 6.92 (d, 4H, J = 7 Hz),
3.89ꢀ3.69 (m, 4H), 1.93ꢀ1.79 (m, 2H), 1.65ꢀ1.45 (m, 2H),
1.34ꢀ1.18 (m, 2H), 1.01 (d, 6H, J = 5.2 Hz), 0.95 (t, 6H, J = 5 Hz).
13C NMR (100 MHz, CDCl3) δ 159.7, 156.8, 150.0, 136.7, 129.6, 128.7,
121.9, 115.0, 73.2, 34.7, 26.1, 16.5, 11.3. HR-FAB MS m/z 568.1811
(calcd m/z 568.1811 for [M + H]+). Anal. Calcd for C29H34N3O4Br: C,
61.27; H, 6.03; N, 7.39. Found: C, 61.05; H, 6.03; N, 7.36.
m/z 1499.9436 for [M + H]+). Anal. Calcd for C94H126N6O8S H2O: C,
3
74.37; H, 8.50; N, 5.54; S, 2.11. Found: C, 74.49; H, 8.46; N, 5.64;
S, 2.33.
Luminescence quantum yields in solution were calculated relative to
diphenylanthracene in cyclohexane (Φ = 0.95).14 Luminescence quan-
tum yields were taken as the average of three separate determinations
and were reproducible to within 10%. Corrected emission spectra were
used for the quantum yield measurements. Luminescence quantum
yields of toluene gels were measured at 293 K with an integrating sphere.
Luminescence lifetimes were determined on a time-correlated pulsed
single-photon-counting instrument.
Samples for transmission electron microscopy (TEM) images were
prepared by drop casting the gelator solution in toluene on carbon-
coated copper grids (200 mesh), and the TEM images were obtained
without staining. Samples for atomic force microscopy (AFM) measure-
ments were analyzed by a magnetic tapping mode AFM. Silicon
cantilevers with a force constant of 10ꢀ130 N/m and resonance
frequency of 204ꢀ497 kHz were used for the AFM observations in
air. The scan rate was varied from 0.3 to 1.0 Hz. Height and phase
images were simultaneously obtained. The samples were prepared by
drop casting of toluene solution of gelators on a freshly cleaned silicon
wafer substrate and dried under vacuum for 24 h prior to imaging.
Powder X-ray diffractions were measured with the films prepared by
drop casting the gelator solution on a glass substrate and dried under
vacuum using a Philips X’Pert PRO diffractometer with Ni-filtered Cu
KR radiation.
PM18. Under an atmosphere of nitrogen, a 100-mL Schlenk flask
equipped with a magnetic stir bar and a reflux condenser was charged
with 4 (0.23 g, 0.7 mmol), 8 (1.4 g, 1.5 mmol), Pd(PPh3)4 (81 mg, 0.07
mmol), CuI (13 mg, 0.07 mmol), and iPr2NH (50 mL). The mixture was
refluxed for 24 h. After reaction, the volatile solvent was removed under
reduced pressure. Subsequently, water (100 mL) was added and the
brown suspension was extracted with CH2Cl2 (100 mL ꢁ 3). The
organic layer was collected, dried over MgSO4, filtered through a short
neutral alumina column, and then evaporated to dryness. The resulting
residue was redissolved in THF and slowly precipitated with CH3CN in
1
a freezer to afford a yellow solid (0.47 g, 33%). H NMR (400 MHz,
CDCl3) δ 9.42 (s, 4H), 8.35 (s, 4H), 7.67ꢀ7.49 (m, 12H), 7.43ꢀ7.33
(m, 6H), 6.70 (d, 8H, J = 8.6 Hz), 3.82 (t, 8H, J = 6.5 Hz), 1.82ꢀ1.69 (m,
8H), 1.51ꢀ1.17 (m, 120H), 0.86 (t, 12H, J = 6.5 Hz). 13C NMR (100
MHz, CDCl3) δ 160.6, 156.5, 149.7, 134.3, 132.0, 130.6, 129.4, 128.6,
127.9, 126.8, 121.7, 114.9, 100.7, 92.8, 89.3, 80.8, 73.4, 34.9, 29.7, 26.3,
16.5, 11.3. HR-MALDI MS m/z 2058.1670 (calcd m/z 2058.3638 for
[M + Na]+). Anal. Calcd for C134H182N6O8S 6H2O: C, 75.03; H, 9.12;
3
The mole fraction of aggregate (Ragg(T)) was estimated by tempera-
ture-dependent UVꢀvis absorption spectra of coassembled PM18 (1 ꢁ
10ꢀ3 M) and PM-chiral (5 mol %) using the equation shown below5e
N, 3.92; S, 1.49. Found: C, 75.03; H, 9.04; N, 3.90; S, 1.84.
PM-chiral. Under an atmosphere of nitrogen, a 100-mL Schlenk flask
equipped with a magnetic stir bar and a reflux condenser was charged
with 4 (0.23 g, 0.7 mmol), S-9 (0.85 g, 1.5 mmol), Pd(PPh3)4 (81 mg,
0.07 mmol), CuI (13 mg, 0.07 mmol), and iPr2NH (50 mL). The
mixture was refluxed for 24 h. After reaction, the volatile solvent was
removed under reduced pressure. Subsequently, water (100 mL) was
added and the brown suspension was extracted with CH2Cl2 (100mLꢁ 3).
The organic layer was collected, dried over MgSO4, filtered through a
short neutral alumina column, and then evaporated to dryness. The
resulting residue was redissolved in THF and slowly precipitated with
CH3CN in a freezer to afford a yellow solid (0.32 g, 35%). 1H NMR (400
MHz, CDCl3) δ 9.43 (s, 4H), 8.41 (s, 4H), 7.72ꢀ7.49 (m, 12H),
7.46ꢀ7.33 (m, 6H), 6.75 (d, 8H, J = 8.4 Hz), 3.84ꢀ3.58 (m, 8H),
1.92ꢀ1.78 (m, 4H), 1.36ꢀ1.14 (m, 8H), 1.09ꢀ0.85 (m, 24H). 13C
NMR (100 MHz, CDCl3) δ 160.5, 156.2, 149.5, 134.2, 132.0, 130.4,
129.5, 128.6, 127.8, 126.7, 126.4, 121.6, 114.6, 100.6, 96.1, 92.7, 89.1,
80.7, 68.3, 32.6, 31.9, 29.7, 29.6, 29.4, 26.1, 22.7, 14.1. HR-MALDI MS
m/z 1308.6215 (calcd m/z 1307.5680 for [M + H]+). Anal. Calcd for
C82H78N6O8S 4H2O CH3OH: C, 70.62; H, 6.43; N, 5.95; S, 2.27.
RaggðTÞ ꢂ ðAðTÞ ꢀ AmonÞ=ðAagg ꢀ Amon
Þ
where Ragg(T) is the mole fraction of aggregate at temperature T and
Amon, A(T), and Aagg are the absorbance at 400 nm for the monomer, the
solution at temperature T, and the pure aggregate solution, respectively.
Computational Analysis. Molecular mechanics and dynamics
simulations on the gelator molecules were performed using the Dreiding
force field implemented in the Materials Studio package.15,16 The detailed
computational analysis is described in the Supporting Information.
’ ASSOCIATED CONTENT
S
Supporting Information. Computational analysis, gela-
b
tion properties, and optical spectra. This material is available free
of charge via the Internet at http://pubs.acs.org.
3
3
’ AUTHOR INFORMATION
Found: C, 70.96; H, 6.06; N, 5.91; S, 2.59.
Corresponding Author
*E-mail: sssun@chem.sinica.edu.tw; 068204@mail.fju.edu.tw.
TM12. Under an atmosphere of nitrogen, a 100-mL Schlenk flask
equipped with a magnetic stir bar and a reflux condenser was charged
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The Journal of Organic Chemistry
ARTICLE
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We thank the National Council of Taiwan (Grant No. 97-
2628-M-001-015-MY3), Academia Sinica, and Fu-Jen Catholic
University for support of this research.
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