Self-assembly of oligothiophene chromophores by m -calix[3]amide scaffold

Article abstract of DOI:10.1021/jo102160x

m-Calix[3]amides carrying the bithiophene chromophore (BTC3A) and terthiophene chromophore (TTC3A) were synthesized by the cyclic trimerization of m-aminobenzoic acid esters for the purpose of the control and understanding of the self-assembly of oligothiophene chromophores. Polymers and model compounds were also prepared for comparison. From the ¹H NMR experiments, cyclic trimer BTC3A showed the syn/anti equilibrium in solution, and the syn/anti conformer ratio (76/24 in CDCl₃) was influenced by the solvent character. Namely, the population of the syn conformer was lowest (70%) in THF-d₈ and was highest (86%) in CDCl₃/CD₃OD (1/1 in volume). On the other hand, the population of the syn conformer of cyclic trimer TTC3A was high (84%) even in CDCl₃. In a CHCl ₃ solution of cyclic trimer BTC3A, the absorption maximum (342 nm) blue-shifted and the emission maximum (448 nm) red-shifted compared with those of polymer BTPA and model compound BTM. The solvent character also had an impact on the optical properties of cyclic trimer BTC3A. The red-shifted emission maximum (481 nm) of cyclic trimer BTC3A in CH₃OH indicated the interaction between three bithiophene chromophores. The emission maxima of cyclic trimer TTC3A (486 nm) demonstrated a small red-shift from model compound TTM (477 nm), and no solvent dependency was observed, unlike cyclic trimer BTC3A.

Full text of DOI:10.1021/jo102160x

ARTICLE
pubs.acs.org/joc
Self-Assembly of Oligothiophene Chromophores by m-Calix[3]amide
Scaffold
Koji Takagi,* Shinri Sugimoto, Ryohei Yamakado, and Katsuya Nobuke
Department of Materials Science and Engineering, Nagoya Institute of Technology Gokiso, Showa, Nagoya 466-8555, Japan
S Supporting Information
b
ABSTRACT: m-Calix[3]amides carrying the bithiophene chromo-
phore (BTC3A) and terthiophene chromophore (TTC3A) were
synthesized by the cyclic trimerization of m-aminobenzoic acid esters
for the purpose of the control and understanding of the self-assembly
of oligothiophene chromophores. Polymers and model compounds
were also prepared for comparison. From the 1H NMR experiments,
cyclic trimer BTC3A showed the syn/anti equilibrium in solution,
and the syn/anti conformer ratio (76/24 in CDCl3) was influenced by
the solvent character. Namely, the population of the syn conformer
was lowest (70%) in THF-d8 and was highest (86%) in CDCl3/
CD3OD (1/1 in volume). On the other hand, the population of the syn conformer of cyclic trimer TTC3A was high (84%) even in
CDCl3. In a CHCl3 solution of cyclic trimer BTC3A, the absorption maximum (342 nm) blue-shifted and the emission maximum
(448 nm) red-shifted compared with those of polymer BTPA and model compound BTM. The solvent character also had an impact
on the optical properties of cyclic trimer BTC3A. The red-shifted emission maximum (481 nm) of cyclic trimer BTC3A in CH3OH
indicated the interaction between three bithiophene chromophores. The emission maxima of cyclic trimer TTC3A (486 nm)
demonstrated a small red-shift from model compound TTM (477 nm), and no solvent dependency was observed, unlike cyclic
trimer BTC3A.
’ INTRODUCTION
Cyclic molecules are useful building blocks in the supramole-
cular chemistry and have attracted increasing attention as one
of the leading player in molecular recognition events.1 Among
them, cyclic oligoamides2 and oligopeptides3 are of interest from
the material and biological viewpoints as represented by self-
assembling peptide nanotubes. In these classes of molecules, the
intermolecular hydrogen bonding between N—H and CdO has
a crucial role to permit the supramolecular association. Mean-
while, cyclic aromatic triamides made of three N-alkyl benzanilide
units, abbreviated hereafter as calix[3]amides, have also constituted
a new class of cyclic oligomers.4 In contrast to the secondary amide
counterpart, N-alkyl benzanilide preferentially adopts the cis-amide
structure5 that enables the cyclic trimerization through the self-
condensation of N-alkylaminobenzoic acids.6 Thus, calix[3]amides
were obtained in good yields by using tetrachlorosilane or dichlor-
otriphenylphosphorane as the condensation reagents. Especially,
the single crystal X-ray structure analysis and the relationship
between the solvent character and the conformation of m-calix-
[3]amides whose amide nitrogen and carbonyl group are located at
the meta-position are well-decumented.4c In view of the supramo-
lecular chemistry, however, the inner cavities provided by m-calix-
[3]amide hosts might be too small to encapsulate guest molecules.
Yokozawa and co-workers reported the synthesis of para-linked
cyclic aromatic triamide with the large triangular cavity by inserting
a phenylene-ethynylene unit as the additional linker between
the amide and phenylene groups.7 On the other hand, bowl-shaped
Figure 1. Chemical structure of m-calix[3]amides bearing bithiophene
and terthiophene chromophore.
m-calix[3]amides would be expected as a reliable template for funct-
ional groups to be located in close proximity and to enjoy intimate
interactions with each other. To the best of our knowledge, however,
there are few examples installing a functional group into the m-
calix[3]amide skeleton.8
π-Conjugated oligomers with the tailored molecular length
and the minimum structural defect play a central role in molecular
devices including light-emitting diodes9 and field-effect transistors10
because of the feasible tuning of optoelectronic properties. A
precision assembly of conjugated oligomers is of much importance
for understanding the nanostructure of these molecules and ensur-
ing the best performances in the solid state. Along this line,
substantial efforts have been paid to obtain new (macro)molecules
Received: October 30, 2010
Published: March 14, 2011
r
2011 American Chemical Society
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Scheme 1. Synthetic Route of Monomers 4 and 5
Scheme 2. Synthetic Route of Cyclic Trimers and Polymers from Monomers 4 and 5
that attain the programmed arrangement of multichromophores
at the defined positions.11 Oligothiophenes and polythiophenes
are important classes of π-conjugated organic molecules that have
been extensively investigated and explored as the active material for
optoelectronic devices.12 Thus, we became interested in investigating
the alignment of oligothiophene chromophores in a controlled
fashion by utilizing the m-calix[3]amide scaffold. In this context,
we have prepared m-calix[3]amides carrying bithiophene and terthi-
ophene chromophore in a confined space (Figure 1) and studied
their conformation in solution. Polymers and model compounds
were also prepared for comparison. The absorption/emission prop-
erties of these materials were carefully investigated to disclose a
potential utility of the m-calix[3]amide framework. Especially, the
polymers carrying multiple chromophores were examined in order to
highlight the character of m-calix[3]amides although there is a room
for discussion about the conformation of N-substituted poly-m-
benzamides.
intensity corresponding to the cyclic trimer was high in the
MALDI-TOF-MS spectrum, uncharacterizable peaks and higher
molecular weight cyclic oligomers were also detected (Figure
S10). Thus, the isolated yield of a target m-calix[3]amide (BTC3A)
was low (15%), which was performed by SiO2 chromatography and
subsequent preparative GPC. The narrow melting temperature
range, the 1H NMR spectrum, and the MALDI-TOF-MS spectrum
(Figure 2) indicated the isolation of the cyclic trimer. Likewise,
cyclic trimer TTC3A carrying the terthiophene chromophore was
synthesized from monomer 5 (Figures S14ꢀS16).
For more detailed investigation into the characteristics of the
m-calix[3]amide scaffold, polymers were also prepared for com-
parison. Following the conditions of the chain-growth polycon-
densation reported by Yokozawa et al.,13 monomer 4 dissolved in
THF was slowly added to a THF solution of LiHMDS and
phenyl benzoate (Scheme 2, right arrow). The obtained product
was purified by preparative GPC to isolate polymer BTPA having
the number-averaged molecular weight of 5300. The molecular
weight distribution (Mw/Mn = 1.59) was larger than that of N-
substituted poly(m-benzamide)s without the bithiophene chro-
mophore (Mw/Mn < 1.19). The MALDI-TOF-MS spectrum of
the lower molecular weight part recovered from preparative GPC
indicated the formation of cyclic trimer BTC3A. These results
indicate that the initiator (phenyl benzoate) does not fulfill an
ideal role and the self-condensation of monomer 4 may take
place. Since the measurement of the MALDI-TOF-MS spectrum
was not available, the chemical structure of the polymer termini
’ RESULTS AND DISCUSSION
1. Synthesis and Characterization of Materials. Methyl
3-(nonylamino)benzoate carrying the bithiophene chromo-
phore at the 5-position (4) was synthesized from 3-bromo-5-
nitrobenzoic acid in four steps (Scheme 1). The dropwise
addition of lithium bis(trimethylsilyl)amide (LiHMDS) into a
dilute THF solution of monomer 4 gave a crude mixture of
oligomeric products (Scheme 2, left arrow).7 Although the peak
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could not be determined. Since the narrow molecular weight
distribution is not a prerequisite factor in the present research,
the optimization of the ester groups in monomer 4 and the
initiator was not attempted. In the 1H NMR spectrum of polymer
BTPA, the signal of methyl ester at the propagating end was
detected at 3.91 ppm. Interestingly, there was noticeable differ-
ence on the chemical shift for methylene protons adjacent to the
amide nitrogen between cyclic trimer BTC3A and polymer
BTPA. Cyclic trimer BTC3A showed the bimodal signal at
around 3.59ꢀ4.11 ppm (Figure S11), while polymer BTPA
showed the single broad signal at the relatively higher magnetic
field region (3.57 ppm) (Figure S13). The different peak position
might have arisen from the conformation of the materials and the
magnetic environment of the methylene protons that will be
clarified in the future. A model compound bearing the bithiophene
chromophore (BTM) was also synthesized as shown in Scheme 3.
Polymer TTPA (Mn = 7000, Mw/Mn = 1.45) and model compound
TTM carrying the terthiophene chromophore were likewise
prepared.
The original m-calix[3]amide without any chromophore on
the benzene ring is known to have two conformers in solution.4c
Namely, the syn conformer has three benzene rings in the same
orientation relative to the amide bond, and the anti conformer
has one benzene ring turning in other direction. To determine
the syn/anti conformer ratio at various temperatures, cyclic trimer
BTC3A was subjected to the variable temperature (VT) NMR
measurement in a CDCl3 solution (Figure S23). The minor signal
assignable to a benzene proton of the anti conformer was observed
at 6.39 ppm at 293 K,14 and the signal intensity was increased at
low temperature (263 K) (Figure 3). The corresponding proton
signal of the syn conformer was buried in other aromatic proton
signals, which made the calculation of the activation energy from
one conformer to another difficult. The syn/anti conformer ratio
was 76/24 at 293 K, calculated from the integral ratio of this minor
proton signal, and the population of the syn conformer was
decreased to reach 66% at 233 K. The population of the syn
conformer was increased to reach 86% at 293 K in a CDCl3/
CD3OD solution (1/1 in volume) in good agreement with the
trend of m-calix[3]amide without the bithiophene chromophore,
and on the other hand, the value was decreased to 70% at 293 K in a
THF-d8 solution (Figure S24). This phenomenon seems to be
related to the acceptor number of solvents15 (8.0 for THF, 23 for
CHCl3, and 41 for CH3OH) rather than the dielectric constant of
solvents (7.5 for THF, 4.8 for CHCl3, and 33 for CH3OH). The
carbonyl stretching vibration signal of cyclic trimer BTC3A actually
shifted from 1659 cmꢀ1 in THF to 1648 cmꢀ1 in CHCl3, from
which the solvent interaction with the amide carbonyl group
was suggested. Although the cis or trans structure of the amide
moiety is unknown for the anti conformer of m-calix[3]amide,
the solvent character would influence the dihedral angle
between the amide plane and the benzene ring through the
interaction with the carbonyl group to eventually impact the
syn/anti conformer ratio of the material. The syn/anti con-
former ratio for cyclic trimer TTC3A was 84/26 at 293 K in a
CDCl3 solution. Since the bowl-shaped m-calix[3]amide in
the syn conformation has a truncated cone structure (pseudo-
C3 symmetry),4c three oligothiophene units would adopt a
nonparallel arrangement even in the self-assembled state and
the π-stacking of chromophores could not be confirmed by
the peak shift in the NMR measurement.
2. Optical Properties of Materials. The UV spectra of
bithiophene-carrying materials (cyclic trimer BTC3A, polymer
BTPA, and model compound BTM) were collected in a CHCl3
solution. The absorption maximum of cyclic trimer BTC3A
(342 nm) shifted to the shorter wavelength region compared
with those of polymer BTPA (348 nm) and model compound
BTM (351 nm) (Figure 4A). On the other hand, the PL spectra
demonstrated a marked difference among three materials (see
also Figure S25). The emission maximum red-shifted in the order
of model compound BTM (422 nm), polymer BTPA (431 nm),
and cyclic trimer BTC3A (448 nm) (Figure 4B).16 These peak
shifts do not have a simple correlation with the number of
Figure 2. MALDI-TOF-MS spectrum of cyclic trimer BTC3A.
Scheme 3. Synthetic Route of Model Compounds
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the bithiophene chromophore (3mer for cyclic trimer BTC3A,
13mer for polymer BTPA,17 and 1mer for model compound
BTM). The full-width at half-maximum (fwhm) of the PL spec-
trum of cyclic trimer BTC3A (113 nm) was quite larger than that
of model compound BTM (64 nm). One plausible reason is that
the syn and anti conformers of cyclic trimer BTC3A have the
different electronic structure at the excited state, and they emit
fluorescence with the different wavelength (vide infra).
Since Shudo et al. reported the twisted intramolecular charge
transfer (TICT) fluorescence at the longer wavelength region
(518 nm) for acyclic N-methylbenzanilide especially in nonpolar
solvents,18 the emission properties of cyclic trimer BTC3A are
of much interest. In order to gain deeper insight into the large
wavelength shift of the emission maximum of cyclic trimer BTC3A,
the UV and PL spectra of cyclic trimer BTC3A and model com-
pound BTM were collected in various solvents. As a result, the UV
and PL spectra of model compound BTM showed a small shift on
going from a CHCl3 solution to a CH3OH solution probably
because the hydrogen bonding interaction of CH3OH with the
amide carbonyl group has an influence upon the electronic structure
of the bithiophene chromophore (Figure S26). In contrast, cyclic
trimer BTC3A showed the noticeable solvato(fluoro)chromic be-
havior. The absorption maxima blue-shifted from 342 nm in CHCl3
to 336 nm in CH3OH, while the emission maxima showed the
pronounced and opposite shift from 448 nm in CHCl3 to 481 nm in
CH3OH (Figure 5). The emission maxima demonstrated hypso-
chromic shifts when the spectra were collected in THF (430 nm)
and in methylcyclohexane (MCH) (420 nm). These emission wave-
length shifts seem to have a good correlation with the population of
the syn conformer in solution although the value in MCH is not
available. Taking the fact that cyclic trimer BTC3A preferably adopts
the syn conformation in a CDCl3/CD3OD solution (vide supra) into
account, the self-assembly of the bithiophene segments enables the
chromophore interaction in a CH3OH solution. Three bithiophene
chromophores included in the syn conformer, however, take the
nonparallel arrangement, and they cannot enjoy the greatest benefit
of the π-electron cloud overlap. Nonetheless, the obvious red-shift of
the PL spectra indicates that an intramolecular interaction between
three bithiophene chromophores gives an emission at the longer
wavelength in CH3OH. Neckers et al. reported the preparation and
optical properties of bithiophene-functionalized metal nanoparti-
cles (NPs), where 5-mercapto-2,20-bithiophene (BTSH) and 5-(5-
mercaptopentyl)-2,20-bithiophene (BTC5SH) were assembled on
the NP surface.19 The NP decorated with BTSH showed a blue-shift
in the UV spectra and red-shift in the PL spectra as compared
with the NP bearing BTC5SH with a flexible methylene chain. They
suggest that trans-BTSHs on the NP surface interact through
intermolecular van der Waals forces to restrict isomerization giving
enhanced blue emission. The type of self-assembled structure is
different; however, a similar intramolecular interaction between
three bithiophene chromophores likely exists in cyclic trimer
BTC3A. The PL spectrum collected in a MCH solution showed a
smooth shoulder at ca. 480 nm, probably ascribed to the emission
from the syn conformer, that became the maximum peak when the
spectrum was measured in a CH3OH solution. The emission
maximum wavelength of cyclic trimer BTC3A in a spin-coated thin
film (494 nm) showed a further red-shift from that in a CH3OH
solution due to the intermolecular chromophore interaction besides
the intramolecular one.
Figure 3. VT NMR spectra of cyclic trimer BTC3A in CDCl3 (top, 323 K;
middle, 293 K; and bottom, 263 K).
Figure 4. UV (A) and PL (B) spectra of cyclic trimer BTC3A (O), polymer BTPA (4), and model compound BTM (0) in CHCl3 at 298 K (10ꢀ5 M).
The excitation wavelengths were those of absorption maxima.
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Figure 5. UV (A) and PL (B) spectra of cyclic trimer BTC3A in MCH (4), THF (]), CHCl3 (O), and CH3OH (0) at 298 K (10ꢀ5 M). The excitation
wavelengths were those of absorption maxima.
Figure 6. Excitation spectra of cyclic trimer BTC3A in MCH (4), THF
Figure 7. PL spectra of cyclic trimer TTC3A (O), polymer TTPA (4),
(]), CHCl3 (O), and CH3OH (0) at 298 K (10ꢀ5 M).
and model compound TTM (0) in CHCl3 at 298 K (10ꢀ5 M). The
excitation wavelengths were those of absorption maxima.
The excitation spectra of cyclic trimer BTC3A were also measured
in the same series of solvents, and the maximum wavelengths were
observed at 357 nm (MCH and THF), 349 nm (CHCl3), and
338 nm (CH3OH) (Figure 6). There was a small wavelength shift
between the absorption maximum (336 nm) and the excitation
maximum (338 nm) in the case of a CH3OH solution. In a MCH
solution, on the other hand, the excitation maximum was observed at
357 nm that was red-shifted compared with that of absorption maxi-
mum (342 nm). Otsubo et al. described the preparation and proper-
ties of a family of [n.n]quinquethiophenophanes as a useful π-dimer
model.11b They pointed out that the blue-shifted absorption max-
imum as compared with that of monomeric quinquethiophene could
stem from the nonbonded interaction between face-to-face chromo-
phores. With this report in mind, the population of the syn conformer
with three bithiophene chromophores in close proximity might be
low in the excited state rather than the ground state. We now
speculate that the photoexcitation of cyclic trimer BTC3A induces
the flip of the bithiophene chromophore enabling the conversion
from the syn conformer to the anti one especially in a MCH solution.
Finally, the optical properties of terthiophene-carrying materi-
als (cyclic trimer TTC3A, polymer TTPA, and model compound
TTM) were investigated in a CHCl3 solution. As expected, the
absorption maxima of these materials are red-shifted compared
with those of bithiophene-carrying analogues. The absorption
maximum of cyclic trimer TTC3A (379 nm) was observed at
the shorter wavelength region compared to those of polymer
TTPA (386 nm) and model compound TTM (390 nm), which is
similar to the trend of cyclic trimer BTC3A. However, the
emission maximum of cyclic trimer TTC3A was detected at
486 nm (Figure 7), and the shift width from that of model
compound TTM was smaller (9 nm) than that of cyclic trimer
BTC3A (24 nm) in spite of the higher population of the syn
conformer (vide supra). Since the m-calix[3]amide framework
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has a truncated cone structure,4c the edge-to-edge distance between
neighboring terthiophene chromophores in cyclic trimer TTC3A
would be longer than that of bithiophene-carrying cyclic trimer
BTC3A. It is thus considered that the intramolecular interaction
between the self-assembled chromophores does not effectively
work in cyclic trimer TTC3A. The emission maximum was likewise
observed at 486 nm when the PL spectrum was measured in a
CH3OH solution.
was purified by SiO2 chromatography (CH2Cl2, Rf = 0.7) to obtain a
colorless solid in 0.20 g (56% yield). Mp 65ꢀ66 °C. 1H NMR (δ, 200
MHz, CDCl3) 7.44 (s, 1H), 7.15 (t, J = 1.5 Hz, 1H), 6.87 (t, J = 1.8 Hz,
1H), 3.89 (s, 3H), 3.82 (br s, 1H), 3.10 (t, J = 7.0 Hz, 2H), 1.62 (m, 2H),
1.46ꢀ1.18 (12H), 0.89 (t, J = 6.0 Hz, 3H). IR (cmꢀ1) 3395, 2924, 2847,
2360, 1710, 1512, 1323, 1246, 765.
For methyl 3-(nonylamino)-5-(20-(50,200-bithienyl))benzoate (4), to
a THF (30 mL) solution of 3 (1.1 g, 3.0 mmol) and 2-(5,20-bithienyl)boro-
nic acid24 (0.63 g, 3.0 mmol) were added 2 M aq K2CO3 (12 mL) and
Pd(PPh3)4 (35 mg, 30 μmol), and the system was heated to reflux overnight.
After the aqueous phase was extracted with CH2Cl2, a combined organic
phase was dried over MgSO4. Solvents were removed by a rotary evaporator.
The crude product was purified by SiO2 chromatography (CH2Cl2, Rf = 0.6)
followed by recrystallization from hexane to obtain pale green crystals in 0.54
g (41% yield). Mp 74ꢀ75 °C. 1HNMR(δ, 200 MHz, CDCl3) 7.59(s, 1H),
7.24ꢀ7.08 (5H), 7.02 (dd, J = 3.5 Hz, 5.0 Hz, 1H), 6.95 (t, J = 1.9 Hz, 1H),
3.92 (s, 3H), 3.82 (br s, 1H), 3.18 (t, J = 6.9 Hz, 2H), 1.64 (m, 2H),
1.48ꢀ1.16 (12H), 0.87 (t, J = 6.7 Hz, 3H). 13C NMR (δ, 50 MHz, CDCl3)
167.2, 148.9, 142.6, 137.3, 136.7, 134.9, 131.6, 127.8, 124.4, 124.3, 124.0,
123.6, 115.5, 113.5, 112.4, 52.1, 43.8, 31.8, 29.5, 29.4, 29.2, 27.1, 22.6, 14.1. IR
(cmꢀ1) 3403, 2924, 1703, 1600, 1251, 802, 688. Anal. Found: C, 67.64; H,
6.86; N, 3.06%. Calcd for C25H31NO2S2: C, 67.99; H, 7.07; N, 3.17%.
HRMS (EI) Calcd for C25H31NO2S2: 441.1796. Found: 441.1792.
For methyl 3-(nonylamino)-5-(20-(50,200,500,2000-terthienyl))benzoate (5),
the material was similarly prepared from 3 and 2-(5,20,50,200-terthienyl)boro-
nic acid24 in 31% yield. Mp 88ꢀ89 °C. 1H NMR (δ, 200 MHz, CDCl3) 7.59
(s,1H),7.24ꢀ7.08(7H),7.02(dd,J= 3.6 Hz, 5.0 Hz, 1H), 6.95 (t, J=1.9Hz,
1H), 3.92 (s, 3H), 3.89ꢀ3.70 (br s, 1H), 3.18 (t, J = 7.0 Hz, 2H), 1.64 (m,
2H), 1.48ꢀ1.18 (12H), 0.89 (t, J = 6.7 Hz, 3H). 13C NMR (δ, 50 MHz,
CDCl3) 167.1, 148.8, 142.7, 137.0, 136.4, 136.1, 136.0, 134.8, 131.6, 127.8,
124.4, 124.3, 124.1, 123.6, 115.4, 113.5, 112.5, 52.1, 43.8, 31.8, 29.5, 29.4, 29.2,
27.1, 22.6, 14.1. IR (cmꢀ1) 3385, 2921, 2850, 1719, 1598, 1451, 1254, 789,
765. HRMS (EI) Calcd for C29H33NO2S3: 523.1673. Found: 523.1681.
2. Synthesis of Cyclic Trimers and Polymers. For the cyclic
trimer of 4(BTC3A),7 to a THF (2 mL) solution of monomer 4(0.17 g, 0.40
mmol) was added dropwise LiHMDS (1.0 M in THF, 0.64 mL, 0.64 mmol)
at 0 °C, and the system was stirred for 2 h. After saturated aq NH4Cl was
added, the aqueous phase was extracted with CHCl3. A combined organic
phase was dried over MgSO4, and solvents were removed by a rotary evapora-
tor. The crude product was purified by SiO2 chromatography (CH2Cl2/
In conclusion, we herein prepared two m-calix[3]amides
bearing the oligothiophene unit to accomplish the self-assembly
of chromophores. The conformational study was carried out
1
using H NMR spectra. The syn/anti conformer ratio of m-
calix[3]amide carrying the bithiophene chromophore was influ-
enced by the solvent character. The UV and PL spectra were
measured to know a relationship between the conformation and
the optical properties of materials. The absorption and emission
maxima of m-calix[3]amide carrying the bithiophene chromo-
phore shifted from those of polymer and model compound. The
emission maximum wavelengths were dramatically influenced by
the solvent character. On the other hand, m-calix[3]amide
carrying the terthiophene chromophore showed a relatively small
shift of the emission maxima compared with the model com-
pound, and the maximum wavelength was independent upon the
solvent character. These results indicate that the m-calix[3]amide
framework would be the intriguing scaffold for the self-assembly
of π-conjugated chromophores.
’ EXPERIMENTAL SECTION
1. Monomer Synthesis. For methyl 3-bromo-5-nitrobenzoate
(1),20 to a MeOH (15 mL) solution of 3-bromo-5-nitrobenzoic acid
(0.25 g, 1.0 mmol)21 was added SOCl2 (0.11 mL, 1.5 mmol) at 0 °C.
After the mixture was heated to reflux for 6 h, MeOH was evaporated.
Then, saturated aq NaHCO3 was added, and the system was extracted
with ethyl acetate. The organic phase was dried over MgSO4, and
solvents were removed by a rotary evaporator. The crude product was
recrystallized from EtOH to obtain colorless crystals in 0.33 g (63%
yield). Mp 71ꢀ72 °C. 1H NMR (δ, 200 MHz, CDCl3) 8.79 (d, J = 1.6
Hz, 1H), 8.55 (d, J = 1.9 Hz, 1H), 8.49 (t, J = 1.5 Hz, 1H), 4.00 (s, 3H).
13C NMR (δ, 50 MHz, CDCl3) 163.6, 148.6, 138.1, 133.1, 130.3, 123.0,
122.9, 53.0. IR (cmꢀ1) 3089, 1727, 1531, 1452, 1345, 1276, 1197, 1153,
983, 735.
3
acetone = 3/1 in volume, Rf =0.7),followedbypreparativeGPC(CHCl as an
eluent) to obtain yellow solid in 0.02 g (15% yield). Mp 51ꢀ53 °C. 1H NMR
(δ, 200 MHz, CDCl3) 7.95ꢀ6.32 (24H), 4.11ꢀ3.59 (br m, 6H), 1.82ꢀ1.51
(br s, 6H), 1.49ꢀ1.10 (36H), 1.05ꢀ0.76 (br, 9H). 13C NMR (δ, 50 MHz,
CDCl3) 169.7, 142.9, 139.8, 139.4, 138.2, 136.6, 135.3, 127.7, 127.6, 125.0,
124.6, 124.5, 124.3, 124.2, 123.8, 49.6, 31.8, 29.5, 29.2, 27.6, 26.8, 22.6, 14.1. IR
(cmꢀ1) 2923, 2852, 2360, 1650, 1585, 1387, 688. MALDI-TOF-MS Calcd
for C72H82N3O3S6 [M þ H]þ: 1229.82. Found: 1229.65.
For methyl 3-amino-5-bromobenzoate (2),22 to an EtOH (30 mL)
solution of SnCl2 (52 g, 0.23 mol) was added dropwise 1 (12 g, 46
mmol) dissolved in THF/EtOH (30 mL/30 mL) under cooling in a
water bath. After the addition was completed, the mixture was heated to
reflux for 6 h. Then, saturated aq NaHCO3 was added, and a precipitate
was filtered off. The filtrate was washed with water, and the aqueous
phase was extracted with ethyl acetate. A combined organic phase was
dried over MgSO4, and solvents were removed by a rotary evaporator.
The crude product was recrystallized from hexane to obtain colorless
For the polymer of 4 (BTPA),13 to a THF (0.4 mL) solution of
phenyl benzoate (1.6 mg, 8.0 μmol) mixed with LiHMDS (1.0 M in
THF, 0.44 mL, 0.44 mmol) was added dropwise a THF (0.4 mL)
solution of monomer 4 (0.18 g, 0. 40 mmol) at 0 °C. After a few hours,
saturated aq NH4Cl was added, and the aqueous phase was extracted
with CHCl3. A combined organic phase was dried over MgSO4, and
solvents were removed by a rotary evaporator. In order to remove low
molecular weight oligomers, the crude product was purified by pre-
parative GPC (CHCl3 as an eluent) to obtain brown solid in 93 mg (56%
1
crystals in 8.7 g (82% yield). Mp 92ꢀ93 °C. H NMR (δ, 200 MHz,
CDCl3) 7.52 (d, J = 1.3 Hz, 1H), 7.26 (s, 1H), 6.99 (t, J = 1.8 Hz, 1H),
3.89 (s, 3H). 13C NMR (δ, 50 MHz, CDCl3) 166.0, 147.7, 132.4, 122.8,
122.0, 121.5, 114.5, 52.3. IR (cmꢀ1) 3409, 1708, 1569, 1430, 1307, 1241,
1114, 1003, 852, 766.
1
For methyl 3-(nonylamino)-5-bromobenzoate (3),23 to a THF
(3.2 mL) solution of 2 (0.23 g, 1.0 mmol), nonanal (0.18 mL, 1.0
mmol), and AcOH (32 μL, 0.55 mmol) was added NaBH(OAc)3 (0.26
g, 1.2 mmol) at room temperature. The system was stirred overnight.
After saturated aq NaHCO3 was added, the aqueous phase was extracted
with ethyl acetate. A combined organic phase was dried over MgSO4,
and solvents were removed by a rotary evaporator. The crude product
yield). H NMR (δ, 200 MHz, CDCl3) 8.05ꢀ6.60 (8H), 3.91 (br,
small), 3.80ꢀ3.35 (br, 2H), 1.80ꢀ1.42 (br, 2H), 1.40ꢀ0.96 (12H),
0.92ꢀ0.72 (br, 3H). IR (cmꢀ1) 2924, 2360, 1648, 1581, 1258, 687. GPC
(THF, PSt standard) Mn = 5300, Mw/Mn = 1.59.
For the cyclic trimer of 5 (TTC3A),7 the material was similarly prepared
from monomer 5 in 13% yield. Mp 183ꢀ185 °C. 1H NMR (δ, 200 MHz,
CDCl3) 8.00ꢀ6.35 (30H), 4.02ꢀ3.52 (br m, 6H), 1.85ꢀ1.52 (br s, 6H),
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The Journal of Organic Chemistry
ARTICLE
1.50ꢀ1.05 (36H), 1.00ꢀ0.72 (br, 9H). 13C NMR (δ, 50 MHz, CDCl3)
169.8, 143.0, 139.9, 139.4, 138.2, 137.0, 136.6, 135.2, 128.0, 127.9, 125.0,
124.8, 124.7, 124.6, 124.5, 124.4, 124.3, 124.2, 123.7, 123.6, 49.6, 31.9, 29.6,
29.3, 27.7, 26.9, 22.7, 14.1. IR (cmꢀ1) 2923.6, 2360.4, 1651.7, 1585.2,
1387.5, 785.9. MALDI-TOF-MS Calcd for C84H87N3O3S9 [M þ H]þ:
1476.19. Found: 1476.66.
This material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
takagi.koji@nitech.ac.jp
For the polymer of 5 (TTPA),13 the material was similarly prepared
from monomer 5 in 56% yield. 1H NMR (δ, 200 MHz, CDCl3) 7.95ꢀ
6.45 (10H), 3.90 (br, small), 3.82ꢀ3.25 (br, 2H), 1.81ꢀ1.42 (br, 2H),
1.40ꢀ0.96 (12H), 0.92ꢀ0.72 (br, 3H). IR (cmꢀ1) 2923, 2360, 1647,
1583, 789. GPC (THF, PSt standard) Mn = 7000, Mw/Mn = 1.45.
3. Synthesis of Model Compound. 3-(N-Nonyl-N-benzoyla-
mino)-5-bromo-N0-methylbenzanilide (6) A pyridine (4 mL) solution
of 3 (0.36 g, 1.0 mmol) and BzCl (1.5 mL, 1.2 mmol) was heated at
80 °C for 2 h.25 After pouring into iced-water, the aqueous phase was
extracted with ethyl acetate. The organic phase was washed with 1 M
HCl and subsequently with saturated aq. NaHCO3. From the organic
phase dried over MgSO4, solvents were removed by a rotary evaporator
to obtain methyl 3-(N-nonyl-N-benzoylamino)-5-bromobenzoate as
pale brown viscous oil which was used without further purification. To
a THF (1.6 mL) solution of 3-(N-nonyl-N-benzoylamino)-5-bromobenzo-
ate (0.36 g, 0.78 mmol) and N-methylaniline (86 μL, 0.79 mmol) was
added dropwise LiHMDS (1.0 M in THF, 0.78 mL, 0.78 mmol) at 0 °C,
and the system was stirred for 2 h. After saturated aq. NH4Cl was added, the
aqueous phase was extracted with ethyl acetate. A combined organic phase
was dried over MgSO4 and solvents were removed by a rotary evaporator to
obtain pale brown viscous oil in 0.41 g (98% yield). 1H NMR (δ, 200 MHz,
CDCl3) 7.40ꢀ6.80 (13H), 3.60 (t, J= 8.1 Hz, 2H), 3.44 (s, 3H), 1.50ꢀ1.10
(14H), 0.87 (t, J = 6.5 Hz, 3H).
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1
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viscous oil in 45 mg (29% yield). H NMR (δ, 200 MHz, CDCl3)
7.40ꢀ6.80 (18H), 3.67 (t, J = 7.8 Hz, 2H), 3.49 (s, 3H), 1.43 (m, 2H),
1.33ꢀ1.10 (12H), 0.87 (t, J= 6.5 Hz, 3H). 13C NMR(δ, 50 MHz, CDCl3)
170.1, 169.0, 144.5, 143.4, 140.6, 137.7, 137.4, 136.9, 135.8, 134.5, 129.6,
129.3, 128.5, 127.8, 126.9, 126.3, 125.7, 124.7, 124.5, 124.4, 123.9, 50.1,
38.3, 31.8, 29.5, 29.3, 29.2, 27.6, 26.8, 22.6, 14.0. IR (cmꢀ1) 3726, 2924,
2360, 1644, 1586, 1494, 1446, 1378, 694. Anal. Found: C, 73.32; H, 6.36;
N, 4.42%. Calcd for C38H40N2O2S2: C, 73.51; H, 6.49; N, 4.51%. HRMS
(EI) Calcd for C38H40N2O2S2: 620.2531. Found: 620.2515.
For 3-(N-nonyl-N-benzoylamino)-5-(20-(50,200,500,2000-terthienyl))-
N0-methylbenzanilide (TTM), the material was similarly prepared from
7 in 57% yield. 1H NMR (δ, 200 MHz, CDCl3) 7.40ꢀ6.80 (20H), 3.67
(t, J = 7.7 Hz, 2H), 3.49 (s, 3H), 1.43 (m, 2H), 1.33ꢀ1.10 (12H), 0.87 (t,
J = 6.6 Hz, 3H). 13C NMR (δ, 50 MHz, CDCl3) 170.1, 169.0, 144.5,
143.5, 140.7, 137.5, 137.3, 136.8, 136.6, 135.8, 135.5, 134.4, 129.6, 129.4,
128.5, 127.8, 126.9, 126.3, 125.8, 124.6, 124.5, 124.4, 124.3, 123.8, 50.1,
38.3, 31.8, 29.5, 29.3, 29.2, 27.6, 26.8, 22.6, 14.1. IR (cmꢀ1) 2924.5,
1645.0, 1583.3, 1374.0, 787.8, 695.2. HRMS (EI) Calcd for C42H42N2O2S3:
702.2408. Found: 702.2389.
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’ ASSOCIATED CONTENT
S
Supporting Information. Spectroscopic data (NMR and
b
MALDI-TOF-MS) of materials. Conformational study of cyclic
trimer BTC3A using VT NMR spectra. Optical properties of
materials bearing bithiophene chromophore in various solvents.
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ARTICLE
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