Photoresponsive two-component organogelators based on trisphenylisoxazolylbenzene

Article abstract of DOI:10.1039/c3ob00041a

Photochromic tris(phenylisoxazolyl)benzene 1 and bispyridine derivatives 2a-e were mixed in a certain ratio to generate stable gels in benzyl alcohol, 4-methoxybenzyl alcohol, and aniline. Supramolecular assembly of 1 in solution was confirmed by ¹H NMR study. The T_gel value was saturated in a 2:3 ratio of 1 and 2c. The intermolecular hydrogen bonds OH...N and salt bridge O^-...H-N⁺ between 1 and 2c coexisted evidently, and these hydrogen bonds contributed to the stabilization of the gel networks. The lengths of alkyl chains of 2a-e governed the stabilities of the gels. The gel formations were driven by the morphological transition of 1 before and after the addition of 2a-e. Mixtures of 1 and 2a-e led to the well developed fibrillar networks, generating a lot of voids that are responsible for immobilizing solvent molecules. When the benzyl alcohol gel was irradiated at 360 nm, the gel turned to the sol. The sol was reversed to the gel by warming. This gel-to-sol phase transition was completely reversible.

Full text of DOI:10.1039/c3ob00041a

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Photoresponsive two-component organogelators
based on trisphenylisoxazolylbenzene†
Cite this: DOI: 10.1039/c3ob00041a
Takeharu Haino,* Yuko Hirai, Toshiaki Ikeda and Hiroshi Saito
Photochromic tris(phenylisoxazolyl)benzene 1 and bispyridine derivatives 2a–e were mixed in a certain
ratio to generate stable gels in benzyl alcohol, 4-methoxybenzyl alcohol, and aniline. Supramolecular
assembly of 1 in solution was confirmed by 1H NMR study. The Tgel value was saturated in a 2 : 3 ratio
of 1 and 2c. The intermolecular hydrogen bonds OH⋯N and salt bridge O−⋯H–N+ between 1 and 2c
coexisted evidently, and these hydrogen bonds contributed to the stabilization of the gel networks. The
lengths of alkyl chains of 2a–e governed the stabilities of the gels. The gel formations were driven by
the morphological transition of 1 before and after the addition of 2a–e. Mixtures of 1 and 2a–e led to
the well developed fibrillar networks, generating a lot of voids that are responsible for immobilizing
solvent molecules. When the benzyl alcohol gel was irradiated at 360 nm, the gel turned to the sol. The
sol was reversed to the gel by warming. This gel-to-sol phase transition was completely reversible.
Received 9th January 2013,
Accepted 10th April 2013
DOI: 10.1039/c3ob00041a
www.rsc.org/obc
Two-component LMOGs6 functionalized with a photochromic
moiety are synthetically more accessible than a conventional
Introduction
Molecular organogels of low-molecular-weight organogelators LMOG—the photochromic unit and a long alkyl side chain are
(LMOGs) are thermally reversible viscoelastic materials, separately placed in each of the components that are con-
formed by self-assembly via noncovalent interactions.1 The nected through noncovalent interaction.7
aggregation of gelators forms the entangled fibers, giving rise
We have previously reported that an isoxazolyl ring is a key
to the three-dimensional network.2 Solvent molecules are functionality for generating molecular assemblies,8 e.g. tris-
immobilized in voids of the network, which are responsible (phenylisoxazolyl)benzenes assembled to form fibrillar gel net-
for gelation. The properties of LMOGs rely on the nature of works in common organic solvents,9 and an azobenzene func-
their resulting three-dimensional supramolecular organiz- tionalized gelator10 showed a photoresponsive nature. Here,
ations in which the molecular constituents are spatially orga- we report a new class of two-component photochromic LMOGs
nized.3 Control of these organization processes by chemical or composed of photochromic tris(phenylisoxazolyl)benzene 110
physical stimuli represents a prime scientific challenge to and bispyridines 2a–e (Scheme 1). 1 has three phenolic
develop stimuli-responsive functional materials.4 Integration hydroxyl groups that are responsible for hydrogen bonding
of photochromic units as an addressable functionality onto interactions. Long alkyl chains are introduced onto the bispyri-
the molecular constituents offers potential access to achieve dine unit. When 1 and 2a–e are blended in a certain ratio, the
the reversible control of the organization process that induces fibrous assemblies of 1 should be cross-linked by 2a–e,
a sol-to-gel transition.5 Therefore, LMOGs possessing photo- forming hydrogen bonds between the phenolic hydroxyl group
chromic units have become a groundbreaking area in the field and the pyridine nitrogen.
of material chemistry. The development of a desired photo-
chromic LMOG requires a lot of synthetic efforts to provide
structural variants, because a tiny structural modification
of a gelator can appreciably influence its gelation ability.
Result and discussion
Self-assembling behavior
The self-assembling behavior of 1 was examined in DMSO-d6
using 1H NMR spectroscopy. Aromatic protons Ha–Hf appeared
Department of Chemistry, Graduate School of Science, Hiroshima University,
1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8526, Japan.
in a common aromatic region at concentrations lower than
1 mmol L−1 (Fig. 1). Upon concentrating the solution of 1,
E-mail: haino@hiroshima-u.ac.jp; Fax: +81-82-424-0724; Tel: +81-82-424-7427
†Electronic supplementary information (ESI) available: Analysis of self-associ-
ation by 1H NMR experiments, gelation properties, UV/vis absorption spectra,
AFM images, and 1H and 13C NMR spectra of all new compounds. See DOI:
10.1039/c3ob00041a
every aromatic resonance shifted upfield, suggesting that 1
assembled as piles in which each aromatic proton experiences
the shielding effect of the neighboring aromatic groups.
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Fig. 2 Gelation temperatures (Tgel) of solutions of 1 (3 g L−1) in p-methoxy-
benzyl alcohol (a) in the presence of 2c, and (b) in the presence of 2a–e in a
ratio of 2 : 3 for 1 and 2a–e.
gelation was confirmed by the absence of the gravitational
flow of solvents when the test tube was inverted. The gelation
properties of 1, 2a–e, and their mixtures were examined in
twenty-nine solvents (Table S1†). 1 and 2a–e were not gelators.
The mixtures of 1 and 2a–e formed gels in benzyl alcohol, in
aniline, and in p-methoxybenzyl alcohol.
Scheme 1 Photochromic tris(phenylisoxazolyl)benzene 1 and bispyridines 2a–e,
and the schematic representation of gel formation.
To discuss the gel stability upon mixing 1 and 2c, the sol–
gel phase transitions were examined by measuring the gel
melting temperature (Tgel) in p-methoxybenzyl alcohol and
benzyl alcohol (Fig. 2a and S1†). The solution of 1 ([1] = 3 g L−1
)
became viscous upon the addition of 2c, and Tgel values were
determined. The gelation was appreciably influenced by ratios
of 1 and 2c. With increasing the concentration of 2c, the gel
became stable. The highest Tgel value was obtained in a
2 : 3 ratio of 1 and 2c. Further addition of 2c did not influence
the gel stability. These values provide quite a reasonable
agreement with the ratio of the numbers of the acidic phenol
units to the basic pyridyl units, implying that hydrogen bonds
between the phenolic hydroxyl and the pyridyl moieties most
likely contribute to the stabilization of the gel networks.
Fig. 1 1H NMR spectra of 1 at concentrations of (a) 1.0, (b) 3.0, (c) 5.0, and
(d) 10.0 mmol L−1 in DMSO-d6.
To confirm the formation of the hydrogen bonding between
the phenolic hydroxyl and the basic nitrogen of pyridyl ring,
titration experiments were carried out in THF. 1 has a strong
UV-vis absorption band at 367 nm, which are sensitive to
hydrogen bonding interaction with the hydroxyl groups.11 Bis-
pyridine 2c has a UV-vis absorption band at approximately
370 nm, which was completely overlapped with that of 1.
Then, 4-dimethylaminopyridine (DMAP) was employed for the
titration of 1 instead of 2c. Upon the addition of DMAP, the
absorption maximum of 1 red-shifted from 367 nm to 374 nm
with isosbestic point, indicating the formation of the inter-
molecular OH⋯N hydrogen bond (Fig. S2a†). This spectral
characteristic was highly influenced by solvent properties; in
benzyl alcohol, the absorption band at 371 nm decreased
while the new band at 475 nm emerged upon the addition of
DMAP (Fig. S2b†). The same characteristics of the spectral
Plotting the chemical shift changes of the protons versus the
concentration of 1 produced hyperbolic curves. By applying
the isodesmic model (see the ESI†), nonlinear regression
analysis of the curves gave rise to the estimated complexation-
induced shifts (Δδ = −1.04, −1.01, −0.70, −0.60, −0.36, and
−0.17 ppm for Ha, Hb, Hc, Hd, He, and Hf) and the association
constant of 87 5 L mol−1. The complexation-induced shifts
decreased with increasing distance of the protons from the C3
axis of 1, implying that 1 stacked as piles along the C3 axis.
This can lead to the formation of polymeric fibrillar
assemblies.
Gelation properties
The gelation tests of 1, 2a–e, and their mixtures were per- shifts were observed when sodium hydroxide was added
formed using the “invert test-tube” method. The compounds instead of DMAP (Fig. S2c†). The traits support that the
and solvents were placed in a screw-capped test tube and phenolic protons of the azobenzene units were partially
warmed until the solids dissolved. The solution was then removed by DMAP; as a result, the intermolecular OH⋯N
cooled to 298 K and left for 2 h under ambient conditions. The hydrogen bond and the salt bridge O−⋯H–N+ coexisted.
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The gelation properties are also governed by the dimen-
sions of the alkyl chains of 2a–e. With increasing the length of
the side chains, the gels were thermally stabilized (Fig. 2b).
The gel stabilities were maximized in the presence of 2c,d,
whereas 2e reduced the stability. 2e showed lower solubility to
the solvents than 2c,d; thereby, the highly lipophilic nature of
2e resulted in its quick precipitation before the gel formed.
Morphologies
To obtain a detailed insight into the two-component gel
system, morphologies of the films prepared by casting solu-
tions of 1, 2a–e, and mixtures of 1 and 2a–e were investigated
by scanning electron microscopy (SEM). Fig. 3a and b showed
microcrystalline and tape-like morphologies, which most prob-
ably resulted from the self-assembly of 1. Morphologies of
films of 2a–e were altered by the dimensions of the alkyl side
chains. n-Butyl and n-hexyl side chains were probably too short
to form well-developed three-dimensional nanostructures
(Fig. 3c–f). By contrast, flower-like morphologies were found in
the film, prepared from a benzyl alcohol solution of 2c.
Aniline solvent facilitated the anisotropic growth of 2c that
resulted in the helical tape-like nanostructures (Fig. 3h). n-Tetra-
decyl side chains of 2d stabilized the helical tape-like nano-
structures, the entanglement of which generated the well
developed three dimensional networks (Fig. 3i,j). 2e mostly
produced the film-like morphologies in both solvents (Fig. 3k,l).
The fibrillar morphologies were partially found, and bundled
into film-like morphologies. The stability of the helical tape-
like nanostructures was apparently determined by the dimen-
sions of the aliphatic side chains. The self-assembly of 2c,d is
most probably driven by the phase separation of the aliphatic
and the aromatic moieties. The rigid aromatic cores can be
capable of assembling with the assistance of aromatic stacking
interaction, and the assemblies are thereby surrounded by
long alkyl chains. The helical tape-like nanostructures perhaps
result from further aggregation of the rod-like supramolecular
structures in the solid state.
Upon mixing azobenzene 1 and bispyridines 2a–e in a ratio
of 2 : 3 in benzyl alcohol and in aniline, the xerogels resulted
in dramatic morphological changes. The helical, flower-like,
and tape-like morphologies turned into highly developed and
entangled fibrillar networks that were confirmed by the SEM
images (Fig. 4a–j). The anisotropic growth of the assemblies of
mixtures of 1 and 2a–e generated the long and entangled gel
fibers that gave rise to a lot of voids. Especially, a mixture of 1
and 2d or 2e gave rise to well-developed three-dimensional
networks.
Employing atomic force microscopy measurements of cast
films of 1 with or without 2c gained an insight into the supra-
molecular assemblies of 1 and 2c. The assembly of 1 gave rise
to the well developed fibers that bundled with an average
cross-section of 1.5 0.1 nm (Fig. 5a, S3†), whereas cast-films
from solutions of 2c provided only amorphous morphologies
(Fig. S4†). By contrast, the presence of bispyridyl linker 2c led
Fig. 3 SEM images of cast-films of (a, b) 1, (c, d) 2a, (e, f) 2b, (g, h) 2c, (i, j) 2d,
and (k, l) 2e in (a, c, e, g, i, k) benzyl alcohol and (b, d, f, h, j, l) aniline.
sections increased to be more than 2.5 nm in THF. Benzyl
alcohol and aniline solvents produced further growth of the
fibers, the cross-section of which reached more than 3.0 nm
(Fig. S6†). Fig. 5c,d indicates that the interconnection of the
fibrillar assemblies promoted bundling of them to form
thicker supramolecular networks, which should be facilitated
by the bispyridyl linkages.
Photoisomerization
1 to thicker sheet-like morphologies in which fibers could Photoisomerization of trans-isomer of 1 was monitored by UV-
directionally align to form bundles (Fig. 5b, S5†). The cross- vis absorption spectroscopy (Fig. 6). A solution of trans-isomer
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Fig. 5 AFM images of cast-films on mica prepared from solutions of (a) 1 in
THF (1 μm × 1 μm) and 1 with 2c (b) in THF (5 μm × 5 μm), (c) in benzyl alcohol
(2.5 μm × 2.5 μm), and (d) in aniline (1 μm × 1 μm).
Fig. 6 Absorption spectra of trans-isomer of 1 (8.4 × 10−6 mol L−1) in THF:
(left) the process of trans–cis isomerization under irradiation with 360 nm light;
(right) the subsequent reverse isomerization process under irradiation with
450 nm light. (a–e) 0, 5, 10, 15, 20 min; (f–j) 0, 5, 10, 30, 60 min.
Fig. 4 SEM images of cast-films of 1 in the presence of (a, b) 2a, (c, d) 2b, (e, f)
2c, (g, h) 2d, and (i, j) 2e in (a, c, e, g, i) benzyl alcohol and (b, d, f, h, j) aniline.
in THF showed a sharp absorption band at approximately
360 nm and a broad band around 450 nm, assigned as the
π–π* and n–π* transitions of the azobenzene moieties. Upon
irradiation at 360 nm, the band at 360 nm decreased and a
new broad band simultaneously emerged at 445 nm. These
changes produced the isosbestic points at 320 and 431 nm,
indicating that the photoisomerization was a unimolecular
process in which only two chemical species existed. Accord-
ingly, the trans-isomer was converted to the cis-isomer as a
primary product. The cis-isomer turned back to the trans-
isomer by irradiation of 460 nm light. These processes showed
complete reversibility.
Fig. 7 The gel-to-sol transition of a mixture of 1 and 2c in benzyl alcohol at
room temperature. The pictures are: (left) before UV irradiation, (middle) after
UV irradiation, and (right) after warming.
In our previous study, the cis-isomer is not capable of gen- down (Fig. 7, left). Under the irradiation of UV light at 365 nm
erating stacked supramolecular assemblies.10 Therefore, the for several hours, the gel became transparent sol (Fig. 7,
sol-to-gel transition can be switchable in the two component middle), indicating that the trans-isomer isomerized to the cis-
organogelators through the photo-induced structural isomeri- isomer, collapsing the stable gel. Once the resulting sol was
zation. The turbid gel prepared from a solution of 1 and 2c in warmed up, the cis-to-trans thermal isomerization was pro-
benzyl alcohol was stable when the tube was turned upside moted, and the trans-isomers gave rise to the turbid gel (Fig. 7,
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right). The effective self-assembling of the trans-isomer is most HRMS (ESI+) calcd for C44H64O8I2Na m/z 997.2583 [M + Na]+,
likely responsible for the gel formation, whereas the reason- found m/z 997.2582; Anal. calcd for C44H64O8I2 C 54.21,
ably weaker molecular interaction of the cis-isomer destroys H 6.62, found C 54.32, H 6.52%.
the higher order of supramolecular assemblies even though
1,4-Diiodo-2,5-bis{[3,4,5-tri(hexoxy)phenyl]methoxy}benzene
they are connected by the bispyridyl linker via hydrogen (4). 2,5-Diiodohydroquinone (543 mg, 1.50 mmol), 3,4,5-tri-
bonds.
(hexoxy)benzyl chloride (1.41 g, 3.30 mmol), potassium car-
bonate (1.3 g, 9.0 mmol), and 15 mL DMF were mixed in a
round bottom flask, and the mixture was stirred at 50 °C for
24 h under an argon atmosphere. The reaction mixture was
cooled to room temperature, and poured into 250 mL of ice-
Conclusions
Photoresponsive organogelators were synthetically accessible cold water. The aqueous layer was extracted with chloroform
through the two-component system composed of tris(phenyl- twice. The combined organic layer was washed with brine
isoxazolyl)benzene 1 and bispyridines 2a–e acting as a supra- (50 mL), dried over anhydrous sodium sulfate, and concen-
molecular linker that connected the fibrillar assemblies of 1. trated. The crude product was purified by column chromato-
The gel-to-sol phase changes were successfully controlled graphy on silica gel (5% ethyl acetate–hexane) to obtain the
through the photo-induced structural isomerization of the azo- pure product as a white powder (1.57 g, 91%). M.p. 71–74 °C;
benzene moieties. These results propose a way of exploiting 1H NMR (300 MHz, chloroform-d1) δ 7.27 (s, 2H), 6.69 (s, 4H),
new photoresponsive low-molecular-weight organogelators.
4.97 (s, 4H), 4.00 (t, 8H, J = 6.5 Hz), 3.95 (t, 4H, J = 6.5 Hz),
1.69–1.86 (m, 12H), 1.41–1.58 (m, 12H), 1.24–1.39 (m, 24H),
and 0.85–0.95 (m, 18H) ppm; 13C NMR (75 MHz, chloroform-
d1) δ 153.2, 152.7, 137.7, 131.1, 123.6, 105.6, 86.6, 73.4, 72.1,
69.1, 31.7, 31.5, 30.2, 29.3, 25.8, 22.7, 22.6, 14.1, and
14.0 ppm; HRMS (ESI+) calcd for C56H88O8I2Na m/z 1165.4461
Experimental
General
All chemicals were used without further purification unless [M + Na]+, found m/z 1165.4464; Anal. calcd for C56H88O8I2
otherwise specified. Flash column chromatography was per- C 58.84, H 7.76, found C 59.11, H 7.74%.
formed employing 200–300 mesh silica gel. Proton and carbon
1,4-Diiodo-2,5-bis{[3,4,5-tri(tetradecoxy)phenyl]methoxy}-
NMR spectra were recorded on a Varian Mercury-300 spectro- benzene (5). 2,5-Diiodohydroquinone (108 mg, 0.297 mmol),
meter. IR spectra were obtained on a JASCO FT/IR-420S. UV-vis 3,4,5-tri(tetradecoxy)benzyl chloride (500 mg, 0.654 mmol),
absorption spectra were measured on a JASCO V-560 spectro- potassium carbonate (0.31 g, 1.7 mmol), and 3 mL DMF were
meter. Mass spectra were reported with a Thermo Fisher Scien- mixed in a round bottom flask, and the mixture was stirred at
tific LTQ Orbitrap XL. Melting points were measured with an 50 °C for 24 h under an argon atmosphere. The reaction
AS ONE micro melting point apparatus and uncorrected. mixture was cooled to room temperature, and poured into
Elemental analyses were performed on
a Perkin-Elmer 250 mL of ice-cold water. The aqueous layer was extracted with
2400CHN elemental analyser. Atomic Force Microscopy chloroform twice. The combined organic layer was washed
measurements were carried out by using an Agilent 5100 AFM with brine (50 mL), dried over anhydrous sodium sulfate, and
system. SEM images were obtained by Hitachi S-5200 field concentrated. The crude product was purified by column
emission scanning electron microscopy.
chromatography on silica gel (5% ethyl acetate–hexane) to
1,4-Diiodo-2,5-bis{[3,4,5-tri(butoxy)phenyl]methoxy}benzene obtain the pure product as a white powder (362 mg, 69%).
(3). 2,5-Diiodohydroquinone (517 mg, 1.43 mmol), 3,4,5-tri- M.p. 57–60 °C; 1H NMR (300 MHz, chloroform-d1) δ 7.27 (s,
(butoxy)benzyl chloride (1.22 g, 3.56 mmol), potassium car- 2H), 6.69 (s, 4H), 4.96 (s, 4H), 3.99 (t, 8H, J = 6.5 Hz), 3.95 (t,
bonate (1.2 g, 8.56 mmol), and 15 mL DMF were mixed in a 4H, J = 6.5 Hz), 1.69–1.86 (m, 12H), 1.41–1.58 (m, 12H),
round bottom flask, and the mixture was stirred at 50 °C for 1.24–1.39 (m, 120H), and 0.85–0.95 (m, 18H) ppm; 13C NMR
24 h under an argon atmosphere. The reaction mixture was (75 MHz, chloroform-d1) δ 153.2, 152.7, 137.8, 131.1, 123.6,
cooled to room temperature, and poured into 250 mL of ice- 105.6, 86.6, 73.4, 72.1, 69.1, 31.9, 31.9, 30.3, 29.8, 29.7, 29.7,
cold water. The aqueous layer was extracted with ethyl acetate 29.6, 29.4, 29.4, 26.1, 22.7, and 14.1 ppm; HRMS (ESI+) calcd
twice. The combined organic layer was washed with brine for C104H184O8I2Na m/z 1838.1923 [M + Na]+, found m/z
(50 mL), dried over anhydrous sodium sulfate, and concen- 1838.1974; Anal. calcd for C104H184O8I2 C 68.77, H 10.21,
trated. The crude product was purified by column chromato- found C 69.11, H 9.92%.
graphy on silica gel (5% ethyl acetate–hexane) to obtain the
1,4-Diiodo-2,5-bis{[3,4,5-tri(octadecoxy)phenyl]methoxy}-
pure product as a white powder (995 mg, 71%). M.p. 84–85 °C; benzene (6). 2,5-Diiodohydroquinone (254 mg, 0.701 mmol),
1H NMR (300 MHz, chloroform-d1) δ 7.27 (s, 2H), 6.69 (s, 4H), 3,4,5-tri(octadecoxy)benzyl chloride (1.63 g, 1.75 mmol),
4.97 (s, 4H), 4.01 (t, 8H, J = 6.5 Hz), 3.97 (t, 4H, J = 6.5 Hz), potassium carbonate (0.50 g, 4.2 mmol), and 3 mL DMF were
1.67–1.85 (m, 12H), 1.43–1.60 (m, 12H), 0.97 (t, 12H, J = 7.4 mixed in a round bottom flask, and the mixture was stirred at
Hz), and 0.96 (t, 6H, J = 7.4 Hz) ppm; 13C NMR (75 MHz, 50 °C for 24 h under an argon atmosphere. The reaction
chloroform-d1) δ 153.2, 152.7, 137.8, 131.1, 123.7, 105.7, 86.6, mixture was cooled to room temperature, and poured into
73.0, 72.2, 68.8, 32.3, 31.4, 19.3, 19.2, 13.9, and 13.9 ppm; 250 mL of ice-cold water. The aqueous layer was extracted with
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chloroform twice. The combined organic layer was washed C70H97O8N2 m/z 1093.7239 [M + H]+, found m/z 1093.7236;
with brine (50 mL), dried over anhydrous sodium sulfate, and Anal. calcd for C70H96O8N2·0.2H2O C 76.63, H 8.86, N 2.55,
concentrated. The crude product was purified by column found C 76.27, H 9.06, N 2.50%.
chromatography on silica gel (5% ethyl acetate–hexane) to
1,4-Bis(4′-pyridylethynyl)-2,5-bis{[3,4,5-tri(dodecoxy)phenyl]-
obtain the pure product as a white powder (1.24 g, 82%). methoxy}benzene (2c). A mixture of 1,4-diiodo-2,5-bis{[3,4,5-
M.p. 70–73 °C; 1H NMR (300 MHz, chloroform-d1) δ 7.27 tri(dodecoxy)phenyl]methoxy}benzene12 (706 mg, 0.429 mmol),
(s, 2H), 6.69 (s, 4H), 4.96 (s, 4H), 3.99 (t, 8H, J = 6.5 Hz), 3.95 4-ethynylpyridine (111 mg, 1.07 mmol), PdCl2(PPh3)2 (15 mg,
(t, 4H, J = 6.5 Hz), 1.69–1.86 (m, 12H), 1.41–1.58 (m, 12H), 21 μmol), and CuI (4.0 mg, 21 μmol) in dry THF (11 mL) and
1.24–1.39 (m, 168H), and 0.85–0.95 (m, 18H) ppm; 13C NMR dry diisopropylamine (1.2 mL) was stirred for 6 h at rt. The
(75 MHz, chloroform-d1) δ 153.2, 152.7, 137.8, 131.1, 123.6, reaction mixture was diluted with ethyl acetate, and the result-
105.6, 86.6, 73.4, 72.2, 69.1, 31.9, 30.3, 29.7, 29.7, 29.5, 29.4, ing insoluble solid was filtered off. The organic layer was
26.1, 22.7, and 14.1 ppm; HRMS (ESI+) calcd for washed with aqueous ammonium chloride solution, dried over
C
128H232O8I2Na m/z 2174.5729 [M + Na]+, found m/z 2174.5732; anhydrous sodium sulfate, and concentrated. The crude
Anal. calcd for C56H88O8I2 C 71.41, H 10.86, found C 71.36, product was purified through recrystallization from ethyl
H 10.93%. acetate to give a yellow powder (300 mg, 43%). M.p. 78–81 °C;
1,4-Bis(4′-pyridylethynyl)-2,5-bis{[3,4,5-tri(butoxy)phenyl]- 1H NMR (300 MHz, chloroform-d1) δ 8.60 (d, 4H, J = 5.9 Hz),
methoxy}benzene (2a). A mixture of 4 (550 mg, 0.564 mmol), 7.43 (d, 4H, J = 5.9 Hz), 7.13 (s, 2H), 6.68 (s, 4H), 5.06 (s, 4H),
4-ethynylpyridine (175 mg, 1.69 mmol), PdCl2(PPh3)2 (20.1 mg, 3.95 (t, 4H, J = 6.5 Hz), 3.92 (t, 8H, J = 6.5 Hz), 1.62–1.81
28 μmol), and CuI (5.3 mg, 28 μmol) in dry THF (6 mL) and (m, 12H), 1.15–1.56 (m, 108H), and 0.82–0.92 (m, 18H) ppm;
dry diisopropylamine (1.6 mL) was stirred for 6 h at rt. The 13C NMR (75 MHz, chloroform-d1) δ 153.8, 153.3, 149.7, 138.0,
reaction mixture was diluted with ethyl acetate, and the result- 131.4, 131.1, 125.3, 117.8, 114.3, 105.7, 92.6, 90.0, 73.4, 71.7,
ing insoluble solid was filtered off. The organic layer was 69.1, 31.9, 30.3, 29.7, 29.6, 29.6 29.4, 29.3, 26.1, 26.1, 22.6, and
washed with aqueous ammonium chloride solution, dried over 14.0 ppm; HRMS (ESI+) calcd for C106H169O8N2 m/z 1598.2874
anhydrous sodium sulfate, and concentrated. The crude [M + H]+, found m/z 1598.2872; Anal. calcd for C106H168O8N2
product was purified through recrystallization from ethyl acetate C 79.65, H 10.59, N 1.75, found C 79.33, H 10.68, N 1.59%.
to give a yellow powder (480 mg, 53%). M.p. 165–167 °C;
1,4-Bis(4′-pyridylethynyl)-2,5-bis{[3,4,5-tri(tetradecoxy)phenyl]-
1H NMR (300 MHz, chloroform-d1) δ 8.59 (d, 4H, J = 5.9 Hz), methoxy}benzene (2d). A mixture of 5 (362 mg, 0.210 mmol),
7.34 (d, 4H, J = 5.9 Hz), 7.13 (s, 2H), 6.69 (s, 4H), 5.06 (s, 4H), 4-ethynylpyridine (65.0 mg, 0.61 mmol), PdCl2(PPh3)2 (7.5 mg,
3.96 (t, 4H, J = 6.5 Hz), 3.92 (t, 8H, J = 6.5 Hz), 1.65–1.78 11 μmol), and CuI (2.0 mg, 11 μmol) in dry THF (2.1 mL) and
(m, 12H), 1.36–1.58 (m, 12H), 0.95 (t, 6H, J = 7.4 Hz), and 0.92 dry diisopropylamine (0.6 mL) was stirred for 6 h at rt. The
(t, 12H, J = 7.4 Hz) ppm; 13C NMR (75 MHz, chloroform-d1) reaction mixture was diluted with ethyl acetate, and the result-
δ 153.8, 153.3, 149.7, 138.1, 131.4, 131.3, 125.4, 117.9, 114.3, ing insoluble solid was filtered off. The organic layer was
105.8, 92.6, 90.2, 73.1, 71.8, 68.9, 32.3, 31.4, 19.2, 19.2, 13.9, washed with aqueous ammonium chloride solution, dried over
and 13.8 ppm; HRMS (ESI+) calcd for C58H73O8N2 m/z anhydrous sodium sulfate, and concentrated. The crude
925.5361 [M + H]+, found m/z 925.5358; Anal. calcd for product was purified through recrystallization from ethyl
C58H72O8N2 C 75.29, H 7.84, N 3.03, found C 75.60, H 8.17, acetate to give a yellow powder (160 mg, 60%). M.p. 72–76 °C;
N 3.07%.
1H NMR (300 MHz, chloroform-d1) δ 8.59 (d, 4H, J = 5.9 Hz),
1,4-Bis(4′-pyridylethynyl)-2,5-bis{[3,4,5-tri(hexoxy)phenyl]- 7.34 (d, 4H, J = 5.9 Hz), 7.13 (s, 2H), 6.69 (s, 4H), 5.06 (s, 4H),
methoxy}benzene (2b). A mixture of 5 (627 mg, 0.549 mmol), 3.95 (t, 4H, J = 6.5 Hz), 3.91 (t, 8H, J = 6.5 Hz), 1.62–1.81
4-ethynylpyridine (170 mg, 1.64 mmol), PdCl2(PPh3)2 (20 mg, (m, 12H), 1.15–1.56 (m, 132H), and 0.82–0.92 (m, 18H) ppm;
28 μmol), and CuI (5.3 mg, 28 μmol) in dry THF (5 mL) and 13C NMR (75 MHz, chloroform-d1) δ 153.8, 153.3, 149.7, 138.0,
dry diisopropylamine (1.5 mL) was stirred for 6 h at rt. The 131.4, 131.3, 125.6, 117.8, 114.3, 105.7, 92.6, 90.2, 73.4, 71.8,
reaction mixture was diluted with ethyl acetate, and the result- 69.2, 31.9, 30.3, 29.7, 29.7, 29.6, 29.4, 29.4, 26.1, 26.1, 22.7,
ing insoluble solid was filtered off. The organic layer was and 14.1 ppm; HRMS (ESI+) calcd for C118H193O8N2 m/z
washed with aqueous ammonium chloride solution, dried over 1766.4752 [M
+
H]+, found m/z 1766.4758; Anal. calcd
anhydrous sodium sulfate, and concentrated. The crude for C118H192O8N2 C 80.22, H 10.95, N 1.59, found C 79.91,
product was purified through recrystallization from ethyl H 11.09, N 1.47%.
acetate to give a yellow powder (478 mg, 80%). M.p. 82–85 °C;
1,4-Bis(4′-pyridylethynyl)-2,5-bis{[3,4,5-tri(octadecoxy)phenyl]-
1H NMR (300 MHz, chloroform-d1) δ 8.59 (d, 4H, J = 5.9 Hz), methoxy}benzene (2e). A mixture of 6 (1.04 g, 0.481 mmol),
7.34 (d, 4H, J = 5.9 Hz), 7.13 (s, 2H), 6.69 (s, 4H), 5.06 (s, 4H), 4-ethynylpyridine (174 mg, 1.69 mmol), PdCl2(PPh3)2 (17.1 mg,
3.95 (t, 4H, J = 6.5 Hz), 3.91 (t, 8H, J = 6.5 Hz), 1.66–1.85 24 μmol), and CuI (4.7 mg, 24 μmol) in dry THF (5 mL) and
(m, 12H), 1.21–1.54 (m, 12H), 0.90 (t, 6H, J = 7.4 Hz), and 0.88 dry diisopropylamine (1.3 mL) was stirred for 6 h at rt. The
(t, 12H, J = 7.4 Hz) ppm; 13C NMR (75 MHz, chloroform-d1) reaction mixture was diluted with ethyl acetate, and the result-
δ 153.8, 153.3, 149.7, 138.0, 131.5, 131.3, 125.4, 117.9, 114.3, ing insoluble solid was filtered off. The organic layer was
105.7, 92.6, 90.2, 73.5, 71.8, 69.2, 31.8, 31.5, 30.3, 29.3, 25.8, washed with aqueous ammonium chloride solution, dried
25.7, 22.7, 22.6, 14.1, and 14.0 ppm; HRMS (ESI+) calcd for over anhydrous sodium sulfate, and concentrated. The crude
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product was purified through recrystallization from ethyl
acetate to give a yellow powder (480 mg, 48%). M.p. 101–104 °C;
1H NMR (300 MHz, chloroform-d1) δ 8.60 (d, 4H, J = 5.9 Hz),
7.33 (d, 4H, J = 5.9 Hz), 7.13 (s, 2H), 6.69 (s, 4H), 5.06 (s, 4H),
3.95 (t, 4H, J = 6.5 Hz), 3.91 (t, 8H, J = 6.5 Hz), 1.62–1.81
(m, 12H), 1.15–1.56 (m, 156H), and 0.82–0.92 (m, 18H) ppm;
13C NMR (75 MHz, chloroform-d1) δ 153.9, 153.3, 149.7, 138.1,
131.4, 131.3, 125.4, 117.9, 114.3, 105.8, 94.4, 92.7, 73.5, 71.9,
69.2, 31.9, 30.4, 29.8, 29.7, 29.7, 29.4, 29.4, 26.1, 26.1, 22.7,
and 14.1 ppm; HRMS (ESI+) calcd for C142H241O8N2 m/z
2102.8508 [M + H]+, found m/z 2102.8529; Anal. calcd for
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C142H240O8N2 C 81.08, H 11.50, N 1.33, found C 81.20,
H 11.53, N 1.21%.
Acknowledgements
This work was supported by Grant-in-Aids for Scientific
Research (B) (No. 24350060) and Challenging Exploratory
Research (No. 23655105) from Japan Society for the Promotion
of Science (JSPS).
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