510
S. Okada et al.
irradiation of UV light at 254 nm, no absorption peaks were observed for the nanoaggregates in the same condition, indicating different stacking structures between the
crystals and the nanoaggregates. The charge-transfer complex of 6 with 2,5-difluoro7,7,8,8-tetracyanoquinodimethane (F 2 TCNQ) in the nanoaggregate states was also
prepared by the reprecipitation method using acetone solution of 6 and F 2 TCNQ
in the mixing ratio of 1:1 for injection to pure water. The nanoaggregate size was
approximately 140 ± 70 nm. Since the absorption bands in the visible-NIR spectra,
assigned to TTF radical cation and F 2 TCNQ radical anion, were confirmed, the
charge-transfer complex seemed to be formed. However, upon UV irradiation, the
complexed monomer showed absorption decrease suggesting that the charge-transfer
state was decomposed and the regular solid-state polymerization did not progress at
least.
24.3 Monomers Showing Fibrous Morphology
When we can prepare fibrous crystals of butadiyne monomers and stimulate the
solid-state polymerization along the fibrous direction, fibers with large mechanical
strength may be realized. In addition, they may be also used as conducting wires
for molecular electronics, if fiber diameters are down to a nanoscale and appropriate
doping is carried out. When nanowires are prepared in solvent in high concentration,
the gel state generally appears. Although some gel-formable polydiacetylenes have
been reported [36–38], the monomer structures were slightly complicated. Thus,
simplified structures were designed. Since 3,4,5-alkyloxyphenyl group, which can
be derived from gallic acid, is a useful substituent for nanoassembling of functional
species, it was introduced at both ends of the butadiyne monomers [39, 40]. Urethane
or amide groups were placed between the end groups and the central butadiyne moiety
to ensure the formation of the polymerizable stacks by intermolecular hydrogen
bonding. Structures of the related monomers are shown in Fig. 24.7.
In monomers 7 and 8, the methylene numbers between butadiyne and urethane
moieties are different, i.e., four for 7 and three for 8, respectively. The C=O vibration of 7 and 8 with dodecyloxy groups is approximately 1700 cm
−1 , while that of
the corresponding methoxy derivatives is approximately 1725 cm
−1 , indicating that
intermolecular hydrogen bonding becomes stronger by attaching long alkyl chains.
However, there is large difference in the melting points of 7 and 8, i.e., 74 and 109 °C,
respectively, and stacking difference depending on the methylene chain number was
found to be also an important factor for determining the physical properties besides
the hydrogen bonding. Upon UV irradiation, the absorption bands at the longest
wavelength of both monomers appear approximately at 580 nm. Conversion from a
monomer to the corresponding polymer by γ -ray irradiation of 7 was higher than
that of 8. For monomers 9–11, the hydrogen-bonding group was changed to amide
group, and its direction and position were changed. The melting points reflecting
crystallization states were investigated using DSC in detail, and, at least, two polymorphs were found for each of 9–11. Upon UV irradiation, the absorption bands
S. Okada et al.
irradiation of UV light at 254 nm, no absorption peaks were observed for the nanoaggregates in the same condition, indicating different stacking structures between the
crystals and the nanoaggregates. The charge-transfer complex of 6 with 2,5-difluoro7,7,8,8-tetracyanoquinodimethane (F 2 TCNQ) in the nanoaggregate states was also
prepared by the reprecipitation method using acetone solution of 6 and F 2 TCNQ
in the mixing ratio of 1:1 for injection to pure water. The nanoaggregate size was
approximately 140 ± 70 nm. Since the absorption bands in the visible-NIR spectra,
assigned to TTF radical cation and F 2 TCNQ radical anion, were confirmed, the
charge-transfer complex seemed to be formed. However, upon UV irradiation, the
complexed monomer showed absorption decrease suggesting that the charge-transfer
state was decomposed and the regular solid-state polymerization did not progress at
least.
24.3 Monomers Showing Fibrous Morphology
When we can prepare fibrous crystals of butadiyne monomers and stimulate the
solid-state polymerization along the fibrous direction, fibers with large mechanical
strength may be realized. In addition, they may be also used as conducting wires
for molecular electronics, if fiber diameters are down to a nanoscale and appropriate
doping is carried out. When nanowires are prepared in solvent in high concentration,
the gel state generally appears. Although some gel-formable polydiacetylenes have
been reported [36–38], the monomer structures were slightly complicated. Thus,
simplified structures were designed. Since 3,4,5-alkyloxyphenyl group, which can
be derived from gallic acid, is a useful substituent for nanoassembling of functional
species, it was introduced at both ends of the butadiyne monomers [39, 40]. Urethane
or amide groups were placed between the end groups and the central butadiyne moiety
to ensure the formation of the polymerizable stacks by intermolecular hydrogen
bonding. Structures of the related monomers are shown in Fig. 24.7.
In monomers 7 and 8, the methylene numbers between butadiyne and urethane
moieties are different, i.e., four for 7 and three for 8, respectively. The C=O vibration of 7 and 8 with dodecyloxy groups is approximately 1700 cm
−1 , while that of
the corresponding methoxy derivatives is approximately 1725 cm
−1 , indicating that
intermolecular hydrogen bonding becomes stronger by attaching long alkyl chains.
However, there is large difference in the melting points of 7 and 8, i.e., 74 and 109 °C,
respectively, and stacking difference depending on the methylene chain number was
found to be also an important factor for determining the physical properties besides
the hydrogen bonding. Upon UV irradiation, the absorption bands at the longest
wavelength of both monomers appear approximately at 580 nm. Conversion from a
monomer to the corresponding polymer by γ -ray irradiation of 7 was higher than
that of 8. For monomers 9–11, the hydrogen-bonding group was changed to amide
group, and its direction and position were changed. The melting points reflecting
crystallization states were investigated using DSC in detail, and, at least, two polymorphs were found for each of 9–11. Upon UV irradiation, the absorption bands