504
S. Okada et al.
24.2 Aryl-Substituted Butadiyne Monomers
In order to develop materials for all-optical switching devices, studies on further
improvement of the third-order nonlinear optical properties of polydiacetylenes were
performed. Although it was clearly demonstrated that the large χ
(3) s were originated
from polarization along the π-conjugated backbones, their enhancement has not been
easy because the substituents of the conventional polydiacetylenes are composed of
methylene chains and the π-conjugated backbone structures are quite similar among
them. Thus, attachment of π-conjugated substituents to the backbone to modify
the π-conjugated structures was proposed to increase χ
(3) s. However, in the early
stage of the research on polydiacetylenes, only few diphenylbutadiyne derivatives
were known to be polymerizable in the solid state [12, 13]. Many of diphenylbutadiyne monomers do not align in the polymerizable stack in the crystals resulting in
stable compounds. In order to obtain polymerizable butadiyne monomers with one
aromatic ring at least, key structures for the polymerizable stacks were extracted from
the crystal structures of the polymerizable monomers. They were methylene group
with the bent structure for easy stacking, the alkyl chain for intermolecular packing,
urethane or amide groups to form intermolecular hydrogen bonding, and fluorinated
aromatics with the characteristic electronic effect [14]. By using these structural
features, various polydiacetylenes with π-conjugation between the backbone and the
substituents have been prepared and characterized [15]. For example, symmetrical
diphenylbutadiyne derivatives with fluorinated substituents such as fluorine atoms or
trifluoromethyl groups were often found to be polymerizable [16] although polymerization probabilities of asymmetrical derivatives with one fluorinated phenyl group
became low [17]. Introduction of urethane group in the alkyl substituent has been
known to be effective to obtain polydiacetylenes from symmetrically substituted
monomers [18], and polymerization probabilities of arylbutadiyne derivatives were
found to be improved by attaching the alkyl-urethane group [19, 20]. By using this
urethane substituent effect, the solid-state polymerization of butadiyne derivatives
with electron-donating aromatic rings were studied.
24.2.1 Aniline and Carbazole Derivatives
Aniline and carbazole rings work as electron-donating substituents. Thus,
4-(dimethylamino)phenyl [21, 22], 4-(N-carbazolyl)phenyl [23], and 3-(Nphenyl)carbazolyl [24] groups were introduced as one of the butadiyne substituents,
and the other substituent contained butylene and urethane groups (Fig. 24.2).
Although all compounds prepared showed absorption in the visible region after
UV irradiation, their diffuse reflectance spectra were able to be roughly classified
into two types. One is the spectra with absorption maxima in the wavelength range
between 580 and 672 nm (Fig. 24.3a). This type of absorption is typical for polydiacetylenes as mentioned in the introduction. The other spectra showed absorbance
S. Okada et al.
24.2 Aryl-Substituted Butadiyne Monomers
In order to develop materials for all-optical switching devices, studies on further
improvement of the third-order nonlinear optical properties of polydiacetylenes were
performed. Although it was clearly demonstrated that the large χ
(3) s were originated
from polarization along the π-conjugated backbones, their enhancement has not been
easy because the substituents of the conventional polydiacetylenes are composed of
methylene chains and the π-conjugated backbone structures are quite similar among
them. Thus, attachment of π-conjugated substituents to the backbone to modify
the π-conjugated structures was proposed to increase χ
(3) s. However, in the early
stage of the research on polydiacetylenes, only few diphenylbutadiyne derivatives
were known to be polymerizable in the solid state [12, 13]. Many of diphenylbutadiyne monomers do not align in the polymerizable stack in the crystals resulting in
stable compounds. In order to obtain polymerizable butadiyne monomers with one
aromatic ring at least, key structures for the polymerizable stacks were extracted from
the crystal structures of the polymerizable monomers. They were methylene group
with the bent structure for easy stacking, the alkyl chain for intermolecular packing,
urethane or amide groups to form intermolecular hydrogen bonding, and fluorinated
aromatics with the characteristic electronic effect [14]. By using these structural
features, various polydiacetylenes with π-conjugation between the backbone and the
substituents have been prepared and characterized [15]. For example, symmetrical
diphenylbutadiyne derivatives with fluorinated substituents such as fluorine atoms or
trifluoromethyl groups were often found to be polymerizable [16] although polymerization probabilities of asymmetrical derivatives with one fluorinated phenyl group
became low [17]. Introduction of urethane group in the alkyl substituent has been
known to be effective to obtain polydiacetylenes from symmetrically substituted
monomers [18], and polymerization probabilities of arylbutadiyne derivatives were
found to be improved by attaching the alkyl-urethane group [19, 20]. By using this
urethane substituent effect, the solid-state polymerization of butadiyne derivatives
with electron-donating aromatic rings were studied.
24.2.1 Aniline and Carbazole Derivatives
Aniline and carbazole rings work as electron-donating substituents. Thus,
4-(dimethylamino)phenyl [21, 22], 4-(N-carbazolyl)phenyl [23], and 3-(Nphenyl)carbazolyl [24] groups were introduced as one of the butadiyne substituents,
and the other substituent contained butylene and urethane groups (Fig. 24.2).
Although all compounds prepared showed absorption in the visible region after
UV irradiation, their diffuse reflectance spectra were able to be roughly classified
into two types. One is the spectra with absorption maxima in the wavelength range
between 580 and 672 nm (Fig. 24.3a). This type of absorption is typical for polydiacetylenes as mentioned in the introduction. The other spectra showed absorbance