Six
butadiyne monomers with (dimethylamino)phenyl and N-substituted urethane substituents were synthesized and their crystal
structures and solid-state polymerization were investigated. In five
of the six monomers, directions of the butadiyne stacking and the
intermolecular hydrogen bonding between urethane groups coincided,
and translational distance d between adjacent butadiyne
moieties was around 5 Å. Among them, four monomers showed angle
θ between the translation axis of the monomers and the butadiyne
moiety of around 45°, which is appropriated for regular 1,4-addition
polymerization. These geometries resulted in formation of polydiacetylenes
with characteristic excitonic absorption and relatively high conversion.
One monomer was found to have large θ, and the regular polymerization
was not recognized to be quite low conversion. However, in the remaining
one monomer among six, the directions of butadiyne stacking and intermolecular
hydrogen bonding were different and d was much longer
than 5 Å. However, distance between reacting carbons for 1,4-addition
was short enough resulting in comparable conversion without regular
polymerization. Although introduction of urethane group is effective
to increase probability of the solid-state polymerization of butadiynes,
hydrogen bonding direction, methylene chain conformation, and disorder
of the aromatic rings were found to afford the variation from the
appropriate conditions.
Four diacetylene derivatives with an N-carbazolylphenyl group as a donor moiety have been synthesized and subsequently characterized. These diacetylene derivatives undergo solid-state polymerization via UV irradiation, although these compounds have relatively large π-conjugated aromatic groups. The polymerization behaviors of these derivatives were confirmed by distinct absorption bands for polydiacetylenes. The reactive process is strongly influenced by the slightly differing side groups. Single crystal growth of the two compounds was successful and their crystal structure analyses revealed large differences in the molecular conformations and intermolecular geometries caused by a methylene unit. The HOMO population of the monomers is predominantly expressed in the phenyl carbazole unit, while each polymer showed differing HOMO energies with some polymers exhibiting high-lying HOMO levels.
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