RECENT PROGRESS IN POLYDIACETYLENE MATERIAL RESEARCH FOR NONLINEAR OPTICS

In order to enhance the third-order nonlinear optical susceptibilities (χ(3) s ) of polydiacetylenes, polydiacetylenes with π-conjugation between polymer backbone and acetylenic substituents were synthesized. In the case of hexatriyne monomer, solid-state polymerization proceeded via 1, 4-addition to give polydiacetylene with directly bound ethynyl substituents. Also 1, 4-addition polymerization took place in the case of octatetrayne and dodecahexayne monomers and gave polydiacetylenes with butadiynyl and octatetraynyl substituents, respectively. These butadiynyl and octatetraynyl moieties of the latter two polymers could thermally be polymerized furthermore. Especially, in the case of dodecahexayne, formation of an interesting ladder polymer with π-conjugation between two polydiacetylene backbones were confirmed by the solid-state NMR. The effective χ(3)(−3ω; ω, ω, ω) value in three-photon resonant region of the π-conjugation system of polydiacetylenes with butadiynyl substituents was elucidated to be about 10−9 esu. The ratio of χ(3) to absorption at the THG wavelength in near-resonant region was found to be larger than that in resonant region. Aiming at obtaining sharp excitonic absorption of polydiacetylenes, polydiacetylene microcrystals with controlled molecular weight distribution, i.e., uniform electronic structure in the polymer backbones, were also examined.