PI-CONJUGATED SOLUBLE POLY(ARYLENEETHYNYLENE) TYPE POLYMERS - PREPARATION BY PALLADIUM-CATALYZED COUPLING REACTION, NONLINEAR-OPTICAL PROPERTIES, DOPING, AND CHEMICAL-REACTIVITY

Palladium-catalyzed polycondensation between dihalo aromatic compounds X-Ar-X (3-hexyl-2,5-diiodothiophene, 2,5-dibromoselenophene, and 3,4-dinitro-2,5-dibromothiophene) and diethynyl aromatic compounds HC=C-Ar'-C=CH (2,5-diethynylpyridine, 3-hexyl-2,5-diethynylthiophene, and p-diethynylbenzene) in the presence of triethylamine gives soluble pi-conjugated poly(aryleneethynylene) (PAE) type polymers (-Ar-C=C-Ar'-C=C-). when Ar and/or Ar' contains the long alkyl substituent and/or pyridine ring. The PAE type polymers are obtained in high yields (86-100%), have molecular weights of 9.6 x 10(4)-369 x 10(4) and rho(v) (degree of depolarization) values of 0.005-0.034 as determined by the light scattering method, and show absorption bands in the range 350-462 nm, which are shifted from the absorption bands of the corresponding aromatic units (HArH and HAr'H), indicating the occurrence of pi-conjugation along the polymer chain. The polymers exhibit fluorescence in solutions, and the lambda(max) position of the fluorescence is shifted to a longer wavelength in films of the polymers, suggesting the formation of excimer-like adducts in the solid state. The polymer films give a chi((3)) (third-order nonlinear optical susceptibility) value of about 5 x 10(-11) esu when the Ar group has the hexyl group. Cyclic voltammetry of the PAE type polymers indicates that they receive reduction (n-doping) at about -2 V vs Ag/Ag+ whereas oxidation (p-doping) of the polymer is difficult presumably due to the electron-withdrawing effect of the -C=C- group. HBr addition to the -C=C- group of the polymer gives a polymer having a -CH=CH(Br)- group, which can be further converted into ester and amide groups.