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-d iethynylbenzene) in the presence of triethylamine gives soluble pi-con jugated poly(aryleneethynylene) (PAE) type polymers (-Ar-C=C-Ar'-C=C-) . when Ar and/or Ar' contains the long alkyl substituent and/or pyridi ne 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 o f depolarization) values of 0.005-0.034 as determined by the light sca ttering method, and show absorption bands in the range 350-462 nm, whi ch are shifted from the absorption bands of the corresponding aromatic units (HArH and HAr'H), indicating the occurrence of pi-conjugation a long the polymer chain. The polymers exhibit fluorescence in solutions , and the lambda(max) position of the fluorescence is shifted to a lon ger wavelength in films of the polymers, suggesting the formation of e xcimer-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-dopi ng) at about -2 V vs Ag/Ag+ whereas oxidation (p-doping) of the polyme r is difficult presumably due to the electron-withdrawing effect of th e -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 int o ester and amide groups.