SYNTHESIS AND OPTICAL-PROPERTIES OF THERMOTROPIC POLYTHIOPHENE AND POLY(P-PHENYLENE) DERIVATIVES

Thermotropic nematic and chiral-nematic conjugated polymers consisting of polythiophene and poly(p-phenylene) backbones carrying cyanobiphen yl and (-)-cholesterol as pendant groups were synthesized and characte rized as a new class of optical polymers; Spontaneous assembly of the conjugated backbone was promoted by liquid crystalline mesomorphism on the part of the pendants, thereby allowing uniaxially and helically a ligned glassy films to be prepared for polarized photoluminescence (PL ) studies. In the thiophene series, the conjugated backbone was found to yield an absorption peak red-shifted from those of the monomers and pendant groups. This permitted selective photoexcitation of the polyt hiophene backbone to be accomplished. In the p-phenylene series, the c onjugated backbone did not give rise to a unique absorption peak. Howe ver, with excitation at the long wavelength edge of the absorption pea k, PL of the poly(p-phenylene) backbone was found to be 1 order of mag nitude stronger than that of the pendant cyanobiphenyl group. These or dered solid films produced significant degrees of linearly and circula rly polarized FL. Existing theories were;Found to be capable of repres enting the experimental results with independently measured absorption coefficient, average refractive index, and optical birefringence.