Abstract: Poly(1-alkyne) with octoxy spacer —?[HC=C(CH2)8O—terphenyl—CN]?n—(PA8CN) and terphenyl liquid crystalline pendant was synthesized, and the effects of structure on the optical properties, especially the liquid crystallinity behavior of the polymer and monomer were investigated. The monomer was prepared in high yields(92.30%) by coupling and etherification reactions and successfully polymerized in the presence of Rh catalyst and Et3N cocatalyst in high yields with trans-rich(86.27%) stereoregular structure. Compared to the monomer showing mixed monolayer structure, its corresponding polymer PA8CN formed homogeneous monolayer arrangement. Upon photoexcitation, strong blue emission peak of PA8CN appeared at 413 nm[fluorescence quantum yield, ?F =  68% when excited at 330 nm in tetrahydrofuran(THF) solution]. Compared with its solid film photoexcitated at 330 nm at room temperature, the UV light-emitting band of PA8CN solid film from its liquid crystalline with liquid nitrogen quenched rapidly at 236 ?C was red-shift 10 nm with higher intensity, which may be ascribed to the fact that the effectual conjugation and the order degree of the molecule in the liquid crystalline state of the polymer were enhanced, the energy loss caused by the thermal vibration was decreased, thus resulting in the observed hyperchromic effect.

Key words: Polyacetylene, Liquid crystallinity, Phase transition, Photoluminescence