Unique liquid crystalline behavior of conducting polyacetylene derivatives

Unique liquid crystalline behaviors have been observed in polyacetylene derivatives substituted with long side chains containing mesogen unit such as poly [5-(p-(trans-4'-n-octylcyclohexyl)phenoxy)-1-pentyne](PPCH803A) with phenylcyclohexyl mesogenic moiety. Texture typical to smectic liquid crystal has been confirmed by optical microscopic observation. Smectic structure has also been confirmed by X-ray diffraction. Anisotropy of optical absorption spectrum consistent with X-ray diffraction has been observed, from which the band gap of PPCH803A has also been evaluated to be 2.7 eV. Dielectric constant of PPCH803A in the smectic phase (90-150 degrees C) is about 2.8 and changes at phase transition temperature in step wise. The mixture of PPCH803A with ferroelectric liquid crystal of low molecular weight exhibits large dielectric constant and unique ferroelectric behavior in the temperature range of the smectic phase of PPCH803A.