Liquid Crystalline Behaviors of Conducting Polyacetylene Derivative with Mesogenic Substituent and Its Mixture with Ferroelectric Liquid Crystal

Abstract

Liquid crystalline behavior has been studied in a polyacetylene derivative substituted with long side chains containing phenylcyclohexyl mesogenic units such as poly [5-( p-( trans-4'- n-octylcyclohexyl)phenoxy)-1-pentyne] (PPCH803A). A texture typical of smectic liquid crystal has been observed using an optical microscope. The smectic layer structure has also been confirmed by X-ray diffraction. Anisotropy of the optical absorption spectrum of the smectic phase, which is consistent with the results of the X-ray diffraction measurements, has been observed. The band gap of PPCH803A in the liquid crystalline phase has been evaluated as 2.9 eV, which is smaller than that in the isotropic liquid phase. The dielectric constant of PPCH803A changes stepwise at the phase transition temperatures. A mixture of PPCH803A with a ferroelectric liquid crystal of low molecular weight exhibits a large dielectric constant and unique ferroelectric behavior.