Liquid Crystal Transitions ofp-Sexiphenyl

Abstract

Vorlander,¹ studying the melting behavior of various polyphenyl compounds, reported that both p-quinquephenyl and p-sexiphenyl exhibited liquid crystalline behavior. Based on these early qualitative observations and subsequent melting point determinations,² specific mesophase transitions were designated for each compound in the extensive compilations by Demus.³ Transformation temperatures for solid-to-nematic and nematic-to-isotropic states were assigned for p-quinquephenyl. On the other hand, two liquid crystal transitions, solid-to-smectic and smectic-to-nematic, were assigned to p-sexiphenyl. Since there is no direct evidence to confirm the nature of these phases and since the occurrence of a smectic transition for p-sexiphenyl is inconsistent with recent liquid crystal theory,₄ we have reexamined the melting behavior of p-sexiphenyl with the aid of hot-stage polarized light microscopy and differential scanning calorimetry (DSC). The results provide definitive proof for the nature of the liquid crystalline states of p-sexiphenyl.