Design of Liquid Crystals with 'de Vries-Like' Properties: Organosiloxane Mesogen with a 5-Phenylpyrimidine Core

摘要

Ferroelectric liquid crystals (FLC) have generated a considerable amount of research activity over the past 30 years, ranging from fundamental studies on the molecular origins of spontaneous polar ordering to the commercial development of high-resolution reflective liquid-crystal-on-silicon (LCOS) microdisplays with switching times in the range of microseconds. Materials used in FLC microdisplay applications are normally composed of an achiral liquid crystal mixture with an isotropic-nematic-smectic A-smectic C (INAC) phase sequence and a chiral dopant that induces a ferroelectric polarization P_s in the tilted smectic C phase. Coupling of P_s to an applied electric field enables switching of the ferroelectric SmC~* phase between opposite tilt orientations, thereby producing an ON-OFF light shutter between crossed polarizers. One major problem in formulating FLC mixtures for display devices is the layer contraction caused by the tilting of molecules upon transition from the orthogonal SmA phase to the SmC phase (Figure la), which results in a buckling of the smectic layers into a chevron geometry and the formation of "zigzag" defects that reduce the optical quality of the FLC film.