Improving FLC Properties. Simplicity, Planarity, and Rigidity in New Chiral Oxazoline Derivatives
作者:Jose Luis Serrano、Teresa Sierra、Yolanda Gonzalez、Carsten Bolm、Konrad Weickhardt、Angelika Magnus、Guido Moll
DOI:10.1021/ja00137a003
日期:1995.8
In an attempt to develop new dopants for improved ferroelectric properties in liquid crystals, aryloxazolines have been chosen as chiral moieties. They were prepared in optically active form from (s)-beta-amino alcohols via a short stereospecific synthesis and incorporated into mesogenic systems. Mesogenic and ferroelectric properties of 11 compounds in five series of chiral oxazoline derivatives [I(OH), I(H), II(OH), II(H), and III(OH)] have been studied. In order to establish the relationship between the molecular structure and ferroelectric properties, an in-depth structural investigation of both H-bonded and non-H-bonded phenyloxazoline moieties was carried out (by means of semiempirical calculations-AM1-and spectroscopic studies-IR, UV and H-1 NMR). These studies have proved a planar structure for both types of structures, which should have a strong influence on ferroelectric properties. These properties have been evaluated in 10 mol % binary mixtures. The highest Ps values were measured for compounds of series I(OH) [P-s max(I(OH)a) = 16.7 nC/cm(2), P-s max(I(OH)b) = 13.2 nC/cm(2)] containing a hydrogen bond, which makes the chiral part of the molecule more rigid. Compound III(OH)a shows a wide SmC* phase range which supercools well below room temperature, and it has been studied as a ferroelectric liquid crystal in the pure state. The P-s max measured is appreciably high: 225 nC/cm(2). Its special thermal behavior (showing a glass transition at -28 degrees C) makes this compound very interesting from the point of view of practical applications and will be the target of further studies.