Improving FLC properties. Simplicity, planarity, and rigidity in new chiral oxazoline derivatives

Article abstract of DOI:10.1021/ja00137a003

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)-β-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 indepth structural investigation of both H-bonded and non-H-bonded phenyloxazoline moieties was carried out (by means of semiempirical calculations - AMI - and spectroscopic studies - IR, UV and ¹H 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) [P₅ max_I(OH)a = 16.7 nC/cm², P_s max_I(OH)b = 13.2 nC/cm²] 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/cm². Its special thermal behavior (showing a glass transition at -28 °C) makes this compound very interesting from the point of view of practical applications and will be the target of further studies.