IMPROVING FLC PROPERTIES - SIMPLICITY, PLANARITY, AND RIGIDITY IN NEWCHIRAL OXAZOLINE DERIVATIVES

In an attempt to develop new dopants for improved ferroelectric proper ties in liquid crystals, aryloxazolines have been chosen as chiral moi eties. They were prepared in optically active form from (s)-beta-amino alcohols via a short stereospecific synthesis and incorporated into m esogenic systems. Mesogenic and ferroelectric properties of 11 compoun ds 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 rel ationship between the molecular structure and ferroelectric properties , an in-depth structural investigation of both H-bonded and non-H-bond ed 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. Thes e properties have been evaluated in 10 mol % binary mixtures. The high est Ps values were measured for compounds of series I(OH) [P-s max(I(O H)a) = 16.7 nC/cm(2), P-s max(I(OH)b) = 13.2 nC/cm(2)] containing a hy drogen bond, which makes the chiral part of the molecule more rigid. C ompound III(OH)a shows a wide SmC phase range which supercools well b elow room temperature, and it has been studied as a ferroelectric liqu id crystal in the pure state. The P-s max measured is appreciably high : 225 nC/cm(2). Its special thermal behavior (showing a glass transiti on at -28 degrees C) makes this compound very interesting from the poi nt of view of practical applications and will be the target of further studies.