Studies on electrically switchable bent core liquid crystals for molecular switches

Abstract

This dissertation comprises synthesis and characterization of four series of structurally asymmetric bent-core compounds. These four series comprises twenty five different compounds, each series is differentiated by the different substituents, asymmetry in linking group, asymmetry in terminal chain and asymmetry in both linking group and terminal chains. Accordingly, series I contains five compounds designed as various substituents (H, COOCH3, Cl and NO2) to find the effect of substituent on the mesophase. Series II is designed as five rings containing bent-shape mesogen with unsymmetrical linking groups (with linking group and without linking group) and the terminal chain variations. Series III and IV contain thirteen compounds reported which are consisting of asymmetrical mesogens. Asymmetric compounds were studied by introducing assymetry in the bentcore of the molecules using ester and azomethine linking groups but with symmetrical terminal chains (6-12) and the molecules have asymmetric core by ester and azomethine linking group as well as asymmetric terminal chains (6-12) respectively. Polarizing Optical Microscopic (POM) observations were performed to confirm the existence of a mesomorphic behavior of the compounds. Most of the compounds in the four series exhibited enantiotropic liquid crystalline properties in both heating and cooling processes. In third series of compounds, exhibit mesophase at different temperature and these phases are enantiotropic in nature except compound IIIa. The compounds IIIb and IIIc showed B1 (Colr) phase while higher alkyl chain containing compounds IIId to IIIg exhibited B2 (SmCP) type mesophase. The results revealed that the compounds in the first series exhibit nematic and B1 phases and these phases are not switchable phase under electric field. Second, third and fourth series of compounds shows switchable B2 phase. It is found to be nearly 936 nCcm-2. It is observed that high spontaneous polarization and lowering the melting point is the highlight of this investigation