Synthesis, Characterization Mesomorphic Studies of New Liquid Crystal Compounds with Coumarin Moiety

Abstract

In this thesis , the present work includes synthesis three series of novel heterocyclic Coumarin liquid crystals. These liquid crystals containing 3-acetyl-7-hydroxy-2H-Chromine-2-one, usually known as coumarin within the central moiety. The syntheses of these liquid crystalline compounds involved alkylation (2a-2i), esterification (3a-3i) and Schiff-base reactions. The structure of all the liquid crystals compounds that have been synthesized has been elucidated by CHN Element analysis, FT-IR, 1HNMR and 13C NMR technique. The liquid crystal properties are studied by conducted several methods such as DSC and POM. Where the DSC results, it reveals the presence of phase transitions in material by detecting the enthalpy change associated with each phase transition, by observation under POM. The first series of novel coumarin derivatives dimers (4a-4i) have synthesized from the reactions of derivatives coumarin (3a-3i) with benzidine and terminal chains in odd or even parity. Compound (4a) with shorter terminal alkyl chains show the liquid crystal phase during heating and cooling cycle and obtained nematic mesophase. The heating and cooling scans of compounds (4b-4d) are non mesogenic. The nematic mesophase was observed for compounds (4e-4i) during heating and cooling scans. A second series, a series of new derivatives of coumarin dimers (5a 5i) have been synthesized by reaction coumarin derivatives (3a-3i) with o diansidine. The compounds (5a-5i) had a long terminal alkyl chain ranging from (C= 6-14), molecules (5a-5d) are non-mesogenic and they have shown only crystal-isotropic liquid transitions which are revealed by POM and DSC. Compounds (5e-5i) with increasing the carbons in the alkyl chains (C=C10-C14) exhibited nematic phases V during heating and cooling cycles except for compound (5e). Compound (5e) shows monotropic nematic phase on cooling scan, while compounds (5f-5i) exhibited enantiotropic nematic phase. The third series of compounds (6a-6i), where synthesized by the reaction of p-phenylenediamine with derivatives coumarin (3a-3i), and terminal chains in odd or even parity. Compounds (6a-6d) with short terminal alkyl chains showed non-mesogenic. While compounds (6e-6i) exhibited stable enantiotropic phases obtained during heating and cooling process. The following Scheme shows the preparation of the three series of liquid crystalline compounds.