Synthesis And Properties Of Novel Schiff Base Chiral Liquid Crystal Compounds

With the development of liquid crystal material,the design and synthesis of novel liquid crystal compound have drawn much attention.The swallow-tailed and the star-shaped liquid crystal are two novel liquid crystal compounds.The swallow-tailed liquid crystal is a novel multi-arm liquid crystal compound combined with multiple flexible substituents at both ends of the rod-shaped molecules.The star-shaped liquid crystal compound is a multi-arm liquid crystal molecular consisted of central atoms or groups and several mesogenic units.In this thesis,the central molecule cholic acid was used to synthesize swallow-tailed and star-shaped Schiff base chiral liquid crystal compounds.It can enrich the varieties of liquid crystal compounds,and provide the theoretical basis for design and synthesis of novel liquid crystal compounds with specific properties.Based on the related literature,we have designed and synthesized five kinds of Schiff base liquid crystal arms,swallow-tailed Schiff base chiral liquid crystal compounds and star-shaped Schiff base chiral liquid crystal compounds.This thesis contains two parts.The first part introduces the design and synthesis of the swallow-tailed Schiff base chiral liquid crystal compounds.They were perpared by introducing the Schiff base mesogenic units into chiral core cholic acid by esterification reaction.The five kinds of the swallow-tailed Schiff base chiral macromolecules were tris(4-toluicacid)-(4-p-methylbenzene Schiff base phenol)cholate(C1),tris(4-chloro benzoic-acid)-(4-p-chlorobenzene Schiff base phenol)cholate(C2),tris(4-methoxy benzoicacid)-(4-p-methoxybenzene Schiff base phenol)cholate(C3),tris(4-methoxy benzoicacid)-(4-pmethoxybenzene Schiff base phenol)cholate(C4)and tris(4-methoxy benzoicacid)-(4-pchlorobenzene Schiff base phenol)cholate(C5).The results showed that the structure conformed to the molecular design characterized by FT-IR and 1H-NMR.The liquid crystal properties were confirmed by use of DSC and POM.It showed that liquid crystal compounds C1-C5 were thermotropic nematic phase liquid crystal compounds with schlieren and filamentous texture.The liquid crystal ranges of C1,C2 and C5 were from 10℃ to 70℃,and the liquid crystal ranges of C3 and C4 were from 110℃ to 130℃.When the substituent group was electron-donating group(-OCH3),the liquid crystal range became the widest with heating liquid crystal interval was 124.4℃ and the cooling was 129.0℃.The design and synthesis of five kinds of schiff base liquid crystal arms and five kinds of star-shaped Schiff base chiral liquid crystal moleculars are in the second part.The five kinds of Schiff base liquid crystal arms were:4-p-methylbenzene Schiff base benzene oxygen formyl pentanoic acid(B1),4-p-methoxybenzene Schiff base benzene oxygen formyl pentanoic acid(B2),4-p-chlorobenzene Schiff base benzene oxygen formyl pentanoic acid(B3),4-p-methyl benzene Schiff base benzene oxygen formyl heptylic acid(B4)and 4-p-methylbenzene Schiff base benzene oxygen formyl pelargonic acid(B5).Star-shaped liquid crystal macromolecules were synthesized by the esterification reaction of above five kinds of Schiff base liquid crystal arms and cholic acid,and then reintroduced to Schiff base phenolic compound A.The intermediates of five kinds of star-shaped Schiff base chiral liquid crystal macromolecules were tris(4-p-methylbenzene Schiff base benzene oxygen formyl pentanoic acid)cholate(Q1),tris(4-p-methoxybenzene Schiff base benzene oxygen formyl pentanoic acid)cholate(Q2),tris(4-p-chlorobenzene Schiff base benzene oxygen formyl pentanoic acid)cholate(Q3),tris(4-p-methylbenzene Schiff base benzene oxygen formyl heptylic acid)cholate(Q4)and tris(4-p-methylbenzene Schiff base benzene oxygen formyl pelargonic acid)cholate(Q5).The five kinds of star-shaped Schiff base chiral liquid crystal compounds were tris(4-p-methylbenzene Schiff base benzene oxygen formyl pentanoic acid)-(4-p-methylbenzene Schiff base phenol)cholate(D1),tris(4-p-methoxybenzene Schiff base benzene oxygen formyl pentanoic acid)-(4-p-methoxy benzene Schiff base phenol)cholate(D2),tris(4-p-chlorobenzene benzene Schiff base benzene oxygen formyl pentanoic acid)-(4-p-chlorobenzene Schiff base phenol)cholate(D3),tris(4-p-methylbenzene Schiff base benzene oxygen formyl heptylic acid)-(4-p-methyl-benzene Schiff base phenol)cholate(D4)and tris(4-p-methylbenzene Schiff base benzene oxygen formyl pelargonic acid)-(4-p-methylbenzene Schiff base phenol)cholate(D5).The results showed that their structure conformed to the molecular design characterized by FT-IR and 1H-NMR.Liquid crystal properties were confirmed by use of DSC and POM,which showed that liquid crystal compounds D1,D3,D4 and D5 were thermotropic schlieren and filamentous texture nematic phase liquid crystal.D1 was thermotropic oil and fingerprint texture cholesteric liquid crystal.The liquid crystal ranges of D1,D2 and D3 were from 50 to 70℃,and the liquid crystal ranges of D4 and D5 were from 20 to 30℃.D1,D2 and D3 had optical rotation.With the increase of the flexible chain of the liquid crystal arm,the rigidity decreased,the liquid crystal range became shorter and the melting point decreased.Macromolecules with strongly polar terminal groups were obviously red-shifted on UV absorption.