Synthesis And Characterization Of Liquid Crystal Dimers Containing Various Chiral Centers

Three series of symmetric liquid crystal(LC)dimers have been synthesized in this dissertation.The effects of the chiral center,flexible spacer and the rigidity of the LC arm on the performance of the dimers have been studied.In this dissertation,five intermediate compounds have been successfully synthesized,termed as 10-oxo-10-((4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’biphenyl]-4-yl)oxy)decanoic acid(TBDA),4-((4-fluorobenzoyl)oxy)benzoic acid(1F2B),4’-((4-fluorobenzoyl)oxy)-[1,1’-biphenyl]-4-carboxylic acid(1F3B),4-((4-(trifluoromethyl)benzoyl)oxy)benzoic acid(3F2B),4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-carboxylic acid(3F3B).In the second chapter,four symmetric dimers containing TBDA as the LC arm,and respectively taking propane-1,2-diol((R,S)-PD)、(R)-propane-1,2-diol((R)-PD)、hexahydrofuro[3,2-b]furan-3,6-diol(HD)and(S)-1-phenylethane-1,2-diol((S)-PE),as chiral centers,have been successfully synthesized,termed as propane-1,2-diyl bis(10-oxo-10-((4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’biphenyl]-4-y1)oxy)decanoate)(TBDA-(R,S)-PD)、(R)-propane-1,2-diyl bis(10－oxo-10-((4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-yl)oxy)decanoate)(TBDA-(R)-PD)、O’1,O1-((3 R)-hexahydrofuro[3,2-b]furan-3,6-diyl)bis(10-oxo－10-((4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-yl)oxy)decanoate)(TBDA-HD)、(S)-l-phenylethane-1,2-diyl bis(10-oxo-10-((4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-yl)oxy)decanoate)(TBDA-(S)-PE).In the third chapter,a series of symmetric dimers containing 3F3B as the LC arm,and respectively taking(R,S)-PD、(R)-PD、HD and(S)-PE as chiral centers,have been successfully synthesized,termed as propane-1,2-diyl bis(4’-((4－(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-carboxylate)(3F3B-(R,S)-PD)、(R)-propane-1,2-diyl bis(4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]－4-carboxylate)(3F3B-(R)-PD)、hexahydrofuro[3,2-b]furan-3,6_diyl bis(4’-((4(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-carboxylate)(3F3B-HD)and(S)-1-phenylethane-1,2-diyl bis(4’-((4-(trifluoromethyl)benzoyl)oxy)[1,1’-biphenyl]-4-carboxylate)(3F3B-(S)-PE).In the fourth chapter,a series of symmetric dimers with the same chiral center((S)-PE),taking 1F2B、1F3B、3F2B and 3F3B as LC arms,respectively,have been successfully synthesized,termed as(S)-1-phenylethane-1,2-diyl bis(4((4-fluorobenzoyl)oxy)benzoate)(1F2B-(S)-PE)、(S)-1-phenylethane-1,2-diyl bis(4’-((4-fluorobenzoyl)oxy)-[1,1’-biphenyl]-4-carboxylate)(1F3B,(S)-PE)、(S)-1-phenylethane-1,2-diyl bis(4-((4-(trifluoromethyl)benzoyl)oxy)benzoate)(3F2B-(S)-PE)and(S)-1-phenylethane-1,2-diyl bis(4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-carboxylate)(3F3B-(S)-PE).The chemical structures and LC properties of the intermediates and three series of dimers were investigated by FTIR,differential scanning calorimetry(DSC),polarised optical microscopy(POM)and X-ray diffractometer(XRD).The molecular structures of all the intermediates and LC dimers are all consistent with the designs.TBDA-(R,S)-PD、TBDA-(R)-PD、TBDA-HD and TBDA一(S)-PE in the second chapter are thermotropic enantiotropic smectic A LCs.This may be due to the longer methylene flexible spacers,which weakened the effect of the chiral center on the molecular conformation by intramolecular rotation.Besides,the hydrogen bond between F of the trifluoromethyl group and H of the adjacent molecule causes a large intermolecular force to help to form the smectic phase.For the four LC dimers in the third chapter,which the flexible spacers have been removed,3F3B-(R,S)-PD is a thermotropic enantiotropic smectic LC,3F3B-(R)-PD、3F3B-HD and 3F3B-(S)-PE are thermotropic enantiotropic cholesteric LCs.This indicates that the larger rigidity side arm with a chiral center containing a larger chirality is more conducive to maintaining the asymmetric structure of the chiral center,which is conducive to the formation of the cholesteric phase.From the viewpoint of the liquid crystal performance,the liquid crystal dimer 3F3B-(S)-PE with(S)-PE as the chiral center has better LC properties and with wider cholesteric liquid crystal range.Therefore in the fourth chapter four LC dimers have been synthesized by maintaining(S)-PE as the chiral center,changing the structure of the terminal fluorine-containing groups and the rigidity of the side arms.Among the obtained four LC dimers,1F3B-(S)-PE is a thermotropic monotropic cholesteric LC,1F2B,(S)-PE、3F2B-(S)-PE and 3F3B-(S)-PE are thermotropic enantiotropic cholesteric LCs.And the 1F2B-(S)-PE has the widest LC range.The results indicate that proper reduction of the rigidity of the side arms and the F number in the fluorine-containing groups did not affect the formation of the cholesteric phase,even widen the LC range of the cholesteric phase.