Study On The Synthesis And Performance Of Liquid Crystal Materials Containing Multiple Chiral Centers With Selective Reflection

Chiral liquid crystals(CLCs)are LC materials that contain asymmetric chiral center and the molecular arrangement presents unique helical structure.They exhibit unique optical properties,such as selective reflection properties,optical rotation,and circular dichroism.Among them,CLCs with N*phase have received extensive attention in the research field because of their excellent selective reflection characteristics,and have already exerted great application value in color recording,medical field,anti-counterfeiting mark,instrument detection and daily life.Currently,the design and synthesis of new CLCs,the discussion on the influence of structural changes on the performance of CLCs,and the improvement on the performance of CLCs through blending and doping are the main research directions of CLCs.In the present dissertation,the new CLCs were designed based on L-menthol and cholesterol containing multiple chiral centers as chiral motifs,and the selective reflection characteristics of the new CLCs were discussed in depth.Three series of CLC compounds containing menthol and one series of CLC compounds containing cholesterol were designed and synthesized.The chemical structures and properties of CLC compounds were characterized and analyzed by Fourier transform infrared(FT-IR),nuclear magnetic resonance(NMR),differential scanning calorimetry(DSC),polarizing optical microscopy(POM)and ultraviolet-visible(UV/Vis).The specific research contents and results are as follows:(1)Two series of CLC compounds Mt4OP-R and Mt4OB-R(R=M,OM,CN,F,CF,OCF)were synthesized by using menthol as the chiral center and introducing different rigid LC cores and terminal groups.Mt4OP-M,Mt4OP-OM,Mt4OB-M and Mt4OB-OM whose terminal groups are flexible alkyl chains or alkoxy chains exhibited blue phase(BP Ⅰ/Ⅱ),Mt4OB-F,Mt4OB-CF,and Mt4OB-OCF whose rigid LC core is-/-ArCOOAr-Ar-/-exhibited SmA*phase,Mt4OP-CN exhibited SmC*phase during cooling course.CLC compounds with fluorine-based or cyano in the terminal group had the higher clearing point(Ti).Mt4OP-OM showed selective reflection characteristics in the N*phase temperature range.(2)One series of CLC compounds Mt4OP-nAB(n=2,4,6,8,10,12,14,16,18)were synthesized by using menthol as the chiral center,selecting-/-ArCOOArOOCAr-/-as the LC core and introducing acyloxy groups of different lengths as terminal groups,Mt4OP-nAB(n≤6)exhibits enantiotropic N*phase.Mt4OP-nAB(n≥10)exhibits enantiotropic N*phase and SmC*phase,Mt4OP-8AB exhibits enantiotropic N*phase and monotropic SmC*phase,and all CLC compounds in this series exhibited blue phase(BP Ⅰ/Ⅱ).As the length of the acyloxy group is varied,the clearing point(Ti)showed a downward trend,the SmC*phase gradually widens,and the N*phase gradually narrows.Mt4OP-nAB(n≤8)showed selective reflection characteristics in the N*phase temperature range.(3)One series of CLC compounds Chol-nOB(n=3,4,5,6,7,8,10,12,14)were synthesized by using cholesterol as the chiral center and introducing alkoxy groups of different lengths as terminal groups.Chol-nOB(n≤7)exhibited enantiotropic N*phase,Chol-nOB(n≥8)exhibited enantiotropic N*phase and SmC*phase,Chol-120B and Chol-14OB exhibited blue phase(BP Ⅰ/Ⅱ).The clearing point(Ti)of Chol-nOB(n=3-8)exhibited an odd-even effect as the length of alkoxy group is varied and the even members gave higher values than the corresponding odd-parity compounds.All CLC compounds in this series showed selective reflection characteristics in the N*phase temperature range.