Synthesis And Characterization Of Asymmetric Dimers Containing Mandelic Acid

In this thesis,the structure of dimers and the introduction of mandelic acid as the chiral center were adopted to design and synthesize three series(DBM-nC2B series,DBBM-nC2B series and DBBM-nFmB series),15 kinds asymmetric liquid crystal dimers.The effects of the length of the flexible terminal group,the rigidity of the side arm and the polarity of the fluorine-containing group on the performance of the dimers have been investigated respectively.Infrared spectroscopy(IR),differential scanning calorimeter(DSC),polarised optical microscopy(POM)and other test methods were used to characterize and analyze the structure,thermal properties,and liquid crystal properties of the intermediate and liquid crystal dimers.It is confirmed that all the target products are consistent with the molecular design.In the second chapter,the study of the DBM-nC2B series shows that DBM-0C2B,DBM-1C2B,DBM-2C2B,DBM-3C2B and DBM-4C2B are all nematic liquid crystal dimers,indicating the length of the flexible terminal group only affects the thermal performance of DBM-nC2B series while it does not affect the type of liquid crystal phase in this study.Although the dimers of DBM-nC2B series contain chiral centers,they do not exhibit chiral liquid crystal phases.It may be due to insufficient rigidity of the mesogenic unit connecting to the chiral C,which causes the intramolecular rotation,so that the chiral center fails to induce the dimer to display chiral liquid crystal phase.Therefore,the DBBM-nC2B series are designed by increasing rigidity of mesogenic unit connecting to the chiral C.Besides,the result that DBM-0C2B with the smallest molecular weight displays the highest melting point in this series reveals that the influence of the molecular configuration on the thermal properties of the dimer.In the third chapter,the study of the DBBM-nC2B series shows that DBBM-0C2B,DBBM-1C2B,DBBM-2C2B,DBBM-3C2B and DBBM-4C2B are all chiral nematic liquid crystal dimers,indicating that increasing the rigidity of mesogenic unit connecting to the chiral C reduces the intramolecular spin,so that the series of dimers exhibit the chiral liquid crystal phase.The result also shows that for this series,the length of the flexible terminal group has no effect on the type of the liquid crystal phase of the dimers.The result of the melting temperatures shows a trend of increasing with the increase of molecular weight.For confirming that the side arm DBBM can provide sufficient chirality to form a chiral nematic phase,the next step is to change the rigidity of the other side arm and introduce fluorine-containing group with different polarity to explore its effect on liquid crystal properties.In the fourth chapter,the study of the DBBM-nFmB series shows that DBBM-0F1B,DBBM-1F1B,DBBM-1F2B,DBBM-1F3B and DBBM-3F2B are all chiral nematic liquid crystal dimers,indicating that when the rigidity of the mesogenic unit connecting the chiral C is enough,the introduction of F or CF3 terminal group does not change the liquid crystal phase type of this series dimers;at the same time,the changing of the rigidity of the other side arm does not affect the formation of chiral nematic phase,but plays the influence on the thermal properties of the dimers.