The Synthesis Of Chiral (S)-1, 2-Propanediol Derivatives And Study On Helical Twisting Behavior Of Induced Chiral Nematic Liquid Crystals

Chiral dopant is an integral part of the chiral nematic liquid crystal materials, and the molecular structure of the chiral dopant has an intense influence on helical twisting behavior of induced N*-LCs. Therefore design and synthesis of a new-style chiral dopant molecule, investigation into the relationship of molecular structure and helical twisting behavior of induced N*-LCs have become a hot topic in the field of liquid crystal science.A novel series of chiral (S)-1, 2-propanediol derivatives with single or double chiral centers (CRDB, CnTC, CSTC) were designed, synthesized and characterized. The piches of induced N*-LCs in different temperature were tested; besides, the influences of terminal alkyl chain length, the nature of terminal substitutional group and numbers of the chiral centers on the pitch of induced N*-LCs, the molecular twisting powerβand PC of the chiral molecule, respectively.The structure validity of chiral compounds were characterized by FT-IR, 1H NMR, and the pitches of N*-LCs were tested by means of Cano, the texture of liquid crystal was observed by POM.The results are as following: (1) The pitches of N*-LC induced by CnTC,βand PC (absolute value) were all decreased with the increasing length of terminal alkyl chain, and there is a odd-even effect on the changements. (2) The piches of N*-LCs induced by the chiral dopants (CnTC, CSTC and CRDB) increased with the increasing temperature and the former with a smaller pitch. In addition,βand PC (absolute value) of three kinds of derivatives were also increased with the increasing temperature but latter two with higher value. (3) To our surprise, the phenomenon of a helix inversion with temperature variation was observed in the N*-LCs induced by C3FTC; besides, the pitches of N*-LCs induced by C3FDB decreased with the increasing temperature, accordingly,βand PC (absolute value) of C3FDB increased with the increasing temperature. (4) For the chiral derivatives with different chiral center number (CNTC and CNDB), the former with a smaller P, the latter with a higher PC (absolute value) andβ, so it indicates that there is a plus property on the chiral center.