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Chiral symmetry breaking in achiral bent-core molecules

2008년 8월 12일 08시 15분 14초
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목 14시 : 50분
고분자화학 - New Design Concept and Frontier Technology of Liquid Crystals
저자 및
최석원, Hideo Takezoe1
경희대학교 환경응용화학대학 디스플레이재료공학과, Korea
1Dep. of organic and polymeric materilas, Tokyo Institute of Technology, Japan, Japan
Achiral bent-core mesogens have opened a new era in liquid-crystal science from viewpoints of chirality. Since the constituent molecules do not have a chiral carbon, the presence of chiral phases is fascinating chemists and physicists in the field of liquid crystals. Particularly, inherent chirality in the B4 phase (or unidentified analogous phases) has been reported intensively; large optical rotation (OR) and chiral nonlinear optical (NLO) effects and so on. Moreover, large chiral Pockels (electrogyration) constant observed in the B4 phase of the classic bent-core molecule is nearly equal to that of LiNbO3, which allows promising electrooptical applications if large uniform chiral domains could be obtained. However, bent-core molecules without chiral carbon behave like a racemic mixture, when spontaneous symmetry breaking occurs. Thus, spontaneous degeneracy is inevitably formed; the ratio of the positive and negative domains is approximately 50:50. Hence macroscopic chirality is cancelled out. Herein, in this talk, methods for controlling the chirality and enlarging the chiral domain size in achiral bent-core liquid crystal phases are introduced, in which spontaneous chiral micro-segregation occurs; i.e., (1) use of chiral surface, (2) irradiation of circularly polarized light, and (3) use of twisted cell geometry. Particular attentions will be paid to the methods (2) and (3), since they can provide almost 100% enantiomeric excess.