Comprehensive Understanding of Host- and Guest-Dependent Helix Inversion in Chiral Nematic Liquid Crystals: Experimental and Molecular Dynamics Simulation Study
Authors:
- Jun YoshidaJYJun Yoshida
- Syuhei TamuraSTSyuhei Tamura
- Keisuke HoshinoKHKeisuke Hoshino
- Hidetaka YugeHYHidetaka Yuge
- Hisako SatoHSHisako Sato
- Akane YamazakiAYAkane Yamazaki
- Shigetaka YonedaSYShigetaka Yoneda
- Go WatanabeGo Watanabe
- 24 October 2018
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry B
- Vol. 122 (46) , 10615-10626
Abstract
Nematic liquid crystals (N-LCs) are known to transform into chiral nematic liquid crystals (N*-LCs) with helical structures upon doping with enantiomeric compounds (chiral dopants or guests). Here, we investigated the mechanism of host LC- and guest-dependent helix inversion by using octahedral metal complexes as guests. The helical twisting powers (HTPs /μm-1) of eight metal complexes with ΔΛ chirality were examined in five nematic LC hosts. For example, Δ-[Ru(acac)2(trop)] (Ru-trop, Hacac=2,4-pentanedione, Htrop=tropolone) induces a left-handed (M) helix upon doping with N-(4-methoxybenzylidene)-4-butylaniline (MBBA), whereas it induces an opposite right-handed (P) helix in 4-cyano-4'-pentylbiphenyl (5CB). Further, the monobrominated complex of Ru-trop, Δ-[Ru(acac)2(Brtrop)] (Ru-Br1trop, HBr1trop = 5-bromotropolone), induces P helices in both MBBA and 5CB, while the dibrominated complex, Δ-[Ru(acac)2(Br2trop)] (Ru-Br2trop, HBr2trop=3,7-dibromotroplone) induces M helices in both the media. Molecular dynamics simulation performed in parallel confirmed the drastic effect of the bromo group in guest complexes on the microscopic ordering direction of them in nematics. Further, HTPs of all Δ isomers of metal complexes investigated were found to shift in the positive direction as the dielectric constant anisotropy (Δε) of the host LCs increases (and vice versa for Λ isomers). These experimental and calculated results highlight the interplay of steric (exclusive volume effect) and electrostatic (dipole-dielectric body) interactions between the host LCs and guest metal complexes.Keywords
Funding Information
- Kitasato University
- Japan Society for the Promotion of Science (JP16K21353, JP17H03038, JP17H03044, JP17K14465)
- Iketani Science and Technology Foundation
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