title: Directed metalation route to ferroelectric liquid crystals with a chiral fluorenol core: the effect of restricted rotation on polar order.
abstract: A new series of smectic C* (SmC*) mesogens containing a chiral (R)-2-octyloxy side chain and either a fluorenone (2a-e) or chiral fluorenol (3a-e) core were synthesized using a combined directed ortho metalation-directed remote metalation strategy. The SmC phase formed by the fluorenol mesogens is more stable and has a wider temperature range than that formed by the fluorenone mesogens, which may be ascribed to intermolecular hydrogen bonding according to variable-temperature FT-IR measurements. The C11 fluorenol mesogens (R,R)-3d and (S,R)-3d were obtained in diastereomerically pure form and gave reduced polarization (Po) values of +106 and +183 nC/cm2, respectively, at 10 K below the SmA*-SmC* phase transition temperature. The difference in Po values suggests that the chiral fluorenol core contributes to the spontaneous polarization of the SmC* phase. This is ascribed to the bent shape of the fluorenol core, which should restrict its rotation with respect to the side chains in the SmC* phase and favor one orientation of its transverse dipole moment along the polar axis, and to steric coupling of the core to the chiral 2-octyloxy side chain.
authors.affiliation: Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6.
authors.forename: J Adam
authors.initials: JA
authors.lastname: McCubbin
authors.forename: Xia
authors.initials: X
authors.lastname: Tong
authors.forename: Ruiyao
authors.initials: R
authors.lastname: Wang
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhao
authors.forename: Victor
authors.initials: V
authors.lastname: Snieckus
authors.forename: Robert P
authors.initials: RP
authors.lastname: Lemieux