Directed Metalation Route to Ferroelectric Liquid Crystals with a Chiral Fluorenol Core: The Effect of Restricted Rotation on Polar Order

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.