Unveiling the Racemization in Ferroelectrics with Coupled Ferroelectricity and Optical Activity

The most distinctive features of
ferroelectrics are spontaneous
polarization and depolarization. Ferroelectricity was first observed
in Rochelle salt, a compound with a chiral component in which the
molecular chirality is not affected by depolarization. For structurally
chiral ferroelectrics (SCFs), such as triglycine sulfate, which lacks
chiral components, the depolarization effect on chirality presents
an intriguing and unexplored topic. In this study, we focus on a newly
proposed chiral optical topic in optically active ferroelectrics with
coupled ferroelectricity and optical activity. We examined the depolarization
effect on the optical activity in these ferroelectric materials and
employed chiral-environment crystallization and solid-state circular
dichroism (CD) techniques to elucidate the racemization-depolarization
mechanism in an SCF for the first time. For polar and nonchiral optically
active ferroelectrics, optical activity is averaged out in the powder
state, resulting in no CD signal. Additionally, we experimentally
validated the consistency between CD measurements and optical activity
theory across the four optically active point groups (m, mm2, 4̅, 4̅2m). These
findings could advance the development of chiral spintronic devices
by leveraging coupled ferroelectricity and optical activity to tune
the spin selectivity.