Chiral Switchable Low-Dimensional Perovskite Ferroelectrics

Low-dimensional
hybrid organic–inorganic perovskites (HOIPs)
possess more localized electronic states and narrower conduction and
valence bands to promote self-trapping of excitons and stronger exciton
emission; therefore, they are widely used as building blocks for various
applications in the fields of optoelectronics, photovoltaics, light-emitting
diodes, luminescence, fluorescence, and so forth. Despite the past
decades of intensive study, the discovered low-dimensional chiral
HOIPs are rare as of the 1D chiral HOIP single crystals reported in
2003, as well as the low-dimensional chiral HOIP ferroelectrics are
particularly scarce since the first chiral two-dimensional (2D) and/or
one-dimensional (1D) HOIP ferroelectrics reported. Herein, two new
low-dimensional HOIPs with the same conformational formula [R-MPA]2CdCl4 (R-MPA+ = (R)-(−)-1-methyl-3-phenylpropylamine)
were successfully synthetized by means of regulating the stoichiometric
proportion of R-MPA and CdCl2 in two ways of 1:1 (1) and 2:1 (2). By combining single-crystal X-ray
diffraction, circular dichroism (CD) spectroscopy, differential scanning
calorimetry, temperature-dependent dielectric constant, temperature-dependent
second-harmonic generation (SHG) effect, polarization-dependent SHG
response, and P–E hysteresis
loop, we reveal that 1 is a 1D nonchiral molecular ferroelectric
and 2 is the first zero-dimensional (0D) chiral ferroelectric
with distinct CD signals; meanwhile, 2 exhibits increased
properties of high-Tc, large dielectric
constant, SHG isotropy, and ferroelectricity than that of 1. These results not only shed light on the high tunability of the
low-dimensional HOIP ferroelectrics but also open up an avenue to
explore multifunctional chiral ferroelectrics.