Exceptional Three-Level Switching Behaviors of Quadratic Nonlinear Optical Properties in a Tristable Molecule-Based Dielectric

Significant
progress on a new brilliant scheme for the solid phase
transition has opened up new possibilities of highly efficiently switching
the quadratic nonlinear optical (NLO) properties. However, the NLO
switching capacities of previously reported solid-state materials
were restrictively modulated between the conventional bistable states.
Exploring NLO tristability is strongly required for multistep operations
in multilevel memory elements and optoelectronic devices. Here, we
first report a tristable molecule-based dielectric, dipropylammonium
trichloroacetate (DPA-TCA), which shows an exceptional three-level
switching of quadratic NLO effects (i.e., NLO-off, low-NLO, and high-NLO
states). This unprecedented three-level switching of the NLO effect
originates from the stepwise ordering of the dynamic molecular components
in DPA-TCA, associated with the tristability of dielectric phase transitions
at 142 and 228 K. It is believed that this finding will shed light
on the further design of new multilevel NLO switching materials and
promote their prospective device applications.