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.