Hydrogen-Bonded Switchable Dielectric Material Showing the Bistability of Second-Order Nonlinear Optical Properties

Abstract

Physical properties of phase transition materials are directly linked to the transformation of structural moieties. Here, we report a new hydrogen-bonded binary crystal of cyclohexylaminium chlorodifluoroacetate (1), consisting of two distinct types of the anion–cationic structural moieties, which shows an order–disorder phase transition around 153 K (phase transition point, Tc). Thermal analyses, dielectric, and second-order nonlinear optical (NLO) measurements solidly confirm the symmetry transformation from the point group mmm to mm2. It is noteworthy that 1 exhibits a coexistence of switchable dielectric behaviors and bistable NLO effects. In detail, it is NLO-active below Tc, while its quadratic NLO effects completely disappear above Tc. Such a change reveals the bistable feature of its quadratic NLO properties. Further, variable-temperature structure analyses reveal that the emergence of NLO effects below Tc is ascribed to partial ordering of anions and small-angle reorientation of cations. This mec...