Triethylammonium picrate: An above-room-temperature phase transition material to switch quadratic nonlinear optical properties

To switch quadratic nonlinear optical (NLO) effects has become an exciting branch of the NLO material science. However, solid-State molecular crystals showing tunable and switchable NLO behaviors remain scarce. Here, we report an organic picrate-based binary molecular crystal, triethylammonium picrate (TEAP), which undergoes an above-room-temperature phase transition at T-c=319 K, being solidly confirmed by the thermal and dielectric measurements. A large thermal hysteresis of similar to 7 K discloses the first-order feature for its phase transition. More strikingly, the quadratic NLO effects of TEAP can be switched in the vicinity of T-c. That is, TEAP exhibits NLO-active response of similar to 1.5 times as large as that of KDP below T-c (i.e., NLO-on state), while its NLO effects totally disappear above T-c (NLO-off state). Structure analyses disclose that the order-disorder transformations of triethylammonium cations and picrate anions collectively contribute to its phase transition, as well as switchable NLO behaviors. This work opens up a new pathway to the designing and assembling of stimuli-responsive materials. (C) 2017 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.