Ferroelectric Property, Switchable Dielectric, and Excellent Second Harmonic Generation Response in a Homochiral Organic Salt: l-Prolinammonium 1-Adamantane Carboxylate

Abstract

Molecular ferroelectrics have attracted increasing interest recently; however, the research on homochiral molecular ferroelectrics based on organic salts is relatively spare. Here we present a novel homochiral molecular ferroelectric [Hpla]·[ac] (Hpla = protonated l-prolinammonium, ac = deprotonated 1-adamantane carboxylate), 1, which goes through a reversible phase transition in the vicinity of 140 K. The distinct dielectric and heat anomalies further confirm the reversible phase transition. Single crystal X-ray diffraction analysis before and after the phase transition temperature indicates that 1 belongs to the P21 chiral space group, and the synergetic motions from the hydrogen bond and disorder–order of adamantane grids triggered the phase transition. The polarization–electric hysteresis loop shows that 1 has spontaneous polarization of 0.15 muC/cm2. Notably, compound 1 displays ultralarge second harmonic generation signals (9.1 a.u.), approximately equal to three times that of potassium dihydrogen p...