Nopinic acid is an unprecedented homochiral single-component organic ferroelectric

Abstract

Since the first homochiral ferroelectric crystal Rochelle salt (NaKC4H4O6•4H2O) was discovered in 1921 by Valasek, the single-component homochiral organic molecular ferroelectrics still remain unexplored although a number of molecular ferroelectrics were discovered in the past decade. Here we present the first example of homochiral single component organic ferroelectric, nopinic acid, (2-hydroxy-6, 6-dimethyl bicycle [3, 1, 1] heptane-2-carboxylic acid), 1, which experiences a unique ferroelectric to ferroelectric phase transition around 161 K from space group C2 to P1. The heat anomaly, switchable dielectric and varied SHG responses dependence on temperatures directly confirm its reversible phase transition behavior. The further X-ray single crystal diffraction analysis indicates that with the temperature changes the relative displacement motions of H-proton caused the collective shift along the direction of double helical nopinic acid chains, and results the reversible phase transition. The piezo-response force microscopy (PFM) measurements on thin films of 1 probed and switched the local ferroelectric polarization at the nanoscale, and directly proved its ferroelectricity. Because of its inherent chirality, flexibility, environment-friendly, easy process ability, and room-temperature polarization switching, we believe these finding affords a new venue to explore for high performance ferroelectrics.