The First Kleinman‐type Second‐Harmonic Generation Circular Dichroism On/Off Switchable Ferroelectrics
Hang Peng, Yan Qin, Xiaogang Chen, Xian‐Jiang Song, Ren‐Gen Xiong, Wei‐Qiang Liao
Abstract
Chiral ferroelectrics have recently received considerable interest due to their unique chiroptical properties. They can adopt Kleinman symmetry second-harmonic generation (SHG)-active chiral-polar point groups in the ferroelectric phase while Kleinman symmetry SHG-inactive chiral-nonpolar point groups in the paraelectric phase, providing a great opportunity to realize on/off switching of SHG circular dichroism (SHG-CD) response. However, the SHG-CD effect was rarely explored in chiral ferroelectrics, and the on/off switchable SHG-CD has never been reported. Herein, we report the first crown ether-based chiral ferroelectrics (R/S-CS)Ca(18-crown-6) (CS=camphor-10-sulfonic acid), which undergo a 422F2 type ferroelectric phase transition at around 336 K from Kleinman symmetry SHG-active point group 2 to Kleinman symmetry SHG-inactive point group 422. Notably, they exhibit obvious SHG-CD responses with an anisotropy factor of up to 0.31. More importantly, the SHG-CD response can be switched between SHG-CD active (SHG-CD on) and inactive (SHG-CD off) states during the ferroelectric phase transition, which is unprecedented. To the best of our knowledge, this is the first example of Kleinman-type SHG-CD on/off switchable ferroelectric. Our findings open up a new way to switch SHG-CD response based on chiral ferroelectrics, which would greatly inspire the further exploration of switchable SHG-CD effects in chiral ferroelectrics.