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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.
Peng et al. (Tue,) studied this question.