A Chiral Organic Radical Ferroelectric with Magnetic Circular Dichroism

Chiral ferroelectrics are attracting tremendous interest because of their unique intrinsic chirality and various intriguing optical properties, such as natural circular dichroism (NCD) effects. However, the magnetic CD (MCD), a kind of important magneto-optical effect, has never been explored in chiral ferroelectrics. Herein, through implementing a homochiral strategy on organic radical charge-transfer complexes, we designed a pair of chiral organic radical ferroelectric crystals, R- and S-[TBSQ][TCNQ] (TBSQ = 3-((tert-butyldimethylsilyl)oxy)quinuclidine, TCNQ = tetracyanoquinodimethane), which show both paramagnetism and ferroelectricity at room temperature. Notably, the chiral transfer from homochiral R/S-TBSQ⁺ to TCNQ•^- radical makes R- and S-[TBSQ][TCNQ] can produce remarkable NCD signal in the absorbance region of TCNQ•^- radical. More importantly, the CD signal can be modulated and reversed by an external magnetic field of 1.6 T, showing a remarkable magneto-optical response. The magnetic circular dichroism (MCD) effect is further demonstrated with the strength g_MCD being ∼1 × 10^-4 T^-1 at about 600 nm. To the best of our knowledge, this is the first report on chiral ferroelectrics with MCD effect. Our findings shed light on the exploration of magneto-optical effects in chiral ferroelectrics and stimulate further study on the chemical design of chiral radical ferroelectrics.