Unprecedented 2D Homochiral Hybrid Lead‐Iodide Perovskite Thermochromic Ferroelectrics with Ferroelastic Switching

Chiral perovskites have emerged as a significant class of materials showing promising optoelectronic and spintronic applications. Reports of chiral perovskite ferroelectrics, however, have been scarce. In this work, we have successfully synthesized homochiral lead–iodide perovskite ferroelectrics [(R)‐N‐(1‐phenylethyl)ethane‐1,2‐diaminium]PbI4 and [(S)‐N‐(1‐phenylethyl)ethane‐1,2‐diaminium]PbI4 by introducing a methyl group into the organic cation of the parent (N‐benzylethane‐1,2‐diaminium)PbI4. Vibrational circular dichroism spectra identify the chiral mirroring relationship. They both undergo 222F2‐type paraelectric–ferroelectric behavior at around 378 K coupled with clear ferroelastic domain “ON/OFF” switching. Besides, they exhibit an evident thermochromism with color change from orange–yellow to orange–red. To our knowledge, the discovery of integrated ferroelectricity, ferroelasticity, and reversible thermochromism in chiral perovskites is unprecedented.