Strain-Driven Solid−Solid Crystal Conversion in Chiral Hybrid Perovskites with Paramagnetic-To-Ferromagnetic Transition

Hybrid organic−inorganic perovskites (HOIPs) are promising stimuli-responsive materials (SPMs) owing to their molecular softness and tailorable structural dimensionality. The design of mechanically responsive HOIPs requires an in-depth understanding of how lattice strain induces intermolecular rearrangement that impacts physical properties. While chirality transfer from an organic cation to an inorganic lattice is known to influence chiral-optical properties, its effect on strain-induced phase conversion has not been explored. As opposed to achiral or racemic organic cations, chiral organic cations can potentially afford a new dimension in strain-responsive structural change. Herein, we demonstrate that mechanical strain induces a solid phase crystal conversion in chiral halide perovskite single crystals (<i>R</i>/<i>S</i>)-(FE)₂CuCl₄ (FE = (4-Fluorophenyl)ethylamine) from a 0D isolated CuCl4 tetrahedral to 1D corner-sharing CuFCl₅ octahedral framework via the incorporation of Cu...F interaction and N−H...F hydrogen bonding. This strain-induced crystal-to-crystal conversion involves the connection of neighboring 0D CuCl₄ tetrahedra via Cu²⁺−Cl⁻−Cu²⁺ linkages as well as the incorporation of an F-terminated organic cation as one of the X atoms in BX₆ octahedra, leading to a reduced band gap and paramagnetic-to-ferromagnetic conversion. Control experiments using nonchiral or racemic perovskite analogs show the absence of such solid phase conversion. To demonstrate pressure-sensitive properties, the 0D phase is dispersed in water-soluble poly(vinyl alcohol) (PVA) polymer, which can be applied to a large-scale pressure-induced array display on fibrous Spandex substrates via a screen-printing method.<br/><b>Reference:</b><br/>Zheng H.; Zhang R.; Wu X.; Zhang Q.; Wu Z.; Wong P. D. W.; Chen J.; Xu Q.; Loh K. P. <i>J. Am. Chem. Soc. </i>2023, 145, 3569−3576.