Strain-Driven Solid–Solid Crystal Conversion in Chiral Hybrid <i>Pseudo</i>-Perovskites with Paramagnetic-to-Ferromagnetic Transition
Haining Zheng, Rongrong Zhang, Xiao Wu, Qihan Zhang, Zhenyue Wu, Walter P. D. Wong, Jingsheng Chen, Qing‐Hua Xu, Kian Ping Loh
Abstract
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 pseudo -perovskite single crystals ( R / S )-(FE) 2 CuCl 4 (FE = (4-Fluorophenyl)ethylamine) from a 0D isolated CuCl 4 tetrahedral to 1D corner-sharing CuFCl 5 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 CuCl 4 tetrahedra via Cu 2+ –Cl – –Cu 2+ linkages as well as the incorporation of a F-terminated organic cation as one of the X atoms in BX 6 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.